Method and system for adjustable gradient patterning using shadow mask

Abstract

The present invention relates to methods and systems for achieving adjustable gradient patterning using shadow masks. A method for manufacturing a diffractive structure with a varying diffractive element depth includes providing a shadow mask having a first region and a second region, the first region having a first aperture size to aperture period ratio, and the second region having a second aperture size to aperture period ratio less than the first aperture size to aperture period ratio. The method also includes positioning the shadow mask adjacent to a substrate. The substrate includes an etching mask corresponding to the diffractive structure. The method further includes: exposing the substrate to an etchant; etching the substrate to form a diffractive element having a first depth adjacent to the first region; and etching the substrate to form a diffractive element having a second depth less than the first depth adjacent to the second region.

Description

[0001] This application is a divisional application of an application with an application date of November 6, 2018, PCT international application number of PCT / US2018 / 059440, Chinese national phase application number of 201880071255.3, and invention name of “Method and system for achieving adjustable gradient patterning using shadow mask”.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims the benefit of and priority to U.S. Provisional Patent Application Serial No. 62 / 582,082, filed on November 6, 2017, the entire contents of which are incorporated herein by reference for all purposes. Background Art

[0004] Modern computing and display technologies have facilitated the development of systems for so-called "virtual reality" or "augmented reality" experiences, in which digitally reproduced images, or portions thereof, are presented to a user in a manner that appears to be, or can be perceived to be, real. Virtual reality or "VR" scenarios generally involve presenting digital or virtual image information opaque to other actual real-world visual input, and augmented reality "AR" scenarios generally involve presenting digital or virtual image information as an enhancement to a visualization of the actual real world surrounding the user.

[0005]

[0006] Despite the advances that have been made in these display technologies, there is a need in the art for improved methods and systems relating to augmented reality systems, and particularly display systems. Summary of the invention

[0006] The present disclosure relates to virtual reality and augmented reality imaging and visualization systems. The present disclosure generally relates to methods and systems related to the manufacture of such diffraction structures: in the diffraction structure, the diffraction elements have a depth that varies according to the position. The embodiments described herein can be applied in the context of a diffraction grating-based waveguide display for near-eye display. In certain embodiments, gratings with gradient depth distribution are used to improve field uniformity and increase light outcoupling efficiency. As described herein, some embodiments utilize shadow masks and dry etching processes to manufacture gratings with gradient depth distributions achieved by controlling the plasma density on the surface of the substrate. The present disclosure is applicable to various applications in computer vision and image display systems.

[0007] According to one embodiment of the present invention, a method for manufacturing a diffractive structure having a varying diffractive element depth is provided. The method includes: providing a shadow mask, the shadow mask having a first region and a second region, the first region having a first aperture size and aperture period ratio, the second region having a second aperture size and aperture period ratio less than the first aperture size and aperture period ratio; and positioning the shadow mask adjacent to a substrate, wherein the substrate includes an etching mask corresponding to the diffractive structure. The method also includes: exposing the substrate to an etchant; etching the substrate to form a diffractive element having a first depth adjacent to the first region; and etching the substrate to form a diffractive element having a second depth less than the first depth adjacent to the second region.

[0008] According to another embodiment of the present invention, a method for manufacturing a mother substrate is provided. The method includes providing a shadow mask, the shadow mask having a first area and a second area, the first area being characterized by a first gradient aperture size and aperture period ratio in at least a first direction, and the second area being characterized by a second gradient aperture size and aperture period ratio in at least a second direction. The method also includes providing a substrate, the substrate having an etching mask characterized by a diffraction feature, a first exposure area, and a second exposure area. The method further includes positioning the shadow mask adjacent to the substrate. The first area is aligned with the first exposure area, and the second area is aligned with the second exposure area. In addition, the method includes: performing a plasma etching process on the substrate; etching a first diffraction element adjacent to the first area. The first diffraction element is characterized by a first gradient depth distribution in the at least first direction. In addition, the method includes etching a second diffraction element adjacent to the second area. The second diffraction element is characterized by a second gradient depth distribution in the at least second direction.

[0009] According to a specific embodiment of the present invention, a method of depositing a variable thickness material is provided. The method includes providing a substrate and providing a shadow mask, the shadow mask having a first region and a second region, the first region having a first aperture size to aperture period ratio, the second region having a second aperture size to aperture period ratio that is less than the first aperture size to aperture period ratio. The method also includes positioning the shadow mask adjacent to the substrate, and performing a plasma deposition process on the substrate to deposit the variable thickness material. The thickness of the layer adjacent to the first region is greater than the thickness of the layer adjacent to the second region.

[0010] In one embodiment, the substrate includes a growth surface, the growth surface includes a diffraction structure, and the diffraction structure may include a diffraction grating. The variable thickness material may include a conformal layer. In another embodiment, the shadow mask includes a plurality of holes and a surface parallel to the plurality of holes, the substrate includes a deposition surface, and positioning the shadow mask adjacent to the substrate includes placing the surface of the shadow mask parallel to the deposition surface. The shadow mask may be characterized by an aperture size and an aperture period ratio that vary in two directions. In addition, in one embodiment, the substrate includes a uniform diffraction structure, the uniform diffraction structure includes a plurality of diffraction elements, and the variable thickness material is characterized by a first diffraction element depth in a first region and a second diffraction element depth in a second region that is less than the first diffraction element depth. In addition, in another embodiment, the substrate includes a uniform diffraction structure, the uniform diffraction structure includes a plurality of diffraction elements, and the variable thickness material is characterized by a first diffraction element width in a first region and a second diffraction element width in a second region that is less than the first diffraction element width.

[0011] According to another specific embodiment of the present invention, a method for manufacturing a mother substrate is provided. The method includes providing a shadow mask, the shadow mask having a first area and a second area, the first area being characterized by a first gradient aperture size and aperture period ratio in at least a first direction, and the second area being characterized by a second gradient aperture size and aperture period ratio in at least a second direction. The method also includes providing a substrate, the substrate having a mask characterized by a diffraction feature, a first exposure area and a second exposure area. The method also includes positioning the shadow mask adjacent to the substrate. The first area is aligned with the first exposure area, and the second area is aligned with the second exposure area. In addition, the method includes performing at least one of a plasma coating or a deposition process on the substrate, and coating a first diffraction element adjacent to the first area. The first diffraction element is characterized by a first gradient depth and a first line width distribution in the at least first direction. The method also includes coating a second diffraction element adjacent to the second area. The second diffraction element is characterized by a second gradient depth and a second line width distribution in the at least second direction.

[0012] In one embodiment, the first gradient depth is greater than the second gradient depth. In another embodiment, the first line width distribution is characterized by a first width, and the second line width distribution is characterized by a second width less than the first width.

