Simultaneous film thickness and refractive index measurement using a constrained fitting method in a white light...

Area of Science:

• Optoelectronics and Semiconductor Manufacturing
• Optical Metrology
• Thin Film Characterization

Background:

• Accurate measurement of film thickness and refractive index is crucial for optoelectronic and semiconductor industries.
• Existing methods often require known dispersion models and initial parameter values, limiting their applicability.
• Compatibility with surface topography measurement is often lacking in current techniques.

Purpose of the Study:

• To develop a novel method for simultaneous measurement of film thickness and refractive index.
• To overcome the limitations of existing measurement techniques, such as the need for a priori information.
• To integrate film property measurement with surface topography reconstruction.

Main Methods:

• A constrained nonlinear fitting method applied to white-light spectral interferometry.
• Utilizing spectral phase-shifting to extract nonlinear phase information.
• Employing vertical scanning interferometry (VSI) for constraint acquisition and surface topography reconstruction.

Main Results:

• Simultaneous measurement of thickness and refractive index without requiring a dispersion model or initial values.
• Achieved high measurement repeatability for refractive index (10^-3).
• Demonstrated compatibility with VSI for reconstructing both top and bottom surface topography.
• Validated measurements on SiO2 and polymer films against theoretical values and commercial instruments.

Conclusions:

• The proposed constrained nonlinear fitting method offers a robust and versatile approach for thin film characterization.
• This technique eliminates the need for a priori knowledge, making it suitable for a wider range of materials.
• The integrated system provides comprehensive film analysis, including thickness, refractive index, and surface topography.