U.S. patent application number 11/488150 was filed with the patent office on 2007-07-12 for plating apparatus and method for controlling plating solution.
Invention is credited to Masao Hodai, Hiroyuki Kanda, Takashi Kawakami, Mizuki Nagai, Tsutomu Nakada.
Application Number | 20070158202 11/488150 |
Document ID | / |
Family ID | 37915997 |
Filed Date | 2007-07-12 |
United States Patent
Application |
20070158202 |
Kind Code |
A1 |
Nagai; Mizuki ; et
al. |
July 12, 2007 |
Plating apparatus and method for controlling plating solution
Abstract
A plating apparatus can keep concentrations of components of a
plating solution constant over a long period of time and can stably
form a plated film having a more uniform thickness on a surface of
a substrate while minimizing an amount of the plating solution
used. The plating apparatus includes a plating cell for carrying
out electroplating of a surface of a substrate with a space between
the surface of the substrate, serving as a cathode, and an
insoluble anode filled with a plating solution, a plating solution
circulation system for supplying the plating solution to the
plating cell and recovering the plating solution in a circulatory
manner, and a plating solution component replenishment system for
supplying a replenisher solution, containing a component of the
plating solution in a higher concentration than that in the plating
solution, to the plating solution which circulates in the plating
solution circulation system, thereby maintaining the concentration
of the component in the plating solution within a predetermined
range.
Inventors: |
Nagai; Mizuki; (Tokyo,
JP) ; Hodai; Masao; (Tokyo, JP) ; Kanda;
Hiroyuki; (Tokyo, JP) ; Nakada; Tsutomu;
(Tokyo, JP) ; Kawakami; Takashi; (Tokyo,
JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
37915997 |
Appl. No.: |
11/488150 |
Filed: |
July 18, 2006 |
Current U.S.
Class: |
205/101 |
Current CPC
Class: |
C25D 17/001 20130101;
H01L 21/2885 20130101; C25D 21/14 20130101; C25D 21/18 20130101;
C25D 17/002 20130101; C25D 7/123 20130101; H01L 21/76877
20130101 |
Class at
Publication: |
205/101 |
International
Class: |
C25D 21/18 20060101
C25D021/18 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 19, 2005 |
JP |
2005-209236 |
Dec 15, 2005 |
JP |
2005-362314 |
Claims
1. A plating apparatus comprising: a plating cell for carrying out
electroplating of a surface of a substrate with a space between the
surface of the substrate, serving as a cathode, and an insoluble
anode filled with a plating solution; a plating solution
circulation system for supplying the plating solution to the
plating cell and recovering the plating solution in a circulatory
manner; and a plating solution component replenishment system for
supplying a replenisher solution, containing a component of the
plating solution in a higher concentration than that in the plating
solution, to the plating solution which circulates in the plating
solution circulation system, thereby maintaining the concentration
of the component in the plating solution within a predetermined
range.
2. The plating apparatus according to claim 1, further comprising a
plating solution discharge system for discharging a predetermined
amount of the plating solution from the plating solution
circulation system.
3. The plating apparatus according to claim 1, wherein the plating
solution circulation system includes a plating solution buffer tank
for recovering the plating solution after its use in plating in the
plating cell, a plating solution adjustment tank, connected to the
plating solution buffer tank, for replenishing the plating solution
with the replenisher solution, and a plating solution supply tank,
connected to the plating solution adjustment tank, for storing the
plating solution which has been adjusted in the plating solution
adjustment tank and supplying the plating solution to the plating
cell.
4. The plating apparatus according to claim 1, wherein the
component contained in the replenisher solution, supplied to the
plating solution by the plating solution component replenishment
system, comprises an organic additive comprising at least one of a
reaction accelerator, a reaction suppressor and a leveler, a metal
ion, a supporting electrolyte and a halogen ion.
5. The plating apparatus according to claim 1, wherein the
replenishment quantity of the replenisher solution is determined
based on a cumulative quantity of electricity taken for
electroplating.
6. The plating apparatus according to claim 1, wherein the
replenisher solution contains one component of the plating solution
in a higher concentration than that in the plating solution, and is
supplied to the plating solution from a replenisher solution
tank.
7. The plating apparatus according to claim 1, wherein the plating
cell has a high-resistance structure disposed between the insoluble
anode and the substrate which serves as a cathode.
8. The plating apparatus according to claim 1, wherein the
replenishment quantity of the replenisher solution is determined by
using a consumption coefficient determined by the current density
of electric current applied to carry out plating in the plating
cell and by the time of application of the electric current.
9. The plating apparatus according to claim 8, wherein the plating
cell is divided into an anode chamber and a cathode side area by
the high-resistance structure disposed between the insoluble anode
and the substrate which serves as a cathode, and the replenishment
quantity of the replenisher solution is determined individually for
the anode chamber and for the cathode side area, and the respective
values obtained are summed up.
10. The plating apparatus according to claim 8, wherein the
component of the plating solution, contained in the replenisher
solution whose replenishment quantity is determined by using the
consumption coefficient determined by the current density and the
time of application of the electric current, is a reaction
accelerator.
11. The plating apparatus according to claim 3, wherein the plating
solution adjustment tank has a liquid level sensor for measuring a
liquid level of the plating solution in the plating solution
adjustment tank.
12. The plating apparatus according to claim 1, further comprising
a plating solution analyzer for sampling the plating solution to be
supplied to the plating cell, and analyzing the concentrations of
the components of the plating solution.
13. A method for controlling a plating solution, comprising:
replenishing a plating solution, to be used in plating, with a
replenisher solution containing a component of the plating solution
in a higher concentration than that in the plating solution,
thereby maintaining the concentration of the component in the
plating solution within a predetermined range.
14. The method for controlling a plating solution according to
claim 13, wherein the replenishment quantity of the replenisher
solution is determined based on a cumulative quantity of
electricity taken for electroplating.
15. The method for controlling a plating solution according to
claim 13, wherein the replenishment quantity of the replenisher
solution is determined by using a consumption coefficient
determined by the current density of electric current applied to
carry out plating in the plating cell and by the time of
application of the electric current.
16. The method, for controlling a plating solution according to
claim 15, wherein the plating cell is divided into an anode chamber
and a cathode side area by a high-resistance structure disposed
between an insoluble anode and a substrate which serves as a
cathode, and the replenishment quantity of the replenisher solution
is determined individually for the anode chamber and for the
cathode side area, and the respective values obtained are summed
up.
17. The method for controlling a plating solution according to
claim 15, where in the replenishment quantity of the replenisher
solution is determined based on a cumulative quantity of
electricity taken for electroplating.
18. The method for controlling a plating solution according to
claim 13, wherein a plating metal is copper, and the plating
solution having a copper ion concentration of 20-60 g/L is
replenished with an aqueous solution of copper sulfate having a
copper sulfate concentration of 200 g/L to saturation
concentration, thereby maintaining the concentration of copper ion
in the plating solution within a predetermined range.
19. The method for controlling a plating solution according to
claim 13, wherein the plating solution contains sulfuric acid as a
supporting electrolyte, and the plating solution having a sulfuric
acid concentration of 10-100 g/L is replenished with sulfuric acid
having a concentration of 20-98 wt %, thereby maintaining the
concentration of sulfuric acid in the plating solution within a
predetermined range.
20. The method for controlling a plating solution according to
claim 13, wherein the plating solution contains chlorine as a
halogen ion, and the plating solution having a chlorine
concentration of 30-90 mg/L is replenished with hydrochloric acid
having a concentration of 1-36 wt %, thereby maintaining the
concentration of chlorine in the plating solution within a
predetermined range.
21. A method for controlling a plating solution, comprising:
recovering a plating solution, which has been used in plating in a
plating cell, in a plating solution buffer tank; sending the
plating solution in the plating solution buffer tank to a plating
solution adjustment tank, and replenishing the plating solution in
the plating solution adjustment tank with a replenisher solution
containing a component of the plating solution in a higher
concentration than that in the plating solution, thereby
maintaining the concentration of the component in the plating
solution within a predetermined range; sending the plating solution
in the plating solution adjustment tank to a plating solution
supply tank; and supplying the plating solution in the plating
solution supply tank to the plating cell.
22. The method for controlling a plating solution according to
claim 21, where in the replenishment quantity of the replenisher
solution is determined based on a cumulative quantity of
electricity taken for electroplating.
23. The method for controlling a plating solution according to
claim 21, where in the replenishment quantity of the replenisher
solution is determined by using a consumption coefficient
determined by the current density of electric current applied to
carry out plating in the plating cell and by the time of
application of the electric current.
24. The method for controlling a plating solution according to
claim 23, wherein the plating cell is divided into an anode chamber
and a cathode side area by a high-resistance structure disposed
between an insoluble anode and a substrate which serves as a
cathode, and the replenishment quantity of the replenisher solution
is determined individually for the anode chamber and for the
cathode side area, and the respective values obtained are summed
up.
25. The method for controlling a plating solution according to
claim 23, wherein the component of the plating solution, contained
in the replenisher solution whose replenishment quantity is
determined by using the consumption coefficient determined by the
current density and the time of application of the electric
current, is a reaction accelerator.
26. The method for controlling a plating solution according to
claim 21, wherein a plating metal is copper, and the plating
solution having a copper ion concentration of 20-60 g/L is
replenished with an aqueous solution of copper sulfate having a
copper sulfate concentration of 200 g/L to saturation
concentration, thereby maintaining the concentration of copper ion
in the plating solution within a predetermined range.
