Patent Publication Number: US-2022238295-A1

Title: Shadow mask apparatus and methods for variable etch depths

Description:
RELATED APPLICATION 
     This application claims priority to and is a divisional application of U.S. Non-Provisional patent application Ser. No. 16/789,591, filed on Feb. 13, 2020, entitled “S HADOW  M ASK  A PPARATUS  &amp; M ETHODS FOR  V ARIABLE  E TCH  D EPTHS ,” which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure generally relates to processing of grating materials. More specifically, the disclosure relates to apparatuses and methods of producing variable-depth grating materials. 
     BACKGROUND OF THE DISCLOSURE 
     Optical elements such as optical lenses have long been used to manipulate light for various advantages. Recently, micro-diffraction gratings have been utilized in holographic and augmented/virtual reality (AR and VR) devices. One particular AR and VR device is a wearable display system, such as a headset, arranged to display an image within a short distance from a human eye. Such wearable headsets are sometimes referred to as head mounted displays, and are provided with a frame displaying an image within a few centimeters of the user&#39;s eyes. The image can be a computer-generated image on a display, such as a micro display. The optical components are arranged to transport light of the desired image, where the light is generated on the display to the user&#39;s eye to make the image visible to the user. The display where the image is generated can form part of a light engine, so the image generates collimated light beams guided by the optical component to provide an image visible to the user. 
     The optical components may include structures with different slant angles, such as fins of one or more gratings, on a substrate, formed using an angled etch system. One example of an angled etch system is an ion beam chamber that houses an ion beam source. The ion beam source is configured to generate an ion beam, such as a ribbon beam, a spot beam, or full substrate-size beam. The ion beam chamber is configured to direct the ion beam at an angle relative to a surface normal of a substrate to generate a structure having a specific slant angle. Changing the slant angle of the structure to be generated by the ion beam requires substantial hardware reconfiguration of the of the ion beam chamber. 
     Forming optical devices that include different structures having different depths across the surface of substrate has conventionally been performed using gray-tone lithography. However, gray-tone lithography is a time-consuming and complex process, which adds considerable costs to any devices fabricated using the process. 
     Accordingly, improved methods and related equipment are needed for forming optical devices that include different structures with different slant angles and/or different depths across a single substrate. 
     SUMMARY 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended as an aid in determining the scope of the claimed subject matter. 
     According to one embodiment, a method may include providing an etching material atop a substrate, and positioning a shadow mask between the etching material and an ion source, wherein the shadow mask is separated from the etching material by a distance. The method may further include etching the etching material using an ion beam passing through a set of openings of the shadow mask, wherein a first depth of a first portion of the etching material is different than a second depth of a second portion of the etching material. 
     According to another embodiment, a shadow mask apparatus may include a shadow mask positioned over a grating material, wherein the shadow mask is separated from the grating material by a distance. The shadow mask apparatus may further include a plurality of openings provided through the shadow mask, each of the plurality of openings defined by a leading edge and a trailing edge relative to a direction of travel of an ion beam, wherein the leading edge and the trailing edge of at least one opening of the plurality of openings vary from one another in height, the height relative to a top surface of the grating material. 
