Vertical Trench DMOSFET with Integrated Enhancement Diodes
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Solution Overview
Problem
Modern semiconductor devices, such as power MOSFETs, face challenges with high breakdown voltage due to gate oxide damage from electric field buildup, particularly as device size decreases and gate oxide thickness diminishes.
Innovation Solution
The implementation of epitaxial layer enhancement portions with the same carrier type as the epitaxial layer, disposed below contact trenches, reduces the breakdown voltage by forming Schottky diodes with lower breakdown voltage than the body diode, preventing electric field-induced damage to the gate oxide.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If device size decreases and gate oxide thickness diminishes, then high current conduction and power dissipation are achieved, but gate oxide becomes more easily damaged during operation
Solution Approach 1:
A P-type intermediary layer is introduced between the N-type epitaxial layer and the N+ drain contact. This P-type layer acts as a mediator that reduces the breakdown voltage at the drain contact region, thereby preventing excessive electric field buildup that would otherwise damage the gate oxide during high current conduction and power dissipation operations
Solution Approach 2:
The breakdown voltage of the drain contact region is deliberately reduced by introducing the P-type layer with different doping characteristics. This parameter change creates a lower breakdown voltage path that protects the gate oxide from high electric fields while allowing the device to maintain high current conduction and power dissipation capabilities
2Reliability
If breakdown voltage is reduced to protect gate oxide, then electric field-induced damage is prevented, but device voltage handling capability decreases
Solution Approach 1:
The P-type layer is selectively positioned only at the drain contact region where it is needed to reduce breakdown voltage and protect the gate oxide. The rest of the device structure maintains its original high breakdown voltage characteristics, allowing the device to have both protective low breakdown voltage at critical points and high voltage handling capability elsewhere
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 effectively reduces the breakdown voltage of MOSFET devices, as demonstrated by a decrease from 38V to 22V, enhancing device efficiency and performance by allowing the Schottky diode to dissipate charges before damaging the gate oxide.
Implementation Method 1
forming Schottky diodes with lower breakdown voltage than the body diode, preventing electric field-induced damage to the gate oxide
Data Source
AI summary
Fabricating a semiconductor device comprises: forming a gate trench in an epitaxial layer overlaying a semiconductor substrate; depositing gate material in the gate trench; forming a body in the epitaxial layer; forming a source embedded in the body; forming a contact trench that extends through the source and at least part of the body; disposing an implant at least along a contact trench wall; and disposing an epitaxial enhancement portion below the contact trench and in contact with the implant.