U.S. patent application number 11/890997 was filed with the patent office on 2009-02-12 for electroplating aqueous solution and method of making and using same.
This patent application is currently assigned to eMAT TECHNOLOGY, LLC.. Invention is credited to James D. Blanchard, Valery M. Dubin, Yingxiang Tao, Xingling Xu.
Application Number | 20090038947 11/890997 |
Document ID | / |
Family ID | 40341973 |
Filed Date | 2009-02-12 |
United States Patent
Application |
20090038947 |
Kind Code |
A1 |
Dubin; Valery M. ; et
al. |
February 12, 2009 |
Electroplating aqueous solution and method of making and using
same
Abstract
In one embodiment of the invention, an electroplating aqueous
solution is disclosed. The electroplating aqueous solution includes
at least two acids, copper, at least one accelerator agent, and at
least two suppressor agents. The at least one accelerator agent
provides an acceleration strength of at least about 2.0 and the at
least two suppressor agents, collectively, provide a suppression
strength of at least about 5.0. Methods of making and using such an
electroplating aqueous solution are also disclosed.
Inventors: |
Dubin; Valery M.; (Portland,
OR) ; Tao; Yingxiang; (Moses Lake, WA) ; Xu;
Xingling; (Moses Lake, WA) ; Blanchard; James D.;
(Soap Lake, WA) |
Correspondence
Address: |
GRAYBEAL JACKSON LLP
155 - 108TH AVENUE NE, SUITE 350
BELLEVUE
WA
98004-5973
US
|
Assignee: |
eMAT TECHNOLOGY, LLC.
|
Family ID: |
40341973 |
Appl. No.: |
11/890997 |
Filed: |
August 7, 2007 |
Current U.S.
Class: |
205/101 ;
205/210; 205/291; 205/297; 205/80 |
Current CPC
Class: |
C25D 5/00 20130101; C25D
21/02 20130101; C25D 3/38 20130101 |
Class at
Publication: |
205/101 ;
205/210; 205/291; 205/297; 205/80 |
International
Class: |
C25D 21/18 20060101
C25D021/18; C25D 3/38 20060101 C25D003/38; C25D 5/34 20060101
C25D005/34 |
Claims
1. An electroplating aqueous solution, comprising: at least two
acids; copper; at least one accelerator agent that provides an
acceleration strength of at least about 2.0; and at least two
suppressor agents that collectively provide a suppression strength
of at least about 5.0.
2. The electroplating aqueous solution of claim 1 wherein the at
least two acids comprise one or more of the following acids:
sulfuric acid; hydrochloric acid; hydroiodic acid; hydroboric acid;
and fluoroboric acid.
3. The electroplating aqueous solution of claim 1 wherein the at
least two acids comprise: sulfuric acid present in a concentration
from about 5 grams per liter to about 20 grams per liter; and
hydrochloric acid present in a concentration from about 20
milligrams per liter to about 100 milligrams per liter.
4. The electroplating aqueous solution of claim 1 wherein the
copper is present in a concentration from about 50 grams per liter
to about 100 grams per liter.
5. The electroplating aqueous solution of claim 1 wherein the
concentration is at least about 85 grams per liter.
6. The electroplating aqueous solution of claim 1 wherein the at
least one accelerator agent comprises at least one of: a sulfide
compound; a selenium-containing anion; and a tellurium-containing
anion.
7. The electroplating aqueous solution of claim 1 wherein the at
least two suppressor agents comprise one or more of the following
suppressor agents: a surfactant; a chelating agent; a leveler
agent; and a wetting agent.
8. The electroplating aqueous solution of claim 1 wherein the at
least two suppressor agents comprise one or more of the following
suppressor agents: a quaternized polyamine; a polyacrylamide; a
cross-linked polyamide; a phenazine azo-dye; an alkoxylated amine
surfactant; a polyether surfactant; a non-ionic surfactant; a
cationic surfactant; an anionic surfactant; a block copolymer
surfactant; polyacrylic acid; a polyamines; aminocarboxylic acid;
hydrocarboxylic acid; citric acid; entprol; edetic acid; and
tartaric acid.
