SAW VELOCITY-MEASUREMENT OF CRYSTALS AND THIN-FILMS BY THE PHASE-VELOCITY SCANNING OF INTERFERENCE-FRINGES

We present principle and application of a novel noncontact velocity me asurement of surface acoustic waves (SAW) on crystals and thin films u sing laser interference fringes scanned at the phase velocity of SAW. The scanning interference fringes (SIF) are produced by intersecting t wo laser beams with a frequency difference. The SAW velocity within th e laser beam spot is measured as the ratio of observed SAW frequency a nd predetermined wave number of the SIF. The frequency measurement can be quite precise because of a large number of generated SAW carriers and amplitude enhancement effect. The SAW velocity measurement is free from the water loading effect accompanying the leaky SAW measurements . This principle was successfully applied to evaluate Si3N4 and SiO2 f ilms deposited on Si (001) surface.