U.S. patent application number 11/117391 was filed with the patent office on 2005-11-03 for plasma processing apparatus and plasma processing method.
This patent application is currently assigned to TOKYO ELECTRON LIMITED.. Invention is credited to Saito, Hitoshi, Sasaki, Kazuo, Sato, Ryo, Satoyoshi, Tsutomu.
Application Number | 20050241769 11/117391 |
Document ID | / |
Family ID | 35185885 |
Filed Date | 2005-11-03 |
United States Patent
Application |
20050241769 |
Kind Code |
A1 |
Satoyoshi, Tsutomu ; et
al. |
November 3, 2005 |
Plasma processing apparatus and plasma processing method
Abstract
A plane parallel plasma processing apparatus includes an
impedance adjustment unit having a capacitive component, which is
disposed between a lower electrode and a processing chamber. The
impedance adjustment unit adjusts the value of the impedance over
the path extending from an upper electrode to a grounded casing of
a matching circuit via plasma, the lower electrode and the wall of
the processing chamber to a level lower than the value of the
impedance over the path extending from the upper electrode to the
grounded casing of the matching circuit via the plasma and the wall
of the processing chamber, and thus, highly uniform plasma can be
generated by minimizing the generation of plasma in the space
between the cathode electrode and the processing chamber wall.
Inventors: |
Satoyoshi, Tsutomu;
(Yamanashi, JP) ; Sato, Ryo; (Yamanashi, JP)
; Sasaki, Kazuo; (Yamanashi, JP) ; Saito,
Hitoshi; (Yamanashi, JP) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER
LLP
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Assignee: |
TOKYO ELECTRON LIMITED.
|
Family ID: |
35185885 |
Appl. No.: |
11/117391 |
Filed: |
April 29, 2005 |
Current U.S.
Class: |
156/345.44 ;
216/67 |
Current CPC
Class: |
H01J 37/32183 20130101;
H01J 37/32082 20130101 |
Class at
Publication: |
156/345.44 ;
216/067 |
International
Class: |
C23F 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 30, 2004 |
JP |
JP2004-136566 |
Dec 28, 2004 |
JP |
JP2004-381290 |
Claims
What is claimed is:
1. A plasma processing apparatus for processing a substrate with
plasma generated from a process gas by supplying high-frequency
power into a processing chamber, comprising: a cathode electrode
and an anode electrode facing opposite each other on an upper side
and a lower side inside the processing chamber and insulated from
the processing chamber; a high-frequency power source having one
end thereof connected to the cathode electrode via a matching
circuit; and an impedance adjustment unit having one end thereof
connected to the anode electrode and another end thereof connected
to the processing chamber and containing a capacitive component,
wherein: the substrate is placed on either the cathode electrode or
the anode electrode that is located on the lower side; and the
impedance adjustment unit adjusts a value of impedance occurred in
a path extending from the cathode electrode to a grounded casing of
the matching circuit via the plasma, the anode electrode and a wall
of the processing chamber to a level lower than a value of
impedance occurred in a path extending from the cathode electrode
to the grounded casing of the matching circuit via the plasma and
the wall of the processing chamber.
2. The plasma processing apparatus according to claim 1, wherein:
the impedance adjustment unit adjusts the value of the impedance
occurred in the path extending from the cathode electrode to the
grounded casing of the matching circuit via the plasma, the anode
electrode and the wall of the processing chamber so as to
minimize.
3. The plasma processing apparatus according to claim 1, wherein:
the impedance adjustment unit sets the value of the impedance
occurred in the path extending from the cathode electrode to the
grounded casing of the matching circuit via the plasma, the anode
electrode and the wall of the processing chamber so as to flow a
current to the anode electrode within a range of 10% of a maximum
value of the current flowing to the anode electrode by adjusting
the value of the impedance by controlling the current flowing to
the anode electrode.
4. The plasma processing apparatus according to claim 1, wherein:
the impedance adjustment unit is constituted so as to be eneble to
vary the value of the impedance.
5. The plasma processing apparatus according to claim 1, further
comprising: a control unit memorizing impedance adjustment data
related to various plasma processing types, reading out the
impedance adjustment data corresponding to a plasma processing type
selected from the various plasma processing types and outputting a
control signal for adjusting the value of the impedance to the
impedance adjustment unit based on the impedance adjustment
data.
6. The plasma processing apparatus according to claim 1, wherein:
the impedance adjustment unit is constituted with a dielectric
member having the capacitive component and be located between the
anode electrode and the processing chamber.
7. The plasma processing apparatus according to claim 1, wherein: a
plurality of impedance adjustment units are provided and the
plurality of the impedance adjustment units are individually
connected on one end thereof to the anode electrode at positions
distanced from one another along the longish side of the anode
electrode.
8. A plasma processing apparatus for processing a substrate with
plasma generated from a process gas by supplying high-frequency
power into a processing chamber, comprising: an upper electrode and
a lower electrode facing opposite each other on an upper side and a
lower side inside the processing chamber and insulated from the
processing chamber; a first high-frequency power source having one
end thereof connected to the upper electrode via a first matching
circuit and supplying the high-frequency power within a range of 10
MHz to 30 MHz; a second high-frequency power source having one end
thereof connected to the lower electrode via a second matching
circuit and supplying the high-frequency power within a range of 2
MHz to 6 MHz; a first impedance adjustment unit having one end
thereof connected to the lower electrode and another end thereof
connected to the processing chamber and containing a capacitive
component; and a second impedance adjustment unit having one end
thereof connected to the upper electrode and another end thereof
connected to the processing chamber and containing a capacitive
component, wherein: the substrate is placed on the lower electrode;
the first impedance adjustment unit adjusts a value of impedance
occurred in a path extending from the upper electrode to a grounded
casing of the first matching circuit via the plasma, the lower
electrode and a wall of the processing chamber by the
high-frequency power of the first high-frequency power source to a
level lower than a value of impedance occurred in a path extending
from the upper electrode to the grounded casing of the first
matching circuit via the plasma and the wall of the processing
chamber by the high-frequency power of the first high-frequency
power source; and the second impedance adjustment unit adjusts a
value of impedance occurred in a path extending from the lower
electrode to a grounded casing of the second matching circuit via
the plasma, the upper electrode and the wall of the processing
chamber by the high-frequency power of the second high-frequency
power source to a level lower than a value of impedance occurred in
a path extending from the lower electrode to the grounded casing of
the second matching circuit via the plasma and the wall of the
processing chamber by the high-frequency power of the second
high-frequency power source.
9. The plasma processing apparatus according to claim 8, wherein:
the first impedance adjustment unit adjusts the value of the
impedance occurred in the path extending from the upper electrode
to the grounded casing of the first matching circuit via the
plasma, the lower electrode and the wall of the processing chamber
by the high-frequency power of the first high-frequency power
source so as to minimize; and the second impedance adjustment unit
adjusts the value of the impedance occurred in the path extending
from the lower electrode to the grounded casing of the second
matching circuit via the plasma, the upper electrode and the wall
of the processing chamber by the high-frequency power of the second
high-frequency power source so as to minimize.
10. The plasma processing apparatus according to claim 8, wherein:
the first impedance adjustment unit sets the value of the impedance
so as to flow a current to the lower electrode within a range of
10% of a maximum value of the current flowing to the lower
electrode by adjusting the value of the impedance by controlling
the current of the frequency of the first high-frequency power
source; and the second impedance adjustment unit sets the value of
the impedance so as to flow a current to the upper electrode within
a range of 10% of a maximum value of the current flowing to the
upper electrode by adjusting the value of the impedance by
controlling the current of the frequency of the second
high-frequency power.
11. The plasma processing apparatus according to claim 8, wherein:
the first impedance adjustment unit and the second impedance
adjustment unit are constituted so as to be enable to vary the
value of the impedance corresponding to the frequency of the first
high-frequency power source and the value of the impedance
corresponding to the frequency of the second high-frequency power
source respectively.
12. The plasma processing apparatus according to claim 8, further
comprising: a control unit memorizing impedance adjustment data for
the first impedance adjustment unit and impedance adjustment data
for the second impedance adjustment unit related to various plasma
processing types, reading out the impedance adjustment data for the
first impedance adjustment unit and the impedance adjustment data
for the second impedance adjustment unit corresponding to a plasma
processing type selected from the various plasma processing types
and outputting a control signal for adjusting the value of the
impedance to the first impedance adjustment unit and the second
impedance adjustment unit based on the impedance adjustment data
for the first impedance adjustment unit and the impedance
adjustment data for the second impedance adjustment unit.
13. The plasma processing apparatus according to claim 8, wherein:
the first impedance adjustment unit is constituted with a
dielectric member having the capacitive component and be located
between the lower electrode and the processing chamber; and the
second impedance adjustment unit is constituted with a dielectric
member having the capacitive component and be located between the
upper electrode and the processing chamber.
14. The plasma processing apparatus according to claim 8, wherein:
a plurality of first impedance adjustment units are provided and
the plurality of the first impedance adjustment units are
individually connected on one end thereof to the lower electrode at
positions distanced from one another along the longish side of the
lower electrode; and a plurality of second impedance adjustment
units are provided and the plurality of the second impedance
adjustment units are individually connected on one end thereof to
the upper electrode at positions distanced from one another along
the longish side of the upper electrode.
