Patent Publication Number: US-2013242149-A1

Title: Solid-state imaging element and method for manufacturing same

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation application of PCT Application No. PCT/JP2011/004340 filed Jul. 29, 2011, designating the United States of America, the disclosure of which, including the specification, drawings and claims, is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a solid-state imaging device having microlenses formed on color filters and also relates to a method for manufacturing such a solid-state imaging device. 
     DESCRIPTION OF THE RELATED ART 
     Solid-state imaging devices are employed in digital still cameras, digital movie cameras, camera-equipped mobile phones, and so on. With the prevalence of these devices, there is a growing demand that solid-state imaging devices offer higher resolution and have a greater number of pixels. In response to this demand, an effort is underway to make pixels smaller and smaller. 
     Generally, a solid-state imaging device has: a semiconductor substrate in which a matrix of photoelectric converters is disposed, a transparent insulating layer having wiring liens embedded therein and disposed on the semiconductor substrate; color filters of colors determined for the respective photoelectric converters; and a plurality of microlenses disposed on the respective color filters (see Patent Literature 1, for example). A microlens is a convex lens for collecting incident light. Conventionally, microlenses are manufactured by a method involving a thermal reflow process in which, for example, a transparent resin material is melted by heat and then the surface tension of the molten material forms the curved surface of a lens. 
     The progress toward smaller pixels in recent years has also accelerated the progress toward smaller microlenses, as small as the order of a few micrometers in lens diameter. 
     CITATION LIST 
     Patent Literature 
     
         
         [Patent Literature 1] 
         Japanese Patent Application Publication No. 3-183165 
       
    
     SUMMARY 
     In order to collect incident light to the photoelectric converters, desirable solid-state imaging devices are configured such that each microlens has a focus within the corresponding photoelectric converter disposed in the semiconductor substrate. 
     However, since the curved surfaces of the microlenses are formed through the thermal reflow process, it is difficult to control the formation of the microlenses to obtain a precise shape. Therefore, there may a case where the focus of a microlens falls in the corresponding color filter, which is located above the transparent insulating layer having wiring embedded therein. Naturally, light incident on a microlens is once converged and then diverged after it passes through the focus of the microlens. Therefore, when the focus is positioned in the color filter, a problem arises that divergence of light after it exits from the color filter becomes large. 
     This increase the risk of a phenomenon called “color crosstalk”, which is caused when the light exits from the color filter travels toward the wiring lines embedded in the transparent insulating layer and is reflected by the wiring liens to fall on the adjacent photoelectric converter. In the case where the solid-state imaging device is a CCD solid-state imaging device, the above problem leads to another risk that light may enter the vertical CCDs provided adjacent to each array of photoelectric converters, which results in occurrence of a phenomena called smear. 
     The present disclosure is made in view of the above and aims to provide a solid-state imaging device capable of suppressing divergence of light after the light exits a color filter, even if the focus of a microlens falls in the color filter. The present disclosure also aims to provide a method for manufacturing such a solid-state imaging device. 
     In order to solve the problems noted above, one aspect of the present disclosure provides a solid-state imaging device including: a semiconductor substrate including a matrix of photoelectric converters disposed therein; a transparent insulating layer disposed on the semiconductor substrate and including wiring lines embedded therein; a color filter layer disposed on the transparent insulating layer and including a color filter for each of a plurality of colors of the respective photoelectric converters; and a plurality of microlenses disposed on the color filter layer, one for each color filter. In a plan view, the color filter of at least one color is smaller in area size than the corresponding microlens. In the color filter layer, the color filter of the at least one color is surrounded by a low-refractive-index material having a lower refractive index than a refractive index of the color filter. 
     In another aspect, the present disclosure provides a manufacturing method for a solid-state imaging device, the manufacturing method including: a first step of forming a matrix of photoelectric converters in a semiconductor substrate; a second step of forming, on the semiconductor substrate, a transparent insulating layer containing wiring lines embedded therein; a third step of forming, on the transparent insulating substrate, a color filter layer including a color filter for each of a plurality of colors of the respective photoelectric converters; and a fourth step of forming a plurality of microlenses, one for each color filter. The third step includes: a step of forming the color filters each in a size smaller than the corresponding microlens in a plan view; and a step of disposing a low-refractive-index material to surround each color filter, the low-refractive-index material having a refractive index lower than a refractive index of the color filter. 
     In the solid-state imaging device having the above structure, the color filters of at least one color are each surrounded by a low-refractive-index material having a refractive index of the color filters themselves. Hence, the color filters of at least one color each act as a waveguide. 
     Therefore, even if the focus of a microlens is within such a color filter, light once converged at the focus is guided downward through the color filter. As a result, the divergence of light is suppressed as compared with the case where light diverges immediately after passing through the focus. 
     Consequently, the amount of light traveling toward wiring lines embedded in the transparent insulating layer is reduced, which is effective to suppress occurrence of color crosstalk resulting from light reflected by the wiring lines toward adjacent photoelectric converters. In addition, in the case of CCD solid-state imaging devices, the above structure is also effective to suppress occurrence of smear. 
     The manufacturing method for a solid-state imaging device having the above structure achieves the same advantageous effect as those achieved by the solid-state imaging device described above. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIGS. 1A-1C  are views showing a structure of a solid-state imaging device according to a first embodiment of the present disclosure. 
         FIG. 2A  is a view illustrating how light diverges after passing through the focus in a conventional solid-state imaging device, and  FIG. 2B  is a view illustrating how light diverges after passing through the focus in the solid-state imaging device of the first embodiment. 
         FIGS. 3A and 3B  are sectional views showing the electric field intensity distributions indicating the result of simulation run to confirm an effect to suppress divergence of light. 
         FIGS. 4A and 4B  are views illustrating steps of a manufacturing method for the solid-state imaging device according to the first embodiment of the present disclosure. 
         FIGS. 5A and 5B  are views illustrating subsequent steps of the manufacturing method shown in  FIGS. 4A and 4B . 
         FIGS. 6A and 6B  are views illustrating subsequent steps of the manufacturing method shown in  FIGS. 5A and 5B . 
         FIGS. 7A and 7B  are views illustrating subsequent steps of the manufacturing method shown in  FIGS. 6A and 6B . 
         FIGS. 8A and 8B  are views illustrating subsequent steps of the manufacturing method shown in  FIGS. 7A and 7B . 
         FIGS. 9A and 9B  are views illustrating subsequent steps of the manufacturing method shown in  FIGS. 8A and 8B . 
         FIGS. 10A-10C  are views showing a structure of a solid-state imaging device according to a second embodiment of the present disclosure. 
