Method for fabricating oblique gratings with variable etching depth - Patents.com

Abstract

To provide a method that produces gratings with a trench having a variable height.SOLUTION: In one example, a method of forming a diffracted optical element 400 may include: providing an optical grating layer 407 on a substrate 402; patterning a hardmask on the optical grating layer; and forming a sacrificial layer on the hardmask, in which the sacrificial layer has a non-uniform height measured from a top surface of the optical grating layer. To form an optical grating 445, the method may further include etching a plurality of angled trenches in the optical grating layer, in which a first depth of a first trench 428A of the plurality of trenches is different from a second depth of a second trench 428B of the plurality of trenches.SELECTED DRAWING: Figure 4D-4F

Description

[Technical field]

[0001]

[0001] Embodiments of the present disclosure relate generally to methods for fabricating optical gratings, and more particularly, to methods for fabricating oblique optical gratings having trenches with variable depths. [Background technology]

[0002] Optical elements such as optical lenses have long been used to manipulate light to obtain various advantages. Recently, micro-diffraction gratings have been utilized in holographic and augmented / virtual reality (AR and VR) devices. One type of AR and VR device is a wearable display system, such as a headset, arranged to display an image within a short distance of the human eye. Such wearable headsets, often referred to as head-mounted displays, include a frame that displays an image within a few centimeters of the user's eye. The image may be a computer-generated image on a display, such as a microdisplay. The optics are arranged to transport light of a desired image generated on the display to the user's eye so that the image is visible to the user. The display on which the image is generated may form part of a light engine, so that the image generates a collimated light beam that is guided by the optics to provide the image that is visible to the user.

[0003]

[0003] Various types of optical components have been used to convey images from a display to the human eye. To function properly in an augmented reality lens or combiner, the geometry of the optical grating can be designed to achieve various effects. In some devices, multiple distinct regions, such as two or more distinct regions, are formed on the surface of the lens, and the geometry of the grating in one region is different from the geometry of the grating in another region.

[0004]

[0004] Angled surface relief optical gratings can be fabricated by etching angled trenches directly into a substrate or a film stack on a substrate. One of the parameters that controls the efficiency of the optical grating is the depth of the trench. Unfortunately, current approaches to creating optical gratings with varying heights, widths, and / or shapes in the diffraction field and field of view have proven difficult.

[0005] Therefore, there is a need for an improved method for fabricating gratings having trenches of variable depth. Summary of the Invention

[0006]

[0006] 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.

[0007]

[0007] An embodiment of the present disclosure provides a method of forming a diffractive optical element, the method including providing an optical grating layer over a substrate, patterning a hard mask over the optical grating layer, and forming a sacrificial layer over the hard mask, the sacrificial layer having a non-uniform height measured from a top surface of the optical grating layer. The method may further include etching a plurality of angled trenches in the optical grating layer to form the optical grating, a first depth of a first trench of the plurality of trenches being different from a second depth of a second trench of the plurality of trenches.

[0008]

[0008] An embodiment of the present disclosure further provides a method of forming a diffractive optical element including providing an optical grating layer over a substrate, providing a hard mask over the optical grating layer, the hard mask including a series of openings, and forming a sacrificial layer over the hard mask. The method may further include forming recesses in the sacrificial layer, the recesses causing the sacrificial layer to have a non-uniform height measured from a top surface of the optical grating layer, and etching a plurality of angled trenches through the optical grating layer to form the optical grating, wherein a first depth of a first trench of the plurality of angled trenches is different from a second depth of a second trench of the plurality of trenches.

[0009]

[0009] An embodiment of the present disclosure further provides a method of forming a diffractive optical element, the method including providing an optical grating layer over a substrate, patterning a hard mask over the optical grating layer, and depositing a sacrificial layer over the hard mask. The method may further include removing a portion of the sacrificial layer to form trenches in the sacrificial layer, the trenches including a sloped bottom surface defining a first plane, the first plane being non-parallel to a second plane defined by a top surface of the optical grating layer, and etching a plurality of angled trenches in the optical grating layer to form the optical grating, the first depth of a first trench of the plurality of trenches being different from a second depth of a second trench of the plurality of trenches.

