High resolution fresnel zone plates for soft x-rays (original) (raw)

Process optimization for production of sub-20 nm soft x-ray zone plates

We report here the optimization of processes for producing sub-20 nm soft x-ray zone plates, using a general purpose electron beam lithography system and commercial resist technologies. We have critically evaluated the failure point of the various process steps and where possible chosen alternate methods, materials, or otherwise modified the process. Advances have been made in most steps of the process, including the imaging resist, pattern conversion for electron beam exposure, and pattern transfer. Two phase shifting absorber materials, germanium and nickel, were compared. Zone plates with 30 nm outer zones have been fabricated in both germanium and nickel with excellent quality using polymethyl methyl accrylate and zones as small as 20 nm have been fabricated in nickel using the calixarene resist. The total efficiency as well as the efficiency of different regions of the zone plates were measured. All zone plates have demonstrated good efficiencies, with nickel zone plates performing better than germanium zone plates.

A New Lithographic Technique for the Manufacture of High Resolution Zone Plates for Soft X-Rays

Le Journal de Physique Colloques

-Une technique de lithographie utilisant un microscope électronique à balayage en transmission est en développement. Cette technique est capable de dessiner avec précision sur des petites surfaces, des motifs dont l'épaisseur des lignes est inférieure à 50 nm. On décrit la méthode et on discute de ses applications à la fabrication de composants d'optique pour la diffraction desrayons-X mous.

High-efficiency Fresnel zone plates for hard X-rays by 100 keV e-beam lithography and electroplating

Journal of Synchrotron Radiation, 2011

The fabrication and characterization of Fresnel zone plates (FZPs) for hard X-ray microscopy applications are reported. High-quality 500 nm-and 1 mmthick Au FZPs with outermost zone widths down to 50 nm and 70 nm, respectively, and with diameters up to 600 mm were fabricated. The diffraction efficiencies of the fabricated FZPs were measured for a wide range of X-ray energies (2.8-13.2 keV) showing excellent values up to 65-75% of the theoretical values, reflecting the good quality of the FZPs. Spatially resolved diffraction efficiency measurements indicate the uniformity of the FZPs and a defect-free structure.

Fabrication of Fresnel zone plates for hard X-rays

Microelectronic Engineering, 2007

A method to fabricate gold structures with high aspect ratio is presented. Fresnel zone plates with an outermost zone width of 100 nm and structures of 1 lm height are fabricated. Preliminary focusing results at an X-ray energy of 8 keV are presented and ways to improve the zone plate parameters are discussed.

Progress in the fabrication of high-aspect-ratio zone plates by soft x-ray lithography

Design and Microfabrication of Novel X-Ray Optics, 2002

Fabrication of Fresnel zone plates for the hard x-ray spectral region combines the challenge of high lateral resolution (~100 nm) with a large thickness requirement for the phase-shifting material (0.5-3 µm). For achieving a high resolution, the initial mask was fabricated by e-beam lithography and gold electroforming. To prevent the collapse of the structures between the developing and electroforming processes, drying was completely eliminated. Fabrication errors, such as nonuniform gold electroplating and collapse of structures, were systematically analyzed and largely eliminated. We optimized the exposure and developing processes for 950k and 2200k polymethylmethacrylate of different thicknesses and various adhesion promoters. We discuss the effects of these fabrication steps on the zone plate's resolution and aspect ratio. Fresnel zone plates with 110 nm outermost zone width, 150 µm diameter, and 1.3 µm gold thickness were fabricated. Preliminary evaluation of the FZPs was done by scanning electron microscopy and atomic force microscopy. The FZP focusing performance was characterized at the Advanced Photon Source at Argonne National Laboratory.

Towards 10-nm Soft X-Ray Zone Plate Fabrication

2011

In this paper the latest efforts to improve our nanofabrication process for soft x-ray zone plates is presented. The resolving power, which is proportional to the smallest outermost zone width of the zone plate, is increased by introducing cold development of the electron beam resist that is used for the patterning. With this process we have fabricated Ni zone plates with 13-nm outermost zone and shown potential for making 11-nm half-pitch lines in the electron beam resist. Maintaining the diffraction efficiency of the zone plate is a great concern when the outermost zone width is decreased. To resolve this problem we have developed the so-called Ni-Ge zone plate in which the zone plate is build up by Ni and Ge, resulting in an increase of the diffraction efficiency. In a proof-of-principle experiment with 25nm Ni-Ge zone plates, we have shown a doubling of the diffraction efficiency. When combined with cold development, the Ni-Ge process has been shown to work down to 16-nm half-pitch. It is plausible that further refinement of the process will make it possible to go to 10-nm outermost zone widths.

High-efficiency and low-absorption Fresnel compound zone plates for hard X-ray focusing

Design and Microfabrication of Novel X-Ray Optics, 2002

Circular and linear zone plates have been fabricated on the surface of silicon crystals for the energy of 8 keV by electron beam lithography and deep ion plasma etching methods. Various variants of compound zone plates with first, second, third diffraction orders have been made. The zone relief height is about 10 mkm, the outermost zone width of the zone plate is 0.4 mkm. The experimental testing of the zone plates has been conducted on SPring-8 and ESRF synchrotron radiation sources. A focused spot size and diffraction efficiency measured by knife-edge scanning are accordingly 0.5 mkm and 39% for the first order circular zone plate.

Zone-doubled fresnel zone plates for scanning transmission X-ray microscopy

AIP Conference Proceedings, 2010

We demonstrate the highest spatial resolution reported in scanning transmission x-ray microscopy to date. For the first time in x-ray microscopy, features below 10 nm in width were resolved in the soft x-ray regime (1.2 keV) and 20-nm lines and spaces were visible at multi-keV photon energies (6.2 keV). These achievements were accomplished using zone-doubled Fresnel zone plates. These lenses were fabricated by combining electron-beam lithography and atomic layer deposition of iridium. Diffraction efficiencies up to 8% were measured for zone-doubled Fresnel zone plates with an outermost zone width of 25 nm at 6.2-keV photon energy.

X-ray lithography fabrication of a zone plate for X-rays in the range from 15 to 30 keV

Microelectronic Engineering, 2002

Progress on the fabrication of zone plates for hard X-rays is reported. The issue of achieving a high aspect ratio for lithographic structures has been addressed by developing a specific fabrication protocol based on the combined use of electron beam and proximity X-ray lithography. An example of a 1 mm diameter wide zone plate, optimized for a 23 keV X-ray beam, is presented, showing an aspect ratio of the outermost zone of up to 10. The most critical steps of the fabrication process are discussed on the basis of the results.

Development of laser deposited multilayer zone plate structures for soft X-ray radiation

Applied Surface Science, 2011

As a novel approach, the combination of pulsed laser deposition and focused ion beam was applied to fabricate different types of multilayer zone plate structures for soft X-ray applications. For this purpose, high quality non-periodic ZrO 2 /Ti multilayers were deposited by pulsed laser deposition on planar Si substrates and on rotating steel wires with layer thicknesses according to the Fresnel zone plate law. Linear focusing optics were fabricated by cutting slices out of the multilayers by focused ion beam and placing them directly over pinholes within Si 3 N 4 substrates. Additionally, it was shown that laser deposition of depth-graded multilayers on a wire is also a promising way for building up multilayer zone plates with point focus. First experiments using a table-top X-ray source based on a laser-induced plasma show that the determined focal length and spatial resolution of the fabricated multilayer Laue lens corresponds to the designed optic.