U.S. patent application number 11/360685 was filed with the patent office on 2006-07-06 for substrate plating method and apparatus.
Invention is credited to Akihisa Hongo, Tetsuma Ikegami, Hiroaki Inous, Ryoichi Kimizuka, Megumi Maruyama, Koji Mishima, Mizuki Nagai, Naoaki Ogure, Shuichi Okuyama, Satoshi Sendai.
Application Number | 20060144714 11/360685 |
Document ID | / |
Family ID | 27286894 |
Filed Date | 2006-07-06 |
United States Patent
Application |
20060144714 |
Kind Code |
A1 |
Hongo; Akihisa ; et
al. |
July 6, 2006 |
Substrate plating method and apparatus
Abstract
A method and apparatus plate a substrate to form wiring by
efficiently filling a fine recess formed in a semiconductor
substrate with plating metal without a void or contamination. The
plating of the substrate to fill a wiring recess formed in the
semiconductor substrate with plating metal includes performing an
electroless plating process of forming an initial layer on the
substrate, and performing an electrolytic plating process of
filling the wiring recess with the plating metal, while the initial
layer serves as a feeding layer.
Inventors: |
Hongo; Akihisa; (Tokyo,
JP) ; Ogure; Naoaki; (Tokyo, JP) ; Inous;
Hiroaki; (Tokyo, JP) ; Sendai; Satoshi;
(Tokyo, JP) ; Ikegami; Tetsuma; (Tokyo, JP)
; Mishima; Koji; (Tokyo, JP) ; Okuyama;
Shuichi; (Tokyo, JP) ; Nagai; Mizuki; (Tokyo,
JP) ; Kimizuka; Ryoichi; (Tokyo, JP) ;
Maruyama; Megumi; (Kanagawa, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
27286894 |
Appl. No.: |
11/360685 |
Filed: |
February 24, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09762582 |
Apr 12, 2001 |
7033463 |
|
|
PCT/JP99/04349 |
Aug 11, 1999 |
|
|
|
11360685 |
Feb 24, 2006 |
|
|
|
Current U.S.
Class: |
205/296 ;
205/291; 257/E21.175; 257/E21.585 |
Current CPC
Class: |
C23C 18/1682 20130101;
C25D 7/123 20130101; H05K 3/107 20130101; H01L 21/76874 20130101;
H01L 21/2885 20130101; H05K 3/241 20130101; C23C 18/38 20130101;
H01L 21/76877 20130101; H05K 3/423 20130101; C25D 3/38 20130101;
H01L 2221/1089 20130101; C23C 18/1653 20130101; C23C 18/1632
20130101; H01L 21/76843 20130101; H01L 21/76873 20130101; C25D
17/001 20130101 |
Class at
Publication: |
205/296 ;
205/291 |
International
Class: |
C25D 3/38 20060101
C25D003/38 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 11, 1998 |
JP |
10-239490 |
Feb 8, 1999 |
JP |
11--30230 |
Aug 3, 1999 |
JP |
11-220363 |
Claims
1-11. (canceled)
12. A method of plating a substrate to fill a wiring recess formed
in the substrate with copper, said method comprising: performing an
electrolytic plating process to fill the wiring recess with copper
while using an electrolytic plating liquid including: i) copper
sulfate (CuSO.sub.4.5H.sub.2O) having a concentration of 100 to 250
g/l, ii) sulfuric acid (H.sub.2SO.sub.4) having a concentration of
10 to 100 g/l, iii) chlorine ions having a concentration of 0 to
100 mg/l, iv) a sulfur compound having a concentration of at least
0.14 to 70 .mu.mol/l, v) a macromolecular compound having a
concentration of 10 to 5000 mg/l, and vi) a nitrogen compound
having a concentration of 0.01 to 100 mg/l.
13. The method as recited in claim 12, wherein the sulfur compound
is expressed by a formula X-L-(S).sub.n-L-X where L is an alkyl
group having a carbon number of 1 to 6 which is substituted by a
lower alkyl group, a lower alkoxyl group, a hydroxyl group, or a
halogen atom; n is an integer; and X is a hydrogen atom, a
--SO.sub.3M group, or a --PO.sub.3M group; and M indicates a
hydrogen atom, an alkali metal atom, or an amino group.
14. The method as recited in claim 12, wherein the macromolecular
compound is expressed by a formula ##STR2## where R.sub.1 indicates
a residue of a higher alcohol group having a carbon number of 8 to
25, a residue of an alkyl phenol with an alkyl group having a
carbon number of 1 to 25, a residue of an alkyl naphthol with an
alkyl group having a carbon number of 1 to 25, a residue of a fatty
acid amide having a carbon number of 3 to 22, a residue of an
alkylamine having a carbon number of 2 to 4, or a hydroxyl group;
R.sub.2 and R.sub.3 indicate a hydrogen atom or a methyl group; and
m and k indicate an integer from 1 to 100.
Description
[0001] This application is a divisional application of application
Ser. No. 09/762,582, which is a U.S. national stage application of
International Application Serial No. PCT/JP99/04349, filed Aug. 11,
1999.
TECHNICAL FIELD
[0002] The present invention relates to a method and apparatus for
plating a substrate, and more particularly to a method and
apparatus for plating a substrate to fill a wiring recess formed in
a semiconductor substrate with wiring metal such as copper, copper
alloy, or the like.
BACKGROUND ART
[0003] Conventionally, in order to form a wiring circuit on a
semiconductor substrate, a layer of Al or Al alloy is deposited on
a surface of a substrate by a sputtering process or the like, and
then unnecessary portions are removed from the layer by a chemical
dry etching process using a photoresist or the like for a mask
pattern. However, as the level of integration of circuits
increases, the width of wiring becomes narrower to thus increase
current density, resulting in generating thermal stress in the
wiring and increasing temperature of the wiring. As a result, the
layer of Al or Al alloy becomes thinner due to stress migration or
electromigration, and finally to cause a breaking of the
wiring.
[0004] Hence, copper has been drawn much attention as a wiring
material because of its lower resistance and higher reliability.
However, it is difficult to form wiring by etching after a layer is
deposited on a surface of a substrate and then performing a
patterning process, which is different from a conventional method
using Al. Therefore, there has been attempted a damascene process
in which a wiring groove is preformed in a substrate and filled
with copper by chemical vapor deposition (CVD), sputtering,
plating, or the like, and then unnecessary portions are removed
from the surface of the substrate by chemical mechanical polishing
(CMP), for thereby forming wiring in the groove.
[0005] Among these processes for filling a wiring groove with
copper, the plating process has drawn much attention because of the
following advantages. The processing cost is lower than that in
other processes, and pure copper material can be obtained, and the
process can be performed at such a low temperature that a substrate
is not damaged. The plating process mainly comprises an electroless
plating process, which is mainly performed by a chemical process,
and an electrolytic plating process, which is performed by an
electrochemical process. The electrolytic plating process is
generally more efficient than the electroless plating process.
[0006] Since copper is liable to be oxidized and corroded and
diffused into SiO.sub.2, wiring is generally formed after a wiring
portion on a base material of the substrate is covered with a
barrier layer of metal nitride such as TiN, TaN, and WN. Since the
sheet resistance of this barrier layer is prohibitively larger than
the resistance of the plating liquid, it has been difficult to
perform uniform electrolytic plating on the barrier layer formed
over the surface of the substrate.
