Table of contents

Boron nitride films were deposited using electron cyclotron resonance (ECR) plasma and RF substrate bias. The authors investigated the mechanical properties and adherence of BN films for various self-bias. The structure and stress of BN films depended on the negative self-bias. These results are analysed by a peening mechanism of compressive stress in films.

High density plasma production using m=+1 and m=-1 helicon waves is studied. Characteristics of cylindrical helicon waves including effects of a vacuum gap between the plasma and the conducting wall and of a non-uniform density profile are presented. The m=+1 and m=-1 helicon modes are separately excited by a helical antenna, and the dependences of plasma density and antenna loading resistance on RF power are different for these modes.

The Si etching characteristic in helicon wave plasma was studied. The Si etch rate showed a very critical pressure dependence. Low-temperature etching at liquid-nitrogen temperature offered directional etching with a rate of 3500 AA min^-1. The etching uniformity was also studied on the two points of the magnetic field and the tube diameter.

Silicon oxide films were prepared in an RF capacitive plasma using hexamethyldisiloxane. The films deposited on c-Si, quartz plate, glass and polycarbonate at room temperature were studied by means of IR absorption, ESCA and optical transmission spectra. The processing plasmas were also monitored spectroscopically.

Two methods of treatment on Si substrate surface were attempted to investigate the effect of mechanical treatment on the substrate surface in the process of diamond nucleation by the RF plasma CVD method. In the first method, a great number of defects were made on the Si substrate surface by mechanical treatment using SiC powders. A large diamond particle was grown on a defect, and many small diamond particles were grown around it. In the second method, the Si substrate was bent by deposition of an a-C:H film on the back side of the substrate. For bending angles less than 18 degrees , the number density of diamond particles was almost constant and of the order of 10⁶ cm^-2. When the bending angle increased, the density tended to increase until an order of 10⁷ cm^-2 was attained. The formation of a SiC intermediate layer between the diamond phase and the Si substrate was confirmed for large bending angles (more than 18 degrees ).

The hydrogen content of a-Si:H films prepared at a fixed substrate temperature varies over a wide range when silane is diluted using a rare gas (He, Ne, Ar, Kr, Xe) during PECVD. A possible explanation, based on known differences in the branching ratios on collision of electronically excited rare gas atoms with silane molecules, is suggested.

The effect of excitation frequency in processing plasmas of the very-high-frequency band has been studied by plasma diagnostics including Langmuir probe and optical emission spectroscopy. The ECR plasma has been implemented in the VHF (144 MHz) range. Properties of hydrogenated amorphous silicon films have also been studied. High-quality interfaces have been demonstrated through the characteristics of thin-film transistors prepared by VHF plasma CVD.

Pulse-discharge (PD) CVD techniques were applied to deposition of hydrogenated amorphous silicon germanium (a-SiGe:H) films. In the PD-CVD, high-voltage rectangular pulses with a small duty cycle were applied periodically to a parallel plate electrode system, and SiH₄-GeH₄ gas mixtures were decomposed in the pulse discharge. The film quality improved remarkably with decreasing electrode gap. To understand this, experimental and theoretical analyses were carried out. The primary radicals generated by electron impact dissociation of source molecules are the key for improving the quality of the film: when the primary radical is the dominant precursor for film deposition, the film quality improves.

Growth kinetics and behaviours of particles in a He-SiH₄ plasma are observed using the RF modulation method together with two in situ laser diagnostic methods. Particles tend to be sustained around the plasma/sheath boundary near the RF electrode, their size and density being 60-180 nm and 10⁸-10⁹ cm^-3, and larger particles exist in a higher electric field region near the RF electrode. The particle growth rate is explained by taking into account the contribution of radical ion and/or radical fluxes. The particle trapping around the sheath edge is explained by balance between the electrostatic force and the ion drag force. An effect of the viscous force on the particles and a suppression mechanism for RF-modulated discharges are also discussed.