15. A plasma processing apparatus for processing a substrate with
plasma generated from a process gas by supplying high-frequency
power into a processing chamber, comprising: an upper electrode and
a lower electrode facing opposite each other on an upper side and a
lower side inside the processing chamber and insulated from the
processing chamber; a first high-frequency power source having one
end thereof connected to the lower electrode via a first matching
circuit and supplying the high-frequency power within a range of 10
MHz to 30 MHz; a second high-frequency power source having one end
thereof connected to the lower electrode via a second matching
circuit and supplying the high-frequency power within a range of 2
MHz to 6 MHz; and a first impedance adjustment unit and a second
impedance adjustment unit having one end thereof connected to the
upper electrode and another end thereof connected to the processing
chamber and containing a capacitive component respectively,
wherein: the substrate is placed on the lower electrode; the first
impedance adjustment unit adjusts a value of impedance occurred in
a path extending from the lower electrode to a grounded casing of
the first matching circuit via the plasma, the upper electrode and
a wall of the processing chamber by the high-frequency power of the
first high-frequency power source to a level lower than a value of
impedance occurred in a path extending from the lower electrode to
the grounded casing of the first matching circuit via the plasma
and the wall of the processing chamber by the high-frequency power
of the first high-frequency power source; and the second impedance
adjustment unit adjusts a value of impedance occurred in a path
extending from the lower electrode to a grounded casing of the
second matching circuit via the plasma, the upper electrode and the
wall of the processing chamber by the high-frequency power of the
second high-frequency power source to a level lower than a value of
impedance occurred in a path extending from the lower electrode to
the grounded casing of the second matching circuit via the plasma
and the wall of the processing chamber by the high-frequency power
of the second high-frequency power source.
16. The plasma processing apparatus according to claim 15, wherein:
the first impedance adjustment unit adjusts the value of the
impedance occurred in the path extending from the lower electrode
to the grounded casing of the first matching circuit via the
plasma, the upper electrode and the wall of the processing chamber
by the high-frequency power of the first high-frequency power
source so as to minimize; and the second impedance adjustment unit
adjusts the value of the impedance occurred in the path extending
from the lower electrode to the grounded casing of the second
matching circuit via the plasma, the upper electrode and the wall
of the processing chamber by the high-frequency power of the second
high-frequency power source so as to minimize.
17. The plasma processing apparatus according to claim 15, wherein:
the first impedance adjustment unit sets the value of the impedance
so as to flow a current to the upper electrode within a range of
10% of a maximum value of the current flowing to the upper
electrode by adjusting the value of the impedance by controlling
the current of the frequency of the first high-frequency power
source; and the second impedance adjustment unit sets the value of
the impedance so as to flow a current to the upper electrode within
a range of 10% of a maximum value of the current flowing to the
upper electrode by adjusting the value of the impedance by
controlling the current of the frequency of the second
high-frequency power source.
18. The plasma processing apparatus according to claim 15, wherein:
the first impedance adjustment unit and the second impedance
adjustment unit are constituted so as to be enable to vary the
value of the impedance corresponding to the frequency of the first
high-frequency power source and the value of the impedance
corresponding to the frequency of the second high-frequency power
source respectively.
19. The plasma processing apparatus according to claim 15, further
comprising: a control unit memorizing impedance adjustment data for
the first impedance adjustment unit and impedance adjustment data
for the second impedance adjustment unit related to various plasma
processing types, reading out the impedance adjustment data for the
first impedance adjustment unit and the impedance adjustment data
for the second impedance adjustment unit corresponding to a plasma
processing type selected from the various plasma processing types,
outputting a control signal for adjusting the value of the
impedance to the first impedance adjustment unit and outputting a
control signal for adjusting the value of the impedance to the
second impedance adjustment unit.
20. The plasma processing apparatus according to claim 15, wherein:
the first impedance adjustment unit is constituted with a
dielectric member having the capacitive component and be located
between the upper electrode and the processing chamber; and the
second impedance adjustment unit is constituted with a dielectric
member having the capacitive component and be located between the
upper electrode and the processing chamber.
21. The plasma processing apparatus according to claim 15, wherein:
a plurality of first impedance adjustment units are provided and
the plurality of the first impedance adjustment units are
individually connected on one end thereof to the lower electrode at
positions distanced from one another along the longish side of the
lower electrode; and a plurality of second impedance adjustment
units are provided and the plurality of the second impedance
adjustment units are individually connected on one end thereof to
the lower electrode at positions distanced from one another along
the longish side of the lower electrode.
22. The plasma processing apparatus according to claim 1, wherein:
an area of the substrate is equal to or greater than 1 m.sup.2.
23. The plasma processing apparatus according to claim 8, wherein:
an area of the substrate is equal to or greater than 1 m.sup.2.
24. The plasma processing apparatus according to claim 15, wherein:
an area of the substrate is equal to or greater than 1 m.sup.2.
25. The plasma processing apparatus according to claim 22, wherein:
a sum of the high-frequency power used in the plasma processing
apparatus is equal to or greater than 10 kW.
26. The plasma processing apparatus according to claim 23, wherein:
a sum of the high-frequency power used in the plasma processing
apparatus is equal to or greater than 10 kW.
27. The plasma processing apparatus according to claim 24, wherein:
a sum of the high-frequency power used in the plasma processing
apparatus is equal to or greater than 10 kW.
28. The plasma processing apparatus according to claim 1, wherein:
the cathode electrode and the anode electrode respectively
constitute an upper electrode and a lower electrode; the frequency
of the high-frequency power source is within a range of 10 MHz to
30 MHz; an area of the substrate is equal to or greater than 1
m.sup.2; a distance between the upper electrode and the lower
electrode is within a range of 50 mm to 300 mm; a processing
pressure is set at a value within a range of 13 Pa to 27 Pa; and
the substrate is etched by using a process gas containing
halogen.
29. The plasma processing apparatus according to claim 1, wherein:
the cathode electrode and the anode electrode respectively
constitute a lower electrode and an upper electrode; the frequency
of the high-frequency power source is within a range of 10 MHz to
30 MHz; an area of the substrate is equal to or greater than 1
m.sup.2; a distance between the upper electrode and the lower
electrode is within a range of 200 mm to 700 mm; a processing
pressure is set at a value within a range of 0.7 Pa to 13 Pa; and
the substrate is etched by using a process gas containing
halogen.
30. The plasma processing apparatus according to claim 8, wherein:
an area of the substrate is equal to or greater than 1 m.sup.2; the
first high-frequency power source is connected to the upper
electrode; a distance between the upper electrode and the lower
electrode is within a range of 50 mm to 300 mm; a processing
pressure is set at a value within a range of 13 Pa to 27 Pa; and
the substrate is etched by using a process gas containing
halogen.
31. The plasma processing apparatus according to claim 15, wherein:
an area of the substrate is equal to or greater than 1 m.sup.2; the
first high-frequency power source is connected to the lower
electrode; a distance between the upper electrode and the lower
electrode is within a range of 200 mm to 700 mm; a processing
pressure is set at a value within a range of 0.7 Pa to 13 Pa; and
the substrate is etched by using a process gas containing
halogen.
32. A plasma processing method for processing a substrate with
plasma generated from a process gas by supplying high-frequency
power into a processing chamber, wherein: disposing a cathode
electrode and an anode electrode so as to face opposite each other
on an upper side and a lower side inside the processing chamber and
insulating the cathode electrode and the anode electrode from the
processing chamber; connecting a high-frequency power source to one
end of the cathode electrode via a matching circuit; placing the
substrate on either the cathode electrode or the anode electrode
that is located on the lower side; disposing an impedance
adjustment unit containing a capacitive component with one end
thereof connected to the anode electrode and another end thereof
connected to the processing chamber; and adjusting a value of
impedance occurred in a path extending from the cathode electrode
to a grounded casing of the matching circuit via the plasma, the
anode electrode and a wall of the processing chamber to a level
lower than a value of impedance occurred in a path extending from
the cathode electrode to the grounded casing of the matching
circuit via the plasma and the wall of the processing chamber by
the impedance adjustment unit.
33. A plasma processing method for processing a substrate with
plasma generated from a process gas by supplying high-frequency
power into a processing chamber, wherein: disposing an upper
electrode and a lower electrode so as to face opposite each other
on an upper side and a lower side inside the processing chamber and
insulating the upper electrode and the lower electrode from the
processing chamber; connecting a first high-frequency power source
for supplying the high-frequency power within a range of 10 MHz to
30 MHz to one end of the upper electrode via a first matching
circuit; connecting a second high-frequency power source for
supplying the high-frequency power within a range of 2 MHz to 6 MHz
to one end of the lower electrode via a second matching circuit
and; placing the substrate on the lower electrode; disposing a
first impedance adjustment unit containing a capacitive component
with one end thereof connected to the lower electrode and another
end thereof connected to the processing chamber; disposing a second
impedance adjustment unit containing a capacitive component with
one end thereof connected to the upper electrode and another end
thereof connected to the processing chamber; and adjusting a value
of impedance occurred in a path extending from the upper electrode
to a grounded casing of the first matching circuit via the plasma,
the lower electrode and a wall of the processing chamber by the
high-frequency power of the first high-frequency power source to a
level lower than a value of impedance occurred in a path extending
from the upper electrode to the grounded casing of the first
matching circuit via the plasma and the wall of the processing
chamber by the first impedance adjustment unit; and adjusting a
value of impedance occurred in a path extending from the lower
electrode to a grounded casing of the second matching circuit via
the plasma, the upper electrode and a wall of the processing
chamber by the high-frequency power of the second high-frequency
power source to a level lower than a value of impedance occurred in
a path extending from the lower electrode to the grounded casing of
the second matching circuit via the plasma and the wall of the
processing chamber by the second impedance adjustment unit.
