Study of work function of CVD WSix thin film on high K dielectric.

ABSTRACTTo meet requirements of CMOS circuits at sub 45nm scale, gate oxide thickness shall decrease. Thus high K materials are needed as dielectric gate. In this setting, due to gate depletion effect, metallic material should be used as an alternative to poly silicon gate. Moreover, specifications on threshold voltage require modulation of gate material work function with respect to nMOS or pMOS transistor. WSix work function is known to be sensitive to material stoichiometry. In this work, WSix thin films with x between 2.2 and 2.5 are evaluated as metal gate on HfO2 and SiO2 dielectric. Film chemical characteristics are correlated with work function measurements.Thin films are deposited using WF6 and dichlorosilane on a 200mm wafer industrial chamber. Thermal treatments are applied to sample in order to recrystallise the film and confirm it stability. MOS Capacitors are processed. Electrical characterizations (capacitance vs voltage) are used to extract work function with respect to film composition.Films are chemically and morphologically stable up to 800°C. A W/Si ratio gradient is observed between surface and dielectric/film interface. Whatever the nominal stoichiometry, Si/W ratio is constant at this interface. This result is correlated with identical work function measurement for different nominal stoichiometry. Moreover no differences are observed between Vfb vs equivalent oxide thickness curves for HfO2 and SiO2 dielectric. High EOT variations have been identified for SiO2 capacitors in contrast with SiO2/HfO2 capacitors. These results characterize WSix as a suitable metal gate for nMOS transistors.

Studies on the perovskite-based La4Srn−4TinO3n+2

Perovskite titanates with nominal stoichiometry ABO3+Δ are frequently reported in SOFC literature as having O3 stoichiometry. Such phases often exhibit quite interesting properties, but are not stoichiometric and the structural characterisation is usually not rigorous. Here we demonstrate how oxygen excess can be incorporated in a titanate perovskite-based lattice as crystallographic oxygen shears giving rise to the homologous series La4Srn−4TinO3n+2. The layered structure is lost for the n=12 member (La4Sr8Ti12O38−Δ), although the oxygen excess is accommodated within the perovskite framework in randomly distributed short-range linear defects. This compound was studied as potential fuel electrode due to its high total conductivity and stability in the most reducing conditions.

Synthesis, Structure and Magnetic Properties of the Group IV Ternary Nitrides, AMN2 (A = Alkaline Earth Metal, M = Transition Metal)

The ternary transition metal nitrides of general formulation AMN2 (A = alkaline earth metal, M = transition metal) have been systematically studied. These compounds have been synthesised by high temperature solid state reaction from their component binary nitrides in sealed systems. The structures of these materials have been determined by powder X-ray diffraction (PXD) and two layered structure-types (α-NaFeO2-type and KCoO2-type) have been observed, thus far. Intriguingly, magnetic measurements performed on nitride samples indicate they may not be diamagnetic (d = 0, S = 0) as their nominal stoichiometry suggests.

Parallel Electron Energy Loss Spectroscopy of a Cu-Be Alloy

Although the Cu-Be binary system has been studied by previous investigators and recently reviewed, no direct measurements have been made concerning the chemistry of the γ-phase, which has a nominal stoichiometry CuBe. Quantitative parallel electron energy loss spectroscopy (PEELS) has been used in this investigation of a Cu, 1.8 wt.% Be, 0.3 wt.% Co alloy to determine a section of the γ/(α+γ) phase boundary of the Cu-Be phase diagram. Sections of alloy (in sheet form) were encapsulated in evacuated quartz capsules to prevent oxidation and isothermally aged in the temperature range 400 - 600°C. TEM specimens were prepared by punching disks from the sheet, dimpling and ion milling. Spectra were acquired using a Philips EM400 TEM/STEM in the TEM image mode, and with a Gatan parallel recording EELS spectrometer. The acquisition mode allowed for the use of a relatively large (yet accurately known) collection angle. The incident beam convergence angle was also determined, so that a beam convergence correction could be used to calculate the true collection angle.

Einfluß der Dotierung von BaPb0,75Bi0,25O3 mit K, Rb und Cs auf dessen supraleitende Eigenschaften

xIn the series with nominal stoichiometry Ba1-xAxPb0,75Bi0,25O3 (A = K, Rb with = 0.1, 0.2, 0.3, and A = Cs with x = 0.1) solid solutions were prepared. The composition of the samples obtained was verified by X -ray techniques. All compounds crystallize tetragonally with a 3-dimensional array of Pb(Bi) - O6 octahedra and Pb(Bi) -O -Pb(Bi) bonding angles of 180° (c-axis) and 165° (xK = 0.3) 168° (xRb = 0.3 and xCs = 0.1) within the a/b plane. Superconducting transition temperatures o f Ba1-xAxPb0,75Bi0,25O3 with Te = 12 (“onset”) were determined using a SQUID magnetometer.

Preparation and Characterization of La1Sr2Nb5O10−x Specimens

ABSTRACTRecently Ogushi et al reported a La-Sr-Nb-O compound with a superconducting temperature of about 225 K. The possibility of having superconductors with such a high temperature is certainly technologically relevant. We prepared specimens with the same nominal stoichiometry and performed characterization by SEM, high resolution TEM, Scanning Auger and X-rays.

Preparation and characterization of the superconducting system Bi1−xPbxSrCaCu2Oy

The superconducting properties of the system Bi1−xPbxSrCaCu2Oy have been studied as a function of lead concentration and preparation conditions. Energy dispersive x-ray analysis indicates the nominal stoichiometry is preserved up to x = 0.2 and for this concentration, zero resistance occurs at 97 K. Magnetically modulated microwave absorption measurements provide a global probe of the samples and show that resistance measurements alone can give a false impression of the quality of the materials.

Phase chemistries in a precipitation-strengthened superalloy

The majority of Ni-base superalloys are strengthened by precipitation of the γ' phase, which has a coherent ordered Ll2 structure based on Ni3(Al,Ti). However, a few superalloys, most notably Inconel 718, are strengthened instead by a γ" phase, which is a metastable coherent ordered DO22 precipitate with a tetragonal unit cell and nominal stoichiometry Ni3(Nb,Ta). The γ' phase generally precipitates homogeneously in the form of spheres or cubes, whereas the γ" phase occurs as disks with the (001) γ" plane parallel to one of the {100} planes of the cubic matrix. Thus, three variants of γ" are possible. The γ" phase is generally metastable and is replaced on extended aging by the δ phase, which is also Ni3(Nb,Ta) but which has a Cu3Ti-ordered orthorhombic structure.It has been shown that the type of precipitate formed in Ni-base alloys is a sensitive function of overall alloy chemistry. In particular, the Ti+Al/Nb+Ta ratio has a strong effect, with increases in this ratio favoring γ and decreases γ'.