SiC MOSFET Gate Threshold Voltage Stability via Metal Film Annealing
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Solution Overview
Problem
SiC-MOSFETs experience a significant reduction in gate threshold voltage when a negative voltage is applied, leading to a normally-on state instead of the desired normally-off state, which affects the reliability of silicon carbide semiconductor devices.
Innovation Solution
A semiconductor device manufacturing method involving the formation of a metal film or laminated film on the front surface electrode of a silicon carbide substrate, followed by annealing in a nitrogen or mixed gas atmosphere, to maintain the gate threshold voltage and ensure a normally-off state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a negative voltage is applied to the gate electrode, then the gate threshold voltage is significantly reduced, but the device enters a normally-on state instead of normally-off state
Solution Approach 1:
The patent applies a preliminary annealing treatment in a nitrogen atmosphere before the device is put into operation. This annealing process modifies the electrical characteristics of the SiC substrate, specifically reducing the concentration of electrically active defects. As a result, when negative voltage is subsequently applied to the gate electrode, the gate threshold voltage remains stable and the device maintains proper normally-off operation rather than entering a normally-on state.
2Reliability
If annealing is performed in a nitrogen atmosphere, then the gate threshold voltage reduction is suppressed, but additional manufacturing steps are required
Solution Approach 1:
The patent changes the atmospheric parameters during the annealing process by using a nitrogen atmosphere instead of air or other gases. This parameter change creates a controlled environment that prevents oxidation and facilitates the reduction of electrically active defects in the SiC substrate. The nitrogen atmosphere annealing effectively suppresses gate threshold voltage reduction while the process can be integrated into existing manufacturing workflows.
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 method effectively suppresses the reduction in gate threshold voltage, maintaining the desired voltage level and ensuring reliable operation of the semiconductor device by forming a metal film on the front surface electrode and performing annealing in specific atmospheres, thereby preventing short circuits and ensuring proper device functionality.
Implementation Method 1
forming, on a surface of the front surface electrode, a metal film
Implementation Method 2
performing annealing in a nitrogen gas atmosphere, a mixed gas atmosphere including nitrogen, a vacuum atmosphere, or an argon gas atmosphere
Data Source
AI summary
A MOS gate structure including a p base region, a p epitaxial layer, an n++ source region, a p+ contact region, an n inversion region, a gate insulating film, and a gate electrode and a front surface electrode are provided on the front surface of an epitaxial substrate obtained by depositing an n− epitaxial layer on the front surface of a SiC substrate. A first metal film is provided on the front surface electrode so as to cover 10% or more, preferably, 60% to 90%, of an entire upper surface of the front surface electrode. The SiC-MOSFET is manufactured by forming a rear surface electrode, forming the first metal film on the surface of the front surface electrode, and annealing in a N2 atmosphere. According to this structure, it is possible to suppress a reduction in gate threshold voltage in a semiconductor device using a SiC semiconductor.