Study of reticle cleaning process for 130nm lithography and beyond

Three cleaning methods were examined to check their strong points. Cleaning results were analyzed from the aspects on removal of particles and chemicals. Starlight inspection results showed that conventional wet cleaning based on chemicals, such as H2SO4 and NH4OH, could remain small particles on chrome-oxide (CrOX). DUV irradiation could assist this traditional SC-1 (mixture of NH4OH and H2O2 and H2O) cleaning in removing these sticking particles. Electrolyzed water, contained anode and cathode water, showed same tendency as SC-1 treatment, which could easily attract particles to CrOX surface. Mechanism of particle removal and attraction was considered from the aspect on electrostatic reaction between particles and photomask surface. ArF (lambda =193nm) lithography could cloud quartz surface with crystallized substances. Analytical results implied that they had been generated by optical-chemical reaction between ArF light and chemical residue after cleaning. Experimental results showed that DW treatment before cleaning was effective to prevent reticle surface from chemical contamination. From the above knowledge, suggestion about reticle cleaning process for ArF lithography is described as a conclusion.