[0010]

[0010] The accompanying drawings illustrate exemplary approaches of the present disclosure, including practical applications of its principles, as follows: [Brief description of the drawings]

[0011] [Figure 1] 1 is a schematic cross-sectional view of a display device according to an embodiment of the present disclosure. [Figure 2A] FIG. 1 illustrates a cross-sectional side view of an optical grating component according to an embodiment of the present disclosure. [Figure 2B] FIG. 2B is a top view of the optical grating component of FIG. 2A in accordance with an embodiment of the present disclosure. [Figure 3A] FIG. 1 shows a schematic diagram of a processing apparatus according to an embodiment of the present disclosure. [Figure 3B] FIG. 13 illustrates a top view of an extraction plate assembly and substrate according to an embodiment of the present disclosure. [Figure 4A-4C] 1A-1C are side cross-sectional views illustrating the formation of angled structures according to embodiments of the present disclosure. [Fig. 4D-4F] 1A-1C are side cross-sectional views illustrating the formation of angled structures according to embodiments of the present disclosure. [Figure 5A-5C] 1A-1C are side cross-sectional views illustrating the formation of angled structures according to embodiments of the present disclosure. [Fig. 5D-5F] 1A-1C are side cross-sectional views illustrating the formation of angled structures according to embodiments of the present disclosure. [Fig. 5G-5H] 1A-1C are side cross-sectional views illustrating the formation of angled structures according to embodiments of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012]

[0018] The drawings are not necessarily to scale. The drawings are merely representational and are not intended to depict specific parameters of the present disclosure. The drawings are intended to depict exemplary embodiments of the present disclosure and therefore should not be considered limiting in scope. In the drawings, like numbering represents like elements.

[0013]

[0019] Additionally, certain elements in some of the drawings may be omitted or may be drawn out of scale for illustrative clarity. The cross-sectional views may be in the form of "slices," or "myopic" cross-sectional views, in which certain background lines that are otherwise visible in a "true" cross-sectional view are omitted for illustrative clarity. Additionally, reference numbers may be omitted in some of the drawings for clarity.

[0014]

[0020] The method according to the present disclosure will now be described more fully with reference to the accompanying drawings, in which embodiments of the method are shown. The method may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Instead, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the systems and methods to those skilled in the art.

[0015]

[0021] 1 is a schematic cross-sectional view of a waveguide 104 implemented in a display device 100. The display device 100 can be configured for augmented reality, virtual reality, and mixed or blended reality applications, as well as other display applications, such as handheld display devices.

[0016]

[0022] The display device 100 uses a waveguide 104 to view an ambient environment 130 through the waveguide 104, such as for a user to view the environment 130 from a user viewpoint 101. When implemented in the display device 100, a first surface 122 of the waveguide 104 is disposed adjacent to and facing the user's eye 111. A second surface 124 of the waveguide 104 is disposed opposite the first surface 122, adjacent to and facing the ambient environment 130. Although illustrated planar, the waveguide 104 may be curved depending on the desired application.

[0017]

[0023] The display device 100 further includes an image microdisplay 128 for guiding the generated virtual image light 120 to the waveguide 104. The virtual image light 120 propagates through the waveguide 104. In general, the waveguide 104 includes an input coupling region 106, a waveguide region 108, and an output coupling region 110. The input coupling region 106 receives the light 120 (virtual image) from the image microdisplay 128, and the light 120 travels through the waveguide region 108 to the output coupling region 110 where the virtual image can be visualized overlaid with the surrounding environment 130 according to the user's viewpoint 101 and field of view. The image microdisplay 128 is a high resolution display generator such as a liquid crystal on silicon microdisplay operable to project the virtual image light into the waveguide 104.

[0018]

[0024] The waveguide 104 includes an input grating structure 112 and an output grating structure 114. The input grating structure 112 is formed in an area of ​​the waveguide 104 that corresponds to the in-coupling region 106. The output grating structure 114 is formed in an area of ​​the waveguide 104 that corresponds to the out-coupling region 110. The input grating structure 112 and the output grating structure 114 affect the light propagation within the waveguide 104. For example, the input grating structure 112 in-couples light from the image microdisplay 128 and the output grating structure out-couples light to the user's eye 111.

[0019]

[0025] For example, the input grating structure 112 affects the field of view of the virtual image displayed at the user's eye 111. The output grating structure 114 affects the amount of light 120 collected and outcoupled from the waveguide 104. Additionally, the output grating structure 114 modulates the field of view of the virtual image from the user's viewpoint 101, increasing the viewing angle at which the user can view the virtual image from the image microdisplay 128. In another embodiment, a grating structure (not shown) is also formed in the waveguide region 108 between the input coupling region 106 and the out coupling region 110. Additionally, the display device 100 can be formed using multiple waveguides 104, each having a desired grating structure formed therein.

