Fast surface measurement using wavelength scanning interferometry with compensation of environmental noise

We introduce a new optical interferometry system for fast areal surface measurement of microscale
and nanoscale surfaces that are immune to environmental noise. Wavelength scanning interferometry
together with an acousto-optic tunable filtering technique is used to measure surfaces with large
step heights. An active servo control system serves as a phase-compensating mechanism to eliminate
the effects of environmental noise. The system can be used for online or in-process measurement on
a shop floor. Measurement results from two step height standard samples and a structured surface
of a semiconductor daughterboard are presented. In comparison with standard step height specimens,
the system achieved nanometer measurement accuracy. The measurement results of the semiconductor daughterboard, under mechanical disturbance, showed that the system can withstand environmental
noise.