Münster 1999 – scientific programme
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HL: Halbleiterphysik
HL 9: Diamant
HL 9.4: Talk
Monday, March 22, 1999, 16:45–17:00, H3
Ion energy distributions in the bias enhanced nucleation of CVD diamond — •Szabolcs Kátai1,2 and Péter Deák2 — 1Walter Schottky Institut, Technische Universität München, Am Coulombwall, 85748 Garching — 2Department of Atomic Physics, Technical University of Budapest, Budafoki út 8, 1111 Budapest, Hungary
Ions play an important role in the bias enhanced nucleation (BEN) of the chemical vapor deposition (CVD) of diamond. The mechanism of BEN is not yet clear; models depend on the assumptions made on the ion energies. We have developed a mass selective energy alalyzer for in situ plasma diagnosis, and measured the ion energy distributions and ion fluxes during the BEN process for H2/CH4 plasmas at 25 mbar. We have shown that several CxHy+ (0≤x≤3, 0≤y≤6) species arrive at the substrate surface in substantial quantities and that most ion energy distributions have a peak at 30-45% of the bias voltage with FWHM of about 15-20% and a smaller high energy tale up to about 80% of the bias. H+ is an exception showing a wide distribution between 10-80% of the bias voltage. Ion fluxes show a maximum as a function of the bias voltage for several species. Hydrogen depleted, thus chemically more reactive ions are more abundant at higher bias (C+, CH+, C2+, C2H+ and C2H2+ dominate at -200V). Ion energies decrease with increasing methane concentration in the feed gas. At low methane concentrations the overall flux of hydrogen species are higher than that of hydrocarbon species, above 0.5% methane concentration hydrocarbon species start to dominate the spectrum. We have shown that there is a correlation between the experimentally observed lowest limit of bias for nucleation enhancement and the low energy limit for ion subplantation below the surface.