Proceedings PaperDirect measurement of H-atom sticking coefficient during diamond film growth
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In previous work it has been demonstrated that diamond thin films can be grown in a heated quartz flowtube by adding organic molecules to a stream of atomic hydrogen. In this system, the pattern of diamond film growth may be used to obtain information about the growth kinetics. In the present work, a thin, moveable catalytic probe that detects hydrogen atoms has been added. Since the flowtube is at a uniform temperature and has a high flowspeed, the rate of decay of H-atoms down the tube may be converted to a sticking coefficient, after making a small correction for diffusive mass transfer. The data were taken at a tube temperature of 800 Celsius and a pressure of 3.7 torr, with 1 SCCM of methane injected into a flow of 150 SCCM of 90% argon, 10% hydrogen. Calibration of the H-atom probe indicates that all the hydrogen is initially nearly dissociated. The probe measurements give a sticking coefficient at 800 Celsius of about 3 X 10-4 for the silicon/diamond substrates. During diamond deposition, i.e., when methane is flowing, the apparent sticking coefficient rises to 2.5 X 10-3, although this includes the effect of gas phase reaction as well as wall loss. We will discuss how these numbers shed light on proposed mechanisms for diamond formation.