Imec has obtained “promising results” with EUV pellicles made from carbon nanotubes (CNTs). Exposing the photomask-protecting membranes on an ASML NXE:3300 scanner, the Leuven research institute found that up to 97 percent of the EUV light was transmitted in a single pass while having no problematic impact on imaging and being able to survive scanner power beyond 600 watts.
A pellicle is mounted a few millimeters above the surface of the photomask so that if particles land on it during semiconductor manufacturing, they’ll be too far out of focus to print. Developing such an EUV pellicle is very challenging since 13.5 nanometer light is absorbed by most materials. In addition, stringent thermal, chemical and mechanical requirements must be met.
A first generation of EUV pellicles, based on silicon, was developed by ASML, but according to a recent report, they’re not quite ready for high-volume manufacturing. TSMC disclosed in a July blog post that it has chosen to use EUV masks without pellicles “to enhance optical transmittance, thus reducing energy loss during the exposure process.” Last year, ASML reported a transmission of 83 percent.
Imec thinks its CNT pellicle will be ready for the fab soon. “We’ve seen tremendous progress in carbon nanotube membrane development in the past year and are confident it will result in a high-performance pellicle solution in the near future,” says Emily Gallagher, principal member of technical staff at Imec.