Patterning of high refractive index glass by plasma etching.

Abstract

To provide favorable patterning of high refractive index glasses by plasma etching.SOLUTION: Plasma etching processes for forming patterns in high refractive index glass substrates, e.g., for use as waveguides, are provided herein. The substrates may be formed of a glass having a refractive index greater than or equal to about 1.65 and containing less than about 50 wt.% of SiO2. The plasma etching processes may include both chemical and physical etching components. In some embodiments, the plasma etching processes can include forming a patterned mask layer on at least a portion of the high refractive index glass substrate and exposing the mask layer and high refractive index glass substrate to plasma to remove the high refractive index glass from the exposed portions of the substrate. Any remaining mask layer is subsequently removed from the high refractive index glass substrate. The removal of the glass forms a desired patterned structure, such as a diffractive grating, in the high refractive index glass substrate.SELECTED DRAWING: Figure 9B

Description

[Technical Field]

[0001] (Priority Claim) This application claims the benefit of priority under 35 U.S.C. § 119(e) to U.S. Provisional Application No. 62 / 442,809, filed January 5, 2017, the entirety of which is incorporated herein by reference.

[0002] (Incorporated by reference) This application incorporates by reference each of the following patent applications in their entirety: U.S. Application No. 14 / 555,585, filed November 27, 2014 (published July 23, 2015 as U.S. Application Publication No. 2015 / 0205126); U.S. Application No. 14 / 690,401, filed April 18, 2015 (published October 22, 2015 as U.S. Application Publication No. 201 No. 5 / 0302652; U.S. Application No. 14 / 212,961, filed March 14, 2014 (now U.S. Patent No. 9,417,452, issued August 16, 2016); and U.S. Application No. 14 / 331,218, filed July 14, 2014 (published October 29, 2015 as U.S. Application Publication No. 2015 / 0309263).

[0003] This disclosure relates to display systems, and more particularly to high-resolution patterning of high refractive index glass for use therein. [Background technology]

[0004] Modern computing and display technology has facilitated the development of systems for so-called "virtual reality" or "augmented reality" experiences, in which digitally reproduced images or portions thereof are presented to a user in a manner that appears or can be perceived as real. Virtual reality, or "VR," scenarios typically involve the presentation of digital or virtual image information without transparency to other actual real-world visual input, while augmented reality, or "AR," scenarios typically involve the presentation of digital or virtual image information as an augmentation to the user's visualization of the real world around them. Mixed reality, or "MR," scenarios are a type of AR scenario that typically involve virtual objects integrated into and responsive to the natural world. For example, MR scenarios may include AR image content that appears blocked by or is perceived to otherwise interact with objects in the real world.

[0005] Referring to FIG. 1 , an augmented reality scene 1 is depicted. A user of AR technology sees a real-world park-like setting 1100 featuring people, trees, a building in the background, and a concrete platform 1120. The user also perceives that they are "seeing" "virtual content," such as a robotic figure 1110 standing on the real-world platform 1120 and a flying, cartoon-like avatar character 1130 that appears to be an anthropomorphic bumblebee. These elements 1130, 1110 are "virtual" in that they do not exist in the real world. Due to the complexity of the human visual perception system, producing AR technology that facilitates a comfortable, natural-feeling, and rich presentation of virtual image elements among other virtual or real-world image elements is challenging.

[0006] The systems and methods disclosed herein address various challenges associated with AR or VR technology. Summary of the Invention [Means for solving the problem]

[0007] According to some aspects, a method for forming one or more diffraction gratings in a waveguide is disclosed. In some embodiments, the method may include providing a waveguide having a refractive index of about 1.65 or greater. In some embodiments, more than 50% by weight of the waveguide is formed from one or more of BO, AlO, ZrO, LiO, NaO, KO, MgO, CaO, SrO, BaO, ZnO, LaO, NbO, TiO, HfO, and SbO. In some embodiments, the method may further include providing a mask layer over the waveguide, the mask layer having a pattern corresponding to the one or more diffraction gratings, the pattern selectively exposing a portion of the waveguide, and anisotropically etching the exposed portion of the waveguide to define the one or more diffraction gratings in the waveguide.

[0008] In some embodiments, providing the mask layer includes providing a pattern comprising a first diffraction grating pattern across a first region of the waveguide and a second diffraction grating pattern in a second region, the second region extending across a majority of the area of the surface of the waveguide. In some embodiments, the first diffraction grating pattern corresponds to an internal coupling optical element, and the second diffraction grating pattern corresponds to an external coupling optical element. In some embodiments, providing the mask layer includes providing a pattern comprising a third diffraction grating pattern across a third region of the waveguide, the third diffraction grating pattern corresponding to an orthogonal pupil expander configured to redirect light from the internal coupling optical element to the upper coupling optical element. In some embodiments, the one or more diffraction gratings comprise substantially parallel lines, each line having a critical dimension less than about 1 micron and an aspect ratio of about 1:10 to about 10:1. In some embodiments, each line has a critical dimension less than about 300 nm.

[0009] According to some aspects, a plasma etching process for forming features in a high refractive index glass substrate is provided. In some embodiments, the process may include providing a patterned mask layer over at least a portion of the high refractive index glass substrate, the substrate being formed from glass having a refractive index of about 1.65 or greater and comprising less than about 50% by weight of SiO2, and exposing the mask layer and the high refractive index glass substrate to a plasma etch comprising chemical and physical etching species to selectively remove the exposed high refractive index glass from the high refractive index glass substrate, thereby etching the features into the substrate.

[0010] In some embodiments, the high refractive index glass substrate comprises less than about 30% SiO2 by weight. In some embodiments, more than 50% by weight of the high refractive index glass substrate is formed from one or more of B2O3, Al2O3, ZrO2, Li2O, Na2O, KO, MgO, CaO, SrO, BaO, ZnO, La2O3, Nb2O5, TiO2, HfO, and Sb2O3. In some embodiments, the high refractive index glass substrate has a refractive index of about 1.70 or greater. In some embodiments, exposing the mask layer and the high refractive index glass substrate to plasma etching includes anisotropically removing the high refractive index glass from exposed surfaces of the high refractive index glass substrate.

[0011] In some embodiments, the plasma is generated in situ in a reaction chamber housing the high refractive index glass substrate. In some embodiments, the source gas comprises SF and Ar gas. In some embodiments, the source gas comprises BCl, HBr, and Ar gas. In some embodiments, the source gas comprises CF, CHF, and Ar gas. In some embodiments, the reaction chamber is the reaction chamber of an inductively coupled plasma (ICP) reactor. In some embodiments, the reaction chamber is the reaction chamber of a dual-frequency ICP reactor. In some embodiments, the features each have a critical dimension less than about 100 nm. In some embodiments, the features each have an aspect ratio of about 1:10 to about 10:1. In some embodiments, the features are sized and spaced to form a diffraction grating. In some embodiments, the mask layer comprises a polymer resist layer. In some embodiments, the process may further include removing the remaining mask layer from the high refractive index glass substrate after exposing the mask layer and the high refractive index glass substrate to the plasma.

[0012] According to some aspects, a process for forming features in a high refractive index glass substrate is provided. In some embodiments, the process may include selectively exposing a portion of the high refractive index glass substrate to a plasma in a reaction chamber to selectively remove high refractive index glass from the high refractive index glass substrate, the high refractive index glass substrate comprising less than about 50% by weight SiO2 and having a refractive index of about 1.65 or greater.

[0013] In some embodiments, the high-index glass substrate comprises one or more of BO, AlO, ZrO, LiO, NaO, KO, MgO, CaO, SrO, BaO, ZnO, LaO, NbO, TiO, HfO, and SbO. In some embodiments, selectively exposing portions of the high-index glass substrate defines a pattern of protrusions in the substrate, the protrusions forming an optical grating. In some embodiments, the process may further include depositing a mask layer on the substrate and patterning the mask layer to define a first set of spaced apart lines in a first region across the substrate and a second set of spaced apart lines in a second region across the substrate, wherein selectively exposing portions of the high-index glass substrate includes etching the substrate through the mask layer to form an optical in-coupling grating in areas of the substrate corresponding to the first regions and an optical out-coupling grating in areas of the substrate corresponding to the second regions. In some embodiments, patterning the mask layer further defines a third set of spaced apart lines in a third region across the substrate, and selectively exposing portions of the high refractive index glass substrate includes etching the substrate through the mask layer to form an orthogonal pupil expander corresponding to the third region.

[0014] According to another aspect, a method for forming an optical waveguide structure is provided. The method includes identifying desired dimensional characteristics of a first feature to be formed in a high-index glass substrate and identifying an etching characteristic of an etching process to be used to form at least the first feature in the high-index glass substrate. Based on the identified etching characteristic, a bias dimensional characteristic is determined for a second feature of a patterned layer to be formed on the high-index glass substrate prior to forming the first feature in the high-index glass substrate. The patterned layer is formed on the high-index glass substrate. Forming the patterned layer includes forming a second feature in the patterned layer, the second feature having the bias dimensional characteristic. The method also includes using an etching process to transfer the pattern of the second feature having the bias dimensional characteristic into the high-index glass, thereby forming a first feature having the desired dimensional characteristic in the high-index glass substrate.

