KEYWORDS: Interferometers, Nanofabrication, Mirrors, Actuators, Near field optics, Control systems, Manufacturing, Nanotechnology, Physics, Atomic force microscopy
Although the field of optical lithography is highly investigated and numerous improvements are made, structure sizes smaller than 20 nm can only be achieved by considerable effort when using conventional technology. To cover the upcoming tasks in future lithography, enormous exertion is put into the development of alternative fabrication technologies in particular for micro- and nanotechnologies that are capable of measuring and patterning at the atomic scale in growing operating areas of several hundred square millimetres. Many new technologies resulted in this process, and are promising to overcome the current limitations1, 2, but most of them are demonstrated in small areas of several square micrometers only, using state-of-the-art piezo stages or the like. At the Technische Universitat Ilmenau, the NanoFabrication Machine 100 (NFM-100) was developed, which serves as an important experimental platform for basic research in the field of scale-spanning AFM tip-based and laser-based nanomeasuring and nanofabrication for simultaneous subnanometre measuring and structuring on surfaces up to Ø100 mm. This machine can be equipped with several probing systems like AFM, laser focus probes and 3D-micro probes as well as tools for different nanofabrication technologies like tip-based technologies, optical technologies and mechanical two-dimensional technologies in a large working range with subnanometre reproducibility and uncertainty. In this paper, the specifics and advantages of the NFM-100 will be described as well as nanofabrication technologies that are currently worked on e.g. advanced scanning proximal probe lithography based on Fowler-Nordheim-electron-field emission, direct laser writing and UV-nanoimprint lithography.
Nanometre accuracy and resolution metrology over large areas is becoming more and more a necessity for the progress of precision and especially for nano manufacturing. In recent years, the TU Ilmenau has succeeded in developing the scientific-technical basics of new ultra-high precision, so called nanopositioning and nanomeasuring machines. In further development of the first 25 mm machine, known as NMM-1 from SIOS Meßtechnik GmbH, we have developed and built new machines having measuring ranges of 200 mm x 200 mm x 25 mm at a resolution of 20 pm and enable measuring reproducibility of up to 80 pm. This means a relative resolution of 10 decades. The enormous accuracy is only made possible by the consistent application of error-minimum measurement principles, highly accurate interferometric measurement technology in combination with highly developed measurement signal processing and comprehensive error correction algorithms. The probing of the measurement objects can optionally be carried out with the aid of precision optical, interference-optical, tactile or atomic force sensors. A complex 3D measurement uncertainty model is used for error analysis. The high performance could be demonstrated as an example in step height measurements with a reproducibility of only 73 pm. The achieved resolution of 10-10 also presents new challenges for the frequency stability of the He-Ne lasers used. Here, the approach of direct coupling of the lasers to a phase-stabilized optical frequency comb synchronized with an atomic clock is pursued. The frequency stability is thus limited by the relative stability of the RFreference to better than 4•10-12 (1s).
Cost-effective generation of single-digit nano-lithographic features could be the way by which novel nanoelectronic devices, as single electron transistors combined with sophisticated CMOS integrated circuits, can be obtained. The capabilities of Field-Emission Scanning Probe Lithography (FE-SPL) and reactive ion etching (RIE) at cryogenic temperature open up a route to overcome the fundamental size limitations in nanofabrication. FE-SPL employs Fowler-Nordheim electron emission from the tip of a scanning probe in ambient conditions. The energy of the emitted electrons (<100 eV) is close to the lithographically relevant chemical excitations of the resist, thus strongly reducing proximity effects. The use of active, i.e. self-sensing and self-actuated, cantilevers as probes for FE-SPL leads to several promising performance benefits. These include: (1) Closed-loop lithography including pre-imaging, overlay alignment, exposure, and post-imaging for feature inspection; (2) Sub-5-nm lithographic resolution with sub-nm line edge roughness; (3) High overlay alignment accuracy; (4) Relatively low costs of ownership, since no vacuum is needed, and ease-of-use. Thus, FE-SPL is a promising tool for rapid nanoscale prototyping and fabrication of high resolution nanoimprint lithography templates. To demonstrate its capabilities we applied FE-SPL and RIE to fabricate single electron transistors (SET) targeted to operate at room temperature. Electrical characterization of these SET confirmed that the smallest functional structures had a diameter of only 1.8 nanometers. Devices at single digit nano-dimensions contain only a few dopant atoms and thus, these might be used to store and process quantum information by employing the states of individual atoms.
High Performance Single Nanometer Lithography (SNL) is an enabling technology for beyond CMOS and future
nanoelectronics. To keep on with scaling down nanoelectronic components, novel instrumentation for nanometer precise
placement, overlay alignment and measurement are an essential pre-requirement to realize Next Generation Lithography
(NGL) systems. In particular, scanning probe based methods for surface modification and lithography are an emerging
method for producing sub-10 nm features. In this study, we demonstrate nano-scale lithography using a scanning probe
based method in combination with a Nanopositioning and Nanomeasuring Machine. The latter one has a measuring
range of 25 mm x 25 mm x 5 mm, 0.1 nanometer resolution and outstanding nanometer accuracy. The basic concept
consists of a special arrangement allowing Abbe error free measurements in all axes over the total scan range.
