<title>EUV multilayers for solar physics</title>

Emerging Lithographic Technologies IV, 2000

Extensive optimization on the fabrication of Mo/Si multilayer systems is carried out at the FOM Institute Rijnhuizen using e-beam evaporation. The process is being optimized including parameters such as variation of the mirror's centre wavelength, the metal fraction, deposition parameters, and the layer composition. Reflectivities of 69.5 % are demonstrated at normal incidence, with values of 67 to 69% being routinely achieved, demonstrating the capabilities of the deposition process. Some evidence of smoothening to interface roughness values lower than the roughness of the initial substrate is given. Furthermore, investigation of the temporal behaviour of the coatings does not indicate any loss of reflectivity over an eight-month period. An analysis of the multilayer composition and the interface roughness is given. The reflectivity measurements have been carried out at the PTB facilities at the electron storage rings BESSY I and BESSY II in Berlin. The results of measurements at both facilities are found to be identical and accuracy is discussed in detail.

2020

Space optic instrumentation for the sun observation in the Extreme Ultraviolet (EUV) spectral region is often based on multilayer coating technology. Such coatings have not negligible bandwidth, and therefore, often the detected signal is due to the contribution of different very close spectral lines. In this work we present a study of innovative capping layer structures covering the multilayer coating able to improve the rejection of the unwanted lines and at the same time preserving the reflectivity peak at the working wavelength.

Optics Express, 2011

Novel capping layer structures have been deposited on periodic Mo/Si multilayers to optimize reflectance at 30.4 nm. Design, deposition and characterization of such coatings are presented. Most of the structures proposed show improved performance with respect to standard Mo/Si multilayers and are stable over time. Reflectance at 121.6 nm and in the visible spectral range have been also tested to explore the applicability of such coatings to the Multi Element Telescope for Imaging and Spectroscopy (METIS) instrument, a coronagraph being developed for the ESA Solar Orbiter platform.

2000

Extensive optimization on the fabrication of Mo/Si multilayer systems is carried out at the FOM Institute Rijnhuizen using e-beam evaporation. The process is being optimized including parameters such as variation of the mirror's center wavelength, the metal fraction, deposition parameters, and the layer composition. Reflectivities of 69.5% are demonstrated at normal incidence, with values of 67 to 69% being routinely achieved, demonstrating the capabilities of the deposition process. Some evidence of smoothening to interface roughness values lower than the roughness of the initial substrate is given. Furthermore, investigation of the temporal behavior of the coatings does not indicate any loss of reflectivity over an eight-month period. An analysis of the multilayer composition and the interface roughness is given. The reflectivity measurements have been carried out at the PTB facilities at the electron storage rings BESSY I and BESSY II in Berlin. The results of measurements at both facilities are found to be identical and accuracy is discussed in detail.

X-Ray Optics, Instruments, and Missions III, 2000

We discuss the development of X-ray multilayer coatings for use as broad-band reflectors operating at energies above 100 keV. Such coatings can be used to produce hard X-ray telescopes that will make possible a variety of entirely new astronomical observations. We summarize our recent investigation into the growth, structure and hard X-ray performance of depth-graded W/Si multilayers, present follow-up information on Cu/Si multilayers, and discuss preliminary results obtained with Ni/Si, Ni .8 Cr .2 /Si, and Ni .93 V .07 /Si multilayers.

Proceedings of the …, 2002

In this paper we will give an overview of the preparation, characterization and typical results of nm-multilayer coatings prepared by pulsed laser deposition (PLD) and magnetron sputter deposition (MSD). We have achieved particularly outstanding results for the Ni/C and Mo/Si material systems, e.g. extreme ultraviolet (EUV) reflectances of >71% with Mo/Si. The thickness deviations of the multilayer period on flat and curved substrates with macroscopic dimensions (150mm diameter) are reduced down to <0.05%. The standard deviation of the thicknesses from run-to-run is <0.2%. High-Precision nm-Coatings for EUV and X-Ray Optical Applications, Proc. NanoFair (2002) the accurate characterization of multilayers on curved substrates. Additionally, a stand-alone reflectometer for the EUV range has been developed, which permits the characterization of EUV optics at the working wavelength directly in the coating laboratories.

