Angela Duparré

Light scattering from the volume of optical thin films: theory and experiment

A theoretical model is presented that describes the volume scattering in thin optical films, particularly in typical columnar structures. It is based on a first-order perturbation theory that concerns the fluctuation of the dielectric permittivity in the film. For evaporated PbF(2) films that show a pronounced columnar morphology, angular as well as total integrated scattering measurements at lambda = 633 nm have been performed on a special layer design to suppress roughness-induced scattering. A comparison of the predicted theoretical and the measured experimental values leads to such structural parameters as packing density and the evolutionary exponent of the columns.

Relation Between Light Scattering and Morphology of Columnar Structured Optical Thin Films

Abstract A statistical model is presented describing the surface roughness of columnar structured thin films. Based on this model, a formula has been derived relating total integrated light scattering to the evolutionary exponent that represents a quantitative characterization of the evolution of the columns with film thickness. The examination of evaporated PbF2 films offers the opportunity to test the suitability of the theoretical considerations by comparing results calculated from scattering data with transmission electron microscopy observations.

Roughness characterization of EUV multilayer coatings and ultra-smooth surfaces by light scattering

Optical components for the extreme ultraviolet (EUV) face stringent requirements for surface finish, because even small amounts of surface and interface roughness can cause significant scattering losses and impair image quality. In this paper, we investigate the roughness evolution of Mo/Si multilayers by analyzing the scattering behavior at a wavelength of 13.5 nm as well as taking atomic force microscopy (AFM) measurements before and after coating. Furthermore, a new approach to measure substrate roughness is presented, which is based on light scattering measurements at 405 nm. The high robustness and sensitivity to roughness of this method are illustrated using an EUV mask blank with a highspatial frequency roughness of as low as 0.04 nm.

Effect of Film Thickness and Interface Roughness Correlation on the Light Scattering from Amorphous and from Columnar Structured Optical Films

Abstract The dependence of total integrated light scattering on film thickness is investigated for evaporated PbF2-films and magnetron sputtered Nb2O5-films. The experimental results are discussed on the basis of theoretical model assumptions, relating the scattering behaviour to interface roughness cross-correlation effects as well as to the evolution of film morphology with increasing film thickness. Electron microscopy examinations serve to make evident the different film structures responsible for the specific scattering properties observed.

Scattering reduction or enhancement by a dielectric single layer

On decrit un modele decrivant la rugosite statistique de la couche mince. En se basant sur ce modele on est capable de prevoir les conditions pour obtenir une reduction de la diffusion

Determination of thin-film roughness and volume structure parameters from light-scattering investigations

Light scattering measurements can be used for determining roughness as well as volume structure parameters of optical thin films. A method of structural analysis is outlined, which allows a quantitative estimation of roughness parameters, mean columnar diameter, packing density, and the evolutionary exponent, respectively.

Modification Of The Statistical Microroughness Of Surfaces By Thin Film Deposition: A Model

A model describing the modification of a surface roughness profile due to thin film deposition is presented. Surface smoothing as well as roughening are found to be significant effects. Conclusions which can be drawn from the roughness model with respect to related light scattering make it possible to interpret film scattering experimentally observed.

New light absorbing material for grazing angles

One of the largest challenges for optical systems is eliminating stray light generated by reflections off the walls and other optical elements of the device. Most black coatings are not sufficiently effective at grazing angles. Acktar’s black coatings exhibit particularly low residual reflectance and have been implemented in various instruments. The new proposed material exhibits particularly low hemispherical and specular reflectance – especially at grazing angles.

Light scattering techniques for the characterization of optical components

The rapid developments in optical technologies generate increasingly higher and sometimes completely new demands on the quality of materials, surfaces, components, and systems. Examples for such driving applications are the steadily shrinking feature sizes in semiconductor lithography, nanostructured functional surfaces for consumer optics, and advanced optical systems for astronomy and space applications. The reduction of surface defects as well as the minimization of roughness and other scatter-relevant irregularities are essential factors in all these areas of application. Quality-monitoring for analysing and improving those properties must ensure that even minimal defects and roughness values can be detected reliably. Light scattering methods have a high potential for a non-contact, rapid, efficient, and sensitive determination of roughness, surface structures, and defects.