34. A plasma processing method for processing a substrate with
plasma generated from a process gas by supplying high-frequency
power into a processing chamber, wherein: disposing an upper
electrode and a lower electrode so as to face opposite each other
on an upper side and a lower side inside the processing chamber and
insulating the upper electrode and the lower the electrode from the
processing chamber; connecting a first high-frequency power source
for supplying the high-frequency power within a range of 10 MHz to
30 MHz to one end of the lower electrode via a first matching
circuit; connecting a second high-frequency power source for
supplying the high-frequency power within a range of 2 MHz to 6 MHz
to one end of the lower electrode via a second matching circuit
and; placing the substrate on the lower electrode; disposing a
first impedance adjustment unit containing a capacitive component
with one end thereof connected to the upper electrode and another
end thereof connected to the processing chamber; disposing a second
impedance adjustment unit containing a capacitive component with
one end thereof connected to the upper electrode and another end
thereof connected to the processing chamber; and adjusting a value
of impedance occurred in a path extending from the lower electrode
to a grounded casing of the first matching circuit via the plasma,
the upper electrode and a wall of the processing chamber by the
high-frequency power of the first high-frequency power source to a
level lower than a value of impedance occurred in a path extending
from the lower electrode to the grounded casing of the first
matching circuit via the plasma and the wall of the processing
chamber by the first impedance adjustment unit; and adjusting a
value of impedance occurred in a path extending from the lower
electrode to a grounded casing of the second matching circuit via
the plasma, the upper electrode and a wall of the processing
chamber by the high-frequency power of the second high-frequency
power source to a level lower than a value of impedance occurred in
a path extending from the lower electrode to the grounded casing of
the second matching circuit via the plasma and the wall of the
processing chamber by the second impedance adjustment unit.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The disclosure of Japanese Patent Application No.
JP2004-381290, filed Dec. 28, 2004, entitled "plasma processing
apparatus" and Application No. JP2004-136566, filed Apr. 30, 2004,
entitled "plasma processing apparatus". The contents of that
applications are incorporated herein by reference in their
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a plasma processing
apparatus and a plasma processing method to be adopted when
executing a process such as etching on a substrate with plasma
generated from a process gas by applying high-frequency power.
[0004] 2. Description of Related Art
[0005] During the production of semiconductor devices and flat
panel devices such as liquid crystal display devices, plasma
processing apparatuses including plasma etching apparatuses and
plasma CVD (Chemical Vapor Deposition) film forming apparatuses are
utilized to execute an etching process, a film forming process and
the like on workpieces such as semiconductor wafers and glass
substrates.
[0006] FIG. 17 shows a plane parallel plasma processing apparatus
used in the related art. This plasma processing apparatus includes
an upper electrode 12 disposed in a processing chamber 11
constituted of, for instance, aluminum and utilized as a gas shower
head through which a gas is supplied and a lower electrode 13
disposed in the processing chamber 11 so as to face opposite the
upper electrode 12 and utilized as a stage on which a substrate 10
is placed. The upper electrode 12, which is set by an insulating
member 14 in a fully floating state electrically relative to the
processing chamber 11, is connected to a high-frequency power
source 17 via a matching circuit 15 to constitute a cathode
electrode.
[0007] The lower electrode is connected to the processing chamber
11 via a conductive passage 18 to constitute an anode electrode.
The conductive passage 18 in this example is constituted with a
shaft 18a, a support plate 18b and a bellows member 18c. The upper
side of the processing chamber 11 is connected with the
high-frequency power source 17 via a matching box 16 which is a
grounded casing, and more specifically, it is grounded through its
connection to the outer layer of the coaxial cable connecting the
high-frequency power source 17 and the matching box 16.
[0008] FIG. 18 is an equivalent circuit diagram of the conductive
path through which a high-frequency current flows in the plasma
processing apparatus shown in FIG. 17. Since the upper electrode 12
and the lower electrode 13 are capacitively coupled while plasma is
generated inside the processing chamber 11, the high-frequency
current from the high-frequency power source 17 flows through the
path extending from the high-frequency power source 17 to the
ground sequentially via the matching circuit 15, the upper
electrode 12, the lower electrode 13 via the plasma, the conductive
passage 18, the wall of the processing chamber 11 and the matching
box 16.
[0009] The size of glass substrates for flat panels used in liquid
crystal displays and the like among substrates that are processed
in plasma processing apparatuses is expected to further increase
and glass substrates as large as 1.5 m.sup.2 must be processed in
plasma processing apparatuses in the near future. As a larger
processing chamber 11 is utilized to handle such large glass
substrates, the inductance component in the processing chamber 11
is bound to increase, to result in weaker coupling of the upper
electrode 12 and the lower electrode 13, which leads to a concern
that plasma may be generated between the upper electrode 12 and the
wall of the processing chamber 11 (shown as capacitive coupling in
FIG. 18). If plasma is generated in this manner, the distribution
of plasma inside the processing chamber 11 becomes uneven with more
plasma concentrating in the periphery to give rise to problems in
that the processed substrate 10 does not achieve a high level of
planar uniformity and in that the inner wall of the processing
chamber 11, the internal parts and the like become damaged readily
or become worn out faster.
[0010] Patent Reference Literature 1 discloses a technology for
controlling the diffusion of the plasma by providing an impedance
adjustment circuit between the lower electrode and the ground.
However, this technology whereby different settings are selected at
the impedance adjustment circuit for a film forming process and for
a cleaning process so as to achieve plasma conditions matching the
individual processes, does not address the problems discussed above
and Patent Reference Literature 1 does not disclose any solutions
to these problems.
[0011] (Patent Reference Literature 1) Japanese Laid Open Patent
Publication No. H11-31685, paragraph (0014)
SUMMARY OF THE INVENTION
[0012] An object on the present invention, which has been completed
with the background described above, is to provide a plasma
processing apparatus and a plasma processing method that prevent
generation of plasma between the cathode electrode and the wall of
the processing chamber and make it possible to execute plasma
processing on the substrate to achieve a high level of planar
uniformity by generating a uniform field of plasma.
[0013] The present invention provides a plasma processing apparatus
for processing a substrate with plasma generated from a process gas
by supplying high-frequency power into a processing chamber,
comprising a cathode electrode and an anode electrode facing
opposite each other on an upper side and a lower side inside the
processing chamber and insulated from the processing chamber a
high-frequency power source having one end thereof connected to the
cathode electrode via a matching circuit, and an impedance
adjustment unit having one end thereof connected to the anode
electrode and another end thereof connected to the processing
chamber and containing a capacitive component, is characterized in
that the substrate is placed on either the cathode electrode or the
anode electrode that is located on the lower side, and the
impedance adjustment unit adjusts a value of impedance occurred in
a path extending from the cathode electrode to a grounded casing of
the matching circuit via the plasma, the anode electrode and a wall
of the processing chamber to a level lower than a value of
impedance occurred in a path extending from the cathode electrode
to the grounded casing of the matching circuit via the plasma and
the wall of the processing chamber.
[0014] The cathode electrode and the anode electrode are described
above as being "insulated from the processing chamber," which means
that they are in a fully floating state electrically relative to
the processing chamber over the area excluding the impedance
adjustment unit.
[0015] It is to be noted that the path extending from the cathode
electrode to the grounded casing of the matching circuit via the
plasma, the anode electrode and the wall of the processing chamber
may also be referred to as the path extending along the direction
in which the plasma achieves uniformity relative to the substrate.
In addition, the path extending from the cathode electrode to the
grounded casing of the matching circuit via the plasma and the wall
of the processing chamber may also be referred to as the path along
which the plasma density becomes higher relative to the wall of the
processing chamber (i.e., the path extending along the direction in
which the plasma distribution becomes non-uniform relative to the
substrate).
[0016] In another aspect of the present invention, a plasma
processing apparatus for processing a substrate with plasma
generated from a process gas by supplying high-frequency power into
a processing chamber containing a process gas, comprising a cathode
electrode and an anode electrode facing opposite each other on an
upper side and a lower side within the processing chamber and
insulated from the processing chamber, a high-frequency power
source having one end thereof connected to the cathode electrode
via a matching circuit and an impedance adjustment unit having a
capacitive component with one end thereof connected to the anode
electrode and another end thereof connected to the processing
chamber, is characterized in that the substrate is placed on either
the cathode electrode or the anode electrode that is located on the
lower side and that the impedance adjustment unit adjusts the value
of the impedance over a path extending from the cathode electrode
to the grounded casing of the matching circuit via the plasma, the
anode electrode and the wall of the processing chamber so as to
achieve a minimum impedance value. Through the adjustment of "the
impedance over the path extending from the cathode electrode to the
grounded casing f the matching circuit via the plasma, the anode
electrode and the wall of the processing chamber so as to achieve a
minimum impedance value", the value of the impedance may be
adjusted substantially to the minimum value and may be adjusted to
a value within a 2% range (namely, 0.98x-1.02x: x=the minimum
value) with respect to the minimum value.
[0017] A plasma processing apparatus for processing a substrate
with plasma generated from a process gas by supplying
high-frequency power into a processing chamber, comprising an upper
electrode and a lower electrode facing opposite each other on an
upper side and a lower side inside the processing chamber and
insulated from the processing chamber, a first high-frequency power
source having one end thereof connected to the upper electrode via
a first matching circuit and supplying the high-frequency power
within a range of 10 MHz to 30 MHz, a second high-frequency power
source having one end thereof connected to the lower electrode via
a second matching circuit and supplying the high-frequency power
within a range of 2 MHz to 6 MHz, a first impedance adjustment unit
having one end thereof connected to the lower electrode and another
end thereof connected to the processing chamber and containing a
capacitive component, and a second impedance adjustment unit having
one end thereof connected to the upper electrode and another end
thereof connected to the processing chamber and containing a
capacitive component, is characterized in that the substrate is
placed on the lower electrode, the first impedance adjustment unit
adjusts a value of impedance occurred in a path extending from the
upper electrode to a grounded casing of the first matching circuit
via the plasma, the lower electrode and a wall of the processing
chamber by the high-frequency power of the first high-frequency
power source to a level lower than a value of impedance occurred in
a path extending from the upper electrode to the grounded casing of
the first matching circuit via the plasma and the wall of the
processing chamber by the high-frequency power of the first
high-frequency power source, and the second impedance adjustment
unit adjusts a value of impedance occurred in a path extending from
the lower electrode to a grounded casing of the second matching
circuit via the plasma, the upper electrode and the wall of the
processing chamber by the high-frequency power of the second
high-frequency power source to a level lower than a value of
impedance occurred in a path extending from the lower electrode to
the grounded casing of the second matching circuit via the plasma
and the wall of the processing chamber by the high-frequency power
of the second high-frequency power source.
