U.S. patent application number 12/407922 was filed with the patent office on 2009-09-24 for plasma processing apparatus.
This patent application is currently assigned to TOKYO ELECTRON LIMITED. Invention is credited to Shinji Himori, Tatsuo MATSUDO.
Application Number | 20090236043 12/407922 |
Document ID | / |
Family ID | 41051678 |
Filed Date | 2009-09-24 |
United States Patent
Application |
20090236043 |
Kind Code |
A1 |
MATSUDO; Tatsuo ; et
al. |
September 24, 2009 |
PLASMA PROCESSING APPARATUS
Abstract
A plasma processing apparatus includes a processing gas
supplying unit for supplying a desired processing gas to a
processing space between an upper electrode and a lower electrode
which are disposed facing each other in an evacuable processing
chamber. The plasma processing apparatus further includes a radio
frequency (RF) power supply unit for applying an RF power to one of
the lower and the upper electrode to generate plasma of the
processing gas by RF discharge and an electrically conductive RF
ground member which covers a periphery portion of the electrode to
which the RF power is applied to receive RF power emitted outwardly
in radial directions from the periphery portion of the electrode to
which the RF power is applied and send the received RF power to a
ground line.
Inventors: |
MATSUDO; Tatsuo; (Nirasaki
City, JP) ; Himori; Shinji; (Nirasaki City,
JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
TOKYO ELECTRON LIMITED
Tokyo
JP
|
Family ID: |
41051678 |
Appl. No.: |
12/407922 |
Filed: |
March 20, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61092626 |
Aug 28, 2008 |
|
|
|
Current U.S.
Class: |
156/345.43 ;
118/723E; 204/298.02; 204/298.31 |
Current CPC
Class: |
H01J 37/32577 20130101;
H01J 37/32091 20130101; H01J 37/32642 20130101; H01L 21/3065
20130101 |
Class at
Publication: |
156/345.43 ;
118/723.E; 204/298.02; 204/298.31 |
International
Class: |
C23F 1/08 20060101
C23F001/08; C23C 16/54 20060101 C23C016/54 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 21, 2008 |
JP |
2008-073376 |
Claims
1. A plasma processing apparatus comprising: an evacuable
processing chamber; a lower electrode for mounting thereon a
substrate in the processing chamber; an upper electrode facing the
lower electrode in parallel in the processing chamber; a processing
gas supplying unit for supplying a processing gas to a processing
space between the upper electrode and the lower electrode; a radio
frequency (RF) power supply unit for applying an RF power to one of
the lower and the upper electrode to generate a plasma of the
processing gas by RF discharge; and an electrically conductive RF
ground member which covers a periphery portion of the electrode to
which the RF power is applied to receive RF power emitted outwardly
in radial directions from the periphery portion of the electrode to
which the RF power is applied and send the received RF power to a
ground line.
2. The plasma processing apparatus of claim 1, wherein the
electrode to which the RF power is applied is the lower
electrode.
3. The plasma processing apparatus of claim 2, wherein a dielectric
material is interposed between the lower electrode and the RF
ground member.
4. The plasma processing apparatus of claim 2, wherein a surface of
the RF ground member is covered by an insulating film.
5. The plasma processing apparatus of claim 2, wherein an annular
gas exhaust path for connecting the processing space to a gas
exhaust port provided at a bottom portion of the processing chamber
is formed between the RF ground member and an inner wall of the
processing chamber, and wherein a plurality of conductive fin
members, which is electrically grounded and vertically extending,
for promotion of extinction of a plasma diffused from the
processing space is provided at an upper region of the gas exhaust
path.
6. The plasma processing apparatus of claim 5, wherein the
plurality of fin members is seamlessly molded as a single unit with
or attached to an electrically conductive exhaust ring provided
annularly at the upper region of the gas exhaust path.
7. The plasma processing apparatus of claim 6, wherein surfaces of
the fin members are covered by insulating films.
8. The plasma processing apparatus of claim 5, wherein the fin
members are radially disposed at regular intervals in a
circumferential direction of the gas exhaust path.
9. The plasma processing apparatus of claim 2, wherein a dielectric
material having a thickness distribution in which the dielectric
material is thickest in the central portion of the lower or the
upper electrode and is thinnest in an edge portion of the lower or
the upper electrode is prepared at the top surface region of the
lower electrode or a bottom surface region of the upper
electrode.
10. The plasma processing apparatus of claim 1, wherein the RF
power has a frequency equal to or higher than 80 MHz.
