During Ru etch with oxygen-based plasma, strong emission lines have been observed in the region of 340-390 nm with the most prominent peak at 373 nm. These are attributed to the emission of neutral Ru. We have shown that the emission can be used for end-point detection for Ru patterning by plasma etch as well as for highly sensitive in situ monitoring of the etch chamber cleaning after Ru processing. (c) 2005 The Electrochemical Society.