[en] To gain more insight into fundamental aspects of the etching behavior of Hf-based high-k materials in plasma etch reactors, HfO₂ films were etched in a multiple-beam setup consisting of a low energy Ar⁺ ion beam and a XeF₂ radical beam. The etch rate and etch products were monitored by real-time ellipsometry and mass spectrometry, respectively. Although etching of HfO₂ in XeF₂/Ar⁺ chemistry is mainly a physical effect, an unambiguous proof of the ion-radical synergistic effect for the etching of HfO₂ is presented. The etch yield for 400 eV Ar⁺ ions at a substrate temperature of 300 deg. C was 0.3 atoms/ion for Ar⁺ sputtering and increased to 2 atoms/ion when XeF₂ was also supplied. The etch yield proved to follow the common square root of ion energy dependence both for pure sputtering and radical enhanced etching, with a threshold energy at room temperature of 69±17 eV for Ar⁺ ions and 54±14 eV for Ar⁺ ions with XeF₂