KMS Chongqing Institute of Green and Intelligent Technology, CAS
| 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
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| 2022-08-01 | |
| 摘要 | 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 2 pi. 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. |
| 关键词 | Broadband light interferometric microscopy Phaseshift interferometry Phase unwrapping Three-dimensional topography measurement |
| DOI | 10.3964/j.issnA000-0593(2022)08-2411-07 |
| 发表期刊 | SPECTROSCOPY AND SPECTRAL ANALYSIS
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| ISSN | 1000-0593 |
| 卷号 | 42期号:8页码:2411-2417 |
| 通讯作者 | Wang Jin-yu(Jinyu.wang@cigit.ac.cn) |
| 收录类别 | SCI |
| WOS记录号 | WOS:000852883200014 |
| 语种 | 英语 |
