Variable height slanted grating method

Abstract

An apparatus having a grating structure and a method for forming the same are disclosed. The grating structure includes forming a recess in a grating layer. A plurality of channels are formed in the grating layer to define a slanted grating structure in the grating layer. The recess and slanted grating structure are formed using a selective etching process.

Description

[0001] This application is a divisional application of the invention patent application filed on July 1, 2019, with application number 201980047037.0 and invention title "Method for Oblique Grating with Variable Height". background

[0002] field

[0003] The embodiments of this disclosure generally relate to methods and apparatus for use in display devices. More specifically, this disclosure relates to grating structures for use in waveguides.

[0004] Description of related technologies

[0005] Virtual reality is generally considered to be a computer-generated simulated environment in which the user has a tangible physical presence. Virtual reality experiences can be generated in 3D and viewed using head-mounted displays (HMDs) (such as glasses, or other wearable display devices with near-eye display panels that act as lenses) to display a virtual environment that replaces the real environment.

[0006] However, augmented reality enables an experience in which users can still view their real surroundings through the display lenses of glasses or other HMD devices, and see images of virtual objects generated for the display and appearing as part of the real environment. Augmented reality can incorporate any type of input, such as sound and touch, as well as virtual images and videos, to enhance or augment the environment experienced by the user. As an emerging technology, augmented reality faces many challenges and design limitations.

[0007] One challenge is displaying virtual images overlaid on the surrounding environment while maintaining sufficient clarity from various user viewing angles. For example, if a user's eye is not precisely aligned with the displayed virtual image, they may see a distorted, blurry image, or may not be able to view the image completely. Furthermore, the image may be blurry and have lower-than-expected resolution from suboptimal viewing angles.

[0008] Therefore, there is a need for improved methods of manufacturing augmented reality display devices. Summary of the Invention

[0009] This disclosure generally relates to methods and apparatus for use in display devices. More specifically, this disclosure relates to grating structures for use in waveguides.

[0010] In one embodiment, a structure for use in a waveguide is provided. The structure has a substrate on which a grating layer is formed. A recess having a first end and a second end is formed in the grating layer. The depth of the recess varies from the first end to the second end. A plurality of channels are formed in the grating layer. Each channel partially defines a portion of a plurality of grating structures. The plurality of grating structures also have a depth variation from the first end to the second end defined by the recess.

[0011] In another embodiment, a structure for use in a waveguide is provided. The structure includes a substrate on which a grating layer is present. Recesses are formed in the grating layer in a first direction and a second direction. The recesses have a depth that varies in the first and second directions, defining a three-dimensional shape. A plurality of channels are formed in the grating layer. Each channel partially defines a portion of a plurality of grating structures. The plurality of grating structures also have a depth that varies in the first and second directions as defined by the recesses.

[0012] In another embodiment, a method for forming a grating structure is provided. The method includes forming a recess in a grating layer, forming a hard mold and a photoresist stack above the grating layer, etching the photoresist stack, and forming a plurality of grating structures in the grating layer. Brief description of the attached figures

[0013] A more specific description of the present disclosure, which has been briefly summarized above, can be obtained by referring to embodiments (some of which are illustrated in the accompanying drawings), thus allowing for a detailed understanding of the aforementioned features of the present disclosure. However, it should be noted that the drawings illustrate exemplary embodiments only and should not be construed as limiting the scope of the embodiments, as the present disclosure allows for other equivalent embodiments.

[0014] Figure 1 This is a schematic cross-sectional view of a display device according to one embodiment described herein.

[0015] Figure 2 This is an enlarged cross-sectional view of a portion of a waveguide according to one embodiment described herein, the waveguide having a wedge-shaped recess structure formed in the waveguide.

[0016] Figure 3 yes Figure 2 A magnified cross-sectional view of a waveguide, on which a photoresist stack structure is formed.

[0017] Figure 4 yes Figure 3 A magnified cross-sectional view of a waveguide, on which a patterned hard mode is formed.

