Nanopositioning and Nanomeasuring Technology

Due to steady advances in nanotechnology—with structures becoming ever smaller—the need to detect, measure, and manipulate these minute structures has emerged in recent decades. High-resolution techniques (STM, AFM) have been available for this purpose since the 1980s; however, they can typically only be applied to very small areas and require significant effort to perform metrologically traceable measurements. To enable the measurement of even large objects with nanometer resolution, the IPMS developed the NMM-1 nanomeasuring machine. It offers a previously unmatched measurement range of 25 mm × 25 mm × 5 mm with a resolution of 0.1 nm.

A distinctive feature of all IPMS nanomeasuring machines is the arrangement of the miniature interferometers used for length measurement. Their measurement axes intersect virtually at the point of contact between the probe and the measurement object, ensuring abbe-error-free measurement in all three coordinate axes.

The NMM-1 can be used for a wide range of measurement tasks, including, for example,

• the positioning, manipulation, machining, and measurement of objects in microelectronics, micromechanics, optics, molecular biology, and microsystems technology
• the measurement of precision parts, membranes, and microlenses
• the calibration of step height standards and pitch standards

References:

• Jäger, G.; Manske, E.; Hausotte, T. & Büchner, H.-J.: Nano Measuring Machine for Zero Abbe Offset Coordinate Measurement In: tm Technisches Messen—Platform for Methods, Systems, and Applications in Measurement Technology, 2000, 67, 319
• Manske, E.; Theska, R. & Schott, W.: Nanopositioning and Nanomeasuring Machines—Universal Cross-Scale Tools for Micro-Nano Integration. In: GMM Technical Report—Micro-Nano Integration, VDE VERLAG GmbH, 2010
• Füßl, R., Manske, E.: Metrology and Measurement Uncertainty of Nanopositioning and Nanomeasuring Machines In: Sensors and Measurement Systems 2010, VDE VERLAG GmbH, 2010
• Jäger, G.; Manske, E.; Hausotte, T. & Büchner, H.-J.: The Metrological Basis and Operation of the NMM-1 Nanopositioning and Nanomeasuring Machine, Metrological Principles and Mode of Operation of the NMM-1 Nanopositioning and Measuring Machine. In: tm—Technical Measurement: A Platform for Methods, Systems, and Applications in Measurement Technology, 2009, 76, 227–234
• Manske, E.; Hausotte, T.; Mastylo, R.; Machleidt, T.; Franke, K. & Jäger, G.: New Applications of the Nanopositioning and Nanomeasuring Machine Using Advanced Tactile and Non-Tactile Probes

The NMM-1 has long been used successfully in various national metrology institutes for the calibration of standards in micro- and nanometrology. However, due to growing demands, it became necessary to develop a new nanopositioning and nanomeasuring machine, the NPMM-200. This machine has a measurement and positioning range of 200 mm x 200 mm x 25 mm and a resolution of 0.02 nm. Its features reflect the consistent application of the significantly improved metrological concept of the NMM-1.

To further minimize length measurement errors in all three coordinate axes compared to the NMM-1, the NPMM-200 continuously measures the angular deviations of the machine table using additional laser interferometers and maintains a constant angular orientation through a complex control system. This allows the errors of the NPMM-200’s mechanical system to be nearly completely eliminated through continuous control.

External disturbances have an enormous influence on the ongoing measurement at the nanometer scale. For this reason, the NPMM-200 is housed in a sealed, temperature-controlled chamber that provides temperature control as well as acoustic and thermal insulation. In addition, a vacuum can be generated inside the chamber, which allows influences from airborne sound, airflows, and changes in the refractive index to be virtually completely suppressed. A key requirement in the implementation of the NPMM-200 design was therefore that all machine components be vacuum-compatible.

