Abstract:
A monolithic polarizing diffractive structure includes a system having at least two parallel continuous planar surfaces, a diffractive pattern on one of the at least two parallel continuous surfaces, the diffractive pattern including at least two diffractive elements integral with the one of the at least two continuous surfaces, the at least two diffractive elements defining a monolithic diffractive pattern, and a polarizing pattern on one of the at least two parallel continuous surfaces. The polarizing pattern includes at least two polarizing elements, each polarizing element corresponding to a respective diffractive element, the at least two polarizing elements outputting polarizations rotated with respect to one another, the at least two polarizing elements defining a monolithic polarizing pattern.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation application based on pending application Ser. No. 11/711,854, filed Feb. 28, 2007, which in turn is a continuation-in-part application of PCT Application No. PCT/US2005/030780, filed Aug. 30, 2005, which claims priority under 35 U.S.C. §119(e) to Provisional U.S. Patent Application Ser. No. 60/714,506, filed Aug. 31, 2004. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    Embodiments are related to a polarizing diffractive structure and a method of manufacturing such a polarizing diffractive structure. More particularly, embodiments are related to a monolithic polarizing diffractive structure and a method of manufacturing such a polarizing diffractive structure. 
         [0004]    2. Description of Related Art 
         [0005]    Diffusers use diffractive elements to control an angle of illumination in a variety of systems, e.g., in a lithographic system. As a critical dimension in micro-lithography continues to be reduced, the effect of polarization on imaging performance in lithographic systems becomes more influential. If these effects are not accounted for, the imaging enhancement expected from using a higher numerical aperture (N.A.) lens system and/or immersion lithography may not be realized. If the polarization state of illumination could be optimized while controlling the angular distribution of the illumination, the adverse affects of the polarization may be minimized. 
         [0006]    One solution involves creating an array of micro-optics, each providing a particular angular distribution, arranged at varying orientations, in combination with an array of polarizers arranged at varying orientations. For example, to create quadrupole illumination where the two poles on the vertical axis have a different polarization state than the two poles on the horizontal axis, the micro-optic array would include dipole micro-optics with every other micro-optic oriented to spread the light vertically. A polarization controlling element, such as a half-wave plate, is then diced into similarly sized portions as each micro-optic to create mini-polarizers. These mini-polarizers are then also arranged in an array. A certain orientation of the mini-polarizers is associated with each particular angular distribution of the micro-optics. For this particular example, each micro-optic providing a dipole along an x-axis could be provided with a mini-polarizer having a vertical polarization and each micro-optic providing a dipole along a y-axis could be provided with a mini-polarizer having a horizontal polarization. Accordingly, a quadrupole illumination profile where the vertical and horizontal dipoles have different polarizations is realized. 
         [0007]    However, this solution requires assembly of numerous small pieces, e.g., 2 mm, making the solution difficult to implement. Given the size and the number of the pieces being assembled into two corresponding arrays, the possibility of errors in such arrangement is not negligible. Further, the alignment of the micro-optics and mini-polarizers, both linearly and angularly, would need to be maintained to insure proper correspondence of angular distribution and polarization state. Additionally, the diced parts would have edge chips or bevels that would increase scatter and thus decrease efficiency of the part. Any gaps between the elements of the array could increase the amount of light in the zero order, which is typically to be minimized in illumination systems for lithography. 
       SUMMARY OF THE INVENTION 
       [0008]    It is therefore a feature of the present invention to provide a polarizing diffractive structure and a method of manufacturing such a polarizing diffractive structure, which substantially overcomes one or more of the problems noted above in connection with the related art. 
         [0009]    It is a feature of an embodiment of the present invention to provide a polarizing diffractive structure that is monolithic. As used herein, “monolithic” is to mean that the elements of the diffractive element and the polarization control are each provided on a continuous surface, rather than separating the elements into pieces and then assembling them back together. Thus, while the monolithic polarizing diffractive structure may be realized on a single surface, it is not to be so limited, and the diffractive elements and the polarization elements may be on different surfaces of a substrate or even on different substrates. 
         [0010]    It is another feature of an embodiment of the present invention to provide a polarizing diffractive structure that maintains its efficiency. 
