Abstract: An apparatus for cleaning a substrate has a process bowl that has a first circumferential zone and a second circumferential zone. That apparatus also has a support located in the process bowl that supports a substrate, and a megasonic transmitter located in the first circumferential zone. The apparatus also comprises a cleaning liquid dispenser that includes an outlet. The dispenser is mounted on the process bowl and is configured to apply liquid to a surface of the substrate through the outlet. The dispenser is positioned in the second circumferential zone. The first circumferential zone and the second circumferential zone are selected to minimize non-uniformity of the propagation of megasonic energy caused by the dispensing of cleaning liquid onto the substrate.