Solid-State Imaging Device Gate Insulating Film Configuration
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Solution Overview
Problem
In solid-state imaging devices, the use of silicon oxynitride films as gate insulating layers in CMOS sensors leads to increased tunnel currents and deterioration of photoelectric conversion performance due to fixed charges, affecting image quality and transistor characteristics.
Innovation Solution
Implementing a silicon oxynitride film as the gate insulating layer in peripheral circuit transistors and replacing it with an oxide film above the photoelectric conversion portion, while maintaining silicon oxynitride films in the pixel portion to prevent tunnel current generation and fixed charge-related defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon oxynitride film is used as the gate insulating film in the peripheral circuit portion to suppress tunnel current, then transistor performance is improved, but photoelectric conversion performance deteriorates due to fixed charge
Solution Approach 1:
The patent applies different gate insulating film configurations to different regions: silicon oxynitride films are used in the peripheral circuit portion for reliable transistor operation, while the photoelectric conversion portion uses a structure without silicon oxynitride films (using only silicon oxide films and silicon nitride films) to avoid fixed charge effects. This spatial differentiation of material properties resolves the contradiction between transistor performance and photoelectric conversion quality.
2Reliability
If a silicon oxynitride film remains on the photoelectric conversion portion, then gate insulating film function is provided, but white defect deterioration occurs due to fixed charge
Solution Approach 1:
The patent extracts the harmful silicon oxynitride film from the photoelectric conversion portion while maintaining gate insulating film functionality through alternative structures. The photoelectric conversion portion uses silicon oxide films and silicon nitride films instead, eliminating the source of fixed charge that causes white defects while still providing necessary electrical isolation and insulation functions.
3Object-affected harmful factors
If a multiple structure of silicon oxide film/silicon nitride film/silicon oxide film/silicon oxynitride film is formed, then antireflection function is provided, but ripple property in light dispersion deteriorates
Solution Approach 1:
The patent removes the silicon oxynitride film layer from the antireflection film structure on the photoelectric conversion portion, simplifying the multiple-layer structure to eliminate the source of dispersion ripple while maintaining the antireflection functionality through the remaining silicon oxide and silicon nitride film layers.
4Reliability
If a silicon oxynitride film is used as gate insulating film, then tunnel current is suppressed, but optimization becomes complicated due to multiple structure
Solution Approach 1:
The patent segments the device into two distinct regions with different gate insulating film structures: the peripheral circuit portion uses silicon oxynitride films for tunnel current suppression, while the photoelectric conversion portion uses a simplified structure without silicon oxynitride films. This segmentation allows each region to be optimized independently, reducing overall device complexity while maintaining both tunnel current suppression and photoelectric conversion quality.
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 enhances transistor performance, reduces tunnel currents, and improves image quality by minimizing white defects and dark currents, thereby optimizing the imaging device's performance.
Implementation Method 1
a pixel portion provided with a photoelectric conversion portion, which photoelectrically converts incident light to obtain an electric signal
Data Source
AI summary
A solid-state imaging device includes, in a semiconductor substrate, a pixel portion provided with a photoelectric conversion portion, which photoelectrically converts incident light to obtain an electric signal and a peripheral circuit portion disposed on the periphery of the pixel portion, wherein a gate insulating film of aMOS transistor in the peripheral circuit portion is composed of a silicon oxynitride film, a gate insulating film of aMOS transistor in the pixel portion is composed of a silicon oxynitride film, and an oxide film is disposed just above the photoelectric conversion portion in the pixel portion.