U.S. patent number RE42,175 [Application Number 12/470,231] was granted by the patent office on 2011-03-01 for electrostatic chucking stage and substrate processing apparatus.
This patent grant is currently assigned to Canon Anelva Corporation, NHK Spring Co., Ltd.. Invention is credited to Masayoshi Ikeda, Tadashi Inokuchi, Kazuaki Kaneko, Takashi Kayamoto, Takuji Okada, Yasumi Sago, Toshihiro Tachikawa.
United States Patent |
RE42,175 |
Sago , et al. |
March 1, 2011 |
Electrostatic chucking stage and substrate processing apparatus
Abstract
This application discloses the structure of an ESC stage where a
chucking electrode is sandwiched by a moderation layer and a
covering layer. The moderation layer and the covering layer have
the thermal expansion coefficients between the dielectric plate and
the chucking electrode. This application also discloses the
structure of an ESC stage where a chucking electrode is sandwiched
by a moderation layer and a covering layer, which have internal
stress directed oppositely to that of the chucking electrode. This
application further discloses a substrate processing apparatus for
carrying out a process onto a substrate as the substrate is
maintained at a temperature higher than room temperature,
comprising the electrostatic chucking stage for holding the
substrate during the process.
Inventors: |
Sago; Yasumi (Tokyo,
JP), Kaneko; Kazuaki (Tokyo, JP), Okada;
Takuji (Kawasaki, JP), Ikeda; Masayoshi (Tokyo,
JP), Tachikawa; Toshihiro (Isehara, JP),
Inokuchi; Tadashi (Yasu, JP), Kayamoto; Takashi
(Isehara, JP) |
Assignee: |
Canon Anelva Corporation
(Kawasaki-shi, JP)
NHK Spring Co., Ltd. (Yokohama-shi, JP)
|
Family
ID: |
29395712 |
Appl.
No.: |
12/470,231 |
Filed: |
May 21, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
10413136 |
Apr 15, 2003 |
07220319 |
May 22, 2007 |
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Foreign Application Priority Data
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Apr 16, 2002 [JP] |
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2002-113563 |
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Current U.S.
Class: |
118/725; 279/128;
361/234; 118/728; 156/345.53; 118/724 |
Current CPC
Class: |
B25B
11/002 (20130101); Y10T 279/23 (20150115) |
Current International
Class: |
H01L
21/00 (20060101); C23C 16/00 (20060101); C23C
14/00 (20060101) |
Field of
Search: |
;361/234 ;279/128
;156/345.51,345.53 ;118/724 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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09-045757 |
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Feb 1997 |
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JP |
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10-041377 |
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Feb 1998 |
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JP |
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10-270540 |
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Oct 1998 |
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JP |
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11-157953 |
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Jun 1999 |
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JP |
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11-168134 |
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Jun 1999 |
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JP |
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2001-223261 |
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Aug 2001 |
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JP |
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2002-033376 |
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Jan 2002 |
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JP |
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Primary Examiner: Kackar; Ram N.
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper &
Scinto
Claims
What is claimed is:
1. An electrostatic chucking stage for electro-statically chucking
an object, comprising: a dielectric plate on which the object is
chucked; a chucking electrode to which voltage for dielectrically
polarizing the dielectric plate is applied; a moderation layer
provided between the dielectric plate and the chucking electrode,
and having a thermal expansion coefficient between a thermal
expansion coefficient of the dielectric plate and a thermal
expansion coefficient of the chucking electrode; a covering layer
provided on the chucking electrode at a side opposite to the
dielectric plate so that the chucking electrode is sandwiched by
the moderation layer and the covering layer, said covering layer
having a thermal expansion coefficient between the thermal
expansion coefficient of the dielectric plate and the thermal
expansion coefficient of the chucking electrode; and wherein the
moderation layer and the covering layer have structures comprising
metal filled into porous bulks made of ceramic, wherein the thermal
expansion coefficients of the moderation layer and the covering
layer are obtained by adjusting volume opening ratios of the porous
bulks, wherein the chucking electrode has a flange part at a
periphery thereof and is fixed to a metallic main body by screwing
at the flange part, and the covering layer is inserted between the
chucking electrode and the main body in an interfacial recess inner
to the flange part, wherein the moderation layer and the covering
layer are separated so as not to cover an end of the electrode, and
wherein the electrode and the metallic main body are electrically
conducted through the metal filled into the porous ceramic of the
covering layer to apply the voltage for chucking without a
connecting line through the covering layer.
2. An electrostatic chucking stage for electro-statically chucking
an object as claimed in claim 1, wherein the dielectric plate is
made of magnesia, the chucking electrode is made of aluminum, and
the moderation layer and the covering layer are made of composite
of aluminum and ceramic.
3. An electrostatic chucking stage for electro-statically chucking
an object as claimed in claim 2, wherein the dielectric plate and
the moderation layer are brazed with a brazing material containing
aluminum as a main component.
4. An electrostatic chucking stage for electro-statically chucking
an object as claimed in claim 2, wherein the dielectric plate and
the moderation layer are soldered with solder containing tin as a
main component.
5. An electrostatic chucking stage for electro-statically chucking
an object as claimed in claim 2, wherein the dielectric plate and
the moderation layer are soldered with solder containing lead as a
main component.
6. An electrostatic chucking stage for electro-statically chucking
an object as claimed in claim 1, wherein the dielectric plate is
made of alumina, the chucking electrode is made of aluminum, and
the moderation layer and the covering layer are made of composite
of aluminum and ceramic.
7. An electrostatic chucking stage for electro-statically chucking
an object as claimed in claim 6, wherein the dielectric plate and
the moderation layer are brazed with a brazing material containing
indium as a main component.
