Backside illuminated image sensor with reduced dark current

Abstract

A backside illuminated image sensor comprises a sensor layer implementing a plurality of photosensitive elements of a pixel array, and an oxide layer adjacent a backside surface of the sensor layer. The sensor layer comprises a seed layer and an epitaxial layer formed over the seed layer, with the seed layer having a cross-sectional doping profile in which a designated dopant is substantially confined to a pixel array area of the sensor layer. The doping profile advantageously reduces dark current generated at an interface between the sensor layer and the oxide layer. The image sensor may be implemented in a digital camera or other type of digital imaging device.

1 . An image sensor having a pixel array configured for backside illumination, comprising:
 a sensor layer comprising a plurality of photosensitive elements of the pixel array; and   an oxide layer adjacent a backside surface of the sensor layer;   wherein the sensor layer comprises a seed layer and an epitaxial layer formed over the seed layer, the seed layer having a cross-sectional doping profile in which a designated dopant is substantially confined to a pixel array area of the sensor layer.   
     
     
         2 . The image sensor of  claim 1  wherein the dopant is an n-type dopant comprising one of arsenic and phosphorus. 
     
     
         3 . The image sensor of  claim 1  wherein the dopant is a p-type dopant comprising one of boron and indium. 
     
     
         4 . The image sensor of  claim 1  wherein the dopant is implanted into the seed layer through a sacrificial oxide layer that is formed over the seed layer and removed prior to formation of the epitaxial layer over the seed layer. 
     
     
         5 . The image sensor of  claim 1  wherein the dopant is implanted into the seed layer through an opening etched in a sacrificial oxide layer in the pixel array area and wherein the sacrificial oxide layer is removed prior to formation of the epitaxial layer over the seed layer. 
     
     
         6 . The mage sensor of  claim 1  wherein said image sensor comprises a CMOS image sensor. 
     
     
         7 . A digital imaging device comprising:
 an image sensor having a pixel array configured for backside illumination; and   one or more processing elements configured to process outputs of the image sensor to generate a digital image;   wherein said image sensor comprises:   a sensor layer comprising a plurality of photosensitive elements of the pixel array; and   an oxide layer adjacent a backside surface of the sensor layer;   wherein the sensor layer comprises a seed layer and an epitaxial layer formed over the seed layer, the seed layer having a cross-sectional doping profile in which a designated dopant is substantially confined to a pixel array area of the sensor layer.   
     
     
         8 . The digital imaging device of  claim 7  wherein said imaging device comprises a digital camera.