Patent Publication Number: US-2015070532-A1

Title: Solid state imaging device and method for manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2013-189393, filed on Sep. 12, 2013; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a solid sate imaging device and a method for manufacturing the same. 
     BACKGROUND 
     High definition is desirable in a solid state imaging device such as, for example, a CMOS image sensor, a CCD image sensor, etc. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view showing a solid state imaging device according to a first embodiment; 
         FIG. 2  is a schematic plan view showing the solid state imaging device according to the first embodiment; 
         FIG. 3  is a flowchart showing operations of the solid state imaging device according to the first embodiment; 
         FIG. 4  is a schematic cross-sectional view showing a solid state imaging device according to the first embodiment; 
         FIG. 5  is a schematic cross-sectional view showing a solid state imaging device according to the first embodiment; 
         FIG. 6  is a schematic cross-sectional view showing a solid state imaging device according to the first embodiment; 
         FIG. 7  is a flowchart showing a method for manufacturing a solid state imaging device according to a second embodiment; 
         FIG. 8A  to  FIG. 8C  are schematic cross-sectional views in order of the processes, showing the method for manufacturing the solid state imaging device according to the second embodiment; 
         FIG. 9  is a flowchart showing the method for manufacturing the solid state imaging device according to the second embodiment; and 
         FIG. 10A  to  FIG. 10C  are schematic cross-sectional views in order of the processes, showing the method for manufacturing the solid state imaging device according to the second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     According to one embodiment, a solid state imaging device includes an imaging substrate unit, a lens unit, and a color filter unit. The imaging substrate unit has a major surface including a first region and a second region. The first region includes a plurality of pixels, and the second region includes a plurality of pixels. The lens unit is separated from the major surface in a first direction perpendicular to the major surface. The lens unit includes a first lens and a second lens. The first lens overlaps the plurality of pixels of the first region when projected onto the major surface. The second lens overlaps the plurality of pixels of the second region when projected onto the major surface. The color filter unit is provided between the imaging substrate unit and the lens unit and is separated from the imaging substrate unit. The color filter unit includes a first color filter and a second color filter. The first color filter is provided between the first region and the first lens and has a first color. The second color filter is provided between the second region and the second lens and has a second color different from the first color. 
     Various embodiments will be described hereinafter with reference to the accompanying drawings. 
     The drawings are schematic or conceptual; and the relationships between the thicknesses and widths of portions, the proportions of sizes between portions, etc., are not necessarily the same as the actual values thereof. Further, the dimensions and/or the proportions may be illustrated differently between the drawings, even for identical portions. 
     In the drawings and the specification of the application, components similar to those described in regard to a drawing thereinabove are marked with like reference numerals, and a detailed description is omitted as appropriate. 
     First Embodiment 
       FIG. 1  is a schematic cross-sectional view showing a solid state imaging device according to a first embodiment. 
       FIG. 2  is a schematic plan view showing the solid state imaging device according to the first embodiment. 
       FIG. 1  is a cross-sectional view along line A 1 -A 2  of  FIG. 2 . 
     As shown in  FIG. 1  and  FIG. 2 , the solid state imaging device  110  according to the embodiment includes an imaging substrate unit  10 , a lens unit  20 , and a color filter unit  30 . 
     The imaging substrate unit  10  includes multiple pixels  12 . The imaging substrate unit  10  has a major surface  10   a.  The multiple pixels  12  are disposed in a plane parallel to the major surface  10   a.    
     A direction perpendicular to the major surface  10   a  is taken as a Z-axis direction (a first direction D1). One direction perpendicular to the Z-axis direction is taken as an X-axis direction. A direction perpendicular to the Z-axis direction and the X-axis direction is taken as a Y-axis direction. 
     The major surface  10   a  includes, for example, multiple regions. The major surface  10   a  includes, for example, a first region  11   a,  a second region  11   b,  and a third region  11   c.    
     The first region  11   a  includes the multiple pixels  12 . The second region  11   b  includes the multiple pixels  12 . The third region  11   c  includes the multiple pixels  12 . 
     The pixel  12  includes, for example, a photodiode including a p-n junction. The configuration of the pixel  12  is arbitrary. The pixel  12  converts, for example, an optical signal of visible light and/or infrared light into an electrical signal. For example, a silicon substrate is used as the imaging substrate unit  10 . Other than the pixels  12 , a circuit unit including CMOS elements, etc., may be provided in the imaging substrate unit  10 . The circuit unit may include a signal processor  70  described below. 
