Plasma-chemical processes in microwave plasma-enhanced chemical vapor deposition reactors operating with C/H/Ar gas mixtures

Microwave (MW) plasma-enhanced chemical vapor deposition (PECVD) reactors are widely used for growing diamond films with grain sizes spanning the range from nanometers through microns to millimeters. This paper presents a detailed description of a two-dimensional model of the plasma-chemical activation, transport, and deposition processes occurring in MW activated H/C/Ar mixtures, focusing particularly on the following base conditions: 4.4%CH(4)/7%Ar/balance H(2), pressure p=150 Torr, and input power P=1.5 kW. The model results are verified and compared with a range of complementary experimental data in the companion papers. These comparators include measured (by cavity ring down spectroscopy) C(2)(a), CH(X), and H (n=2) column densities and C(2)(a) rotational temperatures, and infrared (quantum cascade laser) measurements of C(2)H(2) and CH(4) column densities under a wide range of process conditions. The model allows identification of spatially distinct regions within the reactor that support net CH(4)-> C(2)H(2) and C(2)H(2)-> CH(4) conversions, and provide a detailed mechanistic picture of the plasma-chemical transformations occurring both in the hot plasma and in the outer regions. Semianalytical expressions for estimating relative concentrations of the various C(1)H(x) species under typical MW PECVD conditions are presented, which support the consensus view regarding the dominant role of CH(3) radicals in diamond growth under such conditions. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3035850]