Yuji Kataoka

Transmission electron microscopy study on the crystallization and boron distribution of CoFeB/MgO/CoFeB magnetic tunnel junctions with various capping layers

High-resolution transmission electron microscopy and electron energy-loss spectroscopy (EELS) were used to study the microstructural properties of CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) with various capping layers. Crystallization of CoFeB layers was strongly dependent on the capping materials, and was affected by B diffusion. With NiFe-cap MTJs, CoFeB crystallized from the cap interface and formed a fcc structure; on the other hand, with Ta- and Ti-cap MTJs, CoFeB crystallized from the MgO interface and formed a bcc structure. EELS analysis showed that B mainly diffused to the capping layers and rarely to the MgO layers with increasing temperature. With Ti-cap MTJs, B diffusion caused hcp-Ti crystals to form an amorphous structure and CoFeB crystallized at lower temperature.

Analytical Model for Redistribution Profile of Ion-Implanted Impurities During Solid-Phase Epitaxy

We evaluated the redistribution profiles of ion-implanted impurities during solid-phase epitaxy using Rutherford backscattering spectrometry (RBS). RBS data revealed that the As concentration changes only near the moving amorphous/crystal interface. We derived an analytical model for the redistribution profiles using a segregation coefficient m between amorphous and crystalline Si, introduced a parameter of reaction length l that is the distance where impurities were exchanged, and obtained good agreement with experimental data with an m value of 3 and an l value of 1 nm for As. Furthermore, we applied our model to P and B redistribution profiles and obtained good agreement with corresponding m value of 4 and l value of 1 nm for P and m value of 0.3 and l value of 1 nm for B

High activity of B during solid-phase epitaxy in a pre-amorphized layer formed by Ge ion implantation and deactivation during a subsequent thermal process

We have shown that ion-implanted boron (B) in an amorphous layer formed through Ge ion implantation becomes highly active during solid-phase epitaxy. The activated B concentration reaches about 10/sup 20/ cm/sup -3/ and is almost completely independent of the temperature. This active concentration corresponds to the solid solubility at 900/spl deg/C, hence the B becomes active at levels greater than the solid solubility below this temperature. This activated B was deactivated as a result of the subsequent thermal process in which the diffusion length reached about 10 nm. A low-resistance shallow junction can thus be realized in the low-temperature region provided we end the annealing before the onset of the rise in resistance.

Evaluation of PZT capacitors with Pt/SrRuO3 electrodes for feram

Abstract (Pb, La)(Zr, Ti)O3[PLZT] films were prepared by CSD on sputtered electrodes of Pt/IrO2 on SiO2/Si wafers. Top electrodes consisting of Pt/SrRuO3(SRO) were sputter deposited and the Pt/SRO/PLZT/Pt capacitors were annealed at 600°C. Evaluation of fatigue endurance revealed that more than 6% excess Pb was necessary to produce a fatigue free capacitor. However, the FeCap leakage current increased in proportion to the film excess Pb content. SIMS analysis of the FeCap containing 10% excess Pb revealed that Sr from the 70 nm thick SRO electrode diffused into the PLZT film to the bottom electrode during the anneal resulting in high leakage. FeCap leakage current was greatly reduced by decreasing the PLZT film excess Pb content and SRO film thickness. SRO electrodes with thicknesses of 5 and 15 nm were found to be sufficient to produce a capacitor with high fatigue endurance and little static imprint. These results indicate that the PLZT leakage current was greatly influenced by the Sr interdiffusion and...

Surprisingly large apparent profile shifts of As and Sb markers in Si bombarded with ultra-low-energy Cs ion beams

Shallow arsenic implantation distributions and narrowly spaced antimony delta markers in silicon were used to explore near-surface changes of the sputtering yield under ultra-low-energy Cs + bombardment (0.25-1 keV) at impact angles 0 between 0° (normal incidence) and 60°, i.e. below the critical angle for ripple formation. In all cases, the profiles were found to be shifted towards the surface, with shifts ranging from about 1 nm (250 eV, 0-15°) up to 4 nm ( 1 keV, 0°). These artefacts are attributed to unexpectedly high sputtering yields during Cs build-up in silicon. In most cases, the yields became stationary at sputtered depths of less than 5 nm. Using the mean erosion rate between 0 and 5 nm and the stationary rate above 5 nm to define sputtering yields, the initial yield enhancement η = / Y∞ for 1 kev Cs + was found to be as large as 3.2 at 15°, decreasing to about 1.6 at 60°. Between 30 and 60° the η-values for 250 and 500 eV were only slightly less than at 1 keV. Significantly lower values derived at angles 0 < 30° are probably due to the fact that the respective transition depths are significantly smaller than 5 nm. The results imply that depth profiles previously observed under the conditions of this study suffer from serious depth calibration errors.

