U.S. patent application number 13/893940 was filed with the patent office on 2013-11-21 for plating apparatus and plating solution management method.
This patent application is currently assigned to EBARA CORPORATION. The applicant listed for this patent is EBARA CORPORATION. Invention is credited to Yuji ARAKI, Masashi SHIMOYAMA.
Application Number | 20130306483 13/893940 |
Document ID | / |
Family ID | 48463682 |
Filed Date | 2013-11-21 |
United States Patent
Application |
20130306483 |
Kind Code |
A1 |
ARAKI; Yuji ; et
al. |
November 21, 2013 |
PLATING APPARATUS AND PLATING SOLUTION MANAGEMENT METHOD
Abstract
A plating apparatus plates a substrate with Sn alloy to form an
Sn alloy film on a surface of the substrate. The apparatus
includes: a plating bath for retaining a plating solution therein,
the substrate being immersed in the plating solution in a position
opposite to an insoluble anode; a plating solution dialysis line
for extracting the plating solution from the plating bath and
returning the plating solution to the plating bath; a dialysis cell
provided in the plating solution dialysis line and configured to
remove a free acid from the plating solution by dialysis using an
anion exchange membrane; a free acid concentration analyzer; and a
controller for controlling a flow rate of the plating solution
flowing through the plating solution dialysis line based on the
concentration of the free acid measured by the free acid
concentration analyzer.
Inventors: |
ARAKI; Yuji; (Tokyo, JP)
; SHIMOYAMA; Masashi; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EBARA CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
EBARA CORPORATION
Tokyo
JP
|
Family ID: |
48463682 |
Appl. No.: |
13/893940 |
Filed: |
May 14, 2013 |
Current U.S.
Class: |
205/81 ; 204/234;
205/99 |
Current CPC
Class: |
C25D 3/30 20130101; C25D
3/60 20130101; C25D 21/14 20130101; C25D 17/008 20130101; C25D
21/22 20130101; C25D 21/12 20130101; C25D 17/001 20130101 |
Class at
Publication: |
205/81 ; 204/234;
205/99 |
International
Class: |
C25D 21/22 20060101
C25D021/22; C25D 3/60 20060101 C25D003/60 |
Foreign Application Data
Date |
Code |
Application Number |
May 15, 2012 |
JP |
2012-111115 |
Claims
1. A plating apparatus for plating a substrate with Sn alloy to
form an Sn alloy film on a surface of the substrate, comprising: a
plating bath for retaining a plating solution therein and having an
insoluble anode disposed in the plating solution, the substrate
being immersed in the plating solution in a position opposite to
the insoluble anode; a plating solution dialysis line for
extracting the plating solution from the plating bath and returning
the plating solution to the plating bath; a dialysis cell provided
in the plating solution dialysis line and configured to remove a
free acid from the plating solution by dialysis using an anion
exchange membrane; a free acid concentration analyzer configured to
measure a concentration of the free acid in the plating solution;
and a controller for controlling a flow rate of the plating
solution flowing through the plating solution dialysis line, based
on the concentration of the free acid measured by the free acid
concentration analyzer.
2. The plating apparatus according to claim 1, further comprising:
a plating solution circulation line for extracting the plating
solution from the plating bath and returning the plating solution
to the plating bath during plating of the substrate, the plating
solution dialysis line being coupled to the plating solution
circulation line.
3. The plating apparatus according to claim 1, wherein the
controller is configured to control the flow rate of the plating
solution flowing through the plating solution dialysis line such
that the concentration of the free acid in the plating solution
lies in a range of 60 to 250 g/L.
4. The plating apparatus according to claim 1, wherein the plating
solution dialysis line is provided with a plating solution flow
control mechanism located between the plating bath and the dialysis
cell, and the controller is configured to control the plating
solution flow control mechanism such that a coefficient lies in a
range of 0.3 to 0.7, the coefficient being determined by dividing
an effective area (m.sup.2) of the anion exchange membrane by the
flow rate (L/h) of the plating solution.
5. The plating apparatus according to claim 4, further comprising:
a water supply line coupled to the dialysis cell and provided with
a water flow control mechanism, wherein the controller is
configured to control the water flow control mechanism such that a
flow rate of water, supplied through the water supply line into the
dialysis cell, is 30% to 100% of the flow rate of the plating
solution supplied through the plating solution dialysis line into
the dialysis cell.
6. A plating apparatus for plating a substrate with Sn alloy to
form an Sn alloy film on a surface of the substrate, comprising: a
plating bath for retaining a plating solution therein and having an
insoluble anode disposed in the plating solution, the substrate
being immersed in the plating solution in a position opposite to
the insoluble anode; a plating solution dialysis line for
extracting the plating solution from the plating bath and returning
the plating solution to the plating bath; a dialysis cell provided
in the plating solution dialysis line and configured to remove a
free acid from the plating solution by dialysis using an anion
exchange membrane; and a controller for controlling a flow rate of
the plating solution flowing through the plating solution dialysis
line, based on an integrated value of a quantity of electricity
applied to the plating solution in the plating bath.
7. The plating apparatus according to claim 6, further comprising:
a plating solution circulation line for extracting the plating
solution from the plating bath and returning the plating solution
to the plating bath during plating of the substrate, the plating
solution dialysis line being coupled to the plating solution
circulation line.
8. The plating apparatus according to claim 6, wherein the
controller is configured to control the flow rate of the plating
solution flowing through the plating solution dialysis line such
that a concentration of the free acid in the plating solution lies
in a range of 60 to 250 g/L.
9. The plating apparatus according to claim 6, wherein the plating
solution dialysis line is provided with a plating solution flow
control mechanism located between the plating bath and the dialysis
cell, and the controller is configured to control the plating
solution flow control mechanism such that a coefficient lies in a
range of 0.3 to 0.7, the coefficient being determined by dividing
an effective area (m.sup.2) of the anion exchange membrane by the
flow rate (L/h) of the plating solution.
10. The plating apparatus according to claim 9, further comprising:
a water supply line coupled to the dialysis cell and provided with
a water flow control mechanism, wherein the controller is
configured to control the water flow control mechanism such that a
flow rate of water, supplied through the water supply line into the
dialysis cell, is 30% to 100% of the flow rate of the plating
solution supplied through the plating solution dialysis line into
the dialysis cell.
11. A plating solution management method comprising: forming an Sn
alloy film on a surface of a substrate by applying a voltage
between an insoluble anode and the substrate disposed opposite to
each other in a plating solution retained in a plating bath;
measuring a concentration of a free acid in the plating solution by
a free acid concentration analyzer; extracting the plating solution
from the plating bath through a plating solution dialysis line and
then returning the plating solution to the plating bath; and
removing the free acid from the plating solution flowing through
the plating solution dialysis line by a dialysis cell having an
anion exchange membrane, while controlling a flow rate of the
plating solution flowing through the plating solution dialysis line
based on the concentration of the free acid measured by the free
acid concentration analyzer.
