Crystal interface-enhanced thermal stability of CrAlN/SiNx multilayer films

Abstract

The phase structure, residual stress, and thermal stability of CrAlN/SiNx multilayer films with different phase structures of a SiNx sublayer were studied. The crystal SiNx sublayer was transformed into an amorphous structure as the layer thickness increased from 0 to 1.7 nm. Multilayer films exhibited higher compressive residual stress and hardness than the monolithic CrAlN film, and the film with a 0.9 nm nanocrystalline-SiNx sublayer exhibited the highest value of −5.9 ± 0.2 GPa and 37.9 ± 2.5 GPa respectively. Phase transition was not detected in the nanocrystalline multilayer films, and the sublayer remained intact after vacuum annealing at 900 °C for 1 h. However, sublayer interface thermal dissolution in the film with a 1.7 nm amorphous SiNx sublayer resulted in a pitch-off effect at the grain boundary and the formation of w-AlN under the same condition. There was a slight decrease of hardness in all films after annealing and the film with a 0.9 nm nanocrystalline-SiNx sublayer still exhibited the highest hardness of 36.7 ± 3.7 GPa. Therefore, CrAlN/SiNx multilayer films with a crystalline interface are excellent candidates for achieving high thermal stability.