SiC Trench MOSFET Gate Insulating Film Reliability
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Solution Overview
Problem
Trench SiC-MOSFETs face increased electric field strength on the gate insulating film, reducing its reliability, while planar SiC-MOSFETs have high channel resistance.
Innovation Solution
A silicon carbide semiconductor device with a trench structure where the MOS channel is formed along the side surfaces of the trench, reducing channel resistance and suppressing electric field strength on the gate insulating film by forming a well layer along the trench side and bottom surfaces, and using a gate insulating film that reaches the source region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a trench structure is used to reduce channel resistance, then channel resistance is reduced, but electric field strength on the gate insulating film increases reducing its reliability
Solution Approach 1:
The gate insulating film is designed with different thicknesses at different locations: a first thickness on the side surfaces of the trench and a second thickness on the bottom surface. This local variation in film thickness allows the structure to reduce electric field strength on the gate insulating film while maintaining low channel resistance, resolving the contradiction between reliability and harmful electric field effects.
Solution Approach 2:
The invention transitions from a conventional planar gate structure to a three-dimensional trench structure with a gate insulating film that has varying thickness in the vertical dimension. By forming the gate insulating film with different thicknesses on side surfaces versus bottom surface, the solution utilizes dimensional variation to simultaneously achieve low channel resistance and reduced electric field stress on the insulating film.
2Reliability
If the gate insulating film is made thinner to reduce electric field strength, then reliability improves, but insulation performance deteriorates
Solution Approach 1:
The gate insulating film thickness is optimized locally: thinner on the bottom surface to reduce electric field strength and improve reliability, and appropriately thick on the side surfaces to maintain insulation performance. This spatially differentiated design resolves the contradiction between reliability and insulation strength.
Data Source
AI summary
It is an object of the present invention to provide a silicon carbide semiconductor device that reduces a channel resistance and increases reliability of a gate insulating film. The present invention includes a trench partially formed in a surface layer of an epitaxial layer, a well layer formed along side surfaces and a bottom surface of the trench, a source region formed in a surface layer of the well layer on the bottom surface of the trench, a gate insulating film, and a gate electrode. The gate insulating film is formed along the side surfaces of the trench and has one end formed so as to reach the source region. The gate electrode is formed along the side surfaces of the trench and formed on the gate insulating film.