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High-Resolution Nanostructuring for Soft X-Ray Zone-Plate Optics
KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Biomedicinsk fysik och röntgenfysik.
2011 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Diffractive zone-plate lenses are widely used as optics in high-resolution x-ray microscopes. The achievable resolution in such microscopes is presently not limited by the x-ray wavelength but by limitations in zone-plate nanofabrication. Thus, for the advance of high-resolution x-ray microscopy, progress in zone-plate nanofabrication methods are needed.

 

This Thesis describes the development of new nanofabrication processes for improved x-ray zone-plate optics. Cold development of the electron-beam resist ZEP7000 is applied to improve the resolution of soft x-ray Ni zone plates. The influence of developer temperature on resist contrast, resolution, and pattern quality is investigated. With an optimized process, Ni zone plates with outermost zone widths down to 13 nm are demonstrated. To enhance the diffraction efficiency of Ni zone plates, the concept of Ni-Ge zone plates is introduced. The applicability of Ni-Ge zone plates is first demonstrated in a proof-of-principle experiment, and then extended to cold-developed Ni zone plates with outermost zone widths down to 13 nm. For 15-nm Ni-Ge zone plates a diffraction efficiency of 4.3% at a wavelength of 2.88 nm is achieved, which is about twice the efficiency of state-of-the-art 15-nm Ni zone plates. To further increase both resolution and diffraction efficiency of soft x-ray zone plates, a novel fabrication process for W zone plates is developed. High resolution is provided by salty development of the inorganic electron-beam resist HSQ, and cryogenic RIE in a SF6 plasma is investigated for high-aspect-ratio W structuring. We demonstrate W zone plates with 12-nm outermost zone width and a W height of 90 nm, resulting in a 30% increase in theoretical diffraction efficiency compared to 13-nm efficiency-enhanced Ni-Ge zone plates. In addition to soft x-ray zone plates, some lenses for hard x-ray free-electron-laser applications were also fabricated during this Thesis work. Fabrication processes for the materials W, diamond, and Pt were developed. We demonstrate Pt and W-diamond zone plates with 100-nm outermost zone width and respective diffraction efficiencies of 8.2% and 14.5% at a photon energy of 8 keV.

Ort, förlag, år, upplaga, sidor
Stockholm: KTH Royal Institute of Technology , 2011. , s. xii, 70
Serie
Trita-FYS, ISSN 0280-316X ; 2011:55
Nyckelord [en]
zone plates; x-ray optics; x-ray microscopy; high resolution; nanofabrication; electron beam lithography; reactive ion etching; tungsten; nickel; germanium
Nationell ämneskategori
Fysik
Identifikatorer
URN: urn:nbn:se:kth:diva-47409ISBN: 978-91-7501-175-2 (tryckt)OAI: oai:DiVA.org:kth-47409DiVA, id: diva2:455111
Disputation
2011-12-02, FA31, Roslagstullsbacken 21, KTH/Albanova, Stockholm, 10:00 (Engelska)
Opponent
Handledare
Anmärkning
QC 20111114Tillgänglig från: 2011-11-14 Skapad: 2011-11-08 Senast uppdaterad: 2011-11-14Bibliografiskt granskad
Delarbeten
1. Sub-25-nm laboratory x-ray microscopy using a compound Fresnel zone plate
Öppna denna publikation i ny flik eller fönster >>Sub-25-nm laboratory x-ray microscopy using a compound Fresnel zone plate
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2009 (Engelska)Ingår i: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 34, nr 17, s. 2631-2633Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Improving the resolution in x-ray microscopes is of high priority to enable future applications in nanoscience. However, high-resolution zone-plate optics often have low efficiency, which makes implementation in laboratory microscopes difficult. We present a laboratory x-ray microscope based on a compound zone plate. The compound zone plate utilizes multiple diffraction orders to achieve high resolution while maintaining reasonable efficiency. We analyze the illumination conditions necessary for this type of optics in order to suppress stray light and demonstrate microscopic imaging resolving 25 nm features.

