Abstract:
A single plate system color solid-state image pick-up device of a microlens loading type, the device comprising: a semiconductor substrate; a plurality of light receiving portions formed in a two-dimensional array in a surface portion of the semiconductor substrate; color filters each of which is for any of red, green and blue colors; and microlenses, wherein each of the color filters and each of the microlenses are laminated above on each of the light receiving portions, wherein first ones of the microlenses, corresponding to ones of the light receiving portions on which ones for the red color of the color filters are laminated, have smaller light receiving areas than those of second ones of the microlenses, corresponding to ones of the light receiving portions on which ones for the green color of the color filters are laminated.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a single plate system color solid-state image pick-up device of a microlens loading type which is provided in an image input device such as a digital camera and more particularly to a single plate system color solid-state image pick-up device of a microlens loading type in which color shading is caused with difficulty and an image input device comprising the same. 
     2. Description of the Related Art 
     A single plate system solid-state image pick-up device of a CCD type or a CMOS type is loaded onto an image input device such as a digital camera. In the single plate system solid-state image pick-up device, a large number of pixels are arranged like a tetragonal lattice or a honeycomb, and a color filter for transmitting one of red (R), green (G) and blue (B) colors is laminated on each of the pixels. A microlens is loaded every pixel in such a manner that a light is efficiently incident on an opening of each pixel. 
     For example, in a solid-state image pick-up device described in JP-A-5-75085, a microlens is loaded every pixel, and furthermore, a shape of a corresponding microlens is changed for each color of a color filter depending on an angle of incidence from a lens optical system for collecting a light onto a tip surface of the solid-state image pick-up device onto each pixel, thereby compensating for a variation in a sensitivity unevenness generated by shading of the lens and changing a curvature of the microlens for each color of the color filter to compensate for a variation in the sensitivity unevenness. 
     In a recent solid-state image pick-up device, an increase in pixels has been developed and a dimension of one pixel has been reduced very greatly. For this reason, the influence of the shading of an incident light through an opening of a light receiving surface in a terminal portion of an incident optical path of each pixel (an opening of a shielding film) is greater than that of shading caused by the microlens provided on the entry of the incident optical path of each pixel. Consequently, there is a problem in that color shading is generated. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a single plate system color solid-state image pick-up device of a microlens loading type which can suppress the generation of color shading and an image input device using the same. 
     The invention provides a single plate system color solid-state image pick-up device of a microlens loading type, the device comprising: a semiconductor substrate; a plurality of light receiving portions formed in a two-dimensional array in a surface portion of the semiconductor substrate; color filters each of which is for any of red, green and blue colors; and microlenses, wherein each of the color filters and each of the microlenses are laminated above on each of the light receiving portions, wherein first ones of the microlenses, corresponding to ones of the light receiving portions on which ones for the red color of the color filters are laminated, have smaller light receiving areas than those of second ones of the microlenses, corresponding to ones of the light receiving portions on which ones for the green color of the color filters are laminated. 
     The invention provides the single plate system color solid-state image pick-up device of a microlens loading type, 
     wherein second light receiving areas of the second ones of the microlenses are set to be larger corresponding to a reduction in first light receiving areas of the first ones of the microlenses. 
     The invention provides the single plate system color solid-state image pick-up device of a microlens loading type, wherein, a light receiving area of one of the first ones of the microlenses is gradually reduced toward a peripheral part of the solid-state image pick-up device. 
     The invention provides the single plate system color solid-state image pick-up device of a microlens loading type, wherein when the color filters for at least two of red, green and blue colors are arranged to form a stripe pattern, ones of the microlenses, corresponding to ones, for a color having a longer color wavelength of a light to be transmitted, of the color filters, have smaller light receiving areas. 
     The invention provides an image input device comprising: any of the single plate system color solid-state image pick-up devices of a microlens loading type described above; and a signal processing section that corrects detection signals from ones of the light receiving portions, which detects an amount of an incident light having a red color, with first light receiving areas of the first ones of the microlenses. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a structure of a digital still camera according to an embodiment of the invention, 
         FIG. 2  is a typical view showing a surface of a solid-state image pick-up device illustrated in  FIG. 1 , 
         FIG. 3  is a typical sectional view corresponding to one pixel of the solid-state image pick-up device illustrated in  FIG. 1 , 
         FIG. 4  is a view showing a relationship between an opening and a collecting point corresponding to one pixel of the solid-state image pick-up device illustrated in  FIG. 1 , and 
         FIGS. 5A to 5C  are views showing a difference between a G pixel and an R pixel in the solid-state image pick-up device illustrated in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An embodiment of the invention will be described below with reference to the drawings. 
       FIG. 1  is a diagram showing a structure of a digital still camera according to an embodiment of the invention which is an example of an image input device. While the description will be given by taking the digital still camera as an example in the embodiment, the invention can also be applied to a digital video camera, an electronic apparatus having a camera such as a cell phone having a camera and a scanner. 