[0020]

[0026] FIG. 2A is a side cross-sectional view of an optical grating component 200 according to an embodiment of the present disclosure. FIG. 2B is a top view of the optical grating component 200. The optical grating component 200 can be used as an optical grating disposed on glasses or can be integrally formed on glasses according to various embodiments of the present disclosure. The optical grating component 200 includes a substrate 202 and an optical grating 206 disposed on the substrate 202. The optical grating 206 can be the same as or similar to the input grating structure 112 and / or the output grating structure 114 of FIG. 1. In some embodiments, the substrate 202 is an optically transparent material such as glass, as is known. In some embodiments, the substrate 202 is silicon. In the latter case, the substrate 202 is silicon, and a separate process can be used to transfer the grating pattern to a film on the surface of another optical substrate, such as glass or quartz. It should be noted that the present embodiment is not limited in this context. The optical grating 206 can be disposed on an optical grating layer 207, as described further below. 2A and 2B, optical grating component 200 further includes an etch stop layer 204 disposed between substrate 202 and optical grating layer 207. According to some embodiments of the present disclosure, optical grating layer 207 may be an optically transparent material such as silicon oxide, silicon nitride, glass, TiO2, or other materials.

[0021]

[0027] According to some embodiments of the present disclosure, the optical grating 206 may include a grating height H in the range of 100 nm to 1000 nm. Thus, the optical grating 206 may be suitable for use in an eyepiece of an AR&VR device. The embodiments herein are not limited in this context. According to some embodiments, the etch stop layer 204 may be an optically transparent material and may have a thickness of 10 nm to 100 nm. The embodiments are not limited in this context. Examples of materials suitable for the etch stop layer 204 include SiN, SiO2, TiN, SiC, and other materials. In embodiments in which the optical grating 206 is applied to or incorporated into an eyepiece of a pair of glasses, particularly suitable materials are optically transparent materials. In embodiments in which the optical grating component 200 forms a master for manufacturing an optical grating for an eyepiece, the etch stop layer 204 does not need to be optically transparent. Furthermore, the etch stop layer 204 may be omitted in some embodiments.

[0022]

[0028] As further shown in FIG. 2A, the optical grating 206 may include a plurality of angled structures, shown as angled pieces or structures 212, arranged at a non-zero tilt angle with respect to a normal to the plane of the substrate 202 (e.g., the xy plane). The angled structures 212 may be included in one or more fields of the diagonal grating, which together form a "microlens." In the example of FIG. 2A, a first direction (y-axis) defines a uniform height along a direction parallel to the y-axis of the illustrated Cartesian coordinate system, which is parallel to the plane of the substrate 202, in this case the xy plane. In other embodiments, the angled structures 212 may define variable heights along a direction parallel to the y-axis. The plurality of trenches 214 may be arranged at a non-zero tilt angle with respect to a normal to a plane, such as the top surface of the substrate 202 or the top surface of the optical grating layer 207. As will be described in more detail below, one or more of the trench depths "d" and / or widths "w" of the plurality of trenches 214 may be varied by the presence of a mask or sacrificial layer disposed over the optical grating 206 prior to etching.

[0023]

[0029] In some embodiments, the width of the optical grating 206 along the Y direction may be on the scale of several millimeters to several centimeters, while the grating height H may be on the scale of one micrometer or less. Thus, the change in grating height H may range on the scale of hundreds of nanometers or less. Examples of smooth changes in grating height H or depth d include changes in grating height H or depth d between adjacent lines of the grating of less than 10%, less than 5%, or less than 1%. The present embodiment is not limited thereto. Thus, in an eyepiece, the grating height H may vary continuously and non-stepwise in a given direction along the surface of the eyepiece over a distance of, for example, millimeters to centimeters. More specifically, a 50% change in grating height H over a distance of 5 mm is approximately 5×10 with a pitch of 1 micrometer. 3 This may involve a continuous change in the grating height H across the line. This change is 0.5 / 5×10 4 or with an average change in the relative height of adjacent lines of about 0.01%.

[0024]

[0030] Reference is now made to FIG. 3A, which shows a schematic depiction of a processing apparatus 300. Processing apparatus 300 represents a processing apparatus for etching a portion of a substrate or depositing on a substrate, for example to produce the optical grating of the present embodiment. Processing apparatus 300 may be a plasma-based processing system having a plasma chamber 302 for generating a plasma 304 therein by any convenient method known in the art. To reactively etch or deposit an optical grating layer 207 (FIGS. 2A-2B), an extraction plate 306 having extraction apertures 308 through which non-uniform etching or non-uniform deposition may take place may be provided as shown. In process chamber 324, for example, a substrate 202 including an optical grating structure as described above is placed. The substrate plane of substrate 202 is represented by the XY plane of the illustrated Cartesian coordinate system, with the normal to the plane of substrate 202 being along the Z axis (Z direction).

[0025]

[0031] 3A, similar to known systems, the ion beam 310 may be extracted when a voltage difference is applied between the plasma chamber 302 and the substrate 202 or substrate platen 314 using a bias supply 320. The bias supply 320 may be coupled to the process chamber 324, for example, such that the process chamber 324 and the substrate 202 are held at the same potential.

