Imprint techniques in nanolithography of optical devices

Abstract

The present disclosure generally describes methods and systems for manufacturing high quality surface relief waveguides for eyepieces. In particular, this disclosure describes techniques for fabricating waveguides with surface relief features (e.g., diffraction gratings) to achieve various optical effects using nanolithography imprinting techniques that reduce or eliminate the presence of gaps in the imprinted features by using optimized droplet patterns for dispensing photoresist. Furthermore, the present disclosure describes techniques for manufacturing surface relief waveguides having a gradient, such as a substantially continuous gradient or slope, between regions of dispensed photoresist having different residual layer thicknesses and / or between regions of surface features having different heights (or depths). This gradient can reduce or eliminate adverse optical effects that may result from more sudden transitions between regions and improve the optical efficiency of the completed waveguide.

Description

Technical Field

[0001] Embodiments described herein generally relate to systems and methods for fabricating surface-relief waveguides for eyepieces, and the optical devices created thereby. Background Art

[0002] When fabricating waveguides, eyepieces, and other types of optical devices, performance considerations can be important. For example, minute defects in the fabricated device can have a disproportionate impact on the optical performance of the device, resulting in reduced optical power, light loss, artifacts, etc. Performance considerations can be traded off against the cost of fabricating the device (e.g., the cost of component materials, fabrication, testing, etc.). Thus, manufacturers of high-performance optical devices have traditionally pursued various techniques to improve the quality of the fabricated device while avoiding excessive increases in manufacturing costs. Summary of the Invention

[0003] The present disclosure generally describes methods and systems for fabricating high-quality surface-relief waveguides for eyepieces. Specifically, the present disclosure describes techniques for fabricating waveguides having surface-relief features (e.g., diffraction gratings) using nanoimprint lithography techniques to achieve various optical effects, the nanoimprint lithography techniques reducing or eliminating the presence of gaps in the imprinted features. Additionally, the present disclosure describes techniques for fabricating surface-relief waveguides having a gradient between regions of dispensed photoresist having different residual layer thicknesses and / or between regions of surface features having different heights (or depths), e.g., a substantially continuous gradient or slope. Such a gradient can reduce or eliminate adverse optical effects that may be caused by more abrupt transitions between regions and improve the optical efficiency of the completed waveguide.

[0004] Embodiments include a method performed by a system for manufacturing an optical device, the method including: determining a dispense pattern for droplets of photoresist to form one or more surface features on at least one surface of a substrate, wherein determining the droplet pattern includes: determining a grid of available droplet locations based at least in part on one or more constraints on droplet location, wherein the one or more constraints are based on a configuration of one or more of: i) a dispenser assembly of the system that dispenses droplets of the photoresist, or ii) a stage assembly of the system that stabilizes the substrate during dispensing; for each of a plurality of candidate dispense patterns, predicting a spread pattern of the droplets dispensed according to the respective candidate dispense pattern, wherein each of the plurality of candidate dispense patterns includes a subset of the available droplet locations, and wherein the spread 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; and determining the dispense pattern corresponding to the best spread pattern from among the plurality of spread patterns predicted based on the plurality of candidate dispense patterns; dispensing droplets of the photoresist onto the at least one surface of the substrate or onto a template usable to mold the one or more surface features according to the dispense pattern; applying the template to mold the dispensed photoresist into the one or more surface features on the at least one surface of the substrate; curing the dispensed photoresist to form the one or more surface features; and separating the substrate to create an optical device including the one or more surface features.

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

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

[0007] 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.

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

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

[0010] In some embodiments, the one or more surface features are located on two surfaces of the substrate.

[0011] In some embodiments, the one or more diffraction gratings include one or more of the following: an input coupling grating (ICG), an orthogonal pupil expander (OPE), an exit pupil expander (EPE), or a combined pupil expander (CPE).

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

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

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

[0015] In some embodiments, the one or more constraints include one or more of the following: the range of the moving speed of the stage assembly, and the available moving directions of the stage assembly.

[0016] In some embodiments, determining the dispensing pattern corresponding to the optimal diffusion pattern includes: identifying the optimal diffusion pattern that minimizes one or more of the following: 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, the at least one surface of the substrate includes: a first region and a second region that does not overlap with the first region; and the one or more surface features include: a first set of surface features in the first region and a second set of surface features in the second region.

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

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

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

[0021] In some embodiments, the at least one surface of the substrate includes a third region between the first region and the second region; and the third region includes third nanostructures, the height of which continuously varies from the first height near the boundary of the third region and the first region to the second height near the boundary of the third region and the second region.

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

[0023] Embodiments include an optical device, the optical device including: a substrate; and surface features formed by photoresist disposed on at least one surface of the substrate, the surface features including: a first set of surface features in a first region of the at least one surface of the substrate, wherein the first set of surface features has a first height; a second set of surface features in a second region of the at least one surface of the substrate, wherein the second region does not overlap with the first region, and wherein the second set of surface features has a second height different from the first height; and a third set of surface features in a third region of the at least one surface of the substrate, wherein the third region is located between the first region and the second region, and wherein the third set of surface features has a varying height that continuously varies from the first height near the boundary of the third region and the first region to the second height near the boundary of the third region and the second region.

[0024] In some embodiments, the first set of surface features includes a first residual layer of the photoresist having the first height, the first height being the first residual layer thickness RLT in the first region; the second set of surface features includes a second residual layer of the photoresist having the second height, the second height being the second RLT in the second region, the second RLT being different from the first RLT; and the third set of surface features includes a third residual layer of the photoresist having a varying height, the varying height being a gradient RLT that continuously varies from the first RLT near the boundary of the third region and the first region to the second RLT near the boundary of the third region and the second region.

[0025] In some embodiments, the first set of surface features includes first nanostructures having the first height relative to the at least one surface; the second set of surface features includes second nanostructures having the second height relative to the at least one surface; and the third set of surface features includes third nanostructures having a varying height that continuously varies from the first height near the boundary of the third region and the first region to the second height near the boundary of the third region and the second region.

[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 the following: an input coupling grating (ICG), an orthogonal pupil expander (OPE), an output pupil expander (EPE), or a combined pupil expander (CPE).

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

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

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

[0031] Embodiments include a method for manufacturing an optical device, the method comprising: determining a dispensing pattern for droplets of a photoresist to form surface features on at least one surface of a substrate; dispensing the droplets of the photoresist onto the at least one surface of the substrate or onto a template usable to mold the surface features according to the dispensing pattern; applying the template to mold the dispensed photoresist into the surface features on the at least one surface of the substrate; curing the dispensed photoresist to form the surface features; and separating the substrate to create the optical device including the surface features; wherein the surface features include: a first set of surface features in a first region of the at least one surface of the substrate, wherein the first set of surface features has a first height; a second set of surface features in a second region of the at least one surface of the substrate, wherein the second region does not overlap with the first region, and wherein the second set of surface features has a second height different from the first height; and a third set of surface features in a third region of the at least one surface of the substrate, wherein the third region is located between the first region and the second region, and wherein the third set of surface features has a varying height that continuously varies from the first height near the boundary of the third region and the first region to the second height near the boundary of the third region and the second region.

[0032] In some embodiments, the first set of surface features includes a first residual layer of the photoresist having the first height, where the first height is the first residual layer thickness (RLT) in the first region; the second set of surface features includes a second residual layer of the photoresist having the second height, where the second height is the second RLT in the second region, and the second RLT is different from the first RLT; and the third set of surface features includes a third residual layer of the photoresist having a varying height, where the varying height is a gradient RLT that continuously varies from the first RLT near the boundary of the third region and the first region to the second RLT near the boundary of the third region and the second region.

[0033] In some embodiments, the first set of surface features includes a first nanostructure having the first height relative to the at least one surface; the second set of surface features includes a second nanostructure having the second height relative to the at least one surface; and the third set of surface features includes a third nanostructure having the varying height that continuously varies from the first height near the boundary of the third region and the first region to the second height near the boundary of the third region and the second region.

[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 the following: an input coupling grating (ICG), an orthogonal pupil expander (OPE), an exit pupil expander (EPE), or a combined pupil expander (CPE).

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

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

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

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

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

[0041] In some embodiments, the etching modifies one or more of the following: the first height in the first region, the second height in the second region, or the varying height in the third region.

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

[0043] In some embodiments, the method includes the step of depositing a film on the pattern on the substrate (e.g., post-processing) to define a replication template associated with the waveguide and / or the optical device, provided that once the pattern is defined using the master pattern and the droplet pattern (e.g., for RLT), the pattern can be further replicated into other substrates or films for further replication or fabrication into an optical device (e.g., a waveguide).

