Imprinting techniques in nanolithography for optical devices

Abstract

To provide methods and systems for fabrication of high quality surface relief waveguides for eyepieces.SOLUTION: Techniques are for manufacturing waveguides with surface relief features, such as diffractive gratings to achieve various optical effects, using nanolithography imprinting techniques that reduce or eliminate the presence of gaps in imprinted features through the use of optimized drop patterns for dispensing photoresist. Moreover, the techniques are for manufacturing surface relief waveguides having a gradation, for example a substantially continuous grade or slope, between zones that have different residual layer thickness of the dispensed photoresist, and / or between zones having surface features of different height (or depth).SELECTED DRAWING: None

Description

[Technical Field]

[0001] Technical Field SUMMARY OF THE INVENTION The embodiments described herein generally relate to systems and methods for fabricating surface relief waveguides for eyepieces and optical devices made thereby. [Background technology]

[0002] background When manufacturing waveguides, eyepieces, and other types of optical devices, performance considerations can be important. For example, small scratches on a manufactured device can disproportionately affect the optical performance of the device, reducing optical power, optical loss, artifacts, etc. Performance considerations may be balanced against the manufacturing costs of the device, including the costs of component materials, fabrication, testing, etc. Therefore, manufacturers of high-performance optical devices have traditionally pursued various techniques to increase the quality of manufactured devices while avoiding excessive increases in manufacturing costs. Summary of the Invention [Means for solving the problem]

[0003] overview This disclosure generally describes methods and systems for fabricating high-quality surface-relief waveguides for eyepieces. In particular, this disclosure describes techniques for fabricating waveguides with surface-relief features, such as diffraction gratings, to achieve various optical effects using nanolithography imprinting techniques that reduce or eliminate the presence of gaps within the imprinted features. Furthermore, this disclosure also describes techniques for fabricating surface-relief waveguides with gradations, e.g., substantially continuous slopes or ramps, between zones with different residual layer thicknesses of dispensed photoresist and / or between zones with surface features of different heights (or depths). Such gradations can reduce or eliminate adverse optical effects that can be caused by more abrupt transitions between zones, increasing the optical efficiency of the finished waveguide.

[0004] An embodiment includes a method performed by a system for manufacturing an optical device, the method comprising: determining a dispensing pattern for dispensing drops of photoresist to form one or more surface features on at least one surface of a substrate, wherein determining the drop pattern includes determining a grid of available drop locations based at least in part on one or more constraints on the drop locations, the one or more constraints being based on a configuration of one or more of: i) a dispenser component of a system that dispenses the drops of photoresist; or ii) a stage component of a system that stabilizes the substrate during dispensing; and for each of a plurality of candidate dispensing patterns, predicting a spreading pattern of drops dispensed according to the respective candidate dispensing pattern, wherein each of the plurality of candidate dispensing patterns is based on a grid of available drop locations. the method includes: predicting a diffusion pattern based at least in part on one or more surface features to be formed on at least one surface of the substrate, the diffusion pattern including a subset of locations; determining a distribution pattern corresponding to an optimal diffusion pattern from among a plurality of diffusion patterns predicted based on a plurality of candidate distribution patterns; dispensing droplets of photoresist according to the distribution pattern onto at least one surface of the substrate or onto a template usable to mold the one or more surface features; applying the template to mold the dispensed photoresist into the one or more surface features on the at least one surface of the substrate; hardening the dispensed photoresist to form the one or more surface features; and isolating the substrate to create an optical device including the one or more surface features.

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

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

[0007] In some embodiments, curing the photoresist comprises 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, one or more surface features are on one surface of the substrate.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0024] In some embodiments, the first set of surface features comprises a first residual layer of photoresist having a first height that is a first residual layer thickness (RLT) in the first zone, the second set of surface features comprises a second residual layer of photoresist having a second height that is a second RLT in the second zone, where the second RLT is different from the first RLT, and the third set of surface features comprises a third residual layer of photoresist having a variable height that is a graduated RLT that varies continuously from the first RLT near the boundary between the third zone and the first zone to the second RLT near the boundary between the third zone and the second zone.

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

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

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

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

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

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

[0031] An embodiment includes a method for manufacturing an optical device, the method including: determining a dispensing pattern for dispensing drops of photoresist to form surface features on at least one surface of a substrate; dispensing the drops of photoresist according to the dispensing pattern onto at least one surface of the substrate or onto a template usable to shape the surface features; applying the template to shape the dispensed photoresist into the surface features on the at least one surface of the substrate; hardening the dispensed photoresist to form the surface features; and isolating the substrate to produce an optical device including the surface features, wherein the surface features are formed on at least one surface of the substrate. a first set of surface features within a first zone of at least one surface of the substrate, the first set having a first height; a second set of surface features within a second zone of at least one surface of the substrate, the second zone not overlapping the first zone and the second set of surface features having a second height different from the first height; and a third set of surface features within a third zone of at least one surface of the substrate, the third zone being between the first zone and the second zone, the third set of surface features having a variable height that varies continuously from a first height near the boundary between the third zone and the first zone to a second height near the boundary between the third zone and the second zone.

[0032] In some embodiments, the first set of surface features comprises a first residual layer of photoresist having a first height that is a first residual layer thickness (RLT) in the first zone, the second set of surface features comprises a second residual layer of photoresist having a second height that is a second RLT in the second zone, where the second RLT is different from the first RLT, and the third set of surface features comprises a third residual layer of photoresist having a variable height that is a graduated RLT that varies continuously from the first RLT near the boundary between the third zone and the first zone to the second RLT near the boundary between the third zone and the second zone.

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

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

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

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

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

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

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

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

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

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

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

[0044] Embodiments include a method of preparing a template for imprinting, the method including providing a carrier substrate with an overlay of blank (e.g., oxide or nitride) material, dispensing drops of photoresist on the overlay according to a drop pattern, imprinting the photoresist to provide a pattern on the substrate, the pattern including a stepped RLT, and etching (e.g., dry etching) the pattern to a final pattern, the final pattern having a substantially flat top area.

