U.S. patent application number 14/968662 was filed with the patent office on 2016-04-14 for low copper/high halide electroplating solutions for fill and defect control.
The applicant listed for this patent is Novellus Systems, Inc.. Invention is credited to Erik A. Edelberg, Jonathan David Reid, Jian Zhou.
Application Number | 20160102416 14/968662 |
Document ID | / |
Family ID | 55655057 |
Filed Date | 2016-04-14 |
United States Patent
Application |
20160102416 |
Kind Code |
A1 |
Zhou; Jian ; et al. |
April 14, 2016 |
LOW COPPER/HIGH HALIDE ELECTROPLATING SOLUTIONS FOR FILL AND DEFECT
CONTROL
Abstract
Certain embodiments herein relate to a method of electroplating
copper into damascene features using a low copper, high halide
concentration electrolyte having between about 4-10 g/L copper
ions, between about 150-400 ppm halide ions, and about 2-15 g/L
acid. Using the low copper electrolyte produces a relatively high
overpotential on the plating substrate surface, allowing for a slow
plating process with few fill defects. The low copper electrolyte
may have a relatively high cloud point. The use of a relatively
high halide ion concentration may promote improved nucleation on a
seed layer, resulting in fewer and less significant voids within
the features.
Inventors: |
Zhou; Jian; (West Linn,
OR) ; Reid; Jonathan David; (Sherwood, OR) ;
Edelberg; Erik A.; (Lake Oswego, OR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Novellus Systems, Inc. |
Fremont |
CA |
US |
|
|
Family ID: |
55655057 |
Appl. No.: |
14/968662 |
Filed: |
December 14, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13753333 |
Jan 29, 2013 |
|
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|
14968662 |
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Current U.S.
Class: |
205/123 ;
205/136 |
Current CPC
Class: |
C25D 17/001 20130101;
H01L 21/2885 20130101; C25D 5/02 20130101; C25D 3/38 20130101; C25D
7/123 20130101; C25D 5/48 20130101; C25D 21/12 20130101; H01L
21/76877 20130101; C25D 5/10 20130101; C25D 5/18 20130101 |
International
Class: |
C25D 7/12 20060101
C25D007/12; C25D 5/02 20060101 C25D005/02; C25D 3/38 20060101
C25D003/38 |
Claims
1. A method of plating copper into damascene features, comprising:
receiving a substrate having a seed thickness of about 200
nanometers, on average, or thinner; electrically biasing the
substrate while immersing the substrate in an aqueous low copper
acid-containing electrolyte comprising (i) between about 4-10 grams
per liter copper cations, (ii) between about 150-400 ppm chloride
ions, and (iii) at least one suppressor compound, whereby the
electrolyte induces a cathodic overpotential on the seed sufficient
to protect the seed from dissolution by acid in the electrolyte
during immersion; electroplating copper in a process comprising:
(a) a first plating phase to fill the substrate features with
copper via a bottom-up fill mechanism, wherein a first current
density during the first plating phase is between about 0.5-10
mA/cm.sup.2, and (b) a second plating phase to deposit an
overburden layer of copper on the substrate, wherein a second
current density during the second plating phase is greater than the
first current density, and wherein the first and second plating
phases are part of a single electroplating process; and removing
the substrate from the electrolyte.
2. The method of claim 1, wherein the electrolyte further comprises
about 2-15 grams per liter acid.
3. The method of claim 2, wherein the electrolyte further comprises
about 5-10 grams per liter acid.
4. The method of claim 1, wherein the electrolyte further comprises
about 10-500 ppm active organic additives.
5. The method of claim 4, wherein the active organic additives
comprise one or more accelerator compound.
6. The method of claim 4, wherein the suppressor compound is a
polymeric compound.
7. The method of claim 4, wherein the active organic additives
comprise one or more leveler compound.
8. The method of claim 4, wherein the concentration of accelerator
is less than about 100 Ppm.
9. The method of claim 1, wherein the electrolyte comprises between
about 150-300 ppm chloride ions.
10. The method of claim 1, wherein the electrolyte comprises
between about 200-300 ppm chloride ions.
11. The method of claim 1, wherein the substrate has at least some
features with openings smaller than about 20 nanometers.
12. The method of claim 1, wherein the electrolyte has a cloud
point of about 50.degree. C. or higher, and wherein electroplating
occurs at a temperature that is at least about 20.degree. C. lower
than the cloud point of the electrolyte.
13. The method of claim 1, wherein the second current density is
between about 10 and 15 mA/cm.sup.2.
14. The method of claim 1, wherein the pH of the electrolyte is
between about 0.2 and 2.
15. The method of claim 1, wherein the substrate is a 450 mm
semiconductor wafer.
16. A method of plating copper into damascene features, comprising:
receiving a substrate having a seed thickness of about 200
nanometers, on average, or thinner; electrically biasing the
substrate while immersing the substrate in an aqueous low copper
acid-containing electrolyte comprising (i) between about 4-10 grams
per liter copper ions, (ii) between about 150-400 ppm chloride
ions, (iii) at least one suppressor compound, and (iv) at least one
accelerator compound, during the immersing, electroplating copper
into the features by a bottom-up fill mechanism at a first current
density, wherein electroplating occurs sufficiently slowly in the
electrolyte at the first current density to allow the suppressor
and accelerator to adsorb onto the seed and thereby enable
bottom-up fill during immersion; and removing the substrate from
the electrolyte.
17. The method of claim 16, wherein the first current density is
between about 0.5-10 mA/cm.sup.2.
