Polymer patterned disk stack manufacturing

Abstract

To provide a method of aligning a stencil to an eyepiece wafer.SOLUTION: A method includes determining locations of at least two stencil apertures 402. The method also includes providing an eyepiece wafer 302. The eyepiece wafer 302 includes at least two eyepiece waveguides, each eyepiece waveguide including an incoupling grating 606 and a corresponding diffraction pattern 622. The method further includes directing second light from one or more light sources to impinge on each of the corresponding diffraction patterns 622, imaging light diffracted from each incoupling grating 606, determining locations of at least two incoupling grating 606, determining offsets between corresponding stencil 402 aperture locations and incoupling grating 606 locations, and aligning the stencil 402 to the eyepiece wafer 302 on the basis of the determined offsets.SELECTED DRAWING: Figure 6C

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of priority to U.S. Provisional Patent Application No. 62 / 865,715, entitled “POLYMER PATTERNED DISK STACK MANUFACTURING,” filed June 24, 2019, and U.S. Provisional Patent Application No. 62 / 892,427, entitled “POLYMER PATTERNED DISK STACK MANUFACTURING,” filed August 27, 2019, the entire contents of which are incorporated herein by reference for all purposes. [Background technology]

[0002] BACKGROUND OF THEINVENTION Modern computing and display technologies have facilitated the development of systems for "virtual reality" or "augmented reality" experiences, in which digitally reproduced images, or portions thereof, are presented to the viewer in a way that they appear to be real, or can be perceived as real. Virtual reality, or "VR", scenarios typically involve the presentation of digital or virtual image information without transparency to other actual real-world visual inputs, while augmented reality, or "AR", scenarios typically involve the presentation of digital or virtual image information as an extension to the visualization of the real world around the viewer.

[0003] Despite the advances made in these display technologies, a need exists in the art for improved methods and systems related to augmented reality systems. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] US Patent Application Publication No. 2019 / 0111642 [Patent Document 2] US Patent Application Publication No. 2018 / 0329132 Summary of the Invention [Means for solving the problem]

[0005] (Summary of the invention) SUMMARY OF THE DISCLOSURE Embodiments of the present invention relate to assembly tools and methods for making and assembling multi-layer eyepieces.

[0006] Systems and methods for manufacturing multi-layer polymer eyepiece stacks are described. In particular, a stored tool for performing one or more fabrication and / or assembly steps is described. In some embodiments, the stored tool is configured to manufacture multi-layer polymer eyepieces. The stored tool can include equipment or stations used to perform fabrication and assembly steps related to casting, curing, coating, aligning, stacking, singulating, and / or edge finishing of the multi-layer polymer eyepiece stack. Performing multiple fabrication steps within the stored tool can improve the output quality of the multi-layer polymer eyepiece stack by limiting contamination of the eyepieces by dust or other particles in the fabrication area. An additional advantage of an integrated stored tool is that throughput can be increased by synchronizing fabrication and assembly steps. Cost savings can be achieved using the stored tool by eliminating the need for a cleanroom fabrication and assembly environment.

[0007] According to an embodiment of the present invention, a method of aligning a stencil to an eyepiece wafer is provided. The method includes providing a stencil, positioning the stencil relative to a first light source, and determining locations of at least two stencil holes. The method also includes providing an eyepiece wafer. The eyepiece wafer includes at least two eyepiece waveguides, each eyepiece waveguide including an input coupling grating and a corresponding diffraction pattern. The method further includes directing light from one or more second light sources to impinge on each of the corresponding diffraction patterns, imaging the light diffracted from each input coupling grating, determining locations of the at least two input coupling gratings, determining an offset between the corresponding stencil hole locations and the input coupling grating locations, and aligning the stencil to the eyepiece wafer based on the determined offset.

[0008] According to another embodiment of the invention, a system is provided. The system includes a first chuck operable to support a stencil including a plurality of holes, a wafer chuck operable to support and move a wafer including a plurality of in-coupling gratings, and a first light source operable to direct light to impinge on a first surface of the stencil. The system also includes one or more second light sources operable to direct light to impinge on the wafer, and one or more lens and camera assemblies. The one or more camera assemblies are operable to receive light from the first light source that has passed through the plurality of holes in the stencil and to receive light from the one or more second light sources that has been diffracted from the plurality of in-coupling gratings in the wafer. The system further includes an alignment system operable to move the wafer relative to the stencil to reduce misalignment between the locations of the holes and the locations of the in-coupling gratings.

[0009] According to certain embodiments of the present invention, an assembly system is provided. The assembly system includes a wafer casting station, a stencil placement station, and a deposition station. The assembly system also includes a stencil separation station, a first inspection station, a layer assembly station, and a second inspection station. In an embodiment, the stencil placement station includes a first chuck operable to support a stencil including a plurality of holes, a wafer chuck operable to support and move a wafer including a plurality of in-coupling gratings, a first light source operable to direct light to impinge on a first surface of the stencil, and one or more second light sources operable to direct light to impinge on the wafer. The stencil placement station also includes one or more lens and camera assemblies operable to receive light from the first light source that has passed through the plurality of holes in the stencil and receive light from the one or more second light sources that have been diffracted from the plurality of in-coupling gratings in the wafer. The stencil placement station further includes an alignment system operable to move the wafer relative to the stencil to reduce misalignment between the locations of the holes and the locations of the in-coupling gratings.

[0010] Numerous benefits are achieved by the methods of the present invention over prior art. For example, embodiments of the present invention provide methods and systems that allow for the creation of multi-layer eyepieces with high precision, particularly with respect to alignment between layers. Moreover, embodiments of the present invention take advantage of optical diffractive structures present within the eyepiece, allowing for a self-aligning assembly process. These and other embodiments of the present invention, along with many of the advantages and features of the present invention, are described in more detail in the text below and in conjunction with the accompanying drawings. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 shows an exemplary diagram of the equipment within a housed fabrication and assembly tool in accordance with an embodiment of the present invention.

[0012] [Diagram 2] FIG. 2 shows a cross-sectional view of a polymer wafer casting station according to an embodiment of the present invention.

