Substrate composition effects on the interfacial fracture of tantalum nitride films

In this study we combined nanoscratch testing with a multilayer sapphire and aluminum nitride single-substrate system to determine the effects of interface composition and structure on susceptibility to fracture of hard, thin tantalum nitride films. Nanoindentation tests showed that the elastic moduli of the tantalum nitride and aluminum nitride films, as well as the sapphire substrate, were essentially equal at 400 GPa. On both portions of the substrate, these tests also showed that near surface hardness was near 35 GPa. Nanoscratch tests triggered long blisters and circular spalls on both the sapphire and aluminum nitride portions of the substrate. The blisters showed that the tantalum nitride film was subjected to a compressive residual stress of −6.7 GPa. The spalls showed that failure occurred along the tantalum nitride film-substrate interface regardless of substrate composition. Most importantly, the blisters and spalls showed that the mode I componentof the fracture energies was essentially equal on both substrate materials at a value near 3.1 J/m². These energies are on the order of the energies for metallic bonding.