Current Optics and Photonics

Optical Society of Korea (한국광학회)
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In Situ Sensing of Copper-plating Thickness Using OPD-regulated Optical Fourier-domain Reflectometry

  • Nayoung, Kim (Department of Cogno-Mechatronics Engineering, Pusan National University) ;
  • Do Won, Kim (Department of Advanced Circuit Interconnection, Pusan National University) ;
  • Nam Su, Park (Department of Advanced Circuit Interconnection, Pusan National University) ;
  • Gyeong Hun, Kim (Engineering Research Center for Color-Modulated Extra-Sensory Perception Technology, Pusan National University) ;
  • Yang Do, Kim (School of Materials Science and Engineering, Pusan National University) ;
  • Chang-Seok, Kim (Department of Cogno-Mechatronics Engineering, Pusan National University)
  • Received : 2022.11.03
  • Accepted : 2022.12.28
  • Published : 2023.02.25
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Abstract

Optical Fourier-domain reflectometry (OFDR) sensors have been widely used to measure distances with high resolution and speed in a noncontact state. In the electroplating process of a printed circuit board, it is critically important to monitor the copper-plating thickness, as small deviations can lead to defects, such as an open or short circuit. In this paper we employ a phase-based OFDR sensor for in situ relative distance sensing of a sample with nanometer-scale resolution, during electroplating. We also develop an optical-path difference (OPD)-regulated sensing probe that can maintain a preset distance from the sample. This function can markedly facilitate practical measurements in two aspects: Optimal distance setting for high signal-to-noise ratio OFDR sensing, and protection of a fragile probe tip via vertical evasion movement. In a sample with a centimeter-scale structure, a conventional OFDR sensor will probably either bump into the sample or practically out of the detection range of the sensing probe. To address this limitation, a novel OPD-regulated OFDR system is designed by combining the OFDR sensing probe and linear piezo motors with feedback-loop control. By using multiple OFDR sensors, it is possible to effectively monitor copper-plating thickness in situ and uniformize it at various positions.

Keywords

Acknowledgement

2-Year Research Grant of Pusan National University.

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