Backside Illuminated Image Sensor Trench Isolation
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Solution Overview
Problem
Existing backside illuminated (BSI) image sensor devices face challenges in scaling down while maintaining image quality, particularly in reducing dark current and white pixel defects due to etching damage during the fabrication process.
Innovation Solution
The method involves forming a substrate with a pixel region and a periphery region, where a plurality of first trenches are etched in the periphery region and second trenches with reduced depth are etched in the pixel region, along with the formation of spacers and isolation features, to minimize etching damage and enhance image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If device scaling is performed to achieve lower fabrication costs and higher integration density, then productivity and integration density are improved, but manufacturing precision deteriorates due to increased etching damage
Solution Approach 1:
The patent divides the substrate into distinct pixel regions and periphery regions, with different trench depths for each region. This segmentation allows optimized etching parameters for each area, reducing overall etching damage while maintaining high integration density in the pixel regions.
Solution Approach 2:
The patent implements different trench depths (first trenches in periphery region with depth D1, second trenches in pixel region with depth D2 where D1 > D2) tailored to specific functional requirements of each region, minimizing etching damage locally while maintaining overall device performance.
2Reliability
If etching depth is increased to improve isolation effectiveness, then reliability is improved, but manufacturing precision deteriorates due to increased etching damage and white pixel defects
Solution Approach 1:
The patent applies different trench depths to different regions: deeper first trenches in the periphery region for maximum isolation effectiveness, and shallower second trenches in the pixel region to provide sufficient isolation while minimizing etching damage and white pixel defects.
Solution Approach 2:
The patent converts the potentially harmful deep etching process into a beneficial selective isolation method by using different etching depths for different regions, where the deeper etching in periphery regions provides enhanced isolation without affecting pixel regions.
3Manufacturing precision
If trench depth is reduced to minimize etching damage, then manufacturing precision is improved, but reliability deteriorates due to reduced isolation effectiveness
Solution Approach 1:
The patent segments the isolation trenches into two types with different depths: first trenches in periphery regions with greater depth for maximum isolation, and second trenches in pixel regions with reduced depth to minimize etching damage. This segmentation ensures both reliability and manufacturing precision are achieved in their respective regions.
Data Source
AI summary
A method of forming of an image sensor device includes a substrate having a pixel region and a periphery region. A plurality of first trenches is etched in the periphery region. Each of the first trenches has a depth D1. A mask layer is formed over the substrate. The mask layer has a plurality of openings in the pixel region. A spacer is formed in an interior surface of each opening. A plurality of second trenches is etched through each opening having the spacer in the pixel region. Each of the second trenches has a depth D2. The depth D1 is larger than the depth D2.