Nanofabrication of multilayer zone plates by helicon plasma sputtering

Multilayer zone plates whose outermost zone widths are less than 100 nm have been fabricated. Alternate deposition of Ag and Al layers has been performed using a helicon plasma sputtering technique, in which Ar gas pressure was less than 1 x 10(-3) Torr, which is one order lower than in conventional magnetron sputtering. More than 100 Ag/Al layers were deposited, with the thickness of each layer being monitored and controlled by a computer, The multilayered plane was sliced vertically and thinned after the deposition. The multilayer zone plate combined with a crystal acts as a monochromatizing and focusing device for hard X-rays, i.e., a Bragg-Fresnel lens.