9. The electroplating aqueous solution of claim 1 wherein: the at
least one accelerator agent is present in a concentration from
about 10 milligrams per liter to about 1000 milligrams per liter;
and the at least two suppressor agents are collectively present in
a concentration from about 10 milligrams per liter to about 1000
milligrams per liter.
10. The electroplating aqueous solution of claim 1 wherein: the at
least two acids are, collectively, present in a concentration from
about 5 grams per liter to about 20 grams per liter; and the copper
is present in a concentration from about 50 grams per liter to
about 100 grams per liter.
11. A method of electroplating, comprising: immersing a substrate
in an electroplating aqueous solution, the electroplating aqueous
solution comprising: at least two acids; copper; at least one
accelerator agent that provides an acceleration strength of at
least about 2.0; and at least two suppressor agents that
collectively provide a suppression strength of at least about 5.0;
and electroplating at least a portion of the copper from the
electroplating aqueous solution onto the substrate.
12. The method of claim 11, further comprising linearly oscillating
the substrate in the electroplating aqueous solution during the act
of electroplating.
13. The method of claim 12 wherein linearly oscillating the
substrate in the electroplating aqueous solution comprises:
linearly oscillating the substrate in the bath at a rate of about
10 millimeters per second to about 1000 millimeters per second.
14. The method of claim 11, further comprising rotating the
substrate in the electroplating aqueous solution during the act of
electroplating.
15. The method of claim 14 wherein rotating the substrate in the
electroplating aqueous solution comprises: rotating the substrate
in the electroplating aqueous solution at a rate of about 150
revolutions per minute to about 300 revolutions per minute.
16. The method of claim 14: wherein the substrate comprises a
surface to be electroplated with the copper; and further comprising
orienting the surface in an upwardly facing direction or downwardly
facing direction.
17. The method of claim 14: wherein the substrate comprises a
surface to be electroplated with the copper; further comprising
moving the substrate in a manner that maintains the surface
substantially parallel to a longitudinal axis of an anode immersed
in the electroplating aqueous solution.
18. The method of claim 11 wherein electroplating at least a
portion of the copper from the electroplating aqueous solution onto
the substrate comprises: depositing the copper on the substrate as
a substantially dendrite-free film at a deposition rate of at least
10 micrometers per minute.
19. The method of claim 11, further comprising adding additional
copper to the electroplating aqueous solution provided from a
consumable anode immersed in the electroplating aqueous
solution.
20. The method of claim 11, further comprising replenishing the
electroplating aqueous solution with additional copper introduced
into the electroplating aqueous solution.
21. The method of claim 11, further comprising: prior to immersing
the substrate in the electroplating aqueous solution, cleaning the
substrate in a cleaning solution that includes at least one
suppressor agent having the same composition as one of the at least
two suppressor agents of the electroplating aqueous solution.
22. The method of claim 11, further comprising maintaining the
electroplating aqueous solution at a temperature between about
20.degree. Celsius to about 60.degree. Celsius.
23. The method of claim 11: wherein the substrate comprises a
surface to be electroplated with the copper; and further comprising
spacing the surface a distance of about 0.1 centimeter to about 10
centimeter from an anode immersed in the electroplating aqueous
solution.
24. The method of claim 11 wherein the at least two acids of the
electroplating aqueous solution comprise one or more of the
following acids: sulfuric acid; hydrochloric acid; hydroiodic acid;
hydroboric acid; and fluoroboric acid.
25. The method of claim 11 wherein the at least two acids of the
electroplating aqueous solution comprise: sulfuric acid present in
a concentration from about 5 grams per liter to about 20 grams per
liter; and hydrochloric acid present in a concentration from about
20 milligrams per liter to about 100 milligrams per liter.
26. The method of claim 11 wherein the copper of the electroplating
aqueous solution is present in a concentration from about 50 grams
per-liter to about 100 grams per liter.
27. The method of claim 11 wherein the at least one accelerator
agent of the electroplating aqueous solution comprises at least one
of: a sulfide compound; a selenium-containing anion; and a
tellurium-containing anion.
28. The method of claim 11 wherein the at least two suppressor
agents of the electroplating aqueous solution comprise one or more
of the following suppressor agents: a surfactant; a chelating
agent; a leveler agent; and a wetting agent.
