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Integral Insulated Support Structures for Ion Optics

IP.com Disclosure Number: IPCOM000051200D
Original Publication Date: 1982-Aug-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 3 page(s) / 67K

Publishing Venue

IBM

Related People

Kaufman, HR: AUTHOR [+3]

Abstract

Multiple aperture ion optics are used to extract broad ion beams from plasma ion sources. The ability to extract large ion beam currents at low ion energies depends on maintaining a small gap between the grids over a large beam area. The use of interelectrode insulating supports is an attractive means of maintaining a small gap. Practical problems of fabricating small shadow-shielded insulators have, until the present, prevented their widespread use. The use of microfabrication techniques permits practical support designs with integral insulators and self aligning features in an extremely small space.

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Integral Insulated Support Structures for Ion Optics

Multiple aperture ion optics are used to extract broad ion beams from plasma ion sources. The ability to extract large ion beam currents at low ion energies depends on maintaining a small gap between the grids over a large beam area. The use of interelectrode insulating supports is an attractive means of maintaining a small gap. Practical problems of fabricating small shadow-shielded insulators have, until the present, prevented their widespread use. The use of microfabrication techniques permits practical support designs with integral insulators and self aligning features in an extremely small space.

Ion optics for broad ion beams require the use of closely spaced multi-aperture grids. The performance of such grids is approximated with Child's law the one-dimensional planar solution for space charge j = (4E (o)/9) (2q/m) /1/2/(V/3/2//X) where j is the current density in A/m, E(o) is 8.85 x 10 /-12/, is the charge to mass ratio in C/kg, and X is the acceleration distance in m. When this equation is used to approximate the acceleration of charged particles between a pair of grids, V is taken as the voltage between the grids and X is the spacing between them.

A frequent case of interest is a large ion beam current at low energies. The ion-optics configuration required for such an operating condition must have a large ion beam area and a small spacing between the grids. The beam area of such a configuration is normally limited by the permissible span between the grid supports.

The use of insulating grid supports within the active beam area has been an attractive concept for extending the beam area for a given spacing. In practice, the fabrication of such supports within the beam area bas proven difficult. The need to shadow-shield the insulators against sputtered material has resulted in large structures, which have seriously Interfered with beam uniformity.

For optimum extraction of the ions from the discharge chamber, it is necessary to align the grids very accurately. Failure to do so causes nonuniformity in the beam as well as sputtering of the grids due to ions striking the grids. Presently, the grids are aligned by manually moving the grids while observing them under a microscope. Insulated grid supports with self alignment features would allow fast and much more precise alignment of the grids, thus allowing optimum performance of the ion sources.

The proposed technique is indicated in Figs. 1 through 4. The two grids 1 and 2 are covered with an insulating layer 3 Where they come together and touch. The ions are extracted from a plasma 4 and follow trajectories 5 through the apertures 6.

By employing the techniques and materials found in the microelectronics industry, it has become possible to fabricate interelectrode supports far smaller than possible using conventional machining techniques. The proposed technique uses configurations suitable for microfabrication.

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