Image Sensor DTI Layout for Pixel Isolation and Electron Interflow
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Solution Overview
Problem
Existing CMOS image sensors face issues with deep trench isolation (DTI) structures that result in low etching quality and undesired profiles, affecting pixel-to-pixel isolation and electron interflow between sub-pixels, leading to blooming and reduced quantum efficiency.
Innovation Solution
A simplified DTI architecture is implemented with lower etching bias, removing DTI structures between sub-pixels and allowing electron interflow regions to be arranged at any depth, enhancing pixel isolation and electron transfer flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If deep trench isolation (DTI) structures are used for pixel-to-pixel isolation, then pixel isolation is improved, but etching quality deteriorates and undesired profiles are created
Solution Approach 1:
The patent removes the DTI structure from between sub-pixels while maintaining it between adjacent pixels. This extraction of the isolation structure from specific locations (between sub-pixels) eliminates the etching quality problems and undesired profiles in those regions while preserving the necessary pixel-to-pixel isolation functionality where it remains.
Solution Approach 2:
The patent applies different isolation strategies to different spatial locations: DTI structures are maintained between adjacent pixels for proper pixel-to-pixel isolation, but removed between sub-pixels to eliminate etching problems. This local differentiation of isolation quality resolves the contradiction by optimizing each region's specific requirements.
2Reliability
If DTI structures are used for pixel isolation, then pixel-to-pixel isolation is improved, but electron interflow between sub-pixels is blocked
Solution Approach 1:
The patent extracts the DTI structure from the regions between sub-pixels where electron interflow is needed, while maintaining it between adjacent pixels. This selective removal allows electron interflow between sub-pixels to proceed unblocked while preserving pixel-to-pixel isolation where DTI structures remain.
3Reliability
If DTI structures are implemented with high etching bias, then pixel isolation is improved, but etching damage increases
Solution Approach 1:
By removing DTI structures from between sub-pixels, the patent eliminates the source of etching damage in those regions. The high etching bias process is no longer applied where it causes harm, while pixel isolation is maintained in regions where DTI structures remain between adjacent pixels.
Data Source
AI summary
An image sensor includes first photosensing regions, second photosensing regions, a first deep well region, a first isolation structure and second isolation structures. The first and second photosensing regions are disposed within a substrate, and have a first conductivity type. The substrate includes a first surface and a second surface opposite to the first surface. The first deep well region has a second conductivity type, and is extending from the first surface to the second surface and physically separating the first photosensing regions from one another, and physically separating the second photosensing regions from one another. The first isolation structure is extending from the first surface to the second surface and laterally surrounding the first and second photosensing regions. The second isolation structures are extending from the first surface to the second surface, and disposed in between the first and second photosensing regions.