         [0011]    It is yet another feature of an embodiment of the present invention to provide a polarization controlled angle diffuser that minimizes zero order light. 
         [0012]    It is still another feature of an embodiment of the present invention to provide a polarizing diffractive structure that may readily be interchanged with current diffusers. 
         [0013]    It is yet another feature of an embodiment of the present invention to provide a polarizing diffractive structure that may easily be manufactured. 
         [0014]    It is still another feature of an embodiment of the present invention to provide a polarizing diffractive structure in a lithographic system. 
         [0015]    At least one of the above and other features and advantages of the present invention may be realized by providing a monolithic polarizing diffractive structure including a system having at least two parallel, planar surfaces, a diffractive pattern on one of the at least two parallel surfaces, the diffractive pattern including at least two diffractive elements integral with the one of the at least two continuous surfaces, the at least two diffractive elements defining a monolithic diffractive pattern, and a polarizing pattern on one of the at least two surfaces, the polarizing pattern including at least two polarizing elements, the at least two polarizing elements outputting polarizations rotated with respect to one another, each of the at least two polarizing elements corresponding to a respective one of the at least two diffractive elements. 
         [0016]    The system may include a substrate on which the polarizing pattern is formed. At least one of the at least two polarizing elements may be featureless. The polarizations of the at least two polarizing elements may be rotated by 90° with respect to one another. 
         [0017]    The polarizing pattern may have a subwavelength structure. The polarizing pattern may have varied etch depths. The etch depth d may be determined by the equation: 
         [0000]        d=λ/ 2Δ n  
 
         [0000]    where λ is a wavelength at which the diffuser is to be used and Δn is a difference between refractive indices of the substrate for orthogonal polarization states of the polarizing pattern. A period of the polarizing pattern may be selected to maximize Δn. 
         [0018]    The substrate on which the polarizing pattern is formed may be birfringent. An etch depth may be determined in accordance with a difference between an ordinary refractive index and an extraordinary refractive index of the substrate. The period of the polarizing pattern may be selected to equal a size of one of the at least two controlled angle diffuser elements. 
         [0019]    The diffractive elements may on the same substrate as the polarizing elements, either on the same side of the substrate or on opposite sides of the substrate. The diffractive pattern may include an alternating array of x dipoles and y dipoles. 
         [0020]    At least one of the above and other features and advantages of the present invention may be realized by providing a method of making a monolithic polarizing diffractive structure including creating a diffractive design having at least two diffractive elements, creating a polarizing pattern having at least two polarizing elements, the at least two polarizing elements outputting polarizations rotated with respect to one another, transferring the diffractive design to a surface of a system having at least two surfaces to form a diffractive pattern having at least two diffractive elements integral with one of the at least two continuous surfaces, the at least two diffractive elements defining a monolithic diffractive pattern, and transferring the polarizing pattern to one of the at least two surfaces, each of the at least two polarizing elements corresponding to a respective one of the at least two diffractive elements, the at least two controlled polarizing elements defining a monolithic polarizing pattern. 
         [0021]    Transferring the polarizing pattern may include etching a substrate of the system to an etch depth d determined by the equation: 
         [0000]        d=λ/ 2 Δn    
         [0000]    where λ is a wavelength at which the diffuser is to be used and Δn is a different between refractive indices of the substrate for orthogonal polarization states of the polarizing pattern. The period of the polarizing pattern may be selected to maximize Δn. 
         [0022]    Transferring the polarizing pattern may include etching a birefringent substrate to an etch depth determined in accordance with a difference between an ordinary refractive index and an extraordinary refractive index of the birefringent substrate. The period of the polarizing elements is selected to equal a size of one of the at least two controlled angle diffuser elements. 
