Hiroaki Nishikawa

Heteroepitaxy of perovskite-type oxides on oxygen-annealed SrTiO3(1 0 0). Important factors for preparation of atomically flat oxide thin films

Abstract Thin film growth of perovskite-type oxides, CaTiO 3 and La 0.7 Sr 0.3 MnO 3 , on atomically smooth SrTiO 3 (1 0 0) substrate has been studied by in-situ reflection high-energy electron diffraction (RHEED) and ex-situ atomic force microscope (AFM) in order to understand the key points to keep the surface flatness. It is found out that the termination of substrate surface by AO layer of perovskite structure (ABO 3 ), i.e., CaO, SrO and BaO, is quite effective to prepare the atomically flat thin films. Among these top layers, the SrO termination gives the best result. CaTiO 3 film on SrTiO 3 (1 0 0) can keep the atomically flat surface in spite of large lattice mismatch (∼ 2.3%), while La 0.7 Sr 0.3 MnO 3 needs more strict lattice matching to keep the flat surface. Structure and orientation of SrO are analyzed by only in-situ RHEED observation as the first step of real-time growth control. Furthermore, the migration process of Sr supplied by laser ablation is studied by time-resolved measurement of RHEED intensity. The growth process of thin film by laser ablation method is discussed with this experiment.

Cobalt(III) Complexes with N,N′-Ethylene-bis(salicylideneaminate) and a Related Quadridentate Ligand

Abstract Numerous six-coordinate cobalt(III) complexes with N,N′-ethylene-bis(salicylideneaminate) and N,N′-ethylene-bis [2-hydroxynaphthyl (1) -methyleneaminate], abbreviated as salen and nalen, respectively, have been synthesized and characterized. The complexes prepared are of the types [Co(salen)L2]X, MI [CoX2(salen)], [CoX(salen)H2O], [Co(nalen)L2] and [CoX(nalen)L], where X and L denote a univalent anion and a neutral unidentate li-gand, respectively. All these complexes are diamagne-tic and trans-six-coordinate.

Basic Study on Etching Selectivity of Plasma Chemical Vaporization Machining by Introducing Crystallographic Damage into Work Surface

Plasma chemical vaporization machining (PCVM) is a high-speed plasma etching method using atmospheric-pressure plasma. Although it does not leave an affected layer on the processed surface because of the small ion energy owing to the small mean free path of gas molecules, it is not suitable for planarization because of its isotropic etching. Thus, a combination of PCVM and a mechanical machining process is proposed. The convex parts of a substrate surface are considered to be affected by mechanical machining and are removed preferentially by PCVM. In this report, it is investigated whether etching rate of the affected layer becomes larger or not. As a result, it was found that the etching rate increased in the first 100 nm depth of the mechanically polished substrate, which corresponds to the thickness of the heavily damaged layer observed by cross-sectional transmission electron microscopy.

Plasma Chemical Vaporization Machining of Silicon Carbide Wafer Using Flat-Bar Electrode with Multiple Gas Nozzles

Silicon carbide (SiC) power devices have received much attention in recent years because they enable the fabrication of devices with a low power consumption. To reduce the on-resistance in vertical power transistors, backside thinning is required after device processing. However, it is difficult to thin a SiC wafer with a high removal rate by conventional mechanical machining because its high hardness and brittleness cause cracking and chipping during thinning. We have attempted to thin a SiC wafer by plasma chemical vaporization machining (PCVM), which is plasma etching using atmospheric-pressure plasma. In this paper, we describe a machining property using a newly developed flat-bar electrode with multiple gas nozzles for thinning a SiC wafer.

Dicing of SiC Wafer by Atmospheric-Pressure Plasma Etching Process with Slit Mask for Plasma Confinement

Silicon carbide (SiC) is a promising semiconductor material for high-temperature, high-frequency, high-power, and energy-saving applications. However, because of the hardness and chemical stability of SiC, few conventional machining methods can handle this material efficiently. A plasma chemical vaporization machining (PCVM) technique is an atmospheric-pressure plasma etching process. We previously proposed a novel style of PCVM dicing using slit apertures for plasma confinement, which in principle can achieve both a high removal rate and small kerf loss, and demonstration experiments were performed using a silicon wafer as a sample. In this research, some basic experiments were performed using 4H-SiC wafer as a sample, and a maximum removal rate of approximately 10 μm/min and a narrowest groove width of 25 μm were achieved. We also found that argon can be used for plasma generation instead of expensive helium gas.

