In numerous interferometric applications of nanopositioning and nanomeasuring technology, plane mirrors are used as
flatness or straightness standards for the movement of a positioning device. During this process, the shape deviations of
the mirrors used lead to systematic errors of the position measurements, which can be corrected in later applications if
known. Most often the effective shape deviations are described sufficiently well by profile deviations along a profile line
which is fixed by the movement of the positioning or measuring device.
The novel precision device - a so-called interferometric nanoprofilometer - for measuring the profile deviations of plane
mirrors presented in this paper is based on the comparison of the profile line of the mirror to be tested with a straightness
standard embodied by a mirror of very high flatness. A specially designed point-based measuring interferometer is
moved along the profile line. As the measurement is directly referenced to the straightness standard, the influence of the
guide errors was greatly reduced. The uniform movement of the interferometer is ensured through a linear measurement
table, which is driven using speed control and pulse-width modulation. Apart from the mechanical and optical design of
the interferometric nanoprofilometer, a hardware module was assembled which enables the control of the linear
measurement table and the extraction of pulses for the synchronous acquisition of position and profile deviation values.
In addition, a software tool was developed for configuring the measurement process and for data recording as well as a
program to perform various analyses of the profile deviations.
In measurements performed with the interferometric nanoprofilometer covering the maximum scanning length with
lx=250 mm under laboratory conditions, the expanded uncertainty was U(l)=7.8 nm at a confidence level of p=95%
(k=2).
Due to the development and progress in micro- and nanotechnology the range of measuring tasks is becoming ever more
varied and multifaceted. Decreasing structure widths in combination with large area measurements or complex 3D-micro-
and nanostructures with high aspect ratios not only on flat but also on curved surfaces are some of these
measurement challenges. In order to solve the problems arising within this application spectrum a multi-sensor platform
based on a laser focus probe was developed. This platform is integrated in the Nanopositioning and Nanomeasuring
Machine developed mainly at the Institute of Process Measurement and Sensor Technology at the Ilmenau University of
Technology with a measuring range of 25 mm x 25 mm x 5 mm and subnanometre resolution.
Dimensional measurements of microstructures with uncertainties below 50nm require both nanopositioning and
nanomeasuring machines (NPMMs) as well as appropriate microprobes. This paper introduces a novel 3-D tactile
microprobe system developed at the Ilmenau University of Technology, Institute of Process Measurement and
Sensor Technology, and contains an analysis of its metrological characteristics.
This microprobe system uses a silicon membrane to induce the measurement force and to operate as the
damping system for the stylus. This damping is entirely brought about by internal friction. An optical detection
system measures the deflection of the membrane and thus of the stylus. The optical detection system uses a
single laser beam, focused on the backside of the silicon membrane. The reflected beam is split, with one part
being used to measure the tilt about the x- and y-axes and the other part being fed back into an interferometer
for deflection measurement in the z-direction. Thus, the deflection of the membrane can be measured with
sub-nanometre resolution.
An NPMM was used to analyse the metrological characteristics of the microprobe system and to calibrate
it. This paper focuses on a detailed analysis of the three-dimensional reproducibility for point measurements
by obtaining and evaluating a directional response pattern. This pattern is then compared to the behaviour of
other microprobe systems. Furthermore, the work shows that the microprobe system can be applied successfully
to scanning measurements and satisfactory results obtained. These results indicate that the microprobe system
is well-suited for universal measurement tasks in dimensional metrology.
The interferometric length measurement value in multi-axis positioning and measuring systems is directly influenced
by the topography of reference mirrors. Form deviations of the mirror plane can cause systematic
measurement errors because the specimen geometry is superimposed upon the topography of reference mirrors.
This article discusses the complete acquisition of the topography of a special mirror arrangement with the help
of a Fizeau interferometer to correct systematic measurement errors after the raw measurement using the expanded
three-flat test. Furthermore, other influencing factors are presented in the article, e.g., measurement
errors caused by the Fizeau interferometer. Additionally, temporal changes of the reference mirror topography
are detected by regularly occurring measurements, and the topography data used as the correction reference are
updated accordingly.
