Optical waveguide manufacturing method

Abstract

A method for manufacturing an optical waveguide is disclosed, the method comprising the steps of: receiving a master template having a plurality of individual waveguide structures imprinted thereon; coating the master template with a curable master template stamp material; curing the master template stamp material to form a master template stamp; separating the master template stamp from the master template; imprinting the master template stamp onto one or more first substrates having an imprintable coating to form one or more master template replicas, wherein a plurality of individual waveguide structure replicas are imprinted on each master template replica; curing the one or more master template replicas; separating the master template stamp from the one or more master template replicas; coating one of the one or more master template replicas with a curable processing stamp material; curing the processing stamp material to form a processing stamp for manufacturing optical waveguides; and separating the master template replica from the processing stamp.

Description

Technology Field

[0001] The present invention generally relates to nanoimprint lithography methods, and more specifically to the manufacture of optical waveguides for augmented reality devices. Background Technology

[0002] Augmented reality systems can be worn on a user's head to enhance their perception of the real world by supplying additional light. Known head-mounted systems include glasses and helmet structures. Augmented reality systems also include head-up displays that can be implemented in vehicles, such as in the cockpits of cars, trucks, or aircraft.

[0003] Augmented reality light can be provided to users using waveguide structures. Diffraction gratings are positioned on or within the waveguides to couple light from a projector into the waveguides. Additional diffraction grating structures may be used to couple light from the waveguides toward the user. Other augmented reality technologies may be used to produce similar results. In these applications, optical elements such as waveguides or prisms are typically transparent, allowing the user to see light from the projector as well as light from their external environment.

[0004] Waveguides typically include diffraction grating structures fabricated using nanoimprint replication processes and direct etching. These grating structures may be multiple teeth or pins (also known as mesas) and may be formed from a low-exponential material, a high-exponential material, or a combination of low and high-exponential materials on a substrate such as glass or silicon.

[0005] The known manufacturing methods involve using lithography, etching, and imprinting techniques to create waveguide master patterns, and using the master patterns to perform imprint replication to form an etching mask to form a waveguide grating, a waveguide structure, or to create waveguide gratings through a subsequent etching process. The imprinting techniques used to create waveguides include nanoimprint lithography, which can effectively replicate detailed nanostructures for diffraction gratings.

[0006] The object of the present invention is to improve the capabilities of manufacturing methods while maintaining effective nanoreplication of detailed diffraction grating waveguide structures.

[0007] According to an aspect of the present invention, a method for manufacturing an optical waveguide is provided. The present method comprises the steps of: receiving a master template imprinted with a plurality of individual waveguide structures; coating the master template with a curable master template stamp material; curing the master template stamp material to form a master template stamp; separating the master template stamp from the master template; imprinting the master template stamp onto one or more first substrates having an imprintable coating to form one or more master template copies—each master template copy having a plurality of individual waveguide structure copies imprinted on it—curing the one or more master template copies; separating the master template stamp from the one or more master template copies; and among the one or more master template copies The method includes the steps of coating one with a curable working stamp material, curing the working stamp material to form a working stamp for manufacturing optical waveguides, and separating the master template replica from the working stamp.

[0008] In this way, processing stamps used to form production optical waveguides are created from replicas of a master template. In known production processes, processing stamps are formed directly from the master template. However, it has been found that imprinting techniques cause the quality of the master template and / or processing stamp to degrade with use. Therefore, it has been found that forming processing stamps from replicas of the master template provides an optimal balance to ensure the lifespan of the master template while minimizing the nanoreplication degradation effects that may occur with multiple imprints. This not only increases the yield from a single master template but also lowers manufacturing costs.

[0009] Each of the plurality of individual waveguide structures imprinted on the master template replica is substantially identical to each of the plurality of individual waveguide structure replicas on the master template. Nevertheless, the imprinted structure or nanostructure from the stamp may often contain defects or inconsistencies when compared to the original structure or nanostructure from which the stamp was created. Due to current monitoring techniques and production methods, shape deviation of the imprinted structure may not be easily detectable until the final product (optical waveguide) is manufactured. It has also been found that the processing stamp can be used up to 100 times (typically between 50 and 100 times) before the mold structure / shape in the stamp is deformed and low-quality optical waveguides are produced—in this case, the optical performance of the waveguide structures and / or individual waveguides on the production wafer differs significantly from the original waveguide structure in the master template. Therefore, to optimize the production efficiency of the master template, it was advantageously found that the processing stamps used to create production waveguides can be formed from a replication of the master template.

