U.S. patent application number 14/194591 was filed with the patent office on 2015-09-03 for methods for electrochemical deposition of multi-component solder using cation permeable barrier.
This patent application is currently assigned to APPLIED MATERIALS, INC.. The applicant listed for this patent is APPLIED Materials, Inc.. Invention is credited to Marvin L. Bernt, Ross Kulzer.
Application Number | 20150247251 14/194591 |
Document ID | / |
Family ID | 53946088 |
Filed Date | 2015-09-03 |
United States Patent
Application |
20150247251 |
Kind Code |
A1 |
Bernt; Marvin L. ; et
al. |
September 3, 2015 |
METHODS FOR ELECTROCHEMICAL DEPOSITION OF MULTI-COMPONENT SOLDER
USING CATION PERMEABLE BARRIER
Abstract
Processes and systems for electrochemical deposition of a
multi-component solder by 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 a cation permeable
barrier layer. The cation permeable barrier layer separates the
first processing fluid from the second processing fluid while
allowing certain cationic species to transfer between the two
fluids.
Inventors: |
Bernt; Marvin L.;
(Kalispell, MT) ; Kulzer; Ross; (Condon,
MT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
APPLIED Materials, Inc. |
Santa Clara |
CA |
US |
|
|
Assignee: |
APPLIED MATERIALS, INC.
Santa Clara
CA
|
Family ID: |
53946088 |
Appl. No.: |
14/194591 |
Filed: |
February 28, 2014 |
Current U.S.
Class: |
205/136 |
Current CPC
Class: |
C25D 5/10 20130101; C25D
3/60 20130101; C25D 17/002 20130101; C25D 5/02 20130101; C25D 7/123
20130101 |
International
Class: |
C25D 5/02 20060101
C25D005/02 |
Claims
1. A process for electrolytically processing a microfeature
workpiece as the working electrode in a first processing fluid and
a counter electrode in a second processing fluid, the method
comprising: (a) contacting a surface of the microfeature workpiece
with the first processing fluid, the first processing fluid
including a first metal cation; (b) contacting the counter
electrode with a second processing fluid, the second processing
fluid including a second metal cation and having a pH in the range
of about 1 to about 3; (c) allowing the second metal cation to move
from the second processing fluid to the first processing fluid, but
substantially preventing movement of the first metal cation from
the first processing fluid to the second processing fluid by
providing a cation permeable barrier between the first processing
fluid and the second processing fluid, wherein the primary mass
transport of the second metal cation from the second processing
fluid to the first processing fluid is across the cation permeable
barrier; and (d) electrolytically depositing the first and second
metal cations onto the surface of the microfeature workpiece.
2. The process of claim 1, wherein the cation permeable barrier is
a cation exchange membrane.
3. The process of claim 1, further comprising producing an
electrochemical reaction at the counter electrode to produce the
second metal cation.
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 1, wherein the first processing fluid is
dosed with the first metal cation.
6. The process of claim 1, wherein the counter electrode is a
consumable electrode.
7. The process of claim 1, wherein either or both of the first and
second processing fluids is dosed with the second metal cation.
8. The process of claim 7, wherein dosing in either or both of the
first and second processing fluids with the second metal cation is
not the major source of the second metal cation in the first
processing fluid.
9. The process of claim 1, wherein the first metal cation
concentration in the first processing fluid is in the range of
about 0.1 g/L to about 5.0 g/L.
10. The process of claim 1, wherein the second metal cation
concentration in the first processing fluid is selected from the
group consisting of in the range of about 40 to about 80 g/L, about
40 to about 120 g/L, and about 40 to about 150 g/L.
11. The process of claim 1, wherein the pH of the second processing
fluid is higher than the pH of the first processing fluid.
12. The process of claim 1, wherein the pH of the second processing
fluid is selected from the group consisting of about 1.0 to about
2.0, about 1.2 to about 1.8, about 1.5 to about 2.2, greater than
about 2.0, about 1.0 to about 3.0, and about 2.0 to about 3.0.
13. The process of claim 12, wherein the pH of the first processing
fluid is selected from the group consisting of less than or equal
to 1.0, less than or equal to 0.5, and in the range of 0 to
1.0.
14. The process of claim 1, wherein the first metal cation is
selected from the group consisting of copper ion, lead ion, gold
ion, tin ion, silver ion, bismuth ion, indium ion, platinum ion,
ruthenium ion, rhodium ion, iridium ion, osmium ion, rhenium ion,
palladium ion, and nickel ion.
15. The process of claim 1, wherein the second metal cation is
selected from the group consisting of copper ion, lead ion, tin
ion, bismuth ion, indium ion, silver ion, platinum ion, ruthenium
ion, rhodium ion, iridium ion, osmium ion, rhenium ion, palladium
ion, and nickel ion.
16. The process of claim 1, further comprising a third metal cation
selected from the group consisting of copper ion, lead ion, gold
ion, tin ion, silver ion, bismuth ion, indium ion, platinum ion,
ruthenium ion, rhodium ion, iridium ion, osmium ion, rhenium ion,
palladium ion, nickel ion.
17. (canceled)
18. The process of claim 1, wherein at least one of the first
processing fluid and the second processing fluid includes an
antioxidant.
19. (canceled)
20. The process of claim 1, where the second processing fluid is
not dosed into the first processing fluid.
21. A process for electrolytically processing a microfeature
workpiece as the working electrode with a first processing fluid
and a counter electrode, comprising: (a) contacting a surface of
the microfeature workpiece with the first processing fluid, the
first processing fluid comprising first processing fluid species
including a first metal cation; (b) contacting the counter
electrode with a second processing fluid, the second processing
fluid having a pH in the range of about 1 to about 3; (c) producing
an electrochemical reaction at the counter electrode to produce a
second metal cation; (d) providing a cation exchange membrane to
allow the second metal cation to move from the second processing
fluid to the first processing fluid, but to substantially prevent
movement of the first metal cation from the first processing fluid
to the second processing fluid when electrolytically processing the
microfeature workpiece; and (e) separating the second processing
fluid from the membrane when not electrolytically processing the
microfeature workpiece.
22. A process for electrolytically processing a microfeature
workpiece as the cathode with a first processing fluid and an
anode, comprising: (a) contacting a surface of the microfeature
workpiece with the first processing fluid, the first processing
fluid comprising first processing fluid species including a first
metal cation; (b) contacting the anode with a second processing
fluid, the second processing fluid having a pH in the range of
about 1 to about 3; (c) consuming the anode to produce a second
metal cation; (d) providing a cation exchange membrane to allow the
second metal cation to move from the second processing fluid to the
first processing fluid, but to substantially prevent movement of
the first metal cation from the first processing fluid to the
second processing fluid, wherein the second processing fluid is not
dosed in the first processing fluid; and (e) electrolytically
depositing the first and second metal cations onto the surface of
the microfeature workpiece.
Description
TECHNICAL FIELD
[0001] Embodiments of the present invention relate to electrolytic
processing of microfeature workpieces and electrolytic treatment
processes that utilize a cation permeable barrier.
BACKGROUND
[0002] 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.
[0003] 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.
[0004] 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.
[0005] 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.
[0006] 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 properties, such as resistivity, within
desired ranges.
[0007] In wafer level packaging (WLP) electrochemical deposition
(ECD), near eutectic tin-silver (Sn-Ag) is currently the alloy of
choice for lead-free solder bumping and copper pillar capping. In
current tin-silver plating processes, a liquid tin ion doping
concentrate is added to the catholyte to replenish the tin ions
consumed in the deposition process. However, tin ion concentrate
tends to be more significantly more expensive than solid tin, and
because of additives in the concentrate, results in reduced control
over the stability and the lifetime of the catholyte.
[0008] Therefore, there exists a need for an electrochemical
deposition method for plating more than one metal onto a
microfeature workpiece, for example, as a multi-component solder,
that uses a source of primary ions that is easier to control than a
liquid doping concentrate added to the catholyte. Embodiments of
the present disclosure are directed to fulfilling this and other
needs.
SUMMARY
[0009] The embodiments described herein relate to processes for
electrolytically processing a microfeature workpiece to deposit or
remove materials from surfaces of microfeature workpieces. The
processes described herein are capable of producing deposits
exhibiting properties, such as 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 acceptable deposits 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.
[0010] 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
non-cationic, e.g., anionic species between the first processing
fluid and the second processing fluid. In certain embodiments, the
first processing fluid can be a low pH processing fluid, the second
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.
[0011] 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 a cation permeable barrier
between the first processing fluid and the second processing fluid.
The cation permeable barrier allows cations, e.g., hydrogen ions,
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.
