Image sensor and method for fabricating the same

Abstract

An image sensor and a method for fabricating the same are disclosed, in which an impurity implantation layer having a predetermined thickness is formed on a source diffusion layer, thereby controlling a substantial contact point between a contact plug and the source diffusion layer upward from a surface of a semiconductor substrate. As a result, it is possible to minimize a length of an open hole, which is a main channel of the contact plug, so that the open hole has the sufficiently large size, thereby inducing the improvement of the contact quality between the contact plug and the source diffusion layer. Also, in case of the CMOS image sensor, in state the impurity implantation layer having the impurity selectively implanted is formed on the source diffusion layer, the impurity implantation layer is electrically connected with the source diffusion layer. Accordingly, without the additional process such as highly-impurity implantation and formation of salicide layer, it is possible for the source diffusion layer to increase the impurity concentration of impurity therein. Eventually, in case of realizing the image sensor according to the present invention, it is possible to the greatest contact quality between the contact plug and the source diffusion layer. In case of realizing the greatest contact quality between the contact plug and the source diffusion layer with the additional formation of the impurity implantation layer, for example, the source diffusion layer normally performs the function of converting the optical charges generated by the photodiode to voltage constituents. Thus, the completed image sensor according to the present invention realizes the great image quality.

1 . An image sensor comprising:
 a photodiode formed in an active area of a semiconductor substrate, for receiving incident light from the external and generating optical charges;   a transistor having an impurity diffusion layer being electrically connected with the photodiode, for transferring/discharging the optical charges generated by the photodiode to a signal processing circuit;   an impurity implantation layer formed on the impurity diffusion layer;   an insulating interlayer formed above the semiconductor substrate to cover the photodiode, the transistor, and the impurity implantation layer;   an open hole penetrating the insulating interlayer to open the impurity diffusion layer; and   a contact plug for filling the open hole, and electrically connecting the impurity diffusion layer.   
   
   
       2 . The image sensor of  claim 1 , wherein the impurity implantation layer is formed of an epitaxial silicon layer. 
   
   
       3 . The image sensor of  claim 1 , wherein the impurity implantation layer is formed by highly implanting impurity. 
   
   
       4 - 5 . (canceled) 
   
   
       6 . The image sensor of  claim 1 , wherein the photodiode comprises a P-type impurity diffusion layer and an N-type impurity diffusion layer. 
   
   
       7 . The image sensor of  claim 6 , wherein the impurity diffusion layer makes a junction with the P-type impurity diffusion layer and the N-type impurity diffusion layer. 
   
   
       8 . The image sensor of  claim 1 , wherein the insulating interlayer is comprised of a BPSG layer and a TEOS layer. 
   
   
       9 . The image sensor of  claim 1 , wherein the image sensor further comprises a barrier layer formed in the interface between the semiconductor substrate and the insulating interlayer. 
   
   
       10 . The image sensor of  claim 9 , wherein the barrier layer comprises SiN. 
   
   
       11 . The image sensor of  claim 1 , wherein the contact plug comprises tungsten. 
   
   
       12 . The image sensor of  claim 1 , wherein the image sensor further comprises a metal layer formed above the contact plug.