U.S. patent application number 10/739891 was filed with the patent office on 2005-06-23 for method and apparatus for acid and additive breakdown removal from copper electrodeposition bath.
This patent application is currently assigned to APPLIED MATERIALS, INC.. Invention is credited to Kovarsky, Nicolay Y., Lubomirsky, Dmitry.
Application Number | 20050133374 10/739891 |
Document ID | / |
Family ID | 34677745 |
Filed Date | 2005-06-23 |
United States Patent
Application |
20050133374 |
Kind Code |
A1 |
Kovarsky, Nicolay Y. ; et
al. |
June 23, 2005 |
Method and apparatus for acid and additive breakdown removal from
copper electrodeposition bath
Abstract
A method and apparatus for removing waste material from a
plating solution is disclosed. The invention generally provides a
plating cell having an electrolyte inlet and an electrolyte drain,
an electrolyte storage unit in fluid communication with the
electrolyte inlet, and a diffusion dialysis chamber in fluid
communication with the electrolyte drain and the electrolyte
storage unit. The diffusion dialysis chamber is generally
configured to receive at least a portion of used electrolyte
solution and remove waste material therefrom in order to provide a
refreshed electrolyte solution to the electrolyte storage unit. A
method generally includes supplying an electrolyte solution to a
copper plating cell, plating copper onto a substrate in the plating
cell with the electrolyte solution, removing used electrolyte
solution from the plating cell, and refreshing a portion of the
used electrolyte solution with a diffusion dialysis device.
Inventors: |
Kovarsky, Nicolay Y.;
(Sunnyvale, CA) ; Lubomirsky, Dmitry; (Cupertino,
CA) |
Correspondence
Address: |
MOSER, PATTERSON & SHERIDAN, LLP
APPLIED MATERIALS, INC.
3040 POST OAK BOULEVARD, SUITE 1500
HOUSTON
TX
77056
US
|
Assignee: |
APPLIED MATERIALS, INC.
|
Family ID: |
34677745 |
Appl. No.: |
10/739891 |
Filed: |
December 18, 2003 |
Current U.S.
Class: |
205/99 ;
204/237 |
Current CPC
Class: |
C25D 21/22 20130101 |
Class at
Publication: |
205/099 ;
204/237 |
International
Class: |
C25D 021/18 |
Claims
1. An electrochemical plating system, comprising: a plating cell;
and a diffusion dialysis device in fluid communication with the
plating cell, the diffusion dialysis device configured to remove
waste material from an electrolyte solution.
2. The plating system of claim 1, wherein the diffusion dialysis
device comprises alternating diluted acid cells and electrolyte
cells separated by anionic membranes, the electrolyte cells passing
the electrolyte solution therethrough and the diluted acid cells
removing the waste material.
3. The plating system of claim 2, wherein the anionic membrane
comprises a matrix having a positive charge inside and a selected
porosity for selectively passing acids and at least some organic
molecules.
4. The diffusion dialysis device of claim 2, wherein the pore size
of the anionic membrane is between 50 and 100 angstroms.
5. The plating system of claim 2, wherein the anionic membranes
allow negatively charged ions and at least some waste material
within the electrolyte solution to diffuse therethrough into the
diluted acid cells.
6. The plating system of claim 2, wherein the waste material
comprises organic additive breakdown product.
7. The plating system of claim 2, wherein the anionic membranes are
more permeable to accelerator and its breakdown products than
leveler and its breakdown products and less permeable to suppressor
and its breakdown products.
8. The plating system of claim 2, wherein the anionic membranes
prevent positively charged copper ions from passing
therethrough.
9. The plating system of claim 2, wherein the diffusion dialysis
devise comprises between about 25 and about 100 total collective
electrolyte cells and diluted acid cells.
10. The plating system of claim 1, wherein the plating cell is
divided into a catholyte compartment and an anolyte compartment by
a cation membrane, the catholyte compartment for circulating the
electrolyte solution therethrough.
