Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
1999-05-10
2001-07-10
Berman, Jack (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S492200, C250S398000, C134S001100, C134S001200, C134S022100
Reexamination Certificate
active
06259105
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of ion implanters, and more specifically to an improved system and method for cleaning silicon coated surfaces of an ion implanter.
BACKGROUND OF THE INVENTION
Ion implantation has become the technology preferred by industry to dope semiconductors with impurities in the large-scale manufacture of integrated circuits. Ion dose and ion energy are the two most important variables used to define an implant step. Ion dose relates to the concentration of implanted ions for a given semiconductor material. Typically, high current implanters (generally greater than 10 milliamps (mA) ion beam current) are used for high dose implants, while medium current implanters (generally capable of up to about 1 mA beam current) are used for lower dose applications.
Ion energy is the dominant parameter used to control junction depth in semiconductor devices. The energy levels of the ions which make up the ion beam determine the degree of depth of the implanted ions. High energy processes such as those used to form retrograde wells in semiconductor devices require implants of up to a few million electron volts (MeV), while shallow junctions may only demand ultra low energy (ULE) levels below one thousand electron volts (1 KeV).
A typical ion implanter comprises three sections or subsystems: (i) an ion source for outputting an ion beam, (ii) a beamline including a mass analysis magnet for mass resolving the ion beam, and (iii) a target chamber which contains the semiconductor wafer or other substrate to be implanted by the ion beam. Ion sources in ion implanters typically generate an ion beam by ionizing within a source chamber a source gas, a component of which is a desired dopant element, and extracting the ionized source gas in the form of an ion beam.
Internal parts of ion implanters located along the beamline and in the target chamber may become contaminated during the course of continued operation. In high current ion implanters, for example, target wafers are positioned on the periphery of an aluminum disk within the target chamber. The disk is both rotated and translated past a stationary ion beam so that the beam implants ions into the entire surface of the wafer. As a result, portions of the disk not covered by a wafer become implanted with the dopant element, which can be problematic for two reasons.
First, because ion implanters are operated using a variety of process recipes, different types of source gases are run in the source to obtain ion beams comprising the desired species of dopant ions. If, however, the target disk (or other beamline component) becomes contaminated by implantation of a species during a previous process recipe (e.g., one involving phosphorous), a later process recipe (e.g., one involving arsenic) may be adversely effected by this cross-contamination. Second, for a particular process recipe, aluminum contamination may present a problem if the ion beam impact with the disk surface causes sputtering of the disk material.
A known solution to the problem of disk surface material sputtering is to coat the disk with silicon. However, the coated disk still presents cross-contamination problems as the silicon layer on the disk is implanted with the particular species being run. Accordingly, it is an object of the present invention to provide a system and method for cleaning surfaces to remove contaminants therefrom. It is a further object to provide such a system and method for use in cleaning surfaces of components in ion implanters or other vacuum processing equipment. It is still a further object to provide such a system and method for cleaning an ion implanter target disk.
SUMMARY OF THE INVENTION
A method and system for controllably stripping a portion of silicon from a silicon coated surface, for example, from an interior portion of an ion implanter. The system comprises (i) a source of gas comprised at least partially of a reactive gas, such as fluorine; and (ii) a dissociation device such as a radio frequency (RF) powered plasma source located proximate the silicon coated surface for converting the source gas to a plasma of dissociated reactive gas atoms and for directing the dissociated reactive gas atoms in the plasma toward the silicon coated surface to be stripped. A control system determines the rate of removal of the silicon from the surface by controlling (i) a rate of source gas flow into and the amount of power supplied to the dissociation device, and (ii) the time of exposure of the silicon coated surface to the plasma. The invention is useful, among other things, for removing a contaminant-laden layer of silicon from a wafer-supporting disk in an ion implanter, wherein the silicon coated surface has been formed by applying a layer of silicon onto the surface by a plasma enhanced physical vapor deposition (PECVD) process.
REFERENCES:
patent: 4923828 (1990-05-01), Gluck et al.
patent: 5554854 (1996-09-01), Blake
patent: 5633506 (1997-05-01), Blake
patent: 5779849 (1998-07-01), Blalock
patent: 5843239 (1998-12-01), Shrotriya
Eddy Ronald J.
Kopalidis Peter M.
Axcelis Technologies Inc.
Berman Jack
Kastelic John A.
Wells Nikita
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