Andreas Leson

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?).

Multi component EUV multilayer mirrors

It is well known that molybdenum and silicon is the combination with the highest EUV reflectivity of two-component multilayers in the wavelength range lambda=12.5-20nm. Using the magnetron sputter deposition method multilayers with reflectivities of typically 69% can be prepared. A further increase to R=70% was demonstrated by the introduction of tiny barrier layers (C and/or B4C) between the Mo and Si layers, which reduce the interdiffusion of both chemical elements. However, still higher reflectivities are desirable for the use of the multilayers as reflectors for EUV lithography. From model considerations we have concluded that the replacement of the Mo absorber layer by a multi-component layer consisting of two or three layers could result in an EUV reflectivity increase of up to 0.5% compared to the pure Mo/Si system assuming sharp interfaces without any roughness. Particularly Ag and Ru are promising candidates as additional elements within the absorber. Therefore we have systematically changed the thicknesses of the individual layers under the boundary condition of a fixed period thickness of dp=(6.90±0.05)nm. Microstructure and optical parameters of the multilayers have been investigated by HRTEM, X-ray diffractometry and Cu-Ka reflectometry. The most promising multilayers have also been characterized by EUV reflectometry.

Full-field X-ray microscopy with crossed partial multilayer Laue lenses

We demonstrate full-field X-ray microscopy using crossed multilayer Laue lenses (MLL). Two partial MLLs are prepared out of a 48 μm high multilayer stack consisting of 2451 alternating zones of WSi2 and Si. They are assembled perpendicularly in series to obtain two-dimensional imaging. Experiments are done in a laboratory X-ray microscope using Cu-Kα radiation (E = 8.05 keV, focal length f = 8.0 mm). Sub-100 nm resolution is demonstrated without mixed-order imaging at an appropriate position of the image plane. Although existing deviations from design parameters still cause aberrations, MLLs are a promising approach to realize hard X-ray microscopy at high efficiencies with resolutions down to the sub-10 nm range in future.

Highly reflective coatings for micromechanical mirror arrays operating in the DUV and VUV spectral range

High reflecting low-stress optical coatings for the next-generation of micro mechanical mirrors have been developed. The optimized metal systems are applicable from VUV and DUV down to the UV and VIS spectral region and can be integrated in the technology of MOEMS, such as spatial light modulators (SLM) and micro scanning mirrors. This optimized metal designs enable to reconcile high optical performances with adequate mechanical properties and convenient CMOS compatibility. Currently, micro-mirror arrays with enhanced highly reflective coatings for DUV (λ = 193 nm) and VUV (λ = 157 nm) exist as prototypes.

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.

Ptychography with multilayer Laue lenses.

Two different multilayer Laue lens designs were made with total deposition thicknesses of 48 µm and 53 µm, and focal lengths of 20.0 mm and 12.5 mm at 20.0 keV, respectively. From these two multilayer systems, several lenses were manufactured for one- and two-dimensional focusing. The latter is realised with a directly bonded assembly of two crossed lenses, that reduces the distance between the lenses in the beam direction to 30 µm and eliminates the necessity of producing different multilayer systems. Characterization of lens fabrication was performed using a laboratory X-ray microscope. Focusing properties have been investigated using ptychography.

Ion beam sputter deposition of x-ray multilayer optics on large areas

Most important requirements for the deposition of x-ray optical multilayers are a) using a stable and reproducible deposition technique and b) to find growth conditions where the interfaces between adjacent layers are abrupt (no interdiffusion σd) and smooth (no roughness σr). The interface width σ (σ2 = σd 2 + σr 2) becomes increasingly important for smaller period thicknesses. Furthermore, the kinetic energies of the condensing particles on the substrate surface are of special importance for the interface formation. The ion beam sputter deposition technique (IBSD) provides stable and well adjustable particle energies combined with medium to high deposition rates allowing the fabrication of precise multilayer stacks for x-ray optical applications. We will present our newly installed large area IBSD facility with 400 x 100 mm2 linear ion sources and substrate sizes of up to 200 mm diameter (circular) or 500 x 100 mm2 (rectangular) and its characteristics concerning thickness homogeneity and process stability. First experimental results of metal/non-metal multilayer depositions with thickness uniformities of 99,9% over the entire substrate area are discussed. Different material combinations (Ni/B4C, Ni/C, Mo/Si) with period thicknesses between 2 nm and 10 nm have been fabricated and characterized by x-ray and EUV reflectometry. Interface widths are typically in the order of 0.3 nm. For the Ni-based multilayers Cu-Kα reflectances of R > 80 % can be obtained with period thicknesses dP greater than or equal to 2.5 nm (Ni/B4C) and dP greater than or equal to 3.0 nm (Ni/C). EUV reflectances of the Mo/Si multilayers are as high as R = 68,0 % at λ = 13,5 nm (incidence angle α = 5 deg).