Nyckelord
resolution
Identifikatorer
urn:nbn:se:kth:diva-18788 (URN)10.1364/OL.34.002631 (DOI)000270114400031 ()19724514 (PubMedID)2-s2.0-69549105762 (Scopus ID)
Anmärkning
QC 20100525Tillgänglig från: 2010-08-05 Skapad: 2010-08-05 Senast uppdaterad: 2020-03-09Bibliografiskt granskad
2. High-aspect-ratio germanium zone plates fabricated by ractive ion etching in chlorine
Öppna denna publikation i ny flik eller fönster >>High-aspect-ratio germanium zone plates fabricated by ractive ion etching in chlorine
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2009 (Engelska)Ingår i: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 27, nr 2, s. L1-L3Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

This article describes the fabrication of soft x-ray germanium zone plates with a process based on reactive ion etching (RIE) in Cl-2. A high degree of anisotropy is achieved by sidewall passivation through cyclic exposure to air. This enables structuring of higher aspect ratios than with earlier reported fabrication processes for germanium zone plates. The results include a zone plate with a 30 nm outermost zone width and a germanium thickness of 310 tun having a first-order diffraction efficiency of 70% of the theoretical value. 25 nm half-pitch gratings were also etched into 310 nut of germanium. Compared to the electroplating process for the commonly used nickel zone plates, the RIE process with Cl-2, for germanium is a major improvement in terms of process reproducibility.

Nyckelord
x-ray optics; nickel; ti
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:kth:diva-9806 (URN)10.1116/1.3089371 (DOI)000265839400001 ()2-s2.0-64549134292 (Scopus ID)
Anmärkning
QC 20100728Tillgänglig från: 2009-01-07 Skapad: 2009-01-07 Senast uppdaterad: 2020-01-30Bibliografiskt granskad
3. Nickel-germanium soft x-ray zone plates
Öppna denna publikation i ny flik eller fönster >>Nickel-germanium soft x-ray zone plates
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2009 (Engelska)Ingår i: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 27, nr 3, s. L5-L7Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

This article presents a fabrication process for soft x-ray zone plates in which nickel and germanium are combined to achieve high diffraction efficiency. A nickel zone plate is first fabricated on a germanium film and then used as a hardmask for a CHF3-plasma etch into the germanium. Zone plates with 50-60 nm nickel and 110-150 nm of germanium are presented. The measured diffraction efficiencies were 10%-11% at lambda=2.88 nm, which shows that high efficiency is possible even with thin nickel. Thus, the method has a potential for improving the efficiency of high-resolution zone plates for which the high-aspect-ratio structuring of nickel is difficult.

Nyckelord
elemental semiconductors; germanium; light diffraction; nanofabrication; nickel; semiconductor thin films; X-ray microscopy; X-ray optics; zone plates
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:kth:diva-9807 (URN)10.1116/1.3117256 (DOI)000266500300001 ()2-s2.0-70449726046 (Scopus ID)
Anmärkning
Tidigare titel: High-efficency nickel-germanium soft x-ray zone plates QC 20100728Tillgänglig från: 2009-01-07 Skapad: 2009-01-07 Senast uppdaterad: 2020-01-30Bibliografiskt granskad
4. Cold-developed electron-beam-patterned ZEP 7000 for fabrication of 13 nm nickel zone plates
Öppna denna publikation i ny flik eller fönster >>Cold-developed electron-beam-patterned ZEP 7000 for fabrication of 13 nm nickel zone plates
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2009 (Engelska)Ingår i: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 27, nr 6, s. 2593-2596Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Cold development was applied to improve the resolution in a trilayer resist that is used for the fabrication of state-of-the-art soft x-ray microscopy zone plates. By decreasing the temperature of the hexyl acetate developer to -50 degrees C, 11 nm half-pitch gratings have been resolved in the electron-beam resist ZEP 7000. 12 nm half-pitch gratings have been successfully transferred, via the intermediate SiO2 hardmask, into the bottom polyimide layer by CHF3 and O-2 reactive ion etching. The trilayer resist, including optimized cold development, has finally been used in an electroplating-based process for the fabrication of nickel zone plates. Zone plates with down to 13 nm outermost zone width have been fabricated and 2.4% average groove diffraction efficiency has been measured for zone plates with 15 nm outermost zone width and a nickel height of 55 nm.