[0013] Many benefits over conventional techniques are achieved through the present disclosure. For example, embodiments of the present invention provide methods and systems suitable for current plasma-based systems and tools for etching and / or deposition systems to achieve improved control of plasma density / energy, including controlled changes in plasma density / energy near the target surface. In addition, embodiments improve the uniformity of plasma-enhanced etching or deposition of current systems, including systems with various levels of non-uniformity due to plasma density, gas flow, etc. In addition, embodiments of the present invention are characterized by reduced system complexity and reduce the manufacturing cost of gradient pattern templates for contact nanolithography and microlithography processes. By utilizing readily available materials and systems, embodiments of the present invention enable the manufacture of masks / templates and materials that can be used to change plasma density / energy in a controlled manner. In addition, embodiments can produce nano / micro structures with gradient depths. By utilizing the shadow mask described herein, structures with variable depths can be achieved with a single etching step, thereby avoiding multiple lithography-etching processes, thereby saving time and cost. The above and other embodiments of the present disclosure and their numerous advantages and features are described in more detail in conjunction with the following and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1A Schematically illustrated are optical paths in a viewing optics assembly (VOA) that may be used to present a digital or virtual image to a viewer according to embodiments described herein.

[0015] Figure 1B is a simplified cross-sectional view of a diffractive structure according to an embodiment of the present invention.

[0016] Figure 2 is a simplified cross-sectional diagram illustrating variable depth etching using a shadow mask in accordance with an embodiment of the present invention.

[0017] Figure 3A is a simplified plan view of a substrate and exemplary shadow mask features in accordance with an embodiment of the present invention.

[0018] Figure 3B According to an embodiment of the present invention Figure 3A A close-up view of a portion of the area shown.

[0019] Figure 3C According to another embodiment of the present invention, Figure 3A A close-up view of a portion of the area shown.

[0020] Figure 4A is an image showing a portion of an eyepiece including a variable height grating structure according to an embodiment of the present invention.

[0021] Figures 4B to 4D yes Figure 4A Illustration of SEM cross sections of a grating tooth at the three measurement positions shown.

[0022] Figure 4E It shows that as the distance Figure 4A A graph of the grating etching depth as the distance from the eyepiece edge is shown.

[0023] Figures 5A to 5C is a plan view showing a diffraction structure manufactured using conventional technology.

[0024] Figures 5D to 5F is a plan view showing a diffractive structure having a one-dimensional or two-dimensional profile manufactured according to an embodiment of the present invention.

[0025] Fig. 6A is a simplified cross-sectional view of a diffractive structure with a grating height gradient according to an embodiment of the present invention.

[0026] Figure 6B is a simplified plan view illustrating a digital dispensing pattern with varying dispensing volumes in accordance with an embodiment of the present invention.

[0027] Figure 6C is a hybrid interface region according to an embodiment of the present invention Fig. 6A Simplified cross-sectional view of the diffractive structure shown in .

[0028] Figure 7 A simplified process flow diagram illustrating a method of manufacturing a shadow mask in accordance with an embodiment of the present invention is shown.

[0029] Figure 8 is a simplified diagram illustrating the use of a shadow mask master to fabricate a substrate having variable depth diffractive elements in accordance with an embodiment of the present invention.

[0030] Fig. 9 is a simplified cross-sectional view showing a variable thickness deposition layer according to an embodiment of the present invention.

[0031] Fig.10 is a flow chart illustrating a method of manufacturing a diffractive structure with varying diffractive element depth according to an embodiment of the present invention.

[0032] Fig.11 is a flowchart illustrating a method of manufacturing a mother substrate according to an embodiment of the present invention.

[0033] Fig.12 is a flow chart illustrating a method of depositing a variable thickness material according to an embodiment of the present invention.

[0034] Fig.13 is a flowchart illustrating a method of manufacturing a mother substrate according to an embodiment of the present invention. DETAILED DESCRIPTION

[0035] In some conventional diffraction-based waveguide optical displays, a nanometer / micrometer grating pattern with a fixed height is used. However, depending on the incident angle of the light when it interacts with the grating pattern, the intensity of light coupled out toward the user's eye can vary significantly. For example, the light intensity measured across the user's field of view may be non-uniform in the near-field and / or far-field images.

[0036] Embodiments of the present invention improve the user experience by reducing image intensity non-uniformity using a waveguide structure with a diffractive element depth (e.g., grating depth) that varies with position (e.g., gradually varies). These nanometer-scale adjustments effectively adjust the diffraction efficiency to provide a more uniform view for the user.

[0037] Figure 1A Schematically illustrates an optical path in an observation optical assembly (VOA) that can be used to present a digital or virtual image to a viewer according to one embodiment. The VOA includes an eyepiece 100 that can be worn by a viewer and a projector 101. In some embodiments, the projector 101 may include a group of red LEDs, a group of green LEDs, and a group of blue LEDs. For example, the projector 101 may include two red LEDs, two green LEDs, and two blue LEDs. The eyepiece 100 may include one or more eyepiece layers. In one embodiment, the eyepiece 100 includes three eyepiece layers, one eyepiece layer for each of the three primary colors (red, green, and blue). In another embodiment, the eyepiece 100 may include six eyepiece layers, one group of eyepiece layers for each of the three primary colors is configured to form a virtual image at one depth plane, and another group of eyepiece layers for each of the three primary colors is configured to form a virtual image at another depth plane. In yet another embodiment, the eyepiece 100 may include three or more eyepiece layers for each of the three primary colors for three or more different depth planes. Each eyepiece layer includes a planar waveguide and may include an in-coupling grating (ICG) 107, an orthogonal pupil expander (OPE) region 108, and an exit pupil expander (EPE) region 109.

[0038] The projector 101 projects image light onto the ICG 107 in the eyepiece 100. The ICG 107 couples the image light from the projector 101 into a planar waveguide that propagates in a direction toward the OPE region 108. The waveguide propagates the image light in a horizontal direction by total internal reflection (TIR). The OPE region 108 also includes a diffraction element that multiplies the image light from the ICG 107 propagating in the waveguide and redirects it to the EPE region 109. In other words, the OPE region 108 multiplies the small beams delivered to different parts of the EPE in an orthogonal direction. The EPE region 109 includes a diffraction element that couples out a portion of the image light propagating in the waveguide and guides it to the viewer's eye 102. In this way, the viewer's eye 102 can view the image projected by the projector 101.

[0039] As described above, the image light produced by projector 101 may include light of three primary colors, i.e., blue (B), green (G), and red (R). This image light may be separated into component colors so that the image light of each component color may be coupled to a corresponding waveguide in the eyepiece. Embodiments of the present disclosure are not limited to use with the projector shown, and other types of projectors may be utilized in various embodiments of the present disclosure.

[0040] Although projector 101 includes an LED light source 103 and a liquid crystal on silicon (LCOS) spatial light modulator (SLM) 104, embodiments of the present disclosure are not limited to this projector technology and may include other projector technologies, including fiber scanning projectors, deformable mirror devices, micromechanical scanners, use of laser light sources instead of LEDs, and other arrangements of optics, waveguides, and beam splitters (including front illumination designs), etc.

