454-zheng-jes-1990-2812 - JOURNAL SOLID-STATE -AND OF" THE...

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JOURNAL OF" THE ELECTROCHEMICAL SOCIETY SOLID-STATE SCIENCE ---- AND TECHNOLOGY ~ SEPTEMBER L1 D ~""~" , 1990 Oxidation of Single-Crystal Silicon Carbide Part II. Kinetic Model Z. Zheng, R. E. Tressler, and K. E. Spear Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802 ABSTRACT The oxidation of single-crystal SiC in dry oxygen (10-3-1 atm and 1200~176 followed parabolic kinetics. The oxy- gen partial pressure dependence of the oxidation rate of the (0001) carbon face decreased with increasing temperature (from 0.6 at 1200~ to 0.3 at 1500~ A kinetic model based on parallel transport of oxidants through the oxide via molecu- lar and ionic oxygen diffusion mechanisms fits the observed oxidation behavior. Both diffusivity and activation energy values for oxidants permeating through the oxide derived from the model using the experimental data are similar to those for molecular oxygen permeating through vitreous SIO2. Ionic oxygen diffusion inward via the lattice presumably via a vacancy mechanism becomes more important when oxidation takes place at higher temperatures and at low oxygen par- tial pressures. Both diffusivity and activation energy values for the ionic oxidant diffusion derived from the model using the experimental data are similar to those values for the diffusion of oxygen through silica reported in the literature. In a companion paper we have concluded that the oxida- tion of single-crystal SiC in dry oxygen (10-3-1 arm and 1200~176 followed parabolic kinetics (1). Two different apparent activation energies were calculated for oxidation of the (0001) C faces of SiC (around 120 kJ/mol below 1350~ and 260 kJ/mol above 1350~ Two regimes were not apparent for oxidation of the (0001) Si faces, and appar- ent activation energies lie between 223-298 kJ/mol. Double oxidation experiments using 160~ and 1802 indicated that the process is dominated by the transport of molecular ox- ygen at lower temperatures with a substantial contribution due to diffusion of ionic oxygen at higher temperatures. Epitaxially grown SiI3C films on alpha-Si~2C substrates via CVD were used to study carbon transport behavior during oxidation of SiC. SIMS analyses showed that carbon can transport quickly through the oxide layer, which elimi- nates the possibility that transport of carbonaceous spe- cies is rate controlling in the oxidation of SiC. The oxida- tion mechanisms of SiC were hypothesized to be parallel transport of oxidants through the growing oxide layer via molecular oxygen and ionic oxygen diffusion mech- anisms. The change of activation energies in lower and higher oxidation temperature regimes listed above agrees with other observations reported in the literature (2-4) with the reported activation energy values increasing from around 120 kJ/mol below 1400~ to around 250-500 kJ/mol above this temperature. The activation energy values around 120 kJ/mol in the lower temperature range are very similar to the activation energy values reported for the oxidation of silicon (5), which corresponds to the activation energy for
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This note was uploaded on 12/10/2009 for the course IF PFIS1200 taught by Professor Antonio during the Spring '09 term at Universidade Federal do Rio de Janeiro.

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454-zheng-jes-1990-2812 - JOURNAL SOLID-STATE -AND OF" THE...

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