Lithographic projection system and projection lens polarization sensor
Abstract
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Expired 13 June 2026, 0.3 years ago.
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22 claims: 13 independent, 9 dependent
- 1放射ビームを調整する照明システムと、 前記放射ビームにその断面にてパターンを付与して、パターニングされた放射ビームを形成することができるパターニングデバイスを支持するサポートと、 基板を保持する基板テーブルと、 前記放射ビームを前記基板のターゲット部分に投影する投影システムと、 前記照明システム又は前記投影システムを通過した前記放射ビームをコリメートするコリメーションレンズと、 前記コリメートされた放射ビームを前記照明システムの光軸に対して垂直方向に反射する反射部材と、 前記反射部材で反射された放射ビームを受ける、 調整可能な偏光変換素子と、 前記偏光変換素子を通過した放射ビームを受ける、 偏光 子 と、 前記偏光子を通過した放射ビームの強度を測定するディテクタと、 を備え、 前記コリメーションレンズ、前記反射部材、 前記偏光変換素子 、及び 前記偏光 子 が、 キャリア上に配置され、 前記キャリアが、 前記パターニングデバイスが前記サポートによって支持されるレベルに 前記パターニングデバイスと交換可能に 配置され、 前記コリメーションレンズ、前記反射部材、前記偏光変換素子、及び前記偏光子が、前記レベルにて移動可能であり、前記照明システム又は前記投影システムの瞳座標に対応する複数の位置において、前記偏光変換素子及び前記偏光子を通過した放射ビームの強度を測定可能である、 リソグラフィ装置。
- 2前記偏光変換素子が、回転自在 及び / 又は 交換自在であることにより調整可能である、請求項1に記載のリソグラフィ装置。
- 3前記偏光変換素子が、四分の一波長板である、請求項1 又は 2に記載のリソグラフィ装置。
- 4前記偏光 子 が、直線偏光子である、請求項1 乃至3のいずれか1項 に記載のリソグラフィ装置。
- 5前記偏光 子 が、空間的に相互に分離された2つの直交する直線偏光放射コンポーネントを出力する偏光ビームスプリッタである、請求項1 乃至3のいずれか1項 に記載のリソグラフィ装置。
- 6前記偏光 子 が、本質的に 燐酸カリウム からなる、請求項5に記載のリソグラフィ装置。
- 7放射ビームを調整する照明システムと、 前記放射ビームにその断面にてパターンを付与して、パターニングされた放射ビームを形成することができるパターニングデバイスを支持するサポートと、 基板を保持する基板テーブルと、 前記放射ビームを前記基板のターゲット部分に投影する投影システムと、 前記投影システムの前に配置された、前記放射ビームを偏光させるための調整可能な偏光子と、 前記パターニングデバイスのレベルにて、前記偏光子を通過した放射ビームを受け、前記放射ビームを調整して前記投影システムの瞳を過充填するためのピンホール板と、 前記基板のレベルで前記放射ビームの波面を測定するための干渉センサであって、 前記ピンホール板及び前記投影システムを通過した放射ビームを受ける格子、及び前記格子を通過した放射ビームを受ける ディテクタを有する干渉センサと、 を備えるリソグラフィ装置。
- 8前記偏光子が、直線偏光子であり、回転自在 及び 交換自在の少なくともいずれか一方であることにより調整可能であり、2つの異なる方向に前記放射を順次偏光させる、請求項7に記載のリソグラフィ装置。
- 9前記ディテクタにより前記測定の結果を取得し、前記 偏光 子を制御し、前記 照明システム又は前記投影システム の少なくとも1つの偏光特性を計算するためのコントローラをさらに備える、請求項1 乃至 8のいずれか1項に記載のリソグラフィ装置。
- 10前記コントローラが、前記 照明システム又は前記投影システム の少なくとも1つの計算された偏光特性に応答して前記 照明システム又は前記投影システム の1つ 又は 複数の素子をさらに制御する、請求項9に記載のリソグラフィ装置。
- 11リソグラフィ装置の少なくとも1つの偏光特性を判定するための方法であって、 前記リソグラフィ装置の投影システムの前に配置された、放射ビームを偏光させるための調整可能な偏光子に放射ビームを照射することと、 前記リソグラフィ装置に配置されるパターニングデバイスのレベルにて、ピンホール板で、前記偏光子を通過した放射ビームを受け、前記放射ビームを調整して前記投影システムの瞳を過充填することと、 前記リソグラフィ装置の基板ステージのレベルで、前記放射ビームの波面を測定するための干渉センサであって、前記ピンホール板及び前記投影システムを通過した放射ビームを受ける格子、及び前記格子を通過した放射ビームを受けるディテクタを有する干渉センサで前記放射ビームを受光することと、 を含み、 前記調整可能な偏光子の少なくとも2つの異なる設定に対する前記放射ビームのそれぞれの波面を 前記干渉センサで 測定 し 、 前記波面測定値から、前記投影システムの偏光に影響する特性に関する情報を判定すること、 を含む方法。
- 12前記投影システムの偏光に影響する特性に関する前記情報が、ジョーンズ行列の少なくとも1つの要素として表される、請求項 11 に記載の方法。
- 13前記 格子 が、シアリングの方向に相互に変位された少なくとも2つの波面の間でシアリング干渉測定を提供する、請求項 11又は12 に記載の方法。
- 14前記調整可能な偏光子の前記少なくとも2つの異なる設定が、前記シアリングの方向に沿った直線偏光と、前記シアリングの方向に垂直の直線偏光とを含む、請求項 13 に記載の方法。
- 15前記投影システムの瞳の中の強度振動の振幅の空間分布、 及び 前記調整可能な偏光子の前記少なくとも2つの異なる設定の各々に対する平均強度を測定することをさらに含む、請求項 13又は14 に記載の方法。
- 16前記投影システムの瞳の中の前記調整可能な偏光子の前記少なくとも2つの異なる設定の各々に対する強度振動の位相の空間分布を測定することをさらに含む、請求項 15 に記載の方法。
- 17放射ビーム内のフィールドの偏光を分析するための 、イルミネータ及び投影システムを有するリソグラフィ装置の 偏光アナライザであって、 前記イルミネータ及び前記投影システムの間に配置される 第1の ピンホール板と 、 前記イルミネータ及び前記投影システムの間に配置され、 前記 第1のピンホール板を通過した 放射ビームを 受ける偏光変換素子と、 前記イルミネータ及び前記投影システムの間に配置され、前記偏光変換素子を通過した放射ビームを受けるウォラストンプリズムと、 前記投影システムの焦点に配置され、前記第1のピンホール板の一方の偏光画像を選択的に送信し、他方の偏光画像を遮蔽する第2のピンホール板と、 前記リソグラフィ装置の投影システムの焦点から外れた位置に配置された光強度ディテクタと、 を備え る 偏光アナライザ。
- 18前記第1のピンホール板、前記偏光変換素子及び前記ウォラストンプリズムを保持するキャリアを更に備える、請求項17のアナライザ。
- 19前記キャリアが、前記イルミネータの光軸に対して垂直方向に移動可能である、請求項18に記載のアナライザ。
- 20前記第2のピンホール板が、前記投影システムの光軸に対して垂直方向に移動可能である、請求項17乃至19のいずれか1項に記載のアナライザ。
- 21前記偏光変換素子の高速軸を回転可能である、請求項17乃至20のいずれか1項に記載のアナライザ。
- 22前記偏光変換素子が四分の一波長板である、請求項17乃至21のいずれか1項に記載のアナライザ。
Independent claims22
165 paragraphs, as filed
(Related application) [001] This application claims the priority of US Patent Application No. 11 / 361,049 filed February 24, 2006. U.S. Patent Application No. 11 / 361,049 is a partial continuation of U.S. Patent Application No. 11 / 065,349 entitled "Lithographic Capsule" filed February 25, 2005. The contents of both applications shall be incorporated herein by reference in their entirety. This application also claims the priority of US Patent Application No. 60 / 689,800 filed June 13, 2005, which is incorporated herein by reference in its entirety.
[002] The present invention relates to a lithography apparatus, a method for determining polarization characteristics, a projection lens polarization sensor, a lithography projection system, a method for determining a polarization state, an active reticle tool, a patterning method for a device, a passive reticle tool, a polarization analyzer, and the like. And the polarization sensor.
[003] A lithographic device is a machine that attaches a desired pattern to a substrate, usually a target portion of the substrate. Lithographic equipment can be used, for example, in the manufacture of integrated circuits (ICs). In that case, a patterning device, also called a mask or reticle, can be used to generate radiation patterns that correspond to the circuit patterns formed on the individual layers of the IC. This pattern can be transferred to a target portion (eg, including a portion, one or more dies) on a substrate (eg, a silicon wafer). Pattern transfer is usually performed by imaging onto a layer of radiation sensitive material (resist) provided on the substrate. Generally, one substrate contains a network of adjacent target portions that are continuously patterned. Well-known lithographic devices use a so-called stepper that illuminates each target area by exposing the entire pattern onto the target area at once, and a radiation beam that scans the pattern in a given direction (the "scanning" direction) in this direction. Includes a so-called scanner that illuminates each target portion by scanning the substrate synchronously or antiparallel to. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern on the substrate.
[004] A well-known wafer scanner (European Patent Application No. EP 1037117), which is incorporated herein by reference in its entirety, comprises an illuminator and a projection lens. During operation, a reticle with a circuit pattern in cross section is placed between the illuminator and the projection lens. The wafer is arranged so that an image of the circuit pattern on the reticle is formed on the surface of the wafer by radiation passing through the illuminator, reticle, and projection lens, respectively.
[005] The demand for miniaturization of features that can be imaged by lithography equipment such as steppers and scanners has led to the use of projection systems with an ever-increasing numerical aperture (NA). The angle of radiation in the projection device with respect to the optical axis increases with increasing NA. The vector nature of light is important for imaging. This is because only the same polarization components of electromagnetic waves interfere with each other. Therefore, it is not only the wave surface quality that determines the contrast of the image, but also the polarization has a considerable effect on the contrast of the image.
[006] Due to production restrictions, the imaging characteristics of a projection lens change when the polarization state of light changes. The imaging performance of a wafer scanner with a projection lens operating at a large numerical aperture (NA) is significantly dependent on the polarization state of the light emitted by the illuminator (combined with the polarization-dependent imaging characteristics of the projection lens). Dependent. One effect is that the image of the circuit pattern on the reticle (formed by the wafer) is in focus at the distance z1 between the projection lens and the wafer in the first polarization state. In the second polarized state, the image is in focus at the distance z2 between the projection lens and the wafer. The wafer is placed on z1 to focus the image of the radiation circuit pattern of the first polarized state on the wafer, while the portion of the image formed by the light with the second polarized state is not focused and is a line. Wider width. By improving the control of polarization, the roughness of the line edge of minute features and the control of CD can be improved.
[007] The current tendency to increase the NA value of a projection lens leads to a decrease in image quality at the wafer level as the quality of the polarized state deteriorates.
[008] In addition, illumination radiation with a particularly desired state of polarization in a particular region is increasingly being used to image features aligned in a particular direction. As a result, it is desirable to know the polarization state of the radiation incident on the patterning device such as a reticle. It is also desirable to know the effect on the state of polarization caused by the projection system (projection lens, etc.). Existing radiation sensors built into lithographic devices are usually insensitive to polarization. Moreover, the polarization state of the illumination radiation at the level of the patterning device may not be easily or cost-effectively measured at the substrate level without knowing the effect of the projection system on the polarization.
[009] The polarization of the radiation incident on the wafer is determined by the polarization of the radiation after it has partially passed through the illuminator. In order to measure the polarization of radiation with an illuminator, a polarization analyzer must be installed between the illuminator and the projection lens.
[010] As the quality level of polarization control improves, it is desirable to know the polarization at different positions in the plane perpendicular to the optical axis of the illuminator. Measurements that provide position-dependent information are called field decomposition measurements.
When field-resolved polarization measurements are required, the polarization analyzer required for each polarization measurement must include a polarization element and a motor that moves to the field position where the polarization element is analyzed. Alternatively, it is necessary to have several polarizing elements at different field positions to analyze and the same amount of shutters to select one polarizing element. By opening the shutter at a desired field position and closing the shutter at another position, the polarization at that position can be measured. The combination of a motor or some polarizing elements and some shutters inevitably provides a large amount of space between the illuminator and the projection lens.
