Variable height slanted grid method

Abstract

To provide an apparatus with a grating structure and a method for forming the grating structure.SOLUTION: A method of forming grating structures 280 includes forming a recess 220 in a grating layer 206. A plurality of channels 270 is formed in the grating layer to define slanted grating structures therein. The recess and the slanted grating structures are formed using a selective etching process.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE Embodiments of the present disclosure relate to methods and apparatus for use in displays. More particularly, the present disclosure discloses grating structures for use in waveguides. [Background technology]

[0002] Virtual reality is generally considered to be a computer-generated simulated environment in which the user is physically present. Virtual reality experiences can be generated in 3D and viewed on a head-mounted display (HMD), such as glasses or other wearable display devices with near-eye display panels as lenses to display the virtual environment that replaces the real environment.

[0003] Augmented reality, however, allows for an experience in which a user can still see the real surroundings through the display lenses of glasses or other HMD devices, but in addition can see images of virtual objects that are generated for display and appear as part of the real environment. Augmented reality can include any type of input, such as voice input and haptic input, as well as virtual images and video that enhance or extend the environment experienced by the user. As an emerging technology, augmented reality presents many challenges and design constraints.

[0004] One such challenge is displaying a virtual image superimposed on the surrounding environment with sufficient clarity from a user's various viewpoints. For example, if a user's eye is not precisely aligned with the virtual image being displayed, the user may see a distorted or unclear image, or may not be able to see the entire image. Furthermore, the image may be blurry and of less than the desired resolution from a non-optimal viewing angle.

[0005] Therefore, there is a need for improved methods for manufacturing augmented reality displays. Summary of the Invention

[0006] The present disclosure relates generally to methods and apparatus for use in displays, and more particularly to grating structures for use in waveguides.

[0007] In one embodiment, a grating structure for use in a waveguide is provided. The structure includes a substrate having a grating layer disposed thereon. The grating layer has recesses formed therein, the recesses having a first end and a second end. The recesses vary in depth 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 vary in depth from the first end to the second end defined by the recesses.

[0008] In another embodiment, a structure for use in a waveguide is provided. The structure includes a substrate having a grating layer disposed thereon. Recesses are formed in the grating layer in a first direction and a second direction. The recesses vary in depth in the first direction and the second direction and define 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 vary in depth in the first direction and the second direction as defined by the recesses.

[0009] In yet another embodiment, a method of forming a grating structure is provided that includes forming recesses in a grating layer, forming a hard mask and a photoresist stack over the grating layer, etching the photoresist stack, and forming a plurality of grating structures in the grating layer.

[0010] So that the above-mentioned features of the present disclosure can be understood in detail, a more particular description of the present disclosure, briefly summarized above, will be obtained by reference to embodiments, some of which are illustrated in the accompanying drawings. It should be noted, however, that the accompanying drawings depict only exemplary embodiments and therefore should not be considered as limiting its scope, as the present disclosure may admit of other equally effective embodiments. [Brief description of the drawings]

[0011] [Figure 1] 1 shows a schematic cross-sectional view of a display device according to an embodiment described herein; [Diagram 2] FIG. 2 is an enlarged cross-sectional view of a portion of a waveguide having a wedge-shaped recessed structure formed therein according to one embodiment described herein. [Diagram 3] 3 is an enlarged cross-sectional view of the waveguide of FIG. 2 with a photoresist stack formed thereon; [Figure 4] FIG. 4 is an enlarged cross-sectional view of the waveguide of FIG. 3 with a patterned hard mask formed thereon. [Diagram 5] 5 is an enlarged cross-sectional view of the waveguide of FIG. 4 in which a grating structure is formed. [Figure 6] FIG. 2 is a flow diagram of a method for fabricating a waveguide, according to one embodiment. [Figure 7A] 1A-1C are enlarged cross-sectional views of example recessed structure geometries according to embodiments described herein. [Figure 7B] 1A-1C are enlarged cross-sectional views of example recessed structure geometries according to embodiments described herein. [Figure 7C] 1A-1C are enlarged cross-sectional views of example recessed structure geometries according to embodiments described herein. [Figure 8A] FIG. 2 is a perspective view of a three-dimensional shape of a recessed structure according to one embodiment described herein. [Figure 8B] FIG. 2 is a perspective view of a three-dimensional shape of a recessed structure according to one embodiment described herein. [Figure 8C] FIG. 2 is a perspective view of a three-dimensional shape of a recessed structure according to one embodiment described herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] For ease of understanding, wherever possible, the same reference numerals have been used to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

[0013] A device comprising a lattice structure and a method of forming the lattice structure are disclosed. The lattice structure includes recesses in a lattice layer. A plurality of channels are formed in the lattice layer to define a tilted lattice structure in the lattice layer. The recesses and the tilted lattice structure are formed using a selective etching process.

