Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2000-02-07
2004-02-17
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S492210
Reexamination Certificate
active
06693289
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to ion implantation and in particular to an operationally positional source magnetic field for an ion implantation system.
2. Description of the Related Art
Ion implantation systems are utilized for implanting ions in a substance. For example, ion implantation systems can be used to implant impurity ions in a semiconductor substrate of a wafer to form doped regions.
FIG. 1
is a diagram of an example of an ion implantation system for implanting ions into a target semiconductor wafer. Ion implantation system
101
includes an ion source system
105
, an analyzing magnet
107
, resolving aperture
109
, and an acceleration tube
111
. Ion implantation system
101
also includes a scanning system to distribute ions uniformly over a target wafer
131
. In
FIG. 1
, the scanning system includes focus lens
112
, neutral beam trap and beam gate
108
, Y axis scanner
113
, beam trap and gate plate
115
, and X-axis scanner
119
. Ion implantation system
101
also includes a system end station
132
. End station
132
includes an area defining aperture
135
, a Faraday cup and current integrator (which directly measures the implant dose by collecting the beam current and integrating over the implant time), and a subsystem that loads, holds, and positions the target wafer
131
for ion implementation. The Faraday cup nearly surrounds target wafer
131
and has an opening around aperture
135
. Ion implantation system
101
also includes a vacuum system
133
for evacuating various chambers and components of the ion system. Ion implantation system
101
further includes a system controller
143
for controlling the operation of the ion implantation system. A further description of an example of an ion implantation system can be found in the
Silicon Processing for the VLSI Era
, by S. Wolf and R. N. Tauber, Vol. 1, 1986, pages 308-317. Other examples of ion implantation systems can be found in Plumb et al, U.S. Pat. No. 4,743,767; Aitken U.S. Pat. No. 5,300,785; Tanaka et al., U.S. Pat. No. 5,306,921; Mekenna et al., U.S. Pat. No. 4,757,208; Aitken et al., U.S. Pat. No. 5,389,793; Wong, U.S. Pat. No. 5,675,152; all of which are incorporated by reference in their entirety.
FIG. 2
is an illustrative diagram of an example of an ion source system of an ion implantation system. Ion source system
201
is a Bernas type ion source system. Located within arc chamber
203
is pig tail type filament
205
and repeller plate
207
. A current provided through filament
205
generates thermal electrons which are accelerated through a gas species to collide with atoms of the gas species to produce ions. The gas species material is provided from a feed source (not shown) via the gas feed inlet
211
. Ions exit the chamber through extraction slit
227
.
The ion source system shown includes two source magnet poles that generate a magnetic field (designated as the dashed arrows) in arc chamber
203
. The magnetic field alters the electron paths (e.g., path
222
) to increase the probability of collisions with source material gas species atoms, thereby producing more ions. Source magnet poles for conventional ion implantation systems are operationally fixed with respect to the arc chamber such that they are capable of providing a magnetic field in only one position with respect to the arc chamber. Some ion implantation systems include the ability to vary the magnetic field provided by the source magnet poles
217
and
219
. Varying the magnetic field allows the field strength to be set to a value that provides the maximum ion output for the source magnet core poles as positioned.
Because the magnetic field generated by a source magnet affects the ionization in the arc chamber, the magnetic field may create “hot spots” of ion plasma in the arc chamber which can shorten the life of the filament in the chamber.
SUMMARY OF THE INVENTION
It has been discovered that providing an ion implantation system with source magnetic structures that are operationally positionable with respect to an arc chamber advantageously provides the ion implantation system with the ability to move a magnetic field to maximize ion generation efficiency. Moving a magnetic field with respect to the arc chamber may also allow potential hot spots in the ion chamber to be moved within the chamber, thereby extending the operating life of the filament.
In one aspect of the invention, a method for generating ions includes generating ions from an arc chamber with source magnet poles providing a magnetic field in a first position with respect to the arc chamber. The method also includes positioning the source magnet poles to provide a magnetic field in a second position. The second position is different from the first position. The method further includes generating ions from the arc chamber with the magnetic field in the second position.
In another aspect, the invention includes an ion source system for an ion implantation system. The ion source system includes an arc chamber and a source magnet assembly including at least two magnetic poles that are positionable with respect to the arc chamber to provide a plurality of operational magnetic field positions with respect to the arc chamber.
In another aspect of the invention, an ion implantation system includes a ion source system including an arc chamber. The ion implantation system also includes means for providing a magnetic field for the ion source system in a plurality of operational positions with respect to the arc chamber.
REFERENCES:
patent: 3845312 (1974-10-01), Allison, Jr.
patent: 4578589 (1986-03-01), Aitken
patent: 4743767 (1988-05-01), Plumb et al.
patent: 4743806 (1988-05-01), Gyulai et al.
patent: 4754200 (1988-06-01), Plumb et al.
patent: 4757208 (1988-07-01), McKenna et al.
patent: 4847504 (1989-07-01), Aitken
patent: 5130552 (1992-07-01), Bright et al.
patent: 5300785 (1994-04-01), Aitken
patent: 5306921 (1994-04-01), Tanaka et al.
patent: 5389793 (1995-02-01), Aitken et al.
patent: 5675152 (1997-10-01), Wong
patent: 5886355 (1999-03-01), Bright et al.
patent: 5914494 (1999-06-01), Abbott
patent: 5973329 (1999-10-01), Kim
patent: 6222196 (2001-04-01), Mack
S. Wolf and R.N. Tauber;Silicon Processing for the VLSI Era; vol. 1-Process Technology; 1986; 308-317. (Copy Enclosed).
March Marvin G.
Toy Stephen W.
Campbell Stephenson Ascolese LLP
Lee John R.
NEC Electronics Inc.
Quash Anthony
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