THE CHARACTERIZATION OF SPUTTERED POLYCRYSTALLINE ALUMINUM NITRIDE ONSILICON BY SURFACE-ACOUSTIC-WAVE MEASUREMENTS

Polycrystalline aluminum nitride films were deposited on Si3N4 coated (100) silicon substrates by the reactive sputtering method. We have ca rried out experiments to evaluate the effect of ALN material parameter s on the SAW characteristics. The SAW transducers were fabricated by f orming interdigitated Al electrodes on top of the AlN films and transm ission measurements made over the frequency range from 50 MHz to 1.5 G Hz. The SAW characteristics were correlated with material parameters o f crystallite orientation, grain size, surface morphology and oxygen c oncentration. A key material parameter affecting the SAW characteristi cs was found to be the preferred degree of crystallite orientation wit h the c-axis normal to the plane of the substrate. The better oriented the AlN grains, the stronger the SAW response, the higher the SAW pha se velocity, and the lower the insertion and propagation losses over t he entire frequency range of measurement. Above 500 MHz the propagatio n losses of the well oriented films followed a frequency squared depen dence only slightly higher than the reported values for the best epita xial films. The coupling factors deduced from the transducer character istics are in the upper range of values reported by Tsubouchi for epit axial AlN films deposited on the basal plane of sapphire. There was a strong correlation between the x-ray diffraction intensity from the (0 02) planes and the oxygen content in the films.