MULTISCALE ROUGHNESS IN OPTICAL MULTILAYERS - ATOMIC-FORCE MICROSCOPYAND LIGHT-SCATTERING

We have previously shown that macroscopic roughness spectra measured w ith light scattering at visible wavelengths were perfectly extrapolate d at high spatial frequencies by microscopic roughness spectra measure d with atomic force microscopy [Europhys. Lett. 22, 717 (1993); Proc. SPIE 2253, 614 (1994)]. These results have been confirmed by numerous experiments [Proc. SPIE 2253, 614 (1994)] and allow us today to charac terize thin films microstructure from a macroscopic to a microscopic s cale. In the first step the comparison of light scattering and atomic force microscopy is completed by optical measurements at UV wavelength s that allow us to superimpose (and no longer extrapolate) the spectra measured by the two techniques. In the second step we extract multisc ale parameters that describe the action of thin-film coatings on subst rate roughness in all bandwidths. The results obviously depend on mate rials and substrates and deposition techniques. Electron-beam evaporat ion, ion-assisted deposition, and ion plating are compared, and the co nclusions are discussed in regard to the deposition parameters. Finall y, special attention is given to the limits and performances of the tw o characterization techniques (light scattering and atomic force micro scopy) that may be sensitive to different phenomena. (C) 1996 Optical Society of America