Abstract:
A multi-layered lens having a substrate with opposing first and second surfaces. The substrate is formed of a plurality of discrete polymer layers. A cavity is formed into the first surface and is defined by a non-planar cavity surface that acts as a lens surface. The cavity extends into and exposes each of the plurality of polymer layers. The compositions of the polymer layers can vary to provide optimized focal properties. Alignment marks in the form of cavities or protrusions can be formed at the first surface or the second surface, so that multiple lenses can be stacked together in an aligned manner to form a stacked lens assembly.

Description:
FIELD OF THE INVENTION 
     The present invention relates to lenses, and more particularly to lenses used in mobile devices such as cell phone cameras. 
     BACKGROUND OF THE INVENTION 
     CMOS image sensor chips are typically used in mobile devices such as cell phone cameras to capture images (e.g. cell phone camera or video functionality). These image sensors are usually very small and compact, given the limited size and weight requirements for mobile devices. The image sensor chip includes one or more lenses that are used to focus the incoming light onto a light sensor. The light sensor converts the incoming light into electronic signals that represent the image formed by the incoming light. 
     Lenses are often made of glass or polymer, and are typically made using a molding process. For example, polymer lenses are typically manufactured using molding techniques such as stamping, injection molding and transfer molding. Injection molding, for example, involves injecting polymer in a liquid state into a mold cavity. The polymer is then cooled so that it solidifies in the shape of the mold. The polymer is then removed from the mold in the form of a lens. 
     Molded lenses are easily mass-produced. For example, pluralities of molds are simultaneously injected with fluid state material, then cooled, resulting in simultaneous formations of lenses. The quality of lenses needs to be high and consistent. However, as lenses get smaller and smaller, it has become harder to maintain quality with molded lenses because of the difficulty in forming multiple molds with exactly the same dimensions. Additionally, molds can fatigue over time and thus can produce lenses with declining quality over time. Lastly, injection molded lenses are monolithic, meaning that the possible optical properties achieved from molded lenses are limited. Multiple monolithic lenses can be stacked to achieve more varies optical properties, but with incrementally larger overall sizes and cost. 
     There is a need for an improved lens and manufacturing technique for making the lens that provides superior quality, uniformity and diverse optical performance over molded lenses, without adding significant cost. 
     BRIEF SUMMARY OF THE INVENTION 
     The aforementioned problems and needs are addressed by a multi-layered lens that includes a substrate having opposing first and second surfaces (wherein the substrate is formed of a plurality of discrete polymer layers), and a cavity formed into the first surface and including a non-planar cavity surface in the substrate, wherein the cavity extends into each of the plurality of polymer layers. 
     In another aspect of the present invention, a method of forming a lens includes forming a first polymer layer, forming a first cavity into a top surface of the first polymer layer, forming a second polymer layer on the top surface of the first polymer layer, and forming a second cavity into a top surface of the second polymer layer that extends through the second polymer layer to the first cavity, wherein the first and second cavities together include a non-planar cavity surface. 
     In yet another aspect of the present invention, a method of forming a lens includes forming a first polymer layer, forming a first cavity into a top surface of the first polymer layer, altering a shape of a sidewall of the first cavity, forming a second polymer layer on the top surface of the first polymer layer, forming a second cavity into a top surface of the second polymer layer, and altering a shape of a sidewall of the second cavity, wherein the second cavity includes a first non-planar cavity surface. 
     In still yet another aspect of the present invention, a lens assembly includes a plurality of lenses and a layer of material. Each of the plurality of lenses includes a substrate having opposing first and second surfaces and an outer edge, wherein the substrate is formed of a plurality of discrete polymer layers, and a cavity formed into the first surface and including a non-planar cavity surface in the substrate, wherein the cavity extends into each of the plurality of polymer layers. The plurality of lenses are stacked together such that adjacent ones of the plurality of lenses are affixed to each other by a bonding material. The layer of material extends around and between the outer edges of the substrates. 
     Other objects and features of the present invention will become apparent by a review of the specification, claims and appended figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1K  are cross sectional side views showing in sequence the steps in forming the multi-layered lens. 
         FIGS. 2A-2N  are cross sectional side views showing in sequence the steps in forming an alternate embodiment of the multi-layered lens. 
