A Study On SiO₂/SiC Interface Characteristics

In this paper, the SiO2/SiC interfacial characteristics are systemically investigated in detail.Poisson's equation in space charge region (SCR) of SiC MOS devices is built by taking some factors, e.g. incomplete ionization of impurity, Pool-Frenkel effect and generation rate of minority carriers, into account. The electrical characteristics of SiC MOS devices are studied by solving the Poisson's equation. The results show that the impurity in SiC can't be completely ionized at room temperature and the ionized ratio increases as temperature increases. Based on these, potential distribution in SCR, ideal high/low-frequency C-V curves and flatband-voltage equation for SiC MOS capacitors are obtained. Considering SiC's wide bandgap and its different molecule structure from Si, origination of interface traps is discussed. Interface-state density and border trap density for SiC MOS devices are measured by modifying measurement methods for Si MOS devices and considering electrical and physical properties of SiC.A comprehensive Semi-empirical model for inversion channel electron mobility of SiC n-MOSFET is proposed on the basis of semiconductor device physics. Effects of lattice, ionized impurities, surface phonon, interface charges and surface roughness scatterings on the mobility are considered in this model, where the interface-charge scattering mechanism includes electrically-shielded effect of carriers. The model can be used to study and analyze influences of interface characteristics on electron mobility and is also a basis of circuit simulations in the future. The model can be well used for device simulation. Influences of some factors, such as interface states, surface roughness and so on, on the mobility are investigated using the model. Simulated results indicate that the interface charges and surface roughness are major factors of affecting inversion-channel electron mobility, in which the maximum mobility depends on the interface-state density, and surface-roughness scattering limits electron mobility under high field.A new process of oxidizing SiC in dry O2 + trichloroethylene (TCE) is presented for the first time to prepare gate dielectrics of 6H-SiC MOS devices. As compared to the conventional dry O2 oxidation, the O2 + TCE oxidation not only increases the oxidation rate of SiC, but also results in lower interface-state density, border trap density, effective oxide-charge density and enhanced device reliability. These improvements are probably related to Cl2 and HCl decomposed by TCE at high temperature. Moreover, post-oxidation NO anneal, especially in a wet ambient, can further decreases the interface-state density, border trap density and effective oxide-charge density, and enhance the interface reliability. The involved physical mechanisms can be attributed to steam-enhanced NO passivation.