     According to yet another embodiment, a method of forming an optical grating may include providing an optical grating material atop a substrate, and positioning a shadow mask between the grating material and an ion source, wherein the shadow mask is separated from the optical grating material by a distance. The method may further include forming a plurality of structures by etching the optical grating material using an ion beam passing through a set of openings of the shadow mask, wherein a first depth of a first portion of the optical grating material is different than a second depth of a second portion of the optical grating material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate exemplary approaches of the disclosure, including the practical application of the principles thereof, as follows: 
         FIG. 1  is a perspective, frontal view of an optical device, according to embodiments of the present disclosure; 
         FIG. 2A  is a side, schematic cross-sectional view of an angled etch system, according to embodiments of the present disclosure; 
         FIG. 2B  is a top, schematic cross-sectional view of the angled etch system shown in  FIG. 2A , according to embodiments of the present disclosure; 
         FIG. 3A  depicts a side, cross sectional view of an optical grating component formed from a grating material, according to embodiments of the disclosure; 
         FIG. 3B  depicts a frontal view of the optical grating component of  FIG. 3A , according to embodiments of the present disclosure; 
         FIG. 4  depicts a frontal view a shadow mask apparatus, according to embodiments of the present disclosure; 
         FIG. 5A  depicts a side, cross-sectional view along cut line  5 A- 5 A of  FIG. 4 , according to embodiments of the present disclosure; 
         FIG. 5B  depicts a side cross-sectional view along cut line  5 B- 5 B of  FIG. 4 , according to embodiments of the present disclosure; 
         FIG. 6A  depicts a side, cross-sectional view of a mask and grating material, according to embodiments of the present disclosure; 
         FIG. 6B  depicts a frontal view of the mask and grating material of  FIG. 6A , according to embodiments of the present disclosure; 
         FIG. 7A  depicts a side, cross-sectional view of a mask and grating material, according to embodiments of the present disclosure; 
         FIG. 7B  depicts a frontal view of the mask and grating material of  FIG. 7A , according to embodiments of the present disclosure; 
         FIG. 8A  depicts a side, cross-sectional view of a mask and grating material, according to embodiments of the present disclosure; 
         FIG. 8B  depicts a frontal view of the mask and grating material of  FIG. 8A , according to embodiments of the present disclosure; 
         FIG. 9A  depicts a side, cross-sectional view of a mask and grating material, according to embodiments of the present disclosure; 
         FIG. 9B  depicts a frontal view of the mask and grating material of  FIG. 9A , according to embodiments of the present disclosure; 
         FIG. 10A  depicts a side, cross-sectional view of a mask and grating material, according to embodiments of the present disclosure; 
         FIG. 10B  depicts a frontal view of the mask and grating material of  FIG. 10A , according to embodiments of the present disclosure; 
         FIG. 11A  depicts a side, cross-sectional view of a raised surface feature, according to embodiments of the present disclosure; 
         FIG. 11B  depicts a frontal view of the raised surface feature of  FIG. 11A , according to embodiments of the present disclosure; and 
         FIG. 12  is a flowchart of a method, according to embodiments of the present disclosure. 
     
    
    
     The drawings are not necessarily to scale. The drawings are merely representations, not intended to portray specific parameters of the disclosure. The drawings are intended to depict exemplary embodiments of the disclosure, and therefore are not be considered as limiting in scope. In the drawings, like numbering represents like elements. 
     Furthermore, certain elements in some of the figures may be omitted, or illustrated not-to-scale, for illustrative clarity. The cross-sectional views may be in the form of “slices”, or “near-sighted” cross-sectional views, omitting certain background lines otherwise visible in a “true” cross-sectional view, for illustrative clarity. Furthermore, for clarity, some reference numbers may be omitted in certain drawings. 
     DETAILED DESCRIPTION 
     Apparatuses, systems, and methods in accordance with the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, where various embodiments are shown. The apparatuses, systems, methods may be embodied in many different forms and are not to be construed as being limited to the embodiments set forth herein. Instead, these embodiments are provided so the disclosure will be thorough and complete, and will fully convey the scope of the apparatuses, systems, and methods to those skilled in the art. 
       FIG. 1  is a perspective, frontal view of a device  100 , such as an optical device, according to embodiments of the present disclosure. Examples of the optical device  100  include, but are not limited to, a flat optical device and a waveguide (e.g., a waveguide combiner). The optical device  100  includes one or more structures, such as gratings. In one embodiment, which can be combined with other embodiments described herein, the optical device  100  includes an input grating  102 , an intermediate grating  104 , and an output grating  106 . Each of the gratings  102 ,  104 ,  106  includes corresponding structures  108 ,  110 ,  112  (e.g., fins). In one embodiment, which can be combined with other embodiments described herein, the structures  108 ,  110 ,  112  and depths between the structures include sub-micron critical dimensions (e.g., nano-sized critical dimensions), which may vary in one or more dimensions across the optical device  100 . 
       FIG. 2A  is a side, schematic cross-sectional view and  FIG. 2B  is a top, schematic cross-sectional view of an angled etch system (hereinafter “system”)  200 , such as the Varian VIISta® system available from Applied Materials, Inc. located in Santa Clara, Calif. It is to be understood that the system  200  described below is an exemplary angled etch system and other angled etch systems, including angled etch systems from other manufacturers, may be used to or modified to form the structures described herein on a substrate. 
