Embedded CMOS Light Shield Structure for Crosstalk and Blooming
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Solution Overview
Problem
Complementary metal-oxide semiconductor (CMOS) image sensors face challenges in reducing crosstalk and blooming among photodetectors due to the thickness of the buffer layer, which affects quantum efficiency and sensitivity, especially in low light environments.
Innovation Solution
A light shield structure is disposed within the buffer layer overlying a first photodetector and laterally offset from adjacent photodetectors, reducing quantum efficiency of the first photodetector while maintaining optical isolation, thereby decreasing crosstalk and blooming, and increasing sensitivity by embedding the light shield structure within the buffer layer to reduce the distance to the back-side surface of the semiconductor substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the buffer layer thickness is increased to reduce crosstalk and blooming, then optical isolation between photodetectors is improved, but quantum efficiency and sensitivity deteriorate due to increased distance from the light shield structure to the back-side surface
Solution Approach 1:
The light shield structure is embedded within the buffer layer rather than being placed above it, creating a nested configuration where the light shield is surrounded by the buffer layer material. This nesting approach reduces the distance between the light shield and the back-side surface of the semiconductor substrate, improving quantum efficiency and sensitivity while maintaining optical isolation to reduce crosstalk and blooming effects between adjacent photodetectors.
2Measurement precision
If the light shield structure is positioned closer to the back-side surface to improve sensitivity, then quantum efficiency increases, but optical isolation and crosstalk reduction deteriorate
Solution Approach 1:
By nesting the light shield structure within the buffer layer, the design achieves close proximity to the back-side surface for improved sensitivity while the surrounding buffer layer material provides the necessary optical isolation. This resolves the contradiction by allowing the light shield to be positioned deep within the buffer layer structure, maintaining both high sensitivity and effective crosstalk reduction.
Solution Approach 2:
The buffer layer acts as an intermediary medium between the light shield structure and the external environment. By embedding the light shield within this intermediary layer, the system achieves both close coupling to the photodetector (improving sensitivity) and optical isolation from adjacent structures (reducing crosstalk), as the buffer layer material provides the necessary optical barrier properties.
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 allows for increased exposure times and improved sensitivity in low light conditions while minimizing crosstalk and blooming, enhancing the overall performance of the image sensor.
Implementation Method 1
The light shield structure is configured to block at least a portion of incident light from reaching the first photodetector
Implementation Method 2
embedding the light shield structure within the buffer layer to reduce the distance to the back-side surface of the semiconductor substrate
Data Source
AI summary
In some embodiments, an image sensor is provided. The image sensor comprises a first photodetector disposed within a front-side surface of a semiconductor substrate. A trench isolation structure is disposed over a back-side surface of the semiconductor substrate. The trench isolation structure includes a buffer layer and a dielectric liner. The buffer layer covers the back-side surface of the semiconductor substrate and fills trenches that extend downward into the back-side surface of the semiconductor substrate. The dielectric liner is disposed between the buffer layer and the semiconductor substrate. A composite grid structure has composite grid segments that are aligned over the trenches, respectively. The buffer layer separates the dielectric liner from the composite grid structure. A light shield structure is disposed within the buffer layer and directly overlies the first photodetector.