SILICON SILICON-OXIDE AND SILICON SILICON-NITRIDE MULTILAYERS FOR EXTREME ULTRAVIOLET OPTICAL APPLICATIONS

Si/SiO2 and Si/Si3N4 multilayers have been fabricated using a locally made reactive diode rf-sputtering system. The layer alternation is obtained by modulating a partial pressure of oxygen or nitrogen near the sample using a silicon target with argon as sputtering gas. O2 and N2 partial pressure conditions were optimized to deposit stoichiometric SiO2 and Si3N4 films without significant reaction with the silicon target. In situ kinetic ellipsometry was used to monitor both thick film and multilayer deposition. The different interfaces appear very sharp with a little contamination of the silicon layers especially using oxygen. The multilayers were characterized by grazing x-ray reflection (Cu-K-alpha-line), and the reflectivity was measured in the soft x-ray range (120-350 angstrom) by synchrotron radiation. Both Si/SiO2 and Si/Si3N4 multilayers exhibit well-defined Bragg peaks with very narrow bandpasses (two to three times lower than the conventional Mo/Si multilayer), and high absolute reflectivities (up to congruent-to 22% at 130 angstrom). Finally, thermal stability of Si/Si3N4 multilayers was evaluated. We did not find any degradation after annealing up to 800-degrees-C, which is extremely high compared to conventional Mo/Si multilayers, which are generally destroyed above 500-degrees-C.