A proprietary metrological scanning probe microscope (SPM) with an interferometer, developed by the Institute of
Process Measurement and Sensor Technology at the Ilmenau University of Technology (IPMS), is used as a stationary
probe system in the nanomeasuring and nanopositioning machine (NPMM). Due to the movements of the NPMM, the
total microscope measuring range is 25mm × 25mm × 5mm with a positioning resolution of less than 0.1nm. Examples
for specimens are step height standards and one-dimensional gratings. The repeatability has been determined at less than
0.5nm for measurements on calibrated step height standards and less than 0.2nm for the gratings. The measurement
results of these samples are always directly related to the corresponding measurement uncertainty, which can be
calculated using an uncertainty budget. A new traceable method has been developed using a vectorial modular model.
With this approach, it is possible to quickly insert new sub-models and to individually analyze their effects on the total
measurement uncertainty. The analysis of these effects with regard to their uncertainties is done by Monte Carlo
Simulation (MCS), because some models have partially or fully nonlinear character of which one example is the
interferometer model of the metrological SPM. The complete development and analysis of these models is presented for
one specific measurement task. The measurement results and the corresponding measurement uncertainty were obtained
by Monte Carlo Simulation. Comparisons with the GUM have shown that the proposed procedure is a good alternative to
achieve reasonable measurement results with uncertainty estimation.
A three-degree-of-freedom measurement system for the acquisition of the straightness and roll errors of a moving linear
stage is described. The horizontal (Δx) and vertical (Δy) straightness errors are obtained by measuring the lateral displacement
of a triple prism with a laser beam and position sensitive detectors. From two simultaneously performed vertical
straightness measurements the roll angle (Θz) can be calculated. The system consists of a cable-free reflector head
and a detector head. The position sensitive detectors have been calibrated using a precision x,y-stage equipped with two
plane mirror interferometers. Different position sensitive detectors are compared with regard to position sensitivity, linearity,
null-shift stability and sensitivity to the intensity profile of the detected laser beam. In combination with an already
known triple-beam plane mirror interferometer, additional information about the linear position (Δz) and the pitch (Θx)
and yaw (Θy) angle can be obtained from three parallel linear measurements. Thus all six-degree-of-freedom geometric
errors can be measured simultaneously.
Systematic errors of the three-degree-of-freedom measurement due to misalignment of the laser beams and geometric
errors of the triple reflectors are discussed. An approach for correction of those errors caused by the triple reflectors is
shown. The method is based on determination of the reflector geometry and calculation using the additional information
(Δz) acquired by the interferometer. Furthermore the metrological properties of the proposed system for the measurement
of straightness and roll are compared to other measurement principles. Experimental results demonstrate the
measurement capabilities of the system.
Laser interferometric methods are employed in precision measurements and positioning tasks, since they provide the
means for attaining high metric resolution and precision, even over large measurement ranges. The most important
fundamental principles of heterodyne and homodyne interferometers are discussed. A metrological analysis makes it
possible to describe the advantages and limits of laser interferometry. The design and functionality of fibre-coupled
miniature interferometers are described. The broad applicability of interferometers to microtechnology, nanotechnology
and precision mechatronics is explained.
This paper presents measurements of calibrated step height and pitch standards using a homodyne interferometer-based
metrological scanning probe microscope (SPM) and a nanopositioning and nanomeasuring machine (NPM machine).
These devices were developed at the Institute of Process Measurement and Sensor Technology of the Technische
Universität Ilmenau. Together these devices are capable of highly exact dimensional and traceable long-range
positioning and measurement with a resolution of 0.1 nm over the positioning and measurement range of
25 mm × 25 mm × 5 mm.
Measurements of different calibrated step height and pitch standards were completed in order to test the
repeatability and accuracy of the metrological SPM. The deviations between the calibrated and measured values were
smaller than the uncertainty values determined by the Physikalisch-Technische Bundesanstalt (PTB) calibration. The
extended uncertainty of the measurement results (step height or mean pitch value) was less than 1 nm.
