Patterned grid element polarizer

The present invention relates to polarized optical elements.

Polarizer The simplest grid element deflector is a device consisting of a grid of parallel conductive wires. When light enters the grid, each orthogonal component of the irradiation intersects differently with the wire grid polarizer. The components of the field parallel to the wires drive electrons along the longitudinal direction of each wire, which produces an electric current. The electrons also collide with the lattice atoms, giving them energy, which heats the wire. In this way energy is transferred from the field to the grid. Furthermore, the electrons accelerating parallel to the wire radiate both forward and backward. The incident wave tends to be offset by the wave radiated forward, so that component of the field is opaque or almost impervious. Radiation propagating backwards simply appears as a reflected wave. Conversely, the components of the wave perpendicular to the wire propagate through the grid virtually unchanged. (Eugene Hecht, Optics, Chapter 8, pp.333-334, Addison Wesley, San Francisco (2002)) George R. in 1960. Bird and Maxfield Parish, Jr. disclose a grid polarizer for use in the microwave region with 2160 wires per mm (GR Bird and M. Parish, Jr., J. Opt. Soc). . Am. 50: 886 (1960)). According to this publication, this was achieved by depositing a gold (or aluminum) atomic stream on a plastic grating replica at a close angle of incidence. The metal deposited along the edges of each step of the grating forms a thin microscopic wire, the width and spacing of which wire is smaller than the wavelength.

Grid polarizers have been developed for use in both IR and visible spectrum. For example, US Pat. No. 6,122,103 states that a wire grid polarizer is prefixed to the visible spectrum. This polarizer has a plurality of stretching elements supported on the substrate. U.S. Pat. No. 5,748368 also describes a wire grid polarizer that polarizes light into the visible light spectrum.

In order to form faster and more sophisticated circuits than lithographs, the semiconductor manufacturing industry continues to strive to reduce the size of circuit elements. The circuit is basically manufactured by a photolithography. In this process, the circuit is printed on a semiconductor wafer by exposing a coating of photosensitive material to light. Photosensitive materials are often referred to as "photoresists" or resists. A mask made of chrome or other opaque material is formed on the transparent substrate. Passing light through this mask produces the desired circuit pattern. The mask can also be formed by a pattern of relatively high and relatively low regions etched on the surface of the transparent substrate. Alternatively, these two technologies can be combined. Subsequently, only exposed or unexposed parts of the resist (depending on the material) are removed by thermal or chemical processes, leaving exposed substrate areas. This area is used in the manufacture of electronic circuits in further processes.

Polarization in the reticle affects the lithograph capability of the lens in many ways. First of all, if the future of the reticle is, for example, a chrome density line, the intersection of this with the illumination will change with polarized light. As a result, the transmission and scattering of the mask depends on the polarization of the light and the future of the mask. Second, reflections on the surface of lenses and mirrors are polarized dependent, so apodization and, to a lesser extent, wave planes in projected optics (PO) are polarized. The reflection from the resist surface also depends on the polarization, which is also a polarization-dependent apodization. Finally, when the light rays diffracted from the reticle are returned to the wafer together, this also interferes with the formation of the image. However, since only the parallel components of the electric field interfere with each other, the polarization state of each light beam on the wafer affects the coherent image. Even with a perfect lens, the three-dimensional geometry of the light rays arriving at the wafer can reduce contrast.

The first reason to consider polarized illuminators is to improve the image formed on the wafer by improving the interference of the light rays diffracted by the wafer. This is especially advantageous for systems with large numerical apertures. Consider dipole illumination incident on a binary mask of density lines. Each small area in the illuminator pupil (ie, each pole of the low sigma dipole) is not coherent with the other areas in the pupil and forms a unique image on the wafer. Therefore, it can be regarded as a single pole for dipole lighting. Light is diffracted from the reticle and the density lines form a dense diffracted array. For small futures, only two diffraction sequences are allowed for PO. On the wafer, these diffraction sequences recombine to form a mask image. The image of the mask depends on the contrast, and this contrast depends on the polarization.

