U.S. patent application number 10/742767 was filed with the patent office on 2004-08-05 for plating method.
Invention is credited to Kanda, Hiroyuki, Mishima, Koji, Nagai, Mizuki.
Application Number | 20040149584 10/742767 |
Document ID | / |
Family ID | 32766684 |
Filed Date | 2004-08-05 |
United States Patent
Application |
20040149584 |
Kind Code |
A1 |
Nagai, Mizuki ; et
al. |
August 5, 2004 |
Plating method
Abstract
An object of the present invention is to provide a plating
method which can form defect-free, completely-embedded
interconnects of a conductive material in recesses in the surface
of a substrate even when the recesses are of a high aspect ratio,
and which can improve the flatness of a plated film on the
substrate even when narrow trenches and broad trenches are
co-present in the surface of the substrate. A plating method
according to the present invention includes: providing a high
resistance structure between a surface of a substrate, said surface
being connected to a cathode electrode, and an anode electrode;
filling the space between the substrate and the anode electrode
with a plating solution while applying a voltage between the
cathode electrode and the anode electrode; and growing a plated
film on the surface of the substrate while controlling an electric
current flowing between the cathode electrode and the anode
electrode at a constant value.
Inventors: |
Nagai, Mizuki; (Tokyo,
JP) ; Mishima, Koji; (Tokyo, JP) ; Kanda,
Hiroyuki; (Tokyo, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
32766684 |
Appl. No.: |
10/742767 |
Filed: |
December 23, 2003 |
Current U.S.
Class: |
205/103 ;
205/104 |
Current CPC
Class: |
C25D 17/001 20130101;
C25D 5/18 20130101; C25D 5/50 20130101; C25D 5/34 20130101; C25D
21/12 20130101 |
Class at
Publication: |
205/103 ;
205/104 |
International
Class: |
C25D 005/18 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 2002 |
JP |
2002-382405 |
Claims
What is claimed is:
1. A plating method, comprising: providing a high resistance
structure between a surface of a substrate, said surface being
connected to a cathode electrode, and an anode electrode; filling
the space between the substrate and the anode electrode with a
plating solution while applying a voltage between the cathode
electrode and the anode electrode; and growing a plated film on the
surface of the substrate while controlling an electric current
flowing between the cathode electrode and the anode electrode at a
constant value.
2. The plating method according to claim 1, wherein the voltage is
applied for 100 to 2000 msec after the electric current begins to
flow between the cathode electrode and the anode electrode.
3. The plating method according to claim 1, wherein the voltage
applied is such as to allow an electric current with an average
cathodic current density, with respect to the surface of the
substrate, of 1 to 30 mA/cm.sup.2 to flow.
4. The plating method according to claim 3, wherein the voltage is
applied for 100 to 2000 msec after the electric current begins to
flow between the cathode electrode and the anode electrode.
5. A plating method, comprising: providing a high resistance
structure between a surface of a substrate, said surface being
connected to a cathode electrode, and an anode electrode; filling
the space between the substrate and the anode electrode with a
plating solution; and growing a plated film on the surface of the
substrate while controlling an electric current flowing between the
cathode electrode and the anode electrode at stepwise changing
constant values.
6. The plating method according to claim 5, wherein the plating
solution is changed for a different plating solution in the process
of film formation.
7. The plating method according to claim 6, wherein the surface of
the substrate is cleaned in the process of film formation.
8. The plating method according to claim 5, wherein the value of
the electric current flowing between the cathode electrode and the
anode electrode is increased stepwise.
9. The plating method according to claim 8, wherein the plating
solution is changed for a different plating solution in the process
of film formation.
10. The plating method according to claim 9, wherein the surface of
the substrate is cleaned in the process of film formation.
11. A plating method, comprising: providing a high resistance
structure between a surface of a substrate, said surface being
connected to a cathode electrode, and a anode electrode; filling
the space between the substrate and the anode electrode with a
plating solution; growing a plated film on the surface of the
substrate while controlling an electric current flowing between the
cathode electrode and the anode electrode at a constant value;
reversing the direction of the electric current flowing between the
cathode electrode and the anode electrode to etch away the surface
of the plated film; and further growing the plated film on the
surface of the substrate while controlling an electric current
flowing between the cathode electrode and the anode electrode at a
constant value.
12. The plating method according to claim 11, wherein the step of
etching the surface of the plated film and the subsequent step of
growing the plated film are carried out repeatedly.
13. A plating method, comprising: filling the space between a
surface of a substrate, said surface being connected to a cathode
electrode, and an anode electrode with a plating solution while
applying a voltage between the cathode electrode and the anode
electrode; and growing a plated film on the surface of the
substrate while controlling an electric current flowing between the
cathode electrode and the anode electrode at a constant value.
14. The plating method according to claim 13, wherein the voltage
is applied for 100 to 200 msec after the electric current begins to
flow between the cathode electrode and the anode electrode.
15. The plating method according to claim 13, wherein the voltage
applied is such as to allow an electric current with an average
cathodic current density, with respect to the surface of the
substrate, of 1 to 30 mA/cm.sup.2 to flow.
16. The plating method according to claim 15, wherein the voltage
is applied for 100 to 2000 msec after the electric current begins
to flow between the cathode electrode and the anode electrode.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a plating method, and more
particularly to a plating method for filling a conductive metal
such as copper (Cu) or the like in fine interconnection patterns
(recesses) formed in a substrate such as a semiconductor wafer to
form interconnects.
[0003] 2. Description of the Related Art
[0004] In recent years, instead of using aluminum or aluminum
alloys as a material for forming interconnection circuits on a
semiconductor substrate, there is an eminent movement towards using
copper (Cu) that has a low electric resistivity and high
electromigration endurance. Copper interconnects are generally
formed by filling copper into fine recesses formed in the surface
of a substrate. Various techniques for forming such copper
interconnects are known, including CVD, sputtering, and plating.
According to any such techniques, a copper film is formed in the
substantially entire surface of a substrate, followed by removal of
unnecessary copper by performing chemical mechanical polishing
(CMP).
[0005] FIGS. 21A through 21C illustrate, in sequence of basic
process steps, an example for producing a semiconductor device
having copper interconnects by performing copper plating onto a
surface of a substrate. As shown in FIG. 21A, an insulating film 2,
such as a silicon oxide film of SiO.sub.2 or a film of low-k
material, is deposited on a conductive layer 1a in which electronic
devices are formed, which is formed on a semiconductor base 1. Fine
recesses 5 composed of contact holes 3 and trenches 4 for
interconnects are formed in the insulating film 2 by a
lithography/etching technique. A barrier layer 6 of TaN or the like
is formed on the entire surface of the insulating film 2.
[0006] Then, as shown in FIG. 21B, copper plating is performed onto
a surface of the semiconductor substrate W to fill the recesses
(holes) 5 of the semiconductor substrate W with copper and, at the
same time, deposit a copper film 7 on the barrier layer 6.
Thereafter, the copper film 7 and the barrier layer 6 on the
insulating film 2 are removed by performing chemical mechanical
polishing (CMP) so as to make the surface of the copper filled in
the contact holes 3 and the trenches 4 for interconnects and the
surface of the insulating film 2 lie substantially on the same
plane. Embedded interconnects composed of the copper film 7, as
shown in FIG. 21C, are thus formed.
[0007] In the embedding of copper film 7 e.g. by an electroplating
method in the fine recesses 5 provided in the surface of the
semiconductor substrate W, it is widely practiced, in advance of
the copper plating, to form a seed layer 8 e.g. by sputtering or
CVD on the surface of the barrier layer 6 formed in the surface of
the semiconductor substrate W, as shown in FIG. 22. The main
objective of the seed layer 8 is to make the surface of the seed
layer 8 serve as an electrical cathode to supply a sufficient
electrical current for reducing metal ions in a plating solution
and depositing the metal ions as a solid metal.