27. The method for controlling a plating solution according to
claim 21, wherein the plating solution contains sulfuric acid as a
supporting electrolyte, and the plating solution having a sulfuric
acid concentration of 10-100 g/L is replenished with sulfuric acid
having a concentration of 20-98 wt %, thereby maintaining the
concentration of sulfuric acid in the plating solution within a
predetermined range.
28. The method for controlling a plating solution according to
claim 21, wherein the plating solution contains chlorine as a
halogen ion, and the plating solution having a chlorine
concentration of 30-90 mg/L is replenished with hydrochloric acid
having a concentration of 1-36 wt %, thereby maintaining the
concentration of chlorine in the plating solution within a
predetermined range.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a plating apparatus and a
method for controlling a plating solution, and more particularly to
a plating apparatus useful for filling fine interconnect recesses
(circuit pattern) formed in a surface of a substrate, such as a
semiconductor wafer, with a metal (interconnect material), such as
copper, to form interconnects, and also to a method for controlling
a plating solution, which is suited for controlling the components
of a plating solution for use in the plating apparatus.
[0003] 2. Description of the Related Art
[0004] In recent years, as the processing speed and integration of
a semiconductor chip becomes higher, there has been a growing
tendency to replace aluminum or aluminum alloy with copper (Cu)
having a low electric conductivity and a high electromigration
resistance as metallic materials for forming interconnect circuits
on the substrate such as semiconductor wafer. Copper interconnects
are generally formed by filling copper into fine interconnect
recesses formed in the surface of the substrate. There are known
various techniques for forming such copper interconnects, including
CVD, sputtering, and plating. Plating is generally used.
[0005] FIGS. 1A through 1C illustrate, in a sequence of process
steps, an example of forming such a substrate having copper
interconnects. First, as shown in FIG. 1A, an insulating film 2,
such as an oxide film of SiO.sub.2 or a film of low-k material, is
deposited on a conductive layer 1a on a semiconductor base 1 on
which semiconductor devices are formed. Contact holes 3 and
trenches 4 are formed in the insulating film 2 by performing a
lithography/etching technique so as to provide interconnect
recesses. Thereafter, a barrier layer 5 of TaN, TiN, or the like is
formed on the insulating film 2, and a seed layer 7 as an electric
supply layer for electroplating is formed on the barrier layer 5 by
sputtering, CVD, or the like.
[0006] Then, as shown in FIG. 1B, copper plating is performed onto
a surface of the seed layer 7 of the substrate W to fill the
contact holes 3 and the trenches 4 with copper and, at the same
time, deposit a copper film 6 on the insulating film 2. Thereafter,
the copper film 6, the seed layer 7 and the barrier layer 5 on the
insulating film 2 are removed by chemical mechanical polishing
(CMP) so as to make the surface of the copper film 6 filled in the
contact holes 3 and the trenches 4, and the surface of the
insulating film 2 lie substantially on the same plane.
Interconnects composed of the copper film 6 are thus formed in the
insulating film 2, as shown in FIG. 1C.
[0007] In a plating processing, as described above, a plating
solution is generally used which contains three organic additives,
i.e., a reaction accelerator for accelerating a plating reaction, a
reaction suppressor for suppressing a plating reaction and a
leveler for leveling a surface of a plated film, in addition to a
salt of copper, the object metal, a supporting electrolyte, a
halogen ion, such as a chlorine ion, which functions, for example,
to keep an additive retained on a surface of a substrate, and
water.
[0008] With the recent movement toward smaller-sized chips, printed
wiring or LSI interconnects in semiconductor devices are becoming
finer. Electroplating of such a fine structure necessitates
enhanced embedding of a plated film in fine recesses. In order to
carry out such electroplating, it is necessary to keep the
concentrations of the components (a metal ion, a supporting
electrolyte, a halogen ion and various additives) of a plating
solution constant in the plating apparatus used over a long period
of time, including the time of plating operation.
[0009] In an electroplating apparatus is generally used for an
anode a metal which generates the same metal ion as that contained
in a plating solution. For example, in an electroplating apparatus
which uses a plating solution mainly comprising copper sulfate and
sulfuric acid, and thus containing copper ions therein,
phosphorus-containing copper containing a small amount of
phosphorus is used for an anode. When electroplating is carried out
by an electroplating apparatus that employs such an anode, the
metal of the anode, for example copper, gradually dissolves in a
plating solution, so that the anode gradually decreases while
changing its shape. As the shape of the anode changes, variation in
a thickness of a plated film formed on the cathode side becomes
larger. It is therefore necessary to periodically replace the
anode. Further, in the case of an anode of phosphorus-containing
copper, a black sludge, called black film, is formed on a surface
of the anode. The black film can adversely affect a plated film
formed on the cathode side, causing a defect, e.g., in
interconnects formed in interconnect recesses formed in a
substrate.
[0010] An electroplating apparatus has therefore been developed
which uses an insoluble anode, for example, comprising a titanium
base coated with iridium oxide or the like, and performs plating of
a surface of a substrate by feeding electricity between the
insoluble anode and the substrate surface, serving as a cathode,
while filling the space between them with a plating solution.
Unlike a phosphorus-containing copper anode, an insoluble anode is
free from the formation, on its surface, of a black sludge called a
black film, and does not dissolve in a plating solution during
plating. An insoluble anode thus has the advantage of no need for
its replacement, involving less time and effort for its maintenance
and management.
[0011] An automatic analysis means has recently been developed
which automatically analyzes the concentration of an additive
contained in a plating solution by using an electrochemical method
(CVS: Cyclic Voltammetry Stripping). It is a conventional practice
to analyze the concentration of an additive in a plating solution
by using an automatic analysis means and, based on the analytical
results, replenish the plating solution with a shortage of the
component, thereby keeping the concentration of the additive in the
plating solution constant.
SUMMARY OF THE INVENTION
[0012] The amount of plating solution necessary for one plating
operation is generally small with an electroplating apparatus that
holds a substrate in a face-up manner, i.e., with the front surface
(surface to be plated) facing upwardly. A so-called one-pass
(throwaway) method, in which a plating solution is thrown away
after each plating operation, is therefore employed. The one-pass
method, however, involves the use of a large amount of plating
solution, leading to a high running cost.
[0013] It may therefore be considered to employ a so-called
circulation method in which a plating solution is recovered and
reused in a circulatory manner. A plating solution
circulation/recovery system adapted for such a circulation method
is generally provided with a circulation tank for circulating a
plating solution while recovering the plating solution after use in
plating, and is designed to supply a predetermined amount of the
plating solution, which has been recovered in the circulation tank,
to a surface (surface to be plated) of a substrate to carry out
plating of the substrate surface, and recover the plating solution,
remaining on the plated surface after plating, in the circulation
tank.
[0014] In order to form a good plated film stably on a surface of a
substrate, it is required to keep the concentrations of the
components of a plating solution constant over a long period of
time, including the time of plating operation. In a plating
apparatus that uses an insoluble anode, the concentrations of the
components of a plating solution are known to change gradually due
to consumption of a metal, such as copper, decomposition of an
additive, generation of hydrogen ion, etc. with the progress of
plating. Thus, when recovering a plating solution after plating in
a circulation tank and reusing the plating solution, the
concentrations of the components of the plating solution recovered
in the circulation tank change gradually. Accordingly, in order to
keep the concentration of each component of the plating solution
constant over a long period of time, including the time of plating
operation, it is necessary to appropriately replenish the plating
solution with each component.
[0015] Replenishment of the intended metal ion in a plating
apparatus that uses an insoluble anode is generally practiced by
putting a powdery metal salt into a circulation tank, or by
dissolving metal flakes in a separate tank before replenishing the
metal ion. The supply of a powdery metal salt into a plating
solution, however, increases fine particles in the plating
solution, and there is a fear that the increased fine particles may
cause a defect in the plated surface of a substrate. On the other
hand, the method of dissolving metal flakes in a separate tank
before replenishing the metal ion necessitates a complicated
apparatus construction with an increased apparatus cost.
[0016] With respect to the above-described method of analyzing the
concentration of an additive in a plating solution by using an
automatic analysis means and, based on the analytical results,
replenishing the plating solution with a shortage of the additive,
thereby keeping the concentration of the additive in the plating
solution constant, such an automatic analysis means generally needs
a considerable time for measurement. Thus, a plating solution will
be replenished with an additive after elapse of a considerable
time. Further, the amount of an additive to be replenished needs to
be varied depending on the plating conditions, such as a large
amount when forming a thick plated film and a small amount when
forming a thin plated film. There is thus a large change in the
concentration of an additive in a plating solution before and after
replenishment of the plating solution with the additive, and the
change can vary largely depending on the plating conditions.
[0017] The present invention has been made in view of the above
situations. It is therefore an object of the present invention to
provide a plating apparatus which can keep the concentrations of
the components of a plating solution constant over a long period of
time and can stably form a plated film having a more uniform
thickness on a surface of a substrate while minimizing the amount
of the plating solution used, and a method for controlling a
plating solution for use in the plating apparatus.
