EP3956258A1

EP3956258A1 - Substrate modification by femto-second laser to achieve variable etch depth in dry etching

Info

Publication number: EP3956258A1
Application number: EP20723733.0A
Authority: EP
Inventors: Serol TURKYILMAZ; Giuseppe Calafiore
Original assignee: Facebook Technologies LLC
Current assignee: Meta Platforms Technologies LLC
Priority date: 2019-04-15
Filing date: 2020-04-14
Publication date: 2022-02-23
Also published as: WO2020214608A1; CN113677619A

Abstract

An artificial reality system, such as a head-mounted display (HMD) or heads-up display (HUD) system, generally includes a near-eye display (e.g., a headset or a pair of glasses) configured to present content to a user via an electronic or optic display within, for example, about 10-20 mm in front of the user's eyes. Such a system may include a variable-etch-depth structures. The present invention provides a method of fabricating a variable-etch-depth structure in a substrate, the method comprising: exposing a surface of the substrate to femto-second laser pulses, wherein an exposure dose of the femto-second laser pulses on the surface of the substrate varies across the surface of the substrate; depositing an etch mask layer on the substrate; forming a two- dimensional pattern in a lithography layer on the etch mask layer; transferring the two- dimensional pattern into the etch mask layer to form an etch mask; and etching the substrate using the etch mask to form the variable-etch-depth structure in the substrate.

Description

SUBSTRATE MODIFICATION BY FEMTO-SECOND LASER TO

ACHIEVE VARIABLE ETCH DEPTH IN DRY ETCHING

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority from U.S. Application No. 62/834,289, filed on April 15, 2019, the contents of which are incorporated by reference in their entirety herein for all purposes.

APPENDIX

[0002] Appendix A is being filed as part of this application. The contents of Appendix A are part of this application. The entire contents of Appendix A are also incorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

[0003] An artificial reality system, such as a head-mounted display (HMD) or heads-up display (HUD) system, generally includes a near-eye display (e.g., a headset or a pair of glasses) configured to present content to a user via an electronic or optic display within, for example, about 10-20 mm in front of the user’s eyes. The near-eye display may display virtual objects or combine images of real objects with virtual objects, as in virtual reality (VR), augmented reality (AR), or mixed reality (MR) applications. For example, in an AR system, a user may view both images of virtual objects (e.g., computer-generated images (CGIs)) and the surrounding environment by, for example, seeing through transparent display glasses or lenses (often referred to as optical see-through).

[0004] One example of an optical see-through AR system may use a waveguide-based optical display, where light of projected images may be coupled into a waveguide (e.g., a transparent substrate), propagate within the waveguide, and be coupled out of the waveguide at different locations. In some implementations, the light of the projected images may be coupled into or out of the waveguide using a diffractive optical element, such as a grating. Various techniques can be used to fabricate the grating or to fabricate a mold for imprinting the grating. However, these techniques are generally incapable of etching a grating structure with a desired height or depth profile that is non-uniform over the area of the grating. BRIEF SUMMARY OF THE INVENTION

[0005] This disclosure relates generally to techniques for fabricating variable-etch-depth structures. According to a first aspect of the present invention, there is provided a method of fabricating a variable-etch-depth structure in a substrate, the method comprising: exposing a surface of the substrate to femto-second laser pulses, wherein an exposure dose of the femtosecond laser pulses on the surface of the substrate varies across the surface of the substrate; depositing an etch mask layer on the substrate; forming a two-dimensional pattern in a lithography layer on the etch mask layer; transferring the two-dimensional pattern into the etch mask layer to form an etch mask; and etching the substrate using the etch mask to form the variable-etch-depth structure in the substrate.

[0006] The variable-etch-depth structure may be a variable-etch-depth grating structure for a waveguide-based near-eye display system.

[0007] The substrate may comprise a dielectric material and/or a semiconductor material.

[0008] The etch mask layer may comprise one or more of: a metal, molybdenum silicide, a polymer, a metal oxide and a combination thereof. The metal may comprise chromium, platinum, palladium and/or titanium.

[0009] The etch mask layer may be deposited on the substrate before exposing the surface of the substrate to femto-second laser pulses.

[0010] The exposure to femto-second laser pulses may occur from a backside of the substrate. The backside may be the side or surface opposed to the side or surface on which the etch mask layer is deposited.

[0011] The two-dimensional pattern may be formed in the lithography layer using electron beam lithography, photolithography and/or nanoimprint lithography.

[0012] The pattern in the lithography layer may be transferred into the etch mask layer using a dry etching technique, a wet etching technique, a physical etching technique and/or chemical etching technique. [0013] The substrate may be etched using the etch mask with dry etching. The substrate may be etched using the etch mask with inductively coupled plasma etching, capacitively coupled plasma etching reactive ion etching, ion beam etching, ion milling and/or chemical reactive ion etching.

[0014] According to a second aspect of the present invention, there is provided a variable-etch- depth structure fabricated using the method of the first aspect.

[0015] According to a third aspect of the present invention, there is provided a system for performing the method of the first aspect.

[0016] This summary is neither intended to identify key or essential features of the claimed subject matter, nor is it intended to be used in isolation to determine the scope of the claimed subject matter. The subject matter should be understood by reference to appropriate portions of the entire specification of this disclosure, any or all drawings, and each claim. The foregoing, together with other features and examples, will be described in more detail below in the following specification, claims, and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Illustrative embodiments are described in detail below with reference to the following figures.

[0018] FIG. 1 is a simplified block diagram of an example of an artificial reality system environment including a near-eye display according to certain embodiments.

[0019] FIG. 2 is a perspective view of an example of a near-eye display in the form of a head- mounted display (HMD) device for implementing some of the examples disclosed herein.

[0020] FIG. 3 is a perspective view of an example of a near-eye display in the form of a pair of glasses for implementing some of the examples disclosed herein.

[0021] FIG. 4 illustrates an example of an optical see-through augmented reality system using a waveguide display according to certain embodiments.

[0022] FIG. 5 illustrates an example of a slanted variable-etch-depth grating coupler in a waveguide display according to certain embodiments. [0023] FIG. 6 illustrates an example of a method of fabricating a variable-etch-depth structure according to certain embodiments.

[0024] FIG. 7 is a simplified block diagram of an example electronic system of an example near-eye display according to certain embodiments.

[0025] The figures depict embodiments of the present disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated may be employed without departing from the principles, or benefits touted, of this disclosure.

[0026] In the appended figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar

components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.

DETAILED DESCRIPTION

[0027] This disclosure relates generally to techniques for fabricating variable-etch-depth structures, such as a variable-etch-depth grating structure for a waveguide-based near-eye display system. Various inventive embodiments and examples are described herein, including devices, systems, methods, and the like.

[0028] Gratings may be used in a waveguide-based near-eye display system for coupling light into or out of a waveguide. Achieving spatially variable etch depth (VED) gratings with precise control of pattern height can be very useful in waveguide technology to tune the diffraction efficiency and/or the angular and/or spectral response of the diffractive grating. For example, in some waveguide-based near-eye display system, in order to improve the performance of the grating, such as different diffraction characteristics (e.g., diffraction efficiencies and/or diffraction angles) at different areas of the grating, the depth of the grating may need to vary across the area of the grating. In non-diffractive (e.g., refractive or reflective) devices, achieving spatially varying three-dimensional structures is also very useful. However, it is difficult to pattern nanoscale features and spatially control the geometry of the nanoscale features with a high accuracy.

[0029] While conventional lithographic techniques (e.g. photolithography, electron-beam lithography, etc.) can produce gratings with a highly customizable duty cycle and/or grating period, these lithographic techniques generally are not capable of modulating the vertical dimension (i.e., etch depth) of the grating relative to the surface-normal of the substrate over the entire area of the substrate. Techniques, such as the use of movable blades during etch to control etch time (and depth) spatially, the use of double mask and grey-tone lithography, and the like, may be used to fabricate variable etch depth structures. However, these techniques may need a long development cycle to develop and may be difficult to control the different variations of the etch depth over a two dimensional area to achieve full three-dimensional VED structure.