       FIGS. 2A-2B  show a device  205  disposed on a platen  206 . The device  205  may include a substrate  210 , an etch stop layer  211  disposed over the substrate  210 , a etching layer to be etched, such as a grating material  212  disposed over the etch stop layer  211 , and a hardmask  213  disposed over the grating material  212 . It will be appreciated that the device  205  may include different layering materials and/or combinations in other embodiments. For example, the etching layer may be a blanket film to be processed, such as a photoresist-type material or an optically transparent material (e.g., silicon or silicon nitride). The blanket film may be processed using a selective area processing (SAP) etch cycle(s) to form one or more sloped or curved surfaces of the device  205 . 
     To form structures (e.g., fins) having slant angles, the grating material  212  may be etched by the system  200 . In one embodiment, the grating material  212  is disposed on the etch stop layer  211  disposed on the substrate  210 . In one embodiment, the one or more materials of the grating material  212  are selected based on the slant angle of each structure to be formed and the refractive index of the substrate  210 . In some embodiments, the grating material  212  includes one or more of silicon oxycarbide (SiOC), titanium dioxide (TiO 2 ), silicon dioxide (SiO 2 ), vanadium (IV) oxide (VOx), aluminum oxide (Al 2 O 3 ), indium tin oxide (ITO), zinc oxide (ZnO), tantalum pentoxide (Ta 2 O 5 ), silicon nitride (Si 3 N 4 ), titanium nitride (TiN), and/or zirconium dioxide (ZrO 2 ) containing materials. The grating material  212  can have a refractive index between about 1.5 and about 2.65. 
     In some embodiments, the patterned hardmask  213  is a non-transparent hardmask that is removed after the device  205  is formed. For example, the non-transparent hardmask  213  can include reflective materials, such as chromium (Cr) or silver (Ag). In another embodiment, the patterned hardmask  213  is a transparent hardmask. In one embodiment, the etch stop layer  211  is a non-transparent etch stop layer that is removed after the device  205  is formed. In another embodiment, the etch stop layer  211  is a transparent etch stop layer. 
     The system  200  may include an ion beam chamber  202  that houses an ion beam source  204 . The ion beam source  204  is configured to generate an ion beam  216 , such as a ribbon beam, a spot beam, or full substrate-size beam. The ion beam chamber  202  is configured to direct the ion beam  216  at a first ion beam angle α relative to a surface normal  218  of substrate  210 . Changing the first ion beam angle α may require reconfiguration of the hardware of the ion beam chamber  202 . The substrate  210  is retained on a platen  206  coupled to a first actuator  208 . The first actuator  208  is configured to move the platen  206  in a scanning motion along a y-direction and/or a z-direction. In one embodiment, the first actuator  208  is further configured to tilt the platen  206 , such that the substrate  210  is positioned at a tilt angle β relative to the x-axis of the ion beam chamber  202 . In some embodiments, the first actuator  208  can further be configured to tilt the platen  206  relative to the y-axis and/or z-axis. 
     The first ion beam angle α and the tilt angle β result in a second ion beam angle ∂ relative to the surface normal  218  of the substrate  210  after the substrate  210  is tilted. To form structures having a slant angle relative to the surface normal  218 , the ion beam source  204  generates an ion beam  216  and the ion beam chamber  202  directs the ion beam  216  towards the substrate  210  at the first ion beam angle α. The first actuator  208  positions the platen  206 , so that the ion beam  216  contacts the grating material  212  at the second ion beam angle ∂′ and etches the grating material  212  to form the structures having a slant angle on desired portions of the grating material  212 . 
     Conventionally, to form a portion of structures with a slant angle than different than the slant angle of an adjacent portion of structures, or to form structures having a different slant angle on successive substrates, the first ion beam angle α is changed, the tilt angle ( 3  is changed, and/or multiple angled etch systems are used. Reconfiguring the hardware of the ion beam chamber  202  to change the first ion beam angle α is complex and time-consuming. Adjusting tilt angle ( 3  to modify the ion beam angle ∂ results in non-uniform depths of structures across portions of the substrate  210  as the ion beam  216  contacts the grating material  212  with different energy levels. For example, a portion positioned closer to the ion beam chamber  202  will have structures with a greater depth than structures of an adjacent potion positioned further away from the ion beam chamber  202 . Using multiple angled etch systems increases the fabrication time and increases costs due the need of multiple chambers. To avoid reconfiguring the ion beam chamber  202 , adjusting the tilt angle β to modify the ion beam angle ∂, and using multiple angled etch systems, the angled etch system  200  may include a second actuator  220  coupled to the platen  206  to rotate the substrate  210  about the x-axis of the platen  206  to control the slant angle of structures. 
