Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2001-12-26
2003-11-25
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S492100
Reexamination Certificate
active
06653643
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to ion implantation systems, and more particularly to methods and apparatus for improved ion acceleration in an ion implantation system.
BACKGROUND OF THE INVENTION
In the manufacture of semiconductor devices, ion implantation is used to dope semiconductors with impurities. A high energy (HE) ion implanter is described in U.S. Pat. No. 4,667,111, assigned to the assignee of the present invention, which is hereby incorporated by reference as if fully set forth herein. HE ion implanters are used for deep implants into a substrate in creating, for example, retrograde wells. Such implanters typically perform implants at energies between at least 300 keV and 700 keV. Some HE ion implanters are capable of providing ion beams at energy levels up to 5 MeV.
Referring to
FIG. 1
, one implementation of high energy ion implanter
10
is illustrated, having a terminal
12
, a beamline assembly
14
, and an end station
16
. The terminal
12
includes an ion source
20
powered by a high voltage power supply
22
. The ion source
20
produces an ion beam
24
, which is provided to the beamline assembly
14
. The ion beam
24
is then directed toward a target wafer
30
in the end station
16
. The ion beam
24
is conditioned by the beamline assembly
14
, which comprises a mass analysis magnet
26
and a radio frequency (RF) linear accelerator (linac)
28
. The mass analysis magnet
26
passes only ions of an appropriate charge to-mass ratio to the linac
28
.
The linac
28
includes a series of accelerating stages or modules
28
a
-
28
n,
each of which further accelerates ions beyond the energies they achieve from prior modules. The accelerator modules
28
a-
28
n
in the implementation of
FIG. 1
are individually energized by dedicated, fixed-frequency RF amplifiers and resonator circuits (not shown). The linear accelerator modules
28
a
-
28
n
in the high energy ion implanter
10
individually include an RF amplifier, a resonator, and an energizable electrode, wherein the resonators operate at a fixed frequency in order to accelerate ions of the beam
24
to energies over one million electron volts per charge state.
The accelerator
28
of
FIG. 1
may be adapted to efficiently accelerate various ion species through adjustment of the relative phase between adjacent accelerator modules
28
a
-
28
n.
However, the adjustments in the individual accelerator modules
28
a
-
28
n
must be made carefully in order to provide for proper acceleration of ions through the entire accelerator
28
. Thus, sophisticated controls and/or trial and error methodologies are commonly employed in order to tune such multi-variable accelerator systems
28
for specific acceleration energies, and for specific ion species. In addition, the provision of multiple fixed-frequency amplifiers associated with individual accelerating stages
28
a
-
28
n
is costly and such dedicated amplifiers and associated resonator circuits occupy a significant amount of space in conventional ion implantation systems. Thus, there remains a need for improved ion acceleration apparatus and methodologies to facilitate low cost, simplified ion implantation systems.
SUMMARY OF THE INVENTION
The present invention is directed to an ion accelerator for use in an ion implantation system, as well as methodologies for accelerating ions in such a system, which reduce or overcome the problems and shortcomings found in conventional accelerators. In particular, an ion accelerator is provided, comprising a plurality of energizable electrodes energized by a variable frequency power source or amplifier, in order to accelerate ions from an ion source. The employment of a variable frequency power source allows the ion accelerator to be adapted to accelerate a wide range of ion species to desired energy levels for implantation onto a workpiece. The single power source reduces the cost and complexity of the ion accelerator and associated controls compared with conventional accelerators, and additionally reduces the size thereof. The invention further includes methodologies for accelerating ions in an ion implantation system, which may be employed to achieve performance and cost advantages over conventional methodologies.
One aspect of the invention provides an ion accelerator for accelerating ions traveling along a path in an ion implantation system. The accelerator includes one or more accelerating stages, each stage having one or more energizable electrodes and a variable frequency RF system, such as a variable frequency power source and an associated variable frequency resonator. The accelerator stage or stages may comprise constant potential (e.g., grounded) electrodes interleaved between the energizable electrodes, where the RF system energizes all the energizable electrodes in phase with one another. Alternatively, alternating energizable electrodes can be connected to a first RF system terminal, with the remaining electrodes connected to a second terminal, for instance, such that adjacent energizable electrodes are energized 180 degrees out of phase.
The accelerator may also comprise a variable frequency buncher stage located upstream of the initial accelerating stage to provide bunched ions thereto. Reliability in such an implementation may be improved in accordance with the present invention, since only two RF systems are required (e.g., such as a high power RF system for the accelerating stage and a lower power RF system for the buncher stage). Moreover, the reduced number of independent RF systems (e.g. power sources and resonators) simplifies associated control systems and may reduce the time and effort required to tune ion implantation systems. Where multiple accelerating stages are used, or where a buncher stage is provided, the stages are operable at the same frequency or one stage may be operated at a harmonic of the frequency of another stage. In addition, the relative phasing between multiple stages, and/or between accelerating stages and a buncher stage may be controlled at a fixed relationship, or may be adjustable.
Because a single variable frequency power source is used to energize a series of energizable electrodes, the system cost and size are significantly reduced compared with conventional ion accelerators having an RF system for each energizable electrode. In addition, the invention provides an accelerator which is much easier to tune and control, particularly where an ion implantation system is used to implant different ion species at different energy levels. Thus, the system complexity is reduced along with the complexity of associated controls, whereby reduced setup and/or tuning time is achieved. In addition, where previous systems may have been limited in their ability to support a wide range of ion species and energy levels (e.g., due to the complexity involved in tuning the individual resonators and fixed frequency amplifiers), the present invention provides an accelerator with fewer system variables, which is adaptable to support a wide range of ion species and energy levels.
The variable frequency power source, moreover, may be adjustable to provide RF energy to the energizable electrodes in a frequency range appropriate to support commonly used ion species and acceleration energy levels. For instance, the power source may be adjustable in a range of from about 1 to 10 times a given frequency, such as from about 4 MHz to about 40 MHz. The invention comprises any number of such energizable electrodes in a given accelerating stage. The invention may thus provide significant cost and space savings over existing high energy ion implantation systems and linear accelerators.
Another aspect of the invention provides an ion implantation system comprising an ion accelerator as described above having one or more energizable electrodes energized with a variable frequency power source, as well as an ion source providing an ion beam to the accelerator, an end station adapted to position a workpiece so that accelerated ions impact the workpiece, and a controller oper
DiVergilio William F.
Saadatmand Kourosh
Axcelis Technologies Inc.
Eschweiler & Associates LLC
Kalivoda Christopher M.
Lee John R.
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