Backside Deep Trench Isolation Bi-Layer for Small-Pixel Image Sensors
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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 its effective size, 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
1Volume of moving object
If pixel regions are scaled down to reduce device size, then device compactness 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 architecture to a three-dimensional stacked architecture, placing photodiodes above transistors in the vertical dimension. This allows pixel regions to be scaled down in the lateral plane while maintaining sufficient active area through vertical stacking, thereby preserving quantum efficiency despite reduced device footprint.
Solution Approach 2:
The pixel region is segmented into distinct functional layers: photodiode layer for light detection, transistor layer for signal processing, and isolation structures. This segmentation allows optimization of each layer's function and enables the photodiode to capture maximum photons while the transistor processes signals, maintaining quantum efficiency in scaled-down devices.
2Reliability
If high aspect ratio backside deep trench isolation structures are formed to isolate pixel regions, then isolation effectiveness is improved, but manufacturing difficulty increases and available space for image sensing elements is reduced
Solution Approach 1:
The isolation structure extends vertically into the substrate from the backside, utilizing the depth dimension to achieve effective isolation without requiring large lateral dimensions. This vertical isolation approach maintains pixel separation effectiveness while preserving lateral space for image sensing elements and simplifying the formation process.
Solution Approach 2:
An intermediary isolation layer is introduced between the photodiode and the deep trench isolation structure. This intermediary layer protects the photodiode from damage during deep trench formation and provides a transition zone that simplifies the manufacturing process while maintaining effective isolation.
3Area of moving object
If isolation epitaxial bi-layer is implemented with same doping type as image sensing element, then effective size of image sensing element is increased, but device complexity increases
Solution Approach 1:
The isolation epitaxial layer with the same doping type as the image sensing element is merged with the photodiode region, effectively extending the light-sensitive area. This merging increases the effective size of the image sensing element without requiring additional separate structures, thereby maintaining relatively simple device architecture.
Solution Approach 2:
The epitaxial bi-layer serves multiple functions: it acts as isolation material between pixel regions while simultaneously extending the light-sensitive area of the photodiode. This multi-functionality increases the effective sensing area without proportionally increasing device complexity, as the same structure performs both isolation and light detection functions.
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 BDTI structure enhances the quantum efficiency of pixel regions by increasing the effective size of image sensing elements and improves full well capacity, maintaining performance despite reduced pixel size, while also facilitating efficient charge storage and defect passivation.
Implementation Method 1
a first isolation epitaxial layer with the same doping type as the image sensing element increases its effective size
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.