Microroughness analysis of thin film components for VUV applications

For the roughness characterization of optical surfaces a new procedure based on the analysis of their power spectral density (PSD) functions has been developed. The method consists of the fitting of the PSD obtained from Atomic Force Microscopy measurements at different scan sizes to mathematical models. With this procedure the micro- structural properties of optical surfaces and coatings can be represented by a reduced set of numbers that correspond to the characteristic parameters of the mathematical models. For optical coatings this method allows a separate study of the influence of the substrate and layers on the overall sample roughness. As an example, the method is applied to MgF2 and LaF3 films for VUV applications. We investigated a set of single layers deposited onto superpolished Caf2, fused silica and Si substrates. The samples were deposited by ion beam sputtering, boat and e- beam evaporation. A comparison of the influence of the substrate on the development of the roughnesses and lateral structures has been performed, as well as a study of the dependence of the roughness properties of the coatings on the deposition process. Complementary investigations of roughness-related scattering consisting of measurements of Total Scatter at 193 nm and 633 nm and calculation of expected scattering based on the theory are presented.

[1]  Norbert Kaiser,et al.  Surface finish and optical quality of CaF2 for UV lithography applications , 1998, Advanced Lithography.

[2]  H Truckenbrodt,et al.  Interfacial roughness and related scatter in ultraviolet optical coatings: a systematic experimental approach. , 1998, Applied optics.

[3]  Etienne Quesnel,et al.  New procedure for the optical characterization of high-quality thin films , 2000, SPIE Optics + Photonics.

[4]  Gunther Notni,et al.  Multitype surface and thin film characterization using light scattering, scanning force microscopy, and white light interferometry , 1999, Optics + Photonics.

[5]  J. Stover.  Optical Scattering: Measurement and Analysis , 1990 .

[6]  E. Church.  Fractal surface finish. , 1988, Applied optics.

[7]  Salvador Bosch,et al.  UV-optical and microstructural properties of MgF2-coatings deposited by IBS and PVD processes , 1999, Optical Systems Design.

[8]  J. Bennett,et al.  Relation between the angular dependence of scattering and the statistical properties of optical surfaces , 1979 .

[9]  Ekaterina V. Kostyukevich,et al.  Light scattering of thin dielectric films: self-assembled monolayers on the surface of polycrystalline gold , 1999, Correlation Optics.

[10]  E. Quesnel,et al.  Microstructure and composition of MgF2 optical coatings grown on Si substrate by PVD and IBS processes , 2000 .

[11]  E. L. Church,et al.  The Prediction Of BRDFs From Surface Profile Measurements , 1990, Optics & Photonics.

[12]  J. Bennett,et al.  Introduction to Surface Roughness and Scattering , 1999 .

[13]  Adolf Canillas,et al.  Effective dielectric function of mixtures of three or more materials: a numerical procedure for computations , 2000 .

[14]  Etienne Quesnel,et al.  DUV light scattering and morphology of ion beam sputtered fluoride coatings , 1999, Optical Systems Design.

[15]  D. Rönnow.  Elastic light scattering by thin films : spectroscopic measurements and analysis , 1996 .

[16]  P. Roche,et al.  Scattering from multilayer thin films: theory and experiment , 1981 .