Trench MOSFET Guard Ring Reinforcement for Breakdown Voltage
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Solution Overview
Problem
Trench MOSFET structures experience low breakdown voltage in the trench gate area, leading to avalanche occurrence when reverse bias between the drain and gate/source increases, and existing solutions like guard rings and thick field oxides are either inadequate or require additional manufacturing steps.
Innovation Solution
A trench MOS structure with a novel guard ring and reinforcement structure, including an epitaxial layer, trench gate, source, drain, and a reinforcement structure within the guard ring, which features a second conductivity type and an electrically insulating material to increase breakdown voltage, and a method for manufacturing that involves implantation, etching, and oxidizing steps to form the structure compatible with current processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a guard ring is constructed using thick field oxide and N+ epitaxial region, then the breakdown voltage protection is improved, but the manufacturing process complexity increases due to additional steps
Solution Approach 1:
The invention merges the guard ring formation with the existing trench isolation oxidation process. The field oxide layer serves dual purposes: as the trench isolation and as the guard ring structure, eliminating the need for separate thick field oxide growth and N+ epitaxial region formation steps.
Solution Approach 2:
The field oxide layer is given multiple functions: it acts as both the trench isolation structure and the guard ring for breakdown voltage protection. This multi-functional approach reduces the total number of manufacturing steps while maintaining both isolation and protection functions.
2Reliability
If a guard ring is constructed using thick field oxide and N+ epitaxial region, then the breakdown voltage protection is improved, but the manufacturing time increases due to additional steps
Solution Approach 1:
The guard ring formation is merged into the trench isolation oxidation process, allowing both structures to be formed simultaneously in a single oxidation step rather than requiring separate processing steps for thick field oxide and epitaxial region formation.
Solution Approach 2:
The field oxide layer is formed preliminarily as part of the trench isolation process, and then the same layer serves as the guard ring structure. This preliminary formation of the field oxide eliminates the need for subsequent separate guard ring formation steps, reducing total manufacturing time.
3Ease of manufacture
If conventional trench MOS structure is used, then the manufacturing process is simple, but the breakdown voltage is low due to avalanche at trench bottom
Solution Approach 1:
The field oxide layer is selectively grown at the trench periphery regions where the guard ring is needed, while the trench bottom maintains its original structure for current conduction. This local differentiation provides breakdown protection at the perimeter without affecting the central current-carrying region.
Solution Approach 2:
The field oxide layer acts as an intermediary structure that provides electrical isolation and breakdown protection at the trench periphery. It mediates between the high-field region at the trench bottom and the surrounding substrate, preventing avalanche breakdown while maintaining manufacturing simplicity.
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
The proposed structure significantly raises the breakdown voltage of the trench MOSFET by incorporating a reinforcement structure within the guard ring, enhancing the protection against avalanche and maintaining process compatibility with existing manufacturing methods.
Implementation Method 1
a reinforcement structure within the guard ring... which features a second conductivity type and an electrically insulating material to increase breakdown voltage
Implementation Method 2
construct a doped region, called a guard ring... protected by the native bias of different doping regions
Data Source
AI summary
A trench MOS structure is provided. The trench MOS structure includes a substrate, an epitaxial layer, a trench, a gate isolation, a trench gate, a guard ring and a reinforcement structure within the guard ring. The substrate has a first conductivity type, a first side and a second side opposite to the first side. The epitaxial layer has the first conductivity type and is disposed on the first side. The trench is disposed in the epitaxial layer. The gate isolation covers the inner wall of the trench. The trench gate is disposed in the trench and has the first conductivity type. The guard ring has a second conductivity type and is disposed within the epitaxial layer. The reinforcement structure has an electrically insulating material and is disposed within the guard ring.