U.S. patent application number 13/336202 was filed with the patent office on 2012-06-28 for electroplating method.
Invention is credited to Yuji ARAKI, Jumpei Fujikata, Nobutoshi Saito.
Application Number | 20120160696 13/336202 |
Document ID | / |
Family ID | 46315372 |
Filed Date | 2012-06-28 |
United States Patent
Application |
20120160696 |
Kind Code |
A1 |
ARAKI; Yuji ; et
al. |
June 28, 2012 |
ELECTROPLATING METHOD
Abstract
A substrate with a through-hole is immersed in a plating
solution in a plating tank. A pair of anodes are disposed in the
plating solution in the plating tank in facing relation to face and
reverse sides, respectively, of the substrate in the plating
solution. A plurality of plating processes are performed on the
face and reverse sides by supplying pulsed currents respectively
between the face side of the substrate and one of the anodes which
faces the face side of the substrate, and between the reverse side
of the substrate and the other anode which faces the reverse side
of the substrate. A reverse electrolyzing process is performed on
the face and reverse sides between adjacent plating processes by
supplying currents in an opposite direction to the pulsed currents
respectively between the face side of the substrate and one of the
anodes, and between the reverse side of the substrate and the other
anode.
Inventors: |
ARAKI; Yuji; (Tokyo, JP)
; Saito; Nobutoshi; (Tokyo, JP) ; Fujikata;
Jumpei; (Tokyo, JP) |
Family ID: |
46315372 |
Appl. No.: |
13/336202 |
Filed: |
December 23, 2011 |
Current U.S.
Class: |
205/171 |
Current CPC
Class: |
C25D 5/18 20130101; C25D
11/024 20130101; H01L 21/2885 20130101; H01L 21/76898 20130101 |
Class at
Publication: |
205/171 |
International
Class: |
C25D 5/18 20060101
C25D005/18; C25D 11/02 20060101 C25D011/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 2010 |
JP |
2010-291656 |
Claims
1. An electroplating method comprising: immersing a substrate with
a through-hole defined therein in a plating solution in a plating
tank; disposing a pair of anodes in the plating solution in the
plating tank in facing relation to face and reverse sides,
respectively, of the substrate in the plating solution; performing
a plurality of plating processes, each for a predetermined period,
on the face and reverse sides of the substrate by supplying pulsed
currents respectively between the face side of the substrate and
one of the anodes which faces the face side of the substrate, and
between the reverse side of the substrate and the other of the
anodes which faces the reverse side of the substrate; and
performing a reverse electrolyzing process on the face and reverse
sides of the substrate between adjacent ones of the plating
processes by supplying currents in an opposite direction to the
pulsed currents in the plating processes respectively between the
face side of the substrate and one of the anodes which faces the
face side of the substrate, and between the reverse side of the
substrate and the other of the anodes which faces the reverse side
of the substrate.
2. An electroplating method according to claim 1, wherein each of
the pulsed currents comprises a PR pulsed current represented by an
alternate repetition of a current flowing in a forward direction
and a current flowing in a reverse direction.
3. An electroplating method according to claim 1, wherein each of
the pulsed currents comprises an on/off pulsed current represented
by an alternate repetition of the supply and non-supply of a
plating current which flows in a forward direction.
4. An electroplating method according to claim 1, wherein each of
the pulsed currents comprises a composite pulsed current
represented by a combination of two pulsed currents having
different current values.
5. An electroplating method according to claim 1, wherein the
plating processes together with the reverse electrolyzing process
are performed to gradually increase an average current density as
the substrate is progressively plated.
6. An electroplating method according to claim 1, wherein the
reverse electrolyzing process is performed a plurality of times
before and after a normal electrolyzing cycle in which a pulsed
current is supplied in the forward direction.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an electroplating method
for simultaneously plating both the face and reverse sides of a
substrate which has a through-hole vertically penetrating in its
interior to fill a plated film of metal such as copper or the like
into the through-hole.
[0003] 2. Description of the Related Art
[0004] A technique of forming a plurality of through-vias of a
metal, vertically penetrating through a substrate, is known as a
method to electrically connect the layers of a multi-layer stack of
substrates such as semiconductor substrates. It is customary to
make vertical through-vias in a substrate by simultaneously plating
both the face and reverse sides of a substrate, which has
through-holes vertically penetrating in its interior, thereby to
fill a plated film of metal into the through-holes.
[0005] There is known an electroplating apparatus for producing
through-vias (see Japanese Patent No. 4138542). This electroplating
apparatus includes a substrate holder for holding a substrate while
exposing certain areas on its face and reverse sides and sealing
peripheral areas around the certain areas, and a pair of anodes
disposed in facing relation to the face and reverse sides,
respectively, of the substrate that is held by the substrate
holder. The substrate held by the substrate holder and the anodes
are immersed in a plating solution, and then voltages are applied
between the substrate and the anodes to simultaneously plate the
face and reverse sides of the substrate, which has vertical
through-holes defined therein, embedding metal such as copper in
the through-holes.
[0006] FIGS. 1A through 1D are diagrams illustrating, in a sequence
of process steps, a process for filling a plated film into a
through-hole defined in a substrate to form a through-via therein
(see Japanese Patent No. 4248353).
[0007] As shown in FIG. 1A, a substrate W is prepared which
includes a base 100 with a vertical through-hole 100a defined
therein, and a barrier layer 102 made of Ti or the like and a seed
layer 104, as an electric feed layer, which cover all the surfaces
of the base 100 including inner surfaces of the through-hole 100a.
The face and reverse sides of the substrate W are simultaneously
plated to deposit a plated film 106 of metal such as copper or the
like on the face and reverse sides of the substrate W and in the
through-hole 100a, as shown in FIG. 1B. The plated film 106 in the
through-hole 100a has its maximum thickness at its center along the
in-depth direction thereof. Then, as shown in FIG. 1C, the plated
film 106 is grown until the tip ends of layers of the plated film
106 that have grown from the wall surfaces of the through-hole 100a
are joined to each other at the center of the through-hole 100a
along the in-depth direction thereof. The center of the
through-hole 100a along the in-depth direction thereof is thus
blocked by the plated film 106, forming recesses 108 above and
below the closed region. The plating process is further continued
to grow the plated film 106 in the recesses 108 until the recesses
108 are filled up with the plated film 106, as shown in FIG. 1D. In
this manner, a through-via made up of the plated film 106 is
produced in the substrate W.
