Yasuyoshi Nagai

ROLE OF VACANCY-SOLUTE COMPLEX IN THE INITIAL RAPID AGE HARDENING IN AN Al-Cu-Mg ALLOY

Abstract We have investigated the origin of the initial rapid hardening of an Al–1.3 at.% Mg–1.7 at.% Cu alloy by coincidence Doppler broadening of positron annihilation radiation and positron lifetime spectroscopy. Quenched-in vacancies are bound to Mg atoms rather than Cu atoms initially and the vacancy–Mg complexes easily migrate to vacancy sinks at 150°C. Vacancy–Mg–Cu complexes form during the initial 1 min aging at vacancy sinks, meanwhile vacancy density decreases rapidly. These results support that the dislocation–solute interaction is the origin of the initial rapid hardening.

Dopant distributions in n-MOSFET structure observed by atom probe tomography

The dopant distributions in an n-type metal-oxide-semiconductor field effect transistor (MOSFET) structure were analyzed by atom probe tomography. The dopant distributions of As, P, and B atoms in a MOSFET structure (gate, gate oxide, channel, source/drain extension, and halo) were obtained. P atoms were segregated at the interface between the poly-Si gate and the gate oxide, and on the grain boundaries of the poly-Si gate, which had an elongated grain structure along the gate height direction. The concentration of B atoms was enriched near the edge of the source/drain extension where the As atoms were implanted.

Positron annihilation study of vacancy-type defects in high-speed deformed Ni, Cu and Fe

Abstract Vacancies and vacancy clusters in Ni, Cu, and Fe induced by high- and low-speed deformations are studied systematically by positron annihilation techniques and are compared with those induced by the conventional-rolling. To clarify the nature of the defects, the experimental results are compared with our superimposed-atomic-charge calculations of the positron lifetimes in the vacancy clusters as a function of their size. It is found that the deformation-induced defects in the fcc and bcc metals are significantly distinct. In the fcc metals of Ni and Cu, monovacancies with high number densities are induced by the high- and low-speed deformations and by heavy conventional-rolling (>10% in Ni and >40% in Cu). Vacancy clusters are observed after the high- and low-speed deformation for Ni and after the conventional-rolling for Cu. On the contrary, dislocations and vacancy clusters are introduced in bcc Fe regardless of the type or degree of deformation.

Dopant distribution in gate electrode of n- and p-type metal-oxide-semiconductor field effect transistor by laser-assisted atom probe

Three dimensional dopant distributions in polycrystalline Si gate of n-type (n-) and p-type (p-) metal-oxide-semiconductor field effect transistor (MOSFET) structure were investigated by laser-assisted three dimensional atom probe. The remarkable difference in dopant distribution between n-MOSFET and p-MOSFET was clearly observed. In n-MOSFET gate, As and P atoms were segregated at grain boundaries and the interface between gate and gate oxide. No diffusion of As and P atoms into the gate oxide was observed. On the other hand, in p-MOSFET, no segregations of B atoms at grain boundaries or the interface were observed, and diffusion of B atoms into the gate oxide was directly observed.

Origin of characteristic variability in metal-oxide-semiconductor field-effect transistors revealed by three-dimensional atom imaging

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.

Depth and lateral resolution of laser-assisted atom probe microscopy of silicon revealed by isotopic heterostructures

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.

Monolayer segregation of As atoms at the interface between gate oxide and Si substrate in a metal-oxide-semiconductor field effect transistor by three-dimensional atom-probe technique

Atom-probe technique was applied to analyze three-dimensional dopant distribution in Si substrate of metal-oxide-semiconductor field effect transistor (MOSFET) structure. As a result, three-dimensional As atom distribution implanted in Si was obtained. The quantification of the As atom distribution in a depth direction was confirmed as compared with the one-dimensional distribution measured by secondary ion mass spectroscopy. Moreover, monolayer segregation of As atoms at the interface between gate oxide and Si substrate was clearly observed. This result shows the possibility to clarify discrete dopant distribution in Si substrate related to the characteristic variation of MOSFETs.

Interlaboratory comparison of positron annihilation lifetime measurements for synthetic fused silica and polycarbonate

Interlaboratory comparison of positron annihilation lifetime measurements using synthetic fused silica and polycarbonate was conducted with the participation of 12 laboratories. By regulating procedures for the measurement and data analysis the uncertainties of the positron lifetimes obtained at different laboratories were significantly reduced in comparison with those reported in the past.

Correlation between threshold voltage and channel dopant concentration in negative-type metal-oxide-semiconductor field-effect transistors studied by atom probe tomography

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.

Positron and positronium studies of irradiation-induced defects and microvoids in vitreous metamict silica

Abstract To study irradiation-induced defects and structural microvoids in vitreous silica (v-SiO2), positron lifetime, angular correlation of positron annihilation radiation (ACAR), and electron spin resonance (ESR) were measured on v-SiO2 and quartz (c-SiO2) samples irradiated with fast neutrons up to a dose of 4.1×1020 n/cm2. Two kinds of positron-trapping defects have been found to form in v-SiO2 by fast neutron irradiation: type-I and type-II defects. Similar defects also appear in the irradiated c-SiO2, indicating that both the defects are common in v-SiO2 and c-SiO2. The detailed annealing and photo-illumination studies of positron annihilation and ESR for these two defects suggest that the type-I defects are non-bridging oxygen hole centers (NBOHC), while the type-II defects are oxygen molecules which cannot be detected by ESR. Higher dose irradiation than 1.0×1020 n/cm2 causes c-SiO2 to change to metamict (amorphous) phase (m-SiO2). Positronium (Ps) atoms are found to form in microvoids with an average radius of about 0.3 nm in the v-SiO2 and m-SiO2. This suggests that microvoids proved by Ps are structurally intrinsic open spaces and reflect the topologically disordered structure of these phases in the subnanometer scale.