11. The system of claim 1, further comprising an electrodialysis
cell that receives the electrolyte solution from the diffusion
dialysis device.
12. The system of claim 11, wherein the electrodialysis cell
comprises at least one cationic membrane between cells having an
electrolyte solution containing waste material and cells having a
refreshed electrolyte solution.
13. The plating system of claim 1, further comprising an
electrolyte storage unit.
14. A diffusion dialysis device for extracting waste material from
an electrolyte solution, comprising: a housing having a plurality
of anionic membranes positioned therein to define alternating
electrolyte cells and diluted acid cells; and a deionized water
loop comprising: a supply conduit that supplies a controlled
concentration of acid to the diluted acid cells; and a return
conduit that receives an outflow from the diluted acid cells.
15. The diffusion dialysis device of claim 14, wherein each anionic
membrane comprises a matrix having a positive charge inside and a
selected porosity to extract waste material comprising organic
breakdown product and acid.
16. The diffusion dialysis device of claim 15, wherein the anionic
membranes allow negatively charged ions and at least some of the
waste material within the electrolyte solution to diffuse
therethrough into the diluted acid cells.
17. The plating system of claim 15, wherein the anionic membranes
are more permeable to accelerator and its breakdown products than
leveler and its breakdown products and less permeable to suppressor
and its breakdown products.
18. The diffusion dialysis device of claim 15, wherein the anionic
membranes prevent positively charged copper ions from passing
therethrough.
19. The diffusion dialysis device of claim 15, wherein the pore
size of the anionic membranes is between 50 and 100 angstroms.
20. A method for plating copper, comprising: supplying an
electrolyte solution to a plating cell; plating onto a substrate in
the plating cell with the electrolyte solution; removing used
electrolyte solution from the plating cell; and refreshing a
portion of the used electrolyte solution with a diffusion dialysis
device.
21. The method of claim 20, wherein the refreshing a portion of the
used electrolyte with the diffusion dialysis devise comprises:
receiving the used electrolyte solution in an electrolyte cell of
the diffusion dialysis device; urging negative sulfate ions and
organic additive breakdown waste material through an anionic
membrane into a diluted acid cell; and removing a refreshed
electrolyte solution from the electrolyte cell.
22. The method of claim 21, wherein urging comprises maintaining a
concentration gradient across the electrolyte cell and the diluted
acid cell.
23. The method of claim 20, further comprising receiving the
refreshed electrolyte solution in an electrodialysis cell that
removes additional organic additives and organic additive breakdown
products from the refreshed electrolyte solution.
24. The method of claim 20, wherein the plating cell is divided
into a catholyte compartment and an anolyte compartment by a cation
membrane, the catholyte compartment for circulating the electrolyte
solution therethrough.
25. A method for replenishing a copper plating solution,
comprising: receiving a portion of a used electrolyte solution in
an electrolyte cell of a diffusion dialysis device; urging
negatively charged sulfate ions and organic additive breakdown
waste material into a diluted acid cell adjacent the electrolyte
cell to provide a refreshed electrolyte solution, wherein the
diluted acid cell and the electrolyte cell are separated by an
anionic membrane; and returning the refreshed electrolyte solution
to the copper plating solution.
26. The method of claim 25, wherein urging comprises maintaining a
concentration gradient across the electrolyte cell and the diluted
acid cell.
27. The method of claim 25, wherein the receiving step comprises
receiving the used electrolyte solution in up to 100 electrolyte
cells within a single diffusion dialysis device.
28. The method of claim 25, wherein a collective total of the
electrolyte cells and the diluted acid cells is between about 25
and about 100.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] Embodiments of the invention generally relate to removing
organic waste material and acid from semiconductor electrolyte
solutions.