11. A plasma processing apparatus comprising: an evacuable
processing chamber; a lower electrode for mounting thereon a
substrate in the processing chamber; an upper electrode facing the
lower electrode in parallel in the processing chamber; a processing
gas supplying unit for supplying a processing gas to a processing
space between the upper electrode and the lower electrode; a radio
frequency (RF) power supply unit for applying an RF power to one of
the lower and the upper electrode to generate a plasma of the
processing gas by RF discharge; and a grounded electrically
conductive RF ground member which covers a periphery portion of a
top or a bottom surface and a side surface of the electrode to
which the RF power is applied.
12. The plasma processing apparatus of claim 11, wherein the
electrode to which the RF power is applied is the lower
electrode.
13. The plasma processing apparatus of claim 12, wherein the RF
ground member covers a substantially entire region of the top
surface of the lower electrode projecting outwardly in radial
directions from the substrate.
14. The plasma processing apparatus of claim 12, wherein a
dielectric material is interposed between the lower electrode and
the RF ground member.
15. The plasma processing apparatus of claim 12, wherein a surface
of the RF ground member is covered by an insulating film.
16. The plasma processing apparatus of claim 12, wherein an annular
gas exhaust path for connecting the processing space to a gas
exhaust port provided at a bottom portion of the processing chamber
is formed between the RF ground member and an inner wall of the
processing chamber, and wherein a plurality of conductive fin
members, which is electrically grounded and vertically extending,
for promotion of extinction of a plasma diffused from the
processing space is provided at an upper region of the gas exhaust
path.
17. The plasma processing apparatus of claim 16, wherein the
plurality of fin members is seamlessly molded as a single unit with
or attached to an electrically conductive exhaust ring provided
annularly at the upper region of the gas exhaust path.
18. The plasma processing apparatus of claim 17, wherein surfaces
of the fin members are covered by insulating films.
19. The plasma processing apparatus of claim 16, wherein the fin
members are radially disposed at regular intervals in a
circumferential direction of the gas exhaust path.
20. The plasma processing apparatus of claim 12, wherein a
dielectric material having a thickness distribution in which the
dielectric material is thickest in the central portion of the lower
or the upper electrode and is thinnest in an edge portion of the
lower or the upper electrode is prepared at the top surface region
of the lower electrode or a bottom surface region of the upper
electrode.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a technique for performing
a plasma processing on a substrate to be processed, and more
particularly, to a capacitively coupled plasma processing
apparatus.
BACKGROUND OF THE INVENTION
[0002] In a manufacturing process of a semiconductor device or an
FPD (flat panel display), a plasma is often used in the process,
e.g., etching, deposition, oxidation, sputtering or the like, in
order to allow a processing gas to react efficiently at a
relatively low temperature. Conventionally, a capacitively coupled
plasma processing apparatus is mainly used to easily realize a
plasma having a large diameter for a single-wafer plasma processing
apparatus.
[0003] In general, in a capacitively coupled plasma processing
apparatus, an upper electrode and a lower electrode are disposed in
parallel with each other in a vacuum processing chamber, and a
target substrate (e.g., a semiconductor wafer, a glass substrate or
the like) is mounted on the lower electrode, while a radio
frequency (RF) power is applied between both electrodes. Then,
electrons accelerated by an RF electric field formed between the
electrodes, electrons emitted from the electrodes, or heated
electrons collide with molecules of a processing gas to ionize them
to thereby generate plasma of the processing gas, and accordingly,
a desired microprocessing, e.g., etching, is performed on a
substrate surface by radicals and ions in the plasma.
[0004] Here, the electrode to which the RF power is applied serves
as a cathode (negative pole) that is connected to an RF power
supply via a blocking capacitor in a matching unit. A cathode
coupling type in which an RF power is applied to the lower
electrode which mounts thereon a substrate and serves as a cathode
can perform a well directed anisotropic etching by substantially
vertically attracting ions in the plasma toward the substrate by
using a self-bias voltage generated in the lower electrode.
[0005] Along with the recent trend for miniaturization of a design
rule in manufacturing a semiconductor device or the like, an ever
increasingly high dimensional accuracy is required especially in
the plasma etching and, hence, selectivity against an etching mask
and an underlying layer and/or in-plane uniformity in the etching
has to be improved. Accordingly, there arises a demand for lowering
ion energy as well as pressure in a processing region inside the
chamber. For that reason, an RF power of about 40 MHz or greater
has been applied, which is significantly higher than that applied
in a conventional case.
