Silicon/silicon oxide and silicon/silicon nitride multilayers for extreme ultraviolet

Abstract

Si/SiO₂ and Si/Si₃N₄ multilayers have been fabricated using a locally made reactive diode ri-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 α line), and the reflectivity was measured in the soft x-ray range (120-350 Å) 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 ≅22% at 130 Å). Finally, thermal stability of Si/Si₃N₄ multilayers was evaluated. We did not find any degradation after annealing up to 800°C, which is extremely high compared to conventional Mo/Si multilayers, which are generally destroyed above 500°C.