Generation and detection of 400-MHz-band surface acoustic waves using the phase velocity scanning method

We succeeded in generating and detecting high-frequency surface acoustic waves (SAWs) UP to 400 MHz by improving an apparatus for the scanning interference fringes (SIF) approach of the phase velocity scanning method using an optical knife-edge technique with a single lens. Using the new SIF apparatus, we confirmed that we are able to measure the SAW velocity anisotropy of a single-crystal Si(001) wafer within 0.1% relative error. We also measured the velocity anisotropy of Sezawa waves on a Si(001) wafer with a 1430-nm-thick Cu film and estimated Young's modulus and thickness of the Cu film by an inverse analysis. The estimated Young's modulus was close to that of bulk Cu (129.8 GPa). On a single-crystal Si(001) wafer with thinner Cu films (270-700 nm), we measured the SAW velocity along the [110] direction of the Si substrate by the time-off-light method. The measured velocities decreased with increasing film thickness. The measured velocity for the thicker sample approximated the group velocity calculated from the estimated value for 1430-nm-thick Cu film by the inverse analysis.