[0044] Embodiments include a method of creating a template for imprinting, the method including: providing a carrier substrate having a cover layer of a blank (e.g., oxide or nitride) material; dispensing droplets of photoresist onto the cover layer according to a droplet pattern; imprinting the photoresist to provide a pattern on the substrate, the pattern including a gradient RLT; and etching the pattern (e.g., dry etching) into a final pattern, wherein the final pattern has a substantially flat upper extent.

[0045] Embodiments include a method of creating a template for imprinting, the method including: providing a carrier substrate having a cover layer of a blank (e.g., oxide or nitride) material; creating regions of photoresist on the substrate that will not be etched or removed in subsequent steps (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 inverted dome-shaped deposition profile in the cover layer using a controlled plasma; performing a blank etch to reduce the remaining portion of the cover layer to a specific depth; performing a photo etch to create features in the carrier substrate; performing photolithography to provide a pattern (e.g., an ICG pattern); and etching the pattern and stripping at least a portion of the resist to provide the template.

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

[0047] Figure 1 An example system for manufacturing an optical device is depicted.

[0048] Figure 2A and 2B A schematic diagram depicting an example template configuration and operation is shown.

[0049] Figure 3 A flowchart depicting an example process for determining a droplet pattern for manufacturing an optical device.

[0050] Figure 4 A schematic diagram depicting an example grid for determining a small droplet pattern.

[0051] Figure 5A and 5B respectively depict an example droplet pattern and an example of a fluid dispensing pattern based on the droplet pattern.

[0052] Figure 6 A flowchart depicting an example process for creating surface features on a substrate.

[0053] Figures 7A - 7D A schematic diagram showing an example template and an example grating pattern created by applying the template.

[0054] Figure 8A and 8B show schematic diagrams of example grating patterns.

[0055] Figures 9 to 12 A diagram depicting an example process for creating a template.

[0056] Figure 13 Depicts an example computing system. DETAILED DESCRIPTION

[0057] This disclosure describes various embodiments of methods and systems for manufacturing high-quality optical devices. Optical devices created using the techniques described herein are suitable for virtual reality (VR), augmented reality (AR), and / or mixed reality (MR) systems, and / or other suitable optical applications. For example, an optical device can be incorporated into a wearable (e.g., head-mounted) display system to provide an AR experience for a wearer. In such a system, the eyepiece can be transparent to allow the wearer to view the physical environment, while the waveguide of the eyepiece transmits light for presenting graphical objects as an overlay of 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 specific distance from the wearer, e.g., at different depth planes or focal lengths. In some examples, the waveguides can be arranged in a waveguide stack, where different waveguides are configured to present graphical objects at different depth planes and / or transmit light in different wavelength ranges (e.g., red, green, and blue).

[0058] The optical device includes a high-quality surface-relief waveguide, which can be used alone or in a stacked configuration of multiple waveguides in an eyepiece. The optical features in the surface-relief waveguide have a residual layer thickness (RLT) with high nano-feature fidelity and high uniformity in one or more regions, which may have different requirements for the resist volume considering the surface features (such as diffraction gratings) to be created in each region. In some embodiments, the features can be fabricated by dispensing, patterning, and curing a high refractive index nanoimprint fluid, which can also be described as a photoresist, resist, or resin. The features can be created on one or both surfaces of a wide, substantially flat transparent substrate, and the substrate serves as a waveguide to transmit light by total internal reflection (TIR).

[0059] The surface features created on one or more surfaces of the substrate can include diffraction gratings, which have optical functions that can affect the light passing through the substrate. Such diffraction gratings can include, but are not limited to, input coupling gratings (ICGs), output coupling gratings (OCGs), orthogonal pupil expanders (OPEs), exit pupil expanders (EPEs), combined pupil expanders (CPEs), and / or other types of gratings. The substrate and the fabricated eyepiece 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 various suitable glasses and polymers. For example, the substrate can be composed of inorganic amorphous materials (such as, dense tantalum flint glass TADF55, quartz, etc.), crystalline materials (such as, LiNbO3, LiTaO3, SiC, etc.), high refractive index polymers (such as, containing sulfur, aromatic, etc.), and / or other polymer materials (such as, polycarbonate (PC), polyethylene terephthalate (PET), etc.).

[0061] The embodiments described herein employ a drop-on-demand, controlled-volume dispensing technique to dispense a fluid onto the substrate, precisely controlling the volume of the droplets (also referred to as microdroplets) of the dispensed fluid and their dispensing positions on the substrate. 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 optics.

[0062] The fluid can be dispensed onto an optically transparent substrate that serves as a waveguide, and the dispensed fluid can be imprinted with a template and then cured to create the desired nano-features (such as diffraction gratings) on one or more surfaces of the transparent substrate. As used herein, optically transparent generally refers to the physical property of allowing 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 substrate thickness in a series of point measurements over the dimension of the substrate. For a substrate having a patterned surface on which a diffraction grating has been created, the TTV refers to an approximation 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 range from about 10 nanometers (nm) to 150 nm. This thickness is determined by the trench depth of the template, which can vary by 10% (e.g., 1 nm to 15 nm). The TTV of an unpatterned substrate typically exceeds 100 nm and is sometimes on the micron scale. Thus, the additional variation in the thickness of the patterned substrate introduced by the pattern features can be neglected and can be ignored as an approximation. Accordingly, the thickness of the patterned substrate evaluated at a location including a protrusion can be approximated by subtracting a given feature thickness from the evaluated thickness to obtain an adjusted thickness, while the thickness of the patterned substrate evaluated at a location without a protrusion remains unchanged. That is, the TTV of a substrate having a patterned surface can be calculated using the adjusted (e.g., reduced) thickness of the feature regions and the original thickness of the unpatterned regions. The low TTV values described herein result at least in part from flat optical-grade glass substrates (which are polished to meet the required 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 can be imparted to polymer substrate materials and achieved from the mold surface when molding (e.g., injection molding, ultraviolet (UV) or thermoplastic, extrusion, etc.) such substrates, which are composed of a base material of a high refractive index polymer (e.g., containing sulfur, aromatic, etc.) and other polymer materials (e.g., polycarbonate).

[0064] As used herein, RLT refers to the thickness of a (e.g., polymer) photoresist deposited onto a substrate in a region that is free of surface features (e.g., gratings) and / or in a region that has surface features but is located between specific nano-geometries of the surface features. The RLT may be substantially similar across the finished eyepiece, or different regions of the eyepiece may have different RLTs. In some embodiments, across at least a portion of the eyepiece, the RLT may have a substantially continuous and / or gradual variation. In some embodiments, different regions may have different RLTs, and in a transition region from one region having one RLT to another region having a different RLT, the RLT may have a continuous gradient (e.g., slope). The embodiments described herein enable fine-tuning of the RLT to achieve various desired optical performance characteristics in the finished eyepiece.

[0065] Figure 1FIG. 0 depicts an example system 100 for manufacturing an optical device by dispensing a fluid 106 (e.g., a nanoimprint lithography resist 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 (e.g., a waveguide or an eyepiece).

[0066] As Figure 1 shown, system 100 can operate on a substrate 102 that is supported by a stage 104. The stage 104 can also be described as a chuck. The substrate 102 can be composed of any suitable material (e.g., glass or polymer). The substrate 102 can take any suitable form, including a sheet, a wafer, a film, etc. In some examples, a portion of the substrate 102 (e.g., a wafer) can include multiple regions, each region corresponding to an eyepiece that will be cut out from the substrate 102 after other manufacturing steps to create a desired pattern (e.g., a diffraction grating) on one or more surfaces of the substrate 102.

[0067] The stage 104 can be configured to support and stabilize the substrate 102 during fluid dispensing, imprinting, curing, etching, and / or other manufacturing operations. The stage 104 can be configured to fix the substrate 102 to the stage 104, e.g., by using a vacuum pump to generate suction to hold the substrate 102 on the stage 104. The stage 104 can be moved to move between different stations of the manufacturing system 100, as in the example shown, where the stage moves from a fluid dispensing station to an imprinting station to an etching station, etc. The stage 104 can also be configured to move in various directions when it is in a position close to (e.g., below) one of the stations. For example, if the stage 104 is holding the substrate 102, the surface of the substrate 102 is substantially flat and includes an X-axis and a Y-axis, as shown, then the stage 104 can be configured to move in the X direction and / or the Y direction below the stage. In some embodiments, the stage 104 can also be configured to move in the Z direction to increase or decrease the distance between the substrate 102 and a particular device (e.g., a fluid dispenser 112, an imprinting mechanism 116, an etching mechanism 122, etc.) that performs an operation on the substrate 102. In some embodiments, the stage 104 is configured to support the substrate 102 by the edge of the substrate 102 such that both wide surfaces of the substrate 102 are available for such operations. In some embodiments, the stage 104 can be configured to flip the substrate 102 in the Z direction so that two opposite sides of the substrate 102 are available for fluid dispensing, imprinting, curing, etching, and / or other operations.

