AVS 47th International Symposium
    Surface Science Monday Sessions
       Session SS2+NS+TF-MoM

Paper SS2+NS+TF-MoM8
Ultra-thin Al Films Grown Epitaxially on CaF@sub 2@/Si(111)

Monday, October 2, 2000, 10:40 am, Room 209

Session: Nucleation and Growth
Presenter: Y.V. Shusterman, Rensselaer Polytechnic Institute
Authors: Y.V. Shusterman, Rensselaer Polytechnic Institute
N.L. Yakovlev, Rensselaer Polytechnic Institute
L.J. Schowalter, Rensselaer Polytechnic Institute
Correspondent: Click to Email
Electron scattering at metal boundaries becomes increasingly important as interconnect structures shrink further. To improve our understanding of this phenomenon, studies of electron transport through ultra-thin metal films are needed. In such experiments, it is desirable to have smooth, single crystal metal layers grown on an insulating substrate. For this reason, we are studying epitaxial growth of Al on CaF@sub 2@/Si(111), with metal thickness as low as several nanometers. The structures discussed in this work were grown by molecular beam epitaxy and investigated by reflection high-energy electron diffraction (RHEED), scanning tunneling microscopy (STM) and atomic force microscopy (AFM). Hydrogen-terminated Si(111) was used as a substrate. The CaF@sub 2@/Si interface was formed at 700°C, followed by fluoride overgrowth at temperatures below 200°C, which resulted in improved continuity of the subsequent Al layer. The roughness of the final CaF@sub 2@ surface was below 1nm, as measured by AFM. The Al films grew epitaxially, as revealed by RHEED patterns that only contained streaks. The spacing between the streaks from Al was about 4/3 times larger than that from CaF@sub 2@, in agreement with bulk lattice mismatch. The growth proceeded through formation of 3-dimentional islands that then coalesced as the thickness increased. Using an Al deposition rate above 1nm/s at room temperature, we were able to obtain continuous films as thin as 10nm with roughness less then 2nm. The STM images of these films showed atomic steps, some of them originating at screw dislocations. The density of these dislocations was around 10@super 11@ cm@super -2@. The dependence of Al conductivity on film thickness will also be presented.