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Imec, SUSS MicroTec to develop EUV mask tech

Posted: 14 Jul 2011 ?? ?Print Version ?Bookmark and Share

Keywords:EUV? lithography? photomask? mask integrity?

Imec International has expanded its research agreement with SUSS MicroTec AG to develop a complete mask management system that will offer a complex approach to preserve mask integrity prior to exposure using extreme ultraviolet (EUV) lithography. The two companies have previously collaborated in mask cleaning processes of record (POR). They are now extending the scope of their research to focus on mask cleanliness during in-fab transportation and storage.

EUV masks are different from photomasksused in optical lithographyin that they will not have the protection of a pellicle, making them sensitive to particle and organic contamination. A higher cleaning frequency will be required to lessen the risk of wafer loss and yield loss from contamination of the patterned side of the mask. However, a bigger issue is the contamination on the backside of the mask that could transfer to the reticle clamp if introduced into the scanner, causing serious overlay problem. To clean the reticle clamp the scanner would require a costly extensive downtime to the semiconductor manufacturer.

Last year, Imec's mask cleaning program reached significant milestones in the development of PORs for EUV mask cleaning, using SUSS' MaskTrack Pro photomask cleaning system that was installed in Imec's 300mm cleanroom in 2009. The developed PORs are effective in removing the contamination, but 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 performed to keep the overlay performance of the EUV scanner. Imec achieved a particle removal efficiency (PRE) of the backside of an alpha demo tool (ADT) reticle of up to 80 percent. To reach a PRE of 100 percent, particles coming from handling, transportation and storage need to be avoided. Therefore, a controlled mask management environment is necessary from the time the mask enters the fab and throughout the entire lifetime of the mask. This is the goal of the broadened research scope geared toward total automated handling for the recently installed NXE-3100 using the SUSS MaskTrack Pro InSync in-fab mask management system.

Particle removal efficiency

Particle Removal Efficiency (PRE) of the backside of an ADT (alpha demo tool) reticle of up to 80 percent (1x clean).

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 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. It will provide the foundation for further development of the mask integrity infrastructure at Imec.

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