STRUCTURE AND COMPOSITION OF ALN FILMS PREPARED BY RF REACTIVE SPUTTERING

III-V compound of AlN with good thermal and chemical stability shows good thermal conductivity and high electrical resistivity. Thus AlN films can be a useful material in electrical and optical applications. The purpose of this work is to study the dependence of deposition conditions on the crystallographic structure and the composition of rf reactive sputtered AlNx films. AlNx films were deposited onto slide glasses at room temperature by rf sputtering of pure Al disk (70 mm in diameter) with Ar + N2 mixed gas. The total gas pressure was kept at 0.4 Pa through out this work. The N2 partial pressure-to-total pressure ratio in the sputtering gas, P(N2)/P(total), was changed from 0.0 to 1.O. The structure and the composition of films were characterized by X-ray diffractometry and Auger electron spectroscopy, respectively. The deposition rate decreased gradually with increasing P(N2)/P(total), and decreased drastically when P(N2)/P(total) increased above a threshold value. This threshold value of P(N2)/P(total) was about 0.5 at rf power of 300 W, and decreased with decreasing the applied rf power. It is shown that the films prepared at above the threshold value were transparent and have an AlN single phase. The film prepared nearly at the threshold value has a highly distorted AlN structure. Quadrupole mass analysis of exhaust gas showed that N2 molecules scarcely existed below the threshold value. The spectroscopic measurement of glow discharge plasma during sputtering suggested that N2+ species might have an important role in the deposition of AlN single phase films.