[0018] Figure 5 yes Figure 4A magnified cross-sectional view of a waveguide in which a grating structure is formed.

[0019] Figure 6 This is a flowchart of a method for manufacturing a waveguide according to one embodiment described herein.

[0020] Figures 7A to 7C This is an enlarged cross-sectional view of an example of the shape of the recessed structure according to the embodiments described herein.

[0021] Figures 8A to 8C This is a perspective view of an example of the three-dimensional shape of the recessed structure according to the embodiments described herein.

[0022] For ease of understanding, the same reference numerals have been used as much as possible to designate common elements in the figures. Elements and features of one embodiment may be advantageously incorporated into other embodiments without further description. Detailed Implementation

[0023] A device having a grating structure and a method for forming the device are disclosed. The grating structure includes recesses in a grating layer. A plurality of channels are formed in the grating layer to define a slanted grating structure within the grating layer. The recesses and the slanted grating structure are formed using a selective etching process.

[0024] Figure 1 This is a schematic cross-sectional view of the waveguide 104 implemented in the display device 100. The display device 100 is configured for augmented reality applications, virtual reality applications, and mixed or combined reality applications, as well as other display applications such as handheld display devices.

[0025] Display device 100 utilizes waveguide 104 to allow viewing of the surrounding environment 130 through the waveguide 104, for example, allowing a user to view the surrounding environment 130 from the user's perspective 101. When implemented in display device 100, a first surface 122 of waveguide 104 is positioned adjacent to and facing the user's eye 111. A second surface 124 of waveguide 104 is positioned opposite to and adjacent to the first surface 122, facing the surrounding environment 130. Although waveguide 104 is illustrated as planar, it is conceivable that waveguide 104 may be curved or angled depending on the desired application.

[0026] Display device 100 further includes an image microdisplay 128 to guide a beam 120 of a generated virtual image into a waveguide 104. The beam 120 of the virtual image propagates in the waveguide 104. Generally, 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 beam 120 (virtual image) from the image microdisplay 128, and the beam 120 travels through the waveguide region 108 to the output coupling region 110, where the user's viewing angle 101 and field of view enable visualization of the virtual image overlaid on the surrounding environment 130. The image microdisplay 128 is a high-resolution display generator, such as a liquid crystal on a silicon microdisplay, which projects the beam 120 of the virtual image into the waveguide 104.

[0027] Waveguide 104 includes an input grating structure 112 and an output grating structure 114. The input grating structure 112 is formed on waveguide 104 in a region corresponding to the input coupling region 106. The output grating structure 114 is formed on waveguide 104 in a region corresponding to the output coupling region 110. The input grating structure 112 and the output grating structure 114 affect light propagation within waveguide 104. For example, the input grating structure 112 couples in light (such as beam 120) from the image microdisplay 128, while the output grating structure couples the light outward to the user's eye 111.

[0028] 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 beam 120 collected from and outcoupled from the waveguide 104. Furthermore, the output grating structure 114 modulates the field of view of the virtual image from the user's viewing angle 101 and increases the viewing angle at which the user can view the virtual image from the image microdisplay 128. In another example, a grating structure (not shown) is also formed in the waveguide region 108 between the input coupling region 106 and the output coupling region 110. Additionally, a plurality of waveguides 104 (each waveguide 104 having the desired grating structure formed in it) can be used to form the display device 100.

[0029] Figure 2 It is a magnified portion of the cross-section of waveguide 200, which is used to form a grating structure 280 in the waveguide. Figure 5In this example, waveguide 200 has a substrate 202 on which an etch stop layer 204 is formed. The substrate 202 is made of an optically transparent material, such as silicon. The etch stop layer 204 is formed over the substrate 202. The etch stop layer 204 is formed, for example, by a chemical vapor deposition (CVD) process, a physical vapor deposition (PVD) process, or a spin coating process. The etch stop layer 204 is formed of a material such as titanium nitride or tantalum nitride, which is resistant to etching processes.

