(361e) New Insight Into the Reaction Mechanism of SiC Oxidation and Nitridation: A Density Functional Theory Study of β-SiC (001) Surface

Wide interest in detailed investigations of SiC can be divided into two major areas: exploring their potential as high-frequency materials in electronic applications and assessing their continuous stability when exposed to high temperature environments. One common factor in both types of applications is the importance of SiC oxidation. The mechanism of this process likely proceeds via a complex set of serial and parallel reaction steps, and while predicting all of them is challenging mapping a comprehensive set computationally would offer significant insight into the dominant adsorption and reaction chemistry of gaseous species interacting with SiC surfaces. In this work, reaction pathways leading to active/passive oxidation of SiC surfaces were investigated systematically using density functional theory. First, adsorption of gaseous species (small molecules containing O, C, H and N) interacting in different orientations and positions on the β-SiC (001) surface was studied. Based on the most favorable adsorption configurations, various reaction channels were explored by identifying transition state structures.  Interactions with both the carbon and silicon layers of SiC were analyzed. Interactions with the carbon layer were found to be important for NO dissociation leading to Si-C bond breaking by insertion. The observations made for atomic and multiatomic species adsorption on the SiC surface were extended to form reaction pathways resulting in SiC oxidation products, including CO, SiO₂ and SiO. Rate constants were calculated with transition state theory, and microkinetic modeling was carried out to identify the dominant pathways that were mapped. The thermodynamic data was interpreted to understand the role of temperature in the formation of SiO instead of SiO₂.