Optical dual-probe measurement system and method of thicknesses ranging from nanometer to millimeter (<italic>invited</italic>)

ObjectiveThere is an urgent demand for precision measurement of the thickness of nano- to millimeter-scale transparent materials in fields such as semiconductor and optical manufacturing. However, existing single thickness measurement devices struggle to balance wide-range and high-precision detection. Traditional dispersive confocal method and interferometric spectroscopy both offer advantages including non-contact measurement and simple structure, but the former is difficult to measure nano-scale thin films, while the latter is only applicable to nano-scale transparent thin films—neither of which can meet the needs of multi-scale measurement. To overcome this limitation, this paper proposes a dual-probe composite thickness measurement system integrating interferometric spectroscopy and dispersive confocal method, enabling cross-scale and high-precision thickness detection.MethodsThe composite measurement system proposed in this study comprises two main modules: A dispersive confocal module and an interferometric spectroscopy module. For the dispersive confocal module, a dispersive objective lens group with a theoretical chromatic dispersion range of 349 μm in the 480-680 nm wavelength range is designed. For the interferometric spectroscopy module, a hybrid optimization algorithm integrating the simulated annealing algorithm with the genetic algorithm is proposed. Furthermore, the spectral fitting optimization algorithm, envelope algorithm, extreme value algorithm, and dispersive confocal thickness calculation algorithm are employed to process materials of different thickness scales. Refractive index compensation and accurate calibration for thickness measurement are realized.Results and discussionsFor SiO2 materials, the optical dual-probe thickness measurement system has a theoretical thickness measurement range of 10 nm-0.5 mm. Repeated measurements were conducted on a SiO2 thin film with a thickness of 60.135 nm, and the results showed that its average measured thickness was 60.115 nm with a repeatability of 0.813 nm. In addition, repeated measurements were performed on a SiC wafer with a nominal thickness of 350 μm, which gave an average measured thickness of 348.9 μm and a repeatability of 0.8 μm.ConclusionsTo address the issue that existing single thickness measurement devices struggle to balance wide-range and high-precision thickness detection, this study developed a dual-probe composite thickness measurement system. The system overcomes the application limitations of single measurement methods and exhibits cross-scale detection capability for multi-scale transparent samples ranging from nanometers to millimeters. The proposed dual-probe composite thickness measurement system can be applied to the thickness detection of transparent materials such as semiconductor wafer surface films, SiC wafer substrates, and quartz glass, demonstrating significant practical application value.