8. A substrate processing apparatus for processing onto a substrate
as the substrate is maintained at a temperature higher than room
temperature, comprising an electrostatic chucking stage as claimed
in claim 1 for holding the substrate during process.
9. A substrate processing apparatus as claimed in claim 8,
comprising a plasma generator for generating plasma at a space
facing the substrate, wherein the process utilizes the plasma.
10. An electrostatic chucking stage for electro-statically chucking
an object, comprising: a dielectric plate on which the object is
chucked; a chucking electrode to which voltage for dielectrically
polarizing the dielectric plate is applied; a moderation layer
provided between the dielectric plate and the chucking electrode,
and having a thermal expansion coefficient between a thermal
expansion coefficient of the dielectric plate and a thermal
expansion coefficient of the chucking electrode, said moderation
layer having a peripheral side open for thermal expansion without
being covered by the dielectric plate; a covering layer provided on
the chucking electrode at a side opposite to the moderation layer
so that the chucking electrode is sandwiched by the moderation
layer and the covering layer, said covering layer having a thermal
expansion coefficient between the thermal expansion coefficient of
the dielectric plate and the thermal expansion coefficient of the
chucking electrode; and a protection ring surrounding a peripheral
side of the chucking electrode, and being provided separately from
the dielectric plate and the moderation layer, wherein the
moderation layer and the covering layer have structures comprising
metal filled into porous bulks made of ceramic, wherein the thermal
expansion coefficients of the moderation layer and the covering
layer are obtained by adjusting volume opening ratios of the porous
bulks, wherein the chucking electrode has a flange part at a
periphery thereof and is fixed to a metallic main body by screwing
at the flange part, and the covering layer is inserted between the
chucking electrode and the main body in an interfacial recess inner
to the flange part, wherein the moderation layer and the covering
layer are separated so as not to cover an end of the electrode and
so as to allow the electrode thermally expand at the end thereof,
and wherein the electrode and the metallic main body are
electrically conducted through the metal filled into the porous
ceramic of the covering layer to apply the voltage for chucking
without a connecting line through the covering layer.
11. An electrostatic chucking stage for electro-statically chucking
an object as claimed in claim 10, wherein the dielectric plate is
made of magnesia, the chucking electrode is made of aluminum, and
the moderation layer and the covering layer are made of composite
of aluminum and ceramic.
12. An electrostatic chucking stage for electro-statically chucking
an object as claimed in claim 11, wherein the dielectric plate and
the moderation layer are brazed with a brazing material containing
aluminum as a main component.
13. An electrostatic chucking stage for electro-statically chucking
an object as claimed in claim 11, wherein the dielectric plate and
the moderation layer are soldered with solder containing tin as a
main component.
14. An electrostatic chucking stage for electro-statically chucking
an object as claimed in claim 11, wherein the dielectric plate and
the moderation layer are soldered with solder containing lead as a
main component.
15. An electrostatic chucking stage for electro-statically chucking
an object as claimed in claim 10, wherein the dielectric plate is
made of alumina, the chucking electrode is made of aluminum, and
the moderation layer and the covering layer are made of composite
of aluminum and ceramic.
16. An electrostatic chucking stage for electro-statically chucking
an object as claimed in claim 15, wherein the dielectric plate and
the moderation layer are brazed with a brazing material containing
indium as a main component.
17. A substrate processing apparatus for processing a substrate as
the substrate is maintained at a temperature higher than room
temperature, comprising an electrostatic chucking stage as claimed
in claim 10 for holding the substrate during process.
18. A substrate processing apparatus as claimed in claim 17,
comprising a plasma generator for generating plasma at a space
facing the substrate, wherein the process utilizes the plasma.
.Iadd.19. An electrostatic chucking stage for electro-statically
chucking an object, the stage comprising: a dielectric plate for
chucking the object; a chucking electrode for receiving a voltage
for dielectrically polarizing the dielectric plate; a first layer
provided between the dielectric plate and the chucking electrode,
and having a thermal expansion coefficient between a thermal
expansion coefficient of the dielectric plate and a thermal
expansion coefficient of the chucking electrode; a second layer
provided on the chucking electrode so that the chucking electrode
is sandwiched by the first layer and the second layer, the second
layer having a thermal expansion coefficient between the thermal
expansion coefficient of the dielectric plate and the thermal
expansion coefficient of the chucking electrode; and a main body
supporting the second layer, wherein the first and second layers
and the main body are electroconductive, and wherein for connecting
electrical power to the chucking electrode, an electrical power
providing portion is connected to the main body, which conducts to
the chucking electrode through the second layer. .Iaddend.
.Iadd.20. An electrostatic chucking stage for electro-statically
chucking an object according to claim 19, wherein the dielectric
plate is made of magnesia, the chucking electrode is made of
aluminum, and each of the first layer and the second layer is made
of a composite of aluminum and ceramic. .Iaddend.
.Iadd.21. An electrostatic chucking stage for electro-statically
chucking an object according to claim 20, wherein the dielectric
plate and the first layer are brazed with a brazing material
containing aluminum as a main component. .Iaddend.
.Iadd.22. An electrostatic chucking stage for electro-statically
chucking an object according to claim 20, wherein the dielectric
plate and the first layer are soldered with solder containing tin
as a main component. .Iaddend.
.Iadd.23. An electrostatic chucking stage for electro-statically
chucking an object according to claim 20, wherein the dielectric
plate and the first layer are soldered with solder containing lead
as a main component. .Iaddend.
.Iadd.24. An electrostatic chucking stage for electro-statically
chucking an object according to claim 19, wherein the dielectric
plate is made of alumina, the chucking electrode is made of
aluminum, and each of the first layer and the second layer is made
of a composite of aluminum and ceramic. .Iaddend.
.Iadd.25. An electrostatic chucking stage for electro-statically
chucking an object according to claim 24, wherein the dielectric
plate and the first layer are brazed with a brazing material
containing indium as a main component. .Iaddend.
