Gate Trench MOSFET Shielding Layout for Gate Oxide Field Stress
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Solution Overview
Problem
Power MOSFETs with gate trench designs face reliability issues due to high electric fields in the gate oxide layer, leading to breakdown and device failure, particularly in reverse blocking operations, where electric field crowding increases the stress on the oxide layer.
Innovation Solution
The formation of trench shielding regions with deep implantation of second conductivity type dopants simultaneously with well regions, eliminating the need for masking and allowing deeper shielding without impacting the doping concentration of channel regions, and an oxidation process to convert sidewalls and bottoms of trenches into oxide material for enhanced protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If trench shielding regions are formed using conventional ion implantation with masking, then the gate oxide layer is protected from electric field stress, but the fabrication process becomes complex and the shielding depth is limited
Solution Approach 1:
The patent combines the formation of well regions and trench shielding regions into a single ion implantation step. By using the source region as a natural mask, the process merges two previously separate fabrication steps into one, reducing process complexity while achieving both well formation and deep trench shielding simultaneously
Solution Approach 2:
The source region serves a dual function: as the active source electrode and as the masking layer during ion implantation. This self-service approach eliminates the need for separate masking layers, simplifying the fabrication process while enabling deep implantation for enhanced electric field protection
2Reliability
If deeper trench shielding regions are formed, then electric field stress on the gate oxide layer is reduced, but the doping concentration of channel regions is impacted
Solution Approach 1:
The ion implantation process creates different doping profiles in different regions: the source region acts as a mask protecting the channel region from excessive doping, while allowing deep implantation in the trench shielding region. This local differentiation enables deep shielding without compromising channel region doping precision
Solution Approach 2:
The source region is formed first with appropriate doping concentration before the trench shielding region implantation. This preliminary action creates a protective mask that prevents subsequent deep ion implantation from affecting the channel region doping, thereby maintaining manufacturing precision while achieving deep shielding
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 approach significantly simplifies the fabrication process, allows for deeper trench shielding regions, and enhances the reliability of gate trench power MOSFETs by reducing electric field stress on the gate oxide layer, thereby increasing the device's operational lifetime.
Implementation Method 1
Second conductivity type dopants are implanted into the wide band-gap semiconductor layer structure to simultaneously form both a well region underneath the source region and a trench shielding region underneath the trench
Implementation Method 2
an oxidation process to convert sidewalls and bottoms of trenches into oxide material for enhanced protection
Data Source
AI summary
A wide band-gap semiconductor layer structure is provided that comprises a drift region having a first conductivity type and a plurality of source regions having the first conductivity type on the drift region. A plurality of trenches are provided in an upper surface of the wide band-gap semiconductor layer structure. Second conductivity type dopants are implanted into the wide band-gap semiconductor layer structure to simultaneously form well regions underneath the source regions and trench shielding regions underneath the trenches, the well regions and the trench shielding regions each having a second conductivity type.