SURFACE SEGREGATION OF SUBSTRATE ELEMENT ON METAL-FILMS IN FILM SUBSTRATE COMBINATIONS WITH NB, TI AND CU

The surface segregation of the substrate element on metal film by diffusion through the film was studied. Six film/substrate couples---Nb/Ti, Ti/Nh, Cu/Nb, Nb/Cu, Cu/Ti and Ti/Cu-deposited by rf magnetron sputtering were applied to investigate segregation behaviour, as well as Nb/Ti and Ti/Nb deposited by electron beam. The segregation behaviour of the substrate element by diffusion through the films was monitored at the film surface by AES. For Nb/Ti, Cu/Nb, Cu/Ti and Ti/Cu, the substrate element segregated on the film surface by diffusing through the film with a diffusion coefficient much larger than that corresponding to volume diffusion in the bulk. The segregation of Cu on Ti film was affected by an exposure of 2.6 x 10(-6) Pa oxygen during heating. The activation energy for this diffusion was approximately 60% of that in the bulk and the diffusion path seems to be the grain boundaries. The occurrence of this segregation via grain boundary diffusion did not depend on the film preparation process. From these results, the driving force of the segregation via grain boundary diffusion may be the decrease of the surface free energy of film by the segregation of substrate element on grain boundaries and surfaces of films.