29. The method of claim 11 wherein the at least two suppressor
agents of the electroplating aqueous solution comprise one or more
of the following suppressor agents: a quaternized polyamine; a
polyacrylamide; a cross-linked polyamide; a phenazine azo-dye; an
alkoxylated amine surfactant; a polyether surfactant; a non-ionic
surfactant; a cationic surfactant; an anionic surfactant; a block
copolymer surfactant; polyacrylic acid; a polyamines;
aminocarboxylic acid; hydrocarboxylic acid; citric acid; entprol;
edetic acid; and tartaric acid.
30. The method of claim 11 wherein: the at least one accelerator
agent is present in a concentration from about 10 milligrams per
liter to about 1000 milligrams per liter; and the at least two
suppressor agents are collectively present in a concentration from
about 10 milligrams per liter to about 1000 milligrams per
liter.
31. The method of claim 11 wherein: the at least two acids of the
electroplating aqueous solution are, collectively, present in a
concentration from about 5 grams per liter to about 20 grams per
liter; and the copper of the electroplating aqueous solution is
present in a concentration from about 50 grams per liter to about
100 grams per liter.
32. A method of making an electroplating aqueous solution,
comprising: maintaining an electroplating aqueous solution at a
first temperature, the electroplating aqueous solution including:
at least two acids; copper present in a concentration below a
copper solubility limit, at the first temperature, of the at least
two acids; heating the electroplating aqueous solution to a second
temperature that is greater than the first temperature; and
introducing additional copper from a copper source to the
electroplating aqueous solution when the electroplating aqueous
solution is at the second temperature so that the electroplating
aqueous solution exhibits a copper concentration of at least about
50 grams per liter.
33. The method of claim 32 wherein introducing additional copper
from a copper source comprises: introducing additional copper in a
concentration that is less than a copper solubility limit of the at
least two acids at the electroplating temperature.
34. The method of claim 32 wherein introducing additional copper
comprises: introducing the additional copper into the
electroplating aqueous solution in an amount so that the copper
concentration is about 50 grams per liter to about 100 grams per
liter at the second temperature.
35. The method of claim 32 wherein introducing additional copper
from a copper source comprises: introducing the additional copper
into the electroplating aqueous solution in an amount so that the
copper concentration is about 85 grams per liter or more at the
second temperature.
36. The method of claim 32 wherein the copper source comprises at
least one of: a copper salt; copper oxide; and copper
hydroxide.
37. The method of claim 31 wherein the electroplating aqueous
solution comprises at least one accelerator agent that provides an
acceleration strength of at least about 2.0 and at least two
suppressor agents that collectively provides a suppression strength
of at least about 5.0.
Description
TECHNICAL FIELD
[0001] Embodiments of the invention relate to an electroplating
aqueous solution for electroplating copper, a method of making such
an electroplating aqueous solution, and a method of electroplating
copper onto a substrate.
BACKGROUND
[0002] 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.
[0003] Interconnects in an IC 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.
[0004] 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.
[0005] 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 aqueous solution that includes
copper. The substrate functions as a cathode of an electrochemical
cell in which the electroplating aqueous solution functions as an
electrolyte, and the copper from the electroplating aqueous
solution is electroplated in 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").
[0006] 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 aqueous
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 aqueous solutions be capable of depositing copper in
a uniform manner (i.e., high throwing power) and at a
high-deposition rate.
[0007] A number of electroplating aqueous solutions are currently
available for electroplating copper. For example, sulfate-based
electroplating aqueous solutions are commonly used for
electroplating copper. Some alkaline copper electroplating aqueous
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 aqueous solutions can diffuse into silicon
substrates and are deep-level impurities in silicon that can
compromise transistor performance. Fluoroborate electroplating
aqueous solutions can be used for high-speed deposition of copper.
However, fluoroborate electroplating aqueous solutions can be more
expensive than, more traditional, sulfate-based solutions.
Moreover, fluoroborate electroplating aqueous solutions may be more
hazardous and difficult to dispose of than many other
electroplating aqueous solutions for electroplating copper.
