Electric lamp and discharge devices: systems – High energy particle accelerator tube – Magnetic field acceleration means
Reexamination Certificate
1998-12-23
2001-03-27
Arroyo, Teresa M. (Department: 2881)
Electric lamp and discharge devices: systems
High energy particle accelerator tube
Magnetic field acceleration means
C250S492210, C333S202000, C333S219000
Reexamination Certificate
active
06208095
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to high-energy ion implantation systems and more particularly to a compact helical resonator coil for use in a linear accelerator in such systems.
BACKGROUND OF THE INVENTION
Ion implantation has become the technology preferred by industry to dope semiconductors with impurities in the large-scale manufacture of integrated circuits. High-energy ion implanters are used for deep implants into a substrate. Such deep implants are required to create, for example, retrograde wells. Eaton GSD/HE and GSD/VHE ion implanters are examples of such high-energy implanters. These implanters can provide ion beams at energy levels up to 5 MeV (million electron volts). U.S. Pat. No. 4,667,111, assigned to the assignee of the present invention, Eaton Corporation, and describing such an high-energy ion implanter, is incorporated by reference herein as if fully set forth.
A block diagram of a typical high-energy ion implanter
10
is shown in FIG.
1
. The implanter
10
comprises three sections or subsystems: a terminal
12
including an ion source
14
powered by a high-voltage supply
16
to produce an ion beam
17
of desired current and energy; an end station
18
which contains a rotating disc
20
carrying wafers W to be implanted by the ion beam; and a beamline assembly
22
, located between the terminal
12
and the end station
18
, which contains a mass analysis magnet
24
and a radio frequency (RF) linear accelerator (linac)
26
. A final energy magnet (not shown in
FIG. 1
) may be positioned between the linac
26
and the rotating disc.
The RF linac
26
comprises a series of resonator modules
30
a
through
30
n
, each of which functions to further accelerate ions beyond the energies they achieve from a previous module.
FIG. 2
shows a known type of resonator module
30
, comprising a large inductive coil L having a circular cross section and being contained within a resonator cavity housing
31
(i.e., a “tank” circuit). A radio frequency (RF) signal is capacitively coupled to a high-voltage end of the inductor L via capacitor C
c
. An accelerating electrode
32
is directly coupled to the high-voltage end of the inductor L. Each accelerating electrode
32
is mounted between two grounded electrodes
34
and
36
, and separated by gaps
38
and
40
, respectively.
FIG. 3
shows a simple lumped parameter equivalent circuit for the resonator geometry of FIG.
2
. The capacitance C includes the capacitance of the high voltage electrode with respect to ground, the stray capacitance of the coil and electrode stem with respect to ground, and the inter-turn coil capacitance.
Values for C and L are chosen for the circuit to achieve a state of resonance so that a sinusoidal voltage of large amplitude may be achieved at the accelerating electrode
32
. The accelerating electrode
32
and the ground electrodes
34
and
36
operate in a known “push-pull” manner to accelerate the ion beam passing therethrough, which has been “bunched” into “packets”. During the negative half cycle of the RF sinusoidal electrode voltage, a positively charged ion packet is accelerated (pulled by the accelerating electrode
32
) from the first grounded electrode
34
across gap
38
. At the transition point in the sinusoidal cycle, wherein the electrode
32
is neutral, the packet drifts through the electrode
32
(also referred to as a “drift tube”) at constant velocity.
During the positive half cycle of the RF sinusoidal electrode voltage, positively charged ion packets are further accelerated (pushed by the accelerating electrode
32
) toward the second grounded electrode
36
across gap
40
. This push-pull acceleration mechanism is repeated at subsequent resonator modules having accelerating electrodes that also oscillate at a high-voltage radio frequency, thereby further accelerating the ion beam packets by adding energy thereto. The RF phase of successive accelerating electrodes in the modules is independently adjusted to insure that each packet of ions arrives at the appropriate gap at a time in the RF cycle that will achieve maximum acceleration.
Referring to
FIG. 3
, it is convenient for analysis to replace the three circuit values R, L and C by the parameters &ohgr; (the resonant frequency), Q (the quality factor), and Z (the characteristic impedance), where: &ohgr;=(LC)
−½
, Q=R/(&ohgr;L), and Z=&ohgr;L=1/(&ohgr;C)=(LC)
½
. Note that &ohgr; is the radial frequency, equal to 2 &pgr; times the conventional frequency (Hertz).
To minimize the power required to obtain a given electrode voltage, the product of the quality factor Q and the characteristic impedance Z must be maximized. Prior art resonators such as that shown in
FIG. 4
are designed using known design principles for high Q resonators. Such designs utilize a circular cross section conductor for the coil. By utilizing a rectangular cross section conductor, as is contemplated by the present invention, with the short dimension parallel to the coil axis
47
, higher impedance coils may be realized while still maintaining a high quality factor Q. The shorter conductor dimension parallel to the coil axis allows smaller winding pitch, i.e., a shorter coil, which has less capacitance with respect to ground (the resonator housing
31
). Thus, the ratio of the coil inductance to the coil capacitance is increased.
SUMMARY OF THE INVENTION
A compact coil design is provided for a linear accelerator resonator capable of resonating at a predetermined frequency. The coil comprises a plurality of generally circular coil segments, each of the coil segments having a polygonal cross section wherein flat surfaces of adjacent coil segments face each other. The polygonal cross section may take the form of a rectangle having dimensions of length x and width y, wherein dimension x section defines the flat surfaces of adjacent coil segments. The coil segments are provided with a dual channel construction for providing the introduction of a cooling medium into the coil. The dual channel construction comprises an inlet passageway and an outlet passageway having a separate inlet and outlet, respectively, at a first end of the coil, and wherein the inlet and outlet passageways are connected and in communication with each other at a second end of the coil.
REFERENCES:
patent: 4700158 (1987-10-01), Dorsey
patent: 5344815 (1994-09-01), Su et al.
patent: 5351023 (1994-09-01), Niiranen
patent: 5418508 (1995-05-01), Puurunen
patent: 5445153 (1995-08-01), Sugie et al.
patent: 5546743 (1996-08-01), Conner
Divergilio William F.
Quinn Stephen M.
Saadatmand Kourosh
Arroyo Teresa M.
Axcelis Technologies Inc.
Kastelic John A.
Wells Nikita
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