U.S. patent application number 12/443766 was filed with the patent office on 2010-01-07 for electroplating method.
This patent application is currently assigned to Seizo MIYATA. Invention is credited to Seizo Miyata, Tetsuya Shimizu, Masato Sone, Hisayoshi Tajima.
Application Number | 20100000872 12/443766 |
Document ID | / |
Family ID | 39268378 |
Filed Date | 2010-01-07 |
United States Patent
Application |
20100000872 |
Kind Code |
A1 |
Shimizu; Tetsuya ; et
al. |
January 7, 2010 |
ELECTROPLATING METHOD
Abstract
The surface of a metal base is electroplated by utilizing an
induction codeposition phenomenon using at least one of carbon
dioxide and inert gas, an electroplating liquid containing a metal
powder dispersed therein, and a surfactant in a supercritical state
or a subcritical state. The concentration of the metal in the
electroplating liquid is in a saturated or supersaturated state.
Accordingly, the dissolution speed of the metal base can be
suppressed, and, at the same time, a plating layer having a smooth
surface can be formed in a short time by utilizing an induction
codeposition phenomenon. The electroplating method can be applied
even when the metal base is formed of a metallic thin film provided
on a surface of an insulating film provided on the substrate, or
even when the metal is copper, zinc, iron, nickel, or cobalt. The
above constitution can provide an electroplating method which, in
electroplating on the surface of a metal base, can prevent the
dissolution of the metal base to realize normal electroplating even
in the case of a very thin metal base.
Inventors: |
Shimizu; Tetsuya;
(Iruma-shi, JP) ; Tajima; Hisayoshi; (Iruma-shi,
JP) ; Miyata; Seizo; (Nishitokyo-shi, JP) ;
Sone; Masato; (Konganei-shi, JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW, SUITE 700
WASHINGTON
DC
20036
US
|
Assignee: |
MIYATA; Seizo
Nishitokyo-shi, Tokyo
JP
S.E.S. CO., LTD.
Oume-shi, Tokyo
JP
|
Family ID: |
39268378 |
Appl. No.: |
12/443766 |
Filed: |
April 2, 2007 |
PCT Filed: |
April 2, 2007 |
PCT NO: |
PCT/JP2007/068380 |
371 Date: |
June 3, 2009 |
Current U.S.
Class: |
205/98 |
Current CPC
Class: |
H01L 21/2885 20130101;
C25D 15/02 20130101; C25D 5/003 20130101; H01L 21/76877 20130101;
C25D 3/38 20130101 |
Class at
Publication: |
205/98 |
International
Class: |
C25D 21/14 20060101
C25D021/14 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 2, 2006 |
JP |
2006-270762 |
Claims
1. A method for electroplating the surface of a metal base, the
method characterized in comprising: performing electroplating by
utilizing an induction codeposition phenomenon in a supercritical
or a subcritical state using at least one of carbon dioxide and an
inert gas, as well as an electroplating solution containing a metal
powder which are added in an amount equal to or greater than the
amount at which the plating metal could no longer be dissolved
dispersed therein, and a surfactant, said metal powder being
comprising the same metal as at least on of the metal base and a
metal film obtained in electroplating.
2. (canceled)
3. The electroplating method according to claim 1, characterized in
that the average particle diameter of said metal powder is from 1
.mu.m or greater to 100 .mu.m or less.
4. The electroplating method according to claim 1, characterized in
that the average particle diameter of said metal powder is from 1
nm or greater to less than 1 .mu.m.
5. The electroplating method according to claim 1, characterized in
that a voltage at which said metal base does not dissolve is
applied before said metal base is immersed into said electroplating
solution.
6. The electroplating method according to claim 3, characterized in
that a voltage at which said metal base does not dissolve is
applied before said metal base is immersed into said electroplating
solution.
7. The electroplating method according to claim 4, characterized in
that a voltage at which said metal base does not dissolve is
applied before said metal base is immersed into said electroplating
solution.
Description
TECHNICAL FIELD
[0001] The present invention relates to an electroplating method
for electroplating the surface of a metal base, and particularly
relates to an electroplating method in which the dissolution of the
metal base that has not yet been electroplated can be prevented,
and a uniform film can be obtained by electroplating in a short
time using an induction codeposition phenomenon even on a very thin
metal base.