12. The plating solution management method according to claim 11,
wherein the flow rate of the plating solution flowing through the
plating solution dialysis line is controlled such that the
concentration of the free acid in the plating solution lies in a
range of 60 to 250 g/L.
13. The plating solution management method according to claim 11,
wherein the plating solution dialysis line is provided with a
plating solution flow control mechanism located between the plating
bath and the dialysis cell, and the plating solution flow control
mechanism is controlled such that a coefficient lies in a range of
0.3 to 0.7, the coefficient being determined by dividing an
effective area (m.sup.2) of the anion exchange membrane by the flow
rate (L/h) of the plating solution.
14. The plating solution management method according to claim 13,
wherein a water supply line provided with a water flow control
mechanism is coupled to the dialysis cell, and the water flow
control mechanism is controlled such that a flow rate of water,
supplied through the water supply line into the dialysis cell, is
30% to 100% of the flow rate of the plating solution supplied
through the plating solution dialysis line into the dialysis
cell.
15. A plating solution management method comprising: forming an Sn
alloy film on a surface of a substrate by applying a voltage
between an insoluble anode and the substrate disposed opposite to
each other in a plating solution retained in a plating bath;
extracting the plating solution from the plating bath through a
plating solution dialysis line and then returning the plating
solution to the plating bath; and removing a free acid from the
plating solution flowing through the plating solution dialysis line
by a dialysis cell having an anion exchange membrane, while
controlling a flow rate of the plating solution flowing through the
plating solution dialysis line based on an integrated value of a
quantity of electricity applied to the plating solution in the
plating bath.
16. The plating solution management method according to claim 15,
wherein the flow rate of the plating solution flowing through the
plating solution dialysis line is controlled such that a
concentration of the free acid in the plating solution lies in a
range of 60 to 250 g/L.
17. The plating solution management method according to claim 15,
wherein the plating solution dialysis line is provided with a
plating solution flow control mechanism located between the plating
bath and the dialysis cell, and the plating solution flow control
mechanism is controlled such that a coefficient lies in a range of
0.3 to 0.7, the coefficient being determined by dividing an
effective area (m.sup.2) of the anion exchange membrane by the flow
rate (L/h) of the plating solution.
18. The plating solution management method according to claim 17,
wherein a water supply line provided with a water flow control
mechanism is coupled to the dialysis cell, and the water flow
control mechanism is controlled such that a flow rate of water,
supplied through the water supply line into the dialysis cell, is
30% to 100% of the flow rate of the plating solution supplied
through the plating solution dialysis line into the dialysis cell.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This document claims priority to Japanese Patent Application
No. 2012-111115, filed May 15, 2012, the entire contents of which
are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a plating apparatus useful
for forming a plating film of an Sn alloy, such as lead-free Sn--Ag
having good soldering properties, on a substrate surface, and to a
management method of a plating solution for use in the plating
apparatus.
[0004] 2. Description of the Related Art
[0005] As is known in the art, a plating film of an Sn alloy (e.g.,
Sn--Ag), formed on a substrate surface by electroplating, can be
used for lead-free solder bumps. An insoluble anode is typically
used as an electrode in plating the substrate surface with the Sn
alloy. The Sn alloy plating film is formed on the substrate surface
by applying a voltage between the insoluble anode and the substrate
surface, which are disposed opposite to each other and immersed in
a plating solution. The insoluble anode is also typically used as
an electrode when plating the substrate surface with Sn--Cu or
Sn--Bi which is the Sn alloy.
[0006] A known method of successively carrying out plating of
substrates with the Sn alloy, such as Sn--Ag, uses a plating
solution containing: (i) a salt or complex formed from the reaction
of Sn ion (Sn.sup.2+) and an acid or a complexing agent (e.g., tin
methanesulfonate) capable of forming a water-soluble salt or
complex with Sn ion (Sn.sup.2+); and (ii) a salt or complex formed
from the reaction of Ag ion (Ag.sup.+) and an acid or a complexing
agent (e.g., silver methanesulfonate) capable of forming a
water-soluble salt or complex with Ag ion (Ag.sup.+). In this
method, the salt(s) or complex(es) is supplied to the plating
solution so as to replenish the plating solution with those metal
ions (Sn ions and Ag ions) which have been consumed with the
progress of plating (see Japanese Patent No. 4698904).
[0007] Such a metal ion replenishing method has a problem that,
because the metal ion and the free acid (e.g., methanesulfonic
acid) are separated from each other and the metal ions are consumed
by the plating process, a concentration of the free acid in the
plating solution gradually increases as the plating process
progresses. In order to solve such a problem, there has been
proposed a method in which the free acid is removed from a part of
the plating solution using an ion-exchange resin, electrodialysis,
or diffusion dialysis (see Japanese Laid-Open Patent Publication
No. H1-312099).
[0008] Another proposed method using the insoluble anode involves
subjecting a plating solution, which is being circulated, to
diffusion dialysis to remove the free acid from the plating
solution, thereby controlling a pH of the plating solution (see
Japanese Laid-Open Patent Publication No. S57-29600). Japanese
Laid-Open Patent Publication No. S59-28584 discloses optimization
of liquid supply to an electrolytic cell or a dialysis cell, and
Japanese Patent Laid-Open Publication No. H9-75681 discloses
recovery of an acid using the diffusion dialysis while causing
water to flow in a direction opposite to a flow direction of a raw
liquid.
[0009] The method described in the aforementioned Japanese
Laid-Open Patent Publication No. S57-29600 removes the free acid
from the plating solution by dialysis so as to control the pH of
the plating solution without measuring the concentration of the
free acid in the plating solution. It is therefore possible that
when plating of substrates is carried out successively while
replenishing the plating solution with metal ions, a too large
amount of the free acid may be removed, resulting in a too low
concentration of the free acid in the plating solution, or
conversely, a too small amount of the free acid may be removed,
resulting in a too high concentration of the free acid in the
plating solution. Use of the plating solution having a too low or
too high concentration of the free acid could result in a poor
appearance of a plating film and/or non-uniform film thickness.
Such plating solution must be discarded and as a result process
costs increase. The same holds true for the other prior art
techniques disclosed in the above documents.
SUMMARY OF THE INVENTION
[0010] The present invention has been made in view of the above
situation. It is therefore an object of the present invention to
provide a plating apparatus and a plating solution management
method which can use a plating solution for a longer period of time
by controlling a concentration of free acid in the plating solution
within a preferable range.
[0011] In order to achieve the object, the present invention
provides a plating apparatus for plating a substrate with Sn alloy
to form an Sn alloy film on a surface of the substrate, including:
a plating bath for retaining a plating solution therein and having
an insoluble anode disposed in the plating solution, the substrate
being immersed in the plating solution in a position opposite to
the insoluble anode; a plating solution dialysis line for
extracting the plating solution from the plating bath and returning
the plating solution to the plating bath; a dialysis cell provided
in the plating solution dialysis line and configured to remove a
free acid from the plating solution by dialysis using an anion
exchange membrane; a free acid concentration analyzer configured to
measure a concentration of the free acid in the plating solution;
and a controller for controlling a flow rate of the plating
solution flowing through the plating solution dialysis line, based
on the concentration of the free acid measured by the free acid
concentration analyzer.
