Proceedings Volume 5193

Advances in Mirror Technology for X-Ray, EUV Lithography, Laser, and Other Applications

cover
Proceedings Volume 5193

Advances in Mirror Technology for X-Ray, EUV Lithography, Laser, and Other Applications

View the digital version of this volume at SPIE Digital Libarary.

Volume Details

Date Published: 13 January 2004
Contents: 6 Sessions, 24 Papers, 0 Presentations
Conference: Optical Science and Technology, SPIE's 48th Annual Meeting 2003
Volume Number: 5193

Table of Contents

icon_mobile_dropdown

Table of Contents

All links to SPIE Proceedings will open in the SPIE Digital Library. external link icon
View Session icon_mobile_dropdown
  • Mirror Fabrication and Metrology I
  • Mirrors, Coatings, and Multilayers I
  • Mirror Fabrication and Metrology II
  • Mirror Fabrication and Metrology III
  • Mirrors, Coatings, and Multilayers I
  • Mirrors, Coatings, and Multilayers II
  • Posters - Thursday
  • Mirror Fabrication and Metrology I
  • Mirrors, Coatings, and Multilayers II
  • Posters - Thursday
Mirror Fabrication and Metrology I
icon_mobile_dropdown
Fabrication and metrology of 10X Schwarzschild optics for EUV imaging
Louis A. Marchetti
ASML Optics recently completed two sets of 10X Schwarschild optics for use in an EUV imaging application. The 10X system consists of two spherical elements - a primary, convex element fabricated from fused silica and a secondary, concave element fabricated from Zerodur. This paper outlines the fabrication process, and discusses the challenges to optical metrology due to the particular form factor and the exacting tolerances placed on the optics. These challenges were met using a variety of metrology tools including full-aperture metrology, phase measuring microscopy (PMM), atomic force microscopy (AFM), and a new mid-frequency interferometer (SASHIMI). A comparison of the recently completed optics is made to the set of 10X optics previously fabricated and delivered in early 1999.
Fabrication and metrology of diffraction-limited soft x-ray optics for the EUV microlithography
Udo Dinger, Guenther Seitz, Stefan Schulte, et al.
EUVL, i.e. microlithography at 13nm is one of the most likely technologies to satisfy the requirements for the 45nm-node and below of the IC-manufacturing roadmap. The development of the first step and scan machines meeting production requirements of field size and resolution is in progress. A key component of these machines will be a diffraction limited, off-axis mirror system with aspherical surfaces. The optical surfaces of these mirrors have to be fabricated and measured with unprecedented accuracy. In recent years, technology development at Carl Zeiss SMT AG was focussed on the on-axis aspheres of the NA=0.30 micro exposure tool (MET). Presently this technology is transferred to the surfaces of a NA=0.25 off-axis, large field system The current status of the fabrication and metrology of both on-axis and off-axis mirrors will be reviewed.
Fabrication of EUV components with MRF
Magneto-rheological finishing (MRF) is a deterministic figuring process capable of quickly achieving extreme surface accuracies. The commercially available Q22 has been instrumental in the manufacture of DUV lithography optics to better than 30 nm P-V figure and 1.0 nm rms microroughness. The requirements for EUV optics, photomask substrates, and silicon-on-insulator (SOI) wafers, however, have taken "extreme accuracy" to new levels. Surface quality is specified over a broad range of spatial frequencies, and allowable error magnitudes shrink ever smaller. These specifications expose some limitations of sub-aperture tool technologies. MRF capabilities, recent developments, and future system improvements that address these concerns are described. We present polishing results on photomasks that pass flatness requirements until year 2010. We further demonstrate extreme precision figure correction capability on SOI wafers, achieving thickness uniformity of better than 2 nm PV and 0.3 nm rms.
Mirrors, Coatings, and Multilayers I
icon_mobile_dropdown
Smoothing of diamond-turned substrates for extreme-ultraviolet lithography illuminators
Regina Soufli, Eberhard Spiller, Mark A. Schmidt, et al.