[0008] Therefore, there is still a need for an electroplating
aqueous solution for electroplating copper that can deposit a
high-quality film of copper at a high-speed.
SUMMARY
[0009] In one embodiment of the invention, an electroplating
aqueous solution is disclosed. The electroplating aqueous solution
includes at least two acids, copper, at least one accelerator
agent, and at least two suppressor agents. The at least one
accelerator agent provides an acceleration strength of at least
about 2.0 and the at least two suppressor agents, collectively,
provide a suppression strength of at least about 5.0.
[0010] In another embodiment of the invention, a method of
electroplating is disclosed. A substrate is immersed in an
electroplating aqueous solution. The electroplating aqueous
solution includes at least two acids, copper, at least one
accelerator agent, and at least two suppressor agents. The at least
one accelerator agent provides an acceleration strength of at least
about 2.0 and the at least two suppressor agents, collectively,
provide a suppression strength of at least about 5.0. At least a
portion of the copper from the electroplating aqueous solution is
electroplated onto the substrate.
[0011] In yet another embodiment of the invention, a method of
making an electroplating aqueous solution is disclosed. An
electroplating aqueous solution maintained at a first temperature
may be provided. The electroplating aqueous solution includes at
least two acids and copper present in a concentration below a
copper solubility limit, at the first temperature, of the at least
two acids. The electroplating aqueous solution is heated to a
second temperature that is greater than the first temperature.
Additional copper from a copper source is introduced into the
electroplating aqueous solution when the electroplating aqueous
solution is at the second temperature so that the electroplating
aqueous solution exhibits a copper concentration of at least about
50 grams per liter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The drawings illustrate various embodiments of the
invention, wherein like reference numerals refer to like elements
or features in different views or embodiments shown in the
drawings.
[0013] FIGS. 1A and 1B are schematic cross-sectional views of an
electroplating system that may be used for practicing embodiments
for electroplating copper onto a substrate according to various
methods of the invention.
[0014] FIG. 2 is graph illustrating an example of a forward-pulse
current density waveform that may be used to electroplate copper
from any of the disclosed electroplating aqueous solutions.
[0015] FIG. 3 is graph illustrating an example of a reverse-pulse
current density waveform that may be used to electroplate copper
from any of the disclosed electroplating aqueous solutions.
DETAILED DESCRIPTION
[0016] Embodiments of the invention are directed to electroplating
aqueous solutions for electroplating copper, methods of making such
electroplating aqueous solutions, and methods of electroplating
copper onto a substrate using such electroplating aqueous
solutions. The disclosed electroplating aqueous solutions may be
used for electroplating copper onto a substrate as a film that is
substantially-free of dendrites and at a high-deposition rate
(e.g., about 10 .mu.m per minute or more) for forming electrical
interconnects used in ICs, solar cells, and many other
applications.
[0017] According to various embodiments of the invention, an
electroplating aqueous solution includes at least two acids, copper
in the form of cupric ions (Cu.sup.2+), at least one accelerator
agent that provides an acceleration strength of at least about 2.0,
and at least two suppressor agents that collectively provide a
suppression strength of at least about 5.0. The at least two acids
and the copper collectively form an electrolyte. The at least two
acids may be selected from two or more of the following acids:
sulfuric 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 two acids includes
sulfuric acid present in a concentration from about 5 grams per
liter ("g/L") to about 20 g/L and hydrochloric acid present in a
concentration from about 20 mg/L to about 100 mg/L. In addition to
the aforementioned at least two acids, in certain embodiments of
the invention, the electroplating aqueous solution may further
include a supplemental acid selected to increase the solubility of
the copper in the at least two acids of the electroplating aqueous
solution. 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 two acids of the
electroplating aqueous solution.
[0018] The copper may be present in the electroplating aqueous
solution 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 85 g/L to about 100 g/L.
[0019] As discussed above, the electroplating aqueous solution
includes additives, such as suppressor and accelerator agents that
improve certain electroplating characteristics of the
electroplating aqueous solution. As used throughout this disclosure
and claims, the phrase "virgin make solution" ("VMS") refers to an
electroplating aqueous solution without any suppressor agents and
accelerator agents. For the electroplating aqueous solution
embodiments described herein, the VMS includes the at least two
acids and the copper dissolved therein. As used throughout this
disclosure and claims, "suppression strength" of one or more
suppressor agents of an electroplating aqueous solution 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 aqueous solution
embodiments described herein, a suppressed solution includes the at
least two acids, the copper, and the at least two suppressor
agents. 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.