     The lens unit  20  is separated from the major surface  10   a  in the first direction D1. The first direction D1 (the Z-axis direction) is perpendicular to the major surface  10   a.  The lens unit  20  includes multiple lenses  21   o  (e.g., a first lens  21   a,  a second lens  21   b,  a third lens  21   c,  etc.). 
     The first lens  21   a  overlaps the multiple pixels  12  of the first region  11   a  when projected onto the major surface  10   a . The second lens  21   b  overlaps the multiple pixels  12  of the second region  11   b  when projected onto the major surface  10   a . The third lens  21   c  overlaps the multiple pixels  12  of the third region  11   c  when projected onto the major surface  10   a.    
     The lenses  21   o  include a light-transmissive material. The lenses  21   o  are, for example, made of a light-transmissive resin. The resin  21   o  may be an acrylic resin, an epoxy resin, etc. Glass, etc., may be used as the lenses  21   o.    
     The color filter unit  30  is provided between the imaging substrate unit  10  and the lens unit  20 . The color filter unit  30  is separated from the imaging substrate unit  10 . The color filter unit  30  includes multiple color filters  31   o  (e.g., a first color filter  31   a,  a second color filter  31   b,  a third color filter  31   c , etc.). 
     The first color filter  31   a  is provided between the first region  11   a  and the first lens  21   a.  The first color filter  31   a  has a first color. 
     The second color filter  31   b  is provided between the second region  11   b  and the second lens  21   b.  The second color filter  31   b  has a second color. The second color is different from the first color. 
     The third color filter  31   c  is provided between the third region  11   c  and the third lens  21   c.  The third color filter  31   c  has a third color. The third color is different from the first color and different from the second color. 
     For example, the first color, the second color, and the third color correspond respectively to red, green, and blue. In the embodiment, the first color, the second color, and the third color are arbitrary. For example, the peak wavelength absorbed by the second color filter  31   b  is different from the peak wavelength absorbed by the first color filter  31   a.  For example, the peak wavelength absorbed by the third color filter  31   c  is different from the peak wavelength absorbed by the first color filter  31   a  and different from the peak wavelength absorbed by the second color filter  31   b.  For example, the peak wavelength transmitted by the second color filter  31   b  is different from the peak wavelength transmitted by the first color filter  31   a.  For example, the peak wavelength transmitted by the third color filter  31   c  is different from the peak wavelength transmitted by the first color filter  31   a  and different from the peak wavelength transmitted by the second color filter  31   b.    
     The color filter  31   o  includes, for example, a resin, and a colorant dispersed in the resin. The resin may, for example, be an acrylic resin, an epoxy resin, a polyimide resin, etc. For example, a pigment, a dye, etc., is used as the colorant. The thickness (the length along the Z-axis direction) of the color filter  31   o  is, for example, not less than 0.5 micrometers (μm) and not more than 5 μm. 
     A resin layer  41  is provided in the example. The resin layer  41  is provided between the imaging substrate unit  10  and the color filter unit  30 . The resin layer  41  is light-transmissive. The resin layer  41  includes an acrylic resin, an epoxy resin, etc. In the example, the refractive index of the resin layer  41  is about 1.5. 
     The color filter unit  30  is separated from the imaging substrate unit  10  by the resin layer  41 . Thereby, the lens unit  20  also is separated from the imaging substrate unit  10 . 
     A distance Ds1 along the first direction (the Z-axis direction) between the imaging substrate unit  10  and the lens unit  20  is, for example, not less than 10 μm and not more than 80 μm. In the example, the distance Ds1 is not less than 45 μm and not more than 55 μm (about 50 μm). 
     As shown in  FIG. 2 , the multiple lenses that are included in the lens unit  20  are disposed in a hexagonal configuration. The embodiment is not limited thereto; and the disposition and planar configuration of the multiple lenses are arbitrary. 
     In the example, the size of the second lens  21   b  is the same as the size of the first lens  21   a.  In the example, the size of the third lens  21   c  is the same as the size of the first lens  21   a.    
     The size (the width) of the lens  21   o  of the lens unit  20  is larger than the size of the pixel  12 . One direction perpendicular to the first direction D1 is taken as a second direction D2. The second direction D2 is parallel to the major surface  10   a.  In the example, the width of the lens  21   o  is a maximum in the second direction D2. 
     A lens length L1 is the length along the second direction D2 of the lens  21   o  (e.g., the first lens  21   a ). The lens length L1 is, for example, not less than 10 μm and not more than 100 μm. In the example, the lens length L1 is not less than 25 μm and not more than 35 μm (e.g., 30 μm). 
