IGBT Guard Ring Mesa Structure for Carrier Control
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Solution Overview
Problem
Conventional power control semiconductor devices, such as IGBTs and PiN diodes, face issues with reduced withstanding capability due to carrier accumulation and electric field concentration in the guard ring region, leading to thermal destruction and lowered reverse recovery withstand capability.
Innovation Solution
The semiconductor device design includes a guard ring region with a modified structure, where the collector layer is removed from the lower part of the guard ring, and an impurity layer with higher concentration is formed on the bottom part of the drift layer, preventing carrier accumulation and electric field concentration, thereby allowing for a narrower guard ring width.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional IGBT structure with uniform impurity concentration is used, then the device can be manufactured with standard processes, but carrier accumulation occurs in the guard ring region causing thermal destruction and reduced withstanding capability
Solution Approach 1:
The patent applies local quality by creating a non-uniform impurity concentration distribution in the drift layer. Specifically, the impurity concentration is increased in the guard ring region compared to the cell region, forming a localized modification that prevents carrier accumulation. This local variation in material properties (impurity concentration) directly addresses the harmful effect of carrier accumulation without requiring a complete structural redesign.
Solution Approach 2:
The patent changes the physical parameter of impurity concentration in the drift layer to resolve the technical contradiction. By increasing the impurity concentration in the guard ring region, the electrical properties of the material are modified to reduce carrier accumulation. This parameter change (from uniform to non-uniform impurity concentration) directly improves withstanding capability while preventing thermal destruction.
2Reliability
If the guard ring width is increased to prevent electric field concentration, then withstanding capability is improved, but the device area increases and productivity decreases
Solution Approach 1:
The patent uses local quality by modifying the impurity concentration specifically in the guard ring region of the drift layer. This localized parameter modification allows the guard ring to perform its protective function more efficiently, enabling a reduction in guard ring width while maintaining withstanding capability. The local variation in impurity concentration creates a more effective electric field distribution that prevents concentration effects with a narrower structure.
Solution Approach 2:
The patent changes the impurity concentration parameter in the drift layer to alter the electric field distribution characteristics. By increasing impurity concentration in the guard ring region, the electric field is better controlled and concentrated less, allowing for a narrower guard ring width. This parameter change enables improved area utilization while maintaining reliability.
3Reliability
If holes are absorbed into the p type well in the outermost periphery during turn-off, then carrier removal is achieved, but thermal destruction occurs when hole amount exceeds a certain value
Solution Approach 1:
The patent applies local quality by creating a localized region of higher impurity concentration in the drift layer beneath the guard ring. This local modification changes the carrier distribution and recombination characteristics in that specific area, reducing the number of holes that must flow to the outermost p type well during turn-off. The localized material property change prevents excessive hole accumulation and associated thermal destruction.
Solution Approach 2:
The patent changes the impurity concentration parameter in the drift layer to modify carrier behavior during turn-off operations. By increasing impurity concentration in the guard ring region, the recombination of carriers is enhanced locally, reducing the total number of holes that need to be removed through the outermost p type well. This parameter change prevents thermal destruction by limiting hole accumulation.
Data Source
AI summary
A carrier is prevented from being stored in a guard ring region in a semiconductor device. The semiconductor device has an IGBT cell including a base region and an emitter region formed in an n− type drift layer, and a p type collector layer arranged under the drift layer with a buffer layer interposed therebetween. A guard ring region having a guard ring is arranged around the IGBT cell. A lower surface of the guard ring region has a mesa structure provided by removing the collector layer.