Effects of sputtering pressure and nitrogen concentration on the preferred orientation of AIN thin films

Aluminium-nitride films were prepared on glass substrates by reactive radio frequency (r.f.) magnetron sputtering in argon/nitrogen gas mixtures containing 25 ~ 75 1/2; nitrogen at substrate temperatures below 150C. It is important to control the crystallographic orientation and the surface morphology of the films with the deposition parameters for surface-acoustic-wave (SAW) devices. The change of crystallographic orientation with the sputtering pressure and the nitrogen concentration was calculated from the texture coefficient of the (0002) plane based on X-ray diffraction (XRD) patterns. It was found that a change of the c-axis from a parallel to a normal orientation, with respect to the substrate surface, occurred with a decrease in the sputtering pressure and an increase in the nitrogen concentration. From observations of the cross-section and the surface morphology, aluminium-nitride films exhibited a columnar structure and the grain size at the film surface increased an increase in the sputtering pressure and with a decrease in the nitrogen concentration.