Ion beam synthesis of aluminium nitride: characterisation of thin AIN layers formed in microelectronics aluminium

Abstract

Buried AlN thin layers have been formed by high dose N⁺ ion implantation into microelectronics grade Al films (containing 1 at.-%Si), which were deposited on Si wafers. The structures obtained have been characterised by spreading resistance measurements, transmission electron microscopy, secondary ion mass spectrometry, X-ray diffraction, and X-ray photoelectron spectroscopy. The results show the formation of buried dielectric precipitates of crystalline AlN at implantation doses below the threshold and a continuous polycrystalline AlN layer at doses above the threshold. The AlN grains have the wurtzite structure, sizes of about 10–15 nm, and a preferred orientation in relation to the Al matrix, namely, <110>_AIN parallel to <110>_Al. The data also show that, under certain conditions, the main impurities (Si and O) are gettered in the buried layer. Moreover, for thin Al films, the formation of a Si rich surface layer is observed. This surface layer is formed by Si diffusion from the substrate, probably due to the penetration of N⁺ ions into the Si substrate. The distribution and evolution of these impurities and the different phases formed are studied as a function of the thickness and grain size of the Al film, as well as of the annealing processes.

MST/3304