Optical element stack assemblies

Optics Stack Assemblies

OPTICAL ELEMENT STACK ASSEMBLIES

The present invention relates to optical element stack assemblies.

For example, various optoelectronic modules are used in imaging applications, such as three-dimensional (3D) imaging, or distance measurement applications, such as proximity sensing and time-of-flight (TOF) sensing. In some applications, an optical emitter component is operable to emit a structured optical pattern that can be used in imaging and distance sensing applications. Structured light can cause a pattern of discrete features (ie, texture) to be projected onto an object. Light reflected by the object can be directed back towards an image sensor (where the light is sensed). The sensed signal can be used for distance calculation. In some cases, structured light provides additional texture for matching pixels in stereoscopic imaging applications. In some modules, an optical element, such as a diffractive optical element (DOE), is introduced into the path of light emitted by a light source, such as a vertical cavity semiconductor emitting laser (VCSEL) or VCSEL array. DOEs can be used to generate structured light patterns. It can also contribute to the multiplication of a structured light pattern produced by a VCSEL or other light source. Various methods are available for fabricating optical element stack assemblies. In some cases, an optical element stack is formed. However, various problems arise in some known manufacturing techniques. For example, in many applications it may be desirable to control the vertical height (z-height) of stacked components. However, adhesives at the interface of the wafers used to form the stacked components can cause excessive height variation between components. Additionally, in some cases, the adhesive can migrate into an adjacent surface (eg, one of the optical components) and interfere with its optical properties. Additionally, in some instances the surface of the optical element(s) cannot be completely isolated from the atmosphere. In fact, sometimes only a small amount of the adhesive is provided at the interface between the wafers in order to avoid the adhesive migrating into the surface of the optical element. However, using such a small amount of adhesive can make it more difficult to achieve an effective seal.

This disclosure describes optical stack assemblies and techniques for their fabrication that may in some implementations overcome or alleviate some or all of the above-mentioned problems. In one aspect, an optical element stack assembly includes a first subassembly and a second subassembly, each of which includes a substrate and a substructure secured to the respective substrate. At least one of the first substructure or the second substructure includes an optical element. The optical element stack assembly further includes a spacer laterally surrounding and molded to the first subassembly and the second subassembly. Each of the substructures includes a respective first edge feature and a respective second edge feature protruding away from the substrate of the substructure. Each second edge feature is disposed laterally closer to an outer periphery of the respective substructure than the first edge feature of the same substructure. The first edge feature of the first substructure is in direct contact with the first edge feature of the second substructure, and the second edge feature of the first substructure and the second edge feature of the second substructure Attached to each other by adhesive. In some implementations, the first edge features in direct contact with each other can help establish the z-height of the component. The spacer laterally surrounding the subassemblies can help keep the subassemblies together and can help protect the optical elements from, for example, water, moisture, and/or dust. Some implementations include one or more of the following features. For example, the spacer may encapsulate the peripheral side edges of the substrates and may also partially overlap the upper and lower surfaces of the substrates. In some instances, there is a space separating the first edge feature and the second edge feature of the first substructure from each other. In some cases, adhesive may be present in the space separating the first edge feature and the second edge feature of the first substructure. In some embodiments, the optical element is adjacent to a substructure of which the optical element is a part. Additionally, in some instances, both substructures have an optical element. Thus, the first substructure may contain an optical element on the same side as its first and second edge features; likewise, the second substructure may include an optical element on the same side as its first and second edge features An optical element is included on the side of the feature. In some cases, the optical element of the first substructure is adjacent to the first edge feature and the second edge feature of the first substructure, and the optical element of the second substructure is adjacent to the second substructure The first edge feature and the second edge feature are adjacent. In another aspect, the disclosure describes a wafer-level method of fabricating an optical element stack assembly. The method includes providing a first wafer having a plurality of first substructures thereon, wherein each first substructure includes a respective optical element and a respective edge feature protruding away from the first wafer. The method further includes providing a second wafer having a plurality of second substructures thereon, wherein each second substructure includes a respective optical element and a respective edge feature protruding away from the second wafer. The edge features of the first substructures are attached to the edge features of the second substructures by an adhesive to form a wafer stack. Spacers laterally surrounding the first substructures and the second substructures in the wafer stack are provided using a vacuum injection molding technique. Subsequently, the wafer stack is separated into individual optical element stack assemblies. In yet another aspect, the disclosure describes a method of making a master mold. The method includes: providing a wafer having an optical element structure thereon; and repeatedly performing the following to build up one or more edge features laterally surrounding the optical element structure: (a) applying a photoresist layer thereto on the side of the wafer having the optical element structure thereon; and (b) selectively removing portions of the photoresist layer. Other aspects, features, and advantages will be readily apparent from the following detailed description, drawings, and claims.

