Compact encoder head for interferometric encoder system

0001In some cases, the interferometric measurement system monitors changes in the relative position of the object under test based on the optical interference signal. For example, an interferometer superimposes a measurement beam reflected from an object to be measured with a second beam, which is sometimes called a "reference beam," and causes them to interfere with each other to generate an optical interference signal. The reference beam is obtained from a common light source. The change in the relative position of the object to be measured corresponds to the change in the phase of the measured optical interference signal.

0002An example of such an interference type measurement system is an interference type encoder system, which evaluates the movement of an object by tracking a measurement scale called an encoder scale. In general, an interferometric encoder system includes an encoder scale and an encoder head. The encoder head is an assembly that includes an interferometer. The interferometer directs the measurement beam to the encoder scale, where the light is diffracted. The interferometer combines the diffracted measurement beam with the reference beam to form an output beam that includes the phase related to the position of the object. Encoder systems are widely used in lithographic applications to monitor the movement of movable stages within lithographic tools. Encoder systems can be useful in such applications because they are relatively insensitive to atmospheric fluctuations.

<p num="0003"> The present application relates to a small encoder head. Various aspects of the present invention are summarized as follows. In general, in a first aspect, the subject matter of the present application can be embodied in an encoder head for use with an encoder scale, the encoder head synthesizing each of a plurality of double diffraction measurement beams with a corresponding reference beam. The encoder head contains a monolithic optical component with multiple facets, i) receiving multiple single diffraction measurement beams from the surface of the encoder scale. , Ii) Configured to redirect multiple single-diffraction measurement beams back to the surface of the encoder scale, the encoder scale is positioned within the path of the single-diffraction measurement beam to generate a double-diffraction measurement beam. To do.</p><p num="0004"> In other embodiments, the subject matter of the present application can be embodied in an encoder system, the encoder system comprising an encoder scale and an encoder head, wherein the encoder head corresponds to each of a plurality of double diffraction measurement beams. Configured to combine with and to form multiple output beams, the encoder head contains a monolithic optical component with multiple facets, which receives multiple single diffraction measurement beams from the surface of the encoder scale. Arranged to divert multiple single-diffraction measurement beams back to the surface of the encoder scale, the encoder scale is positioned within the path of the single-diffraction measurement beam to generate a double-diffraction measurement beam. The encoder system can further include a plurality of detection elements positioned to detect the output beam and an electronic processor, which is an interference signal from each of the detection elements and is a double diffraction measurement. It is configured to receive interference signals that include the phase for the optical path difference between one of the beams and the corresponding reference beam and determine information about the degree of freedom of the encoder scale based on the phase for each interference signal. To.</p><p num="0005"> The implementation of the system can include one or more of the following features and / or features of other aspects. For example, monolithic optics can take the shape of a cube. In some implementations, monolithic optics take the form of a rectangular parallelepiped.</p><p num="0006"> In some implementations, the monolithic optics include a first facet configured to receive a non-diffraction measurement beam and emit a double diffraction measurement beam. The first facet is capable of substantially transmitting radiation propagating in the direction perpendicular to the first facet and substantially reflecting radiation incident on the first facet at an angle of inclination. The monolithic optics can include a second facet configured to receive a single or double diffraction measurement beam from the encoder scale. The second facet can substantially transmit radiation propagating in the direction perpendicular to the second facet. The second facet can be placed opposite the first facet and facing the first facet.</p><p num="0007"> Alternatively, the second facet can be placed perpendicular to the first facet. The second facet reflects the radiation incident on the second facet with respect to the second facet in the first tilt angle range and the second with respect to the second facet in the second different tilt angle range. It can be configured to transmit radiation incident on the facets.</p><p num="0008"> In some implementations, the side facets of monolithic optics substantially reflect radiation incident on the side facets at an angle of inclination. In some implementations, the encoder scale includes a 1D or 2D grid. The grid can consist of grooves extending along the first direction. In some cases, the plane containing the side facets of the monolithic optics can be oriented at an angle of inclination with respect to the first direction.</p><p num="0009"> In some implementations, the monolithic optics can include regular hexagonal prisms or regular pentagonal prisms. In certain embodiments, the encoder head can be configured to direct the non-diffraction measurement beam along the first beam path to the encoder scale, where the first beam path of the non-diffraction measurement beam is monolithic optics. It is on the outside of the part. The encoder scale can be positioned so that the incident beam is diffracted along the second beam path with respect to the monolithic optical component, and the second beam path of the diffracted incident beam is outside the monolithic optical component.</p><p num="0010"> In some embodiments, the single diffraction measurement beam is a first single diffraction measurement beam obtained from a positive diffraction order from the encoder scale and a second one obtained from a negative diffraction order from the encoder scale. Includes diffraction measurement beam. The first and second single diffraction measurement beams can include positive and negative diffraction orders in the first plane. The first diffraction measurement beam is a third and fourth first diffraction measurement beam containing a positive diffraction order and a negative diffraction order from the encoder scale in the second plane perpendicular to the first plane, respectively. Further can be included.</p><p num="0011"> In some implementations, the system receives an input beam and, from this input beam, obtains (1) a corresponding reference beam for each double diffraction measurement beam and (2) an incident measurement beam. It further includes a plurality of configured optical elements. The optics can include multiple beam splitters and retroreflectors.</p><p num="0012"> In some implementations, the monolithic optics receive an input beam from which it obtains (1) a corresponding reference beam for each double diffraction measurement beam and (2) an incident measurement beam. It is configured as follows. Monolithic optics can include beam separation facets, which separate the input beam based on the polarization of the input beam and the specified angle of incidence for the beam separation facet, at angles of incidence other than the specified angle of incidence. It is configured to reflect the light incident on the beam separation facets. The system can further include a reference grid that receives the reference beam from the monolithic optics and is positioned to divert the diffracted reference beam into the monolithic optics.</p><p num="0013"> In other embodiments, the subject matter of the present application can be embodied in a system, the system comprising a movable stage and an encoder system, in which either the encoder system or the object under test is attached to the movable stage. The encoder system can include an encoder scale and an encoder head, in which the encoder head combines the double diffraction measurement beams of each of the multiple double diffraction measurement beams with the corresponding reference beam to form multiple output beams. It is configured as follows. In some embodiments, the encoder head comprises a monolithic optic with multiple facets, which receives multiple single-diffraction measurement beams from the surface of the encoder scale and receive multiple single-diffraction measurement beams. Arranged to turn around to return to the surface of the encoder scale. In some implementations, the encoder scale is positioned within the path of the single diffraction measurement beam to generate the double diffraction measurement beam. The encoder system can further include multiple detection elements positioned to detect the output beam and an electronic processor configured to receive interference signals from each of the detection elements, each interference signal being 2 Includes the phase with respect to the optical path difference between one of the diffraction measurement beams and the corresponding reference beam. The electronic processor can be further configured to determine information about encoder scale degrees of freedom based on the phase for each interference signal.</p><p num="0014"> In other embodiments, the subject matter of the present application can be embodied in a lithography system, which is an encoder system and a mobile stage to which either the encoder system or an object to be measured is mounted. A lighting system connected to the encoder system, a detector that detects the output beam from the encoder system during operation of the lithography system, and an electronic processor that adjusts the position of the stage based on information about the displacement of the encoder scale. Includes a positioning system configured to. The lighting system can include a radiation source, which directs the radiation to the encoder system during the operation of the lithography system. The encoder system can include an encoder scale and an encoder head configured to combine each of the plurality of double diffraction measurement beams with a corresponding reference beam to produce a plurality of output beams. The encoder head can include monolithic optics with multiple facets, which receive multiple single-diffraction measurement beams from the surface of the encoder scale and multiple single-diffraction measurement beams on the surface of the encoder scale. Arranged to turn around to return to. The encoder scale is positioned in the path of the single diffraction measurement beam and can generate the double diffraction measurement beam. The encoder system can further include a plurality of detection elements positioned to detect the output beam and an electronic processor, which is an interference signal from each of the detection elements and is a double diffraction measurement. receiving an interference signal that comprises a phase related to an optical path difference between one corresponding reference beam of the beam based on the phase of the interference signal, encoder configured to determine information about the degree of freedom of Dasukeru.</p><p num="0015"> Advantages of the various aspects of the subject matter disclosed herein include, for example, that the interferometric encoder system requires fewer optics and / or separate encoder heads for position measurement. Can be done. Other benefits include, for example, low cost and / or simple design for interferometric encoder systems and / or encoder heads.</p><p num="0016"> Details of one or more embodiments are provided in the accompanying drawings and in the description below. Other features and advantages will become apparent from the description, drawings and claims.</p>

