Vertical MOSFET Fin Structure With Schottky Shielding
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Solution Overview
Problem
Power MOSFETs with vertical channel regions face challenges in short-circuit strength and switching behavior due to the slow response of space charge zones based on pn junctions, which affects their ability to withstand full system voltage and switch off quickly.
Innovation Solution
Incorporating a Schottky junction at the base of the fins, which eliminates the need for complex and expensive p+-doping of shielding elements, allows for quicker depletion of the region under the fins, enhancing short-circuit strength and switching behavior by forming a space charge zone faster than a pn junction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pn junction is used to form the space charge zone under the fins, then the transistor structure can provide shielding, but the space charge zone forms slowly due to minority charge carriers, reducing short-circuit strength and switching speed
Solution Approach 1:
The patent changes the fundamental parameter of the junction type from pn junction to Schottky junction. This parameter change transforms the charge carrier mechanism from minority carrier diffusion (slow) to majority carrier drift (fast), enabling rapid space charge zone formation and improving both short-circuit strength and switching speed
Solution Approach 2:
The patent substitutes the pn junction mechanism with a Schottky junction mechanism. The Schottky junction uses a metal-semiconductor interface instead of a semiconductor-semiconductor interface, replacing the slow minority carrier-based space charge formation with a fast majority carrier-based depletion region formation
2Reliability
If p+-doping is used to create shielding regions under the fins, then the transistor can achieve adequate shielding effect, but the manufacturing process becomes complex and expensive
Solution Approach 1:
The patent extracts and removes the complex p+-doping process for creating shielding regions. By introducing a Schottky contact, the patent eliminates the need for separate shielding region doping steps, simplifying the manufacturing process while maintaining or improving the shielding effect
Solution Approach 2:
The Schottky contact serves multiple functions simultaneously: it provides the shielding effect, enables fast space charge zone formation for short-circuit protection, and simplifies the manufacturing process. This multi-functionality replaces what previously required separate dedicated shielding structures
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
The Schottky junction improves short-circuit strength and switching behavior by enabling faster space charge region formation, increasing breakdown strength and reliability, and reducing voltage transients and overvoltages during commutation.
Implementation Method 1
Inserting a Schottky contact at the base of the fins, the complex and expensive p+-doping of the shielding elements can be dispensed with. By suitably arranging the Schottky contact, the region under the fins can be depleted more quickly.
Data Source
AI summary
A vertical field-effect transistor structure, and a method for producing the structure. The structure includes a semiconductor body having a first terminal zone, a drift zone, and a second terminal zone of a first conductivity type; a channel zone, between the first and the second terminal zone, of the first or second conductivity type; first trenches extending into the semiconductor body, which extend from the second terminal zone into the drift zone and form fins of the channel and second terminal zones; a control electrode arranged in the first trenches, adjacent to the channel zone and insulated from the semiconductor body; and a current path connected between the first and the second terminal zone and in parallel with the channel zone, the current path having at least one Schottky junction and which conducts when a reverse voltage between the first and the second terminal zones is reached.