Trench MOSFET Guard Ring Breakdown Voltage
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Solution Overview
Problem
Trench MOSFET structures experience low breakdown voltage due to deeper trench depths in contacted trench gate areas, leading to avalanche occurrence during reverse bias between drain and gate/source, as a result of wider trench widths allowing more etching gas penetration during the dry etching process.
Innovation Solution
A trench MOSFET structure with a guard ring wrapped around the contacted trench gate, forming a drift region between the guard ring and the substrate with a height greater under the center of the trenched contact gate than under its sidewalls, enhancing breakdown voltage by creating a region with decreasing doping concentration from the sidewall to the center of the trenched contact gate bottom.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the trench width is increased to allow more open area for metal contact, then the ease of manufacture and electrical connection are improved, but the trench depth increases which causes lower breakdown voltage and avalanche occurrence
Solution Approach 1:
The invention divides the trench structure into two distinct types: active area trenches with standard depth for transistor operation, and contact trenches with greater depth for metal connection. This segmentation allows each trench type to be optimized independently - contact trenches can be deeper to accommodate metal contacts while active trenches maintain standard depth to ensure proper breakdown voltage characteristics.
Solution Approach 2:
The invention applies different trench depth characteristics to different spatial locations on the device. Contact trenches located in the termination area have greater depth to facilitate metal contact formation, while active area trenches maintain standard depth to preserve breakdown voltage. This local differentiation resolves the contradiction by allowing deeper trenches only where needed for electrical connection without compromising the overall device reliability.
2Reliability
If the trench depth is increased to reach the substrate for proper electrical contact, then the electrical connection is improved, but the breakdown voltage decreases due to avalanche occurrence at the trench bottom
Solution Approach 1:
The invention segments the device into active area and termination area with different trench depth requirements. Contact trenches in the termination area extend deeper to reach the substrate for proper electrical connection, while active area trenches maintain standard depth. This segmentation isolates the deeper trench structure to locations where electrical connection is prioritized over breakdown voltage, preventing avalanche issues in the active transistor regions.
Solution Approach 2:
The invention introduces a lightly-doped drift region as an intermediary layer between the heavily-doped substrate and the contact trench bottom. This drift region acts as a buffer that prevents direct high-field stress at the trench bottom, thereby reducing avalanche breakdown while still allowing the trench to reach deep enough for proper electrical connection to the substrate.
3Ease of operation
If the trench width is increased to improve metal contact tolerance and alignment, then the ease of operation is improved, but the etching gas penetration increases causing deeper trench depth and lower breakdown voltage
Solution Approach 1:
The invention separates contact trenches from active trenches, allowing contact trenches to be wider for better alignment tolerance while active trenches maintain standard dimensions. The segmentation enables independent optimization of each trench type - contact trenches can be designed with greater width and depth for robust metal contact formation without affecting the breakdown voltage characteristics of active trenches.
Solution Approach 2:
The invention applies different geometric characteristics to different trench locations. Contact trenches in the termination area have both greater width and depth to accommodate metal contacts with alignment tolerance, while active area trenches maintain standard width and depth to ensure proper breakdown voltage. This local quality differentiation resolves the contradiction by confining the wider, deeper trench structure to areas where it provides benefit without causing harm.
Data Source
AI summary
A trench Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) structure with guard ling, includes: a substrate including an epi layer region on the top thereof a plurality of source and body regions formed in the epi layer; a metal layer including a plurality of metal layer regions which are connected to respective source and body regions forming metal connections of the MOSFET; a plurality of metal contact plugs connected to respective metal layer regions; an insulating layer deposited on the epi layer formed underneath the metal layer with a plurality of metal contact holes therein for contacting respective source and body regions; and a guard ring wrapping around the trench gates with contact metal plug underneath the gate metal layer.