A novel approach for film thickness measurements based on fs-laser generated ramp structures

Abstract

Accurate determination of thin film thickness is essential in coating research and process development. Established methods such as focused ion beam (FIB) cross-sectioning provide high accuracy but are time- and resource-intensive, while more accessible techniques like the calotte grinding method often suffer from limited reproducibility and throughput. In this work, a method for rapid and laterally resolved film thickness measurement is presented, based on femtosecond laser-induced ramp structures. Shallow ramps are ablated into the coating, exposing the film–substrate interface over a defined lateral distance. The local film thickness is determined from the step height perpendicular to the interface using 3D confocal laser scanning microscopy. The use of ultrashort laser pulses enables material removal with limited thermal impact, resulting in well-defined interfaces between coating and substrate. Due to the small feature size and high processing speed, multiple ramp structures can be generated across the sample surface, enabling statistical analysis and spatial mapping of thickness variations. To improve efficiency and reproducibility, an automated data evaluation workflow was developed. Image analysis is used to identify the film–substrate interface within the confocal datasets, allowing automated extraction of thickness values from 3D surface reconstructions and facilitating batch processing. The applicability of the method is demonstrated for both planar and curved substrates, indicating its suitability for more complex geometries. Overall, the approach provides a combination of speed, lateral resolution, and automation, representing a practical alternative to conventional thickness measurement techniques.