U.S. patent application number 14/570602 was filed with the patent office on 2015-04-09 for methods for electroplating copper.
The applicant listed for this patent is Moses Lake Industries, Inc.. Invention is credited to James D. Blanchard, Valery M. Dubin, Yingxiang Tao, Xingling Xu.
Application Number | 20150096894 14/570602 |
Document ID | / |
Family ID | 41132259 |
Filed Date | 2015-04-09 |
United States Patent
Application |
20150096894 |
Kind Code |
A1 |
Dubin; Valery M. ; et
al. |
April 9, 2015 |
METHODS FOR ELECTROPLATING COPPER
Abstract
Embodiments of the invention are directed to methods of
electroplating copper onto at least one surface of a substrate in
which more uniform electrical double layers are formed adjacent to
the at least one surface being electroplated (i.e., the cathode)
and an anode of an electrochemical cell, respectively. In one
embodiment, the electroplated copper may be substantially-free of
dendrites, exhibit a high-degree of (111) crystallographic texture,
and/or be electroplated at a high-deposition rate (e.g., about 6
.mu.m per minute or more) by electroplating the copper under
conditions in which a ratio of a cathode current density at the at
least one surface to an anode current density at an anode is at
least about 20. In another embodiment, a porous anodic film may be
formed on a consumable copper anode using a long conditioning
process that promotes forming a more uniform electrical double
layer adjacent to the anode.
Inventors: |
Dubin; Valery M.; (Portland,
OR) ; Xu; Xingling; (Moses Lake, CN) ; Tao;
Yingxiang; (Moses Lake, CN) ; Blanchard; James
D.; (Soap Lake, WA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Moses Lake Industries, Inc. |
Moses Lake |
WA |
US |
|
|
Family ID: |
41132259 |
Appl. No.: |
14/570602 |
Filed: |
December 15, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13452139 |
Apr 20, 2012 |
8911609 |
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14570602 |
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12080680 |
Apr 4, 2008 |
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13452139 |
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Current U.S.
Class: |
205/96 |
Current CPC
Class: |
C25D 5/02 20130101; H01L
21/67011 20130101; C25D 3/38 20130101; H05K 3/241 20130101; C25D
17/10 20130101; C25D 5/00 20130101; Y02E 10/50 20130101; C25D
17/001 20130101; H01L 31/022425 20130101; C25D 17/12 20130101; H01L
21/2885 20130101; C25D 5/18 20130101 |
Class at
Publication: |
205/96 |
International
Class: |
C25D 3/38 20060101
C25D003/38; C25D 5/02 20060101 C25D005/02 |
Claims
1. A method, comprising: forming an electrochemical cell including
at least one surface of a substrate, an anode, and an
electroplating solution in contact with the at least one surface
and the anode, wherein the electroplating solution includes at
least one suppressor agent; and electroplating copper onto the at
least one surface under conditions in which a ratio of a cathode
current density at the at least one surface to an anode current
density at the anode is at least about 20.
2. The method of claim 1 wherein electroplating copper onto the at
least one surface under conditions in which a ratio of a cathode
current density at the surface to an anode current density at the
anode is at least about 20 comprises electroplating the copper onto
the at least one surface under conditions in which the ratio is
about 20 to about 100.
3. The method of claim 1 wherein electroplating copper onto the at
least one surface under conditions in which a ratio of a cathode
current density at the surface to an anode current density at the
anode is at least about 20 comprises electroplating the copper onto
the at least one surface under conditions in which the ratio is
about 40 to about 100.
4. The method of claim 1 wherein electroplating copper onto the at
least one surface under conditions in which a ratio of a cathode
current density at the surface to an anode current density at the
anode is at least about 20 comprises electroplating the copper onto
the at least one surface under conditions in which the ratio is
about 60 to about 100.
5. The method of claim 1 wherein electroplating copper onto the at
least one surface under conditions in which a ratio of a cathode
current density at the surface to an anode current density at the
anode is at least about 20 comprises: selecting a strength and a
concentration of the at least one suppressor agent, and a surface
area of the anode so that the ratio is established during the act
of electroplating copper.
6. The method of claim 1 wherein: the anode comprises an inert
anode; and electroplating copper onto the at least one surface
comprises electroplating the copper from dissolved copper in the
electroplating solution.
7. The method of claim 1 wherein: the anode comprises a
copper-containing anode; and electroplating copper onto the at
least one surface comprises electroplating the copper provided from
the copper-containing anode.
8. The method of claim 1 wherein the anode comprises a
copper-containing anode.
9. The method of claim 8 wherein the copper-containing anode
comprises: a porous mass of copper particles; a grooved body
comprising copper; a porous mass of sintered copper-containing
particles; or a mesh comprising copper.
10. (canceled)
11. The method of claim 1 wherein electroplating copper comprises
applying a time-varying voltage between the anode and the at least
one surface of the substrate.
12. The method of claim 1 wherein forming an electrochemical cell
including at least one surface of a substrate, an anode, and an
electroplating solution in contact with the at least one surface
and the anode comprises forming the electrochemical cell to include
the at least one surface, the anode, and the electroplating
solution having dissolved copper therein present in a concentration
from about 50 grams per liter to about 100 grams per liter.
13. The method of claim 1 wherein the at least one suppressor agent
of the electroplating solution comprises one or more of the
following suppressor agents: a surfactant; a chelating agent; a
leveler agent; and a wetting agent.
14. The method of claim 1 wherein the electroplating solution
comprises at least one accelerator agent.
15. The method of claim 14 wherein the at least one accelerator
agent is substantially free of at least one type of alkali
element.
16. The method of claim 1, further comprising linearly oscillating
the substrate in the electroplating solution during the act of
electroplating copper.
17. The method of claim 1, further comprising rotating the
substrate in the electroplating solution during the act of
electroplating copper.
18. (canceled)
19. The method of claim 1 wherein electroplating copper comprises
depositing the copper onto the at least one surface of the
substrate as a substantially dendrite-free film at a deposition
rate of at least about 6 .mu.m per minute.
20. The method of claim 1 wherein the at least one suppressor agent
provides a suppression strength of at least about 5.0.