Thinning of a Two-Inch Silicon Carbide Wafer by Plasma Chemical Vaporization Machining Using a Slit Electrode

In recent years, silicon (Si) has been mainly used in power devices, but the limit of its performance is being reached. Therefore, silicon carbide (SiC) power devices have been attracting attention because they enable the fabrication of devices with low power consumption. To reduce the on-resistance in vertical power transistors, backside thinning is required after device processing. However, it is difficult to thin a SiC wafer with a high removal rate by conventional mechanical processing because its high hardness and brittleness cause cracking and chipping during thinning. Therefore, we have attempted to thin a SiC wafer using plasma chemical vaporization machining (PCVM), which is plasma etching using atmospheric-pressure plasma. In this study, we describe a machining property using a newly developed slit electrode that is composed of two parts and has a slit that allows for a new gas to pass.

A data-driven execution control scheme and its experimental study

The authors have proposed a high-level parallel processing system representing the data-drive principle (including history-sensitive processing by diagrammatical language) and have been investigating its realization. Realization of high-level processing by the data-driven principle requires a load and function distribution scheme to secure the smooth data flow corresponding to the input stream into the system. Together with the results of experiment, this paper describes a systematic control scheme for load and function distribution of the data-driven execution function through the construction of clusters adapted to the hierarchical diagrammatical program structure. In other words, the proposed system realizes the data-driven execution functions of the hierarchical system by an iterative structure composed of fundamental functions, namely input-output, function processing, history-sensitive processing and firing control. This paper first describes the load and function distribution scheme for the fundamental function in the data-driven execution control. Then, using an experimental system with common-bus multiprocessor structure, it is shown that the proposed system is useful in realizing high-level parallel processing. Lastly, based on the geometrical connection structure of the diagrammatical program, a semiquantitative guideline is presented for the distributed assignment of fundamental functions in the hierarchical cluster structure.

Basic Experiment on Atmospheric-Pressure Plasma Etching with Slit Aperture for High-Efficiency Dicing of SiC Wafer

Silicon carbide (SiC) is a promising semiconductor material for high-temperature, high-frequency, high-power, and energy-saving applications. However, because the hardness and chemical stability of SiC are high, few conventional machining methods can handle this material efficiently. We previously developed a plasma chemical vaporization machining (PCVM) technique, which is an atmospheric-pressure plasma etching process, and investigated its application to the processing of SiC substrates. In this paper, we propose a novel style of PCVM technique for dicing, using slit apertures to confine the plasma. From experiments by means of an apparatus with a one-slit aperture formed by two masks, it was found that the kerf loss was almost proportional to the slit width, and that the etching depth increased with RF power. Furthermore, from experiments on a SiC wafer, we obtained a 130-μm etching depth and 300-μm kerf loss for an 11-min processing time and 200-μm slit width.

Back-Side Thinning of Silicon Carbide Wafer by Plasma Etching Using Atmospheric-Pressure Plasma

Silicon carbide (SiC) power devices have received much attention in recent years because they enable the fabrication of devices with low power consumption. To reduce the on-resistance in vertical power transistors, back-side thinning is required after device processing. However, it is difficult to thin a SiC wafer with a high removal rate by conventional mechanical machining because its high hardness and brittleness cause cracking and chipping during thinning. In this study, we attempted to thin a SiC wafer by plasma chemical vaporization machining (PCVM), which is plasma etching using atmospheric-pressure plasma. The wafer level thinning of a 2-inch 4H-SiC wafer has been possible without a removal thickness distribution caused by the circular shape of the wafer using the newly developed PCVM apparatus for back-side thinning with a spatial wafer stage.

Co-Ordination Chemistry of Metal Complexes of Salicylideneimines and β-Ketoimines

Co(II), Ni(II), Cu(II), Pd(II) and Pt(II) complexes of N-substituted salicylideneimines [I] and β-ketoimines [II], including a number of new compounds, have been prepared and their configuration examined mostly on the basis of their electronic spectra. The main results of the examination, which are summarized as follows, are understood in terms of the nature of the metalligand bond and of the electronic structure of the metal ions.