         FIGS. 11A and 11B  are views illustrating steps of a manufacturing method for the solid-state imaging device according to the second embodiment of the present disclosure. 
         FIGS. 12A and 12B  are views illustrating subsequent steps of the manufacturing method shown in  FIGS. 11A and 11B . 
         FIGS. 13A-13C  are views showing a structure of a solid-state imaging device according to a third embodiment of the present disclosure. 
         FIGS. 14A-14C  are views showing a structure of a solid-state imaging device according to a fourth embodiment of the present disclosure. 
         FIGS. 15A-15C  are views showing a structure of a solid-state imaging device according to a fifth embodiment of the present disclosure. 
         FIGS. 16A-16C  are views showing a structure of a solid-state imaging device according to a sixth embodiment of the present disclosure. 
         FIGS. 17A-17C  are views showing a structure of a solid-state imaging device according to a seventh embodiment of the present disclosure. 
         FIG. 18  is a sectional view showing the electric field intensity distributions indicating the result of simulation run to confirm an effect to suppress divergence of light. 
     
    
    
     DETAILED DESCRIPTION 
     The following specifically describes embodiments of the present disclosure, with reference to the accompanying drawings. 
     First Embodiment 
     Overall Structure 
     A solid-state imaging device according to a first embodiment of the present disclosure is a CCD solid-state imaging device and includes a matrix of pixels, such as 2048×1536 pixels (about three million pixels), for example. 
       FIG. 1A  is a top view showing part of the solid-state imaging device according to the first embodiment. More specifically, a region corresponding 2×2 pixels are shown, out of the plurality of pixels.  FIG. 1B  is a sectional view taken along the arrowed line A 1 -A 1  of  FIG. 1A , whereas  FIG. 1C  is a sectional view taken along the arrowed line B 1 -B 1  of  FIG. 1A . 
     As shown in  FIG. 1A , the solid-state imaging device  1  has red pixels  30 R, green pixels  30 Gr and  30 Gb, and blue pixels  30 B. These pixels  30 R,  30 Gr,  30 Gb, and  30 B are arranged in a Bayer array. 
     As shown in  FIGS. 1B and 1C , the solid-state imaging device  1  includes a silicon substrate  2 , which is a semiconductor substrate. The silicon substrate  2  has an N-type region  2   a  and a P-type well region  2   b  that is on the N-type region  2   a.    
     The P-type well region  2   b  has a two-layer structure formed form a first well region  2   b   1  on the N-type region  2   a  and a second well region  2   b   2  on the first well region  2   b   1 . Disposed in the second well region  2   b   2  are photodiodes  3 , transfer channels  4 , Vt control regions  5 , channel stop regions  6 , and P+ layers  7 . 
     The photodiodes  3  are arranged in a matrix. The transfer channels  4  are shaped into straight lines and disposed adjacent to the respective arrays of the photodiodes  3 . The transfer channels  4  constitute part of vertical CCDs. 
     Each Vt control region  5  is disposed between a photodiode  3  and a transfer channel  4  adjacent to the photodiode  3 . Each channel stop region  6  is disposed at the side of a photodiode  3  opposite from the Vt control region  5 . The P+ layers  7  are disposed on the respective photodiodes  3  to extend internally along the upper surface of the silicon substrate  2 . 
     An insulating film  8  made from silicon oxide is disposed on the silicon substrate  2 . On the insulating film  8 , transfer electrodes  9  are disposed one for each photodiode  3  and at a location corresponding to a gap between two adjacent arrays of the photodiodes  3 . Together with the transfer channels  4  of each array, the transfer electrodes  9  in the corresponding array constitute the vertical CCDs. 
     A transparent insulating layer  10  made from silicon oxide is disposed on the transfer electrodes  9  and the insulating film  8 . In the transparent insulating layer  10 , first wiring lines  11  and second wiring lines  12  are embedded. 
     The first wiring lines  11  are provided for the respective rows of the transfer electrodes  9 . To read out signal charge generated by the photodiodes  3 , a drive pulse is applied to the respective transfer electrodes  9  via the first wiring lines  11 . The second wiring lines  12  are provided for the respective first wiring lines  11  and connected in parallel to the respective first wiring line  11 . 
     The first and second wiring lines  11  and  12  are made of copper and coated with a barrier film  13 . The barrier film  13  is provided for preventing copper contained in the wiring lines  11  and  12  from diffusing into silicon oxide constituting the transparent insulating layer  10 . 
     A color filter layer  20  is disposed on the transparent insulating layer  10 , and the color filter layer  20  includes color filters  21 R,  21 Gr,  21 Gb, and  21 B provided for the respective photodiodes  3 . In the following description, the color filters  21 R,  21 Gr,  21 Gb, and  21 B may be collectively referred to as the “color filters  21 ”. 
     Disposed on the color filter layer  20  are microlenses  14  provided for the respective color filters  21 . 
     &lt;Structure of Microlenses&gt; 
     Each microlens  14  is a convex lens formed from a transparent resin material by a thermal reflow process. The microlens  14  has a diameter d 1  that measures 1.5 VIM. 
     The microlens  14  has a curved surface, the shape of which is determined depending on the balance between the surface tension and the dead weight of the transparent resin material in the thermally molten state. That is, for a lens of a smaller diameter, the weight of the transparent resin material is lighter, which naturally leads a relatively greater surface tension. Thus, the surface (curvature) of the resulting lens approaches a spherical shape, which means that the focal length of the lens is shorter. 
     To collect light to the photodiodes  3 , it is ideal that the focus position of each microlens  14  is located in a photodiode  3 . According to the present embodiment, however, the diameter d 1  of each microlens  14  is as short as 1.5 μm and the focal length is shorter than the distance from the microlens  14  to the photodiode  3 . That is to say, the position of the focus F 1  of the microlens  14  is not within the photodiode  3  but above the photodiode  3 . The description of the present embodiment is given on condition that the position of the focus F 1  of each microlens  14  is in a corresponding one of the color filters  21 . 
     In the case where light converges to one point, the term “focus of a microlens” refers to that point. In the case where light does not converges to one point due to spherical aberration of the lens, the term refers to a central point of where the light most tightly converges. 
     &lt;Structure of Color Filters&gt; 
     The following now describes the color filter layer  20 . 
     The color filters  21 R,  21 Gr,  21 Gb, and  21 B all have the same dimensions and a square shape in a plan view. The width w 1  of the squared shaped color filters  21 R,  21 Gr,  21 Gb, and  21 B is smaller than the diameter d 1  of the microlenses  14 . 