BACKGROUND ART
[0002] In conventional methods for forming a fine metal wiring
within a semiconductor element, a thin aluminum film is first
formed, for example, on a substrate by sputtering; a photoresist is
then applied; a pattern is formed by exposure and development; and
a designated wiring is formed by etching. However, such wiring
methods have come to be difficult to use with the progress in the
increased integration and miniaturization of semiconductor circuit
elements, prompting wider use of so-called Damascene methods, in
which a wiring groove or hole is formed in advance; aluminum is
embedded in the groove or hole by chemical vapor deposition (CVD),
sputtering, plating, or another method; and the surface is then
polished by chemical mechanical polishing (CMP) to form a wiring.
One of the Damascene methods, referred to as the dual Damascene
method, is one in which a hole for connecting the bottom layer to
the wiring is formed at the time the groove is formed, the
connecting hole and groove are filled with aluminum or copper at
the same time, and a wiring is formed.
[0003] A Damascene method in which electroplating is used has
recently become popular as a step for forming wiring in a
semiconductor device (see Patent Documents 1 and 2 below).
Following is a description, made with reference to FIGS. 3 and 4,
of a method for forming a wiring in a semiconductor device for
three-dimensional mounting by using the Damascene method disclosed
as a prior-art example in Patent Document 1. In this wiring method,
a hole 72 is formed by, for example, lithography or etching in the
surface of a silicon substrate or other substrate 70, as shown in
FIG. 3A; an insulating film 74 composed of SiO.sub.2 is
subsequently formed by, for example, CVD on the surface of the
substrate 70, as shown in FIG. 3B; the surface of the hole 72 is
covered with the insulating film 74 to thereby prevent leakage of
electricity; and a seed layer 76 is further formed by, for example,
CVD or sputtering as an electroplating feeder layer on the
insulating film 74, as shown in FIG. 3C.
[0004] The surface of the substrate 70 is electroplated with copper
as shown in FIG. 3D, the interior of the hole 72 in the substrate
70 is filled with copper, a copper plating film 78 is deposited on
the insulating film 74, the copper plating film 78 and the
insulating film 74 are then removed from the substrate 70 by CMP as
shown in FIG. 3E, and the surface of the copper plating film 78 in
the hole 72 is made substantially coplanar with the surface of the
substrate 70 to form an embedded wiring.
[0005] In the embedded wiring disclosed in Patent Document 1, the
diameter W of the hole 72 is about 5 to 20 .mu.m, and the wiring is
applicable to cases in which the depth D is about 50 to 70 .mu.m.
In the step in which copper is electroplated in the manner shown in
FIG. 3D according to the invention disclosed in Patent Document 1,
a step is added in which part of the plating film is etched during
the electroplating step, as shown in FIG. 4B, in order to prevent
situations in which the copper creates an overhang in proximity to
the entrance to the hole 72, as shown in FIG. 4A, and voids (air
holes) are formed inside the copper wiring. The groove 72 is filled
with copper 78, as shown in FIG. 4E, by further repeating the
electroplating step and the plating film etching step the desired
number of times, as shown in FIGS. 4C and 4D.
[0006] Thus, using inventions such as the one disclosed in Patent
Document 1 makes it difficult to fill copper without voids into a
narrow groove or hole that measures about 0.20 .mu.m or less.
Therefore, this problem is solved in the invention disclosed in
Patent Document 2 below by adjusting the composition of the plating
solution and adjusting the metal deposition rate at the bottom and
entrance of the groove or hole.
[0007] Patent Document 1: Japanese Laid-Open Patent Application No.
2003-96596 (claims; paragraphs [0003] to [0010], [0011]; FIGS. 4,
6, 8)
[0008] Patent Document 2: Japanese Laid-Open Patent Application No.
2005-259959 (claims; paragraphs [0011], [0013], [0029]; FIGS. 1 and
2)
[0009] Patent Document 3: Japanese Laid-Open Patent Application No.
2003-321798 (paragraphs [0001] to [0009])
[0010] Patent Document 4: Japanese Laid-Open Patent Application No.
2005-154816 (claim 15, paragraphs [0023] to [0036], FIG. 1)
[0011] Patent Document 5: Japanese Laid-Open Patent Application No.
7-268696 (claims; paragraphs [0021] to [0022]; FIGS. 1 and 2)
DISCLOSURE OF THE INVENTION
Problems the Invention is Intended to Solve
[0012] As described above, in the Damascene method or the dual
Damascene method, a seed layer, namely, a very thin metal base, is
formed on the surface of the insulating film as an electroplated
feed layer by CVD or sputtering, and a similar metal is also
electroplated onto the surface of the metal base. Our experiments
showed, however, that when this metal base was immersed into an
electroplating solution to electroplate a similar metal, the metal
base was often dissolved even if the metal base was a thick plate,
and the plating failed without producing a smooth, normal surface.
