SiC Trench Gate Structure With Corner Guard Regions
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Solution Overview
Problem
In silicon carbide semiconductor devices with trench structures, there is a trade-off between reducing on-resistance and maintaining high breakdown voltage, and the electric field in the insulating film can lead to leakage currents and device malfunction, requiring careful design of the trench layout and guard regions to alleviate these issues.
Innovation Solution
The silicon carbide semiconductor device features a trench structure with a gate electrode embedded in an insulating film, where the current diffusion region is separated from one side surface and the guard region covers all corners of the trench bottom, allowing for a thicker insulating film on one side surface to alleviate the electric field and reduce on-resistance while maintaining breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a p type layer is formed to cover the entire bottom of the trench to alleviate electric field, then the breakdown voltage is maintained, but the cell pitch increases and on-resistance increases
Solution Approach 1:
The patent applies local quality by forming the guard region only at specific corner portions of the trench bottom rather than covering the entire bottom surface. This localized approach provides electric field relief where it is most needed (at corners where field concentration occurs) while minimizing the area occupied by the guard region, thus reducing cell pitch and preventing on-resistance increase.
Solution Approach 2:
The patent segments the guard region into discrete portions positioned at specific corner locations of the trench bottom. Instead of a continuous p-type layer covering the entire bottom, the guard regions are segmented and placed only where corner electric field concentration occurs, achieving effective field relief with minimal area occupation.
2Reliability
If a p type layer is formed between trenches to prevent gate insulating film breakdown, then the reliability is improved, but the cell pitch increases
Solution Approach 1:
The patent applies preliminary action by providing electric field relief at the trench corners through guard regions before the high-voltage stress occurs. This preventive measure at the most vulnerable locations (corners) eliminates the need for additional p-type layers between trenches, as the corner guard regions already prevent field concentration that would lead to insulating film breakdown.
3Productivity
If the trench interval is reduced to decrease cell pitch, then the productivity is improved, but the JFET resistance increases
Solution Approach 1:
The patent applies local quality by concentrating the guard region structure at the corner portions of the trench bottom rather than extending it across the entire trench bottom or into the JFET region. This localized placement provides electric field relief without encroaching on the JFET region, allowing tighter trench spacing without increasing JFET resistance.
Data Source
AI summary
A silicon carbide semiconductor device comprises: a trench formed in an upper surface of a semiconductor layer and having first and second lateral surfaces opposing each other in a first direction along an upper surface of the semiconductor layer; a gate electrode on the inside of the trench with an insulating film therebetween; a body layer adjoining the first lateral surface; a current spread region adjoining each of the first and second lateral surfaces; and a guard region covering corners of a bottom surface of the trench on the first lateral surface side and spaced apart from corners of the bottom surface of the trench on the second lateral surface side. In a first direction, the film thickness of the insulating film covering the second lateral surface is greater than the film thickness of the insulating film covering the first lateral surface.