Abstract
A three-dimensional kinetic Monte Carlo model has been developed to simulate the chemical vapor deposition of a diamond (100) surface under conditions used to grow single-crystal diamond (SCD), microcrystalline diamond (MCD), nanocrystalline diamond (NCD), and ultrananocrystalline diamond (UNCD) films. The model includes adsorption of CHx (x = 0, 3) species, insertion of CHy (y = 0-2) into surface dimer bonds, etching/desorption of both transient adsorbed species and lattice sidewalls, lattice incorporation, and surface migration but not defect formation or renucleation processes. A value of ∼200 kJ mol(-1) for the activation Gibbs energy, ΔG(‡) etch, for etching an adsorbed CHx species reproduces the experimental growth rate accurately. SCD and MCD growths are dominated by migration and step-edge growth, whereas in NCD and UNCD growths, migration is less and species nucleate where they land. Etching of species from the lattice sidewalls has been modelled as a function of geometry and the number of bonded neighbors of each species. Choice of appropriate parameters for the relative decrease in etch rate as a function of number of neighbors allows flat-bottomed etch pits and/or sharp-pointed etch pits to be simulated, which resemble those seen when etching diamond in H2 or O2 atmospheres. Simulation of surface defects using unetchable, immobile species reproduces other observed growth phenomena, such as needles and hillocks. The critical nucleus for new layer growth is 2 adjacent surface carbons, irrespective of the growth regime. We conclude that twinning and formation of multiple grains rather than pristine single-crystals may be a result of misoriented growth islands merging, with each island forming a grain, rather than renucleation caused by an adsorbing defect species.
Highlights
The chemical vapor deposition (CVD) of diamond is well-developed with many existing and potential commercial applications in electronics, mechanical parts/tools, sensors, and optics.1 The CVD process involves a low pressure reactor into which a small amount of a hydrocarbon gas and molecular hydrogen (H2) is introduced
The base set of conditions used in these simulations was those for deposition of standard microcrystalline diamond (MCD) in a hot filament reactor, given in Ref. 20, Table I
It was found that the growth rates and surface roughness are most sensitive to the concentration of CH3 and to the desorption rate constant, because the interplay between these parameters directly affects the rate of adsorption
Summary
The chemical vapor deposition (CVD) of diamond is well-developed with many existing and potential commercial applications in electronics, mechanical parts/tools, sensors, and optics. The CVD process involves a low pressure reactor into which a small amount of a hydrocarbon gas (usually CH4) and molecular hydrogen (H2) is introduced. Hydrocarbon species that adsorb onto this surface are treated as a 1 × 1 × 1 block, which may migrate around the surface in the x and y directions, be etched away, or meet and add to an existing sidewall so propagating the layer of growth This 3D cubic grid model is clearly less realistic than the full 3D diamond structures adopted by Grujicic and Lai and Netto and Frenklach in their previous KMC simulations. B. Etching/desorption of surface species In previous models of etching, the rate constant, ketch, for etching isolated adspecies was initially considered to adopt a value based on an Arrhenius law with a pre-exponential factor equivalent to the collision frequency (assumed to be ∼1013 s−1) and activation barrier, ∆G‡etch, equivalent to the C–C bond energy (348 kJ mol−1).
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