50nm particle removal from EUV mask blank using standard wet clean

Readiness of defect free mask supply is one of the critical challenges for the insertion of extreme ultra violet lithography (EUVL) into high volume semiconductor manufacturing for 32 nm half pitch (HP) and beyond. According to ITRS updated in 2008, the defect size which is needed to remove is 25 nm for 32 nm HP [1]. On the other hand, in the presentation published in 2008, critical defect size for absorber defect on EUV mask was described around 24 nm for 32 nm HP line and space patterns, meaning that the particles having the equivalent size are necessary to be removed [2]. In such a stringent defect requirement, cleaning process must play critical role to remove such tiny particulate defects. However, EUV mask cleaning faces unique challenges related to the reflective mask structure, new material such as ruthenium (Ru) capping layer and more frequent cleaning due to the lack of pellicle protection. Consequently, it must be gentle enough not to damage fragile patterns and surfaces on EUV mask, particularly the very thin Ru capping layer. The competing demand makes the EUV mask cleaning more challenging. We have reported comprehensive evaluation of cleaning related issues using the blank inspection tool M1350 with 80 nm sensitivity [3, 4]. In this paper we extend our effort to much smaller defects using the new blank inspection tool M7360 with 50 nm sensitivity.