Yosuke Ono

Development of closed-type EUV pellicle

In this study, we fabricated a closed type EUV pellicle without any gaps by using the mask adhesive, forming the vent holes in the Si border part and putting the sufficiently wide area filters on the top side of Si border. Ventilation performance of closed EUV pellicle was examined during pumping and ventilation condition. As the result, we found that the closed EUV pellicle has enough ventilation performance under the practical pumping down condition. Furthermore, as for EUV pellicle, contamination growth on mask surface during EUV exposure should be suppressed. We fabricated EUV pellicle with coated adhesive as the mask adhesive to suppress the outgas generation which causes the contamination on mask during EUV exposure. EUV irradiation was performed to the base plate which has similar component of the EUV mask surface inside the pellicle space. Contamination growth was not observed for the sample with coated adhesive, but observed for the sample with general adhesive as mask adhesive. Coated adhesives for mask adhesive of EUV pellicle, which keep the adhesive properties, will be suitable for fixing method to suppress the mask contamination during EUV exposure.

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.

Development of a novel closed EUV pellicle for EUVL manufacturing

As for the EUV pellicle, closed pellicle structure with the filters which has fundamentally no penetration path of particles is needed to keep the clean reliability level of photomask equivalent to the current photolithography. We proposed a novel closed EUV pellicle equipped with filters which has not only the particle intrusion prevention but also the ventilation performance. Full-size closed EUV pellicle was fabricated by forming the vent holes in the Si border part and putting the wide filters on the top side of Si border. As the result, we experimentally confirmed the suppression of the membrane deflection under the practical pumping down condition.