Verein Deutscher Ingenieure

Optical measurement of microtopography - Calibration of confocal microscopes and depth setting standards for roughness measurement
 N VDI/VDE 2655 BLATT 1.2

Annotation

The present guideline applies to confocal microscopes for measuring the topography of technical surfaces. The procedures described for the calibration can be compared with the methods which have already proved their worth and have therefore been incorporated in the guidelines (DKD-R 4-2, EAL G-20) on the traceability of stylus instruments , see Figure 1. Accordingly, also the standards tested there (optical flats, gratings, depth setting standard, roughness standard) are adopted to the extent possible.

This guideline is limited to the basic calibration of imaging confocal microscopes. By confocal microscopes measuring instruments are understood whose underlying principle relies on the imaging of a point source onto the sample to be calibrated in the illumination branch and the imaging of the light, returning onto a corresponding point-type intensity sensor in the detection branch. The focus here lies on the measurement of three-dimensional surface topographies. The guideline deals with the required traceability to the unit of length via the measurement on depth setting standards that have been traced back. This is illustrated by the right-hand vertical path in Figure 1. These measurement processes furnish the derivation for the evaluation of the measurement uncertainty in instrument calibration and that of the measurement on depth setting standards.

This guideline relates to the measurement of uncoated samples. The influence of sample coatings as well as the measurement of layer thicknesses of transparent materials are not dealt with in this guideline. Similarly, it is assumed that the samples used for calibration do not show material contrasts.

It is to be ensured that the objective used is operated in conformity with its specifications. Measurement methods using fluorescence and stitching methods to enlarge the measuring field have not been taken into account due to the complexity of potential error influences.