Noncontact characterization of crystal surface and thin films by the phase velocity scanning of laser interference fringes

We present the first application of a novel noncontact velocity measurement method of surface acoustic waves (SAW) to evaluation of thin films. This method uses laser interference fringes scanned at the phase velocity of SAW. The scanning interference fringes (SIF) are produced by intersecting two laser beams with a frequency difference. It was found that the Si
₃
N
₄
film prepared by low pressure CVD had similar elastic properties to that of a sintered body. The dispersive Sezawa waves on the flame hydrolysis deposited SiO
₂
films on Si (100) surface were detected. Comparing the measured Sezawa wave velocity with calculated velocity, the films were found to be much softer than bulk SiO
₂
(fused quartz)