July 12, 2011 – Suss Microtec has joined imec’s research program to develop an in-fab approach to EUV lithography mask integrity. The work, which builds on a collaboration in mask cleaning processes between Suss unit Hamatech APE and imec since 2009, will focus on mask cleanliness during in-fab transportation and support, aiming to develop a holistic mask management system and a sophisticated approach to preserving mask integrity prior to exposure.
EUV masks don’t offer protection of pellicles, so they are more sensitive to contamination (particles and organics) on the mask patterns. A higher cleaning frequency will be needed to mitigate risk to wafers and yields, but the backside of the mask is also a concern — in the scanner it could transfer contaminants to the reticle clamp and result in serious overlay issues. Cleaning the reticle clamp means bringing the critical litho tool offline, causing delays and costs.
imec installed the Suss MaskTrack Pro photomask cleaning system in its 300mm fab in 2009, and the two have pushed ahead with processes-of-record (POR) for EUV mask cleaning, that are effective in removing those contaminants but are gentle enough to be applied repeatedly. Shifting attention to the wafer backside, they have achieved up to 80% particle removal efficiency on an alpha demo reticle; reaching 100% will require avoidance of artifacts caused by handling, transportation, and storage, i.e. a more controlled mask management environment throughout the mask’s use in the fab. To this end, imec has added Suss’ InSync fab management system to its NXE-3100 EUV tool. EUV masks are automatically transferred into and out of the dual pod; the inner pod can be stored inside the InSync environment. Functioning as a loadport the system can accept a reticle dual pod directly from the scanner for transfer to the mask cleaning tool.
Particle removal efficiency (PRE) of the backside of an ADT (alpha demo tool) reticle of up to 80%. (1