[0012] Another aspect of the present invention provides a plating
apparatus for plating a substrate with Sn alloy to form an Sn alloy
film on a surface of the substrate, including: a plating bath for
retaining a plating solution therein and having an insoluble anode
disposed in the plating solution, the substrate being immersed in
the plating solution in a position opposite to the insoluble anode;
a plating solution dialysis line for extracting the plating
solution from the plating bath and returning the plating solution
to the plating bath; a dialysis cell provided in the plating
solution dialysis line and configured to remove a free acid from
the plating solution by dialysis using an anion exchange membrane;
and a controller for controlling a flow rate of the plating
solution flowing through the plating solution dialysis line, based
on an integrated value of a quantity of electricity applied to the
plating solution in the plating bath.
[0013] Still another aspect of the present invention provides a
plating solution management method including: forming an Sn alloy
film on a surface of a substrate by applying a voltage between an
insoluble anode and the substrate disposed opposite to each other
in a plating solution retained in a plating bath; measuring a
concentration of a free acid in the plating solution by a free acid
concentration analyzer; extracting the plating solution from the
plating bath through a plating solution dialysis line and then
returning the plating solution to the plating bath; and removing
the free acid from the plating solution flowing through the plating
solution dialysis line by a dialysis cell having an anion exchange
membrane, while controlling a flow rate of the plating solution
flowing through the plating solution dialysis line based on the
concentration of the free acid measured by the free acid
concentration analyzer.
[0014] Still another aspect of the present invention provides a
plating solution management method including: forming an Sn alloy
film on a surface of a substrate by applying a voltage between an
insoluble anode and the substrate disposed opposite to each other
in a plating solution retained in a plating bath; extracting the
plating solution from the plating bath through a plating solution
dialysis line and then returning the plating solution to the
plating bath; and removing a free acid from the plating solution
flowing through the plating solution dialysis line by a dialysis
cell having an anion exchange membrane, while controlling a flow
rate of the plating solution flowing through the plating solution
dialysis line based on an integrated value of a quantity of
electricity applied to the plating solution in the plating
bath.
[0015] According to the present invention, the flow rate of the
plating solution, supplied to the dialysis cell for removing the
free acid from the plating solution, is controlled based on the
analytical value of the concentration of the free acid in the
plating solution or based on the integrated value of the quantity
of electricity applied to the plating solution in the plating bath.
Therefore, plating can be performed while controlling the
concentration of the free acid in the plating solution in a
preferable range. This makes it possible to extend a life of the
plating solution and to form a plating film with good appearance
and good in-plane uniformity of thickness stably over a longer
period of time.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a schematic view of a plating apparatus according
to an embodiment of the present invention;
[0017] FIG. 2 is a schematic perspective view of a substrate
holder;
[0018] FIG. 3 is a plan view of the substrate holder shown in FIG.
2;
[0019] FIG. 4 is a right side view of the substrate holder shown in
FIG. 2;
[0020] FIG. 5 is an enlarged view of a portion A of FIG. 4;
[0021] FIG. 6 is a schematic view of the plating apparatus
according to another embodiment of the present invention;
[0022] FIG. 7 is a schematic view of the plating apparatus
according to yet another embodiment of the present invention;
[0023] FIG. 8 is a graph showing a relationship between an
integrated value (Ah/L) of a quantity of electricity applied to a
plating solution and a concentration of free acid in the plating
solution (g/L), as observed when plating is carried out while
performing dialysis of the plating solution, and also showing the
same relationship but observed when plating is carried out without
dialysis of the plating solution;
[0024] FIG. 9 is a graph showing a relationship between the
integrated value (Ah/L) of the quantity of electricity applied to
the plating solution and an in-plane uniformity (%) of heights of
bumps (thickness of plating film) on a substrate, as observed when
plating is carried out while performing dialysis of the plating
solution, and also showing the same relationship but observed when
plating is carried out without dialysis of the plating
solution;
[0025] FIGS. 10A through 10F are diagrams each illustrating a
change in a cross-sectional shape of a bump with the increase in
the integrated value of the quantity of electricity applied to the
plating solution, as observed when plating is carried out while
performing dialysis of the plating solution;
[0026] FIGS. 11A through 11D are diagrams each illustrating a
change in the cross-sectional shape of the bump with the increase
in the integrated value of the quantity of electricity applied to
the plating solution, as observed when plating is carried out
without dialysis of the plating solution;
[0027] FIG. 12 is a graph showing a relationship between a
coefficient a (=A/v) [A (m.sup.2) represents an effective area of
an anion exchange membrane, and v (L/h) represents a flow rate of
the plating solution supplied to a dialysis cell] and a removal
rate (%) of the free acid, as observed when plating is carried out
while performing dialysis of the plating solution in the dialysis
cell;
[0028] FIG. 13 is a graph showing a relationship between a ratio
V/v [V (L/h) represents a flow rate of water supplied to the
dialysis cell, and v (L/h) represents the flow rate of the plating
solution supplied to the dialysis cell] and the removal rate (%) of
the free acid, as observed when the flow rate of water supplied to
the dialysis cell is constant; and
[0029] FIG. 14 is a graph showing a relationship between the ratio
V/v [V (L/h) represents the flow rate of water supplied to the
dialysis cell, and v (L/h) represents the flow rate of the plating
solution supplied to the dialysis cell] and the removal rate (%) of
the free acid, as observed when the flow rate of the plating
solution supplied to the dialysis cell is constant.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] Preferred embodiments of the present invention will now be
described in detail with reference to the drawings. The following
description illustrates an example in which a plating film of
Sn--Ag alloy is formed on a substrate surface by using a plating
solution using tin methanesulfonate solution as a supply source of
Sn ion (Sn.sup.2+) and silver methanesulfonate solution as a supply
source of Ag ion (Ag.sup.+). The same reference numerals are used
in FIGS. 1 through 7 to refer to the same or like elements, and
duplicate descriptions thereof are omitted.
[0031] FIG. 1 is a schematic view of a plating apparatus according
to an embodiment of the present invention. As shown in FIG. 1, the
plating apparatus includes a plating bath 10 for retaining a
plating solution Q therein, an anode holder 14 for holding an
insoluble anode 12 (which may be made of titanium) and disposing it
at a predetermined position in the plating bath 10 while immersing
the insoluble anode 12 in the plating solution Q, and a substrate
holder 16 for removably holding a substrate W and disposing it at a
predetermined position, opposite to the insoluble anode 12, in the
plating bath 10 while immersing the substrate in the plating
solution Q.