The influence of driving frequency on discharge structure and production efficiency has been investigated in Ar over the frequency range from 13.56 MHz to 100 MHz in terms of the relaxation continuum model. Under constant RF voltage, the plasma density increases in proportion to the square of the driving frequency. The net ionization and excitation rates, and the power density, show the same frequency dependence, although the collisional production efficiency per input power density is almost invariant with change of frequency. This has the great advantage for plasma processing and deposition from plasmas that parallel plate discharge in very high frequency (VHF) will lead to the system being rather free from ion damage or effects of confined plasma volume as compared with those in high frequency (HF) and microwave (MW).

An apparatus is developed which prepares clusters by means of arc-discharge-heated expanding plasma jet, and as a test of the apparatus carbon clusters are prepared from the carbon cathode, which is heated and vaporized by arc discharge. Vaporized carbon atoms and helium plasma are ejected from a higher pressure discharge chamber into a lower pressure vessel through a tiny nozzle with plasma. After the carbon atoms get into the lower pressure vessel, they are cooled and clustered. It is expected that the size and shape of clusters can be controlled by changing the pressure ratio across the nozzle. It is confirmed that the apparatus can run without plugging the nozzle. The pressure region in which it runs stably is also investigated. Experiments are made with a view to preparing C₆₀ ('Buckminsterfullerene'), which looks like a soccer ball and is considered an important material with various applications.

The electron paramagnetic resonance (EPR) spectral features of several plasma-irradiated fibrous polypeptides (scleroproteins), such as silk, wool, and collagen vary with materials, but remain unchanged during the course of plasma irradiation in each case. Unlike for many other synthetic and natural homopolymers, it is difficult to identify the full structures of polypeptide radicals from EPR spectroscopic evidence alone, since proteins consist of many kinds of amino acid units. Nevertheless, systematic computer simulations indicated that plasma susceptibility for radical formation is rather specific in amino acids, that is glycine-derived, radicals (-CHNHCO-) in silk and collagen, and sulphide radicals (-RS) in wool as a major radical.

A thermal plasma has high potential to instigate a refractory chemical reaction because it has a high temperature and high energy. So thermal plasmas have been utilized for some high-temperature processes in which a chemical reaction occurs, although so far chemical application of thermal plasmas has not been sufficient and their use should be promoted more. In this paper, the homogeneous and heterogeneous chemical processes in a thermal plasma are described, and its application to the environment problem is mentioned as a recent topic. Lastly the problems which must be solved to promote chemical applications of thermal plasmas are shown

The decomposition process of chlorofluorocarbons by water plasma was investigated by thermodynamic analysis. The optimized point for maximizing the fraction of CFCs is n_CCl3F:n_H2O = 1:2. Conditions with more CFCs than at this point lead to the recombination of CFCs. With more O₂, Cl₂ is produced. The energy needed to heat water and CFC11 to 10000 K is 2.4 MJ mol^-1. The ionization of the mixture begins at 9000 K, which is 1000 K lower than Ar plasma

A numerical approach is presented for the analysis of the dynamic behaviour of the induction thermal plasma under step-like change of the sustaining magnetic field. The time-dependent energy conservation equation which includes thermal conduction, radiation and convection loss terms was solved numerically in conjunction with the continuity equation and Maxwell's electromagnetic field equations. A one-dimensional model with radial direction is adopted for the first approximation to analyse the transient aspects of the radial distributions of the temperature, the penetrating electromagnetic fields and the input and losses. Calculations were carried out for an Ar-induction thermal plasma with a diameter from 2 to 7 cm, operated at a frequency of 3 MHz and a pressure of 760 Torr. Special attention was given to the time constant which is a measure of the time necessary for the plasma to converge to a new steady state. The response time of the induction thermal plasma was a few milliseconds and had a strong dependence upon the diameter of the plasma across which the mass and energy diffusions take place under the off-balancing condition between the input and the loss. The transient aspect of a high-power induction plasma operated with a low frequency of 300 kHz is also discussed.