[0068] The fluid dispenser 112 is configured to dispense droplets (or small droplets) of a fluid 106 (e.g., a resist) onto a substrate 102. The fluid dispenser 112 may include one or more printheads (or nozzles) for dispensing (e.g., ejecting) droplets of the fluid 106. The fluid 106 is held in a reservoir 108, which is connected to the fluid dispenser 106 via one or more channels (e.g., tubes, conduits, etc.) of a suitable type, material, and size. One or more fluid pumps 110 operate to circulate the fluid 106 between the reservoir 108 and the fluid dispenser 112. The system 100 may also include various other suitable devices, such as pumps, pressure sensors, flow sensors, filters, etc., which are arranged to provide a reliable flow of the fluid 106 to the fluid dispenser 112.

[0069] The fluid dispenser 112 can dispense a certain number of droplets of the fluid 106 onto a specific location on the surface of the substrate 102 at any suitable dispensing round, at any suitable position, and with any suitable droplet size or volume. The fluid 106 can be dispensed according to a determined droplet pattern to optimize the use of the fluid 106, minimize the presence of air gaps in the cured grating, and / or precisely control the RLT of the dispensed fluid. Such droplet patterns will be described further below.

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

[0071] In some embodiments, the fluid dispensing and imprinting are performed according to drop-on-demand jetting and flash imprint lithography (J-FIL) techniques to dispense the fluid 106 and imprint a desired pattern into the 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", the entire content of which is incorporated herein by reference.

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

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

[0074] Although Figure 1 An example of the system 100 including a single fluid dispenser 112 is shown, but other embodiments are possible. For example, the system 100 can include multiple fluid dispensers 112 (e.g., print heads) to increase the throughput of the system 100 and / or distribute the fluid 106 to additional locations on the substrate 102. The system 100 can similarly include multiple imprint stations, each having 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 higher refractive index material are incorporated. Alternatively, the resist can be a polymer-based resin without NPs incorporated. Incorporating NPs can increase the overall refractive index of the material, which is beneficial for more closely matching the refractive index of the substrates described herein. However, incorporating NPs can also cause Rayleigh scattering of light in the resist. Thus, the choice of using a resist that includes NPs or omits NPs may be based on balancing considerations such as a higher refractive index versus more scattering. For example, a resist with a refractive index of 1.6 or 1.7 and without NPs can provide optimal performance, providing a higher refractive index (e.g., closer to the refractive index of the substrate) while avoiding scattering caused by the presence of NPs.

[0076] The refractive index of organic (meth)acrylate monomers and oligomers at a wavelength of 532 nm is typically about 1.5. Sulfur atoms and aromatics both have a relatively high polarizability and can be added to these acrylate components to increase the refractive index of the formulation. This effect is limited due to the fluid viscosity limit of the jetting process being less than 20 to 25 cP and the upper limit of the refractive index of sulfur-containing molecules. This method can produce a jetable and imprintable resist with a refractive index of up to 1.72 at a wavelength of 532 nm.

[0077] The addition of inorganic nanoparticles (NPs) such as ZrO2 and TiO2 can further significantly increase the refractive index. Pure ZrO2 and TiO2 crystals can achieve refractive indices of 2.2 and 2.4 - 2.6 respectively at 532 nm. For 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 agglomerate in the polymer matrix. Surface modification of the NPs can be used to overcome this problem. In this technique, the hydrophilic surface of ZrO2 is modified to be compatible with organic substances, enabling the NPs to be uniformly mixed with the polymer. This modification can be accomplished using capping agents containing silanes and carboxylic acids. One end of the capping agent bonds to the ZrO2 surface; the other end of the capping agent either contains functional groups that can participate in acrylate crosslinking or contains non-functional organic moieties. Examples of surface-modified sub-10 nm ZrO2 particles are those provided by Pixelligent Technologies TM and Cerion Advanced Materials TM These functionalized nanoparticles are typically sold as a homogeneous suspension in a solvent in the form of a uniform mixture and can be combined with other base materials to produce a resist formulation with a jetable viscosity and an increased refractive index.

[0078] When the stage 104 moves the substrate 102 from one station to another, the system 100 can also include other stations and other devices for performing other operations on the substrate 102. In some embodiments, the system 100 includes a station for curing the dispensed fluid 106 after it has been molded into the desired shape at the imprinting station. This curing can be performed by any suitable technique, depending on the specific fluid 106 used, such as applying heat, radiation (e.g., ultraviolet light), and / or pressure. The system 100 can also include a station for dividing (e.g., cutting) the substrate 102 into the shape of an eyepiece required for an optical device. The system 100 can also include a station for inspecting the substrate 102 at one or more stages of manufacture, such as by the operation of an imaging camera.

[0079] Figure 2A and 2BA schematic diagram depicting an example template configuration and operation is shown. Schematic diagram 200 shows a substrate 102 with droplets of fluid 106 dispensed on its surface, and a template 118 is being applied to shape the fluid 106 into a desired grating on the surface of the substrate 102. As shown, the template includes the (e.g., negative) form of the grating pattern 202 to be applied. In this example, the template 118 is a flexible, rollable template that is applied to the substrate 102 through the operation of a roller device 204, which can be a component of an imprinting mechanism 116. The roller device 204 can move in a direction 206 that is substantially parallel to the surface of the substrate 102 to press the template onto the substrate 102 and mold the dispensed fluid 106 into the desired nano-geometry for the grating. Schematic diagram 210 shows a subsequent state where the template 118 is fully pressed onto the substrate 102 and a grating has been formed by applying the template.

[0080] In some embodiments, the template is a coated resist template (CRT). The template can be fabricated by imprinting onto any suitable substrate, including plastics (e.g., PC, PET, etc.), glass, silicon, etc. The substrate can be a wafer, sheet, webroll, or other suitable form. Once the surface is imprinted (e.g., after appropriate adhesion surface treatment), a patterned polymer resist can be conformally coated with materials such as SiO2, Al2O3, Al, Ag, TiN, Cr by 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. The coated surface can also be treated with a release fluoropolymer material to improve the release performance during demolding in the imprinting process (e.g., when the template is separated from the waveguide substrate, a diffraction grating is formed on the waveguide substrate by applying the template).

[0081] Although this example depicts a rollable template configuration for the imprinting step, the embodiments are not limited thereto. Other types of templates, such as the template 118, which presses down (e.g., in the Figure 1 Z direction) onto the surface of the substrate 102 rather than moving laterally in the X-Y plane parallel to the surface of the substrate 102. In some embodiments, the template 118 has been etched or otherwise imprinted onto the surface of a cylindrical drum that imprints the desired pattern into the fluid 106 as the drum rolls over the substrate and dispenses the fluid 106. In such embodiments, the imprinting direction 106 can be perpendicular to the axis of rotation of the cylinder. In some embodiments, the template is applied in a spherical shape such that pressure is initially applied to press the template onto the substrate at or near the center of the substrate portion (e.g., wafer) to be imprinted, and then outward from the center.

[0082] Multiple eyepieces can be fabricated from a particular substrate wafer. For example, six eyepieces can be fabricated from the wafer (e.g., 6-up configuration) or four eyepieces can be fabricated from the wafer (e.g., 4-up configuration). In some embodiments, the fluid dispensing step dispenses fluid to all the eyepieces on the wafer in one operation or a set of operations. Alternatively, the fluid dispensing operation can be performed separately for each eyepiece, where the stage rotates the substrate under the fluid dispenser between dispensing operations to move different eyepiece regions under the dispenser. Similarly, the imprinting step can be performed for all the eyepieces on the wafer simultaneously using a template arranged to imprint all the eyepieces at the same time. Alternatively, the template can be arranged to imprint a single eyepiece, and each eyepiece can be imprinted separately, where the stage (or the template) moves from one eyepiece to another accordingly.

[0083] In some embodiments, the fluid 106 is dispensed onto the template 116, rather than onto the surface of the substrate 102, or in addition to being dispensed onto the surface of the substrate 102, it is also dispensed onto the template 116. The techniques described herein operate in a similar manner in such embodiments, where a droplet pattern of fluid droplets is dispensed onto the surface of the template 116, which surface includes features (e.g., negative) to be imprinted onto the substrate 102.

