Masahito Nawata

Transparent conducting ZnO thin films prepared by XeCl excimer laser ablation

Highly conductive and transparent aluminum- and gallium-doped zinc oxide (ZnO:Al and ZnO:Ga) thin films in place of indium tin oxide films have been prepared by using XeCl excimer laser ablation at relatively low temperatures. The impurity content of Al or Ga in the ZnO target was optimized on the basis of the measurements of resistivity, carrier concentration, and Hall mobility of the deposited transparent conducting ZnO films. The effects of substrate temperature on the properties of ZnO films were investigated. The crystalline, electrical and optical properties of the films were found to depend directly on substrate temperature during deposition. The minimum resistivity of 1.4×10−4 Ω cm was obtained for the ZnO:Al film prepared at a substrate temperature of 300 °C using a ZnO target with an Al2O3 content of 1% by weight (wt %). Moreover, the ZnO:Al film prepared at a substrate temperature of 100 °C showed a low resistivity value of 2.5×10−4 Ω cm. As for the ZnO:Ga film, on the other hand, the minimum r...

Formation of polytetrafluoroethylene thin films by using CO2 laser evaporation and XeCl laser ablation

Laser evaporation and laser ablation methods were applied to the preparation of polytetrafluoroethylene (PTFE) thin films. In the case of the laser evaporation method, PTFE targets were evaporated by a continuous wave (cw) CO2 laser (10.6 μm), and fluorocarbon thin films were formed at a deposition rate of as high as 2 μm/min for a laser power of 10 W. The chemical composition and structure of the deposited film corresponded to those of a PTFE target, which was confirmed by x‐ray photoelectron spectroscopy and Fourier transform infrared absorption spectroscopy analyses. In the laser ablation method, PTFE targets were ablated by a XeCl excimer laser (308 nm). It is found that the deposited films contained a small amount of fluorine atoms on the surface. From these experiments, the successful formation of PTFE thin films was demonstrated for the first time using cw CO2 laser evaporation method.

Formation of Si-based organic thin films with low dielectric constant by using remote plasma enhanced chemical vapor deposition from hexamethyldisiloxane

Abstract New interlayer insulating thin films with low dielectric constant were proposed for multilevel interconnection of ultralarge scale integration circuits. Hexamethyldisiloxane (HMDSO) monomer was used as an organic source and fluorinated Si based organic thin films were prepared by plasma enhanced chemical vapor deposition employing radio frequency inductively coupled plasma (ICP) with CF 4 . Moreover, Si based organic thin films containing benzene rings (phenyl groups) were deposited from a HMDSO/toluene (C 6 H 5 CH 3 ) source mixture employing an O 2 ICP. From Fourier transform infrared spectroscopy, films had methyl-siloxane structure containing Si O Si and Si CH 3 bonds mainly. The dielectric constants of the films deposited from HMDSO/CF 4 and HMDSO/toluene/O 2 at a substrate temperature of 200 °C were 2.9 and 2.8, respectively.

Hydrogen‐radical‐assisted radio‐frequency plasma‐enhanced chemical vapor deposition system for diamond formation

Diamond was successfully synthesized using an improved radio‐frequency (rf) plasma‐enhanced chemical vapor deposition system. In this system, conventional capacitively coupled parallel‐plate rf (13.56 MHz) discharge plasma was assisted by a compact microwave (2.45 GHz) H2 plasma as a remote hydrogen radical source, and substrate heating was carried out using CO2 laser irradiation. Plasma control in rf discharge region for diamond formation was performed using the hydrogen radical source in this system. This was discussed with optical emission spectroscopy. The hydrogen radical source was improved. When water vapor was mixed to the microwave H2 plasma, namely, using water‐vapor‐enhanced hydrogen radical source, diamond films were grown at a low substrate temperature of 450 °C.

Detection of C2 radicals in low-pressure inductively coupled plasma source for diamond chemical vapor deposition

Abstract The C 2 radical density was measured in a low-pressure, radio frequency (rf), inductively coupled plasma (ICP) employing a CH 3 OH/H 2 /H 2 O mixture. Measurement was carried out under the conditions where predominantly diamond can be formed. At the typical growth conditions for the low-pressure, rf ICP reactor used for diamond formation, the C 2 radical density in the ICP region was of the order of 10 13 cm −3 . The correlation between the C 2 radical density and the quality of diamond films was investigated.

