Effects of ruthenium mirror contamination and tin laser produced plasma debris for extreme ultraviolet lithography

Major challenges for commercial integration of extreme ultraviolet lithography (EUVL) hinge on the development of effective optics and optimized source generation. The goal of this work is to further develop the understanding of these critical research thrusts, optics behavior, and source generation for EUVL. This is accomplished through experimental work conducted with a unique EUV reflectometer and in-situ materials characterization system for optics performance analysis and a laser produced plasma system employing the use of an Nd:YAG laser at fundamental, second, and fourth harmonic wavelengths as well as a CO2 laser in conjunction with a high vacuum chamber. The EUV reflectivity analysis of ruthenium mirrors was conducted in view of sample contamination driven through EUV-related dissociation of chamber water vapor and hydrocarbons in conjunction with reflectometer generated secondary photoelectrons. In particular, oscillations in EUV reflectivity were observed as a function of sample oxidation and surface carbon growth in the presence of secondary photoelectrons. Furthermore, tin LPP debris generation is investigated as a function of the incident laser wavelength optimized for higher conversion efficiency. The CO2 laser is seen to generate less atomic debris than Nd:YAG and the Nd:YAG debris exhibits forward bias not observed by CO2. Debris particle size is investigated with SEM, and seen to be similar for both sources, regardless of the excitation source employed