Yo-han Ahn

ArF pellicle degradation mechanism for resolving CD variation

With the introduction of ArF laser, a binary mask is preferred because a PSM mask is still weak to the crystal defect called as photomask haze although extensive studies trying to resolve the haze impact to a photomask have been performed by various researchers in company and school. However, a new problem was happened after a binary mask introduction that CD variation in an exposure shot is appeared and is gradually increased. And finally, CD variation considerably causes defects in wafer level. It was proven that CD variation is closely related to the change of the reticle transmittance by a lot of researches. In this study, the mechanism of ArF pellicle degradation is focused on because the pellicle degradation affects a reticle transmittance in direct. The components outgassed from a pellicle by the high photon energy of ArF laser, for example carbon or fluorine, are absorbed on the surface of the reticle, so that the transmittance of the reticle is decreased. The phenomena of the pellicle degradation have been studied by the various viewpoints, theoretical background, experiment and results tested in mass production line in this study. Therefore, this study has the important meaning by providing the substantial clues to resolve CD variation problem in a near future.

Effects of exposure environment on pellicle degradation in ArF lithography

With the introduction of ArF laser, its high photon energy affects the pellicle degradation in direct. The components outgassed from the damaged pellicle have the effect on the CD variation of reticle. In order to resolve this new inevitable problem, the method of dry gas purge has been proposed among the various solutions recently. Dry gas purge method is generally applied to two applications. It can be applied to a storage environment such as reticle stocker, reticle SMIF pod and reticle library in scanner and to the exposure chamber inside of a scanner during ArF laser exposure phase directly. In this case, it is quite important technologically that which gas is determined as dry purge gas, pure nitrogen or CDA (clean dry air). In this study, the effects of exposure environment on pellicle degradation according to dry purge gas and their mechanism has been investigated to propose strategies and solutions of dry gas purge technology.