Simulations of CVD Diamond Film Growth Using a Simplified Monte Carlo Model
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1203-J16-02
Simulations of CVD Diamond Film Growth Using a Simplified Monte Carlo Model Paul W. May1, Jeremy N. Harvey1, Neil L. Allan1, James C. Richley1 and Yuri M. Mankelevich2 1
School of Chemistry, University of Bristol, Bristol BS8 1TS, United Kingdom.
2
Skobel’tsyn Institute of Nuclear Physics, Moscow State University, Vorob’evy gory, Moscow
119991, Russia. ABSTRACT A simple 1-dimensional kinetic Monte Carlo (KMC) model has been developed to simulate the chemical vapour deposition (CVD) of a diamond (100) surface. The model considers adsorption, etching/desorption, lattice incorporation, and surface migration along and across the dimer rows. The reaction probabilities for these processes are re-evaluated in detail and their effects upon the predicted growth rates and morphology are described. We find that for standard CVD diamond conditions, etching of carbon species from the growing surface is negligible. Surface migration occurs rapidly, but is mostly limited to CH2 species oscillating rapidly back and forth between two adjacent radical sites. Despite the average number of migration hops being in the thousands, the average surface diffusion length for a surface species before it either adds to the diamond lattice or is removed back to the gas phase is 700°C) allows migration of the adsorbed C species until they meet a step-edge and
add to the diamond lattice. Another role for the atomic H is to etch back into the gas phase any adsorbed carbon groups that have deposited as non-diamond phases. It is believed that hydrocarbons CxHy with 2 or more carbons (x ≥2) are prevented from contributing to the growth by the ‘β-scission’ reaction which is a rapid, low energy, efficient process that stops the build up of polymer chains on the growing surface. Diamond growth is therefore seen as competition between etching and deposition, with carbons being added to the diamond on an atom-by-atom basis. Our group recently developed a modified version of the standard growth model which considers the effects of all the C1 hydrocarbon radicals (CH3, CH2, CH and C atoms) on both monoradical and biradical sites on a (100) diamond surface [6]. Our growth model also relies upon surface migration of CH2 groups along and across the reconstructed dimer rows in order to predict growth rates to within a factor of two of experimental observations. Using the model we derived expressions for the fraction of surface radical sites based upon the substrate temperature, Ts, and the concentrations of H and H2 above the surface. Under typical CVD diamond conditions with Ts~900°C and 1%CH4/H2 around 10% of the surface carbon atoms support radical sites. Despite these successes, evidence for surface migration, nucleation processes, the effects of gas impurities and gas-surface reactions are sparse and mostly circumstantial. To investigate these ideas we developed a simplified one-dimensional Monte Carlo (MC) model of the growth of diamond films [7] for a fixed set of process conditions and substrate temperature. Although the model was only
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