Image Sensor Pixel Isolation Layout for Void-Free Dark Current Control
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Solution Overview
Problem
Current image sensor fabrication processes face challenges in achieving high production yield and clear image quality due to issues such as direct contact between pixels and structural defects like voids in the pixel isolation portion, leading to dark current and manufacturing defects.
Innovation Solution
The image sensor design incorporates a pixel isolation portion with a sequential arrangement of conductive patterns and insulating isolation patterns, where the conductive patterns are spaced apart from the substrate, and the insulating isolation pattern is between the substrate and the conductive pattern, including a polycrystalline semiconductor layer with varying grain sizes to prevent void formation and ensure uniform negative bias application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional pixel isolation structure is used, then the fabrication process is simple, but direct contact between pixels occurs leading to dark current and reduced image quality
Solution Approach 1:
The pixel isolation portion is divided into multiple discrete conductive patterns (first, second, and third conductive patterns) arranged sequentially on the side surface of the insulating isolation pattern. This segmentation prevents direct contact between pixels while maintaining structural integrity and reducing dark current through distributed electrical isolation.
Solution Approach 2:
The conductive patterns are arranged in a sequential configuration along the vertical dimension (side surface) of the insulating isolation pattern rather than only in horizontal planes. This three-dimensional arrangement provides comprehensive pixel isolation while maintaining fabrication feasibility and reducing structural complexity compared to traditional approaches.
2Productivity
If the conductive pattern is placed directly on the substrate, then the structure is simple, but voids form leading to manufacturing defects and reduced production yield
Solution Approach 1:
The insulating isolation pattern serves as an intermediary layer positioned between the substrate and the conductive patterns. This intermediate structure prevents direct contact that would cause void formation, eliminates manufacturing defects, and enables successful fabrication while maintaining a relatively simple overall device architecture.
Solution Approach 2:
The insulating isolation pattern is placed in advance between the substrate and conductive patterns to prevent the formation of voids before they can occur during fabrication. This preventive approach eliminates manufacturing defects and ensures high production yield by addressing potential failure points before they manifest.
3Reliability
If a single-layer conductive pattern is used, then the fabrication process is simple, but negative bias application is inconsistent leading to operational performance issues
Solution Approach 1:
The conductive pattern is segmented into multiple distinct layers (first, second, and third conductive patterns) arranged sequentially on the side surface of the insulating isolation pattern. This multi-layer segmentation enables consistent negative bias application across different regions, improving operational performance while maintaining fabrication simplicity through a systematic manufacturing approach.
Solution Approach 2:
Different conductive patterns are positioned at different locations (first, second, and third conductive patterns at progressively higher positions on the side surface) to provide localized electrical isolation and consistent negative bias application where needed. This localized approach ensures uniform operational performance without complicating the overall fabrication process.
Data Source
AI summary
An image sensor may include a substrate having a first surface and a second surface, which are opposite to each other, and micro lenses on the second surface, interconnection lines on the first surface, and a pixel isolation portion in the substrate, the pixel isolation portion configured to isolate pixels from direct contact with each other. The pixel isolation portion may include an insulating isolation pattern and a conductive pattern, wherein the conductive pattern is spaced apart from the substrate, and the insulating isolation pattern is between the substrate and the conductive pattern. The conductive pattern may include a sequential arrangement of a first conductive pattern, a second conductive pattern, and a third conductive pattern on a side surface of the insulating isolation pattern.