DIAMOND DEPOSITION IN A HOT-FILAMENT REACTOR USING DIFFERENT HYDROCARBON PRECURSOR GASES

A hot-filament reactor Was used to deposit polycrystalline diamond fil ms upon single-crystal Si substrates using hydrocarbon/H-2 gas mixture s. We studied the effect upon the deposition process and resulting fil m properties by varying the hydrocarbon gas from C1Hx to C4Hx alkanes. This was done maintaining a constant carbon-to-hydrogen ratio, but us ing a substantially lower-than-normal filament temperature (1500-degre es-C) in order to highlight differences in activation barriers and in the chemistry of the diamond-forming step. It was found that with incr easing hydrocarbon chain length the deposition rate decreased, from a value of about 0.4 mum h-1 for methane/H-2 Mixtures to less than 0.07 mum h-1 for butane/H-2. This was accompanied by an increase in the rel ative proportion of amorphous carbon to diamond present in the films. After one hour deposition the diamond grain size remained constant at about 20 nm, irrespective of the precursor gas. The measured Knoop har dness of the films also decreased when using process gases other than methane. We also studied the effect of changing the bond order in C2Hx precursor gases (ethane, ethene, ethyne) but found that this had no e ffect on either the deposition rate or the film quality.