Abstract:
A solid-state image sensing device having an effective pixel area and an optical black area disposed on one principal surface of a substrate, includes photoelectric converter elements, a wiring part containing a plurality of wiring layers disposed on the one principal surface of the substrate, in which in the optical black area more wiring layers are disposed than in the effective pixel area, an interlayer dielectric disposed between, among the plurality of wiring layers, a topmost first wiring layer and a second wiring layer disposed beneath the first wiring layer, a passivation film disposed on the interlayer dielectric in the effective pixel area and disposed on the first wiring layer in the optical black area, and inner lenses disposed at least at positions on the passivation film that corresponds to the effective pixel area, a thickness of the passivation film being equal to or less than a thickness of the first wiring layer.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a solid-state image sensing device, and more particularly, to a solid-state image sensing device equipped with an inner lens. 
   BACKGROUND OF THE INVENTION 
   Recently, solid-state image sensing devices have come to be used in image input apparatuses such as digital cameras, video cameras and image readers. As such solid-state image sensing devices, there are CCD image sensors as well as such non CCD-type image sensors as bipolar transistor-type image sensors, field effect transistor-type image sensors and CMOS image sensors. With such image input apparatuses, optical image information (an optical image) is converted into electrical signals by a photoelectric converter and the converted electrical signals are signal-processed and displayed on a display unit, recorded on a storage medium, and so forth. 
   To obtain a higher performance solid-state image sensing device, it is desirable to reduce the surface area (pixel surface area) of the light-receiving surface of the photoelectric conversion element that is the photoelectric converter that actually converts the optical image into electrical signals and increase the number of photoelectric converter elements deployed, while at the same time reducing the solid-state image sensing device chip size. 
   However, with continued advances in high-density pixel integration and chip size reduction, the quantity of light that a single photoelectric converter element which constitutes a pixel can receive decreases as the surface area of the light-receiving surface decreases, and thus decreasing the sensitivity of the device. To remedy this situation, a technology is known that reduces the decrease in sensitivity by forming a microlens on a flattened protective film provided on the light-receiving surface and concentrating incoming light on the light-receiving surface. 
   In addition, with the demand for even further high-density pixel integration and chip size reduction, the need to provide an inner lens between the microlens and the photoelectric converter element, composed of a film having a refractive index different from those of the adjacent layers, increases. 
   For example, Japanese Patent Application Laid-Open No. 2005-012189 discloses a solid-state image sensing device having a microlens and an inner convex lens. A brief description is given of the configuration of the solid-state image sensing device disclosed in Japanese Patent Application Laid-Open No. 2005-012189 using  FIG. 15 . 
   In  FIG. 15 , reference numeral  13  indicates a semiconductor member,  1  indicates photoelectric converter elements formed within the semiconductor member and  2  represents an element separation area. Reference numeral  4  indicates a first wiring pattern and  6  indicates a second wiring pattern, with the first wiring pattern  4  and the second wiring pattern  6  separated by a first dielectric  3  and a second dielectric  5 . A third dielectric  7  above the second wiring pattern  6  is flattened, after which the inner convex lens  8  are formed. Further, the tops of the inner convex lens  8  are flattened by a first flattening film  9 , after which a color filter layer  10  is formed, further flattened by a second flattening film  11 , and microlenses  12  formed thereafter. Reference numeral  14  indicates a pad part. With such a technique, it is said, the inner convex lens  8  can be formed with precision, enabling the light collecting efficiency to be increased without substantially reducing sensitivity. 
   A description is now given of an instance in which a solid-state image sensing device having a light-shielded area on an edge part of the photoelectric converter element is designed on the basis of Japanese Patent Application Laid-Open No. 2005-012189, with reference to  FIG. 16 . 
     FIG. 16  shows a sectional view of the edge of a solid-state image sensing device including a light-receiving area and a light-shielded area. In  FIG. 16 , reference numeral  101  indicates a light-shielded area pixel,  102  indicates a light-receiving area pixel,  103  indicates photosensitive areas (photoelectric converter elements),  104  indicates a first metal wiring layer,  105  indicates a second metal wiring layer, and  106  indicates a third metal wiring layer that blocks incoming light. Most of the photoelectric converter elements  103 , the first metal wiring layer  104 , the second metal wiring layer  105  and the third metal wiring layer  106  are physically and electrically separated from each other by interlayer dielectrics, with portions connected by contact plugs and via plugs. It should be noted that the pixel shielded from incoming light by the third metal wiring layer  106  becomes the light-shielded area pixel, with the third metal wiring layer  106  configured so as not to intrude upon the light-receiving area pixel  102 . In addition, reference numeral  112  indicates a flattening film that covers the height difference created by the third metal wiring layer  106 , and is formed so as to provide a uniform surface for the formation of inner lenses  108  described later. Reference numeral  107  indicates a passivation layer and  108  indicates the inner lenses. After formation of the inner lenses  108 , a flattening film  109  is formed to attain a flat surface, on which a color filter layer  110  is. Thereafter further flattening is performed using flattening layer  109  is further formed to attain a flat surface, on which microlenses  111  are formed. 