         FIGS. 3-4  are cross sectional side views of a lens assembly of a plurality of stacked multi-layered lenses. 
         FIG. 5  is a cross sectional side view of the lens assembly (of a plurality of stacked multi-layered lenses) mounted on an image sensor assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is a multi-layer lens, and the method of manufacturing the same. The number of layers, and the composition of each layer, can be varied to achieve the desired optical properties of the lens. 
       FIGS. 1A-1K  illustrate the sequence of steps for manufacturing a multi-layer lens. In this example, the resulting lens will comprise three layers of material. The process begins by providing a smooth carrier  10  (e.g. Teflon), which is used as a lens carrier during the manufacturing process. As a non-limiting example, carrier  10  can be round (6 to 12 inches in diameter), with sidewalls  12  extending up from its upper surface  14  to contain the lens materials on the upper surface  14 , as illustrated in  FIG. 1A . While preferably a plurality of lenses are formed on carrier  10  simultaneously, for simplicity, the remaining figures illustrate the formation of a single lens on just a portion of carrier  10 . 
     A first polymer layer  16  is formed on surface  10 . Preferably, polymer formation is done by spray coating deposition, due to its even coating property. Polymer deposition is followed by a curing process. Polymer layer  16  can be epoxy silicone monomer, cycloaliphatic epoxy compounds, UV curable polymers, acrylate polymer, PMMA, COP, PC, ORNOCOMP or any other well-known optical polymer with desirable optical properties. A photo-resist layer  18  is formed over polymer layer  16 , for example, by spray coating, spin coating or any other photo-resist deposition process (which are known in the art). The photo-resist layer is then patterned using a photo-lithography exposure and development process (which are all well known in the art), leaving portions of the polymer layer  16  exposed. The resulting structure is shown in  FIG. 1B . 
     An isotropic etch process is next performed to selectively etch the exposed portions of polymer layer  16 . For example, a wet isotropic etching process involving a wet bath of etch agent for the polymer of layer  16  can be used, which dissolves unprotected portions of layer  16  to create cavity  20  formed into the upper surface of layer  16  in the form of a ring around the optical area), as illustrated in  FIG. 1C . The curvature of cavity  20  can be controlled by the pattern of photo-resist  18  and the etching solution used. 
     After photo-resist  18  is removed, the cavity  20  is filled with photo-resist  22 . A second polymer layer  24  is then formed over polymer layer  16  (and photo-resist  22 ). Polymer layer  24  can be formed with the same material(s) or different material(s) (and same or different thickness) as polymer layer  16 , depending upon the desired optical properties provided by itself and/or in combination of the other polymer layers. A photo-resist layer  26  is then formed over polymer layer  24 , and patterned to expose portions of polymer layer  24  (in this example those portions disposed over photo-resist  22 ), as illustrated in  FIG. 1D . Photo-resist  26  is different from (i.e. etch selective relative to) photo-resist  22 . 
     An isotropic etch process is next performed to selectively etch the exposed portions of polymer layer  24 . For example, a wet isotropic etching process involving a wet bath of etch agent for the polymer of layer  24  can be used, which dissolves unprotected portions of layer  24  such that cavity  20  extends up through layer  24 , as illustrated in  FIG. 1E . The curvature and angle of the walls of cavity  20  as they extend through layer  24  can be controlled by the thickness of polymer layer  24 , the pattern of photo-resist  26  and the etching solution used. 
     After photo-resist  26  is removed, the cavity  20  (as expanded through layer  24 ) is filled with photo-resist  22 . A third polymer layer  28  is then formed over polymer layer  24  (and photo-resist  22 ). Polymer layer  28  can be formed with the same material(s) or different material(s) (and same or different thickness) as polymer layers  16  and/or  24 , depending upon the desired optical properties provided by itself and/or in combination of the other polymer layers. A photo-resist layer  30  is then formed over polymer layer  28 , and patterned to expose portions of polymer layer  28  that are disposed over photo-resist  22 , as illustrated in  FIG. 1F . Photo-resist  30  is different from (i.e. etch selective relative to) photo-resist  22 . 
