U.S. patent application number 12/879926 was filed with the patent office on 2010-12-30 for plasma processing apparatus.
This patent application is currently assigned to TOKYO ELECTRON LIMITED. Invention is credited to Keizo Hirose, Akira Koshiishi.
Application Number | 20100326601 12/879926 |
Document ID | / |
Family ID | 34317719 |
Filed Date | 2010-12-30 |
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United States Patent
Application |
20100326601 |
Kind Code |
A1 |
Koshiishi; Akira ; et
al. |
December 30, 2010 |
PLASMA PROCESSING APPARATUS
Abstract
In the plasma processing apparatus of the present invention, a
first electrode (21) for connecting a high frequency electric power
source (40) in a chamber is arranged to be opposed to a second
electrode (5). A substrate (W) to be processed is placed between
the electrodes. There is provided a harmonic absorbing member (51)
for being able to absorb harmonics of the high frequency electric
power source (40) so as to come in contact with a peripheral
portion or circumference of a face of the first electrode 21, which
is opposite the second electrode (5). The harmonic absorbing member
absorbs the reflected harmonic before the harmonic returns to the
high frequency electric power source. By absorbing the harmonic in
this manner, the standing wave due to the harmonic will be
effectively prevented from being generated, and the density of
plasma is made even.
Inventors: |
Koshiishi; Akira; (Kofu-shi,
JP) ; Hirose; Keizo; (Nirasaki-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, L.L.P.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
TOKYO ELECTRON LIMITED
Minato-ku
JP
|
Family ID: |
34317719 |
Appl. No.: |
12/879926 |
Filed: |
September 10, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10984943 |
Nov 10, 2004 |
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12879926 |
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09959745 |
Nov 5, 2001 |
7537672 |
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PCT/JP00/02770 |
Apr 27, 2000 |
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10984943 |
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Current U.S.
Class: |
156/345.44 |
Current CPC
Class: |
B23K 10/00 20130101;
H01J 37/32082 20130101; H01J 37/321 20130101; H01J 37/32165
20130101 |
Class at
Publication: |
156/345.44 |
International
Class: |
C23F 1/08 20060101
C23F001/08 |
Foreign Application Data
Date |
Code |
Application Number |
May 6, 1999 |
JP |
11-125637 |
May 7, 1999 |
JP |
11-126878 |
May 11, 1999 |
JP |
11-129696 |
May 21, 1999 |
JP |
11-141209 |
Claims
1. A plasma etching apparatus comprising: a chamber maintained at a
reduced pressure; a first electrode and a second electrode arranged
to be opposed to each other in the chamber; a process gas source
connected to the chamber; a first high frequency electric source
connected to the first electrode; and a direct current voltage
source connected to the first electrode wherein plasma is generated
by applying high frequency electric power from the first high
frequency electric source to the first electrode, and wherein a
substrate to be processed which is supported by the second
electrode is subject to plasma etching processing in a state where
thicker plasma sheath is generated by applying direct current
voltage from the direct current voltage source to the first
electrode.
2. A plasma etching apparatus according to claim 1, further
comprising a harmonic absorbing member arranged to come into
contact with one of an outer periphery and an outer face on an
opposing face, which is opposed to the second electrode, of the
first electrode, wherein the harmonic absorbing member absorbs a
harmonic generated by the high frequency electric power applied by
the high frequency electric source.
3. A plasma etching apparatus according to claim 2, wherein the
harmonic absorbing member is laminated harmonic absorbing members
having frequency characteristics different from each other.
4. A plasma etching apparatus according to claim 2, wherein the
harmonic absorbing member has magnetic resonance loss effect.
5. A plasma etching apparatus according to claim 4, wherein the
harmonic absorbing member contains ferrite.
6. A plasma etching apparatus according to claim 1, further
comprising an electrode plate, the electrode plate comprising: an
outer portion constituted by conductor or semiconductor, formed in
a ring-shape; and a central portion constituted by a dielectric
member or a high resistance member with higher resistivity than
that of the outer portion, formed in a disk-shape fitted to an
inner circumference of the ring-shape of the outer portion.
7. A plasma etching apparatus according to claim 6, wherein the
central portion of the electrode plate is formed of the high
resistance member and a skin depth .delta. expressed by the
following formula (1) is larger than the central portion of the
electrode plate thickness. .delta.=(2/.omega. .PHI. .mu.).sup.1/2
[where .omega.=2.pi.f (f is frequency), .PHI. is conductivity, .mu.
is magnetic permeability]
8. A plasma etching apparatus according to claim 6, wherein both
the outer portion and the central portion of the electrode plate
are formed form silicon, and the outer portion having low
resistivity and the central portion having high resistivity are
formed by differentiating doping amounts of dopant into the outer
portion and the central portion.
9. A plasma etching apparatus according to claim 8, further
comprising: an electrode plate formed of conductor or semiconductor
provide on the side of an opposing face, which si opposed to the
second electrode, of the first electrode; and one of a dielectric
member and a high resistance member having higher resistivity than
that of the electrode plate provided so as to come in contact with
a central portion of a non-opposing face, which is not opposed to
the second electrode of the electrode plate.
10. A plasma etching apparatus according to claim 9, where a skin
depth .delta. expressed by the following formula (1) is large than
the electrode plate in thickness. .delta.=(2/.omega. .PHI.
.mu.).sup.1/2 [where .omega.=2.pi.f (f is frequency), .PHI. is
conductivity, .mu. is magnetic permeability]
11. A plasma etching apparatus according to claim 9, wherein a
diameter of one of the dielectric member and the high resistance
member is 50-220 mm.
12. A plasma etching apparatus according to claim 9, wherein
resistivity of the electrode plate is 1-100 .OMEGA.-m.
13. A plasma etching apparatus according to claim 1, further
comprising an electrode plate formed of conductor or semiconductor
which is provided on the side of an opposing face, which is opposed
to the second electrode of the first electrode; and an insulating
layer formed on the side of an opposing face, which is opposed to
the second electrode of the first electrode.
14. A plasma etching apparatus according to claim 1, further
comprising: an electrode plate formed of conductor or semiconductor
provided on the side of an opposing face which is opposed to the
second electrode of the first electrode; and a member having an
electromagnetic wave absorbing effect provided so as to come in
contact with a central portion of an non-opposing face which is not
opposed to the second electrode of the electrode plate.
15. A plasma etching apparatus according to claim 1, further
comprising: an electric power supplying rod connected to a central
portion of the side of a non-opposing face, which is not opposed to
the second electrode of the first electrode, the electric supplying
rod supplying the high frequency electric power supplied from the
high frequency electric source, a conductive cylindrical member
arranged near the electric power supplying rod so as to enclose the
electric power supplying rod the conductive cylindrical member
being grounded; and a conductive plate-like member electrically
connected to the conductive cylindrical member and grounded.
16. A plasma etching apparatus according to claim 1, further
comprising: an electric power supplying rod connected to a position
shifted from a center to an outer periphery of the side of a
non-opposing face, which is not opposed to the second electrode of
the first electrode, the electric power supplying rod supplying the
high frequency electric power supplied from the high frequency
electric source; a conductive cylindrical member arranged near the
electric power supplying rod so as to enclose the electric power
supplying rode, the conductive cylindrical member being grounded; a
conductive plate-like member electrically connected to the
conductive cylindrical member and grounded; and phase adjusting
means connected to the first electrode at one terminal and grounded
at the other one terminal, for adjusting a phase voltage and
current of the high frequency electric power supplied to the first
electrode.
17. A plasma etching apparatus according to claim 16, wherein the
phase adjusting means is an LC circuit arranged on the side of the
non-opposing face of the first electrode at an opposite position to
a connected position of the electric power supplying rod with
respect to a center of the non-opposing face.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 10/984,943, filed on Nov. 10, 2004, which is a
continuation of U.S. patent application Ser. No. 09/959,745, filed
on Nov. 5, 2001, which is a national stage application of
PCT/JP00/02770, filed on Apr. 27, 2000. This PCT application claims
priority to Japanese patent application numbers JP 11-125637, filed
on May 6, 1999; JP 11-126878, filed on May 7, 1999; JP 129696,
filed on May 11, 1999; and JP 11-141209, filed on May 21, 1999. The
entire contents of these applications are incorporated by reference
herein.
TECHNICAL FIELD
[0002] The present invention relates to a plasma processing
apparatus for performing etching and film forming on a substrate
such as a semiconductor substrate by plasma processing.
BACKGROUND ART
[0003] In a process for manufacturing semiconductor devices,
various plasma processing such as etching, film forming by
sputtering or CVD film forming (Chemical Vapor Depositing) have
been frequently employed.
[0004] There have been known various types of plasma processing
apparatuses, among which a capacitive coupling type parallel plate
plasma processing apparatus is the apparatus the most popularly
distributed and used.
