U.S. patent application number 12/458956 was filed with the patent office on 2010-02-11 for electrolytic processing apparatus and electrolytic processing method.
Invention is credited to Hiroyuki Kanda, Junko Mine, Tsutomu Nakada, Akira Susaki.
Application Number | 20100032315 12/458956 |
Document ID | / |
Family ID | 41651898 |
Filed Date | 2010-02-11 |
United States Patent
Application |
20100032315 |
Kind Code |
A1 |
Mine; Junko ; et
al. |
February 11, 2010 |
Electrolytic processing apparatus and electrolytic processing
method
Abstract
An electrolytic processing apparatus, prior to carrying out
plating directly on, e.g., a ruthenium film of a substrate using
the ruthenium film as a seed layer, can securely remove a passive
layer formed on a surface of the ruthenium film even when the
substrate is a large-sized high-resistance substrate, such as a
300-mm wafer, thereby reducing the terminal effect during the
subsequent plating, improving the quality of a plated film and
enabling filling of a void-free plated film into a fine
interconnect pattern. The electrolytic processing apparatus
includes: an anode disposed opposite a seed layer of a noble metal
or a high-melting metal, formed on a substrate; a porous body
impregnated with an electrolytic solution, disposed in a space,
filled with the electrolytic solution, between the substrate and
the anode; and a control section for controlling an electric field
on a surface of the seed layer so that a reduction reaction takes
place in the seed layer, thereby electrolytically and
electrochemically removing a passive layer formed in the surface of
the seed layer.
Inventors: |
Mine; Junko; (Tokyo, JP)
; Susaki; Akira; (Tokyo, JP) ; Kanda;
Hiroyuki; (Tokyo, JP) ; Nakada; Tsutomu;
(Tokyo, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
1030 15th Street, N.W.,, Suite 400 East
Washington
DC
20005-1503
US
|
Family ID: |
41651898 |
Appl. No.: |
12/458956 |
Filed: |
July 28, 2009 |
Current U.S.
Class: |
205/666 ;
204/230.2 |
Current CPC
Class: |
C25F 5/00 20130101; H01L
21/76873 20130101; H01L 21/76861 20130101; H01L 21/02068
20130101 |
Class at
Publication: |
205/666 ;
204/230.2 |
International
Class: |
C25F 3/02 20060101
C25F003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 8, 2008 |
JP |
2008-205193 |
Claims
1. An electrolytic processing apparatus comprising: an anode
disposed opposite a seed layer of a noble metal or a high-melting
metal, formed on a substrate; a porous body impregnated with an
electrolytic solution, disposed in a space, filled with the
electrolytic solution, between the substrate and the anode; and a
control section for controlling an electric field on a surface of
the seed layer so that a reduction reaction takes place in the seed
layer, thereby electrolytically and electrochemically removing a
passive layer formed on the surface of the seed layer.
2. The electrolytic processing apparatus according to claim 1,
wherein a shield plate for limiting the area of electrolytic
processing is disposed between the porous body and the anode.
3. The electrolytic processing apparatus according to claim 1,
wherein the anode is comprised of a disk-shaped anode, or one or
more ring-shaped anodes, or a combination thereof.
4. The electrolytic processing apparatus according to claim 1
further comprising a gas removal mechanism for removing a gas
generated from the surface of the seed layer during the
electrolytic processing.
5. The electrolytic processing apparatus according to claim 1,
wherein the seed layer is comprised of a ruthenium film or a
ruthenium alloy film having a thickness of not more than 10 nm.
6. An electrolytic processing method comprising: disposing a porous
body between a substrate having a seed layer of a noble metal or a
high-melting metal and an anode disposed opposite the seed layer;
filling an electrolytic solution into a space between the substrate
and the anode while impregnating the porous body with the
electrolytic solution; and electrolytically and electrochemically
removing a passive layer formed on a surface of the seed layer
while controlling an electric field on the surface of the seed
layer so that a reduction reaction takes place in the seed
layer.
7. The electrolytic processing method according to claim 6, wherein
the voltage or electric current applied between the seed layer and
the anode is gradually increased in accordance with the
electrolytic processing area of the substrate.
8. The electrolytic processing method according to claim 6, wherein
a shield plate is disposed between the anode and the porous body to
limit the area of electrolytic processing.
9. The electrolytic processing method according to claim 6, wherein
the seed layer is comprised of a ruthenium film or a ruthenium
alloy film having a thickness of not more than 10 nm.
10. An electrolytic processing method comprising: filling an
electrolytic solution containing sulfuric acid as an electrolyte
into a space between a substrate, having a seed layer of a noble
metal or a high-melting metal, and an anode disposed opposite the
seed layer; and applying an electric current between the seed layer
and the anode in such a manner as to satisfy the following formula
(1), thereby electrolytically and electrochemically removing a
passive layer formed on a surface of the seed layer:
A.gtoreq.1.15.times.B+5 (1) wherein "A" represents the sulfuric
acid concentration of the electrolytic solution (g/L), and "B"
represents current density (mA/cm.sup.2).
11. The electrolytic processing method according to claim 10,
wherein the seed layer is comprised of a ruthenium film or a
ruthenium alloy film having a thickness of not more than 10 nm.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an electrolytic processing
apparatus and an electrolytic processing method, and more
particularly to an electrolytic processing apparatus and an
electrolytic processing method which are useful for removing a
passive layer from a surface of a ruthenium film, e.g., having a
thickness of not more than 10 nm, formed on a surface of a
substrate, such as a semiconductor wafer, prior to carrying out
copper plating on the substrate surface using the ruthenium film as
a seed layer to form LSI interconnects of copper on the surface of
the ruthenium film.
[0003] 2. Description of the Related Art
[0004] Copper plating is generally employed as a method for forming
LSI interconnects when copper is used instead of aluminum as an
interconnect material.