[0012] 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 a cation permeable barrier is located between the first
processing fluid and the second processing fluid.
[0013] 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 a cation permeable barrier is
located between the processing unit and the counter electrode unit.
The system also includes a source of complexing agent. The chamber
further includes a source of metal ion in fluid communication with
the processing unit or the counter electrode unit and a source of a
pH adjustment agent in fluid communication with the processing
unit.
[0014] Through the use of processes described above and the system
described above, metals such as copper, nickel, lead, gold, silver,
tin, platinum, ruthenium, rhodium, iridium, osmium, rhenium, and
palladium can be deposited onto surfaces of a microfeature
workpiece. Such surfaces can take the form of seed layers or
barrier layers.
[0015] The process embodiments and systems 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.
[0016] Accordingly, in another embodiment, a surface of a
microfeature workpiece is contacted with a first processing fluid
that includes hydrogen ion and a counter ion to a metal on the
surface. A cathode is contacted with a second processing fluid also
containing hydrogen ion, and a cation 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 first processing fluid to provide
hydrogen ions. Hydrogen ions from the first processing fluid are
passed through the cation permeable barrier to the second
processing fluid. In accordance with this embodiment, metals from
the surface of the microfeature workpiece are electrolytically
dissolved, i.e., oxidized and deplated.
[0017] 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. A
cation 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 hydrogen ions in
fluid communication with the processing unit, and a source of pH
adjustment agent in fluid communication with the counter-electrode
unit.
[0018] 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.
[0019] In accordance with another embodiment of the present
disclosure, a process for electrolytically processing a
microfeature workpiece as the working electrode with a first
processing fluid and a counter electrode is provided. The process
generally includes contacting a surface of the microfeature
workpiece with the first processing fluid, the first processing
fluid comprising first processing fluid species including at least
one metal cation, an anion, and a complexing agent. The process
further includes contacting the counter electrode with a second
processing fluid, producing an electrochemical reaction at the
counter electrode, and electrolytically depositing the metal cation
onto the surface of the microfeature workpiece. The process further
includes substantially preventing movement of anionic and
complexing agent species between the first processing fluid and the
second processing fluid.
[0020] In accordance with another embodiment of the present
disclosure, a process for electrolytically processing a
microfeature workpiece as the working electrode with a first
processing fluid and a counter electrode is provided. The process
generally includes contacting a surface of the microfeature
workpiece with the first processing fluid, the first processing
fluid comprising first processing fluid species including at least
one metal cation, an anion, and at least one organic component
selected from the group consisting of accerators, suppressors, and
levelers. The process further includes contacting the counter
electrode with a second processing fluid, producing an
electrochemical reaction at the counter electrode, and
electrolytically depositing the metal cation onto the surface of
the microfeature workpiece. The process further includes providing
a cation exchange membrane to substantially prevent movement of
anionic species and the at least one organic component between the
first processing fluid and the second processing fluid.
[0021] In accordance with yet another embodiment of the present
disclosure, a process for electrolytically processing a
microfeature workpiece as the working electrode with a first
processing fluid and a counter electrode is provided. The process
includes contacting a surface of the microfeature workpiece with
the first processing fluid, the first processing fluid comprising
first processing fluid species including a metal cation, an anion,
and a complexing agent. The process further includes contacting the
counter electrode with a second processing fluid, producing an
electrochemical reaction at the counter electrode, and
electrolytically depositing the metal cation onto the surface of
the microfeature workpiece. The process further includes providing
a cation permeable barrier between the first processing fluid and
the second processing fluid to substantially prevent the movement
of anionic and complexing agent species between the first
processing fluid and the second processing fluid, wherein the
cation permeable barrier is oriented in a substantially horizontal
configuration.
[0022] In accordance with another embodiment of the present
disclosure, a process for electrolytically processing a
microfeature workpiece as the working electrode in a first
processing fluid and a counter electrode in a second processing
fluid is provided. The process generally includes: contacting a
surface of the microfeature workpiece with the first processing
fluid, the first processing fluid including a first metal cation;
contacting the counter electrode with a second processing fluid,
the second processing fluid including a second metal cation and
having a pH in the range of about 1 to about 3; allowing the second
metal cation to move from the second processing fluid to the first
processing fluid, but substantially preventing movement of the
first metal cation from the first processing fluid to the second
processing fluid by providing a cation permeable barrier between
the first processing fluid and the second processing fluid, wherein
the primary mass transport of the second metal cation from the
second processing fluid to the first processing fluid is across the
cation permeable barrier; and electrolytically depositing the first
and second metal cations onto the surface of the microfeature
workpiece.
[0023] In accordance with another embodiment of the present
disclosure, a process for electrolytically processing a
microfeature workpiece as the working electrode with a first
processing fluid and a counter electrode is provided. The process
includes: contacting a surface of the microfeature workpiece with
the first processing fluid, the first processing fluid comprising
first processing fluid species including a first metal cation;
contacting the counter electrode with a second processing fluid,
the second processing fluid having a pH in the range of about 1 to
about 3; producing an electrochemical reaction at the counter
electrode to produce a second metal cation; providing a cation
exchange membrane to allow the second metal cation to move from the
second processing fluid to the first processing fluid, but to
substantially prevent movement of the first metal cation from the
first processing fluid to the second processing fluid when
electrolytically processing the microfeature workpiece; and
separating the second processing fluid from the membrane when not
electrolytically processing the microfeature workpiece.
[0024] In accordance with another embodiment of the present
disclosure, a process for electrolytically processing a
microfeature workpiece as the cathode with a first processing fluid
and an anode is provided. The process generally includes:
contacting a surface of the microfeature workpiece with the first
processing fluid, the first processing fluid comprising first
processing fluid species including a first metal cation; contacting
the anode with a second processing fluid, the second processing
fluid having a pH in the range of about 1 to about 3; consuming the
anode to produce a second metal cation; providing a cation exchange
membrane to allow the second metal cation to move from the second
processing fluid to the first processing fluid, but to
substantially prevent movement of the first metal cation from the
first processing fluid to the second processing fluid, wherein the
second processing fluid is not dosed in the first processing fluid;
and electrolytically depositing the first and second metal cations
onto the surface of the microfeature workpiece.
[0025] In accordance with any of the process described herein, the
cation permeable barrier may be a cation exchange membrane.
[0026] In accordance with any of the process described herein, the
process may further comprise producing an electrochemical reaction
at the counter electrode to produce the second metal cation.
[0027] In accordance with any of the process described herein, the
working electrode may be a cathode, and the counter electrode may
be an anode.
[0028] In accordance with any of the process described herein, the
first processing fluid may be dosed with the first metal
cation.
[0029] In accordance with any of the process described herein, the
counter electrode may be a consumable electrode.
[0030] In accordance with any of the process described herein,
either or both of the first and second processing fluids may be
dosed with the second metal cation.
[0031] In accordance with any of the process described herein,
dosing in either or both of the first and second processing fluids
with the second metal cation may not be the major source of the
second metal cation in the first processing fluid.
[0032] In accordance with any of the process described herein, the
first metal cation concentration in the first processing fluid may
be in the range of about 0.1 g/L to about 5.0 g/L.
[0033] In accordance with any of the process described herein, the
second metal cation concentration in the first processing fluid may
be selected from the group consisting of in the range of about 40
to about 80 g/L, about 40 to about 120 g/L, and about 40 to about
150 g/L.
[0034] In accordance with any of the process described herein, the
pH of the second processing fluid may be higher than the pH of the
first processing fluid.
[0035] In accordance with any of the process described herein, the
pH of the second processing fluid may be selected from the group
consisting of about 1.0 to about 2.0, about 1.2 to about 1.8, about
1.5 to about 2.2, greater than about 2.0, about 1.0 to about 3.0,
and about 2.0 to about 3.0.
[0036] In accordance with any of the process described herein, the
pH of the first processing fluid may be selected from the group
consisting of less than or equal to 1.0 and less than or equal to
0.5, and in the range of 0 to 1.0.
[0037] In accordance with any of the process described herein, the
first metal cation may be selected from the group consisting of
copper ion, lead ion, gold ion, tin ion, silver ion, bismuth ion,
indium ion, platinum ion, ruthenium ion, rhodium ion, iridium ion,
osmium ion, rhenium ion, palladium ion, and nickel ion.
[0038] In accordance with any of the process described herein, the
second metal cation may be selected from the group consisting of
copper ion, lead ion, tin ion, bismuth ion, indium ion, silver ion,
platinum ion, ruthenium ion, rhodium ion, iridium ion, osmium ion,
rhenium ion, palladium ion, and nickel ion.
