Fabrication of multilayer Fresnel zone plate for hard X-ray microscopy by atomic layer deposition and focused ion beam milling

Abstract

Fresnel zone plate (FZP) is a widely used optics in X-ray microscopy. In contrast to soft X-ray, high aspect ratio is essential for FZP to focus hard X-ray efficiently. Multilayer FZP (ML-FZP) is a promising solution to fabricate high-aspect-ratio FZP due to the unique sputter-sliced technique. In this work, atomic layer deposition (ALD) and focused ion beam (FIB) milling were utilized to prepare ML-FZP for hard X-ray microscopy. Al2O3/HfO2 ML-FZP with total zone thickness 10 μm was successfully obtained. The zone thickness is much greater than the reported ML-FZPs fabricated by the same method and of great significance to the increase of FZP active region. The ML-FZP with outermost zone width 40 nm and aspect ratio 157 was also tested in transmission X-ray microscopy (TXM) at 9 keV and achieved a 29 nm half-pitch cut-off resolution.