[0006] Here, it becomes difficult to make a plasma of a uniform
density in a processing space of the chamber (particularly in a
radial direction). In other words, when the frequency of the RF
power for plasma generation is increased, the plasma density
becomes non-uniform by having a mountain-shaped profile in which
the plasma density is maximized mostly above a central portion of a
substrate and is minimized mostly above an edge portion of the
substrate by a wavelength effect by which a standing wave is
produced in the chamber and/or a skin effect by which the RF power
is concentrated on a central portion of an electrode surface. If
the plasma density is non-uniform above the substrate, a plasma
process also becomes non-uniform, which leads to a reduced
production yield of devices.
[0007] Various studies on electrode structures have been made to
overcome such a problem. For example, Japanese Patent Laid-open
Application No. 2004-363552 (Corresponding to U.S. Patent
Application Publication No. 2005/0276928 A1) discloses a plasma
processing apparatus in which a dielectric material is embedded at
a main surface of an electrode facing a processing space and
impedance of the RF power emitted from the electrode main surface
to the processing space is made to be relatively large at a central
portion of the electrode and relatively small at an edge portion of
the electrode, thereby improving uniformity of a plasma density
distribution.
[0008] At a certain frequency range, the method of embedding the
dielectric material at the electrode main surface as described
above can be employed to effectively transform, to a flat (uniform)
profile, a mountain-like profile of the plasma density distribution
on a subject substrate, which has its peak at the central portion
of the substrate and becomes gradually getting low toward an edge
portion of the substrate. However, if a frequency of the employed
RF power is increased further, variation of the plasma density
distribution (altitude difference in the mountain-like
distribution) becomes larger in proportion to the increased
frequency, thereby making it difficult to flattening the plasma
density distribution. In addition, a cathode-coupled plasma
processing apparatus is disadvantageous in that, if a frequency of
the RF power exceeds about 80 MHz, a plasma density distribution
produced by an RF power of a certain power level becomes to have a
W-like profile in which the plasma density is high above the
central portion and the edge portion of a substrate and low above
the portion therebetween. Such a W-like profile cannot be dealt
with the method of flattening the mountain-like profile.
SUMMARY OF THE INVENTION
[0009] In view of the above, the present invention provides a
plasma processing apparatus capable of improving in-plane
uniformity of a plasma process in wide RF frequency and power
ranges.
[0010] In accordance with a first aspect of the invention, there is
provided a plasma processing apparatus including: an evacuable
processing chamber; a lower electrode for mounting thereon a
substrate in the processing chamber; an upper electrode facing the
lower electrode in parallel in the processing chamber; a processing
gas supplying unit for supplying a processing gas to a processing
space between the upper electrode and the lower electrode; a radio
frequency (RF) power supply unit for applying an RF power to one of
the lower and the upper electrode to generate a plasma of the
processing gas by RF discharge; and an electrically conductive RF
ground member which covers a periphery portion of the electrode to
which the RF power is applied to receive RF power emitted outwardly
in radial directions from the periphery portion of the electrode to
which the RF power is applied and send the received RF power to a
ground line.
[0011] The electrode to which the RF power is applied may be the
lower electrode.
[0012] In this configuration, when the RF power from the RF power
supply unit goes around into the electrode main surface (top
surface) along a surface layer of the lower electrode, a part of
the RF power is emitted out of the periphery portion of the top
surface of the electrode. Since the RF ground member receives the
part of the RF power and sends it to the ground line, the part of
the RF power makes no contribution to discharge of the processing
gas, i.e., plasma generation. Thus, a plasma generation region in
the processing space is confined to a region right above or near
the substrate to be processed and a profile of the plasma density
distribution on the substrate can be stabilized.
[0013] In accordance with a second aspect of the invention, there
is provided a plasma processing apparatus including: an evacuable
processing chamber; a lower electrode for mounting thereon a
substrate in the processing chamber; an upper electrode facing the
lower electrode in parallel in the processing chamber; a processing
gas supplying unit for supplying a processing gas to a processing
space between the upper electrode and the lower electrode; a radio
frequency (RF) power supply unit for applying an RF power to one of
the lower and the upper electrode to generate a plasma of the
processing gas by RF discharge; and a grounded electrically
conductive RF ground member which covers a periphery portion of a
top or a bottom surface and a side surface of the electrode to
which the RF power is applied.
[0014] The electrode to which the RF power is applied may be the
lower electrode.
[0015] In this configuration, when the RF power from the RF power
supply unit goes around into the electrode main surface (top
surface) along a surface layer of the lower electrode, a part of
the RF power is emitted out of the periphery portion of the top
surface and a side surface of the electrode. Since the RF ground
member receives the part of the RF power and sends it to the ground
line, the part of the RF power makes no contribution to discharge
of the processing gas, i.e., plasma generation. Thus, a plasma
generation region in the processing space is confined to a region
right above or near the substrate to be processed and a profile of
the plasma density distribution on the substrate can be stabilized.
