Structure and chemical characteristics of tin oxide films prepared by reactive-ion-assisted deposition as a function of oxygen ion beam energy

Tin oxide films were deposited on amorphous SiO2/Si and Si (100) substrates by ion-assisted deposition (IAD) at various ion beam potentials (V-I) at r oom temperature and a working pressure of 8 x 10(-5) ton. The structural an d chemical properties of the as-grown tin oxide films were investigated to determine the effects of the oxygen ion/atom arrival ratio (R-i). X-ray dif fraction patterns indicated that the as-grown films with different average energy per atom (E-ave) showed different growth directions. The as-grown fi lms with oxygen/Sn ratio (N-O/N-Sn) of 2.03 and 2.02 had preferred orientat ion of (101) and (002), respectively. In addition, the as-grown film with l ow R-i was amorphous. Comparison of the observed d spacings with those for standard SnO2 samples, indicated that the crystalline as-grown films had co mpressive and tensile stress depending on E-ave. In transmission electron m icroscopy analysis, a buffer layer of amorphous tin oxide was observed at t he interface between the substrate and the film, and the crystalline grains were grown on this buffer layer. The crystalline grains were arranged in l arge spherical clusters, and this shape directly affected surface roughness . Rutherford backscattering spectroscopy spectra showed that the tin oxide thin films were inhomogeneous. The density of films decreased and the poros ity and oxygen trapped in the films increased with increasing R-i. The dens est film had about 6% porosity.