[0030] According to certain embodiments, a method of fabricating VED structures may include modifying the etch selectivity of the surface region of a substrate (e.g., quartz) using femto-second laser pulses before etching, and then using a dry etch process to etch the modified substrate to achieve spatially varying geometry with nanoscale or micro-scale features.

[0031] In the following description, for the purposes of explanation, specific details are set forth in order to provide a thorough understanding of examples of the disclosure. However, it will be apparent that various examples may be practiced without these specific details. For example, devices, systems, structures, assemblies, methods, and other components may be shown as components in block diagram form in order not to obscure the examples in unnecessary detail. In other instances, well-known devices, processes, systems, structures, and techniques may be shown without necessary detail in order to avoid obscuring the examples. The figures and description are not intended to be restrictive. The terms and expressions that have been employed in this disclosure are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof. The word“example” is used herein to mean“serving as an example, instance, or illustration.” Any embodiment or design described herein as“example” is not necessarily to be construed as preferred or advantageous over other embodiments or designs. [0032] FIG. 1 is a simplified block diagram of an example of an artificial reality system environment 100 including a near-eye display 120 in accordance with certain embodiments. Artificial reality system environment 100 shown in FIG. 1 may include near-eye display 120, an optional external imaging device 150, and an optional input/output interface 140 that may each be coupled to an optional console 110. While FIG. 1 shows example artificial reality system environment 100 including one near-eye display 120, one external imaging device 150, and one input/output interface 140, any number of these components may be included in artificial reality system environment 100, or any of the components may be omitted. For example, there may be multiple near-eye displays 120 monitored by one or more external imaging devices 150 in communication with console 110. In some configurations, artificial reality system environment 100 may not include external imaging device 150, optional input/output interface 140, and optional console 110. In alternative configurations, different or additional components may be included in artificial reality system environment 100.

[0033] Near-eye display 120 may be a head-mounted display that presents content to a user. Examples of content presented by near-eye display 120 include one or more of images, videos, audios, or some combination thereof. In some embodiments, audios may be presented via an external device (e.g., speakers and/or headphones) that receives audio information from near-eye display 120, console 110, or both, and presents audio data based on the audio information. Neareye display 120 may include one or more rigid bodies, which may be rigidly or non-rigidly coupled to each other. A rigid coupling between rigid bodies may cause the coupled rigid bodies to act as a single rigid entity. A non-rigid coupling between rigid bodies may allow the rigid bodies to move relative to each other. In various embodiments, near-eye display 120 may be implemented in any suitable form-factor, including a pair of glasses. Some embodiments of neareye display 120 are further described below with respect to FIGS. 2-4. Additionally, in various embodiments, the functionality described herein may be used in a headset that combines images of an environment external to near-eye display 120 and artificial reality content (e.g., computergenerated images). Therefore, near-eye display 120 may augment images of a physical, real- world environment external to near-eye display 120 with generated content (e.g., images, video, sound, etc.) to present an augmented reality to a user. [0034] In various embodiments, near-eye display 120 may include one or more of display electronics 122, display optics 124, and an eye-tracking unit 130. In some embodiments, neareye display 120 may also include one or more locators 126, one or more position sensors 128 , , and an inertial measurement unit (IMU) 132. Near-eye display 120 may omit any of these elements or include additional elements in various embodiments. Additionally, in some embodiments, near-eye display 120 may include elements combining the function of various elements described in conjunction with FIG. 1.

[0035] Display electronics 122 may display or facilitate the display of images to the user according to data received from, for example, console 110. In various embodiments, display electronics 122 may include one or more display panels, such as a liquid crystal display (LCD), an organic light emitting diode (OLED) display, an inorganic light emitting diode (ILED) display, a micro light emitting diode (mLED) display, an active-matrix OLED display

(AMOLED), a transparent OLED display (TOLED), or some other display. For example, in one implementation of near-eye display 120, display electronics 122 may include a front TOLED panel, a rear display panel, and an optical component (e.g., an attenuator, polarizer, or diffractive or spectral film) between the front and rear display panels. Display electronics 122 may include pixels to emit light of a predominant color such as red, green, blue, white, or yellow. In some implementations, display electronics 122 may display a three-dimensional (3D) image through stereoscopic effects produced by two-dimensional panels to create a subjective perception of image depth. For example, display electronics 122 may include a left display and a right display positioned in front of a user’s left eye and right eye, respectively. The left and right displays may present copies of an image shifted horizontally relative to each other to create a stereoscopic effect (i.e., a perception of image depth by a user viewing the image).

[0036] In certain embodiments, display optics 124 may display image content optically (e.g., using optical waveguides and couplers) or magnify image light received from display electronics 122, correct optical errors associated with the image light, and present the corrected image light to a user of near-eye display 120. In various embodiments, display optics 124 may include one or more optical elements, such as, for example, a substrate, optical waveguides, an aperture, a Fresnel lens, a convex lens, a concave lens, a filter, input/output couplers, or any other suitable optical elements that may affect image light emitted from display electronics 122. Display optics 124 may include a combination of different optical elements as well as mechanical couplings to maintain relative spacing and orientation of the optical elements in the combination. One or more optical elements in display optics 124 may have an optical coating, such as an anti-reflective coating, a reflective coating, a filtering coating, or a combination of different optical coatings.

[0037] Magnification of the image light by display optics 124 may allow display electronics 122 to be physically smaller, weigh less, and consume less power than larger displays.

Additionally, magnification may increase a field of view of the displayed content. The amount of magnification of image light by display optics 124 may be changed by adjusting, adding, or removing optical elements from display optics 124. In some embodiments, display optics 124 may project displayed images to one or more image planes that may be further away from the user’s eyes than near-eye display 120.

[0038] Display optics 124 may also be designed to correct one or more types of optical errors, such as two-dimensional optical errors, three-dimensional optical errors, or a combination thereof. Two-dimensional errors may include optical aberrations that occur in two dimensions. Example types of two-dimensional errors may include barrel distortion, pincushion distortion, longitudinal chromatic aberration, and transverse chromatic aberration. Three-dimensional errors may include optical errors that occur in three dimensions. Example types of three-dimensional errors may include spherical aberration, comatic aberration, field curvature, and astigmatism.

[0039] Locators 126 may be objects located in specific positions on near-eye display 120 relative to one another and relative to a reference point on near-eye display 120. In some implementations, console 110 may identify locators 126 in images captured by external imaging device 150 to determine the artificial reality headset’s position, orientation, or both. A locator 126 may be a light emitting diode (LED), a comer cube reflector, a reflective marker, a type of light source that contrasts with an environment in which near-eye display 120 operates, or some combinations thereof. In embodiments where locators 126 are active components (e.g., LEDs or other types of light emitting devices), locators 126 may emit light in the visible band (e.g., about 380 nm to 750 nm), in the infrared (IR) band (e.g., about 750 nm to 1 mm), in the ultraviolet band (e.g., about 10 nm to about 380 nm), in another portion of the electromagnetic spectrum, or in any combination of portions of the electromagnetic spectrum. [0040] External imaging device 150 may generate slow calibration data based on calibration parameters received from console 110. Slow calibration data may include one or more images showing observed positions of locators 126 that are detectable by exteral imaging device 150. External imaging device 150 may include one or more cameras, one or more video cameras, any other device capable of capturing images including one or more of locators 126, or some combinations thereof. Additionally, external imaging device 150 may include one or more filters (e.g., to increase signal to noise ratio). External imaging device 150 may be configured to detect light emitted or reflected from locators 126 in a field of view of external imaging device 150. In embodiments where locators 126 include passive elements (e.g., retroreflectors), external imaging device 150 may include a light source that illuminates some or all of locators 126, which may retro-reflect the light to the light source in exteral imaging device 150. Slow calibration data may be communicated from external imaging device 150 to console 110, and external imaging device 150 may receive one or more calibration parameters from console 110 to adjust one or more imaging parameters (e.g., focal length, focus, frame rate, sensor temperature, shutter speed, aperture, etc.).

