Using Atomic Force Microscopy for Engineering Low Scatter Thin Film Optics (AN21)

The quality of optical components used in complex applications such as lasers, microscopes, and lithography systems, is critically influenced by surface morphology. The majority of these components - lenses, mirrors, beamsplitters, polarizers, etc.- are covered by thin film optical coatings. Hence, important properties of the optical elements such as optical scattering, are significantly affected by the surface microstructure of the thin film coating. With the ongoing trend of today's optical lithography towards shorter wavelengths (e.g. lithographic objective shifting from 248nm to 193nm), thin film research and industry are facing drastically increasing requirements for low-scatter optics in the UV, and deep UV, spectral region.1

The surface microstructure of a thin film coating can be advantageously measured with an Atomic Force Microscope (AFM) and the information obtained can substantially contribute to successful development of low-scatter optical coatings. This, however, requires good understanding of some basic relationships between microstructures and optical scatter, as well as the use of appropriate AFM data analysis and interpretation concepts.