U.S. patent application number 14/029196 was filed with the patent office on 2014-02-13 for plasma generator.
This patent application is currently assigned to NISSIN ION EQUIPMENT CO., LTD. The applicant listed for this patent is NISSIN ION EQUIPMENT CO., LTD. Invention is credited to Hideki FUJITA, Tetsuya IGO.
Application Number | 20140042902 14/029196 |
Document ID | / |
Family ID | 50065702 |
Filed Date | 2014-02-13 |
United States Patent
Application |
20140042902 |
Kind Code |
A1 |
FUJITA; Hideki ; et
al. |
February 13, 2014 |
PLASMA GENERATOR
Abstract
A plasma generator generates a plasma by ionizing a gas with a
high-frequency discharge in a plasma generating chamber so that
electrons from the plasma are emitted outside the plasma generator
through an electron emitting hole. The plasma generator includes an
antenna that is provided in the plasma generating chamber and that
emits a high-frequency wave, and an antenna cover that is made of
an insulating material and that covers an entire body of the
antenna. A plasma electrode having the electron emitting hole is
made of a conductive material. A frame cover with a protrusion
ensures conductivity by preventing an insulating material from
accumulating on a surface of the plasma electrode on a plasma side
in sputtering by the plasma.
Inventors: |
FUJITA; Hideki; (Kyoto,
JP) ; IGO; Tetsuya; (Kyoto, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NISSIN ION EQUIPMENT CO., LTD |
Kyoto-shi |
|
JP |
|
|
Assignee: |
NISSIN ION EQUIPMENT CO.,
LTD
Kyoto-shi
JP
|
Family ID: |
50065702 |
Appl. No.: |
14/029196 |
Filed: |
September 17, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13198429 |
Aug 4, 2011 |
8569955 |
|
|
14029196 |
|
|
|
|
Current U.S.
Class: |
315/34 |
Current CPC
Class: |
H05H 2001/463 20130101;
H05H 2001/4667 20130101; H01J 37/3211 20130101; H05H 1/46 20130101;
H01J 37/32357 20130101; H01J 37/32541 20130101 |
Class at
Publication: |
315/34 |
International
Class: |
H05H 1/46 20060101
H05H001/46 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 24, 2010 |
JP |
2010-186824 |
Claims
1. A plasma generator that ionizes a gas using high-frequency
discharge within a plasma generating chamber to generate plasma and
discharges electrons externally using that plasma through an
electron discharge hole, wherein the plasma generator is equipped
with an antenna installed in the plasma generating chamber that
radiates high-frequency waves and an antenna cover that covers the
entire antenna and is comprised of an insulating material, in a
plasma generator in which the plasma electrode material that has
the electron discharge hole is comprised of conductive material,
between the plasma electrode and the antenna, in the cylindrical
frame region, a frame cover is provided that has protrusions of
different thicknesses that are on the inner side or the inner and
outer sides of the frame, the material of the frame cover being an
insulating material, the ones of the protrusions near a top surface
of the plasma electrode and near the frame cover forming shadows
near the top surface of the plasma electrode, the formed shadows
configured to prevent accumulation of the insulating material on
the plasma electrode, the accumulation being associated with
sputtering by the plasma.
2. The plasma generator recited in claim 1, wherein the material of
the frame cover is made of carbon and the frame cover is
electrically connected to one of the plasma generating chamber and
the plasma electrode.
3. A plasma generator that ionizes a gas using high-frequency
discharge within a plasma generating chamber to generate plasma and
discharges electrons externally using that plasma through an
electron discharge hole comprising a plasma electrode, wherein the
plasma generator is equipped with an antenna installed in the
plasma generating chamber that radiates high-frequency waves and an
antenna cover that covers the entire antenna and is comprised of an
insulating material, in a plasma generator in which the plasma
electrode material that has the electron discharge hole is
comprised of conductive material, between the plasma electrode and
the antenna, in the cylindrical frame region, a frame cover is
provided that has protrusions of different thicknesses that are on
the inner side or the inner and outer sides of the frame, the
material of the frame cover comprising carbon, the frame cover
being electrically connected to one of the plasma generating
chamber and the plasma electrode, the frame cover protrusions
forming shadows on the inner wall of the frame cover, and the
formed shadows configured to prevent accumulation of the insulating
material of the frame cover, the accumulation being associated with
sputtering by the plasma.