[0005] This type of plasma processing apparatus has a pair of
parallel flat plate electrodes (upper and lower electrodes) in a
reduced-pressure chamber. A semiconductor wafer to be processed is
placed between the electrodes, then process gas (treatment gas) is
introduced into the chamber and electric power with high frequency
is applied to one of the electrodes. A high frequency electric
field generated between the electrodes generates plasma from the
process gas to perform plasma processing on the semiconductor
wafer.
[0006] In etching an oxide film or the like formed on a
semiconductor wafer with use of such a plasma processing apparatus,
the pressure in the chamber is set at an intermediate level to
generate plasma having an intermediate density, thereby the optimum
radical control can be attained. In such a condition, the optimum
plasma can be obtained to realize etching with good stability and
reproducibility at a high selective ratio.
[0007] In accordance with the downsizing of a device, however, the
request for the ultra-integration of a circuit is increased. There
are also design rule constraints on features like the contact hole.
The contact hole is required to be thin and deep, i.e., to have
higher aspect ratio. The conventional oxide film etching method is,
therefore, beginning to be not good enough to satisfy the demands
of the market.
[0008] To cope with such recent requests, the frequency of the
electric power applied to the electrode is set at a higher level to
generate plasma having a higher density, so as to maintain good
dissociation. By generating the plasma in such a manner, suitable
plasma can be generated in a lower pressure, and thus the device
with a smaller design rule can be manufactured.
[0009] With the conventional plasma processing apparatus, however,
the upper electrode is formed from a conductor or semiconductor.
Therefore, when the frequency of the electric power applied to the
upper electrode is set at a high level, the inductance on the
surface of the electrode will be increased so as not to be
neglected, whereby the electric field in the opposite direction
will be uneven.
[0010] Further, such a higher density of the plasma by the higher
frequency remarkably causes non-linear characteristics of the
plasma, so that a harmonic may be easily interposed on the
reflected wave form the plasma. Particularly, with use of the
electrode having a diameter of 250 to 300 mm, it has been found
from experience that such a harmonic generates a standing wave on
the surface of the electrode, which makes the electric field on the
surface of the electrode uneven.
[0011] If the electric field is made uneven in such a manner, the
density of plasma will be also made uneven, with the result that
the etching rate of etching will be uneven. Accordingly, it is
essential to make the etching rate even by eliminating the causes
of the uneven electric field. The above-mentioned problems in
generating a high-density plasma, however, have not been recognized
clearly, and thus a proposal for preventing the above-mentioned
uneven electric field has not sufficiently been presented yet.
[0012] Further, according to the conventional plasma processing
apparatus, the electric power is applied to the upper electrode
with use of an electric power applying rod, and thus a box having a
size substantially equal to a chamber encloses the electric power
applying rod to shield electromagnetic wave.
[0013] However, since the inductance of the electric power applying
rod is very high, if the frequency of the high frequency power
supplied to the upper electrode is set at a higher level in order
to increase the plasma density, the harmonic of the wave reflected
from the plasma is reflected due to the inductance component of the
electric power applying rod. Further, reflection is caused at every
portions within the box in which the electric power applying is
disposed, and the resultant reflected harmonic backs to the surface
of the upper electrode exposed to the plasma.
[0014] With the electrode having a diameter of 250 mm to 300 mm, a
standing wave will be easily generated on the surface of the
electrode due to the higher harmonic (higher harmonic), which makes
the electric field on the surface of the electrode uneven.
[0015] The electric power applying rod is provided to the center of
the upper electrode on the rear surface thereof. When the frequency
of the electric power applied to the electrode is increased to
generate high-density plasma, the high frequency current flows only
on the surface of the electrode. The high frequency electric power
applied from the electric power applying rod to the upper electrode
flows through the rear surface of the electrode to the outer
periphery of the round electrode to be supplied from the outer
periphery to the center of the electrode.
[0016] The outer periphery of the electrode is enclosed by an
insulator (capacity component) and the chamber enclosing the
insulator is grounded. With this structure, the standing wave is
generated on the plasma contacting face of the upper electrode by
the interference, which makes the electric field on the electrode
in the direction of the diameter uneven. The unevenness of the
electric field also makes the density of the plasma uneven, which
causes an uneven etching rate. Accordingly, these causes need to be
eliminated to make the etching rate even.
[0017] However, as mentioned before, the problems in generating the
high-density plasma, have not been recognized clearly, and thus a
proposal for preventing the above-mentioned uneven electric field
has not been sufficiently presented yet.
DISCLOSURE OF INVENTION
[0018] The present invention is intended to provide a plasma
processing apparatus capable of making the density of plasma even
by suppressing the unevenness of the electric field on the surface
of an electrode in the plasma processing using high-density plasma
with use of which a device can be formed finer.
[0019] In order to attain the above-mentioned object, the present
invention provides a plasma processing apparatus comprising a
chamber containing a substrate to be processed; a first electrode
and a second electrode arranged to be opposed to each other in the
chamber; high frequency electric power applying means for applying
high frequency electric power to the first electrode; a harmonic
absorbing member arranged to come into contact with one of an outer
periphery and an outer peripheral face on an opposing face (on
which the first electrode faces the second electrode) of the first
electrode being opposed to the second electrode, for absorbing a
harmonic generated by the high frequency electric power applied by
the high frequency electric power applying means; exhaust means for
exhausting the chamber to maintain a pressure in the chamber at a
reduced level; and process gas introducing means for introducing
process gas into the chamber, wherein in a state that one of the
first and second electrodes is caused to hold the substrate to be
processed, while the harmonic absorbing member absorbs the harmonic
generated by the high frequency electric power, a high frequency
electric field is formed between the first and the second
electrodes to generate plasma of the process gas, and the substrate
to be processed is subjected to plasma processing with the plasma
while the harmonic absorbing member absorbs the harmonic generated
by the high frequency electric power.
[0020] In the plasma processing apparatus of the present invention,
high frequency electric power is applied to the first electrode.
There is provided a harmonic absorbing member for absorbing a
harmonic of the high frequency electric power source so as to come
into contact with a peripheral portion or circumference of a face
of the first electrode, which is opposite to the second electrode.
The harmonic absorbing member absorbs a harmonic reflected from
plasma before the harmonic returns to the high frequency electric
power source. By absorbing the harmonic in this manner, the
standing wave due to the harmonic will be effectively prevented
from being generated, and the density of plasma is made even. With
such a structure, the standing wave due to the harmonic can be
prevented to suppress the unevenness of the electric field on the
surface of the electrode due to the standing wave, with the result
that the density of plasma can be made even.
BRIEF DESCRIPTION OF DRAWINGS
[0021] FIG. 1 is a sectional view showing the plasma etching
apparatus according to the first embodiment of the present
invention.
[0022] FIG. 2 is a schematic view for explaining the cause of the
standing wave formed on the electrode applied with a high frequency
wave.
[0023] FIG. 3 is a sectional view showing an example of an
arrangement of a high frequency wave absorbing member.
[0024] FIG. 4 is a graph showing frequency characteristics of
return loss when a ferrite sinter having a thickness of 7 mm is
used as the high frequency wave absorbing member.
[0025] FIG. 5 is a graph showing frequency characteristics of
return loss when a ferrite sinter having a thickness of 4.5 mm is
used as the high frequency wave absorbing member.
[0026] FIG. 6 is a sectional view showing the plasma etching
apparatus according to the second embodiment of the present
invention.
[0027] FIG. 7 is a sectional view schematically showing the supply
path of the high frequency electric power on the electrode.
[0028] FIG. 8 is a bottom view schematically showing the supply
path of the high frequency electric power on the electrode.
[0029] FIG. 9 is a sectional view schematically showing a first
example of the upper electrode according to the second embodiment
of the present invention.
[0030] FIG. 10 is a sectional view schematically showing a second
example of the upper electrode according to the second embodiment
of the present invention.
[0031] FIG. 11 is a sectional view schematically showing a supply
path of the high frequency electric power in the second example of
the upper electrode according to the second embodiment of the
present invention.
[0032] FIG. 12 is a sectional view schematically showing a third
example of the upper electrode according to the second embodiment
of the present invention.
[0033] FIG. 13 is a sectional view schematically showing a fourth
example of the upper electrode according to the second embodiment
of the present invention.
[0034] FIG. 14 is a sectional view schematically showing a fifth
example of the upper electrode according to the second embodiment
of the present invention.
[0035] FIG. 15 is a sectional view schematically showing a sixth
example of the upper electrode according to the second embodiment
of the present invention.
[0036] FIG. 16 is a sectional view showing the plasma etching
apparatus according to the third embodiment of the present
invention.
[0037] FIGS. 17A and 17B are schematic views for explaining the
principle of the third embodiment of the present invention.
[0038] FIG. 18 is a sectional view showing the plasma etching
apparatus according to the fourth embodiment of the present
invention.
[0039] FIG. 19 is a sectional view showing the plasma etching
apparatus according to the fifth embodiment of the present
invention.