[0003] 2. Description of the Related Art
[0004] Metallization for sub-quarter micron sized features is a
foundational technology for present and future generations of
integrated circuit manufacturing processes. More particularly, in
devices such as ultra large scale integration-type devices, i.e.,
devices having integrated circuits with more than a million logic
gates, the multilevel interconnects that lie at the heart of these
devices are generally formed by filling high aspect ratio
interconnect features with a conductive material, such as copper or
aluminum. Conventionally, deposition techniques such as chemical
vapor deposition (CVD) and physical vapor deposition (PVD) have
been used to fill these interconnect features. However, as
interconnect sizes decrease and aspect ratios increase, void-free
interconnect feature fill via conventional metallization techniques
becomes increasingly difficult. As a result, plating techniques
such as electrochemical plating (ECP) and electroless plating have
emerged as viable processes for filling sub-quarter micron sized
high aspect ratio interconnect features in integrated circuit
manufacturing processes.
[0005] In an ECP process, sub-quarter micron sized high aspect
ratio features formed on a substrate surface may be efficiently
filled with a conductive material, such as copper. ECP plating
processes are generally two stage processes, wherein a seed layer
is first formed over the surface features of the substrate, and
then the surface features of the substrate are exposed to an
electrolyte solution, while an electrical bias is applied between
the substrate and an anode positioned within the electrolyte
solution. The electrolyte solution is generally rich in ions to be
plated onto the surface of the substrate, and therefore, the
application of the electrical bias causes these ions to be urged
out of the electrolyte solution and to be plated as a metal on the
seed layer. The plated metal, e.g., copper, grows in thickness and
forms a copper layer over the seed layer that operates to fill the
features formed on the substrate surface. The concentration of
chemicals in the electrolyte solution must be maintained within a
narrow operation window to achieve void free filling of the
features.
[0006] In order to facilitate and control this plating process,
several additives may be utilized in the electrolyte plating
solution. For example, a typical electrolyte solution used for
copper electroplating may consist of copper sulfate solution, which
provides the copper to be plated, having sulfuric acid and copper
chloride added thereto. The sulfuric acid may generally operate to
modify the acidity and conductivity of the solution. The
electrolytic solutions also generally contain various organic
molecules, which may be accelerators, suppressors, levelers,
brighteners, etc. These organic molecules are generally added to
the plating solution in order to facilitate formation of void-free
high aspect ratio features and planarized copper deposition.
Accelerators, for example, may be sulfide-based molecules that
locally accelerate electrical current at a given voltage where they
absorb. Suppressors may be polymers of polyethylene glycol,
mixtures of ethylene oxides and propylene oxides, or block
copolymers of ethylene oxides and propylene oxides which tend to
reduce electrical current at the sites where they absorb (the upper
edges/corners of high aspect ratio features), and therefore, slow
the plating process at those locations, which reduces premature
closure of the feature before the feature is completely filled.
Levelers may be nitrogen containing, long chain polymers which
operate to facilitate planar plating. Additionally, the plating
bath usually contains a small amount of chloride, generally between
about 20 and about 60 ppm, which provides negative ions needed for
adsorption of suppressor molecules on the cathode, while also
facilitating proper anode corrosion.
[0007] Although the various organic additives facilitate the
plating process and offer a control element over the interconnect
formation process, they also present a challenge since the
additives are known to eventually break down and become waste
material in the electrolyte solution that is no longer useful and
may even be a contaminant. Conventional plating systems
traditionally dealt with these organic waste materials via bleed
and feed methods (periodically replacing a portion of the
electrolyte), extraction methods (filtering the electrolyte with a
charcoal filter), photochemical decomposition methods (using UV in
conjunction with ion exchange and acid-resistant filters), and/or
ozone treatments (dispensing ozone into the electrolyte). However,
these conventional methods are known to be inefficient, expensive
to implement and operate, bulky, and/or tend to generate hazardous
materials or other kinds of contaminants as byproducts.
[0008] Recently, electrodialysis cells (EDC) have been used to
substantially remove all of the organic additives from at least a
portion of the electrolyte solution in the plating process as
discussed in detail in U.S. patent application Ser. No. 10/074,569,
which is herein incorporated by reference in its entirety.