[0018] The present invention provides a plating apparatus
including: a plating cell for carrying out electroplating of a
surface of a substrate with a space between the surface of the
substrate, serving as a cathode, and an insoluble anode filled with
a plating solution; a plating solution circulation system for
supplying the plating solution to the plating cell and recovering
the plating solution in a circulatory manner; and a plating
solution component replenishment system for supplying a replenisher
solution, containing a component of the plating solution in a
higher concentration than that in the plating solution, to the
plating solution which circulates in the plating solution
circulation system, thereby maintaining the concentration of the
component in the plating solution within a predetermined range.
[0019] The amount of the plating solution used can be minimized by
recovering and reusing the plating solution in a circulatory
manner. Further, the use of an insoluble anode can eliminate the
need for anode replacement, thus facilitating the maintenance and
management of the anode. In addition, by using an insoluble anode
and also by maintaining the concentration of a component of a
plating solution, which concentration will change with circulation
and reuse of the plating solution, within a predetermined range by
replenishing the plating solution with a replenisher solution
containing the component in a higher concentration than that in the
plating solution, it becomes possible to prevent an increase of
fine particles in the plating solution in association with the
replenishment of the component of the plating solution and to avoid
complication of the apparatus.
[0020] Preferably, the plating apparatus further comprises a
plating solution discharge system for discharging a predetermined
amount of the plating solution from the plating solution
circulation system.
[0021] By discharging a predetermined amount of plating solution
from the plating solution circulation system, the amount of the
plating solution in the plating solution circulation system can be
regulated so that the necessary amount of a replenisher solution
for maintaining the concentration of a component of the plating
solution within a predetermined range is secured, for example.
[0022] In a preferred aspect of the present invention, the plating
solution circulation system includes a plating solution buffer tank
for recovering the plating solution after its use in plating in the
plating cell, a plating solution adjustment tank, connected to the
plating solution buffer tank, for replenishing the plating solution
with the replenisher solution, and a plating solution supply tank,
connected to the plating solution adjustment tank, for storing the
plating solution which has been adjusted in the plating solution
adjustment tank and supplying the plating solution to the plating
cell.
[0023] By sending a plating solution after its use in plating to
the plating solution adjustment tank after recovering the plating
solution in the plating solution buffer tank, replenishing the
plating solution in the plating solution adjustment tank with a
replenisher solution to adjust the concentration of a component of
the plating solution, storing the plating solution containing the
component in the adjusted concentration in the plating solution
supply tank, and then supplying the plating solution to the plating
cell for plating, it becomes possible to supply to the plating cell
a plating solution having a more constant concentration of the
intended component.
[0024] The component contained in the replenisher solution,
supplied to the plating solution by the plating solution component
replenishment system, comprises, for example, an organic additive
comprising at least one of a reaction accelerator, a reaction
suppressor and a leveler, a metal ion, a supporting electrolyte and
a halogen ion.
[0025] For example, a plating solution for use in embedding of
copper generally contains three organic additives, i.e., a reaction
accelerator, a reaction suppressor and a leveler, in addition to a
metal (copper) ion, a supporting electrolyte and a halogen ion. The
concentrations of the components in the plating solution gradually
change with the progress of plating using an insoluble anode. Thus,
the concentration of each component in the plating solution can be
maintained within a predetermined range by replenishing the plating
solution with a replenisher solution containing the component in a
higher concentration than that in the plating solution.
[0026] The replenishment quantity of the replenisher solution is
determined, for example, based on a cumulative quantity of
electricity taken for electroplating.
[0027] In electroplating using a plating solution in a circulatory
manner, a change in the quantity of a component in the plating
solution with the progress of plating (i.e., consumption of the
component) is generally determined by the quantity of electricity
that has been supplied for plating. Thus, the replenishment
quantity of a component of the plating solution can be calculated
from a cumulative quantity of electricity taken for electroplating.
The calculation of the replenishment quantity of, e.g., an additive
in the plating solution can be made in a shorter time than the
analysis time of an automatic analysis means. This makes it
possible to replenish the additive with a smaller change in the
concentration of the additive in the plating solution during
determination of the replenishment quantity.
[0028] Preferably, the replenisher solution contains one component
of the plating solution in a higher concentration than that in the
plating solution, and is supplied to the plating solution from a
replenisher solution tank.
[0029] For example, in the case of maintaining the concentrations
of six components, a metal ion, a supporting electrolyte, a halogen
ion, a reaction accelerator, a reaction suppressor and a leveler,
in a plating solution respectively within a predetermined range,
the concentration of each component in the plating solution can be
controlled individually by individually storing replenisher
solutions each containing only one of the six components and
supplying the replenisher solutions to the plating solution.
[0030] In a preferred aspect of the present invention, the plating
cell has a high-resistance structure disposed between the insoluble
anode and the substrate which serves as a cathode.
[0031] By disposing the high-resistance structure, which has a
higher resistance than the resistance of a plating solution,
between the insoluble anode and the substrate which serves as a
cathode, it becomes possible to make the influence of the
resistance of, e.g., a seed layer, formed in the surface (surface
to be plated) of the substrate, as small as negligible, thereby
reducing an in-plane difference in the current density due to the
electric resistance of the substrate surface and improving the
in-plane uniformity of a plated film.
[0032] The replenishment quantity of the replenisher solution may
also be determined by using a consumption coefficient determined by
the current density of electric current applied to carry out
plating in the plating cell and by the time of application of the
electric current.
[0033] There are some additives, for use in a plating solution,
whose consumption will differ by a difference in the current
density of electric current applied during plating and by a
difference in the time of application of the electric current.
Thus, if the replenishment quantity is calculated only on the basis
of the cumulative quantity of electricity, a difference will be
produced between the calculated replenishment quantity and the
actual consumption. The consumption of such an additive can be
determined more precisely by using a consumption coefficient as
determined by the current density of electric current applied to
carry out plating and by the time of application of the electric
current.
[0034] In a preferred aspect of the present invention, the plating
cell is divided into an anode chamber and a cathode side area by
the high-resistance structure disposed between the insoluble anode
and the substrate which serves as a cathode, and the replenishment
quantity of the replenisher solution is determined individually for
the anode chamber and for the cathode side area, and the respective
values obtained are summed up.
[0035] In the case where the plating cell is divided into the anode
chamber and the cathode side area, an additive, which is contained
in a plating solution and whose consumption is affected by the
current density, is consumed differently in the anode chamber and
in the cathode side area. Therefore, the consumption of the
additive can be determined more precisely by individually
determining the consumptions in the anode chamber and in the
cathode side area, and summing up the determined consumptions.
[0036] The component of the plating solution, contained in the
replenisher solution whose replenishment quantity is determined by
using the consumption coefficient determined by the current density
and the time of application of the electric current, is, for
example, a reaction accelerator.
[0037] The concentration in a plating solution of a reaction
accelerator, whose consumption is affected by the current density,
can thus be controlled more strictly. This enables uniform copper
plating or the like, thereby producing highly-reliable copper
interconnects or the like.
[0038] In a preferred aspect of the present invention, the plating
solution adjustment tank has a liquid level sensor for measuring a
liquid level of the plating solution in the plating solution
adjustment tank.
[0039] By measuring the liquid level of the plating solution stored
in the plating solution adjustment tank, the amount of the plating
solution stored in the plating solution adjustment tank can be
maintained in a certain range.
[0040] Preferably, the plating apparatus further comprises a
plating solution analyzer for sampling the plating solution to be
supplied to the plating cell, and analyzing the concentrations of
the components of the plating solution.
[0041] By sampling the plating solution at specified time intervals
and analyzing the concentrations of the components in the plating
solution by the plating solution analyzer, and replenishing the
plating solution with deficient components, it becomes possible to
deal with a case in which the consumptions of the components of the
plating solution become imbalanced, e.g., due to a change in the
plating conditions with time.
[0042] The present invention provides a method for controlling a
plating solution comprising replenishing a plating solution, to be
used in plating, with a replenisher solution containing a component
of the plating solution in a higher concentration than that in the
plating solution, thereby maintaining the concentration of the
component in the plating solution within a predetermined range
[0043] The present invention provides another method for
controlling a plating solution comprising recovering a plating
solution, which has been used in plating in a plating cell, in a
plating solution buffer tank, sending the plating solution in the
plating solution buffer tank to a plating solution adjustment tank,
and replenishing the plating solution in the plating solution
adjustment tank with a replenisher solution containing a component
of the plating solution in a higher concentration than that in the
plating solution, thereby maintaining the concentration of the
component in the plating solution within a predetermined range,
sending the plating solution in the plating solution adjustment
tank to a plating solution supply tank, and supplying the plating
solution in the plating solution supply tank to the plating
cell.
[0044] In a preferred aspect of the present invention, a plating
metal is copper, and the plating solution having a copper ion
concentration of 20-60 g/Lis replenished with an aqueous solution
of copper sulfate having a copper sulfate concentration of 200 g/L
to saturation concentration, thereby maintaining the concentration
of copper ion in the plating solution within a predetermined.
[0045] In a preferred aspect of the present invention, the plating
solution contains sulfuric acid as a supporting electrolyte, and
the plating solution having a sulfuric acid concentration of 10-100
g/L is replenished with sulfuric acid having a concentration of
20-98 wt %, thereby maintaining the concentration of sulfuric acid
in the plating solution within a predetermined range.
[0046] In a preferred aspect of the present invention, the plating
solution contains chlorine as a halogen ion, and the plating
solution having a chlorine concentration of 30-90 mg/L is
replenished with hydrochloric acid having a concentration of 1-36
wt %, thereby maintaining the concentration of chlorine in the
plating solution within a predetermined range.
