U.S. patent application number 10/788306 was filed with the patent office on 2004-08-26 for plasma producing device.
This patent application is currently assigned to SHIMADZU CORPORATION. Invention is credited to Suzuki, Masayasu, Ueda, Masahiro.
Application Number | 20040163767 10/788306 |
Document ID | / |
Family ID | 29543042 |
Filed Date | 2004-08-26 |
United States Patent
Application |
20040163767 |
Kind Code |
A1 |
Ueda, Masahiro ; et
al. |
August 26, 2004 |
Plasma producing device
Abstract
A plasma source includes a plasma source cavity having a tubular
shape for forming plasma, an exciting coil for forming a radio
frequency magnetic field, and a magnetic path structure for guiding
magnetic flux of the radio frequency magnetic field. The magnetic
flux extends from an end surface of the plasma source cavity to a
side surface of the plasma source cavity and from the side surface
of the plasma source cavity to the end surface of the plasma source
cavity.
Inventors: |
Ueda, Masahiro; (Atsugi-shi,
JP) ; Suzuki, Masayasu; (Hadano-shi, JP) |
Correspondence
Address: |
HAUPTMAN KANESAKA BERNER PATENT AGENTS, LLP
Suite 310
1700 Diagonal Road
Alexandria
VA
22314
US
|
Assignee: |
SHIMADZU CORPORATION
|
Family ID: |
29543042 |
Appl. No.: |
10/788306 |
Filed: |
March 1, 2004 |
Current U.S.
Class: |
156/345.49 |
Current CPC
Class: |
H01J 37/321
20130101 |
Class at
Publication: |
156/345.49 |
International
Class: |
C23F 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 1, 2002 |
JP |
2002-129714 |
Claims
What is claimed is:
1. A plasma source, comprising: a plasma source cavity with a
tubular shape for producing plasma having an end surface and a side
surface, an exciting coil placed adjacent to the plasma source
cavity for forming a radio frequency magnetic field, and a magnetic
path structure placed outside the plasma source cavity for forming
a path of magnetic flux of the radio frequency magnetic field
extending from the end surface to the side surface and returning
from the side surface to the end surface to thereby provide a
uniform distribution of the radio frequency magnetic field in the
plasma source cavity.
2. A plasma source according to claim 1, wherein said magnetic path
structure includes a first soft magnetic material member placed
inside the exciting coil adjacent to the end surface of the plasma
source cavity for guiding the magnetic flux into an inside of the
plasma source cavity through the end surface thereof; a second soft
magnetic material member disposed adjacent to the side surface of
the plasma source cavity for guiding the magnetic flux from the
inside of the plasma source cavity to the second soft magnetic
material member through the side surface of the plasma source
cavity; and a third soft magnetic material member disposed at a
side opposite to the end surface of the plasma source cavity with
the first soft magnetic material member interposed therebetween for
guiding the magnetic flux to the first soft magnetic material
member from the second soft magnetic material member.
3. A plasma source according to claim 2, wherein said first soft
magnetic material member projects from the third soft magnetic
material member, and the exciting coil is located between the first
soft magnetic material member and the second soft magnetic material
member.
4. A plasma source according to claim 3, wherein said first to
third soft magnetic material members are formed in single piece.
Description
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
[0001] The present invention relates to a plasma source, and more
specifically, to a radio frequency wave inductively coupled plasma
source.
[0002] Many of electronic device fabrication methods utilize plasma
to provide various processes such as etching and sputter deposition
which are applied to a substrate wafer of semiconductor, glass and
other materials. An inductively coupled plasma source is known as
one of those plasma activation methods. In most cases of such a
plasma source, an excitation coil is located adjacent to a plasma
cavity and driven by radio frequency generator to supply
electromagnetic power into the cavity. The radio frequency
electromagnetic energy will be inductively delivered to ionize
source gas and keep activating the plasma in the cavity.