0017<figref num="1">It is the schematic of the interference type encoder system as an example.</figref><figref num="2A">It is the schematic of the cross section of the optical component as an example.</figref><figref num="2B">It is a three-dimensional (3D) schematic diagram of the optical component shown in FIG. 2A.</figref><figref num="2C">It is a 3D schematic diagram of an optical component as an example.</figref><figref num="3A">It is a 3D schematic diagram of a monolithic optical component as an example.</figref><figref num="3B">It is a 3D schematic diagram of a monolithic optical component as an example.</figref><figref num="4A">It is the schematic of the cross section of the optical component as an example.</figref><figref num="4B">It is a 3D schematic view of the optical component shown in FIG. 4A.</figref><figref num="5">It is a 3D schematic diagram of an optical component as an example.</figref><figref num="6">It is a 3D schematic diagram of an optical component as an example.</figref><figref num="7">It is a 3D schematic diagram of an optical component as an example.</figref><figref num="8">It is the schematic of the interference type encoder head as an example.</figref><figref num="9">It is the schematic of the interference type encoder head as an example.</figref><figref num="10">It is a 3D schematic diagram of the interference type encoder head as an example.</figref><figref num="11">It is the schematic of the interference type encoder head as an example.</figref><figref num="12">It is the schematic of the interference type encoder head as an example.</figref><figref num="13">It is the schematic which shows the use example of the optical element for separating a desirable output beam from an undesired output beam of an interference type encoder head.</figref><figref num="14">It is the schematic of the lithography tool as an example.</figref><figref num="15A">It is a flowchart of the manufacturing sequence of a semiconductor device.</figref><figref num="15B">It is a flowchart which shows the detail of a wafer process.</figref><figref num="16A">It is a schematic diagram which shows an example of the encoder head which uses the patch of the transmission type and the reflection type lattice.</figref><figref num="16B">It is a schematic diagram which shows an example of the encoder head which uses the patch of the transmission type and the reflection type lattice.</figref><figref num="16C">It is a 3D schematic view of the encoder head shown in FIG. 16B.</figref>

0018Referring to FIG. 1, the interferometric encoder system 100 includes a light source module 120 (eg, including a laser), an optical assembly 110, an object 101 to be measured, and a detector module 130 (eg, a polarizer and a photodetector). And the electronic processor 150. In general, the light source module 120 includes a light source and also includes beam forming optics (eg, optical collimating optics), light guide components (eg, fiber waveguides), and / or polarization control optics (eg, polarizers and). Other components such as / or wave plate) can also be included. Various embodiments of the optical assembly 110 will be described below. In some implementations, the optical assembly may also be referred to as an "encoder head". A Cartesian coordinate system is shown for reference and the Y direction (not shown) extends into the page.

0019The object 101 to be measured is positioned along the Z axis at a nominal distance from the optical assembly 110. In many applications, for example, when an encoder system is used to monitor the position of a wafer stage or reticle stage within a lithography tool, the object 101 moves in the x and / or y directions with respect to the optical assembly 110. On the other hand, the z-axis is nominally (nominally) kept at a constant distance from the optical assembly. This constant distance can be relatively small (eg, a few centimeters or less). However, in such applications, the position of the object to be measured can generally change by a small amount from a nominally constant distance, and the relative orientation of the object to be measured in the Cartesian coordinate system can also change by a small amount. During operation, the encoder system 100 includes one or more of these degrees of freedom of the object 101 with respect to the optical assembly 110, including the position of the object 101 with respect to the x-axis, as well as the y-axis and / or z. Monitor, including the position of the object 101 with respect to the axis and / or the angular orientation of the pitch and yaw.

0020To monitor the position of the object 101 to be measured, the light source module 120 directs the input beam 122 to the optical assembly 110. The optical assembly 110 obtains the measurement beam 112 from the input beam 122 and directs the measurement beam 112 toward the object 101 to be measured. The optical assembly 110 also obtains a reference beam (not shown) from the input beam 122 and directs the reference beam along a different path than the measurement beam. For example, the optical assembly 110 can include a beam splitter that splits the input beam 122 into a measurement beam 112 and a reference beam. The measurement and reference beams can have orthogonally polarized light (eg, orthogonally linearly polarized light).

0021The object 101 to be measured includes an encoder scale 105, which is a measurement scale that diffracts, for example, a measurement beam from an encoder head into one or more diffraction orders. In general, encoder scales can include a wide variety of diffraction structures, such as lattice or holographic diffraction structures. Examples of grids include sinusoidal grids, rectangular grids, or serrated grids. Lattice can be characterized not only by a periodic structure with a constant pitch, but also by a more complex periodic structure (eg, a chirp lattice). In general, encoder scales can diffract a measurement beam into multiple planes. For example, the encoder scale can be a two-dimensional grid that diffracts the measurement beam to the diffraction order in the xz and yz planes. The encoder scale extends in the xy plane over a distance corresponding to the range of movement of the object 101 to be measured.

0022In this embodiment, the encoder scale 105 is a grid whose grid lines extend perpendicular to the plane of the page and parallel to the y-axis of the Cartesian coordinate system as shown in FIG. The grid lines are periodic along the x-axis. The lattice plane of the encoder scale 105 corresponds to the xy plane, and the encoder scale diffracts the measurement beam 112 to one or more diffraction orders in the yz plane.

0023At least one of these diffraction orders of the measurement beam (eg, +1 or -1st order diffraction) (indicated as beam 114) returns to optical assembly 110, where the diffraction measurement beam is referenced using optics. Combined with the beam, the output beam 132 is formed. Alternatively, the optics in assembly 110 are used to redirect the diffracted measurement beam back to the encoder scale for a second diffraction before being combined with the reference beam.

0024The output beam 132 contains phase information regarding the difference in optical path length between the measurement beam and the reference beam. The optical assembly 110 directs the output beam 132 to the detector module 130, which detects the output beam and sends a signal to the electronic processor 150 in response to the detected output beam. The electronic processor 150 receives and analyzes the signal to determine information about one or more degrees of freedom of the object 101 to be measured with respect to the optical assembly 110. An example of an exemplary technique for determining information about one or more degrees of freedom based on a detected output beam can be found in U.S. Pat. No. 8,300,233, which is hereby incorporated by reference in its entirety. ..

0025In certain embodiments, the measurement and reference beams have a small frequency difference (eg, a difference in the kHz to MHz range) that produces an interfering signal of interest at a frequency that generally corresponds to this frequency difference. .. This frequency will be referred to below interchangeably with the "heterodyne" frequency. The information about the change in the relative position of the object under test generally corresponds to the phase of the interfering signal at this heterodyne frequency. This phase can be extracted using signal processing techniques. In general, this phase term changes over time depending on the movable object to be measured. In this regard, the first-order time derivative of the motion of the object under test shifts the frequency of the interference signal by a certain amount from the heterodyne frequency, which is referred to herein as a "Doppler shift".

0026Different frequencies of the measurement and reference beams are generated, for example by Zeeman separation of the laser, by acoustic optics modulation, using two different laser modes, or inside the laser using a birefringent element, and by other techniques. it can. Orthogonal polarization allows a polarization beam splitter to direct the measurement and reference beams along different paths and combine them to form an output beam, because the output beam then passes through the polarizer and mixes with the orthogonally polarized components. , These can interfere. Without the movement of the target, the interference signal oscillates at the heterodyne frequency, which is exactly the difference between the optical frequencies of the two components. Given the movement of the target, this heterodyne frequency causes a change in target velocity through the well-known Doppler relationship. Therefore, by monitoring the change in heterodyne frequency, the movement of the target with respect to the optical assembly can be monitored.

0027In the embodiments described below, the "input beam" generally refers to a beam emitted from a light source module. For heterodyne detection, the input beam contains components with slightly different frequencies, as described above.

0028In certain embodiments, the interferometer system is designed so that it does not work with the retrow. For example, in general, the measurement beam is incident on the object 101 at a certain angle of incidence, and the once-diffracted measurement beam does not satisfy the Littrow condition. The retrow condition refers to the orientation of a diffractive structure such as a grid with respect to an incident beam such that the diffractive structure returns the diffracted beam toward a light source. In other words, in the encoder system 100, the single diffraction measurement beam does not satisfy the retrow condition because it is not co-linear with the measurement beam before the single diffraction measurement beam is diffracted on the encoder scale.