[0084] Droplet pattern determination

[0085] Embodiments provide techniques for determining a droplet pattern for dispensing fluid 106 onto a substrate 102 (or onto a template) to create desired surface features on the substrate 102. The droplet pattern is determined such that the unfilled (e.g., air gaps) in the fluid 106 that diffuses upon application of the template 118 are minimized or eliminated, thereby minimizing or eliminating surface features formed by the cured fluid. The droplet pattern is also determined to provide a controlled, and in some cases ultrathin, RLT in the resulting waveguide.

[0086] During imprinting using previously available techniques, void defects can occur due to air entrainment in the resist during dispensing and imprinting. These defects are referred to as unfilled in nanolithography and are regions not filled with resist (e.g., at least partially inside the imprinted and cured nano-features). A previous method to prevent such defects was to dispense an additional volume of resist into the region to ensure that all gaps were filled. Unfortunately, the additional volume can result in an undesirably large RLT, which can have an adverse effect on the optical performance of the finished waveguide. Embodiments determine a droplet pattern that is capable of effectively filling the grating pattern of the applied template without increasing the volume of resist dispensed.

[0087] When air is trapped by the fluid front during the application of the template 118, for example, when the fluid 106 is pressed between the substrate 102 and the template 118 (also known as the superstrate), and the air cannot escape from the fluid 106 before curing, void defects (e.g., air gaps) will be generated in the cured resist structure. The grating being created can have a grating direction, which is the axis along which the grating pattern is arranged. For example, the grating can include long channels along the grating direction, and these channels are separated by ridges. Void or unfilled defects are more likely to be generated when the grating direction is substantially perpendicular to the imprint direction (e.g., the direction 206 in which the roller device 204 moves to apply the template 118) compared to when the grating direction is parallel to the imprint direction. In some cases, unfilled defects are more likely to be generated when the grating direction is substantially parallel to the imprint direction. Substantially perpendicular or substantially parallel can mean that the angular deviation from perpendicular or parallel is within a suitable radian angle (e.g., within one degree, within five degrees, within ten degrees, etc.).

[0088] To address this issue and eliminate or mitigate air gaps, the implementation determines the optimal droplet pattern, which takes into account the diffusion characteristics of the fluid 106 on the substrate 102 and is predicted based on the specific pattern being imprinted, fluid and substrate characteristics, imprint direction, and / or other variables. The 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, with other variables remaining unchanged, the diffusion rates of dome (e.g., convex or concave) glass and silicon substrates can be similar, and flat glass can exhibit a greater diffusion rate. Therefore, the optimized droplet pattern may be different for glass substrates with different TTVs. The diffusion rate can also vary with different imprint speeds (e.g., the speed of applying the template). For example, the faster the imprinting, the more difficult it may be for air to escape and the easier it may be to form void defects.

[0089] The diffusion rate is defined as the ratio of the width (e.g., lateral diffusion) of the diffused elliptical droplet to the length (e.g., longitudinal diffusion) of the diffused elliptical droplet. Alternatively, this ratio can be defined as the ratio of longitudinal diffusion to lateral diffusion. If the lateral and longitudinal diffusion of a specific resist material on a specific substrate is known, and further based on the knowledge of how the resist fluid diffuses and / or interacts with the template (e.g., through capillary filling, etc.), such information can be used to modify the droplet pattern for imprinting in lithography techniques (e.g., J-FIL).

[0090] The grating direction is the direction along (e.g., substantially parallel to) the long axis of the features present in the imprinted grating. The direction perpendicular to the grating direction is referred to as the lateral direction. In some embodiments, the imprint direction is the grating direction, but embodiments support any imprint direction at any angle relative to the grating direction. The imprint direction can be the lateral direction to more effectively spread the fluid across the boundaries between channels. The distance between droplets in the lateral direction or between different rows of droplets is referred to as the lateral spread distance. The minimum available distance of such a distance is referred to as the minimum lateral spread distance (MLSD). This value may be limited by the printhead geometry (e.g., the distance between the nozzles of the fluid dispenser 112). A smaller MLSD can help avoid void defects because the fluid tends to spread along the grating features (e.g., in the grating direction) and is less likely to spread across the grating features (e.g., in the lateral direction). To help the fluid merge in the lateral direction and eliminate air traps, a smaller MLSD can be used in the droplet pattern. However, if the MLSD is too small, it may result in a larger separation between droplets in the gradient direction, which may also cause defects. Therefore, embodiments model different droplet patterns and are able to select a droplet pattern to achieve optimal spread with minimal or no gaps. The optimal droplet pattern can also reduce the total volume of the dispensed resist (e.g., 50% less compared to previous techniques) because the optimal droplet pattern enables the droplets to fill the grating volume optimally and provide the required RLT outside the grating region. The droplet pattern for imprinting is further described in U.S. Patent No. 8,119,052, entitled "Droplet Pattern Generation for Imprint Lithography," the entire content of which is incorporated herein by reference.

[0091] Figure 3 A flowchart depicting an example process 300 for determining a droplet pattern for manufacturing an optical device is shown. The operations of the process can be performed by software executing on one or more suitable computing devices. The various operations can be performed in any suitable order. Some operations can be combined into a single operation. The operations can be performed sequentially and / or in parallel to suit a particular operation.

[0092] At 302, various grating patterns and unpatterned regions to be created on the substrate 102 are determined. Such patterns (or non-patterns) may be present in one or more regions on the substrate 102.

[0093] At 304, based on the volume of the grating pattern to be filled as defined by the template, plus the regions in the unpatterned regions that may receive various thicknesses of resist, and the required RLT in the patterned and / or unpatterned regions, the total volume of fluid to be dispensed is determined.

[0094] At 306, based on the configuration of the fluid dispenser 112, various constraints of the possible droplet patterns are determined. These constraints can include the number of nozzles of the dispenser, the spacing between the nozzles, and the available dispensing frequencies. The dispensing frequency is the frequency at which the nozzles can dispense droplets (e.g., the ejection frequency). In some examples, the dispensing frequency can be specified as a range of frequencies. The range of the dispensing frequency can have a defined upper limit based on the dispenser configuration (e.g., the ejection speed is as fast as possible), and no defined lower limit (or the lower limit is zero).

[0095] At 308, based on the configuration of the stage 104, various constraints of the possible droplet patterns are determined, such as the available movement speed and the available movement directions of the stage 104. In some embodiments, the information accessed at 302, 304, 306, and / or 308 can be input into the process as input parameters or otherwise specified.

[0096] At 310, a grid is generated that specifies the available droplet positions based on the constraints accessed at 306 and 308. Figure 4 An example of such a grid is shown. Each vertex of the grid indicates a position where the dispenser can dispense the fluid 106 as droplets on the substrate 102.

[0097] At 312, each of a plurality of possible droplet patterns (e.g., dispensing patterns) can be analyzed, and the process can be performed to predict the diffusion pattern of the fluid 106 dispensed according to the corresponding droplet pattern. The prediction can be made based on the specific droplet pattern and the volume of the fluid 106 to be dispensed, the specific geometry of the grating to be created, the fluid properties of the fluid 106, the properties of the 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, which is determined by the direction in which the fluid front moves (e.g., based on the template imprinting direction), and the droplets will diffuse once the template starts to push the droplets onto the surfaces of the template and the substrate.

[0098] At 314, each predicted diffusion pattern in each analyzed droplet pattern can be evaluated, and the best diffusion pattern can be determined. The best diffusion pattern can be a diffusion pattern that includes the fewest air gaps, the smallest air gap, and / or the smallest total air gap volume. In some embodiments, each diffusion pattern can be scored based on a metric that takes into account the number and / or size of the air gaps, and the diffusion pattern with the highest score can be designated as the best.

[0099] At 316, the droplet pattern corresponding to the optimal diffusion pattern is identified and designated as the droplet pattern for dispensing fluid 106 before imprinting and curing to create the desired surface features. In some embodiments, the analysis to determine the optimal droplet pattern can be performed manually by visually inspecting the various resulting diffusion patterns presented on a suitable display of a computing device. Alternatively, the algorithm can be executed iteratively to automatically search for the optimal diffusion pattern based on the computed scores as described above, and the droplet pattern to be used can be automatically identified as the droplet pattern corresponding to the optimal diffusion pattern.

[0100] Figure 4 A schematic diagram of an example grid 400 for determining a droplet pattern is depicted. Each vertex of the grid 400 (e.g., where the lines intersect) can be considered a possible location for dispensing a droplet onto the substrate 102 (or onto the template 118). As described above, the possible locations for dispensing are determined based on the configuration of the dispenser (e.g., the distance between the nozzles and the range of available nozzle ejection frequencies) and the configuration of the stage (e.g., the speed and direction in which the stage can move beneath the dispenser). Other factors can also be considered, such as the number of passes that can be made with the stage at different locations beneath the dispenser. The MLSD 404 is shown separating the vertical rows of droplet positions horizontally (along the lateral direction) by a distance. The spacing along such vertical rows can be based on the ejection frequency of the nozzles and the speed at which the stage moves beneath the nozzles. In this example, four droplet positions 406 have been selected for analysis by the process described in Figure 3 These droplet positions can be modeled to determine the final diffusion pattern as described above.