Nyckelord
electron beam lithography, nickel, optical fabrication, resists, zone, plates, x-ray microscopy, resolution, poly(methylmethacrylate), temperature, dynamics
Identifikatorer
urn:nbn:se:kth:diva-19051 (URN)10.1116/1.3237140 (DOI)000272803400055 ()2-s2.0-72849123318 (Scopus ID)
Anmärkning
QC 20100525Tillgänglig från: 2010-08-05 Skapad: 2010-08-05 Senast uppdaterad: 2020-01-30Bibliografiskt granskad
5. Process development for improved soft X-ray zone plates
Öppna denna publikation i ny flik eller fönster >>Process development for improved soft X-ray zone plates
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2010 (Engelska)Ingår i: Microelectronic Engineering, ISSN 0167-9317, E-ISSN 1873-5568, Vol. 87, nr 5-8, s. 1583-1586Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We demonstrate two nanofabrication methods which improve the diffraction efficiency of high-resolution soft X-ray nickel zone plates. First, pulse electroplating is shown to result in uniform diffraction efficiency over the entire zone-plate area. A resulting enhancement of the total efficiency of 20% compared to conventional DC plating was measured. Second, we demonstrate that a high-resolution cold development process can be combined with efficiency-enhancing dry etching into an underlying germanium film. We present 16 nm half-pitch gratings composed of 50 nm nickel on top of 50 nm germanium.

Nyckelord
Zone plate, Electroplating, Diffraction efficiency, microscopy
Nationell ämneskategori
Annan teknik
Identifikatorer
urn:nbn:se:kth:diva-19377 (URN)10.1016/j.mee.2009.11.012 (DOI)000276300700230 ()2-s2.0-76949092001 (Scopus ID)
Anmärkning
QC 20100525 35th International Conference on Micro-and Nano-Engineering, Ghent, BELGIUM, SEP 28-OCT 01, 2009Tillgänglig från: 2010-08-05 Skapad: 2010-08-05 Senast uppdaterad: 2020-01-30Bibliografiskt granskad
6. 13 nm high-efficiency nickel-germanium soft x-ray zone plates
Öppna denna publikation i ny flik eller fönster >>13 nm high-efficiency nickel-germanium soft x-ray zone plates
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2011 (Engelska)Ingår i: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 29, nr 1, s. 011012-Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Zone plates are used as objectives for high-resolution x-ray microscopy. Both high resolution and high diffraction efficiency are crucial parameters for the performance of the lens. In this article, the authors demonstrate the fabrication of high-resolution soft x-ray zone plates with improved diffraction efficiency by combining a nanofabrication process for high resolution with a process for high diffraction efficiency. High-resolution Ni zone plates are fabricated by applying cold development of electron-beam-patterned ZEP 7000 in a trilayer-resist process combined with Ni-electroplating. High-diffraction-efficiency Ni-Ge zone plates are realized by fabricating the Ni zone plate on a Ge film and then using the finished zone plate as etch mask for anisotropic CHF3 reactive ion etching into the underlying Ge, resulting in a Ni-Ge zone plate with improved aspect ratio and zone plate efficiency. Ni-Ge zone plates with 13 nm outermost zone width composed of 35 nm Ni on top of 45 nm Ge were fabricated. For comparable Ni and Ni-Ge zone plates with an outermost zone width of 15 nm, the diffraction efficiency was measured to be 2.4% and 4.3%, respectively, i.e., an enhancement of a factor of 2.

Nyckelord
Crucial parameters, Etch mask, Ge films, High efficiency, High resolution, Nanofabrication process, Resist process, Soft X-ray, Trilayers, X ray microscopy, Zone plates, Aspect ratio, Diffraction efficiency, Fabrication, Germanium, Optical instruments, Reactive ion etching, X ray diffraction, X rays
Nationell ämneskategori
Annan teknik
Identifikatorer
urn:nbn:se:kth:diva-31321 (URN)10.1116/1.3520457 (DOI)000286679400015 ()2-s2.0-79551627215 (Scopus ID)
Forskningsfinansiär
VetenskapsrådetKnut och Alice Wallenbergs Stiftelse
Anmärkning
QC 20110318Tillgänglig från: 2011-03-18 Skapad: 2011-03-14 Senast uppdaterad: 2020-01-30Bibliografiskt granskad
7. Twelve nanometer half-pitch W–Cr–HSQ trilayer process for soft x-ray tungsten zone plates
Öppna denna publikation i ny flik eller fönster >>Twelve nanometer half-pitch W–Cr–HSQ trilayer process for soft x-ray tungsten zone plates
2011 (Engelska)Ingår i: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 29, nr 6, s. 06FG02-1-06FG02-4Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The authors describe a new W–Cr–HSQ trilayer nanofabrication process for high-resolution and high-diffraction-efficiency soft x-ray W zone-plate lenses. High-resolution HSQ gratings were first fabricated by electron-beam lithography and high-contrast development in a NaCl/NaOH solution. The HSQ pattern was then transferred to the Cr layer by RIE with Cl2/O2, and subsequently to the W layer by cryogenic RIE with SF6/O2. The anisotropy of the W etch as a function of substrate temperature was investigated, and the best etch profile was achieved at −50 °C. Using this optimized process, W gratings with half-pitches down to 12 nm and a height of 90 nm were fabricated. For a zone plate with corresponding parameters, this would result in a theoretical diffraction efficiency of 9.6% (at λ = 2.48 nm), twice as high as has been reported previously.

