Yoon-Kee Kim

Effects of argon and oxygen addition to the CH4-H2 feed gas on diamond synthesis by microwave plasma enhanced chemical vapor deposition

In order to investigate the effects of argon and oxygen on diamond synthesis, the behaviors of diamond deposition using microwave plasma chemical vapor deposition method have been studied by varying the concentrations of argon and oxygen in the methane-hydrogen gas mixture. Diamond films were deposited on silicon wafer under the conditions of substrate temperatures: 1073 ∼ 1173 K, total reaction pressure: 5333 Pa (40 Torr), methane concentrations: 0.5 ∼ 5.0%, and they were characterized by scanning electron microscopy, Raman spectroscopy and optical emission spectroscopy. The deposition rates of diamond films were enhanced by adding argon into the methane-hydrogen system, but nondiamond carbon phases in the films also increased. It resulted from the increase of hydrocarbon radicals in the plasma. As oxygen was added, the quality of deposited diamond films was improved due to the decrease of C2 radicals and increase of OH radicals in the plasma. Simultaneous addition of 0.3% oxygen and 20% argon has been able to effectively suppress the formation of nondiamond carbon components and increase the deposition rate of diamond films. It appears that the ionized argon (Ar+) and excited argon atoms (Ar*) may activate the various chemical species and promote the reactions between the gas phase species and oxygen in the plasma.

The effects of a negative bias on the nucleation of oriented diamond on Si

Abstract The highly oriented diamond film was deposited on Si(001) substrate using the bias enhanced nucleation (BEN) proceeded at −250 V for 10 min in 3%CH4/H2 plasma at substrate temperature 750°C. The {111} X-ray pole figure of the oriented diamond film with a thickness of ca 5 μm is clearly dominated by the four {111} peaks of diamond. The full width at half maximum of the peaks in azimuth rotation and tilt are below 9 and 10°, respectively. Negative bias effects on heteroepitaxial nucleation of diamond have been investigated. It is found that the heteroepitaxial SiC was formed on the Si substrate and the high dose (ca 4 × 1016per cm2s−1) of positive ions bombarded the substrate during the bias treatment. In previous work, it was also found that the concentrations of activated atomic hydrogen and carbonaceous radical in the dense plasma were increased by negative bias. From the results, we try to combine the information based on surface and bulk analytical data and that based on the plasma analysis during the BEN process in order to explain the oriented nucleation of diamond on the Si substrate. It is suggested that the heteroepitaxial diamond can be obtained by the combination of forming heteroepitaxial SiC on the Si substrate, selective etching of Si in the SiC network, filling the vacant Si sites by carbonaceous ions, adding hydrocarbon radicals to the oriented sp3 bond carbon clusters and etching non-diamond carbon components and misoriented sp3 bond carbon clusters during the BEN process.

Formation of highly oriented diamond film on (100) silicon

Highly oriented diamond particles are deposited on mirror-polished (100) silicon substrates in a bell-jar-type microwave plasma deposition system using a three-step process consisting of carburization, bias-enhanced nucleation and growth. By adjusting the geometry of the substrate and substrate holder, very dense disk-shaped plasma is formed over the substrate when the bias voltage is below −200 V. This dense plasma is a prerequisite for the high orientation and is not obtained simply by increasing microwave power, but is obtained by introducing a graphite block between the substrate and the substrate holder. The plasma is concentrated over the substrate with a thickness of several millimeters. From the results of the optical emission spectra of the disk-shaped dense plasma, it is found that the concentrations of atomic hydrogen and hydrocarbon radicals are increased with negative bias voltage. It is also found that the highly oriented diamonds are deposited in the region, where the intensity ratios of ca...

The effect of SiC codeposition on the oxidation behavior of carbon/carbon composites prepared by chemical vapor deposition

Abstract The effects of SiC codeposition on the oxidation kinetics and oxidized surface morphology of carbon/carbon composites prepared by chemical vapor deposition have been investigated in the temperature range 600 to 1350°C in air. The oxidation rate of SiC-codeposited C/C composites is slower than that of SiC-free C/C composites below 800°C. However, the C/C composites have nearly the same apparent activation energies for oxidation, regardless of SiC codeposition. It is suggested that SiC particles in C/C composites affect the growth of oxidized pits, not the oxidation mechanism of the composites. The SiC particles are unable to act as an oxygen diffusion barrier, so the oxidation of C/C composites is not retarded by SiC particles above 800°C. SiC particles react with oxygen to produce glassy SiO2 and join to form a skeleton of the initial fiber mat after full oxidation above 1000°C.