In addition, the RF ground member may preferably covers a
substantially entire region of the top surface of the lower
electrode projecting outwardly in radial directions from the
substrate.
[0016] A dielectric material may be interposed between the lower
electrode and the RF ground member. Further, a surface of the RF
ground member is covered by an insulating film.
[0017] It is preferable that an annular gas exhaust path for
connecting the processing space to a gas exhaust port provided at a
bottom portion of the processing chamber may be formed between the
RF ground member and an inner wall of the processing chamber, and a
plurality of conductive fin members, which is electrically grounded
and vertically extending, for promotion of extinction of a plasma
diffused from the processing space is provided at an upper region
of the gas exhaust path. This plasma extinction promotion function
of the fin members may reduce plasma existing near or above the
entrance of the gas exhaust path, thereby relatively increasing the
plasma density of a region right above the wafer while reducing
altitude differences in the plasma density distribution.
[0018] The plurality of fin members may be seamlessly molded as a
single unit with or attached to an electrically conductive exhaust
ring provided annularly at the upper region of the gas exhaust path
and surfaces of the fin members are covered by insulating films.
Further, the fin members are radially disposed at regular intervals
in a circumferential direction of the gas exhaust path.
[0019] Further, by providing the RF ground member, a plasma density
distribution on the substrate can have the mountain-like profile in
a wide RF power range. In order to correct the profile to make it
more flattened, it is preferable that a dielectric material having
a thickness distribution in which the dielectric material is
thickest in the central portion of the lower or the upper electrode
and is thinnest in an edge portion of the lower or the upper
electrode may be prepared at a top surface region of the lower
electrode or a bottom surface region of the upper electrode.
[0020] The RF power may have a frequency equal to or higher than 80
MHz. With such configuration, it is possible to improve in-plane
uniformity of a plasma density and a plasma process in wide RF
power ranges. Further, another RF power is applied to the lower
electrode to attract ions in the plasma mainly towards the
substrate disposed on the lower electrode from another RF power
supply unit.
[0021] In accordance with the plasma processing apparatus of the
present invention with the above-described configuration and
operation, it is possible to improve in-plane uniformity of a
plasma process in wide RF frequency and power ranges.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The objects and features of the present invention will
become apparent from the following description of embodiments,
given in conjunction with the accompanying drawings, in which:
[0023] FIG. 1 is a vertical cross sectional view showing a
configuration of a capacitively coupled plasma etching apparatus in
accordance with an embodiment of the present invention;
[0024] FIG. 2 is a partially-enlarged sectional view showing an
enlarged configuration of a main part in the capacitively coupled
plasma etching apparatus in accordance with the embodiment of the
present invention;
[0025] FIG. 3 is a view for explaining operation and function of an
RF ground member in accordance with the embodiment of the present
invention;
[0026] FIG. 4 is a perspective view showing an example of a
configuration of a fin member in accordance with the embodiment of
the present invention;
[0027] FIG. 5 is a partially-enlarged sectional view of a
comparative example showing a main part of a configuration with no
RF ground member and no fin member in the plasma etching apparatus
shown in FIG. 1;
[0028] FIGS. 6A to 6C show an example of an etching rate
distribution characteristic obtained from the configuration of the
apparatus in accordance with the embodiment of the present
invention;
[0029] FIGS. 7A to 7C show an etching rate distribution
characteristic of a comparative example obtained from the
configuration of the apparatus shown in FIG. 5;
[0030] FIG. 8 is a partially-enlarged sectional view showing a
configuration of a main part of a modification of the plasma
etching apparatus in accordance with the embodiment of the present
invention;
[0031] FIG. 9 is a partially-enlarged sectional view showing a
configuration of a main part of another modification of the plasma
etching apparatus in accordance with the embodiment of the present
invention; and
[0032] FIG. 10 is a partially-enlarged sectional view showing a
configuration of a main part of still another modification of the
plasma etching apparatus in accordance with the embodiment of the
present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0033] Hereinafter, embodiments of the present invention will be
described with reference to the accompanying drawings which form a
part hereof.
[0034] FIG. 1 shows a configuration of a plasma etching apparatus
in accordance with an embodiment of the present invention. The
plasma processing apparatus is configured as a capacitively coupled
plasma etching apparatus of a cathode coupling type (lower
electrode dual frequency application type) in which dual radio
frequency (RF) powers are applied to a lower electrode, and
includes a cylindrical chamber (processing chamber) 10 made of
metal such as aluminum, stainless steel or the like. The chamber 10
is frame grounded.