18. The method of claim 16, wherein electroplating copper into the
features is performed during a first plating phase, and further
comprising a second plating phase comprising electroplating copper
to deposit an overburden layer of copper on the substrate at a
second current density, wherein the second current density is
higher than the first current density.
19. The method of claim 16, wherein the electrolyte further
comprises about 2-15 grams per liter acid.
20. The method of claim 16, wherein the electrolyte between about
4-6 grams per liter copper ions.
21. An electrolyte comprising: between about 1 and 10 grams per
liter copper cations; between about 2 and 15 grams per liter acid;
between about 150-400 ppm chloride ions; one or more suppressor
compound; one or more accelerator compound; and the electrolyte
having a cloud point above 50.degree. C.
22. The electrolyte of claim 21, wherein the acid is sulfuric
acid.
23. The electrolyte of claim 21, wherein the acid is
methanesulfonic acid.
24. The electrolyte of claim 21, wherein the chloride ions are
provided at a concentration between about 150-300 ppm.
25. The electrolyte of claim 21, wherein the copper cations are
provided in a compound that dissociates into cations and anions,
and wherein the anions associated with the copper cations are the
same species as anions formed from the acid.
26. The electrolyte of claim 21, wherein the concentration of
accelerator compound in the electrolyte is less than about 100 ppm.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 13/753,333, filed Jan. 29, 2013, and titled
"LOW COPPER ELECTROPLATING SOLUTIONS FOR FILL AND DEFECT CONTROL,"
which is herein incorporated by reference in its entirety and for
all purposes.
FIELD OF THE INVENTION
[0002] The present disclosure relates generally to copper
electroplating of damascene interconnects, and more specifically,
to a low-copper, low acid electrolyte having a high concentration
of halide ions, and a method for using the electrolyte under
conditions that enhance suppression of copper plating to promote
void-free fill of submicron damascene features.
BACKGROUND
[0003] Electrolytes used in electroplating copper into damascene
interconnects typically contain a copper salt, an acid, halide
ions, an accelerator, a suppressor and a leveler. The copper salt
is the copper source for the deposition. Acid is generally used to
control the conductivity of the plating bath. Halide ions may act
as bridges to assist the adsorption of certain organic additives
(e.g., accelerator, suppressor and/or leveler) onto a substrate
surface to encourage a bottom-up fill mechanism, described
herein.
[0004] Example copper salts include, but are not limited to, copper
sulfate, copper methanesulfonate, copper pyrophosphate, copper
propanesulfonate, etc. As used herein, the concentration of copper
ions reflects the concentration (mass per volume) of copper
cations, and does not include the mass of any anions associated
with the copper cations. Example acids include, but are not limited
to, sulfuric acid and methanesulfonic acid. As used herein, the
concentration of acid reflects the concentration (mass per volume)
of the entire acid molecule, not the mass of hydrogen cations
alone. Example halide ions include, but are not limited to,
chloride, bromide, iodide, and combinations thereof.
[0005] It may be desirable to strongly polarize the substrate in
the cathodic direction, particularly during the initial stages of
electroplating onto a seed layer. Such polarization may protect the
seed layer from dissolution. One way to achieve such polarization
is by providing a strong "suppressor" in the electrolyte.
[0006] FIG. 2 shows a copper wafer 201 plated in an electrolyte
containing a strong suppressor. It is a high molecular weight
suppressor with high ratio of hydrophobic propylene oxide versus
hydrophilic ethylene oxide. The cloud point of the electrolyte is
27.degree. C., and plating occurred at 21.degree. C. The plated
wafer contains visible streaks caused by non-uniform suppressor
adsorption on the wafer due to suppressor agglomeration. The use of
some electrolytes may result in more subtle forms of such defects
that are not detectable by visual inspection, but which are
detectable through common defect metrology such as the AIT, SP1, or
SP2 series of tools from KLA-Tencor of San Jose, Calif.
[0007] Another technique for increasing the polarization of a
substrate is to increase halide ion concentrations or change the
halide ion composition. This technique is further described in U.S.
Pat. No. 8,268,155, incorporated by reference herein. The halide
may affect the suppressing effect of a suppressor or other
additive. However, the increase in overpotential that may be gained
by changing halide ion concentration or composition is limited, and
may not sufficient to provide the conditions needed for a uniform,
reproducible fill of small 10-20 nm features. Further, the
concentration of halide ions should be relatively low in the
electrolyte in order to avoid incorporation of the halides into the
plated films or the formation of center voids due to insufficient
bottom-up fill by over-suppression of copper deposition.
[0008] While conventional electroplating solutions have worked well
for previous generations of damascene interconnect fabrication
processes, new challenges are emerging as smaller features and
thinner seed layers are used. Thus, it has recently been found that
there exists a need for a method of electroplating damascene
interconnects that better protects the seed layer from dissolution
and allows the deposition to occur over a longer timeframe to
achieve a more reproducible, more uniform fill of features.
SUMMARY
[0009] Various embodiments herein relate to methods and apparatus
for electroplating copper into damascene features, as well as
electrolytes for such electroplating processes. In a number of
implementations, a particular electrolyte is used during
electroplating. The electrolyte may be acidic, may have a
relatively low concentration of copper ions, and may have a
relatively high concentration of chloride ions. The electrolyte may
also include organic additives such as suppressor, accelerator,
and/or leveler. The disclosed methods, apparatus, and electrolyte
are particularly useful for filling small (e.g., in some cases
10-20 nm) features using bottom-up fill to produce high quality
plating results.