[0045] Embodiments include a method of creating a template for imprinting, the method including providing a carrier substrate with an overlay of blank (e.g., oxide or nitride) material; creating areas of photoresist on the substrate that will not be etched or removed in a subsequent step (e.g., spin-coated); removing portions of the photoresist (e.g., using wet etching, dry etching, and / or stripping); creating a dome or inverted dome shaped deposition profile in the overlay using a controlled plasma; performing a blank etch to reduce the remainder of the overlay to a specified depth; performing photolithography to create features in the carrier substrate; performing lithography 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 and drawings, and from the claims. The present invention provides, for example, the following. (Item 1) 1. A method performed by a system for manufacturing an optical device, the method comprising: determining a dispensing pattern for dispensing droplets of photoresist to form one or more surface features on at least one surface of the substrate, wherein determining the droplet pattern includes: determining a grid of available drop locations based at least in part on one or more constraints on the drop locations, the one or more constraints being based on a configuration of one or more of: i) a dispenser component of the system that dispenses the photoresist drops; or ii) a stage component of the system that stabilizes the substrate during dispensing; predicting, for each of a plurality of candidate dispensing patterns, a spreading pattern of drops dispensed according to the respective candidate dispensing pattern, wherein each of the plurality of candidate dispensing patterns includes a subset of the available drop locations, and the spreading pattern is predicted based at least in part on the one or more surface features to be formed on the at least one surface of the substrate; determining a distribution pattern corresponding to an optimal spreading pattern from a plurality of spreading patterns predicted based on the plurality of candidate distribution patterns; and dispensing the drops of photoresist according to the dispensing pattern onto the at least one surface of the substrate or onto a template that can be used to mold the one or more surface features; applying the template to shape 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; isolating the substrate to create an optical device including the one or more surface features; and A method comprising: (Item 2) Item 10. The method according to item 1, wherein the substrate is made of glass or a polymer. (Item 3) 3. The method of any of items 1 or 2, wherein the photoresist is a polymer fluid. (Item 4) 4. The method of any of items 1 to 3, wherein curing the photoresist comprises one or more of applying ultraviolet radiation to the dispensed photoresist or applying heat to the dispensed photoresist. (Item 5) 5. The method of any of items 1 to 4, wherein the one or more surface features include one or more diffraction gratings. (Item 6) Item 6. The method of item 5, wherein the one or more diffraction gratings include one or more of an incoupling grating (ICG), an orthogonal pupil expander (OPE), an exit pupil expander (EPE), or a compound pupil expander (CPE). (Item 7) 7. The method of any of items 1 to 6, wherein the one or more constraints include one or more of a number of nozzles of the dispenser component, a spacing between the nozzles of the dispenser component, and a range of dispensing frequencies of the nozzles of the dispenser component. (Item 8) 8. The method of any of items 1 to 7, wherein the one or more constraints include one or more of a range of speeds of movement of the stage component and available directions of movement of the stage component. (Item 9) 9. The method of any of items 1 to 8, wherein determining the distribution pattern corresponding to the optimal diffusion pattern includes identifying the optimal diffusion pattern that minimizes one or more of the number of void gaps in the diffusion pattern, the size of the void gaps in the diffusion pattern, and the total volume of the void gaps in the diffusion pattern. (Item 10) the at least one surface of the substrate includes a first zone and a second zone that does not overlap the first zone; the one or more surface features include a first set of surface features in the first zone and a second set of surface features in the second zone; 10. The method according to any one of items 1 to 9. (Item 11) the first set of surface features includes a first residual layer of the photoresist having a first residual layer thickness (RLT) in the first zone; the second set of surface features includes a second residual layer of the photoresist having a second RLT in the second zone, the second RLT being different from the first RLT; Item 11. The method according to item 10. (Item 12) the at least one surface of the substrate includes a third zone between the first zone and the second zone; the third zone includes a third residual layer of the photoresist having a gradational RLT that continuously changes from the first RLT near the boundary between the third zone and the first zone to the second RLT near the boundary between the third zone and the second zone; Item 12. The method according to item 11. (Item 13) the first set of surface features includes a first nanostructure having a first height relative to the at least one surface; the second set of surface features includes second nanostructures having a second height relative to the at least one surface; 13. The method according to any one of items 10 to 12. (Item 14) the at least one surface of the substrate includes a third zone between the first zone and the second zone; the third zone includes a third nanostructure having a height that varies continuously from the first height near the boundary between the third zone and the first zone to the second height near the boundary between the third zone and the second zone; Item 14. The method according to item 13. (Item 15) 15. The method of any of items 1 to 14, wherein the optical device is a waveguide. (Item 16) 16. The method of any of items 1 to 15, wherein the one or more surface features are on one surface of the substrate. (Item 17) 16. The method of any of items 1 to 15, wherein the one or more surface features are on two or more surfaces of the substrate. (Item 18) 18. The method of any of items 1 to 17, wherein the one or more surface features include at least one non-diffractive pattern. (Item 19) Item 19. The method of item 18, wherein the one or more surface features include an anti-reflective pattern. [Brief explanation of the drawings]

[0047] [Figure 1] FIG. 1 illustrates an example of a system for manufacturing an optical device.

[0048] [Figure 2A] 2A and 2B depict schematic diagrams of example template configurations and operations. [Figure 2B] 2A and 2B depict schematic diagrams of example template configurations and operations.

[0049] [Figure 3] FIG. 3 depicts a flow diagram of an example of a process for determining a drop pattern for use in manufacturing an optical device.

[0050] [Figure 4] FIG. 4 depicts a schematic diagram of an example of a grid for determining a drop pattern.

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

[0052] [Figure 6] FIG. 6 depicts a flow diagram of an example process for creating surface features on a substrate.

[0053] [Figure 7A] 7A-7D show schematic diagrams of an example template and an example grid pattern created by application of the template. [Figure 7B]7A-7D show schematic diagrams of an example template and an example grid pattern created by application of the template. [Figure 7C] 7A-7D show schematic diagrams of an example template and an example grid pattern created by application of the template. [Figure 7D] 7A-7D show schematic diagrams of an example template and an example grid pattern created by application of the template.