         [0023]    The at least two surfaces may be on a single substrate. The polarizing elements and the controlled angle diffuser elements may be on the same side or on opposite sides of the substrate. The transferring of the polarizing pattern may occur before transferring the controlled angle diffuser design. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the attached drawings, in which: 
           [0025]      FIG. 1  illustrates a cross-sectional view of a model of a pattern in accordance with an embodiment of the present invention; 
           [0026]      FIG. 2  is a plot of duty cycle versus index of refraction for both polarizations and both grating periods for the model of  FIG. 1 ; 
           [0027]      FIG. 3  illustrates a cross-sectional view of a half wave plate in accordance with an embodiment of the present invention; 
           [0028]      FIG. 4  illustrates a schematic cross-sectional view of a half-wave plate in accordance with an embodiment of the present invention; 
           [0029]      FIG. 5  illustrates a schematic top view of outputs of individual portions of an example of a controlled angle diffuser pattern; 
           [0030]      FIG. 6  illustrates an output of the controlled angle diffuser pattern of  FIG. 5  in conjunction with a polarizing pattern of an embodiment of the present invention; 
           [0031]      FIG. 7  illustrates a top view of the controlled angle diffuser pattern providing the outputs of  FIG. 5 ; 
           [0032]      FIG. 8  illustrates a front view of a controlled angle diffuser; 
           [0033]      FIG. 9  illustrates an annular target pattern; and 
           [0034]      FIG. 10  illustrates a side view of a lithographic system in which a controlled angle diffuser in accordance with any of the embodiment of the present invention may be used. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0035]    The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the figures, the dimensions of layers and regions are exaggerated for clarity of illustration. Like reference numerals refer to like elements throughout. 
         [0036]    In accordance with the present invention, the polarization of the diffuser may be controlled in accordance with an etch depth of the material. This polarization control pattern may be on the same surface, on an opposite surface of the same substrate or even on different substrates, as the controlled angle diffuser pattern. The surfaces on which the controlled angle diffuser and the polarization pattern are to be formed may be parallel and planar to one another. Examples of appropriate controlled angle diffusers may be found in U.S. Pat. No. 5,850,300, the entire contents of which are herein incorporated by reference for all purposes, and as illustrated in  FIG. 8 , and discussed in detail below. If the polarization control pattern is on an opposite side of a substrate from the controlled angle diffuser pattern, then front to back alignment will be needed. 
         [0037]    Polarization Control 
         [0038]    The polarization control may be realized in two manners. First, if the substrate is a non-birefringent material, e.g., fused silica, then a sub-wavelength structure may be designed to change or rotate the polarization state. A model for creating such a structure is shown in  FIG. 1 . The birefringent curves from this structure are shown in  FIG. 2 . A structure for a half-wave plate created based on this model is shown in  FIG. 3 . 
         [0039]    In  FIG. 1 , the reflection of a diffractive pattern  10 , here a binary pattern, in a fused silica substrate  20  was modeled for both parallel and perpendicular polarizations. A duty cycle of this pattern was varied from 0 to 100% at 1% increments for both polarizations. A period of this pattern was checked for 0.9 and 0.5 of the wavelength of interested in the substrate material. When the wavelength of interest is in the deep ultraviolet (DUV), e.g., 193 nm, and fused silica, have an index of refraction of about 1.56, is the substrate material, these wavelengths are about 111 nm and 61 nm, respectively. As can be seen from  FIG. 2 , the greatest birefringence occurs at about a 44% duty cycle using 111 nm as the grating period. Thus, these parameters are selected for creating a half-wave plate  30  shown in  FIG. 3 . The half-wave plate  30  includes a pattern  32  of depth d, a period of 111 nm and a duty cycle of 44%. For the half-wave plate  30 , the depth d is set to be λ/(2Δn), where Δn is the difference in refractive indices for the different polarization states. In fused silica, for the period of 111 nm, this difference is 0.16. 
         [0040]    If the material of the substrate is birefringent, e.g., crystal quartz or calcium fluoride (CaF), such patterning is not needed. Instead, this material only needs to be selectively etched for every other part to an appropriate depth to realize the desired polarization rotation. No high resolution patterns are needed, as with the sub-wavelength pattern of the first embodiment. An example of this is shown in  FIG. 4 , in which a half-wave plate  40  includes etched portions  42  and unetched portions  44  to provide the different rotations. Thus, the unetched portions  44  may be featureless. While no pattern is required, the etch depth to realize the desired rotations are typically an order of magnitude higher than for the patterned approach, e.g., on the order of several microns. The etch depth is determined in accordance with the refractive index difference between the ordinary and extraordinary direction in the birefringent material. 
