Light guide array for an image sensor

Abstract

An image sensor pixel that includes a photoelectric conversion unit supported by a substrate and an insulator adjacent to the substrate. The pixel includes a cascaded light guide that is located within an opening of the insulator and extends above the insulator such that a portion of the cascaded light guide has an air interface. The air interface improves the internal reflection of the cascaded light guide. The cascaded light guide may include a self-aligned color filter having air-gaps between adjacent color filters. These characteristics of the light guide eliminate the need for a microlens. Additionally, an anti-reflection stack is interposed between the substrate and the light guide to reduce backward reflection from the image sensor. Two pixels of having different color filters may have a difference in the thickness of an anti-reflection film within the anti-reflection stack.

1 . A method of forming an image sensor that comprises a pixel array, comprising:
 providing a substrate;   forming a plurality of photoelectric conversion units across said substrate; and,   forming a plurality of color filters, each of said color filters being coupled to transmit a light to one of said photoelectric conversion units, an air gap being between each of said color filters and an adjacent one of said color filters, said air gap comprising air or a gas, said air gap having a width of 0.45 um or less.   
     
     
         2 . The method of  claim 1 , wherein said air gap has a depth of at least a wavelength in air of a visible light. 
     
     
         3 . The method of  claim 2 , wherein said wavelength in air is 650 nm. 
     
     
         4 . The method of  claim 2 , further comprising:
 forming a plurality of light guides each being between one of said photoelectric conversion units and a corresponding one of said color filters.   
     
     
         5 . The method of  claim 4 , wherein the light guides comprise silicon nitride. 
     
     
         6 . The method of  claim 4 , wherein no microlens is formed on an opposite side of each of said color filters away from a corresponding one of said photoelectric conversion units.