SiC defect density reduction by epitaxy on porous surfaces

The presence of micropipes and dislocations in SiC wafers used as substrates for SIC epitaxial growth may cause formation of lattice defects in the epi-layers. In this research a chemical vapor deposition (CVD) process on porous SiC (PSC) buffer layers was developed to reduce structural defect concentrations in SiC epi-layers. One possible mechanism for defect reduction is nano-scale lateral epitaxial overgrowth whereby the pores serve as regions to relieve stress at the growth surface. Previous X-ray diffraction, RHEED, SEM and AFM characterization has demonstrated good surface quality of these films gown on PSC substrates compared with conventional (control) substrates. For this study, the porous substrate surface was fabricated by surface anodization on half of a commercial 4H-SiC (0001) Si-face off-axis wafer. The other half of each wafer was protected by wax during this process and served as a control substrate. 4H-SiC epitaxial layers of thickness ranging from 4 to 10 mum were then grown on the processed substrates by atmospheric pressure CVD. LTPL data taken at 2K shows virtually no evidence of the L(1) line for the film grown on PSC while the line is clearly evident in the spectra from films grown on the control substrate. The LI line appears in rapid CVD growth and is related to intrinsic defects in films grown too quickly. It appears from this preliminary work that epitaxial films gown on porous SiC buffer lavers have a lower density of defects than identical epitaxial firms grown on commercially available SiC substrates.