BRIEF DESCRIPTION OF THE DRAWINGS
[0047] FIG. 1A through 1C are diagrams illustrating, in a sequence
of steps, an example for forming copper interconnects by plating
process;
[0048] FIG. 2 is an overall plan view of a substrate processing
apparatus provided with a plating apparatus according an embodiment
of the present invention;
[0049] FIG. 3 is a plan view of a plating cell of the plating
apparatus shown in FIG. 2;
[0050] FIG. 4 is an enlarged sectional view of a substrate holder
and a cathode portion of the plating cell of the plating apparatus
shown in FIG. 2;
[0051] FIG. 5 is a front view of a pre-coating/recovering arm of
the plating cell of the plating apparatus shown in FIG. 2;
[0052] FIG. 6 is a plan view of the substrate holder of the plating
cell of the plating apparatus shown in FIG. 2;
[0053] FIG. 7 is a cross-sectional view taken along line B-B of
FIG. 6;
[0054] FIG. 8 is a cross-sectional view taken along line C-C of
FIG. 6;
[0055] FIG. 9 is a plan view of a cathode portion of the plating
cell of the plating apparatus shown in FIG. 2;
[0056] FIG. 10 is a cross-sectional view taken along line D-D of
FIG. 9;
[0057] FIG. 11 is a plan view of an electrode arm section of the
plating cell of the plating apparatus shown in FIG. 2;
[0058] FIG. 12 is a cross-sectional diagram schematically showing
an electrode head and the substrate holder of the plating cell of
the plating apparatus shown in FIG. 2 upon electroplating;
[0059] FIG. 13 is a diagram schematically showing the plating
apparatus shown in FIG. 2 upon plating;
[0060] FIG. 14 is a diagram schematically showing the plating
apparatus shown in FIG. 2 upon replacement of a plating solution in
the electrode head;
[0061] FIG. 15 is a diagram schematically showing a plating
apparatus according to another embodiment of the present invention
upon plating;
[0062] FIG. 16 is a diagram schematically showing the plating
apparatus according to another embodiment of the present invention
upon replacement of a plating solution in an electrode head;
[0063] FIG. 17 is a diagram schematically showing a plating
apparatus according to yet another embodiment of the present
invention upon plating;
[0064] FIG. 18 is a diagram schematically showing the plating
apparatus according to yet another embodiment of the present
invention upon replacement of a plating solution in an electrode
head;
[0065] FIG. 19 is a graph showing a change in the consumption rate
(consumption coefficient) of a reaction accelerator with current
density and with the time of application of electric current;
[0066] FIGS. 20A and 20B are graphs showing the relationship
between the number of wafers processed and the concentrations of
the components of a plating solution in Example 2;
[0067] FIGS. 21A and 21B are graphs showing the relationship
between the number of wafers processed and the concentrations of
the components of a plating solution in Example 3; and
[0068] FIG. 22 is a graph showing the relationship between the
number of wafers processed and the concentration of a reaction
accelerator in a plating solution in Example 4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0069] Preferred embodiments of the present invention will be
described below with reference to the drawings. The following
embodiments show examples in which copper is embedded in fine
interconnect recesses formed in a surface of a semiconductor
substrate so as to form interconnects composed of copper.
[0070] FIG. 2 is a plan view showing a substrate processing
apparatus incorporating a plating apparatus according to an
embodiment of the present invention. As shown in FIG. 2, this
substrate processing apparatus houses therein two loading/unloading
units 10 for housing a plurality of substrates W therein, two
plating cells 12 for performing plating process, a transfer robot
14 for transferring substrates W between the loading/unloading
units 10 and the plating cells 12, and plating solution supply
facility 18, having a plating solution adjustment tank 16, for
supplying a plating solution to the plating cells 12.
[0071] The plating cell 12, as shown in FIG. 3, is provided with a
substrate processing section 20 for performing plating process and
processing incidental thereto, and a plating solution tray 22 for
storing a plating solution is disposed adjacent to the substrate
processing section 20. There is also provided an electrode arm
portion 30 having an electrode head 28 which is held at the front
end of a swing arm 26 swingable about a rotating shaft 24 and which
is swung between the substrate processing section 20 and the
plating solution tray 22. Furthermore, a pre-coating/recovering arm
32, and fixed nozzles 34 for ejecting pure water or a chemical
liquid such as ion water, and also a gas or the like toward a
substrate are disposed laterally of the substrate processing
section 20. In this embodiment, three of the fixed nozzles 34 are
disposed, and one of them is used for supplying pure water.
[0072] The substrate processing section 20, as shown in FIG. 4, has
a substrate holder 36 for holding a substrate W with its surface
(surface to be plated) facing upwardly, and a cathode portion 38
located above the substrate holder 36 so as to surround a
peripheral portion of the substrate holder 36. Further, a
substantially cylindrical bottomed cup 40 surrounding the periphery
of the substrate holder 36, for preventing scatter of various
chemical liquids used during processing, is provided so as to be
vertically movable by an air cylinder (not shown).
[0073] The substrate holder 36 is adapted to be raised and lowered
by the air cylinder 44 to and from a lower substrate transfer
position A, an upper plating position B, and a
pretreatment/cleaning position C that is intermediate positions A
and B. The substrate holder 36 is also adapted to rotate at an
arbitrary acceleration and an arbitrary velocity, integrally with
the cathode portion 38 by a rotating motor and a belt (not shown).
Substrate carry-in and carry-out openings (not shown) are provided
in confrontation with substrate transfer position A in a side panel
of the plating cell 12 facing the transfer robot 14. When the
substrate holder 36 is raised to plating position B, a sealing
member 90 and cathode electrodes 88 (to be described below) of the
cathode portion 38 are brought into contact with the peripheral
portion of the substrate W held by the substrate holder 36. On the
other hand, the cup 40 has an upper end located below the substrate
carry-in and carry-out openings, and when the cup 40 ascends, the
upper end of the cup 40 reaches a position above the cathode
portion 38 closing the substrate carry-in and carry-out openings,
as shown by imaginary lines in FIG. 4.
[0074] The plating solution tray 22 serves to replace part of the
plating solution in the electrode head 28 with a new plating
solution while positioning the electrode head 28 in the plating
solution tray 22, when plating has not been performed. The plating
solution tray 22 is set at a size in which the high-resistance
structure 110 can be accommodated, and the plating solution tray 22
has a plating solution supply port and a plating solution drainage
port (not shown). A photo-sensor, for measuring a liquid level of
the plating solution, is attached to the plating solution tray
22.
[0075] The electrode arm portion 30 is vertically movable by a
vertical movement motor (not shown), which is a servomotor, and a
ball screw, and swingable between the plating solution tray 22 and
the substrate processing section 20 by a swing motor (not shown) in
this example. A pneumatic actuator may be used instead of the
motor.
[0076] As shown in FIG. 5, the pre-coating/recovering arm 32 is
coupled to an upper end of a vertical support shaft 58. The
pre-coating/recovering arm 32 is swingable by a rotary actuator 60
and is also vertically moveable by an air cylinder (not shown) The
pre-coating/recovering arm 32 supports a pre-coating nozzle 64 for
discharging a pre-coating liquid, on its free end side, and a
plating solution recovery nozzle 66 for recovering the plating
solution, on a portion closer to its proximal end. The pre-coating
nozzle 64 is connected to a syringe that is actuatable by an air
cylinder, for example, for intermittently discharging a pre-coating
liquid from the pre-coating nozzle 64. The plating solution
recovery nozzle 66 is connected to a pump 134 (see FIG. 13)
provided in a plating solution recovery pipe 130 to draw the
plating solution on the substrate from the plating solution
recovery nozzle 66 by actuation of the pump 134.
[0077] As shown in FIGS. 6 through 8, the substrate holder 36 has a
disk-shaped substrate stage 68 and six vertical support arms 70
disposed at spaced intervals on the circumferential edge of the
substrate stage 68 for holding a substrate W in a horizontal plane
on respective upper surfaces of the support arms 70. A positioning
plate 72 is mounted on an upper end one of the support arms 70 for
positioning the substrate by contacting the end face of the
substrate. A pressing finger 74 is rotatably mounted on an upper
end of the support arm 70, which is positioned opposite to the
support arm 70 having the positioning plate 72, for abutting
against an end face of the substrate W and pressing the substrate W
to the positioning plate 72 when rotated. Chucking fingers 76 are
rotatably mounted on upper ends of the remaining four support arms
70 for pressing the substrate W downwardly and gripping the
circumferential edge of the substrate W.
[0078] The pressing finger 74 and the chucking fingers 76 have
respective lower ends coupled to upper ends of pressing pins 80
that are normally urged to move downwardly by coil springs 78. When
the pressing pins 80 are moved downwardly, the pressing finger 74
and the chucking fingers 76 are rotated radially inwardly into a
closed position. A support plate 82 is disposed below the substrate
stage 68 for engaging lower ends of the opening pins 80 and pushing
them upwardly.
[0079] When the substrate holder 36 is located in substrate
transfer position A shown in FIG. 4, the pressing pins 80 are
engaged and pushed upwardly by the support plate 82, so that the
pressing finger 74 and the chucking fingers 76 rotate outwardly and
open. When the substrate stage 68 is elevated, the opening pins 80
are lowered under the resiliency of the coil springs 78, so that
the pressing finger 74 and the chucking fingers 76 rotate inwardly
and close.
