THE INITIAL-STAGES OF DIAMOND GROWTH - AN ADSORPTION STUDY OF HOT-FILAMENT ACTIVATED METHANE AND HYDROGEN ON SI(100)

The adsorption of hot filament ''activated'' methane and hydrogen on Si(100) has been probed with Auger electron and thermal desorption spectroscopies. Whilst the molecular forms of these gases do not adsorb, bound hydrocarbon species are formed on the Si surface after flowing methane over a tantalum filament held at 2200 K. Adsorbed ethylene and acetylene are both present. The reactions promoted in this adsorbed layer by impinging atomic hydrogen have been studied. Atomic hydrogen abstraction leads to the conversion of all adsorbed ethylene into acetylene. Further atomic hydrogen abstraction enables catenation to occur, most probably from an acetylenic intermediate plus adsorbed methyl species, giving rise to C3 forms. This information provides the first direct experimental insight into the surface reactions which occur during the onset of hot filament activated CVD diamond formation on silicon. The surface will be host to both ethylene and acetylene species, but the former will play an insignificant role in nucleation since under growth conditions these will be converted to acetylene. The results also indicate that C-C bond formation on the silicon surface can occur through the atomic hydrogen driven addition of hydrogenated forms. The concentration of the adsorbed species observed will be low under the high temperatures pertaining during diamond growth; thus, nucleation on Si(100) would be expected to be very slow, as is typically found, if this means of carbon layer formation dominates over the simple thermal decomposition of bound hydrocarbons.