     On the other hand, a pixel length d1 is the length along the second direction of each of the multiple pixels  12 . The pixel length d1 is, for example, not less than 0.5 μm and not more than 3 μm. In the example, the pixel length d1 is, for example, not less than 1.0 μm and not more than 1.5 μm (e.g., 1.4 μm). 
     A pixel pitch p1 is the pitch of the multiple pixels  12  in the second direction. The pixel pitch p1 is, for example, not less than 1 μm and not more than 5 μm. In the example, the pixel pitch p1 is, for example, not less than 2.0 μm and not more than 3.0 μm (e.g., 2.8 μm). 
     For example, the lens length L1 is not less than 6 times and not more than 100 times the pixel length d1. In the example, the lens length L1 is not less than 7 times and not more than 72 times the pixel length d1. 
     For example, the lens length L1 is not less than 3 times and not more than 50 times the pixel pitch p1. 
     For example, the distance Ds1 is not less than 0.5 times and not more than 5 times the lens length L1. 
     In the solid state imaging device  110  according to the embodiment, the light passes through the lens unit  20  and the color filter unit  30  to be incident on the pixels  12 . The electrical signals obtained at the pixels  12  change according to the intensity of the light incident on the pixels  12 . 
       FIG. 3  is a flowchart showing operations of the solid state imaging device according to the first embodiment. 
       FIG. 3  shows processing implemented by the signal processor  70  (referring to  FIG. 1 ). 
     As shown in  FIG. 3 , in the embodiment, an image is generated based on luminance information (step S 10 ). Then, color information is added to the generated image data (step S 20 ). 
     For example, the signal processor  70  implements first processing. In the first processing, the image data is generated based on the first luminance information included in the first signals obtained from the multiple pixels  12  included in the first region  11   a  and the second luminance information included in the second signals obtained from the multiple pixels  12  included in the second region  11   b.  The signal processor  70  further implements second processing. In the second processing, the color information is added to the generated image data. 
     For example, a reference example may be considered in which the distance information is reconfigured by deriving differences of the data corresponding to mutually-adjacent microlenses based on the luminance information and the color information. In such a case, the processing is complex because data processing relating to the color information should be performed. 
     Conversely, in the embodiment, first, the image data is generated by reconfiguring the distance information based on the luminance information. The color information is added subsequently. Thereby, the processing when reconfiguring is simple and advantageous. 
     In the solid state imaging device  110  according to the embodiment, one color filter  31   o  is provided to have a large surface area that includes multiple pixels  12 . The effect of the error of the position of the color filter  31   o  on the detection signal is small. 
     For example, there is a reference example in which the color filters are provided to correspond respectively to the pixels  12 . In such a case, the pitch of one color filter is the same as the pixel pitch. Color mixing occurs easily in the case where the positional precision of the color filters is low. The color mixing becomes pronounced as the pixels have higher definition. Accordingly, high definition is difficult in such a reference example. 
     On the other hand, in the embodiment, one color filter  31   o  is provided to have a large surface area that includes multiple pixels  12 . The positional shift of the one color filter  31   o  for one pixel  12  is reduced. Therefore, the color mixing due to the error of the position of the color filter  31   o  is suppressed. In other words, in the embodiment, the color mixing does not occur easily even in the case where the pixels  12  are small. According to the embodiment, high definition is easy to obtain because the color mixing is suppressed. 
     In the embodiment as shown in  FIG. 1 , the upper surfaces of the lenses  21   o  have protruding configurations; and the lower surfaces of the lenses  21   o  are planes. In other words, the first lens  21   a  has a first surface  21   aa  and a second surface  21   ab . The first surface  21   aa  opposes the color filter unit  30 . The second surface  21   ab  is on the side opposite to the first surface  21   aa . The first surface  21   aa  is parallel to the major surface  10   a.  The first surface  21   aa  is a plane. The second surface  21   ab  includes a portion having a curved surface. 
     The first surface  21   aa  is a plane; and the color filter  31   o  also has a planar configuration. The thickness of the color filter  31   o  is substantially uniform in the surface (in the X-Y plane). The optical characteristics (e.g., the color) of the color filter  31   o  can easily be set to be uniform inside the surface. 
     In the embodiment, the light that passes through a first portion inside the surface of one color filter  31   o  is incident on one of the multiple pixels  12 . The light that passes through a second portion inside the surface of the one color filter  31   o  is incident on one other of the multiple pixels  12 . The color of the light incident on the multiple pixels  12  is made uniform by increasing the uniformity of the color inside the surface of the one color filter  31   o.  Thereby, imaging having good color characteristics is possible. 
       FIG. 4  is a schematic cross-sectional view showing another solid state imaging device according to the first embodiment. 
