U.S. patent application number 14/103767 was filed with the patent office on 2014-06-19 for sn alloy plating apparatus and method.
The applicant listed for this patent is EBARA CORPORATION. Invention is credited to Yuji ARAKI, Jumpei FUJIKATA, Toshiki MIYAKAWA, Masashi SHIMOYAMA, Masamichi TAMURA.
Application Number | 20140166492 14/103767 |
Document ID | / |
Family ID | 50929683 |
Filed Date | 2014-06-19 |
United States Patent
Application |
20140166492 |
Kind Code |
A1 |
SHIMOYAMA; Masashi ; et
al. |
June 19, 2014 |
Sn ALLOY PLATING APPARATUS AND METHOD
Abstract
An Sn alloy plating apparatus includes: a plating bath having a
cathode chamber for holding therein an Sn alloy plating solution in
which the substrate is to be immersed and an anode chamber for
holding therein an anolyte containing Sn ions and an acid; an Sn
anode located in the anode chamber; and an electrolytic solution
supply line configured to supply an electrolytic solution
containing the acid into the anode chamber such that a Sn ion
concentration of the anolyte in the anode chamber is kept not less
than a predetermined value and a concentration of the acid in the
anolyte is kept not less than a predetermined acceptable value. The
electrolytic solution supply line supplies the electrolytic
solution into the anode chamber to increase an amount of the
anolyte in the anode chamber and supply the anolyte into the Sn
alloy plating solution by the increased amount.
Inventors: |
SHIMOYAMA; Masashi; (Tokyo,
JP) ; FUJIKATA; Jumpei; (Tokyo, JP) ; ARAKI;
Yuji; (Tokyo, JP) ; TAMURA; Masamichi; (Tokyo,
JP) ; MIYAKAWA; Toshiki; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EBARA CORPORATION |
Tokyo |
|
JP |
|
|
Family ID: |
50929683 |
Appl. No.: |
14/103767 |
Filed: |
December 11, 2013 |
Current U.S.
Class: |
205/82 ; 204/225;
205/148; 205/81 |
Current CPC
Class: |
C25D 17/008 20130101;
C25D 21/10 20130101; C25D 3/30 20130101; C25D 17/002 20130101; C25D
5/003 20130101; C25D 17/001 20130101; C25D 21/14 20130101; C25D
21/18 20130101 |
Class at
Publication: |
205/82 ; 204/225;
205/148; 205/81 |
International
Class: |
C25D 21/14 20060101
C25D021/14; C25D 3/30 20060101 C25D003/30 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 13, 2012 |
JP |
2012-272168 |
Claims
1. An Sn alloy plating apparatus for electrodepositing an alloy of
Sn and a metal which is nobler than Sn on a surface of a substrate,
the apparatus comprising: a plating bath whose interior is
separated by an anion exchange membrane into a cathode chamber for
holding therein an Sn alloy plating solution in which the
substrate, serving as a cathode, is to be immersed and an anode
chamber for holding therein an anolyte containing Sn ions and an
acid that forms a complex with a divalent Sn ion; an Sn anode
located in the anode chamber; and an electrolytic solution supply
line configured to supply an electrolytic solution containing the
acid into the anode chamber such that a Sn ion concentration of the
anolyte in the anode chamber is kept not less than a predetermined
value and a concentration of the acid in the anolyte is kept not
less than a predetermined acceptable value, the electrolytic
solution supply line being configured to supply the electrolytic
solution into the anode chamber to increase an amount of the
anolyte in the anode chamber and supply the anolyte into the Sn
alloy plating solution by the increased amount.
2. The Sn alloy plating apparatus according to claim 1, wherein the
electrolytic solution supply line is configured to supply the
electrolytic solution into the anode chamber to increase an amount
of the anolyte in the anode chamber to thereby cause the anolyte to
overflow the anode chamber into the Sn alloy plating solution.
3. The Sn alloy plating apparatus according to claim 1, further
comprising: an overflow bath configured to store the Sn alloy
plating solution that has overflowed the cathode chamber; and a
plating solution circulation line configured to return the Sn alloy
plating solution in the overflow bath to the cathode chamber to
thereby circulate the Sn alloy plating solution.
4. The Sn alloy plating apparatus according to claim 1, further
comprising: a pure water supply line configured to supply pure
water into the anode chamber.
5. The Sn alloy plating apparatus according to claim 1, further
comprising: an acid concentration measuring device configured to
measure the concentration of the acid in the anolyte in the anode
chamber.
6. The Sn alloy plating apparatus according to claim 1, further
comprising: a dialysis cell configured to draw out a part of the Sn
alloy plating solution from the cathode chamber, remove at least a
part of the acid from the Sn alloy plating solution, and then
return the Sn alloy plating solution to the cathode chamber.
7. The Sn alloy plating apparatus according to claim 1, further
comprising: an N.sub.2 gas supply line configured to supply
nitrogen gas into the anolyte in the anode chamber to form nitrogen
gas bubbles in the anolyte.
8. The Sn alloy plating apparatus according to claim 1, further
comprising: an auxiliary electrolytic cell configured to supply an
anolyte having an increased concentration of Sn ions to the Sn
alloy plating solution, the auxiliary electrolytic cell including
an auxiliary anode chamber for holding an anolyte therein, an
auxiliary cathode chamber for holding a catholyte therein, an anion
exchange membrane separating the auxiliary anode chamber and the
auxiliary cathode chamber from each other, an auxiliary Sn anode
located in the auxiliary anode chamber, an auxiliary cathode
located in the auxiliary cathode chamber, and an auxiliary power
source configured to apply a voltage between the auxiliary Sn anode
and the auxiliary cathode when the auxiliary Sn anode is immersed
in the anolyte and the auxiliary cathode is immersed in the
catholyte to produce the anolyte having the increased concentration
of Sn ions.
9. An Sn alloy plating method of electrodepositing an alloy of Sn
and a metal which is nobler than Sn on a surface of a substrate,
the method comprising: providing a plating bath whose interior is
separated by an anion exchange membrane into a cathode chamber and
an anode chamber; supplying an Sn alloy plating solution into the
cathode chamber; immersing the substrate in the Sn alloy plating
solution; supplying an anolyte, containing Sn ions and an acid that
forms a complex with a divalent Sn ion, into the anode chamber to
immerse an Sn anode in the anolyte; supplying an electrolytic
solution containing the acid into the anode chamber such that a Sn
ion concentration of the anolyte in the anode chamber is kept not
less than a predetermined value and a concentration of the acid in
the anolyte is kept not less than a predetermined acceptable value;
and applying a voltage between the Sn anode and the substrate
serving as a cathode to plate the surface of the substrate, while
supplying the electrolytic solution into the anode chamber to
increase an amount of the anolyte in the anode chamber and
supplying the anolyte into the Sn alloy plating solution by the
increased amount.
10. The Sn alloy plating method according to claim 9, wherein the
supplying the electrolytic solution into the anode chamber to
increase an amount of the anolyte in the anode chamber and the
supplying the anolyte into the Sn alloy plating solution by the
increased amount comprises supplying the electrolytic solution into
the anode chamber to increase an amount of the anolyte in the anode
chamber to thereby cause the anolyte to overflow the anode chamber
into the Sn alloy plating solution.
11. The Sn alloy plating method according to claim 9, further
comprising: circulating the Sn alloy plating solution in the
cathode chamber.
12. The Sn alloy plating method according to claim 9, further
comprising: controlling an amount of the electrolytic solution or
pure water to be supplied into the anode chamber based on the
concentration of the acid in the anolyte held in the anode
chamber.
13. The Sn alloy plating method according to claim 9, further
comprising: determining the concentration of the acid in the
anolyte from an initial acid concentration of the anolyte, a
quantity of electricity and a current efficiency at the Sn anode,
an amount of the electrolytic solution supplied, and a permeability
of the anion exchange membrane with respect to methanesulfonic acid
that passes through the anion exchange membrane and migrates from
the cathode chamber into the anode chamber.
14. The Sn alloy plating method according to claim 9, further
comprising: drawing out a part of the Sn alloy plating solution
from the cathode chamber; removing at least a part of the acid from
the Sn alloy plating solution that has been drawn out; and then
returning the Sn alloy plating solution to the cathode chamber.
15. The Sn alloy plating method according to claim 9, further
comprising: supplying nitrogen gas into the anolyte in the anode
chamber to form nitrogen gas bubbles in the anolyte.
16. The Sn alloy plating method according to claim 9, further
comprising: immersing an auxiliary Sn anode in an anolyte held in
an auxiliary anode chamber; immersing an auxiliary cathode in a
catholyte held in an auxiliary cathode chamber that is separated
from the auxiliary anode chamber by an anion exchange membrane;
applying a voltage between the auxiliary Sn anode and the auxiliary
cathode to produce the anolyte having an increased concentration of
Sn ions; and supplying the anolyte having the increased
concentration of Sn ions into the Sn alloy plating solution.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This document claims priority to Japanese Patent Application
No. 2012-272168 filed Dec. 13, 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 an Sn alloy plating
apparatus and method useful for forming a metal film of an alloy of
Sn and a metal which is nobler than Sn (e.g., a lead-free Sn--Ag
alloy having good soldering properties) on a substrate surface.
