Abstract:
A photoelectric converting layer lamination type solid-state image pick-up device comprises: a semiconductor substrate; at least three layers of photoelectric converting layers each of which is interposed between a common electrode layer and pixel electrode layers, the pixel electrode layers corresponding to pixels respectively, wherein said at least three layers of photoelectric converting layers are laminated through insulating layers, said at least three layers of photoelectric converting layers being above the semiconductor substrate, and wherein each of said at least three layers of photoelectric converting layers is separated into layers corresponding the pixels respectively.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a solid-state image pick-up device in which a photoelectric converting layer for generating a signal charge corresponding to a quantity of an incident light is laminated on a semiconductor substrate on which a signal reading circuit is formed, and more particularly to a photoelectric converting layer lamination type solid-state image pick-up device in which S/N of an image signal obtained by a photoelectric converting layer is enhanced. 
     2. Description of the Related Art 
     A prototype unit of a photoelectric converting layer lamination type solid-state image pick-up device has been described in JP-A-58-103165, for example. The solid-state image pick-up device has a structure that three photosensitive layers are laminated on a semiconductor substrate and respective electric signals for red (R), green (G) and blue (B) colors detected by each photosensitive layer are read by an MOS circuit formed on a surface of the semiconductor substrate. 
     The solid-state image pick-up device having such a structure was proposed in the past. Subsequently, a CCD type image sensor and a CMOS type image sensor in which a large number of light receiving portions (photodiodes) are integrated on a surface portion of the semiconductor substrate and color filters for red (R), green (G) and blue (B) colors are laminated on each light receiving portion have progressed remarkably. At present, an image sensor in which several million light receiving portions (pixels) are integrated on a chip is mounted on a digital still camera. 
     However, the techniques of the CCD type image sensor and the CMOS type image sensor have progressed to an almost limit and a size of an opening of one light receiving portion has been close to a wavelength order of an incident light, that is, approximately 2 μm. For this reason, they have been confronted with a problem in that a manufacturing yield is poor. 
     Moreover, an upper limit of a quantity of optical charges stored in one light receiving portion which is microfabricated is small, that is, approximately 3000 electrons. Consequently, it has also been difficult to finely represent 256 gradations. For this reason, it has been hard to expect a more excellent image sensor of a CCD type or a CMOS type in respect of picture quality or a sensitivity. 
     As a solid-state image pick-up device for solving these problems, a solid-state image pick-up device proposed in JP-A-58-103165 has been reconsidered. Consequently, image sensors described in Japanese Patent No. 3405099 and JP-A-2002-83946 have been proposed newly. 
     The image sensor described in Japanese Patent No. 3405099 has such a structure that hyperfine particles of silicon are dispersed in a medium to form a photoelectric converting layer and three photoelectric converting layers having sizes of the hyperfine particles changed are laminated on a semiconductor substrate, and electric signals corresponding to quantities of received lights for red, green and blue colors are generated from each of the photoelectric converting layers. 
     Also in the image sensor described in JP-A-2002-83946, three nanosilicon layers having different particle sizes are laminated on a semiconductor substrate and each of electric signals for red, green and blue colors which are detected in the respective nanosilicon layers is read onto a storage diode formed in a surface portion of the semiconductor substrate. 
       FIG. 5  is a typical sectional view corresponding to two pixels for the related-art photoelectric converting layer lamination type solid-state image pick-up device. In  FIG. 5 , a high concentration impurity region  2  for storing a red signal, an MOS circuit  3  for reading a read signal, a high concentration impurity region  4  for storing a green signal, an MOS circuit  5  for reading a green signal, a high concentration impurity region  6  for storing a blue signal and an MOS circuit  7  for reading a blue signal are formed on a surface portion of a P well layer  1  provided on an n-type silicon substrate. 
     Each of the MOS circuits  3 ,  5  and  7  is constituted by impurity regions for a source and a drain which are formed on the surface of the semiconductor substrate and a gate electrode formed through a gate insulating layer  8 . An insulating layer  9  is laminated on the gate insulating layer  8  and the gate electrodes and is flattened and a shielding layer  10  is laminated thereon. In many cases, the shielding layer is formed by a thin metal layer. Therefore, an insulating layer  11  is further formed thereon. 
