Backside Image Sensor Structure for Low Reflection and Pixel Isolation
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Solution Overview
Problem
Conventional semiconductor image sensors face challenges in maximizing quantum efficiency due to light reflection and cross-talk between pixels, limiting their performance in capturing photons efficiently.
Innovation Solution
The semiconductor image-sensing structure incorporates a substrate with photodiode regions, an isolation structure, an anti-reflection structure comprising pillars, and optical elements like color filters and micro lenses, which reduce light reflection and enhance pixel isolation, thereby improving quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional frontside illumination design is used, then the device complexity is reduced, but the quantum efficiency deteriorates due to high reflection and optical cross-talk
Solution Approach 1:
The patent inverts the conventional frontside illumination design by implementing backside illumination. The photodiode regions are positioned to receive light from the backside of the substrate, with the isolation structure extending from the frontside through the backside to surround each photodiode region. This inversion allows light to enter the photodiode regions without passing through the isolation structure first, thereby reducing optical cross-talk and reflection while maintaining effective pixel isolation.
2Reliability
If the isolation structure extends only partially through the substrate, then the manufacturing precision is improved, but the optical cross-talk between pixels increases
Solution Approach 1:
The isolation structure is segmented into two distinct parts: a first portion extending from the frontside surface into the substrate, and a second portion extending from the backside surface into the substrate. These two portions are positioned on opposite sides of each photodiode region, with gaps between them. This segmentation allows each portion to be formed using standard shallow trench isolation processes without requiring deep through-substrate etching, while the combined effect of both portions provides complete optical isolation between adjacent pixels.
3Reliability
If no anti-reflection structure is implemented, then the device complexity is reduced, but the reflection loss increases significantly
Solution Approach 1:
An anti-reflection structure is implemented on the backside surface of the substrate, specifically positioned to cover the photodiode regions where light enters. This local application of anti-reflection properties targets the critical areas needing protection against reflection loss, while leaving other regions of the backside surface without this additional structure. The anti-reflection structure may consist of a dielectric layer or textured surface pattern that reduces the reflection coefficient at the air-substrate interface.
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 increases quantum efficiency by more than 2%, reducing light reflection and optical cross-talk, and allowing specific wavelengths to be directed accurately to their corresponding photodiode regions, enhancing the overall performance of the image sensor.
Implementation Method 1
an anti-reflection structure with pillars and a hybrid low-n grid, along with color filters and micro lenses, to minimize reflection and optical cross-talk
Implementation Method 2
photodiodes and transistors that can absorb radiation projected toward the substrate and convert the sensed radiation into electrical signals
Data Source
AI summary
A semiconductor image sensing structure includes a substrate, an isolation structure, an anti-reflection structure, at least one optical element and a transistor. The substrate has at least one photodiode region. The isolation structure is disposed in the substrate and surrounds the photodiode region. The anti-reflection structure covers the photodiode region. The optical element is disposed over the anti-reflection structure and corresponds to the photodiode region. The transistor is disposed under the photodiode region.