Deep Pixel Isolation Structure for Low-Defect CMOS Image Sensors
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Solution Overview
Problem
Current CMOS image sensors face challenges in reducing defects and achieving high integration due to issues with deep isolation patterns and dielectric materials, which affect pixel performance and lead to increased dark current and white spots.
Innovation Solution
The proposed solution involves a CMOS image sensor with a deep isolation pattern that includes a semiconductor pattern penetrating the substrate and a dielectric pattern with distinct material parts, where the first part is nitrided to prevent impurity diffusion and reduce thickness, thereby enhancing pixel integration and reducing defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a uniform dielectric pattern is used in the deep isolation structure, then the manufacturing process is simpler, but impurity diffusion occurs between pixel regions leading to increased dark current and white spots
Solution Approach 1:
The dielectric pattern is divided into two distinct parts: a first dielectric material adjacent to the semiconductor pattern and a second dielectric material between the first dielectric and the substrate. This local differentiation prevents impurity diffusion at the interface while maintaining manufacturing feasibility through a structured approach.
2Reliability
If the dielectric pattern thickness is increased to prevent impurity diffusion, then pixel performance improves, but the integration density decreases and manufacturing complexity increases
Solution Approach 1:
The first dielectric material is positioned specifically where impurity diffusion is most critical (adjacent to the semiconductor pattern), providing targeted protection with minimal thickness. The second dielectric material fills the remaining space, achieving both protection and space efficiency for high integration density.
Solution Approach 2:
The dielectric pattern is segmented into two functional parts with different materials and thicknesses, allowing each part to perform its specific function optimally while collectively achieving the goals of impurity suppression and high integration.
3Ease of manufacture
If a single material is used for the entire dielectric pattern, then material deposition is easier, but interface defects increase leading to white spots
Solution Approach 1:
The dielectric pattern uses a composite structure with two different dielectric materials. The first dielectric material (e.g., silicon nitride or silicon oxynitride) provides a high-quality interface with the semiconductor pattern, while the second dielectric material (e.g., silicon oxide) fills the remaining space. This composite approach maintains manufacturing ease while significantly improving interface quality and reducing white spot defects.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in a highly integrated image sensor with reduced defects, improved dark current management, and prevention of white spots, leading to enhanced performance and reliability.
Implementation Method 1
nitriding a surface of the dielectric layer by performing a nitridation process
Data Source
AI summary
An image sensor includes a substrate including a plurality of pixel regions, and a deep isolation pattern in the substrate between the pixel regions. The deep isolation pattern includes a semiconductor pattern penetrating at least a portion of the substrate, and a dielectric pattern disposed between the substrate and the semiconductor pattern. The dielectric pattern includes a first part disposed adjacent to the semiconductor pattern, and a second part disposed between the substrate and the first part. The semiconductor pattern includes a first semiconductor pattern and a second semiconductor pattern. The first semiconductor pattern is disposed between the dielectric pattern and the second semiconductor pattern. The first part of the dielectric pattern includes a material different from a material of the second part of the dielectric pattern. A thickness of the first part of the dielectric pattern is less than a thickness of the second part of the dielectric pattern.