EFFECT OF REACTANT DEPLETION ON THE MICROSTRUCTURE AND PREFERRED ORIENTATION OF POLYCRYSTALLINE SIC FILMS BY CHEMICAL-VAPOR-DEPOSITION

Polycrystalline SiC films were deposited on graphite substrates from the gaseous mixture of CH3SiCl3 and H-2 at temperatures ranging from 1273 to 1673 K by low-pressure chemical vapor deposition. Variations of deposition rate, surface morphology and preferred orientation of the films with temperature and depletion of reactants (distance from inlet in the isothermal zone of the reactor) have been studied. The deposition had two growth kinetics evidently. The first is controlled by surface reaction for 1273-1473 K and the second by mass transport for 1523-1673 K. For each growth region, depletion of reactants is correlated to the decrease of the deposition rate and for the surface reaction region to the decrease of the activation energy. The change of the surface morphology of the films with depletion is shown by scanning electron microscopy. From X-ray diffraction experiments, it is concluded that the growth direction of the SiC films is always [111] for the surface reaction control but changes from [220] to [111] with depletion of the reactants for the mass transport control.