.Iadd.26. An electrostatic chucking stage for electro-statically
chucking an object, the stage comprising: a dielectric plate for
chucking the object; a chucking electrode for receiving a voltage
for dielectrically polarizing the dielectric plate; a first layer
provided between the dielectric plate and the chucking electrode,
and having a thermal expansion coefficient between a thermal
expansion coefficient of the dielectric plate and a thermal
expansion coefficient of the chucking electrode; a second layer
provided on the chucking electrode so that the chucking electrode
is sandwiched by the first layer and the second layer, the second
layer having a thermal expansion coefficient between the thermal
expansion coefficient of the dielectric plate and the thermal
expansion coefficient of the chucking electrode; and a main body
supporting the second layer, wherein the first layer and the second
layer have structures comprising metal filled into porous bulks
made of ceramic, wherein the thermal expansion coefficients of the
first layer and the second layer are obtained by adjusting volume
opening ratios of the porous bulks, wherein the first and second
layers and the main body are electroconductive, and wherein for
connecting electrical power to the chucking electrode, an
electrical power providing portion is connected to the main body,
which conducts to the chucking electrode through the second layer.
.Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electrostatic chucking (ESC) stage for
holding a board-shaped object such as a substrate, and a substrate
processing apparatus comprising the ESC stage.
2. Description of the Related Art
The ESC stages for chucking substrates by electrostatic force are
used widely in the field of substrate processing. In manufacturing
electronic devices such as LSIs (Large-Scale Integrate circuits)
and display devices such as LCDs (Liquid Crystal Displays), for
example, there are many steps of processing substrates that are
bases for products. In these steps, ESC stages are used for
securing process uniformity and process reproducibility. Taking the
plasma etching as an example, a substrate is etched, utilizing
functions of ions and activated species produced in plasma. In
this, an ESC stage is used for holding the substrate at an optimum
position against the plasma.
Generally, an ESC stage comprises a chucking electrode to which
voltage for chucking is applied, and a dielectric plate that is
polarized by the voltage applied to the chucking electrode. The
held substrate is in contact with the dielectric plate, and chucked
by static electricity induced on the surface of the dielectric
plate.
ESC stages are demanded to chuck substrates with making them
stable. If a substrate is displaced or changes the posture on an
ESC stage while a process is carried out, it might bring the
problem of degrading the process uniformity and the process
reproducibility. Thermal transformation and thermal expansion of an
ESC stage could be critical in substrate processing in view of
process homogeneity and process reproducibility. Temperatures of
substrates during processes are often higher than room temperature.
This is usually from process conditions, otherwise because of
environments in process chambers in which processes are carried
out. Anyway, when temperature of a substrate rises up, temperature
of the ESC stage rises up as well. If thermal transformation or
thermal expansion of the ESC stage takes place from the temperature
rise, the held substrate might be transformed or displaced.
SUMMARY OF THE INVENTION
The invention of this application is to solve the above described
subjects, and has the advantage of presenting a high-performance
ESC stage capable of preventing transformation and displacement of
a held substrate. Concretely, the invention presents the structure
of an ESC stage where a chucking electrode is sandwiched by a
moderation layer and a covering layer. The moderation layer and the
covering layer have the thermal expansion coefficient between the
dielectric plate and the chucking electrode. The invention also
presents the structure of another ESC stage where a chucking
electrode is sandwiched by a moderation layer and a covering layer,
which have internal stress directed oppositely to that of the
chucking electrode. This invention also presents a substrate
processing apparatus for carrying out a process onto a substrate as
the substrate is maintained at a temperature higher than room
temperature, comprising an ESC stage for holding the substrate
during the process.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a schematic front cross-sectional view of the ESC stage
as the embodiment of the invention.
FIG. 2 schematically explains the advantage of the ESC stage shown
in FIG. 1.
FIG. 3 is a schematic front cross-sectional view of the substrate
processing apparatus as the embodiment of the invention.
FIG. 4, FIG. 5, FIG. 6 and FIG. 7 schematically show the result of
an experiment for confirming the effect obtained from the structure
of the embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The preferred embodiments of this invention will be described as
follows. First, the ESC stage of the embodiment will be described.
FIG. 1 is a schematic front cross-sectional view of the ESC stage
of the embodiment. The ESC stage comprises a main body 41, a
dielectric plate 42 on which an object 9 is chucked, and a chucking
electrode 43 to which voltage for chucking is applied.
The ESC stage is table-like as a whole, and holds the board-shaped
object 9 on the top surface. The main body 41 is made of metal such
as aluminum or stainless-steel. The main body 41 is low column
shaped. The chucking electrode 43 is fixed on the main body 41. As
shown in FIG. 1, the chucking electrode 43 has a flange-shaped part
431 at bottom end. This part 431 is hereinafter called "electrode
flange". The chucking electrode 43 is fixed on the main body 41 at
the electrode flange 431 by screwing. The chucking electrode 43 is
electrically shorted with the main body 41.
A protection ring 49 is provided, surrounding the screwed electrode
flange 431. The protection ring 49 is made of insulator such as
silicon oxide. The protection ring 49 is to protect the side of the
chucking electrode 43 and the electrode flange 431 by covering
them.
The dielectric plate 42 is located at the upside of the chucking
electrode 43. As shown in FIG. 1, the chucking electrode 43 is
formed of an upward convex part and a flange-like part surrounding
the convex part. The dielectric plate 42 is almost the same in
diameter as the chucking electrode 43.