As mentioned above, the polarization state of the illumination in the reticle can improve the image formed on the wafer in the lithograph. Since lithographs use light in the UV spectrum, a polarizing device is needed for such UV applications. The inventor recognizes the advantages of wire grid polarizers. This type of polarizing device can customize the pattern to the element according to the application. Such a polarizing device is necessary, for example, to form a polarization pattern in the pupil of an illuminator of an optical system or in a projection optical system of a lithograph system.<patcit num="1"><text>U.S. Pat. No. 6122103</text></patcit><patcit num="2"><text>U.S. Pat. No. 5,748368</text></patcit><patcit num="3"><text>U.S. Pat. No. 4049944</text></patcit><patcit num="4"><text>U.S. Pat. No. 4514479</text></patcit><nplcit num="1"><text>Eugene Hecht, Optics, Chapter 8, pp.333-334, Addison Wesley, San Francisco (2002)</text></nplcit><nplcit num="2"><text>GR Bird and M. Parish, Jr. J. Opt. Soc. Am. 50: 886 (1960)</text></nplcit><nplcit num="3"><text>Grid polarizings for the visible spectral region, Proceedings of the SPIE, vol.2213, pp.288-296</text></nplcit>

<p> An object of the present invention is to provide a patterned grid polarizing device having high transmission efficiency over the ultraviolet spectrum.</p>

<p> According to the present invention, the patterned grid polarizing device used for the lithograph has (a) a substrate that is transparent to ultraviolet (UV) light and (b) an array of patterned elements on the substrate. , This element is solved by polarization the ultraviolet light.</p>

The grid polarizing device of the present invention generally consists of a substrate having a patterned element. The polarization of the light emitted from the polarizer of the present invention depends on the pattern of the elements on this substrate.

In the embodiment, the elements are grouped and arranged radially around the optical axis to form tangentially polarized emitted light. In another embodiment, the elements are patterned around the optical axis as concentric circles to form an emitted light that is polarized in the radial direction.

The present invention further provides an optical system including a squirrel graph system having the polarizing device of the present invention. Such a squirrel graph system benefits from a polarization pattern that enhances imaging on the wafer.

Further embodiments, futures, advantages, and structures and operations of the various embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

In one embodiment a patterned grid polarizer is provided for use in lithographs. Such a polarizing device has a substrate that is transparent to ultraviolet light and an array of elements that are patterned on the substrate, and these elements polarize the ultraviolet light.

Grid Element Pattern The present invention provides a UV polarizing device including elements patterned on a substrate by various methods. In the present invention, the pattern of elements on the substrate is configured to define the polarization of the light emitted from the polarizer.

Having a polarization pattern in the pupil of the illuminator of the optical system of the lithograph system or the illuminator of the projection optical system is advantageous for imaging for various reasons. For example, such a polarization pattern can provide a relatively large contrast to the wafer for good imaging.

According to an embodiment of the present invention, the polarizing device of the present invention has an element patterned on a substrate to form polarized light, and the polarization pattern of the light is defined by the pattern of the element.

For example, the element can be patterned on a substrate to form tangentially polarized (ie, tangential to the cylindrical symmetry of the polarizer) emitted light from incoming unpolarized light. The light arriving here enters the polarizing device and exits the polarizing device.

Alternatively, the element can be patterned on the substrate to form an emitted light that is radially polarized (ie, radial relative to the cylindrical symmetry of the polarizer) from the incoming unpolarized light. The light arriving here enters the polarizing device and exits the polarizing device.

However, the present invention is not limited to the formation of tangentially or radially polarized light. The present invention also includes a polarizer whose element pattern changes depending on the application of a specific lithograph. Such patterns can be obtained by using software applications or other design techniques for forming custom patterns. Therefore, the present invention provides an ultraviolet polarizing device having an element pattern dedicated to a predetermined lithograph application.

FIG. 1 generally shows an embodiment of the wire grid polarizing device of the present invention by 100. In this embodiment, the element pattern on the wire grid polarizing device is configured to form tangentially polarized light. As shown, element 105 is linear and is patterned into multiple groups (eg, two groups 120 and 125). Here, each group consists of a plurality of elements, and the groups are arranged in a circular pattern centered on the optical axis (OA). The dashed line 115 indicates a dividing line between the elements. In this example, the elements in one group are not parallel to the elements in the other adjacent group. For example, group 120 is adjacent to group 125, the elements in group 120 are parallel to each other, and not parallel to the elements in group 125.

In the polarizing device of FIG. 1, a plurality of extended conductive elements 105 are supported by a transparent substrate 110. The dimensions of the element and the dimensions of the element placement are determined by the wavelength used and are adapted for the full spectrum of UV light or for a wide spectrum. In a given group, the elements are not all the same length, but relatively shorter towards the edges of the group. In this way, each group 120, 125 has a suitable "edge" shape, and these groups can be arranged in a radial circular pattern about the optical axis OA.