[0008] The seed layer 8 is formed usually by sputtering, CVD or the
like. As interconnects are now becoming highly densified and finer,
the aspect ratios of contact holes and via holes are becoming
higher. For example, as shown in FIG. 22, when a seed layer 8 e.g.
of copper is formed over a recess (hole) 5 having a diameter of
about 0.15 .mu.m and an aspect ratio of about 6, the ratio
B.sub.1/A.sub.1(side coverage), i.e. the ratio of the film
thickness B.sub.1 of the seed layer 8 on the internal side surface
of the recess 5 to the film thickness A.sub.1 of the seed layer 8
on the external surface of the substrate W, is about 5 to 10%.
Further, in this case, it is difficult to form a continuous seed
layer 8. This is considered to be partly due to cohesion of
sputtered copper atoms upon film formation. In addition, there is a
current tendency that the film thickness A.sub.1 of the seed layer
8 on the external substrate surface is becoming as thin as no more
than 80-100 nm, particularly even no more than 40-60 nm, and
accordingly, the film thickness B.sub.1 of the seed layer 8 on the
internal side surface of the recess 5 is also becoming thinner.
[0009] A plating solution, in general, is composed of copper
sulfate, sulfuric acid, chlorine and several types of additives,
and is strongly acidic. Thus, a plating solution has the nature of
dissolving the seed layer 8 of copper. Accordingly, as shown in
FIG. 23, in carrying out electroplating of the substrate W, having
on its surface the above-described seed layer 8, to form copper
interconnects, the seed layer 8 can be dissolved by the plating
solution upon contact of the substrate W with the plating solution.
In particular, the seed layer 8 can be dissolved out in the
sidewalls of fine holes or trenches, especially at portions near
the bottoms of the holes or trenches, resulting in electrical
non-conductivity and formation of voids at those portions.
[0010] If the film thickness A.sub.1 of the seed layer 8 on the
external substrate surface, shown in FIG. 22, is made large for the
purpose of ensuring the side coverage, the substantial aspect ratio
of the recess 5 should then be increased. Further, blockage of the
opening of the hole could occur upon embedding of copper, whereby a
void will be formed in the hole, leading to a decreased yield.
[0011] On the other hand, when a barrier layer 6 is formed on the
surface of a substrate W in which relatively small and large fine
recesses, e.g. narrow trenches 5a and broad trenches 5b, are
co-present in the surface, as shown in FIG. 24A, and a seed layer 8
is formed on the barrier layer 6, as shown in FIG. 24B, and then
copper is embedded in the trenches 5a, 5b by copper plating, as
shown in FIG. 24C, the growth of plating tends to be promoted over
the narrow trenches 5a, whereby the plated copper film 7 is likely
to be raised even when the plating solution or an additive in the
plating solution is optimized, whereas plating with a sufficiently
high leveling cannot be effected in the broad trenches 5b,
resulting in an insufficient embedding of copper.
[0012] In this regard, it may be considered to increase the overall
thickness of embedded copper film in order to prevent the
insufficient embedding. When considering a later CMP processing for
flattening the surface of the substrate W, however, a thicker
plated film necessarily increases the polishing amount, thus
necessarily prolonging the processing time. Increasing a CMP rate
to avoid the processing time prolongation could cause dishing in
the broad trenches 5b during the CMP processing.
[0013] In order to solve these problems, it is necessary to make
the thickness of a plated film as thin as possible, and reduce or
eliminate the raised portions and recesses in the plated film even
when narrow trenches and broad trenches are co-present in the
surface of a substrate to thereby improve the flatness of the
plated film. At present, however, when performing plating using,
for example, a copper sulfate plating bath, it is not possible to
simultaneously decrease the raised portions and decrease the
recesses solely by the action of the plating solution or an
additive.
SUMMARY OF THE INVENTION
[0014] The present invention has been made in view of the above
situation in the related art. It is therefore an object of the
present invention to provide a plating method which can form
defect-free, completely-embedded interconnects of a conductive
material in recesses in the surface of a substrate even when the
recesses are of a high aspect ratio, and which can improve the
flatness of a plated film on the substrate even when narrow
trenches and broad trenches are co-present in the surface of the
substrate, enabling a later CMP processing to be carried out in a
short time while preventing dishing during the CMP processing.
[0015] In order to achieve the above object, the present invention
provides a plating method, comprising: providing a high resistance
structure between a surface of a substrate, said surface being
connected to a cathode electrode, and an anode electrode; filling
the space between the substrate and the anode electrode with a
plating solution while applying a voltage between the cathode
electrode and the anode electrode; and growing a plated film on the
surface of the substrate while controlling an electric current
flowing between the cathode electrode and the anode electrode at a
constant value.
[0016] This method can prevent a seed layer from being dissolved by
a plating solution that is supplied onto the surface of a substrate
to perform plating, and can therefore enable a plated film to grow
on the seed layer to effect embedding of e.g. copper.
[0017] In a preferred embodiment of the present invention, the
voltage applied is such as to allow an electric current with an
average cathodic current density, with respect to the surface of
the substrate, of 1 to 30 mA/cm.sup.2 to flow.
[0018] The voltage is preferably applied for 100 to 2000 msec after
the electric current begins to flow between the cathode electrode
and the anode electrode.
[0019] The present invention provides another plating method,
comprising: providing a high resistance structure between a surface
of a substrate, said surface being connected to a cathode
electrode, and an anode electrode; filling the space between the
substrate and the anode electrode with a plating solution; and
growing a plated film on the surface of the substrate while
controlling an electric current flowing between the cathode
electrode and the anode electrode at stepwise changing constant
values.
[0020] It becomes possible with this plating method to carry out a
first-step plating at a low electric current to reinforce a seed
layer on a substrate and carry out a second-step plating to grow a
plated film on the seed layer to effect embedding of e.g. copper.
Such a stepwise plating makes it possible to form defect-free,
completely-embedded interconnects of a conductive material, such as
copper, in recesses in the surface of a substrate even when the
recesses are of a high aspect ratio.
[0021] In a preferred embodiment of the present invention, the
value of the electric current flowing between the cathode electrode
and the anode electrode is increased stepwise.
[0022] In a preferred embodiment of the present invention, the
plating solution is changed for a different plating solution in the
process of film formation.
[0023] In a preferred embodiment of the present invention, the
surface of the substrate is cleaned in the process of film
formation.
[0024] The present invention also provides yet another plating
method, comprising: providing a high resistance structure between a
surface of a substrate, said surface being connected to a cathode
electrode, and a anode electrode; filling the space between the
substrate and the anode electrode with a plating solution; growing
a plated film on the surface of the substrate while controlling an
electric current flowing between the cathode electrode and the
anode electrode at a constant value; reversing the direction of the
electric current flowing between the cathode electrode and the
anode electrode to etch away the surface of the plated film; and
further growing the plated film on the surface of the substrate
while controlling an electric current flowing between the cathode
electrode and the anode electrode at a constant value.
[0025] According to this method, the surface of a plated film is
etched away between plating processings to flatten the plated film,
whereby the flatness of the final plated film can be improved.
[0026] In a preferred embodiment of the present invention, the step
of etching the surface of the plated film and the subsequent step
of growing the plated film are carried out repeatedly.
[0027] The present invention also provides yet another plating
method, comprising: filling the space between a surface of a
substrate, said surface being connected to a cathode electrode, and
an anode electrode with a plating solution while applying a voltage
between the cathode electrode and the anode electrode; and growing
a plated film on the surface of the substrate while controlling an
electric current flowing between the cathode electrode and the
anode electrode at a constant value.
[0028] The above and other objects, features, and advantages of the
present invention will be apparent from the following description
when taken in conjunction with the accompanying drawings that
illustrates preferred embodiments of the present invention by way
of example.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is an overall plan view of a substrate processing
apparatus provided with a plating apparatus for carrying out a
plating method according to the present invention;
[0030] FIG. 2 is a plan view of the plating apparatus shown in FIG.
1;
[0031] FIG. 3 is an enlarged sectional view of the substrate holder
and the electrode portion of the plating apparatus shown in FIG.