[0041] In some eyepiece layers, the grating structure can have spatially uniform diffraction efficiency and optical phase across the entire surface of the grating structure. Figure 1A In the case of the OPE shown, this invariance can result in coherence artifacts when the substrate is substantially flat. These coherence artifacts are caused by interference effects associated with the multiple propagation paths that light may take within the OPE grating region, which can manifest as strong modulations of the output intensity at the exit of the grating region. These modulations produce dark bands, often referred to as "fringe," in the output image produced by the eyepiece, which appear at different angles as the viewing position changes. Additionally, the invariance of the diffraction efficiency can result in the output intensity decreasing exponentially with propagation distance into the grating structure.

[0042] Therefore, embodiments of the present invention reduce or eliminate these interference effects by making the diffraction efficiency vary with position, thereby reducing these and other image artifacts. As described herein, the variation in diffraction efficiency, also known as coupling efficiency, can be achieved by modifying the grating height to vary with position, thereby obtaining the desired variation in diffraction efficiency. For example, when the coherence between all possible optical paths in the OPE is reduced, the variable distribution of grating heights in the OPE will disturb the optical phase and will reduce interference-based image artifacts of the output image. In addition, the gradient variation of grating height in the EPE will result in increased brightness uniformity across the entire field of view in the output image and at different eye positions, thereby preventing the intensity from decreasing with position as light propagates through the grating (which is a characteristic of a uniform diffraction efficiency structure).

[0043] Figure 1B is a simplified cross-sectional view of a diffraction structure according to an embodiment of the present invention. Figure 1B As shown, the diffractive elements (i.e., grating teeth) are characterized by a depth / height that varies with position measured along the x-axis. As described above, if Figure 1A The EPE portion of the eyepiece shown is utilized Figure 1B With the diffraction structure shown, the outcoupled light intensity that varies with position (which may decrease with position when using a traditional grating) can be characterized by increased uniformity, thereby improving the user experience.

[0044] If a template is used to fabricate the grating structure, the imprinted waveguide in the template can be selectively tuned during the template etching process. Figure 1B If the grating structure is fabricated directly, the grating depth gradient can be selectively adjusted during fabrication (e.g., during etching) using the methods and systems described herein. In one embodiment, a structure with a varying grating depth (i.e., the depth is measured relative to the planar surface 160 of the substrate) is used as a master to imprint replicas that will include gratings with varying heights. Of course, other designs in which the master has a varying grating height (i.e., the height is measured relative to an inclined plane aligned with the bottom of the grating teeth) can also be used.

[0045] Embodiments of the present invention overcome the problem observed in conventional methods that the uniformity of near-field images and far-field images cannot be simultaneously addressed. In addition, in conventional methods (including step-based (i.e., digital) variation methods that can be manufactured using multi-step etching, or sequentially performing electron beam lithography and etching), step-based variations result in scattering due to clear boundaries between digital steps and / or steps of different sizes. Using embodiments of the present invention, a predetermined analog variation of the depth of the diffraction element with position is achieved, as well as benefits that cannot be obtained from conventional step-based grating depth variations. As described above, the methods and systems described herein enable the grating coupling coefficient to vary according to position, thereby improving brightness uniformity and user experience.

[0046] Figure 2 is a simplified cross-sectional diagram illustrating variable depth etching using a shadow mask according to an embodiment of the present invention. Figure 2 In the embodiment of the present invention, a shadow mask 210 is placed adjacent to a substrate 205 on which an etch mask 207 has been patterned. The etch mask 207 may be referred to as a hard mask. In some embodiments, the plane of the shadow mask having the holes is positioned parallel to the top surface of the substrate, and the distance D between the top surface of the etch mask and the shadow mask may be in the range of about 100 μm to several centimeters, for example, about 1 mm. The plasma 220 passes through the shadow mask 210 and causes etching of the substrate 205 at portions of the substrate not covered by the etch mask 207. It should be understood that the dimensions of the etch mask 207 are typically on the order of sub-micron geometric dimensions. Therefore, the drawings are not drawn to scale. Figure 2 , because the center distance between holes and the aperture size are several orders of magnitude larger than the etching mask size.

[0047] Shadow mask 210 has been fabricated to have apertures 212, 214, 216, and 218 whose sizes vary according to the x-direction. Figure 2In the example shown, the width of hole 212 is 30 μm, the width of hole 214 is 60 μm, the width of hole 216 is 90 μm, and the width of hole 218 is 120 μm. In this example, the center distance 215 of the aperture is 150 μm, but this is not required by the present invention, and other aperture spacings and aperture widths can be used. Due to the varying aperture sizes, the plasma density reaching the substrate surface varies across the substrate, with a higher plasma density adjacent to the wider aperture 218 and a lower plasma density adjacent to the narrower aperture 212. The plasma density is affected by the diffusion process. Therefore, although the holes have different sizes, the diffusion of the plasma in the x-direction and the y-direction will cause the plasma density to vary approximately continuously depending on the position on the substrate surface. It will be apparent to those skilled in the art that four holes 212 to 218 are shown to illustrate holes of varying sizes depending on the position, and the present invention is not limited to such a small number of holes. Instead, a large number of holes (each with a small variation) are used to provide a series of holes of increasing width, for example, approximately 65 holes on 150 μm centers may be used to vary the pore width from 30 μm to 120 μm, which may have a micrometer-scale increase in width from hole to hole. Figure 2 In the embodiment of the present invention, the variation of the aperture size with respect to the mask period is linear with position (i.e., in the x-direction), but this is not required by the present invention. In other embodiments, the variation with position is nonlinear. Since the plasma density at the etched surface is a function of the size and spacing of the holes in the shadow mask, in addition to using holes with equal spacing but varying sizes, other embodiments may also vary the spacing of the holes with equal aperture sizes. In addition, the aperture size and spacing may be varied simultaneously to achieve a desired aperture to mask area ratio and obtain a desired plasma density at the substrate surface. Those of ordinary skill in the art will recognize many variations, modifications, and alternatives.

[0048] As will be apparent to one skilled in the art, the chemical / physical etch rate that affects the grating depth is a function of the plasma density reaching the substrate surface. Figure 2 As shown, the grating depth H2 adjacent to the wider hole 218 is greater than the grating depth H1 adjacent to the narrower hole 212. Therefore, embodiments of the present invention utilize shadow masks to generate a plasma density that varies with position, which results in a change in the depth / height of the diffractive element with position on the substrate (the change can be a gradual change or a simulated change). After etching the diffractive element (e.g., grating teeth), the etch mask 207 can be removed.