[0014] 1 is a schematic cross-sectional view of a waveguide 104 implemented in a display device 100. The display device 100 is configured for augmented reality, virtual reality, mixed or blended augmented and virtual reality applications, and other display applications, such as handheld display devices.

[0015] The display device 100 utilizes a waveguide 104 for see-through viewing of the surrounding environment 130 via the waveguide 104, for example, for a user viewing the surrounding environment 130 from the user's viewpoint 101. When implemented in the display device 100, a first surface 122 of the waveguide 104 is disposed proximate to and facing the user's eye 111. A second surface 124 of the waveguide 104 is disposed opposite the first surface 122 and proximate to and facing the surrounding environment 130. Although illustrated as planar, it is contemplated that the waveguide 104 may be curved or angled depending on the desired application.

[0016] The display device 100 further comprises an image microdisplay 128 for directing the light beam 120 of the generated virtual image into the waveguide 104. The virtual image light beam 120 propagates in 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 beam 120 (virtual image) from the image microdisplay 128, which passes through the waveguide region 108 to the output coupling region 110, where the user's viewpoint 101 and field of view allow visualization of the virtual image superimposed on the surrounding environment 130. The image microdisplay 128 is a high-resolution display generator, such as a liquid crystal on silicon microdisplay, which projects the virtual image light beam 120 into the waveguide 104.

[0017] The waveguide 104 includes an input grating structure 112 and an output grating structure 114. The input grating structure 112 is formed in a region on the waveguide 104 that corresponds to the input coupling region 106. The output grating structure 114 is formed in a region on the waveguide 104 that corresponds to the output coupling region 110. The input grating structure 112 and the output grating structure 114 affect the propagation of light within the waveguide 104. For example, the input grating structure 112 couples light from an image microdisplay 128, such as light beam 120, and the output grating structure couples out the light to a user's eye 111.

[0018] 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 rays 120 that are focused and emitted from the waveguide 104. In addition, the output grating structure 114 changes the field of view of the virtual image from the user's viewpoint 101 to increase the viewing angle at which the user can see the virtual image on 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, multiple waveguides 104, each with a desired grating structure formed therein, can be used to form the display device 100.

[0019] FIG. 2 is a cross-sectional view of an enlarged portion of a waveguide 200 for forming a grating structure 280 (FIG. 5) therein. In this example, the 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 on 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-on process. The etch stop layer 204 is made of a material that is resistant to the etching process, such as titanium nitride, tantalum nitride, among others.

[0020] A grating layer 206 is formed on the etch stop layer 204. The grating layer 206 is formed of an optically transparent material. In one example, the grating layer 206 is made 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 more, even more than 1.5. Typically, the grating layer 206 has a thickness of less than about 1 micron, such as between about 150 microns and about 700 microns. For example, the grating layer 206 has a thickness of between about 200 nm and about 600 nm, such as between about 300 nm and about 500 nm, such as about 400 nm.

[0021] After the lattice layer 206 is formed, a recess 220 is formed in the lattice layer 206. The recess 220 may have any suitable recess structure and shape, such as, but not limited to, a wedge shape, a frustum shape, or a cone shape. As shown in FIG. 2, the recess 220 has a planar, scalene wedge-shaped structure and has 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. In the embodiment of FIG. 2, the length L is substantially larger than the depth D. For example, the length L is about 25 mm, but the depth D at the first end 230 is between about 0 nm and about 50 nm, and the depth D at the second end 232 is between about 250 nm and about 700 nm. Thus, the recess 220 is a substantially shallow slope, shown as an angle θ measured between a surface of the recess 220 and a 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 degree, such as about 0.0005 degrees. The slope of the recess 220 is shown here with an exaggerated angle θ for clarity.