     An isotropic etch process is next performed to selectively etch the exposed portions of polymer layer  28 . For example, a wet isotropic etching process involving a wet bath of etch agent for the polymer of layer  28  can be used, which dissolves unprotected portions of layer  28  (i.e. leaving cavity  20  extending up through layer  28 ). The curvature and angle of the walls of cavity  20  as they extend through layer  28  can be controlled by the thickness of polymer layer  28 , the pattern of photo-resist  30  and the etching solution used. Photo-resist  30  and  22  are then removed, leaving the structure illustrated in  FIG. 1G . In this example, cavity  20  is no longer in the shape of a ring, but is now circular with a non-planar cavity surface  20   a  that extends through (i.e. is defined by) all three polymer layers  16 ,  24  and  28 . The cavity surface  20   a  defines the lens surface as further explained below. 
     A soft isotropic etch can be performed to smooth out any roughness on the cavity surface  20   a , as well as any steps or gaps between polymer layers  16 / 24 / 28  along the cavity surface  20   a . A similar optional surface polishing may be performed on the lens backside (i.e. the bottom surface of polymer layer  16  abutting carrier  10  after removal from the carrier  10 ). 
     Surface  20   a  can be optionally coated with an IR coating, which can include Copper (Cu), Gold, Hafnium Oxide (HfO2), ITO (Indium Tin Oxide), Magnesium Oxide (MgO), Nickel (Ni), Silicon Monoxide (SiO), Silver, Titanium Dioxide (TiO2), Tantalum Oxide (Ta2O5), Zirconium Oxideany and/or any other appropriate IR coating material. The IR coating can be applied using standard deposition techniques which are well known in the art. Similarly, the back surface (i.e. bottom surface of polymer layer  16  abutting the carrier  10 ) can be optionally coated with an AR coating (after removal from the carrier  10 ) using antireflection materials that are well known in the art. 
     Alignment marks are then formed on or in the top surface of polymer layer  28 . If the alignment marks  32  are formed on the polymer layer  28  top surface (as shown in  FIG. 1H ), they can be formed with a polymer, an epoxy, a resin, a metal, etc. as a protrusion that preferably extends from the polymer layer  28  top surface with a height of at least 3 μm. If the alignment marks  32  are formed into the polymer layer  28  top surface (as shown in  FIG. 1I ), they can be formed as a cavity or trench using a laser preferably having a depth of at least 3 μm. Alignment marks can have any desired shape, such as for example circular, rectangular, cross shaped, T-shaped, etc. Alignment marks  32  can additionally or alternately be formed on or in the bottom surface of polymer layer  16 . 
     The carrier  10  is then removed, and the structure is then diced along dicing lines  34  as illustrated in  FIG. 1J  to separate each individual lenses  36 . The final lens  36  is illustrated in  FIG. 1K . 
     Lens  36  is a substrate formed of discrete layers of polymer material. Lens  36  includes a lens surface  20   a  having a very specific shape in order to produce the desired optical focusing for light passing through lens  36 . The shape of lens surface  20   a  can be consistently and precisely controlled using the polymer deposition, photo-lithography and etch processes described above. By varying the compositions of the three layers  16 ,  24  and  28  relative to each other, as well as optionally continuing to add additional discrete layers to the three described above in a similar manner, more complex and diverse optical focusing performance can be achieved. 
       FIGS. 2A-2N  illustrate the sequence of steps for manufacturing an alternate embodiment multi-layer lens. The process begins with the structure of  FIG. 1B , except for the relative locations of the exposed portions of polymer layer  16 , as illustrated in  FIG. 2A . An anisotropic etch is then performed to selectively etch the exposed portions of polymer layer  16 . For example, a plasma or wet anisotropic etching process removes portions of layer  16  to form an annular trench-shaped cavity  40  into the upper surface of layer  16  (i.e. in the form of a ring around the optical area). The photo-resist  18  is then removed, leaving the structure illustrated in  FIG. 2B . 
     A photo-resist layer  42  is deposited over the structure (including inside cavity  40 ). A photolithography process is used to remove selective portions of photo-resist layer  42  (along the inner sidewall of cavity  40 , and that portion on the upper surface of polymer layer  16  that is adjacent the inner sidewall of cavity  40 ), as illustrated in  FIG. 2C . An isotropic etching process, such as a wet bath of polymer etch agent, is used to dissolve exposed portions of polymer layer  16 , creating a curved shaped to the inner-sidewall  40   a  of cavity  40 . The resulting structure is illustrated in  FIG. 2D  (after photo-resist  42  is removed). The curvature and angle of the inner-sidewall  40   a  of cavity  40  can be controlled by the thickness of polymer layer  16 , the pattern of photo-resist  42  and the etch material. 