[0015] According to yet another aspect, a method for patterning a glass substrate is provided. The method includes providing an etching mask over a glass substrate formed from glass having a refractive index of 1.65 or greater. Features in the etching mask are larger than a desired size of the corresponding features for defining corresponding features in the glass substrate. The method also includes etching the glass substrate through the etching mask to define the features in the glass substrate. The present invention provides, for example, the following. (Item 1) 1. A method for forming one or more diffraction gratings in a waveguide, the method comprising: providing a waveguide having a refractive index of about 1.65 or greater, wherein greater than 50% by weight of the waveguide is formed from one or more of B2O3, Al2O3, ZrO2, Li2O, Na2O, K2O, MgO, CaO, SrO, BaO, ZnO, La2O3, Nb2O5, TiO2, HfO, and Sb2O3; providing a mask layer over the waveguide, the mask layer having a pattern corresponding to the one or more diffraction gratings, the pattern selectively exposing portions of the waveguide; anisotropically etching the exposed portion of the waveguide to define the one or more diffraction gratings within the waveguide; A method comprising: (Item 2) 2. The method of claim 1, wherein providing a mask layer includes providing a pattern comprising a first diffraction grating pattern across a first region of the waveguide and a second diffraction grating pattern in a second region, the second region extending across a majority of an area of a surface of the waveguide. (Item 3) Item 3. The method of item 2, wherein the first diffraction grating pattern corresponds to an internal coupling optical element and the second diffraction grating pattern corresponds to an external coupling optical element. (Item 4) Item 4. The method of item 3, wherein providing a mask layer includes providing a pattern comprising a third diffraction grating pattern across a third region of the waveguide, the third diffraction grating pattern corresponding to an orthogonal pupil expander configured to redirect light from the inner coupling optical element to an upper coupling optic. (Item 5) Item 10. The method of item 1, wherein the one or more diffraction gratings comprise a plurality of substantially parallel lines, each line having a critical dimension of less than about 1 micron and an aspect ratio of about 1:10 to about 10:1. (Item 6) Item 6. The method of item 5, wherein each line has a critical dimension of less than about 300 nm. (Item 7) Item 6. The method of item 5, wherein the mask layer comprises a lower mask layer and an upper conformal layer of mask layer material. (Item 8) 1. A plasma etching process for forming features in a high refractive index glass substrate, the process comprising: providing a patterned mask layer on at least a portion of the high refractive index glass substrate, the substrate being formed from glass, the glass having a refractive index of about 1.65 or greater and comprising less than about 50% by weight SiO2; etching the features into the substrate by exposing the mask layer and the high index glass substrate to a plasma etch comprising chemical and physical etching species to selectively remove exposed high index glass from the high index glass substrate; The process includes: (Item 9) Item 9. The plasma etching process of item 8, wherein the high refractive index glass substrate comprises less than about 30% SiO2 by weight. (Item 10) Item 9. The plasma etching process of item 8, wherein greater than 50 wt. % of the high refractive index glass substrate is formed from one or more of B2O3, Al2O3, ZrO2, Li2O, Na2O, KO, MgO, CaO, SrO, BaO, ZnO, La2O3, Nb2O5, TiO2, HfO, and Sb2O3. (Item 11) 9. The plasma etching process of claim 8, wherein the high refractive index glass substrate has a refractive index of about 1.70 or greater. (Item 12) 9. The plasma etching process of claim 8, wherein exposing the mask layer and high refractive index glass substrate to plasma etching comprises anisotropically removing high refractive index glass from exposed surfaces of the high refractive index glass substrate. (Item 13) 9. The plasma etching process of claim 8, wherein the plasma is generated in situ in a reaction chamber containing the high refractive index glass substrate. (Item 14) Item 14. The plasma etching process of item 13, wherein the source gas comprises SF6 and Ar gas. (Item 15) Item 14. The plasma etching process of item 13, wherein the source gas comprises BCl3, HBr, and Ar gas. (Item 16) Item 14. The plasma etching process of item 13, wherein the source gas comprises CF4, CHF3, and Ar gas. (Item 17) 9. The plasma etching process of claim 8, wherein the reaction chamber is an inductively coupled plasma (ICP) reactor reaction chamber. (Item 18) Item 18. The plasma etching process of item 17, wherein the reaction chamber is a reaction chamber of a dual frequency ICP reactor. (Item 19) Item 9. The plasma etching process of item 8, wherein the features each have a critical dimension of less than about 100 nm. (Item 20) 20. The plasma etching process of claim 19, wherein each of the features has an aspect ratio of about 1:10 to about 10:1. (Item 21) 20. The plasma etching process of claim 19, wherein the features are sized and spaced to form a diffraction grating. (Item 22) Item 9. The plasma etching process of item 8, wherein the mask layer comprises a polymer resist layer. (Item 23) 9. The plasma etching process of claim 8, further comprising removing the remaining mask layer from the high refractive index glass substrate after exposing the mask layer and the high refractive index glass substrate to the plasma. (Item 24) 1. A process for forming features in a high refractive index glass substrate, the process comprising: selectively exposing a portion of the high refractive index glass substrate to a plasma in a reaction chamber to selectively remove high refractive index glass from the high refractive index glass substrate; Including, The high refractive index glass substrate comprises less than about 50% by weight SiO2 and has a refractive index of about 1.65 or greater. (Item 25) 25. The process of claim 24, wherein the high refractive index glass substrate comprises one or more of B2O3, Al2O3, ZrO2, Li2O, Na2O, K2O, MgO, CaO, SrO, BaO, ZnO, La2O3, Nb2O5, TiO2, HfO, and Sb2O3. (Item 26) Item 25. The process of item 24, wherein selectively exposing portions of the high refractive index glass substrate defines a pattern of protrusions in the substrate, the protrusions forming an optical diffraction grating. (Item 27) depositing a mask layer on the substrate; patterning the mask layer to define a first set of spaced apart lines in a first region across the substrate and a second set of spaced apart lines in a second region across the substrate; further comprising selectively exposing a portion of the high refractive index glass substrate by etching the substrate through the mask layer; an optical incoupling grating in an area of the substrate corresponding to the first region; an optical outcoupling grating in an area of the substrate corresponding to the second region; 27. The process of claim 26, comprising forming (Item 28) patterning the mask layer further defines a third set of spaced apart lines in a third region across the substrate; 28. The process of claim 27, wherein selectively exposing portions of the high refractive index glass substrate comprises etching the substrate through the mask layer to form an orthogonal pupil expander corresponding to the third region. (Item 29) 1. A method of forming an optical waveguide structure, the method comprising: identifying desired dimensional characteristics of a first feature to be formed in a high refractive index glass substrate; identifying an etching characteristic of an etching process used to form at least the first feature in the high refractive index glass substrate; determining bias dimensional characteristics of a second feature of a patterned layer to be formed on the high refractive index glass substrate based on the identified etching characteristics prior to forming the first feature in the high refractive index glass substrate; forming the patterned layer on the high refractive index glass substrate, the forming including forming the second feature in the patterned layer, the second feature having the bias dimensional characteristic; transferring the pattern of the second features having the bias dimensional characteristics into the high refractive index glass using the etching process to form the first features having the desired dimensional characteristics in the high refractive index glass substrate; A method comprising: (Item 30) 1. A method for patterning a glass substrate, the method comprising: providing an etching mask over a glass substrate formed from glass having a refractive index of 1.65 or greater, wherein features in the etching mask for defining corresponding features in the glass substrate are larger than a desired size of the corresponding features; etching the glass substrate through the etch mask to define the features in the glass substrate; A method comprising: (Item 31) Providing an etching mask comprises: forming an initial etching mask; increasing the size of features of the initial etching mask to form the etching mask; Item 31. The method according to Item 30, comprising: (Item 32) Item 32. The method of item 31, wherein the etching mask comprises a resist, and forming the initial etching mask includes imprinting the resist. (Item 33) Item 32. The method of item 31, wherein increasing the size of the features of the initial etching mask comprises depositing a conformal film onto the initial etching mask. (Item 34) Item 31. The method of item 30, wherein the glass substrate comprises less than about 50% by weight of SiO2, and greater than 50% by weight of the high refractive index glass substrate is formed from one or more of B2O3, Al2O3, ZrO2, Li2O, Na2O, KO, MgO, CaO, SrO, BaO, ZnO, La2O3, Nb2O5, TiO2, HfO, and Sb2O3. (Item 35) Item 31. The method of item 30, wherein the etch mask comprises a carbon-based polymer, chromium, or silicon oxide. (Item 36) Item 31. The method of item 30, wherein etching the glass substrate comprises performing ion beam milling to remove material of the glass substrate. (Item 37) Item 37. The method of item 36, wherein etching the glass substrate forms openings having a depth of 50 nm or more in less than 20 seconds. (Item 38) Item 38. The method of item 37, wherein etching the glass substrate forms the opening in less than 10 seconds. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 illustrates a user's view of an augmented reality (AR) device.

[0017] [Figure 2] FIG. 2 illustrates an example of a wearable display system.

[0018] [Figure 3] FIG. 3 illustrates a conventional display system for simulating a three-dimensional image for a user.

[0019] [Figure 4] FIG. 4 illustrates aspects of an approach for simulating a three-dimensional image using multiple depth planes.

[0020] [Figure 5] 5A-5C illustrate the relationship between the radius of curvature and the radius of focus.

[0021] [Figure 6] FIG. 6 illustrates an embodiment of a waveguide stack for outputting image information to a user.

[0022] [Figure 7] FIG. 7 illustrates an example of an output beam output by a waveguide.

[0023] [Figure 8] FIG. 8 illustrates an example of a stacked waveguide assembly in which each depth plane contains an image formed using multiple different primary colors.

[0024] [Figure 9A] FIG. 9A illustrates a cross-sectional side view of an example of a set of stacked waveguides, each containing an internal coupling optical element.

[0025] [Figure 9B] FIG. 9B illustrates a perspective view of the multiple stacked waveguide embodiment of FIG. 9A.

[0026] [Figure 9C] FIG. 9C illustrates a top-down plan view of the multiple stacked waveguide embodiment of FIGS. 9A and 9B.

[0027] [Figure 10] FIG. 10 is a process flow diagram for an example plasma etching process, according to some embodiments.

[0028] [Figure 11A]FIG. 11A illustrates a cross-sectional side view of an embodiment of a glass substrate with an overlying etch mask.

[0029] [Figure 11B] FIG. 11B illustrates a cross-sectional side view of an example of the structure of FIG. 11A undergoing directional etching.

[0030] [Figure 11C] FIG. 11C illustrates a cross-sectional side view of an example structure of FIG. 11B after etching the glass substrate and removing the top etch mask.

[0031] [Figure 12A] FIG. 12A illustrates a cross-sectional side view of another embodiment of an etch mask on top of a glass substrate.

[0032] [Figure 12B] FIG. 12B illustrates a cross-sectional side view of an example of the structure of FIG. 12A after expanding the size of the features of the etch mask.

[0033] [Figure 12C] FIG. 12C illustrates a cross-sectional side view of an example of the structure of FIG. 12B undergoing a directional etch.

[0034] [Figure 12D] FIG. 12D illustrates a cross-sectional side view of an example structure of FIG. 12B after etching the glass substrate and removing the top etch mask. DETAILED DESCRIPTION OF THE INVENTION

[0035] The drawings are provided to illustrate example embodiments described herein and are not intended to limit the scope of the present disclosure. The drawings are not necessarily drawn to scale.

[0036] VR and AR display systems may utilize high-index glass substrates as waveguides for providing image information to a user in the form of light. A high-index substrate provides desirable optical properties, including allowing light to exit the substrate at a wide range of angles and promoting total internal reflection (TIR) of light within the substrate. It should be understood that optical elements may be provided on the surface of the substrate to, for example, incouple light for TIR within the substrate and / or outcouple light to a user. As an example, these optical elements may take the form of a diffraction grating.

[0037] However, etching optical elements such as diffraction gratings directly into the body of a high-refractive-index glass substrate is difficult. Substrate materials with high refractive indexes are difficult to etch, especially at the dimensions desired for optical elements, due to the small amount of silicon oxide in the substrate. However, the optical properties of optical elements depend significantly on the regularity, size, and shape of the elements. Typical wet chemical etching or reactive ion etching has been found to have insufficient high resolution and / or not produce features with sufficiently vertical or straight sidewalls and / or sufficient aspect ratios for use as optical diffraction gratings.

[0038] As a result, a conventional approach to forming such optical elements is to deposit the material to form the optical element on a substrate. For example, the material may be evaporated and patterned. As another example, the optical element may be formed in a separate film that is attached to the substrate. However, such deposition or attachment can be undesirable, add manufacturing complexity, and introduce optical artifacts. For example, the interface between the substrate and the deposited layer or film, and any adhesive layer joining the film to the substrate, can cause reflections, which in turn cause optical artifacts.

[0039] According to some embodiments, the etching process provides high resolution and selectivity while allowing features to be formed directly within the body of the high-index glass substrate. In some embodiments, the etching process is a plasma etching process that includes forming a patterned mask layer on at least a portion of the surface of the high-index glass substrate and exposing the mask layer and the high-index glass substrate to a plasma in a reaction chamber to remove a desired amount of high-index glass from the exposed portion of the surface of the substrate. The removal leaves behind features or structures having a desired pattern. The features may form optical elements, such as diffraction gratings, on the surface of the high-index glass substrate. In some embodiments, any remaining mask layer of material may be removed from the surface of the substrate.