[0020] As used throughout this disclosure and claims, "acceleration
strength" of one or more accelerator agents of an electroplating
aqueous solution 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 aqueous solution embodiments described herein,
an accelerated solution includes the at least two acids, the
copper, 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 acceleration strength of
2.0.
[0021] The at least one accelerator agent of the electroplating
aqueous solution is formulated to increase the deposition rate of
copper onto a substrate and present in the electroplating aqueous
solution 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 and other qualities, such as decreasing void concentration in
the electroplated copper film. The at least bne accelerator agent
may be present in the electroplating aqueous solution in
concentration from about 10 mg/L to about 1000 mg/L. According to
various embodiments of the invention, 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,
acetylthiourea, 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
aqueous solution, decrease hydrogen evolution that can increase the
porosity in the electroplated copper film, 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.
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 aqueous solutions having an
accelerator agent that is substantially free of alkali elements
will also be substantially-free of alkali elements.
[0022] The at least two suppressor agents of the electroplating
aqueous solution are formulated to substantially suppress formation
of dendrites during electroplating copper from the electroplating
aqueous solution and improve other qualities of an electroplated
copper film, such as surface roughness, ductility, brightness, and
electrical conductivity. The at least two suppressor agents may be,
collectively, present in the electroplating aqueous solution in
concentration from about 10 mg/L to about 1000 mg/L. Together, the
at least two suppressor agents are present in the electroplating
aqueous solution in an amount sufficient to provide a suppression
strength of at least about 5.0. The suppressor agents 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 two suppressor agents may be selected
from two 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.
[0023] The electroplating aqueous solutions may be manufactured
according to a number of different embodiments. According to one
embodiment of the invention, a container may be provided that
contains an electrolyte including the at least two acids and copper
dissolved in the at least two acids. The electrolyte is maintained
at a first temperature that may be, for example, about room
temperature (e.g., about 20.degree. C.). The copper may be present
in the electrolyte in a concentration that is at or below a
solubility limit, at the first temperature, of the copper in the
electrolyte. For example, the copper may be present in the
electrolyte in a concentration that is at or below 50 g/L. Next,
the electrolyte is heated to a second temperature that is greater
than the first temperature. At the second temperature, the copper
has a higher solubility in the electrolyte. The second temperature
may be a temperature at which a copper electroplating process may
be performed, such as about 50.degree. C. or more.
[0024] Then, additional copper from a copper source is added to the
electrolyte while the electrolyte is maintained at the second
temperature. The copper source may be one or more of the following
copper sources: a copper salt (e.g., copper sulfate), copper oxide,
and copper hydroxide. The amount of the additional copper may be
selected so that the copper concentration in the electrolyte is at
or approaches the copper solubility limit, at the second
temperature, for the electrolyte. For example, the additional
copper may be added to the electrolyte to increase the copper
concentration thereof to about 50 g/L to about 100 g/L. In certain
embodiments of the invention, the additional copper may be added to
the electrolyte so that the copper concentration of the
electrolyte, at the second temperature, is at least about 85 g/L.
The at least one accelerator agent and the at least two suppressor
agents may be mixed with the electrolyte prior to heating the
electrolyte to the second temperature or after adding the
additional copper.
[0025] When precipitation of copper is not a concern, the
electroplating aqueous solution may be formulated merely by mixing
the selected at least two acids, copper salt, at least one
accelerator agent, and the at least two suppression agents. For
example, when the fluoroboric acid comprises one of the at least
two acids, the solubility of copper therein is sufficiently high at
room temperature so that additional copper does not need to be
added at a higher temperature to increase the copper concentration
to a desired level.
[0026] FIG. 1A is a schematic cross-sectional view of an
electroplating system 100 that may be used for practicing
embodiments for electroplating copper onto a substrate according to
various methods of the invention. The electroplating system 100 may
include a number of linearly spaced and isolated containers.
