U.S. patent application number 12/036177 was filed with the patent office on 2009-08-27 for convenient replacement of anode in semiconductor electroplating apparatus.
This patent application is currently assigned to NOVELLUS SYSTEMS, INC.. Invention is credited to Mitchell Gee, Robert Rash, Frederick Wilmot.
Application Number | 20090211900 12/036177 |
Document ID | / |
Family ID | 40997249 |
Filed Date | 2009-08-27 |
United States Patent
Application |
20090211900 |
Kind Code |
A1 |
Rash; Robert ; et
al. |
August 27, 2009 |
Convenient Replacement of Anode in Semiconductor Electroplating
Apparatus
Abstract
The convenient replacement of an anode in a semiconductor
electroplating apparatus is disclosed. For example, in one
disclosed embodiment, an electroplating system comprises an
electroplating cell having an anode chamber, a cathode chamber, a
selective transport barrier separating the anode chamber and the
cathode chamber, and an anode disposed within the anode chamber.
The anode comprises a plurality of pieces of anode material
disposed within a removable anode holder.
Inventors: |
Rash; Robert; (Portland,
OR) ; Wilmot; Frederick; (Gladstone, OR) ;
Gee; Mitchell; (Keizer, OR) |
Correspondence
Address: |
ALLEMAN HALL MCCOY RUSSELL & TUTTLE LLP
806 SW BROADWAY , SUITE 600
PORTLAND
OR
97205
US
|
Assignee: |
NOVELLUS SYSTEMS, INC.
Tualatin
OR
|
Family ID: |
40997249 |
Appl. No.: |
12/036177 |
Filed: |
February 22, 2008 |
Current U.S.
Class: |
204/276 |
Current CPC
Class: |
C25D 17/10 20130101;
H01L 21/67011 20130101; C25D 21/12 20130101 |
Class at
Publication: |
204/276 |
International
Class: |
C25B 9/00 20060101
C25B009/00 |
Claims
1. An electroplating system, comprising: an electroplating cell
comprising an anode chamber, a cathode chamber, and a selective
transport barrier separating the anode chamber and the cathode
chamber; and an anode disposed within the anode chamber and
comprising a plurality of pieces of anode material disposed within
a removable anode holder.
2. The electroplating system of claim 1, wherein the anode pieces
comprise copper pieces.
3. The electroplating system of claim 2, wherein the copper pieces
have a rounded shape with a radius in the range of 0.5-0.75
inches.
4. The electroplating system of claim 1, wherein the anode holder
comprises a titanium basket.
5. The electroplating system of claim 1, wherein the anode holder
comprises a plurality of elongate openings to admit a flow of an
anolyte.
6. The electroplating system of claim 1, further comprising a
plurality of anode holders.
7. The electroplating system of claim 1, wherein the anode holder
is at least partially coated with a protective coating.
8. The electroplating system of claim 1, further comprising a
charge plate on which the anode holder rests.
9. The electroplating system of claim 8, wherein the charge plate
comprises one or more openings configured to pass a flow of plating
solution received through the bottom surface of the anode holder,
and wherein the electroplating system further comprises a filter
disposed between the anode holder and a plating solution
outflow.
10. An electroplating system, comprising: an electroplating cell
comprising an anode chamber, a cathode chamber, and a selective
transport barrier separating the anode chamber and the cathode
chamber; a plurality of removable anode holders disposed within the
anode chamber, each anode holder comprising a basket with one or
more faces having a plurality of openings configured to admit a
flow of anolyte through the anode holder; and a plurality of copper
anode pieces disposed loosely within each anode holder.
11. The electroplating system of claim 10, wherein the removable
anode holders each comprise titanium baskets.
12. The electroplating system of claim 10, wherein at least some
openings in the anode holders have an elongate shape with a small
dimension that is smaller than an average smallest dimension of a
used anode piece.
13. The electroplating system of claim 12, wherein the openings
have an oval or rectangular shape.
14. The electroplating system of claim 10, wherein the anode holder
is at least partially coated in a protective polymer coating.