Condenser optics in extreme ultraviolet lithography (EUVL) systems are subjected to frequent replacement as they are positioned close to the illumination source, where increased heating and contamination occur. In the case of aspherical condenser elements made by optical figuring/finishing, their replacement can be very expensive (several hundred thousand dollars). One approach to this problem would be to manufacture inexpensive illuminator optics that meet all required specifications and could be replaced at no substantial cost. Diamond-turned metal substrates are a factor of 100 less expensive than conventional aspherical substrates but have insufficient finish, leading to unacceptably low EUV reflectance after multilayer coating. In this work it is shown that, by applying a smoothing film prior to multilayer coating, the high spatial frequency roughness of a diamond-turned metal substrate is reduced from 1.76 to 0.27 nm rms while the figure slope error is maintained at acceptable levels. Metrology tests performed at various stages of the fabrication of the element demonstrated that it satisfied all critical figure and finish specifications as illuminator. Initial experimental results on the stability and performance of the optic under a real EUVL plasma source environment show no accelerated degradation when compared to conventional substrates.
Mirror Fabrication and Metrology II
icon_mobile_dropdown
EUV collectors: design, development, fabrication, and testing
Wilhelm J. Egle, Wolfgang Hafner, Axel Matthes, et al.
EUV sources are designed to emit radiation around 13.5 nm wavelength into a solid angle of up to 2π sr. With a suitable Wolter type 1 grazing incidence optic such EUV photons can be collected with high efficiency and focussed onto a preferred target. Such Wolter type 1 collectors are characterized by densely nested concentric and confocal mirror shells with fixed distance from the source and the intermediate image. In this paper we will report on optical and mechanical design, development, fabrication and testing of nested Wolter type 1 collectors, capable of collecting and imaging EUV photons at 13.5 nm wavelength with high efficiency.
Fabrication of meter-scale laser-resistant mirrors for the National Ignition Facility: a fusion laser
Christopher J. Stolz, Carolyn L. Weinzapfel, Amy L. Rigatti, et al.
Large-aperture laser-resistant mirrors are required for the construction of the National Ignition Facility, a 1.8 MJ laser. In order to fabricate the 1408 mirrors, a development program was started in 1994 to improve coating quality, manufacturing rate, and lower unit cost. New technologies and metrology tools were scaled to meter size for facilitization in 1999 at Spectra-Physics and the Laboratory of Laser Energetics at the University of Rochester. Pilot production, to fabricate 5-10% of each component, commenced in 2001 and full production rates were achieved in 2002. Coating production will be completed in 2008 with the coating of 460 m2 of high-damage-threshold precision coatings on 100 tons of BK7 glass with yields exceeding 90%.
Mirror Fabrication and Metrology III
icon_mobile_dropdown
Replicated multilayer x-ray mirrors
Ladislav Pina, Adolf Inneman, Rene Hudec, et al.
We report on the progress in innovative X-ray mirror development with focus on deposition and replication of multilayers. These mirrors are expected to find applications in the fields of X-ray astrophysics as well as in various fields in the laboratory.
EUV spectral purity filter: optical and mechanical design, grating fabrication, and testing
Holger Kierey, Klaus F. Heidemann, Bernd H. Kleemann, et al.
The radiation emitted from an EUV source is collected and focused by a suitable collector system. A reflective blazed grating is used in -1st diffraction order to select a definite spectral band around 13.5 nm wavelength from the broad-band emission spectrum of the source. The effective grating area is segmented into a set of different plane gratings, mounted on a common base plate. In order to focus the light from the collector system, the grating segments are tilted and form a best-fit polygon surface. A specific groove density variation on the grating segments significantly improves the imaging performance. In this paper, we report on design, fabrication and testing of the grating system.
