SiC Trench MOSFET Sidewall Angle Optimization
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In vertical MOSFETs with a trench structure, achieving high channel mobility and breakdown voltage is challenging due to electric field concentration at the trench bottom and thinning of the gate oxide film, which affects the sidewall angle and curvature of the trench corners.
Innovation Solution
The semiconductor device features a trench with distinct sidewall angles, where the sidewall angle at the second wide bandgap semiconductor layer is 80° to 90° and the angle deeper than the boundary is 65° to 89°, differing by 1° to 25°, to mitigate electric field concentration and maintain uniform gate oxide film thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the trench sidewall angle is made nearly perpendicular (80° to 90°) to improve channel mobility and reduce ON resistance, then channel mobility increases, but the curvature of the trench bottom corners decreases causing breakdown voltage to decrease due to electric field concentration
Solution Approach 1:
The patent applies local quality by creating different sidewall angles at different depths of the trench. The upper portion (first region) has a first sidewall angle of 80° to 90° to maximize channel mobility, while the lower portion (second region) has a second sidewall angle of 45° to 75° to increase corner curvature and reduce electric field concentration. This local differentiation allows each region to optimize for its specific functional requirement.
Solution Approach 2:
The trench structure is segmented into two distinct regions with different sidewall angles. The first region extends from the semiconductor surface to a first depth, and the second region extends from the first depth to a second depth. This segmentation allows independent optimization of each region's geometry to address the conflicting requirements of channel mobility and breakdown voltage.
2Reliability
If the trench formation conditions are set to achieve large curvature at the bottom of the trench to increase breakdown voltage, then the sidewall angle becomes obtuse, but channel mobility decreases
Solution Approach 1:
The patent resolves this contradiction by applying different sidewall angles to different regions. The lower region (second region) uses a smaller sidewall angle (45° to 75°) to create large corner curvature and increase breakdown voltage, while the upper region (first region) uses a larger sidewall angle (80° to 90°) to maintain high channel mobility. Each region's geometry is locally optimized for its specific function.
Solution Approach 2:
The trench is divided into two segments with distinct geometric characteristics. The first segment (upper region) prioritizes channel mobility with a near-perpendicular sidewall, while the second segment (lower region) prioritizes breakdown voltage with a more gradual sidewall angle. This segmentation allows both conflicting requirements to be satisfied in their respective regions.
3Manufacturing precision
If the trench sidewall angle is made nearly perpendicular and a deposited oxide film is used for the gate oxide film, then the thickness of the gate oxide film decreases with proximity to the bottom of the trench, but the gate oxide film is easily destroyed at locations where it is thin
Solution Approach 1:
The patent addresses this issue by creating a gradual transition in sidewall angle through the two-region structure. The first region (80° to 90° sidewall angle) maintains sufficient gate oxide film thickness for proper electrical isolation, while the second region (45° to 75° sidewall angle) provides mechanical support and stress distribution. This local differentiation prevents the gate oxide film from becoming too thin and vulnerable to destruction.
Data Source
AI summary
On a surface of an n-type silicon carbide epitaxial layer on an n+-type silicon carbide substrate, first and second p+-type base regions are formed in the n-type silicon carbide epitaxial layer, an n-type region is formed in the n-type silicon carbide epitaxial layer, a p-type base layer is formed on the n-type region, an n+-type source region and a p++-type contact region are formed in the p-type base layer, and a trench is formed to a position shallower than the second p+-type base region and penetrates the p-type base layer. A first sidewall angle of the trench at a position of the p-type base layer is 80° to 90° with respect to a main surface. A difference of the first sidewall angle and a second sidewall angle of the trench at a position deeper than a boundary of the p-type base layer and the n-type region is 1° to 25°.