Surface recovery algorithm in white light interferometry based on combined white light phase shifting and fast Fourier transform algorithms

Abstract

Quality control of micro-nano structured and freeform surfaces is becoming increasingly important, which leads to challenging requirements in the measurement and characterization of rough and highly reflective surfaces. As an important measurement technique, white light scanning interferometry (WLSI) is a fast noncontact method to measure three-dimensional (3D) surface profiles. Nevertheless, the existing WLSI 3D surface reconstruction algorithms are prone to environmental vibrations and phase changes caused by reflections on the tested surface. A novel peak detecting algorithm that combines the white light phase-shifting interferometry (WLPSI) method and fast Fourier transform (FFT) coherence-peak-sensing technique is proposed in this paper, which can accurately determine the local fringe peak and improve the vertical resolution of the measurement. A microcomponent (10 μm standard step height) and a spherical surface were used as test specimens to evaluate the proposed method. Both simulated and experimental results show that the proposed algorithm improves the precision and anti-interference ability of the WLPSI and FFT methods, which can effectively reduce the batwing effects at the edges and solve the problem of positioning error in the maximum modulation.

Nanoscale surface characterization using laser interference microscopy

“…It could be easily achieved in laboratories with AFM and SEM but industrial application AFM and SEM as the in-line tool is limited due to high cost and of low operating speed measurements. That is why optical measurement tools seem more promising for the inline metrology; the traditional WLI methods meet the requirements of low cost and high operating speed it also widely uses for vertical dimensions measurements and provides <1 nm uncertainty [26,27]. Table 2 demonstrates the results of lateral dimensions measurements experiment.…”

Application of Clustering Filter for Noise and Outlier Suppression in Optical Measurement of Structured Surfaces

“…Specifically, the two profiles obtained from the envelope and phase evaluations at the best focus position are compared at each point and then the batwing effect is removed in the phase unwrapping procedure. Vo et al [18] proposed another algorithm which combines white light phase shifting algorithm and fast Fourier Transform (FFT) coherence peak sensing techniques to effectively solve the problem of positioning error in the maximum modulation and remove the batwing effect at the step edges. Niehues et al [19] proposed a dual-wavelength phase unwrapping technique to correct the batwings and ghost peaks by adding a second LED (with a different mean wavelength) in the vertical scanning interferometry and comparing the measurement results from two different illumination schemes.…”

“…The visibility falls quickly when the OPD increases. Surface topography can be acquired after tracking all coherence peaks or phase retrieval within the field of view of the objective [12], [18].…”

Robust 3D surface recovery by applying a focus criterion in white light scanning interference microscopy

“…(1), in which the position where the fringe visibility is maximum corresponds to the best focus position and hence the pixel depth. Although there are many methods for processing WLSI signals [20], we use here the maximum intensity detection because it is fast, requires little data storage, and has been shown to yield accurate results in surfaces of relatively high slope scanned with fine vertical stepping [1].…”