Ion-assisting magnetron sources: Principles and uses

The design and performance of magnetron sources which provide at the substrate not only the flux of sputtered atoms but also fluxes of electrons and ions from the plasma are described. This energetic particle bombardment (which is directed to the substrate by an unbalanced magnetic field design) can be beneficial, as when it is used to ion assist the growth of the depositing thin film, or deleterious, e.g., by providing extra heating. Applications of unbalanced magnetrons to investigate the technology of magnetron sputtering are described. Ion assistance of the growing film increases the biaxial compressive stress in the growing film due to an atomic peening process. The lattice strain produced by the stress can be measured using x-ray diffraction, and can be used to quantify the degree of ion assistance. Effects studied in films of refractory metals include the increase in stress until plastic flow occurs during growth, changes in preferential orientation, the effectiveness of the different gases Ar and Xe in producing stress, energetic neutral bombardment, and moderation of sputtered atoms. New results are presented here for the temperature dependence of the stress production in molybdenum films. The application of unbalanced magnetrons to industrial deposition processes is discussed.