New diamond nanofabrication process for hard x-ray zone plates

The authors report on a new tungsten-hardmask-based diamond dry-etch process for fabricating diamond zone plate lenses with a high aspect ratio. The tungsten hardmask is structured by electron-beam lithography, together with Cl-2/O-2 and SF6/O-2 reactive ion etching in a trilayer resist-chromium-tungsten stack. The underlying diamond is then etched in an O-2 plasma. The authors demonstrate excellent-quality diamond gratings with half-pitch down to 80 nm and a height of 2.6 mu m, as well as zone plates with a 75 mu m diameter and 100nm outermost zone width. The diffraction efficiency of the zone plates is measured to 14.5% at an 8 keV x-ray energy, and the imaging properties were investigated in a scanning microscope arrangement showing sub-100-nm resolution. The imaging and thermal properties of these lenses make them suitable for use with high-brightness x-ray free-electron laser sources. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3656055]