[0080] As shown in FIGS. 9 and 10, the cathode portion 38 comprises
an annular frame 86 fixed to upper ends of vertical support columns
84 mounted on the peripheral edge of the support plate 82 (see FIG.
8), a plurality of, six in this embodiment, cathode electrodes 88
attached to a lower surface of the annular frame 86 and projecting
inwardly, and an annular sealing member 90 mounted on an upper
surface of the annular frame 86 in covering relation to upper
surfaces of the cathode electrodes 88. The sealing member 90 is
adapted to have an inner peripheral edge portion inclined inwardly
downwardly and progressively thin-walled, and to have an inner
peripheral end suspending downwardly.
[0081] When the substrate holder 36 has ascended to plating
position B, as shown FIG. 4, the cathode electrodes 88 are pressed
against the peripheral portion of the substrate W held by the
substrate holder 36 for thereby allowing electric current to pass
through the substrate W. At the same time, an inner peripheral end
portion of the sealing member 90 is brought into contact with an
upper surface of the peripheral portion of the substrate W under
pressure to seal its contact portion in a watertight manner. As a
result, the plating solution supplied onto the upper surface
(surface to be plated) of the substrate W is prevented from seeping
from the end portion of the substrate W, and the plating solution
is prevented from contaminating the cathode electrodes 88.
[0082] In this embodiment, the cathode portion 38 is vertically
immovable, but rotatable in a body with the substrate holder 36.
However, the cathode portion 38 may be arranged such that it is
vertically movable and the sealing member 90 is pressed against the
surface to be plated of the substrate W when the cathode portion 38
is lowered.
[0083] As shown in FIGS. 11 and 12, the electrode head 28 of the
electrode arm section 30 includes a electrode holder 94 which is
coupled via a ball bearing 92 to the free end of the swing arm 26,
and a high-resistance structure 110 of porous material, which is
disposed such that it closes the bottom opening of the electrode
holder 94. The electrode holder 94 has a downward-open and cup-like
bottomed configuration having at its lower inside an recess portion
94a, while the high-resistance structure 110 has at its top a
flange portion 110a. The flange portion 110a is inserted into the
recess portion 94a. Thus, the plating cell 12 is divided into an
anode chamber 100 and a cathode side area 101 in the electrode
holder 94 by the high-resistance structure 110.
[0084] The high-resistance structure 110 is composed of porous
ceramics such as alumina, SiC, mullite, zirconia, titania or
cordierite, or a hard porous material such as a sintered compact of
polypropylene or polyethylene, or a composite material comprising
these materials. The high-resistance structure 110 may be composed
of a woven fabric or a non-woven fabric. In case of the
alumina-based ceramics, for example, the ceramics with a pore
diameter of 30 to 200 .mu.m is used. In case of the SiC, SiC with a
pore diameter of not more than 30 .mu.m, a porosity of 20 to 95%,
and a thickness of about 1 to 20 mm, preferably 5 to 20 mm, more
preferably 8 to 15 mm, issued. The high-resistance structure 110,
in this embodiment, is constituted of porous ceramics of alumina
having a porosity of 30%, and an average pore diameter of 100
.mu.m. The porous ceramic plate per se is an insulator, but the
high resistance structure is constituted to have lower electric
conductivity than that of the plating solution by causing the
plating solution to enter its interior complicatedly and follow a
considerably long path in the thickness direction.
[0085] The high-resistance structure 110, which has the high
resistance, is thus disposed between the anode chamber 100 and the
cathode side area 101. Hence, the influence of the resistance of
the seed layer 7 (see FIG. 1) becomes a negligible degree.
Consequently, the difference in current density over the surface of
the substrate due to electrical resistance on the surface of the
substrate W becomes small, and the uniformity of the plated film
over the surface of the substrate can be improved.
[0086] In the anode chamber 100 and located above the
high-resistance structure 110 is disposed an insoluble anode 98
having a large number of vertically-extending through-holes 98a
therein. The electrode holder 94 has a plating solution discharge
outlet 103 for discharging by suction a plating solution in the
anode chamber 100. The plating solution discharge outlet 103 is
connected to a plating solution discharge pipe 106 connecting with
a waste liquid tank 160. Further, a plating solution supply inlet
104, positioned beside the insoluble anode 98 and the
high-resistance structure 110 and vertically penetrating the
peripheral wall of the electrode holder 94, is provided within the
peripheral wall of the electrode holder 94. The plating solution
supply inlet 104 is connected to a plating solution supply pipe 102
extending from the plating solution adjustment tank 16.
[0087] The plating solution supply inlet 104 is to supply a plating
solution from the side of the insoluble anode 98 and the
high-resistance structure 110 into the cathode side area 101
between the substrate W and the high-resistance structure 110 when
the substrate holder 36 is in the plating position B (see FIG. 4)
and the electrode head 28 is in such a lowered position that the
distance between the substrate W held by the substrate holder 36
and the high-resistance structure 110 is, for example, about 0.5 to
3 mm. The lower-end nozzle portion of the plating solution supply
inlet 104 opens to the cathode side area 101 between the sealing
member 90 and the high-resistance structure 110. A rubber shielding
ring 112 for electrical shielding is attached to the
circumferential surface of the high-resistance structure 110.
[0088] The plating solution, supplied from the plating solution
supply inlet 104, flows in one direction along the surface of the
substrate W, and by the flow of the plating solution, air in the
cathode side area 101 between the substrate W and the
high-resistance structure 110 is forced out of the area. The
cathode side area 101 defined by the substrate W and the sealing
member 90 is thus filled with the fresh, composition-adjusted
plating solution supplied from the plating solution supply inlet
104, and the plating solution is stored in the cathode side area
101 defined by the substrate W and the sealing member 90.
[0089] The insoluble anode 98 is composed of an insoluble metal,
such as platinum, titanium, etc. or a material comprising a base of
such a metal and a coating of iridium oxide. The insoluble anode 98
is free from the formation on its surface of a black sludge called
black film and will not dissolve in a plating solution during
plating. The use of the insoluble anode 98 can thus eliminate the
need for anode replacement. For reasons of easy passage of plating
solution, etc., the insoluble anode 98 may have a net-like
structure.
[0090] As shown in FIG. 13, the plating solution supply facility 18
includes a plating solution supply pipe 102 extending from the
plating solution adjustment tank 16 and connected to the plating
solution supply inlet 104 (see FIG. 12), and a plating solution
recovery pipe 130 extending from the plating solution adjustment
tank 16 and connected to the plating solution recovery nozzle 66
(see FIG. 5). The plating solution supply pipe 102 and the plating
solution recovery pipe 130 are provided with pumps 132, 134,
respectively. A plating solution circulation system 136 is thus
constructed. In particular, the pump 132 provided in the plating
solution supply pipe 102 is driven to supply a predetermined amount
of the plating solution in the plating solution adjustment tank 16
to that area of the surface (surface to be plated) of the substrate
W, held by the substrate holder 36, which is surrounded by the
sealing member 90. After the completion of plating, the pump 134
provided in the plating solution recovery pipe 130 is driven to
suck the plating solution, remaining on the surface of the
substrate W, by the plating solution recovery nozzle 66 and recover
the plating solution in the plating solution adjustment tank 16 for
reuse of the plating solution.
[0091] The plating solution supply facility 18 also includes a
plating solution component replenishment system 138 for supplying
replenisher solutions, each containing a component of the plating
solution in a higher concentration than that in the plating
solution, to the plating solution in the plating solution
adjustment tank 16 so as to maintain the concentration of the
component in the plating solution within a predetermined range. In
particular, the plating solution in this embodiment contains three
organic additives, a reaction accelerator, a reaction suppressor
and a leveler, in addition to copper ions in a concentration of
20-60 g/L, sulfuric acid as a supporting electrolyte in a
concentration of 10-100 g/L, and chlorine as a halogen ion in a
concentration of 30-90 mg/L.
[0092] The replenishment system 138 includes a replenisher solution
tank 140 storing an aqueous solution of copper sulfate having a
copper sulfate concentration of 200 g/L to saturation
concentration, a replenisher solution tank 142 storing sulfuric
acid having a concentration of 20-98 wt %, a replenisher solution
tank 144 storing hydrochloric acid having a concentration of 1-36
wt %, a replenisher solution tank 146 storing a reaction
accelerator solution of a commercial concentration, a replenisher
solution tank 148 storing a reaction suppressor solution of a
commercial concentration, and a replenisher solution tank 150
storing a leveler solution of a commercial concentration. The
replenisher solutions are supplied from the replenisher solution
tanks 140-150 to the plating solution in the plating solution
adjustment tank 16, and pure water (DIW) is also supplied through a
pure water replenishment pipe 152 to the plating solution, thereby
maintaining the concentrations of the components of the plating
solution recovered in the plating solution adjustment tank 16 each
within a predetermined range before reusing the plating solution.
The plating solution adjustment tank 16 is provided with a liquid
level sensor 154 for measuring a liquid level of the plating
solution stored therein.
[0093] The concentration of copper sulfate in the replenishing
aqueous solution of copper surface is preferably in the range of
250-300 g/L, the concentration of the replenishing sulfuric acid is
preferably in the range of 50-98 wt % from the viewpoint of
reducing the replenishment quantity, and the concentration of the
replenishing chlorine is preferably in the range of 5-20 wt %
because of easier handling.
