Toshiba Nanoanalysis Corporation

Mg diffusion is a common problem in GaN devices with p–n junctions. Although this impurity diffusion is reported to occur through threading dislocations (TDs), no direct evidence has yet been obtained. Therefore, we tried the direct observation of Mg diffusion by atom probe tomography (APT) analysis. The n-type drift layer of the fabricated p–n diode was exposed, and etch pits were formed on the drift layer to identify the TD position. The APT analysis around TDs was carried out by lifting out the drift layer around specific etch pits using a focused ion beam to include TDs. The relationship between the etch pit shape and the TD type was confirmed by cross-sectional scanning transmission electron microscopy observation. The APT analysis of two types of etch pits formed on the mixed dislocations was performed, and Mg diffusion was clearly observed through the mixed dislocations. In this work, we show direct evidence of Mg diffusion via mixed dislocations in GaN p–n diodes and its effect on reverse leakage current.

We fabricate $\mathrm{C}\mathrm{o}\mathrm{F}\mathrm{e}/{\mathrm{A}\mathrm{l}\mathrm{O}}_{x}/\mathrm{C}\mathrm{o}\mathrm{F}\mathrm{e}/{\mathrm{A}\mathrm{l}\mathrm{O}}_{x}/\mathrm{C}\mathrm{o}\mathrm{F}\mathrm{e}$ ferromagnetic double tunnel junctions and observe spin-dependent tunneling phenomena. A middle CoFe layer becomes discontinuous by forming CoFe particles two dimensionally, of which the average diameter is evaluated to be 2.0--4.5 nm from cross-sectional transmission electron microscopy images. Below 50 K, a Coulomb gap is observed in current-voltage curves, and both magnetoresistance ratios and resistances are found to increase significantly with decreasing temperature. This indicates that a cotunneling process is dominant within the gap, which agrees very well with theoretical prediction [Phys. Rev. Lett. 80, 1758 (1998)].

We report on a direct comparison of the depth and lateral resolution of the current state-of-the-art laser-assisted atom probe microscopy analysis of single-crystalline silicon. The isotopic heterostructures composed of 5–15 nm-thick S28i- and S30i-enriched layers were measured to reconstruct three-dimensional images of S28i and S30i stable isotope distributions in the surface perpendicular and parallel directions for the analysis of the depth and lateral resolution, respectively. The decay length experimentally obtained for the lateral direction is only about twice longer than in the direction, meaning that the lateral resolution is higher than obtained by secondary ion mass spectrometry.

The greater variability in the electrical properties of n-type metal-oxide-semiconductor field-effect transistors (MOSFETs) compared with those of p-type MOSFETs poses problems for scaling of silicon based large-scale integration technology. We have elucidated the origin of the variability difference between n- and p-type transistors by using laser-assisted atom probe tomography to directly count the number of discrete atoms in local regions. We found that ion implantation and activation annealing for source/drain extension fabrication enhances anomalous dopant fluctuations of boron atoms in n-MOSFET channel regions, interpreted by fast migration of boron atoms.

Laser-assisted atom probe microscopy of 2 nm period Si28∕Si30 isotope superlattices (SLs) is reported. Three-dimensional distributions of Si28 and Si30 stable isotopes are obtained with sub-nanometer spatial resolution. The depth resolution of the present atom probe analysis is much higher than that of secondary ion mass spectrometry (SIMS) even when SIMS is performed with a great care to reduce the artifact due to atomic mixing. Outlook of Si isotope SLs as ideal depth scales for SIMS and three-dimensional position standards for atom probe microscopy is discussed.

Recent experiments suggest that Mg condensation at threading dislocations induces current leakage, leading to degradation of GaN-based power devices. To investigate this, we perform first-principles total-energy electronic-structure calculations for various Mg and dislocation complexes. We find that threading screw dislocations (TSDs) indeed attract Mg impurities, and that the electronic levels in the energy gap induced by the dislocations are elevated toward the conduction band as the Mg impurity approaches the dislocation line, indicating that the Mg-TSD complex is a donor. The formation of the Mg-TSD complex is unequivocally evidenced by atom probe tomography in which Mg condensation around the [0001] screw dislocation is observed in a p–n diode. These findings provide a picture in which the Mg, being a p-type impurity in GaN, diffuses toward the TSD and then locally forms an n-type region. The appearance of this region along the TSD results in local formation of an n–n junction and leads to an increase in the reverse leakage current.

The 31 P-NMR spectra of europium complexes with β-diketones and phosphine oxides in CDCl 3 , DMSO- d 6 , toluene- d 8 with dissolved fluorinated polymers, and fluorinated solvent were investigated as well as the temperature dependence of these spectra. When a mixture of europium complex 1 and 1.0 molar equivalent of trioctylphosphine oxide and triphenylphosphine oxide was dissolved in a fluorinated solvent, europium complex 2 with two types of phosphine oxides was formed at room temperature. In CDCl 3 and toluene- d 8 solutions, however, this complex was identified only at low temperatures. This difference is thought to be due to the differences in the speed of ligand exchanges. In DMSO- d 6 solution, no signal corresponding to the europium complex with phosphine oxides was observed. This implies that the major portion of phosphine oxides is not coordinated with europium ions in DMSO- d 6 solution. The fluorescence intensity of each europium complex in a solvent was correlated to the solvent and the 31 P-NMR spectrum. It was found that the fluorescence intensity was the highest in the fluorinated solvent.

