U.S. patent application number 12/788396 was filed with the patent office on 2010-12-02 for circular ring-shaped member for plasma process and plasma processing apparatus.
This patent application is currently assigned to TOKYO ELECTRON LIMITED. Invention is credited to Hideki Mizuno, Koichi Yatsuda.
Application Number | 20100300622 12/788396 |
Document ID | / |
Family ID | 43218877 |
Filed Date | 2010-12-02 |
United States Patent
Application |
20100300622 |
Kind Code |
A1 |
Yatsuda; Koichi ; et
al. |
December 2, 2010 |
CIRCULAR RING-SHAPED MEMBER FOR PLASMA PROCESS AND PLASMA
PROCESSING APPARATUS
Abstract
A plasma processing apparatus includes a processing chamber the
inside of which is maintained in a vacuum; a mounting table
configured to mount a target substrate and serve as a lower
electrode in the processing chamber; a circular ring-shaped member
provided at the mounting table so as to surround a peripheral
portion of the target substrate; an upper electrode arranged to
face the lower electrode thereabove; and a power feed unit for
supplying a high frequency power to the mounting table. The
apparatus performs a plasma process on the target substrate by
plasma generated in the processing chamber. The circular
ring-shaped member includes at least one ring-shaped groove
configured to adjust an electric field distribution to a desired
distribution in a plasma generation space, and the groove is formed
in a surface of the circular ring-shaped member and the surface is
on an opposite side to the plasma generation space.
Inventors: |
Yatsuda; Koichi; (Tokyo,
JP) ; Mizuno; Hideki; (Nirasaki, JP) |
Correspondence
Address: |
PEARNE & GORDON LLP
1801 EAST 9TH STREET, SUITE 1200
CLEVELAND
OH
44114-3108
US
|
Assignee: |
TOKYO ELECTRON LIMITED
Tokyo
JP
|
Family ID: |
43218877 |
Appl. No.: |
12/788396 |
Filed: |
May 27, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61228636 |
Jul 27, 2009 |
|
|
|
Current U.S.
Class: |
156/345.44 ;
156/345.1 |
Current CPC
Class: |
H01J 37/32642 20130101;
H01J 37/32091 20130101 |
Class at
Publication: |
156/345.44 ;
156/345.1 |
International
Class: |
C23F 1/08 20060101
C23F001/08 |
Foreign Application Data
Date |
Code |
Application Number |
May 27, 2009 |
JP |
2009-128355 |
Claims
1. A circular ring-shaped member for a plasma process provided to
surround a peripheral portion of a target substrate to be
plasma-processed, the member comprising: at least one ring-shaped
groove configured to adjust an electric field distribution to a
desired distribution in a plasma generation space, wherein the
groove is formed in a surface of the circular ring-shaped member
and the surface is on an opposite side to the plasma generation
space.
2. The circular ring-shaped member of claim 1, wherein the groove
is formed in an inner peripheral portion of the circular
ring-shaped member.
3. The circular ring-shaped member of claim 1, wherein impedance of
the circular ring-shaped member is adjusted to be a desired value
depending on a shape of the groove.
4. The circular ring-shaped member of claim 1, wherein the groove
is formed to have a predetermined width, starting from a position
between an inner end of the circular ring-shaped member and a
position in a range of about 30% or less of a width of the circular
ring-shaped member in a diametric direction.
5. The circular ring-shaped member of claim 1, wherein the groove
is formed to have a predetermined width which is about 80% or less
of a width of the circular ring-shaped member, starting from an
inner end of the circular ring-shaped member in a diametric
direction.
6. The circular ring-shaped member of claim 1, wherein a depth of
the groove is about 70% or less of a thickness of the circular
ring-shaped member.
7. The circular ring-shaped member of claim 1, wherein the circular
ring-shaped member is made of at least one of quartz, carbon,
silicon, silicon carbide, and a ceramic material.
8. A plasma processing apparatus comprising: a processing chamber
the inside of which is maintained in a vacuum condition; a mounting
table configured to mount thereon a target substrate and serve as a
lower electrode in the processing chamber; a circular ring-shaped
member provided at the mounting table so as to surround a
peripheral portion of the target substrate; an upper electrode
arranged to face the lower electrode thereabove; and a power feed
unit for supplying a high frequency power to the mounting table,
wherein the plasma processing apparatus performs a plasma process
on the target substrate by plasma generated in the processing
chamber, the circular ring-shaped member includes at least one
ring-shaped groove configured to adjust an electric field
distribution to a desired distribution in a plasma generation
space, and the groove is formed in a surface of the circular
ring-shaped member and the surface is on an opposite side to the
plasma generation space.
9. The plasma processing apparatus of claim 8, wherein the groove
is formed in an inner peripheral portion of the circular
ring-shaped member.
10. The plasma processing apparatus of claim 8, wherein impedance
of the circular ring-shaped member is adjusted to be a desired
value depending on a shape of the groove.
11. The plasma processing apparatus of claim 8, wherein the groove
is formed to have a predetermined width, starting from a position
between an inner end of the circular ring-shaped member and a
position in a range of about 30% or less of a width of the circular
ring-shaped member in a diametric direction.
12. The plasma processing apparatus of claim 8, wherein the groove
is formed to have a predetermined width which is about 80% or less
of a width of the circular ring-shaped member, starting from an
inner end of the circular ring-shaped member in a diametric
direction.
