U.S. patent application number 09/827307 was filed with the patent office on 2002-02-21 for plasma processing apparatus and plasma processing method.
Invention is credited to Hirayama, Masaki, Kaihara, Ryuu, Ohmi, Tadahiro.
Application Number | 20020020497 09/827307 |
Document ID | / |
Family ID | 18506369 |
Filed Date | 2002-02-21 |
United States Patent
Application |
20020020497 |
Kind Code |
A1 |
Ohmi, Tadahiro ; et
al. |
February 21, 2002 |
Plasma processing apparatus and plasma processing method
Abstract
A substrate (101) subjected to a plasma process is placed on a
first electrode (102). A magnetic field is applied to a surface of
the substrate to which the plasma process is applied by magnetic
field applying means (103). An auxiliary electrode (104) is
provided on an outer periphery of the first electrode (102) to
excite plasma on a back surface (105) thereof. Electrons in the
plasma are caused to drift from a front surface (106) to a back
surface (105) of the auxiliary electrode (104) and from the back
surface (105) to the front surface (106) of the auxiliary electrode
(104).
Inventors: |
Ohmi, Tadahiro; (Sendai-Shi,
JP) ; Hirayama, Masaki; (Sendai-Shi, JP) ;
Kaihara, Ryuu; (Sendai-Shi, JP) |
Correspondence
Address: |
PILLSBURY WINTHROP LLP
1600 TYSONS BOULEVARD
MCLEAN
VA
22102
US
|
Family ID: |
18506369 |
Appl. No.: |
09/827307 |
Filed: |
April 6, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09827307 |
Apr 6, 2001 |
|
|
|
PCT/JP00/08247 |
Nov 22, 2000 |
|
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|
Current U.S.
Class: |
156/345.12 |
Current CPC
Class: |
H01J 37/3266 20130101;
H01J 37/32697 20130101; H01J 37/32587 20130101; H01J 37/32623
20130101; H01J 37/32082 20130101 |
Class at
Publication: |
156/345 |
International
Class: |
C23F 001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 25, 1999 |
JP |
11-375974 |
Claims
1. A plasma processing apparatus comprising a first electrode (102)
on which a substrate (101; 807) subjected to a plasma process is
placed and magnetic field applying means (103) for applying a
magnetic field to a surface of the substrate (101; 807) to which
the plasma process is applied, characterized in that: an auxiliary
electrode (104) is provided on an outer periphery of said first
electrode (102) to excite plasma by the auxiliary electrode (104)
so as to cause electrons in the plasma to drift from a front
surface (106) to a back surface (105) of said auxiliary electrode
(104) and from the back surface (105) to the front surface (106) of
said auxiliary electrode (104).
2. The plasma processing apparatus as claimed in claim 1,
characterized in that the front surface (106) of said auxiliary
electrode (104) is covered by an insulating material (902).
3. The plasma processing apparatus as claimed in claim 1 or 2,
characterized in that a level of a surface of the substrate (101)
placed on said first electrode (102) and a level of the front
surface of said auxiliary electrode (104) are equal to each other
or within .+-.2 mm.
4. The plasma processing apparatus as claimed in claim 1 or 2,
characterized in that said magnetic field applying means (103)
comprises a dipole ring-magnet.
5. The plasma processing apparatus as claimed in claim 1 or 2,
characterized in that a frequency f1 of a radio frequency applied
to said first electrode (102) and a frequency f2 of a radio
frequency applied to said auxiliary electrode (104) are equal to
each other and phases thereof are different from each other.
6. The plasma processing apparatus as claimed in claim 1 or 2,
characterized in that a frequency f2 of a radio frequency applied
to said auxiliary electrode (104) is higher than a frequency f1 of
a radio frequency applied to said first electrode (102)
(f2>f1).
7. A plasma processing method performed in a plasma processing
apparatus comprising a first electrode (102) on which a substrate
(101) subjected to a plasma process is placed and magnetic field
applying means (103) for applying a magnetic field to a surface of
the substrate (101) to which the plasma process is applied,
characterized by: exciting plasma on at least a back surface (105)
of an auxiliary electrode (104) provided on an outer periphery of
said first electrode; and cause electrons in the plasma to drift
from a front surface (106) to the back surface (105) of said
auxiliary electrode (104) and from the back surface (105) to the
front surface (106) of said auxiliary electrode (104).
Description
TECHNICAL FIELD
[0001] The present invention generally relates to a plasma
processing apparatus and, more particularly, to a plasma processing
apparatus which applies a magnetic field to a surface of a
substrate to which a plasma process is applied and a plasma
processing method performed b such a plasma processing
apparatus.