15. The electroplating system of claim 10, further comprising a
charge plate on which the anode holder rests, wherein the charge
plate comprises one or more openings configured to pass a flow of
plating solution received through a bottom of the anode holder, and
wherein the electroplating system further comprises a filter
disposed between the anode holder and a plating solution
outflow.
16. In an electroplating system having an electroplating cell
comprising an anode chamber, a cathode chamber separated from the
anode chamber by a selective transport barrier, and an anode
comprising a plurality of anode pieces contained within an anode
holder, a method of servicing the anode, comprising: removing
electroplating fluids from the cathode chamber and the anode
chamber; opening an access to the anode chamber; removing the anode
holder from the electroplating cell; removing at least some used
anode pieces from the anode holder; adding at least some
replacement anode pieces to the anode holder; closing the access
between the cathode chamber and the anode chamber; and adding
electroplating fluids to the cathode chamber and the anode
chamber.
17. The method of claim 16, wherein opening an access between the
cathode chamber and the anode chamber comprises removing the
selective transport barrier.
18. The method of claim 16, wherein the anode pieces comprise
copper pieces.
19. The method of claim 16, wherein the anode comprises a plurality
of anode holders, and wherein removing the anode holder from the
electroplating cell comprises removing each anode holder from the
plating cell.
20. The method of claim 16, wherein the electroplating system
comprises a filter disposed fluidically between the anode holder
and an electroplating fluid outlet, and further comprising
replacing the filter before adding electroplating fluid to the
anode chamber.
Description
BACKGROUND
[0001] Electroplating is commonly used in integrated circuit
manufacturing processes to form electrically conductive structures.
For example, in a copper damascene process, electroplating is used
to form copper lines and vias within channels previously etched
into a dielectric layer. In such a process, a seed layer of copper
is first deposited into the channels and on the substrate surface
via physical vapor deposition. Then, electroplating is used to
deposit a thicker copper layer over the seed layer such that the
channels are completely filled. Excess copper is then removed by
chemical mechanical polishing, thereby forming the individual
copper features.
[0002] Some electroplating processes utilize consumable copper
anodes. As copper is reduced out of solution at the substrate
(cathode) surface, copper at a consumable anode is oxidized,
thereby adding copper ions to the solution and reducing the mass of
the anode. A consumable anode may be periodically replaced to
replenish the mass of copper at the anode. Anode replacement
generally involves bringing an electroplating system generally
off-line during replacement, and therefore may reduce system
throughput. To mitigate this by lessening the frequency at which
replacement is performed, anodes having a large mass of copper may
be used. However, such anodes may be expensive to produce due to
the cost of the raw material and to the machining used to produce
the anodes. Further, such anodes may be heavy and difficult to
handle during replacement.
SUMMARY
[0003] Accordingly, the convenient replacement of an anode in a
semiconductor electroplating apparatus is disclosed herein. For
example, in one disclosed embodiment, an electroplating system
comprises an electroplating cell having an anode chamber, a cathode
chamber, a selective transport barrier separating the anode chamber
and the cathode chamber, and an anode disposed within the anode
chamber. The anode comprises a plurality of pieces of anode
material disposed loosely within a removable anode holder.
[0004] This Summary is provided to introduce a selection of
concepts in a simplified form that are further described below in
the Detailed Description. This Summary is not intended to identify
key features or essential features of the claimed subject matter,
nor is it intended to be used to limit the scope of the claimed
subject matter. Furthermore, the claimed subject matter is not
limited to implementations that solve any or all disadvantages
noted in any part of this disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 shows a block diagram of an embodiment of a
semiconductor electroplating system.
[0006] FIG. 2 shows a view of an embodiment of a portion of an
anode in a semiconductor electroplating system.
[0007] FIG. 3 shows an exploded view of the embodiment of FIG.
2.
[0008] FIG. 4 shows a flow diagram depicting an embodiment of a
method of changing an anode in a semiconductor electroplating
system.
DETAILED DESCRIPTION
[0009] Prior to discussing the convenient replacement of an anode
in a semiconductor electroplating assembly, an example use
environment is described. FIG. 1 shows a block diagram of an
embodiment of a semiconductor electroplating system 100.
