In accordance with one embodiment there is provided a method of improving the performance of a substrate cleaner of the type having a megasonic probe with a probe shaft extending generally parallel to a surface of a rotating substrate, and at least one dispenser for applying a cleaning liquid onto the surface of the substrate, wherein the megasonic probe agitates the liquid on the surface. The method comprising dissolving gas in the liquid before the liquid reaches the dispenser. In accordance with another embodiment, an apparatus for cleaning substrates comprises a rotary fixture which is adapted to support a substrate and rotate the substrate about a first axis, a probe having a probe shaft extending generally parallel to a surface of the substrate, and a megasonic transducer in acoustically coupled relation to the probe. The apparatus further comprises at least one dispenser that applies a cleaning liquid drawn from a cleaning liquid supply onto a surface of the substrate, and a gasifier operatively associated with the cleaning liquid supply. The gasifier causes gas to dissolve in the cleaning liquid.