Improvement in high-k (HfO2/SiO2) reliability by incorporation of fluorine

In this letter, we demonstrate that negative bias temperature instability of high-kappa (HfO2/SiO2) gate dielectric stacks can be greatly improved by incorporating fluorine and engineering its concentration depth profile with respect to HfO2/SiO2 interface. It was found that fluorine is easily incorporated in HfO2/SiO2 at low temperatures (<= 400 degrees C) by F-2 anneal in the presence of UV radiation. Fluorine tends to segregate at the HfO2/SiO2 interface and, to a lesser extent, diffuses into the underlying SiO2/Si interface. The HfO2/SiO2 stacks with F addition show significantly reduced (< 50 %) positive charge trapping and interface states generation compared to control samples without F.