Substantially all of the additives are removed since membranes used
in the EDC are sufficiently dense such that the additives fail to
penetrate through the membranes. The EDC requires an electrical
supply and may lack the ability to remove acids. However, it may be
desirable to remove acids that accumulate during the plating
process and to remove certain organic additives and/or organic
waste at a faster rate than other organic additives based on the
breakdown rates of the various organic additives. For example, the
accelerators breakdown faster than the levelers which breakdown
faster than the suppressors. Further, it may be desirable in
certain applications to remove only a percentage of the organic
additives and/or organic waste from the entire electrolyte solution
rather than all of the organic additives from a portion of the
electrolyte solution.
[0009] Therefore, there exists a need for a method and apparatus
for removing additive breakdown waste material from semiconductor
electroplating baths, wherein the method and apparatus addresses
the deficiencies of conventional devices.
SUMMARY OF THE INVENTION
[0010] The invention generally provides a plating cell having an
electrolyte inlet and an electrolyte drain, an electrolyte storage
unit in fluid communication with the electrolyte inlet, and a
diffusion dialysis chamber in fluid communication with the
electrolyte drain and the electrolyte storage unit. The diffusion
dialysis chamber is generally configured to receive at least a
portion of used electrolyte solution and remove waste material
therefrom in order to provide a refreshed electrolyte solution to
the electrolyte storage unit. The method generally includes
supplying an electrolyte solution to a copper plating cell, plating
copper onto a substrate in the plating cell with the electrolyte
solution, removing used electrolyte solution from the plating cell,
and refreshing a portion of the used electrolyte solution with a
diffusion dialysis device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] So that the manner in which the above recited features of
the invention can be understood in detail, a more particular
description of the invention, briefly summarized above, may be had
by reference to embodiments, some of which are illustrated in the
appended drawings. It is to be noted, however, that the appended
drawings illustrate only typical embodiments of this invention and
are therefore not to be considered limiting of its scope, for the
invention may admit to other equally effective embodiments.
[0012] FIG. 1 illustrates an exemplary plating system incorporating
a diffusion dialysis device (DDD).
[0013] FIG. 2 illustrates a schematic view of the DDD in FIG.
1.
[0014] FIG. 3 illustrates an exemplary plating system incorporating
the DDD and an electrodialysis cell (EDC).
[0015] FIG. 4 illustrates a schematic view of the EDC shown in FIG.
3.
[0016] FIG. 5 illustrates a schematic view of an alternative
EDC.
[0017] FIG. 6 illustrates an alternative plating system
configuration that incorporates the DDD.
[0018] FIG. 7 is a graph showing the rate of removal by the DDD of
sulfuric acid from an electrolyte solution.
[0019] FIG. 8 is a graph showing the rate of removal of additives
and breakdown products from the additives by the DDD from the
electrolyte solution.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0020] The invention generally relates to removal of organic waste
material and acid from an electrolyte solution during a plating
process with a diffusion dialysis device (DDD). FIG. 1 illustrates
an exemplary plating system 100 that includes a diffusion dialysis
device (DDD) 110 in conjunction with a plating cell 101 such as an
electrochemical plating (ECP) cell, an electroless plating cell, or
other plating cell configuration. The plating cell 101 includes a
fluid inlet 105 configured to deliver an electrolyte solution or
plating processing fluid to the plating cell 101 and a fluid outlet
or drain 106 configured to receive the electrolyte solution from
the plating cell 101. The electrolyte solution enters the plating
cell 101 via the inlet 105 that is in fluid communication with an
electrolyte solution storage unit 102. A fluid pump 104 positioned
between the storage unit 102 and the plating cell 101 circulates
the electrolyte solution to the plating cell 101. The fluid outlet
106 of the plating cell 101 returns used electrolyte solution to
the storage unit 102 through a fluid conduit 11 1. The fluid
conduit 111 may include a slipstream, bypass, or diverter fluid
conduit 112 attached thereto. The diverter fluid conduit 112
receives a portion of or the entire used electrolyte solution
returned from the processing cell 101 to the storage unit 102 via
the drain 106. The diffusion dialysis device 110 positioned along
the diverter fluid conduit 112 includes an input for accepting the
electrolyte solution flowing through the diverter fluid conduit 112
and an output coupled to a fluid conduit 113 for returning the
electrolyte solution to the storage unit 102. In this manner, the
electrolyte solution continually circulates through an electrolyte
circulation loop.
