A short-pulsed laser cleaning system for EUVL tool

A traditional method of reticle protection, using a pellicle, is thought to be difficult to apply to EUVL tool. There is a possibility that some particles adhere to the surface of a reticle. In order to resolve this reticle issue, we are investigating in-situ short-pulsed laser cleaning system. In order to confirm whether it can be applied to EUVL tool or not, we have to verify experimentally that it is possible to remove particles in vacuum without any damage to a Mo/Si multilayer. In this work, as a short-pulsed laser, a Q-switched YAG Laser (wavelength: 266 similar to 1064 nm, pulse duration time: similar to 7 ns) has been used. As experimental results, at the pressure on the order of 10(-3) Pa, around 100% removal rate to PSL (organic) particles can be achieved without particular damage using a DUV laser. And also, it is found that a laser cleaning method in vacuum is easier to remove particles on a surface than that in atmosphere and for SiO2 and Ni (inorganic) particles, this method is particularly effective. This reason can be explained that the drag force exerted to a particle by the surrounding gas molecules is neglected at the pressure on the order of 10(-3) Pa because a gas is in free molecule regime.