U.S. patent application number 11/299293 was filed with the patent office on 2006-07-20 for electrolytic process using anion permeable barrier.
This patent application is currently assigned to Semitool, Inc.. Invention is credited to Rajesh Baskaran, Robert W. JR. Batz, Kyle M. Hanson, Bioh Kim, John L. Klocke, Tom L. Ritzdorf.
Application Number | 20060157355 11/299293 |
Document ID | / |
Family ID | 36682748 |
Filed Date | 2006-07-20 |
United States Patent
Application |
20060157355 |
Kind Code |
A1 |
Baskaran; Rajesh ; et
al. |
July 20, 2006 |
Electrolytic process using anion permeable barrier
Abstract
Processes and systems for electrolytically processing a
microfeature workpiece with a first processing fluid and an anode
are described. Microfeature workpieces are electrolytically
processed using a first processing fluid, an anode, a second
processing fluid, and an anion permeable barrier layer. The anion
permeable barrier layer separates the first processing fluid from
the second processing fluid while allowing certain anionic species
to transfer between the two fluids. The described processes produce
deposits over repeated plating cycles that exhibit resistivity
values within desired ranges.
Inventors: |
Baskaran; Rajesh;
(Kalispell, MT) ; Batz; Robert W. JR.; (Kalispell,
MT) ; Kim; Bioh; (Kalispell, MT) ; Ritzdorf;
Tom L.; (Bigfork, MT) ; Klocke; John L.;
(Kalispell, MT) ; Hanson; Kyle M.; (Kalispell,
MT) |
Correspondence
Address: |
CHRISTENSEN, O'CONNOR, JOHNSON, KINDNESS, PLLC
1420 FIFTH AVENUE
SUITE 2800
SEATTLE
WA
98101-2347
US
|
Assignee: |
Semitool, Inc.
Kalispell
MT
|
Family ID: |
36682748 |
Appl. No.: |
11/299293 |
Filed: |
December 8, 2005 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11296574 |
Dec 7, 2005 |
|
|
|
11299293 |
Dec 8, 2005 |
|
|
|
10861899 |
Jun 3, 2004 |
|
|
|
11296574 |
Dec 7, 2005 |
|
|
|
09872151 |
May 31, 2001 |
|
|
|
10861899 |
Jun 3, 2004 |
|
|
|
10729357 |
Dec 5, 2003 |
|
|
|
11299293 |
Dec 8, 2005 |
|
|
|
10729349 |
Dec 5, 2003 |
|
|
|
11299293 |
Dec 8, 2005 |
|
|
|
10059907 |
Jan 29, 2002 |
|
|
|
11299293 |
Dec 8, 2005 |
|
|
|
09531828 |
Mar 21, 2000 |
6368475 |
|
|
10059907 |
Jan 29, 2002 |
|
|
|
Current U.S.
Class: |
205/674 ;
257/E21.175 |
Current CPC
Class: |
H05K 3/423 20130101;
H01L 21/76843 20130101; C25D 17/001 20130101; C25D 5/022 20130101;
H01L 21/76846 20130101; C25F 7/00 20130101; H01L 21/76868 20130101;
C25D 17/002 20130101; C25D 3/02 20130101; C25D 3/38 20130101; H01L
21/2885 20130101; C25F 3/02 20130101; H01L 21/76873 20130101; C25D
7/123 20130101 |
Class at
Publication: |
205/674 |
International
Class: |
B23H 5/00 20060101
B23H005/00 |
Claims
1. A process for electrolytically processing a microfeature
workpiece as the working electrode with a first processing fluid
and a counter electrode comprising: contacting a surface of the
microfeature workpiece with the first processing fluid, the first
processing fluid comprising first processing fluid species
including a cation, an anion, and a complexing agent; contacting
the counter electrode with a second processing fluid; producing an
electrochemical reaction at the counter electrode; and
substantially preventing movement of cationic species between the
first processing fluid and the second processing fluid species.
2. The process of claim 1, wherein the step of substantially
preventing movement of cationic species between the first
processing fluid and the second processing fluid comprises
providing an anion permeable barrier between the first processing
fluid and the second processing fluid.
3. The process of claim 2, wherein the anion permeable barrier is
an anion exchange membrane.
4. The process of claim 1, wherein the working electrode is a
cathode, and the counter electrode is an anode.
5. The process of claim 4, wherein the cation of the first
processing fluid is a metal ion, and further comprising the step of
electrolytically depositing the metal ion onto the surface of the
microfeature workpiece.
6. The process of claim 5, wherein the first processing fluid
further includes a counter anion of the metal ion and the process
further comprises the step of passing the counter anion from the
first processing fluid to the second processing fluid through the
anion exchange membrane.
7. The process of claim 4, wherein the anode is an inert anode.
8. The process of claim 4, wherein the anode is a consumable
anode.
9. The process of claim 3, further comprising the step of passing
the anion between the first processing fluid and the second
processing fluid through the anion exchange membrane.
10. The process of claim 1, wherein the first processing fluid has
a pH greater than 7.0.
11. The process of claim 5, wherein the metal ion is a cation of a
metal salt.
12. The process of claim 1, further comprising the step of adding a
metal ion to the first processing fluid.
13. The process of claim 12, wherein the metal ion is added to the
first processing fluid by adding a metal salt to the first
processing fluid.
14. The process of claim 1, wherein the first processing fluid
species further include a pH adjustment agent and a buffer.
15. The process of claim 14, further comprising the step of adding
a pH adjustment agent to the second processing fluid.
16. The process of claim 14, wherein the second processing fluid
comprises a pH adjustment agent and a buffer.
17. The process of claim 16, wherein buffer concentration in the
first processing fluid is equal to or less than buffer
concentration in the second processing fluid.
18. The process of claim 1, wherein the concentration of the anion
in the first processing fluid is greater than the concentration of
the anion in the second processing fluid.
19. The process of claim 1, wherein the complexing agent is
selected from the group consisting of ethylene diamine, ethylene
diamine tetraacetic acid and its salts, cyclam, porphrin,
bipyridyl, pyrolle, thiophene, and polyamines.
20. The process of claim 1, wherein the complexing agent is
selected from compounds that contain a nitrogen-containing
chelating group R--NR.sub.2--R.sub.1, where R is any alkyl or
aromatic group and R.sub.1 and R.sub.2 are H, alkyl or aryl organic
groups or polymer chains.
21. The process of claim 1, wherein the complexing agent includes
chemical compounds having at least one part with the chemical
structure COOR.sub.1--COHR.sub.2R.sub.3 where R.sub.1 is an organic
group covalently bound to the carboxylate group (COO), R.sub.2 is
either hydrogen or an organic group, and R.sub.3 is either hydrogen
or an organic group.
22. The process of claim 21, wherein the complexing agent is
selected from the group consisting of citric acid and salts
thereof, tartaric acid and salts thereof, diethyltartrate,
diisopropyltartrate, and dimethyltartrate.
23. The process of claim 1, wherein pH of the first processing
fluid is substantially equal to pH of the second processing
fluid.
24. The process of claim 1, further comprising the step of
depositing the cation onto the surface of the microelectronic
workpiece.
25. The process of claim 24, wherein the surface onto which the
cation is deposited comprises a seed material.
26. The process of claim 24, wherein the surface onto which the
cation is deposited comprises a barrier material.
27. The process of claim 1, wherein the cation is selected from the
group consisting of copper ion, gold ion, tin ion, silver ion,
platinum ion, ruthenium ion, rhodium ion, iridium ion, osmium ion,
rhenium ion, palladium ion, and nickel ion.
28. A process for electrolytically processing a microfeature
workpiece with a first processing fluid and an inert anode
comprising: contacting a surface of the microfeature workpiece with
the first processing fluid, the first processing fluid including a
metal ion to be deposited onto the surface of the microfeature
workpiece, a counter anion to the metal ion, and a complexing
agent; contacting the inert anode with a second processing fluid,
an anion permeable barrier located between the first processing
fluid and the second processing fluid; producing an oxidizing agent
at the inert anode; adding a metal ion to the first processing
fluid; passing the counter anion from first processing fluid to the
second processing fluid through the anion permeable barrier; and
depositing the metal ion onto the surface of the microelectronic
workpiece.
29. A process for electrolytically processing a microfeature
workpiece with a first processing fluid and an inert anode
comprising: contacting a surface of the microfeature workpiece with
the first processing fluid, the first processing fluid comprising
first processing fluid species including a metal ion to be
deposited onto the surface of the microelectronic workpiece; and
contacting the inert anode with a second processing fluid that
includes a buffer and a pH adjustment agent, an ion permeable
barrier located between the first processing fluid and the second
processing fluid.