[0026]

[0032] According to various embodiments, the ion beam 310 may be extracted along a normal line 326 or may be extracted at a non-zero angle of incidence, shown as φ, relative to the normal line 326 .

[0027]

[0033] The trajectories of the ions in the ion beam 310 may be parallel to each other or may be in a narrow angular spread, such as 10 degrees or less, from each other. In other embodiments, as described below, the trajectories of the ions in the ion beam 310 may converge or diverge from each other, for example, in a fan shape. Thus, the value of φ may represent an average value of the incidence angle where the individual trajectories vary from the average value by a few degrees. In various embodiments, the ion beam 310 may be extracted as a continuous beam or as a pulsed ion beam, as in known systems. For example, the bias supply 320 may be configured to supply a voltage difference between the plasma chamber 302 and the process chamber 324 as a pulsed DC voltage, and the voltage, pulse frequency, and duty cycle of the pulsed voltage may be adjusted independently of each other.

[0028]

[0034] In various embodiments, gases, such as reactive gases, may be supplied to the plasma chamber 302 by a source 322. The plasma 304 may generate various etching or deposition species, depending on the exact composition of species supplied to the plasma chamber 302.

[0029]

[0035] In various embodiments, the ion beam 310 may be provided as a ribbon reactive ion beam with a long axis extending along the X direction of the Cartesian coordinate system shown in FIG. 3B. The ion beam 310 may etch or deposit on the substrate 202 by scanning the substrate platen 314 containing the substrate 202 relative to the extraction aperture 308 and thus the ion beam 310 along a scan direction 330. The ion beam 310 may be comprised of any convenient gas mixture including inert gases, reactive gases, and in some embodiments may be provided in combination with other gas species. In certain embodiments, the ion beam 210 and other reactive species may be provided as an etch recipe for the substrate 202 to perform a directional reactive ion etch (RIE) of a layer such as the optical grating layer 207. The etch recipe may use known reactive ion etch chemistries for etching materials such as oxides or other materials as is known in the art. In other embodiments, where the ion beam 310 is provided to etch the substrate 202, or more specifically, the optical grating layer 207, by physical sputtering as the substrate 202 is scanned relative to the ion beam 310, the ion beam 310 may be formed of an inert species.

[0030]

[0036] In the example of Figure 3B, the ion beam 310 is provided as a ribbon reactive ion beam that extends to a beam width along the X direction that is sufficient to expose the entire width of the substrate 202 even at its widest portion along the X direction. Exemplary beam widths may range from 10 cm, 20 cm, 30 cm, or more, while exemplary beam lengths along the Y direction may range from 2 mm, 3 mm, 5 mm, 10 mm, or 20 mm. The present embodiment is not limited in this context.

[0031]

[0037] In particular, the scan direction 330 may represent a scan of the substrate 202 in two opposing (180 degree) directions along the Y direction, or simply a scan to the left or to the right. As shown in Figure 3B, the long axis of the ion beam 310 extends along the X direction, perpendicular to the scan direction 330. Thus, if a sufficient length of scanning is performed from the left side to the right side of the substrate 202 along the scan direction 330 of the substrate 202, the entire substrate 202 may be exposed to the ion beam 310.

[0032]

[0038] Lattice features such as the angled structures 212 of FIGS. 2A-2B may be achieved by scanning the substrate 202 relative to the ion beam 310 using a process recipe. Briefly, the process recipe may involve varying at least one process parameter of a set of process parameters that have the effect of varying, for example, the etching rate or deposition rate caused by the ion beam 310 during scanning of the substrate 202. The process parameters may include the scanning speed of the substrate 202, the ion energy of the ion beam 310, the duty cycle of the ion beam 310 if provided as a pulsed ion beam, the spread angle of the ion beam 310, and the rotational position of the substrate 202. In at least some embodiments herein, the process recipe may further include the material(s) of the optical grating layer 207 and the chemistry of the etching ions of the ion beam 310. In still other embodiments, the process recipe may include the starting geometry of the optical grating layer 207, including dimensions and aspect ratios. The present embodiments are not limited in this context.

[0033]

[0039] 4A-4E are diagrams illustrating a process for forming a diffractive optical element 400 according to an embodiment of the present disclosure. As shown in FIG. 4A, an optical grating layer 407 may be formed on a substrate 402, and a hard mask layer 410 may be formed on the optical grating layer 407. Although not shown, in some embodiments, an etch stop layer may be provided between the substrate 402 and the optical grating layer 407. The etch stop layer may be formed of a material that is resistant to the etching process, such as titanium nitride or tantalum nitride, among others. The substrate 402 may be made of an optically transparent material, such as glass. The optical grating layer 407 and / or the hard mask 410 may be formed, for example, by a chemical vapor deposition (CVD) process, a physical vapor deposition (PVD) process, or a spin-on process.

