Kenichi Uemura

Bi‐Functional Oxygen Electrode Using Large Surface Area La1 − x Ca x CoO3 for Rechargeable Metal‐Air Battery

In order to develop an air electrode to be used for rechargeable metal‐air batteries, gas‐diffusion type carbon‐based electrodes have been tested for the electrochemical reduction and evolution of oxygen. The electrode, loaded with a large surface area of catalyst was found to show high bifunctional performance, i.e., 3000 mA/cm2 (oxygen reduction) and 1000 mA/cm2 (oxygen evolution) at −125 and +700 mV vs. , respectively, in 30 w/o at 25°C. The oxide catalyst is considered to decompose effectively , an intermediate appearing in both oxygen reduction and oxygen evolution reactions. The air electrode was stable for 100 cycles of charge‐discharge test at a current density of 100 mA/cm2.

Adsorption Species of Transition Metal Ions on Silicon Wafer in SC‐1 Solution

Adsorption of transition metal ions such as Fe(III), Ni(II), and Zn(II) on silicon wafers in ammoniac hydrogen peroxide solution (SC-1 solution) has been studied. It was found by comparing the experimental results with the equilibrium calculations that the main adsorption species is the dissolved neutral hydroxide complex. This was supported by the calculated free energy change of adsorption of hydroxide complexes.

Error factors in quantitative total reflection x-ray fluorescence analysis

This paper reviews and discusses the error factors in quantitative total reflection x-ray fluorescence analysis, primarily with regard to the surface contamination of silicon wafers. The error factors were classified into three origins: instrumental, sample and data processing. The instrumental error factors originate from source x-ray stability, accuracy of the mechanical glancing angle, position accuracy of sample stage and spurious peaks from the detection system. The sample error factors arise from lateral and depth distribution of the analyte, surface roughness and diffraction of the primary x-rays. The data processing error factors are from interfering peaks and background definition. The accuracy and detection limit are affected by all the error sources listed above. Of these factors, the depth distribution of the analyte is the most important, because this factor is often overlooked and because it is difficult to control. Copyright

A depth profile fitting model for a commercial total reflection X-ray fluorescence spectrometer

Abstract We have proposed a practical depth profiling model for a commercial Total Reflection X-Ray Fluorescence (TXRF) spectrometry instrument. The model includes three factors peculiar to a commercial TXRF instrument: (a) the irradiated X-ray photon density on the sample surface depends on a glancing angle, (b) the X-ray irradiated area becomes smaller than the detector view over a certain glancing angle, and (c) the incident X-ray has angular divergence. This model was optimized by comparing the measured Si-Kα for a silicon wafer with the calculated one. The results indicated that all of the three factors are indispensable for our instrument. We have applied this model to a surface contaminant and discussed its adequacy.

A method of locating dried residue on a semiconductor wafer in vapor phase decomposition-total-reflection X-ray fluorescence spectrometry by monitoring scattered X-rays

Abstract Vapor phase decomposition-total-reflection X-ray fluorescence spectrometry (VPD-TXRF) is used in the analysis of whole-surface trace metal contamination on silicon wafers at a very high sensitivity. In VPD-TXRF, locating the exact position of dried residue is critical for obtaining a reliable analysis. To locate the residue, the fluorescence from the internal element added as standard reference for quantification is most commonly used as a search marker. However, the added internal standard reference sometimes interferes with the determination of analytes. To avoid such interference, we introduce a new method of locating the residue that utilizes the scattered X-rays from it. Basic experiments have shown that scattered X-rays can be used as markers of residue position instead of the fluorescence from an internal standard reference. An x – y –θ-controlled stage has been proven to be preferable in the application of this locating method than an r –θ-controlled stage. The repeatability of our method is the same as that of the conventional internal standard reference method. There are many advantages in our new method: no interference with analytes of interest, speed, and ease of application. In addition, the method is compatible with the conventional internal standard reference method.

Total-reflection X-ray fluorescence analysis for semiconductor process characterization

Abstract Semiconductor process characterization techniques based on total-reflection X-ray fluorescence (TXRF) analysis are reviewed and discussed. One of the most critical factors in obtaining reliable determinations by TXRF is the reliability of the standard samples that are used. Conventional physisorption standard samples such as spin coat wafers have two potential drawbacks: reproducibility of depth profile and stability. A method of chemisorption called ‘immersion in alkaline hydrogen peroxide solution (IAP)’ was proposed that provides answers to these two problems. IAP standard samples were used to experimentally examine three methods of TXRF application: Straight-TXRF, VPD-TXRF, and Sweeping-TXRF. In the application of Straight-TXRF, the linearity of Cu at a level of 10 9 atoms cm −2 is examined. In the application of VPD-TXRF, test results of VPD-TXRF for both transition metals and light elements are shown. Finally, a new measurement protocol called Sweeping-TXRF is proposed to conduct whole-surface analysis without chemical preconcentration.