We present an analysis of the quality of white light interferometric measurements using an optical profiler with increased scan speeds up to 100 microns per second. A centroid approach was chosen for the white light fringe analysis because it is among the quickest to compute. The increase in speed requires a decrease in the spectral bandwidth of the illumination source. Only certain sampling rates (scanner speeds) yield suitable results for finding the position of the white light fringe envelope. Sampling rate, spectral bandwidth, noise, vibration and camera integration time all influence the quality of the measurements. Although precisely calibrating the scanner is one approach for achieving accurate measurements, our preferred method is determining the scanner speed during the measurement and then utilizing this information in the algorithm. Besides assuring highly accurate measurements this method avoids the delicacy and fine tuning that accompanies the calibration of the scanner. Our optical profiler system allows variable scan rates from 4.8 microns per second all the way up to 100 microns per second, which yields very precise measurements when a slower scan rate is used, extremely fast measurements with still high repeatability or any combination of speed and accuracy depending on the scan rate. We find that this combination of precision and speed make this system quite well suited for industrial measurement of a wide range of sample heights from hundreds of nanometers up to eight millimeters.

Date Published: 30 May 2003
PDF: 11 pages
Proc. SPIE 5144, Optical Measurement Systems for Industrial Inspection III, (30 May 2003); doi: 10.1117/12.501035

Published in SPIE Proceedings Vol. 5144:
Optical Measurement Systems for Industrial Inspection III
Wolfgang Osten; Malgorzata Kujawinska; Katherine Creath, Editor(s)