Solid state image pickup device and its manufacture method

Abstract

A solid state image pickup device is provided which includes: charge accumulation regions disposed in a semiconductor substrate in a matrix shape; a plurality of vertical transfer channels formed in the semiconductor substrate each in a close proximity to each column of the charge accumulation regions; vertical transfer electrodes formed above the vertical transfer channels; a channel protective impurity layer formed just under the vertical transfer channel and surrounding the charge accumulation region; one or more pixel separation impurity layers formed under the channel protective impurity layer and at a position facing the channel protective impurity layer; an overflow barrier region having a peak position of an impurity concentration at a position deeper than the pixel separation impurity layer, the peak position of the impurity concentration being at a depth of 3 μm or deeper from a surface of the semiconductor substrate; and a horizontal CCD for transferring signal charges transferred from the vertical transfer channels in a horizontal direction.

1 . A solid state image pickup device comprising: 
 charge accumulation regions of a first conductivity type disposed in a semiconductor substrate in a matrix shape, said charge accumulation region accumulating signal charges photoelectrically converted from incidence light;    a plurality of vertical transfer channels of the first conductivity type formed in said semiconductor substrate each in a close proximity to each column of said charge accumulation regions and extending in a column direction as a whole;    vertical transfer electrodes formed above said vertical transfer channels, said vertical transfer electrodes controlling a potential of said vertical transfer channels and a potential of a region between said charge accumulation region and said vertical transfer channel to read the signal charges accumulated in said charge accumulation regions and transfer the signal charges along the column direction;    a channel protective impurity layer of a second conductivity type opposite to the first conductivity type formed in said semiconductor substrate just under said vertical transfer channel and surrounding said charge accumulation region;    one or more pixel separation impurity layers of the second conductivity type formed in said semiconductor substrate, under said channel protective impurity layer and at a position facing said channel protective impurity layer;    an overflow barrier region of the second conductivity type formed in said semiconductor substrate and having a peak position of an impurity concentration at a position deeper than said pixel separation impurity layer, said peak position of the impurity concentration being at a depth of 3 μm or deeper from a surface of said semiconductor substrate; and    a horizontal CCD for transferring signal charges transferred from said vertical transfer channels in a horizontal direction.    
     
     
         2 . The solid state image pickup device according to  claim 1 , wherein an impurity concentration of said pixel separation impurity layer is lower than an impurity concentration of said channel protective impurity layer.  
     
     
         3 . The solid state image pickup device according to  claim 1 , wherein the impurity concentration of said pixel separation impurity layer is lower than an impurity concentration of said overflow barrier region.  
     
     
         4 . The solid state image pickup device according to  claim 1 , wherein said charge accumulation regions disposed in the matrix shape include first charge accumulation regions disposed in a first square matrix shape and second charge accumulation regions disposed in a second square matrix shape at positions between lattice points of said first charge accumulation regions disposed in the first square matrix shape.  
     
     
         5 . The solid state image pickup device according to  claim 1 , wherein the first conductivity type is an n-type.  
     
     
         6 . A manufacture method for a solid state image pickup device comprising steps of: 
 (a) implanting, into a whole surface of a semiconductor substrate of a first conductivity type, impurity ions of a second conductivity type opposite to the first conductivity type, to form an overflow barrier region;    (b) implanting impurity ions of the second conductivity type into said semiconductor substrate above said overflow barrier region to form a first pixel separation impurity layer;    (c) epitaxially growing a semiconductor layer on said semiconductor substrate to form an epitaxial substrate;    (d) implanting impurity ions of the second conductivity type into said epitaxial substrate above said first pixel separation impurity layer to form a channel protective impurity layer surrounding a region where a charge accumulation region is to be formed;    (e) implanting impurity ions of the first conductivity type into said epitaxial substrate above said channel protective impurity layer to form vertical transfer channels;    (f) forming vertical transfer electrodes above said vertical transfer channel; and    (g) implanting impurity ions of the first conductivity type into said epitaxial substrate in a region surrounded by said channel protective impurity layer to form the charge accumulation region, a peak position of an impurity concentration in said overflow barrier region being eventually set to a depth of 3 μm or deeper from a surface of said epitaxial substrate.    
     
     
         7 . The manufacture method for a solid state image pickup device according to  claim 6 , wherein said step (d) comprises: 
 (d1) implanting impurity ions of the second conductivity type into said epitaxial substrate above said first pixel separation impurity layer to form a second pixel separation impurity layer;    (d2) epitaxially growing a semiconductor layer on said epitaxial substrate; and    (d3) implanting impurity ions of the second conductivity type into said epitaxial substrate above said first and second pixel separation impurity layers to form said channel protective impurity layer surrounding the region where said charge accumulation region is to be formed.    
     
     
         8 . The manufacture method for a solid state image pickup device according to  claim 6  or  7 , wherein implanting impurity ions of the second conductivity type at said step (b) is performed at a first dose, and implanting impurity ions of the second conductivity type at said step (d) or (d3) is performed at a second dose larger than the first dose.  
     
     
         9 . The manufacture method for a solid state image pickup device according to  claim 7 , wherein implanting impurity ions of the second conductivity type at said step (d1) is performed at a third dose, and implanting impurity ions of the second conductivity type at said step (d3) is performed at the second dose larger than the third dose.  
     
     
         10 . The manufacture method for a solid state image pickup device according to  claim 6 , wherein implanting impurity ions of the second conductivity type at said step (a) is performed at a fourth dose, and implanting impurity ions of the second conductivity type at said step (b) is performed at the first dose smaller than the fourth dose.  
     
     
         11 . The manufacture method for a solid state image pickup device according to  claim 7 , wherein implanting impurity ions of the second conductivity type at said step (a) is performed at a fourth dose, and implanting impurity ions of the second conductivity type at said step (d1) is performed at the third dose smaller than the fourth dose.  
     
     
         12 . The manufacture method for a solid state image pickup device according to  claim 6 , wherein at said step (g) said charge accumulation regions are formed in a matrix shape as viewed along a normal direction of said semiconductor substrate.  
     
     
         13 . The manufacture method for a solid state image pickup device according to  claim 12 , wherein at said step (g) said charge accumulation regions are formed in a matrix shape as viewed along a normal direction of said semiconductor substrate, the matrix shape including a first square matrix and a second square matrix formed at positions between lattice points of the first square matrix.  
     
     
         14 . The manufacture method for a solid state image pickup device according to  claim 6 , wherein the first conductivity type is an n-type.