CMOS image sensor and method of fabrication

Abstract

A CMOS imaging device including a two pixel detection system for red, green, and blue light. One pixel detects red and blue light and another pixel detects green light. The detection of red and blue is based on wavelength and the device is structured such that in the red/blue pixel, detection of blue light is at a shallow substrate depth, while detection of red is at a deeper substrate depth. The pixel array is structured such that the red/blue pixel is adjacent to the green pixel and alternates between red/blue and green pixels. The invention is also related to methods of forming such an imager array and pixels.

1 - 118 . (canceled) 
   
   
       119 . A two color pixel comprising:
 a substrate having a surface;   a first color photoconversion device located below the surface of said substrate at a first absorption depth for a first wavelength of light; and   a second color photoconversion device located below the surface of said substrate at a second absorption depth for a second wavelength of light;   wherein said first color photoconversion device and said second color photoconversion device overlap within said substrate such that the first color photoconversion device is located closer to the surface of the substrate than the second color photoconversion device and said first and second color photoconversion devices are spaced apart vertically by a region of said substrate that does not produce photogenerated charges.   
   
   
       120 . The two color pixel of  claim 119 , wherein said first and second color photoconversion devices are photodiodes. 
   
   
       121 . The two color pixel of  claim 120 , wherein said first and second photodiodes are PIN photodiodes. 
   
   
       122 . The two color pixel of  claim 119 , wherein said first color photoconversion device is a blue light sensor. 
   
   
       123 . The two color pixel of  claim 122 , wherein said blue light sensor has a p-n junction located at a depth of from about 0.5 μm to about 1.0 μm from a top surface of the substrate. 
   
   
       124 . The two color pixel of  claim 119 , wherein said second color photoconversion device is a red light sensor. 
   
   
       125 . The two color pixel of  claim 124 , wherein said red light sensor has a p-n junction located at a depth of about 2.0 μm or greater from a top surface of the substrate. 
   
   
       126 . The two color pixel of  claim 124 , wherein said red light sensor has a p-n junction located at a depth of about 5.0 μm or greater from a top surface of the substrate. 
   
   
       127 . The two color pixel of  claim 119 , wherein a doped region connects said first color photoconversion device to a ground circuit. 
   
   
       128 . The two color pixel of  claim 127 , wherein said doped region is a p+ doped region. 
   
   
       129 . The two color pixel of  claim 119 , wherein a doped region connects said second color photoconversion device to a ground circuit. 
   
   
       130 . The two color pixel of  claim 129 , wherein said doped region is a p+ doped region. 
   
   
       131 . The two color pixel of  claim 119 , wherein said first and second color photoconversion devices comprise respective charge generating regions that are not coincident in size when viewed from the top. 
   
   
       132 . The two color pixel of  claim 131 , wherein said respective charge generating region of the first color photoconversion device occupies a smaller area than said respective charge generating region of the second color photoconversion device when viewed from the top. 
   
   
       133 . An array of pixel sensor cells comprising:
 a substrate having a top surface and comprising a plurality of first pixels for sensing a first color of light and a second color of light and second pixels for sensing a third color of light, said first pixels and said second pixels being arranged in an array of rows and columns;   said first pixel comprising a first photoconversion device located below the top surface of said substrate at a first depth and a second photoconversion device located below the top surface of said substrate at a second depth;   said first photoconversion device and said second photoconversion device being stacked below the top surface of the substrate and separated by a region of said substrate that does not produce photogenerated charges.   
   
   
       134 . The array of  claim 133 , wherein said first pixel senses red and blue colors of light. 
   
   
       135 . The array of  claim 133 , wherein said first photoconversion device is a blue light sensor. 
   
   
       136 . The array of  claim 135 , wherein said blue light sensor has a p-n junction located at a depth of from about 0.5 μm to about 1.0 μm from the top surface of the substrate. 
   
   
       137 . The array of  claim 133 , wherein said second photoconversion device is a red light sensor. 
   
   
       138 . The array of  claim 137 , wherein said red light sensor has a p-n junction located at a depth of about 2.0 μm or greater from the top surface of the substrate. 
   