BACKGROUND ART
[0002] Etching of a silicone oxidization film or a polycrystalline
silicon film is one of the most important process in production of
a semiconductor, and plasma etching has been used as such etching.
In order to form a fine pattern of 1.0 .mu.m or less by plasma
etching, plasma having an ion current density of 1 mA/cm.sup.2 or
more and an electron density of 1 10 cm.sup.-3 or more is required
under a process pressure of 0.5 Pa or less. However, a
conventionally used RIE apparatus of a parallel plate type was not
able to generate plasma of such conditions.
[0003] In order to achieve the above-mentioned plasma performance,
a plasma generating apparatus using a magnetic field has been
developed. As an apparatus provided with such a plasma generating
apparatus, Japanese Laid-Open Patent Application No. 6-37056
discloses a magnetron plasma etching apparatus using a dipole
ring-magnet.
[0004] The magnetron plasma etching apparatus using a dipole-ring
magnet is able to generate low pressure and high-density plasma.
However, it is difficult to control the plasma generated on a
substrate with high accuracy. That is, it becomes difficult to
attain equalization of the plasma density on a substrate and
equalization of a self-bias voltage by introducing a horizontal
magnetic field on the substrate.
[0005] As solution which attains equalization of plasma density and
a self-bias voltage, a method of giving a slope to a magnetic field
(Japanese Laid-Open Patent Application No. 62-21062) or a method of
rotating a magnetic field introduced into a process space (Japanese
Laid-Open Patent Application No. 61-208223) is suggested. However,
the solution suggested in Japanese Laid-Open Patent Application No.
62-21062 has a problem in that the optimum value of a slope
magnetic field changes when a process pressure etc. is changed.
Additionally, although the solution suggested in Japanese Laid-Open
Patent Application No. 61-208223 apparently achieves equalization
of plasma with respect to a substrate being processed, the
mechanism for rotating the magnetic field is required, and there is
a problem in that a miniaturization of the whole plasma apparatus
is difficult.
[0006] In order to solve the above-mentioned problems, the method
of equalizing plasma by generating a uniform horizontal magnetic
field by applying a high frequency electric power to an auxiliary
electrode. In this solution method, an electron drift is generated
in a direction opposite to an electron drift generated on a surface
of the substrate placed on a lower electrode so as to promote
circulation of electrons in the plasma, which prevents deviation of
electrons. According to this solution, even if it is the case where
process pressure etc. is changed, it is possible to attain
equalization of plasma by changing the electric power of the radio
frequency applied to the auxiliary electrode. Additionally, since
it is not necessary to rotate a magnetic field, it is possible to
attain a miniaturization of the plasma apparatus.
[0007] However, in association with increase of sizes of
semiconductor chips such as DRAM or MPU, the diameter of the
silicone substrate used as a base thereof has become large
gradually. For example, in order to suppress a pressure
distribution to less than several percent in the plasma apparatus
which processes a substrate having a diameter of 300 mm or more, it
is necessary to set a distance between the substrate and an upper
electrode as 30 mm or more. In such a distance, diffusion of
electrons which go from the surface of the substrate to the surface
of the auxiliary electrode and from the auxiliary electrode to the
surface of the substrate is suppressed. As a result, a movement of
electrons is prevented and it is difficult to equalize the
plasma.
[0008] Additionally, in the conventional sputter apparatus using a
magnetron plasma source, an amount of reduction of a target
material is uneven, and there is a problem in that an efficiency of
use of the target is less than 50%. In order to solve such a
problem, a method of using a generally uniform parallel magnetic
field is considered. In such a case, it is necessary to rotate eh
magnetic field or the substrate during a process. Therefore, the
stress in a thin film formed on the substrate spreads to the
entire-substrate, and there is a problem in that the substrate is
deformed due to relaxation of the stress during a machining process
as a post process. Further, since the surface of the substrate is
exposed to uneven plasma during film deposition process, a control
of a film quality on the entire surface of the substrate is very
difficult. For example, in a sputter apparatus which forms copper
wiring, there is a problem in that the resistance of the formed
copper wiring is as large as several times of a target value
(theoretical value).
DISCLOSURE OF INVENTION
[0009] It is a general object of the present invention to provide
an improved and useful plasma processing apparatus in which the
above-mentioned problems are eliminated.
