Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – With means applying electromagnetic wave energy or...
Patent
1997-05-19
1999-06-01
Jenkins, Daniel J.
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
With means applying electromagnetic wave energy or...
42218605, B01J 1912
Patent
active
059086025
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an apparatus for generation of a linear arc discharge for plasma processing, particularly for surface processing of solid substrates.
BACKGROUND OF THE INVENTION
Because of high ion density of produced plasmas the arc discharges represent very powerful tools in the plasma processing technology. Arc sources are used for generation of reactive plasmas in a working gas, they can produce plasma which contains particles of sputtered and/or evaporated electrodes, or chemical compounds of these particles with the working gas. Properties of arc discharges depend on energies and densities of the generated ions and electrons, which are affected by the pressure of the working gas. A wide variety of gas plasmatrons use arc discharges at atmospheric pressures, because of simple arrangement without vacuum pumps. However, generation of an arc based on a non-isothermal plasma with controllable ion energies requires low gas pressures. Different types of arc discharges are used for this purpose. Most of them are generated by direct current (DC), high power generators. A typical low pressure source for plasma processing is a cascaded arc (European patent 0297637) which produces a flow of an active plasma in a working gas. Metal ions in plasmas are generated usually from an electrode which is sputtered and/or evaporated by the arc discharge, see D. M. Sanders et al., IEEE Trans. Plasma Sci. 18, 883-894 (1990). The eroded electrode is usually a planar cathode in the DC arc circuit with an electrically grounded anode. The cathode is water cooled and the content of undesirable micro droplets--"macroparticles" present in the evaporated cathode material is reduced by steering the cathode spot motion on the cathode surface. In recent cathodic arc sources the macroparticles are filtered by an auxiliary magnetic field filter (U.S. Pat. No. 5,279,723). The content of macroparticles is usually lower when the consumable electrode is heated up to melting temperature. It is also possible to utilize arc arrangements with a consumable anode instead of the cathode, see e.g. M. Mausbach et al., Vacuum 41, 1393-1395 (1990). Cold consumable cathodes are of limited size and require the magnet filtering, which limits possibility of scaling these sources up. Consumable electrodes containing liquid metal crucibles can be installed only in restricted positions. Most arc sources require an additional switch to start the discharge.
A generation of an arc discharge is very efficient in hollow cathodes. The principle of the hollow cathode gas discharge generated by a direct current has been reported first by F. Paschen, Ann. Physik 50, 901-940 (1916). From that time a great number of investigations about this discharge have been reported, see reviews e.g. J-L. Delcroix and A. R. Trindade, Advances in Electronics and Electron Phys. 35, 87-190 (1974), M. E. Pillow, Spectrochimica Acta 36B, no.8, 821-843 (1981), and R. Mavrodineanu, J. Res. Nat. Bureau of Standards 89, no. 2, 143-185 (1984). In DC hollow cathodes an arc discharge can be generated at high DC power. The wall of the hollow cathode must be heated up to high temperatures strongly enhancing thermionic emission of electrons. Moreover, a substantial portion of ions is produced by an erosion of the hollow cathode surface. At these conditions the DC current in the arc circuit grows up rapidly, while the voltage at the cathode falls down to values of the order of the minimum ionizing or minimum exciting potential of the gas or metal vapor. The arc is a self-sustained discharged capable of supporting large currents by providing its own mechanism of electron emission from the negative electrode (see "Handbook of Plasma Processing Technology" ed. by S. Rossnagel et al., Noyes Publ. 1990, Chapter 18 by D. Sanders). Until this condition is not reached the discharge in the hollow cathode cannot be assumed as an arc. It is rather a normal or anomalous glow, even if some parts of the cathode walls are hot, particularly in cathodes fabricated from a
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Barankova Hana
Bardos Ladislav
Jenkins Daniel J.
Surfcoat Oy
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