International Conference on Space Optics — ICSO 2006

Extreme UltraViolet instrumentation often requires the use of multilayer coated optics. Such coatings have a limited working bandwidth, and therefore are optimized to perform in correspondence of specific EUV spectral lines. Nevertheless, contemporary observations of the same target in other spectral region would strongly improve scientific knowledge. In this work we present a study on multilayers optimized to achieve high efficiency also in other spectral bands. These coatings would allow the realization of very compact instruments, such as UVCI on board of the Solar Orbiter.

Microelectronic Engineering, 2001

In the past, the successful application of PLD for X-ray multilayer synthesis has already been demonstrated for C-spacer systems. Recently, the method has also been tested for Mo / Si layer stacks. A UHV-coating machine has been used to prepare X-ray mirrors on 4 in. substrates. The ablation of both Mo and Si targets was carried out by Nd:YAG laser irradiation using the third harmonic (l 5 355 nm) with a pulse energy E 5 275 mJ and a pulse width t 5 4. .. 6 ns. p Multilayers of 10. .. 50 periods have been synthesized. Soft X-ray measurements in the EUV-range at near normal incidence show reflectivities R of typically 60%. From HRTEM, a high stack regularity and minimum interface roughness can be s deduced. In contrast to conventional technologies (coating by sputtering or e-beam evaporation) the formation of a MoSi-interface layer happens only when depositing Mo on Si. Extremely sharp interface transitions from one individual x layer to the other are observed and the total period is represented by a three-layer system. From TEM results, a structure model for PLD-prepared Mo / Si-multilayers has been deduced. The optical parameters of the layers were adapted by reflectivity curve fitting, so that the results measured in the EUV-range can be explained. Using this model, predictions of the ratio of the number of atoms N /N for the total stack were made and are in good agreement with results of RBS Si Mo measurements. The use of the multilayers as X-ray optics requires an excellent homogeneity of the layer thickness across the entire mirror. It can be shown that the PLD technique is able to realize film uniformities with a standard deviation of the period thickness of less than 0.5%. This was confirmed by Cu-Ka-reflectometry and by near normal incidence measurements in the EUV range on 4 in. samples.

SPIE Proceedings, 2004

We have determined experimentally optical constants for eight thin film materials that can be used in hard Xray multilayer coatings. Thin film samples of Ni .97 V .03 , Mo, W, Pt, C, B 4 C, Si and SiC were deposited by magnetron sputtering onto superpolished optical flats. Optical constants were determined from fits to reflectance-vs-incidence angle measurements made using synchrotron radiation over the energy range E=35-180 keV. We have also measured the Xray reflectance of a prototype W/SiC multilayer coating over the energy range E=35-100 keV, and we compare the measured reflectance with a calculation using the newly derived optical constants.

AIP Conference Proceedings, 2007

The topic of this paper is the fabrication and characterization of EUV reflective coatings based on molybdenum/silicon (Mo/Si) multilayers. For the fabrication of such nanometer structures, the technologies of magnetron sputter deposition (MSD) and ion beam sputter deposition (IBSD) are used in IWS Dresden. The main challenges for extreme ultraviolet (EUV) optics are high reflectance, precise thickness profiles, low internal stress and long-term stability. Reflectances > 70 %, uniformities > 99.9 % and overall internal stresses < 20 MPa have been reached. In addition to sophisticated deposition technologies, precise metrology tools are mandatory for the characterization of the coatings. Together with a number of partners, IWS Dresden has developed a stand-alone EUV reflectometer that makes it possible to measure EUV reflectance R and peak position O on substrates with diameters of up to 500 mm. Current improvements of the reflectometer resulted in differences compared to calibrated measurements at PTB/BESSY of 'R = -0.2…-0.6 % and 'O 50 = +4…+9 pm.