Image sensor and manufacturing method therefor

Abstract

The present disclosure relates to the technical field of semiconductors, and discloses an image sensor and a manufacturing method therefor. The image sensor includes: a semiconductor substrate; a first active region located on the semiconductor substrate; a doped semiconductor layer located on the first active region; and a contact located on the semiconductor layer, where the first active region includes: a first doped region and a second doped region abutting against the first doped region, wherein the second doped region is located at an upper surface of the first active region, and wherein the second doped region is formed by dopants in the semiconductor layer that are annealed to be diffused to a surface layer of the first doped region. The present disclosure may reduce leakage current and improve device performances.

What is claimed is: 
     
         1 . An image sensor, comprising:
 a semiconductor substrate;   a first active region located on the semiconductor substrate;   a doped semiconductor layer located on the first active region; and   a contact located on the semiconductor layer,   wherein the first active region comprises: a first doped region and a second doped region abutting against the first doped region,   wherein the second doped region is located at an upper surface of the first active region, and   wherein the second doped region is formed by dopants in the semiconductor layer that are annealed to be diffused to a surface layer of the first doped region.   
     
     
         2 . The image sensor according to  claim 1 , wherein a conductivity type of the first doped region is contrary to a conductivity type of the second doped region. 
     
     
         3 . The image sensor according to  claim 1 , wherein the semiconductor layer comprises polysilicon. 
     
     
         4 . The image sensor according to  claim 1 , wherein the first active region further comprises:
 a third doped region abutting against the first doped region,   wherein a conductivity type of the third doped region is contrary to a conductivity type of the first doped region.   
     
     
         5 . The image sensor according to  claim 4 , further comprising:
 a first gate structure located on the first active region and above a portion at which the first doped region abuts against the third doped region.   
     
     
         6 . The image sensor according to  claim 5 , further comprising:
 a spacer located on the first active region and at a side surface of the first gate structure, the spacer separating the semiconductor layer and the first gate structure.   
     
     
         7 . The image sensor according to  claim 5 , wherein
 the first active region further comprises: a fourth doped region abutting against the third doped region and separated from the first doped region, a part of the fourth doped region being located below the first gate structure,   wherein a conductivity type of the fourth doped region is contrary to a conductivity type of the third doped region.   
     
     
         8 . The image sensor according to  claim 5 , further comprising:
 a barrier layer covering a part of the first gate structure, the semiconductor layer, and the first active region, wherein the contact passes through the barrier layer so as to be in contact with the semiconductor layer.   
     
     
         9 . The image sensor according to  claim 1 , further comprising:
 a second active region located on the semiconductor substrate and separated from the first active region, and   a third active region located on the semiconductor substrate and separated from the second active region,   wherein the second active region comprises a fifth doped region, the third active region comprises a sixth doped region, and a conductivity type of the sixth doped region is contrary to a conductivity type of the fifth doped region.   
     
     
         10 . The image sensor according to  claim 9 , further comprising:
 a second gate structure located on the second active region, and a third gate structure located on the third active region;   a first source electrode and a first drain electrode in the second active region and located at two sides of the second gate structure, the first source electrode and the first drain electrode abutting against the fifth doped region, separately; and   a second source electrode and a second drain electrode in the third active region and located at two sides of the third gate structure, the second source electrode and the second drain electrode abutting against the sixth doped region, separately.   
     
     
         11 . A method for manufacturing an image sensor, comprising:
 providing a semiconductor structure, wherein the semiconductor structure comprises: a semiconductor substrate and a first active region located on the semiconductor substrate, the first active region comprising a first doped region;   forming a doped semiconductor layer on the first active region;   annealing to diffuse dopants in the semiconductor layer to a surface layer of the first doped region, so as to form a second doped region, wherein the second doped region is located at an upper surface of the first active region; and   forming a contact connected to the semiconductor layer.   
     
     
         12 . The method according to  claim 11 , wherein forming a doped semiconductor layer comprises:
 forming an undoped semiconductor layer on the first doped region; and   executing a first doping to the undoped semiconductor layer so as to form the doped semiconductor layer, the first doping enabling a conductivity type of the semiconductor layer to be contrary to the conductivity type of the first doped region.   
     
     
         13 . The method according to  claim 11 , wherein a conductivity type of the first doped region is contrary to a conductivity type of the second doped region. 
     
     
         14 . The method according to  claim 11 , wherein material of the semiconductor layer comprises polysilicon. 
     
     
         15 . The method according to  claim 12 , wherein the first doping is executed using an ion implantation, and energy of the ion implantation is determined according to thickness of the semiconductor layer, so that depth of the ion implantation does not exceeds the semiconductor layer. 
     
     
         16 . The method according to  claim 12 , further comprising:
 before the doped semiconductor layer is formed, forming a first gate structure located on the first active region.   
     
     
         17 . The method according to  claim 16 , further comprising:
 before the doped semiconductor layer is formed, forming a spacer layer on the semiconductor structure and the first gate structure and partially etching the spacer layer to expose a part of the first doped region; and   wherein forming the doped semiconductor layer comprises: forming the doped semiconductor layer on the exposed part of the first doped region.   
     
     
         18 . The method according to  claim 17 , wherein in the step of partially etching the spacer layer, the spacer layer covering a side surface of the first gate structure is etched to form a first part of the spacer;
 wherein in the step of forming the semiconductor layer, the first part of the spacer separates the semiconductor layer and the first gate structure; and   wherein the method further comprises: after the undoped semiconductor layer is formed, and before the first doping is executed to the undoped semiconductor layer, etching a remaining spacer layer so as to form a second part of the spacer covering the side surface of the first gate structure.   
     
     
         19 . The method according to  claim 16 , wherein the first active region further comprises:
 a third doped region abutting against the first doped region,   wherein a conductivity type of the third doped region is contrary to a conductivity type of the first doped region, and the first gate structure is above a portion at which the first doped region abuts against the third doped region.   
     
     
         20 . The method according to  claim 19 , wherein the first active region further comprises:
 a fourth doped region abutting against the third doped region and separated from the first doped region, a part of the fourth doped region being located below the first gate structure,   wherein a conductivity type of the fourth doped region is contrary to the conductivity type of the third doped region.   
     
     
         21 . The method according to  claim 11 , wherein
 a temperature range of the annealing is from 700° C. to 1000° C., and   a time range of the annealing is from 5 min to 1 h.   
     
     
         22 . The method according to  claim 16 , wherein the method further comprises: after the annealing is executed and before the contact is formed, forming a barrier layer on a part of the first gate structure, the semiconductor layer, and the first active region; and
 wherein forming the contact comprises: etching the barrier layer to form an opening exposing a part of the semiconductor layer, and forming, in the opening, the contact connected to the semiconductor layer.   
     
     
         23 . The method according to  claim 11 , wherein the method further comprises:
 forming a second active region located on the semiconductor substrate and separated from the first active region, and forming a third active region located on the semiconductor substrate and separated from the second active region,   wherein the second active region comprises a fifth doped region, the third active region comprises a sixth doped region, and a conductivity type of the sixth doped region is contrary to a conductivity type of the fifth doped region.   
     
     
         24 . The method according to  claim 23 , wherein the method further comprises:
 forming a second gate structure located on the second active region, and a third gate structure located on the third active region; and   after the annealing and before the contact is formed:
 executing a second doping to the second active region, so as to form, in the fifth doped region, a first source electrode and a first drain electrode at two sides of the second gate structure, separately; and 
 executing a third doping to the third active region, so as to form, in the sixth doped region, a second source electrode and a second drain electrode at two sides of the third gate structure, separately.