[0013] [Diagram 3] FIG. 3 illustrates a top view of an exemplary polymer wafer with an eyepiece molded therein, according to an embodiment of the present invention.

[0014] [Figure 4] FIG. 4 illustrates a top view of an exemplary coating stencil according to an embodiment of the present invention.

[0015] [Diagram 5] FIG. 5 illustrates an exemplary process flow for stencil alignment in accordance with an embodiment of the present invention.

[0016] [Figure 6A] FIG. 6A shows a cross-sectional view of an alignment station in a first process step according to an embodiment of the present invention.

[0017] [Figure 6B] FIG. 6B shows an example image of a backlit stencil cutout in accordance with an embodiment of the present invention.

[0018] [Figure 6C] FIG. 6C shows a cross-sectional view of the alignment station in a second process step according to an embodiment of the present invention.

[0019] [Figure 6D] FIG. 6D shows an example image of an illuminated input coupling grating illustrated in accordance with an embodiment of the present invention.

[0020] [Figure 6E] FIG. 6E shows a cross-sectional view of the alignment station in a second process step according to another embodiment of the present invention.

[0021] [Figure 6F] FIG. 6F is an exploded perspective view of a clamping system according to an embodiment of the present invention.

[0022] [Figure 7] FIG. 7 illustrates a cross-sectional view of an exemplary stencil and wafer assembly in a coating deposition station in accordance with an embodiment of the present invention.

[0023] [Figure 8] FIG. 8 shows a top view of a coated polymer wafer according to an embodiment of the present invention.

[0024] [Figure 9] FIG. 9 shows a cross-sectional view of the coated polymer wafer of FIG.

[0025] [Figure 10] FIG. 10 illustrates a top view of an exemplary spacer according to an embodiment of the present invention.

[0026] [Figure 11] FIG. 11 illustrates a top view of an exemplary multi-layer polymer wafer stack according to an embodiment of the present invention.

[0027] [Figure 12] FIG. 12 shows a cross-sectional view of the multi-layer polymer wafer stack of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS SUMMARY OF THE DISCLOSURE Embodiments of the present invention relate to assembly tools and methods for making and assembling multi-layer eyepieces.

[0029] FIG. 1 shows an exemplary diagram of equipment within a housed fabrication and assembly tool in accordance with an embodiment of the present invention. Referring to FIG. 1, an exemplary housed multi-layer polymer eyepiece fabrication and assembly tool 110 is shown. The tool 110 includes an enclosure 112 that houses equipment for fabricating and assembling a polymer eyepiece stack. In some embodiments, the enclosure 112 is sealed to prevent particles and contaminants from entering the interior where the fabrication and assembly takes place. The enclosure 112 can house machines that perform various fabrication and assembly steps. For example, the enclosure 112 can include one or more of a wafer casting station 200, an annealing station 120, a stencil placement station 125, a metal deposition station 130, a stencil separation station 135, a layer assembly station 145, and an inspection station 140. Although each of these steps is depicted as a separate station, it is possible to combine multiple tasks or functions into a single station or to subdivide a task into one or more steps.

[0030] 2 shows a cross-sectional view of a polymer wafer casting station according to an embodiment of the invention. Wafer casting station 200 receives curable polymer resin material from a polymer material supply 101 (shown in FIG. 1) located either within enclosure 112 or external to enclosure 112. Casting station 200 produces a patterned polymer wafer. The curable polymer resin can be a multi-part (e.g., two-part or three-part or more) polymer mixture that is cured in the mold using at least one of UV light and / or thermal energy.

[0031] Wafer casting station 200 includes two mold structures 204a and 204b (also referred to as "optical flats") that are clamped (e.g., via clamps 202a and 202b) to actuated stages 212a and 212b, respectively. In some cases, clamps 202a and 202b can be magnetic (e.g., electromagnets) and / or pneumatic clamps that allow mold structures 204a and 204b to be reversibly mounted to and removed from actuated stages 212a and 212b. In some cases, clamps 202a and 202b can be controlled by switches and / or by control module 210 (e.g., by selectively applying electricity to electromagnets of clamps 202a and 202b and / or by selectively activating pneumatic mechanisms to engage or disengage the mold structures).

[0032] A curable polymer 214 (e.g., a photopolymer or a light-activated resin that hardens when exposed to light) is deposited on mold structure 204b in the opening 216 between mold structure 204a and mold structure 204b. In some embodiments, the polymer material to be cured can have a refractive index greater than about 1.5 (e.g., about 1.65 or higher). Mold structures 204a and 204b are moved closer together (e.g., by moving actuated stages 212a and / or 212b vertically along support frame 208 using motor assembly 218) such that curable material 214 is enclosed by surface 220a of mold structure 204a and surface 220b of mold structure 204b. To provide a predefined spacing between mold structures 204a and 204b, a spacer 224 can be utilized, with a top surface 226 of spacer 224 contacting surface 220a of mold structure 204a when in position to form a mold. Curable material 214 is then cured (e.g., by exposing curable material 214 to light from light sources 206a and / or 206b) to form a thin film having one or more features defined by mold structures 204a and 204b. After curable material 214 is cured, mold structures 204a and 204b are moved away from one another (e.g., by moving actuated stages 212a and / or 212b vertically along support frame 208) and the film is removed. In some embodiments, the thin film can be a polymer wafer 302 as shown in FIG. 3 with one or more eyepieces 304a, 304b, 304c, and 304d molded therein. The eyepieces 304a, 304b, 304c, and 304d can be referred to as eyepiece waveguides. More or less than four eyepieces can be molded into the wafer. As an example, six eyepieces oriented at 60° angular intervals can be utilized in a manner similar to the four eyepieces 304a, 304b, 304c, and 304d oriented at 90° angular intervals as illustrated in FIG. 3.Thus, embodiments of the present invention are not limited to this particular implementation, and other numbers of eyepieces can be fabricated on the polymer wafer 302. Alternatively, in some embodiments, a single polymer eyepiece layer can be produced in a cast-to-shape manner, and the subsequent singulation step can be omitted. Additional information regarding casting equipment and methods is available in U.S. Patent Application Publication No. 2019 / 0111642, filed October 17, 2018, which is incorporated by reference in its entirety.