[0004] 2. Description of the Related Art
[0005] As is known in the art, a plating film of an alloy of Sn
(tin) and a metal which is nobler than Sn (e.g., an Sn--Ag alloy
which is an alloy of Sn and silver), formed by electroplating on a
substrate surface, can be used for lead-free solder bumps. Sn--Ag
alloy plating is typically carried out by applying a voltage
between an anode and a substrate surface, which are disposed
opposite to each other and immersed in an Sn--Ag alloy plating
solution containing Sn ions and Ag ions, thereby forming an Sn--Ag
alloy film on the substrate surface. Other than the Sn--Ag alloy,
an Sn--Cu alloy which is an alloy of Sn and Cu (copper), an Sn--Bi
alloy which is an alloy of Sn and Bi (bismuth), and the like can be
used as an alloy of Sn and a metal which is nobler than Sn.
[0006] An insoluble anode is often used in plating of such an alloy
of Sn and a metal which is nobler than Sn. This is because, if a
soluble anode made of Sn (i.e., Sn anode) is used, displacement
deposition of the nobler metal on the surface of the Sn anode will
occur, leading to unstable concentration of metal component and
contamination of the plating solution.
[0007] Various Sn alloy plating apparatuses and methods using a
soluble anode made of Sn (Sn anode) have been proposed. For
example, a plating method has been proposed which involves
separating an anode chamber, in which an Sn anode is disposed, from
a plating bath by using an anion exchange membrane, and putting an
Sn plating solution and an acid or a salt thereof into the anode
chamber and putting an Sn alloy plating solution into the plating
bath (see Japanese Patent No. 4441725). The Sn ion-containing
solution in the anode chamber can be supplied through a supply line
to the Sn alloy plating solution in the plating bath. A plating
method has been proposed which comprises carrying out plating of a
plating object in a plating bath by using an Sn anode which is
isolated by an anode bag or box formed of a cation exchange
membrane (see Japanese Patent No. 3368860).
[0008] Further, an Sn--Ag alloy plating method has been proposed
which involves providing a plating bath with an auxiliary cell,
having a cathode chamber and an anode chamber which are separated
by a diaphragm so that a substance that can cause deterioration of
a plating solution will not diffuse into the cathode chamber, and
supplying Sn ions to the plating solution (anolyte) in the anode
chamber in the auxiliary bath (see Japanese Patent Laid-Open
Publication No. H11-21692).
[0009] The abovementioned Japanese Patent No. 4441725 describes the
method including the steps of separating an anode chamber and a
cathode chamber by an anion exchange membrane, putting an Sn anode
into an electrolytic solution (anolyte) containing Sn ions and an
acid or a salt thereof, held in the anode chamber, to allow
dissolution of Sn ions from the Sn anode into the anolyte, and
supplying the Sn ion in the anode chamber to the cathode chamber.
In this method, it has been found by the present inventors that it
is important to control the acid concentration of the anolyte in
the anode chamber in order to achieve stable dissolution of Sn ions
into the anolyte in the anode chamber. The method described in this
Japanese Patent No. 4441725 necessitates a supply line and a supply
device, such as a pump, to supply the Sn ion to the cathode
chamber, leading to a complicated construction of the
apparatus.
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 an Sn alloy plating apparatus and method which
appropriately control a concentration of Sn ions and a
concentration of an acid that forms a complex with a divalent Sn
ion in an anolyte to be supplied to an Sn alloy plating solution,
to thereby enable relatively easy control of the Sn alloy plating
solution and simplified construction of the apparatus.
[0011] An Sn alloy plating apparatus for electrodepositing an An Sn
alloy plating apparatus for electrodepositing an alloy of Sn and a
metal which is nobler than Sn on a surface of a substrate is
provided. The apparatus comprises: a plating bath whose interior is
separated by an anion exchange membrane into a cathode chamber for
holding therein an Sn alloy plating solution in which the
substrate, serving as a cathode, is to be immersed and an anode
chamber for holding therein an anolyte containing Sn ions and an
acid that forms a complex with a divalent Sn ion; an Sn anode
located in the anode chamber; and an electrolytic solution supply
line configured to supply an electrolytic solution containing the
acid into the anode chamber such that a Sn ion concentration of the
anolyte in the anode chamber is kept not less than a predetermined
value and a concentration of the acid in the anolyte is kept not
less than a predetermined acceptable value, the electrolytic
solution supply line being configured to supply the electrolytic
solution into the anode chamber to increase an amount of the
anolyte in the anode chamber and supply the anolyte into the Sn
alloy plating solution by the increased amount.
[0012] According to the apparatus as described above, the Sn ion
concentration of the anolyte and the concentration of the acid that
forms a complex with a divalent Sn ion are controlled
appropriately, the anolyte, having a high Sn ion concentration and
in which divalent Sn ions exist stably, is supplied to the Sn alloy
plating solution. Therefore, it is possible to supply Sn ions to
the Sn alloy plating solution stably.
[0013] In an embodiment, the electrolytic solution supply line is
configured to supply the electrolytic solution into the anode
chamber to increase an amount of the anolyte in the anode chamber
to thereby cause the anolyte to overflow the anode chamber into the
Sn alloy plating solution.
[0014] According to this embodiment, the anolyte, having a high Sn
ion concentration and in which divalent Sn ions exist stably, can
be supplied to the Sn alloy plating solution without use of any
power.
[0015] In an embodiment, the Sn alloy plating apparatus further
includes: an overflow bath configured to store the Sn alloy plating
solution that has overflowed the cathode chamber; and a plating
solution circulation line configured to return the Sn alloy plating
solution in the overflow bath to the cathode chamber to thereby
circulate the Sn alloy plating solution.
[0016] According to this embodiment, the Sn alloy plating solution
in the cathode chamber circulates through the plating solution
circulation line, so that the plating solution can be agitated.
[0017] In an embodiment, the Sn alloy plating apparatus further
includes a pure water supply line configured to supply pure water
into the anode chamber.
[0018] By adjusting the amount of pure water to be supplied through
the pure water supply line into the anode chamber or the amount of
the electrolytic solution to be supplied through the electrolytic
solution supply line into the anode chamber, the concentration of
the acid in the anolyte can be controlled in a preferable
range.
[0019] In an embodiment, the Sn alloy plating apparatus further
comprises an acid concentration measuring device for measuring the
concentration of the acid in the anolyte in the anode chamber.
[0020] In an embodiment, the Sn alloy plating apparatus further
comprises a dialysis cell configured to draw out a part of the Sn
alloy plating solution from the cathode chamber, remove at least a
part of the acid from the Sn alloy plating solution, and then
return the Sn alloy plating solution to the cathode chamber.
[0021] When the concentration of the acid in the Sn alloy plating
solution is too high, at least a part of the acid can be removed
from the Sn alloy plating solution by the dialysis cell so as to
adjust the acid concentration to a preferable range.
[0022] In an embodiment, the Sn alloy plating apparatus further
comprises an N.sub.2 gas supply line configured to supply nitrogen
gas into the anolyte in the anode chamber to form nitrogen gas
bubbles in the anolyte.
[0023] According to this embodiment, the anolyte in the anode
chamber can be sufficiently agitated with the bubbles of the
nitrogen gas, so that Sn ions and the acid can be uniformly
distributed in the anolyte. In addition, the bubbles of the
nitrogen gas can prevent oxidation of the Sn ions in the
anolyte.
[0024] In an embodiment, the Sn alloy plating apparatus further
comprises an auxiliary electrolytic cell configured to supply an
anolyte having an increased concentration of Sn ions to the Sn
alloy plating solution. The auxiliary electrolytic cell includes an
auxiliary anode chamber for holding an anolyte therein, an
auxiliary cathode chamber for holding a catholyte therein, an anion
exchange membrane separating the auxiliary anode chamber and the
auxiliary cathode chamber from each other, an auxiliary Sn anode
located in the auxiliary anode chamber, an auxiliary cathode
located in the auxiliary cathode chamber, and an auxiliary power
source configured to apply a voltage between the auxiliary Sn anode
and the auxiliary cathode when the auxiliary Sn anode is immersed
in the anolyte and the auxiliary cathode is immersed in the
catholyte to produce the anolyte having the increased concentration
of Sn ions.
[0025] In the event of a shortage of Sn ions in the entire system,
the shortage can be compensated for by the supply of the anolyte,
having a high Sn ion concentration, from the auxiliary anode
chamber.
[0026] An Sn alloy plating method of electrodepositing an alloy of
Sn and a metal which is nobler than Sn on a surface of a substrate,
the method comprising: providing a plating bath whose interior is
separated by an anion exchange membrane into a cathode chamber and
an anode chamber; supplying an Sn alloy plating solution into the
cathode chamber; immersing the substrate in the Sn alloy plating
solution; supplying an anolyte, containing Sn ions and an acid that
forms a complex with a divalent Sn ion, into the anode chamber to
immerse an Sn anode in the anolyte; supplying an electrolytic
solution containing the acid into the anode chamber such that a Sn
ion concentration of the anolyte in the anode chamber is kept not
less than a predetermined value and a concentration of the acid in
the anolyte is kept not less than a predetermined acceptable value;
and applying a voltage between the Sn anode and the substrate
serving as a cathode to plate the surface of the substrate, while
supplying the electrolytic solution into the anode chamber to
increase an amount of the anolyte in the anode chamber and
supplying the anolyte into the Sn alloy plating solution by the
increased amount.