[0040] Preferably, the high-index glass substrate has a refractive index of about 1.65 or greater or 1.75 or greater and less than about 50% by weight of SiO2. In some embodiments, greater than 50% by weight of the substrate is formed from one or more of B2O3, Al2O3, ZrO2, Li2O, Na2O, KO, MgO, CaO, SrO, BaO, ZnO, La2O3, Nb2O5, TiO2, HfO, and Sb2O3. In some embodiments, the plasma etching is performed using very high frequency (VHF) inductively coupled plasma (ICP). In some embodiments, the VHF power is in the range of 10-2500 W and the RF power is in the range of 10-500 W. Preferably, the etching process includes both chemical and physical etching components. In some embodiments, the etching chemistry includes one or more halogen-containing compounds and one or more inert gases. Examples of halogen-containing compounds include CF, CHF, SF, O, Cl, BCl, and HBr, and examples of inert gases include Ar, He, and N. The plasma may be conducted at a temperature in the range of -150 to 50°C.

[0041] In some embodiments, features having critical dimensions of about 10 to 500 nm, including about 10 to 100 nm, may be etched into high refractive index glass substrates and may have aspect ratios in the range of about 1:10 to about 10:1. Additionally, the etched features may have substantially straight sidewalls. In some embodiments, these features may be utilized in various applications, such as optical applications, including as waveguides for VR and AR display systems. For example, the etched features may form internal coupling optical elements, external coupling optical elements, or light dispersive elements. In some embodiments, the plasma etching process may be utilized to etch any desired pattern into high refractive index glass substrates for other applications where high-resolution patterning is desired.

[0042] Advantageously, plasma etching processes, according to some embodiments, enable high-resolution patterning and etching of high-index glass substrates, forming features directly into the body of the substrate. The ability to directly etch the substrate can simplify the manufacture of devices utilizing such features by eliminating the need to separately form and attach a film containing the features to the substrate. In some embodiments, optical performance can be improved by eliminating the presence of interfaces formed by separately attaching a film.

[0043] In some embodiments, an etch mask used to pattern an underlying high-refractive index glass substrate may be biased, with etch mask features having dimensional characteristics that compensate for the characteristics of the etchant used to etch the pattern into the substrate. For example, the size of the features in the etch mask may be larger (e.g., wider and / or taller) than the desired size of the features to be etched into the substrate, thereby compensating for the etching of the etch mask itself over the course of etching the substrate, such that the features formed in the substrate are of the desired size, even with the etching of the mask itself. In some embodiments, the features in the etch mask may be patterned with sizes larger than the desired size of the features in the substrate. In some other embodiments, the size of the features in the etch mask may be increased by depositing a layer of material to augment the features and / or chemically react with the features to increase their size. In some embodiments, the substrate may be patterned through the etch mask using plasma-based etching as disclosed herein. In some other embodiments, the substrate may be patterned using ion beam milling. Advantageously, a biased etch mask precisely forms features of the desired dimensions while facilitating high-speed patterning of high-refractive index glass substrates.

[0044] Reference is now made to the drawings, wherein like reference numerals refer to like features throughout. Exemplary Display Systems

[0045] FIG. 2 illustrates an example of a wearable display system 80 in which an etched high-index glass substrate may be incorporated. The display system 80 includes a display 62 and various mechanical and electronic modules and systems to support the functionality of the display 62. The display 62 may be coupled to a frame 64, which is wearable by a display system user or viewer 60 and configured to position the display 62 directly in front of the user's 60 eyes. The display 62 may, in some embodiments, be considered eyewear. In some embodiments, a speaker 66 is coupled to the frame 64 and positioned adjacent to the user's 60 ear canal (another speaker, not shown, may optionally be positioned adjacent the user's other ear canal to provide stereo / adjustable sound control). The display system may also include one or more microphones 67 or other devices to detect sound. In some embodiments, the microphone may be configured to allow a user to provide input or commands (e.g., voice menu command selections, natural language questions, etc.) to the system 80 and / or enable audio communication with other persons (e.g., other users of similar display systems).

[0046] 2, the display 62 is operatively coupled by a communications link 68, such as a wired lead or wireless connectivity, to a local data processing module 70, which may be mounted in a variety of configurations, such as fixedly attached to the frame 64, fixedly attached to a helmet or hat worn by the user, built into headphones, or otherwise removably attached to the user 60 (e.g., in a backpack-style configuration, in a belt-coupled configuration). The local processing and data module 70 may include a hardware processor and digital memory, such as non-volatile memory (e.g., flash memory or a hard disk drive), both of which may be utilized to aid in processing, caching, and storing data. The data includes a) data captured from sensors (e.g., which may be operatively coupled to frame 64 or otherwise attached to user 60), such as image capture devices (such as cameras), microphones, inertial measurement units, accelerometers, compasses, GPS units, wireless devices, gyroscopes, and / or other sensors disclosed herein, and / or b) data obtained and / or processed using a remote processing module 72 and / or a remote data repository 74 (including data related to the virtual content), possibly for processing or retrieval and passage to display 62. The local processing and data module 70 may be operatively coupled to the remote processing module 72 and the remote data repository 74 by communication links 76, 78, such as via wired or wireless communication links, such that these remote modules 72, 74 are operatively coupled to each other and available as resources to the local processing and data module 70. In some embodiments, the local processing and data module 70 may include one or more of an image capture device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a wireless device, and / or a gyroscope.In some other embodiments, one or more of these sensors may be mounted on the frame 64 or may be stand-alone structures that communicate with the local processing and data module 70 via wired or wireless communication paths.

[0047] 2 , in some embodiments, remote processing module 72 may comprise one or more processors configured to analyze and process data and / or image information. In some embodiments, remote data repository 74 may comprise a digital data storage facility, which may be available through the Internet or other networking configuration in a “cloud” resource configuration. In some embodiments, remote data repository 74 may include one or more remote servers, which provide information, e.g., information for generating augmented reality content, to local processing and data module 70 and / or remote processing module 72. In some embodiments, all data is stored and all calculations are performed in the local processing and data module, allowing for fully autonomous use from the remote module.

[0048] Referring now to FIG. 3, the perception of an image as being “three-dimensional” or “3-D” may be achieved by providing a slightly different presentation of the image to each eye of a viewer. FIG. 3 illustrates a conventional display system for simulating a three-dimensional image for a user. Two distinct images 5, 7 (one for each eye 4, 6) are output to the user. The images 5, 7 are spaced from the eyes 4, 6 by a distance 10 along an optical axis, or z-axis, parallel to the viewer's line of sight. The images 5, 7 are flat, and the eyes 4, 6 can focus on the images by assuming a single accommodation state. Such a system relies on the human visual system to combine the images 5, 7 and provide the perception of depth and / or scale for the combined image.

[0049] However, it will be appreciated that the human visual system is more complex and providing a realistic perception of depth is more difficult. For example, many viewers of conventional “3-D” display systems find such systems uncomfortable or may not perceive any sense of depth at all. Without being limited by theory, it is believed that viewers of an object may perceive the object as “three-dimensional” due to a combination of vergence and accommodation. Vergence of the two eyes relative to one another (i.e., rotation of the eyes such that the pupils move toward or away from one another, converging the lines of sight of the eyes, and fixating on an object) is closely linked to the focusing (or “accommodation”) of the eye lenses and pupils. Under normal conditions, a change in the focus of the eye lenses or accommodation of the eye to change focus from one object to another at a different distance will automatically produce a matching change in vergence at the same distance, a relationship known as the “accommodation-vergence reflex” and pupil dilation or constriction. Similarly, changes in vergence-divergence will induce matching changes in accommodation in lens shape and pupil size under normal conditions. As described herein, many stereoscopic, or "3-D," display systems display a scene to each eye using slightly different presentations (and therefore slightly different images) so that a three-dimensional perspective is perceived by the human visual system. However, such systems are uncomfortable for many viewers because, among other things, they simply provide different presentations of the scene but counter the "accommodation-vergence-divergence reflex," in which the eyes view all image information in a single accommodation state. Display systems that provide better matching between accommodation and vergence-divergence create more realistic and comfortable simulations of three-dimensional images.

[0050] FIG. 4 illustrates aspects of an approach for simulating a three-dimensional image using multiple depth planes. Referring to FIG. 4 , objects at various distances from the eyes 4, 6 on the z-axis are accommodated by the eyes 4, 6 so that the objects are in focus. The eyes (4 and 6) assume particular accommodated states, focusing objects at different distances along the z-axis. Consequently, a particular accommodated state may be said to be associated with a particular one of the depth planes 14, having an associated focal length, such that an object or portion of an object at that particular depth plane is in focus when the eye is in the accommodated state for that depth plane. In some embodiments, a three-dimensional image may be simulated by providing a different presentation of an image to each of the eyes 4, 6, and also by providing a different presentation of an image corresponding to each of the depth planes. While shown as separate for clarity of illustration, it will be understood that the fields of view of the eyes 4, 6 may overlap, for example, as the distance along the z-axis increases. Additionally, although shown as flat for ease of illustration, it will be understood that the contour of the depth plane may be curved in physical space so that all features within the depth plane are in focus with the eye in a particular accommodated state.

[0051] The distance between an object and eye 4 or 6 can also change the amount of light emitted from the object as viewed by that eye. Figures 5A-5C illustrate the relationship between distance and light ray divergence. The distance between an object and eye 4 is represented in the order of decreasing distances R1, R2, and R3. As shown in Figures 5A-5C, light rays become more divergent as the distance to the object decreases. As the distance increases, the light rays become more collimated. In other words, the light field generated by a point (an object or part of an object) can be said to have a spherical wavefront curvature that is a function of the distance the point is from the user's eye. As the curvature increases, the distance between the object and eye 4 decreases. As a result, the degree of divergence of light rays also varies at different depth planes, and the degree of divergence increases as the distance between the depth plane and the viewer's eye 4 decreases. Although only a single eye 4 is shown in Figures 5A-5C and other figures herein for clarity of illustration, it will be understood that the discussion regarding eye 4 may apply to both eyes 4 and 6 of the viewer.

[0052] Without being limited by theory, it is believed that the human eye can typically interpret a finite number of depth planes to provide depth perception. As a result, a highly realistic simulation of perceived depth can be achieved by providing the eye with different representations of images corresponding to each of these limited number of depth planes. The different representations can be focused separately by the viewer's eyes, thereby serving to provide depth cues to the user based on the ocular accommodation required to focus on different image features for a scene located on different depth planes and / or based on the observation of different image features on different depth planes that are out of focus.

[0053] FIG. 6 illustrates an example of a waveguide stack for outputting image information to a user. Display system 1000 includes a stack of waveguides or stacked waveguide assembly 178 that can be utilized to provide a three-dimensional perception to the eye / brain using multiple waveguides 182, 184, 186, 188, 190. In some embodiments, display system 1000 is system 80 of FIG. 2 , and FIG. 6 diagrammatically illustrates some portions of system 80 in greater detail. For example, waveguide assembly 178 may be part of display 62 of FIG. 2 . It will be understood that display system 1000 may, in some embodiments, be considered a light field display.