21. The method of claim 1 wherein forming an electrochemical cell
including at least one surface of a substrate, an anode, and an
electroplating solution in contact with the at least one surface
and the anode comprises immersing the substrate in the
electroplating solution.
22. A method, comprising: forming an electrochemical cell including
a cathode, a consumable copper-containing anode, and an
electroplating solution in contact with the cathode and the
consumable copper-containing anode; and forming a porous anodic
film on the consumable copper-containing anode by generating a
current through the electrochemical cell for a time sufficient to
pass at least about 1000 coulombs per liter of the electroplating
solution through the electroplating solution.
23-34. (canceled)
Description
BACKGROUND
[0001] Copper-based materials have currently supplanted
aluminum-based materials as the material of choice for
interconnects in integrated circuits ("ICs"). Copper offers a lower
electrical resistivity and a higher electromigration resistance
than that of aluminum, which has historically been the dominant
material used for interconnects.
[0002] Interconnects in ICs are becoming one of the dominant
factors for determining system performance and power dissipation.
For example, the total length of interconnects in many currently
available ICs can be twenty miles or more. At such lengths,
interconnect resistance-capacitance ("RC") time delay can exceed a
clock cycle and severely impact device performance. Additionally,
the interconnect RC time delay also increases as the size of
interconnects continues to relentlessly decrease with corresponding
decreases in transistor size. Using a lower resistivity material,
such as copper, decreases the interconnect RC time delay, which
increases the speed of ICs that employ interconnects formed from
copper-based materials. Copper also has a thermal conductivity that
is about two times aluminum's thermal conductivity and an
electromigration resistance that is about ten to about one-hundred
times greater than that of aluminum.
[0003] Copper-based interconnects have also found utility in other
applications besides ICs. For example, solar cells, flat-panel
displays, and many other types of electronic devices can benefit
from using copper-based interconnects for the same or similar
reasons as ICs.
[0004] Due to difficulties uniformly depositing and void-free
filling trenches and other small features with copper using
physical vapor deposition ("PVD") and chemical vapor deposition
("CVD"), copper interconnects are typically fabricated using a
Damascene process. In the Damascene process, a trench is formed in,
for example, an interlevel dielectric layer, such as a carbon-doped
oxide. The dielectric layer is covered with a barrier layer formed
from, for example, tantalum or titanium nitride to prevent copper
from diffusing into the silicon substrate and degrading transistor
performance. A seed layer is formed on the barrier layer to promote
uniform deposition of copper within the trench. The substrate is
immersed in an electroplating solution that includes copper. The
substrate functions as a cathode of an electrochemical cell in
which the electroplating solution functions as an electrolyte, and
the copper from the electroplating solution or a consumable anode
is electroplated into the trench responsive to a voltage applied
between the substrate and an anode. Then, copper deposited on
regions of the substrate outside of the trench is removed using
chemical-mechanical polishing ("CMP").
[0005] Regardless of the particular electronic device in which
copper is used as a conductive structure, it is important that an
electroplating process for copper be sufficiently fast to enable
processing a large number of substrates and have an acceptable
yield. Additionally, the cost of the electroplating solution is
also another factor impacting overall fabrication cost of
electronic devices using copper. This is particularly important in
the fabrication of solar cells, which have to cost-effectively
compete with other, potentially more cost-effective, energy
generation technologies. Thus, it is desirable that copper
electroplating solutions be capable of depositing copper in a
uniform manner (i.e., high-throwing power) and at a high-deposition
rate.
[0006] A number of electroplating solutions are currently available
for electroplating copper. For example, sulfate-based
electroplating solutions are commonly used for electroplating
copper. Some alkaline copper electroplating solutions have a
high-throwing power, but are not capable of rapidly depositing
copper without compromising the deposited film quality. At
high-deposition rates, the copper may grow as dendrites as opposed
to a more uniformly deposited film. Additionally, alkali elements
(e.g., sodium and potassium) in such alkaline copper electroplating
solutions can diffuse into silicon substrates and are deep-level
impurities in silicon that can compromise transistor performance.
Fluoroborate electroplating solutions can be used for high-speed
deposition of copper. However, fluoroborate electroplating
solutions can be more expensive than, more traditional,
sulfate-based solutions. Moreover, fluoroborate electroplating
solutions may be more hazardous and difficult to dispose of than
many other electroplating solutions for electroplating copper.
SUMMARY
[0007] Embodiments of the invention are directed to methods of
electroplating copper onto at least one surface of a substrate in
which more uniform electrical double layers are formed adjacent to
the at least one surface being electroplated (i.e., the cathode)
and an anode of an electrochemical cell, respectively. The
electroplated copper may be of high-quality and electroplated at a
high-deposition rate so that the electroplated copper may be used,
for example, in electrical interconnects for ICs, solar cells, and
many other applications.
[0008] In one embodiment of the invention, a method is disclosed in
which the electroplated copper may be substantially-free of
dendrites, exhibit a high-degree of (111) crystallographic texture,
and/or be electroplated at a high-deposition rate (e.g., about 6
.mu.m per minute or more) by electroplating copper under conditions
in which a ratio of a cathode current density at the at least one
surface of the substrate being electroplated to an anode current
density at an anode is at least about 20. In such an embodiment,
the method includes forming an electrochemical cell comprising at
least one surface of a substrate, an anode, and an electroplating
solution in contact with the at least one surface and the anode,
wherein the electroplating solution includes at least one
suppressor agent. The method further includes electroplating copper
onto the at least one surface under conditions in which a ratio of
a cathode current density at the surface to an anode current
density at the anode is at least about 20.
[0009] In another embodiment of the invention, a method includes
forming an electrochemical cell comprising a cathode, a consumable
copper-containing anode, and an electroplating solution in contact
with the cathode and the consumable copper-containing anode. The
method further includes forming a porous anodic film on the
consumable copper-containing anode by generating a current through
the electrochemical cell for a time sufficient to pass at least
about 1000 coulombs per liter through the electroplating solution.
In one embodiment, the cathode may be a conditioning cathode that
is replaced with a substrate having at least one surface to be
electroplated that functions as a cathode. In such an embodiment,
the method also includes electroplating copper onto the at least
one surface of the substrate. In another embodiment, the consumable
copper-containing anode may be conditioned to form the porous
anodic film in a separate electrochemical cell, and subsequently
removed and employed in a plating electrochemical cell in which at
least one surface of a substrate to be electroplated functions as
the cathode.