Monte Carlo Simulation of Ion Implantation Profiles Calibrated for Various Ions over Wide Energy Range

Monte Carlo simulation is widely used for predicting ion implantation profiles in amorphous targets. Here, we compared Monte Carlo simulation results with a vast database of ion implantation secondary ion mass spectrometry (SIMS), and showed that the Monte Carlo data sometimes deviated from the experimental data. We modified the electron stopping power model, calibrated its parameters, and reproduced most of the database. We also demonstrated that Monte Carlo simulation can accurately predict profiles in a low energy range of around 1 keV once it is calibrated in the higher energy region.

Direct Observation of Atomic Ordering and Interface Structure in Co2MnSi/MgO/Co2MnSi Magnetic Tunnel Junctions by High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy

The atomic ordering of Co2MnSi (CMS) full-Heusler film and the interface structure of CMS/MgO/CMS magnetic tunnel junctions (MTJs) were investigated by high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM). We observed the atomic ordering of L21 and B2 structures of CMS from the atomic number (Z) contrast STEM images. We also confirmed that the interface structure consists of the layer next to the Co layer terminating in the CMS to MgO layer from the layer periodicity along the [001] direction, however, site-disorder exists between two atomic layers at the termination of CMS, including locally L21-ordered MnSi terminated structure.

Compact model for amorphous layer thickness formed by ion implantation over wide ion implantation conditions

In this paper, a through dose parameter /spl Phi//sub a/c/, which is defined by the dose of ions passing through the amorphous/crystal (a/c) interface, is proposed, and the use of /spl Phi//sub a/c/ combined with parameters for ion-implantation profiles to model the thickness of the amorphous layer d/sub a/ is demonstrated. It is shown that /spl Phi//sub a/c/ is independent of ion-implantation conditions but depends on the impurities. /spl Phi//sub a/c/ for Ge, Si, As, P, B, In, and Sb is evaluated. Consequently, d/sub a/ over a wide range of ion-implantation conditions for various ions was predicted.

Quantitative analysis of nitrogen in oxynitrides on silicon by MCs+ secondary ion mass spectrometry?

The use of MCs+ secondary ion mass spectrometry for quantitative analysis of nitrogen in oxynitride layers on silicon was studied using Cs+ primary ions at energies between 250 eV and 1 keV and impact angles between 0° (normal incidence) and 80°. To achieve constant signal levels in the SiO2 layer, the oxide was chosen to be comparatively thick (4.9 nm). Due to differences in cesium surface coverage, the yields of the reference species Cs+ and SiCs+ varied with depth by up to three orders of magnitude, depending on the beam energy and the angle of incidence. Large differences in ion formation probability by up to a factor of 10 became evident from angular dependent changes of the OCs+/SiCs+ signal ratio in the oxide. Based on the observation that the depth dependent variations of the Cs+ and the SiCs+ signals are quite similar, attempts were made to rationalize the SiCs+ and OCs+ yields by normalizing to the Cs+ yields and the apparent target current. By way of scaling the NCs+ signals to the normalized O...

Analysis of EEL spectrum of low-loss region using the Cs-corrected STEM–EELS method and multivariate analysis

We analyzed a Si/SiO(2) interface using multivariate analysis and spherical aberration-corrected scanning transmission electron microscopy-electron energy loss spectroscopy which is characterized by using the electron energy loss spectrum of the low-loss region. We extracted the low-loss spectra of Si, SiO(2) and an interface state. Even if the interface is formed from materials with different dielectric functions, the present method will prove suitable for obtaining a more quantitative understanding of the dielectric characteristic.