Electroplating system 100 comprises an electroplating cell 102 with
an anode chamber 104 and a cathode chamber 106. The anode chamber
104 is defined by a selective transport barrier 108 that separates
the anode chamber 104 from the cathode chamber 106, and includes an
anode indicated schematically at 110.
[0010] The anode chamber 104 comprises an anolyte solution
associated with the anode 110. The cathode chamber 106 comprises a
"plating bath", or catholyte, associated with a cathode 112. In one
embodiment, the cathode 112 comprises a semiconductor wafer having
trenches etched on its surface for damascene processing.
[0011] During electroplating, an electric field is established
between the anode 110 and the cathode 112. This field drives
positive ions from the anode chamber 104 through the selective
transport barrier 108 and into the cathode chamber 106 and onto
cathode 112. At the cathode, an electrochemical reaction takes
place in which metal cations are reduced to form a solid layer of
the metal on the surface of the cathode 112. An anodic potential is
applied to the anode 110 via an anode electrical connection 114,
and a cathodic potential is provided to the cathode 112 via a
cathode electrical connection 116. In one embodiment, the metal
ions are copper ions and copper metal is deposited in the trenches
on the semiconductor wafer. In some embodiments, the
cathode/substrate may be rotated during plating.
[0012] The selective transport barrier 108 allows a separate
chemical and/or physical environment to be maintained within the
anode chamber 104 and the cathode chamber 106. For example, the
selective transport barrier 108 may be configured to prevent
non-ionic organic species from crossing the barrier while allowing
metal ions to cross the barrier. The catholyte may contain various
organic additives, such as levelers, accelerators and suppressors,
that aid in plating copper onto the cathode 112 but that may poison
the anode 110 or otherwise harm anode performance. Therefore, the
selective transport barrier 108 may be configured to prevent such
organic additives in the catholyte from contaminating the anolyte
while allowing copper from the anolyte to reach the catholyte.
[0013] The selective transport barrier 108 may be made from any
suitable material or materials. In some embodiments, the selective
transport barrier may be made from a material or material that is
porous and that allows passage of both anions and cations. Examples
of suitable materials include, but are not limited to, porous
glasses, porous ceramics (e.g. alumina and zirconia), silica
aerogels, organic aerogels, and porous polymeric materials such as
Kynar, sintered polyethylene or sintered polypropylene. For many
materials, the thickness, pore size, etc. can be adjusted to
increase ionic conductance or decrease non-ionic diffusion.
Generally, reducing the thickness and increasing pore size may
increase the ionic conductance while also increasing non-ionic
diffusion. Likewise, increasing the thickness and reducing pore
size may decrease both of these parameters. Therefore, suitable
thickness and/or pore sizes may be selected depending upon a
desired balance between these characteristics.
[0014] In yet other embodiments, a multi-layer structure comprising
one or more layers of a material with smaller pores and one or more
layers of a material with larger pores may be used. For example, in
one specific embodiment, the selective transport barrier 108 has a
three-layer structure comprising a thin small pore size material
sheet sandwiched between two thicker larger pore size material
sheets. In a specific embodiment, the thin small pore size material
is a sheet of porous polyolefin (such as polypropylene) having a
thickness of approximately 10-50 microns and an average pore size
of less than about 0.5 microns (e.g. 0.01-0.2 microns), while the
thicker, large pore size material is a sheet of polyolefin having
an average pore size of approximately 5-20 microns. The middle
layer provides a large resistance to fluid flow through the
selective transport barrier (due to the small pore size) while
allowing good ionic conductivity (due to thickness), while the
outer layers provide mechanical strength and extra resistance to
flow.
[0015] The catholyte may be circulated between the cathode chamber
106 and a catholyte reservoir 120. The temperature and composition
of the catholyte may be controlled within the catholyte reservoir
120. For example, concentrations of non-ionic organic plating
additives may be controlled in the catholyte reservoir 120.
Catholyte may be circulated between the catholyte reservoir 120 and
the cathode chamber 106 via a combination of gravity and one or
more pumps 122.
