BSI Image Sensor Isolation Structure for Parasitic Light Blocking
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Solution Overview
Problem
Existing backside illuminated (BSI) image sensors face challenges in preventing parasitic light from entering storage nodes, which affects their performance, especially as device scaling-down continues.
Innovation Solution
The implementation of a front side isolation structure and a backside isolation structure around the light-sensing region in BSI image sensors. These isolation structures, made of materials like nitride, oxide, or metal, prevent parasitic light from entering the storage node, while allowing light to incident on the light-sensing region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If device scaling-down continues in BSI image sensors, then integration density improves, but parasitic light interference worsens
Solution Approach 1:
The isolation structure is divided into a first isolation structure (e.g., dielectric material) and a second isolation structure (e.g., metal material), where each segment addresses different aspects of light blocking and electrical isolation. This segmented approach allows effective prevention of parasitic light interference while maintaining compact design for high integration density.
Solution Approach 2:
The isolation structure uses composite materials combining different properties - a dielectric material for electrical isolation and light blocking, combined with a metal material for enhanced light absorption and additional electrical isolation. This composite structure effectively counters parasitic light interference in scaled-down devices.
2Object-affected harmful factors
If isolation structures are added around light-sensing region, then parasitic light interference is reduced, but device complexity increases
Solution Approach 1:
The first isolation structure and second isolation structure are merged into a unified isolation structure that performs both dielectric and metal functions. This merging reduces the number of separate components and simplifies the overall device structure while maintaining effective parasitic light interference prevention.
Solution Approach 2:
The combined isolation structure serves multiple functions simultaneously: it provides electrical isolation between pixels, blocks parasitic light from reaching storage nodes, and absorbs stray light. This multi-functionality reduces the need for separate structures, thereby reducing device complexity.
3Productivity
If storage node is positioned near light-sensing region, then signal transfer efficiency improves, but susceptibility to parasitic light increases
Solution Approach 1:
The isolation structure acts as an intermediary element positioned between the light-sensing region and the storage node. It allows efficient signal transfer (electrons) from the light-sensing region to the storage node while simultaneously blocking parasitic light from reaching the storage node, thus resolving the contradiction between proximity benefits and light interference risks.
Data Source
AI summary
Image sensor structures are provided. In some embodiments, an image sensor structure is provided. The image sensor structure includes a substrate and a light-sensing region formed in the substrate and extending from the top surface to the bottom surface of the substrate. The image sensor structure further includes a first isolation structure extending from the top surface of the substrate to a middle portion of the substrate and a second isolation structure formed extending from the bottom surface of the substrate to the middle portion of the substrate and in contact with the first isolation structure. The image sensor structure further includes a gate structure overlapping the light-sensing region, the first isolation structure, and the second isolation structure and a cap layer overlapping the gate structure, the light-sensing region, the first isolation structure, and the second isolation structure in a top view.