Shielded Trench MOSFET Layout for Gate Dielectric Field Relief

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Solution Overview

Problem

Silicon carbide MOSFET devices face challenges in protecting gate-dielectric regions from high electrical fields, leading to reliability issues and reduced breakdown voltage due to manufacturing inaccuracies causing asymmetry in gate dielectric electrical fields.

Innovation Solution

The introduction of self-aligned shielding regions underneath the gate electrodes in the MOSFET device, which reduces the electrical field intensity at the gate dielectrics and ensures proper alignment during manufacturing, thereby enhancing reliability and miniaturization without increasing on-state resistance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional manufacturing methods are used for trench-gate MOSFETs, then gate dielectric regions are exposed to high electrical fields in reverse-biasing conditions, but reliability deteriorates due to field-induced breakdown and asymmetric electrical behavior

Engineering Contradiction:

Improvegate dielectric reliabilityVSAvoidelectrical field intensity at gate dielectric

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

A shielding region with third-type conductivity is introduced as an intermediary element between the first and second gate dielectric regions. This shielding region acts as a mediator that reduces the electrical field intensity at the gate dielectric interfaces during reverse-biasing conditions, preventing field-induced breakdown and ensuring symmetric electrical behavior without affecting the conductive channels

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The shielding region is positioned and configured in advance to counteract the harmful electrical fields before they can cause damage to the gate dielectric regions. By establishing this protective structure during manufacturing, the device is pre-equipped to withstand reverse-biasing conditions without jeopardizing gate dielectric integrity

Inventive Principle:

Principle #9Preliminary anti-action

2Area of moving object

If the distance between gate regions is reduced for miniaturization, then device density increases, but manufacturing precision deteriorates due to alignment sensitivity

Engineering Contradiction:

Improvedevice footprint areaVSAvoidgate region alignment precision

Core Design Contradiction:

Area of moving objectVSManufacturing precision

Solution Approach 1:

The shielding region is designed with asymmetric positioning relative to the gate regions, extending preferentially towards one gate region rather than being symmetrically distributed. This asymmetric configuration reduces sensitivity to alignment variations during manufacturing, allowing smaller distances between gate regions while maintaining manufacturing feasibility and electrical symmetry

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The shielding region provides localized field reduction specifically at the gate dielectric interfaces where it is most needed, rather than uniformly distributed protection. This localized approach allows miniaturization by concentrating the protective function where critical, enabling closer gate spacing without compromising overall device reliability

Inventive Principle:

Principle #3Local quality

3Reliability

If shielding regions are added to protect gate dielectrics, then reliability improves, but device complexity increases

Engineering Contradiction:

Improvebreakdown voltageVSAvoidstructural complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The shielding region functionality is merged with the existing doping structure of the MOSFET device. Rather than adding a completely separate protective component, the shielding region utilizes the doping framework already present in the device architecture, achieving field protection while maintaining structural integration and minimizing complexity increases

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The shielding region serves multiple functions simultaneously: it reduces electrical field intensity at gate dielectric interfaces, ensures symmetric electrical behavior, and can be integrated with existing doping processes. This multi-functionality achieves reliability improvement without proportionally increasing device complexity

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS12148824B2MOSFET device with shielding region and manufacturing method thereof

Publication Date: 2024.11.19 STMICROELECTRONICS SRL

AI summary

A MOSFET device comprising: a structural region, made of a semiconductor material having a first type of conductivity, which extends between a first side and a second side opposite to the first side along an axis; a body region, having a second type of conductivity opposite to the first type, which extends in the structural region starting from the first side; a source region, having the first type of conductivity, which extends in the body region starting from the first side; a gate region, which extends in the structural region starting from the first side, traversing entirely the body region; and a shielding region, having the second type of conductivity, which extends in the structural region between the gate region and the second side. The shielding region is an implanted region self-aligned, in top view, to the gate region.