Image sensor grid and method of fabrication of same

Abstract

A method incudes forming a plurality of photodiodes in a substrate; forming an interconnect structure on a front-side of the substrate; forming a barrier layer on a back-side of the substrate; depositing a metal layer over the barrier layer; forming an adhesion enhancement layer over the metal layer; forming an oxide layer over the adhesion enhancement layer; etching the oxide layer, the adhesion enhancement layer, the metal layer, and the barrier layer to form an oxide grid, an adhesion enhancement grid, a metal grid, and a barrier grid, respectively, wherein the barrier grid and the adhesion enhancement grid have a same chemical element.

What is claimed is: 
     
         1 . A method, comprising:
 forming a plurality of photodiodes in a substrate;   forming an interconnect structure on a front-side of the substrate;   forming a barrier layer on a back-side of the substrate;   depositing a metal layer over the barrier layer;   forming an adhesion enhancement layer over the metal layer;   forming an oxide layer over the adhesion enhancement layer; and   etching the oxide layer, the adhesion enhancement layer, the metal layer, and the barrier layer to form an oxide grid, an adhesion enhancement grid, a metal grid, and a barrier grid, respectively, wherein the barrier grid and the adhesion enhancement grid have a same chemical element.   
     
     
         2 . The method of  claim 1 , wherein the chemical element comprises nitrogen. 
     
     
         3 . The method of  claim 1 , wherein the adhesion enhancement layer is made of silicon nitride. 
     
     
         4 . The method of  claim 1 , wherein the barrier layer is made of a metal-containing nitride material. 
     
     
         5 . The method of  claim 1 , wherein the adhesion enhancement layer has a refractive index in a range from about 1.5 to about 2.5. 
     
     
         6 . The method of  claim 1 , wherein the adhesion enhancement grid has a thickness less than a thickness of the metal grid. 
     
     
         7 . The method of  claim 1 , wherein the adhesion enhancement grid has a thickness in a range from about 230 angstroms to about 300 angstroms. 
     
     
         8 . The method of  claim 1 , wherein the adhesion enhancement grid comprises gridlines each having a width that increases as a distance from the semiconductor substrate increases. 
     
     
         9 . The method 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. 
     
     
         10 . The method of  claim 1 , wherein the metal layer is made of tungsten. 
     
     
         11 . An method, comprising:
 forming a plurality of image sensing elements in a semiconductor substrate;   forming an interconnect structure on a front-side of the semiconductor substrate; and   forming a composite grid structure on a back-side of the semiconductor substrate, wherein the composite grid structure comprises a plurality of metal gridlines laterally extending over the back-side of the semiconductor substrate, a plurality of oxide gridlines laterally extending over the metal gridlines, and a plurality of silicon nitride gridlines laterally extending between the metal gridlines and the oxide gridlines.   
     
     
         12 . The method of  claim 11 , wherein the silicon nitride gridlines form nitride/metal interfaces with top surfaces of the metal gridlines. 
     
     
         13 . The method of  claim 11 , wherein the silicon nitride gridlines form nitride/oxide interfaces with bottom surfaces of the oxide gridlines. 
     
     
         14 . The method of  claim 11 , wherein the composite grid structure is devoid of an oxide/metal interface. 
     
     
         15 . The method of  claim 11 , wherein the silicon nitride gridlines each has a thickness less than thicknesses of the oxide gridlines. 
     
     
         16 . An image sensor structure, comprising:
 a semiconductor substrate;   a plurality of image sensing elements formed in the semiconductor substrate;   an interconnect structure on a front-side of the semiconductor substrate;   a buffer grid on a back-side of the semiconductor substrate;   a barrier grid over the buffer grid;   a metal grid over the barrier grid; and   a nitride grid over the metal grid.   
     
     
         17 . The image sensor structure of  claim 16 , further comprising:
 an oxide grid over the nitride grid.   
     
     
         18 . The image sensor structure of  claim 17 , further comprising:
 an oxynitride grid over the oxide grid.   
     
     
         19 . The image sensor structure of  claim 16 , wherein the nitride grid has a sheet resistance in a range from about 80Ω per unit square area to about 120Ω per unit square area. 
     
     
         20 . The image sensor structure of  claim 16 , wherein the buffer grid is made of oxide.