Dual-wavelength vertical scanning low-coherence interferometric microscope.

White-light interferometry has turned into a standard tool in the field of high-accuracy topography measurements. Nevertheless, surfaces with relatively large local surface tilts or height steps often give rise to systematic measuring errors. The reasons are diffraction and dispersion effects, which cause deviations between height values obtained from the envelope maximum of the white-light interference signal and those obtained from the signal's phase. In certain cases this may result in ghost steps appearing in the measured topography. To identify and eliminate these ghost steps we use a second LED emitting light at a different mean wavelength. This now allows the measurement of curved or structured specular surfaces with high resolution, which up to now was restricted by the mentioned effects.