| Zugriffsnummer | 18802 |
| Dokumenttyp | Konferenzartikel in Zeitschrift |
| Sprache | Englisch |
| Titel | Overview of the metrological scanning probe microscopes at PTB |
| Autor(in); Institution |
Danzebrink, Hans-Ulrich; 5.1, Nano- und Mikrometrologie, PTB-Braunschweig
Dai, Gaoliang; 5.1, Nano- und Mikrometrologie, PTB-Braunschweig
Pohlenz, Frank; 5.1, Nano- und Mikrometrologie, PTB-Braunschweig
Wilkening, Günter; 5.1, Nano- und Mikrometrologie, PTB-Braunschweig
|
| Quelle/Jahr | Microscopy and Microanalysis: 11 (2005), Suppl. 3, 2 - 5 |
| ISSN | 1431-9276 (PRINT) ; 1435-8115 (ONLINE) |
| DOI | |
| Verlag | New York, NY: Cambridge Univ. Press |
| Konferenzangaben | Third Latin American Symposium on Scanning Probe Microscopy (III LASPM), Ouro Preto, 18-20, April, 2005, Brazil |
| Freie Schlagworte | Nanometrology ; SPM metrology ; Scanning probe microscopy ; SPM ; Scanning force microscopy ; SFM ; Probing systems ; Interferometry |
| Zusammenfassung | Quantitative dimensional measurements of micro- and nanometre-sized structures are urgently required from science and industry. Due to their very high vertical resolution (down to sub- anometres) and high lateral resolution (<10 nm) scanning probe microscopes (SPMs) are of great interest for such metrological applications. Additionally, SPM methods are able to measure surfaces in a number of modes like contact, intermittent-contact and non-contact mode. The forces between tip and sample are low during the measurement and, even in contact mode, reach only a few nanonewtons. This fact prevents scratching of the measured surface during the SPM scanning procedure even when very sharp tips are used. Earlier SPMs derived the surface topography from the voltage applied to the piezoelectric transducers. However, the poor behaviour of the piezos, such as creep, nonlinearity and hysteresis, limited the accuracy of these SPMs. As SPMs are used increasingly for industrial applications and asked to give quantitative dimensional results, a fundamental requirement for precise metrology using SPMs is, however, the addition of a length measuring system to the microscope system. For this purpose, the piezo actuators which serve for the scanning of sample or SPM tip, are in many cases position-controlled via additional sensors (strain gauges, capacitive or inductive sensors) by which the disadvantages of the piezo elements are compensated. Furthermore, in order to trace back the measurement results to the SI unit "metre", SPMs - so called "metrological SPMs" - with high demands on the uncertainty are equipped with laser interferometers. PTB's activities in the field of SPM metrology include the development of high-resolution probing systems as well as of complete metrological SPMs. The main focus of the development of the probing systems is aimed at constructing and optimising SPM heads for their use in dimensional nanometrology. In addition to the properties important from the viewpoint of metrology such as stability, sensitivity and noise behaviour, different other aspects have been incorporated into PTB's development: - The combination of SPM heads with optical microscopes: here, the optical function extends from visualisation to quantitative dimensional or analytical methods - The use of different detection principles: the movement and position of the sensor tip is measured by an external optical method or via an intrinsic electrical measuring principle - The use of different tip materials: in recent developments, special diamond tips are used in addition to conventional silicon and silicon nitride tips The development of SPM-based probing systems ranges from compact "sensor objectives" with optical beam deflection detection to self-sensing systems based on piezoresistive cantilevers or tuning forks with attached diamond tips. The following part of the paper will concentrate on complete metrological SPMs which are equipped with laser interferometers for position control and measurement, and which are thus capable of performing quantitative traceable dimensional measurements. Up to now three metrological SPMs have been built up at PTB. Two of these metrological SPMs are capable of measuring in a volume of 70 μ × 15 μm × 15 μm along x-, y- and z-axes. These SPMs are referred to as “Veritekt B” and “Veritekt C”. The third system allows measurements in a volume of 25 mm × 25 mm × 5 mm, referred to as the metrological large range SPM (LR-SPM). All these devices have been designed in a way that metrological principles, like minimisation of Abbe errors and tilting angles were complied with. In this paper the LR-SPM (see Figure 1) will be highlighted and discussed in more details. Conventional SPMs currently available often have scanning ranges of only tens of micrometres. Compared to stylus or optical methods, these small scanning ranges limit the further applications, e.g. in the field of roughness measurement. To exceed this limitation, the LR-SPM has been built up at PTB. The LR-SPM is based on the scanning sample principle. The image is formed by monitoring the deflection of the cantilever as the sample is scanned beneath the tip. In order to obtain the large range scanning capability, the sample is moved by a combined motion system which consists of a fast z-piezo positioning stage (z-PPS) and a ball-bearing positioning stage (NMM). The motion servo controllers of the z-PPS and the NMM are executed in parallel. As a benefit, both a large measurement range and a high measurement speed can be achieved using such a configuration. The topography of the surface, derived from the position of the sample, is traceably measured by integrated laser interferometers along the x, y and z-axes. The specifications of the LR-SPM are summarised in Table 1. The metrological frame of the instrument (see Figure 2) mainly consists of a metrological base (Zerodur frame), a mirror corner and the measurement systems including three interferometers and two angle sensors. The mirror corner, which comprises three high precision planar mirrors attached orthogonally to each other, is fixed to the motion stage of the NMM. This motion stage is moved by ball bearing guidances driven by electrodynamic motors (not shown in Figure 2). All six degrees of freedom of the motion stage are measured directly by interferometers (with a resolution of 0.08 nm) and angle sensors (with a resolution < 0.01 arcseconds). Based on these measurement values, a servo controller is addressed by the NMM controller for controlling its position and orientation. Due to the fact that during the measurement process, the SPM probe tip and therefore the measurement point is always located at the intersection point of the three interferometer beams this arrangement reduces the Abbe-error to a minimum. A number of extensive investigations, calibrations, PTB-internal and international comparisons have been carried out using the described metrological SPMs. Calibrations on a number of standards, like flatness standards, one-dimensional and two-dimensional gratings, nano and micro roughness standards, nano and micro step height standards (or depth setting standards, film thickness standards) have been successfully performed. As an example, some measurement results are shown in Figure 3. Presently, these metrological SPMs at PTB serve for versatile calibrations of standards, international comparisons and general characterisations of micro and nano structures. |
