U.S. patent application number 11/984972 was filed with the patent office on 2008-04-10 for method of plasma processing.
This patent application is currently assigned to KAWASAKI MICROELECTRONICS, INC. Invention is credited to Hiroyoshi Aoki, Satoru Hiraoka, Koji Mori, Takayuki Shimizu, Katsunori Suzuki.
Application Number | 20080083703 11/984972 |
Document ID | / |
Family ID | 34879694 |
Filed Date | 2008-04-10 |
United States Patent
Application |
20080083703 |
Kind Code |
A1 |
Suzuki; Katsunori ; et
al. |
April 10, 2008 |
Method of plasma processing
Abstract
Plasma processing apparatus and plasma processing methods
capable of maintaining etching characteristics and to prevent
degradation of a lower electrode even when the focus ring is
severely eroded by the plasma are disclosed. According to an
exemplary embodiment, a side-surface protecting ring formed of a
ceramic material having an erosion rate by the plasma lower than an
erosion rate of the material of the focus ring is provided to cover
the side surface of the lower electrode. As a result, it becomes
possible to prevent the side surface of the lower electrode from
being exposed to the plasma and maintain the etching
characteristics even after the focus ring is severely eroded.
Further, degradation of the lower electrode is decreased.
Inventors: |
Suzuki; Katsunori;
(Mihama-ku, JP) ; Shimizu; Takayuki; (Mihama-ku,
JP) ; Aoki; Hiroyoshi; (Mihama-ku, JP) ; Mori;
Koji; (Mihama-ku, JP) ; Hiraoka; Satoru;
(Mihama-ku, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 320850
ALEXANDRIA
VA
22320-4850
US
|
Assignee: |
KAWASAKI MICROELECTRONICS,
INC
Mihama-ku
JP
261-8501
|
Family ID: |
34879694 |
Appl. No.: |
11/984972 |
Filed: |
November 26, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11057164 |
Feb 15, 2005 |
|
|
|
11984972 |
Nov 26, 2007 |
|
|
|
Current U.S.
Class: |
216/67 |
Current CPC
Class: |
H01J 37/32642 20130101;
H01L 21/67069 20130101 |
Class at
Publication: |
216/067 |
International
Class: |
C23F 1/00 20060101
C23F001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 2004 |
JP |
2004-053275 |
Claims
1. A method of processing a substrate using a plasma, comprising:
providing a lower electrode in a processing chamber, the lower
electrode having a supporting surface for supporting the substrate
and a side surface connected to an outer perimeter of the
supporting surface, the supporting surface having a size
approximately the same as, or smaller than, a size of the
substrate; supporting the substrate on the supporting surface;
covering the side surface of the lower electrode by a side surface
protecting ring formed of a ceramic material; positioning an outer
perimeter of the most outside part of the side surface protecting
ring inside an outer perimeter of the substrate supported on the
supporting surface; surrounding the side surface of the lower
electrode, which is covered by the side surface protecting ring, by
a focus ring formed of a first material different from the ceramic
material; and processing a surface of the substrate by generating a
plasma in the processing chamber, the processing including:
preventing, by the side surface protecting ring, the plasma from
touching the side surface of the lower electrode; and preventing,
by the substrate supported on the supporting surface, charged
particles in the plasma accelerated toward a direction
perpendicular to the surface of the substrate from irradiating the
side surface protecting ring.
2. The method according to claim 1, wherein: the focus ring
prevents the plasma from touching the side surface protecting ring
before the focus ring is eroded by the plasma; and the side surface
protecting ring prevents the plasma from touching the side surface
of the lower electrode even after the focus ring is eroded by the
plasma to an extent that the focus ring cannot prevent the plasma
from touching the side surface of the lower electrode.
3. The method according to claim 1, wherein the ceramic material
has a different secondary electron emission coefficient than that
of the first material.
4. The method according to claim 1, wherein the side surface
protecting ring is prevented by the substrate from being irradiated
by the charged particles in the plasma accelerated toward the
direction perpendicular to the surface of the substrate, even after
the focus ring is eroded.
5. The method according to claim 1, wherein said covering includes
fitting the side surface protecting ring, which is prepared
separately from the lower electrode, to the side surface of the
lower electrode.
6. The method according to claim 1, wherein: the ceramic material
is selected from the group consisting of alumina, aluminum nitride,
silicon carbide, silicon nitride, zirconia, titanium nitride, YAG,
alumina-silicate solid solution, and alumina-silicon nitride solid
solution; and the first material is selected from a group
consisting of quartz, silicon, and engineering plastics.
7. The method according to claim 1, wherein the ceramic material is
alumina and the first material is quartz.
8. A method of processing a substrate using a plasma, comprising:
providing a lower electrode in a processing chamber, the lower
electrode having a supporting surface for supporting the substrate
and a side surface connected to an outer perimeter of the
supporting surface, the supporting surface having a size smaller
than a size of the substrate; supporting the substrate on the
supporting surface; covering the side surface of the lower
electrode by a side surface protecting ring formed of a ceramic
material; positioning an outer perimeter of the most outside part
of the side surface protecting ring inside an outer perimeter of
the substrate supported on the supporting surface; surrounding the
side surface of the lower electrode, which is covered by the side
surface protecting ring, by a focus ring formed of quartz;
processing a surface of the substrate by generating a plasma in the
processing chamber, the processing including: preventing, by the
side surface protecting ring, the plasma from touching the side
surface of the lower electrode; and preventing, by the substrate
supported on the supporting surface, charged particles in the
plasma accelerated toward a direction perpendicular to the surface
of the substrate from irradiating the side surface protecting
ring.
9. The method according to claim 8, wherein the ceramic material is
selected from a group consisting of alumina, aluminum nitride,
silicon carbide, silicon nitride, zirconia, titanium nitride, YAG,
alumina-silicate solid solution, and alumina-silicon nitride solid
solution.
10. The method according to claim 8, wherein the ceramic material
is alumina.
11. The method according to claim 8, wherein said covering includes
fitting the side surface protecting ring, which is prepared
separately from the lower electrode, to the side surface of the
lower electrode.
Description
[0001] This is a Division of application Ser. No. 11/057,164 filed
Feb. 15, 2005. The entire disclosure of the prior applications is
hereby incorporated by reference herein in its entirety. This
invention is first described in a Japanese Application No.
2004-53275, which is incorporated by reference in its entirety.
