Influence of oxygen and argon on the crystal quality and piezoelectric response of AlN sputtered thin films

In this work we have investigated the effect of oxygen and argon impurities on the residual stress, crystal structure and piezoelectric response of sputtered AlN thin films for surface acoustic wave applications. The AlN films were deposited on Si (100) wafers by RF sputtering of an Al target in an Ar/N-2 gas mixture. The substrate bias voltage and the pressure were adjusted to obtain films with pure c-axis orientation. The crystal quality and the grain size of the films were assessed by X-ray diffractometry. The Al:N atomic ratio and the Ar content were measured by Rutherford backscattering spectrometry. The oxygen content was determined by an improved particle-induced gamma-ray emission method. Our results indicate that the residual stress is associated with the presence of Ar in the film but not with oxygen contamination. There is also a correlation between the Ar content and the crystal quality The grain size depends on the oxygen contamination, but is also affected by other factors. Finally, the electromechanical coupling factor decreases significantly with oxygen content but is independent of Ar impurities. (C) 2003 Elsevier B.V. All rights reserved.