[0027] In an embodiment, the supplying the electrolytic solution
into the anode chamber to increase an amount of the anolyte in the
anode chamber and the supplying the anolyte into the Sn alloy
plating solution by the increased amount comprises supplying the
electrolytic solution into the anode chamber to increase an amount
of the anolyte in the anode chamber to thereby cause the anolyte to
overflow the anode chamber into the Sn alloy plating solution.
[0028] In an embodiment, the Sn alloy plating method further
includes circulating the Sn alloy plating solution in the cathode
chamber.
[0029] In an embodiment, the Sn alloy plating method further
includes controlling an amount of the electrolytic solution or pure
water to be supplied into the anode chamber based on the
concentration of the acid in the anolyte held in the anode
chamber.
[0030] In an embodiment, the Sn alloy plating method further
includes determining the concentration of the acid in the anolyte
from an initial acid concentration of the anolyte, a quantity of
electricity and a current efficiency at the Sn anode, an amount of
the electrolytic solution supplied, and a permeability of the anion
exchange membrane with respect to methanesulfonic acid that passes
through the anion exchange membrane and migrates from the cathode
chamber into the anode chamber.
[0031] In an embodiment, the Sn alloy plating method further
includes drawing out a part of the Sn alloy plating solution from
the cathode chamber; removing at least a part of the acid from the
Sn alloy plating solution that has been drawn out; and then
returning the Sn alloy plating solution to the cathode chamber.
[0032] In an embodiment, the Sn alloy plating method further
includes supplying nitrogen gas into the anolyte in the anode
chamber to form nitrogen gas bubbles in the anolyte.
[0033] In an embodiment, the Sn alloy plating method further
includes immersing an auxiliary Sn anode in an anolyte held in an
auxiliary anode chamber; immersing an auxiliary cathode in a
catholyte held in an auxiliary cathode chamber that is separated
from the auxiliary anode chamber by an anion exchange membrane;
applying a voltage between the auxiliary Sn anode and the auxiliary
cathode to produce the anolyte having an increased concentration of
Sn ions; and supplying the anolyte having the increased
concentration of Sn ions into the Sn alloy plating solution.
[0034] According to the present invention, the electrolytic
solution containing the acid that forms a complex with a divalent
Sn ion is supplied into the anode chamber so that the Sn ion
concentration of the anolyte in the anode chamber is kept not less
than a predetermined value and the concentration of the acid does
not become lower than an acceptable value. The concentration of Sn
ions and the concentration of the acid in the anolyte can thus be
appropriately controlled. Further, the anolyte, whose amount has
been increased by the supply of the electrolytic solution, in the
anode chamber is supplied to the Sn alloy plating solution. Thus,
the anolyte, having a high Sn ion concentration and in which
divalent Sn ions exist stably, is supplied to the Sn alloy plating
solution. This makes it possible to stably replenish the Sn alloy
plating solution with Sn ions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIG. 1 is a schematic view of an Sn alloy plating apparatus
according to an embodiment;
[0036] FIG. 2 is a perspective view of an exemplary anode bath
configured to cause an anolyte to overflow the bath;
[0037] FIG. 3 is a cross-sectional view of a main portion of
another exemplary anode bath configured to cause an anolyte to
overflow the bath;
[0038] FIG. 4 is a perspective view of a main portion of yet
another exemplary anode bath configured to cause an anolyte to
overflow the bath;
[0039] FIG. 5 is a schematic perspective view of a substrate holder
shown in FIG. 1;
[0040] FIG. 6 is a plan view of the substrate holder shown in FIG.
1;
[0041] FIG. 7 is a right side view of the substrate holder shown in
FIG. 1;
[0042] FIG. 8 is an enlarged view of the portion A of FIG. 7;
[0043] FIG. 9 is a diagram illustrating a main portion of the Sn
alloy plating apparatus when performing the plating process;
[0044] FIG. 10 is a graph showing a theoretical Sn ion
concentration of an anolyte in an anode chamber, calculated from a
quantity of electricity, in comparison with actually measured Sn
ion concentration of the anolyte;
[0045] FIG. 11 is a schematic view of another example of a plating
bath;
[0046] FIG. 12 is a schematic view of an Sn alloy plating apparatus
according to another embodiment;
[0047] FIG. 13 is a schematic view of an Sn alloy plating apparatus
according to yet another embodiment;
[0048] FIG. 14 is a schematic view of an Sn alloy plating apparatus
according to yet another embodiment; and
[0049] FIG. 15 is a schematic view of an Sn alloy plating apparatus
according to yet another embodiment.
DETAILED DESCRIPTION
[0050] Embodiments will now be described in detail with reference
to the drawings. The same reference numerals are used in the
figures and descriptions to refer to the same or like members,
components, etc., and duplicate descriptions thereof are
omitted.
[0051] The following embodiment illustrates an exemplary case where
Ag (silver) is used as a metal which is nobler than Sn (tin) and a
film of an Sn--Ag alloy is formed on a substrate surface.
Methanesulfonic acid is used as an acid that forms a complex with a
divalent Sn ion. Thus, an Sn--Ag alloy plating solution is used
which contains tin methanesulfonate as a source of Sn ions
(Sn.sup.2+) and silver methanesulfonate as a source of Ag ions
(Ag.sup.+). It is also possible to use silver alkylsulfonate as a
source of Ag ions (Ag.sup.+).
[0052] FIG. 1 is a schematic view of an Sn alloy plating apparatus
according to an embodiment. As shown in FIG. 1, the Sn alloy
plating apparatus includes a plating bath 16 in which a box-shaped
anode bath 10 is disposed. The interior of the plating bath 16 is
divided by the anode bath 10 into a cathode chamber 12 and an anode
chamber 14 which is defined in the anode bath 10.
[0053] The cathode chamber 12 is coupled via an overflow bath 36,
which will be described later, to a plating solution supply line 20
extending from a plating solution supply source 18. The cathode
chamber 12 is configured to hold an Sn--Ag alloy plating solution
(hereinafter referred to simply as a plating solution) Q therein. A
substrate W, which is detachably held by a substrate holder 22 and
serves as a cathode during plating thereof, is put at a
predetermined position in the cathode chamber 12 and immersed in
the plating solution Q when plating of the substrate W is
performed.
[0054] An anolyte supply line 23, an electrolytic solution supply
line 24, a pure water supply line 26, and a liquid discharge line
28 are coupled to the anode chamber 14. The anode chamber 14 is
configured to hold an anolyte E therein. A soluble Sn anode 32,
which is made of Sn and held by an anode holder 30, is disposed at
a predetermined position in the anode chamber 14 and immersed in
the anolyte E. Further, an N.sub.2 gas supply line 33 for supplying
nitrogen gas into the anolyte E to form nitrogen gas bubbles in the
anolyte E is provided at a bottom of the anode chamber 14.
[0055] In this embodiment, a solution, containing Sn ions and
methanesulfonic acid that forms a complex with a divalent Sn ion
and not containing Ag ions, is used as the anolyte E. A part of
methanesulfonate ions in the anolyte E surrounds the divalent Sn
ion to form the complex with the Sn ion, while the other part of
methanesulfonate ions exists as a free acid in the anolyte E. The
methanesulfonic acid concentration herein refers to the
concentration of the free acid unless otherwise stated. Because of
the absence of Ag ions in the anolyte E, there is no possibility of
a reaction between Ag ions and the Sn anode 32, and a consequent
displacement deposition of Ag on the surface of the Sn anode 32
does not occur when the Sn anode 32 is immersed in the anolyte E.
An aqueous solution containing methanesulfonic acid (i.e., an
aqueous methanesulfonic acid solution) is used as the electrolytic
solution which is supplied into the anode chamber 14 through the
electrolytic solution supply line 24.
[0056] When carrying out plating of the substrate W, the Sn anode
32 is electrically connected to a positive pole of a plating power
source 34, and a conductive layer (not shown), such as a seed
layer, formed on the surface of the substrate W is electrically
connected to a negative pole of the plating power source 34. As a
result, a metal film of an Sn--Ag alloy is formed on the surface of
the conductive layer. This metal film may be used for lead-free
solder bumps.
[0057] The plating bath 16 is provided with the overflow bath 36
which is located adjacent to the cathode chamber 12. The plating
solution Q is allowed to overflow the top of the cathode chamber 12
into the overflow bath 36. One end of a plating solution
circulation line 46 is coupled to the bottom of the overflow bath
36, and the other end of the plating solution circulation line 46
is coupled to the bottom of the cathode chamber 12. The plating
solution circulation line 46 is provided with a pump 38, a heat
exchanger (temperature regulator) 40, a filter 42, and a flow meter
44. The plating solution supply line 20 extending from the plating
solution supply source 18 is coupled to the top of the overflow
bath 36.
[0058] A regulation plate 50 for regulating a distribution of
electric potential in the cathode chamber 12 is disposed in the
cathode chamber 12. This regulation plate 50 is located between the
substrate holder 22, disposed in the cathode chamber 12, and the Sn
anode 32. In this embodiment, the regulation plate 50 is made of
vinyl chloride, which is a dielectric material, and has a central
hole 50a having such a size as to sufficiently restrict spreading
of an electric field. A lower end of the regulation plate 50
reaches the bottom plate of the cathode chamber 12.
