Ion sources optimization for high energy ion implantation by computer simulation
Results of the computer simulation for ion sources optimization used for ion implantations have been done. The highly stripped ion source has been designed to provide high current beams of multiply charged P and B ions for high energy ion implantation. However, the total current transport efficiency...
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Litovko, I.V. Gushenets, V.I. 2017-01-06T11:44:37Z 2017-01-06T11:44:37Z 2008 Ion sources optimization for high energy ion implantation by computer simulation / I.V. Litovko, V.I. Gushenets // Вопросы атомной науки и техники. — 2008. — № 6. — С. 138-140. — Бібліогр.: 3 назв. — англ. 1562-6016 PACS: 52.65.-y https://nasplib.isofts.kiev.ua/handle/123456789/110769 Results of the computer simulation for ion sources optimization used for ion implantations have been done. The highly stripped ion source has been designed to provide high current beams of multiply charged P and B ions for high energy ion implantation. However, the total current transport efficiency was about 30%. The modified computer code Kobra has been used to simulate processes of ion extraction by dc-acceleration systems as well as beam transport and thus to determine main reasons for ion beam losses. The calculations indicated that the losses of extracted ion beam mainly occur in the transport channel and magnetic separator. The computer modeling allows find optimal geometry for ion-optical system. Several ion-optical systems were designed and also changed the design of the initial section of the beam transport channel. Furthermore, the simulation for original way of compensating the parasitic beam deflection has been executed. Results of experiments with the modified geometry are supported simulation results. With the optimization of geometries of the ion-optical system and experimental setup, the maximum current transport for Boron ions has been attained. It should be noted that the maximum attainable percentage of singly charged B ions was 65% and the total current transport was about 60%. Приведено результати чисельного моделювання оптимізації іонного джерела для іонної імплантації. Для отримання високо-енергійних іонів фосфору і бору було створено іонне джерело, однак, його ефективність була дуже низькою. Для знаходження каналів втрат було здійснено комп’ютерне моделювання на основі модифікованого коду Кобра, яке довело, що головні втрати зв’язані з транспортним каналом та з магнітним сепаратором. Завдяки моделюванню було знайдено оптимальну геометрію джерела, а також шляхи компенсації відхилення пучку у магнітному полі. Здійснена на основі розрахунків модифікація іонного джерела дозволила отримати максимальний струм для пучків бору та підвищити ефективність іонного джерела більш ніж вдвічі. Приведены результаты численного моделирования оптимизации ионного источника для ионной имплантации. Для получения высокоэнергетичных пучков фосфора и бора был создан ионный источник, однако, его эффективность была крайне низкой. Для нахождения возможных каналов потерь было проведено компьютерное моделирование на основе модифицированного кода Кобра, которое показало, что основные потери связаны с транспортным каналом и магнитным сепаратором. Благодаря моделированию была найдена оптимальная геометрия источника, а также пути компенсации отклонения пучка в магнитном поле. На основе полученных результатов источник был модифицирован, что позволило достичь максимального тока для пучков однозарядного бора и повысить эффективность источника более чем вдвое. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Plasma electronics Ion sources optimization for high energy ion implantation by computer simulation Оптимізація іонного джерела для високодозної імплантації Оптимизация ионного источника для высокодозной имплантации Article published earlier |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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DSpace DC |
| title |
Ion sources optimization for high energy ion implantation by computer simulation |
| spellingShingle |
Ion sources optimization for high energy ion implantation by computer simulation Litovko, I.V. Gushenets, V.I. Plasma electronics |
| title_short |
Ion sources optimization for high energy ion implantation by computer simulation |
| title_full |
Ion sources optimization for high energy ion implantation by computer simulation |
| title_fullStr |
Ion sources optimization for high energy ion implantation by computer simulation |
| title_full_unstemmed |
Ion sources optimization for high energy ion implantation by computer simulation |
| title_sort |
ion sources optimization for high energy ion implantation by computer simulation |
| author |
Litovko, I.V. Gushenets, V.I. |
| author_facet |
Litovko, I.V. Gushenets, V.I. |
| topic |
Plasma electronics |
| topic_facet |
Plasma electronics |
| publishDate |
2008 |
| language |
English |
| container_title |
Вопросы атомной науки и техники |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| format |
Article |
| title_alt |
Оптимізація іонного джерела для високодозної імплантації Оптимизация ионного источника для высокодозной имплантации |
| description |
Results of the computer simulation for ion sources optimization used for ion implantations have been done. The highly stripped ion source has been designed to provide high current beams of multiply charged P and B ions for high energy ion implantation. However, the total current transport efficiency was about 30%. The modified computer code Kobra has been used to simulate processes of ion extraction by dc-acceleration systems as well as beam transport and thus to determine main reasons for ion beam losses. The calculations indicated that the losses of extracted ion beam mainly occur in the transport channel and magnetic separator. The computer modeling allows find optimal geometry for ion-optical system. Several ion-optical systems were designed and also changed the design of the initial section of the beam transport channel. Furthermore, the simulation for original way of compensating the parasitic beam deflection has been executed. Results of experiments with the modified geometry are supported simulation results. With the optimization of geometries of the ion-optical system and experimental setup, the maximum current transport for Boron ions has been attained. It should be noted that the maximum attainable percentage of singly charged B ions was 65% and the total current transport was about 60%.