[0033] In some embodiments, two or three or more casting stations 200 can be included within the enclosure 112 of the tool 110. Such a configuration can allow for increased wafer production and can also allow each casting station to make polymer wafers from different polymer chemistries. For example, a first casting station can make wafers from a first polymer formulation, a second casting station can make wafers from a second polymer formulation that is different from the first polymer formulation, etc.

[0034] After the molded polymer wafer is removed from the casting station, the polymer wafer optionally moves to an annealing station 120 where the wafer is heated to reduce material stress in the wafer, increase the thermal stability of the polymer material, and / or fine-tune the contour or flatness of the wafer. In some embodiments, the polymer wafer is placed on a substrate (e.g., a thermally conductive plate such as aluminum) that has a surface roughness of 100 nm or higher to prevent the polymer material from sticking to the substrate. It is desirable for the polymer wafer to be able to freely expand and / or contract during the annealing process so that the polymer wafer can conform to the shape of the substrate. In some embodiments, the substrate is flat and has low local thickness variation (LTV) and low total thickness variation (TTV). Alternatively, at least a portion of the substrate can include a concave or convex curved surface, and the curvature is imparted to the polymer wafer during annealing.

[0035] During annealing, gravity may be sufficient to cause the polymer wafer to conform to the shape of the annealing substrate; however, to increase conformity, a second substrate may be used as a weight on top of the polymer wafer, and the wafer is sandwiched between the two substrates. The second substrate may also be a thermally conductive plate, or the second substrate may be an optical flat of fused quartz coated with a conductive metal layer or a mixed layer of metal / metal oxide.

[0036] The specific annealing method may depend on the specific polymer material. In some embodiments, the annealing step may include exposing the polymer wafer to a temperature above the glass transition temperature of the wafer (e.g., about 100° C. for some materials). The reduction in temperature to room temperature may occur slowly (e.g., at a rate of less than about 2° C. per minute) near the glass transition temperature to reduce the risk of warping or distortion of the polymer wafer.

[0037] The annealing step can be performed in a dedicated annealing station 120, but it is also possible for the annealing to be performed while the cast polymer wafer is moved (e.g., on a moving conveyor belt or other transport mechanism) between the casting station 200 and the stencil placement station 125.

[0038] Figure 3 shows a top view of an exemplary polymer wafer with an eyepiece molded therein according to an embodiment of the present invention, and Figure 4 shows a top view of an exemplary coating stencil according to an embodiment of the present invention.

[0039] 3 and 4, the stencil placement station 125 receives the polymer wafer 302 directly or indirectly from the casting station 200, and also receives the stencil 402 from a stencil supply 103 located either inside or outside the enclosure. An alignment step is performed at the stencil placement station 125 to determine the orientation of the stencil 402 to the wafer 302 by rotation or translation. In some embodiments, the alignment is done using computer vision algorithms that reference reference markers and features on the wafer and on the stencil. The precise alignment between the stencil and the wafer causes certain portions of the wafer 302 to remain exposed after the stencil is placed on the wafer. For example, a particular pattern or part of a pattern (e.g., a diffraction grating) molded into each eyepiece 304a, 304b, 304c, 304d is aligned with and exposed by the holes 404 in the stencil. The remainder of the wafer 302 is covered by the stencil.

[0040] In some embodiments, each hole 404 on the stencil is aligned with a set of input coupling gratings (ICGs) molded into each eyepiece 304 on the polymer wafer 302. In some embodiments, the holes 404 are smaller than the ICG area, and only a portion of the ICG area is exposed. Once aligned, the stencil 402 is removably coupled to the wafer 302 using any suitable means to prevent movement between the stencil and the wafer. As discussed more fully in connection with FIG. 6F, in some embodiments, the stencil is clamped to the wafer using a magnetic clamp. Although four holes 404 are illustrated in FIG. 4 in association with the four eyepieces 304a, 304b, 304c, and 304d illustrated in FIG. 3, embodiments of the present invention are not limited to this particular implementation and other numbers of hole / eyepiece pairs can be utilized, for example, six hole / eyepiece pairs can be utilized. While some embodiments discuss aligning the wafer to the stencil, in other embodiments, the wafer may be aligned first and then the stencil may be aligned to the wafer. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.

[0041] FIG. 5 illustrates an exemplary process flow for stencil alignment according to an embodiment of the present invention. FIG. 6A illustrates a cross-sectional view of an alignment station in a first process step according to an embodiment of the present invention. FIG. 6B illustrates an exemplary image of a backlit stencil cutout according to an embodiment of the present invention. FIG. 6C illustrates a cross-sectional view of an alignment station in a second process step according to an embodiment of the present invention. FIG. 6D illustrates an exemplary image of an illuminated in-coupling grating illustrated according to an embodiment of the present invention.

[0042] Referring to FIG. 5, an example of an alignment process flow 500 is shown in relation to an exemplary stencil placement station 125, which is shown in two process steps in FIG. 6A and FIG. 6C. In the process 500, a stencil 402 is received by the stencil placement station 125 (502 in FIG. 5). The stencil can be made of a ferromagnetic metal or otherwise include portions of a ferromagnetic metal and is configured to attract magnetic materials. The stencil 402 is opaque, and light does not pass through the stencil material. The stencil 402 includes at least one hole 404, also referred to as a cutout. In some embodiments, the stencil 402 includes at least one hole 404 for each input coupling grating formed on each of the eyepieces 304a / 304b / 304c / 304d on the wafer 302.

