A QUASI-EQUILIBRIUM MODEL FOR THE PREDICTION OF INTERLAYER CHEMISTRY DURING DIAMOND CHEMICAL-VAPOR-DEPOSITION

The chemistry of the intermediate layer that develops at the interface between diamond and a non-diamond substrate during diamond chemical v apor deposition is analyzed using a thermodynamic quasi-equilibrium mo del. Substrates of Si, Mo, W, Ti, Ta, Fe and Ni are examined, and the physical parameters such as substrate temperature, reactor pressure, a nd CH4/H-2 ratio in the gas phase required for the growth of respectiv e metal carbides/solid carbon as intermediate layers between the subst rate and diamond is predicted. The intermediate layers that are consid ered to be formed on Si, Mo, W, Ti, Ta, Fe, and Ni are SiC, Mo2C, WC, TiC, TaC, Fe3C, and Ni3C, respectively, in addition to diamond and gra phite. A quasi-equilibrium treatment of heterogeneous reactions at the gas-substrate interface is used to compute the desorption rates of vo latile species formed in the reaction of gaseous H-2/H with the substr ate. A phase diagram is obtained for the hydrogen and metal carbides/s olid carbon (graphite, diamond). Good qualitative agreement is obtaine d between the model predictions and existing experimental data for the chemistry of the intermediate layer formed on the substrate at variou s temperatures and pressures commonly employed during diamond chemical vapor deposition. (C) 1998 Elsevier Science S.A. All rights reserved.