Backside Illuminated Image Sensor Pixel Isolation Grooves
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Solution Overview
Problem
Backside illuminated CMOS image sensors face challenges due to partial obstruction of pixel areas by metalization and polysilicon features on the front side, leading to reduced light sensitivity and increased cross-talk between pixels, which affects color fidelity and introduces noise.
Innovation Solution
A deep-groove isolation structure is formed by etching into the backside of the substrate using a chemical solution, such as KOH or TMAH, to separate pixels and prevent electron-hole pair diffusion, enhancing the barrier between pixels and reducing cross-talk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a backside illuminated structure is used to improve light sensitivity, then light sensitivity is improved, but cross-talk between pixels increases
Solution Approach 1:
The pixel array is divided into individually isolated photodiode regions separated by deep isolation grooves. These grooves physically segment the continuous substrate into discrete pixel units, preventing electron-hole pair diffusion between adjacent pixels while maintaining full light sensitivity from the backside illumination.
Solution Approach 2:
The isolation structure is applied locally at the boundaries between pixels rather than uniformly across the entire substrate. The deep isolation grooves are positioned specifically where needed to block carrier diffusion between pixels, while the bulk photodiode regions maintain their light-sensitive properties.
2Object-generated harmful factors
If deep isolation grooves are etched to reduce cross-talk, then cross-talk is reduced, but manufacturing complexity increases
Solution Approach 1:
The complex multi-step isolation process is replaced by a single wet chemical etching step using KOH or TMAH solutions. This chemical etching method automatically forms the isolation grooves based on crystallographic planes, eliminating the need for multiple mechanical or photolithographic steps while achieving the same cross-talk reduction effect.
Solution Approach 2:
The etching process parameters (chemical solution type, temperature, concentration) are optimized to achieve self-aligned deep groove formation. By controlling these parameters, the isolation structures are formed with precise depth and orientation without requiring complex masking or multiple etching steps.
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 deep-groove isolation structure effectively reduces cross-talk and noise, improving the sensitivity and color fidelity of the image sensor by preventing light leakage and electron-hole pair diffusion between pixels.
Implementation Method 1
An isolation structure is formed by etching into the backside of the substrate using a chemical solution to separate the second pixel from the first pixel
Data Source
AI summary
Systems and methods are provided for fabricating a backside illuminated image sensor including an array of pixels. An example image sensor includes a first pixel, a second pixel, and an isolation structure. The first pixel is disposed in a front side of a substrate and is configured to generate charged carriers in response to light incident upon a backside of the substrate. The second pixel is disposed in the front side of the substrate and is configured to generate charged carriers in response to light incident upon the backside of the substrate. The isolation structure is disposed to separate the second pixel from the first pixel, and extends from the backside of the substrate toward the front side of the substrate. The isolation structure includes a sidewall substantially vertically to the front side of the substrate.