BACKGROUND
[0002] This invention relates to a plasma processing apparatus for
processing a surface of a substrate using plasma and also relates
to methods of plasma processing a surface of a substrate.
[0003] Plasma processing techniques, such as, for example, dry
etching techniques, have been widely used for manufacturing
semiconductor devices such as semiconductor integrated circuits.
The plasma processing processes various films formed on a surface
of a substrate to be processed, such as a semiconductor wafer,
using reactive gases activated by plasma. The dry etching, for
example, etches various films and forms fine circuit patterns such
as electrode and wiring patterns using resist patterns formed by
the lithography as masks.
[0004] In any application of the plasma processing, it is
inevitable that the reactive gas activated by the plasma touches
and erodes components within the processing chamber. Especially,
the processing of silicon oxide films requires high radio frequency
power, because the bonding energy of Si--O bonds is high.
Accordingly, the processing of silicon oxide films causes severe
damage to the components.
[0005] In general, so-called parallel-plate RIE (Reactive Ion
Etching) apparatus is mainly used as the dry etching apparatus for
processing silicon oxide films. In the parallel-plate RIE
apparatus, radio-frequency power is applied to an upper and a lower
electrode that face in parallel with each other. In such an
apparatus, usually, the wafer to be processed is placed on the
lower electrode and the plasma is concentrated between the
electrodes to process the surface of the wafer.
[0006] In order to concentrate the plasma between the electrodes,
peripheries of the upper and the lower electrodes are surrounded by
ring-shaped components formed of, for example, quartz. Hereafter,
the ring-shaped components that surrounds the upper electrode will
be called "shield ring", while the ring-shaped component that
surround the lower electrode will be called "focus ring".
[0007] Moreover, in order to improve processing accuracy, an
electro-static chuck has been widely employed as the means to hold
the wafer on the wafer-supporting surface of the plasma processing
apparatus. Compared with a mechanical chuck, the electro-static
chuck improves the uniformity of the surface temperature of the
wafer and improves the uniformity of the processing.
[0008] Electro-static chucks are generally classified into two
types. One is formed of fluorocarbon resin, and the other is formed
of ceramics. The dry etching apparatus for processing silicon oxide
films mainly utilize the electro-static chuck formed of
fluorocarbon resin, in which a conductive film is inserted into a
fluorocarbon resin film. A high DC voltage is applied to the
conductive film, and the wafer is chucked onto the upper surface of
the electro-static chuck by the Coulomb force generated between the
wafer and the conductive film.
[0009] FIG. 10 is a partial cross-sectional view showing the
periphery of the lower electrode of a plasma processing apparatus.
As shown in FIG. 10, the upper surface 118a of the lower electrode
118 has an electro-static chuck 120, which is formed of, for
example, a fluorocarbon resin film 120a and a conductive film 120b
inserted within the resin film 120a. The fluorocarbon resin film
120a also covers the side surface 118b of the lower electrode
118.
[0010] A focus ring 124 is detachably placed so as to surround the
periphery of the lower electrode 118. The height of the upper
surface 124b of the focus ring 124 generally matches the height of
the upper surface 118a of the lower electrode 118. The wafer W to
be processed is placed on the upper surface, or the
wafer-supporting surface, 118a of the lower electrode 118 and is
chucked by the electro-static chuck 120.
[0011] In the dry etching apparatus for processing silicon oxide
films described above, a component that is generally most severely
damaged by the plasma is the focus ring 124 that surrounds the
lower electrode 118. When the focus ring is continuously used in
the processing apparatus, it gradually erodes. The erosion
generally proceeds in the vertical direction, mainly at the stepped
region 124a near the inner perimeter of the focus ring 124, and a
groove is formed. In other words, the erosion proceeds mainly at
the area near the outer perimeter of the wafer W.
[0012] When the erosion reaches the extent shown in FIG. 11, the
side surface of the lower electrode 118b becomes exposed to the
plasma. Thereafter, the plasma may influence the temperature of the
wafer W chucked by the electro-static chuck 120 onto the supporting
surface 118a of the lower electrode 118.
[0013] As discussed above, the control of the wafer temperature is
crucial for etching fine patterns. However, as discussed above, the
amount of plasma radiation to the lower electrode 118 increases as
the erosion of the focus ring 124 increases. The increased plasma
radiation increases the surface temperature of the wafer W,
especially at the region near the edge. As a result, it becomes
difficult to maintain an acceptable uniformity of etching.
[0014] Moreover, exposure of the lower electrode 118 to the plasma
accelerates the degradation and shortens the usable life of the
lower electrode 118. The lower electrode 118, to which the
electrostatic chuck 120 is attached, is one of the most expensive
components in the dry etching apparatus. Therefore, the shortened
life of the lower electrode 118 markedly increases the operation
cost of the apparatus.
[0015] As such, the erosion of the focus ring 124 causes two
problems, change of the etching characteristics, and rapid
degradation of the lower electrode 118. Therefore, the focus ring
124 is generally replaced or repaired at short intervals before it
becomes severely damaged. As a result, the replacement and/or
repair of the focus ring has to be made frequently, and the
throughput and the cost of production of semiconductor devices by
the processing apparatus are thus adversely affected.
[0016] In regards to the focus ring that is eroded by the plasma,
various improvements have been proposed in, for example, the
following references:
[0017] Japanese Laid-open Patent No. 2003-100713 (Patent Document
1) discloses an electrode cover which is divided into an inner
portion and an outer portion. The inner portion, which is further
divided into a plurality of sections in the circumferential
direction, surrounds the side surface of the lower electrode. The
outer portion is attached to the outside of the inner portion.
Thereby, a plurality of sections and portions are combined to form
a cover, or a focus ring, having an inner periphery that surrounds
closely the side surface of the lower electrode.
[0018] Japanese Laid-open Patent No. 8-339895 (Patent Document 2)
discloses a quartz component, or a focus ring, coated with an
insulating film having a high resistance to the erosion by the
plasma.
[0019] The focus ring disclosed in Patent Document 1 aims to
minimize the clearance between the lower electrode and the focus
ring, but does not suppress the erosion of the focus ring.
[0020] In the quartz component disclosed in Patent Document 2, the
insulating film having a high erosion resistance is coated on the
surface of a quartz component, which is designed to have a shape
suitable to be used in a processing apparatus. Therefore, the
thickness of the resistive coating film is limited so that the
coating film does not materially change the shape of the component.
Therefore, the ability to improve the erosion resistance is
limited.