[0018] A plasma processing apparatus according to the present
invention for processing a substrate with plasma generated from a
process gas by supplying high-frequency power into a processing
chamber containing the process gas achieved in another aspect of
the present invention adopted in an upper electrode/lower electrode
two-frequency system, comprising an upper electrode and a lower
electrode facing opposite each other on an upper side and a lower
side inside the processing chamber and insulated from the
processing chamber, a first high-frequency power source that
supplies 10 MHz to 30 MHz power with one end thereof connected to
the upper electrode via a first matching circuit, a second
high-frequency power source that supplies 2 MHz to 6 MHz power with
one end thereof connected to the lower electrode via a second
matching circuit, a first impedance adjustment unit having a
capacitive component with one end thereof connected to the lower
electrode and another end thereof connected to the processing
chamber and a second impedance adjustment unit having a capacitive
component with one end thereof connected to the upper electrode and
another end thereof connected to the processing chamber, is
characterized in that the substrate is placed on the lower
electrode, that the first impedance adjustment unit adjusts the
value of the impedance at the frequency of the first high-frequency
power source over a path extending from the upper electrode to a
grounded casing of the first matching circuit via the plasma, the
lower electrode and the wall of the processing chamber so as to
achieve a minimum impedance value and that the second impedance
adjustment unit adjusts the value of the impedance at the frequency
of the second high-frequency power source over a path extending
from the lower electrode to a grounded casing of the second
matching circuit via the plasma, the upper electrode and the
processing chamber wall so as to achieve a minimum impedance
value.
[0019] The present invention may also be adopted in a lower
electrode two-frequency system having a first high-frequency power
source and a second high-frequency power source connected to the
lower electrode. In such an application, A plasma processing
apparatus for processing a substrate with plasma generated from a
process gas by supplying high-frequency power into a processing
chamber, comprising, an upper electrode and a lower electrode
facing opposite each other on an upper side and a lower side inside
the processing chamber and insulated from the processing chamber, a
first high-frequency power source having one end thereof connected
to the lower electrode via a first matching circuit and supplying
the high-frequency power within a range of 10 MHz to 30 MHz, a
second high-frequency power source having one end thereof connected
to the lower electrode via a second matching circuit and supplying
the high-frequency power within a range of 2 MHz to 6 MHz, and a
first impedance adjustment unit and a second impedance adjustment
unit having one end thereof connected to the upper electrode and
another end thereof connected to the processing chamber and
containing a capacitive component respectively, is characterized in
that the substrate is placed on the lower electrode, the first
impedance adjustment unit adjusts a value of impedance occurred in
a path extending from the lower electrode to a grounded casing of
the first matching circuit via the plasma, the upper electrode and
a wall of the processing chamber by the high-frequency power of the
first high-frequency power source to a level lower than a value of
impedance occurred in a path extending from the lower electrode to
the grounded casing of the first matching circuit via the plasma
and the wall of the processing chamber by the high-frequency power
of the first high-frequency power source, and the second impedance
adjustment unit adjusts a value of impedance occurred in a path
extending from the lower electrode to a grounded casing of the
second matching circuit via the plasma, the upper electrode and the
wall of the processing chamber by the high-frequency power of the
second high-frequency power source to a level lower than a value of
impedance occurred in a path extending from the lower electrode to
the grounded casing of the second matching circuit via the plasma
and the wall of the processing chamber by the high-frequency power
of the second high-frequency power source.
[0020] Another plasma processing apparatus according to the present
invention for processing a substrate with plasma generated from a
process gas by supplying high-frequency power into a processing
chamber containing the process gas, adopted in a lower electrode
two-frequency system and comprising an upper electrode and a lower
electrode facing opposite each other on an upper side and a lower
side inside the processing chamber and insulated from the
processing chamber, a first high-frequency power source that
supplies 10 MHz to 30 MHz power with one end thereof connected to
the lower electrode via a first matching circuit, a second
high-frequency power source that supplies 2 MHz to 6 MHz power with
one end thereof connected to the lower electrode with a second
matching circuit and a first impedance adjustment unit and a second
impedance adjustment unit each having a capacitive component with
one end thereof connected to the upper electrode and another end
thereof connected to the processing chamber, is characterized in
that the substrate is placed on the lower electrode, that the first
impedance adjustment unit adjusts the value of the impedance over a
path extending from the lower electrode to a grounded casing of the
first matching circuit via the plasma, the upper electrode and the
wall of the processing chamber so as to achieve a minimum impedance
value and that the second impedance adjustment unit adjusts the
value of the impedance over a path extending from the lower
electrode to a grounded casing of the second matching circuit via
the plasma, the upper electrode and the processing chamber wall so
as to achieve a minimum impedance value.
[0021] In each of the plasma processing apparatuses described
above, the following control may be executed by the individual
units in the plasma processing apparatus when adjusting the value
of the impedance over the path extending along the direction in
which the plasma achieves uniformity relative to the substrate to a
level lower than the value of the impedance over the path through
which the plasma density increases relative to the wall (i.e., the
path extending along the direction in which the plasma distribution
becomes non-uniform relative to the substrate) and when adjusting
the value on the impedance over the path through which the plasma
becomes distributed more evenly relative to the substrate so as to
achieve the minimum impedance value.
[0022] Namely, it is desirable that an impedance value, which will
provide a value within a 10% range with respect to the maximum
high-frequency current value when the value of the high-frequency
current at a specific frequency flowing to the anode electrode is
altered by adjusting the value of the high-frequency impedance at
the frequency, be set at each impedance adjustment unit. If the
anode electrode constitutes the lower electrode, for instance, the
impedance adjustment unit should be connected on its other end to
the bottom of the processing chamber. To make the most of the
impedance adjustment unit, it should be ensured that the other end
of the impedance adjustment unit and the processing chamber are
connected with each other in an area considerably distanced from
the cathode electrode to avoid plasma generation occurring between
the cathode electrode and the connecting area. Accordingly, the
connection may be achieved at a position achieving a height equal
to the height of the anode electrode in the processing chamber, or
at a position on the side opposite from the side on which the anode
electrode is present (e.g., on the lower side when the anode
electrode constitutes the lower electrode, and on the upper side
when the anode electrode constitutes the upper electrode).
[0023] The impedance adjustment unit may be constituted by using,
for instance, a variable-capacity capacitor so as to allow the
impedance value to be varied, or it may be achieved by using, for
instance, a dielectric plate constituting a capacitive component
disposed between the anode electrode and the inner surface of the
processing chamber. By using an impedance adjustment unit that
allows the impedance value to be varied, a plasma processing
apparatus according to the present invention may adopt a structure
having a control unit having stored therein data correlating each
plasma processing type with the impedance adjustment value of the
impedance adjustment unit (correlating each plasma processing type
with an adjustment value at the first impedance adjustment unit and
an adjustment value at the second impedance adjustment unit when
the plasma processing apparatus includes the first and second
impedance adjustment units), which outputs a control signal to be
used to adjust the impedance adjustment unit by reading out an
impedance adjustment value corresponding to a selected plasma
processing type.
[0024] It is desirable that the plasma processing apparatus
according to the present invention include a plurality of impedance
adjustment units with the individual impedance adjustment units
connected on one end to the anode electrode at positions distanced
from one another along the longish side of the anode electrode. In
an application in an upper electrode/lower electrode two-frequency
system, the plasma processing apparatus should include a plurality
of first impedance adjustment units with the individual impedance
adjustment units connected on one end thereof to the lower
electrode at positions distanced from one another along the longish
side of the lower electrode and a plurality of second impedance
adjustment units with the individual impedance adjustment units
connected on one end thereof to the upper electrode at positions
distanced from one another along the longish side of the upper
electrode. In addition, according to the present invention adopted
in a lower electrode two-frequency system, the plasma processing
apparatus should include a plurality of first impedance adjustment
units with the individual impedance adjustment units connected on
one end thereof to the lower electrode at positions distanced from
one another along the longish side of the lower electrode and a
plurality of second impedance adjustment units with the individual
impedance adjustment units connected on one end thereof to the
lower electrode at positions distanced from one another along the
longish side of the lower electrode.
[0025] The plasma processing apparatus having a plurality of
impedance adjustment units as described above is ideal in an
application in which a substrate with an area equal to or greater
than 1 m.sup.2, e.g., a large rectangular substrate, and is
particularly effective when the sum of the high-frequency power
used in the apparatus is equal to or greater than 10 kW.