[0094] Though the plating solution used in this embodiment contains
the three organic additives, a reaction accelerator, a reaction
suppressor and a leveler, it is also possible to use a plating
solution containing one or two of the organic additives and
replenish the component(s) of the plating solution with the
replenisher solution(s).
[0095] The plating solution supply facility 18 also includes a
plating solution discharge system 162 for discharging the plating
solution, which circulates in the plating solution circulation
system 136, into the waste liquid tank 160. In particular, a
branching three-way valve 164 is provided in the plating solution
recovery pipe 130, and a waste liquid pipe 166, branched by the
three-way valve 164, is connected to the waste liquid tank 160.
[0096] Thus, when sucking the plating solution remaining on the
surface (surface to be plated) of the substrate W by the plating
solution recovery nozzle 66 and recovering the plating solution in
the plating solution adjustment tank 16 by driving the pump 134,
provided in the plating solution recovery pipe 130, after the
completion of plating, part of the plating solution is discharged
through the waste liquid pipe 166 to the waste liquid tank 160.
[0097] As shown in FIG. 14, the plating solution discharge pipe
106, connected to the plating solution discharge outlet 103 (see
FIG. 12), is connected to the waste liquid tank 160, and the
plating solution discharge pipe 106 is provided with a pump 170.
When the high-resistance structure 100 of the electrode head 28 is
immersed in the plating solution in the plating solution tray 22,
the pump 132 provided in the plating solution supply pipe 102 is
driven to supply the plating solution in the plating solution
adjustment tank 16 into the plating solution tray 22 while the pump
170 provided in the plating solution discharge pipe 106 is driven
to draw the plating solution from the anode chamber 100, thereby
carrying out replacement of the plating solution, with which the
high-resistance structure 110 is impregnated, with a new plating
solution and discharge of the old plating solution.
[0098] When carrying out plating, the cathode electrodes 88 are
electrically connected to the cathode of the plating power source
114, and the insoluble anode 98 to the anode of the plating power
source 114. The plating power source 114 may be one which can
change the direction of electric current so that the plating
apparatus has an etching function of etching a plated film.
[0099] The operation of the substrate processing apparatus
incorporating the plating apparatus according to an embodiment of
the present invention will now be described.
[0100] First, a substrate W to be plated is taken out from one of
the loading/unloading units 10 by the transfer robot 14, and
transferred, with the surface (surface to be plated) facing
upwardly, through the substrate carry-in and carry-out opening
defined in the side panel of a frame, into one of the plating cell
12. At this time, the substrate holder 36 is in lower substrate
transfer position A. After the hand of the transfer robot 14 has
reached a position directly above the substrate stage 68, the hand
of the transfer robot 14 is lowered to place the substrate W on the
support arms 70. The hand of the transfer robot 14 is then
retracted through the substrate carry-in and carry-out opening.
[0101] After the hand of the transfer robot 14 is retracted, the
cup 40 is elevated. Then, the substrate holder 36 is lifted from
substrate transfer position A to pretreatment/cleaning position C.
As the substrate holder 36 ascends, the substrate W placed on the
support arms 70 is positioned by the positioning plate 72 and the
pressing finger 74, and then reliably gripped by the chucking
fingers 76. When the ascending movement of the cup 40 is completed,
the substrate carry-in and carry-out opening in the side panel is
closed by the cup 40, isolating the atmosphere in the side panel
and the atmosphere outside of the side panel from each other.
[0102] Meanwhile, the electrode head 28 of the electrode arm
portion 30 is in a normal position over the plating solution tray
22 now as shown in FIG. 14, and the high-resistance structure 110
is immersed in the plating solution in the plating solution tray
22. In this state, replacement of the plating solution, with which
the high-resistance structure 110 is impregnated, with a new
plating solution is carried out by supplying a plating solution
into the plating solution tray 22 and discharging the plating
solution in the anode chamber 100.
[0103] When the cup 4 is elevated, the pre-coating step is
initiated. Specifically, the substrate holder 36 that has received
the substrate W is rotated, and the pre-coating/recovering arm 32
is moved from the retracted position to a position confronting the
substrate W. When the rotational speed of the substrate holder 36
reaches a preset value, the pre-coating nozzle 64 mounted on the
tip end of the pre-coating/recovering arm 32 intermittently
discharges a pre-coating liquid which comprises a surfactant, for
example, toward the surface of the substrate W. At this time, since
the substrate holder 36 is rotating, the pre-coating liquid spreads
all over the surface of the substrate W. Then, the
pre-coating/recovering arm 32 is returned to the retracted
position, and the rotational speed of the substrate holder 36 is
increased to spin the pre-coating liquid off and dry the surface of
the substrate W.
[0104] After the completion of the pre-coating step, the plating
step is initiated. First, the substrate holder 36 is stopped
against rotation, or the rotational speed thereof is reduced to a
preset rotational speed for plating. In this state, the substrate
holder 36 is lifted to plating position B. Then, the peripheral
portion of the substrate W is brought into contact with the cathode
electrodes 88, when it is possible to pass an electric current, and
at the same time, the sealing member 90 is pressed against the
upper surface of the peripheral portion of the substrate W, thus
sealing the peripheral portion of the substrate W in a watertight
manner.
[0105] Based on a signal indicating that the pre-coating step for
the loaded substrate W is completed, the electrode arm portion 30
is swung in a horizontal direction to displace the electrode head
28 from a position over the plating solution tray 22 to a position
over the plating processing position. After the electrode head 28
reaches this position, the electrode head 28 is lowered toward the
cathode portion 38. The electrode head is stopped when the
high-resistance structure 110 does not contact with the surface of
the substrate W but is held closely to the surface of the substrate
W at a distance ranging from 0.1 mm to 3 mm. Next, the cathode side
area 101 between the substrate W and the high-resistance structure
110 and surrounded by the sealing member 90 is filled with the
plating solution by supplying a predetermined amount of plating
solution from the plating solution supply pipe 102, as shown in
FIG. 13.
[0106] Then, the cathode electrodes 88 are connected to the cathode
of the plating power source 114 and the insoluble anode 98 is
connected to the anode of the plating power source 114 to carry out
plating onto the surface (surface of the seed layer 7) of the
substrate W while integrating the quantity of electricity taken for
plating. After the completion of plating, the plating power source
114 is disconnected from the cathode electrodes 88 and the
insoluble anode 98, and the electrode arm section 30 is raised and
pivoted to return the electrode head 28 to above the plating
solution tray 22 and is then lowered to the normal position.
[0107] Next, the pre-coating/recovery arm 32 is moved from the
retreat position to the position opposite to the substrate W and
lowered. The pump 134 provided in the plating solution recovery
pipe 130 is then driven to recover most of the plating solution on
the substrate W from the plating solution recovery nozzle 66 into
the plating solution adjustment tank 16 while discharging part of
the plating solution into the waste liquid tank 160. After
completion of the recovery of the plating solution, the
pre-coating/recovery arm 32 is returned to the retreat position.
The plated surface of the substrate W is then rinsed by spraying
pure water from the fixed nozzle 34 for spraying pure water onto
the center of the substrate W while rotating the substrate holder
36 at an increased speed, thereby replacing the plating solution on
the surface of the substrate W with pure water. By thus carrying
out rinsing of the substrate W, the cathode electrodes 88 of the
cathode section 38 can be prevented from being contaminated with
the plating solution due to splashing of the plating solution upon
lowering of the substrate holder 36 from the plating position
B.
[0108] After completion of the rinsing, the washing with water step
is initiated. That is, the substrate holder 36 is lowered from
plating position B to pretreatment/cleaning position C. Then, while
pure water is supplied from the fixed nozzle 34 for supplying pure
water, the substrate holder 36 and the cathode portion 38 are
rotated to perform washing with water. At this time, the sealing
member 90 and the cathode electrodes 88 can also be cleaned,
simultaneously with the substrate W, by pure water directly
supplied to the electrode potion 38, or pure water scattered from
the surface of the substrate W.
[0109] After washing with water is completed, the drying step is
initiated. That is, supply of pure water from the fixed nozzle 34
is stopped, and the rotational speed of the substrate holder 36 and
the cathode portion 38 is further increased to remove pure water on
the surface of the substrate W by centrifugal force and to dry the
surface of the substrate W. The sealing member 90 and the cathode
electrodes 88 are also dried at the same time. Upon completion of
the drying, the rotation of the substrate holder 36 and the cathode
portion 38 is stopped, and the substrate holder 36 is lowered to
substrate transfer position A. Thus, the gripping of the substrate
W by the chucking fingers 76 is released, and the substrate W is
just placed on the upper surfaces of the support arms 70. At the
same time, the cup 40 is also lowered.
[0110] All the steps for one substrate including the plating step,
the pretreatment step accompanying to the plating step, the
cleaning step, and the drying step are now finished. The transfer
robot 14 inserts its hand through the substrate carry-in and
carry-out opening into the position beneath the substrate W, and
raises the hand to receive the plated substrate W from the
substrate holder 36. Then, the transfer robot 14 returns the plated
substrate W received from the substrate holder 36 to one of the
loading/unloading units 10.
