Image Sensor Pad Isolation Structure for Dark Current Reduction
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Solution Overview
Problem
Existing image sensors face challenges in reducing dark current and white spots, which affect their reliability and performance.
Innovation Solution
The image sensor design includes a semiconductor substrate with specific pad and pixel separation patterns, a through via, and a fixed charge layer to reduce dark current and white spots, featuring a first pad separation pattern with a liner insulation and buried insulation, and a second pad separation pattern with a fixed charge layer and buried insulation, all of which are strategically positioned to enhance electrical signal transformation and isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional image sensor structures are used, then manufacturing is simpler, but dark current and white spots increase reducing reliability
Solution Approach 1:
The pad separation pattern is divided into multiple segments extending from different surfaces of the semiconductor substrate toward each other. These segmented patterns meet within the substrate to form complete separation, allowing isolation to be achieved through distributed structures rather than a single complex layer, thereby improving reliability while managing structural complexity
Solution Approach 2:
The pad separation pattern extends in the depth dimension (z-axis) from both the first and second surfaces of the semiconductor substrate, rather than only in the planar dimensions. This three-dimensional approach enables effective pad isolation and dark current reduction by creating separation barriers that traverse the substrate thickness, resolving the contradiction between reliability improvement and structural complexity
2Object-affected harmful factors
If pad separation patterns extend from both surfaces, then dark current is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The pixel separation pattern serves as an intermediary reference structure that mediates the alignment between the first and second pad separation patterns. By using the pixel separation pattern (formed from the second surface) as a common reference, the alignment precision requirements are managed through a shared intermediary structure, enabling dark current reduction while controlling manufacturing precision demands
3Reliability
If through via is spaced apart from pad separation patterns, then electrical isolation is improved, but device area increases
Solution Approach 1:
The through via is positioned at a specific optimized distance from the pad separation patterns, creating a localized isolation zone where electrical isolation is most critical. This local quality approach concentrates isolation efforts where needed (near the pad separation patterns) while minimizing the overall area occupied by the pad zone, resolving the contradiction between electrical isolation improvement and area increase
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 design increases the reliability of the image sensor, decreases dark current, and effectively reduces white spots, leading to improved performance in electrical signal transformation and image quality.
Implementation Method 1
The photodiode serves to transform incident light into an electrical signal
Data Source
AI summary
Disclosed are image sensors and methods of fabricating the same. The image sensor includes a semiconductor substrate including a pixel zone and a pad zone and having a first surface and a second surface opposing each other, a first pad separation pattern on the pad zone and extending from the first surface of the semiconductor substrate toward the second surface of the semiconductor substrate, a second pad separation pattern extending from the second surface toward the first surface of the semiconductor substrate on the pad zone the second pad and in contact with the first pad separation pattern, and a pixel separation pattern on the pixel zone and extending from the second surface of the semiconductor substrate toward the first surface of the semiconductor substrate.