Effects of annealing on the microstructures and mechanical properties of UN/A1N nano-multilayer films prepared by ion-beam assisted deposition

Abstract

High temperature stability of superlattice films of TiN/AlN nano-multilayers was investigated. TiN/AlN multilayers with bilayer periods from 2.9 to 32 nm were prepared on (100) Si wafer by an ion-beam assisted deposition (IBAD) process, alternatively evaporating Ti and Al metals with the bombardment of ions of nitrogen and argon mixed gases. They were annealed at temperatures from 800 to 1100 degreesC under Ar atmosphere using rapid thermal process (RTP). Changes in microstructure and lattice structure were investigated using high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). Hardness of the films both before and after the annealing was measured using nano-indentation. The hardness of films with lambda less than or equal to 3.2 nm was higher than 30 GPa, while those with larger layer thickness were approximately 20 GPa. When annealing the superlattice film, its microstructure remained unchanged at temperatures up to 1000 T. Its hardness was also maintained after annealing. However, annealing above 1100 degreesC modified the microstructure abruptly, which caused the loss of hardness enhancement due to the superlattice formation. (C) 2002 Elsevier Science B.V. All rights reserved.