FUNDAMENTAL GAS PROCESSES FOR THE CVD DIAMOND GROWTH FROM H-2 C2H2/O-2 AND AR/C2H2/O-2 MIXTURES/

Acetylene/oxygen gas mixtures with and without additional H-2 are succ essfully used for diamond deposition experiments using microwave excit ation. The changing gas phase processes are analyzed as function of ox ygen addition using mass (MS) and optical emission spectroscopy (OES). The analysis of these unconventional gas mixtures allows insight into the fundamental processes and in the determination of the essential g as phase species for diamond synthesis. The diamond film quality, howe ver, as judged by Raman spectroscopy is inferior to the conventional H -2/CH4 system. MS and OES data demonstrate that the concentration of C 2H2 (C-2) has to be reduced below a specific level in order to obtain the diamond phase. The reduction of C2H2 species by oxygen is much hig her than that of CH4. Atomic H is for oxygen containing source gases n ot the essential species which determines the phase quality of the dep osited films. For H-2/C2H2/O-2 and Ar/C2H2/O-2 the measured H concentr ation is nearly independent of the oxygen addition. Thermodynamical eq uilibrium calculations suggest that for hydrogen-rich and, with some l imitations, also hydrogen-poor systems (Ar/C2H2/O-2) can be successful ly modeled assuming a gas phase temperature of 1300 K. In order to det ermine the concentration of atomic H a 500 K higher temperature is req uired.