Nanomeasuring Machine Research Articles

High-precision and low-cost vibration generator for low-frequency calibration system

Low-frequency vibration is one of the harmful factors that affect the accuracy of micro-/nano-measuring machines because its amplitude is significantly small and it is very difficult to avoid. In this paper, a low-cost and high-precision vibration generator was developed to calibrate an optical accelerometer, which is self-designed to detect low-frequency vibration. A piezoelectric actuator is used as vibration exciter, a leaf spring made of beryllium copper is used as an elastic component, and a high-resolution, low-thermal-drift eddy current sensor is applied to investigate the vibrator’s performance. Experimental results demonstrate that the vibration generator can achieve steady output displacement with frequency range from 0.6 Hz to 50 Hz, an analytical displacement resolution of 3.1 nm and an acceleration range from 3.72 mm s−2 to 1935.41 mm s−2 with a relative standard deviation less than 1.79%. The effectiveness of the high-precision and low-cost vibration generator was verified by calibrating our optical accelerometer.

Development of a 3D Tunneling Current Probing System for Micro- and Nano-Coordinate Metrology

The demands for precision measurement of three dimensional micro-and nanogeometries over a large area have rapidly increased during the last few years. To meet such requirements, many different nanometre resolving 3D capable probing sensors and corresponding 3D positioning systems to operate the sensors for 3D measurements have been developed. The mechanical contact-free, electrical work piece probing based on the scanning tunneling microscopy principle offers new possibilities for 3D micro coordinate measurements as well as for nanometre resolved topography measurements in micro-and nanometrology. This paper introduces an updated version of this probing sensor system extended with a 3D movable piezo scanner to directly detect its probing direction. With the magnitude and the direction of the contact vector forwarded to the position control of the nanopositioning and nanomeasuring machine NMM-1 all of the 3D measurement commands of NMM-1 can be utilized, allowing 3D surface scans and especially 3D free-form surface scans.

Overview of 3D Micro- and Nanocoordinate Metrology at PTB

Improved metrological capabilities for three-dimensional (3D) measurements of various complex micro- and nanoparts are increasingly in demand. This paper gives an overview of the research activities carried out by the Physikalisch-Technische Bundesanstalt (PTB), the national metrology institute of Germany, to meet this demand. Examples of recent research advances in the development of instrumentation and calibration standards are presented. An ultra-precision nanopositioning and nanomeasuring machine (NMM) has been upgraded with regard to its mirror corner, interferometers and angle sensors, as well as its weight compensation, its electronic controller, its vibration damping stage and its instrument chamber. Its positioning noise has been greatly reduced, e.g., from 1σ = 0.52 nm to 1σ = 0.13 nm for the z-axis. The well-known tactile-optical fibre probe has been further improved with regard to its 3D measurement capability, isotropic probing stiffness and dual-sphere probing styli. A 3D atomic force microscope (AFM) and assembled cantilever probes (ACPs) have been developed which allow full 3D measurements of smaller features with sizes from a few micrometres down to tens of nanometres. In addition, several measurement standards for force, geometry, contour and microgear measurements have been introduced. A type of geometry calibration artefact, referred to as the “3D Aztec artefact”, has been developed which applies wet-etched micro-pyramidal marks for defining reference coordinates in 3D space. Compared to conventional calibration artefacts, it has advantages such as a good surface quality, a well-defined geometry and cost-effective manufacturing. A task-specific micro-contour calibration standard has been further developed for ensuring the traceability of, e.g., high-precision optical measurements at microgeometries. A workpiece-like microgear standard embodying different gear geometries (modules ranging from 0.1 mm to 1 mm) has also been developed at the Physikalisch-Technische Bundesanstalt.

