Pixel Isolation Air Gap Structure for Low-Dark-Current Image Sensors
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Solution Overview
Problem
Current image sensors face challenges in achieving optimal electrical and optical characteristics, particularly in reducing dark current and improving quantum efficiency, due to limitations in pixel isolation structures and photoelectric conversion regions.
Innovation Solution
The image sensor incorporates a semiconductor substrate with a pixel isolation structure that includes an air gap, a liner insulating pattern, and a capping pattern, which reduces dark current and enhances quantum efficiency by reflecting incident light and preventing absorption, while also using impurities of a second conductivity type in photoelectric conversion regions to form pn junctions for efficient light conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional pixel isolation structures are used, then manufacturing is simpler, but dark current increases and quantum efficiency decreases
Solution Approach 1:
The pixel isolation structure is segmented into multiple functional layers: a first pixel isolation structure in the light-receiving region and a second pixel isolation structure in the light-blocking region. This segmentation allows each layer to be optimized for its specific function, improving overall quantum efficiency while managing complexity through functional division.
Solution Approach 2:
Different regions of the pixel isolation structure have different properties: the first pixel isolation structure in the light-receiving region uses an air gap for optimal light transmission and quantum efficiency, while the second pixel isolation structure in the light-blocking region uses a sacrificial pattern for effective light blocking. This local differentiation resolves the contradiction by optimizing each region for its specific purpose.
2Object-generated harmful factors
If pixel isolation structure encloses photoelectric conversion region, then dark current is reduced, but light absorption increases
Solution Approach 1:
The pixel isolation structure applies different materials and configurations to different regions: the first pixel isolation structure uses an air gap configuration that minimizes light absorption in the light-receiving region, while the second pixel isolation structure uses a sacrificial pattern that provides effective isolation in the light-blocking region. This local differentiation allows dark current reduction without compromising quantum efficiency.
Solution Approach 2:
The pixel isolation structure acts as an intermediary element between the light-receiving region and the light-blocking region, providing electrical isolation while maintaining optical performance. The air gap and sacrificial pattern configurations serve as intermediate structures that prevent direct contact between regions, reducing dark current while allowing optimal light transmission to the photoelectric conversion regions.
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 configuration improves the electrical and optical characteristics of the image sensor by reducing dark current and increasing quantum efficiency, leading to enhanced performance in converting optical signals to electrical signals.
Implementation Method 1
enhances quantum efficiency by reflecting incident light and preventing absorption
Implementation Method 2
photoelectric conversion region having an impurity of a second conductivity type... efficient light conversion
Data Source
AI summary
An image sensor includes: a semiconductor substrate of a first conductivity type, the semiconductor substrate including: a first surface, a second surface opposite to the first surface, a pixel region, and a pixel isolation structure; and a photoelectric conversion region in the pixel region, the photoelectric conversion region having an impurity of a second conductivity type, wherein the pixel isolation structure is configured to enclose the photoelectric conversion region, and wherein the pixel isolation structure comprises: an air gap, a liner insulating pattern between the air gap and the semiconductor substrate, and a capping pattern adjacent to the second surface of the semiconductor substrate.