the cleaning results of a traveling and a standing wave, the damping
material was exchanged with a reflector plate, while the wafer
angle of incidence was maintained at 30. The distance to the
reflector plate was adjusted so that the power reflected back into
the transducer amplifier was smaller than 1 W/cm2
, which is comparable
to the case when damping material is present in the cleaning
tank. For the standing wave case, the average PRE was reduced
to 6.7%. As a result, cleaning is optimized when the traveling wave
component is maximized.