HIGH-FREQUENCY ULTRASONIC CLEANING TANK UTILIZING OBLIQUE-INCIDENCE

Transmission characteristics of a double-structured tank, used for hig h-frequency (1 MHz range) ultrasonic cleaning of semiconductor wafers and substrates, were improved by utilizing oblique incidence of ultras onic waves. As the sound transmittivity through a plate in water varie s with the angle of incidence, the bottom of the Pyrex glass inner con tainer was slanted at the angle where strong transmission occurred. In the slant-bottom container, an intensive and uniform sound pressure d istribution was measured with a polyvinylidene fluoride (PVDF) hydroph one probe. In comparison with the conventional horizontal-bottom conta iner, it was shown that the distributions as well as amplitude of soun d pressure were remarkably improved by slanting the bottom of the inne r container at the proper angle.