Egbert Buhr

Physikalisch-Technische Bundesanstalt, Brunswyck, Lower Saxony, Germany

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Publications (70)59.12 Total impact

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    Full-text · Article · Mar 2016 · Measurement Science and Technology
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    ABSTRACT: The European Metrology Research Programme participating countries and the European Union jointly fund a three year project to address the need of the automotive industry for a metrological sound base for exhaust measurements. The collaborative work on particle emissions involves five European National Metrology Institutes, the Tampere University of Technology, the Joint Research Centre for Energy and Transport and the Leibniz Institute for Tropospheric Research. On one hand, a particle number and size standard for soot particles is aimed for. Eventually this will allow the partners to provide accurate and comparable calibrations of measurement instruments for the type approval of Euro 5b and Euro 6 vehicles. Calibration aerosols of combustion particles, silver and graphite proof partially suitable. Yet, a consensus choice together with instrument manufactures is pending as the aerosol choice considerably affects the number concentration measurement. Furthermore, the consortium issued consistent requirements for novel measuring instruments foreseen to replace today's opacimeters in regulatory periodic emission controls of soot and compared them with European legislative requirements. Four partners are conducting a metrological validation of prototype measurement instruments. The novel instruments base on light scattering, electrical, ionisation chamber and diffusion charging sensors and will be tested at low and high particle concentrations. Results shall allow manufacturers to further improve their instruments to comply with legal requirements.
    Full-text · Article · Jan 2014 · The European Physical Journal Conferences
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    ABSTRACT: Optical vision systems require both unidirectional and bidirectional measurements for the calibrations and the verification of the tool performance to enable accurate measurements traceable to the SI unit Metre. However, for bidirectional measurements up to now the national metrology institutes are unable to provide internationally recognized calibrations of suitable standards. Furthermore often users are not aware of the specific difficulties of these measurements. In this paper the current status and limitations of bidirectional optical measurements at the industrial level are summarised and compared to state-of-the-art optical linewidth measurements performed at PTB on measurement objects of semiconductor industry. It turns out, that for optical widths measurements at an uncertainty level below 1 μm edge localisation schemes are required, which are based on tool and sample dependent threshold values, which usually need to be determined by a rigorous simulation of the microscopic image. Furthermore the calibration samples and structures must have a sufficient quality, e. g. high edge angle and low edge roughness and the structure materials and their material parameters have to be known. The experience obtained within the accreditation process of industrial labs for width calibrations shows that, in order to be able to achieve a desired measurement uncertainties of about 100 nm, the imaging system needs to have a monochromatic Koehler illumination, numerical aperture larger than 0.5, a magnification greater than 50x and the ability to control the deviation of the focus position to better than 100 nm.
    No preview · Conference Paper · May 2013
  • Chapter: TSEM
    Tobias Klein · Egbert Buhr · Carl Georg Frase

    No preview · Chapter · Dec 2012
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    ABSTRACT: Within the European iMERA-Plus project 'Traceable Characterisation of Nanoparticles' various particle measurement procedures were developed and finally a measurement comparison for particle size was carried out among seven laboratories across six national metrology institutes. Seven high quality particle samples made from three different materials and having nominal sizes in the range from 10 to 200 nm were used. The participants applied five fundamentally different measurement methods, atomic force microscopy, dynamic light scattering (DLS), small-angle x-ray scattering, scanning electron microscopy and scanning electron microscopy in transmission mode, and provided a total of 48 independent, traceable results. The comparison reference values were determined as weighted means based on the estimated measurement uncertainties of the participants. The comparison reference values have combined standard uncertainties smaller than 1.4 nm for particles with sizes up to 100 nm. All methods, except DLS, provided consistent results.
    No preview · Article · Nov 2012 · Measurement Science and Technology
  • B. Bdermann · Egbert Buhr · Zhi Li · Harald Bosse
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    ABSTRACT: IntroductionQuantitative Optical MicroscopyComparison MeasurementsRecent Development Trends: DUV MicroscopyPoints to Address for the Further Development of Quantitative Optical MicroscopyReferences
    No preview · Article · Aug 2012
  • T Klein · E Buhr · K-P Johnsen · C G Frase
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    ABSTRACT: Traceable size measurements of nanoparticles are accomplished by means of a calibrated scanning electron microscope operated in transmission mode (TSEM). An image analysis tool was developed which individually determines the boundary and size of every particle based on modelled TSEM signals obtained by Monte Carlo simulations. The model relies on first-principle electron scattering theory taking into account particle and instrument properties. A series of TSEM images containing thousands of particles can be analysed in automated batch processing to attain a particle size distribution. As examples, nanoparticles of three different material classes (gold, silica, latex) with sizes ranging from about 5 to 60 nm are analysed. An uncertainty analysis reveals expanded measurement uncertainties (95% confidence interval) of the mean diameter in the range of 1 to 3 nm.
    No preview · Article · Aug 2011 · Measurement Science and Technology

