Study of Bubble Activity in a Megasonic Field Using an Electrochemical Technique

摘要

In the megasonic cleaning of wafers, size and motion of cavitating bubbles and fluid flow due to acoustic streaming play a very important role. In this paper, chronoamperometric technique has been used to seek information on acoustic streaming and bubble activity in a 1 MHz sound field. Specifically, current transients during reduction of potassium ferricyanide were recorded. Data collected at 1–6 MHz sampling rate using a 25 $mu{rm m}$ platinum electrode show current “peaks” indicative of the approach of oscillating bubbles to the electrode and current “valleys” due to blocking of the electrode by bubbles. Acoustic streaming velocity $({sim}{rm 1.5}~{rm cm}/{rm s})$ and bubble size (maximum radius of ${sim}{rm 1}~mu{rm m}$ for oscillating bubbles) have been estimated from local current transients caused by bubble activity near the electrode.