Annealing effects of tantalum thin films sputtered on [001] silicon substrate

Tantalum is an important barrier material for copper metalization in integr ated-circuit fabrication. A nano-structured tantalum film of 550 nm thickne ss was grown on [001] Si substrate. This Ta/Si system was then annealed fro m 500 degreesC to 750 degreesC under various vacuum conditions. Tbe phases and microstructures of the as-deposited and annealed films were analyzed by grazing incident angle (3 degrees) X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The interface of tantalum and substrate was ana lyzed by secondary-ion mass spectrometry (SIMS). The inter-diffusion behavi or happened at the Ta/Si interface when annealed at a temperature lower tha n 600 degreesC, and the tetragonal Ta5Si3 was formed after annealing at 750 degreesC. In addition, Ta surface oxidation has been detected after anneal ing in a vacuum as low as 2 X 10(-4) Torr. The increase of oxygen content i n Ta films caused higher compressive stress and resulted in film peeling fr om the substrate. The residual oxygen in vacuum may build up stress in Ta t hin films during thermal processes, which can cause major reliability probl ems in electronic and X-ray optics applications. (C) 2001 Elsevier Science B.V. All rights reserved.