Multiwavelength phase unwrapping and aberration correction using depth filtered digital holography

Area of Science:

• Metrology
• Optical Engineering
• Holography

Background:

• Standard spectral domain optical coherence tomography (OCT) offers limited axial resolution with intensity-based processing.
• Phase-based OCT achieves subwavelength accuracy but restricts resolvable step heights to half the system's wavelength.
• A significant metrology gap exists between intensity- and phase-based OCT methods for step height measurements.

Purpose of the Study:

• To address the metrology gap in optical coherence tomography (OCT).
• To develop a new data processing approach for OCT systems.
• To enable accurate step height measurements beyond the limitations of existing methods.

Main Methods:

• Implementation of depth filtered digital holography (DFDH) for OCT data processing.
• Integration of multiwavelength phase unwrapping techniques.
• Correction of measurement data for optical aberrations.

Main Results:

• Successful proof-of-concept measurements were performed on a structured semiconductor sample.
• The combined DFDH and multiwavelength phase unwrapping approach effectively bridges the metrology gap.
• Aberration correction enhanced the accuracy of the measurements.

Conclusions:

• The presented method successfully combines DFDH with multiwavelength phase unwrapping to overcome OCT metrology limitations.
• This approach offers a viable solution for precise step height measurements in metrology.
• Further applications in semiconductor metrology and other fields are anticipated.