A traceable calibration setup for investigation of the quasi-static and the dynamic performance of nano-positioning
stages is detailed, which utilizes a differential plane-mirror interferometer with double-pass configuration from the
National Physical Laboratory (NPL). An NPL-developed FPGA-based interferometric data acquisition and decoding
system has been used to enable traceable quasi-static calibration of nano-positioning stages with high resolution. A lockin
based modulation technique is further introduced to quantitatively calibrate the dynamic response of moving stages
with a bandwidth up to 100 kHz and picometer resolution. First experimental results have proven that the calibration
setup can achieve under nearly open-air conditions a noise floor lower than 10 pm/sqrt(Hz). A pico-positioning stage,
that is used for nanoindentation with indentation depths down to a few picometers, has been characterized with this
Based upon the micro-fabrication technology, a series of MEMS scanning probe microscopes (MEMS-SPM) have been developed in the national metrology institute Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig. In comparison with those traditional AFMs, the MEMS-SPM features generally a vertical deflection up to 10 μm with a resolution of 0.2 nm, a non-linearity less than 0.03%, and a testing force up to several hundreds of μN with a force resolution down to 1 nN by means of a capacitive displacement sensing technique. As a result, these MEMS-SPMs can be successfully applied in the field of nanodimensional and nanomechanical metrology. Mechanical design of the MEMS-SPM is reported in this manuscript. Proof-of-principle measurements using a prototype of the MEMS-SPM are detailed in this manuscript, verifying the capabilities of the MEMS-SPM.
The paper summarize the PTB activities in the field of silicon sensors for dimensional metrology especially roughness measurements and silicon calibration standards developed during the past ten years. A focus lies in the development of 2D silicon microprobes which enable roughness measurements in nozzles as small as 100 μm in diameter. Moreover these microprobes offer the potential for very fast tactile measurements up to 15 mm/s due to their tiny mass and therefore small dynamic forces. When developing high precision tactile sensors care has to be taken, not to scratch the often soft surfaces. Small probing forces and well defined tip radii have to be used to avoid surface destruction. Thus probing force metrology and methods to determine the radius and form of probing tips have been developed. Silicon is the preferred material for the calibration of topography measuring instruments due to its excellent mechanical and thermal stability and due to the fabrication and structuring possibilities of silicon microtechnology. Depth setting standards, probing force setting standards, tip radius and tip form standards, reference springs and soft material testing artefacts will be presented.
Free-standing thin membranes have now been widely applied in various research and industrial fields. As one of the key parameters of thin membranes, the membrane thickness is demanded to be precisely determined. A traceable membrane thickness measurement system is presented in this paper. It utilizes a pair of micro-machined nano-force transducers to actively detect both surfaces of a free-standing micro-machined membrane. Thanks to the high force sensitivity (down to a few Nanonewton) and a relatively large movement range (up to 10 μm) of the MEMS transducers in use, the proposed thickness measurement micro-system is capable of measuring membranes with small open aperture and membrane thicknesses down to sub-100 nm. In addition, the in-plane movement of the MEMS-transducers is measured in real-time by a single-frequency laser interferometer with nanometric resolution, which is traceable to the SI unit. Numerical analysis of the tip-membrane mechanical contact at nano-scale has been undertaken, which guides the selection of appropriate stylus radius used for experiments. Design and construction of the miniature thickness measurement system are detailed in this paper, including the first measurement results, which prove the feasibility of the proposed measurement system.
