Soft x-ray reduction lithography using multilayer mirrors

TLDR

The authors propose new telecentric optics to enable a practical soft‑x‑ray reduction lithography system. They selected 45–130 Å wavelengths, designed Schwarzschild demagnifying optics with a ring field, and performed experiments at KEK‑PF, estimating a numerical aperture >0.0125 (or 0.0325 at 130 Å) to achieve 0.2 µm resolution. Experimental results confirm that multilayer‑mirror soft‑x‑ray lithography can replicate 0.2 µm patterns and produce demagnified exposure patterns below 0.5 µm, demonstrating the method’s feasibility.

Abstract

A soft x-ray lithograpy using multilayer mirrors for demagnifying optics and a reflecting mask has been designed and studied experimentally. In this system, a wavelength of 45–130 Å has been selected based on the optical characteristics, the exposed depth of the resist film, and the reflectivity of the multilayer mirror. To obtain a replication pattern resolution of 0.2 μm, the numerical aperture required is estimated to be greater than 0.0125 or 0.0325 for a wavelength of 50 or 130 Å, respectively. These values show that the multilayer optics using two mirrors can be realized to replicate a 0.2 μm pattern. The experiments were performed on the SR beamline BL-1 of the KEK-PF storage ring. The Schwarzschild demagnifying optics with a ring field were designed and fabricated. Demagnified exposure patterns of less than 0.5 μm have been obtained using a reflecting mask. The feasibility of the soft x-ray reduction method using multilayer mirrors has been confirmed. Furthermore, new telecentric optics are proposed to realize a practical reduction lithography system.