30. The process of claim 29 wherein the buffer is boric acid.
31. The process of claim 29 wherein the pH adjustment agent is
tetramethylammonium hydroxide.
32. A system for electrolytically processing a microfeature
workpiece with a first processing fluid comprising: a chamber
including: a processing unit for receiving the first processing
fluid; a counter electrode unit for receiving a second processing
fluid; an counter electrode in the counter electrode unit; an anion
permeable barrier between the processing unit and the counter
electrode unit; a source of complexing agent; a source of a metal
ion in fluid communication with the processing unit; and a source
of a pH adjustment agent in fluid communication with the counter
electrode unit.
33. The process of claim 1, wherein the counter electrode comprises
multiple electrodes.
34. The process of claim 1, wherein the working electrode comprises
multiple electrodes.
35. The process of claim 1, wherein the working electrode is an
anode, and the counter electrode is a cathode.
36. The process of claim 35, wherein the first processing fluid
comprises a cation and an anion, and further comprising
electrolytic dissolution of metal on the surface of the
microfeature workpiece.
37. The process of claim 35, wherein the cathode is an inert
electrode in contact with the second processing fluid.
38. The process of claim 37, wherein the second processing fluid
includes an anion and a cation.
39. The process of claim 38, wherein reduction of chemical species
in the second processing fluid occurs at the cathode.
40. The process of claim 39, wherein the non-anionic chemical
species in the first processing fluid are separated from the inert
cathode by an anion permeable barrier.
41. The process of claim 35, wherein the second processing fluid
further includes a counter anion of a metal present on the surface
of the microfeature workpiece and the process further comprises
passing the counter anion from the second processing fluid to the
first processing fluid through an anion permeable barrier.
42. The process of claim 35, wherein the first processing fluid has
a pH less than 7.0.
43. The process of claim 35, wherein the cation is a metal ion of a
metal salt.
44. The process of claim 35, further comprising the step of adding
an anion to the second processing fluid.
45. The process of claim 44, wherein the anion is added to the
second processing fluid by adding an acid to the second processing
fluid.
46. The process of claim 35, wherein the first processing fluid
species further include a pH adjustment agent and a buffer.
47. The process of claim 46, further comprising the step of adding
a pH adjustment agent to the second processing fluid.
48. The process of claim 46, wherein the second processing fluid
comprises a pH adjustment agent and a buffer.
49. The process of claim 48, wherein buffer concentration in the
first processing fluid is equal to or greater than buffer
concentration in the second processing fluid.
50. The process of claim 1, wherein the cation is a metal ion of a
metal salt and the anion is a counter ion of the metal salt, the
second processing fluid comprising the anion, concentration of the
anion in the second processing fluid being greater than
concentration of the anion in the first processing fluid.
51. The process of claim 1, further comprising the step of
electrolytically dissolving metal from the surface of the
microfeature workpiece.
52. A process for electrolytically processing a microfeature
workpiece with a first processing fluid and cathode comprising:
contacting a surface of the microfeature workpiece with the first
processing fluid, the first processing fluid including an anion;
contacting the cathode with a second processing fluid containing
the anion, an anion permeable barrier located between the first
processing fluid and the second processing fluid; reducing chemical
species in the second processing fluid; adding acid to the second
processing fluid; passing the anion from the second processing
fluid to the first processing fluid through the anion permeable
barrier; and electrolytically dissolving metal from the surface of
the microfeature workpiece.
53. A system for electrolytically processing a microfeature
workpiece with a first processing fluid comprising: a chamber
including: a processing unit for receiving the first processing
fluid; a counter electrode unit for receiving a second processing
fluid; a cathode in the counter electrode unit; an anion permeable
barrier between the processing unit and the counter electrode unit;
a source of metal counter ion in fluid communication with the
counter electrode unit; and a source of a pH adjustment agent in
fluid communication with the processing unit.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of U.S.
application Ser. No. ______, filed Dec. 7, 2005, entitled
Electrolytic Process Using Anion Permeable Barrier, Attorney Docket
No. SEMT-1-25721, naming Rajesh Baskaran, Robert W. Batz., Jr.,
Bioh Kim, and Tom L. Ritzdorf as inventors, priority from the
filing date of which is hereby claimed under 35 U.S.C.
.sctn.120.
FIELD OF THE INVENTION
[0002] The present invention relates to electrolytic processing of
microfeature workpieces and an electrolytic treatment process that
utilizes an anion permeable barrier.
BACKGROUND OF THE INVENTION
[0003] Microfeature devices, such as semiconductor devices,
imagers, displays, thin film heads, micromechanical components,
microelectromechanical systems (MEMS), and large through-wafers
vias are generally fabricated on and/or in microfeature workpieces
using a number of machines that deposit and/or etch materials from
the workpieces. Many current microfeature devices require
interconnects and other very small, submicron sized features (e.g.,
45-250 nanometers) formed by depositing materials into small
trenches or holes. One particularly useful process for depositing
materials into small trenches and/or vias is electrolytic
processing, e.g., electroplating. Typical electrolytic processing
techniques include electroplating processes that deposit copper,
nickel, lead, gold, silver, tin, platinum, and other materials onto
microfeature workpieces and etching processes that remove metals
from microfeature workpiece surfaces.
[0004] In certain electroplating or etching processes, chelants or
complexing agents are used to affect the electric potential at
which metal ions are deposited onto or removed from surfaces of
microfeature workpieces. Other components that may be present in
the processing fluids include accelerators, suppressors, and
levelers which can affect the results of the electroplating or
electroetching process. Although these types of materials can
positively influence the electroplating or electroetching
processes, their use is not without drawbacks. For example, it is
possible for these components to have an adverse impact on the
electrolytic process as a result of reactions or other interactions
with electrodes used in the electrolytic process.
[0005] Another challenge in depositing metals into narrow, deep
trenches or vias is that it is difficult to completely fill the
small features without creating voids or other nonuniformities in
the deposited metal. For example, when depositing metal into a
trench having a critical dimension of 45 nanometers to 250
nanometers, an ultrathin seed layer may be used, but care must be
taken to ensure sufficient vacant space in the trench for the
subsequently deposited bulk metal. In addition, ultrathin seed
layers may be problematic because the quality of the deposited seed
layer may not be uniform. For example, ultrathin seed layers may
have voids or other nonuniform physical properties that can result
in nonuniformities in the material deposited onto the seed layer.
Such challenges may be overcome by enhancing the seed layers or
forming a seed layer directly on a barrier layer to provide
competent seed layers that are well suited for depositing metals
into trenches or holes with small critical dimensions. One
technique for enhancing the seed layer or forming a seed layer
directly on a barrier layer is to electroplate a material using a
processing solution with a low conductivity. Such low conductivity
processing fluids have relatively low hydrogen ion (H.sup.+)
concentrations, i.e., relatively high pH. Suitable electrochemical
processes for forming competent seed layers using low conductivity
processing fluids are disclosed in U.S. Pat. No. 6,197,181, which
is herein incorporated by reference.
[0006] Electroplating onto seed layers or electroplating materials
directly onto barrier layers using low conductivity/high pH
processing fluids presents additional challenges. For example,
inert anodes are generally required when high pH processing fluids
are used because the high pH tends to passivate consumable anodes.
Such passivation may produce metal hydroxide particles and/or
flakes that can create defects in the microfeatures. Use of inert
anodes is not without its drawbacks. The present inventors have
observed that when inert anodes are used, the resistivity of the
deposited material increases significantly over a relatively small
number of plating cycles. One way to combat this increase in the
resistivity of the deposited material is to frequently change the
processing fluid; however, this solution increases the operating
cost of the process.
[0007] As a result, there is a need for electrolytic processes for
treating microfeature workpieces that reduce adverse impacts
created by the presence of complexing agents and/or other additives
and also maintain deposit resistivity within desired ranges.
SUMMARY
[0008] The embodiments described herein relate to processes for
electrolytically processing a microfeature workpiece to deposit or
remove materials from surfaces of microfeature workpieces. In
certain embodiments, the processes are capable of producing
deposits that exhibit resistivity values within desired ranges over
an extended number of plating cycles. The embodiments described
herein also relate to processes that reduce the adverse impacts
created by the presence of complexing agents and/or other additives
in processing fluids used to electrolytically process a
microfeature workpiece. In some embodiments, the described
processes employ low conductivity/high pH processing fluids without
suffering from the drawback of defect formation in the deposited
material resulting from the presence of metal hydroxide particles
or flakes present in processing fluids in contact with the
microfeature workpiece. Processors of microfeature workpieces will
find certain processes described herein desirable because the
processes produce high yields of deposits that exhibit resistivity
values within acceptable ranges without requiring costly frequent
replacement of processing fluids. Reducing adverse impacts created
by the presence of complexing agents and/or other additives in the
processing fluids may also be considered desirable by users of the
electrolytic processes described herein.
