Imprint Technology in Nanolithography for Optical Devices

Abstract

This disclosure generally describes methods and systems for fabricating high-quality surface relief waveguides for an eyepiece. In particular, this disclosure uses nanoimprint lithography imprinting techniques that reduce or eliminate the presence of gaps within the imprinted features by using a droplet pattern optimized for dispensing photoresist to achieve various optical effects, such as manufacturing waveguides having surface relief features such as diffraction gratings. Further, this disclosure also describes techniques for manufacturing surface relief waveguides having a gradient, such as a substantially continuous gradient or slope, between zones having different residual layer thicknesses of the dispensed photoresist and / or between zones having surface features of different heights (or depths).

Description

Technical Field

[0001] Technical Field The embodiments described herein generally relate to systems and methods for fabricating surface relief waveguides for an eyepiece lens, and to optical devices created thereby.

Background Art

[0002] Background When manufacturing waveguides, eyepiece lenses, and other types of optical devices, it can be important to consider performance. For example, small scratches in the manufactured device can have a disproportionate impact on the optical performance of the device, potentially reducing light power, light loss, artifacts, etc. Performance considerations may balance the manufacturing cost of the device, such as the cost of component materials, fabrication, testing, etc. Thus, manufacturers of high-performance optical devices have conventionally pursued various techniques to enhance the quality of the manufactured device while avoiding an excessive increase in manufacturing cost.

Summary of the Invention

Means for Solving the Problems

[0003] Summary This disclosure generally describes methods and systems for fabricating high-quality surface relief waveguides for an eyepiece lens. In particular, this disclosure describes techniques for manufacturing waveguides having surface relief features, such as diffraction gratings, to achieve various optical effects using nanoimprint lithography techniques that reduce or eliminate the presence of gaps within the imprinted features. Further, this disclosure also describes techniques for manufacturing surface relief waveguides having a gradient, such as a substantially continuous slope or incline, between zones having different residual layer thicknesses of the dispensed photoresist and / or between zones having surface features of different heights (or depths). Such gradients can reduce or eliminate optical adverse effects caused by more abrupt transitions between zones and can enhance the optical efficiency of the completed waveguide.

[0004] The embodiment includes a method executed by a system for manufacturing an optical device, the method comprising determining a dispensing pattern for dispensing drops of photoresist so as to form one or more surface features on at least one surface of a substrate, wherein determining the drop pattern comprises determining a grid of available drop locations based at least in part on one or more constraints for the drop locations, wherein the one or more constraints are based on one or more of i) a dispenser component of a system for dispensing drops of photoresist, or ii) a stage component of a system for stabilizing the substrate during dispensing, predicting a diffusion pattern of drops dispensed according to each of a plurality of candidate dispensing patterns, wherein each of the plurality of candidate dispensing patterns includes a subset of available drop locations and the diffusion pattern is predicted based at least in part on one or more surface features to be formed on at least one surface of the substrate, determining a dispensing pattern corresponding to an optimal diffusion pattern from among the plurality of diffusion patterns predicted based on the plurality of candidate dispensing patterns, dispensing drops of photoresist according to the dispensing pattern on at least one surface of the substrate or on a template usable for shaping one or more surface features, applying a template to shape the dispensed photoresist into one or more surface features on at least one surface of the substrate, curing the dispensed photoresist to form one or more surface features, and isolating the substrate to create an optical device including the one or more surface features.

[0005] In some embodiments, the substrate is composed of glass or a polymer.

[0006] In some embodiments, the photoresist is a polymer fluid.

[0007] In some embodiments, curing the photoresist includes applying ultraviolet radiation to the dispensed photoresist, or applying heat to the dispensed photoresist, or one or more of these.

[0008] In some embodiments, one or more surface features include one or more diffraction gratings.

[0009] In some embodiments, one or more surface features are on one surface of the substrate.

[0010] In some embodiments, one or more surface features are on both sides of the substrate.

[0011] In some embodiments, one or more diffraction gratings include one or more of an in-coupling grating (ICG), an orthogonal pupil expander (OPE), an exit pupil expander (EPE), or a compound pupil expander (CPE).

[0012] In some embodiments, one or more surface features include a non-diffractive pattern.

[0013] In some embodiments, one or more surface features include an anti-reflection pattern.

[0014] In some embodiments, one or more constraints include one or more of the number of nozzles of the dispenser component, the spacing between the nozzles of the dispenser component, and the range of dispensing frequencies of the nozzles of the dispenser component.

[0015] In some embodiments, one or more constraints include one or more of the range of movement speeds of the stage component and the available movement directions of the stage component.

[0016] In some embodiments, determining a distribution pattern corresponding to an optimal diffusion pattern includes identifying an optimal diffusion pattern that minimizes one or more of the number of void gaps in the diffusion pattern, the size of the void gaps in the diffusion pattern, and the total volume of the void gaps in the diffusion pattern.

[0017] In some embodiments, at least one surface of a substrate includes a first zone and a second zone that does not overlap with the first zone, and one or more surface features include a first set of surface features within the first zone and a second set of surface features within the second zone.

[0018] In some embodiments, the first set of surface features includes a first residual layer of photoresist having a first residual layer thickness (RLT) within the first zone, the second set of surface features includes a second residual layer of photoresist having a second RLT within the second zone, and the second RLT is different from the first RLT.

[0019] In some embodiments, at least one surface of a substrate includes a third zone between the first zone and the second zone, and the third zone includes a third residual layer of photoresist having a gradient-like RLT that continuously changes from a first RLT near the boundary between the third zone and the first zone to a second RLT near the boundary between the third zone and the second zone.

[0020] In some embodiments, the first set of surface features includes a first nanostructure having a first height with respect to at least one surface, and the second set of surface features includes a second nanostructure having a second height with respect to at least one surface.

[0021] In some embodiments, at least one surface of a substrate includes a third zone between the first zone and the second zone, and the third zone includes a third nanostructure having a height that continuously changes from a first height near the boundary between the third zone and the first zone to a second height near the boundary between the third zone and the second zone.

[0022] In some embodiments, the optical device is a waveguide.

[0023] Embodiments include an optical device comprising a substrate and surface features formed from a photoresist disposed on at least one surface of the substrate, the surface features including a first set of surface features within a first zone of at least one surface of the substrate, the first set having a first height; a second set of surface features within a second zone of at least one surface of the substrate, the second zone not overlapping the first zone, the second set of surface features having a second height different from the first height; and a third set of surface features within a third zone of at least one surface of the substrate, the third zone being between the first zone and the second zone, the third set of surface features having a variable height that varies continuously from the first height near the boundary between the third zone and the first zone to the second height near the boundary between the third zone and the second zone.

[0024] In some embodiments, the first set of surface features includes a first residual layer of photoresist having a first height that is a first residual layer thickness (RLT) within the first zone, the second set of surface features includes a second residual layer of photoresist having a second height that is a second RLT within the second zone, the second RLT being different from the first RLT, and the third set of surface features includes a third residual layer of photoresist having a variable height that is a gradation-like RLT that varies continuously from the first RLT near the boundary between the third zone and the first zone to the second RLT near the boundary between the third zone and the second zone.

[0025] In some embodiments, the first set of surface features includes a first nanostructure having a first height with respect to at least one surface, the second set of surface features includes a second nanostructure having a second height with respect to at least one surface, and the third set of surface features includes a third nanostructure having a variable height that continuously changes from the first height near the boundary between the third zone and the first zone to the second height near the boundary between the third zone and the second zone.

[0026] In some embodiments, the surface features include one or more diffraction gratings.

[0027] In some embodiments, the one or more diffraction gratings include one or more of an incoupling grating (ICG), an orthogonal pupil expander (OPE), an exit pupil expander (EPE), or a compound pupil expander (CPE).

[0028] In some embodiments, the substrate is composed of glass or a polymer.

[0029] In some embodiments, the photoresist is a polymer fluid.

[0030] In some embodiments, the optical device is a waveguide.

[0031] An embodiment includes a method for manufacturing an optical device, the method comprising determining a dispensing pattern for dispensing drops of photoresist so as to form surface features on at least one surface of a substrate; dispensing drops of photoresist according to the dispensing pattern on at least one surface of the substrate or on a template that can be used to shape the surface features; applying a template to shape the dispensed photoresist into surface features on at least one surface of the substrate; curing the dispensed photoresist to form the surface features; and isolating the substrate to create an optical device including the surface features, wherein the surface features include a first set of surface features within a first zone of at least one surface of the substrate, the first set having a first height; a second set of surface features within a second zone of at least one surface of the substrate, the second zone not overlapping the first zone and the second set of surface features having a second height different from the first height; and a third set of surface features within a third zone of at least one surface of the substrate, the third zone being between the first zone and the second zone and the third set of surface features having a variable height that continuously changes from the first height near the boundary between the third zone and the first zone to the second height near the boundary between the third zone and the second zone.

[0032] In some embodiments, the first set of surface features includes a first residual layer of photoresist having a first height that is a first residual layer thickness (RLT) within the first zone, the second set of surface features includes a second residual layer of photoresist having a second height that is a second RLT within the second zone, the second RLT being different from the first RLT, and the third set of surface features includes a third residual layer of photoresist having a variable height that is a gradation-like RLT that continuously changes from the first RLT near the boundary between the third zone and the first zone to the second RLT near the boundary between the third zone and the second zone.

[0033] In some embodiments, the first set of surface features includes a first nanostructure having a first height with respect to at least one surface, the second set of surface features includes a second nanostructure having a second height with respect to at least one surface, and the third set of surface features includes a third nanostructure having a variable height that varies continuously from the first height near the boundary between the third zone and the first zone to the second height near the boundary between the third zone and the second zone.