Description
BACKGROUND OF THE INVENTION
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 13/198,429, filed Aug. 4, 2011, claiming
priority to Japanese Patent Application No. 2010-186824, filed Aug.
24, 2010, the contents of which is incorporated by reference in its
entirety.
[0002] 1. Field of the Invention
[0003] The present invention relates to a high-frequency discharge
plasma generator that is used for suppressing an electrostatic
charge (charge-up), etc., on a surface of a substrate when ion beam
irradiation is carried out in an ion beam irradiation device that
performs ion implantation, etc., by, for example, irradiating the
substrate with an ion beam.
[0004] 2. Description of the Related Art
[0005] A plasma generator is disclosed in Japanese Patent
Application Laid-open No. 2002-324511 (Paragraphs 0031 to 0038 and
FIG. 1) as an example of a high-frequency discharge plasma
generator described above used for suppressing an electrostatic
charge on a surface of a substrate. The disclosed plasma generator
generates a plasma by ionizing a gas with a high-frequency
discharge in a plasma generating chamber. As a result, electrons
from the plasma are emitted outside the plasma generating chamber
through electron emitting holes. In this plasma generator, an inner
wall and an antenna of the plasma generating chamber are covered
with an insulator to prevent metal contamination produced in
sputtering by the plasma and adhering of the conductive sputtered
material to the antenna.
[0006] The principal object of providing the insulator on the inner
wall is to prevent contamination (that is, metallic contamination)
of the plasma from occurring. That is, to prevent particles of
metal constituting the inner wall being discharged in the plasma
from the antenna in sputtering by the plasma.
[0007] Alumina, etc., is used as the material of the insulator. An
extracting power supply 56 is connected between a plasma electrode
16, which has electron emitting holes, and a target chamber 8. The
plasma electrode 16 is made of a conductive material such as
carbon. A current that flows through the extracting power supply 56
is called a PFG current Ipfg and is a measure of the electrons that
are emitted to the outside through electron emitting holes 18.
[0008] The plasma electrode 16 is in contact with a plasma 20 and
is operative to ensure an electric potential of the plasma 20. The
electric potential of the plasma electrode 16 is set the same as
that of a plasma generating chamber 12. When the plasma generating
chamber 12 is internally completely covered with the insulator, no
conductor is in contact with the plasma 20, no current flows in the
plasma 20, and the electrons can hardly be extracted from the
plasma 20. However, the plasma electrode 16 can prevent such
situations from occurring.
[0009] If the plasma generator 10 is driven for a prolonged period
(for example, approximately a few hundred hours to a few thousand
hours), the PFG current decreases to such an extent so as to be of
no use.
[0010] If the PFG current Ipfg decreases as described above and
neutralization of charge-up of the substrate cannot be performed
adequately, the plasma generator has to be removed for clearing the
insulating material accumulated on the plasma electrode 16. This
results in stoppage of the ion beam irradiation device for
maintenance for a long time.
[0011] A plasma is a good conductor and by itself is quasi-neutral.
Therefore, an electron current lost from the plasma and an ion
current are always equal in magnitude. Because a decrease in plasma
electrons takes place due to extraction of an electron current from
a PFG (PFG current Ipfg), the same amount of ions needs to be lost
from the plasma.
[0012] Although the ions can obtain the electrons by recombining in
the plasma, the electron current lost from the plasma cannot be
compensated. An ion current flow is initiated only when the ions
collide against the wall, releasing the electrons from the
wall.
[0013] When the ions collide against the wall, the ions recombine
with the electrons at the wall and are converted back into a
neutral gas. These electrons are supplied by a PFG power supply 30
through a conductive wall. The PFG power supply 30 also extracts
electrons from the PFG, and supplies an amount of electrons to a
PFG plasma via the ions that is equal to the amount of electrons
that flow into a vacuum chamber. As a result, an outflow current is
maintained equal to a feedback current of the power supply.