Rapid advances in nano-positioning/motion technology have offered metrologists in the field of precision engineering
larger and larger potential measurement range. A concept of micro-SPM head array is proposed in this paper to enhance
the performance of the currently available nano-measuring machines and effectively reduce the measurement time for
large specimen. The proposed micro-SPM head array consists of 1 × N ( N = 7 in our case) micro-SPM heads/units,
which are realized in one chip by MEMS technique. The kern of each SPM head is an electrostatic comb-drive actuator,
whose main shaft protrudes out of the MEMS chip to sense the surface topography of a specimen under test. To further
improve the lateral resolution of the micro-SPM head, an AFM tip can then be mounted onto the end of the actuator's
main shaft. To ensure the traceability of the measurement results from micro-SPM head, a fiber-based interferometer
array is considered to be integrated within the micro-SPM head array so as to in-situ calibrate the in-plane displacement
sensing system of the micro-SPM head. Design and simulation of the mico-SPM head array together with the
corresponding micro-interferometer will be detailed in this manuscript.
Accurate measurement of the mechanical properties of materials with micro-/nanoindentation methods demands precise
knowledge of tip geometry of the indenters in use. An optical microform calibration system for ball-shaped indenters,
and Rockwell indenter in particular, is therefore developed in Physikalisch-Technische Bundesanstalt. The calibration
system is fundamentally realized on basis of an optical confocal microscope. By means of investigating the spherical
aberration introduced by the object under test, the calibration system has the capability to quantitatively determine the
averaging radius of a spherical body (up to 300 μm) with an uncertainty of ~ 6 x 10-3.
To apply the calibration system for characterization of a partial spherical object, e.g. a Rockwell indenter, a simple
method has been proposed to improve the possible resolution of the calibration system. The basic configuration of the
calibration system and preliminary experimental results are detailed in this paper. Further extension of the functionality
of the calibration system is outlined.
A novel optical critical dimension (CD) metrology tool equipped with a 193 nm laser source and a high numerical
aperture objective (NA=0.9) is under development at the Physikalisch-Technische Bundesanstalt (PTB), the National
Metrology Institute of Germany. The CD tool is designed for characterization of photomasks up to 6-inch and offers "atwavelength"
measurements for current and future 193 nm lithography. Design, construction and realisation of the CD
metrology tool is presented in this paper. The illumination system, which employs a multi-mode DUV fiber to reduce the
lateral coherence of the laser beam, is detailed with numerical simulation and experimental investigation. Combined with
precision optical modelling, this optical CD tool will be applicable for quantitative determination of the microstructures
on 32 nm node photomasks with uncertainty less than 10 nm.
Nanoindentation testing has proved to be an effective tool to determine the mechanical properties of small volumes of
materials applied in various micro-systems, including hardness, indentation modulus, creep and so on. Nowadays, with
the help of advanced numerical methods, especially the finite element analysis (FEA) technique, further mechanical
properties of the material under test (e.g. tensile strength, etc.) can be interpreted from the typical indentation curve.
However, the reliability and accuracy of these analytical models have to be well tested.
Recently, the deformed topography of the interlayer surface within the tip-film-substrate system has been proposed to be
the reference for the evaluation of FEA and other mathematic models for indentation testing. Here an in-situ interlayer
deformation imaging system based on differential confocal microscopy is therefore developed, which has the capability
to measure in-situ the real-time topography deformation within a layered specimen during nanoindentation testing.
By means of linear regression and interpolation of the linear region of the standard confocal microscopy, differential
confocal microscopy (DCM) can achieve a very high resolution for topography measurements. However, the actual
capability and measurement uncertainty of DCM would be subject to those common-mode error sources like surface
heterogeneity, intensity fluctuation of the light source, etc. In this paper an improved DCM is proposed, which
introduces an additional point detector to the conventional DCM, creating dual confocal signals with slight relative axial
shifting. The real topography of the surface under test can then be easily deconvoluted from the dual differential signals,
whilst the common-mode errors within the measurement are eliminated.
A prototype was developed and applied for measuring a step-height composed of two different materials and for in-situ
inspection of the interlayer deformation during nanoindentation testing. Preliminary experimental results verify the
feasibility and accuracy of the proposed method.