   However, as shown in  FIG. 16 , if the solid-state image sensing device is configured using the technique shown in  FIG. 15 , the distance from the light-receiving surface to the bottom of the inner lenses lengthens, and conversely light collecting efficiency worsens. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in consideration of the above-described situation, and has as its object to shrink the distance from the light-receiving surface to the bottom of the inner lens and to increase light-collecting efficiency without decreasing sensitivity. 
   According to the present invention, the foregoing object is obtained by providing a solid-state image sensing device having an effective pixel area that carries out photoelectric conversion according to a quantity of incident light and an optical black area for creating a reference signal, the effective pixel area and the optical black area disposed on one principal surface of a substrate, the solid-state image sensing device comprising: 
   photoelectric converter elements; 
   a wiring part containing a plurality of wiring layers disposed on the one principal surface of the substrate, in which in the optical black area more wiring layers are disposed than in the effective pixel area; 
   an interlayer dielectric disposed between, among the plurality of wiring layers, a topmost first wiring layer and a second wiring layer disposed beneath the first wiring layer; 
   a passivation film disposed on the interlayer dielectric in the effective pixel area and disposed on the first wiring layer in the optical black area; and 
   inner lenses disposed at least at positions on the passivation film that corresponds to the effective pixel area, 
   wherein a thickness of the passivation film is equal to or less than a thickness of the first wiring layer. 
   Other features and advantages of the present invention will be apparent from the following description when taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
       FIG. 1  is a sectional view of the configuration of a solid-state image sensing device according to a first embodiment of the present invention; 
       FIG. 2  is a diagram illustrating the improvement effect of the solid-state image sensing device according to the first embodiment of the present invention; 
       FIG. 3  is a diagrams illustrating a method of manufacturing the solid-state image sensing device shown in  FIG. 1 ; 
       FIG. 4  is a diagrams illustrating the method of manufacturing the solid-state image sensing device shown in  FIG. 1 ; 
       FIG. 5  is a diagrams illustrating the method of manufacturing the solid-state image sensing device shown in  FIG. 1 ; 
       FIG. 6  is a diagrams illustrating the method of manufacturing the solid-state image sensing device shown in  FIG. 1 ; 
       FIG. 7  is a diagrams illustrating the method of manufacturing the solid-state image sensing device shown in  FIG. 1 ; 
       FIG. 8  is a diagrams illustrating the method of manufacturing the solid-state image sensing device shown in  FIG. 1 ; 
       FIG. 9  is a diagrams illustrating the method of manufacturing the solid-state image sensing device shown in  FIG. 1 ; 
       FIG. 10  is a diagrams illustrating the method of manufacturing the solid-state image sensing device shown in  FIG. 1 ; 
       FIG. 11  is a sectional view of the configuration of a solid-state image sensing device according to a second embodiment of the present invention; 
       FIG. 12  is a diagram illustrating a method of manufacturing the solid-state image sensing device shown in  FIG. 11 ; 
       FIG. 13  is a sectional view of a configuration of another solid-state image sensing device of the present invention; 
       FIG. 14  is a sectional view of a configuration of another solid-state image sensing device of the present invention; 
       FIG. 15  is a sectional view of the configuration of a conventional solid-state image sensing device; and 
       FIG. 16  is a sectional view of the configuration of a solid-state image sensing device designed on the basis of a conventional example. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings. However, the dimensions, shapes and relative positions of the constituent parts shown in the embodiments should be changed as convenient depending on various conditions and on the structure of the apparatus adapted to the invention, and the invention is not limited to the embodiments described herein. 
   First Embodiment 
   A description will now be given of a first embodiment of the present invention. 
     FIG. 1  is a diagram showing a sectional view of a solid-state image sensing device of a first embodiment of the present invention. It should be noted that, in  FIG. 1 , elements that are the same as those shown in  FIG. 16  are assigned the same reference characters and a description thereof is omitted. In the configuration shown in  FIG. 1 , the flattening using the flattening film  112  shown in  FIG. 16  is not performed and the passivation film part  107  is formed directly on the interlayer dielectric and the third metal wiring layer  106 , with the height difference with the third metal wiring layer  106  not covered but left as is. 