     During use, the ion beam  216  may be extracted when a voltage difference is applied using a bias supply between the ion beam chamber  202  and substrate  210 , or substrate platen, as in known systems. The bias supply may be coupled to the ion beam chamber  202 , for example, where the ion beam chamber  202  and substrate  210  are held at the same potential. 
     The trajectories of ions within the ion beam  216  may be mutually parallel to one another or may lie within a narrow angular spread range, such as within 10 degrees of one another or less. In other embodiments, the trajectory of ions within the ion beam  216  may converge or diverge from one another, for example, in a fan shape. In various embodiments, the ion beam  216  may be provided as a ribbon reactive ion beam extracted as a continuous beam or as a pulsed ion beam, as in known systems. 
     In various embodiments, gas, such as reactive gas, may be supplied by a source to the ion beam chamber  202 . The plasma may generate various etching species or depositing species, depending upon the exact composition of species provided to the ion beam chamber  202 . The ion beam  216  may be composed of any convenient gas mixture, including inert gas, reactive gas, and may be provided in conjunction with other gaseous species in some embodiments. In some embodiments, the ion beam  216  and other reactive species may be provided as an etch recipe to the substrate  210  so as to perform a directed reactive ion etching (RIE) of a layer, such as the grating material  212 . Such an etch recipe may use known reactive ion etch chemistries for etching materials such as oxide or other material, as known in the art. In other embodiments, the ion beam  216  may be formed of inert species where the ion beam  216  is provided to etch the substrate  210  or more particularly, the grating material  212 , by physical sputtering, as the substrate  210  is scanned with respect to ion beam  216 . 
     As further shown, the system  200  may include one or more proximity or shadow masks  225  positioned between the ion beam chamber  202  and the device  205 . The shadow mask (hereinafter “mask”)  225  may include a plurality of openings formed therethrough, which permit passage of the ion beam  216  towards the substrate  210 . The mask  225  may be separated from a top surface  213  of the grating material  212  by a gap or distance  215 . Stated another way, the mask  225  is not typically formed directly atop the device  205 . However, in an alternative embodiment, the mask  225  may be in direct physical contact with the device  205 , while one or more edges defining at least one of the plurality of openings through the mask  225  is spaced apart or raised above the device  205  to create a shadow effect, as will be described in greater detail herein. 
       FIG. 3A  depicts a side cross sectional view of an optical grating component  300  formed from the grating material  312  according to embodiments of the disclosure.  FIG. 3B  depicts a frontal view of the optical grating component  300 . As shown, the optical grating component  300  includes a substrate  310 , and the optical grating material  312  disposed on the substrate  310 . The optical grating component  300  may be the same or similar to the input grating  102 , the intermediate grating  104 , and/or the output grating  106  of  FIG. 1 . In some embodiments, the substrate  310  is an optically transparent material, such as a known glass. In some embodiments, the substrate  310  is silicon. In the latter case, the substrate  310  is silicon, and another process is used to transfer grating patterns to a film on the surface of another optical substrate, such as glass or quartz. The embodiments are not limited in this context. In the non-limiting embodiment of  FIG. 3A  and  FIG. 3B , the optical grating component  300  further includes an etch stop layer  311 , disposed between the substrate  310  and the grating material  312 . 
     In some embodiments, the optical grating optical grating component  300  may include a plurality of angled structures, shown as angled components or structures  322  separated by trenches  325 A- 325 N. The structures  322  may be disposed at a non-zero angle of inclination (ϕ) with respect to a perpendicular to a plane (e.g., y-z plane) of the substrate  310  and the top surface  313  of the grating material  312 . The angled structures  322  may be included within one or more fields of slanted gratings, the slanted grating together forming “micro-lenses.” 
     In the example of  FIG. 3A , the angled structures  322  and the trenches  325 A- 325 N define a variable height along the direction parallel to the y-axis. For example, a depth ‘d 1 ’ of a first trench  325 A in a first portion  331  of the optical grating component  300  may be different than a depth ‘d 2 ’ of a second trench  325 B in a second portion  333  of the optical grating component  300 . In some embodiments, a width of the angled structures  322  and/or the trenches  325  may also vary, e.g., along the y-direction. 