     Signal charges stored in the high concentration impurity regions  2 ,  4  and  6  for storing the color signals are read to an outside by the MOS circuits  3 ,  5  and  7 . 
     A pixel electrode layer  12  divided for each pixel is formed on the insulating layer  11  shown in  FIG. 5 . The pixel electrode layer  12  for each pixel is conducted through a columnar electrode  13  to the high concentration impurity region  2  for storing a red signal for each pixel. The columnar electrode  13  is electrically insulated from components other than the pixel electrode layer  12  and the high concentration impurity region  2 . 
     A photoelectric converting layer  14  for detecting a red color is laminated on the pixel electrode layer  12  in a one-sheet structure in common to each pixel, and furthermore, a transparent common electrode layer  15  is formed thereon in a one-sheet structure in common to each pixel. 
     Similarly, a transparent insulating layer  16  is formed on the common electrode layer  15  and a transparent pixel electrode layer  17  divided for each pixel is formed thereon. Each pixel electrode layer  17  and the high concentration impurity region  4  for storing a green signal for each pixel corresponding thereto are conducted through a columnar electrode  18 . The columnar electrode  18  is electrically insulated from components other than the pixel electrode layer  17  and the high concentration impurity region  4 . A photoelectric converting layer  19  for detecting a green signal is formed on each pixel electrode layer  17  in a one-sheet structure in the same manner as the photoelectric converting layer  14 , and a transparent common electrode layer  20  is formed thereon. 
     A transparent insulating layer  21  is formed on the common electrode layer  20  and a pixel electrode layer  22  divided for each pixel is formed thereon. The pixel electrode layer  22  is conducted to the high concentration impurity region  6  for storing a blue signal for each pixel corresponding thereto through a columnar electrode  26 . The columnar electrode  26  is electrically insulated from components other than the pixel electrode layer  22  and the high concentration impurity region  6 . A photoelectric converting layer  23  for detecting a blue signal is laminated on the pixel electrode layer  22  in a one-sheet structure in common to each pixel, a transparent common electrode layer  24  is formed thereon and a transparent protective layer  25  is formed as an uppermost layer. 
     When a light is incident on the solid-state image pick-up device, optical charges corresponding to the quantities of incident lights having blue, green and red colors are excided in each of the photoelectric converting layers  23 ,  19  and  14 . A voltage is applied between the common electrode layers  24 ,  20  and  15  and the pixel electrode layers  22 ,  17  and  12  so that the respective optical charges flow into the high concentration impurity regions  2 ,  4  and  6  and are read as blue, green and red signals to an outside through the MOS circuits  3 ,  5  and  7 . 
     In the related-art photoelectric converting layer lamination type solid-state image pick-up device shown in  FIG. 5 , there is a problem in that a difference in a sensitivity for each color is made and a color balance of a pick-up image is thus lost to cause a deterioration in picture quality if the photoelectric converting efficiencies of the photoelectric converting layers  14 ,  19  and  23  are not equal to each other. Moreover, there is also a problem in that S/N is reduced because of an insufficient pixel separation of a detection signal through each pixel electrode layer. Furthermore, there is also a problem in that a quantity of a received light in a peripheral part of the solid-state image pick-up device is smaller than that in a central part thereof and shading is thus generated in an incorporation in a digital still camera in some cases. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a photoelectric converting layer lamination type solid-state image pick-up device capable of increasing a pixel separation performance of a detection signal to enhance S/N and suppressing a difference in a sensitivity for each color to improve picture quality, and furthermore, preventing shading from being generated. 
     The invention provides a photoelectric converting layer lamination type solid-state image pick-up device comprising: a semiconductor substrate; at least three layers of photoelectric converting layers each of which is interposed between a common electrode layer and pixel electrode layers, the pixel electrode layers corresponding to pixels respectively, wherein said at least three layers of photoelectric converting layers are laminated through insulating layers, said at least three layers of photoelectric converting layers being above the semiconductor substrate, and wherein each of said at least three layers of photoelectric converting layers is separated into layers corresponding the pixels respectively. 
     By this structure, a pixel separation performance of an image signal (a detection signal) detected from each pixel can be improved and S/N of the detection signal can be enhanced. 
