Role of kinetic energy of sputtered particles in thin film formation

Abstract

Dynamic processes of thin film growth by the sputter deposition method have been studied with special emphasis on the effects of the kinetic energies of sputtered particles on thin film properties. Regardless of the thin film preparation method, the thin film process is comprised of three elementary stages: decomposition, transport, and nucleation and growth mechanisms. During the decomposition stage, starting materials in the form of a gas, liquid or solid are decomposed into various fragments of neutrals or ions in the form of atoms, molecules, clusters or powders by external powers of plasma, laser, ion, microwave and thermal energies. The fragments thus formed have various kinetic energies depending on the decomposition mechanism. During sputter deposition, the primary ions with kinetic energies more than several hundred electron volts formed in a plasma bombarded the targets surface, giving rise to secondary sputtered particles with kinetic energies of 10–20 eV. This dynamic process of energy transfer from primary ions to the target was analyzed in detail by the precise measurement of kinetic energies of the sputtered particles. The particles formed by sputtering will travel through the media of sputtering gas and approach the substrate. This phase is referred to as the transport stage of the thin film process. Monte Carlo simulations are helpful in understanding the dynamic energy transport mechanisms. Finally, the chemical reaction between the fragments and the transport gas or adsorbed molecules on the substrate is also important in obtaining superior thin film properties. Consequently, it has become possible to control the thin film microstructure using the kinetic energies of the sputtered particles. Practical applications of high quality electrical films such as SiO 2 and NiSiB are real evidence for the sophisticated thin film technology of sputtering.