Hermann Mai

Mo/Si Multilayers with Different Barrier Layers for Applications as Extreme Ultraviolet Mirrors

Pulsed laser deposition (PLD) and magnetron sputter deposition (MSD) have been used to prepare different types of Mo/Si multilayers for the extreme ultraviolet (EUV) spectral range. In the case of PLD prepared Mo/Si multilayers the deposition of 0.3?0.5 nm thick carbon barrier layers at the interfaces leads to a substantial improvement of the interface quality. This can be deduced from Cu-K? reflectivity measurements and HRTEM observations. Consequently the EUV reflectivity has been substantially increased. For pure Mo/Si-multilayers prepared by MSD the deposition parameters have been optimized so that a normal incidence reflectivity of REUV=68.7% could be realized. Although this is one of the best experimental results achieved so far, there is still a gap between this experimental value and the theoretical limit (REUV=75.5%). One of the main reasons for this discrepancy is the formation of intermixing zones at the interfaces. With B4C and C barrier layers at the interfaces interdiffusion can be reduced. The resulting EUV reflectivity of this new type of EUV multilayers is 69.8% (?=13.42 nm, ?=1.5?) and 71.4% (?=12.52 nm, ?=22.5?).

Thermal stability of Mo/Si multilayers with boron carbide interlayers

Abstract Mo/Si multilayer systems with boron carbide (B 4 C) diffusion barrier layers were deposited on sapphire and silicon substrates by DC magnetron sputtering. Samples were subsequently annealed in vacuum at temperatures between 100 and 800 °C for duration of between 20 min and 30 h. Thermally stimulated solid state reactions have been characterized by X-ray analysis methods. Mo/Si multilayers without barrier layers are stable up to 100 °C. Interdiffusion was observed to start by 150 °C. It was found that B 4 C diffusion barrier layers with thicknesses between 0.3 and 1.0 nm, depending on the stack sequence, give rise to an increase of the thermal stability up to 400 °C. The impact of thermal treatments, at various temperatures and annealing times, on thickness and composition of the interdiffusion layers was investigated by X-ray reflectometry, wide angle X-ray scattering, cross-sectional high resolution transmission electron microscopy and fluorescence extended X-ray absorption fine structure measurements in combination with excitation of X-ray standing waves. The last method was used to investigate the short-range order of Mo/Si multilayers depth-resolved.

Comparative study of interfaces of Fe–Al multilayers prepared by direct and crossed-beam pulsed laser deposition

Abstract Fe/Al multilayers with different composition were prepared by conventional, direct-pulsed laser deposition (DPLD) and crossed-beam pulsed laser deposition (CBPLD). Films were studied by means of X-ray reflectometry, wide-angle X-ray scattering and X-ray absorption fine structure experiments. Ballistic simulations of the deposition processes were performed. It is found that adjacent Fe and Al layers are partially intermixed during the deposition, forming Fe–Al transition layers of a few nm in thickness. Both DPLD and CBPLD multilayers have comparable interfaces. In Fe-rich layers, a b.c.c. solid solution is formed. Al-rich layers of approximately 5 nm in nominal thickness are amorphous. DPLD samples have a higher Al content and a significant number of incorporated Al droplets.

New laboratory EUV reflectometer for large optics using a laser plasma source

The quality assurance for production of optical components for EUV lithography strongly requires at-wavelength metrology. Presently, at-wavelength characterizations of mirrors and masks are done using the synchrotron radiation of electron storage rings, e.g. BESSY II. For the production process of EUV optics, however, the immediate access to metrology tools is necessary and availability of laboratory devices is mandatory. Within the last years a stand alone laboratory EUV reflectometer for large samples has been developed It consists of a laser produced plasma (LLP) radiation source, a monochromator and a large goniometer systme. The manipulation system of the reflectometer can handle samples with diameters of up to 500 mm, thicknesses of up to 200 mm and weights of up to 30 kg. The wavelength can be varied from 10 nm to 16 nm. The spot size on the sample surface is about 2mm. The angle of incidence can be varied from 3° to 60°. In this paper, we describe the laboratory reflectometer in detail and discuss the achieved performance. First measurements of 4 inch mirrors are presented and discussed in comparison to the results obtained at the PTB soft x-ray radiometry beamline at BESSY II.

Pulsed laser deposition of x-ray optical layer stacks with atomically flat interfaces

Pulsed laser deposition is described as a technique for the synthesis of multilayers showing X- ray optical quality. The state of the art is characterized by results that demonstrate a development of the instrument basis superior to that of conventional PLD systems. Multilayers of the Ni/C, Mo/Si- and W/C-types prove the versatility of the method and the output of layer stack characterization by HREM, SPM, XD, AES, XPS, ellipsometry and image processing ensures a high quality with regard to stack regularity, layer homogeneity and interface smoothness.