[0032] When plating of the substrate W is performed, the insoluble
anode 12 is electrically connected to a positive electrode of a
plating power source 18, while a conductive layer (not shown), such
as a seed layer, formed on a surface of the substrate W is coupled
to a negative electrode of the plating power source 18. A plating
film of Sn--Ag alloy is formed by plating on the surface of the
conductive layer. This plating film can be used for production of
lead-free solder bumps.
[0033] The plating bath 10 includes an inner bath 20 for storing
the plating solution Q therein, and an overflow bath 22 surrounding
the inner bath 20. The plating solution Q overflows a top of the
inner bath 20 into the overflow bath 22. One end of a plating
solution circulation line 32 is coupled to a bottom of the overflow
bath 22. This plating solution circulation line 32 is provided with
a pump 24, a heat exchanger (heat regulator) 26, a filter 28, and a
flow meter 30. The other end of the plating solution circulation
line 32 is coupled to a bottom of the inner bath 20 via a plating
solution return pipe 34.
[0034] In the plating bath 10, a regulation plate 36 for regulating
an electric potential distribution in the plating bath 10 is
disposed between the insoluble anode 12 and the substrate holder 16
disposed in the plating bath 10. In this embodiment the regulation
plate 36 is made of polyvinyl chloride, which is a dielectric
material, and has a central opening 36a having such a size so as to
sufficiently regulate expansion of an electric field. The
regulation plate 36 has its lower end that reaches the bottom of
the plating bath 10.
[0035] Located between the substrate holder 16 and the regulation
plate 36 in the plating bath 10, there is provided a
vertically-extending agitating paddle (agitating tool) 38 which
reciprocates parallel to the substrate W, held by the substrate
holder 16, to agitate the plating solution Q existing between the
substrate holder 16 and the regulation plate 36. By agitating the
plating solution Q by means of the agitating paddle 38, a
sufficient amount of ions can be supplied uniformly to the surface
of the substrate W.
[0036] A plating solution supply pipe 44 for supplying the plating
solution Q to a dialysis cell 42, which has an anion exchange
membrane 40 therein, is coupled to the plating solution return pipe
34 of the plating solution circulation line 32. A plating solution
discharge pipe 46 extending from the dialysis cell 42 is coupled to
a top of the overflow bath 22. The plating solution supply pipe 44
and the plating solution discharge pipe 46 constitute a plating
solution dialysis line 48, which is coupled to the plating solution
circulation line 32 and takes a part of the plating solution Q out
of the plating solution circulation line 32 to allow the plating
solution to circulate therethrough. The plating solution supply
pipe 44 is provided with a flow meter 50 and a plating solution
flow control valve 52 as a plating solution flow control mechanism.
A water supply line 54 for supplying water (pure water) into the
dialysis cell 42 is coupled to the dialysis cell 42. The water
supply line 54 is provided with a flow meter 56 and a water flow
control valve 58 as a water flow control mechanism. A drainage line
60 is coupled to the dialysis cell 42.
[0037] The plating solution Q, flowing through the plating solution
dialysis line 48, is supplied into the dialysis cell 42, where a
free acid (e.g., methanesulfonic acid) is removed by dialysis using
the anion exchange membrane 40. The plating solution Q after
dialysis is returned to the overflow bath 22. The free acid that
has been removed from the plating solution Q by the dialysis
diffuses in the water (the pure water) supplied into the dialysis
cell 42 through the water supply line 54, and is discharged to the
exterior of the dialysis cell 42 through the drainage line 60.
[0038] The anion exchange membrane 40 used in this embodiment is
DSV (an effective area is 0.0172 m.sup.2) manufactured by AGC
Engineering Co., Ltd. An arbitrary number (e.g., 19) of such
membranes may be incorporated in the dialysis cell 42 depending on
the amount of the plating solution to be dialyzed (the amount of
the free acid to be removed).
[0039] A plating solution extraction pipe 66 of a plating solution
analysis line 64, which is provided with a free acid concentration
analyzer 62, is coupled to the plating solution return pipe 34 of
the plating solution circulation line 32. An extract discharge pipe
68 extending from the free acid concentration analyzer 62 is
coupled to the top of the overflow bath 22. A part of the plating
solution Q, circulating through the plating solution circulation
line 32, is extracted through the plating solution extraction pipe
66 and fed to the free acid concentration analyzer 62, where the
concentration of the free acid in the plating solution Q is
measured. The plating solution after measurement is returned to the
overflow bath 22.
[0040] A replenisher solution supply line 69 for supplying a
replenisher solution is coupled to the top of the overflow bath 22.
A plating solution and metal ion (i.e., tin methanesulfonate
solution as a supply source of Sn ion Sn.sup.2+ and silver
methanesulfonate solution as a supply source of Ag ion Ag.sup.+)
are supplied through the replenisher solution supply line 69 into
the plating solution Q circulating through the plating solution
circulation line 32.
[0041] Results of analysis (analytical value of the concentration
of the free acid) by the free acid concentration analyzer 62 and
results of measurement by the flow meters 30, 50, 56 are inputted
into a controller 70. Based on outputs from the controller 70, an
opening degree of the plating solution flow control valve (the
plating solution flow control mechanism) 52 and an opening degree
of the water flow control valve (the water flow control mechanism)
58 are adjusted so as to regulate the flow rate of the plating
solution Q flowing through the plating solution dialysis line 48
into the dialysis cell 42 and the flow rate of the water flowing
through the water supply line 54 into the dialysis cell 42.
[0042] As shown in FIGS. 2 through 5, the substrate holder 16
includes a first holding member (base holding member) 154 having a
rectangular plate shape and made of e.g., vinyl chloride, and a
second holding member (movable holding member) 158 rotatably
coupled to the first holding member 154 through a hinge 156 which
allows the second holding member 158 to open and close with respect
to the first holding member 154. Although in this embodiment the
second holding member 158 is configured to be openable and closable
through the hinge 156, it is also possible to dispose the second
holding member 158 opposite to the first holding member 154 and to
move the second holding member 158 away from and toward the first
holding member 154 to thereby open and close the second holding
member 158.
[0043] The second holding member 158 includes a base portion 160
and a ring-shaped seal holder 162. The seal holder 162 is made of
vinyl chloride so as to enable a retaining ring 164, which will be
described later, to slide well. A substrate-side sealing member 166
is fixed to an upper surface of the seal holder 162. This
substrate-side sealing member 166 is placed in pressure contact
with a periphery of the surface of the substrate W to seal a gap
between the substrate W and the second holding member 158 when the
substrate W is held by the substrate holder 16. A holder-side
sealing member 168 is fixed to a surface, facing the first holding
member 154, of the seal holder 162. This holder-side sealing member
168 is placed in pressure contact with the first holding member 154
to seal a gap between the first holding member 154 and the second
holding member 158. The holder-side sealing member 168 is located
outwardly of the substrate-side sealing member 166.