     In the color filter layer  20 , each color filter  21  is surrounded on the four sides by a low-refractive-index material  22 , which is a material having a refractive index lower than that of the color filters  21 . With this arrangement, the color filters  21  act as waveguides that guide light incident on the respective color filters  21  to a downward position by confining the light due to total reflection or Fresnel reflection at the boundaries with the low-refractive-index material  22 . 
     In one example, the color filters  21  are made from an organic material containing pigments dispersed therein, and the low-refractive-index material  22  is a transparent material such as organic glass material. 
     In the present embodiment, the refractive index of the color filters  21  is in the range of 1.4 to 1.9, while the refractive index of the low-refractive-index material  22  is in the range of 1.0 to 1.2. 
     In addition, the central axis c 1  of each color filter  21  is set to be coaxial with the optical axis c 2  of the corresponding microlens  14  and also with the central axis c 3  of the corresponding photodiode  3  (see the pixel  30 Gb shown in  FIG. 1B ). Note that the optical axis c 2  is set to pass the center of the microlens  14  in a plan view (i.e., the areal gravity center of the microlens  14 ) and to be perpendicular to the upper surface of the silicon substrate  2 . 
     The “central axis c 1  of a color filter  21 ” refers to the axis that passes through the center of the color filter  21  in a plan view (i.e., the areal gravity center of the color filter  21 ) and is perpendicular to the upper surface of the silicon substrate  2 . In addition, the “central axis c 3  of a photodiode  3 ” refers to the axis that passes through the center of the photodiode  3  in a plan view (i.e., the areal gravity center of the photodiode  3 ) and is perpendicular to the upper surface of the silicon substrate  2 . 
     In addition, the phrase that “the central axis c 1  is coaxial with the optical axis c 2  and the central axis c 3 ” encompasses not only the positional relation in which the central axis c 1  is completely coaxial with the optical axis c 2  and the central axis c 3  but also the positional relation involving some deviation due to, for example, manufacturing errors, despite that the intended designed is to have the completely coaxial positional relation. Note that the all of the pixels of the solid-state imaging device  1  may be designed to ensure that “the central axis c 1  is coaxial with the optical axis c 2  and the central axis c 3 ” or alternatively, such design may be applied only to some of pixels of the solid-state imaging device  1 . Suppose, for example, that the solid-state imaging device  1  is applied to a digital camera. In this case, it is preferable that some of the pixels of the solid-state imaging device  1 , more specifically, those pixels located in a central region of the pixel matrix have the completely coaxial positional relation. In this case, it is also preferable that the rest of the pixels (those located in the peripheral region of the pixel matrix) be structured such that the optical axis c 2  is inclined relative to the central axes c 1  and c 3  by 8 degrees or so, in consideration of the fact that light from the camera lens enters those peripheral pixels at an angle. 
     According to the present embodiment, the width w 1  of the color filters  21  is in a range of 0.4 to 1.0 μm, which is smaller than the diameter d 1 , and the thickness t 1  of the color filters  21  is in a range of 0.4 to 0.9 μm. 
     Here, the width w 1  of the color filters  21  is not merely smaller than the diameter d 1 . Rather, the width w 1  is set to be the size comparable to the wavelength of visible light (0.4 to 1.0 μm). This arrangement is preferable in that propagation of light within the color filters  21  acting as waveguides is ensured to be single-mode propagation or nearly single-mode propagation. 
     ADVANTAGE 
     Even with the solid-state imaging device  1  having the above structure, it still holds that light once converged by each microlens  14  diverges after it passes through the focus F 1  located in the corresponding color filter  21 . Yet, since the color filters  21  are surrounded by the low-refractive-index material  22  and thus act as waveguides, the divergence of light passing through the color filters is smaller than that observed in a conventional solid-state imaging device. 
     This effect to suppress divergence of light is described in detail with reference to  FIG. 2 . 
       FIG. 2A  illustrates how light diverges after passing through the focus in a conventional solid-state imaging device.  FIG. 2B  illustrates how light diverges after passing through the focus in the solid-state imaging device  1  according to the present embodiment. The solid-state imaging devices shown in  FIGS. 2A and 2B  differ in the structure of the color filters and identical in the other respects. 
     The conventional solid-state imaging device  100  shown in  FIG. 2A  has a color filter  121  having a width equal to the diameter of the microlens  14 . That is, the color filter  121  is not constructed to act as a waveguide. The focus F 2  of the microlens  14  is located in the color filter  121 . In the conventional solid-state imaging device  100 , for example, rays of incident light L 2  pass through the focus F 2  and keep traveling straight. Therefore, rays of light converged to the focus F 2  by the microlens  14  diverge after passing through the focus F 2 . In the solid-state imaging device  1  according to the present embodiment, although rays of incident light L 1  are converged to the focus F 1  by the microlens  14  and then diverge, as shown in  FIG. 2B , the rays of incident light L 1  are thereafter reflected from the boundaries between the color filter  21  and the low-refractive-index material  22  due to total reflection or Fresnel reflection. That is, the divergence of light passing through the color filter is made smaller as compared with that observed in the conventional solid-state imaging device  100 . 
     As a consequence, the amount of light, such as the rays of incident light L 2  shown in  FIG. 2A , traveling toward the wiring lines  11  and  12  embedded in the transparent insulating layer  10  is reduced. This leads to suppress occurrences of color crosstalk resulting from that light is reflected by the wiring lines  11  and  12  and enters into an adjacent photodiode  3 . In addition, the amount of light traveling toward the transfer channel  4  of the vertical CCD that is adjacent to the photodiode  3  is also reduced. This leads to suppress occurrences of smear. It reversely means that the amount of light traveling toward the photodiode  3  is increased, so that the collection efficiency of light to the photodiode  3  is improved. 
     The following describes the result of simulation run to confirm the effect to suppress divergence of light. 
     This simulation was performed to obtain electric field intensity distributions of a working example that is a solid-state imaging device having a color filter acting as a waveguide and of a comparative example that is a solid-state imaging device having a color filter not acting as a waveguide. 
     More specifically, the electric field intensity distributions in a red pixel region exhibited upon receipt of red light (at a wavelength of 600 nm) were simulated on the respective solid-state imaging devices of the working example and comparative example. 
       FIGS. 3A and 3B  are obtained through the simulations. More specifically,  FIG. 3A  is a sectional view showing the electric field intensity distribution simulated for the comparative example, and  FIG. 3B  is a sectional view showing the electric field intensity distribution simulated for the working example. The vertical axis represents the height or equivalently the depth from the top surface of the silicon substrate. The horizontal axis represents the distance from the central axis c 1  of the photodiode  3 . 
