Materials Science Forum Vols. 449-452

Abstract: The ionic valence of Ti changed with electrorefining process of Ti in a bath equi-molar mixture of NaCl-KCl containing TiCl_n (n=2 or 3); The average valence was about 2.3 initially, and became about 2.1 after electrolysis. The cathodic current efficiency was getting better with electrolysis. It should be necessary to maintain the average ionic valence lower for efficient electrolysis in the molten salt. The dominant Ti ion and its electrode reaction changed with the addition of NaF-KF in the molten salt; The average valence shifted from about 2 to about 3, and the total amount of Ti in the bath decreased. The result indicates the disproportionation reaction: 3Ti²⁺ = Ti + 2Ti³⁺ is induced by the fluoride addition. The quantity of electricity for Ti deposition changed consequently, and the purity of the Ti deposit was also affected.

Abstract: Copper (Cu) thin films have been deposited onto titanium nitride (TiN) layer which was previously prepared by flow modulation chemical vapor deposition (FMCVD technology. The diffusion barrier properties of the TiN layer to Cu have been studied depending upon the post-annealing and the sample preparation conditions of the TiN layer. The Cu deposition has performed by RF magnetron sputtering with 5N target in the high vacuum ambient. The FMCVD process has carried out in a single CVD chamber by switching TiCl₄ flow to the argon flow cyclically, which creates sequential deposition of TiN layer and chlorine reduction process. The higher flow modulation cycle and Ar purge time during the TiN layer growth have been observed to provide the better diffusion barrier property in Auger depth profile and X-ray diffraction analysis.

Abstract: We would like to report on the development of our new ultra fine crystalline CVD diamond film and some applications. CVD Diamond films have good wear resistance, but the crystal size is too large. Therefore, in case of application of diamond films for cutting tools, we cannot get fine surface finish on work materials. Recently we succeed in production ultra fine crystalline CVD diamond film and various cutting tools as taps, drills and end mills. Aluminum alloys have lately been consumed more than ever in airplanes and automobiles for the purpose of decreasing the weight of structural materials.Copper alloys are used for the electrode of electric discharge machines (EDM) recently. EDM electrodes are required fine surface finish because the surface quality of mold depends on accuracy of EDM electrodes. Soft materials such as aluminum and copper alloys have high viscosity and additionally activity. So during cutting aluminum and copper alloys we have sometimes adhesion between cutting tools and work pieces. Diamond film on tools is able to improve the reactivity to aluminum and copper alloys. But up to now the diamond film has a lot of course crystal and tend to supply rough surface finish on work pieces. We developed ultra fine crystalline diamond film on end mills by plasma chemical vapor deposition (CVD) method. Now our aircraft, automotive and molding customers can get smooth surface finish of work pieces.Keeping ISO14001, we recommend oil free cutting with ultra fine crystalline diamond coated cutting tools. Here I introduce background of the development and cutting examples with new fine diamond coated end mills.

Abstract: c-BN film was synthesized using ME-ARE on Si substrate. The deposition process was optimized via the Taguchi method. The optimized conditions were as follows: substrate temperature, anode (plasma) current, Ar/N2 ratio, pulse frequency, duty frequency, bias voltage and deposition time were 500°C, 15A, 3, 1 kHz, 50%, -130V and 15 min, respectively. The crosssectional TEM observation revealed that the c-BN films with a thickness of 100nm ~300nm were composed of two layers, a columnar h-BN layer with a thickness of 30nm~40 nm normal to Si substrate and a c-BN structure.

Abstract: Indium-zinc oxide (IZO), with Zn/(Zn+In)=0.33 - 0.78, films were deposited by the sol-gel method. Effects of Zn/(Zn+In) atomic ratio and annealing temperature on the structural, electrical and optical properties of IZO thin film were investigated. Films of Zn/(Zn+In)=0.33 prepared at 600°C had the lowest resistivity value, 4.48X10 ^-2 Ω cm (carrier concentration=3.83X 10¹⁸ cm^-3 and mobility=25.54 cm2/Vs), and the structure of these films matched that of Zn₂In₂O₅ film. Average optical transmittances of all films were above 80% in the visible range. The highest average transmittance was observed at Zn/(Zn+In)=0.5, with 86.8% in the visible range.

Abstract: The characteristics of plasma are important for the deposition of SiOC(-H) low dielectric thin film. The effect of UV light illumination on the plasma parameter in the capacitive coupled plasma chemical vapor deposition (CCP-CVD) system is investigated. The electron density is almost not changed, but the electron temperature decreases by UV light illumination. The deposition rate increases and the dielectric constant of the film is lowered with UV light.

Abstract: Ferroelectric characteristics of the 400 nm-thick Sr_xBi_2.4Ta₂O₉(0.7≤x≤1.3) thin films processed by metalorganic decomposition were investigated, and electrical properties of the Pt/Sr_0.85Bi_2.4Ta₂O₉/TiO₂/Si structure prepared using TiO₂ buffer layer were characterized. The Sr-deficient Sr_xBi_2.4Ta₂O₉ films exhibited well-developed ferroelectric hysteresis curves compared to those of the Sr-excess films. The Sr0.85Bi2.4Ta2O9 film exhibited optimum ferroelectric properties, such as high remanent polarization and low leakage current density, among Sr_xBi_2.4Ta₂O₉ films. A memory window of the Pt/SrxBi2.4Ta2O9/TiO2/Si structure was dependent upon the coercive field of the Sr_xBi_2.4Ta₂O₉ film, and the Pt/Sr_xBi_2.4Ta₂O₉/TiO₂/Si exhibited a maximum memory window of 1.3 V at the sweeping voltage of ±5 V.

Abstract: ITO films were deposited on the Corning 1737 glass by the RF-magnetron sputtering method with and without external heating as a function of deposition time. The as-grown ITO film, deposited on room temperature substrate without external heating for 10 min, was amorphous in nature. Continuous deposition over 20 min resulted in the development of crystallization of the films. The crystallization by prolonged deposition was initiated from the top surface of the film where energetic ions bombard. When the films were deposited with external heating, the crystallization was initiated from the beginning of the deposition at the surface of the substrate.

Abstract: We investigated the effects of hydrogen annealing process on ferroelectricity in SrBi₂Ta₂O₉(SBT) capacitors. The hydrogen-induced degradation of SBT capacitors was found after a hydrogen annealing process. The degraded properties could be recovered by re-crystallization annealing process in O₂ ambient for 30 min. In order to prevent the catalyst reaction of Pt electrode known as an origin of hydrogen-induced degradation, Au top electrode was used. It was confirmed that Au electrode effectively prevented capacitors from degrading during hydrogen process.