Effects of annealing with CO and CO2 molecules on oxygen vacancy defect density in amorphous SiO2 formed by thermal oxidation of SiC

Abstract

SiO2 formed by the thermal oxidation of SiC has numerous defects, and the stoichiometry of the SiO2 near the SiC/SiO2 interface differs from that of SiO2 near the Si/SiO2 interface. We assume that, during the oxidation of SiC, CO and CO2 molecules are released, and that these molecules interact with the SiO2 and form defects. Considering the Gibbs free energy of these molecules, we found that CO molecules reduce part of the amorphous SiO2 at high temperatures, resulting in the formation of oxygen vacancy defects concomitant with the formation of CO2 molecules. In particular, when the partial pressure of the CO molecules is higher than that of the CO2 molecules, the number of oxygen vacancy defects increases. This means that post-oxidation annealing with CO molecules induces defects and degrades the breakdown field of SiO2. On the other hand, when the partial pressure of the CO2 molecules is larger than that of the CO molecules, reduction by the CO molecules does not occur, and the CO2 molecules can oxidize oxygen vacancy defects in SiO2. This means that post-oxidation annealing with CO2 molecules enables recovery of the oxygen vacancy defects and improves the breakdown field and flatband shift of SiO2 gate dielectrics. Accordingly, it is possible to reduce the formation of oxygen vacancies in amorphous SiO2 by performing post-oxidation annealing in a CO2 gas ambient.