[0009] In one embodiment, a surface of a microfeature workpiece is
contacted with a first processing fluid that includes first
processing fluid species, such as a cation, an anion, and a
complexing agent. A counter electrode is in contact with a second
processing fluid and an electrochemical reaction occurs at the
counter electrode. The process effectively prevents movement of
cationic species between the first processing fluid and the second
processing fluid. In certain embodiments, the first processing
fluid can be a high pH processing fluid, the cation can be a metal
ion to be deposited onto the surface of the microfeature workpiece,
and the counter electrode can be an inert electrode.
[0010] In another embodiment, a surface of a microfeature workpiece
is contacted with a first processing fluid that includes a metal
ion to be deposited onto the surface of the microfeature workpiece.
In addition, the first processing fluid includes a complexing agent
and a counter anion to the metal ion. An inert anode is in contact
with a second processing fluid, and an oxidizing agent is produced
at the inert anode. The process employs an anion permeable barrier
between the first processing fluid and the second processing fluid.
The anion permeable barrier allows counter anions to pass from the
first processing fluid to the second processing fluid. In this
embodiment, metal ions in the first processing fluid are deposited
onto the surface of the microelectronic workpiece. In certain
embodiments, the first and second processing fluids can be high pH
processing fluids.
[0011] In a further embodiment, a surface of a microfeature
workpiece is contacted with a first processing fluid that includes
a metal ion to be deposited onto a surface of the microelectronic
workpiece. In this embodiment, an inert anode is in contact with a
second processing fluid that includes a buffer and pH adjustment
agent and an anion permeable barrier is located between the first
processing fluid and the second processing fluid.
[0012] The processes summarized above can be carried out in a
system for electrolytically processing a microfeature workpiece.
The system includes a chamber that has a processing unit for
receiving a first processing fluid and counter electrode unit for
receiving a second processing fluid. A counter electrode is located
in the counter electrode unit, and an anion permeable barrier is
located between the processing unit and the counter electrode unit.
The chamber further includes a source of metal ion in fluid
communication with the processing unit and a source of a pH
adjustment agent in fluid communication with the counter electrode
unit.
[0013] Through the use of processes described above and the system
described above, metals such as copper, nickel, lead, gold, silver,
tin, and platinum can be deposited onto surfaces of a microfeature
workpiece. Such surfaces can take the form of seed layers or
barrier layers.
[0014] The process embodiments and system described above can be
used to electroplate materials onto a surface of a microfeature
workpiece or used to electroetch or deplate materials from a
surface of a microfeature workpiece. When the process is used to
electroplate materials, the microfeature workpiece will function as
a cathode, and the counter electrode will function as an anode. In
contrast, when deplating is carried out, the microfeature workpiece
will function as an anode, and the counter electrode will function
as a cathode.
[0015] Accordingly, in another embodiment, a surface of a
microfeature workpiece is contacted with a first processing fluid
that includes a counter ion to a metal on the surface. A cathode is
contacted with a second processing fluid also containing a counter
ion, and an anion permeable barrier is located between the first
processing fluid and the second processing fluid. Chemical species
in the second processing fluid are reduced, and an acid is
introduced to the second processing fluid. Counter ions from the
second processing fluid are passed through the anion permeable
barrier to the first processing fluid. In accordance with this
embodiment, metals from the surface of the microfeature workpiece
are electrolytically dissolved, i.e., oxidized and deplated.
[0016] The process summarized in the previous paragraph can be
carried out in a system for electrolytically processing a
microfeature workpiece that includes a chamber that has a
processing unit for receiving a first processing fluid and a
counter electrode unit for receiving a second processing fluid. An
anion permeable barrier is positioned between the processing unit
and the counter electrode unit. The system further includes a
cathode in the counter electrode unit, a source of metal counter
ions in fluid communication with the counter electrode unit, and a
source of pH adjustment agent in fluid communication with the
processing unit.
[0017] Through the use of the processes and systems described above
for removing materials from surfaces of a microfeature workpiece,
metals such as copper, nickel, lead, gold, silver, tin, and
platinum can be deplated from a microfeature workpiece surface.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The foregoing aspects and many of the attendant advantages
of the processes described herein will become more readily
appreciated as the same become better understood by reference to
the following detailed description, when taken in conjunction with
the accompanying drawings, wherein:
[0019] FIG. 1 is a schematic illustration of a reactor for carrying
out processes described herein;
[0020] FIG. 2 graphically illustrates deposit resistivity as a
function of bath age for a deposit formed using processing fluids
separated by an anion permeable barrier and a deposit formed using
a processing fluid without an anion permeable barrier;
[0021] FIG. 3 is a schematic illustration of a chamber for carrying
out processes described herein;
[0022] FIG. 4 is a schematic illustration of the chemistry and
chemical reactions occurring in one embodiment of the processes for
electroplating a metal described herein;
[0023] FIG. 5 is a schematic illustration of the chemistry and
chemical reactions occurring in one embodiment of the processes for
electroplating two metals described herein using an inert
anode;
[0024] FIG. 6 is a schematic illustration of the chemistry and
chemical reactions occurring in one embodiment of the processes for
electroplating two metals described herein using a consumable
anode;
[0025] FIG. 7 is a schematic illustration of the chemistry and
chemical reactions occurring in one embodiment of the processes for
deplating a metal described herein;
[0026] FIG. 8 is a schematic illustration of a tool that includes
chambers for carrying out processes described herein;
[0027] FIGS. 9A-9C are schematic illustrations of one embodiment of
the processes described herein for electrolytically treating a seed
layer; and
[0028] FIGS. 10A and 10B are schematic illustrations of one
embodiment of the processes described herein for electrolytically
treating a barrier layer.
DETAILED DESCRIPTION
[0029] As used herein, the terms "microfeature workpiece" or
"workpiece" refer to substrates on and/or in which micro devices
are formed. Such substrates include semiconductive substrates
(e.g., silicon wafers and gallium arsenide wafers), nonconductive
substrates (e.g., ceramic or glass substrates), and conductive
substrates (e.g., doped wafers). Examples of micro devices include
microelectronic circuits or components, micromechanical devices,
microelectromechanical devices, micro optics, thin film recording
heads, data storage elements, microfluidic devices, and other small
scale devices.
[0030] In the description that follows regarding electroplating a
metal onto a microfeature workpiece, specific reference is made to
copper as an example of a metal ion that can be electroplated onto
a microfeature workpiece. The reference to copper ions is for
exemplary purposes, and it should be understood that the following
description is not limited to copper ions. Examples of other metal
ions useful in the processes described herein include gold ions,
tin ions, silver ions, platinum ions, lead ions, cobalt ions, zinc
ions, nickel ions, ruthenium ions, rhodium ions, iridium ions,
osmium ions, rhenium ions, and palladium ions.
[0031] In the description that follows regarding electroplating
more than one metal onto a microfeature workpiece, specific
reference is made to a tin-silver solder system as an example of
metal ions that can be electroplated onto a microfeature workpiece
to form a composite deposit. The reference to deposition of a
tin-silver solder is for exemplary purposes, and it should be
understood that the description is not limited to tin and silver
ions.
[0032] With respect to the description that follows regarding
deplating a metal from a microfeature workpiece, specific reference
is made to copper as an example of a metal ion that can be deplated
from a microfeature workpiece. The reference to copper is for
exemplary purposes, and it should be understood that the
description regarding deplating are not limited to the removal of
copper. Examples of other metals that can be removed from a
microfeature workpiece in accordance with embodiments described
herein include gold ions, tin ions, silver ions, platinum ions,
lead ions, cobalt ions, zinc ions, nickel ions, ruthenium ions,
rhodium ions, iridium ions, osmium ions, rhenium ions, and
palladium ions.
[0033] Processes described herein can be carried out in an
electrochemical reactor, e.g., an electroplating or deplating
reactor, such as the one described below with reference to FIG. 1.