[0039] In accordance with any of the process described herein, the
process may further include depositing a third metal cation
selected from the group consisting of copper ion, lead ion, gold
ion, tin ion, silver ion, bismuth ion, indium ion, platinum ion,
ruthenium ion, rhodium ion, iridium ion, osmium ion, rhenium ion,
palladium ion, nickel ion.
[0040] In accordance with any of the process described herein, the
process may further include depositing a co-deposited metal.
[0041] In accordance with any of the process described herein, the
first processing fluid may include an antioxidant.
[0042] In accordance with any of the process described herein, the
second processing fluid may include an antioxidant.
[0043] In accordance with any of the process described herein,
where the second processing fluid may not be dosed into the first
processing fluid.
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] 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:
[0045] FIG. 1 is a schematic illustration of a reactor for carrying
out processes described herein;
[0046] FIG. 2 is a schematic illustration of the chemistry and
chemical reactions occurring in one embodiment of the processes for
electroplating a metal using an inert anode described herein;
[0047] FIG. 3 is a schematic illustration of the chemistry and
chemical reactions occurring in another embodiment of the processes
for electroplating a metal using a consumable anode described
herein;
[0048] FIGS. 4A-4C are schematic illustrations of one embodiment of
the processes described herein for electrolytically treating a seed
layer;
[0049] FIGS. 5A and 5B are schematic illustrations of one
embodiment of the processes described herein for electrolytically
treating a barrier layer;
[0050] 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 an inert
anode;
[0051] FIG. 7 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;
[0052] FIG. 8 is a schematic illustration of a reactor for carrying
out processes described herein;
[0053] FIG. 9 is a schematic illustration of a tool that includes
chambers for carrying out processes described herein;
[0054] FIG. 10 is a schematic illustration of the chemistry and
chemical reactions occurring in one embodiment of the processes for
deplating a metal described herein;
[0055] FIG. 11 is a graphical representation of the relationship
between the molar concentration of tin ions in the anolyte and the
pH of the anolyte;
[0056] FIG. 12A and 12B are graphical representations of the
relationship between pH and tin concentration in the catholyte and
the anolyte; and
[0057] FIG. 13 is a graphical representation of the relationship
between the pH and conductivity of the anolyte in view of MSA
concentration.
DETAILED DESCRIPTION
[0058] 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.
[0059] 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.
[0060] 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.
[0061] 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.
[0062] Processes described herein can be carried out in an
electroplating or deplating reactor, such as the one described
below with reference to FIG. 1. Referring to FIG. 1,
electrochemical deposition chamber 400 includes an upper processing
unit 404 containing a first processing fluid 406 (e.g., a catholyte
in an electroplating process or an anolyte in a deplating process)
and a counter electrode unit 410 below the processing unit 404 that
contains a second processing fluid 412 (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 406. Processing unit 404 receives a working
electrode 408 (e.g., a microfeature workpiece) and delivers first
processing fluid 406 to the working electrode 408. Counter
electrode unit 410 includes a counter electrode 414 that is in
contact with the second processing fluid 412. When copper is to be
deposited onto working electrode 408, working electrode 408 is the
cathode and counter electrode 414 is the anode. Accordingly, in
plating application, first processing fluid 406 is a catholyte, and
second processing fluid 412 is an anolyte. The catholyte 406
typically contains components in the form of ionic species such as
acid ions and metal ions, as described below in more detail.
[0063] In general, the catholyte contains components in the form of
ionic species, such as acid ions (e.g., H.sup.+), hydroxyl ions,
and metal ions, and complexing agent(s) 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 (e.g., H.sup.+), 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.
[0064] When copper is to be deplated from working electrode 408,
working electrode 408 is the anode, and counter electrode 414 is
the cathode. Accordingly, in deplating applications, the first
processing fluid 406 is an anolyte, and the second processing fluid
412 is a catholyte.
[0065] Reactor 400 also includes a nonporous cation permeable
barrier 402 between first processing fluid 406 and the second
processing fluid 412. Nonporous cation permeable barrier 402 allows
cations (e.g., H.sup.+ and Cu.sup.2+) to pass through the barrier
while inhibiting or substantially preventing non-cationic
components, such as organic components (e.g., accelerators,
suppressors, and levelers) and anionic components from passing
between the first and second processing fluids. By inhibiting or
substantially preventing non-cationic components from passing
between the first processing fluid 406 and second processing fluid
412, adverse effects on the deposited material resulting from the
presence of unwanted non-cationic components, such as unwanted
anions or organic bath components, in the first processing fluid
406 can be avoided. As such, nonporous cation permeable barrier 402
separates first processing fluid 406 and second processing fluid
412 such that first processing fluid 406 can have different
chemical characteristics and properties than second processing
fluid 412. For example, the chemical components of first processing
fluid 406 and second processing fluid 412 can be different, the pH
of first processing fluid 406 and second processing fluid 412 can
be different, and concentrations of components common to both first
processing fluid 406 and second processing fluid 412 can be
different.
[0066] In the following description of a copper electroplating
process, for consistency, working electrode 408 will be referred to
as the cathode, and counter electrode 414 will be referred to as
the anode. Likewise, first processing fluid 406 will be referred to
as the catholyte, and second processing fluid 412 will be referred
to as the anolyte. When reactor 400 is used to electrolytically
process a microfeature workpiece to deposit metal ions thereon, an
electric potential is applied between anode 414 and cathode 408.
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 positively charged cations
through the cation permeable barrier 402 from anolyte 412 to the
catholyte 406. An electrochemical reaction (e.g., losing or gaining
electrons) occurs at cathode 408, resulting in metal ions being
reduced (i.e., gaining electrons) to metal on surfaces of cathode
408.
[0067] Reactor 400 effectively maintains the concentration of metal
ions in catholyte 406 during the electroplating process in the
following manner. As metal ions are deposited onto the surface of
cathode 408, in addition to the metal ions passing from the anolyte
412 to the catholyte 406, additional metal ions can be introduced
to catholyte 406 from a source of metal ions 130, which is in fluid
communication with processing unit 404. As explained below in more
detail, these metal ions can be provided by delivering a metal salt
solution to processing unit 404. Processing unit 404 can also be in
fluid communication with sources of other components that need
replenishment. In a similar fashion, counter electrode unit 410 may
be in fluid communication with sources of components that require
replenishment. For example, counter electrode unit 410 can be in
fluid communication with a source of pH adjustment agent 132.
Likewise, both processing unit 404 and electrode unit 410 can
include conduits or other structures for removing portions of
catholyte 406 from processing unit 404 or portions of anolyte 412
from counter electrode unit 410.
[0068] Anode 414 may be a consumable anode or an inert anode.
Exemplary consumable anodes and inert anodes are described below in
more detail.
[0069] Cation permeable barrier 402 provides several advantages by
substantially preventing certain anionic species and organic
components from migrating between the catholyte and the anolyte.
For example, organic components from the catholyte are unable to
flow past the anode and decompose into products that may interfere
with the plating process. Second, because organic components do not
pass from the catholyte to the anolyte, they are consumed at a
slower rate so that it is less expensive and easier to control the
concentration of organic components in the catholyte. Third, the
risk of passivation by reaction of the anode with organic
components is reduced or eliminated. In addition, the presence of
the cation permeable barrier reduces the chances that metal flakes
or small particles resulting from anode passivation (when a
consumable anode is used in combination with a high pH, low
conductivity, low acid anolyte) reach the workpiece where the
flakes or particles may adversely impact the deposited metal.
Another benefit of using the cation membrane is that gases
generated at the anode are prevented from passing into the
catholyte where they may contact with the workpiece surface.
[0070] Exemplary chemistries present in processing unit 404 in FIG.
1 and counter electrode unit 410 of FIG. 1 are described below with
reference to FIG. 2. It should be understood that by describing
chemical reactions that are believed to occur within reactor 400,
the processes described herein are not limited to processes wherein
these reactions occur.
[0071] FIG. 2 schematically illustrates an example of the operation
of reactor 400 using a cation permeable barrier 422 and an inert
anode 424 in combination with a low conductivity/high pH catholyte
426 and a low conductivity/high pH anolyte 428. In the description
that follows, catholyte 426 in processing unit 430 contains a metal
ion (M.sup.+), e.g., copper ion (Cu.sup.2+), a counter ion
(X.sup.-) for the metal ion, e.g., sulfate ion (SO.sub.4.sup.2-), a
complexing agent (CA), 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.sup.- 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 and pH of catholyte 426 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. Low conductivity, low acid anolyte 428 in electrode
unit 432 includes an aqueous solution of an acid, e.g., sulfuric
acid that dissociates into hydrogen ion (H.sup.+) and sulfate ions
(SO.sub.4.sup.2-). Anolyte 428 may also include a buffer. The
hydrogen ion concentration of anolyte 428 is preferably greater
than the hydrogen ion concentration of catholyte 426, although this
is not required as explained below in more detail. This
differential encourages the movement of hydrogen ions from the
anolyte 428 to the catholyte 426. In order to account for this
increasing hydrogen ion concentration in catholyte 426, pH
adjustment agents can be added to catholyte 426. Hydrogen ions from
anolyte 428 that migrate across cation permeable barrier 422 to
catholyte 426 are replenished in anolyte 428 by the oxidation of
water at anode 424, which produces hydrogen ions.