Such a phenomenon can be clearly observed in particular in the case
of an electroplating method (see Patent Documents 3 and 4 above)
conducted using a supercritical fluid or subcritical fluid in which
the metal base has a high dissolution rate.
[0013] As a result of repeated experiments conducted on the premise
that plating failures such as those described above could be
suppressed if the dissolution of the metal base in the
electroplating solution could be reduced, the inventors completed
the present invention upon discovering that by adding a powdered
plating metal to the electroplating solution in advance in an
amount equal to or greater than the amount (solubility) at which
the plating metal could no longer be dissolved, stirring the
solution to supersaturation, and performing other operations, the
powdered plating metal is dispersed into the electroplating
solution, and the metal is electroplated in a dispersed state,
whereupon electroplating could be performed in a regular manner and
a uniform film could be obtained in a short time by using an
induction codeposition phenomenon because the metal base did not
readily dissolve in the electroplating solution even if the metal
base was immersed into the electroplating solution.
[0014] Namely, an object of the present invention is to provide an
electroplating method wherein dissolution of the metal base prior
to electroplating can be prevented; the electrode, i.e., the not
yet electrodeposited metal base, can be prevented from dissolving;
and a uniform film can be obtained by electroplating in a short
time by using the induction codeposition phenomenon even if the
metal base is very thin.
[0015] Patent Document 5 discloses an invention wherein granular or
pulverulent nickel is directly added into a dissolution bath in
order to adjust the concentration of nickel in a nickel plating
solution, but no description of an electroplating bath is given,
and it is clear that the resulting nickel plating solution is fed
to a separate electroplating bath to perform electroplating.
Means for Solving the Abovementioned Problems
[0016] Aimed at achieving the aforementioned object, the
electroplating method of the present invention is a method for
electroplating the surface of a metal base, the method
characterized in comprising: performing electroplating by utilizing
the induction codeposition phenomenon in a supercritical or a
subcritical state using at least one of carbon dioxide and an inert
gas, as well as an electroplating solution containing a metal
powder dispersed therein, and a surfactant. In the present
specification, "induction codeposition phenomenon" refers to a
phenomenon in which a portion of metal powder is also
simultaneously incorporated into the plating film during
electroplating.
[0017] The electroplating method of the present invention is also
characterized in that the metal powder comprises the same metal as
at least one of the metal base and a metal film obtained in
electroplating.
[0018] The electroplating method of the present invention is also
characterized in that the average particle diameter of the
abovementioned metal powder is from 1 .mu.m or greater to 100 .mu.m
or less.
[0019] The abovementioned electroplating method of the present
invention is characterized in that the average particle diameter of
the metal powder is from 1 nm or greater to less than 1 .mu.m.
[0020] The electroplating method of the present invention is also
characterized in that a voltage at which the metal base does not
dissolve is applied before the metal base is immersed into the
electroplating solution.
[0021] The electroplating method of the present invention is also
characterized in that the voltage at which the metal base does not
dissolve is the voltage used during electroplating.
EFFECT OF THE INVENTION
[0022] By adopting a method such as the one described above, the
present invention provides excellent effects as described
hereinafter. In other words, when the surface of a metal base is
electroplated according to the electroplating method of the present
invention, the electroplating solution and the metal base are in
contact with each other in an emulsion state because an arrangement
is adopted in which electroplating is performed by utilizing the
induction codeposition phenomenon using at least one of a carbon
dioxide and an inert gas, as well as an electroplating solution
containing a metal powder dispersed therein, and a surfactant in a
supercritical or a subcritical state. For this reason, the
electroplating solution rapidly penetrates into fine holes and
grooves, and even a metal base having a complex shape can therefore
be effectively electroplated in applications in which fine metal
wiring is formed in highly integrated, miniaturized semiconductor
circuit elements.
[0023] According to the electroplating method of the present
invention, electroplating is performed in a state in which the
metal powder is dispersed in the electroplating solution, and the
concentration of the metal in the electroplating solution therefore
corresponds to a saturated or supersaturated state. Therefore, the
dissolution rate of the metal base can be reduced when the metal
base is immersed into the electroplating solution, and a uniform
film can be obtained by electroplating in a short time by using the
induction codeposition phenomenon.
[0024] According to the electroplating method of the present
invention, the dissolution rate of the metal base can be reduced
when the metal base is immersed into the electroplating solution,
for which reason electroplating can be performed in the regular
manner even if the metal base is a thin metal film formed on the
surface of an insulating film provided on a substrate. In
particular, effective use can be made of the method in a Damascene
method, dual Damascene method, or other application in which fine
wiring is formed in miniaturized semiconductor circuit
elements.