[0003] FIGS. 6(a) and 6(b) describe typical examples of
conventional inductively coupled plasma sources. The one shown in
FIG. 6(a) uses a solenoid coil 100 as the excitation coil, whereas
the other shown in FIG. 6(b) uses a flat coil 104. In the plasma
source shown in FIG. 6(a), the solenoid coil 100 is wound around a
tubular chamber 103 which works as a plasma source cavity. The
solenoid coil 100 is driven by a radio frequency generator 102
through an impedance matching device 101, so that an alternate
current induces a magnetic field along the solenoid coil 100 axis
in the tubular chamber 103. As a result, plasma P is activated in
the tubular chamber 103.
[0004] In the plasma source shown in FIG. 6(b), a flat coil 104 is
mounted closely outside the feed through port 106 which is located
at the top of the chamber. The radio frequency magnetic field
induced by the flat coil 104 penetrates into the chamber 105
through the feed through port 106, so that plasma P is activated
inside the chamber 105.
[0005] Recently, the wafer size of the electronic device industries
is getting larger. The larger wafer size results in demands for a
larger plasma effective area which needs to cover the whole surface
of the work wafer in the plasma process equipment as described
above. From this point of view, in the case of a plasma source with
a solenoid coil 100 shown in FIG. 6(a), it is necessary to increase
the diameter of the coil as well as the number of turns,
corresponding to a large diameter size, to induce a sufficient
magnetic flux density.
[0006] The larger coil has disadvantages in energy loss and
impedance matching stability. The energy loss may increase as the
coil wire length becomes longer because of the larger resistive
element. The impedance matching condition may become critical
because the larger reactance and the larger stray capacity of the
larger coil size require smaller matching capacitance of the
impedance matching network 101 at the fixed frequency, which may
reduce the head room for the stable plasma operation condition.
[0007] In the case of a plasma source with a flat coil 104 shown in
FIG. 6(b), the induced magnetic flux from a larger coil in both its
size and the number of turns converges around the central part of
the spiral, which results in a poorer uniformity of the plasma
intensity as well as unsuccessful enlargement of the plasma
effective area. In addition, it is hard to improve the energy
transfer efficiency because the positioning of the plasma source
cavity and the flat coil is single sided with each other.
[0008] In view of the above problems, the present invention has
been made, and an object of the invention is to provide a radio
frequency wave inductively coupled plasma source, wherein the
plasma area can be increased without reducing the energy efficiency
and uniform plasma can be formed.
[0009] Further objects and advantages of the invention will be
apparent from the following description of the invention.
SUMMARY OF THE INVENTION
[0010] In order to attain the objects described above, according to
an embodiment of the present invention, a radio frequency wave
inductively coupled plasma source includes a plasma source cavity
having a tubular shape for forming plasma; an exciting coil for
forming a radio frequency magnetic field; and a magnetic path
structure for guiding magnetic flux of the radio frequency magnetic
field from an end surface of the plasma source cavity to a side
surface of the plasma source cavity and from the side surface of
the plasma source cavity to the end surface of the plasma source
cavity.