[0101] Figure 5A and 5B respectively depict examples of an example droplet pattern 500 and a fluid dispensing pattern 510 that may result from the diffusion of droplets of fluid 106 dispensed according to the droplet pattern after application of the template 118. As shown in this example, each droplet 502 may diffuse into an elongated shape 504 according to the specific geometry of the grating. The diffusion of the various droplets 502 may leave one or more air gaps 506 that are not filled with the fluid 106. As described above, the techniques described herein reduce or eliminate the number and volume of such air gaps to ensure optimal performance of the finished optical device.

[0102] Figure 6 A flowchart of an example process 600 for creating surface features on a substrate is depicted. The operations of the process can be performed by one or more components of the system 100, such as under the control of the control device 120. The various operations can be performed in any suitable order. Some operations can be combined into a single operation. The operations can be performed sequentially and / or in parallel to suit the particular operation.

[0103] At 602, the droplet pattern is determined as described above. At 604, the fluid 106 is dispensed onto the substrate 102 according to the droplet pattern. As described above, in some embodiments, the fluid 106 is dispensed onto the template 118 according to the droplet pattern. At 606, the template 118 is applied to mold the dispensed fluid into the desired surface features (e.g., diffraction gratings) on one or more surfaces of the substrate. In embodiments where the template is a roll and / or flexible template (such as the examples of Figure 2A and 2B ), or a roll cylindrical template as described above, the rolling direction can be any suitable direction relative to the grating direction and / or the lateral direction.

[0104] In the case where the template is a cylindrical roll template applied to the substrate, the fluid front of the droplet diffusion can be substantially linear (e.g., perpendicular to the imprinting direction of the template). In some examples, the template moves vertically downward onto the substrate to press on the substrate (e.g., not a cylindrical roll), and the fluid front of the droplet diffusion can be more circular rather than a linear fluid front between the template and the substrate interface. In this case, for determining the droplet pattern design and placement, considering the specific nano or micro pattern to be applied during imprinting, the droplet diffusion rate may be less dependent on the imprinting direction. For an imprinting process where the template contacts the center or is close to the center of the wafer, advantages include a lower dependence of the diffusion rate on a specific imprinting direction (e.g., there is no one direction, but rather a more 360-degree outward imprinting action), and this technique can help maintain equivalent optical performance on the eyepieces distributed in a pinwheel configuration (e.g., having rotational symmetry). During the imprinting process, as the roll rolls from one end (e.g., the leading edge) to the other end (e.g., the trailing edge), the eyepieces at different positions on the wafer may exhibit different performance characteristics in the final product.

[0105] At 608, heat, ultraviolet light, pressure, and / or some other technique is used to cure the dispensed fluid. At 610, in some embodiments, the imprinted and cured surface features can be etched to modify the surface features and / or fine-tune them into the final shape. This etching will be described in more detail below. At 612, the substrate 102 can be segmented (e.g., cut) to create one or more eyepieces from the substrate 102.

[0106] As described herein, the air entrapment problem in the finished surface features is solved through droplet pattern optimization to determine a droplet pattern that reduces or eliminates air gaps in the cured, dispensed photoresist of the nano-geometry forming the diffraction grating. Determining the required amount of the fluid 106 is at least in part a geometric calculation, where the volume of the fluid is calculated to be sufficient to form the desired surface features, plus the volume to be deposited on the non-grating portions (if any) of the substrate, plus the required RLT in one or more regions of the substrate 102.

[0107] Different droplet pattern solutions may not all have similar filling efficiencies for the desired geometries for filling the grating. In the grating, according to the capillary flow of fluid 106 along the direction of the grating channels, the droplets tend to flow along the grating (e.g., along the grating direction) rather than across the grating (e.g., along the transverse direction). For deeper and / or narrower channels, this effect may be stronger. In contrast, fluid 106 is less able to flow in the vertical direction between the channels. The flow differences can be compensated by determining the specific droplet placement positions in the droplet pattern. For example, for deep and / or narrow grating channels, the optimal droplet pattern can include a larger spacing between droplets in the grating direction and a smaller spacing between droplets in the transverse direction (e.g., as Figure 5A shown). In other words, in a flat surface or other surfaces with similar features in two perpendicular directions, the droplet pattern can be a square pattern with similar droplet spacings along both directions.

[0108] In some embodiments, the droplet size is in the tens of micrometers (e.g., diameter), and the channel width of the grating channels can be less than one micrometer. The spacing between the droplets depends on the dispenser and / or stage configuration as described above. In some examples, given such a configuration, the closest droplets that can be dispensed are separated by about 10 micrometers, approximately the diameter of the droplets. In a dispenser with a multi-nozzle configuration, in some examples, the nozzle spacing is about 100 micrometers along the printhead direction (e.g., the transverse direction), and this also limits the spacing in that direction to about 100 micrometers. To achieve a closer spacing in the transverse direction, the stage can be moved to a position closer to the printhead in subsequent dispensing rounds. The droplet spacing along the direction in which the nozzle moves relative to the substrate (or vice versa) can be limited by combining the nozzle firing frequency 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 where droplets need to be dispensed (e.g., the stage movement speed) can be from 100 mm / s to 400 mm / s. The imprinting speed at which the droplets are merged into different nano-patterned grooves between the template and the substrate can vary from 1 mm / s to 40 mm / s.

[0109] The droplet pattern determination process can consider various constraints based on the configuration of the dispense and stage settings and the desired nano-geometry of the grating to be created. Other factors can include the volume of fluid 106 to be dispensed and the desired throughput of system 100 for manufacturing the eyepieces. For example, multiple stage placements are possible, but the more steps of moving the stage and dispensing additional droplets, the longer the time required to process each substrate section, thus reducing the overall throughput of the system. The overall optimal droplet pattern can be based on determining which droplet pattern results in the minimum number and / or volume of air gaps, as well as the droplet pattern that minimizes the dispense rounds and / or stage movements to ensure that the throughput of the system is within an acceptable range.

[0110] In some embodiments, a portion of substrate 102 to be imprinted (e.g., a wafer) can include multiple regions, each corresponding to an eyepiece to be cut out from substrate 102. In such embodiments, each eyepiece region can be modeled separately to determine the optimal droplet pattern for that region, and the overall dispense can be based on the overall droplet pattern for the combination of droplet patterns for each region. Alternatively, the eyepiece regions can be modeled, and the determined droplet patterns can be applied separately to each eyepiece region, where stage 104 moves substrate 102 between rounds to apply the droplet pattern to each eyepiece region of the wafer.

[0111] As described above, due to the configuration of the stage and / or the nozzle of the dispenser, the droplet pattern may be limited to certain types of gratings (meshes). 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 of four eyepieces (e.g., 4-up configuration), or the wafer can include a layout of six eyepieces (e.g., 6-up configuration), where, for example, the eyepieces are parallel to each other (e.g., linear array configuration) or arranged in a rotation relative to each other (e.g., pinwheel configuration). This can lead to complications in modeling. Figure 4 The grating shown has vertices separated by lines at 60 degrees relative to each other and is based on a 6-up configuration where each eyepiece is imprinted separately and stage 104 rotates (e.g., 60 degrees) between imprinting different eyepieces. As another example, a 4-up configuration may result in a grating more like a square pattern. The individual eyepieces in any layout configuration can also be imprinted in a single process step without rotating the wafer and / or the stage.

[0112] In some embodiments, an optimal droplet pattern can be determined for a substrate to be imprinted, where a particular eyepiece is divided into different regions. Each region can have a different RLT and / or different heights (or depths) of the nano-features forming the grating. In some embodiments, the imprinting can also create a transition region between regions having different RLTs and / or different feature heights, and the transition region can provide a gradual change (e.g., slope) of the RLT and / or feature height between the regions. Such embodiments that provide a continuously varying gradient pattern are further described below. The above droplet pattern determination process can take this design into account and determine an optimal droplet pattern to create multiple regions having different RLTs and / or feature heights and transition regions to provide a gradual change of the RLT and / or feature height between the regions.