[0040] FIG. 20 is a circuit diagram showing an equivalent circuit
of an electric power supplying rod and a cylindrical conductive
member in the plasma etching apparatus according to the fifth
embodiment of the present invention.
[0041] FIG. 21 is a circuit diagram showing an equivalent circuit
of an upper surface of the upper electrode (electrode supporting
body) and a plate-like conductive member in the plasma etching
apparatus according to the fifth embodiment of the present
invention.
[0042] FIG. 22 is a sectional view showing the plasma etching
apparatus according to the sixth embodiment of the present
invention.
BEST MODE FOR CARRYING OUT OF THE INVENTION
[0043] The present invention can be more fully understood from the
following detailed description of embodiments of the invention in
conjunction with the accompanying drawings.
[0044] FIG. 1 is a sectional view schematically showing the plasma
etching apparatus according to the first embodiment of the present
invention.
[0045] A plasma processing apparatus 1 is constituted as a
capacitive coupling type parallel plate etching apparatus having
two electrode plates being opposed to each other (arranged in
parallel and facing each other) one of which is connected to a
plasma generating electric power source.
[0046] The plasma processing apparatus 1 has a chamber 2 formed of
aluminum in a cylinder shape the surface of which is processed
(subjected to an anodic oxidation process) to form alumite. The
chamber 2 is grounded.
[0047] The chamber 2 is provided on the bottom face with an
insulator 3, such as a ceramic, upon which a suscepter supporting
body 4 formed in a substantially columnar shape is placed, for
mounting an object to be processed, such as a semiconductor wafer
(hereinafter referred to as "wafer") W. There is further provided
on the suscepter supporting body 4 a suscepter 5 constituting a
lower electrode. The suscepter 5 is connected to a high-pass filter
(HPF) 6.
[0048] The suscepter supporting body 4 contains a refrigerant
passage 7 into which a refrigerant such as liquid nitrogen is
introduced through a refrigerant pipe 8 and circulates therein. The
coldness of the refrigerant is transmitted to the wafer W via the
suscepter 5 to control the surface of the wafer W which is to be
processed at a desired temperature.
[0049] The suscepter 5 is formed in a disk-like shape the center of
the upper side of which protrudes upwards, and mounts the wafer W
and an electrostatic chuck 11. The electrostatic chuck 11 has an
electrode 12 implanted in the body formed of an insulator, and
electrostatically holds the wafer W with use of the Coulomb force
or the like when the electrode 12 is applied with a direct voltage
of 1.5 kV, for example, by a direct voltage source 13.
[0050] The insulating plate 3, the suscepter supporting body 4, the
suscepter 5, and the electrostatic chuck 11 is provided with a gas
path 14 for supplying a temperature transmission medium such as He
gas to the rear surface of the wafer W, via which the coldness of
the suscepter 5 is transmitted to the wafer W to control the wafer
W at a predetermined temperature. The suscepter 5 is provided on
the outer periphery of the upper surface with a circular focus ring
15 to surround the wafer W mounted on the electrostatic chuck 11.
The focus ring 15 is formed of a conductive material such as
silicon and facilitates even etching of the wafer.
[0051] The suscepter 5 functions as the lower electrode. There is
provided an upper electrode 21 above and opposite the suscepter
5.
[0052] The faces of the suscepter 5 and the upper electrode 21
which face each other are referred to as "opposing faces"
hereinafter. The faces not being opposed to each other are referred
to as non-opposing faces.
[0053] The opposing face of the upper electrode 21 is formed as an
electrode plate 23 having a number of delivery holes 24. The
electrode plate 23 is fixed to an electrode supporting body 22. The
body 22 is a water-cooled structure formed from a conductive
material such as aluminum the surface of which has been processed
to form alumite. The upper electrode 21 according the embodiments
to be described below is comprised by the electrode plate 23 and
the electrode supporting body 22.
[0054] The outer periphery of the upper electrode 21 is provided
with insulating member 25 formed in a ring-like shape to be placed
therein.
[0055] There is provided a harmonic absorbing member 51 formed in a
ring-shape so as to come in contact with the outer peripheries of
the electrode plate 23 and the insulating member 25. There is also
provided an insulating member 52 formed in a ring-shape so as to
bridge the electrode plate 23 and the insulating member 25 and
cover the harmonic absorbing member 51.
[0056] With this structure, the upper electrode 21 is fixed to on
the chamber 2 to be put into the insulating material 52. The
suscepter 5 is separated from the upper electrode 21 by around 10
to 60 mm.
[0057] The harmonic absorbing member 51 is designed to absorb or
attenuate the harmonic generated by the high frequency electric
power reflected by plasma by using the magnetic resonance loss
effect. As a material absorbing the harmonic, ferrite is
well-known, and thus the harmonic absorbing member 51 is formed of
a material containing ferrite. By varying the thickness and the
material of the harmonic absorbing member 51, the frequency band of
the harmonic to be absorbed can be adjusted.
[0058] On the other hand, the frequency band of the harmonic to be
absorbed can be widened by forming the harmonic absorbing member 51
of laminated materials having different frequency characteristics.
In this manner, a standing wave can be prevented by absorbing and
attenuating the harmonic having the desired frequency.
[0059] The electrode supporting body 22 of the upper electrode 21
is provided with a gas inlet 26 connected to a gas supplying pipe
27. The gas supplying pipe 27 is connected to a process gas source
30 via a valve 28 and a mass flow controller 29. The process gas
source 30 supplies process gas for plasma processing such as
etching.
[0060] The gas conventionally employed in the plasma processing can
be employed as the process gas. It is preferable to employ gas
containing elements of the halogen series, such as fluorocarbon gas
(CxFy) or hydrofluorocarbon gas (CpHqFr). The rare gas such as Ar,
He, and the like and N.sub.2 can be added, of course. The bottom
portion of chamber 2 is provided with an exhaust pipe 31 connected
to an exhaust system 35. The exhaust system 35 has a vacuum pump
such as a turbo molecule pump which can reduce the pressure in the
chamber 2 to a predetermined pressure such as 1 Pa or less.
[0061] The chamber 2 is provided with a gate valve 32 on a
sidewall. When the gate valve 32 is opened, the wafer W is conveyed
to/from a load lock chamber (not shown) adjacent to the chamber
2.
[0062] The upper electrode 21 is connected to a high frequency
electric power source 40 for generating plasma via a matching
device 41. The electric power from the high frequency electric
power source 40 is supplied to the upper electrode 21 via an
electric power supplying rod 33.
[0063] The upper electrode 21 is connected to a low pass filter
(LPF) 42. The high frequency electric power source 40 supplies
electric power having a frequency of 27 MHz or higher. By applying
electric power having such a high frequency, a high density plasma
can be generated so as to maintain the chamber 2 at a good
dissociation condition to enable plasma processing under a low
pressure.
[0064] In this example, an electric power source 40 supplies
electric power having a frequency of 60 MHz. The suscepter 5 as the
lower electrode is connected to a high frequency electric power
source 50 via a matching device 51 on the supplying line.
[0065] The high frequency electric power source 50 supplies high
frequency electric power having an arbitrary frequency within a
range of 100 kHz to 10 MHz. By applying the electric power within
such a frequency band, a suitable ion effect can be applied to the
wafer W without any damage. In this embodiment, an electric power
source for supplying electric power having a frequency of 2 MHz is
used as the high frequency electric power source 50.
[0066] The process using the plasma etching apparatus 1 constituted
as above will be described below.
[0067] After the gate valve 32 is opened, the wafer W is conveyed
to the chamber 2 from the load lock chamber (not shown) to be
mounted on the electrostatic chuck 11. The direct voltage source 13
then applies a direct voltage to electrostatically absorb the wafer
W on the electrostatic chuck 11.
[0068] The gate valve 32 is then closed and the exhaust system 35
reduces the pressure in the chamber 2 to the desired level.
[0069] Subsequently, the valve 28 is opened to introduce the
process gas into the upper electrode 21 from the process gas source
30 through the process gas supplying pipe 27 and the gas inlet 26
while the gas flow rate is controlled by the mass flow controller
29. The process gas passes through the delivery holes 24 of the
electrode plate 23 and is delivered evenly to the wafer W as
indicated by an arrow shown in FIG. 1 so as to maintain the
pressure in the chamber 2 at a predetermined value.
[0070] The high frequency electric power source 40 applies electric
power having a high frequency no lower than 27 MHz, for example, 60
MHz, to the upper electrode 21. By applying the high frequency wave
in such a manner, a high frequency electric field is generated
between the upper electrode 21 and the suscepter 5 as the lower
electrode. The process gas is dissociated to be plasma in the
electric field, and the plasma etches the wafer W.