[0041] Position sensors 128 may generate one or more measurement signals in response to motion of near-eye display 120. Examples of position sensors 128 may include accelerometers, gyroscopes, magnetometers, other motion-detecting or error-correcting sensors, or some combinations thereof. For example, in some embodiments, position sensors 128 may include multiple accelerometers to measure translational motion (e.g., forward/back, up/down, or left/right) and multiple gyroscopes to measure rotational motion (e.g., pitch, yaw, or roll). In some embodiments, various position sensors may be oriented orthogonally to each other.

[0042] IMU 132 may be an electronic device that generates fast calibration data based on measurement signals received from one or more of position sensors 128. Position sensors 128 may be located external to IMU 132, interal to IMU 132, or some combination thereof. Based on the one or more measurement signals from one or more position sensors 128, IMU 132 may generate fast calibration data indicating an estimated position of near-eye display 120 relative to an initial position of near-eye display 120. For example, IMU 132 may integrate measurement signals received from accelerometers over time to estimate a velocity vector and integrate the velocity vector over time to determine an estimated position of a reference point on near-eye display 120. Alternatively, IMU 132 may provide the sampled measurement signals to console 110, which may determine the fast calibration data. While the reference point may generally be defined as a point in space, in various embodiments, the reference point may also be defined as a point within near-eye display 120 (e.g., a center of IMU 132).

[0043] Eye-tracking unit 130 may include one or more eye-tracking systems. Eye tracking may refer to determining an eye’s position, including orientation and location of the eye, relative to near-eye display 120. An eye-tracking system may include an imaging system to image one or more eyes and may optionally include a light emitter, which may generate light that is directed to an eye such that light reflected by the eye may be captured by the imaging system. For example, eye-tracking unit 130 may include a non-coherent or coherent light source (e.g., a laser diode) emitting light in the visible spectrum or infrared spectrum, and a camera capturing the light reflected by the user’s eye. As another example, eye-tracking unit 130 may capture reflected radio waves emitted by a miniature radar unit. Eye-tracking unit 130 may use low-power light emitters that emit light at frequencies and intensities that would not injure the eye or cause physical discomfort. Eye-tracking unit 130 may be arranged to increase contrast in images of an eye captured by eye-tracking unit 130 while reducing the overall power consumed by eyetracking unit 130 (e.g., reducing power consumed by a light emitter and an imaging system included in eye-tracking unit 130). For example, in some implementations, eye-tracking unit 130 may consume less than 100 milliwatts of power.

[0044] Near-eye display 120 may use the orientation of the eye to, e.g., determine an inter- pupillary distance (IPD) of the user, determine gaze direction, introduce depth cues (e.g., blur image outside of the user’s main line of sight), collect heuristics on the user interaction in the VR media (e.g., time spent on any particular subject, object, or frame as a function of exposed stimuli), some other functions that are based in part on the orientation of at least one of the user’s eyes, or some combination thereof. Because the orientation may be determined for both eyes of the user, eye-tracking unit 130 may be able to determine where the user is looking. For example, determining a direction of a user’s gaze may include determining a point of convergence based on the determined orientations of the user’s left and right eyes. A point of convergence may be the point where the two foveal axes of the user’s eyes intersect. The direction of the user’s gaze may be the direction of a line passing through the point of convergence and the mid-point between the pupils of the user’s eyes.

[0045] Input/output interface 140 may be a device that allows a user to send action requests to console 110. An action request may be a request to perform a particular action. For example, an action request may be to start or to end an application or to perform a particular action within the application. Input/output interface 140 may include one or more input devices. Example input devices may include a keyboard, a mouse, a game controller, a glove, a button, a touch screen, or any other suitable device for receiving action requests and communicating the received action requests to console 110. An action request received by the input/output interface 140 may be communicated to console 110, which may perform an action corresponding to the requested action. In some embodiments, input/output interface 140 may provide haptic feedback to the user in accordance with instructions received from console 110. For example, input/output interface 140 may provide haptic feedback when an action request is received, or when console 110 has performed a requested action and communicates instructions to input/output interface 140.

[0046] Console 110 may provide content to near-eye display 120 for presentation to the user in accordance with information received from one or more of external imaging device 150, neareye display 120, and input/output interface 140. In the example shown in FIG. 1, console 110 may include an application store 112, a headset tracking module 114, an artificial reality engine 116, and eye-tracking module 118. Some embodiments of console 110 may include different or additional modules than those described in conjunction with FIG. 1. Functions further described below may be distributed among components of console 110 in a different manner than is described here.

[0047] In some embodiments, console 110 may include a processor and a non-transitory computer-readable storage medium storing instructions executable by the processor. The processor may include multiple processing units executing instructions in parallel. The non- transitory computer-readable storage medium may be any memory, such as a hard disk drive, a removable memory, or a solid-state drive (e.g., flash memory or dynamic random access memory (DRAM)). In various embodiments, the modules of console 110 described in conjunction with FIG. 1 may be encoded as instructions in the non-transitory computer-readable storage medium that, when executed by the processor, cause the processor to perform the functions further described below.

[0048] Application store 112 may store one or more applications for execution by console 110. An application may include a group of instructions that, when executed by a processor, generates content for presentation to the user. Content generated by an application may be in response to inputs received from the user via movement of the user’s eyes or inputs received from the input/output interface 140. Examples of the applications may include gaming applications, conferencing applications, video playback application, or other suitable applications.

[0049] Headset tracking module 114 may track movements of near-eye display 120 using slow calibration information from external imaging device 150. For example, headset tracking module 114 may determine positions of a reference point of near-eye display 120 using observed locators from the slow calibration information and a model of near-eye display 120. Headset tracking module 114 may also determine positions of a reference point of near-eye display 120 using position information from the fast calibration information. Additionally, in some embodiments, headset tracking module 114 may use portions of the fast calibration information, the slow calibration information, or some combination thereof, to predict a future location of near-eye display 120. Headset tracking module 114 may provide the estimated or predicted future position of near-eye display 120 to artificial reality engine 116.

[0050] Headset tracking module 114 may calibrate the artificial reality system environment 100 using one or more calibration parameters, and may adjust one or more calibration parameters to reduce errors in determining the position of near-eye display 120. For example, headset tracking module 114 may adjust the focus of external imaging device 150 to obtain a more accurate position for observed locators on near-eye display 120. Moreover, calibration performed by headset tracking module 114 may also account for information received from IMU 132.

Additionally, if tracking of near-eye display 120 is lost (e.g., external imaging device 150 loses line of sight of at least a threshold number of locators 126), headset tracking module 114 may recalibrate some or all of the calibration parameters.

[0051] Artificial reality engine 116 may execute applications within artificial reality system environment 100 and receive position information of near-eye display 120, acceleration information of near-eye display 120, velocity information of near-eye display 120, predicted future positions of near-eye display 120, or some combination thereof from headset tracking module 114. Artificial reality engine 116 may also receive estimated eye position and orientation information from eye-tracking module 118. Based on the received information, artificial reality engine 116 may determine content to provide to near-eye display 120 for presentation to the user. For example, if the received information indicates that the user has looked to the left, artificial reality engine 116 may generate content for near-eye display 120 that mirrors the user’s eye movement in a virtual environment. Additionally, artificial reality engine 116 may perform an action within an application executing on console 110 in response to an action request received from input/output interface 140, and provide feedback to the user indicating that the action has been performed. The feedback may be visual or audible feedback via near-eye display 120 or haptic feedback via input/output interface 140.

