SiC Trench Gate Withstand Voltage via Segmented Termination
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Solution Overview
Problem
Conventional trench gate type silicon carbide semiconductor devices face limitations in withstand voltage due to early avalanche breakdown in the protective diffusion layer and uneven electric field distribution, particularly in the outermost peripheral protective diffusion layer, which can lead to dielectric breakdown before the gate insulating film fails.
Innovation Solution
The silicon carbide semiconductor device incorporates a termination trench and termination diffusion layer with a lower impurity concentration surrounding the protective diffusion layer, extending the depletion layer to relax electric fields and suppress avalanche breakdown, thereby enhancing the withstand voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the impurity concentration of the protective diffusion layer is gradually increased to relax electric field concentration in the trench corner, then the withstand voltage is improved, but the avalanche breakdown voltage of the protective diffusion layer decreases
Solution Approach 1:
The protective diffusion layer is divided into multiple regions with different impurity concentrations: a first protective diffusion layer with higher concentration near the trench corner, and a second protective diffusion layer with lower concentration extending outward. This segmentation allows each region to perform its specific function - the first region relaxes electric field concentration while the second region maintains higher avalanche breakdown voltage.
Solution Approach 2:
Different impurity concentrations are applied to different spatial locations of the protective diffusion layer. The region closer to the trench corner has higher impurity concentration to relax electric field concentration, while the outer region has lower impurity concentration to maintain high avalanche breakdown voltage. This local quality differentiation resolves the contradiction between these two requirements.
2Strength
If a protective diffusion layer with high impurity concentration is provided in the lower portion of the trench, then the electric field concentration in the trench corner is relaxed, but the outermost peripheral protective diffusion layer experiences increased electric field and earlier avalanche breakdown
Solution Approach 1:
The protective diffusion layer has non-uniform impurity concentration distribution with higher concentration near the trench corner and lower concentration in the outermost peripheral region. This local quality differentiation ensures that the inner region effectively relaxes electric field concentration while the outer region maintains high avalanche breakdown voltage, preventing premature breakdown in the peripheral area.
Solution Approach 2:
The protective diffusion layer is segmented into an inner region (first protective diffusion layer) and an outer region (second protective diffusion layer) with different impurity concentrations. The inner segment handles electric field relaxation while the outer segment is optimized for high breakdown voltage, resolving the contradiction between these competing requirements.
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 effectively relaxes electric fields in the protective diffusion layer and termination diffusion layer, reducing the risk of avalanche breakdown and enhancing the overall withstand voltage of the semiconductor device.
Implementation Method 1
extending the depletion layer to relax electric fields and suppress avalanche breakdown
Implementation Method 2
suppress avalanche breakdown, thereby enhancing the withstand voltage
Data Source
AI summary
A silicon carbide semiconductor device includes a drift layer of a first conductivity type, a source region of the first conductivity type, an active trench formed in penetration through the source region, a base region, a termination trench formed around the active trench, a gate insulating film formed on a bottom surface, a side surface of the active trench, a gate electrode embedded and formed in the active trench with the gate insulating film interposed therebetween, a protective diffusion layer of a second conductivity type formed in a lower portion of the active trench and a part of a lower portion of the termination trench and having a first impurity concentration, and a termination diffusion layer of the second conductivity type formed on an outside of the protective diffusion layer in the lower portion of the termination trench and having a second impurity concentration lower than the first impurity concentration.