Indashsitu X-ray reflectivity investigation of growth and surface morphology evolution during Fe chemical vapor deposition on Si(001)

Abstract

We used in situ X-ray reflectivity (XRR) to study the kinetics and structural evolution in the early stages of Fe deposition from the thermal decomposition of Fe(CO) 5 in the temperature range 90–220°C. We simultaneously measured the polycrystalline Fe film thicknesss (extending up to 60 Å thick films) as well as the Fe surface roughness and Fe Si interface width as a function of exposure. From the thickness measurements, we were able to separate the nucleation and growth 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 growth representing Fe deposition on Fe. The incubation period decreased with increasing temperature. Using a modified version of classical nucleation theory to model the evolution of film thickness for the initial stages of film growth, we found a difference in the activation energies 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 nucleation at higher temperatures. The evolution of the roughness is in agreement with a simple model of nucleation and coalescence of three-dimensional islands. The large difference in activation energies for nucleation and growth is responsible for the behavior of both the time dependence of the deposition rate and morphology evolution. A relatively narrow Fe Si interface width indicates that very little intermixing occurs in this temperature regime.