     The angled structures  322  may be accomplished by scanning the substrate  310  with respect to the ion beam using a processing recipe. In brief, the processing recipe may entail varying at least one process parameter of a set of process parameters, having the effect of changing, e.g., the etch rate or deposition rate caused by the ion beam during scanning of the substrate  310 . Such process parameters may include the scan rate of the substrate  310 , the ion energy of the ion beam, duty cycle of the ion beam when provided as a pulsed ion beam, the spread angle of the ion beam, and rotational position of the substrate  310 . The etch profile may be further altered by varying the ion beam quality across the mask. Quality may include intensity/etch rate such as varying current with duty cycle or beam shape for different angles. In at least some embodiments herein, the processing recipe may further include the material(s) of the grating material  312 , and the chemistry of the etching ions of the ion beam. In yet other embodiments, the processing recipe may include starting geometry of the grating material  312 , including dimensions and aspect ratios. The embodiments are not limited in this context. 
     Turning now to  FIG. 4 , there is shown a front view of a shadow mask apparatus (hereinafter “apparatus”)  430  according to embodiments of the present disclosure. As shown, the apparatus may include a shadow mask (hereinafter “mask”)  425  positioned over a grating material  412  disposed on a substrate. The mask  425  may include a plurality of openings  432 A- 432 D provided therethrough. Each of the plurality of openings  432 A- 432 D may be defined by a leading edge  434  (e.g., relative to a direction of travel of and an ion beam  416 ) opposite a trailing edge  436 . Each of the plurality of openings  432 A- 432 D may be further defined by a first side edge  438  opposite a second side edge  440 . Although shown as four (4) rectangles, it&#39;ll be appreciated that the plurality of openings  432 A- 432 D may take on virtually any number, shape, or configuration. Furthermore, it&#39;ll be appreciated that one or more openings of the plurality of openings  432 A- 432 D may take on a unique or different shape/configuration than the rest of the openings. Embodiments herein are not limited in this context. 
     As shown in  FIGS. 4, 5A, and 5B , the apparatus  430  may further include a plurality of raised surface features  450 A-D along the trailing edge  436  and/or the leading edge  434  of one or more of the plurality of openings  432 A- 432 D. The raised surface features  450 A- 450 D may extend above a plane (e.g., y-z) defined by a top surface  441  of the mask  425 . In some embodiments, the apparatus  430  may further include a second set of surface features  454  extending below a plane (e.g., y-z) defined by a bottom surface  443  of the mask  425 . The raised surface features  450 A-D and the second set of surface features  454  may partially block the ion beam  416 , thus influencing an amount, angle, and/or depth of the ion beam  416  passing through respective openings  432 A- 432 D and impacting the grating material  412 . In one example, increasing a height ‘H’ of a particular surface feature may decrease an amount of etching to the grating material  412  proximate the trailing edge  436 . As shown, steeper angles in the ion beam  416  may be blocked by the mask  425  and raised surface features  450 A-D, while the relatively shallower angles of the ion beam  416  etch the grating material  412  through the opening  432 . Additional etching examples/variations will be described below. 
     As shown in  FIGS. 5A-5B , the apparatus  430  may include a plurality of optical gratings  453  across the grating material  412 . The plurality of optical gratings  453  may represent input gratings, intermediate gratings, output gratings, or a combination thereof. In some embodiments, the ion beam  416  passing through a single opening of the set of openings  432 A-D may simultaneously impact at least two of the optical gratings  453 . 
     In some embodiments, one or more of the raised surface features  450 A- 450 D may have a non-uniform height ‘H’ along a length, e.g., along the z-direction, which may generally be perpendicular to a direction of travel of the ion beam  416 . For example, as best shown in  FIG. 5B , raised surface feature  450 C may have a sloped or triangular profile in the x-z plane. Meanwhile, raised surface feature  450 D may have a curved profile in the x-z plane defined by a set of peaks  451  and a central depression  452 . Although non-limiting, the raised surface feature  450 D may result in a parabolic shaped grating material  412  having a depressed central area. The raised surface features  450 A-D may take on virtually any variety of shapes or dimensions in various embodiments. Although not shown, one or more of the raised surface features  450 A- 450 D may additionally, or alternatively, have a varied thickness, e.g., along the y-direction and/or the z-direction. 