[0007] Conventionally, a seed layer of copper is formed on the
barrier layer by a sputtering process or a CVD process, and then
plated with copper by an electrolytic plating process to fill fine
recesses formed in the substrate with copper. However, it is
difficult to uniformly deposit a layer on a wall of the fine recess
by the sputtering process, and the CVD process introduces
impurities into the deposited layer. Further, when the design rule
is further decreased from about 0.18 .mu.m to 0.10 .mu.m, there is
no dimensional margin to form a seed layer having a thickness of
0.02 to 0.05 .mu.m within the recess.
[0008] On the other hand, in the electroless plating process, since
the plating layer is grown in isogonic directions from a side wall
or a bottom surface of the fine recess, an inlet of the recess is
covered with metal grown from the side wall and hence, a void tends
to be formed in the recess. In addition, since the plating rate of
the electroless plating process is about one-tenth as slow as that
of the electrolytic plating process, the electroplating process is
inefficient.
SUMMARY OF THE INVENTION
[0009] It is therefore an object of the present invention to
provide a method and apparatus for plating a substrate to form
wiring by efficiently filling a fine recess formed in a
semiconductor substrate with plating metal without a void or
contamination.
[0010] When formalin (HCHO) is used in the electroless plating
process as a reducing agent, hydrogen gas (H.sub.2) is generated
according to the following reaction. Cu 2 + + 2 .times. H .times.
.times. C .times. .times. H .times. .times. O + 4 .times. O .times.
.times. H - -> Cu 2 + + 2 .times. H .times. .times. C .times.
.times. H .times. .times. O .times. .times. O - + H 2 + 2 .times. H
2 .times. O + 2 .times. e - -> Cu + 2 .times. H .times. .times.
C .times. .times. O .times. .times. O - + H 2 + 2 .times. H 2
.times. O ##EQU1##
[0011] When a plating surface of a substrate W faces downwardly or
sideways, as shown in FIGS. 16A and 16B, bubbles 98 are generated
by hydrogen gas (H.sub.2) in a plating liquid Q within recesses 42,
such as fine grooves or the like, formed in the substrate, and
these bubbles cause a plating defect 99. In order to prevent the
generation of these plating defects 99, a pump or air is generally
used to agitate the plating liquid in the conventional plating
process. However, as shown in FIG. 16B, unevenly plated portions
100 are generated on a plating surface 97 of the substrate W in the
direction that the hydrogen gas bubbles 98 move, indicated by an
arrow A.
[0012] In order to remove the bubbles 98 from the plating surface
97, the conventional methods employ a jig to grip or suspend the
plating substrate W, while a shock is applied externally to the jig
to separate the bubbles from the plating surface 97. However, since
there is risk that the shock will damage the jig or the plating
substrate, this method is not desirable.
[0013] A conventional electroless plating apparatus comprises a
plating processing tank and a plating liquid circulating tank, and
a plating liquid is circulated during the plating process. The
plating liquid is prepared in a special preparation bath or in the
circulating tank. Therefore, problematic reactions specific to the
electroless copper plating, such as a Cannizzaro reaction or a
disproportionation, occur in the electroless plating liquid
immediately after preparation to cause deterioration of the plating
liquid and changes in concentration of the plating liquid
composition.
[0014] Accordingly, it is another object of the present invention
to provide a method and apparatus for electroless plating which can
minimize the amount of plating defects and unevenly plated portions
and can prevent deterioration of a plating liquid and changes in
concentration of the plating liquid composition to perform a
plating process with a highly stable quality.
[0015] In the conventional electrolytic plating, in order to grow a
uniform layer in through holes formed in a printed circuit board
using copper plating, the concentration of copper in the plating
liquid is lowered to improve the throwing power (in a high throwing
power bath). This is because the overvoltage of a cathode is
increased by increasing the polarization of the cathode to improve
the throwing power. A degree of liquid flow through the holes can
be expected when the dimensions of the holes in the printed circuit
board are about 50 to 100 .mu.m.
[0016] The wiring grooves or holes formed in a surface of a
semiconductor wafer have a width or diameter of 0.2 .mu.m or less
and do not pass through the substrate. Hence, it is impossible to
flow a liquid through such fine grooves or holes. Further, the
electrophoresis speed generated by the electric field is
numerically small, and hence the holes are filled with copper ions
almost entirely by the diffusion of ion concentration. The amount
of diffusion of copper ions in the holes decreases in proportion to
the second power of the hole diameter (the area of the inlet of the
hole) as the hole diameter decreases.
[0017] In contrast, the amount of deposition of copper ions in the
hole grows smaller in proportion to the diameter of the hole.
Accordingly, copper ions can be expected to be diffusion-controlled
in grooves and holes, as semiconductor devices become more
integrated and the width of grooves and diameters of holes become
smaller in the future. When the hole diameters drop below 0.15
.mu.m, in particular, copper ions tend to be diffusion-controlled
depending on a methods of agitating plating liquid for a large
aspect ratio.
[0018] Therefore, it is another object of the present invention to
provide a method and apparatus of electrolytic plating capable of
sufficiently filling a fine groove and a hole formed in a surface
of a substrate using a copper plating without copper ions becoming
diffusion-controlled in the groove and the hole, even when the
width of the groove and the diameter of the hole become smaller and
the integration in the semiconductor devices increases.
[0019] According to a first aspect of the present invention, there
is provided a method of plating a substrate to fill a wiring recess
formed in a semiconductor substrate with plating metal, the method
comprising: performing an electroless plating process of forming an
initial layer on a substrate; and performing an electrolytic
plating process of filling the wiring recess with plating metal
while the initial layer serves as a feeding layer.
[0020] With this method, an initial plating layer (seed layer) is
formed with an electroless plating process, and then the recess in
the substrate is filled with electrolytic plating metal while the
initial layer serves as the feeding layer. Accordingly, an
electroless plating process with high uniformity is combined with
an electrolytic plating process having good qualities in leveling
and high-speed filling. The recess having a barrier layer of a high
electrical resistance can efficiently be filled with a void-free
wiring metal, without the sputtering process or the CVD process in
a series of plating processes. By filling the greatest portion of
the recess formed on the feeding layer with the electrolytic
plating, it is possible to maintain a high plating speed and
increase throughput.
[0021] The electroless plating process and the electrolytic plating
process may be performed in the same plating processing tank or in
separate processing tanks. Further, the same plating liquid may be
used in the same plating processing tank to perform both of the
electroless plating process for forming an initial layer serving as
a feeding layer and the electrolytic process for filling the
recess. With this method, both of the plating processes can
continuously be performed without changing the processing tank or
the plating liquid, for thereby simplifying the apparatus and
process while achieving the above effects.
[0022] According to a second aspect of the present invention, there
is provided an apparatus for plating a substrate to fill a wiring
recess in a semiconductor substrate with plating metal, the
apparatus comprising: an electroless plating tank for forming an
initial layer on a substrate by electroless plating; an
electrolytic plating tank for filling the wiring recess with
plating metal while the initial layer serves as a feeding layer;
and transfer means for transferring a substrate between the
tanks.