[0071] On the other hand, the high frequency electric power source
50 applies electric power having high frequency within the range of
100 kHz to 10 MHz, for example, 2 MHz, to the suscepter 5. By
applying the high frequency wave in such a manner, the ions in the
plasma are introduced into the side of the suscepter 5, and
anisotropic property of the etching is improved by the ion
assistance.
[0072] By setting the frequency of the high frequency electric
power applied to the upper electrode 21 at 27 MHz or higher, the
density of plasma can be increased. However, merely by setting the
frequency of the high frequency electric power applied to the upper
electrode at the high level, the harmonic is reflected from the
plasma. The reflected harmonic generates the standing wave under
the electrode plate 23, which causes the unevenness of the electric
field under the electrode plate 23.
[0073] More specifically, when the high frequency wave of 27 MHz or
higher is employed to generate plasma, a harmonic n times higher
than the frequency of the applied electric power will be easily
generated by plasma. When the harmonic backs to the high frequency
wave source from the upper electrode 21, the harmonic is reflected
at the portions such as a border between the upper electrode 21 and
the insulating member 25 as indicated as A and B and the electric
power supplying position indicated as C in FIG. 2, and generates
the standing wave between these portions and the center of the
upper electrode 21 indicated as D.
[0074] When the wavelength of the standing wave equals to 1/4 times
of a wavelength .lamda. of a harmonic, i.e., .lamda./4, the density
of plasma is increased near the center of the upper electrode 21,
which will cause uneven plasma. For example, when a high frequency
wave having a frequency of 60 MHz is employed as the high frequency
electric power source 40, the wavelength of the high frequency wave
is 5 m. Assuming that the distance between the portions A to D is
set at 0.14 m, the calculation indicates that the harmonic of the
ninth degree will be easily generated.
[0075] In consideration of the wavelength shortening rate
proportional to the 1/2th power of the dielectric constant of high
frequency wave path material, the harmonic of the third to sixth
degree will be easily generated. When the distance between the
portions A to D is set at 0.07 m, however, the similar problem will
occur even using the high frequency wave of 13.56 MHz.
[0076] In contrast, according to the present embodiment, the
harmonic back to the high frequency electric power source 40 is
absorbed by providing the harmonic absorbing member 51 to the
electrode plate 23 on the side of the opposing face, thereby the
generation of the standing wave can be prevented.
[0077] The harmonic absorbing member 51 is formed in a ring-like
shape in the present embodiment to improve the harmonic absorbing
effect. It goes without saying that the shape of the harmonic
absorbing member 51 is not limited to a ring. The same effect can
be also attained by providing the harmonic absorbing member 51 to
the outer periphery of the upper electrode 21, as shown in FIG.
3.
[0078] When the harmonic absorbing member 51 is formed of ferrite
sinter, the harmonic absorbing member 51 can absorb and attenuate
harmonic using the magnetic resonance loss effect, as described
above. In this case, the frequency band that can be attenuated will
be shifted by the thickness of the harmonic absorbing member 51.
When the thickness of the harmonic absorbing member 51 is halved,
the frequency band that can be attenuated will be doubled.
[0079] More specifically, when the thickness of the harmonic
absorbing member 51 is 7 mm, the harmonic of 200 to 800 MHz can be
attenuated by 20 dB, as shown in FIG. 4. When the thickness of the
harmonic absorbing member 51 is 4.5 mm, the harmonic of 700 MHz to
3 GHz can be attenuated by 20 dB, as shown in FIG. 5. The frequency
band that can be attenuated can be widened by laminating ferrite
layers having different frequency characteristics. For example,
when the above-mentioned layers having a thickness of 7 mm and 4.5
mm are laminated, the harmonic having a wide frequency band from
200 MHz to 3 GHz can be attenuated.
[0080] The present embodiment will not be limited to the first
embodiment and various modifications can be attained.
[0081] For example, the case where the upper electrode is applied
with electric power having high frequency of 27 MHz is described in
the first embodiment, but the frequency lower than 27 MHz is also
effective.
[0082] Further, in the present embodiment, the upper and lower
electrodes are applied with electric power having high frequency in
the first embodiment, the type that only the upper electrode is
applied with electric power having high frequency may be employed.
The present embodiment can be applied to the apparatus wherein the
lower electrode is applied with electric power having high
frequency. In this case, the harmonic absorbing member is arranged
to come into contact with the edge portion of the face of the lower
electrode, which is opposed to the upper electrode, or the
periphery of the lower electrode.
[0083] In addition, the case where the semiconductor wafer is used
as the substrate to be processed and etched is described in this
embodiment, but the substrate is not limited to the semiconductor
wafer, but the other substrate such as a liquid display apparatus
(LCD) or the like may be processed. The plasma processing is not
limited to the etching, but an other processing such as sputtering,
CVD, or the like may be performed.
[0084] According to the present embodiment, the first electrode is
applied with electric power having high frequency, and the harmonic
absorbing member for absorbing harmonic having frequency of the
high frequency wave electric power applied by the high frequency
wave electric power applying means is arranged to come in contact
with the edge portion of the face of the first electrode, which is
opposed to the second electrode, or the periphery of the first
electrode. With this method, the harmonic reflected by plasma
passes through the electrode and reaches the harmonic absorbing
member before returning to the high frequency electric power
source, where the harmonic will be absorbed.
[0085] Accordingly, the standing wave due to the harmonic will be
prevented from being generated, and the unevenness of the electric
field on the surface of the electrode, which is caused by the
standing wave, can be suppressed to make the density of plasma
even.
[0086] FIG. 6 shows an example of a constitution of a plasma
processing apparatus according to the second embodiment of the
present invention, used as a capacitive coupling type parallel
plate etching apparatus. The constituent elements as the main
feature of the apparatus according to the present embodiment will
be described below, and the same constituent elements as those of
the first embodiment shown in FIG. 1 will be denoted by the same
symbols and the description thereof will be omitted.
[0087] The upper electrode 21 of this etching apparatus 102 is
arranged on the upper portion in the chamber 2 to be opposed to a
suscepter 5 via an insulating member 25 covering the electrode like
a ring along the outer periphery thereof. The upper electrode 21 is
constituted by the electrode plate 23 having numerous delivery
holes 24 and the electrode supporting body 22 so as to be
integrated.
[0088] The upper electrode of the present embodiment does not have
the harmonic absorbing member 51 or the insulating member 52
described in the first embodiment, but is attached directly to the
chamber 2 by the insulating member 25. The other structure is the
same as that described in the first embodiment.
[0089] The structure of the upper electrode 21 will be described
below in detail.
[0090] The electrode 23 of the upper electrode 21 is normally
formed of a conductor or semiconductor such as Si, SiC or the like.
When the frequency of the high frequency electric power 40 supplied
via the electric power supplying rod 33 is increased, the skin
effect will be generated to supply electric power only to the
surface of the electrode. As shown in FIG. 7, the electric power
passes the surface of the electric power supplying rod 33, the
upper surface of the electrode supporting body 22, the side face of
the electrode supporting body 22, and the side face of the
electrode plate 23, and reaches the lower surface of the electrode
plate 23, which is a plasma contacting face.
[0091] In this case, the electric power supplying rod 33 is
connected to the center of the non-opposing face of the upper
electrode 21, and thus the electric power has the same phase
anywhere in the edge portion on the opposing face of the electrode
plate 23. As shown in FIG. 8, the electric power having the same
phase is supplied gradually toward the center of the opposing face
from the edge portion of the electrode plate 23. With this
constitution, the phase difference d/.lamda. (.lamda. is the
wavelength of the electric wave on the electrode, and d is a radius
of the electrode) is generated between the center and the edge
portion of the electrode plate 23.
[0092] When the frequency of the high frequency electric power
applied is increased, the inductance (L.omega.j.OMEGA.) in the
direction in which the electrode plate 23 is opposed to the
suscepter 5 is not neglected. The impedance at the center of the
opposing face of the electrode plate 23 will be decreased due to
the interference by the phase difference d/.lamda., thereby the
strength of the electric field of the center of the electrode plate
23 is higher than that of the edge portion. The center of the
electrode plate 23 comes in contact with plasma, and thus is an
open-circuit terminal of an RF equivalent circuit.
[0093] Accordingly, the electric field supplied to plasma is
similar to the standing wave, which causes the unevenness of the
density of plasma.
[0094] In the first example to solve the unevenness of the density
of plasma, the opposing face of the electrode plate 23 is
constituted by an outer portion 61 formed in a ring shape having a
circumference corresponding to the outer periphery of the electrode
plate 23 and made of a conductor or semiconductor having a low
resistivity of around 50 m.OMEGA.cm and a central portion 62 formed
of a dielectric, as shown in FIG. 9. By forming the central portion
62 of dielectric, the capacitance between the plasma and the
dielectric is added at the portion. The impedance Z will be
expressed as follows:
Z=.omega.L-(1/C.omega.)j
[where .omega.=2.pi.f (f: frequency)] The inductance component
(L.omega.) in the direction of the diameter of the electrode plate
23 in the impedance Z can be thus offset by the capacitance
component (-1/C.omega.) of the capacitance C of the dielectric
member 62.
