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A host of complementary imaging techniques (Scanning Electron Microscopy), surface
analytical technique (Auger Electron Spectroscopy, AES), chemical analytical and
speciation techniques (Grazing Incidence Reflectance Fourier-Transform Infrared
Spectroscopy, GIR-FTIR; and Raman spectroscopy) have been assessed for their
sensitivity and effectiveness in analyzing contamination on three EUV reticles that were
contaminated to varying degrees. The first reticle was contaminated as a result of its
exposure experience on the SEMATECH EUV Micro Exposure Tool (MET) at Lawrence
Berkeley National Laboratories, where it was exposed to up to 80 hours of EUV radiation.
The second reticle was a full-field reticle, specifically designed to monitor molecular
contamination, and exposed to greater than 1600J/cm2 of EUV radiation on the ASML Alpha Demo Tool (ADT) in Albany Nanotech in New York. The third reticle was intentionally contaminated with hydrocarbons in the Microscope for Mask Imaging and
Contamination Studies (MIMICS) tool at the College of Nanoscale Sciences of State
University of New York at Albany. The EUV reflectivities of some of these reticles were
measured on the Advanced Light Source EUV Reflectomer at Lawrence Berkeley
National Laboratories and PTB Bessy in Berlin, respectively. Analysis and
characterization of thin film contaminants on the two EUV reticles exposed to varying
degrees of EUV radiation in both MET and ADT confirm that the two most common
contamination types are carbonization and surface oxidation, mostly on the exposed areas
of the reticle, and with the MET being significantly more susceptible to carbon
contamination than the ADT. While AES in both surface scanning and sputter mode is
sensitive and efficient in analyzing thin contaminant films (of a few nanometers), GIRFTIR
is sensitive to thick films (of order of a 100 nm or more on non-infra-red reflecting
substrates), Raman spectroscopy is not compatible with analyzing such contaminants because of laser-induced evaporation of the contaminant film. SEM and EUV reflectometry are effective in quantifying the impact of contamination on imaging performance and reflectivity, respectively.
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