Silica imprint templates with concave patterns from single-digit nanometers fabricated by electron beam lithography involving argon ion beam milling

To maintain the silica surface of imprint templates without a fluorine-containing passivation layer on sidewalls after dry etching, we investigated whether a physical dry etching process entailing exposure to Ar ion beam is useful for the fabrication of silica templates. An almost same etching rate of a positive-tone electron beam (EB) resist as silica in Ar ion beam milling allowed for the fabrication of bar-shaped patterns with micrometer lengths and widths for moire alignment and of hole patterns with diameters of around 20 nm in silica templates. The EB resist layer of 40 nm thickness generated partially non-etched defects of 10-nm-diameter holes in silica templates because the Ar ion beam was completely unable to reach silica surfaces through resist sidewalls with a depth of 40 nm. The break-through etching of a hard mask sacrifice Cr layer with a thickness of 5 nm by Ar ion milling and the subsequent inductively coupled plasma etching of silica enabled the fabrication of silica hole templates with diameters of 7–20 nm and depths of 20–30 nm.