Fast Recovery of Elasticity of Cu Thin Films at Room Temperature Studied by Resonant-Ultrasound Spectroscopy

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In this study, we investigate the behavior of the room-temperature recovery of elastic constants of Cu thin films by monitoring the mechanical resonance frequencies of the film/substrate specimen throughout the deposition process using resonant-ultrasound spectroscopy. The thin films were deposited on a (001) Si substrate located on a needle tripod transducer set in a vacuum chamber. The free-vibration resonance frequencies of the Cu/Si specimen were measured before, during, and after magnetron-sputtering deposition, yielding the evolution of the elastic constants of the Cu thin films. Recovery of the elastic constants of Cu thin films is completed in a much shorter time than that for bulk Cu; after the deposition, the elastic constants $C_{11}$ and $C_{66}$ increased by 1.0–2.4% and 2.2–5.3%, respectively, within 20 min. The recovery behaviors are well explained by the dislocation-damping theory. The recovery rate is larger than that of bulk Cu by a factor of 100, indicating much lower activation energies for point defect migration and dislocation sliding in the film.
2007-07-30