13 nm high-efficiency nickel-germanium soft x-ray zone plates

Zone plates are used as objectives for high-resolution x-ray microscopy. Both high resolution and high diffraction efficiency are crucial parameters for the performance of the lens. In this article, the authors demonstrate the fabrication of high-resolution soft x-ray zone plates with improved diffraction efficiency by combining a nanofabrication process for high resolution with a process for high diffraction efficiency. High-resolution Ni zone plates are fabricated by applying cold development of electron-beam-patterned ZEP 7000 in a trilayer-resist process combined with Ni-electroplating. High-diffraction-efficiency Ni–Ge zone plates are realized by fabricating the Ni zone plate on a Ge film and then using the finished zone plate as etch mask for anisotropic CHF3 reactive ion etching into the underlying Ge, resulting in a Ni–Ge zone plate with improved aspect ratio and zone plate efficiency. Ni–Ge zone plates with 13 nm outermost zone width composed of 35 nm Ni on top of 45 nm Ge were fabricated. For comparable Ni and Ni–Ge zone plates with an outermost zone width of 15 nm, the diffraction efficiency was measured to be 2.4% and 4.3%, respectively, i.e., an enhancement of a factor of 2. © 2011 American Vacuum Society. DOI: 10.1116/1.3520457