Growth and properties of sputtered highly (100)-oriented oxygenated AlN thin films for SAW sensing applications

A method for growth of highly (100)-oriented aluminum nitride (AlN) thin films on (100) Si substrate, in poor vacuum systems, by radio frequency magnetron sputtering was developed. This method allows prediction for near ideal deposition conditions in which high quality films with good stoichiometry Al/N (≈1:1) and low oxygen concentration (< 10%) are produced. During the depositions, the substrate was fed by floating potential. The temperature, the nitrogen flow, RF power and sputtering pressure were fixed, whereas the target-substrate distance and the deposition time were varied. Rutherford backscattering spectroscopy (RBS) measurements estimated film thicknesses of 170 nm, 255 nm, and 480 nm and the amount of oxygen incorporated of 43.32%, 29.80%, and 24.67%, respectively. XRD analysis revealed that films grown with substrate placed near the region of the cathodic sheath are amorphous. However, the other three samples exhibited good crystallinity and orientation (100). Surface properties of the films have been also examined by Fourier transform infrared and Raman spectroscopy. Overall, the characteristics of the obtained highly (100)-oriented AlN films evidence their potential to fabricate surface acoustic wave (SAW) sensing devices.