BSI Image Sensor Isolation Stack for Near-Infrared Cross-Talk
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Solution Overview
Problem
BSI image sensors face challenges in reducing cross-talk between adjacent pixel structures, which affects their precision and quantum efficiency due to light interference.
Innovation Solution
Incorporating a stack of isolation structures, including shallow trench isolation (STI) and deep trench isolation (DTI) with a metal fill layer, and grooved regions on the back-side surface of the substrate to optically isolate pixel structures, minimizing light leakage and enhancing quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If isolation structures are added to reduce cross-talk, then quantum efficiency is improved, but device complexity increases
Solution Approach 1:
The isolation structure is divided into multiple segments: a first isolation structure extending from the front surface to a first depth, and a second isolation structure extending from the front surface to a second depth greater than the first depth. This segmentation allows each isolation structure to perform specific functions in reducing cross-talk at different depths, thereby improving quantum efficiency while maintaining manageable structural complexity.
Solution Approach 2:
Different regions of the substrate are treated with different isolation structures based on local requirements. The first and second isolation structures are positioned at specific locations between adjacent pixel structures where cross-talk is most problematic. This localized approach targets cross-talk reduction precisely where needed, improving quantum efficiency without unnecessarily complicating the entire device structure.
2Measurement precision
If deeper isolation structures are used to reduce cross-talk, then quantum efficiency is improved, but manufacturing difficulty increases
Solution Approach 1:
The isolation approach is segmented into two distinct structures with different depths. The first isolation structure provides baseline isolation, while the second, deeper isolation structure provides enhanced isolation in specific regions. This segmentation allows manufacturers to implement a staged isolation strategy that achieves superior cross-talk reduction through the second structure while using the simpler first structure as a foundation, balancing manufacturing complexity with performance improvement.
Solution Approach 2:
The first isolation structure is formed as a preliminary step before forming the second isolation structure. This preliminary action establishes a foundation that simplifies subsequent manufacturing steps. By first creating the shallower isolation structure and then adding the deeper second isolation structure in specific regions, the manufacturing process is broken into manageable stages, reducing overall difficulty while achieving the quantum efficiency improvements needed for near-infrared detection.
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
The solution significantly improves quantum efficiency by reducing cross-talk, particularly in the near-infrared region, by up to 1.5 times compared to BSI image sensors without these features, while maintaining a compact size and manageable manufacturing costs.
Implementation Method 1
isolation structures disposed between adjacent pixel structures to optically isolate the adjacent pixel structures from each other
Implementation Method 2
absorb (e.g., sense) the incoming radiation and convert it into electrical signals
Data Source
AI summary
An optical device with isolation structures and a method of fabricating the same are disclosed. The optical device includes a substrate having a first surface and a second surface opposite to the first surface, first and second radiation sensing devices disposed in the substrate, a first isolation structure disposed in the substrate. The first isolation structure has a first surface and a second surface opposite to the first surface. The optical device further includes a second isolation structure disposed in the substrate and on the first surface of the first isolation structure. The second isolation structure includes a metal structure and a dielectric layer surrounding the metal structure. The second isolation structure vertically extends over the first surface of the substrate.