Characteristics of SnOx films deposited by reactive-ion-assisted deposition

SnOx films were deposited on glass, amorphous SiO2/Si, and Si(100) substrates by oxygen ion-assisted deposition at various ion beam potentials (V-l) at room temperature and a working pressure of 8 x 10(-5) Torr. The structural, chemical, and optical properties of the as-grown tin oxide films were investigated to determine the effects of the oxygen ion energy (E-ave) and ion/atom arrival ratio (R-i). X-ray diffraction (XRD) patterns indicated different growth directions with various E-ave. The as-grown films with oxygen/Sn ratio (N-O/N-Sn) of 2.03 and 2.02 had preferred orientation of (101) and (002), respectively. In addition, the as-grown film with low R-i was amorphous. Comparing the observed d spacings with those for standard SnO2 samples, the as-grown films, which were crystalline had compressive and tensile stress depending on E-ave. The grain size increased from 7 to 11 nm with increasing ion beam potential for glass substrates. The crystalline grains were arranged in large spherical clusters. Such clusters play an important role in optical scattering. In transmission electron microscopy analysis, a buffer layer of amorphous tin oxide was observed at the interface between the substrate and the film, and the crystalline grains were grown on this buffer layer. The crystalline grains were arranged in large spherical clusters, and this shape directly affected surface roughness. Scanning electron microscopy images suggested that the small grain size and very dense grain structure might be due to the ion bombardment effects at the initial stage of film growth. Root mean square roughness values from atomic force microscopy showed that the surface roughness increased with increasing R-i, while the roughness decreased at R-i = 1.39 because the high bombarding ion energy broke the SnO2 grains on the substrate, resulting in small grains. X-ray photoelectron spectroscopy peaks showed different N-O/N-Sn, (1.51, 2.03, 2.02, and 1.96) for different Values of R-i. Rutherford backscattering spectroscopy spectra showed that the tin-oxide thin films were inhomogeneous. The density of films decreased and the porosity and oxygen trapped in the films increased with increasing R-i. The densest film had about 6% porosity. The refractive index of films decreased with increase of the ion beam energy due to an increase in porosity. The degree of the dispersion of the refractive index and extinction coefficient decreased with increasing ion beam energy. A formula for the atomic elastic force was derived from the dispersion of the refractive index and d spacings derived from the XRD analysis. The atomic bonding force increased, and the stress of films was changed from compressive to tensile stress with increasing ion energy. [S0163-1829(99)03539-0].