SUMMARY
[0021] Accordingly, in order to solve the above-mentioned problems,
an exemplary object of this invention is to provide a processing
apparatus and methods of plasma processing to maintain acceptable
etching characteristics, even when the focus ring is severely
eroded by the plasma. Another exemplary object of this invention is
to provide an apparatus and methods that diminish the degradation
of the lower electrode even when the focus ring is severely eroded.
Another exemplary object of this invention is to provide an
apparatus and methods to leave the plasma discharge conditions used
in the conventional apparatus and methods substantially unchanged,
while maintaining acceptable etching characteristics, even when the
focus ring is severely eroded. In order to solve the
above-mentioned problems, various exemplary embodiments according
to this invention provide an exemplary plasma processing apparatus
for processing a substrate using plasma. The exemplary apparatus
includes a lower electrode comprising a supporting surface for
supporting the substrate and a side surface connected to an outer
perimeter of the supporting surface, a side surface protecting ring
that covers the side surface of the lower electrode, and a focus
ring that surrounds the side surface of the lower electrode covered
by the side surface protecting ring. The supporting surface may
have a dimension approximately the same as, or smaller than, that
of the substrate. The side surface protecting ring may be formed of
a ceramic material, and an outer perimeter of the side surface
protecting ring may be approximately aligned with, or inside of, an
outer perimeter of the substrate supported on the supporting
surface. The focus ring is formed of a first material, and the
ceramic material has an erosion rate by the plasma lower than that
of the first material.
[0022] In the exemplary apparatus, an outer perimeter of the side
surface protecting ring may be positioned inside of an outer
perimeter of the substrate supported on the supporting surface.
[0023] In order to solve the above-mentioned problems, various
exemplary embodiments according to this invention provide an
exemplary plasma processing apparatus for processing a substrate
using plasma. The exemplary apparatus includes a lower electrode
comprising a supporting surface for supporting the substrate and a
side surface connected to an outer perimeter of the supporting
surface, a side surface protecting ring that covers the side
surface of the lower electrode, and a focus ring that surrounds the
side surface of the lower electrode covered by the side surface
protecting ring. The supporting surface may have a dimension
approximately the same as, or smaller than, that of the substrate.
The side surface protecting ring may be formed of a ceramic
material selected from a group consisting of alumina, aluminum
nitride, silicon carbide, silicon nitride, zirconia, titanium
nitride, YAG, alumina-silicate solid solution, and alumina-silicon
nitride solid solution, and an outer perimeter of the side surface
protecting ring may be approximately aligned with, or inside of, an
outer perimeter of the substrate supported on the supporting
surface. The focus ring may be formed of a first material selected
from a group consisting of quartz, silicon, and engineering
plastics.
[0024] In order to solve the above-mentioned problems, various
exemplary embodiments according to this invention provide an
exemplary plasma processing apparatus for processing a substrate
using plasma. The exemplary apparatus includes a lower electrode
comprising a supporting surface for supporting the substrate and a
side surface connected to an outer perimeter of the supporting
surface, a side surface protecting ring that covers the side
surface of the lower electrode, and a focus ring that surrounds the
side surface of the lower electrode covered by the side surface
protecting ring. The supporting surface may have a dimension
approximately the same as, or smaller than, that of the substrate.
The side surface protecting ring may be formed of a ceramic
material, and an outer perimeter of the side surface protecting
ring may be positioned inside of an outer perimeter of the
substrate supported on the supporting surface. The focus ring is
formed of a first material different from the ceramic material.
[0025] In order to solve the above-mentioned problems, various
exemplary embodiments according to this invention provide an
exemplary plasma processing method of processing a substrate using
plasma. The exemplary method includes providing a lower electrode
in a processing chamber, the lower electrode having a supporting
surface and a side surface connected to an outer perimeter of the
supporting surface, covering the side surface of the lower
electrode by a side surface protecting ring formed of a ceramic
material, and surrounding the side surface of the lower electrode,
which is covered by the side surface protecting ring, by a focus
ring formed of a first material. The supporting surface may have a
dimension approximately the same as, or smaller than, that of the
substrate, and the ceramic material may have an erosion rate by the
plasma lower than that of the first material. The exemplary method
further includes supporting the substrate on the supporting
surface, and processing a surface of the substrate by generating
plasma in the processing chamber. Processing the surface includes
i) preventing, by the side surface protecting ring, the plasma from
touching the side surface of the lower electrode, and ii)
preventing, by the substrate supported on the supporting surface,
charged particles in the plasma accelerated toward a direction
perpendicular to the surface of the substrate from irradiating the
side surface protecting ring.
[0026] In the exemplary method, the focus ring may prevent the
plasma from touching the side surface protecting ring before the
focus ring is eroded by the plasma; and the side surface protecting
ring may prevent the plasma from touching the side surface of the
lower electrode even after the focus ring is eroded by the plasma
to an extent that the focus ring cannot prevent the plasma from
touching the side surface of the lower electrode.
[0027] Furthermore, in the exemplary method, the covering may
include positioning an outer perimeter of the side surface
protecting ring inside of an outer perimeter of the substrate
supported on the supporting surface.
[0028] In order to solve the above-mentioned problems, various
exemplary embodiments according to this invention provide an
exemplary plasma processing method of processing a substrate using
plasma. The exemplary method includes providing a lower electrode
in a processing chamber, the lower electrode having a supporting
surface and a side surface connected to an outer perimeter of the
supporting surface, covering the side surface of the lower
electrode by a side surface protecting ring formed of a ceramic
material selected from the group consisting of alumina, aluminum
nitride, silicon carbide, silicon nitride, zirconia, titanium
nitride, YAG, alumina-silicate solid solution, and alumina-silicon
nitride solid solution, and surrounding the side surface of the
lower electrode, which is covered by the side surface protecting
ring, by a focus ring formed of a first material selected from a
group consisting of quartz, silicon, and engineering plastics. The
supporting surface may have a dimension approximately the same as,
or smaller than, that of the substrate. The exemplary method
further includes supporting the substrate on the supporting
surface, and processing a surface of the substrate by generating
plasma in the processing chamber. The processing includes i)
preventing, by the side surface protecting ring, the plasma from
touching the side surface of the lower electrode, and ii)
preventing, by the substrate supported on the supporting surface,
charged particles in the plasma accelerated toward a direction
perpendicular to the surface of the substrate from irradiating the
side surface protecting ring.
