Development of an abrasive-free polishing method for optical material using pure water and Ni catalyst

摘要

Recently, short-wavelength lights of extreme ultraviolets (EUVs) and X-rays have attracted attention because of their excellent properties to achieve microscopy and/or lithography with an extremely high spatial resolution and a higher photon energy phenomenon [1,2]. In the short-wavelength range, reflective optics are generally utilized since they have a significantly large absorption loss. However, from the viewpoint of fabrication, the surfaces of optical components for EUVs and/or X-rays become difficult to manage because they require unprecedentedly high precision and smoothness. The level of smoothness demanded at the atomic level is a root-mean-square (rms) roughness at several tens of pico-meters and needs to be realized on free-form surfaces. The chemical mechanical polishing (CMP) method is currently utilized as a final surfacing method [3,4]. In CMP, a slurry is used that includes chemicals and abrasives. The workpiece surface is chemically modified and removed with abrasives [5,6]. Due to the usage of abrasives, physical damages onto the surface are unavoidable. The damaged layer significantly reduces the optical reflectance--especially in the short wavelength range [7]. In addition, the abrasives remaining on the surface after the CMP processing are difficult to remove and can cause yield reductions to the products.