Ultra-low density, nanostructured free-standing films for EUV Pellicles

A new process was developed to manufacture large size (up to 300 x 300 mm) free-standing nanoparticle films with areal densities as low as 0.2 μg/cm2 (2x of a graphene monolayer). For this process, a variety of nanoparticles with high aspect ratio can be used i.e. single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNT) and multi-walled carbon nanotubes (MWCNT) or even non-carbon-based materials such as boron nitride nanotubes (BNNT). The precursor material can be purified prior-fabrication of the film greatly reducing the concentration of contaminants such as catalyst particles (< 0.5 wt.%). DWCNT films made through this method have shown an EUV (13.5 nm) transparency higher than 98% with scattering of only 0.2% and practically zero reflectance. Due to a high surface area to volume ratio, these films show strong adhesion force (higher than the film tensile strength) to virtually any substrate allowing it to instantaneously adhere to a silicon-based border without any special adhesive or surface treatment. This facilitates the mounting of these films on standard pellicle borders. CNT films showed a deflection of only 0.05 mm under pumping down at a rate of 3.5 mbar/s, indicating good mechanical stability for EUV pellicle applications. Also, LINTEC has developed a technology to conformally coat CNT films which can greatly increase its resistance against hydrogen radicals/ions etching.