[0043] The stencil 402 is positioned over the first light source 610 (504 in FIG. 5) and the apparatus illustrated in FIG. 6A is utilized to determine the location of the holes 404 in the stencil 402. In some embodiments, a screen 612 is positioned between the first light source 610 and the stencil 402 to diffuse the light from the first light source 610. Thus, the first light source 610 in combination with the screen 612 provides a diffuse image of the holes 404. The first light source 610 can be implemented as an LED, an LED array, or other suitable light source, and the first light source 610 can be turned on (510 in FIG. 5) and can shine light toward the stencil 402 through the holes 604a and 604b, which may also be referred to as cutouts, and into at least one lens and camera assembly 614 / 615. With reference to FIG. 4 and FIG. 6A, the holes 604a and 604b shown in FIG. 6A correspond to two of the holes 404 illustrated in FIG. 4. Because FIG. 6A is a cross-sectional view, the other two holes 404 illustrated in FIG. 4 are positioned such that one hole is in front of the plane of the figure and the other hole is located behind the plane of the figure. As described more fully in connection with FIG. 6C, in some implementations, the wafer 302 including the input coupling gratings 606a and 606b is positioned above the stencil 402 during imaging of the holes 604a and 604, but the inventors have determined that the presence of the input coupling gratings 606a and 606b positioned between the holes 604a and 604b and the lens and camera assembly 614 / 615 does not inhibit imaging of the holes. In some implementations, the wafer 302 can be positioned as illustrated in FIG. 6C after imaging of the holes 404. Those skilled in the art will recognize many variations, modifications, and alternatives.

[0044] With reference to FIG. 4, holes 404 illustrated in FIG. 4 are shown as holes 604 and 604b in FIG. 6A. To obtain the locations of at least two stencil holes, the light from the first light source passing through the stencil holes can be imaged using one or more cameras (512 in FIG. 5). While some configurations can include a single camera and capture the light shining through multiple cutouts, other configurations can include two or more cameras, each of which can be configured to separately capture the light from each cutout as shown in FIG. 6A with lens and camera assemblies 614 and 615. An exemplary image of the backlight captured by the lens and camera assemblies through the stencil cutouts is shown in FIG. 6B. Once the image of the cutouts is captured by the camera, the first light source can be turned off (514 in FIG. 5).

[0045] The images from the lens and camera assemblies 614 and 615 are provided as inputs to an alignment system 616, which may include an alignment algorithm where the center of each imaged illuminated portion corresponding to the center of each imaged stencil cutout is identified in coordinate points. For example, the alignment algorithm may calculate the center of each cutout in x, y and theta coordinates. In other embodiments, the shape of the imaged holes may be characterized by width and height, and the width and height may then be used to calculate the center. In some embodiments, in addition to the two holes 604a and 604b illustrated in FIG. 6A, additional cutouts (not shown) are utilized to improve alignment accuracy. For example, four cutouts, six cutouts, etc. may be utilized in the alignment process. As described more fully herein, the locations of the holes will be used in aligning the stencil 402 to the wafer 302, for example, by minimizing the misalignment between the corresponding holes and the input coupling grid. As an example, the location of each hole (e.g., location in xy coordinates or pixel coordinates) can be compared to the location of a corresponding input coupling grid, and the average distance between the location of each hole and the location of the corresponding input coupling grid can be minimized.

[0046] Referring to FIG. 6C, a wafer is received (506 in FIG. 5) and positioned over the stencil, and the diffraction grating intended to be coated or metallized is present in the wafer and adapted to face the stencil (508 in FIG. 5). A small gap (e.g., on the order of a few hundred microns to a few millimeters) is provided between the wafer 302 and the stencil 402, so that the position of the wafer can be adjusted without damaging the surface of the wafer or the grating placed thereon. The wafer is generally aligned with the stencil along its longitudinal axis 618. To ensure that the input coupling gratings 606a / 606b are aligned with the openings in the stencil, one or more second light sources 620 / 621, such as red, green or blue LED light, illuminate the wafer in the area of ​​the diffraction pattern 622a / 622b (516 in FIG. 5). The diffraction pattern 622a can be, for example, a diffraction grating configured to diffract the incident light from the second light source 620 directly or indirectly (e.g., via total internal reflection inside the wafer) to the input coupling grating 606a. The diffraction pattern 622b can be, for example, a diffraction grating configured to diffract the incident light from the second light source 621 directly or indirectly (e.g., via total internal reflection inside the wafer) to the input coupling grating 606b. Thus, the input coupling grating 606a and the diffraction pattern 622a can be considered to correspond to each other, and the input coupling grating 606b and the diffraction pattern 622b can be considered to correspond to each other.

[0047] In use, each of the diffraction patterns 622a and 622b can be a compound pupil expander (CPE) that forms an output coupling grating that can be used to direct image light generated by the projector and diffracted into the plane of an eyepiece waveguide located in the wafer to a user's eye via the corresponding input coupling grating 606a / 606b. As will be apparent to one skilled in the art, the illumination of the diffraction pattern 622a / 622b with the second light source 620 / 621, the propagation through TIR to the input coupling grating 606a / 606b, and the diffraction of the light from the second light source to the lens and camera assembly 614 / 615 utilizes the propagation of light along an optical path that is opposite to the optical path utilized during use of the eyepiece waveguide (during use of the eyepiece waveguide, input coupling to the eyepiece waveguide occurs at the diffraction grating 622a / 622b used for output coupling to the user, and output coupling occurs from the input coupling grating 606a / 606b used for input coupling from the projector). One skilled in the art will recognize many variations, modifications, and alternatives.

[0048] When light from the diffraction pattern 622a / 622b reaches the input coupling grating 606a / 606b, at least some of the light exits the input coupling grating 606a / 606b toward the lens and camera assembly 614 / 615, where an image of the input coupling grating 606a / 606b is captured (518 in FIG. 5). An example image of the illuminated input coupling grating is shown in FIG. 6D. It should be noted that the lens and camera assembly 614 / 615 has a sufficient depth of field to image both the stencil 402 and the wafer 302 despite the gap between their elements during the alignment process. Although separate lens and camera assemblies 614 and 615 are illustrated in FIG. 6A, embodiments of the present invention are not limited to the use of multiple cameras, and a single lens and camera assembly having a field of view that includes the element to be imaged can be utilized as an alternative to the illustrated separate lens and camera assemblies 614 and 615.