     A second polymer layer  44  is next formed over polymer layer  16  (filling cavity  40 ). Polymer layer  44  can be formed with the same material(s) or different material(s) (and same or different thickness) as polymer layer  16 , depending upon the desired optical properties provided by itself and/or in combination of the other polymer layers. A photo-resist layer  46  is then formed over polymer layer  44 , and patterned to expose portions of polymer layer  44 , as illustrated in  FIG. 2E . 
     An anisotropic etch is then performed to selectively etch the exposed portions of polymer layer  44 . For example, a plasma or wet anisotropic etching process removes portions of layer  44  to form an annular trench-shaped cavity  48  into the upper surface of layer  44  (i.e. in the form of a ring around the optical area). After the photo-resist  46  is removed, a photo-resist layer  50  is deposited over the structure (including inside cavity  48 ). A photolithography process is used to remove selective portions of photo-resist layer  50  (along the inner sidewall of cavity  48 , and that portion on the upper surface of polymer layer  44  that is adjacent the inner sidewall of cavity  48 ), as illustrated in  FIG. 2F . An isotropic etching process, such as a wet bath of polymer etch agent, is used to dissolve exposed portions of polymer layer  44 , creating a curved inner-sidewall  48   a  to cavity  48 . The resulting structure is illustrated in  FIG. 2G  (after photo-resist  50  is removed). The curvature and angle of inner-sidewall  48   a  of cavity  48  can be controlled by the thickness of polymer layer  44 , the pattern of photo-resist  50 , and the etch material. 
     A third polymer layer  52  is next formed over polymer layer  44  (filling cavity  48 ). Polymer layer  52  can be formed with the same material(s) or different material(s) (and same or different thicknesses) as polymer layers  16  and  44 , depending upon the desired optical properties provided by itself and/or in combination of the other polymer layers. A photo-resist layer  54  is then formed over polymer layer  52 , and patterned to expose portions of polymer layer  52 , as illustrated in  FIG. 2H . 
     An anisotropic etch is then performed to selectively etch the exposed portions of polymer layer  52 . For example, a plasma or wet anisotropic etching process removes portions of layer  52  to form an annular trench-shaped cavity  56  into the upper surface of layer  44  (i.e. in the form of a ring around the optical area). After the photo-resist  54  is removed, a photo-resist layer  58  is deposited over the structure (including inside cavity  56 ). A photolithography process is used to remove selective portions of photo-resist layer  56  (along the inner sidewall of cavity  56 , and that portion on the upper surface of polymer layer  52  that is adjacent the inner sidewall of cavity  56 ), as illustrated in  FIG. 2I . An isotropic etching process, such as a wet bath of polymer etch agent, is used to dissolve exposed portions of polymer layer  52 , creating a curved inner-sidewall  56   a  to cavity  56 . The resulting structure is illustrated in  FIG. 2J  (after photo-resist  58  is removed). The curvature and angle of the inner-sidewall  56   a  of cavity  56  can be controlled by the thickness of polymer layer  52 , the pattern of photo-resist  58 , and the etch material. Surface  56   a  defines the lens surface. 
     A soft isotropic etch can be performed to smooth out any roughness on surface  56   a , as well as any steps or gaps between polymer layers  16 / 44 / 52 . A similar surface polishing may be (i.e. optional) performed on the lens backside (i.e. the bottom surface of polymer layer  16  abutting carrier  10  after removal from the carrier  10 ). 
     Surface  56   a  can be optionally coated with an IR coating, and the back surface of polymer layer  16  (i.e. bottom surface of polymer layer  16  abutting the carrier  10 ) can be optionally coated with an AR coating, as described above. Alignment marks  32  can be formed on or in the top surface of polymer layer  52  as described above, and shown in  FIGS. 2K and 2L . Alignment marks  32  could additionally or alternately be formed on or in the bottom surface of polymer layer  16 . 