Referring to FIG. 1, reactor 10 includes an upper processing unit
12 containing a first processing fluid 14 (e.g., a catholyte in an
electroplating process or an anolyte in a deplating process) and a
counter electrode unit 18 below the processing unit 12 that
contains a second processing fluid 20 (e.g., anolyte in an
electroplating process or a catholyte in a deplating process) which
may be different in composition and/or properties from the first
processing fluid 14. Processing unit 12 receives a working
electrode 16 (e.g., a microfeature workpiece) and delivers first
processing fluid 14 to the working electrode 16. Counter electrode
unit 18 includes a counter electrode 22 that is in contact with the
second processing fluid 20. When copper is to be deposited onto
working electrode 16, working electrode 16 is the cathode and
counter electrode 22 is the anode. Accordingly, in plating
applications, first processing fluid 14 is a catholyte, and second
processing fluid 20 is an anolyte. In general, the catholyte
contains components in the form of ionic species, such as acid
ions, hydroxyl ions, and metal ions, and a complexing agent capable
of forming a complex with the metal ions. The catholyte may also
include organic components, such as accelerators, suppressors, and
levelers that improve the results of the electroplating process. In
addition, the catholyte may include a pH adjustment agent to affect
the pH of the catholyte. The anolyte generally includes ionic
species as well, such as acid ions, hydroxyl ions, and metal ions.
The catholyte may also include a pH adjustment agent. Additional
details regarding the various components in the catholyte and
anolyte are provided below.
[0034] When copper is to be deplated from working electrode 16,
working electrode 16 is the anode, and counter electrode 22 is the
cathode. Accordingly, in deplating applications, the first
processing fluid 14 is an anolyte, and the second processing fluid
20 is a catholyte.
[0035] Reactor 10 also includes a nonporous anion permeable barrier
24 between the first processing fluid 14 and the second processing
fluid 20. Nonporous anion permeable barrier 24 allows anions to
pass through the barrier while inhibiting or substantially
preventing non-anionic components, such as cations, from passing
between the first processing fluid 14 and second processing fluid
20. By inhibiting or substantially preventing nonionic components
from passing between the first processing fluid 14 and second
processing fluid 20, adverse effects on the deposited material
resulting from the presence of unwanted nonanionic components, such
as cations, in the first processing fluid 14 can be avoided. As
such, nonporous anion permeable barrier 24 separates first
processing fluid 14 and second processing fluid 20 such that first
processing fluid 14 can have different chemical characteristics and
properties than second processing fluid 20. For example, the
chemical components of first processing fluid 14 and second
processing fluid 20 can be different, the pH of first processing
fluid 14 and second processing fluid 20 can be different, and
concentrations of components common to both first processing fluid
14 and second processing fluid 20 can be different.
[0036] In the following description of an electroplating process,
for consistency, working electrode 16 will be referred to as the
cathode, and counter electrode 22 will be referred to as the anode.
Likewise, first processing fluid 14 will be referred to as the
catholyte, and second processing fluid 20 will be referred to as
the anolyte. When reactor 10 is used to electrolytically process a
microfeature workpiece to deposit metal ions thereon, an electric
potential is applied between anode 22 and cathode 16. Copper ions
in the catholyte are consumed by the deposition of copper ions onto
the cathode. Meanwhile, the anode becomes positively charged and
attracts negatively charged ions to its surface. For example,
hydroxyl ions in the anolyte are attracted to the anode where they
react to liberate oxygen and produce water. The foregoing results
in a gradient of charge in the anolyte with unbalanced positively
charged species in the anolyte solution, and negatively charged
species in the catholyte solution. This charge imbalance encourages
the transfer of negatively charged anions through the anion
permeable barrier 24 from catholyte 14 to the anolyte 20. An
electrochemical reaction (e.g., losing or gaining electrons) occurs
at cathode 16, resulting in metal ions being reduced (i.e., gaining
electrons) to metal on surfaces of cathode 16.
[0037] Reactor 10 effectively maintains the concentration of metal
ions in catholyte 14 during the electroplating process in the
following manner. As metal ions are deposited onto the surface of
cathode 16, additional metal ions are introduced to catholyte 14
from a source of metal ions 130, which is in fluid communication
with processing unit 12. As explained below in more detail, these
metal ions can be provided by delivering a metal salt solution to
processing unit 12. Processing unit 12 can also be in fluid
communication with sources of other components that need
replenishment. In a similar fashion, counter electrode unit 18 may
be in fluid communication with sources of components that require
replenishment. For example, counter electrode unit 18 can be in
fluid communication with a source of pH adjustment agent 132.
Likewise, both processing unit 12 and electrode unit 18 can include
conduits or other structures for removing portions of catholyte 14
from processing unit 12 or portions of anolyte 20 from counter
electrode unit 18.
[0038] Anode 22 may be a consumable anode or an inert anode.
Exemplary consumable anodes and inert anodes are described below in
more detail.
[0039] Referring to FIG. 4, the chemistry present in processing
unit 12 and counter electrode unit 18 are described in more detail
along with various chemical reactions that are believed to occur.
It should be understood that by describing chemical reactions that
are believed to occur within reactor 10, the processes described
herein are not limited to processes wherein these reactions
occur.
[0040] FIG. 4 schematically illustrates an example of the operation
of reactor 10 using an anion permeable barrier 24 and an inert
anode 22 in combination with a low conductivity/high pH first
processing fluid and a low conductivity/high pH second processing
fluid suitable for processing copper seed layers or plating
directly onto a barrier layer. In the description that follows,
high pH first processing fluid 14 in processing unit 12 is a
catholyte containing a metal ion (M.sup.+), e.g., copper ions
(Cu.sup.2+), a counter ion (X.sup.-) for the metal ion, e.g.,
sulfate ions (SO.sub.4.sup.2-), a complexing agent CA, as described
below, chelated with the metal ions, a pH buffer such as boric acid
(H.sub.3BO.sub.3) that dissociates into hydrogen ions (H.sup.+) and
H.sub.2BO.sub.3-, and a pH adjustment agent, such as
tetramethylammonium hydroxide (TMAH) that dissociates into hydroxyl
ion (OH.sup.-) and TMA.sup.+. The specific hydrogen ion
concentration in catholyte 14 can be chosen taking into
consideration conventional factors such as complexing ability of
the complexing agent, buffering capability of the buffer, metal ion
concentrations, volatile organics concentrations, deposition
potential of the complex at the particular pH, solubility of the
catholyte constituents, stability of the catholyte, desired
characteristics of the deposits, and diffusion coefficients of the
metal ions.
[0041] For example, for electroplating embodiments, high pH second
processing fluid 20 in counter electrode unit 18 is an anolyte.
Anolyte 20 can have a concentration of H.sup.+ that is
approximately equal to the concentration of H.sup.+ in catholyte
14, although this is not required. By adjusting H.sup.+
concentration in anolyte 20 to be approximately equal to the
concentration of H.sup.+ in catholyte 14, transfer of negatively
charged hydroxyl ions from catholyte 14 to anolyte 20 through anion
permeable membrane 24 during electroplating is inhibited. By
inhibiting the transfer of negatively charged hydroxyl ions from
catholyte 14 to anolyte 20, a more constant catholyte pH can be
maintained. By maintaining pH of the catholyte relatively constant,
the need to add pH adjustment agent to the catholyte is reduced or
eliminated. This simplifies maintenance of the catholyte and helps
to maintain the conductivity of the catholyte relatively stable
through repeated plating cycles. In the description that follows
with reference to FIG. 4, anolyte 20 includes a pH adjustment
agent, such as TMAH, and a buffer, such as boric acid.
[0042] As mentioned above, during a plating cycle, an electric
potential is applied between cathode 16 and anode 22. As copper
ions are reduced and electroplated onto cathode 16, sulfate ions
(SO.sub.4.sup.2-) accumulate in the catholyte near a first surface
32 of anion permeable barrier 24. Additionally, depending on the pH
of the anolyte at positively charged anode 22, hydroxyl ions
(OH.sup.-) are converted to water (H.sub.2O) and oxygen (O.sub.2)
and/or water is decomposed to hydrogen ions (H.sup.+) and oxygen.
The resulting electrical charge gradient causes the negatively
charged sulfate ions to move from first surface 32 of anion
permeable barrier 24 to the second surface 34 of anion permeable
barrier 24. The transfer of negatively charged sulfate ions from
catholyte 14 to anolyte 20 during the plating cycle maintains the
charge balance of reactor 10. To maintain the concentration of the
negatively charged ions resulting from the dissociation of boric
acid in catholyte 14 during electroplating, the concentration of
boric acid in the anolyte may be set so it is significantly greater
than the concentration of boric acid in the catholyte. This
concentration differential inhibits the negatively charged ions
resulting from the dissociation of boric acid in catholyte 14 from
moving through anion permeable membrane 24 to anolyte 20 during
electroplating.
