Source-Down Trench MOSFET With Split Gate Field Plate
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Solution Overview
Problem
Existing MOSFET structures with source-down configuration face challenges such as increased chip size, complex fabrication processes, and limited space for field plates due to the use of dedicated trenches and four epitaxial layers.
Innovation Solution
A novel trench MOSFET structure where the source terminal is accessible from the bottom of the chip, with a conductive field plate element that splits the gate material into two electrodes and extends into the substrate to short the body region, allowing for improved electric field distribution and reduced resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If dedicated trenches are used for shorting source to body region, then source-down configuration is achieved, but chip size increases
Solution Approach 1:
The cell trench serves multiple functions: it acts as the isolation structure between adjacent MOSFET cells, provides the pathway for the field plate element, and enables the source-body shorting connection. By making the trench multi-functional, the patent eliminates the need for separate dedicated trenches for source-body shorting, thereby avoiding additional chip area consumption while still achieving the source-down configuration.
Solution Approach 2:
The patent combines the field plate element with the source-body shorting structure within the same cell trench. The conductive field plate element is positioned to extend from the trench opening through the drift region and make contact with the source region, simultaneously providing field plate functionality and source-body shorting in a single integrated structure rather than separate components.
2Ease of operation
If four epitaxial layers are used with silicide deep in trenches, then source-down configuration is achieved, but fabrication process complexity increases
Solution Approach 1:
The patent extracts and eliminates the requirement for four complex epitaxial layers and deep trench silicide formation. Instead, it uses a simplified structure where the cell trench extends through the drift region to contact the source region, and the field plate element provides the necessary electrical connection. This extraction of unnecessary complexity simplifies the fabrication process while maintaining the source-down configuration functionality.
Solution Approach 2:
The patent changes the structural parameters by reducing the number of epitaxial layers from four to a simpler configuration, and by modifying the trench depth and field plate element positioning to achieve source-body shorting without requiring deep silicide formation. These parameter changes simplify the fabrication process while achieving the desired source-down configuration.
3Ease of operation
If dedicated trenches and four epitaxial layers are used, then source-down configuration is achieved, but field plate placement space is limited
Solution Approach 1:
The cell trench is designed to serve as both the isolation structure and the housing for the field plate element. By making the trench multi-functional, the patent creates space within the existing trench structure for the field plate element to be positioned and extend through the drift region, eliminating the need for additional dedicated space that would be required if separate structures were used.
Solution Approach 2:
The field plate element is nested within the cell trench structure. The trench provides the containing structure, and the field plate element is positioned inside and extends through the trench, efficiently utilizing the available space within the trench volume rather than requiring separate external space for the field plate.
Data Source
AI summary
The structure of a field-effect transistor with a source-down configuration and process of making the transistor are described in this paper. The transistor is built in a semiconductor chip with a trench extending from top chip surface towards the bottom surface. The trench contains a conductive gate material embedded in a dielectric material in the trench. A conductive field plate is also embedded in the trench and extends from the top surface of the chip towards the bottom surface of the chip and splits the conductive gate electrode into two halves. The conductive field plate penetrates the trench and makes electrical contact with the heavily doped substrate near the bottom surface of the chip.