Приведено результати чисельного моделювання оптимізації іонного джерела для іонної імплантації. Для отримання високо-енергійних іонів фосфору і бору було створено іонне джерело, однак, його ефективність була дуже низькою. Для знаходження каналів втрат було здійснено комп’ютерне моделювання на основі модифікованого коду Кобра, яке довело, що головні втрати зв’язані з транспортним каналом та з магнітним сепаратором. Завдяки моделюванню було знайдено оптимальну геометрію джерела, а також шляхи компенсації відхилення пучку у магнітному полі. Здійснена на основі розрахунків модифікація іонного джерела дозволила отримати максимальний струм для пучків бору та підвищити ефективність іонного джерела більш ніж вдвічі.
Приведены результаты численного моделирования оптимизации ионного источника для ионной имплантации. Для получения высокоэнергетичных пучков фосфора и бора был создан ионный источник, однако, его эффективность была крайне низкой. Для нахождения возможных каналов потерь было проведено компьютерное моделирование на основе модифицированного кода Кобра, которое показало, что основные потери связаны с транспортным каналом и магнитным сепаратором. Благодаря моделированию была найдена оптимальная геометрия источника, а также пути компенсации отклонения пучка в магнитном поле. На основе полученных результатов источник был модифицирован, что позволило достичь максимального тока для пучков однозарядного бора и повысить эффективность источника более чем вдвое.
|
| issn |
1562-6016 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/110769 |
| citation_txt |
Ion sources optimization for high energy ion implantation by computer simulation / I.V. Litovko, V.I. Gushenets // Вопросы атомной науки и техники. — 2008. — № 6. — С. 138-140. — Бібліогр.: 3 назв. — англ. |
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AT litovkoiv ionsourcesoptimizationforhighenergyionimplantationbycomputersimulation AT gushenetsvi ionsourcesoptimizationforhighenergyionimplantationbycomputersimulation AT litovkoiv optimízacíâíonnogodžereladlâvisokodoznoíímplantacíí AT gushenetsvi optimízacíâíonnogodžereladlâvisokodoznoíímplantacíí AT litovkoiv optimizaciâionnogoistočnikadlâvysokodoznoiimplantacii AT gushenetsvi optimizaciâionnogoistočnikadlâvysokodoznoiimplantacii |
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2025-11-25T01:12:37Z |
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2025-11-25T01:12:37Z |
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| fulltext |
ION SOURCES OPTIMIZATION FOR HIGH ENERGY
ION IMPLANTATION BY COMPUTER SIMULATION
I.V. Litovko1, V.I. Gushenets2
1Institute of Nuclear Research NASU, 47 pr. Nauki, 03028 Kiev, Ukraine, ilitovko@kinr.kiev.ua;
2High Current Electronic Institute SB RAS, 2/3 Academichesky ave.,Tomsk, 634055 Russia
Results of the computer simulation for ion sources optimization used for ion implantations have been done. The
highly stripped ion source has been designed to provide high current beams of multiply charged P and B ions for high
energy ion implantation. However, the total current transport efficiency was about 30%. The modified computer code
Kobra has been used to simulate processes of ion extraction by dc-acceleration systems as well as beam transport and
thus to determine main reasons for ion beam losses. The calculations indicated that the losses of extracted ion beam
mainly occur in the transport channel and magnetic separator. The computer modeling allows find optimal geometry for
ion-optical system. Several ion-optical systems were designed and also changed the design of the initial section of the
beam transport channel. Furthermore, the simulation for original way of compensating the parasitic beam deflection has
been executed. Results of experiments with the modified geometry are supported simulation results. With the
optimization of geometries of the ion-optical system and experimental setup, the maximum current transport for Boron
ions has been attained. It should be noted that the maximum attainable percentage of singly charged B ions was 65%
and the total current transport was about 60%.