FIG. 2 typically illustrates another embodiment of the wire grid polarizing device of the present invention by 200. In this embodiment, the pattern of elements 250 on the wire grid polarizing device is configured to form radialally polarized light. As shown, a plurality of elements 250 are concentrically patterned on the substrate 255. Again, the dimensions of the elements, and the dimensions of the element placement, are determined by the wavelength used and are optimized for the entire spectrum of UV light or for a wider spectrum.

Grid Element and Substrate In the embodiments of the present invention, the element is patterned on the substrate and is formed from a conductive material, such as metal. The element can be formed from, for example, aluminum, silver or gold. Such elements include, but are not limited to, wires or microwires.

In another embodiment of the invention, the substrate of the polarizing device is either all or partially transparent to UV light. Also, but not limited to, the substrate is formed from any of quartz glass, calcium fluoride, sapphire, quartz and magnesium fluoride. The present invention is not limited to this, and other thicknesses and materials can be used as will be apparent to those skilled in the art.

The spacing between the elements is determined by the wavelength used. The spacing between the elements is called the pitch for the elements in the concentric pattern. This pitch is the distance between the corresponding points on two adjacent elements.

In the examples of the present invention, the distance between the elements is smaller than the wavelength of light. Thus the pitch can be approximately less than 200 nm for a parallel or concentric element and less than 200 nm for a parallel element at the widest point between two adjacent non-parallel elements. In the embodiment, the elements are spaced between 1/10 of the wavelength of ultraviolet light and twice the wavelength.

The spacing between the elements can be smaller than the wavelength of light, but the present invention is not limited to this. The spacing between elements, and especially the boundaries between zones of parallel elements, can be greater than the wavelength of light.

In the examples, the elements of the polarizing device of the present invention have a period of about 1/4 of the ultraviolet wavelength, or a period between about 45 nm and 95 nm. However, it is not limited to this, and other periods and wavelengths can be used.

In the examples, the pitch is approximately 1/10 or 100 nm of the light wavelength. A grid with a relatively long period (approximately more than twice the wavelength of light) acts as a diffraction grating. A grid with a relatively short period (approximately 1/2 of the optical wavelength) acts as a polarizing device. The period grid in the region between the two periods then acts as a diffraction grating, characterized by sudden changes or anomalies relative to resonance. In addition, the elements of the polarizing device have regular or equal spacing. Alternatively, the present invention is not limited to this, and may have irregular intervals.

In the embodiments of the present invention where the elements are linear, the elements are relatively long and thin. For example, each element can generally have a length longer than the UV wavelength. In the examples, this element has a length approximately between 400 nm and 60 nm, but may be longer.

In addition, each element has a width of 10% to 90% of the pitch. Therefore, this element has a thickness greater than about 10 nm and is thinner than about 200 nm. Advantageously, this element has a thickness approximately between 20 nm and 100 nm.

The element width can be selected to optimize the performance of the polarizing device for a given application. In general, increasing the element width relative to the pitch can increase the reflectivity to parallel polarized light up to almost 100%. On the other hand, the reflectivity to orthogonally polarized light also increases from the ideal value of 0%. Therefore, typically increasing the ratio of element width to spacing results in a high absorption ratio for transmitted light. This is because parallel polarized light does not pass through. However, high efficiency is not required because part of the orthogonally polarized light is reflected. Conversely, in general, if the ratio of the element width to the pitch is small, a high absorption ratio is generated with respect to the reflected beam, but high efficiency is not required at that time. The overall efficiency, defined as the product of the reflectance for parallel beams and the transmittance for orthogonal beams, is best when the ratio of element width to element pitch is 40% to 60%.

Device The present invention further provides a device using the polarizing device of the present invention. For example, the polarizing device of the present invention can be used as a device for polarized ultraviolet light. Such a device has, for example, a light source that forms a light beam having at least one wavelength in the ultraviolet spectrum, and also has a substrate, which substrate is transparent to light in the ultraviolet spectrum and has an optical beam path. It has an element array that is lithograph-etched on the substrate. Here, the element array etched by lithograph on the substrate forms polarized emitted light.

In the embodiment, the ultraviolet light emitted from the light source has at least two polarization directions, and the wire grid polarizer reflects most of the light in the first polarization direction and transmits most of the light in the second polarization direction. ..

The present invention also comprises a wire grid polarizer and an illuminator to provide a device for supplying an exposure beam along the optical axis. Here, the polarizing device has a substrate transparent to ultraviolet light and an element array patterned on the substrate, the element polarizes the ultraviolet light, and the polarizing device forms a polarization pattern in the pupil of the illuminator. ..