[0026] According to the present invention, the generation of plasma
between the cathode electrode and the wall of the processing
chamber is controlled and, as a result, a plasma process can be
executed on the substrate to achieve a high level of planar
uniformity by generating evenly distributed plasma.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a longitudinal cross section, schematically
illustrating the overall structure of the plasma processing
apparatus achieved in a first embodiment of the present
invention;
[0028] FIG. 2 is a circuit diagram of a circuit equivalent to the
embodiment;
[0029] FIG. 3A shows an example of a structure that may be adopted
in the impedance adjustment unit in the embodiment;
[0030] FIG. 3B shows another example of a structure that may be
adopted in the impedance adjustment unit in the embodiment;
[0031] FIG. 3C shows yet another example of a structure that may be
adopted in the impedance adjustment unit in the embodiment;
[0032] FIG. 3D shows yet another example of a structure that may be
adopted in the impedance adjustment unit in the embodiment;
[0033] FIG. 3E shows yet another example of a structure that may be
adopted in the impedance adjustment unit in the embodiment;
[0034] FIG. 4 shows an example of a structure that may be adopted
in the embodiment;
[0035] FIG. 5A is a longitudinal cross section, schematically
showing the overall structure of the plasma processing apparatus
achieved as a variation of the embodiment;
[0036] FIG. 5B shows how the substrate may be divided in the
embodiment;
[0037] FIG. 6 is a circuit diagram of a circuit equivalent to the
embodiment in FIG. 5A;
[0038] FIG. 7A is a longitudinal cross section, schematically
showing the overall structure of the plasma processing apparatus
achieved as a variation of the embodiment;
[0039] FIG. 7B is a longitudinal cross section, schematically
showing another overall structure of the plasma processing
apparatus achieved as a variation of the embodiment;
[0040] FIG. 7C is a longitudinal cross section, schematically
showing another overall structure of the plasma processing
apparatus achieved as a variation of the embodiment;
[0041] FIG. 8 is a longitudinal cross section, schematically
showing the overall structure of the plasma processing apparatus
achieved as a variation of the embodiment;
[0042] FIG. 9 is a longitudinal cross section, schematically
showing the overall structure of the plasma processing apparatus
achieved in a second embodiment of the present invention;
[0043] FIG. 10 is a longitudinal cross section, schematically
showing the overall structure of the plasma processing apparatus
achieved in a third embodiment of the present invention;
[0044] FIG. 11 illustrates the installation positions for the
impedance adjustment units set in correspondence to specific points
on the substrate;
[0045] FIG. 12 is a circuit diagram of the circuit constituted with
the impedance adjustment units used in a test conducted to verify
the advantages of the embodiments of the present invention;
[0046] FIG. 13 presents data indicating the overall results of the
test;
[0047] FIG. 14 shows the relationship between the adjustment
position assumed at the impedance adjustment unit and the
high-frequency current, indicated as the results of the test;
[0048] FIG. 15 shows the relationship between the adjustment
position assumed at the impedance adjustment unit and the
high-frequency voltage, indicated as the results of the test;
[0049] FIG. 16 is a characteristics diagram indicating the silicon
etching rate and the etching rate consistency within the plane of
the substrate, indicated as the results of another test;
[0050] FIG. 17 is a longitudinal cross section, schematically
showing the overall structure of a plasma processing apparatus in
the related art; and
[0051] FIG. 18 is a circuit diagram of a circuit equivalent to the
plasma processing apparatus in the related art.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
[0052] The plasma processing apparatus achieved in the first
embodiment of the present invention as an etching apparatus for
etching a glass substrate for a liquid crystal display device is
now explained. Reference numeral 2 in FIG. 1 indicates a processing
chamber assuming the shape of an angular tube, which is constituted
of, for instance, aluminum with anodized surfaces. On the upper
side inside the processing chamber 2, an upper electrode 3 also to
be used as a gas shower head through which a process gas is
supplied is disposed, and an insulating member 31 disposed along
the opening edge of an opening 30 at the upper surface of the
processing chamber 2 sets the upper electrode 3 in a fully floating
state electrically relative to the processing chamber 2. In
addition, the gas shower head constituted with the upper electrode
3 is connected with a process gas supply unit 33 via a gas supply
passage 32 and includes numerous gas holes 34 through which the gas
supplied via the gas supply passage 32 is delivered into the
processing chamber 2.
[0053] The upper electrode 3 is connected with a high-frequency
power source 4 via a matching circuit 41 and a conductive passage
40. In addition, a matching box 42 is disposed so as to surround
the opening 30 at the processing chamber 2 and to hold therein the
matching circuit 41. The top portion of the matching box 42 extends
as an outer layer portion 43 which constitutes, together with the
conductive passage 40, a coaxial cable 44, and the outer layer
portion 43 is grounded. In this example, the matching box 42
constitutes a grounded casing of the matching circuit.
[0054] In the processing chamber 2, a lower electrode 5 to be also
used as a stage on which a substrate 10 is placed is disposed at
the bottom, and the lower electrode 5 is supported at a support
portion 51 via an insulating member 50. Thus, the lower electrode 5
is fully floating with respect to the processing chamber 2
electrically. At the center of the lower surface of the support
portion 51, a protective pipe 52 passing through an opening 20
formed at the bottom wall of the processing chamber 2 and extending
downward is disposed. The protective pipe 52 is supported on its
bottom side by a conductive support plate 53 having a diameter
larger than that of the protective pipe 52, which also seals the
pipe. At the peripheral edge of the support plate 53, the lower end
of a conductive bellows member 54 is fixed, and the upper end of
the bellows member 54 is fixed to the opening edge of the opening
20 at the processing chamber 2. The bellows member 54 pneumatically
seals the inner space in which the protective pipe 52 is disposed
from the atmosphere side space, and the stage 5 is allowed to move
up/down by an elevator mechanism (not shown) via the support plate
53.
[0055] One end of a conductive passage 55 disposed within the
protective pipe 51 is connected to the lower electrode 5, with an
impedance adjustment unit 6 disposed in the conductive passage 55.
Another end of the conductive passage 55 is connected to the bottom
of the processing chamber 2 via the support plate 53 and the
bellows member 54. A portion of the processing chamber 2 located in
the vicinity of the upper electrode 3, e.g., the upper surface of
the processing chamber 2, is grounded via the matching box 42 and
then the outer layer portion 43 of the coaxial cable 44, as
explained earlier. The upper electrode 3 and the lower electrode 5
are respectively equivalent to a cathode electrode and an anode
electrode in this example.
[0056] An evacuation passage 21 is connected to the side wall of
the processing chamber 2, with a vacuum evacuation means 22
connected to the evacuation passage 21. In addition, a gate valve
24 used to open/close a transfer port 23 through which the
substrate 10 is transferred is disposed at the side wall of the
processing chamber 2.
[0057] In the structure described above, a high-frequency current
flows through the path extending from the high-frequency power
source 4 to the ground sequentially via the matching circuit 41,
the upper electrode 3, the plasma, the lower electrode 5, the
impedance adjustment unit 6, the processing chamber 2, the matching
box 42 and the outer layer portion 43 of the coaxial cable 44.
Since there is a concern that the high-frequency current may flow
to the wall of the processing chamber 2 from the upper electrode 3
via the plasma as explained in reference to the related art, the
impedance in the path (the return path) extending from the lower
electrode 5 to the top of the processing chamber 2 is adjusted with
the impedance adjustment unit 6.
[0058] FIG. 2 presents a diagram of a circuit equivalent to the
high-frequency current circuit in the plasma processing apparatus
shown in FIG. 1. Since the processing chamber 2 can be regarded as
an inductance component, it is shown as an inductor. C1 indicates a
capacitive component representing the plasma present between the
upper electrode 3 and the lower electrode 5, whereas C2 indicates a
capacitive component representing the plasma present between the
upper electrode 3 and the wall of the processing chamber 2.
[0059] The object of the embodiment is to adjust the impedance j
(-1/.omega.C1+.omega.L-1/.omega.C) over the path extending from the
lower electrode 5 to the top of the processing chamber 2 to a level
lower than the impedance over the path extending from the upper
electrode 3 through the plasma and then the wall of the processing
chamber 2 through which the plasma density increases relative to
the wall by canceling out the capacitance (C1) of the plasma and
the inductance (L) in the path extending from the lower electrode 5
to the top of the processing chamber 2 with the capacitive
component (C) of the impedance adjustment unit 6. For these
purposes, the impedance adjustment unit 6 includes a capacitive
component. Such an impedance adjustment unit 6 may be achieved by
adopting any of various modes. For instance, the impedance
adjustment unit 6 may be constituted by using a variable-capacity
capacitor 61, as shown in FIG. 3A, by using a capacitor 62 with a
fixed capacity in combination with a variable-capacity capacitor
61, as shown in FIG. 3B, by using a capacitor 62 with a fixed
capacity, as shown in FIG. 3C, by using a variable-capacity
capacitor 61 in combination with an inductor 63, as shown in FIG.
3D or by using an inductor 64 which allows the inductance to be
varied in combination with a capacitor 62 with a fixed capacity, as
shown in FIG. 3E. Even in a plasma processing apparatus having the
fixed capacity capacitor 62 alone, the impedance value can be
adjusted by replacing the capacitor 62 with a capacitor having a
different capacity.
[0060] While the impedance in the path extending along the
direction in which the plasma becomes more uniform relative to the
substrate should be ideally reduced by ascertaining the values of
the electrical current flowing through the path in correspondence
to varying impedance values assumed at the impedance adjustment
unit 6 through tests conducted as detailed later and selecting an
impedance value corresponding to the maximum current value, i.e.,
by setting a value that will minimize the impedance in the path
extending along the direction in which the plasma becomes more
uniform relative to the substrate, it is desirable to ensure that a
value corresponding to a current value within a 2% range with
respect to the maximum value or at least a 10% range with respect
to the maximum current value in a practical application.
[0061] The functions and the advantages of the embodiment described
above are now explained. After the substrate 10 is transferred into
the processing chamber 2 on a transfer arm (not shown) from a load
lock chamber (not shown) by opening the gate valve 24, the
substrate 10 is transferred onto the lower electrode 5 through
cooperation of the transfer arm and an elevator pin (not shown)
passing through the lower electrode 5. Then, the gate valve 24 is
closed, the process gas is supplied into the processing chamber 2
from the process gas supply unit 33 via the upper electrode 3, and
the pressure inside the processing chamber 2 is maintained at a
predetermined level by evacuating the processing chamber 2
vacuously with the vacuum evacuation means 22. The process gas
becomes excited as 10 kW high-frequency power at, for instance, 10
MHz to 30 MHz frequency from the high-frequency power source 4 is
applied between the upper electrode 3 and the lower electrode 5,
thereby generating plasma. The process gas may be constituted with,
for instance, a gas containing halogen such as a gas containing a
halogen compound, an oxygen gas and an argon gas or the like.