[0023] With this apparatus, an initial plating layer (seed layer)
is formed with an electroless plating process, and then the recess
in the substrate is filled with electrolytic plating metal while
the initial layer serves as the feeding layer. Accordingly, the
recess having a barrier layer of a high electrical resistance can
efficiently be filled with a void-free wiring metal, without the
sputtering process or the CVD process in a series of plating
processes. The electroless plating tank and the electrolytic
plating tank should preferably be disposed in close proximity to
each other within the same space and separated by a partition.
[0024] By providing a substrate transfer means in addition to the
electroless tank and the electrolytic plating tank, it is possible
to continue from one process to the next process without changing
the state of the surface of the substrate when transferring the
substrate. Specifically, the electroless plating tank, the
electrolytic plating tank, and required rinse tanks should
preferably be arranged in close proximity to each other, and the
substrate should be transferred after the plating process or the
rinsing process, without exposing the surface of the substrate to
the air. Such a function may also be provided in the transfer means
itself.
[0025] According to a third aspect of the present invention, there
is provided a method or apparatus for plating a substrate according
to the first or second aspect, comprising in the electroless
plating process or the electroless plating bath: means for
disposing a substrate to be plated in such a state that a surface
to be processed thereof faces upwardly, and forming a hermetically
sealed space by the surface to be processed; and plating liquid
supply means for supplying an electroless plating liquid to the
hermetically sealed space to perform an electroless plating
process.
[0026] By facing the plating surface of the substrate to be plated
upwardly, nitrogen gas bubbles certainly generated in the plating
liquid in the electroless plating process will moved upwardly due
to buoyancy. Accordingly, the number and the amount of bubbles
remaining on the plating surface of the plating substrate and in
the fine groove and hole can be reduced, thereby reducing the
plating defects.
[0027] According to a fourth aspect of the present invention, there
is provided a method or apparatus for plating a substrate according
to the third aspect, wherein the minimum amount of electroless
plating liquid required for performing a predetermined plating on
the substrate to be plated is supplied to the hermetically sealed
space, and the electroless plating process is performed with the
electroless plating liquid in a static state. Since this method
does not move the nitrogen gas bubbles over the plating surface, it
is possible to minimize the unevenly plated portions that are
generated on the plating surface, as shown in FIG. 17.
[0028] According to a fifth aspect of the present invention, there
is provided a method or apparatus for plating a substrate according
to the third or fourth aspects, further comprising: pressure
pulsation means for generating a pressure in the hermetically
sealed space that is higher than atmospheric pressure and for
pulsating the pressure.
[0029] According to the present invention, since the hydrogen gas
bubbles can be encouraged to dissolve into the electroless plating
liquid by pressurization, it is possible to encourage the nitrogen
gas bubbles to separate from the plating surface. Specifically, the
nitrogen gas bubbles 98 attached to the plating surface 97 of the
plating substrate W, as shown in FIG. 11A, are contracted by
pressurization, as shown in FIG. 11B, to separate from the plating
surface 97. The nitrogen gas bubbles 98 are expanded by
decompression, as shown in FIG. 11C, to separate completely from
the plating surface 97.
[0030] According to a sixth aspect of the present invention, there
is provided a method or apparatus for plating a substrate according
to any one of the third through fifth aspects, further comprising a
preparation bath disposed in the vicinity of the hermetically
sealed space for supplying the minimum amount of prepared
electroless plating liquid to the hermetically sealed space just
prior to the electroless plating process.
[0031] According to the present invention, the plating process is
completed before an occurrence of problematic reactions specific to
the electroless copper plating, such as a Cannizzaro reaction or a
disproportionation, which cause deterioration of the plating liquid
and changes in concentration of the plating liquid composition
immediately after the preparation. Therefore, the plating process
can be performed with a highly stable quality.
[0032] According to a seventh aspect of the present invention,
there is provided a method or apparatus for plating a substrate
according to the sixth aspect, wherein the electroless plating
liquid is processed as a waste liquid without circulating the
electroless plating liquid after performing the electroless plating
process with the minimum amount of electroless plating liquid.
[0033] According to the present invention, since the amount of
plating liquid used per deposition (deposition of plating layer)
can be maintained to be the minimum required amount, it is possible
to avoid increases in cost with the waste liquid and an excessive
burden on the environment.
[0034] The plating substrate may be held on a turntable in the
electroless plating tank to be rinsed and dried after the plating
process. With this arrangement, the plating, rinsing, and drying
processes can all be performed in the same area, thereby reducing
the space required for device installation and making the device
suitable for installation in a clean room.
[0035] A hot bath for maintaining temperature may be provided in
the electroless plating tank in the vicinity of the top of the
hermetically sealed space, and a heater for maintaining temperature
may be disposed below the plating substrate. With this arrangement,
it is possible to maintain a fixed plating temperature, which is
one of the most important factors governing the quality (uniformity
of layer thickness, reproducibility, electric conductivity of the
plating layer, etc.) of electroless plating.
[0036] In the electroless plating process, the minimum required
amount of electroless plating liquid may be set within a range of
amount of liquid that includes ions of solutes 1.5 to 20 times as
many as a predetermined deposited metal equivalent. In the
electroless plating process, the pressure pulsation means may be
configured to generate pressure pulsations having an amplitude of 0
to 1 MPa and a frequency of 0 to 10 Hz.
[0037] According to an eighth aspect of the present invention,
there is provided a method or apparatus for plating a substrate
according to the first or second aspects, wherein the plating
liquid used in the electroless plating process or the electroless
plating bath comprises copper sulfate (CuSO.sub.4.5H.sub.2O) having
a concentration of 100 to 250 g/l, sulfuric acid (H.sub.2SO.sub.4)
having a concentration of 10 to 100 g/l, and chlorine ions having a
concentration of 0 to 100 mg/l.
[0038] According to a ninth aspect of the present invention, there
is provided a method or apparatus for plating a substrate according
to the eighth aspect, wherein the electrolytic plating liquid
further comprises at least 0.14 to 70.mu. mol/l of a sulfur
compound expressed by a formula [A] below, 10 to 5000 mg/l of a
macromolecular compound expressed in a formula [B] below, and 0.01
to 100 mg/l of a nitrogen compound; wherein L is an alkyl group
having a carbon number of 1 to 6 which is substituted by a lower
alkyl group, a lower alkoxyl group, a hydroxyl group, or a halogen
atom; and X is a hydrogen atom, a --SO.sub.3M group, or a
--PO.sub.3M group (M indicating a hydrogen atom, an alkali metal
atom, or an amino group) in the formula [A]; and R.sub.1 indicates
a residue of a higher alcohol group having a carbon number of 8 to
25, a residue of an alkyl phenol with an alkyl group having a
carbon number of 1 to 25, a residue of an alkyl naphthol with an
alkyl group having a carbon number of 1 to 25, a residue of a fatty
acid amide having a carbon number of 3 to 22, a residue of an
alkylamine having a carbon number of 2 to 4, or a hydroxyl group;
R.sub.2 and R.sub.3 indicate a hydrogen atom or a methyl group; and
m and k indicate an integer from 1 to 100 in the formula [B].