The present invention further provides a device for supplying an exposure beam along the optical axis, which device comprises a wire grid polarizing device and a projection optical system. Here, the polarizing device has a substrate transparent to ultraviolet light and an array of elements patterned on the substrate, the elements polarize the ultraviolet light, and the polarizer forms a polarization pattern in the projection optical system.

The wire grid polarizers of the present invention are particularly advantageous in the field of lithographs, where polarized light can be used to form relatively large contrasts on wafers, resulting in improved imaging. Polarization generally has four effects on the lithograph. These are (1) transmission and diffraction of reticle features, (2) Fresnel loss at the projection optics lens, (3) Fresnel reflection at the resist surface, and (4) vector interference. Considering these four factors, the ideal pattern of polarization for a lithograph can be varied for a given reticle and lighting conditions.

The ideal polarization pattern for the lithograph can be varied, but tangential polarization is often a satisfactory option. The reticle has a repeating structure and usually intersects the mask horizontally or vertically. This structure is repeated on the reticle in another orientation as well. Iterating the structure can be done like a one-dimensional grating, diffracting light into a small number of dense beams in one row. When both of these beams are returned to the wafer, a good image can be obtained if they interfere well. It is the most difficult to image a very small future. By repeating the structure of a very small future, two diffraction sequences are formed at the opposite edges of the projection optics pupil. Tangent polarization is often advantageous for imaging such futures.

Similarly, radial polarization is also advantageous in certain situations. Frennel loss can be minimized, for example by using radial polarization, which further increases the light intensity. Therefore, radial polarization is advantageous when high light intensity is desired. In another embodiment, radial polarization is advantageous for imaging futures that already have good contrast. On the other hand, when imaging a future with limited contrast (usually a very small future), tangential polarization is desired.

Accordingly, the present invention provides an optical lithograph system 300 for exposing a layer of photosensitive material on a semiconductor wafer, which lithograph system includes the polarizing device of the present invention. As shown in FIG. 3, such a system 300 advantageously comprises a light source 310 as a radiant energy source, a wire grid polarizing device 100 of the present invention, a mask 320, a projection optics 330 such as a lens system, and a photosensitive material. Has a wafer containing layer 340 of. In the embodiment, the radiant energy from the light source passes through the polarizing device 100, the polarizing device polarizes the light in a predetermined direction, and outputs the polarized radiant energy beam 318 to the mask 320. The polarized radiant energy beam 318 passes through the mask 320 and exposes layer 3340 in a predetermined pattern.

It should be mentioned that lithographs often do not use the entire pupil. Therefore, only a predetermined area of the pupil is illuminated by applying a predetermined lithograph. For example, in "dipole" lighting, only two areas are illuminated at the edge of the pupil. Therefore, in certain embodiments of the lithograph system, not all of the beams emitted from the polarizer are used. For example, the pattern of polarization is not uniform or incomplete throughout the pupil. In such cases, only part of the pupil with the desired polarization is used.

In another embodiment of the invention, the arcs that the wire grid polarizers 100,200 can have allow for very wide angles. This allows the polarization pattern to be introduced into any pupillary surface of the optical system. Since the grid element acts as a polarizer, an unpolarized beam can be used upstream for further simplification. Both polarization patterns are easily achieved by selecting a pattern for the wire grid elements.

Method Arranging an array of conductive elements on a substrate can be performed by a number of well-known techniques. For example, U.S. Pat. No. 4,409944 and U.S. Pat. No. 4,514,479 use a hologram interference lithograph to form a fine lattice structure on a photoresist, which is then etched by an ion beam to form the underlying metal. It is described to convert to film. Stenkamp is (Grid Polarizer for the visible spectral region, Proceedings of the SPIE, vol.2213, pp.288-296) discloses that a resist pattern is formed using a direct e-beam lithograph and then the pattern is converted to a metal film by reactive ion etching. Other high resolution lithograph techniques, including EUV lithographs and X-ray lithographs, and X-ray hologram interference lithographs, can also be used to form resist patterns. Other techniques, including other etching mechanisms and lift-off processes, can also be used to convert the pattern from resist to metal film. The exact process used to form the array of conductive elements is not important to the present invention.

<figref num="1">It is a figure which shows typically the Example of the polarizing device of this invention.</figref><figref num="2">It is a figure which shows generally another Example of the polarizing device of this invention.</figref><figref num="3">It is a figure which shows schematicly the lithograph system including the polarizing device of this invention.</figref>