0029Although the encoder scale 105 is depicted in FIG. 1 as a unidirectionally periodic structure, more generally, the object under test can include a variety of different diffractive structures that appropriately diffract the measurement beam. In some embodiments, the object under test can include a diffraction structure (eg, encoder scale) that is periodic in two directions (eg, along the x and y axes), and the measurement beam is placed in two orthogonal planes. Diffract to the inner beam. In general, encoder-scale diffraction structures and light source modules are geometrically constrained by the encoder system. Within constraints), it is selected to provide one or more diffraction measurement beams of sufficient intensity to establish one or more detectable interferometric signals when combined with the corresponding reference beam. .. In some embodiments, the light source module supplies an input beam having a wavelength in the range of 400 nm to 1,600 nm. For example, the input beam can have a wavelength of about 633 nm or about 980 nm. It should be noted that in general, as a result of frequency division of heterodyne sources, the difference between the wavelengths of the two components of the input beam is very small, so even if the input beam is not strictly monochromatic, it is still the input beam. It is realistic to characterize with one wavelength. In some embodiments, the light source module includes a heat source such as a gas laser (eg, a HeNe laser), a laser diode or other solid state laser source, a light emitting diode, or a halogen lamp with or without a filter for spectral bandwidth modulation. be able to.

0030In general, the diffraction structure (eg, lattice pitch) can be varied depending on the wavelength of the input beam and the diffraction order used to arrange and measure the optical assembly. In some embodiments, the diffraction structure is a grid with a pitch in the range of about 1λ to about 20λ, where λ is the wavelength of the light source. The grid pitch can be from about 0.5 μm to about 10 μm. Another embodiment of the interferometric optical encoder system and operation is described in US Pat. No. 8,300,233, which is hereby incorporated by reference in its entirety.

0031As mentioned above, the object under test diffracts the incident measurement beam into a beam in one or more planes (eg, two orthogonal planes). These diffracted beams may include, for example, a beam from a positive diffraction order and a beam from a negative diffraction order. In some embodiments, the diffracted beam is combined with the corresponding reference beam to generate multiple output beams, feed the beam to the encoder scale, and receive a once-diffracted beam from the encoder scale. Multiple components are used to divert the first diffracted beam towards the encoder scale to allow the second diffraction to occur and to receive the twice-diffracted beam. Such systems can be complicated in arrangement and expensive to configure and manufacture, depending on the number of parts required to receive and redirect each of the diffracted beams.

0032In order to reduce the cost of the system, simplify the system design, and streamline the use of light energy, the multiple components used to receive and divert the diffraction measurement beam are effectively retroreflected. It can be replaced with a monolithic optical component that has two or more combinations of various optical surfaces. In some implementations, the single diffractive beam enters the monolithic optics and is redirected back to the grating by the surface and / or facets of the monolithic optics, causing two or more double diffractive beams in the grating. Will be generated. In some embodiments, the surface and / or facet of the monolithic optics takes the measurement beam from the input beam and redirects the measurement beam towards the encoder scale to produce a single diffraction measurement beam.<u style="single">Get</u>It is configured to. The double diffracted beams can be interfered with each other or by the corresponding reference beam to produce an output beam, the output beam being recorded by the detector. After that, the interference signal obtained from the detector can be used to determine the position information regarding the grid position based on the phase information from the interference signal. At least N measurement beams are required to measure changes in the position of the encoder scale in the N dimension. The system disclosed herein has one input as compared to a configuration that requires multiple separate input beams and one diffraction order for each input beam is detected from multiple separate input beams. The beam can be used to obtain different diffraction orders and therefore the light source can be used efficiently. Therefore, in some implementations, the power required to make the measurements can be saved. Alternatively, in some implementations, position measurement can be performed with lower noise.

0033Similarly, in some implementations, the surface and / or facets of monolithic optics are configured to receive and orient a 1-diffraction and / or 2-diffraction reference beam from a reference grid. In some cases, the surface and / or facets of the monolithic optics are configured to acquire a reference beam prior to diffraction from the input beam.

0034For the purposes of the present disclosure, it is understood that a monolithic optical component means an optical device including one or more optical elements constituting a single continuous component. In some implementations, single components can be formed joints or seamlessly. In some implementations, a single component can include facets that extend through at least a portion of that component, which is a single continuous component that fuses or glues two separate optics together. Is formed by (eg, using an optical adhesive). For example, a single component can include a polarizing beam splitter, whose facets extending from the beam splitter body propagate an incident beam of orthogonal polarization into two separate beams that propagate in different directions based on the different polarizations of the input beam. Separate with.

0035Diffraction measurements and / or reference beams can be received and redirected using a single monolithic optic, but with one or more beam steering, beam separation and / or beam compositing components. An implementation is also possible that is arranged to provide a compact optical device for measuring relative position changes of the encoder scale in N dimensions.

0036Minimalistic optical design for optical encoder heads allows for multiple retroreflective elements, which can be any single cubic, rectangular parallelepiped (rectangular surface). Hexagon with), right angle prisms (eg prisms with inclusion angles of 45 °, 45 °, 90 ° or prisms with inclusion angles of 30 °, 60 °, 90 °) or multiple retroreflections on the optical surface. Includes any other monolithic component with a combination. The embodiments disclosed herein can be used to capture and evaluate two or four diffraction orders of a 1D or 2D grid, respectively, and therefore capture less than two or four diffraction orders. Efficiency can be improved compared to the configuration. In addition, each of the embodiments described herein can be used for both homodyne and heterodyne light sources.

0037In an exemplary embodiment, four diffraction measurement beams can be controlled using a single monolithic glass cube and an encoder scale (eg, a 2D grating). When the input measurement beam is supplied to the glass cube, the input measurement beam passes through the cube and collides with the encoder scale at a non-littrow angle, resulting in at least four first-order diffraction orders (eg, for example). It is divided into +1 and -1 order in the first plane and +1 and -1 order in the second plane orthogonal to each other. The four diffracted beams re-enter the cube, are retroreflected near the four corners of the cube and return to the encoder scale, where the beam is again diffracted at the non-retro-angle and out of the diffracted beam. The four beams are spatially separated and propagate in the opposite direction of the initial input beam. The double diffracted beam passes through the cube and is ready to interfere with one or more reference beams. The above arrangement provides four phase measurements and therefore the position of the encoder head or encoder scale can be calculated with some redundancy in all three dimensions.

0038FIG. 2A is a schematic cross-sectional view of a monolithic optical component 200 as an example for use in an encoder head of an interferometric encoder system similar to the exemplary embodiment described above. The optical component 200 is configured to receive a plurality of single-diffraction beams from the encoder scale 105 and redirect these single-diffraction beams back to the encoder scale. Other components of the interference encoder system have been omitted from the figure for clarity. Optics 200 includes a monolithic cube having a top facet 202, a bottom facet 204, and four side facets 206. Encoder scale 105 includes a 2D grid.

0039From the light source during operation of the interference encoder system<u style="single">Get</u>The measurement beam 201 is incident on the upper facet 202 of the optical component 200, at which time the measurement beam 201 is perpendicular to the surface of the facet 202. The measurement beam 201 passes through the top facet 202 and the bottom facet 204 to reach the encoder scale 105 at a non-retrorow angle. Due to the diffraction characteristics of the encoder scale 105, the measurement beam 201 is diffracted into a plurality of diffraction orders. Diffraction beams can be, for example, one or more first beams obtained from the positive diffraction order of the encoder scale and one or more second beams obtained from the negative diffraction order from the encoder scale 105. Correspond. For example, the encoder scale 105 propagates the measurement beam 201 through two beams propagating in the XY plane (eg, +1st order diffraction and -1st order diffraction) and two beams propagating in the YZ plane (eg, +1st order diffraction). And -1st order diffraction).

0040The single diffraction beam 203 returns to the optical component 200, and the beam enters the optical component 200 again from the bottom facet 204. The single diffraction beam 203 is then reflected by the side facets 206 and the top facets 202 of the optical component 200 and returned to the bottom facets 204. The first diffracted beam 203 passes through the lower surface facet 204 and is directed toward the encoder scale 105, and the encoder scale 105 diffracts the measured beam for the second time under non-retrow conditions. The double diffraction beam 205 then returns towards the optical component 200 in a direction substantially opposite to the direction of the incident beam 201. After passing through the optics 200, each of the double diffracted beams 205 is combined with the corresponding reference beam (omitted for clarity) to form the corresponding output beam, which is the detection module (excluded for clarity). For example, it is received by a polarizer and a photodetector). An electronic processor connected to the detector analyzes the interference signal from each detector to extract phase information about the relative position of the encoder scale and / or encoder head.