[0054] [Figure 8A] 8A and 8B show schematic diagrams of an example of a grid pattern. [Figure 8B] 8A and 8B show schematic diagrams of an example of a grid pattern.

[0055] [Figure 9] 9-12 depict diagrams of an example process for creating a template. [Figure 10] 9-12 depict diagrams of an example process for creating a template. [Figure 11] 9-12 depict diagrams of an example process for creating a template. [Figure 12] 9-12 depict diagrams of an example process for creating a template.

[0056] [Figure 13] FIG. 13 illustrates an example of a computing system. DETAILED DESCRIPTION OF THE INVENTION

[0057] Detailed Description 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 use in virtual reality (VR), augmented reality (AR), and / or mixed reality (MR) systems, and / or other suitable optical applications. For example, the optical device may be incorporated into a wearable (e.g., head-mountable) display system that provides an AR experience to the wearer. In such a system, the eyepiece can be transparent to allow the wearer to see the physical environment, while the eyepiece's waveguide transmits light used for graphical objects presented as an overlay on the view of the physical environment. In some examples, the waveguides are configured to present graphical objects at multiple depth planes, allowing the wearer to perceive the graphical objects as if they were at a particular 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, with different ones of the waveguides 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 that can be used in an eyepiece, either alone or in a stacked configuration of multiple waveguides. The optical features within the surface-relief waveguide have high nanofeature fidelity and high uniformity of residual layer thickness (RLT) within one or more zones, which may have different requirements for resist volume given the surface features (e.g., one or more diffraction gratings) to be created within each zone. In some embodiments, the features may be fabricated by dispensing, patterning, and curing a high-index nanoimprintable fluid, which may also be described as a photoresist, resist, or resin. The features may be fabricated on one or both sides of a large, substantially flat substrate that is transparent and acts as a waveguide for transmitting light through total internal reflection (TIR).

[0059] The surface features fabricated on one or more surfaces of the substrate can include diffraction gratings that optically function to affect light passing through the substrate. Such diffraction gratings can include, but are not limited to, incoupling gratings (ICGs), outcoupling gratings (OCGs), orthogonal pupil expanders (OPEs), exit pupil expanders (EPEs), compound pupil expanders (CPEs), and / or other types of gratings. The substrate, and the resulting eyepiece, can include any suitable number and type of such gratings in any suitable combination to achieve the desired optical performance.

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

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

[0062] A fluid may be dispensed onto an optically transparent substrate that acts as a waveguide, and the dispensed fluid can be imprinted with a template and then cured to create desired nanofeatures (e.g., 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 thickness values of a substrate in a series of point measurements across a dimension of the substrate. For a substrate having a patterned surface on which a diffraction grating is fabricated, TTV refers to an approximation estimated by ignoring the contribution of pattern features to thickness. For example, the thickness (or height) of a typical feature on a patterned substrate may be in the range of approximately 10 nanometers (nm) to 150 nm. The thickness is governed 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 is typically greater than 100 nm and can be on the order of microns. Therefore, any additional variation in the thickness of a patterned substrate introduced by pattern features is negligibly small and can be ignored as an approximation. Therefore, the thickness of a patterned substrate estimated at locations including protrusions can be approximated by subtracting a given feature thickness from the estimated thickness to obtain an adjusted thickness, while the thickness of a patterned substrate estimated at locations without protrusions is not altered. That is, the adjusted (e.g., reduced) thickness of the feature areas and the intrinsic thickness of the unpatterned areas can be used to calculate the TTV of a substrate having a patterned surface. The low TTV values described herein result, at least in part, from flat optical-grade glass substrates polished to a desired flatness and the methods described herein for minimizing or reducing non-uniform material shrinkage during curing. Low TTV can also be imparted to inorganic material substrates by extrusion. Furthermore, low TTV can also be imparted to polymer substrate materials and achieved from mold surfaces while forming such substrates from base materials consisting of high refractive index polymers (e.g., containing sulfur, aromatic groups, etc.) and other polymeric materials such as polycarbonates (e.g., by injection molding, ultraviolet (UV) or thermoforming, extrusion, etc.).

[0064] As used herein, RLT refers to the thickness of (e.g., polymer) photoresist deposited on a substrate in areas where surface features (e.g., gratings) are absent and / or where surface features are present but between the specific nanogeometric structures of the surface features. The RLT may be substantially similar across the finished eyepiece, or different zones of the eyepiece may have different RLTs. In some embodiments, there may be a substantially continuous and / or gradual change in RLT across at least a portion of the eyepiece. In some embodiments, different zones may have different RLTs, and there may be a continuous gradation (e.g., slope) of RLT in the transition area from one zone having one RLT to another zone having a different RLT. The embodiments described herein allow for fine tuning of the RLT to achieve various desired optical performance characteristics in the finished eyepiece.

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

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

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

[0068] The fluid dispenser 112 is configured to dispense drops (or droplets) of a fluid 106, such as a resist, onto the substrate 102. The fluid dispenser 112 may include one or more print heads (or nozzles) that dispense (e.g., eject) the droplets of the fluid 106. The fluid 106 is held in a reservoir 108, which is connected to the fluid dispenser 106 by one or more channels (e.g., tubes, conduits, etc.) of a suitable type, material, and dimensions. 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., arranged to provide a reliable flow of the fluid 106 to the fluid dispenser 112.

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

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

[0071] In some embodiments, the fluid dispenser and imprinting are performed according to drop-on-demand jet and flash imprint lithography (J-FIL) techniques to dispense the fluid 106 and imprint the 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," which is incorporated by reference in its entirety into this disclosure.