[0029] In order to solve the above-mentioned problems, various
exemplary embodiments according to this invention provide an
exemplary plasma processing method of processing a substrate using
plasma. The exemplary method includes providing a lower electrode
in a processing chamber, the lower electrode having a supporting
surface and a side surface connected to an outer perimeter of the
supporting surface, covering the side surface of the lower
electrode by a side surface protecting ring formed of a ceramic
material, and surrounding the side surface of the lower electrode,
which is covered by the side surface protecting ring, by a focus
ring formed of a first material different from the ceramic
material. The supporting surface has a dimension approximately the
same as, or smaller than, that of the substrate. The exemplary
method may further include supporting the substrate on the
supporting surface, and processing a surface of the substrate by
generating plasma in the processing chamber. The processing
includes i) preventing, by the side surface protecting ring, the
plasma from touching the side surface of the lower electrode, and
ii) preventing, by the substrate supported on the supporting
surface, charged particles in the plasma accelerated toward a
direction perpendicular to the surface of the substrate from
irradiating the side surface protecting ring.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a schematic drawing of an exemplary plasma
processing apparatus according to an exemplary embodiment of this
invention;
[0031] FIG. 2 is a magnified view showing the relationship between
the focus ring and the lower electrode, to which the ceramic ring
is fitted, in the plasma processing apparatus shown in FIG. 1;
[0032] FIG. 3 is a curve illustrating a relationship between the
amount of erosion of the focus ring and the cumulative RF discharge
time of the focus ring in a conventional plasma processing
apparatus;
[0033] FIG. 4 is a curve illustrating a relationship between the
temperature near the edge of a wafer and the cumulative RF
discharge time of the focus ring in a conventional plasma
processing apparatus;
[0034] FIG. 5 is a cross-sectional view showing the structure of a
wafer W processed in an exemplary plasma processing apparatus;
[0035] FIG. 6 is a curve illustrating a relationship between the
etching rate of silicon dioxide film near the edge of the wafer and
the cumulative RF discharge time of the focus ring in a
conventional plasma processing apparatus;
[0036] FIG. 7 is a curve illustrating a relationship between the
etching rate of silicon dioxide film near the edge of the wafer and
the cumulative RF discharge time of the focus ring in an exemplary
plasma processing apparatus according to this invention;
[0037] FIG. 8 is a curve illustrating a relationship between the
silicon dioxide etching rate near the edge of the wafer and the
cumulative RF discharge time of two focus rings used alternately in
the exemplary plasma processing apparatus according to this
invention;
[0038] FIG. 9 is a curve illustrating a relationship between the
amount of erosion of the ceramic ring and the cumulative RF
discharge time of the ceramic ring;
[0039] FIG. 10 is a magnified view showing the relationship between
an uneroded focus ring and the lower electrode in a conventional
plasma processing apparatus; and
[0040] FIG. 11 is a magnified view showing the relationship between
an eroded focus ring and the lower electrode in a conventional
plasma processing apparatus.
DETAILED DESCRIPTION OF EMBODIMENTS
[0041] An exemplary plasma processing apparatus and plasma
processing methods according to this invention are explained in
detail with reference to various exemplary embodiments shown in the
drawings.
[0042] FIG. 1 is a schematic drawing of an exemplary plasma
processing apparatus according to this invention. As shown in FIG.
1, an exemplary plasma processing apparatus 10 is a dry etching
apparatus for manufacturing semiconductor devices. The apparatus 10
may have a narrow-gap parallel-plate construction and etches oxide
films such as silicon oxide films using high-frequency (radio
frequency) plasma.
[0043] The processing chamber 12 for accommodating a wafer W, which
is a substrate to be processed, can be evacuated to a pressure of,
for example, about 10.sup.-6 Torr (10.sup.-4 Pa). Various
components are provided within the chamber 12.
[0044] In the upper center of the chamber 12, an upper electrode
16, which is connected to a gas inlet 14 for introducing an etching
gas, is provided. In the lower center of the chamber 12, a lower
electrode 18 is provided.
[0045] According to various exemplary embodiments, the lower
electrode 18 is formed of alumite-coated aluminum. The upper
surface, a wafer-supporting surface 18a of the lower electrode 18,
has a dimension approximately the same as or is slightly smaller
than the dimension of the wafer W. The inside of the lower
electrode 18 has a circulation path for circulating coolant
supplied from the chiller (not shown), which is placed outside the
chamber 12. Thereby, the upper surface 18a of the lower electrode
18 can be maintained to a desired temperature.
[0046] According to various exemplary embodiments, on the upper
surface 18a of the lower electrode 18, an electro-static chuck 20
for chucking the wafer W is provided. The electro-static chuck 20
is formed of a fluorocarbon resin film in which a metal film is
inserted. The fluorocarbon resin film, forming the electro-static
chuck 20, also covers the side surface 18b of the lower electrode
18.
[0047] Applying a voltage to the metal film from a high voltage DC
power source (not shown), which is placed outside of the chamber
12, produces a Coulomb force between the metal film and the wafer
20. Thereby, the wafer W is chucked on the upper surface of the
electro-static chuck 20. That is, the wafer W is chucked on the
wafer-supporting surface 18a of the lower electrode 18 by the
electro-static chuck 20.
[0048] According to various exemplary embodiments, the lower
electrode 18 also has passages (not shown) to supply He gas.
Supplying He gas to the rear side of the wafer W chucked on the
electro-static chuck 20 improves the thermal conduction between the
wafer W and the lower electrode 18. The passages are divided into
two groups so that the pressures of He gas supplied to the central
portion and to the outer portion of the wafer W can be controlled
independently.
[0049] According to various exemplary embodiments, on the side
surface 18b of the lower electrode 18, a side-surface protecting
ring 30 formed of a ceramic material (which will be called as a
"ceramic ring" hereinafter) is placed. That is, the ceramic ring 30
covers the side surface 18b of the lower electrode 18, or, more
exactly, the fluorocarbon resin film 20a covering the side surface
18b of the lower electrode 18.
[0050] A shield ring 22 and a focus ring 24 may surround
peripheries of the upper electrode 16 and of the lower electrode
18, respectively. The shield ring 22 and the focus ring 24
concentrate the plasma between the parallel-plate electrodes. The
shield ring 22 and the focus ring 24 are detachable in order to
perform, for example, a mechanical cleaning.