[0034] In some embodiments, the surface features include one or more diffraction gratings.

[0035] In some embodiments, the one or more diffraction gratings include one or more of an in-coupling grating (ICG), an orthogonal pupil expander (OPE), an exit pupil expander (EPE), or a compound pupil expander (CPE).

[0036] In some embodiments, the optical device is a waveguide.

[0037] In some embodiments, the substrate is composed of glass or a polymer.

[0038] In some embodiments, the photoresist is a polymer fluid.

[0039] In some embodiments, curing the photoresist includes one or more of applying ultraviolet radiation to the dispensed photoresist or applying heat to the dispensed photoresist.

[0040] In some embodiments, the method further includes etching at least one of the surface features to modify at least one of the surface features after curing.

[0041] In some embodiments, the etching modifies one or more of the first height in the first zone, the second height in the second zone, or the variable height in the third zone.

[0042] In some embodiments, the method includes a step of etching (e.g., post-processing) into the substrate or into a film coating on the substrate.

[0043] In some embodiments, the method includes a step of depositing (e.g., post-processing) a film over a pattern on a substrate to define a replication template and / or an optical device associated with the waveguide, and when the pattern is defined by a master pattern and a droplet pattern (e.g., in the case of RLT), the pattern can be further replicated to another substrate or film for further replication or fabrication as an optical device (e.g., a waveguide).

[0044] Embodiments include a method of creating a template for imprinting, the method comprising providing a carrier substrate with an overlay of a blank (e.g., oxide or nitride) material, dispensing droplets of photoresist onto the overlay according to a droplet pattern, imprinting the photoresist to provide a pattern on the substrate, where the pattern includes a stepwise RLT, and etching the pattern to a final pattern (e.g., dry etching), where the final pattern has a substantially flat upper extent.

[0045] An embodiment includes a method of creating a template for imprinting, the method comprising providing a carrier substrate with an overlay of a blank (e.g., oxide or nitride) material, creating on the substrate an area of photoresist that is not to be etched or removed in a subsequent step (e.g., spin-coated), removing a portion of the photoresist (e.g., using wet etching, dry etching, and / or lift-off), creating a dome or inverse dome-shaped deposition profile within the overlay using a controlled plasma, performing a blank etch to reduce the remaining portion of the overlay to a specific depth, performing photolithography to create features within the carrier substrate, performing lithography to provide a pattern (e.g., an ICG pattern), etching the pattern and removing at least a portion of the resist to provide the template.

[0046] Other features and advantages will be apparent from the following detailed description and the drawings, and from the claims.

Brief Description of the Drawings

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[0057] Detailed Description This disclosure describes various embodiments of methods and systems for manufacturing high-quality optical devices. The optical devices created using the techniques described herein are suitable for use in virtual reality (VR), augmented reality (AR), and / or mixed reality (MR) systems, and / or other suitable optical applications. For example, the optical device can be incorporated into a wearable (e.g., head-mounted) display system that provides an AR experience to the wearer. In such a system, the eyepiece lens can be transparent to allow the wearer to see the physical environment, while the waveguide of the eyepiece lens transmits light used for graphic objects presented as an overlay on the view of the physical environment. In some examples, the waveguide is configured to present graphical objects at multiple depth planes, such that the wearer can perceive the graphical objects as if the objects were at a particular distance from the wearer, e.g., at different depth planes or focal distances. In some examples, the waveguides can be arranged within a waveguide stack, and different ones of the waveguides are configured to present graphical objects at different depth planes and / or to transmit light in different wavelength ranges (e.g., red, green, and blue).

[0058] The optical device includes high-quality surface relief waveguides that can be used in an eyepiece lens, either alone or in a stacked configuration of multiple waveguides. The optical features within the surface relief waveguide have high nano-feature fidelity and high uniformity of residual layer thickness (RLT) within one or more zones that can have different requirements with respect to the resist volume, given the surface features (e.g., one or more diffraction gratings) to be created within each zone. In some embodiments, the features may be manufactured by dispensing, patterning, and curing a high refractive index nanoimprintable fluid that can also be described as a photoresist, resist, or resin. The features can be created on one or both sides of a broad substantially flat substrate that is transparent and acts as a waveguide for transmitting light through total internal reflection (TIR).

[0059] The surface features created on one or more surfaces of the substrate can include diffraction gratings that optically function to affect the light passing through the substrate. Such diffraction gratings can include, but are not limited to, an incoupling grating (ICG), an outcoupling grating (OCG), an orthogonal pupil expander (OPE), an exit pupil expander (EPE), a compound pupil expander (CPE), and / or other types of gratings. The substrate, and the manufactured eyepiece lens, can include any suitable number and type of such gratings in any suitable combination to achieve the desired optical performance.

[0060] The substrate can be composed of any suitable material including a variety of suitable glasses and polymers. For example, the substrate can be composed of an inorganic amorphous material (e.g., heavy tantalum flint glass TADF55, quartz, etc.), a crystalline material (e.g., LiNbO3, LiTaO3, SiC, etc.), a high refractive index polymer (e.g., containing sulfur, aromatic groups, etc.), and / or other polymer materials such as polycarbonate (PC), polyethylene terephthalate (PET).

[0061] The embodiments described herein employ a drop-on-demand volume control dispensing technique for dispensing fluid onto a substrate by precisely controlling the volume of droplets (also referred to as liquid droplets) of the fluid to be dispensed and the location on the substrate where the droplets are dispensed. The dispensed fluid can then be imprinted to create a patterned optical device suitable for use in AR systems, MR systems, and / or other suitable optical applications.

[0062] The fluid may be dispensed onto an optically transparent substrate that acts as a waveguide, and after imprinting the dispensed fluid with a template, it can be cured to create desired nano-features (e.g., diffraction gratings) on one or more surfaces of the transparent substrate. As used herein, optically transparent generally refers to the physical property that allows light to pass through a material without being scattered or absorbed.

[0063] As used herein, total thickness variation (TTV) refers to the difference between the maximum and minimum values of the thickness of a substrate in a series of point measurements across the entire dimension of the substrate. In the case of a substrate having a patterned surface on which a diffraction grating is created, TTV refers to an approximation that is evaluated by ignoring the contribution of the pattern features to the thickness. For example, the thickness (or height) of typical features on a patterned substrate may be in the range of approximately 10 nanometers (nm) to 150 nm. The thickness can vary by 10% (e.g., 1 nm to 15 nm) and is governed by the trench depth of the template. The TTV of an unpatterned substrate typically exceeds 100 nm and can be on the order of microns. Therefore, the additional variation in the thickness of a patterned substrate introduced by the pattern features is negligibly small and can be ignored as an approximation. Thus, the thickness of a patterned substrate evaluated at a location containing protrusions can be approximated by subtracting a given feature thickness from the evaluated thickness to obtain an adjusted thickness, while the thickness of a patterned substrate evaluated at a location without protrusions remains unchanged. That is, the adjusted (e.g., reduced) thickness of the feature area and the inherent thickness of the unpatterned area can be used to calculate the TTV of a substrate having a patterned surface. The low TTV values described herein result at least in part from flat optical grade glass substrates polished to meet the desired flatness and the methods described herein for minimizing or reducing non-uniform material shrinkage during curing. Low TTV can also be imparted to inorganic material substrates by extrusion. Additionally, low TTV is imparted to polymer substrate materials and can be achieved from a mold surface while molding such substrates (e.g., injection molding, ultraviolet (UV) or thermoforming, extrusion, etc.) from base materials consisting of other polymer materials such as high refractive index polymers (e.g., containing sulfur, aromatic groups, etc.) and polycarbonates.

[0064] As used herein, RLT refers to the thickness of a (e.g., polymer) photoresist deposited on a substrate in areas where there are no surface features (e.g., gratings), and / or in areas where there are surface features but between specific nanogeometry structures of the surface features. The RLT may be substantially the same across the finished eyepiece, or different zones of the eyepiece may have different RLTs. In some embodiments, there may be a substantially continuous and / or gradual change in the RLT across at least a portion of the eyepiece. In some embodiments, different zones may have different RLTs, and there may be a continuous gradation (e.g., slope) in the RLT in a transition area from one zone having one RLT and another zone having a different RLT. The embodiments described herein enable fine-tuning of the RLT to achieve various desired optical performance characteristics in the finished eyepiece.

[0065] FIG. 1 depicts an exemplary system 100 for manufacturing an optical device by dispensing a fluid 106 (e.g., a nanoimprint photoresist fluid) onto a substrate 102 and imprinting the dispensed fluid 106 to create a pattern on the substrate 102. As shown in this example, system 100 can include various components that perform various operations to manufacture an optical device such as a waveguide or an eyepiece.

[0066] As shown in FIG. 1, system 100 can operate on substrate 102 while the substrate is supported by a stage 104. Stage 104 can also be described as a chuck. Substrate 102 may be composed of any suitable material such as glass or polymer. Substrate 102 may be in any suitable form and may include sheets, wafers, films, etc. In some examples, a portion of substrate 102 (e.g., a wafer) may include a plurality of regions each corresponding to an eyepiece to be cut out from substrate 102 according to other manufacturing steps to create a desired pattern (e.g., a diffraction grating) on one or more surfaces of substrate 102.

