Advanced Processes for 193-nm Immersion Lithography

Resist Leaching and Water UptakeOne unique aspect of 193i lithography is the use of water situated between the final lens element and the resist.The resist stack (with or without topcoat) on the wafer is dynamically exposed through this water with the step-and-scan process.The photoacid generator (PAG), quencher, and other small molecular components of the resist may leach into this water.These leached components contaminate the water and may degrade resist performance.This contaminated water can additionally contaminate the lens and wafer stage of the scanner.To master these leaching problems, we must understand the dynamics of resist leaching, transportation of leached contaminates in the immersion water, and the impact of these contaminants on the lens during exposure.Additionally, water can penetrate the topcoat and diffuse into the resist film.This penetration and diffusion of water can cause the topcoat or the resist to swell, which will affect their lithographic performance.This chapter specifically addresses the following issues: (1) leaching test methods, (2) leaching dynamics, (3) leaching with 193-nm exposure, (4) pre-rinse to partially remove leached contaminants, (5) lens contamination caused by resist leaching, and (6) water uptake in resist film.