[0113] Continuous gradient pattern

[0114] Embodiments also provide a technique for creating surface features with continuous (e.g., pseudo-gray scale) nano-scale gradients using jet-based nanoimprint lithography. Embodiments provide a technique for generating a continuous gradient pattern within the constraints of a physical device (e.g., jet nozzle spacing) and droplet volume. Generating the continuous gradient pattern can be the above-described grating (e.g., unit cell grid) and droplet pattern optimization (e.g., unit cell fluid pattern optimization), and in some embodiments, unit cell boundary smoothing. If desired, the continuous gradient jetable pattern can be used to imprint nano-patterns and / or micro-patterns over a larger area while still maintaining a constant RLT. Generally, the technique provides finer control of the RLT over one or more regions being imprinted. Embodiments can be used to create a simulated continuous gradient pattern in the final imprint, and in some cases, an additional etching step can be used to fine-tune the imprinted pattern to the final pattern of the eyepiece. This provides an efficient surface relief waveguide with good image uniformity, which can be used in fabricated optical devices. As described above, the optical devices (e.g., waveguides and / or eyepieces) can be used in AR, MR, or VR solutions, or other types of optical systems.

[0115] Embodiments also have the following advantage: (as Figure 9 shown in the example) creating a substantially continuously varying RLT over a defined region, which can then be used to etch a continuous pattern defined by the RLT into a material (e.g., SiO2, Si3N4, etc.) to create a submaster template from a template starting at a single depth that rides on the continuously varying RLT. If a template with continuously varying features is fabricated (as Figures 10 - 12 shown) and the pattern is replicated onto a suitable substrate (e.g., plastic, glass, etc.) using J-FIL, the droplet pattern used can match the continuously varying pattern to be applied to the substrate.

[0116] The substrate can be imprinted in multiple regions, and each region can include different surface features (such as diffraction gratings) with different configurations and / or different RLTs in each region. Traditionally, attempts to fabricate waveguides with a fine grid of regions have been limited by two factors. The first factor is the inaccuracy of the master template alignment and / or the jet head or nozzle alignment in the nanoimprint tool. The second factor is the feature fabrication accuracy during the etching step. During imprinting from a rigid template or a soft master template (such as a CRT) onto a substrate (such as a wafer), the transition region between regions with different grating features (such as different discrete gradient heights and / or linewidth regions) can fill a small volume of resist with non-uniform RLT below the pattern created by using the template. Such irregularities in the underlying RLT can lead to undesirable optical artifacts, thereby degrading the performance of the finished optical device.

[0117] These problems can be mitigated or eliminated by using an analog or at least partially analog continuous gradient pattern in the regions (such as the transition regions) on the substrate that are located between regions with different gratings and / or different RLTs. Using jet imprint lithography techniques (such as J-FIL), a low-viscosity UV-curable resist (polymer resin) can be dispensed onto any suitable type of substrate (such as a roll, sheet, wafer, rigid, flexible, organic, inorganic, etc.), and the desired (nano or micro) pattern can be transferred from the template mold to the substrate quickly and at low cost, such as in the above process. Drop-on-demand jetting techniques pattern the substrate surface using discrete droplets according to a previously determined droplet (dispensing) pattern. One of the challenges of jetting techniques for ultraviolet nanoimprint lithography is that the dispensed droplets can coalesce based on a large number of variables, such as droplet volume, contact angle, surface energy, nano features created in the grating, capillary forces, evaporation of the resist liquid, and / or the stiffness of the template and / or the substrate.

[0118] When imprinting from a soft master template onto a processed substrate portion (such as a wafer), the transition region between regions can be filled with a small volume of additional resist. To reduce such artifacts, multiple regions can be used in the master template design to reduce the feature height step between regions. Figure 7A Such an example is shown in the schematic diagram 700. In this example, the template 118 includes multiple regions 708, each having a different grating feature height. Applying the template to the fluid 106 dispensed onto the substrate 102 creates features 702 for the different regions. At the boundary 706 between regions, there may be a certain amount of excess resist fluid 704 after imprinting. To improve uniformity and reduce or eliminate the presence of this excess fluid 704, the technique employs a more gradual transition between the regions 708 by using a (such as a pseudo-gray scale) continuous gradient pattern in the template 118. Figure 7BSuch an example is shown in the schematic diagram 710. As shown in this example, the template 118 includes a more continuous variation in feature height rather than a sudden transition between regions of different feature heights. The final feature 712 imprinted on the substrate 102 also exhibits such a continuous variation without Figure 7A the spikes of the excess resist 704 that occur in the example.

[0119] Instead of or in addition to different regions of an imprinted grating having different feature heights, as Figure 7A shown, different regions can have different RLTs. Figure 7C Example 720 is shown, in which the template 118 includes different regions 708 having different RLTs, which can be used to imprint onto the substrate 102 to create imprinted RLTs 722 having different heights in the different regions 708. As described above, such a sudden transition between regions of different RLTs can result in adverse optical effects in an optical device. To avoid such adverse effects, the transition between regions can be more gradual, as Figure 7D shown in example 730. In this example, a transition region 724 is inserted between the regions 708 of different RLTs, where the RLT varies slightly more gradually between the regions of different RLTs.

[0120] In addition to the benefits of a smoother imprint transition and relaxed alignment requirements, this can also allow for the use of finer gratings in the optical design and provide a method for fabricating a continuous master template. When the template and / or the master template having the master pattern to be replicated have discrete regions, the alignment requirements between droplet dispensing and template-to-substrate registration can be more stringent. This is because the droplet volume in a region that requires less fluid volume may not be in a region having a higher droplet volume requirement. In some cases, the spacing between regions can be in the range of 100 nanometers to 1 micrometer. For droplet sizes on the order of 100 micrometers, the process can be fine-tuned based on fluid diffusion and alignment. For example, when the transition between two such regions is smoother, such as a transition region being about 10 to 1000 micrometers wide, the droplet diffusion does not change suddenly, and a smoother transition in the RLT is provided as well as maintaining the desired RLT range.

[0121] Using such a gradient can enhance the virtual image brightness (e.g., efficiency) without sacrificing image uniformity (e.g., the degree to which the image fills the corners and the center of the field of view). However, if photolithography using an etching mask creates a gradient in the template, the boundary between two gradient step regions may cause the RLT to change over a larger area (e.g., ~10 - 100 microns) compared to the region transition boundary (e.g., <1 micron). Specifically, a certain volume of resist can enter the shallower adjacent region, thereby increasing the RLT of that adjacent region. Similarly, the resin volume from the shallow region may cause the RLT to thin and / or non - filling in the higher adjacent region.

[0122] The regions described herein can be located on one or both surfaces of the substrate. In some examples, the different regions do not overlap, such that the regions are separated from each other. Alternatively, the different regions can at least partially overlap. The different regions can be adjacent or separated by a suitable distance. The regions can have any reasonable shape and / or size, having any suitable dimensions to cover a portion of the region of at least one surface of the substrate.

[0123] Figure 8A Schematic 800 is depicted, which shows an example where different regions 802 and 804 of surface features on substrate 102 have features with different heights and / or different RLTs, and a portion 808 of the resin fluid has flowed from one region across a sharp (e.g., sudden, discontinuous) transition boundary between the regions into the other region. Figure 8B Schematic 810 is depicted, which shows an example where a transition region 806 is created between regions with different feature heights. In the transition region 806, the feature height changes more slowly between the higher feature region 802 and the lower feature region 804, thereby avoiding an undesired flow of the resin 808. Test results show that the image uniformity is improved in the design created in the second example as Figure 8B shown. In the Figure 8A example, the test results show that there are unwanted high - frequency artifacts in the finished optical device. Such dominant high - frequency image fringes can be undesirable and difficult to color - correct in the final device and / or a large number of devices because these fringes may not always appear in the same positions. As Figure 8B shown, the gradient pattern can mitigate or eliminate such artifacts, thereby providing an analog region transition region where the eyebox efficiency is the same, but the contrast and sharpness are improved.

