The characterization of sputtered polycrystalline aluminum nitrideon silicon by surface acoustic wave measurements

摘要

Polycrystalline aluminum nitride films were deposited on Si3nN4 coated (100) silicon substrates by the reactivensputtering method. We have carried out experiments to evaluate theneffect of AlN material parameters on the SAW characteristics. The SAWntransducers were fabricated by forming interdigitated Al electrodes onntop of the AlN films and transmission measurements made over thenfrequency range from 50 MHz to 1.5 GHz. The SAW characteristics werencorrelated with material parameters of crystallite orientation, grainnsize, surface morphology and oxygen concentration. A key materialnparameter affecting the SAW characteristics was found to be thenpreferred degree of crystallite orientation with the c-axis normal tonthe plane of the substrate. The better oriented the AlN grains, thenstronger the SAW response, the higher the SAW phase velocity, and thenlower the insertion and propagation losses over the entire frequencynrange of measurement. Above 500 MHz the propagation losses of the wellnoriented films followed a frequency squared dependence only slightlynhigher than the reported values for the best epitaxial films. Thencoupling factors deduced from the transducer characteristics are in thenupper range of values reported by Tsubouchi for epitaxial AlN filmsndeposited on the basal plane of sapphire. There was a strong correlationnbetween the X-ray diffraction intensity from the (002) planes and thenoxygen content in the films