A High Precision and Large Range Measuring Method for Broadband Light Interferometric Microscopy Based on Phase Unwrapping and
Stitching Algorithm
ZHAO Wen-hao1, 2, LI Jun1, DU Kai1, XIONG Liang1, YIN Shao-yun1, HU Jian-ming3, WANG Jin-yu1, 2*
1. Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714, China
2. University of Chinese Academy of Sciences, Beijing 100049, China
3. College of Physics and Electronic Engineering，Chongqing Normal University，Chongqing 401331，China
Abstract：Broadband light interferometric microscopy is widely used for high precision profile measurement in the industry field. Vertical scanning interferometry (VSI) is usually used to measure the submicron to millimeter level features, and phase shift interferometry (PSI) to measure the nanoscale features. Among them, the precision of PSI is of nanoscale order, while its measurable range is limited because the phase changes corresponding to the height variations of the sample surface should be limited within the scope of 2π.A large amount of phase unwrapping algorithms are developed to extend the range of PSI. However, they are only suitable to smooth surfaces. When the height fluctuations exceed the limited range determined by the focal depth or the coherent length of the light source, the interference fringes will be blurred. Even the contrast will be lost. Thereafter, great measurement errors will be introduced to the calculated results. This paper proposesa high precision and large range broadband light interferometric microscopy measurement method based on the phase unwrapping and stitching algorithm. The fringe modulation value quantified the fringe quality at a given focal plane, the areas with the high modulation values generally correspond to the regions of interests （ROI） with high contrast and clear image. The ideal regions (IRs) are defined as the ROI with a modulation value greater than a given threshold within the current focal plane. Meanwhile, the problem regions (PRs) are defined as the ROI with a modulation value lower than the given threshold. Only the true phase distribution in IRs is calculated with the phase unwrapping algorithm. By vertically moving the focal plane of the objective with a translation stage at a reasonable step length, the IRs of the adjacent focal plane will be partially overlapped. According to the differences between the phase of the overlapped IRs of the adjacent focal plane, the corresponding unwrapped phase of the adjacent plane can be stitched together with high precision. Finally, the complete profile distribution of the sample is restored according to the stitched true phase with high precision. The proposed method for broadband light interferometric microscopy avoids the error caused by the phase unwrapping in the PRs. Through simulation and experiments results, we demonstrate that the proposed method maintains the nanoscale precision of PSI in broadband light interferometric microscopy and extends its range from hundreds of nanometers to several micrometers. Moreover, its accuracy does not depend on the displacement precision of the focal planes by translation stages. Theoretically, the range of our proposed method can be extended to the total working distance of the microscopic objective.
赵文豪，李 俊，杜 凯，熊 亮，尹韶云，胡建明，王金玉. 基于相位展开及拼接算法的一种高精度大量程宽光谱干涉显微术[J]. 光谱学与光谱分析, 2022, 42(08): 2411-2417.
ZHAO Wen-hao, LI Jun, DU Kai, XIONG Liang, YIN Shao-yun, HU Jian-ming, WANG Jin-yu. A High Precision and Large Range Measuring Method for Broadband Light Interferometric Microscopy Based on Phase Unwrapping and
Stitching Algorithm. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2022, 42(08): 2411-2417.
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