[0035] A circular plate-shaped lower electrode or a susceptor 12
for mounting thereon a substrate to be processed, e.g., a
semiconductor wafer W, is installed in the chamber 10. The
susceptor 12 is made of a conductive material, e.g., aluminum, and
is supported by the bottom wall of the chamber 10 through a
cylindrical support 14 made of an insulating material, e.g.,
alumina.
[0036] An RF ground member 18 is vertically extended from a bottom
wall of the chamber 10. The RF ground member 18 covers a side
surface, preferably the entire side surface, and a periphery
portion (edge portion) of a top surface (hereinafter, referred to
as "top periphery portion") of the susceptor 12 with a dielectric
material 16 interposed therebetween. The dielectric material 16 is
made of, e.g., quartz. A lower portion of the dielectric material
16 is connected to an upper portion of the cylindrical insulating
support 14, while an upper portion thereof is bent approximately at
a right angle toward the center of the susceptor 12 so as to cover
the top periphery portion of the susceptor 12. The RF ground member
18 is made of aluminum whose surface is covered by an anodic oxide
film or an insulating film 19 (see FIG. 2, illustration of the
insulating film 19 will be omitted in other figures.) such as
Y.sub.2O.sub.3 or the like. A lower portion of the RF ground member
18 is connected to the bottom wall of the chamber 10 and an upper
portion of the RF ground member 18 is bent approximately at a right
angle toward the center of the susceptor 12 so as to cover the top
periphery portion of the susceptor 12 via the dielectric material
16.
[0037] A gas exhaust path 20 is annularly formed between the RF
ground member 18 and the inner wall of the chamber 10. In addition,
an exhaust ring (baffle plate) 22 of a conical shape is annularly
attached near the entrance or at an upper portion of the gas
exhaust path 20 and a gas exhaust port 24 is provided at a bottom
portion of the gas exhaust path 20. Further, a gas exhaust unit 28
is connected to the gas exhaust port 24 via a gas exhaust pipe 26.
The gas exhaust unit 28 has a vacuum pump so that a processing
space in the chamber 10 can be depressurized to a desired vacuum
level. Attached to an outer sidewall of the chamber 10 is a gate
valve 30 for opening and closing a loading/unloading port for the
semiconductor wafer W.
[0038] A first RF power supply 32 for RF discharge is electrically
connected to the susceptor 12 via a first matching unit 34 and a
power feed rod 36. The first RF power supply 32 applies a first RF
power having a relatively high frequency appropriate for plasma
generation, e.g., 100 MHz, to the lower electrode, i.e., the
susceptor 12. A shower head 38 to be described later, serving as an
upper electrode of a ground potential, is provided in a ceiling
portion of the chamber 10. With this configuration, the first RF
power from the first RF power supply 32 is capacitively applied
between the susceptor 12 and the shower head 38.
[0039] Moreover, a second RF power supply 70 is electrically
connected to the susceptor 12 via a second matching unit 72 and the
power feed rod 36. The second RF power supply 70 outputs a second
RF power having a relatively low frequency appropriate for ion
attraction, e.g., 3.2 MHz.
[0040] An electrostatic chuck 40 for attracting and holding the
semiconductor wafer W by an electrostatic attractive force is
provided on the top surface of the susceptor 12. The electrostatic
chuck 40 is formed by embedding an electrode made of a sheet or
mesh-like conductive material in an insulating film. This electrode
is electrically connected with a DC power supply 42 via a switch 43
and an electric wire. By a Coulomb force generated by a DC voltage
from the DC power supply 42, the semiconductor wafer W can be
attracted to be held by the electrostatic chuck 40.
[0041] Installed in the susceptor 12 is a coolant chamber 44
extended in, e.g., a circumferential direction. In the coolant
chamber 44, a coolant of a predetermined temperature, e.g., cooling
water, from a chiller unit 46 is circulated via lines 48 and 50. A
process temperature of the semiconductor wafer W on the
electrostatic chuck 40 can be controlled based on the temperature
of the coolant. Further, a heat transfer gas, e.g., He gas, from a
heat transfer gas supply unit 52 is supplied between the top
surface of the electrostatic chuck 40 and the backside of the
semiconductor wafer W via a gas supply line 54.
[0042] The shower head 38 on the ceiling portion includes an
electrode plate 56 having a plurality of gas injection holes 56a in
the bottom surface and an electrode support 58 for detachably
supporting the electrode plate 56. A buffer chamber 60 is provided
within the electrode support 58, and a gas supply line 64 extending
from a processing gas supplying unit 62 is connected to a gas inlet
port 60a of the buffer chamber 60.
