Introducing the EUV CNT pellicle

摘要

EUV lithography insertion is anticipated at the 7 nm node and below; however, defects added to the mask during use is a lingering concern. Defectivity in the scanner is non-zero and an EUV pellicle membrane to protect the mask for high volume manufacturing power levels does not yet exist. The EUV photons are strongly absorbed by all materials. Si-based membranes leverage the low absorption coefficient k value (k = 0.0018 at 13.5 nm) for reasonable transmission, but poly Si becomes fragile and wrinkles during the high temperatures associated with exposure. An alternate approach to high transmission is deploying very thin or porous layers so that there are fewer atoms to absorb light. For example, carbon nanomaterials have a reasonably low k value (k = 0.0069), but are strong enough to be fabricated in very thin layers. Graphene, graphite, carbon-nanosheets and carbon nanotubes are all candidate carbon nanomaterials for this application, but we focus here on carbon nanotubes (CNTs). Our first measurements on CNT films of~60 nm thick were found to have 96.5% transmission at 13.5 nm. Adding CNT layers also enhanced the strength of a thin SiN membrane significantly. In this paper, critical pellicle metrics will be evaluated in more detail: EUV transmission, bulge test for mechanical strength, emissivity measurements for heat management, and exposure testing in a hydrogen environment.