[0067] The stage 104 is configured to support the substrate 102 and to stabilize the substrate 102 during fluid dispensing, imprinting, curing, etching, and / or other manufacturing processes. The stage 104 may be configured to fix the substrate 102 to the stage 104, such as by using a vacuum pump to create a suction force that holds the substrate 102 to the stage 104. The stage 104 may be movable to move between different stations of the manufacturing system 100, as in the illustrated example, in which case the stage is moved from a fluid dispensing station to an imprinting station, to an etching station, etc. Also, the stage 104 may be configured to move in various directions while in a position proximate to (e.g., below) one of the stations. For example, as illustrated, when the stage 104 holds a substrate 102 having a substantially planar surface that includes the X-axis and the Y-axis, the stage 104 may be configured to move in the X direction and / or the Y direction below the station. In some embodiments, the stage 104 may be configured to be movable in the Z direction to increase or decrease the distance between the substrate 102 and a particular device (e.g., the fluid dispenser 112, the imprinting mechanism 116, the etching mechanism 122, etc.) that performs operations on the substrate 102. In some embodiments, the stage 104 is configured to support the substrate 102 by its edges such that both broad surfaces of the substrate 102 are accessible for such operations. In some embodiments, the stage 104 may be configured to invert the substrate 102 in the Z direction to make both sides of the substrate 102 available for fluid dispensing, imprinting, curing, etching, and / or other operations.

[0068] The fluid dispenser 112 is configured to dispense drops (or droplets) of a fluid 106, such as a resist, onto a substrate 102. The fluid dispenser 112 can include one or more print heads (or nozzles) that dispense (e.g., eject) drops of the fluid 106. The fluid 106 is held within a reservoir 108, and the reservoir 108 is connected to the fluid dispenser 106 by one or more channels (e.g., tubes, conduits, etc.) of a suitable type, material, and dimension. One or more fluid pumps 110 operate to circulate the fluid 106 between the reservoir 108 and the fluid dispenser 112. Also, the system 100 can include various other suitable devices, such as pumps, pressure sensors, flow sensors, filters, etc., arranged to provide a reliable flow of the fluid 106 to the fluid dispenser 112.

[0069] The fluid dispenser 112 may dispense several drops of the fluid 106 at specific locations on the surface of the substrate 102 at any suitable location and drop diameter or volume within any suitable number of dispensing passes. The fluid 106 may be dispensed according to a determined drop pattern in order to optimize the use of the fluid 106, minimize the presence of voids within the cured lattice, and / or accurately control the RLT of the dispensed fluid. Such drop patterns are further described below.

[0070] After the fluid has been dispensed, the stage 104 may move (114) to the next station where the template 118 is applied to the fluid 106 by the imprint mechanism 116. The template 118 may be applied to create a desired surface feature 124 (e.g., a lattice) on the surface of the substrate 102.

[0071] In some embodiments, the fluid dispenser and the imprint are performed according to drop-on-demand jet and flash imprint lithography (J-FIL) techniques to dispense fluid 106 and imprint a desired pattern onto fluid 106 to create surface features such as diffraction gratings. Such techniques are described in U.S. Patent No. 7,077,992, entitled "Step and Repeat Imprint Lithography Processes," which is hereby incorporated by reference in its entirety.

[0072] In some embodiments, after imprinting, stage 104 may move (126) to the next station where an etching mechanism performs one or more etching operations to modify the imprinted pattern. Such etching is further described below.

[0073] Control device 120 is communicatively coupled to various other devices of system 100 that perform actions on substrate 102 to manufacture an optical device including stage 104, fluid dispenser 112, imprint mechanism 116, etching mechanism 122, etc. Control device 120 can send signals to various other devices to control their operations. In some embodiments, control device 120 is any suitable type of computing device including at least one processor and memory. The memory can store a computer program including instructions that cause the processor to execute operations for controlling the devices of system 100 during the manufacturing process when executed by at least one processor. Control device 120 may be any suitable type of computing device, such as a personal computer, and may communicate with other computing devices to receive instructions and provide data, etc.

[0074] FIG. 1 shows an example of a system 100 that includes a single fluid dispenser 112, although other embodiments are possible. For example, the system 100 may include multiple fluid dispensers 112 (e.g., print heads) in order to improve the throughput of the system 100 and / or to dispense fluid 106 to additional locations on the substrate 102. The system 100 may similarly include multiple imprint stations, each with an associated imprint mechanism 116 and / or template 118.

[0075] Embodiments support the use of various suitable types of photoresist fluid 106. In some embodiments, the resist is a polymer-based resin in which nanoparticles (NPs) of a high refractive index material are incorporated. Alternatively, the resist can be a polymer-based resin without incorporated NPs. Incorporation of NPs may increase the overall refractive index of the material, which provides an advantage in more closely matching the refractive index of the substrate as described herein. However, incorporation of NPs can also cause Rayleigh scattering of light in the resist. Thus, the choice of using a resist with or without NPs can be based on considerations such as a balance of higher refractive index versus more scattering. For example, a resist having a refractive index of 1.6 or 1.7 and without NPs can provide optimal performance with a higher refractive index (e.g., closer to the refractive index of the substrate) while avoiding scattering caused by the presence of NPs.

[0076] Organic (meth)acrylate monomers and oligomers typically have a refractive index of approximately 1.5 at a wavelength of 532 nm. Both sulfur atoms and aromatic groups have high polarizabilities and can be incorporated into these acrylate components to increase the refractive index of the formulation. This effect is limited by the fluid viscosity limit of less than 20 - 25 cP for the inkjet process and by the refractive index upper limit of sulfur-containing molecules. This approach results in a printable and imprintable resist having a refractive index of about 1.72 at a wavelength of 532 nm light.

[0077] Incorporating inorganic nanoparticles (NPs) such as ZrO2 and TiO2 can significantly further increase the refractive index. Pure ZrO2 and TiO2 crystals can reach refractive indices of 2.2 and 2.4 - 2.6 at 532 nm, respectively. In the preparation of optical nanocomposites of acrylate monomers and inorganic nanoparticles, the particle size is less than 10 nm to avoid excessive Rayleigh scattering. Due to its high specific surface area, high polarity, and incompatibility with the crosslinked polymer matrix, ZrO2 NPs tend to aggregate in the polymer matrix. To overcome this problem, surface modification of the NPs can be used. In this technique, the hydrophilic surface of ZrO2 is modified to be compatible with organic substances, thus enabling the NPs to be uniformly mixed with the polymer. Such modification can be carried out using silane and carboxylic acid-containing capping agents. One end of the capping agent is bonded to the ZrO2 surface, and the other end of the capping agent contains either a functional group or a non-functional organic moiety that can participate in acrylate crosslinking. Examples of surface-modified ZrO2 particles less than 10 nm are those supplied by Pixelligent Technologies (trademark) and Cerion Advanced Materials (trademark). These functionalized nanoparticles are typically sold as a homogeneous formulation uniformly suspended in a solvent and can be combined with other substrates to obtain a resist formulation with a printable viscosity and an increased refractive index.

[0078] System 100 may include other stations and other devices that perform additional operations on substrate 102 when stage 104 moves substrate 102 between stations. In some embodiments, system 100 includes a station for curing fluid 106 dispensed after being shaped into a desired form at an imprint station. Such curing may be by any suitable technique depending on the particular fluid 106 being used, such as application of heat, radiation (e.g., UV light), and / or pressure. System 100 can also include a station that isolates (e.g., cuts) substrate 102 into an eyepiece lens shape desirable for an optical device. System 100 can also include a station for inspecting substrate 102 at one or more stages in manufacturing, such as by operation of an imaging camera.

[0079] Figures 2A and 2B depict schematic views of an exemplary template configuration and operation. Schematic view 200 shows substrate 102 with droplets of fluid 106 dispensed on its surface, and template 118 being applied to form fluid 106 into a desired lattice on the surface of substrate 102. As shown, the template includes the (e.g., negative) form of lattice pattern 202 to be applied. In this example, template 118 is a flexible rollable template that is applied to substrate 102 by operation of roller device 204, which may be a component of imprint mechanism 116. Roller device 204 moves in a direction 206 substantially parallel to the surface of substrate 102 to press the template onto substrate 102 and shape the dispensed fluid 106 into the desired nanogeometry for the lattice. Schematic view 210 shows the state after template 118 has been fully pressed onto substrate 102 and the lattice has been formed by application of the template.

[0080] In some embodiments, the template is a coated resist template (CRT). The template can be manufactured by imprinting on any suitable substrate including plastic (e.g., PC, PET, etc.), glass, silicon, etc. The substrate can be in the form of a wafer, sheet, web roll, or other suitable format. Once the surface is imprinted (e.g., after appropriate adhesive surface treatment), the patterned polymer resist can be conformally coated with a material such as SiO2, Al2O3, Al, Ag, TiN, Cr, etc. by deposition using any suitable technique (e.g., PVD sputtering, CVD-ALD, APPECVD, etc.). This patterned polymer can now be used as a template or mold for nanoimprinting. Also, the coated surface may be treated with a release fluoropolymer material to improve the mold release performance during demolding in the imprint process (e.g., when the template is separated from a waveguide substrate on which a diffraction grating is formed by template application).

[0081] This example depicts a rollable template configuration for use in the imprint step, but embodiments are not so limited. Other types of templates are, for example, a template 118 that presses downward (e.g., in the Z direction of FIG. 1) onto the surface of the substrate 102 instead of having a lateral movement in the X - Y plane parallel to the surface of the substrate 102. In some embodiments, the template 118 is etched or otherwise imprinted on the surface of a cylindrical drum, and the cylindrical drum imprints the desired pattern onto the fluid 106 when the drum rolls over the substrate and the dispensed fluid 106. In such embodiments, the imprint direction 106 can be perpendicular to the axis of rotation of the cylinder. In some embodiments, the template is applied spherically such that pressure is first applied to the substrate at or near the center of the portion of the substrate (e.g., a wafer) where the imprint is initially made, and then pressure is applied outward from the center.