[0010] In one aspect of the disclosed embodiments, a method of
plating copper into damascene features is provided, the method
including: receiving a substrate having a seed thickness of about
200 nanometers, on average, or thinner; electrically biasing the
substrate while immersing the substrate in an aqueous low copper
acid-containing electrolyte including (i) between about 4-10 grams
per liter copper cations, (ii) between about 150-400 ppm chloride
ions, and (iii) at least one suppressor compound, whereby the
electrolyte induces a cathodic overpotential on the seed sufficient
to protect the seed from dissolution by acid in the electrolyte
during immersion; electroplating copper in a process including: (a)
a first plating phase to fill the substrate features with copper
via a bottom-up fill mechanism, where a first current density
during the first plating phase is between about 0.5-10 mA/cm.sup.2,
and (b) a second plating phase to deposit an overburden layer of
copper on the substrate, where a second current density during the
second plating phase is greater than the first current density, and
where the first and second plating phases are part of a single
electroplating process; and removing the substrate from the
electrolyte.
[0011] As mentioned, the electrolyte may have a particular
composition. In some cases, the electrolyte further includes about
2-15 grams per liter acid, in some cases between about 5-10 grams
per liter acid. The electrolyte may include between about 10-500
ppm active organic additives. In some cases, the active organic
additives include one or more accelerator compound. The
concentration of the accelerator compound may less than about 100
ppm. The suppressor compound may be a polymeric compound. In
certain implementations, the active organic additives include one
or more leveler compound. The concentration of chloride ions may be
between about 150-300 ppm in some cases, for example between about
200-300 ppm. The pH of the electrolyte may be between about
0.2-2.
[0012] As mentioned, the substrate may include relatively small
features that are to be filled with copper. In some embodiments,
the substrate has at least some features with openings smaller than
about 20 nanometers. In some such cases, all of the features on the
substrate may have openings smaller than about 20 nm. The
electroplating may occur at a particular temperature. In certain
embodiments, the electrolyte has a cloud point of about 50.degree.
C. or higher, and electroplating occurs at a temperature that is at
least about 20.degree. C. lower than the cloud point of the
electrolyte. The second current density may be between about 10-15
mA/cm.sup.2 in some embodiments. The substrate may be a 300 mm or
450 mm semiconductor substrate in some cases.
[0013] In a further aspect of the disclosed embodiments, a method
of plating copper into damascene features is provided, the method
including: receiving a substrate having a seed thickness of about
200 nanometers, on average, or thinner; electrically biasing the
substrate while immersing the substrate in an aqueous low copper
acid-containing electrolyte including (i) between about 4-10 grams
per liter copper ions, (ii) between about 150-400 ppm chloride
ions, (iii) at least one suppressor compound, and (iv) at least one
accelerator compound, during the immersing, electroplating copper
into the features by a bottom-up fill mechanism at a first current
density, where electroplating occurs sufficiently slowly in the
electrolyte at the first current density to allow the suppressor
and accelerator to adsorb onto the seed and thereby enable
bottom-up fill during immersion; and removing the substrate from
the electrolyte.
[0014] In certain implementations, the first current density may be
between about 0.5-10 mA/cm.sup.2. Electroplating copper into the
features may be performed during a first plating phase. The method
may also include a second plating phase including electroplating
copper to deposit an overburden layer of copper on the substrate at
a second current density, where the second current density is
higher than the first current density.
[0015] The electrolyte may further include between about 2-15 g/L
acid. In some embodiments, the electrolyte includes between about
4-6 g/L copper, or between about 4-5 g/L copper.
[0016] In another aspect of the disclosed embodiments, an
electrolyte is provided, including: between about 1 and 10 grams
per liter copper cations; between about 2 and 15 grams per liter
acid; between about 150-400 ppm chloride ions; one or more
suppressor compound; one or more accelerator compound; and the
electrolyte having a cloud point above 50.degree. C.
[0017] In some embodiments, the acid is sulfuric acid or
methanesulfonic acid. The chloride ions may be provided at a
concentration between about 150-300 ppm, or between about 200-300
ppm. The copper cations may be provided in a compound that
dissociates into cations and anions, where the anions associated
with the copper cations are the same species as anions formed from
the acid. In various embodiments, the concentration of accelerator
compound in the electrolyte may be about 100 ppm or less.
[0018] These and other features will be described below with
reference to the associated drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 shows 100 nm trenches plated at constant currents
between 1 and 4 Amps, for a fixed amount of charge passed.
[0020] FIG. 2 shows a copper wafer that was plated at 21.degree. C.
in a plating bath containing a strong suppressor with a low cloud
point of 27.degree. C. Polymer agglomeration defects are
visible.
[0021] FIG. 3 shows galvanic polarization results collected on
copper coated platinum rotating disk electrodes in three copper
sulfate solutions, both with and without organic additives. The
graphs illustrate increases in polarization resulting from
decreases in copper ion concentration and acid concentration.
[0022] FIG. 4A is a graph demonstrating increased uniformity of
fill fraction (and therefore fill rate) between upstream and
downstream features on a substrate at low copper ion concentrations
as opposed to high copper ion concentrations in electrolyte.
[0023] FIG. 4B is a graph showing current density over time for
substrates plated in a variety of electrolytes having different
halide ion concentrations.
[0024] FIG. 4C is a graph representing the polarization rate
achieved for the various electrolytes tested in relation to FIG.
4B.