Nanopositioning and nanomeasuring machine NPMM-200—a new powerful tool for large-range micro- and nanotechnology

High-precision metrology has emerged as an enabling technology for modern key technologies. Therefore, at the Technische Universität Ilmenau, a new nanopositioning and nanomeasuring machine NPMM-200 with a measuring range of 200 mm × 200 mm × 25 mm, and a resolution of 0.02 nm was developed. The machine represents the great improvement of the extended three-dimensional Abbe comparator principle to achieve nanometre accuracy. All six degrees of freedom of the mirror plate with the measuring object are measured by fibre-coupled laser interferometers, the signals of which are then used together with the probe system signals for a high-precision position and orientation control and surface and coordinate measurements. This paper presents the metrological concept, the realized design as well as the metrological parameters.

High-speed metrological large range AFM

A high-speed metrological large range AFM (Met. LR-AFM) which is capable of fast, accurate, and large range measurements of surfaces and nanostructures is presented. In its design, the z scanner is realized by combining a piezo stage and a large range mechanical stage (referred to as a nanopositioning and nanomeasuring machine, NMM) which move the sample in parallel, thus providing both a high dynamic positioning capability and a large motion range. A contact mode AFM which offers both a short response time and a large sensing range is applied for measuring the surfaces of interest. Sensor signals from the AFM, the piezo stage, and the NMM are combined to derive the surface topography, thus offering high bandwidth for high-speed measurements. To reduce the distortion in the measured profiles, the time delay of the sensors is corrected as well as the displacements of the AFM and the piezo stage being traceably calibrated referring to the z-interferometer of the NMM in situ. Experimental results have demonstrated the high image quality obtainable at a scan speed of 500 μm s−1. The measurement repeatability at different scan speeds ranging from 10 μm s−1 to 1000 μm s−1 reaches nm for step height measurements and × 10−6 for grating pitch measurements, respectively. The study has improved the measurement speed of the Met. LR-AFM by a factor of more than 20, and thus significantly enhanced its measurement throughput and reduced its measurement drift.

Study on Spatial Frequency Domain Algorithm and White Light Interference System Based on NMM

White light interference technique for topography measurement effectively avoids phase ambiguity in phase-shifting interferometry. The spatial frequency domain algorithm based on scanning white light interference technique has the advantage of insensitivity to noise and higher calculation accuracy compared with other methods. The white light interference sensor is constructed based on nano positioning and nano measuring machine (NMM), the calibrated step height standard of 100±3nm is measured. The spatial frequency domain algorithm is adopted for data processing, the repetitive test result of 97.9nm and standard deviation of 0.48nm are achieved. To verify the measuring ability of complex device, the number ‘242’ on ink box is measured and three-dimensional reconstruction is conducted. The high precision and traceable measurements of micro/nano scale step height standard and complex devices are realized by the white light interference system based on NMM with steady frequency laser interferometer built-in.

Setup and evaluation of a sensor tilting system for dimensional micro- and nanometrology

Sensors in micro- and nanometrology show their limits if the measurement objects and surfaces feature high aspect ratios, high curvature and steep surface angles. Their measurable surface angle is limited and an excess leads to measurement deviation and not detectable surface points. We demonstrate a principle to adapt the sensor's working angle during the measurement keeping the sensor in its optimal working angle. After the simulation of the principle, a hardware prototype was realized. It is based on a rotary kinematic chain with two rotary degrees of freedom, which extends the measurable surface angle to ±90° and is combined with a nanopositioning and nanomeasuring machine. By applying a calibration procedure with a quasi-tactile 3D sensor based on electrical near-field interaction the systematic position deviation of the kinematic chain is reduced. The paper shows for the first time the completed setup and integration of the prototype, the performance results of the calibration, the measurements with the prototype and the tilting principle, and finishes with the interpretation and feedback of the practical results.

