ELECTRON-BEAM GENERATED PHASE ZONE PLATES WITH 30 NM ZONEWIDTH FOR HIGH-RESOLUTION X-RAY MICROSCOPY

We report the manufacture of germanium phase zone plates as objective lenses for high resolution X-ray imaging at 2.4 ran wavelength. The phase shifting properties of the germanium can be used to enhance the diffraction efficiency of a zone plate. Zone plate patterns with structure widths down to 30 nm are generated by low distortion electron beam lithography. The structures are transferred into a 280 nm thick layer of germanium by reactive ion etching (RIE) using a highly selective trilevel mask. 100 rim thick boron doped silicon windows made from single crystal wafers serve as high transmission support membranes. Measurements at the BESSY storage ring proved diffraction efficiencies up to 6.2 %. X-ray imaging of a test object showed clearly resolved 30 nm features.