Low-distortion electron-beam lithography for fabrication of high-resolution germanium and tantalum zone plates

Abstract

In this work, an e-beam tool consisting of a commercial pattern generator and a scanning electron microscope is used for the fabrication of high-resolution zone plates for x-ray microscopy applications. In order to avoid misplacement of the zone plate structures, which would result in a deterioration of the imaging properties, various possible distortions of the lithography system are investigated. Misscaling and nonorthogonality of the deflection axes are eliminated by a simple alignment routine using contamination marks. Drift is found to be sufficiently small after several hours of thermal stabilization. The nonlinearity error is measured by the exposure of Moiré patterns. We were able to reduce the total misplacement of the zone plate structures to less than 3×10−4 of the zone plate’s diameter. The resist patterns can be transferred in germanium and tantalum by reactive ion etching using trilevel processes resulting in structures with linewidths down to 26 nm. The quality of the dry etching process is shown by measurement of the x-ray diffraction efficiency. Imaging an e-beam-generated test object with the fabricated zone plates at λ=2.4 nm proves that the total distortions of the e-beam tool were sufficiently reduced.