Traceability is a fundamental issue for nanoscale dimensional metrology. The lack of traceability in measurements inhibits the comparison of tools from different manufacturers and limits knowledge about the real size of fabricated features. Two approaches for realizing traceability in nanometrology, referred to as a top-down approach and a bottom-up approach, are presented. Following the top-down approach, for instance, realized using metrological atomic force microscopes, the dimension of nanostructures is derived from the displacement of the scanner, which is directly measured by laser interferometers whose optical frequency is calibrated to an iodine frequency-stabilized laser. Thus, the measurement result is directly traceable with an unbroken chain to the International System of Units—the meter. However, to achieve subnanometer measurement accuracy, which is far smaller than the optical wavelength (632.8 nm in this study), the subdivision of the interference fringe is essential for obtaining desired measurement resolution and accuracy. On the contrary, with the bottom-up approach, the dimension of nanostructures is determined using the silicon crystal lattice as an internal ruler. Due to the small dimension of the crystal lattice constant (e.g., $d111=0.313nm$), the bottom-up approach offers measurements with potential highest accuracy. The crystal lattice constant can be traceably calibrated to the meter by, e.g., a combined optical and x-ray interferometer; thus, the traceability of the bottom-up approach is also ensured. The consistency of the two approaches is experimentally confirmed in this paper.

A new three-dimensional atomic force microscopy (3D-AFM) for true 3D measurements of nanostructures has been developed at Physikalisch Technische Bundesanstalt (PTB), the national metrology institute of Germany. In its configuration, two piezo actuators are applied to drive the AFM cantilever near its vertical and torsional resonant frequencies. In such a way, the AFM tip can probe the surface with a vertical and/or a lateral oscillation, offering high 3D probing sensitivity. For enhancing measurement flexibility as well as reducing tip wear, a vector approach probing (VAP) method is applied. The sample is measured point by point using this method. At each probing point, the tip is approached toward the surface in its normal direction until the desired tip-sample interaction is detected and is then immediately withdrawn from the surface. Preliminary experimental results show promising performance of the PTB system. The measurement of an IVPS 100 sample using a flared AFM tip showed a repeatability of its 3D profiles better than 1 nm (p-v). A single crystal critical dimension reference material having features with almost vertical sidewalls was also measured using a flared AFM tip. These results show that the feature has average left and right sidewall angles of 89.5 and 89.4, respectively. However, the nonuniformity of the feature width within the measurement window of 1 μm may be up to 10 nm. The standard deviation of the average middle CD values from 10 repeated measurements is 0.1 nm. In addition, an investigation of long-term measurement stability was performed on a PTB photomask. The results changed at a rate of about 0.00033 nm per line, which confirms the high measurement stability and the very low tip wear of the system.

Advanced manufacturing has been identified as one of the key enabling technologies with applications in multiple industries. The growing importance of advanced manufacturing is reflected by an increased number of publications on this topic in recent years. Advanced manufacturing requires new and enhanced metrology methods to assure the quality of manufacturing processes and the resulting products. However, a high-level coordination of the metrology community is currently absent in this field and consequently this limits the impact of metrology developments on advanced manufacturing. In this article we introduce the new European Metrology Network (EMN) for Advanced Manufacturing within EURAMET, the European Association of National Metrology Institutes (NMIs). The EMN is intended to be operated sustainably by NMIs and Designated Institutes in close cooperation with stakeholders interested in advanced manufacturing. The objectives of the EMN are to set up a permanent stakeholder dialogue, to develop a Strategic Research Agenda for the metrology input required for advanced manufacturing technologies, to create and maintain a knowledge sharing programme and to implement a web-based service desk for stakeholders. The EMN development is supported by a Joint Network Project within the European Metrology Programme for Innovation and Research.

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.