[0021] During typical operational periods, the plating cell 101 may
receive and/or circulate therethrough approximately 100 liters of
electrolyte solution per hour. Thus, the DDD 110 receives any
portion of this used electrolyte solution or the entire used
electrolyte solution. As the used electrolyte solution passes
through the DDD 110, the DDD 110 removes a portion of the organic
additives, waste material from the organic additive breakdown, and
acid from the used electrolyte solution to provide a refreshed
electrolyte solution. The refreshed electrolyte solution is
reintroduced into the fluid storage unit 102 for subsequent use in
plating operations. The DDD 110 captures the extracted acids and
waste material for disposal. In this manner, the DDD 110 operates
to decrease or eliminate the frequency of replacement of the
electrolyte solution by retaining copper ions within the
electrolyte solution, removing organic additive breakdown waste
material, and removing acid accumulated in the electrolyte
solution. If needed, acid and additives may be reintroduced to the
refreshed electrolyte solution in order to compensate for the loss
of these components by the DDD 110.
[0022] FIG. 2 illustrates a schematic view of the DDD 110 shown in
FIG. 1. The DDD 110 includes an outer housing 200 having a
plurality of anionic membranes 206 that separate and define
electrolyte cells 202 and diluted acid cells 204 within the DDD
110. The electrolyte cells 202 and the diluted acid cells 204
alternate across the DDD 110. Although only four electrolyte cells
202 and diluted acid cells 204 are shown, the DDD 110 may include
any number of anionic membranes 206 that define any number of
alternating electrolyte cells 202 and diluted acid cells 204. For
example, embodiments of the DDD 110 may include between 3 and about
500 total number of electrolyte cells 202 and diluted acid cells
204. Configuration of the anionic membranes 206 within the housing
200 of the DDD 110 may include any known configuration for
diffusion dialysis currently used for free acid recovery.
[0023] The anionic membranes 206 can be any type of anion-exchange
membrane such as any one of many commercially available membranes.
For example, Asahi Glass Company produces a wide range of
polystyrene based ion-exchange membranes under the trade name
Selemion such as anion membranes AMV, AMT, and AMD. Other companies
manufacture similar ion-exchange membanes, such as Solvay (France),
Sybron Chemical Inc. (USA), Ionics (USA), and FuMA-Tech (Germany)
etc. Each anionic membrane 206 comprises a matrix having a positive
charge inside and a selected porosity for selectively passing
molecules therethrough. In one embodiment, the pore size of the
anionic membrane is preferably greater than 50 angstroms and most
preferably about 100 angstroms. Thus, the anionic membrane 206
permits water, hydrogen ion, disassociated sulfate ion, and organic
additive penetration due to the negative or neutral charge and/or
size of these molecules. However, disassociated copper ion
penetration is negligible since the copper ions are repelled by the
anionic membrane 206 having the same charge. The diffusion rate of
the different organic additives through the anionic membranes 206
varies depending on the size and charge of the organic additives.
For example, small and negative or neutral charged organic
additives such as sulfur containing accelerators and brighteners
penetrate through the anionic membrane 206 faster than the organic
additives containing nitrogen such as levelers. Further, the
polymeric structures of some organic additives such as suppressors
substantially lack the ability to pass through the anionic
membranes 206 due to their large sizes. Since the contamination
material from the various organic additives is caused by their
breakdown, the contamination material typically has a smaller chain
length than the original organic additive. Thus, the smaller chain
length of the contamination material permits the contamination
material to penetrate through the anionic membranes 206.