[0054] Continuing with reference to FIG. 6 , the waveguide assembly 178 may also include multiple features 198, 196, 194, 192 between the waveguides. In some embodiments, the features 198, 196, 194, 192 may be one or more lenses. The waveguides 182, 184, 186, 188, 190 and / or multiple lenses 198, 196, 194, 192 may be configured to transmit image information to the eye using various levels of wavefront curvature or ray divergence. Each waveguide level may be associated with a particular depth plane and configured to output image information corresponding to that depth plane. Image injection devices 200, 202, 204, 206, 208 may act as light sources for the waveguides and may be utilized to inject image information into waveguides 182, 184, 186, 188, 190, each configured to distribute incident light across each individual waveguide for output toward eye 4, as described herein. Light exits output surfaces 300, 302, 304, 306, 308 of image injection devices 200, 202, 204, 206, 208 and is injected into corresponding input surfaces 382, 384, 386, 388, 390 of waveguides 182, 184, 186, 188, 190. In some embodiments, each input surface 382, 384, 386, 388, 390 may be an edge of the corresponding waveguide or may be a portion of a major surface of the corresponding waveguide (i.e., one or both of the waveguide surfaces that directly face the world 144 or the viewer's eye 4). In some embodiments, a single beam of light (e.g., a collimated beam) may be launched into each waveguide, outputting a total field of cloned collimated beams that are directed toward the eye 4 at a particular angle (and divergence) corresponding to the depth plane associated with the particular waveguide. In some embodiments, a single one of the image launch devices 200, 202, 204, 206, 208 may be associated with and launch light into multiple (e.g., three) waveguides 182, 184, 186, 188, 190.

[0055] In some embodiments, image input devices 200, 202, 204, 206, 208 are each discrete displays that generate image information for input into their respective corresponding waveguides 182, 184, 186, 188, 190. In some other embodiments, image input devices 200, 202, 204, 206, 208 are outputs of a single multiplexed display that may, for example, send image information to each of image input devices 200, 202, 204, 206, 208 via one or more optical conduits (such as fiber optic cables). It should be understood that the image information provided by image input devices 200, 202, 204, 206, 208 may include light of different wavelengths or colors (e.g., different primary colors, as discussed herein).

[0056] In some embodiments, the light injected into the waveguides 182, 184, 186, 188, 190 is provided by a light projector system 2000, which includes a light module 2040, which may include a light emitter such as a light emitting diode (LED). The light from the light module 2040 may be directed and modified by a light modulator 2030, e.g., a spatial light modulator, via a beam splitter 2050. The light modulator 2030 may be configured to vary the perceived intensity of the light injected into the waveguides 182, 184, 186, 188, 190. Examples of spatial light modulators include liquid crystal displays (LCDs), including liquid crystal on silicon (LCOS) displays.

[0057] In some embodiments, display system 1000 may be a scanning fiber display comprising one or more scanning fibers configured to project light in various patterns (e.g., raster scan, spiral scan, Lissajous pattern, etc.) into one or more waveguides 182, 184, 186, 188, 190 and ultimately to a viewer's eye 4. In some embodiments, the illustrated image injection devices 200, 202, 204, 206, 208 may diagrammatically represent a single scanning fiber or a bundle of scanning fibers configured to inject light into one or more waveguides 182, 184, 186, 188, 190. In some other embodiments, the illustrated image injection devices 200, 202, 204, 206, 208 may diagrammatically represent multiple scanning fibers or multiple bundles of scanning fibers, each configured to inject light into an associated one of waveguides 182, 184, 186, 188, 190. It should be understood that one or more optical fibers may be configured to transmit light from the optical module 2040 to one or more waveguides 182, 184, 186, 188, 190. It should be understood that one or more intervening optical structures may be provided between the scanning fiber(s) and one or more waveguides 182, 184, 186, 188, 190, for example, to redirect light exiting the scanning fiber into one or more waveguides 182, 184, 186, 188, 190.

[0058] The controller 210 controls the operation of one or more of the stacked waveguide assemblies 178, including the operation of the image input devices 200, 202, 204, 206, 208, the light source 2040, and the light modulator 2030. In some embodiments, the controller 210 is part of the local data processing module 70. The controller 210 includes programming (e.g., instructions in a non-transitory medium) that coordinates the timing and provision of image information to the waveguides 182, 184, 186, 188, 190, for example, according to any of the various schemes disclosed herein. In some embodiments, the controller may be a single integrated device or a distributed system connected by a wired or wireless communication channel. The controller 210 may, in some embodiments, be part of the processing module 70 or 72 (FIG. 1).

[0059] Continuing with reference to FIG. 6 , the waveguides 182, 184, 186, 188, and 190 may be configured to propagate light within each individual waveguide by total internal reflection (TIR). Each of the waveguides 182, 184, 186, 188, and 190 may be planar or have another shape (e.g., curved) with major top and bottom surfaces and edges extending between the major top and bottom surfaces. In the illustrated configuration, the waveguides 182, 184, 186, 188, and 190 may each include outcoupling optical elements 282, 284, 286, 288, and 290 configured to extract light from the waveguides by redirecting the light, causing it to propagate within each individual waveguide, and outputting image information from the waveguides to the eye 4. The extracted light may also be referred to as outcoupling light, and the outcoupling optical element light may also be referred to as a light extraction optical element. The extracted beams of light are output by the waveguides at locations where light propagating within the waveguides strikes the light-extraction optical elements. The outcoupling optical elements 282, 284, 286, 288, 290 may be gratings, for example, including diffractive optical features, as discussed further herein. While shown disposed on the bottom major surfaces of the waveguides 182, 184, 186, 188, 190 for ease of explanation and clarity of drawing, in some embodiments, the outcoupling optical elements 282, 284, 286, 288, 290 may be disposed on the top and / or bottom major surfaces and / or directly within the volume of the waveguides 182, 184, 186, 188, 190, as discussed further herein. In some embodiments, the outcoupling optical elements 282, 284, 286, 288, 290 may be formed within a layer of material that is attached to a transparent substrate and forms the waveguides 182, 184, 186, 188, 190. In some other embodiments, the waveguides 182, 184, 186, 188, 190 may be monolithic material components, and the outcoupling optical elements 282, 284, 286, 288, 290 may be formed on and / or within the material components.

[0060] Continuing with reference to FIG. 6 , as discussed herein, each waveguide 182, 184, 186, 188, 190 is configured to output light and form an image corresponding to a particular depth plane. For example, the waveguide 182 closest to the eye may be configured to deliver collimated light (injected into such waveguide 182) to the eye 4. The collimated light may represent an optical infinity focal plane. The next upper waveguide 184 may be configured to send collimated light that passes through a first lens 192 (e.g., a negative lens) before reaching the eye 4. Such first lens 192 may be configured to generate a slight convex wavefront curvature so that the eye / brain interprets light emerging from the next upper waveguide 184 as emerging from a first focal plane closer inward from optical infinity toward the eye 4. Similarly, the third upper waveguide 186 passes its output light through both the first lens 192 and the second lens 194 before reaching the eye 4. The combined refractive power of the first lens 192 and the second lens 194 may be configured to produce another, increasing amount of wavefront curvature such that the eye / brain interprets the light emerging from the third waveguide 186 as originating from a second focal plane that is closer inward from optical infinity towards the person than was the light from the next upper waveguide 184.

[0061] The other waveguide layers 188, 190 and lenses 196, 198 are similarly configured, with the highest waveguide 190 in the stack sending its output through all of the lenses between it and the eye for a collective focal power representing the focal plane closest to the person. To compensate for the stack of lenses 198, 196, 194, 192 when viewing / interpreting light originating from the world 144 on the other side of the stacked waveguide assembly 178, a compensating lens layer 180 may be placed on top of the stack to compensate for the collective power of the lower lens stacks 198, 196, 194, 192. Such a configuration provides as many perceived focal planes as there are available waveguide / lens pairs. Both the outcoupling optical elements of the waveguides and the focusing sides of the lenses may be static (i.e., not dynamic or electro-active). In some alternative embodiments, one or both may be dynamic using electro-active features.

[0062] In some embodiments, two or more of the waveguides 182, 184, 186, 188, 190 may have the same associated depth plane. For example, multiple waveguides 182, 184, 186, 188, 190 may be configured to output images set at the same depth plane, or multiple subsets of the waveguides 182, 184, 186, 188, 190 may be configured to output images set at the same depth planes, with one set per depth plane. This may provide the advantage of forming tiled images to provide an extended field of view at those depth planes.

[0063] Continuing with reference to FIG. 6 , the outcoupling optical elements 282, 284, 286, 288, and 290 may be configured to redirect light from their respective waveguides and output the light with an appropriate amount of divergence or collimation for a particular depth plane associated with the waveguide. As a result, waveguides with different associated depth planes may have different configurations of outcoupling optical elements 282, 284, 286, 288, and 290, which output light with different amounts of divergence depending on the associated depth plane. In some embodiments, the light-extraction optical elements 282, 284, 286, 288, and 290 may be volume or surface features, which may be configured to output light at specific angles. For example, the light-extraction optical elements 282, 284, 286, 288, and 290 may be volume holograms, surface holograms, and / or diffraction gratings. In some embodiments, features 198, 196, 194, 192 may not be lenses. Rather, they may simply be spacers (e.g., cladding layers and / or structures for forming air gaps).

[0064] In some embodiments, the outcoupling optical elements 282, 284, 286, 288, 290 are diffractive features that form a diffraction pattern or "diffractive optical element" (also referred to herein as a "DOE"). Preferably, the DOE has a sufficiently low diffraction efficiency so that only a portion of the light in the beam is deflected toward the eye 4 at each intersection of the DOE, while the remainder continues traveling through the waveguide via total internal reflection. The light carrying the image information is thus split into several related output beams that exit the waveguide at various locations, resulting in a very uniform pattern of output emission toward the eye 4 for this particular collimated beam bouncing within the waveguide.

[0065] In some embodiments, one or more DOEs may be switchable between an "on" state in which they actively diffract and an "off" state in which they do not significantly diffract. For example, a switchable DOE may comprise a layer of polymer-dispersed liquid crystal in which microdroplets comprise a diffractive pattern in a host medium, and the refractive index of the microdroplets may be switched to substantially match the refractive index of the host material (in which case the pattern does not significantly diffract incident light), or the microdroplets may be switched to a refractive index that does not match that of the host medium (in which case the pattern actively diffracts incident light).

[0066] In some embodiments, a camera assembly 500 (e.g., a digital camera, including visible and infrared light cameras) is provided to capture images of the eye 4 and / or tissue surrounding the eye 4 and may detect, for example, user input. As used herein, a camera may be any image capture device. In some embodiments, the camera assembly 500 may include an image capture device and a light source that projects light (e.g., infrared light) onto the eye, which may then be reflected by the eye and detected by the image capture device. In some embodiments, the camera assembly 500 may be mounted to the frame 64 ( FIG. 2 ) and may be in electrical communication with processing modules 70 and / or 72, which may process image information from the camera assembly 500. In some embodiments, one camera assembly 500 may be utilized for each eye, monitoring each eye separately.