         [0041]    As a specific example, polarized quadrupole illumination may be realized in accordance with an embodiment of the present invention. First, a dipole illuminator would be designed. Such a dipole illuminator may be designed using a diffractive approach, as set forth in U.S. Pat. No. 5,850,300. As shown in  FIG. 5 , an output of each cell of an array of cells  50  includes a plurality of x dipole illumination cells  52 , which are oriented along the x-axis, and a plurality of y dipole illumination cells  54 , which are oriented along the y-axis. These x dipole illumination cells  52  and y dipole illumination cells  54  are arranged in a two-dimensional array of alternating x and y orientations. 
         [0042]    If the substrate is not a birefringent material, and the input light is to be polarized, then a polarizing pattern rotating the polarization may be provided for every other illumination cell, i.e., all dipole illumination cells of the same orientation. The polarizing pattern would be created using the design technique of  FIG. 3  and then transferred to a surface and aligned with the controlled angle diffuser pattern. Of course, if the incoming light is not polarized, the polarizing pattern may include a polarization element for each dipole illumination cell. If the substrate is birefringent, every other illumination cell, i.e., all dipole illumination cells of the same orientation, would have an etched portion as taught in connection with  FIG. 4 . 
         [0043]    The composite output of a substrate having this controlled angle diffuser pattern therein would be a quadrupole  60  as shown in  FIG. 6 , without the arrows indicating polarization orientation in the quadrupole  60 . In the particular example shown in  FIG. 6 , the polarization is rotated by 90° in the quadrupole  60 . An x dipole illumination  62  and a y dipole illumination  64  have orthogonal polarizations, as indicated by the arrows therein. 
         [0044]    An example of an actual mask  70  used to create the illumination shown in  FIGS. 5 and 6  is illustrated in  FIG. 7 . Here, the mask  70  includes a plurality of x dipole illuminators  72 , which are oriented along the x-axis, and a plurality of y dipole illuminators  74 , which are oriented along the y-axis. Each dipole illuminator  72 ,  74  of this array would have the desired dimensions of the conventional individual elements, e.g., about 2 mm. 
         [0045]    The controlled angle diffuser pattern of the mask  70  may then be transferred to a substrate, e.g., by lithography or replication, followed by etching. The polarization pattern in accordance with either embodiment of the present invention may be transferred to either the same or the opposite surface of the substrate, e.g., by lithography or replication, followed by etching. Alternatively, the transfer of the polarizing pattern may be transferred to another substrate. These substrates may be secured together. This securing may occur on a wafer level, after which the secured wafers may be vertically separated to form dies including at least two controlled angle diffuser elements and at least two polarizing elements. Each of the two controlled diffuser elements may output different angular distributions. Each polarizing element may correspond to a respective controlled angle diffuser element. Each of the two polarizing elements may output polarizations rotated with respect to one another. 
         [0046]    Controlled Angle Diffuser 
         [0047]    A front view of an exemplary embodiment of a controlled angle diffuser  84  is shown in  FIG. 8 . The controlled angle diffuser  84  of  FIG. 8  may have been arbitrarily designated to have an array of facet areas, or facets,  86 , arranged in a 4×4 array as shown by dotted lines in  FIG. 8 . These dotted lines are not structure on the controlled angle diffuser, but are used to designate a facet area or a facet, which is a convenient way to refer to an area of the controlled angle diffuser  84 . Each facet area  86  has irregularly patterned plateaus  80  and vias  82 . No sharp edges or breaks appear between facet areas  86 . 
         [0048]    Facet area, for purposes of the description, refers to an area of arbitrarily designated size on the controlled angle diffuser  84 . It is used as a convenient way to refer to an area of irregularly shaped or patterned diffractive fringes  88  (irregularly shaped or patterned plateaus and vias in this exemplary embodiment) on the controlled angle diffuser. A controlled angle diffuser has at least two facet areas. In the exemplary embodiment, no two facet areas  86  contain a pattern of plateaus  80  and vias  82  that are alike. The pattern within one facet area  86  is nominally correlated to itself and nominally uncorrelated to the pattern in all other facet areas. Therefore, each facet area  86  within the controlled angle diffuser  84  may direct light to an entire target area of an output plane. 