[0025] FIG. 4D presents data related to polarization vs. time for
several different electroplating processes using electrolytes
having differing concentrations of halide ions.
[0026] FIG. 4E is a graph depicting the steady state polarization
achieved in the various electrolytes tested in relation to FIG.
4D.
[0027] FIG. 4F presents four graphs describing impurities in copper
films deposited in various electrolytes having different
concentrations of halide ions.
[0028] FIG. 4G summarizes the impurity data shown in FIG. 4F.
[0029] FIG. 4H illustrates several defect maps for substrates
plated in a variety of electrolytes having different halide ion
concentrations, using three different recipes.
[0030] FIGS. 5A and 5B are graphs describing the fill fraction for
patterned substrates that were electroplated in a variety of
electrolytes having different halide ion concentrations.
[0031] FIG. 6 is a graph showing the voided fraction within the
features vs. the concentration of chloride ions in electrolyte for
several substrates plated in different electrolytes.
[0032] FIG. 7 shows a flowchart of a method of electroplating
copper according to the embodiments herein.
[0033] FIG. 8 shows the fill of 48 nm trenches plated in three
electrolytes. The left panel corresponds to a film plated in a high
copper, high acid electrolyte, the middle panel corresponds to a
film plated in a low copper, high acid electrolyte, and the right
panel corresponds to a film plated in a low copper, low acid
electrolyte.
[0034] FIG. 9 shows a schematic of a top view of an example
electrodeposition apparatus.
[0035] FIG. 10 shows a schematic of a top view of an alternative
example electrodeposition apparatus.
DETAILED DESCRIPTION
[0036] In this application, the terms "semiconductor wafer,"
"wafer," "substrate," "wafer substrate," and "partially fabricated
integrated circuit" are used interchangeably. One of ordinary skill
in the art would understand that the term "partially fabricated
integrated circuit" can refer to a silicon wafer during any of many
stages of integrated circuit fabrication thereon. Further, the
terms "electrolyte," "plating bath," "bath," and "plating solution"
are used interchangeably. The term "low copper electrolyte" is
understood to mean "electrolyte having a low concentration of
copper ions." A low concentration of copper ions is understood to
mean a concentration of less than about 10 g/L copper ions. The
following detailed description assumes the invention is implemented
on a wafer. However, the invention is not so limited. The work
piece may be of various shapes, sizes, and materials. In addition
to semiconductor wafers, other work pieces that may take advantage
of this invention include various articles such as printed circuit
boards and the like.
[0037] In the following description, numerous specific details are
set forth in order to provide a thorough understanding of the
presented embodiments. The disclosed embodiments may be practiced
without some or all of these specific details. In other instances,
well-known process operations have not been described in detail to
not unnecessarily obscure the disclosed embodiments. While the
disclosed embodiments will be described in conjunction with the
specific embodiments, it will be understood that it is not intended
to limit the disclosed embodiments.
[0038] The embodiments herein utilize a low copper concentration
electrolyte having a high concentration of halide ions to achieve a
high overpotential plating environment. For example, the copper
concentration for low copper electrolytes may be about 75% to 90%
lower than the nominal mass/volume concentration used in
conventional copper plating baths. In certain applications, the
copper ion concentration is less than about 10 g/L or less than
about 5 g/L. In these or other applications, the copper ion
concentration may be about 4 g/L or higher. In some examples, the
copper ion concentration may be between about 4-10 g/L, or between
about 4-5 g/L. The electrolyte may have a halide ion concentration
between about 150-300 ppm, for example between about 200-300 ppm.
This halide ion concentration is higher than halide ion
concentrations previously used in low copper electrolytes. The high
halide ion concentration can promote increased suppression (as well
as an increased rate at which suppression takes effect), leading to
higher quality bottom-up fill results. The role of halide ions is
further discussed below.
[0039] Some embodiments also utilize a low acid concentration
electrolyte to further increase the overpotential. For example, the
electrolyte may be between about 2-15 g/L, between about 5-10 g/L,
less than about 10 g/L, and/or less than about 5 g/L acid. The
increased overpotential provides various advantages such as
allowing plating to occur at a slower rate, thereby making the
deposition easier to control and resulting in a more uniform, more
easily reproducible fill. By increasing the total amount of plating
time, the influence of initial plating non-uniformities that occur
during immersion become less important, and a more uniform fill
results.
[0040] Typically, the copper electroplating solution includes
organic bath additives to permit controlled high quality
electrofill of recesses in a damascene substrate. Such additives
typically include a suppressor and an accelerator and possibly a
leveler. One role of the suppressor is to suppress electroplating
and increase the surface polarization of the plating substrate.
Before further describing the use of low copper, high halide
concentration electroplating solutions, a discussion of plating
additives is presented. As used herein, many additive
concentrations are recited in parts per million (ppm). This unit is
equivalent to mg/L for the purpose of determining additive
concentration in solution.
Suppressors
[0041] While not wishing to be bound to any theory or mechanism of
action, it is believed that suppressors (either alone or in
combination with other bath additives) are surface-kinetic
polarizing compounds that lead to a significant increase in the
voltage drop across the substrate-electrolyte interface, especially
when present in combination with a surface chemisorbing halide
(e.g., chloride or bromide). The halide may act as a bridge between
the suppressor molecules and the wafer surface. In conventional
electroplating solutions, the concentration of halide ions is
typically relatively low (e.g., often below 100 ppm, in various
cases below 50 ppm). This low halide concentration may promote
formation of a relatively smoother film and/or minimize
incorporation of impurities (e.g., halides or halide-containing
compounds) in the film. However, in low copper electrolytes, higher
concentrations of halide ions may be used to increase suppression
without increasing film contamination. These surprising results are
discussed further below.
