Fast template matching method in white-light scanning interferometry for 3D micro-profile measurement.

White-light scanning interferometry (WLSI) is an important measurement technique that has been widely used in three-dimensional profile reconstruction. Because of the effects of environmental noise and phase changes caused by surface reflection, existing WLSI algorithms have problems in measurement accuracy and measurement speed. Addressing these problems, this paper proposes a fast template matching method to determine precisely the zero optical path difference (ZOPD) position in the WLSI. Due to the uniform shape of the interference signals, a template interference signal can be obtained in advance by performing a least-square fitting or Fourier interpolation on an interference signal of one pixel. In the method, the ZOPD position is initially obtained by the centroid method. Then, the ZOPD position is determined by a precise matching process through moving the template interference signal on the measured interference signal. Through the two-step processes, the ZOPD position can be obtained precisely with much less time. The method was simulated and verified through the measurement of a spherical surface, a 1.8-µm-height standard step and a flip-chip substrate. The experimental results show that the proposed algorithm can achieve both high precision and fast measurement.