[0072] During a plating cycle, an electric potential is applied
between cathode 434 and inert anode 424. As metal ions are reduced
and electroplated onto cathode 434, hydrogen ions (H.sup.+)
accumulate in the anolyte 428 near a first surface 436 of cation
permeable barrier 422. The resulting electrical charge gradient and
concentration gradient causes the positively charged hydrogen ions
to move from first surface 436 of cation permeable barrier 422 to
the second surface 438 of cation permeable barrier 422 that is in
contact with catholyte 426. The transfer of positively charged
hydrogen ions from anolyte 428 to catholyte 426 during the plating
cycle maintains the charge balance of reactor 400. The electrical
charge gradient created by applying an electric potential between
cathode 434 and anode 424 also hinders the migration of cations,
e.g., metal ions M.sup.+ and cations of pH adjustment agent from
transferring from catholyte 426 to anolyte 428 through cation
permeable barrier 422. In order to avoid the build up of counter
ions (X.sup.-) of the metal ions and cations of the pH adjustment
agent in the catholyte, these ionic and cationic species can be
removed from the catholyte 426.
[0073] Continuing to refer to FIG. 2, during a plating cycle, as
explained above, metal ions in catholyte 426 are reduced at cathode
434 and are deposited as metal. Metal ions that are consumed by the
electroplating are replenished by the addition of a solution of
metal salt (MX) to catholyte 426.
[0074] While operating reactor 400 with the hydrogen ion
concentration of anolyte 428 greater than the hydrogen ion
concentration of catholyte 426 is preferred in order to promote
transfer of hydrogen ions from the anolyte 428 to catholyte 426
through cation permeable membrane 422, it is also possible to
operate reactor 400 with the hydrogen ion concentration of the
anolyte 428 being less than the hydrogen ion concentration in the
catholyte 426. Providing such a hydrogen ion concentration gradient
would reduce the driving force promoting transport of hydrogen ions
from anolyte 428 to catholyte 426 in favor of the transport of
other cationic species that may be present in catholyte 426 in
order to provide the necessary charge balance. The transport of
such metal cations from catholyte 428 to anolyte 426 would be
promoted by the electrical charge gradient between anode 424 and
cathode 434. Under such circumstances, it may be necessary to add
pH adjustment agents to anolyte 428 in order to maintain the
hydrogen ion concentration in anolyte 428 below the hydrogen ion
concentration of catholyte 426.
[0075] Metals may also be deposited using a cation permeable
barrier and a consumable anode. Referring to FIG. 3, reactor 450,
that includes a cation permeable barrier 452, a consumable anode
454, a low conductivity/high pH catholyte 456 and a low
conductivity/high pH anolyte 458, is illustrated. For the
embodiment of FIG. 3, catholyte 456 can have a composition that is
similar to the composition of catholyte 426 described with
reference to FIG. 2. Anolyte 458 includes hydrogen ions (H.sup.+)
and metal ions (M.sup.+) from dissolution of consumable anode 454.
Anolyte 458 can also include a buffer and dissociation products of
pH adjustment agent. It is preferred that positively charged metal
ions (M.sup.+) transfer across cation permeable barrier 454 as
opposed to positively charged hydrogen ions (H.sup.+). Accordingly,
it is preferred that anolyte 458 be a low acid/high pH anolyte so
that there is an absence of a hydrogen ion concentration gradient
between catholyte 456 and anolyte 458 that would promote the
migration of the hydrogen ions from anolyte 458 to catholyte 456.
Furthermore, by inhibiting the transfer of positively charged
hydrogen ions from anolyte 458 to catholyte 456, a more constant
catholyte pH can be maintained and the need to add a pH adjusting
agent to the catholyte can be reduced. As noted above, this
simplifies maintenance of the catholyte and helps to maintain the
conductivity of the catholyte relatively stable during repeated
plating cycles.
[0076] Continuing to refer to FIG. 3, during a plating cycle, an
electric potential is applied between cathode 460 and anode 454.
Metal is oxidized at anode 454 and metal ions (M.sup.+) accumulate
in the anolyte near a first surface 462 of cation permeable barrier
452. The resulting electrical charge gradient causes the positively
charged metal cations (M.sup.+) to move from the first surface 462
of cation permeable barrier 452 to the second surface 464 of cation
permeable barrier 452. The transfer of positively charged metal
ions from anolyte 458 to catholyte 456 during the plating cycle
maintains the charge balance of reactor 450. It should be
understood that hydrogen ions will also transfer from anolyte 458
through cation exchange membrane 452 to catholyte 456, the
magnitude of such transport being dictated in part by the hydrogen
ion concentration gradient between anolyte 458 and catholyte 456 as
described above. During the plating cycle, metal ions (M.sup.+) in
catholyte 456 are reduced at cathode 460 and deposited as
metal.
[0077] 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. 4A-4C, one sequence of steps for electrolytically processing
a seed layer using a process described herein is provided.
[0078] Referring to FIG. 4A, 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. 4A, 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.
[0079] 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. 4B. 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. 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.
[0080] 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. 4C, 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.
[0081] 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.
[0082] 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. 5A, 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. 5A, thin barrier
layer 210 is deposited over the surface of a semiconductor device
or, as illustrated in FIG. 5A, over a layer of dielectric 208, such
as silicon dioxide. Barrier layer 210 can be deposited as described
above with reference to FIG. 4A 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.
[0083] 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 (pH<7) 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.
[0084] 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.
[0085] 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 or hydrogen 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,
diisopropyltartrate, 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 group, aromatic group, or polymer chain and R.sub.1 and
R.sub.2 are H, alkyl or aryl organic groups. 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.
[0086] 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.
[0087] For acidic processing fluids (low pH, high conductivity,
high acid), useful pH adjustment agents include materials capable
of adjusting the pH of the first and second processing fluid to
below 7. Useful complexing agents for acid processing fluids
include pyrophosphate, citric acid, ethylene diamine, ethylene
diamine tetraacetic acid, polyimines, and polyamines.
[0088] Useful buffers for both alkaline and acidic processing
fluids 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 0.001 to about 0.5M in the catholyte for
plating applications. Exemplary buffer concentrations for the
anolyte range from about 0.001 to about 1.0M.
[0089] 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.
[0090] The catholyte can also include other additives such as an
additive or combination of additives that suppresses the growth of
metal nuclei on itself while permitting metal deposition onto the
treated barrier layers. Through the use of such additives or
additive combinations, nucleation of deposit metal on barrier
layers can be promoted over growth of the metal itself. By
promoting the nucleation of the metal to be deposited on the
barrier layer as opposed to the growth of metal nuclei itself,
metal deposition that is conformal (i.e., uniformly lines that
feature) and continuous at small dimensions, e.g., thicknesses can
be promoted.
[0091] Useful cation permeable barriers are generally selective to
positively charged ions, e.g., hydrogen ions and metal ions;
therefore, hydrogen ions and metal ions may migrate through the
useful cation permeable barriers.
[0092] Useful cation permeable barriers include nonporous barriers,
such as semi-permeable cation exchange membranes. A semi-permeable
cation exchange membrane allows cations to pass but not
non-cationic species, such as anions. The nonporous feature of the
barrier inhibits fluid flow between first processing fluid 406 and
second processing fluid 412 within reactor 400 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 cations across a
cation 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.
[0093] 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. Examples of useful
cation permeable barriers include commercially available cation
permeable membranes. For example, Tokuyama Corporation manufactures
and supplies various hydrocarbon membranes for electrodialysis and
related applications under the trade name Neosepta.TM..
Perfluorinated cation membranes are generally available from DuPont
Co. as Nafion.TM. membranes N-117, N-450, or from Asahi Glass
company (Japan) under the trade name Flemion.TM. as Fx-50, F738,
and F893 model membranes. Asahi Glass Company also produces a wide
range of polystyrene based ion-exchange membranes under the trade
name Selemion.TM., which can be very effective for
concentration/desalination of electrolytes and organic removal
(cation membranes CMV, CMD, and CMT and anion membranes AMV, AMT,
and AMD). There are also companies that manufacture similar
ion-exchange membranes (Solvay (France), Sybron Chemical Inc.