##STR1##
[0039] Since increases in copper concentration in the plating
liquid generate proportional increases in the diffusion speed, it
is possible to prevent copper ions from becoming
diffusion-controlled in the groove and the hole, even when the
width of the groove and the diameter of the hole become smaller and
the integration in the semiconductor devices increases. Of course,
it is also possible to produce a thinner diffusion layer and
suppress the current density by agitating the plating liquid.
[0040] FIG. 18 is a graph comparing diffusion amount and deposition
amount in a hole H of 1.2 .mu.m shown in FIG. 19. In FIG. 18, the
vertical axis represents the amount of copper deposition and the
amount of copper diffusion (g/s), and the horizontal axis
represents the diameter .phi. (.mu.m) of the hole H. Here, the
diffusion coefficient is set at 0.72.times.10.sup.-9 m.sup.2/s and
the diffusion layer thickness at 5 .mu.m. When the diffusion amount
is greater than the deposition amount, the ions become
reaction-controlled to prevent a depletion in copper ions in the
hole H and the generation of voids therein. When the diffusion
layer is less than the deposition amount, the ions become
diffusion-controlled, and voids are generated in the hole H. As
seen in FIG. 18, higher concentrations of copper sulfate are
advantageous when the hole diameter becomes finer, while the
sulfuric acid concentration relatively declines due to the
relationship with saturated concentration. By reducing the sulfuric
acid concentration, the electrical resistance of the plating liquid
increases, improving the uniformity of the deposited layer
thickness.
[0041] In FIG. 18, a curve A indicates the diffusion amount (per
second) when the copper sulfate concentration is 225 g/l, a curve B
indicates the deposition amount (per second) when the current
density is 3 A/dm.sup.2, a curve C indicates the deposition amount
(per second) when the current density is 2.5 A/dm.sup.2, a curve D
indicates the deposition amount (per second) when the current
density is 2 A/dm.sup.2, and a curve E indicates the diffusion
amount (per second) when the copper sulfate concentration is 75
g/l.
[0042] As described above, the plating liquid includes the sulfur
compound shown in equation [A] of 0.14 to 40 .mu.mol and the
macromolecular compound shown in equation [B]. This sulfur compound
can achieve a fine deposition. Some examples of these compounds
include N,N-dimethyldithiocarbamylpropylsulfonic acid,
O-ethyl-S-(3-propylsulfonic acid)-dithiocarbonate,
bis-(sulfopropyl) disulfide, and their salts.
[0043] In the present invention, the amount of additive in the
sulfur compound should preferably be 0.14 to 70 .mu.mol/l, since
the amount of copper sulfate is greater than the amount of sulfuric
acid. The amount of additive in the sulfur compound is less than
that in the case where a solution with a low concentration of
copper sulfate is used because the cathode vicinity is rich in
copper ions, requiring less sulfur compound as an accelerating
agent.
[0044] Some examples of a macromolecular organic additive contained
in the plating liquid are PPG and PEG, their random or block
polymers, or a derivative thereof, such as a polyether type. The
amount of macromolecular organic additive is about 10 to 5000
mg/l.
[0045] A leveler is added to the above plating liquid to further
control the copper deposition and accelerate plating growth in the
bottom of the hole. The leveler is a nitrogen compound containing a
polyalkylene imine, such as a phenazine compound, a phthalocyanine
compound, a polyethylene imine, and a polybenzyl ethylene imine, or
a derivative thereof, or a thiourea derivative such as an N-dye
substitute compound, a safranine compound, such as a
phenosafranine, a safranine azo naphthol, a diethyl safranine azo
phenol, and a dimethyl safranine dimethyl aniline, or a
polyepichlorohydrine or a derivative thereof, or a phenylthiazonium
compound such as a thioflavine, or a amide type, such as an
acrylamide, a propylamide, and a polyacrylic acid amide. This
nitrogen compound of about 0.01 to 100 mg/l is added as a
leveler.
[0046] According to the present invention defined in a tenth
aspect, there is provided an apparatus for plating a substrate to
fill a wiring recess formed in a semiconductor substrate with
plating metal, the apparatus comprising: one processing tank having
an electroless plating liquid supply path for supplying an
electroless plating liquid to form an initial layer on a substrate
by an electroless plating process, and an electrolytic plating
liquid supply path for supplying an electrolytic plating liquid to
fill the wiring recess by electrolytic plating while the initial
layer serves as a feeding layer; wherein the two paths are
selectively switchable.
[0047] Hence, an initial plating layer (seed layer) is formed with
an electroless plating process, and then the recess in the
substrate is filled with electrolytic plating metal while the
initial layer serves as the feeding layer. Accordingly, the recess
having a barrier layer of a high electrical resistance can
efficiently be filled with a void-free wiring metal, without the
sputtering process or the CVD process in a series of plating
processes. Since both of the electroless plating process for
forming the initial layer and the electrolytic plating process for
filling the recess can be performed continuously in the same
processing tank, the equipment and time required to transfer the
substrate can be minimized and the state of the surface of the
substrate can be prevented from changing. A cleaning liquid supply
path for cleaning a substrate may be disposed to perform a cleaning
process in the same processing tank.
[0048] The processing tank may be hermetically sealed with a
parallel flow. With this arrangement, a plating liquid can flow
along the surface of the substrate at a high speed even in a small
space to thus perform the efficient plating with sufficient
flowability of the plating liquid.
[0049] According to an eleventh aspect of the present invention,
there is provided a method or apparatus for plating a substrate
according to any one of the first through tenth aspects, wherein
the plating liquid used in the method or apparatus does not include
an alkali metal as a pH regulator.
BRIEF DESCRIPTION OF DRAWINGS
[0050] FIG. 1 is a plan view showing a whole structure of a plating
apparatus according to a first embodiment of the present
invention;
[0051] FIG. 2 is a side view showing a processing tank used in the
plating apparatus of FIG. 1;
[0052] FIG. 3 is a cross-sectional view taken along a line A-A of
the processing tank in FIG. 2;
[0053] FIG. 4 is a schematic view showing the processing tank used
in the plating apparatus in FIG. 1 and circulating paths of a
processing liquid;
[0054] FIG. 5 is a side view of the plating apparatus in FIG.
1;
[0055] FIG. 6 is a flowchart showing processes performed with the
plating apparatus in FIG. 1;
[0056] FIGS. 7A through 7D are schematic diagrams explanatory of a
process of plating a recess formed in a substrate;
[0057] FIG. 8 is a schematic view showing a processing tank used in
a plating apparatus according to a second embodiment of the present
invention;
[0058] FIG. 9 is a plan view showing a whole structure of a plating
apparatus according to a third embodiment of the present
invention;
[0059] FIG. 10 is a schematic view showing a structure of an
electroless plating device in FIG. 9;
[0060] FIGS. 11A through 11C are schematic diagrams explanatory of
the behavior of hydrogen gas bubbles when pressure of a
hermetically sealed space in the electroless plating device is
pulsed;
[0061] FIG. 12 is a schematic view showing a structure of the
electroless plating device in FIG. 9;
[0062] FIG. 13 is a schematic view showing a structure of an
electrolytic plating device in FIG. 9;
[0063] FIG. 14 is an enlarged view of an area B indicated in FIG.
