Investigation of Contamination Removal from Finished EUVL Mask

During extreme ultraviolet lithography, the surfaces of the imaging optics and mask become contaminated with organic compounds. As more and more contaminants are deposited on a Mo/Si multilayer, the reflectivity and exposure intensity become lower, and the resolution of the imaging optics is degraded. A novel in-situ method of removing contaminants without heating has been developed. In an O2 atmosphere at a pressure of 5.0 × 10-2 Pa and at an electron beam current of the synchrotron storage ring of 150 mA, it removes a 0.1-μm-thick layer of contamination in 7 hours. The removal of the contamination restores the reflectivity of a Mo/Si multilayer without causing any surface damage.