     The respective solid-state imaging devices of the working example and the comparative example differ in the structure of the color filters and identical in the other respects. In addition, as shown in  FIG. 3B , the solid-state imaging device of the working example is basically identical in structure to the solid-state imaging device  1  shown in  FIGS. 1A-1C , except that intra-layer lenses  16  are embedded in the transparent insulating layer  10 . The solid-state imaging device of the comparative example also has intra-layer lenses  16  embedded in the transparent insulating layer  10 . Therefore, the presence of intra-layer lenses is considered to have no substantial impact on the comparison of the working example and the comparative example for their respective effects to suppress divergence of light. 
     The width w 1  of the color filter  21 R used in the working example is 0.75 μm. The width of the color filter  121 R used in the comparative example was equal to the diameter d 1  (1.5 μm) of the microlens  14 . In addition, the thickness t 1  of the color filters  21 R and  121 R was 0.75 μm. The refractive index of the color filters  21 R and  121 R was 1.6, and the refractive index of the low-refractive-index material  22  was 1.2. 
     In  FIGS. 3A and 3B , the electric field intensity distributions are shown by contour lines. In addition, to clearly show the region where the electric field intensity is high, “bold lines” are used to indicate the highest electric field intensity, “broken lines” are used to indicate the second-highest electric field intensity, and “thin lines” are used for all the other contour lines. In other words, a region bounded by a bold line is where the light intensity is highest. 
     First, the electric field intensity distribution of light within each color filter is discussed. 
     In the color filter  121 R of the comparative example shown in  FIG. 3A , regions s 4  and s 5  bounded by a bold line are where the electric field intensity is high. One of the regions s 4  and s 5  appears to surround the focus F 2 , and the other appears below the focus F 2 . On the other hand, in the color filter  21 R of the working example shown in  FIG. 3B , regions s 1 , s 2 , and s 3  bounded by a bold line are where the electric field intensity is high. One of the regions s 1 , s 2 , and s 3  appears to surround the focus F 1  and the others appear below the focus F 1 . The regions s 1 -s 3  are significantly larger in size than the regions s 4  and s 5  observed in the comparative example. This result indicates that the divergence of light was duly suppressed. More specifically, in the working example, the divergence of light having passed through the focus F 1  was suppressed, so that loss of light intensity within the color filter  21 R was prevented and hence the electric field intensity was maintained high. 
     Note that the focus F 1  of the working example is at a height (position) different from the focus F 2  of the comparative example. This is because, unlike the comparative example, the working example is configured such that a portion of light incident on the microlens enters the color filter via a low-refractive-index material. 
     In addition, the color filter  21 R of the working example exhibited the electric field intensity distribution in which a plurality of horizontally elongated regions bounded by a broken line (i.e., the regions with second-highest electric field strength) appear at locations along a vertical direction (Z-axis direction) from one edge to the other edge of the color filter  21 . This indicates the occurrence of standing waves within the color filter  21 R. 
     Next, the electric field intensity distribution of light emerging from each color filter is discussed. 
     In the transparent insulating layer  10  of the comparative example shown in  FIG. 3A , a portion of light from the color filter  121 R diverges to travel toward the wiring line  11  (at the divergent angle θ 2 ). To permit easy comparison with the working example, the “divergent angle” used herein is the “divergent angle” of a region bounded by a broken line. 
     In the transparent insulating layer  10  of the working example shown in FIG.  3 B, on the other hand, light from the color filter  21 R diverges to some extent (with the divergent angle θ 1 ), none of the light travels toward the wiring line  11 . As clarified above, the working example succeeded in keeping the divergent angle θ 1  of light emerged from the color filter smaller than the divergent angle θ 2  in the comparative example. 
     The following are assumed to be the reason that the working example successfully suppressed the divergence of light. 
     The width w 1  of the color filter  21 R of the working example was 0.75 μm, which was close to the size of the wavelength of red light being incident light (600 nm). As a consequence, the propagation mode of the color filter  21 R acting as a waveguide was ensured to be single-mode propagation or nearly single-mode propagation, which is advantageous for suppressing divergence of light. 
     More specifically, the single-mode propagation is known to have an electric field intensity distribution which is analogous to the Gaussian distribution. In accordance with the Gaussian distribution, the electric field intensity within the waveguide is highest at its center and gradually becomes lower toward the periphery. Here, looking at the inside of the color filter  21 R (the region below the focus F 1 ) in  FIG. 3B , it is noted that the central portion of the color filter  21 R includes regions s 1 -s 3  bounded by a bold line, and those regions s 1 -s 3  are surrounded by regions bounded by a broken lines. That is, the electric field intensity within the color filter  21 R is gradually lower from the center toward the periphery. Therefore, the electric field intensity distribution shown in  FIG. 3B  is considered to be analogous to the Gaussian distribution, which leads to a conclusion that the propagation mode of the working example is single-mode propagation or nearly single-mode propagation. In the single-mode propagation, the intensity of light within the waveguide is lower at the peripheral portion that at the central portion. Therefore, divergence of light is said to be smaller in the single-mode propagation than that in multi-mode propagation. In addition, although light emitted from the waveguide still diverges due to diffraction, the influence of diffraction remains small because the intensity of light at the peripheral portion is lower and thus the extent of light divergence is kept small. 
     The simulation results described above confirm that the effect to suppress divergence of light is achieved by the present embodiment. 
     &lt;Manufacturing Method&gt; 
     Next, a description is given of a manufacturing method for the solid-state imaging device  1  according to the present embodiment. 
       FIGS. 4-9  are schematic sectional views used to explain the manufacturing method for the solid-state imaging device  1 .  FIG. 4A  includes a top view of the solid-state imaging device  1  as well as two sectional views, one taken along the arrowed line A 1 -A 1  and the other along the arrowed line B 1 -B 1  of the top view. The same applies to  FIG. 4B  and also to  FIGS. 5-9 . 
     &lt;&lt;First Step&gt;&gt; 
     First, the respective regions, such as photodiodes  3 , are formed in the silicon substrate  2  ( FIG. 4A ). 
     &lt;&lt;Second Step&gt;&gt; 
     Subsequently, an insulating film, transfer electrodes  9 , wiring lines  11  and  12 , and a transparent insulating layer  10  are formed over (i.e., on or above) the silicon substrate  2  ( FIG. 4A ). 
     &lt;&lt;Third Step&gt;&gt; 
     The next step is to form color filter layers  20 . 
     (First Sub-Step of Disposing Low-Refractive-Index Material) 
     First, a low-refractive-index material  22   a  is applied to the entire upper surface of the transparent insulating layer  10  ( FIG. 4B ), and then a resist pattern  40  is formed on the low-refractive-index material  22   a  ( FIG. 5A ). 
