Sub-microstructure and surface topography of reactive unbalanced magnetron sputtered titanium and titanium compound thin films

Abstract

Physical vapour deposition techniques (PVD) are non-equilibrium processes that often produce non-equilibrium microstructures. Nucleation occurs at many sites in close proximity over the substrate surface and is similar to electro deposition within an electrolyte in this respect. Thin film growth advances from the substrate to form a dense columnar structure with a growth direction parallel to the flux of incident energetic particles. Growth is usually along one of the preferred close packed crystal directions and results in a high degree of crystallographic texture within the deposit. In this study, titanium was sputtered with different nitrogen flow rates to vary the film composition from Ti to stoichiometric TiN. The thin films were grown at different DC pulse frequencies ranging between 100 kHz and 350 KHz using an Advanced Energy Pinnacle Plus power supply. For comparison purposes, films were also grown in DC mode. Electron microscopy revealed that TiN and titanium metal grow as individual crystallites within sub stoichiometric TiN. Furthermore the growth direction of these crystallites was found to be influenced by deposition conditions. It was also found that the growth direction alters radically for cylindrical substrates rotated in front of a titanium cathode target.