A chucking power source 40 is connected with the above-described
ESC stage. The type of the chucking power source 40 depends on that
of the electrostatic chucking. The ESC stage of this embodiment is
the mono-electrode type. A positive DC power source is adopted as
the chucking power source 40. The chucking power source 40 is
connected with the main body 41, applying the positive DC voltage
to the chucking electrode 43 via the main body 41. The applied
voltage to the chucking electrode 43 causes dielectric
polarization, which enables to chuck the object 9. In this
embodiment, because the positive DC voltage is applied, positive
charges are induced on the surface of the dielectric plate 42,
thereby chucking the object 9 electro-statically.
Two mechanisms of the electro-static chucking have been known. One
is by Coulomb force, and the other one is by Johnson-Rahbeck force.
Johnson-Rahbeck force is the chucking force generated by
convergence of currents at micro-regions. The surfaces of the
dielectric plate 42 and the objects 9 are microscopically uneven.
Micro-protrusions on the both surfaces contact with each other.
When the electrostatic charges are induced by the chucking power
source 40, the flowing currents converge at the protrusions
contacting with each other, thereby generating the Johnson-Rahbeck
force. The Johnson-Rahbeck force is dominant in such an ESC stage
as this embodiment. Still, the present invention is not limited to
the one where the Johnson-Rahbeck force is dominant.
One of points greatly characterizing the ESC stage of this
embodiment is in the structure where thermal displacement and
thermal transformation of the object 9 are effectively prevented.
This point will be described as follows. The ESC stage of this
embodiment is supposedly used at a hot temperature environment.
This would happen in case, for example, the object 9 is subjected
to a test under a hot temperature environment, other than the case
that the object 9 is a substrate to be processed, as described
later. In the ESC stage of this embodiment, thermal displacement
and thermal transformation are prevented even if it is used at a
high-temperature environment.
Concretely, as shown in FIG. 1, a moderation layer 44 is provided
between the dielectric plate 42 and the chucking electrode 43. The
moderation layer 44 moderates difference of the thermal expansion
coefficients between the dielectric plate 42 and the chucking
electrode 43 so that thermal displacement and thermal
transformation of the object 9 can be prevented. More concretely,
the moderation layer 44 has an intermediate value of the thermal
expansion coefficient between that of the dielectric plate 42 and
that of the chucking electrode 43. "Intermediate value of the
thermal expansion coefficient" just means: if the thermal expansion
coefficient of the chucking electrode 43 is higher than the
dielectric plate 42, then it is lower than the chucking electrode
43 and higher than the dielectric plate 42; and if the thermal
expansion coefficient of the dielectric plate 42 is higher than the
chucking electrode 43, then it is lower than the dielectric plate
42 and higher than the chucking electrode 43.
In this embodiment, specifically, the chucking electrode 43 is made
of aluminum, and the dielectric plate 42 is made of magnesia (MgO).
The moderation layer 44 is made of composite of ceramic and metal.
As composite having the thermal expansion coefficient between
aluminum and magnesia, we can name composite of silicon carbide and
aluminum, which hereinafter called "SiC--Al composite". The thermal
expansion coefficient of aluminum is 0.237.times.10.sup.-4/K, and
that of magnesia is 14.times.10.sup.-6/K. In this case, the SiC--Al
composite having the thermal expansion coefficient of about
10.times.10.sup.-6/K is preferably chosen as material of the
moderation layer 44. This kind of SiC--Al composite is manufactured
by poring melting aluminum into porous SiC bulk and fill out it.
The porous SiC bulk is prepared by the hot-temperature
high-pressure sinter-molding of SiC powder. After cooling pored
aluminum, the moderation layer 44 shaped as in Fin. 1 is obtained
by such machine work as cutting. The volume opening ratio of the
porous SiC--Al bulk is adjusted by choosing an adequate temperature
and an adequate pressure in the sinter-molding, which enables to
adjust the volume of filled aluminum. The volume opening ratio is
obtained by comparing density of the porous bulk with that of a
non-porous one of the same size. The thermal expansion coefficient
of the SiC--Al composite manufactured in the described manner
depends on the component ratio of aluminum against SiC. The
described thermal expansion coefficient of 10.times.10.sup.-6/K is
obtained by adjusting the component ratio.
In addition in the ESC stage of this embodiment, a covering layer
45 is provided on the chucking electrode 43 at the opposite side to
the moderation layer 44. In other words, the ESC stage has the
structure where the chucking electrode 43 is sandwiched by the
moderation layer 44 and the covering layer 45. The covering layer
45 is inserted between the chucking electrode 43 and the main body
41. This covering layer 45 is also made of material of which
thermal expansion coefficient is between the dielectric plate 42
and the chucking electrode 43. This is enabled by adopting the same
material as of the moderation layer 44. Still, different material
may be adopted for the covering layer 45.
The structure where the chucking electrode 43 is sandwiched by the
moderation layer 44 and the covering layer 45 having the in-between
thermal-expansion-coefficient enables to prevent displacement and
transformation of the chucked objected 9. This point will be
described in detail as follows, referring FIG. 2. FIG. 2
schematically explains the advantage of the ESC stage shown in FIG.
1.
Generally, there is large difference of the thermal expansion
coefficients between material of the chucking electrode, i.e.
metal, and material of the dielectric plate 42, i.e. dielectric. In
the prior-art structure where the dielectric plate 42 is fixed on
the chucking electrode 43, when the ESC stage is heated up to a hot
temperature, large transformation of the chucking electrode 43
would take place easily from its thermal expansion difference from
the dielectric plate 42. As a result, the dielectric plate 42 would
be also transformed to be convex as shown in FIG. 2(1), or to be
concave as shown in FIG. 2(2). Such a transformation of the
dielectric plate 42 would bring displacement or transformation of
the object 9 being chucked.