     According to the invention, there is provided the photoelectric converting layer lamination type solid-state image pick-up device, wherein an area of each of said at least three layers of photoelectric converting layers is set corresponding to each of photoelectric converting characteristics of said at least three layers of photoelectric converting layers. 
     By this structure, the sensitivities of a layer for photoelectrically converting a red light, a layer for photoelectrically converting a green light and a layer for photoelectrically converting a blue light can be made uniform in each pixel so that a difference in the sensitivity for each color is eliminated. Consequently, it is possible to pick up a color image having a high color balance and high picture quality. 
     According to the invention, there is provided the photoelectric converting layer lamination type solid-state image pick-up device, wherein an area of each of said at least three layers of photoelectric converting layers for a pixel in a peripheral part of the solid-state image pick-up device is set to be larger than that of each of said at least three layers of photoelectric converting layers for a pixel in a central part of the solid-state image pick-up device. 
     By this structure, it is possible to avoid the generation of shading. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a typical sectional view corresponding to one pixel of a photoelectric converting layer lamination type solid-state image pick-up device according to a first embodiment of the invention; 
         FIG. 2  is a typical sectional view corresponding to one pixel of a photoelectric converting layer lamination type solid-state image pick-up device according to a second embodiment of the invention; 
         FIG. 3  is a typical view showing a surface of a photoelectric converting layer lamination type solid-state image pick-up device according to a third embodiment of the invention; 
         FIGS. 4A and 4B  are typical sectional views showing photoelectric converting layer portions of the photoelectric converting layer lamination type solid-state image pick-up devices according to the third and fourth embodiments of the invention; and 
         FIG. 5  is a typical sectional view corresponding to two pixels of the related-art photoelectric converting layer lamination type solid-state image pick-up device. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An embodiment of the invention will be described below with reference to the drawings. 
       FIG. 1  is a typical sectional view corresponding to one pixel of a photoelectric converting layer lamination type solid-state image pick-up device according to a first embodiment of the invention. A signal reading circuit is formed in a surface portion of a semiconductor substrate  100 . The signal reading circuit may be constituted by an MOS transistor circuit in the same manner as in  FIG. 5  or may be constituted by the same charge transfer path as that in the related-art CCD type image sensor as shown in  FIG. 1 . 
     In the photoelectric converting layer lamination type solid-state image pick-up device shown in  FIG. 1 , a P well layer  102  is formed in the surface portion of the n-type semiconductor substrate  100 , and furthermore, a diode portion  141  to be a first color charge storage region, a diode portion  142  to be a second color charge storage region and a diode portion  143  to be a third color charge storage region are formed in a P region  103  in the surface portion and charge transfer paths  151 ,  152  and  153  are formed between the diode portions. A channel stopper  106  formed by a p+ region is provided between the diode portion  141  and the charge transfer path  151 , the diode portion  142  and the charge transfer path  152 , and the diode portion  143  and the charge transfer path  153  which make pairs. 
     An insulating layer  107  is laminated on the surface of the semiconductor substrate  100  and charge transfer electrodes  181 ,  182  and  183  are formed on the charge transfer paths  151 ,  152  and  153  in the insulating layer  107 , and furthermore, electrodes  191 ,  192  and  193  to be connected to the diode portions  141 ,  142  and  143  are buried. The electrodes  191 ,  192  and  193  according to the embodiment also serve as shielding layers in such a manner that an incident light (mainly, an infrared ray because a visible light portion in the incident light is absorbed by a photoelectric converting layer to be an upper layer) is not incident on the signal reading circuit provided on the surface of the semiconductor substrate. 
     A pixel electrode layer  111  for a first color which is divided for each pixel is laminated on the insulating layer  107 . The pixel electrode layer  111  is formed by a transparent material. 
     A first layer photoelectric converting layer  112  for photoelectrically converting an incident light having a first color provided for each pixel and is laminated on each pixel electrode layer  111 , and a transparent common electrode layer (a counter electrode layer of the pixel electrode layer  111 )  113  is laminated on the first layer photoelectric converting layer  112 . 
     A transparent insulating layer  114  is laminated on the common electrode layer  113 , and furthermore, a transparent pixel electrode layer  115  for a second color which is divided for each pixel is laminated thereon. Then, a second layer photoelectric converting layer  116  for photoelectrically converting an incident light having a second color is divided for each pixel and is laminated on each pixel electrode layer  115 , and a transparent common electrode layer (an opposed layer to the pixel electrode layer  115 )  117  is laminated on the second layer photoelectric converting layer  116 . 
