Vertical Transfer Gate Overlap for Pixel Isolation Without Cracking
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
CMOS image sensors face issues with light leakage and cross-talk due to incomplete backside isolation structures, which can lead to cracking and reduced optical and electrical isolation, affecting image quality and manufacturing yield.
Innovation Solution
Implementing backside trench isolation structures that extend partially into the semiconductor substrate with a vertical overlap with the transfer gate electrode, providing enhanced optical and electrical isolation while minimizing the risk of substrate cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If backside trench isolation structures are extended deeper into the substrate to improve optical and electrical isolation between pixels, then isolation performance is improved, but the risk of substrate cracking increases
Solution Approach 1:
The patent merges the backside trench isolation structure with the vertical transfer gate electrode by making them substantially co-located. The isolation structure and the transfer gate share the same vertical path through the substrate, allowing the transfer gate to provide structural support while the isolation structure provides optical and electrical isolation. This combination achieves deep isolation without increasing substrate stress, as the transfer gate acts as a reinforcing element.
2Productivity
If backside trench isolation structures are made shallower to reduce substrate stress and prevent cracking, then manufacturing yield is improved, but optical and electrical isolation between pixels deteriorates
Solution Approach 1:
By merging the isolation structure with the vertical transfer gate, the patent achieves effective isolation with reduced trench depth. The transfer gate electrode, extending vertically through the substrate, provides both the isolation function and structural reinforcement, eliminating the need for deep trenches that would compromise substrate strength.
Solution Approach 2:
The vertical transfer gate electrode serves dual functions: it acts as the functional transfer gate for pixel operation and simultaneously provides structural reinforcement to prevent substrate cracking. This multi-functionality allows the isolation structure to be shallower while maintaining both isolation performance and substrate integrity.
3Ease of manufacture
If incomplete backside isolation structures are used to simplify manufacturing, then ease of manufacture is improved, but light leakage and cross-talk between pixels increase
Solution Approach 1:
The patent combines the formation of the backside trench isolation structure with the formation of the vertical transfer gate electrode. Since both structures require vertical etching through the substrate, they can be formed in the same etching step, simplifying the manufacturing process while achieving complete isolation that prevents light leakage and cross-talk.
Data Source
AI summary
Some embodiments are directed towards an image sensor device. A photodetector is disposed in a semiconductor substrate, and a transfer transistor is disposed over photodetector. The transfer transistor includes a transfer gate having a lateral portion extending over a frontside of the semiconductor substrate and a vertical portion extending to a first depth below the frontside of the semiconductor substrate. A gate dielectric separates the lateral portion and the vertical portion from the semiconductor substrate. A backside trench isolation structure extends from a backside of the semiconductor substrate to a second depth below the frontside of the semiconductor substrate. The backside trench isolation structure laterally surrounds the photodetector, and the second depth is less than the first depth such that a lowermost portion of the vertical portion of the transfer transistor has a vertical overlap with an uppermost portion of the backside trench isolation structure.