[0025] According to the electroplating method of the present
invention, because the average particle diameter of the metal
powder is set within a range of from 1 .mu.m or greater to 100
.mu.m or less and the solubility of metal powder in the
electrolytic solution is high, metal ions can be efficiently fed to
the electrolytic solution. In this case, the substrate
microstructure to be deposited must be precise to 1 .mu.m or more.
An average particle diameter of the metal powder exceeding 100
.mu.m is not preferred because the dissolution rate of the metal
powder will be low.
[0026] According to the electroplating method of the present
invention, the average particle diameter of the metal powder is set
within a range of from 1 nm or greater to less than 1 .mu.m.
Therefore, the metal powder can be easily dispersed into the
electrolytic solution, not only making aggregation more difficult,
but also facilitating electroplating in microstructures having a
precision of less than 1 .mu.m.
[0027] The present invention is particularly suited for
applications involving formation of fine wiring. The reason is that
because a voltage at which the metal base will not dissolve is
applied before the metal base is immersed into the electroplating
solution, the metal base will not dissolve even if the metal base
is immersed into the electroplating solution, and the voltage
required for electroplating can be applied once a sufficiently
stable state is established after the metal base has been immersed
into the electroplating solution.
[0028] According to the present invention, because the
electroplating voltage is applied before the metal base is immersed
into the electroplating solution, the surface of the metal base is
electroplated immediately after the metal base is immersed into the
electroplating solution, and the designated electroplating layer
can therefore be obtained in a short time.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is a schematic view of an electroplating device used
in the experimental examples;
[0030] FIG. 2 is a view showing the relationship between the amount
of copper dissolved from an electrolytic copper sample and the
elapsed time;
[0031] FIG. 3A through 3E are views showing steps for forming a
wiring in a semiconductor device for three-dimensional mounting in
a prior-art example; and
[0032] FIG. 4 is a view showing the void suppression step employed
by the prior art shown in FIG. 3.
KEY TO SYMBOLS
[0033] 10 electroplating device [0034] 11 pressure-resistant
electroplating chamber [0035] 12 carbon dioxide cylinder [0036] 13
high-pressure pump unit [0037] 14 valve [0038] 15 lid [0039] 16
entrance [0040] 17 exit [0041] 18 pressure adjustment unit [0042]
19 electroplating solution [0043] 20 stirrer [0044] 21 oven [0045]
22 metal base sample [0046] 23 counter electrode [0047] 24 direct
current power source
BEST MODE FOR CARRYING OUT THE INVENTION
[0048] Preferred embodiments for implementing the present invention
will be described in detail hereinafter with reference to the
experimental examples and the drawings, but the experimental
examples described below are not intended to limit the present
invention to those described herein, and the present invention is
equally applicable to various modifications that do not depart from
the technical spirit described in the claims. FIG. 1 is a schematic
view of an electroplating device used in the experimental examples,
and FIG. 2 is a view showing the relationship between the amount of
copper dissolved from an electrolytic copper sample and the elapsed
time.
[Electroplating Solution]
[0049] Described below are the composition of the electroplating
solution for copper applications that was used in the experimental
examples, and the constitution of the experimental system.
Electroplating Solution Composition
TABLE-US-00001 [0050] Copper sulfate (CuSo.sub.4.cndot.5H.sub.2O)
70 g/L Sulfuric acid (H.sub.2SO.sub.4) 180 g/L Chlorine ions
(Cl.sup.-) 50 mg/L Nonionic surfactant 10 mL/L
Hereinafter, an electroplating solution for copper having the
above-mentioned composition is referred to as a "high-throw
bath."
[Electroplating Apparatus]
[0051] A pressure-resistant electroplating chamber 11 was used in
an electroplating apparatus 10 in order to be able to perform
electroplating using a supercritical fluid or subcritical fluid, as
shown in FIG. 1. Carbon dioxide can be fed as necessary from a
carbon dioxide cylinder 12 through a high-pressure pump unit 13 and
a valve 14 to the entrance 16 provided in a cover 15 on the upper
part of the pressure-resistant electroplating chamber 11. The
carbon dioxide can also be released into the surrounding atmosphere
through a pressure adjustment unit 18 from an exit 17 provided in
the cover 15 on the upper part.
[0052] Removing the cover 15 of the pressure-resistant
electroplating chamber 11 allows a predetermined amount of an
electroplating solution 19 to be injected into the chamber, and a
stirrer 20 is inserted as stirring means into the
pressure-resistant electroplating chamber 11. The
pressure-resistant electroplating chamber 11 is configured so as to
be placed inside an oven 21 and to allow the electroplating
solution 19 inside the chamber to be kept at a constant
temperature.
