Polysilicon Shield Trench MOSFET Reliability

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Solution Overview

Problem

Power semiconductor devices with trench gates face reliability and fabrication challenges due to thick shielded gate structures, particularly regarding shield oxide and reliability issues, which are not adequately addressed by existing technologies.

Innovation Solution

The introduction of a poly shield region made of polycrystalline silicon, laterally confined by insulators, and an underlying P-type polysilicon PN junction type shielding structure, which replaces traditional shielded MOS gates to enhance reliability and simplify fabrication.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional shielded MOS gate structures are used, then breakdown voltage and on resistance performance are achieved, but shield oxide reliability issues and fabrication complexity arise

Engineering Contradiction:

Improveshield oxide reliabilityVSAvoidfabrication complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent extracts and removes the problematic shield oxide layer from the traditional shielded MOS gate structure, replacing it with a polysilicon-filled trench structure. This extraction eliminates the reliability issues associated with shield oxide while maintaining the electrical shielding function through the polysilicon region.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent changes the material parameter of the shield region from oxide-based (in traditional MOS gates) to polysilicon-based. This parameter change transforms the electrical and mechanical properties of the shield, eliminating oxide-related reliability issues while providing stable electrical characteristics for voltage blocking and shielding functions.

Inventive Principle:

Principle #35Parameter changes

2Strength

If thick shielded gate structures are implemented, then high voltage breakdown capability is achieved, but fabrication difficulties and reliability issues increase

Engineering Contradiction:

Improvebreakdown voltage capabilityVSAvoidfabrication ease

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

The patent employs a composite structure combining the polysilicon shield region with the surrounding semiconductor layers (drift region, body region, source region). This composite approach distributes the voltage blocking function across multiple materials and layers, achieving high breakdown voltage capability while simplifying the fabrication process compared to traditional thick oxide shields.

Inventive Principle:

Principle #40Composite materials

3Reliability

If traditional shielded gate structures are used, then voltage blocking function is provided, but shield oxide reliability issues occur under high current and voltage conditions

Engineering Contradiction:

Improvedevice reliability under high current and voltageVSAvoidshield oxide degradation

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent replaces the fragile shield oxide layer with a more robust polysilicon structure that can withstand high current and voltage stress. The polysilicon-filled trench acts as a durable, replaceable structure that eliminates the degradation issues inherent in thin oxide layers under electrical stress.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

The polysilicon shield region provides inherent electrical and mechanical cushioning against voltage spikes and current surges before they can damage other device components. The structure is designed to absorb and distribute electrical stress, protecting the overall device reliability under extreme operating conditions.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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 solution effectively eliminates shield oxide-related reliability issues and improves the robustness of power semiconductor devices under high current and voltage conditions, ensuring reliable operation and extended device lifespan.

Implementation Method 1

an underlying P-type polysilicon PN junction type shielding structure, which replaces traditional shielded MOS gates

Methodology Applied

Scientific EffectElectrostatic shielding: Faraday Cage

Data Source

PatentUS11538911B2Shielded trench devices

Publication Date: 2022.12.27 IPOWER SEMICON

AI summary

A shield trench power device such as a trench MOSFET or IGBT employs a gate structure with an underlying polysilicon shield region overlying a shield region in an epitaxial or crystalline layer of the device. The polysilicon region may be laterally confined by spacers in a gate trench and may contact or be isolated from the underlying shield region. Alternatively, the polysilicon region may be replaced with an insulating region.