FIG. 1 illustrates an example of an optical element stack assembly 20 comprising a first subassembly 22A held together to form a stack comprising one or more optical elements (eg, refractive or diffractive optical elements) 24A, 24B. and the second subassembly 22B. Each subassembly 22A, 22B includes a glass or other substrate 26A, 26B that is substantially transmissive to radiation of a particular wavelength or range of wavelengths (eg, in the visible, infrared, or near-infrared portions of the spectrum). Each optical element 24A, 24B may be part of a respective substructure 28A, 28B secured to a respective one of the substrates 26A, 26B. For example, each optical element 24A, 24B may be formed as a part adjacent to a respective substructure 28A, 28B. In some cases, each optical element 24A (or 24B) and the remainder of the respective substructure 28A (or 28B) form an integral molded part. For example, the optical elements 24A, 24B and other portions of the respective substructures 28A, 28B may be composed of an epoxy that is substantially transmissive to the particular wavelength or range of wavelengths of interest. In some instances, only one of the subassemblies 22A (or 22B) includes an optical element 24A (or 24B). In that case, another subassembly would contain the remainder of structure 28A (or 28B), but without the optical elements. The two subassemblies 22A, 22B are held together by a molded spacer 30 laterally surrounding one of the subassemblies. Spacers 30 may also encapsulate the peripheral side edges of the glass substrates 26A, 26B and partially overlap the upper and lower surfaces of the substrates, which may help hold the components together. To facilitate providing the aforementioned features, the lateral dimensions of the substructures 28A, 28B may be made slightly smaller than the lateral dimensions of the substrates 26A, 26B. Spacer 30 (which, in some cases, may be composed of a polymeric material that is substantially opaque to a particular wavelength or range of wavelengths of interest) may help protect optical elements 24A, 24B from water, moisture, and/or dust. influences. The spacer 30 also helps to hold the first subassembly 22A and the second subassembly 22B together. Each substructure 28A, 28B includes a respective edge feature that protrudes away from the substrate 26A, 26B of the corresponding subassembly and exists on the same side as the substructure of the optical element 24A, 24B of the corresponding subassembly. In particular, the first substructure 28A includes a first edge feature 32A having a surface 34A that directly contacts an opposing surface 34B of the first edge feature 32B of the second substructure 28B to establish the z of the assembly 20. high. Each of the substructures 28A, 28B includes a respective second edge feature 36A, 36B closer to its perimeter than a corresponding first edge feature 32A, 32B. Adhesive 38 may be present between opposing surfaces 44A, 44B of second edge features 36A, 36B and helps hold the subassemblies together. In some cases, a portion of adhesive 38 may be present in reservoir region 42A that defines a space between a first edge feature and a second edge feature (eg, between edge features 32A, 36A of first substructure 28A). , 42B. Edge features 32A, 36A laterally surround optical element 24A. Likewise, edge features 32B, 36B laterally surround optical element 24B. Edge features 32A, 32B (or 36A, 36B) in combination define an interior space 50 in which optical elements 24A, 24B are positioned. Multiple devices 20 may be formed simultaneously (ie, in parallel) as part of a wafer-level process. In general, a wafer refers to a substantially disc-shaped or plate-shaped article that extends less in one direction (z-direction or vertical) than in the other two directions (x-lateral and y-direction). The amount of extension in the transverse direction). In some implementations, the diameter of the wafer is between 5 cm and 40 cm, and can, for example, be between 10 cm and 31 cm. A wafer can be a cylinder having a diameter of, for example, 2 inches, 4 inches, 6 inches, 8 inches, or 12 inches, with 1 inch being approximately 2.54 cm. In some embodiments of a wafer level process, at least 10 modules may be provided in each lateral direction, and in some cases at least 30 or even 50 or more modules may be provided in each lateral direction. Group. 2-3 illustrate steps in a process for securing the first subassembly 22A and the second subassembly 22B together to form an optical element stack assembly 20 . Although shown for fabrication of subassemblies of a single assembly 20, the steps may form part of a wafer level process in which multiple assemblies are fabricated in parallel. First, the two subassemblies 22A, 22B are stacked on top of each other such that the edge feature surface 34A of the first substructure 28A is in contact with the edge feature surface 34B of the second substructure 28B. Adhesive 38 is then provided between opposing surfaces 44A, 44B of edge features 36A, 36B. Surfaces 44A, 44B are spaced apart from each other by a small gap because first edge features 32A, 32B extend further from their respective substrates 26A, 26B than second edge features 36A, 36B. An adhesive can be used, for example, by screen printing the adhesive into the reservoir 42A (eg, using a high viscosity adhesive) or spraying the adhesive into a reservoir 42A (eg, using a low viscosity adhesive). agent) to apply the adhesive. Adhesive 38 helps to hold subassemblies 22A, 22B in place during subsequent processing steps. During subsequent processing (ie, prior to forming the molded spacer 30 ), only a small amount of adhesive is required to hold the subassemblies 22A, 22B together. In addition, the reservoir 42A in the space between the first edge feature 32A and the second edge feature 36A can accommodate the overflow of the adhesive 38, if present, thereby preventing excess adhesive from flowing onto the optical elements 24A, 24B. . In some cases, rather than depositing adhesive 38 directly onto opposing edge feature surfaces 44A, 44B, the adhesive may be deposited within reservoir 42A such that a portion of the adhesive subsequently flows onto surfaces 44A, 44B. . Spacers 30 