Mo-Si Interface Formation by Ion Beam Sputter Deposition

Abstract

Molybdenum-silicon (Mo-Si) multilayers for EUV lithography were prepared by ion beam sputter deposition at room temperature. The multilayer structure was determined by X-ray-diffraction and transmission electron microscopy. Textured molybdenum layers with preferential (110) orientation normal to the surface are observed. At the interfaces of all Mo-Si and Si-Mo pairs additional intermixing resulting in molybdenum silicide layers were noticed. These layers have a thickness of about 0.7 and 1.5 nm each, respectively. Due to this intermixing, the nominal thickness of the Mo and Si layers is reduced. The optical index contrast at the interface is also expected to decrease. This is in accordance with the obtained EUV reflectivity results of 64–65% at 13.4 nm which remains below the theoretical value of 74%. The formation of the silicide interface layers is discussed and an optimized deposition process focused on narrowing these transition layers is suggested.