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Faraday Cup Configuration for Ion Beam Measurement

IP.com Disclosure Number: IPCOM000085208D
Original Publication Date: 1976-Mar-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 3 page(s) / 45K

Publishing Venue

IBM

Related People

Keller, JH: AUTHOR [+3]

Abstract

Monitoring of ion implantation currents or dosages with Faraday cages is known in the art. The text, "Ion Beams With Applications to Ion Implantation", R. C. Wilson and C. R. Brewer (1973, pp. 446 - 449, 451 - 452, and 457) discusses the conventional utilization of the Faraday cage for ion-beam current or dosage monitoring. In such monitoring, the cage may be a separate unit retractably inserted between the target and the beam for occasional monitoring, or the Faraday cage may consist of the actual target in combination with the housing walls for continuous monitoring during the ion implantation operation.

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Faraday Cup Configuration for Ion Beam Measurement

Monitoring of ion implantation currents or dosages with Faraday cages is known in the art. The text, "Ion Beams With Applications to Ion Implantation", R.
C. Wilson and C. R. Brewer (1973, pp. 446 - 449, 451 - 452, and 457) discusses the conventional utilization of the Faraday cage for ion-beam current or dosage monitoring. In such monitoring, the cage may be a separate unit retractably inserted between the target and the beam for occasional monitoring, or the Faraday cage may consist of the actual target in combination with the housing walls for continuous monitoring during the ion implantation operation.

In either case, the actual target or the target plate (in the case of the retractable cage) is fully insulated from the cage walls.

In such conventional Faraday cage monitoring in the case of the ion beams which are always positively charged, the target is conventionally maintained at a potential which is positive with respect to the cage walls maintained at a negative voltage level. In such a structure, the cage walls purportedly function to suppress secondary electrons created at the target back toward the target, so that the loss of such electrons will not affect the target current which is the only current measured by an ammeter in determining current or dosage.

A Faraday cup for ion implantation current measurement has been proposed wherein the target is at a negative potential, the cage walls are at ground, and the beam current being measured is taken both from both the walls and target so as to include all secondary electrons repelled from target toward the walls.

Further, in order to reduce the extent of the beam divergence after the mass- defining slit, use of a short Faraday cage is preferred since operation occurs with the minimum of the beam diameter at the mass-defining slit. It has been foun...