[0049] although Figure 2 A change in a single direction (ie, the x direction) is shown, but embodiments of the present invention are not limited to this example, and changes in two dimensions (eg, the x direction and the y direction) are included within the scope of the present invention. Figure 2The grating depth is shown to increase approximately linearly from left to right, but the grating depth can be varied in another predetermined manner to achieve a desired depth profile. For example, the grating depth can vary in a linearly decreasing, linearly increasing, non-linear, sinusoidal manner as the depth changes, etc. (e.g., deep grating first, followed by shallower grating, followed by darker grating, or any particular pattern). In some embodiments, these varying grating depth profiles can be controlled by the spacing of the holes used to create the shadow of the grating and / or by the etch rate of the etchant used to create the grating. Those of ordinary skill in the art will recognize many variations, modifications, and alternatives.

[0050] In addition, despite Figure 2 A structure is shown in which a hard mask for diffractive elements is patterned and then a shadow mask is used to form a diffractive element with varying depth, but this is not required by the present invention. Other embodiments may utilize a process flow in which a diffractive element (e.g., a uniform grating pattern) is formed, the hard mask is removed, and then a shadow mask is used to selectively remove portions of the diffractive element to form a diffractive structure with varying height. An etching mask may be used in embodiments where varying depth is desired. In addition, although the periodic diffractive grating structure is composed of Figure 2 The etching mask 207 in FIG. 1 is limited, but this is not necessary for the present invention, and other nanostructures are included within the scope of the present invention, including columns or holes (with different cross-sectional shapes, including circular, polygonal, etc.), discontinuous gratings, sinusoidal wave lines and intervals, line segments, etc.

[0051] A shadow mask can be made using various materials that are etch resistant in a plasma etching environment and provide mechanical rigidity. For example, a shadow mask can be made using a silicon wafer that is patterned using photolithography and then etched to provide variable-sized openings on the wafer surface. A shadow mask can also be made using laser ablation of a portion of a silicon wafer. A stainless steel mesh or an anodized aluminum mesh can also be formed and used as a shadow mask. In addition, a protective coating such as Al2O3, SiO2, ZnO, TiO2, Au, Ag, Cu, Pt, Ir, etc. can be formed over the mesh (e.g., silicon) to protect materials that are not preferentially etched.

[0052] Some embodiments of the present invention are discussed with respect to use during dry etching processes, but embodiments of the present invention are applicable to various semiconductor manufacturing processes in which diffusion control of the etching / growth environment is used to make the manufacturing process (including other plasma etching processes) vary with position. As a further example, embodiments of the present invention are applicable to plasma deposition (e.g., sputtering, chemical vapor deposition (CVD), low pressure CVD (LP-CVD), plasma enhanced CVD (PECVD), etc.) used to form highly variable features, wet etching processes including metal-assisted chemical etching, other manufacturing processes in which the concentration of precursors or chemical species on the surface affects the deposition / etching rate, etc.

[0053] Figure 3A is a simplified plan view of a substrate and example shadow mask features in accordance with an embodiment of the present invention. Figure 3A The example shadow mask 310 shown illustrates how different aperture sizes with x,y position can be used to vary the etch depth, and the specific apertures shown are not limiting of embodiments of the present invention. Figure 3A , three different regions of a shadow mask 310 are shown: a first region 312 having small apertures, a second region 314 having intermediate apertures, and a third region 316 having large apertures.

[0054] In the example shadow mask 310 shown in FIG3 , the center distance between the holes (also referred to as the aperture period) is 150 μm, but this is merely exemplary. In addition, although the holes in the shadow mask are shown as square, this is merely exemplary, and other hole geometries may be utilized, including rectangular, polygonal, circular, elliptical, etc. The aperture size may range from several microns (e.g., 10 μm) to several millimeters, and the thickness of the shadow mask may range from 1 μm to several millimeters. Reference Figure 3A , the shadow mask shown is 80 μm thick, the center distance between holes (i.e., the aperture period) is 150 μm, and the aperture size ranges from 30 μm to 120 μm. Different regions of the shadow mask can be associated with different optical structures, including an orthogonal pupil expander 322 and an exit pupil expander 324. For example, one or more regions of the shadow mask can be associated with one or more optical structures.

[0055] refer to Figure 3A, each region of the shadow mask is characterized by an aperture size to aperture period ratio. For apertures having equal sizes in the x-direction and the y-direction (i.e., square or circular apertures), the aperture size to aperture period ratio may be equal in the x-direction and the y-direction, but this is not required by the present invention, and the ratio may be different in different directions. Region 312 has a low aperture size to aperture period ratio due to the small aperture size, while region 316 has a higher aperture size to aperture period ratio in contrast where the aperture period between regions 312 and 316 is constant (i.e., the center distance between the apertures is constant). Although the aperture size to aperture period ratio is shown as being uniform within each of regions 312, 314, and 316, this is exemplary only, and it should be understood that the ratio may vary within each region and between regions, such as as the size gradually changes.

[0056] Figure 3B is a close-up view of a portion of regions 312 and 316 according to an embodiment of the present invention. In some embodiments, for example, Figure 3B As shown, the aperture size in one region (e.g., x1 in region 316a) is larger than the aperture size in a second region (e.g., x2 in region 312a), and the aperture center distance (e.g., p1 in regions 316a and 312a) is constant, thereby providing a change in the ratio (e.g., R1 in region 316a and R2 in region 312a). Figure 3C is a close-up view of a portion of regions 312 and 316 in another embodiment of the present invention. Figure 3C In the illustrated embodiment, the aperture center distance in the first region (e.g., p1 in region 316b) is less than the aperture center distance in the second region (e.g., p2 in region 312b), and the aperture size in both regions (e.g., x1 in regions 316b and 312b) is constant, thereby providing a variation in the ratio (e.g., R1 in region 316b and R2 in region 312b). The ratio may be varied appropriately at different portions of the eyepiece depending on the particular application. For example, in FIG3, the orthogonal pupil expander 322 has little variation in aperture size or period in the y-direction and therefore has a constant ratio, but in the negative x-direction, the aperture size to aperture spacing ratio increases. On the other hand, the exit pupil expander 324 has a substantially linear variation in the y-direction, but little variation in the x-direction.

[0057] although Figure 3AThe regions of the shadow mask are shown as discrete elements, but it should be understood that these discrete regions are only used to illustrate the portion of the shadow mask whose aperture size gradually increases from region 312 to region 316. As the aperture size increases (which can be controlled during shadow mask manufacturing), the plasma density at the substrate surface corresponding to region 312 of the shadow mask 310 will be less than the plasma density at the substrate surface in the region corresponding to region 316 of the shadow mask 310. Therefore, the etching rate of the substrate area corresponding to region 316 is higher than the etching rate of the substrate area corresponding to region 312, thereby enabling the formation of a diffraction element with a grating depth and coupling coefficient that varies with position. Therefore, the shadow mask with varying size holes enables the plasma density to be adjusted as a function of position, thereby adjusting the etching depth as a function of position. Therefore, Figure 3A The illustration of discrete regions 312, 314, and 316 is intended only to illustrate that the aperture size varies (eg, gradually) across the shadow mask, thereby enabling the etch rate and grating depth to vary with position on the substrate (since the plasma density varies with position).