[0010] Preferably, the present method further comprises the steps of: imprinting the processing stamp onto a second substrate having an imprintable coating to form an optical waveguide wafer—where a plurality of optical waveguides are imprinted on the optical waveguide wafer—curing the optical waveguide wafer, separating the processing stamp from the optical waveguide wafer, and cutting the optical waveguide wafer to separate each optical waveguide from the plurality of optical waveguides. In this manner, optical waveguides are formed and cut from wafers for further stacking or assembly. For example, the optical waveguides can be assembled to construct an augmented reality display system.

[0011] Preferably, the present method further comprises the step of optically testing at least one of the one or more master template replicas. In this way, the master template replica can be optically tested and quality evaluated to monitor and predict optical performance during the production of optical waveguides. The master template replica can be optically tested using non-destructive testing techniques. The optical test can be performed as an inline production step in the optical waveguide manufacturing method to provide a quality control monitoring step.

[0012] Preferably, at least one of the one or more master template replicas is made of a substantially optically transparent material. In this way, the master template replica can be optically functional and tested to provide optical performance results for production optical waveguides. Optical testing can reveal defects, imperfections, or features of the waveguide structure that can be adjusted or modified to change the performance of the production optical waveguide. Preferably, the master template replica comprises a glass substrate coated with an optical polymer. In other words, the substantially optically transparent material may be a glass substrate coated with an optical polymer.

[0013] Preferably, at least one of the one or more master template replicas comprises a silicon substrate. Preferably, at least one of the one or more master template replicas comprises a polymer material for nano-replication. The polymer material for nano-replication may be a different polymer material used for optical testing. In other words, the nano-replication polymer material may be different from the optical polymer described above. In this way, master template replicas can be formed in a material having good nano-replication properties. Such replicas may not be optically functional. Typically, known materials that are more robust in maintaining nanostructures may be used.

[0014] Preferably, the present method further comprises the step of controlling the shape of at least one of the plurality of individual waveguide structure replicas. In this way, the critical nanostructure dimensions of the waveguide structure can be adjusted or controlled in various ways to increase or decrease the size of specific features in each waveguide structure. Preferably, controlling the shape or critical nanostructure dimensions includes a coating deposition technique and / or a plasma treatment technique. For example, plasma treatment may be used to reduce specific critical dimensions of the lattice nanostructures. Alternatively, deposition techniques may be used to compensate for polymer shrinkage. Other nanostructure dimension control techniques readily available to a skilled person may also be used to control the shape of the waveguide lattice nanostructures in the master template replicas. The present method may comprise the step of applying plasma treatment to control the critical nanostructure dimensions. To ensure high-quality separation of the stamps, an anti-stick layer may be provided on the master templates and master template replicas.

[0015] Preferably, the method further comprises the step of applying an anti-sticking layer (ASL). The anti-sticking layer (ASL) may be used at any of the described stages when a separation event occurs (e.g., when separating a stamp or mold structure from a cured material). The ASL facilitates smooth separation between two structures. A parent structure (e.g., a template structure or a stamp structure) may be coated with an anti-sticking layer before a curable material is applied thereon or before being imprinted with a curable material.

[0016] Preferably, the master template can also be formed by a step-and-repeat nanoimprint process. In this way, the surface of the wafer can be optimally utilized so that multiple waveguide structures are provided on a single wafer. The step-and-repeat process uses a single waveguide master stamp (i.e., a stamp for a single waveguide structure) and imprints the single waveguide master stamp multiple times across the surface of the wafer coated with an imprintable material to form a master template (i.e., a master step-and-repeat template containing multiple waveguide structures). Brief explanation of the drawing

[0017] Now, embodiments of the present invention will be described merely as examples with reference to the accompanying drawings. Figures 1a and 1b illustrate schematic representations of different profiles of optical waveguide lattice nanostructures. Figure 2 illustrates a schematic representation of a step-and-repeat master template. FIG. 3a illustrates a schematic representation of forming a template stamp from a master template. FIG. 3b illustrates a schematic representation of forming a master template replica using a master template stamp. FIG. 3c illustrates a schematic representation of forming a processing stamp from a master template replica. Figure 4a illustrates a schematic representation of manufacturing optical waveguides using a processing stamp. Figure 4b illustrates another schematic representation of manufacturing optical waveguides. FIG. 4c illustrates a schematic representation of optical waveguides cut from a production optical wafer. FIG. 5 is a flowchart illustrating a method for creating a processing stamp according to the present invention. Specific details for implementing the invention

[0018] The methods provided herein improve the efficiency of fabricating optical waveguides by nanoimprint lithography processes by reducing not only the structural degradation of lattice structures but also significantly reducing manufacturing costs and steps.

