SiC Trench-Gate MOSFET Sidewall Doping for Current Uniformity
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Solution Overview
Problem
Trench-gate SiC-MOSFETs formed on off-angle substrates exhibit variations in drain current and threshold voltage due to differences in sidewall crystal surfaces, leading to unstable dynamic characteristics and current concentration issues.
Innovation Solution
A silicon carbide semiconductor device with a trench-gate structure featuring a drift region, well region, source region, and doped regions with varying acceptor concentrations on sidewall surfaces to adjust the ON state of each sidewall surface, including a low-channel doped region with higher concentration on one sidewall and a high-channel doped region with lower concentration on the other, to stabilize current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a trench-gate SiC-MOSFET is formed on a substrate having an off-angle, then the device can be manufactured with standard processes, but variations in drain current and threshold voltage occur due to different crystal surfaces of sidewall surfaces
Solution Approach 1:
The patent applies local quality by forming different doped regions (low-channel doped region and high-channel doped region) at different locations within the well region. Specifically, a first doped region with lower impurity concentration is formed near the first sidewall surface, while a second doped region with higher impurity concentration is formed near the second sidewall surface. This local variation in doping concentration compensates for the crystal surface orientation differences, ensuring uniform electrical characteristics across all sidewall surfaces without requiring changes to the overall manufacturing process.
2Device complexity
If a trench-gate SiC-MOSFET is formed on a substrate having an off-angle, then the device structure can be simplified, but current concentration occurs in a channel surface of a particular sidewall surface
Solution Approach 1:
The patent introduces local quality variations through selectively doped regions positioned at different distances from the sidewall surfaces. The low-channel doped region is formed closer to the first sidewall surface while the high-channel doped region is formed closer to the second sidewall surface. This creates a non-uniform doping profile that compensates for the inherent non-uniformity caused by off-angle crystal surfaces, distributing current evenly across all sidewall channels without complicating the basic trench-gate structure.
Solution Approach 2:
The patent applies preliminary anti-action by pre-compensating for the expected current concentration issue through asymmetric doping. Before the device operates, different impurity concentrations are introduced at different sidewall regions to counteract the crystal orientation effects. This preliminary compensation prevents current concentration from occurring during device operation, maintaining uniform current distribution across all sidewall surfaces.
Data Source
AI summary
It is an object of the present invention to provide a silicon carbide semiconductor device that reduces an influence of an off-angle of a silicon carbide substrate on characteristics of the semiconductor device and achieves improved operational stability and reduced resistance. In a trench-gate silicon carbide MOSFET semiconductor device formed on the silicon carbide semiconductor substrate having the off-angle, a low-channel doped region is provided on a first sidewall surface side of the trench in a well region, and a high-channel doped region having an effective acceptor concentration lower than that of the low-channel doped region is provided on a second sidewall surface side of the trench in the well region.