High-precision vibration measurement in multilayer structures using low-coherence two-wave mixing interferometry

Vibration measurements are critical for non-destructive evaluation of mechanical properties and defect detection in multilayer semiconductor devices. Current optical vibrometers struggle with weak signals and echo overlapping in thin-layer structures, limiting measurement accuracy (yielding errors exceeding 3% for a 150 µm layer). This study presents an optical method for high-precision vibration measurement and acoustic velocity characterization in multilayer structures based on low-coherence two-wave mixing interferometry. The system synergistically integrates the spatial selectivity of low-coherence interferometry with the adaptive noise suppression and signal amplification capabilities of two-wave mixing in a photorefractive crystal. Through comprehensive theoretical modeling and numerical simulations, the method demonstrates accurate extraction of surface vibrations and subsequent computation of layer-specific acoustic velocities. Simulation results yielded sound velocity measurements with errors of 1.6%, 3.5%, and 9.4% for successive layers, confirming the method's potential for high accuracy. This non-contact, high-resolution approach provides a robust simulation-backed solution for mechanical property evaluation and defect detection in TSVs and other complex multilayer systems, with significant potential for enhancing reliability assurance in 3D integrated circuits.