Trench MOSFET Polysilicon Structure for Lower Rdson
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Solution Overview
Problem
Existing semiconductor devices face challenges in reducing the drain-source on resistance (Rdson) due to fixed drain side substrate spreading resistance, which increases total Rdson, especially for low breakdown voltage classes.
Innovation Solution
A semiconductor device structure featuring a silicon substrate with a channel and drift region, including multiple polysilicon layers isolated by gate oxide and RESURF oxide, which creates a bi-directional MOSFET device that skips substrate spreading resistance, allowing for a single bi-directional switch instead of two unidirectional switches in series, reducing Rdson.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If backside metallization and deep implants are used to reduce bidirectional resistance and drain side EPI spreading resistance, then these resistances are reduced, but drain side substrate spreading resistance cannot be managed and adds directly to technology Rdson
Solution Approach 1:
The patent introduces a third polysilicon layer positioned in the drift region that extends laterally beyond the channel region, creating a three-dimensional configuration. This lateral extension into the drift region allows the control electrode to influence the electric field distribution in a new spatial dimension, effectively reducing substrate spreading resistance without requiring complex backside metallization or deep implants.
2Reliability
If multiple polysilicon layers are used to reduce substrate spreading resistance, then Rdson is reduced, but device structure becomes more complex
Solution Approach 1:
The control electrode is segmented into three distinct polysilicon layers positioned at different locations: one in the channel region and two in the drift region. This segmentation allows each layer to independently influence specific regions of the electric field, with the third layer specifically targeting substrate spreading resistance reduction. The segmented structure achieves superior electrical performance while maintaining manufacturing feasibility through standardized layer deposition processes.
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
This configuration significantly reduces Rdson by eliminating substrate spreading resistance, enhancing thermal and electrical efficiency and increasing breakdown voltage, resulting in improved semiconductor device performance.
Implementation Method 1
The semiconductor device comprises a first polysilicon layer and the second polysilicon layer and the third polysilicon layer that are isolated by a gate oxide and a RESURF oxide respectively, from the channel and from the drift and from each other
Data Source
AI summary
The present disclosure proposes a semiconductor device including a silicon substrate; a channel positioned on the top surface of the substrate; a drift region positioned on the top of the channel; a trench; a first polysilicon layer positioned within the channel and the drift region on the bottom of the trench; a second polysilicon layer positioned on the top of the first polysilicon layer, and positioned within the drift region inside of the trench; a third polysilicon layer positioned on the top of the second polysilicon layer, and positioned within the drift region inside of the trench. The first polysilicon layer and the second polysilicon layer and the third polysilicon layer are isolated by a gate oxide and a RESURF oxide respectively, from the channel and from the drift and from each other forming at least partially three separated structures.