Optical method for simultaneous thickness measurements of two layers with a significant thickness difference

Area of Science:

• Optics and Photonics
• Materials Science
• Metrology

Background:

• Accurate thickness measurement of multi-layered materials is crucial in various scientific and industrial applications.
• Existing methods often face limitations in range, precision, or simultaneous measurement capabilities.

Purpose of the Study:

• To propose and validate a novel optical method for simultaneous, broad-range thickness measurements of two distinct layers.
• To enhance measurement accuracy and reduce errors compared to conventional techniques.

Main Methods:

• Integration of a spectroscopic reflectometer and a spectral-domain interferometer into a single optical system.
• Optimization of optical configuration including spectral band, beam paths, and illumination.
• Development of a model-based analysis algorithm for high-precision substrate thickness measurement, minimizing thin-film interference.

Main Results:

• Successful simultaneous thickness measurement of a 100 nm and 150 nm silicon dioxide thin film and a 450 µm silicon substrate.
• Demonstrated significant reduction in measurement error (< 8 nm) compared to Fourier-transform analysis.
• Achieved low measurement uncertainties: 0.12 nm (thin film), 0.094 µm (substrate in thin-film specimen), and 0.076 µm (single substrate).

Conclusions:

• The proposed integrated optical system enables accurate and simultaneous thickness measurements across a wide range of scales.
• The developed model-based algorithm significantly improves precision for thin-film and substrate characterization.
• The method's performance was validated against standard equipment, confirming its reliability for multi-scale thickness metrology.