Multifunctional nanoanalytics and long-range scanning probe microscope using a nanopositioning and nanomeasuring machine

An interferometer-based metrological scanning probe microscope (SPM) is successfully integrated into our nanopositioning and nanomeasuring machine (NPM machine) for high-precision measurements with nanometre uncertainty over a range of 25 mm × 25 mm × 5 mm. Both devices were developed at the Institute of Process Measurement and Sensor Technology of Ilmenau University of Technology, Germany. Outstanding results were achieved for different measurement tasks. With the NPM machine, truly long-range and long-term measurements are possible. Due to the tip wear, an automatic SPM cantilever replacement is preferable. Such a tip replacement is also required for the integration of multifunctional nanoanalytics. For example, for Kelvin probe force microscopy (KPFM), the measurement of topography and surface potential with different SPM tips is necessary. For this purpose, an electromagnetic tip changer was designed. The tip changer comprises three SPM probes. In order to retrieve the previous tip positions, additional fiducial marks were developed. The repeatability of relocation is less than 10 nm. The automatic tip changer and fiducial marks are integrated into a sample holder. The tip changer in combination with fiducial marks allows scanning distances three times longer (with the same type of SPM probes) and multifunctional nanoanalytics (with different SPM probes with special properties). Sample KPFM measurements are demonstrated. The developed tip changer, including special fiducial marks, improves the performance and functionality of the NPM machine crucially.

Optical system for trapping particles in air

An innovative optical system for trapping particles in air is presented. We demonstrate an optical system specifically optimized for high precision positioning of objects with a size of several micrometers within a nanopositioning and nanomeasuring machine (NPMM). Based on a specification sheet, an initial system design was calculated and optimized in an iterative design process. By combining optical design software with optical force simulation tools, a highly efficient optical system was developed. Both components of the system, which include a refractive double axicon and a parabolic ring mirror, were fabricated by ultra-precision turning. The characterization of the optical elements and the whole system, especially the force simulations based on caustic measurements, represent an important interim result for the subsequently performed trapping experiments. The caustic of the trapping beam produced by the system was visualized with the help of image processing techniques. Finally, we demonstrated the unique efficiency of the configuration by reproducibly trapping fused silica spheres with a diameter of 10μm at a distance of 2.05mm from the final optical surface.

Dimensional metrology in the macroscopic range with sub-nanometre resolution

Nanomeasuring machines are devices for solving various positioning and measuring problems in a range of several millimetres with sub-nanometre resolution. These devices are used for positioning, probing and measurements. The combination of this machine with a scanning force microscope leads to improved quality in the calibration of standards. The measurement accuracy and stability of the scanning force microscope are important for the achievable measurement uncertainty. Many systems are influenced by the creep, hysteresis and bending of the included piezo actuators. A scanning force microscope head with a combined deflection detection system that comprises an interferometer and a beam deflection system was developed. Due to this system, it is possible to simultaneously measure the displacement, bending and torsion of the cantilever with only one focussed beam. An additional high-speed piezoelectric actuator for the vertical motion of the cantilever was integrated and is controlled by the bending signal. The outcome of this additional control system is a much higher scan speed. The interferometer system can be used for precise measurement of the vertical cantilever motion. Hence, non-linearity and hysteresis in the actuator do not affect the measurement. The device was used for several calibration measurements on step height and lateral standards. This article deals with the set-up, function and application of a scanning force microscope head for dimensional metrology with the nanomeasuring machines.

Modular Family of Sensors for a Nanopositioning and Nanomeasuring Machine

This article presents a modular sensor family and her integration into a Nanopositioning and Nanomeasuring Machine (NPM Machine). More and more flexible data acquisition is necessary in high-precision metrology of micro- and nanostructured parts with increasing complexity and 3-D dimensionality of the geometry. Sensing of most various surfaces and structures with nanometer resolution is an important issue. Because of different capabilities of divers optical probes among each other, but also of tactile and atomic force sensors a multiple sensor concept on the basis of a modular family of sensors is proposed. The combination of the several probes is realized by a microscope revolver system. The centerpiece of the metrology system is a Nanopositioning and Nanomeasuring Machine with sub-nanometer resolution in a measuring range of several millimeters.