[0124] Generating a continuous gradient pattern employs the above-described gratings (e.g., unit cell grids) and droplet pattern optimization (e.g., unit cell fluid pattern optimization), as well as such unit cell boundary smoothing. Techniques such as J-FIL are applicable to such gradients as they can distribute the target droplet volume over a large area, where, for example, the resist volume can gradually increase (or decrease) from one side of the distribution area to the other. In some embodiments, a random or quasi-random droplet pattern can be used to fill a specific area, such as the CPE area of an eyepiece. Using a random droplet pattern to gradually adjust the dispensed resist volume to match the grating depth in the area, due to the simulated gradient defined in the imprint, the area boundaries defined by the droplet pattern may not be distinct. In some embodiments, the droplet diffusion rate in each unit cell can be used as a function of grating orientation, feature height, dispensed resist type, and / or substrate type to further optimize the droplet pattern to better reduce or eliminate the presence of unfilled defects. The entire wafer can be divided into small unit cells, and the feature geometry (including residual layer thickness, grating duty cycle, feature height profile, grating orientation, etc.), unit cell size, and droplet volume determine the number of droplets within each unit cell. The calculated number of droplets can be provided as an input to a Centroidal Voronoi Tessellation (CVT) loop for position optimization. CVT is a special type of Voronoi tessellation where the generating point of each Voronoi unit cell is also its centroid (e.g., the center of mass). It can be regarded as the optimal partition corresponding to the optimal distribution of the generators. At a sufficient number of iterations and a sufficient resolution, the distribution of droplets can reach a locally minimum position in the CVT loop. The unit cell can be defined as a repeating droplet pattern, which can be placed on the underlying grating pattern, which can be defined by various tool constraints (e.g., the constraints described herein), including droplet nozzle spacing, dispense frequency, dispense speed, etc.

[0125] Unit cells optimized for different feature heights are similar to mosaics with different thicknesses on the boundary. If the grid (e.g., grating) is fine enough and the unit cell size is small enough, the thickness difference can be ignored to obtain the desired low-resolution imprint. However, with a given number of droplets in the unit cell and a fixed droplet volume, the grid fineness is limited. Therefore, for high-resolution imprinting, other methods can be used to optimize the pattern. To smooth the boundaries between different unit cells, the droplet positions can be randomized within a certain range, centered on the originally determined droplet positions in the X and Y directions. Then the randomized pattern can be transferred across the entire wafer. After imprinting and optical measurement, the droplet pattern can be adjusted and optimized again based on the measurement feedback. Thus, this randomization, measurement, and re-randomization can be performed as a Figure 3 modification of the process.

[0126] Gradientized RLT imprinting can also be used to fabricate templates (e.g., mother and daughter templates), the corresponding gradient trends of which are mainly defined by the dispensed and imprinted droplet patterns. Etching can also be employed in this process. When using dry etching RIE technology to etch SiO2, RLT can be used as an etching mask to perform secondary gradient etching on, for example, SiO2 (thermal oxide on Si). Adjusting gases (such as CHF3, CF4, C4F8, Ar, O2, SF6, etc.) can be used to control the etching selectivity to etch organic imprints or SiO2. In this way, templates can be fabricated to include multi-step regions with simulated area transitions and / or simulated gradient patterns to provide mother molds for replication. By adjusting the volume of the resist dispensed into each region, dry etching with different depths can be achieved in template materials (such as SiO2, Si3N4, Si, etc.). Creating templates using lithography techniques such as J-FIL can also transfer various geometries, such as serrations, multi-steps, etc., during the dry etching process.

[0127] This process can significantly reduce the cost and complexity of wafer templates of various sizes (e.g., 2 inches, 4 inches, 6 inches, 8 inches, 12 inches, etc.) used in etching lithography. Using an imprinting process (such as J-FIL) that dispenses a curable resist on demand, a dispense pattern with random or quasi-random droplet positions and / or multi-region (e.g., 8 or more regions) droplet patterns can be dispensed or coated onto the target waveguide substrate to transfer the waveguide pattern from the mother mold.

[0128] Figure 9 An example process for fabricating a complex (e.g., 6-up) template with simulated (or at least partially simulated) gradients and / or other specific nano-features is shown. At 900, a carrier substrate 912 with a blank oxide or nitride material 902 overcoat is provided. At 910, resist 904 droplets are dispensed onto the overcoat 902, for example, according to the droplet patterns described herein. At 920, the resist is imprinted to provide a pattern 906 with gradientized RLT as shown. At 930, dry etching is performed to etch the pattern 906 into a final pattern 908. As shown in the example of Figure 9 , the etching can create a final pattern 908 that can have a substantially flat or horizontal upper height on various features that may have different feature depths relative to the gradientized RLT.

[0129] Surface features can include multiple regions, each region having a different RLT and / or different patterns with different height / depth features. Embodiments provide for the use of such regions, but with a gradual change in RLT and / or feature height between the regions, as described herein, to mitigate various negative effects that may occur due to abrupt changes between the regions. Example RLTs can be in the range of 10 - 35 nanometers (nm). Feature creation can also include the step of etching features after dispensing and imprinting using a template. Previously available methods using imprinting plus etching were costly due to the additional etching step. Embodiments described herein for droplet pattern optimization can reduce costs by providing an initial imprint pattern that is more accurate and / or closer to the final pattern than that created without using optimized droplet pattern creation. Etching can then be employed to fine-tune the pattern and turn it into its final form. Using an optimized droplet pattern can also eliminate the need to perform one or more additional imprint steps using a mother and daughter template.

[0130] The algorithms described above for determining optimized droplet patterns can also consider boundary regions where the transition between regions is gradual in terms of RLT change and / or feature height change. For example, as shown in FIG. 8, the dispensed volumes of regions 802 and 804 may be different, and the transition region 806 can have a droplet pattern where the droplets are spaced further apart towards 804 than towards 802. The droplet volume is generally controlled by droplet size, droplet number, droplet density on the transition region (e.g., along the XY pitch), etc.

[0131] As described above, a continuous analog gradient or analog transition between regions of different RLT and / or surface feature height helps to achieve high efficiency and uniform images in optical devices employing planar waveguides with relief nanostructures. The techniques described herein can also be used for curved waveguides and provide similar advantages. Such a gradient avoids abrupt transitions between regions, which can lead to reduced image uniformity and reduced contrast and sharpness (due to changes in RLT). Using such a gradient can also avoid the complexity of template fabrication and increased manufacturing costs while achieving similar eye-box efficiency goals in the manufactured eyepiece. Embodiments provide for the manufacture of such templates for nanoimprint lithography, using plasma-controlled deposition and etching methods. The resulting advantages include reduced template gradient complexity in manufacturing and cost, reduced non-uniformity of the final image displayed through the eyepiece, and improved image quality (e.g., contrast and sharpness) of the final pattern created on the waveguide substrate using J-FIL technology.

[0132] Figure 10An example process for fabricating an imprint template with an analog gradient using deposition and etching methods is shown. This process achieves a smooth transition between regions of different feature heights without the use of multiple masks, photolithography, and etching steps that would otherwise be required to fabricate such a multi-region master template. For analog gradients using previously available stepwise photolithographic exposure processes, the number of steps would be very large and costly.

[0133] Similar to the example of Figure 9 At 1000, a carrier substrate 1002 is provided, which is covered with a blank oxide or nitride 1004. At 1010, photolithography can be performed to create a region 1006. The top region 1006 can be a spin-coated photoresist to create a region that will not be etched or removed in subsequent steps.

[0134] At 1020, operations are performed to develop, wet or dry etch, and strip a portion of the photoresist. At 1030, operations are performed to create a rounded-dome-shaped deposition profile in the oxide / nitride layer using a controlled plasma. At 1040, in some examples, a blank etch can be performed to reduce the remaining overlay (e.g., oxide or nitride) profile to a desired depth. The blank etch can be done using a wet (e.g., using buffered oxide etch or HF for SiO2, etc.) or dry (e.g., RIE, ICP-RIE, IBE, etc.) etching process. At 1050, photolithography can be performed to create the desired features in the oxide / nitride carrier substrate. Photolithography is not limited to photolithography and can also use electron beam lithography or UV / thermal nanoimprint lithography. At 1060, a lithography step (e.g., 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 portion of the resist can be stripped to demonstrate that the template is suitable for imprinting on a waveguide substrate to create a patterned waveguide.

[0135] The method can be used to fabricate rounded-dome or normal-dome-shaped deposition profiles, and a shadow mask can be used to mask the deposition material density or change the plasma density for plasma-enhanced deposition processes such as plasma-enhanced chemical vapor deposition (PE-CVD). Figure 11Shows an example of a method of manipulating deposition by using a shadow mask in a plasma head or deposition source to create a dome or inverted dome shape on a substrate. Example materials used in the deposition may include, but are not limited to, SiO2, Si3N4, or Al2O3. As shown in Example 1100, a shadow mask 1102 with holes of different diameters may be used, and the deposition plasma 1104 may reach the sample 1106 through the holes in the mask. In Example 1110, a shadow mask 1102 is employed where the density of the plasma-enhanced deposition density changes. The position and density of the holes determine how much plasma and chemical reactants are exposed to different regions, thus causing chemical reaction deposition or being removed in the case of etching.

[0136] The embodiments also provide a continuous gradient method of using subtractive gradient etching of a substrate to generate a continuous gradient template, which can improve the field of view uniformity and optimize the eyepiece efficiency. Previous techniques involved creating a nanoscale pattern with a flat top and a gradient bottom on the template. The embodiments improve this technique by creating a nanoscale pattern with a flat bottom and a gradient top on the template. This can avoid RLT non-uniformity on the imprinted resist and improve the field of view uniformity.

