U.S. patent application number 12/647719 was filed with the patent office on 2010-04-22 for electrostatic chuck.
This patent application is currently assigned to CANON ANELVA CORPORATION. Invention is credited to Yoshiki ARUGA, Kazuaki Kaneko, Eitarou Morimoto, You Tanaka.
Application Number | 20100096262 12/647719 |
Document ID | / |
Family ID | 40452008 |
Filed Date | 2010-04-22 |
United States Patent
Application |
20100096262 |
Kind Code |
A1 |
ARUGA; Yoshiki ; et
al. |
April 22, 2010 |
ELECTROSTATIC CHUCK
Abstract
An electrostatic chuck (8) includes a dielectric board (14)
having an upper surface on which a plurality of projections (17a)
for supporting a substrate on top surfaces and recesses (17b)
surrounding the projections (17a) are formed, an electrode (15)
formed inside the dielectric board (14), and an external power
supply (15) which applies a voltage to the electrode (15). The
dielectric board (14) includes a conductor film (19) formed on at
least the top surface of each projection (17a), and has a
three-dimensional structure which causes the conductor film (19) to
generate a Johnson-Rahbeck force between the substrate (9) and
conductor film (19) when a voltage is applied to the electrode
(15).
Inventors: |
ARUGA; Yoshiki;
(Hachioji-shi, JP) ; Morimoto; Eitarou;
(Kunitachi-shi, JP) ; Tanaka; You; (Fuchu-shi,
JP) ; Kaneko; Kazuaki; (Fuchu-shi, JP) |
Correspondence
Address: |
BUCHANAN, INGERSOLL & ROONEY PC
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Assignee: |
CANON ANELVA CORPORATION
Kawasaki-shi
JP
|
Family ID: |
40452008 |
Appl. No.: |
12/647719 |
Filed: |
December 28, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2008/066340 |
Sep 11, 2007 |
|
|
|
12647719 |
|
|
|
|
Current U.S.
Class: |
204/298.08 |
Current CPC
Class: |
H01L 21/6875 20130101;
C23C 14/541 20130101; H02N 13/00 20130101; C23C 14/50 20130101;
H01L 21/6833 20130101 |
Class at
Publication: |
204/298.08 |
International
Class: |
C23C 14/35 20060101
C23C014/35 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 11, 2007 |
JP |
2007-234968 |
Claims
1. A sputtering apparatus including a vessel which is configured to
be evacuated by an external evacuating mechanism, a target arranged
in said vessel and connected to a sputtering power supply which
applies a voltage, a magnet fixed to a lower surface side of said
target, and an electrostatic chuck arranged in a position facing an
upper surface side of said target and configured to support a
substrate thereon, wherein said electrostatic chuck comprises a
dielectric board having an upper surface formed with a plurality of
projections for supporting the substrate on top surfaces thereof
and recesses around the projections, and an electrode formed in
said dielectric board and receiving a voltage from an external
power supply, said dielectric board comprises a conductor film
formed on at least the top surface of each projection, and the top
surface of each projection having said conductor film has a
three-dimensional pattern whose Ry (maximum surface roughness) is
not more than 2.5 m and Ra (central line average roughness) is not
more than 0.25 m.
Description
[0001] This application is a continuation of PCT/JP2008/066340,
filed on Sep. 10, 2008, which claims the benefit of Japanese Patent
Application No. 2007-234968, filed Sep. 11, 2007, which is hereby
incorporated by reference herein in its entirety.
TECHNICAL FIELD
[0002] The present invention relates to an electrostatic chuck to
be used to hold a substrate on a support member when processing the
substrate in a semiconductor fabrication step or in an electronic
part manufacturing step which manufactures a magnetic head or the
like and has a step similar to the semiconductor fabrication
step.
BACKGROUND ART
[0003] Conventionally, an electrostatic chuck disclosed in, for
example, patent reference 1 is known as an electrostatic chuck.
This electrostatic chuck includes a dielectric board having
projections and recesses formed on the upper surface by embossing,
an electrode formed inside the dielectric board, and an external
power supply for applying a voltage to the electrode. Also, the top
surface (substrate supporting surface) of each projection is
covered with a conductor line. This conductor line electrically
connects the substrate supporting surfaces of the projections, and
the electrostatic chuck has a switch for grounding or floating the
conductor line. Furthermore, those portions of the electrode which
are close to the individual projections are removed in one-to-one
correspondence with the projections.