Precision mechatronics is defined in the paper as the science and engineering of a new generation of high precision systems and machines. Nanomeasuring and nanopositioning engineering represents important fields of precision mechatronics. The nanometrology is described as the today's limit of the precision engineering. The problem, how to design nanopositioning machines with uncertainties as small as possible will be discussed. The integration of several optical and tactile nanoprobes makes the 3D-nanopositioning machine suitable for various tasks, such as long range scanning probe microscopy, mask and wafer inspection, nanotribology, nanoindentation, free form surface measurement as well as measurement of microoptics, precision molds, microgears, ring gauges and small holes.
The paper describes traceable nanometrology based on a nanopositioning machine with integrated nanoprobes. The operation of a high-precision long range three-dimensional nanopositioning and nanomeasuring machine (NPM-Machine) having a resolution of 0,1 nm over the positioning and measuring range of 25 mm x 25 mm x 5 mm is explained. An Abbe offset-free design of three miniature plan mirror interferometers and applying a new concept for compensating systematic errors resulting from mechanical guide systems provide very small uncertainties of measurement. The NPM-Machine has been developed by the Institute of Process Measurement and Sensor Technology of the Technische Universitaet Ilmenau and manufactured by the SIOS Messtechnik GmbH Ilmenau. The machines are operating successfully in several German and foreign research institutes including the Physikalisch-Technische Bundesanstalt (PTB), Germany. The integration of several, optical and tactile probe systems and nanotools makes the NPM-Machine suitable for various tasks, such as large-area scanning probe microscopy, mask and wafer inspection, nanostructuring, biotechnology and genetic engineering as well as measuring mechanical precision workpieces, precision treatment and for engineering new material. Various developed probe systems have been integrated into the NPM-Machine. The measurement results of a focus sensor, metrological AFM, white light sensor, tactile stylus probe and of a 3D-micro-touch-probe are presented. Single beam-, double beam- and triple beam interferometers built in the NPM-Machine for six degrees of freedom measurements are described.
A new traceable method has been developed and investigated to experimentally determine the total amount of measuring deviations arising through the capture and demodulation of plane-mirror interferometer signals. The basic principle for such an analysis is the precise specification of length variations. However, either a measuring system of excellent accuracy or accurately defined movements within a stable platform are required. A common measuring motion can be achieved through the displacement of a reflecting wedge plate, which creates a constant step-down. The interferometer to be analyzed is used to determine the change in the wedge plate's thickness, which is caused by lateral movements controlled by another interferometer. The wedge's sampled surfaces demand high planarity as the change of thickness acts as the material measure. These conditions can be achieved by using the Nanopositioning and Nanomeasuring Machine in conjunction with a 0.5-degree tilted mirror placed on it. The interferometer to be analyzed is aligned with this mirror. To provide the highest possible linearity for lateral motion, the only measuring points are in nearly error-free lambda/2 steps of the interferometer. The NPM machine's already small deviations in positioning will only affect the evaluation of measuring errors of the reduced interferometer by a factor of about one-hundredth. This is one of the main advantages of the method. The interferometer to be analyzed - like the entire measuring setup - features a compact assembly and high mechanical and thermal stability. The measured deviations in linearity provide excellent verification of the prospected error influences.
Many scanning probe microscopes (SPMs) are used as image acquisition tools in such industries as microelectronics, micromechanics, lithography and biotechnology. Conventional SPMs use piezoelectric actuators in order to move either the sample or the probe. The voltage across the piezos is taken as a position indicator. However, it is known that piezos suffer from hysteresis, and from time- and temperature-dependent creep. A solution to this problem is provided by accurate, traceable measurement of the cantilever position. An exact dimensional measurement can only take place via direct comparison with a well-known reference. The traceability of the SPM can be achieved using an interferometer, traceable to the 633 nm wavelength of the He-Ne laser. For accurate measurements the position of the cantilever must be measured in addition to the torsion and bending.
This article shows the basic SPM principle as well as the addition of a cantilever position detection system. This system has been realized with a special interferometer with a quadrant diode to detect the cantilever torsion and bending. The measuring beam is focused on the cantilever backside using a lens. The reflected laser beam is split and evaluated; one part of the beam is used for the interferometrical position measurement with the other part focused onto a quadrant diode. Due to the structure of the interferometrical SPM, it can be installed in many different positioning systems with large measuring ranges, including a nanopositioning and nanomeasuring machine (NPM machine), developed at the Institute of Process Measurement and Sensor Technology of the Technische Universitaet Ilmenau.
