Recent advances in traceable nanoscale dimension and force metrology in the UK (original) (raw)
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Developments in Metrology in Support of Nanotechnology
Nanotechnology in Construction 3, 2009
Nanotechnology emerges out of fundamental science through capability for accurate, repeatable and reproducible measurements on the nanoscale which allows scientists and engineers to accumulate knowledge. Understanding the measurement science is the first step towards development of new ideas. This paper describes some research initiatives which underpin the development of nanotechnology. Programs underway at the National Research Council of Canada include: development of metrological scanning-probe microscope instrumentation for dimensional calibration, materials characterization, development of artefacts designed specifically for dimensional calibration, investigation of metrology for application to soft materials and investigation of intrinsic length standards for realization of the SI metre at the nanoscale.
2014
Reliability of measurement is a crucial element of both research and industry. Metrological traceability to the SI unit metre guarantees commensurate units, also at nanometre range. In this thesis, a traceability chain is established for nanometre scale measurements. Measurement instruments and methods were developed for accurate measurements, calibration of instruments and transfer standards, and uncertainty estimations. A metrological atomic force microscope (MAFM) was developed and characterized. The MAFM can be used in the calibration of transfer standards and in accurate AFM measurements. Calibration methods for commercial AFMs were developed. A laser diffractometer was also developed for accurate calibration of 1-D and 2-D gratings with a standard uncertainty of several tens of picometres. Laser interferometric position measurement with a calibrated vacuum wavelength is directly traceable to the realization of the metre if measuring full interferometer fringes, but there is small nonlinearity in sub-fringe measurements. Therefore, in sub-nanometre measurements the nonlinearity of the interferometer needs to be corrected. A method for this correction was developed. Laser diffraction measurement is a very accurate method for characterization of grating pitch. One of the main uncertainty sources is the uncertainty of the measured diffraction angle. Therefore, a method for calibration of the rotary table of the laser diffraction setup was developed. The method can be used also in the realization of angle scale. Methods for transfer standard calibration were developed for both pitch and step height calibration by MAFM. An acoustic method was developed for compensation of the refractive index of air in interferometric measurements. Sub-nanometre uncertainty can be reached with this method. Characterization of instruments, validation of methods and uncertainty estimations are a crucial part of traceability. Therefore, uncertainty estimates based on the characterization of the instruments are given for all measurements in this thesis. Comparisons between laboratories are the best way to ensure commensurate measurements. International comparison results between national metrology institutes for pitch and step height transfer standards are listed. I would like to thank all my colleagues at MIKES, especially MSc Jeremias Seppä, Mr Asko Rantanen, PhD Hannu Husu and MSc Aarni Iho, and the whole length group. It has been a pleasure working with you. Many thanks to PhD Mikko Merimaa for the discussions and comments on the thesis. Thanks also to PhD Kaj Nyholm for his valuable comments. I am grateful to Mr Leonid Mihaljov and AcWaCo Ltd for their kind cooperation. I would like to thank all my international colleagues for their cooperation and valuable input throughout the years. I am also thankful to the University of Helsinki, Department of Physics, and Professor Juhani Keinonen for the inspiring atmosphere during my studies and initial years in the academic world, and to Professor Jyrki Räisänen for his support at the very end of the work. Many thanks to the preliminary examiners Professor Janne Ruokolainen and Professor Markus Ahlskog for their effort. Thanks to Adelaide Lönnberg for revising the English language of the thesis. I would like to acknowledge the Academy of Finland for the financial support, and NGS-NANO for their support. Finally, I would thank my family, Ilkka and Lassi, for their encouragement and support.
Traceability of small force measurements and the future international system of units (SI)
International Journal of Metrology and Quality Engineering, 2016
The unit of force is connected to the international prototype of the kilogramme, unit of mass in the international system of units (SI), via dead weight machines using calibrated masses. However, forces below 10 mN, ubiquitous in nature and in some devices cannot be measured with a traceability to the SI. The measurement, with the uncertainty of these forces has implications for both basic and applied science. Today, many emerging sectors in micro/nanotechnology and biotechnology have started producing and using systems to implement low forces that, for various reasons, require them to be traceable. Also, the revision of the SI, scheduled for 2018 year, of linking the definitions of the kilogramme, the ampere, the kelvin and the mole to fixed numerical values of fundamental constants, has aroused particular interest in the measurement and calibration of small forces. In this paper, we will give some indications of the state of the art on the small force with a focus on the development of a force sensor using a photoelastic crystal as a monolithic solid-state laser. Basically, the force to be measured is applied to the crystal induces a birefringence in the laser medium which in turn manifests itself by the appearance of a splitting between the frequencies associated with the two polarization components of the oscillating laser mode. This difference is then exploited because, within the elastic limit of the crystal, it is proportional to the force acting on the laser.
