Novel metrology for mask degradation: IR-AFM, XPS depth profiling and HAXPES

Given the impracticality of using full-size masks for many analytical instruments due to their size and cost constraints, a critical first step towards advancing novel metrology for mask degradation was to develop and validate a dicing procedure suitable for (EUV-)exposed samples. Small markers were engraved prior to the dicing to facilitate precise navigation to locations of interest in the metrology tools, and allow correlation of metrology results with both each other and the EUV dose. Our investigation revealed no discernible changes induced by the dicing process, as confirmed by light microscopy, XPS and AFM analysis. Two samples were used in this study: a multilayer blank and an absorber blank. Once these blanks were diced, novel methods for mask degradation were tested on thermally degraded mask samples: IR-AFM for detection of (near-)surface morphological and chemical changes. XPS-depth profiling with Al Kα (conventional) and Ag Lα (hard) x-ray sources was used to study the sub-surface and the multilayer below the absorber. We show that IR-AFM analysis produces clear signals, but data interpretation is challenging, and its sensitivity to degradation seems limited, possibly as a result of hydrocarbon contamination. For hard XPS (HAXPES), we found that the signal-to-noise ratio in our instrument is too low to detect the changes induced by thermal annealing. XPS depth profiling on the other hand has very clear potential. Upon annealing, it revealed several changes within the sample, both close to the surface and deeper in the samples.