Journal
JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B
Volume 26, Issue 6, Pages 2225-2229Publisher
A V S AMER INST PHYSICS
DOI: 10.1116/1.3021368
Keywords
atomic force microscopy; chemical interdiffusion; chemisorption; etching; masks; oxidation; plasma materials processing; ruthenium; surface morphology; surface roughness; transmission electron microscopy; ultraviolet lithography; X-ray photoelectron spectra
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Contamination removal from extreme ultraviolet (EUV) mask surfaces is one of the most important aspects to improve reliability for the next generation of EUV lithography. The authors report chemical and morphological changes of the ruthenium (Ru) mask surface after oxygen plasma treatment using surface sensitive analytical methods: x-ray photoelectron spectroscopy (XPS), atomic force microscopy, and transmission electron microscopy (TEM). Chemical analysis of the EUV masks shows an increase in the subsurface oxygen concentration, Ru oxidation, and surface roughness. XPS spectra at various photoelectron takeoff angles suggest that the EUV mask surface was covered with chemisorbed oxygen after oxygen plasma treatment. It is proposed that the Kirkendall effect is the most plausible mechanism that explains the Ru surface oxidation. The etching rate of the Ru capping layer by oxygen plasma was estimated to be 1.5 +/- 0.2 A/min, based on TEM cross sectional analysis.
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