CMOS Image Sensor Trench Layout for Dark Current Suppression
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Solution Overview
Problem
The existing solid-state imaging devices experience deterioration in dark characteristics due to weakened pinning on the silicon substrate, leading to issues like white spots and dark current generation, particularly when a P-type diffusion layer is formed on the light entrance side.
Innovation Solution
A solid-state imaging device design that includes a photoelectric conversion section and a charge retaining section, with a trench formed in the semiconductor substrate between them, where the trench is either higher or lower than the photoelectric conversion section, to create a strong electric field region and prevent electric charge from flowing into the photodiode, thus maintaining charge pinning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a P-type diffusion layer is formed on the light entrance side to increase saturation charge amount, then the saturation charge amount Qs increases, but pinning on the silicon substrate weakens causing dark current and white spots
Solution Approach 1:
The patent divides the semiconductor substrate into multiple depth regions with different trench configurations. Some pixels have trenches extending to the back surface (first trench configuration) while others have trenches not reaching the back surface (second trench configuration). This segmentation allows different pixels to have different charge retention mechanisms, enabling the system to achieve high saturation charge amount while maintaining good dark characteristics through the combined effect of both configurations.
Solution Approach 2:
The patent applies different trench structures to different local regions of the pixel array. The first trench configuration (reaching back surface) provides strong charge pinning for pixels where dark characteristics are prioritized, while the second trench configuration (not reaching back surface) provides adequate charge retention for pixels where saturation charge amount is prioritized. This local differentiation resolves the contradiction by allowing each region to optimize for its specific requirements.
2Reliability
If a trench is formed between photoelectric conversion section and charge retaining section, then charge pinning is maintained, but device structure becomes more complex
Solution Approach 1:
The patent designs the trench structure to serve multiple functions simultaneously. The trenches between the photoelectric conversion section and charge retaining section not only maintain charge pinning but also act as isolation structures and define pixel boundaries. The same trench configuration that provides pinning also serves as the inter-pixel isolation structure, reducing the need for additional separate structures and thereby limiting the increase in device complexity.
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 configuration effectively prevents deterioration in dark characteristics by maintaining charge pinning and reducing the occurrence of white spots and dark current, enhancing the imaging device's performance.
Implementation Method 1
a photoelectric conversion section that performs photoelectric conversion
Implementation Method 2
a strong electric field region is formed to retain electric charge
Data Source
AI summary
The present technology relates to a solid-state imaging device capable of suppressing deterioration in dark characteristics, and an electronic apparatus. The present invention is provided with: a photoelectric conversion section that performs photoelectric conversion; a charge retaining section that temporarily retains electric charge converted by the photoelectric conversion section; and a first trench formed in a semiconductor substrate between the photoelectric conversion section and the charge retaining section, the first trench being higher than the photoelectric conversion section in a depth direction of the semiconductor substrate. Alternatively, the first trench is lower than the photoelectric conversion section and higher than the charge retaining section in the depth direction of the semiconductor substrate. The present technology can be applied to, for example, a back-illuminated CMOS image sensor.