[0004] The above-mentioned electrostatic chuck has as its main
purpose to prevent the generation of particles by friction between
a substrate and the projections, and prevents the electrostatic
chucking force from acting between the substrate supporting
surfaces of the projections and a substrate. That is, when holding
a substrate by applying a voltage to the electrode, the substrate
supporting surface of each projection and the lower surface of the
substrate in contact with the substrate supporting surface are set
at the same potential by moving electric charge through the
conductor line, thereby preventing the Johnson-Rahbeck force from
acting between them (see paragraph [0022] of patent reference 1).
The substrate is held by the spatial Coulomb force between the
recesses of the upper surface of the dielectric board and the lower
surface of the substrate (see paragraph [0040] of patent reference
1). Also, when unloading the substrate, the substrate can be
separated by rapidly moving electric charge by grounding the
conductor line (see paragraph of patent reference 1).
[0005] Furthermore, in an electrostatic chuck disclosed in patent
reference 2, an arrangement in which a separation mask has an
insulating material such as diamond and a mask made of a metal such
as titanium or titanium nitride is disclosed. [0006] Patent
reference 1: Japanese Patent Laid-Open No. 2004-22889 [0007] Patent
reference 2: Japanese Patent Laid-Open No. 10-70180
DISCLOSURE OF INVENTION
Problems that the Invention is to Solve
[0008] In patent reference 1, however, the Johnson-Rahbeck force
acting between the substrate supporting surface of each projection
and the lower surface of a substrate in contact with the substrate
supporting surface is a very large chucking force. Therefore, the
chucking force is often insufficient in a conventional
electrostatic chuck in which no Johnson-Rahbeck force acts. This
problem can be solved by allowing the Johnson-Rahbeck force to act
by removing the conductor line covering the substrate supporting
surfaces of the projections. When removing the conductor line
covering the substrate supporting surfaces of the projections,
however, electric charge cannot rapidly be moved any longer by
grounding the conductor line by the switch. Consequently, the
residual electric charge delays the time at which the substrate can
be separated. In addition, to remove electric charge when unloading
a substrate, the conventional electrostatic chuck must have a
special wiring structure in which the conductor line covering and
electrically connecting the substrate supporting surfaces of the
projections is formed and connected to the switch. This complicates
the structure.
[0009] Also, when a material different from the material of the
electrostatic chuck is used as the insulating material as disclosed
in patent reference 2, electric charge on the lower surface of a
substrate is trapped, and as a consequence the residual chucking
force remains on the substrate. This makes the separation of the
substrate from the electrostatic chuck unstable.
Means of Solving the Problems
[0010] The present invention has been made in consideration of the
above conventional problems, and has as its object to obtain a
sufficient electrostatic chucking force and achieve rapid unloading
of a substrate from an electrostatic chuck (improve the stability
of substrate separation) by a simple structure.
[0011] An electrostatic chuck according to the present invention
which achieves the above object is comprises a dielectric board
having an upper surface on which a plurality of projections for
supporting a substrate on top surfaces and recesses surrounding the
projections are formed, an electrode formed inside the dielectric
board, and an external power supply which applies a voltage to the
electrode, wherein the dielectric board includes a conductor film
formed on at least the top surface of each projection, and has a
three-dimensional structure which causes the conductor film to
generate a Johnson-Rahbeck force between the substrate and the
conductor film when a voltage is applied to the electrode.
EFFECTS OF THE INVENTION
[0012] A gap is formed between the recess around the projection on
the upper surface of the dielectric board and the lower surface of
a substrate. Therefore, when different electric charges are stored
on the upper surface of the dielectric board and the lower surface
of the substrate by applying a voltage to the electrode, the
spatial Coulomb force acts between the recess of the upper surface
of the dielectric board and the lower surface of the substrate.
