Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Patent
1998-06-11
1999-12-07
Nguyen, Kiet T.
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
2504922, 2502521, H01J 37317
Patent
active
059987987
ABSTRACT:
An ion implanter includes an dosage control apparatus for measuring and controlling ion beam dosage applied to workpieces disposed in an implantation station of the implanter. The dosage control apparatus permits the direct calculation of a calibration function. The calibration function includes at least one calibration factor, called a K value. The K value is used by dosage control circuitry of the dosage control apparatus to convert from a measured ionized beam current, I.sup.f, as measured by a Faraday cage disposed in the implantation station, to a true or effective beam current, I.sup.T. The K value is determined from a relationship between the measured ionized beam current, I.sup.+, and a pressure, P, in the implantation station. The relationship between the effective beam current, I.sup.T, the measured ionized beam current, I.sup.f, and the implantation station pressure, P, will normally take the form of an exponential relationship, e.g., I.sup.T =I.sup.f [e.sup.-(KP) ]. The K value is determined by measuring the pressure and corresponding ionized beam currents I.sup.f+, for several pressures and applying a curve fitting algorithm to determine the K value that best fits the data points. The effective beam current, I.sup.T, accounts for neutral atoms in the ion beam which are effective species in the implantation of the workpieces but that are not measured by the Faraday cage. The K value depends upon particular gas encountered along the ion beam beam line. Thus, different K values are advantageously calculated during calibration for different residual gas components expected during a production run. During a production run, the proper K value or values are selected and used by the dosage control electronics to determine the effective beam current of the ion beam and, thereby, to accurately control ion beam dosage utilizing the effective beam current. During a calibration run, a restriction plate having a narrow aperture is positioned in the beam line between an ion beam source and the implantation station.
REFERENCES:
patent: 4539217 (1985-09-01), Farley
patent: 4587433 (1986-05-01), Farley
patent: 5130552 (1992-07-01), Bright et al.
Halling Alfred Mike
Krull Wade
Eaton Corporation
Nguyen Kiet T.
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