Method for repairing Mo/Si multilayer thin film phase defects in reticles for extreme ultraviolet lithography

Abstract

The development of a nearly defect-free reticle blank is an important challenge facing extreme ultraviolet lithography (EUVL). The core element of an EUVL reticle blank is the reflective Mo/Si multilayer film, and deposition of Mo/Si on very small substrate defects can result in critical Mo/Si phase defects. In this article we present a method for repairing Mo/Si multilayer film phase defects in EUVL reticle blanks. An electron beam is used to deposit energy in the immediate vicinity of the defect, producing a small local contraction of the layer thicknesses due to silicide formation at the Mo/Si interfaces. We show in simulations that this contraction can significantly reduce the original structural deformation. We also present experimental results showing that it is possible to use an electron beam to controllably produce depressions in Mo/Si with nanometer-scale depths, and that this can be achieved without significantly impairing the reflective properties of the Mo/Si multilayer films.