[0005] FIGS. 1A through 1C illustrate, in a sequence of process
steps, an exemplary process for manufacturing a substrate having
such copper interconnects. First, as shown in FIG. 1A, an
insulating film 2, e.g., an SiO.sub.2 oxide film or a film of low-k
material, is deposited on a conductive layer 1a, in which
semiconductor elements has been formed, on a semiconductor base 1;
and via holes 3 and trenches 4 as interconnect recesses are formed
in the insulating film 2 by the lithography/etching technique. A
barrier layer 5 is then formed on an entire surface of the
substrate, and a seed layer 7, which serves as a feeding layer
during electroplating, is formed on the barrier layer 5. A metal,
such as tantalum, titanium, tungsten or ruthenium, or a nitride
thereof, is generally used for the barrier layer 5.
[0006] Subsequently, as shown in FIG. 1B, copper plating is carried
out onto a surface of the seed layer 7 of the substrate W to
deposit a copper film 6 on the insulating film 2 while filling
copper into the via holes 3 and the trenches 4. Thereafter, the
copper film 6, the seed layer 7 and the barrier layer 5 on the
insulating film 2 are removed by chemical mechanical polishing
(CMP) to make a surface of the copper film 6, embedded in the via
holes 3 and the trenches 4, approximately flush with the surface of
the insulating film 2, thereby forming interconnects composed of
the copper film 6 in the insulating film 2, as shown in FIG.
1C.
[0007] In conventional copper plating processes, a copper seed
layer formed by, for example, sputtering, CVD, ALD or electroless
plating is widely used as the seed layer 7. As interconnects are
becoming increasingly finer, the copper seed layer 7 is becoming
thinner year by year.
[0008] In particular, a thickness of a copper seed layer in the
field region of a substrate is around 600 angstroms in the
manufacturing of the 65-nm generation of semiconductor devices. A
thickness of a copper seed layer is expected to be not more than
500 angstroms in the 45-nm generation of semiconductor devices, and
not more than 300 angstroms in the 32-nm and the subsequent
generations of semiconductor devices. The side coverage of a copper
seed layer, as formed by the most-prevalent sputtering method, is
generally 10 to 15%. Therefore, a copper seed layer used in the
manufacturing of the 32-nm and the subsequent generations of
semiconductor devices will have a very small thickness on the order
of tens of angstroms in its portions lying on the sidewalls of via
holes or trenches. The continuity of a seed layer will therefore be
lost and the function of a seed layer will be insufficient, leading
to significantly poor filling of copper into the recesses. There is
therefore a movement to use, instead of sputtering, a more
conformal film-forming method, such as CVD or ALD, to form a copper
seed layer.
[0009] On the other hand, there is an attempt to eliminate a copper
seed layer and carry out copper plating directly on a surface of a
barrier layer, e.g., composed of a ruthenium film, using the
barrier layer as a seed layer (feeding layer) during
electroplating. This is partly because of instability of a copper
material in an atmospheric environment. Thus, copper is easily
oxidized in the air, forming a natural oxide film (copper oxide),
having a thickness of a few angstroms to a few tens of angstroms,
on a surface of a copper seed layer. Copper oxide is not
electrically conductive and is easily soluble in an acidic plating
solution.
[0010] When copper plating is carried out directly on a surface of
a barrier layer, e.g., composed of a ruthenium film, using the
barrier layer as a seed layer, there is a case, depending on the
material of the barrier layer, in which a copper plated film with
good morphology as formed by copper electroplating on a copper seed
layer cannot be obtained, or a case in which the plated copper film
has poor adhesion to the barrier layer. Further, in next-generation
semiconductor devices, a thickness of a barrier layer will become
tens of angstroms and the sheet resistance of a barrier layer will
become tens of Q/sq to hundreds of Q/sq. Therefore, compared to the
case of carrying out plating on a surface of a copper seed layer,
the problem of terminal effect will become more serious when
carrying out plating directly on a surface of a barrier layer using
the barrier layer as a seed layer.
[0011] A technique for direct plating on a barrier layer has been
proposed which involves adjusting deposition potentials of barrier
layer/copper and copper/copper using a copper sulfate plating
solution containing additives, and gradually increasing the
electric current applied, thereby filling copper into interconnect
recesses covered with a barrier layer (see US Patent Publication
No. 2004/0069648 and U.S. Pat. No. 6,974,531). Though this
technique enables uniform filling of copper into interconnect
recesses covered with a barrier layer, however, a global thickness
of a copper plated film, formed on a substrate, differs between the
center portion and the edge portion of the film especially when the
substrate is a large 300-mm wafer (substrate), which may cause a
problem in a later CMP process which is generally carried out after
plating.
[0012] When there is a passive layer (ruthenium oxide) formed on a
surface of a ruthenium film as a barrier layer, copper will be
deposited in a particulate form upon direct copper plating on the
surface of the ruthenium film (barrier layer) using the ruthenium
film as a seed layer, which can cause voids in copper embedded in a
fine interconnect pattern and surface roughness of the plated film
on the substrate. There is a report that to solve such problems, it
is effective to carry out pretreatment (electrolytic processing),
prior to copper plating, by using a mixed solution of 1.8 mol/L
(17.6 wt %) of sulfuric acid and 1 mmol/L of NaCl as a pretreatment
solution (electrolytic solution) and applying a voltage with a
ruthenium film as a cathode (see T. P. Moffat et al.,
"Electrodeposition of Cu on Ru Barrier Layers for Damascene
Processing", journal of the Electrochemical Society, 153(1) C37-C50
(2006)). This pretreatment (electrolytic processing), because of
sodium contained in the pretreatment solution (electrolytic
solution), however, is generally difficult to use in a
semiconductor manufacturing process.
[0013] Further, it has been proposed to remove an oxide film formed
on a surface of a metal film, such as a ruthenium film, by carrying
out a cathodic treatment (pretreatment) at a voltage, e.g., in the
range of about 0V to about -0.5V or at a current density, e.g., in
the range of 0.05 mA/cm.sup.2 to about 1 mA/cm.sup.2 (see Published
Japanese Translation of International Patent Publication No.