[0030] A grating layer 206 is formed above the etch stop layer 204. The grating layer 206 is formed of an optically transparent material. In one example, the grating layer 206 is formed of 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 206 has a high refractive index, such as about 1.3 or higher, for example, 1.5 or even higher. Generally, the thickness of the grating layer 206 is less than about 1 micrometer, such as between about 150 nm and about 700 nm. For example, the thickness of the grating layer 206 is between about 200 nm and about 600 nm, such as between about 300 nm and about 500 nm, such as about 400 nm.

[0031] After forming the grating layer 206, recesses 220 are formed within the grating layer 206. The recesses 220 can be any suitable recessed structure and shape, including but not limited to: wedge-shaped, frustum-like, conical, or similar shapes. Figure 2 As depicted, the recess 220 has a planar and irregularly scaled triangular wedge-shaped structure and a length L between a first end 230 and a second end 232. The depth D of the recess 220 increases from the first end 230 to the second end 232. That is, the depth D of the recess 220 is minimum at the first end 230 and maximum at the second end 232. The depth D is in the range of about 0 nm to about 700 nm, such as between about 100 nm and about 600 nm, such as between about 200 nm and about 500 nm. For example, the depth D is between about 300 nm and about 400 nm, such as about 350 nm. Figure 2In this embodiment, the length L is significantly larger than the depth D. For example, the length L is approximately 25 mm, while the depth D at the first end 230 is between approximately 0 nm and approximately 50 nm, and the depth D at the second end 232 is between approximately 250 nm and approximately 700 nm. Therefore, the recess 220 has a substantially shallow bevel (shown as angle Θ), which is measured between the surface of the recess 220 and the plane defined by the surface 206a of the grating layer 206. In this example, the angle Θ is less than 1 degree, such as less than 0.1 degrees, e.g., approximately 0.0005 degrees. For clarity, the bevel of the recess 220 is shown here with an exaggerated angle Θ.

[0032] In one example, the recess 220 is formed by selectively etching a region of the grating layer 206. For example, a first portion 220a of the recess 220 is formed by etching the grating layer 206 at a low etch rate and / or low power. A second portion 220b is formed by etching the grating layer 206 at an increased etch rate and / or power than portion 220a. Similarly, a third portion 220c is formed by etching the grating layer 206 at a higher etch rate and / or power than portions 220a and 220b. Here, three portions are used for illustration. However, any desired number of portions can be used to form the recess 220, and any desired number of portions can be etched in a single operation step or in multiple steps. Additionally, etching can occur at steadily increasing intervals (i.e., etch rate and / or power) such that the recess 220 has a smooth surface. In one example, a region for the grating structure 280 is defined prior to the formation of the recess 220, achieved, for example, by using a mask (e.g., a photolithographic mask or a proximity mask) or an etching beam. Forming a recess 220 with a smooth profile improves image quality compared to a rough (i.e., stepped or similar) structure by better controlling the diffraction and projection of the light beam. Consequently, the power of light coupled outward across the grating structure 280 is significantly more uniform.

[0033] Figure 3This is a cross-section of waveguide 200, on which a photoresist stack structure 250 is formed. A conformal hard mold 208 is formed above grating layer 206. The hard mold 208 is formed, for example, from titanium nitride using a chemical vapor deposition process. In one example, the thickness of the hard mold 208 is between about 30 nm and about 50 nm, such as between about 35 nm and about 45 nm. The photoresist stack structure 250 includes a back anti-reflective coating (BARC) 210, a silicon anti-reflective coating (SiARC) 212, and photoresist 214. BARC 210 is formed using a spin coating process such that the upper surface 210a of BARC 210 is generally planar (i.e., parallel to the surface 202a of substrate 202). By using a spin coating process to form BARC 210, no etching or polishing process is required to planarize BARC 210, which eliminates the possibility of over-etching or damaging the thin BARC 210 and / or the underlying grating layer 206.