[0053] A metal base sample 22 and a counter electrode 23 are
electrically insulated and placed in the upper part of the
pressure-resistant electroplating chamber 11. The metal base sample
22 is electrically connected to the negative terminal of a direct
current power source 24, and the counter electrode 23 is connected
to the positive terminal of the direct current power source 24. A
copper plate or a thin copper film formed on the surface of TaN
film is used in the experimental examples, examples, and the like
described hereinafter; and commercial-grade high phosphorous copper
is used as the counter electrode.
[0054] To conduct an experiment in a supercritical or subcritical
state in the electroplating apparatus 10, the carbon dioxide
cylinder 12, the high-pressure pump unit 13, the valve 14, and the
pressure adjustment unit 18 were operated to maintain the pressure
in the pressure-resistant electroplating chamber 11 at 8 to 10 MPa;
the oven 21 was operated to heat the electroplating solution 19 to
40.degree. C.; and a supercritical or a subcritical state was
created inside the pressure-resistant electroplating chamber 11. To
conduct an experiment under one atmosphere of pressure, the carbon
dioxide cylinder 12, the high-pressure pump unit 13, the valve 14,
and the pressure adjustment unit 18 were operated to open the
interior of the pressure-resistant electroplating chamber 11 to
atmospheric pressure, and the oven 21 was operated to heat the
electroplating solution 19 to a designated temperature.
EXPERIMENTAL EXAMPLE 1 THROUGH 3
[0055] In Experimental Examples 1 through 3, the solubility of the
metal base was investigated when electroplating was conducted in a
supercritical state using the high-throw bath. A base obtained by
forming a thin copper film having a thickness of 65 nm on a TaN
film by sputtering was used as the metal base sample 22. This metal
base sample 22 was pretreated by acid pickling and placed together
with the counter electrode 23 in the upper part of the
electroplating solution 19 in the pressure-resistant plating
chamber 11 to as not to be in contact with the electroplating
solution 19. The amount of the electroplating solution 19 used was
set at 30 mL.
[0056] In this state, the electroplating solution in the
pressure-resistant electroplating chamber 11 was heated to a
temperature of 40.degree. C.; the electroplating solution 19 was
not stirred by the stirrer 20; and the carbon dioxide cylinder 12,
the high-pressure pump unit 13, the valve 14, and the pressure
adjustment unit 18 were operated to increase the pressure inside
the pressure-resistant electroplating chamber 11 to 10 MPa. The
electroplating solution 19 was stirred by the stirrer 20 at the
same time as the pressure inside the pressure-resistant
electroplating chamber 11 reached 10 MPa.
[0057] When this was done, the critical pressure of the carbon
dioxide was about 7.38 MPa when the temperature of the
electroplating solution 19 was 40.degree. C. Therefore, the
interior of the pressure-resistant electroplating chamber 11 was
substantially in a supercritical or a subcritical state under the
abovementioned temperature and pressure conditions, the
electroplating solution 19 was substantially emulsified by the
presence of the surfactant in the electroplating solution 19, and
the electroplating solution 19 in the emulsion state was poured
into the pressure-resistant electroplating chamber 11 and brought
into adequate contact with the metal base sample 22 and the counter
electrode 23.
[0058] The plating state on the surface of the metal base sample 22
was then investigated under the following three conditions.
Experimental Example 1
[0059] Five minutes after the pressure inside the
pressure-resistant electroplating chamber 11 became 10 MPa, an
electroplating voltage was applied between the metal base sample 22
and the counter electrode 23 from the direct current power source
24.
Experimental Example 2
[0060] At the same time the pressure inside the pressure-resistant
electroplating chamber 11 became 10 MPa, an electroplating voltage
was applied between the metal base sample 22 and the counter
electrode 23 from the direct current power source 24.
Experimental Example 3
[0061] At the same time the pressure inside the pressure-resistant
electroplating chamber 11 began rising, an electroplating was
applied between the metal base sample 22 and the counter electrode
23 voltage from the direct current power source 24.
[0062] The results are described in Table 1 below.
TABLE-US-00002 TABLE 1 Voltage application time Plating state
Experimental Five minutes after Dissolution Example 1
pressurization Experimental Immediately after Partial plating
Example 2 pressurization Experimental At same time pressure
Nonuniform plating layer Example 3 starts rising formed
[0063] Namely, under the conditions in Experimental Example 1, the
metal base sample 22 comprising a thin copper film was completely
dissolved before the plating voltage was applied, and no copper
plating film was obtained. Under the conditions in Experimental
Example 2, a sizable portion of the metal base sample 22 comprising
a thin copper film was dissolved, but the partially remaining
portion was electroplated. Also, under the conditions in
Experimental Example 3, a film was obtained, but the film was
nonuniform and irregular.
