Optical precision profilometer using the differential method

Area of Science:

• Optical Engineering
• Metrology
• Surface Science

Background:

• Vertical vibrations significantly impact the accuracy of optical precision profilometry.
• Existing methods often struggle to compensate for environmental disturbances during high-precision measurements.

Purpose of the Study:

• To propose a novel optical precision profilometer design.
• To achieve height measurements that are nearly independent of vertical vibrations.
• To demonstrate the instrument's capability for precise surface analysis.

Main Methods:

• Development of an optical profilometer incorporating simultaneous measurement of the target and its surroundings.
• Implementation of digital subtraction to eliminate the influence of ambient vibrations.
• Characterization of the profilometer's noise level under controlled vibration conditions (0.4 gal).

Main Results:

• The proposed profilometer demonstrates near-independence from vertical vibrations.
• A low noise level of 0.05 nm root mean square was achieved under steady vibrations.
• Successful measurements were performed on an optical flat and a silicon (Si) wafer.

Conclusions:

• The novel optical profilometer offers a robust solution for high-precision surface metrology.
• The digital subtraction technique effectively mitigates vibration-induced errors.
• The instrument is suitable for characterizing delicate optical surfaces and semiconductor wafers.