Application of e-beam lithography and reactive ion etching to the fabrication of masks for projection x-ray lithography

Abstract

Mo/Si multilayer mirrors deposited on silicon wafers by triode sputtering were patterned by electron‐beam lithography and etched by reactive ion etching in a fluorinated plasma with an intermediate metallic mask made by the lift‐off process. The etch rate and etch profile were investigated as a function of the gas mixture, pressure, and plasma rf power. The groove depth was monitored by following the reflectivity of the structure with a helium‐neon laser during etching and comparing it with an optical model. Large structures consisting of gratings and Fresnel zone plates with potential applications to high‐resolution alignment for projection x‐ray lithography were fabricated in Mo/Si. The fabrication feasibility of finer structures such as gratings with 0.3–0.5 μm pitch and linewidths smaller than 100 nm as well as linear and circular Fresnel zone plates with a 0.4‐μm‐wide outer zones were investigated in the similar Mo/C multilayer system.