Kohgi Kato

Electron-temperature control for plasmas passing through a negatively biased grid

Electron‐temperature control is performed on plasmas passing through a coarse mesh grid from a discharge region. By increasing a negative potential applied to the grid, the electron temperature is continuously decreased in a very wide range covering almost two orders of magnitude down to the value nearly equal to the background gas temperature in case of direct current argon or helium gas discharge. The temperature decrease is accompanied by an increase in the electron density. This method of electron‐temperature control can also be applied to plasmas produced by radio‐frequency and electron cyclotron resonance discharges.

Electron temperature control by varying size of slits made in a grid

Electron temperature is controlled by varying the length of slits made in a grid immersed in a weakly ionized discharge plasma. The grid, which is kept at floating potential, has six slits in this experiment. With a decrease in the slit length from 6 to 0 cm, the electron temperature decreases from 2.1 to 0.09 eV, being accompanied by an electron-density increase from 0.32×109 to 1.53×109 cm−3 at argon gas pressure of 1.5 mTorr. This method of electron–temperature control is applicable to reactive plasmas in which grids are often covered by insulators.

Electron and Ion Energy Controls in a Radio Frequency Discharge Plasma with Silane

Electron and ion energy distribution functions are controlled in a radio-frequency (rf) discharge plasma with silane for production of hydrogenated amorphous silicon films. We apply the grid-bias method to an rf silane plasma in order to obtain a low electron-temperature (T e ≃ 0.2 eV) and low ion-temperature (T i ≃ 0.1 eV) plasma. The ion beam energy is controlled by biasing the substrate. We find that the room temperature hole drift mobility is increased by two orders of magnitude compared to the conventional value at an ion beam energy between 23 eV and 24eV.

High quality diamond formation by electron temperature control in methane-hydrogen plasma

We report a new method for the nucleation and growth of diamonds by employing an electron-temperature control technique in CH4/H2 radio frequency glow discharge plasma under a low gas pressure of 100 mTorr. The electron temperature in the plasma is controlled under constant gas pressure in a range from 0.5 to 2.5 eV continuously by changing the open area of the slits situated around a grid that is kept at the floating potential. It is observed that the film quality is changed in accordance with the variation of electron temperature, and we can produce high quality diamond in a low electron temperature plasma, even though usually only graphite film is deposited, unless the electron temperature is controlled.

Negative Hydrogen Ions Produced by Electron Temperature Control in an RF Plasma

The formation of negative hydrogen ions is investigated in a pure hydrogen RF plasma using a grid-method for electron temperature control. Using the grid method we produce both high and low electron temperature plasmas in the separated regions in the chamber, in which the electron temperature in the downstream region is controlled by the grid potential. The production rate of negative ions depends strongly on the grid potential. We observe efficient negative hydrogen ion production in the downstream region when the grid is negatively biased in the hydrogen pressure range of 2–5 mTorr.

Formation of Nanoparticles by Control of Electron Temperature in Hollow-Typed Magnetron Radio Frequency CH4/H2 Plasma

In this study, we investigate the effects of electron temperature Te on the production of nanoparticles by using the grid-biasing method in hollow-typed magnetron radio frequency (RF) CH4/H2 plasma. We find that nanoparticles are produced in low-Te plasma. On the other hand, thin film depositions, such as nanowalls, are mainly observed and almost no nanoparticles are created in high-Te plasma. This implies that a reduction in the CH2/CH3 radical ratio is important for producing nanoparticles, together with a reduction in sheath potential in front of the substrate. The change in electron temperature in plasma has a marked effect on film quality.

Electron temperature and ion energy control in modified magnetron-typed RF discharge

The basic properties of the control of electron temperature and ion energy in modified magnetron-typed (MMT) radio-frequency (RF) plasma are investigated by using the grid and double-plasma methods, respectively. By changing the open area of the slots situated on a cylindrical grid, the electron temperature in the center region is controlled continuously in the range from 0.5 to 2.4 eV. On the other hand, by changing the plasma potential of an ion-beam source, we control the ion energy from 0 to 30 eV.

Control of Electron Temperature by Varying DC Voltage to a Mesh Grid Blanketed with Thin Film in Plasmas

The basic characteristics of control of electron temperature in weakly ionized plasma have been investigated in the absence of magnetic field using a grid-bias method. To control the electron temperature, dc voltage is applied to a mesh grid covered with a thin film. Although the grid is covered with a thin film made of a diamond-like carbon known as an insulating material, the electron temperature can still be controlled from 1.0 to 0.045 eV by varying the dc voltage of the grid from 40 to -10 V at an argon gas pressure of 20 mTorr accompanied by an electron density increase in a cold-cathode discharge plasma. We also provide theoretical discussions to clarify how the resistance of the film deposited on the metal grid affects the efficiency of the control of electron temperature in the case of the grid-bias method. This technique of electron-temperature control is available for reactive plasmas in which grids are often deposited by thin films made of hydrogenated amorphous substance, diamond-like carbon and so forth.

Control of fine particles by time-averaged external forces in plasmas

A technique for the control of fine particle behavior is developed and demonstrated experimentally. In this method positive pulses are applied to two point-electrodes placed with some distance in plasmas containing fine particles. When the positive pulses are applied to these electrodes alternatively with a repetition period that is shorter than the particle response time, the particles feel only time-averaged force because of their large mass and are gradually transported toward the middle point between two point-electrodes wherever they are distributed initially. This method is quite effective for converging fine particles in the plasma.

Efficient production of negative hydrogen ions in RF plasma by using a self-biased grid electrode

Volume production of negative hydrogen ions is established efficiently in a pure hydrogen RF discharge plasma by using a self-biased grid electrode for production of low electron-temperature and high density plasma. Using this electrode both high and low electron temperature plasmas are produced in the regions separated by the grid electrode in the chamber, in which the electron temperature in the downstream region is controlled by the mesh size and plasma production parameters. The production rate of negative ions depends strongly on the electron temperature varied by the RF input power and hydrogen pressure. In the case of the grid electrode with the 5 mesh/in., the negative hydrogen ions are produced effectively in the downstream region in the hydrogen pressure range of 0.9 − 2.7 Pa. In addition, the production rate of the negative ion H raises from 62 % to 87 % at 0.9 Pa by changing the RF power from 20 W to 80 W.