A measurement system for surface topography based on three-wavelength interferometry

Optical microscopic interferometry is an important measurement method for surface topography. There is usually contradiction between enlargement of measuring interval and improvement of measuring precision. In this paper, a three- wavelength interference measurement system for surface topography based on wavelength switch and phase shift scanning is proposed. A data processing method for three- wavelength interference images is proposed, which use the phase extraction and recognition algorithm based on elliptic fitting and combined size scales of phase difference. The method can effectively improve the overall precision of surface topography measurement and expand measuring interval to nearly 27 times that of single wavelength 640 nm. Experimental results have shown that the relative measurement error of surface roughness of square wave specimen with multiple grooves is only 4.1% compared to the calibrated data which is produced by China National Institute of Metrology. Therefore, the three-wavelength interferometry method can realize high precision measurement for surface topography in a certain measuring interval.