Trenched MOSFET Guard Ring Channel Stop Breakdown Voltage
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Solution Overview
Problem
The existing trenched MOSFET structures experience low breakdown voltage and current leakage due to deeper trench depths in wider trenches, leading to early avalanche occurrence and instability in termination areas, primarily caused by high epi resistivity and the formation of leakage paths.
Innovation Solution
A trenched MOSFET structure with a guard ring wrapped around the contacted trenched gate and a channel stop, featuring heavier N-type doping regions and polysilicon-filled trenches, which enhances breakdown voltage and reduces on-resistance by preventing negative charge-induced positive charges at the silicon/dielectric interface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the trench width is increased to allow more open area for etching, then the trench depth becomes deeper, but the breakdown voltage decreases due to early avalanche occurrence at the trench bottom
Solution Approach 1:
The patent applies local quality by creating a guard ring structure with different doping characteristics specifically at the trench bottom region. The guard ring has a first doping concentration in the drift region and a second doping concentration in the termination region, with the second concentration being higher. This localized doping variation addresses the specific problem at the trench bottom without affecting the overall trench geometry or etching process.
2Length of stationary object
If the trench depth is increased to accommodate wider trenches, then more etching gas can enter during dry etching, but avalanche occurs earlier at the deeper trench bottom
Solution Approach 1:
The patent changes the doping concentration parameter locally at the trench bottom by forming a guard ring with a second doping concentration that is higher than the first doping concentration in the drift region. This parameter change in the doping concentration modifies the electric field distribution and prevents early avalanche occurrence at the deeper trench bottom, allowing the trench depth to be maintained without the harmful avalanche effect.
3Reliability
If high epi resistivity is used in the termination area, then breakdown voltage increases, but negative charge in the dielectric layer induces positive charge at the silicon/dielectric interface creating leakage paths
Solution Approach 1:
The patent introduces a guard ring structure as an intermediary element between the drift region and the termination region. This guard ring with its specific doping concentrations acts as a mediator that prevents the formation of leakage paths caused by charge induction at the silicon/dielectric interface, while still allowing the high epi resistivity to provide the desired breakdown voltage enhancement.
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 solution effectively improves breakdown voltage stability and reduces on-resistance while preventing leakage paths, thereby enhancing the overall performance of the MOSFET structure.
Implementation Method 1
preventing negative charge-induced positive charges at the silicon/dielectric interface
Data Source
AI summary
A trenched MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) with a guard ring and a channel stop, including: 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, and gate regions forming metal connections of the MOSFET; a plurality of metal contact plugs connected to respective metal layer regions; a plurality of gate structure filled with polysilicon to form a plurality of trenched gates on top of epi layer; 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; a guard ring wrapping around the metal layer corresponding to the gate region at the termination; and a channel stop which is a heavier N-type doping region aside the guard ring at the termination; Wherein the contact plugs connecting to the top metal layer are corresponding to the source and the body regions.