[0095] Accordingly, the change of the impedance Z due to the phase
is prevented almost perfectly in the opposing face of the electrode
plate 23, thereby the electric field strength of the center of the
opposing face of the electrode plate 23 is decreased, which makes
the electric field applied to plasma from the lower face of the
electrode even, and the density of plasma can be also made
even.
[0096] The diameter of the central portion 62 formed of dielectric
is preferably 10 to 50 mm.PHI. when the diameter of the electrode
plate 21 is set at 300 mm.PHI.. The dielectric constant of the
dielectric comprising the central portion 62 needs to be set merely
enough to offset the inductance component L.omega., and thus the
central portion 62 may be formed from a polyimide resin having a
dielectric constant of 3, for example. The outer portion 61 can be
formed from conductor or semiconductor such as Si, SiC or the like,
which is normally used to form an electrode plate.
[0097] The second example of the upper electrode 21 will be
described below.
[0098] According to the second example, the electrode plate 23 is
constituted by an outer portion 63 formed of conductor or
semiconductor having relatively low resistivity of 50 m.OMEGA.cm
for example, and a central portion 64 formed of high resistant
member having relatively high resistivity of 1 to 100 .OMEGA.cm, as
shown in FIG. 10.
[0099] By forming the central portion 64 of such a high resistant
member, the thickness of the portion supplied with electric power
at the portion, i.e., so-called skin depth .delta. will be varied.
More specifically, the skin depth .delta. can be expressed as
.delta.=(2/.omega. .sigma. .mu.).sub.1/2
[where .sigma. is conductivity, .mu. is magnetic permeability] When
the resistance becomes larger to decrease the conductivity .sigma.,
the skin depth .delta. will become larger.
[0100] When the skin depth .delta. of the high resistance member 64
increases more than the thickness of the high resistance member 64,
the high frequency electric power reaches the rear face
(non-opposing face) of the high resistance member 64 to be supplied
there as shown in FIG. 11. On the way from the rear face to the
lower face of the high resistance member 64, the high frequency
electric power will be discharged as Joule heat.
[0101] By virtue of the heat discharge, the electric field strength
of the center of the opposing face of the electrode plate 23 is
made even, as the result, the electric field applied to plasma from
the opposing face of the electrode plate 23 is made even, and the
density of plasma can be also made even.
[0102] The diameter of the central portion of the high resistance
member 64 is preferably 50 to 220 mm.PHI. when the diameter of the
electrode 21 is set at 300 mm.PHI.. It is preferable that the high
resistance member (central portion) 64 is formed from Si since the
resistance can be adjusted merely by adjusting the amount of the
dopant such as boron.
[0103] The outer portion 63 can be formed from a conductor or
semiconductor such as Si, SiC or the like, which is normally used
to form an electrode plate. It is easier to form the entire
electrode plate 23 from Si and form the outer portion 63 and the
high resistance member 64 by changing the doping amount of the
dopant such as boron.
[0104] The third example of the upper electrode 21 will be
described below.
[0105] According to the present example, a dielectric member 65 is
provided to the electrode plate 23 to come in contact with the
center of the non-opposing face of the electrode plate 23, as shown
in FIG. 12. In this example, the electrode plate 23 is formed of
conductor or semiconductor having resistivity within 1 to 100
.OMEGA.cm, such that the skin depth .delta. is larger than the
thickness of the electrode plate 23.
[0106] By forming the electrode plate 23 in such a manner, the high
frequency electric power reaches the rear face (non-opposing face)
of the electrode plate 23 to be supplied there. By arranging the
dielectric member 65 on the central portion of the rear surface of
the electrode plate 23, the capacitance between the plasma and the
dielectric is added at the portion.
[0107] Accordingly, as in the first example, the inductance
component (.omega.L) in the direction of the diameter in the
impedance Z can be thus offset by the capacitance component
(-1/C.omega.) of the capacitance C of the dielectric member 62. The
change of the impedance Z due to the phase is thus decreased in the
central portion of the opposing face of the electrode plate 23,
thereby the electric field strength of the center of the opposing
face of the electrode plate 23 is decreased, which makes the
electric field applied to plasma from the lower face of the
electrode even, and the density of plasma can be also made
even.
[0108] In the third example, the electrode plate 23 need not be
divided into two portions, unlike the first and second examples,
and the conventional integrated electrode plate formed of a
conductor and semiconductor can be employed.
[0109] The diameter of the dielectric member 65 formed of a
dielectric is preferably 50 to 220 mm.PHI. when the diameter of the
electrode 21 is set at 300 mm.PHI.. The dielectric constant of the
dielectric member 65 needs to be set merely enough to offset the
inductance component L.omega., and thus the dielectric member 65
may be formed from a polyimide resin having a dielectric constant
of 3, for example.
[0110] The fourth example of the upper electrode 21 will be
described below.
[0111] According to the present example, a high resistant member 66
is provided to the electrode plate 23 to come in contact with the
center of the rear face of the electrode plate 23, as shown in FIG.
13. According to the fourth example, the high resistance member 60
electrode plate 23 is formed of a high resistant member having
resistivity within a range of 1 to 100 .OMEGA.cm and the skin depth
.delta. is larger than the thickness of the electrode plate 23.
[0112] By forming the electrode plate 23 in this manner, the high
frequency electric power reaches the non-opposing face of the
electrode plate 23 to be supplied there. By arranging the high
resistant member 66 in the central portion of the rear face of the
electrode plate 23, the high frequency electric power supplied
thereto will be discharged as Joule heat. By virtue of the heat
discharge, the electric field strength of the center of the
opposing face of the electrode plate 23 is decreased. Accordingly,
the electric field applied to plasma from the opposing face of the
electrode is made even, and the density of plasma can be also made
even. Also in the fourth example, the electrode plate 23 needs not
to be divided into two portions, unlike the first and second
examples, and the conventional integrated electrode plate formed of
conductor and semiconductor can be employed.
[0113] The diameter of the high resistant member 66 formed of
dielectric is preferably 50 to 220 mm.PHI. when the diameter of the
electrode 21 is set at 300 mm.PHI.. It is preferable that the high
resistant member 66 is formed from Si since the resistance can be
adjusted merely by adjusting the amount of the dopant such as
boron.
[0114] The fifth example of the upper electrode 21 will be
described below.
[0115] According to the present example, an insulating layer 67 is
provided on the opposing face of the electrode plate 23, as shown
in FIG. 14. The insulating layer 67 can be formed by the frame
spraying of ceramic or the like, but can also be formed in other
ways. By forming the insulating layer 67 in this manner, the
capacitive coupling is formed between plasma and the electrode
plate 23 via the insulating layer 67.
[0116] In other words, there are a plenty of capacitors between the
electrode plate 23 and plasma in an RF equivalent circuit. As a
result, the inductance component (.omega.L) in the direction in
which the suscepter 5 and the electrode plate 23 are opposed to
each other can be thus offset by the capacitance component
(-1/C.omega.) of the insulating layer 67. The change of the
impedance Z due to the phase is thus prevented almost perfectly on
the opposing face of the electrode plate 23, thereby the electric
field applied to plasma from the opposing face of the electrode is
made even, and the density of plasma can be also made even.
[0117] The material and the thickness of the insulating layer 67
are determined such that the capacitance of the insulating layer is
set high enough to offset the inductance component (.omega.L).
[0118] The unevenness of the electric field on the opposing face of
the electrode plate 23 of the upper electrode 21 is caused not only
by the change in direction of the inductance on the surface of the
electrode when the frequency of the electric power applied to the
electrode is increased. The unevenness of the electric field on the
opposing face of the electrode plate 23 will be caused also in the
case where the non-linear characteristics of plasma remarkably
appears, a harmonic of the reflection wave from plasma is
increased, and the harmonic generates a standing wave on the
surface of the electrode.
[0119] More specifically, the reflection wave of the high frequency
electric power from the plasma contains so much amount of
harmonics. The harmonics are further reflected by the inductance
component of the electric power supplying rod 33. Some of the
harmonics contain the reflection waves reflected by the rod 33
having a wavelength for forming the standing wave when the diameter
of the electrode 21 is set at 250 to 300 mm.PHI., the standing wave
is formed on the opposing face of the electrode plate 23 to
increase the electric field strength in the central portion of the
surface of the electrode plate 23.
[0120] In order to solve the above-mentioned problem, according to
the sixth example of the upper electrode 21, a member 68 having an
electromagnetic wave absorbing effect, such as ferrite sinter, is
provided to the electrode plate 23 so as to come in contact with
the central portion of the non-opposing face of the electrode plate
23, as shown in FIG. 15. With use of such a member 68, the harmonic
from plasma is absorbed. By absorbing the harmonic in this manner,
the standing wave can be prevented from being generated, the
electric field on the opposing face of the electrode plate 23 is
made even, and the density of plasma can be made even.