13. The plasma processing apparatus of claim 8, wherein a depth of
the groove is about 70% or less of a thickness of the circular
ring-shaped member.
14. The plasma processing apparatus of claim 8, wherein the
circular ring-shaped member is made of at least one of quartz,
carbon, silicon, silicon carbide, and a ceramic material.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of Japanese Patent
Application No. 2009-128355 filed on May 27, 2009, and U.S.
Provisional Application Ser. No. 61/228,636 filed on Jul. 27, 2009,
the entire disclosures of which are incorporated herein by
reference.
FIELD OF THE INVENTION
[0002] The present disclosure relates to a circular ring-shaped
member for a plasma process configured to surround a peripheral
portion of a target substrate on which a plasma process is
performed in a plasma processing chamber, and a plasma processing
apparatus including the same.
BACKGROUND OF THE INVENTION
[0003] In a manufacturing process of a semiconductor device or a
FPD (Flat Panel Display), there has been widely used a plasma
processing apparatus for etching, deposition, oxidation,
sputtering, or the like. As one of the plasma processing
apparatuses, there has been known a plasma etching apparatus in
which an upper electrode and a lower electrode are arranged
parallel to each other within a processing vessel or reaction
chamber, a target substrate (semiconductor wafer, glass substrate
or the like) is mounted on the lower electrode, and a high
frequency voltage for plasma generation is applied to either or
both of the upper electrode and the lower electrode via a matching
unit in most cases.
[0004] Generally, a plurality of gas discharge holes is provided in
the upper electrode and an etching gas excited into plasma is
discharged to the entire substrate through the gas discharge holes
so as to etch the entire surface of the target substrate at the
same time.
[0005] Typically, in a parallel plate type plasma etching
apparatus, an upper electrode and a lower electrode are arranged
parallel to each other, and a high frequency voltage for generating
plasma is applied to the upper electrode or the lower electrode via
a matching unit. Electrons accelerated by a high frequency electric
field between both the electrodes, secondary electrons emitted from
the electrodes, or heated electrons collide with molecules of a
processing gas and are ionized, so that the processing gas is
excited into plasma. By radicals or ions in the plasma, a required
microprocessing such as an etching process is performed on a
surface of a substrate.
[0006] As semiconductor integrated circuits are miniaturized, high
density plasma under a low pressure is required in a plasma
process. For example, in a capacitively coupled plasma processing
apparatus, a plasma process of a higher efficiency, a higher
density, and a lower bias power is required. Further, as
semiconductor chips become large-sized and target substrates have
large diameters, plasma of a larger diameter is required, and,
thus, chambers (processing vessels) also become scaled up.
[0007] However, in the large-diameter plasma processing apparatus
along with the large-diameter target substrate, an intensity of an
electric field at a central portion of an electrode (upper
electrode or lower electrode) tends to be higher than that of an
electric field at an edge portion thereof. As a result, there is a
problem in that a density of the generated plasma at the central
portion of the electrode is different from a plasma density at the
edge portion thereof. Therefore, a resistivity of the plasma
becomes low at a portion in which plasma density is high, and a
current is also concentrated on a corresponding portion of a facing
electrode. Accordingly, there is a problem in that a non-uniformity
of the plasma density becomes serious.
[0008] Furthermore, as the chamber becomes scaled up along with the
large-diameter target substrate, there is a problem in that a
plasma density at a central portion of the target substrate is
different from a plasma density at a peripheral portion thereof in
an actual etching process due to a flow of a processing gas caused
by a temperature distribution.
[0009] The non-uniformity of the plasma density causes a difference
in an etching rate of the target substrate, and particularly, it
causes a deterioration of a device yield obtained from the
peripheral portion of the target substrate.
[0010] In this regard, various researches for a configuration of an
electrode have been conducted until now. For example, in order to
solve the above-described problem, there has been known a technique
of providing a high resistance member at a central portion of a
main surface of a high frequency electrode (see Patent Document 1).
According to this technique, the high resistance member is provided
at the central portion of the main surface (plasma contact surface)
of the electrode connected with a high frequency power supply, so
that an intensity of an electric field at the central portion of
the main surface of the electrode is relatively lowered as compared
to an intensity of an electric field at an outer peripheral portion
thereof. Therefore, non-uniformity of an electric field
distribution can be corrected.
[0011] Further, in a plasma processing apparatus disclosed in
Patent Document 2, a dielectric member is embedded in a main
surface of an electrode facing a processing space such that
impedance against a high frequency power supplied from the main
surface of the electrode to the processing space is relatively high
at an central portion of the electrode and relatively low at an
edge portion of the electrode. With this configuration, uniformity
of an electric field distribution can be improved.
[0012] Meanwhile, in order to improve uniformity of a plasma
density distribution at the edge portion of a target substrate, the
plasma processing apparatus includes a circular ring-shaped member
such as a focus ring, provided so as to surround an outer periphery
of a wafer mounted on a mounting table within the processing
chamber. By way of example, the focus ring may have a double-circle
structure including a ring-shaped inner focus ring positioned on
inner side and a ring-shaped outer focus ring positioned so as to
surround an outer periphery of the inner focus ring. Generally, the
inner focus ring may be made of a conductive material such as
silicon and the outer focus ring may be made of an insulating
material such as quartz.
[0013] The inner focus ring has a function to concentrate plasma on
the wafer, and the outer focus ring serves as an insulator
confining the plasma on the wafer.
