Two-Layer Trench Isolation in Image Sensors to Prevent Cross-Talk
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Solution Overview
Problem
Existing image sensors face challenges in achieving increased reliability, particularly in maintaining performance and preventing cross-talk between unit pixel regions.
Innovation Solution
The image sensor incorporates a substrate with unit pixel regions and a semiconductor pattern that defines these regions, including a first semiconductor pattern with side and bottom portions, and a second semiconductor pattern that extends towards the substrate's second surface, ensuring effective pixel isolation and preventing void formation in trenches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer semiconductor pattern is used to define unit pixel regions, then the structure is simpler, but cross-talk between neighboring pixel regions increases and reliability decreases
Solution Approach 1:
The semiconductor pattern is divided into two distinct layers: a first semiconductor pattern that defines the upper boundaries of unit pixel regions, and a second semiconductor pattern that defines the lower boundaries. This segmentation creates a more effective isolation structure between neighboring pixels by preventing photocharge diffusion through multiple isolation barriers, thereby resolving the contradiction between improved pixel isolation and structural complexity.
2Reliability
If the semiconductor pattern extends closer to the substrate surface, then pixel isolation is improved, but void formation in trenches increases
Solution Approach 1:
The isolation structure is extended into the vertical dimension by creating a two-layer semiconductor pattern with different heights and positions. The first semiconductor pattern is positioned higher and the second semiconductor pattern is positioned lower, filling the trench space vertically. This dimensional approach prevents void formation by ensuring complete trench filling while maintaining effective pixel isolation, resolving the contradiction between isolation effectiveness and void prevention.
Data Source
AI summary
An image sensor including a substrate having first and second surfaces that are opposite to each other. The substrate includes unit pixel regions having photoelectric conversion regions. A semiconductor pattern is disposed in a first trench defined in the substrate and defines the unit pixel regions. The semiconductor pattern includes a first semiconductor pattern and a second semiconductor pattern disposed on the first semiconductor pattern. A back-side insulating layer covers the second surface of the substrate. The first semiconductor pattern includes a side portion extended along an inner side surface of the first trench and a bottom portion connected to the side portion and disposed closer to the second surface of the substrate than the side portion. The second semiconductor pattern extends toward the second surface of the substrate and is spaced apart from the back-side insulating layer with the bottom portion of the first semiconductor pattern interposed therebetween.