KEYWORDS: Calibration, Standards development, 3D metrology, Solids, 3D image processing, Neodymium, Time metrology, Mirrors, 3D imaging standards, Metrology
Two kinds of 3D label free Bio-Transfer-Standards (BTS) have been further developed at the University of Helsinki (UH). The first one, NanoRuler, is a staircase BTS featuring eight fatty acid bilayers which allows vertical calibration in the range of 5 to 40 nm. The second one, NanoStar, is a V-shaped BTS featuring two 5 nm tall bilayers that overlap at 10° angle. This standard enables the determination of the Instrument Transfer Function (ITF). A stability test was conducted on the BTSs, during which the standards were stored in laboratory conditions, and were profiled each week. Profiling was done using a custom-built Scanning White Light Interferometer (SWLI). The stability of NanoStar was ± 0.3 nm, and of NanoRuler ± 0.5 nm to ± 2.5 nm. The BTSs maintained their specified properties for at least six months and therefore allow vertical calibration and ITF determination. In addition, changes in surface morphology of one NanoRuler subjected to water immersion are presented. This paper reports intermediate findings during an ongoing stability test that will run for 24 months.
A V-shape Bio-Transfer-Standard (V-BTS), developed and produced at the University of Helsinki (UH), was measured in two laboratories. In comparison to Siemens Star calibration specimens, the V-BTS performs better at high lateral frequencies close to the diffraction limit of the optical instrument. This permits determining of the Instrument Transfer Function (ITF). The V-BTS features two lipid bilayer steps that partly overlap each other at an angle of 20°, with an average height of 4.6 ± 0.1 nm. The Round Robin (RR) test aims to determine whether the V-BTS and the developed application protocol work with different optical profilers in different laboratories. First the artefact was measured at Sensofar-Tech, S.L. using an S-neox profiler working in Phase Shifting Interferometry mode. Then V-BTS was measured at UH using a custom-built Scanning White Light Interferometer. All measurements done by four different operators at the two laboratories have a range or standard deviation of ±0.1 nm which agrees with the theoretical estimates and with measurements done using an atomic force microscope and with a surface plasmon resonance based instrument. The RR results show the applicability of the V-BTS for calibration and for ITF characterization of 3D optical profilers.
Confocal microscopes are widely used for areal measurements thanks to its good height resolution and the capability to
measure high local slopes. For the measurement of large areas while keeping few nm of system noise, it is needed to use
high numerical aperture objectives, move the sample in the XY plane and stitch several fields together to cover the
required surface. On cylindrical surfaces a rotational stage is used to measure fields along the round surface and stitch
them in order to obtain a complete 3D measurement. The required amount of fields depends on the microscope’s
magnification, as well as on the cylinder diameter. However, for small diameters, if the local shape reaches slopes not
suitable for the objective under use, the active field of the camera has to be reduced, leading to an increase of the
required number of fields to be measured and stitched. In this paper we show a new approach for areal measurements of
cylindrical surfaces that uses a rotational stage in combination with a slit projection confocal arrangement and a highspeed
camera. An unrolled confocal image of the cylinder surface is built by rotating the sample and calculating the
confocal intensity in the centre of the slit using a gradient algorithm. A set of 360º confocal images can be obtained at
different heights of the sample relative to the sensor and used to calculate an unrolled areal measure of the cylinder. This
method has several advantages over the conventional one such as no stitching required, or reduced measurement time. In
addition, the result shows less residual flatness error since the surface lies flat in the measurement direction in
comparison to field measures where the highest slope regions will show field distortion and non-constant sampling. We
have also studied the influence on the areal measurements of wobble and run-out introduced by the clamping mechanism
and the rotational axis.
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