IN-SITU X-RAY REFLECTIVITY INVESTIGATION OF GROWTH AND SURFACE-MORPHOLOGY EVOLUTION DURING FE CHEMICAL-VAPOR-DEPOSITION ON SI(001)

We used in situ X-ray reflectivity (XRR) to study the kinetics and str uctural evolution in the early stages of Fe deposition from the therma l decomposition of Fe(CO)(5) in the temperature range 90-220 degrees C . We simultaneously measured the polycrystalline Fe film thicknesss (e xtending up to 60 Angstrom thick films) as well as the Fe surface roug hness and Fe/Si interface width as a function of exposure, From the th ickness measurements, we were able to separate the nucleation and grow th regimes and find direct evidence for an autocatalytic growth effect : an induction period indicative of the rate-limiting nucleation of Fe islands on the Si(001) substrate followed by a linear increase in gro wth representing Fe deposition on Fe. The incubation period decreased with increasing temperature. Using a modified version of classical nuc leation theory to model the evolution of film thickness for the initia l stages of film growth, we found a difference in the activation energ ies for the thermal decomposition of the Fe(CO)(5) precursor on Si(001 ) and Fe, 0.78+/-0.09 eV and 0.20+/-0.02 eV, respectively. The surface roughness decreased with increasing temperature due to enhanced nucle ation at higher temperatures. The evolution of the roughness is in agr eement with a simple model of nucleation and coalescence of three-dime nsional islands. The large difference in activation energies for nucle ation and growth is responsible for the behavior of both the time depe ndence of the deposition rate and morphology evolution. A relatively n arrow Fe/Si interface width indicates that very little intermixing occ urs in this temperature regime. (C) 1997 Elsevier Science B.V.