Backside Image Sensor Pixel Layout 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 increase saturation charge amount, then the electric charge retention capability is improved, but the dark characteristics deteriorate due to weakened electric charge pinning
Solution Approach 1:
The diffusion layer structure is segmented into distinct P-type and N-type regions with defined spatial separation. The P-type diffusion layer is positioned between the N-type diffusion layer and the backside Si interface, creating a segmented architecture that prevents direct contact between the N-type layer and the interface, thereby resolving the contradiction between charge retention and dark characteristic maintenance
Solution Approach 2:
The P-type diffusion layer acts as an intermediary barrier between the N-type diffusion layer and the backside Si interface. This intermediate P-type region prevents the N-type layer from reaching the interface, maintaining electric charge pinning at the interface while allowing the N-type layer to extend sufficiently deep to increase saturation charge amount
2Quantity of substance
If the N-type solid-phase diffusion layer contacts the backside Si interface to maximize charge storage capacity, then the charge retention is improved, but dark current increases due to pinning weakness
Solution Approach 1:
The diffusion structure is divided into functionally distinct P-type and N-type regions. The P-type region serves as a separator that prevents the N-type diffusion layer from contacting the backside Si interface, thereby maintaining low dark current while allowing the N-type layer to extend deep enough to provide sufficient charge storage capacity
Solution Approach 2:
Different regions of the diffusion structure are assigned different doping types and properties. The P-type region near the backside interface maintains strong pinning to suppress dark current, while the N-type region extends deeper into the substrate to maximize charge storage capacity, creating local quality variations that resolve the contradiction
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 and reducing dark current, enhancing the imaging performance of the solid-state imaging apparatus.
Implementation Method 1
A P-type solid-phase diffusion layer 13 and an N-type solid-phase diffusion layer 14 are formed between the PD 11 and the DTI 12 in the stated order from the DTI 12 to the PD 11. Specifically, the P-type solid-phase diffusion layer 13 and the N-type solid-phase diffusion layer 14 are formed along the DTI 12, held in contact with a backside Si interface 20 of the Si substrate 10. With this, 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 light-shielding film 15 is formed on a back side (lower side in the figure) of the DTI 12. The light-shielding film 15 prevents leakage of light to neighboring pixels. The light-shielding film 15 is, for example, made of metal material such as W (tungsten). An on-chip lens (OCL) 16 is formed on a back side of the Si substrate 10. The OCL 16 converges incident light to the PD 11.
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.