[0044] As shown in FIG. 5, the substrate-side sealing member 166 is
sandwiched between the seal holder 162 and a first mounting ring
170a which is secured to the seal holder 162 by fastening tools
169a, such as bolts. The holder-side sealing member 168 is
sandwiched between the seal holder 162 and a second mounting ring
170b which is secured to the seal holder 162 by fastening tools
169b, such as bolts.
[0045] The seal holder 162 of the second holding member 158 has a
stepped portion at a periphery thereof, and the retaining ring 164
is rotatably mounted to the stepped portion via a spacer 165. The
retaining ring 164 is inescapably held by an outwardly projecting
retaining plates 172 (see FIG. 3) mounted to a side surface of the
seal holder 162. This retaining ring 164 is made of a material
(e.g., titanium) having high rigidity and excellent acid and alkali
corrosion resistance and the spacer 165 is made of a material
having a low friction coefficient, for example PTFE, so that the
retaining ring 164 can rotate smoothly.
[0046] Inverted L-shaped dampers 174, each having an inwardly
projecting portion and located outside of the retaining ring 164,
are provided on the first holding member 154 at equal intervals
along a circumferential direction of the retaining ring 164. The
retaining ring 164 has outwardly projecting portions 164b along the
circumferential direction of the retaining ring 164 at positions
corresponding to positions of the dampers 174. A lower surface of
the inwardly projecting portion of each damper 174 and an upper
surface of each projecting portion 164b of the retaining ring 164
are tapered in opposite directions along the rotational direction
of the retaining ring 164. A plurality (e.g., three) of upwardly
protruding dots 164a are provided on the retaining ring 164 in
predetermined positions along the circumferential direction of the
retaining ring 164. The retaining ring 164 can be rotated by
pushing and moving each dot 64a from a lateral direction by means
of a rotating pin (not shown).
[0047] When the second holding member 158 is open, the substrate W
is inserted into the central portion of the first holding member
154, and the second holding member 158 is then closed through the
hinge 156. Subsequently the retaining ring 164 is rotated clockwise
so that each projecting portion 164b of the retaining ring 164
slides into the inwardly projecting portion of each damper 174. As
a result, the first holding member 154 and the second holding
member 158 are fastened to each other and locked by engagement
between the tapered surfaces of the retaining ring 164 and the
tapered surfaces of the dampers 174. The lock can be released by
rotating the retaining ring 164 counterclockwise and to disengage
the projecting portions 164b of the retaining ring 164 from the
inverted L-shaped dampers 174. When the second holding member 158
is locked in the above-described manner, the lower end of the inner
downwardly-protruding portion of the substrate-side sealing member
166 is placed in pressure contact with the periphery of the surface
of the substrate W held by the substrate holder 16, while the lower
end of the outer downwardly-protruding portion of the holder-side
sealing member 168 is placed in pressure contact with the surface
of the first holding member 154, whereby the sealing members 166
and 168 are uniformly pressed to seal the gap between the substrate
W and the second holding member 158 and the gap between the first
holding member 154 and the second holding member 158,
respectively.
[0048] A protruding portion 182 is formed on the central portion of
the first holding member 154 so as to protrude in a ring shape
corresponding to a size of the substrate W. The protruding portion
182 has a support surface 180 which is placed in contact with the
periphery of the substrate W to support the substrate W. The
protruding portion 182 has recesses 184 arranged at predetermined
positions along a circumferential direction of the protruding
portion 182.
[0049] As shown in FIG. 3, a plurality of electrical conductors
(electrical contacts) 186 (e.g., 12 conductors as illustrated),
coupled respectively to wires extending from external contacts
provided in a hand 190, are disposed in the recesses 184 of the
protruding portion 182. When the substrate W is placed on the
support surface 180 of the first holding member 154, ends of the
electrical conductors 186 are exposed in a springy state on the
surface of the first holding member 154 at positions beside the
substrate W to contact lower portions of the electrical contacts
188 shown in FIG. 5.
[0050] The electrical contacts 188, to be electrically connected to
the electrical conductors 186, are secured to the seal holder 162
of the second holding member 158 by fastening tools 189, such as
bolts. The electrical contacts 188 each have a leaf spring-like
contact portion lying outside the substrate-side sealing member 166
and projecting inwardly. This contact portion is springy and bends
easily. When the substrate W is held by the first holding member
154 and the second holding member 158, the contact portions of the
electrical contacts 188 make elastic contact with the peripheral
surface of the substrate W supported on the support surface 180 of
the first holding member 154.
[0051] The second holding member 158 is opened and closed by a
not-shown pneumatic cylinder and by the weight of the second
holding member 158 itself. More specifically, the first holding
member 154 has a through-hole 154a, and a pneumatic cylinder is
provided so as to face the through-hole 154a. The second holding
member 158 is opened by extending a piston rod of the pneumatic
cylinder to lift up a pressing rod through the through-hole 154a to
push up the seal holder 162 of the second holding member 158. The
second holding member 158 is closed by its own weight when the
piston rod is retracted.
[0052] A pair of approximately T-shaped hands 190 is connected to
the ends of the first holding member 154 of the substrate holder
16. These hands 190 serve as a support when the substrate holder 16
is transported and when the substrate holder 16 is held in a
suspended state.
[0053] In this embodiment the opening degree of the plating
solution flow control valve 52 and the opening degree of the water
flow control valve 58 are adjusted based on the concentration of
the free acid measured by the free acid concentration analyzer 62
so as to control the flow rate of the plating solution Q flowing
through the plating solution dialysis line 48 into the dialysis
cell 42 and the flow rate of water flowing through the water supply
line 54 into the dialysis cell 42, thereby controlling the amount
of the free acid removed. The concentration of the free acid in the
plating solution Q for use in the plating process is controlled in
the preferable range of, e.g., 60 to 250 g/L.
[0054] In operation, while the pump 24 is driven and the plating
solution Q in the plating bath 10 circulates through the plating
solution circulation line 32, the substrate W held by the substrate
holder 16 is disposed at a predetermined position in the plating
bath 10, and the insoluble anode 12 is connected to the positive
electrode of the plating power source 18 and a surface conductive
layer, such as a seed layer, of the substrate W is connected to the
negative electrode of the plating power source 18 to thereby
initiate plating of the substrate W. At this time, the plating
solution flow control valve 52 and the water flow control valve 58
are in a closed state.
[0055] As the plating solution Q in the plating bath 10 circulates
through the plating solution circulation line 32 in this manner, a
part of the plating solution Q is extracted through the plating
solution extraction pipe 66 and fed to the free acid concentration
analyzer 62, where the concentration of the free acid in the
plating solution Q is analyzed several times a day, for example.
The results of analysis (the analytical values of the concentration
of the free acid) are inputted into the controller 70.
