The Early Days of R&D on EUV Lithography and Future Expectations

Abstract

Extreme Ultraviolet Lithography (EUVL) is will soon be fully practically applicable to the high volume manufacture of semiconductor chips. This paper describes the establishment of soft X-ray or EUV optical technology utilizing multilayer optical elements and the early stages of research regarding its application as a lithographic technique. The technology was established through the demonstration of three fundamental properties of optics: imaging, interference, and polarization in the soft X-ray region by multilayer optical elements. In imaging optics, we have demonstrated EUVL's feasibility as a lithographic candidate by establishing a design employing two-aspherical mirror optics, processing the aspherical mirrors with a multilayer coating, devising an assembly technology for imaging optics, and realizing an illumination system for large exposure area. This result showing the possibility of large-area exposure constitutes an epoch that strongly promotes the practical application of EUVL. Also, at-wavelength metrology in the EUV wavelength region, such as mask inspection based on a Mirau interferometric microscope, or thin film analysis based on a soft X-ray ellipsometer has contributed greatly to the practical application of EUVL.