2008-502806). However, it is considered that when a high-resistance
substrate having a surface ruthenium film, e.g., with a thickness
of not more than 10 nm, especially a large-sized one such as a
300-mm wafer, is subjected to the cathodic treatment (pretreatment)
using such a voltage or current density, because of the terminal
effect, it will be difficult to uniformly process the entire
substrate surface.
[0014] The applicant has proposed a method in which a passive layer
formed on a surface of a ruthenium film is electrochemically
removed by electrolytic processing using an electrolytic solution
having an electric conductivity of not more than 0.4/.OMEGA.cm,
such as sulfuric acid having a concentration of not more than 10 wt
% (see Japanese Patent laid-Open Publication No. 2008-98449).
However, it has turned out that though this method is effective for
a relatively small-sized substrate such as a test chip, in the case
of a large-sized high-resistance substrate, such as a 300-mm wafer,
having a surface ruthenium film, e.g., with a thickness of not more
than 10 nm, due to the terminal effect, it is difficult to
uniformly process the entire substrate surface.
SUMMARY OF THE INVENTION
[0015] When carrying out copper plating directly on a surface of a
barrier layer using the barrier layer as a seed layer (feeding
layer), especially when carrying out copper electroplating directly
on a surface of a ruthenium film having a thickness of not more
than 10 nm, which is expected to be used in the 32-nm generation of
semiconductor devices, using the ruthenium film as a seed layer, it
is necessary to remove a passive layer (ruthenium oxide), formed on
a surface of the ruthenium film, prior to the copper plating.
Especially, with the progress toward a thinner ruthenium film, the
proportion of a passive layer (ruthenium oxide) in a ruthenium film
becomes larger. Therefore, the necessity for removal of a passive
layer (ruthenium oxide) from a surface of a ruthenium film will
become higher.
[0016] This is because a passive layer (ruthenium oxide) has a very
high electric resistance. If copper plating is carried out directly
on a ruthenium film, which itself has a high resistance, with a
passive layer formed on a surface, because of increased terminal
effect due to the passive layer, it is difficult to form a copper
plated film with high in-plane uniformity of a film thickness
especially on a large-sized high-resistance substrate, such as a
300-mm wafer. In addition, plated copper will deposit in a
particulate form on the surface of the passive layer (ruthenium
oxide), which may cause the formation of voids in copper embedded
in a fine interconnect pattern and also cause surface roughness of
a plated film formed on the substrate surface.
[0017] The present invention has been made in view of the above
situation. It is therefore an object of the present invention to
provide an electrolytic processing apparatus and an electrolytic
processing method which, prior to carrying out plating directly on,
e.g., a ruthenium film of a substrate using the ruthenium film as a
seed layer, can securely remove a passive layer (ruthenium oxide)
formed on a surface of the ruthenium film even when the substrate
is a large-sized high-resistance substrate, such as a 300-mm wafer,
thereby reducing the terminal effect during the subsequent plating,
improving the quality of a plated film and enabling filling of a
void-free plated film into a fine interconnect pattern.
[0018] In order to achieve the object, the present invention
provides an electrolytic processing apparatus comprising: an anode
disposed opposite a seed layer of a noble metal or a high-melting
metal, formed on a substrate; a porous body impregnated with an
electrolytic solution, disposed in a space, filled with the
electrolytic solution, between the substrate and the anode; and a
control section for controlling an electric field on a surface of
the seed layer so that a reduction reaction takes place in the seed
layer, thereby electrolytically and electrochemically removing a
passive layer formed on the surface of the seed layer.
[0019] The resistance between the substrate and the anode can be
increased by disposing the porous body impregnated with an
electrolytic solution in a space, filled with the electrolytic
solution, between the substrate and the anode. This can reduce the
terminal effect during the electrolytic processing. In addition, in
the electrolytic processing to electrochemically remove a passive
layer formed on a surface of a seed layer, the voltage or electric
current applied between the anode and the seed layer may be
gradually increased. This can remove the passive layer on the
surface of the seed layer gradually from the periphery toward the
center of the substrate while reducing the terminal effect, thus
enabling uniform electrolytic processing of the entire surface of
the substrate even when the substrate is a large-sized
high-resistance substrate, such as a 300-mm wafer.
[0020] Preferably, a shield plate for limiting the area of
electrolytic processing is disposed between the porous body and the
anode.
[0021] By limiting the electrolytic processing area of a substrate
by the shield plate, it becomes possible to lower the maximum
applied voltage or the maximum applied current necessary for the
cathodic processing of the entire substrate from the peripheral
portion to the central portion. The shield plate preferably has a
diaphragm mechanism capable of adjusting the aperture area
corresponding to the electrolytic processing area.
[0022] The anode is comprised, for example, of a disk-shaped anode,
or one or more ring-shaped anodes, or a combination thereof.
[0023] For example, the anode may be comprised of a combination of
a disk-shaped divided anode and a plurality of ring-shaped divided
anodes. By independently controlling the respective divided anodes,
it becomes possible to easily control the electric field on a
surface of a seed layer, enabling more uniform processing of the
entire substrate.
[0024] Preferably, the electrolytic processing apparatus further
comprises a gas removal mechanism for removing a gas generated from
the surface of the seed layer during the electrolytic
processing.
[0025] The gas removal means is, for example, means for circulating
the cathode-side electrolytic solution, means for rotating the
substrate during electrolytic processing or means for vertically
moving or tilting a head holding the anode.
[0026] The seed layer is, for example, comprised of a ruthenium
film or a ruthenium alloy film having a thickness of not more than
10 nm.
[0027] The present invention also provides an electrolytic
processing method comprising: disposing a porous body between a
substrate having a seed layer of a noble metal or a high-melting
metal and an anode disposed opposite the seed layer; filling an
electrolytic solution into a space between the substrate and the
anode while impregnating the porous body with the electrolytic
solution; and electrolytically and electrochemically removing a
passive layer formed on a surface of the seed layer while
controlling an electric field on the surface of the seed layer so
that a reduction reaction takes place in the seed layer.
