Steven R. Lange

The analysis of EUV mask defects using a wafer defect inspection system

EUVL is the strongest candidate for a sub-20nm lithography solution after immersion double-patterning. There are still critical challenges for EUVL to address to become a mature technology like todays litho workhorse, ArF immersion. Source power and stability, resist resolution and LWR (Line Width Roughness), mask defect control and infrastructure are listed as top issues. Source power has shown reasonably good progress during the last two years. Resist resolution was proven to resolve 32nm HP (Half Pitch) lines and spaces with good process windows even though there are still concerns with LWR. However, the defectivity level of blank masks is still three orders of magnitude higher than the requirement as of today. In this paper, mask defect control using wafer inspection is studied as an alternative solution to mask inspection for detection of phase defects on the mask. A previous study suggested that EUVL requires better defect inspection sensitivity than optical lithography because EUVL will print smaller defects. Improving the defect detection capability involves not only inspection system but also wafer preparation. A few parameters on the wafer, including LWR and wafer stack material and thickness are investigated, with a goal of enhancing the defect capture rate for after development inspection (ADI) and after cleaning inspection (ACI). In addition to defect sensitivity an overall defect control methodology will be suggested, involving mask, mask inspection, wafer print and wafer inspection.