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

[0073] Control device 120 is communicatively coupled to various other devices of system 100 that perform actions on substrate 102 to fabricate optical devices, including stage 104, fluid dispenser 112, imprint mechanism 116, etching mechanism 122, etc. Control device 120 can send signals to the various other devices to control their operation. In some embodiments, control device 120 is any suitable type of computing device that includes at least one processor and memory. The memory can store computer programs that include instructions that, when executed by the at least one processor, cause the processor to perform operations to control the devices of system 100 during the manufacturing process. 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, etc.

[0074] 1 shows an example of system 100 including a single fluid dispenser 112, other implementations are possible. For example, system 100 may include multiple fluid dispensers 112 (e.g., print heads) to increase the throughput of system 100 and / or to dispense fluid 106 to additional locations on substrate 102. System 100 may also include multiple imprint stations, each with an associated imprint mechanism 116 and / or template 118.

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

[0076] Organic (meth)acrylate monomers and oligomers typically have refractive indices of approximately 1.5 at a wavelength of 532 nm. Sulfur atoms and aromatic groups, both highly polarizable, can be incorporated into these acrylate components to increase the refractive index of the formulation. This effect is limited due to the fluid viscosity limit of less than 20-25 cP for inkjet processing and by the upper refractive index limit of sulfur-containing molecules. This approach results in jettable and imprintable resists with refractive indices as low as 1.72 at wavelengths of 532 nm light.

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

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

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

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

[0081] While this example depicts a rollable template configuration for use in the imprint step, embodiments are not so limited. Other types of templates include, for example, template 118 that, instead of moving laterally in an XY plane parallel to the surface of substrate 102, pushes downward (e.g., in the Z direction in FIG. 1 ) onto the surface of substrate 102. In some embodiments, template 118 is etched or otherwise imprinted onto the surface of a cylindrical drum that imprints the desired pattern into fluid 106 as the drum rolls over the substrate and dispensed fluid 106. In such embodiments, imprint direction 106 may be perpendicular to the axis of rotation of the cylinder. In some embodiments, the template is applied spherically so that pressure is first applied to press the template against the substrate at or near the center of the portion of the substrate (e.g., a wafer) being imprinted, and then pressure is applied outward from the center.

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

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

[0084] Embodiments provide techniques for determining a drop pattern for dispensing fluid 106 onto a substrate 102 (or onto a template) to create desired surface features on the substrate 102. The drop pattern is determined to minimize or eliminate non-filled areas (e.g., voids) from the spread fluid 106 upon application of the template 118, thus minimizing or eliminating surface features formed from the hardened fluid. The drop pattern is also determined to provide a controlled, and potentially ultra-thin, RLT in the resulting waveguide.

[0085] During imprinting using conventionally available techniques, void defects can result from air entrapment in the resist during dispensing and imprinting. These defects, referred to as non-fills in nanolithography, are areas that are not filled with resist (e.g., at least partially inside an imprinted and cured nanofeature). A previous method for preventing such defects was to dispense an extra volume of resist in the area to ensure all gaps were filled. Unfortunately, the extra volume can result in an undesirably large RLT, which can result in poor optical performance in the finished waveguide. Embodiments determine a drop pattern that allows for efficient filling of the grating pattern of an applied template without the need to increase the volume of dispensed resist.

[0086] When the fluid front traps air as the template 118 is being applied, for example, when the fluid 106 is pressed between the substrate 102 and the template 118 (also referred to as a superstrate) and the air cannot escape from the fluid 106 before hardening, void defects (e.g., voids) can occur in the hardened resist structure. The created grating 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, separated by ridges. Voids or unfilled defects can be more likely to occur when the grating direction is substantially perpendicular to the imprint direction (e.g., the direction 206 in which the rolling device 204 is moving to apply the template 118) compared to when the grating direction is parallel to the imprint direction. In some examples, unfilled defects can be more likely to occur when the grating direction is substantially parallel to the imprint direction. Substantially perpendicular or substantially parallel can refer to an angular deviation from perpendicular or parallel within an appropriate arc angle (e.g., within 1 degree, within 5 degrees, within 10 degrees, etc.).

[0087] To address this issue and eliminate or mitigate voids, embodiments determine an optimal drop pattern that takes into account the predicted diffusion characteristics of the fluid 106 on the substrate 102 according to the specific pattern to be imprinted, fluid and substrate properties, imprint direction, and / or other variables. The drop diffusion characteristics are related to resist properties (e.g., viscosity), substrate surface properties, template properties (e.g., the grating to be created), and imprint conditions. For example, the diffusion rate may be similar for domed (e.g., convex or concave) glass and silicon substrates, while flat glass may exhibit a greater diffusion rate, other variables held constant. Thus, for glass substrates with different TTVs, the optimized drop pattern may be different. The diffusion rate may also vary with different imprint speeds (e.g., the speed at which the template is applied). For example, the faster the imprint, the less air can escape, making void defects more likely to form.

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

[0089] The grid direction is the direction along (e.g., substantially parallel to) the long axis of the features present in the imprinted grid. The direction perpendicular to the grid direction is referred to as the lateral direction. In some embodiments, the imprint direction is the grid direction, but embodiments support any imprint direction at any angle relative to the grid direction. The imprint direction may be lateral to more effectively spread fluid across the boundaries between channels. The distance between drops in the lateral direction, or the distance between different rows of drops, is referred to as the lateral spreading distance. Such a minimum available distance is referred to as the minimum lateral spreading distance (MLSD). This value may be constrained by the geometry of the printhead, for example, the distance between the nozzles of the fluid dispenser 112. Considering that fluids tend to spread along (e.g., in the grid direction) and difficult to spread across (e.g., laterally) grid features, a smaller MLSD can help avoid void defects. A smaller MLSD can be used in the drop pattern to help fluids merge laterally and eliminate air traps. However, too small an MLSD can lead to large separation between drops in the grid direction, which can also cause defects. Therefore, embodiments model different drop patterns and allow for the selection of a drop pattern that results in optimal spreading with minimal or no gaps. An optimal drop pattern can also result in a reduction in the total volume of dispensed resist (e.g., a 50% reduction compared to previous techniques), given that the optimal drop pattern allows drops to be positioned to optimally fill the grid volume and provide the desired RLT outside the gridded area. Drop patterns for imprinting are further described in U.S. Pat. No. 8,119,052, entitled "Drop Pattern Generation For Imprint Lithography," the entirety of which is incorporated herein by reference.

