Raised Isolation Structure in Image Sensors for Lower Photodetector Crosstalk
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Solution Overview
Problem
Cross talk between adjacent photodetectors in complementary metal-oxide semiconductor (CIS) image sensors is high due to the relatively low height of the isolation structure, leading to decreased quantum efficiency and overall performance.
Innovation Solution
The image sensor incorporates an isolation structure that protrudes above the semiconductor substrate into the upper dielectric structure, increasing its height to reduce cross talk by providing a shorter path for oblique incident light, and includes a metal grid structure to further direct light towards the photodetectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the isolation structure height is increased to reduce cross talk, then cross talk between adjacent photodetectors is reduced, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The isolation structure is divided into multiple segments: a first isolation structure extending from the first dielectric layer to a first depth, and a second isolation structure extending from the first dielectric layer to a second depth greater than the first depth. This segmentation allows each isolation structure to perform isolation functions at different levels, effectively reducing cross talk between adjacent photodetectors while maintaining manageable structural complexity
Solution Approach 2:
The patent introduces vertical dimensionality by creating isolation structures at different depths within the semiconductor substrate. The first and second isolation structures are positioned at different vertical levels, creating a multi-layered isolation architecture that reduces cross talk by blocking oblique incident light paths without requiring excessive lateral space or overall device height
2Measurement precision
If the isolation structure height is increased to reduce cross talk, then quantum efficiency is improved, but manufacturing precision requirements increase
Solution Approach 1:
The isolation structure is segmented into first and second isolation structures with different depths. The first isolation structure extends to a first depth and the second isolation structure extends to a second depth greater than the first depth. This segmentation allows for staged manufacturing processes where each isolation structure can be formed with controlled precision requirements, reducing the overall manufacturing difficulty compared to forming a single deep isolation structure
Solution Approach 2:
The first isolation structure is formed first, extending from the first dielectric layer to the first depth. Subsequently, the second isolation structure is formed, extending from the first dielectric layer to the second depth. This preliminary action approach allows the shallower first isolation structure to be established before adding the deeper second isolation structure, enabling better control over the final isolation heights and improving manufacturing precision
3Reliability
If the isolation structure height is increased to reduce cross talk, then overall performance is improved, but fabrication complexity increases
Solution Approach 1:
The isolation architecture is segmented into first and second isolation structures formed at different depths. This segmentation enables the use of standard semiconductor fabrication techniques for each isolation structure independently, such as separate etching and filling processes, which are more easily manufactured than a single complex deep isolation structure
Solution Approach 2:
By utilizing the vertical dimension to create multi-level isolation structures at different depths within the substrate, the patent achieves effective cross talk reduction without requiring increased lateral dimensions or excessive overall device height. This vertical stacking approach is compatible with standard planar fabrication processes, maintaining ease of manufacture while improving performance
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 decreases cross talk among photodetectors, enhances quantum efficiency, and improves overall performance of the image sensor while maintaining structural integrity and facilitating device scaling.
Implementation Method 1
increasing its height to reduce cross talk by providing a shorter path for oblique incident light
Implementation Method 2
includes a metal grid structure to further direct light towards the photodetectors
Data Source
AI summary
Various embodiments of the present disclosure are directed towards an image sensor having a photodetector disposed within a semiconductor substrate. A dielectric structure is disposed on a first side of the semiconductor substrate. An isolation structure extends from the dielectric structure into the first side of the semiconductor substrate. The isolation structure laterally wraps around the photodetector and comprises an upper portion disposed above the first side of the semiconductor substrate and directly contacting sidewalls of the dielectric structure. The isolation structure comprises a first material different from a second material of the dielectric structure.