Optimized EUV scatterometry measurements with tunable high harmonic generation and the Fisher information matrix

We present the use of high harmonic generation (HHG) to achieve sub-nanometer sensitivity to out-of-plane geometric features on an industrially relevant damascene sample with extreme ultraviolet (EUV) scatterometry. We also demonstrate a methodology to take advantage of the tuneability of HHG by selecting experimental conditions that maximize the sensitivity of EUV scatterometry. The method uses the Fisher information matrix to encode prior knowledge about the sample into a robust mathematical framework that enables automated selection of the optimal experimental conditions such as wavelength and incidence angles. Importantly, HHG allows us to use wavelength tunability across the EUV spectrum through precisely controlled phase matching to achieve these conditions. We apply this to our damascene sample to show that EUV light at ~13nm will maximize the sensitivity of our scatterometry measurements and the angle selection will break correlations between parameters to enable a reliable solution to the inverse problem. Using this approach, we are able to take full advantage of the wavelength tunability of HHG based EUV sources to support accurate metrology for next generation semiconductor devices.