Also, the same electric charge as that on the upper surface of the
dielectric board is stored on the upper surface of the conductor
film. Between the conductor film on the top surface of the
projection and the lower surface of the substrate, fine
three-dimensional structures of the top surfaces microscopically
form contact points and a fine gap. Accordingly, the
Johnson-Rahbeck force acts in this fine gap between the conductor
film and substrate. That is, in the present invention, the
substrate is chucked by both the spatial Coulomb force acting
between the recess of the upper surface of the dielectric board and
the lower surface of the substrate, and the Johnson-Rahbeck force
acting between the conductor film on the projection of the upper
surface of the dielectric board and the lower surface of the
substrate. As a consequence, a sufficient substrate holding force
is obtained in the present invention.
[0013] On the other hand, when the voltage application to the
electrode is stopped, the lower surface of the substrate and the
conductor films on the top surfaces of the plurality of projections
are going to have the same potential via the contact points between
the conductor films and the lower surface of the substrate, thereby
removing electric charge. This makes it possible to eliminate the
residual chucking force on the substrate, and rapidly unload the
substrate after the voltage application to the electrode is
stopped. To enable rapid charge removal, it is advantageous to
increase the number of contact points between the substrate and
conductor films, and the conductor films are preferably as smooth
as possible. Even when the conductor films are smoothened, the gap
between the conductor films and the lower surface of the substrate
does not microscopically disappear, but the width of the gap
further decreases, and the Johnson-Rahbeck force acting in this gap
increases.
[0014] Furthermore, the generation of particles can be suppressed
by selecting a film having a high wear resistance as the conductor
film.
BRIEF DESCRIPTION OF DRAWINGS
[0015] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate embodiments of
the invention and, together with the description, serve to explain
the principles of the invention.
[0016] FIG. 1 is an exemplary sectional view of a sputtering
apparatus including an electrostatic chuck according to an
embodiment of the present invention;
[0017] FIG. 2 is a partially enlarged exemplary sectional view of
the electrostatic chuck according to the embodiment of the present
invention;
[0018] FIG. 3 is a partially enlarged exemplary sectional view of
an electrostatic chuck according to another embodiment of the
present invention;
[0019] FIG. 4A is a view showing the states of electric charge on
the upper surface of a conductor film of the electrostatic chuck
shown in FIG. 2 and the lower surface of a substrate when it is
chucked;
[0020] FIG. 4B is a view showing the states of electric charge on
the upper surface of the conductor film of the electrostatic chuck
shown in FIG. 2 and the lower surface of a substrate when it is
separated;
[0021] FIG. 5A is a view showing the states of electric charge on
the upper surface of a conductor film of the electrostatic chuck
shown in FIG. 3 and the lower surface of a substrate when it is
chucked;
[0022] FIG. 5B is a view showing the states of electric charge on
the upper surface of the conductor film of the electrostatic chuck
shown in FIG. 3 and the lower surface of a substrate when it is
separated;
[0023] FIG. 6 is a graph showing the states of the supporting force
(chucking force) when the conductor film is formed and not
formed;
[0024] FIG. 7 is a graph plotting the results of calculations of
the chucking forces of a projection and recess in the electrostatic
chuck based on this embodiment; and
[0025] FIG. 8 is a graph showing the results of measurements of
times before a substrate can be separated by applying a reverse
voltage to the electrostatic chuck for a predetermined time
immediately before an external power supply is turned off.
BEST MODE FOR CARRYING OUT THE INVENTION
[0026] Embodiments of the present invention will be explained in
detail below. However, constituent elements described in the
embodiments are merely examples, and the technical scope of the
present invention is determined by the scope of the appended claims
and is not limited by the following individual embodiments.
[0027] An electrostatic chuck of the present invention will be
explained below by taking a case in which the electrostatic chuck
is applied to a sputtering apparatus as an example.
[0028] FIG. 1 is an exemplary sectional view of a sputtering
apparatus including an electrostatic chuck according to an
embodiment of the present invention. FIG. 2 is a partially enlarged
exemplary sectional view of the electrostatic chuck according to
the embodiment of the present invention. FIG. 3 is a partially
enlarged exemplary sectional view of an electrostatic chuck
according to another embodiment of the present invention. FIG. 4A
is a view showing the states of electric charge on the upper
surface of a conductor film of the electrostatic chuck shown in
FIG. 2 and the lower surface of a substrate when it is chucked.
