PHASE-TRANSITION OF CU/SI SYSTEM OBTAINED BY ION-BEAM-ASSISTED DEPOSITION

Cu films were formed on Si(100) substrates using three different methods: physical vapor deposition (PVD), ion beam assisted deposition (IBAD), and a combined IBAD-PVD technique. Epsilon-phase (Cu15Si4) was formed directly at the interface of the 14 keV Ar+ IBAD Cu film (350 nm) and the Si substrates during the deposition processes. In the combined film [IBAD Cu (20 nm)+PVD Cu (350 nm)] no new phase was observed until the sample had undergone an annealing treatment (300-degrees-C 30 min), in which the epsilon phase was formed. The phase sequence of the Cu-Si system in combined films of our experiments is quite different from those observed in a typical annealing process. From discussion the nucleation of epsilon phase is the key factor to obtain a thermodynamically stable phase at the Cu-Si interface during the annealing process.