Transparent X-Ray Lithography Masks

Abstract

With a view to producing a rigid and optically-transparent mask for use in X-ray lithography, the membrane strength was theoretically analyzed as a function of the residual stress in films. In silicon nitride films, reduction of the residual stress resulted in an increase in membrane strength accompanied by a decrease in optical Transparency. Silicon nitride film was then combined with transparent silicon dioxide film and an Si3N4/SiO2/Si3N4 sandwich-structure membrane was developed. In this membrane, the compressive film force approached the tensile film force closely, keeping the membrane under tension. This produced an optically-transparent, rigid, smoothly stretched-out membrane. An X-ray lithography mask with 0.8 µm thick gold absorber patterns on this membrane was successfully used for four-level multiple-pattern replications using an optical auto-alignment system.