Research on rapid and high-sensitivity ellipsometry employing multi-harmonic terms of dual cascade photoelastic modulators

In the fields of film coating, microelectronics, biosensing, and nanomaterial characterization, there is a growing demand for rapid and highly sensitive ellipsometry. Photoelastic modulation ellipsometry has emerged as a method capable of achieving unparalleled measurement speeds and sensitivities. However, the performance of this ellipsometry technique is contingent upon the precise calibration and long-term stability control of photoelastic modulation modulator (PEM). In this study, a differential frequency photoelastic modulation ellipsometry was proposed. Two PEMs operating at distinct frequencies were cascaded, and multi -harmonic terms of the modulation signals were extracted using digital phase -locking technology. Real-time/in-situ calibration and control of PEM was accomplished within a single Field -Programmable Gate Array. The developed system facilitated high-speed and high -sensitivity ellipsometric parameter measurements. To validate the proposed methodology, an experimental system was meticulously constructed, and performance tests were conducted on air and SiO2 film samples. Additionally, a tensile force experiment was performed on a Cu/polyimide film. Results demonstrated that the proposed approach achieved highly sensitive ellipsometry measurements within milliseconds. The system exhibited repeatability and sensitivity up to 10-3 degrees with an integration time of 200 ms. This research provided valuable insights into high -precision, high -sensitivity, and rapid in -situ ellipsometry measurements, offering promising applications in online real-time film technology detection.