   With such a construction, the configuration shown in  FIG. 1  of the present embodiment can be made thinner by an amount equal to the flattening film  112  that covers the height difference of the topmost metal layer. Therefore, compared to the configuration shown in  FIG. 16 , the height from the photoelectric converter element  103  of the light-receiving area pixel  102  to the bottom of the inner lens  108  can be lowered. As a result, the light collecting efficiency can be increased, and in particular a decrease in sensitivity when the F number is small can be remedied. 
     FIG. 2  shows the F number dependency characteristics of the configuration of the present embodiment and the configuration shown in  FIG. 16 . As shown in  FIG. 2 , with the configuration of the first embodiment the sensitivity when the F number is small is improved compared to the configuration employing the conventional technique shown in  FIG. 16 . 
   Next, a description will be given of steps in the production of the solid-state image sensing device according to the first embodiment of the present invention shown in  FIG. 1 , with reference to  FIGS. 3 through 10 . 
   First, as shown in  FIG. 3 , a semiconductor member  121  composed of a silicon wafer or the like is prepared and an element separation area  122  is formed on the semiconductor member  121  by LOCOS (LOCal Oxidation of Silicon), STI (Shallow Trench Isolation) or the like. Next, a photo-resist pattern is formed, ion-injection and heating processes are performed, and, for example, a diffusion layer that becomes the cathode or the anode of a photodiode (photoelectric converter element  103 ) is formed on the semiconductor member  121 . 
   Then, by thermal oxidation, CVD (Chemical Vapor Deposition), sputtering, coating or the like, a first dielectric  123  is formed on the semiconductor member  121 . The top surface of the first dielectric  123  is flattened by CMP (Chemical Mechanical Planarization) or the like, enabling the accuracy of the patterning of the next process to be improved. 
   Next, a metal film consisting of Al, Mo, W, Ta, Ti or Cu, or an alloy composed chiefly of these elements, is formed on the first dielectric  123  by sputtering, CVD, electro-plating or the like. Further, by removing by etching a portion located above the light-receiving surface of the photoelectric converter element  103 , a first pattern (first metal wiring layer)  104  of a desired shape is formed. 
   Next, a second dielectric  124  consisting of SiO or a material composed chiefly of SiO is formed on the first dielectric  123  and the first metal wiring layer  104  by CVD. The top surface of the second dielectric  124  is flattened by CMP or the like to enable the accuracy of the patterning of the next process to be improved. 
   Next, a metal film consisting, like the first metal wiring layer  104 , of Al, Mo, W, Ta, Ti or Cu, or an alloy composed chiefly of these elements, is formed on the second dielectric  124  by sputtering, CVD, electro-plating or the like. Further, by removing by etching a portion located above the light-receiving surface of the photoelectric converter element  103 , a second pattern (second metal wiring layer)  105  of a desired shape is formed. 
   It should be noted that the first and second metal wiring layers  104 ,  105 , in addition to functioning as wiring used in the transmission of electrical signals from the photoelectric converter element  103 , also functions as light-shielding planes that prevents light that should enter one photoelectric converter element  103  from entering another photoelectric converter element  103 . 
   Next, a third dielectric  125  consisting of SiO or a material composed chiefly of SiO is formed on the second dielectric  124  and the second metal wiring layer  105  by CVD. The top surface of the third dielectric  125  is flattened by CMP or the like, enabling the accuracy of the patterning of the next process to be improved. 
   Next, a metal film consisting, like the first pattern  104  and the second pattern  105 , of Al, Mo, W, Ta, Ti or Cu, or an alloy composed chiefly of these elements, is formed on the third dielectric  125  by sputtering, CVD, electro-plating or the like. Further, by removing by etching a portion located above the light-receiving surface of the photoelectric converter element  103 , a third pattern (third metal wiring layer)  106  of a desired shape is formed. The third metal wiring layer  106  is formed in an area outside an effective pixel area and also includes a light-shielding member for forming a light-shielded area (optical black) for creating a reference signal. 
   Next, a passivation layer/inner lens formation film  107 ′ composed of SiN, SiON or SiO and the like is formed on the third metal wiring layer  106  and the third dielectric  125  by CVD. 
   Then, as shown in  FIG. 3 , an etching mask  126  for forming the inner lens  108  is formed on the passivation layer/inner lens formation film  107 ′ by photolithography. Thereafter, as shown in  FIG. 4 , the etching mask  126  is heated and reflowed to form a convex lens having substantially the same shape as the shape of the inner lens  108 . It should be noted that, in the present embodiment, the inner lens is also formed in the light-shielded area. 