1;
[0032] FIG. 4 is a front view of the pre-coating/recovering arm of
the plating apparatus shown in FIG. 1;
[0033] FIG. 5 is a plan view of the substrate holder of the plating
apparatus shown in FIG. 1;
[0034] FIG. 6 is a cross-sectional view taken along the line B-B of
FIG. 5;
[0035] FIG. 7 is a cross-sectional view taken along the line C--C
of FIG. 5;
[0036] FIG. 8 is a plan view of the electrode portion of the
plating apparatus shown in FIG. 1;
[0037] FIG. 9 is a cross-sectional view taken along the line D-D of
FIG. 8;
[0038] FIG. 10 is a plan view of the electrode arm section of the
plating apparatus shown in FIG. 1;
[0039] FIG. 11 is a schematic sectional view illustrating the
electrode head and the substrate holder of the plating apparatus
shown in FIG. 1 upon electroplating;
[0040] FIG. 12 is a graph showing the relationship between electric
current and time in a control method (plating method) as carried
out by the plating apparatus shown in FIG. 1;
[0041] FIG. 13 is a graph showing the relationship between electric
current and time in another control method (plating method) as
carried out by the plating apparatus shown in FIG. 1;
[0042] FIG. 14 is a graph showing the relationship between electric
current and time in yet another control method (plating method) as
carried out by the plating apparatus shown in FIG. 1;
[0043] FIG. 15 is a graph showing the relationship between electric
current and time in yet another control method (plating method) as
carried out by the plating apparatus shown in FIG. 1;
[0044] FIG. 16 is a graph showing the relationship between electric
current and time in yet another control method (plating method) as
carried out by the plating apparatus shown in FIG. 1;
[0045] FIGS. 17A through 17C are diagrams illustrating a series of
a first-step plating, an intermediate etching step and a
second-step plating, the etching step being carried out by applying
a reverse current;
[0046] FIG. 18 is a schematic diagram illustrating another plating
apparatus;
[0047] FIG. 19 is an overall plan view of another substrate
processing apparatus provided with a plating apparatus useful for
carrying out a plating method according to the present
invention;
[0048] FIG. 20 is a block diagram illustrating a substrate
processing process as carried out by the substrate processing
apparatus shown in FIG. 19;
[0049] FIGS. 21A through 21C are diagrams illustrating, in a
sequence of process steps, an example of the formation of copper
interconnects by plating;
[0050] FIG. 22 is a diagram illustrating the formation of a seed
layer on the surface of a recess (hole) having a high aspect
ratio;
[0051] FIG. 23 is a diagram illustrating the problem of dissolution
of the seed layer shown in FIG. 22 upon its contact with a plating
solution; and
[0052] FIGS. 24A through 24C are diagrams illustrating the
formation of embedded interconnects by copper plating of a
substrate as carried out by a conventional method.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0053] Preferred embodiments of the present invention will now be
described in detail with reference to the drawings. The following
embodiments relate to the application of the present invention
useful for forming interconnects of copper by embedding copper in
fine recess for interconnects formed in a surface of the
substrate.
[0054] FIG. 1 is a plan view showing a substrate processing
apparatus incorporating a plating apparatus for performing a
plating method according to the present invention. As shown in FIG.
1, this substrate processing apparatus has a rectangular facility
which houses therein two loading/unloading units 10 for housing a
plurality of substrates W therein, two plating apparatuses 12 for
performing plating process, a transfer robot 14 for transferring
substrates W between the loading/unloading units 10 and the plating
apparatuses 12, and plating solution supply equipment 18 having a
plating solution tank 16.
[0055] The plating apparatus 12, as shown in FIG. 2, is provided
with a substrate processing section 20 for performing plating
process and processing incidental thereto, and a plating solution
tray 22 for storing a plating solution is disposed adjacent to the
substrate processing section 20. There is also provided an
electrode arm portion 30 having an electrode head 28 which is held
at the front end of an arm 26 swingable about a rotating shaft 24
and which is swung between the substrate processing section 20 and
the plating solution tray 22. Furthermore, a pre-coating/recovering
arm 32, and fixed nozzles 34 for ejecting pure water or a chemical
liquid such as ion water, and further a gas or the like toward a
substrate are disposed laterally of the substrate processing
section 20. In this embodiment, three of the fixed nozzles 34 are
disposed, and one of them is used for supplying pure water.
[0056] The substrate processing section 20, as shown in FIG. 3, has
a substrate holder 36 for holding a substrate W with its surface
(plating surface) facing upward, and a electrode portion 38 located
above the substrate holder 36 so as to surround a peripheral
portion of the substrate holder 36. Further, a substantially
cylindrical bottomed cup 40 surrounding the periphery of the
substrate holder 36 for preventing scatter of various chemical
liquids used during processing is provided so as to be vertically
movable by an air cylinder (not shown).
[0057] The substrate holder 36 is adapted to be raised and lowered
by the air cylinder 44 between a lower substrate transfer position
A, an upper plating position B, and a pretreatment/cleaning
position C intermediate between these positions. The substrate
holder 36 is also adapted to rotate at an arbitrary acceleration
and an arbitrary velocity integrally with the electrode portion 38
by a rotating motor and a belt (not shown). Substrate carry-in and
carry-out openings (not shown) are provided in confrontation with
the substrate transfer position A in a side panel of the plating
apparatus 12 facing the transfer robot 14. When the substrate
holder 36 is raised to the plating position B, a sealing member 90
and cathode electrodes 88 (to be described below) of the electrode
portion 38 are brought into contact with the peripheral edge
portion of the substrate W held by the substrate holder 36. On the
other hand, the cup 40 has an upper end located below the substrate
carry-in and carry-out openings, and when the cup 40 ascends, the
upper end of the cup 40 reaches a position above the electrode
portion 38 closing the substrate carry-in and carry-out openings,
as shown by imaginary lines in FIG. 3.
[0058] The plating solution tray 22 serves to wet a high resistance
structure 110 and an anode electrode 98 (to be described later on)
of the electrode arm portion 30 with a plating solution, when
plating has not been performed. The plating solution tray 22 is set
at a size in which the high resistance structure 110 can be
accommodated, and the plating solution tray 22 has a plating
solution supply port and a plating solution drainage port (not
shown). A photo-sensor is attached to the plating solution tray 22,
and can detect brimming with the plating solution in the plating
solution tray 22, i.e., overflow, and drainage.
[0059] The electrode arm portion 30 is vertically movable by a
vertical movement motor 132, which is a servomotor, and a ball
screw 134, and swingable between the plating solution tray 22 and
the substrate processing section 20 by a swing motor, in this
embodiment, as described bellow. A compressed actuator may be
used.
[0060] As shown in FIG. 4, the pre-coating/recovering arm 32 is
coupled to an upper end of a vertical support shaft 58. The
pre-coating/recovering arm 32 is swingable by a rotary actuator 60
and is also vertically moveable by an air cylinder (not shown). The
pre-coating/recovering arm 32 supports a pre-coating nozzle 64 for
discharging a pre-coating liquid, on its free end side, and a
plating solution recovering nozzle 66 for recovering the plating
solution, on a portion closer to its proximal end. The pre-coating
nozzle 64 is connected to a syringe that is actuatable by an air
cylinder, for example, for intermittently discharging a pre-coating
liquid from the pre-coating nozzle 64. The plating solution
recovering nozzle 66 is connected to a cylinder pump or an
aspirator, for example, to draw the plating solution on the
substrate from the plating solution recovering nozzle 66.
[0061] As shown in FIGS. 5 through 7, the substrate holder 36 has a
disk-shaped substrate stage 68 and six vertical support arms 70
disposed at spaced intervals on the circumferential edge of the
substrate stage 68 for holding a substrate W in a horizontal plane
on respective upper surfaces of the support arms 70. A positioning
plate 72 is mounted on an upper end one of the support arms 70 for
positioning the substrate by contacting the end face of the
substrate. A pressing finger 74 is rotatably mounted on an upper
end of the support arm 70, which is positioned opposite to the
support arm 70 having the positioning plate 72, for abutting
against an end face of the substrate W and pressing the substrate W
to the positioning plate 72 when rotated. Chucking fingers 76 are
rotatably mounted on upper ends of the remaining four support arms
70 for pressing the substrate W downwardly and gripping the
circumferential edge of the substrate W.
