Surface roughness in sputtered SnO2 films studied by atomic force microscopy and spectroscopic light scattering

In this paper we study the growth of surface roughness during sputtering of transparent SnO2 films onto rough glass substrates. Films in the thickness range 50-1200 nm were produced, and the optical characterization was made with a spectroscopic total integrating scattering instrument in the wavelen gth range 0.35 <lambda < 1.0 mu m. Optical constants for the different SnO2 films were determined. The observed spectral behavior of the diffuse refle ctance (transmittance), as compared to the total reflectance (transmittance ), could be explained by first-order vector perturbation theory in conjunct ion with a surface growth model incorporating both smoothing and roughening effects. Good agreement between calculated and measured reflectance and tr ansmittance spectra was found, only by assuming partially correlated interf ace roughness. The scattering calculations rely on atomic force microscope measurements of the glass substrate and the front surfaces of the films, an d a model of the cross correlation that describes the propagation of surfac e features through the new layer. The obtained replication factor gave addi tional information on the contribution of the substrate roughness to the fi lm front surfaces. (C) 2000 American Institute of Physics. [S0021-8979(00)0 3809-3].