FIG. 4B is a view showing the states of electric charge on the
upper surface of the conductor film of the electrostatic chuck
shown in FIG. 2 and the lower surface of a substrate when it is
separated. FIG. 5A is a view showing the states of electric charge
on the upper surface of a conductor film of the electrostatic chuck
shown in FIG. 3 and the lower surface of a substrate when it is
chucked. FIG. 5B is a view showing the states of electric charge on
the upper surface of the conductor film of the electrostatic chuck
shown in FIG. 3 and the lower surface of a substrate when it is
separated.
[0029] First, an outline of the sputtering apparatus will be
explained with reference to FIG. 1. The sputtering apparatus shown
in FIG. 1 includes a vessel 1 that can be evacuated by an external
evacuating mechanism (not shown), and a target 3 attached to the
ceiling of the vessel 1 with a ring-like insulating member 2
interposed between them. Magnets 5 fixed on a yoke plate 4 are
arranged to face the lower surface of the target 3. Also, a
sputtering power supply 6 for applying a voltage is connected to
the target 3.
[0030] In a position opposite to the target 3, an electrostatic
chuck 8 is installed on a substrate temperature adjusting unit 7
fixed to the bottom of the vessel 1, and a substrate 9 is placed on
the electrostatic chuck 8. In addition, a cylindrical shielding
member 10 is formed along the inner surface of the circumferential
wall of the vessel 1 between the target 3 and electrostatic chuck
8.
[0031] The substrate temperature adjusting unit 7 is a member that
controls the temperature of the substrate 9 via the electrostatic
chuck 8, and includes a thermocouple 12 and heating/cooling
portions 13 connected to a temperature control power supply
mechanism 11. In the substrate temperature adjusting unit 7, the
temperature control power supply mechanism 11 operates the
heating/cooling portions 13 based on a temperature detected by the
thermocouple 12, thereby heating or cooling the electrostatic chuck
8.
[0032] The electrostatic chuck 8 installed on the substrate
temperature adjusting unit 7 includes a dielectric board 14 having
an embossed surface (upper surface), an electrode 15 formed inside
the dielectric board 14, and an external power supply 16 for
applying a predetermined voltage to the electrode 15.
[0033] The upper surface of the dielectric board 14 has a plurality
of projections 17a and surrounding recesses 17b formed by
embossing. On the edge of the upper surface of the dielectric board
14, an outer periphery protruding portion 18 is formed to surround
the region where the projections 17a and recesses 17b are formed.
The projections 17a and outer periphery protruding portion 18 have
top surfaces on which the substrate 9 is placed, and have almost
the same height.
[0034] A conductor film 19 is formed to cover at least the top
surface of each projection 17a, except for the recesses 17b. Each
conductor film 19 has a three-dimensional structure that generates
the Johnson-Rahbeck force between the substrate 9 and conductor
film 19 when a voltage is applied to the electrode 15 (to be
described later). This three-dimensional structure functions as a
Johnson-Rahbeck force generating portion. Each conductor film 19
may cover not only the top surface of the projection 17a but also
its circumferential surface. However, each conductor film 19 is not
formed in the recess 17b and is electrically isolated from other
conductor films 19.
[0035] In the example shown in FIG. 1, the conductor film 19 is
formed on the top surface of the outer periphery protruding portion
18 as well. The conductor film 19 on the outer periphery protruding
portion 18 is preferably formed to facilitate equalizing the
overall heights of the outer periphery protruding portion 18 and
projections 17a, but may also be omitted.
[0036] The electrode 15 is a monopolar electrode and connected to
the external power supply 16 as a DC power supply via a switch 20.
A predetermined negative voltage is applied to the electrode 15 by
turning on the switch 20. Although the electrode 15 shown in FIG. 1
is a monopolar electrode, it is also possible to form bipolar
electrodes on the inner and outer peripheries of the dielectric
board 14, and apply a negative voltage to one electrode and a
positive voltage to the other. Furthermore, the electrode 15 has a
diameter smaller than that of the outer periphery protruding
portion 18. Therefore, the electrode 15 exists only below the
region where the projections 17a and recesses 17b are formed, and
does not exist near the portion immediately below the outer
periphery protruding portion 18. Since the electrode 15 does not
exist below the outer periphery protruding portion 18, the outer
periphery protruding portion 18 does not contribute to chucking of
the substrate 9.