13;
[0064] FIG. 15 is a schematic view showing a processing tank used
in the plating apparatus and circulating paths of a processing
liquid according to the third embodiment of the present
invention;
[0065] FIGS. 16A and 16B are schematic diagrams explanatory of the
behavior of hydrogen gas bubbles in electroless plating, FIG. 16A
shows the behavior of the hydrogen gas bubbles when a plating
surface of a plating substrate faces downwardly, and FIG. 16B shows
the behavior of the hydrogen gas bubbles when the plating surface
of the plating substrate faces sideways;
[0066] FIG. 17 is a schematic diagram explanatory of unevenly
plated portions generated on a plating surface of a plating
substrate by the behavior of hydrogen gas bubbles in electrolytic
plating;
[0067] FIG. 18 is a graph comparing diffusion amount and deposition
amount in holes formed in a plating substrate; and
[0068] FIG. 19 is a schematic view showing an example of a shape of
a hole formed in a surface of a plating substrate.
DETAILED DESCRIPTION OF THE INVENTION
[0069] Embodiments according to the present invention will be
described below with reference to the accompanying drawings. A
plating apparatus is disposed in a rectangular installation frame
10, as shown in FIG. 1. The plating apparatus has a clean zone 13
at one side of the installation frame 10, and load/unload units
14a, 14b and two cleaning and drying devices 60 for post-processing
a substrate, after the plating process, are disposed at the clean
zone 13. A transfer device (first transfer robot) 61 for
transferring a substrate is provided among the load/unload units
14a, 14b and the cleaning and drying devices 60. The plating
apparatus has a contaminated zone 12 at the other side of the
installation frame 10, and a second transfer robot 62 movable on a
rail is disposed at the central portion of the contaminated zone
12. An SnCl.sub.2 solution tank 16 containing SnCl.sub.2 solution
used as an activator in plating, a rinse tank 17, a PdCl.sub.2
solution tank 18 containing PdCl.sub.2 solution used as a catalyst
in electroless plating, and a rinse tank 19 are disposed in order
on one side with respect to the second transfer robot 62. An
electroless plating tank 20, a rinse tank 21, an electrolytic
plating tank 22, and a rinse tank 23 are disposed in order on the
other side with respect to the second transfer robot 62. The rinse
tanks 17, 19, 21 and 23 may be provided as needed.
[0070] Each of these processing tanks 16-23 has the same basic
shape and structure, and comprises a processing container body 50
having a rectangular plate shape and a recess 50a forming a
processing chamber 52 therein, and a cover 51 capable of opening
and closing a front opening of the processing container body 50, as
shown in FIG. 2. A packing 53 is mounted at the peripheral portion
of the processing container body 50 to maintain the water-tightness
of the processing container body 50 when the cover 51 is closed and
brought into close contact with the processing container body 50. A
holding member for detachably holding a substrate W is provided on
the inner side of the cover 51, and the cover 51 is provided with a
sensor (not shown) for detecting the existence of a substrate W on
the holding member.
[0071] In the processing tank (electrolytic plating tank) 22 for
performing electrolytic plating, a plate-like anode 54 is mounted
on the bottom of the recess 50a in the processing container body 50
in parallel with the processing chamber 52, and a shielding plate
55 made of dielectric material is disposed at the opening end of
the recess 50a. The shielding plate 55 has an opening 55a therein
for regulating the electric field on a plating surface of the
substrate W. The other processing tanks are not provided with the
anode 54 or the shielding plate 55.
[0072] An upper header 56 and a lower header 57 are mounted on the
top and bottom of the processing container body 50 and communicate
with the processing chamber 52 via a plurality of through-holes
56a, 57a, respectively. Thus, for example, a processing liquid is
supplied from the lower header 57 to the upper header 56 to thus
generate a parallel flow along the surface of the substrate to be
plated, as shown in FIG. 3. As shown in FIG. 4, processing liquid
circulating devices 33 each having a reservoir tank 31 and a
circulating pump 32 are provided below the processing tanks 16-23,
and a supply pipe 34 and a return pipe 35 extending from the
processing liquid circulating device 33 are connected to the lower
header 57 and the upper header 56.
[0073] Since, as described above, the plating tanks 20, 22 are
hermetically sealed with a parallel flow, a plating liquid can flow
along the surface of the substrate at a high speed even in a small
space to thus perform the efficient plating with sufficient
flowability of the plating liquid. Further, each of the processing
tanks 16-23 is vertically positioned, and hence bubbles in fine
recesses formed in the substrate W can easily flow out therefrom
during the plating process or the like. Therefore, uniformity of
the plating reaction and the processing rate can be increased, and
simultaneously the installation area of the processing tanks 16-23
can be reduced, resulting in an efficient arrangement of the
processing tanks.
[0074] In this embodiment, the transfer robot 62 comprises a
hexaxial robot having a plurality of arms 63 and a hand 64 which is
provided on the end of the arms 63 and is capable of opening and
closing (see FIG. 5). A plurality of rollers 65 are rotatably
supported on the inner surface of the hand 64. A temporary holding
stage 66 having a plurality of supports is provided in the clean
zone 13 and used for temporarily holding a substrate W to be
transferred between the clean zone 13 and the contaminated zone
12.
[0075] Next, the plating process according to the plating apparatus
thus constructed will be described below with reference to FIGS. 6
and 7. The first transfer robot 61 takes out a substrate W held on
the load/unload unit 14a, 14b and places the substrate W on the
temporary holding stage 66. The second transfer robot 62 transfers
the substrate W to the contaminated zone 12, and, when necessary,
the substrate W is inserted into the processing container body 50
of the activation tank 16 and activated by a processing liquid
containing an activator such as SnCl.sub.2. Next, the substrate W
is transferred to the adjacent rinse tank 17 to be rinsed, and then
transferred to the catalyst application tank 18 to receive a
catalyst application.
[0076] In this process, Sn.sup.2+ ions from the activator are
adsorbed by the surface of the substrate W in the activation tank
16, and these ions are oxidized in the catalyst application tank 18
to be Sn.sup.4+. On the other hand, Pd.sup.2+ ions are reduced to
Pd metal, and the Pd metal is deposited on the surface of the
substrate W to serve as a catalyst in the following electroless
plating process. A single catalyst containing Pd/Sn colloids may be
used in this process. In this embodiment, the catalyst application
process described above is performed in the activation tank 16 and
the catalyst application tank 18 belonging to a portion of the
plating apparatus. However, the catalyst application process may be
performed in a separate apparatus, and then the substrate W may be
transferred to the plating apparatus. It is possible to dispense
with the activation process and/or the catalyst application process
in some cases, depending on a material or a state of the inner
surface of the recess formed in the semiconductor substrate.
[0077] The second transfer robot 62 further transfers the substrate
W to the electroless plating tank 20, where the electroless plating
process is performed with a predetermined reducing agent and a
predetermined plating liquid. With this process, as shown in FIGS.
7A and 7B, an electroless plating layer 41 is formed on the inner
surface of a barrier layer 40. In this case, electrons generated at
the solid-liquid interface due to decomposition of the reducing
agent are applied to the Cu.sup.2+ via the catalyst on the surface
of the substrate, and hence Cu metal is deposited on the catalyst
to form the copper layer 41. In addition to Pd, other transition
metals such as Fe, Co, Ni, Cu, and Ag may be used as the
catalyst.