Control of nanopositioning and nanomeasuring machines with a modular FPGA based data processing system

For precise length measuring techniques, highly dynamic positioning stages are used to measure and manipulate objects with a resolution in subnanometer range. The position and the orientation of these systems have to be controlled permanently to compensate external disturbances such as sound waves, thermal expansion of the mechanical components, and ground motion. Because of new applications in the area of microsensing devices the dynamic or path accuracy is in addition to the stationary accuracy a critical feature. To improve the dynamic behavior of these machines, an efficient friction compensation as well as a high perfomance signal- and data processing system is necessary. This work presents a realization of a control system with friction compensation for a nanopositioning and nanomeasuring machine based on FPGA technology. Particular attention was paid to the obtainable sampling rate and its impact on the attainable path accuracy.

Low coherent Linnik interferometer optimized for use in nano-measuring machines**This article was presented at the 56th International Scientific Colloquium on ‘Precision Engineering and Precision Measurement Technology’ held at Ilmenau University of Technology, Germany, and submitted for publication in the July 2012 special issue of this journal devoted to papers from that meeting.

The precise acquisition of three-dimensional geometrical data in micro- and nanotechnologies plays a crucial role in advanced fabrication processes. Scanning white-light interferometry achieves nanometer resolution in the axial direction, but the lateral resolution is far more critical. The requirements for an area-based optical sensor in a nano-measuring machine are very high. The resolution in every dimension and the working distance have to be as high as possible. In contrast to a Mirau interferometer, a Linnik interferometer does not need any optical components in front of the objective lens. This benefit permits both a long working distance and a high lateral resolution. In the EC-funded project ‘NanoCMM’ we developed a Linnik interferometer providing a working distance of more than 5 mm and a lateral resolution of 0.44 µm. This is achieved by near-UV illumination. The interferometer measures the full modulation depth and the rectangular shape of a pitch standard with 0.6 µm pitch length.

Fibre-coupled monochromatic zero-point sensor for precision positioning systems using laser interferometers

This paper focuses on a novel fibre-coupled monochromatic zero-point reference sensor for high-precision measurement and positioning tasks, especially for use in nanopositioning and nanomeasuring machines. The motivation for this development and the basic concept of the confocal-based sensor are explained in detail. Differences from other similar systems also realizing the confocal principle through fibre coupling are pointed out. Furthermore, the optical system design is described. Initial experimental results using this sensor as a probe system in a nanopositioning and nanomeasuring machine, and investigations into the metrological properties are discussed, which underscore the great potential for utilization as a reference sensor.

Area-based optical 2.5D sensors of a nanopositioning and nanomeasuring machine

At the Ilmenau University of Technology, work has been continuing on nanopositioning and nanomeasuring machines (NPMMs), which allow users to perform highly exact dimensional and traceable positioning with sub-nanometre resolution and nanometre uncertainty within a measuring volume of 25 mm × 25 mm × 5 mm. The NPMM can work with various probe systems operating in the z-direction, including atomic force microscopes, focus sensors and tactile probes. However, point-by-point measurement of the entire 25 mm × 25 mm area would take a prohibitively long time. This paper presents two area-based optical sensors as an alternative scanning approach. The use of these sensors can significantly reduce the time required for measurements of the entire scannable area. The methods used are white light interferometry and depth from focus. The use of the NPMM for these tasks adds the ability for high-accuracy positioning, which is necessary in order to use several special stitching methods which can reduce the propagation of uncertainty normally introduced by standard stitching.

Design and performance evaluation of an interferometric controlled planar nanopositioning system