[0010] Other embodiments of the invention relate to methods of
synthesizing an accelerator agent that is substantially free of
alkali elements for use in an electroplating solution.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The drawings illustrate various embodiments of the
invention, wherein identical reference numerals refer to identical
elements or features in different views or embodiments shown in the
drawings.
[0012] FIG. 1 is a schematic cross-sectional view of an embodiment
of an electroplating apparatus that may be used for electroplating
copper onto at least one surface of a substrate according to
embodiments of methods of the invention.
[0013] FIG. 2 is a cross-sectional view of a consumable, copper
anode including a mass of copper particles enclosed in a porous
membrane according to an embodiment of the invention.
[0014] FIG. 3 is a side elevation view of a consumable, copper
anode made from sintered copper particles according to an
embodiment of the invention.
[0015] FIG. 4 is an isometric view of a consumable, copper anode
comprising a body having a plurality of grooves formed therein
according to an embodiment of the invention.
[0016] FIGS. 5A-5E are cross-sectional views illustrating various
stages in a to method of electroplating bumps according to an
embodiment of the invention.
DETAILED DESCRIPTION
[0017] Embodiments of the invention are directed to methods of
electroplating copper onto at least one surface of a substrate in
which more uniform electrical double layers are formed adjacent to
the at least one surface being electroplated (i.e., the cathode)
and an anode of an electrochemical cell, respectively. The
electroplated copper may be used in electrical interconnects for
ICs, solar cells, and many other applications. For example, in an
embodiment, the electroplated copper may be substantially-free of
dendrites, exhibit a high-degree of (111) crystallographic texture,
and/or be electroplated at a high-deposition rate (e.g., about 6
.mu.m per minute or more) by electroplating the copper under
conditions in which a ratio of a cathode current density at the at
least one surface to an anode current density at an anode is at
least about 20. In another embodiment, a porous anodic film may be
formed on a consumable copper anode using a long-conditioning
process that promotes forming a more uniform electrical double
layer adjacent to the anode during electroplating.
Electroplating Apparatuses for Practicing Described Electroplating
Methods
[0018] FIG. 1 is a schematic cross-sectional view of an embodiment
of an electroplating apparatus 100 that may be employed for
practicing embodiments of methods of the invention. The
electroplating apparatus 100 includes a container 102 holding an
electroplating solution 104 comprising at least one suppressor
agent and having a high-surface area anode 106 immersed therein.
Although not shown in FIG. 1, the electroplating apparatus 100 may
include a heating unit configured to maintain the electroplating
solution 104 at a temperature of about 20.degree. C. to about
60.degree. C. and, more specifically, at about 40.degree. C. A
substrate holder 108 is configured to hold a substrate 110, having
at least one surface 112, to be electroplated in the electroplating
solution 104. The substrate holder 108 may be configured according
to any conventional or subsequently developed substrate holder.
Although only a single substrate is illustrated in FIG. 1 for
simplicity, many commercially available substrate holders are
configured to hold multiple substrates. Additionally, as used
herein, the term "substrate" refers to any workpiece capable of
being electroplated. For example, suitable substrates include, but
are not limited to, semiconductor substrates (e.g., single-crystal
silicon wafers, single-crystal gallium arsenide wafer, etc.) with
or without active and/or passive devices (e.g., transistors,
diodes, capacitors, resistors, etc.) formed therein and with or
without at least one surface coated with a seed layer, printed
circuit boards, flexible polymeric substrates, and many other types
of substrates. As will be discussed in more detail below, the
electroplating solution 104 is formulated and the anode 106 is
configured so that a generally uniform electrical double layer is
formed at both the surface 112 being electroplated and the anode
106 so that a more uniform current density is developed at both the
surface 112 (i.e., cathode) and the anode 106.
[0019] A power supply 114 is electrically connected to the anode
106 and, through electrical contacts (not shown) in the substrate
holder 108, to the surface 112 of the substrate 110 to be
electroplated. The power supply 114 may be operable to apply a
selected voltage waveform between the anode 106 and substrate 110,
such as a constant voltage, a time-varying voltage waveform, or
both. Thus, the surface 112 of the substrate 110 defining a
cathode, the anode 106, and the electroplating solution 104 form an
electrochemical cell 115.
[0020] Still referring to FIG. 1, a movable arm 116 is connected to
the substrate holder 108 and may orient the surface 112 of the
substrate 110 downwardly, and further is operably connected to an
actuator system 118. The surface 112 may be spaced from the anode
106 by a spacing S of about 0.5 to about 50 centimeters ("cm"). The
actuator system 118 is operable to selectively move the movable arm
116 in directions V.sub.1 and V.sub.2 to enable immersing and
removal of the substrate holder 108 carrying the substrate 110 from
the electroplating solution 108. Additionally, the actuator system
118 may be operable to controllably move the movable arm 116 in
directions H.sub.1 and H.sub.2 in a linearly oscillatory manner to
move the substrate 110 in the directions H.sub.1 and H.sub.2,
rotate the movable arm 116 and the substrate holder 108 connected
thereto in a direction R, or both during electroplating.
[0021] The electroplating apparatus 100 may also include a number
of containers (not shown) holding different solutions, such as a
cleaning solution, drying solution, rinsing solution, etc.
Furthermore, a variety of different fluid supply systems may be
employed to supply the various fluids in the containers and,
optionally, to re-circulate the electroplating solution 104 to
provide a generally laminar flow of the electroplating solution 104
over the substrate 110. Such fluid supply systems, container
configurations, and cleaning/drying/rinsing solutions are
well-known and in the interest of brevity are not described in
detail herein.
