Tino Hausotte

Recent developments and challenges of nanopositioning and nanomeasuring technology

Rapid progress in several high-tech industries has significantly increased the need for dimensional micro- and nano-metrology. Structures to be measured are becoming more complex with smaller structure widths and higher aspect ratios in increasingly larger surface regions and potentially highly curved surfaces. Significant international effort can be seen to develop high-capacity measuring machines with nanometre precision in growing measuring ranges up to hundreds of millimetres. This paper begins with an outline of the requirements stemming from high-tech developments currently being done or expected in the future and discusses recent developments in the field of nanopositioning and nanomeasuring technology with respect to basic measurement approaches, laser interferometer systems. The large range of nanoprobe systems usable in nanomeasuring machines is discussed, such as optical focus sensors, white light interferometer microscopes, CCD camera microscopes using the depth from the focus method, tactile stylus probes, atomic force microscopes (AFMs) and 3D microprobes. The versatile properties of these sensors allow the machine to be used in many different metrological applications. The paper also introduces a multi-sensor approach using a microscope revolver. It concludes with an illustration of metrologically challenging measurements, e.g., scanning micro-structures of curved optical surfaces or performing AFM scans of very large regions with significant data volume.

New applications of the nanopositioning and nanomeasuring machine by using advanced tactile and non-tactile probes

With the nanopositioning and nanomeasuring machine (NPM-Machine) developed at the Technische Universitat Ilmenau, subnanometre resolution and nanometre uncertainty in a measuring volume of 25 × 25 × 5 mm3 have been demonstrated in the last few years. This machine allows the most various measuring problems to be solved. In practice, however, there are too many different requirements for sensing surfaces or for detecting structures. So, this paper deals with the development and also the improvement of several optical and tactile probes for application in the NPM-Machine. A focus probe with a spot size of approximately 0.5 µm, a working distance of 1.5 mm and a resolution of less than 1 nm was developed and adopted in the NPM-Machine. In the next step, the working distance was improved to exploit the full vertical range of the NPM-Machine of 5 mm. To realize tactile sensing, an atomic force probe and tactile stylus probe were developed on the basis of the focus probe. These probing systems can acquire measuring data only by scanning the surface sequentially and point-by-point. To increase data acquisition, we realized a sensor based on a white-light interference microscope and parallel sampling of 1600 × 1200 data points. First results of fringe evaluation with laser interferometer reference are presented.

Tactile 3D microprobe system with exchangeable styli

Over the past decade a trend of component miniaturization can be observed both in industry and in the laboratory, which involves an increasing demand for nanopositioning and nanomeasuring machines as well as for miniature tactile probes for measuring complex three-dimensional objects. The challenge is that these components—for example, diesel injectors, microgears and small optics—feature dimensions in the micrometre range with associated dimensional tolerances below 100 nm. For this reason, a significant number of research projects have dealt with microprobes for performing the dimensional measurements of microstructures with the goal of achieving measurement uncertainties in the nanometre range. This paper introduces an updated version of a 3D microprobe with an optical detection system developed at the Institute of Process Measurement and Sensor Technology. It consists of a measuring head and a separate probe system. The mechanical design of the probe system has been completely overhauled to enable the exchange of the stylus separately from the flexure elements. This is very important for the determination of the probing spheres roundness deviations. The silicon membranes used in the first system design are therefore replaced by metal membranes. A new design of these membranes, optimized for isotropic probing forces and locking parasitic movements, is presented. Regarding the measuring head, the optical design has been redesigned to eliminate disruptive interference on the quadrant photodiode used for deflection measurement and to improve adjustment. Its dimensioning is discussed, especially the influence of the laser beam diameter on the interference contrast due to the parallel misalignment of the collimated laser beam. Initial measurement results are presented to prove functionality.

Investigations and calculations into decreasing the uncertainty of a nanopositioning and nanomeasuring machine (NPM-Machine)

Continuously increasing demands on nanopositioning and nanomeasuring (NPM) machines require a detailed analysis of and a decrease in measurement uncertainty. Initial studies have been done in the field of length and angle measurement. The analysis resulted in updated assemblies, which were investigated further. Significant improvements in mechanical stability, drift behaviour and temperature dependence were produced. To minimize the undesired heat production by the non-self-locking vertical linear drive systems, an improved weight force compensation arrangement adaptable to different object masses was developed and tested. Also, the systems natural frequencies were analysed. A modified structure with increased stiffness of the vertical drive system was designed to improve the NPMs dynamic behaviour.

Advanced three-dimensional scan methods in the nanopositioning and nanomeasuring machine

The nanopositioning and nanomeasuring machine developed at the Ilmenau University of Technology was originally designed for surface measurements within a measuring volume of 25 mm ? 25 mm ? 5 mm. The interferometric length measuring and drive systems make it possible to move the stage with a resolution of 0.1 nm and a positioning uncertainty of less than 10 nm in all three axes. Various measuring tasks are possible depending on the installed probe system. Most of the sensors utilized are one-dimensional surface probes; however, some tasks require measuring sidewalls and other three-dimensional features. A new control system, based on the I++ DME specification, was implemented in the device. The I++ DME scan functions were improved and special scan functions added to allow advanced three-dimensional scan methods, further fulfilling the demands of scanning force microscopy and micro-coordinate measurements. This work gives an overview of these new functions and the application of them for several different measurements.

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.

Application of a positioning and measuring machine for metrological long-range scanning force microscopy

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.

Novel control scheme for a high-speed metrological scanning probe microscope

Some time ago, an interferometer-based metrological scanning probe microscope (SPM) was developed at the Institute of Process Measurement and Sensor Technology of the Ilmenau University of Technology, Germany. The specialty of this SPM is the combined deflection detection system that comprises an interferometer and a beam deflection. Due to this system it is possible to simultaneously measure the displacement, bending and torsion of the probe (cantilever). The SPM is integrated into a nanopositioning and nanomeasuring machine (NPM machine) and allows measurements with a resolution of 0.1 nm over a range of 25 mm ? 25 mm ? 5 mm. Excellent results were achieved for measurements of calibrated step height and lateral standards and these results are comparable to the calibration values from the Physikalisch-Technische Bundesanstalt (PTB) (Dorozhovets N et al 2007 Proc. SPIE 6616 661624?1?7). The disadvantage was a low attainable scanning speed and accordingly large expenditure of time. Control dynamics and scanning speed are limited because of the high masses of the stage and corner mirror of the machine. For the vertical axis an additional high-speed piezoelectric drive is integrated in the SPM in order to increase the measuring dynamics. The movement of the piezoelectric drive is controlled and traceable measured by the interferometer. Hence, nonlinearity and hysteresis in the actuator do not affect the measurement. The outcome of this is an improvement of the bending control of the cantilever and much higher scan speeds of up to 200 ?m?s?1.

FRICTION IDENTIFICATION AND COMPENSATION ON NANOMETER SCALE

This work concerns the modelling and experimental verification of the highly nonlinear friction behavior in positioning on the nanometer scale. The main goal of this work is to adjust and identify a simple dynamic friction model which allows a model-based estimation of the friction force in combination with the system inertia against displacement. Experiments in the pre-sliding and sliding friction regimes are conducted on an experimental setup. A hybrid two-stage parameter estimation algorithm is used to fit the model parameters based on the experimental data. Finally, the identified friction model is utilized as a model-based feedforward controller combined with a classical feedback controller to compensate the nonlinear friction force and reduce tracking errors.

Metrological scanning probe microscope

Todays 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.