High technology applications for example in the semiconductor or the optical industry require positioning systems providing repeatability and uncertainty in the range of nanometers together with x-, y-travel ranges of several hundreds of millimeters. We contribute in this research by investigating the applicability of integrated planar direct drives for the realization of nanopositioning- and nanomeasuring machines (NPM/NMM). The paper introduces the concept of planar integrated direct drives and explains the engineering design of the realized system for a 100 mm circular travel range in x and y. It presents the drive system parameters and the arrangement and interaction of the main components. The results of the initial operation are presented with a special focus on the question how the closed loop system can be taken into operation with a free floating slider. The evaluation of the positioning performance leads to the result that a 2D servo error of less than exy = 1.3 nm is achieved at arbitrary positions within the travel range. As a result of repeated step response tests, the positioning resolution is 0.5 nm. The measurement of the coincidental z-movement of the aerostatically supported slider yields a z-vibration with a standard deviation of σz = 0.45 nm. Regarding the drive system these results represent the limit of what can be reached with this setup as the measured error motions are in the range of the noise of the fixed environment setup. By measuring the characteristics of the aerostatic slider support at the fully assembled system the present air bearing stiffness is determined and based on a FEM-simulation of the slider eigenfrequencies the influence on the force transfer behavior is expected to be only marginal.

Interference signal demodulation for nanopositioning and nanomeasuring machines

The nanopositioning and nanomeasuring machine NMM-1 developed at the Ilmenau University of Technology was designed for measurements within a measuring volume of 25 × 25 × 5 mm3. The interferometric length measuring and drive systems make it possible to move the stage and corner mirror with a resolution of 0.1 nm in all three axes. The object being measured is placed on the corner mirror and can be measured with different probe systems. The high precision of the machine can be attributed to several factors. The most important is the accuracy of the interferometric measuring systems. Starting with a short description of NMM-1 and an improved equation for length calculation, this paper describes a small detail of the measurement uncertainty analysis for a displacement measurement using two positions of the measuring mirror. The overall 3D uncertainty for measurements carried out with the machine depends on the machine itself and the probe system in use as well as the specific measuring task. In particular, this paper discusses only the influence of the interference signal demodulation for homodyne interferometers.

A Multi-Sensor Approach for Complex and Large-Area Applications in Micro and Nanometrology

Abstract:In micro and nanotechnology, the metrological demands are increasing. The structures to be measured are becoming more complex with smaller structure widths, increasingly larger surface regions, and thousands of inspection features. In order to solve the problems, it has become desirable and even necessary to combine multi-sensor technology with high precision nanopositioning and nanomeasuring technology. The Nanopositioning and Nanomeasuring Machine NMM-1 with a measuring range of 25 mm × 25 mm × 5 mm and sub-nanometer resolution allows the application of several optical, tactile and atomic force probes. The combination of several sensor technologies in a multi-sensor approach for application with the NMM-1 is demonstrated.

Surface and coordinate measurements with nanomeasuring machines

The nanomeasuring machine (NMM-1) was designed for surface and coordinate measurements within a measurement volume of 25 mm × 25 mm × 5 mm. The machine is equipped with three homodyne plane-mirror miniature interferometers for the measurement of the displacement of a movable corner mirror. The object being measured is placed on the corner mirror, which is positioned by a three-axis drive system. Various measurement tasks are possible depending on the probe system installed. Most of the sensors utilised are one-dimensional tactile or optical surface sensors or probes. In recent years, measurements of three-dimensional features and sidewalls are becoming more important. For these more complex measurements, probe systems with two or three directions of sensitivity are necessary and were therefore integrated into the NMM-1. The article gives an overview of the operation and properties of the NMM-1, its use for surface and coordinate measurements, of integrated probe systems and of two probing systems developed.

Measuring value correction and uncertainty analysis for homodyne interferometers

The Nanopositioning and Nanomeasuring Machine (NMM-1) developed at the Ilmenau University of Technology is equipped with three homodyne plane-mirror miniature interferometers for the measurement of the displacement of a movable corner mirror. The object being measured is placed on the corner mirror, which is positioned by a three-axis drive system. The uncertainty of interferometric length measurements is dependent on several factors. Starting with an improved equation for calculating length, this paper describes a part of the determination of the measurement uncertainty for a displacement measurement using two positions of the measuring mirror. The new approach separates the correlated influencing factors for three positions of the measuring mirror: for the position where the interferometer counter is reset to zero and the other two positions of two measured points. Additionally, the work takes into account the influence of the dead path length and its determination.