Single Hf atoms inside the ultrathin SiO2 interlayer between a HfO2 dielectric film and the Si substrate: How do they modify the interface?

We show that individual Hf atoms may get incorporated into the SiO2 interlayer which is formed between the HfO2 dielectric film and the Si substrate during rapid thermal annealing. We report atomically-resolved Z-contrast images of a Si/SiO2/HfO2 structure together with first-principles calculations which demonstrate that single Hf atoms are in fact present in the interlayer. The location of individual Hf atoms within the interlayer oxide is closely related to the structure of the amorphous oxide near the Si/SiO2 interface. The Hf defects may affect channel mobility and leakage currents in the HfO2/Si electronic devices.