[0028] Preferably, the voltage or electric current applied between
the seed layer and the anode is gradually increased in accordance
with the electrolytic processing area of the substrate.
[0029] A shield plate may be disposed between the anode and the
porous body to limit the area of electrolytic processing.
[0030] The present invention provides another electrolytic
processing method comprising: filling an electrolytic solution
containing sulfuric acid as an electrolyte into a space between a
substrate, having a seed layer of a noble metal or a high-melting
metal, and an anode disposed opposite the seed layer; and applying
an electric current between the seed layer and the anode in such a
manner as to satisfy the following formula (1), thereby
electrolytically and electrochemically removing a passive layer
formed on a surface of the seed layer:
A.gtoreq.1.15.times.B+5 (1)
wherein "A" represents the sulfuric acid concentration of the
electrolytic solution (g/L), and "B" represents current density
(mA/cm.sup.2).
[0031] According to the present invention, a passive layer
(ruthenium oxide) formed on a surface of a ruthenium film can be
electrochemically removed over an entire surface of a substrate
even when the substrate is a large-sized high-resistance substrate,
such as a 300-mm wafer, having the ruthenium film with a thickness
of not more than 10 nm, and subsequently copper electroplating can
be carried out directly on the surface of the ruthenium film using
the ruthenium film as a seed layer. This makes it possible to
reduce the terminal effect during plating, speed up plating and
shorten time taken for plating to reach the center of a substrate
and, in addition, form a fine metal plated film, such as a copper,
with a uniform thickness over the entire substrate surface while
filling the plating metal into a fine interconnect pattern without
forming voids in the embedded metal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIGS. 1A through 1C are diagrams illustrating, in a sequence
of process steps, a conventional process for the formation of
copper interconnects;
[0033] FIG. 2 is a layout plan view of a substrate processing
apparatus incorporating an electrolytic processing apparatus
according to an embodiment of the present invention;
[0034] FIG. 3 is a schematic cross-sectional view of the
electrolytic processing apparatus shown in FIG. 2;
[0035] FIG. 4 is a graph showing the relationship between the
sulfuric acid concentration of an electrolytic solution for use in
the present invention and current density between an insoluble
anode and a ruthenium film;
[0036] FIG. 5 is a flow chart of a process as carried out in the
substrate processing apparatus shown in FIG. 2;
[0037] FIGS. 6A and 6B are diagrams showing the morphology of a
copper plated film as formed by first carrying out electrolytic
processing to electrochemically remove a passive layer formed on a
surface of a ruthenium film, and subsequently carrying out copper
electroplating on the ruthenium film using the ruthenium film as a
seed layer;
[0038] FIG. 7 is a graph showing the bottom-up performance of
plating, determined by chip test for samples as prepared by first
carrying out electrolytic processing of an interconnect substrate
having a ruthenium film with varying current densities and varying
sulfuric acid concentrations, using the electrolytic processing
apparatus shown in FIG. 3, to electrochemically remove a passive
layer formed on the surface of the ruthenium film, and subsequently
carrying out copper plating on the ruthenium film using the
ruthenium film as a seed layer;
[0039] FIG. 8 is a diagram explaining the bottom-up
performance;
[0040] FIG. 9 is a schematic view of the main portion of an
electrolytic processing apparatus according to another embodiment
of the present invention;
[0041] FIG. 10 is a graph showing change with time in current value
during electrolytic processing in the electrolytic processing
apparatus shown in FIG. 9; and
[0042] FIG. 11 is a schematic diagram showing another insoluble
anode.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] Preferred embodiments of the present invention will now be
described with reference to the drawings. The following description
illustrates an exemplary case in which a substrate W, having a
ruthenium film as the barrier layer 5 shown in FIG. 1A, is
prepared, and a copper film 6 (see FIG. 1B) is formed directly on a
surface of the ruthenium film (barrier layer 5), without forming
the seed layer 7 shown in FIG. 1A, by carrying out copper
electroplating using the ruthenium film as a seed layer. The
present invention may also be applied to a case in which instead of
a ruthenium film, a ruthenium alloy film or a film of another noble
metal or high-melting metal is used as a seed layer during
electroplating, and a plated film is formed directly on a surface
of the seed layer.
[0044] FIG. 2 shows a layout plan of a substrate processing
apparatus incorporating an electrolytic processing apparatus
according to an embodiment of the present invention. As shown in
FIG. 2, the substrate processing apparatus includes a rectangular
apparatus frame 12 having a control panel 10. In the apparatus
frame 12 are disposed two loading/unloading sections 14 for
carrying in a substrate cassette in which a plurality of substrates
are housed, two bevel etching/back surface cleaning apparatuses 16,
a substrate station 18, a rinsing/drying apparatus 20, one
electrolytic processing apparatus 22 and four copper electroplating
apparatuses 24. A first transport robot 26 is movably disposed
between the loading/unloading sections 14, the bevel etching/back
surface cleaning apparatuses 16, the substrate station 18 and the
rinsing/drying apparatus 20, and a second transport robot 28 is
movably disposed between the substrate station 18, the
rinsing/drying apparatus 20, the electrolytic processing apparatus
22 and the copper electroplating apparatuses 24.
[0045] FIG. 3 shows a schematic view of the electrolytic processing
apparatus 22 shown in FIG. 2. The electrolytic processing apparatus
22 is to electrolytically and electrochemically remove, prior to
copper electroplating, a passive film (ruthenium oxide) formed on a
surface of a ruthenium film which serves as a seed layer during
copper electroplating, and is comprised mainly of a substrate
holding section 30 and an anode head 32. The substrate holding
section 30 includes a substrate stage 34 for holding, e.g., by
attraction, a substrate W with its front surface (with ruthenium
film formed) facing upwardly. The substrate stage 34 is coupled to
an upper end of a rotating shaft 36 extending from a rotation
mechanism (not shown). By thus connecting the substrate stage 34 to
the upper end of the rotating shaft 36 and rotating the substrate W
by rotating the rotating shaft 36, hydrogen gas generated during
electrolytic processing of a ruthenium film is removed from a
surface of the ruthenium film. A gas removal mechanism is thus
constructed.
