Nanoindentation investigation of Ti/TiN multilayers films

The hardness of Ti/TiN nanolaminated films is investigated in this study. Monolithic Ti and TiN films and Ti/TiN multilayers were deposited on silicon substrates by radio-frequency sputtering. The period thickness of multilayers was decreased from 20 to 2.5 nm. Grazing x-ray reflectometry showed that the modulation of composition of Ti/TiN multilayers exists for all the period thickness considered. From nanoindentation measurements, we determined the hardness and Young’s modulus of multilayers. Hardness increased with decreasing period thickness to go beyond the rule-of-mixture value for samples with period thickness of $\text{Λ⩽5}$ nm. The maximum hardness, 1.6 times higher than the value obtained by the rule of mixture, is obtained for $\text{Λ=2.5}$ nm. Our results are compared to a dislocation-based model previously introduced by Lehoczky.