[0043] Continuing to refer to FIG. 4, during a plating cycle, as
explained above, copper ions in catholyte 14 are reduced at cathode
16 and are deposited as copper. Copper ions that are consumed by
the electroplating are replenished by the addition of a solution of
copper sulfate to the catholyte. During the plating cycle, sulfate
ions which are introduced to catholyte 14 as a result of adding the
copper sulfate transfer across anion permeable barrier 24 to
anolyte 20. Portions of the anolyte can be removed from counter
electrode unit (18 in FIG. 1) in order to avoid the excessive build
up of sulfate ions in the anolyte 20. Non-anionic components in
catholyte 14 (e.g., Cu.sup.2+, H.sup.+, TMA.sup.+, H.sub.3BO.sub.3,
and Cu(ED).sub.2.sup.2+) generally do not pass through anion
permeable membrane 24 and thus remain in catholyte 14. As described
above, transfer of the hydroxyl (OH.sup.-) ion from the catholyte
to the anolyte is minimized by maintaining pH of anolyte 20 at
substantially the same level as pH of catholyte 14. Since hydroxyl
ions are consumed at anode 22, a pH adjustment agent, such as
TMAOH, may be added to anolyte 20 as described above to maintain
the pH of the anolyte at desired levels.
[0044] Microfeature workpieces that can be processed using
processes described herein can include different structures on
their surfaces that can be electrolytically processed to deposit
materials thereon. For example, a semiconductor microfeature
workpiece can include seed layers or barrier layers. Referring to
FIGS. 9A-9C, one sequence of steps for electrolytically processing
a seed layer using a process described herein is provided.
[0045] Referring to FIG. 9A, a cross-sectional view of a
microstructure, such as trench 105 that is to be filled with bulk
metallization is illustrated and will be used to describe use of
processes described herein to enhance a seed layer. As shown, a
thin barrier layer 110, for example, titanium nitride or tantalum
nitride, is deposited over the surface of a semiconductor device
or, as illustrated in FIG. 9A, over a layer of dielectric 108 such
as silicon dioxide. Any known technique such as chemical vapor
deposition (CVD) or physical vapor deposition (PVD), can be used to
deposit barrier layer 110.
[0046] After deposition of barrier layer 110, an ultrathin copper
seed layer 115 is deposited on barrier layer 110. The resulting
structure is illustrated in FIG. 9B. Seed layer 115 can be formed
using a vapor deposition technique also, such as CVD or PVD.
Alternatively, seed layer 115 can be formed by direct
electroplating onto barrier layer 110 as described below in more
detail. Owing to the small dimensions of trench 105, techniques
used to form ultrathin seed layer 115 should be capable of forming
the seed layer without closing off small geometry trenches. In
order to avoid closing off small geometry trenches, seed layer 115
should be as thin as possible while still providing a suitable
substrate upon which to deposit bulk metal. For example, ultrathin
seed layer 115 can have a thickness of about 50 to about 500
angstroms, about 100 to about 250 angstroms, or specifically about
200 angstroms.
[0047] The use of ultrathin seed layer 115 introduces its own set
of drawbacks. For example, ultrathin seed layers may not coat the
barrier layer in a uniform manner. For example, voids or
non-continuous seed layer regions on the sidewalls of the trenches
such as at 120, can be present in ultrathin seed layer 115. The
processes described herein can be used to enhance seed layer 115 to
fill the void or non-continuous regions 120 found in ultrathin seed
layer 115. Referring to FIG. 9C, to achieve this enhancement, the
microfeature workpiece is processed as described herein to deposit
a further amount of metal 118 onto ultrathin seed layer 115 and/or
portions of underlying barrier layer 110 that are exposed at voids
or non-continuous portions 120.
[0048] Preferably, this seed layer enhancement continues until a
sidewall step coverage, i.e., the ratio of seed layer 115 thickness
at the bottom sidewall regions to the nominal thickness of seed
layer 115 at the exteriorly disposed side of the workpiece,
achieves a value of at least 10%. More preferably, the sidewall
step coverage is at least about 20%. Preferably, such sidewall step
coverage values are present in substantially all of the recessed
structures of the microfeature workpiece; however, it will be
recognized that certain recessed structures may not reach such
sidewall step values.
[0049] Another type of feature on the surface of a microfeature
workpiece that can be electrolytically treated using processes
described herein is a barrier layer. Barrier layers are used
because of the tendency of certain metals to diffuse into silicon
junctions and alter the electrical characteristics of semiconductor
devices formed in a substrate. Barrier layers made of materials
such as titanium, titanium nitride, tantalum, tantalum nitride,
tungsten, and tungsten nitride are often laid over silicon
junctions and any intervening layers prior to depositing a layer of
metal. Referring to FIG. 10A, a cross-sectional view of a
microstructure, such as trench 205 that is to be filled with bulk
metallization is illustrated, and will be used to describe the
formation of a metal layer directly onto a barrier layer using
processes described herein. As illustrated in FIG. 10A, thin
barrier layer 210 is deposited over the surface of a semiconductor
device or, as illustrated in FIG. 10A, over a layer of dielectric
208, such as silicon dioxide. Barrier layer 210 can be deposited as
described above with reference to FIG. 9A using CVD or PVD
techniques. After barrier layer 210 is deposited, the microfeature
workpiece is processed as described herein to form a metal feature
215 over barrier layer 210. The resulting structure can then be
further processed to deposit bulk metal (not shown) to fill the
trench 205.
[0050] The pH of processing fluids described herein can vary from
alkaline to acidic. The low conductivity/high pH processing fluids
described herein are distinct from low pH processing fluids such as
acidic electroplating baths. The concentration of H.sup.+ useful in
high pH processing fluids may vary with those providing pHs above
7, preferably above 8 and most preferably above 9 being examples of
useful high pH processing fluids.
[0051] As noted above, processes described herein are useful to
electroplate metals other than copper, for example, gold, silver,
platinum, nickel, tin, lead, ruthenium, rhodium, iridium, osmium,
rhenium, and palladium. Metal ions useful in the catholyte can be
provided from a solution of a metal salt. Exemplary metal salts
include gluconates, cyanides, sulfamates, citrates, fluoroborates,
pyrophosphates, sulfates, chlorides, sulfides, chlorites, sulfites,
nitrates, nitrites, and methane sulfonates. Exemplary
concentrations of metal salts in the catholyte used for plating
applications range from about 0.03 to about 0.25M.
[0052] The ability to electroplate metal ions can be affected by
chelating the metal ion with a complexing agent. In the context of
the electroplating of copper, copper ions chelated with ethylene
diamine complexing agent exhibit a higher deposition potential
compared to copper ions that have not been chelated. Complexing
agents useful for chelating and forming complexes with metal ions
include chemical compounds having at least one part with the
chemical structure COOR.sub.1--COHR.sub.2R.sub.3 where R.sub.1 is
an organic group covalently bound to the carboxylate group (COO),
R.sub.2 is either hydrogen or an organic group, and R.sub.3 is
either hydrogen or an organic group. Specific examples of such type
of complexing agents include citric acid and salts thereof,
tartaric acid and salts thereof, diethyltartrate,
diisoproyltartrate, and dimethyltartrate. Another type of useful
complexing agent includes compounds that contain a nitrogen
containing chelating group R--NR.sub.2--R.sub.1, wherein R is any
alkyl or aromatic group, and R.sub.1 and R.sub.2 are H, alkyl, or
aryl organic groups or polymer chains. Specific examples of these
types of complexing agents include ethylene diamine, ethylene
diamine tetraacetic acid and its salts, cyclam, porphrin,
bipyridyl, pyrolle, thiophene, and polyamines. In plating
embodiments, suitable ratios between the concentration of metal
ions and concentrations of complexing agents in the catholyte can
range from 1:25 to 25:1; for example, 1:10 to 10:1 or 1:5 to
5:1.
[0053] Useful pH adjustment agents include materials capable of
adjusting the pH of the first processing fluid and the second
processing fluid, for example, to above 7 to about 13, and more
specifically, above about 9.0. When ethylene diamine or citric acid
are used as a complexing agent for copper ions, a pH of about 9.5
is useful. When ethylene diamine tetraacetic acid is used as a
complexing agent for copper ions, a pH of about 12.5 is suitable.
Examples of suitable pH adjustment agents include alkaline agents
such as potassium hydroxide, ammonium hydroxide, tetramethyl
ammonium hydroxide, sodium hydroxide, and other alkaline metal
hydroxides. A useful amount and concentration of pH adjustment
agents will depend upon the level of pH adjustment desired and
other factors, such as the volume of processing fluid and the other
components in the processing fluid. Useful pH adjustment agents
also include materials capable of adjusting the pH of the first and
second processing fluid to below 7.