Nyckelord
zone plates; x-ray optics; tungsten; electron beam lithography; HSQ; reactive ion etching; nanofabrication
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:kth:diva-47400 (URN)10.1116/1.3643760 (DOI)000298538800085 ()2-s2.0-84255172356 (Scopus ID)
Anmärkning
QC 20111114Tillgänglig från: 2011-11-08 Skapad: 2011-11-08 Senast uppdaterad: 2020-01-30Bibliografiskt granskad
8. Platinum zone plates for hard X-ray applications
Öppna denna publikation i ny flik eller fönster >>Platinum zone plates for hard X-ray applications
Visa övriga...
2011 (Engelska)Ingår i: Microelectronic Engineering, ISSN 0167-9317, E-ISSN 1873-5568, Vol. 88, nr 10, s. 3123-3126Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We describe the fabrication and evaluation of platinum zone plates for 5–12 kV X-ray imaging and focusing. These nano-scale circular periodic structures are fabricated by filling an e-beam generated mold with Pt in an electroplating process. The plating recipe is described. The resulting zone plates, having outer zone widths of 100 and 50 nm, show good uniformity and high aspect ratio. Their diffraction efficiencies are 50–70% of the theoretical, as measured at the European Synchrotron Radiation Facility. Platinum shows promise to become an attractive alternative to present hard X-ray zone plate materials due to its nano-structuring properties and the potential for zone-plate operation at higher temperatures.

Nyckelord
zone plate, x-ray optics, electroplating, electron beam lithography, platinum, hard x-rays
Nationell ämneskategori
Teknik och teknologier
Identifikatorer
urn:nbn:se:kth:diva-47405 (URN)10.1016/j.mee.2011.06.011 (DOI)000297400900014 ()2-s2.0-80052786408 (Scopus ID)
Forskningsfinansiär
EU, Europeiska forskningsrådet, FP7/2007-2013 226716
Anmärkning
QC 20111109Tillgänglig från: 2011-11-08 Skapad: 2011-11-08 Senast uppdaterad: 2020-01-30Bibliografiskt granskad
9. New diamond nanofabrication process for hard x-ray zone plates
Öppna denna publikation i ny flik eller fönster >>New diamond nanofabrication process for hard x-ray zone plates
Visa övriga...
2011 (Engelska)Ingår i: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 29, nr 6, s. 06FG03-1-06FG03-4Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The authors report on a new tungsten-hardmask-based diamond dry-etch process for fabricating diamond zone plate lenses with a high aspect ratio. The tungsten hardmask is structured by electron-beam lithography, together with Cl2/O2 and SF6/O2 reactive ion etching in a trilayer resist-chromium-tungsten stack. The underlying diamond is then etched in an O2 plasma. The authors demonstrate excellent-quality diamond gratings with half-pitch down to 80 nm and a height of 2.6 μm, as well as zone plates with a 75 μm diameter and 100 nm outermost zone width. The diffraction efficiency of the zone plates is measured to 14.5% at an 8 keV x-ray energy, and the imaging properties were investigated in a scanning microscope arrangement showing sub-100-nm resolution. The imaging and thermal properties of these lenses make them suitable for use with high-brightness x-ray free-electron laser sources.

Nyckelord
zone plate; reactive ion etching; electron beam lithography; diamond; tungsten; nanofabrication; aspect ratio; x-ray free-electron laser; x-ray optics
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:kth:diva-47402 (URN)10.1116/1.3656055 (DOI)000298538800086 ()2-s2.0-84255168525 (Scopus ID)
Anmärkning
QC 20111114Tillgänglig från: 2011-11-08 Skapad: 2011-11-08 Senast uppdaterad: 2020-01-30Bibliografiskt granskad

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