SiC Device Interface Trap Engineering for Normally-Off Operation
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Solution Overview
Problem
Silicon carbide semiconductor devices face a trade-off between channel mobility and threshold voltage, where reducing interface traps to increase channel mobility results in lower threshold voltage, making it difficult to achieve normally-off characteristics.
Innovation Solution
A silicon carbide semiconductor device structure is designed with a specific distribution of interface traps, utilizing defects such as bonds between silicon and hydrogen to increase the density of traps at deeper energy levels, thereby maintaining high channel mobility while elevating the threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If interface traps are reduced to increase channel mobility, then channel mobility increases, but threshold voltage decreases making normally-off characteristics difficult to achieve
Solution Approach 1:
The patent applies local quality by creating non-uniform distribution of interface traps across different energy levels. Specifically, it reduces interface traps at shallow energy levels (0.2 eV or shallower from conduction band end) while maintaining or increasing interface traps at deeper energy levels (0.5 eV or deeper). This localized differentiation allows channel mobility to improve without sacrificing threshold voltage, as shallow traps affect mobility while deep traps contribute to threshold voltage.
Solution Approach 2:
The patent changes the energy level distribution parameter of interface traps rather than uniformly reducing all interface traps. By controlling the energy level at which interface traps are formed (using specific heat treatment temperatures and gas atmospheres), the patent transforms the interface trap profile from a uniform high-density state to a differentiated state where shallow traps are reduced and deep traps are maintained, thereby resolving the trade-off between mobility and threshold voltage.
2Reliability
If threshold voltage is highly maintained, then normally-off characteristics are achieved, but channel mobility is low
Solution Approach 1:
The patent applies local quality by creating non-uniform distribution of interface traps across different energy levels. Specifically, it reduces interface traps at shallow energy levels (0.2 eV or shallower from conduction band end) while maintaining or increasing interface traps at deeper energy levels (0.5 eV or deeper). This localized differentiation allows channel mobility to improve without sacrificing threshold voltage, as shallow traps affect mobility while deep traps contribute to threshold voltage.
Solution Approach 2:
The patent changes the energy level distribution parameter of interface traps rather than uniformly reducing all interface traps. By controlling the energy level at which interface traps are formed (using specific heat treatment temperatures and gas atmospheres), the patent transforms the interface trap profile from a uniform high-density state to a differentiated state where shallow traps are reduced and deep traps are maintained, thereby resolving the trade-off between mobility and threshold voltage.
Data Source
AI summary
A silicon carbide semiconductor device capable of effectively increasing a threshold voltage and a method for manufacturing the silicon carbide semiconductor device. The silicon carbide semiconductor device includes a gate insulating film formed on part of surfaces of the well regions and the source region; and a gate electrode formed on a surface of the gate insulating film so as to be opposite to an end portion of the source region and the well regions. Furthermore, the gate insulating film has, in an interface region between the well regions and the gate insulating film, defects that each form a first trap having an energy level deeper than a conduction band end of silicon carbide and that include a bond between silicon and hydrogen.