     Here, regions of the low-refractive-index material  22   a  each corresponding to where the respective color filters  21  are to be formed in a matrix are referred to as formation regions K. Regions between any two adjacent rows of formation regions K are referred to as row-spacing regions G 1 -G 3 . Regions between any two columns of adjacent formation regions K are referred to as column-spacing regions R 1 -R 3 . Then, the resist pattern  40  is formed to cover even-numbered row-spacing regions and even-numbered column-spacing regions (that is, the row-spacing region G 2  and the column-spacing region R 2 ). 
     Then, the low-refractive-index material  22   a  is processed by dry etching with the use of the resist pattern  40  to remove exposed regions of the low-refractive-index material  22   a , namely the formation regions K for the color filters  21 , row-spacing regions G 1  and G 3 , and column-spacing regions R 1  and R 3  ( FIG. 5B ). 
     In this manner, since the regions to be removed are made greater by including the row-spacing regions G 1  and G 3  and the column-spacing regions R 1  and R 3  of the low-refractive-index material  22   a  as well as the formation regions K of the color filters  21 , the etching is carried out more easily. This arrangement helps to accurately reserve the formation regions K for the color filters  21  and thus helps to accurately form the color filters  21 . 
     (Color Filter Forming Step) 
     First, a green color filter material  41  containing photosensitizer is applied to the regions of the transparent insulating layer  10  excluding where low-refractive-index material  22   a  is present ( FIG. 6A ). Then, the color filter material  41  is exposed to a pattern of light to form color filters  21 Gr and  21 Gb ( FIG. 6B ). 
     Next, a blue color filter material  42  containing photosensitizer is applied to the regions of the transparent insulating layer  10  excluding where the low-refractive-index material  22   a  and the color filters  21 Gr and  21 Gb are present ( FIG. 7A ). Then, the color filter material  42  is patterned to form color filters  21 B ( FIG. 7B ). 
     Next, a red color filter material  43  containing photosensitizer is applied to the regions of the transparent insulating layer  10  excluding where the low-refractive-index material  22   a  and the color filters  21 Gr,  21 Gb, and  21 B are present ( FIG. 8A ). Then, the color filter material  43  is patterned to form color filters  21 R ( FIG. 8B ). 
     The color filters  21  of the respective colors are formed such that the width w 1  of the color filters  21  is smaller than the diameter d 1  of the microlenses  14 . The order in which the respective color filters  21  are formed is not limited to the order described above. 
     (Second Sub-Step of Disposing Low-Refractive-Index Material) 
     First, low-refractive-index material  22   b  of identical compositions as the low-refractive-index material  22   a  is applied to the regions of the transparent insulating layer  10  excluding where the low-refractive-index material  22   a  and the color filters  21  are present ( FIG. 9A ). Through this sub-step, the color filters  21 R,  21 Gr,  21 Gb, and  21 B are surrounded by the low-refractive-index material  22 , which has been applied as the low-refractive-index materials  22   a  and  22   b.    
     &lt;&lt;Fourth Step&gt;&gt; 
     Finally, microlenses  14  are formed on the respective color filters  21 R,  21 Gr,  21 Gb, and  21 B ( FIG. 9B ). 
     Through the above steps, the solid-state imaging device  1  is manufactured. 
     Second Embodiment 
     Schematic Structure 
     Next, a description is given of a solid-state imaging device  51  according to a second embodiment of the present disclosure, with reference to  FIGS. 10A-10C . 
       FIG. 10A  is a top view showing part of the solid-state imaging device according to the second embodiment.  FIG. 10B  is a sectional view taken along the arrowed line A 2 -A 2  of  FIG. 10A , whereas  FIG. 10C  is a sectional view taken along the arrowed line B 2 -B 2  of  FIG. 10A . 
     According to the first embodiment, the respective color filters  21 R- 21 B are all equal in thickness. Yet, the present embodiment differs from the first embodiment in that the thickness t 2  of red color filters  61 R is greater than the thickness t 3  of green and blue color filters  61 Gr- 61 B. For the sake of simplicity, the components identical to those of the solid-state imaging device  1  shown in  FIGS. 1A-1C  are denoted by the same reference signs and a description thereof is omitted. 
     &lt;Structure of Color Filters&gt; 
     The color filter layer  60  includes the red color filters  61 R as well as the color filters  61 Gr- 61 B of the other colors all disposed on the transparent insulating layer  10 . That is, the color filters  61 R, which are thicker, project upwardly beyond the color filters  61 Gr- 61 B. In order to provide the color filter layer  60  with a flat surface, a low-refractive-index material  62  surrounding the color filters  61  is filled to the same height as the upper surfaces of the color filters  61 R. 
     The following describes the reason for forming the color filters  61 R to have a thickness different from the thickness of the color filters  61 Gr- 61 B of the other colors. 
     Preferably, the thickness of a color filter is set according to the wavelength of light that can transmit the color filter. More specifically, the preferable thickness of a color filter is an integral multiple of a half of the wavelength of transmission light of the color filter. Note that the “wavelength of transmission light of the color filter” refers to the dominant wavelength of light that can transmit the color filter and that calculated in consideration of the refractive-index of the color filter. 
     That is, light that transmits the respective color filters is a mixture of light that exits from the color filter without being reflected at the boundary at the bottom surface of the color filter and light that exits from the color filter after being reflected back and force within the color filter. The thickness of the color filter is defined so as not to cause phase difference between the respective rays of light and thereby to amplify the respective rays of light transmitted. As a result, the amount of light to be transmitted is increased. 
     However, the following should be noted in manufacturing of the color filters of the respective colors having different thickness. That is, since a step of providing a flat surface (by filing with low-refractive-index material, for example) needs to be performed separately for the color filters of the respective thicknesses, the manufacturing load increases. In order to suppress the manufacturing load, the present embodiment limits the number of different thicknesses of the color filters. More specifically, the present embodiment provides the color filters in two different thicknesses (namely, the red color filters in a certain thickness, and the color filters of the other colors in a different thickness). The following describes the reason for providing the red color filters in a thickness that is different from the color filters of the other colors. That is, since its wavelengths are longer than light of other colors, red light is diffracted more than other colors of light when passing through a color filter. Naturally, the amount of light traveling toward the corresponding photodiode is smaller as compared with light of the other colors. To compensate for the loss, it is preferable to increase the amount of light to transmit the red filters. From the viewpoint of increasing the amount of light transmitted, it is preferable that the color filters have different thicknesses for the respective colors. 