  • No preview · Article · Jun 2011
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    ABSTRACT: In this paper we will provide an overview of methods and instruments developed and applied at the National Metrology Institute of Germany (Physikalisch Technische Bundesanstalt—PTB) for high-precision dimensional (linear and angular) measurements and discuss some challenges for future developments in this important area of metrology. Key wordsdimensional (linear and angular) metrology-micrometrology-nanometrology-signal modeling
    Full-text · Article · Aug 2010 · Optoelectronics Instrumentation and Data Processing
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    ABSTRACT: Stochastic sub-wavelength structures with lateral sizes of below 100nm and heights of about 250nm were produced on polymer surfaces by plasma treatment. From these master samples, an embossing nickel tool was manufactured, which, in turn, was used to replicate the master surface form by hot embossing in plastic materials. The geometry of the produced nanostructures was quantified by scanning electron microscopy. The optical surface reflectance of both the master and the replicated samples were measured in the visible wavelength range. A significant reduction of optical reflectance from the expected 4% of untreated surfaces, to less than 0.5% of the master samples, and to values between 1% and 2% of the replicated samples was achieved. The optical reflectance of the stochastic structures was calculated by a finite element-based rigorous solution of the Maxwell equations. The modeled results show a good agreement with experimental data.
    No preview · Article · Oct 2009 · Plasma Processes and Polymers
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    ABSTRACT: In preparation for the international Nano1 linewidth comparison on photomasks between nine national metrology insti-tutes, the National Institute of Standards and Technology (NIST) and the Physikalisch-Technische Bundesanstalt (PTB), initiated a bilateral linewidth comparison in 2008, independent of and prior to the Nano1 comparison in order to test the suitability of the mask standards and the general approach to be used for the Nano1 comparison. This paper reports on the current status of the bilateral comparison. In particular the methods for linewidth metrology applied at NIST and PTB and its major uncertainty contributions will be discussed based on actual measurements results for both of the mask standards chosen for the bilateral comparison.
    Full-text · Article · Oct 2009 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: A conventional scanning electron microscope operated in transmission mode (TSEM) was used for imaging silica, gold and latex nanoparticles. Particles were applied to conventional transmission electron microscope (TEM) grids with different supporting films. A semiconductor detector capable of accomplishing both bright-field and dark-field imaging was used to record transmitted electrons. Particle diameter was determined from the images by comparing measured data with the results of corresponding Monte Carlo simulations which took into account particle and instrument properties. Measured and simulated line profiles agreed well; the method is sensitive to changes in diameter in the nano- and sub-nanometre range. It is concluded that TSEM imaging is a promising tool for dimensional characterization of nanoparticles. Necessary extensions to the technique in order to achieve traceable measurements are discussed.
    No preview · Article · Aug 2009 · Measurement Science and Technology
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    ABSTRACT: A new deep UV transmission microscope for traceable micro- and nanometrology is currently being set up at the Physikalisch-Technische Bundesanstalt (PTB), the National Metrology Institute of Germany. The new microscope is especially designed to enable linewidth measurements of micro- and nanostructures with an unsurpassed absolute measurement uncertainty of down to 10 nm (95% confidence interval). The optical resolution is about 100 nm. The main field of this tool will be critical dimension (CD) metrology of photomasks used in optical lithography. In particular, this system offers the possibility of 'at-wavelength' metrology for the currently applied 193 nm lithography technology. The high lateral resolution will be attained by means of 193 nm excimer laser radiation for illumination in conjunction with a high-aperture objective (NA = 0.9). The illumination and imaging system will provide various imaging modalities, ranging from ordinary brightfield to specially structured illumination schemes. Traceability to the SI unit 'meter' will be accomplished by means of laser interferometry. The mechanical set-up is characterized by an ultra-stable bridge construction on a granite base and has been designed with special emphasis on realizing a positioning stability in the nanometer range. The instrument is being set up in the Clean Room Centre of the PTB and will be ready for operation in mid 2009. Simulation calculations, based on a rigorous optical modeling of the expected microscope images, are presented. These simulations are made for the important application of measuring Cr structures on quartz photomasks. Based on these simulations and on available data of the uncertainties of various experimental parameters—including instrument and sample parameters—expected uncertainty budgets for the measurement of the width of Cr lines on quartz substrates are estimated.
    No preview · Article · Jun 2009 · Measurement Science and Technology
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    ABSTRACT: This paper reports results of an international comparison of one-dimensional (1D) grating pitch calibration by optical diffraction. Comparison results are analysed and discussed following the recommended guidelines for the analysis of CIPM key comparisons. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by SIM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).
    No preview · Article · Jan 2009 · Metrologia
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    ABSTRACT: In preparation of the international Nano1 linewidth comparison on photomasks between 9 national metrology institutes, NIST and PTB have started a bilateral linewidth comparison in 2008, independent of and prior to the Nano1 comparison in order to test the suitability of the mask standards and the general approach to be used for the Nano1 comparison. This contribution describes the rationale of both comparisons, the design of the mask comparison standards to be used and the measurement methods applied for traceable photomask linewidth metrology at NIST and PTB.
