The Influence of Standing Waves on Cleaning with a Megasonic Nozzle

A non uniform sound field distribution can be a problem in a megasonic cleaning system, since a higher sound intensity can cause damage, while areas exposed to a lower intensity will be insufficiently cleaned. These non uniformities can be the result of sound field reflection, leading to standing waves, and the interference related to the near field. In a single wafer tool with a transducer facing the wafer a small height difference will have a large impact on the cleaning efficiency if standing waves are present. Here we study the impact of the wafer transducer height in a cleaning system using a megasonic nozzle above a rotating wafer.