No abstract

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

The authors report on the chemical bonding structure of the HfO2∕Si (001) stack after the SiO2 interfacial layer (IL) is partially removed by a reactive titanium metal overlayer. Using synchrotron photoelectron spectroscopy, they found that ultrathin SiO2-like IL ∼6.5Å thick, which is significantly less than the initial SiO2 IL thickness of ∼15Å, exists at the HfO2∕Si interface with an overlying Ti electrode. The dissociated Si from SiO2 IL is believed to go onto Si substrate where it regrows epitaxially. The interfacial trap density of the Ti-electrode sample was extracted to be ∼1.6×1011eV−1cm−2 near the midgap of Si, which was comparable to that of the control sample with W electrode.

We report the chemical bonding structure and valence band alignment at the HfO2∕Ge(001) interface by systematically probing various core level spectra as well as valence band spectra using soft x rays at the Stanford Synchrotron Radiation Laboratory. We investigated the chemical bonding changes as a function of depth through the dielectric stack by taking a series of synchrotron photoemission spectra as we etched through the HfO2 film using a dilute hydrogen fluoride solution. We found that a very nonstoichiometric GeOx layer exists at the HfO2∕Ge interface. The valence band spectra near the Fermi level in each different film structure were carefully analyzed, and as a result, the valence band offset between Ge and GeOx was determined to be ΔEv (Ge–GeOx)=2.2±0.15eV, and that between Ge and HfO2, ΔEv (Ge–HfO2)=2.7±0.15eV.

In this letter, we demonstrate that formation of a Zr-silicate interfacial layer between ZrO2 and Si substrate can be controlled by the solid state reaction between Zr and an underlying SiO2/Si substrate through in situ vacuum anneals and subsequent UV oxidation. By investigating the chemical shifts of Si2p, Zr3d, and O1s features using x-ray photoelectron spectroscopy, the formation of a Zr-silicide phase after in situ vacuum anneals of the Zr/chemical SiO2/Si gate stack at 200 °C was confirmed. The Zr-silicide was oxidized to form a Zr-silicate phase in the subsequent UV-ozone oxidation treatment. According to spectroscopic analyses, Zr-silicate bonding occurred in the interfacial layer for the in situ vacuum annealed samples. Vacuum annealed samples containing the silicate interface layer exhibited excellent dielectric characteristics, such as negligible capacitance–voltage hysteresis (∼10mV), lower fixed charge density, and reduced equivalent oxide thickness compared to unannealed samples.