Crystallographic and morphological characterization of reactively sputtered Ta, Ta-N and Ta-N-O thin films

This paper concentrates on the deposition of Ta, Ta-N and Ta-N-O thin films by r.f. magnetron sputtering in Ar/N-2/O-2 gas mixtures. The film properties and their suitability as diffusion barriers and protective coatings in silicon devices were characterized using four-point probe measurements, Auger electron spectroscopy, Rutherford backscattering, glancing angle X-ray diffractometry, atomic force microscopy and scanning electron microscopy. With the addition of N-2 to the gas mixture a transition from tetragonal Ta to b.c.c.-Ta(N) was detected, leading to the nanocrystalline metastable b.c.c.-Ta(N) phase with approximately 20 at.% interstitially incorporated nitrogen. Increasing the nitro en flow above a critical value, an abrupt transition between metal-sputtering to nitride-sputtering mode was observed, resulting in a sharp increase in the N:Ta atomic ratio slightly above the stoichiometric value for the TaN phase, which was found to exhibit f.c.c. structure. With the addition of oxygen at fixed nitrogen flow the films tend to grow in an amorphous state. Due to the lack of short-circuit diffusion paths, the as-deposited amorphous Ta(N,O) films are considered as excellent candidates for ultra-thin diffusion barriers and protection layers in future Cu-metallized ULSI devices. (C) 1997 Elsevier Science S.A.