FCC tantalum thin films deposited by magnetron sputtering

Tantalum (Ta) exists in body-centered cubic (alpha phase), tetragonal (beta phase), and face-centered cubic (fcc) crystal structures. The beta phase is a metastable structure formed in thin films and is often mixed with the alpha phase. The fcc phase has only previously been reported as dispersed fine grains embedded in alpha or beta phase. In this study, Ta thin films were deposited on silicon substrates by magnetron sputtering. A mixture of alpha and beta phases was observed in the films when the deposition temperature was lower than 400 degrees C. The beta phase content decreased gradually with the increase in deposition temperature, and completely disappeared at 400 degrees C. It is interesting that when the deposition temperature reached 500 degrees C, both alpha and beta phases disappeared, and Ta films became a fcc structure. The structure and the stabilization of the fcc Ta thin films were further investigated using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy, and the results are presented in the present paper. This new finding would open new research and application directions for Ta materials.