[0019] FIGS. 1a and FIGS. 1b illustrate different exemplary optical waveguide grating profiles. FIGS. 1a illustrates an optical waveguide (100) having a transparent substrate (102) and a grating structure (104) formed on the substrate (102). A resin remnant layer (not shown) may also be provided under the grating structure. The grating structure (104) may be a diffraction grating configured to input and / or output light into the optical waveguide (100), and the grating structure (104) may have structural features in the micrometer and nanometer range to manipulate incoupled or outcoupled light. As illustrated in FIGS. 1b, the optical waveguide (150) may have a grating structure (154) on a substrate (152) having a plurality of features as obvious to a person skilled in the art of diffraction gratings.

[0020] Optical waveguides (100, 150) can be formed using nanoimprinting and / or etching processes, wherein mask layers and pattern or stack layers are used to control the shape and structure of the lattices. The mask layer can be made from metal or metal oxide or metal nitride such as titanium nitride or tantalum nitride or carbon or other etch-resistant materials using thin-film deposition techniques such as chemical vapor deposition, physical vapor deposition or atomic layer deposition.

[0021] If lattice structures are generated using nanoimprinting, pattern / stack layers can be made of an imprintable resist material with a high refractive index.

[0022] A hard master can be made of materials that are more robust than those typically used for optical waveguides (100, 150) and may not be optically functional or transparent. Hard masters or master patterns are used in imprint replication processes, such as nanoimprint lithography for manufacturing optical waveguides, as described below.

[0023] FIG. 2 illustrates a schematic representation of a step-and-repeat (SnR) master template, wherein a step-and-repeat stamp (200) of a single optical waveguide grating structure (which is the inverse of a hard master template) is repeatedly imprinted step-by-step across a wafer (202). This is known as a step-and-repeat (SnR) nanoimprint lithography process. The wafer (202) is a spin-coated wafer having a substrate layer, a primer layer, and an imprint resist layer. The imprint resist is a curable monomer or polymer material that can be modified to create an inverse or negative replica of the step-and-repeat stamp (200) within the imprint resist layer. Heat or UV light is applied to the imprint resist layer to cure (harden) it. Other suitable coated wafers will be obvious to those skilled in the art.

[0024] In a step-and-repeat nanoimprint lithography process, a step-and-repeat stamp (200) is imprinted and cured by heat and / or UV light and separated multiple times on the wafer (202) to cover the wafer (202) with cured imprints (204) of the optical waveguide structure. This step-and-repeat process is repeated across the surface of the wafer (202) to provide an imprinted wafer (206) by optimally utilizing and arranging the maximum number of cured imprints (204) on the wafer (202). FIG. 2 also illustrates an exemplary top view of the imprinted wafer (206). The imprinted wafer (206) is an SnR master template on which a plurality of individual waveguide structures are imprinted. The number of imprinted structures on the wafer may vary depending on the grid structure and / or the size of the wafer, as recognized by a skilled person.

[0025] In this particular example, the imprinted wafer (206) is typically not optically functional, whereby the imprint resist material used is selected to have optimal nanoreplication properties intended to maintain the detailed structure of the optical waveguide structure. Alternatively, the imprinted wafer (206) may be optically functional or substantially transparent so that an optical test can determine the optical performance of the individual lattice structures (204) imprinted on the wafer (206).

[0026] FIG. 3a illustrates a process (300) having steps (302, 304) in a schematic form, wherein a master template (306) having a plurality of individual waveguide structures (308) is used to form a master template stamp (310). The master template (306) is a hard master template or an SnR master template as described with reference to FIG. 2, and a top view of the master template (306) is also shown in FIG. 3a.

[0027] In step (302), a curable template stamp material (312) is applied over the master template (308). This can be done by a spin coating method or other methods known in the art. As the stamp material (312) is applied over the template (306), it flows over and fills any voids or spaces between the waveguide structures (308) to form a mold or inverse copy of the shape of the waveguide structures. As seen in step (302), the height of the applied template stamp material (312) exceeds the maximum height of the waveguide structures (308), so that there is a layer of a predetermined thickness (314) or template stamp material (312) that is not shaped by the waveguide structures (308). The unformed thickness of the template stamp material (312) provides a base layer (316) on which a mold of waveguide structures (308) is formed.

[0028] In step (304), a first substrate (320) is applied to a curable template stamp material (312). In this example, the first substrate (32) is a flexible foil that comes into contact with the curable template stamp material (312). The first substrate may also be a rigid material such as glass or silicon, or even a semi-rigid material such as polydimethylsiloxane (PDMS). Heat and / or UV light (318) is applied to the curable template stamp material (312) and the first substrate (320) to cure and harden the material. After curing, the curable template stamp material (312) is hardened into a cured template stamp material.

