Decoupled measurement of silicon-based film and substrate thickness by hybrid reflectance spectroscopy

Semiconductor manufacturing requires accurate measurement of film thickness, which significantly impacts the performance and reliability of device based on multilayer film structures. In this study, to simultaneously analyze multilayer films with significant thickness differences, a hybrid reflectance spectroscopy was proposed by combining differential reflectance spectroscopy (DRS) for thin films and reflectance spectroscopy (RS) for thick substrate. By integrating visible and near-infrared light, a comprehensive system is developed with microscopic imaging, DRS, and RS techniques. Furthermore, a practical algorithm was proposed to obtain the thickness differences of multilayer structure like Silicon-on-Insulator (SOI), with thickness of layers ranging from nanometers to micrometers and substrate thickness at hundreds of micrometers. The ability of wide range measurement and repeatability was verified by experiment conducted on SiO₂/Si samples, with thickness compared to nominal thickness by commercial ellipsometer across a range of 12 nm to 500 nm. The decouple of multilayer thickness was validated by experiment conducted on SOI, comparing to nominal thickness by scanning electron microscope (SEM).