We demonstrate that interfacial SiO₂, usually formed during high-k oxide growth on silicon using ozone (O₃), is suppressed during Al₂O₃ atomic layer deposition (ALD) by decreasing the O₃ flow rate. First-principles calculations indicate that oxygen introduced by the first low-dose O₃ exposure is inserted into the surface nucleation layer rather than the Si lattice. Subsequent Al₂O₃ deposition further passivates the surface against substrate oxidation. Aluminum methoxy [–Al₂OCH₃)₂] and surface Al–O–Al linkages formed after O₃ pulses are suggested as the reaction sites for trimethylaluminum during ALD of Al₂O₃.