Holography in the extreme ultraviolet region: A new fabrication technique for high resolution Fresnel zone plates

Fresnel Zone Plates (FZPs) are essential components for high resolution x-ray microscopy. An FZP is a diffractive lens that focuses an incident light beam to a small focal spot whose width is related to the smallest feature of the FZP pattern. In this work, we present two different holographic techniques for fabrication of FZPs using extreme ultraviolet (EUV) light (λ = 13.5 nm). The first of the two techniques involves recording the interference pattern of two spherical beams generated by two parent zone plates when illuminated with coherent EUV radiation. In the second approach, a frequency-doubled self-image of the zone plate structure is recorded. In both cases the recorded FZP pattern has half the size of the corresponding features of the parent FZP. The smallest line-width recorded so far by the techniques is below 30 nm. Photon based EUV lithography offers potential for high resolution pattern fabrication and high throughput. The technique also uses the polychromatic nature of the radiation, enabling the use of broad band sources.