Growth Rate Enhancement of Silicon-Carbide Oxidation in Thin Oxide Regime

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Among wide band-gap semiconductor materials, only silicon carbide (SiC) can have SiO2 layers, known as superior insulating films for metal-oxide-semiconductor (MOS) applications, on its surface by thermally oxidizing it, similarly to Si (2). In addition, its physical properties, such as high-breakdown electric field and high thermal conductivity, compared with Si, are suitable for high-speed switching and low-power-loss electronic devices. For these reasons, SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) are expected to have superior specifications that cannot be obtained using Si. However, the electrical characteristics of SiC MOSFETs, such as on-resistance, are seriously poorer than those predicted from SiC bulk properties (1). It has been considered that these poor characteristics result from a high interface state density (3). Therefore, the clarification of the structure of SiC–oxide interfaces or the formation mechanism of the interface layer is one of the most important subjects to be studied to improve the electrical characteristics of SiC MOS devices. In a previous work, we have performed real-time observation of SiC thermal oxidation using an in-situ ellipsometer (4). The results show that the oxidation-time dependence of oxide thickness can be represented using the Deal-Grove (D-G) model (5), which has been originally proposed for the explanation of Si oxidation. Song et al. (6) have modified the D-G model for application to SiC oxidation taking the presence of carbon into account. They have concluded that a linear-parabolic formula can also be applicable to SiC oxidation, although the parabolic term includes the contribution from the diffusion of CO or CO2 molecules from the SiC–oxide interface to the surface as well as that of oxygen from the surface to the interface. On the other hand, it is well known that the oxidation behavior of Si cannot be explained using the D-G model, i.e., a simple linear-parabolic model, particularly at the initial oxidation stage. Accordingly, several models have been proposed for the explanation of Si oxidation (7–12). In this work, we have studied 4H-SiC oxidation at the initial stage in more detail by performing in-situ spectroscopic ellipsometry and discussed the oxidation mechanism of SiC by comparing it with that of Si. 4