Segmented Deep Trench Isolation for BSI Image Sensors
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Solution Overview
Problem
Backside illuminated (BSI) image sensor devices face issues with dark current and optical crosstalk due to the loading effect during the formation of deep trench isolations, which affects the isolation between image pixels and leads to noise and performance degradation.
Innovation Solution
A pattern of deep trench isolations (DTIs) with segmented strips and continuous strips is implemented, where intersections are designed to avoid crossover regions, reducing the loading effect and ensuring uniform depth, thereby minimizing defects and dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If deep trench isolations are formed in the substrate to isolate neighboring image pixels, then isolation between image pixels is improved, but loading effect occurs during formation causing non-uniform depth and increased defects
Solution Approach 1:
The patent divides the continuous deep trench isolation structure into multiple segmented trenches. Instead of forming one deep trench that crosses the entire substrate, the isolation is achieved through multiple shallower segmented trenches that are distributed across the substrate. This segmentation approach eliminates the loading effect that occurs during formation of continuous deep trenches, as each segmented trench can be formed independently with uniform depth control, while still achieving the desired isolation between image pixels.
2Object-affected harmful factors
If deep trench isolations are formed to reduce optical crosstalk, then crosstalk between pixels is reduced, but dark current increases due to loading effect and defects
Solution Approach 1:
The patent segments the deep trench isolation structure into multiple shallower trenches. This segmentation reduces the loading effect during formation, leading to more uniform trench depth and fewer defects. Consequently, dark current is reduced while maintaining effective isolation against optical crosstalk between pixels.
Solution Approach 2:
The patent applies different trench depths locally across the substrate. Instead of uniform deep trenches everywhere, the isolation structure is optimized locally with segmented trenches positioned strategically to provide sufficient isolation where needed while minimizing the loading effect and associated defects that generate dark current.
Data Source
AI summary
A back side illuminated (BSI) image sensor device, includes: a substrate including a front side and a back side opposite to the front side; a radiation-sensing region disposed in the substrate; and a deep trench isolation (DTI) grid disposed in the substrate and defining the radiation-sensing region. The DTI grid extends from the back side toward the front side, and includes a segmented strip in a top view from the back side.