White-light colorimetric interferometry for measurement of thickness and topography on semiconductor structures

Reflectometry and white-light interferometry (WLI) have attracted significant attention due to their high-resolution capability in measuring thickness and topography. In this report, we demonstrated the colorimetric WLI with reflectometry by using a color camera and multi-bandpass filter to obtain not only topography but also thickness of the thin film which is less than 100 nm. The 3D metrological images of thin-film silicon dioxide (SiO₂)/silicon (Si) mesa structures were measured with optical microscopic lateral resolution less than 1 μm. The measured SiO₂ thickness ranges from 20 to 150 nm on top of Si mesa structures with heights of a few nanometers. The thickness of the thin film was determined by colorimetric reflectometry and fixed during the fitting process of colorimetric WLI to extract the bottom and top surface topographies. Using this method, it was possible to measure vertically the over-etched depth of the silicon substrate on the order of a few nanometers. The measured optical 3D images agree significantly with the measurement from the transmission electron microscopy (TEM) and the atomic force microscopy (AFM). Thus, the results have demonstrated that the proposed colorimetric methods can measure the topography and thickness of films as thin as 20 nm in a single measurement.