[0043] Two ring magnets 66a and 66b annularly or concentrically
extending are disposed around the chamber 10 and magnetic fields
are generated at a peripheral region of a processing space PS
between the susceptor 12 and the upper electrode 38. These ring
magnets 66a and 66b are arranged to be rotated by a rotation
mechanism (not shown).
[0044] A controller 68 is provided to control operation of each
unit in the plasma etching apparatus such as the gas exhaust unit
28, the first RF power supply 32, the first matching unit 34, the
switch 43 for the electrostatic chuck, the chiller unit 46, the
heat transfer gas supply unit 52, the processing gas supplying unit
62, the second RF power supply 70, the second matching unit 72 and
the like. In addition, the controller 68 is connected to a host
computer (not shown) and the like.
[0045] To carry out an etching process in the plasma etching
apparatus, first, the gate valve 30 is opened. Next, the
semiconductor wafer W to be processed is loaded into the chamber 10
to be mounted on the electrostatic chuck 40. Thereafter, an etching
gas (generally a gaseous mixture) is introduced at a predetermined
flow rate from the processing gas supplying unit 62 into the
chamber 10 and the internal pressure of the chamber 10 is set to a
preset value by the gas exhaust unit 28. Moreover, the first RF
power is supplied with a predetermined power from the first RF
power supply 32 to the susceptor 12 while the second RF power is
supplied with a predetermined power from the second RF power supply
70 to the susceptor 12. Further, a DC voltage is applied from the
DC power supply 42 to the electrode of the electrostatic chuck 40,
thus attracting and holding the semiconductor wafer W on the
electrostatic chuck 40. The etching gas injected through the shower
head 38 is converted to a plasma between both electrodes 12 and 38
by the first RF discharge, and the main surface of the
semiconductor wafer W is etched into a desired pattern by radicals
or ions generated by the plasma.
[0046] In the plasma etching apparatus, by applying the first RF
power having a radio frequency (preferably 80 MHz or higher)
significantly higher than that applied in the conventional
techniques from the first RF power supply 32 to the susceptor
(lower electrode) 12, a high-density plasma in a desirable
dissociated state can be generated even at a lower pressure. At the
same time, by applying the second RF power having a relatively low
frequency (e.g., 3.2 MHz) appropriate for ion attracting to the
susceptor 12, an anisotropic etching with high selectivity for a
film to be processed on a semiconductor wafer W can be performed.
While the first RF power for plasma generation is always used in
all plasma processes, the second RF power for ion attraction may or
may not be used depending on a process.
[0047] The main feature of this capacitively coupled plasma etching
apparatus lies in the configuration that the electrically
conductive RF ground member 18 covers the side surface and the top
periphery portion of the susceptor 12 via the dielectric material
16, as shown in an enlarged partial view in FIG. 2.
[0048] Now, operation and function of the RF ground member 18 will
be described with reference to FIG. 3. The ion attraction by the
second RF power has no particular relation to the operation of the
RF ground member 18, and therefore, the second RF power supply 70
is not shown in FIG. 3.
[0049] In FIG. 3, the first RF power outputted from the first RF
power supply 32 is transmitted to the bottom center of the
susceptor 12 through a surface layer of the circumferential surface
of the power feed rod 36 to propagate outwardly in radial
directions along a surface layer of the bottom surface of the
susceptor therefrom, and reaches to the top surface of the
susceptor by flowing through the outer circumferential surface
(side surface) of the susceptor. At the top surface of the
susceptor 12, the first RF power goes out of the semiconductor
wafer W and is emitted into the processing space PS while
propagating inwardly in the inverse radial directions from the top
periphery portion to the central portion of the top surface
(hereinafter, referred to as "top central portion") of the
susceptor. The first RF power emitted into the processing space PS
collides with molecules of the processing gas, thereby ionizing or
dissociating the gas molecules. Here, if the frequency of the first
RF power exceeds about 80 MHz, a percentage of the first RF power
escaping through the outer circumferential surface (side surface)
or the top periphery portion of the susceptor 12 before the first
RF power reaches to a portion below the semiconductor wafer W,
i.e., the top surface of the susceptor 12 is measurably
increased.
[0050] In the present embodiment, the RF', the part of the first RF
power escaping through the outer circumferential surface (side
surface) or the top periphery portion of the susceptor 12, enters
into the RF ground member 18 immediately after escaping from the
dielectric material 16, propagates to the bottom wall of the
chamber 10 along a surface layer of the inner side of the RF ground
member 18, and then flows into a ground line therefrom.