[0034]

[0040] The grating layer 407 may be formed from an optically transparent material. In one example, the grating layer 407 is formed from a silicon-based material, such as silicon nitride or silicon oxide, or a titanium-based material, such as titanium oxide. The material of the grating layer 407 has a high refractive index, such as about 1.3 to 2.4, or higher. Typically, the grating layer 407 has a thickness of less than about 1 micrometer, such as about 150 nm to 700 nm. However, embodiments herein are not limited in this context.

[0035]

[0041] As shown in FIG. 4B, the hard mask 410 may be patterned to form a series of openings or gaps 411 therein. In some embodiments, the hard mask 410 is formed from a photoresist stack (not shown), where the hard mask layer is conformally formed over the grating layer 407. The hard mask 410 may be formed from titanium nitride, for example, using a chemical vapor deposition process. As shown, the hard mask 410 is formed as a plurality of hard mask elements 412 separated from one another by gaps 411. Each gap 411 may be formed using an etching process selective to the top surface 413 of the optical grating layer 407. In some embodiments, the hard mask elements 412 are formed by etching a photoresist stack. In some embodiments, the hard mask elements 412 have the same height and / or width. In other embodiments, one or more of the hard mask elements 412 have different or non-uniform heights and / or thicknesses.

[0036]

[0042] As shown in FIG. 4C, a sacrificial layer 420 may then be formed over the optical grating layer 407 and the hard mask 410. In some embodiments, the sacrificial layer 420 is a mask deposited over the optical grating layer 407 and the hard mask 410. In a non-limiting embodiment, the sacrificial layer 420 may be a photoresist-type material formed over the diffractive optical element 400 using, for example, 3D printing. In other embodiments, the sacrificial layer 420 may be an optically transparent material such as silicon. In one non-limiting embodiment, the sacrificial layer 420 may be silicon nitride, which advantageously provides uniform properties in both vertical and angled etching.

[0037]

[0043] As shown in FIG. 4D, the sacrificial layer 420 may be recessed using a subtractive process 425, such as ion etching, reactive etching, or sputtering. In the illustrated embodiment, the subtractive process 425 may be a reactive ion etch (RIE) transversely along a direction 426, which produces a sacrificial layer 420 having a variable height "H" relative to the top surface 413 of the optical grating layer 407. For example, the sacrificial layer 420 may be processed to form a recess or trench 421 having a sloped bottom surface 422. As shown, the sloped bottom surface 422 may define a plane that is non-parallel to the plane defined by the top surface 413 of the optical grating layer 407. Without limitation, the sloped bottom surface 422 may be generally planar and / or curved. Furthermore, the gradient direction of the sloped bottom surface 422 need not be aligned with the lattice vector of the subtractive process 425.

[0038]

[0044] As shown in FIG. 4E, the diffractive optical element 400 is then etched 427 to form a plurality of angled trenches 428 through the sacrificial layer 420 and the optical grating layer 407. In some embodiments, the etch 427 is an angled ion etch, where the angled ion etch is performed by a reactive ion beam. The substrate 402 may be scanned along a scanning direction relative to the reactive ion beam. As shown, the etch 427 may be delivered at a non-zero angle (θ) relative to a normal 433 to a plane defined by the top surface 413 of the optical grating layer 407. During the etching process, the hard mask 410 and the sacrificial layer 420 act as pattern guides to form a plurality of diagonal grating structures 430 from the optical grating layer 407. It will be appreciated that more complex and / or nuanced shapes of the diagonal grating structures 430 may be achieved by first forming a non-uniform sacrificial layer 420 and then performing additional selective area processing (SAP) etching cycles during the etch 427.

[0039]

[0045] The sacrificial layer 420 and hard mask 410 may then be removed from over each diagonal grating structure 430, resulting in the optical grating 445 shown in Figure 4F. In some embodiments, due to the variable height of the sacrificial layer 420, a first depth of a first trench 428A of the plurality of trenches is different from a second depth of a second trench 428B.

[0040]

[0046] 5A-5H illustrate a process for forming a diffractive optical element 500 according to an embodiment of the present disclosure. As shown in FIG. 5A, an optical grating layer 507 may be formed on a substrate 502, and a hard mask layer 510 may be formed on the optical grating layer 507. The diffractive optical element 500 may further include an etch stop layer 505 disposed between the substrate 502 and the optical grating layer 507. The substrate 502 may be made of an optically transparent material, such as silicon. In some embodiments, the etch stop layer 505 may be formed by, for example, a chemical vapor deposition (CVD) process, a physical vapor deposition (PVD) process, or a spin-on process. The etch stop layer 505 is formed of a material that is resistant to the etching process, such as titanium nitride or tantalum nitride, among others.