[0016] Likewise, the anolyte in the anode chamber 104 may be stored
in and replenished from an anolyte reservoir 124. The temperature
and composition of the anolyte may be controlled in the anolyte
reservoir 124. Anolyte may be circulated through the anolyte
reservoir 124 and the anode chamber 104 via a combination of
gravity and one or more pumps 126. In some embodiments, anolyte
from the anolyte reservoir 124 is introduced into the anode
chambers via one or more outlets arranged to create a flow of
anolyte laterally across the anode. This may facilitate mixing and
help prevent any impurities present from poisoning the anode
surface.
[0017] It will be understood that in some integrated circuit
fabrication systems, plating operations maybe performed in parallel
on multiple wafers using multiple electrofill modules. In such
cases, central catholyte and/or anolyte reservoirs may supply
multiple plating cells with catholyte and/or anolyte.
[0018] FIG. 2 shows a cut-away view of the plating cell 102
depicting anode 110 in more detail, and FIG. 3 shows an exploded
view of the anode 110. In these views, the selective transport
barrier 108, cathode 112, and other structures are omitted for
clarity. The anode comprises a plurality of anode holders 202, one
of which is shown in FIG. 2 and all of which are shown in FIG. 3,
each containing a plurality of pieces of an anode material, which
are referred to hereinafter as anode pieces 204. The anode holders
202 rest on a charge plate 206 configured to conduct electrical
current to/from the anode holders 202 and the anode pieces 204.
Further, a porous filter 208 is disposed between the charge holder
and an anolyte outlet that leads to the anolyte reservoir 124.
[0019] The anode pieces 204 are disposed loosely within the anode
holders 202 in that they are not connected to the anode holders 202
with bolts or other fasteners. The use of an anode holder 202 to
hold loose anode pieces 204 offers various advantages compared to
the use of a solid anode. For example, as mentioned above, a solid
anode of sufficient thickness for high-volume industrial use may be
quite heavy (e.g. greater than 60 lbs. for a 300 mm wafer plating
cell), and therefore difficult to handle during installation.
Further, the costs of machining such an anode may be quite
expensive. Even when divided into a number of smaller segments (for
example, three wedge-shaped segments each comprising 120 degrees of
a cylindrical anode), the individual pieces still may be difficult
to machine and handle. Additionally, solid anodes are generally
connected to the anode chamber wall via fasteners such as bolts.
Therefore, changing such an anode generally involves unbolting the
used anode and then reinstalling the bolts to secure the new anode
in place.
[0020] In contrast, the use of anode pieces 204 loosely disposed
within an anode holder 202 may greatly reduce replacement and
servicing costs. For example, such anode pieces 204 may be easily
handled relative to large, solid anodes. Further, whereas solid
anodes are generally bolted to a bottom portion of a plating cell,
the anode holders 204 on the bottom of the plating cell. Therefore,
servicing the anode 110 involves simply lifting the anode holders
202 out of the plating cell 102 via a handle 210 on each anode
holder 202, pouring out the anode pieces, and then adding
replacement anode pieces, without removing/reinstalling any bolts
or other fasteners.
[0021] The anode pieces may have any suitable shape or size.
Examples of suitable anode pieces include, but are not limited to,
generally rounded or oval anode pieces having an average radius of
approximately 0.5-0.75 inch. In one specific embodiment, the anode
pieces have a generally rounded shape with an average diameter of
approximately 1/2 inch. The use of relatively larger anode pieces
204 may facilitate the flow of anolyte solution through the anode
pieces, while the use of relatively smaller anode pieces 204 may
increase the mass of copper that can be held within the anode
holders 202, and therefore reduce a frequency at which anode
servicing is performed. It will be understood that the
above-specified shapes and size ranges are disclosed for the
purpose of example, and that anode pieces may have any other
suitable shape and/or size.
