Comparative study of the interface roughness of Ag/Au and Cu/Au multilayers with scanning tunneling microscopy and x-ray diffraction

The interface roughness is a very important parameter determining the performances of multilayered structures. Ag/Au and Cu/Au textured multilayers have been produced by thermal evaporation in an ultrahigh vacuum chamber. After deposition of the Au, Ag, or Cu layer, the surface roughness at different sampling lengths was probed in situ by scanning tunneling microscopy. After completion of the multilayers, the samples were taken from the ultrahigh vacuum chamber and measured in an x-ray-diffraction unit. Low-angle as well as high-angle specular x-ray-diffraction curves were analyzed using a refinement program which takes into account layer thickness fluctuations, interface roughness, and crystalline disorder. The average interface roughness, obtained from fitting the x-ray-diffraction profiles, is then compared to the roughness of the film growth front, which was probed with the scanning tunneling microscope. The roughness obtained from the x-ray-diffraction profiles corresponds to a lateral sampling scale which is in good agreement with the average grain size within the layers, indicating that x rays scatter coherently over a volume which is relatively small. Our work also shows the complementarity of the scanning tunneling microscopy and x-ray-diffraction technique to probe interface roughness of multilayers. (C) 1996 American Vacuum Society.