T. Tanimura

Control of oxidation and reduction reactions at HfSiO∕Si interfaces through N exposure or incorporation

Using synchrotron-radiation photoemission spectroscopy, we have investigated oxidation and reduction reactions of HfSiO(N)∕Si gate stack structures annealed in a N2 or O2 atmosphere. It is found that both oxidation and reduction reactions can be suppressed by using nitrogen-incorporated HfSiO films in the annealing process at proper partial pressure of N2 gas (PN2∼100Torr). The detailed analysis of “SiO2 equivalent thicknesses” for annealed HfSiO and HfSiON films reveals that ambient N2 gas suppresses only the reduction reaction, while nitrogen atoms incorporated in dielectrics suppress both oxidation and reduction reactions.

Annealing effects of in-depth profile and band discontinuity in TiN/LaO/HfSiO/SiO2/Si gate stack structure studied by angle-resolved photoemission spectroscopy from backside

We have investigated annealing effects on in-depth profile and band discontinuity for a metal gate/high-k gate stack structure on a Si substrate using backside angle-resolved photoemission spectroscopy with synchrotron radiation. In-depth profiles analyzed from angle-resolved photoemission spectroscopy show that La atoms diffuse through the HfSiO layer and reach interfacial SiO2 layers by rapid thermal annealing. Chemical shift of Si 2p core-level spectra suggests that there are changes in the band discontinuity at the high-k/SiO2 interface, which is well related to the Vth shift based on the interface dipole model.

Photoinduced charge-trapping phenomena in metal/high-k gate stack structures studied by synchrotron radiation photoemission spectroscopy

We have demonstrated photoinduced charge-trapping phenomena in metal/high-k gate stack structures using time-dependent photoemission spectroscopy with synchrotron radiation. Pt metal gate electrode with a large work function releases trapped negative charges near the surface of the HfSiON film while TiN metal gate electrode with a lower work function keeps negative charges in the HfSiON film. The release of negative trapped charges reveals a possibility of positive charge trapping at the interface in the HfSiON film. The location of energy level for negative charges is concluded to be between Pt and TiN Fermi-level in the band gap of the HfSiON film.

Thermal stability in a-Si/HfSiO(N)/Si gate stack structures studied by photoemission spectroscopy using synchrotron radiation

We have investigated thermal stability in amorphous-Si/HfSiO(N) gate stack structures using synchrotron-radiation photoemission spectroscopy. Core-level photoemission spectra depending on annealing temperature have revealed the mechanism of metallization reaction at the upper interface between a-Si cap layer and HfSiO(N) films under ultrahigh vacuum annealing. Silicidation reaction starts by annealing at 700 °C for both HfSiO and HfSiON films. By annealing at 800 °C, metallization reaction is rapidly promoted for the HfSiO film, while the Hf-silicide component changes into the Hf-nitride component due to its thermal stability and metallization reaction mildly proceeds for the HfSiON films.

Relationship between band alignment and chemical states upon annealing in HfSiON/SiON stacked films on Si substrates

We have investigated the relationship between band alignment and chemical states in HfSiON/SiON stacked films on Si substrates by photoemission spectroscopy and x-ray absorption spectroscopy. Valence-band maxima mainly derived from N 2p states in HfSiON films are closely related to N–Hf bonding configurations. The valence-band offset for a thick HfSiON film is smaller than that for a thin HfSiON film, due to the amount of N–Hf bonding states. Since N–Hf bonding states decrease upon annealing, thickness dependence of valence-band offset can be eliminated. On the other hand, the conduction-band offset does not depend on either the thickness or annealing.

Depth profiling of chemical states and charge density in HfSiON by photoemission spectroscopy using synchrotron radiation

We have investigated chemical states and charge density in HfSiON films as a function of depth using x-ray irradiation time-dependent photoemission spectroscopy. N 1s core-level photoemission spectra deconvoluted into three components depend on HfSiON thickness, indicating the component, which is attributed to the N atoms bonded to Hf atoms, has peak near the surface. On the other hand, charge density estimated from band bending in Si from Si 2p photoemission spectra is also distributed mainly near the surface. These results indicate that the origin of the negative charge trapping can be directly related to the presence of Hf–N bonds.

Effects of thermal annealing on charge density and N chemical states in HfSiON films

We have investigated the charge density and N chemical states in HfSiON films annealed at various oxygen gas pressures by time-dependent photoemission spectroscopy. The Si 2p core-level spectra and the sample current reveal that annealing these films at low oxygen partial pressures affects the number of inherent fixed charges and annealing at high oxygen partial pressures results in a decrease in the number of trapped charges. The N 1s spectra of the annealed HfSiON samples indicate a decrease in Hf–N bonds due to the substitution of N by O along with a decrease in the number of trapped charges.

Interfacial reactions in Ru metal-electrode/HfSiON gate stack structures studied by synchrotron-radiation photoelectron spectroscopy

We have investigated the thermal stability and interfacial reactions of a Ru/HfSiON gate stack structure, annealed in a nitrogen ambient, using synchrotron-radiation photoelectron spectroscopy. We find that in HfSiON films with Ru metal, competition between catalyst-induced oxidation and oxygen or SiO desorption arises upon high-temperature annealing, unlike in the same films without Ru. The desorption reaction during high-temperature annealing at 1050 °C could be caused by the decomposition of an unstable Si oxide component, formed by catalytic oxidation at the interface between the HfSiON layer and the Si substrate after annealing below 850 °C.