SiC Gate Trench MOSFET Support Shields for Lower Oxide Field Stress

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Solution Overview

Problem

Power MOSFETs with gate trenches face reliability issues due to high electric fields in the gate oxide layers, leading to degradation and potential breakdown, which can result in device failure.

Innovation Solution

The implementation of a silicon carbide based semiconductor layer structure with a drift region, a well layer, and a support shield of a second conductivity type, along with a gate trench design that includes a trench shielding region and a buried lateral support shield extension, to reduce electric field levels and enhance reliability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If gate trenches are implemented in power MOSFETs, then switching speed and integration density are improved, but electric field concentration in gate oxide layers increases leading to reliability degradation

Engineering Contradiction:

Improveswitching speedVSAvoidgate oxide layer reliability

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

A support shield structure with second conductivity type is introduced as an intermediary element between the gate trench and the drift region. This support shield redistributes the electric field lines, preventing excessive concentration in the gate oxide layer while maintaining the gate trench's switching performance benefits

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The support shield is strategically positioned only in regions where electric field concentration is most problematic, allowing local modification of the electric field distribution without altering the overall gate trench structure or sacrificing switching speed

Inventive Principle:

Principle #3Local quality

2Reliability

If support shields are added to reduce electric field, then reliability is improved, but device complexity and manufacturing difficulty increase

Engineering Contradiction:

Improvedevice reliabilityVSAvoidstructure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The support shield formation process is merged with existing device fabrication steps, particularly combining it with ion implantation processes already used for creating other doped regions. This integration adds minimal complexity while achieving the reliability improvement

Inventive Principle:

Principle #5Merging (Combining)

3Reliability

If support shields are added to reduce electric field, then reliability is improved, but manufacturing process difficulty increases

Engineering Contradiction:

Improvegate oxide layer reliabilityVSAvoidfabrication ease

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The support shield is formed preliminarily during the device fabrication sequence, utilizing ion implantation through masks that are already in place for other doping steps. This preliminary action avoids the need for separate, complex manufacturing steps

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS20250120119A1Gate trench power semiconductor devices having shaped deep support shields that reduce cell pitch and on-state resistance

Publication Date: 2025.04.10 WOLFSPEED INC

AI summary

A semiconductor device comprises a silicon carbide based semiconductor layer structure and a first gate trench extending into an upper portion of the semiconductor layer structure. The semiconductor layer structure comprises a drift region having a first conductivity type, a well layer having a second conductivity type, and a support shield having the second conductivity type. A width of a first segment of the support shield that is deeper in the semiconductor layer structure than the well layer and less deep in the semiconductor layer structure than a bottom of the first gate trench decreases with increasing distance from the well region.