[0012] In well-known lithographic equipment, the space between the illuminator and the projection lens is rather small and is occupied by a reticle stage compartment. This reticle stage section is an area where the reticle stage moves. No other component can enter the area due to the risk of collision with the reticle stage.
[0013] Similarly, if the radiation must pass through the projection lens before measuring the polarization state of the projected beam, the wafer stage consumes the space required by the polarization analyzer.
<p>As a result, there is no space left in such a lithographic apparatus for inserting a polarization analyzer that provides field resolution measurements of the projected beam of radiation.</p>
<p>[0015] In one embodiment, the radiation received from the illuminator has a predetermined well-known polarization state. The following embodiments include methods and devices for adjusting the illuminator using a polarization sensor to improve polarization quality.</p><p>[0016] In one embodiment, the polarization sensor generally consists of two parts. That is, some optical elements (retarders, polarizers) that process the polarization of the illuminator light, and a detector that measures the intensity of the processed light. From the intensity measurements, four parameters S<sub>0</sub>~ S<sub>3</sub>A Stokes vector consisting of can be derived. The field point is the position in the cross section perpendicular to the optical axis of the radiating beam passing through the illuminator. The light at each field point can be measured using the field stop at that point where the narrow light beam travels. The light emitted from the field stop is detected by a detector such as a 2-d detector. The intensity detected by the 2-d detector includes a sequence of sub-intensity measurements collected at each individual xy position corresponding to the pupil coordinates in the illuminator. An intensity measurement of 3 or more per field point is sufficient to measure the polarization of light at that field point. From three or more intensity measurements collected at each xy position by the detector, a polarized pupil map containing the Stokes vector of each measured pupil position in the illuminator where the light from it passes through the field stop can be created. You can fine-tune the polarization settings of the illuminator using the measurement information about the polarization at the field point. In addition, the polarization state can be measured at different times and the illuminator output can be monitored over a period of time. In addition, the measured values can be obtained at a series of field points, and these measured values can be used to map the polarization state of radiation as a function of the field point position.</p><p>The contribution of the projection lens to polarization can be measured using additional optics. The polarization state of light at the wafer level can be monitored over a period of time, taking into account, for example, the drift effect of the illuminator and / or lens.</p><p>[0018] Therefore, in the configuration of the present invention described below, both the illuminator and the projection lens polarization sensor can include an optical element that processes and analyzes the polarization state of light and a detector that measures the intensity of light.</p><p>[0019] In addition to knowing the polarization state of the illumination radiation, it is also desirable to obtain information about the effect of the illumination radiation on the polarization state caused by the projection system.</p><p>[0020] According to one aspect of the present invention, an illumination system configured to adjust the radiated beam and a patterning device capable of imparting a pattern to the radiated beam in cross section to form a patterned radiated beam. A support configured to support, a substrate table configured to hold the substrate, a projection system configured to project a patterned radiation beam onto the target location of the substrate, and a radiation projection system. A lithography system including a detector configured to measure the intensity of radiation after passing through, an adjustable polarization conversion element, and a polarization analyzer in which the polarization conversion element and the polarization analyzer are supported by a patterning device. There is provided a lithography system that is sequentially arranged in the path of the radiated beam at a certain level.</p><p>[0021] According to another aspect of the invention, a lighting system configured to adjust the radiated beam and a patterning device capable of imparting a pattern to the radiated beam in cross section to form a patterned radiated beam. At the substrate level, with a support configured to support, a substrate table configured to hold the substrate, and a projection system configured to project a patterned radiated beam onto the target location of the substrate. An interference sensor configured to measure the wave front of a radiated beam, which has a detector and works in conjunction with the source module at the level of a patterning device to adjust the radiation and flood it from the pupil of the projection system. A lithography system is provided that includes a sensor and an adjustable polarizer configured to polarize the radiation in front of the projection system.</p><p>[0022] According to another aspect of the present invention, a method for determining the polarization characteristics of a lithography apparatus, the detector is used to obtain intensity measurements for a plurality of different settings of the polarization conversion element of the lithography apparatus. A method is provided that includes a step and a step of determining information about the polarization state of the radiation from the intensity measurements prior to encountering the polarization converting element.</p><p>[0023] According to another aspect of the present invention, a method for determining the polarization characteristics of a lithography apparatus, which is located in the lithography apparatus in front of the projection system of the lithography apparatus by using the interference sensor of the lithography apparatus. Steps to measure each wave plane of the radiation beam at the device substrate level for at least two different settings of the adjustable polarizer, and to determine information about the polarization-affecting properties of the projection system from the wave plane measurements. Methods are provided that include.</p><p>[0024] According to another aspect of the present invention, the projection lens polarization sensor configured to measure the polarization contribution generated from the projection lens of the lithography apparatus. A pinhole provided in a reticle arranged to be present in the reticle stage of a lithographic apparatus, configured to receive radiation from an illuminator, the radiation having a first polarization state, and a projection lens. With pinholes configured to transmit the first radiating beam through A first optical element located at the wafer level of the lithographic apparatus and configured to reflect the first radiated beam to generate a second radiated beam. A second optic configured to direct the second radiating beam to another component, A polarizer arranged to polarize the radiation received from the second optical element, A projection lens polarization sensor with a detector arranged to receive polarized radiation is provided.</p><p>[0025] According to another aspect of the invention, an illuminator configured to provide illuminator radiation with a first polarization state to the reticle level and radiation with a second polarization state projected onto the wafer level. The projection lens configured as described above and the pinhole provided in the reticle of the lithography apparatus to receive radiation from the illuminator having the first polarization state and transmit the first radiation beam through the projection lens. The first optical element, which is located at the wafer level and is configured to reflect the first radiation beam to generate a second radiation beam, and the second radiation beam are separated. A second optical element configured to direct the component of, a polarizer arranged to polarize the radiation received from the second optical element, and a detector arranged to receive the polarized radiation. Provided is a lithography projection system including a lithography projection system in which a projection lens sensor is configured to measure the polarization contribution generated from a projection lens.</p><p>[0026] According to another aspect of the present invention, there is a method of measuring the polarization state of radiation passing through a projection lens, the step of determining the input polarization state of the first radiation beam and the first through the projection lens. The step of directing the first radiated beam in the direction of, and the step of reflecting the first radiated beam as the second radiated beam in the second direction, which is almost opposite to the first direction at the wafer level, and the polarization at the reticle level. A method is provided that includes a step of reflecting the second radiated beam through the child as a third radiated beam and a step of measuring the intensity of the third radiated beam with a detector.</p><p>[0027] According to another configuration of the present invention, an active reticle tool having a carrier configured to couple to the reticle stage of a lithography apparatus, the first polarized light received from the illuminator at the first field point. A pinhole configured to receive a radiating beam with a state, a retarder rotatably coupled to a carrier and configured to delay the first polarization state of the radiating beam with a first polarization state. It comprises a polarizer configured to receive a delayed polarized beam and direct radiation in a predetermined polarization state to the detector, the detector being configured to perform multiple intensity measurements of radiation with a predetermined polarization state. Active reticle tools are provided.</p><p>[0028] According to the additional configuration of the present invention, an illuminator configured to supply radiation to the reticle stage and a radiation beam having a first polarization state received from the illuminator at the first field point are accepted. It has an active reticle tool with pinholes configured in, and a retarder rotatably coupled to the carrier and configured to delay the first polarization state of the radiating beam with the first polarization state. It comprises a polarizer configured to receive a delayed polarized beam and direct radiation in a predetermined polarization state towards the detector, the detector being configured to perform multiple intensity measurements of radiation with a predetermined polarization state. A lithography device is provided.</p><p>[0029] According to an additional aspect of the invention, a method of patterning a device in a lithography tool that includes a step of receiving radiation at the reticle stage corresponding to a first field point in the illuminator field is a first field. A step of applying a plurality of polarization delay conditions to the radiation corresponding to a point, and a step of directing a plurality of radiation beams derived from the plurality of polarization delay conditions toward a polarizing element configured to emit radiation having a predetermined polarization. And the step of measuring the radiation intensity of each of the plurality of radiation beams transmitted from the polarizing element, the step of determining the polarization condition of the radiation located at the first field point in the illuminator field, and the determined polarization condition. It features a step of adjusting the illuminator based on.</p><p>[0030] According to another aspect of the invention is a passive reticle tool comprising a carrier configured to be present in the reticle stage of a lithography apparatus and an array of polarization sensor modules associated with the carrier, the polarization sensor. A detector in which an array of modules is configured to receive illuminator radiation from an illuminator at multiple field points and an array of polarization sensor modules is configured to perform a set of intensity measurements of polarization derived from the illuminator radiation. A passive reticle tool is provided that is configured to output radiation to multiple delay conditions in which a set of intensity measurements is applied to the illumination radiation by an array of polarization sensor modules.</p><p>[0031] According to another configuration of the present invention, an illuminator configured to supply radiation towards the reticle stage and a passive reticle tool having a carrier located on the reticle stage of the lithographic apparatus and a carrier association. A lithography system including an array of polarization sensor modules, the array of polarization sensor modules is configured to receive illumination radiation from the illuminator at multiple field points, and the array of polarization sensor modules is derived from the illuminator radiation. Provided by a lithographic device configured to output radiation to a detector configured to perform a set of polarization intensity measurements and a set of intensity measurements corresponding to multiple delay conditions applied to the illumination radiation. Will be done.</p><p>[0032] According to another aspect of the invention, a method of patterning a device within a lithography tool, including a step of receiving radiation in a reticle stage corresponding to a first field point in the illuminator field. A step of providing an array of sensors configured to provide the polarization delay condition of the light to the received radiation, and a plurality of emission beams corresponding to the plurality of polarization delay conditions by scanning the array of sensors through the first field point. And the step of directing a plurality of radiating beams to a polarizing element configured to transmit radiation having a predetermined polarization, and measuring the radiant intensity of each of the plurality of radiating beams transmitted from the polarizing element. A method is provided that includes a step, determining the polarization conditions of the radiation located at the first field point in the illuminator field, and adjusting the illuminator based on the determined polarization conditions.</p><p>[0033] According to another aspect of the invention, a polarization analyzer that analyzes the polarization of a field in a radiation beam, having a first field stop arranged to pass through in a first region. The base member comprises a polarizing element arranged to polarize the radiated beam transmitted through the first region of the field stop, and the base member is analyzed by the first stage of the lithography apparatus in the first region of the field stop. A polarization analyzer is provided that is transferred to a position that matches the field to be used.</p><p>[0034] The polarization analyzer comprises a base member located so as to be located by the reticle stage (or substrate stage) of the lithography apparatus. The base member itself has a field stop and a polarizing element.</p><p>[0035] The field stop transmits radiation in the first region. Due to field stops, polarization state analysis is primarily concerned with information about the radiation transmitted by the first region.</p><p>[0036] The polarizing element polarizes the radiation transmitted from the field stop so that the polarized radiation can be used for analysis.</p><p>[0037] During production, the reticle stage of the lithographic apparatus places the reticle in the desired position with respect to the projection lens and illumination unit of the lithographic apparatus so that the pattern on the reticle is imaged on the substrate by the projection lens.</p><p>[0038] Using a polarization analyzer, the reticle stage transfers the field stop to the desired location within the radiation beam where the polarization radiation needs to be analyzed. Similarly, during manufacturing, the substrate stage transfers the substrate to the required location.</p><p>[0039] Therefore, the polarization analyzer is transferred to the reticle stage compartment without the risk of collision between the polarization analyzer and the reticle stage or substrate. That is, by transferring the polarization analyzer in the first stage, it is not necessary to place additional motors or combinations of some polarizing elements and some shutters in the area required by the first stage.</p><p>[0040] According to another aspect of the invention, a polarization sensor for a lithography apparatus comprising a polarization analyzer, which is arranged to measure radiant intensity in a measurement plane after passing through a field stop. The second stage of is provided with a polarization sensor characterized by a detector located in place in the radiant beam.</p><p>Transferring the detector in the second stage eliminates the need to place additional motors or combinations of some polarizing elements and some shutters in the area that the second stage also needs.</p><p>Embodiments of the present invention will be described below with reference to the accompanying schematics showing the corresponding parts with the corresponding reference numerals, but this is merely an example.</p>
[0062] In one embodiment, the polarization state is well defined and known during wafer exposure. Therefore, the image quality at the wafer level can be improved, and the line width becomes smaller especially with a projection lens having a large NA value. To measure and monitor the exact polarization state of the light used in wafer exposure, a wafer scanner must perform the polarization measurement. To quantify and monitor the illuminator with respect to polarization, the sensor can be placed at the reticle level. In addition, additional optics may be implemented at the wafer level to monitor or quantify the polarization behavior of the projection lens.
