Isolation Epitaxial Bi-Layer for CMOS Pixel Quantum Efficiency
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Solution Overview
Problem
As CMOS image sensors are scaled down, the smaller size of pixel regions leads to decreased quantum efficiency due to reduced incident photons reaching the image sensing elements, and forming high aspect ratio backside deep trench isolation (BDTI) structures becomes challenging, limiting the available space for image sensing elements.
Innovation Solution
A BDTI structure with an isolation epitaxial bi-layer is implemented, where a first isolation epitaxial layer with the same doping type as the image sensing element increases the effective size of the image sensing element, and a second isolation epitaxial layer with a different doping type serves as a passivation layer and facilitates depletion, improving quantum efficiency and full well capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixel regions are scaled down to increase integration density, then device integration density is improved, but quantum efficiency deteriorates due to reduced incident photons reaching the image sensing elements
Solution Approach 1:
The patent transitions from planar pixel arrangement to a three-dimensional stacked architecture with multiple imaging stacks vertically arranged. Each stack contains multiple pixel layers separated by isolation epitaxial bi-layers, enabling light detection from multiple depths and angles simultaneously. This vertical dimensionality increase allows higher integration density while maintaining sufficient light capture volume for quantum efficiency.
Solution Approach 2:
The patent implements nested isolation structures where the isolation epitaxial bi-layer is formed within trenches that are themselves within the pixel region. The bi-layer structure (first epitaxial layer with same doping type as pixel, second epitaxial layer with opposite doping type) is nested within the trench structure, creating concentric isolation zones that maintain pixel performance while enabling dense packing.
2Reliability
If backside deep trench isolation structures are formed with high aspect ratio to improve isolation effectiveness, then isolation quality is improved, but manufacturing difficulty increases and available space for image sensing elements decreases
Solution Approach 1:
The patent changes the geometric parameters of the isolation structure by forming trenches with controlled depth and width ratios. The isolation epitaxial bi-layer is deposited within these trenches to create a structure that achieves effective isolation without requiring extreme aspect ratios. The doping type alternation in the bi-layer enhances isolation effectiveness at moderate geometric dimensions.
Solution Approach 2:
The patent uses composite material structure in the isolation epitaxial bi-layer, combining two different doped semiconductor layers. The first epitaxial layer has the same doping type as the pixel region, while the second epitaxial layer has the opposite doping type, creating a composite structure that provides superior isolation and passivation properties compared to single-material isolation structures.
3Reliability
If isolation epitaxial bi-layer is implemented with alternating doping types to increase effective pixel size, then quantum efficiency is improved, but device complexity increases
Solution Approach 1:
The patent segments the isolation layer into two distinct epitaxial layers with alternating doping types. The first epitaxial layer (same doping type as pixel) and second epitaxial layer (opposite doping type) are formed as separate segments within the trench structure. This segmentation allows each layer to perform specific functions: the first layer maintains electrical characteristics matching the pixel, while the second layer provides passivation and depletion, achieving enhanced quantum efficiency through functional division.
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 enhances the quantum efficiency of pixel regions by increasing the effective size of image sensing elements and improves full well capacity by effectively managing charge storage, thus maintaining performance despite reduced pixel size.
Implementation Method 1
a first isolation epitaxial layer with the same doping type as the image sensing element increases the effective size of the image sensing element
Implementation Method 2
a second isolation epitaxial layer with a different doping type serves as a passivation layer and facilitates depletion
Data Source
AI summary
In some embodiments, the present disclosure relates to an integrated chip, including a substrate, a first image sensing element and a second image sensing element arranged next to one another over the substrate, the first image sensing element and the second image sensing element having a first doping type, and a backside deep trench isolation (BDTI) structure arranged between the first and second image sensing elements and including a first isolation epitaxial layer setting an outermost sidewall of the BDTI structure and having the first doping type, a second isolation epitaxial layer arranged along inner sidewalls of the first isolation epitaxial layer and having a second doping type different than the first doping type, and an isolation filler structure filling between inner sidewalls of the second isolation epitaxial layer.