[0014] During a plasma process, a temperature of the outer focus
ring increases due to heat transferred from the plasma. If the
temperature is not stable, a radical density in the vicinity of the
outer focus ring becomes non-uniform and a plasma density at an
outer peripheral portion of the wafer becomes non-uniform as well.
As a result, an effect of the plasma process at the central portion
of the wafer is different from that at the outer peripheral portion
thereof, and, thus, it becomes difficult to perform the plasma
process on the wafer uniformly.
[0015] Therefore, in Patent Document 3, a ring-shaped groove is
formed in an outer focus ring so as to reduce a heat capacity of
the outer focus ring, so that a temperature of the outer focus ring
is rapidly increased and is easily maintained high by heat
transferred from plasma. With this configuration, uniformity of the
plasma density at a peripheral portion of the wafer can be achieved
and deposits on the focus ring can be removed at the earliest stage
of a production lot.
[0016] Patent Document 1: Japanese Laid-open Publication No.
2000-323456 [0017] Patent Document 2: Japanese Laid-open
Publication No. 2004-363552 [0018] Patent Document 3: Japanese
Laid-open Publication No. 2007-67353
[0019] However, in a high frequency discharge type plasma
processing apparatus as disclosed in Patent Documents 1 and 2,
since a high resistance member is provided at a central portion of
a main surface of a high frequency electrode, there is a problem in
that a large quantity of a high frequency power is consumed (energy
loss) due to Joule's heat.
[0020] In accordance with a technique in which a dielectric member
is embedded in the main surface of an electrode as disclosed in
Patent Documents 1 and 2, a characteristic of an impedance
distribution on the main surface of the electrode is determined by
a material and a shape profile of the dielectric member. Therefore,
there is a problem in that such a technique can not respond
flexibly to various kinds of processes or variation of process
conditions.
[0021] Further, in Patent Document 3, a groove is formed in an
outer focus ring so as to reduce a heat capacity. Accordingly,
uniformity of a plasma density distribution at a peripheral portion
of a wafer can be obtained due to increase and stabilization of a
temperature in a short time.
[0022] However, in order to obtain the uniformity of the plasma
density distribution at the peripheral portion of the wafer, not
only the temperature needs to be stabilized but a distribution or
an intensity of an electric field at the peripheral portion of the
wafer also need to be adjusted to a desired level.
[0023] In Patent Document 3, by providing the groove in the outer
focus ring so as to reduce the heat capacity, stability of the
temperature can be obtained. However, the uniformity of the plasma
density distribution caused by the stability of the temperature is
obtained only while the temperature is stabilized, which does not
mean that the distribution or intensity of the electric field is
adjusted to a desired level. Therefore, in Patent Document 3, a
problem of adjusting the electric field distribution to a desired
level can not be solved.
[0024] Furthermore, in Patent Document 3, the groove is formed in
the outer focus ring so as to reduce the heat capacity, so that
uniformity of the plasma density distribution can be obtained.
However, in order to secure an etching rate or a deposition rate of
a desired level at the end portion of the wafer, an electric field
distribution on a top surface in the vicinity of the end portion of
the wafer needs to be adjusted to a desired level, which has not
been solved in Patent Document 3.
BRIEF SUMMARY OF THE INVENTION
[0025] In view of the foregoing, the present disclosure provides a
circular ring-shaped member for a plasma process capable of
improving uniformity and production yield in the plasma process by
adjusting an electric field distribution at a peripheral portion of
a wafer to a desired level, and a plasma processing apparatus.
[0026] In accordance with an aspect of the present disclosure,
there is provided a circular ring-shaped member for a plasma
process to surround a peripheral portion of a target substrate to
be plasma-processed. The circular ring-shaped member includes at
least one ring-shaped groove configured to adjust an electric field
distribution to a desired distribution in a plasma generation
space. The groove may be formed in a surface of the circular
ring-shaped member and the surface may be on an opposite side to
the plasma generation space. Since the ring-shaped groove is formed
in the circular ring-shaped member configured to surround the
peripheral portion of the target substrate to be plasma-processed,
the electric field distribution at the peripheral portion of the
target substrate can be changed.
[0027] The groove may be formed in an inner peripheral portion of
the circular ring-shaped member. Since the groove is formed in the
circular ring-shaped member in contact with the target substrate,
it is possible to adjust the electric field distribution at the
peripheral portion of the target substrate more favorably.
[0028] Further, impedance of the circular ring-shaped member may be
adjusted to be a desired value depending on a shape of the groove.
The impedance varies depending on the shape of the groove, thereby
adjusting the electric field distribution.
[0029] The groove may be formed to have a predetermined width,
starting from a position between an inner end of the circular
ring-shaped member and a position in a range of about 30% or less
of a width of the circular ring-shaped member in a diametric
direction. If the groove is formed at a position exceeding about
30% of the width of the circular ring-shaped member, starting from
the inner end of the circular ring-shaped member in contact with
the target substrate, it becomes difficult to adjust the electric
field distribution at the peripheral portion of the target
substrate.
[0030] Further, the groove may be formed to have a predetermined
width which is about 80% or less of a width of the circular
ring-shaped member, starting from an inner end of the circular
ring-shaped member in a diametric direction. If the groove is
formed to exceed about 80% of the width of the circular ring-shaped
member, starting from the inner end of the circular ring-shaped
member in contact with the target substrate, the groove has less
effect on the electric field distribution at the peripheral portion
of the target substrate.