[0014] If the material of the frame cover is conductive and made of
carbon and electrically connected to the plasma generating chamber
or plasma electrode, then even if plasma is not in contact with
plasma electrode 16, if the inner wall of the frame cover made by
the frame cover protrusions does not become insulating and is in
contact with plasma, and PFG current Ipfg will flow.
SUMMARY OF THE INVENTION
[0015] One plasma generator according to this invention makes the
PFG current Ipfg not decrease by ionizing a gas using
high-frequency discharge within a plasma generating chamber to
generate plasma and discharge electrons externally from that plasma
through an electron discharge hole, equipping the plasma generator
with an antenna installed in the plasma generating chamber that
radiates high-frequency waves and an antenna cover that covers the
entire antenna and is comprised of an insulating material, in a
plasma generator in which the plasma electrode material that has
the electron discharge hole is comprised of conductive material,
between the plasma electrode and the antenna, in the cylindrical
frame region, a frame cover is provided that has protrusions of
different thicknesses that are on the inner side or the inner and
outer sides of the frame, the material of the frame cover being an
insulating material, the frame cover protrusions that are near the
top surface of the plasma electrode that is near the frame cover
forming shadows near the top surface of the plasma electrode, and
those shadows preventing accumulation of insulating material on the
plasma electrode due to sputtering by the plasma.
[0016] The frame cover should preferably be made of a conductive
material such as carbon. The frame cover should also be
electrically connected to the plasma generator or the plasma
electrode. The conductive frame cover also functions as an
electrode, increasing a surface area of the conductive wall, and as
a result, increasing the PFG current Ipfg. The PFG current Ipfg
flows until a point in time at which the entire surface of the
plasma electrode and the frame cover are coated with the insulating
material. Thus, the life of the plasma generator can be prolonged
not only by preventing the insulation of the plasma electrode but
also by increasing the PFG current Ipfg. The carbon can be
pyrolytic graphite having strong plasma resistant properties.
[0017] Another plasma generator according to this invention makes
the PFG current Ipfg not decrease by ionizing a gas using
high-frequency discharge within a plasma generating chamber to
generate plasma and discharge electrons externally from that plasma
through an electron discharge hole, equipping the plasma generator
with an antenna installed in the plasma generating chamber that
radiates high-frequency waves and an antenna cover that covers the
entire antenna and is comprised of an insulating material, in a
plasma generator in which the plasma electrode material that has
the electron discharge hole is comprised of conductive material,
between the plasma electrode and the antenna, in the cylindrical
frame region, a frame cover is provided that has protrusions of
different thicknesses that are on the inner side or the inner and
outer sides of the frame, the material of the frame cover being
made of carbon, the frame cover being electrically connected to the
plasma generating chamber or the plasma electrode, the frame cover
protrusions forming shadows on the inner wall of the frame cover,
and those shadows preventing accumulation of the insulating
material of the frame cover due to sputtering by the plasma.
[0018] In view of the above discussion, because the object is to
only increase the surface area that is in contact with the plasma,
the plasma electrode can be arranged at any position as long as it
is in contact with the plasma, for example, at the edge of the
plasma.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a cross-sectional view of a plasma generator
according to an embodiment of the present invention;
[0020] FIG. 2 is a cross-sectional view taken along a line A-A of
FIG. 1;
[0021] FIG. 3 shows how the shadow of the frame cover protrusion is
formed near the top surface of the plasma electrode and on the
inner wall of the frame cover.
[0022] FIG. 4 is a graph that depicts a change in a PFG current
before and after the implementation of the invention;
[0023] FIGS. 5A to 5D are drawings that depict examples of shapes
of a frame cover with protrusion;
[0024] FIG. 6 is a drawing that depicts an example of a shape of
the frame cover with protrusion that is outwardly convex;
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] Exemplary embodiments of a plasma generator according to the
present invention are explained below with reference to the
accompanying drawings. In FIGS. 1 and 2, a configuration is
explained as an example in which a plasma generator 10 is used in
an ion beam irradiation device (this device is called an ion
implantation apparatus when ion implantation is performed) that
performs a process of ion implantation, etc., into a substrate 4 by
irradiating the substrate (for example, semiconductor substrate) 4
with an ion beam 2 in a target chamber 8. The plasma generator 10
is attached outside the target chamber 8 located in the vicinity of
an upstream side of the substrate 4 via an insulator 54.