The use of homodyne interferometers has been limited to vibration measurements at objects with high surface reflectivity. This paper presents the modification of a homodyne Michelson laser interferometer that has been designed for vibration analysis at objects with industrial rough surfaces. High linearity, wide measurement range and low measurement uncertainty are the main features of this system. Experiments on an atomic force microscope (AFM) demonstrate the capability of the system.
Today's technological progress calls for metrologically accurate object measurement, positioning and scanning with nanometre precision and over large measuring ranges. In order to meet that requirement a nanopositioning and nanomeasuring machine (NPM machine) was developed at the Institute of Process Measurement and Sensor Technology of the Technische Universitaet Ilmenau. This device is capable of highly exact long-range positioning and measurement of objects with a resolution of less than 0.1 nm. Due to the structure of the machine many different probe systems can be
installed, including scanning probe microscopes (SPMs). A few SPMs have outstanding metrological characteristics and many commercial microscopes only perform as image acquisition tools. Commercial SPMs use piezoelectric actuators in order to move either the sample or the probe. The position measurement sometimes results from the applied voltage to the piezoelectric actuators or from the strain gauge or capacitive displacement sensor data. This means that they suffer from hysteresis, creep, nonlinear characteristics and Abbe offsets. For an accurate measurement the position of the cantilever must be measured in addition to the torsion and bending. The best solution is a combined detection system with a single laser beam. This system has been realized with a special interferometer system, in which the measuring beam is focused on the cantilever backside using a lens. The reflected beam is split with a part being detected by a quadrant photo-diode and the other part being fed back into the
interferometer for position measurement. The quadrant photo-diode is used to detect the cantilever torsion and bending.
The paper describes the operation of a high-precision long range three-dimensional nanopositioning and nanomeasuring
machine (NPM-Machine). The NPM-Machine has been developed by the Institute of Process Measurement and Sensor
Technology of the Technische Universität Ilmenau. The machine was successfully tested and continually improved in the
last few years. The machines are operating successfully in several German and foreign research institutes including the
Physikalisch-Technische Bundesanstalt (PTB). Three plane mirror miniature interferometers are installed into the NPM-machine
having a resolution of less than 0,1 nm over the entire positioning and measuring range of 25 mm x 25 mm x 5
mm. An Abbe offset-free design of the three miniature plane mirror interferometers and applying a new concept for
compensating systematic errors resulting from mechanical guide systems provide extraordinary accuracy with an
expanded uncertainty of only 5 - 10 nm.
The integration of several, optical and tactile probe systems and nanotools makes the NPM-Machine suitable for various
tasks, such as large-area scanning probe microscopy, mask and wafer inspection, nanostructuring, biotechnology and
genetic engineering as well as measuring mechanical precision workpieces, precision treatment and for engineering new
material. Various developed probe systems have been integrated into the NPM-Machine. The measurement results of a
focus sensor, metrological AFM, white light sensor, tactile stylus probe and of a 3D-micro-touch-probe are presented.
Single beam-, double beam- and triple beam interferometers built in the NPM-Machine for six degrees of freedom
measurements are described.
Driven by increasing precision and accuracy requirements due to miniaturization and performance enhancement, measuring technologies need alternative ways of positioning, probing and measurement strategies. The paper describes the operation of the high-precision wide scale three-dimensional nanopositioning and nanomeasuring machine (NPM-Machine) having a resolution of 0.1 nm over the positioning and measuring range of 25 mm x 25 mm x 5 mm. The NPM-Machine has been developed by the Technische Universitat Ilmenau and manufactured by the SIOS Messtechnik GmbH Ilmenau. Three plane-mirror miniature interferometers and two angular sensors are arranged, to realize in all three coordinates zero Abbe offset measurements. Therefore, this device closes a gap in coordinate-measuring technique regarding resolution, accuracy and measuring range. The machines are operating successfully in several German and foreign research institutes including the Physikalisch-Technische Bundesanstalt (PTB). The integration of several, optical and tactile probe systems and scanning force microscopes makes the NPM-Machine suitable for various tasks, such as large-area scanning probe microscopy, mask and water inspection, circuit testing as well as measuring optical and mechanical precision work pieces such as micro lens arrays, concave lenses, step height standards.