[0010] A more specific object of the present invention is to
provide a plasma processing apparatus which can equalize the
generation plasma density with respect to a surface of a substrate
and a self-bias potential while maintaining a pressure distribution
on the substrate uniform.
[0011] Another object of the present invention is to provide a
plasma processing apparatus which can perform uniform etching
without a charge-up damage to a substrate.
[0012] A further object of the present invention is to provide a
plasma processing apparatus which can perform sputter which is
uniform with respect to a substrate and does not generate a
stress.
[0013] In order to achieve the above-mentioned objects, there is
provided a plasma processing apparatus a plasma processing
apparatus comprising a first electrode on which a substrate
subjected to a plasma process is placed and magnetic field applying
means for applying a magnetic field to a surface of the substrate
to which the plasma process is applied, characterized in that: an
auxiliary electrode is provided on an outer periphery of the first
electrode to excite plasma by the auxiliary electrode so as to
cause electrons in the plasma to drift from a front surface to a
back surface of the auxiliary electrode and from the back surface
to the front surface of the auxiliary electrode.
[0014] The front surface of the auxiliary electrode may be covered
by an insulating material. Additionally, it is preferable that a
level of a surface of the substrate placed on the first electrode
and a level of the front surface of the auxiliary electrode are
equal to each other or within .+-.2 mm. The magnetic field applying
means may comprise a dipole ring-magnet. It is preferable that a
frequency f1 of a radio frequency applied to the first electrode
and a frequency f2 of a radio frequency applied to the auxiliary
electrode are equal to each other and phases thereof are different
from each other. Further, it is preferable that a frequency f2 of a
radio frequency applied to the auxiliary electrode is higher than a
frequency f1 of a radio frequency applied to the first electrode
(f2>f1).
[0015] Other objects, features and advantages of the present
invention will become more apparent from the following detailed
description when read in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0016] FIG. 1 is a structural diagram of a plasma processing
apparatus according to a first embodiment of the present
invention.
[0017] FIG. 2 is a perspective view of a substrate, a first
electrode and an auxiliary electrode of the plasma processing
apparatus shown in FIG. 1.
[0018] FIG. 3 is a plane view of the auxiliary electrode.
[0019] FIG. 4 is a plane view showing a variation of the auxiliary
electrode.
[0020] FIG. 5 is a graph showing a self-bias potential measured in
the plasma processing apparatus according to the first embodiment
of the present invention.
[0021] FIG. 6 is a graph showing an ion current density measured in
the plasma processing apparatus according to the first embodiment
of the present invention.
[0022] FIG. 7 is a structural diagram of a plasma sputter film
deposition apparatus according to a second embodiment of the
present invention.
[0023] FIG. 8 is a cross-sectional view of an auxiliary electrode
in a third embodiment of the present invention.
[0024] FIG. 9 is a graph showing a radio frequency electric power
applied to an auxiliary electrode, which can make a self-bias
potential the most uniform in cases where a surface of the
auxiliary electrode is covered or not covered by an insulating
material.
[0025] FIG. 10 is a graph showing an amount of consumption of an
inner wall of a process chamber.
[0026] FIG. 11 is a graph showing a result of measurement of an
amount of consumption of the auxiliary electrode by applying a
radio frequency electric power, of which frequency is higher than a
radio frequency electric power applied to the first electrode, to
the auxiliary electrode.
[0027] FIG. 12 is a graph showing a change in the radio frequency
electric power applied to the auxiliary electrode needed to uniform
the self-bias potential by a difference in a height between an
upper surface of the first electrode and an upper surface of the
auxiliary electrode.
[0028] FIG. 13 is an illustration showing an action of an electron
drift when the surface of the first electrode is higher than the
surface of the auxiliary electrode.
[0029] FIG. 14 is an illustration showing an action of an electron
drift when the surface of the first electrode is lower than the
surface of the auxiliary electrode.
BEST MODE FOR CARRYING OUT THE INVENTION
[0030] A description will be given below, with reference to the
drawings, of embodiments of the present invention.
[0031] FIG. 1 is a structural diagram of a plasma processing
apparatus according to a first embodiment of the present invention.
In the plasma processing apparatus shown in FIG. 1, a substrate 101
to which a plasma process is applied is placed on an electrode 102.
A plasma process applied to the substrate 101 by exciting plasma on
the surface of the substrate 101. The dipole ring-magnet 103 is
provided in the circumference of a process chamber 108 in which the
substrate 101 is accommodated as a means to apply a magnetic field.
As a means to apply a magnetic field, although a permanent magnet
or an electromagnet may be used, it is preferable to use a dipole
ring-magnet when installation capacity, electric power consumption,
magnetic field leakage, etc. are taken into consideration.