[0121] In this case, the member 68 having the electromagnetic wave
absorbing effect is formed from the material having a property that
absorbs the harmonic from plasma but does not absorb the frequency
of the higher frequency electric power. The frequency band to be
absorbed by the member 68 can be adjusted by the type of material
and component.
[0122] The above-mentioned first to sixth examples of the upper
electrodes in the second embodiment is effective particularly in
the case where the frequency of the electric power applied to the
electrode is 27 MHz or more, and the density of plasma is as high
as 1.times.10.sup.11/cm.sup.3 or higher.
[0123] Next, the etching apparatus according to the second
embodiment will be described about the example in which an oxide
film formed on the wafer W is etched.
[0124] As in the first embodiment, the wafer W is transferred into
the chamber 2 to be electrostatically attached to an electrostatic
chuck 11. After the pressure of the chamber 2 is reduced to a
predetermined level, the process gas is introduced into the chamber
2 to be blown to the wafer W under a predetermined pressure.
[0125] Subsequently, a high frequency electric power having
frequency of 60 MHz is applied to the upper electrode 21 from the
high frequency electric power source 40. By applying such a high
frequency electric power, a high frequency electric field is
generated between the upper electrode 21 and the suscepter (lower
electrode) 5, and the process gas is dissociated therein to be
plasma. On the other hand, the high frequency electric power source
50 applies electric power having high frequency within the range of
1 to 4 MHz, for example, 2 MHz, to the suscepter 5 as a lower
electrode. By applying the high frequency wave in such a manner,
the ions in the plasma are introduced into the side of the
suscepter 5, and anisotropy of the etching is improved by the ion
assistance.
[0126] By setting the frequency of the high frequency electric
power applied to the upper electrode 21 at 27 MHz or higher, the
density of plasma can be increased. However, in the conventional
constitution of the upper electrode, the unevenness of the electric
field on the opposing face of the electrode plate 23 will be caused
due to the standing wave, as described before.
[0127] According to the present embodiment, any of the causes of
the unevenness of the electric field on the opposing face of the
electrode plate 23 can be eliminated by constituting the upper
electrode 21 as described in the first to sixth examples.
Accordingly, the electric field on the opposing face of the
electrode plate 23 can be made even more than the conventional one,
thereby the density of plasma can be made more even.
[0128] More specifically, with the above-mentioned constitution of
the upper electrode, the frequency of the high frequency electric
power is increased, and the problem unique to the case when the
density of plasma is increased can be solved, thereby high-density
and an even plasma can be generated.
[0129] Therefore, according to the present embodiment, the evenness
of the etching can be improved to suitably cope with the downsizing
of the design rule.
[0130] When the frequency of the electric power applied to the
electrode is 27 MHz or more, and the density of plasma is as high
as 1.times.10.sup.11/cm.sup.3 or higher, unevenness will easily
occur. The above-mentioned upper electrode according to the present
embodiment is effective particularly in such a case.
[0131] The present embodiment is not be limited to the
above-mentioned examples, and various modifications can be made.
For example, the upper and lower electrodes are applied with
electric power having a high frequency, only the upper electrode
may be applied with electric power having a high frequency.
Further, the case where the upper electrode is applied with
electric power having a high frequency of 27 to 50 MHz is described
in the first embodiment, but the frequency is not limited to this
range. In addition, the case where the semiconductor wafer is used
as the substrate to be processed and etched is described in this
embodiment, but the substrate is not limited to the semiconductor
wafer, but another substrate, such as a liquid display apparatus
(LCD) or the like, may be processed. The plasma processing is also
not limited to etching, but another processing such as sputtering,
CVD, or the like may be performed. The above-mentioned examples of
the upper electrodes shown in the present embodiment can be
employed together.
[0132] FIG. 16 shows an example of a constitution of a plasma
processing apparatus according to the third embodiment of the
present invention, used as a capacity coupling parallel plate
etching apparatus. The same constituent elements as those of the
first embodiment shown in FIG. 1 will be denoted by the same
symbols and the description thereof will be omitted.
[0133] The etching apparatus 103 is different in that the electrode
rod on the side of the upper electrode 21 is removed and the
chamber 2 covering the rod is formed in a different shape. The
upper electrode 21 is connected to a direct voltage source 43 for
boosting a self bias voltage (Vdc) of the upper electrode 21 via a
low pass filter (LPF) 44 for transmitting only a direct
voltage.
[0134] The matching device 41 is provided therein with a capacitor
(not shown) connected in series, and thus the high frequency
electric power source 40 and the direct voltage source 43 will not
conflict with each other.
[0135] The outer periphery of the upper electrode 21 is provided
with an insulating member 25 formed in a ring-like shape along, the
periphery. The insulating member 25 is air-tightly attached at the
outer peripheral face to the inner sidewall of the chamber 2. With
this constitution, the harmonic absorbing member 51 is not provided
to the apparatus of the present embodiment.
[0136] The operation of the plasma etching apparatus 103
constituted as above will be described below.
[0137] As in the first embodiment, the wafer W is transferred into
the chamber 2 to be electrostatically attached to the electrostatic
chuck 11. After the pressure of the chamber 2 is reduced to a
predetermined level, the process gas is introduced into the chamber
2 to be blown to the wafer W under a predetermined pressure.
[0138] Subsequently, high frequency electric power having a
frequency of 27 MHz or more, for example, 60 MHz, is applied to the
upper electrode 21 from the high frequency electric power source
40. By applying such high frequency electric power, plasma is
generated between the upper electrode 21 and the suscepter 5 to
etch the wafer W. On the other hand, the high frequency electric
power source 50 applies electric power having a high frequency of 2
MHz, for example, to the suscepter 5, and an etching with excellent
anisotropy by ion assistance is performed.
[0139] Also in the present embodiment, the unevenness of the
electric field will occur on the opposing face of the electrode
plate 23, as in the first embodiment.
[0140] More specifically, when the high frequency electric power is
applied only by the high frequency electric power source 40, the
harmonic from the plasma generates a standing wave on the opposing
face of the upper electrode 21, and an unevenness of the electric
field will occur on the opposing face of the upper electrode 21.
When the frequency of the high frequency electric power applied to
the upper electrode is increased to 27 MHz or higher, the self bias
voltage (Vdc) of the upper electrode 21 is decreased thereby. As a
result, the thickness of the entire plasma sheath S of the upper
electrode 21 will be decreased as shown in FIG. 17A. Due to the
unevenness of the electric field by the standing wave, the plasma
sheath of the central portion of the electrode will be further
decreased in thickness. The change ratio of the thickness of the
overall portion of the plasma sheath is increased in such a manner,
and the self bias voltage (Vdc) on the surface of the upper
electrode 21 will be made uneven. As a result, the evenness of
plasma will be deteriorated.
[0141] In contrast, by applying a high frequency electric power
having a frequency higher than 27 MHz to the upper electrode 21
from the high frequency electric power source 40 and applying a
direct voltage from the direct voltage source 43, the self bias
voltage (Vdc) will be increased by the valve of the direct voltage
as shown in FIG. 17B. The increased voltage S1 forms a thicker
plasma sheath S', which can suppress the influence of the
unevenness of the self bias voltage (Vdc) and the plasma
sheath.
[0142] With this method, even if the unevenness occurs in the
plasma density, the influence thereof will be suppressed at the
minimum level, and the etching rate can be regarded to be even in
the practical level.
[0143] For example, when high frequency electric power of 60 MHz
and 1 kW is applied to the upper electrode 21 from the high
frequency electric power source 40, the relationship Vdc=-100 V
will be attained. Assuming the fluctuation of Vdc is around.+-.10
V, the fluctuation rate will be as large as.+-.10%, which will
deteriorate the evenness of plasma.
[0144] However, when a direct voltage of -400 V, for example, is
applied from the direct voltage source 43, the total sum of the
self bias voltage (Vdc) will be increased to -(100+400).+-.10 V. As
a result, the fluctuation rate will be decreased to.+-.2%, and the
evenness of Vdc will be improved. The evenness of plasma can be
considered to be also improved thereby.
[0145] The fourth embodiment of the present invention will be
described below.
[0146] FIG. 18 shows an example of a constitution of a plasma
processing apparatus according to the fourth embodiment of the
present invention, used as a capacity coupling parallel plate
etching apparatus. The same constituent elements as those of the
second embodiment shown in FIG. 16 are denoted by the same symbols
and the description thereof is omitted.
[0147] In the etching apparatus 104, the upper electrode 21 is
connected to two high frequency electric power sources. One is the
first high frequency electric power source 70 for generating plasma
connected to the upper electrode 21 via a high pass filter (HPF) 72
and a matching device 71. The other is the second high frequency
electric power source 73 connected to the upper electrode 21 via a
low pass filter (LPF) 75 and a matching device 74.
