A large-planar (22 cm diam.) high-density ( ∼2×1012 cm-3) plasma is produced in argon gas at 140 Pa by 2.45 GHz–1 kW discharges, using a microwave launcher of small slot antennas. The two-dimensional distributions of optical emission intensities as well as microwave field intensities are measured near the plasma surface irradiated with microwaves. Both the optical emission and the microwave field clearly show stationary patterns of azimuthal mode m=3 and radial mode n=3 at higher pressures (140 Pa), while a mode change to m=6 and n=2 is observed at lower pressures (44 Pa). These patterns are attributed to the excitation and absorption of standing surface waves near the cutoff layer.

For the practical application of end-point detection of etching using plasma-impedance monitoring, the factors determining the impedance were clarified using an electric circuit model of a reaction chamber. In the model, plasma is approximated by a conductor, and the floating capacitance and wafer of a powered electrode, as well as the powered-electrode sheath (the sheath formed between the plasma and powered electrode), are approximated by capacitors. Calculated values obtained using the model agree well with measured values obtained by an impedance monitor installed between the powered electrode and the matching network. Based on this result, it was inferred that the impedance depends on the powered-electrode sheath-voltage and electron density, as well as on the floating capacitance and area of the powered electrode, the dielectric constant and thickness of the wafer, and the electron temperature. Next, the end-point detection method of etching by impedance monitoring was applied to reactive ion etching of SiO2 films, and the following finding was confirmed: the change in the impedance significantly depends on the RF power and the exposed area ratio (the ratio of etched area to wafer area) on the wafer. In addition, the feasibility of detecting the point of change of the exposed area ratio on the wafer, where the area size varies during etching, by detecting microchanges in the impedance, was demonstrated. As a result, the possibility of highly accurate end-point detection of etching by impedance monitoring was confirmed.

An inductively coupled plasma source with an internal straight antenna was developed. By inserting an antenna into plasma, the induction of a strong electric field in the plasma and the efficient transmissions of power to plasma is enabled. However, there was a practical problem in that antenna sputtering occurred. Suppression of antenna sputtering and methods of insulating the antenna were studied. Consequently, it was found that sputtering impurities were reduced by covering the straight antenna with a quartz pipe. Furthermore, the amount of quartz pipe etching could be reduced to as little as 1/10th the original value. As a result of fabricating and evaluating the plasma source in which four straight antennas were arranged in parallel, electron density was determined to be as high as 1011 cm-3 even at a pressure as low as 4 mTorr. When the processing performance of the plasma source was evaluated, the ashing rate of the photoresist and the etching rate of the poly-Si were, respectively, 4.8 µm/min and 450 nm/min. These values are at practically applicable levels.

A decaborane-based boronization system has been installed in the JT-60U tokamak in order to reduce the influx of impurities during plasma discharges. Boronization has been performed under a glow discharge using a helium-decaborane gas mixture. The properties of the boron films deposited through boronization and the effects of boronization on the tokamak discharges were investigated. It was found that the deposition of a boron layer with high purity was achieved with few impurities other than hydrogen through boronization, and that the present boronization deposited toroidally nonuniform boron film. It was also found that the decaborane-based boronization resulted in good plasma performance similar to that of conventional boronization.

We propose to describe the dynamics of unstable particles in relativistic quantum field theory in terms of semigroups of transformations of the observables. This leads, in contrast to the usual Hilbert space level treatment, to a complete and consistent description of the irreversible dynamics of decay processes. The scheme is explicitly worked out for the massive scalar quantum field and the evolution of the particle density and its higher moments is computed.

A new boronization technique based on pyrolysis of boron hydrides on hot walls was investigated in a laboratory experiment. The deposition rate of boron films through pyrolysis of decaborane was high enough to apply the pyrolysis to actual fusion devices bakable to 300°C. The hydrogen concentration of boron films prepared by the pyrolysis or conventional plasma-assisted boronization at various temperatures was measured with 15N nuclear reaction and/or IR absorption methods. The hydrogen content markedly decreased with increasing wall temperature, where decaborane always gives higher H content than diborane. Oxygen gettering and hydrogen recycling in a boronized vessel were evaluated by pulsed glow discharge in O2/He and D2, respectively. The results were compared between the pyrolysis and the plasma-based boronizations in decaborane or diborane at various wall temperatures.

No abstract

No abstract