Angle and wavelength resolved light scattering measurement of optical surfaces and thin films

Abstract

Light scattering metrology has become more and more important with the development of cutting-edge optical components and systems. Light scattering is also a very versatile tool for the characterization of nanostructures and defects. While optical engineering and manufacturing are striving for ever increasing resolution of optical devices and lowest optical losses, the demands for highly resolved light scattering metrology have become extremely challenging. In this sense, “highly resolved” means: (i) measurements with high angular resolution, not just in one plane but within the entire scattering sphere, (ii) small near-angle limits, (iii) highest sensitivities and lowest instrument signatures close to or even below the Rayleigh scattering limit, as well as (iv) at-wavelength operation and, more recently, spectral resolution. Instruments for scatter measurements developed at Fraunhofer IOF to meet these demands are presented together with practical examples of application comprising roughness, sub-surface damage, and defects of polished surfaces and thin film coatings. Compact tools like a table-top 3D scatterometer and a CMOS-based scatter sensor are presented. Finally, we report on the development of a new instrument for spectroscopic angle resolved scatter measurements based on an OPO tunable laser.