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

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

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

[0093] At 306, various constraints on the drop pattern that may exist based on the configuration of the fluid dispenser 112 are determined. Such constraints may include the number of nozzles in the dispenser, the spacing between the nozzles, and the available dispensing frequency. The dispensing frequency is the frequency at which the nozzles can dispense drops (e.g., firing frequency). In some examples, the dispensing frequency may be specified as a range of frequencies. The range of dispensing frequencies may have a defined upper limit (e.g., as fast as they can fire) and no defined lower limit (or a zero lower limit) based on the dispenser configuration.

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

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

[0096] At 312, each of a plurality of possible drop patterns (e.g., dispensing patterns) can be analyzed, and a process can be performed to predict the spreading pattern of the fluid 106 dispensed according to each drop pattern. This prediction can be made based on the particular drop pattern, along with the volume of fluid 106 to be dispensed, the particular 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 spreading rate of the drop, such that it is governed by the direction in which the fluid front moves and spreads (e.g., based on the template imprint direction) once the template begins to push the drop across the surface of the template and substrate.

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

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

[0099] FIG. 4 depicts a schematic diagram of an exemplary grid 400 for determining a drop pattern. Each vertex of the grid 400, e.g., where lines intersect, can be considered a possible location for dispensing a drop onto the substrate 102 (or onto the template 118). As previously described, the possible locations for dispensing are determined based on the configuration of the dispenser, such as the distance between nozzles and the available range of nozzle firing frequencies, and the configuration of the stage, such as how quickly and in what direction the stage can move beneath the dispenser. Other factors, such as the number of passes that can be made with the stage at different positions beneath the dispenser, can also be considered. MLSD 404 is shown as the horizontal distance apart from the vertical columns of drop locations. The spacing along these columns can be based on the nozzle firing frequency and the speed at which the stage moves beneath the nozzles. In this example, four drop locations 406 are selected for analysis according to the process described in FIG. 3. These drop locations can be modeled to determine the resulting spreading pattern, as previously described.

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

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

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

[0103] If the template is a cylindrically rolled template applied to the substrate, the droplet spreading fluid front can be substantially linear (e.g., perpendicular to the imprint direction of the template). In some instances, if the template is moved vertically downward over the substrate to press against it (e.g., not cylindrically rolled), the droplet spreading fluid front can be more circular rather than a linear fluid front between the template and substrate interface. In this case, to determine the design and placement of the droplet pattern, the droplet spreading rate may be less dependent on the imprint direction given the specific nano- or micropattern to be applied during imprinting. For imprint processes in which the template contacts or is close to the center of the wafer, advantages include less dependency of the spreading rate on the specific imprint direction (e.g., more 360-degree outward imprint action rather than one direction), and such a technique can help maintain comparable optical performance across eyepieces distributed in a pinwheel configuration (e.g., with rotational symmetry). In the case of an imprint process in which a roller rolls from one edge (e.g., the leading edge) to the other edge (e.g., the trailing edge), eyepieces at different locations on the wafer can exhibit different performance characteristics in the final product.

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

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

[0106] Different drop pattern solutions do not all have the same packing efficiency for filling the desired geometry of a lattice. In a lattice, droplets tend to flow along the lattice (e.g., in the lattice direction) rather than across it (e.g., laterally), due to the capillary flow of fluid 106 along the direction of the lattice's channels, which extend in the lattice direction. For deeper and / or narrower channels, this effect may be stronger. In contrast, fluid 106 cannot flow vertically between channels. Flow differences can be compensated for by determining specific drop placement locations within the drop pattern. For example, for deep and / or narrow lattice channels, an optimal drop pattern may include greater spacing between droplets in the lattice direction and closer spacing between droplets in the lateral direction (e.g., as shown in Figure 5A). In other words, on a flat or other surface with similar features in both vertical directions, the drop pattern may be a square pattern with similar drop spacing along both directions.

[0107] In some embodiments, the droplet size may be on the order of tens of microns (e.g., diameter), and the channel width of the grid channels may be less than 1 micron. Droplet spacing depends on the dispenser and / or stage configuration, as discussed above. In some examples, given this configuration, the closest droplets that can be dispensed are about 10 microns apart, approximately the droplet diameter. In dispensers with multi-nozzle configurations, the nozzle separation in some examples is about 100 microns along the printhead direction (e.g., lateral direction), which also constrains the separation in that direction to about 100 microns. To achieve closer separation in the lateral direction, the stage can be shifted to provide a closer location below the printhead in subsequent dispense passes. Droplet spacing along the direction in which the nozzle is moving relative to the substrate (or vice versa) can be constrained by the nozzle firing frequency combined with the speed at which the stage can move in that direction. In some examples, the firing frequency can range from 4 kHz to 14 kHz, and the relative speed between the dispenser and the substrate at which droplets need to be dispensed (e.g., stage movement speed) can be from 100 mm / s to 400 mm / s. The imprint speed, at which the droplets merge into different nanopattern grooves between the template and the substrate, can vary from 1 mm / s to 40 mm / s.

[0108] The drop pattern determination process can consider various constraints based on the configuration of the dispensing and stage setup, along with the desired nanogeometry of the grating to be created. Other factors include the volume of fluid 106 to be dispensed and the desired throughput of the system 100 for manufacturing the eyepiece. For example, while multiple stage configurations may be possible, a greater number of steps of moving the stage to dispense additional drops may increase the time it takes to process each portion of the substrate, thus reducing the overall throughput of the system. The overall optimal drop pattern may be based on determining which drop pattern results in the smallest number and / or volume of voids and the drop pattern that minimizes the number of passes for dispensing and / or stage movement, so that the system throughput is within an acceptable range.