[0041]

[0047] 5B, the hard mask 510 may be patterned to form openings or gaps 511 therein. In some embodiments, the hard mask 510 is formed from a photoresist stack (not shown), and a hard mask layer is conformally formed over the grating layer 507. The hard mask layer 510 is formed from titanium nitride, for example, using a chemical vapor deposition process. In some embodiments, the gaps 511 may be formed using an etching process selective to the top surface 513 of the optical grating layer 507.

[0042]

[0048] 5B, a sacrificial layer 520 can be formed over the optical grating layer 507 and the patterned hard mask 510. In some embodiments, the sacrificial layer 520 is a mask deposited over the optical grating layer 507 and the hard mask 510. In a non-limiting embodiment, the sacrificial layer 520 can be a photoresist-type material formed over the diffractive optical element 500 using, for example, 3D printing. In other embodiments, the sacrificial layer 520 can be an optically transparent material, such as a silicon-based material, such as silicon nitride or silicon oxide, or a titanium-based material, such as titanium oxide.

[0043]

[0049] 5C, the sacrificial layer 520 may be recessed using a subtractive process 525, such as ion etching, reactive or sputtering. In the illustrated embodiment, the subtractive process 525 may be RIE traversed along a direction 526 to produce a sacrificial layer 520 having a variable height "H" relative to the top surface 513 of the optical grating layer 507. For example, the sacrificial layer 420 may be processed to form a recess or trench 521 having a sloped bottom surface 522. As shown, the sloped bottom surface 522 may define a plane that is non-parallel to the plane defined by the top surface 513 of the optical grating layer 507. Without limitation, the sloped bottom surface 522 may be generally planar and / or curved.

[0044]

[0050] In some embodiments, as shown in FIG. 5D, a sacrificial layer 520 including trenches 521 and sloped bottom surfaces 522 can be transferred to the optical grating layer 507. In some embodiments, a variable etch depth (VED) profile, e.g., a two-dimensional wedge shape, can be formed using vertical etching with a graytone screen (not shown), an optical device and method of variable exposure of photoresist to achieve variable depth. More specifically, graytone lithography is a technique for photolithography of a resist film to form a three-dimensional profile in the photoresist in a single exposure process. Graytone lithography can be combined with RIE to convert the resist profile into a three-dimensional structure.

[0045]

[0051] As shown, the subtractive process 561 extends the trenches 521 further into the optical grating layer 507 to form the sloped bottom surface 532 of the optical grating layer 507. Without limitation, the sloped bottom surface 532 may be generally planar and / or curved. By first shaping the sacrificial layer 520, precision in the optical grating layer 507 may be improved.

[0046]

[0052] 5E, any remaining portions of the sacrificial layer 520 may be removed, and a second hard mask 534 is formed in the trench 521. As shown, the second hard mask 534 is deposited over the sloped bottom surface 532.

[0047]

[0053] Next, as shown in Figure 5F, an optical planarization layer (OPL) 538 and a photoresist (PR) 540 may be formed over the first hard mask 510 and the second hard mask 534. A plurality of vertical trenches 544 may then be formed through the OPL 538, the PR 540, and the second hard mask 534. In some embodiments, the vertical trenches 544 are formed by vertical RIE selective to the top surface 513 of the optical grating layer 507. The OPL 538 and the PR 540 are removed, resulting in the diffractive optical element 500 shown in Figure 5G.

[0048]

[0054] As shown in FIG. 5H, the diffractive optical element 500 is then etched 527 to form a plurality of angled trenches 528A-N through the optical grating layer 507. In some embodiments, the etch 527 is an angled ion etch, which is performed by a reactive ion beam selective to the etch stop layer 505. The substrate 502 can be scanned along a scanning direction relative to the reactive ion beam. As shown, the etch 527 can be delivered at a non-zero angle relative to a normal to a plane defined by the top surface 513 of the optical grating layer 507. During the etch 527, the second hard mask 534 serves as a pattern guide to form a plurality of diagonal grating structures 530. As shown, a first depth of a first trench 528A of the plurality of trenches is different from a second depth of a second trench 528B due to the etch 527. The first and second hard masks 510, 534 are then removed, resulting in a structure similar to the device 400 of FIG. 4F.