Embodiments of Methods for Electroplating Copper
[0022] Referring to FIG. 1, according to an embodiment of a method
of the invention, the electrochemical cell 115 is formed by
immersing the substrate holder 108 carrying the substrate 110 in
the electroplating solution 104 so that the surface 112 and anode
106 are in contact with the electroplating solution 104. As will be
discussed in more detail below, the electroplating solution 104 is
formulated with at least one suppressor agent to promote forming a
more uniform electrical double layer adjacent to the surface 112
during electroplating. That is, the resistance drop across the
electrical double layer in the electroplating solution 104 adjacent
to the surface 112 is more uniform in a direction generally
parallel to the surface 112. Additionally, the high-surface area
anode 106 is configured to provide a more uniform electrical double
layer adjacent to the anode 106 during electroplating. That is, the
resistance drop across the electrical double layer in the
electroplating solution 104 adjacent to the anode 106 is more
uniform in a direction along the length of and about the anode
106.
[0023] A copper film 120 is electroplated onto the surface 112 of
the substrate 110 under conditions in which a ratio of a cathode
current density at the surface 112 to an anode current density at
the anode 106 is at least about 20 (e.g., about 20 to about 200) by
application of a selected voltage waveform between the surface 112
and the anode 106 using the power supply 114. Furthermore, the
ratio may be about 20 to about 100, more particularly about 40 to
about 100, even more particularly about 60 to about 100, and yet
even more particularly about 80 to about 100. The surface area of
the anode 106 relative to the surface area of the surface 112 being
electroplated, and the suppression strength of the at least one
suppressor agent are selected to that the above ratios may be
maintained during electroplating of the copper film 120. The
electroplating copper that forms the copper film 120 may be
provided from the anode 106 when the anode 106 is a consumable
anode or may be provided from copper intentionally added to the
electroplating solution 104.
[0024] During electroplating of the copper film 120, the substrate
110 may be linearly oscillated at a rate of about 10 millimeters
per second ("mm/s") to about 1000 mm/s back and forth in the
directions H.sub.1 and H.sub.2. In another embodiment, the
substrate holder 108 and substrate 110 may be rotated in the
direction R as a unit while the surface 112 of the substrate 110 is
maintained generally parallel to a longitudinal axis of the anode
106. For example, the substrate holder 108 and substrate 110 may be
rotated in the direction R as a unit at a rotational speed of about
150 revolutions per minute ("RPM") to about 300 RPM and, more
particularly, about 200 RPM. In other embodiments of the invention,
a combination of linear oscillatory movement of the substrate
holder 108 and substrate 110 as a unit in the directions H.sub.1
and H.sub.2 and rotational movement in the direction R may be used.
Utilizing any of the above-described techniques for linearly
oscillating and/or rotating the substrate 110 enables increasing
the limiting current density at the substrate 110 that is limited
by diffusion of cupric ions within the electroplating solution 104
to the surface 112 of the substrate 110.
[0025] During the electroplating process, in one embodiment of the
invention, the power supply 114 may apply a generally constant
voltage between the surface 112 of the substrate 110 and the anode
106. In another embodiment of the invention, the power supply 114
may apply time-varying voltage to impose a forward-pulse current
density on the substrate 110 to promote forming a finer grain size
in the copper film 120. Representative cathode current densities at
the surface 112 of the substrate 110 (i.e., the cathode) for a
forward-pulse current density waveform may be about 200 mA/cm.sup.2
to about 2000 mA/cm.sup.2, while anode current densities at the
anode 106 may be about 10 mA/cm.sup.2 or less. In another
embodiment, the power supply 114 may apply a time-varying voltage
to impose a reverse-pulse current density waveform on the surface
112 of the substrate 110 or a combination of a forward-pulse and
reverse-pulse current density waveform. Representative current
densities at the surface 112 of the substrate 110 (i.e., the
cathode) for the forward pulse of a forward-pulse/reverse-pulse
current density waveform may be increased to about 10 A/cm.sup.2
with a pulse duration of about 0.1 ms to about 100 ms. In the
above-described time-varying voltage waveforms, the ratio of the
cathodic current density to the anodic current density is
determined by the peak current density at the cathode (i.e., the
surface 112 of the substrate 110) to the corresponding peak current
density at the anode 106.
[0026] The described embodiments of electroplating the copper film
120 that utilize the selectively formulated electroplating solution
104 in combination with the high-surface area anode 106 enables
electroplating the copper film 120 at a high-deposition rate, such
as about 6 .mu.m per minute or more and, more particularly, about 9
.mu.m per minute. Additionally, the electroplated copper film 120
may be substantially free of dendrites and exhibit a high-degree of
(111) crystallographic texture that is more resistant to
stress-induced voiding than other crystallographic textures.
Embodiments of Consumable Copper Anodes
[0027] In an embodiment of the invention, the anode 106 may be a
consumable, copper-containing anode. Referring to FIG. 2, in one
embodiment, the anode 106 may be configured as a porous mass of
copper particles 200 enclosed in a suitable polymeric membrane 202
that is permeable to cupric ions (Cu.sup.2+) and the electroplating
solution 104. Referring to FIG. 3, in another embodiment, the anode
106 may be configured as porous mass 300 of sintered-together
copper particles. Referring to FIG. 4, in another embodiment, the
anode 106 may be configured as a rod 400 or body of other geometry
made from copper that includes a plurality of grooves 402 formed
therein. In yet another embodiment, the anode 106 may be configured
as a copper mesh. In any of the above-described embodiments for the
anode 106, the anode 106 provides the copper to be deposited onto
the surface 112 of the substrate 110. Application of the selected
voltage waveform between the anode 106 and the surface 112 of the
substrate 110 causes copper from the consumable anode 106 to
oxidize, dissolve in the electroplating solution 104, and be
electroplated onto the surface 112.
Embodiments of Electroplating Solutions
[0028] The electroplating solution 104 may formulated from at least
one acid and at least one suppressor agent. In some embodiments of
the invention, the electroplating solution 104 may also include at
least one accelerator agent. The at least one acid may be selected
from one or more of the following acids: sulfuric acid, methane
sulfonic acid, hydrochloric acid, hydroiodic acid, hydroboric acid,
fluoroboric acid, and any other suitable acid. In a more specific
embodiment of the invention, the at least one acid includes
sulfuric acid present in a concentration of about 100 grams per
liter ("g/L") or less (e.g., about 5 g/L to about 100 g/L) and
hydrochloric acid present in a concentration from about 20 mg/L to
about 100 mg/L. In addition to the aforementioned acids, in certain
embodiments of the invention, the electroplating solution 104 may
further include a supplemental acid selected to increase the
solubility of the copper from the consumable anode 106 in the at
least one acid. For example, the supplemental acid may be selected
from alkane sulfonic acid, methane sulfonic acid, ethane sulfonic
acid, propane sulfonic acid, buthane sulfonic acid, penthane
sulfonic acid, hexane sulfonic acid, decane sulfonic acid, dedecane
sulfonic acid, fluoroboric acid, mixtures of any of the preceding
supplemental acids, or another suitable acid selected to increase
the solubility of the copper in the at least one acid of the
electroplating solution 104.