0041In the example shown in FIG. 2A, the top facet 202 transmits radiation that is perpendicular to the surface of the facet 202, while radiation that is incident on the surface of the facet 202 at an angle of inclination with respect to the surface of the facet. Is configured to reflect. This property of the top facet 202 can be established using a multi-layer coating on the facet (eg, multiple alternating layers of different thin film materials). By manipulating the thickness and composition of each layer in the multi-layer stack, the reflection characteristics can be tailored to a particular angle of incidence. That is, the coating should have antireflection properties for radiation that is vertically incident radiation and high reflectance for radiation incident at one or more tilt angles with respect to the surface of the facet 202. Can be optimized for. For example, if all tilted beams that collide with the top facet 202 have the same angle of incidence with respect to the facet surface, then the layer thickness of the multilayer coating at a certain angle of incidence and wavelength is a quarter of the reflectivity for that tilted beam. It can be configured to behave like a one-wavelength stack, and for vertically incident light, behave like a transmissive half-wavelength stack. The angle dependence of surface reflections is due to changes in the difference in optical path length between reflections from various interlayer interfaces.

0042For coatings configured to maximize the transmission of a vertically incident beam, the incident beam angle tolerance of this coating can be up to about +/- 10 ° from the vertical. For coatings configured to maximize the reflectance of sloping beams (ie, beams that are non-perpendicular and non-parallel to the plane of incidence), the incident beam angle tolerance of this coating is approximately + from the desired angle. It can be from / -2 ° to about +/- 5 °. For coatings that substantially transmit the incident beam at a particular angle, the coating is at least 75% (eg, at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, or) of the incident beam. At least 99%) can be transmitted. For a coating that substantially reflects an incident beam at a particular angle, this coating will be at least 75% (eg, at least 80%, at least 85%, at least 90%, at least 95%) of the incident beam at a given angle. At least 98%, or at least 99%) can be reflected. Materials for such coatings can include, for example, zinc sulfide, titanium dioxide, magnesium fluoride, and / or silicon dioxide. An example of a multi-layer coating that reflects only about 1.2% for vertical beams and 95.2% for tilted beams at 27.82 ° in BK7 glass is a stack of ABCBCBCBA, where A is a 57 nm magnesium fluoride layer and B is 942 nm zinc sulfide. Zinc layer, C is a magnesium fluoride layer of 1149 nm. Other guidelines on how to design such multilayer films are described, for example, in E. Hecht, Optics, 4th Edition, Addison Wesley, 2003. The entire contents are incorporated herein by reference. Multilayer coatings can also be used in other embodiments, including the following examples:

0043Unlike the top facet 202, the bottom facet 204 is configured to transmit incident radiation perpendicular or oblique to the surface of the bottom facet. In some implementations, the facet 204 is configured to include a multilayer coating for a wide angle of incidence in order to facilitate transmission from the underside facet 204. Alternatively, the underside facet 204 can be configured to include a multi-layer coating optimized for a particular angle of incidence (eg, vertical incidence and incident at one tilt angle) and a particular wavelength or wavelength range. The side facets 206 are naturally reflective due to total internal reflection (ie, the outer region of the part 200 has a lower refractive index than the inner region of the part 200). However, the side facets 206 can also be configured to include a highly reflective coating.

00442B and 2C are three-dimensional (3D) schematic views of the optical component 200 shown in FIG. 2A. As shown in FIGS. 2B and 2C, the optics 200 is the bottom edge of the side facet 206. The orientation is such that the edge) does not match the edge of the encoder scale 105. In this example, the encoder scale 105 includes a grid composed of a set of grooves extending along a direction parallel to at least two edges of the portion of the encoder scale 105 shown in the figure. Rotating the optics 200 so that the lower edge of the side facet 206 is at an angle of inclination with respect to the edge of the encoder scale and therefore at an angle to the direction in which the groove extends ensures that the single diffraction beam is It can be roughly propagated toward the corners of the optical component 200, and the corners of the optical component 200 cause retroreflection. Figure 2B shows a more general case of the angle at which the optics 200 can rotate with respect to the encoder grid, while in Figure 2C the angle is just 45 °. That is, the single-diffraction beam 203 passes through the lower surface facet 204 and then propagates toward the edge formed by the intersection of the side facets 206. As a result, it is possible to maintain a certain degree of symmetry of the polarization characteristics and the beam path between various beams.

0045In some embodiments, the optics prevent the single diffraction beam from colliding on the edges formed by the intersections of the side facets, while at least some single diffraction beams are such. It can be configured to prevent such an incident on the edge. FIG. 3A is a 3D schematic view of the monolithic optics 300 as an example, which prevents the diffracted beam from colliding with the edges formed by the intersections of the side facets 306. To achieve this effect, the optics 300 are configured to be a rectangular parallelepiped oriented at 45 ° with respect to the grid direction of the encoder scale 105 (ie, the direction in which the elongated portion of the grid extends). There is. FIG. 3B is a 3D schematic of a cube rotated 30 ° with respect to the grid direction to prevent the single diffracted beam from hitting the faceted edges.

0046For clarity, the other components of the interference system and the reference beam are omitted in Figure 3. Similar to the optics 200 in FIG. 2, the optics 300 can be made of glass and include multilayer coatings on different facets to increase the transmission of incident radiation at a specified angle and / or at another specified angle. The reflection of incident radiation can be increased. In some implementations, component 300 or component 200 can also be configured to increase the spatial separation between beams incident on the facet surface. Each separated beam can then be directed towards a different region of optics 300 or 200 (eg, towards the facets or sides of optics 300 or 200). Physical separation allows the facet or surface on which each separated beam is incident to include a corresponding local reflective or transmissive coating for that beam. By increasing the spatial separation between the beams, the spacing between the local antireflection / transmissive coatings formed on the optics can also be increased, and therefore the complexity of manufacturing different coatings in close proximity to each other. Is reduced. Various parameters can be adjusted to obtain the spacing between beams that allows the formation of a local coating, for example this is the aspect ratio of the optics, between the encoder scale 105 and the optics 300 or 200. Distance, pitch between the grid grooves of the encoder scale 105, and / or rotation of the encoder scale 105 in the grid direction with respect to the optics.

0047In some embodiments, it is advantageous to feed and detect the measurement beam along a direction parallel to the plane containing the encoder scale 105. FIG. 4A receives a measurement beam 401 propagating along a direction parallel to the plane containing the encoder scale 105, redirects the measurement beam 401 towards the encoder scale, and along a direction parallel to the plane containing the encoder scale 105. It is the schematic of the cross section of the optical component 400 by an example for outputting a plurality of double diffraction measurement beams 405. The shape of the optical component 400 corresponds to a monolithic triangular prism. For clarity, Figure 4A omits the other optics of the interferometric system and shows only one double diffracted beam. However, the optics 400 can redirect a plurality of double diffracted beams, the double diffracted beam being composed of one or more first beams obtained from the positive diffraction order from the encoder scale 105. Includes one or more second beams obtained from negative diffraction order from encoder scale 105. As shown in FIG. 4, the measurement beam incident on the encoder scale 105 does not satisfy the retrow condition.

0048The optics 400 can be made of any suitable material that is substantially transparent to the wavelength of the measurement beam (eg, glass for light in the visible wavelength range) and receives the incident measurement beam 401, 2 Includes a first facet 402 for transmitting the diffraction measurement beam 405. The first facet 402 can also include a thin film multilayer coating (not shown) configured to reflect radiation incident on the facet surface at an angle of inclination. The second facet 404 can include a thin film multilayer coating configured to allow transmission or reflection of incident radiation depending on the angle of incidence. For example, as shown in FIG. 4A, the second facet 404 is a thin film multilayer coating that maximizes the transmission of radiation perpendicular to the surface of the second facet 404 and incident at the first tilt angle (shown). ) May be included. However, the second facet 404 reflects radiation incident on the facet surface at a second tilt angle different from the first, which is made possible by either a multi-layer coating or a total internal reflection phenomenon. The third facet 406 includes a thin film coating (not shown) configured to substantially reflect radiation to its surface at any angle. For example, the thin film coating of the third facet 406 can include a thin film layer of silver or gold.

0049FIG. 4B is a 3D schematic view of the optical component 400. In some implementations, component 400 is rotated with respect to the grid direction of the encoder scale 105. For example, the lower edge of part 400 formed by the intersection of side facets 406 and facets 404 is non-parallel to the groove direction of the grid (eg, non-parallel to the direction in which the elongated portion of the groove extends). Can be rotated like this. Rotating the optics 400 non-parallel to the grooves ensures that the one-time diffracted beam propagates roughly towards the corners of the optics 400 in some implementations.