References:

• Jäger, G.; Manske, E.; Hausotte, T.; Müller, A. & Balzer, F.: Nanopositioning and nanomeasuring machine NPMM-200—a new powerful tool for large-range micro- and nanotechnology In: Surface Topography: Metrology and Properties, IOP Publishing, 2016, 4, 034004
• Manske, E.; Fröhlich, T.; Füßl, R.; Mastylo, R.; Blumröder, U.; Köchert, P.; Birli, O.; Ortlepp, I.; Pruß, C.; Schwesinger, F. & Meister, A.; Lehmann, P.; Osten, W. & Jr., A. A. G. (Eds.): Scale-Spanning Subnanometer Metrology Up to Ten Decades In: Optical Measurement Systems for Industrial Inspection XI, SPIE, 2019, 11056, 130–136
• Manske, E.; Fröhlich, T.; Füßl, R.; Ortlepp, I.; Mastylo, R.; Blumröder, U.; Dontsov, D.; Kühnel, M. & Köchert, P.: Progress of nanopositioning and nanomeasuring machines for cross-scale measurement with sub-nanometer precision In: Measurement Science and Technology, IOP Publishing, 2020, 31, 085005
• Osten, W.; Józwik, M.; Jaroszewicz, L. R. & Kujawińska, M. (Eds.): Optical Metrology: The Long and Unstoppable Path to Becoming an Outstanding Measuring Tool. In: Speckle 2018: VII International Conference on Speckle Metrology, SPIE, 2018

In the optical industry, optical components with free-form surfaces play a central role in various applications, as they significantly improve the performance of optical systems.

The manufacturing process for free-form optics often consists of successive measurement and machining steps. During measurements, it is essential that the sensor system always be aligned perpendicular to the surface of the optic; otherwise, additional measurement errors will occur. This also means that the sensor system is not rigidly mounted on the nanomachining system but must be swiveled according to the local inclination of the measurement object. To address this, the Nanomeasuring Machine 1 (NMM-1) was upgraded with two rotational axes as part of the NanoFab Graduate College, enabling the sensor to be aligned orthogonally to the surface of the measured object at all times. As a result, the excellent metrological properties of the NMM-1 could be extended to highly curved surfaces. To account for the imperfections of the mechanical swivel axes during measurement, a reference measurement system has been integrated.  This allows the systematic and random path deviations of the rotational systems to be detected and the resulting undesirable displacement of the measurement point to be corrected.

References:

• Fern, F.; Füßl, R. & Schienbein, R.: Influence of additional rotational movements on the measurement uncertainty of nanomeasuring, nanopositioning, and nanofabrication machines. In: Sensors and Measurement Systems, VDE Verlag GmbH, 2018, 168–171
• Fern, F.; Schienbein, R.; Füßl, R. & Theska, R.: Ultra-precise motion error measurement of rotational kinematics for integration into nanomeasuring and nanofabrication machines. In: Proceedings of the 33rd ASPE Annual Meeting, 2018

A major challenge in precision length metrology—driven by the ever-increasing size of measurement objects—lies in the growing measurement volumes, coupled with ever-stricter precision requirements in the nanometer and subnanometer ranges. However, the scanning-stage principle typically used for these applications—as found in the NMM-1 and NPMM-200—is reaching fundamental limits for future measurement ranges due to two conflicting requirements: Measurement objects of increasing size and mass must be moved with high dynamics and precision, together with a correspondingly large and heavy machine stage (approx. 450 kg for a measurement range of 700 mm x 700 mm x 100 mm). At the same time, the dynamics of the measurement must be increased compared to today’s typical parameters in order to keep measurement times within an acceptable range. To address this challenge, IPMS is developing a concept for an NPMM based on an inverse kinematic design.

The basic approach involves reversing the kinematic configuration, such that the large and heavy precision mirrors, as well as the large and heavy measurement object, are fixed in space. The measurement object is probed by a movable probe system, whose position is measured using several laser interferometers. This measurement concept reduces the moving mass from over 400 kg (mirror + measurement object) to approximately 1 kg (miniature interferometer + probe). This enables very high measurement dynamics and positioning accuracy.