[0029] As discussed above, the electroplating solution 104 may
include additives, such as a suppressor agent, an accelerator
agent, or both that improve certain electroplating characteristics
of the electroplating solution 104. As used herein, the phrase
"virgin make solution" ("VMS") refers to an electroplating solution
104 without any suppressor agents and accelerator agents. For the
electroplating solution 104 described herein, the VMS includes the
at least one acid. As used herein, "suppression strength" of one or
more suppressor agents of an electroplating solution 104 is
determined by a decrease in current density at a cathode of an
electrochemical cell that includes a suppressed solution containing
VMS and the one or more suppressor agents compared to current
density at a cathode of an electrochemical cell that includes a
solution containing generally only the VMS, with each current
density measured at about -0.7 volts relative to a mercurous
sulfate electrode ("MSE"). For the electroplating solution 104
described herein, a suppressed solution includes the at least one
acid and the at least one suppressor agent. As merely an example,
when a current density at a cathode of an electrochemical cell
utilizing a suppressed solution is five times lower than a current
density of an electrochemical cell utilizing a VMS, a suppressor
agent provides a suppression strength of 5.0.
[0030] As used herein, "acceleration strength" of one or more
accelerator agents of an electroplating solution 104 is measured by
an increase in current density at a cathode of an electrochemical
cell that includes an accelerated solution containing VMS and the
one or more accelerator agents compared to current density at a
cathode of an electrochemical cell that includes the
above-described suppressed solution, with each current density
measured at about -0.7 volts relative to a MSE. For the
electroplating solution 104 described herein, an accelerated
solution includes the at least one acid and the at least one
accelerator agent. As merely an example, when a current density at
a cathode of an electrochemical cell utilizing an accelerated
solution is two times higher than a current density of an
electrochemical cell utilizing a suppressed solution, an
accelerator agent provides an acceleration strength of 2.0.
[0031] The at least one suppressor agent of the electroplating
solution 104 is formulated to substantially suppress formation of
dendrites during electroplating copper from the electroplating
solution 104 and improve other qualities of an electroplated copper
film, such as surface roughness, ductility, brightness, and
electrical conductivity. The at least one suppressor agent may be
present in the electroplating aqueous solution in concentration
from about 10 mg/L to about 1000 mg/L. In some embodiments, the at
least suppressor agent is present in the electroplating solution
104 in an amount sufficient to provide a suppression strength of at
least about 5.0. The at least one suppressor agent may be a
surfactant, a leveler agent, a wetting agent, a chelating agent, or
an additive that exhibits a combination of any of the foregoing
functionalities. The at least one suppressor agent may be selected
from one or more of the following suppressor agents: a quaternized
polyamine, a polyacrylamide, a cross-linked polyamide, a phenazine
azo-dye (e.g., Janus Green B), an alkoxylated amine surfactant, a
polyether surfactant, a non-ionic surfactant, a cationic
surfactant; an anionic surfactant, a block copolymer surfactant,
polyacrylic acid, a polyamine, aminocarboxylic acid,
hydrocarboxylic acid, citric acid, entprol, edetic acid, tartaric
acid, and any other suitable suppressor agent.
[0032] When present, the at least one accelerator agent of the
electroplating solution 104 is formulated to increase the
deposition rate of copper onto the surface 112 of the substrate 110
and present in the electroplating solution 104 in an amount
sufficient to provide an acceleration strength of at least about
2.0. The at least one accelerator agent may further increase the
brightness of the electroplated copper film 120 and other
qualities, such as decreasing void concentration in the
electroplated copper film 120. The at least one accelerator agent
may be present in the electroplating solution 104 in concentration
from about 10 mg/L to about 1000 mg/L. According to various
embodiments, the at least one accelerator agent may be selected
from an organic sulfide compound, such as
bis(sodium-sulfopropyl)disulfide, 3-mercapto-1-propanesulfonic acid
sodium salt, N,N-dimethyl-dithiocarbamyl propylsulfonic acid sodium
salt, 3-S-isothiuronium propyl sulfonate, or mixtures of any of the
preceding chemicals. Additional suitable accelerator agents
include, but are not limited to, thiourea, allylthiourea,
acetyithiourea, pyridine, mixtures of any of the preceding
chemicals, or another suitable accelerator agent. The at least one
accelerator may also comprise an inorganic compound selected to
increase the deposition rate of the copper from the electroplating
solution 104, decrease hydrogen evolution that can increase the
porosity in the electroplated copper film 120, or both. For
example, suitable inorganic compounds may comprise
selenium-containing anions (e.g., SeO.sub.3.sup.2- and Se.sup.2-),
tellurium-containing anions (e.g., TeO.sub.3.sup.2- and Te.sup.2-),
or both.
[0033] Additionally, many of the disclosed accelerator agents may
be substantially-free of alkali elements (e.g., sodium and
potassium), which can be detrimental to the performance of
semiconductor devices used in ICs. Accordingly, a copper film
deposited from one of the disclosed electroplating solutions having
an accelerator agent that is substantially free of alkali elements
will also be substantially-free of alkali elements.
[0034] For example, in an embodiment of the invention, a
substantially sodium-free accelerator agent of
3,3'-Dithio-1,1'-propanedisulfonic acid may be synthesized. As
shown in reaction (1) below, thiourea or N-substituted derivatives
of thiourea having at least one hydrogen atom attached to one or
both of the nitrogen atoms may be reacted with the 1,3-propane
sultone to form S-thiuronium alkane sulfonate, which is a
derivative of thiourea containing a sulfonic acid group.