[0032] An auxiliary electrode 104 is installed on an outer
periphery of the first electrode 102. The auxiliary electrode may
surround the entire periphery or a part of the periphery of the
first electrode 102. The auxiliary electrode 104 is provided so
as-to excite plasma in the vicinity of the back surface 105 and the
front surface 106 thereof.
[0033] FIG. 2 is a perspective view of the substrate 101, the first
electrode 102 and the auxiliary electrode 104 of the plasma
processing apparatus shown in FIG. 1. An arrow 204 shows the drift
of electrons to the front surface 106 from the back surface 105 of
the auxiliary electrode 104, and an arrow 205 shows the drift of
electrons to the back surface 105 from the front surface 106 of the
auxiliary electrode 104. An arrow 206 indicated by the dotted line
shows the drift of electrons in the vicinity of the back surface
105 of the auxiliary electrode 104, and an arrow 207 shows the
drift of electrons in the vicinity of the surface of the substrate
101 and the front surface 106 of the auxiliary electrode 104. The
drift of electrons indicated by arrows 204, 205, 206 and 207 is
generated by the interaction of a magnetic field or a magnetic
field and substrate and a sheath electrode generated between the
substrate and the auxiliary electrode.
[0034] In the conventional magnetron plasma apparatus, the drift of
electrons shown by arrows 204, 205 and 206 hardly occurs, but only
the drift of electrons shown by the arrow 207 occurs. For this
reason, electrons in the plasma shift toward the W-pole, which
results in generation of uneven plasma.
[0035] In the plasma processing apparatus according to the present
embodiment, electrons generated by the surface of the substrate 101
and the auxiliary electrode 104 flow according to the electron
drift on the surface of the substrate and the front surface of the
auxiliary electrode 104 (indicated by the arrow 207, the electron
drift from the front surface 106 to the back surface 105 of the
auxiliary electrode 104 (indicated by the arrow 205), the electron
drift on the back surface 106 of the auxiliary electrode 104
(indicated by the arrow 206), the electron drift from the back
surface 105 to the front surface 106 of the auxiliary electrode 104
(indicated by the arrow 204) and diffusion movement of electrons.
According to the flow of electrons, electrons in the plasma are
prevented from moving in a certain direction of the applied
magnetic field, thereby achieving uniformization of the entire
plasma.
[0036] As mentioned above, the plasma processing apparatus shown in
FIG. 1 comprises: the first electrode 102 on which the substrate
101 to which a plasma process is applied is placed; the magnetic
field applying means 103 for applying a magnetic field to the
surface to which the plasma process is applied; and the auxiliary
electrode 104 provided on an outer periphery of the first electrode
102, wherein electrons in the plasma is caused to drift from the
front surface 106 to the back surface 105 of the auxiliary
electrode 104 and from the back surface 105 to the front surface
106 of the auxiliary electrode 104 by exciting plasma on the front
surface 106 and the back surface 105 of the auxiliary electrode
104.
[0037] A description will now be given of a structure of the plasma
processing apparatus shown in FIG. 1 in the case of using the
plasma processing apparatus as a plasma etching apparatus. The
process chamber 108 shown in FIG. 1 is made of aluminum, and the
turbo-molecular pump 302 is provided on the bottom thereof as an
exhaust means. The turbo-molecular pump 302 exhausts and
depressurizes the gas from inside a chamber 301. Additionally, a
gas introduction port is provided in the process chamber 108 as a
gas introduction means so as to introduce gas, such as
C.sub.4F.sub.8, carbon monoxide, oxygen or xenon, into process
chamber 108 through the gas introduction port 303. The inside of
the process chamber 108 is maintained at a desired pressure by the
introduction of the gas and the exhaust of the gas by the turbo
numerator pump 302. The combination of the above-mentioned gases is
not limited to eh above mentioned combination, and as other
examples there are C4F8, carbon monoxide, oxygen, argon, etc.
Additionally, since C.sub.4F.sub.8, carbon monoxide, oxygen and
xenon are preferable since they suppresses an excessive
dissociation of gas and improve the etching characteristic.
[0038] The first electrode 102 is connected to a radio frequency
power supply 306 having a frequency of 13.56 MHz via a matching
circuit 305. Although the frequency of the radio frequency power
supply can also be set to 27.12 MHz or 40 MHz, a radio frequency of
about 13.56 MHz is preferable, when etching of an oxidization film
is performed, at which a self-bias potential of the plasma becomes
large. In etching of an insulated film, it is preferable to set a
high self-bias at an initial stage so as to etch at a high speed,
and to set a low self-bias at an etching end stage. Accordingly, a
damage of the background of the insulated film can be reduced.
