Lateral Transistor Wedge Trench Layout for Low RDSon and Breakdown
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Solution Overview
Problem
Existing lateral field-effect transistors face challenges in achieving low on-state resistance (RDSon) while maintaining high breakdown voltage, particularly for voltages above 20V, due to limitations in field compensation structures and oxide geometry in silicon semiconductor devices.
Innovation Solution
The introduction of a transistor device with a shallow trench isolation structure featuring a wedge-shaped trench and a superjunction structure, along with a field plate arrangement, to enhance electrical performance and reduce RDSon. This includes a gate dielectric on the main surface and a shallow trench filled with insulating material, with a base extending at an inclined angle and a field plate covering at least 50% of the trench length, coupled with a superjunction structure under the trench.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thicker LOCOS field oxide is used to increase breakdown voltage, then the breakdown voltage is improved, but the on-state resistance increases
Solution Approach 1:
The patent changes the geometric parameters of the field oxide structure by introducing a tapered profile with specific angles (α1 and α2) instead of a uniform thickness. This parameter change allows the field oxide to provide adequate breakdown voltage protection while reducing the maximum thickness to maintain low on-state resistance, directly resolving the technical contradiction between these two opposing requirements
Solution Approach 2:
The patent introduces asymmetric tapering of the field oxide structure with different angles (α1 at the source side and α2 at the drain side) to optimize the electric field distribution. This asymmetric geometry allows the structure to simultaneously achieve high breakdown voltage through increased thickness in critical regions while maintaining low on-state resistance through reduced thickness in current-carrying regions
2Object-affected harmful factors
If a field plate structure is added to lower on-state resistance, then the on-state resistance is improved, but the device complexity increases
Solution Approach 1:
The patent merges the field plate function with the gate electrode by extending the gate electrode to form an integrated field plate structure. This merging eliminates the need for separate field plate structures and additional processing steps, thereby reducing device complexity while still achieving the benefit of lowered on-state resistance through field effect
3Reliability
If the field oxide thickness is increased to improve breakdown voltage, then the breakdown voltage is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The patent introduces dynamic geometry to the field oxide structure through tapering, where the thickness varies continuously along the lateral direction according to specific angles. This dynamic profile is more robust to manufacturing variations than a uniform thickness design because the gradual transition reduces sensitivity to local thickness control errors, thereby improving manufacturing precision while maintaining breakdown voltage
Data Source
AI summary
A transistor device includes a semiconductor body having a substantially planar main surface, a source region extending to the main surface and having a first conductivity type, a body region extending to the main surface and having a second conductivity type, a drain region extending to the main surface and having the first conductivity type, a drift region having the first conductivity type, and a gate electrode arranged on the main surface laterally between the source and drain regions and electrically insulated from the semiconductor body by an insulation structure. The insulation structure includes a gate dielectric arranged on the main surface and a shallow trench arranged in the drift region and filled with electrically insulating material. The shallow trench has at least partly a wedge shape and the electrically insulating material has an upper surface that is substantially planar and extends substantially parallel to the main surface.