[0078] Next, the substrate W is transferred to the electrolytic
plating tank 22 by the transfer robot, and the copper layer 41
formed by the electroless plating process is connected to an
electrode to perform the electrolytic plating process with a
predetermined plating liquid, for thereby filling the recess 42
with electrolytic plating metal 43, as shown in FIGS. 7C and
7D.
[0079] After the electrolytic plating process is completed, the
substrate is taken out by the second transfer robot and transferred
to the rinse tank to be rinsed and then placed on a second
temporary holding stage 67. The substrate is held by the first
transfer robot 61 and transferred to the cleaning and drying device
60 to be cleaned and dried for finishing, and returned to the
load/unload unit 14a, 14b. The substrate is finally transferred to
a chemical mechanical polishing apparatus (CMP) to remove
unnecessary plating metal from the surface of the substrate with
the chemical mechanical polishing process.
[0080] FIG. 8 shows a plating apparatus according to another
embodiment of the present invention. The plating apparatus
comprises a vertical processing tank 24 as in the previous
embodiment, and processing liquid circulating devices 33a, 33b, 33c
for circulating and supplying a respective processing liquid
(electroless copper plating liquid, rinse water, and electrolytic
copper plating liquid) to the processing tank 24. Supply of the
processing liquid can be switched by switching valves 36a through
36c and 37a through 37c. The processing tank 24 comprises a
processing container base 50 having an anode 54 and a shielding
plate 55 therein, as in the example shown in FIG. 2, and can
perform the electrolytic plating process.
[0081] In this embodiment, for example, after the electroless
plating process is completed, the plating liquid is returned to the
reservoir tank 31a. A rinse water circulating pump 32b is operated
to introduce rinse water into the processing tank 24, and then an
electrolytic plating liquid is introduced from the reservoir tank
31c into the processing tank 24. After the electrolytic plating
process is completed, a rinsing process is similarly performed.
Thus, it is possible to eliminate such problems that plating
liquids are mixed with each other. In this embodiment, the
electroless copper plating process, the rinsing process, the
electrolytic copper plating process, the rinsing process, and other
processes can be continuously performed in the same processing tank
24 without transferring a substrate, simply by changing processing
liquids. Therefore, the present embodiment can decrease the number
of the required tanks compared with the previous embodiment and can
eliminate the need of a transfer robot for transferring a substrate
between tanks, for thereby compacting a installation frame.
Further, throughput is increased as the transferring time can be
eliminated.
[0082] FIG. 9 shows a plating apparatus according to still another
embodiment of the present invention. A transferring rail 61a is
extended from one side of a rectangular frame to the other side of
the frame, and a transfer device (transfer robot) 61 is movably
provided on the transferring rail 61a. A load/unload unit 41, a
pre-treatment unit 68, an electroless plating unit 69, a first spin
drying unit 70A, an electrolytic plating unit 71, and a second spin
drying unit 70B are clockwise disposed in order so that these units
surround the transfer robot 61. The pre-treatment unit 68 comprises
an activator (SnCl.sub.2 solution) tank or a catalysis (PdCl.sub.2
solution) tank, for example.
[0083] FIG. 10 is a schematic view showing a configurational
example of the electroless plating unit 69 shown in FIG. 9. The
electroless plating unit 69 has a turntable 72 for holding a
substrate W to be plated such as a semiconductor substrate thereon.
A heater 73 for maintaining temperature is provided in the
turntable 72, and the turntable 72 can be moved vertically via a
ball screw 85 by a motor 86 and rotated via a timing belt 83 by a
motor 84.
[0084] A plating cell 92 having an opening in its lower surface is
disposed above the turntable 72, and a seal packing 91 which is
brought into close contact with the plating substrate W held by a
housing 96 is provided at the outer edge of the lower end of the
plating cell 92. Specifically, when the turntable 72 is upwardly
moved, a hermetically sealed space is formed in the plating cell 92
in such a state that the surface of the plating substrate W is
brought into close contact with the seal packing 91. The
hermetically sealed space has a volume sufficient for accommodating
the minimum amount of plating liquid (electroless plating liquid)
required for performing a predetermined plating on the surface of
the plating substrate W, as described later.
[0085] A preparation bath 74 is disposed in the vicinity of the
upper portion of the plating cell 92 and supplied with plating
liquids A, B, C, and pure water D. An impeller 76a connected to an
agitator 76 is disposed in the preparation bath 74, and a heater 81
is disposed in the preparation bath 74. A plating liquid in the
preparation bath 74 is supplied to the plating cell 72 via a
plating liquid supply valve 79.
[0086] A hot bath 75 is disposed in the vicinity of the outer
portion of the preparation bath 74 so as to surround the
preparation bath 74. An impeller 77a connected to an agitator 77 is
disposed in the hot bath 75, and a heater 82 is disposed in the hot
bath 75. The reference numeral 80 denotes a plating liquid
discharge valve for discharging a plating liquid after the plating
process is completed in the plating cell 92. A plating liquid
discharged through the plating liquid discharge valve 80 flows into
a waste liquid tank 93. The reference numeral 78 denotes a pressure
supply valve for supplying pressure into the plating cell 92. The
pressure in the plating cell 92 can be pulsed via the pressure
supply valve 78 by a pressure pulsation generator 94.
[0087] The pressure pulsation generator 94 comprises a pressure
regulator valve 87 for high pressure, a pressure regulator valve 88
for low pressure, a switching valve 89 for switching pressure, and
a pneumatic pressure source 90, and can generate pressure
pulsations having an amplitude of 0 to 1 MPa and a frequency of 0
to 10 Hz. The reference numerals P1, P2 denote pressure gauges.
[0088] In the electroless plating apparatus thus constructed, when
a substrate W is plated, the plating substrate W is held in a
predetermined position on the upper surface of the turntable 72
positioned below the plating cell 92. In this state, the turntable
72 is moved upwardly via the ball screw 85 by the motor 86 to thus
bring the upper surface of the plating substrate W into close
contact with the seal packing 91, thereby closing the lower opening
of the plating cell 92 to form a hermetically sealed space therein.
At this time, the supply valve 79 is opened to supply the plating
liquid Q in the preparation bath 74 to the plating cell 92.
[0089] The interior of the plating cell 92 has a volume sufficient
for accommodating the minimum amount of plating liquid Q required
for performing a predetermined plating on the surface of the
plating substrate W, and this minimum required amount of plating
liquid Q is accommodated in the interior of the plating cell 92.
Here, the minimum required amount of electroless plating liquid is
set within a range of amount of liquid that includes ions of
solutes 1.5 to 20 times as many as a predetermined deposited metal
equivalent. In the plating process, the pressure pulsation
generator 94 applies a pressure pulsation to the plating cell 92
via the pressure supply valve 78 at a predetermined amplitude and a
predetermined frequency.
[0090] As shown in FIGS. 11A through 11C, since the plating
substrate W is held on the upper surface of the turntable 72 in
such a state that the surface to be plated faces upwardly, hydrogen
gas bubbles 98 certainly generated in the plating liquid Q in the
electroless plating process are moved upwardly due to buoyancy.
Therefore, the number and the amount of bubbles remaining on the
plating surface 97 of the plating substrate W and in fine grooves
and holes are reduced, for thereby reducing the plating defects.