In the prior-art structure where the moderation layer 44 having the
in-between thermal-expansion-coefficient is inserted between the
dielectric plate 42 and the chucking electrode 43, the difference
of the thermal expansion coefficients is moderated, thereby
suppressing transformation of the dielectric plate 42. From the
research by the inventors, it has turned out that transformation of
the dielectric plate 42 is further suppressed when a layer similar
to the moderation layer 44 is provided at the opposite side in
addition, as shown in FIG. 2(4). Though the reason of this has not
been clarified completely, it is considered that thermal expansion
at the both sides of the chucking electrode 43 would be in a
balanced state when it is sandwiched by the layers having the
in-between thermal-expansion-coefficients. It is further considered
that internal-stress of the chucking electrode 43 would be balanced
by the both-sides layers having the similar thermal expansion
coefficients.
Respecting to thermal stress, it also could be considered that
thermal stress within the moderation layer 44 and the covering
layer 45 would function so as to restrain the transformation of the
chucking electrode 43. For example, when the chucking electrode 43
would be transformed to be convex upward, internal thermal stress
of the moderation layer 44 and the covering layer 45 could function
so as to transform it in the opposite way, i.e. making it convex
downward. In addition, it could take place that when compression
stress is produced within the chucking electrode 43, tensile stress
is produced within the moderation layer 44 and the covering layer
45. Inversely, compression stress could be produced within the
moderation layer 44 and the covering layer 45 when tensile stress
is produced within the chucking electrode 43. Generally, it can be
expressed that the moderation layer 44 and the covering layer 45
could have stress opposite against stress within the chucking
electrode 43. "Opposite" in this does not always mean that stress
is directed completely to an opposite direction. Expressing by
vectors, vectors of stress within the moderation layer 44 and the
covering layer 45 make an angle over 90 degrees against the vector
of stress within the chucking layer 43.
Anyway, provision of the covering layer 45 further restrains
transformation of the chucking electrode 43 and the consequent
transformation of the dielectric plate 42. As a result,
displacement and transformation of the object 9 can be restrained
as well. The point that the covering layer 45 has a similar
thermal-expansion-coefficient does not means complete
correspondence of the thermal expansion coefficient, but just means
that the covering layer 45 is similar to the moderation layer 44 in
view of having the in-between thermal-expansion-coefficient.
Although, the same ceramic-metal composite as of the moderation
layer 44, e.g. SiC-Al composite, may be employed as material of the
covering layer 45. The composite for the covering layer 45 is
conductive, having sufficient metal content. This is not to
insulate the chucking electrode 43 from the main body 41.
Structure for fixing the dielectric plate 42 is also significant in
view of restraining transformation of the dielectric plate 42. If
the dielectric plate 42 is fixed locally, e.g. by screwing, thermal
transformation of the dielectric plate 42 would be aggravated
because it is in a state pinched at the fixation points and thermal
conductivity is enhanced locally at the fixation points. In this
embodiment, the dielectric plate 42 is in junction with the
chucking electrode 43 by such brazing material as one of which main
component is aluminum or indium. "Main component" here implies pure
aluminum or pure indium, in addition to one including some
additive. For example, the junction is performed by whole-surface
brazing. Concretely, a thin sheet made of aluminum or indium is
inserted between the dielectric plate 42 and the moderation layer
44. By cooling them after heating them up a required hot
temperature, the dielectric plate 42 is fixed with the moderation
layer 44. In this blazing, it is preferable that pressure ranging
from 1 MPa to 2 MPa is mechanically applied with the heating at a
temperature ranging from 570.degree. C. to 590.degree. C., in view
of enhancing the thermal contact and the mechanical strength. Such
the junction by brazing restrains transformation of the dielectric
plate 42 further effectively. It is also practical to braze the
moderation layer 44 and the chucking electrode 43, and to braze the
chucking electrode 43 and the covering layer 45, in the same way.
The dielectric plate 42 and the moderation layer 44 may be soldered
by solder of which main component is tin or lead.
Next will be described the embodiment of the substrate processing
apparatus of the invention. The apparatus of the present invention
is to process a substrate, maintaining it at a temperature higher
than room temperature. In the following description, a plasma
etching apparatus is adopted as an example of substrate processing
apparatuses. Also in the following description, "object" is
replaced with "substrate" that is the sub-concept of it.
FIG. 3 is a schematic front cross-sectional view of the substrate
processing apparatus as the embodiment of the invention. The
apparatus shown in FIG. 3 comprises a process chamber in which
plasma etching is carried out onto the substrate 9, a process-gas
introduction line 2 to introduce a process gas into the process
chamber 1, a plasma generator 3 to generate plasma in the process
chamber 1 by applying energy to the introduced process gas, and an
ESC stage 4 to hold the substrate 9 by chucking it
electro-statically at a position where the substrate 9 can be
etched by a function of the plasma. The ESC stage 4 is almost the
same as the described embodiment.
The process chamber is the air-tight vacuum vessel, which is pumped
by a pumping line 11. The process chamber 1 is made of metal such
as stain-less steel and electrically grounded. The pumping line 11
comprises a vacuum pump 111 such as dry pump and a pumping speed
controller 112, thereby being capable of maintaining pressure in
the process chamber 1 at 10-3 Pa to 10 Pa.
The process-gas introduction line 2 is capable of introducing the
process gas for the plasma etching at a required flow-rate. In this
embodiment, such a reactive gas as CHF3 is introduced into the
process chamber 1 as the process gas. The process-gas introduction
line 2 comprises a gas bomb filled with the process gas, and a
feeding pipe interconnecting the gas bomb and the process chamber
1.
The plasma generator 3 generates the plasma by applying
radio-frequency (RF) energy to the introduced process gas. The
plasma generator 3 comprises an opposed electrode 30 facing to the
ESC stage 4, and an RF power source 31 to apply RF voltage to the
opposed electrode 30. The RF power source 31 is hereinafter called
"plasma-generation source". Frequency of the plasma-generation
source 31 ranges from 100 kHz to several tens MHz. The
plasma-generation source 31 is connected with the opposed electrode
30 interposing a matching circuit (not shown). Output of the
plasma-generation source 31 may range from 300 W to 2500 W. The
opposed electrode 30 is installed air-tightly with the process
chamber 1, inserting an insulator 32.