[0082] The plurality of eyepieces may be manufactured from a particular wafer of the substrate. For example, 6 eyepieces may be made from one wafer (e.g., 6-up configuration), or 4 eyepieces may be made from one wafer (e.g., 4-up configuration). In some embodiments, the fluid dispensing step dispenses fluid for all of the eyepieces on the wafer in one operation or set of operations. Alternatively, the stage can rotate the substrate below the fluid dispenser between dispensing operations while moving different eyepiece regions below the dispenser, and the fluid dispenser operations can be performed separately for each eyepiece. Similarly, the imprinting step may be performed simultaneously for all of the eyepieces on the wafer using a template arranged to imprint all of the eyepieces simultaneously. Alternatively, the template may be arranged to imprint a single eyepiece, and each eyepiece may be imprinted separately with the stage (or template) moving accordingly from eyepiece to eyepiece.

[0083] In some embodiments, the fluid 106 is dispensed onto the template 116 instead of or in addition to being dispensed onto the surface of the substrate 102. The techniques described herein operate similarly in such embodiments, and the droplet pattern of fluid droplets is dispensed onto the surface of the template 116 that includes the features (e.g., negative features) to be imprinted onto the substrate 102. Droplet Pattern Determination

[0084] Embodiments provide techniques for determining a droplet pattern for dispensing fluid 106 onto the substrate 102 (or onto a template) to create a desired surface feature on the substrate 102. The droplet pattern is determined such that non-fill (e.g., voids) is minimized or eliminated from the fluid 106 spread by the application of the template 118, and thus surface features formed from the cured fluid are minimized or eliminated. Also, the droplet pattern is determined to provide a controlled, and in some cases ultrathin, RLT in the resulting waveguide.

[0085] During imprinting using previously available techniques, void defects can result from the distribution and entrapment of air within the resist during imprinting. These defects, referred to as non-fill in nanolithography, are areas that are not filled with resist (e.g., at least partially internally within the imprinted and cured nano-features). Previous methods for preventing such defects were to dispense an extra volume of resist into the area so that all gaps were filled. Unfortunately, the extra volume can result in an undesirably large RLT, which can result in poor optical performance in the completed waveguide. Embodiments determine a droplet pattern that enables efficient filling of the lattice pattern of the applied template without increasing the volume of resist to be dispensed.

[0086] When the fluid front entraps air as the template 118 is applied, for example, when the fluid 106 is being pressed between the substrate 102 and the template 118 (also referred to as superstrate) and the air cannot be discharged from the fluid 106 before curing, void defects (e.g., voids) can be introduced into the cured resist structure. The created lattice can have a lattice direction that is the axis along which the lattice pattern is arranged. For example, the lattice may include long channels along the lattice direction separated by ridges. Voids or non-fill defects can be more likely to result when the lattice direction is substantially perpendicular to the imprint direction (e.g., the direction 206 in which the rolling device 204 is moving to apply the template 118) compared to when the lattice direction is parallel to the imprint direction. In some examples, non-fill defects can be more likely to result when the lattice direction is substantially parallel to the imprint direction. Substantially perpendicular or substantially parallel can mean an angular deviation from perpendicular or parallel within an appropriate arc angle (e.g., within 1 degree, within 5 degrees, within 10 degrees, etc.).

[0087] To address this problem and eliminate or mitigate voids, embodiments determine an optimal droplet pattern that takes into account the diffusion characteristics of fluid 106 on substrate 102, which are predicted according to the specific pattern to be imprinted, the characteristics of the fluid and the substrate, the imprint direction, and / or other variables. Droplet diffusion characteristics are related to resist characteristics (e.g., viscosity), substrate surface characteristics, template characteristics (e.g., the grating to be created), and imprint conditions. For example, the diffusion rate can be similar for dome-shaped (e.g., convex or concave) glass and silicon substrates, with other variables kept constant, and planar glass may exhibit a greater diffusion rate. Thus, for glass substrates with different TTVs, the optimized droplet pattern may vary. Also, the diffusion rate can change with different imprint speeds (e.g., the speed at which the template is applied). For example, the faster the imprint, the more difficult it is for air to escape and the more likely void defects are to form.

[0088] The diffusion rate is defined as the ratio of the width of the diffused elliptical droplet (e.g., lateral diffusion) to the length of the diffused elliptical droplet (e.g., longitudinal diffusion). Alternatively, the ratio can be defined as the longitudinal diffusion to the lateral diffusion. If the lateral-to-longitudinal diffusion is known for a specific resist material over a particular substrate, and further based on knowledge of how the resist fluid diffuses and / or interacts with the template (e.g., via capillary filling, etc.), such information can be used to modify the droplet pattern for imprinting in lithography techniques such as J-FIL.

[0089] The lattice direction is the direction along the major axis of the features present in the imprinted lattice (e.g., substantially parallel to the major axis). The direction perpendicular to the lattice direction is referred to as the lateral direction. In some embodiments, the imprint direction is the lattice direction, although embodiments support any imprint direction at any angle with respect to the lattice direction. The imprint direction may be the lateral direction to more effectively diffuse the fluid across the boundaries between channels. The distance between drops in the lateral direction, or the distance between different rows of drops, is referred to as the lateral diffusion distance. Such an available minimum distance is referred to as the minimum lateral diffusion distance (MLSD). This value can be constrained by the geometry of the print head, e.g., the distance between the nozzles of the fluid dispenser 112. Considering that the fluid diffuses easily along the lattice features (e.g., in the lattice direction) and less easily across the lattice features (e.g., in the lateral direction), a smaller MLSD can help avoid void defects. A smaller MLSD can be used in the drop pattern to help the fluid merge in the lateral direction and eliminate air traps. However, if the MLSD is too small, it may lead to a large separation between drops in the lattice direction, which may also cause defects. Thus, embodiments enable the modeling of different drop patterns and the selection of a drop pattern that results in optimal diffusion with minimal or no gaps. The optimal drop pattern can also result in a reduction in the total volume of resist dispensed (e.g., a 50% reduction compared to prior art), considering that the optimal drop pattern is arranged such that the drops optimally fill the volume of the lattice and provide the desired RLT outside the lattice region. The drop pattern for imprinting is further described in U.S. Patent No. 8,119,052, entitled "Drop Pattern Generation For Imprint Lithography", which is hereby incorporated by reference in its entirety.

[0090] FIG. 3 depicts a flowchart of an exemplary process 300 for determining a droplet pattern for use in manufacturing an optical device. The operations of the process may be performed by software executed on one or more suitable computing devices. The various operations may be performed in any suitable order. Some operations may be combined into a single operation. The operations may be performed sequentially and / or in parallel as appropriate for a particular operation.

[0091] At 302, various grating patterns and non-patterned areas to be created on substrate 102 are determined. Such patterns (or non-patterns) may be present in one or more zones on substrate 102.

[0092] At 304, the total volume of fluid to be dispensed is determined based on the volume of the grating pattern to be filled as defined by the template, the desired RLT in the patterned and / or non-patterned zones, and the area of the non-patterned area that can receive resists of various thicknesses.

[0093] At 306, various constraints on the possible droplet patterns are determined based on the configuration of fluid dispenser 112. Such constraints can include the number of nozzles of the dispenser, the spacing between nozzles, and the available dispensing frequency. The dispensing frequency is the frequency at which a nozzle can dispense droplets (e.g., the emission frequency). In some examples, the dispensing frequency can be specified as a range of frequencies. The range of dispensing frequencies may not have a defined upper limit (e.g., as fast as possible to emit) and a defined lower limit (or a lower limit of 0) based on the dispenser configuration.

[0094] At 308, various constraints on the droplet patterns that can exist based on the configuration of stage 104, such as the available movement speed and available movement directions of stage 104, are determined. In some embodiments, the information accessed at 302, 304, 306, and / or 308 may be input into the process as input parameters or otherwise specified.

[0095] At 310, a grid is generated that specifies the available droplet locations based on the constraints accessed at 306 and 308. An example of such a grid is shown in FIG. 4. Each vertex of the grid indicates a location on substrate 102 where the dispenser can dispense droplets of fluid 106.

[0096] At 312, each of a plurality of possible droplet patterns (e.g., dispensing patterns) can be analyzed, and the process can be executed to predict the diffusion pattern of fluid 106 dispensed according to each droplet pattern. This prediction can be made based on a particular droplet pattern, along with the volume of fluid 106 to be dispensed, the specific geometric shape of the grid to be created, the fluid properties of fluid 106, the properties of substrate 102 (e.g., coefficient of friction, etc.), and / or other variables. In some embodiments, the process also takes into account the diffusion rate of the droplets such that the direction in which the fluid front moves and diffuses (e.g., based on the template imprint direction) when the template begins to push droplets across the surface of the template and the substrate.

[0097] At 314, each predicted diffusion pattern from each analyzed droplet pattern can be evaluated, and an optimal diffusion pattern can be identified. The optimal diffusion pattern can be a pattern that includes the fewest voids, smallest voids, and / or the smallest total volume of voids. In some embodiments, each diffusion pattern can be scored based on such metrics that take into account the number and / or size of the voids, and the diffusion pattern with the best score can be designated as optimal.

[0098] In 316, the droplet pattern corresponding to the optimal diffusion pattern is identified and designated as the droplet pattern to be used for dispensing fluid 106 prior to imprinting and curing to create the desired surface features. In some embodiments, the analysis for determining the best droplet pattern can be performed manually by human inspection of the diffusion patterns resulting as various results presented on a suitable display of a computing device. Alternatively, an algorithm can be iteratively executed to automatically search for the optimal diffusion pattern based on the scores calculated as described above, and the droplet pattern to be used can be automatically identified as the droplet pattern corresponding to the optimal diffusion pattern.

