Semiconductor device provided with photodiode, manufacturing method thereof, and optical disc device

Abstract

A semiconductor device includes: a P-type semiconductor substrate; a first P-type semiconductor layer formed on the P-type semiconductor substrate; a second P-type semiconductor layer formed on the first P-type semiconductor layer and having a lower P-type impurity concentration than the first P-type semiconductor layer; an N-type semiconductor layer, which will form a cathode region, formed on the second P-type semiconductor layer; a first P-type diffusion layer formed by diffusing a P-type impurity in a partial region of the second P-type semiconductor layer; a second P-type diffusion layer formed by diffusing a P-type impurity in the second P-type semiconductor layer so as to be present adjacently beneath the first P-type diffusion layer at a lower P-type impurity concentration than the first P-type diffusion layer; and a photodiode formed in such a manner that the N-type semiconductor layer and the first P-type diffusion layer are isolated from each other.

What is claimed is: 
     
         1 . A semiconductor device comprising:
 a second semiconductor layer ( 12 ) of a first conductivity type (P-type) between a first semiconductor layer ( 11 ) of the first conductivity type (P-type) and a cathode region ( 22 ) of a second conductivity type (N-type), said cathode region ( 22 ) touching said second semiconductor layer ( 12 ) and a surface of a semiconductor substrate;   a first diffusion layer ( 19 ) of a first conductivity type (P-type) touching said second semiconductor layer ( 12 ) and said surface of the semiconductor substrate, said second semiconductor layer ( 12 ) physically separating said cathode region ( 22 ) from said first diffusion layer ( 19 );   a second diffusion layer ( 15 ) of the first conductivity type (P-type) between said first diffusion layer ( 19 ) and said second semiconductor layer ( 12 ), said second semiconductor layer ( 12 ) physically separating said first semiconductor layer ( 11 ) from said second diffusion layer ( 15 ),   wherein an impurity concentration of the first conductivity type (P-type) in said second diffusion layer ( 15 ) is lower than an impurity concentration of the first conductivity type (P-type) in said first diffusion layer ( 19 ).   
     
     
         2 . The semiconductor device according to  claim 1 , wherein said first conductivity type (P-type) is P-type. 
     
     
         3 . The semiconductor device according to  claim 1 , wherein said second conductivity type (N-type) is N-type. 
     
     
         4 . The semiconductor device according to  claim 1 , wherein a conductivity of the first conductivity type (P-type) is opposite to a conductivity of the second conductivity type (N-type). 
     
     
         5 . The semiconductor device according to  claim 1 , wherein said second diffusion layer ( 15 ) touches said first diffusion layer ( 19 ) and said second semiconductor layer ( 12 ). 
     
     
         6 . The semiconductor device according to  claim 1 , wherein said second semiconductor layer ( 12 ) touches said second diffusion layer ( 15 ) and said first semiconductor layer ( 11 ). 
     
     
         7 . The semiconductor device according to  claim 1 , wherein said second semiconductor layer ( 12 ) is between said first semiconductor layer ( 11 ) and said second diffusion layer ( 15 ). 
     
     
         8 . The semiconductor device according to  claim 1 , wherein said second semiconductor layer ( 12 ) is between said cathode region ( 22 ) and said first diffusion layer ( 19 ). 
     
     
         9 . The semiconductor device according to  claim 1 , wherein an impurity concentration of the first conductivity type (P-type) in said second semiconductor layer ( 12 ) being lower than said impurity concentration of the first conductivity type (P-type) in said first diffusion layer ( 19 ). 
     
     
         10 . The semiconductor device according to  claim 9 , wherein said impurity concentration of the first conductivity type (P-type) in said second semiconductor layer ( 12 ) is lower than an impurity concentration of the first conductivity type (P-type) in said first semiconductor layer ( 11 ). 
     
     
         11 . The semiconductor device according to  claim 1 , wherein a side end of the cathode region ( 22 ) is physically separated along an X axis direction from a side end of the first diffusion layer ( 19 ) by a distance alpha, said X axis direction being parallel to said surface of the semiconductor substrate. 
     
     
         12 . The semiconductor device according to  claim 11 , wherein said cathode region ( 22 ) terminates in said X axis direction at said side end of the cathode region ( 22 ). 
     
     
         13 . The semiconductor device according to  claim 11 , wherein said first diffusion layer ( 19 ) terminates in said X axis direction at said side end of the first diffusion layer ( 19 ). 
     
     
         14 . The semiconductor device according to  claim 11 , wherein said distance alpha is 3.0 μm to 4.0 μm. 
     
     
         15 . The semiconductor device according to  claim 11 , wherein said side end of the first diffusion layer ( 19 ) is offset along said X axis direction from a side end of the second diffusion layer ( 15 ) by a distance beta. 
     
     
         16 . The semiconductor device according to  claim 15 , wherein said second diffusion layer ( 15 ) terminates in said X axis direction at said side end of the second diffusion layer ( 15 ). 
     
     
         17 . The semiconductor device according to  claim 15 , wherein said side end of the second diffusion layer ( 15 ) is separated along the X axis direction from said cathode region ( 22 ) by a sum total of the distance alpha and the distance beta. 
     
     
         18 . The semiconductor device according to  claim 15 , wherein said distance beta is 1.0 μm to 2.0 μm. 
     
     
         19 . An electronic device comprising:
 the semiconductor device according to  claim 1 ;   a processor ( 61 ) configured to electronically process an electric signal,   wherein said semiconductor device is configured to receive light and to convert said light into said electric signal.   
     
     
         20 . The electronic device according to  claim 19 , wherein said processor ( 61 ) is configured to perform an intensity detection process, said intensity detection process using said electric signal to detect an intensity of the light. 
     
     
         21 . The electronic device according to  claim 20 , wherein said processor ( 61 ) is configured to adjust said intensity of the light after performing said intensity detection process.