[0042] The suppressor both (1) increases the local polarization of
the substrate surface at regions where the suppressor is present
relative to regions where the suppressor is absent, and (2)
increases the polarization of the substrate surface generally. The
increased polarization (local and/or general) corresponds to
increased resistivity/impedance and therefore slower plating at a
particular applied potential.
[0043] It is believed that suppressors are not incorporated into
the deposited film, though they may slowly degrade over time.
Suppressors are often relatively large molecules, and in many
instances they are polymeric in nature (e.g., polyethylene oxide,
polypropylene oxide, polyethylene glycol, polypropylene glycol,
etc). Other examples of suppressors include polyethylene and
polypropylene oxides with S- and/or N-containing functional groups,
block polymers of polyethylene oxide and polypropylene oxides, etc.
The suppressors can have linear chain structures or branch
structures. It is common that suppressor molecules with various
molecular weights co-exist in a commercial suppressor solution. Due
in part to suppressors' large size, the diffusion of these
compounds into a recessed feature is relatively slow.
Accelerators
[0044] While not wishing to be bound by any theory or mechanism of
action, it is believed that accelerators (either alone or in
combination with other bath additives) tend to locally reduce the
polarization effect associated with the presence of suppressors,
and thereby locally increase the electrodeposition rate. The
reduced polarization effect is most pronounced in regions where the
adsorbed accelerator is most concentrated (i.e., the polarization
is reduced as a function of the local surface concentration of
adsorbed accelerator). Example accelerators include, but are not
limited to, dimercaptopropane sulfonic acid, dimercaptoethane
sulfonic acid, mercaptopropane sulfonic acid, mercaptoethane
sulfonic acid, bis-(3-sulfopropyl) disulfide (SPS), and their
derivatives. Although the accelerator may become strongly adsorbed
to the substrate surface and generally laterally-surface immobile
as a result of the plating reactions, the accelerator is generally
not incorporated into the film. Thus, the accelerator remains on
the surface as metal is deposited. As a recess is filled, the local
accelerator concentration increases on the surface within the
recess. Accelerators tend to be smaller molecules and exhibit
faster diffusion into recessed features, as compared to
suppressors.
Levelers
[0045] While not wishing to be bound by any theory or mechanism of
action, it is believed that levelers (either alone or in
combination with other bath additives) act as suppressing agents to
counteract the depolarization effect associated with accelerators,
especially in the field region and at the side walls of a feature.
The leveler may locally increase the polarization/surface
resistance of the substrate, thereby slowing the local
electrodeposition reaction in regions where the leveler is present.
The local concentration of levelers is determined to some degree by
mass transport. Therefore levelers act principally on surface
structures having geometries that protrude away from the surface.
This action "smooths" the surface of the electrodeposited layer. It
is believed that leveler reacts or is consumed at the substrate
surface at a rate that is at or near a diffusion limited rate, and
therefore, a continuous supply of leveler is often beneficial in
maintaining uniform plating conditions over time.
[0046] Leveler compounds are generally classified as levelers based
on their electrochemical function and impact and do not require
specific chemical structure or formulation. However, levelers often
contain one or more nitrogen, amine, imide or imidazole, and may
also contain sulfur functional groups. Certain levelers include one
or more five and six member rings and/or conjugated organic
compound derivatives. Nitrogen groups may form part of the ring
structure. In amine-containing levelers, the amines may be primary,
secondary or tertiary alkyl amines. Furthermore, the amine may be
an aryl amine or a heterocyclic amine. Example amines include, but
are not limited to, dialkylamines, trialkylamines, arylalkylamines,
triazoles, imidazole, triazole, tetrazole, benzimidazole,
benzotriazole, piperidine, morpholines, piperazine, pyridine,
oxazole, benzoxazole, pyrimidine, quonoline, and isoquinoline.
Imidazole and pyridine may be especially useful. Leveler compounds
may also include ethoxide groups. For example, the leveler may
include a general backbone similar to that found in polyethylene
glycol or polyethyelene oxide, with fragments of amine functionally
inserted over the chain (e.g., Janus Green B). Example epoxides
include, but are not limited to, epihalohydrins such as
epichlorohydrin and epibromohydrin, and polyepoxide compounds.
Polyepoxide compounds having two or more epoxide moieties joined
together by an ether-containing linkage may be especially useful.
Some leveler compounds are polymeric, while others are not. Example
polymeric leveler compounds include, but are not limited to,
polyethylenimine, polyamidoamines, and reaction products of an
amine with various oxygen epoxides or sulfides. One example of a
non-polymeric leveler is 6-mercapto-hexanol. Another example
leveler is polyvinylpyrrolidone (PVP).
Bottom-Up Fill
[0047] In the bottom-up fill mechanism, a recessed feature on a
plating surface tends to be plated with metal from the bottom to
the top of the feature, and inward from the side walls towards the
center of the feature. It is important to control the deposition
rate within the feature and in the field region in order to achieve
uniform filling and avoid incorporating voids into the features.
The three types of additives described above are beneficial in
accomplishing bottom-up fill, each working to selectively increase
or decrease the polarization at the substrate surface.
[0048] After the substrate is immersed in electrolyte, the
suppressor adsorbs onto the surface of the substrate, especially in
exposed regions such as the field region. At the initial plating
stages, there is a substantial differential in suppressor
concentration between the top and bottom of a recessed feature.