[0064] The above experiment results indicate that a good
electroplating film could not be obtained because the reaction
between the electroplating solution and the metal base comprising a
thin copper film proceeded too rapidly when a commonly employed
high-throw bath was used to electroplate copper onto a metal base
composed of copper in a supercritical state or a subcritical
state.
Experimental Example 4
[0065] Thus, in Experimental Example 4, the electroplating state
was investigated under conditions in which a high-throw bath was
used and noncritical pressure was applied. Namely, 40 mL of the
high-throw bath was injected into the pressure-resistant
electroplating chamber 11 as the electroplating solution, and the
electroplating solution 19 in the pressure-resistant electroplating
chamber 11 was heated to a temperature of 40.degree. C. Next, using
the metal base sample 22 comprising a thin copper film similar to
the one described above, the metal base sample 22 comprising a thin
copper film was arranged so as to be immersed into the
electroplating solution 19.
[0066] In this state, the electroplating solution 19 was not
stirred by the stirrer 20, and the carbon dioxide cylinder 12, the
high-pressure pump unit 13, the valve 14, and the pressure
adjustment unit 18 were operated to increase the pressure inside
the pressure-resistant electroplating chamber 11 to 5 MPa. The
electroplating solution 19 was stirred by the stirrer 20 at the
same time as the pressure inside the pressure-resistant
electroplating chamber 11 reached 5 MPa, and the electroplating
voltage was applied from the direct current power source 24 to
between the metal base sample 22 and the counter electrode 23.
[0067] In a state pressurized to 5 MPa, the critical condition is
not achieved at 40.degree. C., and the high-throw bath is therefore
in a liquid state. Even in this case, a large portion of the metal
base comprising a thin copper film dissolved before the direct
current voltage was applied, and the electroplated film was
obtained only partially.
Experimental Example 5
[0068] Because the results of Experimental Examples 1 through 4
showed that a metal base composed of copper rapidly dissolved in a
high-throw bath, which is an electroplating solution for copper
applications, the composition of the electroplating solution was
investigated further. Namely, sulfuric acid and chlorine ions were
added to the high-throw bath for stabilization purposes. Thus, an
experiment was conducted as Experimental Example 5 by using an
electroplating solution having a composition such as the one
described below in which sulfuric acid and chlorine ions were
excluded in order to reduce the dissolution rate of the metal based
composed of copper. The surfactant was the same as the one
described above.
Electroplating Solution Composition
TABLE-US-00003 [0069] Copper sulfate (CuSo.sub.4.cndot.5H.sub.2O)
70 g/L Sulfuric acid (H.sub.2SO.sub.4) 0 g/L Chlorine ions
(Cl.sup.-) 0 mg/L Nonionic surfactant 10 mL/L
[0070] Using the electroplating apparatus 10 shown in FIG. 1, 40 mL
of an electroplating solution having the abovementioned composition
was injected into the pressure-resistant electroplating chamber 11,
and the electroplating solution in the pressure-resistant
electroplating chamber 11 was heated to a temperature of 40.degree.
C. Next, using the same metal base sample 22 comprising a thin
copper film as the one used in Experimental Examples 1 through 4,
the metal base sample 22 was arranged so as to be immersed into the
electroplating solution 19. In this state, the electroplating
solution 19 was stirred by the stirrer 20 under atmospheric
pressure without the application of any particular pressure, and an
electroplating voltage was applied between the metal base sample 22
and the counter electrode 23 from the direct current power source
24.
[0071] In Experimental Example 5, some of the thin copper film had
eluted from the metal base sample 22, and a plated film was
obtained only partially. Thus, it was confirmed that elution of the
thin copper film occurred even when sulfuric acid and chlorine ions
were excluded from the conventional copper electroplating solution,
and that electroplating could not be conducted in the regular
manner.
Experimental Example 6
[0072] The results from Experimental Examples 1 through 5 showed
that reducing the rate at which copper dissolves in the
electroplating solution for copper applications was necessary in
order to electroplate copper on a metal base composed of copper.
Thus, the rate at which copper dissolves in a copper electroplating
solution was investigated as Experimental Example 6. First, a 2
cm.times.2 cm.times.5 mm electrolytic copper sample was provided,
40 mL of the copper electroplating solution comprising a high-throw
bath used in Experimental Examples 1 through 4 was injected into
the pressure-resistant electroplating chamber 11, this electrolytic
copper sample was immersed into the copper electroplating solution
19, and the dissolution rate under one atmosphere of pressure at
60.degree. C. was investigated. The amount of copper dissolved from
the electrolytic copper sample was evaluated by conducting a weight
measurement. FIG. 2 shows the relationship between the amount of
copper dissolved and the elapsed time.