References:

• Straube, G.; Calderón, S. F.; Ortlepp, I. & Manske, E.: Fundamentals of Dynamic Sensor Positioning with Nanoscale Accuracy by an Inverse Kinematic Concept In: AMA Service GmbH, Von-Münchhausen-Str. 49, 31515 Wunstorf, Germany, 2020
• Ortlepp, I.; Manske, E. & Füßl, R.: Dynamic sensor positioning in large measuring volumes using an inverse kinematic concept. In: Journal of Physics: Conference Series, IOP Publishing, 2018, 1065, 142009

Unlike continuous-wave He-Ne laser sources, an optical frequency comb (OFC) is a mode-locked pulsed laser—typically based on fiber lasers—that can be stabilized to a highly stable reference in the optical or radio frequency range (e.g., an atomic clock or hydrogen maser). The commercial availability of frequency comb technology in recent years has opened up new possibilities for tracing the wavelength back to the meter definition. The use of this technology not only enables highly accurate frequency measurements over a broad wavelength range but also offers the potential for direct coupling of the laser frequency to the second standard of an atomic clock. This allows the stability of the time source (e.g., an atomic clock via a GPS-disciplined oscillator (GPSDO) with a relative frequency stability in the range of 10⁻¹²) to be transferred to a He-Ne gas laser via the frequency comb.

The goal of the “Metrobase” research project, funded by the Carl Zeiss Foundation, is therefore to establish a new metrological basis that will reduce the current measurement uncertainty of the laser interferometers in nanomeasuring machines by up to three orders of magnitude. This is to be achieved through the installation of frequency comb technology at the Technical University of Ilmenau. The plan is to directly couple the helium-neon lasers of the NPMM-200 to the optical frequency comb, thereby achieving a new level of traceability for the unit of length. The combination of frequency comb technology and nanopositioning technology will, overall, raise the standard of dimensional metrology at the Technical University of Ilmenau and open the door to novel concepts for coupling frequency comb and nanomeasurement technologies.

References:

• S. Cundiff, T. Steven, J. Ye, Colloquium: Femtosecond optical frequency combs. Reviews of Modern Physics, 2003, Vol. 75, No. 1, p.
• S. Schilt, et al: Noise properties of an optical frequency comb from a SESAM-mode-locked 1.5-μm solid-state laser stabilized to the 10−13 level. Applied Physics B, 2012, Vol. 109, No. 3, pp. 391–402.
• P. Köchert, U. Blumröder, E. Manske: Ultrastable metrology laser at 633 nm using an optical frequency comb. In: Optical Micro-and Nanometrology VII. International Society for Optics and Photonics, 2018. p. 106780S.
• Manske, E., et al: Progress of nanopositioning and nanomeasuring machines for cross-scale measurement with sub-nanometer precision. Measurement Science and Technology, 2020, Vol. 31, No. 8, p. 085005

Nano- and micro-coordinate measuring machines have been developed for the precise measurement of complex microcomponents. To capture the smallest structures, the probes used by these machines require contact balls with diameters smaller than 300 µm. A significant source of uncertainty in such measuring instruments is caused by the shape of the probe ball. However, given the required level of uncertainty, there is currently no suitable method for characterizing such balls.

The institute is therefore currently developing and investigating strategies for the precise measurement of microspheres. Among other things, a method based on surface scans with atomic force microscopes has been developed. This method enables precise, high-resolution characterization of the radius and roundness of a large set of spheres with diameters smaller than 300 µm. Further work is focused on extending the method to characterize the entire sphere, as well as on developing alternative methods.

