Unlike photomasks used in optical lithography today, EUV masks will not have the protection of a pellicle, making it sensitive to particle and organic contamination. A higher cleaning frequency will be required to mitigate the risk of wafer loss and yield loss from contamination of the patterned side of the mask. However, of increasing concern is contamination on the backside of the mask which, if introduced into the scanner, could transfer to the reticle clamp causing serious overlay issues. To clean the reticle clamp the scanner would require extensive downtime at a considerable cost to the semiconductor manufacturer.
Over the last year, imec’s mask cleaning program reached significant milestones in the development of processes of record (PORs) for EUV mask cleaning, using the SUSS MaskTrack Pro photomask cleaning system, which was installed in imec’s 300mm clean room in 2009. The developed PORs are effective in removing the contamination of interest, yet are gentle enough to be applied repeatedly without reducing mask lifetime. Investigation and optimization of EUV reticle backside cleaning processes, which do not influence the front-side, were developed and demonstrated to keep the overlay performance of the EUV scanner in spec. Imec achieved a Particle Removal Efficiency (PRE) of the backside of an ADT (alpha demo tool) reticle of up to 80%. To reach a PRE of 100% we need to avoid artifacts caused by handling, transportation and storage. Therefore, a controlled mask management environment is necessary from the time the mask enters the fab throughout the entire lifetime of the mask. Exactly this assurance is the main trigger for our broadened research scope towards totally automated handling for the recently installed NXE-3100 using the SUSS MaskTrack Pro InSync (InSync) in-fab mask management system.
InSync is designed to meet the strictest EUV mask integrity requirements prior-to-exposure. The exclusive InSync provides a highly controlled environment to automatically transfer EUV masks into [and out of] the dual pod, eliminating the risk of contamination from manual handling and transfer. The critical inner pod can be stored inside of the InSync environment. Functioning as a loadport, InSync can accept a reticle dual pod directly from the scanner for transfer to the MaskTrack Pro cleaning tool. InSync will provide the foundation for further development of the mask integrity infrastructure at imec.
Kurt Ronse, program director advanced lithography at imec said, “Our goal to provide an EUV infrastructure that delivers a defect-free mask at point-of-exposure, has not changed. Building on our important progress on mask cleaning, we are excited to expand the scope of our research to deliver a holistic mask management system. The installation of the MaskTrack Pro InSync and our on-going collaborative research efforts with SUSS Microtech provides a world-class team and resources focused on mask integrity for the advancement of EUV technology.”
“We are very pleased to continue our collaboration with imec on an EUV mask integrity infrastructure for next generation lithography,” said Frank P. Averdung, President and CEO of SUSS MicroTec AG . “The MaskTrack Pro InSync, is the only mask management system available that can automatically interface with the unique EUV dual pod in a fully-controlled environment. Designed to cluster EUV mask cleaning, transfer and storage in a pristine environment, InSync provides a holistic approach to mask management throughout the life of the mask.”