Back-Side Deep Trench Isolation for Image Sensor Pixel Crosstalk
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Solution Overview
Problem
The challenge in image sensor technology is achieving improved electrical and optical isolation between neighboring pixels to reduce blooming and crosstalk, particularly with the scaling down of device geometries, which complicates the fabrication process and reduces photodiode area and full well capacity.
Innovation Solution
The implementation of a back-side deep trench isolation (BDTI) structure with a doped liner, which eliminates the need for deep implantation, allowing for a shorter and simplified implantation process, expanding the lateral area of photodiodes and improving exposure resolution and full well capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If deep implantation is used to achieve electrical and optical isolation between pixels, then isolation performance is improved, but photodiode area is reduced and full well capacity decreases
Solution Approach 1:
The patent extracts the deep implantation process from the isolation structure formation, replacing it with a back-side deep trench isolation approach. This removes the harmful deep implantation step that was consuming photodiode area while still achieving the desired electrical and optical isolation between pixels through the trench structure filled with dielectric material.
Solution Approach 2:
The patent transitions from front-side deep implantation to back-side trench isolation, changing the dimensional approach from horizontal implantation to vertical trench formation. This dimensional shift allows isolation to be achieved through depth (z-dimension) rather than lateral expansion, preserving photodiode area while maintaining isolation effectiveness.
2Reliability
If deep implantation is performed to isolate pixels, then electrical isolation is improved, but fabrication complexity increases
Solution Approach 1:
The patent removes the complex deep implantation process from the fabrication sequence and replaces it with trench formation and filling operations. This extraction simplifies the fabrication workflow by eliminating the need for precise deep ion implantation while achieving equivalent or superior electrical isolation through the physical separation provided by the deep trench structure.
3Productivity
If device geometries are scaled down to increase pixel density, then integration density is improved, but achieving isolation becomes more difficult and photodiode area is reduced
Solution Approach 1:
The patent addresses the scaling challenge by moving the isolation mechanism to the vertical dimension through deep trench formation from the back side. This allows maintaining effective isolation between pixels even as lateral dimensions are reduced to increase pixel density, since the trench depth provides isolation independent of the reduced pixel pitch.
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 approach enhances exposure resolution and full well capacity by reducing crosstalk and blooming, while simplifying the fabrication process and minimizing photodiode area reduction, thereby improving the overall performance of the image sensor.
Implementation Method 1
The BDTI structure comprises a doped liner with the second doping type and a dielectric fill layer, the doped liner lining a sidewall surface of the deep trench
Implementation Method 2
The pixel sensors measure incident radiation (e.g., light) and convert to digital data
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.