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Browse Prior Art Database

RF Ion Source

IP.com Disclosure Number: IPCOM000049249D
Original Publication Date: 1982-Apr-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 3 page(s) / 38K

Publishing Venue

IBM

Related People

Guarnieri, CR: AUTHOR [+2]

Abstract

An electron bombardment source is described wherein a discharge chamber is operated with RF heating of the plasma rather than the usual DC heating and the RF energy is coupled capacitively with the discharge plasma with the frequency high enough so that most of the energy comes from resistive heating of the plasma.

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RF Ion Source

An electron bombardment source is described wherein a discharge chamber is operated with RF heating of the plasma rather than the usual DC heating and the RF energy is coupled capacitively with the discharge plasma with the frequency high enough so that most of the energy comes from resistive heating of the plasma.

The electron bombardment ion source is shown in Fig. 1, wherein gas to be ionized 1 is introduced into the outer shell of the discharge chamber 2, where electrons emitted from the cathode 3 pass through the enclosed volume to the anode 4. With the low gas pressures normally used within the discharge chamber (10-3 torr, or less), the probability of ionizing electron collisions is enhanced by arranging a magnetic field 5 so that electrons must cross magnetic field lines to reach the anode. This magnetic field orientation can be generated by a field coil (not shown) external to the ion source. The magnetic field strength must be sufficiently large so that the field lines cannot be crossed without the electrons first undergoing collisions, either collective or individual, with other particles (atoms, molecules, ions, or other electrons) within the discharge chamber. Some of the ions generated by collisions arrive at the screen grid 6, which is located at one end of the discharge chamber and connected to the outer shell 2. A negative potential on the accelerator grid accelerates the ions that pass through the apertures in the screen grid. The apertures in the two grids are aligned so that the accelerated ions leave the ion source in small beamlets 8. At a sufficient distance from the ion source the beamlets coalesce to form a single composite ion beam.

The radio frequency power is applied across the two discharge chamber electrodes 3 and 4. Electrode 3 is more substantial than a thin wire. The outer shell 2 and the screen grid 7 are biased negative or left at a floating potential, to avoid the concentration of power input where electrodes 3 and 4 approach the outer shell and the screen grid. The electrodes 3 and 4 can be made of a material that enhances secondary electron emission, such as aluminum, platinum, or magnesium oxide. With capacitive coupling to the discharge plasma, conducting surfaces are not required for electrodes 3 and 4. The combination of a high frequency with an electrode material that...