[0051] Therefore, among the first RF power supplied to the
susceptor 12, only the power emitted from the top surface of the
susceptor 12 into the processing space PS through the semiconductor
wafer W contributes effectively to the ionization or dissociation
of the processing gas, i.e., the plasma generation, and a region
for plasma generation in the processing space PS is ideally
confined to a region right above the semiconductor wafer W. In
other words, plasma generation in a region at an outer side in a
radial direction other than the region right above the
semiconductor wafer W in the processing space PS is extremely
limited, and any influence from adjacent regions on the plasma
density distribution of the region right above the wafer is
suppressed. Accordingly, the plasma density distribution on the
semiconductor wafer W mounted on the susceptor 12 can hardly have a
W-like profile in which the plasma density distribution is
increased at its edge portion as well as its central portion and is
sunk at the portion therebetween.
[0052] Further, another feature of the capacitively coupled plasma
etching apparatus to improve a plasma density distribution
characteristic is a plurality of plate-like fin members 25 each
having vertical flat surfaces. The fin members 25 are seamlessly
molded as a single unit with or attached to the baffle plate 22
disposed near the entrance of the gas exhaust path 20. As shown in
FIG. 4, the fin members 25 are radially disposed at regular
intervals in the circumferential direction of the baffle plate 22.
Moreover, vent holes 22a are formed in the bottom wall of the
baffle plate 22. Each of the fin members 25 and the baffle plate 22
is made of an electrically conductive material, e.g., aluminum
whose surface is covered by an anodic oxide film or an insulating
film 23 (see FIG. 2, illustration of the insulating film 23 in
other figures is omitted) such as Y.sub.2O.sub.3 and is
electrically grounded via the chamber 10 or the RF ground member
18.
[0053] The fin members 25 have no effect on inherent functions
(vacuum exhaust stabilization function and processing space
pressure control function) of the baffle plate 22 and have a
function to promote extinction of plasma being diffused from the
processing space PS to the gas exhaust path 20. This plasma
extinction promotion function of the fin members 25 may reduce the
amount of the plasma existing near or above the entrance of the gas
exhaust path 20, thereby relatively increasing the plasma density
of a region right above the wafer while reducing altitude
differences in a mountain-like profile.
[0054] FIGS. 6A to 6C show an example of an in-plane distribution
characteristic of an etching rate obtained in the etching process
using the plasma etching apparatus shown in FIG. 1 in accordance
with the embodiment. The main etching conditions are as
follows:
[0055] Wafer diameter: 300 mm
[0056] Film to be etched: photoresist (blanket film)
[0057] Processing gas: O.sub.2 100 sccm
[0058] Internal pressure of chamber: 5 mTorr
[0059] RF power: 100 MHz/3.2 MHz=500 to 2000/0 W
[0060] Temperature: upper electrode/sidewall of chamber/lower
electrode=60/60/20.degree. C.
[0061] Heat transfer gas (He gas) supply pressure: central
portion/edge portion=10/50 Torr
[0062] FIGS. 7A to 7C show a comparative example of an in-plane
distribution characteristic of an etching rate under the same
etching conditions as the above for a configuration having neither
RF ground member 18 nor fin members 25 in the plasma etching
apparatus shown in FIG. 1, that is, the configuration of
surrounding of the susceptor 12, as shown in FIG. 5.
[0063] In FIG. 5, a dielectric material 16' covers the top
periphery portion of the susceptor 12 and is exposed to oppositely
face the upper electrode 38, the ceiling or inner wall of the
chamber 10. A focus ring 80 made of, e.g., Si, SiC or the like is
mounted on the dielectric material 16' so as to surround a wafer
mount region on the top surface of the susceptor 12. A grounded
cylindrical conductor 82 covering a side surface of the dielectric
material 16' forms a wall of the gas exhaust path 20, but does not
cover the top of the susceptor 12 and the dielectric material
16'.
[0064] When the RF ground member 18 and the fin members 25 are not
provided, as shown in FIGS. 7A to 7C, in-plane uniformity of an
etching rate is significantly deteriorated from .+-.28.8% to
.+-.39.6% and .+-.46.5% respectively as the first RF (100 MHz)
power for plasma generation is increased from 500 W to 1000 W and
2000 W. On the other hand, an etching rate distribution for a low
power level of 500 W is increased in an edge portion as well as a
central portion on the substrate so that the etching rate
distribution in a middle portion between the edge and central
portion is sunk. Therefore, a W-like profile is produced.