[0052] Eye-tracking module 118 may receive eye-tracking data from eye-tracking unit 130 and determine the position of the user’s eye based on the eye tracking data. The position of the eye may include an eye’s orientation, location, or both relative to near-eye display 120 or any element thereof. Because the eye’s axes of rotation change as a function of the eye’s location in its socket, determining the eye’s location in its socket may allow eye-tracking module 118 to more accurately determine the eye’s orientation.

[0053] In some embodiments, eye-tracking module 118 may store a mapping between images captured by eye-tracking unit 130 and eye positions to determine a reference eye position from an image captured by eye-tracking unit 130. Alternatively or additionally, eye-tracking module 118 may determine an updated eye position relative to a reference eye position by comparing an image from which the reference eye position is determined to an image from which the updated eye position is to be determined. Eye-tracking module 118 may determine eye position using measurements from different imaging devices or other sensors. For example, eye-tracking module 118 may use measurements from a slow eye-tracking system to determine a reference eye position, and then determine updated positions relative to the reference eye position from a fast eye-tracking system until a next reference eye position is determined based on measurements from the slow eye-tracking system.

[0054] Eye-tracking module 118 may also determine eye calibration parameters to improve precision and accuracy of eye tracking. Eye calibration parameters may include parameters that may change whenever a user dons or adjusts near-eye display 120. Example eye calibration parameters may include an estimated distance between a component of eye-tracking unit 130 and one or more parts of the eye, such as the eye’s center, pupil, cornea boundary, or a point on the surface of the eye. Other example eye calibration parameters may be specific to a particular user and may include an estimated average eye radius, an average corneal radius, an average sclera radius, a map of features on the eye surface, and an estimated eye surface contour. In

embodiments where light from the outside of near-eye display 120 may reach the eye (as in some augmented reality applications), the calibration parameters may include correction factors for intensity and color balance due to variations in light from the outside of near-eye display 120. Eye-tracking module 118 may use eye calibration parameters to determine whether the measurements captured by eye-tracking unit 130 would allow eye-tracking module 118 to determine an accurate eye position (also referred to herein as“valid measurements”). Invalid measurements, from which eye-tracking module 118 may not be able to determine an accurate eye position, may be caused by the user blinking, adjusting the headset, or removing the headset, and/or may be caused by near-eye display 120 experiencing greater than a threshold change in illumination due to external light. In some embodiments, at least some of the functions of eyetracking module 118 may be performed by eye-tracking unit 130.

[0055] FIG. 2 is a perspective view of an example of a near-eye display in the form of a head- mounted display (HMD) device 200 for implementing some of the examples disclosed herein. HMD device 200 may be a part of, e.g., a virtual reality (VR) system, an augmented reality (AR) system, a mixed reality (MR) system, or some combinations thereof. HMD device 200 may include a body 220 and a head strap 230. FIG. 2 shows a top side 223, a front side 225, and a right side 227 of body 220 in the perspective view. Head strap 230 may have an adjustable or extendible length. There may be a sufficient space between body 220 and head strap 230 of HMD device 200 for allowing a user to mount HMD device 200 onto the user’s head. In various embodiments, HMD device 200 may include additional, fewer, or different components. For example, in some embodiments, HMD device 200 may include eyeglass temples and temples tips as shown in, for example, FIG. 2, rather than head strap 230.

[0056] HMD device 200 may present to a user media including virtual and/or augmented views of a physical, real-world environment with computer-generated elements. Examples of the media presented by HMD device 200 may include images (e.g., two-dimensional (2D) or three- dimensional (3D) images), videos (e.g., 2D or 3D videos), audios, or some combinations thereof. The images and videos may be presented to each eye of the user by one or more display assemblies (not shown in FIG. 2) enclosed in body 220 of HMD device 200. In various embodiments, the one or more display assemblies may include a single electronic display panel or multiple electronic display panels (e.g., one display panel for each eye of the user). Examples of the electronic display panel(s) may include, for example, a liquid crystal display (LCD), an organic light emitting diode (OLED) display, an inorganic light emitting diode (ILED) display, a micro light emitting diode (mLED) display, an active-matrix organic light emitting diode (AMOLED) display, a transparent organic light emitting diode (TOLED) display, some other display, or some combinations thereof HMD device 200 may include two eye box regions.

[0057] In some implementations, HMD device 200 may include various sensors (not shown), such as depth sensors, motion sensors, position sensors, and eye tracking sensors. Some of these sensors may use a structured light pattern for sensing. In some implementations, HMD device 200 may include an input/output interface for communicating with a console. In some implementations, HMD device 200 may include a virtual reality engine (not shown) that can execute applications within HMD device 200 and receive depth information, position

information, acceleration information, velocity information, predicted future positions, or some combination thereof of HMD device 200 from the various sensors. In some implementations, the information received by the virtual reality engine may be used for producing a signal (e.g., display instructions) to the one or more display assemblies. In some implementations, HMD device 200 may include locators (not shown, such as locators 126) located in fixed positions on body 220 relative to one another and relative to a reference point. Each of the locators may emit light that is detectable by an external imaging device.

[0058] FIG. 3 is a perspective view of an example of a near-eye display 300 in the form of a pair of glasses for implementing some of the examples disclosed herein. Near-eye display 300 may be a specific implementation of near-eye display 120 of FIG. 1, and may be configured to operate as a virtual reality display, an augmented reality display, and/or a mixed reality display. Near-eye display 300 may include a frame 305 and a display 310. Display 310 may be configured to present content to a user. In some embodiments, display 310 may include display electronics and/or display optics. For example, as described above with respect to near-eye display 120 of FIG. 1, display 310 may include an LCD display panel, an LED display panel, or an optical display panel (e.g., a waveguide display assembly).

[0059] Near-eye display 300 may further include various sensors 350a, 350b, 350c, 350d, and 350e on or within frame 305. In some embodiments, sensors 350a-350e may include one or more depth sensors, motion sensors, position sensors, inertial sensors, or ambient light sensors. In some embodiments, sensors 350a-350e may include one or more image sensors configured to generate image data representing different fields of views in different directions. In some embodiments, sensors 350a-350e may be used as input devices to control or influence the displayed content of near-eye display 300, and/or to provide an interactive VR/AR/MR experience to a user of near-eye display 300. In some embodiments, sensors 350a-350e may also be used for stereoscopic imaging.

[0060] In some embodiments, near-eye display 300 may further include one or more illuminators 330 to project light into the physical environment. The projected light may be associated with different frequency bands (e.g., visible light, infra-red light, ultra-violet light, etc.), and may serve various purposes. For example, illuminators) 330 may project light in a dark environment (or in an environment with low intensity of infra-red light, ultra-violet light, etc.) to assist sensors 350a-350e in capturing images of different objects within the dark environment. In some embodiments, illuminator(s) 330 may be used to project certain light pattern onto the objects within the environment. In some embodiments, illuminator(s) 330 may be used as locators, such as locators 126 described above with respect to FIG. 1.

[0061] In some embodiments, near-eye display 300 may also include a high-resolution camera 340. Camera 340 may capture images of the physical environment in the field of view. The captured images may be processed, for example, by a virtual reality engine (e.g., artificial reality engine 116 of FIG. 1) to add virtual objects to the captured images or modify physical objects in the captured images, and the processed images may be displayed to the user by display 310 for AR or MR applications.