[0067] 7, an example of an output beam output by a waveguide is shown. While one waveguide is illustrated, it should be understood that other waveguides in waveguide assembly 178 (FIG. 6) may function similarly, and that waveguide assembly 178 includes multiple waveguides. Light 400 is launched into waveguide 182 at input surface 382 of waveguide 182 and propagates within waveguide 182 by TIR. At the point where light 400 impinges on DOE 282, a portion of the light exits the waveguide as output beam 402. Output beam 402 is illustrated as being approximately parallel, but may be redirected to propagate to eye 4 at an angle (e.g., forming a diverging output beam), as discussed herein and depending on the depth plane associated with waveguide 182. It should be understood that a nearly collimated exit beam may refer to a waveguide with outcoupling optics that outcouples light to form an image that appears to be set at a depth plane at a large distance (e.g., optical infinity) from the eye 4. Other waveguides or other sets of outcoupling optics may output a more divergent exit beam pattern, which would require the eye 4 to accommodate to a closer distance and focus on the retina, and would be interpreted by the brain as light from a distance closer to the eye 4 than optical infinity.

[0068] In some embodiments, a full-color image may be formed at each depth plane by overlaying an image in each of the primary colors, for example, three or more primary colors. FIG. 8 illustrates an example of a stacked waveguide assembly, with each depth plane including an image formed using multiple different primary colors. The illustrated embodiment shows depth planes 14a-14f, but more or fewer depths are also contemplated. Each depth plane may have three or more primary color images associated with it, i.e., a first image in a first color G, a second image in a second color R, and a third image in a third color B. Different depth planes are indicated in the diagram by different numbers for diopters (dpt) following the letters G, R, and B. By way of example only, the number following each of these letters indicates the diopter (1 / m), i.e., the inverse distance of the depth plane from the viewer, and each box in the diagram represents an individual primary color image. In some embodiments, the exact locations of the depth planes for the different primary colors may vary to account for differences in the eye's focusing of light of different wavelengths. For example, different primary color images for a given depth plane may be placed on depth planes corresponding to different distances from the user. Such an arrangement may increase visual acuity and user comfort.

[0069] In some embodiments, light for each primary color may be output by a single dedicated waveguide, such that each depth plane may have multiple waveguides associated with it. In such embodiments, each box in the diagram containing the letter G, R, or B may be understood to represent an individual waveguide, and three waveguides may be provided per depth plane, resulting in three primary color images per depth plane. While the waveguides associated with each depth plane are shown adjacent to each other in this drawing for ease of illustration, it should be understood that in a physical device, the waveguides may all be arranged in a stack with one waveguide per level. In some other embodiments, multiple primary colors may be output by the same waveguide, such that, for example, only a single waveguide may be provided per depth plane.

[0070] 8, in some embodiments, G is green, R is red, and B is blue. In some other embodiments, other colors associated with other wavelengths of light, including magenta and cyan, may be used in addition to or replace one or more of red, green, or blue.

[0071] It should be appreciated that references to a given color of light throughout this disclosure will be understood to encompass light of one or more wavelengths within the range of wavelengths of light that are perceived by a viewer to be of that given color. For example, red light may include one or more wavelengths of light within a range of about 620-780 nm, green light may include one or more wavelengths of light within a range of about 492-577 nm, and blue light may include one or more wavelengths of light within a range of about 435-493 nm.

[0072] Referring now to FIG. 9A , in some embodiments, light impinging on a waveguide may need to be redirected to incoupling the light into the waveguide. An incoupling optical element may be used to redirect and incoupling the light into its corresponding waveguide. FIG. 9A illustrates a cross-sectional side view of an example of a plurality or set 1200 of stacked waveguides, each including an incoupling optical element. The waveguides may each be configured to output light of one or more different wavelengths or one or more different wavelength ranges. While stack 1200 may correspond to stack 178 ( FIG. 6 ), and the illustrated waveguides of stack 1200 may correspond to a portion of multiple waveguides 182, 184, 186, 188, 190, it should be understood that light from one or more of image injection devices 200, 202, 204, 206, 208 is injected into the waveguide from a location requiring the light to be redirected for incoupling.

[0073] The illustrated set 1200 of stacked waveguides includes waveguides 1210, 1220, and 1230. Each waveguide includes an associated internal coupling optical element (which may also be referred to as the light input area on the waveguide), for example, internal coupling optical element 1212 is disposed on a major surface (e.g., the top major surface) of waveguide 1210, internal coupling optical element 1222 is disposed on a major surface (e.g., the top major surface) of waveguide 1220, and internal coupling optical element 1232 is disposed on a major surface (e.g., the top major surface) of waveguide 1230. In some embodiments, one or more of the internal coupling optical elements 1212, 1222, 1232 may be disposed on the bottom major surface of the respective waveguides 1210, 1220, 1230 (particularly, one or more of the internal coupling optical elements is a reflective polarizing optical element). As shown, the internal coupling optical elements 1212, 1222, 1232 may be disposed on the upper major surface of their respective waveguides 1210, 1220, 1230 (or on top of the next lower waveguide), and in particular, the internal coupling optical elements are transmissive turning optical elements. In some embodiments, the internal coupling optical elements 1212, 1222, 1232 may be disposed within the body of the respective waveguides 1210, 1220, 1230. In some embodiments, as discussed herein, the internal coupling optical elements 1212, 1222, 1232 are wavelength selective such that they selectively redirect one or more wavelengths of light while transmitting other wavelengths of light. Although illustrated on one side or corner of the respective waveguides 1210, 1220, 1230, it should be understood that the internal coupling optical elements 1212, 1222, 1232 may be located within other areas of the respective waveguides 1210, 1220, 1230 in some embodiments.

[0074] As shown, the in-coupling optical elements 1212, 1222, 1232 may be laterally offset from one another. In some embodiments, each in-coupling optical element may be offset to receive light without that light passing through another in-coupling optical element. For example, each in-coupling optical element 1212, 1222, 1232 may be configured to receive light from a different image input device 1213, 1223, 1233 and may be separated (e.g., laterally spaced) from the other in-coupling optical elements 1212, 1222, 1232 so as to substantially not receive light from others of the in-coupling optical elements 1212, 1222, 1232.

[0075] Each waveguide also includes an associated optically dispersive element, for example, optically dispersive element 1214 is disposed on a major surface (e.g., the top major surface) of waveguide 1210, optically dispersive element 1224 is disposed on a major surface (e.g., the top major surface) of waveguide 1220, and optically dispersive element 1234 is disposed on a major surface (e.g., the top major surface) of waveguide 1230. In some other embodiments, optically dispersive elements 1214, 1224, 1234 may be disposed on the bottom major surfaces of the associated waveguides 1210, 1220, 1230, respectively. In some other embodiments, the optically dispersive elements 1214, 1224, 1234 may be disposed on both the top and bottom major surfaces of the associated waveguides 1210, 1220, 1230, respectively, or the optically dispersive elements 1214, 1224, 1234 may be disposed on different ones of the top and bottom major surfaces in different associated waveguides 210, 1220, 1230, respectively.

[0076] Waveguides 1210, 1220, 1230 may be spaced apart and separated, for example, by gas, liquid, and / or solid layers of material. For example, as shown, layer 1218a may separate waveguides 1210 and 1220, and layer 1218b may separate waveguides 1220 and 1230. In some embodiments, layers 1218a and 1218b are formed from a low refractive index material (i.e., a material having a lower refractive index than the material forming the immediately adjacent ones of waveguides 1210, 1220, 1230). Preferably, the refractive index of the material forming layers 1218a, 1218b is less than the refractive index of the material forming waveguides 1210, 1220, 1230 by 0.05 or more, or 0.10 or more. Advantageously, the lower refractive index layers 1218a, 1218b may function as cladding layers that promote total internal reflection (TIR) of light through the waveguides 1210, 1220, 1230 (e.g., TIR between the top and bottom major surfaces of each waveguide). In some embodiments, the layers 1218a, 1218b are formed from air. Although not shown, it should be understood that the top and bottom of the illustrated set of waveguides 1200 may include immediate cladding layers.

[0077] Preferably, for ease of manufacturing and other considerations, the materials forming the waveguides 1210, 1220, 1230 are similar or the same, and the materials forming the layers 1218a, 1218b are similar or the same. In some embodiments, the materials forming the waveguides 1210, 1220, 1230 may differ between one or more waveguides, and / or the materials forming the layers 1218a, 1218b may differ while still maintaining the various refractive index relationships discussed above.

[0078] 9A, light rays 1240, 1242, 1244 enter waveguide set 1200. It should be understood that light rays 1240, 1242, 1244 may be injected into waveguides 1210, 1220, 1230 by one or more image injection devices 200, 202, 204, 206, 208 (FIG. 6).

[0079] In some embodiments, light rays 1240, 1242, 1244 have different properties, e.g., different wavelengths or different wavelength ranges, which may correspond to different colors. Each of the in-coupling optical elements 1212, 1222, 1232 deflects incident light such that the light propagates through a respective one of the waveguides 1210, 1220, 1230 by TIR. In some embodiments, each of the in-coupling optical elements 1212, 1222, 1232 selectively deflects light of one or more particular wavelengths while transmitting other wavelengths to the underlying waveguide and associated in-coupling optical element.

[0080] For example, internal coupling optical element 1212 may be configured to deflect light ray 1240, having a first wavelength or range of wavelengths, while transmitting light rays 1242 and 1244, having different second and third wavelengths or ranges of wavelengths, respectively. Transmitted light ray 1242 then impinges on and is deflected by internal coupling optical element 1222, which is configured to selectively deflect light of the second wavelength or range of wavelengths. Light ray 1244 is transmitted by internal coupling optical element 1222 and continues to impinge on and be deflected by internal coupling optical element 1232, which is configured to selectively deflect light of a third wavelength or range of wavelengths.

[0081] 9A , the deflected light rays 1240, 1242, 1244 are deflected to propagate through the corresponding waveguides 1210, 1220, 1230. That is, the in-coupling optical element 1212, 1222, 1232 of each waveguide deflects the light into its corresponding waveguide 1210, 1220, 1230, in-coupling the light into the corresponding waveguide. The light rays 1240, 1242, 1244 are deflected at an angle that causes the light to propagate through the respective waveguides 1210, 1220, 1230 by TIR. The light rays 1240, 1242, 1244 propagate through the respective waveguides 1210, 1220, 1230 by TIR until they impinge on the corresponding optical dispersive element 1214, 1224, 1234 of the waveguide.

[0082] 9B, a perspective view of the multiple stacked waveguide embodiment of FIG. 9A is illustrated. As previously described, the in-coupled light rays 1240, 1242, and 1244 are deflected by the in-coupling optical elements 1212, 1222, and 1232, respectively, and then propagate by TIR within the waveguides 1210, 1220, and 1230, respectively. The light rays 1240, 1242, and 1244 then impinge on the optically dispersive elements 1214, 1224, and 1234, respectively. The optically dispersive elements 1214, 1224, and 1234 deflect the light rays 1240, 1242, and 1244 to propagate toward the out-coupling optical elements 1250, 1252, and 1254, respectively.