     In the present embodiment, it is preferable that the thickness t 2  of the color filters  61 R fall in the range of 0.8 to 0.9 μm, and that the thickness t 3  of the green color filters  61 Gr and  61 Gb as well as of the blue color filters  61 B fall in the range of 0.4 to 0.6 μm. In the case of forming the green color filters and the blue color filters to have mutually different thicknesses, it is preferable that the thickness of the green color filters  61 Gr and  61 Gb fall in the range of 0.4 to 0.5 μm, and the thickness of the blue color filters  61 B fall in the range of 0.5 to 0.6 μm. 
     As described above, the solid-state imaging device  51  has the red color filters having a thickness determined according to the wavelengths of light that can pass through the red color filters. With this arrangement, the amount of light that transmits the red color filters is increased as compared with that in the solid-state imaging device  1  according to the first embodiment and the loss of collection efficiency of light to the photodiodes is further prevented. 
     &lt;Manufacturing Method&gt; 
     Next, a description is given of a manufacturing method for the solid-state imaging device  51  according to the present embodiment. 
       FIGS. 11-12  are schematic sectional views used to explain the manufacturing method for the solid-state imaging device  51 . 
     The manufacturing method of the solid-state imaging device  51  is identical to the manufacturing method of the solid-state imaging device  1  according to the first embodiment in that both the methods commonly have: the first step of manufacturing a matrix of photodiodes in the silicon substrate; the second step of forming the transparent insulating layer  10  in which the wiring lines are embedded; the third step of forming the color filter layer  60  including the color filters  61 ; and the fourth step of forming microlenses. 
     On the other hand, the difference with the manufacturing method of the solid-state imaging device  1  according to the first embodiment lies in that the red color filters of the solid-state imaging device  51  are formed to have a thickness t 2  that is greater than the thickness t 3  of the green and blue color filters  61 Gr- 61 B. For the sake of simplicity, no description is given of the same steps as those in the manufacturing method of the solid-state imaging device  1  shown in  FIGS. 4-9 . The following description begins with the step of forming red color filters  61 R, which is one step in the third step. 
     &lt;&lt;Third Step&gt;&gt; 
     (Color Filter Forming Step) 
     A red color filter material  80  containing photosensitizer is applied to the regions of the transparent insulating layer  10  excluding where the low-refractive-index material  62   a  and the color filters  61 Gr,  61 Gb, and  61 B are present ( FIG. 11A ). In this step, the color filter material  80  is applied until the height of the applied material  80  is greater than that of the color filters  61 Gr,  61 Gb, and  61 B (until reaching the height t 2  measured from the transparent insulating layer  10 ). 
     Then, the color filter material  80  is patterned to form color filters  61 R ( FIG. 11B ). 
     (Second Sub-Step of Disposing Low-Refractive-Index Material) 
     First, low-refractive-index material  62   b  of identical compositions as the low-refractive-index material  62   a  is applied to the regions of the transparent insulating layer  10  excluding where the low-refractive-index material  62   a  and the color filters  61 Gr,  61 Gb, and  61 B are present ( FIG. 12A ). In this step, the low-refractive-index material  62   b  is applied until the upper surface of the applied material  62   b  reaches the height equal to the upper surfaces of the color filters  61 R (i.e., equal to the height t 2  measured from the transparent insulating layer  10 ). Through this sub-step, the color filters  61 R,  61 Gr,  61 Gb, and  61 B are surrounded by the low-refractive-index material  62 , which has been applied as the low-refractive-index materials  62   a  and  62   b.    
     &lt;&lt;Fourth Step&gt;&gt; 
     Finally, microlenses  14  are formed on the respective color filters  61 R,  61 Gr,  61 Gb, and  61 B ( FIG. 12B ). 
     Through the above steps, the solid-state imaging device  51  is manufactured. 
     Third Embodiment 
     Schematic Structure 
     Next, a description is given of a solid-state imaging device  151  according to a third embodiment of the present disclosure, with reference to  FIGS. 13A-13C . 
       FIG. 13A  is a top view showing part of the solid-state imaging device according to the third embodiment.  FIG. 13B  is a sectional view taken along the arrowed line A 3 -A 3  of  FIG. 13A , whereas  FIG. 13C  is a sectional view taken along the arrowed line B 3 -B 3  of  FIG. 13A . 
     The present embodiment is identical to the second embodiment in that the red color filters are thicker than the color filters of the other colors. 
     Yet, the present embodiment differs from the second embodiment according to which the microlenses  14  are disposed on the flat surface of the color filter layer  60 , the flat surface being formed by filling with the low-refractive-index material  62  to reach the height of the top surfaces of the red color filters  61 R. In contrast, according to the present embodiment, the low-refractive-index material  162  is filled to reach the height of the top surfaces of the color filters other than red (namely to the top surfaces of the color filters  161 Gr- 161 B). That is, the red color filters  161 R projects beyond the other regions, which means that the surface of the color filter layer  160  has projections and depressions. The microlenses are disposed on that uneven surface of the color filter layer  160 . For the sake of simplicity, the components identical to those of the solid-state imaging device  51  shown in  FIGS. 10A-10C  are denoted by the same reference signs and a description thereof is omitted. 
     &lt;Structure of Color Filters&gt; 
     According to the present embodiment, the refractive index of the color filters  161 R is 1.9, whereas the refractive index of the color filters  161 Gr,  161 Gb, and  161 B is 1.5. 
     On the color filter layer  160 , first microlenses  154  are disposed one for each of the color filters  161 Gr- 161 B, which are of the colors other than red, and also second microlenses  155  are disposed one for each of the red color filters  161 R. 
     Each second microlens  155  has a concaved portion  155   a  formed in the bottom surface and the concaved portion  155   a  is shaped to conform to the projecting portion  161 R 1  of the color filter  161 R. The projecting portion  161 R 1  is received within the concaved portion. 
     The first and second microlenses  154  and  155  are made from a transparent organic material having the refractive index 1.5. That is, the projecting portion  161 R 1  of each color filter  161 R is surrounded by the materials having a lower refractive index than that of the color filters  161 R themselves. Therefore, the entire color filter  161 R including the projecting portion  161 R 1  acts as a waveguide. 
     In the manner described above, in the case where the color filters of different thicknesses are provided, portions of the thicker color filters (i.e., portions projecting beyond the height of the thinner color filters) may be located inside the microlenses. This embodiment achieves the same advantages as that achieved by the second embodiments. In addition, this embodiment achieves that the overall height h 1  of the color filter layers and the microlenses is smaller as compared with the second embodiment, because portions of the thicker color filters are located inside the microlenses. This advantage is effective for downsizing the solid-state imaging device. 