     A transparent insulating layer  118  is laminated on the common electrode layer  117 , and furthermore, a transparent pixel electrode layer  119  for a third color which is divided for each pixel is laminated thereon. Then, a third layer photoelectric converting layer  120  for photoelectrically converting an incident light having a third color is divided for each pixel and is laminated on each pixel electrode layer  119 , and a transparent common electrode layer (an opposed electrode to the pixel electrode layer  119 )  121  is laminated on the third layer photoelectric converting layer  120 . In some cases, moreover, a protective layer is formed thereon, which is not shown. 
     The pixel electrode layer  111  for a first color is electrically connected to the electrode  191  of the diode portion  141  for storing an electric charge having a first color through a longitudinal wiring (a columnar electrode)  122 , the pixel electrode layer  115  for a second color is electrically connected to the electrode  192  of the diode portion  142  for storing an electric charge having a second color through a longitudinal wiring (a columnar electrode)  123 , and the pixel electrode layer  119  for a third color is electrically connected to the electrode  193  of the diode portion  143  for storing an electric charge having a third color through a longitudinal wiring  124 . The longitudinal wirings  122 ,  123  and  124  are insulated from components other than the electrodes  191 ,  192  and  193  and the pixel electrode layers  111 ,  115  and  119  corresponding thereto. 
     The materials of the photoelectric converting layers  112 ,  116  and  120  to be the layers may be organic or inorganic but preferably have a thin layer structure of a direct transition type, a fine particle structure or a Gratzel structure. In case of the fine particle structure, it is possible to control a band gap end. By controlling a nano particle diameter of CdSe, InP, ZnTe or ZnSe, for example, it is possible to control a wavelength region to be converted photoelectrically. 
     It is assumed that the first color is red (R), the second color is green (G) and the third color is clue (B). When a light is incident on the photoelectric converting layer lamination type solid-state image pick-up device, a light in a wavelength region having the blue color in the incident light is absorbed in the third layer photoelectric converting layer  120  so that an electric charge corresponding to a quantity of the absorbed light is generated and flows from the pixel electrode layer  119  into the diode portion  143  through the longitudinal wiring  124  and the electrode  193 . 
     Similarly, a light in a wavelength region having the green color in the incident light is transmitted through the third layer photoelectric converting layer  120  and is absorbed in the second layer photoelectric converting layer  116  so that an electric charge corresponding to a quantity of the absorbed light is generated and flows from the pixel electrode layer  115  into the diode portion  142  through the longitudinal wiring  123  and the electrode  192 . 
     Similarly, a light in a wavelength region having a red color in the incident light is transmitted through the third and second layer photoelectric converting layers  120  and  116  and is absorbed in the first layer photoelectric converting layer  112  so that an electric charge corresponding to a quantity of the absorbed light is generated and flows from the pixel electrode layer  111  into the diode portion  141  through the longitudinal wiring  122  and the electrode  191 . 
     A signal can be fetched from each of the diode portions  141 ,  142  and  143  by a method in accordance with the fetch of a signal from an ordinary light receiving unit formed of silicon. For example, a constant quantity of bias charges are injected into the diode portions  141 ,  142  and  143  (a refresh mode) and constant charges are stored by a light incidence (a photoelectric converting mode), and a signal charge is then read. An organic light receiving unit itself can be used as a storage diode and the storage diode can also be provided separately. It is possible to apply a reading method of a CCD or CMOS sensor to the read of the signal charge. 
     Although the photoelectric converting layers to be the first, second and third layers in the related-art photoelectric converting layer lamination type solid-state image pick-up device have a one-sheet structure in common to the respective pixels, they are separated and formed every pixel in the photoelectric converting layer lamination type solid-state image pick-up device according to the embodiment as described above. Therefore, the pixel separation performance of optical charges flowing into the diodes  141 ,  142  and  143 , that is, image signals (detection signals) can be improved so that S/N can also be enhanced. 
