Linearizing the vertical scale of an interferometric microscope and its effect on step-height measurement

Area of Science:

• Metrology
• Optical Engineering
• Surface Science

Background:

• Accurate vertical scale calibration is crucial for traceable surface topography measurements.
• Existing methods for interferometric microscopes have limitations in full vertical scan motion calibration.

Purpose of the Study:

• To develop a calibration procedure for the entire vertical scan motion of coherent scanning interferometric microscopes.
• To establish traceability of surface topography measurements to the SI unit of length, the meter.

Main Methods:

• Utilized a flat mirror artifact, spectral filter, and aperture.
• Varied interferogram center within the scan range by adjusting microscope head height.
• Determined local interferogram frequency by fitting to sinusoidal functions.

Main Results:

• Developed a method to yield the response curve for the entire vertical scan motion.
• Quantified nonlinearity in vertical scan motion, enabling estimation of measurement uncertainty.
• Demonstrated that correcting for nonlinearity improves step height measurement reproducibility by a factor of three.

Conclusions:

• The described calibration procedure is effective for coherent scanning interferometric microscopes.
• The method enhances the accuracy and reliability of surface topography measurements.
• Correction for scan motion nonlinearity significantly improves measurement reproducibility.