[0037] As described previously, the substrate 9 is placed on the
top surfaces of the projections 17a and outer periphery protruding
portion 18. Between the substrate 9 and dielectric board 14,
therefore, the recesses 17b form a gap in the region surrounded by
the outer periphery protruding portion 18. A gas supply source 22
is connected to this gap via a gas supply path 21, so a gas (e.g.,
argon gas) can be supplied to the gap. By thus supplying the gas to
the gap, it is possible to conduct the heat of the substrate
temperature adjusting unit 7 to the substrate 9 by thermal
conduction of the electrostatic chuck 8 and the gas in the gap,
thereby maintaining the substrate 9 at a predetermined
temperature.
[0038] The electrostatic chuck 8 will be explained in more detail
below with reference to FIGS. 1 to 3. The projection 17a is
normally a column and preferably has a diameter of 0.7 mm or less.
The lower limit is determined by, for example, the necessary
mechanical strength of the projection 17a and the limitations on
processing, and generally about 0.3 mm. If the diameter of the
projection 17a increases, it becomes difficult to rapidly remove
electric charge when separating the substrate 9. This is so
presumably because many contact points between the substrate 9 and
the conductor films 19 formed on the top surfaces of the
projections 17a achieve rapid charge removal, although details are
unknown. When the diameter of the projection 17a is small, the
maximum surface roughness (Ry) of the microscopic three-dimensional
structure, which functions as a Johnson-Rahbeck force generating
portion, of the top surface of the projection 17a decreases from
the viewpoint of probability, and the upper surface smoothness of
the conductor film 19 increases. This perhaps increases the number
of contact points between the substrate 9 and conductor film 19.
When the smoothness of the conductor film 19 increases, the width
of the gap formed by the microscopic three-dimensional structure,
which functions as a Johnson-Rahbeck force generating portion, of
the top surface of the projection 17a decreases, and the
Johnson-Rahbeck force acting between the substrate 9 and conductor
film 19 increases.
[0039] To obtain favorable chucking and separating actions, the top
surface of the projection 17a preferably has a smooth surface, and
preferably has an Ry (maximum surface roughness) of 2.5 .mu.m or
less and an Ra (central line average roughness) of 0.25 .mu.m or
less. Since it is practically impossible to form a completely
smooth surface, the lower limit is not particularly restricted.
From the viewpoint of a practical smoothing limit, however, the Ry
is 0.2 .mu.m or more, and the Ra is 0.02 .mu.m or more.
[0040] The height of the projections 17a and outer periphery
protruding portion 18 is preferably 15 .mu.m or less, provided that
the chucked substrate 9 is not in contact with the recesses 17b.
The Coulomb force acting between the substrate 9 and recesses 17b
can be increased by decreasing the height of the projections 17a
and outer periphery protruding portion 18. The lower limit of the
height is generally about 6.5 .mu.m.
[0041] To obtain an appropriate chucking force and achieve rapid
charge removable, the projections 17a are preferably formed such
that the total area of the top surfaces of the projections 17a is
1% to 2% of the overall planar area of the dielectric board 14.
[0042] The conductor film 19 is made of, for example, a metal,
metal oxide, or metal nitride as an electrical conductor having a
resistivity of 10E.sup.-4 .mu..OMEGA.cm or less, and the
resistivity is preferably 400 .mu..OMEGA.cm or less, and
particularly preferably, 350 .mu..OMEGA.cm or less. The
electrostatic chuck according to this embodiment is formed as a
bulk (plate). Therefore, it is unnecessary to use any dissimilar
insulating material unlike in the separation mask of patent
reference 2 described earlier. The material of the electrostatic
chuck has a volume resistivity capable of achieving a
Johnson-Rahbeck force of E+8 to E+10 .OMEGA.cm. It is normally
possible to maintain a predetermined chucking force by the
Johnson-Rahbeck force and spatial Coulomb force without any
conductor film on the upper surface of an electrostatic chuck (back
side pressure=30 to 50 torr). The conductor film stores the same
electric charge as that on the dielectric surface of the
electrostatic chuck, and secures the chucking force when there is
no conductor film. In addition, during substrate separation in
which a substrate is unloaded from the electrostatic chuck, the
residual chucking force of the substrate is eliminated by setting
the substrate lower surface and conductor film at the same
potential. By thus eliminating the residual chucking force of the
substrate, it is possible to smoothly unload the substrate from the
electrostatic chuck, that is, increase the stability of substrate
separation.
