Cleaning Challenges of EUV Mask Substrates, Blanks, and Patterned Mask

SEMATECH has been a pioneer in EUV mask substrate and blank cleaning since early 2003. Nevertheless, EUV mask blank defectivity remains one of the main challenges in realizing EUV lithography. EUV masks have their own cleaning challenges that are partly related to introducing new materials and partly related to cleaning-induced EUV reflectivity changes in the multilayer structure. Removal of sub-20 nm particles from the surface of EUV mask substrates without leaving pits is a major challenge along with maintaining Ru cap durability over multiple cleanings and removing sub-20 nm particles from the inside of contact holes and trenches. The goal of this paper is to introduce challenging problems in EUV mask cleaning to researchers and technologists whose research can accelerate the mitigation of EUV mask defects.