[0059] A vertically-extending agitating paddle 52 serving as an
agitating tool is disposed in the cathode chamber 12 at a position
between the substrate holder 22, disposed in the cathode chamber
12, and the regulation plate 50. This agitating paddle 52 is
configured to make a reciprocating movement parallel to the
substrate W so as to agitate the plating solution Q that exists
between the substrate holder 22 and the regulation plate 50. By
agitating the plating solution Q with the agitating paddle
(agitating tool) 52 during plating, a sufficient amount of metal
ions can be supplied uniformly to the surface of the substrate
W.
[0060] An anion exchange membrane 54 is incorporated in a
cathode-chamber-side wall 10a of the anode bath 10 which divides
the interior of the plating bath 16 into the cathode chamber 12 and
the anode chamber 14. The cathode chamber 12 and the anode chamber
14 are isolated by the anion exchange membrane 54. A
commercially-available product AAV manufactured by AGC Engineering
Co., Ltd., for example, can be used as the anion exchange membrane
54. The number of anion exchange membranes 54 and their arrangement
may be arbitrarily adjusted depending on the necessary membrane
area and an amount of permeation of water molecules, which will be
described later. The anion exchange membrane 54 is incorporated
into the wall 10a in a liquid-tight manner, e.g., by use of an
O-ring so that the plating solution Q in the cathode chamber 12
will not enter the anode chamber 14.
[0061] The wall 10a and the anion exchange membranes 54 are
arranged between the Sn anode 32 and the substrate W. The wall 10a
functions as an overflow weir which stems the anolyte E in the
anode chamber 14 and allows the anolyte E to overflow the top of
the wall 10a into the cathode chamber 12. Specifically, the anolyte
E is stemmed by the wall (overflow weir) 10a and stored in the
anode chamber 14 at a predetermined liquid level H (see FIG. 9).
After the liquid level H is reached, the anolyte E overflows the
top of the wall 10a into the anode chamber 14.
[0062] A plating solution supply pipe 64 for supplying the plating
solution Q to a dialysis cell 62, which has an anion exchange
membrane 60 therein, is coupled to the plating solution circulation
line 46. This plating solution supply pipe 64 is located downstream
of the flow meter 44. A plating solution discharge pipe 66,
extending from the dialysis cell 62, is coupled to a top of the
overflow bath 36. The plating solution supply pipe 64 and the
plating solution discharge pipe 66 constitute a plating solution
dialysis line 68 that is coupled to the plating solution
circulation line 46 and takes in a part of the plating solution Q
from the plating solution circulation line 46 to cause the plating
solution Q to circulate therethrough. A pure water supply line 70
for supplying pure water into the dialysis cell 62 and a pure water
drainage line 72 for discharging the pure water from the dialysis
cell 62 are coupled to the dialysis cell 62.
[0063] The plating solution Q, flowing through the plating solution
dialysis line 68, is supplied into the dialysis cell 42, where at
least a part of the methanesulfonic acid as a free acid is removed
by dialysis using the anion exchange membrane 60. The plating
solution Q after dialysis is returned to the overflow bath 36. The
methanesulfonic acid that has been removed from the plating
solution Q by the dialysis diffuses into the pure water supplied
into the dialysis cell 62 through the pure water supply line 70,
and is discharged to the exterior of the dialysis cell 62 through
the pure water drainage line 72.
[0064] The anion exchange membrane 60 used in this embodiment is
DSV manufactured by AGC Engineering Co., Ltd. An arbitrary number
of anion exchange membranes 60 may be incorporated in the dialysis
cell 62 depending on the amount of the plating solution to be
dialyzed (i.e., the amount of the methanesulfonic acid to be
removed).
[0065] In this embodiment, at least a part of the methanesulfonic
acid as a free acid in the plating solution Q is removed by using
the dialysis cell 62 that employs the diffusion dialysis. It is
also possible to remove at least a part of the methanesulfonic acid
from the plating solution Q by using a free-acid removal cell that
employs electrodialysis or an ion-exchange resin method.
[0066] The plating solution circulation line 46 is provided with an
Sn ion concentration measuring device 74 for measuring the Sn ion
concentration of the plating solution Q flowing through the plating
solution circulation line 46. The plating solution circulation line
46 is further provided with a methanesulfonic acid concentration
measuring device 76 for measuring the methanesulfonic acid
concentration of the plating solution Q flowing through the plating
solution circulation line 46. The output of the Sn ion
concentration measuring device 74 and the output of the
methanesulfonic acid concentration measuring device 76 (i.e.,
concentration measurement values) are inputted into the plating
solution supply source 18 and a controller 80.
[0067] FIG. 2 is a perspective view of the anode bath 10. As shown
in FIG. 2, in an off-centered position at the top of the wall 10a
of the anode bath 10 that functions as the overflow weir, there is
provided a cutout portion 10b which serves as an outlet for
allowing the anolyte E to overflow the anode chamber 14. The liquid
level H (see FIG. 9) of the anolyte E held in the anode chamber 14
is determined by the position of a lower end of the cutout portion
10b.
[0068] The electrolytic solution supply line 24 extends downward
along the side of the anode bath 10. The electrolytic solution
supply line 24 has at its lower end an electrolytic solution supply
outlet 24a for supplying the electrolytic solution (aqueous
methanesulfonic acid solution) into the anode chamber 14. This
electrolytic solution supply outlet 24a reaches the bottom of the
anode bath 10 and opens in a horizontal direction. Similarly, the
pure water supply line 26 extends downward along the side of the
anode bath 10. The pure water supply line 26 has at its lower end a
pure water supply outlet 26a for supplying pure water into the
anode chamber 14. This pure water supply outlet 26a reaches the
bottom of the anode bath 10 and opens in a horizontal direction.
The electrolytic solution supply outlet 24a and the pure water
supply outlet 26a may open in a downward direction.
[0069] When the anode bath 10 is projected onto a horizontal plane,
the electrolytic solution supply outlet 24a and the pure water
supply outlet 26a are diagonally opposite to the cutout portion 10b
of the wall 10a so that when the pure water or the electrolytic
solution is supplied into the anode chamber 14 through the pure
water supply line 26 or the electrolytic solution supply line 24,
the anolyte E containing Sn ions is agitated sufficiently by the
supplied pure water or electrolytic solution and then overflows the
cutout portion 10b into the cathode chamber 12.
[0070] The N.sub.2 gas supply line 33 extends downward along the
side of the anode bath 10 to reach the bottom of the anode bath 10,
and further extends horizontally over approximately the entire
length of the anode bath 10 in its longitudinal direction. Nitrogen
gas is released or ejected upward through jet orifices 33a, which
are provided in the N.sub.2 gas supply line 33, to cause the
anolyte E to bubble, thereby sufficiently agitating the anolyte E
in the anode chamber 14. The bubbles of the nitrogen gas can
promote uniform distribution of the Sn ions and the methanesulfonic
acid throughout the anolyte E in the anode chamber 14 and, in
addition, can prevent oxidation of the Sn ions in the anolyte E. In
view of this, the nitrogen gas is preferably supplied into the
anolyte E at the bottom of the anode chamber 14 to cause the
bubbling of the anolyte E from the bottom of the anode chamber
14.
[0071] It is preferred to stop the supply of the nitrogen gas
immediately before the pure water or the electrolytic solution is
supplied into the anode chamber 14 so as not to carry out the
bubbling of the anolyte E with the nitrogen gas during the supply
of the pure water or the electrolytic solution. This enables the
anolyte E, containing Sn ions in a sufficiently dispersed state, to
overflow the wall 10a into the cathode chamber 12 while preventing
the anolyte E from being excessively diluted with the pure water or
the electrolytic solution supplied.
[0072] In order to detect a decrease in the amount of the anolyte E
in the anode chamber 14 due to its evaporation, a liquid level
detection sensor 82 for detecting the liquid level of the anolyte E
in the anode chamber 14 is provided above the anode chamber 14.
Upon detection of the decrease in the amount of the anolyte E due
to its evaporation, the pure water may be supplied into the anolyte
E in the anode chamber 14 through the pure water supply line 26.
This makes it possible to keep the anolyte E in the anode chamber
14 at a constant liquid level. Further, it is possible to control
the amount of Sn ions to be supplied to the cathode chamber 12 with
the amount of the pure water or the electrolytic solution to be
supplied into the anode chamber 14.
[0073] A mechanical structure may be used to cause the anolyte E in
the anode chamber 14 to overflow into the cathode chamber 12. For
example, as shown in FIG. 3, a float 84 may be put on the anolyte E
in the anode chamber 14 and may be submerged into the anolyte E so
as to cause the anolyte E to overflow into the cathode chamber 12
with an amount corresponding to a volume of the float 84. This
structure involves no supply of pure water or the electrolytic
solution, and thus no introduction of water into the anolyte E.
Therefore, the anolyte E can be supplied into the cathode chamber
12 without dilution of the anolyte E.
[0074] As shown in FIG. 4, a vertically movable weir 86 may be
provided in a rectangular cutout portion 10c that is formed in the
top of the wall 10a that serves as the overflow weir. In this
example shown in FIG. 4, the anolyte E can be supplied into the
cathode chamber 12 by lowering the movable weir 86. This structure
also has the advantage of no dilution of the anolyte E when
supplied into the cathode chamber 12.
[0075] In the event of a shortage of Sn ions in the entire system,
it is necessary to replenish the plating solution Q with Sn ions. A
conceivable Sn ion replenishing method is to supply an Sn
replenishing solution having a high Sn ion concentration to the
plating solution Q. However, such a high-concentration Sn
replenishing solution is generally expensive, and therefore incurs
high costs. Thus, in this embodiment, an auxiliary electrolytic
cell 100 for replenishment of the Sn ions is provided separately
from the plating bath 16.
