Silica films on silicon carbide: a review of electrical properties and device applications

This paper reviews the present knowledge on silica films (SiO2) on silicon carbide (SiC). First, kinetic of thermal oxidation of SiC is described, and the effects of a great number of parameters (various SiC polytypes, substrate type, substrate orientation...) are discussed. Mainly, thermal oxides grown on SiC are close to stoichiometric silica and the oxidation rate depends on the terminal face of the SiC monocrystal. The next four sections discuss the electrical properties of the oxide, and of the oxide/SiC interface, and especially the effects of materials and technological process on the interface state density and the effective oxide charge (Section 5), and the origin of the interface states are discussed in detail (Section 6). Oxides grown on n-type SiC have electrical properties (in terms of dielectric strength, leakage currents, interface trap, and oxide charges) measured by means of metal-oxide-semiconductor (MOS) structures, similar to oxides grown on silicon. Until recently, p-type SiC MOS structures have had a large equivalent oxide charge and larger interface state densities in spite of many efforts, compared to silicon MOS structures. It seems nevertheless that recent studies have improved the SiO2/SiC interfacial quality. Aluminum, carbon and alkali species are ihs main suspected contaminants. Finally, Section 7 presents the applications of oxide films in SE-based devices: MOS capacitors and MOS field effect transistors (MOSFETs) for microelectronics, MOSFETs for power electronics, and some applications using silica layers as a passivation layer. In spite of a smaller than required carrier mobility in the inversion layer, MOS field effect transistors (MOSFETs) have been demonstrated to operate up to 650 degreesC and integrated circuits based on NMOS and PMOS technologies have been successfully operated up to 300 degreesC. Vertical power MOSFETs are also of importance but their performances are still limited by a specific on-resistance larger than device requirements. The effect of charges present in the oxide on the electrical properties of high voltage diodes is also briefly discussed. (C) 2001 Elsevier Science B.V. All rights reserved.