Indentation-induced intercolumnar shearing in AlN thin films grown on Si(111) substrate

The interrelations between microstructure and deformation behaviors induced by using nanoindentation in AlN thin films deposited on Si(111) substrates are investigated with a Berkovich indenter in this study. The AlN thin films prepared by helicon sputtering are having apparent columnar grain structure (∼20–40 nm in diameter) with thickness of about 350 nm. The cross-sectional transmission electron microscopy (XTEM) observations performed on Berkovich nanoindentation-induced deformation region revealed evidence of cracks resulted from intercolumnar shearing in AlN thin film. Moreover, sharp shearing-induced steps at the film/substrate interface were observed, which was found to intimately correlate with the multiple pop-ins phenomena appearing in the loading part of load-displacement curve. The XTEM results also indicated that, within the Si(111) substrate, in addition to the slip bands appearing on {111} planes, there exists a nanoindentation-induced phase transformation zone containing the metastable phases of Si-III and Si-XII, accompanying with substantial amorphous regions. An indentation-energy model based on the shearing crack driving deformation is proposed to evaluate the intercolumnar shear stress for AlN thin film.