Anti-reflective image sensor

Abstract

An anti-reflective image sensor and method of fabrication are provided, the sensor including a substrate; first color sensing pixels disposed in the substrate; second color sensing pixels disposed in the substrate; third color sensing pixels disposed in the substrate; a first layer disposed directly on the first, second and third color sensing pixels; a second layer disposed directly on the first layer overlying the first, second and third color sensing pixels; and a third layer disposed directly on portions of the second layer overlying at least one of the first or second color sensing pixels, wherein the first layer has a first refractive index, the second layer has a second refractive index greater than the first refractive index, and the third layer has a third refractive index greater than the second refractive index.

What is claimed is: 
     
         1 . A method of forming an anti-reflective image sensor, comprising:
 forming pluralities of first, second and third color sensing pixels in a substrate, respectively;   depositing a first layer disposed directly on the pluralities of first, second and third color sensing pixels;   depositing a second layer disposed directly on the first layer overlying the pluralities of first, second and third color sensing pixels; and   depositing a third layer disposed directly on portions of the second layer overlying at least one of the pluralities of first or second color sensing pixels,   wherein the first layer has a first refractive index, the second layer has a second refractive index greater than the first refractive index, and the third layer has a third refractive index greater than the second refractive index.   
     
     
         2 . The method of  claim 1 , wherein the first color is red, the second color is green, and the third color is blue. 
     
     
         3 . The method of  claim 1 , wherein the first color is magenta, the second color is yellow, and the third color is cyan. 
     
     
         4 . The method of  claim 1 , wherein the first layer comprises SiO2, the second layer comprises Si3N4, and the third layer comprises TiO2 or heat-treated SiON. 
     
     
         5 . The method of  claim 1 , wherein the first layer has a refractive index between about 1.45 and about 1.50, and the second layer has a refractive index between about 1.95 and about 2.05. 
     
     
         6 . The method of  claim 1 , wherein the first layer has a thickness of about 15 nm, the second layer has a thickness of about 7 nm, and the third layer has a thickness of about 15 nm. 
     
     
         7 . The method of  claim 1 , wherein the first layer is a gate dielectric layer or an insulating layer. 
     
     
         8 . The method of  claim 1 , further comprising forming a fourth layer on the exposed second and third layers, the fourth layer comprising the same material as the second layer. 
     
     
         9 . The method of  claim 1 , further comprising:
 forming a first inter-layer dielectric region on the second and third layers in a sensor array region; and   forming a second inter-layer dielectric region in a peripheral circuit region,   wherein a top of the first inter-layer dielectric region is lower than a top of the second inter-layer dielectric region.   
     
     
         10 . The method of  claim 1 , further comprising:
 forming a first inter-layer dielectric region under the first layer in a sensor array region; and   forming at least one micro-lens above the second and third layers for backside illumination.   
     
     
         11 . The method of  claim 1 , wherein the third layer is disposed on all of the first or second color sensing pixels, and disposed on some of the second or first color sensing pixels, respectively. 
     
     
         12 . The method of  claim 1 , wherein the first layer comprises a Silicon Oxide compound, the second layer comprises a Silicon Nitride compound, and the third layer comprises a heat-treated Silicon Oxy-Nitride compound.