Full-field chromatic confocal microscopy for surface profilometry with sub-micrometer accuracy

In various manufacturing processes like semiconductor fabrication, highly accurate and efficient surface pro-filometry on microstructures is critically demanded. This article presents a quasi-area-scan chromatic confocal microscopy for full-field surface profilometry with high precision and accuracy for in-line automated optical in-spection (AOI). Unlike conventional confocal microscopy, the proposed opto-mechatronic confocal measuring system does not require mechanical scanning of the test object. Moreover, it is bi-telecentric to satisfy full-field measurement without optical aberration. Optical line-scan illumination and imaging modules are integrated with an electrically driven galvanometer to perform line scanning. Most importantly, the proposed system is superior to traditional chromatic confocal scanning in that positioning uncertainties can be avoided, and high-speed de-tection with a large field of view and high accuracy can be achieved. Pre-calibrated step-height gauges were experimentally measured to verify the precision and accuracy of the developed probe. Results showed measure-ment bias kept below 0.239 mu m with a standard deviation of 0.126 mu m. When the Galvanometer reaches its design specifications, the measuring speed of the system can exceed 8000 lines/s.

Automated summary

This article introduces a quasi-area-scan chromatic confocal microscopy for full-field surface profilometry which achieves high precision, accuracy, and high-speed measurement without mechanical scanning. By combining electrically driven galvanometer with optical line-scan illumination and imaging modules, the proposed system can measure with a large field of view and high accuracy. Experimental results show measurement bias below 0.239 μm and a standard deviation of 0.126 μm, with a measuring speed exceeding 8000 lines/s when the Galvanometer reaches its design specifications.