[0008] There has been proposed an electroplating method for filling
through-holes defined in a substrate with a plated film of metal
(see Japanese Patent Laid-Open Publication No. 2008-513985).
According to this electroplating method, a forward pulsed current
is supplied to flow between a substrate as a cathode and an anode,
and a reverse pulsed current, which flows in an opposite direction
to the forward pulsed current, is also is supplied to flow between
the substrate and the anode, for thereby fully or substantially
fully filling the center of the through-hole.
[0009] There has also been proposed a method to prevent whiskers
from being generated in plating a printed wiring substrate or the
like with copper (see Japanese Patent Laid-Open Publication No.
2010-95775). According to this method, a DC power source for
applying a DC voltage between a cathode and an anode has its
polarity reversible. The printed wiring substrate is electroplated
alternately under a normal DC voltage and a reversed DC voltage,
i.e., alternately in a normal electrolyzing cycle in which the
printed wiring substrate serves as a cathode and a reverse
electrolyzing cycle in which the printed wiring substrate serves as
an anode.
SUMMARY OF THE INVENTION
[0010] In order to form a through-via in the form of a plated film
free of defects such as voids or the like therein in a substrate,
as shown in FIGS. 1A through 1D, it is ideal that the plated film
be grown preferentially at the center of the through-hole along the
in-depth direction thereof until the center of the through-hole
100a is blocked by the plated film 106, and then the plating
process be further continued. However, it is generally practically
difficult to attempt to meet the ideal requirements and at the same
time to fill the plated film efficiently into the through-hole to
shorten the time required to perform the plating process. Stated
otherwise, the conventional electroplating processes have failed to
achieve both the ideal filling of the plated film into the
through-hole and the efficient filling of the plated film into the
through-hole with a higher average plating current during
plating.
[0011] The present invention has been made in view of the above
situation. It is therefore an object of the present invention to
provide an electroplating method for efficiently filling a plated
film into a through-hole with a higher average plating current
during plating to shorten the time required to perform the plating
process and also ideally filling the plated film into the
through-hole.
[0012] In order to achieve the above object, the present invention
provides an electroplating method comprising: immersing a substrate
with a through-hole defined therein in a plating solution in a
plating tank; disposing a pair of anodes in the plating solution in
the plating tank in facing relation to face and reverse sides,
respectively, of the substrate in the plating solution; performing
a plurality of plating processes, each for a predetermined period,
on the face and reverse sides of the substrate by supplying pulsed
currents respectively between the face side of the substrate and
one of the anodes which faces the face side of the substrate, and
between the reverse side of the substrate and the other of the
anodes which faces the reverse side of the substrate; and
performing a reverse electrolyzing process on the face and reverse
sides of the substrate between adjacent ones of the plating
processes by supplying currents in an opposite direction to the
pulsed currents in the plating processes respectively between the
face side of the substrate and one of the anodes which faces the
face side of the substrate, and between the reverse side of the
substrate and the other of the anodes which faces the reverse side
of the substrate.
[0013] Since the plural plating processes are performed, each for a
predetermined period, on the face and reverse sides of the
substrate by supplying pulsed currents respectively between the
face side of the substrate and one of the anodes which faces the
face side of the substrate, and between the reverse side of the
substrate and the other of the anodes which faces the reverse side
of the substrate, it is possible to fill a plated film into the
through-hole efficiently with an increased average current value
for thereby shortening a period of time required to plate the
substrate. The reverse electrolyzing process performed between the
plating processes is effective to dissolve plated films deposited
on corners of the through-hole. Therefore, it is possible to
ideally fill the plated film into the through-hole by growing the
plated film preferentially at the center of the through-hole along
the in-depth direction thereof.
[0014] In a preferred aspect of the present invention, each of the
pulsed currents comprises a PR pulsed current represented by an
alternate repetition of a current flowing in a forward direction
and a current flowing in a reverse direction.
[0015] The reverse electrolyzing process is repeatedly performed
between the plating processes using the PR pulsed currents, thereby
preventing fine irregularities from being produced by an abnormal
deposition on microscopic surfaces of the plated film and hence
preventing fine voids from being formed in the plated film due to
such fine irregularities.
[0016] In a preferred aspect of the present invention, each of the
pulsed currents comprises an on/off pulsed current represented by
an alternate repetition of the supply and non-supply of a plating
current which flows in a forward direction.
[0017] Since the on/off pulsed current provides non-plating periods
for supplying no plating current in the plating process, the metal
ion concentration in the plating solution within the through-hole
is recovered in the non-plating period for thereby preventing
defects such as voids or the like from being formed in the plated
film.
[0018] In a preferred aspect of the present invention, each of the
pulsed currents comprises a composite pulsed current represented by
a combination of two pulsed currents having different current
values.
[0019] Since the plated film is continuously grown in the plating
process with the composite pulsed current, the plated film is
prevented from being dissolved into the plating solution in the
plating process.
[0020] In a preferred aspect of the present invention, the plating
processes together with the reverse electrolyzing process are
performed to gradually increase an average current density as the
substrate is progressively plated.
[0021] As the through-hole is gradually filled with the plated film
in the plating process, the substantive aspect ratio of the
through-hole changes. When the substantive aspect ratio of the
through-hole changes, it is possible to efficiently fill the plated
film into the through-hole in a manner to match the changing
substantive aspect ratio by increasing the average current density
in the plating process. Consequently, the period of time required
to plate the substrate can be further shortened.
[0022] In a preferred aspect of the present invention, the reverse
electrolyzing process is performed a plurality of times before and
after a normal electrolyzing cycle in which a pulsed current is
supplied in the forward direction.
[0023] The reverse electrolyzing process is performed with a
negative cathode current density in the range from -30 to -40 ASD
at a pulse pitch in the range from 0.1 to 10 ms, for example.
Depending on the aspect ratio of a through-hole defined in the
substrate, it may not be possible to ideally fill a plated film
preferentially at the center of the through-hole in the in-depth
direction thereof according to a reverse electrolyzing process at a
pulse pitch that is shorter than 1.0 ms. However, if the reverse
electrolyzing process is repeatedly performed a plurality of times
at a pulse pitch shorter than 1.0 ms before and after a normal
electrolyzing cycle in which a pulsed current is supplied in the
forward direction, then it is possible to ideally fill a plated
film into such a through-hole.