[0039] A grounded second electrode 307 is provided above the first
electrode 102. Although parallel plate type electrode is used as
the second electrode 307 in the present embodiment, a plasma source
electrode such as a multi-target type, a microwave excitation type,
an electron cyclotron resonance type or an induction coupling type
may be used. In order to improve the etching characteristic, the
parallel plate type is preferable. The substrate 101 of silicon
which has a silicon oxidization film is placed on the surface of
the first electrode 102.
[0040] The auxiliary electrode 104 is connected to a radio
frequency power supply 311 having a frequency of 100 MHz via a
matching circuit 310. The magnetic field applying means 103 in the
present embodiment is a dipole ring-magnet of 12 mT (120
Gausses).
[0041] FIG. 3 is a plan view of the auxiliary electrode 104.
Although the ring-shaped auxiliary electrode 104 is used in the
present embodiment, the auxiliary electrode 104 may be divided into
four parts like an auxiliary electrode 104A as shown in FIG. 4. In
this case, a distance D between the divided parts is preferably
within 2 mm which is within an electron cycloid radius.
[0042] As shown in FIG. 2, by arranging the auxiliary electrode 104
on the outer periphery of the first electrode 102, the drift
(indicated by the arrow 207) of electrons from the E-pole to the
W-pole in the applied magnetic field occurs on the surface of the
substrate 101 and the front surface 106 of the auxiliary electrode
104, and the drift (indicated by the arrow 206) of electrons from
the W-pole to the E-pole of the applied magnetic field occurs on
the back surface 105 of the auxiliary electrode 104. Moreover, on
the W-pole side of the auxiliary electrode 104, the drift
(indicated by the arrow 205) of electrons from the back surface 105
to the front surface 106 occurs, and the drift (indicated by the
arrow 204) of electrons from the back surface 105 to the front
surface occurs on the E-pole side of the auxiliary electrode 104.
By such electron drift, deviation of electrons can be prevented by
the electron being caused to flow, and uniformization of plasma is
achieved.
[0043] FIG. 5 is a graph showing the self-bias potential-measured
in the plasma processing apparatus according to the present
embodiment. Measurements were taken for the case where the
auxiliary electrode 104 is provided and the case where the
auxiliary electrode 104 is not provided. In the case where the
auxiliary electrode 104 is not provided, the structure is the same
as that of a regular magnetron plasma apparatus. As appreciated
from FIG. 5, when the auxiliary electrode 104 was not provided, a
self-bias potential difference of 20 V occurred between the E-pole
side and the W-pole side on the substrate. However, self-bias
potential difference was able to be set to 2 V by providing the
auxiliary electrode 104 on the outer periphery of the first
electrode 102 as in the present embodiment.
[0044] FIG. 6 is a graph showing an ion current density measured in
the plasma processing apparatus according to the present
embodiment. When the auxiliary electrode 104 was not provided, the
ion current density dropped extremely on the E-pole side. However,
like the present embodiment, by providing the auxiliary electrode
104 on the outer periphery of the first electrode, the drop of the
ion current on the side of the E-pole was able to be eliminated,
and was able to achieve a uniform ion current density on the
substrate.
[0045] Using the plasma etching apparatus according to the present
invention, a silicon substrate was etched by introducing a mixed
gas of C.sub.4F.sub.8, carbon monoxide, oxygen, and xenon into the
process chamber 108 and setting the chamber pressure to 5 Pa. The
silicone substrate had a silicone oxidization film with a thickness
of 1.6 micrometers formed on the surface thereof, and the diameter
was 200 mm. When a radio frequency electric power of 1500 W was
supplied to the first electrode 102 and a high frequency electric
power of 200 W was supplied to the auxiliary electrode 104, the
uniformity of the etching rate was .+-.2%.
[0046] A description will now be given, with reference to FIG. 7,
of a second embodiment of the present invention. FIG. 7 is a
structural diagram of a plasma sputtering apparatus according to
the second embodiment of the present invention. In FIG. 7, parts
that are the same as the parts shown in FIG. 1 are given the same
reference numerals, and descriptions thereof will be omitted.
