Youji Kawasaki

Immersion defect performance and particle control method for 45nm mass production

Water-based immersion technology has overcome various challenges and is starting to be used for the 45nm-node mass production. However, even though immersion technology is being used in memory device production, significant improvement in defect performance is needed before the technology can be used for logic devices. Canon has developed an immersion exposure system, the FPA-7000AS7, with numerical aperture of 1.35. In the AS7 immersion tool, there is little influence of vibration and evaporative cooling. The AS7 has an in-situ cleaning system in order to remove particles carried into the exposure tool. We evaluated the contamination of the projection lens and immersion nozzle due to photoacid generator (PAG) leaching from resist to water. We evaluated the cleaning effects of various cleaning processes and found the suitable processes for cleaning the projection lens and immersion nozzle from the view that it does not adversely affect the exposure tool: damage-free and easy drainage treatment. In addition, we evaluated the influence of particles on the wafer stage, since there is a major concern that particles entering the water may increase the defects. The number of particles adhering on the wafer during an exposure sequence can be reduced with the wafer stage cleaning. Periodical cleaning keeps the wafer stage clean, thus preventing the increase of exposure defects caused by particles. We performed a defect evaluation with the AS7. The average defect density was 0.042/cm2 in the continuous exposure process of 25 wafers with a developer-soluble topcoat. Circle defects and bubble defects were not observed.

Contamination and Particle Control System in Immersion Exposure Tool

Water-based immersion technology has overcome various obstacles and is approaching the mass production phase. Canon is in the process of developing an ArF immersion exposure tool, FPA-7000AS7 (NA>1.3), to meet both mass production of the 65nm HP and development of the 45nm HP, which starts in 2007. In the Canon immersion nozzle, there is little influence of vibration on the lens and the stage, and particle generation from the nozzle during treatment of the nozzle in the manufacturing process has successfully been prevented. We evaluated contamination due to leaching and cleaning technology with a test bench. Contamination due to PAG (Photo-acid Generator) leaching from resist to water could be completely eliminated by dipping it into a cleaning fluid. With periodic cleaning, it is possible to keep the projection lens clean and to prevent particle generation from the immersion nozzle. The defect was evaluated with FPA-6000AS4i (NA0.85) that had the same type of immersion nozzle as that of FPA-7000AS7. The level of defect density was stable in a continuous exposure process of 25 wafers with a developer-soluble topcoat. The defect density was 0.030/cm2 with a topcoat-less resist.