Nobuhiro Ishikawa

Aging behavior of photoluminescence in porous silicon

The aging phenomena of porous silicon (PS) over a 192 day time span have been studied using photoluminescence (PL) spectroscopy, Fourier transform infrared spectroscopy, and transmission electron microscopy. As-prepared PS exhibits red PL peaking near 650 nm. The PL intensity increases with time to some equilibrium value. The PL peak shows no blueshift during aging. Infrared analysis reveals that the Si–O bond content in PS increases with time and correlates to the PL intensity. The PL lifetime increases with aging and its values range from 3 to 37 μs. Transmission electron microscopic observations indicate the presence of Si nanoparticles and amorphous substances in the PS layer. These results suggest that the PL from aged PS might be attributed to the combined effects of quantum confinement in Si nanoparticles and some defect in Si oxide covering the nanoparticles.

HRTEM analysis of solid precipitates in Xe-implanted aluminum

High-resolution TEM was carried out to determine shape and atomic arrangement of solid Xe precipitates in Al. Polycrystalline Al TEM specimens were implanted with 30 keV Xe{sup +} at RT to a dose of 3x10{sup 20} ions/m{sup 2} and then annealed at 523 K. Below a size 4 nm dia, the Xe precipitates are solid with an fcc crystal structure mesotacticly aligned with the Al lattice. In HRTEM along [011] projection, the difference in the lattice parameters of solid Xe and Al produces a precipitate image dominated by a 2-D Moire pattern that repeats in both the and directions every 3 Al (or 2 Xe) lattice spacings. Multi-slice image simulations, using a 3-D atomic model, demonstrates that the precipitates are tetradecahedra with faces parallel to the dense {l_brace}111{r_brace} planes and the {l_brace}100{r_brace} planes. Off-Bragg illumination of the precipitates minimizes Al lattice fringes and generates precipitate images which are in good agreement with the model.

Effect of the Purity of Plating Materials on the Reduction of Resistivity of Cu wires for Future LSIs

Resistivity difference between Cu wires made with plating using high purity (new plating process) and conventional purity (conventional process) materials has been evaluated in order to develop the process for the realization of high performance LSIs. This resistivity difference is relatively small, i.e., 8% when line width is wide (200 nm). However, it increases with the decrease in line width, and it reaches about 20%, i.e., 2.8 μΩ cm for the former and 3.5 μΩ cm for the latter at 50 nm line width. A 50 nm wide Cu wire formed with the new plating process had more uniform and larger grain sizes and lower impurity concentrations than the wire formed with the conventional process.

A new phenomenon in the floating-zone (FZ) growth of Si nanowires

Silicon nanowires have been fabricated with the floating-zone melt-vapor method. The growth-time dependence of the size and morphology of Si nanowires was shown to reflect the dynamic behavior of nanowire growth with an oxide-assisted growth mechanism. A new long-time growth phenomenon for silicon nanowires was discovered and a related model was proposed.

Dual ion beam irradiation system interfaced with a transmission electron microscope and the observation of defect evolution in Ni during irradiation

Abstract A dual ion beam accelerator interfaced with a transmission electron microscope (TEM) has been built for in-situ analysis of structural evolution during irradiation. Both ion accelerators were designed for 100 kV heavy ions and 30 kV gas ions, respectively. The ion fluxes from both systems were up to more than 10 18 ions m −2 s −1 at the specimen position. This paper describes the equipment of this facility and presents experimental results of 10 keV H + and 70 keV Ar + ion beam implantation into Ni at room temperature.

High resolution transmission electron microscopy of defect clusters in aluminum during electron and ion irradiation at room temperature

Defect clusters in Al during electron and ion irradiation have been investigated using high-resolution transmission electron microscopy (HRTEM). An ION/HVEM system which consists of a high-voltage TEM and ion implanters was used for in-situ observation of damage evolution under 1,000 keV electrons and 15 keV He{sup +} irradiation at room temperature. HRTEM of Al in [110] orientation showed many planar defects along {l_brace}111{r_brace} planes during electron irradiation, while a high density of small polyhedron-shaped cavities (He-bubbles) was observed in addition to the planar defects after He{sup +} irradiation. Multi-slice image simulation of various models of dislocation loops indicated the planar defect as an interstitial-type Frank loop.