##STR00001##
[0035] As shown below in reaction (2) below, S-thiuronium alkane
sulfonate may be reacted with an aqueous solution of ammonia to
produce guanidinium 3-mercapto-alkanesulfonate.
##STR00002##
[0036] As shown in reaction (3) below, the quanidinium
3-mercapto-alkanesulfonate so-formed may be passed through a
cationic ion exchange resin so that quanidinium ions are replaced
by hydrogen ions to form 3-mercapto-1-propanesulfonic acid.
##STR00003##
[0037] Then, the 3-mercapto-1-propanesulfonic acid so-formed may be
dissolved in water in an amount, for example, to form a 10 percent
by mass solution. Diethylamine (e.g., about 0.25 g/mol) may be
added to the solution. The mixture may be heated to reflux and
while being mixed (e.g., by stirring) a small about (e.g., 0.05
g/mol) of powdered sulfur may be added to the mixture. Then, the
mixture may be refluxed for a sufficient time (e.g., 8 to 10 hours)
until the reaction is completed. The water may be evaporated in
vacuum. The chemical reaction is shown in reaction (4) and the
bis(diethylammonium) 3,3'-dithio-1,1'-dipropanedisulfonate
so-formed is typically a brown viscous syrup.
##STR00004##
[0038] The bis(diethylammonium)
3,3'-dithio-1,1'-dipropanedisulfonate is dissolved in water to
obtain, for example, a 10 percent by mass solution. As shown in
reaction (5) below, this solution may be passed through an ion
exchange resin of, for example, Amberlite IR-120 ion exchange resin
operating in its acid cycle or another suitable ion exchange resin.
After washing the ion exchange resin with water until the pH of the
effluate is about 5 to about 6, the aqueous effluates may be
combined and evaporated in vacuum until substantially all the water
is removed from the reaction product, which is
3,3'-Dithio-1,1'-propanedisulfonic acid in the form of a
light-brown viscous syrup.
##STR00005##
[0039] In another embodiment of the invention, an accelerator agent
of substantially sodium-free 3,3'-Dithio-1,1'-propanedisulfonic
acid may be synthesized directly via an ion exchange process. For
example, bis(sodium-sulfopropyl)disulfide may be passed through a
suitable ion exchange medium to remove substantially all of the
sodium and form substantially sodium-free
3,3'-Dithio-1,1'-propanedisulfonic acid according to reaction (6)
below.
##STR00006##
[0040] Referring again to FIG. 1, in other embodiments of the
invention, the anode 106 may be configured as an inert anode, such
as a platinum anode (e.g., a porous platinum anode) having a
selected surface area relative to the surface 112 of the substrate
110 being electroplated so that in combination with the chemistry
of the electroplating solution 104 the ratio of the cathode current
density at the surface 112 to the anode current density at the
anode 106 is at least about 20. In such an embodiment, the
electroplating solution 104 includes copper in the form of cupric
ions (Cu.sup.2+) dissolved therein from another copper source
besides the anode 104. The copper may be present in the
electroplating solution 104 in a concentration of at least about 50
g/L and, more particularly, from about 50 g/L to about 100 g/L. In
a more specific embodiment of the invention, the concentration of
the copper may be at least about 75 g/L to about 100 g/L, and more
particularly about 75 g/L. The copper may be provided from a copper
source, such as one or more of the following copper sources: copper
sulfate, copper polyphosphate, copper sulfamate, copper alkane
sulfonate, copper chloride, copper acetate, copper formate, copper
fluoride, copper nitrate, copper oxide, copper tetrafluoroborate,
copper trifluoromethanesulfonate, copper trifluoroacetate, copper
hydroxide, and any other suitable copper source.
[0041] One application of the above-described embodiments of
electroplating methods is for electroplating copper to form bumps
(also known as pillars) on a semiconductor substrate. FIGS. 5A-5E
are cross-sectional views illustrating various stages in a method
of electroplating bumps according to an embodiment of the
invention. Referring to FIG. 5A, in one embodiment of the
invention, a semiconductor substrate 500 (e.g., a single crystal
silicon substrate) having a surface 502 is provided. Referring to
FIG. 5B, a seed layer 504 may be deposited onto the surface 502 of
the substrate 500 using, for example, CVD, PVD, or another suitable
deposition technique. For example, the seed layer 504 may comprise
tungsten, copper, or another suitable seed layer that promotes the
deposition of copper. Although not shown, an adhesion layer made
from titanium, tungsten, alloys thereof, or another suitable
material may be deposited onto the surface 502, and the seed layer
504 may be deposited onto the adhesion layer to improve adhesion of
the seed layer 504.
[0042] Referring to FIG. 5C, a photoresist may be applied to the
seed layer 504 and photolithographically patterned to form a mask
layer 506 having a plurality of openings 508 therein. Referring to
FIG. 5D, copper may be electroplated into the plurality of openings
508 and on the exposed portions of the seed layer 506 to form a
plurality of bumps 510. The copper may be electroplated into the
plurality of openings 508 and onto surfaces 509 exposed through the
mask layer 506 using any of the previously described embodiments of
methods described herein. The surface area of the anode 106 and
surface area of respective surfaces 509 are selected in combination
with the chemistry of the electroplating solution 104 so that the
copper is plated under conditions in which a ratio of a cathode
current density at the respective surfaces 509 to an anode current
density at the anode 106 is at least about 20.
[0043] The geometry of the bumps 510 may be selectively controlled
by the concentration of the accelerator agent and the at least one
acid (e.g., sulfuric acid) in the electroplating solution 104. In
an embodiment, the electroplating solution 104 may include an
accelerator agent concentration between about 10 to about 120 parts
per million ("ppm"). The bumps 510 exhibit hemispherical-type
geometry (i.e., convexly curved) at high accelerator agent
concentrations, a dimpled geometry at low accelerator agent
concentrations, and a substantially planar upper surface (shown in
FIGS. 5D and 5E) at accelerator agent concentrations in between 10
ppm and 120 ppm. For example, for a given accelerator agent
concentration, a sulfuric acid concentration of 60 g/L in the
electroplating solution 104 may result in generally flat bumps 510,
while a sulfuric acid concentration of about 30 g/L may result in
dimpled bumps 510.
