White light interferometry with spectral-temporal demodulation for large-range thickness measurement

Yunlong Zhu; Zhuoran Li; Xu Lu; Yonggui Yuan; Jun Yang

doi:10.3788/COL202220.091201

Chinese Optics Letters, Volume. 20, Issue 9, 091201(2022)

White light interferometry with spectral-temporal demodulation for large-range thickness measurement

Yunlong Zhu^1,2, Zhuoran Li^1,2, Xu Lu^1,2, Yonggui Yuan^1,2,*, and Jun Yang^2,3,4,**

¹Key Laboratory of In-fiber Integrated Optics, Ministry of Education of China, Harbin Engineering University, Harbin 150001, China

²College of Physics and Optoelectronic Engineering, Harbin Engineering University, Harbin 150001, China

³Guangdong Provincial Key Laboratory of Information Photonics Technology (Guangdong University of Technology), Guangzhou 510006, China

⁴School of Information Engineering, Guangdong University of Technology, Guangzhou 510008, China

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Film thickness measurement can be realized using white light interferometry, but it is challenging to guarantee high precision in a large range of thicknesses. Based on scanning white light interferometry, we propose a spectral-temporal demodulation scheme for large-range thickness measurement. The demodulation process remains unchanged for either coatings or substrate-free films, while some adjustments are made according to the estimated optical thickness. Experiments show that the single-point repeatabilities for 500 nm ${SiO}_{2}$ coating and 68 µm substrate-free Si film are no more than 0.70 nm and 1.22 nm, respectively. This method can be further developed for simultaneous measurement of surface profile and film thickness.

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spectral-temporal demodulation thickness measurement thin film white light interferometry

1. Introduction

Thin films play important roles in the fields of semiconductors, optoelectronics, integrated optics, etc. Following the increasing demand on thin film quality^[1], precise measurement of film thickness is crucial to provide valuable feedback for the fabrication process. While dealing with transparent thin films, commercial ellipsometry systems^[2] can give good results of film thickness, yet they can hardly measure surface profile and film thickness at the same time. On the contrary, white light interferometry (WLI) is well-known for surface profile measurement with high precision, and it shows great potential for simultaneous measurement of film thickness and surface profile^[3], yet it is hard to measure a large range of thickness with high accuracy.

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Yunlong Zhu, Zhuoran Li, Xu Lu, Yonggui Yuan, Jun Yang. White light interferometry with spectral-temporal demodulation for large-range thickness measurement[J]. Chinese Optics Letters, 2022, 20(9): 091201

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