[0054] Useful buffers include materials that maintain the pH
relatively constant, preferably at a level that facilitates complex
formation and desirable complexed species. Boric acid was described
above as an example of a suitable buffer. Other useful buffers
include sodium acetate/acetic acid and phosphates. Exemplary
concentrations of buffer range from about 0.01 to about 0.5M in the
catholyte for plating applications.
[0055] The catholyte can include other additives such as those that
lower the resistivity of the fluid, e.g., ammonium sulfate; and
those that increase the conformality of the deposit, e.g., ethylene
glycol. For plating applications, exemplary concentrations of
resistivity effecting agents in the catholyte range from about 0.01
to about 0.5M. For conformality affecting agents concentrations
ranging from about 0 to 1.0M are exemplary.
[0056] Useful anion permeable barriers include nonporous barriers,
such as semi- permeable anion exchange membranes. A semi-permeable
anion exchange membrane allows anions to pass but not non-anionic
species, such as cations. The nonporous feature of the barrier
inhibits fluid flow between first processing fluid 14 and second
processing fluid 20 within reactor 10 in FIG. 1. Accordingly, an
electric potential, a charge imbalance between the processing
fluids, and/or differences in the concentrations of substances in
the processing fluids can drive anions across an anion permeable
barrier. In comparison to porous barriers, nonporous barriers are
characterized by having little or no porosity or open space. In a
normal electroplating reactor, nonporous barriers generally do not
permit fluid flow when the pressure differential across the barrier
is less than about 6 psi. Because the nonporous barriers are
substantially free of open area, fluid is inhibited from passing
through the nonporous barrier. Water, however, may be transported
through the nonporous barrier via osmosis and/or electro-osmosis.
Osmosis can occur when the molar concentration in the first and
second processing fluids are substantially different.
Electro-osmosis occurs as water is carried through the nonporous
barrier with current-carrying ions in the form of a hydration
sphere. When the first and second processing fluids have similar
molar concentrations and no electrical current is passed through
the processing fluids, fluid flow between the first and second
processing fluids via the nonporous barrier is substantially
prevented.
[0057] A nonporous barrier can be hydrophilic so that bubbles in
the processing fluids do not cause portions of the barrier to dry,
which reduces conductivity through the barrier. Exemplary nonporous
barriers include Ionac.RTM. membranes manufactured by Sybron
Chemicals, Inc., and NeoSepta.RTM. manufactured by Asahi Kasei
Company.
[0058] In addition to the nonporous barriers described above, anion
permeable barrier can also be a porous barrier. Porous barriers
include substantial amounts of open area or pores that permit fluid
to pass through the porous barrier. Both ionic materials and
nonionic materials are capable of passing through a porous barrier;
however, passage of certain materials may be limited or restricted
if the materials are of a size that allows the porous barrier to
inhibit their passage. While useful porous barriers may limit the
chemical transport (via diffusion and/or convection) of some
materials in the first processing fluid and the second processing
fluid, they allow migration of anionic species (enhanced passage of
current) during application of electric fields associated with
electrolytic processing. In the context of electrolytic processing
a useful porous barrier enables migration of anionic species across
the porous barrier while substantially limiting diffusion or mixing
(i.e., transport across the barrier) of larger organic components
and other non-anionic components between the anolyte and catholyte.
Thus, porous barriers permit maintaining different chemical
compositions for the anolyte and the catholyte. The porous barriers
should be chemically compatible with the processing fluids over
extended operational time periods. Examples of suitable porous
barrier layers include porous glasses (e.g., glass frits made by
sintering fine glass powder), porous ceramics (e.g., alumina and
zirconia), silica aerogel, organic aerogels (e.g., resorcinol
formaldehyde aerogel), and porous polymeric materials, such as
expanded Teflon.RTM. (Gortex.RTM.). Suitable porous ceramics
include grade P-6-C available from CoorsTek of Golden, Colo. An
example of a porous barrier is a suitable porous plastic, such as
Kynar.TM., a sintered polyethylene or polypropylene. Suitable
materials can have a porosity (void faction) of about 25%-85% by
volume with average pore sizes ranging from about 0.5 to about 20
micrometers. Such porous plastic materials are available from
Poretex Corporation of Fairburn, Ga. These porous plastics may be
made from three separate layers of material that include a thin,
small pore size material sandwiched between two thicker, larger
pore-sized sheets. An example of a product useful for the middle
layer having a small pore size is CelGard.TM. 2400, made by CelGard
Corporation, a division of Hoechst, of Charlotte, N.C. The outer
layers of the sandwich construction can be a material such as
ultra-fine grade sintered polyethylene sheet, available from
Poretex Corporation. Porous barrier materials allow fluid flow
across themselves in response to the application of pressures
normally encountered in an electrochemical treatment process, e.g.,
pressures normally ranging from about 6 psi and below.
[0059] Inert anodes useful in processes described herein are also
referred to as non-consumable anodes and/or dimensionally stable
anodes and are of the type that when an electric potential is
applied between a cathode and an anode in contact with an
electrolyte solution, that there is no dissolution of the chemical
species of the inert anode. Exemplary materials for inert anodes
include platinum, ruthenium, ruthenium oxide, iridium, and other
noble metals.
[0060] Consumable anodes useful in processes described herein are
of the type that when an electric potential is applied between a
cathode and an anode in contact with an electrolyte solution,
dissolution of the chemical species making up the anode occurs.
Exemplary materials for consumable anodes will include those
materials that are to be deposited onto the microfeature workpiece,
for example, copper, gold, tin, silver, lead, platinum, nickel,
cobalt, zinc, and the like.
[0061] The temperature of the processing fluids can be chosen
taking into consideration conventional factors such as complexing
ability of the complexing agent, buffering capability of the
buffer, metal ion concentration, volatile organics concentration,
deposition potential of the complexed metal at the particular pH,
solubility of the processing fluid constituents, stability of the
processing fluids, desired deposit characteristics, and diffusion
coefficients of the metal ions. Generally, temperatures ranging
from about 20.degree. C.-35.degree. C. are suitable, although
temperatures above or below this range may be useful.
[0062] As described above in the context of an electroplating
process, oxidation of hydroxyl ions or water at the anode produces
oxygen capable of oxidizing components in the catholyte. When an
anion permeable barrier is absent, oxidation of components in the
electrolyte can also occur directly at the anode. Oxidation of
components in the electrolyte is undesirable because it is believed
that the oxidized components contribute to variability in the
properties (e.g. resistivity) of the metal deposits. Through the
use of an anion permeable barrier, as described above, transfer of
oxygen generated at the anode from the anolyte to the catholyte is
minimized and/or prevented, and, thus, such oxygen is not available
to oxidize components that are present in the catholyte. As
discussed above, one way to address the problem of oxygen generated
at the anode oxidizing components in the processing fluid is to
frequently replace the processing fluid. Because of the time and
cost associated with frequently replacing the processing fluid, the
processes described herein provide an attractive alternative by
allowing the processing fluids to be used in a large number of
plating cycles without replacement. Use of the anion permeable
barrier also isolates the anode from non-anionic components in the
catholyte, e.g., complexing agent, that may otherwise be oxidized
at the anode and adversely affect the ability of the catholyte to
deposit features having resistivity properties that fall within
acceptable ranges.
[0063] The resistivity of deposited metals as a function of the age
of the processing fluid from which the deposit was formed is
illustrated in FIG. 2. FIG. 2 illustrates how the use of processes
described herein to deposit copper significantly extends the useful
operating life of a catholyte compared to conventional processes
using similar chemistries without an anion permeable barrier. FIG.
2 illustrates test results evaluating the resistivity of several 20
nanometer copper seed layers deposited using the same chemistry in
contact with the workpiece. One set of copper seed layers was
formed using a process that did not employ an anion permeable
barrier and a second set of copper seed layers was formed using a
process that employed an anion permeable barrier in accordance with
a process described herein. More specifically the resistivity of a
deposit was measured using a 4-pt resistivity probe from Creative
Design Engineering, Inc. that measures the sheet resistance of a
substrate. The resistivity of the copper films was obtained as the
product of sheet resistance and thickness of the thin film. Several
wafers with the same seed layer resistance were obtained, and their
sheet resistance was pre-measured (R.sub.PVD). The wafers were then
plated in a chamber with no membranes, inert anodes, and a 9.5 pH
electrolyte. A fixed amp time was applied for each wafer (0.7
amp-min for a 300 mm wafer corresponding to 20 nm Cu thickness),
and a theoretical amount of Cu film deposited on the seed layer was
obtained at the same current density. The wafers were then rinsed
and dried in a spin rinse dryer. The wafers were then measured in
the 4-pt probe again. This provided a post sheet resistance
measurement (R.sub.total). With the two sheet resistance
measurements, the sheet resistance of just the film deposited was
obtained through the method of parallel subtraction using the
formula shown below and the sheet of resistance of the
electrodeposited seed layer was obtained. R.sub.ECD
Seed=(R.sub.PVD*R.sub.total)/(R.sub.PVD-R.sub.total)
[0064] The resistivity of the deposited film was obtained by
multiplying the thickness by the sheet resistance calculated
above.