[0062] The pressing finger 74 and the chucking fingers 76 have
respective lower ends coupled to upper ends of pressing pins 80
that are normally urged to move downwardly by coil springs 78. When
the pressing pins 80 are moved downwardly, the pressing finger 74
and the chucking fingers 76 are rotated radially inwardly into a
closed position. A support plate 82 is disposed below the substrate
stage 68 for engaging lower ends of the opening pins 80 and pushing
them upwardly.
[0063] When the substrate holder 36 is located in the substrate
transfer position A shown in FIG. 3, the pressing pins 80 are
engaged and pushed upwardly by the support plate 82, so that the
pressing finger 74 and the chucking fingers 76 rotate outwardly and
open. When the substrate stage 68 is elevated, the opening pins 80
are lowered under the resiliency of the coil springs 78, so that
the pressing finger 74 and the chucking fingers 76 rotate inwardly
and close.
[0064] As shown in FIGS. 8 and 9, the electrode portion 38
comprises an annular frame 86 fixed to upper ends of vertical
support columns 84 mounted on the peripheral edge of the support
plate 82 (see FIG. 7), a plurality of, six in this embodiment,
cathode electrodes 88 attached to a lower surface of the annular
frame 86 and projecting inwardly, and an annular sealing member 90
mounted on an upper surface of the annular frame 86 in covering
relation to upper surfaces of the cathode electrodes 88. The
sealing member 90 is adapted to have an inner peripheral edge
portion inclined inwardly downwardly and progressively thin-walled,
and to have an inner peripheral end suspending downwardly.
[0065] When the substrate holder 36 has ascended to the plating
position B, as shown FIG. 3, the cathode electrodes 88 are pressed
against the peripheral edge portion of the substrate W held by the
substrate holder 36 for thereby allowing electric current to pass
through the substrate W. At the same time, an inner peripheral end
portion of the sealing member 90 is brought into contact with an
upper surface of the peripheral edge of the substrate W under
pressure to seal its contact portion in a watertight manner. As a
result, the plating solution supplied onto the upper surface
(plating surface) of the substrate W is prevented from seeping from
the end portion of the substrate W, and the plating solution is
prevented from contaminating the cathode electrodes 88.
[0066] In the present embodiment, the electrode portion 38 is
vertically immovable, but rotatable in a body with the substrate
holder 36. However, the electrode portion 38 may be arranged such
that it is vertically movable and the sealing member 90 is pressed
against the surface, to be plated, of the substrate W when the
electrode portion 38 is lowered.
[0067] As shown in FIGS. 10 and 11, the electrode head 28 of the
electrode arm section 30 includes a housing 94 which is coupled via
a ball bearing 92 to the free end of the pivot arm 26, and a high
resistance structure 110 which is disposed such that it closes the
bottom opening of the housing 94. The housing 94 has at its lower
end an inwardly-projecting portion 94a, while the high resistance
structure 110 has at its top a flange portion 110a. The flange
portion 110a is engaged with the inwardly-projecting portion 94a
and a spacer 96 is interposed therebetween. The high resistance
structure 110 is thus held with the housing 94, while a hollow
plating solution chamber 100 is defined in the housing 94.
[0068] The high resistance structure 110 is composed of porous
ceramics such as alumina, SiC, mullite, zirconia, titania or
cordierite, or a hard porous material such as a sintered compact of
polypropylene or polyethylene, or a composite material comprising
these materials. In case of the alumina-based ceramics, for
example, the ceramics with a pore diameter of 30 to 200 .mu.m is
used. In case of the SiC, SiC with a pore diameter of not more than
30 .mu.m, a porosity of 20 to 95%, and a thickness of about 1 to 20
mm, preferably 5 to 20 mm, more preferably 8 to 15 mm, is used. The
high resistance structure 110, in this embodiment, is constituted
of porous ceramics of alumina having a porosity of 30%, and an
average pore diameter of 100 .mu.m. The porous ceramic plate per se
is an insulator, but the high resistance structure is constituted
by causing the plating solution to enter its interior complicatedly
and follow a considerably long path in the thickness direction.
[0069] The high resistance structure 110, which has the high
resistance, is disposed in the plating solution chamber 100. Hence,
the influence of the resistance of the seed layer 8 (see FIG. 22)
becomes a negligible degree. Consequently, the difference in
current density over the surface of the substrate due to electrical
resistance on the surface of the substrate W becomes small, and the
uniformity of the plated film over the surface of the substrate
improves.
[0070] In the plating solution chamber 100, there is disposed an
anode electrode 98 held in abutment against an lower surface of a
plating solution introduction pipe 104 disposed above the anode
electrode 98. The plating solution introduction pipe 104 has a
plating solution introduction port 104a connected to a plating
solution supply pipe 102 which extends from the plating solution
supply unit 18 (see FIG. 1). A plating solution discharge port 94b
provided in an upper plate of the housing 94 is connected to an
plating solution discharge pipe 106 communicating with the plating
solution chamber 100.
[0071] A manifold structure is employed for the plating solution
introduction pipe 104 so that the plating solution can be supplied
uniformly onto the plating surface of the substrate. In particular,
a large number of narrow tubes 112, communicating with the plating
solution introduction pipe 104, are connected to the pipe 104 at
predetermined positions along the long direction of the pipe 104.
Further, small holes are provided in the anode electrode 98 and the
high resistance structure 110 at positions corresponding to the
narrow tubes 112. The narrow tubes 112 extend downwardly in the
small holes and reach the lower surface or its vicinity of the high
resistance structure 110.
[0072] Thus, the plating solution, introduced from the plating
solution supply pipe 102 into the plating solution introduction
pipe 104, passes through the narrow tubes 112 and reaches the
bottom of the high resistance structure 110, and pass through the
high resistance structure 110 and fills the plating solution
chamber 100, whereby the anode electrode 98 is immersed in the
plating solution. The plating solution is discharged from the
plating solution discharge pipe 106 by application of suction to
the plating solution discharge pipe 106.
[0073] In order to suppress slime formation, the anode electrode 98
is made of copper (phosphorus-containing copper) containing 0.03 to
0.05% of phosphorus. It is also possible to use an insoluble
material for the anode electrode 98.
[0074] The cathode electrodes 88 are electrically connected to the
negative pole of a plating power source 114, and the anode
electrode 98 is electrically connected to the positive pole of the
plating power source 114. The plating power source 114 can change
the direction of current flow alternatively.
[0075] The ball bearing 92 is coupled to the pivot arm 26 via a
support member 124. The pivot arm 26 is vertically movable by a
vertical movement motor 132, which is a servomotor, and a ball
screw 134. It is also possible to use a compressed air actuator to
constitute a vertical movement mechanism.
[0076] When carrying out electroplating, the substrate holder 36 is
positioned at the plating position B (see FIG. 3). As shown in FIG.
11, the electrode head 28 is lowered until the distance between the
substrate W held by the substrate holder 36 and the high resistance
structure 110 becomes e.g. about 0.1 to 3 mm. A plating solution is
supplied from the plating solution supply pipe 102 to the upper
surface (plating surface) of the substrate W while impregnating the
high resistance structure 110 with the plating solution and filling
the plating solution chamber 100 with the plating solution to carry
out plating of the plating surface of the substrate W.
[0077] The operation of the substrate processing apparatus
incorporating the above-described plating apparatus will now be
described by furthermore referring to FIG. 12.
[0078] First, a substrate W to be plated is taken out from one of
the loading/unloading units 10 by the transfer robot 14, and
transferred, with the surface to be plated facing upward, through
the substrate carry-in and carry-out opening defined in the side
panel, into one of the plating apparatuses 12. At this time, the
substrate holder 36 is in the lower substrate transfer position A.
After the hand of the transfer robot 14 has reached a position
directly above the substrate stage 68, the hand of the transfer
robot 14 is lowered to place the substrate W on the support arms
70. The hand of the transfer robot 14 is then retracted through the
substrate carry-in and carry-out opening.