References:

• Oertel, E.; Manske, E.: Radius and roundness measurement of microspheres based on a set of AFM surface scans, In: Measurement Science and Technology, DOI: 10.1088/1361-6501/abcff4

For more than 40 years, research into the development of fiber-coupled interferometers has been conducted at the Institute of Precision Measurement Technology under the leadership of Professors G. Jäger and E. Manske.  In this process, both the supply of laser light to the interferometers and the scanning of the interferograms are carried out using optical fibers. In this way, only a minimal amount of power is transmitted into the measurement environment. At the same time, there is virtually no interference with the measurement from external electromagnetic fields. Fiber-optic scanning of the interferograms requires the generation of interference fringe patterns. To achieve this, one of the superimposed wavefronts is tilted by a millirad. Technically, this is accomplished through the special geometric design of the optical interfaces. As an alternative to fiber scanning, high-resolution scanning of the interference images is possible using matrix or line scan cameras. Through algorithmic evaluation, this enables measurement path resolutions and reproducibility in the range of a few femtometers. Current research focuses on the development of miniature interferometers with a modular design, in which functionality is achieved using a minimal number of optical components. State-of-the-art methods of optical component fabrication are used for this purpose.

A wide variety of sensors can be used to probe the test specimens in the nanopositioning and nanomeasuring machine. In addition to mechanical probing—for example, using atomic force sensors—optical probing offers several advantages. For this reason, an optical probe based on the focus principle was developed and integrated into the nanopositioning and nanomeasuring machine as a so-called zero indicator.

At the heart of the sensor is a so-called hologram laser unit derived from conventional DVD technology. It contains a semiconductor laser diode, photodiodes for focus error detection, and their preamplifiers. A small hologram located directly in front of the laser unit performs the various functions of beam splitting, division, and deflection. This multifunctional component made it possible to achieve extreme miniaturization of the sensor.

To track the location of the optical scanning on the specimen surface, the focus sensor was combined with a CCD camera microscope. This makes it very easy to locate and relocate areas of interest on the specimen surface.

Based on the focus sensor, two additional tactile sensors were developed: the focus-stylus sensor and the focus-AFM sensor. In this setup, the deflection of the probing tip (stylus or cantilever) is recorded directly and non-contact using the focused laser beam from the focus sensor.

The measurement and metrological characteristics of the developed focus sensor were comprehensively investigated. The resolution of the focus sensor is < 1 nm. Measurements on calibrated step-height standards showed a high degree of agreement with PTB calibration values of < 1 nm. Reproducibility in the picometer range can be achieved: for example, 20 pm was achieved for a 5-mm step height measurement. Scan speeds of up to 10 mm/s with subnanometer reproducibility are achievable.

References:

[1] R. Mastylo, D. Dontsov, E. Manske, G. Jäger: A focus sensor for an application in a nanopositioning and nanomeasuring machine. Optical Measurement Systems for Industrial Inspection IV, Proceedings of SPIE, June 13–17, 2005, Munich, Volume 5856, pp. 238–244

[2] E. Manske, T. Hausotte, R. Mastylo, T. Machleidt, K.-H. Franke, and G. Jäger, “New applications of the nanopositioning and nanomeasuring machine using advanced tactile and non-tactile probes,” Meas. Sci. Technol., vol. 18, no. 2, pp. 520–527, 2007.

[3] R. Mastylo. Optical and Tactile Nanosensors Based on the Focus Method for Use in Nanopositioning and Nanomeasuring Machines. PhD thesis, TU Ilmenau, 2011.

[4] R. Mastylo, E. Manske, T. Fröhlich “Versatile applications of laser focus probes in precision measurement technology: 11th IMEKO TC14 Symposium on Laser Metrology for Precision Measurement and Inspection in Industry (LMPMI 2014) (2014), pp. 29–34

Confocal sensors are considered an alternative to the focus sensor developed at the Technical University of Ilmenau.

