Mitigation of surface contamination from resist outgassing in EUV lithography

Contamination of optics and mask is one of the possible show stoppers for Extreme Ultraviolet Lithography. One of the important sources of hydrocarbon contamination is the outgassing of photoresist coated wafers. Due to the vacuum conditions, these hydrocarbons can freely travel to coat the first optical component they encountcr. This leads to unacceptably short life times which should be increased with 5 orders of magnitude. A new gas lock system is presented to prevent this type of contamination and which eliminates the need for a window between the optics and the wafer. Experimental results are in agreement with numerical calculations and an analytical model. Based on agreement between the experiments and the models, it is predicted that in realistic EUV tools this method can give 5 orders of magnitude debris suppression at 15 mbar·1/s flow with 5% absorption of EUV.