[0063] In some configurations of the present invention, the polarization sensor has two parts. The first part comprises an optical element (eg, a retarder or a polarization beam splitter) that processes the polarization of the illuminator light, which is referred to herein as a polarization sensor module. The second part has a detector. The detector measures the intensity of the light being processed. The polarization sensor module can include a group of parts that are physically contained together. The detector can be located at a relatively long distance from the polarization sensor module. However, in some configurations of the invention, the detector can be accommodated or placed in the vicinity of a component that includes a polarization sensor module.
[0064] Several field points are defined on the pupil to obtain a polarization map of the illuminator pupil. Polarization is measured at each field point using a minimum of three different configurations of polarization sensor modules. Three different measurements can define a polarized state if it is not related to a non-polarized state. Considering the unpolarized state, measurements obtained with four different configurations of the polarization sensor module are needed. Here, each configuration has different delay characteristics and belongs to a particular input polarization state. In general, the detector measures different intensities for all configurations for measuring each field point. Comparing the intensity measurements for each field point reveals the original polarization state of the light at that particular field point using calculations based on the Stokes vector. This can be done for all field points and a polarization map of the pupil can be created. The reason for using Stokes instead of Jones is that the Stokes vector contains unpolarized light, while the Jones vector does not.
The Stokes parameter can be derived from the measured intensity of the polarization spot in a certain combination between the input illumination polarization mode and the optical configuration of the polarization sensor module. The Stokes vector has four parameters S<sub>0</sub>~ S<sub>3</sub>(See Equation 1). SOP means a polarized state.<maths num="1"><img file="JP4717112B2_D0001.tif" /></maths>
[0066] Stokes parameters can be calculated, for example, by measuring and calculating the intensity transmitted by horizontal, vertical, 45 ° and combinations of left and right circular ligands. Four measurements per field point can be used to decompose all four components of the Stokes vector. Stokes vectors can be converted to Jones vectors using their respective E-field equations. Here, Δφ = φ<sub>y</sub>-φ<sub>x</sub>Represents the phase difference between normal and abnormal conditions (see Equation 2).<maths num="2"><img file="JP4717112B2_D0002.tif" /></maths>
[0067] To facilitate visualization, the polarization state is often defined by the polarization ellipse, especially its orientation and elongation. General parameterization uses the azimuth (or "rotation") angle α, which is the angle between the long and x-axis of the ellipse, and the ellipse angle ε, where tan (ε) is the ratio of the two axes. The ellipticity of tan (ε) = +/- 1 corresponds to perfect circular polarization. The relationship between this expression and the Stokes parameter is shown in Equation 3.<maths num="3"><img file="JP4717112B2_D0003.tif" /></maths>
[0068] Incident light Stokes vector S<sub>in</sub>Output state from S<sub>out out</sub>The optical component that changes the incident polarization state (due to reflection, transmission or scattering) can be described by the 4 × 4 Müller matrix M. This conversion is shown in Equation 4. M<sub>tot</sub>Is the product of n cascade components Mi.<maths num="4"><img file="JP4717112B2_D0004.tif" /></maths>
[0069] For example, in a system consisting of a rotational retarder and a polarizer, the output Stokes vector can be calculated using Equation 5 after multiplication of the individual Muller matrices. Where M<sub>pol</sub>And M<sub>ret</sub>Is the Muller matrix of the polarizer and the retarder, respectively. R (α) is a function of the angle of rotation α and is a rotation matrix representing the rotation of the retarder.<maths num="5"><img file="JP4717112B2_D0005.tif" /></maths>
[0070] As mentioned above, the unknown S<sub>in</sub>Use at least 3 measurements to resolve the 4 parameters of the vector. As mentioned above, there are four Stokes parameters, but there is some redundancy between them. Therefore, three measurements are sufficient to determine them in a normalized state, at least with respect to the overall intensity of radiation. In one embodiment, the unknown S<sub>in</sub>Use 4 measurements to solve the 4 parameters of the vector. Muller matrix M, each belonging to a different set of optical components in a defined manner<sub>tot</sub>By changing the contents of, four formulas can be obtained, from which the system of four unknown parameters can be solved. It will be apparent to those skilled in the art that more measurements can be used to resolve the four unknown parameters.
It should be understood that even when using less than two measurements, those measurements can be used to characterize the polarization state of the illuminator or projection lens. For example, a change in the polarization state of a wafer scanner when a single measurement is taken, i.e. when a fixed polarization state measurement is made and the measurement is repeated over a period of time, eg, between two wafer batches in a wafer fab. Can be detected. If this change exceeds a certain threshold, the wafer scanner may be calibrated or maintained.
[0072] The polarized light from the illuminator enters the polarization sensor module at an angle corresponding to the numerical aperture (NA). This is shown in Fig. 1. The polarized light passes through a first collimating lens, a mirror and a positive lens, both of which form beam shaping and collimating optics. A collimating lens is placed to radiate a parallel beam to the mirror. Mirrors are arranged to reflect light in the desired direction. The desired direction is perpendicular to the optical axis of the projection system. Due to the vertical and parallel beams, the polarization sensor module has a relatively low height (the optical axis of the projection system and the values along the sensor increase mechanically). The light then passes through the positive lens, field stop and lens and collimates the light again. A specific field point is selected using a field stop.
After passing through the beam shaping and collimating optics, the light enters the polarization state analyzer. A set of optics that affect the delay of light is used to switch the polarization state of incident light in a defined way. That is, the Tm and Te waves move to each other, resulting in a pure phase difference. The polarizer then selects one polarization. In the second part of the polarization sensor, the intensity of the desired polarization mode is detected by the camera.
Other locations of field stops are possible, but those skilled in the art will appreciate this.
[0075] FIG. 3 is a chart that discloses the interrelationship of features associated with a polarizing sensor arranged according to some embodiments of the present invention.
[0076] One difference is the polarization of the light passing through the projection lens and the polarization sensor module (A. Illuminator polarization sensor) configured to quantify the polarization of the light emitted from the illuminator on the one hand. Differences from polarization sensors configured to monitor / quantify (B. Projection Lens Polarization Sensors).
[0077] In one embodiment of the invention, the reticle tool comprises a carrier and a polarization sensor module. The polarization sensor can be equipped with additional wafer-level components (see Figure 2). The "wafer level" is the level at which the wafer is located during normal operation. "Reticle level" means the position between the illuminator of the lithographic apparatus and the projection lens. The reticle is at the "reticle level" during normal operation of the wafer scanner when illuminating the wafer.
[0078] The wafer scanner includes a reticle stage RS that supports and places the reticle R. In one embodiment of the invention, the reticle tool is configured to replace the reticle on the reticle stage. That is, the mechanical interface between the reticle stage and the reticle is the same as the mechanical interface between the reticle stage and the reticle tool. As a result, the reticle tool can be mounted in the manner of a product reticle. Therefore, the reticle tool is compatible with existing wafer scanners. The reticle tool is independent of the wafer scanner. Also, reticle tool authorization and calibration procedures can be performed outside the wafer scanner. The reticle tool can include one or more polarization sensor modules. The carrier of the reticle tool comprises a layer of well-known reticle material used in product reticle with circuit patterns during operation of the wafer scanner. Well-known reticle materials are extremely stable even with temperature changes, so the position of the module is stable. In addition, the reticle tool comprises marks configured to measure the position of the sensor module and the deformation of the reticle tool. Such measurements are performed on well-known sensors of European Patent Application EP 1267212, which are incorporated herein by reference.
[0079] Aspects of the present invention using the illuminator sensor polarization module (A) are classified into an active reticle configuration (1) and a passive reticle configuration (2). Active means that some parts of the polarization sensor module are movable and / or rotatable during polarization measurements, and passive means that all parts are on the carrier. It means that it is fixed to.
[0080] As shown in FIG. 3, in embodiments of the present invention, both the active reticle tool and the passive reticle tool can include retarders and wedge prisms (shown in FIG. 3 as "the same combination as the active reticle"). .. Alternatively, the passive reticle tool can include a birefringence prism.
[0081] In the configuration of the present invention where the camera (or other polarization detector) is located at the wafer level WS (see Figure 2), for example, with respect to the active reticle tool (Figure 3), the reticle tool is power, No interface is required for control signals (such as triggers to start measurement) and measurement results. Alternatively, with the active reticle tool, the camera may be installed at the reticle level.
[0082] In addition, FIG. 3 lists various types of projection lens polarization sensors (B) according to another embodiment of the present invention. The three common configurations shown in the figure are based on whether the light beam passes through the projection lens (PL) once, twice, or three times. In the projection lens polarization module, in addition to the components located at the reticle level, there are some additional optics at the wafer level.
A. Illuminator polarization sensor [0083] In the following embodiments, active and passive reticle tools including a collimation lens and a folding mirror are disclosed. By collimating the light received from the illuminator and reflecting it in the direction perpendicular to the optical axis of the illuminator, the reticle tool has a relatively low overall height and the tool has the same mechanical interface as the reticle stage. This allows the active or passive reticle tool to be used as a substitute for the product reticle on the reticle stage without having to reconfigure the reticle stage.
1. Active reticle tool [0084] According to one configuration of the present invention, the active reticle tool 40 (see FIG. 4) includes one optical channel with an active rotary retarder. The light emitted from the illuminator enters the collimating lens CL, is reflected by the prism PR1 at an angle of 90 °, exits from the positive lens PL1, and passes through the field stop (pinhole) FS. Light passes through the positive lens PL2 and the rotating retarder R, which can be configured, for example, as a quarter wave plate. The blue star plate (or "blue star element") BP is used as a polarizer, and the angle of the BP is at the blue star angle so as to reflect the polarized light while passing the light of another polarized state. Be placed. The blue star plate BP can be configured to reflect from the surface of the plate or as a prism that reflects polarized light on the inner surface of the prism. The light reflected on the surface of the BP is reflected by the mirror M, passes through the lenses L1 and L2, and enters the prism PR2. Light is directed to the lower detector D within the prism PR2. In one configuration, the detector D is a CCD chip. The reticle tool 40 also has a drive motor MR that can rotate the optical system. In different configurations, different types of motors are possible.
[0085] Preferably, the active reticle tool is configured to be coupled to the reticle stage of the lithographic apparatus, at which the active reticle tool is replaced with a reticle patterning on the substrate. In addition, the complete optical system of the reticle tool is preferably configured to rotate about the z-axis with respect to the carrier of the reticle tool. By rotating the optical system of the reticle tool, the first collimating lens changes its x and y axis positions. This is to measure some field points and assemble a polarized pupil map. Within the wafer scanner, the reticle tools are placed on a reticle stage configured to be movable in the y direction. The y-direction movement of the reticle stage supporting the reticle tool facilitates measurements at more positions. This means the active rotation of the field point on the reticle covering the field of x (eg by two DC motors) and the current reticle-y-motion that positions the channel in the y direction. In addition, dedicated data acquisition circuitry, power and communication are provided to allow two active rotations.
[0086] A camera (eg, a CCD chip) can be placed on a reticle-shaped tool, or a wafer level camera can also be used.
[0087] In this embodiment, the reticle tool 40 includes a first collimation lens CL and a folding mirror M. By collimating the light and reflecting it in the direction perpendicular to the optical axis of the illuminator, the reticle tool has a relatively low overall height and the tool has the same mechanical interface as the reticle stage. That is, the reticle tool can be placed on the reticle stage configured to support the product reticle without changing the reticle stage.
[0088] Obtaining data for this embodiment is relatively straightforward. Also, the intensity of the image does not have to be continuous. For example, parcelization does not affect the determination of the polarization state.
It will be apparent to those skilled in the art that the use of one optical channel for the measurement of several polarization states can reduce the calibration requirements. In addition, reticle tool calibration can be performed outside the machine using a defined light source.
Rotating retarder [0090] FIG. 5 (a) is a diagram showing a part of a polarization sensor including a rotary retarder R according to an embodiment of the present invention. For a rotary retarder (eg, a quarter wave), the delay of all incident light is affected by the same amount at at least four angles around its axis (Figure 5a). The rotational movement can be performed, for example, by a tiny worm wheel structure.