Calibration of step heights and roughness measurements with atomic force microscopes
Precision Engineering, 2003
In this paper we present a method for the vertical calibration of a metrological atomic force microscope (AFM), which can be applied to most AFM systems with distance sensors. A thorough analysis describes the physical z-coordinate of an imaged surface as a function of the observed and uncorrected z-coordinate and the horizontal position. The three most important correction terms in a Taylor expansion of this function are identified and estimated based on series of measurements on a calibrated step height and a flat reference surface. Based on this calibration a number of step heights are calibrated by the AFM with measured values consistent with reference values, where available. Relative standard uncertainty of about 0.5% is achieved for step heights above 200 nm. For step heights below 50 nm, the standard uncertainty is about 0.5 nm. While a calibration of step heights done by AFM and interference microscopy can be compared directly as demonstrated here, this is not straightforward for roughness measurement. To asses this, the exact same area on an important applied surface (a hip joint prosthesis) was measured by both AFM and interference microscopy. Similarities in the images were seen; however, the calculated roughness was significantly different (R q = 3 and 1.5 nm). Applying a low-pass filter with a cut-off wavelength of λ c = 1.5 m, the appearance of the images and the calculated roughness become almost identical. This strongly suggests that the two methods are consistent, and that the observed differences in shape and roughness in the nanometer range can be explained by the limited lateral resolution of the interference microscope.
Calibrated scanning force microscope with capabilities in the subnanometre range
Surface and Interface Analysis, 2002
This paper refers to quantitative scanning force microscopy (SFM) and dimensional measurement being traceable to metrological standards. The traceability to the unit of length is achieved by calibration of several thousands of selected and sufficiently defined reference positions within the three-dimensional measuring range by three miniature laser interferometers and their output signals at distances of λ/2 (λ corresponds to the wavelength of the He/Ne laser radiation). The expanded uncertainty U of the laser interferometer output signals is estimated to be ⩽1 nm. The results reported here refer to the reduction of uncertainty in the subnanometre range by comparisons of measured periods of one-dimensional sinusoidal gratings using optical diffractometry with expanded uncertainties ⩽0.1 nm, as well as SFM with an uncertainty originally estimated to be 1 nm. The goal is to reduce as far as possible the uncertainty of the SFM measurement results, e.g. the thickness of films or the pitch of gratings. The present state of work allows to estimate an expanded uncertainty of <0.4 nm and it is hoped to reach a value near the picometre range.The practical goal is to apply this microscopy to evaluations (calibrations) of dimensional parameters of objects in the semiconductor technology and other dimensional micro- and nanostructures. Copyright © 2002 John Wiley & Sons, Ltd.
Design of a large-scanning-range contact probe for nano-coordinate measurement machines
Optical Engineering, 2012
A new high-precision contact probe with a large scanning range is proposed and validated, which is able to measure miniature components on a micro/nano-coordinate measuring machine (CMM). This scanning probe is composed of a fiber stylus with a ball tip, a mechanism with a wire-suspended floating plate, a two-dimensional (2-D) angle sensor, and a miniature Michelson linear interferometer. The stylus is attached to the floating plate. The wires experience elastic deformation when a contact force is applied, and then the mirrors mounted on the plate are displaced; the displacements can be detected by corresponding sensors. According to industrial demands, such as scanning range, resolution, equal stiffness, contact force, and probe size, several constrained conditions are established, and the optimal structure parameters of the probe are selected. Each component of the probe is designed, fabricated, and assembled in this research. Simulation and experimental results show that the probe can achieve uniform stiffness, AE20-μm scanning range, and 1-nm resolution in x , y , and z directions. The contact force is about 40 μN when the tip ball is displaced 20 μm. It can be used as a contact and scanning probe on a micro/nano-CMM.
CALIBRATION OF MICROFABRICATED CANTILEVERS FOR SI TRACEABLE SMALL FORCE MEASUREMENT
A procedure is described by which the spring constant of a microfabricated cantilever bea m can be calibrated for the measurement of small forces i n an atomic force microscope (AFM) or other device. The procedure utilizes dynamic force instrumented indentation to determine the mechanical properties of the beam by applying a well-characterized oscillating f orce and measuring resulting displacement of the system. An uncertainty analysis is carried out, and by intercomparison with the U.S. National Institute of Standards and Technology (NIST) Electrostatic Force Balance (EFB). The spring constants determined usi ng the indentation method agree within 2 % of the valu es determined using the EFB for spring constants as lo w as 2 N/m.
SI traceability: Current status and future trends for forces below 10 microNewtons
Measurement, 2010
Measurements related to nano-and micro-scale science, technology, and manufacturing are pushing the limits of detectable mechanical, electrical, and chemical quantities to ever smaller values, raising questions about traceability on such scales. The case in small force measurement is illustrative. At present, the mechanical unit of force is linked to the International Prototype Kilogram, or a deadweight force of nearly 10 N. Although known with exquisite accuracy on this scale, such a mass-based force standard is of little use to investigators and manufacturers using instruments that can determine quantities twelve orders of magnitude smaller. Recognizing this situation, the world congress of the International Measurement Confederation (IMEKO) convened a round table of researchers from National Metrology Institutes representing the US, Europe, and Asia to provide an overview of the emerging field of low-force metrology. This paper captures the information shared in that round table and amplifies on its content.