(USA), Ionics (USA), and FuMA-Tech (Germany), etc.). Bipolar
membranes, such as models AQ-BA-06 and AQ-BA-04, for example, are
commercially available from Aqualitics (USA) and Asahi Glass
Company may also be useful.
[0094] In addition to the nonporous barriers described above,
cation 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 cationic
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 cationic 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 cationic species across the porous barrier while substantially
limiting diffusion or mixing (i.e., transport across the barrier)
of larger organic components and other non-cationic 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 fits 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, North Carolina. 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.
[0095] 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.
[0096] 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.
[0097] Exemplary materials for consumable anodes will include those
materials that are to be deposited onto the microfeature workpiece,
for example, copper, tin, silver, lead, nickel, cobalt, zinc, and
the like.
[0098] 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.
[0099] 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 a
cation permeable barrier is absent, oxidation of components in the
electrolyte can also occur directly at the anode. Oxidation of
components in an 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 cation 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 cation permeable
barrier also isolates the anode from non-cationic 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 acceptable properties such as resistivity
properties that fall within acceptable ranges.
[0100] Another advantage of employing a cation permeable barrier in
the processes described herein is that the barrier prevents bubbles
from the oxygen or hydrogen 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.
[0101] 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 gold and hydrogen ions would migrate across the
cationic 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 catholyte resulting from migration of hydrogen ions from
the anolyte to the catholyte. If needed an agent to counteract the
loss of hydrogen ions from the anolyte can be added to the anolyte.
As with the copper example described above, in the gold embodiment
using an inert anode, 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.
[0102] 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.
[0103] 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. Multi-component plating systems can use inert
or consumable anodes. The use of consumable anodes could cause
stability issues resulting from plating/reacting of one of the
metals 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 species, e.g., Sn(II) to the more stable
species, e.g., Sn(IV) ion, which is more difficult to plate onto a
workpiece.
[0104] Referring to FIG. 6, a schematic illustration is provided
for the operation of reactor 610 using a cation permeable barrier
624 and an inert anode 622 in combination with a first processing
fluid 614 and a second processing fluid 620 suitable for depositing
tin-silver solder. In the description that follows, processing
fluid 614 in processing unit 612 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, hydrogen ions and hydroxyl
ions. As discussed above in the context of the electroplating of
copper, the specific hydrogen ion concentration in catholyte 614
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.
[0105] The discussions above regarding the concentration of H.sup.+
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.
[0106] As with the copper plating process, an electric potential
applied between cathode 616 and anode 622 results in tin ions and
silver ions being reduced at cathode 616 and deposited thereon. The
hydrogen ion (H.sup.+) accumulates in the anolyte near a first
surface 632 of cation permeable barrier 624. As with the copper
system, at positively charged inert anode 622, water is converted
to hydrogen ions (H.sup.+) and oxygen. The resulting electrical
charge gradient urges positively charged hydrogen ions (H.sup.+) to
move from first surface 632 of cation permeable barrier 624 to the
second surface 634 of cation permeable barrier 624. The transfer of
positively charged hydrogen ions from anolyte 620 to catholyte 614
during the plating cycle maintains the charge balance of reactor
610. As noted in FIG. 6, the concentration of hydrogen ion in
anolyte 620 is higher than the concentration of hydrogen ion in
catholyte 614. This concentration gradient also urges hydrogen ions
to transfer from anolyte 620 to catholyte 614 through cation
permeable barrier 624. Tin and silver ions that are deposited onto
cathode 616 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
614 as a result of the addition of the tin MSA and silver MSA build
up and must eventually be removed. Portions of the catholyte can be
removed from processing unit 612 to address the buildup of MSA ions
in the catholyte.
[0107] Alternatively, the tin and/or silver ions could be added to
anolyte 620 under conditions wherein the hydrogen ion concentration
in the catholyte 614 is greater than the hydrogen ion concentration
of anolyte 620. Under these conditions, movement of hydrogen ions
from anolyte 620 to catholyte 614 is inhibited by the hydrogen ion
concentration gradient and the metal ions in the anolyte transfer
to the catholyte and contribute to maintaining the charge balance
of the reactor. Under these conditions, steps can be taken to
mitigate any issues created by metal ions oxidizing in anolyte
620.
[0108] Referring to FIG. 7, in a different embodiment,
electroplating of two metals, e.g., tin and silver, can also be
achieved using a consumable anode 722. Referring to FIG. 7, the
catholyte 714 in processing unit 712 is similar to the catholyte
described with reference to FIG. 6. In the process depicted in FIG.
7, metal ion M.sub.2.sup.+ is introduced into processing unit 712
from source 700, metal ion M.sub.1.sup.+ is supplied to counter
electrode unit 718 through oxidation of metal making up consumable
anode 722. Metal ion M.sub.1.sup.+ in anolyte 716 moves across
cation permeable barrier 720 into catholyte 714. Movement of metal
ion M.sub.1.sup.+ helps to maintain the charge balance of reactor
730. In addition, movement of metal ion M.sub.1.sup.+ from anolyte
716 to catholyte 714 is also promoted by a metal ion M.sub.1.sup.+
concentration gradient between anolyte 716 and 714, i.e., metal ion
M.sub.1.sup.+ concentration in anolyte 716 is greater than the
metal ion M.sub.1.sup.+ concentration in catholyte 714. Metal ions
M.sub.1.sup.+ and M.sub.2.sup.+ can be reduced at cathode 724 and
deposited thereon as described above with reference to FIG. 6. In
accordance with this embodiment, complexing agents (CA) are present
in catholyte 714 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 730 can be maintained
through the transfer of positively charged metal ion M.sub.1.sup.+
in counter-electrode unit 718 across cation permeable membrane 720
into processing unit 712. In this system, movement of hydrogen ions
from anolyte 716 to catholyte 714 in order to provide charge
balance is inhibited (in favor of transfer of M.sub.1.sup.+) by
providing a higher concentration of hydrogen ion in catholyte 714
than in anolyte 716. In such a system, metal ion M.sub.2.sup.+ does
not come into contact with anode 722 where it may undesirably
deposit depending upon the deposition potentials of metal ion
M.sub.2.sup.+ and metal ion M.sub.1.sup.+.
[0109] It is contemplated that cations in addition to metal ion
M.sub.1.sup.+ could pass through cation permeable barrier 720 from
anolyte 716 to catholyte 714, for example by reversing the hydrogen
ion concentration gradient described above. When the hydrogen ion
concentration gradient is reversed, e.g., the hydrogen ion
concentration of the anolyte is greater than the hydrogen ion
concentration of the catholyte, hydrogen ions will more readily
transfer from anolyte 716 to catholyte 714. In addition, it is
contemplated that other metal ions in addition to M.sub.1.sup.+
could be added to anolyte 716 and transfer from anolyte 716 to
catholyte 714 through cation permeable barrier 720.
[0110] 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. 60/739,343, filed on Nov. 23, 2005, entitled
Apparatus and Method for Agitating Fluids and the Processing of
Microfeature Workpieces.
[0111] 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.
10, a microfeature workpiece 516 is provided that carries a metal
M, e.g., copper, on its surface. Microfeature workpiece 516 is
contacted with a first processing fluid 514 in processing unit 512.
Processing fluid 514 includes metal ions M.sup.+, e.g., copper
ions; a complexing agent CA, e.g., ethylene diamine tetraacetic
acid; a metal salt MX, e.g., copper sulfate or copper phosphate; a
complexed metal ion M(CA).sup.+; hydroxyl ions; a buffer, and a
counter ion X.sup.-, e.g., phosphate or sulfate ion. Processing
unit 512 is separated from a counter electrode unit 518 by cation
permeable membrane 524. Counter electrode unit 518 includes counter
electrode 522 and a second processing fluid 520. In a deplating
process, microfeature workpiece 516, the working electrode, is an
anode, and counter electrode 522 is the cathode. Processing unit
512 is also in fluid communication with a source 530 of complexing
agent CA and a source 532 of hydrogen ions. Counter electrode unit
518 is in fluid communication with a source 550 of pH adjustment
agent. Through the application of an electric potential between
anode 516 and cathode 522, hydrogen ions are reduced at the cathode
522 to produce hydrogen gas. Metal on the surface of microfeature
workpiece 516 is oxidized resulting in metal ions being removed
from the surface of the microfeature workpiece. The charge balance
within reactor 540 is maintained through the transfer of hydrogen
ions from catholyte 520 to anolyte 514 through cation permeable
membrane 524.