         [0049]    When an incident optical beam, e.g., a collimated beam, illuminates the facet areas, or facets,  86  of the controlled angle diffuser  84 , the irregularly patterned plateaus  80  and vias  82  provide no regular, undesired structure to transmit regular, undesired intensity variation (not shown) in the output plane. An additional advantage of the present embodiment is that departing from designing each individual facet  86  to designing facet areas or entire holograms provides greater freedom of design that allows the designer to reduce undesired intensity variation in the output plane by making adjustments to the plateaus  80  and vias  82 , as sharp breaks or edges provide much less design freedom in relation to those sharp breaks or edges. Further, by designing facet areas or entire holograms provides greater freedom of design that allows greater freedom to create output beams of arbitrary shapes, such as rings and cross-hairs. 
         [0050]    In the embodiment shown in  FIG. 8 , when an input beam illuminates the facet area  86 , and the facet area  86  transmits a beam having a preselected angular spread in the output plane. Those of ordinary skill in the art of this invention are familiar with angular spread. Angular spread, or angular divergence, is the increase in nominal beam size over a finite propagation distance expressed as an angle in radians or degrees. In any given facet area  86 , the plateaus  80  and vias  82  diffract the input beam such that transmitted portions of the beam have a preselected angular spread. The angular spread provided by a facet area  86  is selected by the designer of the controlled angle diffuser  84  such that a desired output beam may illuminate the output plane. The designer may preselect an angular spread of from e.g., about ±0° to about ±90°. 
         [0051]    The choice of angular spread depends upon the application for which the controlled angle diffuser is used and the desired output beam. The angular spread is selected by the designer as needed for the application at hand. For example, an illumination system for machine vision may require uniform illumination across a 10°×15° degree rectangular area. The designer would chose angular spread for the controlled angle diffuser to obtain such a desired illumination. 
         [0052]    With a facet area  86  that transmits a beam with a predesigned angular spread, the designer can control the angle over which the transmitted light is spread. The facet areas  86  of the controlled angle diffuser  84  may provide angular spread such that the target area illuminated on the output plane is larger than the illuminated facet areas  86 . 
         [0053]    The controlled angle diffuser  84  may also homogenize spatial power over a preselected target area. That is, a constant, preselected power distribution at the output plane may be provided even if the power distribution of a beam incident upon the surface of the controlled angle diffuser  84  deviates from design parameters. 
         [0054]    The designer can choose any particular shape for the target area. The designer may design the plateaus  80  and vias  82  such that a target pattern of a desired shape may be projected upon the output plane from the controlled angle diffuser  84 . The spatial frequency content of the hologram is designed to produce a desired pattern. That is, the size and orientation of the plateaus  80  and vias  82  are designed to produce a desired pattern. Preferably, the design takes place using a computer. 
         [0055]    By transmitting light at various, predetermined angular spreads, the facet areas  86  of the controlled angle diffuser  84  project spatial power in predetermined target patterns onto the output plane. Essentially, a target pattern may be composed of illuminated areas of the output plane adjacent to non-illuminated areas of the output plane. The controlled angle diffuser  54  may be designed such that substantially all of the spatial energy is transmitted to predetermined target areas of the output plane and relatively no spatial energy is transmitted to other predetermined areas of the output plane, thus projecting a predetermined target pattern onto the output plane. 
         [0056]    The target pattern formed by the controlled angle diffuser  84  in  FIG. 8  is a circular pattern. Other patterns, such as the one shown in  FIG. 9 , may be selected by the designer of the controlled angle diffuser  84 .  FIG. 9  illustrates an annular target pattern  92  at an output plane  94 . That is,  FIG. 9  illustrates a preselected power distribution pattern in which the spatial power is distributed at the output plane  98  such that a relatively non-illuminated circular area  96  is surrounded by a ring of illuminated area  97 , which is in turn adjacent to a relatively non-illuminated area  98 . Non-circular patterns, such as the shape of a flower or rectangle, may also be chosen. 
         [0057]    Use in a Lithographic System 
         [0058]    Any of the embodiments of the present invention may be particularly useful for in lithographic systems, e.g., photolithographic exposure systems, which may be used to image a pattern of a mask onto a wafer to expose resist on the wafer in a pre-determined pattern. Subsequent processing of the wafer results in the completion of layers that eventually form the desired device, such as an integrated circuit. 