       FIG. 4  is a cross-sectional view corresponding to line A 1 -A 2  of  FIG. 2 . 
     In the solid state imaging device  111  according to the embodiment as shown in  FIG. 4 , a microlens unit  50  is further provided in addition to the imaging substrate unit  10 , the lens unit  20 , and the color filter unit  30 . The microlens unit  50  is provided between the imaging substrate unit  10  and the color filter unit  30 . Otherwise, the solid state imaging device  111  is similar to the solid state imaging device  110 . 
     The microlens unit  50  includes multiple microlenses  52 . The multiple microlenses  52  are disposed respectively between the color filter unit  30  and the multiple pixels  12 . 
     In the example, the resin layer  41  is provided; and the microlens unit  50  is provided between the imaging substrate unit  10  and the resin layer  41 . The multiple microlenses  52  are disposed respectively between the resin layer  41  and the multiple pixels  12 . 
     The microlenses  52  concentrate the light onto, for example, the photosensitive portions of the pixels  12 . Thereby, the sensitivity increases. 
     The refractive index of the multiple microlenses  52  is higher than, for example, the refractive index of the resin layer  41 . Thereby, the light can be concentrated by utilizing the refraction effect of the light. 
     For example, the refractive index of the resin layer  41  is about 1.5. In such a case, the refractive index of the microlenses  52  is set to be higher than 1.5. For example, silicon nitride (or silicon oxynitride) or the like is used as the microlenses  52 . In such a case, the refractive index of the microlenses  52  is about 2.2. 
     In the solid state imaging device  111  as well, a solid state imaging device in which high definition is possible can be provided. The sensitivity can be increased by providing the microlenses  52 . 
       FIG. 5  is a schematic cross-sectional view showing another solid state imaging device according to the first embodiment. 
       FIG. 5  is a cross-sectional view corresponding to line A 1 -A 2  of  FIG. 2 . 
     In the solid state imaging device  112  according to the embodiment as shown in  FIG. 5  as well, the imaging substrate unit  10 , the lens unit  20 , and the color filter unit  30  are provided. In the example, the region between the imaging substrate unit  10  and the color filter unit  30  is a gap  42 . Otherwise, the solid state imaging device  112  is similar to the solid state imaging device  110 . 
     The region (the gap  42 ) between the imaging substrate unit  10  and the color filter unit  30  is filled with, for example, air, an inert gas, etc. 
     For example, the lens length L1 is about 30 μm in the example. In such a case, the distance Ds1 is about 30 μm. The distance Ds1 is, for example, not less than 25 μm and not more than 35 μm. The distance Ds1 is, for example, not less than 28 μm and not more than 32 μm. 
     In the solid state imaging device  112  as well, a solid state imaging device in which high definition is possible can be provided. 
       FIG. 6  is a schematic cross-sectional view showing another solid state imaging device according to the first embodiment. 
       FIG. 6  is a cross-sectional view corresponding to line A 1 -A 2  of  FIG. 2 . 
     In the solid state imaging device  113  according to the embodiment as shown in  FIG. 6 , the region between the imaging substrate unit  10  and the color filter unit  30  is the gap  42 . Also, the microlens unit  50  is provided. Otherwise, the solid state imaging device  113  is similar to the solid state imaging device  110 . 
     In the solid state imaging device  113  as well, a solid state imaging device in which high definition is possible can be provided. 
     Second Embodiment 
     The embodiment relates to a method for manufacturing a solid state imaging device. 
       FIG. 7  is a flowchart showing the method for manufacturing the solid state imaging device according to the second embodiment. 
     In the manufacturing method according to the embodiment as shown in  FIG. 7 , the resin layer  41  is formed (step S 110 ). Then, the color filter unit  30  is formed (step S 120 ). Then, the lens unit  20  is formed (step S 130 ). An example of such processing will now be described. 
       FIG. 8A  to  FIG. 8C  are schematic cross-sectional views in order of the processes, showing the method for manufacturing the solid state imaging device according to the second embodiment. 
     As shown in  FIG. 8A , the imaging substrate unit  10  includes the first region  11   a  including the multiple pixels  12 , and the second region  11   b  including the multiple pixels  12 . The resin layer  41  that is light-transmissive is formed on the major surface  10   a  of the imaging substrate unit  10 . 
     As shown in  FIG. 8B , the color filter unit  30  is formed on the resin layer  41 . The color filter unit  30  includes the first color filter  31   a  and the second color filter  31   b.  The first color filter  31   a  overlaps the first region  11   a  when projected onto the major surface  10   a.  The first color filter  31   a  has the first color. The second color filter  31   b  overlaps the second region  11   b  when projected onto the major surface  10   a.  The second color filter  31   b  has the second color that is different from the first color. 
