Scanless areal surface topography measurement based on reabsorption-coupled two-color fluorescence signals

Abstract

This paper presents a single-shot surface topography measurement method based on two-color laser-induced fluorescence, targeting in-situ and on-machine metrology under nonuniform illumination conditions arising from the excitation light distribution and contamination in the optical path. The proposed approach exploits the intensity ratio of two fluorescence emissions with spectral reabsorption, enabling effective cancellation of spatial variations in excitation light intensity. The measurement principle is theoretically formulated, demonstrating that the fluorescence intensity ratio maintains a unique dependence on fluorescent film thickness while remaining independent of incident light intensity. A scanless full-field measurement system using a color CMOS camera is developed, together with an in-situ calibration scheme employing a reference step height. Experimental validations using a nominally flat silicon wafer confirm a significant improvement in measurement uniformity, reducing apparent height variations from over 10 μm to within ±0.5 μm. Further demonstrations on an aluminum Japanese one-yen coin show that the proposed method robustly suppresses illumination- and scattering-induced artifacts while accurately capturing surface features. These results establish two-color fluorescence as a robust and practical approach for areal surface metrology, offering strong potential for in-process measurement and advanced manufacturing applications.