[0079] After the hand of the transfer robot 14 is retracted, the
cup 40 is elevated. Then, the substrate holder 36 is lifted from
the substrate transfer position A to the pretreatment/cleaning
position C. As the substrate holder 36 ascends, the substrate W
placed on the support arms 70 is positioned by the positioning
plate 72 and the pressing finger 74, and then reliably gripped by
the chucking fingers 76.
[0080] On the other hand, the electrode head 28 of the electrode
arm portion 30 is in a normal position over the plating solution
tray 22 now, and the high resistance structure 110 or the anode
electrode 98 is positioned in the plating solution tray 22. At the
same time that the cup 40 ascends, the plating solution starts
being supplied to the plating solution tray 22 and the electrode
head 28. Until the step of plating the substrate W is initiated,
the new plating solution is supplied, and the plating solution
discharge pipe 106 is evacuated to replace the plating solution in
the high resistance structure 110 and remove air bubbles from the
plating solution in the high resistance structure 110. When the
ascending movement of the cup 40 is completed, the substrate
carry-in and carry-out opening in the side panel is closed by the
cup 40, isolating the atmosphere in the side panel and the
atmosphere outside of the side panel from each other.
[0081] When the cup 40 is elevated, the pre-coating step is
initiated. Specifically, the substrate holder 36 that has received
the substrate W is rotated, and the pre-coating/recovering arm 32
is moved from the retracted position to a position confronting the
substrate W. When the rotational speed of the substrate holder 36
reaches a preset value, the pre-coating nozzle 64 mounted on the
tip end of the pre-coating/recovering arm 32 intermittently
discharges a pre-coating liquid which comprises a surface active
agent, for example, toward the plating surface of the substrate W.
At this time, since the substrate holder 36 is rotating, the
pre-coating liquid spreads all over the plating surface of the
substrate W. Then, the pre-coating/recovering arm 32 is returned to
the retracted position, and the rotational speed of the substrate
holder 36 is increased to spin the pre-coating liquid off and dry
the plating surface of the substrate W.
[0082] After the completion of the pre-coating step, the plating
step is initiated. First, the substrate holder 36 is stopped
against rotation, or the rotational speed thereof is reduced to a
preset rotational speed for plating. In this state, the substrate
holder 36 is lifted to the plating position B. Then, the peripheral
edge of the substrate W is brought into contact with the cathode
electrodes 88, when it is possible to pass an electric current, and
at the same time, the sealing member 90 is pressed against the
upper surface of the peripheral edge of the substrate W, thus
sealing the peripheral edge of the substrate W in a watertight
fashion.
[0083] Based on a signal indicating that the pre-coating step for
the loaded substrate W is completed, the electrode arm portion 30
is swung in a horizontal direction to displace the electrode head
28 from a position over the plating solution tray 22 to a position
over the plating processing position. After the electrode head 28
reaches this position, the electrode head 28 is lowered toward the
electrode portion 38. At this time, the high resistance structure
110 does not contact with the plating surface of the substrate W,
but is held closely to the plating surface of the substrate W at a
distance ranging from 0.1 mm to 3 mm. When the descent of the
electrode head 28 is completed, the plating process is
initiated.
[0084] In particular, as shown in FIG. 12, the negative pole of the
plating power source 114 is connected to the cathode electrodes 88
and the positive pole is connected to the anode electrode 98, and a
constant voltage is applied between the cathode electrodes 88 and
the anode electrode 98, i.e. constant voltage control is carried
out, while a plating solution is supplied from the plating solution
supply pipe 102 into the electrode head 28, so that the plating
solution is supplied onto the upper surface (plating surface) of
the substrate W while the high resistance structure 110 is
impregnated with the plating solution and the plating solution
chamber 100 is filled with the plating solution (t.sub.0-t.sub.1).
The voltage is preferably such as to allow an electric current with
an average cathodic current density, with respect to the surface of
the substrate W, of 1 mA/cm.sup.2 to 30 mA/cm.sup.2 to flow. The
time period for applying the voltage is generally 100 to 2000 msec,
preferably 300 to 1000 msec from the moment at which the electric
current begins to flow between the cathode electrodes 88 and the
anode electrode 98.
[0085] According to this embodiment, the moment at which the
electric current begins to flow between the cathode electrodes 88
and the anode electrode 98 is deemed as a liquid-contact point.
However, it is also possible, for example, to allow a weak direct
current or alternating current to flow between the cathode
electrodes 88 and the anode electrode 98 in advance, and determine
a liquid-contact point by detecting a change in voltage.
[0086] By thus supplying the plating solution while carrying out a
constant voltage control, i.e. applying a constant voltage between
the cathode electrodes 88 and the anode electrode 98, the drawback
of dissolution of seed layer 8 in the prior art as illustrated in
FIG. 23 can be overcome. Thus, according to a conventional plating
method, as shown in FIG. 23, a seed layer 8 on a substrate W can be
dissolved by a plating solution upon contact of the substrate W
with the plating solution. In particular, the seed layer 8 can be
dissolved out in the sidewalls of fine holes or trenches,
especially at portions near the bottoms of the holes or trenches,
resulting in non-conductivity at those portions. Such a drawback
can be overcome by the present method, and plating can be initiated
in such a state that a seed layer 8 is present over the entire
surfaces of recesses 5, as shown in FIG. 22.
[0087] After completion of the filling of plating solution, a
plated film is allowed to grow on the surface (seed layer 8) of the
substrate while carrying out constant current control, i.e.,
applying a constant electric current between the cathode electrodes
88 and the anode electrode 98. In particular, at the initial stage,
a low constant current ii, for example at about 1 to 10
mA/cm.sup.2, preferably at about 3 to 7 mA/cm.sup.2, is applied so
as to gradually grow a plated film (t.sub.1-t.sub.2). When the
thickness of the plated film has reached a predetermined value, for
example about 0.05 to 0.5 .mu.m, preferably about 0.1 to 0.2 .mu.m,
a high constant current i.sub.2 (i.sub.2>i.sub.1), for example
at about 10 to 40 mA/cm.sup.2, preferably at about 25 mA/cm.sup.2,
is applied so as to rapidly grow the plated film, thereby effecting
embedding of copper. During the plating, the substrate holder 36 is
rotated at a low speed, according to necessity.
[0088] The seed layer 8, which can be prevented from being
dissolved with the plating solution as described above, is thus
reinforced in the first-step plating carried out with a low
electric current, and the plated film is allowed to grow in the
second-step plating whereby embedding of copper is effected. Such a
two-step plating can form defect-free, completely-embedded
interconnects of a conductive material, such as copper, in recesses
in the surface of a substrate even when the recesses are of a high
aspect ratio.
[0089] When the plating process is completed, the electrode arm
portion 30 is raised and then swung to return to the position above
the plating solution tray 22 and to lower to the ordinary position.
Then, the pre-coating/recovering arm 32 is moved from the retreat
position to the position confronting to the substrate W, and
lowered to recover the remainder of the plating solution on the
substrate W by a plating solution recovering nozzle 66. After
recovering of the remainder of the plating solution is completed,
the pre-coating/recovering arm 32 is returned to the retreat
position, and pure water is supplied from the fixed nozzle 34 for
supplying pure water toward the central portion of the substrate W
for rinsing the plated surface of the substrate. At the same time,
the substrate holder 36 is rotated at an increased speed to replace
the plating solution on the surface of the substrate W with pure
water. Rinsing the substrate W in this manner prevents the
splashing plating solution from contaminating the cathode
electrodes 88 of the electrode portion 38 during descent of the
substrate holder 36 from the plating position B.
[0090] After completion of the rinsing, the washing with water step
is initiated. That is, the substrate holder 36 is lowered from the
plating position B to the pretreatment/cleaning position C. Then,
while pure water is supplied from the fixed nozzle 34 for supplying
pure water, the substrate holder 36 and the electrode portion 38
are rotated to perform washing with water. At this time, the
sealing member 90 and the cathode electrodes 88 can also be
cleaned, simultaneously with the substrate W, by pure water
directly supplied to the electrode potion 38, or pure water
scattered from the surface of the substrate W.