[0076] A box-shaped cathode bath 102 is disposed in the auxiliary
electrolytic cell 100, whereby the interior of the auxiliary
electrolytic cell 100 is divided into an anode chamber (i.e.,
auxiliary anode chamber) 104 and a cathode chamber (i.e., auxiliary
cathode chamber) 106 defined in the cathode bath 102. An anion
exchange membrane 108 is incorporated in an anode-chamber-side wall
102a of the cathode bath 102 which divides the interior of the
auxiliary electrolytic cell 100 into the anode chamber 104 and the
cathode chamber 106. The anode chamber 104 and the cathode chamber
106 are isolated by the anion exchange membrane 108.
[0077] An anolyte supply line 110 for supplying an anolyte A
containing Sn ions and methanesulfonic acid and not containing Ag
ions, and an electrolytic solution supply line 112 for supplying an
electrolytic solution comprising an aqueous solution containing
methanesulfonic acid (i.e., aqueous methanesulfonic acid solution)
are coupled to the anode chamber 104. An Sn anode (i.e., auxiliary
Sn anode) 118, which is held by an anode holder 116, is disposed in
the anode chamber 104 and immersed in the anolyte A. One end of an
Sn ion replenishing line 114 is coupled to the anode chamber 104,
and the other end of the Sn ion replenishing line 114 is coupled to
the top of the overflow bath 36 of the plating bath 16. The Sn ion
replenishing line 114 is provided with a pump 120.
[0078] A catholyte supply line 122 for supplying a catholyte B
comprising an aqueous solution containing methanesulfonic acid
(i.e., aqueous methanesulfonic acid solution), and a liquid
discharge line 124 for discharging the catholyte B are coupled to
the cathode chamber 106. A cathode (i.e., an auxiliary cathode)
128, which is made of e.g. SUS and held by a cathode holder 126, is
disposed in the cathode chamber 106 and immersed in the catholyte
B. The above-described wall 102a and the anion exchange membrane
108 are located between the Sn anode 118 and the cathode 128.
[0079] In operation of the auxiliary electrolytic cell 100, the
anolyte A, containing Sn ions at a high concentration (e.g. 220 g/L
to 350 g/L) and methanesulfonic acid and not containing Ag ions, is
supplied into the anode chamber 104 through the anolyte supply line
110, thereby immersing the Sn anode 118 in the anolyte A. The
catholyte B containing an aqueous methanesulfonic acid solution is
supplied into the cathode chamber 106 through the catholyte supply
line 122, thereby immersing the cathode 128 in the catholyte B.
[0080] In this state, a positive pole and a negative pole of an
auxiliary power source 130 are electrically connected to the Sn
anode 118 and the cathode 128, respectively, to start electrolysis.
Once the electrolysis is started, the Sn ion concentration of the
anolyte A increases as a result of the dissolution of Sn ions from
the Sn anode 118. Because the anode chamber 104 and the cathode
chamber 106 are isolated by the anion exchange membrane 108, the Sn
ions do not migrate into the cathode chamber 106 and therefore the
cathode 128 is not plated. Because the anolyte A does not contain
Ag ions, displacement deposition of Ag on the surface of the Sn
anode 118 does not occur. The Sn ions in the anolyte A are supplied
through the anolyte supply line 110 before the start of
electrolysis, while the Sn ions are supplied by the dissolution
from the Sn anode 118 after the start of electrolysis.
[0081] After a predetermined Sn ion concentration is reached in the
anolyte A, the pump 120 is driven to supply the anolyte A into the
overflow bath 36 of the plating bath 16 through the Sn ion
replenishing line 114. The amount of the anolyte A in the anode
chamber 104 decreases as a result of the supply of the anolyte A to
the overflow bath 36. Thus, the electrolytic solution, in an amount
that compensates for the decrease in the amount of the anolyte A,
is supplied into the anode chamber 104 through the electrolytic
solution supply line 112. The Sn ion concentration of the anolyte A
is preferably as high as possible from the viewpoint of decreasing
the amount of waste liquid discharged from the entire system.
[0082] Methanesulfonate ions contained in the catholyte B in the
cathode chamber 106 pass through the anion exchange membrane 108
and migrate into the anode chamber 104. Accordingly, the
conductivity of the catholyte B in the cathode chamber 106
decreases with time. Therefore, a fresh catholyte B is supplied
into the cathode chamber 106 through the catholyte supply line 122,
while discharging the catholyte B from the cathode chamber 106 to
the exterior through the liquid discharge line 124 so that the
catholyte B does not overflow.
[0083] As shown in FIGS. 5 through 8, the substrate holder 22
includes a first holding member 154 having a rectangular plate
shape and made of e.g., vinyl chloride, and a second 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.
[0084] 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. An annular substrate-side sealing
member 166 (see FIGS. 7 and 8) 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 22. An annular holder-side sealing member 168 (see FIGS. 7
and 8) 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.
[0085] As shown in FIG. 8, 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.
[0086] 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 through a spacer 165.
The retaining ring 164 is inescapably held by an outwardly
projecting retaining plates 172 (see FIG. 6) 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.
[0087] Inverted L-shaped clampers 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 arranged
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 164a from a lateral direction by means
of a rotating pin (not shown).
[0088] 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 of the second holding
member 158 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.
[0089] When the second holding member 158 is locked in the
above-described manner, the 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. The
substrate-side sealing member 166 is pressed uniformly against the
substrate W to thereby seal the gap between the periphery of the
surface of the substrate W and the second holding member 158.
Similarly, when the second holding member 158 is locked, the
downwardly-protruding portion of the holder-side sealing member 168
is placed in pressure contact with the surface of the first holding
member 154. The sealing holder-side sealing member 168 is uniformly
pressed against the first holding member 154 to thereby seal the
gap between the first holding member 154 and the second holding
member 158.
[0090] A pair of T-shaped holder hangers 190 are provided on end
portions of the first holding member 154. These holder hangers 190
serve as a support when the substrate holder 22 is transported and
when the substrate holder 22 is held in a suspended state. A
protruding portion 182 is formed on the upper surface 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 an
annular 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.
[0091] As shown in FIG. 6, a plurality of electrical conductors
(electrical contacts) 186 (e.g., 12 conductors as illustrated),
coupled respectively to wires extending from external contacts (not
shown) provided in the holder hanger 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,
end portions of the electrical conductors 186 resiliently contact
the lower portions of the electrical contacts 188 shown in FIG.
8.
[0092] The electrical contacts 188, which are 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.
[0093] 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 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.
[0094] Next, operations of the plating apparatus according to the
embodiment will be described. The pump 38 is set in motion to
circulate the plating solution Q in the cathode chamber 12 through
the plating solution circulation line 46 to thereby agitate the
plating solution Q. In this state, the substrate W, held by the
substrate holder 22, is put at the predetermined position in the
cathode chamber 12 and immersed in the plating solution Q. The
anode chamber 14 is filled with the initial anolyte E so that the
Sn anode 32 is immersed in the anolyte E.
[0095] In this state, the Sn anode 32 is electrically connected to
the positive pole of the plating power source 34, and a conductive
layer, such as a seed layer, formed on the surface of the substrate
W is electrically connected to the negative pole of the plating
power source 34 to start plating of the surface of the substrate W.
During the plating, the agitating paddle (agitating tool) 52
reciprocates or oscillates parallel to the substrate W, as
necessary, to agitate the plating solution Q in the cathode chamber
12. At the same time, the nitrogen gas is supplied into the anolyte
E through the N.sub.2 gas supply line 33 to form the bubbles of the
nitrogen gas in the anolyte E in the anode chamber 14.
[0096] During the plating, Sn ions dissolve from the Sn anode 32
into the anolyte E in the anode chamber 14 as shown in FIG. 9. The
dissolution of the Sn ions occurs every time plating of a substrate
is performed, and therefore the Sn ion concentration of the anolyte
E in the anode chamber 14 increases. Further, the volume of the
anolyte E in the anode chamber 14 increases when the electrolytic
solution or the pure water is supplied into the anode chamber 14
from the electrolytic solution supply line 24 or the pure water
supply line 26. When the liquid level of the anolyte E in the anode
chamber 14 rises over the predetermined liquid level H by .DELTA.H,
the anolyte E overflows the cutout portion 10b (see FIG. 2) formed
in the wall 10a of the anode chamber 14 and flows into the cathode
chamber 12 by an amount corresponding to the increase .DELTA.H in
the liquid level. Therefore, some of the Sn ions in the anode
chamber 14 are supplied into the cathode chamber 12, and can
compensate for the shortage of the Sn ions that have been consumed
in plating of the substrate W. In view of the increase in the
amount of the plating solution Q when the anolyte E is supplied to
the plating solution Q, the plating solution Q is discharged in
advance by an amount corresponding to the amount of the anolyte E
supplied into the cathode chamber 12.
[0097] When an electric field is formed between the Sn anode 32 and
the substrate W as a cathode, the methanesulfonic acid in the
cathode chamber 12, together with water molecules, passes through
the anion exchange membrane 54 into the anode chamber 14. This
migration also increases the amount of the anolyte E in the anode
chamber 14, and as a result the anolyte E overflows the wall 10a
into the cathode chamber 12 by an amount exceeding the
predetermined liquid level H. In this manner, the Sn ions in the
anode chamber 14 can be supplied into the cathode chamber 12.