[0024] In operation, the conduit 112 supplies used electrolyte
solution from the plating cell 100 (shown in FIG. 1) to each of the
electrolyte cells 202 through inlets 205 along the housing 200 of
the DDD 110. In one embodiment, the inlets 205 are integral with
the housing 200 such that the conduit 112 supplies used electrolyte
solution to one location along the housing 200. The housing 200
includes individual frame chambers that sandwich the anionic
membranes 206 between adjacent frame chambers. Passages through the
walls of each frame chamber align with apertures in the anionic
membranes 206 and passages in adjacent frame chambers to pass the
used electrolyte solution across the length of the DDD 110. Ports
connecting the interior of the frame chambers or the electrolyte
cells 202 to the appropriate passages in the housing 200 provide
the individual inlets 205. This design may be used for all of the
inlets and outlets to the DDD 110 described herein.
[0025] As shown, the used electrolyte solution includes
disassociated copper ions (Cu.sup.2+), hydrogen ions (H.sup.+),
disassociated sulfate ions (SO.sub.4.sup.2-), and organic additives
and their breakdown products (Org). A diluted acid solution having
a higher pH than the electrolyte solution circulates through the
diluted acid cells 204. The diluted acid solution circulates
through the DDD 110 by use of a supply tank 208, a pump 210, and
fluid conduits connecting the supply tank 208 to inlets 201 and
outlets 203 disposed in the housing 200 to provide flow through
each of the diluted acid cells 204. SO.sub.4.sup.2-, H.sup.+, and
Org within the electrolyte cells 202 migrate across the anionic
membranes 206 based on diffusion across the concentration gradient
between the electrolyte cells 202 and the diluted acid cells 204.
The diffusion of SO.sub.4.sup.2-, H.sup.+, and Org from the
electrolyte cells 202 to the diluted acid cells 204 effectively
removes a portion of the acid and the organic additives from the
electrolyte solution while leaving the Cu.sup.2+ min the
electrolyte solution. The amount of the various organic additives
(e.g. accelerator, leveler, and suppressor) extracted from the
electrolyte solution depends on their diffusion rate through the
anionic membranes 206. During operation, the electrolyte solution
passes through the electrolyte cells 202 where a portion of the
SO.sub.4.sup.2-, H.sup.+, and Org is removed prior to the refreshed
electrolyte solution exiting the electrolyte cells 202 through
outlets 207 along the housing 200 of the DDD 110.
[0026] The supply tank 208, the conduits, the pump 210, and the
diluted acid cells 204 provide a deionized (DI) water loop that
circulates through the diluted acid cells 204 of the DDD 110. To
maintain the concentration level of the acid circulating through DI
water loop, the supply tank 208 refreshes by draining and
discarding the diluted acid solution that contains acids and
organic additives extracted from the electrolyte solution. Fresh
deionized (DI) water adds to the supply tank to maintain the total
volume of the diluted acid solution. In this manner, the
concentration of acid within the supply tank 208 and diluted acid
cells 204 remains sufficiently low to promote diffusion across the
anionic membranes 206. Preferably, the supply tank 208 refreshes
when the acid concentration therein reaches more than about 1 to 10
grams per liter.
[0027] FIG. 3 illustrates the plating system 100 of FIG. 1
incorporating the DDD 110 in conjunction with an electrodialysis
cell (EDC) 103. The plating system 100 functions the same as
described above except that the refreshed electrolyte solution that
exits the DDD 110 first passes through the EDC prior to returning
to the storage unit 102. The DDD 110 removes part of the organic
additives and acid as described herein. Next, the EDC 103
completely removes the organic additives and returns the copper
sulfate and the remaining acid to the storage tank 102 for reuse.
In this manner, a combination of the DDD 110 and the EDC 103
removes a portion of the acid and all the organic additives. Since
the DDD 110 substantially lacks the ability to remove some of the
levelers and polymeric organic additives such as suppressors, the
combination of the DDD 110 and EDC 103 provides for their removal
from the electrolyte solution.