     Furthermore, although shown in this embodiment along the trailing edges  436  of the openings  432 A- 432 D, it will be appreciated that raised or protruding surface features may additionally, or alternatively, be formed along or proximate the first side edge  438 , the second side edge  440 , and/or the leading edge  434 . For example, as best shown in  FIGS. 5A-5B , the second set of surface features  454 , which generally extend in an opposite direction (e.g., negative x-direction) from the raised surface features  450 A- 450 D, may be located adjacent the leading edge  434  of one or more of the openings  432 A- 432 D. 
     Turning now to  FIG. 6A , a simplified, cross-sectional view of an example mask  625  and grating material  612  according to embodiments of the present disclosure will be described. As shown, the mask  625  includes an opening  632  defined by a leading edge  634  and a trailing edge  636 . The opening  632  may have a dimension or distance ‘D’ between the leading edge  634  and the trailing edge  636 . The mask  625  may be positioned over a grating material  612  and a substrate (not shown). The grating material  612  may be defined by first and second grating edges  655 ,  656  positioned on opposite sides of an approximate midpoint ‘MP’. As shown, a center of the opening  632  may be positioned substantially above the midpoint. 
     The mask  625  may be separated from the grating material  612  by a constant or varied distance. For example, the leading edge  634  may be separated from the grating material  612  by a leading edge height ‘LH’ and the trailing edge  636  may be separated from the grating material  612  by a trailing edge height ‘TH’. In this embodiment, LH=TH. 
     During use, the ion beam  616  is delivered towards the grating material  612  at a non-zero angle of inclination (ϕ) with respect to a perpendicular  623  to a plane extending parallel to a the top surface  660  of the mask  625 . The ion beam  616  impacts (e.g., etches) the grating material  612  in a processing area  658 , which may be defined by a downstream boundary or edge  664  and an upstream boundary or edge  665 . In some embodiments, the non-zero angle of inclination is constant as the ion beam  616  passes over the mask  625 . In some embodiments, a power (e.g., voltage and/or current) applied to generate the ion beam  616  can be constant or varied. Although not shown, the processing area  658  may include a plurality of angled structures and corresponding trenches as a result of an etch process by the ion beam  616 . 
     As demonstrated in  FIG. 6B , due to the angle of the ion beam  616 , the grating material  612  of the processing area  658  will be recessed faster/deeper in a first area  661  near the leading edge  634  than in a second area  662  near the trailing edge  636 . As a result, the first area  661  of the processing area  658  may have a deeper depth (e.g., in the x-direction) than in the second area  662 . As shown, the downstream edge  664  of the processing area  658  may extend beneath and beyond (e.g., along the y-direction) the leading edge  634  of the mask  625  due to the angle of the ion beam  616  and positioning/size of the opening  632  relative to the grating material  612 . In the case the grating material  612  includes a plurality of fins and trenches, the trenches in the first area  661  may be deeper than the trenches in the second area. Beam power may further be varied (e.g., increased) as the ion beam  616  moves from the trailing edge  636  towards the leading edge  634  to increase the depth in the first area  661 . 
     As shown in  FIGS. 7A-7B , to further increase etching of the grating material  612 , a distance ‘D 1 ’ of the opening  632  between the leading edge  634  and the trailing edge  636  of the mask  625  may be increased by shifting, e.g., along the negative y-direction, the trailing edge  636  of the mask  625  to be closer to the first grating edge  655 . More specifically, the trailing edge  636  of the mask  625  may be relatively closer to the first grating edge  655  of the grating material  612  than the leading edge  634  of the mask  625  is to the second grating edge  656  of the grating material  612 . As a result, the ion beam  616  may have a greater impact (e.g., increased/deeper etching) on the grating material  612 , particularly in the first area  661  of the processing area  658 . An overall size of the processing area  658  may also be increased by increasing the size of the opening  632 , as evidenced by a grating distance ‘GD’ between the first and second grating edges  655 ,  656 . In this embodiment, LH=TH. As further shown, the downstream edge  664  of the processing area  658  may extend beneath and beyond (e.g., along the y-direction) the leading edge  634  of the mask  625  due to the angle of the ion beam  616  and positioning/size of the opening  632  relative to the grating material  612 . 