[0058] Figure 4A is an image showing a portion of an eyepiece including a variable height grating structure according to an embodiment of the present invention. Figure 4A As shown, three measurement locations 410, 412, and 414 are shown. Figures 4B to 4D They are Figure 4A Illustration of an SEM cross section of a grating tooth at three measurement locations 410, 412 and 414 are shown. Figure 4E Is to show the distance Figure 4A A graph of grating etch depth varying with distance from the edge 405 of the eyepiece is shown.

[0059] refer to Figures 4B to 4D , the grating etch depth was measured at three locations on the eyepiece. Using the shadow mask technique described in this paper, a simulated gradient diffraction structure was fabricated. FIG. 4A to FIG. 4E , an etch depth gradient of a silicon wafer having a one-dimensional gradient is shown, but it should be understood that this is only an example and other gradient structures (including two-dimensional structures) can be fabricated using other materials.

[0060] To manufacture Figures 4A to 4D For the structure shown, an etching mask of thermally grown SiO2 on a silicon wafer is first etched without a shadow mask to produce the grating teeth. Then, a shadow mask with a one-dimensional variation in aperture size is placed 2 mm from the silicon wafer surface and the silicon wafer is etched. The depth of the grating etching is measured relative to the distance from the eyepiece edge 405. Figure 4B As shown, a grating depth d1 of about 60 nm is generated at position 410. Figure 4CAs shown, a grating depth d2 of about 78 nm is generated at position 412, and as shown in Figure 4D As shown in FIG. 4 , a grating depth d1 of about 100 nm is generated at position 414. The variation of grating etching depth with distance is shown in FIG. Figure 4E , where the grating depth ranges from about 60 nm to about 110 nm on a 35 mm sized eyepiece. In contrast to conventional techniques that typically produce steps or lines visible on the eyepiece, embodiments of the present invention provide a substantially gradual grating depth variation with position. Thus, embodiments of the present invention enable smooth near-field and far-field images to be achieved in the virtual image displayed to the user's eye.

[0061] In addition to the one-dimensional variation shown in FIG. 1 , embodiments of the present invention can also utilize a shadow mask with two-dimensional variation to fabricate a structure characterized by a hybrid gradient grating depth / height variation of a 2D profile. Figures 5A to 5C is a plan view showing a diffraction structure manufactured using conventional technology. Figures 5D to 5F is a plan view showing a diffractive structure with a one-dimensional or two-dimensional profile manufactured according to an embodiment of the present invention. By controlling the size, duty cycle (i.e., spacing) of the holes in the shadow mask, a one-dimensional or two-dimensional pattern can be manufactured with a predetermined etching depth gradient. Compared with conventional techniques such as one-dimensional step profiles, embodiments of the present invention achieve challenging two-dimensional profiles. Therefore, the shadow mask technology described herein not only achieves two-dimensional profile drawing or customization based on a specific design of the shadow mask aperture distribution, but also can blend boundaries to achieve a predetermined gradient profile that cannot be obtained using conventional techniques.

[0062] refer to Figures 5A to 5C , showing a one-dimensional ( Figure 5A ), 2D( Figure 5B ) and round ( Figure 5C ) profile. Darker gray areas are associated with darker etch profiles, and lighter gray areas are associated with lighter etch profiles. The steps or boundaries between adjacent parts are obvious. During use, diffractive structures with these obvious boundaries will produce changes or scattering of far-field and / or near-field image intensity at the boundaries, thereby negatively affecting image quality and user experience. In contrast to these traditional results, embodiments of the present invention provide a one-dimensional ( Figure 5D ), 2D( Figure 5E ) and round ( Fig. 5F )contour.

[0063] Fig. 6A is a simplified cross-sectional view of a diffractive structure with a grating height gradient according to an embodiment of the present invention. Figure 6Bis a simplified plan view illustrating a digital dispensing pattern with varying dispensing volumes in accordance with an embodiment of the present invention. Figure 6C is a hybrid interface region according to an embodiment of the present invention Fig. 6A Simplified cross-sectional view of the diffractive structure shown in .

[0064] refer to Fig. 6A , the diffractive structure includes grating teeth with varying depths as described herein. The structure, which may also include variations in a second dimension, may be fabricated using the techniques described herein. In some embodiments, the diffractive structure is made of silicon, SiO2, etc., and is used as a template in a nanoimprint lithography process (e.g., a jet and rapid imprint lithography (J-FIL) process). Figure 6B As shown, a resist pattern or other suitable liquid can be dispensed in a droplet pattern by a print head that can utilize hundreds of nozzles. Thus, the dispense pattern can include droplets having an adjustable finite volume. However, in some embodiments, the droplet volume cannot be continuously adjusted. Figure 6B 6, a volume of liquid is dispensed in a digital dispensing pattern with a predetermined volume in each of portions 620, 622, 624, and 626. For example, if the drop volume is 1 pL, portion 620 will have 9 pL of liquid, portion 622 will have 16 pL of liquid, portion 624 will have 25 pL of liquid, and portion 626 will have 36 pL of liquid. Thus, each portion has a predetermined residual layer thickness (RLT) that is a function of the drop volume and the number of drops per portion. After the initial dispensing is complete, the different volumes in each portion will result in steps 630 between adjacent portions.

[0065] refer to Figure 6C , showing that one can use Fig. 6A The simulated gradient template shown is printed by imprinting Figure 6B Cross-section of the diffraction grating formed by the volume of the patterned droplet shown. During imprinting, as the liquid expands in each section and spreads across the section, the RLT near the edge of the section (not discontinuous) will be as shown in Figure 1. Figure 6C As shown, the grating teeth height changes smoothly from shallower to deeper as measured relative to the base of the substrate. Thus, the expansion of liquid (e.g., resist) at the edge of a portion boundary (e.g., boundary 632) will cause the RLT to mix at the interface region between the portions. Due to the smooth transition at the portion boundary, light scattering at the boundary will be reduced compared to structures with discrete boundaries. The change from shallower to deeper grating tooth height measured relative to the base of the substrate will be associated with the increase in liquid volume from portion 620 to portion 626.

[0066] Figure 7A simplified process flow chart showing a method of making a shadow mask according to an embodiment of the present invention is shown. The process begins with a silicon-on-insulator (SOI) substrate having a chrome etch mask layer 738 deposited thereon (710). The SOI substrate includes a silicon handle wafer 730, a buried oxide layer 732, a single crystal silicon layer 734, and a back oxide layer 736. Although a silicon shadow mask is shown in the flow chart, this is not required by the present invention, and other materials including SiO2, metals, other dielectric materials, etc. are also suitable for use as a shadow mask.