0050In some embodiments, the monolithic optics can be configured to work with an encoder scale having a one-dimensional (1D) pattern, eg, a 1D grid. FIG. 5 is a 3D schematic of the optical component 500 used in the encoder head of an interferometric encoder system, where the optical component 500 receives multiple single diffraction beams from an encoder scale 105 with a 1D grid. Arranged to divert the diffracted beam back to the encoder scale 105. In the implementation shown in FIG. 5, the single diffraction beam 503 received by component 500 includes beams obtained from both positive and negative diffraction orders along the same plane. The optical component 500 is a monolithic regular hexagonal prism, which can be made of a material that is substantially transparent to the wavelength of the measurement beam (eg, glass for a measurement beam in the visible wavelength range). Basically, the prism shape shown in FIG. 5 is passed by the measurement beam (including the incident measurement beam and the 1st and 2nd diffraction measurement beams) and / or by the plane of the rectangular prism that reflects the measurement beam. The part of the rectangle that is defined and is not passed by the measurement beam or does not reflect the measurement beam has been removed.

0051In the examples shown in FIGS. 2-5, the incident measurement beam and the double diffraction beam travel through the monolithic optics. However, in some embodiments, these beams may propagate to and from the encoder scale 105 without propagating through the optics. FIG. 6 is a 3D schematic view of an optical component 600 in which neither the incident measurement beam 601 nor the double diffraction measurement beam propagates through the component 600. For clarity, other components of the interferometric encoder system and the reference beam have been omitted.

0052As shown in FIG. 6, the incident measurement beam 601 propagates toward the encoder scale 105 outside the component 600. The single-diffraction beam obtained from the diffraction of each measurement beam on the encoder scale 105 then propagates into the component 600, and the single-diffraction beam at the component 600 is reflected by the facet of the component 600 to the encoder scale 105. The direction is changed back to, and the second diffraction is performed without satisfying the Litro condition. The double diffraction beam 605 then propagates in the opposite direction, substantially parallel to the incident measurement beam 601 without passing through the optics 600. The advantage of a configuration in which the incident and double diffracted beams do not pass through the monolithic optics, such as the component 600 shown in FIG. 6, is that one or more surfaces of the optics, which are used only for reflection, The point is that it can be configured to have a high reflectance. Since it is not necessary to allow the beam to pass through these surfaces, these surfaces can be formed to have a highly reflective coating, thus improving the efficiency of reflecting light. Increasing the amount of reflected light can improve the signal that is ultimately detected by the photodetector module.

0053In some embodiments, monolithic optics with transmissive / reflective facets deviate from the shape of a rectangular parallelepiped or right angle prism. The optical component 700 described below is an example of such a component. In some cases, such other shapes can also be used to extract phase difference information. That is, the optics can be configured so that the plurality of measurement beams interfere with each other, thus eliminating the need to obtain another reference beam from the light source. The encoder position information is then based on the phase of the interfering beam, which is related to the optical path difference (OPD) between the measured beams.

0054FIG. 7 is a 3D schematic of a monolithic optical component 700 as an example, in which the monolithic optical component 700 synthesizes and interferes with multiple measurement beams to generate an output beam, from which the phase information and therefore the output beam. It is configured to be able to extract position information related to the encoder scale. For clarity, the other components of the interference system are omitted in Figure 7. In this example, the optical component 700 has a shape corresponding to a regular pentagonal prism and can be formed of glass.

0055During operation, the incident measurement beam 701 propagating along the direction perpendicular to the surface of the top facet 702 travels through the top facet 702 and bottom facet 704 of component 700. The incident beam 701 is diffracted by an encoder scale (including a diffraction grating line) at the first position 720 without satisfying the retrow condition, and generates a plurality of diffracted beams corresponding to different diffraction orders of the incident measurement beam 701. For example, the encoder scale diffracts the measurement beam 701 into two beams propagating in the first plane and two beams propagating in the second orthogonal plane. For clarity, only two of the diffracted beams generated at position 720 are shown, and each of the single diffracted beams propagates in a different plane. The single-diffraction beam is redirected by the facets of the optical component 700, and both of the redirected single-diffraction beams are incident on the second position 730 of the encoder scale, which is the first position. Is different. At the second position 730, the single-diffraction measurement beam does not meet the Litro condition and is diffracted again, causing the double-diffraction beam 705 to propagate parallel to and in the opposite direction to the incident measurement beam 701. The double diffraction beam 705 is also in line so that it interferes when the double diffraction beam 705 reaches the detector module (not shown) of the interference system. Upon receiving the interfering double diffract beam 705, the detector module can generate an electronic interference signal. An electronic processor connected to the detector module can analyze the interference signal to extract phase information and determine the position of the encoder scale with respect to the encoder head (ie, monolithic optics) from the phase information.

0056Various embodiments of an interference encoder system that utilizes monolithic optical components are possible. For example, in some embodiments, the interferometric encoder system includes a beam separating component (eg, a polarized and unpolarized beam splitter) and a beam steering component. Components) (eg, mirrors, lenses, prisms, retroreflectors), and / or polarization control components can be included in addition to monolithic optics. An additional beam separator and / or beam steering element provides a fixed number of reference beams at a specified position, which is combined with the diffraction measurement beam obtained using monolithic optics. For example, in some embodiments, a beam composite component can be used to combine one or more double diffraction measurement beams with one or more reference beams, respectively, and these composite beams are in the detector module. Interfere with. In some embodiments, the beam separator and / or beam steering component is arranged so that the measurement and reference beams remain parallel to each other, even with poor angular alignment of the initial source input beam. it can. In some embodiments, one or more gratings on the encoder scale can be used to diffract the reference beam back to the monolithic optics. The use of additional grids can provide the configuration of compact interferometric encoder systems in some implementations, which is very spatially efficient for grids to generally generate multiple beams from one beam. This is because it is a high-level means (see, for example, Fig. 9).

0057Beam-splitting combining components disclosed herein can also include beam separating elements such as, for example, polarized or unpolarized beam separating prisms. Other beam separators can also be used, such as half mirrors or dichroic mirror prisms. Beam steering components disclosed herein include retroreflectors such as corner cube reflectors and / or prisms such as right angle triangular prism prisms. Examples of polarization state changing devices disclosed herein include, but are not limited to, linear polarizers, quarter wave plates, and half wave plates.

0058FIG. 8 shows an embodiment of an interferometric encoder system that includes a beam steering component and a beam compositing component in addition to a monolithic optical component to acquire a double diffraction measurement beam. In particular, FIG. 8 is a schematic cross-sectional view of the interference encoder head 810, which includes a monolithic optical component 800 for receiving multiple diffracted beams from the encoder scale and a first beam splitter / It includes a combiner component 812, a second beam splitting component 814, a third beam splitting component 816, and a retroreflector 818. In some embodiments, the encoder head also includes a polarization control component 820 (eg, a quarter wave-plate (QWP), a half-wave plate, or a polarizing rotator).

0059In certain embodiments, the polarization state of the beam is generally such that the beam is diffracted twice by the lattice and passed through the air-glass interface multiple times and is uncoated with monolithic optics or other optics in the interferometer system. It may be generally oval after multiple internal reflections from the surface and the coated surface. In some cases, such changes in polarization state will ultimately reduce the efficiency of the entire interferometer system, considering that less light will reach the detector module, and / or position detection. Accuracy may be reduced. Polarizing elements such as the polarization control component 820 can be added to the encoder head device and positioned to compensate for changes in the polarization state. Compensating elements can be placed between monolithic optics (eg, rectangular parallelepipeds or right angle prisms) and encoder scales (and / or reference grids) and / or on surfaces that are part of a retroreflector. For example, as shown in FIG. 8, the encoder head 810 has a first QWP 820a on the first surface of the beam separator 812 and a second QWP on the second surface of the beam splitter 812. Includes 820b. The first QWP 820a is located between the beam separator 812 and the retroreflector 818, whereas the second QWP 820b is located between the beam separator 812 and the monolithic optics 800.

0060During the operation of the interferometric encoder system utilizing the encoder head 810, the input beam 825 is supplied from the light source to the third beam separation component 816. The third beam splitter 816 splits the incident beam 825 into a measurement beam (solid line) and a reference beam (dashed line). For example, the beam splitter 816 can include a polarizing beam splitter, which can split an input beam composed of orthogonally polarized beam components (eg, s and p polarized beam components) into a polarized beam of reference and measurement beams. Split into reference and measurement beams based on the differences. Both the reference beam and the measurement beam pass through the second beam separator 814.

0061The measurement beam passes through the second beam separation component 814 without changing the first beam separation component 812, and the measurement beam then redirects towards the monolithic optics 800 and encoder scale 105 at the beam separation interface. Will be done. With optics 800, the measurement beam is diffracted multiple times at a non-retroangle angle to produce two or more double diffraction measurement beams.