     In another example, as shown in  FIGS. 8A-8B , a distance ‘D 2 ’ of the opening  632  between the leading edge  634  and the trailing edge  636  of the mask  625  may be increased by shifting, e.g., along the y-direction, the leading edge  634  of the mask  625  to be closer to the second grating edge  656 . In this embodiment, the leading edge  634  of the mask  625  may be relatively closer to the second grating edge  656  of the grating material  612  than the trailing edge  636  of the mask  625  is to the first grating edge  655  of the grating material  612 . Furthermore, the midpoint ‘MP’ of the grating material  612  may be relatively closer to the trailing edge  636  than the leading edge  634 . As a result, the ion beam  616  may have a greater impact (e.g., increased/deeper etching) on the grating material  612 , particularly in the first area  661  of the processing area  658 . An overall size of the processing area  658  may also be increased, as evidenced by grating distance ‘GD 2 ’ between the first and second grating edges  655 ,  656 . In this embodiment, LH=TH. As further shown, the downstream edge  664  of the processing area  658  again may extend beneath and beyond (e.g., along the y-direction) the leading edge  634  of the mask  625  due to the angle of the ion beam  616  and positioning/size of the opening  632  relative to the grating material  612 . 
     As shown in  FIGS. 9A-9B , etching of the processing area  658  may be modified by varying (e.g., decreasing) the leading edge height ‘LH’ at the leading edge  634  relative to the trailing edge height ‘TH’ at the trailing edge  636 . In this embodiment, LH&lt;TH. As a result, less of the ion beam  616  may be permitted to travel through the opening  632  to impact the processing area  658 , particularly downstream of the downstream edge  664 . A variable etch depth may still be achieved, however, with the first area  661  of the processing area  658  being etched more/faster than the second area  662 . 
     As shown in  FIGS. 10A-10B , etching of the processing area  658  may alternatively be modified by varying (e.g., increasing) the leading edge height ‘LH’ at the leading edge  634  relative to the trailing edge height ‘TH’ at the trailing edge  636 . In this embodiment, LH&gt;TH. As a result, more of the ion beam  616  may be permitted to travel through the opening  632  to impact the processing area  658 , including downstream of the downstream edge  664 . A variable etch depth may be increased in this embodiment, with the first area  661  of the processing area  658  being etched significantly greater/faster than the second area  662 . 
     Turning now to  FIGS. 11A-11B , a set of surface features  1150 A- 1150 B according to embodiments of the disclosure is shown. In this embodiment, the surface feature  1150 A may be positioned proximate the trailing edge  1136  of the mask  1125 , while the surface feature  1150 B may be positioned proximate the leading edge  1134  of the mask  1125 . In this non-limiting embodiment, the surface features  1150 A generally extend in the positive x-direction, while the surface features  1150 B generally extend in the negative x-direction. As shown, both surface features  1150 A- 1150 B may include a series of peaks  1170  and valleys  1172 . During processing of the grating material  1112 , the peaks  1170  generally will block the ion beam, while the valleys  1172  will permit the ion beam to pass through. Although non-limiting, the shape, configuration, and number of peaks  1170  and valleys  1172  may differ between the raised surface features  1150 A- 1150 B. Embodiments herein are not limited in this context. 
     Turning to  FIG. 12 , a method  1200  according to embodiments of the present disclosure will be described. As shown, at block  1201 , the method  1200  may include providing an etching material atop a substrate. In some embodiments, the etching material may be a grating material, e.g., an optical grating material including one or more of silicon oxycarbide (SiOC), titanium dioxide (TiO 2 ), silicon dioxide (SiO 2 ), vanadium (IV) oxide (VOx), aluminum oxide (Al 2 O 3 ), indium tin oxide (ITO), zinc oxide (ZnO), tantalum pentoxide (Ta 2 O 5 ), silicon nitride (Si 3 N 4 ), titanium nitride (TiN), and/or zirconium dioxide (ZrO 2 ) containing materials. 
     At block  1202 , the method  1200  may include positioning a shadow mask between the etching material and an ion source, wherein at least a portion of the shadow mask is separated from the etching material by a distance. In some embodiments, multiple shadow masks may be positioned between the etching material and the ion source. In some embodiments, the shadow mask may be provided directly atop a portion of the etching material, wherein one or more sections, e.g., sections near shadow mask openings, may be spaced apart from the etching material by a gap. 
