Plasma Chemistry and Plasma Processing, Vol. 18, No. 3, 1998 Modeling of H2 and H2 /CH4 Moderate-Pressure Microwave Plasma Used for Diamond Deposition1 K. Hassouni,2 O. Leroy, S. Farhat,2 and A. Gicquel2 Received October 8, 1997; revised December 4, 1997 One-dimensional transport models of moderate-pressure H2 and H2/CH4 plasmas obtained in a diamond deposition microwave reactor are presented. These models describe the plasma as a thermochemically nonequilibrium flow with three different energy modes. The solution of the one-dimensional plasma transport equations enabled the estimation of plasma species concentrations and temperatures on the axis of the reactor. As far as pure H2 plasmas are concerned, results showed that the model predictions of gas and vibration temperatures are in good agreement with experimental measurements. The model also yields a relatively good qualitative prediction of the variations of H-atom mole fraction with the power density absorbed by the plasma. The results obtained for H2/CH4 discharges showed that the model prediction on the variations of H-atom mole fraction with methane percentage in the discharge is in good qualitative agreement with experimental results. They also showed that methane is rapidly converted to acetylene before reaching the discharge zone. The concentrations of neutral hydrocarbon species in the reactor are mainly governed by thermal chemistry. The addition of methane strongly affects the ioniza- tion kinetics of the plasma. Three major ions are generally obtained in H2/CH4 plasmas: C2H2, C 2 H3 , and C2 H5 . The relative predominance of these ions depends on the considered plasma region and on the discharge conditions. The ionic species concentrations are also mainly governed by chemistry, except very near the sub- strate surface. Finally the use of this transport model along with the surface chem- istry model of Goodwin(1) enabled us to estimate the diamond growth rate for several discharge conditions. KEY WORDS: Microwave plasma; diamond deposition; modeling. 1. INTRODUCTION Moderate-pressure H2/CH4 microwave plasmas are now routinely used for the chemical vapor deposition of diamond films. Usually, the deposition process is characterized by a pressure ranging between 20 and 120 torr, an 1invited lecture presented at the 13th International Symposium on Plasma Chemistry, Beijing, PRC, August 18-22, 1997. 2LIMHP, CNRS-UPN, Avenue 3. B. Clement 93430 Villetaneuse, France. 325 0272-4324/98/0900-0325$15.00/0 © 1998 Plenum Publishing Corporation