Hiroshi Nohira

High resolution-high energy x-ray photoelectron spectroscopy using third-generation synchrotron radiation source, and its application to Si-high k insulator systems

High-resolution x-ray photoelectron spectroscopy (XPS) at 6 keV photon energy has been realized utilizing high-flux-density x rays from the third generation high-energy synchrotron radiation facility, SPring-8. The method has been applied to analysis of high-k HfO2/interlayer/Si complementary metal–oxide–semiconductor gate-dielectric structures. With the high energy resolution and high throughput of our system, chemical-state differences were observed in the Si 1s, Hf 3d, and O 1s peaks for as-deposited and annealed samples. The results revealed that a SiOxNy interlayer is more effective in controlling the interface structure than SiO2. Our results show the wide applicability of high resolution XPS with hard x rays from a synchrotron source.

Characterization of ALCVD-Al2O3 and ZrO2 layer using X-ray photoelectron spectroscopy

The atomic layer chemical vapor deposition (ALCVD) deposited Al 2 O 3 and ZrO 2 films were investigated by ex situ X-ray photoelectron spectroscopy. The thickness dependence of band gap and valence band alignment was determined for these two dielectric layers. For layers thicker than 0.9 nm (Al 2 O 3 ) or 0.6 nm (ZrO 2 ), the band gaps of the Al 2 O 3 and ZrO 2 films deposited by ALCVD are 6.7 ± 0.2 and 5.6 ± 0.2 eV, respectively. The valence band offsets at the Al 2 O 3 /Si and ZrO 2 /Si interface are determined to be 2.9 ± 0.2 and 2.5 ± 0.2 eV, respectively. Finally, the escape depths of Al2p in Al 2 O 3 and Zr 3p3 in ZrO 2 are 2.7 and 2.0 nm, respectively.

Surface preparation and interfacial stability of high-k dielectrics deposited by atomic layer chemical vapor deposition

The effects of various interface preparations on atomic layer chemical vapor deposition (ALCVD) deposited Al2O3 and ZrO2 dielectrics properties were investigated by X-ray photoelectron spectroscopy (XPS), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), medium energy ion scattering (MEIS) and transmission electron microscopy (TEM). H-terminated Si, SiO2 and SiOxNy surfaces were used as substrates upon which the dielectric was deposited. Thermal annealing of SiO2 in NH3 forms an oxynitride; subsequent deposition of a ZrO2/Al2O3 bi-layer stack resulted in a capacitor structure with an equivalent oxide thickness (EOT) of ˜ 0.8 nm and a leakage current of 3 × 10-4 A/cm2 at - 1 + Vfb. This is in contrast to capacitor structures grown on H-terminated Si where high leakage was found. The growth of additional interfacial SiO2 during processing, a critical problem in nano-electronic device applications, is temperature dependent with ZrO2 exhibiting a higher oxygen permeability than Al2O3. Use of a polysilicon cap was shown to be effective at blocking oxygen absorption and transport through the high-k dielectrics, with stability up to 1100 °C.

Initial stage of oxidation of hydrogen-terminated silicon surfaces

Abstract Structural changes produced by the oxidation of hydrogen-terminated Si(111)-1 × 1 and Si(100)-2 × 1 surfaces at 300°C in dry oxygen under a pressure of 1 Torr were investigated by X-ray photoelectron spectroscopy (XPS) and multiple internal reflection infrared absorption spectroscopy (MIR-IRAS). Following results are obtained from the analysis and simulation of the experimental results: (1) the layer-by-layer oxidation reaction occurs locally at SiO 2 Si (111) interface, while that does not occur at SiO 2 Si (100) interface, however, (2) the oxidation on Si(100) surface proceeds more uniformly in atomic scale than that on Si(111) surface.

Accurate determination of SiO2 film thickness by x-ray photoelectron spectroscopy

We established the number of Si 2p photoelectrons emanating from a Si(100) substrate covered with a silicon–oxide film as a function of azimuthal and polar angles using the oxide film thickness as a parameter. The elastic and inelastic scattering cross sections of Si 2p photoelectrons in silicon oxide were deduced by reproducing the experimental results with Monte Carlo simulation for the path of Si 2p photoelectrons in silicon oxide. Based on the simulation, we found that the elastic scattering of Si 2p photoelectrons in silicon oxide could effectively be neglected in several specific directions. We also found that an emitting direction different to these specific directions is indispensable when precisely determining the thickness using XPS with a large receiving angle.