[0091] After washing with water is completed, the drying step is
initiated. That is, supply of pure water from the fixed nozzle 34
is stopped, and the rotational speed of the substrate holder 36 and
the electrode portion 38 is further increased to remove pure water
on the surface of the substrate W by centrifugal force and to dry
the surface of the substrate W. The sealing member 90 and the
cathode electrodes 88 are also dried at the same time. Upon
completion of the drying, the rotation of the substrate holder 36
and the electrode portion 38 is stopped, and the substrate holder
36 is lowered to the substrate transfer position A. Thus, the
gripping of the substrate W by the chucking fingers 76 is released,
and the substrate W is just placed on the upper surfaces of the
support arms 70. At the same time, the cup 40 is also lowered.
[0092] All the steps including the plating step, the pretreatment
step accompanying to the plating step, the cleaning step, and the
drying step are now finished. The transfer robot 14 inserts its
hand through the substrate carry-in and carry-out opening into the
position beneath the substrate W, and raises the hand to receive
the plated substrate W from the substrate holder 36. Then, the
transfer robot 14 returns the plated substrate W received from the
substrate holder 36 to one of the loading/unloading units 10.
[0093] FIG. 13 shows another control method (plating method) as
carried out by the plating apparatus. According to this method, the
negative pole of the plating power source 114 is connected to the
cathode electrodes 88 and the positive pole is connected to the
anode electrode 98, and a voltage (e.g. constant voltage) is
applied between the cathode electrodes 88 and the anode electrode
98, while a plating solution is supplied from the plating solution
supply pipe 102 into the electrode head 28, so that the plating
solution is supplied onto the upper surface (plating surface) of
the substrate W while the high resistance structure 110 is
impregnated with the plating solution and the plating solution
chamber 100 is filled with the plating solution
(t.sub.0-t.sub.4).
[0094] After completion of the filling of plating solution, a
plated film is allowed to grow on the surface of the substrate W
while carrying out constant current control, i.e., applying a
constant electric current between the cathode electrodes 88 and the
anode electrode 98. In particular, at the initial stage, a low
constant current i.sub.3, for example at about 1 to 10 mA/cm.sup.2,
preferably at about 3 to 7 mA/cm.sup.2, is applied so as to
gradually grow a plated film (t.sub.4-t.sub.5). When the thickness
of the plated film has reached a predetermined value, for example
about 0.05 to 0.5 .mu.m, preferably about 0.1 to 0.2 .mu.m, the
electric current (voltage) is switched so that the cathode
electrodes 88 becomes an anode and the anode electrode 98 becomes a
cathode, and a constant current (-i.sub.4) is applied between the
cathode electrodes 88 and the anode electrode 98 so as to etch away
the surface of the plated film and flatten the plated film
(t.sub.5-t.sub.6). Thereafter, the electric current (voltage) is
switched so that the cathode electrodes 88 becomes a cathode and
the anode electrode 98 becomes an anode, and a high constant
current i.sub.5 (i.sub.5>i.sub.3), for example at about 10 to 40
mA/cm.sup.2, preferably at about 25 mA/cm.sup.2, is applied so as
to rapidly grow the plated film, thereby effecting embedding of
copper.
[0095] By thus etching away the surface of a plated film between
the plating steps to flatten the plated film, the flatness of the
final plated film can be improved. In this connection, when a
barrier layer 6 is formed on the surface of a substrate W in which
relative small and large fine recesses, e.g. narrow trenches 5a and
broad trenches 5b, are co-present in the surface, as shown in FIG.
17A, and a seed layer 8 is formed on the barrier layer 6, and then
copper plating is carried out to grow a plated film to effect
embedding of copper film 7, the growth of plating tends to be
promoted over the narrow trenches 5a whereby the copper film 7 is
likely to be raised, even when the seed layer 8 can be prevented
from being dissolved with the plating solution as described above.
According to the present method, the raised portions 7a of the
plated copper film 7, shown by the broken line in FIG. 17B, are
etched away and a plated film is further grown on the flattened
copper film 7b to finally form a copper film 7c. The flatness of
the plated film (copper film 7) can thus be improved.
[0096] FIG. 14 shows yet another method (plating method) as carried
out by the plating apparatus. According to this method, the
negative pole of the plating power source 114 is connected to the
cathode electrodes 88 and the anode electrode 98, i.e. constant
voltage control is carried out, while a plating solution is
supplied from the plating solution supply pipe 102 into the
electrode head 28, so that the plating solution is supplied onto
the upper surface (plating surface) of the substrate W while the
high resistance structure 110 is impregnated with the plating
solution and the plating solution chamber 100 is filled with the
plating solution (t.sub.0-t.sub.8).
[0097] After completion of the filling of plating solution, a
plated film is allowed to grow on the surface (seed layer 8) of the
substrate while carrying out constant current control, i.e.,
applying a constant electric current between the cathode electrodes
88 and the anode electrode 98. In particular, at the initial stage,
a low constant current i.sub.6, which is lower than the electric
current applied between the cathode electrodes 88 and the anode
electrode 98 upon the constant voltage control, for example at
about 1 to 10 mA/cm.sup.2, preferably at about 3 to 7 mA/cm.sup.2,
is applied so as to gradually grow a plated film (t.sub.8-t.sub.9).
When the thickness of the plated film has reached a predetermined
value, for example about 0.05 to 0.5 .mu.m, preferably about 0.1 to
0.2 .mu.m, a high constant current i.sub.6 (i.sub.6>i.sub.5),
for example at about 10 to 40/cm.sup.2, preferably at about 25
mA/cm.sup.2, is applied so as to rapidly grow the plated film,
thereby effecting embedding of copper. During the plating, the
substrate holder 36 is rotated at a low speed, according to
necessity.
[0098] FIG. 15 shows yet another control method (plating method) as
carried out by the plating apparatus. According to this method, the
negative pole of the plating power source 114 is connected to the
cathode electrodes 88 and the positive pole is connected to the
anode electrode 98, and a constant voltage is applied between the
cathode electrodes 88 and the anode electrode 98, i.e. constant
voltage control is carried out, while a plating solution is
supplied from the plating solution supply pipe 102 into the
electrode head 28, so that the plating solution is supplied onto
the upper surface (plating surface) of the substrate W while the
high resistance structure 110 is impregnated with the plating
solution and the plating solution chamber 100 is filled with the
plating solution (t.sub.0-t.sub.11).
[0099] After completion of the filling of plating solution, a
plated film is allowed to grow on the surface (seed layer 8) of the
substrate while carrying out constant current control, i.e.,
applying a constant electric current between the cathode electrodes
88 and the anode electrode 98. In particular, at the initial stage,
a low constant current i.sub.8, which is higher than the electric
current applied between the cathode electrodes 88 and the anode
electrode 98 upon the constant voltage control, for example at
about 1 to 10 mA/cm.sup.2, preferably at about 3 to 7 mA/cm.sup.2,
is applied so as to gradually grow a plated film
(t.sub.11-t.sub.12). When the thickness of the plated film has
reached a predetermined value, for example about 0.05 to 0.5 .mu.m,
preferably about 0.1 to 0.2 .mu.m, a high constant current i.sub.9
(i.sub.9>i.sub.8), for example at about 10 to 40 mA/cm.sup.2,
preferably at about 25 mA/cm.sup.2, is applied so as to rapidly
grow the plated film, thereby effecting embedding of copper. During
the plating, the substrate holder 36 is rotated at a low speed,
according to necessity.
[0100] FIG. 16 shows yet another control method (plating method) as
carried out by the plating apparatus. This method effects embedding
of copper by using two plating solutions of different compositions.
In particular, the negative pole of the plating power source 114 is
connected to the cathode electrodes 88 and the positive pole is
connected to the anode electrode 98, and a constant voltage is
applied between the cathode electrodes 88 and the anode electrode
98, i.e. constant voltage control is carried out, while a plating
solution is supplied from the plating solution supply pipe 102 into
the electrode head 28, so that the plating solution is supplied
onto the upper surface (plating surface) of the substrate W while
the high resistance structure 110 is impregnated with the plating
solution and the plating solution chamber 100 is filled with the
plating solution (t.sub.0-t.sub.14).