         [0059]    When the mask is used in a projection lithography system, such as a laser stepper with a 5:1 or 10:1 reduction ratio, the mask is often referred to as a reticle. The reticle or mask is typically formed by chrome regions on a transparent substrate. The chrome regions of the mask block the incident light, thereby imposing the pattern of the mask as an intensity variation on the light. In a 5× laser stepper, the pattern of the reticle is reduced by a factor of 5 as imaged onto a wafer. Typically, in this application, the beam illuminating the diffractive is relatively uniform and has a rather narrow cone angle of divergence, i.e., limited spatial and angular energy distributions. 
         [0060]    Embodiments of the present invention allow for the control of the angular distribution of the light on the wafer. By modifying the particular angular distribution of the light illuminating the wafer, the depth of the field and resolving power of photolithographic exposure systems may be extended. Additionally, when any of the embodiments of the present invention also homogenize the beam, the system may be relatively insensitive to fluctuations in positioning of the incident beam and to fluctuations in the spatial energy distributions of the incident beam. Further, a polarization state may be optimized. 
         [0061]    By using embodiments of the present invention, the intensity, angular frequency content, pupil pattern shape, and polarization of the exposure light used in photolithography can be controlled. Such control can improve the resolution of the image of the master pattern on the integrated circuit wafer. It has been found that for some master patterns, it is better for the light to illuminate at certain angles, ranges of angles or polarizations. The controlled angle diffuser according to embodiments of the present invention may provide light at that angle while homogenizing the spatial energy provided, as well as providing control of other attributes of the exposure light. Such control may improve yields in semiconductor chip manufacturing and other areas in which photolithography is used. 
         [0062]    For example, referring to  FIG. 10 , a light source  100  may illuminate a controlled angle diffuser  110  (shown in side view) of any of the embodiments of the present invention, with or without polarization control, with a collimated input beam  114 . The controlled angle diffuser  110  may transmit a majority portion of the incident light to a mask  160  at a desired angular spread, and with a preselected intensity and spatial power distribution, wherein the preselected spatial power distribution is uniform. This transmitted portion  120   f,    120   g  may serve as the exposure light. The mask  160  may be placed close to the controlled angle diffuser  110  such that there is no appreciable change in power distribution between the controlled angle diffuser  110  and the mask  160 , and thus, the beam may be uniform at both the controlled angle diffuser  110  and the mask  160 . The mask  160  may be illuminated with the desired exposure light  120   f,    120   g.    
         [0063]    The portion of the exposure light  120   f,    120   g  that is not blocked  120   h  by the mask  160  may be transmitted by the master  160 , and may illuminate a lens  162 . This portion  20   h  may have the desired, preselected angular spread. The lens  162  in turn transmits the incident light  120   h  such that the mask  160  is imaged onto a mount  164  for receiving a subject wafer having, e.g., photoresist (not shown) thereon. The lens  162  provides a desired reduction factor. This embodiment images the mask  160  onto the subject wafer on the mount  164  in a desired manner, particularly a desired angular spread. Thus, the wafer on the mount  164  may be exposed in the preselected, desired manner with an exposure light with desired and optimized attributes, and a copy may be provided. 
         [0064]    In this manner, by optimizing the exposure light as desired and needed, higher yields during, for example, semi-conductor chip manufacturing may be realized. The controlled angle diffuser  110  may be used to, e.g., block zero to two degrees, allow two to four degrees, and block from four degrees onward. Further, for example, the controlled angle diffuser may form a top-hat, e.g., from plus three degrees to minus three degrees. Control of the angular spread and the frequency content, and the polarization of the transmitted light may be realized by the design of the controlled angle diffuser  110 , preferably using a computer. 
         [0065]    The controlled angle diffuser  110  may also be used in other parts of the lithographic system, and may be designed accordingly. 
         [0066]    Exemplary embodiments of the present invention have been disclosed herein and, although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. For example, the polarizing pattern could be transferred to the substrate before the controlled angle diffuser pattern. Accordingly, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as set forth in the following claims.