[0043] Setting the resistivity of the conductor film at, for
example, 350 .mu..OMEGA.cm or less facilitates setting the lower
surface of the substrate and the conductor film on the upper
surface of the electrostatic chuck at the same potential.
Consequently, it is possible to eliminate the residual chucking
force of the substrate from which electric charge is removed, and
smoothly unload (separate) the substrate from the electrostatic
chuck.
[0044] By contrast, if the resistivity is high, the electric charge
on the substrate lower surface is trapped, and as a consequence the
residual chucking force remains on the substrate. This makes
separation of the substrate from the electrostatic chuck
unstable.
[0045] Examples of the material of the conductor film 19 are metals
such as titanium and tungsten, and oxides or nitrides of these
metals. Materials such as titanium and tungsten are strong against
thermal strain among other metals, and hardly deform because they
have high wear resistances. Accordingly, these materials can
suppress particles generated by, for example, contact between a
substrate and the conductor film of the electrostatic chuck, or
friction caused by a linear expansion difference, and increase the
wear resistance.
[0046] The conductor film 19 can be a single-layered film as shown
in FIG. 2, and can also be a multi-layered film (a first layer 19a
and second layer 19b) as shown in FIG. 3. When depositing the
multilayered film (the first layer 19a and second layer 19b) as
shown in FIG. 3, the first layer 19a as an inside layer is
preferably made of a metal such as titanium or tungsten, and the
second layer 19b formed on the first layer 19a is preferably made
of an oxide or nitride of a metal such as titanium or tungsten. By
using a metal oxide or metal nitride having a high wear resistance
as the second layer 19b, it is possible to suppress the generation
of particles when the substrate 9 is loaded and unloaded, and
increase the wear resistance.
[0047] The conductor film 19 can be formed by a film formation
method such as sputtering or ion plating. The thickness of the
conductor film 19 is preferably 1.5 .mu.m or less in order to
decrease the resistance of the conductor film 19 in the film
thickness direction to about 10.OMEGA.. If the thickness of the
conductor film 19 exceeds 1.5 .mu.m, the resistance of the
conductor film increases, and film pealing readily occurs owing to
the film stress. A practical lower limit is about 0.5 .mu.m.
[0048] The conductor film 19 need only be formed on at least the
top surface of the projection 17a except for the recesses 17b, but
can also be formed to the circumferential surface of the projection
17a as described previously. When the conductor film 19 is formed
to the circumferential surface, the deposition state can be
stabilized. The conductor film 19 may also be formed on the top
surface and side surfaces of the outer periphery protruding portion
18.
[0049] Note that FIG. 1 shows none of a substrate transfer robot, a
loading/unloading gate, lift pins for loading and unloading the
substrate 9 onto and from the electrostatic chuck 8, a mechanism
related to discharge, a discharge gas supply mechanism, and the
like.
[0050] In the sputtering apparatus shown in FIG. 1, the substrate
transfer robot loads the substrate 9 from the loading/unloading
gate onto the electrostatic chuck 8 in the vessel 1. When the
vessel 1 is set in a predetermined vacuum ambient and a voltage is
applied to the electrode 15 by turning on the switch 20, different
electric charges are stored on the upper surfaces of the dielectric
board 14 and conductor films 19 and the lower surface of the
substrate 9. FIGS. 4A and 5A illustrate the states of electric
charge on the upper surface of the conductor film 19 and the lower
surface of the substrate 9 when the switch 20 is turned on. In
these states, the spatial Coulomb force acts between the recesses
17b of the upper surface of the dielectric board 14 and the lower
surface of the substrate 9, and the Johnson-Rahbeck force acts in a
fine gap between the conductor films 19 on the top surfaces of the
projections 17a and the lower surface of the substrate 9. The
substrate 9 is strongly chucked to the electrostatic chuck by the
spatial Coulomb force and Johnson-Rahbeck force.