[0073] The results in FIG. 2 show that because the copper
concentration in the high-throw bath did not reach saturation
concentration even after 31 hours elapsed, considerable time was
required for the copper concentration in the copper electroplating
solution to reach saturation when bulk copper was used.
[0074] Thus, solubility was investigated when copper powder was
further added to the copper electroplating solution used in
Experimental Examples 1 through 4. An electroplating solution in
which the copper powder was present in a dispersed state was
obtained when 300-mesh undersize was used as the copper powder, and
0.3 g was added under stirring to 500 mL of the high-throw bath. It
was thus found that adding copper in a powdered state is preferred
for bringing copper to a saturated state in a conventionally used
electroplating solution for copper applications.
Experimental Examples 7 Through 10
[0075] The solubility of a metal base sample similar to the one
used in Experimental Example 1 through 5 described above was
subsequently investigated when the sample was immersed in a variety
of copper electroplating solutions under atmospheric pressure at
25.degree. C. The four types described in Experimental Examples 7
through 10 below were used as the copper electroplating solutions.
The ratio in which copper powder was added in Experimental Examples
9 and 10 was such that 0.3 g of 300-mesh undersize was added under
stirring to 500 mL of the high-throw bath in the same manner as in
Experimental Example 6. The surfactant used in Experimental Example
10 was the same as the one added to the high-throw bath, and was
directly added into the pressure-resistant electroplating chamber
11.
Experimental Example 7
[0076] High-throw bath
Experimental Example 8
[0077] High-throw bath+electrolytic copper dissolved for 31 hours
(from Experimental Example 6)
Experimental Example 9
[0078] High-throw bath+copper powder
Experimental Example 10
[0079] 0.4 mL of a nonionic surfactant further added to the one in
Experimental Example 9
[0080] 40 mL of each of the four types of copper electroplating
solution described above was injected into the pressure-resistant
electroplating chamber 11, a metal base sample was immersed into
these four types of copper electroplating solution under
atmospheric pressure at 25.degree. C., and each surface state was
investigated after 3, 5, 10, 12, and 15 minutes had elapsed. The
results are summarized in Table 2 below. In the results shown in
Table 2, .largecircle. indicates that no dissolution was found to
have occurred at the copper surface, .DELTA. indicates that a
dissolution state was found to be present at the copper surface,
and x indicates that the copper was completely dissolved.
TABLE-US-00004 TABLE 2 Elapsed Time Composition 3 min 5 min 10 min
12 min 15 min Experimental High-throw X Example 7 bath Experimental
High-throw X Example 8 bath + electrolytic copper Experimental
High-throw .largecircle. .largecircle. .DELTA. .DELTA. X Example 9
bath + copper powder Experimental Experimental .largecircle.
.largecircle. .largecircle. .largecircle. .DELTA. Example 10
Example 9 + nonionic surfactant Key) .largecircle.: No change;
.DELTA.: Surface dissolution; X: Total dissolution
[0081] The results in Table 2 confirmed that elution of a metal
base composed of copper could not be suppressed when bulk
electrolytic copper had been dissolved in a high-throw bath in
advance, but elution of a metal base composed of copper could be
suppressed when copper metal powder was added and dispersed in a
powdered state. The results also confirmed that elution of a metal
base composed of copper could be suppressed further when an extra
amount of surfactant was added.
Experimental Examples 11 and 12
[0082] It is apparent from the results in Table 2 that elution of a
metal base composed of copper can be further suppressed when a
copper electroplating solution is used in a state in which copper
metal powder is added and dispersed in a powdered state, and an
extra amount of surfactant is added. Therefore, the variation in
the state in which copper is eluted from the metal base was
investigated for a case in which the electroplating solution from
Experimental Example 10 was used, and the voltage applied between
the metal base sample and the counter electrode was varied relative
to a metal base sample similar to the one used in Experimental
Examples 1 through 5.
[0083] Namely, no voltage was applied in Experimental Example 11, a
voltage of 1 V was applied in Experimental Example 12, a voltage of
5 V was applied in Experimental Example 12, the electroplating
solution was used in an amount of 40 mL, the temperature of the
electroplating solution was set to 40.degree. C., and the operation
was conducted under stirring in all cases. 1 V is a voltage that is
believed, theoretically, not to cause any copper plating or
dissolution of copper.