[0046] The substrate holding section 30 has a ring-shaped seal ring
38 which is located above the substrate stage 34 and which, when
the substrate W held by the substrate stage 34 is raised, comes
into pressure contact with a peripheral portion of the upper
surface of the substrate W to seal the peripheral portion, and
cathode contacts 40 for contact with the ruthenium film at a
peripheral portion of the upper surface of the substrate W and at
an outer position than the contact portion of the substrate surface
with the seal ring 38, to make the ruthenium film serve as a
cathode. With this structure, when the peripheral portion of the
upper surface of the substrate W is sealed by the seal ring 38, a
substrate-side electrolytic solution chamber, circumferentially
defined by the seal ring 38, is formed over the upper surface of
the substrate W. Because the cathode contacts 40 are located
outside the seal ring 38, contact of the cathode contacts 40 with
an electrolytic solution 62 in the substrate-side electrolytic
solution chamber can be avoided.
[0047] In this embodiment, the seal ring 38 and the cathode
contacts 40, while keeping contact with the peripheral portions of
the upper surface of the substrate W held by the substrate stage
34, are configured to rotate together with the substrate stage
34.
[0048] The anode head 32 includes a vertically-movable lifting
shaft 42, a downwardly-open, bottomed cylindrical housing 44
coupled to a lower end of the lifting shaft 42, and a porous body
46 disposed such that it closes the lower-end opening of the
housing 44. The housing 44, in its inner circumferential surface,
has a recessed portion 44a, while the porous body 46 has at its top
a flange portion 46a. The porous body 46 is held in the housing 44
with the flange portion 46a inserted into the recessed portion
44a.
[0049] A shield ring 48, for preventing an electric current from
flowing out of the circumferential surface of the porous body 46,
is wound around the circumferential surface of the porous body 46.
The shield ring 48 may be made of a flexible material, such as
fluoro rubber. Located in the recessed portion 44a of the housing
44, an O-ring 50 for preventing leakage of the electrolytic
solution is interposed between the flange portion 46a of the porous
body 46 and the housing 44.
[0050] The porous body 46 is, for example, composed of a porous
ceramic, such as alumina, SiC, mullite, zirconia, titania or
cordierite, or a hard porous body, such as a sintered body of
polypropylene or polyethylene, or a composite thereof. The porosity
of the porous body 46 is, for example, not more than 19%. Though
the porous body 46 itself is an insulating material, it has an
electric conductivity when it contains an electrolytic solution
therein. In particular, the electrolytic solution penetrates into
the porous body 46 in the thickness direction through complicated,
fairly long paths of the pores. This can provide the porous body 46
containing the electrolytic solution with an electric conductivity
which is lower than the electric conductivity of the electrolytic
solution.
[0051] The provision of the porous body 46, which thus has a high
electric resistance, at the opening of the housing 44 can make the
influence of the resistance of the ruthenium film as small as
negligible upon electrolytic processing of the ruthenium film.
Thus, a difference in current density in the surface of the
substrate W due to the electric resistance of the substrate surface
can be made small, thereby enhancing the in-plane uniformity of
electrolytic processing.
[0052] The use of the porous body 46, e.g., a porous ceramic having
a porosity of not more than 19%, can separate the electrolytic
solution on the substrate W side from the electrolytic solution on
the insoluble anode 52 side by the porous body 46. This makes it
possible to replace only the electrolytic solution in the
substrate-side electrolytic solution chamber, formed over the
surface of the substrate W and surrounded by the seal ring 38, with
a plating solution and carry out plating after carrying out
electrolytic processing with the electrolytic solution in the
substrate-side electrolytic solution chamber. This method thus
enables electrolytic processing and plating to be carried out
successively in the single electrolytic cell simply by replacement
of processing solutions.
[0053] In the housing 44, an insoluble anode 52 having a large
number of through-holes therein is disposed above the porous body
46 such that it faces the ruthenium film of the substrate W held by
the substrate stage 34. The insoluble anode 52, for example
composed of a titanium base and an iridium oxide coating, does not
dissolve in an electrolytic solution during electrolytic
processing, and therefore is not subject to deformation. The use of
the insoluble anode 52 can therefore render its replacement
unnecessary. In the case where the electrolytic solution is
separated into the cathode-side solution and the substrate
(anode)-side solution by an ion exchanger or the like, a soluble
anode may be used instead of the insoluble anode.
[0054] The insoluble anode 52 is electrically connected to an anode
conducting wire 56a extending from the anode of a power source 54,
while the cathode contacts 40 are electrically connected to a
cathode conducing wire 56b extending from the cathode of the power
source 54. The power source 54 is connected to a control section 58
which controls an electric current or a voltage applied from the
power source 54 to between the insoluble anode 52 and the ruthenium
film which serves as a cathode when in contact with the cathode
contacts 40.
[0055] To the housing 44 is connected an oxygen gas discharge pipe
60 for discharging oxygen, which has accumulated over the
electrolytic solution 62 in the housing 44, to the outside.
Further, though not shown diagrammatically, an electrolytic
solution supply pipe for supplying the electrolytic solution 62
into the housing 44 and an electrolytic solution discharge pipe for
discharging the electrolytic solution 62 in the housing 44 to the
outside are connected to the housing 44. Further, either lateral to
the housing 44 or in the interior of the sidewall of the housing 44
are provided an electrolytic solution supply section for supplying
the electrolytic solution 62 into the space over the surface of the
substrate W and surrounded by the seal ring 38 (substrate-side
electrolytic solution chamber) and an electrolytic solution
discharge section for discharging the electrolytic solution 62 in
the substrate-side electrolytic solution chamber to the outside. In
this embodiment, sulfuric acid having a concentration of not more
than 100 g/L, e.g., 80 g/L, is used as the electrolytic solution
62.