[0051] After the substrate 9 is chucked to the electrostatic chuck
8, the gas supply source 22 supplies a necessary amount of gas to
the gap between the electrostatic chuck 8 and substrate 9. At the
same time, the temperature control power supply mechanism 11
operates the heating/cooling portions 13 to hold the temperature of
the substrate 9 constant, a discharge gas is supplied into the
vessel 1, and sputtering is performed by turning on the sputtering
power supply 6.
[0052] When this sputtering is complete, the sputtering power
supply 6 is turned off, and the voltage application to the
electrode 15 is stopped by turning off the switch 20. Consequently,
the lower surface of the substrate 9 and the conductor films 19 on
the top surfaces of the plurality of projections 17a are going to
have the same potential through the contact points between the
conductor films 19 and the lower surface of the substrate 9,
thereby removing electric charge. Accordingly, the substrate 9 can
be rapidly unloaded after the voltage application to the electrode
15 is stopped. FIGS. 4B and 5B illustrate the states of electric
charge on the upper surface of the conductor film 19 and the lower
surface of the substrate 9 when the switch 20 is turned off.
[0053] By the charge removing action described above, the substrate
9 can be unloaded from the electrostatic chuck 8 within a short
time after the switch 20 is turned off. The substrate transfer
robot carries the unloaded substrate 9 outside the vessel 1 from
the loading/unloading gate.
[0054] Next, a more practical embodiment of the electrostatic chuck
will be explained.
[0055] In this embodiment, 384 columnar projections 17a having a
diameter of 0.4 mm.+-.0.15 mm and a height of 8.5 .mu.m.+-.2 .mu.m
and the outer periphery protruding portion 18 having the same
height as that of the projections 17a and a width of 1 mm.+-.0.3 mm
were formed on the upper surface of the dielectric board 14 of the
electrostatic chuck 8 in order to hold a 300-mm substrate 9
(silicon wafer). The total area of the top surfaces of the
projections 17a was set at 1.5% of the overall planar area of the
dielectric board 14.
[0056] In this embodiment, the electrode 15 of the electrostatic
chuck 8 was not placed immediately below the outer periphery
protruding portion 18 in order to obtain an appropriate holding
force.
[0057] The Ry and Ra of the top surface of each projection 17a were
respectively adjusted to 2.5 .mu.m or less and 0.25 .mu.m or
less.
[0058] Titanium films and titanium nitride films were sequentially
formed as the conductor films 19 near only the top surfaces of the
projections 17a and outer periphery protruding portion 18. The
thickness of the titanium film was 1.0 .mu.m, and that of the
titanium nitride film was 0.3 .mu.m.
[0059] Practical results of the above embodiment will be explained
below with reference to a graph shown in FIG. 6.
[0060] The states of the supporting force (chucking force) when the
conductor films 19 are formed on the top surfaces of the
projections 17a and outer periphery protruding portion 18 and no
conductor films 19 are formed will be explained below with
reference to FIG. 6. A graph shown in FIG. 6 indicates the
relationship between the voltage applied to the electrode 15 of the
electrostatic chuck 8 of the sputtering apparatus as shown in FIG.
1, that is, the chucking voltage (V), and the pressure (Pa) of a
gas (argon gas) sealed between the electrostatic chuck 8 and
substrate 9, that is, the chucking force. The substrate 9 is a
300-mm silicon substrate covered with silicon nitride.
[0061] FIG. 6 reveals that almost identical supporting forces can
be obtained with and without the conductor films 19. A larger
supporting force is obtained with the conductor films 19 in some
measurement points. The supporting force is inversely proportional
to the square of the distance between the electrostatic chuck 8 and
substrate 9. In this embodiment, a 1.3-.mu.m thick conductor film
19 was formed on the top surface of the projection 17a having a
height of 8.5 .mu.m, and the distance was 9.8 .mu.m. Therefore, a
supporting force (obtained by the spatial Coulomb force) F of the
recess 17b of the electrostatic chuck 8 presumably decreases from
1.59E.sup.2 (N) to 1.19E.sup.2 (N) on calculation.