   
       139 . The array of  claim 137 , wherein said red light sensor has a p-n junction located at a depth of about 5.0 μm or greater from the top surface of the substrate. 
   
   
       140 . The array of  claim 133 , wherein said first and second photoconversion devices comprise respective charge generating regions that are not coincident in size when viewed from the top. 
   
   
       141 . The array of  claim 140 , wherein said respective charge generating region of the first photoconversion device occupies a smaller area than said respective charge generating region of the second photoconversion device when viewed from the top. 
   
   
       142 . The array of  claim 133 , wherein each said second pixel senses green color of light. 
   
   
       143 . The array of  claim 133 , wherein said first pixels and second pixels are arranged in a checkerboard pattern across the array. 
   
   
       144 . A method for forming a pixel consisting of two color sensors, comprising:
 forming a first color photoconversion device within a substrate and below the surface of said substrate at a first depth corresponding to an absorption depth for a first wavelength of light; and   forming a second color photoconversion device within said substrate stacked below the first color photoconversion device at a second depth corresponding to an absorption depth for a second wavelength of light, said second depth being further from the surface of the substrate than the first depth, said first and second color photoconversion devices being separated by a region of said substrate that does not produce photogenerated charges.   
   
   
       145 . The method of  claim 144 , wherein said first color photoconversion device is a blue light sensor. 
   
   
       146 . The method of  claim 145 , wherein said blue light sensor has a p-n junction located at a depth of about 0.5 μm to about 1.0 μm from the upper surface of the substrate. 
   
   
       147 . The method of  claim 144 , wherein said second color photoconversion device is a red light sensor. 
   
   
       148 . The method of  claim 147 , wherein said red light sensor has a p-n junction located at a depth of about 2.0 μm or greater from the upper surface of the substrate. 
   
   
       149 . The method of  claim 147 , wherein said red light sensor has a p-n junction located at a depth of about 5.0 μm or greater from the upper surface of the substrate. 
   
   
       150 . The method of  claim 144 , wherein said first and second color photoconversion devices are not coincident in size when viewed from the top. 
   
   
       151 . The method of  claim 150 , wherein the first color photoconversion device occupies a smaller area than the second color photoconversion device when viewed from the top. 
   
   
       152 . A method for forming an array of pixel cells comprising:
 forming a plurality of first pixels for sensing a first color and a second color of light and second pixels for sensing a third color of light, said first pixels and second pixels being arranged in an array of rows and columns across a substrate;   forming a first color photoconversion device in said first pixels at a first depth below a surface of said substrate;   forming a second color photoconversion device in said first pixels at a second depth below the upper surface of said substrate and below the first color photoconversion device, said first color photoconversion device and second color photoconversion devices being separated by a region of said substrate that does not produce photogenerated charges; and   arranging said first and second pixels in an alternating pattern across said array.   
   
   
       153 . The method of  claim 152 , wherein said first color photoconversion device is a blue light sensor. 
   
   
       154 . The method of  claim 153 , wherein said blue light sensor has a p-n junction at a depth of about 0.5 μm to about 1.0 μm from the upper surface of the substrate. 
   
   
       155 . The method of  claim 152 , wherein said second color photoconversion device is a red light sensor. 
   
   
       156 . The method of  claim 155 , wherein said red light sensor has a p-n junction at a depth of about 2.0 μm or greater from the upper surface of the substrate. 
   
   
       157 . The method of  claim 155 , wherein said red light sensor has a p-n junction at a depth of about 5.0 μm or greater from the top surface of the substrate. 
   
   
       158 . The method of  claim 152 , wherein said second pixels sense green light. 
   
   
       159 . The method of  claim 152  wherein said alternating pattern is a checkerboard pattern. 
   
   
       160 . The method of  claim 152 , wherein said first color photoconversion device and said second color photoconversion device are not coincident in size when viewed from the top. 
   
   
       161 . The method of  claim 160 , wherein the first color photoconversion device occupies a smaller area than s the second color photoconversion device when viewed from the top.