Studies On Physical And Radiation Induced Properties Of 6H-SiC MOS Interface

Silicon carbide (SiC) is one of the promising wide bandgap compound semiconductor materials. It is the only compound semiconductor whose native oxide is SiO2. This places SiC in a unique position to fabricate high-temperature, high-frequency, high-power, high voltage and radiation-hard MOS devices with standard silicon MOS techniques. The quality of oxide layer grown on SiC substrate and its interface properties are currently under intensive investigation. In this work, we have fabricated SiC MOS capacitors by oxidizing SiC substrates with dry Oa to form SiO2 layers as gate insulators and studied the physical and radiation induced properties of the SiOa/SiC interface system.The experiments indicated that the large flatband shift was due to the high density of interface states appearing at SiO2/p-SiC interface, rather than the aluminum that were incorporated into the oxide layer. The effective interface state ledge, which appeared in room temperature photo-CV curve, was systematically investigated. The basic conditions needed to observe this interface state ledge and the formulas to calculate the density of effective interface states and fixed oxide charges have been found. The low temperature experiments have showed that the interface states at SiO2/p-SiC interface were donor-type, while at Si02/n-SiC interface were acceptor-type.The SiC MOS capacitors were irradiated with 7 ray with different absorbed doses of 0.2 and 1.0Mrad(SiO2). Positive gate biases were applied during the irradiation. The results presented that SiC MOS capacitors had better irradiation tolerance than Si MOS capacitors and n-SiC capacitors were better than p-SiC capacitors. However, if the MOS devices were taken into account, n-channel would be much better than p-channel devices.XPS and SIMS analyses were also performed to investigate the properties of the oxides on p-type and n-type SiC substrate. The results of XPS measurementsshowed that the quality of SiO2 grown on SiC substrate was inferior to those grown on Si substrate. SIMS results indicated that there was no release of the aluminum incorporated into p-SiC oxides, and the concentration of carbon was higher than that in n-SiC oxides. Therefore, it could be determined that the quality of SiO2/n-SiC interface was much better than SiO2/p-SiC interface, Which also agreed well with the C-V results.