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Unformatted text preview: Silicon oxycarbide formation on SiC surfaces and at the SiC/SiO 2 interface C. O ¨ nneby a) and C. G. Pantano Department of Materials Science and Engineering, The Pennsylvania State University, 102 Materials Research Institute Building, University Park, Pennsylvania 16802 ~ Received 1 October 1996; accepted 11 March 1997 ! Amorphous and single-crystal a-SiC were exposed to various oxygen sources at room temperature. The oxygen sources included the residual gas in an ultrahigh vacuum environment, ambient air, ozone, and oxygen plasma. X-ray photoelectron spectroscopy ~ XPS ! was used to follow changes in the surface composition and to determine the local bonding environment of the Si atoms. It was found that silicon oxycarbide species are formed when these SiC materials are initially exposed to oxygen. With extended exposure to ambient air, a SiO 2 layer is subsequently formed over the silicon oxycarbide. However, the native oxide on the single-crystal SiC consists mainly of silicon oxycarbide species. The thicknesses of these native oxides were calculated using the XPS data. © 1997 American Vacuum Society. @ S0734-2101 ~ 97 ! 59103-2 # I. INTRODUCTION SiC is widely used in microelectronic devices. In these multilayer devices, an oxide layer is often grown over a SiC layer through thermal oxidation, or is deposited onto the SiC using thin-film techniques. The nature of the SiC/SiO 2 inter- face strongly influences the behavior of the device. The pres- ence of a transition oxide at the interface could alter the electronic properties of a multilayer SiC-based electronic de- vice. A more thorough characterization of the interface could help explain the difficulties encountered in producing a high quality oxide on SiC substrates for electronic devices. A study of this nature could also help reveal the reasons for the different oxidation rates of the two polar surfaces of a-SiC. Many studies have been undertaken to investigate the ini- tial stages of SiC oxidation. The definition of initial stages, however, varies from study to study ~ submonolayers up to ; 10 nm ! . In the more recent studies, 1–9 a transition oxide, often termed a ‘‘suboxide,’’ has been observed during the initial stages of SiC oxidation. In studies where the forma- tion of a suboxide was suggested at the SiC/SiO 2 interface, no specific definition of the terms ‘‘suboxide’’ and SiO x were given. This leaves one to assume the same definitions that have been applied to the Si/SiO 2 interface, 10–15 i.e., SiO 2 , SiO, and Si 2 O 3 . However, the formation of suboxides on a SiC substrate is not very likely, since that would involve breaking Si–C bonds in the presence of oxygen and forming Si–Si bonds. The more logical transition species would be the silicon oxycarbides. Hence, the suboxides reported in previous studies of SiC oxidation might actually be silicon oxycarbides. Only recently has the transition oxide been at- tributed to silicon oxycarbide....
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