BSI Image Sensor Dark Current Reduction via Low-Transparent DTI Fill
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Solution Overview
Problem
As image sensor pixels shrink, controlling excessive dark current becomes increasingly difficult, leading to noise issues in image sensors, particularly in back side illuminated (BSI) image sensors where dark current is a significant source of noise even in the absence of photons.
Innovation Solution
The method involves manufacturing a BSI image sensor with a deep trench isolation (DTI) at the back side of the semiconductive substrate, a dielectric layer, a planarization stop layer, and a low-transparent material within the DTI, which helps in reducing light leakage between pixels and improving light separation, thereby minimizing dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixel size is reduced to increase resolution, then imaging resolution is improved, but dark current increases leading to more noise
Solution Approach 1:
The patent divides the semiconductor substrate into isolated pixel regions using deep trench isolation structures. These trenches physically separate adjacent pixels, preventing dark current generated in one pixel from affecting neighboring pixels. The isolation trenches extend through the substrate and are filled with insulating material, creating effective electrical separation between pixels while maintaining optical performance.
Solution Approach 2:
The patent introduces an intermediate layer with specific optical properties between the pixel region and the substrate. This intermediate layer acts as a mediator that allows photons to pass through to the photodetector while blocking or absorbing dark current carriers. The layer is positioned strategically to optimize both light transmission and dark current suppression.
2Object-generated harmful factors
If deep trench isolation is implemented to reduce dark current, then dark current noise is reduced, but device complexity increases
Solution Approach 1:
The patent addresses the complexity issue by optimizing the dimensional parameters of the deep trench isolation structure. By carefully controlling the depth, width, and spacing of the isolation trenches, the patent achieves effective dark current suppression without requiring excessively complex manufacturing processes. The dimensional parameters are selected to balance performance requirements with manufacturability.
3Measurement precision
If pixel density is increased to improve resolution, then imaging resolution is improved, but light separation between pixels becomes difficult leading to increased dark current
Solution Approach 1:
The patent employs a nested structure where the deep trench isolation is integrated within the pixel architecture itself. The isolation trenches are formed between adjacent pixels in a nested manner, allowing each pixel to be surrounded by isolation structures. This nested approach enables effective light and electrical separation even at high pixel densities without requiring additional external components or excessively complex processing steps.
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 effectively reduces dark current noise by enhancing light separation and control within each pixel, improving the overall performance and accuracy of the image sensor.
Implementation Method 1
a low-transparent material within the DTI, which helps in reducing light leakage between pixels
Data Source
AI summary
Some embodiments of the present disclosure provide a back side illuminated (BSI) image sensor. The BSI image sensor includes a semiconductive substrate, a deep trench isolation (DTI) at a back side of the semiconductive substrate, and a dielectric layer. the dielectric layer includes a top portion over the back side, and a side portion lined to a sidewall of the DTI. The BSI image sensor includes a planarization stop layer disposed conformally on top of the dielectric layer. The planarization stop layer includes a top section on the top portion, a side section lined against the side portion, and a first transmittance. The BSI image sensor includes a low-transparent material inside the DTI, and the low-transparent material includes a second transmittance. The second transmittance is lower than the first transmittance.