[0024] According to the present invention, as described above, the
plural plating processes are performed, each for a predetermined
period, on the face and reverse sides of the substrate by supplying
pulsed currents respectively between the face side of the substrate
and one of the anodes which faces the face side of the substrate,
and between the reverse side of the substrate and the other of the
anodes which faces the reverse side of the substrate. Accordingly,
it is possible to fill a plated film into the through-hole
efficiently with an increased average current value for thereby
shortening a period of time required to plate the substrate. The
reverse electrolyzing process performed between the plating
processes is effective to dissolve plated films deposited on
corners of the through-hole. Therefore, it is possible to ideally
fill the plated film into the through-hole by growing the plated
film preferentially at the center of the through-hole along the
in-depth direction thereof.
[0025] The above and other objects, features, and advantages of the
present invention will become apparent from the following
description when taken in conjunction with the accompanying
drawings which illustrate preferred embodiments of the present
invention by way of example.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIGS. 1A through 1D are diagrams illustrating, in a sequence
of process steps, a process for filling a plated film into a
through-hole defined in a substrate to form a through-via
therein;
[0027] FIG. 2 is a vertical sectional front view schematically
showing an electroplating apparatus which is used to carry out an
electroplating method according to the present invention;
[0028] FIG. 3 is a front view of a substrate holder of the
electroplating apparatus shown in FIG. 2;
[0029] FIG. 4 is a plan view of the substrate holder of the
electroplating apparatus shown in FIG. 2;
[0030] FIG. 5 is a bottom view of the substrate holder of the
electroplating apparatus shown in FIG. 2;
[0031] FIG. 6 is a cross-sectional view taken along line K-K of
FIG. 3;
[0032] FIG. 7 is a view of the substrate holder as viewed along the
arrow A in FIG. 6;
[0033] FIG. 8 is a view of the substrate holder as viewed along the
arrow B in FIG. 6;
[0034] FIG. 9 is a view of the substrate holder as viewed along the
arrow C in FIG. 6;
[0035] FIG. 10 is a cross-sectional view taken along line D-D of
FIG. 7;
[0036] FIG. 11 is a cross-sectional view taken along line E-E of
FIG. 7;
[0037] FIG. 12 is a cross-sectional view taken along line F-F of
FIG. 3;
[0038] FIG. 13 is a cross-sectional view taken along line G-G of
FIG. 7;
[0039] FIG. 14 is a cross-sectional view taken along line H-H of
FIG. 8;
[0040] FIG. 15 is a front view of an anode holder, which is holding
an insoluble anode therein, of the electroplating apparatus shown
in FIG. 2;
[0041] FIG. 16 is a cross-sectional view of the anode holder, which
is holding the insoluble anode therein, of the electroplating
apparatus shown in FIG. 2;
[0042] FIG. 17 is an enlarged cross-sectional view of the main
portion of another substrate holder;
[0043] FIG. 18 is an enlarged cross-sectional view of the main
portion of the substrate holder shown in FIG. 17;
[0044] FIG. 19 is an enlarged cross-sectional view of the main
portion of the substrate holder shown in FIG. 17;
[0045] FIG. 20 is a graph showing the relationship between the
cathode current density and time for an example of a plating
current that is supplied between a substrate surface and an
anode;
[0046] FIG. 21 is an enlarged fragmentary cross-sectional view
showing the manner in which a plated film is grown preferentially
at the center of a through-hole along the in-depth direction
thereof when a reverse electrolyzing process is performed after a
plating process;
[0047] FIG. 22 is an enlarged fragmentary cross-sectional view
schematically showing the manner in which fine irregularities are
produced by an abnormal deposition on microscopic surfaces of the
plated film in the plating process;
[0048] FIG. 23 is a graph showing the relationship between the
cathode current density and time for another example of a plating
current that is supplied between a substrate surface and an
anode;
[0049] FIGS. 24A and 24B are enlarged fragmentary cross-sectional
views schematically showing the manner in which a plated film
embedded in a through-hole is excessively dissolved into the
plating solution until finally voids are formed in the plated
film;
[0050] FIG. 25 is a graph showing the relationship between the
cathode current density and time for still another example of a
plating current that is supplied between a substrate surface and an
anode;
[0051] FIG. 26 is a graph showing the relationship between the
cathode current density and time for yet another example of a
plating current that is supplied between a substrate surface and an
anode;
[0052] FIG. 27 is a graph showing the relationship between the
cathode current density and time for yet still another example of a
plating current that is supplied between a substrate surface and an
anode;
[0053] FIG. 28 is a graph showing the relationship between the
cathode current density and time for a further example of a plating
current that is supplied between a substrate surface and an
anode;
[0054] FIG. 29 is a graph showing the relationship between the
cathode current density and time for a still further example of a
plating current that is supplied between a substrate surface and an
anode;
[0055] FIG. 30 is a graph showing the relationship between the
cathode current density and time for a yet further example of a
plating current that is supplied between a substrate surface and an
anode;
[0056] FIG. 31 is a graph showing the relationship between the
cathode current density and time for a yet still further example of
a plating current that is supplied between a substrate surface and
an anode; and
[0057] FIG. 32 is a graph showing the relationship between the
cathode current density and time for another example of a plating
current that is supplied between a substrate surface and an
anode.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0058] Preferred embodiments of the present invention will now be
described with reference to the drawings. FIG. 2 is a vertical
sectional front view schematically showing an electroplating
apparatus 50 which is used to carry out an electroplating method
according to the present invention. As shown in FIG. 2, the
electroplating apparatus 50 includes a plating tank 51 holding a
plating solution Q therein, and a substrate holder 10 holding a
substrate W such as a semiconductor wafer or the like and suspended
vertically in the plating solution Q. The plating solution Q with
the substrate holder 10 immersed therein has a surface level L at
the upper end of the plating tank 51, as shown in FIG. 2. Two
insoluble anodes 52 supported on respective anode holders 58 are
disposed in the plating tank 51 in facing relation to respective
opposite surfaces, i.e., face and reverse sides, of the substrate W
held by the substrate holder 10. As shown in FIG. 3, the substrate
holder 10 includes a first holding member 11 having a circular hole
11a defined therein and a second holding member 12 having a
circular hole 12a defined therein. The first holding member 11 and
the second holding member 12 serve to hold the substrate W
therebetween. The insoluble anodes 52 are circular in shape and
substantially identical in size to the circular holes 11a, 12a in
the first and second holding members 11, 12.
