Synthesis of highly oriented piezoelectric AlN films by reactive sputter deposition

Nucleation and growth of polycrystalline AlN films on thermal and chemical vapor deposited oxide have been studied during rf reactive sputter deposition. The influence of the growth conditions, namely deposition pressure, rf power, Ar/N-2 ratio, and substrate temperature, on film properties has been systematically studied. The properties of interest are crystallinity, degree of orientation, crystallite size, surface roughness, stress, piezoelectric coupling, acoustic velocity, and others. The films have been analyzed with Rutherford backscattering spectroscopy, electron spectroscopy for chemical analysis, x-ray diffraction (XRD), ellipsometry, scanning electron microscopy, atomic force microscopy, stress measurements, etc. It is found that these properties are sensitive functions of all deposition parameters and that there exist optimal deposition conditions under which films of high quality are obtained. The films at optimal conditions were analyzed with the following results: full width half maximum (FWHM) XRD 0.216 degrees, FWHM rocking curve 1.62 degrees, crystallite size 38 nm, optical index 2.15, surface roughness 31 Angstrom, and stress 400 MPa. Further, to study the electroacoustic properties of the films surface acoustic wave filters were fabricated operating at 534 MI-it. The thin film structure consists of AlN/SiO2/Si. The electrodes of the interdigital transducers were made of Al. Examination of the frequency response indicated an acoustic velocity of 4900 m/s and a moderate coupling coefficient. (C) 2000 American Vacuum Society. [S0734-2101(00)09804-3].