Growth of diamond films and characterization by Raman, scanning electron microscopy, and x-ray photoelectron spectroscop
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A. R. Chourasia and D. R. Chopra Department of Physics, East Texas State University, Commerce, Texas 75428
K. K. Mishra Department of Chemistry, The University of Texas at Arlington, Arlington, Texas 76019 (Received 11 April 1990; accepted 9 August 1990) We have deposited diamond films on Si(lll) using hot filament assisted chemical vapor deposition at low pressures —25 Torr. Diamond films deposited at different relative concentrations of methane (ranging from 0.25% to 2.0%) in methane-hydrogen mixtures have been characterized by Raman spectroscopy, scanning electron microscopy, and x-ray photoelectron spectroscopy. With varying methane concentration, Raman spectra show features characteristic of crystalline diamond, diamond-like carbon, and polycrystalline graphite. Scanning electron micrographs show densely packed diamond crystallites. SEM measurements made on diamond films grown as a function of time show that the median grain size of the diamond crystallites increases linearly with time during the initial phase of the growth. X-ray photoelectron spectroscopy reveals differences between the diamond sp3 covalent bonding and sp2 graphitic bonding as well as the extent of s-p hybridization as a function of methane concentration. The plasmon loss shoulder, characteristic of graphite, is absent from the spectrum of 0.25% methane concentration film. But it appears in the XPS spectra of films grown at higher concentrations.
I. INTRODUCTION
The vapor-phase growth of diamond and "diamond-like" carbon (DLC) films and their characterization have generated increasing interest in the scientific community in recent years.1"7 Such a rapid increase in this area of research is obviously due to the potential industrial applications of diamond films which include their use as diffusion barriers for semiconductor products and coatings for optical components and mechanical parts because of their hardness, optical transparency, chemical inertness, high electrical resistivity, thermal conductivity, and dielectric strength. Frequently used deposition techniques utilize (1) low energy carbon ion beams that are guided electrostatically to a substrate.2 This technique provides contaminant-free films by maintaining high vacuum under differentially pumped conditions and by utilizing mass separation of the ionic species. The instrumentation is, however, elaborate and expensive; (2) chemical vapor deposition (CVD) in which the hydrocarbon radicals are produced by thermal decomposition of hydrocarbon
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J. Mater. Res., Vol. 5, No. 11, Nov 1990
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gases with a carefully treated hot filament8'9; (3) microwave plasma enhanced CVD10 in which the microwave power is used to produce hydrocarbon radicals etc.; and (4) laser-induced discharge of carbon ions in which the carbon ions are produced by an intense laser beam incident on graphite.1112 These basic techniques and the properties of some of the films deposited by using different methods have been
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