SiC MOSFET Threshold Voltage Stability via Low-Temperature Nitrogen Annealing
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Solution Overview
Problem
Silicon carbide (SiC) MOSFETs experience instability in threshold voltage when negative voltage is continuously applied at high temperatures, leading to a normally off MOSFET becoming normally on due to high interface state density at the gate oxide film/SiC interface, primarily caused by dangling bonds and the reaction of nitrogen with active hydrogen and holes.
Innovation Solution
A method of manufacturing SiC semiconductor devices involving the formation of a silicon carbide substrate with specific conductivity types, selective region formation, and metal wiring using aluminum, with low temperature nitrogen annealing after metal wiring formation to reduce hydrogen concentration and suppress threshold voltage decrease, including the use of titanium and titanium nitride films to occlude active hydrogen.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If nitrogen annealing is performed to reduce interface state density at the gate oxide film/SiC interface, then the interface state is lowered and channel mobility is improved, but active hydrogen reacts with nitrogen and holes to form NH+ that penetrates to form hole traps, causing threshold voltage to decrease and MOSFET to become normally on
Solution Approach 1:
The patent applies preliminary action by performing nitrogen annealing at a controlled low temperature (300-450°C) for a specific duration (1-10 hours) before the harmful reaction can occur. This preliminary treatment reduces interface state density to acceptable levels while limiting the extent of hydrogen-nitrogen reaction and NH+ formation, thereby preventing excessive threshold voltage degradation and maintaining MOSFET reliability.
2Manufacturing precision
If high concentration nitrogen is introduced to terminate dangling bonds at the interface, then interface state is reduced, but nitrogen takes on positive charge and forms hole traps when active hydrogen and holes are present, leading to threshold voltage decrease
Solution Approach 1:
The patent applies parameter changes by precisely controlling the nitrogen annealing temperature (300-450°C) and duration (1-10 hours) to optimize the balance between interface state reduction and hole trap formation. By adjusting these parameters, the patent achieves sufficient interface quality improvement while limiting the charge state of nitrogen and minimizing NH+ formation that would create harmful hole traps.
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 reduces the hydrogen concentration in the metal wiring and suppresses the decrease in threshold voltage, maintaining the MOSFET's normally off characteristic even under high temperature negative gate voltage application.
Implementation Method 1
the use of titanium and titanium nitride films to occlude active hydrogen
Implementation Method 2
performing low temperature nitrogen annealing after the metal wiring is formed
Implementation Method 3
low temperature nitrogen annealing after the metal wiring formation to reduce hydrogen concentration
Data Source
AI summary
A method of manufacturing a silicon carbide semiconductor device includes forming on a front surface of a silicon carbide substrate of a first conductivity type, a silicon carbide layer of the first conductivity type of a lower concentration; selectively forming a region of a second conductivity type in a surface portion of the silicon carbide layer; selectively forming a source region of the first conductivity type in the region; forming a source electrode electrically connected to the source region; forming a gate insulating film on a surface of the region between the silicon carbide layer and the source region; forming a gate electrode on the gate insulating film; forming a drain electrode on a rear surface of the substrate; forming metal wiring comprising aluminum for the device, the metal wiring being connected to the source electrode; and performing low temperature nitrogen annealing after the metal wiring is formed.