[0062] FIG. 4 illustrates an example of an optical see-through augmented reality system 400 using a waveguide display according to certain embodiments. Augmented reality system 400 may include a projector 410 and a combiner 415. Projector 410 may include a light source or image source 412 and projector optics 414. In some embodiments, image source 412 may include a plurality of pixels that displays virtual objects, such as an LCD display panel or an LED display panel. In some embodiments, image source 412 may include a light source that generates coherent or partially coherent light. For example, image source 412 may include a laser diode, a vertical cavity surface emitting laser, and/or a light emitting diode. In some

embodiments, image source 412 may include a plurality of light sources each emitting a monochromatic image light corresponding to a primary color (e.g., red, green, or blue). In some embodiments, image source 412 may include an optical pattern generator, such as a spatial light modulator. Projector optics 414 may include one or more optical components that can condition the light from image source 412, such as expanding, collimating, scanning, or projecting light from image source 412 to combiner 415. The one or more optical components may include, for example, one or more lenses, liquid lenses, mirrors, apertures, and/or gratings. In some embodiments, projector optics 414 may include a liquid lens (e.g., a liquid crystal lens) with a plurality of electrodes that allows scanning of the light from image source 412.

[0063] Combiner 415 may include an input coupler 430 for coupling light from projector 410 into a substrate 420 of combiner 415. Input coupler 430 may include a volume holographic grating, a diffractive optical element (DOE) (e.g., a surface-relief grating), or a refractive coupler (e.g., a wedge or a prism). Input coupler 430 may have a coupling efficiency of greater than 30%, 50%, 75%, 90% , or higher for visible light. As used herein, visible light may refer to light with a wavelength between about 380 nm to about 750 nm. Light coupled into substrate 420 may propagate within substrate 420 through, for example, total internal reflection (TIR). Substrate 420 may be in the form of a lens of a pair of eyeglasses. Substrate 420 may have a flat or a curved surface, and may include one or more types of dielectric materials, such as glass, quartz, plastic, polymer, poly(methyl methacrylate) (PMMA), crystal, or ceramic. A thickness of substrate 420 may range from, for example, less than about 1 mm to about 10 mm or more.

Substrate 420 may be transparent to visible light. A material may be“transparent” to a light beam if the light beam can pass through the material with a high transmission rate, such as larger than 50%, 40%, 75%, 80%, 90%, 95%, or higher, where a small portion of the light beam (e.g., less than 50%, 40%, 25%, 20%, 10%, 5%, or less) may be scattered, reflected, or absorbed by the material. The transmission rate (i.e., transmissivity) may be represented by either a photopically weighted or an unweighted average transmission rate over a range of wavelengths, or the lowest transmission rate over a range of wavelengths, such as the visible wavelength range.

[0064] Substrate 420 may include or may be coupled to a plurality of output couplers 440 configured to extract at least a portion of the light guided by and propagating within substrate 420 from substrate 420, and direct extracted light 460 to an eyebox 495 where an eye 490 of the user of augmented reality system 400 may be located when augmented reality system 400 is in use. As input coupler 430, output couplers 440 may include grating couplers (e.g., volume holographic gratings or surface-relief gratings), other DOEs, prisms, etc. Output couplers 440 may have different coupling (e.g., diffraction) efficiencies at different locations. Substrate 420 may also allow light 450 from environment in front of combiner 415 to pass through with little or no loss. Output couplers 440 may also allow light 450 to pass through with little loss. For example, in some implementations, output couplers 440 may have a low diffraction efficiency for light 450 such that light 450 may be refracted or otherwise pass through output couplers 440 with little loss, and thus may have a higher intensity than extracted light 460. In some implementations, output couplers 440 may have a high diffraction efficiency for light 450 and may diffract light 450 to certain desired directions (i.e., diffraction angles) with little loss. As a result, the user may be able to view combined images of the environment in front of combiner 415 and virtual objects projected by projector 410.

[0065] In many applications, to diffract light at a desired direction towards the user’s eye, to achieve a desired diffraction efficiency for certain diffraction orders, and to increase the field of view and reduce rainbow artifacts of a waveguide display, a grating coupler (e.g., input coupler 430 or output couplers 440) may include a blazed or slanted grating, such as a slanted surface- relief grating, where the grating ridges and grooves may be tilted relative to the surface normal of the grating coupler or waveguide. In addition, in some embodiments, it may be desirable that the grating has a height or depth profile that is non-uniform over the area of the grating, and/or a grating period or duty cycle that varies across the grating, in order to improve the performance of the grating, such as to achieve different diffraction characteristics (e.g., diffraction efficiencies and/or diffraction angles) at different areas of the grating.

[0066] FIG. 5 illustrates an example of a slanted grating 520 used in an example waveguide display 500 according to certain embodiments. Waveguide display 500 may include slanted grating 520 on a waveguide 510, such as substrate 420. Slanted grating 520 may act as a grating coupler for couple light into or out of waveguide 510. In some embodiments, slanted grating 520 may include a structure with a period p, which may be a constant or may vary across the area of slanted grating 520. Slanted grating 520 may include a plurality of ridges 522 and a plurality of grooves 524 between ridges 522. Each period of slanted grating 520 may include a ridge 522 and a groove 524, which may be an air gap or a region filled with a material with a refractive index different from the refractive index of ridge 522. The ratio between the width of a ridge 522 and the grating period p may be referred to as the duty cycle. Slanted grating 520 may have a duty cycle ranging, for example, from about 30% to about 70%, or from about 10% to about 90% or greater. In some embodiments, the duty cycle may vary from period to period or from area to area. In some embodiments, the period p of the slanted grating may vary from one area to another on slanted grating 520, or may vary from one period to another (i.e., chirped) on slanted grating 520.

[0067] Ridges 522 may be made of a material, such as silicon containing materials (e.g., SiO₂, S13N4, SiC, SiOxNy, or amorphous silicon), organic materials (e.g., spin on carbon (SOC) or amorphous carbon layer (ACL) or diamond like carbon (DLC)), or inorganic metal oxide layers (e.g., TiOx, AlOx, TaOx, HfOx, etc.). Each ridge 522 may include a leading edge 530 with a slant angel a and a trailing edge 540 with a slant angle b. In some embodiments, leading edge 530 and trailing edge 540 of each ridge 522 may be parallel to each other. In some embodiments, slant angle a may be different from slant angle b. In some embodiments, slant angle a may be approximately equal to slant angle b. For example, the difference between slant angle a and slant angle b may be less than 20%, 10%, 5%, 1%, or less. In some embodiments, slant angle a and slant angle b may range from, for example, about 30° or less to about 70° or larger. In some embodiments, slant angle a and/or slant angle b may also vary from ridge to ridge in slanted grating 520.

[0068] Each groove 524 may have a depth d in the z direction, which may be a constant or may vary across the area of slanted grating 520. In some embodiments, the depths of grooves 524 may vary across the area of slanted grating 520 according to a pattern or a depth profile 550. In some embodiments, the depths of grooves 524 may include multiple depth levels, such as 8 depth levels, 16 depth levels, 32 depth levels, or more. In some embodiments, the depths of grooves 524 may vary from 0 to about 100 nm, 200 nm, 300 nm, or deeper. In some implementations, grooves 524 between ridges 522 may be over-coated or filled with a material having a refractive index higher or lower than the refractive index of the material of ridges 522. For example, in some embodiments, a high refractive index material, such as Hafnia, Titania, Tantalum oxide, Tungsten oxide, Zirconium oxide, Gallium sulfide, Gallium nitride, Gallium phosphide, silicon, or a high refractive index polymer, may be used to fill grooves 524. In some embodiments, a low refractive index material, such as silicon oxide, alumina, porous silica, or fluorinated low index monomer (or polymer), may be used to fill grooves 524. As a result, the difference between the refractive index of the ridges and the refractive index of the grooves may be greater than 0.1, 0.2, 0.3, 0.5, 1.0, or higher.

[0069] As such, slanted grating 520 may have a 3-D structure, the physical dimensions of which may vary in the x, y, and/or z directions. For example, the grating period or duty cycle of slanted grating 520 may vary in the x-y plane and may also vary in the z-direction if slant angle a is different from slant angle b. The depths of grooves 524 in the z direction may vary in the x and/or y directions. In some embodiments, the slant angle a and/or b with respect to the z direction may also vary along the x and/or y directions in slanted grating 520.

