Haruaki Akashi

One-dimensional modelling of low-frequency and high-pressure Xe barrier discharges for the design of excimer lamps

A self-consistent one-dimensional modelling of a Xe gas discharge between electrodes covered with dielectric barrier is presented for power frequencies from 50 kHz to 1 MHz and gas pressures from 10 to 400 Torr. Spatiotemporal profiles of the concentration of electrons, ions, excited atoms and excimers are obtained. Excimers are mainly produced in the sheath regions. The efficiencies of spontaneous emission from excimers and resonance-state atoms increase with an increase in the input powers for gas pressures higher than 50 Torr. A characteristic period during which the barrier wall charge significantly influences the electric field in bulk region was found, and discharge properties in the period are discussed.

An output power stabilized erbium-doped fiber amplifier with automatic gain control

Based on the cross-saturation between two different-wavelength optical signals in an erbium-doped fiber amplifier (EDFA), we have developed an output power stabilized EDFA system with automatic gain control. The developed system shows 18.5-dB dynamic range of the output power limitation with the ability to set the output power level arbitrarily. When a temporally varying optical signal is input, the system works as a fluctuation remover for the input signal modulated at low frequency up to 1 kHz and does not have any deteriorative effect on high-frequency modulated optical signals. The degree of modulation in the fluctuated optical signal can be reduced down to as low as 0.003.

Dependence of Frequency and Pressure on Electron Energy Distribution Functions in Low Pressure Plasma

The electron energy distribution functions (EEDF), ionization frequency R i and mean electron energy e in a low pressure high frequency (13.56 MHz–1 GHz) discharge in Ar gas have been examined using Monte Carlo method. The dependence of driving frequency on the EEDF, R i and e is calculated. As the frequency increases, the lower energy electrons increase significantly because they can not follow the applied high frequency electric field. Then, R i and e decrease with increasing frequency. The dependence of pressure on EEDF, R i and e under applied frequencies of UHF (500 MHz) and RF (13.56 MHz) is also investigated for actual etching pressures. The EEDF, R i and e in the UHF plasma do not depend on the pressure, whereas those in the RF plasma are strongly influenced by the pressure. It is considered that the driving frequency (UHF) is higher than the electron collision frequency in the plasma.

Modeling of multifilaments formation in dielectric barrier discharge excimer lamp

Formation of multifilaments in dielectric barrier discharge (DBD) excimer lamp has been simulated using two dimensional fluid model. The simulation had started from a small cluster of electron-ion pair in the middle of discharge gap. After the first streamer arrived at the cathode, the discharge expanded on the surface of the dielectric toward the lateral direction until the polarity of the discharge voltage change. The edges of this surface discharge become the start point of next second and third filaments. Within one and half cycles of the discharge voltage waveform, five filaments are formed in stably in 3-cm discharge space.

Modelling of the initiation and development of a filamentary discharge in XeCl excimer lasers

The dynamics of a filamentary discharge in discharge-excited XeCl excimer laser has been examined using a two dimensional fluid model. The entire process of the filamentary discharge, from its initiation and development, is presented and the role of protrusions on a cathode surface to induce a filamentary discharge is discussed. The filament develops in the direction of the anode, assisted by a space-charge induced local high electric field. The features of the spatio-temporal evolution of the filament, including the gas temperature rise are discussed comparing the ArF discharge case and experimental observation.

Effects of discharge frequency on plasma characteristics and etching characteristics in high density Cl/sub 2/ plasma: comparison of ultrahigh-frequency plasma and radio-frequency plasma

We investigated the effects of discharge frequency on the characteristics of polycrystalline-silicon etching rates and on the etching selectivity on the gate oxide (SiO/sub 2/). An ultrahigh-frequency (UHF) plasma excited at 500 MHz was found to possess a wider process window for highly selective polycrystalline silicon etching than did an inductively coupled plasma excited at 13.56 MHz. The ionization rate in the UHF plasma is nearly constant at discharge pressures from 3-20 mtorr because the discharge frequency is higher than the electron-collision frequency in that plasma.

Development of Streamers in Dielectric-Barrier-Discharge Excimer Lamp

The development of streamers in a dielectric-barrier-discharge (DBD) excimer lamp has been simulated by using a 2-D fluid model. The DBD is composed of streamer and surface discharges, and the surface discharge significantly affected the shape of the discharge-current waveform. The spatial distributions of electron density, electric field, and excimer density showed the dynamics of the streamer developments, and the behavior of streamers in DBD was clarified in detail.

Various Kinds of Streamers in Atmospheric Pressure Oxygen Dielectric Barrier Discharge

An atmospheric pressure oxygen dielectric barrier discharge had been simulated using two dimensional fluid model. Three kinds of streamers had been obtained, and they are primary, small and secondary streamers. The electron density of small and secondary streamers is lower than that of primary streamers. But it was found that generation of ozone was significantly affected by these three streamers.

Modeling of filament discharge development in a XeCl excimer laser

Dynamics of a filament discharge in a discharge-excited XeCl excimer laser medium has been simulated for a sequence of discharge pulses (shots). In the present model a filament discharge is triggered at a microprotrusion on a cathode surface. After the first discharge initiation, a hot spot is created near the cathode, then filament develops toward the anode in the second shot. Images of the filament discharge development and its properties in a XeCl excimer laser are presented.

Modeling of a filamental discharge formation and development in ArF excimer laser

Dynamics of a constricted filamental discharge in a discharge- excited ArF excimer laser have been examined using a two dimensional fluid model. An entire process of the filamental discharge, from its initiation and development to extinction, is shown. The filamental discharge is triggered at protrusions which would always exist on cathode surfaces, and develops in the direction of the anode assisted by the high field induced by space charge. The gas temperature in the filamental discharge in the vicinity of the cathode is found to rise. This temperature is shown to play an important role in development of the filamental discharge. The effect of preionization electron density ne0 is also examined, and significant development of the filamental discharge toward the anode is seen when the ne0 becomes lower. The results are examined properly in connection with experimental observations.