Abstract
This paper presents an advanced technique to determine all independent elastic constants C_<ij> of thin films. Many polycrystalline films exhibit elastic anisotropy between the film-growth direction and in-plane direction, and macroscopically possess five independent elastic constants; they are denoted by C_<11>, C_<33>, C_<13>, C_<44>, and C_<66> when the x_3 axis is chosen along the film-growth direction. All of C_<ij> of thin film affect the mechanical resonance frequencies of a film/substrate specimen. Measuring them permits us to determine the film C_<ij> with known density, dimensions, and the elastic constants of the substrate. It is necessary to measure the resonance frequencies with a high accuracy, because the contributions of the film C_<ij> to the resonance frequencies are normally small. We made this possible using the piezoelectric tripod, which consists of two piezoelectric pinducers and a supporting pin. The specimen is held on the tripod and only the specimen weight makes the acoustic coupling. This weak but stable coupling measures the resonance frequencies with a high accuracy. We applied our technique to copper thin films and found anisotropy between C_<11> and C_<33>.