[0028] FIG. 4 shows a schematic view of the EDC 103 for use with
the DDD 110 as illustrated in FIG. 3. The '569 application that is
incorporated by reference and entitled "Apparatus and Method for
Removing Contaminants from Semiconductor Copper Electroplating
Baths" describes the use of the EDC for removal of waste material.
The used electrolyte solution enters the EDC 103 via conduit 408
from the DDD 110. The conduit 408 supplies the used electrolyte
into a plurality of depletion cells or chambers 405 in the EDC 103.
While the used electrolyte is supplied to the depletion cells 405,
a cathode 402 and an anode 403 apply an electrical bias across the
EDC 103. The application of the electrical bias across the EDC 103
operates to urge ions in the used electrolyte solution towards the
respective poles, i.e., positive ions urge in the direction of the
cathode, while negative ions urge in the direction of the anode.
Therefore, the Cu.sup.2+ along with the H.sup.+ urge in the
direction of the cathode 402. Similarly, the SO.sub.4.sup.2- urges
in the direction of the anode 403. However, although the respective
ions are urged in the direction of the respective poles, the linear
distance the respective ions travel is limited by the positioning
of anionic and cationic membranes 409, 410. More particularly, the
positive copper and hydrogen ions in depletion cells 405 urge
towards cathode 402 and pass into the neighboring concentration
chambers 404 since the membranes separating depletion chambers 405
and concentration chambers 404 are cationic membranes 410.
Similarly, the negatively charged sulfate ions urge towards the
anode 403 and pass through the anionic membranes 409 into the
neighboring concentration chambers 404. As a result of the
alternating positioning of the cationic and anionic membranes 410,
409, positive copper ions and negative sulfate ions diffuse into
concentration chambers 404 where these ions combine to form
concentrated copper sulfate-sulfuric acid solution
(CuSO.sub.4/H.sub.2SO.sub.4). The electrolyte solution waste
material (organic breakdown products, impurities, solid particles,
etc.) remain in depletion chambers 405 and are discarded via
conduit 413. The concentrated copper sulfate within the
concentration chambers 404 may then be removed via conduit 414 and
returned to the storage unit 102 (shown in FIG. 3) for reuse.
[0029] FIG. 5 shows a schematic view of an alternative EDC 500
which may be used with the DDD 110 as illustrated in FIG. 3.
Anionic membranes 509 used in the EDC 500 may not possess a
sufficiently small porosity to completely prevent the passage of
organics such as breakdown products from accelerator and leveler
into the purified electrolyte. Unlike the configuration of the EDC
103 shown in FIG. 4, at least one cation membrane 510 separates the
organic additives within depletion cells 505 from purified
electrolyte cells 504 that contain the electrolyte for reuse.
Therefore, the EDC 500 operates to provide a purified electrolyte
solution based on the non-permeability of cation membranes 510 with
respect to the organics such as accelerator and high-molecular
weight leveler. A conduit 408 supplies the used electrolyte into a
plurality of depletion cells 505 in the EDC 500. While the used
electrolyte is supplied to the depletion cells 505, a cathode 502
and an anode 503 apply an electrical bias across the EDC 500 to
urge ions in the used electrolyte solution towards the respective
poles. Therefore, the Cu.sup.2+ along with the H.sup.+ urge in the
direction of the cathode 502, and the SO.sub.4.sup.2- urges in the
direction of the anode 503. The positive copper and hydrogen ions
in depletion cells 505 urge towards cathode 502 and pass into the
neighboring purified electrolyte cells 504 since the membranes
separating depletion cells 505 and purified electrolyte cells 504
are cationic membranes 510. The negatively charged sulfate ions and
some of the organic additives and their breakdown products within
the depletion cells 505 urge towards the anode 503 and pass through
the anionic membrane 509 into a neighboring waste cell 507. Acid at
a controlled concentration (e.g. 5-50 g/L) and supplied via conduit
508 circulates through acid cells 506 adjacent the purified
electrolyte cells 504 and opposite the depletion cells 505. The
sulfate ions within the acid cells 506 pass through the anionic
membranes 509 separating the acid cells 506 and the purified
electrolyte cells 504 in order to replenish the purified
electrolyte. DI water may enter the waste cells 507 and the
purified electrolyte cells 504 to aid flow through the EDC 500. The
electrolyte solution waste material (organic breakdown products,
impurities, solid particles, etc.) that remains in depletion cells
505 or is transferred to waste cells 507 is discarded via conduit
511. In this manner, the EDC 500 may return more than 95% of
purified CuSO.sub.4/H.sub.2SO.sub.4 for reuse through conduit 414
to the storage unit 102 (shown in FIG. 3).