A lens focuses a divergent beam (e.g., a laser beam) onto the measurement object as a point within its focal plane. The light reflected by the measurement object is collected by the lens and directed via a beam splitter into a pinhole aperture positioned in front of the detector. The pinhole aperture is responsible for the system’s confocal property. Information that does not originate from the focal plane of the microscope objective is blocked by this pinhole aperture. Light from the focal plane is focused onto the detector pinhole and thus detected by the detector. This ability to block out information above and below the focal plane enables the confocal microscope to establish a depth range and thus perform optical tomography.

The most common application of a confocal microscope is the laser scanning microscope. In this process, an image is constructed from a set of data, with the object being scanned sequentially point by point and line by line. The optical section generated in this way is a high-contrast, high-resolution image of the object being measured in the X, Y, and Z directions.

The resolution of the confocal scanning microscope depends on the microscope objective and light source used and can reach up to 1 nm in the Z-direction and approximately 0.5 µm laterally.

References:

[1] Belkner J, Manske E (2021). “Method and Apparatus for Compensating for Transient Aberrations in Confocal Measurement of a Sample Surface,” priority: March 26, 2020, published: July 15, 2021, DE102020108333B3, assignee: Technische Universität Ilmenau, 98693 Ilmenau

[2] Belkner J, Ortlepp I, Gerhardt U, Manske E (2021). "Compensating aberration-induced error in differential confocal microscopy," Proc. SPIE 11782, Optical Measurement Systems for Industrial Inspection XII, 117820P (June 20, 2021); https://doi.org/10.1117/12.2592392

[3] J. Kirchner, Fundamental Developments and Investigations into Micro- and Nanostructuring via Direct Laser Writing in Nanopositioning and Nanomess Machines. PhD thesis, TU Ilmenau, 2020.

Interferometric microscopy is another noncontact method used for topographic measurements. Various types of interferometers are used here: the Fizeau interferometer, the Michelson interferometer, the Mirau interferometer, and the Linnik interferometer. In these methods, the phenomenon of interference is used to determine the topography over a large area.

White-light interference microscopy is an imaging two-beam interference measurement method that uses light from a spectrally broadband source. The light emitted by the white-light source is focused by various imaging optics and passes through the interferometer objective (Mirau objective). The reflected light is directed onto a CCD camera via a beam splitter. Inside the Mirau objective, a beam splitter plate splits the light into object and reference beams, which are reflected at the measurement surface and the flat reference mirror, respectively. The interference patterns are recorded using a CCD camera. During the measurement, the object or the Mirau objective is moved in fine increments in the Z-direction. This results in white-light interference patterns that move across the object. A stack of images is acquired, and each individual point on the object is analyzed in parallel but independently of the others. Advantages include very short measurement times as well as peak values in height resolution of < 0.1 nm.

References:

[1] D. Kapusi, T. Machleidt, E. Manske, K-H. Franke, R. Jahn: White light interferometry utilizing the large measuring volume of a nanopositioning and nanomeasuring machine, Conference: Proc. 12th Int. Colloquium on Surfaces (Chemnitz, January 28–29, 2008), pp. 210–7.

[2] T. Machleidt, E. Sparrer, E. Manske, D. Kapusi, K-H. Franke: Area-based optical 2.5D sensors of a nanopositioning and nanomeasuring machine, In: Measurement Science and Technology, Vol. 23, 2012, p. 074010 (6 pp.).

[3] E. Manske: Modular Family of Sensors for a Nanopositioning and Nanomeasuring Machine, In: International Journal of Optomechatronics, Vol. 7, 2013, pp. 122–135.

The Nanofabrication Machine 100 serves as an important experimental platform for basic research in the field of tip- and laser-based nanofabrication for sub-10-nm structuring on surfaces up to Ø100 mm. This platform enables the “NanoFab” Graduate Research Training Program to push the boundaries of nanofabrication into new, cutting-edge territories with reproducibility and uncertainty in the subnanometer range. The currently installed AFM system can also be used for field-emission scanning probe lithography (FESPL), thereby enabling new methods of nanostructuring that will be investigated on the machine. It will support the research work of the DFG Research Training Group Nano-Fab (GRK 2182/1) conducted by 13 doctoral students over three cohorts (9 years). The instrument is unique and unparalleled internationally and is based on many years of research conducted by SFB 622 (2002–2013).

