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).
We propose a wavelength standard for highly precise dimensional measurements. An internal-mirror helium-neon laser is offset-locked to a frequency comb line in order to carry out a secondary standard with reduced phase noise and high optical power. Additional lasers can be traced back to this secondary standard, which will enable us to disseminate the accuracy and stability to the metrology lasers of our nanopositioning and -measuring machine, the so-called NPMM-200. First measurements revealed that the stability of the secondary standard is restricted by the time standard of the optical frequency comb to a value of 2.4·10-12 (τ = 1 s), which is a significant improvement in comparison to the stability of the existing metrology lasers. In further measurements a metrology laser was locked onto the secondary standard with a relative instability of 0.6·10-15 (τ = 1000 s).
The paper describes recent improvements of Physikalisch-Technische Bundesanstalt's (PTB) reference measuring instrument for length graduations, the so-called nanometer comparator, intended to achieve a measurement uncertainty in the domain of 1 nm for a length up to 300 mm. The improvements are based on the design and realization of a new sample carriage, integrated into the existing structure and the optimization of coupling this new device to the vacuum interferometer, by which the length measuring range of approximately 540 mm with sub-nm resolution is given. First, measuring results of the enhanced nanometer comparator are presented and discussed, which show the improvements of the measuring capabilities and verify the step toward the sub-nm accuracy level.