[0062] As the plasma is generated, the high-frequency current flows
through the path extending from the upper electrode 3 to the ground
sequentially via the plasma, the lower electrode 5, the impedance
adjustment unit 6, the processing chamber 2, the matching box 42
and the outer layer portion 43 of the coaxial cable 44 along the
direction in which the plasma becomes more uniform relative to the
substrate. Since the value of the impedance in the path is set
substantially to the minimum value, smaller than the value of the
impedance in the path extending from the upper electrode 3 to the
ground sequentially via the plasma, the processing chamber 2, the
matching box 42 and the outer layer portion 43 of the coaxial cable
44, plasma is not generated readily between the upper electrode 3
and the wall of the processing chamber 2. As a result, the plasma
is allowed to concentrate in the space between the upper electrode
3 and the lower electrode 5 and the plasma present above the
substrate 10 achieves a high level of planar uniformity. As the
surface of the substrate 10 is etched with this plasma achieving a
high level of planar uniformity, the etching rate sustains a high
level of consistency and thus, uniform etching is achieved within
the plane. In addition, the damage to or wear of the inner wall of
the processing chamber 2 and internal parts is minimized.
[0063] In the embodiment, optimal adjustment values to be set at
the impedance adjustment unit 6 in correspondence to various types
of processing may be stored in memory as, for instance, a table at
a storage unit of a control unit 7, the optimal adjustment value
corresponding to a specific processing type having been selected
may be read out from the data, e.g., the table and a control signal
may be output from the control unit 7 to an actuator at the
impedance adjustment unit 6 which may be a motor for driving the
trim mechanism of the variable-capacity capacitor, as shown in FIG.
4. More specifically, such optimal value settings may be determined
in correspondence to various etching processes which are executed
continuously to one another, or the optimal value settings may be
determined in correspondence to different film forming processes
which are executed continuously to one another.
[0064] In the embodiment, when processing the substrate with plasma
generated by applying high-frequency power to the space between the
cathode electrode and the anode electrode, the impedance adjustment
unit having a capacitive component, which is disposed between the
anode electrode (constituted with the electrode facing opposite the
electrode connected with the high-frequency power source) and the
processing chamber, adjusts the value of the impedance in the path
extending from the cathode electrode to the grounded casing of the
matching circuit via the plasma, the anode electrode and the
processing chamber wall to a level lower than the value of the
impedance in the path extending from the cathode electrode to the
grounded casing of the matching circuit via the plasma and the
processing chamber wall. As a result, plasma is not generated
readily in the space between the cathode electrode and the
processing chamber wall and plasma with highly consistent
distribution is generated to enable plasma processing with a high
level of planar uniformity at the substrate.
[0065] (Variations of the First Embodiment)
[0066] In a variation of the embodiment, the plasma processing
apparatus include a plurality of impedance adjustment units e.g.,
impedance adjustment units 6A, 6B and 6C, as shown in FIGS. 5A and
5B. It is desirable that the individual impedance adjustment units
6A, 6B and 6C be connected on one end thereof to the lower
electrode 5 at positions PA, PB and PC distanced from one another
along the longish side of the lower electrode 5 (along the lateral
direction). To explain this in specific terms, a rectangular
substrate 10 is divided into three separate areas, as indicated by
the chain lines in FIG. 5B, for instance, and the impedance in the
path between each divided area and the processing chamber 2 is set
to an optimal value. The term "optimal value" refers to a value at
which highly consistent plasma is achieved, and such an optimal
value is determined for each of the impedance adjustment units 6A,
6B and 6C in correspondence to each type of processing through, for
instance, repeated tests conducted in advance.
[0067] To explain the plasma processing apparatus in further detail
in reference to a specific example, if the plasma intensity is high
around the center, the capacitive value at the impedance adjustment
unit 6B corresponding to the central area is increased so as to
raise the value of the impedance between the lower electrode 5 and
the processing chamber 2 over the central area and the capacity
values at the impedance adjustment units 6A and 6C corresponding to
the peripheral areas are reduced so as to shift the plasma with the
high intensity from the center toward the periphery. It is a
prerequisite in such an embodiment that the impedance values at the
individual impedance adjustment units 6A, 6B and 6C be set so as to
adjust the value of the impedance over the path extending along the
direction in which the plasma becomes more uniform relative to the
substrate as described earlier, including the value of the
impedance at the parallel connection circuit constituted with the
impedance adjustment unit 6A, 6B and 6C to a level lower than the
value of the impedance over the path extending from the upper
electrode 3 and then through the plasma and along the wall of the
processing chamber 2, through which the plasma density increases
relative to the wall. The intensity of the plasma over the plane of
the substrate 10 can be fine-adjusted by adjusting the impedance
values at the individual impedance adjustment units while
satisfying the prerequisite, which proves extremely effective for
generating highly consistent plasma to process large size
substrates. Bearing in mind that it is difficult to sustain plasma
in a uniform state over the plane of a large size substrate with an
area of 1 m.sup.2 or more, e.g., a rectangular substrate used for a
flat panel display, the inventor learned that the plasma
consistency can be improved and any abnormal discharge that might
otherwise occur locally can be prevented by fine-adjusting the
plasma distribution. The structure having a plurality of impedance
adjustment units is particularly effective when the sum of the
high-frequency power is significant at 10 kW or more, since an
abnormal discharge tends to occur readily under such
circumstances.
[0068] As shown in FIGS. 5A and 5B, the impedance adjustment units
6A, 6B and 6C are enclosed inside protective pipes 52A, 52B and 52C
respectively, extending from the lower surface of a support portion
51 at positions corresponding to the positions PA, PB and PC
mentioned earlier. Support plates 53, which are independent of one
another, are each provided in correspondence to one of the
protective pipes 52A to 52C and a bellows member 54 is provided
between each support plate 53 and the processing chamber 2 as has
been described in reference to FIG. 1.
[0069] When dividing the lower electrode 5 into separate impedance
adjustment areas, as described above, it does not need to be
divided into three areas and instead, it may be halved both
longitudinally and laterally to form four divided areas, for
instance, and in such a case, an impedance adjustment unit should
be provided in correspondence to each of the four divided
areas.
[0070] In this embodiment, too, adjustment values to be selected
for the individual impedance adjustment units 6A, 6B and 6C should
be stored in memory at the storage unit of the control unit 7 in
correspondence to each type of processing and the optimal impedance
values should be set at the individual impedance adjustment units
6A, 6B and 6C in correspondence to a selected processing type, as
shown in FIG. 6.
[0071] In addition, instead of using a capacitive element such as a
variable-capacity capacitor or a fixed capacity capacitor to
constitute an impedance adjustment unit 6, a dielectric plate or
the like that constitutes a capacitive component may be used as
shown in FIGS. 7A to 7C. In the example presented in FIG. 7A, an
impedance adjustment unit constituted with a dielectric plate 8 is
detachably mounted between the lower electrode 5 and the bottom of
the processing chamber 2. The capacitive value of the dielectric
plate 8 is set to a level at which the prerequisite conditions with
regard to the impedance value over the path are satisfied mentioned
earlier.
[0072] In the example presented in FIG. 7B, which corresponds to
the example presented in FIG. 5A showing a plurality of impedance
adjustment units 6A, 6B and 6C, the capacity at the dielectric
plate over the central area (e.g., a rectangular area in a plan
view) is varied from the capacity in the peripheral area (the
angular ring-shaped area in a plan view), by using two different
types of dielectric plates 8A and 8B. While the different
capacities are achieved by using different materials and sustaining
a consistent thickness for the entire dielectric plate, different
capacities may instead be achieved for the central area and the
peripheral area by, for instance, increasing the thickness of the
lower electrode 5 over the central area and thus reducing the
thickness of the dielectric plate 8 over the corresponding area in
the example presented in FIG. 7C.
[0073] While the high-frequency power source 4 is connected to the
upper electrode 3 in the embodiment described above, the
high-frequency power source 4 may instead be connected to the lower
electrode 5. In such a case, the impedance adjustment unit 6 should
be connected between the upper electrode 3 and an upper portion of
the processing chamber 2, e.g., the upper surface of the processing
chamber 2. While the impedance adjustment unit 6 may be disposed
between the upper electrode 3 and the side wall of the processing
chamber 2 under these circumstances, it is not desirable to dispose
the impedance adjustment unit at a position lower than the upper
electrode 3. FIG. 8 shows an apparatus of this type having three
impedance adjustment units 6A to 6C. The three impedance adjustment
units 6A to 6C may be installed at positions corresponding to PA to
PC in FIGS. 5A and 5B, for instance. However, the number of
impedance adjustment units 6 is not limited to three and the
apparatus may include two impedance adjustment units 6 or four or
more impedance adjustment units 6. In addition, the apparatus may
include a single impedance adjustment unit 6 instead of a plurality
of impedance adjustment units.
[0074] By adopting the variation in which a plurality of impedance
adjustment units are employed with the individual impedance
adjustment units connected on one side to the anode electrode at
positions distanced from one another along the longish side of the
anode electrode and the impedance can be thus adjusted individually
for each of the plurality of divided areas of the anode electrode
defined along the plane of the substrate, the plasma distribution
can be adjusted more accurately compared to an impedance adjustment
over a single area and, as a result, highly consistent plasma is
achieved. For instance, as it becomes difficult to achieve a highly
consistent plasma state within the plane when handling a large
substrate with an area of 1 m.sup.2 or more, the plasma consistency
can be improved and also an abnormal discharge that might otherwise
occur locally can be prevented by fine-adjusting the plasma
distribution. The structure having a plurality of impedance
adjustment units is particularly effective when the sum of the
high-frequency power is significant at 10 kW or more since an
abnormal discharge tends to occur readily under such
circumstances.
Second Embodiment
[0075] The second embodiment of the present invention is adopted in
an upper electrode/lower electrode two-frequency type plasma
processing apparatus having a high-frequency power source 4
disposed in conjunction with the upper electrode 3 and a
high-frequency power source 100 disposed in conjunction with the
lower electrode 5, as shown in FIG. 9. In this plasma processing
apparatus, a conductive passage 101 is wired inside the protective
pipe 52B located on the lower side in the structure shown in FIG.
