Nucleation and stress generation in thin films deposited with a pulsed energetic deposition flux

Abstract: This thesis presents fundamental mechanisms of nucleation and early growth of and stress generation in thin polycrystalline metal films deposited using pulsed energetic deposition fluxes. The effects of a pulsed deposition flux and energetic bombardment on film nucleation was investigated using in situ stress measurements and in situ ellipsometry to determine the film thickness at which the films become continuous. Ag films where deposited using high power impulse magnetron sputtering (HiPIMS) in two series - one with constant low pulse power to minimize energetic bombardment while varying the pulse frequency and one with a constant pulse frequency while varying the pulse power, resulting in different amounts of energetic bombardment and different deposition rates - to separate the effects of a pulsed deposition flux and energetic bombardment. The thickness at which the film becomes continuous was found to decrease both with increasing pulse frequency and increasing pulse power. The effects of the increased energetic bombardment and deposition rate cannot be separated due to their coupling. Adatom lifetimes and the coalescence times for islands where calculated for different coverages and island sizes and compared to the time between pulses. It was found that the time between pulses was lower than the adatom lifetimes for certain conditions; this leads to an increase in the adatom density and therefore an increase of the nucleation density resulting in smaller thicknesses for the formation of continuous film. It was also found that the coalescence time for clusters becomes longer than the time between pulses, retarding the coalescence process; this leads to formation of long lived elongated clusters also resulting in a decrease of the thickness at which the films become continuous.Energetic bombardment during growth of Mo films using HiPIMS is found to result in large compressive stresses without the commonly observed defect induced associated lattice expansion seen when depositing films using energetic bombardment. This and a correlation between the magnitude of the compressive stress and the film density allow us to conclude that the compressive stress is generated by grain boundary densification. Two mechanisms leading to grain boundary densification and thus generation of compressive stresses are proposed.