[0051] According to various exemplary embodiments, a RF power
splitter 26 and a RF power source 28 are placed outside of the
chamber 12. The RF power source 28 supplies a high-frequency (radio
frequency) power to the RF power splitter 26, and the RF power
splitter 26 applies RF power to both the lower electrode 18 and the
upper electrode 16. Thus, RF plasma is generated within the chamber
12 and dry etching is performed.
[0052] The plasma processing apparatus 10 shown in FIG. 1 employs,
as an example, a split-coupling configuration by using the RF power
splitter 26. However, any one of the configurations including an
anode-coupling, a cathode-coupling, or a split-coupling
configurations may be selected.
[0053] FIG. 2 is a magnified view showing the relationship between
the lower electrode 18, to which the ceramic ring 30 is fitted, and
the focus ring 24.
[0054] According to various exemplary embodiments, the ceramic ring
30 has a ring shape, and is formed of a ceramic material having an
erosion rate by the plasma lower than that of the material forming
the focus ring 24.
[0055] According to various exemplary embodiments, the side surface
18b of the lower electrode 18 is covered with the fluorocarbon
resin film 20a that constitutes the electro-static chuck 20, and is
surrounded by the focus ring 24. The ceramic ring 30 is inserted
between the fluorocarbon resin film 20a covering the side surface
18b of the lower electrode 18 and the inner-side surface of the
focus ring 24. That is, the side surface 18b of the lower electrode
18 is covered by the fluorocarbon resin film 20a and further by the
ceramic ring 30, and then surrounded by the focus ring 24.
[0056] In the exemplary plasma processing apparatus 10 shown in
FIG. 2, the ceramic ring 30 has a thickness (a dimension
perpendicular to the side surface 18b of the lower electrode) such
that it is fitted inside the outer perimeter of the wafer W.
[0057] When the erosion of the focus ring 24 reaches a certain
extent, the ceramic ring 30 becomes directly exposed to the plasma.
Therefore, the ceramic ring 30 should preferably have a sufficient
thickness in order to improve the durability and the mechanical
strength.
[0058] However, if the ceramic ring 30 is too thick and extends
outwardly from the outer perimeter of the wafer W, charged
particles, which are accelerated toward a direction perpendicular
to the surface of the wafer W, may irradiate the surface of the
ceramic ring 30. As a result, the plasma characteristics may change
due to the difference between the secondary electron emission
coefficients of the ceramic ring 30 and the quartz focus ring 24.
Such change in the plasma characteristics changes the etching
characteristics. Thus, the etching condition should be adjusted
differently. Further, depending on the etching process, small
particles emitted from the ceramic ring may alter the electrical
characteristics of the semiconductor device processed by the
apparatus.
[0059] Thus, it may be preferable to make the dimension of the
wafer-supporting surface 18a of the lower electrode 18 smaller than
that of the wafer W, and position the outer surface of the ceramic
ring 30 approximately aligned with, or inside of, the outer
perimeter of the wafer W.
[0060] According to the various exemplary embodiments of this
invention, the fluorocarbon resin coating film 20a on the side
surface 18b of the lower electrode 18 may be omitted. The material
of the focus ring 24 is not limited to quartz. For example, silicon
may be used as the material to form the focus ring 24. Other kinds
of engineering plastics having high operation temperatures, which
are also called super engineering plastics, may also be used. For
example, Vespel.RTM. Polyimide from DuPont, and Celazole.RTM.
PolyBenzlmidazole from Celanese Advanced Materials may be used.
[0061] The material of the side-surface protecting ring 30 may
preferably be, for example, alumina, but is not limited to specific
materials among various ceramic materials. Other ceramic materials
such as aluminum nitride, silicon nitride, and silicon carbide may
also be used. Further, at least in processing apparatus for use in
BEOL (Back-end of the line) processes in the semiconductor device
production, zirconia, titanium nitride, and YGA
(Y.sub.3Al.sub.5O.sub.12) may also be used. Moreover, solid
solutions including one or more of these materials, such as solid
solutions of alumina and silicates, alumina and silicon nitride,
and the like, may also be used. These ceramic materials may also
contain various additives.
[0062] Generally, these ceramic materials have lower erosion rates
that those of the materials used for forming the focus ring 24,
although the ratios between erosion rates are different for
different combinations of materials. The ratio for a specific
combination also varies depending on various conditions such as the
etching gas and the plasma discharge condition.
[0063] According to various exemplary embodiments, in order to
perform etching using the plasma processing apparatus 10, after
evacuating the chamber 12 to a predetermined pressure, a
fluorocarbon-based etching gas is introduced from the gas inlet 14,
and an etching gas atmosphere with a predetermined pressure is
produced within the space between the electrodes 16 and 18. By
applying an RF power, through the RF power splitter 26, to the
electrodes 16 and 18 between which the etching gas atmosphere is
produced, fluorocarbon-based plasma is generated. As a result,
charged particles within the plasma are accelerated toward the
direction perpendicular to the surface of the wafer W placed on the
wafer-supporting surface 18a of the lower electrode 18, and the
surface of the wafer W becomes etched.
[0064] In the various exemplary embodiments according to this
invention, the side surface of the lower electrode 18 is protected
by a ceramic ring 30 formed of a material having a lower erosion
rate than that of the material of the focus ring 24. Therefore,
even after the focus ring 24 is severely eroded, the side surface
18b of the lower electrode 18 is not exposed to the plasma and is
not damaged. As a result, increase of the surface temperature near
the edge of the wafer W is diminished, and the etching
characteristics can be maintained.
[0065] Moreover, because the etching characteristics can be
maintained even after the focus ring is severely eroded, the
interval for replacing the focus ring 24 can be extended. As a
result, the costs incurred for the maintenance is reduced.
[0066] Furthermore, because the ceramic ring 30 protects the side
surface 18b of the lower electrode 18, the mechanical damage to the
fluorocarbon resin film covering the side surface 18b of the lower
electrode 18 during the attaching and detaching of the focus ring
34 is prevented.
[0067] In the exemplary plasma processing apparatus, before the
erosion of the focus ring proceeds, the wafer W and the focus ring
24 prevent the ceramic ring 30 and the side surface 18b of the
lower electrode 18 from being exposed to the plasma. After the
focus ring 24 is eroded to an extent that it cannot prevent the
ceramic ring 30 from being exposed to the plasma, the ceramic ring
30 then prevents the side surface 18b of the lower electrode 18
from being exposed to the plasma. In other words, after the focus
ring 24 is eroded to an extent that the focus ring 24 alone cannot
prevent the side surface 18b of the lower electrode 18 from being
exposed to the plasma, the ceramic ring 30 prevents the side
surface 18b of the lower electrode 18 being exposed to the
plasma.