[0056] FIG. 4 shows the relationship between the sulfuric acid
concentration of the electrolytic solution 62 and current density
between the insoluble anode 52 and the ruthenium film in contact
with the cathode contacts 40 and serving as a cathode. In this
embodiment, an electric current is applied between the insoluble
anode 52 and the ruthenium film, in contact with the cathode
contacts 40 and serving as a cathode, in such a manner as to
satisfy the following formula (1), thereby electrolytically and
electrochemically removing a passive layer (ruthenium oxide) formed
on the surface of the ruthenium film:
A.gtoreq.1.15.times.B+5 (1)
wherein "A" represents the sulfuric acid concentration of the
electrolytic solution 62 (g/L), and "B" represents current density
(mA/cm.sup.2).
[0057] The operation of the electrolytic processing apparatus 22
will now be described. First, the substrate W is held with its
front surface (with the ruthenium formed) facing upwardly by the
substrate stage 34 which attracts thereto the lower surface of the
substrate W. At this moment, the substrate W is in a lowered
position. The substrate stage 34 is then raised to bring the
peripheral portion of the upper surface of the substrate W, held by
the substrate stage 34, into pressure contact with the seal ring
38, thereby forming the substrate-side electrolytic solution
chamber, circumferentially defined by the seal ring 38, over the
upper surface of the substrate W. At the same time, the ruthenium
film, at the peripheral portion of the upper surface of the
substrate W and at the outer position than the seal ring 38, is
brought into contact with the cathode contacts 40.
[0058] Next, the anode head 32 in a raised position is lowered, and
the lowering of the anode head 32 is stopped when the porous body
46 has reached a position not into contact with but close to the
upper surface of the substrate W. The narrower the gap "G" between
the porous body 46 and the substrate W held by the substrate stage
34 is, the larger is the terminal effect reducing effect of the
porous body 46. Therefore, the gap "G" is preferably not more than
10 mm, more preferably not more than 0.5 mm. In the anode head 32,
the electrolytic solution 62 is supplied into the housing 44 while
drawing the electrolytic solution 62 from the housing 44, thereby
impregnating the porous body 46 with the electrolytic solution
62.
[0059] The electrolytic solution 62 is injected into the region
(substrate-side electrolytic solution chamber) surrounded by the
seal ring 38 to fill the space between the substrate W and the
porous body 46 with the electrolytic solution 62. If necessary, the
electrolytic solution 62 is withdrawn by suction form the
substrate-side electrolytic solution chamber and returned to the
chamber in a circulatory manner. In this state, while rotating the
substrate stage 34, thereby rotating the substrate W together with
the seal ring 38 and the cathode contacts 40, the insoluble anode
52 is electrically connected to the anode of the power source 54
and the cathode contacts 40 to the cathode of the power source 54
to carry out electrolytic processing of the substrate surface,
thereby electrolytically and electrochemically removing a passive
film (ruthenium oxide) present on the surface of the ruthenium film
serving as a cathode. Thus, in this embodiment, water is subjected
to cathodic electrolysis with the electrolytic solution 62,
consisting of sulfuric acid having a concentration of not more than
100 g/L, to generate hydrogen. The hydrogen electrochemically
removes the passive film (ruthenium oxide) present on the surface
of the ruthenium film. The hydrogen generated at this time is
removed from the surface of the ruthenium film by the rotation of
the substrate W.
[0060] During the electrolytic processing, the voltage or electric
current applied between the insoluble anode 52 and the ruthenium
film serving as a cathode is gradually increased from a low value
in accordance with the electrolytic processing area by the control
section 58 so that the passive layer on the surface of the
ruthenium film is removed gradually from the periphery toward the
center of the substrate W.
[0061] As described above, the resistance between the substrate W
and the insoluble anode 52 is increased by disposing the porous
body 46 impregnated with the electrolytic solution in the space,
filled with the electrolytic solution 62, between the substrate
Wand the insoluble anode 52. This can reduce the terminal effect
upon the electrolytic processing. In addition, in the electrolytic
processing to electrochemically remove the passive layer formed on
the surface of the ruthenium film, the voltage or electric current
applied between the insoluble anode 52 and the ruthenium film is
gradually increased. This can remove the passive layer on the
surface of the ruthenium film gradually from the periphery toward
the center of the substrate while reducing the terminal effect,
thus enabling uniform electrolytic processing of the entire surface
of the substrate even when the substrate is a large-sized
high-resistance substrate, such as a 300-mm wafer.
[0062] After completion of the electrolytic processing, the
insoluble anode 52 and the cathode contacts 40 are disconnected
from the power source 54, and the rotation of the substrate stage
34 is stopped. After raising the anode head 32, the electrolytic
solution 62 remaining on the upper surface of the substrate W is
removed and recovered, e.g., by suction, and the substrate W after
electrolytic processing is transported for the next process
step.
[0063] The operation of the substrate processing apparatus shown in
FIG. 2 will now be described with reference to FIG. 5. First, a
substrate cassette, in which a plurality of substrates W are
housed, is carried into the loading/unloading section 14 in the
apparatus frame 12. The first transport robot 26 takes one
substrate W out of the substrate cassette carried into the
loading/unloading section 14 and transports the substrate W to the
substrate station 18. The second transport robot 28 receives the
substrate W from the substrate station 18 and transfers the
substrate W to the substrate stage 34 of the electrolytic
processing apparatus 22.