     Fourth Embodiment 
     Schematic Structure 
     Next, a description is given of a solid-state imaging device  201  according to a fourth embodiment of the present disclosure, with reference to  FIGS. 14A-14C . 
       FIG. 14A  is a top view showing part of the solid-state imaging device according to the fourth embodiment.  FIG. 14B  is a sectional view taken along the arrowed line A 4 -A 4  of  FIG. 14A , whereas  FIG. 14C  is a sectional view taken along the arrowed line B 4 -B 4  of  FIG. 14A . 
     Different from the first embodiment according to which the color filters  21 R- 21 B are all equal in width, the color filters according to the present embodiment have different widths for the respective colors. For the sake of simplicity, the components identical to those of the solid-state imaging device  1  shown in  FIGS. 1A-1C  are denoted by the same reference signs and a description thereof is omitted. 
     &lt;Structure of Color Filters&gt; 
     According to the present embodiment, the refractive index of the color filters  221 R is 1.9, whereas the refractive index of the color filters  221 Gr,  221 Gb, and  221 B is 1.5. 
     In the color filter layer  220 , the width w 2 B of the blue color filters  221 B is smaller than the width w 2 G of the green color filters  221 Gr and  221 Gb. In addition, the width w 2 G of the green color filters  221 Gr and  221 Gb is smaller than the width w 2 R of the red color filters  221 R. Yet, the widths w 2 R, w 2 B, and w 2 G are all smaller than the diameter d 1  of the microlenses  14 . 
     In the present embodiment, the width w 2 G of the green color filters  221 Gr and  221 Gb is 0.6 μm, whereas the width of the red color filters  221 R is 0.8 μm and the width w 2 B of the blue color filters  221 B is 0.45 μm. 
     As described above, the widths w 2 R-w 2 B are determined to be close to the sizes of the respective wavelengths (which are computed in consideration of the respective refractive indexes) of light that passes through the respective color filters  221 R- 221 B. This ensures the propagation mode of each of the color filters  221 R- 221 B to be single-mode propagation or nearly single-mode propagation, thereby ensuring divergence of light having passed the respective color filters  221 R- 221 B to be suppressed. 
     With respect to the red color filters  221 R, in addition, the single-mode propagation or nearly single-mode propagation is also effective to suppress occurrence of flare. The details of this advantage are described below. 
     For example, digital cameras are provided with an infrared cut-off filter disposed between the camera lens and the solid-state imaging device housed in the casing. The infrared cut-off filter reflects infrared radiation while allowing visible light to pass through. Yet, depending on the angle of incidence, the infrared cut-off filter may reflect a portion of visible light, the portion being closer to the infrared wavelengths. 
     Of the light incident on the infrared cut-off filter from the camera lens, visible light passes through the infrared cut-off filter. Yet, a portion of the transmitted visible light is reflected and diffracted by the microlenses disposed on the chip surface and travels back toward the infrared cut-off filter. Such a portion of light is reflected by the infrared cut-off filter and enters the solid-state imaging device at an angle to be ultimately received by the photoelectric converter regions. Reception of such light results in occurrence of flare, which is a type of noise. 
     Note that the blue pixels as well as the green pixels of the solid-state imaging device are associated with little risk of flare caused by oblique incidence of red light because the blue or green color filters of the respective pixels absorb red light. On the other hand, the red pixels involve a higher risk of flare caused by oblique incidence of red light because the red filters of the respective pixels passes red light. 
     Therefore, by ensuring the propagation mode in the red color filters  221 R to be nearly single-mode propagation, red light obliquely incident is eliminated by interference of light within the color filters  221 R. This is effective to suppress occurrence of flare. 
     Fifth Embodiment 
     Next, a description is given of a solid-state imaging device  251  according to a fifth embodiment of the present disclosure, with reference to  FIGS. 15A-15C . 
       FIG. 15A  is a top view showing part of the solid-state imaging device according to the fifth embodiment.  FIG. 15B  is a sectional view taken along the arrowed line A 5 -A 5  of  FIG. 15A , whereas  FIG. 15C  is a sectional view taken along the arrowed line B 5 -B 5  of  FIG. 15A . 
     According to the fourth embodiment, all the color filters  221  have a width that is smaller than the diameter d 1  of the microlenses  14  and are surrounded by the low-refractive-index material  222 . In contrast, according to the present embodiment, while the red color filters  261 R have the width w 3  that is smaller than the diameter d 1  of the microlenses  14  and are surrounded by the low-refractive-index material  262 , the green and blue color filters  261 Gr- 261 B have the width w 4  that is equal to the diameter d 1  and are not surrounded by the low-refractive-index material  262 . For the sake of simplicity, the components identical to those of the solid-state imaging device  201  shown in  FIGS. 14A-14C  are denoted by the same reference signs and a description thereof is omitted. 
     In the manner described above, depending on the specifications and applications of the solid-state imaging device, it may be applicable to surround only the red color filters  261 R by the low-refractive-index material  262 . 
     In the present embodiment, the width w 3  of the red color filters  261 R is in the range of 0.4 to 0.6 μm, and the width w 4  of the green and blue color filters  261 Gr- 261 B is in the range of 1.5 μm. 
     Sixth Embodiment 
     Next, a description is given of a solid-state imaging device  301  according to a sixth embodiment of the present disclosure, with reference to  FIGS. 16A-16C . 
       FIG. 16A  is a top view showing part of the solid-state imaging device according to the sixth embodiment.  FIG. 16B  is a sectional view taken along the arrowed line A 6 -A 6  of  FIG. 16A , whereas  FIG. 16C  is a sectional view taken along the arrowed line B 6 -B 6  of  FIG. 16A . 
     According to the fourth embodiment, all the color filters  221  have a width that is smaller than the diameter d 1  of the microlenses  14  and are surrounded by the low-refractive-index material  222 . In contrast, the present embodiment differs in that: the green color filters  321 Gr and  321 Gb have the width w 5 G that is equal to the diameter d 1  and not surrounded by a low-refractive-index material; and that the red and blue color filters  321 R and  321 B respectively have the widths w 5 R and w 5 B that are smaller than the diameter d 1  of the microlenses  14  and are surrounded by a green color filter material  322  that is identical to the material of the color filters  321 Gr and  321 Gb. For the sake of simplicity, the components identical to those of the solid-state imaging device  201  shown in  FIGS. 14A-14C  are denoted by the same reference signs and a description thereof is omitted. 