Further, the minimum required amount of plating liquid Q is
supplied to the hermetically sealed space in the plating cell 92,
and the substrate is plated in a stationary state. Hence, the
hydrogen gas bubbles 98 are not moved on the plating surface 97,
thereby minimizing the amount of unevenly plated portions generated
on the plating surface.
[0091] The pressure of the hermetically sealed space in the plating
cell 92 is set to be higher than atmospheric pressure and pulsed by
the pressure pulsation generator 94. Hence, as described above, the
hydrogen gas bubbles 98 can be encouraged to dissolve into the
electroless plating liquid Q by pressurization and simultaneously
encouraged to separate from the plating surface 97 by pressure
pulsation, as shown in FIGS. 11A through 1C.
[0092] The preparation bath 74 is disposed in the vicinity of the
upper portion of the plating cell 92, and the minimum required
amount of plating liquid prepared in the preparation bath 74 is
supplied to the plating cell 92 just before the substrate W is
plated. Hence, the plating process is completed before the
occurrence of problematic reactions specific to the electroless
copper plating, such as a Cannizzaro reaction or a
disproportionation, which cause deterioration of the plating liquid
and changes in concentration of the plating liquid composition
after the preparation. Therefore, the plating process can be
performed with a highly stable quality.
[0093] The plating liquid Q used for plating is discharged from the
plating cell 92 via the plating discharge valve 80 into the waste
liquid tank 93, where the plating liquid Q is processed as a waste
liquid. Hence, the plating process can be performed with a highly
stable quality. In addition, since the amount of plating liquid
used per deposition is maintained to be the minimum required
amount, it is possible to avoid increases in cost with the waste
liquid and an excessive burden on the environment. Further, since
the hot bath 75 is disposed above the plating cell 92 and the
heater 73 for maintaining temperature is disposed below the
turntable 72, it is possible to maintain a fixed plating
temperature, which is one of the most important factors governing
the quality (uniformity of layer thickness, reproducibility,
electric conductivity of the plating layer, etc.) of electroless
plating.
[0094] After the plating process is completed, as described above,
the plating liquid discharge valve 80 is opened to discharge the
plating liquid in the plating cell 92 to the waste liquid tank 93.
The turntable is moved downwardly via the ball screw 85 by the
motor 86, and a cleaning liquid (mainly pure water) is ejected from
a cleaning nozzle 95 shown in FIG. 12 to the plating surface of the
plating substrate W to clean the plating surface. In this cleaning
process, a cleaning nozzle 95 is swung, and the plating substrate W
is slowly rotated via the timing belt 83 by the motor 84. After the
cleaning process is completed, the plating substrate W is rotated
at a high speed to spin off the cleaning liquid attached to the
plating substrate W by centrifugal force.
[0095] After a seed layer is formed on the barrier layer in the
wiring grooves by the electroless plating process, the substrate W
is transferred to the first spin drying unit 70A by the transfer
robot 61 and completely dried therein. Then, the substrate W is
transferred to the electrolytic plating unit 71, where the
electrolytic plating process is performed. The electrolytic plating
process will be described below with reference to FIGS. 13 and
14.
[0096] As shown in FIG. 13, the electrolytic plating unit 71
comprises a plating tank 110, and the plating tank 110 comprises a
plating tank body 111 and a substrate holding member 112 for
holding a plating substrate W such as a semiconductor substrate in
the plating tank body 111. The substrate holding member 112 has a
substrate holding portion 112-1 and a shaft portion 112-2, and the
shaft portion 112-2 is rotatably supported in an inner wall of a
cylindrical guide member 114 via bearings 115, 115. The guide
member 114 and the substrate holding member 112 are vertically
movable at a predetermined stroke by a cylinder 116 provided on the
top of the plating tank body 111.
[0097] The substrate holding member 112 is rotated in a direction
indicated by the arrow A via the shaft portion 112-2 by a motor 118
provided on the inner side of the upper portion of the guide member
114. A space C is formed in the substrate holding member 112, and a
substrate presser member 117 having a substrate presser portion
117-1 and a shaft portion 117-2 is accommodated in the space C. The
substrate presser member 117 is vertically movable at a
predetermined stroke by a cylinder 119 provided on the top of the
shaft portion 112-2 in the substrate holding member 112.
[0098] An opening 112-1a communicating with the space C is formed
below the substrate holding portion 112-1 of the substrate holding
member 112, and, as shown in FIG. 14, a step portion 112-1b on
which the peripheral portion of the plating substrate W is placed
is formed at the upper portion of the opening 112-1a. The
peripheral portion of the plating substrate W is placed on the step
portion 112-1b, and the upper surface of the plating substrate W is
pressed by the substrate presser portion 117-1 of the substrate
presser member 117, for thereby clamping the peripheral portion of
the plating substrate W between the substrate presser portion 117-1
and the step portion 112-1b. The lower surface (plating surface) of
the plating substrate W is exposed to the opening 112-1a. FIG. 14
is an enlarged view of the area B indicated in FIG. 13.
[0099] A flat plating liquid chamber 120 is provided below the
substrate holding portion 112-1 of the plating tank body 111, i.e.,
below the plating surface of the plating substrate W exposed to the
opening 112-1a, and a flat plating liquid introduction chamber 122
is provided below the plating liquid chamber 120 via a perforated
plate 121 having a large number of holes 121a. The recovery gutter
123 for recovering a plating liquid Q overflowing the plating
liquid chamber 120 is provided outside of the plating liquid
chamber 120.
[0100] The plating liquid Q recovered in the recovery gutter 123 is
returned to a plating liquid tank 124. The plating liquid Q in the
plating liquid tank 124 is horizontally introduced to the plating
liquid chamber 120 from both sides thereof by a pump 125. The
plating liquid Q introduced to the plating liquid chamber 120 from
both sides thereof flows vertically into the plating liquid chamber
120 through the holes 121a formed in the perforated plate 121. A
distance between the perforated plate 121 and the plating substrate
W is set to be 5 to 15 mm. The flow of the plating liquid Q passed
through the holes 121a formed in the perforated plate 121 is
brought into contact with the plating surface of the plating
substrate W in such a state that the plating liquid Q flows
upwardly as a uniform flow. The plating liquid Q overflowing the
plating liquid chamber 120 is recovered in the recovery gutter 123
and flows into the plating liquid tank 124. Specifically, the
plating liquid Q is circulated between the plating liquid chamber
120 in the plating tank body 111 and the plating liquid tank
124.
[0101] The plating liquid level L.sub.Q in the plating liquid
chamber 120 is higher than the plating surface level L.sub.W of the
plating substrate W by a slight distance .DELTA.L, and the plating
liquid Q is brought into contact with the whole surface of the
plating substrate W.
[0102] An electrical contact 127 for electrically connecting with a
connecting portion of the plating substrate W is provided in the
step portion 112-1b of the substrate holding portion 112-1 in the
substrate holding member 112. The electrical contact 127 is
connected to a cathode of an external plating power supply (not
shown) via a brush 126. An anode 128 is provided on the bottom of
the plating liquid introduction chamber 122 in the plating tank
body 111, in confrontation with the plating substrate W. The anode
128 is connected to an anode of the plating power supply. A
transfer slit 129 for inserting and removing the plating substrate
W with a substrate transfer jig such as a robot arm is formed at a
predetermined position in the wall of the plating tank body
111.
