Coating apparatus – Gas or vapor deposition – With treating means
Reexamination Certificate
1999-08-06
2001-05-29
Mills, Gregory (Department: 1763)
Coating apparatus
Gas or vapor deposition
With treating means
C118S7230AN, C118S728000
Reexamination Certificate
active
06237527
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of plasma immersion ion implantation systems, and more specifically to an improved system and method for maintaining uniform implant energy distribution and minimizing charge accumulation of a substrate implanted by such a system.
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 is one of two important variables in defining a particular implant process (the other being ion energy, which determines implant depth). Ion dose relates to the concentration of implanted ions for a given area or volume of 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.
A conventional 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. The ion beam is directed along an evacuated beam path provided by the beamline. Energetic ions within the beam strike the substrate within the target chamber and are implanted therein. It is important in such an implantation system to insure that the implanted ions do not charge the surface of the wafer to such an extent that circuit components on the wafer are damaged. To prevent such detrimental effects of wafer charge accumulation, beam neutralization mechanisms are often implemented in an ion implanter. In addition, the energy of the implanted ions must be controlled in order to assure a uniform and desired energy distribution for the implant.
Plasma immersion ion implantation (PI-cubed or PI
3
) is an emerging technology wherein a substrate such as a wafer on a platen is immersed within a plasma in a chamber. Thus, the chamber functions as both the processing chamber and the plasma source. Typically, a voltage differential is periodically established between the walls of the chamber and the platen to attract ions in the plasma toward the substrate. A sufficient voltage differential will result in a pulsed ion implantation into the surface of the substrate.
As in conventional ion implantation systems, it is important to insure that wafer charging is minimized. In a PI-cubed system, wafer charging may be caused by either (i) accumulated charge from the implant pulses or (ii) exposure to the plasma in the chamber between implant pulses. In addition, as in conventional ion implantation systems, it is important to insure that only ions within a specific energy range are implanted into the wafer to yield a uniform implant energy distribution.
Accordingly, it is an object of the present invention to provide a system and method for maintaining a uniform implant energy distribution and for minimizing charge accumulation of a substrate implanted by a plasma immersion ion implantation system.
SUMMARY OF THE INVENTION
A plasma immersion ion implantation method and system is provided for maintaining uniformity in implant energy distribution and for minimizing charge accumulation of an implanted substrate such as a wafer. An improved voltage modulator applies a pulsed voltage signal to a platen in a process chamber that contains a plasma, so that ions in the plasma are attracted by and implanted into a wafer residing on the platen. The voltage modulator comprises: (i) a first switch disposed between a power supply and the platen for momentarily establishing a connection therebetween and supplying the pulsed voltage signal to the platen; (ii) a second switch disposed between the platen and ground for at least momentarily closing to discharge residual voltage from the platen after the first switch opens and the connection between the power supply and the platen is broken; and (iii) a controller for controlling sequential operation of the first and second switches.
By closing second switch and grounding the platen the number of ions with energy less than the applied pulse voltage are reduced, thus improving the implant energy distribution. Further, wafer charging due to implantation of positive ions is neutralized by allowing electrons in the plasma to flow toward the wafer between implant pulses. Upon opening, second switch permits the platen to float to achieve the floating potential of the plasma, thus minimizing voltage stresses on devices in the wafer. Alternatively, the platen may be positively biased to the plasma floating potential.
REFERENCES:
patent: 4438315 (1984-03-01), Toyoda et al.
patent: 4912065 (1990-03-01), Mizuno et al.
patent: 4937205 (1990-06-01), Nakayama et al.
patent: 5110437 (1992-05-01), Yamada et al.
patent: 5573597 (1996-11-01), Lantsman
patent: 5585012 (1996-12-01), Wu et al.
patent: 5654043 (1997-08-01), Shao et al.
patent: 5674321 (1997-10-01), Pu et al.
patent: 5690781 (1997-11-01), Yoshida et al.
patent: 5711812 (1998-01-01), Chapek et al.
patent: 5717294 (1998-02-01), Sakai et al.
patent: 6070550 (2000-06-01), Ravi et al.
Bernstein James D.
Denholm A. Stuart
Kellerman Peter L.
Alejandro Luz L.
Axcelis Technologies Inc.
Kastelic John A.
Mills Gregory
LandOfFree
System for improving energy purity and implant consistency,... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with System for improving energy purity and implant consistency,..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and System for improving energy purity and implant consistency,... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2513552