[0059] Two regulation plates 60 made of an insulating material are
disposed between the substrate holder 10 and the respective
insoluble anodes 52 in the plating tank 51. The regulation plates
60 have respective circular holes defined therein which are similar
in shape to the circular holes 11a, 12a in the first and second
holding members 11, 12. The insoluble anodes 52 are electrically
connected to respective wires 61a extending from respective
terminals of plating power sources 53 each capable of changing the
direction in which a current supplied thereby and also changing the
value of the current. The plating power sources 53 have other
terminals electrically connected to respective wires 61b which are
connected respectively to terminal plates 27, 28 (see FIG. 3) of
the substrate holder 10. The plating power sources 53 are also
electrically connected to a controller 59 which individually
controls the plating power sources 53.
[0060] Two stirring paddles 62 are disposed between the substrate W
held by the substrate holder 10 and the respective regulation
plates 60 in the plating tank 51. The stirring paddles 62 are
movable back and forth parallel to the substrate W held by the
substrate holder 10 for stirring the plating solution Q. The
electroplating apparatus 50 also includes an outer tank 57 disposed
around the plating tank 51 for holding the plating solution Q which
has overflowed the plating tank 51. The plating solution Q, which
has overflowed the plating tank 51 into the outer tank 57, is
circulated through a constant-temperature unit 55 and a filter 56
back into the plating tank 51 from its bottom by a plating solution
circulation pump 54.
[0061] FIG. 3 is a front view of a substrate holder 10. FIG. 4 is a
plan view of the substrate holder 10. FIG. 5 is a bottom view of
the substrate holder 10. FIG. 6 is a cross-sectional view taken
along line K-K of FIG. 3. FIG. 7 is a view of the substrate holder
10 as viewed along the arrow A in FIG. 6. FIG. 8 is a view of the
substrate holder 10 as viewed along the arrow B in FIG. 6. FIG. 9
is a view of the substrate holder 10 as viewed along the arrow C in
FIG. 6. FIG. 10 is a cross-sectional view taken along line D-D of
FIG. 7. FIG. 11 is a cross-sectional view taken along line E-E of
FIG. 7. FIG. 12 is a cross-sectional view taken along line F-F of
FIG. 3. FIG. 13 is a cross-sectional view taken along line G-G of
FIG. 7. FIG. 14 is a cross-sectional view taken along line H-H of
FIG. 8.
[0062] As shown in FIG. 3, the first holding member 11 and the
second holding member 12, each of a planar shape, of the substrate
holder 10 have respective lower ends pivotally coupled to each
other by a hinge mechanism 13. The hinge mechanism 13 has two hooks
13-1 of synthetic resin, e.g., HTPVC, which are fixed to the second
holding member 12. The hooks 13-1 are angularly movable supported
on a lower end of the first holding member 11 by a hook pin 13-2
made of stainless steel, e.g., SUS 303. The first holding member 11
is made of synthetic resin, e.g., HTPVC, and has a substantially
pentagonal shape. The circular hole 11a is centrally defined in the
first holding member 11, as shown in FIG. 7. As shown in FIG. 3, a
T-shaped hanger 14 made of synthetic resin, e.g., HTPVC, is
integrally formed with an upper end of the first holding member 11.
The second holding member 12 is made of synthetic resin, e.g.,
HTPVC, and has a substantially pentagonal shape. The circular hole
12a is centrally defined in the second holding member 12.
[0063] When the first holding member 11 and the second holding
member 12 are turned about the hinge mechanism 13 into superposed
relation to each other, i.e., when the substrate holder 10 is
closed, the first holding member 11 and the second holding member
12 are held together by left and right clamps 15, 16. The left and
right clamps 15, 16, each made of synthetic resin, e.g., HTPVC,
have respective groove 15a, 16a for receiving therein the side
marginal edges of the first holding member 11 and the second
holding member 12 that are superposed one on the other. The left
and right clamps 15, 16 have lower ends angularly movably supported
on the lower ends of the opposite sides of the first holding member
11 by respective pins 17, 18.
[0064] As shown in FIG. 7, a seal ring 19 is mounted on a surface
of the first holding member 11 which faces the second holding
member 12, and extends around the hole 11a. As shown in FIG. 9, a
seal ring 20 is mounted on a surface of the second holding member
12 which faces the first holding member 11, and extends around the
hole 12a. The seal rings 19, 20 are made of rubber, e.g., silicone
rubber. An O-ring 29 is mounted on the surface of the second
holding member 12 which faces the first holding member 11, and
extends around the seal ring 20.
[0065] The seal rings 19, 20, each of a rectangular cross-sectional
shape, have respective ridges 19a, 20a projecting radially inwardly
from and extending along inner circumferential edges thereof. When
the first holding member 11 and the second holding member 12 are
superposed one on the other with the substrate W interposed
therebetween, the ridges 19a, 20a press the respective surfaces of
the substrate W and are held in close contact therewith, defining a
watertight space free of the plating solution Q between the O-ring
29 and the ridges 19a, 20a that are positioned radially outwardly
of the holes 11a, 12a. As shown in FIGS. 7 and 10, eight substrate
guide pins 21 for positioning the substrate W are mounted on the
surface of the first holding member 11 which faces the second
holding member 12, radially outwardly of the hole 11a, and project
through the seal ring 19.
[0066] As shown in FIGS. 7, 11 and 12, six conductive plates 22 are
mounted on the surface of the first holding member 11 which faces
the second holding member 12 around the hole 11a. As shown in FIG.
11, three out of the six conductive plates 22 are held in electric
contact with the seed layer 104 (see FIGS. 1A through 1D) on one of
the surfaces, e.g., the face side, of the substrate W through
conductive pins 23. As shown in FIG. 12, the other three conductive
plates 22 held in electric contact with the seed layer 104 on the
other surface, e.g., the reverse side, of the substrate W through
conductive pins 23.