[0099] FIG. 4 depicts a schematic view of an exemplary grid 400 for determining a droplet pattern. For example, each vertex of grid 400 where lines intersect can be considered a possible location for dispensing a droplet onto substrate 102 (or onto template 118). As described above, the possible locations for dispensing are determined based on the configuration of the dispenser, such as the distance between nozzles and the available range of nozzle firing frequencies, and the configuration of the stage, such as how fast and in what directions the stage can move below the dispenser. Other factors can also be considered, such as the number of paths that can be made using the stage at different positions below the dispenser. MLSD 404 is shown as the horizontal (along the lateral direction) distance separate from the vertical columns of droplet locations. The spacing along such vertical columns may be based on the nozzle firing frequency and the speed of the stage moving below the nozzle. In this example, four droplet locations 406 are selected for analysis by the process described in FIG. 3. These droplet locations can be modeled to determine the resulting diffusion pattern as described above.

[0100] Figures 5A and 5B depict, respectively, an exemplary droplet pattern 500 and an example of a fluid dispersion pattern 510 that can result from the diffusion of droplets of fluid 106 distributed according to a droplet pattern after application of template 118. As shown in this example, each droplet 502 can diffuse into an elongated shape 504 according to a particular geometry of the lattice. The diffusion of the various droplets 502 can leave one or more voids 506 that are not filled with fluid 106. As described above, the techniques described herein reduce or eliminate the number and volume of such voids to ensure optimal performance of the completed optical device.

[0101] Figure 6 depicts a flow diagram of an exemplary process 600 for creating surface features on a substrate. The operations of the process may be performed by one or more components of system 100 under the control of, for example, control device 120. The various operations can be performed in any suitable order. Some operations can be combined into a single operation. The operations may be performed sequentially and / or in parallel as appropriate for a particular operation.

[0102] At 602, a droplet pattern is determined as described above. At 604, fluid 106 is dispensed onto substrate 102 according to the droplet pattern. As described above, in some embodiments, fluid 106 is dispensed onto template 118 according to the droplet pattern. At 606, template 118 is applied to shape the dispensed fluid into a desired surface feature (e.g., a diffraction grating) on one or more surfaces of the substrate. In embodiments where the template is a rolled and / or flexible template such as the examples of FIGS. 2A and 2B, or a rolled cylindrical template as described above, the rolling direction may be in any suitable direction with respect to the grating direction and / or the lateral direction.

[0103] When the template is a cylindrically rolled template applied to a substrate, the fluid front of the droplet diffusion can be substantially linear (e.g., perpendicular to the imprint direction of the template). In some examples, when the template is moved vertically downward across the substrate to press the substrate (e.g., not cylindrically rolled), the droplet diffusion fluid front can be more circular rather than a linear fluid front between the template and the substrate interface. In this case, in order to determine the design and placement of the droplet pattern, the droplet diffusion rate may be less dependent on the imprint direction when a given specific nanopattern or micropattern to be applied during imprinting is provided. In the case of an imprint process where the template contacts or is near the center of the wafer, the advantages include less dependence of the diffusion rate on a specific imprint direction (e.g., rather than a one-directional, there are more 360-degree outward imprint actions), and such techniques can help maintain equivalent optical performance across the eyepieces distributed in a pinwheel configuration (e.g., having rotational symmetry). In the case of an imprint process where the roller rolls from one end (e.g., the leading edge) to the other end (e.g., the trailing edge), the eyepieces at different locations on the wafer can exhibit different performance characteristics in the final product.

[0104] At 608, the dispensed fluid is cured using heat, UV light, pressure, and / or some other technique. At 610, in some embodiments, the imprinted and cured surface features can be etched to modify the surface features and / or fine-tune them to their final shape. Such etching will be described in more detail below. At 612, the substrate 102 can be isolated (e.g., cut) to create one or more eyepieces from the substrate 102.

[0105] As described herein, the problem of air entrapment into the finished surface features is addressed by drop pattern optimization to determine a drop pattern that reduces or eliminates the presence of voids in the cured and dispensed photoresist formed into a nanometric structure for a diffraction grating. Determining the amount of fluid 106 required is, at least in part, a geometric calculation where the volume of fluid is calculated as a volume sufficient to form the desired surface features, as a volume deposited (if any) in the non-grated portions of the substrate, and as a desired RLT in one or more zones of the substrate 102.

[0106] Different drop pattern solutions do not all have the same filling efficiency for filling the desired geometry of the grating. In a grating, the drops tend to flow along the grating (e.g., in the grating direction) rather than across the grating (e.g., in the lateral direction) following the capillary flow of fluid 106 along the direction of the channels of the grating that extend in the grating direction. In the case of deeper and / or narrower channels, the effect can be stronger. In contrast, fluid 106 cannot flow vertically between channels. The difference in flow can be compensated for by determining specific drop placement locations within the drop pattern. For example, in the case of deep and / or narrow grating channels, the optimal drop pattern may include a greater spacing between drops in the grating direction and a closer spacing between drops in the lateral direction (e.g., as shown in FIG. 5A). Stated another way, on a flat or other surface having similar features in both vertical directions, the drop pattern can be a square pattern having similar drop spacing along both directions.

[0107] In some embodiments, the droplet diameter can be on the order of several tens of microns (e.g., diameter), and the channel width of the lattice channels can be less than 1 micron. The droplet spacing depends on the dispenser and / or stage configuration as described above. In some examples, considering this configuration, the closest droplets that can be dispensed are separated by about 10 microns, which is approximately the diameter of the droplet. In a dispenser having a multi-nozzle configuration, the nozzle separation in some examples is about 100 microns along the print head direction (e.g., lateral direction), which also constrains the separation in that direction to about 100 microns. To achieve closer separation in the lateral direction, the stage can be shifted to bring it closer under the print head in subsequent dispensing passes. The droplet spacing along the direction in which the nozzle is moving relative to the substrate (or vice versa) can be constrained by the nozzle firing frequency combined with the speed at which the stage can move in that direction. In some examples, the firing frequency range can be from 4 kHz to 14 kHz, and the relative speed between the dispenser and the substrate (e.g., stage movement speed) required to dispense droplets can be from 100 mm / s to 400 mm / s. The imprint speed at which the droplets are merged into different nanopatterned grooves between the template and the substrate can vary from 1 mm / s to 40 mm / s.

[0108] The droplet pattern determination process can take into account various constraints based on the configuration of the dispensing and stage setup, along with the desired nanogeometry of the lattice to be created. Other factors can include the volume of the fluid 106 to be dispensed and the desired throughput of the system 100 for manufacturing the eyepiece. For example, while it may be possible to arrange multiple stages, a greater number of steps to move the stage to dispense additional droplets can increase the time taken to process each part of the substrate and thus reduce the overall throughput of the system. The overall optimal droplet pattern may be determined based on which droplet pattern results in the minimum number and / or minimum volume of voids and minimizes the number of passes for dispensing and / or stage movement, such that the throughput of the system remains within an acceptable range.

[0109] In some embodiments, a portion of the substrate 102 to be imprinted (e.g., a wafer) can include a plurality of regions each corresponding to an eyepiece lens cut out from the substrate 102. In such embodiments, each eyepiece lens region may be modeled separately to determine the optimal droplet pattern for that region, and the overall dispensing may follow an overall droplet pattern that is a combination of the droplet patterns of each region. Alternatively, the eyepiece lens regions may be modeled, and the determined droplet patterns may be applied separately to each eyepiece lens region, in which case the stage 104 moves the substrate 102 between passes to apply the droplet pattern to each eyepiece lens region of the wafer.

[0110] As described above, due to the configuration of the dispenser stage and / or nozzle, the droplet pattern can be constrained to a particular type of grid (mesh). The droplet pattern may also depend on the layout of the wafer of the substrate being processed. For example, the wafer can include a layout for four eyepiece lenses (e.g., a 4-up configuration), or the wafer can include a layout for six eyepiece lenses (e.g., a 6-up configuration) where the eyepiece lenses are arranged parallel to each other (e.g., a linear array configuration) or rotatably with respect to each other (e.g., a pinwheel configuration). This can lead to complexity in the modeling. The grid shown in FIG. 4 has vertices separated by lines at an angle of 60 degrees to each other and is based on a 6-up configuration where the stage 104 rotates (e.g., 60 degrees) between imprints of different eyepiece lenses and each eyepiece lens is imprinted separately. As another example, a 4-up configuration can result in a grid that is a more square pattern. The individual eyepiece lenses of any layout configuration can also be imprinted in a single process step without rotating the wafer and / or the stage.

[0111] In some embodiments, an optimal droplet pattern can be determined for a substrate to be imprinted, where a particular eyepiece is divided into different zones. The various zones may have different RLTs and / or different heights (or depths) of the nano-features forming the lattice. In some embodiments, the imprint can also create a transition zone between zones of different RLTs and / or different feature heights, and the transition zone can result in a gradual change (e.g., a slope) in the RLT and / or feature height between the zones. Such embodiments that result in a continuously varying gradation pattern are further described below. The aforementioned droplet pattern determination process can take such a design into account and determine an optimal droplet pattern for creating a plurality of zones of different RLTs and / or different feature heights, and transition zones that result in a gradual change in the RLT and / or feature height between the zones. Continuous gradation pattern

[0112] Embodiments also provide for creating continuous (e.g., pseudo - grayscale) nanoscale gradations of surface features using inkjet - based nanoimprint lithography. Embodiments provide techniques for generating continuous gradation patterns within the constraints of physical device (e.g., inkjet nozzle spacing) and droplet volume. Generating a continuous gradation pattern can perform the aforementioned grid (e.g., unit cell mesh) and droplet pattern optimization (e.g., optimization of the unit cell fluid pattern), and in some embodiments, unit cell boundary smoothing. If desired, the continuous gradation ejectable pattern can be applied to imprint nano - patterns and / or micro - patterns over a large area while keeping the RLT constant. Generally, the technique provides more precise control of the RLT over one or more zones to be imprinted. In some examples, embodiments for creating an analog continuous gradation pattern in the final imprint can be used, using additional etching steps to fine - tune the imprinted pattern to the final pattern for an eyepiece. This provides a high - efficiency surface relief waveguide with good image uniformity for use in fabricated optical devices. As described above, optical devices (e.g., waveguides and / or eyepieces) can be used in AR, MR, or VR solutions, or in other types of optical systems.

