Development of EUV pellicle for suppression of contamination, haze, and outgas generation

In the existing DUV pellicle, haze generation risk on mask surface during DUV exposure exists due to the reaction of out gas in an exposure atmosphere. It is well known fact that outgas is generated not only from pellicle in itself but also by stray light being irradiated adhesive parts. As for EUV pellicle, problems of the exposure defect such as haze generation and reflectance reduction of mask will be anticipated because EUV has higher photon energy compared with DUV and diffusion of the outgas is promoted in high vacuum condition. In this study, similar to the pelliclized EUV mask structure was constructed by using the full-size EUV pellicle frame stacked on a base plate which has similar component of the EUV mask surface, and dummy plate placed on the membrane side of the frame. Contamination growth behavior was examined by irradiating the EUV light to the base plate inside pellicle via EUV transparent membrane on dummy plate. Adhesion of the contamination on base plate was observed in EUV irradiation area in the case of the pellicle sample using commercially available adhesive as the mask adhesive. So, general commercially available adhesives will not be suitable for mask adhesive of pellicle. We found that generation of the contamination was not observed for pellicle sample with coated adhesive materials as the mask adhesive, which has both outgas suppressing and EUV light screening function. Coated adhesives for mask adhesive of pellicle, which keep the adhesive properties, will be suitable for fixing method to suppress the contamination growth during EUV exposure.