[0049]

[0055] For convenience and clarity, terms such as "top," "bottom," "upper," "lower," "vertical," "horizontal," "transverse," "length" and the like are used herein to describe the relative placement and orientation of components illustrated in the figures and their component parts. These terms are intended to include the words specifically mentioned, derivatives thereof, and words of similar import.

[0050]

[0056] As used herein, elements or steps described in the singular and preceded by the word "a" or "an" should be understood to include a plurality of elements or steps, unless expressly stated to the contrary. Moreover, references to "one embodiment" of the present disclosure are not intended to be limiting; additional embodiments may incorporate the recited features.

[0051]

[0057] Furthermore, the terms "substantial" or "substantially" as well as the terms "approximately" or "about" can be used interchangeably in some embodiments and can be described using any relative measure accepted by those of skill in the art. For example, these terms can serve as a comparison to a reference parameter to indicate a deviation that can provide a given function. Without being limiting, the deviation from the reference parameter can be, for example, an amount of less than 1%, less than 3%, less than 5%, less than 10%, less than 15%, less than 20%, etc.

[0052]

[0058] Furthermore, those skilled in the art will understand that when an element, such as a layer, region, or substrate, is referred to as being formed, deposited, or disposed "on" another element, the element may be directly on the other element, or there may be intervening elements. In contrast, when an element is referred to as being "directly on" another element, there are no intervening elements present.

[0053]

[0059] As used herein, "deposited" and / or "deposited" may include any now known or later developed technique suitable for the material to be deposited, including, for example, but not limited to, chemical vapor deposition (CVD), low pressure CVD (LPCVD), and plasma enhanced CVD (PECVD). "Deposited" and / or "deposited" may also include semi-atmospheric CVD (SACVD) and high density plasma CVD (HDPCVD), rapid thermal CVD (RTCVD), ultra-high vacuum CVD (UHVCVD), limited reaction processing CVD (LRPCVD), and metal organic CVD (MOCVD), etc. "Deposited" and / or "deposited" may also include sputtering deposition, ion beam deposition, electron beam deposition, laser assisted deposition, thermal oxidation, thermal nitridation, spin-on techniques, and physical vapor deposition (PVD). "Deposited" and / or "deposited" may also include atomic layer deposition (ALD), chemical oxidation, molecular beam epitaxy (MBE), plating, and evaporation.

[0054]

[0060] In various embodiments, a design tool is provided and may be configured to create a data set used to pattern layers of the diffractive optical elements 400 and 500, for example, as described herein. For example, the data set may be created to generate a photomask used during a lithography process to pattern layers for structures as described herein. Such a design tool may include a collection of one or more modules, or may be configured in hardware, software, or a combination thereof. Thus, for example, a tool may 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 may be a computing device or other appliance that executes software, or may be implemented in hardware.

[0055]

[0061] As used herein, a module may be implemented using any form of hardware, software, or combination thereof. For example, one or more processors, controllers, ASICs, PLAs, logic components, software routines, or other mechanisms may be implemented to constitute a module. In implementations, the various modules described herein may be implemented as separate modules, or the described functions and features may be shared in part or in whole between one or more modules. In other words, the various features and functionality described herein may be implemented in any given application, as would be apparent to one of ordinary skill in the art after reading this specification. Furthermore, the various features and functionality may be implemented in one or more separate or shared modules in various combinations and permutations. Although various features or elements of functionality may be described or claimed separately as separate modules, one of ordinary skill in the art will understand that these features and functionality may be shared between one or more common software and hardware elements.

[0056]

[0062] By using the embodiments described herein, a waveguide having an oblique optical grating structure is formed. A first technical advantage of the oblique grating structure of the present embodiment includes improving the performance of the waveguide by better collecting and guiding the light passing through the waveguide, thus improving the clarity of the projected image. A second technical advantage of the oblique grating structure of the present embodiment includes improving the manufacturing efficiency of the waveguide by eliminating more time-consuming and difficult processes. Furthermore, a third technical advantage of the oblique grating structure of the present embodiment includes providing two-dimensional or three-dimensional shapes, allowing the waveguide to be used in a wider range of applications.

[0057]

[0063] The present disclosure is not limited in scope by the specific embodiments described herein. Indeed, in addition to those described herein, various other embodiments and modifications of the present disclosure will become apparent to those skilled in the art from the foregoing description and the accompanying drawings. Accordingly, such other embodiments and modifications are intended to be included within the scope of the present disclosure. Furthermore, the present disclosure has been described herein in the context of specific implementations in specific environments for specific purposes. Those skilled in the art will recognize that its usefulness is not limited thereto, and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Accordingly, the following claims should be construed in light of the full breadth and spirit of the present disclosure as described herein.