[0067] The three conductive plates 22 which are held in electric
contact with the seed layer 104 on one of the surfaces, e.g., the
face side, of the substrate W are electrically connected to
respective electrode terminals 27a, 27b, 27c (see FIG. 4) provided
on the terminal plate 27 of the hanger 14 through insulative
covered wires 26 extending through a wire slot 25 (see FIG. 13).
The other three conductive plates 22 which are held in electric
contact with the seed layer 104 on the other surface, e.g., the
reverse side, of the substrate W are electrically connected to
respective electrode terminals 28a, 28b, 28c (see FIG. 4) provided
on the other terminal plate 28 of the hanger 14 through insulative
covered wires 26 extending through a wire slot 25 (see FIG. 13). As
shown in FIGS. 7 and 13, the insulative covered wires 26 are held
in position by wire holders 30 made of a synthetic resin, e.g.,
PVC.
[0068] The substrate holder 10 operates as follows: When the first
holding member 11 and the second holding member 12 are turned about
the hinge mechanism 13 away from each other, i.e., when the
substrate holder 10 is open, the substrate W is placed in an area
on the first holding member 11 which is surrounded by the eight
substrate guide pins 21. The substrate W is now positioned in place
on the first holding member 11. The first holding member 11 and the
second holding member 12 are turned about the hinge mechanism 13
toward each other, i.e., the substrate holder 10 is closed. The
left and right clamps 15, 16 are then angularly moved about the
pins 17, 18 until the side marginal edges of the first holding
member 11 and the second holding member 12 are inserted in the
respective grooves 15a, 16a of the left and right clamps 15, 16.
The substrate W, which is positioned in place on the first holding
member 11, is now held between the first holding member 11 and the
second holding member 12.
[0069] The O-ring 29 and the ridges 19a, 20a of the seal rings 19,
20 jointly define a watertight space free of the plating solution Q
therebetween. At this time, the outer circumferential edge area of
the substrate W, which is positioned radially outwardly of the
ridges 19a, 20a, is positioned in the watertight space, and the
surface areas of the opposite surfaces of the substrate W, which
are coextensive with the holes 11a, 12a of the first holding member
11 and the second holding member 12, are exposed to the holes 11a,
12a. The three of the six conductive plates 22, which are held in
electric contact with the seed layer 104 on one of the surfaces of
the substrate W, are electrically connected to the electrode
terminals 27a, 27b, 27c provided on the terminal plate 27 of the
hanger 14, and the other three conductive plates 22, which are held
in electric contact with the seed layer 104 on the other surface of
the substrate W, are electrically connected to the electrode
terminals 28a, 28b, 28c provided on the terminal plate 28 of the
hanger 14.
[0070] FIG. 15 is a front view of the anode holder 58, which is
holding the insoluble anode 52 therein, of the electroplating
apparatus shown in FIG. 2, and FIG. 16 is a cross-sectional view of
FIG. 15. In this embodiment, in order to prevent anodes from being
dissolved by an additive(s) of the plating solution, the insoluble
anodes 52, each of which comprises an anode body of titanium coated
with iridium oxide, for example, are used.
[0071] As shown in FIGS. 15 and 16, each of the anode holders 58
includes a holder body 70 having a central hole 70a defined
therein, a closure plate 72 disposed on a reverse side of the
holder body 70 and closing the central hole 70a, a circular support
plate 74 disposed in the central hole 70a of the holder body 70 and
holding the insoluble anode 52 on its surface such that the
insoluble anode 52 is positioned in the central hole 70a, and an
annular anode mask 76 mounted on a face side of the holder body 70
in surrounding relation to the central hole 70a. The support plate
74 has a channel 74a defined therein which houses therein a
conductive plate 78 which is electrically connected to the wire 61a
extending from the plating power source 53. The conductive plate 78
extends to a central area of the support plate 74 where the
conductive plate 78 is electrically connected to the insoluble
anode 52.
[0072] A separating membrane 80 in the form of a neutral membrane
is disposed in covering relation to the surface of the insoluble
anode 52 that is positioned in the central hole 70a of the holder
body 70. The separating membrane 80 has its peripheral edge gripped
in position by the holder body 70 and the anode mask 76, and is
fastened to the holder body 70. The anode mask 76 is fastened to
the holder body 70 by screws 82, and the closure plate 72 is also
fastened to the holder body 70 by screws.
[0073] When the anode holder 58 is immersed in the plating solution
Q, the plating solution Q enters a gap between the insoluble anode
52 and the support plate 74 in the central hole 70a of the holder
body 70.
[0074] The insoluble anode 52 and the separating membrane 80 are
used for the following reasons: An additive to be added to the
plating solution Q includes a component for promoting the formation
of monovalent copper, which impairs the function of other additives
because it causes oxidative decomposition of the other additives.
As a result, soluble anodes cannot be used. When insoluble anodes
are used, the insoluble anodes produce an oxygen gas in the
vicinity thereof, and part of the produced oxygen gas is dissolved
into the plating solution Q, increasing the concentration of
dissolved oxygen. The increased concentration of dissolved oxygen
tends to cause oxidative decomposition of the additives. Therefore,
the separating membrane 80 in the form of a neutral membrane is
desirably disposed in covering relation to the surface of the
insoluble anode 52 to prevent the components of the additives near
the substrate W from being adversely affected even if they are
subject to oxidative decomposition in the vicinity of the insoluble
anode 52.
[0075] It is also desirable to bubble or aerate the plating
solution Q in the vicinity of the insoluble anode 52 with air or
nitrogen supplied via, e.g., an aeration tube, not shown, for
preventing the concentration of dissolved oxygen from being unduly
rising on the insoluble anode 52 side.
[0076] Since the surface of the insoluble anode 52 held by the
anode holder 58 is covered with the separating membrane 80 and the
insoluble anode 52 is disposed to allow the separating membrane 80
to face the substrate W that is held by the substrate holder 10 and
disposed in the plating tank 51, it is possible to prevent an
oxygen gas from being produced in the vicinity of the insoluble
anode 52 and dissolving into the plating solution when the plating
solution Q is bubbled or aerated and hence to prevent the
concentration of dissolved oxygen in the plating solution Q from
increasing.