[0031] A depth of the groove may be about 70% or less of a
thickness of the circular ring-shaped member. When the groove is
formed in the circular ring-shaped member, if the depth of the
groove (a length in a vertical direction when the circular
ring-shaped member is provided in a horizontal direction) exceeds
about 70% of the thickness of the circular ring-shaped member, a
lifetime of the circular ring-shaped member is shortened by
abrasion caused by a plasma impact.
[0032] Further, the circular ring-shaped member may be made of at
least one of quartz, carbon, silicon, silicon carbide, and a
ceramic material.
[0033] In accordance with another aspect of the present disclosure,
there is provided a plasma processing apparatus including a
processing chamber the inside of which is maintained in a vacuum
condition; a mounting table configured to mount thereon a target
substrate and serve as a lower electrode in the processing chamber;
a circular ring-shaped member provided at the mounting table so as
to surround a peripheral portion of the target substrate; an upper
electrode arranged to face the lower electrode thereabove; and a
power feed unit for supplying a high-frequency power to the
mounting table. The plasma processing apparatus performs a plasma
process on the target substrate by plasma generated in the
processing chamber. The circular ring-shaped member may include at
least one ring-shaped groove configured to adjust an electric field
distribution to a desired distribution in a plasma generation
space. The groove may be formed in a surface of the circular
ring-shaped member and the surface may be on an opposite side to
the plasma generation space. Since the ring-shaped groove is formed
in the circular ring-shaped member configured to surround the
peripheral portion of the target substrate to be plasma-processed,
the electric field distribution at the peripheral portion of the
target substrate can be changed.
[0034] The groove may be formed in an inner peripheral portion of
the circular ring-shaped member. Since the groove is formed in the
circular ring-shaped member in contact with the target substrate,
it is possible to adjust the electric field distribution at the
peripheral portion of the target substrate more favorably.
[0035] Further, impedance of the circular ring-shaped member may be
adjusted to be a desired value depending on a shape of the groove.
The impedance varies depending on the shape of the groove, thereby
adjusting the electric field distribution.
[0036] The groove may be formed to have a predetermined width,
starting from a position between an inner end of the circular
ring-shaped member and a position in a range of about 30% or less
of a width of the circular ring-shaped member in a diametric
direction. If the groove is formed at a position exceeding about
30% of the width of the circular ring-shaped member, starting from
the inner end of the circular ring-shaped member in contact with
the target substrate, it becomes difficult to adjust the electric
field distribution at the peripheral portion of the target
substrate.
[0037] Further, the groove may be formed to have a predetermined
width which is about 80% or less of a width of the circular
ring-shaped member, starting from an inner end of the circular
ring-shaped member in a diametric direction. If the groove is
formed to exceed about 80% of the width of the circular ring-shaped
member, starting from the inner end of the circular ring-shaped
member in contact with the target substrate, the groove has less
effect on the electric field distribution at the peripheral portion
of the target substrate.
[0038] A depth of the groove may be about 70% or less of a
thickness of the circular ring-shaped member. When the groove is
formed in the circular ring-shaped member, if the depth of the
groove (a length in a vertical direction when the circular
ring-shaped member is provided in a horizontal direction) exceeds
about 70% of the thickness of the circular ring-shaped member, a
lifetime of the circular ring-shaped member is shortened by
abrasion caused by a plasma impact.
[0039] Further, the circular ring-shaped member may be made of at
least one of quartz, carbon, silicon, silicon carbide, and a
ceramic material.
[0040] In accordance with the plasma processing apparatus of the
present disclosure, the etching rate or deposition rate at the
peripheral portion of the wafer can be adjusted easily and freely
by adjusting the electric field distribution at the peripheral
portion of the wafer, thereby improving uniformity or production
yield in the plasma process.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] The disclosure may best be understood by reference to the
following description taken in conjunction with the following
figures:
[0042] FIG. 1 is a longitudinal cross sectional view showing a
configuration of a plasma processing apparatus in accordance with
an embodiment of the present disclosure;
[0043] FIG. 2A is a cross sectional view of a conventional focus
ring;
[0044] FIG. 2B is a cross sectional view of a groove-formed focus
ring;
[0045] FIGS. 3A to 3C show shapes of grooves;
[0046] FIG. 4 is a graph showing an etching rate of an oxide
film;
[0047] FIG. 5 is a graph showing an etching rate of a nitride
film;
[0048] FIGS. 6A and 6B provide graphs showing a characteristic of a
sputtering rate; and
[0049] FIGS. 7A and 7B provide graphs showing a characteristic of a
deposition rate.
DETAILED DESCRIPTION OF THE INVENTION
[0050] Hereinafter, an embodiment applying a plasma processing
apparatus in accordance with the present disclosure to an etching
apparatus will be described in detail with reference to the
accompanying drawings. However, the present disclosure is not
limited thereto.
[0051] FIG. 1 shows a schematic overall configuration of a plasma
processing apparatus 1 in accordance with the embodiment of the
present disclosure. The plasma processing apparatus includes a
cylindrical processing chamber the inside of which can be
airtightly sealed and is made of, e.g., aluminum or stainless
steel. In this case, a capacitively coupled plasma processing
apparatus of a lower electrode dual frequency application type is
employed, but the present disclosure is not limited thereto. For
example, a plasma processing apparatus of an upper and lower
electrode dual frequency application type or a plasma processing
apparatus of a single frequency application type may be
employed.