[0070] It may be challenging to fabricate the slant grating shown and described above with respect to FIG. 5. For example, many grating etching processes may only uniformly etch a substrate to fabricate a grating with a uniform thickness or depth. In some etching processes, the etch rate and thus the depth of the grating may depend on the duty cycle of the grating to be etched. As such, even if non-uniform depths can be achieved using such etching processes, the etch depths may depend on other physical dimensions (e.g., the duty cycle or period) of the grating and thus the grating may not have the desired 3-D profile.

[0071] While conventional lithographic techniques (e.g. photolithography, electron-beam lithography, etc.) can produce gratings with a highly customizable duty cycle and/or grating period, these lithographic techniques generally are not capable of modulating the vertical dimension (i.e., etch depth) of the grating relative to the surface-normal of the substrate over the entire area of the substrate. Techniques, such as the use of movable blades during etch to control etch time (and depth) spatially, the use of double mask and grey-tone lithography, and the like, may be used to fabricate variable etch depth structures. However, these techniques may need a long development cycle to develop and may be difficult to control the different variations of the etch depth over a two dimensional area to achieve full three-dimensional VED structure.

[0072] According to certain embodiments, a method of fabricating VED structures may include modifying the etch selectivity of the surface region of a substrate (e.g., quartz) using femto-second laser pulses before etching, and then using a dry etch process to etch the modified substrate to achieve spatially varying geometry with nanoscale or micro-scale features. The modifying of the etch selectivity of the surface region of the substrate using femto-second laser pulses can be performed before or after a lithography process.

[0073] The femto-second laser pulses are used to directly and locally modify the etch selectivity of the substrate and define a VED function or profile in the substrate, which allows for a mask-less grey-scale level etching. A nanoscale or microscale lithography can be used to define a two-dimensional diffractive, refractive, or reflective pattern of an optical device used in, for example, a near-eye display device. Due to the different femto-second laser modifications of different two-dimensional regions of the substrate, the two-dimensional patterns may be transferred into the substrate at different depth levels in different regions, depending on the femto-second laser pulse energy each respective region of the substrate has been exposed to and thus the etch selectivity at the respective region.

[0074] FIG. 6 is a flow chart 600 illustrating an example of a method of fabricating a variable- etch-depth grating according to certain embodiments. The operations described in flow chart 600 are for illustration purposes only and are not intended to be limiting. In various implementations, modifications may be made to flow chart 600 to add additional operations or to omit some operations. The operations described in flow chart 600 may be performed by, for example, one or more semiconductor fabrication systems that include a patterning system, a deposition system, an etching system, or any combination thereof.

[0075] At block 610, a surface of a substrate may be exposed to femto-second laser pulses. As described above, the substrate may include one or more types of dielectric materials or semiconductor materials, such as glass, quartz, plastic, polymer, poly(methyl methacrylate) (PMMA), crystal, Si3N4, SiC, AI2O3, or ceramic. The exposure times at different regions of the surface of the substrate may be different, such that the exposure dosage at different regions of the surface of the substrate may be different, which may modify the etch selectivity of the substrate differently at different regions.

[0076] At block 620, an etch mask layer (e.g., a hard mask layer) may be deposited on the substrate. The etch mask layer may include, for example, Cr, Pt, Pd, Ti, MoSi, polymer, another metal material, a metal-oxide, or any combination thereof. In some embodiments, etch mask layer may be deposited on the substrate before exposing the surface of the substrate to femtosecond laser pulses, where the exposure to femto-second laser pulses may occur from the backside of the substrate..

[0077] At block 630, a two-dimensional pattern may be formed in a lithography layer on top of the etch mask layer. The pattern may include a nanoscale or microscale grating. The lithography layer may include, for example, a photoresist. The pattern may be formed in the lithography layer using, for example, electron beam lithography (EBL), photolithography, nanoimprint lithography, and the like.

[0078] At block 640, the pattern in the lithography layer may be transferred into the etch mask layer, for example, using various dry etching, wet etching, physical etching, or chemical etching techniques, to form an etch mask.

[0079] At block 650, the substrate may be etched using the etch mask by dry etching, such as inductively coupled plasma (ICP) etching, capacitively coupled plasma (CCP) etching, reactive ion etching (RIE), ion beam etching (IBE), ion milling, Chemical-RIE, and the like. Regions of the substrate that are exposed to higher femto-second laser pulse dose may be etch faster than regions of the substrate that are exposed to lower femto-second laser pulse dose. Thus, a variable etch depth profile can be formed in the substrate using dry etching.

[0080] Embodiments of the invention may be used to implement components of an artificial reality system or may be implemented in conjunction with an artificial reality system. Artificial reality is a form of reality that has been adjusted in some manner before presentation to a user, which may include, for example, a virtual reality (VR), an augmented reality (AR), a mixed reality (MR), a hybrid reality, or some combination and/or derivatives thereof. Artificial reality content may include completely generated content or generated content combined with captured (e.g., real-world) content. The artificial reality content may include video, audio, haptic feedback, or some combination thereof, and any of which may be presented in a single channel or in multiple channels (such as stereo video that produces a three-dimensional effect to the viewer). Additionally, in some embodiments, artificial reality may also be associated with applications, products, accessories, services, or some combination thereof, that are used to, for example, create content in an artificial reality and/or are otherwise used in (e.g., perform activities in) an artificial reality. The artificial reality system that provides the artificial reality content may be implemented on various platforms, including a head-mounted display (HMD) connected to a host computer system, a standalone HMD, a mobile device or computing system, or any other hardware platform capable of providing artificial reality content to one or more viewers.

[0081] FIG. 7 is a simplified block diagram of an example electronic system 700 of an example near-eye display (e.g., HMD device) for implementing some of the examples disclosed herein. Electronic system 700 may be used as the electronic system of an HMD device or other near-eye displays described above. In this example, electronic system 700 may include one or more processors) 710 and a memory 720. Processors) 710 may be configured to execute instructions for performing operations at a number of components, and can be, for example, a general-purpose processor or microprocessor suitable for implementation within a portable electronic device. Processor(s) 710 may be communicatively coupled with a plurality of components within electronic system 700. To realize this communicative coupling, processors) 710 may communicate with the other illustrated components across a bus 740. Bus 740 may be any subsystem adapted to transfer data within electronic system 700. Bus 740 may include a plurality of computer buses and additional circuitry to transfer data.

[0082] Memory 720 may be coupled to processors) 710. In some embodiments, memory 720 may offer both short-term and long-term storage and may be divided into several units. Memory 720 may be volatile, such as static random access memory (SRAM) and/or dynamic random access memory (DRAM) and/or non-volatile, such as read-only memory (ROM), flash memory, and the like. Furthermore, memory 720 may include removable storage devices, such as secure digital (SD) cards. Memory 720 may provide storage of computer-readable instructions, data structures, program modules, and other data for electronic system 700. In some embodiments, memory 720 may be distributed into different hardware modules. A set of instructions and/or code might be stored on memory 720. The instructions might take the form of executable code that may be executable by electronic system 700, and/or might take the form of source and/or installable code, which, upon compilation and/or installation on electronic system 700 (e.g., using any of a variety of generally available compilers, installation programs,

compression/decompression utilities, etc.), may take the form of executable code.

[0083] In some embodiments, memory 720 may store a plurality of application modules 722 through 724, which may include any number of applications. Examples of applications may include gaming applications, conferencing applications, video playback applications, or other suitable applications. The applications may include a depth sensing function or eye tracking function. Application modules 722-724 may include particular instructions to be executed by processors) 710. In some embodiments, certain applications or parts of application modules 722-724 may be executable by other hardware modules 780. In certain embodiments, memory 720 may additionally include secure memory, which may include additional security controls to prevent copying or other unauthorized access to secure information.

