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

Abstract

In various manufacturing processes like semiconductor fabrication, highly accurate and efficient surface profilometry 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 inspection (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 detection 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 measurement bias kept below 0.239 µm with a standard deviation of 0.126 µm. When the Galvanometer reaches its design specifications, the measuring speed of the system can exceed 8000 lines/s.