[0030] FIG. 6 illustrates an alternative plating system 500 that
incorporates the DDD 110. The plating system 500 generally includes
a plating cell 501 configured to fluidly isolate an anode 522 of
the plating cell 501 from a cathode 523 or plating electrode of the
plating cell 501 via a cation exchange membrane 512 positioned
between the substrate being plated and the anode 522 of the plating
cell 501. U.S. patent application Ser. No. 10/187,027, entitled
"Electroplating Cell with Copper Acid Correction Module for
Substrate Interconnect Formation," which is herein incorporated by
reference in its entirety, describes in detail a plating system
using this type of divided plating cell. The plating cell 501
provides a first fluid solution (anolyte) to an anolyte compartment
508, i.e., the volume between the upper surface of the anode 522
and the lower surface of the membrane 512, and a second fluid
solution (catholyte) to a catholyte compartment 510, i.e., the
volume of fluid positioned above the upper membrane surface. The
anode 522 may generally be soluble, e.g., a copper anode, or
insoluble, e.g., platinum. The catholyte includes copper sulfate,
sulfuric acid, copper chloride, and additives similar to the
electrolyte solution described in FIG. 1. However, during
electrolysis hydrogen ions and copper ions move through the
membrane 512 into the catholyte compartment 510. As a result, the
concentration of acid in the catholyte increases and must be
removed. Therefore, the use of the DDD 110 as described herein
effectively removes the build up of acid in the catholyte along
with the build up of waste material from the breakdown of the
organic additives.
[0031] FIG. 7 is a graph showing the rate of removal by the DDD 110
of sulfuric acid from an electrolyte solution. The electrolyte
solution used to obtain the graph contained 0.85M CuSO.sub.4 and
0.3M H.sub.2SO.sub.4. In operation, one square meter of anionic
membrane 206 within the DDD 110 extracts between about 20 and 60
grams of acid from the electrolyte solution per hour. The rate of
acid extraction depends on the quality of the anionic membrane 206,
flow rates through the DDD 110, and the concentration of acid
accumulated in the DI water loop. As shown in the graph in FIG. 7,
acid may need to be added to the electrolyte solution if
insufficient acid is not produced during the plating process to
compensate for the loss of acid.
[0032] FIG. 8 is a graph showing the rate of removal of organic
additives and their breakdown products by the DDD from the
electrolyte solution. The electrolyte solution contained 6.5
milliliters per liter of accelerator, 3 milliliters per liter of
suppressor, and 4 milliliters per liter of leveler. As shown, the
DDD 110 removes accelerator faster than leveler and leveler faster
than suppressor. Therefore, the DDD 110 becomes most effective when
the accumulation of accelerator's breakdown is faster than that of
leveler's and negligibly low for suppressor. During typical plating
processes, the breakdown products from accelerator accumulates
faster than the breakdown products from leveler, and the breakdown
products from suppressor accumulates negligibly within the
electrolyte solution. Therefore, the DDD 110 extracts the various
organic breakdown products at a rate that mirrors their rate of
accumulation within the electrolyte solution.
[0033] While the foregoing is directed to embodiments of the
present invention, other and further embodiments of the invention
may be devised without departing from the basic scope thereof, and
the scope thereof is determined by the claims that follow.
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