[0011] In the radio frequency wave inductively coupled plasma
source, the magnetic path structure includes a first soft magnetic
material member placed inside the exciting coil for introducing the
magnetic flux of the radio frequency magnetic field into the plasma
source cavity through the end surface of the plasma source cavity;
a second soft magnetic material member placed outside the tubular
plasma source cavity for introducing the magnetic flux guided into
the plasma source cavity to the side surface of the plasma source
cavity; and a third soft magnetic material member placed on a side
opposite to the end surface of the plasma source cavity to sandwich
the first soft magnetic material member therebetween:for returning
the magnetic flux guided to the side surface of the plasma source
cavity to the first soft magnetic material member through the
second soft magnetic material member.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a block diagram showing a plasma source according
to an embodiment of the present invention;
[0013] FIGS. 2(a) and 2(b) are views showing a magnetic path
structure, wherein FIG. 2(a) shows a first example, and FIG. 2(b)
shows a second example;
[0014] FIGS. 3(a) to 3(c) are views showing a radio frequency
magnetic field in the plasma source according to the present
invention as compared with that in a conventional device, wherein
FIG. 3(a) shows a radio frequency magnetic field of the plasma
source according to the embodiment of the invention; FIG. 3(b)
shows a radio frequency magnetic field of a conventional flat
surface type coil; and FIG. 3(c) shows plasma density
distributions;
[0015] FIG. 4 is a block diagram showing a plasma source;
[0016] FIG. 5 shows a distribution profile of ion beams obtained in
the plasma source shown in FIG. 4; and
[0017] FIGS. 6(a) and 6(b) show conventional plasma sources,
wherein FIG. 6(a) shows a plasma source using a solenoid coil, and
FIG. 6(b) shows a plasma source using a flat coil.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
[0018] Hereunder, embodiments of the present invention will be
explained with reference to the accompanying drawings. FIG. 1 is a
block diagram showing a plasma source according to an embodiment of
the present invention, wherein a portion above a line B constitutes
a plasma source 1. A plasma source cavity main portion 3 forming a
plasma source cavity 2 of a plasma source 1 is placed at an upper
portion of a vacuum chamber 12, i.e. a process chamber. The plasma
source cavity main portion 3 is made of a ceramic material and the
like as used for a feed through port of radio frequency wave power
of a conventional device. A radio frequency magnetic field enters
the plasma source cavity 2 through the plasma source cavity main
portion 3. A vacuum chamber 12 is pumped by a vacuum pump (not
shown) connected to an exhaust port 12a.
[0019] In the plasma source 1 as shown in FIG. 1, the plasma source
cavity main portion 3 has a cylindrical shape, and an exciting coil
6 is provided at an outside of the plasma source cavity main
portion 3 to face a cylindrical end surface thereof. The exciting
coil 6 is a two-turn solenoid type coil, and is connected to an RF
power source 9 through an impedance matching device 8. In the
present embodiment, the exciting coil 6 is the solenoid type coil.
Alternatively, the exciting coil 6 may be, for example, a single
turn flat surface type coil. The RF power source 9 uses a frequency
of 1 MHz to 100 MHz in view of an economical efficiency. In the
present embodiment, a radio frequency power source having a
frequency of 13.56 MHz is used.
[0020] A capacitor for matching impedance is provided in the
impedance matching device 8, and a capacitance of the capacitor is
adjusted to optimize a matching condition. Argon gas is injected
into the plasma source cavity 2 to produce plasma. A magnetic path
structure 7 is provided around the plasma source cavity main
portion 3 for covering the same. The magnetic path structure 7
constitutes a return circuit for magnetic flux generated by the
exciting coil 6 (described later), and is made of a soft magnetic
material such as iron, nickel, cobalt and the like having good
radio frequency properties, i.e. lower loss within an excitation
frequency range.
[0021] A grid type aperture electrode 4 is placed between the
plasma source cavity 2 and the vacuum chamber 12. A voltage Vacc is
applied to the grid 4 from the power source 5. The grid 4 confines
the plasma in the plasma source cavity 2, and the acceleration
voltage Vacc accelerates ions flying out of the plasma. As a
result, the plasma source 1 produces ion beams to be used for
various processes. In the present embodiment, a scanning type
Faraday cup 10 is provided in the vacuum chamber 12 to measure a
current density of the ion beams. An electric current of the ions
is measured by a micro-ammeter 11.
[0022] FIGS. 2(a) and 2(b) are views showing the magnetic path
structure 7. As shown in FIG. 2(a), the magnetic path structure 7
is formed of three functional portions. The first functional
portion is a core portion 7A disposed inside an exciting coil 6 for
concentrating magnetic flux at a center portion of the coil and for
homogenizing a distribution thereof. Magnetic flux 20 enters the
plasma source cavity 2 from a lower end surface of the core portion
7A. The second functional portion is side return portions 7B
covering both of the exciting coil 6 and the plasma source cavity
main portion 3 for guiding the magnetic flux 20 from an end surface
of the core portion 7A to side surfaces of the plasma source cavity
main portion 3. The magnetic flux 20 passes through the side
surfaces of the plasma source cavity main portion 3, and enters
cylindrical side return portions 7B. The third functional portion
is a back return portion 7C for allowing the magnetic flux 20
entered the side return portion 7B to return to the core portion
7A.