[0026] In this example, the ion beam 2 is reciprocally scanned in
an X direction (for example, horizontal direction) by the action of
an electric field or a magnetic field. The substrate 4 is secured
to a holder 6, and reciprocally scanned in a mechanical manner in a
Y direction (for example, orthogonal direction) that crosses the X
direction. Due to the coordination of both of the scanning systems
(hybrid scanning), an entire surface of the substrate 4 is
uniformly irradiated with the ion beam 2, thus enabling a highly
uniform ion implantation to be performed.
[0027] While the substrate 4 is being scanned, electrons in a
plasma emitted from the plasma generator 10 are supplied to the
vicinity of the ion beam 2 or the substrate 4. These electrons
neutralize a positive charge caused by ion beam irradiation,
thereby suppressing an electrostatic charge on the surface of the
substrate 4.
[0028] To cope with the scanning of the ion beam 2 in the X
direction, the plasma generator 10 of the present embodiment has a
structure that is elongated in the X direction. Thus, the electrons
in the plasma that is wide in the X direction are emitted and
uniformly supplied to the vicinity of the ion beam 2 scanned in the
X direction. As a result, the electrostatic charge on the surface
of the substrate 4 can be uniformly suppressed.
[0029] The plasma generator 10 includes a cylindrical plasma
generating chamber 12 (specifically, semicylindrical) that is
elongated along the X direction. The plasma generating chamber 12
is made of a non-magnetic material. The non-magnetic plasma
generating chamber 12 does not disturb a magnetic field 52
generated by a magnet 50, which is described later. A plasma
electrode 16 is also made of a non-magnetic material.
[0030] A gas introducing pipe 22 is connected to one end of the
plasma generating chamber 12 (on a left side in FIG. 1). A gas 24,
for example, xenon, is introduced into the plasma generating
chamber 12 from the gas introducing pipe 22.
[0031] The plasma generating chamber 12 has an opening 14 in a
portion, specifically, on a lower side (the side facing the ion
beam 2) of the plasma generating chamber 12. The plasma electrode
16 is provided in the opening 14. The plasma electrode 16 has an
electron emitting hole 18 through which the electrons in the plasma
generated in the plasma generating chamber 12 are emitted outside
the plasma generating chamber 12. In the present embodiment, the
electron emitting hole 18 includes a plurality of holes (for
example, circular holes or elongated holes) arranged in a line in
the X direction. Alternatively, the electron emitting hole 18 can
be a slit extending along the X direction. The plasma electrode 16
is electrically connected to the plasma generating chamber 12, and
has the same electric potential as the plasma generating chamber
12.
[0032] A straight rod-like antenna 26 is provided in the plasma
generating chamber 12. The antenna 26 extends along a longitudinal
axis of the plasma generating chamber 12, that is, along the X
direction. A length of the antenna 26 in the plasma generating
chamber 12 is, for example, about 80% to 100% of a length of the
plasma generating chamber 12 along the longitudinal axis. The
antenna 26 is inserted into the plasma generating chamber 12, for
example, from the other end (right side in FIG. 1) of the plasma
generating chamber 12. The antenna 26 is made of, for example,
tungsten. The antenna 26 is covered with an antenna cover 42, or
some other insulator (not shown), thereby electrically insulating
the antenna 26.
[0033] A high-frequency wave 28 is supplied from a PFG power supply
30 to the antenna 26 via an impedance matching circuit 32 and a
coaxial cable 34. The high-frequency wave 28 can be a high
frequency wave of approximately 13.56 megahertz (MHz) or a
microwave of a frequency of approximately 2.45 gigahertz (GHz).
That is, high frequency in the present description encompasses
frequencies in the microwave band. A central conductor 36 and an
outer conductor 38 of the coaxial cable 34 are, respectively,
electrically connected to the antenna 26 and the plasma generating
chamber 12.