[0052] Within the processing chamber, a susceptor 2 configured to
support a semiconductor wafer (hereinafter, referred to as "wafer")
15 as a target substrate is horizontally placed. The susceptor 2 is
made of a conductive material such as aluminum and serves as an RF
electrode. Installed on a top surface of the susceptor 2 is an
electrostatic chuck 16 made of a dielectric material such as
ceramic so as to hold the wafer 15 by an electrostatic attracting
force. An internal electrode 17 formed of a conductive film made of
a conductive material such as copper or tungsten is embedded in the
electrostatic chuck 16. The susceptor 2 is supported by a
cylindrical holder 3 made of an insulating material such as
ceramic. The cylindrical holder 3 is supported by a cylindrical
support 4 of the processing chamber. Installed on a top surface of
the cylindrical holder 3 is a focus ring 5 configured to surround
the top surface of the susceptor 2 in a ring shape.
[0053] Around the outside of the focus ring 5, a circular
ring-shaped cover ring 25 is installed.
[0054] The electrostatic chuck 16 is used as a heat exchange plate
for adjusting a temperature of the wafer 15 by exchanging heat with
the wafer 15 in contact with each other. The focus ring 5 serving
as one of circular ring-shaped members for a plasma process is
installed around the outside of the wafer 15. In this embodiment,
the single focus ring 5 is provided, but it may be possible to use
a double focus ring which is divided into an outer focus ring and
an inner focus ring. The focus ring 5 can be made of, e.g., Si,
SiC, C or SiO.sub.2 depending on the wafer 15.
[0055] Between a sidewall of the processing chamber and the
cylindrical support 4, a ring-shaped exhaust line 6 is provided. At
the entrance or on the way to the exhaust line 6, a ring-shaped
baffle plate 7 is provided. A bottom portion of the exhaust line 6
is connected with an exhaust device 9 via an exhaust pipe 8. The
exhaust device 9 includes a vacuum pump such as a turbo molecular
pump, and, thus, a plasma processing space within the processing
chamber can be depressurized to a predetermined vacuum level.
Further, a gate valve 11 configured to open and close a transfer
port 10 for loading/unloading the wafer 15 is installed outside the
sidewall of the processing chamber.
[0056] A rear surface (bottom surface) of the susceptor 2 and an
upper electrode 21 are connected with upper ends of circular
column-shaped or cylindrical-shaped power feed rods 14a and 14b
extending from output terminals of matching units 13a and 13b,
respectively. First and second high frequency power supplies 12a
and 12b used in a dual frequency application type are electrically
connected with the susceptor 2 and the upper electrode 21 via the
matching units 13a and 13b and the power feed rods 14a and 14b,
respectively. The power feed rods 14a and 14b are made of a
conductive material such as copper or aluminum.
[0057] The first high frequency power supply 12a outputs a first
high frequency power having a relatively high frequency of, e.g.,
about 60 MHz for generating plasma above the susceptor 2. The
second high frequency power supply 12b outputs a second high
frequency power having a relatively low frequency of, e.g., about 2
MHz for attracting ions to the wafer 15 on the susceptor 2. The
matching unit 13a performs matching between impedance of the first
high frequency power supply 12a and impedance of a load (mainly,
electrode, plasma, and chamber), and the matching unit 13b performs
matching between impedance of the second high frequency power
supply 12b and the impedance of the load.
[0058] The electrostatic chuck 16 is configured such that the
internal electrode 17 formed of a sheet-shaped or mesh-shaped
conductor is embedded in a film-shaped or plate-shaped dielectric
member. The electrostatic chuck 16 is integrally fixed to or
integrally formed on the top surface of the susceptor 2. The
internal electrode 17 is electrically connected with a DC power
supply and a power feed line such as a coated line provided outside
the processing chamber, and, thus, the wafer 15 can be attracted to
and held on the electrostatic chuck 16 by a Coulomb force generated
by a DC voltage applied from the DC power supply.
[0059] At a ceiling portion of the processing chamber, the upper
electrode 21 is provided to face parallel to the susceptor 2. The
upper electrode 21 is formed in a circular plate shape having a
hollow structure (hollow portion) at the center thereof, and a
plurality of gas discharge holes 22 is formed in its bottom
surface, thereby functioning as a shower head. An etching gas
supplied from a processing gas supply unit is introduced into the
hollow portion in the upper electrode 21 through a gas inlet line
23 and uniformly distributed and supplied from the hollow portion
to the processing chamber through the gas discharge holes 22.
Further, the upper electrode 21 is made of, e.g., Si or SiC.
[0060] A heat transfer gas such as a He gas is supplied between the
electrostatic chuck 16 and the rear surface of the wafer 15 from a
heat transfer gas supply unit (not illustrated) through a gas
supply line 24. The heat transfer gas accelerates heat conduction
in the electrostatic chuck 16, i.e., between the susceptor 2 and
the wafer 15.
[0061] A main feature of this plasma processing apparatus is that
the focus ring 5, in which a circular ring-shaped groove is formed,
is used so as to obtain an impedance characteristic capable of
forming an intensity and distribution of an electric field most
suitable for a characteristic of the wafer 15 or various kinds of
plasma processes.