Texture-controlled diamond films synthesized by microwave plasma-enhanced chemical vapour deposition

Abstract Texture-controlled diamond films are deposited on silicon wafers in a CH4-H2 gas mixture using microwave plasma-enhanced chemical vapour deposition and the quality of the textured films has been investigated using Raman spectroscopy. It is found that the quality of the (100) textured film is better than those of (110) or (111) textured films. The transition of the textures and the growth rates of the diamond film are observed with changing deposition parameters such as the substrate temperature (700–950 °C), total reaction pressure (1333–8000 Pa), methane concentration (0.5–5%) and microwave power (500–1300 W). As the texture of diamond films is changed from 〈100〉 to 〈111〉 or others, the full width at half maximum and I G I D ratio obtained from Raman scattering are increased. It is found that the growth rate of (100) textured film is more sensitive to the parameters of substrate temperature, pressure and methane concentration than microwave power. The growth rate of the (100) textured film is increased with increasing substrate temperature, pressure or methane concentration, and the quality of the (100) textured film is increased with decreasing growth rate. The optimum growth rate maintaining the (100) texture is about 0.6 μm h−1, and its deposition conditions are as follows: substrate temperature, 800 °C; pressure, 4 000 Pa (30 Torr); methane concentration, 2%; microwave power, 1 000 W.

Deposition of heteroepitaxial diamond film on (100) silicon in the dense plasma

Almost perfectly oriented heteroepitaxial diamond film was deposited on the (100)Si substrate by the carburization, bias‐enhanced nucleation, and growth process in a dense plasma using a bell‐jar‐type microwave‐plasma chemical vapor deposition (CVD) system with an ASTeX 1.5 kW magnetron plasma source. This dense plasma was a prerequisite for the perfect orientation and was not obtained simply by increasing microwave power, but was obtained by introducing a graphite block between the substrate and the substrate holder. The plasma was concentrated over the substrate especially at the four corners with a thickness of several millimeters.

Thermal stability and brazing characteristics of Zr–Be binary amorphous filler metals for zirconium alloy

The thermal stability and brazing characteristics of Zr–Be binary amorphous alloys as a new filler metal for joining zirconium alloy were investigated in order to supersede physically vapor-deposited (PVD) beryllium used conventionally with many disadvantages. The Zr1−xBex (0.3≤x≤0.5) binary amorphous alloys were produced by melt-spinning method. In the selected composition range the Zr–Be amorphous alloys have two crystallization modes which are dependent on beryllium content in alloys. The temperatures and activation energies for crystallization depend on crystallization-mode as well as beryllium content. These amorphous alloys were put into practical use in joining bearing pads on zircaloy cladding sheath. Using Zr–Be amorphous alloys as filler metals, the reduction in thickness of cladding sheath wall are prevented. Especially, in the case of using Zr0.65Be0.35 and Zr0.7Be0.3 amorphous alloys, smooth interface and spherical primary α-Zr particles appear in the brazed layer, which is desirable microstructure in the view of the corrosion–resistance.

The effects of oxygen on diamond synthesis by hot-filament chemical vapor deposition

The effects of oxygen addition on the synthesis of diamond are extensively studied by using the hot-filament chemical vapor deposition (HFCVD) method, in which it is simple and easy to control the deposition parameters independently. Diamond films are deposited on silicon wafers under the conditions of substrate temperature 530–950 ‡C; total reaction pressure 700–8000 Pa; and methane concentration 0.4–2.4% in both CH4–H2 and CH4–H2–O2 systems.At deposition conditions of low substrate temperature, high CH4 concentration or high total pressure, soot-like carbon and/or graphite are deposited without oxygen addition. When even a small amount of oxygen (about 0.6%) is added, well-faceted diamond films are observed in scanning electron microscopy micrographs and a sharp diamond peak in the Raman spectra appears. The range of deposition parameters for high-quality diamond syntheses are extended by oxygen addition (low substrate temperature, high methane concentration and high reaction pressure).

The effect of Bi2O3 on the microstructure and electrical conductivity of ZrO2-Y2O3 ceramics

ZrO2-Y2O3 ceramics with varying Bi2O3 contents were prepared and their microstructures and electrical conductivities investigated. The phase stability of cubic fluorite zirconia was disturbed by the introduction of Bi2O3 and tetragonal or monoclinic second phases appeared. The effect of the second phases on the intragrain and the grain boundary conductivities was investigated in the 300–550 ‡C range using complex plane analysis in the frequency range of 5 Hz to 13 MHz. It showed that conductivity data could readily be interpreted in terms of possible physical models and electrical equivalent circuits. Tetragonal phases had a small positive influence on the intragrain conductivity. The grain 9boundary resistivity could be diminished by discrete monoclinic second phases which offered more conductive intergranular contacts.

Nucleation of highly oriented diamond on silicon

Highly oriented diamond particles were deposited on the mirror-polished (100) silicon substrates in the belljar type microwave plasma deposition system. The diamond films were deposited by a three-step process consisting of carburization, bias-enhanced nucleation and growth. The bias-enhanced nucleation was performed under the deposition conditions such as 2-3% of methane concentration in hydrogen, 1333-2666 Pa of total pressure, the negative bias voltage below 200V and the substrate temperature of 1073 K. By adjusting the geometry of the substrate and substrate holder, very dense disc-shaped plasma was formed on the substrate when the bias voltage was below 200V. As characterized by transmission electron microscopy (TEM), almost perfectly oriented diamond particles were obtained only in this dense plasma. From the results of the optical emission spectra of disc-shaped dense plasma, it was found that the concentrations of atomic hydrogen and hydrocarbon radicals were increased with negative bias voltage. As a result, it was suggested that the highly oriented diamonds were obtained by the combination of the high dose of hydrocarbon radicals and the increased hydrogen etching effects.