High-efficiency nickel phase zone plates with 20 nm minimum outermost zone width

Abstract

Fresnel zone plates for high-resolution imaging in the soft x-ray regime were fabricated in nickel by a trilevel process, which makes use of electron-beam lithography, reactive-ion etching, and electrodeposition. In order to improve the zone plate’s resolution, which is determined by its outermost zone width, ZEP-7000 electron-beam resist was employed. Residues, which arose during pattern transfer by reactive-ion etching, and which hindered etching in small structures, were suppressed by a cleaning procedure. For improved electrodeposition process control, a nickel electroplating bath was optimized. Zone plates with minimum outermost zone widths of 20, 25 and 30 nm were fabricated, yielding 9.2%, 16.2% and 18.0% first-order diffraction efficiency, respectively, at λ=2.4 nm.