Solid-State Imaging Device Isolation Region Optimization
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Solution Overview
Problem
In CMOS solid-state imaging devices, as the number of pixels increases and pixels become finer, the isolation region area required for each pixel grows, leading to reduced photodiode area, saturation characteristic, sensitivity, and mixed color issues due to high impurity concentration in isolation regions, which affects the electric field and crystal defects.
Innovation Solution
The implementation of a solid-state imaging device with distinct impurity concentration levels in first and second isolation regions, where the first isolation region between neighboring photodiodes has a low concentration for optimal isolation and a higher concentration in the second isolation region between the photodiode and pixel transistor, allowing for a larger photodiode area and reduced isolation region width.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the isolation region is formed with high impurity concentration to isolate the periphery of the pixel transistor, then the isolation effect is improved, but the effective area of the photodiode is reduced and the saturation signal amount Qs is reduced
Solution Approach 1:
The patent applies local quality by forming two distinct isolation regions with different impurity concentrations: a first isolation region with high impurity concentration to provide strong isolation between the pixel transistor and photodiode, and a second isolation region with low impurity concentration to minimize impact on the photodiode area and saturation signal amount. This localized differentiation allows each region to optimize its function without compromising the other.
2Reliability
If the impurity concentration in the isolation region is increased to improve isolation, then the isolation between source/drain region and photodiode is improved, but the electric field intensity increases and white spots worsen
Solution Approach 1:
The patent differentiates the impurity concentration in isolation regions based on their specific functions: the first isolation region uses high concentration for effective isolation, while the second isolation region uses low concentration to avoid excessive electric field intensity and white spot formation in the floating diffusion region.
Solution Approach 2:
The patent changes the impurity concentration parameter across different isolation regions, using high concentration where isolation is critical and low concentration where electric field intensity must be controlled, thereby optimizing both isolation performance and reduction of harmful effects.
3Manufacturing precision
If the number of pixels is increased and pixels become finer, then the resolution is improved, but the isolation region area increases and sufficient area for photodiodes cannot be obtained
Solution Approach 1:
The patent applies local quality by creating isolation regions with differentiated impurity concentrations that optimize the balance between isolation requirements and photodiode area. The second isolation region with low impurity concentration specifically addresses the need to preserve photodiode area in high-resolution devices while maintaining necessary isolation.
4Reliability
If the impurity concentration in the isolation region is increased to improve isolation, then the isolation effect is improved, but the conversion efficiency is degraded
Solution Approach 1:
The patent uses local quality by forming isolation regions with different impurity concentrations tailored to their specific functions, allowing the second isolation region to maintain low concentration for optimal conversion efficiency while the first isolation region provides necessary isolation with high concentration.
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 enhances pixel characteristics such as saturation characteristic, sensitivity, and mixed color by optimizing impurity concentrations in isolation regions, reducing electric field intensity and crystal defects, and improving conversion efficiency.
Implementation Method 1
a pixel portion where photodiodes which are a photoelectric conversion portion and a plurality of pixels having a plurality of pixel transistors are regularly arranged in two dimensions
Data Source
AI summary
A solid-state imaging device includes: a pixel having a photodiode and a pixel transistor; a first isolation region using a semiconductor region containing impurities formed between neighboring photodiodes; and a second isolation region using an semiconductor region containing impurities formed between the photodiode and the pixel transistor, wherein an impurity concentration of the first isolation region is different from an impurity concentration of the second isolation region.