Boundary-free multi-element barrier films by reactive co-sputtering

Four kinds of alloy thin films were deposited on Si(100) by co-sputtering method with two kinds of metal targets to investigate the formation of boundary-free amorphous structure which may lead to featureless morphology. These thin films, Nb-Cr, Ta-Cr, Ti-Nb, and Zr-Cr, were examined using XRD SEM, XPS, TEM, and four-point probe for resistivity measurement. It was found that the forming ranges of amorphous thin films were related to the difference in atomic size of the paired metals as well as their heat of mixing. The addition of nitrogen gas during deposition caused further amorphization and reduced surface roughness, until nitride phases were formed. For Ta-Cr thin film, the boundary-free amorphous phase was generated with the composition between Ta-82% Cr and Ta-30% Cr. The composition region of the amorphous phase was explained in a ternary system. The barrier property of a Ta-Cr-N amorphous thin film was examined. It was found that a thin TaN layer controlled the reaction of Cr and Si and improved the barrier performance.