[0068] Moreover, in the exemplary embodiment of the plasma
processing apparatus 10, the dimension of the wafer-supporting
surface 18a of the lower electrode 18 is made smaller than the
dimension of the wafer W, and the outer perimeter of the ceramic
ring 30 is positioned approximately aligned with, or inside, the
outer perimeter of the wafer W. Accordingly, it is possible to
prevent charged particles in the plasma accelerated to the
direction perpendicular to the surface of the wafer W from
irradiating the ceramic ring 30, even after the focus ring 24 is
eroded.
[0069] The exemplary plasma processing apparatus and plasma
processing methods according to this invention are not limited to
the embodiments described above. For example, the plasma processing
apparatus may be any type of plasma processing apparatus that
comprises an electrode having a substrate-supporting surface.
Further, the exemplary plasma processing apparatus according to
this invention is not limited to semiconductor manufacturing
apparatuses for processing surfaces of semiconductor substrates,
but may be various apparatuses for processing various other
substrates. Moreover, various reaction gases other than the
fluorocarbon-based gas may be used.
Comparative Example 1
[0070] In order to confirm the effect of the ceramic ring 30 in the
exemplary plasma processing apparatus 10, etching is performed
using a conventional plasma processing apparatus that does not have
a ceramic ring 30.
[0071] FIG. 3 is a curve illustrating a relationship between an
amount of erosion of the focus ring 124 of a conventional plasma
processing apparatus in the vertical direction, or in the direction
perpendicular to the surface of the wafer W supported on the
wafer-supporting surface 18a, and a cumulative RF discharge time of
the focus ring 124 (i.e., a cumulative time of RF discharge made
using the same focus ring 124).
[0072] FIG. 11 described above shows the shape of the focus ring
124 when the amount of erosion is about 1 mm. FIG. 3 indicates that
the focus ring 124 reaches this shape when the cumulative RF
discharge time reaches about 300 hours. It is found that the
desired etching characteristics cannot be maintained when the focus
ring 124 has the shape shown in FIG. 11.
[0073] At first, in order to investigate the relationship between
the surface temperature of the wafer W and the amount of erosion of
the focus ring 124, the surface temperature of the wafer W is
measured while the plasma is generated. Specifically, the surface
temperature of the wafer W at 5 mm from the edge is measured.
[0074] As the dry etching process gas, a mixture of etchant gases
(CF.sub.4 and C.sub.4F.sub.8), CO and Ar is used. Table 1 shows the
plasma discharge condition during the measurement of the surface
temperature. However, the plasma processing apparatus 10 is used
for the production of semiconductor devices with a different
process gas and a different plasma discharge condition shown in
Table 2. That is, the focus ring 124 is mainly eroded by the plasma
with the condition shown in Table 2. TABLE-US-00001 TABLE 1 Coolant
temperature Rear side He Discharge RF Power [.degree. C.] pressure
pressure density Gas flow rate [sccm] upper lower [Torr] [mTorr]
[Wcm.sup.-2] CF.sub.4 C.sub.4F.sub.8 CO Ar electrode electrode
center edge 150 4.65 10 8 120 350 30 -10 10 19
[0075] TABLE-US-00002 TABLE 2 RF Coolant temperature Discharge
Power Gas flow rate [.degree. C.] Rear side He pressure density
[sccm] upper lower pressure [Torr] [mTorr] [Wcm.sup.-2] CF.sub.4
CHF.sub.3 Ar electrode electrode center edge 300 4.65 40 30 500 30
-10 10 22
[0076] FIG. 4 is a curve illustrating the result of measurements,
where the surface temperature near the edge of the wafer W is shown
in relation to the cumulative RF discharge time of the focus ring
124. FIG. 4 indicates that the surface temperature near the edge of
the wafer W increases after the cumulative RF discharge time
exceeds 300 hours.
[0077] A coolant with the temperature shown in Table 1 is
circulated within the lower electrode 118. Because there is a
certain distance between the circulation path and the side surface
118b of the lower electrode 118, however, the temperature of the
lower electrode 118 near the side surface 118b increases when the
side surface 118b is exposed to the plasma. Accordingly, the
temperature of the edge portion of the wafer W increases.
[0078] In order to evaluate the change of etching rate of small
holes near the edge of the wafer W by the increase of the
cumulative RF discharge time of the focus ring, dry etching is
conducted. Specifically, the surface of the wafer W shown in FIG. 5
is etched under the conditions shown in Table 1.
[0079] As discussed above, however, the apparatus is used for the
production with the condition shown in Table 2. Here, the condition
shown in Table 1 is more suitable for etching small holes, but is
more strongly influenced by the surface temperature of the wafer
W.
[0080] According to various exemplary embodiments, in the wafer W
shown in FIG. 5, on a silicon substrate S1, a 2.0 .mu.m thick
silicon dioxide film S2 is formed, and a 1.2 .mu.m thick
photoresist mask pattern M is formed on the silicon dioxide film.
The mask M has 0.30 .mu.m.sup..PHI. holes H. A mixture of etchant
gases (CF.sub.4 and C.sub.4F.sub.8) and CO and Ar is used as the
dry etching process gas. The etching rate is measured at the
position of 5 mm from the edge of the wafer W.
[0081] FIG. 6 is a curve illustrating the change of the silicon
dioxide film etching rate in relation to the cumulative RF
discharge time of the focus ring 124. FIG. 6 shows that the etching
rate near the edge of the wafer W significantly decreases after the
cumulative RF discharge time exceeds 300 hours.
[0082] This result indicates that, 1) when the cumulative RF
discharge time exceeds 300 hours, the focus ring 124 is severely
damaged and irradiation of the plasma to the side surface of the
lower electrode 118 increases, and 2) as a result, the surface
temperature near the edge of the wafer W increases and the etching
rate near the edge of the wafer W decreases. In other words, it is
impossible to maintain desired etching characteristics when the
cumulative RF discharge time exceeds 300 hours.
[0083] Moreover, in the conventional plasma processing apparatus
illustrated in FIG. 10, the lower electrode 118 is also damaged
when the erosion of the focus ring 124 proceeds to the extent shown
in FIG. 11.