[0034] Next, SiARC 212 is formed over BARC 210. SiARC 212 is formed from a silicon-based material using, for example, a chemical vapor deposition process or a spin coating process. Photoresist 214 is formed over SiARC 212. Photoresist 214 is formed from a polymer material using, for example, a lithography process. In one example, the photoresist 214 is formed by spin coating, exposing one or more grating lines, and developing the photoresist 214. After forming the photoresist 214, the photoresist stack structure 250 is patterned using an etching process. It should be understood that patterning with BARC 210 and SiARC 212 is an exemplary method. Other patterning methods may be used in conjunction. The patterning method is generally chosen with respect to the size and shape of the structure to be patterned.

[0035] Figure 4 In etching and removal Figure 3 The cross-section of waveguide 200 following the photoresist stack structure 250. Etching the photoresist stack structure 250 patternes the hard mold 208, as shown. Figure 4 As shown in the diagram. The hard mold 208 serves as a guide for the pattern to form. Figure 5The oblique grating structure 280 is shown. The oblique grating structure 280 is defined between one or more channels 270 formed within the grating layer 206. To form the channels 270, the grating layer 206 is etched again using a selective etching process. In one example, the oblique grating structure 280 is formed using a process similar to (but in reverse order) that is used to form the wedge-shaped recess 220. For example, the region corresponding to the third portion 220c is etched at a low etch rate and / or low power. The region corresponding to the second portion 220b is etched at a higher etch rate and / or power than the third portion 220c. The region corresponding to the first portion 220a is etched at a higher etch rate and / or power than portions 220b and 220c. In one example, the etch stop layer 204 is etched to improve the definition of the oblique grating structure 280. After forming the oblique grating structure 280, an etching process may optionally be used to remove the hard mold 208.

[0036] Each oblique grating structure 280 is formed to have a depth d. For example, the oblique grating structure 280 may have a depth d between about 5 nm and about 700 nm, such as between about 100 nm and about 600 nm, such as about 500 nm. The depth of the oblique grating structure 280 is selected depending on the desired wavelength (i.e., color) for projecting the image onto the user. Figure 5 In this embodiment, the depth d of the oblique grating structure decreases from the first end 230 to the second end 232 of the recess 220 (shown in dashed lines). The upper surface 280a of each oblique grating structure 280 defines an angled plane 290 corresponding to the slope of the recess 220. Furthermore, each oblique grating structure 280 may have an angle Φ measured relative to a plane perpendicular to the surface 204a of the etch-stop layer 204. This angle Φ is, for example, between about 0 degrees and about 70 degrees, such as between about 25 degrees and about 45 degrees, such as about 35 degrees. By forming the oblique grating structure 280 as described herein, the sharpness of the image projected by the waveguide 200 is significantly improved because the diffraction and projection of light toward the desired image plane are improved. Image quality is further improved by controlling the shape of the oblique grating structure 280, thereby controlling the variation in diffraction for different wavelengths (i.e., different colors). Due to the increased control provided by the oblique grating structure 280, optical efficiency (i.e., the projection of the desired wavelength to the user's viewing angle) is significantly improved. Furthermore, the projection of undesirable wavelengths is reduced, thereby increasing the sharpness and quality of the projected image.