[0109] In some embodiments, a portion of substrate 102 (e.g., a wafer) to be imprinted may include multiple regions, each corresponding to an eyepiece to be cut from substrate 102. In such embodiments, each eyepiece region may be modeled separately to determine an optimal drop pattern for that region, and the overall distribution may follow an overall drop pattern that is a combination of the drop patterns for each region. Alternatively, the eyepiece regions may be modeled, and the determined drop pattern may be applied to each eyepiece region separately, with stage 104 moving substrate 102 between passes to apply the drop pattern to each eyepiece region of the wafer.

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

[0111] In some embodiments, an optimal drop pattern can be determined for a substrate to be imprinted, where a particular eyepiece is divided into different zones. The various zones may have different RLTs and / or different heights (or depths) of the nanofeatures forming the grating. In some embodiments, the imprint can also create transition zones between zones of different RLTs and / or different feature heights, which can result in a gradual change (e.g., a slope) in RLT and / or feature height between the zones. Such embodiments for creating continuously varying gradient patterns are further described below. The drop pattern determination process described above can take such designs into account and determine an optimal drop pattern for creating multiple zones of different RLTs and / or feature heights, and transition zones that result in a gradual change in RLT and / or feature height between the zones. Continuous Gradient Pattern

[0112] Embodiments also provide for creating continuous (e.g., pseudo-grayscale) nanoscale gradations of surface features using inkjet-based nanoimprint lithography. Embodiments provide techniques for generating continuous gradient patterns within physical device constraints (e.g., inkjet nozzle spacing) and drop volume constraints. Generating continuous gradient patterns can involve the aforementioned grid (e.g., unit cell mesh) and drop pattern optimization (e.g., unit cell fluid pattern optimization), and in some embodiments, unit cell boundary smoothing. If desired, continuous gradient jettable patterns can be applied to imprint nanopatterns and / or micropatterns over large areas while keeping the RLT constant. In general, the technique provides more precise control of the RLT over one or more zones being imprinted. In some examples, embodiments can be used to create analog continuous gradient patterns in the final imprint, with an additional etching step to fine-tune the imprinted pattern to the final pattern for the eyepiece. This provides highly efficient surface relief waveguides with good image uniformity for use in fabricated optical devices. As previously mentioned, the optical devices (e.g., waveguides and / or eyepieces) can be used in AR, MR, or VR solutions, or in other types of optical systems.

[0113] Embodiments also provide advantages by creating a substantially continuously varying RLT across a defined area (as shown in the example of FIG. 9), which can then be used to etch the continuous pattern defined by the RLT into materials such as SiO2, Si3N4, etc. to create submaster templates from templates starting at a single depth that ride on the continuously varying RLT. When a template with continuously varying features is fabricated (as shown in FIGS. 10-12) and used to pattern replicas onto a suitable substrate (e.g., plastic, glass, etc.) using J-FIL, the drop pattern used can be matched to the continuously varying pattern applied to the substrate.

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

[0115] These problems can be reduced or eliminated by using analog or at least partially analog continuous gradient patterns in regions of the substrate between zones with different gratings and / or different RLTs (e.g., transition zones). Inkjet imprint lithography techniques such as J-FIL can be used to dispense low-viscosity UV-curable resists (polymer resins) onto any suitable type of substrate (e.g., rolls, sheets, wafers, rigid, flexible, organic, inorganic, etc.), allowing for the rapid, low-cost transfer of desired (nano- or micro) patterns from a template mold to the substrate, such as in the aforementioned process. Drop-on-demand inkjet techniques pattern the surface of a substrate with individual droplets according to a previously determined droplet (dispensing) pattern. One challenge with the inkjet method of UV nanoimprint lithography is that dispensed droplets can merge based on numerous variables, such as droplet volume, contact angle, surface energy, nanofeatures created within the grating, capillary forces, evaporation of the resist fluid, and / or the stiffness of the template and / or substrate.

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

[0117] In addition to or instead of different zones having different feature heights of the imprinted grating, the different zones may have different RLTs, as shown in FIG. 7A. FIG. 7C shows an example 720 in which a template 118 includes different zones 708 of different RLTs that can be used to imprint on a substrate 102 to create imprinted RLTs 722 of different heights in the different zones 708. As previously mentioned, such abrupt transitions between zones of different RLTs can result in adverse optical effects in optical devices. To avoid such adverse effects, the transition between zones can be more gradual, as shown in example 730 of FIG. 7D. In this example, the zones 708 of different RLTs are sandwiched between transition zones 724 where the RLT changes somewhat gradually between the zones of different RLTs.

[0118] In addition to the benefits of smoother imprint transitions and relaxed alignment requirements, this also allows for the use of finer grids in optical designs, providing a continuous method for fabricating master templates. When the template bearing the desired master pattern and / or the master template has distinct zones, the alignment requirements between drop dispensing and template-to-substrate alignment can be more stringent. This is because the drop volume in areas with lower fluid volumes may not be present in areas with higher drop volume requirements. In some instances, the separation between zones can range from 100 nm to 1 micron. For drop diameters on the order of 100 microns, the process can be fine-tuned based on fluid diffusion and alignment. For example, when the transition between two such zones is smoother, e.g., when the width of the transition zone is approximately 10 to 1000 microns, the drop diffusion does not change abruptly, providing a smoother transition in RLT and maintaining the desired RLT range.

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

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

[0121] FIG. 8A depicts a schematic diagram 800 illustrating an example in which different zones 802 and 804 of surface features on a substrate 102 have different heights and / or different RLT characteristics, causing a portion of the resin fluid 808 to flow from one zone to another across a sharp (e.g., abrupt, discontinuous) transition boundary between the zones. FIG. 8B depicts a schematic diagram 810 illustrating an example in which a transition area 806 is created between zones of different feature heights. In the transition area 806, the feature height changes more gradually between the higher feature zone 802 and the lower feature zone 804, avoiding undesirable flow of the resin 808. Test results showed improved image uniformity in designs created as in the second example of FIG. 8B. In the example of FIG. 8A, test results indicate the presence of undesirable high-frequency artifacts in the finished optical device. Such dominant high-frequency image fringes can be undesirable, and because these fringes do not always appear in the same location, correcting for color in the final device and / or across multiple devices can be very difficult. A gradient pattern such as that of Figure 8B can reduce or eliminate such artifacts, providing an analog zone transition region with the same eyebox efficiency but improved contrast and sharpness.