References:

• Stauffenberg J, Ortlepp I, Blumröder U, Dontsov D, Schäffel C, Holz M, Rangelow I W, Manske E: Investigations on the positioning accuracy of the Nano Fabrication Machine (NFM-100) / Investigations into the Positioning Accuracy of the Nano Fabrication Machine (NFM-100), Technisches Messen, 2021, https://doi.org/10.1515/teme-2021-0079
• Jaqueline Stauffenberg, Christoph Reuter, Ingo Ortlepp, Mathias Holz, Denis Dontsov, Christoph Schäffel, Jens-Peter Zöllner, Ivo W. Rangelow, Steffen Strehle, and Eberhard Manske: Nanopositioning and -fabrication using the Nano Fabrication Machine with a positioning range up to Ø 100 mm. In: SPIE Advanced Lithography Proceedings, 11610-35 (2021), DOI: 10.1117/12.2583703
• Jaqueline Stauffenberg, Ingo Ortlepp, Christoph Reuter, Mathias Holz, Denis Dontsov, Christoph Schäffel, Steffen Strehle, Jens-Peter Zöllner, Ivo W. Rangelow, Eberhard Manske: Investigations on Long-Range AFM Scans Using a Nano Fabrication Machine (NFM-100). In: 4^th Edition of the nanoFIS-Functional Integrated nanoSystems Conference, Graz, Austria, November 2–4, 2020. MDPI proceedings. 2020. 174–176.
• Ingo Ortlepp, Michael Kühnel, Martin Hofmann, Laura Weidenfeller, Johannes Kirchner, Shradda Supreeti, Rostyslav Mastylo, Mathias Holz, Thomas Michels, Roland Füßl, Ivo W. Rangelow, Thomas Fröhlich, Denis Dontsov, Christoph Schäffel, Eberhard Manske: Tip- and laser-based nanofabrication up to 100 mm with sub-nanometer precision. In: SPIE Advanced Lithography. California, USA. 2020. 11324-8.

Direct laser writing enables the patterning of wafers for electronic circuits, electronic and microsystems components, as well as the fabrication of components with micro- to submicrometer dimensions [1]. The advantage of this approach is that it eliminates the need for the complex fabrication of masks, making the manufacturing process more cost-effective and flexible [2].

In direct laser writing (DLW), the focused laser beam is directed directly onto a substrate coated with photoresist, and a positioning system is used to induce relative motion between the laser beam and the sample [1]. This allows the specified structures to be exposed, so that geometric features—consisting of cured photoresist or grooves—form at the exposed areas. Through a subsequent etching process, the structures are transferred from the photoresist into the substrate in the form of etched grooves [1].

To induce a reaction in the photoresist on the coated substrate—a photoreaction—a certain amount of energy is required, which depends on the energy difference between the ground state and the excited state of the initiator molecule in the photoresist. The energy required for this can be supplied by a single photon [3]. The energy can be provided through the absorption of a single photon (Figure a) or through the quasi-simultaneous absorption of two photons (Figure b) with sufficient energy [4].

References

[1] Combination of two-photon-based direct laser writing with large-area and high-precision nanopositioning, Laura Weidenfeller.

[2] Kenneth H. Church, Charlotte Fore, and Terry Feeley. Commercial applications and review of direct-write technologies. MRS Online Proceedings Library Archive, 624, 2000.

[3] Robert W. Boyd. Nonlinear Optics. Academic Press, 2003.

[4] Shoji Maruo, Osamu Nakamura, and Satoshi Kawata. Three-dimensional microfabrication with two-photon-absorbed photopolymerization. Optics Letters, 22 (2):132–134, 1997.