   Next, etching is performed over the entire passivation layer/inner lens formation film  107 ′, and as shown in  FIG. 5  the convex lens shape of the etching mask  126  is transferred to the passivation layer/inner lens formation film  107 ′ to form the inner lenses  108 . For the etching gas, CF 4 , CHF 3 , O 2 , Ar, He and the like can be used. The portions of the passivation layer/inner lens formation film  107 ′ that remain after etching become the passivation layer  107 . 
   Then, as shown in  FIG. 6 , in order to open a pad part  128 ′ by photolithography, a resist pattern  127  having such an opening pattern is formed on the passivation layer  107  and the inner lenses  108 . Then, as shown in  FIG. 7 , the passivation layer  107  located above the pad part  128  is removed by photolithography. 
   Thereafter, as shown in  FIG. 8 , the first flattening film  109  is formed on the pad part  128 , the passivation layer  107  and the inner lenses  108 , and a color filter layer  110  is formed on the first flattening film  109 . The color filter layer  110  has a color pattern that selects the color of the light stroking on the photoelectric converter elements  103  underneath the color filter layer  110 . 
   Then, as shown in  FIG. 9 , a second flattening film  109  is formed on the color filter layer  110 , and microlenses  111  are formed thereon using resist patterning and reflow. Finally, as shown in  FIG. 10 , the first and second flattening films  109  that remain on the pad part  128  are removed by etching so as to open the pad part  128  upward. 
   Through the steps described above the solid-state image sensing device shown in  FIG. 1  can be manufactured. 
   Second Embodiment 
   Next, a description will be given of a second embodiment of the present invention. 
     FIG. 11  is a diagram showing a sectional view of a solid-state image sensing device according to a second embodiment of the present invention, showing an edge part of an solid-state image sensing device having a light-receiving area and a light-shielded area. In  FIG. 11 , elements identical to those shown in  FIG. 1  are assigned identical reference numerals and descriptions thereof are omitted. 
   In the configuration shown in  FIG. 1 , an inner lens  108  is also formed on the third metal wiring layer  106  that is the light-shielded area, and therefore, in order to prevent the microlens  111  formed at the boundary between the light-receiving area and the light-shielded area from tilting when formed, the first flattening film  109  must be made thick. 
   By contrast, with the configuration of the second embodiment shown in  FIG. 11 , no inner lens  108  is formed on the third metal wiring layer  106  that is the light-shielded area. As a result, the first flattening film  109  can be made thinner than that in the configuration shown in  FIG. 1 . Consequently, light collecting efficiency can be increased, and in particular a decrease in sensitivity when the F number is small can be further remedied. 
   The method of manufacturing the configuration shown in  FIG. 11 , though it differs from the method described above insofar as an etching mask  126  for forming the inner lens  108  is not formed in the light-shielded area as shown in  FIG. 12 , is otherwise the same as the method of manufacturing the first embodiment described above, and therefore a description thereof is omitted here. It should be noted that the step shown in  FIG. 12  corresponds to the step shown in  FIG. 3 . 
   According to the second embodiment, the distance from the photoelectric converter  3  to the microlenses  111  can be reduced, enabling light collecting efficiency to be further increased. 
   (Variations) 
     FIG. 13  shows a sectional view of another solid-state image sensing device of the present invention, showing an edge part of a solid-state image sensing device having a light-receiving area and a light-shielded area. In  FIG. 13 , elements identical to those shown in  FIG. 1  are assigned identical reference numerals and descriptions thereof are omitted. Unlike the first and second embodiments described above, the configuration shown in  FIG. 13  has only the first metal wiring layer  104 , without the second metal wiring layer  105 . 
   In addition,  FIG. 14  shows a sectional view of another solid-state image sensing device of the present invention, showing an edge part of a solid-state image sensing device having a light-receiving area and a light-shielded area. In the configuration shown in  FIG. 14 , the thickness of the third metal wiring layer  206  is thinner than that of the third metal wiring layer  106  of the second embodiment and the thickness of the inner lens  108  is formed substantially the same as the height difference of the passivation layer  107 . 
   Thus, as described above, in the configurations shown in  FIG. 13  and  FIG. 14 , the height from the photoelectric converter element  103  of the light-receiving area pixel  102  to the bottom of the inner lens  108  can be lowered, enabling light collecting efficiency to be increased. 
   As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims. 
   This application claims the benefit of Japanese Patent Application No. 2005-195281 filed on Jul. 4, 2005, which is hereby incorporated herein by reference herein in its entirety.