Alexander Schuler

Development of a tunnelling current sensor for a long-range nano-positioning device

Dimensional micro and nano metrology is gaining enormously in importance with the development and advancement of micro mechanics (e.g., micro gears), micro electronic and mechanical devices (e.g., MEMS, miniaturized sensors), micro optics (e.g., cameras in mobile phones) and nanotechnology (e.g., functional surface layers), but effective and efficient quality control in these fields is hindered today by the lack of powerful, flexible, robust and economic tools for nanometre-resolved 3D metrology. Scanning probe microscopy (e.g., AFM) suffers from small measuring ranges, fragility, a lack of flexibility and usually unsatisfactory metrological properties such as repeatability and linearity. Miniaturized tactile 3D coordinate measuring machines (CMMs) today only deliver very low point rates and are not suitable for measuring surface fine structure due to the characteristics of their probing elements and their dynamic properties. Additionally AFM tips tend to wear and micro CMMs may damage the workpiece. To overcome these limitations a laser-interferometrically controlled 3D nano- positioning and measuring machine (NMM-1) with a measurement range of 25 mm × 25 mm × 5 mm and sub-nanometre positioning resolution has been equipped with a custom made current measuring probing system. The use of electrical probing interaction in the nanoampere order instead of force (tactile probing, AFM) gives much more flexibility for size and shape of the probing element, as gravitational influence and stresses in the probe are not relevant for probing performance. The combined system can be used as a metrological long-range scanning tunnelling microscope, but also as a 3D micro CMM and provides nanometre resolution combined with an outstandingly large measuring range of several millimetres and traceable position measurement via three helium–neon (HeNe) laser interferometers. Results of the experimental set-up show that the combination of laser interferometry and electrical probing can deliver a reproducibility of down to 3 nm at ranges of several millimetres.

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 sensors 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.

Application of sensor tilting for enhanced measurement of microstructures

In the field of tactile surface probing, the contact point between the probing tip and the surface varies depending on the local surface slope. The measurement of high slopes as found in microstructures leads to deviations as the probing point no longer lies on the tip’s apex. A probing principle is investigated that applies a surface slope–dependent sensor rotation to reduce measurement deviation by shape superposition. For planning purposes and the determination of the benefit, a simulation of the probing process was performed. Different kinematic chains to rotate the sensor were investigated, and a stacking of two rotary axes was selected. To compensate systematic positioning deviation, a compensation field is applied, acquired by an in situ calibration method. As a basis for the test stand, a nanometer resolution coordinate measuring machine is used and is combined with a near-tactile micro- and nanosensor based on electrical interactions. The test stand has been completed in a preliminary configuration, and the first results are presented.

Enhanced measurement of steep surfaces by slope-adapted sensor tilting

In the field of tactile surface probing, the contact point between the probing tip and the surface varies depending on the local surface slope. In the case of 2.5D systems such as profilometers or atomic force microscopes, the measurement of high slopes leads to large deviations. Therefore a probing principle is investigated that applies a surface slope-dependent sensor tip rotation to maintain an orthogonal orientation to the measured surface. To realize the tilting system, strategies are necessary to determine the optimal tip rotation angle for each surface point. Possible strategies can be based on a two-pass scan with a priori knowledge of the surface with a pre-scan, a single-pass scan with dynamic extrapolation of already acquired surface points or a combination with multiple strategies. To determine the most suitable strategies and the best algorithms a simulation and analysis environment was developed. The focus of this work is the development and simulation of the strategies.