PACS: 52.65.-y
INTRODUCTION
Various types of ions, but mostly Boron and
Phosphorous are implanted into substrate used in the
construction of semiconductors. The energies range
deferent from as low as 100 eV for shallow surface
implantations, to as high as multi-MeV for deep
implantation into materials. Our task was to develop high
charge state ion sources for high energy implantation in
order to improve upon present day high-energy ion
implanters. The natural way for this purpose was trying to
adapt charge enhancement techniques to ion sources that
generate steady state multi-charged B, P ions [1].
The highly stripped ion source has been designed to
provide high current beams of multiply charged
Phosphorous and Boron ions for high energy ion
implantation. However, the total current transport
efficiency was about 30%. Therefore determine main
reason for ion beam losses and optimization construction
of ion-optical system was main tasks for improving
effective of ion source. The using of computer modeling
for these purposes looks very attractive and easy way in
order to optimize beam parameters as well as geometry of
ion source. As a rule, the applied numerical method based
on solving the Poisson equation with the unknown space
charge term and then the result is used for the solving of
motion equations for charge particles. A repeated iteration
allows achieve self-consistent solution.
The optimization of the geometry of ion-optical
system as well as transport system was made in this work
by consequent numerical simulations with Kobra code
[2]. Algorithms of code are modified for the calculation of
the beam characteristics with the best precision.
MODELLING OF BEAM EXTRACTION
Modified code Kobra is intended for solving three-
dimension stationary problems of forming charged particle
beams in external and self-consistent electric and magnetic
fields. It allows translate the geometry information into mesh
information and take into account plasma source and
acceleration gap geometry as well as physical condition for
beam formation. The plasma is looking as collisionless, fully
ionized. We consider the case of electron emission limited by
space charge. For describing of such plasma model could be
used Poisson equation ρϕ
ε
Δ = , the law of charge
conservation 0j∇ ⋅ = and particles movement equations
( )qd v ι i Ε v Βid t m i
= + ×⎡ ⎤⎣ ⎦
, here ϕ – is the electric
potential, E – the electric field, B- the magnetic induction,
j – the current density, ε – the permittivity, vi, mi and qi –
the velocity, mass and charge for particle of kind i. For
transport high-current ion beam we need take into account
the importance the space charge of the particles
N ji
i 1 i
ρ
ν
= ∑
=
in addition to the external fields and the
magnetic self-field 0
j
B μ μr r
= that may influence the
particles themselves. Here ji is current density; N is
maximum charge of ions in the beam, μ0 μr - the
permeability and r is the perpendicular distance to the
trajectory. The space charge limited current density j
depends on the potential drop ϕ across the extraction gap
width d according to Child-Lengmuir low
2d
23
m
2q
9
4εj 0 ϕ
= . The beam is extracted from plasma
by applying a potential difference between the plasma and
the beam line.
The finite difference method is used for the
discretization of equations system. The highest discretization
should be chosen to translate the physical problem into the
best possible data description, but the Debye length must be
smaller than the character length of mesh discretization.
For solution of the set of algebraic equations an
iterative point-to-point relaxation method is applied. The
first step is solution of the Laplace equation with using
seven point differential schemes. An iteration method
with relaxation of potential is used to find the self-
consistent solution: , n
kjikji
n
kji ,,,,
1
,, )1( ϕααϕϕ −+=+
138 PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2008. № 6.
Series: Plasma Physics (14), p. 138-140.
where n is a number of iteration, α is a coefficient of
relaxation that can change during calculation, φn
i,j,k – old
value of potential, φn+1
i,j,k – new, φi,j,k – evaluated for node
(i,j,k) from calculation for this node and neighbored nodes.
Equations of motion is solving by numerical
integration with repeated interval halving and
extrapolation. The space charge map is created during this
process. A self-consistent solution can be found by
repeated solving of Poisson equation, motion equations
for particles and re-determination of the space charge
distribution on every step. The existing boundaries
between regions with space charge and region with
plasma condition are taken into account.
139
RESULTS OF THE COMPUTER
SIMULATION
The principal schema of ion-optical system for ions
extraction and acceleration is shown at Fig.1.
