INFLUENCES OF DEPOSITION PARAMETERS ON THE CRYSTALLOGRAPHIC ORIENTATION OF REACTIVELY SPUTTERED ALUMINUM NITRIDE THIN-FILMS

Aluminum nitride (AlN) thin films were fabricated on silicon and glass substrates by reactive RF magnetron sputtering in Ar-N2 gas mixtures without substrate heating. It is essential to control the c-axis orien tation of AlN films with deposition parameters for the applications of surface acoustic wave devices, since the piezoelectric properties are strongly dependent upon the crystallographic orientation of AlN film. The influences of sputtering pressure and nitrogen concentration on t he crystallographic orientation are investigated employing X-ray diffr action (XRD), stress measurement and plasma analysis. It is found that the c-axis orientation of deposited film changes from parallel to per pendicular with respect to the substrate surface, as sputtering pressu re decreases and nitrogen concentration increases. The magnitude of co mpressive stress increases with the decrease of sputtering pressure. T he principal effect of decreasing sputtering pressure, therefore, is t he enhancement of mean free path and adatomic mobility at the film sur face. In addition, the cause of high c-axis orientation with the incre ase of nitrogen concentration may be attributed to the increase of N2 and N2+ ions in the plasma, through the plasma analysis.