[0091] In the embodiment shown in FIG. 5 (a), the detector is camera C, but may be a photocell or a photomultiplier tube. It should be understood that any detector configured to detect intensity can be used.
[0092] However, the rotation of the retarder can be measured using other devices such as CCD cameras. The angle of rotation of the retarder does not need to be controlled accurately. This is because the angle of rotation can be checked, for example, by attaching a small radial marker on the retarder and forming the marker on the camera. From this image marker position, the exact rotation of the retarder can be derived and corrected for the future. Placing a small radial marker at a large radial distance from the retarder's axis of rotation can result in a relatively low resolution of the CCD camera, but it is still possible to accurately determine the position of rotation of the retarder.
Iterative measurements of a given rotation angle of the retarder and the optical system of the reticle tool can be performed to average the angle positioning errors that can occur in a single measurement.
[0094] In one embodiment, the detector is located at the wafer level. After passing through the reticle tool, the light will pass through the projection lens system and reach the detector. Light passes through the projection lens system at the same position (ie, the same portion of the projection lens cross section) where the effects of the projection lens system are equal. This is because the polarizer of the reticle tool makes the same rotation with respect to the projection lens system. Therefore, the light passing through the projection lens system is constant.
[0095] FIG. 5 (b) is a diagram showing a spring-loaded retarder 50 configured according to another embodiment of the present invention. In this case, the two separate cylinders 52 each include two optical retarders 54. In the illustrated configuration, the cylinders 52 can be displaced from each other to provide, for example, a possible combination of four retarders of light passing from left to right. As a result, four angles of rotation of light are obtained.
Wedge prism [0096] In another embodiment, instead of using the active rotary retarder described above, two wedge prisms fixed on the reticle (see Figure 6) can be used to cause beam delay.
2. Passive reticle tool Birefringence prism [0097] In one embodiment using wedge prisms, the four thin birefringent wedge prisms BR and the polarizer P are imaged and polarized so that multiple mesh fringes are generated on a detector such as a video camera's CCD image sensor. Built into the child (see Figure 6). The generation of these fringes is based on the fact that the light passing through the wedge prism makes different rotations as a function of position. That is, each wedge prism consists of a pair of wedges of material whose optical axes rotate with each other by, for example, 90 ° between the wedges. Considering only one of the pair of wedges inside the prism, the physical thickness of the wedge changes as a function of position along a given direction, eg, along the y direction in the first wedge prism. Is clear. Therefore, the degree of light delay also changes along the y direction, and the polarization direction of the light emitted from the wedge changes as a function of the y position. As a result, the component of the polarized light parallel to the direction of the polarizer as a function of the y position changes, and the light transmitted by the polarizer as a function of the y position (only the light parallel to the direction of the polarizer is transmitted). ) Changes in strength. The optical orientation of the crystal forming the second wedge is rotated 90 ° with respect to the first wedge so that the effect of changing rotation as a function of position is not canceled by the second wedge. Therefore, although the physical thickness along the Y direction is constant, the effective light rotation may change. Information for determining the two-dimensional distribution of the polarized state can be obtained by Fourier analysis of the obtained fringe. No mechanical or active element is used to analyze the polarization, and all parameters related to the space-dependent monochrome Stokes parameters corresponding to the azimuth and ellipticity angles can be determined from a single frame.
[0098] In the configuration shown in Figure 6, two wedges arranged in series, consisting of a total of four wedge pairs with the high speed axes of the four wedges facing 0 °, 90 °, 45 °, and -45 °. There is a prism. The wedge angles of both prisms shall be small enough to neglect refraction at the inclined contact surfaces. The resulting intensity pattern detected by the detector is usually a mesh shape with intensity varying in the x and y directions. Fourier analysis of the intensity mesh can reconstruct the two-dimensional distribution of the input polarization state of light received through a pinhole at a given field position. The measurement resolution of the two-dimensional polarization state distribution can be optimized by properly selecting the wedge angle that determines how quickly the polarization delay of the emitted light changes with the x and y axis positions and the resolution of the camera.
[0099] In one embodiment, the detector is located at the wafer level. After passing through the reticle tool, the light will pass through the projection lens system and reach the detector. Light passes through the projection lens system at the same position (ie, the same portion of the projection lens cross section) where the effects of the projection lens system are equal. This is because the polarizer of the reticle tool makes the same rotation with respect to the projection lens system. Therefore, the light passing through the projection lens system is constant.
[00100] Iterative measurements of a given rotation angle of the retarder and the optical system of the reticle tool can be performed to average the angle positioning errors that can occur in a single measurement.
[00101] In one embodiment of the invention, the passive reticle shaping tool comprises a plurality of optical channels. First, it is preferred that at least four different channels, each with a different angle of rotation of the retarder, be used for each field point, as described below in connection with FIGS. 8 (b) and 8 (c). .. In addition, these optical channels are copied and placed in the x direction of the reticle to select field points in the x direction. Different channels can be placed in the y direction using the current reticle-y-motion.
[00102] Since different channels are used to measure polarization at one field point, these channels (with optical paths) need to be calibrated.
[00103] There are several variants that are measured after the polarization is split after a retarder delay at a fixed angle. This is done, for example, by a birefringence prism BRFP based on the Blue Star Plate BP (FIG. 7) or the Wallaston prism (FIG. 8 (a)).
[00104] A blue star plate is a plate that operates at a blue star angle (also known as a polarization angle). When light moves between two media with different indices of refraction, p-polarized light with respect to the interface does not reflect off the interface at one particular angle of incidence known as the Bruster angle.
[00105] The calculation formula is as follows. [00106] θ<sub>B</sub>= arctan (n<sub>2</sub>/ n<sub>1</sub>) [00107] However, n1 and n2 are the refractive indexes of the two media.
[00108] Since all p-polarized light is refracted, any light reflected from the interface at this angle must be s-polarized. Therefore, the glass plate arranged at the Blue Star angle in the light beam can be used as a polarizer.
[00109] FIG. 10 is a diagram showing the interaction between the unpolarized wave and the surface. In the case of randomly polarized light incident at the Blue Star angle, the reflected and refracted light forms an angle of 90 ° with each other.
[00110] Air (n<sub>1</sub> 1) Glass medium (n)<sub>2</sub>In the case of 1.5), the blue star angle of visible light is about 56 ° with respect to the perpendicular. The index of refraction of a given medium varies with the wavelength of light, but usually does not vary much. For example, the difference in refractive index between ultraviolet light (about 100 nm) and infrared light (about 1000 nm) inside the glass is about 0.01.
[00111] The Walston prism is a useful optical device for manipulating polarized light. The Walston prism separates randomly polarized or unpolarized incident light into two orthogonal linearly polarized emission beams. Since the beams are separated in space, the intensities of the two different beams can be measured with a detector, from which information about the polarization of the light can be derived. For example, the prism can be configured to output horizontally and vertically polarized beams, with the difference in beam intensity in two different orientations measured by the detector corresponding to the Stokes parameter S1 (see above).
[00112] The Walston prism consists of two orthogonal birefringent prisms, such as the Calcite prism, which is joined on a base to form two right triangle prisms with a vertical optical axis. The emitted light beam diverges from the prism, resulting in two polarized rays whose divergence angle is determined by the wedge angle of the prism and the wavelength of the light. Commercially available prisms with divergence angles of 15 ° to about 45 ° are available.
[00113] The extinction ratio of both devices is estimated to be greater than 1: 300.
[00114] FIG. 8B is a diagram showing a passive reticle system 80 configured according to an embodiment of the present invention. System 80 includes a 3x4 array of polarization sensor modules 82. The sensor module 82 includes a field stop 84 configured to direct light into the sensor module. FIG. 8 (c) is a detailed view of the polarization sensor module 82. The light that passes through the field stop 84 is reflected by the mirror 86, passes through the fixed retarder 87, is reflected by the blue star plate polarizer (prism polarizer), and is emitted from the collimator lens 89. The reticle system 80 is preferably configured to be replaceable with the reticle used in the lithography tool. When the tool 80 is placed in the reticle stage, the field stop 82 samples different field points. In one embodiment of the invention, each of the four sensor modules in the "column" is composed of different effective retarders. That is, the detector that measures the light emitted from all four sensor modules 82 in the column receives four different amounts of delayed light. The reticle system is preferably configured to translate within the illuminator radiation field, for example by applying x or y motion to the reticle stage. 4 Sensor Modules By translating along a direction parallel to the column, each sensor module can block a common field point, a series of four measurements corresponding to each measurement for each sensor module in the column. The value can be recorded. Therefore, four different delay conditions can be recorded for a given field point. In principle, by properly configuring the retarder in each column, complete polarization information corresponding to the position of each column can be obtained. Each polarization sensor module is equipped with a movable shutter that can block radiation from the illuminator to prevent radiation from entering other sensor modules at the same time while receiving radiation from the illuminator at a given time in a single sensor module. As specified
[00115] In one embodiment of the invention, as shown in FIG. 8 (b), the three columns of the sensor module 82 are asymmetrically arranged on the reticle system 80. In this illustrated example, each column represents a fixed Y position with respect to the illuminator. Therefore, the reticle system 80 can be used to measure at least three different Y-field positions. By replacing the reticle system 80 with another 3-column system with different column positions in the Y direction, a total of 6 different y positions can be measured with a single reticle change.
[00116] For example, in one embodiment of the invention shown in FIGS. 7 and 8 (b), the detector can be placed near the collimating lens. However, in some embodiments, the detector is located at the wafer level and receives the radiation reflected by the blue star plate. In the latter case, the reflected light is detected after passing through the projection lens. As described below, in other configurations of the present invention, the effect of the projection lens on the polarization can be measured independently.
B. Projection lens Polarization sensor [00117] In general, a projection lens can affect the polarization state of light passing through the projection lens. The final polarization of light after passing through a projection lens also depends on the polarization settings of the illuminator and which part of the lens is exposed. The contribution of the projection lens to the polarization state can be measured using a reticle-level illuminator polarization sensor (on an active or passive reticle) and an additional optical system that handles reticle and / or wafer-level polarization. Three configurations including a one-pass system, a double-pass system, and a triple-pass system are shown in FIGS. 9a to 9c. For convenience, only one optical path passing through the center of the lens is shown. Preferably, the standard illuminator polarization state is defined and fine-tuned by the illuminator polarization sensor before measuring the contribution to projection lens polarization. Therefore, the input polarization state (polarization state of the light incident on the projection system) can be accurately known. In one aspect of the invention, at least four well-defined input polarization states (in terms of Stokes vectors) are used.
[00118] One-pass system [00119] In a one-pass system (see Figure 9 (a)), the light from the illuminator IL, which has a well-known polarization state, is reticle-level pinhole P, projection lens PL, optional rotary retarder (not shown) and wafer level. It passes through a wafer-level polarizer P at a short distance above the camera C in WS. In one embodiment, the light enters the polarizer after passing through a collimator and a rotary retarder (not shown).
[00120] FIG. 9B is a diagram showing an embodiment of the present invention that employs a double path system. The light passes through the projection lens a second time after being reflected by the mirror located at the wafer level and then through the rotating retarder (not shown for clarity) and the polarizer P at the reticle level, where the camera Measures the intensity of polarized light. This wafer level mirror M displaces the incident beam in the (x, y) (horizontal) direction so that the reflected beam can be received by the reticle level mirror and then detected by the camera. For example, this can be done by configuring the wafer level mirror as a cube edge mirror. The xy shift is minimized to ensure approximately the same optical path through the lens for the first and second light passing through the projection lens. That is, the light incident on the wafer level mirror M can be slightly horizontally displaced at the mirror level and reflected in the opposite direction, but substantially parallel to the incident light. Thus, the optical path length, direction, and position within the projection lens PL are approximately the same for both incident and reflected light. The ability to produce nearly similar incident and reflected beams depends on the position and alignment of the reticle-level mirror with respect to the remaining optics. Precise determination of reticle-level mirror position and alignment for the remaining optics can be performed outside the wafer scanner. As shown in Figure 9 (b), the double path configuration does not require a detector / polarizer system at the wafer stage level.
