Phase Measuring Deflectometry for Wafer Thin-Film Stress Mapping

Area of Science:

• Materials Science
• Optical Engineering
• Semiconductor Manufacturing

Background:

• Wafer-level thin-film stress measurement is critical for semiconductor fabrication.
• Current methods like interferometry and laser scanning have practical limitations (cost, data sparsity).
• A need exists for a high-precision, full-field, and cost-effective stress measurement solution.

Purpose of the Study:

• To develop and validate a phase-measuring deflectometry (PMD) system for full-field wafer stress mapping.
• To address key challenges in adapting PMD for this application.
• To provide an accurate and affordable alternative for production-scale thin-film stress inspection.

Main Methods:

• Developed a PMD system incorporating refined screen positioning via inverse bundle adjustment.
• Utilized a backward-propagation ray-tracing framework with a reprojection constraint strategy to resolve slope-height ambiguity.
• Integrated regional wavefront reconstruction with Hermite interpolation to mitigate edge artifacts.

Main Results:

• Achieved a peak-to-valley error of 0.48 µm for reconstructed topography on a spherical mirror.
• Demonstrated curvature mapping on a 12-inch patterned wafer.
• Validated stress measurements on an 8-inch bare wafer with <5% deviation from standard instrumentation.

Conclusions:

• The proposed PMD system provides an accurate and cost-effective solution for wafer stress mapping.
• The developed methods effectively address PMD implementation challenges.
• The system is suitable for production-scale thin-film stress inspection in semiconductor fabrication.