[0065] On the contrary, in the present embodiment, as shown in
FIGS. 6A to 6C, even when the first RF (100 MHz) power is increased
from 500 W to 1000 W and 2000 W, the in-plane uniformity of the
etching rate is stable with no significant change, changing from
.+-.15.8% to .+-.20.7% and .+-.20.1%, respectively. Further, a
mountain-like profile is constantly produced in any power level
even though each has a different altitude, and a W-like profile is
not produced.
[0066] Since an etching rate of a photoresist generally depends on
electron density, the etching rate distribution characteristics
shown in FIGS. 6A to 6C and FIGS. 7A to 7C may be evaluated by
substituting them with electron density distribution
characteristics.
[0067] As described above, in accordance with the present
invention, even when the RF power for plasma generation has a
substantially high frequency (80 MHz or above), it is possible to
stabilize the in-plane uniformity of the electron density
distribution in a wide RF power range while preventing an irregular
change of an electron density distribution profile (particularly
generation of a W-like electron density distribution profile).
Accordingly, the in-plane uniformity of the plasma etching can be
improved.
[0068] Further, since the electron density distribution has the
mountain-like profile in any RF power level in the plasma etching
apparatus of the above-described embodiment, a configuration in
which a dielectric material 84 is embedded at the top surface of
the susceptor 13 as shown in FIG. 8 may be preferably used to
flatten the mountain-like profile. In this case, the dielectric
material 84 may be prepared such that it has the largest thickness
at the center of the susceptor 12 and is gradually getting thinner
from the center (or from a point off the center) toward an edge
portion of the susceptor 12.
[0069] To the same purpose, a dielectric material 86 may be
embedded at the bottom of the upper electrode 38 as shown in FIG.
9. In this case, similarly, the dielectric material 86 may be
prepared such that it has the largest thickness at the center of
the susceptor 12 and is gradually getting thinner from the center
(or from a point off the center) toward an edge portion of the
susceptor 12.
[0070] Although the embodiment of the present invention has been
illustrated in the above, the present invention is not limited to
the above embodiment, and may be variously modified. Particularly,
various selections and modifications for the RF ground member 18
and the fin members 25 may be made such that they are optimally
combined with other mechanisms in the apparatus.
[0071] For example, as shown in FIG. 9, an appropriate gap may be
prepared between an edge portion of the semiconductor wafer W and
the RF ground member 18 on the top surface of the susceptor 12 and
a cover 88 made of an appropriate material (e.g., Si, SiC or the
like) is provided in the gap in an electrically floating state. In
this case, the RF power is emitted from the top surface of the
susceptor 12 into the processing space PS through the dielectric
material 16 and the cover 88, and plasma is also generated in a
region above the cover 88. Further, the baffle plate 22 may be
configured to have other shape than the conical shape, e.g., a flat
annular shape having a main surface horizontally oriented, and the
upper surfaces of the fin members 25 may be configured to be tilted
as shown in FIG. 9. Further, although not shown, the fin members 25
may be configured to be separated from the baffle plate 22.
[0072] Further, as shown in FIG. 10, the upper surface of the RF
ground member 18 may be covered by a cover 90.
[0073] Moreover, the present invention is not limited to lower
electrode dual frequency application type as in the above
embodiment but may be, e.g., applied to a lower electrode single
frequency application type in which a single RF power is applied to
the susceptor (lower electrode) or a type in which an RF power for
plasma generation is applied to the upper electrode.
[0074] Further, although not shown, in an apparatus in which the RF
power for plasma generation is applied to the upper electrode, an
RF ground member having the same configuration and function as the
RF ground member 18 described in the above embodiment may be
provided in the peripheral region of the upper electrode. By
providing the RF ground member covering a side surface and a
periphery portion of a bottom surface of the upper electrode, even
when a part of the RF power applied to the upper electrode is
emitted or leaked outwardly in radial directions at the side
surface and the periphery portion of the bottom surface of the
upper electrode, the RF ground member can receive the leaked RF
power and send it to the ground line such that a plasma generation
region in the processing space can be confined to a region right
above and near a substrate to be processed.
[0075] The present invention is not limited to a plasma etching
apparatus but may be applied to other plasma processing apparatuses
for performing plasma CVD, plasma oxidation, plasma nitridation,
sputtering and the like. Furthermore, the substrate to be processed
in the present invention is not limited to the semiconductor wafer
but may be various substrates for flat panel displays, photo masks,
CD substrates, printed substrates and so forth.
[0076] While the invention has been shown and described with
respect to the embodiments, it will be understood by those skilled
in the art that various changes and modification may be made
without departing from the scope of the invention as defined in the
following claims.
* * * * *