CMOS Image Sensor

Abstract

A method of fabricating a CMOS image sensor is disclosed, by which image sensor characteristics are enhanced. In one aspect, the method includes forming a plurality of photodiodes in the photodiode region of a semiconductor substrate; stacking a first insulating layer over the semiconductor substrate including the photodiodes; forming a metal pad on the insulating layer in the pad region of the substrate; forming a second insulating layer over the semiconductor substrate including the metal pad; selectively etching exposed portions of the second insulating layer, using a mask, to form simultaneously a pad opening in the pad region and a trench in the photodiode region; selectively etching portions of the second insulating layer and the first insulating layer under the trench; and forming a slope on lateral sides of at least the second insulating layer.

1 . A CMOS image sensor, comprising:
 a semiconductor substrate having a photodiode region and a pad region;   a plurality of photodiodes in the photodiode region;   a first insulating layer over the semiconductor substrate including the photodiodes;   a metal pad on the first insulating layer in the pad region;   a second insulating layer over the semiconductor substrate including the metal pad;   a pad opening in the pad region; and   a trench in the first and second insulating layers in the photodiode region, the trench having a slope on lateral sides of at least the second insulating layer.   
   
   
       2 . The CMOS image sensor of  claim 1 , wherein the trench also has a slope on lateral sides of the first insulating layer. 
   
   
       3 . The CMOS image sensor of  claim 1 , wherein the pad opening also has a slope on its lateral sides. 
   
   
       4 . The CMOS image sensor of  claim 1 , further comprising a plurality of microlenses on the first insulating layer in the photodiode region. 
   
   
       5 . The CMOS image sensor of  claim 4 , wherein the microlenses comprise a resist. 
   
   
       6 . The CMOS image sensor of  claim 4 , wherein the microlenses comprise an oxide layer. 
   
   
       7 . The CMOS image sensor of  claim 6 , wherein the microlenses comprise a tetra-ethyl-ortho-silicate oxide. 
   
   
       8 . The CMOS image sensor of  claim 1 , wherein the second insulating layer comprises an oxide layer and a nitride layer thereon. 
   
   
       9 . The CMOS image sensor of  claim 1 , wherein the semiconductor substrate comprises first and second epitaxial layers. 
   
   
       10 . The CMOS image sensor of  claim 1 , wherein the plurality of photodiodes are adjacent to one another in the photodiode region. 
   
   
       11 . The CMOS image sensor of  claim 1 , wherein the semiconductor substrate comprises a single-crystal silicon wafer. 
   
   
       12 . The CMOS image sensor of  claim 11 , further comprising an epitaxial silicon layer on the single-crystal silicon wafer. 
   
   
       13 . The CMOS image sensor of  claim 1 , wherein the first insulating layer comprises a multi-layer structure. 
   
   
       14 . The CMOS image sensor of  claim 13 , wherein a first layer of the multi-layer structure comprises tetra-ethyl-ortho-silicate oxide. 
   
   
       15 . The CMOS image sensor of  claim 13 , wherein a second layer of the multi-layer structure comprises a borophosphorus silicate glass layer. 
   
   
       16 . The CMOS image sensor of  claim 13 , further comprising a light shielding layer between first and second layers of the multi-layer structure. 
   
   
       17 . The CMOS image sensor of  claim 13 , wherein the multi-layer structure has a thickness of about 1,000 Å. 
   
   
       18 . The CMOS image sensor of  claim 1 , wherein the metal pad comprises aluminum. 
   
   
       19 . The CMOS image sensor of  claim 1 , further comprising a titanium nitride layer on the metal pad. 
   
   
       20 . The CMOS image sensor of  claim 1 , wherein the photodiode region and the pad region have different thicknesses.