SYNCHROTRON-RADIATION STUDIES OF DIAMOND NUCLEATION AND GROWTH ON SI

Valence-band as well as Si(2p) and C(1s) core-level photoemission, Aug er, and near-edge x-ray-absorption fine-structure spectroscopies were used to follow the surface chemistry associated with diamond film depo sition with a filament-assisted chemical-vapor-deposition reactor on a tomically clean and diamond polished Si(100) and Si(111) surfaces. Ram an spectroscopy and atomic force microscopy (AFM) were also used ex si tu to characterize the deposited films. Within 3 min of deposition, a carbon-rich SiC layer, at least 13 Angstrom thick, was observed to dev elop. At early stages of growth (<10 min of deposition), no difference s were observed between the clean and diamond-polished surfaces. With additional deposition, a 20-30-Angstrom-thick amorphous carbon overlay er was deposited on the clean Si surfaces: The amorphous carbon layer did not promote diamond nucleation. Deposition of an a-C:H layer on to p of the amorphous carbon layer also did not promote diamond nucleatio n. In contrast, similar to 500 Angstrom diamond films were deposited w ithin 45-60 min on the diamond-polished surfaces. Two types of nuclei were observed following 20 min of deposition by atomic force microscop y: (1) large (200-300 nm in diameter) nuclei, randomly distributed on the surface; and (2) smaller (50-100 nm) nuclei that show a preference for forming along the scratches. Atomic force micrographs of the orig inally clean surface shaw the formation of sharp relief structures on the surface. These structures, combined with the amorphous carbon over layer, may be responsible for the few sites that do nucleate diamond o n unpolished Si surfaces.