[0083] In some embodiments, the optically dispersive elements 1214, 1224, 1234 are orthogonal pupil expanders (OPEs). In some embodiments, the OPEs both deflect or disperse light into the out-coupling optical elements 1250, 1252, 1254 and increase the beam or spot size of this light as it propagates through the out-coupling optical elements. In some embodiments, for example, if the beam size is already the desired size, the optically dispersive elements 1214, 1224, 1234 may be omitted and the in-coupling optical elements 1212, 1222, 1232 may be configured to deflect light directly into the out-coupling optical elements 1250, 1252, 1254. For example, with reference to FIG. 9A , the optically dispersive elements 1214, 1224, 1234 may be replaced with the out-coupling optical elements 1250, 1252, 1254, respectively. In some embodiments, the outcoupling optical elements 1250, 1252, 1254 are exit pupils (EP) or exit pupil expanders (EPE) that direct light into the viewer's eye 4 (FIG. 7).

[0084] 9A and 9B, in some embodiments, a waveguide set 1200 includes, for each primary color, waveguides 1210, 1220, 1230, in-coupling optical elements 1212, 1222, 1232, optically dispersive elements (e.g., OPEs) 1214, 1224, 1234, and out-coupling optical elements (e.g., EPs) 1250, 1252, 1254. The waveguides 1210, 1220, 1230 may be stacked with an air gap / cladding layer between each one. The in-coupling optical elements 1212, 1222, 1232 redirect or deflect incident light into that waveguide (different in-coupling optical elements receive light of different wavelengths). The light then propagates at an angle that will result in TIR within the individual waveguides 1210, 1220, 1230. In the example shown, light ray 1240 (e.g., blue light) is deflected by the first in-coupling optical element 1212 in the manner previously described, then continues bouncing back down the waveguide, interacting with the optically dispersive element (e.g., OPE) 1214 and then the out-coupling optical element (e.g., EP) 1250. Light rays 1242 and 1244 (e.g., green and red light, respectively) pass through the waveguide 1210, and light ray 1242 will encounter and be deflected by the in-coupling optical element 1222. Light ray 1242 then travels via TIR back down the waveguide 1220, bouncing back down its optically dispersive element (e.g., OPE) 1224 and then to the out-coupling optical element (e.g., EP) 1252. Finally, light ray 1244 (e.g., red light) passes through waveguide 1220 and impinges on light in-coupling optical element 1232 of waveguide 1230. Light in-coupling optical element 1232 deflects light ray 1244 such that it propagates by TIR to light dispersive element (e.g., OPE) 1234 and then by TIR to out-coupling optical element (e.g., EP) 1254. Out-coupling optical element 1254 then finally out-couples light ray 1244 to a viewer, who also receives light out-coupled from the other waveguides 1210, 1220.

[0085] FIG. 9C illustrates a top-down plan view of the multiple stacked waveguide embodiment of FIGS. 9A and 9B. As shown, waveguides 1210, 1220, 1230 may be vertically aligned, along with each waveguide's associated optically dispersive element 1214, 1224, 1234 and associated external coupling optical elements 1250, 1252, 1254. However, as discussed herein, internal coupling optical elements 1212, 1222, 1232 are not vertically aligned. Rather, the internal coupling optical elements are preferably non-overlapping (e.g., laterally spaced apart, as seen in the top-down view). As discussed further herein, this non-overlapping spatial arrangement facilitates the injection of light from different sources into different waveguides on a one-to-one basis, thereby allowing a specific light source to be uniquely coupled to a specific waveguide. In some embodiments, arrays including non-overlapping, spatially separated internal coupling optical elements may be referred to as shifted pupil systems, and the internal coupling optical elements in these arrays may correspond to sub-pupils. (Exemplary Etching for High Refractive Index Glass)

[0086] In some embodiments, microscale and nanoscale features, such as the various diffractive optical elements discussed herein, may be etched directly into a high-index glass substrate. For example, a glass substrate may be used as a waveguide, and a plasma etching process may be used to form the in-coupling optical elements 1212, 1222, 1232, the optically dispersive elements 1214, 1224, 1234, and / or the out-coupling optical elements 1250, 1252, 1254 of FIGS. 9A-9C directly into the substrate.

[0087] The high refractive index glasses forming the substrate may have a relatively low concentration of silicon dioxide (SiO), e.g., less than 50 weight percent (wt %) SiO. Additionally, these high refractive index glasses may comprise 50 wt % or more of one or more metal oxides, such as B2O3, Al2O3, ZrO2, Li2O, Na2O, KO, MgO, CaO, SrO, BaO, ZnO, La2O3, Nb2O5, TiO2, HfO, and Sb2O3. In some embodiments, the glasses may include combinations of these metal oxides.

[0088] Although providing a high refractive index, small amounts of SiO2 and large amounts of other metal oxides can hinder effective etching of substrates formed using these glasses. For example, glasses formed by combinations of such component oxides can be particularly difficult to etch. While specific etching recipes have been developed for the component oxides, these etching recipes may not be effective for high refractive index glasses due to the relatively low concentrations of SiO2 and the different etching rates between the constituent oxides that form the glass.

[0089] In addition, conventional etching processes exhibit various drawbacks. For example, wet chemical etching is typically limited to patterning resolution on the order of a few microns and is isotropic, meaning it cannot form straight sidewalls. Alternatively, ion milling can be used to non-selectively remove material from high-index glass substrates. However, this process significantly limits the achievable resolution and aspect ratio of patterned features. Ion milling can remove material simply by impacting a surface with high-energy particles that physically repel material from the surface. Ion milling requires a hard mask, but it also erodes the hard mask to the point that the process may not be able to maintain the mask for a sufficient duration to form high-aspect ratio features.

[0090] According to some embodiments, as discussed herein, a plasma etching process has been developed for forming features in high-index glass substrates. Features may be formed by using the plasma etching process to transfer a pattern from a mask layer to the high-index glass substrate underlying the mask layer. The plasma etching process may be anisotropic or directional and may be highly selective with respect to the glass substrate relative to the mask layer. Features produced as a result of the plasma etching process may have substantially vertical sidewalls. In some embodiments, the plasma etching process may not be selective with respect to all oxides that may form in high-index glass substrates. In some embodiments, the plasma etching process may include both chemical and physical mechanisms to etch high-index glass, with the physical mechanisms enabling the removal of oxide species that chemical mechanisms may not be very effective at removing. Without being limited by theory, chemical etching of at least some substrate materials may disrupt the physical integrity of the exposed substrate, thereby allowing the physical mechanisms to remove the exposed material with a higher selectivity than would occur without chemical etching. Thus, high-resolution patterns can be transferred into high-index glass substrates via plasma etching processes, even when the high-index glass comprises a complex mixture of oxides.

[0091] In some embodiments, a substrate may be patterned by selectively exposing some areas of the surface of the substrate to reactive species. That is, some areas of the substrate may be etched to form features therein, while other areas may not. For example, an etch-resistant patterned mask material or mask layer may cover the substrate such that areas under the mask layer are not etched, while areas not protected by the mask layer, i.e., left exposed, are etched. The mask layer may then be removed, leaving the etched features on the surface of the substrate.

[0092] As discussed herein, the plasma etching process may be an anisotropic or substantially anisotropic etching process. The directionality of anisotropic etching advantageously enables the formation of substantially straight sidewalls. When etching species are directed toward the substrate in a direction perpendicular to the substrate, the etching process may define features in the substrate with substantially vertical sidewalls. In some embodiments, straight, angled (non-vertical) sidewalls may be formed by directing etching species toward the substrate at an angle other than perpendicular to the substrate.

[0093] In some embodiments, the plasma etching process may etch two or more oxides that comprise high refractive index glass at substantially similar rates, hi some embodiments, the etch rates may be substantially similar for any two or more of SiO2, BO3, Al2O3, ZrO2, Li2O, Na2O, KO, MgO, CaO, SrO, BaO, ZnO, La2O3, Nb2O5, TiO2, HfO, and Sb2O3.

[0094] It should be understood that the term "high refractive index" is used herein to refer to a material, preferably an optically transmissive material such as glass, having a refractive index of 1.65 or greater. In some embodiments, the high refractive index glass may have a refractive index of 1.65 or greater, 1.7 or greater, 1.75 or greater, or 1.8 or greater. In some embodiments, the refractive index may be as noted above and may also be less than 4, less than 3, or less than 2.5. In some other embodiments, the etching processes described herein may be applied to etching substrates having a refractive index lower than 1.65.

[0095] In some embodiments, the high index glass comprises less than about 50 percent by weight (wt%) SiO. In some embodiments, the high index glass may comprise less than about 30 wt% SiO, less than about 25 wt% SiO, or less than about 20 wt% SiO. In some embodiments, the remainder of the high index glass may comprise at least one metal oxide, including multiple metal oxides. That is, the high index glass may comprise greater than about 50 wt% of one or more metal oxides, such as B2O3, Al2O3, ZrO2, Li2O, Na2O, KO, MgO, CaO, SrO, BaO, ZnO, La2O3, Nb2O5, TiO2, HfO, and Sb2O3. In some embodiments, the high index glass may comprise up to about 30 wt% of any one metal oxide.

[0096] According to some embodiments, the high refractive index glass may comprise SiO2, B2O3, TiO2, La2O3, ZrO2, Nb2O5, CaO, and Li2O. For example, the high refractive index glass may comprise about 20 wt% to about 30 wt% SiO2, about 0 wt% to 5 wt% B2O3, about 5 wt% to 10 wt% TiO2, about 20 wt% to 25 wt% La2O3, about 5 wt% to 10 wt% ZrO2, about 10 wt% to 15 wt% Nb2O5, about 15 wt% to 20 wt% CaO, and about 0 wt% to 5 wt% Li2O.

[0097] According to some embodiments, the described plasma etching process may be used to form features having critical dimensions in the range of about 10 nm to about 10 μm. As used herein, critical dimension refers to the smallest dimension of a feature formed in a substrate, as seen in the top and bottom views. For example, the critical dimension of a grating formed by the same elongated feature is the width of one of the features, as seen in the top and bottom views. In some embodiments, the critical dimension of a feature formed in a high refractive index glass substrate may be in the range of about 10 nm to about 500 nm, including about 10 nm to about 100 nm or about 100 nm to about 500 nm. In some embodiments, features formed by the plasma etching process have substantially vertical sidewalls. In some embodiments, the angle formed between a feature formed by the plasma etching process, such as a sidewall, and the horizontal surface of the substrate may be greater than 75°, greater than 80°, or greater than 85°.

[0098] In some embodiments, the plasma etching process may form features having aspect ratios in the range of about 1:10 to about 10:1, about 1:10 to about 3:1, or about 3:1 to about 10:1, where it is understood that aspect ratio is the ratio of the width of the feature to the height of the feature.

[0099] Referring now to FIG. 10 , which shows a process flow diagram for an example of a plasma etching process, according to some embodiments. A substrate comprising high-index glass as described herein is provided in block 1001. A mask layer comprising a pattern of openings is provided on the high-index glass substrate in block 1002, such that at least a portion of the high-index glass substrate is exposed by the mask layer. In some embodiments, the mask layer may comprise a polymer photoresist layer or a hard mask having a desired pattern, such as a binary grating pattern. In some embodiments, blocks 1001 and 1002 may be combined. For example, the etching process may start with a high-index glass substrate in an etching chamber, the substrate having an overlying patterned mask layer.

