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 depositi on. 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, degr ee of orientation, crystallite size, surface roughness, stress, piezoelectr ic coupling, acoustic velocity, and others. The films have been analyzed wi th Rutherford backscattering spectroscopy, electron spectroscopy for chemic al analysis, x-ray diffraction (XRD), ellipsometry, scanning electron micro scopy, atomic force microscopy, stress measurements, etc. It is found that these properties are sensitive functions of all deposition parameters and t hat there exist optimal deposition conditions under which films of high qua lity are obtained. The films at optimal conditions were analyzed with the f ollowing results: full width half maximum (FWHM) XRD 0.216 degrees, FWHM ro cking curve 1.62 degrees, crystallite size 38 nm, optical index 2.15, surfa ce roughness 31 Angstrom, and stress 400 MPa. Further, to study the electro acoustic properties of the films surface acoustic wave filters were fabrica ted operating at 534 MI-it. The thin film structure consists of AlN/SiO2/Si . The electrodes of the interdigital transducers were made of Al. Examinati on 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].