Equal optical path beam splitters by use of amplitude-splitting and wavefront-splitting methods for pencil beam interferometer
A beam splitter to create two separated parallel beams is a critical unit of a pencil beam interferometer, for example the long trace profiler (LTP). The operating principle of the beam splitter can be based upon eitehr amplitude-splitting (AS) or wavefront-splitting (WS). For precision measurements with the LTP, an equal optical path system with two parallel beams is desired. Frequency drift of the light source in a non-equal optical path system will cause the interference fringes to drift. An equal optical path prism beam splitter with an amplitude-splitting (AS-EBS) beam splitter and a phase shift beam splitter with a wavefront-splitting (WS-PSBS) are introduced. These beam splitters are well suited to the stability requirement for a pencil beam interferometer due to the characteristics of monolithic structure and equal optical path. Several techniques to produce WS-PSBS by hand are presented. In addition, the WS-PSBS using double thin plates, made from microscope cover plates, has great advantages of economy, convenience, availability, and ease of adjustment over other beam splitting methods. Comparison of stability measurements made with the AS-EBS, WS-PSBS, and other beam splitters is presented.
Mirrors, Coatings, and Multilayers I
icon_mobile_dropdown
High-performance multilayer coatings for EUV lithography
We review the specification for the coatings in steppers for extreme ultraviolet (EUV) lithography and discuss the deposition methods that have produced such coatings. Thermal deposition by electron beam, magnetron sputtering, and ion beam deposition have all been able to achieve the requirements for future EUV optics. Ion beam sputtering has produced coatings with very few defects and can smooth substrate roughness and mitigate the effects of substrate defects.
Mirrors, Coatings, and Multilayers II
icon_mobile_dropdown
Deposition of multilayer mirrors with arbitrary period thickness distributions
Thomas Foltyn, Stefan Braun, Matthew Moss, et al.
In this paper we will describe a new approach for the deposition of multilayers with arbitrary period thickness distributions. The standard technique of magnetron sputter deposition has been extended to a design where a special mask with lateral varying particle transmission is placed in front of the substrate to be coated. Planar and curved substrates have been used to deposit multilayers with prescribed period thickness gradients. The realized laterally graded multilayer interference mirrors have been investigated by using X-ray and EUV-reflectometry. For the example of Mo/Si multilayers as normal incidence reflectors for EUV light at 13.5 nm it has been demonstrated that high-reflection multilayer mirrors can be deposited using the new deposition technique. Typical EUV reflectance of Mo/Si multilayer with carbon barrier layers are in the order of 70%. In addition, non-uniform masks have been used and several 1- and 2- dimensional period thickness gradients have been coated. The nominal thicknesses were compared with the actual values. Furthermore, steep gradients of the period thickness with thickness changes of typically 5% along a length of 5mm have been prepared and characterized.
Multilayer mirror design for different applications in the XUV using a versatile simulation program
Thomas G. Graf, Alan G. Michette, A. Keith Powell
By combining previous multilayer optics design methods a multilayer mirror program has been developed to provide a versatile tool for multilayer mirror (MLM) design for the XUV range. The optimization program allows variation of the angle of incident radiation, the interface roughness and the number of different materials within the MLM structure. The possibility of optimizing the performance of the MLM using different merit functions or reflectivity profiles has been implemented and makes this program a powerful tool for the design of different multilayer devices. Polarizers have been designed by optimizing at the Brewster angle, and ratios of Rs|Rp around 103 are achieved for specific wavelengths. To select a specific line from a superimposed line and continuum spectrum from an electron impact or laser plasma source, a selective merit function is used. Applications include the calculation of Al Kα and Ti Kα electron impact source radiation monochromators for the use in microbeam radiation experiments. Other ideas for MLMs where the maximal reflected wavelength is dependent on the angle of incidence are currently being studied. These MLMs are planned for the use in achieving tunability of a microscope running with a continuum source.