    Full-text · Article · Oct 2008 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: Today, various types of high resolution dimensional metrology instrumentation are in use for a quantitative characterisation of micro-and nanostructures. Although sophisticated ultra high resolution microscopic techniques like SEM and AFM are available, optical methods like microscopy and scatterometry are still of interest and are important because they are non-destructive, fast and have a good in-line capability. At PTB different optical tools are used for high-resolution metrology. Our standard instrument for CD metrology is a special UV transmission microscope. A new 193nm microscope is currently under development which will meet future requirements at least for the 32nm node as specified in the ITRS roadmap. A special alternating grazing incidence dark field microscope is used to measure the width of single features down to 100nm. For grating structures, we developed an optical diffractometer for pitch calibrations with an uncertainty down to 10 pm. Recently we realised a DUV scatterometer and ellipsometer capable to measure accurately CD, edge profile, layer thickness, and optical parameters. A versatile EUV scatterometer can be used to characterise absorber structures e. g. on EUV photomasks. For accurate measurements a thorough modelling on the basis of rigorous diffraction calculation is essential, which accounts for both polarisation effects and the 3D geometry of the structures. We use the rigorous coupled wave analysis (RCWA) method and the finite elements (FEM) method. We present an overview of PTB's current and future activities in optical high-resolution metrology and how these systems compare to ultra-high resolution microscopy like SEM or AFM.
    Full-text · Article · Sep 2008 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: We measured the pitch of a 144-nm pitch, two-dimensional grid in two different laboratories. Optical Diffraction gave very high accuracy for mean pitch and Atomic Force Microscopy measured individual pitch values, gaining additional information about local pitch variation. The measurements were made traceable to the international meter. Optical diffraction gave mean value 143.928 +/- 0.015 nm (95% confidence limit, per GUM). AFM gave mean value 143.895 +/- 0.079 nm. Individual pitch values had standard deviation 0.55 nm and expanded uncertainty +/- 1.1 nm. Mean values measured by the two methods agreed within 0.033 nm. Because this was less than the uncertainty due to random variation in the AFM results, it suggests that the AFM measuring and analysis procedures have successfully corrected all systematic errors of practical significance in microscopy. We also discuss what precision may be expected from the AFM method when it is applied to measure smaller pitches.
    Preview · Article · Apr 2008 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: We have developed a lateral standard on the nanometre scale for use with high-resolution optical microscopy techniques [U. Huebner, in: Proceedings of the 5th International Euspen Conference, 2005, pp. 185–188; U. Huebner, in: Optical Fabrication Testing, and Metrology II, Proc. SPIE 5965 (2005) 59651W]. The so-called nanoscale linewidth/pitch standard contains structures in the submicron- and sub-100 nm scale and meets the metrological requirements for accurate, easy and traceable optical microscopy measurements. The optical contrast of the pattern in the UV wavelength range makes it suitable for transmission and reflection UV-microscopy and for confocal laser scanning microscopy. The standard can be used for pitch- and linewidth measurements and for quick resolution testing of these instruments. Additionally, the integrated circular gratings provide a new way of calibrating scanning probe microscopes.
    No preview · Article · May 2007 · Microelectronic Engineering
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    ABSTRACT: A new algorithm for SEM CD evaluation of trapezoidal line structures is presented. It is based on the physical modeling of SEM image formation and allows the assignment of top and bottom structural edge positions to the SEM signal. The SEM image profile is described by a set of piecewise continuous functions which is convoluted with the electron probe intensity profile. The resulting function is fitted to the measured signal profile by a least squares algorithm. The fit returns both top and bottom edge positions as well as the electron probe diameter. The algorithm is verified against three different Monte Carlo simulation programs using different physical models of elastic and inelastic electron scattering and secondary electron generation and transport. The effect of the physical modeling on the evaluated critical dimension is discussed and the absolute CD deviation of the algorithm is determined for different sets of specimen and tool parameters like edge slope angle, beam energy, and electron probe diameter.
    No preview · Article · Mar 2007 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: Measurement and control of edge profiles and edge angles is increasingly important in advanced lithography. Especially for critical dimension metrology a sophisticated multi-dimensional shape metrology is highly beneficial. Different types of dimensional metrology instrumentation are in use today for edge profile and edge angle measurement. While destructive cross section SEM measurements often serve as reference, AFM and optical scatterometry systems are commonly used for day-to-day or in-line control. Due to the limitations of these metrology systems (AFM: slow, scatterometry: only integral measurements of periodic structures), the evaluation and modelling of top down SEM images is increasingly considered, too. At the PTB both SEM and AFM as well as optical scatterometry are applied for edge angle and/or edge profile metrology, supported by optical transmission microscopy. At the PTB we have realised a new DUV hybrid scatterometer for measurements over the full range of 6025 format masks which combines essential elements of a reflectometer, an ellipsometer, and a diffractometer. In addition to scatterometric measurements this set-up allows to measure the complete Müller-matrix including transmission, polarisation and depolarisation. This new set-up will be presented in detail. Finally we study the possibilities of evaluating high resolution top down SEM images to determine edge angles. The potential of edge angle evaluation using these new analysis procedures will be discussed. We present an overview of the PTB measurement capabilities with an emphasis on newly developed metrology methods and systems.
    No preview · Article · Mar 2007 · Proceedings of SPIE - The International Society for Optical Engineering