Cold-developed electron-beam-patterned ZEP 7000 for fabrication of 13 nm nickel zone plates

Cold development was applied to improve the resolution in a trilayer resist that is used for the fabrication of state-of-the-art soft x-ray microscopy zone plates. By decreasing the temperature of the hexyl acetate developer to −50 °C, 11 nm half-pitch gratings have been resolved in the electron-beam resist ZEP 7000. 12 nm half-pitch gratings have been successfully transferred, via the intermediate SiO2 hardmask, into the bottom polyimide layer by CHF3 and O2 reactive ion etching. The trilayer resist, including optimized cold development, has finally been used in an electroplating-based process for the fabrication of nickel zone plates. Zone plates with down to 13 nm outermost zone width have been fabricated and 2.4% average groove diffraction efficiency has been measured for zone plates with 15 nm outermost zone width and a nickel height of 55 nm.