[0084] In some embodiments, memory 720 may include an operating system 725 loaded therein. Operating system 725 may be operable to initiate the execution of the instructions provided by application modules 722-724 and/or manage other hardware modules 780 as well as interfaces with a wireless communication subsystem 730 which may include one or more wireless transceivers. Operating system 725 may be adapted to perform other operations across the components of electronic system 700 including threading, resource management, data storage control and other similar functionality.

[0085] Wireless communication subsystem 730 may include, for example, an infrared communication device, a wireless communication device and/or chipset (such as a Bluetooth® device, an IEEE 802.11 device, a Wi-Fi device, a WiMax device, cellular communication facilities, etc.), and/or similar communication interfaces. Electronic system 700 may include one or more antennas 734 for wireless communication as part of wireless communication subsystem 730 or as a separate component coupled to any portion of the system. Depending on desired functionality, wireless communication subsystem 730 may include separate transceivers to communicate with base transceiver stations and other wireless devices and access points, which may include communicating with different data networks and/or network types, such as wireless wide-area networks (WWANs), wireless local area networks (WLANs), or wireless personal area networks (WPANs). A WWAN may be, for example, a WiMax (IEEE 802.16) network. A WLAN may be, for example, an IEEE 802.1 lx network. A WPAN may be, for example, a Bluetooth network, an IEEE 802.15x, or some other types of network. The techniques described herein may also be used for any combination of WWAN, WLAN, and/or WPAN. Wireless communications subsystem 730 may permit data to be exchanged with a network, other computer systems, and/or any other devices described herein. Wireless communication subsystem 730 may include a means for transmitting or receiving data, such as identifiers of HMD devices, position data, a geographic map, a heat map, photos, or videos, using antenna(s) 734 and wireless link(s) 732. Wireless communication subsystem 730, processors) 710, and memory 720 may together comprise at least a part of one or more of a means for performing some functions disclosed herein.

[0086] Electronic system 700 may also include one or more sensors 790. Sensor(s) 790 may include, for example, an image sensor, an accelerometer, a pressure sensor, a temperature sensor, a proximity sensor, a magnetometer, a gyroscope, an inertial sensor (e.g., a module that combines an accelerometer and a gyroscope), an ambient light sensor, or any other similar module operable to provide sensory output and/or receive sensory input, such as a depth sensor or a position sensor. For example, in some implementations, sensor(s) 790 may include one or more inertial measurement units (IMUs) and/or one or more position sensors. An IMU may generate calibration data indicating an estimated position of the HMD device relative to an initial position of the HMD device, based on measurement signals received from one or more of the position sensors. A position sensor may generate one or more measurement signals in response to motion of the HMD device. Examples of the position sensors may include, but are not limited to, one or more accelerometers, one or more gyroscopes, one or more magnetometers, another suitable type of sensor that detects motion, a type of sensor used for error correction of the IMU, or some combination thereof. The position sensors may be located external to the IMU, internal to the IMU, or some combination thereof. At least some sensors may use a structured light pattern for sensing.

[0087] Electronic system 700 may include a display module 760. Display module 760 may be a near-eye display, and may graphically present information, such as images, videos, and various instructions, from electronic system 700 to a user. Such information may be derived from one or more application modules 722-724, virtual reality engine 726, one or more other hardware modules 780, a combination thereof, or any other suitable means for resolving graphical content for the user (e.g., by operating system 725). Display module 760 may use liquid crystal display (LCD) technology, light-emitting diode (LED) technology (including, for example, OLED, ILED, mLED, AMOLED, TOLED, etc.), light emitting polymer display (LPD) technology, or some other display technology.

[0088] Electronic system 700 may include a user input/output module 770. User input/output module 770 may allow a user to send action requests to electronic system 700. An action request may be a request to perform a particular action. For example, an action request may be to start or end an application or to perform a particular action within the application. User input/output module 770 may include one or more input devices. Example input devices may include a touchscreen, a touch pad, microphone(s), button(s), dial(s), switch(es), a keyboard, a mouse, a game controller, or any other suitable device for receiving action requests and communicating the received action requests to electronic system 700. In some embodiments, user input/output module 770 may provide haptic feedback to the user in accordance with instructions received from electronic system 700. For example, the haptic feedback may be provided when an action request is received or has been performed.

[0089] Electronic system 700 may include a camera 750 that may be used to take photos or videos of a user, for example, for tracking the user’s eye position. Camera 750 may also be used to take photos or videos of the environment, for example, for VR, AR, or MR applications. Camera 750 may include, for example, a complementary metal-oxide-semiconductor (CMOS) image sensor with a few millions or tens of millions of pixels. In some implementations, camera 750 may include two or more cameras that may be used to capture 3-D images.

[0090] In some embodiments, electronic system 700 may include a plurality of other hardware modules 780. Each of other hardware modules 780 may be a physical module within electronic system 700. While each of other hardware modules 780 may be permanently configured as a structure, some of other hardware modules 780 may be temporarily configured to perform specific functions or temporarily activated. Examples of other hardware modules 780 may include, for example, an audio output and/or input module (e.g., a microphone or speaker), a near field communication (NFC) module, a rechargeable battery, a battery management system, a wired/wireless battery charging system, etc. In some embodiments, one or more functions of other hardware modules 780 may be implemented in software.

[0091] In some embodiments, memory 720 of electronic system 700 may also store a virtual reality engine 726. Virtual reality engine 726 may execute applications within electronic system 700 and receive position information, acceleration information, velocity information, predicted future positions, or some combination thereof of the HMD device from the various sensors. In some embodiments, the information received by virtual reality engine 726 may be used for producing a signal (e.g., display instructions) to display module 760. For example, if the received information indicates that the user has looked to the left, virtual reality engine 726 may generate content for the HMD device that mirrors the user’s movement in a virtual environment.

Additionally, virtual reality engine 726 may perform an action within an application in response to an action request received from user input/output module 770 and provide feedback to the user. The provided feedback may be visual, audible, or haptic feedback. In some

implementations, processors) 710 may include one or more GPUs that may execute virtual reality engine 726.

[0092] In various implementations, the above-described hardware and modules may be implemented on a single device or on multiple devices that can communicate with one another using wired or wireless connections. For example, in some implementations, some components or modules, such as GPUs, virtual reality engine 726, and applications (e.g., tracking

application), may be implemented on a console separate from the head-mounted display device. In some implementations, one console may be connected to or support more than one HMD.

[0093] In alternative configurations, different and/or additional components may be included in electronic system 700. Similarly, functionality of one or more of the components can be distributed among the components in a manner different from the manner described above. For example, in some embodiments, electronic system 700 may be modified to include other system environments, such as an AR system environment and/or an MR environment.

[0094] The methods, systems, and devices discussed above are examples. Various

embodiments may omit, substitute, or add various procedures or components as appropriate. For instance, in alterative configurations, the methods described may be performed in an order different from that described, and/or various stages may be added, omitted, and/or combined. Also, features described with respect to certain embodiments may be combined in various other embodiments. Different aspects and elements of the embodiments may be combined in a similar manner. Also, technology evolves and, thus, many of the elements are examples that do not limit the scope of the disclosure to those specific examples.

[0095] Specific details are given in the description to provide a thorough understanding of the embodiments. However, embodiments may be practiced without these specific details. For example, well-known circuits, processes, systems, structures, and techniques have been shown without unnecessary detail in order to avoid obscuring the embodiments. This description provides example embodiments only, and is not intended to limit the scope, applicability, or configuration of the invention. Rather, the preceding description of the embodiments will provide those skilled in the art with an enabling description for implementing various embodiments. Various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the present disclosure.