Development of Mo/Si multilayers deposited by low-pressure rotary magnet cathode sputtering for EUV lithography
Mo (molybdenum)/Si (silicon) multilayers were deposited by low-pressure RMC (rotary magnet cathode) sputtering, which can operate at a gas pressure (about 0.1Pa) lower than that conventional magnetron sputtering. We obtained a high EUV (extreme ultraviolet) reflectivity in the Mo/Si multilayers sputtered with low-pressure Xe gas. The measured maximum EUV reflectivity was about 71%. We confirmed that the multilayers sputtered at a low pressure exhibited high EUV reflectivity. From the TEM (transmission electron microscopy) images of the multilayers we observed thinner interdiffusion layers between Mo and Si layers in the multilayers deposited by RMC sputtering than in those deposited by ion-beam sputtering. The Mo single layer deposited by RMC sputtering has tensile stress and the Si single layer has compressive stress. By changing the Γ ratio (the fractional thickness ratio of a Mo layer to the total thickness of a Mo layer and a Si layer) of multilayer coatings, film stress can be converted from tensile to compressive. However, for larger Γ ratio, interface roughness increases and EUV reflectivity decreases. We have developed a doubly stacked multilayer structure that has low stress and high reflectivity. Using this technique, the stress of multilayer coatings can be reduced to -6 MPa.
Enhanced reflectivity and stability of Sc/Si multilayers
Sc/Si multilayers were designed for normal incidence reflectivity in the wavelength range from 35 to 50 nm and were deposited by dc-magnetron sputtering. X-ray scattering of CuKα radiation, transmission electron microscopy, atomic force microscopy and chemical analysis were used for the characterization of the multilayer structures. The normal incidence reflectivity was measured as a function of the wavelength, for different layer thickness ratios, number of layers and some important sputter parameters. Maximum reflectivities of 21% @ 38 nm and 54 % @ 46 nm for Sc/Si multilayer mirrors were achieved. Reflectivity up to 56 % @ 44.7 nm for a Sc/Si multilayers having enhanced interface structure due to Cr diffusion barriers will be under discussion. The increase in reflectivity is consistent with multilayers having sharper and smoother interfaces. The evolutions of optical properties in the temperature range from 50°C to 250°C for classical Sc/Si and interface engineered Sc/Cr/Si/Cr multilayers will be compared.
Posters - Thursday
icon_mobile_dropdown
Development of an extreme-ultraviolet imaging spectrometer for the Mercury mission
Ichiro Yoshikawa, Tetsunori Murachi, Shingo Kameda, et al.
Extreme and far ultraviolet imaging spectrometers will be boarded on the low-altitude satellite of the upcoming mercury msision (the BepiColombo mission) conducted by ISAS and ESA. The UV instrument, consisting of the two spectrometers with common electronics, aims at measuring, (1) emission lines from molecules, atoms and ions present in the Mercury's tenuous atmosphere, and (2) the reflectance spectrum of Mercury's surface. The instrument pursues a complete coverage in UV spectroscopy. The extreme UV spectrometer covers the spectral range of 30-150 nm with the field of view of 5.0 degree, and the spectrum from 130 nm to 430 nm is obtained by the far UV spectrometer. The extreme UV spectrometer employs a Mo/Si multi-layer coating to enhance its sensitivity at particular emission lines. This technology enables us to identify small ionospheric signals such as He II (30.4nm) and Na II (37.2nm), which the previous mission could not identify.
High-performance Cr/Sc multilayers for the soft x-ray range
Results of soft x-ray reflection measurements of Cr/Sc multilayer mirrors close to the Sc absorption edge at 3.11 nm are presented. Improvements in the deposition technology and the adjustment of the multilayer period with an accuracy of better than 0.01 nm to this absorption edge enabled a step forward towards soft x-ray mirrors with an adequate reflectance that allow the realization of normal incidence optical components in the water window. In particular, reflectivity measurements performed at the PTB reflectometer at BESSY II in Berlin revealed a reflectivity of R = 14.8% at an incidence angle of θ = 1.5° and R = 15.0% at θ = 5°. Simulation results show that the interface widths between the Cr and Sc nanolayers are less than 0.4 nm. The annealing effect in short-period Cr/Sc multilayers was studied in the temperature range from 50°C to 500°C by X-ray scattering and transmission electron microscopy. Structural and phase transformations and the corresponding changes of the optical properties are presented and discussed.
Recoating mirrors having a chromium underlayer
Ali M. Khounsary, Peter J. Eng, Lahsen Assoufid, et al.
