Cleaning and liquid contact with solids – Processes – For metallic – siliceous – or calcareous basework – including...
Reexamination Certificate
1999-05-10
2001-04-24
Markoff, Alexander (Department: 1746)
Cleaning and liquid contact with solids
Processes
For metallic, siliceous, or calcareous basework, including...
C134S001000, C134S001100, C134S036000, C250S492200
Reexamination Certificate
active
06221169
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 contaminated 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 1 milliamp (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 or vapor, 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 by the species being implanted during the course of continued operation. Components that are prone to contamination are those that the ion beam impacts during processing. Along the beamline, components which may become contaminated include the strike plate inside the mass analysis magnet, accelerating electrodes, resolving apertures, and plasma flood components. In the target chamber, at least in high current ion implanters, target wafers are positioned on the periphery of an aluminum disk. 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 contaminated with the dopant species.
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 or sputtering 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. For example, phosphorous which has been sputtered onto or implanted into the surface of an aluminum target disk or beamline component may be dislodged by a subsequent arsenic ion beam, resulting in process contamination.
It is known to generate an ion beam comprised of a reactive species, such as fluorine, between successive implant processes to clean internal portions of an ion implanter (see for example, U.S. Pat. No. 5,554,854 to Blake). However, Blake suggests the use of ionized fluorine to effect such cleaning, because the beam must be ionized (positively) to be transported through the implanter. The Blake system does not suggest the use of an atomic neutral reactive species for cleaning the internal components of an ion implanter.
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 a system and method for cleaning the internal components of an ion implanter using the ion beam to generate reactive neutral atomic radicals of a cleaning gas. It is still a further object of the present invention to provide such a system and method for use in cleaning either silicon-coated or uncoated internal implanter components.
SUMMARY OF THE INVENTION
A method and system is provided for cleaning a contaminant from a surface of a vacuum chamber. The method and system include means for (i) generating an ion beam having a reactive species (e.g., fluorine) component; (ii) directing the ion beam toward a surface to be cleaned; (iii) neutralizing the ion beam by introducing, into the chamber proximate the surface to be cleaned, a neutralizing gas (e.g., xenon) such that the ion beam collides with molecules of the neutralizing gas, and, as a result of charge exchange reactions between the ion beam and the neutralizing gas molecules, creates a beam of energetic reactive neutral atoms of the reactive species; (iv) cleaning the surface by allowing the beam of energetic reactive neutral atoms of the reactive species to react with contaminants to create reaction products; and (v) removing from the chamber any volatile reaction products that result from the cleaning process. The neutralizing gas may contain a second reactive species component, such that the neutralizing gas molecules are dissociated into reactive atomic neutral atoms upon colliding with the ion beam.
Alternatively, the method and system include means for (i) generating an energetic non-reactive (e.g., xenon) ion beam; (ii) directing the non-reactive ion beam toward a surface to be cleaned; (iii) introducing a cleaning gas proximate the surface to be cleaned, comprised at least partially of a reactive species (e.g., fluorine) component; (iv) dissociating the cleaning gas using the ion beam to create a supply of energetic reactive neutral atoms of the reactive species; (v) cleaning the surface by allowing the energetic reactive neutral atoms of the reactive species to react with contaminants to create reaction products; and (vi) removing from the chamber any volatile reaction products that result from the cleaning process. The cleaning gas may be characterized by a high sticking coefficient and is allowed to collect onto and adsorb into the surface to be cleaned prior to being dissociated by the ion beam.
REFERENCES:
patent: 4703183 (1987-10-01), Guerra
patent: 5144147 (1992-09-01), Shiozaki et al.
patent: 5554854 (1996-09-01), Blake
patent: 5576538 (1996-11-01), Sakai et al.
patent: 5633506 (1997-05-01), Blake
patent: 5779849 (1998-07-01), Blalock
patent: 5843239 (1998-12-01), Shrotriya
patent: 5940724 (1999-08-01), Warren
patent: 2-155147 (1990-06-01), None
Larson et al, Metallic Impurities and Dopant Cross-Contamination Effects in Ion Implanted Surfaces, MRSSP, vol. 45, pp. 381-388. 1985.
Bernstein James D.
Freer Brian S.
Kopalidis Peter M.
Axcelis Technologies Inc.
Kastelic John A.
Markoff Alexander
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