This article deals with a high-precision three-dimensional positioning and measuring machine and its application as a metrological long-range scanning force microscope. At the Institute of Process Measurement and Sensor Technology of the Technische Universitaet Ilmenau an interferometric nanopositioning and nanomeasuring machine has been developed. Which is able to achieve a resolution of less than 0.1 nm over the entire positioning and measurement range of 25 mm x 25 mm x 5 mm and is traceable to the length standard. The Abbe offset-free design in conjunction with a corner mirror as a reference coordinate system provides extraordinary accuracy. The integration of several probe systems and nanotools (AFM, STM, focus sensor, tactile probes) makes the nanopositioning and nanomeasuring machine suitable for various tasks in the micro- and nanotechnologies. Various probe systems have been integrated in the last few years. For example, a commercial piezo tube AFM was integrated and tested. Additionally, interferometeric measurement systems of the nanopositioning and nanomeasuring machine enables the calibration of probe systems. Also in order to achieve the best possible measurement results special probe systems have been developed and tested and are discussed briefly.
A focus sensor on the basis of a hologram laser unit was developed and successfully tested in a nanopositioning and nanomeasuring machine as a zero indicator. The high resolution of the focus sensor is due to a high-precision optical adjustment and special solutions incorporated into the electronic parts. Thus, any sensor malfunctions caused by back-reflected light inside of the assembly could be completely avoided by means of the special high-frequency modulation and laser power stabilization. Common mode noise reduction provides the high SNR of the output signals. The measurements were made according to a dynamic principle by permanent difference formation between the output signal of the focus sensor and the length value of the z-interferometer of the nanopositioning and nanomeasuring machine. The measuring results are presented, and further possibilities of application are outlined.
The paper describes the design of a high-precision three-dimensional nanopositioning and nanomeasuring machine (NPM-Machine). The NPM-Machine has been developed by the Institute of Process Measurement and Sensor Technology of the Technische Universität Ilmenau and manufactured by the SIOS Meßtechnik GmbH Ilmenau. The machine was successfully tested and continually improved in the last few years. The NPM-Machine has a resolution of less than 0,1 nm over the entire positioning and measuring range of 25 mm x 25 mm x 5 mm. An Abbe offset-free design and the application of a new concept for compensating systematic errors resulting from mechanical bearings provide extraordinary accuracy. An important part of the NPM-Machine is constituted by a mirror corner. The integration of several probe systems and Nanotools makes the NPM-Machine suitable for various tasks, such as large-area scanning probe microscopy, mask and wafer inspection, nanostructuring, biotechnology as well as measuring mechanical precision workpieces a.s.o. Various probe systems have been integrated into the NPM-Machines. The machines are operating successfully in several German and foreign institutes including the Physikalisch-Technische Bundesanstalt (PTB). The article gives basic information on the NPM-Machine and describes the mode of operation and the measurements by means of probe systems.
Laser interferometers are important instruments for the measurement of length in today's mechanical engineering and manufacturing technology. The principle on which interferometers have operated to date is that of interference between beams with the same direction of propagation. However, optical beams can interfere with each other not only in the same direction of propagation but also in opposing directions. The name given to this type of interference is the standing wave. A beam of light strikes a plane mirror at 90° to it, is reflected and interferes with the beam currently being reflected at the mirror. The outcome of the interference is a standing wave in front of the plane mirror. The only way of detecting the maxima and minima of the intensity of a standing wave photoelectrically is to use a photoelectric detector which is partially transparent. The photoelectric detector is placed in path of the standing wave, which propagates through it. Phase-shifted signals can be received if two photoelectric detectors with a phase shift between them are positioned in the standing wave. These enable sin and cos signals to be registered so that bi-directional fringe counting can take place. The authors have named this assembly an optical Standing-Wave Interferometer. The form taken by the partially transparent photoelectric detectors is that of photodiodes based on amorphous silicon, in a TCO-pin-TCO structure. Phase-shifted signals are received by two components with a TCO1-(pin)1-TCO2-(pin)2-TCO3 composition, integrated at the engineering stage, which are called by the authors transparent phase selective photodiodes (TPS). The TPS have been used to carry out measurement of length in a technological setting in such a way that the standing-wave interferometer could be compared with a plane mirror interferometer.
