Anisotropic Elastic Constants of Copper Thin Films: RUS/Laser and Picosecond-Laser Ultrasound

摘要

We propose a combination of the RUS/laser method and picosecond-laser ultrasound method for measuring anisotropic elastic constants of thin films. The RUS/laser method determines the in-plane moduli, C11, C12, and C13, of thin films; and picosecond-laser ultrasound method determines the out-of-plane modulus, C33. Therefore, their combination enables us to evaluate elastic anisotropy of thin films. In this study, we measured the elastic constants of copper thin films. They showed elastic anisotropy between the in-plane and out-of-plane directions. This is attributed to columnar grain structure and noncohesive bonds aligned at the columnar grain. This view is supported by micromechanics calculation.