[0029] The first substrate (320) and the cured template stamp material (312) together form a master template stamp (310), which is used to create one or more copies of the master template (306) as described with reference to FIG. 3b. The master template stamp (310) has a plurality of individual mold structures (322), which are inverse copies of a plurality of individual waveguide structures (308) of the master template (306).

[0030] FIG. 3b illustrates a process (330) having steps (332, 334, 336) in a schematic form, wherein a master template stamp (310) having a plurality of individual mold structures (322) or stamp structures is used to form a master template replica (338).

[0031] In step (332), the master template stamp (310) is lowered onto a second substrate (340) having an imprintable coating (342) (imprint resist layer), so that in step (334), mold structures (322) are imprinted onto the imprintable coating (342) to form waveguide structure replicas (344) of individual waveguide structures (308). This means that the master template stamp (310) is pressed into the imprintable coating (342) up to the base layer (316) of the cured stamp material (312) of the stamp (310). As seen in step (334), the height of the imprintable coating (342) is typically greater than the height of the mold structures (322), so that there is a predetermined thickness (346) of the imprintable coating (342) that is not deformed when the master template stamp (310) is pressed against the second substrate (340).

[0032] After the mold structures (322) are imprinted into the imprintable coating (342), heat and / or UV light (348) is applied to the second substrate (340) to cure and harden the imprintable coating (342). The unaltered thickness of the hardened imprintable coating provides a base layer (350) on which imprinted replicas (344) of the waveguide structures (308) are provided.

[0033] In step (336), the master template stamp (310) is separated from the imprinted second substrate to provide a master template replica (338). FIG. 3b also illustrates a top view of the master template replica (338). The master template replica (338) has a plurality of individual waveguide structures (344) having substantially the same shape as the plurality of individual waveguide structures (308) of the master template (306). According to the present disclosure, the master template replica (338) is used to create a production working stamp as described with reference to FIG. 3c.

[0034] If more than one number of master template replicas (338) are produced, at least one of the master template replicas is used to form a production processing stamp, and another of the master template replicas may be optically tested for quality control to ensure that the waveguide nanostructures are properly replicated. Each master template replica may be optically qualified before it is used to form a processing stamp. It should be understood that the master template replica used to form the production processing stamp may be made of low refractive index materials that are not optically functional and exhibit optimal nanoreplication properties (i.e., robust mechanical and physical properties to maintain the transference to nanostructure details), whereas the master template replica to be optically tested will be made of substantially optically transparent materials so that the optical test determines the optical performance of the individual lattice structures.

[0035] FIG. 3c illustrates a process (360) having steps (362, 364) in a schematic form, wherein a master template duplication (338) is used to form a processing stamp (366) used to create production optical waveguide structures for an augmented reality system. It should be recognized that the formation of the processing stamp (366) follows a process similar to the formation of the master template stamp (310).

[0036] In step (362), a curable processing stamp material (368) is applied over the master template replica (338) to form an inverse replica of the shape of the waveguide structures (344) of the master template replica (338). The curable processing stamp material (368) is selected to have optimal nanoreplication properties intended to maintain the detailed structure of the imprinted waveguide structures (344).

[0037] The curable processing stamp material (368) provides a layer (370) of the processing stamp material (368) that is applied such that its height exceeds the maximum height of the waveguide structures (344) and does not take the shape of the waveguide structures (344). The unshaped layer of the processing stamp material (368) thus provides a base layer (372) on which mold structures (376) of the waveguide structures (344) are formed.

[0038] In step (364), a third substrate is bonded to the curable processing stamp material (368). In this example, the third substrate (378) is a flexible foil applied to the curable stamp material (368) to lift or separate the cured stamp material (368) from the master template replica (338) after curing. Additionally, the third substrate may be a rigid material such as glass or silicon, or even a semi-rigid material such as polydimethylsiloxane (PDMS). Then, heat and / or UV light (374) is applied to the processing stamp material (368) to cure and solidify this material. After curing, the processing stamp material (368) is solidified into the cured template stamp material.

[0039] The third substrate (378) and the cured processing stamp material (368) together form a processing stamp (366) having a plurality of mold structures (376) used to create one or more production optical waveguides as described with reference to FIG. 4.