Claims

1. 1. A method of forming a diffractive optical element, comprising the steps of: providing an optical grating layer over a substrate; patterning a hard mask over the optical grating layer; forming a sacrificial layer over the hard mask, the sacrificial layer having a non-uniform height measured from a top surface of the optical grating layer; after the sacrificial layer is formed, etching a plurality of angled trenches in the optical grating layer to form an optical grating, wherein a first depth of a first trench of the plurality of angled trenches is different from a second depth of a second trench of the plurality of angled trenches, said etching including performing an angled ion etch at a non-zero angle with respect to a normal to a plane defined by a top surface of the optical grating layer; The method includes:

2. forming the sacrificial layer depositing the sacrificial layer over the hard mask; etching the sacrificial layer to form a trench in the sacrificial layer, the trench in the sacrificial layer having a sloped bottom surface; The method of claim 1 further comprising:

3. performing a vertical etch to form the trench in the sacrificial layer. The method of claim 2 further comprising:

4. forming a second hard mask along the sloped bottom surface of the trench in the optical grating layer; forming an optical planarization layer (OPL) and a photoresist (PR) on the hard mask and the second hard mask; Etching a plurality of vertical trenches through the OPL, the PR, and the second hard mask; removing the OPL and the PR, wherein after removing the OPL and the PR, the vertical trenches are etched into the optical grating layer; and The method of claim 2 further comprising:

5. The method of claim 1 , wherein the angled ion etching is performed by a reactive ion beam, and the substrate is scanned along a scan direction relative to the reactive ion beam.

6. The method of claim 1 , further comprising forming an etch stop layer over the substrate, the optical grating layer being formed over the etch stop layer.

7. 1. A method of forming a diffractive optical element, comprising the steps of: providing an optical grating layer over a substrate; providing a hard mask over the optical grating layer, the hard mask including a set of openings; forming a sacrificial layer over the hard mask; forming a recess in the sacrificial layer, the recess causing the sacrificial layer to have a non-uniform height as measured from a top surface of the optical grating layer; forming a trench in the optical grating layer, the trench being recessed below a top surface of the optical grating layer, the trench having a sloped bottom surface; after the trenches are formed, etching a plurality of angled trenches in the optical grating layer to form an optical grating, wherein a first depth of a first trench of the plurality of angled trenches is different from a second depth of a second trench of the plurality of angled trenches, said etching including performing an angled ion etch at a non-zero angle with respect to a normal to a plane defined by a top surface of the optical grating layer; The method includes:

8. forming the sacrificial layer depositing the sacrificial layer over the hard mask; etching the sacrificial layer to form a sloped bottom surface of the recess; The method of claim 7 further comprising:

9. forming a second hard mask along the inclined bottom surface of the recess; forming an optical planarization layer (OPL) and a photoresist (PR) on the hard mask and the second hard mask; Etching a plurality of vertical trenches through the OPL, the PR, and the second hard mask; removing the OPL and the PR, wherein after the removal of the OPL and the PR, the vertical trenches are etched through the optical grating layer; and The method of claim 8 further comprising:

10. The method of claim 7 , wherein the angled ion etching is performed by a reactive ion beam, and the substrate is scanned along a scan direction relative to the reactive ion beam.

11. The method of claim 7 , further comprising forming an etch stop layer over the substrate, the optical grating layer being formed over the etch stop layer.

12. 1. A method of forming a diffractive optical element, comprising the steps of: providing an optical grating layer over a substrate; patterning a hard mask over the optical grating layer; depositing a sacrificial layer over the hard mask; forming a trench in the sacrificial layer, the trench including a sloping bottom surface defining a first plane, the first plane being non-parallel to a second plane defined by a top surface of the optical grating layer; Etching a plurality of angled trenches in the optical grating layer to form an optical grating, wherein a first depth of a first trench of the plurality of angled trenches is different from a second depth of a second trench of the plurality of angled trenches, said etching including performing an angled ion etch at a non-zero angle with respect to a normal to the second plane defined by a top surface of the optical grating layer; The method includes:

13. The method of claim 12 , further comprising forming the sacrificial layer having a non-uniform height measured from a top surface of the optical grating layer.

14. etching the optical grating layer to recess the trenches in the optical grating layer; forming a second hard mask along the sloped bottom surface of the trench; forming an optical planarization layer (OPL) and a photoresist (PR) on the hard mask and the second hard mask; Etching a plurality of vertical trenches through the OPL, the PR, and the second hard mask; removing the OPL and the PR, wherein after removing the OPL and the PR, the vertical trenches are etched into the optical grating layer; and The method of claim 12 further comprising:

15. The method of claim 12 , wherein the angled ion etching is performed by a reactive ion beam, and the substrate is scanned along a scan direction relative to the reactive ion beam.

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