Materials Science and Engineering B61 – 62 (1999) 468 – 471 Mechanistic model for oxidation of SiC N.G. Wright *, C.M. Johnson, A.G. O’Neill Department Of Electrical and Electronic Engineering, The Uniersity of Newcastle upon Tyne, Newcastle NEI 7RU, UK Abstract A mechanistic model for the oxidation of SiC is presented. The model explains the observed anisotropic oxidation rate of SiC in terms of the effect of weakening/strengthening of Si – C bonds arising from the on-going incorporation of highly electronegative oxygen atoms into the crystal lattice. A novel Monte Carlo based oxidation simulator, OXYSIM, is presented and used to explore the proposed SiC oxidation model. The extraction of key process metrics (such as oxide thickness, interface roughness and oxide defect density) is discussed. © 1999 Elsevier Science S.A. All rights reserved. Keywords: SiC; Oxidation rate; OXYSIM 1. Introduction The possibility of metal-oxide-semiconductor (MOS) devices is one of the main forces driving the huge international interest in SiC devices. The desirable high voltage normally-off behaviour of such devices is criti- cally dependent on growing good quality SiO 2 layers on SiC and to date attempts at producing oxide layers have not been particularly successful. Oxides grown on SiC (both the 4H and 6H polytypes) exhibit high fixed charge densities and poor oxide – semiconductor inter- faces with significant roughness [1]. Systematic study of oxidation of the 6H- and 4H-SiC polytypes by various groups has, however, produced a wealth of information about oxidation processes in SiC [2]. For example, it is now well established that different crystal faces of SiC oxidise at different rates resulting (for example) in uneven oxide thickness around an etched trench [3,4]. The lowest/highest oxidation rates are observed on the so-called silicon/carbon faces (the 0001/000 - 1 planes, respectively), with a corresponding increase in oxida- tion rate for planes between the two extremes. Depen- dency of oxidation rate on crystallographic plane is also observed in silicon where it is also explained by argu- ments based on the number of silicon–silicon bonds exposed to various crystal faces. As 0001/000 - 1 planes have the same number of surface bonds but widely differing oxidation rates, such an explanation is not sufficient for SiC. This paper proposes a simple mecha- nistic model which predicts the oxidation rate at differ- ent crystal faces. In order to explore the consequences of the proposed model, a simple Monte Carlo based simulation program was developed. 2. Monte Carlo approach The proposed oxidation model was implemented in the simulator, OXYSIM, which is based on using a Monte Carlo type approach to model the oxidation process at an atomic level. OXYSIM works by consid- ering the interaction between the semiconductor crystal lattice and any oxidising species (note: the model can be adapted to all common oxidising reactants. For simplic- ity of explanation, however, the description is given in terms of dry oxidation, i.e. oxygen atoms reacting with the semiconductor). After the structure of the lattice has been initialized by placing atoms in their correct position and setting relevant bond energies, oxygen atoms (in this case) enter the lattice on calculated trajectories. The oxidation temperature of the simulated process can be used to determine the number and trajectories of the incoming oxygen atoms according to the well-known laws of statistical mechanics governing gases. Those oxygen atoms that come within pre- defined distances of lattice atoms are considered as possible candidates for interaction with the lattice atoms to form bonds (and thus disrupt the original * Corresponding author. 0921-5107/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved. PII:S0921-5107(98)00557-1