[0037] exist Figures 2 to 5In the diagram, the recess 220 is shown as a wedge shape with a planar surface and an irregular triangular shape. However, the etching process described herein advantageously allows the recess 220 to have a slope and / or curvature in one or more directions. Therefore, the recess 220 can have any suitable shape, as described above. Figures 7A to 7C The illustration shows other examples of shapes that can be used for the recess 220. For example, Figure 7A The diagram illustrates a generally isosceles triangular recess 720 in the grating layer 706 of waveguide 700. The recess 720 has two planar inclined portions that extend from corresponding peripheral regions 720a, 720b toward the central region 720c. Figure 7B The diagram illustrates another recess 750 in the grating layer 736 of waveguide 730. The recess 750 has a curved and concave structure, with a shallow depth D in the surrounding regions 750a, 750b, and an increasing depth in the central region 750c. In one example, the recess 750 has a parabolic shape. For instance, the depth D increases non-linearly from the surrounding regions 750a, 750b to the central region 750c. Figure 7C The illustration shows another recess 780 in the grating layer 766 of waveguide 760. Recess 780 has a depth D that oscillates from a first end 780a to a second end 780b, thus forming a cyclic pattern of depth D in recess 780. Recess 780 is shown as a linear, sawtooth oscillation with depth D. However, it is possible to consider that depth D can vary non-linearly, such that recess 780 has a wave-like oscillation of depth D. The depth D of recesses (such as recesses 720, 750, and 780) can vary linearly or non-linearly across the length L of the recess from the first end (i.e., 720a, 750a, 780a) to the second end (i.e., 720b, 750b, 780b).

[0038] In another example, the recess 220 has a three-dimensional shape. That is, the depth varies in more than one direction, such as varying in two directions (i.e., the first direction X and the second direction Y), as in... Figures 8A-8C The example is illustrated in the diagram. Figure 8A The diagram shows the concave portion 820 of a curve with a saddle point shape (i.e., a hyperbolic paraboloid shape). Figure 8B The diagram shows a concave portion 850 with a positive curvature elliptical parabolic shape. Figure 8C The illustration shows a concave portion 880 with an elliptic parabolic shape and negative curvature. The three-dimensional shape of the concave portion is not limited to... Figures 8A to 8C Examples of this approach are also considered, and other desired shapes can be used in conjunction with it, such as parabolas, ellipsoids, and linearly inclined shapes within a square domain with positive or negative curvature. In these cases, the depth of the concave portion varies in both the X and Y directions. Therefore, the upper surface of the oblique grating structure (such as...) Figure 5The upper surface 280a) is curved as defined by the shape of the concave curvature. The shape and / or depth of the concave are not limited to variations in the X and Y directions. For example, the depth of the concave can vary in three directions, four directions, or even more directions. Furthermore, although Cartesian coordinates are used for illustration herein, the wedge structure can be formed using other coordinate systems, such as polar coordinates, cylindrical coordinates, or spherical coordinates. The embodiments described herein can be advantageously used to form any desired shape of the concave.

[0039] Figure 6 This is a flowchart illustrating a method 600 for forming a grating structure in a waveguide, such as forming an oblique grating structure 280. The waveguide is typically formed on a substrate. In one example, the substrate is a silicon-based glass substrate with an optional etch-stop layer and a grating layer. In another example, the substrate is a glass substrate without an etch-stop layer. In such a case, the substrate serves as the grating layer, and the grating structure is formed directly in the substrate. In operation 602, a recess is formed in the grating layer above the optional etch-stop layer. In one example, the recess is formed using an etching process that selectively processes areas of the substrate, as described above. In operation 604, a conformal hard mold is deposited on the grating layer. A photoresist stack structure is formed over the hard mold, the photoresist stack structure including a back anti-reflective coating (BARC), a silicon anti-reflective coating (SiARC), and photoresist. The back anti-reflective coating is formed using a spin-coating technique such that the upper surface of the layer is substantially planar.

[0040] In operation 606, the photoresist stack is etched to form a desired pattern on the hard mold. In operation 608, the hard mold and grating layer are etched using a selective etching process to form a grating structure in the grating layer, as described above. In operation 610, an etch stop layer (if present) is optionally etched to improve the definition of the shape of the grating structure. In operation 612, the hard mold is optionally removed, for example, using an etching process.

