Trench MOSFET Doped Pillar Layout for Corner Oxide Breakdown
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Solution Overview
Problem
Trench MOSFETs using silicon carbide substrates face breakdown voltage limitations due to high electric fields at the corner oxide, which is insufficient for reverse bias operation at 1200 V without additional protection, as the current design does not adequately manage the electric field concentration.
Innovation Solution
The implementation of a trench MOSFET design with p-type and n-type doped pillars of varying depths and dopant concentrations, along with multiple epitaxial layers, to distribute the electric field and enhance breakdown voltage, including the use of p+ and n+ doped regions and a gate oxide within trenches extending into doped pillars, effectively managing the electric field and increasing breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a trench MOSFET design is used with conventional doping structures, then the device can be manufactured with standard processes, but the breakdown voltage is limited to 754 V due to high electric fields at the corner oxide
Solution Approach 1:
The patent applies local quality by creating regions with different doping types and concentrations at specific locations. P-type doped pillars are positioned at the corner oxide regions where electric field concentration occurs, while n-type doped pillars are placed in the trench channel area. This localized doping strategy modifies the electric field distribution specifically at the problematic corner oxide regions without altering the overall device structure, thereby increasing breakdown voltage from 754 V to over 1566 V.
Solution Approach 2:
The patent employs composite doping structures by combining p-type and n-type doped pillars within the same semiconductor device. The p-type doped regions (with dopants such as aluminum or boron) and n-type doped regions (with dopants such as phosphorus or nitrogen) work together to create a composite structure that manages electric field distribution. This composite approach allows the device to achieve high breakdown voltage while maintaining standard manufacturing processes.
2Reliability
If additional protection measures are added to achieve 1200 V reverse bias operation, then the breakdown voltage requirement is met, but the device complexity increases
Solution Approach 1:
The patent achieves 1200 V reverse bias operation capability by changing the doping parameters (type and concentration) rather than adding protective structures. By adjusting the p-type and n-type dopant concentrations in the pillars and modifying the epitaxial layer thickness, the device inherently manages electric field distribution to achieve the required breakdown voltage. This parameter-based approach maintains device simplicity while meeting the 1200 V operation requirement.
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 design significantly increases the breakdown voltage from 754 V to over 1566 V, reducing the maximum electric field at the corner oxide by nearly 50%, thereby ensuring stable operation at 1200 V without additional protection measures.
Implementation Method 1
The first conductivity type doped pillar may be n-type doped with nitrogen and the second conductivity type doped pillars may be p-type doped with aluminum
Data Source
AI summary
Implementations of a semiconductor device may include a trench including a gate and a gate oxide formed therein, the trench extending into a doped pillar of a first conductivity type formed in a substrate material. The device may include a trench channel adjacent to the trench and two doped pillars of a second conductivity type extending on each side of the first conductivity type doped pillar where a ratio of a depth of each of the two second conductivity type doped pillars to a depth of the trench into the substrate material may be at least 1.6 to 1.