[0148] The first high frequency electric power source 70 has a high
frequency of 27 MHz or higher. By applying electric power having
such a high frequency, suitably dissociated and high-density plasma
can be generated in the chamber 2, thereby the plasma processing
under a low pressure can be attained. In this example, the first
high frequency electric power source 70 outputting high frequency
electric power of 60 MHz is employed.
[0149] The second high frequency electric power source 73 outputs
high frequency electric power of a frequency lower than that output
from the first high frequency electric power source 70, preferably,
2 to 10 MHz. In the present embodiment, the second high frequency
electric power source 73 outputting high frequency electric power
of 2 MHz is employed.
[0150] More specifically, the second high frequency electric power
source 73 outputs the high frequency electric power of a frequency
lower than that output from the first high frequency electric power
source 70, and thus functions to boost the self bias voltage (Vdc)
of the upper electrode 21.
[0151] The high pass filter (HPF) 72 is intended to cut the current
having a frequency equal or lower than the frequency of the second
high frequency electric power source 73, and the low pass filter
(LPF) 75 is provided to cut the current having a frequency equal to
or higher than the frequency of the first high frequency electric
power source 70.
[0152] The plasma etching apparatus 104 constituted as above
performs the etching process in basically the same manner as using
the plasma etching apparatus 103 according to the third
embodiment.
[0153] At this time, the density of plasma can be increased by
setting the frequency of the high frequency electric power applied
to the upper electrode 21 at 27 MHz or higher. However, merely by
increasing the frequency, the standing wave is generated on the
opposing face of the electrode plate 23 by a harmonic due to the
reflected wave from the plasma, which will cause unevenness of the
electric field on the opposing face of the electrode plate 23.
[0154] Instead of the application of the direct voltage according
to the third embodiment, according to the fourth embodiment, the
second high frequency electric power source 73 applies the high
frequency electric power having a frequency lower than the
frequency of the first high frequency electric power source 70 to
the upper electrode 21.
[0155] The self bias voltage generated by the high frequency
electric power applied by the second high frequency electric power
source 73 is larger than the self bias voltage generated by the
high frequency electric power applied by the first high frequency
electric power source 70. Therefore, the high frequency electric
power from the first and second high frequency electric power
sources 70 and 73 overlap, as a result, a remarkably high self bias
voltage (Vdc) of the upper electrode 21 can be attained compared
with the case where a high frequency electric power is applied to
the electrode only from the first high frequency electric power
source 60, as indicated in the embodiment described before. The
increased voltage forms a thicker plasma sheath, which can suppress
the influence of the unevenness of the self bias voltage (Vdc) and
the plasma sheath, as in the case shown in FIG. 17(b).
[0156] With this method, the plasma density can be made even, on a
practical basis, and the etching rate can be made even.
[0157] In an example where high frequency electric power of 60 MHz
and 1 kW is applied to the upper electrode 21 from the high
frequency electric power source 70, the relationship Vdc=-100 V
will be attained. Assuming the fluctuation of Vdc is around.+-.10
V, the fluctuation rate will be as large as.+-.10%, which will
deteriorate the evenness of plasma. However, when a high frequency
electric power of 2 MHz and 500 W, for example, is applied to the
upper electrode 21 from the second high frequency electric power
source 73, the self bias voltage (Vdc) generated by the second high
frequency electric power source 73 will be increased to around -400
V, and the total sum of the self bias voltage (Vdc) generated by
the second high frequency electric power source 73 will be
increased to -(100+400) V.+-.10 V. As a result, the fluctuation
rate will be decreased to.+-.2%, and the evenness of Vdc will be
improved. The evenness of plasma can be also improved thereby.
[0158] The fourth embodiment is not be limited to the
above-mentioned examples, and various modifications can be
made.
[0159] For example, the upper and lower electrodes are applied with
electric power having a high frequency, only the upper electrode 21
may be applied with electric power having a high frequency.
[0160] Further, where the oxide film formed on the wafer is etched
using the semiconductor wafer, the present embodiment can be
applied to an etching for an insulating film other than the oxide
film, a polysilicon film, and the like. In addition, the substrate
to be processed is not limited to the semiconductor wafer, and
another substrate, such as a liquid display apparatus (LCD) or the
like may be processed.
[0161] FIG. 19 shows an example of a constitution of a plasma
processing apparatus according to the fifth embodiment of the
present invention, used as a capacitive coupling type parallel
plate etching apparatus. The same constituent elements as those of
the first embodiment shown in FIG. 1 will be denoted by the same
symbols and the description thereof will be omitted.
[0162] The etching apparatus 105 is constituted to have an
electromagnetic wave shielding box 80 for shielding electromagnetic
waves above the non-opposing face of the upper electrode 21 in the
chamber 2.
[0163] In this constitution, the electric power supplying rod 33
for supplying high frequency electric power output from the high
frequency electric power source 40 is connected to the electrode
supporting body 22 of the upper electrode 21.
[0164] There is provided above the electrode supporting body 22
with a conductive plate-like member 82. A cylindrical member 81 and
plate-like member 82 are integrally, and at least electrically
connected with each other, and the plate-like member 82 is
connected to the grounded chamber 2.
[0165] More specifically, the cylindrical member 81 and the
plate-like member 82 are grounded via the chamber 2. The
cylindrical member 81 can decrease the inductance of the electric
power supplying rod 33 as will be described later, and also ground
the harmonics. The plate-like member 82 can also decrease the
inductance of the upper electrode 21, and also ground the
harmonics.
[0166] The other constituent elements are the same as those
described in the first embodiment.
[0167] The operation of the plasma etching apparatus 105
constituted as above will be described below. In this embodiment,
the etching of the film formed on the wafer W will be
described.
[0168] As in the first embodiment, the wafer W is transferred into
the chamber 2 to be electrostatically attached to electrostatic
chuck 11. After the pressure of the chamber 2 is reduced to a
predetermined level, the process gas is introduced into the chamber
2 to be blown to the wafer W under a predetermined pressure.
[0169] Subsequently, high frequency electric power having a
frequency of 27 MHz or more, for example, 60 MHz, is applied to the
upper electrode 21 from the high frequency electric power source
40. By applying such a high frequency electric power, plasma is
generated between the upper electrode 21 and the suscepter 5 to
etch the wafer W. On the other hand, the high frequency electric
power source 50 applies electric power having a high frequency of 2
MHz, for example, to the suscepter 5, and an etching with excellent
anisotropy by ion assistance is performed.
[0170] In general, the density of plasma can be increased by
increasing the high frequency electric power applied to the upper
electrode 21 to 27 MHz or higher, as described before. However, the
inductance of the electric power applying rod is very large, and
thus the harmonic is reflected from the plasma by the inductance
component of the electric power applying rod. The reflected
harmonic is further reflected by the faces of the electromagnetic
wave shielding box 80, and returns to the opposing face of the
upper electrode 21 generating the plasma. Particularly with an
electrode having a diameter of 250-300 mm.PHI., a standing wave
will be easily generated on the surface of the electrode due to the
harmonic, which makes the electric field on the electrode
uneven.
[0171] In contrast, according to the present embodiment, the
conductive cylindrical member 81 is arranged near the electric
power supplying rod 33. This constitution is equivalent to a
circuit having a number of capacitors arranged in parallel between
the cylindrical member 81 and the electric power supplying rod 33,
as shown in FIG. 20. The inductance component of the electric power
supplying rod 33 is cancelled by the capacitance component of the
capacitors to decrease the impedance, with the result that the
inductance component of the electric power supplying rod 33 will be
decreased.
[0172] The cylindrical member 81 is grounded via the chamber 2, and
thus the harmonic reflected by the electric power supplying rod 33
will be grounded through the cylindrical member 81.
[0173] Accordingly, the harmonic from plasma will not be easily
reflected by the electric power supplying rod 33, and the harmonic
itself will be decreased, with the result that a standing wave
generated by the reflection of the harmonic will not be easily
generated on the plasma contacting face (opposing face) of the
electrode plate 23.
[0174] Consequently, the electric field on the plasma contacting
face of the electrode plate 23 can be made more even, which makes
the plasma density even.
[0175] The inductance component on the non-opposing face of the
electrode supporting body 22 will contribute to generate a standing
wave due to the reflection of the harmonic. However, according to
the present embodiment, the plate-like member 82 is arranged near
the non-opposing face of the electrode supporting body 22, which is
equal to the equivalent circuit having a number of capacitors
arranged in parallel between the electrode supporting body 22 and
the plate-like member 62, as shown in FIG. 21. The inductance
component at the portion will be decreased, according to the same
principle as mentioned above. The harmonic will be grounded through
the plate-like member 82.
[0176] Accordingly, the plate-like member 82 will further improve
the standing wave preventing effect.