     The digital still camera shown in  FIG. 1  comprises a photographing lens  10  having a zoom function, a solid-state image pick-up device  11 , a diaphragm  12  provided between both of them, an infrared cut filter  13 , and an optical low-pass filter  14 . A CPU  15  for controlling the whole digital still camera controls a light emitting unit  16  and a light receiving unit  17  for a flashlight, and furthermore, controls a lens driving unit  18  to adjust the zoom and focus positions of the photographing lens  10 , and controls an opening amount of the diaphragm through a diaphragm driving portion  19  to adjust an amount of exposure so as to be proper. 
     Moreover, the CPU  15  drives the solid-state image pick-up device  11  through an image pick-up unit driving portion  20  and outputs, as a color signal, an object image picked up through the photographing lens  10 . Moreover, a user instruction signal is input to the CPU  15  through an operating portion  21  and the CPU  15  carries out various control operations in accordance with the instruction. 
     An electric control system of the digital still camera includes an analog signal processing portion  22  connected to an output of the solid-state image pick-up device  11  and an A/D converting circuit  23  for converting color signals of RGB output from the analog signal processing portion  22  into digital signals, and these are controlled by the CPU  15 . 
     Furthermore, the electric control system of the digital still camera includes a memory control portion  25  connected to a main memory (frame memory)  24 , a digital signal processing portion  26 , a compressing and expanding portion  27  for compressing a pick-up image into a JPEG image and expanding the compressed image, an integrating portion  28  for integrating photometric data and regulating a gain of a white balance, an external memory control portion  30  to which a removable recording medium  29  is connected, and a display control portion  32  to which a liquid crystal display portion  31  loaded onto a back face of the camera is connected, and these are connected mutually through a control bus  33  and a data bus  34  and are controlled in accordance with an instruction sent from the CPU  15 . 
       FIG. 2  is a typical view showing a surface of the solid-state image pick-up device  11  to be used in the embodiment. A row in which an R pixel  42  for detecting a red color (R) and a B pixel  43  for detecting a blue color (B) are alternately arranged is shifted from a row in which a G pixel  41  for detecting a green color (G) is arranged at a 1/2 pixel pitch in a horizontal direction (a so-called honeycomb pixel arrangement). Vertical transfer paths  44  and  45  for transferring signal charges read from the pixels  41 ,  42  and  43  in a vertical direction meander to keep away from the pixels  41 ,  42  and  43  in the vertical direction. 
     While the description will be given by taking, as an example, the solid-state image pick-up device  11  of a CCD type having the honeycomb pixel arrangement in the embodiment, the invention can also be applied to a solid-state image pick-up device of a CCD type having a tetragonal lattice array, and furthermore, the invention can be applied to a solid-state image pick-up device of an MOS type. 
       FIG. 3  is a typical view showing sections of the pixels  41 ,  42  and  43 . A P well layer  50  is formed in a surface portion of an n-type semiconductor substrate on which each of the pixels is provided, and an n region  51  is formed for each pixel in a surface portion of the P well layer  50 . When a light is incident on the pn junction, a photoelectric charge is generated. The photoelectric charge is read onto the vertical transfer path  44  or  45  in  FIG. 2  and is transferred to a horizontal transfer path which is not shown, and is then transferred to the horizontal transfer path and is read from the solid-state image pick-up device  11 . 
     The P well layer  50  of the semiconductor substrate is covered with a shielding film  52  and an opening  53  is formed in a portion of the shielding film  52  which corresponds to a light receiving surface of each pixel. A color filter  54  is laminated on the shielding film  52  through a flattened layer, and a microlens  55  corresponding to each pixel is provided thereon through a flattened layer. 
     It is assumed that a light is incident perpendicularly to the substrate through the microlens  55  shown in  FIG. 3 . In this case, a collecting point  57  (which is not actually a “point” but is a surface having a larger diameter than a wavelength of the incident light) on which a light is collected by the microlens  55  is provided on an inside of the opening  53  as shown in  FIG. 4 . When an angle of incident is changed, however, collecting points  57   a  and  57   a ′ get out of a center of the opening  53  as shown in  FIG. 4 . Consequently, a pixel light receiving portion provided under the opening  53  cannot receive a total amount of a light at the collecting point  57   a  but can receive only an amount of a light in the opening  53  at the collecting point  57   a . So-called shading is generated. 
     When a zoom magnification of the photographing lens  10  shown in  FIG. 1  is changed or the amount of the opening of the diaphragm  12  is regulated, a light is incident more obliquely for a closer pixel to a peripheral portion of the solid-state image pick-up device  11  so that the shading is caused by the opening  53  as described with reference to  FIG. 4 . A green light and a blue light are rarely influenced by the shading. When the shading is generated over a red light, however, color shading becomes conspicuous. For example, when an image of a gray object is picked up by the solid-state image pick-up device  11 , a color of a pick-up image of a pixel in a peripheral portion of the image, that is, on a periphery of the solid-state image pick-up device  11  become slightly magenta or cyan, which is conspicuous. 
