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Improved tungsten nanofabrication for hard X-ray zone plates
KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.ORCID iD: 0000-0001-7569-9408
KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.ORCID iD: 0000-0003-0152-6533
KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
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2016 (English)In: Microelectronic Engineering, ISSN 0167-9317, E-ISSN 1873-5568, Vol. 152, p. 6-9Article in journal (Refereed) Published
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Text
Abstract [en]

We present an improved nanofabrication method of high aspect ratio tungsten structures for use in high efficiency nanofocusing hard X-ray zone plates. A ZEP 7000 electron beam resist layer used for patterning is cured by a second, much larger electron dose after development. The curing step improves pattern transfer fidelity into a chromium hard mask by reactive ion etching using Cl2/O2 chemistry. The pattern can then be transferred into an underlying tungsten layer by another reactive ion etching step using SF6/O2. A 630 nm-thick tungsten zone plate with smallest line width of 30 nm was fabricated using this method and characterized. At 8.2 keV photon energy the device showed an efficiency of 2.2% with a focal spot size at the diffraction limit, measured at Diamond Light Source I-13-1 beamline.

Place, publisher, year, edition, pages
2016. Vol. 152, p. 6-9
Keywords [en]
High aspect ratio, Reactive ion etching, Tungsten, X-ray diffractive optics, Zone plate
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:kth:diva-180917DOI: 10.1016/j.mee.2015.12.015Scopus ID: 2-s2.0-84952359520OAI: oai:DiVA.org:kth-180917DiVA, id: diva2:898484
Note

QC 20160128

Available from: 2016-01-28 Created: 2016-01-25 Last updated: 2018-03-09Bibliographically approved
In thesis
1. High-Aspect Ratio Nanofabrication for Hard X-Ray Zone Plates
Open this publication in new window or tab >>High-Aspect Ratio Nanofabrication for Hard X-Ray Zone Plates
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Hard x-ray nanoimaging enables structural investigations of new materials for many applications. For high-resolution experiments, zone plate x-ray optics are commonly chosen.Two methods of zone plate nanofabrication are presented in this thesis.

Zone plates are circular diffraction gratings with radially decreasing grating period. Their optical resolution depends on the width of the smallest zone, which nowadays can be around 10 nanometers. However, the efficiency of a zone plate depends on its thickness and its material. For hard x-rays, the optimal zone plate thickness is in the order of micrometers. Therefore, high aspect ratio nanofabrication processes are needed.Two such methods are investigated in this study.

First, an existing tungsten nanofabrication process based on reactive ion etching (RIE) was extended to 22:1 aspect ratio structures at 30~nm line width. The core improvement was a resist curing step that enhanced pattern transfer during RIE. Such a zone plate with 200 micrometer diameter and 2.2% efficiency was used in the commissioning experiment of NanoMAX, the nanoimaging beamline at the Swedish synchrotron facility MAX IV. Transmission imaging with 40 nm resolution, as well as the fluorescence imaging modality were demonstrated.

Second, metal-assisted chemical etching (MACE) of silicon using gold catalyst patterns was investigated. MACE dependence on gold pattern geometry, etching solution composition, temperature, and substrate doping is described. The process is characterized in terms of etching rate, directionality, and nanostructure surface roughness.

Finally, the Ronchi test is presented as a way to quickly judge the performance of x-ray optics in terms of present aberrations and x-ray sources in terms of coherence.

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2018. p. 64
Series
TRITA-SCI-FOU ; 2018:09
Keywords
nanofabrication, x-ray optics, zone plate, tungsten, silicon, reactive ion etching, metal-assisted chemical etching, Ronchi test
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-223958 (URN)978-91-7729-700-0 (ISBN)
Public defence
2018-04-06, FB53, Albanova University Center, Roslagstullsbacken 21, Stockholm, 13:00 (English)
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Supervisors
Note

QC 20180312

Available from: 2018-03-12 Created: 2018-03-09 Last updated: 2018-03-12Bibliographically approved

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Parfeniukas, KarolisRahomäki, JussiVogt, Ulrich

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