Nanometeraufgelöste Koordinatenmesstechnik mit elektrischer Werkstückantastung

Zusammenfassung Koordinatenmesstechnik gehört vor allem im Maschinenbau zu den Kernelementen der industriellen Qualitätssicherung. Ihre Anwendung kann auch in der Mikrotechnologie zur Bewältigung zahlreicher Herausforderungen im Bereich der geometrischen Werkstückprüfung beitragen, wenn es gelingt praktische Probleme der taktilen Antastung bei der Messung von Mikromerkmalen zu überwinden. Mit kleiner werdenden Tastelementen — Voraussetzung für die Antastung von Mikromerkmalen — wird es überproportional schwieriger, statische und dynamische Antastkräfte so zu begrenzen, dass Beschädigungen von Werkstück und/oder Tastsystem vermieden werden können. Am Lehrstuhl Qualitätsmanagement und Fertigungsmesstechnik der Universität Erlangen-Nürnberg wurde als Alternative zu taktilen Tastsystemen ein berührungslos arbeitendes, auf elektrischer Wechselwirkung beruhendes 3D-Mikrotastsystem entwickelt und wissenschaftlich untersucht, welches für 3D Mikrokoordinatenmesstechnik und Nanometer-aufgelöste Topographiemessungen eingesetzt werden kann. Abstract In mechanical engineering coordinate metrology belongs to the key elements of quality management. Its application may help to master challenges posed by geometrical testing in micro technology if practical problems of tactile micro probing can be solved. With smaller probing elements — prerequisite for probing micro features — limiting static and dynamic probing forces to a beareable level for workpiece and probing system is getting disproportionately more difficult. A non-contacting 3D micro probing system based on electrical interaction has been developed and investigated at the chair Quality Management and Manufacturing Metrology of university Erlangen-Nuremberg, which can be applied as an alternative to tactile 3D microprobes for 3D imcro coordinate measurements as well as for nanometer resolved topography measurements.

Aspects of micro-tactile dynamic sensor tracking

To reduce measurement deviations of tactile surface measurement systems resulting from high surface angles, a probing principle is investigated based on a dynamic surface slope dependent sensor tip rotation. To research the principle, a simulation environment and methods to calculate an optimal tip rotation angle are developed. The achievable deviation reduction of the principle and the performance of the different angle determination methods are examined based on different sample surfaces. In support of a hardware realisation, parameters of a virtual rotation system are varied, its effectiveness is quantified and the limits are identified.

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.

Schottky emission effect in surface topography: method and application

Presented here is an application of Schottky emission effect in surface topography. Since using current transfer mechanism can detect the metal or semiconductor surface structures in high resolution without contact, the tendency of Schottky emission in surface metrology is obvious. In this study, Schottky emission property in practical condition is compared both theoretically and practically into detail with tunnelling effect and field emission in order to distinguish the observed phenomena. A new developed probing system holding a thick electrical probe is exemplified to demonstrate the Schottky emission effect application in surfaces study. Future prospects of applying Schottky emission to manufacturing metrology are overviewed.

Mikrokoordinatenmesstechnik mit elektrischer WerkstückantastungMicro Coordinate Metrology with Electrical Probing

Zusammenfassung Koordinatenmesstechnik gehört im klassischen Maschinenbau zu den Kernelementen der industriellen Qualitätssicherung. Ihre Anwendung kann auch in der Mikrotechnologie zur Bewältigung zahlreicher Herausforderungen im Bereich der geometrischen Werkstückprüfung beitragen, wenn die Gerätetechnik entsprechend miniaturisiert und die Genauigkeit verbessert werden kann. Während es mehrere kommerzielle Achssysteme für Mikrokoordinatenmessgeräte mit einer Auflösung im Nanometerbereich gibt, bestehen große praktische Beschränkungen bei der nanometeraufgelösten Werkstückantastung. Kein heute verfügbares taktiles oder optisches Mikrotastsystem kann eine vollständige Messung komplexer dreidimensionaler Bauteile leisten, weshalb oftmals aufwendige multisensorische Ansätze verfolgt werden. Elektrische Werkstückantastung bietet eine neue Möglichkeit zu holistischer, nanometeraufgelöster Koordinaten- und Oberflächenmesstechnik mit nur einem Sensor.