[0137] When the master template has patterned features with a flat top and a stepped bottom, the CRT made from the master template correspondingly has a stepped surface. When this CRT is used to imprint on a substrate (such as glass) to generate an eyepiece, the steps cause RLT bulges in the step transaction region, as described above. This may result in field of view uniformity artifacts.

[0138] Figure 12 Shows an example process of creating a template using a subtractive continuous gradient. As shown in 1202, a substrate having a Si layer and a SiO2 layer is received. During dry SiO2 etching, a grid shadow mask 1210 is placed on top of the wafer. By adjusting the grid mask opening duty cycle, the etching rate can be adjusted and a SiO2 layer thickness gradient can be created, as shown in 1204. In this operation, a higher etching rate provides a thinner end of the SiO2 layer. During patterned dry etching, the Si layer can act as an etch stop layer such that the feature depth stops at the SiO2-Si interface, as shown in 1206. Thus, the patterned features have a flat bottom. The CRT made from this template can have a flat surface, as shown in 1208. In some examples, the central platform on the template is away from the patterned area, so it may not affect the imprinting of the patterned area. The grid shadow mask etching gradient method is further described in U.S. Patent No. 10,527,865, titled "Methods and Systems for Tunable Gradient Patterning Using a Shadow Mask", the entire content of which is incorporated herein by reference.

[0139] Example computing system

[0140] Figure 13 FIG. shows a schematic diagram of an example computer system 1300. Various computing devices described herein (e.g., Figure 1 the control device 120 shown in) may be implemented as including one or more components of system 1300.

[0141] 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 is capable of processing instructions executed within system 700. The processor 1310 may include a single-threaded processor and / or a multi-threaded processor. The processor 1310 is capable of processing and executing instructions stored in the memory 1320 and / or on the storage device 1330 to perform various operations, receive and analyze data inputs, generate data outputs, store and retrieve data, present text, graphics, audio, video, images, and / or other types of information via a user interface on the input / output device 1350, and so on.

[0142] The memory 1320 stores information within system 700. In some embodiments, the memory 1320 is a computer-readable medium. In some embodiments, the memory 1320 is a volatile storage unit. In some embodiments, the memory 1320 is a non-volatile storage unit.

[0143] The storage device 1330 provides mass storage for system 700. In some embodiments, the storage device 1330 is a computer-readable medium. In various different embodiments, the storage device 1330 may be a floppy disk device, a hard disk device, a solid state drive, an optical disk device, a tape device, a universal serial bus stick, and / or some other suitable type of storage device.

[0144] The input / output device 1350 provides input / output operations for system 700. The input / output device 1350 may 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 gyroscope sensor, etc.), and / or a game controller. The input / output device 1350 may also include output devices, including but not limited to a display, an audio speaker, a tactile actuator, a printer, etc.

[0145] 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, which is tangibly embodied in an information carrier, e.g., a machine-readable storage device, and executed by a programmable processor; and the method steps of the methods described herein can be executed by a programmable processor, which executes an instruction program to perform the functions of the described embodiments by operating on input data and generating 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 produce a particular result. A computer program can be written in any suitable programming language, including compiled or interpreted languages, 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 a part of one or more computer programs that can be executed by one or more processors.

[0146] Processors suitable for the execution of an instruction program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any type of computer. Generally, 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. Generally, a computer will also include one or more mass storage devices for storing data files, or be operatively coupled to communicate with them. 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 any suitable form of non-volatile memory, including by way of example semiconductor memory devices, such as 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, compact disc read-only memory (CD-ROM) and digital video disc 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).

[0147] For interaction with a user, these features may be implemented on a system having input / output devices, such as a display device. The display device may include any suitable type of display, such as a cathode ray tube (CRT), a liquid crystal display (LCD), etc., for displaying information to the user. Input devices, such as a keyboard, and / or pointing devices, such as a mouse or trackball, enable the user to input to the system.

[0148] These features may be implemented in a computer system that includes backend components, such as a data server, or includes middleware components, such as an application server or an Internet server, or includes 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 may be connected by digital data communication in any form or medium, such as a communication network. Examples of communication networks include a local area network (LAN), a wide area network (WAN), and the computers and networks that form the Internet.

[0149] The computer system may include a client and a server. The client and the server are typically remote from each other and typically interact via a network, such as the networks discussed herein. The relationship between the client and the server is created by computer programs running on their respective computers and they have a client-server relationship with each other. The server may be part of a cloud, which may include ephemeral aspects.

[0150] Although this disclosure contains many specific implementation details, these details should not be construed as limitations on any implementation of the disclosure or on the scope that may be claimed, but rather as descriptions of features specific to example implementations. Certain features described in the context of separate implementations may also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementation may also be implemented separately or in any suitable sub-combination in multiple implementations. Additionally, although features may be described as acting in certain combinations and even initially claimed as such, in some cases, one or more features from a claimed combination may be deleted from the combination, and the claimed combination may be directed to a sub-combination or a variant of a sub-combination.

[0151] Similarly, although the operations are depicted in the figures in a particular order, it should not be understood that these operations are required to be performed in the particular order shown or sequentially, or that all of the illustrated operations are required to achieve the desired result. In some cases, multitasking and parallel processing may be advantageous. Additionally, the separation of various system components in the above-described embodiments should not be understood as requiring such separation in all embodiments, and it should be understood that the program components and systems can generally be integrated in a single software product or packaged into multiple software products. Further, the processes depicted in the figures are not necessarily required to be in the particular order shown or sequential to achieve the desired result. In some embodiments, multitasking and parallel processing may be advantageous.

[0152] 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. Many variations and modifications may occur to those skilled in the art after reading this specification. The breadth and scope of the present invention are not limited by the examples described herein and may be broadly interpreted 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 droplets of photoresist to form one or more surface features on at least one surface of a substrate, wherein determining the droplet pattern comprises: Determining a grid of available droplet positions based at least in part on one or more constraints on the droplet positions, wherein the one or more constraints are based on a configuration of one or more of the following: i) a dispenser component of the system that dispenses the droplets of photoresist, or ii) a stage component of the system that stabilizes the substrate during dispensing; For each of a plurality of candidate dispensing patterns, predicting a diffusion pattern of the droplets dispensed according to the corresponding candidate dispensing pattern, wherein each of the plurality of candidate dispensing patterns comprises a subset of the available droplet positions, and wherein 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; and Determining the dispensing pattern corresponding to the best diffusion pattern from the plurality of diffusion patterns predicted based on the plurality of candidate dispensing patterns; Dispensing droplets of the photoresist onto the at least one surface of the substrate or onto a template usable for molding the one or more surface features according to the dispensing pattern; Applying the template to mold the dispensed photoresist into the one or more surface features on the at least one surface of the substrate; Curing the dispensed photoresist to form the one or more surface features; and Separating the substrate to create an optical device comprising the one or more surface features.

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

3. The method according to claim 1 or 2, wherein The photoresist is a polymeric fluid.

4. The method according to any one of claims 1 to 3, wherein, Curing the photoresist comprises one or more of the following: applying ultraviolet radiation to the dispensed photoresist or applying heat to the dispensed photoresist.

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

6. The method according to claim 5, wherein, The one or more diffraction gratings comprise one or more of the following: an input coupling grating (ICG), an orthogonal pupil expander (OPE), an output pupil expander (EPE), or a combined pupil expander (CPE).

7. The method according to any one of claims 1 to 6, wherein The one or more constraints comprise one or more of the following: 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.

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

9. The method according to any one of claims 1 to 8, wherein, Determining the dispensing pattern corresponding to the best diffusion pattern comprises identifying the best diffusion pattern that minimizes one or more of the following: 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.

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

11. The method according to claim 10, wherein, The first set of surface features includes a first residual layer of the photoresist having a first residual layer thickness (RLT) in the first region; and The second set of surface features includes a second residual layer of the photoresist having a second RLT in the second region, the second RLT being different from the first RLT.

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

13. The method according to any one of claims 10 to 12, wherein, The first set of surface features includes a first nanostructure having a first height relative to the at least one surface; and The second set of surface features includes a second nanostructure having a second height relative to the at least one surface.

14. The method according to claim 13, wherein, At least one surface of the substrate includes a third region between the first region and the second region; and The third region includes a third nanostructure, the height of which continuously changes from the first height near the boundary of the third region and the first region to the second height near the boundary of the third region and the second region.

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 1-15, wherein, The one or more surface features are located 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 located on multiple 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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