Double patterning techniques for forming a deep trench isolation structure

Abstract

Double patterning techniques described herein may reduce corner rounding, etch loading, and/or other defects that might otherwise arise during formation of a deep trench isolation (DTI) structure in a pixel array. The double patterning techniques include forming a first set of trenches in a first direction and forming a second set of trenches in a second direction in a plurality of patterning operations such that minimal to no etch loading and/or corner rounding is present at and/or near the intersections of the first set of trenches and the second set of trenches.

What is claimed is: 
     
         1 . A method, comprising:
 forming a first pattern in a first photoresist layer over a substrate;   etching, based on the first pattern, the substrate to form a first set of trenches in a first direction within the substrate;   removing the first photoresist layer after etching the substrate to form the first set of trenches;   forming a second photoresist layer over the substrate after removing the first photoresist layer;   forming a second pattern in the second photoresist layer; and   etching, based on the second pattern, the substrate to form a second set of trenches in a second direction within the substrate.   
     
     
         2 . The method of  claim 1 , further comprising:
 filling the first set of trenches and the second set of trenches to form a deep trench isolation (DTI) structure of a pixel array.   
     
     
         3 . The method of  claim 2 , further comprising:
 forming photodiodes for pixel sensors of the pixel array; and   wherein the first set of trenches and the second set of trenches are formed in between the photodiodes.   
     
     
         4 . The method of  claim 1 , further comprising:
 forming an antireflective coating (ARC) over the substrate; and   forming the first photoresist layer over the ARC.   
     
     
         5 . The method of  claim 1 , wherein the first direction and the second direction are approximately perpendicular such that the first set of trenches and the second set of trenches intersect at a plurality of locations in the substrate. 
     
     
         6 . The method of  claim 1 , further comprising:
 filling the first set of trenches with a blocking material prior to etching the substrate to form the second set of trenches.   
     
     
         7 . The method of  claim 6 , further comprising:
 removing the blocking material from the first set of trenches after etching the substrate to form the second set of trenches; and   removing the second photoresist layer after etching the substrate to form the second set of trenches.   
     
     
         8 . The method of  claim 1 , wherein a ratio between a depth of the first set of trenches and a width of the first set of trenches is in a range of approximately 20 to approximately 50; and
 wherein a ratio between a depth of the second set of trenches and a width of the second set of trenches is in the range of approximately 20 to approximately 50.   
     
     
         9 . A method, comprising:
 forming a first portion of a pattern in a first direction in a hard mask layer over a substrate;   forming, subsequent to forming the first portion of the pattern, a second portion of the pattern in a second direction in the hard mask layer;   etching, based on the first portion and the second portion of the pattern, the substrate to form a plurality of intersecting trenches in the substrate; and   filling the plurality of intersecting trenches to form a deep trench isolation (DTI) structure in the substrate.   
     
     
         10 . The method of  claim 9 , wherein the DTI structure is included in a pixel array. 
     
     
         11 . The method of  claim 10 , further comprising:
 forming photodiodes for pixel sensors of the pixel array;   wherein forming the plurality of intersecting trenches comprises:
 forming the plurality of intersecting trenches in between the photodiodes. 
   
     
     
         12 . The method of  claim 9 , wherein a ratio between a depth of the DTI structure and a width of the DTI structure is in a range of approximately 20 to approximately 50. 
     
     
         13 . The method of  claim 9 , wherein forming the first portion of the pattern comprises:
 forming a first photoresist layer over the hard mask layer;   forming a first photoresist pattern in the first photoresist layer;   performing, based on the first photoresist pattern, a first etch operation to form the first portion of the pattern in the hard mask layer; and   removing the first photoresist layer.   
     
     
         14 . The method of  claim 13 , wherein forming the second portion of the pattern comprises:
 forming a second photoresist layer over the hard mask layer after removing the first photoresist layer;   forming a second photoresist pattern in the second photoresist layer;   performing, based on the second photoresist pattern, a second etch operation to form the second portion of the pattern in the hard mask layer; and   removing the second photoresist layer.   
     
     
         15 . The method of  claim 14 ; wherein performing the first etch operation comprises:
 etching through the first photoresist layer to a first antireflective coating (ARC) over the hard mask layer; and   wherein performing the second etch operation comprises:
 etching through the second photoresist layer to a second ARC over the hard mask layer. 
   
     
     
         16 . The method of  claim 9 , wherein etching the substrate to form the plurality of intersecting trenches in the substrate comprises:
 etching through an ashing removable dielectric (ARD) layer and into at least a portion of the substrate to form the plurality of intersecting trenches in the substrate.   
     
     
         17 . The method of  claim 16 , further comprising:
 removing the hard mask layer and the ARD layer after etching through the ARD layer and into at least the portion of the substrate to form the plurality of intersecting trenches; and   wherein filling the plurality of intersecting trenches to form the DTI structure in the substrate comprises:
 filling the plurality of intersecting trenches to form the DTI structure in the substrate after removing the hard mask layer and the ARD layer. 
   
     
     
         18 . A method, comprising:
 forming a plurality of photodiodes in a substrate of a pixel array for pixel sensors of a pixel array;   forming, by a double patterning technique, a plurality of trenches in the substrate,
 wherein the plurality of trenches are formed in between the plurality of photodiodes, and 
 wherein the plurality of trenches include a first subset of trenches and a second subset of trenches, and 
 wherein the first subset of trenches and the second subset of trenches are approximately perpendicular; 
   filling the plurality of trenches to form a deep trench isolation (DTI) structure in the substrate;   forming a dielectric layer over the substrate, over the DTI structure, and over the photodiodes;   forming a metal layer over the dielectric layer;   etching through the metal layer and into a portion of the dielectric layer to form a grid structure;   forming color filter regions for the pixel sensors in between the grid structure; and   forming a micro-lens layer of the pixel array over the grid structure and over the color filter regions.   
     
     
         19 . The method of  claim 18 , wherein the double patterning technique comprises:
 forming the first subset of the plurality of trenches based on a first photoresist pattern; and   forming the second subset of the plurality of trenches based on a second photoresist pattern.   
     
     
         20 . The method of  claim 18 , wherein the double patterning technique comprises:
 forming a first portion of a hard mask pattern in a hard mask layer based on a first photoresist pattern;   forming a second portion of the hard mask pattern in the hard mask layer based on a second photoresist pattern; and   forming the plurality of trenches based on the hard mask pattern in the hard mask layer.