[0113] Embodiments also provide advantages by creating an RLT that varies substantially continuously over a defined region (as shown in the example of FIG. 9), where the defined region can then be used to etch a continuous pattern defined by the RLT into a material such as SiO2, Si3N4, etc., to create a sub-master template from a template starting at a single depth riding on the continuously varying RLT. A template having continuously varying features is fabricated (as shown in FIGS. 10 - 12) and used to pattern a replication onto a suitable substrate (e.g., plastic, glass, etc.) using J-FIL. When used, the drop pattern can be made to match the continuously varying pattern applied to the substrate.

[0114] The substrate can be imprinted in a plurality of zones, where each zone may include different surface features (e.g., diffraction gratings) of different configurations and / or different RLTs within various zones. Conventionally, attempts to fabricate waveguides with fine zone meshes have been limited by two factors. The first factor is the inaccuracy in master template alignment in nanoimprint tools and / or inkjet head or nozzle alignment. The second factor is the feature fabrication accuracy during the etching step. During imprinting from a rigid template or a soft master template (e.g., CRT) onto a substrate (e.g., a wafer), the transition area between zones having different grating features (e.g., different discretely stepped heights and / or linewidth zones) can be filled with a small volume of resist having a non-uniform RLT under the pattern created by the imprint using the template. Such irregularities in the underlying RLT can cause undesirable optical artifacts that degrade the performance of the finished optical device.

[0115] These problems can be mitigated or eliminated by using an analog or at least partially analog continuous gradation pattern in regions of the substrate (e.g., transition zones) between zones having different gratings and / or different RLTs. Inkjet imprint lithography techniques such as J-FIL can be used to dispense a low-viscosity UV curable resist (polymer resin) onto any suitable type of substrate (e.g., roll, sheet, wafer, rigid, flexible, organic, inorganic, etc.), and in processes such as the foregoing, a desired (nano or micro) pattern can be rapidly transferred from a template-type to the substrate at low cost. Drop-on-demand inkjet technology patterns the surface of the substrate with individual drops according to a previously determined drop (dispensing) pattern. One challenge in the inkjet method of UV nanoimprint lithography is that the dispensed drops can coalesce based on a number of variables such as drop volume, contact angle, surface energy, nano features created within the grating, capillary forces, evaporation of the resist fluid, and / or the rigidity of the template and / or substrate.

[0116] When imprinting on a portion of a substrate (e.g., a wafer) being processed from a soft master template, the transition area between zones can be filled with a small volume of extra resist. To reduce this artifact, multiple zones can be used in the master template design to reduce the feature height step between zones. FIG. 7A illustrates such an example in schematic diagram 700. In this example, template 118 includes multiple zones 708 each having a different lattice feature height. Application of the template to fluid 106 dispensed on substrate 102 creates features 702 for different zones. At the boundary 706 between zones, an amount of excess resist fluid 704 may be present after imprinting. To improve uniformity and reduce or eliminate the presence of such excess fluid 704, the technique uses a more gradual transition between zones 708 by using a continuous gradation pattern (e.g., a pseudo gray scale) within template 118. FIG. 7B illustrates such an example in schematic diagram 710. As shown in this example, template 118 includes a more continuous change in feature height instead of a sharp transition between zones of different feature heights. The resulting features 712 imprinted on substrate 102 also exhibit such continuous variations without the spikes of excess resist 704 present in the example of FIG. 7A.

[0117] In addition to or instead of different zones having different feature heights of the imprinted lattice, as shown in FIG. 7A, different zones may have different RLTs. FIG. 7C shows an example 720 where template 118 includes different zones 708 of different RLTs that can be used to imprint different heights of imprinted RLTs 722 on different zones 708 on substrate 102. As described above, such a sharp transition between zones of different RLTs can have an adverse optical effect in an optical device. To avoid such an adverse effect, as shown in the example 730 of FIG. 7D, the transition between zones can be more gradual. In this example, the zones 708 of different RLTs are sandwiched by a transition zone 724 where the RLT changes somewhat gradually between zones of different RLTs.

[0118] In addition to the advantages of smoother imprint transfer and relaxed alignment requirements, this also enables the use of finer grids in optical designs and can provide a method for fabricating continuous master templates. When a template and / or master template having a master pattern to be replicated has individual zones, the alignment requirements between droplet dispensing and alignment from the template to the substrate can be more stringent. This is because the droplet volume in regions with a small volume of fluid may not be present in regions with higher droplet volume requirements. In some examples, the separation between zones can range from 100 nm to 1 micron. For droplet diameters on the order of 100 microns, the process can be fine-tuned based on fluid diffusion and alignment. For example, when the transition between two such zones is smoother, e.g., when the width of the transition zone is about 10 to 1000 microns, the droplet diffusion does not change abruptly, giving a smoother transition in the RLT and maintaining the desired RLT range.

[0119] By using such a gradation, the brightness (e.g., efficiency) of the virtual image can be improved without sacrificing the uniformity of the image (e.g., how well the image fills the corners and the center of the field of view). However, when the gradation of the template is created using photolithography involving etching masking, the boundary between two gradation step zones can change the RLT over a wider area (e.g., about 10 to 100 microns) compared to the zone transition boundary (e.g., <1 micron). In particular, the volume of the resist can enter the shallower adjacent zone and thus increase the RLT of that adjacent zone. Similarly, the resin volume from the shallow zone can cause a thinner RLT and / or non-filling in the higher adjacent zone.

[0120] The zones described herein may be on one or both sides of the substrate. In some examples, the different zones do not overlap and the zones are separated from each other. Alternatively, the different zones may at least partially overlap. The different zones can be adjacent or separated at some suitable distance. The zones can be of any reasonable shape and / or size having any suitable dimensions for covering a portion of the area of at least one surface of the substrate.

[0121] FIG. 8A depicts a schematic diagram 800 showing an example where different zones 802 and 804 of surface features on substrate 102 have different heights and / or different RLT characteristics, and a portion 808 of the resin fluid flows from one zone to another across a sharp (e.g., abrupt and discontinuous) transition boundary between the zones. FIG. 8B depicts a schematic diagram 810 showing an example where a transition area 806 is created between zones of different feature heights. In the transition area 806, the feature height changes more gradually between the higher feature zone 802 and the lower feature zone 804, avoiding an undesirable flow of the resin 808. The test results showed an improvement in image uniformity in the design created as in the second example of FIG. 8B. In the example of FIG. 8A, the test results showed the presence of undesirable high-frequency artifacts in the completed optical device. Such major high-frequency image stripes can be undesirable, and since these stripes do not always appear in the same location, it is very difficult to correct the color across the final device and / or multiple devices. A gradation pattern such as in FIG. 8B can reduce or eliminate such artifacts and provide an analog zone transition region with the same eye box efficiency but improved contrast and sharpness.

[0122] For generating a continuous gradation pattern, the aforementioned grid (e.g., unit cell mesh), droplet pattern optimization (e.g., optimization of the unit cell fluid pattern), and such unit cell boundary smoothing are used. Techniques such as J-FIL are suitable for such gradations because, for example, they can distribute the target droplet volume over a wide area where the resist volume can gradually increase (or decrease) from one side of the distribution area to the other side. In some embodiments, a random or quasi-random droplet pattern can be used to fill specific areas such as the area that is the CPE of the eyepiece. By using a random droplet pattern and gradually modulating the resist volume distributed to match the grid depth within the area, the zone boundaries defined by the droplet pattern may be less conspicuous due to the analog gradation defined within the imprint. In some embodiments, the droplet pattern can be further optimized using the droplet diffusion rate within each unit cell as the functional grid orientation, feature height, dispensed resist type, and / or substrate type to better reduce or eliminate the presence of non-fill defects. The entire wafer can be meshed into small unit cells, and the geometric shape of the feature (including the thickness of the residue layer, grid duty cycle, feature height profile, grid orientation, etc.), the size of the unit cell, and the droplet volume determine the number of droplets within each unit cell. The calculated number of droplet depositions can be provided as an input to a centroid Voronoi mosaic processing (CVT) loop for local optimization. CVT is a specific type of Voronoi tessellation where the generation point of each Voronoi cell is also its centroid (e.g., center of mass). It can be regarded as the optimal partition corresponding to the optimal distribution of the generators. The droplet distribution can reach the local minimum within the CVT loop with sufficient iterations and a sufficiently high resolution. The unit cell can be defined as a repeating droplet pattern that can be placed on the underlying grid pattern, which can be defined by various tool constraints such as droplet nozzle spacing, dispense frequency, dispense speed, etc., as described herein.