[0067] A pattern layer 740 is formed on the chrome layer 738, and the pattern layer (e.g., photoresist) is patterned with a predetermined aperture size (712). As described below, apertures of varying sizes with position are defined in this processing step. The chrome layer 738 is etched using the patterned pattern layer, such as using a dry etching process, to transfer the pattern in the pattern layer into the chrome layer (714), which will be used as a hard mask in a subsequent etching process.

[0068] To etch the single crystal silicon layer 734, the patterned chromium layer 742 is used as a hard mask, for example, during plasma etching, and the pattern in the chromium layer will be transferred into the single crystal silicon layer during etching (716). As shown in process step 716, the silicon etching process terminates when the buried oxide layer 732 is reached.

[0069] To define the lateral dimensions of the shadow mask, the back oxide layer 736 is patterned (718). The opening is then used to etch the silicon handle wafer 730 (720) with a deep etch (e.g., dry etch) that terminates at the buried oxide layer 732. The thickness of the silicon handle wafer (e.g., about 80 μm to 800 μm, such as 500 μm) provides mechanical strength and rigidity to the shadow mask. The buried oxide layer 732 is then removed, leaving a grid or mesh pattern in the single crystal silicon layer 734 (722). The manufacturing process is completed by removing the chrome hard mask and the remainder of the pattern layer (724). Illustration 750 shows the holes in the grid pattern shown at processing step 724 in a plan view. It will be apparent to one skilled in the art that the aperture size varies across the shadow mask, and the uniformity of the aperture size shown in illustration 750 is intended only to illustrate a portion of the shadow mask, as the aperture size can, for example, vary slowly across the structure. In addition, although in Figure 7 The exemplary flow charts shown use an SOI substrate, but other materials and processes may be used and are within the scope of the present invention.

[0070] For example, despite Figure 7Dry etching is shown, but other embodiments utilize a wet etching process in which silicon can be anisotropically etched using KOH to create holes in the wafer / sheet. Other metals and dielectric materials can also be wet etched anisotropically or isotropically. In addition, laser drilling / ablation can be used, for example, a laser can be used to drill holes in silicon, metal, glass or other dielectric materials with sub-micron accuracy, which is sufficient for pore sizes greater than micrometers. In addition, a metal-assisted chemical wet etching (MaCe) process can be used, for example, gold (Au) can be used to assist silicon wet etching to produce anisotropic etching.

[0071] Figure 8 is a simplified diagram illustrating the use of a shadow mask master to produce a substrate having variable depth diffractive elements in accordance with an embodiment of the present invention. Figure 8 8, a shadow mask master 805 having a gradient duty cycle aperture is placed adjacent to a substrate 820. In this example, the shadow mask master 805 includes four regions 812, 814, 816, and 818, each region having a varying aperture size to produce a gradient duty cycle aperture, where lighter colors represent larger duty cycles, similar to Figure 3A In the region 316 shown, the darker color indicates a smaller duty cycle, which is similar to Figure 3A Area 312 is shown. In one example, four different eyepieces can be patterned using a shadow mask master.

[0072] The substrate 820 is etched to form a mother substrate 830. Figure 8 As shown, shadow mask master 805 is aligned adjacent to (e.g., above) substrate 820, which is typically protected by resist and is exposed in four regions 822, 824, 826, and 828 corresponding to regions 812, 814, 816, and 818 in shadow mask master 805. Figure 8 In FIG. 8 , darker areas on the mother substrate 830 represent deeper etch depths. By designing specific aperture sizes and varying the duty cycle on the shadow mask master, a targeted etch depth gradient can be etched into the substrate 820 to form a multi-field mother substrate 830. The mother substrate 830 can then be used as a master template for a contact-based nanolithography process (e.g., J-FIL) to imprint on a high refractive index substrate and thus be used as a waveguide, or as a shadow mask when directly etching a high refractive index layer or a substrate to be used as an optical waveguide.

[0073] Fig. 9 is a simplified cross-sectional view showing a variable thickness deposition layer according to an embodiment of the present invention. Fig. 9In the embodiment, a shadow mask (not shown) has been applied to the deposition process to produce a gradually varying deposition layer 910 having a first thickness t1 in a first region and a second thickness t2 in a second region. Fig. 9 As shown, the thickness of the deposited layer in areas adjacent to shadow mask portions having a higher aperture size to aperture period ratio is greater than the thickness of the deposited layer in areas adjacent to shadow mask portions having a lower aperture size to aperture period ratio. Thus, starting with a grating element having a uniform height, the shadow mask technique described herein can be used to form a diffractive element characterized by a first gradient depth in a first area and a second gradient depth in a second area, since the thickness of the deposited layer varies with position. In addition, as Fig. 9 As shown, the diffractive element in the first region is characterized by a line width distribution w1 measured in the x direction, which is wider than the line width distribution w2 in the second region. Therefore, the diffractive element provided by embodiments of the present invention can include depth and width variations with position, which are related to the shadow mask aperture size and aperture period ratio.

[0074] Many plasma assisted deposition processes may be implemented using embodiments of the present invention, including, for example, atmospheric pressure plasma enhanced CVD (APPECVD), traditional physical deposition processes such as sputtering deposition and evaporation. Placing a shadow mask adjacent to a substrate on which a deposited layer is formed will result in a variation in coating / deposition thickness, where for similar aperture spacing, areas with larger apertures are coated with thicker coatings, while areas with smaller apertures are coated with thinner coatings. Thus, a coating thickness gradient is created that is not easily created using traditional deposition techniques. Fig. 9 , a conformal coating produced using APPECVD or sputtering processes on nanopatterns is shown, which nanopatterns can be diffraction gratings or other suitable diffraction structures.

[0075] Fig.10 1 is a flow chart illustrating a method for manufacturing a diffractive structure with a variable diffractive element depth according to an embodiment of the present invention. The method includes providing a shadow mask in step 1005. The shadow mask may have a first area and a second area, the first area having a first aperture size and an aperture period ratio, and the second area having a second aperture size and an aperture period ratio. The second aperture size and the aperture period ratio may be less than the first aperture size and the aperture period ratio. In some embodiments, the first aperture size and the aperture period ratio and the second aperture size and the aperture period ratio are defined by a first aperture size in the first area that is greater than the second aperture size in the second area and a constant aperture center distance. In some embodiments, the first aperture size and the aperture period ratio and the second aperture size and the aperture period ratio are defined by a first aperture center distance in the first area and a second aperture center distance in the second area and a constant aperture size. As used herein, the aperture period may also be referred to as an aperture center distance.

[0076] The method further includes positioning a shadow mask adjacent to the substrate at step 1010. In some embodiments, the shadow mask is characterized by an aperture size to aperture period ratio that varies linearly across the shadow mask. The shadow mask can be fabricated using etch-resistant materials and can include a protective coating to protect materials that are not preferentially etched.