[0064] After receiving the substrate by the substrate stage 34, the
electrolytic processing apparatus 22 carries out electrolytic
processing of the substrate W, held by the substrate stage 34, in
the above-described manner to electrochemically remove a passive
film (ruthenium oxide) present on the surface of the ruthenium
film. If the electrolytic processing apparatus 22 has a function to
rinse with pure water a surface of a substrate after electrolytic
processing and dry the substrate by rotating it at a high speed,
rinsing and drying of the substrate W is carried out in the
electrolytic processing apparatus 22. Otherwise the substrate W
after electrolytic processing is transported by the second
transport robot 28 to the rinsing/drying apparatus 20, where the
substrate is rinsed and dried. It is possible, in some cases, to
omit drying or both rinsing and drying.
[0065] The second transport robot 28 receives the substrate from
the electrolytic processing apparatus 22 or from the rinsing/drying
apparatus 20, and transports the substrate to the substrate stage
of the copper electroplating apparatus 24. After receiving the
substrate by the substrate stage, the copper electroplating
apparatus 24 carries out copper electroplating of the substrate
using the ruthenium film as a seed layer to form a copper plated
film on the surface of the ruthenium film. The substrate after
plating is transported by the second transport robot 28 to the
rinsing/drying apparatus 20, where the substrate is rinsed and
dried. If the copper electroplating apparatus 24 has a function to
rinse with pure water a surface of a substrate after plating and
dry the substrate by rotating it at a high speed, rinsing and
drying of the substrate W may be carried out in the copper
electroplating apparatus 24.
[0066] The first transport robot 26 receives the dried substrate
from the rinsing/drying apparatus 20 and transfers the substrate to
the bevel etching/back surface cleaning apparatus 16. The bevel
etching/back surface cleaning apparatus 16 carries out bevel
etching to etch off a copper plated film, etc. adhering to the
bevel portion of the substrate, and cleaning of the back surface of
the substrate. The first transport robot 26 receives the substrate
from the bevel etching/back surface cleaning apparatus 16 and
returns the substrate to the substrate cassette in the
loading/unloading section 14.
[0067] The sequence of substrate processing steps is thus
completed.
[0068] The above-described substrate processing process can carry
out, in a successive one-by-one manner, copper electroplating of a
substrate after carrying out electrolytic processing of the
substrate to electrochemically remove a passive layer (ruthenium
oxide) formed on a surface of a ruthenium film, e.g., having a
thickness of not more than 10 nm and having a high sheet
resistance. This can prevent an oxide film (ruthenium oxide) from
growing on the surface of the ruthenium film during the period
after the removal of the passive layer until the initiation of
copper plating. Furthermore, it becomes possible to control the
time period after the electrolytic processing until the initiation
of copper electroplating at a constant time.
[0069] FIGS. 6A and 6B show the morphology of a copper plated film
as formed by first carrying out electrolytic processing to
electrochemically remove a passive layer (ruthenium oxide) formed
on a surface of a ruthenium film, and subsequently carrying out
copper electroplating on the ruthenium film using the ruthenium
film as a seed layer. As can be seen from FIGS. 6A and 6B, compared
to the case of forming a copper plated film on a ruthenium film
without electrochemically removing a passive layer from the surface
of the ruthenium film, a fine particulate copper plated film can be
formed uniformly on a substrate surface by electrochemically
removing a passive layer (ruthenium oxide) from the surface of the
ruthenium film in advance.
[0070] FIG. 7 shows the bottom-up performance of a plating,
determined by chip test for samples as prepared by first carrying
out electrolytic processing of an interconnect substrate having a
ruthenium film, having a thickness of 2 nm and a sheet resistance
of 150 .OMEGA./sq, with varying current densities and varying
sulfuric acid concentrations, using the electrolytic processing
apparatus shown in FIG. 3, to electrochemically remove a passive
layer formed on a surface of the ruthenium film, and subsequently
carrying out copper plating on the ruthenium film using the
ruthenium film as a seed layer. As shown in FIG. 8, the bottom-up
performance is determined by the ratio of the thickness "b" of a
plated film in interconnects of a substrate to the thickness "a" of
the plated film in the field area of the substrate (b/a). In the
estimation of interconnect plating, a higher ratio b/a indicates a
better bottom-up performance. All the samples were subjected to
plating, carried out under the same conditions, within 10 minutes
after electrolytic processing.
[0071] The following six combinations of sulfuric acid
concentration and current density were used in the electrolytic
processing:
(1) Sulfuric acid conc. 0.8 (g/L), current density 40 (mA/cm.sup.2)
(2) Sulfuric acid conc. 8 (g/L), current density 40 (mA/cm.sup.2)
(3) Sulfuric acid conc. 8 (g/L), current density 80 (mA/cm.sup.2)
(4) Sulfuric acid conc. 80 (g/L), current density 40 (mA/cm.sup.2)
(5) Sulfuric acid conc. 80 (g/L), current density 80 (mA/cm.sup.2)
(6) Sulfuric acid conc. 80 (g/L), current density 120
(mA/cm.sup.2)
[0072] FIG. 7 depicts a straight line corresponding to the equality
in the above formula (1) (A=1.15.times.B+5). As can be seen from
FIG. 7, the bottom-up performance is poor when the combinations of
low current density and high sulfuric acid concentration, which
fall within the range that does not satisfy the above formula (1)
(A<1.15.times.B+5), are used in the electrolytic processing,
indicating poor removal of the passive layer from the ruthenium
film by electrolytic processing. It is inferred from the data that
a passive layer will not be adequately removed by electrolytic
processing using a sulfuric acid concentration in the range of 10
to 100 g/L and a current density in the range of 0.05 to 1
mA/cm.sup.2, and that the bottom-up performance will be poor in the
subsequent plating.