This differential is present due to the relatively large size of
the suppressor molecule and its correspondingly slow transport
properties. Over this same initial plating time, it is believed
that accelerator accumulates at a low, substantially uniform
concentration over the entire plating surface, including the bottom
and side walls of the feature. Because the accelerator diffuses
into features more rapidly than the suppressor, the initial ratio
of accelerator:suppressor within the feature (especially at the
feature bottom) is relatively high. The relatively high initial
accelerator:suppressor ratio within the feature promotes rapid
plating from the bottom of the feature upwards and from the
sidewalls inwards. Meanwhile, the initial plating rate in the field
region is relatively low due to the lower ratio of
accelerator:suppressor. Thus, in the initial plating stages,
plating occurs relatively faster within the feature and relatively
slower in the field region.
[0049] As plating continues, the feature fills with metal and the
surface area within the feature is reduced. Because of the
decreasing surface area and the accelerator substantially remaining
on the surface, the local surface concentration of accelerator
within the feature increases as plating continues. This increased
accelerator concentration within the feature helps maintain the
differential plating rate beneficial for bottom-up fill.
[0050] In the later stages of plating, particularly as overburden
deposits, the accelerator may build up in certain regions (e.g.,
above filled features) undesirably, resulting in local
faster-than-desired plating. Leveler may be used to counteract this
effect. The surface concentration of leveler is greatest at exposed
regions of a surface (i.e., not within recessed features) and where
convection is greatest. It is believed that the leveler displaces
accelerator, increases the local polarization and decreases the
local plating rate at regions of the surface that would otherwise
be plating at a rate greater than at other locations on the
deposit. In other words, the leveler tends, at least in part, to
reduce or remove the influence of an accelerating compound at the
exposed regions of a surface, particularly at protruding
structures. Without leveler, a feature may tend to overfill and
produce a bump. Therefore, in the later stages of bottom-up fill
plating, levelers are beneficial in producing a relatively flat
deposit.
[0051] The use of suppressor, accelerator and leveler, in
combination, may allow a feature to be filled without voids from
the bottom-up while producing a relatively flat deposited surface.
The exact identity/composition of the additive compounds are
typically maintained as trade secrets by the additive suppliers,
thus, information about the exact nature of these compounds is not
publicly available.
Plating Techniques and Process Considerations
[0052] Typical electroplating baths for filling damascene
interconnects generally contain relatively high concentrations of
copper cations (e.g., 40 g/L). High copper concentrations were
understood to be beneficial because higher copper concentrations
result in higher limiting currents that may be used during plating.
Higher currents were seen as beneficial because they increased the
rate of electrodeposition and thereby decreased processing time.
Moreover, if the concentration of copper is too low, the
electrolyte may experience copper depletion, resulting in
significant fill defects. When the mass transfer of copper to the
plating surface is too low at a given current (e.g., when the
concentration of copper is too low or when the electrolyte is
insufficiently turbulent), there is insufficient copper at the
plating surface to sustain the reduction reaction. Instead, a
parasitic reaction must occur to sustain the current delivered to
the substrate. For example, the electrolyte itself may begin to
decompose and generate gasses at the plating interface, resulting
in significantly non-uniform plating and nodular growths on the
substrate.
[0053] When plating with these high copper electrolytes, small
features tend to fill fairly quickly (e.g., within 1 to 2 seconds).
Because the timeframe for filling the small features is so short,
the resulting fills often contain defects or are otherwise
non-uniform. For example, because of the nature of the physical
vapor deposition (PVD) processes used to deposit a copper seed
layer, the seed thickness is not uniformly distributed, especially
in areas along the sidewall of a feature. In some areas the seed
layer may be so thin that the seed becomes discontinuous, which may
lead to the formation of sidewall voids during subsequent rapid
deposition.
[0054] As indicated, the immersion time is frequently a significant
fraction of the total feature fill time in high copper
electrolytes. Therefore, non-uniformities may be introduced as a
consequence of the time difference between when the leading edge of
a wafer contacts the electrolyte and when the trailing edge of the
wafer contacts the electrolyte. Wafers are frequently immersed at
an angle that deviates from horizontal in order to minimize bubble
creation. In order to reduce non-uniformities introduced by the
time it takes for the wafer to be fully immersed, it would be
desirable to reduce the plating rate in recessed features,
particularly during immersion. Use of a low copper electrolyte
increases the polarization of the seed layer, thereby protecting it
from dissolution without requiring a strong electrical bias. As a
consequence, the low copper electrolyte permits seed layer
protection without rapid electroplating. Non-uniformities are
reduced.
[0055] Further, short feature filling timeframes required with high
copper electrolytes may result in poor fill performance because the
short timeframes are incompatible with the bottom-up fill mechanism
during immersion, which requires some time for the organic
additives to reach and adsorb onto the substrate surface at the
relevant locations described above. As a particular example, when
the accelerator compound(s) do not have time to reach and adsorb
onto the bottom surface of a feature before substantial deposition
begins, the bottom-up fill mechanism will be impaired and the
feature fill will likely be poor. Similarly, bottom-up fill may be
poor if the suppressor does not adsorb onto the field region of a
feature sufficiently quickly. One method of addressing this concern
is to use a high concentration of accelerator and/or suppressor in
the electrolyte. However, high additive concentrations may be
undesirable in particular applications, and it is generally
advantageous to use low concentrations of these additives in order
to lower cost. In certain implementations, the concentration of
accelerator is about 100 ppm or less, for example about 20 ppm or
less, or about 10 ppm or less.