[0056] Based on the results of analysis (analytical values of the
concentration of the free acid) by the free acid concentration
analyzer 62, the controller 70 sends signals respectively to the
plating solution flow control valve 52 and to the water flow
control valve 58 in order to adjust the opening degree of the
plating solution flow control valve 52 and the opening degree of
the water flow control valve 58 so that the concentration of the
free acid in the plating solution Q for use in the plating process
lies in the range of, e.g., 60 to 250 g/L. In this manner, the
concentration of the free acid in the plating solution Q is
controlled, e.g., in the range of 60 to 250 g/L, by controlling the
flow rate of the plating solution which is fed through the plating
solution dialysis line 48 to the dialysis cell 42 that removes the
free acid (methanesulfonic acid) from the plating solution, and
also controlling the flow rate of water for use in the removal of
the free acid (methanesulfonic acid). The opening degree of the
plating solution flow control valve 52 and the opening degree of
the water flow control valve 58 are adjusted every time the
concentration of the free acid in the plating solution Q is
analyzed by the free acid concentration analyzer 62.
[0057] By thus controlling the flow rate of the plating solution
flowing through the plating solution dialysis line 48, which has
the dialysis cell 42 for removing the free acid from the plating
solution, based on the concentration of the free acid measured by
the free acid concentration analyzer 62, plating can be performed
with the controlled concentration of the free acid in the plating
solution, e.g., in the preferable range of 60 to 250 g/L.
[0058] According to this embodiment, the free acid can be removed
from the plating solution under the condition of the controlled
flow rate of the plating solution flowing through the plating
solution dialysis line 48, while the plating solution is
circulating through the plating solution circulation line 32.
[0059] It is preferable to adjust the opening degree of the plating
solution flow control valve 52 such that a coefficient a (=A/v) [A
(m.sup.2) represents the effective area of the anion exchange
membrane 40 of the dialysis cell 42, and v (L/h) represents the
flow rate of the plating solution supplied through the plating
solution dialysis line 48 to the dialysis cell 42] lies in the
range of 0.3 to 0.7 (a=0.3 to 0.7). Further, it is preferable to
adjust the opening degree of the water flow control valve 58 such
that a ratio V/v [V (L/h) represents the flow rate of water
supplied through the water supply line 54 into the dialysis cell
42, and v (L/h) represents the flow rate of the plating solution
supplied through the plating solution dialysis line 48 to the
dialysis cell 42] lies in the range of 0.3 to 1 (V/v=0.3 to 1,
i.e., V is 30% to 100% of v).
[0060] In this embodiment the controller 70 calculates an
integrated value of a quantity of electricity applied to the
plating solution Q in the plating bath 10. The "quantity of
electricity applied to the plating solution Q" herein refers to the
product of an electric current, which flows from the positive
electrode to the negative electrode of the plating power source 18
via the insoluble anode 12, the plating solution Q, and the surface
conductive layer of the substrate W, and a period of time of the
application of the electric current. The "integrated value" herein
refers to the total quantity of electricity applied to the plating
solution Q during a period of time from supply of a fresh plating
solution Q into the plating bath 10 to withdrawal of that plating
solution Q from the plating bath 10. The free acid in the plating
solution Q is produced, as the metal ions in the plating solution Q
are consumed by plating. Thus, the integrated value of the quantity
of electricity applied to the plating solution Q can give an
indication of an increase in the concentration of the free acid.
Therefore, based on the integrated value of the quantity of
electricity applied to the plating solution Q, the controller 70
sends signals respectively to the plating solution flow control
valve 52 and to the water flow control valve 58 in order to adjust
the opening degree of the plating solution flow control valve 52
and the opening degree of the water flow control valve 58 such that
the concentration of the free acid in the plating solution Q lies
in the range of, e.g., 60 to 250 g/L. For example, plating may be
carried out in the following manner. Plating of substrates is
performed successively using a predetermined amount of the plating
solution Q while replenishing it with metal ions. When the
integrated value of the quantity of electricity applied to the
plating solution has reached a predetermined value, the plating
solution flow control valve 52 and the water flow control valve 58
are each opened to a certain degree to carry out dialysis of the
plating solution, so that the free acid is removed.
[0061] Also by thus controlling the flow rate of the plating
solution Q flowing through the plating solution dialysis line 48,
which has the dialysis cell 42 for removing the free acid from the
plating solution, based on the integrated value of the quantity of
electricity applied to the plating solution Q in the plating bath
10, plating can be performed while controlling the concentration of
the free acid in the plating solution in the preferable range of,
e.g., 60 to 250 g/L.
[0062] In this embodiment, based on at least one of the
concentration of the free acid, measured by the free acid
concentration analyzer 62, and the integrated value of the quantity
of electricity applied to the plating solution Q, the controller 70
sends signals respectively to the plating solution flow control
valve 52 and to the water flow control valve 58 in order to adjust
the opening degree of the plating solution flow control valve 52
and the opening degree of the water flow control valve 58 so that
the concentration of the free acid in the plating solution Q lies
in the range of, e.g., 60 to 250 g/L. The plating solution flow
control valve 52 and the water flow control valve 58 may be
controlled based on only one of the concentration of the free acid,
measured by the free acid concentration analyzer 62, and the
integrated value of the quantity of electricity applied to the
plating solution Q.
[0063] Instead of the plating solution flow control valve 52 and
the water flow control valve 58, it is possible to use on-off
valves which are each on-off controllable by means of a timer and
which respectively constitute the plating solution flow control
mechanism and the water flow control mechanism. Thus, the flow rate
of the plating solution Q flowing through the plating solution
dialysis line 48 into the dialysis cell 42 and the flow rate of
water flowing through the water supply line 54 into the dialysis
cell 42 may be controlled by the use of the plating solution flow
control mechanism and the water flow control mechanism, including
the on-off valves.
[0064] FIG. 6 is a schematic view of a plating apparatus according
to another embodiment of the present invention. This embodiment
differs from the embodiment shown in FIG. 1 in that the plating
solution dialysis line 48 is provided with an on-off valve 80 and a
first tube pump 82, both constituting the plating solution flow
control mechanism, instead of the plating solution flow control
valve 52, and that the water supply line 54 is provided with an
on-off valve 84 and a second tube pump 86, both constituting the
water flow control mechanism, instead of the water flow control
valve 58. The controller 70 controls the plating solution flow
control mechanism, i.e., the on-off valve 80 and the first tube
pump 82, and the water flow control mechanism, i.e., the on-off
valve 84 and the second tube pump 86.
[0065] According to this embodiment, the controller 70 can regulate
the flow rate of the plating solution flowing through the plating
solution dialysis line 48 by controlling the first tube pump 82
with the on-off valve 80 opened. The controller 70 can further
regulate the flow rate of the water flowing through the water
supply line 54 by controlling the second tube pump 86 with the
on-off valve 84 opened.
[0066] FIG. 7 is a schematic view of the plating apparatus
according to yet another embodiment of the present invention. This
embodiment differs from the embodiment shown in FIG. 6 in that,
instead of coupling the plating solution supply pipe 44 of the
plating solution dialysis line 48 to the plating solution return
pipe 34 of the plating solution circulation line 32, the plating
solution supply pipe 44 extends from the bottom of the overflow
bath 22. According to this embodiment, a part of the plating
solution Q that has flown into and accumulated in the overflow bath
22 can be supplied through the plating solution dialysis line 48 to
the dialysis cell 42 and, after the free acid is removed by the
dialysis cell 42, can be returned to the overflow bath 22.