[0100] The high-index glass substrate and mask layer are exposed to a plasma in a reaction chamber in block 1003 until a desired amount of high-index glass is removed from a portion or portions of the high-index glass substrate exposed by the openings in the mask layer, thereby forming a desired pattern in the high-index glass substrate. Preferably, the plasma comprises chemical and physical etching species, as discussed herein. Any mask layer remaining over the high-index glass substrate may be removed in block 1004. Such removal may be accomplished, for example, by contacting the remaining mask layer with a solvent that dissolves the layer or by using an ashing process.

[0101] In some embodiments, the mask layer may be patterned by lithographic techniques in block 1002. For example, the mask layer may be patterned by ultraviolet photolithography, nanoimprinting, electron beam lithography, or other techniques to remove material in selected areas of the mask layer and form openings that expose the underlying glass substrate.

[0102] In some embodiments, the mask layer may comprise a polymer, e.g., a polymer resist material, e.g., a photoresist material. In some embodiments, the mask layer may be a hard mask layer. In some embodiments, the hard mask layer may comprise a metal, such as nickel, or amorphous carbon.

[0103] In some embodiments, the mask layer may provide an etch selectivity ratio in the range of about 0.1 to about 10. As used herein, etch selectivity ratio refers to the ratio of the etch rate of the mask layer to the etch rate of the high refractive index glass substrate. In some embodiments, the mask layer may have an etch selectivity ratio greater than about 0.5, greater than about 1, greater than about 2, or greater than about 5, up to about 10. The thickness of the mask layer may be selected based on the depth of the features to be formed by subsequent exposure to the etch species. For example, the thickness may be selected to be sufficiently thick, in light of the selectivity provided by the etch species and etching conditions, so that the mask layer is not worn away by subsequent exposure to the etch species. In some embodiments, the critical dimension or width of the features in the mask layer may also be sufficiently larger than the desired size of the substrate features to be patterned using these mass features to compensate for the width reduction caused by etching with the etch species. In some embodiments, features in a mask layer may be formed to be sufficiently large by first patterning the mask layer and then conformally depositing (e.g., by CVD or ALD) an additional layer of mask material over the features, thereby increasing the size of the features. The additional conformal layer of mask material may be formed from the same or a different material than the underlying patterned mask layer.

[0104] In some embodiments, the patterned mask layer may be on a high refractive index glass substrate. The mask layer may comprise a plurality of substantially parallel lines formed on the surface of the high refractive index glass. In some embodiments, the lines may have a thickness of about 100 nm and a base width of about 135 nm. It should be understood that the mask layer may be patterned to have shapes other than lines. For example, in some embodiments, the mask layer pattern may comprise any pattern, shape, or design and may have a critical dimension of about 10 to 500 nm.

[0105] In some embodiments, the mask layer pattern may comprise a pattern corresponding to an optical element such as a diffraction grating or DOE. In some embodiments, the mask layer pattern may comprise a binary diffraction grating. As discussed herein, in some embodiments, the mask layer pattern may comprise an in-coupling optical element, an out-coupling optical element, or a light-dispersing element, for example, as shown in Figures 9A-9C.

[0106] The high-index glass substrate with the upper mask layer may be provided in a plasma etch chamber of a plasma reactor in block 1003 and then exposed to plasma. Providing the substrate in the reaction chamber may include loading the substrate into the reaction chamber. In some embodiments, the plasma may be generated in the reaction chamber, i.e., in situ. In some embodiments, the plasma may be generated in a second, different chamber upstream of the reaction chamber, such as a remote plasma generator, and provided to the reaction chamber containing the high-index glass substrate. In some embodiments, the plasma reactor may be an inductively coupled plasma (ICP) reactor. In some embodiments, the plasma reactor may be a dual-frequency ICP reactor.

[0107] The plasma to which the high refractive index glass substrate and mask layer are exposed in block 1003 may be plasma generated using a source gas in a plasma reactor. Thus, in some embodiments, the plasma may comprise ions, radicals, atoms, and / or other high-energy reactive species formed from the source gas. In some embodiments, the source gas may be continuously flowed into the plasma etch chamber during the plasma exposure in block 1003.

[0108] The source gas may comprise one or more gases. In some embodiments, the source gas may comprise an inert gas, such as He, Ne, Ar, Kr, or Xe, and one or more of chemically reactive species such as O, N, H, and halide gases, such as XeF, C, F, CF, CHF, CF, Cl, SF, Cl, BCl, and HBr. In some embodiments, the source gas may be flowed into the plasma etch chamber and contacted with the high refractive index glass substrate before the plasma is ignited or generated in the plasma etch chamber.

[0109] As an example, the source gas may comprise SF6 and Ar. In some other examples, the source gas may comprise CHF3 and Ar. In yet other examples, the source gas may comprise CHF3, CF4, and Ar. Another example of a source gas composition may comprise BCl3 and HBr. In other examples, the source gas may comprise BCl3, HBr, and Ar. In some embodiments, the source gas may comprise Ar and at least one other halide gas.

[0110] In some embodiments, exposing the substrate to the plasma may include exposing the substrate to plasma-excited species generated from a noble gas, such as He, Ne, Ar, Kr, or Xe. For example, the plasma-excited species may be in the form of radicals, ions, a plasma, or may be in elemental form. In some embodiments, the plasma may comprise SF radicals, SF molecules, and / or SF plasma. In some embodiments, the plasma may comprise HBr radicals, HBr molecules, and / or HBr plasma. In some embodiments, the plasma may comprise BCl radicals, BCl molecules, and / or BCl plasma. In some embodiments, the plasma may comprise CHF radicals, CHF molecules, and / or CHF plasma. In some other embodiments, the plasma may comprise CF radicals, CF molecules, and / or CF plasma.

[0111] In some embodiments, the total flow rate for the source gases into the plasma etch chamber may be in the range of less than about 1 sccm to about 100 sccm, or about 25 sccm to about 75 sccm. In some embodiments, the flow rate for any one component gas of the source gas may be in the range of about 1 sccm to about 100 sccm. As an example, if the source gas comprises SF and Ar, the flow rate for SF may be in the range of about 1 sccm to about 100 sccm, preferably about 50 sccm, and the flow rate for Ar may be in the range of about 1 sccm to about 100 sccm, preferably about 50 sccm.

[0112] In block 1003, the surface of the high-index glass substrate and the mask layer are exposed to a plasma in a reaction chamber until a desired amount of high-index glass is removed from the portion or portions of the high-index glass substrate left exposed by the patterned mask layer. The removal of material transfers the pattern or structure and forms the mask layer in the high-index glass substrate. In block 1003, the high-index glass substrate and mask layer are exposed to the plasma for a duration that can be readily determined by one skilled in the art depending on the desired amount of material to be removed from the high-index glass substrate. For example, the high-index glass substrate and mask layer may be exposed to the plasma for a duration ranging from less than 1 second to about 1 minute, or from about 5 seconds to about 30 seconds. In some embodiments, plasma exposure times greater than about 1 minute may be used depending on the desired amount of high-index glass material to be removed and the thickness and composition of the mask layer.

[0113] In some embodiments, the mask layer material may be removed by the plasma. Thus, in some embodiments, the plasma exposure duration may be limited by the thickness of the mask layer and / or the mask layer material. For example, the plasma exposure duration may be short enough to avoid the formation of holes that extend through the thickness of the mask layer.

[0114] Without wishing to be limited by theory, as discussed herein, plasma, according to some embodiments, may remove material from high refractive index glass substrates by both physical and chemical etching mechanisms. In some embodiments, the source gas may comprise a gas that, when a plasma is generated in it, may etch the substrate by a physical mechanism, such as Ar, He, or N2, and a gas that, when a plasma is generated in it, may etch the substrate by a chemical mechanism, such as CF4, CHF3, SF6, O2, Cl2, BCl3, HBr, and / or other halide gases.

[0115] The plasma may be generated by applying RF power to a source gas. The RF power may be applied to the source gas flowing through the plasma exposure block 1003 and / or flowing through a remote plasma generator. In some embodiments, the RF power applied to the source gas is in the range of about 10 W to about 500 W, about 100 W to about 200 W, about 200 W to about 500 W, or about 10 W to about 100 W.

[0116] In some embodiments, when a plasma is generated in an ICP reactor, a first ICP power may be applied to a source gas to generate the plasma, and a second RF power may be applied to the source gas and / or the plasma in the reaction chamber to generate a directional electric field therein, for example, to promote anisotropic etching by directing etching species directly toward the substrate. In some embodiments, the ICP power may be in a range from about 10 W to about 2500 W. In some embodiments, the RF power may be in a range from about 10 W to about 500 W, from about 100 W to about 200 W, from about 200 W to about 500 W, or from about 10 W to about 100 W.

[0117] In some embodiments, for example, when a dual-frequency ICP reaction is used to generate a plasma, a first VHF power is applied to a source gas and a second RF power is applied to the source gas and / or plasma in the reaction chamber to generate a directional electric field therein. In some embodiments, the VHF power applied to the source gas may be in the range of about 10 W to about 2500 W. In some embodiments, the RF power may be in the range of about 10 W to about 500 W, about 100 W to about 200 W, about 200 W to about 500 W, or about 10 W to about 100 W.

[0118] According to some embodiments, the plasma may be generated using a plasma etch chamber having a pressure between about 1 mTorr and about 0.1 mTorr. More specifically, the reactor chamber pressure may be within a range between about 5 mTorr and about 20 mTorr or between about 20 mTorr and about 100 mTorr in some embodiments. Without being bound by theory, it is believed that a relatively low reactor chamber pressure compared to other typical plasma etch processes may reduce the tendency of any chemical etching mechanism to isotropically etch portions of the substrate. In some embodiments, a relatively low pressure, for example, a reactor chamber pressure between about 20 mTorr and about 100 mTorr, may promote the formation of features with substantially vertical sidewalls.

[0119] In some embodiments, the plasma may be generated at a temperature in the range of about −150° C. to about 50° C. In some embodiments, the plasma may be generated at a temperature in the range of about −120° C. to about −100° C., about −100° C. to about 0° C., about 0° C. to about 20° C., and about 20° C. to about 50° C.

[0120] 11A-11C, in some embodiments, an etch mask may be biased to facilitate the formation of features of a desired size in a high refractive index glass substrate. Advantageously, the etch mask may be utilized in patterning the underlying glass substrate using conventional directional etching, e.g., ion beam milling and / or the plasma etching processes disclosed herein.

[0121] 11A illustrates a cross-sectional side view of an example glass substrate 1010 having an overlying etch mask 1012. The glass substrate 1010 may be formed from any of the high refractive index glass materials disclosed herein. For example, the material forming the glass substrate may have a refractive index of about 1.65 or greater or 1.75 or greater and less than about 50% SiO by weight. In some embodiments, more than 50% by weight of the substrate is formed from one or more of BO, AlO, ZrO, LiO, NaO, KO, MgO, CaO, SrO, BaO, ZnO, LaO, NbO, TiO, HfO, and SbO.

[0122] 11A , the etch mask 1012 may be formed from a polymer (e.g., a carbon-based polymer), chromium, silicon oxide (SiO ), or other material with sufficient stability and etch resistance to pattern the substrate 1010. In some embodiments, the polymer may form a resist, such as a photoresist or an imprint resist. In some embodiments, the resist may be deposited by jet deposition. As shown, the etch mask comprises a pattern formed from a plurality of spaced features 1013 that will be used to protect portions of the underlying substrate 1010 from etching and to define features within the substrate 1010.