may then be formed, for example, by a vacuum injection molding technique (see FIG. 1 ). Further details of a suitable procedure are described below. The substructures 28A, 28B of the subassemblies 22A, 22B can be formed, for example, using a poly(dimethylsiloxane) ("PDMS") tool that can be made from a master mold. An example of a (positive) master mold 102 is depicted in FIG. 4A, and an example of a (negative) PDMS tool 104 is depicted in FIG. 4B. The substructures 28A, 28B may be formed, for example, using the PDMS tool 104 in a wafer-level replication process. In this replication procedure, a PDMS tool is pressed into an epoxy material on, for example, a glass substrate to form an optical element (eg, 24A). Simultaneously, edge features (eg, 32A and 36A) are formed in the overflow portion of the epoxy material. The size of the edge features can vary depending on the application. However, in some instances, the height of each first edge feature 32A, 32B is about twice the height of each second edge feature 36A, 36B. For example, in some cases, each first edge feature 32A, 32B has a height of about 34 μm and each second edge feature 36A, 36B has a height of about 17 μm, wherein the heights indicate that the edge features protrude beyond the respective How far apart the reservoir area 42A (or 42B) is. Reservoir regions 42A, 42B may have a relatively narrow width (eg, about 15 μm). Figures 5A-5E show an example of how the (positive) master mold 102 of Figure 4A may be made. As indicated by FIG. 5A , a master mold may be fabricated by providing, for example, a glass wafer 110 having a structure 112 corresponding to the formation of an optical element, such as a lens. Structure 112 may be formed, for example, by laser writing or laser engraving of glass wafer 110 . Next, as indicated by FIG. 5B , a photoresist layer (eg, dry photoresist layer) 114 is applied on the side of wafer 110 having structures 112 for optical elements. Next, photoresist 114 is cured, patterned by standard photolithography techniques, and selectively removed (eg, by etching) to build up edge features 116 (see FIG. 5C ). Another photoresist layer 118 is applied over wafer 110 (see FIG. 5D ). Photoresist 118 may be cured, patterned by photolithography, and partially removed to continue building up edge features 120, 122 (FIG. 5E). In some implementations, each photoresist layer 114, 118 has a thickness of one of about 50 μm. Repeat the above steps as needed to stack edge features. As mentioned above, multiple stacked devices 20 may be formed simultaneously as part of a wafer level process. 6A-6G illustrate steps in one example of a wafer-level process for fabricating an optical element stack assembly. In the depicted example of FIGS. 6A-6G , substructures 228A, 228B include edge features 36A, 36B, but do not include edge features 32A, 32B of the FIG. 1 implementation. Thus, in the example depicted, the substructures 228A, 228B also do not include the reservoir regions 42A, 42B of the FIG. 1 embodiment. However, the generally same procedure described in connection with FIGS. 6A-6G can be used for substructures that include both the first edge feature 32A (or 32B) and the second edge feature 36A (or 36B) and a reservoir 42A (or 42B). , as in Figure 1 embodiment. As shown in FIG. 6A, a first glass wafer 226A is provided and has a plurality of substructures 228A formed on one of its surfaces. The glass wafer 226A may be referred to as a first optical element wafer. Each substructure includes an optical element 24A replicated in an epoxy material, the overflow portion of which acts as an edge feature 36A for facilitating stacking. As shown in FIG. 6B , an adhesive (eg, glue) is applied, for example, by screen printing using a pattern template 250 252 is applied to the upper surface of each edge feature 36A. After removal of the template 250, a second optical element wafer comprising a plurality of substructures 228B on the surface of a glass wafer 226B is stacked on the first optical element wafer (see FIG. 6C). Each substructure 228B includes an optical element 24B replicated in an epoxy material, the overflow portion of which acts as an edge feature 36B for facilitating stacking. The first optics wafer and the second optics wafer are aligned such that their respective edge features 36A, 36B are attached to each other by adhesive 252 to thereby form a stack 254 . Next, as shown in Figure 6D, the wafer stack 254 is placed on a substantially flat support 256, and a vacuum injection tool 258 is moved into the contacts on the stack. The vacuum injection tool 258 is separated from the support 256 by a sealing plate 260 . A vacuum pump may be provided near outlet 262 to facilitate the flow of vacuum injected polymer material 264 so that it laterally surrounds stacked substructures 228A, 228B (FIG. 6E). In the example depicted, the vacuum injection tool 258 also includes a space 266 for forming a spacer 268 ( FIG. 6E ) consisting of vacuum injected polymeric material. (FIG. 6D). Spacers 268 can facilitate mounting the resulting stacked assembly on, for example, a printed circuit board. Next, the vacuum injected polymer material can be cured (eg, by UV and/or heat curing). The resulting wafer stack comprising cured vacuum injected polymer material is demolded and removed from vacuum injection tools 256, 258, as shown in Figure 6F. The resulting wafer stack 270 is then separated (eg, by dicing) to form a plurality of stacked components 220 ( FIG. 6G ), each of which includes one or more optical elements (eg, lenses; DOEs). As mentioned above, the generally same procedure described in connection with FIGS. 6A-6G can be used to include both the first edge feature 32A (or 32B) and the second edge feature 36A (or 36B) and a reservoir 42A (or 36B). 42B) substructure, as in Fig. 1 embodiment. Thus, in some cases, wafer-level procedures include the processes described above in connection with FIGS. 2 and 3 . Various modifications can be made to the above described stack assembly and method of manufacture. In some cases, features from different implementations described in detail above may be combined. Accordingly, other implementations are within the scope of this patent application.

