Discontinuous surface measurement by wavelength-tuning interferometry with the excess fraction method correcting...

Area of Science:

• Optical Metrology
• Surface Profilometry
• Interferometry

Background:

• Wavelength-tuning interferometry measures surface shapes with steps using synthetic wavelengths.
• Measurement resolution degrades for larger steps due to increased synthetic wavelength.
• Existing methods struggle with accuracy for significant step heights.

Purpose of the Study:

• To improve the accuracy of two-dimensional surface shape measurements for large step heights.
• To address the resolution decrease issue in wavelength-tuning interferometry.
• To develop a robust method for determining absolute interference order in complex surfaces.

Main Methods:

• Application of the excess fraction method combined with piezoelectric transducer phase shifting.
• Utilizing two-dimensional surface shape measurements.
• Correction of systematic errors from source frequency nonlinearity via fringe correlation analysis.

Main Results:

• Accurate determination of absolute interference order was achieved.
• Successful profiling of a 1mm surface step height.
• Achieved measurement accuracy of 12nm for the 1mm step.

Conclusions:

• The developed method significantly enhances accuracy for measuring large surface steps.
• Absolute interference order determination is key to high-precision profilometry.
• This technique offers a viable solution for precise surface metrology in demanding applications.