Back-Side Deep Trench Isolation for Higher-Capacity Image Sensors
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Solution Overview
Problem
Existing image sensor technologies face challenges in achieving precise electrical and optical isolation between neighboring pixels due to the complexity of deep implantation processes, which result in reduced photodiode area and full well capacity, limiting exposure resolution and performance.
Innovation Solution
The implementation of a back-side deep trench isolation (BDTI) structure with a doped liner in image sensors, which eliminates the need for deep implantation by functioning as both a deep depletion and isolation structure, thereby simplifying the fabrication process and enhancing photodiode area and full well capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If deep implantation processes are used to achieve electrical and optical isolation between neighboring pixels, then isolation effectiveness is improved, but photodiode area and full well capacity are reduced
Solution Approach 1:
The patent extracts the isolation function from the deep implantation process and relocates it to the back-side deep trench isolation structure. By forming trenches from the back side of the substrate, the isolation structures are separated from the photodiode formation area, allowing photodiodes to maintain larger area while achieving effective electrical and optical isolation between pixels through the trench structures extending through the substrate.
Solution Approach 2:
The patent inverts the conventional approach by forming isolation trenches from the back side of the substrate rather than from the front side. This inversion allows the photodiodes to be formed first with maximum area, then the isolation structures are created from the opposite side, eliminating the need to reduce photodiode area to accommodate deep implantation isolation regions.
2Reliability
If deep implantation processes are used to achieve electrical and optical isolation between neighboring pixels, then isolation effectiveness is improved, but fabrication complexity increases
Solution Approach 1:
The patent segments the isolation process into distinct stages: first forming photodiodes on the front side, then forming trenches from the back side, and finally filling trenches with isolation material. This segmentation allows each process to be optimized independently and simplifies fabrication by avoiding the need for complex deep implantation processes that require multiple alignment steps and precise control.
Solution Approach 2:
By inverting the isolation structure formation approach and creating trenches from the back side rather than implanting from the front side, the patent simplifies the fabrication process. The back-side trench approach eliminates the need for complex deep implantation equipment and processes, reducing fabrication complexity while maintaining effective isolation.
3Reliability
If deep implantation processes are used to achieve electrical and optical isolation between neighboring pixels, then isolation effectiveness is improved, but exposure resolution is reduced
Solution Approach 1:
The patent extracts the isolation function from the photodiode formation process and implements it separately through back-side trench structures. This extraction allows photodiodes to be formed with high precision and maximum area without the degradation caused by deep implantation processes, thereby maintaining exposure resolution while achieving effective isolation.
Solution Approach 2:
By inverting the isolation approach to use back-side trenches instead of front-side deep implantation, the patent preserves photodiode area and exposure resolution. The trench structures provide isolation without interfering with the photodiode formation precision, eliminating the trade-off between isolation effectiveness and exposure resolution.
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 with a doped liner improves exposure resolution and full well capacity of the photodiode, reduces blooming and crosstalk between pixels, and simplifies the implantation process, leading to more efficient and effective image sensor performance.
Implementation Method 1
The BDTI structure comprises a doped liner with the second doping type and a dielectric fill layer
Implementation Method 2
A plurality of pixel regions are disposed within the image sensing die and respectively comprises a photodiode configured to convert radiation that enters from the back-side of the image sensor die into an electrical signal
Data Source
AI summary
The present disclosure relates to an image sensor having a photodiode surrounded by a back-side deep trench isolation (BDTI) structure, and an associated method of formation. In some embodiments, a plurality of pixel regions is disposed within an image sensing die and respectively comprises a photodiode configured to convert radiation into an electrical signal. The photodiode comprises a photodiode doping column with a first doping type surrounded by a photodiode doping layer with a second doping type that is different than the first doping type. A BDTI structure is disposed between adjacent pixel regions and extending from the back-side of the image sensor die to a position within the photodiode doping layer. The BDTI structure comprises a doped liner with the second doping type and a dielectric fill layer. The doped liner lines a sidewall surface of the dielectric fill layer.