Multilayer x-ray optics for energies E > 8 keV and their application in x-ray analysis

Performance of Ni/C, Ni/B4C, Mo/B4C and W/B4C multilayers in the energy range E > 8 keV is considered by simulation of x-ray reflectivity and resolution of 1st order Bragg reflection at three different photon energies. The results indicate, that Ni/C and Ni/B4C multilayers show highest theoretical reflectivities of R > 80% for Cu K(alpha) - radiation and also above the Mo K-edge (E equals 20.04 keV) at 30 keV. For Mo K(alpha) -radiation a reflectivity of R > 90% can be achieved by the use of Mo/B4C multilayers. For applications, where period thicknesses d < 3 nm and high reflectivities are required W/B4C multilayers can be used. Theoretical values are compared with X-ray reflectometry results, which were executed at 75 period Ni/C, Ni/B4C and Mo/B4C multilayers, fabricated by pulsed laser deposition (PLD) technology on Si substrates. Amorphous or nanocrystalline structures of single layers, smoothest interfaces and high reproducibility of single layer thickness across the entire layer stack are the results of this high precision PLD process.

Postprocessing of nm-period multilayer structures

We study effects of macro- and micro-postprocessing of multilayered synthetic Ni/C film structures. The structures have nm-period 1D modulation of concentration of the major components. Initially low surface and interface roughness of such structures makes them advantageous for application as a new type of substrates in nanofabrication technologies and for information storage with nm-resolution. Metastability of microstructure and high residual stresses favor the use of the structures themselves as a media for fine-scale processing.

Maßgeschneiderte Innenbeschichtung von Bauteilen mittels Puls Laser Deposition. Tailored internal coating of components by Pulsed Laser Deposition

Die Beschichtung von Bauteilinnenflachen gewinnt mit den zunehmenden Anforderungen an Haltbarkeit und Leistungsfahigkeit der technischen Systeme immer mehr an Bedeutung. Beispiele hierfur sind der Warme- und Oxidationsschutz in Brennkammern und Abgassystemen sowie der Verschleisschutz in durch Reibung beanspruchten Bauteilen wie Dampferrohren oder Gieskokillen. Die zur Verfugung stehenden Verfahren weisen jedoch haufig Nachteile bezuglich der Homogenitat der Beschichtung auf oder sind nur auf bestimmte Bauteilgeometrien anwendbar. Nachfolgend wird ein lasergestutztes Verfahren zur Innenbeschichtung von Bauteilen beschrieben, welches die Beschichtung komplexer Geometrien mit Durchmessern bis hinab in den mm-Bereich erlaubt. Die Kopplung der beiden Teilverfahren der Puls Laser Deposition (PLD), Laserablation und Laserverdampfung, ermoglicht dabei die Herstellung masgeschneiderter Schichtsysteme hinsichtlich Mikrostruktur und Schichtdickenverteilung. Die Funktionsweise des Verfahrens wird anhand der Synthese von Warmedammschichten fur Raketenbrennkammern erlautert. As the requirements on technical systems are growing in terms of durability and efficiency, coating of the inner walls of highly charged parts becomes more and more important. Well known examples are the protection of combustion chambers or exhaust systems against heat and oxidation as well as wear protection of friction loaded parts like shock-absorber tubes or casting moulds. The methods available for internal coating are often limited in the inner diameter of the systems to be coated and it has proven to be very difficult to deposit films homogeneously over a wide range. We present a method for coating of complex internal geometries with diameters down to several millimeters. The combination of classic Pulsed Laser Deposition (PLD) and laser evaporation enables synthesis of tailored film systems in terms of microstructure and distribution of single layer thickness. An example for the application of this method is given by means of the preparation of thermal barrier coatings in rocket combustion chambers.

Morphological transition in Ni/C nanoscale multilayers

Annealing of nanoscale Ni/C multilayers and C/Ni/C trilayers at temperatures above about 670 K leads to the formation of separated Ni particles embedded in carbon. The agglomeration of the Ni layers starts by the formation of holes in the Ni layer and proceeds by hole growth and hole coalescence. Different thermodynamic driving forces and kinetic processes which can affect the observed agglomeration are discussed. The formation of holes by thermal grooving of Ni grain boundaries is analyzed quantitatively.

Microstructure of Mo/Si multilayers with barrier layers

Mo/Si multilayers with and without diffusion barrier layers have been prepared by dc magnetron sputter deposition. The introduction of C and B4C barrier layers reduces the formation of the well-known MoSix intermixing zones on the interfaces and improves the optical contrast between absorber and spacer layers. Using these barriers the EUV reflectivity was increased from 68.7% (λ=13.46nm, α=1.5°) for pure Mo/Si multilayers to 69.9% (λ=13.5nm, α=1.5°) for Mo/B4C/Si/C multilayers. The microstructure of the layers has been investigated by HRTEM, X-ray diffractometry, Cu-Kα-and EUV-reflectometry. The introduction of thin C and B4C barrier layers (d=0.2-0.5nm) on the Mo-on-Si interface shifts the amorphous-to-crystalline transition to Mo layer thicknesses >2nm and reduces the size of the Mo crystallites. In multilayers with period thicknesses between 6.5nm and 7.0nm the optimum Mo layer thickness is close to the transition thickness. Therefore small changes of the ratio =dMo/dperiod result in amorphous or crystalline Mo layers. In both cases EUV reflectivities >69% are observed.