Supercritical Oxynitride Treatment for 4H-SiC/SiO2 Interface
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Solution Overview
Problem
High interface state density at the SiO2/4H—SiC interface limits the mobility and reliability of SiC MOSFETs, with existing high-temperature annealing methods using hazardous gases or causing additional defects, necessitating a low-temperature processing method for improving interface quality.
Innovation Solution
A low-temperature processing method using a supercritical oxynitride environment with nitrogen-oxygen gas in a sealed chamber, where the silicon carbide sample is treated at temperatures from 50° C. to 500° C. and pressures from 10 MPa to 100 MPa to reduce interface state density and enhance oxide layer quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-temperature annealing (1000-1500°C) is used to reduce interface state density, then interface quality improves, but processing temperature and energy consumption increase
Solution Approach 1:
The patent changes the physical-chemical state parameters of the processing environment by using supercritical fluid (temperature 31-200°C, pressure 73-300 atm) instead of conventional gas phase annealing. This parameter change allows the processing to occur at much lower temperatures while maintaining effective interface passivation through the unique solvation and penetration capabilities of supercritical CO2 with dissolved H2S.
Solution Approach 2:
The patent utilizes the phase transition of CO2 to supercritical fluid state under specific temperature and pressure conditions. This phase transition enables the processing medium to achieve both liquid-like density for effective interaction with the interface and gas-like diffusivity for uniform penetration, achieving superior interface quality at low temperatures.
2Reliability
If NO gas is used for annealing to reduce interface state density, then interface quality improves, but safety hazards increase due to toxicity
Solution Approach 1:
The patent replaces toxic NO gas with CO2-H2S supercritical fluid system where CO2 is inert and safe, and H2S is delivered in controlled微量 amounts through the supercritical medium. The CO2 can be easily vented and recovered, making the process safer and more environmentally friendly while maintaining effective interface passivation.
Solution Approach 2:
The supercritical CO2 acts as an intermediary carrier that delivers H2S to the interface region. This intermediary approach allows controlled delivery of the reactive species (H2S) while using the safe, inert CO2 as the primary processing medium, eliminating the need to handle toxic NO gas directly.
3Object-affected harmful factors
If N2O is used instead of NO for safety, then operational safety improves, but interface state reduction effectiveness decreases due to decomposition and reoxidation
Solution Approach 1:
The patent extracts the problematic decomposition behavior of N2O by completely avoiding its use. Instead, the system uses CO2-H2S supercritical fluid where H2S provides the necessary sulfur for interface passivation without decomposition issues, and CO2 remains stable throughout the process, eliminating reoxidation problems.
4Speed
If POCl3 annealing is used to improve mobility, then channel mobility increases, but device threshold shifts negatively and oxide layer reliability decreases
Solution Approach 1:
The patent changes the chemical composition parameters of the processing medium from phosphorus-based (POCl3) to sulfur-based (H2S in CO2). This parameter change achieves effective interface passivation through sulfur bonding without introducing phosphorus contamination that causes threshold voltage shifts and oxide degradation.
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 interface state density, improves oxide layer quality, and increases carrier mobility of SiC MOSFETs without the hazards and defects associated with high-temperature processing, enabling high-performance SiC MOSFETs with reduced leakage current and increased breakdown electric field.
Implementation Method 1
A low-temperature processing method using a supercritical oxynitride environment with nitrogen-oxygen gas in a sealed chamber, where the silicon carbide sample is treated at temperatures from 50° C. to 500° C. and pressures from 10 MPa to 100 MPa
Implementation Method 2
an annealing process after oxidation is mainly used to reduce the interface state density of 4H—SiC/SiO2 and improve characteristics of a MOS interface
Data Source
AI summary
Disclosed are a low-temperature processing method for improving a 4H—SiC/SiO2 interface based on a supercritical oxynitride, and use thereof. The method includes: performing standard cleaning on a silicon carbide sample to be processed; performing dry-oxygen oxidation on the cleaned silicon carbide sample to grow an oxide layer; placing the silicon carbide sample having the oxide layer on a support in a steady-state supercritical chamber; controlling a pressure and injecting nitrogen-oxygen gas into the supercritical device; increasing a temperature in the supercritical device from 23° C. to 500° C.; maintaining the above supercritical state until the processing ends; reducing a temperature of a reactor to room temperature after reaction ends, reducing the pressure to an atmospheric pressure, and taking out the reactor. The present disclosure allows for effective and quick decrease in the 4H—SiC/SiO2 interface state density, and also a significant decrease in the processing temperature.