Point focusing with flat and wedged crossed multilayer Laue lenses

Point focusing measurements using pairs of directly bonded crossed multilayer Laue lenses (MLLs) are reported. Several flat and wedged MLLs have been fabricated out of a single deposition and assembled to realise point focusing devices. The wedged lenses have been manufactured by adding a stress layer onto flat lenses. Subsequent bending of the structure changes the relative orientation of the layer interfaces towards the stress-wedged geometry. The characterization at ESRF beamline ID13 at a photon energy of 10.5 keV demonstrated a nearly diffraction-limited focusing to a clean spot of 43 nm × 44 nm without significant side lobes with two wedged crossed MLLs using an illuminated aperture of approximately 17 µm × 17 µm to eliminate aberrations originating from layer placement errors in the full 52.7 µm × 52.7 µm aperture. These MLLs have an average individual diffraction efficiency of 44.5%. Scanning transmission X-ray microscopy measurements with convenient working distances were performed to demonstrate that the lenses are suitable for user experiments. Also discussed are the diffraction and focusing properties of crossed flat lenses made from the same deposition, which have been used as a reference. Here a focal spot size of 28 nm × 33 nm was achieved and significant side lobes were noticed at an illuminated aperture of approximately 23 µm × 23 µm.

Reflectance and Resolution of Multilayer Monochromators for Photon Energies from 400 – 6000 eV

This paper deals with multilayer monochromators for synchrotron beamlines that are produced by magnetron and ion beam sputter deposition (MSD and IBSD). Different material combinations (W/B4C, W/Si, Mo/B4C, Mo/Si) with period thicknesses between 1 nm and 10 nm have been fabricated and measured at the synchrotron BESSY II (optics and KMC1 beamlines). The main challenge for the deposition of nanometer multilayers is to find growth conditions where the interfaces between adjacent layers are abrupt (no interdiffusion σd) and smooth (no roughness σr). The interface width σ (σ2 = σd2 + σr2) becomes increasingly important for smaller period thicknesses. One decisive point for the interface formation is the kinetic energy distribution of the particles arriving on the substrate surface. In MSD, the sputter gas pressure is the main parameter for influencing the kinetic energy of the particles. In IBSD, an assist ion beam source can be used to bombard the growing film with inert gas atoms of a specific energy. Using...

Ion beam sputtering of x-ray multilayer mirrors

Ion beam sputtering has been applied for polishing, figuring and multilayer coating on silicon and quartz glass substrates for the fabrication of x-ray mirrors. For high-performance x-ray optics extremely low microroughnesses of the substrates have to be achieved. Particularly for low d-spacing multilayers (d = 1...2 nm) even small improvements of the surface quality result in significant performance gains of the mirrors. By ion beam polishing silicon substrate surfaces could be smoothed from 0.18 nm rms to 0.11 nm rms (AFM scan length = 5 μm). Furthermore figuring of spherical substrates into elliptical or parabolic surface contours has been developed and applied. Spherical quartz glass substrates with initial rms roughnesses of 0.73 nm and 0.52 nm show reduced roughnesses after figuring and multilayer coating of 0.26 nm and 0.10 nm using AFM scan lengths of 20 μm and 5 μm, respectively. The testing of the ion beam figured mirrors for the application as parallel beam and focussing optics shows very promising results: The comparison of collimating mirrors, produced either by ion beam figuring or bending, shows very similar x-ray intensities. However, the ion beam figured mirrors open the perspective for further reduced figure errors, improved long-term stability and 2-dimensional focusing.