[0122] The generation of continuous gradient patterns utilizes the aforementioned grid (e.g., unit cell mesh) and drop pattern optimization (e.g., unit cell fluid pattern optimization), as well as unit cell boundary smoothing. Techniques such as J-FIL are well-suited for such gradations, for example, because they can distribute a targeted drop volume over a large area where the resist volume can gradually increase (or decrease) from one side of the dispensed area to the other. In some embodiments, random or quasi-random drop patterns can be used to fill specific regions, such as the CPE of an eyepiece. By using random drop patterns to gradually modulate the dispensed resist volume to match the grating depth within the region, the zone boundaries defined by the drop pattern may not be noticeable due to the analog gradation defined in the imprint. In some embodiments, the drop pattern can be further optimized using the drop spread rate within each unit cell as a function grating orientation, feature height, dispensed resist type, and / or substrate type to better reduce or eliminate the presence of non-filled defects. The entire wafer can be meshed into small unit cells, and the feature geometry (including residue layer thickness, grating duty cycle, feature height profile, grating orientation, etc.), unit cell size, and drop volume determine the number of drops within each unit cell. The calculated drop count can be provided as input to a centroidal Voronoi tessellation (CVT) loop for location optimization. CVT is a specific type of Voronoi tessellation in which the generating point of each Voronoi cell is also its centroid (e.g., center of mass). It can be viewed as an optimal partition corresponding to an optimal distribution of generators. The drop distribution can reach a local minimum within the CVT loop with sufficient iterations and sufficiently high resolution. A unit cell can be defined as a repeating drop pattern that can be arranged on an underlying grid pattern, which can be dictated by various tool constraints, such as those described herein, including drop nozzle spacing, dispense frequency, dispense rate, etc.

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

[0124] Stepwise RLT imprinting can also be used to fabricate templates (e.g., submasters), with the corresponding gradient trend primarily defined by the dispensed drop pattern. Etching can also be used in this process. For example, gradient etching into SiO2 (thermal oxide on Si) can be performed secondary, with RLT acting as an etching cover, when using dry-etching RIE techniques to etch SiO2. Etch selectivity can be controlled with tuning gases such as CHF3, CF4, CF8, Ar, O2, and SF6 to etch either the organic imprint or SiO2. In this way, templates can be fabricated to contain multi-step zones with analog zone transitions and / or analog gradient patterns to provide a master mold ready for replication. By adjusting the resist volume dispensed into various zones, different depths can be dry-etched into the template material (e.g., SiO2, Si3N4, Si, etc.). Creating templates using lithography techniques such as J-FIL also enables the transfer of various shapes, such as sawtooth and multi-step, during the dry-etching process.

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

[0126] FIG. 9 illustrates an exemplary process for fabricating complex (e.g., 6-up) templates with analog (or at least partially analog) gradations and / or other specific nanofeatures. At 900, a carrier substrate 912 is provided with an overlay of blank oxide or nitride material 902. At 910, droplets of resist 904 are dispensed onto the overlay 902, such as according to a droplet pattern described herein. At 920, the resist is imprinted to result in a pattern 906 with a stepped RLT, as shown. At 930, a dry etch is performed to etch the pattern 906 into a final pattern 908. As shown in the example of FIG. 9, the etch can create a final pattern 908 that can have a substantially flat or flat upper height across various features that can have different feature depths relative to the stepped RLT.

[0127] Surface features can include multiple zones with different patterns, each with a different RLT and / or feature height / depth. Embodiments provide for the use of such zones, but with gradual changes in RLT and / or feature height between zones, as described herein, to mitigate various adverse effects that can result from abrupt changes between zones. An example RLT can be in the range of 10 to 35 nanometers (nm). Feature creation can also include etching the features after dispensing and imprinting using a template. Previously available methods using imprint-plus-etch can be costly due to the extra etching step. The described embodiments for drop pattern optimization can reduce costs by providing an initial imprint pattern that is more accurate and / or closer to the final pattern than would be created without the optimized drop pattern. Etching can then be used to refine the pattern into its final form. The use of an optimized drop pattern can also eliminate the need to perform one or more additional imprint steps using a submaster template.

[0128] The above algorithms for determining optimized drop patterns can also take into account boundary areas where the transition between zones is gradual in RLT change and / or feature height change. For example, as shown in Figure 8, the volumes dispensed into zones 802 and 804 may be different, and transition zone 806 may have a drop pattern in which drops toward 804 are spaced further apart than drops toward 802. Drop volume is generally controlled by drop size, drop number, drop density across the transition zone (e.g., along the XY pitch), etc.

[0129] As previously mentioned, continuous analog gradations or transitions between zones of different RLT and / or surface feature heights are useful for enabling efficient, uniform imaging in optical devices using planar waveguides with relief nanostructures. The techniques described herein can also be used with curved waveguides, providing similar benefits. Such gradations avoid sharp transitions between zones that can cause reduced image uniformity and reduced contrast and clarity (due to RLT variations). The use of such gradations can also avoid increased template fabrication complexity and manufacturing costs while achieving similar eyebox efficiency goals in the manufactured eyepiece. Embodiments provide for the fabrication of such templates for nanoimprint lithography using plasma-controlled deposition with etching methods. Resulting benefits include reduced complexity and cost of template gradations in fabrication, reduced non-uniformity in the resulting image viewed through the eyepiece, and improved image quality (e.g., contrast and sharpness) using J-FIL techniques to create the final pattern on the waveguide substrate.

