MOSFET Termination Trench With Thicker Oxide For Breakdown Voltage
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Solution Overview
Problem
Conventional edge termination methods for MOSFET devices with high epitaxial doping density fail to achieve higher breakdown voltages due to incomplete charge balance in the termination area, leading to reduced robustness under high voltage conditions.
Innovation Solution
The formation of a wider termination trench with a thicker oxide layer and polysilicon filling, which supports additional voltage blocked by the drift region, allows for improved charge balance and increased breakdown voltage capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional edge termination methods are used in MOSFET devices with high epitaxial doping density, then the device structure is simple and manufacturing is easier, but the breakdown voltage cannot be increased due to incomplete charge balance in the termination area
Solution Approach 1:
The termination structure is segmented into distinct regions: a first termination region with a first doping type and concentration, and a second termination region with a second doping type and concentration. This segmentation allows each region to perform its specific function in managing electric field distribution and charge balance, enabling higher breakdown voltages while maintaining structural organization
Solution Approach 2:
Different doping types and concentrations are applied to different locations within the termination structure. The first termination region uses one doping configuration while the second termination region uses another, allowing optimal charge balance to be achieved locally in each region rather than using a uniform structure throughout
2Reliability
If the drift region doping density is increased to improve specific on-state resistance, then the on-state resistance decreases, but the breakdown voltage is limited due to high doping density in the epitaxial layer
Solution Approach 1:
The termination structure acts as an intermediary region between the high-doping drift region and the low-doping substrate. By introducing intermediate doping regions with graded concentrations, the structure mediates the transition and enables the drift region to maintain high doping for low on-resistance while the termination regions manage the electric field to achieve high breakdown voltage
3Device complexity
If a simple field plate structure is used for gate control, then the device complexity is reduced, but the breakdown voltage decreases due to incomplete charge balance in the termination area
Solution Approach 1:
The termination regions are formed with specific doping configurations before the field plate is added. This preliminary action of establishing proper charge balance through doped regions ensures that when the field plate is subsequently added, the complete structure can achieve high breakdown voltage without requiring complex gate control mechanisms
Data Source
AI summary
A method, in one embodiment, can include forming a core trench and a termination trench in a substrate. The termination trench is wider than the core trench. In addition, a first oxide can be deposited that fills the core trench and lines the sidewalls and bottom of the termination trench. A first polysilicon can be deposited into the termination trench. A second oxide can be deposited above the first polysilicon. A mask can be deposited above the second oxide and the termination trench. The first oxide can be removed from the core trench. A third oxide can be deposited that lines the sidewalls and bottom of the core trench. The first oxide within the termination trench is thicker than the third oxide within the core trench.