[0022] The anode holders 202 likewise may have any suitable
configuration. Suitable configurations include, but are not limited
to, configurations that permit the free flow of anolyte through the
anode holder and that help to prevent the escape of anode pieces
204 from the anode holder 202 as the anode pieces 204 reduce in
size due to consumption. In the depicted embodiment, the anode
holders 202 each take the form of an open basket defining a
ninety-degree wedge of a circle (due to the circular cross-section
of the plating cell 102). In other embodiments, either more or
fewer anode holders 202 than four may be used, and the anode
holders 202 may other suitable shapes. Generally, the user of
larger anode holders 202 may allow the use of fewer total anode
holders 202. This may allow a greater mass of copper to be held in
the anode, as less total anode space is occupied by the anode
holders 204. However, this also may lead to a greater weight for
each anode holder 202 when loaded with new anode pieces 204, which
may increase the difficulty of handling during anode replenishment.
Likewise, the use of smaller anode holders 202 may increase the
ease of handling during replenishment, but also may reduce the mass
of copper in the anode due to the greater amount of space occupied
by the anode holders 202.
[0023] Each anode holder 202 comprises a plurality of elongate
openings 212 configured to admit a flow of anolyte into and out of
the sides and bottom of the anode holder 202. The depicted openings
212 have a smallest dimension (i.e. the vertical dimension in FIGS.
2-3) configured to prevent used anode pieces 204 of an average
reduced size from passing through the openings 202, and a largest
dimension of sufficient size to avoid any openings being plugged
shut by an anode piece 204. While the depicted openings 212 have an
elongate oval shape, it will be understood that the openings may
have any other suitable shape that enables anolyte flow while
preventing escape of anode pieces and plugging by anode pieces.
Examples include, but are not limited to, rectangular, trapezoidal,
other polygonal shapes, other rounded shapes, and combinations of
all of the above-described shapes.
[0024] The charge plate 206 is configured to be coupled to an
electrical connection to deliver electric charge to the anode
holders 202 and anode pieces 204. In the depicted embodiment, the
anode holders 202 rest on the charge plate 206 without the use of
any fasteners to connect the structures together. This allows the
anode holders to be removed from the charge plate 206 in a quick
and easy manner during anode servicing. However, in other
embodiments, the anode holders 202 may be fastened to the charge
plate 206.
[0025] The charge plate 206 may have any suitable configuration for
transferring charge to the anode holders 202. In the depicted
embodiment, the charge plate 206 comprises two halves 214, 216 each
configured to be fixed within the anode chamber 104 via two bolts
217 (for a total of four bolts 217). In other embodiments, the
charge plate may have a single piece, or more than two pieces.
Further, the charge plate comprises a plurality of support feet 218
configured to support the charge plate 206 against the weight of
the anode holders 202. Additionally, the charge plate 206 defines
openings 220 configured to permit anolyte to flow out of the bottom
of the anode holders 202 and into an anolyte outlet for transport
to the anolyte chamber 124. In the depicted embodiment, the
openings are positioned below a substantial portion of the bottoms
of the anode holders 202, and the charge plate 206 contacts the
anode holders 202 around a perimeter region of the bottom surface
of the anode holders 202. However, the charge plate 206 may have
any other suitable configuration other than that shown. Further,
while the depicted charge plate is fixed within the anode chamber
104 via four bolts 217, it will be understood that either more or
fewer bolts, or any other suitable fastener or fasteners, may be
used.
[0026] The charge plate 206 and anode holders 202 may be made from
any suitable material or materials. Suitable materials include
materials that are inert to the anolyte solution used in a desired
plating process. In the specific example of a copper plating
process that utilizes a sulfuric acid/copper sulfate solution as an
anolyte, one example of a suitable material is titanium. Further,
the anode holders 202 may be partly or fully coated with a
protective coating, such as a PTFE (polytetrafluoroethylene)
coating or other polymer coating, to insulate the anode holder
material from plating solutions, such as a copper sulfate solution.
When the anode pieces become small (i.e. near end of life but
before requiring replenishment), the anode holder 202 may pass
current to a wafer during processing. This may cause electrolysis
in the plating solution, and may introducing air bubbles under the
selective transport barrier 108, which can disrupt the plating
process. By coating a portion of the anode holder with such a
protective coating (for example, the upper 3/4 of the height of the
anode holder), the electrical potential between the wafer and the
anode holder may be reduced, and the anode pieces may remain the
primary electrical source, thereby reducing the production of air
bubbles.