[0123] A unit cell optimized for different feature heights is similar to a mosaic having different thicknesses across the boundaries. If the mesh (e.g., grid) is sufficiently fine and the unit cell size is sufficiently small, the difference in thickness can be ignored for the desired low-resolution imprint. However, for a given number of drops within the unit cell and a constant drop volume, the fineness of the mesh is limited. As a result, for high-resolution imprinting, other methods can be used to optimize the pattern. To smooth the boundaries across different unit cells, the drop locations can be randomized over a range with the original determined drop locations as the center in both the X and Y directions. The randomized pattern can then be transferred across the wafer. After imprinting and optical measurement, the drop pattern can be adjusted and optimized again based on the measurement feedback. Thus, as a modification of the process of FIG. 3, such randomization, measurement, and re-randomization can be performed.

[0124] The stepwise RLT imprint can also be used to fabricate templates (e.g., submasters), and the corresponding gradation tendency is mainly defined by the droplet pattern that is distributed and imprinted. Etching can also be used in this process. For example, gradation etching of SiO2 (thermal oxide on Si) can be performed secondarily by using the RLT as an etching mask when using the dry etching RIE technique for etching SiO2. The etching selectivity can be controlled with adjustment gases such as CHF3, CF4, C4F8, Ar, O2, SF6, etc. for etching either the organic imprint or SiO2. In this way, the template can be fabricated to include multi-step zones with analog zone transitions and / or analog gradation patterns to provide a master mold ready for replication. By adjusting the resist volume distributed to the various zones, dry etching can be performed on the template material to different depths (e.g., SiO2, Si3N4, Si, etc.). When using lithography techniques such as J-FIL to create the template, various shapes such as Sawtooth and multi-step can also be transferred during the dry etching process.

[0125] This process can significantly reduce the cost and complexity of etching wafer templates of various sizes (e.g., 2, 4, 6, 8, 12 inches, etc.) used in lithography. Using an imprint process with on-demand dispensing of a curable resist (such as J-FIL), a dispensing pattern with, for example, random or quasi-random droplet locations and / or a multi-zone (e.g., eight or more zones) droplet pattern can be dispensed or coated onto the target waveguide substrate to transfer the waveguide pattern from the master mold.

[0126] FIG. 9 shows an exemplary process for fabricating a complex (e.g., 6-up) template having analog (or at least partially analog) gradations and / or other specific nano-features. At 900, a carrier substrate 912 having an overlay of a blank oxide or nitride material 902 is provided. At 910, drops of resist 904 are dispensed onto the overlay 902 in accordance with, for example, the drop patterns described herein. At 920, the resist is imprinted to yield a pattern 906 having a stepped RLT as shown. At 930, dry etching is performed to etch the pattern 906 into the final pattern 908. As shown in the example of FIG. 9, the etching can create a final pattern 908 having a substantially flat or planar top height across various features that can have different feature depths for the stepped RLT.

[0127] The surface features can include multiple zones each having a different pattern with different RLTs and / or features of different heights / depths. Embodiments provide for the use of such zones, but with a gradual change in RLT and / or feature height between zones, as described herein, to mitigate various adverse effects that can occur due to abrupt changes between zones. Example RLTs can be in the range of 10 to 35 nanometers (nm). Feature creation can also include the step of etching the features after dispensing and imprinting using a template. Conventional available methods using imprint plus etching can be costly due to the extra etching steps. The embodiments described herein for drop pattern optimization can reduce costs by providing an initial imprint pattern that is more accurate and / or closer to the final pattern than would be created without using an optimized drop pattern. The pattern can then be fine-tuned to its final form using etching. The use of an optimized drop pattern can also eliminate the need to perform one or more additional imprint steps using a sub-master template.

[0128] The above algorithm for determining an optimized drop pattern can also take into account a boundary area where the transition between zones is gradual in terms of RLT change and / or feature height change. For example, as shown in FIG. 8, the volumes allocated to zones 802 and 804 may be different, and the transition zone 806 can have a drop pattern where the drops heading towards 804 are more spaced apart than the drops heading towards 802. The drop volume is generally controlled by, for example, the drop diameter, the number of drops dispensed, the drop density across the transition zone (e.g., along the X-Y pitch).

[0129] As described above, a continuous analog gradation or analog transition between zones of different RLT and / or surface feature heights is useful for enabling highly efficient and uniform images in optical devices using planar waveguides having relief nanostructures. The techniques described herein can also be used in curved waveguides, providing similar advantages. Such gradations avoid sharp transitions between zones that can cause a decrease in image uniformity, contrast, and sharpness (due to variations in RLT). The use of such gradations can also avoid an increase in the complexity of template fabrication and manufacturing costs while achieving similar eye box efficiency goals in the manufactured eyepiece. Embodiments provide the fabrication of such templates for nanoimprint lithography using plasma-controlled deposition by an etching method. The resulting advantages include a reduction in the complexity and cost of template gradation in manufacturing, a reduction in the non-uniformity of the image obtained as a result of being displayed through the eyepiece, and an improvement in image quality (e.g., contrast and sharpness) using J-FIL technology for creating the final pattern on the waveguide substrate.

[0130] FIG. 10 illustrates an exemplary process for fabricating an imprint template having analog graduations using deposition and etching techniques. This process enables a smooth transition between zones of different feature heights without using the multiple masking, lithography, and etching steps that would otherwise be required for fabricating such a multi-zone master template. In the case of analog graduations using the previously available stepwise photolithographic exposure process, the number of steps is very large and costly.

[0131] Similar to the example of FIG. 9, at 1000, a carrier substrate 1002 having an overlay of a blank oxide or nitride 1004 is provided. At 1010, photolithography can be performed to create region 1006. The upper region 1006 can be a spin-coated photoresist for creating an area that is not etched or removed in subsequent steps.

[0132] At 1020, operations for development, wet or dry etching, and partial stripping of the photoresist are performed. At 1030, operations for creating an inverse dome-shaped deposition profile in the oxide / nitride layer using a controlled plasma are performed. At 1040, in some examples, blank etching can be performed to reduce the remaining overlay (e.g., oxide or nitride) profile to a desired depth. The blank etching can be performed using a wet (e.g., buffered oxide etching or HF for SiO2, etc.) or dry (e.g., RIE, ICP-RIE, IBE, etc.) etching process. At 1050, photolithography can be performed to create desired features in the oxide / nitride carrier substrate. The lithography is not limited to photolithography, and electron beam lithography or UV / thermal nanoimprint lithography can also be used. At 1060, a lithography step such as UV nanoimprint lithography can be performed to provide a pattern (e.g., an ICG pattern). At 1070, the pattern can be etched, and at least a part of the resist can be stripped to demonstrate a template suitable for imprinting on the waveguide substrate to create a patterned waveguide.

[0133] This method can be used to create reverse dome or normal dome-shaped deposition profiles, and also uses a shadow mask to mask the deposition material density or change the plasma density for plasma-enhanced deposition processes such as plasma chemical vapor deposition (PE-CVD). FIG. 11 illustrates an example of a method for creating a dome or reverse dome shape on a substrate by manipulating the deposition using a shadow mask within a plasma head or deposition source. Exemplary materials used for deposition can include, but are not limited to, SiO2, Si3N4, or Al2O3. As shown in Example 1100, a shadow mask 1102 having holes of various diameters can be used, and the deposition plasma 1104 can pass through the holes of the mask onto the sample 1106. In Example 1110, the shadow mask 1102 is used while varying the density of the plasma-enhanced deposition density. The location and density of the holes determine to what extent the plasma and reactants are exposed to different regions and thus whether they chemically react to deposit or are removed in the case of etching.

[0134] Embodiments also provide a continuous gradation method that uses a subtractively gradated etching substrate to generate a continuous gradation template, which can improve field uniformity and optimize eyepiece efficiency. Conventional techniques involve creating a nano-pattern with a flat top and a gradation bottom on the template. Embodiments improve this technique by creating a nano-pattern with a flat bottom and a gradation top on the template. This can avoid RLT non-uniformity on the imprinted resist and improve field uniformity.

[0135] If the master template has patterned features with a flat top and a stepped bottom, the CRT made from the master template will have a corresponding stepped surface. When this CRT is used to imprint on a (e.g., glass) substrate to generate an eyepiece lens, the step, as described above, causes the creation of an RLT hump in the step transaction area. This can cause visual uniformity artifacts.

[0136] Figure 12 shows an exemplary process for creating a template using a subtractive continuous gradient. As shown at 1202, a substrate having an Si layer and an SiO2 layer is received. A mesh shadow mask 1210 is placed on top of the wafer during dry SiO2 etching. As shown at 1204, by adjusting the mesh mask aperture duty cycle, the etching rate is adjusted to create a thickness gradient of the SiO2 layer. In this operation, a higher etching rate provides the thinner SiO2 layer end. During pattern dry etching, the Si can layer can function as an etch stop so that, as shown at 1206, the feature depth stops at the SiO2 - Si interface. Thus, the patterned feature has a flat bottom. The CRT made from this template can have a flat surface, as shown at 1208. In some examples, the central plateau on the template is far from the pattern area and may not affect the pattern area imprint. The gradient method of mesh shadow mask etching is further described in U.S. Patent No. 10,527,865, titled "Method and System For Tunable Gradient Patterning Using a Shadow Mask", which is hereby incorporated by reference in its entirety. Exemplary computing system

[0137] FIG. 13 illustrates a schematic diagram of an exemplary computer system 1300. Various computing devices described herein, such as the control device 120 shown in FIG. 1, can be implemented to include one or more of the components of the system 1300.

