The interface between (100)Si and HfO2 grown by atomic layer deposition is strongly influenced by the choice of the oxygen precursor. In particular, the use of oxidants with different oxidizing power such as H2O and O3 produces interfaces differing both in terms of density of electronic traps and defect microstructure. While H2O produces a Si∕SiO2-like interface, characterized by the presence of the Pb0 center, the high reactivity of O3 induces a modification in the defect wavefunction, as revealed by electrically detected magnetic resonance. Post growth annealing in N2 at T⩾600°C allows the recovery of a Si∕SiO2-like interface.