[0098] The present inventors have verified through experiments the
fact that the concentration of methanesulfonic acid as a free acid
in the anolyte E in the anode chamber 14 is important for
stabilizing the Sn ions that have dissolved from the Sn anode. In
particular, an experiment was conducted in which an anolyte of an
aqueous methanesulfonic acid solution, initially having a
methanesulfonic acid concentration of 100 g/L, was supplied in an
anode chamber at the start of electrolysis. In this case, the
anolyte in the anode chamber was found to become cloudy as the
electrolysis was continued. This indicates that Sn ions cannot
exist stably as divalent ions in the anolyte, and precipitate as
metal Sn or tetravalent Sn ions are generated.
[0099] In contrast, in an experiment in which the electrolysis was
started with an initial methanesulfonic acid concentration of 140
g/L, the anolyte in the anode chamber did not become cloudy during
the electrolysis. Moreover, the Sn ion concentration of the anolyte
agreed with a calculation value that was determined on condition
that Sn has dissolved as divalent Sn ions. This indicates that
because of the presence of a sufficient amount of methanesulfonate
ions in the anolyte, divalent Sn ions exist stably in the form of a
complex surrounded by methanesulfonate ions. As will be appreciated
from the foregoing, the methanesulfonic acid concentration of the
anolyte should preferably be controlled in such a range as to allow
the divalent Sn ions to exist stably in the anolyte.
[0100] As described above, by supplying the pure water into the
anode chamber 14 through the pure water supply line 26, the anolyte
E in the anode chamber 14 can overflow into the cathode chamber 12
to supply Sn ions to the cathode chamber 12. The plating apparatus
of this embodiment is also provided with the electrolytic solution
supply line 24 for supplying the electrolytic solution (the aqueous
methanesulfonic acid solution) into the anode chamber 14. This is
because of the following reasons.
[0101] When the pure water is supplied into the anode chamber 14
through the pure water supply line 26 to cause the anolyte E in the
anode chamber 14 to overflow into the cathode chamber 12, the
methanesulfonic acid in the anolyte 14 flows into the cathode
chamber 12, and therefore the methanesulfonic acid concentration of
the anolyte E in the anode chamber 14 decreases. The
methanesulfonic acid in the cathode chamber 12 passes through the
anion exchange membrane 54 and migrates into the anode chamber 14
by forming an electric field between the Sn anode 32 and the
substrate W as a cathode. The transference number of
methanesulfonic acid is not 100%, but can be 50% to 90% due to a
loss, although it depends on conditions. Thus, a ratio of the mol
concentration of the methanesulfonic acid that passes through the
anion exchange membrane 54 into the anode chamber 14 to the mol
concentration of Sn ions that dissolve from the Sn anode 32 into
the anolyte E in the anode chamber 14 will deviate from 1:2.
Consequently, the methanesulfonic acid concentration of the anolyte
E in the anode chamber 14 will decrease, whereby Sn ions in the
anode chamber 14 may become unstable as described above.
[0102] It is therefore necessary to supply the electrolytic
solution containing the methanesulfonic acid into the anode chamber
14 through the electrolytic solution supply line 24 so that the
methanesulfonic acid concentration of the anolyte E in the anode
chamber 14 is not lowered below an acceptable value.
[0103] In order to operate the plating apparatus efficiently, it is
desirable to supply the anolyte E into the cathode chamber 12 by
causing the anolyte E to overflow the anode chamber 14 while
keeping the Sn ion concentration of the anolyte E in the anode
chamber 14 as high as possible. If the anolyte E with a low Sn ion
concentration is supplied into the cathode chamber 12, a larger
amount (overflow amount) of the anolyte E needs to be supplied from
the anode chamber 14 in order to supply a certain amount of Sn ions
into the cathode chamber 12. As a result, a larger amount of the
plating solution Q should be discharged from the circulation system
including the cathode chamber 12, making the plating process
uneconomical.
[0104] Specifically, the Sn ion concentration of the anolyte E in
the anode chamber 14 is controlled typically in the range of 80 g/L
to 500 g/L, preferably in the range of 200 g/L to 400 g/L, more
preferably in the range of 220 g/L to 350 g/L. The Sn ion
concentration of the anolyte E can be determined from the Sn ion
concentration of a fresh anolyte E which has been put into the
anode chamber 14 before the start of plating and the Sn ion
concentration converted from the quantity of electricity at the Sn
anode 32 after the start of plating. The Sn ion concentration of
the anolyte E is of significant importance for controlling the
concentration of Sn ions in the entire plating bath. The Sn ion
concentration of the Sn--Ag plating solution Q is usually 50 g/L to
80 g/L. When the decrease in the Sn ion concentration of the
plating solution Q in the cathode chamber 12 is to be compensated
by the supply of the anolyte E containing the Sn ion in the anode
chamber 14, the use of the anolyte E with a higher Sn ion
concentration can reduce its volume to be supplied into the cathode
chamber 12. The amount of the plating solution Q in the cathode
chamber 12 usually decreases due to evaporation of the solution,
etc. When the anolyte E in the anode chamber 14 is supplied to the
plating solution Q in the cathode chamber 12 in an amount more than
the decrease in the amount of the plating solution Q, the excess
amount of the plating solution Q needs to be finally discharged
from the cathode chamber 12. However, the Sn ion concentration of
the anolyte E cannot be increased to a value more than a saturation
concentration of tin methanesulfonate. Further, the Sn ion
concentration of the anolyte E should be kept less than the
saturation concentration in order for the Sn ions to exist
stably.
[0105] The pure water supply line 26 is used not only for supplying
the pure water into the anode chamber 14 when replenishing the
anode chamber 14 with water by an amount corresponding to the
amount of evaporated water, but also for causing the anolyte E in
the anode chamber 14 to overflow the wall 10a so as to supply the
Sn ions to the cathode chamber 12 when the methanesulfonic acid
concentration of the anolyte E in the anode chamber 14 is
sufficiently high. Further, the pure water supply line 26 is used
for supplying the pure water into the anode chamber 14 so as to
adjust the concentration of a component of the anolyte E in the
anode chamber 14.
[0106] An exemplary operation of the Sn alloy plating apparatus
shown in FIG. 1 will now be described.
[0107] Before starting the operation of the Sn alloy plating
apparatus, the anolyte E, containing Sn ions at a high
concentration (e.g., 220 g/L to 350 g/L) and methanesulfonic acid,
is supplied into the anode chamber 14 to fill the anode chamber 14
with the anolyte E. As described above, it is preferable to supply
the anolyte E at a high Sn ion concentration in the anode chamber
14 into the cathode chamber 12 because the amount of the plating
solution Q to be discharged as waste can be reduced. If the
operation of the apparatus is started with the anolyte E at a low
Sn concentration, it is necessary to wait to supply the anolyte E
into the cathode chamber 12 until a high Sn ion concentration of
the anolyte E is reached.
[0108] The pump 38 is actuated to circulate the plating solution Q
in the cathode chamber 12 through the plating solution circulation
line 46, thereby agitating the plating solution Q in the cathode
chamber 12. In this state, a substrate W, which is held by the
substrate holder 22, is put at a predetermined position in the
cathode chamber 12 and immersed in the plating solution Q.
[0109] The Sn anode 32 is electrically connected to the positive
pole of the plating power source 34, and a conductive layer, such
as a seed layer, formed on the surface of the substrate W is
electrically connected to the negative pole of the plating power
source 34 to start plating of the surface of the substrate W.
During the plating, the agitating paddle (agitating tool) 52 is
caused to make a reciprocating movement parallel to the substrate
W, as necessary, so as to agitate the plating solution Q in the
cathode chamber 12. At the same time, the nitrogen gas is supplied
into the anolyte E in the anode chamber 14 through the N.sub.2 gas
supply line 33 to form nitrogen gas bubbles in the anolyte E.
[0110] While the plating of the substrate W is performed in this
manner, the Sn ion concentration of the plating solution Q is
measured by the Sn ion concentration measuring device 74, and a
signal of the measurement results (i.e., a measurement value) is
sent to the controller 80. In this embodiment, the controller 80
estimates the methanesulfonic acid concentration of the anolyte E
in the anode chamber 14 and, based on the estimated value,
determines whether to supply the electrolytic solution into the
anode chamber 14 through the electrolytic solution supply line 24
or to supply the pure water into the anode chamber 14 through the
pure water supply line 26, or to supply both the electrolytic
solution and the pure water. Specifically, when the concentration
of methanesulfonic acid as a free acid in the anolyte E has been
reduced below a predetermined value, the electrolytic solution,
containing the methanesulfonic acid, is supplied into the anode
chamber 14 through the electrolytic solution supply line 24 so that
the methanesulfonic acid concentration of the anolyte E does not
become lower than a lower limit value. When replenishing the
plating solution Q in the cathode chamber 12 with Sn ions through
the supply of the anolyte E having a sufficiently high
methanesulfonic acid concentration, the pure water is supplied into
the anode chamber 14 through the pure water supply line 26. The
supply of the pure water into the anode chamber 14 causes the
anolyte E to overflow into the cathode chamber 12, thereby
supplying Sn ions to the plating solution Q in the cathode chamber
12.