[0103] When the plating process is performed in the electrolytic
plating unit thus constructed, the substrate holding member 112 is
moved upwardly to a predetermined position (a position at which the
plating substrate W held by substrate holding portion 112-1 opposes
the transfer slit 129) together with the guide member 114 by
actuating the cylinder 116, and simultaneously the substrate
presser member 117 is moved upwardly to a predetermined position (a
position at which the substrate presser portion 117-1 reaches the
upper portion of the transfer slit 129) by actuating the cylinder
119. In this state, the plating substrate W is transferred to the
space C in the substrate holding member 112 by the substrate
transfer jig such as a robot arm and placed on the step portion
112-1b in such a state that the plating surface of the plating
substrate W faces downwardly. At this state, the substrate presser
portion 117-1 is moved downwardly to a position at which the lower
surface of the substrate presser portion 117-1 is brought into
contact with the upper surface of the plating substrate W, by
actuating the cylinder 119, and hence the peripheral portion of the
plating substrate W is clamped between the substrate presser
portion 117-1 and the step portion 112-1b.
[0104] In this state, the substrate holding member 112 is moved
downwardly to a position at which the plating surface of the
plating substrate W is brought into contact with the plating liquid
Q in the plating liquid chamber 120 (a position .DELTA.L lower than
the plating liquid level L.sub.Q) together with the guide member
114 by actuating the cylinder 116. While the substrate holding
member 112 is being moved downwardly, the substrate holding member
112 and the plating substrate W are rotated at a low speed by
actuating the motor 118. The plating liquid chamber 120 is filled
with the plating liquid Q, and the plating liquid passed through
the holes 121a formed in the perforated plate flows vertically
upwardly in the plating liquid chamber 120. In this state, when a
predetermined voltage is applied between the anode 128 and the
electric contact 127 by the plating power supply, a plating current
flows from the anode 128 to the plating substrate W to form the
plating layer on the plating surface of the plating substrate
W.
[0105] During the plating process, the substrate holding member 112
and the plating substrate W are rotated at a low speed by actuating
the motor 118. This rotation at a low speed is set such that the
vertical flow of the plating liquid Q in the plating liquid chamber
120 is not interrupted, and a plating layer having a uniform
thickness can be formed on the plating surface of the plating
substrate W.
[0106] When the plating process is completed, the substrate holding
member 112 and the plating substrate W are moved upwardly by
actuating the cylinder 116. When the lower surface of the substrate
holding portion 112-1 is positioned above the plating liquid level
L.sub.Q, the motor 118 rotates the substrate holding member 112 and
the plating substrate W at a high speed to spin off the plating
liquid attached on the plating surface of the plating substrate W
and the lower surface of the substrate holding portion 112-1. After
the plating liquid is spun off, the plating substrate W is moved
upwardly to a position corresponding to the transfer slit 129. When
the substrate presser portion 117-1 is moved upwardly by actuating
the cylinder 119, the plating substrate W is released from the
substrate presser portion 117-1 in such a state that the plating
substrate W is placed on the step portion 112-1b of the substrate
holding portion 112-1. In this state, the substrate transfer jig
such as a robot arm is inserted from the transfer slit 129 into the
space C in the substrate holding member 112 to pick up the plating
substrate W and transfer it to the exterior.
[0107] With the electrolytic plating unit 71 thus constructed, a
plating substrate W in which holes having a diameter of 0.15 .mu.m
and a depth of 1.2 .mu.m were formed was plated by the electrolytic
plating process to fill the holes with copper. A plating liquid Q
having the following composition, a current density of 2
A/dm.sup.2, and a temperature of 25.degree. C. was used, and a
plating time was set to 150 seconds. The holes were efficiently
filled with copper.
[0108] Composition of Plating Liquid Q TABLE-US-00001
CuSO.sub.4.5H.sub.2O 225 g/l H.sub.2SO.sub.4 55 g/l Cl.sup.- 60
mg/l Sulfur compound (N,N- 5 mg/l
dimethyldithiocarbamylpropylsulfonic acid) Macromolecular compound
(PEG6000) 0.1 g/l Nitrogen compound (safranine compound, janus 2
mg/l green B)
[0109] When a plating liquid having a high concentration of copper
sulfate (CuSO.sub.4.5H.sub.2O) is used, as described above, a hole
having a diameter of 0.15 .mu.m and a depth of 1.2 .mu.m can
efficiently be filled with copper by plating.
[0110] FIG. 15 shows a processing tank 25 which can continuously
perform an electroless plating process and an electrolytic plating
process with the same processing liquid. The processing tank 25 can
perform an electrolytic plating process as with the processing tank
shown in FIG. 8. In this processing tank, the electroless plating
process is performed, and then the electrolytic plating process is
directly performed by energization of a low current of less than
0.2 A/dm.sup.2. In this case, an electroless plating liquid is used
as a plating liquid, and TMAH is used in place of NaOH or KOH
usually used as a pH regulator in the electroless plating process,
in order to prevent the semiconductor substrate from being
contaminated. TMAH is an organic alkali chemical including a methyl
group. It is necessary to avoid using a reducing agent liable to be
decomposed, such as formalin, which has commonly been used.
[0111] Conventionally, in the through hole plating of the printed
circuit board, throwing power has been improved by a high throwing
power bath (CuSO.sub.4.5H.sub.2O 10-80 g/l) having a low Cu
concentration. However, when trenches and via holes of a
semiconductor substrate are plated, not only throwing power but
also leveling of plating is required in order to prevent the
generation of voids. Further, since the high throwing power bath is
easily influenced by the flow of a plating liquid, it is desirable
to use a plating liquid having a mid to high increased
concentration for reducing the possibility of flow effects.
[0112] Various things were examined under the above preconditions.
As a result, conventionally used baths such as a
CuSO.sub.4.5H.sub.2O low concentration (15-80 g/l) bath (high
throwing power bath) superior in throwing power, or a
CuSO.sub.4.5H.sub.2O high concentration (150-220 g/l) bath
(decorative bath) superior in leveling of plating were found not to
be appropriate. A CuSO.sub.4.5H.sub.2O mid concentration (100-150
g/l) bath was found to be appropriate for a damascene plating
process which combines an electroless plating process and an
electrolytic plating process of a semiconductor substrate.
[0113] As described above, according to the present invention, an
initial plating layer (seed layer) is formed with an electroless
plating process, and then the recess in the substrate is filled
with electrolytic plating metal while the initial layer serves as
the feeding layer. Accordingly, the recess having a barrier layer
of a high electrical resistance can efficiently be filled with a
void-free wiring metal, without the sputtering process or the CVD
process in a series of plating processes. Therefore, the present
invention can provide a method and apparatus for plating a
substrate to form wiring by efficiently filling a fine recess
formed in a semiconductor substrate with plating metal without a
void or contamination.
INDUSTRIAL APPLICABILITY
[0114] The present invention is suitable for a method and apparatus
for plating a substrate to fill a wiring recess formed in a
semiconductor substrate with wiring metal such as copper, copper
alloy, or the like.
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