     At block  1203 , the method  1200  may include forming a plurality of structures by etching the etching material using an ion beam passing through a set of openings of the shadow mask, wherein a first depth of a first portion of the etching material is different than a second depth of a second portion of the etching material. In some embodiments, the method  1200  may include etching the etching material to form the plurality of structures and a plurality of trenches. In some embodiments, the method  1200  may include forming the plurality of structures at a non-zero angle with respect to a vertical extending from a top surface of the etching material. 
     In some embodiments, the method  1200  may include providing a raised surface feature along a leading edge or a trailing edge of one or more of the set of openings, wherein the raised surface feature has a non-uniform height along a direction extending parallel to the top surface of the grating material. The raised surface feature(s) may extend above a plane defined by the top surface of the grating material. 
     In some embodiments, the method  1200  may include varying an opening edge height, relative to the top surface of the grating material, between the leading edge and a trailing edge of one or more openings of the set of openings. In some embodiments, the method  1200  may additionally, or alternatively, include varying the opening edge height, relative to the top surface of the grating material, between a first side edge and a second side edge of one or more openings of the set of openings. 
     For the sake of convenience and clarity, terms such as “top,” “bottom,” “upper,” “lower,” “vertical,” “horizontal,” “lateral,” and “longitudinal” will be used herein to describe the relative placement and orientation of components and their constituent parts as appearing in the figures. The terminology will include the words specifically mentioned, derivatives thereof, and words of similar import. 
     As used herein, an element or operation recited in the singular and proceeded with the word “a” or “an” is to be understood as including plural elements or operations, until such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present disclosure are not intended as limiting. Additional embodiments may also incorporate the recited features. 
     Furthermore, the terms “substantial” or “substantially,” as well as the terms “approximate” or “approximately,” can be used interchangeably in some embodiments, and can be described using any relative measures acceptable by one of ordinary skill in the art. For example, these terms can serve as a comparison to a reference parameter, to indicate a deviation capable of providing the intended function. Although non-limiting, the deviation from the reference parameter can be, for example, in an amount of less than 1%, less than 3%, less than 5%, less than 10%, less than 15%, less than 20%, and so on. 
     Still furthermore, one of ordinary skill will understand when an element such as a layer, region, or substrate is referred to as being formed on, deposited on, or disposed “on,” “over” or “atop” another element, the element can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on,” “directly over” or “directly atop” another element, no intervening elements are present. 
     In various embodiments, design tools can be provided and configured to create the datasets used to pattern the layers of the grating material and the diffracted optical elements described herein. For example, data sets can be created to generate photomasks used during lithography operations to pattern the layers for structures as described herein. Such design tools can include a collection of one or more modules and can also be comprised of hardware, software or a combination thereof. Thus, for example, a tool can be a collection of one or more software modules, hardware modules, software/hardware modules or any combination or permutation thereof. As another example, a tool can be a computing device or other appliance running software, or implemented in hardware. 
     As used herein, a module might be implemented utilizing any form of hardware, software, or a combination thereof. For example, one or more processors, controllers, ASICs, PLAs, logical components, software routines or other mechanisms might be implemented to make up a module. In implementation, the various modules described herein might be implemented as discrete modules or the functions and features described can be shared in part or in total among one or more modules. In other words, as would be apparent to one of ordinary skill in the art after reading the description, the various features and functionality described herein may be implemented in any given application. Furthermore, the various features and functionality can be implemented in one or more separate or shared modules in various combinations and permutations. Although various features or elements of functionality may be individually described or claimed as separate modules, one of ordinary skill in the art will understand these features and functionality can be shared among one or more common software and hardware elements. 
     By utilizing the embodiments described herein, a waveguide with regions of variable etch depth is formed. A first technical advantage of the waveguide of the present embodiments includes improved manufacturing efficiency by eliminating more time consuming and difficult processes. Further, a second technical advantage of the grating structures of the present embodiments includes providing a two dimensional or a three-dimensional shape, enabling use of the waveguide in an increased range of applications. 
     The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Furthermore, the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose. Those of ordinary skill in the art will recognize the usefulness is not limited thereto and the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Thus, the claims set forth below are to be construed in view of the full breadth and spirit of the present disclosure as described herein.