TOPOGRAPHICAL DISPLAY USING A CONFOCAL MEASURING MICROSCOPE

The problem: How to display and characterise microtopographies and possible irregularities relatively promptly.

The solution: Equipment surfaces must present the same parameters in respect of texture, smoothness and engraving depth in every product. The human eye can generally recognise mismatches but quantification without a 3D measuring system is only very approximate. In a dual sensor assembly with an interferometric probe and a chromatic distance sensor, we have at our disposal a measuring system for rapid, on-the-spot topography measurements to assess contour and texture in both two- and three-dimensions. The measurement is made by a sensor with a range of 3mm which is capable of a vertical resolution of around 30nm. The appraisal of the measured topographies is performed in conjunction with the analysis program FRT Mark III. This program is installed on the FRT Measuring System for display and analysis of topography data. In this manner, the preparation of histograms, grey-scale images and photorealistic 3D views from any angle is possible.

The illustration below shows the topographical view of the number five as well as its profile. The blue line indicates the profile-section. It can be ascertained from this view that the height of the engraved numeral is about 70 µm.

The method of measuring is based on the principle of chromatic aberration (wavelength-dependent refraction index). Here, white light is focused onto the structural element and the height of the object to be measured is calculated using the prismatic distribution of the light scattered on the surface. The advantage of the measuring principle is that diffused light-rays filtered through an aperture only use the light at the focal point of the objective lens for the image. This operates contact-free both on transparent or reflective and on black or matte surfaces. By using a high resolution we are able to succeed in this way in displaying the smallest of structural features.

For our clients this means that the required texture can be minutely analysed. Should it be on a piece of equipment, we are in a position to measure the pattern afresh and to match it with the client’s sample. Possible deviations can be minimised and ultimately equipment surfaces can be optimally patterned.