[0022] In one example, the recesses 220 are formed by selectively etching regions of the lattice layer 206. For example, a first portion 220a of the recesses 220 is formed by etching the lattice layer 206 at a slow etch rate and / or low power. A second portion 220b is formed by etching the lattice layer 206 at an increased etch rate and / or power relative to portion 220a. Similarly, a third portion 220c is formed by etching the lattice layer 206 at a faster etch rate and / or higher power than portions 220a, 220b. Here, three portions are used for illustration purposes. However, any desired number of portions may be used to form the recesses 220 and etched in a single work step or multiple steps. Additionally, the etching may be performed in smoothly increasing intervals (i.e., etch rate and / or power) such that the recesses 220 have a smooth surface. In one example, the areas for the grating structure 280 are defined prior to the formation of the recesses 220, for example, by utilizing a mask (e.g., a photolithography mask or a proximity mask) or an etching beam. Creating recesses 220 with smooth contours improves image quality by better controlling the diffraction and projection of light compared to rough (i.e., stepped, etc.) structures. Thus, the light output emitted across the grating structure 280 is significantly more uniform.

[0023] 3 is a section of a waveguide 200 on which a photoresist stack 250 is formed. A conformal hard mask 208 is formed on the grating layer 206. The hard mask 208 is made of titanium nitride, for example, using a chemical vapor deposition process. In one example, the hard mask 208 has a thickness between about 30 nm and about 50 nm, for example, between about 35 nm and about 45 nm. The photoresist stack 250 includes a back anti-reflective coating (BARC) 210, a silicon anti-reflective coating (SiARC) 212, and a photoresist 214. The BARC 210 is formed using a spin-on process, such that a top surface 210a of the BARC 210 is substantially flat (i.e., parallel to the surface 202a of the substrate 202). By utilizing a spin-on process to form BARC 210, no etching or polishing processes are required to planarize BARC 210, thereby eliminating the possibility of overetching or damaging the thin BARC 210 and / or the underlying lattice layer 206.

[0024] Next, SiARC 212 is formed on BARC 210. SiARC 212 is formed from a silicon-based material, for example, using a chemical vapor deposition process or a spin-on process. Photoresist 214 is formed on SiARC 212. Photoresist 214 is formed from a polymer material, for example, using a photolithography process. In one example, photoresist 214 is formed using spin-on coating, one or more grid lines are exposed, and photoresist 214 is developed. After photoresist 214 is formed, photoresist stack 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 utilized herein. The patterning method is generally selected in relation to the size and shape of the structure to be patterned.

[0025] FIG. 4 is a cross-sectional view of the waveguide 200 after the photoresist stack 250 of FIG. 3 is etched and removed. Etching the photoresist stack 250 patterns the hard mask 208 as shown in FIG. 4. The hard mask 208 serves as a pattern guide for forming the tilted grating structure 280 shown in FIG. 5. The tilted 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 again etched using a selective etching process. In one example, the tilted grating structure 280 is formed using a process similar to that used to form the wedge-shaped recess 220, but in reverse order. For example, the area corresponding to the third portion 220c is etched at a slower etch rate and / or lower power. The area corresponding to the second portion 220b is etched at a faster etch rate and / or higher power than the third portion 220c. The area corresponding to the first portion 220a is etched at a faster etch rate and / or with a higher power than the portions 220b, 220c. In one example, the etch stop layer 204 is etched to improve the definition of the tilted lattice structure 280. After the tilted lattice structure 280 is formed, the hard mask 208 is optionally removed using an etching process.

[0026] Each tilted grating structure 280 is formed with a depth d. For example, the tilted grating structure 280 may have a depth d between about 5 nm and about 700 nm, between about 100 nm and about 600 nm, for example about 500 nm. The depth of the tilted grating structure 280 is selected according to a desired wavelength (i.e., color) for the projection of an image to a user. In the embodiment of FIG. 5, the depth d of the tilted grating structure decreases from the first end 230 to the second end 232 of the recess 220 (shown in phantom). The top surface 280a of each tilted grating structure 280 defines an angled plane 290 that corresponds to the tilt of the recess 220. Additionally, each tilted grating structure 280 may have an angle φ measured with respect to a plane perpendicular to the surface 204a of the etch stop layer 204. The angle φ is, for example, between about 0 degrees and about 70 degrees, for example, between about 25 degrees and about 45 degrees, for example, about 35 degrees. Forming the grating structure 280 described herein improves the diffraction and projection of light towards the desired image plane, thereby substantially improving the clarity of the image projected by the waveguide 200. By controlling the shape of the tilted grating structure 280, the variation in diffraction of different wavelengths (i.e., different colors) is controlled to improve image quality. Due to the increased control provided by the tilted grating structure 280, the optical efficiency (i.e., the projection of the desired wavelengths to the user's viewpoint) is significantly improved. Furthermore, the projection of undesired wavelengths is reduced, thus increasing the clarity and quality of the projected image.