0062In contrast, the reference beam interacts with the beam separation interface of the second beam separation component 814 to separate it into two separate reference beams. Both reference beams generated by component 814 pass through the first beam separator 812 and are reflected little or no towards the retroreflector 818. The retroreflector 818 redirects each reference beam back towards the first beam separator 812, where the first beam separator 812 combines each reference beam with the corresponding double diffraction measurement beam. , Produce separate output beams 807, 809. As shown in FIG. 8, the two output beams 807, 809 exit from the first beam separator 812. If the encoder scale 105 contains a 2D grid, the encoder head device shown in FIG. 8 may be used to generate an additional output beam, which propagates out of the plane of the figure. In this case, additional beam separators would also have to be used to create additional reference beams. The advantage of the configuration shown in FIG. 8 is that the measurement and reference beams remain parallel to each other within each output beam, even if the initial input beams have poor angular alignment. This is because the measurement beam, and the reference beam, are retroreflected by each of component 800 and component 818, resulting in all output beam angles changing by the same amount as the input beam angles.

0063FIG. 9 is a schematic diagram of an interferometric encoder head 910 as an example, including a monolithic optical component 900 and a reference grid 950. The optics 900 can include, for example, a polarized beam separating component configured to obtain a measurement beam 901 and a reference beam 911 from an input beam 925 supplied from a light source, the input beam 925 from an orthogonally polarized beam component. Become. When the measurement beam 901 is reflected from the beam separation interface 902, it propagates to the encoder scale 105, and the beam 901 at the first position 903 of the encoder scale 105 at a non-retrorow angle has multiple diffraction orders (eg, +). It is diffracted into primary and -1st order diffraction). For clarity, only one diffracted beam is shown at position 903 in FIG.

0064The multiple single diffraction measurement beams (eg, 901') then propagate back to the monolithic optics 900. In optics 900, the single diffraction measurement beam is reflected by the central facet 902 and one or more side facets of component 900, after which the single diffraction measurement beam is in a second position 904 in non-retro state conditions. And the direction is changed to return to the encoder scale 105 at the tilt angle with respect to the encoder scale 105. When the encoder scale is reached for the measurement beam, a second diffraction is performed on a plurality of diffraction orders. Again, for clarity, only one diffracted beam is shown at position 904 in FIG. The double diffraction measurement beam (eg, 901'') propagates back to the optics 900 and is then reflected by the central facet 902 and propagates in parallel and opposite directions to the input beam 925.

0065The central facet 902 is also used to obtain the reference beam 911. The reference beam 911 (dashed line in FIG. 9) propagates through the component 900 to the reference grid 950, and the reference beam is at the first position 906 of the reference grid 950 at multiple diffraction orders at a non-retroangle angle (eg, +). It is diffracted into primary and -1st order diffraction). For clarity, only one diffracted beam 911'is shown at position 906 of reference grid 950 in FIG. One or more of the single diffraction reference beams return to part 900. In optics 900, the single-diffraction reference beam is reflected by the central facet 902 and one or more side facets of component 900, after which the single-diffraction measurement beam is referenced grid at a non-retro angle at second position 907. Turned back to 950.

0066The measurement beam undergoes a second diffraction at one or more diffraction orders (eg, +1 or -1) at the second position 907 of the reflection grid 950. Again, for clarity, only one double-diffraction reference beam 911'' is shown in FIG. Each double-diffraction reference beam then propagates through the beam separator 900 and is combined with the corresponding double-diffraction measurement beam to form the corresponding output beam. The output beam is then received by a detector module (not shown) and in FIG. 9 an exemplary output beam is shown as beam 960. To ensure that the reference and measurement beams are properly reflected or transmitted by the facets of the part, the facets should include a multi-layer coating to reflect and / or transmit the incident radiation at the specified angle of incidence. Can be configured in. In the example shown in FIG. 9, the central facet 902 is configured to act as a beam splitter for radiation incident at 45 ° to the surface of the facet 902 and to reflect incident radiation at other angles. An example of a multi-layer coating that reflects only 3.2% of a 45 ° beam (relative to the interface normal) and 96.8% of a 20 ° beam on the beam separation surface between two blocks of BK7 glass is a stack of ABCBCBCBA. A is a 78 nm magnesium fluoride layer, B is a 756 nm zinc sulfide layer, and C is a 365 nm magnesium fluoride layer.

0067FIG. 10 shows another embodiment of an encoder head that can use a reference grid. In particular, FIG. 10 is a 3D schematic showing an example of the interferometric encoder head 1010, which includes a beam splitter 1002, a reference grid 1050, a measurement block 1060, and a reference block 1070. The measurement block 1060 and the reference block 1070 include optical elements such as a right-angled triangular prism and are fixed to the beam splitter 1002 using, for example, an optical adhesive. The beam splitter 1002 can include, for example, an unpolarized beam splitter or a polarized beam splitter. The measurement block 1060 is positioned to direct the measurement beam toward the encoder scale 105 and receive the 1-fold and 2-diffraction measurement beams from the encoder scale 105. Reference block 1070 is similarly positioned to direct the reference beam towards the reference grid 1050 and receive the one-diffraction and two-fold diffraction reference beams from the reference grid 1050. The beam splitter 1002 receives an input beam 1001 having an orthogonally polarized beam component from a light source (not shown) and splits the input beam 1001 into both a reference beam and a measurement beam. The reference beam and the measurement beam are then redirected by the beam splitter 1002 towards reference block 1070 and measurement block 1060, respectively. The beam splitter 1002 is also configured to combine the double diffracted reference beam and the double reference measurement beam into four separate output beams 1007, the four separate output beams 1007 being transmitted to the detector module. , Interference signals are obtained from four separate output beams 1007, and the relative position of the encoder scale and / or encoder head is determined (eg, based on phase information from the interference signals).

0068FIG. 11 is an example of another embodiment of the encoder head including the reference grid. In particular, FIG. 11 is a schematic view showing a cross-sectional view of the interference type encoder head 1110, in which the interference type encoder head 1110 includes a measurement block 1160 (for example, a rectangular parallelepiped), a reference block 1170 (for example, a rectangular parallelepiped), and a polarizing beam. It includes a splitter 1102, a reference grid 1150, and two quarter wave plates (QWP) 1180.

0069The operation of the encoder head 1110 is similar to the operation of the encoder head 1010 shown in FIG. That is, the beam splitter 1102 receives an input beam 1125 having an orthogonal polarization component, separates the input beam 1125 into a reference beam (broken line) and a measurement beam (solid line), and then the reference beam and the measurement beam are referred to as reference blocks 1170, respectively. Propagate towards measurement block 1160.

0070Initially, the measurement beam passes through measurement blocks 1160 and QWP 1180 and is barely or completely unreflected, with one or more diffraction orders (eg, +1st order, -1st order diffraction) at non-retro angle by encoder scale 105. ) Is diffracted. The single diffraction measurement beam returns to the measurement block 1160, and the single diffraction measurement beam is reflected by the side facets of the measurement block 1160 and returns to the encoder scale 105. As in the other embodiments described above, the measurement block 1160 can include a localized thin film coating configured to reflect a single diffraction measurement beam based on the angle of incidence. The one-time diffraction measurement beam returns to the encoder scale 105, where the beam is diffracted a second time to one or more diffraction orders at a non-retro angle. At least some of the double-diffraction measurement beams propagate back to measurement block 1160 along a direction parallel to the incident measurement beam.

0071Similarly, the incident reference beam is the reference block 1170 and QWP. It passes through 1180 and is hardly or at all reflected and is diffracted by the reference grid 1150 to one or more diffraction orders (eg, +1 or -1). The one-diffraction reference beam returns to reference block 1170, is reflected by the side facets of block 1170, and returns to reference grid 1150. In another embodiment described above, reference block 1170 can include a localized thin film multilayer coating configured to reflect a single diffracted reference beam based on the angle of incidence. The one-diffraction reference beam returns to the reference grid 1150, where the beam is diffracted a second time to one or more diffraction orders. At least some of the double-diffraction reference beams propagate back to reference block 1170 along a direction parallel to the incident reference beam. The double-diffraction reference beam and the double-diffraction measurement beam are then combined in the beam splitter 1102 to form the output beam 1107, which relates to the difference in optical path length between the measurement beam and the reference beam. Includes phase information. A detector module and an electronic processor (not shown) can be used to calculate information about one or more relative degrees of freedom for encoder scale 105 and / or encoder head 1110.