[0067] In order to verify that the free acid (methanesulfonic acid)
in the plating solution can be removed by the apparatus of the
present invention, an experiment was conducted using a dialysis
cell incorporating nine anion exchange membranes, each being a
commercially-available DSV (an effective area is 0.0172 m.sup.2)
manufactured by AGC Engineering Co., Ltd. The plating solution was
supplied to the dialysis cell at a flow rate of 2.9 ml/min, while
pure water was supplied to the dialysis cell at a flow rate of 2.9
ml/min. Thus, the coefficient a (=A/v) [A (m.sup.2) is the
effective area of the anion exchange membrane of the dialysis cell,
and v (L/h) is the flow rate of the plating solution supplied to
the dialysis cell] is 0.9 (a=A/v=0.9). Further, the ratio V/v [V
(L/h) is the flow rate of water supplied to the dialysis cell, and
v (L/h) is the flow rate of the plating solution supplied to the
dialysis cell] is 1 (V/v=1, i.e., V is 100% of v).
[0068] As a result of the experiment, the concentration of the free
acid in the plating solution, which was 242 g/L before dialysis,
decreased to 45 g/L after dialysis. This result showed the fact
that the free acid can be removed from the plating solution.
However, the plating solution after dialysis was so cloudy that it
was not suitable for use in plating. As is appreciated from this
fact, the plating solution containing the free acid with a
concentration of less than 60 g/L is not suitable for use in
plating, and the concentration of the free acid in the plating
solution should preferably be not less than 60 g/L, more preferably
not less than 80 g/L.
[0069] A further experiment for examining the removal of the free
acid from the plating solution was conducted using a dialysis cell
having a reduced total area of ion exchange membranes, more
specifically using a dialysis cell incorporating five anion
exchange membranes, each being a commercially-available DSV (an
effective area is 0.0172 m.sup.2) manufactured by AGC Engineering
Co., Ltd. The plating solution was supplied to the dialysis cell at
a flow rate of 2.9 ml/min, while pure water was supplied to the
dialysis cell at a flow rate of 1.7 ml/min. Thus, the coefficient a
(=A/v) [A (m.sup.2) is the effective area of the anion exchange
membrane of the dialysis cell, and v (L/h) is the flow rate of the
plating solution supplied to the dialysis cell] is 0.45
(a=A/v=0.45). Further, the ratio V/v [V (L/h) is the flow rate of
the water supplied to the dialysis cell, and v (L/h) is the flow
rate of the plating solution supplied to the dialysis cell] is 0.59
(V/v=0.59, i.e., V is 59% of v).
[0070] As a result of the experiment, the concentration of the free
acid in the plating solution, which was 256 g/L before dialysis,
decreased to 115 g/L after dialysis.
[0071] A further experiment was conducted in the same manner as in
the preceding experiment except that the flow rate of the pure
water supplied to the above-described dialysis cell incorporating
five anion exchange membranes was changed from 1.7 ml/min to 1.23
ml/min. The flow rate of the plating solution supplied to the
dialysis cell was maintained at 2.9 ml/min. Thus, the coefficient a
(=A/v) [A (m.sup.2) is the effective area of the anion exchange
membrane of the dialysis cell, and v (L/h) is the flow rate of the
plating solution supplied to the dialysis cell] is 0.45
(a=A/v=0.45). Further, the ratio V/v [V (L/h) is the flow rate of
water supplied to the dialysis cell, and v (L/h) is the flow rate
of the plating solution supplied to the dialysis cell] is 0.42
(V/v=0.42, i.e., V is 42% of v).
[0072] As a result of the experiment, the concentration of the free
acid in the plating solution, which was 256 g/L before dialysis,
decreased to 150 g/L after dialysis. It can be seen from this
result that the free acid removal effect is lowered by reducing the
flow rate of the water supplied to the dialysis cell.
[0073] An experiment was conducted to examine the effect of the
concentration of the free acid in the plating solution on formation
of a plating film on a substrate surface. A plating film, which was
for forming bumps, was formed on a substrate surface in a single
plating bath (volume 28 L). Plating of the substrate was carried
out while applying electricity to the plating solution at 8.7 Ah/L
per day and performing the dialysis (for removing the free acid) of
the plating solution in the dialysis cell. For comparison, plating
of a substrate was carried out without performing the dialysis of
the plating solution. Measurements were made to determine a change
in the concentration of the free acid in the plating solution and a
change in the uniformity (in-plane uniformity) of the heights of
bumps (thickness of the plating film) over the entire substrate
surface with the change (the increase) in the integrated value of
the quantity of electricity applied to the plating solution.
[0074] The dialysis was performed by using a dialysis cell
incorporating 19 anion exchange membranes, each being a
commercially-available DSV (the effective area is 0.0172 m.sup.2)
manufactured by AGC Engineering Co., Ltd. The flow rate of the
plating solution and the flow rate of the water were controlled by
tube pumps so that the plating solution was supplied to the
dialysis cell at a flow rate of 9 to 10 ml/min and the pure water
was supplied to the dialysis cell at a flow rate of 6 to 7 ml/min.
Thus, the coefficient a (=A/v) [A (m.sup.2) is the effective area
of the anion exchange membrane of the dialysis cell, and v (L/h) is
the flow rate of the plating solution supplied to the dialysis
cell] is 0.5 to 0.6 (a=A/v=0.5 to 0.6). Further, the ratio V/v [V
(L/h) is the flow rate of the water supplied to the dialysis cell,
and v (L/h) is the flow rate of the plating solution supplied to
the dialysis cell] is 0.6 to 0.8 (V/v=0.6 to 0.8, i.e., V is 60% to
80% of v).
[0075] The dialysis was started when the integrated value of the
quantity of electricity applied to the plating solution had
exceeded 20 Ah/L. The application of electricity to the plating
solution was stopped when the integrated value of the quantity of
electricity had reached 59 Ah/L because the concentration of the
free acid in the plating solution almost reached 200 g/L. Then the
dialysis of the plating solution was performed for 24 hours without
the application of electricity to thereby lower the concentration
of the free acid in the plating solution.
[0076] FIG. 8 shows a relationship between the integrated value
(Ah/L) of the quantity of electricity applied to the plating
solution and the concentration of the free acid in the plating
solution (g/L), determined by the above experiment in which plating
was carried out while performing the dialysis of the plating
solution, and also shows the same relationship but determined by
the comparative experiment in which plating was carried out without
dialysis of the plating solution. FIG. 9 shows a relationship
between the integrated value (Ah/L) of the quantity of electricity
applied to the plating solution and the in-plane uniformity (%) of
the heights of bumps (i.e., the thickness of the plating film),
determined by the above experiment in which plating was carried out
while performing the dialysis of the plating solution, and also
shows the same relationship but determined by the comparative
experiment in which plating was carried out without dialysis of the
plating solution.