[0047] The process chamber 108 shown in FIG. 7 is made of aluminum,
and a protective film is provided by forming an aluminum fluoride
by applying a fluoride treatment to an inner surface thereof. The
process chamber 108 is not limited to such a structure, and it is
preferable to from an inner wall which discharge an extremely small
amount of gas such as water other than a process gas. Similar to
the plasma processing apparatus shown in FIG. 1, the inside of the
process chamber 108 is depressurized by using the turbo-molecular
pump 302. Additionally, argon gas is introduced into the process
chamber 108 from the gas supply passage 803 as a gas introduction
means. The gas to be used is not limited to argon gas, and a
mixture gas of xenon or krypton and oxygen may be used. Argon is
preferable for a copper sputtering film deposition.
[0048] The first electrode 102 is connected to the radio frequency
power supply 306 having a frequency of 13.56 MHz via the matching
circuit 305. The frequency of the radio frequency power supply 306
is not limited to this frequency and 27.12 MHz or 40 MHz may be
used. As for sputtering, a frequency near 13.56 MHz is preferable
at which the self-bias potential generated on the target surface
becomes large. A substrate 807 as a copper target is attached to a
surface of the first electrode 102. Although the copper target is
used in the present embodiment, the target is not limited to copper
and a material to be deposited can be attached as the target. The
auxiliary electrode 104 is connected to the radio frequency power
supply 311 having a frequency of 100 MHz via the matching circuit
310. The dipole ring-magnet 103 of 12 mTs (120 Gausses) is used as
a magnetic field applying means.
[0049] A second electrode 812 is arranged in the position, which
counters with first electrode 102. A silicon substrate 813 having a
surface on which a silicone oxidization film is formed is placed on
the second electrode 812. Additionally, the second electrode 812 is
connected to a radio frequency power supply 815 having a frequency
of 40 MHz via a matching circuit 814. The frequency of the radio
frequency power supply 815 is not limited to this frequency, and
13.56 MHz or 27.12 MHz may be used. A higher frequency is
preferable in order to increase the quantity of ions which
irradiate the silicon substrate and to reduce the self-bias
potential to be generated.
[0050] Copper sputtering was performed on the silicone substrate
813 by using the sputtering apparatus according to the present
embodiment. Argon gas was introduced into the process chamber 108
and the pressure was set to 0.1 Pa. A radio frequency electric
power of 1500 W was supplied to the first electrode 102, and a
radio frequency electric power of 200 W was supplied to the
auxiliary electrode 104. Consequently, a copper thin film was
formed on the substrate 813, which film has no stress at all and
has a film thickness uniformity of .+-.2% and a resistivity of 2.76
.mu..OMEGA..
[0051] A description will now be given of a plasma etching
apparatus according to a third embodiment of the present invention.
The plasma processing apparatus according to the third embodiment
of the present invention is provided with an auxiliary electrode
having a surface covered by an insulating material instead of the
auxiliary electrode 104.
[0052] FIG. 8 is a cross-sectional view of an auxiliary electrode
901 in the present embodiment. The auxiliary electrode 901 has an
insulator 902 formed on the surface 106 of the auxiliary electrode
104. In the present embodiment, although the insulator 902 is
formed of aluminum nitride AlN, it can be formed of quartz,
alumina, Teflon, polyimide, etc. AlN is preferable because of a
high thermal conductivity and a high plasma resistance. It should
be noted that other parts of the auxiliary electrode 901 are the
same as the parts shown in FIG. 1, and descriptions thereof will be
omitted.
[0053] FIG. 9 is a graph showing a radio frequency electric power
applied to the auxiliary electrode, which can make a self-bias
potential the most uniform in cases where a surface of the
auxiliary electrode is covered or not covered by an insulating
material. When the surface of the auxiliary electrode was not
covered by an insulator, the radio frequency electric power which
can make a self-bias potential uniform was 200 W. On the other
hand, it was 100 W when covered by an insulator.
[0054] Using the plasma etching apparatus according to the present
embodiment, a silicon substrate was etched by introducing a mixed
gas of C.sub.4F.sub.8, carbon monoxide, oxygen, and xenon into the
process chamber 108 and setting the chamber pressure to 5 Pa. The
silicone substrate had a silicone oxidization film with a thickness
of 1.6 .mu.m formed on the surface thereof, and the diameter was
200 mm. A radio frequency electric power of 1500 W was supplied to
the first electrode 102 and a high frequency electric power of 200
W was supplied to the auxiliary electrode 104. As a result, the
uniformity of the etching rate was .+-.2%.
[0055] A further detailed description will be given of a result of
measurement with respect to the plasma etching apparatus according
to the above-mentioned first embodiment.
