Line spectroscopic reflectometry for rapid and large-area thickness measurement.

Thickness measurements in the range of 0.1-1 mm over large optically transparent layers are essential in various manufacturing applications. However, existing non-contact measurement methods, which typically measure a single point or a few points at a time, fall short in their suitability for inline area measurement. Here, we introduce line spectroscopic reflectometry (LSR), an approach that extends the point measurement of traditional SR to line measurement, enabling rapid thickness measurement over large areas. By combining line beam illumination and line spectroscopy, LSR can measure 2048 points simultaneously, thereby boosting the measurement speed by two thousand times. We detail the measurement principle and the optical design in the near-infrared regime, and demonstrate thickness measurements of single-layered and double-layered samples over a measurement line length of up to 68 mm. Furthermore, we showcase the inline area measurement capability of LSR through one-dimensional sample scanning, with measurement rates limited only by camera readout rates.