Fig.1. Construction of ion-optical 3-electrodes system
The ac-dc system is used for saving the space charge
compensation of the extracted ion beam. The beam is
extracted from plasma by applying a potential difference
between the plasma and the beam line. System is in
magnetic field. The aperture sizes of electrodes as well as
distances between them changed during calculation with
aim find optimal construction for extraction of the steady
ion beam with high current, small divergence and
minimizing losses during beam transport.
The calculation has been made for Phosphorus ion
beam with different ion charge state (45% P+1, 45%PP
+2,
10%P+3 on current fractions) and for .Boron beam (70%
В+, 10% F+, 10% BF+ and 10% BF+2). The starting energy
is given by a direct ion drift energy which is determined
by the physics of plasma formation and the ion
temperature. Corresponding data for plasma source have
been taken from experiment [3].
Fig.2. Calculated trajectories of the ion beam along (a)
and across (b) emission slit for initial geometry: size of
emission slit 1x40 (mm), suppressor and accel-electrode
4x44 and 5x45 (mm) consequently
The space charge inside the plasma is compensated
by electrons with Boltzmann density distribution and
temperature about 5 eV. Calculations have been made for
emission current 20 mA and 40 mA, ac-voltage 25−30 kV
and dc-voltage 2−6 kV. System was subdivided on 2
subsystem – extraction subsystem and transport
subsystem. Fig. 2 shows the results of calculation for
these subsystems for initial geometry.
a
b
Fig.3. Calculated trajectories of the ion beam along (a)
and across (b) emission slit for aperture size in emission,
ac- and dc-electrodes 1х16, 4х20, 5х21 mm2. The beam
deflected by the magnetic field of the ion source (b)
It can be seen from the Fig. 2 that part of beam losses
on the walls of the first section due to deflection of the
beam in the magnetic field of the ion source magnet and
losses for the section make up 20−30%. To increase beam
transparency, source aperture was reduced from lx40 mm2
to lx16 mm2 that shows best result under calculation,
besides was reduced aperture’s size for ac- and dc-
electrodes. Fig. 3 shows the result of calculation for
reducing size. Ones can see from Fig.2 and Fig. 3 that
reducing slits sizes allows decrease defocusing influence
of these slits owing to reduce beam divergence and
rejected beam losses on the tube walls. But problem
connected with decreasing beam cross-sectional
dimensions before the entrance aperture of the separator
still exist. We need in beam cross-section at separator
entrance not more than 4.8×16 cm2, but we have total
beam dimensions 8.5×10 cm2 and the losses for a
4.5×10 cm2 beam cross-section area make up 13%.
In analyzing the calculation data, we came to the
conclusion that the maximum decrease in beam cross-
sectional dimensions is attainable not only by decreasing
the vertical dimension of the emission slit of the ion
source, but also by reducing the spacing between the
emission boundary and the entrance aperture of the
separator. Decreasing the spacing by 20 cm must decrease
the cross-sectional dimensions by a factor of >1.5 even
for an ion source with an emission slit of 1x25 mm2.
However in this case, we have to do away with the
positioning unit and resolve the problem of adjusting the
ion beam position, since the deflection of the ion beam in
the self-magnetic field of the source should be
compensated. From Fig.3 (b) we can see that the beam
deflected by the magnetic field of the ion source. The
displacement the suppressor and grounded electrode slits
from the emission slit by 1 mm in the direction of beam
deflection may compensate beam deflection. As a result,
the ion beam shifted to the slit edge and came under the
influence of the transverse electric field, which causes
deflection of the beam ions in a direction perpendicular to
the beam motion and opposite to the deflection produced
by the magnetic field of the ion source. Fig. 4 shows
results of calculation for shifted construction.
a
b
Fig.5. Boron ion beam imprint on the collector plate (Mo)
against the background of the beam line contour of the
separator for the source aperture is 1×25 mm2
It can be seen in the figure that the cross-sectional
dimensions of the beam, particularly its vertical
dimension, were some decreased and were no more than
36×91 mm2. This measuring procedure does not ensure
sufficient accuracy, and hence the above values differ
from those calculated using the computer code Kobra
(Fig. 4) which shows that the full beam dimensions are
8.5×10 cm2 and the losses for 4.5×10 cm2 beam
dimensions make up 13%.