Electrical tree at high temperature in XLPE and effect of oxygen

Effect of degassing treatment on tree initiation voltage was investigated in XLPE specimen with semiconducting electrode at 50/spl deg/C and room temperature. 1. Degassing treatment drastically increases tree initiation voltage of XLPE at room temperature. The same result is obtained in LDPE. 2. However, degassing treatment does not so much increase tree initiation voltage of XLPE at 50/spl deg/C, regardless of degassing temperature. This result is different from the result in LDPE, where tree initiation voltage at elevated temperature is increased by degassing treatment at elevated temperature. 3. It is considered that oxygen deeply trapped in or chemically bonded to XLPE polymer structure is released by combination of electric field and thermal stimulation, and participates in tree initiation process.

Low dielectric constant film formation by oxygen-radical polymerization of laser-evaporated siloxane

Polysiloxane thin films were proposed as low dielectric constant interlayer dielectrics for multilevel interconnection of ultralarge scale integration circuits. The films were prepared using oxygen-radical polymerization of siloxane oligomers. A variety of siloxane oligomers were thermally produced by the decomposition of polysiloxane bulk target using CO2 laser irradiation. Oxygen radicals generated by a remote microwave O2 plasma were injected into the vacuum chamber during film deposition. The films deposited with the oxygen radical injection were transformed from polysiloxane to carbon-deficient silicon oxide with increase of substrate temperature as confirmed by x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy analyses. At a CO2 laser power of 10 W, an O2 pressure of 50 mTorr, a microwave power of 100 W, and a substrate temperature of 100 °C, the dielectric constant of the polysiloxane film was 2.0.

Synthesis of Diamond Using RF Magnetron Methanol Plasma Chemical Vapor Deposition Assisted by Hydrogen Radical Injection.

A new plasma chemical vapor deposition (P-CVD) system was developed for synthesis of diamond. This system consisted of a parallel-plate radio frequency (RF) (13.56 MHz) plasma reactor, with a radical source using a microwave (2.45 GHz) discharge plasma and substrate heating using a cw-CO2 laser. In this system, hydrogen (H) radicals were generated in the microwave H2 plasma and preferentially injected near the substrate in the parallel-plate RF magnetron methanol ( CH3OH) plasma region. By scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses, it was found that diamond was successfully synthesized using this system. The effects of H radical on the diamond formation were also investigated from the results of optical emission measurements in the RF plasma region, thin-film deposition and etching of the nondiamond phases by varying amounts of H radical injection.

Diamond Film Formation by OH Radical Injection from Remote Microwave H2/H2O Plasma into Parallel-Plate RF Methanol Plasma

Diamond film was successfully synthesized for the first time using a parallel-plate radio-frequency (RF 13.56 MHz) methanol ( CH3OH) plasma assisted by injection of hydrogen (H) and hydroxyl (OH) radicals generated by microwave H2/ H2O plasma. OH radical, in addition to H radical, injection into RF CH3OH plasma enhanced selective diamond growth and selective etching of the nondiamond phase. The effects of OH radical injection on the initial and growth stages of the diamond formation were investigated by changing H2O partial pressure in the microwave plasma. It was found that OH radical injection into RF CH3OH plasma enhanced the growth of diamond in the initial stage.

Diamond deposition from methanol–hydrogen–water mixed gas using a low pressure, radio frequency, inductively-coupled plasma

Abstract Diamond was successfully synthesized using a low pressure, radio frequency (r.f.), inductively-coupled plasma (ICP). A source mixture of methanol (CH 3 OH), hydrogen (H 2 ), and water vapor (H 2 O) was introduced into the reaction chamber through a quartz tube of 12 mm inner diameter. A seven-turn r.f. coil was mounted on the quartz tube to produce a high-density plasma. The Si substrate was located in a downstream region. Diamond formation was carried out with varying mixture ratios of source gases at total pressures of 9.3–18.6 Pa, an r.f. power of 500 W, a substrate temperature of 700°C, and a substrate bias of +30 V. Diamond crystals exhibiting a well-defined 1332 cm −1 diamond Raman peak were formed using CH 3 OH/H 2 /H 2 O mixtures at total pressures below 19 Pa.