[0111] The concentration of methanesulfonic acid as a free acid
contained in the anolyte E in the anode chamber 14 is controlled to
be not less than 30 g/L, so that the Sn ions at a high
concentration, e.g., 220 g/L to 350 g/L, can exist stably as
divalent ions. When the methanesulfonic acid concentration of the
anolyte E is high, the supply of the anolyte E to the plating
solution Q can appreciably increase the methanesulfonic acid
concentration of the plating solution Q in the cathode chamber 12,
which may result in poor film-thickness uniformity in the plating
process as will be described later. Therefore, the methanesulfonic
acid concentration of the plating solution Q is controlled so as
not to exceed a particular value which is determined by taking the
actual operating conditions of the apparatus into
consideration.
[0112] The concentration of methanesulfonic acid as a free acid in
the plating solution Q in the cathode chamber 12 varies with the
quantity of electricity and the current efficiency at the Sn anode
32, the amount of the anolyte E that has overflowed into the
plating solution Q, the amount of waste liquid (drain-out)
discharged from the plating solution circulation line 46, and the
permeability of the anion exchange membrane 54 with respect to the
methanesulfonic acid. The film-thickness uniformity in plating of
the substrate tends to be poor when the methanesulfonic acid
concentration of the plating solution Q in the cathode chamber 12
exceeds about 250 g/L. Therefore, when the methanesulfonic acid
concentration measuring device 76 detects that the methanesulfonic
acid concentration of the plating solution Q in the cathode chamber
12 exceeds an upper limit value, the plating solution Q is forced
to flow into the plating solution dialysis line 68 having the
dialysis cell 62, which removes the methanesulfonic acid from the
plating solution Q. The plating solution Q, from which the
methanesulfonic acid has been removed, is returned to the overflow
bath 36. The dialysis of the plating solution Q in the dialysis
cell 62 can adjust the methanesulfonic acid concentration of the
plating solution Q preferably in the range of 60 g/L to 250 g/L,
more preferably in the range of 90 g/L to 150 g/L.
[0113] The concentration of the methanesulfonic acid as a free acid
in the anolyte E during operation of the Sn alloy plating apparatus
may be controlled based on an estimated value of the
methanesulfonic acid concentration of the anolyte E in the anode
chamber 14. This estimated value of the methanesulfonic acid
concentration can be determined theoretically or experimentally
from an initial methanesulfonic acid concentration of the anolyte
E, the quantity of electricity and the current efficiency at the Sn
anode 32, the amount of the electrolytic solution supplied through
the electrolytic solution supply line 24, the amount of pure water
supplied through the pure water supply line 26, and the
permeability of the anion exchange membrane 54 with respect to the
methanesulfonic acid that passes through the anion exchange
membrane 54 and migrates from the cathode chamber 12 into the anode
chamber 14. The Sn ion concentration and the methanesulfonic acid
concentration of the anolyte E in the anode chamber 14 can be
estimated from a curve of the amount of dissolved Sn ions
associated with the quantity of electricity during plating and from
the permeability of the anion exchange membrane with respect to the
acid.
[0114] As described above, before starting the operation of the Sn
alloy plating apparatus, the anolyte E, containing Sn ions at a
high concentration (e.g., 220 g/L to 350 g/L) and methanesulfonic
acid, is supplied into the anode chamber 14. When the Sn ion
concentration of the anolyte E in the anode chamber 14, as
estimated e.g. from the quantity of electricity at the Sn anode and
the efficiency of electrolysis, reaches a predetermined threshold
value (e.g., 300 g/L) during operation of the Sn alloy plating
apparatus, the electrolytic solution is supplied into the anode
chamber 14 through the electrolytic solution supply line 24 to
cause the anolyte E to overflow the wall 10a, thereby replenishing
the plating solution Q in the cathode chamber 12 with Sn ions.
[0115] Although the Sn ion concentration of the anolyte E in the
anode chamber 14 decreases as a result of the supply of the
electrolytic solution, the Sn ion concentration increases gradually
during plating and eventually reaches the threshold value. During
this plating process, Sn ions in the plating solution Q are
consumed in plating of the substrate W. Assuming that the
efficiency of electrolysis at the substrate W is equal to the
efficiency of electrolysis at the Sn anode 32 and that no Sn ions
are discharged out of the system, Sn ions will dissolve from the Sn
anode 32 in an amount equal to the amount of Sn ions consumed in
plating of the substrate W. Thus, the amount of Sn ions in the
entire system is kept constant. In fact, however, the efficiency of
electrolysis decreases with the increase in the Sn ion
concentration of the anolyte E in the anode chamber 14.
Accordingly, the amount of Sn ions that are supplied to the anolyte
E by the dissolution from the Sn anode 32 becomes smaller than the
amount of Sn ions consumed in plating, resulting in a shortage of
Sn ions in the entire system.
[0116] FIG. 10 is a graph showing the theoretical Sn ion
concentration of the anolyte E in the anode chamber 14, calculated
from the quantity of electricity, in comparison with the actually
measured Sn ion concentration of the anolyte E. As can be seen in
FIG. 10, while the efficiency of electrolysis is approximately 100%
when the Sn ion concentration of the anolyte E in the anode chamber
14 is not more than about 130 g/L, the electrolysis efficiency
decreases when the Sn ion concentration is more than about 150 g/L,
and the electrolysis efficiency decreases to about 80% at an Sn ion
concentration of 300 g/L. The data shown in FIG. 10 thus indicates
that when it is intended to control the Sn ion concentration of the
anolyte E at a high level as 220 g/L to 350 g/L, 10% to 20% of Sn
ions will be in short supply in the entire system. It is also noted
that since the anolyte E in the anode chamber 14 overflows into the
cathode chamber 12, the plating solution Q containing the Sn ions
in the cathode chamber 12 or the overflow bath 36 is discharged in
advance, resulting in the shortage of the amount of Sn ions in the
entire system.
[0117] Thus, the Sn alloy plating apparatus of this embodiment
includes the auxiliary electrolytic cell 100 for compensating for
the shortage of the Sn ions in the entire system. The electrolysis
operation of the auxiliary electrolytic cell 100 is started
simultaneously with the start of operation of the Sn alloy plating
apparatus or at an appropriate time. The pump 120 is driven based
on the concentration of Sn ions measured by the Sn ion
concentration measuring device 74 to thereby supply the anolyte A
having a high Sn ion concentration in the anode chamber 104 to the
overflow bath 36 of the plating bath 16. The supply of Sn ions from
the auxiliary electrolytic cell 100 can compensate for the shortage
of Sn ions caused by the difference between the electrolytic
efficiency of plating on the substrate W and the efficiency of
electrolysis at the Sn anode 32 in the anode chamber 14 and by the
discharge of the plating solution Q from the plating bath 16.
[0118] When the Sn alloy plating apparatus is operated over a long
period of time, the Sn ion concentration and the methanesulfonic
acid concentration of the anolyte E in the anode chamber 14 may
deviate from the estimated concentrations. Therefore, the Sn
concentration and the methanesulfonic acid concentration of the
plating solution Q are measured by the Sn ion concentration
measuring device 74 and the methanesulfonic acid concentration
measuring device 76, and their changes are recorded. If the Sn ion
concentration tends to become higher or lower than a concentration
as estimated from the operating conditions, then the efficiency of
Sn ion dissolution, which is used for the estimation of the
concentration, will be changed. If the methanesulfonic acid
concentration tends to become higher or lower than an estimated
concentration, then the permeability of the anion exchange membrane
with respect to the acid will be changed. After changing such a
factor(s), control of the Sn concentration and the methanesulfonic
acid concentration is continued.
[0119] The supply of the anolyte E, containing a high concentration
of Sn ions, from the anode chamber 14 to the cathode chamber 12 is
preferably performed by forcing the anolyte E to overflow the anode
chamber 14, rather than by passing the anolyte E through a pipe
using a dedicated pump. This is because of the following
reasons.
[0120] If the anolyte E containing Sn ions with a high
concentration resides in a pipe for a long time, deposition of a
metal (which is abnormal deposition) on an interior surface of the
pipe will occur even when the surface of the pipe is made of an
insulating material. Once the metal begins to deposit on the
interior surface of the pipe, the metal tends to grow continuously
on the surface. If the supply of the anolyte E from the anode
chamber 14 to the cathode chamber 12 is continued in order to pass
the anolyte E continuously through the pipe, then the total amount
of the liquid in the cathode chamber increases. As a result, it is
necessary to continuously discharge the plating solution Q from the
cathode chamber by the same amount as the amount of the anolyte E
supplied.
[0121] The above-described metal deposition in the pipe can be
avoided by using the overflow method to supply the anolyte E. The
anolyte E in the anode chamber 14 is constantly agitated by
bubbling thereof with the supply of the nitrogen gas. This can
prevent deposition of a metal on the inner surface of the anode
chamber 14. In the embodiment, the anolyte E overflows the anode
chamber 14 as a result of the migration of methanesulfonic acid and
water molecules caused by the electrolysis. The amount or volume of
the anolyte E overflowing into the cathode chamber 12 is exactly
equal to the amount or volume of the methanesulfonic acid and the
water that have passed through the anion exchange membrane 54.
Thus, there is no change in the volume of the plating solution Q in
the cathode chamber 12, and therefore there is no need to discharge
the plating solution Q.