[0027] The filter 208 is configured to prevent any anode pieces or
fragments that escape from the anode holders 202 from being
circulated toward the anolyte chamber 124, as such anode pieces or
fragments may harm the pumping mechanisms used to circulate
anolyte. Any suitable type of filter may be used as filter 208. In
one embodiment, the filter 208 comprises a polypropylene mesh
having a pore size of approximately 120 microns. Other suitable
materials and/or other suitable filter pore sizes may be used in
other embodiments. The depicted filter 208 comprises a plurality of
holes 222 configured to accommodate the bolts 217 that fix the
charge plate within the anode chamber 104, and a plurality of holes
224 configured to accommodate the charge plate support feet 218,
but a filter may accommodate these structures in any other suitable
manner than the depicted holes.
[0028] The filter 208 may be periodically changed to ensure proper
anolyte fluid flow through the filter 208. The filter 208 may be
changed each time the anode pieces 204 are changed, or on either a
more frequent or less frequent basis. Because changing the filter
involves removing only the four bolts 217 that hold the charge
plate in the anode chamber 104, and does not involve the removal of
any other fasteners, the filter change may not add any significant
amount of time to the anode changing process, and therefore may be
performed during anode servicing without substantially adding to
system downtime.
[0029] As described above, the embodiments of anodes described
herein may be easily serviced to replenish the copper mass of the
anode, to replace the filter, and/or to service or change other
parts. FIG. 4 shows an embodiment of a method 400 of changing an
anode in a semiconductor electroplating device. Method 400 first
comprises, at 402 removing electroplating fluids (i.e. the anolyte
and catholyte) from the anode chamber and cathode chamber of a
plating cell. Then, method 400 comprises, at 404, opening an access
into the anode chamber. As described above, the plating cell
embodiments disclosed herein comprise a selective transport barrier
108 that prevent additives in the catholyte from diffusing into the
anolyte. Therefore, opening access to the anode chamber may
comprise removing the selective transport barrier, as indicated at
406, or otherwise opening an access through the selective transport
barrier.
[0030] Once access has been gained to the anode chamber, the anode
holder or holders are removed from the electroplating cell at 408,
and used anode pieces are removed from the anode holder at 410.
Generally, all of the used anode pieces are removed from the anode
holder during anode replacement, but under some circumstances, only
a portion of the used anode pieces may be removed. Also, once the
anode holders are removed from the anode chamber, the charge plate
may be removed, the filter located between the charge plate and an
anolyte outlet may be changed, and then the charge plate may be
replaced.
[0031] Continuing with FIG. 4, method 400 next comprises, at 412,
adding replacement anode pieces to the anode holder. Any suitable
quantity of replacement anode pieces may be added to the anode
holder. For example, if it is desired to maximize the amount of
time or the number of plating cycles that pass between anode
replacement, then the anode holders may be substantially completely
filled with anode pieces. Alternatively, it may be desired under
some circumstances to fill one or more anode holders only partially
with anode pieces.
[0032] After adding replacement anode pieces to the anode chamber,
method 400 next comprises closing access to the anode chamber, as
indicated at 414. Closing access to the anode chamber may comprise,
for example, placing the previously removed selective transport
barrier (or a replacement barrier) back into the cell, as indicated
at 416, or otherwise closing an access through the selective
transport barrier. Then, as indicated at 418, the anolyte and
catholyte electroplating fluids may again be added to the plating
cell.
[0033] It be understood that the configurations and/or approaches
described herein are exemplary in nature, and that these specific
embodiments or examples are not to be considered in a limiting
sense, because numerous variations are possible. The subject matter
of the present disclosure includes all novel and nonobvious
combinations and subcombinations of the various processes, systems
and configurations, and other features, functions, acts, and/or
properties disclosed herein, as well as any and all equivalents
thereof.
* * * * *