[0056] First, a description will be given of a case in which a
radio frequency electric power having a frequency of 13.56 MHz,
which is the same as the radio frequency electric power supplied to
the first electrode 102, is supplied to the auxiliary electrode 104
while varying the phase from 0 degree to 180 degrees.
[0057] FIG. 10 is a graph showing an amount of consumption of the
inner wall of the process chamber in the above-mentioned condition.
After exciting plasma for 24 hours, change of the thickness in the
inner wall of the process chamber was measured. In a case where a
radio frequency of 13.56 MHz was applied to the first electrode 102
in phase of 0 degree, the thickness of the chamber decreased by 30
.mu.m. On the other hand, when the radio frequency was applied with
antiphase of 180 degrees, the thickness of the chamber decreased by
7 .mu.m, and there was least reduction of the thickness of the
chamber.
[0058] Additionally, using the plasma etching apparatus according
to the present embodiment, a silicon substrate was etched 300 times
by introducing a mixed gas of C.sub.4F.sub.8, carbon monoxide,
oxygen, and xenon into the process chamber and setting the pressure
to 5 Pa, the silicone substrate having a silicone oxidization film
with a thickness of 1.6 .mu.m formed on the surface thereof and the
diameter thereof being 200 mm. As a result, the consumption of the
inner wall of the chamber was about 7 .mu.m. In a conventional
etching apparatus, the inner wall of the chamber is consumed about
50 .mu.m in the same condition. Therefore, the consumption of the
inner wall of the chamber was able to be reduced to {fraction
(1/7)} by using the plasma etching apparatus according to the
present embodiment.
[0059] It was found from the above-mentioned results that by
applying a radio frequency electric power having a frequency the
same as that applied to the first electrode 102 but having a
different phase to the auxiliary electrode, the inner wall of the
chamber was prevented from being sputtered and was prevented from
being sputtered at most at the antiphase since the plasma potential
was reduced.
[0060] Next, the amount of consumption of the auxiliary electrode
104 was measured by applying to the auxiliary electrode a radio
frequency electric power having a frequency of 100 MHz which is
higher than the frequency 13.56 MHz of the radio frequency electric
power applied to the first electrode. FIG. 11 is a graph showing
the results of measurement.
[0061] As shown in FIG. 11, by increasing the frequency of the
radio frequency power supply 311 connected to the auxiliary
electrode 104, the self-bias voltage generated in the auxiliary
electrode 104 can be suppressed and an amount of consumption of the
auxiliary electrode 104 sue to sputtering can be reduced. Although
the radio frequency electric powers of 13.56 MHz and 100 MHz were
used in the measurement, the present invention is not limited to
this combination, and a radio frequency electric power of about 27
MHz may be applied to the first electrode 102 and a radio frequency
electric power of 60 MHz may be applied to the auxiliary electrode
104. Alternatively, radio frequency electric powers of 40 MHz and
80 MHz may be applied to the first electrode 102 and the auxiliary
electrode 104, respectively. Although there are various frequencies
of the radio frequency electric power applied to the first
electrode 102 and the auxiliary electrode 104 as mentioned above, a
higher frequency is preferable for the radio frequency applied to
the auxiliary electrode 104.
[0062] As mentioned above, by increasing the frequency of the radio
frequency power supply 311 connected to the auxiliary electrode
104, the self-bias voltage generated in the auxiliary electrode 104
can be suppressed, and the consumption of the auxiliary electrode
104 due to sputtering can be reduced.
[0063] Additionally, using the plasma etching apparatus shown in
FIG. 1, a silicon substrate was etched 300 times by introducing a
mixed gas of C.sub.4F.sub.8, carbon monoxide, oxygen, and xenon
into the process chamber and setting the pressure to 5 Pa. The
silicone substrate had a silicone oxidization film with a thickness
of 1.6 .mu.m formed on the surface thereof and the diameter thereof
was 200 mm. As a result measurement of the amount of consumption of
eh auxiliary electrode 104, the amount of consumption was about 5
mm. Since the amount of consumption in a conventional etching
apparatus is 65 mm, the amount of consumption was reduced to
{fraction (1/13)} of that of the conventional apparatus.
[0064] Next, the radio frequency electric power as investigated,
which is applied to the auxiliary electrode and is able to make the
self-bias potential most uniform by the position relationship
(height relationship) between the surface of the first electrode
102 and the front surface 106 of the auxiliary electrode 104.
