Real-time scanner error correction in white light interferometry

3D microscopes based on white light interferometry (WLI) with vertical scanning have been widely used in many areas of surface measurements and characterizations for decades. This technology provides fast, non-contact, and full-field surface 3D measurements with vertical resolution as low as the sub-nanometer range. Its applications include measurements of step height, surface roughness, film thickness, narrow trench and via depths as well as other geometric and texture parameters. In order to assure the highest accuracy of the measurement, scanner linearity needs to be maintained or monitored so that the nonlinearity can be accounted for during the measurement. This paper describes a method that accounts for nonlinearities in real time without the need to store frame data; in addition this method is shown to be less sensitive to vibrations than previous methods described. The method uses an additional interferometer, a distance measuring interferometer to measure the actual scanner position at each scan step.