Film thickness effects on the fracture of tantalum nitride on aluminum nitride thin film systems
In this study, nanoindentation and nanoscratch testing were combined with transmission electron microscopy to establish the relationship between structure, properties, and fracture resistance of thin tantalum nitride resistor films on aluminum nitride substrates. The films were sputter-deposited to thicknesses of 160, 440, and 500 nm. Nanoindentation was used to determine mechanical properties while nanoscratch tests were used to measure interfacial fracture energies. These tests showed that the measured elastic moduli of all films were independent of indenter depth and approximately equal to the value measured for the aluminum nitride substrates. They also showed that measured hardness values increased with film thickness. More importantly, the fracture energies measured in indentation fracture and nanoscratch tests were essentially equal and independent of film thickness. These results showed that tantalum nitride films and aluminum nitride substrates behaved in an inherently brittle manner. They further showed that fracture was localized along the interface suggesting that adhesion was controlled by the nature of bonding across the interface plane.
Fig. 1. The substrates consist of (a) aluminum nitride and yttrium oxide phases (white grains). Some aluminum nitride grains exhibited a (b) roughening of their surface which served as nucleation sites for a pronounced columnar grain structure in overlying regions of the tantalum nitride film.
Source: Engineering Fracture Mechanics