     The carrier  10  is then removed, and the structure is then diced along dicing lines  34  illustrated in  FIG. 2M  to separate each of the individual lenses  60 . The final lens  60  is illustrated in  FIG. 2N . In this embodiment, lens  60  is a substrate formed of discrete layers of polymer material. Not only can non-planar lens surface  56   a  be precisely shaped and formed to provide the desired focusing effects, but the abutting non-planar surfaces of discretely formed layers  16  and  44 , and the abutting non-planar surfaces of discretely formed layers  44  and  52 , can provide additional light focusing effects when the layers  16 ,  44  and/or  52  are formed of different materials with different light propagating properties (e.g. different effective indices of refraction). 
     Lens assemblies can be formed by stacking a plurality of lenses of similar or dissimilar design to achieve the light focusing performance required for the particular application. For example,  FIG. 3  illustrates five lenses  62   a - 62   e  stacked together using bonding material  64  to form a lens assembly  66 . The number of lenses  62  and lens shapes can vary depending upon the performance requirements of the design. Bonding material  64  can be a polymer, epoxy based, a resin, a metal or any other appropriate bonding material. Preferably, epoxy based adhesive  64  is applied to the non-alignment mark side of lenses  62   a - 62   e . A stacking tool with an alignment camera can be used to align the alignment marks  32  before bonding the lenses  62   a - 62   e  together. 
     After completing the lens stacking and bonding process, a light shielding layer  68  is deposited on the lens stack sidewalls (i.e. extending around and between the outer edges of the lenses), as illustrated in  FIG. 4  (i.e. for lenses having a round outer edge, layer  68  would be in the form of a cylinder). Light shielding layer  68  can be polymer, epoxy based, resin, paint, tape, metal, plastic/metallic enclosure or any other non-transparent material(s). Preferably, light shielding layer  68  is at least 5 μm in thickness and made of polymer based material such as black solder mask. 
       FIG. 5  illustrates the lens assembly  66  bonded to a CMOS image sensor assembly  70  via bond joints  71 . Bond joints  71  can be a polymer, epoxy based, resin, metallic or any other bonding material. Preferably, bond joints  71  are an epoxy based adhesive that is deposited on the bottom side of lens module  66 , where the lens module  66  is then picked up and placed on the CMOS image sensor assembly  70  for bonding. Image sensor assembly  70  generally includes photo detectors  72 , circuitry  74 , color filters  76 , microlenses  78 , contact pads  80 , wires  82 , contact pads  84  and a circuit board  86 . A more detailed discussion of image sensor assembly  70  can be found in co-pending U.S. patent application Ser. No. 13/343,682, which is incorporated herein by reference for all purposes. 
     It is to be understood that the present invention is not limited to the embodiment(s) described above and illustrated herein, but encompasses any and all variations falling within the scope of the appended claims. For example, while lens  36 / 60  are shown and described with three polymer layers, they can contain N polymer layers, where N is any integer 2 or greater. References to the present invention herein are not intended to limit the scope of any claim or claim term, but instead merely make reference to one or more features that may be covered by one or more of the claims. Materials, processes and numerical examples described above are exemplary only, and should not be deemed to limit the claims. Further, as is apparent from the claims and specification, not all method steps need be performed in the exact order illustrated or claimed, but rather in any order that allows the proper formation of the multi-layer lens of the present invention. Lastly, single layers of material could be formed as multiple layers of such or similar materials, and vice versa. 
     It should be noted that, as used herein, the terms “over” and “on” both inclusively include “directly on” (no intermediate materials, elements or space disposed therebetween) and “indirectly on” (intermediate materials, elements or space disposed therebetween). Likewise, the term “adjacent” includes “directly adjacent” (no intermediate materials, elements or space disposed therebetween) and “indirectly adjacent” (intermediate materials, elements or space disposed there between), “mounted to” includes “directly mounted to” (no intermediate materials, elements or space disposed there between) and “indirectly mounted to” (intermediate materials, elements or spaced disposed there between), and “electrically coupled” includes “directly electrically coupled to” (no intermediate materials or elements there between that electrically connect the elements together) and “indirectly electrically coupled to” (intermediate materials or elements there between that electrically connect the elements together). For example, forming an element “over a substrate” can include forming the element directly on the substrate with no intermediate materials/elements therebetween, as well as forming the element indirectly on the substrate with one or more intermediate materials/elements therebetween.