Behaviors of Carbon Atoms during Plasma Oxidation of 4H-SiC(0001) Surfaces near Room Temperature

Abstract

Epitaxial graphene on silicon carbide (SiC) is promising for future electronic devices. A well-known scheme for the epitaxial growth of graphene is to heat a Si-face SiC(0001) surface to 1100-1300°C in ultrahigh vacuum (UHV), which results in the sublimation of Si. However, this simple process produces a SiC surface with a pitted morphology, which degrades the transport properties of graphene on it.The pitted morphology originates from the rapid and random sublimation of Si from the terraces that are not covered by a carbon-rich buffer layer. Thus, a strategy to avoid the pitted morphology is to form a homogeneous buffer layer on the entire SiC surface. For this purpose, a key technique is the deposition of carbon at the monolayer level on a SiC substrate in a controllable manner. Researchers have reported various methods to enrich carbon concentration on a SiC surface with a Si face. Some examples are the direct deposition of carbon onto SiC, the rapid annealing of SiC surfaces, and the enhanced removal of silicon atoms by atomic hydrogen, all of which are based on sophisticated UHV techniques.In this study, we demonstrate that carbon atoms are segregated at the SiO2/SiC interface at the monolayer level when a SiC surface, atomically flattened by a solution-based process[1-3], is oxidized by an atmospheric-pressure plasma (He-based plasma with a small amount of O and OH species) at near room temperature. The behavior of carbon atoms has been an object of study in thermal oxidation of SiC. We discuss the mechanism of carbon aggregation at the SiO2/SiC interface occurring in the plasma oxidation at room temperature. After the plasma oxidation, the sample was etched in HF solution to strip off the oxide layer, which leaves a carbon source for graphene growth on the SiC substrate. And we show the carbon-rich surface yields a surface morphology with reduced pits on graphene when it is treated at elevated temperatures in vacuum. We speculate this is achieved by the additional carbon atoms assisting the formation of the buffer layer more uniformly over the surface prior to graphene growth. [1] K. Arima, K. Endo, K. Yamauchi, K. Hirose, T. Ono, and Y. Sano, J. Phys.: Condens. Matter 23, 394202 (2011).[2] A.N. Hattori, T. Okamoto, S. Sadakuni, J. Murata, K. Arima, Y. Sano, K. Hattori, H. Daimon, K. Endo and K. Yamauchi, Surf. Sci. 605, 597 (2011).[3] K. Nishitani, H. Sakane, A.N. Hattori, T. Okamoto, K. Kawai, J. Uchikoshi, Y. Sano, K. Yamauchi, M. Morita and K. Arima, ECS Transactions, 41(6), 241 (2011).