[0041] By utilizing the embodiments described herein, waveguides with oblique grating structures are formed. The oblique grating structure improves the waveguide's functionality by better collecting and guiding light through it, thereby improving the sharpness of the projected image. The oblique grating structure provides increased control over the wavelength of light projected onto the desired image plane. The power uniformity of the light coupled outward from the waveguide is significantly more uniform. The embodiments described herein further improve waveguide fabrication by eliminating manufacturing processes such as mechanical polishing (which can damage the layers used to form the waveguide). Furthermore, the embodiments described herein allow the grating to have two-dimensional or three-dimensional shapes, which allows for the use of waveguides in an expanded range of applications.

[0042] While the foregoing describes implementations of this disclosure, other and further implementations of this disclosure may be devised without departing from the basic scope of this disclosure, and the scope of this disclosure is defined by the appended claims.

Claims

1. A device having a grating structure, comprising: A substrate having an optically transparent grating layer disposed on the substrate; A recess is formed in the grating layer, the recess having a depth that varies from a first end to a second end; Multiple oblique grating structures are formed in the grating layer below the recess and partially define a portion of the recess. The depth of the multiple oblique grating structures varies from the first end to the second end, and the angle of each of the multiple oblique grating structures relative to a plane perpendicular to the substrate is between 25 degrees and 45 degrees.

2. The device of claim 1, wherein the recess has a planar and irregularly triangular wedge-shaped structure.

3. The device of claim 2, wherein the top surfaces of the plurality of oblique grating structures are coplanar.

4. The device of claim 3, wherein the depth of the plurality of oblique grating structures varies linearly from the first end to the second end.

5. The device of claim 1, wherein the recess has a truncated cone shape or a conical shape.

6. The device of claim 5, wherein the top surface of the plurality of oblique grating structures defines a curvature.

7. The device of claim 6, wherein the depth of the plurality of oblique gratings varies non-linearly from the first end to the second end.

8. The device of claim 1, wherein the recess has a generally isosceles triangular shape.

9. The device of claim 1, wherein the recess has a depth that oscillates from the first end to the second end.

10. A device having a grating structure, comprising: A substrate having an optically transparent grating layer disposed on the substrate; A recess is formed in the grating layer, the recess having a depth that varies in a first direction and a second direction to define a three-dimensional shape; and Multiple oblique grating structures are formed in the grating layer below the recess and partially define a portion of the recess. The depths of the multiple oblique grating structures vary in the first direction and the second direction, and the angle of each of the multiple oblique grating structures relative to a plane perpendicular to the substrate is between 25 degrees and 45 degrees.

11. The device of claim 10, wherein the recess has a parabolic shape.

12. The device of claim 11, wherein the recess has a hyperbolic paraboloid shape.

13. The device of claim 11, wherein the recess has an elliptical parabolic shape.

14. The device of claim 10, wherein the recess has a negative curvature.

15. The device of claim 10, wherein the recess has a positive curvature.

16. A method for forming an apparatus having a grating structure, comprising: An optically transparent grating layer is formed on top of a substrate. The grating layer comprises a silicon-based or titanium-based material and has a thickness of less than 1 µm. A recess is formed in the grating layer by selective etching, the recess having a depth that varies from a first end to a second end; A conformal hard mold is deposited on the grating layer; A photoresist stack structure is formed on top of the conformal hard mold, the photoresist stack structure including a back anti-reflective coating, a silicon anti-reflective coating and photoresist; The photoresist stack structure is etched to form a desired pattern on the hard mold; and The hard mold and the grating layer are selectively etched to form an oblique grating structure in the grating layer.

17. The method of claim 16, further comprising: Before forming the grating layer, an etch stop layer is formed on the substrate, which is formed by chemical vapor deposition (CVD), physical vapor deposition (PVD), or spin coating.

18. The method of claim 16, wherein the back antireflective coating is formed by spin coating and the silicon antireflective coating is formed by chemical vapor deposition or spin coating.

19. The method of claim 16, wherein the recess has a wedge shape, a truncated cone shape, or a conical shape.

20. The method of claim 16, wherein the recess has a three-dimensional parabolic shape.

Images