[00121] In another double-pass configuration, the first light beam incident on the wafer level mirror M is reflected towards the reticle level as a second light beam at the wafer level with virtually no xy translation applied. It almost overlaps with the light beam of 2. In this configuration, the second light beam achieves a different optical attribute than the first light beam, which allows the second light beam to be directed at the polarizer and the camera, as shown in Figure 9 (b). To do. For example, as shown in detail in FIG. 9 (d), a beam splitting polarizer PBS is provided under the pinhole FS supplied to the reticle. In one example, the randomly polarized light 1 incident on the beam splitter PBS is Y-polarized 2 after passing through the polarization beam splitter. After passing through the beam splitter, the light passes through the retarder R (such as a quarter wave plate) and becomes circularly polarized, as shown as right circularly polarized light 3 in FIG. 9 (d). After being reflected by the wafer-level mirror M, the light becomes left-handed circularly polarized 4, passes through the quarter-wave plate, becomes x-polarized 5, and is reflected by the beam splitter PBS to reach the reticle-level detector D. Therefore, the reflected light does not need to be translated in the xy direction at the wafer level to be detected by the reticle level detector. It should be noted that projection lenses can generally affect circular polarization. For example, light can be elliptically polarized. Further, the light 4 incident on the quarter wave plate may be elliptically polarized instead of circularly polarized. However, there is a reason for such an effect, and in fact it provides information about the effect on the polarization of the projection lens.
[00122] In the configuration of the present invention that employs a triple pass system (see FIG. 9 (c)), light passes through the projection lens three times. In the configuration shown in FIG. 9 (c), the light is first reflected by the wafer level mirror M, then reflected a second time by the reticle level mirror M2, and then the light is reflected toward the wafer stage by the mirror M3. It passes through and is processed by the polarizer P and is measured by a detector (such as camera C) at wafer level WS. As shown, the polarizer does not have to be located near the wafer level detector, but may be located at the reticle level.
[00123] Further, a triple-pass system with optics that allow the reflection of the first beam without horizontal displacement is possible, as described above for double-pass systems.
[00124] As shown in Figures 9 (b) and 9 (c), the reticle tool contains almost all optics used to perform polarization measurements on the projection lens, so when no measurements are taken. , They do not have to be in the wafer scanner. The reticle tool can be removed from the wafer scanner, for example, to calibrate the position of the tool's two optical mirrors. This improves the measurement quality.
[00125] Collimating lenses (not shown) can be used in front of the polarizer in all three systems (one-pass, double-pass and triple-pass). This reduces the requirement that the delay error of the polarizing element be small for incident light at high NA values.
[00126] The one-pass system has the advantage that existing cameras can be used at the wafer level. The double pass system uses a different camera at the reticle level. One advantage of the double-pass configuration shown in Figure 9 (b) is that it can mount most of the optical components, including pinholes, polarizers, cameras, and reticle-level mirrors (but not wafer stage reflectors (mirrors)). The point is that it can be configured as part of a reticle shape tool. Since no wafer level camera is used, the reflector can be placed anywhere on the wafer stage.
[00127] Further, it should be noted that in the configuration of the triple-pass system shown in FIG. 9 (c), the measured polarization effect applied by the projection lens is essentially the same as in the double-pass system configuration. That is, the polarizers in FIGS. 9 (b) and 9 (c) are in a position to capture light after passing through the projection lens twice in common. As shown in FIG. 9 (c), the intensity of polarized light emitted by the polarizer and measured by the detector must not be affected by whether or not the light passes through the projection lens.
Those skilled in the art will appreciate that the present invention can be practiced in other particular forms without departing from its spiritual or essential characteristics. Therefore, it should be construed that the embodiments disclosed herein are exemplary in all respects and do not limit the invention. For example, the present invention also applies to wafer scanner lithography equipment or wafer steppers similar to flat panel displays, PCBs and the like. The present invention also applies to catadioptric systems.
[00129] The meaning of its equivalent and all variants within its scope are included in it.
Those skilled in the art will appreciate other embodiments, uses and advantages of the invention in light of the specification and practices of the invention disclosed herein. The specification should be considered merely as an example, and the scope of the present invention is limited only by the appended claims. The above description is an example and does not limit the present invention. Therefore, it will be apparent to those skilled in the art that modifications can be made to the present invention without departing from the scope of the appended claims.
[00131] FIG. 11 is a diagram showing a lithography apparatus according to an embodiment of the present invention. The device of FIG. 11 is configured to support an illumination system (illuminator) IL configured to adjust the emission beam PB (eg UV emission or EUV emission) and a patterning device (eg mask) MA. To hold a support structure (eg, mask table) MT connected to a first positioner PM configured to accurately position the patterning device according to certain parameters, and a substrate (eg, resist coated wafer) W. A substrate table (eg, a wafer table) WT connected to a second positioner PW configured to accurately position the substrate according to certain parameters and applied to the emission beam B by the patterning device MA. It comprises a projection system (eg, a refraction projection lens system) PS configured to project the pattern onto a target portion C (eg, including one or more dies) of the substrate W.
Lighting systems provide various types of optics, such as refraction, reflection, magnetism, electromagnetics, static electricity, or other types of optical components, or any combination thereof, that direct, shape, or control radiation. Can contain components.
[00133] The support structure supports the patterning device, i.e., its weight. The support structure holds the patterning device in different ways depending on the orientation of the patterning device, the design of the lithographic device, and other conditions such as whether the patterning device is held in a vacuum environment or not. The support structure can hold the patterning device using mechanical, vacuum, electrostatic or other clamping techniques. The support structure is, for example, a fixed or movable frame or table as needed. The support structure can ensure that the patterning device is in the desired position, eg, with respect to the projection system. The term "reticle" or "mask" herein is synonymous with the more general term "patterning device".
[00134] The term "patterning device" as used herein should be broadly construed as referring to any device that applies a pattern to the cross section of a radiating beam to form a pattern on the target portion of the substrate. is there. The pattern applied to the radiated beam may not accurately correspond to the desired pattern of the target portion of the substrate. For example, the pattern may include a phase shift function or a so-called assist function. In general, the pattern imparted to the radiated beam corresponds to a particular functional layer within the device created in a target portion such as an integrated circuit.
[00135] The patterning device is transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography and include mask types such as binary, alternating phase shifts, and attenuation phase shifts as well as various hybrid mask types. An example of a programmable mirror array uses a matrix configuration of small mirrors, each tilted to reflect an incident radiating beam in different directions. The tilted mirror imparts a pattern within the radiated beam, which is reflected by the mirror matrix.
[00136] The term "projection system" as used herein refers to refraction, reflection, reflection refraction, magnetic, electromagnetic and electrostatic suitable for the exposure radiation used or other factors such as the use of immersion liquid or vacuum. It should be broadly interpreted as including any type of projection system, including optical systems, or any combination thereof. When the term "projection lens" is used herein, it is always synonymous with the more general term "projection system".
[00137] The apparatus shown herein is a transmissive type (eg, using a transmissive mask). Alternatively, the device may be reflective (eg, using a programmable mirror array of the type described above, or using a reflective mask).
[00138] The lithographic apparatus may be of the type having two (dual stage) or more substrate tables (and / or two or more mask tables). In such a "multistage" machine, additional tables can be used in parallel. Alternatively, the preparatory process can be performed on one or more tables while using one or more other tables for exposure.
[00139] The lithographic apparatus may be of a type in which at least a part of the substrate is covered with a liquid having a relatively high refractive index such as water so as to fill the space between the projection system and the substrate. Immersion techniques that increase the numerical aperture of projection systems are well known in the art. As used herein, the term "immersion" does not mean that a structure such as a substrate must be immersed in a liquid, but simply that the liquid is located between the projection system and the substrate during exposure. is there.
[00140] With reference to FIG. 11, the illuminator IL receives a radiation beam from the radiation source SO. The source and the lithographic apparatus may be different entities, for example, when the source is an excimer laser. In such cases, the source is not considered to form part of the lithography equipment and the radiated beam is lined with the help of a beam transmission system BD, eg, equipped with a suitable induction mirror and / or beam expander. It is transmitted from the source SO to the illuminator IL. In other cases, the source may be an integral part of the lithographic apparatus, for example in the case of a mercury lamp. The source SO and illuminator IL and, if necessary, the beam transmission system BD may be referred to as a radiation system.
[00141] The illuminator IL can include an adjuster AD that adjusts the angular intensity distribution of the radiated beam. In general, at least the outer and / or inner radial ranges of the intensity distribution within the illuminator's pupil plane (commonly referred to as σ-outer and σ-inner, respectively) can be adjusted. In addition, the illuminator IL includes a variety of other components, such as the integrator IN and the capacitor CO. The illuminator can be used to adjust the radiated beam so that it has the desired uniformity and intensity distribution in cross section. The illuminator also controls the polarization of the radiation, which does not have to be uniform across the cross section of the beam.
[00142] The radiated beam B is incident on a patterning device (eg, mask MA) held on a support structure (eg, mask table MT) and is patterned by the patterning device. After passing through the mask MA, the radiated beam B passes through the projection system PS, which focuses this beam on the target portion C of the substrate W. Using a second positioner PW and position sensor IF (eg, interferometer, linear encoder or capacitive sensor), the substrate table WT is precisely placed in the path of the radiation beam B, eg, a different target portion C. Can be moved. Similarly, for example, after mechanically searching from the mask library or during scanning, mask MA with respect to the path of radiated beam B using the first positioner PM and another position sensor (not shown in FIG. 1). Can be placed accurately. In general, the movement of the mask table MT can be achieved with the help of long stroke modules (coarse positioning) and short stroke modules (fine positioning) that form part of the first positioner PM. Similarly, the movement of the substrate table WT can be realized by using the long stroke module and the short stroke module which form a part of the second positioner PW. However, in the case of a stepper (unlike a scanner), the mask table MT may be connected only to the short stroke actuator or may be fixed. The mask MA and the substrate W may be aligned using the mask alignment marks M1 and M2 and the substrate alignment marks P1 and P2. Although the illustrated substrate alignment mark occupies a dedicated target position, it may be placed in the space between the target portions (known as a scribe lane alignment mark). Similarly, in cases where two or more dies are provided on the mask MA, a mask alignment mark can be placed between the dies.
[00143] The illustrated device can be used in at least one of the following modes:
[00144] 1. In step mode, the mask table MT and the substrate table WT are kept essentially stationary and the entire pattern applied to the radiated beam is projected onto the target portion C in one go (ie, single). Static exposure). The substrate table WT is then shifted in the X and / or Y directions to expose different target portions C. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged with a single static exposure.
2. In scan mode, the mask table MT and the substrate table WT are scanned synchronously (ie, single dynamic exposure) while the pattern applied to the emitted beam is projected onto the target portion C. The speed and direction of the substrate table WT with respect to the mask table MT are determined by the magnification (reduction ratio) and image inversion characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width of the target area (width in the non-scanning direction) in a single dynamic exposure, and the length of the scanning motion determines the height of the target area (height in the scanning direction). decide.
[00146] 3. In another mode, the mask table MT is kept essentially stationary to hold the programmable patterning device. The substrate table WT is moved or scanned while the pattern applied to the radiated beam is projected onto the target portion C. In this mode, a pulsed radiation source is typically used. During the scan, the programmable patterning device is updated as appropriate each time the substrate table WT moves or during continuous radiation pulses. This mode of operation is readily applicable to maskless lithography using programmable patterning devices such as the type of programmable mirror array referenced above.
[00147] The combination of usage modes described above and / or a modified form thereof, or a completely different usage mode may be adopted.
[00148] Another embodiment of the present invention is shown in FIG. 12 as a schematic diagram of an arrangement configuration for measuring the polarization state of projected radiation at the reticle level. The illuminator IL and the projection system PS are shown in Figure 11. At the reticle level and in the form of intervening in the beam path, there is an adjustable polarization converter 10 and a polarization analyzer 12 behind it. In this example, the analyzer 12 is a linear polarizer, such as a beam splitter cube with a first fixed rotational orientation that transmits only the radiating component having an electric field vector in a particular direction. The polarization conversion element 10 is a retarder or delay plate, and in one embodiment, is a quarter wave plate of a specific wavelength of illumination radiation. The quarter wave plate introduces a B / 2 relative phase shift between the orthogonal linearly polarized components of the incident radiation. It converts properly oriented linearly polarized radiation into circularly polarized radiation and vice versa. Generally, a quarter wave plate converts a normal elliptically polarized beam into another elliptically polarized beam.
