SiC Trench Gate Sidewall Angle Control for Channel Mobility
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Solution Overview
Problem
Conventional silicon carbide (SiC) semiconductor devices with trench gate structures face challenges in achieving high channel mobility due to inaccuracies in etching trench sidewalls perpendicular to specific crystal planes, such as (11-20) or (1-100), which are crucial for optimal electrical characteristics.
Innovation Solution
The SiC semiconductor device incorporates an off-angle substrate with trenches oriented in a specific direction, where only one sidewall of the trench has a smaller acute angle to these planes, forming a current path on the high-mobility sidewall, thereby enhancing channel mobility while allowing for a wider margin in etching accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If trench etching is performed vertically with high accuracy to achieve (11-20) or (1-100) plane sidewalls, then channel mobility is improved, but manufacturing difficulty increases due to SiC's chemical stability
Solution Approach 1:
The patent changes the substrate orientation parameter by using an off-cut substrate (with a small angle deviation from the ideal orientation) instead of a perfectly oriented substrate. This parameter change allows the trench sidewalls to naturally form at angles that are acceptable for achieving high channel mobility, while significantly easing the etching process due to SiC's chemical stability in the off-cut orientation.
2Reliability
If trench sidewall inclination angle is kept small to maintain channel mobility, then electrical characteristics are improved, but etching control becomes more difficult
Solution Approach 1:
Instead of trying to control the trench etching process to achieve the desired sidewall angle (direct approach), the patent inverts the approach by first selecting a substrate with a specific off-cut angle, which naturally determines the trench sidewall angle after etching. This inversion transfers the angle control from the difficult etching process to the substrate selection stage, where precision is more easily achieved.
3Reliability
If perfect vertical trench etching is attempted to increase channel mobility, then device performance is improved, but process margin is reduced
Solution Approach 1:
By changing the substrate orientation parameter to an off-cut configuration, the patent creates a wider acceptable range (process margin) for trench etching angles. The off-cut substrate ensures that even with variations in etching conditions, the resulting sidewall angles will fall within the range necessary for achieving high channel mobility, thus providing robustness against process variations.
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 configuration achieves high channel mobility over a broader angle range, stabilizing device operation and expanding the process margin for trench etching, even when sidewalls are not perfectly vertical to the substrate surface.
Implementation Method 1
When the gate electrode is applied with a gate voltage, a current path is formed on only the first sidewall in the first and second sidewalls of each of the trenches and electric current flows in the current path
Data Source
AI summary
In a silicon carbide semiconductor device, a plurality of trenches has a longitudinal direction in one direction and is arranged in a stripe pattern. Each of the trenches has first and second sidewalls extending in the longitudinal direction. The first sidewall is at a first acute angle to one of a (11-20) plane and a (1-100) plane, the second sidewall is at a second acute angle to the one of the (11-20) plane and the (1-100) plane, and the first acute angle is smaller than the second acute angle. A first conductivity type region is in contact with only the first sidewall in the first and second sidewalls of each of the trenches, and a current path is formed on only the first sidewall in the first and second sidewalls.