Particle removal challenges with EUV patterned masks for the sub-22 nm HP node

The particle removal efficiency (PRE) of cleaning processes diminishes whenever the minimum defect size for a specific technology node becomes smaller. For the sub-22 nm half-pitch (HP) node, it was demonstrated that exposure to high power megasonic up to 200 W/cm(2) did not damage 60 nm wide TaBN absorber lines corresponding to the 16 nm HP node on wafer. An ammonium hydroxide mixture and megasonics removes >= 50 nm SiO2 particles with a very high PRE. A sulfuric acid hydrogen peroxide mixture (SPM) in addition to ammonium hydroxide mixture (APM) and megasonic is required to remove >= 28 nm SiO2 particles with a high PRE. Time-of-flight secondary ion mass spectroscopy (TOFSIMS) studies show that the presence of O-2 during a vacuum ultraviolet (VUV) (lambda=172 nm) surface conditioning step will result in both surface oxidation and Ru removal, which drastically reduce extreme ultraviolet (EUV) mask life time under multiple cleanings. New EUV mask cleaning processes show negligible or no EUV reflectivity loss and no increase in surface roughness after up to 15 cleaning cycles. Reviewing of defect with a high current density scanning electron microscope (SEM) drastically reduces PRE and deforms SiO2 particles. 28 nm SiO2 particles on EUV masks age very fast and will deform over time. Care must be taken when reviewing EUV mask defects by SEM. Potentially new particles should be identified to calibrate short wavelength inspection tools. Based on actinic image review, 50 nm SiO2 particles on top of the EUV mask will be printed on the wafer.