X-ray mirrors and multilayers are used to reflect, focus, or monochromatize x-ray beams. Substrate materials are typically silicon, fused silica, Zerodur, ULE, or metals such as molybdenum, copper, or stainless steel. Substrates are polished to a few angstroms rms roughness and often coated with one or more layers to provide the desired spectral reflectivity. Coatings can be damaged as a result of mishandling, contamination and/or chemical reaction, prolonged exposure to x-rays, exposure to poor vacuum, aging, or peeling due to poor coating adhesion and/or high stress. Incomplete or out-of-spec coatings may render an optic unacceptable. In all these cases, it is highly desirable to be able to completely strip off a coating and recoat the substrate without the need for repolishing it. This is particularly important for optical substrates that are expensive or have a long fabrication lead-time. This paper describes one such scheme. It involves pre-coating of mirror reflecting surfaces with a thin layer of chromium. Subsequent coatings can be stripped by etching away the chromium underlayer without damaging the substrate. Experimental results show that surface roughness is unaffected by the etching process in silicon and zerodur, the two substrate material tested so far. The process is expected to be equally applicable to other glasses and can be extended to other substrate materials using appropriate underlayer / etchant combinations.
Rigorous wavefront analysis of the visible-light point diffraction interferometer for EUVL
Katsura Otaki, Yucong Zhu, Mikihiko Ishii, et al.
In visible-light point diffraction interferometer (PDI), in order to achieve measurement error <0.1 - 0.2 nm rms, wavefront irregularity from the pinhole must be supressed as 0.05 - 0.1 nm rms in designing. It is so difficult to execute such high accurate (10-4λ) simulation because the numerical electromagnetic simulation shows slow convergence in the visible-region. We discussed this problem by using 2D-model and found simulation conditions to obtain significant results. By using the simulator, several kind of systematic erros have been analyzed and optimized.
Mirror Fabrication and Metrology I
icon_mobile_dropdown
Fabrication technology of hard x-ray aspherical mirror optics and application to nanospectroscopy
Yuzo Mori, Kazuto Yamauchi, Kazuya Yamamura, et al.
We developed ultra-precise fabrication system for x-ray optics, which combined numerically controlled plasma CVM and EEM. In this system, nanometer order form accuracy having atomic order roughness is achieved. And there are no deformed layers on the surface because these fabrication processes utilizes chemical reaction. So, this system is effective for not only reflective optics but also for diffractive optics. Recently, elliptical mirrors having less than 3 nm form accuracy are fabricated by utilizing the above system, and K-B arrangement microfocusing unit for installation of these mirrors are developed. In this unit, micro x-ray beam having the size of 180 (V)×90(H) nm2 is achieved at 15 keV. By scanning irradiation of the micro x-ray beam and by detecting x-ray fluorescence, inside structures of some mammalian cells are observed with resolution of 0.2 μm.
Mirrors, Coatings, and Multilayers II
icon_mobile_dropdown
Development of a figure correction method having spatial resolution close to 0.1 mm
Yuzo Mori, Kazuto Yamauchi, Kazuya Yamamura, et al.
A new figure correction method is applied to fabricate an elliptical mirror to realize a one-dimensionally diverging X-ray beam having high image quality. Mutual relations between figure errors and intensity uniformities of diverging X-ray beams are also investigated using a wave-optical simulator and indicate that figure errors in relatively short spatial wavelength ranges lead to high-contrast interference fringes. By using the microstitching interferometer and elastic emission machining, figure correction of an elliptical mirror with lateral resolution close to 0.1mm was carried out. A one-dimensional diverging X-ray obtained by the fabricated mirror was observed at SPring-8 and evaluated to have a sufficiently flat intensity distribution.
Performance of an adaptive u-focusing Kirkpatrick-Baez system for high-pressure studies at the Advanced Photon Source
Riccardo Signorato, Daniel Hausermann, Maddury Somayazulu, et al.