Coimplantation of heterogeneous dopants in materials can be used to control the principal dopant distribution. We used atom probe tomography (APT) and secondary ion mass spectrometry (SIMS) to investigate the impact of coimplanted carbon on boron diffusion in silicon. After annealing, three-dimensional APT analysis of dopant distributions revealed the presence of carbon–boron coclusters around the projection range of boron. In addition, SIMS depth profiles revealed enhanced boron concentration around the projection range of carbon. These results suggest that the carbon–boron interaction suppresses boron diffusion in silicon.

The correlation between threshold voltage (VT) and channel boron concentration in silicon-based 65 nm node negative-type metal-oxide-semiconductor field-effect transistors was studied by atom probe tomography (APT). VT values were determined for one million transistors in a single chip, and transistors having a ±4σ deviation from the median VT were analyzed using APT. VT and the channel boron concentration were positively correlated. This is consistent with the relationship between the average boron concentration of wafers implanted with different channel doses and the median VT of the million transistors. APT is suitable for the study of dopant-distribution-based device failure mechanisms.

Platinum (Pt) incorporation into nickel silicide (NiSi) films improves silicide characteristics such as lower contact resistance <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> at silicide/Si interface and higher thermal stability. The impact of Pt incorporation is widely accepted and recognized in research field; however, the role of Pt in NiSi films has not been fully clarified so far. In this paper, the spatial distributions of Pt and dopants (i.e., arsenic and boron) in silicide films are studied at an atomic level analysis using local electrode atom probe. In particular, Pt and dopant distributions were investigated in detail both at silicide/Si interface and at silicide-grain boundary. Silicide-grain size was also analyzed at various Pt concentrations in silicide films, and the relationship between the Pt concentration and physical properties of Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sub> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Pt <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Si films is pointed out. Finally, for further CMOS device scaling, the benefit of higher concentration of Pt incorporation into Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Pt <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Si films is described.

We combine time-resolved pump-probe magneto-optical Kerr effect and photoelectron spectroscopy experiments supported by theoretical analysis to determine the relaxation dynamics of delocalized electrons in half-metallic ferromagnetic manganite $\mathrm{L}{\mathrm{a}}_{1\ensuremath{-}x}\mathrm{S}{\mathrm{r}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$. We observe that the half-metallic character of $\mathrm{L}{\mathrm{a}}_{1\ensuremath{-}x}\mathrm{S}{\mathrm{r}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$ determines the timescale of both the electronic phase transition and the quenching of magnetization, revealing a quantum isolation of the spin system in double-exchange ferromagnets extending up to hundreds of picoseconds. We demonstrate the use of time-resolved hard x-ray photoelectron spectroscopy as a unique tool to single out the evolution of strongly correlated electronic states across a second-order phase transition in a complex material.

Platinum (Pt)-incorporation into nickel silicide films is the promising approach to reduce the contact resistance (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> ) at silicide/Si interface. Physical properties of Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Pt <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Si films were investigated by using local electrode atom probe (LEAP); The distributions of Pt and dopants (such as As and B) were analyzed both at silicide/Si interface and at silicide grain boundary. The silicide grain-size miniaturization was clearly observed by Pt-incorporation. The impacts of silicide grain size on electrical properties and thermal stability were clarified depending on the Pt concentration. Finally, R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> reduction depending on the incorporated-Pt concentration was experimentally shown in both nMOSFETs and pMOSFETs.

We studied extremely low interface resistance and thermal stability of the interface of NiSi/Si junctions with Pt (Ni(Pt)Si/Si junctions) based on first-principles calculation. The physical origin of thermal stability of NiSi enhanced by Pt is clarified by the calculations. Our calculations show clear difference of energies for dopant atoms of As and B between PtSi/Si and NiSi/Si. The results obtained theoretically and experimentally in this study demonstrate the dipole comforting Schottky junctions enhanced by PtSi at the interface for extremely low resistance.

Abstract We experimentally studied the optimization of the hot-C + -ion implantation process for forming nano-SiC (silicon carbide) regions in a (100) Si-on-insulator substrate at various hot-C + -ion implantation temperatures and C + ion doses to improve photoluminescence (PL) intensity for future Si-based photonic devices. We successfully optimized the process by hot-C + -ion implantation at a temperature of about 700 °C and a C + ion dose of approximately 4 × 10 16 cm −2 to realize a high intensity of PL emitted from an approximately 1.5-nm-thick C atom segregation layer near the surface-oxide/Si interface. Moreover, atom probe tomography showed that implanted C atoms cluster in the Si layer and near the oxide/Si interface; thus, the C content locally condenses even in the C atom segregation layer, which leads to SiC formation. Corrector-spherical aberration transmission electron microscopy also showed that both 4H-SiC and 3C-SiC nanoareas near both the surface-oxide/Si and buried-oxide/Si interfaces partially grow into the oxide layer, and the observed PL photons are mainly emitted from the surface SiC nano areas.