[0123] In some embodiments where the resist is a photoresist, the etch mask 1012 may be patterned by exposure to light through a reticle. In some embodiments where the resist is an imprint resist, the etch mask 1012 may be patterned by contact with and imprinting an imprint reticle. In some other embodiments, the etch mask 1012 itself may be etched to define a pattern of features within the etch mask. For example, a resist (not shown) may be provided over a layer of material (e.g., chromium, silicon oxide, etc.) to form the etch mask 1012. The resist may be patterned, for example, by photolithography or imprinting, and then the pattern in the resist may be transferred to a layer of material to form the etch mask 1012, and the top resist may be removed, thereby leaving the etch mask 1012.

[0124] Reference is now made to Figure 11B, which is a cross-sectional side view of an example embodiment of the structure of Figure 11A undergoing a directional etch, as shown. As shown, the etch mask 1012 may have a plurality of features 1013, the features having a critical dimension of 1013w. It should be understood that the critical dimension 1013w may be the width of the feature 1013, which may extend out of the plane of the page along its major axis. Preferably, the critical dimension 1013w is larger than the critical dimension 1014w of a corresponding feature 1014 to be etched into the underlying substrate 1010 using the etch mask feature 1013. In some embodiments, critical dimension 1013w may be selected by identifying desired dimensional characteristics of a first feature (e.g., feature 1016 (FIG. 11C)) to be formed in high index glass substrate 1010, identifying etching characteristics of an etching process 1015 to be used to form at least the first feature in the high index glass substrate, and determining bias dimensional characteristics of a second feature (e.g., feature 1013) of a patterned layer (e.g., etch mask 1012) to be formed on the high index glass substrate based on the identified etching characteristics. For example, critical dimension 1013w may be biased to be sufficiently larger than critical dimension 1014w to compensate for etching of etch mask 1012 by the particular etchant selected to etch substrate 1010. Preferably, the size of feature 1013 is large enough so that, when etched by etching process 1015, mask feature 1013 is of a size that forms an opening of a desired size in high index glass substrate 1010. In addition, the height of feature 1013 is also preferably biased to compensate for the removal of material at the top of feature 1013 by etching.

[0125] As shown, substrate 1010 may be etched by exposing the substrate to a directional etch through openings in etch mask 1012. It should be understood that in embodiments where etch mask 1012 does not have openings but does have regions of lesser thickness than feature 1013, the regions of lesser thickness would be removed by etching, subsequently leaving openings that expose portions of substrate 1010 to the etch. The directional etch 1015 may include various particles that contact and remove material from the substrate 1010. In some embodiments, the directional etch comprises ion beam milling. Advantageously, in some embodiments, the directional etch can form openings having a depth of about 50 nm or greater in about 20 seconds or less. In some embodiments, the directional etch can form openings having a depth of about 50 nm or greater in about 10 seconds or less.

[0126] FIG. 11C illustrates a cross-sectional side view of the example structure of FIG. 11B after etching the glass substrate 1010 and removing the overlying etch mask 1012 (FIGS. 11A-11B). In some embodiments, the etch mask 1012 may be removed using an ashing process and / or a wet etch, selected for the material forming the etch mask. The etched substrate 1010 includes a plurality of features 1016 defined by etching 1015. The features have a critical dimension 1016w, which may be substantially equal to the desired critical dimension 1014w (FIG. 11B).

[0127] As discussed herein, in some embodiments, the substrate 1010 may be utilized as a waveguide, and the features 1016 may be optical elements defined on the surface of the waveguide. For example, the features 1016 may form part of the in-coupling optical elements 1212, 1222, 1232, the optical dispersive elements 1214, 1224, 1234, and / or the out-coupling optical elements 1250, 1252, 1254 of FIGS. 9A-9C.

[0128] 11A-11B, feature 1013 may be biased to have a size that is larger than the desired size of feature 1016 that will ultimately be patterned by feature 1013. This larger size may be set by patterning the layer that forms etch mask 1012 to provide a layer having a desired thickness for etch mask 1012. In some other embodiments, features in the etch mask may be extended to increase their size. FIGS. 12A-12D illustrate a process for etching features into a substrate using an extended etch mask.

[0129] 12A, a cross-sectional side view of an example of an etch mask 1012 on top of a high refractive index glass substrate 1010 is shown. The etch mask 1012 includes a feature 1013 having a critical dimension 1013w. It should be understood that the structure shown in FIG. 12A is similar to that shown in FIG. 11A, although the critical dimension 1013w may be smaller than that of FIG. 11A.

[0130] The etch mask 1012 of FIG. 12A may be considered an initial etch mask, and the dimensions of the features 1013 of that etch mask may be subsequently increased. FIG. 12B illustrates a cross-sectional side view of the example structure of FIG. 12A after expanding the size of the features 1013 of the etch mask 1012. In some embodiments, the size expansion may be achieved by depositing a conformal layer 1018 over the etch mask 1012, thereby forming the etch mask 1012′ having features 1013′ with critical dimension 1013w′. For example, the conformal layer 1018 may be a silicon oxide layer deposited by a vapor deposition process such as atomic layer deposition (ALD) or chemical vapor deposition (CVD). In some other embodiments, the size of the features 1013 in the etch mask 1012 ( FIG. 12A ) may be expanded by chemically reacting with the etch mask to form a material that occupies a larger volume. For example, etch mask 1012 may be oxidized to form, for example, layer 1018, thereby forming etch mask 1012' with extended features 1013'. In some embodiments, the chemical reaction may occur to such an extent that layer 1018 may extend substantially throughout the entire etch mask 1012'.

[0131] Referring now to FIG. 12C , a cross-sectional side view of an example of the structure of FIG. 12B undergoing a directional etch 1015 is illustrated. FIG. 12C is similar to FIG. 12B , except that the etch mask comprises a layer 1018, and it should be understood that the directional etch 1015 is preferably selective with respect to the material of the layer 1018 relative to the substrate 1010. The etch mask 1012′ comprises a plurality of features 1013′, the features having a critical dimension 1013w′ that is greater than a critical dimension 1014w of a corresponding feature 1014 to be etched into the underlying substrate 1010 using the etch mask 1012′. As discussed herein, in some embodiments, the directional etch comprises ion beam milling. Advantageously, in some embodiments, the directional etch can form an opening having a depth of about 50 nm or greater in about 20 seconds or less, or in about 10 seconds or less.

[0132] FIG. 12D illustrates a cross-sectional side view of an example of the structure of FIG. 12B after etching the glass substrate 1010 and removing the overlying etch mask 1012′ (FIG. 12C). It should be understood that FIG. 12D is similar to FIG. 11C. For example, the etch mask 1012 may be removed using an ashing process and / or a wet etch that is selective with respect to the material forming the etch mask. The etched substrate 1010 includes a plurality of features 1016 defined by the etch 1015 and having a critical dimension 1016w, which may be substantially equal to the desired critical dimension 1014w (FIG. 11B).

[0133] In the foregoing specification, various specific embodiments have been described. It will be apparent, however, that various modifications and changes can be made therein without departing from the broader spirit and scope of the invention. The specification and drawings are, therefore, to be regarded in an illustrative rather than a restrictive sense.

[0134] Indeed, it should be understood that the systems and methods of the present disclosure each have several innovative aspects, no single one of which is solely responsible for or required for the desirable attributes disclosed herein. The various features and processes described above may be used independently of one another or may be combined in various ways. All possible combinations and subcombinations are intended to fall within the scope of the present disclosure.

[0135] Certain features described herein in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable subcombination. Furthermore, while features may be described above as operative in a combination and may even be initially claimed as such, one or more features from the claimed combination may, in some cases, be deleted from the combination, and the claimed combination may be directed to a subcombination or a variation of the subcombination. No single feature or group of features is required or essential to every embodiment.

[0136] It should be understood that conditional statements used herein, such as "can," "could," "might," "may," "eg," and the like, in particular, are generally intended to convey that certain embodiments include certain features, elements, and / or steps, while other embodiments do not, unless specifically stated otherwise or understood otherwise within the context as used. Thus, such conditional statements are generally not intended to imply that features, elements, and / or steps are in any way required for one or more embodiments, or that one or more embodiments necessarily include logic for determining whether those features, elements, and / or steps are included or should be performed in any particular embodiment, with or without authorial input or prompting. The terms "comprise," "include," "have," and the like are synonymous and used inclusively in a non-limiting manner and do not exclude additional elements, features, acts, operations, etc. Also, the term "or" is used in its inclusive sense (and not its exclusive sense); thus, for example, when used to connect a list of elements, the term "or" means one, some, or all of the elements in the list. Additionally, the articles "a," "an," and "the," as used in this application and the appended claims, should be interpreted to mean "one or more" or "at least one," unless otherwise specified. Similarly, while operations may be depicted in the figures in a particular order, it should be recognized that such operations need not be performed in the particular order shown, or in sequential order, or that all of the depicted operations need not be performed to achieve desirable results. Furthermore, the figures may diagrammatically depict one or more exemplary processes in the form of a flowchart. However, other operations not depicted may be incorporated within the diagrammatically depicted exemplary methods and processes. For example, one or more additional operations may be performed before, after, concurrently with, or during any of the depicted operations.Additionally, operations may be rearranged or reordered in other implementations. In some situations, multitasking and parallel processing may be advantageous. Furthermore, the separation of various system components in the above-described embodiments should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems may generally be integrated together in a single software product or packaged into multiple software products. Additionally, other implementations are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results.

[0137] Thus, the claims are not intended to be limited to the embodiments shown herein but are to be accorded the widest scope consistent with the present disclosure, the principles and novel features disclosed herein.

Claims

1. 1. A method for patterning a glass substrate, the method comprising: providing an etching mask over a glass substrate formed from glass having a refractive index of 1.65 or greater, wherein features in the etching mask for defining corresponding features in the glass substrate are larger than a desired size of the corresponding features; etching the glass substrate through the etch mask to define the features in the glass substrate; Including, The method, wherein etching the glass substrate comprises performing an anisotropic etch.

2. Providing an etching mask comprises: forming an initial etching mask; increasing the size of features of the initial etching mask to form the etching mask; The method of claim 1 , comprising:

3. The method of claim 2 , wherein the etch mask comprises a resist, and forming the initial etch mask comprises imprinting the resist.

4. The method of claim 2 , wherein increasing the size of features of the initial etch mask comprises depositing a conformal film onto the initial etch mask.

5. The glass substrate contains less than about 50% by weight of SiO ２ More than 50% by weight of the glass substrate is B ２ O ３ , Al ２ O ３ , ZrO ２ , Li ２ O, Na ２ O.K. ２ O, MgO, CaO, SrO, BaO, ZnO, La ２ O ３ , Nb ２ O ５ , TiO ２ , HfO, and Sb ２ O ３ The method of claim 1 , wherein the substrate is formed from one or more of:

6. The method of claim 1 , wherein the etch mask comprises a carbon-based polymer, chromium, or silicon oxide.

7. The method of claim 1 , wherein performing the anisotropic etching comprises performing ion beam milling to remove material of the glass substrate.

8. 8. The method of claim 7, wherein etching the glass substrate forms openings having a depth of 50 nm or greater in less than 20 seconds.

9. 9. The method of claim 8, wherein etching the glass substrate forms the opening in less than 10 seconds.

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