Article

Development of a metrological atomic force microscope

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Abstract

Scanning probe microscopes are very well used for characterization at the nanometer scale. To ensure the measurement coherency and the accuracy of the results, those microscopes need to be periodically calibrated. It's done thanks to reference standards whose dimensional characteristics are measured by a metrological atomic force microscope (mAFM) for example. The aim of this thesis work is to develop in France the first metrological atomic force microscope in order to calibrate the reference standards that are used in scanning probe microscopy. Displacement range is about 60 μm in the horizontal plane and 15 μm along the vertical axis. Dimensional measurements of the tip-sample relative position are achieved with four differential interferometers whose laser wavelengths are calibrated in order to perform direct traceability to the length standard. The tip sample relative position uncertainty is about one nanometer for the whole range. The conception of this metrological AFM is lead through four main design rules: (i) the minimization of Abbe errors, (ii) the optimization of the metrological loop, (iii) the reduction of thermal effects during the measurement process and (iv) the optimization of ambient interferometrical measurement.

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Microscope calibration standards in nanometrology were calibrated using a metrological atomic force microscope (metrological AFM) and the validity of calibrated values was shown. The metrological AFM was developed through the modification of a commercial AFM, which replaced the PZT tube scanner with flexure hinge scanners and displacement sensors. These modifications improved the traceability of measured values to metrological primary standards. The grating pitch and step height specimens, which are typical standard artefacts for the calibration of lateral and vertical magnifications of microscopes, were measured using the metrological AFM. The expanded uncertainties (k = 2) of calibrated values were estimated considering the characteristics of the calibration process and were less than 1 nm. The measurement results were compared with those obtained by other metrological methods or the certified values and their consistency was verified by checking the En numbers. These experimental results show that the metrological AFM can be used effectively for the measurements of microscope calibration standards in nanometrology.
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We present a system of positioning and interferometric monitoring of a sample position for measurements and calibration in the nanoscale in metrology. The positioning is based on a three-axis stage which allows replacing scanning by the probe of an atomic force microscope with a system with full interferometric displacement measurement. A stage with 200 µm × 200 µm of horizontal travel extends also the microscope range. The stage allows positioning with sub-nanometer resolution in all three axes under a closed loop control with position detection via capacitive sensors. Interferometric system monitoring all six degrees of freedom of the stage ensures full metrological traceability of the positioning to the fundamental etalon of length and improves resolution and overall precision of the displacement monitoring.
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A differential plane mirror interferometer developed at the NPL has been built into a system designed to calibrate and certify displacement transducers. Two electrical signals generated from the optical outputs of the interferometer and a voltage output of the transducer to be calibrated are read by a computer and mathematically analysed in order to calculate the proportionality and linearity of the displacement transducer. In order to realize the highest measurement accuracy from the interferometer the interferogram signals are analysed and corrected by an optimizing routine in order to interpolate the fractioning of the optical fringes accurately. Without computer optimization of the signals a standard deviation of measurement of a few nanometres is typical, whereas after optimization this is reduced to a fraction of a nanometre. The interferometer has been used to calibrate a high-precision capacitance probe and the results of these measurements are shown and discussed.
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The review will describe the various scanning probe microscopy tips and cantilevers used today for scanning force microscopy and magnetic force microscopy. Work undertaken to quantify the properties of cantilevers and tips, e.g. shape and radius, is reviewed together with an overview of the various tip–sample interactions that affect dimensional measurements.
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The only difference between nanotechnology and many other fields of science or engineering is that of size. Control in manufacturing at the nanometre scale still requires accurate and traceable measurements whether one is attempting to machine optical quality glass or write one's company name in single atoms. A number of instruments have been developed at the National Physical Laboratory that address the measurement requirements of the nanotechnology community and provide traceability to the definition of the metre. The instruments discussed in this paper are an atomic force microscope and a surface texture measuring instrument with traceable metrology in all their operational axes, a combined optical and x-ray interferometer system that can be used to calibrate displacement transducers to subnanometre accuracy and a co-ordinate measuring machine with a working volume of (50 mm)3 and 50 nm volumetric accuracy.
Article
a b s t r a c t A new metrological AFM is developed for the Dutch standards laboratory. This instrument consists of a translation stage with a stroke of 1 Â 1 Â 1 mm and a custom-designed AFM measurement head. Here the design of the translation stage, consisting of elastic straight guides, Lorentz-actuators with weight and stiffness compensation and interferometric translation measurement systems, will be discussed. Some preliminary results on the performance of the actuation system are presented.
Article
The design of a large measurement-volume metrological atomic force microscope (AFM) is presented. The translation of the sample is accomplished with multiple stages which allow for separate 'coarse' and 'fine' motion. Interferometers and autocollimators are used to measure the position and orientation of the sample. The instrument does not attempt to control position via feedback from the interferometers, thereby allowing use of readily available commercial translation stages and controllers.
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In multi-station assembly systems, common for mass-customization manufacturing strategies, the product being assembled is held in a fixture attached to a pallet, and the pallet is conveyed between workstations. In high-precision assembly systems, variation in the position of the pallet is one of the largest sources of variation within the error budget, reducing quality and yields. Conventional approaches to locating pallets use pins and bushings, and a method for predicting their repeatability is presented. This paper also presents an exact constraint approach using a split-groove kinematic coupling, which reduces variation in pallet location by an order of magnitude.