[0044] Referring to FIG. 5E, the mask layer 506 may be stripped
using a suitable solvent and exposed portions of the seed layer 504
may be removed by etching.
Embodiments of Methods for Conditioning a Consumable Copper
Anode
[0045] Referring to again FIG. 1, in another embodiment of the
invention, the anode 106 may be a consumable copper-containing
anode having a surface area of about two times or more than that of
the surface 112 of the substrate 110 being electroplated. For
example, the anode 106 may be configured as a generally flat plate
comprised of copper and having a surface area of about two times or
more than that of the surface 112 of the substrate 110 being
electroplated. Unlike the above-described embodiments, in this
embodiment, the copper film 120 is not electroplated onto the
surface 112 under conditions in which a ratio of a cathode current
density at the surface to an anode current density at the anode is
at least about 20. In this embodiment, the anode 106 is treated to
form a porous anodic film (not shown) that promotes the formation
of a more uniform electrical double layer adjacent to it during the
electroplating of the copper film 120. That is, the porous anodic
film of the anode 106 enables utilizing a high current density
(e.g., about 400 mA/cm.sup.2) at the anode 106 while still
maintaining a relatively uniform electrical double layer in the
electroplating solution 104 adjacent it despite the anode 106
having a generally flat configuration.
[0046] The porous anodic film formed on the anode 106 may comprise
copper oxide, copper chloride, copper phosphide, or combinations of
the foregoing depending upon the chemistry of the electroplating
solution 104. Because the porous anodic film is porous, copper from
the anode 106 may still oxidize during the electroplating process
and dissolve into the electroplating solution 104, and plate onto
the surface 112 of the substrate 110.
[0047] In practice, the porous anodic film may be formed on the
copper anode 106 by passing a charge of about 1000 coulombs per
liter of electroplating solution 104 ("C/L") or more through the
electroplating solution 104 of the electrochemical cell 115 using a
conditioning cathode instead of using the surface 112 of the
substrate 110 as the cathode as depicted in FIG. 1. For example,
the conditioning cathode may be formed from a material that is
relatively chemically inert in the electroplating solution 104. A
charge of about 1000 C/L or more may be generated by applying a
selected voltage waveform, using the power source 114, between the
surface 112 to be electroplated and the anode 106 so that a current
is passed through the electrochemical cell 115 for a time
sufficient to pass 1000 C/L through the electroplating solution 104
and form the porous anodic film.
[0048] After forming the porous anodic film on the anode 106, the
conditioning cathode may be removed and replaced with the surface
112 of the substrate 110 to be electroplated. That is, the surface
112 of the substrate 110 functions as the cathode. Then, a copper
film 120 may be electroplated onto the surface 112, as previously
described, by applying a selected voltage between the surface 112
and the anode 106 having the porous anodic film formed thereon as a
result of the conditioning process. For example, any of the
previously described compositions for the electroplating solution
104 may be used. Furthermore, the substrate 110 may be moved (e.g.,
rotated, linearly oscillated, or both) during electroplating.
[0049] In an embodiment of the invention, the conditioning process
for forming the porous anodic film on the anode 106 may be
performed in a separate conditioning electrochemical cell including
the anode 106, electroplating solution 104, and the conditioning
cathode. Then, the conditioned anode 106 having the porous anodic
film formed thereon may be removed from the conditioning
electrochemical cell used in a separate electroplating
electrochemical cell, such as the electrochemical cell 115 shown in
FIG. 1, for electroplating the copper film 120.
[0050] Utilizing the disclosed electroplating methods in which the
anode 106 has been conditioned, the copper film 120 may be
electroplated onto the surface 112 of the substrate 110 at a
high-deposition rate, such as about 6 .mu.m per minute or more and,
more particularly, about 9 .mu.m per minute. Additionally, the
electroplated copper film 120 may be substantially free of
dendrites and exhibit a high-degree of (111) crystallographic
texture that is more resistant to stress-induced voiding than other
crystallographic textures.
[0051] The disclosed methods may be used for electroplating a
high-quality copper film at a high-deposition rate to form many
different types of electrically conductive structures other than
copper bumps or pillars. For example, copper electroplated
according to methods disclosed herein may be used to form
interconnects for ICs using a Damascene process. Copper
electroplated according to methods disclosed herein may also be
used to form through-substrate interconnects or other metallization
structures in ICs and other electronic devices. Moreover, copper
electroplated according to methods disclosed herein may also be
used to form electrical contacts for solar cells.
[0052] The foregoing, non-limiting, list of applications merely
provides some examples of uses of copper electroplated according to
the embodiments of methods disclosed herein.
WORKING EXAMPLES
[0053] The following working examples set forth methods for
electroplating copper bumps and a method for synthesizing an
accelerator agent composed of 3,3'-Dithio-1,1'-propanedisulfonic
acid that is substantially free of alkali elements. Examples 1 and
2 are working examples of methods for electroplating copper bumps
at a cathode current density to anode current density ratio of
greater than 20. Example 3 is a working example of a method for
electroplating copper bumps using a flat copper anode that has been
conditioned. Example 4 is a working example of a method for forming
an accelerator agent of 3,3'-Dithio-1,1'-propanedisulfonic acid
that is substantially free of alkali elements. The following
working examples provide further detail in connection with the
specific embodiments described above.
Example 1
[0054] A 20 nm thick titanium adhesion layer was deposited onto a
surface of a single-crystal silicon wafer, followed by depositing a
100 nm thick copper seed layer onto the adhesion layer. The
titanium adhesion layer and copper seed layer were each deposited
using PVD. A photoresist was applied to the seed layer and
photolithographically patterned to form a mask layer having a
plurality of openings therein that exposed portions of the seed
layer. An electrochemical cell was formed by immersing the silicon
wafer including the mask layer in an electroplating solution with
an anode. The anode of the electrochemical cell was made from a
grooved copper anode. The electroplating solution had a composition
of 60 g/L of copper, 60 g/L of sulfuric acid, and 50 mg/L
hydrochloric acid. The electroplating solution further included the
following additives: 2 mL/L of eMAT.TM. accelerator/brightener
RB10, 20 mL/L of eMAT.TM. suppressor RS14, and 5 mL/L of eMAT.TM.
leveler RL6.