     In the present embodiment, the refractive index of the color filters  321 R and  321 B is 1.6, and the refractive index of the green color filter material  322  is 1.2. Hence, the refractive index of the color filters  321 Gr and  321 Gb is also 1.2. In this embodiment, the refractive index of the green color filter material  322  is still lower than the refractive index of the color filters  321 R and  321 B, and therefore the color filters  321 R and  321 B act as waveguides. That is, this embodiment achieves the same advantageous effect as that achieved by the color filters  221 R and  221 B according to the fourth embodiment. 
     In the manner described above, the present embodiment uses the green color filter material as a low-refractive-index material, which means that a fewer types of materials are used to manufacture the color filter layer as compared with the fourth embodiment. Therefore, the present embodiment allows the manufacturing steps to be simplified. 
     Seventh Embodiment 
     Next, a description is given of a solid-state imaging device  351  according to a seventh embodiment of the present disclosure, with reference to  FIGS. 17A-17C . 
       FIG. 17A  is a top view showing part of the solid-state imaging device according to the seventh embodiment.  FIG. 17B  is a sectional view taken along the arrowed line A 7 -A 7  of  FIG. 17A , whereas  FIG. 17C  is a sectional view taken along the arrowed line B 7 -B 7  of  FIG. 17A . 
     The present embodiment differs from the first embodiment in that optical waveguide regions  371  are disposed in a transparent insulating layer  370 . More specifically, each optical waveguide region  371  is disposed between a color filter  361  and a photodiode  3 . For the sake of simplicity, the components identical to those of the solid-state imaging device  1  shown in  FIGS. 1A-1C  are denoted by the same reference signs and a description thereof is omitted. 
     The optical waveguide regions  371  are made of silicon nitride (refractive index: 1.9). 
     The regions of the transparent insulating layer  370  other than where the optical waveguide regions  371  are disposed are made of silicon oxide (refractive index: 1.45). That is, the optical waveguide regions  371  are surrounded by silicon oxide having a lower refractive index than that of the optical waveguide regions  371  themselves, so that the boundaries between the optical waveguide regions  371  and the silicon oxide reflect light by total reflection or Fresnel reflection. 
     The upper surface  371   a  of each optical waveguide region  371  is shaped to conform to the bottom surface of a corresponding color filter  361 . The bottom surface  371   b  of the optical waveguide region  371  has the size of the upper surface of a corresponding photodiode  3  and faces toward the photodiode  3  via the insulating film  8 . With this structure, light emitted from the color filters  361  travels toward the photodiodes  3  via the optical waveguide regions  371  without leaking between the color filters  361  and the optical waveguide regions  371  or between the optical guides  371  and the photodiodes  3 . 
     The optical waveguide regions  371  are manufactured by, for example, forming holes in the transparent insulating layer  370  by dry etching and filling the holes with silicon nitride. 
     According to the present embodiment, the optical waveguide regions  371  are provided in the transparent insulating layer  370  that is located between the color filters  361  and the photodiodes  3 . This structure suppresses the divergence of light emitted from the color filters to a greater extent than by the solid-state imaging device  1  according to the first embodiment. Therefore, occurrence of color crosstalk is suppressed even better. 
       FIG. 18  is obtained by the simulation run to confirm the suppression of light divergence by a solid-state imaging device having the optical waveguide regions as described above. For the purpose of comparison, the solid-state imaging device shown in  FIG. 18  is basically identical in structure to the solid-state imaging device shown in  FIG. 3B , except the optical waveguide regions  17  disposed inside the transparent insulating layer  10 . 
     As shown in  FIG. 18 , light as emitted from the color filter  21 R enters the optical waveguide region  17  thorough which the light is guided downward (toward the photodiode  3 ). In comparison with the simulation result shown in  FIG. 3B , the simulation result shown in  FIG. 18  indicates that the divergence of light emitted from the color filter  21 R is suppressed to a greater extent. 
     The above simulation demonstrates that the provision of optical waveguide regions in the transparent insulating layer is effective to better suppress the divergence of light emitted from the color filters. 
     Note that light is shown to be converged in the optical waveguide region  17 , and this convergence of light is by the action of the intra-layer lens  16 . 
     Up to this point, the solid-state imaging devices and manufacturing methods according to the present invention have been described by way of specific embodiments. Naturally, however, the present invention is not limited to those specific embodiments. 
     [Modifications] 
     For example, the following modifications may be made. 
     (1) Although the above embodiments are described by way of the CCD solid-state imaging devices, the present invention is not limited to such and applicable to CMOS solid-state imaging devices as well. 
     (2) The red, green, and blue color filters may mutually differ in refractive index and the refractive indexes may be determined appropriately to the specifications and applications of the solid-state imaging devices. 
     (3) According to the above embodiments, the low-refractive-index material is organic glass material but not limited to such. For example, the low-refractive-index material may be an inorganic transparent material containing silicon oxide. 
     (4) According to the above embodiments, the color filters of the respective colors are surrounded by the low-refractive-index material of the same type. However, the present invention is not limited to such. For example, different low-refractive-index materials may be used for the different colors of the color filters. 
     (5) According to the above embodiments, the photoelectric converters comprise photodiodes. However, the photoelectric converters are not limited to such structure. 
     (6) According to the above embodiments, the manufacturing methods for solid-state imaging devices according to the present invention are described. However, the manufacturing methods of the solid-state imaging devices according to the present invention are not limited to those described above. Depending on the specifications and applications of the solid-state imaging devices, an appropriate manufacturing method therefor can be selected. 
     For example, according to the above embodiments, the low-refractive-index material is formed in the color filter layer through two steps, namely the first and second sub-steps. Alternatively, however, the low-refractive-index material may be formed in a single step. In this modification, the low-refractive-index material may be formed either before or after the step of forming color filters. 
     Note that in the case where a plurality of different low-refractive-index materials are used for, for example, color filters of the respective colors, a step of forming low-refractive-index material needs to be performed for each color. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure is useful to provide solid-state imaging devices offering high image quality. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  solid-state imaging device 
             F 1 , F 2  focus 
               2  silicon substrate 
               3  photodiode 
               4  transfer channel 
               9  transfer electrode 
               10  insulating layer 
               11 ,  12  wiring line 
               14  microlens 
               20  color filter layer 
               21  color filter 
               22  low-refractive-index material 
               22   a ,  22   b  low-refractive-index material 
               30  pixel 
               40  resist pattern 
               51 ,  100 ,  151 ,  201 ,  251 ,  301 ,  351  solid-state imaging device 
               60 ,  160 ,  220  color filter layer 
               61 ,  121 ,  161 ,  221 ,  261 ,  321 ,  361  color filter 
               62 ,  162 ,  222 ,  262  low-refractive-index material 
               154 ,  155  microlens 
               155  microlens 
               370  transparent insulating layer 
               371  optical waveguide region