[0077] As can be seen in FIGS. 8 and 9, the concentration of the
free acid in the plating solution can be controlled at a level of
not more than 200 g/L and the in-plane uniformity of the heights of
bumps can be controlled at a level of not more than 10% by
performing the dialysis of the plating solution (i.e., the removing
process of the free acid). In contrast, without the dialysis of the
plating solution, the concentration of the free acid in the plating
solution exceeds 250 g/L and the in-plane uniformity of the heights
of the bumps exceeds 10% with the increase in the integrated value
of the quantity of electricity applied to the plating solution.
[0078] The in-plane uniformity of the heights of bumps is generally
required to be not more than 10%. As can be seen from the data in
FIGS. 8 and 9, the in-plane uniformity can be controlled at a level
of not more than 10% by controlling the concentration of the free
acid in the plating solution at a level of not more than 250 g/L,
preferably not more than 200 g/L, more preferably not more than 170
g/L. Therefore, in each of the above-described plating apparatuses,
the concentration of the free acid in the plating solution may be
controlled at a level of not more than 250 g/L, preferably not more
than 200 g/L, more preferably not more than 170 g/L. On the other
hand, as described above, the concentration of the free acid in the
plating solution is preferably controlled at a level of not less
than 60 g/L, more preferably not less than 80 g/L in order to
prevent the plating solution from becoming too cloudy for use in
plating.
[0079] FIGS. 10A through 10F each illustrates a change in a
schematic cross-sectional shape of the bump (the plating film) with
the increase in the integrated value of the quantity of electricity
applied to the plating solution, as observed in the above
experiment in which plating was carried out while performing the
dialysis of the plating solution. More specifically, FIGS. 10A
through 10F illustrate the cross-sectional shapes of the bumps (the
plating films) formed on substrates when the integrated value of
the quantity of electricity applied to the plating solution was 0
Ah/L (FIG. 10A), 20 Ah/L (FIG. 10B), 40 Ah/L (FIG. 10C), 59 Ah/L
(FIG. 10D), 80 Ah/L (FIG. 10E), and 130 Ah/L (FIG. 10F),
respectively.
[0080] As can be seen from FIGS. 10A through 10F, the bump (plating
film) has a normal shape or appearance when the integrated value of
the quantity of electricity applied to the plating solution is not
more than 80 Ah/L. A poor appearance of the bump (plating film)
shown in FIG. 10F is considered to be due to the fact that
coarsening of crystal grains occurs when the integrated value of
the quantity of electricity applied to the plating solution reaches
130 Ah/L, resulting in roughened surface of the bump.
[0081] FIGS. 11A through 11D each illustrates the change in the
schematic cross-sectional shape of the bump (plating film) with the
increase in the integrated value of the quantity of electricity
applied to the plating solution, as observed in the above
experiment (comparative test) in which plating was carried out
without the dialysis of the plating solution. More specifically,
FIGS. 11A through 11D illustrate the cross-sectional shapes of the
bumps (plating films) formed on substrates when the integrated
value of the quantity of electricity applied to the plating
solution was 0 Ah/L (FIG. 11 A), 19 Ah/L (FIG. 11B), 59 Ah/L (FIG.
11C), and 100 Ah/L (FIG. 11D), respectively.
[0082] As can be seen from FIGS. 11A through 11D, a roughened
surface of the bump (plating film) was observed when the integrated
value of the quantity of electricity applied to the plating
solution reached 59 Ah/L. A more roughened surface of the bump
(plating film) was observed when the integrated value reached 100
Ah/L. Such a roughened surface of the bump (plating film) is
considered to be due to a decrease in Ag in the bump (plating film)
with the increase in the concentration of the free acid in the
plating solution.
[0083] FIG. 12 is a graph showing a relationship between the
coefficient a (=A/v) [A (m.sup.2) is the effective area of the
anion exchange membrane, and v (L/h) is the flow rate of the
plating solution supplied to the dialysis cell] and a removal rate
(%) of the free acid, determined by the above experiment in which
plating was carried out while performing the dialysis of the
plating solution (i.e., the removing process of the free acid) in
the dialysis cell incorporating the 19 anion exchange membranes.
The flow rate of the water supplied to the dialysis cell was 6.3
ml/min.
[0084] As can be seen from FIG. 12, the removal rate of the free
acid can be controlled in an appropriate range of about 30% to 65%
by controlling the coefficient a (=A/v) in the range of 0.3 to 0.7.
The same holds true for the above-described plating apparatuses.
That is, the removal rate of the free acid can be controlled in the
appropriate range of about 30% to 65% by regulating the opening
degree of the plating solution flow control valve 52 so that the
coefficient a (=A/v) [A (m.sup.2) is the effective area of the
anion exchange membrane 40 of the dialysis cell 42, and v (L/h) is
the flow rate of the plating solution supplied through the plating
solution dialysis line 48 to the dialysis cell 42] lies in the
range of 0.3 to 0.7 (i.e., a=0.3 to 0.7).
[0085] FIGS. 13 and 14 are graphs each showing a relationship
between the ratio V/v [V (L/h) is the flow rate of the water
supplied to the dialysis cell, and v (L/h) represents the flow rate
of the plating solution supplied to the dialysis cell] and the
removal rate of the free acid, determined by the above experiment
in which plating was carried out while performing the dialysis of
the plating solution in the dialysis cell incorporating the 19
anion exchange membranes. FIG. 13 shows the relationship observed
when the flow rate of the plating solution supplied to the dialysis
cell was changed while keeping the flow rate of the water supplied
to the dialysis cell constant at 6.3 ml/min. FIG. 14 shows the
relationship observed when the flow rate of the water supplied to
the dialysis cell was changed while keeping the flow rate of the
plating solution supplied to the dialysis cell constant at 10.3
ml/min.
[0086] As can be seen from FIGS. 13 and 14, the removal rate of the
free acid can be controlled in the appropriate range of about 30%
to 65% by controlling the ratio V/v in the range of 0.3 to 1. The
same holds true for the above-described plating apparatuses. That
is, the removal rate of the free acid can be controlled in the
appropriate range of about 30% to 65% by regulating the opening
degree of the water flow control valve 58 so that the ratio V/v [V
(L/h) is the flow rate of the water supplied through the water
supply line 54 into the dialysis cell 42, and v (L/h) is the flow
rate of the plating solution supplied through the plating solution
dialysis line 48 into the dialysis cell 42] lies in the range of
0.3 to 1 (i.e., V/v=0.3 to 1, i.e., V is 30% to 100% of v).
[0087] While the present invention has been described with
reference to preferred embodiments, it is understood that the
present invention is not limited to the embodiments described
above, but is capable of various changes and modifications within
the scope of the inventive concept as expressed herein.
* * * * *