[0084] The results are summarized in Table 3 below. In Table 3,
.largecircle. indicates that a copper plating film having a normal
visual appearance was formed; .DELTA. indicates that a plating film
was formed, but the film had irregularities; and x indicates that
all copper had dissolved.
TABLE-US-00005 TABLE 3 Voltage Current Elapsed time Composition (V)
(mA) 3 min 5 min 10 min Experimental High-throw -- -- .DELTA. X
Example 11 bath + Copper Experimental powder + 1 30 .DELTA. X
Example 12 Nonionic Experimental surfactant 5 30 .largecircle.
.largecircle. .largecircle. Example 13 Key) .largecircle.: Was
electroplated; .DELTA.: Irregularities present; X: Total
dissolution
[0085] It can be seen from the results in Table 3 that applying the
voltage necessary for electroplating (5 V in this case) before
immersing the metal base into the electroplating solution is
preferred for the copper plating of a metal base composed of copper
by using an electroplating bath to which a large amount of
surfactant has been added and in which copper powder has been added
to a high-throw bath and brought into a suspended state.
Experimental Example 14
[0086] In Experimental Example 14, the conditions of Experimental
Example 13 that had yielded the best results shown in Table 3 were
adopted, the electroplating apparatus 10 shown in FIG. 1 was used,
and electroplating was carried out under supercritical conditions.
Copper powder was added to a high-throw bath and brought to a
suspended state in a manner similar to Experimental Example 13. 30
mL of this copper electroplating solution was injected into the
pressure-resistant electroplating chamber 11, and 0.3 mL of a
nonionic surfactant was further added thereto.
[0087] Next, a base obtained by forming a thin copper film having a
thickness of 65 nm on a 2 cm.times.2 cm TaN substrate by sputtering
was used as the metal base sample 22. This metal base sample 22 was
pretreated by acid pickling and then placed together with the
counter electrode 23 in the upper part of the electroplating
solution 19 in the pressure-resistant plating chamber 11 to as not
to be in contact with the electroplating solution 19. The amount of
the electroplating solution 19 used was set at 30 mL. Next, a metal
base sample 22 similar to the one used in Experimental Examples 1
through 5 was pretreated by acid pickling and then placed together
with the counter electrode 23 in the upper part of the
electroplating solution 19 in the pressure-resistant plating
chamber 11 to as not to be in contact with the electroplating
solution 19.
[0088] In this state, the electroplating solution in the
pressure-resistant electroplating chamber 11 was heated to a
temperature of 40.degree. C.; a voltage of 5 V was applied between
the metal base sample 22 and the counter electrode 23; and the
carbon dioxide cylinder 12, the high-pressure pump unit 13, the
valve 14, and the pressure adjustment unit 18 were operated to
increase the pressure inside the pressure-resistant electroplating
chamber 11 to 10 MPa without initially stirring the electroplating
solution 19 with the stirrer 20. The electroplating solution 19 was
stirred by the stirrer 20 at the same time as the pressure inside
the pressure-resistant electroplating chamber 11 reached 10
MPa.
[0089] By maintaining this state for three minutes and operating
the pressure adjustment unit 18 while applying a voltage of 5 V
between the metal base sample 22 and the counter electrode 23, the
carbon dioxide in the pressure-resistant electroplating chamber 11
was gradually released to reduce the pressure to atmospheric
pressure. A good copper plating film was formed on the surface of
the resulting metal base sample 22. Consequently, it became clear
that a Damascene method or a dual Damascene method based on the use
of a supercritical fluid could also be applied according to the
operating conditions employed in Experimental Example 14.
[0090] Although 300-mesh undersize was used as copper powder in the
experimental examples described above, a smaller particle diameter
is preferred in order to increase the dissolution rate because the
purpose of the copper powder is to keep the copper concentration in
the electroplating solution substantially at a saturation
concentration. In particular, because copper disperses well and
aggregates less readily in the electrolytic solution when particles
smaller than 1 .mu.m are used, electroplating can also easily be
performed on substrate structures whose precision is less than 1
.mu.m. Obtaining fine metal powder in which the metal has an
average particle diameter of less than 1 nm is difficult at the
present time, but an average particle diameter of about 1 nm is
realistic.
[0091] The above experimental examples described cases in which the
metal used in both the metal base and the electroplating metal was
copper, but the electroplating method of the present invention has
the same effect with any other metal base and electroplating metal
as long as they are of the same type. Not only copper but also
zinc, iron, nickel, cobalt, and the like are equally applicable as
the metal base and electroplating metal.
* * * * *