[00149] The polarization conversion element 10 is adjustable so that the induced polarization switching varies. In one form of adjustment, the polarization transforming element 10 is rotatable and its spindle orientation can be adjusted. In another embodiment of this example, the polarization conversion element 10 is replaced by several differently oriented polarization conversion elements that can be inserted into each beam path. The polarization conversion element 10 can be completely removed and replaced with a polarization conversion element 10 having a different orientation, or a plurality of polarization conversion elements having different orientations are integrally provided on a carrier like a reticle, for example, in the form of an array. it can. Next, by translating the carriers, the polarization conversion element corresponding to an arbitrary specific field point can be adjusted.
[00150] In this embodiment of the present invention, a detector 14 is provided that detects the intensity of radiation after it has passed through the projection system PS. The detector 14 can use the pre-detector provided in the base table. One form is a spot sensor that measures the radiant intensity at a particular field point. Another form is a CCD camera provided for wave surface measurement. The CCD camera can have an aperture or pinhole on the focal plane of the projection system to select the desired field point. The CCD sensor itself is then defocused, and each pixel of the CCD detects radiation that crosses a particular path through a projection system and reaches its field point. That is, each pixel corresponds to a point within the pupil plane of the projection system (or the pupil plane of the illuminator).
[00151] A configuration known in the field of ellipsometry is provided with a quarter wave plate followed by a linear polarizer and detector to generate a polarized state of incident radiation, eg, reticle-level radiation. Several intensity measurements are taken in different rotation orientations of the quarter wave plate, and these values are converted and radiated to quantify the polarization state represented according to suitable criteria such as Stokes parameters. A Stokes vector that characterizes is provided. Details on ellipsometry and how to obtain Stokes parameters can be found in any suitable optical textbook such as "Principles of Optics", M Born and E Wolf, 7th Edition, Cambridge University Press (1999). Has been done. At least three intensity measurements are required corresponding to the three rotation positions of the quarter wave plate. There are four Stokes parameters, but there is some redundancy between them. Therefore, three measurements can determine them at least in a normalized state with respect to the overall intensity of radiation.
[00152] According to one embodiment of the invention, the controller 16 receives a measurement from the detector 14, thereby coordinating with the control and / or detection of the adjustment of the polarization transforming element 10, such as the direction of rotation, respectively. Polarized states such as Stokes parameters can be calculated for pupil pixels. You can move the detector to repeat the measurement at different field points.
[00153] The question arises if this is true when the detector 14 is not immediately behind the analyzer 12 (such a position is the ideal detector position). On the contrary, the polarization effect of the projection system PS is unknown. However, it should be understood that the analyzer 12 is immediately after the polarization conversion element 10. Since the detector 14 is not affected by changes in polarization, it does not matter that there is a separate component between the analyzer 12 and the detector 14. This situation can be considered as follows. The radiation emitted from the polarization conversion element 10 is the Stokes vector S.<sub>in</sub>If it has a polarized state represented by, S<sub>out out</sub>The polarization state emitted from the analyzer 12 called the analyzer 12 represents the operation of the analyzer 12 (linear polarizer).<sub>pol</sub>S<sub>in</sub>Obtained by multiplying by. The coordinate system can be arbitrarily selected so that the analyzer 12 is a polarizer in the X direction. Therefore, the polarization state (Stokes vector) of the radiation at the ideal detector position is as follows.<maths num="6"><img file="JP4717112B2_D0006.tif" /></maths>
The irradiance measured by the detector is given by the first component of the Stokes vector and is:<maths num="7"><img file="JP4717112B2_D0007.tif" /></maths>
[00155] In the actual situation shown in Figure 12, the general Muller matrix Mgen can be used to represent the effects of the projection system and the non-ideal state of the detector.<maths num="8"><img file="JP4717112B2_D0008.tif" /></maths>
[00156] Therefore, the irradiance measured by the detector is as follows.<maths num="9"><img file="JP4717112B2_D0009.tif" /></maths>
[00157] m<sub>11</sub>And m<sub>12</sub>Is a divisor (m) that is a component of the Muller matrix that represents the projection system<sub>11</sub>+ m<sub>12</sub>) Aside, this value is equal to the above result for an ideal detector located immediately after the analyzer. Therefore, it is not necessary to know the value of this factor because the measured value detected by the detector 14 is not affected by the calculation of the ellipsometry method, apart from the constant factor. Therefore, the polarization characteristics such as the degree of polarization at the reticle level and the purity of polarization can be completely determined. The effect of the projection system is almost completely eliminated by placing the polarizer 12 at the reticle level. Only strength changes. Therefore, the polarization conversion element 10, the analyzer 12, and the detector 14 all include an illumination polarization sensor having a detector located at the wafer level rather than the reticle level.
[00158] As mentioned above, the factor (m<sub>11</sub>+ m<sub>12</sub>You don't need to know the value of). However, it is useful to obtain this information, especially when the value of this factor is not constant in the pupil region. If this value fluctuates in the region of the pupil, the operator does not know whether this is due to the polarization characteristics of the projection system or due to incomplete illumination radiation. For example, in quadruple illumination mode combined with tangentially polarized light, two poles are less bright than the other two poles. This is due to the asymmetry of the lighting system or the residual linear polarization effect of the projection system. Appropriate correction is possible by identifying the cause. To identify the cause (the asymmetry or the residual polarization effect), the analyzer 12 is rotated to a second fixed direction of rotation and the Stokes parameter is measured again. From the two measurement sets, the contribution of the projection system and the lighting system as separate entities can be identified.
[00159] FIG. 13 shows another embodiment of the present invention. In this example, the polarization converter 10 and analyzer 12 are integrated into a carrier 18 that can be inserted into a lithography system instead of a reticle. The radiation 20 from the illuminator is incident on a pinhole 22 having a diaphragm in an opaque layer such as chromium formed on the upper surface of the carrier 18. In one embodiment, the polarization conversion element 10 is a quarter wave plate such as a low order quarter wave plate that minimizes thickness and is made of a suitable material such as quartz. The analyzer 12 of this embodiment does not simply block or absorb one linearly polarized light component, but is a prism made of birefringent material arranged so that the two orthogonally linearly polarized light components are separated in space, that is, a polarized beam. It is a splitter. According to one form, the prism comprises two wedges of birefringent quartz crystal in contact with each other. However, in one wedge the main optical axis of the crystal is in the X direction and in the other wedge it is in the Y direction (ie, in the shape of a Wollaston prism). A suitable birefringent material that can be used to make prisms and for short wavelength illumination radiation is KDP (potassium phosphate).
[00160] The effect of the polarization beam splitter as the analyzer 12 is that when the illumination radiation is viewed from below, two pinholes are aligned, the radiation from one pinhole is polarized along the X axis, and the radiation from the other pinhole. It means that the radiation is polarized along the Y axis. The second pinhole 24, which is an integral part of the detector, can be placed on the focal plane of the projection system to selectively transmit one polarized image of the first pinhole 22 and block the radiation of the other. .. A defocusing detector 14, such as a CCD, measures the intensity of multiple pixels corresponding to the position of the projection system and illuminator in the pupil plane.
[00161] For one of the polarized images not transmitted by the second pinhole 24, the device can be used to determine the polarization state of the reticle-level illumination radiation in exactly the same way as described with reference to FIG. The carrier 18 can include a plurality of pinholes 22, a polarization conversion element 10, and an analyzer 12, and the polarization conversion element 10 has a high-speed axis in the X direction, the Y direction, and 45 ° with respect to the X and Y directions. Can be turned in various directions, such as pointing. By translating the carrier 18, the polarization conversion element corresponding to a specific field position can be adjusted, and the ellipsometry measurement can be performed in the same manner as described above. The procedure for moving the second pinhole 24 to select orthogonally polarized radiation is equivalent to rotating the analyzer 12 in FIG. 12 by 90 °. Therefore, further measurements can be easily performed to obtain information that characterizes the polarization state of the radiation. As already mentioned with reference to FIG. 12, the contribution of the projection system and the illuminator can be split by using the second pinhole 24 to select two different polarizations, but it is used as the analyzer 12 in FIG. Since the polarization beam splitter functions as two orthogonal linear polarizers at the same time, it is not necessary to have a rotatable or removable / interchangeable analyzer 12 in this case.
[00162] Another embodiment of the present invention for measuring the polarization characteristics of a projection system will be described. A measuring device for measuring the wave surface aberration of a projection system using a principle known as a "shearing interferometer" has been proposed. According to this proposal, different parts of the beam from a particular location at the level of the patterning device are transmitted along different paths through the projection system. This can be achieved by a diffraction element in the beam between the illuminator system and the projection system. Diffractive elements, such as gratings, also known as object gratings, diffract and disperse radiation through a projection system along a number of different paths. The diffraction element is usually placed at a level where a patterning device such as a mask MA is located. Diffractive elements are appropriately sized gratings or arrays of features that can be placed in bright areas within the dark field reticle. This region is small relative to the object field size of the projection system (ie, small enough that the aberration of the image is approximately independent of the position of the object points in that region). Such areas can be embodied as pinholes. As described above, for example, the object lattice or a diffraction feature such as a lattice pattern, or a structure such as a checker board pattern can be provided inside. However, this is in principle an option (eg, in the first embodiment of the invention, a pinhole can be used to select a smaller portion of the field, in one embodiment there is no structure within the pinhole). .. The function of the pinhole and its optional internal structure is to define preselected mutual coherence with a local maximum of mutual coherence within the pupil of the projection system. The preselected mutual coherence is associated with the internal structure of the pinhole and its options by the spatial Fourier transform of the pinhole and its structure. More information about patterns within pinholes can be collected from US Patent Application No. 2002-0001088. It is also possible to associate one or more lenses with the diffraction element.
[00163] With reference to FIG. 14, the source module SM used in one embodiment of the present invention is shown. The source module SM is provided with an opaque chromium layer similar to a reticle on one side, and a pinhole plate PP which is a quartz glass plate in which a pinhole PH is provided in the chromium layer. The source module also includes a lens SL that focuses the radiation on the pinhole. In fact, an array of pinholes and lenses for different field positions and different slit positions is provided, and the lenses can be integrated onto the top of the pinhole plate. Ideally, the source module produces radiation over a wide angular range so that the pupils of the projection system are filled and overfilled with numerical aperture measurements. In one embodiment, the pupil fill should be uniform. Overfilling can be achieved by using the lens SL and the radiation intensity is increased. Pinhole PH limits radiation to specific locations within the field. Another way to obtain uniform pupil fill is to use a diffuser plate (such as an etched frosted glass plate) over a pinhole plate or an array of microlenses (similar to the diffractive optics DOE). Or use a holographic diffuser (similar to the phase shift mask PSM).
[00164] Radiation across the source module and projection system is incident on another diffraction element GR, such as a pinhole or grating known as an image grating. Referring to FIG. 14, another diffraction element GR is mounted on, for example, a crystal carrier plate CP. This other diffraction element acts as a "shearing mechanism" that produces different diffraction orders configured to interfere with each other (by matching the diffraction order to the local maximum of mutual coherence). For example, a zero order can be generated to interfere with the first order. As a result of this interference, a pattern is generated that is detected by the detector to reveal information about the wave surface aberration at a particular location in the image field. The detector DT may be, for example, a CCD or CMOS camera that electronically captures an image of the pattern without the use of a resist. Another diffraction element GR and detector DT are called an interference sensor IS. Traditionally, another diffraction element GR has been placed at the level of the substrate in the best focal plane. Here, the focal plane was located in the conjugate plane with respect to the first mentioned diffraction element in the source module SM. The detector DT is located via a space below another diffraction element GR.
[00165] One self-owned form of interferometer wave surface measurement system implemented on a lithography tool is known as ILIAS , an acronym for Integrated Lens Interferometer At Scanner. This measurement system is routinely provided on lithographic projection equipment. Detailed information on such interferometer systems provided on the lithography scanner device can be collected from US Patent Application No. 2002-0001088 and US Pat. No. 6,650,399 B2, both of which are incorporated herein by reference in their entirety.
[00166] The interference sensor essentially measures the differential phase of the wave front. The detector itself can only measure radiant intensity, but it can convert phase to intensity by using interference. Most interferometers require a secondary reference beam to generate the interference pattern, which is difficult to implement with lithographic projection equipment. However, a class of interferometers that do not have this requirement is shearing interferometers. In the case of lateral shearing, interference occurs between the wave front and the laterally displaced (sheared) copy of the original wave front. In this embodiment, another diffraction element GR divides the wave plane into a plurality of wave planes that are slightly displaced (sheared) from each other. Interference is observed between them. In this example, only zero and +/- 1 diffraction orders are considered. The intensity of the interference pattern is related to the phase difference between the zero and one diffraction orders.
