Six European National Measurement Institutes (NMIs) have joined forces within the European Metrology Research Programme funded project NANOTRACE to develop the next generation of optical interferometers having a target uncertainty of 10 pm. These are needed for NMIs to provide improved traceable dimensional metrology that can be disseminated to the wider nanotechnology community, thereby supporting the growth in nanotechnology. Several approaches were followed in order to develop the interferometers. This paper briefly describes the different interferometers developed by the various partners and presents the results of a comparison of performance of the optical interferometers using an x-ray interferometer to generate traceable reference displacements.

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We have developed a direct optical method for aperture area measurement, based on constant, known irradiance over the aperture. The method is described and results of test measurements are given, including wavelength dependence of the effective aperture area. Systematic uncertainty components are studied experimentally to reach a relative uncertainty of 10 -4 for aperture sizes down to 3 mm in diameter. The most important advantages of the direct optical method are that it does not require any reference aperture, it can be applied to apertures of any shape, and the calibration setup is similar to the actual use of the apertures in filter radiometers.

An optical method for calibration of the aperture area is described and studied both theoretically and experimentally. A spatially uniform, known irradiance is formed over the aperture by overlapping identical, parallel laser beams centred at constant spacing in an orthogonal lattice. The ratio of the throughput power and irradiance gives the area of the aperture. The method has several advantages compared with previous methods: it measures the area of the aperture directly, the shape of the aperture is not limited to a circle, it is relatively inexpensive to establish, it does not damage the edges of the aperture and the calibration set-up is similar to that for the actual use of the aperture. It is estimated that the relative standard uncertainty is 1.6 × 10 −4 in calibration of a circular 3 mm diameter aperture. The results that the present method gave for one aperture have been compared with the result of a mechanical calibration at the National Physical Laboratory (UK). The relative difference between the results was 2.4 × 10 −4 , with a combined standard uncertainty of 2.5 × 10 −4 .

Traceability of measurements and calibration of devices are needed also at the nanometre scale. Calibration of a commercial atomic force microscope (AFM) was studied as part of a dimensional nanometrology project at MIKES. The calibration procedure and results are presented here. The metrological properties of the AFM were characterized by several measurements. A method developed to calibrate the z scale by a laser interferometer during a normal measurement mode of an AFM is presented. x and y movements were studied with a laser interferometer and the scales were also calibrated using a calibration grid, which was calibrated at MIKES using a laser diffraction method. The advantages and disadvantages of the two methods are discussed. Orthogonalities of the axes were determined by calibration grids and an error separation method. Out-of-plane deviation was measured with a flatness standard. Uncertainty estimates for the coordinate system of the AFM scanner are presented.

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