Trench-Structured Passivation Layer for Image Sensor Stress Relief
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Solution Overview
Problem
Camera image sensors experience bubble defects in the periphery-region due to material-induced stress, leading to noise and degraded image quality, particularly as the surface area increases with higher pixel counts.
Innovation Solution
Incorporating trenches in the periphery-region of the semiconductor substrate, where the passivation layer lines the trenches, to relieve stress and prevent bubble defects, and depositing a thin film that conformally covers the trench regions and inter-trench surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the surface area of the passivation layer is increased to accommodate higher pixel counts, then the image sensor can capture higher resolution images, but material-induced stress accumulates and causes bubble defects
Solution Approach 1:
The passivation layer is divided into multiple separate regions by introducing trenches that extend into the semiconductor substrate. These trenches segment the continuous passivation layer into isolated islands, preventing stress accumulation across the entire surface area. Each segmented region can independently accommodate stress without forming bubbles, thus maintaining reliability while allowing the overall device area to increase for higher pixel counts.
Solution Approach 2:
Trenches filled with stress-relief material are introduced as intermediary structures between the passivation layer and the semiconductor substrate. These trenches act as stress-absorbing elements that mediate the mechanical stress between the expanding passivation layer and the rigid substrate, preventing stress-induced bubble defects while allowing the passivation layer to cover larger areas.
2Strength
If the passivation layer is made thicker to improve stress distribution, then stress resistance improves, but manufacturing complexity and cost increase
Solution Approach 1:
Instead of increasing the thickness of the entire passivation layer uniformly, the invention segments the passivation structure by introducing trenches. This allows the passivation layer to maintain optimal thickness in regions where it is present, while the trenches provide additional stress management. This approach achieves improved stress resistance without the manufacturing complexity of depositing uniformly thicker passivation layers across the entire substrate.
Data Source
AI summary
A method for preventing defects in a thin film deposited on a semiconductor substrate includes forming a plurality of trenches on a periphery-region of the semiconductor substrate to yield a trenched surface. The semiconductor substrate includes a pixel array; the periphery-region surrounds the pixel array. The trenched surface includes (i) a plurality of trench regions each forming a respective one of the plurality of trenches and (ii) between each pair of adjacent trenches, a respective one of a plurality of inter-trench surfaces. The method also includes depositing the thin film on the surface such that the thin film covers each inter-trench surface and conformally covers each trench region.