Activated boron and its concentration profiles in heavily doped Si studied by soft x-ray photoelectron spectroscopy and Hall measurements

The chemical bonding states of boron (B) in shallow P+/N junctions on Si substrates were studied by soft x-ray photoelectron spectroscopy (SXPES). This study revealed three chemical bonding states of B embedded in bulk Si. The concentration profiles of B were successfully determined by combining SXPES with step-by-step etching of Si substrates. The concentration profiles of B thus determined were in good agreement with those determined by secondary ion mass spectroscopy. The concentration profiles of holes were also determined by combining Hall measurements with the step-by-step etching of Si substrates. The concentration profiles of B having the lowest binding energy were found to agree well with the concentration profiles of holes. Therefore, B with the lowest binding energy can be assigned as activated B and those having the middle and highest binding energies can be attributed to deactivated B having chemical bonding states different from that of activated B.

Characterization of oxide films on 4H-SiC epitaxial (0001¯) faces by high-energy-resolution photoemission spectroscopy: Comparison between wet and dry oxidation

Wet and dry oxide films-4H-SiC epitaxial (0001¯) C-face interfaces have been characterized by capacitance-voltage (C-V) measurements and soft x-ray excited photoemission spectroscopy (SX-PES) and hard x-ray excited photoemission spectroscopy (HX-PES) using synchrotron radiation. The interface state density for wet oxidation is much smaller than that for dry oxidation at any energy level. In the PES measurements, intermediate oxidation states such as Si1+ and Si3+ were observed. In addition, the areal densities of these states were found to be in a good correspondence with those of the interface states. The reasons for the good electrical characteristics of metal-oxide-semiconductor devices fabricated by wet oxidation are discussed in terms of the depth profiles of oxide films derived from the SX-PES and HX-PES results.

Comprehensive x-ray photoelectron spectroscopy study on compositional gradient lanthanum silicate film

Oxygen bonding in La-silicate film with compositional gradient has been characterized by x-ray photoelectron spectroscopy. Based on an analytical model of bridging and nonbridging oxygen, the O 1s spectra arising from La-silicate layer have been deconvoluted with compositionally dependent parameters. For a composition ratio of 1:1 for SiO2 and LaO1.5 on the surface of the La-silicate layer, negative binding energy shifts of 0.35 and 0.10 eV for bridging and nonbridging oxygen, respectively, have been found to well interpret the angle-resolved spectra. The method has also been applied to characterize the temperature dependence of interface reactions at La2O3/Si with in situ processed Pt electrode. SiO4 molecules combined with bridging and nonbridging oxygen atoms have been found to form by high temperature annealing. The thickness of the silicate layer of 0.4 nm at as-deposited state has been found grow up to 2.8 nm after 500 °C annealing. From rough estimation, it has been revealed that 10% of the newly c...

TOF-SIMS as a rapid diagnostic tool to monitor the growth mode of thin (high k) films

Abstract For deep submicron technologies it is of crucial importance to grow ultra-thin (

X-ray photoelectron spectroscopy study on SiO2/Si interface structures formed by three kinds of atomic oxygen at 300 °C

Using the high-brilliant synchrotron radiation at SPring-8 we have studied the SiO2/Si interface structures, the interface state densities, and the uniformities of ∼1-nm-thick oxide films formed by three kinds of atomic oxygen at 300 °C by measuring Si 2p photoelectron spectra at the photon energy of 1050 eV and the energy loss spectra of O 1s photoelectrons at the photon energy of 714 eV. Among silicon oxide films studied here the abrupt compositional transition at SiO2/Si interface, the smallest deviation in interface state density, the interface state density comparable to that for thermal oxide formed in dry oxygen at 950 °C, and the highest uniformity was obtained with oxide film formed in krypton-mixed oxygen (Kr:O2=97:3) plasma.