Influence of Carbon Cap on Self-Diffusion in Silicon Carbide

Abstract

Self-diffusion of carbon (12C and 13C) and silicon (28Si and 30Si) in 4H silicon carbide has been investigated by utilizing a structure containing an isotope purified 4H-28Si12C epitaxial layer grown on an n-type (0001) 4H-SiC substrate, and finally covered by a carbon capping layer (C-cap). The 13C and 30Si isotope profiles were monitored using secondary ion mass spectrometry (SIMS) following successive heat treatments performed at 2300–2450∘C in Ar atmosphere using an inductively heated furnace. The 30Si profiles show little redistribution within the studied temperature range, with the extracted diffusion lengths for Si being within the error bar for surface roughening during annealing, as determined by profilometer measurements. On the other hand, a significant diffusion of 13C was observed into the isotope purified layer from both the substrate and the C-cap. A diffusivity of D=8.3×106e−10.4/kBT cm2/s for 13C was extracted, in contrast to previous findings that yielded lower both pre-factors and activation energies for C self-diffusion in SiC. The discrepancy between the present measurements and previous theoretical and experimental works is ascribed to the presence of the C-cap, which is responsible for continuous injection of C interstitials during annealing, and thereby suppressing the vacancy mediated diffusion.