Extending the Ruthenium Capping Layer Life Time of Extreme Ultra-Violet Lithography Photomasks in Physical Force Cleaning
The process conditions that create pattern damage on 193i reticles do not necessarily create Ru pits on the EUVL reticles. Physio-chemical effects of cleaning media used with MegaSonic have to be taken into account for effective process development. The chemical nature of the cleaning media defines the cavitation behaviour in MegaSonic and physio-chemical behaviour in Ru pitting. Chemical A based POR shows no pattern damage and zero Ru pitting as compared to SC1 and NH4 OH-DI and has the maximum particle removal efficiency. This new process did not show any absorber CD shift over 50x clean and only showed an EUV-R change of 0.04% per cleaning cycle averaged over 70x cleans.