[0049] Once the illuminated ICG image is captured, the second light source 620 / 621 may be turned off. The captured image of at least one of the illuminated input coupling gratings 606a / 606b is provided to an alignment algorithm 616, and the center of each input coupling grating 606a / 606b is identified at a coordinate point. For example, the alignment algorithm may calculate the center of each input coupling grating in x, y and theta coordinates. The coordinates of the input coupling grating may be compared to the coordinates of the cutout to determine the relative position between the stencil and the wafer (520 in FIG. 5). Any misalignment between the center of the input coupling grating and the center of the corresponding stencil cutout may be calculated and used as a reference to adjust the location of the wafer in the x, y and / or theta directions via an actuated wafer chuck 624, which holds the wafer at its periphery (e.g., using a vacuum gland in contact with the periphery of the wafer) and adjusts the position of the wafer 302 (522 in FIG. 5). One or more of the above alignment steps can be repeated as needed to achieve a relative position between the stencil and the wafer that is within a predefined tolerance.

[0050] In some embodiments, a portion of the number of holes 604a / 604b and the number of input coupling gratings 606a / 606b may be used in the alignment process. For example, a captured image of two illuminated holes 604a / 604b and a captured image of two illuminated input coupling gratings 606a / 606b may be used in the x, y, θ alignment of the wafer to the stencil. In other embodiments, all (e.g., four or six) of the holes 604a / 604b and input coupling gratings 606a / 606b may be used in the alignment process. The use of a larger number of holes and input coupling gratings may be advantageous when the input coupling gratings are misaligned from their intended positions, resulting in registration errors between the misaligned input coupling grating(s) and the corresponding hole(s) in the stencil. Using a larger number of holes and input coupling gratings would allow a global adjustment to address such registration errors, since a best fit between a group of holes and input coupling gratings can be used in the alignment process.

[0051] In a specific embodiment of the invention, the alignment algorithm utilizes the center positions of some or all of the holes and some or all of the input coupling gratings. When utilizing accurate relative position measurements for the holes / input coupling gratings, the positions of the holes / input coupling gratings measured using the lens and camera assembly are utilized in a best-fit algorithm that minimizes the position difference between each hole and the corresponding input coupling grating. As an example, the center of a best-fit circle passing through all of the measured holes can be matched to the center of a best-fit circle passing through all of the measured input coupling gratings. Thus, the minimum average position difference can be utilized in adjusting the wafer position in x, y, and θ coordinates.

[0052] When the alignment is within an acceptable tolerance, the wafer is moved into contact with the stencil and a plate made of a magnetic material or that otherwise contains one or more magnets is placed on top of the wafer, creating a magnetic clamp (524 in FIG. 5). In some implementations, the stencil can be positioned against a reference surface (e.g., a vacuum chuck) using a vacuum. As discussed in connection with FIG. 6F, magnets on the top plate attract the ferromagnetic stencil, holding the wafer in place and preserving the alignment. The assembly can then be moved or repositioned to other areas of the tool without disturbing the precise alignment between the stencil and the wafer.

[0053] In some embodiments, alignment of the stencil and wafer is verified after a magnetic clamp is utilized to clamp the wafer to the stencil, thus providing confirmation that no movement of the wafer relative to the stencil occurred during the clamping process.

[0054] FIG 6E shows a cross-sectional view of an alignment station in a second process step according to another embodiment of the present invention. Rather than injecting light directly into the wafer via the diffraction gratings 622a / 622b as shown in FIG 6E, in the embodiment shown in FIG 6E, light from the second light source 640 / 641 is coupled into the wafer after reflection from the mirrors 636 / 637 and propagates to each input coupling grating 606 via total internal reflection so that the light propagates in the eyepiece waveguide. By injecting light into the wafer 302 as shown in FIG 6E, the second light source 640 / 641 can be positioned on either side of the wafer 302 at a location outside the periphery of the wafer 302, allowing other system elements, including the lens and camera assembly 614 / 615, to be positioned closer to the wafer 302 along the z-axis, etc.

[0055] In a specific embodiment, the mirrors 636 / 637 can be implemented as prisms, although other reflective structures can be utilized. Additionally, in some embodiments, light from the second light source 640 / 641 can be injected into the wafer 302 at grazing incidence, obviating the use of the mirrors 636 / 637. Thus, embodiments of the invention can utilize diffraction gratings 622a / 622b to couple light into the wafer, as illustrated in FIG. 6C, or embodiments of the invention can utilize other methods of injecting light into the wafer, as illustrated in FIG. 6E, to provide light that can be output-coupled from the input-coupling grating 606. Those skilled in the art will recognize many variations, modifications, and alternatives.

[0056] FIG. 6F is an exploded perspective view of a clamping system according to an embodiment of the present invention. As shown in FIG. 6F, a magnetic clamp 650 is utilized with a wafer 652 and a stencil 654 to magnetically clamp the wafer to the stencil using magnetic forces. The magnetic clamp 650 includes a plurality of magnets 651 that are positioned or arrayed at various locations on the top surface of the magnetic clamp. Although twelve magnets 651 are utilized in the illustrated example, the present invention is not limited to this specific number and other numbers can be utilized according to other embodiments. The stencil 654 is made from a magnetic material such as stainless steel, although other suitable materials can be utilized.

[0057] While the magnetic clamp 650 is positioned adjacent to the stencil 654, the wafer 652 is clamped between the magnetic clamp and the stencil, allowing the alignment obtained as discussed in connection with FIG. 5 to be maintained during subsequent processing operations.

[0058] 7 shows a cross-sectional view of an exemplary stencil and wafer assembly in a coating deposition station according to an embodiment of the present invention. As shown in FIG. 7, an assembly 702 is shown that includes a stencil 402 removably coupled to a wafer 302. The assembly 702 can be moved to a deposition station 130 where a coating material 704, such as a metal or high refractive index inorganic material, is deposited over the stencil 402 and through holes 404 onto exposed portions of the polymer wafer 302. The coating deposition process can be carried out in a vacuum deposition chamber in the deposition station 130 (shown in FIG. 1).

[0059] The coating material to be deposited is received from a coating material supply 104 (shown in FIG. 1) by a deposition station 130 and deposited over the stencil to form a layer 706 on one or more regions of the polymer wafer 302 (e.g., forming a layer 706 on at least a portion of the ICG region of each eyepiece). The size and shape of the layer 706 is limited by the size and shape of the holes 404 in the stencil 402. Although circular holes 404 are shown, holes with shapes such as squares, ellipses, rectangles, polygons, etc., or other shapes can also be used. The coating material can be a material such as aluminum, silver, titanium dioxide, zirconium dioxide, or other suitable reflective material.