When the plasma-generation source 31 applies the RF voltage to the
opposed electrode 30, an RF discharge is ignited with the
introduced process gas by RF field provided in the process chamber
1. Through the discharge, the process gas transits to the state of
plasma. In case the process gas is fluoride, ions and activated
species of fluorine or fluoride are profusely produced in the
plasma. Those ions and species reach the substrate 9, thereby
etching the surface of the substrate 9.
Another RF power source 6 is connected with the ESC stage 4,
interposing a capacitor. This RF power source 6 is to make ions
incident onto the substrate 9 efficiently. This RF power source 6
is hereinafter called "ion-incidence source". When the
ion-incidence source 6 is operated in the state the plasma is
generated, self-biasing voltage is provided to the substrate 9. The
self biasing voltage is negative DC voltage that is generated
through the mutual reaction of the plasma and the RF wave. The
self-biasing voltage makes ions incident onto the substrate 9
efficiently, thereby enhancing the etching rate.
In this embodiment, a correction ring 46 is provided with the ESC
stage 4. The correction ring 46 is installed on the flange part of
the dielectric plate 42, being flush with the substrate 9. The
correction ring 46 is made of the same or similar material as the
substrate 9, e.g. silicon mono-crystal. The correction ring 46 is
to prevent non-uniformity or non-homogeneity of the process at the
periphery on the substrate 9. Temperature on the substrate 9 tends
to be lower at the periphery in comparison with the center, because
of heat dissipation from the edge of the substrate 9. For solving
this problem, the correction ring 46 made of the same or similar
material as the substrate 9 is provided surrounding the substrate 9
to compensate the heat dissociation. The plasma is sustained by
ions and electrons released from the substrate 9 during the etching
as well. The plasma density tends to be lower at the space facing
to the periphery of the substrate 9, because a less number of ions
and electrons are released, compared to the center. When the
correction ring 46 made of the same or similar material as the
substrate 9 is provided surrounding it, amount of ions and electros
supplied to the space facing the periphery of the substrate 9 is
increased, thereby making the plasma more uniform and more
homogeneous.
As described above, the ESC stage 4 comprises the protection ring
49. The protection ring 49 protects the side of the chucking
electrode 43 and the electrode flange from the damage by the plasma
or discharge. In case the substrate 9 is made of silicon, the
silicon-oxide-made protection ring 49 reduces probability to
contaminate the substrate 9 even if it is etched.
The ESC stage 4 is installed with the process chamber 1, inserting
an insulator 47. The insulator 47 is made of material such as
alumina, insulating the main body 41 from the process chamber 1 as
well as protecting the main body 41 from the plasma. For preventing
leakage of vacuum from the process chamber 1, vacuum seals such as
O-rings are provided between the ESC stage 4 and the insulator 47,
and between the process chamber 1 and the insulator 47.
The apparatus of this embodiment comprises a temperature controller
5 for controlling temperature of the substrate 9 during the
process. As described, temperature of a substrate to be kept during
a process, which is hereinafter called "optimum temperature", is
often higher than room temperature. In the plasma etching, however,
temperature of the substrate 9 easily exceeds the optimum
temperature by receiving heat from the plasma. For solving this
problem, the temperature controller 5 cools the substrate 9 and
controls temperature of it at the optimum value during the
etching.
As shown in FIG. 3, the chucking electrode 43 has a cavity in
itself. The temperature controller 5 circulates coolant through the
cavity to cool the chucking electrode 43, thereby cooling the
substrate 9 indirectly. The cavity preferably has a complex
configuration so that area for heat exchange by the coolant can be
enlarged. For example, a cavity having complex uneven walls is
formed by making a couple of cooling fin-plates face to each other
with each fin staggered. The temperature controller 51 comprises a
coolant feeding pipe 51 to feed the coolant into the cavity, a
coolant drainage pipe 52 to drain the coolant out of the cavity,
and a circulator 53 to circulate the coolant controlled at a
required low temperature. As the coolant, Fluorinate (trademark of
3M Corporation) is employed, for example. The temperature
controller 51 cools the substrate 9 at a temperature ranging from
80.degree. C. to 90.degree. C. by circulating the coolant of
30.degree. C. to 40.degree. C.
The substrate processing apparatus comprises a heat-transfer gas
introduction line (not shown) to introduce a gas between the
chucked substrate 9 and the dielectric plate 42. The heat-transfer
gas introduction is to enhance heat transfer efficiency between the
chucked substrate 9 and the dielectric plate 42. The back surface
of the substrate 9 and the top surface of the dielectric plate 42
are not completely planar, but rough microscopically. Heat transfer
efficiency is poor at spaces formed of the micro roughness on the
surfaces, because those are at a vacuum pressure. The heat-transfer
gas introduction line introduces a gas of high thermal
conductivity, e.g. helium, into the spaces, thereby improving heat
transfer efficiency.
The ESC stage 4 comprises lift pins 48 in the inside for accepting
and releasing the substrate 9. The lift pins 48 are elevated by an
elevation mechanism (not shown). Though only one lift pin 48
appears in FIG. 3, three lift pins 48 are provided actually.
Next will be described operation of the substrate processing
apparatus of this embodiment. After a transfer mechanism (not
shown) transfers the substrate 9 into the process chamber 1, the
substrate 9 is placed on the ESC stage 4 by operation of the lift
pins 48. With operation of the chucking power source 40, the
substrate 9 is chucked on the ESC stage 4. The process chamber 1
has been pumped at a required vacuum pressure in advance. In this
state, the process-gas introduction line 2 is operated to introduce
the process gas at a required flow-rate. Then, the
plasma-generation source 31 is operated, thereby generating the
plasma. The etching is performed utilizing the plasma as described.
