We report the first study of the effect of in situultrasound treatment (UST) during ion implantation on amorphizationof crystalline silicon. Rutherford backscattering spectroscopy,ion channelling and cross-section transmission electronmicroscopy measurements show that amorphization of Si during Arion implantation is enhanced by UST,especially at ultrasound frequencies around 2 MHz. Theinfluence on the amorphization process depends mainly on ionflux, ion masses and ultrasound frequency. For implantationconditions without amorphization, for example in the case of implantationwith light atoms such as boron, defect concentrations arelower for wafers implanted with UST comparedto reference wafers implanted without UST. Theinfluence of ultrasound is discussed in terms of itsinteraction with point defects and ultrasound-stimulatedenhanced diffusion of interstitials.