<p>20optical element stack assembly&lt;br/&gt;2Afirst subassembly&lt;br/&gt;2Bsecond subassembly&lt;br/&gt;4Aoptical element&lt;br/&gt;4B Optical element&lt;br/&gt;6Asubstrate&lt;br/&gt;6Bsubstrate&lt;br/&gt;8Afirst substructure&lt;br/&gt;8Bsecond substructure&lt;br/&gt;0 Spacer&lt;br/&gt;2AFirst Edge Feature&lt;br/&gt;2BFirst Edge Feature&lt;br/&gt;4ASurface&lt;br/&gt;4BSurface&lt;br/&gt; 6Asecond edge feature&lt;br/&gt;6Bsecond edge feature&lt;br/&gt;8adhesive&lt;br/&gt;2Areservoir region&lt;br/&gt;2B Reservoir area&lt;br/&gt;0internal space&lt;br/&gt;02(positive) master mold&lt;br/&gt;04poly(dimethylsiloxane) (PDMS) tool&lt;br/&gt; /&gt;10wafer&lt;br/&gt;12structure&lt;br/&gt;14photoresist layer&lt;br/&gt;16edge features&lt;br/&gt;18photoresist layer&lt; br/&gt;20edge features&lt;br/&gt;22edge features&lt;br/&gt;20stacked components&lt;br/&gt;26Aglass wafer&lt;br/&gt;26Bglass crystal Circle&lt;br/&gt;28Asubstructure&lt;br/&gt;28Bsubstructure&lt;br/&gt;50template&lt;br/&gt;52adhesive&lt;br/&gt;54wafer Stacking&lt;br/&gt;56Support/Vacuum Injection Tool&lt;br/&gt;58Vacuum Injection Tool&lt;br/&gt;60Sealing Plate&lt;br/&gt;62Outlet&lt;br/&gt;64 Vacuum injection polymer material</p><p>266: space</p><p>268:Spacer</p><p>270: Wafer stacking</p>

FIG. 1 shows an example of an optical element stack assembly. 2 and 3 illustrate the steps of forming the optical element stack assembly of FIG. 1 . Figure 4A shows an example of a master mold, and Figure 4B shows an example of a tool for making substructures of subassemblies. 5A to 5E illustrate an example of how to make a master mold. 6A-6G illustrate an exemplary wafer-level method for fabricating an optical element stack assembly.