[0065] Resistivity of the electrodeposit=Thickness*R.sub.ECD
Seed=20 nm*R.sub.ECD Seed
[0066] Several such wafers were plated periodically, as the bath
ages in terms of amp-min (dummy wafers were plated to age the
bath).
[0067] Similar sets of wafers were plated using an anionic membrane
as described herein. The chamber utilized the same electrolyte as
the catholyte used to plate the first set of wafers described
above. The anolyte was a fluid consisting of buffer, pH adjustment
agent, and of the same pH as the catholyte as described herein. The
wafers were plated with the same amp time as before under
substantially identical conditions.
[0068] Similar calculations were performed and the resistivity of
the electrodeposit was obtained as a function of bath age.
[0069] The resistivity of seed layers deposited using a process
without an anion permeable barrier (line 38), increases rapidly
with the age of the bath, increasing more than three times in under
2000 amp minutes. By comparison, the resistivity of copper seed
layers deposited using a process that employed an anion permeable
membrane as described herein, illustrated by line 40, increases
only gradually over time such that little increase is observed even
after 10,000 amp minutes. These results illustrate how a process
described herein substantially extends the useful life of
processing fluids used to deposit metal features onto a
microfeature workpiece.
[0070] Another advantage of employing an anionic permeable barrier
in the processes described herein is that the barrier prevents
bubbles from the oxygen gas evolved at the anode from transferring
to the catholyte. Bubbles in the catholyte are undesirable because
they can cause voids or holes in the deposited features.
[0071] Another feature of processes described herein is that the pH
adjustment agent, e.g., tetramethyl ammonium hydroxide, does not
accumulate in the first processing fluid. As a result, pH
adjustment agent need not be removed from the first processing
fluid. This simplifies the maintenance of the first processing
fluid.
[0072] In the foregoing descriptions, copper has been used as an
example of a metal that can be used to enhance a seed layer or to
form a metal feature directly onto a barrier layer. However, it
should be understood that the basic principles of the processes
described herein and their use for enhancement of an ultrathin
metal layer prior to the bulk deposition of additional metal or the
direct electroplating of a metal onto a barrier layer can be
applied to other metals or alloys as well as deposition for other
purposes. For example, gold is commonly used on for thin film head
and III-V semiconductor applications. Gold ions can be
electroplated using chloride or sulfite as the counter ion. As with
copper, the chloride or sulfite counter ion would migrate across
the anionic permeable barrier as described above in the context of
copper. Potassium hydroxide could be used as the pH adjustment
agent in a gold electroplating embodiment to counteract a drop in
pH in the anolyte resulting from the oxidation of hydroxyl ions at
the anode. As with the copper example described above, in the gold
embodiment, gold chloride or gold sulfite, in the form of sodium
gold sulfite or potassium gold sulfite could be added to the
catholyte to replenish the gold deposited.
[0073] As mentioned previously, processes described above are
useful for depositing more than one metal ion onto a microfeature
workpiece surface. For example, processes described above are
useful for depositing multi-component solders such as tin-silver
solders. Other types of multi-component metal systems that can be
deposited using processes described above include tin-copper,
tin-silver-copper, lead-tin, nickel-iron, and tin-copper-antimony.
Unlike certain copper features that are formed on the surfaces of
microfeature workpieces, solder features tend to be used in
packaging applications and are thus large compared to copper
microfeatures. Because of their larger size, e.g., 10-200 microns,
solder features are more susceptible to the presence of bubbles in
processing fluids that can become entrapped and affect the quality
of the solder deposits. A tin-silver solder system is an example of
plating of a metal with multiple valence states. Generally, metals
with multiple valence states can be plated from most of their
stable states. Since the charge required to deposit any metal is
directly proportional to the electrons required for the reduction,
metals in their valence states closest to their neutral states
consume less energy for reduction to metal. Unfortunately, most
metals in their state closest to their neutral states are
inherently unstable, and therefore production-worthy plating can be
unfeasible. Through the use of processes for plating metal ions
described above, plating solutions that include metals in this
inherently unstable state can be applied in an effective process to
deposit the desired metal. Through the use of the processes
described above for depositing a metal, less oxidation of the
inherently unstable metal species occurs, thus providing a more
production-worthy process.
[0074] By way of illustration, most tin-silver plating solutions
prefer Sn(II) as the species for tin plating. For such
multi-component plating systems, control of tin and silver ions
needs to be precise, and the use of silver or tin as an anode is
not feasible. The use of such consumable anodes could cause
stability issues resulting from plating/reacting with the anodes,
and they also create issues relating to the ability to uniformly
replenish metal. On the other hand, the use of inert anodes avoids
the foregoing issues, but introduces a new issue associated with
the production of oxygen through the oxidation of water or hydroxyl
ions at the inert anode. Such oxygen not only may oxidize other
components in the plating bath, it may also oxidize the desired
Sn(II) species to the more stable Sn(IV) ion, which is more
difficult to plate onto a workpiece.
[0075] Referring to FIG. 5, a schematic illustration is provided
for the operation of reactor 10 using an anion permeable barrier 24
and an inert anode 22 in combination with a first processing fluid
and a second processing fluid suitable for depositing tin-silver
solder. In the description that follows, processing fluid 14 in
processing unit 12 is a catholyte containing metal ions
M.sub.1.sup.+ and M.sub.2.sup.+, e.g., Sn.sup.2+ and Ag.sup.+ ions;
counter ions X.sub.1.sup.- and X.sub.2.sup.- for the metal ions,
e.g., methane sulfonate CH.sub.3SO.sub.3.sup.-; and complexing
agents CA.sub.1 and CA.sub.2, e.g., proprietary organic additives,
chelated with the metal ions. As discussed above in the context of
the electroplating of copper, the specific hydrogen ion
concentration in catholyte 14 can be chosen taking into
consideration conventional factors such as complexing ability of
the complexing agent, buffering capability of the buffer, metal ion
concentrations, volatile organics concentrations, alloy deposition
potential of the complex at the particular pH, solubility of the
catholyte constituents, stability of the catholyte, desired
characteristics of the deposits, and diffusion coefficients of the
metal ions.
[0076] The discussions above regarding the concentration of H+in
the anolyte and catholyte, relative concentrations of the buffer in
the anolyte and the catholyte, use of the pH adjustment agent,
replenishment of the metal ions, cathodic reduction reactions, and
anodic oxidation reactions in the context of the electroplating of
copper are equally applicable to a tin-silver system. The
particular operating conditions that are most desirable are related
to the specific chemistry being used.
[0077] As with the copper plating process, an electric potential
applied between cathode 16 and anode 22 results in tin ions and
silver ions being reduced at cathode 16 and deposited thereon. The
methane sulfonate (MSA) counter ion (CH.sub.3SO.sub.3.sup.-)
accumulates in the catholyte near a first surface 32 of anion
permeable barrier 24. As with the copper system, at positively
charged anode 22, hydroxyl ions are converted to water and oxygen
and/or water is decomposed to hydrogen ions and oxygen. The
resulting electrical charge gradient causes negatively charged MSA
ions (CH.sub.3SO.sub.3.sup.-) to move from first surface 32 of
anion permeable barrier 24 to the second surface 34 of anion
permeable barrier 24. The transfer of negatively charged MSA ions
(CH.sub.3SO.sub.3.sup.-) from catholyte 14 to anolyte 20 during the
plating cycle maintains the charge balance of reactor 10. Tin and
silver ions that are deposited onto cathode 16 can be replenished
by the addition of a solution of tin methane sulfonate and silver
methane sulfonate to the catholyte. During the plating cycle, MSA
ions that are introduced to catholyte 14 as a result of the
addition of the tin MSA and silver MSA transfer across anion
permeable barrier 24 to anolyte 20. As with the copper process,
portions of the anolyte can be removed from counter electrode unit
18 to avoid the buildup of MSA ions in the anolyte.
[0078] Referring to FIG. 6, in a different embodiment,
electroplating of two metals, e.g., tin and silver, can also be
achieved using a consumable anode 122. Referring to FIG. 6, the
catholyte 14 in processing unit 12 is similar to the catholyte
described with reference to FIG. 5. In the process depicted in FIG.