5A, a matching box 102 is disposed at the lower end of the
protective pipe 52B, a matching circuit 103 connected to the
conductive passage 101 is housed inside the matching box 102 and
the high-frequency power source 100 is connected to the matching
circuit 103. The bottom portion of the matching box 102 extends as
an outer layer portion 105, which constitutes a coaxial cable 104
together with a conductive passage 106 and the outer layer portion
105 is grounded.
[0076] The matching circuits 41 and 103 in this example
respectively constitute a first matching circuit and a second
matching circuit. The high-frequency power sources 4 and 100
respectively constitute a first high-frequency power source and a
second high-frequency power source, and the first high-frequency
power source 4 located on the upper side outputs, for instance, 10
kW high-frequency power with a frequency of 10 MHz to 30 MHz,
whereas the second high-frequency power source 100 located on the
lower side outputs, for instance, 3 kW high-frequency power with a
frequency of 2 MHz to 6 MHz. The high-frequency power output from
the first high-frequency power source 4 activates the process gas,
whereas the power output from the second high-frequency power
source 100 attracts the ions in the plasma toward the substrate 10.
It is to be noted that the matching boxes 42 and 102 respectively
constitute a grounded casing for the first matching circuit and a
grounded casing for the second matching circuit in the embodiment.
Although not shown in FIG. 9, a high pass filter is disposed
between the upper electrode 3 and the matching circuit 41 and a low
pass filter is disposed between the lower electrode 5 and the
matching circuit 103 so as to ensure that the high-frequency
component of the high-frequency power source 4 does not enter the
high-frequency power source 100 and the high-frequency component of
the high-frequency power source 100 does not enter the
high-frequency power source 4. In this example, the lower electrode
5 constitutes an anode electrode in relation to the first
high-frequency power source 4, and the upper electrode 3
constitutes an anode electrode in relation to the second
high-frequency power source 100.
[0077] A plurality of impedance adjustment units 9A and 9C are
disposed between the upper electrode 3 and the matching box 42, and
the impedance adjustment units 9A and 9C are connected to an upper
portion, e.g., the ceiling, of the processing chamber 2 via the
matching box 42. While the illustration includes two impedance
adjustment units 9A and 9C on the upper side and two impedance
adjustment units 6A and 6C on the lower side, three or more
impedance adjustment units may be provided on each side or a single
impedance adjustment unit may be provided on each side. In
addition, the matching box 42 constitutes the grounded casing for
the first matching circuit 41, which allows the high-frequency
current from the first high-frequency power source 4 to return to
the high-frequency power source 4 through the top portion of the
processing chamber 2, and the matching box 102 constitutes the
grounded casing for the second matching circuit 103, which allows
the high-frequency current from the second high-frequency power
source 100 to return to the high-frequency power source 100 from
the bottom portion of the processing chamber 2.
[0078] The lower impedance adjustment units 6A and 6C constitute a
first impedance adjustment units in conjunction with which a filter
for allowing the high-frequency component corresponding to the
high-frequency band of the first high-frequency power source 4
alone to pass through is provided. The upper impedance adjustment
units 9A and 9C constitute second impedance adjustment units in
conjunction with which a filter for allowing the high-frequency
component corresponding to the high-frequency band of the second
high-frequency power source 100 alone to pass through is provided.
Namely, the high-frequency current from the first high-frequency
power source 4 flows through a path extending from the
high-frequency power source 4 to the ground sequentially via the
matching circuit 41, the upper electrode 3, the plasma, the lower
electrode 5, the impedance adjustment units 6A and 6C, the
processing chamber 2, the matching box 42 and the outer layer
portion 43 of the coaxial cable 44, whereas the high-frequency
current from the second high-frequency power source 100 flows
through a path extending from the high-frequency power source 100
to the ground sequentially via the matching circuit 103, the lower
electrode 5, the plasma, the upper electrode 3, the impedance
adjustment units 9A and 9C, the processing chamber 2, the matching
box 102 and the outer layer portion 105 of the coaxial cable
104.
[0079] The first impedance adjustment units 6A and 6B adjust the
value of the impedance at the high-frequency of the first
high-frequency power source 4 over the path extending from the
upper electrode 3 to the matching box 42 (the grounded casing of
the first matching circuit) via the plasma, the lower electrode 5
and the wall of the processing chamber 2 along the direction in
which the plasma becomes more uniform relative to the substrate, to
a level lower than the value of the impedance at the high frequency
of the first high-frequency power source 4 over the path extending
from the upper electrode 3 to the matching box 42 via the plasma
and the wall of the processing chamber 2 along the direction in
which the plasma density increases relative to the wall. While the
impedance in the path extending along the direction in which the
plasma becomes more uniform relative to the substrate should be
ideally reduced by ascertaining the values of the electrical
current flowing from the first high-frequency power source 4
through the path extending along the direction in which the plasma
becomes more uniform relative to the substrate in correspondence to
varying impedance values and selecting an impedance value
corresponding to the maximum current value, i.e., by setting a
value that will minimize the impedance in the path extending along
the direction in which the plasma becomes more uniform relative to
the substrate, it should be insured in a practical application that
a value corresponding to a current value within a 2% range with
respect to the maximum current value or at least within a 10% range
with respect to the maximum current value is set. The value of the
current in the path extending along the direction in which the
plasma becomes more uniform relative to the substrate may be
determined as the sum of the current values provided by, for
instance, ammeters connected to the impedance adjustment units 6A
and 6C.
[0080] The second impedance adjustment units 9A and 9C adjust the
value of the impedance at the high-frequency of the second
high-frequency power source 100 over the path extending from the
lower electrode 5 to the matching box 102 via the plasma, the upper
electrode 3 and the wall of the processing chamber 2 along the
direction in which the plasma becomes more uniform relative to the
substrate to a level lower than the value of the impedance at the
high-frequency of the second high-frequency power source 100 over
the path extending from the lower electrode 5 to the matching box
102 via the plasma and the wall of the processing chamber 2 along
the direction in which the plasma density increases relative to the
wall. While the impedance in the path extending along the direction
in which the plasma becomes more uniform relative to the substrate
should be ideally reduced by ascertaining the values of the
electrical current flowing from the second high-frequency power
source 100 through the path extending along the direction in which
the plasma becomes more uniform relative to the substrate in
correspondence to varying impedance values and selecting an
impedance value corresponding to the maximum current value, it
should be ensured in a practical application that a value
corresponding to a current value within a 2% range with respect to
the maximum value or at least a 10% range with respect to the
maximum current value is set.
Third Embodiment
[0081] The third embodiment of the present invention is adopted in
a lower electrode two-frequency type plasma processing apparatus
having a first high-frequency power source 4 and a second
high-frequency power source 100 both provided in conjunction with
the lower electrode 5, as shown in FIG. 10. In this plasma
processing apparatus, the protective pipe 45 is connected via an
insulating layer 50 to the lower side of the lower electrode 5, the
lower end of the protective pipe 45 passes through the bottom
surface of the processing chamber 2 and a matching box 42 is
connected to the lower end of the protective pipe 45. Two matching
circuits 41 and 103 are disposed inside the matching box 42, with
the matching circuits 41 and 103 individually connected on one end
thereof to the lower electrode 5 respectively via conductive
passages 46 and 101 disposed inside the protective pipe 45 and the
first high-frequency power source 4 and the second high-frequency
power source 100 respectively connected to the other ends of the
matching circuits 41 and 103. Reference numerals 44 and 104
indicate the coaxial cables described earlier. The frequencies and
the power levels of the high-frequency power output from the first
high-frequency power source 4 and the second high-frequency power
source 100 are equal to those in the embodiment shown in FIG.
9.
[0082] A plurality of first impedance adjustment units, e.g., three
impedance adjustment units 6A to 6C, and a plurality of second
impedance adjustment units, e.g., three impedance adjustment units
9A to 9C, are individually connected on one end thereof to the
upper electrode 3, and the ends of the impedance adjustment units
6A to 6C and 9A to 9C on the other side are connected to an upper
portion, e.g., the ceiling, of the processing chamber 2 via a
conductive cover member 56 covering the opening 30 of the
processing chamber 2. Instead of providing three first impedance
adjustment units and three second impedance adjustment units, a
first impedance adjustment unit constituted with a single impedance
adjustment unit and a second impedance adjustment unit constituted
with a single impedance adjustment unit may be used, or the number
of impedance adjustment units included in the first and second
impedance adjustment units may be two or four or more. In this
example, too, a filter for allowing only the high-frequency
component corresponding to the high-frequency band of the first
high-frequency power source 4 to pass through is provided in
conjunction with the first impedance adjustment units 6A to 6C. In
addition, a filter for allowing only the high-frequency component
corresponding to the high-frequency band of the second
high-frequency power source 100 to pass through is provided in
conjunction with the second impedance adjustment units 9A to
9C.
[0083] In addition, the matching box 42 is used both as the
grounded casing for the first matching circuit, which allows the
high-frequency current from the first high-frequency power source 4
to return to the high-frequency power source 4 through the bottom
of the processing chamber 2, and the grounded casing for the second
matching circuit, which allows the high-frequency current from the
second high-frequency power source 100 to return to the
high-frequency power source 100 through the bottom of the
processing chamber 2.
[0084] The high-frequency current from the first high-frequency
power source 4 flows through the path extending from the
high-frequency power source 4 to the matching box 42 sequentially
via the matching circuit 41, the lower electrode 5, the plasma, the
upper electrode 3, the first impedance adjustment units 6A to 6C
and the processing chamber 2, whereas the high-frequency current
from the second high-frequency power source 100 flows through the
path extending from the high-frequency power source 100 to the
matching box 42 sequentially via the matching circuit 103, the
lower electrode 5, the plasma, the upper electrode 3, the second
impedance adjustment units 9A to 9C and the processing chamber
2.
