INITIAL-STAGES IN THE GROWTH OF POLYCRYSTALLINE DIAMOND ON SILICON

Polycrystalline diamond films prepared in a hot filament chemical vapo ur deposition reactor were investigated with Raman Spectroscopy and X- ray photoelectron spectroscopy (XPS) in order to identify chemically a nd structurally distinguishable phases during nucleation and early sta ges of diamond growth. This was achieved by investigating a series of films grown under identical conditions for 5 min to 4 h. In addition, the interface between a solid diamond film and its silicon substrate w as studied after the film had been removed from the substrate. Carbon deposition commences initially with the simultaneous growth of diamond crystallites along scratches and a layer of microcrystalline graphite covering the remainder of the substrate. Small amounts of SiC could a lso be identified during the first 100 min of deposition. Once the ind ividual diamond crystallites have grown together to form a continuous layer, the graphitic phase in the spectra is replaced by an amorphous carbon phase which we attribute to the grain boundaries between the cr ystals. Inspection of the film backside revealed that the amorphous ca rbon had merely overgrown the microcrystalline graphite which was stil l present as the major component. Only after prolonged growth times (2 4 h) did the Raman and XPS spectra exhibit the characteristic diamond features free from any other contributions. On the basis of these obse rvations a model for the initial stages of diamond growth on Si is dev eloped.