Study of SIC oxidation for device application

Abstract

Silicon carbide (SiC) is a wide bandgap semiconductor that exhibits many excellent electrical properties such as high critical field strength and thermal conductivity. As a result, it has attracted a lot of attention for high temperature, high power and high frequency device applications. In addition, SiC can be thermally oxidized to form silicon dioxide (Si02), which is a critical building block of silicon complimentary metal-oxidesemiconductor (MOS) technology. This means that Si CMOS processes can be possibly transferred directly to SiC based CMOS devices. This renders SiC very attractive and offers many great advantages compared to other wide bandgap semiconductors such as gallium nitride (GaN). The development of SiC device applications is further propelled by the fact that high quality 4-inch 4H-SiC substrates are commercially available. To realize SiC based MOS devices, a high quality SiC/Si02 interface is necessary, as in the case of Si based MOS technology. However, at present the SiC/Si02 interface is still too defective for device application. The interface states density (Z)«) and the oxide fixed charge (Q ox) of SiC MOS structure are about two orders higher than those of Si MOS structure. This project aims to investigate the oxidation process of N-type 4H-SiC, such as oxidation temperature and annealing ambient, and their effects on the interface states density and oxide fixed charge. Thermally grown Si0 2 is examined as gate dielectric on N-type 4H-SiC by x-ray photoelectron spectroscopy (XPS), ellipsometry and capacitance-voltage (C-V) measurements. From XPS, it is found that CC bonds only exist at the Si02/SiC interface, whereas SiO x C y and Si-C bonds are only found in the iv ATTENTION: The Singapore Copyright Act applies to the use of this document. Nanyang Technological University Library Si0 2. At points further away from the interface and into the Si0 2 , there are more SiO x C y bonds relative to Si-C bonds. This result can be attributed to the dynamic oxidation process that transforms Si-C bonds into SiO x C y bonds, which are then further oxidized to form Si0 2 bonds. Ellipsometry is used to investigate the optical constants of thermal Si0 2 on 4H-SiC. It is found that there exists a transition layer between Si0 2 and 4H-SiC, which has a higher optical constant than pure Si0 2. The thermal oxidation temperature can influence the composition of the transition layer, especially the SiC volume fraction. Higher oxidation temperature has resulted in a lower SiC volume fraction. Nitridation of the thermal Si0 2 using N 2 0 at different temperatures was also studied. Over the temperature range from 950 °C to 1150 °C, it is found that nitridation at 1050°C gives relatively the lowest interface state density. The trap cross section constant was also investigated by AC conductance method. Higher temperature nitridation is found to result in smaller capture cross-section. Apart from thermal Si0 2 on 4H-SiC, other dielectrics such as silicon nitride (SiN x), tantalum pentoxide (Ta 2 0 5) and aluminum...