Tadashi Sonobe

Chemical Vapor Deposition of a-SiGe:H Films Utilizing a Microwave-Excited Plasma

Hydrogenated amorphous silicon-germanium films were prepared by a chemical vapor deposition method utilizing a microwave-excited plasma produced at low gas pressures (~10-3 Torr). Deposition methods in which SiH4 and GeH4 were decomposed by a plasma stream of Ar or hydrogen or by direct excitation were examined at 200°C and at the pressures optimized for the preparation of hydrogenerated amorphous silicon films. Highly photoconductive narrow gap films (an optical gap of 1.5 eV) with photoconductivity higher than 10-5 S/cm and photosensitivity of about 104 were obtained by these methods, keeping a high deposition rate.

Microwave-Excited Plasma CVD of a-Si:H Films Utilizing a Hydrogen Plasma Stream or by Direct Excitation of Silane

The microwave-excited plasma CVD of a-Si:H films, in which SiH4 was decomposed by a plasma stream of hydrogen or by direct excitation at low gas pressures (10-4 to 10-3 Torr), was examined and compared with a previously studied Ar plasma stream method. It was clarified that an Ar plasma stream was not necessary to obtain highly photoconductive a-Si:H films. However, the deposition characteristics in these deposition methods were different from the Ar plasma stream method. On the other hand, the influence of the hydrogen plasma stream was not apparent when the SiH4 flow rate was high, suggesting an ionization cross-section dependence of the plasma discharge.

Effects of Excited Plasma Species on Silicon Oxide Films Formed by Microwave Plasma CVD

By using a microwave plasma deposition system, effects of highly excited plasma species on the film formation of silicon oxide have been studied and the roles of excited ion and radical species have been investigated by emission spectra of the excited plasma species. A strong correlation was confirmed between film quality and the amount of highly excited ion species transported to the substrate. Furthermore, high quality films could be formed by increasing the amount of the excited species.

Chemical Vapor Deposition of a-Si:H Films Utilizing a Microwave Excited Ar Plasma Stream

A Microwave-excited Ar-plasma stream produced at low gas pressures (10-4 to 10-2 Torr) was applied to a preparation of hydrogenated amorphous silicon films made from SiH4. The electric and optical properties of the films were investigated as functions of the deposition conditions. The film properties greatly depended upon the substrate temperature and the deposition pressure and slightly upon the microwave power. The conductivity of the films prepared at 200°C and at pressures ranging between 0.6 and 0.8 mTorr were about 5×10-10 Scm-1 in the dark and 4×10-4 Scm-1 under AM 1.5 illumination. The films prepared at the lower pressures were porous and contain a large amount of gases; the films prepared at higher pressures were deteriorated in the same way as those prepared by an RF glow discharge from Ar-diluted SiH4.

Effects of Applied Magnetic Fields on Silicon Oxide Films Formed by Microwave Plasma CVD

By using a microwave plasma deposition system in which distributions of applied magnetic fields can be varied, the effects of the ECR position and plasma species on deposition rate and deposited film quality of silicon oxide are studied. The following results are obtained: deposition rate increases when not only O2 but also SiH4 as a material gas are excited by ECR, and high-quality film equivalent to thermal SiO2 film can be formed when the ECR position is located close to the substrate. It is suggested that the process of forming high-quality film is related to highly excited ions transported to the substrate.

Influence of deposition conditions on properties of a-SiGe:H prepared by microwave-excited plasma CVD

The influence of the deposition conditions on properties of a-SiGe:H prepared by the microwave-excited plasma CVD was examined. Highly photoconductive a-SiGe:H alloys were obtained at the pressures lower than 0.8 mTorr when the substrate was heated to 200degC. The photoconductive property of a-SiGe:H deteriorated when the microwave power was decreased. Similar deterioration was observed when the deposition pressure was increased. It was suggested that the deterioration of the photoconductive property was caused by the depression of SiH4 decomposition. The photoconductivity of a-SiGe:H alloys increased with the decrease of the deposition pressure even though the amount of the isolated SiH2 bonds in the film also increased with the decrease of the deposition pressure. The deposition mechanism inducing this deposition pressure dependence was discussed.

Development of a high rigidity superconducting magnet for the Maglev system

A high rigidity type superconducting magnet (SCM) is developed and tested by an electromagnetic vibration simulator which simulates the actual running conditions. To reduce the increase in heat load due to the vibration of the cryostat, several kinds of design concepts are chosen. It is recognized from the experiment result that the most effective design concept is to increase the characteristic frequency in twisting mode of the inner vessel with the high rigidity outer vessel.