SiC MOSFET Breakdown Voltage Holding Layer Design
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Solution Overview
Problem
Silicon carbide (SiC) MOSFETs face challenges in achieving high breakdown voltage due to electric field concentration, which is not adequately addressed by techniques optimized for silicon (Si) MOSFETs, as SiC can withstand higher electric fields, leading to potential breakage at specific positions in the MOSFET structure.
Innovation Solution
A silicon carbide semiconductor device with a specific structure including a silicon carbide film, gate insulating film, and electrodes, featuring breakdown voltage holding layers, charge compensation regions, junction terminal regions, and guard rings, configured to manage electric fields effectively, allowing for higher voltage application while maintaining low on-resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If SiC material is used to withstand high electric field (0.4 MV/cm or more), then the breakdown voltage capability is improved, but electric field concentration at specific positions (trench corner portions) causes breakage and reduces reliability
Solution Approach 1:
The patent applies local quality by creating a guard ring region with different impurity concentration characteristics at the trench corner portion compared to other regions. Specifically, the guard ring region has a first impurity concentration in a vertical direction and a second impurity concentration in a horizontal direction, with the ratio between them being controlled within a specific range. This anisotropic doping creates locally optimized electric field distribution at the critical trench corner region, preventing electric field concentration and subsequent breakage while maintaining high breakdown voltage capability.
2Strength
If breakdown voltage holding region is provided with low impurity concentration, then breakdown voltage is improved, but on-resistance increases
Solution Approach 1:
The patent implements local quality by spatially varying the impurity concentration distribution within the breakdown voltage holding region. The guard ring region employs a specific impurity concentration ratio (vertical to horizontal) that differs from conventional uniform doping. This localized optimization allows the region to simultaneously achieve high breakdown voltage through appropriate doping levels while maintaining low on-resistance through the anisotropic concentration profile that optimizes carrier transport in different directions.
Data Source
AI summary
A silicon carbide film includes a first range having a first breakdown voltage holding layer, a charge compensation region, a first junction terminal region, and a first guard ring region. The silicon carbide film includes a second range having a second breakdown voltage holding layer, a channel forming region, and a source region. The first and second breakdown voltage holding layers constitutes a breakdown voltage holding region having a thickness in an element portion. When voltage is applied to attain a maximum electric field strength of 0.4 MV/cm or more in the breakdown voltage holding region during an OFF state, a maximum electric field strength in the second range within the element portion is configured to be less than ⅔ of a maximum electric field strength in the first range.