A novel way of detecting transient cavitation near a solid surface during megasonic cleaning using electrochemical impedance spectroscopy

Megasonic energy assisted wet cleaning is traditionally used for removal of particulate contaminants from wafer and mask surfaces in semiconductor industry. One of the major issues associated with megasonic cleaning is the damage caused to fragile features due to transient cavitation. Development of a method to monitor transient cavitation events in solutions irradiated with sound energy will allow chemical formulators to fine tune the cleaning chemistry and acoustic field parameters for maximum cleaning efficiency without any feature damage. In this work, a method based on electrochemical impedance spectroscopy (EIS) measurements on a microelectrode has been found to be effective in detection of transient cavity collapses in solutions subjected to ∼1 MHz sound field. Additionally, the technique also provides useful information about the diffusion boundary layer thicknesses in the presence and absence of megasonic field.