[0111] When the insoluble anode 98 is used and the plating solution
is recovered and reused in a circulatory manner, as described
above, the concentrations of the components in the plating solution
recovered in the plating solution adjustment tank 16 change
gradually. According to this embodiment, therefore, the replenisher
solutions, each containing a component of the plating solution in a
higher concentration than that in the plating solution, are
supplied from the plating solution component replenishment system
138 into the plating solution adjustment tank 16 when, after having
processed a plurality of substrates, a cumulative quantity of
electricity taken for plating has reached to a predetermined value,
for example, 50 Ah. In particular, the plating solution in the
plating solution adjustment tank 16 is replenished with: an aqueous
solution of copper sulfate having a copper sulfate concentration of
200 g/L to saturation concentration, supplied from the replenisher
solution tank 140; sulfuric acid having a concentration of 20-98 wt
%, supplied from the replenisher solution tank 142; hydrochloric
acid having a concentration of 1-36 wt %, supplied from the
replenisher solution tank 144; a reaction accelerator solution of a
commercial concentration, supplied from the replenisher solution
tank 146; a reaction suppressor solution of a commercial
concentration, supplied from the replenisher solution tank 148; a
leveler solution of a commercial concentration, supplied from the
replenisher solution tank 150; and pure water (DIW), supplied
through the pure water replenishment pipe 152. The concentrations
of the components of the plating solution recovered in the plating
solution adjustment tank 16 are thus maintained each within a
predetermined range, and the concentration-controlled plating
solution is reused in a circulatory manner.
[0112] The amount of the plating solution used can be minimized by
recovering and reusing the plating solution in a circulatory manner
through the plating solution circulation system 136. Further, the
use of the insoluble anode 98, which needs no replacement, can
facilitate the maintenance and management of the anode. In
addition, by using the insoluble anode 98 and also by maintaining
the concentrations of the components of the plating solution, which
concentrations will change with circulation and reuse of the
plating solution, each within a predetermined range by replenishing
the plating solution with the replenisher solutions, each
containing one of the components in a higher concentration than
that in the plating solution, by the plating solution component
replenishment system 138, it becomes possible to prevent an
increase of fine particles in the plating solution in association
with the replenishment of the components of the plating solution
and to avoid complication of the apparatus.
[0113] The replenishment quantity of each replenisher solution is
determined, for example, based on a cumulative quantity of
electricity taken for plating. In electroplating using a plating
solution in a circulatory manner, a change in the quantity of a
component in the plating solution with the progress of plating is
generally determined by the quantity of electricity that has been
supplied for plating. Thus, on the basis of a predetermined
experimental data for consumption or increase of a component, the
replenishment quantity of the component of the plating solution can
be calculated from a cumulative quantity of electricity taken for
electroplating.
[0114] The calculation of the replenishment quantity of a component
of a plating solution from a cumulative quantity of electricity can
be made in a shorter time than the analysis time of an automatic
analysis means. This makes it possible to replenish, e.g., an
additive with a smaller change in the concentration of the additive
in the plating solution during determination of the replenishment
quantity.
[0115] The plating solution adjustment tank 16 is provided with a
liquid level sensor 154 for measuring a liquid level of the plating
solution stored in the tank 16, so that the plating solution in a
constant amount can be stored in the plating solution adjustment
tank 16 by stopping supply of the replenisher solutions and pure
water when the liquid level of the plating solution in the plating
solution adjustment tank 16 has come up to a predetermined position
by the supply of the replenisher solutions and pure water. When the
plating solution is recovered in the plating solution adjustment
tank 16, part of the plating solution is discharged into the waste
liquid tank 160 by the plating solution discharge system 162. The
amount of the plating solution recovered and reused in the plating
solution circulation system 136 can thus be adjusted, making it
possible to supply the replenisher solutions and pure water in
amounts sufficient for bringing the concentrations of the
components in the plating solution in the plating solution
adjustment tank 16 each into a predetermined range.
[0116] FIGS. 15 and 16 schematically show a plating apparatus
according to another embodiment of the present invention. This
plating apparatus differs from the above-described plating
apparatus in the following respects: The plating solution
circulation system 136 includes a plating solution buffer tank 200
and a plating solution supply tank 202 respectively located on the
upstream side and on the downstream side of the plating solution
adjustment tank 16. The plating solution recovery pipe 130
extending from the plating solution recovery nozzle 66 is connected
to the plating solution buffer tank 200, while the plating solution
supply pipe 102 for supplying a plating solution through the
plating solution supply inlet 114 to the plating cell 12 is
connected to the plating solution supply tank 202. The plating
solution buffer tank 200 is connected to the plating solution
adjustment tank 16 via a communication pipe 206 provided with a
pump 204, and the plating solution adjustment tank 16 is connected
to the plating solution supply tank 202 via a communication pipe
210 provided with a pump 208. To the bottom of the plating solution
adjustment tank 16 is connected one end of a plating solution
withdrawing pipe 214 provided with a pump 212, while the other end
of the plating solution withdrawing pipe 214 is connected to the
waste liquid tank 160. The plating solution discharge system 162 is
thus constructed.
[0117] Further, as shown in FIG. 16, in carrying out replacement of
the plating solution, with which the high-resistance structure 110
of the electrode head 28 is impregnated, with a new plating
solution and discharge of the old plating solution when the
high-resistance structure 110 is immersed in the plating solution
in the plating solution tray 22, the plating solution can be
selectively introduced into the waste liquid tank 160 and disposed
of, or can be introduced into the plating solution buffer tank 200
for recovery and reuse of the plating solution, by a three-way
valve 215.
[0118] The plating apparatus of this embodiment is also provided
with a plating solution analyzer 216 for sampling the plating
solution in the plating solution supply tank 202 and analyzing the
components, and returning the sampled solution after analysis to
the plating solution adjustment tank 16. Further, pure water is
stored in a pure water tank 218 and supplied into the plating
solution adjustment tank 16. The plating solution buffer tank 200
is provided with a liquid level sensor 220 for measuring a liquid
level of the plating solution stored in the plating solution buffer
tank 200.
[0119] According to this embodiment, the plating solution is
recovered in the plating solution buffer tank 200 every time one
substrate is processed in the plating cell 12, and the plating
solution in the plating solution buffer tank 200 is sent to the
plating solution adjustment tank 16 when the amount of the plating
solution recovered in the plating solution buffer tank 200 has
reached a predetermined amount. Part of the plating solution
received by the plating solution adjustment tank 16 is discharged
by the plating solution discharge system 162. Simultaneously with
or after the discharge of the plating solution, as with the
preceding embodiment, the replenisher solutions each containing a
component of the plating solution, in a higher concentration than
that in the plating solution, i.e., an aqueous solution of copper
sulfate, sulfuric acid, hydrochloric acid, a reaction accelerator
solution, a reaction suppressor solution, a leveler solution and
pure water (DIW), are supplied from the plating solution
replenishment system 138 to the plating solution in the plating
solution adjustment tank 16 so that the concentrations of the
components of the plating solution in the plating solution
adjustment tank 16 are kept constant.
[0120] The plating solution, having the adjusted concentrations of
components, is sent from the plating solution adjustment tank 16 to
the plating solution supply tank 202, and a predetermined amount of
the plating solution is sent from the plating solution supply tank
202 to the plating cell 12. In particular, as shown in FIG. 15, a
predetermined amount of the plating solution is sent from the
plating solution supply tank 202 to the area between the substrate
W and the insoluble anode 98 and surrounded by the sealing member
90, and a voltage is applied from the plating power source 114 to
between the insoluble anode 98 and the cathode electrodes 88 to
carry out plating of the surface of the substrate W. Further, as
shown in FIG. 16, a predetermined amount of the plating solution is
sent from the plating solution supply tank 202 into the plating
solution tray 22 while discharging the plating solution in the
anode chamber 100 of the electrode head 28 through the plating
solution discharge pipe 106, thereby carrying out replacement of
the plating solution with which the high-resistance structure 110
is impregnated.
[0121] By thus sending a plating solution after its use in plating
to the plating solution adjustment tank 16 after recovering the
plating solution in the plating solution buffer tank 200,
replenishing the plating solution in the plating solution
adjustment tank 16 with replenisher solutions to adjust the
concentrations of the components of the plating solution, storing
the plating solution containing the components in the adjusted
concentrations in the plating solution supply tank 202, and then
supplying the plating solution to the plating cell 12 for plating,
it becomes possible to supply to the plating cell 12 a plating
solution having a more constant concentration of each
component.
[0122] Further according to this embodiment, the plating solution
in the plating solution supply tank 202 is sampled at specified
time intervals to analyze the concentrations of the components in
the plating solution by the plating solution analyzer 216, and the
plating solution in the plating solution adjustment tank 16 is
replenished with deficient components by the plating solution
component replenishment system 138. This makes it possible to deal
with a case in which the consumptions of the components of the
plating solution become imbalanced, e.g., due to a change in the
plating conditions with time.
[0123] As shown in FIGS. 17 and 18, it is possible to omit the
plating solution buffer tank 200 and the plating solution supply
tank 202, and to connect the plating solution recovery pipe 130
extending from the plating solution recovery nozzle 66, and the
plating solution supply pipe 102 for supplying the plating solution
through the plating solution supply inlet 104 to the plating cell
12, both to the plating solution adjustment tank 16, thereby
simplifying the apparatus.
[0124] In the preceding embodiment, the replenishment quantity of a
component of plating solution is calculated from a cumulative
quantity of electricity taken for plating, based on the fact that
the consumption of a plating solution component is generally
determined by the quantity of electricity during plating. There
are, however, some additives, such as a reaction accelerator, whose
consumption in a plating solution will differ by a difference in
the current density of electric current applied upon plating and by
a difference in the time of application of the electric current.