[0027] 2-5 show planar, tilted, wedge-shaped recesses 220. However, the etching process described herein advantageously allows the recesses 220 to have a tilt and / or curvature in one or more directions. Thus, the recesses 220 may have any suitable shape, as previously described. FIGS. 7A-7C show other examples of shapes that may be utilized for the recesses 220. For example, FIG. 7A shows a substantially isosceles triangular recess 720 in the grating layer 706 of the waveguide 700. The recess 720 has two planar slopes extending from each of the peripheral regions 720a, 720b toward the central region 720c. FIG. 7B shows another recess 750 in the grating layer 736 of the waveguide 730. The recess 750 has a curved, concave structure with a shallow depth D in the peripheral regions 750a, 750b and an increasing depth in the central region 750c. In one example, the recesses 750 are parabolic in shape. For example, the depth D increases nonlinearly from the peripheral regions 750a, 750b to the central region 750c. FIG. 7C illustrates another recess 780 in the grating layer 766 of the waveguide 760. The recesses 780 vary in depth D from a first end 780a to a second end 780b, thus forming a periodic depth D pattern of the recesses 780. The recesses 780 are shown with a linear sawtooth variation in depth D. However, it is contemplated that the depth D may vary nonlinearly, such that the recesses 220 may have a wavy variation in depth D. The depth D of a recess, for example recesses 720, 750, and 780c, may vary linearly or non-linearly over the length L of the recess from a first end (i.e., 720a, 750a, 780a) to a second end (i.e., 720b, 750b, 780b).

[0028] In another example, the recess 220 has a three-dimensional shape, i.e., the depth varies in one or more directions, for example in two directions (i.e., a first direction X and a second direction Y), as shown in the examples of Figures 8A-8C. Figure 8A shows a recess 820 that is curved in a saddle-point shape (i.e., in a hyperbolic paraboloid shape). Figure 8B shows a recess 850 in the shape of an elliptical paraboloid with positive curvature. Figure 8C shows a recess 880 in the shape of an elliptical paraboloid with negative curvature. The three-dimensional shape of the recess is not limited to the examples of Figures 8A-8C. Other desired shapes, for example, paraboloids, ellipsoids, and linearly tapered shapes, among others, in square areas with positive or negative curvature, are also contemplated and may be utilized herein. In these cases, the depth of the recess varies in both the X and Y directions. Thus, the top surface of the tilted lattice structure, e.g., top surface 280a in FIG. 5, is curved as defined by the shape of the curvature of the recesses. The shape and / or depth of the recesses is not limited to variations in the X and Y directions. For example, the depth of the recesses may vary in three directions, four directions, or more directions. Additionally, although illustrated herein using a Cartesian coordinate system, the wedge-shaped structures may be formed using other coordinate systems, e.g., polar, cylindrical, or spherical coordinate systems. The embodiments herein may be advantageously utilized to form desired shapes for the recesses.

[0029] FIG. 6 is a flow chart showing a method 600 for forming a grating structure in a waveguide, for example, a tilted grating structure 280. The waveguide is generally 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 formed thereon. 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 formed directly on the substrate. In step 602, recesses are formed in the grating layer on the optional etch stop layer. In one example, the recesses are formed using an etching process that selectively treats areas of the substrate, as described above. In step 604, a conformal hard mask is deposited on the grating layer. A photoresist stack including a bottom antireflective coating (BARC), a silicon antireflective coating (SiARC), and a photoresist is formed on the hard mask. The bottom antireflective coating is formed using a spin-on technique, which results in a substantially planar surface of the coating.