[0056] The embodiments herein address the bottom-up fill timeframe
issue by plating at a low copper ion concentration and high halide
ion concentration. Electroplating can be accomplished using a low
current density during bottom-up fill, thereby achieving a slower
filling timeframe, especially for small features. The longer
filling timeframe permits the organic additives sufficient time to
diffuse or otherwise travel to their proper locations, adsorb onto
the substrate surface, and promote bottom-up fill during immersion
and before substantial deposition occurs. Further, the high
concentration of chloride ions increases the rate at which certain
additives adsorb onto the substrate, thereby improving
electroplating results (e.g., void formation).
[0057] In order to increase the timeframe over which plating
occurs, a lower current density is desired during bottom-up
plating. Often, electroplating is accomplished using a two-phase
process. A first phase electroplates copper into the features via a
bottom-up fill mechanism, and a second phase electroplates copper
onto the field region after the features are substantially filled.
Typically, the current density is relatively low during the first
phase, and higher during the second phase. Lower current densities
during the first phase may result in higher bottom-up fill
efficiency. FIG. 1 shows the partial fill of 100 nm trenches with a
400A seed layer plated at constant currents between 1 and 4 Amps,
for a fixed amount of charge passed. The trenches plated at the
lower current are more filled because of increased bottom-up fill
efficiency. However, lower current densities result in faster
dissolution of the copper seed layer, leading to sidewall voids.
The minimum current density required for a void-free fill in
conventional electrolytes is still too high to allow good process
control (i.e., plating occurs too quickly to achieve a
reproducible, defect-free fill).
[0058] Typical electroplating baths and methods often cause the
copper seed layer to dissolve/corrode to a certain degree when the
substrate is first immersed in electrolyte. This dissolution may
result in voids or other defects/non-uniformities in the deposit.
The seed dissolution issue is especially problematic for thin seed
layers, as thin layers are more easily dissolved than thicker
layers. To achieve higher performance integrated circuits, many of
the features of the integrated circuits are being fabricated with
smaller feature sizes and higher densities of components. As the
industry moves towards smaller features, the seed layers must
become thinner and thinner to avoid "pinching off" the top of the
feature before the bottom of the feature can be properly filled. In
some damascene processing, for example, copper seed layers on 2
X-nm node features may be as thin as or thinner than 50 .ANG..
Technical challenges arise with smaller feature sizes in producing
metal seed layers and metal interconnects substantially free of
voids or defects.
[0059] One technique for protecting a copper seed layer is to
increase the overpotential of the substrate-electrolyte interface.
The overpotential may be increased in a variety of ways.
[0060] For example, using a stronger suppressor or a higher
concentration of suppressor will result in a higher overpotential.
Unfortunately, suppressors tend to form visible agglomerations
above a threshold temperature, referred to as the cloud point.
These agglomerations result in significant deposition defects
because they can adhere to the surface of the substrate. Although
the cloud point is the temperature at which the agglomerations
become visible, it is believed that agglomerations begin forming at
temperatures lower than the cloud point. Thus, the deposition
process should be run at a temperature that is well below (e.g.,
20.degree. C. or more below) the cloud point of a particular
electrolyte. Stronger suppressors tend to have very low cloud
points (e.g., 27.degree. C. for a proprietary suppressor that has
more than 20 mV higher overpotential as compared to existing
"moderate strength" commercial suppressors). Moreover, higher
concentrations of suppressor result in lower cloud points (i.e.,
the more suppressor present in solution, the easier it is to form
agglomerations at lower temperatures). Thus, although electrolytes
with strong suppressors or high concentrations of weak to moderate
suppressors may exhibit good fill performance, they cannot
generally be used in conventional electroplating methods for small
10-20 nm features because they reduce the electrolyte's cloud point
to an unacceptably low temperature.
[0061] While suppressors may be referred to as "weak" or "strong,"
it should be understood that these terms are relative and may vary
over time. As the industry develops, stronger suppressors are
created, and suppressors that used to be seen as "strong" may now
be considered "moderate" or even "weak." Currently, the Excel
suppressor available from Enthone may be considered a strong
suppressor, while the Extreme Plus suppressor, also available from
Enthone, may be considered a moderate suppressor.
[0062] FIG. 3 shows the overpotential of three electrolytes and
demonstrates that the overpotential may be increased by using
electrolytes with low copper and low acid concentrations. In the
upper panel, the electrolytes do not include organic additives,
while in the lower panel the organic additives (36 ppm or mg/L
Excel accelerator and 200 ppm or mg/L Excel suppressor) are
present. The overpotential is measured by galvanostatic
polarization between a copper coated platinum rotating disk
electrode (RDE) and a Hg/HgSO.sub.4 reference electrode. A thin
layer of 0.66 .mu.m copper is plated on a platinum electrode in an
organic additive-free electrolyte. The electrode is then immersed
in the bath to be tested with a copper sheet as the counter
electrode. The voltage between the copper coated platinum RDE and
the reference electrode is monitored while the electrode is rotated
at 100 RPM at a current density of 10 mA/cm.sup.2. The
overpotential is expressed relative to the open-circuit voltage,
which is the voltage between the copper coated platinum RDE and the
Hg/HgSO.sub.4 reference electrode when no current is passed.