[0084] The fluorocarbon resin film 120a covering the side surface
118b of the lower electrode 118 is not highly resistant to the
plasma. Therefore, when the focus ring 124 is eroded as shown in
FIG. 11, the fluorocarbon resin film 120a on the side surface 118b
of the lower electrode 118 may easily be degraded. Moreover, in the
conventional plasma processing apparatus illustrated in FIGS. 10
and 11, it is difficult to prevent the fluorocarbon resin film 120a
on the side surface 118a from being damaged during attaching and
detaching of the focus ring 124.
[0085] As a result, when the focus ring 124 is severely eroded as
shown in FIG. 11, the fluorocarbon resin film 120a disappears at
least partly on the side surface 118b of the lower electrode 118,
and portions of the side surface 118b of the lower electrode 118
are directly exposed to the plasma. The direct exposure to the
plasma degrades the alumite coating on the side surface 118b of the
lower electrode 118, and causes abnormal discharge, or arcing, from
the portion that is dielectrically destructed.
[0086] When the abnormal discharge occurs, the lower electrode 118
cannot be used anymore. Therefore, the operation of the apparatus
must be stopped, and the replacement to a new lower electrode 118
must be made.
[0087] As discussed above, in the conventional plasma processing
apparatus that does not have the ceramic ring 30, the etching rate
changes and the lower electrode degrades when the focus ring 124 is
eroded. Therefore, the focus ring 124 should be replaced when the
cumulative RF discharge time exceeds 300 hours, or when the amount
of erosion in the vertical direction reaches about 1 mm by a visual
inspection. The used focus ring 124 should be discarded or
repaired.
Example 1
[0088] Using the exemplary plasma processing apparatus 10 shown in
FIG. 1, dry etching of silicon dioxide films S2 on the surface of
the wafers W shown in FIG. 5 is conducted, and the change of the
etching rate is examined.
[0089] As shown in FIG. 2, the ceramic ring 30 has a dimension such
that the outer perimeter of the ceramic ring 30 is positioned
inside of the outer perimeter of the wafer W. Specifically, the
dimension, or the diameter, of the wafer-supporting surface 18a of
the lower electrode 18 is about 6 mm smaller than that of the wafer
W, and the thickness, or the width, of the ceramic ring 30 is 2 mm.
Therefore, the outer perimeter of the ceramic ring 30 is positioned
about 1 mm inside the outer perimeter of the wafer W. In this
example, the material of the ceramic ring is alumina.
[0090] In this example, a focus ring 24 that is already severely
eroded is used. Specifically, a focus ring 24 that is already
eroded to a depth of 3 mm in the vertical direction at the stepped
portion 24a near the inner perimeter, which faces the lower
electrode 18, is used. This amount of erosion corresponds to three
times the maximum allowable erosion depth (1 mm) in a conventional
apparatus. In other words, a focus ring that has been used for a
cumulative RF discharge time of about 900 hours, is used.
[0091] The etching for measuring the etching rate is conducted
using the plasma discharge condition shown in Table 3. The
apparatus 10 is also used for the production of semiconductor
devices using the condition shown in Table 2. TABLE-US-00003 TABLE
3 Coolant temperature Rear side He Discharge RF Power [.degree. C.]
pressure pressure density Gas flow rate [sccm] upper lower [Torr]
[mTorr] [Wcm.sup.-2] CF.sub.4 C.sub.4F.sub.8 CO Ar electrode
electrode center edge 150 4.65 10 8 120 350 30 -10 10 16
[0092] According to various exemplary embodiments, when the ceramic
ring 30 is fitted around the side surface 18b of the lower
electrode 18, the surface temperature within about 5 mm from the
edge of the wafer decreases with an amount of about 5.degree. C. if
the discharge condition shown in Table 1 is used. Such decrease in
the temperature is due to the fact that, different from the
conventional apparatus, the side surface 18b of the lower electrode
18 is not exposed to the plasma, and the thermal conductivity of
the ceramic ring 30 is high. Especially, the fact that the ceramic
ring 30 is made of alumina and has a thermal conductivity more than
20 times higher than that of quartz, which is the material of the
focus ring 30, significantly improves the cooling efficiency of the
edge portion of the wafer W.
[0093] Therefore, according to various exemplary embodiments, in
order to improve the uniformity of the surface temperature of the
wafer W, the condition shown in Table 3 is used to measure the
etching rate. Specifically, as shown in Table 3, the pressure of He
gas supplied to the peripheral portion of the rear side of the
wafer W is decreased to an amount of about 3 Torr, compared to the
condition shown in Table 1. Otherwise the condition shown in Table
3 is the same as that shown in Table 1.
[0094] FIG. 7 is a curve illustrating the change of the silicon
dioxide film etching rate in relation to the cumulative RF
discharge time of the focus ring 24. As shown in FIG. 7, the
etching rate of 0.30 .mu.m.sup..PHI. hole does not significantly
change even when the focus ring 24, which has already been eroded
to the depth of 3 mm, is further used for 400 hours.
[0095] This result indicates that the ceramic ring 30 enables to
maintain a uniform surface temperature of the wafer W and a stable
etching rate irrespective of the amount of erosion of the focus
ring 24. Further, because the etching rate is stable irrespective
of the amount of erosion, the usable life of the focus ring 24 can
be extended.
[0096] That is, according to various exemplary embodiments of this
invention, a protecting ring formed of a ceramic material that has
an erosion rate lower than that of the material of the focus ring
covers the side surface of the lower electrode. Accordingly, even
after the focus ring is severely eroded, the etching
characteristics can be maintained and the degradation of the lower
electrode is prevented. Moreover, an interval to replace the focus
ring can be extended, and a cost incurred for replacing the focus
ring can be reduced.
[0097] Moreover, as discussed above, it is not necessary to
materially change the etching condition when the ceramic ring 30 is
used. Specifically, the etching condition shown in Table 3, which
is the same as the conventional condition shown in Table 1, except
that the pressure of He supplied to the rear side of the wafer W is
adjusted, can be used in the apparatus 10 that utilizes the ceramic
ring 30. This result indicates that the ceramic ring 30 does not
materially influence the plasma characteristics.
[0098] In this exemplary embodiment, because a focus ring 24 that
is already severely eroded is used, the ceramic ring 30 is exposed
to the plasma. Because the outer perimeter of the ceramic ring 30
is positioned inside of the outer perimeter of the wafer W,
however, charged particles in the plasma accelerated toward the
direction perpendicular to the surface of the wafer W do not
irradiate the ceramic ring 30. Accordingly, the ceramic ring 30
does not materially change the plasma characteristics.