[00167] Intensity I is given by the following schematic relational expression.<maths num="10"><img file="JP4717112B2_D0010.tif" /></maths>Where E<sub>0</sub>And E<sub>1</sub>Is the diffraction order of zero and 1, k is the phase stepping distance, p is the periodicity of the grid (in wave units), W is the wave surface aberration (in wave units), and ρ is the position in the pupil. When the shearing distance is short, the wave surface phase difference approaches the wave surface differential value. When the source module SM is slightly displaced with respect to the interferometer IS to perform continuous intensity measurements, the detected radiant intensity is modulated (the phase stepping factor k / p in the above equation changes). The first harmonic of the signal to be modulated (with the period of the grid as the fundamental frequency) corresponds to the diffraction order (0 and +/- 1). The phase distribution (as a function of pupil position) corresponds to the wave plane difference. By shearing in two nearly vertical directions, the wave surface difference between the two directions is taken into account.
[00168] Amplitude measurements can be performed as well as phase measurements on the wave surface above. These are performed using a reticle-level source with a calibrated angular intensity distribution. One example uses an array of effective point sources (dimensions smaller than the wavelength of radiation used) with an intensity distribution in which each point source is effectively uniform over a range of solid angles within the pupil of the projection system. That is. Other sources can also be used. The detected intensity variation is then associated with attenuation along a particular transmission line through the projection system. Detailed information on amplitude measurements and angular transmission characteristics (also referred to as apodization) of projection systems can be found in US Patent Application No. 10 / 935,741, which is incorporated herein by reference in its entirety.
[00169] According to one aspect of the invention, the wave surface measurements (phase and amplitude) described above are performed using a polarized radiation source. In one embodiment shown in FIG. 14, a polarizer 30 such as a beam splitter cube is incorporated in the source module SM. In another embodiment, for example, an independent discrete hot-swappable polarizer that can be inserted at the illuminator or reticle level is used. There is no need to modify the interference sensor IS.
[00170] The shearing interferometer is arranged to provide shearing in the X direction, and the wave surface Wxx is first measured using unidirectionally polarized source radiation, such as in the X direction. The polarizer or source module is rotated or exchanged / displaced so that the radiation is linearly polarized in the Y direction and the new wave surface Wxy is measured. For convenience, unpolarized, X-polarized, and Y-polarized source structures can be provided in a single source module carrier and mounted as a regular reticle. The reticle stage is free to move in the scanning direction and can provide unpolarized, X-polarized, and Y-polarized light source structures (perpendicular to the scanning direction) per field point.
The effect of an optical element, such as a projection system, or a combination of optical elements on polarized radiation can be represented by the Jones matrix. The X and Y components of the electromagnetic field vectors of incoming and outgoing electromagnetic radiation are related by the Jones matrix as follows.<maths num="11"><img file="JP4717112B2_D0011.tif" /></maths>
[00172] In the projection system of a lithographic apparatus, the off-diagonal elements in the Jones matrix are very small (ie, near zero) compared to the diagonal elements, i.e., very small crosstalk in the X and Y polarization states occurs. It is effective to do so. Therefore, an X-polarized source can be used to determine the diagonal element Jxx from the wave surface measurement, and a Y-polarized source can be used to determine the diagonal element Jyy from the wave surface measurement. Both wave surface phase and amplitude measurements are required. This is because each element of the Jones matrix is generally complex.
For a particular field point, a Jones matrix can be calculated for each pupil point in the projection system (each Jones matrix corresponds to the effect of radiation on a particular path through the projection system on polarization). The source module and interferometer can be moved to different field points, resulting in a set of Jones matrices. Each of these combinations of field points and pupil points has its own Jones matrix.
[00174] One question is whether the polarization states are mixed by a device in the source module, such as a diffuser, that ensures that the pupils of the projection system are overfilled. However, this is unlikely to have a significant impact, as the characteristic length scale of small angle diffusers is usually about 0.05 mm. However, even if mixing occurs, it can be easily corrected by combining X and Y wave plane measurements and solving a set of linear forms. Assuming that the decimal part a of the polarization mixture occurs in the source module, the following set of equations is obtained.<maths num="12"><img file="JP4717112B2_D0012.tif" /></maths>
[00175] The mixing factor a is obtained either logically or by calibration (performed offline). The equation is solved to obtain the desired X and Y polarized wave planes Wx and Wy. The same procedure can be applied if the polarizer used does not produce a satisfactory polarization purity.
The display of the polarization state of the substrate level radiated beam can be based on the desired target polarization state designation. Convenient metrics are defined as the polarization purity (PP) or percentage of polarized radiation in a target or preferred polarization state. Mathematically, polarization purity (PP) can be defined by the following formula.<maths num="13"><img file="JP4717112B2_D0013.tif" /></maths>However, E<sub>Target</sub>And E<sub>Actual</sub>Is a unit length electromagnetic field vector.
[00177] PP, although a valuable criterion, does not completely define irradiation radiation. The fractional part of the radiation is undefined or unpolarized, and the electrical vector rotates within a time frame beyond the observation period. This can be classified as unpolarized radiation. Radiation intensity I<sub>polarized</sub>Polarized radiation and intensity I with<sub>unpolarized</sub>It is considered to be the sum of the unpolarized radiation with, and the sum of the intensities is I.<sub>Total</sub>In the case of, the degree of polarization (DOP) can be defined by the following formula.<maths num="14"><img file="JP4717112B2_D0014.tif" /></maths>
[00178] DOP is for explaining unpolarized parts. Since unpolarized (and polarized) radiation can be decomposed into two orthogonal states, the preferred state intensity (IPS) of polarized light as a function of DOP and PP is derived by:<maths num="15"><img file="JP4717112B2_D0015.tif" /></maths>
[00179] In another embodiment of the invention, the measurement method of the aforementioned embodiment related to FIG. 14 is arranged to verify and calculate the spatial distribution of IPS. Similar to the above embodiment, the wave surface Wxx is first measured using the image grid GR in which the line and space are oriented parallel to the Y direction, which is measured using the source radiation linearly polarized in the X direction. .. Therefore, wave plane shearing in the X direction is obtained in the pupil of the projection system. The polarizer 30 is then rotated or exchanged / displaced and the radiation is linearly polarized in the Y direction. In addition, the object grid is similarly arranged in the pupil of the projection system to provide X-direction wave plane shearing and the corresponding linearly polarized wave plane Wxy is measured.
[00180] For example, the X-polarized first pinhole PH1 is used to measure the spatially decomposed aberration of the wave surface Wxx. This process is also performed on another pinhole PH2 in which the orientation of the Y-polarized grid is the same as the orientation provided in pinhole PH1. This performs the second wave surface aberration measurement of the wave surface Wxy. Using this measurement result, the Jones matrix and the intensity (IPS) in the preferable state can be calculated in the state of being spatially decomposed in the pupil.
[00181] This measurement will be described in more detail below. In a conventional shearing interferometer, the phase φ (x, y) of the wave front is measured using an object grid in the pinhole PH to provide preselected spatial coherence and shearing grid in the pupil of the projection system. The shearing grid is the image grid GR described above. The grid GR brings different diffraction orders onto the detector DT. The detector DT detects the intensity of vibration due to the displacement of the grid GR with respect to the pupil. The amplitude of this vibration is also called contrast, and the average intensity (zero amplitude) is also called a DC signal.
[00182] The shearing interference aberration measurement method includes a mixture of electric fields diffracted by a lattice GR including a zero-order diffracted electric field and a first-order diffracted electric field (that is, addition of coherent). The zero-order and first-order diffraction fields are images of the electric field at the pupil of the projection system, respectively, at the pupil position (x, y) in the pupil of the projection system.<sub>0</sub>(x, y) and the electric field E at the "adjacent" pupil position (x + dx, y)<sub>1</sub>Represented by (x + dx, y).
[00183] Here, the electric field is a scalar field (having the same polarization state independent of the X and Y coordinates of the pupil), and the subscript indicates the order of diffraction in the lattice GR. The vector property of polarized light is introduced as follows. Excluding terms that are constant over the wave front from the calculation gives:<maths num="16"><img file="JP4717112B2_D0016.tif" /></maths>
[00184] The detector DT measures the intensity I (x, y) given by the following equation.<maths num="17"><img file="JP4717112B2_D0017.tif" /></maths>
[00185] Intensity I (x, y) has two fields E<sub>0</sub>And E<sub>1</sub>It changes as a cosine regarding the phase difference with. In addition, A<sub>0</sub>= A<sub>0</sub>(x, y) and A<sub>1</sub>= A<sub>1</sub>(x + dx, y). Short notations have been introduced to make the formula clearer. Wave surface measurement is a special, changing "stepping" phase φ<sub>step</sub>Includes steps to measure cosine behavior by including. At each step, a new value of intensity at one pixel of detector DT is measured. φ<sub>step</sub>After stepping 8 times with = k × (2π / 8) (k = 1,2, ..., 8), the following 8 measurements are obtained.<maths num="18"><img file="JP4717112B2_D0018.tif" /></maths>
[00186] From these eight data points, the phase dφ (x, y) = φ (x + dx, y) -φ (x, y) is derived. Alternatively, depending on the signal / noise constraints, data points greater than or equal to 8 can be used. The fit of the detector DT corresponding to the pupil position (x, y) to all eligible pixels results in a complete map dφ (x, y) of the wave plane phase shift.
[00187] For example, in order to explain the birefringence that occurs in the lens element of the projection system, the vector property of the electric field is incorporated. The shearing grid GR shall be unpolarized. Therefore, only the vector properties of the radiation upstream of the lattice GR are verified. REQE<sub>0</sub>And REQE<sub>1</sub>Both have X and Y components parallel to the orthogonal X and Y directions.<maths num="19"><img file="JP4717112B2_D0019.tif" /></maths>and<maths num="20"><img file="JP4717112B2_D0020.tif" /></maths>
[00188] Special phase φ<sub>rei</sub>(x, y) describes the phase delay between the Y components of each electric field, for example for birefringence. The phase delay between the X components is absorbed by the previously introduced phase difference φ (x, y). The intensity measured by the detector pixel of the detector DT is given by the following equation.<maths num="21"><img file="JP4717112B2_D0021.tif" /></maths>However, for example, A<sub>0x</sub>= A<sub>0x</sub>(x, y).
[00189] This result is described by the following equation.<maths num="22"><img file="JP4717112B2_D0022.tif" /></maths>However,<maths num="23"><img file="JP4717112B2_D0023.tif" /></maths>and<maths num="24"><img file="JP4717112B2_D0024.tif" /></maths>
[00190] Special "birefringence term" dφ<sub>BF</sub>(x, y) appears in the cosine. This special phase is detected by shearing interference measurement and weighted by the Zernike coefficient, which represents the waveform aberration in the orthogonal normalized Zernike function.
[00191] According to one aspect of the invention, the electric field E<sub>0</sub>The polarization state of (x, y) is obtained from the interference measurement of intensity I (x, y). This polarization state is given by the Stokes vector CLKE given by the following equation.<sub>0</sub>Defined by.<maths num="25"><img file="JP4717112B2_D0025.tif" /></maths>
[00192] According to one aspect of the invention, the measurement of I (x, y) is two different priors for the radiation incident on the object grid in the pinhole PH of the two corresponding I (x, y) measurements. Includes the step of selecting the selected polarization state.
