EFFECT OF THE SUBSTRATE BIAS VOLTAGE ON THE CRYSTALLOGRAPHIC ORIENTATION OF REACTIVELY SPUTTERED ALN THIN-FILMS

Aluminum nitride (AIN) films have been deposited on negatively biased Si(100) wafers by reactive r.f. magnetron sputtering in a mixed Ar-N2 discharge. It is important to control the crystallographic orientation and the physical properties of the films with deposition parameters for the surface acoustic wave device application. The change in crystallographic orientation with the negative bias voltage has been evaluated from the calculation of the texture coefficient (TC) based on X-ray diffraction patterns. It is found that the TC of the (0002) plane is increased with increase in the bias voltage. With increase in the bias voltage, the compressive stress in the films is gradually relaxed and the column diameter in the films is slowly increased. A possible explanation for the above results is that, as the bias voltage increases, the adatom mobility at growing film surface is enhanced owing to the increase in the kinetic energy and the flux of bombarding positive ions. From the analysis of the plasma, the dominant positive ions in plasma are N2+ ions responsible for the change in the crystallographic orientation of the films with the bias voltage.