On the role of the energetic species in TiN thin film growth by reactive deep oscillation magnetron sputtering in Ar/N-2

The properties of TiN films deposited by direct current magnetron sputtering strongly depends on the composition of the discharge since the N-2 fraction is the main deposition parameter controlling the poisoning of the target and, thus, the flux and energy of the species bombarding the growing films. Accordingly, the properties of the films are also intimately linked to the N-2 fraction. In this work TiN films were deposited by deep oscillation magnetron sputtering, a variant of high power impulse magnetron sputtering, with increasing N-2 content in the discharge gas. The TiN films deposited under relatively low intensity bombardment conditions have surface chemistry processes that favour the formation of [111] preferential orientation. On the contrary, the TiN films deposited at N-2 fraction of 11% and above are grown under heavy bombardment by the plasma species and are less crystalline than at lower N-2 fraction, have high compressive stresses and their grain size decreases. The increased bombardment of the films with increasing N-2 fraction was attributed to changes of N species energy flux as corroborated by the ion energy distributions. The evolution of the films properties was accounted for by assuming that the energetic metallic and monoatomic nitrogen species interact with the growing film through different mechanisms and thus they have differentiated effects on the films properties. The structural properties of the films are mainly influenced by the bombardment by energetic N species while the microstructure of the films and their hardness mainly depends on the bombardment by energetic Ti species. The different roles of the energetic metallic and monoatomic nitrogen species in the growth process of TiN films implies that proper control and balance of the two types of bombardment are mandatory in order to optimize the properties of the TiN for the targeted application.