Particle Cleaning of EUV Reticles

Due to absorption of EUV light, EUV reticles are not likely to have pellicles for particulate contamination protection, thus even nanosize particles on the reticle could result in fatal defects in every printed die. Consequently, measures must be taken to detect and remove particles above a certain critical size that are deposited on the reticle in the course of its use. In this paper we first present the very stringent requirements that a cleaning technique must satisfy in order to be employed for EUV reticle cleaning. The main challenges consist in the capability of removing very small particles (sub-100 nm), in principle of any type (organic/inorganic) and without damage to the reticle. We then focus on two of the techniques that we are investigating, laser shockwave cleaning (LSC) and high voltage cleaning (HVC). Both of them are dry techniques, which is a necessary requirement in view of their potential integration in the lithography tool. We finally present cleaning and damage tests results, including cleaning of 40-nm polystyrene-latex (PSL) spheres on large areas.