An EUV photomask cleaning solution for the removal of tin contaminate

ASML’s extreme ultraviolet (EUV) lithography machines have found widescale adoption in 5 and 3 nm logic nodes and leading-edge DRAM nodes. The tool operates by generating 13.5nm light from a tin plasma source, which is then directed through multiple optics and reflected off the EUV photomask and down to the wafer surface. In the EUV tool, tin and other contaminants are generated, and because no protective pellicle is used in EUV photo-lithography, any contaminate on the EUV photomask will become a defect on the wafer. EUV photomasks therefore need frequent cleaning compared to a traditional photolithography process, which would employ a protective pellicle. Herein, we report on the development of an EUV photomask cleaning solution that was designed to remove Sn, SnO2, and other contaminates from a mask surface without damaging the mask’s tantalum absorber and ruthenium capping layers. Our mask cleaning solution extends photomask lifetime and can improve operational performance and quality control.