Solid-State Imaging Device Impurity Region Design
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Solution Overview
Problem
In solid-state imaging devices, the interface between the oxide film and silicon substrate often generates a high leak current due to crystal defects caused by stress concentration in the element isolation region, leading to noise in the photodiode and floating diffusion, which is exacerbated by the formation of PN junctions with steep concentration gradients.
Innovation Solution
The implementation of a solid-state imaging device design where a first impurity region surrounds the element isolation region and a second impurity region with lower impurity concentration is placed between the first impurity region and the active elements, reducing the concentration gradient and suppressing leak current. Additionally, a third impurity region is provided around the source and drain of transistors to further minimize the electric field strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a PN junction is formed in the interface between oxide film and silicon substrate to isolate elements, then element isolation is achieved, but crystal defects and stress concentration generate high leak current
Solution Approach 1:
The patent applies local quality by forming a P-type semiconductor layer specifically at the interface between the oxide film and silicon substrate in the element isolation region. This localized doping creates a protective P-type region that fills crystal defects and reduces stress concentration at the critical interface, thereby suppressing leak current generation while maintaining element isolation functionality.
Solution Approach 2:
The P-type semiconductor layer acts as an intermediary between the oxide film and the silicon substrate. It mediates the interaction at the interface by filling voids and defects, reducing direct contact between the oxide and substrate that would otherwise generate leak current through crystal defects and stress concentration.
2Reliability
If high concentration P and N type semiconductors are placed adjacent to each other in a PN junction, then strong isolation is achieved, but steep concentration gradient generates strong electric field and increases leak current
Solution Approach 1:
The patent applies parameter changes by introducing an intermediate doping concentration between the high concentration P-type and N-type regions. Specifically, a P-type semiconductor layer with moderate doping concentration is formed at the oxide-silicon interface, creating a gradual transition in doping concentration that reduces the electric field strength while maintaining effective isolation.
3Object-generated harmful factors
If element isolation region interface is covered with P type semiconductor layer, then leak current at interface is suppressed, but PN junction with steep concentration gradient still forms in transistor region
Solution Approach 1:
The patent extends the application of local quality by forming P-type semiconductor layers at multiple locations: at the oxide-silicon interface in the element isolation region, and also in the transistor region surrounding the channel formation region. This multi-location doping strategy addresses both the interface leak current problem and the steep concentration gradient problem in the transistor region simultaneously.
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 design effectively reduces the leak current by relaxing the electric field at the interface, diminishing it to approximately one seventh or one eighth of the original value, thereby minimizing noise and visual perception of white spot defects in the photoreception signal.
Implementation Method 1
a second impurity region with lower impurity concentration is placed between the first impurity region and the active elements, reducing the concentration gradient and suppressing leak current
Data Source
AI summary
A solid-state imaging device including, active elements configured to handle the charge captured in a photoreceiving region, an element isolation region configured to isolate regions of the active element, a first impurity region configured to surround the element isolation region, and a second impurity region including an impurity region lower in impurity concentration than the first impurity region, the second impurity region being provided between the first impurity region and active elements.