Film thickness test method - Interference Microscope

The interference microscope method uses the same sample processing method as the profiler method, that is, a step , and the height of the step is measured by a multi-beam interferometer.

The interferometer has a lens attached to the sample as a flat reference plate. When a beam of monochromatic light is reflected back and forth between the sample and the above-mentioned lens , the interference fringe image can be observed through a low power microscope. If the reference plate is slightly inclined relative to the surface of the sample to be tested, a series of parallel interference fringe lines will be formed. Steps on the sample surface will shift the interference fringes. A fringe spacing offset is equivalent to the vertical displacement of half a wavelength of monochromatic light. The spacing can be observed and measured with a graduated eyepiece micrometer.

This method can be used to measure coatings below 2 μm with high reflectivity. See the international standard ISO3868 metal and other inorganic coating Fizeau (Fizeau) multi-beam interferometry.