6, metal ion M.sub.2.sup.+ is introduced into processing unit 12
from source 200, metal ion M.sub.1.sup.+ is supplied to counter
electrode unit 18 through oxidation of metal making up consumable
anode 122. Metal ion M.sub.1.sup.+ combines with counter ion
X.sub.1.sup.- to form the metal salt M.sub.1X.sub.1 in counter
electrode unit 18 and is then delivered via line 202 to processing
unit 12. Metal salt M.sub.1X.sub.1 delivered to processing unit 12
dissociates therein to provide a source of metal ion M.sub.1.sup.+
that can be reduced at cathode 16 and deposited thereon as
described above with reference to FIG. 5. In accordance with this
embodiment, complexing agents CA.sub.1 and CA.sub.2 are present in
catholyte 14 where they can complex with metal ions M.sub.1.sup.+
and M.sub.2.sup.+. Suitable pH adjustment agents and pH buffers may
be present and/or added to the catholyte and anolyte. The charge
balance within reactor 10 can be maintained through the transfer of
negatively charged counter ion X.sub.1.sup.- in processing unit 12
across anion permeable membrane 24 into counter electrode unit
18.
[0079] Suitable reactors for depositing tin ions and silver ions
includes one designated a Raptor.TM. by Semitool, Inc., of
Kalispell, Mont., or a reactor of the type described in U.S. patent
application Ser. No. ______, filed on Nov. 23, 2005, entitled
Apparatus and Method for Agitating Fluids and the Processing of
Microfeature Workpieces, Attorney Docket No. 29195.8253US, naming
Paul McHugh, Gregory Wilson and Daniel Woodruff as inventors.
[0080] Metal can be deplated from a microfeature workpiece by
reversing the bias of the electric field created between the
microfeature workpiece and the working electrode. Referring to FIG.
7, a microfeature workpiece 416 is provided that carries a metal M,
e.g., copper, on its surface. Microfeature workpiece 416 is
contacted with a first processing fluid 414 in processing unit 412.
Processing fluid 414 includes metal ions M.sup.2-, e.g., copper
ions; a complexing agent CA, e.g., ethylene diamine tetraacetic
acid; a metal salt MX, e.g., copper sulfate; a complexed metal ion
M(CA).sup.2+; hydroxyl ions; a buffer, and a counter ion
X.sup.2.sup.-, e.g., sulfate ion. First processing unit 412 is
separated from a counter electrode unit 418 by anion permeable
membrane 424. Counter electrode unit 418 includes counter electrode
422 and a second processing fluid 420. In a deplating process,
microfeature workpiece 416, the working electrode, is an anode, and
counter electrode 422 is the cathode. Processing unit 412 is also
in fluid communication with a source 430 of complexing agent CA and
hydroxyl ions. In addition, processing unit 412 can be provided
with a mechanism 440 for removing metal salts therefrom. Counter
electrode unit 418 is in fluid communication with a source 450 of
acid. Through the application of an electric potential between
anode 416 and cathode 422, hydrogen ions are reduced at the cathode
422 to produce hydrogen gas. Copper on the surface of microfeature
workpiece 416 is oxidized resulting in copper ions being removed
from the surface of the microfeature workpiece. The charge balance
within reactor 410 is maintained through the transfer of counter
ion X.sup.2+ from catholyte 420 to anolyte 414 through anion
permeable membrane 424.
[0081] Catholyte 420 in counter electrode unit 418 includes
hydroxyl ions, buffer, and counter ion X.sup.2-. The acid that is
added to counter electrode unit 418 can be both a source of counter
ion X.sup.2- as well as a pH adjustment agent. In order to reduce
or eliminate transfer of buffer components across anionic permeable
membrane 424, the buffer concentration in anolyte 414 can be
maintained at a level equal to or greater than the concentration of
buffer in catholyte 420.
[0082] One or more of the reactors for electrolytically treating a
microfeature workpiece or systems including such reactors may be
integrated into a processing tool that is capable of executing a
plurality of methods on a workpiece. One such processing tool is an
electroplating apparatus available from Semitool, Inc., of
Kalispell, Mont. Referring to FIG. 5, such a processing tool may
include a plurality of processing stations 510, one or more of
which may be designed to carry out an electrolytic processing of a
microfeature workpiece with a high pH first processing fluid and an
inert anode as described above. Other suitable processing stations
include one or more rinsing/drying stations and other stations for
carrying out wet chemical processing. The tool also includes a
robotic member 520 that is carried on a central track 525 for
delivering workpieces from an input/output location to the various
processing stations.
[0083] Referring to FIG. 3, a more detailed schematic illustration
of one design of a reactor 100 for electroplating metals onto seed
layers, directly electroplating metal onto barrier layers, or
otherwise depositing materials onto workpieces is illustrated.
Reactor 100 includes a vessel 302, a processing chamber 310
configured to direct a flow of first processing fluid to a
processing zone 312, and an anode chamber 320 configured to contain
a second processing fluid separate from the first processing fluid.
An anion permeable barrier 330 separates the first processing fluid
in the processing unit 310 from the second processing fluid in the
anode chamber 320. Reactor 100 further includes a workpiece holder
340 having a plurality of electrical contacts 342 for applying an
electric potential to a workpiece 344 mounted to workpiece holder
340. Workpiece holder 340 can be a movable head configured to
position workpiece 344 in processing zone 312 of processing unit
310, and workpiece holder 340 can be configured to rotate workpiece
344 in processing zone 312. Suitable workpiece holders are
described in U.S. Pat. Nos. 6,080,291; 6,527,925; 6,773,560, and
U.S. patent application Ser. No. 10/497,460; all of which are
incorporated herein by reference.
[0084] Reactor 100 further includes a support member 350 in the
processing chamber 310 and a counter electrode 360 in the anode
chamber 320. Support member 350 spaces the anion permeable barrier
330 apart from workpiece processing zone 312 by a controlled
distance. This feature provides better control of the electric
field at processing zone 312 because the distance between the anion
permeable barrier 330 and workpiece processing zone 312 affects the
field strength at processing zone 312. Support member 350 generally
contacts first surface 332 of anion permeable barrier 330 such that
the distance between first surface 332 and processing zone 312 is
substantially the same across processing chamber 310. Another
feature of support member 350 is that it also shapes anion
permeable barrier 330 so that bubbles do not collect along a second
side 334 of anion permeable barrier 330.
[0085] Support member 350 is configured to direct flow F.sub.1 of a
first processing fluid laterally across first surface 332 of anion
permeable barrier 330 and vertically to processing zone 312.
Support member 350 accordingly controls the flow F.sub.1 of the
first processing fluid in processing chamber 310 to provide the
desired mass transfer characteristics in processing zone 312.
Support member 350 also shapes the electric field in processing
chamber 310.
[0086] Counter electrode 360 is spaced apart from second surface
334 of anion permeable barrier 330 such that a flow F.sub.2 of the
second processing fluid moves regularly outward across second
surface 334 of anion permeable barrier 330 at a relatively high
velocity. Flow F.sub.2 of the second processing fluid sweeps oxygen
bubbles and/or particles from the anion permeable barrier 330.
Reactor 100 further includes flow restrictor 370 around counter
electrode 360. Flow restrictor 370 is a porous material that
creates a back pressure in anode chamber 320 to provide a uniform
flow between counter electrode 360 and second surface 334 of the
anion permeable barrier 330. As a result, the electric field can be
consistently maintained because flow restrictor 370 mitigates
velocity gradients in the second processing fluid where bubbles
and/or particles can collect. The configuration of counter
electrode 360 and flow restrictor 370 also maintains a pressure in
the anode chamber 320 during plating that presses the anion
permeable barrier 330 against support member 350 to impart the
desired contour to anion permeable barrier 330.
[0087] Reactor 100 operates by positioning workpiece 344 in
processing zone 312, directing flow F.sub.1 of the first processing
fluid through processing chamber 310, and directing the flow
F.sub.2 of the second processing fluid through anode chamber 320.
As the first and second processing fluids flow through reactor 100,
an electric potential is applied to workpiece 344 via electrical
contacts 342 and counter electrode 360 to establish an electric
field in processing chamber 310 and anode chamber 320.
[0088] Another useful reactor for depositing metals using processes
described herein is described in U.S. Patent Application No.
2005/0087439, which is expressly incorporated herein by
reference.
[0089] While a preferred embodiment of the invention has been
illustrated and described, it will be appreciated that various
changes can be made therein without departing from the spirit and
scope of the invention.
* * * * *