[0055] Copper was electroplated into the plurality of openings of
the mask layer and onto the exposed, respective surfaces of the
seed layer by applying a voltage between the anode and the silicon
wafer to impress a cathodic direct current density of about 300
mA/cm.sup.2 to form a plurality of bumps. The ratio of the current
density at the cathode to the current density at the anode was
about 40. The copper was deposited at a rate of about 6 .mu.m per
minute. Examination of the electroplated copper bumps using a
scanning electron microscope showed that the copper bumps were
generally dendrite free, had relatively planar upper surfaces, and
exhibited a surface roughness of less than 20 nm. X-ray diffraction
also showed that the copper bumps had a strong (111)
crystallographic texture.
Example 2
[0056] A 20 nm thick Ti adhesion layer was deposited onto a surface
of a single-crystal silicon wafer, followed by depositing a 100 nm
thick copper seed layer onto the adhesion layer. The titanium
adhesion layer and copper seed layer were each deposited using PVD.
A photoresist was applied to the seed layer and
photolithographically patterned to form a mask layer having a
plurality of openings therein that exposed portions of the seed
layer. An electrochemical cell was formed by immersing the silicon
wafer including the mask layer in an electroplating solution with
an anode. The anode of the electrochemical cell was made from a
grooved copper anode. The electroplating solution had a composition
of 60 g/L of copper, 60 g/L of sulfuric acid, and 50 mg/L of
hydrochloric acid. The electroplating solution further included the
following additives: 2 mL/L of eMAT.TM. accelerator/brightener
RB10, 20 mL/L of eMAT.TM. suppressor RS14, and 5 mL/L of eMAT.TM.
leveler RL6.
[0057] Copper was electroplated into the plurality of openings of
the mask layer and onto the exposed, respective surfaces of the
seed layer by applying a voltage between the anode and the silicon
wafer to impress a cathodic direct current density of about 700
mA/cm.sup.2 to form a plurality of bumps. The ratio of the current
density at the cathode to the current density at the anode was
about 60. The copper was deposited at a rate of about 11 .mu.m per
minute.
[0058] Examination of the electroplated copper bumps using a
scanning electron microscope showed that the copper bumps were
generally dendrite free, had relatively planar upper surfaces, and
exhibited a surface roughness of less than 20 nm. X-ray diffraction
also showed that the copper bumps had a strong (111)
crystallographic texture.
Example 3
[0059] A 20 nm thick titanium-tungsten alloy adhesion layer was
deposited onto a surface of a single-crystal silicon wafer,
followed by depositing a 100 nm thick copper seed layer onto the
adhesion layer. The titanium-tungsten alloy adhesion layer and
copper seed layer were each deposited using PVD. A photoresist was
applied to the seed layer and photolithographically patterned to
form a mask layer having a plurality of openings therein that
exposed portions of the seed layer. An electrochemical cell was
formed by immersing the silicon wafer including the mask layer in
an electroplating solution with an anode. The anode of the
electrochemical cell was made from a piece of flat copper. The
electroplating solution had a composition of 60 g/L of copper, 60
g/L of sulfuric acid, and 50 mg/L of hydrochloric acid. The
electroplating solution further included the following additives: 2
mL/L of eMAT.TM. accelerator/brightener RB10, 20 mL/L of eMAT.TM.
suppressor RS14, and 5 mL/L of eMAT.TM. leveler RL6. The copper
anode was conditioned in the electroplating solution by passing a
charge of about 5000 C/L through the electroplating solution by
impressing a direct current density of 400 mA/cm.sup.2 at the
copper anode.
[0060] Copper was electroplated into the plurality of openings of
the mask layer and onto the exposed, respective surfaces of the
seed layer by applying a voltage between the anode and the silicon
wafer to impress a cathodic direct current density of about 200
mA/cm.sup.2 to form a plurality of bumps. The ratio of the current
density at the cathode to the current density at the anode was
about 4. The copper was deposited at a rate of 7 .mu.m per minute.
Examination of the electroplated copper bumps using a scanning
electron microscope showed that the copper bumps were generally
dendrite free, had relatively planar upper surfaces, and exhibited
a surface roughness of less than 20 nm. X-ray diffraction also
showed that the copper bumps had a strong (111) crystallographic
texture.
Example 4
[0061] Thiourea was reacted with the 1,3-propane sultone to form
S-thiuronium alkane sulfonate. The S-thiuronium alkane sulfonate
so-formed was reacted with an aqueous solution of ammonia to
produce guanidinium 3-mercapto-alkanesulfonate. The quanidinium
3-mercapto-alkanesulfonate so-formed was passed through a cationic
ion exchange resin so that quanidinium ions were replaced by
hydrogen ions to form 3-mercapto-1-propanesulfonic acid. Then, the
3-mercapto-1-propanesulfonic acid so-formed was dissolved in water
in an amount to form a 10 percent by mass solution. Diethylamine in
an amount of about 0.25 g/mol was added to the solution. The
mixture was heated to reflux and, while being mixed by stirring,
about 0.05 g/mol of powdered sulfur was added to the mixture. Then,
the mixture was refluxed for about 8 to 10 hours until the reaction
was completed and bis(diethylammonium)
3,3'-dithio-1,1'-dipropanedisulfonate was formed. The water was
evaporated in vacuum. The bis(diethylammonium)
3,3'-dithio-1,1'-dipropanedisulfonate so-formed was a brown viscous
syrup.
[0062] The bis(diethylammonium)
3,3'-dithio-1,1-dipropanedisulfonate was dissolved in water to
obtain a 10 percent by mass solution. This solution was passed
through an ion exchange resin of Amberlite IR-120 ion exchange
resin operating in its acid cycle. After washing the ion exchange
resin with water until the pH of the effluate was about 5 to about
6, the aqueous effluates were combined and evaporated in vacuum
until all the water was removed from the reaction product and
3,3'-Dithio-1,1'-propanedisulfonic acid was obtained having a
light-brown viscous syrup.
[0063] From the foregoing it will be appreciated that, although
specific embodiments of the invention have been described herein
for purposes of illustration, various modifications may be made
without deviating from the spirit and scope of the invention.
* * * * *