Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2000-09-05
2003-02-04
Anderson, Bruce (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C313S362100, C250S42300F
Reexamination Certificate
active
06515290
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to ion implantation systems, and more specifically to a gas delivery system and method for supplying gas across a voltage gap in an ion implantation system or other type equipment.
BACKGROUND OF THE INVENTION
Ion implanters are used to implant or “dope” silicon wafers with impurities to produce n or p type extrinsic materials. The n and p type extrinsic materials are utilized in the production of semiconductor integrated circuits. As its name implies, the ion implanter dopes the silicon wafers with a selected ion species to produce the desired extrinsic material. Implanting ions generated from source materials such as antimony, arsenic or phosphorus results in n type extrinsic material wafers. If p type extrinsic material wafers are desired, ions generated with source materials such as boron, gallium or indium will be implanted.
The ion implanter includes an ion source for generating positively charged ions from ionizable source materials. The generated ions are formed into a beam and accelerated along a predetermined beam path to an implantation station. The ion implanter includes beam forming and shaping structure extending between the ion source and the implantation station. The beam forming and shaping structure maintains the ion beam and bounds an elongated interior cavity or region through which the beam passes en route to the implantation station. When operating the implanter, the interior region must be evacuated to reduce the probability of ions being deflected from the predetermined beam path as a result of collisions with air molecules.
For high current ion implanters, the wafers at the implantation station are mounted on a surface of a rotating support. As the support rotates, the wafers pass through the ion beam. Ions traveling along the beam path collide with and are implanted in the rotating wafers. A robotic arm withdraws wafers to be treated from a wafer cassette and positions the wafers on the wafer support surface. After treatment, the robotic arm removes the wafers from the wafer support surface and redeposits the treated wafers in the wafer cassette.
FIG. 1
depicts an exemplary ion implanter, shown generally at
10
, which includes an ion source
12
for emitting ions that form an ion beam
14
and an implantation station
16
. Control electronics
11
are provided for monitoring and controlling the ion dosage received by the wafers within a process chamber
17
at the implantation station
16
. The ion beam
14
traverses the distance between the ion source
12
and the implantation station
16
.
The ion source
12
includes a plasma chamber
18
defining an interior region into which source materials are injected. The source materials may include an ionizable gas or vaporized source material. Source material in solid form may be deposited into a pair of vaporizers
19
. Alternatively, gas sources stored either in high pressure or low pressure type containers may be used. The gaseous hydrides arsine (AsH
3
) and phosphine (PH
3
) are used commonly as sources of arsenic (As) and phosphorous (P) in ion implantation. Due to their toxicity, such gaseous sources are often maintained local to the ion source
12
in low pressure SDS (safe delivery system) bottles.
The source material is injected into the plasma chamber and energy is applied to the source materials to generate charged ions in the plasma chamber
18
. The charged ions exit the plasma chamber interior through an elliptical arc slit in a cover plate
20
overlying an open side of the plasma chamber
18
.
The ion beam
14
travels through an evacuated path from the ion source
12
to the implantation station
17
, which is also evacuated via, for example, vacuum pumps
21
. Ions in the plasma chamber
18
are extracted through the arc slit in the plasma chamber cover plate
20
and are accelerated toward a mass analyzing magnet
22
by a set of electrodes
24
adjacent the plasma chamber cover plate
20
. Ions that make up the ion beam
14
move from the ion source
12
into a magnetic field set up by the mass analyzing magnet
22
. The mass analyzing magnet is part of the ion beam forming and shaping structure
13
and is supported within a magnet housing
32
. The strength of the magnetic field is controlled by the control electronics
11
by adjusting a current through the magnet's field windings. The mass analyzing magnet
22
causes the ions traveling along the ion beam
14
to move in a curved trajectory. Only those ions having an appropriate atomic mass reach the ion implantation station
16
. Along the ion beam travel path from the mass analyzing magnet
22
to the implantation station
16
, the ion beam
14
is further shaped, evaluated and accelerated due to the potential drop from the high voltage of the mass analyzing magnet housing
32
to the grounded implantation chamber.
The ion beam forming and shaping structure
13
further includes a quadrupole assembly
40
, a moveable Faraday cup
42
and an ion beam neutralization apparatus
44
. The quadrupole assembly
40
includes set of magnets
46
oriented around the ion beam
14
which are selectively energized by the control electronics (not shown) to adjust the height of the ion beam
14
. The quadrupole assembly
40
is supported within a housing
50
.
Coupled to an end of the quadrupole assembly
40
facing the Faraday flag
42
is an ion beam resolving plate
52
. The resolving plate
52
includes an elongated aperture
56
through which the ions in the ion beam
14
pass as they exit the quadrupole assembly
40
. The resolving plate
52
also includes four counterbored holes
58
. Screws (not shown) fasten the resolving plate
52
to the quadrupole assembly
40
. At the resolving plate
52
the ion beam dispersion, as defined by the width of the envelope D′, D″, is at its minimum value, that is, the width of D′, D″ is at a minimum where the ion beam
14
passes through the resolving plate aperture
56
.
The resolving plate
52
functions in conjunction with the mass analyzing magnet
22
to eliminate undesirable ion species from the ion beam
14
. The quadrupole assembly
40
is supported by a support bracket
60
and a support plate
62
. The support bracket
60
is coupled to an interior surface of the resolving housing
50
.
As stated supra, ion source materials are provided to the ion source
12
in a variety of different ways. Because switching solid source materials is a relatively time-consuming process, use of gaseous source materials is often utilized. Since some of the gaseous ion source materials are toxic, SDS bottles are often utilized which are not pressurized to enhance safety in the event of leakage. Such containers typically are stored in a gas box which is local to or integrated into the ion implanter. Consequently, replacement of the SDS bottles for purposes of ion source material replenishment requires entry into the clean room in which the ion implanter resides, which contributes to machine down time and potential particulate contamination. Therefore it would be desirable to further improve upon present ion source delivery systems.
SUMMARY OF THE INVENTION
The present invention is directed to a gas delivery system for an ion implanter in which a gaseous ion source material is electrically isolated and/or located remote from the ion implanter. The ion source material may reside at a location remote from the ion implanter such as a centralized gas bunker and is maintained at a first voltage potential such as a ground potential. The gaseous ion source material is then delivered to the ion source of the ion implanter which resides at a second potential via a gas delivery network and is coupled to the implanter via an electrically insulative connector. The connector serves as a voltage isolator between the gas storage and/or delivery network provided at the first voltage potential and the ion source of the ion implanter which operates at the second potential.
The gas delivery system of the present invention provide various a
Quill James P.
Rzeszut Richard J.
Anderson Bruce
Axcelis Technologies Inc.
Eschweiler & Associates LLC
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