Zone Plates in Nickel and Germanium for High-Resolution X-Ray Microscopy
New manufacturing processes for highly efficient high resolution phase zone plates in nickel and germanium are described. A high resolution cross-linked PMMA resist has been synthesized and optimized for the generation of zone plate patterns with smallest zone width down to 19 nm by e-beam lithography. The resist shows an increased resolution compared to conventional PMMA for periodic structures with line to space ratio of I: I. For the pattern transfer into the zone plate material a cross-linked polymer has been developed. This polymer can be structured by reactive ion etching (RIE) with oxygen, thereby aspect ratios of up to 6: I can be obtained using a trilevel process. The polymer structures can be used either as galvanoform for electrodeposition of nickel or as an etching mask for structuring germanium zone plates. Electroplated nickel zone plates with outermost zone width of 40 nm and 30 nm have been fabricated and achieve 15% and II % diffraction efficiency. For germanium zone plates with outermost zone width of 40 nm, 30 nm and 19 nm diffraction efficiencies of 14%, 10% and 4% were measured at 2.4 nm wavelength.
KeywordsDiffraction Efficiency Zone Plate Space Ratio Etching Mask Zone Height
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