[0062] FIG. 2A is a cross sectional view of a conventional focus
ring which has been used in a conventional plasma process, and FIG.
2B is a cross sectional view of a groove-formed focus ring in
accordance with an embodiment of the present disclosure. All the
focus rings illustrated in FIGS. 2A and 2B are single (or referred
to as "integrated type") focus rings. However, the present
disclosure is not limited to the single focus ring and, for
example, may be applied to either or both of two separate focus
rings which are divided into an inner focus ring and an outer focus
ring. The focus ring may be made of, for example, the same material
(Si) as the wafer 15, or any one of quartz, carbon, silicon
carbide, and ceramic materials (yttria (Y.sub.2O.sub.3) or silica).
The focus ring 5 is mounted on the electrostatic chuck 16 so as to
support a peripheral end portion of the wafer 15.
[0063] There will be explained the groove-formed focus ring in
accordance with the embodiment of the present disclosure with
reference to FIG. 2B. In the groove-formed focus ring illustrated
in FIG. 2B, a groove 51 is formed on a surface (rear surface of the
focus ring) in contact with the electrostatic chuck 16. Desirably,
such a groove may be formed on the rear surface of the focus ring.
That is because that if a groove-formed surface is exposed to
plasma ions, the groove may be eroded (worn out) by a plasma ion
impact and, thus, a shape of the groove may be deformed. Further,
that is because that if the groove is formed by a cutting process
or the like, dust caused by the plasma ion impact may be highly
generated as compared to the other surface.
[0064] In FIG. 2B, a depth of the groove 51 (length in a vertical
direction when the focus ring 5 is installed in a horizontal
direction) is desirably about 70% or less of a thickness of the
focus ring and more desirably about 50% or less. If the depth of
the groove 51 exceeds about 70%, a lifetime of the focus ring 5 may
be shortened by abrasion caused by a plasma impact. Further, in
order to secure hardness of the focus ring, the depth of the groove
is desirably about 70% or less. Furthermore, the depth of the
groove 51 of the groove-formed focus ring illustrated in FIG. 2B is
about 0.4 mm, which is about one-ninth ( 1/9) of a thickness of the
focus ring 5, i.e., about 3.6 mm.
[0065] Moreover, a width of the groove 51 in a diametric direction
may be about 80% or less of a width of the focus ring in a
diametric direction. For example, the width of the groove 51 of the
groove-formed focus ring illustrated in FIG. 2B is about 40 mm,
which corresponds to about two-fifth ( ) (40%) of a width of the
focus ring 5, i.e., about 100 mm.
[0066] In addition, the groove 51 may be formed from an end of the
focus ring at the install position of the wafer 15 or from a
position in the range of about 30% or less of the width of the
focus ring in a diametric direction. That is because that by
forming the groove 51 from the end portion as close as possible, in
such a range that is not affected by the ion impact, an electric
field distribution on a surface of the wafer 15 can be adjusted
more easily.
[0067] As described above, the groove 51 may be formed in a certain
shape suitable to optimize the electric field distribution on the
surface of the wafer 15. FIGS. 3A to 3C show shapes of grooves in
accordance with the present disclosure. FIG. 3A shows a case where
a groove 51 is formed in a semi-elliptic shape from the vicinity of
an inner end portion of a focus ring 5. FIG. 3B shows a case where
a trapezoid-shaped groove 51 is formed at an inner end portion of a
focus ring 5 and a rectangular groove 51 is formed outside thereof
in a diametric direction. Further, FIG. 3C shows a case where three
circular hollow grooves 51 are successively formed inside a focus
ring 5. The present disclosure is related to a technique of forming
a groove in a focus ring so as to obtain a desired electric field
distribution, and, thus, it may be possible to form an optimal
groove for a desired electric field distribution.
Experimental Example 1
[0068] As a focus ring to be installed in the plasma processing
apparatus 1, a couple of the focus rings 5 illustrated in FIG. 2B
were prepared. A heat transfer sheet having a heat conductivity of
about 1 W/MK was almost fully filled in a groove 51 of one focus
ring. It will be referred to as "groove-formed focus ring of 1 W
type" in the specification hereinafter. Further, a heat transfer
sheet having a heat conductivity of about 17 W/MK was almost fully
filled in a groove 51 of the other focus ring. It will be referred
to as "groove-formed focus ring of 17 W type" in the specification
hereinafter. Furthermore, as a comparative example, the
conventional focus ring illustrated in FIG. 2A was prepared. It
will be referred to as "conventional focus ring" in the
specification hereinafter.
[0069] Then, three sheets of blanket wafers (hereinafter, referred
to as "wafer Ox") having a diameter of about 300 mm with an oxide
film formed thereon and three sheets of blanket wafers
(hereinafter, referred to as "wafer Ni") having a diameter of about
300 mm with a nitride film formed thereon were prepared. The
conventional focus ring, the groove-formed focus ring of 1 W type,
and the groove-formed focus ring of 17 W type were installed around
the blanket wafers Ox and Ni, respectively; a processing gas of
C.sub.4F.sub.6/Ar/O.sub.2(18/225/10) was supplied; and a plasma
process was performed on each of the wafers Ox and the wafers Ni
for about 60 seconds. Here, a temperature of an upper electrode, a
temperature of a wall surface of a processing chamber, and a
temperature of a bottom surface of an electrostatic chuck were
about 60.degree. C., 60.degree. C., and 45.degree. C.,
respectively.
