Deep trench isolation structure for high resolution CIS pixel

A method, comprising:

• forming a mask on a first side of a semiconductor substrate, wherein the mask defines a grid of openings that surround photodetector pixel regions of the semiconductor substrate;
• etching the semiconductor substrate through the openings to form trenches to a first depth segment, wherein the trenches are defined by sidewalls of the semiconductor substrate;
• lining the sidewalls with an etch-resistant coating;
• adding additional depth segments to the trenches by repeating, for at least two additional cycles, (i) etching to break through the etch-resistant coating at bottoms of the trenches and to extend the trenches with a next depth segment while the etch-resistant coating remains along sidewalls of the trenches, and (ii) re-lining the sidewalls with the etch-resistant coating;
• and
• after reaching a target trench depth, removing residual etch-resistant coating from the trenches and filling the trenches to provide an isolation structure that extends between the photodetector pixel regions.

A method, comprising:

• doping a semiconductor substrate from a first side to form an array of photodiodes within the semiconductor substrate;
• thinning the semiconductor substrate from a second side, which is opposite the first side;
• forming a mask on the second side, wherein the mask has openings with segments aligned to areas of the semiconductor substrate between the photodiodes;
• plasma etching the semiconductor substrate through the openings to form trenches having bottoms and sidewalls, wherein the semiconductor substrate provides the bottoms and sidewalls;
• and
• cyclically repeating for at least two cycles a process comprising:
• depositing a coating on the sidewalls of the trenches;
• etching to break through the coating at the bottoms of the trenches;
• and
• plasma etching to deepen the trenches.