0072The measurement block 1160 and the reference block 1170 are aligned so that they overlap when the double-diffraction reference beam and the double-diffraction measurement beam are combined in the beam splitter 1102 (ie, from the beam splitter 1102). It does not have to be the same distance (the same distance from each grid). For example, in some implementations, the distance between the reference block 1170 and the reference grid 1150 can be different from the distance between the measurement block 1160 and the encoder scale 105. In some implementations, the grid pitch on the encoder scale 105 can be different from the pitch on the reference grid 1150. In some implementations, the dimensions of measurement block 1160 can be different from the dimensions of reference block 1170. For example, it may be preferable to minimize the effects of fluctuations by bringing the reference grid 1150 into contact with, or at least very close to, the reference block 1170. In order for the offset between the input and output beams to be the same as in the measurement path, the dimensions and / or grid pitch of reference block 1170 should be different from those used in the measurement path. .. In addition to this, in the configuration shown in FIG. 11, the beam supply and the beam pickup are spatially separated by guiding the output beam 1107 in a direction different from that of the input beam 1125.

0073As mentioned in the embodiments described above, some surfaces of the monolithic optics should be configured to transmit the beam, while other surfaces of the monolithic optics should be configured to reflect the beam. Should be done. One surface of an optical component can reflect or transmit an incident beam at one or more angles by providing a thin film multilayer coating on this surface.

0074In some embodiments, monolithic optics (eg, cubes, rectangular parallelepipeds and right angle prisms) can be formed with a slight angle deviation from their perfect geometry. The loss of symmetry as a result of angular misalignment is spurious reflection. It can help reduce errors in detecting encoder scale positions related to reflection). That is, spurious reflections tend to follow different paths from the measurement beam and therefore do not mismodulate the detected interference signal. For example, the edges on both sides of an originally symmetrical monolithic optic may be parallel to each other and / or to the plane of the encoder scale, subject to manufacturing tolerances, for example greater than 0 ° but greater than about 10 °. It can be shifted by a small amount (eg, about 0.5 °, about 1 °, about 5 °, or about 7 °). One such case is schematically shown in FIG. 12, where the surface 1211 of the glass monolithic optics 1210 facing the encoder scale is an amount, eg 1 °, relative to the encoder scale 105. Only intentionally tilted. The solid line shows the measurement beam and the intended path of the two diffraction events. In contrast, the broken line indicates an unintended spurious beam, which is first diffracted by zero-order diffraction, reflected by the slanted surface 1211, diffracted by first-order diffraction, and including retroreflection, glass monolithic optics 1210. After roughly following the intended measurement path within, the lattice finally undergoes a third diffraction. Since the direction and position of the spurious beam is different from the desired beam direction and position, it is possible to substantially reduce the measurement error that can occur due to the presence of the spurious beam in the detector. On the other hand, if the underside of the glass monolithic optics is parallel to the encoder scale, the spurious beam will be at the same angle and position as the desired measurement beam, which will cause further errors in the position measurement. ..

0075In some embodiments, the encoder head is configured to propagate the measurement and reference beams within the encoder head optics with small separation angles from each other. For example, by including one or more polarized optical components in the beam path of the measurement and reference beams, a small separation angle between the measurement and reference beams (eg, about 0. (Between 05mrad and 20mrad) can be given. By having a small separation angle between the measurement and reference beams, these beams can be distinguished not only by their polarization but also by their propagation angle, resulting in a large periodic error in mixing the polarizations in the encoder head. Is reduced. This is shown in FIG. 13, where box 1310 shows an encoder head containing monolithic optics and / or beam separation optics and retroreflective optics. The two input beams 1301 and 1302, which are intended to be reference and measurement beams, respectively, are orthogonally polarized to each other and are separated by a small angle. The output beams 1303, 1304 from the encoder head still have the same separation angle and are orthogonally polarized to each other, but the desired output in either direction or polarization, depending on the potential leakage of the polarizer in the encoder head. There can be other unintended output beams 1305, 1306 (ie, ghost beams) that are different from beams 1303, 1304. The birefringent beam combiner 1320 can redirect the intended output beams 1303 and 1304, so that the beams 1303 and 1304 are parallel, whereas the unintended beams 1305 and 1306 are beam combiners 1320. Is deflected along substantially different directions. Therefore, the desired output beams 1303, 1304 can reach the detector module 130 (including, for example, the photodetector and the polarizer) at the same angle, while the unwanted beam is a stronger desired beam. Depending on the angle with respect to, the detector module 130 may not be reached or the contrast of the interference fringes may be substantially reduced. Therefore, it is possible to eliminate measurement errors due to the presence of an unwanted beam in the detector.

0076In general, any of the analysis methods described above can be implemented in computer hardware or software, or a combination of both, including determining phase information and encoder-scale freedom information from detected interference signals. For example, in some embodiments, the electronic processor 150 can be installed in a computer and connected to one or more encoder systems to perform analysis of signals from the encoder systems. The analysis can be implemented in a computer program using standard programming techniques according to the methods described herein. The program code is applied to the input data (eg, interference phase information) and the functions described herein are performed to generate output information (eg, degrees of freedom information). The output information is applied to one or more output devices such as display monitors. Each program may be implemented in a higher procedural or object-oriented programming language to communicate with a computer system. However, the program can also be implemented in assembly or machine language if desired. In either case, the language can be a compiled or interpreted language. In addition, the program can be run on a dedicated integrated circuit pre-programmed for that purpose.

0077Each such computer program is preferably stored on a storage medium or device (eg, ROM or magnetic diskette) readable by a general purpose or special purpose programmable computer, and the computer is stored on the storage medium or device. When read by the computer, it is configured or operated to perform the procedures described herein. Computer programs can also be stored in cache or main memory during program execution. Analytical methods can also be implemented as computer-readable storage media configured with a computer program, the storage media so configured as described herein in a computer-specific, pre-determined manner. To execute the function. Application to lithography tools Lithography tools are particularly useful in lithographic applications used in the manufacture of large integrated circuits such as computer chips. Lithography is a key technology driver for semiconductor manufacturing. Overlay improvement is one of the five major challenges for achieving line widths (design rules) of 22 nm or less, for example, International Technology Roadmap for Semiconductors p.58-59 ( 2009).

0078Overlays directly depend on the performance of the measurement system used to position the wafer and reticle (or mask) stages, namely accuracy and precision. Annual production of lithographic tools can amount to $ 50-500 million, and the economic value of improving measurement systems is great. A 1% increase in lithographic tool production will bring about $ 1 million annually to integrated circuit manufacturers, significantly increasing the competitive advantage of lithographic tool suppliers.

0079The function of the lithography tool is to direct spatially patterned radiation to a wafer with a photoresistor coating. This process involves determining which position on the wafer will receive the radiation (alignment) and irradiating the photoresist at that position (exposure).

0080During exposure, the source irradiates a patterned reticle, which scatters the radiation and produces spatially patterned radiation. Reticles are also called masks, and these terms are used interchangeably below. In the case of reduced projection lithography, the reduced projection lens collects the scattered radiation to form a reduced image of the reticle pattern. Alternatively, in the case of proximity printing, the scattered radiation propagates over a short distance (usually on the order of micrometers) and then contacts the wafer to produce a 1: 1 image of the reticle pattern. Radiation initiates a photochemical process within the resist, which transforms the radiation pattern into a latent image within the resist.

0081In order to properly position the wafer, the wafer contains an alignment mark on the surface of the wafer, and the alignment mark can be measured by a dedicated sensor. The position of the measured alignment mark defines the position of the wafer within the tool. This information guides the wafer alignment for spatially patterned radiation, along with the desired patterning specifications for the wafer surface. Based on this information, a translatable stage that supports the photoresist-coated wafer moves the wafer so that radiation exposes the correct position on the wafer. In certain lithographic tools, such as lithographic scanners, the mask is also placed on a translationally movable stage that is moved with the wafer during exposure.

0082Encoder systems such as those described above are important components of a positioning mechanism that controls the position of the wafer and reticle and aligns the reticle image on the wafer. If such an encoder system includes the features described above, the accuracy of the distance measured by the system can be improved and / or it can be retained for a longer period of time without offline maintenance, resulting in. Throughput is improved by increasing production and reducing tool downtime.

0083Lithographic tools, also commonly referred to as exposure systems, typically include a lighting system and a wafer positioning system. The lighting system includes a radiation source that supplies radiation such as ultraviolet, visible, x-ray, electron or ion radiation, and a reticle or mask that patterns the radiation, thereby producing spatially patterned radiation. Will be done. In addition to this, in the case of reduced projection lithography, the lighting system can include a lens assembly for imaging spatially patterned radiation onto the wafer. The imaged radiation exposes the resist coated on the wafer. The lighting system also includes a mask stage that supports the mask and a positioning system for adjusting the position of the mask stage with respect to radiation directed through the mask. The wafer positioning system includes a wafer stage that supports the wafer and a positioning system for adjusting the position of the wafer stage with respect to the imaged radiation. Manufacturing an integrated circuit can include multiple exposure steps. Common references for lithography include, for example, JR Sheets and BW Smith, Microlithography (Science and Technology) (Marcel Dekker). , Inc.) New York, 1998). Its contents are incorporated herein by reference.