[0112] Catholyte 520 in counter electrode unit 518 includes
hydrogen ions, hydroxyl ions, buffer, and counter ion X.sup.-. The
pH adjustment agent that is added to counter electrode unit 518 can
be both a source of counter ion X.sup.- as well as hydrogen ions
(H.sup.+). Over time, metal ion M.sup.+ builds up in concentration
in anolyte 514. Accordingly, periodic purging and replenishing of
anolyte 514 may be necessary. Charge balance within reactor 540 is
maintained by transfer of hydrogen ions from anolyte 514 to
catholyte 520. To further promote movement of hydrogen ions from
anolyte 514 through cation permeable barrier 524 to catholyte 520,
a hydrogen ion concentration gradient can be established between
anolyte 514 and catholyte 520. In other words, the concentration of
hydrogen ions in anolyte 514 can be greater than the concentration
of hydrogen ions in catholyte 520. While it is possible for metal
ion M.sup.+ to also transfer from anolyte 514 to catholyte 520, it
is preferred that the charge balance be maintained primarily
through movement of hydrogen ions as opposed to metal ions. If it
is desired to have the metal ion serve as the major charge carrier
to maintain charge balance within reactor 540, movement of hydrogen
ions across cation permeable barrier 524 can be inhibited by
reversing the hydrogen ion concentration, i.e., hydrogen ion
concentration of the catholyte is greater than the hydrogen ion
concentration of the anolyte.
[0113] Referring to FIG. 8, a more detailed schematic illustration
of one design of a reactor 8 for directly electroplating metal onto
barrier layers or otherwise depositing materials onto workpieces
using a cation permeable barrier is illustrated. Reactor 824
includes a vessel 802, a processing chamber 810 configured to
direct a flow of first processing fluid to a processing zone 812,
and an anode chamber 820 configured to contain a second processing
fluid separate from the first processing fluid. A cation permeable
barrier 830 separates the first processing fluid in the processing
unit 810 from the second processing fluid in the anode chamber 820.
Reactor 820 further includes a workpiece holder 840 having a
plurality of electrical contacts 842 for applying an electric
potential to a workpiece 844 mounted to workpiece holder 840.
Workpiece holder 840 can be a movable head configured to position
workpiece 844 in processing zone 812 of processing unit 810, and
workpiece holder 840 can be configured to rotate workpiece 844 in
processing zone 812. 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.
[0114] Reactor 824 further includes a support member 850 in the
processing chamber 810 and a counter electrode 860 in the anode
chamber 820. Support member 850 spaces the cation permeable barrier
830 apart from workpiece processing zone 812 by a controlled
distance. This feature provides better control of the electric
field at processing zone 812 because the distance between the
cation permeable barrier 830 and workpiece processing zone 812
affects the field strength at processing zone 812. Support member
850 generally contacts first surface 832 of cation permeable
barrier 830 such that the distance between first surface 832 and
processing zone 812 is substantially the same across processing
chamber 810. Another feature of support member 850 is that it also
shapes cation permeable barrier 830 so that bubbles do not collect
along a second side 834 of cation permeable barrier 830.
[0115] Support member 850 is configured to direct flow F.sub.1 of a
first processing fluid laterally across first surface 832 of cation
permeable barrier 830 and vertically to processing zone 812.
Support member 850 accordingly controls the flow F.sub.1 of the
first processing fluid in processing chamber 810 to provide the
desired mass transfer characteristics in processing zone 812.
Support member 850 also shapes the electric field in processing
chamber 810.
[0116] Counter electrode 860 is spaced apart from second surface
834 of cation permeable barrier 830 such that a flow F.sub.2 of the
second processing fluid moves regularly outward across second
surface 834 of cation permeable barrier 830 at a relatively high
velocity. Flow F.sub.2 of the second processing fluid sweeps oxygen
bubbles and/or particles from the cation permeable barrier 830.
Reactor 824 further includes flow restrictor 870 around counter
electrode 860. Flow restrictor 870 is a porous material that
creates a back pressure in anode chamber 820 to provide a uniform
flow between counter electrode 860 and second surface 834 of the
cation permeable barrier 830. As a result, the electric field can
be consistently maintained because flow restrictor 870 mitigates
velocity gradients in the second processing fluid where bubbles
and/or particles can collect. The configuration of counter
electrode 860 and flow restrictor 870 also maintains a pressure in
the anode chamber 820 during plating that presses the cation
permeable barrier 830 against support member 850 to impart the
desired contour to cation permeable barrier 830.
[0117] Reactor 824 operates by positioning workpiece 844 in
processing zone 812, directing flow F.sub.1 of the first processing
fluid through processing chamber 810, and directing the flow
F.sub.2 of the second processing fluid through anode chamber 820.
As the first and second processing fluids flow through reactor 824,
an electric potential is applied to workpiece 844 via electrical
contacts 842 and counter electrode 860 to establish an electric
field in processing chamber 810 and anode chamber 820. 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.
[0118] 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. 9, such a processing tool may
include a plurality of processing stations 910, one or more of
which may be designed to carry out an electrolytic processing of a
microfeature workpiece 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 920 that is carried on a central
track 925 for delivering workpieces from an input/output location
to the various processing stations.
[0119] Processes are further described for depositing more than one
metal ion onto a microfeature workpiece surface. For example, the
processes may be used for depositing multi-component solders.
Although exemplary tin-silver solder plating processes using cation
permeable barriers are described above, additional metals and
processing conditions are described below solder plating. Other
non-limiting examples of multi-component solders may include
tin-silver-copper, tin-bismuth, tin-indium, tin-copper,
tin-bismuth-indium, and tin-bismuth-zirconium.
[0120] The processes described herein may be used for
electrochemical deposition of two or more metals ions. In one
embodiment of the present disclosure, the solder deposited includes
at least first and second metal ions. The first metal ion may be
selected from the group consisting of copper ion, lead ion, gold
ion, tin ion, silver ion, bismuth ion, indium ion, platinum ion,
ruthenium ion, rhodium ion, iridium ion, osmium ion, rhenium ion,
palladium ion, and nickel ion, etc. Likewise, the second metal ion
may be selected from the group consisting of copper ion, lead ion,
tin ion, silver ion, bismuth ion, indium ion, platinum ion,
ruthenium ion, rhodium ion, iridium ion, osmium ion, rhenium ion,
palladium ion, nickel ion, etc.
[0121] In ternary alloys, the solder deposit may include a third
metal ion also selected from the group consisting of copper ion,
lead ion, gold ion, tin ion, silver ion, bismuth ion, indium ion,
platinum ion, ruthenium ion, rhodium ion, iridium ion, osmium ion,
rhenium ion, palladium ion, nickel ion, etc.
[0122] In accordance with one embodiment of the present disclosure,
a process for electrolytically processing a microfeature workpiece
as the working electrode in a first processing fluid and a counter
electrode in a second processing fluid generally includes
contacting a surface of the microfeature workpiece with the first
processing fluid, the first processing fluid including a first
metal cation, and contacting the counter electrode with a second
processing fluid, the second processing fluid including a second
metal cation. The process further includes allowing the second
metal cation to move from the second processing fluid to the first
processing fluid, but substantially preventing movement of the
first metal cation from the first processing fluid to the second
processing fluid. The process further includes electrolytically
depositing the first and second metal cations onto the surface of
the microfeature workpiece.
[0123] In the exemplary tin-silver solder deposition described
above, the first processing fluid is a catholyte and the second
processing fluid is an anolyte. The cathode is the workpiece, and
the anode is either a consumable or inert anode, as discussed in
greater detail below.
[0124] Preventing movement of the first metal cation from the first
processing fluid to the second processing fluid may include the use
of a cation permeable barrier in combination with a suitable charge
balance to prevent movement of the first metal cation from the
first processing fluid to the second processing fluid, but to allow
movement of the second metal cation from the second processing
fluid to the first processing fluid. Useful cation permeable
barriers include nonporous barriers, such as semi-permeable cation
exchange membranes. Suitable cation permeable membranes are
discussed above.
[0125] As discussed above with reference to FIG. 7, electroplating
of two metals, e.g., tin and silver, can be achieved using a
consumable anode 722. (See FIG. 6 and related discussion above
regarding a process using an inert anode.) Referring to FIG. 7, the
catholyte 714 in processing unit 712 is similar to the catholyte
described with reference to FIG. 6. In the process depicted in FIG.