[0101] After completion of the filling of plating solution, a
plated film is allowed to grow on the surface (seed layer 8) of the
substrate while carrying out constant current control, i.e.,
applying a constant electric current between the cathode electrodes
88 and the anode electrode 98. In particular, at the initial stage,
a low constant current i.sub.10, for example at about 3 to 7
mA/cm.sup.2, is applied so as to gradually grow a plated film
(t.sub.14-t.sub.15).
[0102] In the initial stage of plating, a plating solution suited
for embedding of fine (narrow) patterns is employed. The following
is an example of the composition of such plating solution:
1 CuSO.sub.4.5H.sub.2O 200 g/l H.sub.2SO.sub.4 50 g/l HCl 60 mg/l
Organic additive 5 ml/l
[0103] When the thickness of the plated film has reached a
predetermined value, for example about 0.05 to 0.5 .mu.m,
preferably about 0.1 to 0.2 .mu.m, the plating operation is
stopped, and the plating solution is removed and the surface of the
plated film is cleaned e.g. with pure water in the above-described
manner.
[0104] Next, a high constant current ill (i.sub.11>i.sub.10),
for example at about 20 to 40 mA/cm.sup.2, preferably at about 25
MA/cm.sup.2, is applied so as to rapidly grow the plated film,
thereby effecting embedding of copper.
[0105] In the latter stage of plating, a plating solution suited
for embedding of broad patterns, e.g. containing 100 to 300 g/l of
copper sulfate and 10 to 10 g/l of sulfuric acid, is employed. The
following is an example of the composition of such plating
solution:
2 CuSO.sub.4.5H.sub.2O 200 g/l H.sub.2SO.sub.4 50 g/l HCl 100 mg/l
Organic additive 5 ml/l
[0106] FIG. 18 shows another plating apparatus useful for carrying
out the plating method of the present invention. The plating
apparatus includes an upwardly-open cylindrical plating tank 602
for holding a plating solution 600, and a rotatable substrate
holder 604 for detachably holding a substrate W, such as a
semiconductor wafer, with its front surface facing downward and
locating the substrate W at a position at which it closes the top
opening of the plating tank 602. An anode electrode 606 in a flat
plate shape which, when immersed in the plating solution 600,
serves as an anode is disposed horizontally in the plating tank
602. A seed layer, formed in the surface of the substrate W, serves
as a cathode. The anode electrode 606 may be comprised of, for
example, a plate of copper or an aggregate of copper balls.
[0107] A plating solution supply pipe 610, which is provided with a
pump 608 therein, is connected to the center of the bottom of the
plating tank 602. Further, a plating solution receiver 612 is
disposed around the plating tank 602. The plating solution that has
flowed into the plating solution receiver 612 is returned through a
plating solution return pipe 614 to the pump 608.
[0108] In operation, the substrate W, held face down by the
substrate holder 604 and located at an upper position in the
plating tank 602, is rotated and a predetermined voltage is applied
between the anode electrode 606 and the seed layer (cathode
electrode) of the substrate W while the pump 608 is driven to
introduce the plating solution 600 into the plating tank 602,
whereby a plating current is allowed to flow between the anode
electrode 606 and the seed layer of the substrate W, and a plated
copper film is formed on the lower surface of the substrate W.
During the plating, the plating solution 600 overflowing the
plating tank 602 is recovered by the plating solution receiver 612
and circulated.
[0109] An insulator 632 in a flat plate shape is disposed between
the anode electrode 606 immersed in the plating solution 600 in the
plating tank 602 and the substrate W held by the substrate holder
604 and located at an upper position in the plating tank 602. A
plurality of through-holes 632b of any desired sizes (diameters)
are provided at any desired locations in the insulator 632 so that
a plating current can flow only through the through-holes 632b,
making it possible to make a plated copper film thicker at desired
portions of the substrate.
[0110] Also with the plating apparatus of such a construction, by
carrying out the same control as described above, it becomes
possible to form defect-free, completely-embedded interconnects of
a conductive material in recesses in the surface of a substrate
even when the recesses are of a high aspect ratio, and improve the
flatness of a plated film on the substrate even when narrow
trenches and broad trenches are co-present in the surface of the
substrate, enabling a later CMP processing to be carried out in a
short time while preventing dishing during the CMP processing.
[0111] FIG. 19 shows an overall layout plan of another substrate
processing apparatus provided with a plating apparatus for carrying
out a plating method according to the present invention. The
substrate processing apparatus (interconnects-forming apparatus)
includes two loading/unloading sections 202 for carrying a
substrate in and out a main frame 200. Inside the main frame 200
are disposed a heat treatment apparatus 204 for heat-treating
(annealing) a plated film formed on the substrate, a bevel-etching
apparatus 206 for removing a plated film formed on or adhering to a
peripheral portion of the substrate, two cleaning/drying
apparatuses 208 for cleaning the surface of the substrate with a
cleaning liquid, such as a chemical liquid or pure water, and
spin-drying the cleaned substrate, a substrate stage 210 for
temporarily placing the substrate thereon, and two plating
apparatuses 212. Inside the main frame 200 are also provided a
movable first transfer robot 214 for transferring the substrate
between the loading/unloading sections 202 and the substrate stage
210, and a movable second transfer robot 216 for transferring the
substrate between the substrate stage 210, the heat treatment
apparatus 204, the bevel-etching apparatus 206, the cleaning/drying
apparatuses 208 and the plating apparatuses 212. According to this
embodiment, the plating apparatus 212 has a similar construction to
that of the plating apparatus 12 shown in FIGS. 1 through 11.
[0112] The main frame 200 has been made light-shielding so that the
following process steps can be carried out under light-shielded
conditions in the main frame 200, i.e. without irradiation of a
light, such as an illuminating light, onto the interconnects of the
substrate. This prevents corrosion of the interconnects of e.g.
copper due to potential difference that would be produced by light
irradiation onto the interconnects.
[0113] Positioned beside the main frame 200, there is provided a
plating solution control apparatus 224 which includes a plating
solution tank 220 and a plating solution analyzer 222, and which
analyzes and controls the components of a plating solution for use
in the plating apparatuses 212 and supplies the plating solution of
a predetermined composition to the plating apparatuses 212. The
plating solution analyzer 222 includes an organic material analysis
section for analyzing an organic material by cyclic voltammetry
(CVS), liquid chromatography, etc., and an inorganic material
analysis section for analyzing an inorganic material by
neutralization titration, oxidation-reduction titration,
polarography, electrometric titration, etc. The results of analysis
by the plating solution analyzer 222 are fed back to adjust the
components of the plating solution in the plating solution tank
220. The plating solution control apparatus 224 may also be
disposed inside the main frame 200.
[0114] An example of the formation of copper interconnects by the
substrate processing apparatus, as illustrated in FIG. 20, will now
be described.
[0115] First, substrates W having a seed layer 8 (see FIG. 17B) as
an electric feeding layer formed on the surface are prepared, and a
substrate cassette housing the substrates is mounted in the
loading/unloading section 202. One substrate W is taken by the
first transfer robot 214 out of the cassette mounted in the
loading/unloading section 202, and the substrate is carried in the
main frame 200, transferred to the substrate stage 210, and placed
and held on the substrate stage 210. The substrate held on the
substrate stage 210 is transferred by the second transfer robot 216
to one of the plating apparatuses 212.
[0116] In the plating apparatus 212, as with the above-described
embodiment, a pre-plating treatment, such as pre-coating, of the
surface (plating surface) of the substrate W is first carried out.
Thereafter, plating of the substrate is carried out under a
current/voltage control as shown in FIG. 13, for example. Thus, a
plated copper film is first grown gradually on the surface of the
substrate W, the surface of the plated copper film is then etched
away to flatten the plated copper film, and the plated copper film
is then grown rapidly to effect embedding of copper. During the
processing, the composition of the plating solution in the plating
solution tank 220 is analyzed by the plating solution analyzer 222,
and a shortage of a component is replenished in the plating
solution in the plating solution tank 220 so that the plating
solution of a constant composition is supplied to the plating
apparatus 212. After completion of the plating, as with the
above-described embodiment, the plating solution remaining on the
substrate is recovered and the plated surface of the substrate is
rinsed, and the surface of the substrate is cleaned (water-washed)
with e.g. pure water. The substrate after cleaning is transferred
by the second transfer robot 216 to the bevel-etching apparatus
206.