[0060] After the coating deposition step is completed, the stencil 402 is removed from the wafer 302 by lifting the stencil upward in a direction substantially perpendicular to the surface of the wafer coated with layer 706. Such a stencil removal technique can minimize damage to layer 706. The used stencil can be discarded in a used stencil bin 105 (shown in FIG. 1), which can be inside or outside the enclosure 112 of the tool 110. Separation of the stencil can occur in a stencil separation station 135 (shown in FIG. 1).

[0061] Alternative coating materials and methods of depositing flowable coating materials can be used in place of or in addition to the deposition techniques discussed above. Such techniques are described in U.S. Patent No. 10,436,968, filed April 16, 2018, and U.S. Patent Application Publication No. 2018 / 0329132, filed July 23, 2018, each of which is incorporated herein by reference in its entirety.

[0062] Although not shown in Figure 7, an embodiment of the present invention may utilize a magnetic clamp 650, illustrated in Figure 6F. In this embodiment, the magnetic clamp would be positioned under the wafer 302 and would exert a normal force on the wafer 302 to urge the wafer towards the stencil 402, thereby maintaining alignment between the wafer and the stencil.

[0063] FIG. 8 illustrates a plan view of a coated polymer wafer according to an embodiment of the present invention. FIG. 9 illustrates a cross-sectional view of the coated polymer wafer of FIG. 8. As illustrated in FIGS. 8 and 9, an exemplary coated wafer 802 is illustrated following removal of the stencil. Each of the eyepieces 804a, 804b, 804c, and 804d molded into the coated wafer 802 has a coating layer 706 disposed thereon. Although one layer 706 is shown per eyepiece 804, it is possible that multiple layers 706 are deposited on each eyepiece 804, depending on the design of the stencil. In addition, although multiple eyepieces 804 are shown arranged in a pinwheel arrangement, other arrangements are possible, depending on the size and shape of the eyepieces and wafer. The stencil can be correspondingly designed so that the desired areas of the wafer are exposed when the stencil is superimposed on the wafer.

[0064] Referring again to FIG. 1, the tool 110 may include an inspection station 140 that evaluates the coated wafer 802 after removal of the stencil according to various metrics and qualifies the coated wafer 802 to continue with the assembly of the stack. In some embodiments, the inspection unit may perform checks to ensure that the wafer shape, the lattice shape, the lattice position, the deposited layer shape, the deposited layer position, and the deposition layer adhesion are within selected tolerances. In some embodiments, a computer vision system or other suitable metrology tool may be used to obtain those measurements. If the inspection station 140 determines that the coated wafer 802 does not pass the quality standards, the wafer may be pulled off the assembly line and placed in a wafer reject bin 106 (illustrated in FIG. 1), which may be either inside or outside the enclosure 112 of the tool 110. Wafers that pass inspection may proceed further in the tool's workflow.

[0065] The coated wafers are transferred to layer assembly station 145. To begin assembly of the multi-layer polymer stack, a first coated wafer is received at layer assembly station 145. As discussed in more detail below, layer assembly station 145 also receives a first spacer, such as spacer 1002, from spacer preparation station 150, spacer 1002 being shown in plan view in FIG.

[0066] FIG. 10 shows a top view of an exemplary spacer according to an embodiment of the invention. The spacer 1002 can be shaped similarly to a cast polymer wafer; however, the spacer includes cutouts 1004a / 1004b / 1004c / 1004d configured to align with an eyepiece molded into the polymer wafer. The cutouts 1004 are generally slightly smaller than the outer boundary of the eyepiece 804, and the spacer overlaps with the periphery of the eyepiece molded into the wafer at an overlap region 1008. In some embodiments, the overlap region can be less than 1 mm wide, or the overlap region can be between about 1 mm and about 5 mm wide. Other overlap region widths are possible, depending on the amount of edge reinforcement desired in the multi-layer stack.

[0067] The spacers 1002 are aligned over the coated wafer using a computer vision system that recognizes various features or markers on one or more of the spacers and the coated wafer. In embodiments in which at least some of the spacers are transparent substrates, alignment methods can be used such as those discussed in International Patent Application No. PCT / US2019 / 036380, filed June 10, 2019, which is incorporated herein by reference in its entirety.

[0068] The spacer 1002 includes an adhesive material on a first surface (e.g., bottom surface), which faces the coated wafer. Once application and alignment of the spacer over the wafer is complete, the adhesive on the first surface of the spacer is pressed into contact with the wafer, securing the spacer to the wafer. A second wafer can be attached to the second surface (e.g., top surface) of the first spacer using the same method, by pressing the adhesive layer on the spacer into contact with the second wafer and allowing the adhesive to set. Additional layers can be added to the stack in the same manner.

[0069] In some embodiments, the adhesive is a high refractive index adhesive and can be formed as a double-sided adhesive tape. The adhesive can be a UV curable material and can utilize a step of exposing the adhesive to UV light while the spacer and wafer are in contact. The adhesive material can be transparent or can include carbon or color additives to make the adhesive layer optically opaque or translucent. The carbon or color additives can give the adhesive a dark color, such as dark gray or black. The adhesive layer can be on the top and / or bottom of the spacer, whereby the wafer can be adhered to the top and / or bottom surface of the spacer during the stacking assembly process at the layer assembly station 145.

[0070] When the spacers are stored in the spacer supply bin 108 (illustrated in FIG. 1) prior to assembly with the wafer, a protective film can be removably adhered to the adhesive layer on the top and / or bottom surface of the spacer to prevent contaminants from sticking to the spacer's adhesive. The spacer preparation station 150 is configured to remove the first protective film from the first surface (e.g., bottom surface) of the spacer, where the first layer of adhesive is exposed, prior to delivering the spacer to the layer assembly station 145 (both the spacer preparation station 150 and the layer assembly station 145 are illustrated in FIG. 1). In some embodiments, the second protective film remains in place on the second surface (e.g., top surface) of the spacer during transfer and assembly to the first wafer. Once the spacer is aligned and secured to the first wafer at the previously exposed adhesive surface, the layer assembly station can remove the second protective film from the second surface (e.g., top surface) in preparation for attaching the second wafer on top of the spacer. Minimizing the amount of time between removing the protective film and adhering the exposed adhesive to the wafer can be advantageous to reduce the risk of contamination or other damage to the adhesive layer.

