Characterization of thermal plasma CVD diamond coatings and the intermediate SiC phase
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Z. P. Lu, J. Heberlein, and E. Pfender Department of Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota 55455 (Received 14 January 1991; accepted 28 May 1991)
Diamond films have been successfully deposited by DC thermal plasma jet CVD at a rate of 40 /um/h under atmospheric and subatmospheric pressures. Transmission electron microscopy (TEM) has been used for the characterization of the diamond films and the intermediate phase. The orientation and the distribution of /3-SiC at the interface between the diamond and silicon substrate have been observed using selected-area electron diffraction with the associated dark-field images. X-ray diffraction, scanning electron microscopy, and Raman spectroscopy are used for the characterization of the produced diamond films. Potential applications of selected-area channeling patterns are discussed for investigating the correlations between the growth direction and the crystalline perfection.
I. INTRODUCTION There have been an increasing number of research efforts directed toward producing diamond under thermodynamically metastable conditions.1"4 Numerous processes have been reported over the past decade, including hot filament assisted CVD,5 microwave plasma assisted CVD,6 RF plasma assisted CVD, 7 arc discharge assisted CVD, 8 hollow cathode plasma assisted CVD, 9 and oxygen-acetylene combustion flame assisted CVD. 10 Among the various plasma assisted chemical vapor deposition processes, the majority of the research has been conducted under reduced pressures, i.e., 1-100 Torr. Attempts have been made to synthesize diamond at one atmosphere,5 and recently there have been reports on the thermal plasma synthesis of diamond films.7-11"14 Thermal plasmas are by definition in a state of equilibrium or more precisely in Local Thermodynamic Equilibrium (LTE). The high number densities of species associated with LTE plasmas give rise to high collision frequencies and, as a result, the heavy particles (atoms and ions) have essentially the same temperature as the electrons. If such a plasma is rapidly quenched, chemical reactions will be "frozen", resulting in a strong deviation from chemical equilibrium. As a consequence, the hydrogen ions, atoms, or other radicals, such as CH 3 , which are believed to be responsible for the successful synthesis of diamond, will have a much higher concentration than if they would have been in a corresponding equilibrium state. The higher number density of atomic or ionic hydrogen compared to nonequilibrium plasmas (such as low pressure microwave plasma) enables the use of a much higher methane concentration for the diamond deJ. Mater. Res., Vol. 6, No. 10, Oct 1991
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position without sacrificing the film quality. A methane concentration of 5 - 1 5 % u ' 1 4 is common in thermal plasma diamond deposition while a methane concentration of more than 2% will give a very poor film quality in such processes as microwave plasma assisted CVD and hot filament assisted CVD. The combinat
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