Stoichiometric AuCu alloy has been well studied in bulk form. but tile resistivity of very thin films has rarely been reported. In fact, thin copper and gold films show a strong deviation from bulk-resistivity due to the size effect, which motivates us to study CuAu I thin films and understand the properties of nanoscale metallization in more details. Very thin films of ordered CPAu I phase were formed by interdiffusion of Cu/Au bilayers, in which the intermetallic phase formation was characterized by glancing angle x-ray diffraction and transmission electron microscopy. It was found that Kirkendall voids were created during the interdiffusion. Also, as it turned out, the resistivity of such thin CuAu I films changed only slightly with decreasing film thickness. which was different from pure copper and gold thin films. (C) 2004 American Vacuum Society.