[0071] When using an adhesive that requires a UV or heat curing step, the UV or heat exposure can be performed after each step where the wafer and spacer are pressed into contact, or the complete stack of wafer and spacer layers can be assembled prior to delivering the UV and / or heat curing dose.

[0072] With reference to FIG. 1 , a separate spacer preparation station 150 is depicted, however, it is also possible for the layer assembly station 145 to remove the protective film from the spacer layers and discard it, thereby integrating the functionality of the spacer preparation station 150 into the layer assembly station 145.

[0073] A multi-layer polymer eyepiece is assembled by stacking alternating layers of wafers and layers of spacers. In some embodiments, the stack includes at least three wafers and at least two spacers.

[0074] FIG. 11 shows a plan view of an exemplary multi-layer polymer wafer stack according to an embodiment of the present invention. FIG. 12 shows a cross-sectional view of the multi-layer polymer wafer stack of FIG. 11. Thus, FIG. 12 illustrates a multi-layer polymer wafer stack 1102 including a plurality of wafers 802 and spacers 1002. In some embodiments, the multi-layer polymer wafer stack 1102, which may also be referred to as a stack, includes at least six wafers and at least five spacers. Stacks with any number of layers can be assembled. Once the stack is completed, the layer assembly station 145 can optionally cover the top surface 1104 and bottom surface 1206 with a protective film to reduce the risk of damage to the completed stack.

[0075] To provide alignment between the wafer 802 and the spacer 1002, fiducials can be placed on the wafer 802 and the spacer 1002 to facilitate alignment between layers in the multi-layer polymer wafer stack 1102. By way of example, and referring to FIG. 10, fiducials 1010 fabricated on the spacer 1002 can be used in conjunction with corresponding fiducials 810 (shown in FIG. 8) fabricated on the wafer 802. In the illustrated example, the fiducials 810 have a smaller diameter than the fiducials 1010, allowing for alignment of the wafer 802 to the spacer 1002. Although circular fiducials are illustrated, it will be understood that other shapes, dimensions, locations, and numbers of fiducials can be utilized in accordance with embodiments of the present invention.

[0076] As the thickness of the multi-layer polymer wafer stack 1102 increases, an alignment camera with a large depth of field may be utilized to image the fiducials at various depths within the stack. Alternatively, the position of the alignment camera may be modified to provide imaging of the fiducials on the wafers and spacers as the stack is assembled. Those skilled in the art will recognize many variations, modifications, and alternatives. In an alternative embodiment, a cover plate is utilized and attached to the wafers 802a and 802c using appropriate spacers (not shown) to maintain the integrity of the top surface 1104 of the wafer 802a and the bottom surface 1206 of the wafer 802c. As will be apparent to those skilled in the art, the use of a cover plate will allow an air gap to be provided adjacent the input coupling gratings 606a / 606b and the diffraction patterns 622a / 622b, thereby promoting total internal reflection and preventing dust and debris from accumulating on the optical surfaces.

[0077] In the embodiment illustrated in FIG. 12, each instance of layer 706 aligned with the input coupling grating in each of the eyepiece waveguides is aligned along a single axis aligned with the z-axis. In other embodiments, for example to implement subpupil designs, the input coupling gratings and corresponding layers 706 can be spatially offset, i.e., literally offset laterally in the xy plane. In those embodiments, spatially offset fiducials can be utilized on a wafer-by-wafer and spacer-by-spacer basis in a predefined manner to achieve the desired positioning between adjacent input coupling gratings as appropriate for the particular subpupil design. Those skilled in the art will recognize many variations, modifications, and alternatives.

[0078] After assembly of the stack is complete, the stack can optionally be moved to a stack inspection station 155 (shown in FIG. 1). Inspection of the stack can include measuring alignment between layers and / or checking light output metrics such as contrast, uniformity, and / or brightness of an image projected through the stack. Stacks whose measurements are within threshold tolerances can proceed to a completed stack collection bin 109, while stacks that do not pass quality standards can be moved to a waste bin 911 (both completed stack collection bin 109 and waste bin 911 are shown in FIG. 1). The stack collection bin 109 and stack waste bin 111 can be inside or outside the enclosure 112 of the tool 110.

[0079] Several stations are discussed above by describing the various fabrication or assembly steps performed at each station. Transfer of components between stations can be accomplished using conveyors, transfer arms with vacuum attachments, moving stages, or other component transfer means. Components can be moved individually between stations, or components can be collected as a batch at one station and moved to another station. Intermediate containment areas can be provided between any of the described stations to temporarily hold wafers, spacers, and / or assemblies for later batch transfer.

[0080] The completed stack can exit the enclosure 112 of the tool 110 and further processing steps can be performed, such as milling, laser cutting, water jet, singulation by die-cutting (i.e., cutting the stacked wafers into individual eyepieces), or other means of singulation. The edges of the singulated eyepiece stack can be coated with an adhesive material, such as a high refractive index UV-curable adhesive doped with carbon nanopowder, mesoporous carbon, carbon black, various dyes, or combinations thereof.

[0081] The singulation and edge coating steps can be performed outside the enclosure 112 of the tool 110, so that debris created by the singulation process does not contaminate other processes performed within the enclosure 112. However, it is also possible to create one or more containment areas within the enclosure 112, where the singulation and / or edge coating steps can be performed in isolation from other fabrication and assembly steps. Such isolated areas can prevent the transfer of debris, vibrations, or fumes to other areas of the enclosure 112. In some embodiments, the enclosure 112 is substantially similar to a clean room environment. In some embodiments, providing vents to the enclosure 112 and / or isolated areas within the enclosure 112 to the outside of the tool 110 allows for controlled circulation of filtered air to remove contaminants and / or fumes from the interior of the enclosure 112.