[0065] FIG. 12 is graph showing changes in the radio frequency
electric power, which is applied to the auxiliary electrode and
required to uniformize a self-bias potential according to the
difference in the height between the upper surface of first
electrode 102 and the upper surface 106 of the auxiliary electrode
104. When the height of the upper surface of the first electrode
102 and the height of the upper surface 106 of the auxiliary
electrode 104 were equal to each other, the radio frequency
electric power, which is applied to the auxiliary electrode and
required in order to uniformize the self-bias potential, was 100 W.
The radio frequency electric power applied to the auxiliary
electrode and required to uniformize the self-bias potential
increased as the difference in the height was increased, and the
radio frequency electric power was 300 W when the height difference
was 50 mm. Therefore, it was found that the radio frequency
electric power applied to the auxiliary electrode required to
uniformize the self-bias potential can be made the lowest when the
height of the upper surface of the first electrode 102 and the
upper surface 106 of the auxiliary electrode 104 were equal to each
other.
[0066] FIG. 13 is an illustration showing the action of an
electronic drift when the surface of the first electrode 102 is
higher than the front surface 106 of the auxiliary electrode 104.
FIG. 14 is an illustration showing the action of an electronic
drift when the surface of the first electrode 102 is lower than the
front surface 106 of the auxiliary electrode 104.
[0067] As shown in FIG. 13, in order to prevent the drift of
electrons generated on the front surface 106 of the auxiliary
electrode 104 from disappearing due to collision with the first
electrode 102, the difference between the height of the surface of
the first electrode 102 and the height of the position of the
surface 106 of the auxiliary electrode 104 needs to be smaller than
the cycloid radius of the electron drift. Moreover, in order to
prevent the electron drift generated on the surface of the
substrate 101 from disappearing due to collision with the auxiliary
electrode 104, the difference between the height of the surface of
the first electrode 102 and the height of the position of the front
surface 106 of the auxiliary electrode 104 needs to be smaller than
the cycloid radius of the electron drift.
[0068] Therefore, the self-bias potential can be equalized with a
small radio frequency electric power by setting the height of the
surface 106 of the auxiliary electrode 104 equal to the surface of
the substrate 101 or setting the difference between the height of
the front surface 106 of the auxiliary electrode 104 and the height
of the surface of substrate 101 equal to or less than 2 mm.
[0069] Additionally, using the plasma etching apparatus according
to the present embodiment, a silicon substrate was etched by
introducing a mixed gas of C.sub.4F.sub.8, carbon monoxide, oxygen,
and xenon into the process chamber and setting the chamber pressure
to 5 Pa. The silicone substrate had a silicone oxidization film
with a thickness of 1.6 .mu.m formed on the surface thereof, and
the diameter was 200 mm. A radio frequency electric power of 1500 W
was supplied to the first electrode 102 and a high frequency
electric power of 100 W was supplied to the auxiliary electrode
104. As a result, the uniformity of the etching rate was
.+-.2%.
[0070] As explained above, according to the plasma processing
apparatus of the present invention, uniformization of the density
of the generated plasma with respect to the surface of the
substrate and uniformization of the self-bias potential can be
attempted without rotating the magnetic field applying means
independently of the shape of the upper electrode and the distance
thereof while maintaining the pressure distribution on the
substrate uniform, and, thereby, the etching process without a
charge up damage or the sputtering process which is uniform with
respect to the substrate and does not generate a stress can be
performed.
[0071] Additionally, a plasma processing apparatus having a high
radio frequency electric power efficiency can be realizable by
covering the surface of the auxiliary electrode by an insulating
material.
[0072] Further, a plasma processing apparatus having a high radio
frequency electric power efficiency can be realizable by equalizing
the level of the surface of the substrate placed on the first
electrode and the level of the front surface of the auxiliary
electrode or setting the difference of the heights to less than
.+-.2 mm.
[0073] Additionally, a plasma processing apparatus with a small
electric power, a small installation volume and a small magnetic
field leakage can be realized by using a dipole magnet-ring as the
magnetic field applying means.
[0074] Additionally, a plasma processing apparatus in which a
chamber wall is prevented from being sputtered can be realized by
setting a frequency f1 of a radio frequency applied to the first
electrode and a frequency f2 of a radio frequency applied to the
auxiliary electrode equal to each other and differentiating phases
from each other.
[0075] Furthermore, a plasma processing apparatus in which a
consumption of the auxiliary electrode is suppressed is realized by
setting a frequency f2 of a radio frequency applied to the
auxiliary electrode higher than a frequency f1 of a radio frequency
applied to the first electrode (f2>f1).
* * * * *