Minoru Sugawara

Uniform RF Discharge Plasmas Produced by a Square Hollow Cathode with Tapered Shape

A square hollow cathode with a tapered shape (square HCT) is developed in order to produce highly uniform and dense plasmas (density ~ 6×1010 cm-3) with a wide range of operating pressures. It is shown experimentally that the plasma density produced by the HCT is higher than that produced by a plane cathode from 0.02 Torr to 0.2 Torr. It is demonstrated experimentally that uniform plasmas can be produced by modifying the structure of the HCT for different operating pressures. It is shown that an additional outer hollow cathode is useful to compensate the nonuniformity of plasmas due to edge effects. With the use of the outer hollow cathode for the modified HCT, highly uniform plasmas are produced within almost the entire surface of the grounded square electrode.

Determination of Ionization Cross Section for Argon Metastable-Metastable Collision by Means of Afterglow Technique

Subtracting the energy loss rates of electrons from the decay rate of electron temperature in an argon afterglow at pressure 133 Pa (Ar), we have separated the energy gain of electrons, which was assumed to be due to superelastic collisions and energetic electrons created by the metastable-metastable ionizing collisions. The cross section obtained has a value between (1.30±0.11)×10-17 m2 and (1.40±0.12)×10-17 m2, which is greater than the cross section for collisions between unexcited argon atoms.

RF Hollow Cathode Discharges with Tapered Shape

A hollow cathode with tapered shape (HCT) is developed in order to expand the range of operating pressures. Although the plasma density produced by the HCT becomes slightly lower than that by an ordinary hollow cathode, it is demonstrated experimentally that the range of operating pressures for stable RF hollow cathode discharge is expanded. It is shown that the position of the negative glow moves inside the HCT for different operating pressures to sustain the hollow cathode discharge.

Monte Carlo Simulation of RF Plasmas and Trial Investigation of Similarity Rule

Detailed properties of RF plasmas sustained by an RF external source of 13.56 MHz and 270 V are presented using self-consistent Monte Carlo simulations in an Ar-like model gas. It is shown that most of the RF external electric field is absorbed in the sheath regions and ions cannot follow the RF field. The time-dependent distribution of the number of excitation collisions is shown to give a physical picture of the moving sheath boundary which oscillates with the RF electric field. It is shown that a lower gas pressure yields a distribution with a wider sheath region which gives dominantly the capacitive component of impedance. A trial investigation of the similarity rule for the bulk region of RF plasmas is presented with respect to the electric field, the electron density, the conduction current density, and the mean electron velocity in the direction of the current.

Measurements of the Time-Averaged Sheath Drop Using the Gridded Energy Analyzer

The time-averaged sheath drops across the sheath in front of a powered electrode have been determined using the gridded energy analyzer, by estimating the maximum energy of the ions accelerated by the sheath potential. It is observed that from pressure p=0.01 to 1 Torr, the sheath drops decrease slightly with operating pressure, and above p=0.1 Torr, the sheath drops exhibit a sharper decrease. Also, the sheath drops increase sharply with R.F. power input. These results could be explained qualitatively in terms of the variation of R.F. voltage amplitude with pressure and R.F. power.

Measurement of the Expansion Velocity of the Electrode Sheaths in RF Glow Discharge and Its Physical Mechanism

The time-resolved optical technique has been applied to RF glow discharge to measure the expansion velocity of the sheath of the RF glow in conjunction with the applied RF voltage. In the technique, the movement of the edge of the negative glow is assumed to indicate the expansion of the electrode sheath thickness. We have proposed a model of the sheath expansion which takes into account acceleration, by RF voltage, of electrons initially in the region from the sheath edge to the floating potential surface relative to the plasma. The values deduced using the model compare well with the experimental results.