Formation and Annihilation of Carbon Vacancies in 4H-SiC

The carbon vacancy (V C ) is a major point defect in high-purity 4H-SiC epitaxial layers limiting the minority charge carrier lifetime. In layers grown by chemical vapor deposition techniques, the V C concentration is typically in the range of 10 12 cm -3 and after device processing at temperatures approaching 2000 °C, it can be enhanced by several orders of magnitude. In the present contribution, we show that the cooling rate after high-temperature processing has a profound influence on the resulting V C concentration where a slow rate promotes elimination of V C . Further, isochronal annealing of as-grown and as-oxidized epi-layers protected by a carbon-cap was undertaken between 800 °C and 1600 °C. The results reveal that thermodynamic equilibrium of V C is established rather rapidly at moderate temperatures, reaching a V C concentration of only a few times 10 11 cm -3 after 40 min at 1500 °C. Hence, the concept of eliminating V C ’s by annealing at moderate temperatures under C-rich equilibrium conditions shows great promise and enables re-annealing of high-temperature processed wafers, in contrast to the procedures commonly used today to eliminate V C . In-diffusion of carbon interstitials and out-diffusion of V C ’s are discussed as the kinetics processes establishing the thermodynamic equilibrium