Profiles of a high-aspect-ratio grating determined by spectroscopic scatterometry and atomic-force microscopy

Area of Science:

• Metrology and Nanoscale Characterization
• Optical Physics and Scatterometry
• Surface Science and Engineering

Background:

• Accurate characterization of nanostructures is crucial for advanced manufacturing.
• Traditional methods for measuring high-aspect-ratio gratings can be time-consuming or limited in scope.
• Developing fast and reliable metrology techniques is essential for process control and quality assurance.

Purpose of the Study:

• To compare the performance of optical diffraction microscopy (ODM) with atomic-force microscopy (AFM) for metrology.
• To validate ODM as a fast scatterometry method for characterizing nanostructures.
• To assess the accuracy of ODM and AFM in measuring critical dimensions of a high-aspect-ratio grating.

Main Methods:

• Utilized cross-section scanning-electron microscope (SEM) images as a reference standard.
• Employed optical diffraction microscopy (ODM) and atomic-force microscopy (AFM) for grating profile analysis.
• Investigated a high-aspect-ratio grating with a 1000 nm period at various tilt angles to ensure comprehensive AFM tracking.

Main Results:

• Both ODM and AFM provided consistent measurements for grating profile parameters.
• Measured quantities included sidewall angle (gamma ≈ 90°), groove height (h ≈ 2000 nm), and degree of filling (f ≈ 40%).
• Achieved high accuracy with standard uncertainties: u(gamma) ≤ 0.8°, u(h) ≤ 15 nm, and u(f) ≤ 1%.

Conclusions:

• Optical diffraction microscopy is a viable and fast alternative for scatterometry-based metrology.
• ODM and AFM yield consistent results for critical dimensions of nanostructures, despite differing material property responses.
• The study validates ODM for precise characterization of complex grating profiles.