[0117] In the bevel-etching apparatus 206, while rotating the
substrate which is held horizontally, an acid solution is supplied
continuously to the central portion of the front surface of the
substrate and an oxidant solution is supplied continuously or
intermittently to a peripheral portion of the front surface. The
acid solution may be of any non-oxidative acid, such as
hydrofluoric acid, hydrochloric acid, sulfuric acid, citric acid,
oxalic acid, etc. Examples of the oxidant solution include ozone
water, hydrogen peroxide solution, nitric acid solution, and sodium
hypochlorite solution, and a combination thereof. Copper, etc.
formed on or adhering to a peripheral portion (bevel portion) of
the substrate W is rapidly oxidized by the oxidant solution, and
the oxidized product is etched and dissolved out by the acid
solution which is supplied to the central portion of the substrate
and spreads over the entire surface of the substrate.
[0118] During the above etching processing, an oxidant solution and
an etching agent for silicon oxide film may be supplied
simultaneously or alternately to the central portion of the back
surface of the substrate, thereby oxidizing copper etc. in
elemental form adhering to the back surface of the substrate W,
together with the silicon of the substrate, with the oxidant
solution and etching away the oxidized product with the etching
agent.
[0119] The substrate after bevel-etching is transferred by the
second transfer robot 216 to one of the cleaning/drying apparatuses
208, where the surface of the substrate is cleaned with a cleaning
liquid, such as a chemical liquid or pure water, followed by
spin-drying. The dried substrate is transferred by the second
transfer robot 216 to the heat treatment apparatus 204.
[0120] In the heat treatment apparatus 204, heat treatment
(annealing) of the copper film 7 (see FIG. 21B) formed on the
surface of the substrate W is carried out, thereby crystallizing
the copper film 7 forming interconnects. The heat treatment
(annealing) is carried out by heating the substrate, for example,
at 400.degree. C. for about a few tens of seconds to 60 seconds. At
the same time, if necessary, a gas for oxidation inhibition is
introduced into the heat treatment apparatus 204 and is allowed to
flow along the surface of the substrate to prevent oxidation of the
surface of the copper film 7. The heating temperature of the
substrate is generally 100 to 600.degree. C., preferably 300 to
400.degree. C.
[0121] The substrate W after heat treatment is transferred by the
second transfer robot 216 to the substrate stage 210 and held on
the substrate stage 210. The substrate on the substrate stage 210
is transferred by the first transfer robot 214 to the cassette of
the loading/unloading section 202.
[0122] Thereafter, extra metal formed on the insulating film and
the barrier layer are removed by method such as chemical mechanical
polishing (CMP) so as to flatten the surface, whereby forming
interconnects composed of the copper film 7, as shown in FIG.
21C.
[0123] Though in this embodiment copper is used as an interconnect
metal, it is possible to use a copper alloy instead.
[0124] The following Examples illustrate copper plating of the
surface of a substrate by a plating method according to the present
invention.
[0125] In each of the Examples, two types of substrates are used:
silicon wafer (diameter: 200 mm) with holes having a hole diameter
of 0.15-0.50 .mu.m and a depth of 0.8 .mu.m; and silicon wafer
(diameter: 200 mm) with trenches having a width of 0.12-1.0 .mu.m.
Seed layers are formed on the surfaces of these substrates by PVD
to make electrical conduction, followed by copper plating using a
copper sulfate plating solution.
EXAMPLE 1
[0126] A copper sulfate plating solution having the following
composition was used:
3 Copper sulfate pentahydrate: 200 g/L Sulfuric acid: 50 g/L
Chlorine: 60 mg/L Additive: Proper amount
[0127] Ebatoronfil (manufactured by Ebara-Udylite Co., Ltd) was
used as the additive.
[0128] For each of the above-described substrates, electroplating
was carried out in the following manner:
[0129] A voltage of 0.4V had been applied in advance to the
substrate (the current density at the substrate surface upon
contact of the substrate with the plating solution was 7
mA/cm.sup.2), and the plating solution was filled into the space
between the substrate and an anode electrode. The application of
the constant voltage was continued for 500 msec after the filling
of the plating solution. Thereafter, the constant voltage control
was instantaneously changed to constant current control and a
constant current was applied at 7 mA/cm.sup.2 for 30 sec to form a
copper film, and then a constant current was applied at 25
mA/cM.sup.2 for 50 sec to further grow the plated film, thereby
depositing a copper film having a thickness, on the plane of the
substrate, of about 500 nm.
EXAMPLE 2
[0130] The same substrates and the same plating solution as in
Example 1 were used. For each of the substrates, electroplating was
carried out in the following manner:
[0131] A voltage of 1.0V had been applied in advance to the
substrate (the current density at the substrate surface upon
contact of the substrate with the plating solution was 20
mA/cm.sup.2), and the plating solution was filled into the space
between the substrate and an anode electrode. The application of
the constant voltage was continued for 300 msec after the filling
of the plating solution. Thereafter, the constant voltage control
was instantaneously changed to constant current control and a
constant current was applied at 10 mA/cm.sup.2 for 30 sec to form a
copper film, and then a constant current was applied at 20
mA/cm.sup.2 for 53 sec to further grow the plated film, thereby
depositing a copper film having a thickness, on the plane of the
substrate, of about 500 nm.
EXAMPLE 3
[0132] The same substrates and the same plating solution as in
Example 1 were used. For each of the substrates, electroplating was
carried out in the following manner:
[0133] A voltage of 0.7V had been applied in advance to the
substrate (the current density at the substrate surface upon
contact of the substrate with the plating solution was 15
mA/cm.sup.2), and the plating solution was filled into the space
between the substrate and an anode electrode. The application of
the constant voltage was continued for 500 msec after the filling
of the plating solution. Thereafter, the constant voltage control
was instantaneously changed to constant current control and a
constant current was applied at 7 mA/cm.sup.2 for 40 sec to form a
copper film, and then reverse electrolysis was carried out at 20
mA/cm.sup.2 for 4 sec, and then a constant current was applied at
25 mA/cm.sup.2 for 52 sec to further grow the plated film, thereby
depositing a copper film having a thickness, on the plane of the
substrate, of about 500 nm.
COMPARATIVE EXAMPLE 1
[0134] The same substrates and the same plating solution as in
Example 1 were used. For each of the substrates, electroplating was
carried out in the following manner:
[0135] The plating solution was filled into the space between the
substrate and an anode electrode without application of a voltage
therebetween. 500 msec after the filling of the plating solution, a
constant current was applied at 7 mA/cm.sup.2 for 30 sec to form a
copper film, and then a constant current was applied at 25
mA/cm.sup.2 for 50 sec to further grow the plated film, thereby
depositing a copper film having a thickness, on the plane of the
substrate, of about 500 nm.
[0136] A hole portion or a trench portion of each of the substrates
with the plated copper film, obtained in the above Examples 1 to 3
and Comp. Example 1, was cut off by means of FIB (focused in beam)
and the cut surface was observed by SEM (scanning electron
micrograph). As a result, with respect to the substrates of
Examples 1 to 3, no void was observed in the substrates having fine
holes or in the substrates having fine trenches. In contrast
thereto the substrates of Comp. Example 1, many voids were observed
at the bottom portions of fine holes and trenches.
[0137] As described hereinabove, the present invention makes it
possible to form defect-free, completely-embedded interconnects of
a conductive material in recesses in the surface of a substrate
even when the recesses are of a high aspect ratio, and improve the
flatness of a plated film on the substrate even when narrow
trenches and broad trenches are co-present in the surface of the
substrate, enabling a later CMP processing to be carried out in a
short time while preventing dishing during the CMP processing.
[0138] Although certain preferred embodiments of the present
invention have been shown and described in detail, it should be
understood that various changes and modifications may be made
therein without departing from the scope of the appended
claims.
* * * * *