Wafer-scale waveguide sidewall roughness scattering loss characterization by image processing

Area of Science:

• Materials Science
• Optoelectronics
• Nanotechnology

Background:

• Photonic integrated circuits (PICs) are crucial for advanced optoelectronic devices, but optical losses from waveguide imperfections hinder performance.
• Sidewall roughness, caused by fabrication imperfections, is a primary source of scattering losses in thin-film photonic structures.
• Current roughness measurement techniques like Atomic Force Microscopy (AFM) are costly and not scalable for wafer-level characterization.

Purpose of the Study:

• To evaluate sidewall roughness profiles using 2D scanning electron microscope (SEM) imaging for scalable optical loss characterization in PICs.
• To correlate scattering loss estimations from 2D SEM image analysis with theoretical models.
• To establish a new benchmark for low optical loss in visible-wavelength waveguides.

Main Methods:

• Characterization of optical loss in nitride and oxide waveguides on silicon wafers using 2D high-resolution SEM imaging.
• Application of the theoretical Payne model to estimate scattering loss from 2D image-based sidewall profiles.
• Image processing techniques for edge detection and autocorrelation function estimation to quantify roughness.

Main Results:

• Achieved a record low optical loss of 0.075 dB/cm for the fundamental transverse electric (TE0) mode at 633 nm across 24 waveguide devices.
• Demonstrated 100% success in edge detection for all SEM images, enabling accurate autocorrelation and loss estimation.
• Validated the correlation between 2D SEM image-based loss estimation and experimental measurements.

Conclusions:

• 2D SEM imaging provides a scalable and effective method for characterizing waveguide sidewall roughness and estimating optical loss in PICs.
• The developed approach offers valuable insights for optimizing fabrication processes to minimize optical losses.
• This work paves the way for efficient wafer-scale loss characterization in photonic device manufacturing.