[0122] FIG. 11 schematically shows a plating bath 16a which is
another example. An anode holder 30, holding a disk-shaped Sn anode
32, is disposed in the anode chamber 14 of the plating bath 16a. An
annular anode mask 200 for restricting a contact area of the Sn
anode 32 with anolyte E is mounted to a front surface of the anode
holder 30 in a manner such that the annular anode mask 200
hermetically contact a peripheral area of the Sn anode 32. An
opening 10d is formed in the cathode-chamber-side wall 10a of the
anode bath 10. Anion exchange membrane 54 is mounted to the wall
10a along the edge of the opening 10d, with its peripheral portion
held between a mask member 202 and the wall 10a. The mask member
202 is provided for restricting a contact area of the anion
exchange membrane 54 with the plating solution Q. Since the wall
10a and the mask member 202 hold the anion exchange membrane 54
therebetween to seal a gap along the peripheral portion of the
anion exchange membrane 54, a liquid leakage between the cathode
chamber 12 and the anode chamber 14 can be prevented.
[0123] The anion exchange membrane 54 and the opening 10d may have
a rectangular shape, and the mask member 202 may be a rectangular
ring. The opening sizes of the opening 10d and the mask member 202
may be equal to or larger than the inner diameter of the anode mask
200. In order to reduce an overall resistance between the anode and
the cathode, the anion exchange membrane 54 may preferably contact
the anolyte E or the plating solution Q at an area larger than an
area at which the Sn anode 32 contacts the anolyte E.
[0124] An electric field shield 204, having approximately the same
external shape as that of the mask member 202 and having an opening
204a of a circular shape similar to the shape of the substrate W,
is mounted to the front surface of the mask member 202. The
diameter of the opening 204a is smaller than the opening size of
the mask member 202. The electric field shield 204, which is
provided in the cathode chamber 12 at a position near the Sn anode
32, can reduce a thickness of a seed layer formed on the substrate,
making it possible to make the distribution of the film thickness
uniform even in a case where the film thickness would otherwise be
relatively large in a peripheral area of the substrate. The
electric field shield 204 may have a mechanism to change its
opening area in order to control the film-thickness distribution.
The diameter of the opening 204a of the electric field shield 204
is set equal to or smaller than the diameter of the central hole
50a of the regulation plate 50 which is located between the
substrate W and the Sn anode 32. In this embodiment, the regulation
plate 50 includes a plate 206 and a cylindrical member 208 mounted
to the plate 206.
[0125] When the anolyte E in the anode chamber 14 overflows the
wall 10a and is supplied into the cathode chamber 12, not only the
Sn ions but unnecessary water is supplied as well, resulting in a
considerable increase in the amount of the plating solution Q in
the cathode chamber 12 and the overflow bath 36. When the amount of
the plating solution Q exceeds a predetermined value, the excess
solution must be discharged, leading to increased costs. In order
to avoid such an issue, the Sn alloy plating apparatus of this
embodiment has a gas supply unit 210, which is disposed above the
plating bath 16a, for promoting evaporation of water. The gas
supply unit 210 can evaporate water in the cathode chamber 12 with
the same amount as the amount of the anolyte E supplied from the
anode chamber 14. This makes it possible to stably keep the
concentrations of the components of the plating solution Q in the
cathode chamber 12, thereby eliminating the need of discharging the
plating solution Q or reducing the amount of the plating solution Q
to be discharged.
[0126] In order to further reduce the amount of the plating
solution to be discharged, the plating solution circulation line 46
may be provided with a dewatering device, which can remove only
water, so that the plating solution Q passes through the dewatering
device.
[0127] FIG. 12 is a schematic view of the Sn alloy plating
apparatus according to another embodiment. This embodiment differs
from the embodiment illustrated in FIG. 1 in that the plating bath
16b of this embodiment includes an inner bath 220 which is integral
with the anode bath 10, and overflow bath 36 provided around the
inner bath 220, and that a wall 10e, which is adjacent to the
overflow bath 36, of the anode bath 10 functions as an overflow
weir which stems the anolyte E in the anode chamber 14 and allows
the anolyte E to overflow its top into the overflow bath 36. Thus,
the anolyte E is stemmed by the wall (overflow weir) 10e and held
in the anode chamber 14 at a predetermined liquid level H (see FIG.
9). After the liquid level H is reached, the anolyte E overflows
the top of the wall 10e and flows into the overflow bath 36
surrounding the plating bath 16b. Sn ions, which have been thus fed
into the overflow bath 36, are supplied into the cathode chamber 12
via the plating solution circulation line 46.
[0128] FIG. 13 is a schematic view of the Sn alloy plating
apparatus according to yet another embodiment. This embodiment
differs from the embodiment illustrated in FIG. 1 in that the anode
bath 10 of this embodiment is provided with an anolyte circulation
line 230 for drawing out a part of the anolyte in the anode chamber
14 from the bottom of the anode bath 10 and returning the anolyte
to the top of the anode bath 10. The anolyte circulation line 230
is provided with a pump 232 and a methanesulfonic acid
concentration measuring device 234.
[0129] According to this embodiment, the pump 232 is driven to
circulate the anolyte E in the anode chamber 14 through the anolyte
circulation line 230, while the methanesulfonic acid concentration
measuring device 234 can measure the methanesulfonic acid
concentration of the anolyte E continually or periodically.
[0130] FIG. 14 is a schematic view of the Sn alloy plating
apparatus according to yet another embodiment. This embodiment
differs from the embodiment illustrated in FIG. 1 in that the
liquid discharge line 28 of the plating bath 16 and the
electrolytic solution supply line 112 of the auxiliary electrolytic
cell 100, shown in FIG. 1, are coupled by a connection line 242
which is provided with a pump 240, and that the Sn ion replenishing
line 114, extending form the anode chamber 104 of the auxiliary
electrolytic cell 100, is coupled to the top of the anode chamber
14 of the plating bath 16.
[0131] According to this embodiment, the anolyte E in the anode
chamber 14 of the plating bath 16 can be used as an electrolytic
solution to be supplied to the anode chamber 104 of the auxiliary
electrolytic cell 100, while the anolyte A having a high Sn ion
concentration in the anode chamber 104 of the auxiliary
electrolytic cell 100 can be returned to the anode chamber 14 of
the plating bath 16. The circulating anolyte can compensate for the
shortage of Sn ions in the plating system.
[0132] FIG. 15 is a schematic view of the Sn alloy plating
apparatus having a plurality of plating baths, according to yet
another embodiment. As shown in FIG. 15, the Sn alloy plating
apparatus includes a plurality of plating baths 250, each having
the same construction as the plating bath 16 shown in FIG. 1, and a
single reservoir bath 252. The anode chambers of the respective
plating baths 250 coupled to the reservoir bath 252 by an anolyte
supply line 254 and an anolyte recovery line 256. The anolyte
supply line 254 is provided with a pump 258a. The anolyte supply
line 254 branches into branch lines extending to the plating baths
250, respectively. Branch points of the anolyte supply line 254 are
located downstream of the pump 258a. Switching valves 260a are
provided at the branch points of the anolyte supply line 254. The
anolyte recovery line 256 is provided with a pump 258b. The anolyte
recovery line 256 branches into branch lines extending to the
plating baths 250, respectively. Branch points of the anolyte
recovery line 256 are located upstream of the pump 258b. Switching
valves 260b are provided at the branch points of the anolyte
recovery line 256.
[0133] A heater 262 for heating the anolyte is installed in the
reservoir bath 252 in order to raise the temperature of the anolyte
so as to increase the efficiency of electrolysis. The temperature
of the anolyte is controlled e.g., in the range of 26.degree. C. to
40.degree. C.
[0134] According to this embodiment, the Sn ion concentration and
the methanesulfonic acid concentration of the anolyte can be made
equal in all the anode chambers of the plating baths 250 by
circulating the anolyte between the anode chambers of the plating
baths 250 and the reservoir bath 252. Thus, control of the Sn ion
concentration and the methanesulfonic acid concentration of the
anolyte can be performed in a considerably simple manner according
to this embodiment as compared to the case of controlling these
concentrations of the anolyte individually in each of the plating
baths 250.
[0135] In this embodiment, the anolyte circulates between the
reservoir bath 252 and one of the plating baths 250 by using the
two pumps 258a, 258b and operating the switching valves 260a, 260b.
This enables easy control of the anolyte in the anode chamber of
each plating bath 250. Pumps may be provided for the plating baths
250, respectively, in order to circulate the anolyte between the
anode chambers of the plating baths 250 and the reservoir bath 252.
Thus, the circulation of the anolyte between one plating bath 250
and the reservoir bath 252 may be performed independently of the
other baths 250.
[0136] In order to eliminate the shortage of Sn ions caused by the
difference between the electrolytic efficiency of the substrate
plating and the electrolytic efficiency at the Sn anode in each
anode chamber and by the discharge of the plating solution from
each plating bath, the reservoir bath 252 may be provided with an
auxiliary electrolytic cell, having the same construction as the
auxiliary electrolytic cell 100 shown in FIG. 1, so as to
compensate for the shortage of the Sn ions.
[0137] In yet another embodiment, the Sn alloy plating apparatus
may include one outer bath (overflow bath) and a plurality of
cathode chambers. An anolyte is supplied from the outer bath into
each cathode chamber from a bottom of each cathode chamber by means
of a pump, and the liquid in the cathode chamber is returned by
overflow to the outer bath. This configuration enables easy control
of the liquid in the cathode chambers.
[0138] 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.
* * * * *