Image sensor grid and method of fabrication of same

Abstract

An image sensor structure includes a semiconductor device, a plurality of image sensing elements formed in the semiconductor substrate, an interconnect structure formed on the semiconductor substrate, and a composite grid structure over the semiconductor substrate. The composite grid structure includes a tungsten grid, an oxide grid over the tungsten grid, and an adhesion enhancement grid spacing the tungsten grid from the oxide grid.

What is claimed is: 
     
         1 . An image sensor structure, comprising:
 a semiconductor substrate;   a plurality of image sensing elements formed in the semiconductor substrate;   an interconnect structure formed on the semiconductor substrate; and   a composite grid structure over the semiconductor substrate, wherein the composite grid structure comprises a tungsten grid, an oxide grid over the tungsten grid, and an adhesion enhancement grid spacing the tungsten grid from the oxide grid.   
     
     
         2 . The image sensor structure of  claim 1 , wherein the adhesion enhancement grid is formed from a nitride material. 
     
     
         3 . The image sensor structure of  claim 1 , wherein the adhesion enhancement grid comprises gridlines each having a width that increases as a distance from the semiconductor substrate increases. 
     
     
         4 . The image sensor structure of  claim 1 , wherein the tungsten grid comprises gridlines each having a width that decreases as a distance from the semiconductor substrate increases. 
     
     
         5 . The image sensor structure of  claim 1 , wherein the oxide grid comprises gridlines each having a tapered top segment. 
     
     
         6 . The image sensor structure of  claim 1 , wherein the adhesion enhancement grid comprises gridlines each having a width in a range from about 10 angstroms to about 500 angstroms. 
     
     
         7 . The image sensor structure of  claim 1 , wherein the adhesion enhancement grid has a refractive index in a range from about 1.5 to about 2.5. 
     
     
         8 . The image sensor structure of  claim 1 , wherein the adhesion enhancement grid has a sheet resistance in a range from about 80 D per unit square area to about 120 D per unit square area. 
     
     
         9 . The image sensor structure of  claim 1 , wherein the composite grid structure further comprises a barrier grid between the tungsten grid and the semiconductor substrate. 
     
     
         10 . The image sensor structure of  claim 9 , wherein the barrier grid and the adhesion enhancement grid have a same chemical element. 
     
     
         11 . The image sensor structure of  claim 1 , wherein the composite grid structure further comprises an oxynitride grid over the oxide grid. 
     
     
         12 . An image sensor structure, comprising:
 a semiconductor substrate;   a plurality of photodiodes in the semiconductor substrate;   an interconnect structure on the semiconductor substrate; and   a composite grid structure on the semiconductor substrate, wherein the composite grid structure comprises an oxide grid and a metal grid between the oxide grid and the semiconductor substrate, and the composite grid structure is devoid of an oxide/metal interface.   
     
     
         13 . The image sensor structure of  claim 12 , wherein the composite grid structure further comprises a nitride grid forming a nitride/metal interface with a top surface of the metal grid. 
     
     
         14 . The image sensor structure of  claim 13 , wherein the nitride grid further forms a nitride/oxide interface with a bottom surface of the oxide grid. 
     
     
         15 . The image sensor structure of  claim 13 , wherein the nitride grid has a thickness less than a thickness of the metal grid. 
     
     
         16 . The image sensor structure of  claim 13 , wherein the nitride grid has a thickness less than a thickness of the oxide grid. 
     
     
         17 . The image sensor structure of  claim 13 , further comprising:
 a plurality of color filters extending through the nitride grid.   
     
     
         18 . The image sensor structure of  claim 17 , further comprising:
 a plurality of microlenses over the color filters, respectively.   
     
     
         19 . An image sensor structure, comprising:
 a substrate;   a plurality of photodiodes in the substrate;   an interconnect structure on a front-side of the substrate;   a plurality of metal gridlines on a back-side of the substrate;   a plurality of nitride gridlines respectively extending above the metal gridlines; and   a plurality of oxide gridlines respectively extending above the nitride gridlines.   
     
     
         20 . The image sensor structure of  claim 19 , further comprising:
 a plurality of buffer gridlines respectively extending between the metal gridlines and the substrate.