[0077] The electroplating apparatus 50 thus constructed operates as
follows: The substrate holder 10, which is holding the substrate W
whose face and reverse sides are exposed, is placed in the plating
solution Q in the plating tank 51 such that one of the surfaces of
the substrate W, e.g., the face side thereof, faces one of the
insoluble anodes 52 and the other surface of the substrate W, e.g.,
the reverse side thereof, faces the other insoluble anode 52. The
plating power sources 53 supply plating currents that are
controlled by the controller 59 respectively between the face side
of the substrate W and the insoluble anode 52 which faces the face
side of the substrate W, and between the reverse side of the
substrate W and the insoluble anode 52 which faces the reverse side
of the substrate W, thereby simultaneously plating the face and
reverse sides of the substrate W. If necessary, when the face and
reverse sides of the substrate W are plated, the stirring paddles
62 are moved back and forth parallel to the substrate W to stir the
plating solution Q. In this manner, as shown in FIGS. 1A through
1D, a plated film 106 is grown in the through-hole 100a defined in
the substrate W.
[0078] FIGS. 17 through 19 show enlarged cross-sectional views of
another substrate holder taken in different cross-sectional planes,
respectively. The substrate holder shown in FIGS. 17 through 19 is
different from the above-described substrate holder as follows: As
shown in FIG. 17, the substrate holder includes elastic conductive
plates 90, 92 having respective proximal ends fastened to the first
holding member 11 and the second holding member 12, instead of the
conductive pins 22, 23 shown in FIGS. 11 and 12. When the substrate
W is held by the first holding member 11 and the second holding
member 12, distal free ends of the elastic conductive plates 90, 92
are elastically held against the face and reverse sides,
respectively, of the substrate W in electric contact with the seed
layers 104 (see FIGS. 1A through 1D) on the face and reverse sides
of the substrate W.
[0079] As shown in FIGS. 18 and 19, the substrate holder also
includes seal ring holders 94, 96 for holding the seal rings 19,
20, respectively. The seal ring holders 94, 96 are fastened to the
first holding member 11 and the second holding member 12,
respectively. The seal ring holders 94, 96 have respective arrays
of alternate guide teeth 97, 98 for positioning the substrate W,
instead of the substrate guide pins 21 shown in FIGS. 7 and 10. The
guide teeth 97, 98 are disposed at respective positions along the
circumferential direction of the seal ring holders 94, 96. The
guide teeth 97, 98 have respective tapered surfaces 97a, 98a on
inner peripheral surfaces thereof near free ends thereof. When the
substrate W is held by the first holding member 11 and the second
holding member 12, the outer circumferential edge of the substrate
W is held in contact with and guided by the tapered surfaces 97a,
98a to position the substrate W.
[0080] FIG. 20 shows the relationship between the cathode current
density and time for an example of a plating current that is
supplied between a surface of the substrate W and the insoluble
anode 52 disposed in facing relation to the surface of the
substrate W. The plating current, which is supplied between the
reverse side of the substrate W and the insoluble anode 52 which
faces the reverse side of the substrate W, is held in synchronism
with the plating current which is supplied between the face side of
the substrate W and the insoluble anode 52 which faces the face
side of the substrate W. However, these plating currents do not
need to be synchronized with each other, and hence the present
invention should not be limited by whether the above plating
currents are to be synchronized with each other or not. The
relationship between the cathode current density and time will be
described with reference to FIG. 20 for a plating current that is
supplied between a surface of the substrate W and the insoluble
anode 52 disposed in facing relation thereto.
[0081] In the example shown in FIG. 20, a plating process A in
which a pulsed current is supplied between the surface of the
substrate W and the insoluble anode 52 for plating the surface of
the substrate W for a predetermined period of time, and a reverse
electrolyzing process B in which a current is supplied in a
direction opposite to the current supplied in the plating process A
between the surface of the substrate W and the insoluble anode 52
are alternately repeated. The predetermined period of time for
which the plating process A is carried out is in the range from 50
to 100 ms, for example, and the predetermined period of time for
which the reverse electrolyzing process B is carried out is in the
range from 0.1 to 10 ms, or preferably from 0.5 to 1 ms, for
example.
[0082] As indicated by the imaginary lines in FIG. 20, a quiescent
period C of 0.05 ms, for example, in which no current is supplied
between the surface of the substrate W and the insoluble anode 52
may be inserted after the reverse electrolyzing process B and
before the plating process A. The quiescent period C can uniformize
a metal ion distribution in the plating solution Q within the
through-hole for efficiently filling the plated film into the
through-hole. The quiescent period C may be inserted for its
advantages in each of other examples to be described below.
[0083] In the example shown in FIG. 20, the plating process A is
carried out, using a PR pulsed current which is represented by an
alternate repetition of normal electrolyzing cycles at a pulse
pitch P.sub.1 in which the plating current flows in a forward
direction, i.e., a plating direction, with a positive cathode
current density D.sub.1 in the range from 1 to 3 ASD (A/dm.sup.2),
for example, and reverse electrolyzing cycles at a pulse pitch
P.sub.2 in which the plating current flows in a reverse direction
with a negative cathode current density D.sub.2 in the range from
-0.05 to -4 ASD, for example. The pulse pitch P.sub.2 in the
reverse electrolyzing cycles of the PR pulsed current is of 0.5 ms,
for example. The reverse electrolyzing process B is carried out
with a single pulse at a pulse pitch P.sub.3 in the range from 0.1
to 10 ms, preferably from 0.5 to 1 ms, with a negative cathode
current density D.sub.3 in the range from -30 to -40 ASD, for
example.
[0084] Since the reverse electrolyzing process B with the negative
cathode current density D.sub.3 in the range from -30 to -40 ASD,
for example, is carried out after the plating process A, as
indicated by the imaginary lines in FIG. 21, a plated film 106a,
which tends to be deposited at the corners of the through-hole
100a, is dissolved into the plating solution Q, thereby allowing
the plated film 106 to grow preferentially at the center of the
through-hole 100a along the in-depth direction thereof, as
indicated by the solid lines in FIG. 21.
[0085] As schematically shown in FIG. 22, fine irregularities 106b
are liable to be produced by an abnormal deposition on microscopic
surfaces of the plated film 106 in the plating process. However,
those fine irregularities 106b are prevented from being produced by
the reverse electrolyzing cycles with the negative cathode current
density D.sub.2 in the range from -0.05 to -4 ASD, for example,
according to the example shown in FIG. 20. The fine irregularities
106b due to an abnormal deposition would otherwise be joined to
each other, forming fine voids in the plated film.
