SiC MOSFET Gate Stack Nitrogen Density Control
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Solution Overview
Problem
Conventional methods for improving interface characteristics between silicon carbide semiconductor bases and gate insulating films in silicon carbide MOSFETs face limitations in reducing interface state density, leading to low channel mobility due to saturated nitrogen introduction and limited substitution-element surface density.
Innovation Solution
A method involving the formation of a silicon nitride film on the silicon carbide semiconductor base, followed by heat treatment in an oxygen atmosphere to increase nitrogen surface density at the interface, achieving a range of 6×10^14/cm^2 to 1.2×10^15/cm^2, and reducing hydrogen volume density in the gate insulating film to enhance interface characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If heat treatment is performed under a gas atmosphere including nitrogen atoms (such as nitrous oxide or nitric oxide) after forming the silicon oxide film, then nitrogen atoms are introduced at the interface to improve interface characteristics, but the nitrogen introduction becomes saturated and interface state density reduction is limited
Solution Approach 1:
The invention changes the fundamental parameter of nitrogen introduction mechanism from direct gas-phase nitrogen atom diffusion to silicon nitride film formation followed by nitrogen release. This parameter change enables achieving nitrogen surface density of 6×10^14/cm^2 to 1.2×10^15/cm^2 at the interface, surpassing the saturation limit of conventional direct nitrogen introduction methods.
Solution Approach 2:
The invention introduces silicon nitride film as an intermediary substance between the silicon carbide semiconductor base and the gate insulating film. This intermediary film serves as a nitrogen reservoir that releases nitrogen atoms during heat treatment, enabling controlled and enhanced nitrogen introduction at the interface without the saturation limitations of direct gas-phase methods.
2Manufacturing precision
If conventional heat treatment methods are used to introduce nitrogen at the interface, then some interface characteristics are improved, but hydrogen volume density in the gate insulating film remains high, limiting further improvement
Solution Approach 1:
The invention extracts hydrogen from the gate insulating film through the heat treatment process performed after silicon nitride film formation. The heat treatment at elevated temperatures enables hydrogen diffusion and removal from the gate insulating film, reducing hydrogen volume density to 1×10^20/cm^3 or less, thereby improving interface characteristics without the limitations of conventional methods.
3Reliability
If the nitrogen surface density at the interface is increased beyond conventional levels, then channel mobility increases and interface characteristics improve, but conventional methods reach a saturation point
Solution Approach 1:
The invention performs preliminary action by forming the silicon nitride film on the silicon carbide semiconductor base before forming the gate insulating film. This preliminary silicon nitride film formation enables subsequent controlled nitrogen release at the interface during heat treatment, achieving nitrogen surface density of 6×10^14/cm^2 to 1.2×10^15/cm^2 and channel mobility of 25 cm^2/Vs or more, surpassing conventional saturation limits.
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 approach effectively increases channel mobility and improves interface characteristics by increasing nitrogen surface density and reducing hydrogen volume density, surpassing the limitations of conventional techniques.
Implementation Method 1
heat treatment is performed in an atmosphere that includes oxygen, after the second process
Implementation Method 2
nitrogen atoms in the silicon nitride film react with the semiconductor base
Implementation Method 3
hydrogen volume density in the gate insulating film is 1×10^20/cm^3 or less
Data Source
AI summary
A silicon nitride film having a thickness in a range from 1 [nm] to 3 [nm] is deposited on a front surface of a silicon carbide semiconductor base, by an ALD method. Next, on the silicon nitride film, for example, a silicon oxide film having a thickness in a range from 20 [nm] to 100 [nm] is deposited. After deposition of the silicon oxide film, for example, heat treatment is performed at a temperature in a range from 1100 degrees C. to 1350 degrees C., in a gas atmosphere that includes oxygen. By this heat treatment, nitrogen surface density of an interface of the silicon carbide semiconductor base and the silicon oxide film (gate insulating film) is increased, reducing interface state density of the interface of the silicon carbide semiconductor base and the silicon nitride film.