[0082] Although several examples of fabrication and assembly steps for creating a multi-layer polymer eyepiece within a housed tool are discussed herein, equipment stations and process steps can be added or removed to optimize the tool to build a specific product. Numerous changes, modifications, variations, substitutions, and equivalents will be apparent to those skilled in the art that do not depart from the spirit and scope of the present disclosure.

Claims

1. 1. A method of aligning a stencil to an eyepiece wafer, the method comprising: Providing the stencil; Positioning the stencil relative to a first light source; determining locations of at least two stencil holes; providing the eyepiece wafer, the eyepiece wafer including at least two eyepiece waveguides, each eyepiece waveguide including an input coupling grating and a corresponding diffraction pattern; directing light from one or more second light sources to impinge on each of the corresponding diffraction patterns; imaging the light diffracted from each input coupling grating; determining locations of at least two input coupling gratings; determining a deviation between corresponding stencil hole locations and input coupling grating locations; aligning the stencil to the eyepiece wafer based on the determined offset; and A method comprising:

2. The method of claim 1 , wherein the at least two stencil hole locations comprise four hole locations or six hole locations.

3. Determining locations of the at least two stencil holes includes: imaging the light from the first light source using a first camera after the light from the first light source passes through a first one of the at least two stencil holes; imaging the light from the first light source using a second camera after the light from the first light source passes through a second one of the at least two stencil holes; The method of claim 1 , comprising:

4. Determining locations of the at least two stencil holes includes: imaging the light from the first light source using a camera after the light from the first light source passes through a first of the at least two stencil holes; imaging the light from the first light source using the camera after the light from the first light source passes through a second one of the at least two stencil holes; The method of claim 1 , comprising:

5. 2. The method of claim 1 , further comprising redirecting at least a portion of the light from each of the one or more secondary light sources to each of the input coupling gratings via total internal reflection after directing the light from each of the one or more secondary light sources to impinge on the corresponding diffraction pattern.

6. Imaging the light diffracted from each input coupling grating imaging light from a primary light source of the one or more secondary light sources using a first camera after the light from the primary light source is diffracted from a first input coupling grating of the input coupling gratings; imaging the light from a secondary light source of the one or more second light sources using a second camera after the light from the secondary light source passes through a second input coupling grating of the input coupling gratings; The method of claim 1 , comprising:

7. Imaging the light diffracted from each input coupling grating imaging light from a primary light source of the one or more secondary light sources using a camera after the light from the primary light source is diffracted from a first one of the input coupling gratings; imaging the light from a secondary light source of the one or more secondary light sources using the camera after the light from the secondary light source is diffracted from a second one of the input coupling gratings; The method of claim 1 , comprising:

8. The method of claim 1 , wherein aligning the stencil to the eyepiece wafer comprises moving the eyepiece wafer relative to the stencil to reduce the determined misalignment.

9. 9. The method of claim 8, wherein moving the eyepiece wafer comprises rotating and translating the eyepiece wafer, and reducing the determined misalignment comprises minimizing the determined misalignment.

10. 1. A system comprising: a first chuck operable to support a stencil including a plurality of holes; a wafer chuck operable to support and move a wafer including a plurality of input coupling gratings; a first light source operable to direct light to impinge on a first surface of the stencil; one or more second light sources operable to direct light to impinge on the wafer; One or more lens and camera assemblies, the one or more lens and camera assemblies comprising: receiving light from the first light source that has passed through the plurality of holes in the stencil; receiving light from the one or more second light sources diffracted from the plurality of input coupling gratings in the wafer; one or more lens and camera assemblies operable to an alignment system operable to move the wafer relative to the stencil to reduce misalignment between locations of holes and locations of input coupling gratings; The system comprises:

11. The one or more lens and camera assemblies include: a first camera operable to detect a position of a first hole of the plurality of holes; a second camera operable to detect a position of a second hole of the plurality of holes; The system of claim 10, comprising:

12. 11. The method of claim 10, wherein the one or more lens and camera assemblies comprise a single camera operable to detect a position of a first hole of the plurality of holes and a position of a second hole of the plurality of holes.

13. 11. The system of claim 10, wherein the light from the one or more second light sources diffracted from the input coupling grating within the wafer propagates by total internal reflection before being diffracted out of the wafer from the input coupling grating.

14. Moving the wafer relative to the stencil comprises: rotating and translating the wafer; Thereafter, contacting the wafer with the stencil; The system of claim 10 , comprising:

15. The system of claim 10 , wherein the first light source and the one or more second light sources are positioned on opposite sides of the wafer.

16. 1. An assembly system, comprising: a wafer casting station; a stencil placement station; A deposition station; a stencil separation station; a first inspection station; a layer assembly station; A second inspection station and An assembly system comprising:

17. The stencil placement station includes: a first chuck operable to support a stencil including a plurality of holes; a wafer chuck operable to support and move a wafer including a plurality of input coupling gratings; a first light source operable to direct light to impinge on a first surface of the stencil; one or more second light sources operable to direct light to impinge on the wafer; One or more lens and camera assemblies, the one or more lens and camera assemblies comprising: receiving light from the first light source that has passed through the plurality of holes in the stencil; receiving light from the one or more second light sources diffracted from the plurality of input coupling gratings in the wafer; one or more lens and camera assemblies operable to an alignment system operable to move the wafer relative to the stencil to reduce misalignment between locations of holes and locations of input coupling gratings; 17. The assembly system of claim 16, comprising:

18. The one or more lens and camera assemblies include: a first camera operable to detect a position of a first hole of the plurality of holes; a second camera operable to detect a position of a second hole of the plurality of holes; 20. The assembly system of claim 17, comprising:

19. 20. The method of claim 17, wherein the one or more lens and camera assemblies comprise a single camera operable to detect a position of a first hole of the plurality of holes and a position of a second hole of the plurality of holes.

20. 20. The system of claim 17, wherein the light from the one or more second light sources diffracted from the input coupling grating within the wafer propagates by total internal reflection before being diffracted out of the wafer from the input coupling grating.

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