[0077] In some embodiments, the substrate may include a silicon substrate. In other embodiments, the substrate may include any suitable material that can be etched. The substrate may include an etching mask corresponding to the diffraction structure. The etching mask may also be referred to as a hard mask in this article. In some embodiments, the diffraction structure may include a diffraction grating, and the diffraction element includes grating teeth.

[0078] The method further includes exposing the substrate to an etchant at step 1015. In some embodiments, exposing the substrate to the etchant may include performing a plasma etching process. For example, the plasma may pass through a shadow mask and etch the substrate at portions not covered by the etching mask. In other embodiments, any suitable etchant capable of etching a material selected for the substrate may be used.

[0079] The method further includes etching the substrate at step 1020 to form a diffractive element with a first depth adjacent to the first region. The method further includes etching the substrate at step 1025 to form a diffractive element with a second depth adjacent to the second region that is less than the first depth. In some embodiments, the diffractive element varies nonlinearly. In some embodiments, the first depth and the second depth can be in the range of about 10nm to about 150nm. The first and second depths can vary due to the size variation of the holes in the shadow mask, thereby allowing more or less amounts of etchant to contact the substrate.

[0080] In some embodiments, the method further comprises removing the etching mask after etching the diffractive elements in the first region and etching the diffractive elements in the second region. In some embodiments, the method further comprises performing a plasma enhanced coating process on the substrate.

[0081] It should be understood that Fig.10 The specific steps shown provide a specific method for manufacturing a diffractive structure with a varying diffractive element depth according to another embodiment of the present invention. According to alternative embodiments, other step sequences may also be performed. For example, alternative embodiments of the present invention may perform the steps outlined above in a different order. In addition, Fig.10 The various steps shown may include multiple sub-steps, which may be performed in various orders suitable for the various steps. In addition, additional steps may be added or deleted according to specific applications. Those of ordinary skill in the art will recognize many variations, modifications, and substitutions.

[0082] Fig.11 1 is a flow chart illustrating a method for manufacturing a mother substrate according to an embodiment of the present invention. The method includes providing a shadow mask having a first region and a second region at step 1105. The first region can be characterized by a first gradient aperture size and aperture period ratio in at least a first direction. The second region can be characterized by a second gradient aperture size and aperture period ratio in at least a second direction. The shadow mask can include any suitable etch-resistant material. The aperture period can also be referred to herein as an aperture center distance.

[0083] In some embodiments, the first gradient aperture size to aperture period ratio is equal to the second gradient aperture size to aperture period ratio, and the first direction and the second direction are the same direction. In some embodiments, the first gradient aperture size to aperture period ratio may be defined by a constant aperture center distance and a gradually varying aperture size along the first direction, and the second gradient aperture size to aperture period ratio may be defined by a constant aperture center distance and a gradually varying aperture size along the second direction. In some embodiments, the first gradient aperture size to aperture period ratio may be defined by a constant aperture size and a gradually varying aperture center distance along the first direction, and the second gradient aperture size to aperture period ratio is defined by a constant aperture size and a gradually varying aperture center distance along the second direction.

[0084] The method further includes providing a substrate at step 1110. The substrate may have an etching mask characterized by diffraction features, a first exposed area and a second exposed area. The etching mask may also be referred to as a hard mask in this article. In some embodiments, the substrate may include a silicon substrate. In some embodiments, the substrate may include any suitable etchable material.

[0085] The method further includes positioning a shadow mask adjacent to the substrate at step 1115. The first region can be aligned with the first exposed region, and the second region can be aligned with the second exposed region. The method further includes performing a plasma etching process on the substrate at step 1120. According to the process, the plasma can pass through the shadow mask at portions of the substrate not covered by the etching mask.

[0086] The method further includes etching a first diffractive element adjacent to the first region at step 1125. The first diffractive element can be characterized by a first gradient depth distribution in at least the first direction. The method further includes etching a second diffractive element adjacent to the second region at step 1130. The second diffractive element can be characterized by a second gradient depth distribution in at least the second direction. The different depth distributions between the first diffractive element and the second diffractive element can be caused by holes of varying sizes in the shadow mask used in the plasma etching process. For example, a larger aperture can allow more plasma to contact the substrate, while a smaller aperture can allow less plasma to contact the substrate. This may result in a change in the plasma density reaching the surface, thereby forming a diffractive element of varying size and depth.

[0087] In some embodiments, the first diffractive element and the second diffractive element may include grating teeth. In some embodiments, the method further includes removing the etching mask after etching the first diffractive element adjacent to the first region and etching the second diffractive element adjacent to the second region.

[0088] In some embodiments, the first region can be further characterized by a third gradient aperture size to aperture period ratio in a direction at least orthogonal to the first direction, the second region can be further characterized by a fourth gradient aperture size to aperture period ratio in a direction at least orthogonal to the second direction, the first diffraction element is further characterized by a third gradient depth distribution in a direction orthogonal to the first direction, and the second diffraction element is further characterized by a fourth gradient depth distribution in a direction orthogonal to the second direction.

[0089] It should be understood that Fig.11 The specific steps shown provide a specific method of manufacturing a mother substrate according to another embodiment of the present invention. According to alternative embodiments, other step sequences may also be performed. For example, alternative embodiments of the present invention may perform the steps outlined above in a different order. In addition, Fig.11 The various steps shown may include multiple sub-steps, which may be performed in various orders suitable for the various steps. In addition, additional steps may be added or deleted according to specific applications. Those of ordinary skill in the art will recognize many variations, modifications, and substitutions.

[0090] Fig.12 1 is a flow chart illustrating a method of depositing a variable thickness material according to an embodiment of the present invention. The method includes providing a substrate at step 1205. In some embodiments, the substrate may include a growth surface, the growth surface including a diffraction structure. The diffraction structure may include a diffraction grating.

[0091] In some embodiments, the substrate may include a uniform diffractive structure including a plurality of diffractive elements, and the variable thickness material may be characterized by a first diffractive element depth in a first region and a second diffractive element depth in a second region that is less than the first diffractive element depth. In some embodiments, the substrate may include a uniform diffractive structure including a plurality of diffractive elements, and the variable thickness material may be characterized by a first diffractive element width in a first region and a second diffractive element width in a second region that is less than the first diffractive element width.

[0092] The method further includes providing a shadow mask at step 1210. The shadow mask may include a first region having a first aperture size to aperture period ratio and a second region having a second aperture size to aperture period ratio less than the first aperture size to aperture period ratio. In some embodiments, the shadow mask may be characterized by an aperture size to aperture period ratio that varies in two directions.

[0093] The method further includes positioning a shadow mask adjacent to the substrate at step 1215. The method further includes performing a plasma deposition process on the substrate to deposit a variable thickness material at step 1220. The thickness of the layer adjacent to the first region may be greater than the thickness of the layer adjacent to the second region. In some embodiments, the variable thickness material may include a conformal layer.