[0023] The radio frequency energy is emitted from the exciting coil
6 as inductive magnetic field energy, and is supplied to the plasma
in the plasma source cavity 2. Incidentally, in FIG. 2(a), the
magnetic path structure 7 is shown as a member divided into 7A, 7B
and 7C for the respective functions. However, it is not necessarily
to divide the magnetic path structure 7 into three portions, and
the magnetic path structure 7 may be formed in single piece.
[0024] As shown in FIG. 2(a), upper end surfaces of the side return
portions 7B are closely attached to a lower end surface of the back
return portion 7C. Alternatively, as shown in FIG. 2(b), the side
return portions 7B may be separated from the back return portion
7C. The magnetic path structure 7 made of a soft magnetic material
has a magnetic permeability considerably larger than that of air.
Accordingly, almost all the magnetic flux 20 getting out of the
upper end surfaces of the side return portions 7B enters the back
return portion 7C.
[0025] FIGS. 3(a) to 3(c) are views showing a comparison of states
of the radio frequency magnetic field between the plasma source 1
according to the present embodiment and a conventional device using
a flat coil. FIG. 3(a) corresponds to FIG. 2(a). As described
above, the plasma source 1 is provided with the side return
portions 7B, so that the magnetic flux 20 getting out of the lower
end surface of the core portion 7A is guided to the side return
portions 7B. Therefore, it is possible to form the magnetic field
having a uniform intensity in the whole plasma source cavity 2. On
the other hand, FIG. 3(b) shows a state of the magnetic flux in the
conventional device having the flat coil 21. The coil 21 forms the
radio frequency magnetic field as shown by the magnetic flux 22
widely spread not only in the plasma source cavity 23 but also in
the outer space thereof.
[0026] As described above, in the embodiment of the invention as
shown in FIG. 3(a), almost all the magnetic flux 20 getting out of
the lower end surface of the core portion 7A enters the side return
portions 7B, and enters the opposite end surface of the core
portion 7A through the side return portions 7B and the back return
portion 7C. In other words, the magnetic flux 20 is present in the
magnetic path structure 7 except for the plasma space, and the
magnetic field is not formed in an outer space of the device as in
the conventional device shown in FIG. 3(b). As a result, the energy
efficiency transferred to the plasma is improved.
[0027] Further, the side return portions 7B guide the magnetic flux
20 to the plasma source cavity side surfaces to make the flux
density in the plasma source cavity 2 uniform. As a result, the
uniform plasma can be formed over a wide area in the plasma source
cavity 2. FIG. 3(c) shows a distribution of the plasma density,
wherein the horizontal axis represents a position in the plasma
source cavity in a radial direction. A curve L1 represents the
uniform distribution in the device according to the embodiment of
the invention, while a curve L2 represents the widely spread
distribution of the conventional device using the flat surface type
coil as shown in FIG. 3(b). As shown in FIG. 3(c), the plasma
source of the present invention can obtain the uniform distribution
of the flux density as compared with the conventional device.
[0028] According to the embodiment of the invention, the plasma
source is provided with the magnetic path structure 7, so that the
magnetic flux 20 of the radio frequency field formed by the
exciting coil 6 is guided to the side return portions 7B of the
magnetic path structure 7 through the plasma space. Accordingly,
even if the exciting coil 6 does not have a diameter corresponding
to a size of a required plasma area, it is possible to allow the
magnetic flux 20 to cross the whole plasma area. It is not
necessary to increase the diameter of the exciting coil 6.
Therefore, it is possible to prevent reactance change and
resistance loss due to an increased length of the coil wiring,
thereby obtaining stable impedance matching.