[0085] The first impedance adjustment units 6A to 6C adjust the
value of the impedance at the high frequency of the first
high-frequency power source 4 over the path extending from the
lower electrode 5 to the matching box 42 via the plasma, the upper
electrode 3 and the wall of the processing chamber 2 along the
direction in which the plasma becomes more uniform relative to the
substrate to a level lower than the value of the impedance at the
high frequency of the first high-frequency power source 4 over the
path extending from the lower electrode 5 to the matching box 42
via the plasma and the wall of the processing chamber 2 along the
direction in which the plasma density increases relative to the
wall. While the impedance in the path extending along the direction
in which the plasma becomes more uniform relative to the substrate
should be ideally reduced by ascertaining the values of the
electrical current flowing from the first high-frequency power
source 4 through the path extending along the direction in which
the plasma becomes more uniform relative to the substrate in
correspondence to varying impedance values and selecting an
impedance value corresponding to the maximum current value, i.e.,
by setting a value that will minimize the impedance in the path
extending along the direction in which the plasma becomes more
uniform relative to the substrate, it should be insured in a
practical application that a value corresponding to a current value
within a 2% range with respect to the maximum current value or at
least within a 10% range with respect to the maximum current value
is set.
[0086] The second impedance adjustment units 9A to 9C adjust the
value of the impedance at the high frequency of the second
high-frequency power source 100 over the path extending from the
lower electrode 5 to the matching box 42 via the plasma, the upper
electrode 3 and the wall of the processing chamber 2 along the
direction in which the plasma becomes more uniform relative to the
substrate to a level lower than the value of the impedance at the
high frequency of the second high-frequency power source 100 over
the path extending from the lower electrode 5 to the matching box
42 via the plasma and the wall of processing chamber 2 along the
direction in which the plasma density increases relative to the
wall. While the impedance in the path extending along the direction
in which the plasma becomes more uniform relative to the substrate
should be ideally reduced by ascertaining the values of the
electrical current flowing from the second high-frequency power
source 100 through the path extending along the direction in which
the plasma becomes more uniform relative to the substrate in
correspondence to varying impedance values and selecting an
impedance value corresponding to the maximum current value, it
should be ensured in a practical application that a value
corresponding to a current value within a 2% range with respect to
the maximum value or at least a 10% range with respect to the
maximum current value is set.
[0087] It is to be noted that the impedance adjustment units
achieved in the embodiments shown in FIGS. 8 through 10 may each be
constituted with a dielectric material containing a capacitive
component as shown in FIGS. 7A through 7C in reference to which an
explanation has already been provided. In addition, the data
correlating individual plasma processing types with specific
adjustment values to be set at the impedance adjustment units may
be prepared so as to automatically adjust the impedance adjustment
units in correspondence to a given plasma processing type, as shown
in FIG. 4.
[0088] FIG. 11 presents an example of a layout that may be adopted
when providing a plurality of impedance adjustment units. In this
example, impedance adjustment units are disposed at positions
corresponding to five points which include four points P1 to P4 at
the four corners and a point P5 at the center of the rectangular
substrate 10 (over areas in which those five points are
projected).
[0089] The optimal distance between the upper electrode 3 and the
lower electrode 5 and the optimal processing pressure to be assumed
in an apparatus having the high-frequency power source 4 connected
to the upper electrode 3, as shown in FIGS. 1, 5A and 9 are
respectively 50 mm to 300 mm and 13 Pa to 27 Pa (100 mTorr to 200
mTorr). In an apparatus having the high-frequency power source 4
connected to the lower electrode 5, as shown in FIGS. 8 and 10, on
the other hand, it is desirable to set the distance between the
electrodes to a value within a range of 200 mm to 700 mm and the
processing pressure to a level within a range of 0.7 Pa to 13 Pa (5
mTorr to 100 mTorr).
[0090] (Tests)
[0091] Next, tests conducted to verify the advantages of the
embodiments of the present invention are described.
[0092] (Test 1)
[0093] A Test Method
[0094] A plane parallel plasma processing apparatus such as that
shown in FIG. 5A, having four impedance adjustment areas defined at
the lower electrode (the lower electrode in FIG. 5A includes three
divided areas) was used as a test apparatus. Four impedance
adjustment units (6A to 6D) each constituted by connecting in
series an inductor 63 and a variable-capacity capacitor 61 were
connected in parallel to one another, as shown in FIG. 12. It is to
be noted that the capacitive component indicated as C0 in FIG. 12
corresponds to the capacity of the dielectric member between the
lower electrode and the processing chamber.
[0095] The trimmers of the variable-capacity capacitors were
adjusted to various positions so as to set the impedance at the
impedance adjustment units were set to different values. The state
of the plasma generated in the processing chamber was visually
observed, the current flowing through the conductive path extending
between the impedance adjustment units and the processing chamber
(the current flowing to the lower electrode) was detected and the
voltage at the upper electrode was measured at each impedance
setting. The plasma was generated with the distance between the
upper electrode and the lower electrode set to 60 mm, a mixed gas
containing SF6 gas, HCl gas and He gas was used as the plasma
generating gas, the frequency and the level of the power output
from the high-frequency power source set to 13.56 MHz and 7.5 kW
and the pressure set to 20 Pa (150 mTorr).
[0096] B Test Results
[0097] FIG. 13 shows the relationships among the variable-capacity
capacitor trimmer position, the capacity at the capacitor, the
impedance at the capacitor, the impedance value Z (L-C) at the
impedance adjustment unit, the value of the total impedance
including C0 between the lower electrode and the processing
chamber, the value of the current (lower current) flowing to the
lower electrode, the value of the voltage (upper voltage) at the
upper electrode and the visually observed plasma state. The
visually observed plasma state was evaluated by using the following
criterion; highly consistent light emission (.circleincircle.),
fairly good consistency in light emission (.largecircle.), slightly
poor consistency in light emission (.DELTA.) and poor consistency
in light emission (X). In addition, the lower current value and the
upper voltage value in FIG. 13 are graphed respectively in FIGS. 14
and 15. The unit of the capacitive value is pF, the unit of the
impedance at the capacitor and the impedance value is .OMEGA. and
the units of the current value and the voltage value are
respectively A and V.
[0098] As the test results indicate, the lower current peaked at 79
A and the best plasma state was achieved at 79 A. The plasma state
with the lower current at 78 A was evaluated to be fairly good and
the plasma state with the lower current at 72 A was evaluated to be
slightly poor. In addition, the plasma state at 66 A or lower was
very poor. Accordingly, the impedance value should be adjusted so
as to substantially maximize the lower current. With the measuring
error and the like taken into consideration, it is desirable to
ensure that the lower current is within a 10% range with respect to
the maximum value and it is even more desirable to assure a lower
current within a 2% range with respect to the maximum value. When
the lower current value is substantially maximized, the upper
voltage value, too, is substantially maximized, which means that
the value of the impedance between the lower electrode and the
processing chamber is substantially minimized. In other words, when
the lower current value is substantially maximized, the level of
the current flowing from the upper electrode to the wall of the
processing chamber via the plasma is substantially at the minimum
level and, under such circumstances, the plasma consistency is
improved without an electrical discharge occurring between the
upper electrode and the wall of the processing chamber.
[0099] (Test 2)
[0100] A Test Method
[0101] A two-frequency type plane parallel plasma processing
apparatus such as that shown in FIG. 9, having an upper
high-frequency power source 4 and a lower high-frequency power
source 100, was used as a test apparatus to etch a silicon film
formed at the surface of a rectangular substrate with an area of
2000 mm.times.2200 mm. The processing was executed under the
following conditions.
[0102] Process gas: SF6 gas, HCl gas and He gas
[0103] frequency and level of power output from upper
high-frequency
[0104] power source: 13.56 MHz and 20 kW
[0105] frequency and level of power output from lower
high-frequency
[0106] power source: 3.2 MHz and 4 kW
[0107] processing pressure: 20 Pa (150 mTorr)
[0108] In addition, five impedance adjustment units were provided
in conjunction with the high-frequency component from the
high-frequency power source 4 of the upper side at positions
corresponding to the four corners and the center of the rectangular
substrate and likewise, five impedance adjustment units were
provided in conjunction with the high-frequency component from the
high-frequency power source 100 of the lower side at positions
corresponding to the four corners and the center of the rectangular
substrate. Each impedance adjustment unit was constituted by
connecting in series a variable-capacity capacitor and an inductor,
as shown in FIG. 3D. With an ammeter serially inserted at each
impedance adjustment unit, an adjustment point at which the value
of the current (the sum of the current values detected with the
individual ammeters) running toward the lower electrode was at its
lowest was determined. Then, the average of the etching rates at
numerous positions set within the plane of the substrate surface
and the etching rate consistency within the plane at the adjustment
point were ascertained. In addition, the etching rate average and
the etching rate consistency within the plane were investigated in
a similar manner by processing the substrate under conditions
identical to the processing conditions detailed above but without
providing the impedance adjustment units, by setting the power
applied to the lower electrode to 0 and by dispensing with the
high-frequency power source of the lower side.
[0109] B Test Results
[0110] The results of the test are presented in FIG. 16. As the
test results indicate, the etching rate was improved by connecting
a high-frequency power source to the lower electrode as well as to
the upper electrode, over the etching rate of the system having
high-frequency power source connected to the upper electrode alone.
While the etching rate consistency within the plane is compromised
in the upper electrode/lower electrode two-frequency system, the
etching rate consistency within the plane can still be improved by
adjusting the impedance with the impedance adjustment units so as
to minimize the value of the current flowing to the lower
electrode.
[0111] The operations of the individual units in the plasma
processing apparatus achieved in each of the embodiments described
above are related with one another and thus they may be considered
to be steps in an operational sequence. But assuming such a
perspective, the present invention can be embodied as a plasma
processing method.
[0112] While the invention has been particularly shown and
described with respect to preferred embodiments thereof by
referring to the attached drawings, the present invention is not
limited to these examples and it will be understood by those
skilled in the art that various changes in form and detail may be
made therein without departing from the spirit, scope and teaching
of the invention.
* * * * *