[0062] This experimental result will be described below with
reference to a graph shown in FIG. 7.
[0063] FIG. 7 is a graph plotting the results of calculations of
the chucking forces of the projection 17a and recess 17b of the
electrostatic chuck 8 based on this embodiment. The comparison of
the chucking forces of the projection 17a and recess 17b
demonstrates that the chucking force of the projection 17a abruptly
increases when the distance, that is, the microscopically formed
gap decreases. Note that the chucking force (F) is a value obtained
from F=E(V.sup.2/L.sup.2)A/2 (E=dielectric constant of gap,
V=voltage, L=gap (distance), and A=electrode area), and the unit is
Newton (N).
[0064] As already explained, the upper surface roughness of the
projection 17a has a large influence on the chucking force of the
projection 17a. This result indicates that the conductor film 19
formed on the projection 17a improves the upper surface roughness
and increases the chucking force of the projection 17a. That is,
the conductor film 19 does not decrease the chucking force by its
thickness, but has the effect of increasing the chucking force.
[0065] The present inventor has found from the experimental results
that the chucking force remains unchanged even when the conductor
films 19 are formed on the projections 17a, so the electrostatic
chuck 8 of the present invention achieves the chucking force even
with the projections 17a. The conductor film 19 presumably
increases the chucking force by improving the upper surface
roughness of the projection 17a (i.e., shortening the practical
distance between the substrate 9 and the conductor film 19 on the
top surface of the projection 17a). In addition, the substrate 9
and conductor films 19 have many contact points. This perhaps makes
it possible to move the electric charge near the contact points
toward the electrostatic chuck 8 when the external power supply 16
is turned off.
[0066] A graph shown in FIG. 8 indicates the effect of improving
separation, as the effect of the present invention, and explains
the states of separation when the conductor film 19 is formed on
the top surface of the projection 17a and no conductor film 19 is
formed.
[0067] In this experiment, a monopolar electrostatic chuck 8 was
used, and a 300-mm silicon wafer having a lower surface covered
with silicon nitride was used as the substrate 9. A reverse voltage
was applied to the electrostatic chuck 8 for a predetermined time
immediately before the external power supply 16 was turned off, and
the time before the substrate 9 was separated was measured.
[0068] When no conductor film 19 was formed, the separation time
shortened as the reverse voltage was increased to 150 V, but a
separation time of about 5 sec was necessary even when a reverse
voltage of 150 V or more was applied. On the other hand, when the
conductor film 19 was formed, it was possible to separate the
substrate 9 immediately after the external power supply 16 was
turned off regardless of the condition. Also, easy separation was
observed even at 20.degree. C. to -30.degree. C. at which the
volume resistivity increases. As described earlier, this
demonstrates that the residual electric charge, which had a large
influence on chucking, of the projection 17a rapidly reduced, that
is, charge removal was rapidly performed.
[0069] As described above, the electrostatic chuck of the present
invention controls the residual electric charge on the embossed
projection of a Johnson-Rahpeck type electrostatic chuck using a
dielectric material having an appropriately low volume resistivity,
and is applicable to both a monopolar chuck and bipolar chuck. The
electrostatic chuck can be applied not only to a sputtering
apparatus but also to a CVD apparatus for depositing a thin film on
a substrate or an etching apparatus for processing a thin film.
Furthermore, since the electrostatic chuck has an effect on the
separation of a substrate covered with a high-k silicon nitride
film, the electrostatic chuck is also applicable to a substrate,
such as a glass substrate, made of a material having a high-k upper
surface, as well as a silicon substrate.
[0070] The preferred embodiments of the present invention have been
explained above with reference to the accompanying drawings.
However, the present invention is not limited to these embodiments
and can be changed into various forms within the technical scope
grasped from the description of the scope of the appended
claims.
[0071] The present invention is not limited to the above embodiment
and various changes and modifications can be made without departing
from the spirit and scope of the invention. Therefore, to apprise
the public of the scope of the present invention, the following
claims are appended.
* * * * *