Small footprint high-speed optical 3D profiler

摘要

In surface characterization at the micro- and nano level, the most used non-contact techniques are Imaging Confocal Microscopy (ICM), Coherence Scanning Interferometry (CSI) and Focus Variation (FV). Each measuring technology has its benefits and disadvantages. Whereas CSI is the best technique to measure optically polished samples, it does not perform well in rough surfaces due to its inability to recover signal from high slope regions. FV performs, however, very well with rough surfaces but lacks repeatability on smooth samples, and its repeatability depends on the surface roughness. This has improved recently by the introduction of Active illumination Focus Variation (AiFV). Confocal is besides a versatile technique than can retrieve data from surfaces ranging from smooth to rough with a repeatability down to 1 nm, although needs to do in-plane scanning. However, all the mentioned techniques rely on scanning the surface through the optical axis. Measurement speed depends not only on the acquisition framerate and image processing time but also on the mechanical dynamics. In this paper we propose a compact optical 3D profiler that can measure at higher speed thanks to an increase of camera framerate, lower mass and a novel confocal technique that does not need in-plane scanning. This has been achieved by reducing the overall optical path length, which challenges narrower focal lengths and thus higher optical aberrations. The system scans only the objective lens instead of the whole sensor head with a high-speed, 4 mm travel range miniature translation stage. As the sensor scans can be made continuously oscillating the objective lens, real-time 3D topographies can be obtained.