[0070] FIG. 4 is a graph showing etching rates of the wafers Ox and
FIG. 5 is a graph showing etching rates of the wafers Ni under the
above-described plasma process conditions. In the horizontal axis
of the graphs in FIGS. 4 and 5, a point "O" represents a central
point of the wafer and the right and left sides in a diametric
direction from that point are represented in millimeters up to 150
mm. The vertical axis represents an etching rate (nm/min) of an
oxide film or an etching rate (nm/min) of a nitride film.
[0071] As depicted in FIG. 4, when the conventional focus ring was
installed around the wafer Ox and the plasma process was performed
thereon, an etching rate of the oxide film is about 187 nm/min at
the central portion of the wafer and is increased toward the end
portion thereof. At a position about 30 mm away from the end
portion of the wafer, the etching rate has the maximum value of
about 195 nm/min. From that position to the farthest end portion,
the etching rate is approximately constant.
[0072] Meanwhile, when the groove-formed focus ring of 1 W type was
installed around the wafer Ox and the plasma process was performed
thereon, the etching rate is approximately the same as the etching
rate (about 187 nm/min) of the conventional focus ring at the
central portion of the wafer, but the etching rate is increased
toward the end portion thereof. At a position about 30 mm away from
the end portion of the wafer, the etching rate is about 197 nm/min.
From that position to the farthest end portion, the etching rate is
sharply increased and is about 218 nm/min at the farthest end
portion.
[0073] The etching rate of the groove-formed focus ring of 17 W
type has approximately the same characteristic as that of the
groove-formed focus ring of 1 W type as illustrated in FIG. 4.
[0074] FIG. 5 is a graph showing an etching rate of a nitride film
when the conventional focus ring was installed around the wafer Ni
and the plasma process was performed under the above-described
conditions. As shown in FIG. 5, the etching rate is about -2 nm/min
at the central portion of the wafer, which means that CxFy has been
deposited at the central portion of the wafer. Further, the etching
rate is decreased to a larger minus value (deposition rate of CxFy
is increased) toward the end portion thereof. From a position about
50 mm away from the end portion of the wafer to the farthest end
portion, the deposition rate is increased.
[0075] Meanwhile, when the groove-formed focus ring of 1 W type was
installed around the wafer Ni and the plasma process was performed
thereon, the etching rate has a slightly bigger minus value (about
-4 nm/min) at the central portion of the wafer than that of the
conventional focus ring. However, the etching rate comes to have
plus values from minus values as it goes to the end portion. That
is, at a position about 25 mm away from the end portion of the
wafer, the deposition rate and the etching rate becomes
substantially the same, and the etching rate is increased toward
the end portion of the wafer from that position.
[0076] The etching rate of the groove-formed focus ring of 17 W
type on the wafer Ni has a different etching rate but approximately
the same characteristic as that of the groove-formed focus ring of
1 W type.
[0077] In view of the foregoing, the following facts have been
proved. A difference in the heat conductivity of the heat transfer
sheet embedded in the groove 51 does not make a big difference in
the etching characteristic. That is because that the groove 51
formed in the focus ring 5 does not cause a change in its heat
capacity but causes a change in the impedance of the focus ring 5,
so that an electric field distribution in its vicinity is varied by
a change of the impedance. As a result, an intensity of the plasma
(electric charge) impact on the wafer 15 is changed. Therefore, if
a shape of the groove 51 is changed so as to obtain a desired
electric field distribution according to a material to be
plasma-processed, a desired electric field distribution can be
formed at a desired position. Accordingly, the plasma process can
be uniformly performed on the wafer 15.
Experimental Example 2
[0078] Subsequently, as a focus ring 5 to be installed in the
plasma processing apparatus 1, the groove-formed focus ring of 1 W
type and the groove-formed focus ring of 17 W type were prepared in
the same manner as experimental example 1, and as a comparative
example thereof, the conventional focus ring was also prepared to
find characteristics of a sputtering rate.
[0079] Then, three sheets of blanket wafers having a diameter of
about 300 mm were prepared in the same manner as the experimental
example 1. Thereafter, the conventional focus ring, the
groove-formed focus ring of 1 W type, and the groove-formed focus
ring of 17 W type were installed around the blanket wafers,
respectively; a plasma processing chamber was depressurized to
about 35 millitorr; a processing gas of Ar/O.sub.2 (1225/15) was
supplied; and a plasma process was performed on each of the blanket
wafers for about 60 seconds. Here, a temperature of an upper
electrode, a temperature of a wall surface of the processing
chamber, and a temperature of a bottom surface of an electrostatic
chuck were about 60.degree. C., 60.degree. C., and 45.degree. C.,
respectively.
[0080] FIGS. 6A and 6B are graphs each showing a characteristic of
a sputtering rate in case of using the above-described three kinds
of focus rings under the above-stated plasma process conditions. In
the horizontal axis of the graphs in FIGS. 6A and 6B, a point "O"
represents a central point of the wafer and the right and left
sides in a diametric direction from that point are represented in
millimeters up to 150 mm. The vertical axis represents a sputtering
rate in a unit of nm/min.
[0081] As shown in FIG. 6A, when the conventional focus ring was
installed around the blanket wafer and the plasma process was
performed thereon, the sputtering rate is about 15 mm/min at the
central portion of the wafer and is decreased toward the end
portion thereof. From a position about 40 mm away from the end
portion of the wafer, the sputtering rate is sharply decreased and
is about 13 nm/min at the farthest end portion.
