Studies on immersion defects using mimic immersion experiments

Abstract

Top coat process is required for immersion lithography in order to prevent both the chemical contamination of scanner optics with eluted chemicals from resist material and the formation of residual droplet under the immersion exposure with high scanning speed. However, defect density of ArF immersion lithography with alkaline developer soluble type top coat material is much higher than that of ArF dry lithography. Mimic immersion experiments comprised of soaking of exposed conventional dry ArF resist with purified water followed by drying step were performed in order to study the immersion specific defects. It was suggested that the origin of immersion specific defects with alkaline developer soluble type top coat was the remaining water on and in the permeable top coat layer that might interfere the desired deprotection reaction of resist during post exposure bake (PEB). Therefore, application of post exposure rinse process that can eliminate the impact of the residual micro water droplets before PEB is indispensable for defect reduction. Post exposure rinse with optimized purified water dispense sequence was noticed to be valid for defect reduction in mimic immersion lithography, probably in actual immersion lithography.