     In the embodiment, therefore, a light receiving area of a microlens  55   r  provided in an R pixel  42  is set to be smaller than that of a microlens  55   g  provided in a G pixel  41  with an equal curvature maintained as shown in  FIGS. 5A and 5B . Consequently, a diameter of a collecting point  57   r  in the R pixel  42  is smaller than that of a collecting point  57   g  in the G pixel  41 , and the collecting point  57   r  for a red light is simply moved in the opening  53  even if the light is incident obliquely for a peripheral pixel of the solid-state image pick-up device  11  as shown in  FIG. 5C . Thus, shading can be prevented from being caused by the opening  53  so that the generation of the color shading can be suppressed. 
     The light receiving area of the microlens  55   r  in the R pixel  42  is set to be small so that a sensitivity to a red light in the R pixel is lower than that to a green light in a G pixel and a blue light in a B pixel. However, a reduction in the sensitivity is caused by a decrease in the area of the microlens  55   r . For this reason, the degree of the reduction in the sensitivity can be previously known in a design of the microlenses  55   g  and  55   r . If the CPU  15  or the signal processing portions  22  and  26  shown in  FIG. 1  maintain the reduction in the sensitivity as a default value, therefore, it is possible to carry out an image processing in consideration of a reduction in the sensitivity of the red color. In other words, a signal processing section such as the CPU  15  or the signal processing portions  22  and  26  has a function of correcting detection signals from the R pixels (serving as receiving portions), which detect an amount of an incident light having a red color, with (based on the information of) light receiving areas of plural microlenses  55   r . Here, the signal processing section that performs the above-described function(s) is not limited to the above, and may also include a general purpose computer that are well-known in the art. 
     On the other hand, when unintentional shading for the red light is generated by the opening  53 , it is impossible to know the degree of a reduction in the sensitivity which reflects the image processing. In the solid-state image pick-up device  11  according to the embodiment, however, it is possible to avoid the shading of the red light by the opening  53 . Therefore, it is possible to obtain clear image data in which the color shading is suppressed. 
     While the microlenses  55   r  in all of the R pixels of the solid-state image pick-up device  11  are set to be smaller than the microlens  55   g  in the G pixel in the embodiment, a space is formed on a microlens forming layer corresponding to a reduction in the size of the microlens  55   r . Therefore, it is also possible to correspondingly increase the size of the microlens  55   g  in the G pixel to be used for detecting a luminance. In this case, in a Bayer array or the color filter array shown in  FIG. 2 , it is preferable to reduce the size of the microlens in the B pixel to be equal to the size of the microlens  55   r  in the R pixel in order to form the microlens without a clearance over the microlens forming layer. Consequently, it is possible to cause the microlens  55   g  in the G pixel to be the largest. 
     Although the microlenses  55   r  in all of the R pixels of the solid-state image pick-up device  11  are set to be smaller than the microlens  55   g  in the G pixel in the embodiment, moreover, the light is incident obliquely on the peripheral pixels of the solid-state image pick-up device  11  and the degree of the oblique incidence is not great over pixels in a central part. By gradually reducing the area of the microlens  55   r  in the R pixel toward the periphery of the solid-state image pick-up device  11 , therefore, it is also possible to cope with the color shading. Moreover, only the microlenses  55   r  of the R pixels in the peripheral portion may be set to have small areas and the microlenses  55   r  of the R pixels in the central part may be set to be the same as the microlens  55   g  of the G pixel. 
     In some cases in which a color filter is formed on the solid-state image pick-up device  11 , a color filter for each color is formed in a vertical or lateral stripe in place of the Bayer array or the array in  FIG. 2 . Also in these cases, it is preferable to set a color filter for the R pixel to have a smaller area than a color filter for the G pixel in the same manner as in the embodiment. 
     Moreover, it is also possible to employ a structure in which the microlens has a smaller area for a color having a greater wavelength. More specifically, a wavelength is set to be R&gt;G&gt;B. Therefore, the area of the microlens may be set in order of B&gt;G&gt;R. Moreover, the sizes of the microlenses for the G and B pixels may be equal to each other and only the microlens for the R pixel may have a small area. 
     According to the invention, it is possible to prevent color shading from being generated by shading a red color on a pixel (a light receiving portion) in a peripheral region of the solid-state image pick-up device and to pick up an excellent color image. 
     The single plate system color solid-state image pick-up device of a microlens loading type according to the invention has an advantage that color shading can be suppressed, and is useful for an application to an image input device such as a digital camera or a scanner. 
     The entire disclosure of each and every foreign patent application from which the benefit of foreign priority has been claimed in the present application is incorporated herein by reference, as if fully set forth.