[0094] In some embodiments, the shadow mask may include a plurality of apertures and a surface parallel to the plurality of apertures. The substrate may include a deposition surface. In some embodiments, positioning the shadow mask adjacent to the substrate may include placing a surface of the shadow mask parallel to the deposition surface.

[0095] It should be understood that Fig.12 The specific steps shown provide a specific method for depositing a variable thickness material according to another embodiment of the present invention. According to alternative embodiments, other step sequences may also be performed. For example, alternative embodiments of the present invention may perform the steps outlined above in a different order. In addition, Fig.12 The various steps shown may include multiple sub-steps, which may be performed in various orders suitable for the various steps. In addition, additional steps may be added or deleted according to specific applications. Those of ordinary skill in the art will recognize many variations, modifications, and substitutions.

[0096] Fig.13 1 is a flow chart illustrating a method of manufacturing a mother substrate according to an embodiment of the present invention. The method includes providing a shadow mask at step 1305. The shadow mask may have a first region characterized by a first gradient aperture size to aperture period ratio in at least a first direction. The shadow mask may further have a second region characterized by a second gradient aperture size to aperture period ratio in at least a second direction.

[0097] The method further includes providing a substrate at step 1310. The substrate may have a mask characterized by diffractive features, a first exposed area, and a second exposed area. The method further includes positioning a shadow mask adjacent to the substrate at step 1315. The first area may be aligned with the first exposed area, and the second area may be aligned with the second exposed area. The method further includes performing at least one of a plasma coating or a deposition process on the substrate at step 1320.

[0098] The method further includes coating a first diffractive element adjacent to the first region at step 1325. The first diffractive element may be characterized by a first gradient depth and a first line width distribution in at least a first direction. The method further includes coating a second diffractive element adjacent to the second region at step 1330. The second diffractive element may be characterized by a second gradient depth and a second line width distribution in at least a second direction. In some embodiments, the first gradient depth may be greater than the second gradient depth. In some embodiments, the first line width distribution may be characterized by a first width, and the second line width distribution may be characterized by a second width less than the first width. Therefore, the diffractive elements provided by some embodiments of the present invention may include depths and widths that vary with position, and these variations are related to the shadow mask aperture size and aperture period ratio.

[0099] It should be understood that Fig.13 The specific steps shown provide a specific method of manufacturing a mother substrate according to another embodiment of the present invention. According to alternative embodiments, other step sequences may also be performed. For example, alternative embodiments of the present invention may perform the steps outlined above in a different order. In addition, Fig.13 The various steps shown may include multiple sub-steps, which may be performed in various orders suitable for the various steps. In addition, additional steps may be added or deleted according to specific applications. Those of ordinary skill in the art will recognize many variations, modifications, and substitutions.

[0100] It should also be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light of them will be suggested to those skilled in the art and are to be included within the spirit and purview of the present application and the scope of the appended claims.

Claims

1. A method for depositing a material with variable thickness, the method comprising: Providing a substrate including a uniform diffraction structure, wherein the uniform diffraction structure includes a plurality of diffraction elements; providing a shadow mask having a first region having a first aperture size to aperture period ratio and a second region having a second aperture size to aperture period ratio that is smaller than the first aperture size to aperture period ratio; positioning the shadow mask adjacent to the substrate; as well as A deposition process is performed on the substrate to deposit the variable thickness material, wherein a layer thickness adjacent to the first region is greater than a layer thickness adjacent to the second region.

2. The method of claim 1, wherein the substrate comprises SiO2. The method of claim 2 , wherein the uniform diffraction structure comprises a diffraction grating. The method of claim 1 , wherein the variable thickness material comprises a conformal layer.

5. The method according to claim 1, wherein: The shadow mask includes a plurality of apertures and a surface parallel to the plurality of apertures; The substrate comprises a deposition surface; and Positioning the shadow mask adjacent to the substrate includes placing the surface of the shadow mask parallel to the deposition surface.

6. The method of claim 1, wherein the shadow mask is characterized by an aperture size to aperture period ratio that varies in two directions.

7. The method of claim 1, wherein the variable thickness material is characterized by a first diffractive element depth in the first region and a second diffractive element depth in the second region that is less than the first diffractive element depth.

8. The method of claim 1, wherein the variable thickness material is characterized by a first diffractive element width in the first region and a second diffractive element width in the second region that is smaller than the first diffractive element width.

9. The method of claim 1, wherein performing the deposition process on the substrate comprises a plasma deposition process.

10. A method for manufacturing a mother substrate, the method comprising: A shadow mask is provided, the shadow mask comprising: a first region characterized by a first gradient pore size to pore period ratio in at least a first direction; as well as a second region characterized by a second gradient pore size to pore period ratio in at least a second direction; A substrate is provided, the substrate having: a mask characterized by diffractive features; First exposure area; as well as Second exposure area; positioning the shadow mask adjacent the substrate wherein the first region is aligned with the first exposed region and the second region is aligned with the second exposed region; performing a plasma coating or deposition process on the substrate; applying a first diffractive element adjacent to the first region, wherein the first diffractive element is characterized by a first gradient depth and a first linewidth distribution in the at least first direction; as well as A second diffractive element is applied adjacent to the second region, wherein the second diffractive element is characterized by a second gradient depth and a second linewidth distribution in the at least second direction. The method of claim 10 , wherein the first gradient depth is greater than the second gradient depth. 12 . The method of claim 10 , wherein the first line width distribution is characterized by a first width and the second line width distribution is characterized by a second width that is smaller than the first width.

13. The method of claim 10, wherein: The first region is further characterized by a third gradient aperture size to aperture period ratio in a direction at least orthogonal to the first direction; The second region is further characterized by a fourth gradient aperture size to aperture period ratio in a direction at least orthogonal to the second direction; The first diffractive element is further characterized by a third gradient depth profile in a direction orthogonal to the first direction; and The second diffractive element is further characterized by a fourth gradient depth profile in a direction orthogonal to the second direction.

14. The method of claim 10, wherein: The first gradient aperture size to aperture period ratio is equal to the second gradient aperture size to aperture period ratio; and The first direction and the second direction are the same direction.

15. The method of claim 10, wherein: The first gradient aperture size to aperture period ratio is defined by a gradual aperture size along the first direction and a constant aperture center distance; and The second gradient aperture size to aperture period ratio is defined by the gradually changing aperture size and the constant aperture center distance along the second direction.

16. The method of claim 10, wherein: The first gradient aperture size to aperture period ratio is defined by a constant aperture size and a gradient aperture center distance along the first direction; and The second gradient aperture size to aperture period ratio is defined by a constant aperture size and a gradient aperture center distance along the second direction. The method of claim 10 , wherein the substrate comprises a silicon substrate.

18. The method of claim 10, wherein the substrate comprises a diffractive structure comprising a diffraction grating. The method of claim 18 , wherein the deposition process comprises a plasma deposition process.

20. The method of claim 10, wherein the substrate comprises a conformal layer.

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