[0082] Meanwhile, when the groove-formed focus ring of 1 W type was
installed around the blanket wafer and the plasma process was
performed thereon, the sputtering rate is about 17 nm/min at the
central portion of the wafer. From a position about 40 mm away from
the end portion of the wafer, the sputtering rate is gradually
decreased. However, from a position about 10 mm away from the end
portion of the wafer to the farthest end portion, the sputtering
rate is increased and is about 19 nm/min at the farthest end
portion, which shows a characteristic contrary to that of the
conventional focus ring.
[0083] The sputtering rate of the groove-formed focus ring of 17 W
type has approximately the same characteristic as that of the
groove-formed focus ring of 1 W type.
[0084] FIG. 6B is a graph showing normalized sputtering rates in
case of using the three kinds of focus rings illustrated in FIG.
6A. As shown in FIG. 6B, a difference in the heat conductivity of
the heat transfer sheet embedded in the groove 51 does not make a
big difference in the sputtering rate characteristic. Therefore,
the groove 51 formed in the focus ring 5 does not cause a change in
its heat capacity but causes a change in the impedance of the focus
ring 5, so that an electric field distribution in its vicinity can
be varied by the change of the impedance. As a result, it is deemed
that an intensity of the plasma impact is changed, resulting in a
change of the sputtering rate.
Experimental Example 3
[0085] Subsequently, as a focus ring 5 to be installed in the
plasma processing apparatus 1, the groove-formed focus ring of 1 W
type and the groove-formed focus ring of 17 W type were prepared in
the same manner as experimental examples 1 and 2, and as a
comparative example thereof, the conventional focus ring was
prepared to find characteristics of a deposition rate.
[0086] Then, three sheets of blanket wafers having a diameter of
about 300 mm were prepared. The conventional focus ring, the
groove-formed focus ring of 1 W type, and the groove-formed focus
ring of 17 W type were installed around the blanket wafers,
respectively; a plasma processing chamber was depressurized to
about 35 millitorr; a processing gas including C.sub.4F.sub.6/Ar
(18/1225) was supplied; and a plasma process was performed on each
of the blanket wafers for about 60 seconds. Here, a temperature of
an upper electrode, a temperature of a wall surface of the
processing chamber, and a temperature of a bottom surface of an
electrostatic chuck were about 60.degree. C., 60.degree. C., and
45.degree. C., respectively.
[0087] FIGS. 7A and 7B are graphs each showing a characteristic of
a deposition rate when the above-described three kinds of focus
rings, i.e., the conventional focus ring, the groove-formed focus
ring of 1 W type, and the groove-formed focus ring of 17 W type,
were installed around each of the blanket wafers under the
above-stated plasma process conditions. In the horizontal axis of
the graphs in FIGS. 7A and 7B, a point "O" represents a central
point of the wafer and the right and left sides in a diametric
direction from that point are represented in millimeters up to 150
mm. The vertical axis represents a deposition rate in a unit of
nm/min.
[0088] As shown in FIG. 7A, when the conventional focus ring was
installed around the blanket wafer and the plasma process was
performed thereon, the deposition rate is about nm/min at the
central portion of the wafer and is gradually increased toward the
end portion thereof. From a position about 50 mm away from the end
portion of the wafer, the deposition rate is sharply increased and
is about 105 nm/min at the farthest end portion.
[0089] Meanwhile, when the groove-formed focus ring of 1 W type was
installed around the blanket wafer and the plasma process was
performed thereon, at the central portion of the wafer, the
deposition rate is about 80 nm/min, which is approximately the same
deposition rate as that of the conventional focus ring. However, on
the contrary to the conventional focus ring, from a position about
50 mm away from the end portion of the wafer, the deposition rate
is decreased and is about 70 nm/min at the farthest end
portion.
[0090] The deposition rate of the groove-formed focus ring of 17 W
type has approximately the same characteristic as that of the
groove-formed focus ring of 1 W type as depicted in FIG. 7A.
[0091] FIG. 7B is a graph showing normalized deposition rates of
the three kinds of focus rings illustrated in FIG. 7A. As can be
seen from FIG. 7B, a difference in the heat conductivity of the
heat transfer sheet embedded in the groove 51 does not make a big
difference in the deposition rate characteristic as mentioned in
experimental examples 1 and 2. Therefore, the groove 51 formed in
the focus ring 5 does not cause a change in its heat capacity but
causes a change in the impedance of the focus ring 5, so that an
electric field distribution in its vicinity can be varied by the
change of the impedance. As a result, it is deemed that an
intensity of the plasma impact is changed, resulting in a change in
the deposition rate.
[0092] In view of the foregoing, by forming a groove in a focus
ring and changing a shape of the groove, a desired electric field
distribution can be formed at a desired position. Therefore, it is
obvious that an etching rate or a deposition rate can be adjusted
to be a desired value at a desired position.
[0093] The present disclosure is not limited to a plasma etching
apparatus but can be applied to other plasma processing apparatuses
for plasma CVD, plasma oxidation, plasma nitridation, sputtering or
the like. Further, a target substrate of the present disclosure is
not limited to a semiconductor wafer but can be any one of various
kinds of substrates for flat panel display, a photo mask, a CD
substrate, and a print substrate.
* * * * *