SiC Gate Trench MOSFET Shielding for Gate Oxide Breakdown
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Solution Overview
Problem
Power MOSFETs with gate trenches are susceptible to oxide reliability issues due to high electric fields in the gate oxide layers, leading to breakdown and device failure.
Innovation Solution
The semiconductor devices incorporate a silicon carbide based semiconductor layer structure with a drift layer, gate trenches, support shield trenches, and a source metallization layer that extends into the support shield trench, providing enhanced shielding and reduced electric field levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If gate trenches are used in power MOSFETs, then device integration and current handling capability are improved, but oxide reliability deteriorates due to high electric fields causing breakdown
Solution Approach 1:
A support shield structure is introduced as an intermediary element between the gate trench and the drift region. This support shield, formed by depositing conductive material (such as doped polysilicon or metal) into a trench that extends deeper than the gate trench, acts as a mediator to redistribute and reduce the peak electric field in the gate oxide layer, thereby preventing oxide breakdown while maintaining the benefits of gate trench architecture
Solution Approach 2:
The electric field distribution in the gate oxide layer is modified by changing the structural parameters of the device. By extending the support shield trench deeper into the drift region and filling it with conductive material, the electric field parameters are altered to reduce peak values at critical locations, thus improving oxide reliability without sacrificing current handling capability
2Reliability
If support shield trenches are made deeper to improve shielding, then electric field reduction is enhanced, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The device structure is segmented into distinct functional regions: the gate trench containing the gate electrode, and the deeper support shield trench containing conductive material. This segmentation allows each structure to perform its specific function independently - the gate trench for device operation and the support shield trench for electric field management - thereby achieving effective shielding without excessive overall complexity
Solution Approach 2:
The support shield structure serves multiple functions: it provides electric field shielding to reduce peak values in the gate oxide, acts as an additional conductive path for charge distribution, and can serve as a structural support element. This multi-functionality justifies the additional structural element and reduces the net increase in device complexity
Data Source
AI summary
A semiconductor device comprises a silicon carbide based semiconductor layer structure that includes a drift layer having a first conductivity type, a gate trench that extends to a first depth into an upper surface of the semiconductor layer structure, a gate electrode in the gate trench, a support shield trench that extends to a second depth into the upper surface of the semiconductor layer structure, where the second depth is less than the first depth, and a source metallization layer on the upper surface of the semiconductor layer structure and extending into the support shield trench.