[00193] Hereinafter, the radiation across the projection system shall be fully polarized. Therefore, E<sub>0</sub>Polarization degree DOP of (x, y)<sub>E0</sub>Is 1.<maths num="26"><img file="JP4717112B2_D0026.tif" /></maths>
[00194] The intensity (IPS) in the preferred state is equal to the polarization purity (PP) when DOP = 1. In addition, preferred polarization states are defined as fully X-polarized light and fully Y-polarized light. These polarization states correspond to preferred illumination modes that increase the resolution of the lithography printing process. The corresponding values of IPS are as follows.<maths num="27"><img file="JP4717112B2_D0027.tif" /></maths>and<maths num="28"><img file="JP4717112B2_D0028.tif" /></maths>
[00195] It is assumed that the Jones matrix is well known at the preselected position (xp, yp) in the pupil of the projection system. For example, for the axial light along the optical axis of the projection system, the Jones matrix can be assumed to be a single matrix. Therefore, the electric field CLKE<sub>0</sub>(x<sub>p</sub>, y<sub>p</sub>) Is invariant after crossing the reticle + projection system. In this embodiment, a polarizer 30 with a source module SM is used.<sub>0</sub>(x, y) is arranged so that it is linearly polarized in the X direction at the reticle level. Therefore, on the premise of the unitary-Jones matrix, A<sub>0y</sub>= 0. According to equations 17-19, the following parameters are measured by shearing interferometry.<maths num="29"><img file="JP4717112B2_D0029.tif" /></maths><maths num="30"><img file="JP4717112B2_D0030.tif" /></maths>and<maths num="31"><img file="JP4717112B2_D0031.tif" /></maths>
[00196] Here, the subscript ", x" indicates the incident straight line X polarized light. For example, A<sub>1y, x</sub>Is the amplitude of the Y component of the primary diffracted electric field when the incident X polarized radiation is used at the reticle level. The coherent shearing measurements are then repeated, using the corresponding polarizers 30 in the source module arranged in the direction of polarization along the Y direction again, CLKE.<sub>0</sub>The polarization configuration of (x, y) is acquired at the reticle level with linearly polarized light in the Y direction. Similar to the above measurement, A<sub>0x</sub>= 0. The following parameters can be measured using shearing interferometry according to general equations 17-19.<maths num="32"><img file="JP4717112B2_D0032.tif" /></maths><maths num="33"><img file="JP4717112B2_D0033.tif" /></maths>and<maths num="34"><img file="JP4717112B2_D0034.tif" /></maths>
[00197] The subscript ", y" then indicates the linear Y polarization of the incident radiation at the reticle level. For example, A<sub>1x, y</sub>Is the amplitude of the X component of the primary diffracted electric field when incident Y polarized radiation is used. In principle, for incident X-polarized light and incident Y-polarized light CLKE<sub>1</sub>(x<sub>p</sub>+ dx, y<sub>p</sub>) Can determine the perfect polarization state.
[00198] The contrast of the interference pattern is related to the amplitude of the intensity oscillations described in Equations 24-2 and 25-2. Therefore, entity A<sub>BF</sub><sup>2</sup>The measurement of is called a "contrast" measurement. In addition, the "DC" component of the interference fringe pattern is described by Equations 24-3 and 25-3. Therefore, DC<sub>, x</sub>And DC<sub>, y</sub>The measurement of is called a "DC" measurement. As a result of the contrast and DC measurements, four unknown A's<sub>1x, x</sub>, A<sub>1x, y</sub>, A<sub>1y, x</sub>, A<sub>1y, y</sub>We get four equations including.
[00199] Position (x<sub>p</sub>+ dx, y<sub>p</sub>) Is the first position in the pupil (x)<sub>1</sub>, y<sub>1</sub>). The above measurement process is x from the first position<sub>2</sub>= x<sub>1</sub>+ dx, y<sub>2</sub>-y<sub>1</sub>Repeated as it moves to the second position, which is, again using equations 17-19 (replace the subscripts 0 and 1 with 1 and 2, respectively) the corresponding amplitude A.<sub>2x, x</sub>, A<sub>2x, y</sub>, A<sub>2y, x</sub>, A<sub>2y, y</sub>Has been determined and four unknown A's<sub>2x, x</sub>, A<sub>2x, y</sub>, A<sub>2y, x</sub>, A<sub>2y, y</sub>We get four equations including. Similarly, Y-direction shearing can be introduced (using image grid GR so that lines and space are oriented parallel to the X-direction and Y-direction wave plane shearing is obtained in the pupil of the projection system). This will cause type x<sub>2</sub>= x<sub>1</sub>, y<sub>2</sub>= y<sub>1</sub>The transition from the first position to the second position of + dy becomes possible.
[00200] Any such transition to an adjacent position can be repeated any number of times, each time with amplitude A.<sub>ix, x</sub>, A<sub>ix, y</sub>, A<sub>iy, x</sub>, A<sub>iy, y</sub>(i = 1,2,3, ...) is determined, and the state-space distribution of polarized light by integration is effectively mapped. Equations 22 and 23 are used to obtain the corresponding spatial distribution of IPS. For example, measured value A<sub>ix, x</sub>, A<sub>iy, x</sub>(A<sub>0x</sub>, A<sub>0y</sub>IPS) by substituting IPS into Equation 22<sub>x</sub>The distribution of (x, y) is obtained.
[00201] In this embodiment, two different settings of the polarizer 30 include linearly polarized light along the shearing direction and linearly polarized light perpendicular to the shearing direction. However, according to one aspect of the invention, additional settings for the polarizer 30 can be used. For polarization at reticle levels different from either linear X or linear Y polarization, by providing a source module SM in which the polarizer is placed for linear polarization at zero or 90 ° different angles with respect to the 30 shearing direction, described above. Further DC and contrast measurements can be performed. Such additional measurements can be used to increase the accuracy of the process of solving the electric field amplitude equation as described above, or to obtain information about the presence of unpolarized radiation when DOP <1.
[00202] According to another embodiment of the invention, the Jones matrix distribution can be measured as well. As in the above embodiment, it is assumed that DOP = 1. Therefore, the transfer function that describes the change in the polarization state of radiation across the projection system is expressed as the spatial distribution of the complex 2 × 2 Jones matrix. Similar to the above embodiment, the unknown electric field amplitude is determined by measuring the interference mixing data such as the DC component and contrast, and further measuring dφ.
[00203] These measurements are repeated for two incident polarization states (eg, linear X-polarized light and linear Y-polarized light of the above embodiment). Suppose there is a single point in the pupil where the Jones matrix is known. For example, the Jones matrix can be assumed to be a unitary matrix at a point on the optical axis of the projection system.
[00204] The Jones matrix at points in all other pupils is then obtained by an iterative method similar to the iterative method described in the above embodiment. Since each of the four matrix elements of the Jones matrix has a real part and an imaginary part, there are eight unknown elements, and therefore eight equations are needed to solve the unknown elements. Six equations are provided by the adaptation of the coherence data to equations 24-1, 24-2, 24-3 and equations 25-1, 25-2, 25-3. Two additional equations are provided by supplementary measurement of the output intensity for the two polarization states of the radiation incident on the pinhole PH with respect to the primary diffracted beam in the absence of interference with other diffracted beams.
[00205] The analysis in the description of the fourth and fifth embodiments is limited to a combination of two diffraction orders of radiation in the grid GR of the shearling interferometer configuration for clarity. However, according to one aspect of the invention, additional diffraction orders can be considered. For example, electric field CLKE<sub>0</sub>And REQE<sub>1</sub>Besides, the diffraction field corresponding to the position of the "next" pupil (x-dx, y)<sub>-1</sub>May be included in the analysis. This analysis is similar to the analysis of the fourth embodiment.
[00206] polarizers, retarders (quarter-wave plate), in any of the above embodiments which polarization active components, such as a polarization beam splitter is used, heat radiationCarrying anglea large impact on the performance of the components May be given. Therefore, it is advantageous to place these components in a location where the radiation is approximately parallel. As an option, elements such as the polarization conversion element 10 and the analyzer 12 can be placed at appropriate locations within the illuminator where the radiation is already nearly parallel. The second option is to provide optics 40 and 42 that first collimate the radiation and then focus, as shown in FIG. This provides a zone 44 in which the radiation takes the form of a parallel beam and can place polarized active components.
Feedback can be provided using the results of measurements according to any of the above embodiments of the present invention. For example, in a device in which the illuminator sets the desired polarization pattern, one or more actuators can be provided to adjust the components of the lithography device with feedback based on the measurements obtained. FIG. 12 shows that the illuminator IL can be adjusted under the control of controller 16 to correct or compensate for all measured deviations in the desired polarization pattern, but this is merely an example.
[00208] Although this specification contains specific reference materials regarding the use of lithography equipment in IC manufacturing, the lithography equipment described in this specification includes manufacturing of integrated optical systems, guidance and detection patterns of magnetic area memory, and flats. It should be understood that it can be applied to other applications such as panel displays, liquid crystal displays (LCDs), and thin film magnetic heads. For those skilled in the art, the terms "wafer" or "die" used herein are all synonymous with the more general terms "board" or "target portion," respectively, for the other uses described above. You can understand that. The substrates described herein are processed before and after exposure, for example, in a track (usually a tool that applies a resist layer to the substrate and grows the exposed resist), a metrology tool, and / or an inspection tool. You may. The contents disclosed in the present specification can be appropriately applied to the above-mentioned substrate processing tool and other substrate processing tools. Further, since the substrate can be processed a plurality of times, for example, to create a multi-layer IC, the term substrate as used herein can also refer to a substrate that already includes a multiprocessing layer.
[00209] Although the use of embodiments of the present invention in the field of optical lithography has been specifically described above, it should be understood that the present invention can also be used in other applications.
[00210] The terms "radiation" and "beam" as used herein refer to ultraviolet (UV) radiation (eg, having wavelengths at or near 365, 248, 193, 157, or 126 nm), ultraviolet light. Includes (EUV) radiation (eg, having wavelengths in the range of 5-20 nm), and other types of radiation.
[00211] The term "lens" can, in some contexts, refer to any one or combination of various types of optical components, including refracting and reflective optical components.
[00212] Although the specific embodiment of the present invention has been described above, it should be understood that the present invention can be carried out by a method other than the above.
[00213] The above description is an example and does not limit the present invention. Therefore, it will be apparent to those skilled in the art that modifications can be made to the invention described herein without departing from the appended claims.
<figref num="1">[0043] It is a figure which shows the polarized light from the illuminator which is incident on the polarization sensor module at the angle corresponding to the numerical aperture (NA).</figref><figref num="2">[0044] FIG. 6 shows a camera located at the wafer level in a polarization sensor system according to the configuration of the present invention.</figref><figref num="3">[0045] It is a chart that discloses the relationship between the features related to the polarization sensor according to some embodiments of the present invention.</figref><figref num="4">[0046] It is a figure which shows the active reticle tool by one Embodiment of this invention.</figref><figref num="5a">[0047] It is a figure which shows a part of the polarization sensor by the structure of this invention.</figref><figref num="5b">[0048] It is a figure which shows the spring-mounted retarder arranged by another structure of this invention.</figref><figref num="6">It is a figure which shows a part of another polarization sensor by another embodiment of this invention.</figref><figref num="7">[0050] It is a figure which shows a part of another polarization sensor by another embodiment of this invention.</figref><figref num="8a">[0051] It is a figure which shows a part of another polarization sensor by another embodiment of this invention.</figref><figref num="8b">[0052] It is a figure which shows the passive reticle system arranged in one Embodiment of this invention.</figref><figref num="8c">[0053] It is a detailed view of a polarization sensor module.</figref><figref num="9">[0054] FIG. 6 is a schematic representation of three different polarization sensors according to each of the three embodiments of the present invention.</figref><figref num="9d">[0055] A detailed view of a multipath system with a beam split polarizer provided below the pinholes of a reticle.</figref><figref num="10">[0056] It is a figure which shows the interaction between an unpolarized light wave and a wave surface.</figref><figref num="11">[0057] It is a figure which shows the lithography apparatus by one Embodiment of this invention.</figref><figref num="12">[0058] FIG. 6 is a schematic view of a lithography apparatus according to another embodiment of the present invention.</figref><figref num="13">[0059] It is the schematic of the lithography apparatus by the modification of the embodiment shown in FIG.</figref><figref num="14">[0060] It is the schematic of the lithography apparatus according to another embodiment of this invention.</figref><figref num="15">[0061] FIG. 6 is a schematic configuration of a configuration that collimates radiation within a region of a polarized active component.</figref>
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Numbers
- Publication
- 4717112
- Publication, DOCDB
- 4717112
- Publication, EPODOC
- JP4717112B
- Application
- 2008516222
- Application, DOCDB
- 2008516222
- Application, EPODOC
- JP20080516222
Titles2
- Japanese
- 偏光アナライザ、偏光センサおよびリソグラフィ装置の偏光特性を判定するための方法
- English
- Methods for determining the polarization characteristics of polarization analyzers, polarization sensors and lithography equipment
Classification
- CPC, 4
- G01M11/0264
- G03F7/70566
- G03F7/706
- G03F7/7085
- IPC, 3
- H01L21 027
- G03F7 20
- G01M11 02