[0086] FIG. 23 shows the relationship between the cathode current
density and time for another example of a plating current that is
supplied between a surface of the substrate W and the insoluble
anode 52 disposed in facing relation to the surface of the
substrate W. The example shown in FIG. 23 is different from the
example shown in FIG. 20 in that a reverse electrolyzing process
B.sub.1 is carried out by applying two pulses each at a pulse pitch
P.sub.4 in the range from 0.1 to 10 ms, for example, preferably
from 0.5 to 1.0 ms before and after a normal electrolyzing cycle in
which the plating current is applied in the forward direction.
[0087] The reverse electrolyzing process B with the negative
cathode current density D.sub.3 in the range from -30 to -40 ASD,
as shown in FIG. 20, is carried out with the single pulse at the
pulse pitch P.sub.3 in the range from 0.1 to 10 ms. If the pulse
pitch P.sub.3 is greater than 1 ms, then as schematically shown in
FIG. 24A, the plated film 106 is excessively dissolved into the
plating solution, forming excessively dissolved regions 112. As
shown in FIG. 24B, the excessively dissolved regions 112 have their
open ends closed, tending to produce cat-eyed voids 114 within the
plated film 106 embedded in the through-hole 110a. Therefore, the
pulse pitch P.sub.3 should preferably in the range from 0.1 to 1.0
ms, and more preferably in the range from 0.5 to 1.0 ms.
[0088] However, depending on the aspect ratio of a through-hole
defined in the substrate W, it may not be possible to perform an
ideal embedding process for ideally embedding a plated film
preferentially at the center of the through-hole along the in-depth
direction thereof according to a reverse electrolyzing process
using a single pulse having a pulse pitch that is shorter than 1.0
ms. The reverse electrolyzing process B.sub.1 that is carried out
by applying two pulses, each at the pulse pitch P.sub.4 shorter
than 1.0 ms, as shown in FIG. 23, makes it possible to ideally fill
a plated film into such a through-hole.
[0089] FIG. 25 shows the relationship between the cathode current
density and time for still another example of a plating current
that is supplied between a surface of the substrate W and the
insoluble anode 52 disposed in facing relation to the surface of
the substrate W. The example shown in FIG. 25 includes three
different plating processes, i.e., a plating process (first plating
process) A.sub.1 in a first zone until the plated film 106 in the
through-hole 100a is joined substantially at the center thereof
along the in-depth direction of the through-hole 100a, as shown in
FIGS. 1A through 1C, a plating process (second plating process)
A.sub.2 in a second zone for embedding the plated film 106 to a
predetermined thickness in the recesses 108 in the through-hole
100a, as shown in FIGS. 1C and 1D, and a plating process (third
plating process) A.sub.3 in a third zone in which the danger of a
pinch-off is reduced after the stage shown in FIG. 1D.
[0090] In FIG. 25, the first plating process A.sub.1, the second
plating process A.sub.2 and the third plating process A.sub.3 are
shown as being carried out once each before and after the reverse
electrolyzing process B (see FIG. 20). However, each of the first
plating process A.sub.1, the second plating process A.sub.2 and the
third plating process A.sub.3 is actually carried out a number of
times before and after the reverse electrolyzing process B. This
also applies to each of other examples to be described below.
[0091] In the example shown in FIG. 25, each of the first plating
process A.sub.1, the second plating process A.sub.2 and the third
plating process A.sub.3 is carried out with an on/off pulsed
current which is represented by an alternate repetition of the
supply and non-supply of a plating current which flows in the
forward direction, i.e., the plating direction, and has a positive
cathode current density D.sub.1 in the range from 1 to 3 ASD, for
example. The on/off pulsed current in the first plating process
A.sub.1 has a pulse pitch P.sub.5 shorter than the pulse pitch
P.sub.6 of the on/off pulsed current in the second plating process
A.sub.2 (P.sub.5<P.sub.6), and the pulse pitch P.sub.6 of the
on/off pulsed current in the second plating process A.sub.2 is
shorter than the pulse pitch P.sub.7 of the on/off pulsed current
in the third plating process A.sub.3 (P.sub.6<P.sub.7). The
on/off pulsed currents in the first, second and third plating
processes A.sub.1, A.sub.2, A.sub.3 have respective downtime
pitches P.sub.8, P.sub.9, P.sub.10 of the respective on/off pulsed
currents equal to each other (P.sub.8=P.sub.9=P.sub.10). Therefore,
the cathode current density on average increases stepwise.
Alternatively, the cathode current density on average may increase
gradually linearly.
[0092] Since the on/off pulsed currents provide non-plating periods
for supplying no plating current in the overall plating process,
the metal ion concentration in the plating solution within the
through-hole is recovered in the non-plating periods, for thereby
preventing defects such as voids or the like from being formed in
the plated film. As the through-hole is gradually filled with the
plated film in the plating process, the substantive aspect ratio of
the through-hole changes. When the substantive aspect ratio of the
through-hole changes, it is possible to efficiently fill the plated
film into the through-hole in a manner to match the changing
substantive aspect ratio of the through-hole by increasing the
cathode current density on average in the plating process.
Consequently, the period of time required to plate the substrate
can be further shortened.
[0093] It is generally known in the art to increase the plating
current density stepwise as the plating process progresses.
However, it is difficult to inhibit the generation of monovalent
copper over a full range of plating current densities from a low
plating current density to a high plating current density.
According to this example, since the cathode current density has a
constant peak value to inhibit the generation of monovalent copper,
the plating solution can be prevented from being degraded.
[0094] FIG. 26 shows the relationship between the cathode current
density and time for yet another example of a plating current that
is supplied between a surface of the substrate W and the insoluble
anode 52 disposed in facing relation to the surface of the
substrate W. The example shown in FIG. 26 is different from the
example shown in FIG. 25 in that the reverse electrolyzing process
B.sub.1 shown in FIG. 23 is carried out by applying two pulses each
at the pulse pitch P.sub.4 in the range from 0.1 to 10 ms, for
example, preferably from 0.5 to 1.0 ms, instead of the reverse
electrolyzing process B shown in FIG. 25 with the single pulse at
the pulse pitch P.sub.3 in the range from 0.1 to 10 ms, preferably
from 0.5 to 1 ms, for example.