The temperature controller 5 cools the substrate 9 at an optimum
temperature. During the etching, the ion-incidence source 6 is
operated for enhancing the etching efficiency. After performing the
etching for a required period, operations of the process-gas
introduction line 2, the plasma-generation source 31, and the
ion-incidence source 6 are stopped. Then, operation of the chucking
power source 40 is stopped, dissolving the chucking of the
substrate 9. After the process chamber 1 is pumped again, the
substrate 9 is transferred out of the process chamber 1 by the
transfer mechanism.
In the substrate processing apparatus, though the chucking
electrode 43 is heated higher than room temperature, its
transformation is restrained by the moderation layer 44 and the
covering layer as described. Therefore, transformation of the
dielectric plate 42, and displacement or transformation of the
substrate 9 caused thereby are restrained as well, Accordingly, the
process uniformity and the process homogeneity are enhanced.
The advantage of the moderation layer 44 and the covering layer 45
to restrain the transformation is greatly remarkable in the
structure where the correction ring 46 is provided. This point will
be described in detail as follows. The correction ring 46 has the
configuration essentially equivalent to extending the substrate 9
outward. Material of the correction ring 46 is the same as or
similar to the substrate 9. The correction ring 46 is provided on
the flange part of the dielectric plate 42, and chucked on it as
well as the substrate 9. Probability and volume of transformation
of the dielectric plate 42 would be greater at the flange part
comparatively, because the flange part is thin and peripheral. If
displacement or transformation of the correction ring 46 takes
place from transformation of the dielectric part 42, the function
to compensate heat dissociation from the edge of the substrate 9
would become out of uniform. Moreover, heat contact of the
correction ring 46 onto the dielectric plate 42 would be worsened
by the displacement or the transformation, resulting in that
temperature of the correction ring 46 rises higher than the
substrate 9. What is particularly serious is that the heat-contact
deterioration of the correction ring 46 onto the dielectric plate
happens randomly. The function of the correction ring 46 to heat
the substrate 9 compensatively also becomes random when the
heat-contact deterioration of the correction ring 46 becomes
random. This leads to much deteriorating reproducibility of the
temperature condition on the substrate 9 during the process.
In this embodiment, however, the correction ring 46 is hard to be
transformed or displaced, because transformation and displacement
of the dielectric plate 42 are restrained by suppressing
transformation of the chucking electrode 43. Therefore, this
embodiment is free from such the problems as non-uniformity and
non-reproducibility of the substrate temperature.
Next will be described the result of an experiment for confirming
the effect obtained from the structure of the embodiment. FIGS. 4
to 7 schematically show the result of this experiment. In this
experiment, transformation and displacement of the surface of the
dielectric plate 42 were measured under conditions of different
temperatures or different temperature histories on the ESC stages.
The transformation and the displacement are measured by a distance
meter. Setting a reference level above the ESC stage, distance from
each point on the surface of the dielectric plate 42 to the
reference level is measured by the distance meter for detecting
height of each point.
FIG. 4 and FIG. 5 both show heights of points on the surface of the
convex part of the dielectric plate 42. FIG. 4 shows the heights in
case of the prior-art ESC stage without the moderation layer 44 and
the covering layer 45. FIG. 5 shows the heights in case of the ESC
stage of the described embodiment with the moderation layer 44 and
the covering layer 45. FIG. 6 and FIG. 7 both show heights of
points on the surface of the flange part of the dielectric plate
42. FIG. 6 shows the heights in case of the prior-art ESC stage
without the moderation layer 44 and the covering layer 45. FIG. 7
shows the heights in case of the ESC stage of the described
embodiment with the moderation layer 44 and the covering layer 45.
Location of each point on the flange part designated by {circle
around (1)}, {circle around (2)}, {circle around (3)}, {circle
around (4)} in FIG. 6 and FIG. 7 is shown in FIG. 1 by the same
{circle around (1)}, {circle around (2)}, {circle around (3)},
{circle around (4)} respectively.
The experiment was carried out, varying temperature of the ESC
stages. Temperature of an ESO stage is hereinafter called "stage
temperature". In FIGS. 4 to 7, "A" designates data measured at the
stage temperature of 20.degree. C. after leaving the ESC stage at
20.degree. C. for all night long. "B" designates data measured,
keeping the stage temperature at 5.degree. C. "C" designates data
measured at the stage temperature of 20.degree. C. after cooling
the ESC stage at 5.degree. C. "D" designates data measured, keeping
the stage temperature at 50.degree. C. "E" designates data
measured, forcedly cooling the ESC stage at 20.degree. C. after
making the stage temperature 50.degree. C. Though the ESC stage 4
comprises openings for interior members such as the lift pins 48,
data at those openings are omitted in FIGS. 4 to 7.
Commonly in FIGS. 4 to 7, level of the dielectric plate 42 is
higher when the stage temperature is higher. This results from
thermal expansion of the whole ESC stage 4, being natural in a
sense. What is the problem is that displacement or transformation
of the dielectric plate 42 depends on values of the stage
temperature or histories of the stage temperature.
Specifically, each line appearing in FIG. 5 is drawn through points
on the surface of the dielectric plate 42, which is hereinafter
called "surface level distribution". As shown in FIG. 5, the
surface level distribution is elevated up and down, depending on
the stage temperature or the history of the stage temperature, as
it keeps the same figure. In short, it is displaced in parallel.
