Instrumentation and uncertainty evaluation for absolute characterization of thin films and nanostructured surfaces in advanced optical metrology

The importance of traceable measurements is undeniable within an entire metrology community. However, due to their complexity, the optical measurement techniques suffer from the lack of guidelines regarding the measurement uncertainty evaluation. To address this issue, the paper describes the full procedure on how to perform a comprehensive characterization of advanced metrology instrumentation used in reflectometry, spectroscopic Mueller ellipsometry and optical scatterometry. Despite being fast and accurate, these contactless measurement techniques allow obtaining geometry imperfections, layer thicknesses, optical properties, impurities and other features, which can be hardly determined by other measurement techniques. The paper covers specular x-ray reflectometry and extreme ultra violet (EUV)-reflectometry to obtain the information on thin metal film thickness in the range 29 nm to 32 nm with uncertainties below 0.5 nm, as well as roughness values between 0.5 nm and 2 nm with uncertainties below 0.4 nm. The refractive index and extinction coefficient are determined by EUV-reflectometry at wavelengths of 14.5 nm and 15 nm. Furthermore, by using spectroscopic ellipsometry at national metrology institutes and research institutes, we cover the spectral range from 200 nm to 1200 nm, providing traceable measurements of thin film samples with nominal thicknesses of 30 nm as well as determining the refractive index and extinction coefficient of the thin Ru film, which range from 1 to 6 and display a relative standard uncertainty of less than 2%. In addition, the research looks into the reconstruction of the nanostructure geometry by optical scatterometry comparing the measurement results obtained by multiple scatterometry setups. For one dimensional repeated fused silica nanostructure we find height, line width and pitch values of 221.2 nm, 334.6 nm and 674.5 nm, with standard uncertainties of 2.7 nm, 3.6 nm and 3.0 nm. For two dimensional repeated silicon nanostructure we find height and width values of 122.2 nm and 244.9 with standard uncertainty of 2 nm and 1.2 nm. The methodology for uncertainty evaluation is provided together with actual uncertainty budgets and experimental results for each measurement technique. Measurement techniques cover the x-ray to IR spectral range to determine the optical constants through the measurements of layered nano-structures. Moreover, the inverse problem solving for optical measurement methods is explained in detail by providing the most useful approaches. The paper addresses, compares and summarizes the state of the art optical measurement techniques used in nanometrology.