[0095] FIG. 27 shows the relationship between the cathode current
density and time for yet still another example of a plating current
that is supplied between a surface of the substrate W and the
insoluble anode 52 disposed in facing relation to the surface of
the substrate W. The example shown in FIG. 27 is different from the
example shown in FIG. 25 in that the first, second and third
plating processes A.sub.1, A.sub.2, A.sub.3 have respective
processing times which are equal to each other, the on/off pulsed
current in the first plating process A.sub.1 has a pulse pitch
P.sub.5 shorter than the pulse pitch P.sub.6 of the on/off pulsed
current in the second plating process A.sub.2 (P.sub.5<P.sub.6),
the pulse pitch P.sub.o of the on/off pulsed current in the second
plating process A.sub.2 is shorter than the pulse pitch P.sub.7 of
the on/off pulsed current in the third plating process A.sub.3
(P.sub.6<P.sub.7), the downtime pitch P.sub.8 of the on/off
pulsed current in the first plating process A.sub.1 is longer than
the downtime pitch P.sub.9 of the on/off pulsed current in the
second plating process A.sub.2 (P.sub.8>P.sub.9), and the
downtime pitch P.sub.9 of the on/off pulsed current in the second
plating process A.sub.2 is longer than the downtime pitch P.sub.10
of the on/off pulsed current in the third plating process A.sub.3
(P.sub.9>P.sub.10). Therefore, the cathode current density on
average increases stepwise.
[0096] FIG. 28 shows the relationship between the cathode current
density and time for a further example of a plating current that is
supplied between a surface of the substrate W and the insoluble
anode 52 disposed in facing relation to the surface of the
substrate W. The example shown in FIG. 28 is different from the
example shown in FIG. 25 in that it uses a composite pulsed power
source for supplying a first plating current with a positive
cathode current density D.sub.1 ranging from 1 to 3 ASD, for
example, and a second plating current with a positive cathode
current density D.sub.4 ranging from 0.1 to 0.5 ASD, for example,
instead of the power source for supplying the on/off pulsed current
by repeating the supply and non-supply of a plating current which
flows in the forward direction, i.e., the plating direction, and
has a positive cathode current density D.sub.1 in the range from 1
to 3 ASD, for example.
[0097] Since the composite pulsed power source is used to
continuously supply a weak current in the range from 0.1 to 0.5
ASD, for example, rather than stopping to supply the plating
current, the plated film is continuously grown in the plating
process. Therefore, the plated film is prevented from being
dissolved into the plating solution in the plating process.
[0098] FIG. 29 shows the relationship between the cathode current
density and time for a still further example of a plating current
that is supplied between a surface of the substrate W and the
insoluble anode 52 disposed in facing relation to the surface of
the substrate W. The example shown in FIG. 29 is different from the
example shown in FIG. 25 in that a PR pulsed current is supplied by
repeating normal electrolyzing cycles with a positive cathode
current density D.sub.1 in the range from 1 to 3 ASD, for example,
and reverse electrolyzing cycles with a negative cathode current
density D.sub.2 in the range from -0.05 to -4 ASD, for example,
rather than the on/off pulsed current supplied by repeating the
supply and non-supply of a plating current with a positive cathode
current density in the range from 1 to 3 ASD, for example.
[0099] FIG. 30 shows the relationship between the cathode current
density and time for a yet further example of a plating current
that is supplied between a surface of the substrate W and the
insoluble anode 52 disposed in facing relation to the surface of
the substrate W. The example shown in FIG. 30 is different from the
example shown in FIG. 25 in that it carries out first, second and
third plating processes A.sub.1, A.sub.2, A.sub.3 successively, by
supplying a DC plating current with a positive cathode current
density D.sub.1 in the range from 1 to 3 ASD, for example, the
first, second and third plating processes A.sub.1, A.sub.2, A.sub.3
having respective processing times that are progressively longer in
this order (A.sub.1<A.sub.2<A.sub.3).
[0100] Depending on the aspect ratio of a through-hole, the
structure of a plating underlayer, the nature of the plating
solution, etc., there may be no need to provide a quiescent period
between reverse electrolyzing processes. If no quiescent period is
required, then a plating current may be supplied between the
surface of the substrate W and the insoluble anode 52 to achieve
the relationship between the cathode current density and time shown
in FIG. 30 for thereby shortening the time required to perform the
plating process to efficiently fill the plated film into the
through-hole.
[0101] FIG. 31 shows the relationship between the cathode current
density and time for a yet still further example of a plating
current that is supplied between a surface of the substrate W and
the insoluble anode 52 disposed in facing relation to the surface
of the substrate W. The example shown in FIG. 31 is different from
the example shown in FIG. 20 in that when the plated film 106 is
embedded to a predetermined thickness in the recesses 108 in the
through-hole 100a, as shown in FIG. 1D, so that the danger of a
pinch-off is reduced, for example, the reverse electrolyzing
process B is followed by a plating process A.sub.4 which is carried
out by supplying a DC plating current with a positive cathode
current density D.sub.1 in the range from 1 to 3 ASD, for example.
At the stage wherein the danger of a pinch-off is reduced, the
embedding of the plated film in the through-hole 100a in the
substrate W is essentially completed, as shown in FIG. 1D, and
dimples left on the surface of the substrate are to be finally
filled up. At this time, it is not necessary to supply a DC plating
current to equalize the cathode current density with a previous
pulse peak current density, but a DC plating current may be
supplied to make the cathode current density higher than a previous
pulse peak current density, thereby shortening the time required to
perform the plating process.
[0102] FIG. 32 shows the relationship between the cathode current
density and time for another example of a plating current that is
supplied between a surface of the substrate W and the insoluble
anode 52 disposed in facing relation to the surface of the
substrate W. The example shown in FIG. 32 is different from the
example shown in FIG. 27 in that the third plating process A.sub.3
is performed by supplying a DC plating current with a positive
cathode current density D.sub.1 in the range from 1 to 3 ASD, for
example, thereby shortening the time required to perform the
plating process.
[0103] Although certain preferred embodiments of the present
invention have been shown and described in detail, it should be
understood that various changes and modifications may be made
therein without departing from the scope of the appended
claims.
* * * * *