[0138] System 700 includes one or more processors 1310, a memory 1320, a storage device 1330, and an input / output device 1340. Each of the components 1310, 1320, 1330, and 1340 can be interconnected using one or more system buses 1350. The processor 1310 can process instructions for execution within the system 700. The processor 1310 can include a single-threaded processor and / or a multi-threaded processor. The processor 1310 can process and execute instructions stored in the memory 1320 and / or the storage device 1330 to perform various operations, receive and analyze data inputs, generate data outputs, store and retrieve data, and present text, graphics, audio, video, images, and / or other types of information via a user interface on the input / output device 1350.

[0139] The memory 1320 stores information within the system 700. In some embodiments, the memory 1320 is a computer-readable medium. In some embodiments, the memory 1320 is a volatile memory unit. In some embodiments, the memory 1320 is a non-volatile memory unit.

[0140] The storage device 1330 provides a mass storage device for the system 700. In some embodiments, the storage device 1330 is a computer-readable medium. In various different embodiments, the storage device 1330 can be a floppy (registered trademark) disk device, a hard disk device, a solid state drive, an optical disk device, a tape device, a universal serial bus stick, and / or any other suitable type of storage device.

[0141] The input / output device 1350 provides input / output operations to the system 700. The input / output device 1350 can include input devices including, but not limited to, a keyboard, a pointing device, a mouse, a touchpad, a camera, a microphone, an orientation or motion sensor (e.g., an accelerometer, a gyro sensor, etc.), and / or a game controller. The input / output device 1350 can also include output devices including, but not limited to, a display, an audio speaker, a tactile actuator, a printer, etc.

[0142] The described features can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations thereof. The apparatus can be implemented in a computer program product tangibly embodied in an information carrier, e.g., a machine-readable storage device, for execution by a programmable processor; and method steps of the methods described herein can be performed by a programmable processor executing a program of instructions to perform functions of the described embodiments by operating input data to produce output. The described features can advantageously be implemented in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device. A computer program is a set of instructions that can be used, directly or indirectly, in a computer to perform a particular activity or to cause a particular result. The computer program can be written in any appropriate programming language, including a compiled or interpreted language, and can be deployed in any form, including as a stand-alone program, or as a module, component, subroutine, library, or other unit suitable for use in a computing environment. A module is one or more computer programs and / or part of a computer program executable by one or more processors.

[0143] Processors suitable for the execution of a program of instructions include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of computer. In general, a processor can receive instructions and data from a read only memory or a random access memory or both. Elements of a computer are a processor for executing instructions, and one or more memories for storing instructions and data. In general, a computer may also include, or be operatively coupled to communicate with, one or more mass storage devices for storing data files. Such devices can include magnetic disks, such as internal hard disks and removable disks, magneto-optical disks, and / or optical disks. Storage devices suitable for tangibly embodying computer program instructions and data include, by way of example, any suitable form of non-volatile memory including erasable programmable read only memory (EPROM), electrically erasable programmable read only memory (EEPROM), flash memory devices, magnetic disks such as internal hard disks and removable disks, magneto-optical disks, and semiconductor memory devices such as compact disk read only memory (CD-ROM) and digital video disk read only memory (DVD-ROM) disks. The processor and the memory can be supplemented by, or incorporated in, one or more application specific integrated circuits (ASICs).

[0144] To provide for interaction with a user, the features can be implemented on a system having input output devices such as a display device. The display device can include any suitable type of display, such as a cathode ray tube (CRT), liquid crystal display (LCD), for displaying information to a user. Input devices such as a keyboard and / or a pointing device such as a mouse or trackball can enable user input to the system.

[0145] The features can be implemented in a computer system including backend components such as a data server, or including middleware components such as an application server or an Internet server, or including frontend components such as a client computer having a graphical user interface or an Internet browser, or any combination thereof. The components of the system can be connected by digital data communication in any form or medium such as a communication network. Examples of communication networks include, for example, local area networks (LANs), wide area networks (WANs), and the computers and networks forming the Internet.

[0146] A computer system can include clients and servers. Clients and servers are generally remote from each other and typically interact via a network as described herein. The relationship between a client and a server results from computer programs that are executed on respective computers and have a client-server relationship with each other. A server can be part of a cloud that can include a transient aspect.

[0147] Although this disclosure includes many specific implementation details, these should not be construed as limitations on the scope of any implementation of the disclosure or on what can be claimed, but rather as descriptions of features specific to exemplary implementations. Specific features described herein in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementation can also be implemented separately, or in any suitable sub-combination, in multiple implementations. Further, features are described above as acting in certain combinations and may initially be claimed as such, but one or more features from a claimed combination can in some cases be deleted from the combination, and the claimed combination can be directed to a partial combination or a variation of a partial combination.

[0148] Similarly, the operations are depicted in the drawings in a particular order, but it should not be understood that such operations are to be performed in the particular order shown, or in a sequential order, or that all of the illustrated operations are to be performed, to achieve the desired result. In certain circumstances, multitasking and parallel processing may be advantageous. Further, the separation of various system components in the foregoing embodiments should not be understood to require 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. Further, the processes depicted in the figures do not necessarily require the particular order shown, or a sequential order, to achieve the desired result. In certain embodiments, multitasking and parallel processing may be advantageous.

[0149] Although various embodiments of the present invention have been described herein, it should be understood that they have been presented by way of example only, and not limitation. Many variations and modifications will be apparent to persons skilled in the art upon reading the present specification. The breadth and scope of the present invention should not be limited by the examples described herein, but should be construed broadly to include such variations and modifications. The described embodiments and other such embodiments are within the scope of the following claims.

Claims

1. A method performed by a system for manufacturing an optical device, the method comprising: Determining a dispensing pattern for dispensing drops of photoresist so as to form one or more surface features on at least one surface of a substrate, wherein determining the drop pattern comprises: Determining a grid of available drop locations based at least in part on one or more constraints for the drop locations, wherein the one or more constraints are based on one or more of i) a dispenser component of the system for dispensing drops of the photoresist, or ii) a stage component of the system for stabilizing the substrate during dispensing; For each of a plurality of candidate dispensing patterns, predicting a diffusion pattern of drops dispensed according to the respective candidate dispensing pattern, wherein each of the plurality of candidate dispensing patterns includes a subset of the available drop locations, and the diffusion pattern is predicted based at least in part on the one or more surface features to be formed on the at least one surface of the substrate; Determining the dispensing pattern corresponding to an optimal diffusion pattern among the plurality of diffusion patterns predicted based on the plurality of candidate dispensing patterns; and Dispensing drops of the photoresist according to the dispensing pattern on at least one surface of the substrate or on a template usable for shaping the one or more surface features; Applying the template to shape the dispensed photoresist into the one or more surface features on at least one surface of the substrate; Curing the dispensed photoresist to form the one or more surface features; Isolating the substrate to create an optical device including the one or more surface features. A method.

2. The method according to claim 1, wherein the substrate is composed of glass or polymer.

3. The method according to any one of claims 1 or 2, wherein the photoresist is a polymer fluid.

4. Curing the photoresist includes applying ultraviolet radiation to the dispensed photoresist and / or applying heat to the dispensed photoresist, the method according to any one of claims 1 to 3.

5. The method according to any one of claims 1 to 4, wherein the one or more surface features include one or more diffraction gratings.

6. The method according to claim 5, wherein the one or more diffraction gratings include one or more of an in-coupling grating (ICG), an orthogonal pupil expander (OPE), an exit pupil expander (EPE), or a compound pupil expander (CPE).

7. The method according to any one of claims 1 to 6, wherein the one or more constraints include one or more of the number of nozzles of the dispenser component, the spacing between the nozzles of the dispenser component, and the range of the dispensing frequency of the nozzles of the dispenser component.

8. The method according to any one of claims 1 to 7, wherein the one or more constraints include one or more of the range of the moving speed of the stage component and the available moving directions of the stage component.

9. Determining the dispensing pattern corresponding to the optimal diffusion pattern includes identifying the optimal diffusion pattern that minimizes one or more of the number of void gaps in the diffusion pattern, the size of the void gaps in the diffusion pattern, and the total volume of the void gaps in the diffusion pattern, the method according to any one of claims 1 to 8.

10. At least one surface of the substrate includes a first zone and a second zone that does not overlap with the first zone. The one or more surface features include a first set of surface features within the first zone and a second set of surface features within the second zone. The method according to any one of claims 1 to 9.

11. The first set of surface features includes a first residual layer of the photoresist having a first residual layer thickness (RLT) within the first zone. The second set of surface features includes a second residual layer of the photoresist having a second RLT within the second zone, and the second RLT is different from the first RLT. The method according to claim 10.

12. At least one surface of the substrate includes a third zone between the first zone and the second zone. The third zone includes a third residual layer of the photoresist having a gradient-like RLT that continuously changes from the first RLT near the boundary between the third zone and the first zone to the second RLT near the boundary between the third zone and the second zone. The method according to claim 11.

13. The first set of surface features includes a first nanostructure having a first height with respect to the at least one surface. The second set of surface features includes a second nanostructure having a second height with respect to the at least one surface. The method according to any one of claims 10 to 12.

14. At least one surface of the substrate includes a third zone between the first zone and the second zone. The third zone includes a third nanostructure having a height that continuously changes from the first height near the boundary between the third zone and the first zone to the second height near the boundary between the third zone and the second zone. The method according to claim 13.

15. The method according to any one of claims 1 to 14, wherein the optical device is a waveguide.

16. The method according to any one of claims 1 to 15, wherein the one or more surface features are on one surface of the substrate.

17. The method according to any one of claims 1 to 15, wherein the one or more surface features are on two or more surfaces of the substrate.

18. The method according to any one of claims 1 to 17, wherein the one or more surface features include at least one non-diffraction pattern.

19. The method according to claim 18, wherein the one or more surface features include an anti-reflection pattern.

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