A novel interferometer based on sampling the maxima and minima of intensity of an optical standing wave has been developed. The photoelectric detection of the standing wave is performed by using a partially transparent thin-film photodiode. The automatic bidirectional fringe counting is provided by a partially transparent and phase-sensitive detector which is realized by the integration of two stacked transparent photodiodes along the optical axis of the standing wave. To obtain the ideal sine and cosine signals, the transparent phase-sensitive detector has to be optimized by adjusting the thickness of the single layers. Some features of optimization will be presented and explained. Length measurements have been demonstrated by displacing the plane mirror and bidirectional fringe counting within the standing wave.
KEYWORDS: Calibration, Sensors, Interferometers, Interferometry, Digital signal processing, Signal processing, MATLAB, Actuators, Signal detection, Wavefronts
This paper describes the basic principle of an interferometric angle and length sensor and its application. The sensor is the main part of a compact calibration system that can be used to calibrate and test one-dimensional length measurement systems. It is built by integrating the sensor into a positioning stage and setting up a DSP-based hardware and software signal processing system. A PC-based frontend using Matlab allows for easy setup of user-specific scripts for numerous calibration tasks. The sensor's and system's capabilities have been demonstrated using a high-resolution autocollimator, an AFM and an inductive tactile probe as calibration samples. Calibrations are possible with step sizes ranging from 20pm up to ±6μm and several waveforms for dynamic calibrations at frequencies currently up to 2 kHz.
An initial description of the design and operation of compact miniature interferometers that employ fiberoptic lightguides for all of their optical couplings and are suitable for general-purpose use is followed by a metrological analysis of their mode of operation and examples of their broad applicability, based on several typical instrumental setups.
A novel interferometer concept will be presented which is based on an optical standing wave. This standing wave is scanned by a novel, partially transparent photodetector, which is designed as nip-photodiode and contacted with transparent conductive oxide (TCO). Two transparent photodiodes are integrated to a transparent phase-sensitive sensor. The photodiodes are longitudinally arranged on the optical axis of the standing wave and generate a sine and a cosine signal for the up- and down-counting of the intensity maxima and minima of the standing wave. The layer thickness of the transparent photodiodes has been designed so as to take appropriate coating into account. These measures are demonstrated by a number of experimental results. An incorrect phase relation between the photodiodes will be corrected using the Heydemann algorithm. The non-linearity of the interferometer at a length of <λ/2 will be discussed.
At the Institute of Process Measurement and Sensor Technology of the TU Ilmenau, a scanning force microscope (measuring range 15 ?m x 75 tm x 15 ?m) having a laser-interferometric 3D-nanomeasuring system free from Abbe errors has been developed in cooperation with the PTB Braunschweig. The extended measuring uncertainty (K =2) is only 0.2 nm and was obtained with a structure standard. To achieve a considerable extension of the measuring range up to 25 mmx 25 mm x 5 mm, a nanopositioning and —measuring machine was developed. The resolution of the measuring axes is 1.24 nm. The laser-interferometric measurement is free from Abbe errors of 1St order in all measuring axes. The deviations of the guides used are compensated by means of a precision mirror corner.
A laser-interferometric miniature measuring system designed for precision measurements in the fields of micro-, nano- and macro technology is being presented. In measuring ranges of >= 2 m, a resolution of <EQ 1 nm and an accuracy of only a few nanometers can be achieved. On the basis of various practical applications of the 2D- and 3D-nano- measuring and positioning techniques, the particular advantages offered by the optical fiber-coupled laser- interferometric measuring system are explained.
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