0084The encoder system described above can be used to accurately measure the position of each of the wafer and mask stages with respect to other components of the exposure system, such as the lens assembly, source or support structure. In such cases, the optical assembly of the encoder system can be attached to the stationary structure and the encoder scale can be attached to a movable element such as one of the mask and wafer stage. Alternatively, this situation can be reversed, the optical assembly can be attached to a movable object and the encoder scale can be attached to a stationary object.

0085More generally, such an encoder system can also be used to measure the position of any one component in the exposure system with respect to any other component in the exposure system. The optical assembly is attached to or supported by one of those parts and the encoder scale is attached to or supported by the other of those parts.

0086An example of the lithography tool 1400 using the interference system 1426 is shown in FIG. Encoder systems are used to accurately measure the position of wafers (not shown) within an exposure system. Here, stage 1422 is used to position and support the wafer with respect to the exposure station. The scanner 1400 includes a frame 1402, which carries other support structures and various components supported on these support structures. The exposure base 1404 is mounted on the lens housing 1406 on its upper surface, on which the reticle or mask stage 1416 used to support the reticle or mask is mounted. A positioning system for positioning the mask with respect to the exposure station is outlined by element 1417. The positioning system 1417 can include, for example, a piezoelectric transducer element and a corresponding control electronic device. Alternatively, although not shown in the embodiments described herein, a mask stage that requires accurate monitoring of its position during the manufacturing process of the lithographic structure using one or more of the above encoder systems. It can also accurately measure the location of and other movable elements (see Sheats and Smith, Microlithography: Science and Technology, above).

0087A support base 1413 is suspended beneath the exposure base 1404, which carries the wafer stage 1422. Stage 1422 includes an object to be measured 1428 that allows the measurement beam 1454 to be diffracted into the stage by the optical assembly 1426. A positioning system for positioning stage 1422 with respect to optical assembly 1426 is outlined by element 1419. The positioning system 1419 can include, for example, a piezoelectric transducer element and corresponding control electronic components. The object under test diffracts the reflection of the measurement beam back into the optical assembly mounted on the exposure base 1404. The encoder system can be any of the above-described embodiments.

0088During operation, a UV beam from a radiating beam 1410, eg, an ultraviolet (UV) laser (not shown), passes through the beam forming optics assembly 1412, is reflected by the mirror 1414, and then travels downward. The radiated beam then passes through a mask (not shown) carried by mask stage 1416. The mask (not shown) is imaged on a wafer (not shown) on the wafer stage 1422 through the lens assembly 1408 carried by the lens housing 1406. The base 1404 and the various components supported by it are isolated from environmental vibrations by a damping system depicted as a spring 1420.

0089In some embodiments, one or more of the encoder systems described above can be used to measure displacements along multiple axes and angles associated with, for example, but not limited to, wafer and reticle (mask) stages. .. Wafers can also be exposed using other beams instead of UV laser beams, such as X-ray beams, electron beams, ion beams, and visible rays.

0090In certain embodiments, the optical assembly 1426 can be positioned to measure changes in the position of the reticle (or mask) stage 1416 or other movable component such as a scanner system. Finally, encoder systems can be used in a similar manner for lithography systems that include steppers in addition to or instead of scanners.

0091As is well known in the industry, lithography is an important part of the manufacturing process for manufacturing semiconductor devices. For example, US Pat. No. 5,483,343 outlines the steps of such a manufacturing process. These steps are described below with reference to FIGS. 15A and 15B. FIG. 15A is a flowchart of a manufacturing sequence of a semiconductor device such as a semiconductor chip (for example, IC or LSI), a liquid crystal panel, or a CCD. Step 1951 is a design process for designing circuits for semiconductor devices. Step 1952 is the process of manufacturing the mask based on the circuit pattern design. Step 1953 is the process of manufacturing a wafer by using a material such as silicon.

0092Step 1954 is a wafer process called the pre-process, where circuits are formed on the wafer through lithography using such prepared masks and wafers. Interference-based positioning of the lithographic tool wafer is required to form circuits on the wafer that correspond to these patterns on the mask with sufficient spatial resolution. The interfering methods and systems described herein can be particularly beneficial for improving the effectiveness of lithography used in wafer processes.

0093Step 1955 is an assembly step, called a post-process, in which the wafer machined in step 1954 is formed into a semiconductor chip. This step includes assembly (dicing and bonding) and packaging (chip encapsulation). Step 1956 is an inspection step, in which a check of operability, a check of durability, and the like of the semiconductor device produced by step 1955 are executed. Through these steps, the semiconductor device is completed and shipped (step 1957).

0094FIG. 15B is a flowchart showing the details of the wafer process. Step 1961 is an oxidation process for oxidizing the wafer surface. Step 1962 is a CVD process for forming an insulating film on the wafer surface. Step 1963 is an electrode forming process in which electrodes are formed on a wafer by thin film deposition. Step 1964 is an ion driving process for driving ions into the wafer. Step 1965 is a resist process for applying a resist (photosensitive material) to a wafer. Step 1966 is an exposure process for printing a mask circuit pattern onto a wafer through exposure (ie, lithography) using the exposure apparatus described above. Also in the exposure process, as described above, the use of the interferometric systems and methods described herein improves the accuracy and resolution of such lithography steps.

0095Step 1967 is a developing process for developing the exposed wafer. Step 1968 is an etching process for removing parts other than the developed resist image. Step 1969 is a resist separation process for separating the resist material remaining on the wafer after performing the etching process. By repeating these processes, circuit patterns are formed and superposed on the wafer.

0096The encoder system described above can also be used in other applications where the relative position of an object needs to be accurately measured. For example, in applications where a write beam, such as a laser, X-ray, ion, or electron beam, marks a pattern on a substrate while moving either the substrate or the beam, an encoder system is used to transfer the substrate and write beam. Relative movement can be measured.

0097A number of embodiments have been described. Nonetheless, of course, various changes can be made. For example, in some embodiments, the monolithic optics include another beam steering element (eg, a grid and / or a refracting wedge) formed integrally with the component, which makes the beam more desirable. Greater flexibility for orientation to position. Alternatively, or in addition to this, other beam steering elements formed integrally with the monolithic optics allow for a beam shape that makes the interferometric encoder system inherently less susceptible to fluctuations in encoder scale position. Can be.

0098FIG. 16 shows an example of an encoder head that uses a patch of transmission and reflection grids formed integrally with monolithic optics to provide a beam shape that is less susceptible to fluctuations in encoder scale position.

0099Figure 16A shows only one of up to four measurement beams, the measurement beam 1601, guided by the monolithic optics 1610a (eg, a rectangular parallelepiped) towards a two-dimensional (2D) encoder scale (eg, a 2D grid) 105. It is the schematic of the cross section which shows the beam path. The beam 1601 reenters component 1610 after diffraction on the encoder scale 105, is retroreflected by the two side facets and top fat of component 1610a, and then is a patch of transmission grid 1605 integrally formed within component 1610a. Reach (patch). Lattice 1605 directs the single diffracted beam at approximately right angles to the encoder scale 105. The measurement beam is diffracted a second time from the encoder scale 105. The double diffraction measurement beam can be, for example, of the same diffraction order as the single diffraction beam (eg, + 1st order diffraction), and is directed by the transmission grid patch 1605 in the opposite direction to the initial incident beam (beam 1611). The direction is changed.

0100FIG. 16B is an encoder head configuration similar to FIG. 16A, in which the reflection grid 1606 on the top facet of the monolithic optics 1610b (eg, rectangular parallelepiped) provides retroreflection of the single diffraction measurement beam, thereby 1 The diffraction measurement beam is directed to the encoder scale 105. As shown in FIG. 16B, the reflection grid 1606 is laterally offset from the transmission grid 1605 so that the single diffraction measurement beam can pass through the underside facets of component 1610b without changing the beam path. The double diffracted beam is then redirected by the transmission grid 1605 parallel to the incident measurement beam 1601 and along a path opposite to the incident measurement beam 1601 (eg, beam 1611).

0101FIG. 16C is a 3D view of the encoder shown in FIG. 16B, again showing only one measurement beam path. As shown in Figure 16C, the edges of component 1610b are not oriented parallel to the groove in the encoder grid. This configuration allows the diffracted beam to enter the intersection of the two side and top facets of component 1610b.

0102Other embodiments are also within the scope of the claims.