     As shown in  FIG. 8C , the lens unit  20  is formed on the color filter unit  30 . The lens unit  20  includes the first lens  21   a  and the second lens  21   b.  The first lens  21   a  overlaps the first region  11   a  when projected onto the major surface  10   a.  The second lens  21   b  overlaps the second region  11   b  when projected onto the major surface  10   a.    
     In the manufacturing method, the color filter  31   o  that has a large size is formed to include the multiple pixels  12 . The positional precision of the color filter  31   o  is relaxed; and the productivity increases. 
     Any method such as printing, spin coating, etc., may be used to form the resin layer  41 . For example, photolithography may be used to form the resin layer  41 . For example, photolithography, imprinting, etc., may be used to form the lens unit  20 . 
     An example of the method for forming the lens unit  20  will now be described. Imprinting is used in this method. 
       FIG. 9  is a flowchart showing the method for manufacturing the solid state imaging device according to the second embodiment. 
     As shown in  FIG. 9 , in the formation of the lens unit  20  in the manufacturing method according to the embodiment, a resin film is formed (step S 131 ). Then, an unevenness is formed in the resin film (step S 132 ). Then, the resin film is cured (step S 133 ). An example of such processing will now be described. 
       FIG. 10A  to  FIG. 10C  are schematic cross-sectional views in order of the processes, showing the method for manufacturing the solid state imaging device according to the second embodiment. 
     As shown in  FIG. 10A , a resin film  22  is formed on the color filter unit  30 . The resin film  22  is used to form the lenses  21   o  (the first lens  21   a,  the second lens  21   b,  the third lens  21   c , etc.) 
     A mold  60  is prepared as shown in  FIG. 10B . An unevenness  61  is provided in the mold  60 . The configuration of the unevenness  61  corresponds to the configurations of the lenses  210  (the first lens  21   a,  the second lens  21   b,  the third lens  21   c,  etc.). The unevenness  61  of the mold  60  is caused to contact the resin film  22 . 
     As shown in  FIG. 10C , an unevenness  23  that reflects the unevenness  61  is formed in the surface of the resin film  22 . The unevenness  23  of the resin film  22  includes a first lens-shaped unevenness  24   a,  a second lens-shaped unevenness  24   b,  a third lens-shaped unevenness  24   c,  etc. 
     The lenses  210  are formed by curing the resin film  22 . In other words, the first lens  21   a  is formed from the first lens-shaped unevenness  24   a.  The second lens  21   b  is formed from the second lens-shaped unevenness  24   b.  The third lens  21   c  is formed from the third lens-shaped unevenness  24   c.    
     For example, at least one selected from heating and light irradiation is implemented in the curing. The processing of the curing includes processing according to the characteristics of the resin film  22 . At least a portion of the curing is performed, for example, in the state in which the unevenness  61  contacts the resin film  22 . At least a portion of the curing may be performed, for example, in the state in which the unevenness  61  is separated from the resin film  22 . 
     In the example, the formation of the lens unit  20  includes imprinting. In the embodiment, the size of the lens  21   o  is larger than the size of the pixel  12 . Therefore, the precision is relaxed in the formation of the lens  21   o.  Therefore, a method having high productivity can be used. 
     In the embodiment, a solid state imaging device in which high definition is possible can be manufactured with high productivity. 
     According to the embodiments, a solid state imaging device in which high definition is possible and a method for manufacturing the solid state imaging device can be provided. 
     Hereinabove, embodiments of the invention are described with reference to specific examples. However, the embodiments of the invention are not limited to these specific examples. For example, one skilled in the art may similarly practice the invention by appropriately selecting specific configurations of components included in the solid state imaging device such as the imaging substrate unit, the pixel, the microlens, the color filter unit, the color filter, the lens unit, the lens, the signal processor, etc., from known art; and such practice is within the scope of the invention to the extent that similar effects can be obtained. 
     Further, any two or more components of the specific examples may be combined within the extent of technical feasibility and are included in the scope of the invention to the extent that the purport of the invention is included. 
     Moreover, all solid state imaging devices practicable by an appropriate design modification by one skilled in the art based on the solid state imaging devices described above as embodiments of the invention also are within the scope of the invention to the extent that the spirit of the invention is included. 
     Various other variations and modifications can be conceived by those skilled in the art within the spirit of the invention, and it is understood that such variations and modifications are also encompassed within the scope of the invention.