[0177] The distance between the cylindrical member 81 and the
electric power supplying rod 33, and the distance between the
plate-like member 62 and the electrode supporting body 22 need to
be set suitably in accordance with the capacitance necessary for
canceling the standing wave. For example, when the high frequency
electric power is set at 2 kW, the distances need to be set at 8 mm
or more to prevent the breakdown in air.
[0178] In point of view of forming the capacitors, no component
needs to be provided between the cylindrical member 81 and the
electric power supplying rod 33, and the distance between the
plate-like member 62 and the electrode supporting body 22. However,
if the filtering function needs to be improved, an electric wave
absorbing body may be provided therebetween. Similarly, if the
dielectric constant needs to be adjusted, a dielectric such as a
fluoroplastic (trade name: Teflon) may be provided.
[0179] FIG. 22 shows an example of a constitution of a plasma
processing apparatus according to the sixth embodiment of the
present invention, used as a capacitive coupling type parallel
plate etching apparatus. The same constituent elements as those of
the first embodiment shown in FIG. 1 are denoted by the same
symbols and the description thereof is omitted.
[0180] In the etching apparatus 106, an electric power supplying
rod 93 is arranged at a position shifted from the central portion
of the non-opposing face of the upper electrode 21 so as to supply
electric power. According to the fifth embodiment, the electric
supplying rod 93 is arranged at the central portion of the
non-opposing face of the upper electrode 21.
[0181] There is further provided to the non-opposing face of the
upper electrode 21 with an LC circuit 94 in the opposite side of
the position of the electric supplying rod 93. The LC circuit 94
functions to adjust the phase of the voltage and current of the
high frequency electric power supplied to the upper electrode
21.
[0182] The LC circuit 94 is constructed by a coil 95 capable of
varying an inductance and a capacitor 96 capable of varying a
capacitance, and connected in series between the upper electrode 21
and the chamber 2.
[0183] There is provided a conductive cylindrical member 91 near
the electric power supplying rod 93 and a conductive plate-like
member 92 near the upper portion of the electrode supporting body
22. The cylindrical member 91 and the plate-like member 92 are
electrically connected with each other, and the plate-like member
92 is electrically connected to the grounded chamber 2.
[0184] The other constituent elements are the same as those
described in the first embodiment.
[0185] The plasma etching apparatus 106 constituted as above
performs a similar etching process to that performed by the plasma
etching apparatus 105.
[0186] However, when the high frequency electric power applied to
the upper electrode 21 is increased to 27 MHz or higher, a standing
wave will be generated for the same reason as described before, and
unevenness of the electric field on the electrode will occur
thereby.
[0187] When the electric power supplying rod 33 is arranged in the
center of the upper electrode 21, the phase difference d/.lamda.
(.lamda. is the wavelength of the electric wave on the electrode,
and d is a radius of the electrode) is generated between the center
and the edge portion of the electrode plate 23, as shown in FIGS. 7
and 8 before.
[0188] In the equivalent electric circuit, the electric power
applied to the outer portion of the upper electrode 21 is grounded
via an insulator in parallel with the direction in which electric
power is supplied to the plasma, and terminated at characteristic
impedance (50.OMEGA.), and thus the electric field strength Eo at
the outer portion is expressed as
Eo=Ecos (.omega.t)
[0189] The electric field strength Eo at the central portion of the
upper electrode 21 is expressed as
Ec=Ecos (.omega.t+d/.lamda.)
where .lamda. is the (wavelength shortening) wavelength of the high
frequency electric power applied to the electrode and harmonic
generated by the reflection from plasma, and the high frequency
electric power via plasma.
[0190] In this time, the high frequency electric power is gradually
supplied to the central portion from the outer portion, and thus
the voltage and the current will be concentrated at the central
portion from the outer portion in the electrode plate 23. When the
frequency of the high frequency electric power is increased, the
inductance in the direction in which the electrode plate 23 is
opposed to will become too large to be neglected. The impedance at
the center of the opposing face of the electrode plate 23 will be
decreased due to the interference by the phase difference.
[0191] Due to the above-mentioned problems, the strength of the
electric field of the center of the electrode plate 23 is higher
than that of the edge portion. The center of the electrode plate 23
comes in contact with plasma, and thus is an open-circuit edge of
an RF equivalent circuit. Accordingly, a standing wave having a
wavelength .lamda.=2d is generated on the opposing face of the
electrode plate 23, which causes unevenness of the density of
plasma.
[0192] In order to prevent a standing wave generated due to the
above-mentioned problems, according to the present embodiment, high
frequency electric power is supplied to the position shifted from
the central portion to the outer portion of the upper electrode 21
via an electric power supplying rod 93, and an LC circuit 94 as
phase adjusting means is provided opposite the electric power
supplying rod 93 on the non-opposing face of the upper electrode 21
with respect to the center. By constituting the apparatus in this
manner, the phases of the voltage and the current of the high
frequency electric power supplied to the upper electrode 21 are
made uneven on the outer periphery.
[0193] More specifically, by supplying high frequency electric
power to the position shifted from the central portion to the outer
portion of the upper electrode 21, the concentration of the voltage
and current paths on the opposing face of the electrode plate 23 is
prevented. Thereafter, the phases of the voltage and the current of
the high frequency electric power supplied to the upper electrode
21 can be made uneven on the circumference of the electrode plate
23 by adjusting the inductance of the coil 95 and the capacitance
of the capacitor 96 by using the LC circuit 94 so as to shift the
phases of the voltage and the current. By making the phases uneven,
a standing wave which will be caused by the electric power supplied
from the center of the electrode to the opposing face of the
electrode plate 23 can be prevented.
[0194] Accordingly, the electric field on the opposing face, i.e.,
the plasma contacting face of the electrode plate 23, can be made
more even, thereby the evenness of the plasma density can be
attained.
[0195] The apparatus of the present embodiment is provided with the
cylindrical member 91 and the plate-like member 92, similarly to
the first embodiment, and thus the standing wave due to the
reflection of a harmonic cannot be easily generated on the plasma
contacting face (opposing face) of the electrode plate 23, and thus
the electric field on the plasma contacting face of the electrode
plate 23, can be made more even.
[0196] The above-mentioned advantage can be attained at a
predetermined level if the electric power supplying rod 93 is
shifted more or less from the center of the upper electrode 21.
However, when the electrode has a diameter of 250 mm, it is
preferable to shift 60 mm or more the electric power supplying rod
93 from the center of the upper electrode 21.
[0197] In any of the fifth and sixth embodiments, the higher the
frequency of the electric power applied to the electrode, the
easier the standing wave is generated. The inventions are thus
useful particularly in the case where the frequency of the electric
power is 27 MHz or higher. If the frequency of the electric power
used is lower than 27 MHz, however, it cannot be said that there is
no influence of the standing wave, and thus the present invention
will attain a level of advantage.
[0198] Similarly, when the density of plasma is as high as
1.times.10.sup.11/cm.sup.3 or higher, the unevenness will easily
occur. The above-mentioned upper electrode according to the present
embodiment is effective particularly in such a case.
[0199] The fifth and sixth embodiments can be employed to attain
even better evenness of the density of plasma.
[0200] The present embodiment will not be limited to the
above-mentioned examples, and various modifications can be
made.
[0201] For example, the upper and lower electrodes are applied with
electric power having a high frequency, only one of the electrodes
may be applied with electric power having a high frequency.
[0202] Further, the case where the upper electrode is applied with
electric power is described in the present embodiment, but can be
applied to the lower electrode. In addition, the case where the
semiconductor wafer is used as the substrate to be processed and
etched is described in this embodiment, but the substrate is not
limited to the semiconductor wafer, and other substrates, such as a
liquid display apparatus (LCD) or the like, may be processed. The
plasma processing is also not limited to etching, and other
processings such as sputtering, CVD, or the like may be
performed.
INDUSTRIAL APPLICABILITY
[0203] The plasma processing apparatus according to the present
invention us provided with a harmonic absorbing member for
absorbing harmonic having frequency of the high frequency wave
electric power applied by the high frequency wave electric power
applying means is arranged to come in contact with the electrode.
The harmonic absorbing member absorbs the harmonic before returning
to the high frequency electric power source. A standing wave due to
the harmonic is prevented from being generated, and the density of
plasma is even.
[0204] Further, the plasma processing apparatus according to the
present invention has two high frequency electric power sources.
When high frequency electric power having a frequency higher than
27 MHz is applied to the electrode for generating plasma from one
of the high frequency electric power sources, the high frequency
electric power having a lower frequency than that of the above
electric power is applied from the other one of the power sources,
thereby the self bias voltages (Vdc) generated by the power sources
overlap, to attain a high level self bias voltage. By the increased
self bias voltages (Vdc) the plasma sheath is made thicker, which
can suppress the unevenness of the plasma sheath due to the
unevenness of the self bias voltage (Vdc). As a result, evenness
can be attained of the plasma density, and the etching rate can be
made even when the apparatus is used for etching.
* * * * *