However, in other configurations, the containers may be radially
spaced and isolated from each other. For example, the
electroplating system 100 may include a cleaning container 101
holding a cleaning solution 102, a rinse container 103 holding a
rinsing solution 104 (e.g., water), an electroplating container 105
holding an electroplating aqueous solution 106 that may be any of
the previously described embodiments of electroplating aqueous
solutions, a post-plating cleaning container 107 holding a
post-plating cleaning solution 108, and a drying container 109 for
drying a plated substrate after cleaning in the post-plating
cleaning container 107. For example, the cleaning solution 102 may
include one or more suppressor agents. In one embodiment of the
invention, the one or more suppressor agents of the cleaning
solution 102 may have the same composition of one of the suppressor
agents used in the electroplating aqueous solution 106. The drying
container 109 may hold a drying solution 110 (e.g., isopropyl
alcohol ("IPA") in water or other drying solution) to effect
removal any post-plating cleaning solution 108 on the substrate or
the substrate may be spin dried. Although not shown, external
heaters may maintain the temperature of the electroplating aqueous
solution 106 disposed within the electroplating container 105 at a
selected electroplating temperature, such as between about
20.degree. C. to about 60.degree. C.
[0027] The electroplating system 100 further includes an actuator
system 111 that is operably coupled to a substrate holder 112 via a
movable arm 114. The actuator system 111 is operable to
controllably and selectively move the substrate holder 112 upwardly
and downwardly in vertical directions V.sub.1 and V.sub.2 and
horizontally in horizontal directions H.sub.1 and H.sub.2. The
substrate holder 112 is configured to hold a substrate 116 having a
surface 117 on which a copper film 119 is electroplated and further
includes provisions, such as electrical contact pins, that
electrically contact the substrate 116. It should be emphasized
that any suitable substrate holder 114 may be used. Although only a
single substrate is illustrated in FIG. 1A for simplicity, many
commercially available substrate holders are configured to hold
multiple substrates. Additionally, 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, printed circuit boards, flexible polymeric
substrates, and many other types of substrates. Additionally, a
variety of different fluid supply systems may be employed to supply
the various fluids in the containers 101, 103, 105, 107, and 109
and, optionally, to re-circulate the electroplating aqueous
solution 106 to provide a generally laminar flow of the
electroplating aqueous solution 106 over the substrate 116. Such
fluid supply systems and container configurations are well-known
and in the interest of brevity are not described in detail herein.
Referring to FIG. 1B, in other configurations, the substrate holder
112 may be positioned so that the surface 117 of the substrate 116
is oriented in a downward direction (as shown) or an upward
direction, and the actuator system 111 is operable to rotate the
substrate holder 112 and substrate 116 in a direction R.
[0028] The electroplating system 100 further includes a voltage
source 118 that is electrically connected to the substrate holder
112 (i.e., the cathode) and consequently, the substrate 116. The
voltage source 118 is further electrically connected to an anode
120 immersed in the electroplating aqueous solution 106 of the
electroplating bath 105. The anode 120 may be spaced a distance S
from the surface 117 of the substrate 116. For example, the
distance S may be about 0.1 centimeters ("cm") to about 10 cm and,
more specifically about 1 cm. The voltage source 118 is operable to
apply a selected voltage between the substrate 116 and the anode
120.
[0029] Various embodiments of methods of the invention for
electroplating copper onto the substrate 116 will now be discussed
below in more detail in conjunction with FIGS. 1A and 1B. In
practice, the actuator system 111 may immerse the substrate holder
112 carrying the substrate 116 into the cleaning solution 102,
followed by immersing the substrate holder 112 carrying the
substrate 116 into the rinsing solution 104. Next, the actuator
system 111 may immerse the substrate holder 112 carrying the
substrate 116 into the electroplating aqueous solution 106. While
the substrate 116 immersed in the electroplating aqueous solution
106, the voltage source 118 may apply a voltage between the
substrate 116 and the anode 120 to cause copper from the
electroplating aqueous solution 106 to plate onto surface 117 of
the substrate 116 to form the copper film 119.