Thus, if the replenishment quantity is calculated only on the basis
of a cumulative quantity of electricity, a difference will be
produced between the calculated replenishment quantity and the
actual consumption.
[0125] FIG. 19 shows the consumption rate (consumption coefficient)
of a reaction accelerator contained in a plating solution present
in the cathode side area 101 between the substrate W and the
high-resistance structure 110 and surrounded by the sealing member
90, as determined when plating of the substrate surface is carried
out by bringing the electrode head 28 close to the surface of the
substrate W, filling the cathode side area 101 with the plating
solution, and connecting the cathode electrodes 88 and the
insoluble anode 98 respectively to the cathode and the anode of the
plating power source 114, as shown in FIG. 15, and when such
plating is carried out with various current densities and various
times of application of electric current.
[0126] The consumption of such an additive as a reaction
accelerator, whose consumption will differ by a difference in the
current density of electric current applied upon plating and by a
difference in the time of application of the electric current, can
be determined more precisely by predetermining a consumption
coefficient (consumption rate) as shown in FIG. 19, determined by
the current density of electric current applied to carry out
plating and the time of application of the electric current, and
determining the consumption of the reaction accelerator based on
the current density of electric current applied upon actual plating
and the time of application of the electric current.
[0127] By thus more precisely determining the consumption of a
reaction accelerator, and supplying a reaction accelerator solution
in such an amount as to compensate for that consumption from the
replenisher solution tank 146 of the plating solution component
replenishment system 138 to the plating solution in the plating
solution adjustment tank 16, it becomes possible to more strictly
control the concentration in a plating solution of a reaction
promoter whose concentration will be affected by the current
density. This enables uniform copper plating or the like, thereby
producing highly-reliable copper interconnects or the like.
[0128] When recovering part of the plating solution from the anode
chamber 100 to reuse it, as shown in FIG. 16, the plating solution,
in which an additive, e.g., a reaction accelerator, has been
consumed in the anode chamber 100, is returned to the plating
solution buffer tank 200. An additive such as a reaction
accelerator is consumed differently in the anode chamber 100 and in
the cathode side area 101. Thus, the consumption of such an
additive can be determined more precisely by predetermining the
consumption rate (consumption coefficient) of the additive, such as
a reaction accelerator, contained in the plating solution in the
anode chamber 110, as determined when carrying out plating of the
surface of a substrate with various current densities and various
times of application of electric current, determining the
consumption, by plating, of the additive contained in the plating
solution in the anode chamber 100 by using the consumption
coefficient, and adding the thus-determined consumption to the
consumption, by plating, of the additive in the cathode side area
101 as determined in the above-described manner.
EXAMPLE 1
[0129] A 300-mm silicon wafer, having in a surface a barrier layer
and a copper seed layer formed by PVD, was prepared. Using the
plating apparatus shown in FIGS. 2 through 14, a copper plated film
having a thickness of 1 .mu.m was formed on the surface of the
silicon wafer. The same plating operations were carried out
consecutively. The composition of the plating solution used and the
plating conditions are shown below. The quantity of electricity
used for plating was integrated and, every time the cumulative
quantity of electricity has reached 50 Ah, the plating solution was
replenished with the below-described replenisher solutions
(concentration adjustment solutions) so as to adjust the
concentrations of the components of the plating solution in the
plating solution adjustment tank to the initial concentrations. The
replenishment quantity of each replenisher solution containing one
of the components was calculated based on a consumption or an
increase as predetermined experimentally for the component.
Composition of Plating Solution
[0130] Copper sulfate pentahydrate: 200 g/L [0131] Sulfuric acid:
80 g/L [0132] Chlorine: 50 mg/L [0133] Organic additives (reaction
accelerator, reaction suppressor, leveler): predetermined amounts
Plating Conditions [0134] Amount of plating solution: 50.+-.5 L
[0135] Amount of plating solution replaced in the electrode head:
10 ml for each operation [0136] Amount of plating solution
supplied: 100 ml for each operation [0137] Amount of plating
solution recovered: 90 ml for each operation Replenisher Solutions
(Concentration Adjustment Solutions) [0138] Aqueous solution of
copper sulfate pentahydrate: copper ion concentration 73 g/L [0139]
96 wt % sulfuric acid [0140] 10 wt % hydrochloric acid [0141]
Organic additives (reaction accelerator, reaction suppressor,
leveler): commercial concentrations
COMPARATIVE EXAMPLE 1
[0142] The consecutive plating operations, each forming the plated
film on the surface of the silicon wafer, were carried out in the
same manner as in Example 1, but without replenishing the plating
solution with a replenisher solution.
COMPARATIVE EXAMPLE 2
[0143] The consecutive plating operations, each forming the plated
film on the surface of the silicon wafer, were carried out in the
same manner as in Example 1, except that the plating solution
remaining on the silicon wafer after plating was discharged without
recovering it in the plating solution adjustment tank.
[0144] Table 1 shows a change in the concentration of each
component of the plating solution and the amount of the plating
solution discharged, as observed after carrying out consecutive
plating operations in the respective manners of Example 1 and Comp.
EXAMPLES 1 AND 2. TABLE-US-00001 TABLE 1 Amount of Change in
concentration plating Plating Sulfuric solution conditions Copper
acid Chlorine Accelerator Suppressor Leveler discharged Ex. 1
.smallcircle. .smallcircle. .smallcircle. .smallcircle.
.smallcircle. .smallcircle. .smallcircle. (small) Comp. Ex. 1 x x
.quadrature. x .quadrature. .quadrature. .smallcircle. (small)
Comp. Ex. 2 .smallcircle. .smallcircle. .smallcircle. .smallcircle.
.smallcircle. .smallcircle. x (large)
[0145] As will be appreciated from the data in Table 1, the
concentrations of the components of the plating solution can be
maintained each in a predetermined range in Example 1, and the
amount of the plating solution discharged is small. In contrast,
the data for Comp. Example 1 shows a large change in the
concentration of each component of the plating solution. The
concentration of each component decreases or increases with an
increase in the number of the wafers processed, and thus the
initial plating performance cannot be maintained. Though, in Comp.
Example 2 the concentrations of the components of the plating
solution can be maintained each in a predetermined range, the
amount of the plating solution discharged is large and thus is
uneconomical.
EXAMPLE 2
[0146] A 300-mm silicon wafer, having in a surface a barrier layer
and a copper seed layer formed by PVD, was prepared. Using the
plating apparatus shown in FIGS. 15 and 16, a copper plated film
having a thickness of 1 .mu.m was formed on the surface of the
silicon wafer. The same plating operations were carried out
consecutively. The composition of the plating solution used is the
same as in Example 1, and the plating conditions are shown below.
The replenishment quantity of each of the same replenisher
solutions (concentration adjustment solutions) as used in Example 1
was calculated based on a cumulative quantity of electricity and on
a consumption or an increase predetermined experimentally for each
component of the plating solution. The plating solution in the
plating solution adjustment tank was replenished with the
replenisher solutions in the calculated amounts so as to adjust the
concentration of each component of the plating solution to a
predetermined concentration.
Plating Conditions
[0147] Amount of plating solution: 50.+-.5 L Amount of plating
solution replaced in the electrode head: 20 ml for each operation
[0148] Amount of plating solution supplied: 100 ml for each
operation
[0149] FIGS. 20A and 20B show the concentrations of the components
of the plating solution in the plating solution supply tank. The
concentration data shows a constant concentration of each component
of the plating solution in the plating solution supply tank,
indicating constancy of the concentrations of the components of the
plating solution supplied to the plating cell.
EXAMPLE 3
[0150] Plating of wafers was carried out in the same manner as in
Example 1, but using the plating apparatus shown in FIGS. 17 and
18. FIGS. 21A and 21B show the concentrations of the components of
the plating solution in the plating solution adjustment tank. As
will be appreciated from the data, though the concentrations of the
components of the plating solution in the plating solution
adjustment tank, i.e., the plating solution to be supplied to the
plating cell, change respectively, the concentrations can be
adjusted and maintained each in a predetermined range.
EXAMPLE 4
[0151] Plating of wafers was carried out using a plating solution
comprising a copper sulfate solution (Cu: 40 g/L, H.sub.2SO.sub.4:
80 g/L, Cl.sup.-: 50 ppm) and additives (reaction suppressor: 6
ml/L, reaction accelerator: 10 ml/L, leveler: 2 ml/L). After
carrying out plating at a current density of 40 mA/cm.sup.2 for one
hour, plating was further carried out at a current density of 20
mA/cm.sup.2 for one hour. At intervals of 20 minutes, the
consumption of the reaction accelerator was determined by using a
consumption coefficient as determined by the current density and
the time of application of electric current, and the reaction
accelerator in such an amount as to compensate for the consumption
was added to the plating solution. FIG. 22 shows the concentration
of the reaction accelerator in the plating solution during plating.
The data in FIG. 22 demonstrates that the concentration of the
reaction accelerator in the plating solution is kept constant
during plating.
[0152] According to the present invention, a system for recovering
and reusing a plating solution in a circulatory manner is
established, whereby the amount of the plating solution used can be
reduced. Further, the use of an insoluble anode, which needs no
replacement and whose maintenance and management can be made with
ease, can prevent an increase of fine particles in a plating
solution and can avoid complication of the apparatus. In addition,
it becomes possible with the present invention to keep the
concentrations of the components of a plating solution constant
over a long period of time, thus stabilizing the plating properties
of the plating solution.
* * * * *