Solid-State Image Sensor Pixel Structure for Dark Current Suppression
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Solution Overview
Problem
In solid-state imaging apparatuses, the N-type solid-phase diffusion layer reaching the backside Si interface leads to weakened electric charge pinning, causing dark characteristics deterioration such as white spots and dark current generation.
Innovation Solution
A P-type region is introduced between the photoelectric conversion elements and the light incident side interface, preventing the N-type solid-phase diffusion layer from contacting the backside Si interface, thus maintaining electric charge retention and improving dark characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the N-type solid-phase diffusion layer reaches the backside Si interface to form an intense electric field region, then the saturation charge amount Qs of each pixel is increased, but electric charge pinning weakens at the interface causing dark characteristic deterioration
Solution Approach 1:
The diffusion layer structure is segmented into multiple regions with different doping types and concentrations. Specifically, the N-type diffusion layer is divided into a first N-type region (higher concentration) and a second N-type region (lower concentration), creating distinct functional zones that separately address charge retention and pinning requirements
Solution Approach 2:
Different regions of the diffusion layer are assigned different local properties: the first N-type region provides high-concentration charge retention near the photodiode, while the second N-type region provides low-concentration pinning at the backside interface. This local differentiation allows each zone to optimize its specific function without compromising the other
2Reliability
If a P-type solid-phase diffusion layer is formed on the sidewall of the inter-pixel light-shielding wall, then electric charge retention is improved, but the complexity of the device structure increases
Solution Approach 1:
Multiple diffusion layers (P-type and N-type) are merged into a integrated structure where they work together to form the intense electric field region. The P-type diffusion layer on the sidewall combines with the N-type diffusion layers to create a unified charge retention system that leverages the complementary properties of both doping types
Solution Approach 2:
The diffusion layer structure serves multiple functions simultaneously: the P-type and N-type regions collectively provide charge retention, establish electric field distribution, and maintain pinning at the interface. This multi-functionality reduces the need for separate components and simplifies the overall device architecture
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 the deterioration of dark characteristics by maintaining electric charge retention, reducing white spots and dark current, and enhancing the overall performance of the solid-state imaging apparatus.
Implementation Method 1
A PN-junction portion of the P-type solid-phase diffusion layer 13 and the N-type solid-phase diffusion layer 14 is configured to form an intense electric field region to retain electric charge generated in the PD 11
Implementation Method 2
A DTI 12 is formed surrounding a photodiode (PD) 11 that is a photoelectric conversion element of each pixel
Data Source
AI summary
There is provided a imaging device including: an N-type region formed for each pixel and configured to perform photoelectric conversion; an inter-pixel light-shielding wall penetrating a semiconductor substrate in a depth direction and formed between N-type regions configured to perform the photoelectric conversion, the N-type regions each being formed for each of pixels adjacent to each other; a P-type layer formed between the N-type region configured to perform the photoelectric conversion and the inter-pixel light-shielding wall; and a P-type region adjacent to the P-type layer and formed between the N-type region and an interface on a side of a light incident surface of the semiconductor substrate.