ANALYSIS OF THE GROWTH-PROCESSES OF PLASMA-ENHANCED CHEMICAL-VAPOR-DEPOSITED DIAMOND FILMS FROM CO H-2 AND CH4/H-2 MIXTURES USING REAL-TIMESPECTROELLIPSOMETRY/

Real-time spectroscopic ellipsometry (RTSE) has been applied to study the growth of nanocrystalline diamond thin films by microwave plasma-e nhanced chemical vapor deposition on silicon substrates. The goal of t his research is to characterize the diamond film growth process as a f unction of the gas source and substrate temperature, comparing the res ults obtained using various mixtures of CO and H-2 With those Obtained from a standard mixture of CH4 highly diluted in H-2. The capabilitie s of RTSE have been exploited to establish the true near-surface subst rate temperature under the specific diamond film growth conditions, as well as the deposition rates for a succession of films prepared on th e same substrate under different conditions. The latter capability all ows large regions of parameter space to be scanned expeditiously. As a result of this study, a low-temperature growth process has been ident ified that yields high deposition rates (up to 2.5 mu m/h) at relative ly low microwave plasma powers (0.5 kW). In contrast to the commonly-u sed H-2-rich mixtures of CH4 or CO and H-2 that exhibit monotonic redu ctions in the growth rate with decreasing substrate temperature from 8 00 to 400 degrees C, CO-rich mixtures of CO and H-2 exhibit an increas e and a well-defined maximum as the temperature is reduced over this r ange. At a CO/H-2 gas flow ratio of 18, for example, the growth rate p eaks near 450 degrees C and is a factor of similar to 20 higher than t hat obtained with the standard H-2-rich mixtures of CH4/H-2 and CO/H-2 . These observations suggest a different diamond growth mechanism from the CO-rich mixtures of CO/H-2 with potentially important application s for low-temperature substrate materials. (C) 1997 American Vacuum So ciety.