Influence of deposition parameters on the coalescence stage of growth of metal films

Abstract

Growth of vapor-deposited films by coalescence processes in the post-nucleation stage is discussed. It is shown that increasing values of the parameters of rate of deposition, rate of evaporation from the vapor source, substrate temperature, and angle-of-incidence of vapors should produce increasing agglomeration (that is, islands smaller in number but larger in size), characteristic of high surface mobility. These predictions have been verified by the electrical and electron microscope studies on gold and silver films prepared under controlled conditions of rate of evaporation and rate of deposition. The critical thickness t_c at which films become electrically continuous increases with increasing agglomeration. An exponential dependence of t_c on the inverse of the reciprocal of substrate temperature yields two activation energies of 0.26 and 0.85 eV. The smaller activation energy obtained for temperatures below 450°K may be ascribed to thermal diffusion of adatoms, while the higher value is tentatively proposed to be due to the diffusion of subcritical nuclei resulting from thermal motion as well as the momentum transfer from the impinging energetic vapor. Oblique deposition enhances agglomeration. The growth and distribution of islands is found to be isotropic in the plane of the film for angles of incidence of up to 80°. Anisotropic (columnar) growth in the direction of the incident vapor occurs due to self-shadowing only after the film becomes physically continuous.