Electric lamp and discharge devices: systems – Discharge device load with fluent material supply to the... – Electron or ion source
Reexamination Certificate
2000-06-14
2001-09-04
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Discharge device load with fluent material supply to the...
Electron or ion source
C315S111210, C315S111910, C313S359100, C210S198200, C438S692000
Reexamination Certificate
active
06285133
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to semiconductor fabrication, and more particularly to an apparatus for implanting ions that incorporates multiple vacuum chambers.
2. Description of the Related Art
Ion implantation has been used for many years as a means of adding impurity ions into the surfaces of semiconductor wafers and various circuit structures implemented thereon.
In general, ion implantation involves the bombardment of a targeted surface with energetic charged atoms or molecules. During implantation, secondary electrons and other charged species are ejected from the targeted surface. This exodus of negatively charged particles from the targeted surface can lead to a positive charge buildup, particularly where the targeted surface is an insulating film or a polycrystalline silicon film positioned on an underlying oxide film. The positive charge buildup can alter the charge balance in the ion beam and lead to significant dose variations across the substrate. In some circumstances, the charge buildup may damage the surface of the substrate by inducing microscopic craters via oxide breakdown and degrade the transconductance and subthreshold characteristics of the semiconductor device.
One conventional method for addressing the problem of positive charge buildup during implantation involves the use of an electron flood gun. The electron flood gun directs a stream of low energy electrons at the substrate during implantation. The purpose of the low energy electron stream is to neutralize positive charge buildup. In order to attract the flood gun electron beam to the substrate surface, the substrate must be biased relative to the flood gun beam, normally at about 3 to 4 volts for various types of implanters. Depending upon the geometry of the implanted structures, this bias can lead to the trapping of both positive and negative charges, at locally high levels, particularly near edge structures, such as the edges of a gate electrode and the edges of an underlying gate oxide film.
Typical conventional implanters include an ion source and an ion accelerator and a wafer chamber. The wafer chamber and the enclosures for the accelerator and ion source are pumped down to a relatively high vacuum. Pressure levels of 10
−6
torr or lower are typical. The high vacuum is used to minimize the formation of neutrals by collision of beam ions with residual gas atoms. Thus, the conventional implanter contemplates substantial evacuation and thus very low pressures in the wafer chamber and thus very low concentrations of atomic species that might otherwise be utilized to interact with the wafer surface and neutralize charge buildup.
The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, an apparatus for implanting a workpiece with ions is provided that includes a first chamber and a source of accelerated ions for directing a beam of ions through the first chamber toward the workpiece. A second chamber is provided for holding the workpiece. A first bulkhead is positioned between the first chamber and the second chamber and has an aperture enabling fluid communication between the first chamber and the second chamber and the passage of some of the ions therethrough. A first pump is coupled to the first chamber for reducing pressure in the first chamber. A source of gas is coupled to the second chamber. A second pump is coupled to the second chamber for reducing pressure in the second chamber to a higher level than in the first chamber. The higher pressure level in the second chamber enables the gas to be present in the second chamber in sufficient quantities to impact the workpiece and neutralize charge building thereon.
In accordance with another aspect of the present invention, an apparatus for implanting a workpiece with ions is provided that includes a first chamber, a second chamber, a third chamber, and a fourth chamber for holding the workpiece. A source of accelerated ions is provided for directing a beam of ions through the first chamber toward the workpiece. A first pump is coupled to the first chamber for reducing pressure in the first chamber. A first bulkhead is positioned between the first chamber and the second chamber and has a first aperture enabling fluid communication between the first chamber and the second chamber and the passage of some of the ions therethrough. The first aperture restricts the flow of gas therethrough whereby the pressure level in the second chamber is higher than in the first chamber. A second bulkhead is positioned between the second chamber and the third chamber and has a second aperture enabling fluid communication between the second chamber and the third chamber and the passage of some of the ions therethrough. The second aperture restricts the flow of gas therethrough whereby the pressure level in the third chamber is higher than in the second chamber. A third bulkhead is positioned between the third chamber and the fourth chamber and has a third aperture enabling fluid communication between the third chamber and the fourth chamber and the passage of some of the ions therethrough. The third aperture restricts the flow of gas therethrough whereby the pressure level in the fourth chamber is higher than in the third chamber. A source of gas is coupled to the fourth chamber. A second pump is coupled to the fourth chamber for reducing pressure in the fourth chamber. The higher pressure level in the fourth chamber enables the gas to be present in the fourth chamber in sufficient quantities to impact the workpiece and neutralize charge building thereon.
In accordance with another aspect of the present invention, an apparatus for implanting a workpiece with ions is provided that includes a housing enclosing a first chamber. A source of accelerated ions is provided for directing a beam of ions through the first chamber toward the workpiece. A second chamber is provided for holding the workpiece along with a plurality of longitudinally spaced chambers that are defined by the housing and a plurality of longitudinally spaced bulkheads. Each of the bulkheads has an aperture enabling fluid communication between the plurality of longitudinally spaced chambers and the passage of the beam of ions. A source of gas is coupled to the second chamber. A pumping system is provided for evacuating the first chamber, the second chamber and the plurality of longitudinally spaced chambers. The pumping system and the plurality of longitudinally spaced chambers provide an increase in pressure between the first chamber and the second chamber. The higher pressure level in the second chamber enables the gas to be present in the second chamber in sufficient quantities to impact the workpiece and neutralize charge building thereon.
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Lansford Christopher H.
Lansford Jeremy S.
Advanced Micro Devices , Inc.
Honeycutt Timothy M.
Vu Jimmy
Wong Don
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