This supposedly demonstrates the dielectric plate 42 has not been
transformed and has performed the uniform thermal expansion. In
FIG. 4, contrarily, the surface level distribution is elevated up
and down as it changes the figure, depending on the stage
temperature or the history of the stage temperature. In short, it
is not displaced in parallel. This supposedly demonstrates
transformation of the dielectric plate 42 has taken place. What is
the problem in particular that the surface level distribution
changes the figure, depending on the history of the stage
temperature. As shown in FIG. 4, even in the measurements at the
same stage temperature 20.degree. C., the surface level
distribution draws different curves in case it was left at
20.degree. C. all night long and in case it was decreased by the
forced cooling from 50.degree. C.
The same analysis is applicable to the result at the flange part.
As shown in FIG. 6, in case that the moderation layer 44 and the
covering layer 45 are provided, the surface level distribution is
elevated up and down, keeping the same figure. Contrarily, as shown
in FIG. 7, in case that the moderation layer 44 and the covering
layer 45 are not provided, the surface level distribution is
elevated, changing the figure. Also at each different history of
the stage temperature, the surface level distribution draws a
different curve in FIG. 7.
The point that the surface level distribution depends on the
temperature histories would bring a serious problem with respect to
reproducibility of the substrate processing. Substrate processing
apparatuses fabricated at manufactures' factories are installed
into production lines and used after such works as delivery
inspections. However, the temperature histories of the apparatuses
until actual substrate processes are initially started are not the
same among the apparatuses. Even the apparatuses performing the
same processes almost always submit the different temperature
histories through works such as delivery inspections in the
manufactures' factories and test operations at the users' lines.
Moreover, considering each by-piece process of substrates, a
temperature history that the ESO stage has submitted until the
process for a substrate is carried may differ from another
temperature history that the ESO stage has submitted until the
process for another substrate is carried out. For example, a
temperature history that the ESC stage has submitted while the
by-piece processes are continuingly carried out differs from
another temperature history of the ESC stage that is initially used
for the process of the first substrate. Such a situation happens,
for example, when operation of the apparatus is resumed after
suspension for the maintenance.
The point that the surface level distribution depends on the
history of the stage temperature means that the substrate 9 would
be transformed or displaced depending on the history, even if the
ESC stage 4 is controlled at a constant temperature by the
temperature controller 5. This could be the serious problem with
respect to the process reproducibility. In case the moderation
layer 44 and the covering layer 45 are provided, however, the
surface level distribution does not depend on the history of the
stage temperature, with no transformation and no displacement of
the substrate 9. Therefore, processes with high reproducibility are
enabled only by maintaining the ESC stage 4 at a required
temperature.
More-detailed examples belonging to the embodiment will be
described as follows.
EXAMPLE 1
Material of Chucking Electrode 43: Aluminum Material of Dielectric
Plate 42: Magnesia (MgO) Fixation of Dielectric Plate 42: Brazing
by Al at 550.degree. C. Material of Moderation Layer 44: SiC--Al
composite Thickness of Moderation Layer 44: 1.2 mm Material of
Covering Layer 45: SiC--Al composite Thickness of Covering Layer
45: 1.2 mm Chucking Voltage: 500V
EXAMPLE 2
Material of Chucking Electrode 43: Aluminum Material of Dielectric
Plate 42: Alumina (Al.sub.2O.sub.3) Fixation of Dielectric Plate
42: Brazing by In at 120.degree. C. Material of Moderation Layer
44: SiC--Cu composite Thickness of Moderation Layer 44: 1.2 mm
Material of Covering Layer 45: SiC--Cu composite Thickness of
Covering Layer 45: 1.2 mm Chucking Voltage: 500V
In the EXAMPLE 2, "SiC--Cu composite means composite" made of
silicon carbide and cupper. Manufacture of this composite may be
the same process as of the described SiC--Al composite. Magnesia is
superior to alumina in erosion resistance. In case an erosive gas
is used as in the etching, the dielectric plate 42 made of magnesia
is more preferable. Size of the substrate 9 chucked by any one of
the examples is, for example, 300 mm diameter.
Material of the moderation layer 44 and the covering layer 45 is
not limited to described SiC--Al composite or SiC--Cu composite. It
may be another composite of ceramic and metal. For instance, it may
be composite of silicon carbide and nickel, composite of silicon
carbide and Fe--Ni--Co alloy, composite of silicon carbide and
Fe--Ni alloy, composite of silicon nitride (Si.sub.3N.sub.4) and
nickel, or composite of silicon nitride and Fe--Ni alloy. Moreover,
material of moderation layer 44 and the covering layer 45 is not
limited to composite of ceramic and metal. What is required is only
that it has the thermal expansion coefficient between the chucking
electrode 43 and the dielectric plate 42.
There are several types of electrostatic chucking such as the
bi-electrode type and the multi-electrode type, in addition to the
described mono-electrode type. The bi-electrode type comprises a
couple of chucking electrodes, to which voltages of opposite
polarity to each other are applied. The multi-electrode type
comprises multiple couples of chucking electrodes, applying
voltages of opposite polarity to each electrode of each couple. In
these types, the chucking electrodes may be buried within the
dielectric plate 42. In case of the mono-electrode type, negative
DC voltage may be applied for chucking. The present invention is
also enabled in these types. Though the described ESC stage chucks
the object or substrate 9 on the top surface, it may be overturned,
i.e. chucking the object or substrate 9 at the bottom surface.
Moreover, the ESC stage may chuck the object or substrate 9 on the
side surface, making it uprightly.
Though the plasma etching apparatus was adopted as the example of
substrate processing apparatuses in the above description, the
present invention is enabled for other apparatuses such as plasma
chemical vapor deposition (CVD) apparatuses and sputtering
apparatuses. The temperature controller 5 may heat the substrate 9
and maintain it at a required temperature. There are many other
applications of the ESC stage than substrate processing, for
example a test of an object such as an environmental testing
apparatus.
* * * * *