[0030] In step 606, the photoresist stack is etched to form the desired pattern on the hard mask. In step 608, the hard mask and grating layer are etched using a selective etching process to form grating structures in the grating layer, as previously described. In step 610, the etch stop layer, if present, is optionally etched to improve the definition of the shape of the grating structures. In step 612, the hard mask is optionally removed, for example using an etching process.

[0031] Utilizing the embodiments described herein, a waveguide having a tilted grating structure is formed. The tilted grating structure improves the function of the waveguide by better focusing and directing the light transmitted through the waveguide, thus improving the clarity of the projected image. The tilted grating structure provides improved control over the wavelength of light projected onto the desired image surface. The uniformity of the light output emitted by the waveguide is significantly more uniform. The embodiments described herein further improve the fabrication of the waveguide by eliminating fabrication processes, such as mechanical polishing, that can damage the layers utilized to form the waveguide. Additionally, the embodiments described herein allow the grating to have two- or three-dimensional shapes, which allows the waveguide to be utilized in a wider range of applications.

[0032] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, the scope of which is determined by the claims that follow.

Claims

1. 1. A structure for use in a waveguide, comprising: A substrate provided with a lattice layer, the lattice layer having a recessed structure formed therein, the recessed structure comprising: A first end, A second end, and A depth varying from said first end to said second end A substrate comprising: a plurality of channels formed in the lattice layer below the recessed structure, each channel partially defining a portion of a plurality of lattice structures, bottom ends of the plurality of channels being coplanar, top surfaces of the plurality of lattice structures being coplanar and partially defining the varying depth of the recessed structure, the depth of the plurality of lattice structures varying from the first end defined by the recessed structure to the second end, each of the plurality of lattice structures being at an angle between 25 degrees and 45 degrees with respect to a plane normal to the substrate; Including, structure.

2. The structure of claim 1 , wherein the depths of the plurality of grating structures vary linearly from the first end to the second end.

3. 10. The structure of claim 1, wherein each grating structure is between 5 nm and 700 nm deep.

4. The structure of claim 1 , wherein the grating layer is formed from an optically transparent material having a refractive index of 1.3 or greater.

5. 1. A structure for use in a waveguide, comprising: A substrate provided with a grating layer; a recess formed in the lattice layer, the recess having a depth that varies in a first direction, a second direction, and a third direction and that defines a three-dimensional shape; a plurality of channels formed in the lattice layer below the recess, each channel partially defining a portion of a plurality of lattice structures, bottom ends of the plurality of channels being coplanar, depths of the plurality of lattice structures varying in the first direction, the second direction, and the third direction as defined by the recess, each of the plurality of lattice structures being at an angle between 25 degrees and 45 degrees with respect to a plane normal to the substrate; A structure comprising:

6. The structure of claim 5 , wherein the recess is saddle-point shaped.

7. The structure of claim 5 , wherein the recess has a positive curvature.

8. The structure of claim 5 , wherein the recess has a negative curvature.

9. The structure of claim 5 , wherein the grating layer is formed from an optically transparent material having a refractive index of 1.3 or greater.

10. 6. The structure of claim 5, wherein each grating structure is between 5 nm and 700 nm deep.

11. 1. A structure for use in a waveguide, comprising: A substrate provided with a lattice layer, the lattice layer having a recessed structure formed therein, the recessed structure comprising: A first end, A second end, and A depth varying from said first end to said second end A substrate comprising: a plurality of channels formed in the lattice layer below the recessed structure, each channel partially defining a portion of a plurality of lattice structures, bottom ends of the plurality of channels being coplanar, depths of the plurality of lattice structures varying non-linearly from the first end to the second end as defined by the recessed structure, each of the plurality of lattice structures being at an angle between 25 degrees and 45 degrees with respect to a plane normal to the substrate; Including, structure.

12. The structure of claim 11 , wherein the depth of the plurality of grating structures varies from the first end to the second end.

13. 12. The structure of claim 11, wherein the depth of the recessed structure varies in a first direction and a second direction to define a curved shape.

14. 12. The structure of claim 11, wherein each grating structure is between 5 nm and 700 nm deep.

15. 12. The structure of claim 11, wherein the grating layer is formed from an optically transparent material having a refractive index of 1.3 or greater.

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