[0073] Interconnect substrate samples having a ruthenium film,
having a thickness of 2 nm and a sheet resistance of 150
.OMEGA./sq, were subjected to electrolytic processing at a sulfuric
acid concentration of 80 g/L and a current density of 40
mA/cm.sup.2 using a porous body having a porosity of 19%. The
respective substrate samples were then subjected to copper plating
under the same conditions within 10 minutes after the electrolytic
processing to evaluate the bottom-up performance. As a result,
void-free copper was filled into an interconnect pattern with good
bottom-up performance in a 20-mm square test chip sample. On the
other hand, a difference in the bottom-up performance was observed
in a 300-mm wafer substrate: the same bottom-up performance as the
test chip sample was observed in the edge portion of the substrate,
whereas the bottom-up performance was found to be poor in the
center portion of the substrate. This indicates that the
electrolytic processing was not uniformly effected over the entire
substrate surface, i.e., from the edge to the center of the
substrate. In this regard, when the same 300-mm wafer substrate,
having the same ruthenium film (having a thickness of 2 nm and a
sheet resistance of 150 .OMEGA./sq) but whose passive layer had
been confirmed to be removed from the entire surface, was subjected
to copper plating under the same conditions, void-free copper was
filled into an interconnect pattern with good bottom-up performance
in the entire surface from the edge to the center of the
substrate.
[0074] In order to carry out electrolytic processing uniformly from
the edge to the center of a substrate, it is conceivable to
lengthen the processing time or increase the current density. A
long processing time or a high current density, however, may lead
to generation of a considerable amount of gas, which can cause the
formation of voids or cause damage to an edge portion of a
substrate. For a high-resistance substrate, the use of a porous
body alone is not enough to reduce the terminal effect, and thus is
incapable of uniformly processing the entire substrate. The entire
substrate can be processed uniformly by controlling the electric
field on the substrate in addition to the use of a porous body.
[0075] For example, a low voltage or current is first applied
between an anode and a ruthenium film serving as a cathode to
remove a passive layer only in a peripheral portion of a substrate,
and removal of the passive layer is allowed to proceed to the
center of the substrate while increasing the voltage or current
applied between the ruthenium film and the anode with the progress
of removal of the passive layer. By thus removing the passive layer
gradually from the periphery to the center of the substrate, the
substrate resistance can be lowered, whereby the terminal effect
can be reduced. In addition, the maximum applied voltage or the
maximum applied current for electrolytic processing to the center
of the substrate can be lowered.
[0076] FIG. 9 shows the main portion of an electrolytic processing
apparatus according to another embodiment of the present invention.
This embodiment differs from the preceding embodiment in that a
shield plate 70, having a diaphragm mechanism such as an iris
diaphragm, for limiting the area of electrolytic processing is
disposed between the porous body 46 and the insoluble anode 52. The
closer the shield plate 70 is to the porous body 46, the larger is
the effect of the shield plate 70. The distance between the porous
body 46 and the shield plate 70 is therefore preferably not more
than 10 mm, more preferably not more than 0.5 mm. The shield plate
70 may be disposed in contact with the porous body 46.
[0077] In this embodiment, the shield plate 70 has a diaphragm
mechanism which opens from the center toward the periphery. When a
diaphragm mechanism, which opens from the center toward the
periphery, is thus used, a large amount of electric current flows
from the central portion of a substrate, lying right under the
aperture of the shield plate 70. Therefore, the applied current is
increased in accordance with the aperture area as shown by the
curve (A) in FIG. 10. The shield plate 70 may have a diaphragm
mechanism which opens from the periphery toward the center. In this
case, a large amount of electric current flows from the peripheral
portion of a substrate, and the area in which electric current
flows decreases as the diaphragm mechanism closes. Therefore, the
applied current is decreased in accordance with the aperture area
as shown by the curve (B) in FIG. 10. By thus controlling the
aperture of the shield plate 70 and the current value, electrolytic
processing of an entire surface of a substrate becomes
possible.
[0078] It is also possible to install a hollow disk-shaped shield
plate between the insoluble plate and the porous body in order to
prevent concentration of electric current in a peripheral portion
of a substrate W near the cathode contacts 40. In this case, it
becomes possible to control the area of highest electric field by
the inner diameter of the shield plate, thereby lowering the
maximum applied voltage or the maximum applied current necessary
for electrolytic processing of the entire substrate surface from
the edge to the center of the substrate. Further, it is possible to
interpose a shield plate, having holes whose density increases
toward the center, between the insoluble anode and the porous body
to control the electric field distribution on an entire surface of
a substrate.
[0079] FIG. 11 shows another example of an insoluble anode 52 for
use in the present invention. The insoluble anode 52 is comprised
of a disk-shaped first divided anode 52a centrally located, a
ring-shaped second divided anode 52b surrounding the circumference
of the first divided anode 52a, and a ring-shaped third divided
anode 52c surrounding the circumference of the second divided anode
52b. The divided anodes 52a, 52b and 52c are provided with power
sources 54a, 54b and 54c, respectively. The power sources 54a, 54b,
54c are independently controlled by the control section 58.
[0080] When an insoluble anode comprising a combination of divided
anodes is used as in this embodiment, a higher voltage or electric
current may be applied to a divided anode more centrally located
than peripherally located. Thus, in this embodiment, the applied
voltage or electric current may be decreased in the order of the
first divided anode 52a, the second divided anode 52b and the third
divided anode 52c. This can reduce the terminal effect on a
substrate, enabling uniform electrolytic processing of an entire
substrate surface.
[0081] When the shield plate 70 or the divided anodes 52a, 52b, 52c
is used, as described above, the porous body 46 not only has the
effect of reducing the terminal effect of a substrate but has the
effect of facilitating control of the electric field on the
substrate by the shield plate 70 or the divided anodes 52a, 52b,
52c as well. If the porous body 46 is not used, concentration of
electric field, depending on the inner diameter of the shield plate
or on the diameter of a divided anode, will occur, which will make
control of the electric field on a substrate difficult.
[0082] While the present invention has been described with
reference to the embodiments thereof, it will be understood by
those skilled in the art that the present invention is not limited
to the particular embodiments described above, but it is intended
to cover modifications within the inventive concept. For example,
though the use of copper as an interconnect material has been
described, a copper alloy may be used instead of copper.
* * * * *