[0096] Also, some embodiments and examples were described as processes depicted as flow diagrams or block diagrams. Although each may describe the operations as a sequential process, many of the operations may be performed in parallel or concurrently. In addition, the order of the operations may be rearranged. A process may have additional steps not included in the figure. Furthermore, embodiments of the methods may be implemented by hardware, software, firmware, middleware, microcode, hardware description languages, or any combination thereof. When implemented in software, firmware, middleware, or microcode, the program code or code segments to perform the associated tasks may be stored in a computer-readable medium such as a storage medium. Processors may perform the associated tasks.

[0097] It will be apparent to those skilled in the art that substantial variations may be made in accordance with specific requirements. For example, customized or special-purpose hardware might also be used, and/or particular elements might be implemented in hardware, software (including portable software, such as applets, etc.), or both. Further, connection to other computing devices such as network input/output devices may be employed.

[0098] With reference to the appended figures, components that can include memory can include non-transitory machine-readable media. The term“machine-readable medium” and “computer-readable medium” may refer to any storage medium that participates in providing data that causes a machine to operate in a specific fashion. In embodiments and examples provided hereinabove, various machine-readable media might be involved in providing instructions/code to processing units and/or other device(s) for execution. Additionally or alternatively, the machine-readable media might be used to store and/or carry such

instructions/code. In many implementations, a computer-readable medium is a physical and/or tangible storage medium. Such a medium may take many forms, including, but not limited to, non-volatile media, volatile media, and transmission media. Common forms of computer- readable media include, for example, magnetic and/or optical media such as compact disk (CD) or digital versatile disk (DVD), punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a programmable read-only memory (PROM), an erasable

programmable read-only memory (EPROM), a FLASH-EPROM, any other memory chip or cartridge, a carrier wave as described hereinafter, or any other medium from which a computer can read instructions and/or code. A computer program product may include code and/or machine-executable instructions that may represent a procedure, a function, a subprogram, a program, a routine, an application (App), a subroutine, a module, a software package, a class, or any combination of instructions, data structures, or program statements.

[0099] Those of skill in the art will appreciate that information and signals used to

communicate the messages described herein may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0100] Terms,“and” and“of” as used herein, may include a variety of meanings that are also expected to depend at least in part upon the context in which such terms are used. Typically,“or” if used to associate a list, such as A, B, or C, is intended to mean A, B, and C, here used in the inclusive sense, as well as A, B, or C, here used in the exclusive sense. In addition, the term“one or more” as used herein may be used to describe any feature, structure, or characteristic in the singular or may be used to describe some combination of features, structures, or characteristics. However, it should be noted that this is merely an illustrative example and claimed subject matter is not limited to this example. Furthermore, the term“at least one of’ if used to associate a list, such as A, B, or C, can be interpreted to mean any combination of A, B, and/or C, such as A, AB, AC, BC, AA, ABC, AAB, AABBCCC, etc.

[0101] Further, while certain embodiments and examples have been described using a particular combination of hardware and software, it should be recognized that other

combinations of hardware and software are also possible. Certain embodiments and examples may be implemented only in hardware, or only in software, or using combinations thereof. In one example, software may be implemented with a computer program product containing computer program code or instructions executable by one or more processors for performing any or all of the steps, operations, or processes described in this disclosure, where the computer program may be stored on a non-transitory computer readable medium. The various processes described herein can be implemented on the same processor or different processors in any combination.

[0102] Where devices, systems, components or modules are described as being configured to perform certain operations or functions, such configuration can be accomplished, for example, by designing electronic circuits to perform the operation, by programming programmable electronic circuits (such as microprocessors) to perform the operation such as by executing computer instructions or code, or processors or cores programmed to execute code or instructions stored on a non-transitory memory medium, or any combination thereof. Processes can communicate using a variety of techniques, including, but not limited to, conventional techniques for inter-process communications, and different pairs of processes may use different techniques, or the same pair of processes may use different techniques at different times.

[0103] The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. It will, however, be evident that additions, subtractions, deletions, and other modifications and changes may be made thereunto without departing from the broader spirit and scope as set forth in the claims. Thus, although specific embodiments and examples have been described, these are not intended to be limiting. Various modifications and equivalents are within the scope of the following claims. Appendix A

Motivation

Achieving spatially variable etch depth (VED) gratings with high control of pattern height is very important in WG technology to tune the diffraction efficiency and angular/spectral response of the diffractive grating. In non-diffractive solution (refractive/reflective) achieving spatially varying 3D structures is also very important. Unfortunately, there’s not an easy way to patter nanoscale features and spatial control on their geometry on a millimeter-scale. Currently explored solution include the use of movable blades during etch to control etch time (and depth) spatially, use of double mask and grey-tone lithography, etc. However, these techs all require a long development and are hard to control when 2D VED is required.

Invention

The invention include the use of femto-laser pulse modification of substrate surface coupled with a conventional lithography step and dry etch to achieve ANY spatially varying geometry with nanoscale or microscale patterns.

The femto-laser pulses is used to locally modify the etch selectivity of the substrate and “program” a VED function in the substrate directly. This allows for a mask-less grey-tone etch. The nanoscale or microscale lithography is used to define the diffractive/refractive/reflective patterns used by the optical device. Thanks for the femto-laser modification of the substrate, the patterns will etch deeper or shallower depending on the local energy the substrate has been exposed to.

Process steps

1) Expose substrate surface to femto-laser pulses

2) Deposit hard mask. Hard mask (Cr, Pt, Pd, Ti, MoSi, polymer or any metal, metal-oxide combination) may be already present on the substrate. In this case, exposure to fs laser would occur from the backside.

3) Pattern nano- and/or micro-gratings on a lithography layer on top of hard mask (EBL, photolithography, NIL, etc.)

4) Transfer pattern into hard mask.

5) Etch quartz through hard mask. Area of the substrate that were subject to the highest dose are expected to etch faster than un-modified areas. Thus a VED profile can be programmed on the substrate and achieved using dry etching (ICP, CCP, RIE, IBE, ion milling, Chemical-RIE, etc.)

Claims

WHAT IS CLAIMED IS:

1. A method of fabricating a variable-etch-depth structure in a substrate, the method

comprising:

exposing a surface of the substrate to femto-second laser pulses, wherein an exposure dose of the femto-second laser pulses on the surface of the substrate varies across the surface of the substrate;

depositing an etch mask layer on the substrate;

forming a two-dimensional pattern in a lithography layer on the etch mask layer; transferring the two-dimensional pattern into the etch mask layer to form an etch mask; and

etching the substrate using the etch mask to form the variable-etch-depth structure in the substrate.

2. The method of claim 1, wherein the variable-etch-depth structure is a variable-etch-depth grating structure for a waveguide-based near-eye display system.

3. The method of claim 1, wherein the substrate comprises a dielectric material and/or a semiconductor material.

4. The method of claim 1, wherein the etch mask layer comprises one or more of: a metal, molybdenum silicide, a polymer, a metal oxide and a combination thereof.

5. The method of claim 4, wherein the metal comprises chromium, platinum, palladium and/or titanium.

6. The method of claim 1, wherein the etch mask layer is deposited on the substrate before exposing the surface of the substrate to femto-second laser pulses.

7. The method of claim 6, wherein the exposure to femto-second laser pulses occurs from a backside of the substrate.

8. The method of claim 1, wherein the two-dimensional pattern is formed in the lithography layer using electron beam lithography, photolithography and/or nanoimprint lithography.

9. The method of claim 1, wherein the pattern in the lithography layer is transferred into the etch mask layer using a dry etching technique, a wet etching technique, a physical etching technique and/or chemical etching technique.

10. The method of claim 1, wherein the substrate is etched using the etch mask with dry etching.

11. The method of claim 10, wherein the substrate is etched using the etch mask with

inductively coupled plasma etching, capacitively coupled plasma etching reactive ion etching, ion beam etching, ion milling and/or chemical reactive ion etching.

12. A variable-etch-depth structure fabricated using the method of claim 1.

13. A system for performing the method of claim 1.