7, metal ion M.sub.2.sup.+ is introduced into processing unit 712
from source 700, metal ion M.sub.1.sup.+ is supplied to counter
electrode unit 718 through oxidation of metal making up consumable
anode 722. Metal ion M.sub.1.sup.+ in anolyte 716 moves across
cation permeable barrier 720 into catholyte 714. Movement of metal
ion M.sub.1.sup.+ helps to maintain the charge balance of reactor
730. In addition, movement of metal ion M.sub.1.sup.+ from anolyte
716 to catholyte 714 may also be promoted by a metal ion
M.sub.1.sup.+ concentration gradient between anolyte 716 and
catholyte 714, i.e., metal ion M.sub.1.sup.+ concentration in
anolyte 716 may be greater than the metal ion M.sub.1.sup.+
concentration in catholyte 714. However, such metal concentration
gradient may not be required between the anolyte and the catholyte
if the major driving force of metal ion M.sub.1.sup.+ is the
current and not the concentration gradient. In that regard, the
metal ion M.sub.1.sup.+ concentration in anolyte 716 may be less
than the metal ion M.sub.1.sup.+ concentration in catholyte
714.
[0126] Metal ions M.sub.1.sup.+ and M.sub.2.sup.+ can be reduced at
cathode 724 and deposited thereon as described above with reference
to FIG. 6. In accordance with this embodiment, complexing agents
(CA) are present in catholyte 714 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 730 can be maintained
through the transfer of positively charged metal ion M.sub.1.sup.+
in counter-electrode unit 718 across cation permeable membrane 720
into processing unit 712. In this system, movement of hydrogen ions
from anolyte 716 to catholyte 714 in order to provide charge
balance is inhibited (in favor of transfer of M.sub.1.sup.+) by
providing a higher concentration of hydrogen ion in catholyte 714
than in anolyte 716. In such a system, metal ion M.sub.2.sup.+ does
not come into contact with anode 722 where it may undesirably
deposit depending upon the deposition potentials of metal ion
M.sub.2.sup.+ and metal ion M.sub.1.sup.+.
[0127] When the current is running, the first metal cation (such as
silver ion) does not cross the cation permeable barrier from the
first processing fluid into the second processing fluid because of
the charge balance. However, when the current is not running the
first and second processing fluids may need to be separated from
each other to prevent migration of the first metal cation from the
first processing fluid to the second processing fluid and to
prevent the back draft of protons (H+) ions from the catholyte to
the anolyte. Such separation may be achieved by reducing the
anolyte volume in the anolyte chamber such that the upper surface
of the anolyte is no longer in intimate contact with the membrane.
In that regard, when the current is not running in the system, a
valve may be opened to allow anolyte fluid to drain from the
anolyte chamber.
[0128] By preventing the movement of the first metal cation to the
second processing fluid, the anode ideally does not come into
contact with the ions of the more noble metal. In a non-limiting
exemplary silver/tin alloy system using a consumable tin anode, if
silver ions were to contact the tin anode, they would deposit on
the tin anode and continuously be extracted from solution. At the
same time, the tin would become corroded and tin ions would enter
the electrolyte by a displacement reaction. Once silver metal
deposits on a tin anode, it cannot be easily removed
electrolytically. If tin metal is available in the anode and
exposed to the solution, the applied potential will not be
sufficiently anodic to remove the silver. To avoid this
displacement reaction in the exemplary silver/tin alloy system, it
is important that the tin anode avoid contact with the silver ions
in the bath. Therefore, movement of the first metal cation from the
first processing fluid to the second processing fluid is
substantially prevented. In one embodiment of the present
disclosure, a cation selective membrane is used to separate the
catholyte and anolyte. The membrane allows tin ions to pass from
the anolyte to the catholyte to replenish consumed tin in the
deposition chemistry, but the membrane substantially prevents
silver ions from passing from the catholyte to the anolyte.
[0129] For tin ions to pass through the membrane from the anolyte
to the catholyte, the tin ions must be the primary charge carrier.
Because of the level of acidity in an acid-based chemistry system,
protons (H+) tend to be the primary charge carrier instead of tin
ions, except in the case in which there is a higher pH in the
anolyte than in the catholyte (thereby starving the anolyte of
protons). The target pH in the catholyte for exemplary tin/silver
alloy deposition is generally less than 1.0, or less than 0.5. Such
a target pH in the catholyte improves the conductivity of the
chemistry and the solubility for metal ions. And, the pH of the
anolyte is greater than the pH of the catholyte to create a pH
gradient such that the second metal cations (e.g., tin ions) are
the primary charge carrier through the membrane instead of
protons.
[0130] Further complicating the chemistry, tin solubility in a
methane sulfonic acid (MSA) solution decreases dramatically as pH
approaches 2. Therefore, in order to have a higher pH in the
anolyte than in the catholyte, a suitable anolyte solution is
maintained at a pH higher than 1 but less than 2. However, with
chemistry developments, a pH of greater than 2 may be achieved. In
accordance with embodiments of the present disclosure, the
inventors have found that a ratio of at least 30-40 to 1 of metal
ions to protons in the anolyte improves the mass transfer of metal
ions across the membrane. Referring to FIG. 11, which shows the
relationship between the molar concentration of tin ions in the
anlolyte and the pH of the anolyte, the preferred ratio may
correspond to a pH of about 1.8 to 2.0. In another embodiment, a
ratio of at least 100 to 1 of metal ions to protons in the anolyte
improves the mass transfer of metal ions across the membrane.
Referring to FIG. 11, this ratio may correspond to a pH of about
2.2.
[0131] In accordance with embodiments of the present disclosure,
additives in the chemistry may allow the pH of the anolyte may get
close to 2.0 or even exceed 2.0. Suitable additives may include
stabilitizing agents, chelating agents, metal complexing agents,
and/or buffers to help the ions in the anolyte stay in solution,
even though the pH approaches or exceeds 2.0.
[0132] In one embodiment of the present disclosure, the target pH
of the anolyte is in the range of greater than 1.0 to less than
2.0. In another embodiment, the target pH of the anolyte is in the
range of about 1.2 to about 1.8. In another embodiment, the target
pH of the anolyte is greater than about 2.0. In another embodiment,
the target pH of the anolyte is in the range of about 2.0 to about
3.0. In another embodiment, the target pH of the anolyte is in the
range of about 1.0 to about 3.0.
[0133] In another embodiment, the target pH of the anolyte is in
the range of about 1.5 to about 2.2. In this pH range the ratio of
Sn(2+) ions to H+ ions (proton) is solution is about 40 to about
100 to 1. In this pH range and with this ratio of tin to proton
ions, an acceptable range for membrane efficiency may be achieved,
as discussed in greater detail below.
[0134] For complementary catholyte chemistry, in one embodiment of
the present disclosure, the target pH of the catholyte is less than
1.0, and also less than the pH of the anolyte.
[0135] In a different alloy plating system, as described in U.S.
Patent Publication No. US2012/0138471, to Mayer et al. (hereinafter
"Mayer"), a pH gradient is not required because of hardware
differences in the system. In Mayer, fluid from the anolyte is
pumped into the catholyte (see, e.g., conduit 259 in FIGS. 2B, 3,
and 4 of Mayer). Therefore, the movement of tin ions in an
exemplary tin/silver system is primary through conduit 259, and not
across a cation permeable membrane. Rather, the purpose of the
membrane in Mayer is to prevent the movement of silver ions into
the anolyte to keep the silver ions from depositing on the tin
anode.
[0136] In the system taught by Mayer, the tin ion concentration
would be higher in the anolyte, and then the anolyte would be used
to dose the catholyte. Because other chemistry components move when
the anolyte doses the catholyte (for example, excess water,
protons, and chemistry additives) and accumulate in the catholyte,
the catholyte in the Mayer system will likely need to be
occasionally bled and rebalanced to return to its desired
parameters. Although a bleed and feed process is effective for
chemistry control, it wastes material and significantly increases
the operating costs for the system, particularly in cost-sensitive
wafer level packaging applications.
[0137] Because the dominant movement of tin ions in the Mayer
system is through conduit 259 and not across the cation permeable
membrane, a pH gradient between the anolyte and the catholyte is
not needed for tin ion transport across the membrane. Therefore,
the anolyte can be maintained at a pH similar to the pH of the
catholyte.
[0138] Although Mayer discusses a pH range for the anolyte to be
less than 2.0, the examples provided in Mayer have an anolyte pH of
much lower than 1.0, in the range of about 0 to about 0.5. In that
regard, the exemplary anolyte chemistries in Mayer include,
respectively, 40-140, 80, 50, 180-350 g/l of methanesulfonate acid
(MSA). As provided in a graphical representation of anolyte pH data
in FIG. 13, the amount of MSA in the anolyte chemistry
significantly affects pH. Even 1.0 g/l of MSA will bring the pH of
the anolyte well below 2.0. It is estimated that with the amount of
MSA provided in the examples in Mayer, the pH of the anolyte in
Mayer will be in the range of 0 to 0.5.
