Resist elution study for immersion lithography

Resist component elution may have strong impacts on the feasibility and process establishment of immersion lithography. The amount of photo-acid-generator (PAG) fragment was investigated for a series of onium salts by changing the resist formulation and resist process. The extraction was performed in deionized water. The experiments utilized a 193 nm open-frame exposure system and compared a pair of test samples for non- and post-exposures. It was found that the elution of PAG anions indicated two opposite trends of the exposure process by increasing the number of carbon chains. It was also influenced by doping the polymer matrix with fluorine atoms in base polymers. The presoaking method effectively reduced the PAG elution only for non-exposure. The approach with a developable cover material successfully decreased the amount of PAG fragments regardless of exposure step.