Furthermore, the Nanopositioning and Nanomeasuring Machine is able to store the exact location that can be found again
with an accuracy of less than 2.5 nanometers. This system is also predestinated for critical dimension, quality and
overlay control. The integrated scanning probe lithography is based on electric-field-induced patterning of calixarene. As
a result, repeated step response tests are presented in this paper.
A proprietary metrological scanning probe microscope (SPM) with an interferometer, developed by the Institute of
Process Measurement and Sensor Technology at the Ilmenau University of Technology (IPMS), is used as a stationary
probe system in the nanomeasuring and nanopositioning machine (NPMM). Due to the movements of the NPMM, the
total microscope measuring range is 25mm × 25mm × 5mm with a positioning resolution of less than 0.1nm. Examples
for specimens are step height standards and one-dimensional gratings. The repeatability has been determined at less than
0.5nm for measurements on calibrated step height standards and less than 0.2nm for the gratings. The measurement
results of these samples are always directly related to the corresponding measurement uncertainty, which can be
calculated using an uncertainty budget. A new traceable method has been developed using a vectorial modular model.
With this approach, it is possible to quickly insert new sub-models and to individually analyze their effects on the total
measurement uncertainty. The analysis of these effects with regard to their uncertainties is done by Monte Carlo
Simulation (MCS), because some models have partially or fully nonlinear character of which one example is the
interferometer model of the metrological SPM. The complete development and analysis of these models is presented for
one specific measurement task. The measurement results and the corresponding measurement uncertainty were obtained
by Monte Carlo Simulation. Comparisons with the GUM have shown that the proposed procedure is a good alternative to
achieve reasonable measurement results with uncertainty estimation.
The paper deals with the analysis of the uncertainty of high precision long range three-dimensional Nanopositioning and
Nanomeasuring Machines (NPMM). Those high-tech instruments consisting of precision 3d-guides, interferometers, a
3d-reference-mirror and nanoprobes, connected by a stabile frame are subject of research. Especially the interferometer
mirror system characterizes the precision of such machines. Therefore a new vectorial metrological model will be
described to characterize this machine part. Its properties and advantages are shown and the model is used to analyze the
uncertainty budget of a concrete Nanopositioning and Nanomeasuring Machine.
A new traceable method has been developed and investigated to experimentally determine the total amount of measuring deviations arising through the capture and demodulation of plane-mirror interferometer signals. The basic principle for such an analysis is the precise specification of length variations. However, either a measuring system of excellent accuracy or accurately defined movements within a stable platform are required. A common measuring motion can be achieved through the displacement of a reflecting wedge plate, which creates a constant step-down. The interferometer to be analyzed is used to determine the change in the wedge plate's thickness, which is caused by lateral movements controlled by another interferometer. The wedge's sampled surfaces demand high planarity as the change of thickness acts as the material measure. These conditions can be achieved by using the Nanopositioning and Nanomeasuring Machine in conjunction with a 0.5-degree tilted mirror placed on it. The interferometer to be analyzed is aligned with this mirror. To provide the highest possible linearity for lateral motion, the only measuring points are in nearly error-free lambda/2 steps of the interferometer. The NPM machine's already small deviations in positioning will only affect the evaluation of measuring errors of the reduced interferometer by a factor of about one-hundredth. This is one of the main advantages of the method. The interferometer to be analyzed - like the entire measuring setup - features a compact assembly and high mechanical and thermal stability. The measured deviations in linearity provide excellent verification of the prospected error influences.
The paper describes the design of a high-precision three-dimensional nanopositioning and nanomeasuring machine (NPM-Machine). The NPM-Machine has been developed by the Institute of Process Measurement and Sensor Technology of the Technische Universität Ilmenau and manufactured by the SIOS Meßtechnik GmbH Ilmenau. The machine was successfully tested and continually improved in the last few years. The NPM-Machine has a resolution of less than 0,1 nm over the entire positioning and measuring range of 25 mm x 25 mm x 5 mm. An Abbe offset-free design and the application of a new concept for compensating systematic errors resulting from mechanical bearings provide extraordinary accuracy. An important part of the NPM-Machine is constituted by a mirror corner. The integration of several probe systems and Nanotools makes the NPM-Machine suitable for various tasks, such as large-area scanning probe microscopy, mask and wafer inspection, nanostructuring, biotechnology as well as measuring mechanical precision workpieces a.s.o. Various probe systems have been integrated into the NPM-Machines. The machines are operating successfully in several German and foreign institutes including the Physikalisch-Technische Bundesanstalt (PTB). The article gives basic information on the NPM-Machine and describes the mode of operation and the measurements by means of probe systems.
An initial description of the design and operation of compact miniature interferometers that employ fiberoptic lightguides for all of their optical couplings and are suitable for general-purpose use is followed by a metrological analysis of their mode of operation and examples of their broad applicability, based on several typical instrumental setups.
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