[0029] As described above, according to the present embodiment of
the present invention, the plasma source 1 is provided with the
magnetic path structure 7 to increase the magnetic field intensity
induced in the plasma area. In other words, the inductive coupling
efficiency of the radio frequency energy with respect to the plasma
is increased, and the plasma intensity per unit electric power is
increased.
[0030] In the conventional plasma source, the flat coil forms the
inductive magnetic field symmetrical relative to the coil surface.
The plasma source 1 of the invention is provided with the magnetic
path structure 7, so that the asymmetric magnetic field
distribution is obtained as shown in FIG. 3 (a). If the plasma
source 1 is provided with only the coil 6, it is not possible to
obtain such a distribution. In other words, the efficiency of the
radio frequency energy is improved, and unnecessary radiation and
heating are reduced.
[0031] When the coil 6 is the solenoid coil and does not surround
the plasma area, it is still possible to form the induced magnetic
field over the whole plasma area due to the magnetic path structure
7. In other words, the magnetic path structure 7 controls the
distribution of the inductive magnetic field intensity (plasma
intensity distribution) to thereby easily control the uniformity of
the plasma activity distribution.
[0032] FIG. 4 shows a specific example of the plasma source 1,
wherein dimensions of the respective components of the plasma
source are shown. The dimensions of the respective components are
as follows: an inner diameter of the plasma source cavity main
portion 3 is 220 mm; a diameter of the exciting coil is 200 mm; an
outer diameter of the core portion 7A is 180 mm; a diameter of a
grid opening portion of the aperture 4 is 210 mm; and a distance
between the aperture 4 and the Faraday cup 10 is 300 mm.
[0033] The soft magnetic material constituting the magnetic path
structure 7 has relative permeability of 100; the exciting coil 6
has overall self-inductance of 2.0 pH; the radio frequency power
source 11 has a frequency of 13.56 MHz; the input radio frequency
electric power is 500 W; the accelerating voltage Vacc of the power
source 5 is 1.0 kV; and a flow rate of the argon gas is 50
sccm.
[0034] In the structure described above, the Faraday cup 10 was
scanned in the radial direction (horizontal direction in the
drawing) to measure a distribution profile of an ion beam current
density taken out from the plasma source cavity 2. FIG. 5 shows a
distribution profile L3 obtained from the measurement. In FIG. 5,
the vertical axis represents the ion beam current density having an
arbitrary unit (A.U.). The horizontal axis represents a position in
the exciting coil 6 in the radial direction with the origin as the
center of the exciting coil 6 (center of the plasma source cavity
2).
[0035] When a peak of the distribution profile L3 is assumed to
have an intensity of 100%, an area having a relative intensity of
more than 90% has a diameter of 170 mm. An area having a relative
intensity of 50%, i.e. a half maximum full-width, has a diameter of
190 mm. In other words, it is possible to obtain homogeneous ion
beams having a diameter substantially the same as that of the core
portion 7A. When the plasma source is provided in an ion beam
etching device, the ion beams are uniformly irradiated over the
entire area of a base plate having a diameter of about 170 mm, so
that it is possible to perform the etching process at a higher
speed.
[0036] In the embodiment, the plasma source cavity main portion 3
constitutes a plasma source cavity; the core portion 7A constitutes
a first soft magnetic material member; the side return portions 7B
constitute a second soft magnetic material member; and the back
return portion 7C constitutes a third soft magnetic material
member.
[0037] As described above, according to the present invention, the
plasma source cavity is provided with the magnetic path structure
to obtain the uniform distribution of the magnetic flux in a wide
area, so that the plasma is formed in a wide area. Also, the
magnetic flux is intensively distributed in the plasma source
cavity. without spreading into an unnecessary space outside the
plasma source cavity. Therefore, the intensity of the magnetic
field induced into the plasma source cavity is increased. Thus, the
inductive coupling efficiency of the radio frequency energy is
improved with respect to the plasma.
[0038] While the invention has been explained with reference to the
specific embodiments of the invention, the explanation is
illustrative and the invention is limited only by the appended
claims.
* * * * *