[0139] In contrast, in accordance with embodiments of the present
disclosure, tin ions are the dominant ion of mass transfer across
the cationic membrane, thereby substantially reducing the movement
of other chemistry components from the anolyte to the catholyte,
such as water, protons, and chemistry additives.
[0140] In accordance with embodiments of the present disclosure, a
suitable cationic membrane is chemically compatible with MSA and
efficient at transferring tin ions. In one embodiment, the membrane
has high current carrying capability. For example, the tin-silver
deposition process often operates in the range of 30-50 Amps to
achieve high plating rates. Achieving a stable anolyte and
catholyte generally means that for every tin atom plated on the
wafer, one tin ion from the anolyte has to cross the membrane into
the catholyte.
[0141] In the exemplary tin-silver solder deposition in accordance
with embodiments of the present disclosure, the solder may be a
near eutectic solder. A eutectic solder will solidify at a lower
temperature compared to any other composition made up of the same
ingredients. Eutectic tin-silver solder has 3.5% silver content.
Near eutectic may be in the range of about 0.1% to about 5% silver
content, about 0.5% to 5% silver content, about 1% to about 3%
silver, or about 0.8% to about 5% silver content.
[0142] To achieve near eutectic tin-silver solder deposition, the
composition of the catholyte may include a tin ion concentration in
a range of about 40 to about 80 g/L, about 40 to about 120 g/L, or
about 40 to about 150 g/L. As described in greater detail below, if
the anode is a consumable tin anode, the concentration of tin ions
in the anolyte is substantially similar to the concentration in the
catholyte.
[0143] Likewise, the composition of the catholyte may include a
silver ion concentration in a range of about 0.1 to about 5.0 g/L.
Because the silver ion is dosed into the catholyte and the system
substantially prevents movement of the silver metal cation from the
catholyte to the anolyte, there is little to no silver ion
concentration expected in the anolyte.
[0144] In accordance with other embodiments of the present
disclosure, other exemplary solders may include copper-silver-tin,
tin-gold, and tin-bismuth. Near eutectic ranges for an exemplary
solders are about +/-10% of the eutectic ranges. However, it should
be appreciated that the properties of the solders change as the
compositions change. For example, desirable solder properties may
include desirable grain structure, uniform melting point,
malleability, and less brittleness.
EXAMPLES
[0145] Exemplary catholyte and anolyte bath components are provided
in the table below. The acid may be MSA. Notably, the acid content
in the anolyte is in the range of 0.5 to 2.5 g/l to achieve a
suitable pH range for the anolyte according to the graphical
representation of data in FIG. 13.
TABLE-US-00001 Catholyte#1 Catholyte#2 Catholyte#3 Catholyte#4 Bath
(MMCTS507) (MMCTS304) (DowTS4000) (DowTS6000) Anolyte#1 Sn 75-95
g/l 70-85 g/l 50-75 g/l 50 g/l 30-75 g/l Ag 1-2 g/l 2.3-2.6 g/l
0.3-1 g/l .3-.6 g/l 0 g/l Acid 80-350 g/l 100-350 g/l 225 g/l
100-300 g/l 0.5-2.5 g/l
[0146] In addition to multi-component solders having metals that
are deposited using an electrochemical deposition process, the
multi-component solder may also include other co-deposited metals.
Exemplary co-deposited metals may include small amounts of metals
that are too electronegative to be deposited using ECD technology,
for example, in the range of about 1 to about 100 ppm, or in the
range of about 0.1% to about 20% by weight of deposit. An
non-limiting examples, titanium and tantalum may be suitable
co-deposited metals. Other non-limiting examples include vanadium,
chromium, zirconium, niobium, molybdenum, hafnium, and tungsten.
Although the metals cannot be deposited using ECD technology, if
present in the catholyte chemistry, they can be found in the
deposit as a result of physical deposition effects. To achieve a
co-deposition composition of about 1 to about 100 ppm, the
co-deposited metal may be present in the catholyte in a range of
about 0.1 to about 15 g/L.
[0147] As discussed above, the anode may be a consumable anode for
providing a source of metal ions into the anolyte. There are
several advantages to using a consumable anode. For example, the
cost of a tin concentrate solution is at a much higher cost than a
tin consumable anode. Moreover, a consumable anode is a continuous,
stable, self-controlling source of metal ions. In that regard, the
concentration of metal ions in the anolyte is controlled in that
for every ion deposited, one ion is consumed, one ion crosses
membrane, and one ion is dissolved in solution. Through bath
analysis (primarily tin and acid concentration), ion transport
across the membrane against ion loss (plating) in the catholyte and
ion generation in the anolyte can be tracked using Faraday's
Law.
[0148] Experimental results from an exemplary tin/silver deposition
system with a consumable tin anode are provided in FIGS. 12A and
12B. As can be seen in FIG. 12A, as anolyte pH approaches
approximately 0.8 in an exemplary tin/silver deposition system
(moving from left to right on the graph), the tin concentrations in
the catholyte and anolyte start to diverge from the expected
concentrations. Also, as the pH continues to rise from 0.8 and
approaches 1, the tin concentration in the catholyte starts to
increase. Both observations indicate that if the pH is high enough,
the tin ions become the primary charge carrier and start to pass
thru the membrane from the anolyte to catholyte.
[0149] As can be seen in FIG. 12B, which is a graphical
representation of the relationship between pH and tin concentration
in the catholyte and the anolyte, if the anolyte pH in an exemplary
tin/silver deposition system is maintained at a pH above 1, tin
concentration in the catholyte can be maintained at close to target
concentration. This observation indicates that consumed tin in the
catholyte is replenished by tin ions pass thru the membrane from
the anolyte.
[0150] In contrast to a consumable anode, dosing metal ions into
the system has drawbacks. For example, when dosing metal ions into
the anolyte or the catholyte, process control is retroactive,
thereby resulting in a sawtooth concentration profile. Moreover, a
metal ion concentrate may include other components to keep the
metal ions in solution. As tin ions are consumed, these other
components accumulate, affecting both bath stability and bath
lifetime.
[0151] As described above, another advantage of employing a cation
permeable barrier in the processes described herein is that the
barrier prevents bubbles from the oxygen or hydrogen 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.
[0152] In an ideal system using a consumable anode, the charge
balance is such that for each metal ion deposited, one ion crosses
the membrane from the anolyte to the catholyte, and likewise, one
ion is consumed from the consumable anode. However, it should be
appreciated that an ideal system cannot always be achieved. For
example, protons may move across the membrane in lieu of metal
ions. Although the pH gradient between the anolyte and the
catholyte is designed to such that metal ions (such as tin ions)
dominate mass transfer, protons are more mobile, smaller, and move
more easily than metal ions. Because of their mobility, any proton
in the near vicinity of the membrane may carry current across the
membrane.
[0153] In one embodiment of the present disclosure, 85% efficiency
may be achieved. In another embodiment of the present disclosure,
90% efficiency may be achieved. In another embodiment of the
present disclosure, 95% efficiency may be achieved.
[0154] Although the consumable anode may be a source of metal ions,
it may not be the only source of metal ions. In that regard, in
addition to the presence of metal ions from a consumable anode, an
additional source of metal ions may be dosed in the catholyte. In
one embodiment of the present disclosure, the primary source of
metal ions comes from the consumable anode. In one embodiment of
the present disclosure, the primary source of metal ions comes from
dosing in the catholyte.
[0155] Moreover, when the system is starting up, there may be a
need to chemically dose the system with a source of metal ions.
[0156] In accordance with another embodiment of the present
disclosure, the primary source of metal ions may be dosing in the
anolyte. In that regard, the process may include either a
consumable anode or an inert anode.
[0157] Tin oxidation from Sn(II) to Sn(IV) is a common problem in a
chemistry containing tin ions, resulting in a reduction in tin ions
in the chemistry for plating. Tin oxidation can be mitigated by
including antioxidants in the chemistry. Therefore, in accordance
with another embodiment of the present disclosure, the system
includes a method for mitigating oxidation. Antioxidants may be
chemical antioxidants in solution that are sacrificial oxidants to
use up any oxygen in the system before it oxidizes tin.
[0158] Other antioxidants causing anti-oxidizing effects in the
system may include a degassing unit to remove oxygen in the
catholyte and/or the anolyte, or may include nitrogen injection
bubbling into the catholyte and/or the anolyte. The catholyte may
be more prone to oxidation effects than the anolyte because the
catholyte chamber may be open to the atmosphere allowing more
oxygen to dissolve in solution.
[0159] 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 disclosure.
* * * * *