High energy ion characterization of sputtered AlN thin films

Polycrystalline aluminum nitride (AlN) is a piezoelectric material widely used in surface acoustic wave devices. The optimal films have to be (0 0 2) oriented and with a grain size as high as possible. It has been reported that the presence of impurities is directly related with the crystalline properties of the films. In this communication, we present a study of the high energy ion characterization of sputtered AlN thin films. Films are deposited by RF reactive sputtering of a metallic aluminum target in Ar/N, admixtures. The analysis were carried out using the 3 MV Tandem accelerator of the CNA. Rutherford backscattering spectroscopy, nuclear reaction analysis and particle induced gamma-ray emission (PIGE) were used to determine the composition of the films, which was found to be mainly the stoichiometric one, [Al] = [N]. The influence of the substrate bias voltage and the total sputtering pressure in the concentration of impurities in the films is analyzed. Argon content up to 1.6% has been measured being higher as bias voltage is increased. Oxygen concentration below 1% could be detected by PIGE measurements. Problems associated with the determination of small amounts of oxygen in this kind of samples, where the presence of other light elements like N, Al and Si may interfere with the analysis of O-16, are discussed. (C) 2002 Elsevier Science B.V. All rights reserved.