[0030] While the substrate 116 is immersed in the electroplating
aqueous solution 106 and copper is being electroplated onto the
surface 117 of the substrate 116, the actuator system 111 may move
the substrate holder 112 and the substrate 116 in a linear
oscillatory manner in the directions V.sub.1 and V.sub.2. For
example, the substrate 116 may be linearly oscillated at a rate of
about 10 millimeters per second ("mm/s") to about 1000 mm/s and
with a stroke length of about 600 mm. In one embodiment of the
invention, when the substrate 116 has a diameter of about 300 mm,
the substrate 116 is linearly oscillated at a frequency of about
100 strokes/min. In some embodiments of the invention, the stroke
length may be equal to or greater than dimension D of surface 117
to be electroplated.
[0031] With reference to FIG. 1B, in another embodiment of the
invention, the substrate holder 116 and substrate 112 may be
rotated in the direction R as a unit while the surface 117 of the
substrate 116 is maintained generally parallel to a longitudinal
axis of the anode 120. For example, the substrate holder 116 and
substrate 112 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 112 and substrate 116 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
112 enables increasing the limiting current density at the
substrate 116 that is limited by diffusion of cupric ions within
the electroplating aqueous solution 106 to the surface 117 of the
substrate 116. Consequently, increasing the current density at the
substrate 116 increases the electroplating deposition rate of the
copper film 119. For example, utilizing any of the above
substrate-movement techniques in combination with the chemistry of
the electroplating aqueous solution 106 enables the voltage source
118 to impose a current density at the substrate 116 of about 200
milliamps per square centimeter ("mA/cm.sup.2") to about 2000
mA/cm.sup.2. At such high current densities, the deposition rate of
copper onto the surface 117 of the substrate 116 may be 10 .mu.m
per minute or more. Furthermore, the deposited copper film 119 may
be substantially dendrite-free despite being deposited at such a
high-deposition rate.
[0032] When the anode 120 is an inert anode, copper can be
continually added to the electroplating aqueous solution 106 to
maintain a generally constant concentration of copper as the copper
film 119 is deposited. When the anode 120 is a consumable copper
anode, copper from the anode 120 may be oxidized and dissolved in
the electroplating aqueous solution 106 to maintain a generally
constant concentration of copper as the copper film 119 is
deposited.
[0033] In certain embodiments of the invention, the voltage source
118 may apply a time-varying voltage to impose a forward-pulse
current density on the substrate 116 to promote forming a finer
grain size in the copper film 119. For example, FIG. 2 shows one
example of a forward-pulse current density waveform 200 that may be
imposed on the substrate 116 by applying a voltage between the
substrate 116 and the anode 120 using the voltage source 118.
Representative current-densities at the substrate 112 (i.e., the
cathode) for the forward-pulse current density waveform 200 may be
about 200 mA/cm.sup.2 to about 2000 mA/cm.sup.2. In other
embodiments of the invention, the voltage source 118 may apply a
time-varying voltage to impose a reverse-pulse current density
waveform on the substrate 116 or a combination of a forward-pulse
and reverse-pulse current density waveform. For example, FIG. 3
shows one example of a forward-pulse/reverse-pulse current density
waveform 300 in which the current density at the substrate 116 may
be periodically reversed. Representative current densities at the
substrate 112 (i.e., the cathode) for the forward pulse of the
forward-pulse/reverse-pulse current density waveform 300 may be
increased to about 10 A/cm.sup.2 with a pulse duration, t, of about
0.1 ms to about 100 ms.
[0034] After electroplating the copper film 119 onto the substrate
116, the actuator system 111 may move and immerse the substrate
holder 112 and substrate 116 into the post-plating cleaning
solution 108 of the post-plating cleaning container 107. Then, the
actuator system 111 may move and immerse the substrate holder 112
and substrate 116 into the drying solution 110 of the drying
container 109.
[0035] The disclosed electroplating aqueous solutions may be used
for electroplating a high-quality copper film at a high-deposition
rate to form many different types of electrically conductive
structures. 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, through-mask plated films, electroplated bumps for
flip-chip type electrical connections, 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. The foregoing,
non-limiting, list of applications merely provides some examples of
uses of copper electroplated according to methods disclosed
herein.
[0036] 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.
* * * * *