Role of Ions in Bias Enhanced Nucleation of Diamond
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J.M. LANNON, JR.*, J.S. GOLD*, AND C.D. STINESPRING* *Department of Physics, West Virginia University, Morgantown, WV 26506 "**Department of Chemical Engineering, West Virginia University, Morgantown, WV 26506
ABSTRACT Ion-surface interactions are thought to play a role in bias enhanced nucleation of diamond. To explore this hypothesis and understand the mechanisms, surface studies of hydrogen and hydrocarbon ion interactions with silicon and silicon carbide have been performed. The experiments were carried out at room temperature and used in-situ Auger analyses to monitor the surface composition of thin films produced or modified by the ions. Ion energies ranged from 10 to 2000 eV. Hydrogen ions were found to modify silicon carbide thin films by removing silicon and converting the resulting carbon-rich layers to a mixture of sp 2 - and sp 3 -C. The interaction of 3 2 hydrocarbon ions with silicon was shown to produce a thin film containing SiC-, sp -, and sp -C species. In general, the relative amount of each species formed was dependent upon ion energy, fluence, and mass. The results of these studies, interpreted in terms of chemical and energy transfer processes, provide key insights into the mechanisms of bias enhanced nucleation.
INTRODUCTION Control of the nucleation density is a critical issue during plasma-assisted chemical vapor deposition (PACVD) of diamond. For growth on clean silicon, nucleation densities are quite low, and values higher than 107 cm- 2 are typically achieved only by resorting to ex-situ substrate 79 46 abrasion 1 -3 or other "seeding" techniques. - Recently, however, Glass and coworkers, reported enhancement of the nucleation density by five orders of magnitude using an in-situ process called bias enhanced nucleation. This technique involves biasing the silicon substrate at -250 eV while it is immersed in the plasma. Their results suggest that C-C species produced early in the growth process are the precursors to diamond nucleation, and they speculate that the increased flux of hydrogen and hydrocarbon ions in the plasma plays a role in the formation of these precursors. Motivated by these results, we have initiated ultrahigh vacuum (UHV) surface studies to investigate the interactions of hydrogen and hydrocarbon ions with silicon and silicon carbide. This paper briefly reviews our previously reported results for hydrogen ion interactions with silicon carbide1 0 and presents new data concerning hydrocarbon ion interactions with Si(100).
EXPERIMENTAL The UHV growth and analysis system used in these studies included facilities for Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). 10,11 The hydrocarbon species used for thin film growth and surface modification were introduced using an effusive
"177 Mat. Res. Soc. Symp. Proc. Vol. 388 0 1995 Materials Research Society
beam gas source. An ion gun was used to supply argon ions for substrate cleaning and hydrogen or hydrocarbon ions for growth and surface modification. Si(100) 2xl surfaces were prepared from n
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