Three-dimensional dopant distributions in actual n- and p-channel metal–oxide–semiconductor devices of 65 nm node in two kinds of commercially available products were investigated by atom probe tomography (APT). Detailed and quantitative dopant distributions in gate, gate oxide, and channel regions were successfully obtained by APT. In particular, similarities as well as differences in the dopant distributions of these two devices, which were made by different fabrication processes, were clarified in detail by estimating the dopant concentrations in the grain, at the grain boundary, and at the interface of the polycrystalline Si gate individually.

This paper proposes highly reliable, low resistance and cost effective Cu interconnect system for 45nm CMOS device and beyond. Overhang formation and Cu line resistance increase by deposition process variation are serious problems for titanium (Ti) barrier metal (BM). Overhang reduction by surface nitridation of Ti BM has been successfully demonstrated. It has been clarified that Cu resistivity increase with Ti BM is due to insufficient Cu grain growth, not reaction between Ti and Cu. Surface nitridation contributes to Cu line resistance reduction by changing grain growth behavior. Moreover, it also improves oxidation endurance of the BM caused by absorbed moisture from porous low-k ILD. It is concluded that surface nitridation of Ti BM is promising approach as Cu barrier metal for 45nm device and beyond to fabricate Cu interconnect with controlled resistance and high reliability.

We have investigated the reason behind the enhancement of dielectric constant ( ε ), which occurred in CeO 2 directly grown on Si(111). ε of directly grown CeO 2 is enhanced to 52, which is twice as large as the reported value. From in-plane X-ray diffraction measurements and electron diffraction pattern observations using a transmission electron microscope, it has been found that the lattice spacings in CeO 2 were isotopically expanded by 0.6%, as compared with the reported values in bulk CeO 2 . In addition, from X-ray photoelectron spectroscopy measurements, the existence of oxygen defects in CeO 2 was confirmed. The oxygen defects in CeO 2 may cause the decrease in coulomb interaction in the ionic crystal, resulting in the expansion of lattice spacings. The enhancement of ion movability, due to the expansion of lattice spacings is considered as the reason behind the enhancement of ε .

The structures of the defects induced by carbon contamination in epitaxial silicon films grown with monosilane (SiH 4 ) on silicon substrates were investigated. A new formation mechanism of defects associated with carbon in silicon epitaxial growth processes is proposed. The carbon contaminants were introduced prior to the growth by chemical vapor deposition (CVD), where the growth chamber was intentionally contaminated with organic materials. The carbon contaminant concentration was changed by adjusting the annealing conditions at temperatures ranging from 900°C to 1100°C. Silicon epitaxial films were grown by CVD at a temperature of 700°C. In this experiment, we found that pits were formed as dominant surface defects under the condition of a relatively low carbon concentration of less than 4.5×10 13 cm -2 , while mound defects were formed at a carbon concentration of more than 4.5×10 13 cm -2 . These defects can be explained by the formation of silicon carbide (SiC) islands resulting from the carbon contamination.

Abstract The angular distributions of photoelectrons and Auger electrons from single crystal surfaces show characteristic diffraction patterns, which contain information on the local atomic structures surrounding the emitter atoms. Using computational reconstruction processes on the diffraction patterns enables us to determine the local atomic structures of, for example, dopants, catalytic active sites, and surface/interface structures. This method has become known as “photoelectron holography (PEH)”. Several advanced photoelectron analyzers for PEH are now available at beamlines at SPring-8, the world’s largest synchrotron radiation facility. Recently, the use of micron-sized photon beams, as well as pump-and-probe time-resolved techniques has become possible with relatively high energy resolution. Here, the experimental apparatus and some representative applications are introduced.

The strain in Si, on which a single-crystalline gate oxide was epitaxially grown, was investigated by evaluating lattice spacings in and Si. In-plane X-ray diffraction measurements and observations of electron diffraction patterns by a transmission electron microscope were performed to examine the lattice spacings precisely. It was found that the lattice spacings in epitaxial isotropically expanded by ∼1%, compared with those in bulk polycrystalline The oxygen-defect-induced state was observed in the valence bandedge by X-ray photoelectron spectroscopy measurements. The decrease of the coulombic interaction in ionic oxide due to the oxygen defects may induce the expansion of the lattice spacings in It was clarified that Si at 50 nm depth from the interface was tensile strained owing to the expansion of the lattice spacings in Oxygen defects in epitaxial crystalline gate dielectrics must be controlled by taking account of Si channel properties. © 2004 The Electrochemical Society. All rights reserved.