Nowadays microelectromechanical systems (MEMS) have found more and more applications in various fields of
industry and scientific researches. In the meantime, quality control to MEMS devices and equipment gains more and
more importance, in which one of the important tasks is to characterize the in-plane behaviours of MEMS, including the
in-plane displacement/deflection/deformation, vibration amplitude, resonant frequency, etc. However, due to the special
characteristics of MEMS device, this task cannot be fulfilled easily with high resolution and wide bandwidth. In order to
calibrate and to further improve the performance of MEMS actuators and sensors, in this paper, inspection of in-plane
displacement of MEMS on the basis of an atomic force microscope is discussed, in which the lateral interaction between
an AFM cantilever and a electrostatic actuator is investigated, and its potential application to determine the dynamic
behaviour of a MEMS actuators/sensors is demonstrated.
Topography measurements of MEMS devices are one of the helpful approaches for MEMS devices' quality control, performance evaluation, design optimization, etc. In order to fulfill the requirement to determine the surface topography of a MEMS actuator, especially those of comb-drive types, in which the surface under test is in general discontinuous, a novel principle of an optical differential probe is proposed, in which a common-path laser interferometer and a confocal position sensor are integrated. Details of design and development of the novel differential probe are discussed, including the influence of the geometrical dimensions of the microstructure under test onto the measurement results, basic criteria for the design of the afocal subsystem and edge determination with confocal microscopy. Experimental results verify that the proposed novel approach is applicable.
Investigation of surface profiling method for large aspheres becomes more and more important and imperative with the great development of the synchrotron radiaiton facility (SRF), since the latter puts greater demands on surface quality, shape and figure parameters of the optical elements used in itself. MEanwhile, things became more difficult because of the unique characteristics of the optics used in SRF. As a result, novel surface measurement methods and systems have to be developed to cope with such problems.
Instrumented indentation testing in the nano-range with 'nanoindentation instrument' is playing an increasing role in the characterization of the mechanical properties of thin layers used in surface technology, microelectronics, micromechanics, optics etc. Several works concerning calibration of nanoindentation instruments were published in the last years, and the calibration of the performance of the depth sensing system in a nanoindentation instrument is now under way. In this paper, an optical probe interferometer for calibrating the depth measuring system in a Hysitron Triboscope has been presented, the principle and configuration of the interferometer are detailed. Error sources in the interferometry and their contribution to the interferometer performance have been discussed, which proves that the newly developed calibration device possesses the capability of sensing displacement with subnanometric accuracy.
Single-frequency interferometer with bidirectional fringe counting is frequently used in accurate length measurements due to its high resolution, stability and compact hardware. Meanwhile, in order to obtain nanometric path length resolution, corrections have to be introduced to the phase quadrature signals of a real interferometer due to its systematic deviations such as phase quadrature error, dc bias, unequal gains, etc. Conventional approaches to correct nonlinearity in a single frequency interferometer are generally based on ellipse fitting proposed by Heydemann, i.e. fitting an ellipse to instantaneous phase quadrature signals as the interferometer path length is varying. Consequently, when interferometer path length variation is far larger than light wavelength, the highest correction accuracy could be obtained by the largest number of data points.
In some cases like nanoindentation instruments in particular, however, the path length variation of an interferometer cannot be large enough to produce a closed Lissajou figure. Simulation and experimental results show that the accuracy of conventional calibration techniques drops quickly as the range of the optical path length variation reduces.
A new approach to correct nonlinearity in single-frequency interferometry was introduced, which was based on the concept of model reference control technique. Firstly, a Neural Network (NN) model was created and trained to predict the instantaneous phase of an ideal interferometer. And then the NN model was used as a reference model due to such characteristic that its outputs would be quite different from those obtained by conventional instantaneous phase computation methods when the input data were not on an ideal Lissajou figure. Better correction results could be achieved through minimizing the phase error between the NN model outputs and the conventional computation results. Theoretical derivation and analysis of the new approach are detailed in this paper. Simulation and experimental results show that this new