[0040] FIGS. 4a and 4b illustrate, in a schematic form, the use of a processing stamp (366) to form one or more production optical wafers (400). This process is similar to that described above in relation to FIG. 3b, where a master template stamp (310) is used to form one or more master template replicas (338), and where the mold structures (376) of the processing stamp (366) are pressed against a wafer or substrate (402) having an imprintable coating (404) to cure the imprintable coating (404) by heat and / or UV light and separate the processing stamp (366) to provide a production optical wafer (400) having a plurality of individual waveguide structures (404). FIG. 4c illustrates a schematic representation of individual optical waveguides (408) being cut (410) from the production optical wafer (400).

[0041] FIG. 5 illustrates a method (500) for manufacturing an optical waveguide processing stamp.

[0042] In step (505), a master template is received. The master template may be an SnR master template having a plurality of individual waveguide structures on its surface and a plurality of iterative copies of a single waveguide structure.

[0043] In step (510), the master template is coated with a curable template stamp material. After coating the master template, in step (515), the template stamp material is cured by heat and / or UV light to harden the curable template stamp material, and in step (520), the master template stamp is separated from the master template.

[0044] Then, in step (525), the master template stamp is imprinted on one or more substrates (e.g., imprint resist spin-coated wafers) having an imprintable coating to form one or more master template replicas (e.g., SnR master template replicas), and in step (530), the imprinted imprintable coating on the one or more substrates is cured to solidify. In step (535), the master template stamp is separated from the one or more master template replicas.

[0045] In step (540), one of the master template replicas is coated with a curable processing stamp material, is cured in step (545), and in step (550), the master template replica is separated from the cured processing stamp. Then, as will be obvious to those skilled in the art, the processing stamp is used to manufacture optical waveguides.

Claims

Claim 1 A kit comprising a first master template replica imprinted with a plurality of individual waveguide structure replicas and a second master template replica imprinted with a plurality of individual waveguide structure replicas, wherein the first master template replica is formed of a substantially optically transparent material and the second master template replica is formed of a polymer material for nanoreplication, and wherein the first master template replica and the second master template replica are each formed from a common master template stamp. Claim 2 In claim 1, the first master template replication comprises a kit including a glass substrate coated with a photopolymer. Claim 3 In claim 1, the second master template replication is a kit comprising a silicon substrate. Claim 4 A kit according to claim 1, further comprising an anti-adhesion layer disposed on at least one of the first master template replica or the second master template replica. Claim 5 A kit according to any one of claims 1 to 4, wherein the common master template stamp is formed from a master template formed by a step and repeat nanoimprint process. Claim 6 A kit comprising, in any one of claims 1 to 4, a processing stamp formed from a replication of the second master template. Claim 7 A kit according to any one of claims 1 to 4, wherein the plurality of individual waveguide structure replicas of the first master template replica are substantially identical in shape to the plurality of individual waveguide structure replicas of the second master template replica. Claim 8 A method comprising the steps of: receiving a master template having a plurality of individual waveguide structures imprinted thereon; coating the master template with a curable master template stamp material; curing the master template stamp material to form a master template stamp; separating the master template stamp from the master template; imprinting the master template stamp on a first substrate to form a first master template replica formed of a substantially optically transparent material; imprinting the master template stamp on a second substrate to form a second master template replica formed of a polymer material for nanoreplication; optically testing the first master template replica; and coating the second master template replica with a curable processing stamp material to form a processing stamp. Claim 9 A method according to claim 8, further comprising the steps of: curing the processing stamp material to form the processing stamp; imprinting the processing stamp on a third substrate to form a waveguide wafer imprinted with a plurality of waveguides; curing the waveguide wafer; separating the processing stamp from the waveguide wafer; and cutting the waveguide wafer to separate the plurality of waveguides from each other. Claim 10 In claim 8, the method comprises a glass substrate coated with a photopolymer, wherein the first master template replication comprises a glass substrate. Claim 11 In claim 8, the polymer material for nanoreplication of the second master template replication is different from the optical polymer of the first master template replication. Claim 12 A method according to claim 8, further comprising the step of controlling the shape of at least one of the plurality of individual waveguide structure replicas of the second master template replica by a coating deposition technique. Claim 13 In claim 12, the step of controlling the shape comprises a step of applying plasma treatment. Claim 14 A method comprising, in any one of claims 8 to 13, further a step of applying an anti-adhesion layer to at least one of the first substrate, the second substrate, or the master template stamp. Claim 15 A method according to any one of claims 8 to 13, wherein the master template is formed by a step and repeat nanoimprint process. Claim 16 A method according to any one of claims 8 to 13, wherein the step of optically testing the first master template replication comprises a non-destructive testing technique.

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