Pixel sensor including refraction structures

Abstract

A pixel sensor may include a main deep trench isolation (DTI) structure and one or more sub-DTI structures in a substrate of the pixel sensor to increase the quantum efficiency of the pixel sensor at large incident angles. The one or more sub-DTI structures may be located within the perimeter of the main DTI structure and above a photodiode. The one or more sub-DTI structures may be configured to provide a path of travel for incident light into the photodiode from large incident angles in that the one or more sub-DTI structures may be filled with an oxide material to increase light penetration into the one or more sub-DTI structures. This may reduce reflections at a top surface of the substrate, thereby permitting incident light to refract into the substrate and toward the photodiode.

What is claimed is: 
     
         1 . A method, comprising:
 forming, in a substrate of a pixel sensor, a first deep trench isolation (DTI) structure at least partially surrounding a photodiode in the substrate;   forming, in the substrate, a plurality of second DTI structures over the photodiode and within a perimeter of the first DTI structure;   forming, in the substrate, a high absorption region over the photodiode and in between the plurality of second DTI structures; and   filling the first DTI structure, the plurality of second DTI structures, and the high absorption region with an oxide material.   
     
     
         2 . The method of  claim 1 , wherein forming the first DTI structure and forming the plurality of second DTI structures comprise:
 forming the first DTI structure and forming the plurality of second DTI structures using a same photomask.   
     
     
         3 . The method of  claim 1 , wherein filling the first DTI structure, the plurality of second DTI structures, and the high absorption region with the oxide material comprises:
 filling at least the first DTI structure and the plurality of second DTI structures with the oxide material in a same deposition operation.   
     
     
         4 . The method of  claim 1 , wherein forming the plurality of second DTI structures comprises:
 forming the plurality of second DTI structures to a depth, relative to a top surface of the substrate, such that the plurality of second DTI structures do not touch the photodiode.   
     
     
         5 . The method of  claim 4 , wherein the depth of the plurality of second DTI structures is in a range of approximately 300 nanometers to approximately 2000 nanometers; and
 wherein the depth of the plurality of second DTI structures is less than a depth of the first DTI structure.   
     
     
         6 . The method of  claim 1 , wherein forming the plurality of second DTI structures comprises:
 forming the plurality of second DTI structures to a particular width such that an etch rate of the first DTI structure and the plurality of second DTI structures results in the first DTI structure being deeper relative to the plurality of second DTI structures.   
     
     
         7 . The method of  claim 1 , wherein forming the plurality of second DTI structures comprises:
 forming a third DTI structure, of the plurality of second DTI structures, near a first side of the high absorption region;   forming a fourth DTI structure, of the plurality of second DTI structures, near a second side of the high absorption region;   forming a fifth DTI structure, of the plurality of second DTI structures, near a first third of the high absorption region; and   forming a sixth DTI structure, of the plurality of second DTI structures, near a fourth side of the high absorption region.   
     
     
         8 . A method for forming a pixel sensor, comprising:
 forming, in a substrate, a photodiode;   forming, in the substrate, a deep trench isolation (DTI) structure, one or more refraction structures, and an absorption region,
 wherein the DTI structure is formed to at least partially surround the photodiode, the one or more refraction structures are formed within the DTI structure, and the absorption region increases an absorption of an incident light for the photodiode; and 
   filling the DTI structure, the one or more refraction structures, and the absorption region with an oxide material.   
     
     
         9 . The method of  claim 8 , wherein the DTI structure is formed such that a depth of the DTI structure in the substrate is less than a thickness of the substrate. 
     
     
         10 . The method of  claim 8 , wherein the one or more refraction structures are formed such that a depth of the one or more refraction structures in the substrate is less than a depth of the DTI structure in the substrate. 
     
     
         11 . The method of  claim 8 , wherein the one or more refraction structures are formed in the substrate such that a width of the one or more refraction structures in the substrate is less than a width of the DTI structure in the substrate. 
     
     
         12 . The method of  claim 8 , wherein at least one refraction structure of the one or more refraction structures is formed in the substrate such that the at least one refraction structure is in contact with the DTI structure. 
     
     
         13 . The method of  claim 8 , wherein the one or more refraction structures are not in contact with the absorption region. 
     
     
         14 . The method of  claim 8 , wherein the DTI structure, the one or more refraction structures, and the absorption region are formed in the substrate in a single etching operation. 
     
     
         15 . A method for forming a pixel sensor, comprising:
 forming, in a substrate, a deep trench isolation (DTI) structure, a plurality of refraction structures, and an absorption region,
 wherein the DTI structure is formed to at least partially surround a photodiode in the substrate, the plurality of refraction structures and absorption region are formed within the DTI structure, and the absorption region increases an absorption of an incident light for the photodiode; 
   filling the DTI structure, the plurality of refraction structures, and the absorption region with an oxide material; and   forming a micro-lens layer over the DTI structure, the plurality of refraction structures, and the absorption region.   
     
     
         16 . The method of  claim 15 , wherein the absorption region comprises a structure having angled walls such that the structure is approximately triangular shaped. 
     
     
         17 . The method of  claim 15 , wherein the absorption region is formed between the plurality of refraction structures. 
     
     
         18 . The method of  claim 15 , wherein the absorption region is capable of directing the incident light toward a center of the photodiode. 
     
     
         19 . The method of  claim 15 , further comprising:
 forming an antireflective coating layer over the DTI structure, the plurality of refraction structures, and the absorption region,
 wherein the micro-lens layer is formed over the antireflecting coating layer. 
   
     
     
         20 . The method of  claim 15 , further comprising:
 forming a color filter layer over the DTI structure, the plurality of refraction structures, and the absorption region,
 wherein the micro-lens layer is formed over the color filter layer.