Interfacial Microstructure of A6111/Steel Lap Joint Fabricated by Defocused Laser Beam Welding

Lap joining of A6111 alloy and steel (SPCC: Steel Plate Cold-rolled C) plates was performed using a defocused YAG laser beam. A detailed investigation was performed on the intermetallic compound (IMC) layer formed at the weld interface. Two representative joints fabricated under different welding conditions were selected and the effect of the welding conditions on the kind and morphology of the IMC was investigated using a transmission electron microscope (TEM). An electron diffraction pattern method was used to identify IMC. It was found that the morphology and kind of IMC formed at the weld interface were strongly affected by the welding conditions, in particular, by the amount of heat input during welding. The thickness of the IMC layer formed at the weld interface was about 1 μm and the average grain size of the IMC in the layer was less than 300 nm when the joining was carried out with a small amount of heat input. The IMC layer was composed of Fe3Al, FeAl, Al2Fe, Al5Fe2 and Al13Fe4 in this case. However, the thickness of the IMC layer was around 6 μm when the joining was carried out under high heat input conditions. In this case, the IMC layer was composed of coarse Al5Fe2 (5 μm) and Al13Fe4 (1 μm). Therefore, it is considered that the reduced bonding strength of the joint with a thick IMC layer is due not only to the overall morphology of the IMC layer but also to the formation of coarse Al-rich IMCs in the layer.

In situ observation of transformation in α-Fe2O3 under hydrogen implantation

An in situ observation of the α-Fe2O3-to-Fe3O4 transformation has been performed using a dual-ion-beam accelerator interfaced with a transmission electron microscope (TEM). During the hydrogen-ion implantation of α-Fe2O3, transformation into the new phase (γ-Fe2O3 or Fe3O4) was observed. It was also found that the orientation relationship between α-Fe2O3 and the new phase (γ-Fe2O3 or Fe3O4) satisfies the Shoji–Nishiyama relationship, in agreement with previous experiments. It was also found that the nearest interatomic distance does not vary by the implantation until the re-stacked phase appears, although when the re-stacked phase is formed, the lattice expansion is observed in the transformed (re-stacked) phase. Judging from these results, we have concluded that the α-Fe2O3 to Fe3O4 transformation is induced during the hydrogen ion implantation of α-Fe2O3.

Imaging and modeling of nanocrystalline Xe in Al containing defects

Morphological and crystallographic structures of a Xe nanocrystal embedded in Al were determined with off-Bragg high-resolution transmission electron microscopy (OB-HRTEM). The nanocrystals have a size in a range from 1 to 10 nm and precipitate with a FCC structure, mesotactically aligned with Al matrix. OB-HRTEM revealed Xe cuboctahedron crystals with faces parallel to eight Al {111} planes truncated by six {100} planes. Atomic resolution microscopy indicates that the nanocrystals often contain lattice defects, which consist of a stacking fault. Simulated images for a nanocrystal containing a stacking fault agreed well with experimental images. The process of a defect introduction into a nanocrystal was successfully recorded on videotape. A frame by frame analysis shows the introduction of a Shockely partial dislocation to form the fault. This introduction requires the motion of atoms in several layers in one side of the fault, to relax the strain caused by the change in stacking sequence.

The Development of an Innovative Process of Large Grained and Low Resistivity Cu Wires for less than hp 45nm ULSI

We have developed an innovative process to create large grained and low resistivity Cu wires for less than hp 45 nm ULSIs. The resistivity of the 50 nm wide Cu wires by an innovative high purity process is found to be 21% lower than those created by the conventional process. It was also found that Cu wires formed with the new high purity process have larger grains with a smaller spread and a lower impurity concentration than those made with the conventional process. This innovative new process is expected to be a powerful candidate for created Cu wire of less than hp 45 nm ULSIs.