[0034] With the structure described above, the high-frequency wave
28 supplied to the antenna 26 from outside is emitted from the
antenna 26 into the plasma generating chamber 12 and a plasma 20 is
generated by ionizing the gas 24 with a high-frequency discharge in
the plasma generating chamber 12. As a result, the electrons in the
plasma 20 are emitted into the target chamber 8 through the
electron emitting hole 18.
[0035] A negative extracting voltage V.sub.E can be applied to the
plasma generating chamber 12 and the plasma electrode 16 having the
same electric potential as that of the plasma generating chamber
12, using a direct current extracting power supply 56 with an
electric potential of the target chamber 8 as a reference. This
configuration allows easy emission of the electrons from the
electron emitting hole 18.
[0036] With the electric potential of the target chamber 8 as the
reference, a negative reflector voltage V.sub.R can be applied to a
reflector 70 using a power supply 57. As a result, the electrons in
the plasma emitted from the electron emitting hole 18 are reflected
by the reflector 70, and are easily captured by the ion beam 2.
[0037] The entire antenna 26 located inside the plasma generating
chamber 12 is covered with the antenna cover 42 that is made of an
insulating material. The antenna cover 42 is made of ceramic such
as silica and alumina. Thus, contamination in which metal particles
constituting the antenna 26 are discharged from the antenna 26 in
sputtering by the plasma 20, to contaminate the plasma, can be
prevented from occurring.
[0038] According to the present embodiment, it is desirable to
cover an inner wall (that is, an inner wall excluding the opening
14) of the plasma generating chamber 12 with an insulator 48. When
the electron emitting hole 18 is provided on a side face of the
plasma generating chamber 12 instead of providing to the plasma
electrode 16, it is desirable to cover the inner wall of the plasma
generating chamber 12 excluding the electron emitting hole 18 with
the insulator 48. Thus, contamination, in which metal particles
constituting the plasma generating chamber 12 are discharged from
the plasma generating chamber 12 in sputtering by the plasma 20, to
contaminate the plasma, can be prevented from occurring.
[0039] A frame cover 60 with a protrusion 62 is provided inside the
plasma generating chamber 12 so as to cover a periphery of the
plasma electrode 16. Due to this, the insulating material is
prevented from accumulating on the surface of the plasma electrode
16 in sputtering by the plasma 20, and conduction is ensured.
[0040] FIG. 3 illustrates a shadow 31, 33 formed by the protrusion
62 of the frame cover 60 near the top surface of the plasma
electrode 16. The shadow 31, 33 prevents accumulation of insulating
material on the plasma electrode 16 that would typically be
associated with sputtering by the plasma 20. The shadow 31, 33 may
be formed on the inner wall of the frame cover 60, or near the top
surface of the plasma electrode 16.
[0041] According to a first implementation, and as can be seen in
FIG. 3, the plasma generating chamber 12 includes an insulator 48
having the frame cover 60 with the protrusion 62. The frame cover
60 is electrically connected to one of the plasma generating
chamber 12 and the plasma electrode 16. The antenna 26 emits a
high-frequency wave (not shown) that ionizes a gas (not shown), and
generates plasma 20. The protrusion 62 blocks the plasma 20 from
accumulating on the plasma electrode 16 in the shadow region 31, 33
that is formed near the top surface of the plasma electrode 16. By
preventing the accumulation, conduction is ensured.
[0042] In another example implementation, the frame cover 60 may be
made of carbon, and the frame cover 60 is electrically connected to
the plasma generating chamber 12 or the plasma electrode 16.
According to this example implementation, the location of the
shadow 31, 33 is at the inner wall of the frame cover 60, and
prevents accumulation of the insulating material on the frame cover
60.
[0043] When the insulating material accumulates on the plasma
electrode 16, the conductor cannot contact with the plasma 20, the
electric potential cannot be applied to the plasma 20, no current
flows in the plasma 20, and the electrons are hardly extracted from
the plasma 20. The frame cover 60 with the protrusion 62 is located
between the plasma electrode 16 and the antenna 26. The protrusion
62 has different thicknesses inside a frame or inside and outside
the frame within the frame having a tubular frame area.
[0044] FIG. 4 is a graph that depicts a change in a PFG current
Ipfg when the frame cover 60 with the protrusion 62 and when a
frame cover 60 without protrusion are provided. As can be seen from
FIG. 4, when the frame cover 60 with protrusion 62 is provided, a
larger PFG current Ipfg is generated. Therefore, a life of the
plasma generator 10 is increased.