[0130] Figure 10 illustrates an exemplary process for fabricating an imprint template with analog graduations using a deposition and etching approach. This process allows for smooth transitions between zones of different feature heights without the multiple masking, lithography, and etching steps that would otherwise be required to fabricate such a multi-zone master template. For analog gradation using previously available step-by-step optical lithography exposure processes, the number of steps would be prohibitively large and expensive.

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

[0132] At 1020, operations are performed for developing, wet or dry etching, and stripping portions of the photoresist. At 1030, operations are performed for creating an inverted 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 performed using a wet (e.g., buffered oxide etch or HF for SiO, etc.) or dry (e.g., RIE, ICP-RIE, IBE, etc.) etching process. At 1050, photolithography can be performed to create desired features in the oxide / nitride carrier substrate. Lithography is not limited to photolithography, and electron beam lithography or UV / thermal nanoimprint lithography can also be used. At 1060, a lithography step, such as UV nanoimprint lithography, can be performed to provide a pattern (e.g., an ICG pattern). At 1070, the pattern can be etched and at least a portion of the resist can be stripped to reveal a template suitable for imprinting onto a waveguide substrate to create a patterned waveguide.

[0133] This method can be used to create inverted dome or regular dome-shaped deposition profiles. Shadow masks can also be used to mask deposition material density or modify plasma density for plasma-enhanced deposition processes such as plasma-enhanced chemical vapor deposition (PE-CVD). Figure 11 illustrates an example of how to create a dome or inverted dome shape on a substrate by manipulating deposition with a shadow mask in the plasma head or deposition source. Exemplary materials used for deposition can include, but are not limited to, SiO2, Si3N4, or Al2O3. As shown in example 1100, a shadow mask 1102 with holes of various diameters can be used, and the deposition plasma 1104 can pass through the holes in the mask onto the sample 1106. In example 1110, a shadow mask 1102 is used with varying densities for plasma-enhanced deposition. The location and density of the holes determine how much the plasma and chemical reactants are exposed to different areas and therefore chemically react and deposit or, in the case of etching, remove.

[0134] The embodiments also provide a continuous gradation method that uses a subtractively graded, etched substrate to generate a continuous gradation template, which can improve field uniformity and optimize eyepiece efficiency. Conventional techniques involve creating a flat top and a graduated bottom nanopattern on the template. The embodiments improve on this technique by creating a flat bottom and a graduated top nanopattern on the template. This avoids RLT non-uniformities on the imprinted resist and improves field uniformity.

[0135] If a master template has patterned features with a flat top and a stepped bottom, a CRT made from the master template will have a correspondingly stepped surface. When this CRT is used to imprint on a (e.g., glass) substrate to produce an eyepiece, the step will cause the creation of RLT humps in the step transition areas, as previously mentioned. This can cause field uniformity artifacts.

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

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

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

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

[0140] Storage device 1330 provides mass storage for system 700. In some implementations, storage device 1330 is a computer-readable medium. In various different implementations, 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 any other suitable type of storage device.

[0141] The input / output devices 1350 provide input and output operations to the system 700. The input / output devices 1350 may include input devices including, but not limited to, a keyboard, a pointing device, a mouse, a touchpad, a camera, a microphone, orientation or motion sensors (e.g., accelerometers, gyro sensors, etc.), and / or a game controller. The input / output devices 1350 may also include output devices including, but not limited to, a display, audio speakers, haptic actuators, printers, etc.

[0142] The described features can be implemented in digital electronic circuitry, or computer hardware, firmware, software, or combinations thereof. An apparatus can be implemented in a computer program product tangibly embodied in an information carrier, e.g., a machine-readable storage device, for execution by a programmable processor, and the method steps for the methods described herein can be performed by the programmable processor executing a program of instructions that performs the functions of the described embodiments by manipulating input data and generating output. The described features can advantageously be embodied in one or more computer programs executable on a programmable system including at least one programmable processor coupled to receive data and instructions from a data storage system, at least one input device, and at least one output device, and to transmit data and instructions to the data storage system. A computer program is a set of instructions that can be used directly or indirectly in a computer to perform a particular activity or bring about a particular result. Computer programs 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. Modules are one or more computer programs and / or portions of computer programs that are executable by one or more processors.

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

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

[0145] Features may be implemented in a computer system that includes back-end components such as data servers, or includes middleware components such as application servers or Internet servers, or includes front-end components such as client computers having a graphical user interface or Internet browser, or any combination thereof. The components of the system may be connected by any form or medium of digital data communication, such as a communications network. Examples of communications networks include, for example, a local area network (LAN), a wide area network (WAN), and the computers and networks forming the Internet.

[0146] The computer system may include clients and servers. Clients and servers are generally remote from each other and typically interact through a network as described herein. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other. A server may be part of a cloud, which may include a transient aspect.

[0147] While the present disclosure includes many specific implementation details, these should not be construed as limitations on the scope of any implementation of the disclosure or what may be claimed, but rather as descriptions of features specific to exemplary implementations. Certain features described herein in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Furthermore, while features may be described above as acting in a particular combination and initially claimed as such, one or more features from a claimed combination can, in some cases, be deleted from the combination, and the claimed combination may be directed to a partial combination or a variation of the partial combination.

[0148] Similarly, although operations are depicted in the figures in a particular order, this should not be understood as requiring such operations to be performed in the particular order shown, or in a sequential order, or that all of the illustrated operations be performed, to achieve desirable results. In certain situations, multitasking and parallel processing may be advantageous. Furthermore, the separation of various system components in the foregoing embodiments should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems may generally be integrated together in a single software product or packaged in multiple software products. Furthermore, the processes depicted in the figures do not necessarily require the particular order shown, or in a sequential order, to achieve desirable results. In certain embodiments, multitasking and parallel processing may be advantageous.

[0149] While various embodiments of the present invention have been described herein, it should be understood that they are done so by way of example. Many variations and modifications will be apparent to those skilled in the art upon reading this specification. The breadth and scope of the present invention is not limited by the examples set forth herein, but can be broadly construed to include such variations and modifications. The described embodiments and other such embodiments are within the scope of the following claims.

Claims

[Claim 1] The invention described in this specification.

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