X-ray studies of materials in extreme conditions of pressure call for focusing optics able to deliver very clean micron-size focal spots of high energy X-rays with added stringent requirements of flexibility to accommodate different experimental geometries and fast focal spot size adjustment. These requirements are fully met by multi-electrode modular piezoelectric bimorph mirrors (PBMs) in Kirkpatrick-Baez configurations, and these optical systems have already been successfully used for several years at high brilliance 3rd generation synchrotron radiation facilities such as the ESRF and SPring-8. The optical characterization and in-situ X-ray performance of the first pair of modular PBMs installed at the Advanced Photon Source at Argonne national laboratory is reported here. Metrology tests show that the mirrors are able to approximate an arbitrary surface described by a 9th order polynomial in shape with only 100 Å rms shape error over their full optical surface. Full adaptive zonal control allows wave front correction, delivers optimum focal spot profiles (as small as 8.5 (H) x 5.0 (V) μm2 FWHM at a focal distance of 1 m) and fully achieves the creep-free short and long term stability and repeatability required by the experimental program.
Posters - Thursday
icon_mobile_dropdown
A comparison of uranium oxide and nickle as single-layer reflectors from 2.7 to 11.6 nm
Richard L. Sandberg, David D. Allred, J. E. Johnson, et al.
We present the measured reflectances (Beamline 6.3.2, ALS at LBNL) of naturally oxidized uranium and naturally oxidized nickel thin films from 2.7 to 11.6 nm at 5°, 10°, and 15° grazing incidence. These show that uranium, as UO2, can fulfill its promise as the highest known single surface reflector for this portion of the soft x-ray region, being nearly twice as reflective as nickel in the 5-10 nm region. This is due to its large index of refraction coupled with low absorption. Nickel is commonly used in soft x-ray applications in astronomy and synchrotrons. (Its reflectance at 10° exceeds that of Au and Ir for most of this range.) We prepared uranium and nickel thin films via DC-magnetron sputtering of a depleted U target and resistive heating evaporation respectively. Ambient oxidation quickly brought the U sample to UO2 (total thickness about 30 nm). The nickel sample (50 nm) also acquired a thin native oxide coating (<2nm). Though the density of U in UO2 is only half of the metal, its reflectance is high and it is relatively stable against further changes. There are important discrepancies between UO2’s actual reflectance with those predicted by the atomic scattering factor model indicative of the need to determine the actual constants of UO2.
Cooled mirror for a double-undulator beamline
The design of a contact-cooled horizontally reflecting high-heat-load mirror for use as the first optical element on an Advanced Photon Source (APS) beamline is described. The radiation source consists of a set of two collinear undulators producing an x-ray beam with up to 340 W/mm2 peak normal heat flux at the mirror located 30 m from the source. The beam incident angle is 2.6 mrad (0.15°). The mirror is 500 mm long and 75 mm wide. Specifications for this mirror are an rms tangential slope error ≤ 2 μrad and an rms roughness ≤ 2 Å. The mirror substrate is single crystal silicon. To selectively reflect photons with cut-off energies in the 7 to 33 keV range, the central part of the mirror may be coated with strips of Rh, Pt, and Be. Thermal and structural analyses of the mirror (steady state and transient) are reported. Two contact-cooling options considered are back and side cooling. The slope error of side cooling is smaller than that for back cooling. The influence of the mirror thickness and the cooling zone are analyzed. Other options to reduce the slope error are discussed.
Optimized performance of graded multilayer optics for x-ray single-crystal diffraction
Carsten Michaelsen, Joerg Wiesmann, Christian Hoffmann, et al.
We present recent developments in the production of X-ray multilayer optics for Cu Kα laboratory single crystal diffraction equipment for protein crystallography and structural proteomics. The paper shows design, simulations and properties of Montel optics comprised of two elliptically bent focusing multilayers, optimized for the use with modern rotating anode X-ray generators. The multilayers are sputter deposited with a graded d-spacing along the length of the substrate. The various beam properties such as flux density and divergence are investigated in detail. After optimization of the optic for a state-of-the-art rotating anode x-ray generator, we obtain a flux density of 1 x 1010 photons/s/mm2. Results for a typical protein structure will be shown, illustrating the advantage of Montel optics in the field of single-crystal diffraction and protein crystallography for life sciences.