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The growing industrial need for at-wavelength metrology of crucial elements in the EUV production chain, such as EUV masks and pellicles, can only be answered by cost-effective stand-alone tools. Especially the scaling to higher average operating powers of future EUV scanners is a task requiring multiple tools that can investigate not only critical degradation under increased EUV intensities, but also give information about underlying physical mechanisms of degradation and the imposed structural and chemical changes. At RWTH Aachen University, prototype tools are developed that address this challenge.
The realized high-intensity EUV exposure tool, with a tightly focused sub-100 µm EUV spot, provides a unique opportunity to investigate the influence of EUV intensities on the level of the 250 W EUV scanner generation and beyond. With its pulse-to-pulse measurement system, the exposure dose in the tool is controlled with sub-mW/mm2 precision and it is independent from the temporal stability of the source.
The influence of these exposures on the specimen can directly be characterized by the versatile laboratory EUV spectrometer. The tool can perform spectroscopic measurements of reflectance and transmittance under variable incidence angles and operates spectroscopically in the important wavelength range from 9 nm to 17 nm. In reflectance mode, the incidence angle of illumination is adjustable from 5° to 12° grazing with sub-0.1° resolution, which allows extraction of optical constants for reflectance measurements. It uses an EUV-radiation source based on a gas-discharge plasma, whose instabilities are accounted for by permanent reference monitoring during measurements. This in combination with the use of a calibrated reference sample allows to determine reflectivities with an accuracy <1 %. An additional transmission mode for sufficiently thin membranes allows for an independent determination of absorption coefficients of mono- and multi-layered membranes. The developed analysis algorithms allow not only to obtain best-fit layer parameters, but also to analyze the resulting precision and cross-correlations of parameters.
In this contribution, exemplary use-cases of the tools will be presented. The application of the described methods to resist and pellicle investigations and to contamination studies will be introduced and discussed.
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