       FIG. 2  is a typical sectional view showing a main part corresponding to one pixel of a photoelectric converting layer lamination type solid-state image pick-up device according to a second embodiment of the invention. In the photoelectric converting layer lamination type solid-state image pick-up device according to the embodiment, most parts of the structure are the same as those in the structure of the photoelectric converting layer lamination type solid-state image pick-up device according to the first embodiment shown in  FIG. 1 . Therefore, the same components have the same reference numerals and description thereof will be omitted. 
     In the photoelectric converting layer lamination type solid-state image pick-up device according to the first embodiment shown in  FIG. 1 , areas of the first layer photoelectric converting layer  112 , the second layer photoelectric converting layer  116  and the third layer photoelectric converting layer  120  corresponding to one pixel are set to be equal to each other. This structure has no problem if the photoelectric converting efficiencies of the first layer photoelectric converting layer  112 , the second layer photoelectric converting layer  116  and the third layer photoelectric converting layer  120  are identical to each other. 
     Since these three photoelectric converting layers  112 ,  116  and  120  have different wavelength ranges for absorbing a light, however, they are manufactured by different materials and the same photoelectric converting characteristics, particularly, the identical photoelectric converting efficiencies cannot be obtained in some cases. Therefore, the embodiment is characterized in that the areas of the photoelectric converting layers  112 ,  116  and  120  are set to be varied depending on the materials of the photoelectric converting layers. In an example shown in  FIG. 2 , a photoelectric converting layer  116   a  for photoelectrically converting a light for a green color has a high photoelectric converting efficiency and a high sensitivity, and therefore, has an area which is smaller than the areas of the photoelectric converting layers  112  and  120  having other colors. 
     In the photoelectric converting layer lamination type solid-state image pick-up device according to the embodiment, consequently, a difference in a sensitivity among the photoelectric converting layers to be the three layers, that is, a difference in a sensitivity for each color is eliminated. Consequently, a color balance of a pick-up image can be enhanced so that an image of high picture quality can be picked up. 
       FIG. 3  is a typical view showing a surface of a photoelectric converting layer lamination type solid-state image pick-up device according to a third embodiment of the invention. In the photoelectric converting layer lamination type solid-state image pick-up device according to the embodiment, an area of a pixel  202  in a peripheral part of the device is set to be larger than that of a pixel  201  in a central part thereof. In other words, the area of the pixel is gradually increased from the central part of the device toward the peripheral part thereof. 
       FIG. 4A  is a typical sectional view showing photoelectric converting layer portions of the pixel  201  in the central part of the device and the pixel  202  in the peripheral part of the device shown in  FIG. 3 . It is shown that areas of the photoelectric converting layers  112 ,  116  and  120  to be the first, second and third layers of the pixel  202  in the peripheral part of the device are larger than those of the photoelectric converting layers  112 ,  116  and  120  to be the first, second and third layers of the pixel  201  in the central part of the device. 
     According to the photoelectric converting layer lamination type solid-state image pick-up device in accordance with the embodiment, the pixel in the peripheral part of the device has a larger area and a larger light receiving area. Even if a quantity of a light in the peripheral part is reduced, therefore, the light receiving area of the pixel in the peripheral part is increased. Consequently, it is possible to avoid shading. 
       FIG. 4B  is an explanatory view showing a photoelectric converting layer lamination type solid-state image pick-up device according to a fourth embodiment of the invention. The photoelectric converting layer lamination type solid-state image pick-up device according to the embodiment has a structure obtained by combining the second and third embodiments, in which a pixel area is more increased toward a peripheral part of a device and an area of a photoelectric converting layer to be each layer is set corresponding to a sensitivity of the photoelectric converting layer to be each layer. Consequently, shading can be avoided and a light receiving sensitivity of the photoelectric converting layer for each color can be made uniform so that an image of high picture quality can be picked up. 
     According to the invention, the pixel separation performance of the detection signal is increased so that the S/N can be enhanced. Moreover, the difference in the sensitivity for each color is suppressed so that the picture quality can be improved, and furthermore, the generation of the shading can be suppressed. 
     In the photoelectric converting layer lamination type solid-state image pick-up device according to the invention, a pixel separation performance can be enhanced. Consequently, S/N of a detection signal can be enhanced, a color balance can be improved and shading can easily be avoided. Consequently, the photoelectric converting layer lamination type solid-state image pick-up device is useful as a solid-state image pick-up device in place of the related-art image sensor of a CCD type or a CMOS type. 
     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.