Fig.4. The beam deflection is compensated through
displacing the suppressor and the grounded electrode
downwards by 1 mm
Thus displacing the suppressor and the grounded
electrode downwards by 1 mm allows reducing the
spacing between the emission boundary and the separator
about 20 cm and as result greatly decreased beam cross-
sectional dimension. This way of compensating the beam
deflection has a number of shortcomings, among which is
an increase in horizontal beam dimension; however, this
dimension was found to approximate the calculated one.
Moreover, the electrodes of the ion-optical system with
an emission slit of 1×16 mm2 were made. Calculations
showed that the total beam dimensions were decreased down
to 4.2×6 cm2. Actually the vertical dimension of the beam
became much smaller and was no greater than 2.5 cm. Under
different experimental conditions, the current transport
varied between 50% and 60%.
EXPERIMENTAL RESULTS
Two ion-optical systems were designed, of which one
had an emission slit of 1×25 mm2 and the other an
emission slit of 1×16 mm2. We also changed the design of
the initial section of the beam transport channel, which
allowed an increase in the inner diameter of the accel-
electrode from 57 to 74 mm. Thus, the conductivity in the
initial section was doubled, and hence the pressure inside
it was to decrease twofold. Based on the calculations of
the compensating beam deflection way we have revised
our experimental set up and removed the bellows unit
whereby the ion beam position in the entrance aperture
plane of the separator beam line was changed. This made
it possible to reduce the spacing between the emission
boundary and the separator by 17 cm.
CONCLUSION
For optimal ion source parameters, beams more
40 mA were extracted. Singly charged boron made up
over 70% of the total ion beam [3]. To increase beam
transparency, the experimental set up have been
redesigned and source aperture was reduced from
1×40mm2 to l×16mm2. In results this arrangements
allowed the full current transport of boron ion beam to
increase practically twofold.
REFERENCES
1. V.A. Batalin, AS. Bugaev et al. //Rev. Sci. Instrum.
2004, v. 75, p. 1900.
The cross section of the ion beam and its position in
the entrance aperture region of the magnetic separator
beam line were determined from an imprint left on the
molybdenum collector plate. Fig. 5 shows a photo of the
imprint. An ion beam of current irradiated the Mo plate
for an hour. The pressure at the collector site was
9.2×10-5 Torr.
2. I.G. Brown. The physics and technology of ion sources.
Weinheim: “Wiley-VCH Verlag GmbH & Co. KGaA”,
1999, p. 41-60.
3. V. Gushenets et al.//Rev.Sci.Instrum. 2006, v.77, p.109.
Article received 22.09.08.
ОПТИМИЗАЦИЯ ИОННОГО ИСТОЧНИКА ДЛЯ ВЫСОКОДОЗНОЙ ИМПЛАНТАЦИИ
И.В. Литовко, В.И. Гушенец
Приведены результаты численного моделирования оптимизации ионного источника для ионной имплантации. Для
получения высокоэнергетичных пучков фосфора и бора был создан ионный источник, однако, его эффективность была
крайне низкой. Для нахождения возможных каналов потерь было проведено компьютерное моделирование на основе
модифицированного кода Кобра, которое показало, что основные потери связаны с транспортным каналом и
магнитным сепаратором. Благодаря моделированию была найдена оптимальная геометрия источника, а также пути
компенсации отклонения пучка в магнитном поле. На основе полученных результатов источник был модифицирован,
что позволило достичь максимального тока для пучков однозарядного бора и повысить эффективность источника более
чем вдвое.
ОПТИМІЗАЦІЯ ІОННОГО ДЖЕРЕЛА ДЛЯ ВИСОКОДОЗНОЇ ІМПЛАНТАЦІЇ
І.В. Літовко, В.І. Гушенец
Приведено результати чисельного моделювання оптимізації іонного джерела для іонної імплантації. Для
отримання високо-енергійних іонів фосфору і бору було створено іонне джерело, однак, його ефективність була
дуже низькою. Для знаходження каналів втрат було здійснено комп’ютерне моделювання на основі
модифікованого коду Кобра, яке довело, що головні втрати зв’язані з транспортним каналом та з магнітним
сепаратором. Завдяки моделюванню було знайдено оптимальну геометрію джерела, а також шляхи компенсації
відхилення пучку у магнітному полі. Здійснена на основі розрахунків модифікація іонного джерела дозволила
отримати максимальний струм для пучків бору та підвищити ефективність іонного джерела більш ніж вдвічі.
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