SiC MOSFET Gate Oxide Process for Low-Defect Interfaces
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Solution Overview
Problem
Existing methods for reducing interface defect density between a SiO2 film and a SiC substrate in SiC MOSFETs fail to achieve high channel mobility and normally-off characteristics, with previous nitridation methods leading to oxidation and insufficient defect reduction.
Innovation Solution
A manufacturing method involving etching a SiC substrate with H2 gas in a Si-excess atmosphere, depositing a SiO2 film using CVD, and thermally treating the substrate in NO gas atmosphere within specific temperature ranges to reduce interface defects and achieve high channel mobility and normally-off characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a SiO2 film is formed on a SiC substrate by thermal oxidation, then the gate insulating film can be formed, but the interface defect density becomes extremely high
Solution Approach 1:
The SiC substrate surface is etched with H2 gas under Si-excess atmosphere before SiO2 film formation to remove surface contaminants and create a cleaner interface. This preliminary treatment reduces interface defect density before the gate insulating film is formed, resolving the contradiction between ease of manufacture and manufacturing precision.
Solution Approach 2:
The patent applies interface nitridation by thermal treatment in NO gas atmosphere at 1150°C to 1350°C, which changes the chemical composition at the interface by introducing nitrogen. This parameter change (chemical composition) reduces interface defect density while maintaining the gate insulating film structure, resolving the contradiction between ease of manufacture and manufacturing precision.
2Manufacturing precision
If interface nitridation is performed by NO thermal treatment, then interface defect density can be reduced, but oxidation also proceeds and defect density cannot be sufficiently reduced
Solution Approach 1:
The SiC substrate surface is etched with H2 gas under Si-excess atmosphere before SiO2 film formation to remove surface contaminants and create a cleaner interface. This preliminary treatment reduces interface defect density before the gate insulating film is formed, resolving the contradiction between ease of manufacture and manufacturing precision.
Solution Approach 2:
The patent applies interface nitridation by thermal treatment in NO gas atmosphere at 1150°C to 1350°C, which changes the chemical composition at the interface by introducing nitrogen. This parameter change (chemical composition) reduces interface defect density while maintaining the gate insulating film structure, resolving the contradiction between ease of manufacture and manufacturing precision.
3Manufacturing precision
If a SiO2 film is formed on SiC substrate after H2 gas etching and N2 gas thermal treatment, then high channel mobility is obtained, but normally-on characteristics with negative threshold voltage are easily brought
Solution Approach 1:
The patent uses NO gas atmosphere for thermal treatment instead of N2 gas, which introduces nitrogen at the interface through nitridation. This changes the chemical composition and electrical properties at the SiO2-SiC interface, achieving both high channel mobility and proper threshold voltage control for normally-off characteristics.
Solution Approach 2:
The patent creates a composite interface structure with nitrogen-containing compounds at the SiO2-SiC interface through NO thermal treatment. This composite structure combines the benefits of low defect density with controlled electrical properties, achieving both high channel mobility and proper threshold voltage for normally-off operation.
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
The method results in a SiC MOSFET with high channel mobility and normally-off characteristics by significantly reducing interface defect density, as demonstrated by improved transistor characteristics and nitrogen atom distribution.
Implementation Method 1
a step of etching a surface of a SiC substrate with H2 gas under Si-excess atmosphere within a temperature range of 1000° C. to 1350° C.
Implementation Method 2
a step of depositing, by a CVD method, a SiO2 film on the SiC substrate at such a temperature that the SiC substrate is not oxidized
Implementation Method 3
a step of thermally treating the SiC substrate, on which the SiO2 film is deposited, in NO gas atmosphere within a temperature range of 1150° C. to 1350° C.
Data Source
AI summary
A SiC semiconductor device manufacturing method includes a step of etching a surface of a SiC substrate 1 with H2 gas under Si-excess atmosphere within a temperature range of 1000° C. to 1350° C., a step of depositing, by a CVD method, a SiO2 film 2 on the SiC substrate 1 at such a temperature that the SiC substrate 1 is not oxidized, and a step of thermally treating the SiC substrate 1, on which the SiO2 film 2 is deposited, in NO gas atmosphere within a temperature range of 1150° C. to 1350° C.