[0045] FIGS. 4a to 4d are drawings that depict examples of shapes
of the frame cover 60 with the protrusion 62. Protrusions of
various shapes that form a shadow on the periphery of the plasma
electrode 16 are shown in FIGS. 5a to 5d. FIG. 5a illustrates an
example of the protrusion 62 from a top view and a side view. The
protrusion 62 has a substantially rectangular cross-section, and a
substantially rectangular space is formed. FIG. 5b illustrates an
example of the protrusion 62 from a top view and a side view. The
protrusion 62 has a substantially beveled profile, such that the
space formed within the protrusion 62 is substantially rectangular
and beveled. FIG. 5c illustrates an example of the protrusion 62
from a top view and a side view. The protrusion has a diagonally
upward projecting profile, such that the space formed within the
protrusion 62 is substantially rectangular and upwardly projecting.
FIG. 5d illustrates an example of the protrusion 62 from a top view
and a side view. The protrusion has a substantially rectangular
cross section, and the space formed within the protrusion 62 is
substantially circular."
[0046] FIG. 6 is a drawing that depicts an example of a shape of
the frame cover 60 with protrusion 62 that is outwardly convex in a
central portion. Due to spring characteristics of the frame cover
60, electric contact between the frame cover 60 with the protrusion
62 and the plasma generating chamber 12 can be maintained, and
furthermore, the frame cover 60 with protrusion 62 also has the
same electric potential as that of the plasma electrode 16. Because
the plasma 20 is in contact with a conductive wall, the PFG current
Ipfg flows.
[0047] The magnet 50, which generates the magnetic field 52 along
the longitudinal axis of the plasma generating chamber 12, can be
arranged outside the plasma generating chamber 12 as in the present
embodiment or inside the plasma generating chamber 12. In the
present example, the magnet 50 has a semi-cylindrical shape that
conforms with the shape of the plasma generating chamber 12. The
magnet 50 is typically a permanent magnet. Provision of the magnet
50 facilitates capturing of the electrons by the magnetic field 52
generated by the magnet 50, and generation and maintenance of the
plasma 20 inside the plasma generating chamber 12. Therefore, a
high density plasma can be produced by electron cyclotron resonance
(ECR).
[0048] According to an aspect of the present invention, a shadow
near the top surface of a plasma electrode that has an electron
discharge hole can prevent accumulation of insulating material on
the plasma electrode due to sputtering by the plasma, and thereby,
a decrease in the PFG current can be prevented. As a result, a
plasma generator can be used for a prolonged time.
[0049] According to an aspect of the present invention, a shadow
over a plasma electrode having electron emitting holes prevents
accumulation of an alumina insulating material on the plasma
electrode in sputtering by a plasma, and thereby, a decrease in a
PFG current can be prevented. As a result, a plasma generator can
be used for a prolonged time.
[0050] According to another aspect of the present invention, a
frame cover is made of carbon that is electrically conductive. The
conductive frame cover also functions as an electrode, increasing a
surface area of a conductive wall, thus increasing the PFG current.
The PFG current flows until the entire surface of the plasma
electrode and the frame cover are insulated. Thus, the plasma
generator can be used for a prolonged time.
[0051] According to another aspect of the present invention, the
material of the frame cover is made of carbon, the frame cover is
electrically connected to the plasma generator or the plasma
electrode, the frame cover protrusion forms a shadow on inner wall
of the frame cover, and that shadow prevents accumulation of
insulating material on the frame cover inner wall due to sputtering
by the plasma. According to still another aspect of the present
invention, the plasma electrode has a protruding structure. Thus,
even if the frame cover with protrusion is not provided, a decrease
in the PFG current can be prevented. As a result, the plasma
generator can be used for a prolonged time.
[0052] According to still another aspect of the present invention,
the frame cover internally has depressions of a concave shape. The
depressions are not coated with the insulating material easily.
Furthermore, because the frame cover is made of carbon, by
increasing an area of a conductive wall, the PFG current can be
increased.
* * * * *