An etched multilayer as a dispersive element in a curved‐crystal spectrometer: implementation and performance

Jonnard, Philippe; Guen, Karine Le; André, Jean‐Michel; Coudevylle, Jean-René; Isac, N.

doi:10.1002/xrs.2398

Cited by 10 publications

(13 citation statements)

References 22 publications

(51 reference statements)

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“…Due to the low refractive index contrast, the total ML stack generally consists of up to hundreds of bi-layers, resulting in total ML stack heights of ≥ 1 μm. For single-order LMG operation, the required lamel aspect-ratios are in the order of ≥ 10:1, which is well above previously achieved values of ∼ 5:1 [71]. As these structures are used as optical elements, the fabrication should not negatively affect the optical behavior and consequently leave the nanoscale layered arrangement intact.…”

Section: Fabrication Of Gratings In W/si Multilayer Mirrors 41 Introsupporting

confidence: 62%

“…Using the developed process, LMGs with a grating period of only 200 nm and a lamel width of only 60 nm were fabricated in a ML mirror consisting of 400 W/Si bi-layers with a 2.5 nm bi-layer period. The resulting lamel aspect-ratio was 17:1 as compared to previously reported values of ∼5:1 [71]. Etching of the ML was performed using Bosch Deep Reactive Ion Etching (DRIE), which provides directional etching, but also results in typical sidewall scalloping.…”

Section: Discussionmentioning

confidence: 68%

“…Although Reactive Ion Etching (RIE) has been used to etch ML mirrors, this approach generally suffers from a lack of directional etching, resulting in poor critical-dimension (CD) control and a limitation on ML stack heights that can be etched [63,71]. Furthermore, these processes showed strong dependence of the etch results on the grating structure.…”

Section: Fabrication Of Gratings In W/si Multilayer Mirrors 41 Intromentioning

confidence: 99%

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Single-order lamellar multilayer gratings

Meer¹

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Cover: 3D artist impression of a Lamellar Multilayer Grating (LMG). A Transmission Electron Microscope image of an actual LMG is shown on the rear. The grating was etched into a 400 bi-layer W/Si multilayer mirror with a total stack height H of 1 μm and a tungsten layer thickness of only 3 atoms. The grating had a period D of 300 nm and a lamel width ΓD of 75 nm. In comparison to the TEM image on the rear, the red and green layers in the artist impression correspond to tungsten and silicon, respectively. The bi-layer period in the artist impression is overestimated by a factor of 10 for visibility. SummaryA major challenge in the soft x-ray (SXR) and eXtreme UltraViolet (XUV) spectral ranges is the ability to manipulate the incident radiation using optical elements. By patterning conventional multilayer mirrors with nanoscale structures, novel optical elements with a variety of optical properties can be obtained. In this work, the design, fabrication and characterization of Lamellar Multilayer Gratings (LMG) was investigated. Such LMGs are a particular form of the general class of Bragg-Fresnel optics which combine Fresnel optics with Bragg reflection to provide unique dispersive and focusing optics. In particular, LMGs can be used to improve the spectral resolution of x-ray fluorescence techniques.A Coupled Waves Approach (CWA) was derived to simulate the optical performance, in terms of resolution and reflectivity, of LMGs. This CWA allowed to study the physical principles behind LMGs and resulted in the identification of an optimal LMG operating regime. In this regime, the incident beam is reflected in a single diffraction order and is hence referred to as the singleorder regime. Such single-order LMGs were fabricated using UV-NanoImprint Lithography and Bosch Deep Reactive Ion Etching, a process chosen to enable rapid practical development. Single-order operation was experimentally demonstrated and showed an improvement in spectral resolution of a factor of 3.8 with regard to conventional multilayer mirrors. Singe-order excitation of higher diffraction orders was also measured and analyzed.Single-order operation often requires multilayer stacks and grating structures that cannot be fabricated with sufficient accuracy using current technologies. As this invalidates the semi-infinite multilayer approximation, we investigated the optical performance of LMGs with finite multilayer stacks. We determined the ratio between the absorber thickness and bi-layer period of the multilayer stack can be used to further tailor LMG optical performance to maximize bandwidth reduction or minimize peak reflectivity loss. We also investigated various degradation processes that could limit the lifetime of LMGs, which is important for the applicability of such elements. Oxidation of tungsten and silicon as well as changes to the sidewall composition were clearly seen. However, SXR reflectivity remained stable to within measurement accuracy for an extended storage period of 18 months in a 1 atm air environment. The possibility of ...

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Section: Fabrication Of Gratings In W/si Multilayer Mirrors 41 Introsupporting

confidence: 62%

Section: Discussionmentioning

confidence: 68%

Section: Fabrication Of Gratings In W/si Multilayer Mirrors 41 Intromentioning

confidence: 99%

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Single-order lamellar multilayer gratings

Meer¹

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“…Such a 02001-p. 6 UVX 2012 grating has been designed by our team. The diffraction efficiency at the zero th order of a similar grating fabricated in the same conditions has been measured at 182 eV versus the glancing angle at the BEAR beamline of the ELETTRA synchrotron facility [17].…”

Section: Eigenstate Solutions Of the CM Equationsmentioning

confidence: 99%

“…This latter point is important from the practical point of view; indeed recent measurements of the efficiency at the zero th order of a Mo/B 4 C MG [17] have shown that the absolute peak efficiency is smaller and that the bandwidth is notably larger than the expected ones for a perfect LMG as given by the modal theory. One can suspect that these discrepancies can be attributed, at least in part, to a departure of the multilayer pitch from the rectangular shape.…”

Section: Introductionmentioning

confidence: 97%

Analysis by Coupled-Mode Theory of X-ray Multilayer Gratings

André

Jonnard

Guen

2013

UVX 2012 - 11e Colloque Sur Les Sources Cohérentes Et Incohérentes UV, VUV Et X ; Applications Et Développements Récents

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Abstract. Multilayer gratings developed since the end of the ninethies are now used for various purposes in x-uv optics: polychromator, narrow bandpass monochromators. . . We have implemented the Coupled-Mode Theory (CMT) to calculate the performances of these devices (efficiencies, bandwidths. . . ) especially for quasi-lamellar gratings with different shapes of the multilayer pitch. We have fabricated such gratings and compared CMT calculations with measurements obtained at the BEAR beamline of ELETTRA.

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X-ray quasi-lamellar etched multilayers: analysis by coupled-mode theory

2013

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An etched multilayer (EM) is a two-dimensional structure obtained by etching a periodic multilayer following the profile of a grating. Generally a laminar grating shape, i.e. with a rectangular shape, is desired. However, we observe that different EM give different diffraction efficiency curves. We implement the coupled-mode theory to calculate the diffraction pattern of the EM as a function of the shape of the etching profile. Thus, we try to correlate the variability of the experimental reflectivity curves to various shapes of the profiles, rectangular and trapezoidal, and the corresponding simulated reflectivity curves.Keywords: X-ray mirrors, Multilayers, Gratings, Reflectivity, Coupled-mode theory Highlights: Coupled-mode theory is used to calculate the diffraction pattern of the etched multilayers and then compared to experiments. Reflectivity measurements show different curve shapes depending on the sample preparation. This is explained by the various shapes of the etching profile and partially confirmed by the calculations.2

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An etched multilayer as a dispersive element in a curved‐crystal spectrometer: implementation and performance

Cited by 10 publications

References 22 publications

Single-order lamellar multilayer gratings

Single-order lamellar multilayer gratings

Analysis by Coupled-Mode Theory of X-ray Multilayer Gratings

X-ray quasi-lamellar etched multilayers: analysis by coupled-mode theory

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