Radiation Effects of High-k Oxides and HfO₂ Based MOS Device Induced by Heavy Ions

High-k dielectric materials (high-k materials) have become the inevitable choice for gate dielectric layers when device feature sizes shrink to 45 nm and below. Common high-k materials primarily include metal oxides such as HfO₂, ZrO₂, TiO₂ and Al₂O₃. Research on the heavy ion irradiation effects of these materials is of significant importance for evaluating the long-term reliability of novel nanodevices in space radiation environments. Low-energy heavy ions primarily deposit energy in materials through nuclear energy loss, while swift heavy ions mainly cause electronic energy loss. This paper systematically summarizes and discusses the differences in irradiation effects caused by this fundamental distinction between low-energy and swift heavy ions in these materials. Furthermore, practical applications may involve different crystalline states, grain sizes, and crystal phases of these materials. Therefore, this study also comparatively summarizes the responses of high-k materials with varying crystalline states (single crystal, nanocrystalline, amorphous) and even different crystal phases to heavy ion irradiation. Specifically, swift heavy ions can induce phase transformation from monoclinic to tetragonal in bulk ZrO₂ at relatively low ion fluences, which is usually two to three orders of magnitude lower than required by low-energy heavy ions. For nanocrystalline ZrO₂, heavy ions irradiation could cause amorphization. By systematic experimental studies on latent tracks in rutile TiO₂ induced by swift heavy ions, we first observed the fine structure of latent tracks and their morphological evolution along ion penetration depth (or sample thickness). A new mechanism for swift heavy ion track formation is proposed: the combined effect of material melt flow caused by thermal spikes and strong recrystallization capability is the key factor governing such track morphology evolution. This finding challenges the previous theoretical explanation for the absence of fission tracks in bulk UO₂. The irradiation experiments performed at the Heavy Ion Research Facility in Lanzhou support our predictions, demonstrating the good universality of the new mechanism. Finally, taking HfO₂-based MOS devices as an example, we explore the intrinsic relationship between macroscopic electrical characteristic degradation caused by low-energy/swift heavy ions and microscopic material structural damage.