Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2001-06-28
2002-09-17
Nguyen, Kiet T. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S492200
Reexamination Certificate
active
06452198
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to implantation systems used for fabrication of integrated circuits, and more particularly, to mechanisms for minimizing contamination of semiconductor wafers during implantation processes within an implantation chamber of the implantation system.
BACKGROUND OF THE INVENTION
Referring to
FIG. 1
, a conventional implantation system
100
includes an ion beam source
102
, an ion beam line
104
, and an implantation chamber
106
. Dopant ions are generated in the ion source
102
, and the dopant ions travel through the ion beam line
104
to reach the implantation chamber
106
. Upon reaching the implantation chamber
106
, the dopant ions travel through an ion beam aperture
108
for entry into the implantation chamber
106
. The dopant ions then travel though a plasma flood gun
110
which ensures uniform ionization of the dopant ions. The dopant ions are directed toward a semiconductor wafer placed on a wafer platen
112
with a voltage bias on the wafer platen
112
.
The wafer platen
112
holds the semiconductor wafer to be implanted with the dopant ions within the implantation chamber
106
. An ion beam profiler
114
within the implantation chamber
106
measures the dose of the dopant ions near the semiconductor wafer placed on the wafer platen
112
. A dose cup
115
placed behind the wafer platen
112
is used to measure the dose of the dopant ions without the semiconductor wafer on the wafer platen
112
and without the wafer platen
112
within the implantation chamber
106
during characterizing and calibrating of the implantation system
100
, as known to one of ordinary skill in the art of integrated circuit fabrication.
The conventional implantation system
100
with the components including the ion source
102
, the ion beam line
104
, the implantation chamber
106
, the ion beam aperture
108
, the plasma flood gun
110
, the wafer platen
112
, the ion beam profiler
114
, and the dose cup
115
are known to one of ordinary skill in the art of integrated circuit fabrication. An example of such an implantation system is the model VIISta 80 commercially available from Varian Semiconductor Associates, Inc., headquartered in Gloucester, Mass.
Further referring to
FIG. 1
, in the prior art, a lot of a plurality of semiconductor wafers including a first semiconductor wafer
122
and a second semiconductor wafer
124
is processed within the implantation chamber
106
. Each of the semiconductor wafers
122
and
124
is successively placed on the wafer platen
112
within the implantation chamber
106
, and a respective implantation process is performed to implant each of the semiconductor wafers
122
and
124
with dopant ions from the ion source
102
. For example, the first semiconductor wafer
122
is first placed on the wafer platen
112
within the implantation chamber
106
, and a first implantation process is performed to implant the dopant ions into the first semiconductor wafer
122
. After the first implantation process, the first semiconductor wafer
122
is removed from the implantation chamber
106
, and the second semiconductor wafer
124
is placed on the wafer platen
112
within the implantation chamber
106
. A second implantation process is performed to implant the dopant ions into the second semiconductor wafer
124
.
A semiconductor wafer may have a material including a heavy metal compound deposited thereon. For example, oxides (SiO
2
) of such a heavy metal such as oxides of hafnium (Hf), zirconium (Zr), holmium (Ho), molybdenum (Mo), or gadolinium (Gd) are deposited on the semiconductor wafer. Such a heavy metal oxide instead of pure oxide is used to surround interconnect structures of integrated circuits to increase the dielectric constant of the insulating material surrounding the interconnect structures for minimized parasitic capacitance between the interconnect structures.
Referring to
FIG. 1
, the first semiconductor wafer
122
for example may have such a heavy metal compound deposited thereon. When ion beams hit such material on the first semiconductor wafer
122
placed on the wafer platen
112
within the implantation chamber
106
during the first implantation process, the ion beams may detach the heavy metal compound from the first semiconductor wafer
122
to contaminate the implantation chamber
106
with such heavy metal compound landing on inside surfaces of the implantation chamber
106
and on surfaces of the components within the implantation chamber including the ion beam aperture
108
, the plasma flood gun
110
, the wafer platen
112
, the ion beam profiler
114
, and the dose cup
115
. Such contamination is especially prevalent within implantation systems using a high implantation energy such as an implantation energy of about 40 KeV (Kilo-electron Volts).
Referring to
FIG. 1
, when the second semiconductor wafer
124
is placed on the wafer platen
122
of the implantation chamber
106
, the heavy metal compound contaminants within the implantation chamber
106
from the first semiconductor wafer
122
may contaminate the second semiconductor wafer
124
during the second implantation process within the implantation chamber
106
. For example, such heavy metal contaminants may contact and diffuse into a semiconductor wafer within the implantation chamber
106
. Alternatively, such heavy metal contaminants may be incorporated into the dopant ion beam during an implantation process to be implanted into a semiconductor wafer. In addition, the heavy metal contaminant may hit the semiconductor wafer as back-scatter when the dopant ion beam strikes the heavy metal contaminants within the implantation chamber
106
. In any case, as described in the journal article,
Behavior of Molybdenum in Silicon Evaluated for Integrated Circuit Processing
, by J. L. Benton,
Journal of the Electrochemical Society
, 146(5), 1929-1933, 1999, such heavy metal contaminants on a semiconductor wafer may deleteriously affect circuit performance of integrated circuit devices fabricated on the semiconductor wafer such as by increasing the leakage current of MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) or BJTs (Bipolar Junction Transistors).
Thus, a mechanism is desired for minimizing the level of contamination of the implantation chamber from such heavy metals on semiconductor wafers when semiconductor wafers are processed within the implantation chamber.
SUMMARY OF THE INVENTION
Accordingly, in a general aspect of the present invention, the implantation chamber and components within the implantation chamber are coated with additional material to minimize such heavy metal contamination within the implantation chamber.
In one embodiment of the present invention, for minimizing contamination of a semiconductor wafer to be implanted with a fabrication dopant within an implantation system, surfaces of an implantation chamber of the implantation system are coated by performing a first implantation process with a coating dopant before the semiconductor wafer is placed within the implantation chamber. In this manner, contaminants on the surfaces of the implantation chamber are substantially coated with the coating dopant. In addition, surfaces of components disposed within the implantation chamber are coated with the coating dopant during the first implantation process. Thus, contaminants on the surfaces of the components of the implantation chamber are substantially coated with the coating dopant during the first implantation process. After coating the surfaces of the implantation chamber and the components of the implantation chamber, the semiconductor wafer is placed within the implantation chamber, and a second implantation process is performed for doping the semiconductor wafer with the fabrication dopant within the implantation chamber.
In this manner, because the contaminants, on the surfaces of the implantation chamber and on the surfaces of the components of the implantation chamber, are substantially coated with the coating dopant, contamination of the second semi
Mani Balaraman
Ng Che-Hoo
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