SiC Gate Insulating Film Oxynitriding for Low Trap Density
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Solution Overview
Problem
Conventional silicon oxide film forming techniques for SiC surfaces using microwave-excited plasma fail to achieve excellent electrical properties, resulting in high interface trap densities and oxide fixed charge densities, which impede the realization of high-performance SiC MOS transistors.
Innovation Solution
A semiconductor device with a gate insulating film formed by directly oxynitriding the SiC surface using a Kr/O2/NO mixed gas and subsequent annealing, followed by depositing a CVD oxide film, to reduce carbon content and interface trap density, thereby improving electrical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional thermal oxidation or wet oxidation techniques are used to form a silicon oxide film on SiC surface, then the oxidation process can be completed, but the interface trap density becomes extremely high and channel resistance increases
Solution Approach 1:
The patent changes the oxidation mechanism from molecular oxygen (conventional thermal oxidation) to atomic oxygen radicals (plasma oxidation). By introducing a plasma state and using atomic oxygen species, the oxidation process achieves complete carbon removal and forms a high-quality silicon oxide interface with low trap density, resolving the contradiction between achieving oxidation and maintaining interface quality
Solution Approach 2:
The patent replaces the thermal field-based oxidation mechanism with a plasma field-based mechanism. By substituting conventional thermal oxidation with plasma oxidation, the process achieves superior interface quality and eliminates the harmful effects of carbon contamination that plague conventional methods
2Temperature
If microwave-excited plasma oxidation is used on SiC surface, then oxidation can occur at lower temperature, but the electrical properties remain poor with high interface trap density and oxide fixed charge density
Solution Approach 1:
The patent modifies the plasma composition by introducing a mixed gas containing Kr, O2, and NO. The NO component provides nitrogen radicals that passivate carbon atoms at the SiC interface, while the plasma excitation enables low-temperature processing. This compositional change resolves the contradiction by achieving both low temperature and high electrical quality
Solution Approach 2:
The patent creates a composite gate insulating film structure through plasma oxidation in a mixed gas environment. The resulting film contains silicon oxide with nitrogen incorporation, forming a composite material that simultaneously provides low interface trap density, low fixed charge density, and excellent electrical properties that neither pure oxide nor conventional methods could achieve alone
3Ease of manufacture
If conventional oxidation methods are used, then the process is simple, but carbon content in the gate insulating film remains high causing poor electrical characteristics
Solution Approach 1:
The patent uses plasma-generated atomic oxygen radicals as a strong oxidizing agent that completely removes carbon from the SiC surface and prevents carbon incorporation in the gate insulating film. The high reactivity of atomic oxygen species enables thorough oxidation without requiring complex process steps, maintaining ease of manufacture while achieving superior carbon control
Solution Approach 2:
The patent introduces nitrogen radicals from NO gas as an intermediary that passivates carbon atoms at the SiC interface during plasma oxidation. This intermediary mechanism converts harmful carbon into benign carbon-nitrogen complexes, effectively reducing carbon content in the gate insulating film while maintaining process simplicity
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 approach results in a gate insulating film with a carbon content of 1×10^20 atoms/cm^3 or less, oxide fixed charge of 1×10^11 cm^-2 or less, and interface trap density of 1×10^11 cm^-2 or less, enhancing the reliability and performance of SiC MOS transistors.
Implementation Method 1
introduces a Kr/O2/NO mixed gas and supplies a microwave to generate a plasma
Implementation Method 2
oxidizing the silicon surface by atomic oxygen O radicals
Implementation Method 3
supplies a microwave to generate a plasma
Implementation Method 4
subsequent annealing
Implementation Method 5
depositing a CVD oxide film
Data Source
AI summary
A film with small hysteresis and high voltage resistance is obtained by reducing the carbon content in a gate insulating film on a SiC substrate. Specifically, the carbon content in the gate insulating film is set to 1×1020 atoms/cm3 or less. For this, using a plasma processing apparatus, a silicon oxide film is formed on the SiC substrate and then the formed silicon oxide film is reformed by exposure to radicals containing nitrogen atoms. Thus, the gate insulating film excellent in electrical properties is obtained.