EUV time-resolved studies on carbon growth and cleaning

This paper presents first results to assess the feasibility of a cleaning strategy for EUV production tools. The EUV experiments were performed in a dedicated UHV contamination chamber connected to the DLW20 dipole beam line at the PTB laboratories at BESSY II in Berlin. An in-situ reflectometry system has been implemented inside the contamination chamber to allow for real-time detection of mirror reflection changes. The reproducibility of the in-situ reflectometry system has proven to be about 0.03%, allowing the measurement of reflection changes below 0.1%. Cleaning cycles were performed at producation tool power density levels, i,e,, 10-30 mW/mm2 broadband radiation, on capped Mo/Si mirror samples. Carbon was deposited intentionally at ypical hydrocarbon pressures in the 10-8 mbar regime. Cleaning was done at background levels of hydrocarbons and 10-4 mbar molecular oxygen. First results show that cleaning of a mirror at high power densities and typical tool conditions can restore the reflection close to its initial value.