Optical Profilometry

A contact-less investigation of the surface topography is possible by optical profilometry. The vertical resolution can be down to a few nm. The instrument at Tascon GmbH enables both confocal and interferometric analyses.

In confocal microscopy, only light from the focal plane of the microscope reaches the CCD sensor. Light that doesn't originate from the focal plane is not registered by the detector. Usually monochromatic light is used to irradiate the sample. By continuously varying the distance between the sample surface and the optical system the entire sample surface moves through the focal plane. The acquired imaging data from the various planes can be composed into a three dimensional model of the sample surface.

In interferometric analysis, the sample surface is irradiated with monochromatic light. During the measurement the distance between the sample and the objective of the interferometer is increased in small steps. The topography causes differences in the travelling time of the reflected light and a reference light beam. The overlay of both light beams results in an interference pattern that is moving over the surface during the incremental change in the vertical distance to the sample. The results of this series of interference images is an interferogram for each object point, which makes it possible to calculate the sample topography.

Samples with reflecting surfaces and heights up to 2 cm can be analyzed. There are limitations on the analysis of optically transparent sample systems (e.g. mirrors, glasses, etc.). For a precise acquisition of topographic information from these systems it is recommended to coat the surface with a thin reflecting metal film.