Example 2
[0099] Using the plasma processing apparatus 10 shown in FIG. 1, an
exemplary etching process is performed for a plurality of wafers W
having the structure shown in FIG. 5. The thickness of the ceramic
ring 30 is 2 mm. Two focus rings 24, which have not been eroded,
are prepared, and a running experiment is conducted by alternately
using the two focus rings 24. That is, the operation of the
apparatus 10 is stopped every 50 hours of cumulative RF discharge
time for a mechanical cleaning. During the mechanical cleaning, the
focus ring 24 is substituted with another one.
[0100] Measurement of the etching rate of 0.30 .mu.m.sup..PHI. hole
is made with a predetermined interval using the plasma discharge
condition shown in Table 3. The apparatus may be operated for other
purposes with the condition shown in Table 2.
[0101] FIG. 8 is a curve illustrating the change of the etching
rate of 0.30 .mu.m.sup..PHI. hole in relation to the cumulative RF
discharge time of the two focus rings 24 (i.e., the cumulative time
of RF discharge made using the two focus rings 24). FIG. 8 shows
that the change of the etching rate is small even when the
cumulative RF discharge time reaches 1200 hours, or when the
cumulative RF discharge time of each focus ring 24 reaches 600
hours.
[0102] On the other hand, as shown in FIG. 6, the etching rate in
the conventional apparatus changes significantly when the
cumulative RF discharge time of the focus ring exceeds 300 hours.
Accordingly, it can be understood that by employing the ceramic
ring 30, the life, or the maximum usable period of the focus ring
24, can be extended at least by two times.
[0103] During the experiment, the lower electrode 18 is not
damaged. In this experiment, the ceramic ring 30 is prepared
separately from the lower electrode 18 and fitted to the side
surface 18b of the lower electrode 18 when starting the experiment.
Because the ceramic ring 30 has a smaller outer diameter, and a
smaller weight, than those of the focus ring 24, it can be easily
fitted to the lower electrode 18. Therefore, there is no risk of
damaging the fluorocarbon resin film 20a on the side surface 18b of
the lower electrode 18 when fitting the ceramic ring 30. Moreover,
it is not necessary to detach the ceramic ring for mechanical
cleaning.
[0104] Finally, FIG. 9 is a curve illustrating the amount of
erosion of the ceramic ring 30 in relation to the cumulative RF
discharge time of the ceramic ring 30, or the cumulative time of RF
discharge made using the two focus rings 24 and the ceramic ring
30. FIG. 9 indicates that the amount of erosion is about 1 mm when
the cumulative RF discharge time is 1200 hours. That is, for
example, the ceramic ring 30 with a width of 2 mm has a sufficient
shielding ability to prevent the plasma from touching the side
surface 18b of the lower electrode 18, at least to the cumulative
RF discharge time of 1200 hours.
[0105] FIG. 9 shows that, during the initial period before the
cumulative RF discharge time of less than about 300 hours, the
erosion rate of the ceramic material measured by the amount of
erosion of the ceramic ring 30 in the direction perpendicular to
the side surface 18b of the lower electrode 18 is about 25 nm/min.
On the other hand, FIG. 3 shows that, during the same time period,
the erosion rate of quartz measure by the amount of increase in the
erosion of the focus ring in the vertical direction, or in the
direction perpendicular to the surface of the wafer W, is about 56
nm/min. That is, the erosion rate of the ceramic material measured
by the amount of erosion of the ceramic ring 30 in the direction
perpendicular to the side surface 18b of the lower electrode 18 is
less than a half of the erosion rate of quartz measured by the
amount of erosion of the focus ring 24 in the direction
perpendicular to the surface of the wafer W.
[0106] FIG. 9 further indicates that, when the cumulative RF
discharge time increases, the amount of erosion of the ceramic ring
30 tends to saturate. That is, the erosion rate of the ceramic ring
decreases as the cumulative RF discharge time increases. The lower
erosion rate of the ceramic ring 30, compared with that of the
focus ring 24, enables to use the ceramic ring 30 for a long period
even after the focus ring 24 is severely eroded.
[0107] It should be noted that the erosion rates and the ratios
thereof thus calculated from the data shown in FIGS. 3 and 9 are
determined not only by the difference of the properties of the
materials but also by the positions of the ceramic ring 30 and the
focus ring 24 in the plasma processing apparatus 10. In fact, it is
found that the erosion rate of alumina measured by an etching rate
of aluminum oxide film on the surface of a wafer W placed on the
wafer-supporting surface 18b of the plasma processing apparatus 10
is about 30 times lower than the erosion of quartz measured by an
etching ration of silicon dioxide film on the surface of a wafer W
placed on the wafer-supporting surface 18b. It is clear however
that the actual erosion rate in the ceramic ring 30 fitted in the
processing apparatus 10 determines the usable life of the ceramic
ring 30.
[0108] This invention is not limited to the specific embodiments
described above. Various improvements or modifications may be made
within the spirit of this invention.
[0109] For example, in the exemplary embodiment described above, a
lower electrode 18 having a fluorocarbon resin film 20a on the side
surface 18b may be used in order to be compared to the conventional
plasma processing apparatus. However, the ceramic ring 30 prevents
the plasma from touching the side surface 18b of the lower
electrode 18 even after the focus ring 24 is severely eroded.
Therefore, essentially the same usable life of the lower electrode
18 is realized even without the fluorocarbon resin film 20a on the
side surface 18b of the lower electrode 18.
[0110] Further, in the exemplary embodiments described above, the
lower electrode 18 having an electrostatic chuck 20 formed of
fluorocarbon resin is used. However, this invention may also be
applied to an apparatus having an electrostatic chuck formed of
ceramics. In that case, similarly to a case where an electrostatic
chuck formed of fluorocarbon resin is used, a ceramic coating film
on the side surface 18b of the lower electrode 18 is not always
required.
[0111] According to various exemplary embodiments, when the ceramic
coating film on the side surface 18b of the lower electrode 18 is
made, however, the ceramic ring 30 prevents the plasma from
touching the ceramic coating film on the side surface 18b of the
lower electrode 18 even after the focus ring 24 is severely eroded.
Accordingly, the ceramic ring 30 significantly extends the life of
the ceramic coating.
* * * * *