[0063] The three tested electrolytes are all copper sulfate
solutions. The first solution is a baseline solution of 40 g/L
Cu.sup.2+, 10 g/L acid, and 50 ppm Cl.sup.-. The second solution is
a low copper/high acid solution of 10 g/L Cu.sup.2+, 10 g/L acid,
and 50 ppm Cl.sup.-. The third solution is a low copper/low acid
solution of 10 g/L Cu.sup.2+, 5 g/L acid, and 50 ppm Cl.sup.-. As
used herein, "low" and "high" concentrations are compared relative
to one another. In other words, although 10 g/L acid is referred to
as a "high acid" solution, it should be understood that 10 g/L may
not be a high acid solution in absolute terms, but rather, is high
compared to the 5 g/L acid solution.
[0064] Where there were no organic additives present (FIG. 3, upper
panel), the use of the low copper/high acid solution increased the
overpotential by about 30 mV, and the use of the low copper/low
acid solution further increased the overpotential by about another
20 mV. Where the organic additives were present (FIG. 3, lower
panel), the use of the low copper/high acid solution increased the
overpotential by about 50 mV, and the use of the low copper/low
acid solution further increased the overpotential by about another
50 mV. Thus, the use of a low copper, low acid electrolyte may
increase the overpotential by about 100 mV when additives are
present, as compared to conventional electroplating solutions. This
increase in overpotential is larger than the increase typically
achieved by using stronger suppressor formulations or changing the
suppressor concentration in a given electrolyte (e.g., a typical
increase of about 10 to 20 mV). Advantageously, increasing the
concentration of halide ions (e.g., chloride ions) does not
increase the impurities in the plated films, at least in cases
where the electrolyte contains appropriate organic additives that
yield pure films, as shown in FIG. 3. Hence, the high halide ion
concentrations described herein have no negative impact on film
properties or electrical reliability of the processed devices. The
lack of an increase in impurities (and related device
unreliability) at high halide concentrations was surprising.
[0065] Because the low copper concentration electrolytes exhibit
higher overpotential (stronger polarization) at a given current
density, the copper seed dissolution is also slower at a given
current density. Due to the lower seed dissolution rate, lower
current densities may be used without resulting in sidewall voids.
The lower current densities allow the plating to occur more slowly,
resulting in better fills with fewer defects in a more reproducible
process.
[0066] The low copper, higher overpotential electrolyte presents
several significant plating benefits explored in more detail
herein. First, the higher overpotential provides better seed
protection at a given current density. Better seed protection is
especially beneficial for small features (e.g., 10-20 nm nodes)
with thin seeds (e.g., thinner than about 100 .ANG.) which may
otherwise dissolve during plating, resulting in fill defects.
[0067] Next, higher overpotential promotes higher nucleation
density on the copper seed. The high nucleation density is
especially beneficial for thin seeds, especially those that may
have marginal/discontinuous seed coverage. As mentioned above, thin
seeds may have discontinuous coverage on a substrate surface due to
the nature of the PVD process used to deposit the seed layer. The
discontinuities in seed coverage tend to occur on the sidewalls of
features. However, the combination of improved seed protection and
high nucleation density enables plating to occur in small features
with thin seed without the formation of sidewall voids, or at a
minimum, with fewer/smaller voids than occur with conventional
methods. Moreover, the high overpotential at low copper
concentrations promotes high nucleation density at lower current
densities than what is typically used when plating in conventional
electrolytes. The high nucleation density promotes the formation of
a continuous copper film instead of a discontinuous copper film
having islands of copper.
[0068] Another advantage to using a low copper electrolyte is that
it can promote uniform fill across a pattern of dense features.
When many features are positioned near one another on a wafer,
conventional electrolytes often result in non-uniform fills between
the features. As electrolyte flows over the surface of a substrate,
organic additives present in the electrolyte adsorb onto the
surface, both within the features and in the field region. Features
which are relatively upstream in the electrolyte flow path may
therefore experience higher concentrations of additives, while
features which are relatively downstream may experience lower
concentrations of such additives.
[0069] The activity of the suppressor maxes out at a certain
threshold suppressor concentration, referred to herein as the
saturation point or suppressor saturation point. At concentrations
above the saturation point, additional suppressor has very little
or no effect on the overpotential at a fixed current density. It is
desirable for the electrolyte to be near or above the suppressor
saturation point during the initial stage of plating at all
locations on the substrate surface. Thus, the suppressor
concentration differences caused by flow direction (upstream vs.
downstream) and/or pattern density have little or no impact on
overpotential or copper deposition rate. If one location on a
substrate (e.g., an upstream location) experiences a suppressor
concentration above the saturation point, and another location on
the substrate (e.g., a downstream location) experiences a
suppressor concentration below the saturation point (the lower
suppressor concentration being a result of adsorbing suppressor
onto upstream locations more rapidly on the substrate surface), the
difference in additive concentrations/adsorption rates may result
in non-uniform fill between the upstream and downstream features.
This same phenomenon also results in fill differences between
features which are located in areas of dense features vs. features
which are more isolated. The suppressor saturation point increases
with increasing copper ion concentration in the electrolyte. Thus,
in solutions with lower copper ion concentrations, the suppressor
saturation point is lower, and it is easier for the suppressor
concentration to remain above the saturation point at all locations
during the initial stage of plating.
[0070] FIG. 4A shows the fill fraction of 20 nm technology nodes
(i.e., 2 X-nm features) at three locations on a wafer (upstream
edge (LL, 402), center (C, 404), and downstream edge (UR, 406))
when plated at three different copper concentrations (20, 30 and 40
g/L copper ions). The other components of the electrolyte and the
additive concentrations were the same for all three electrolytes.
The fill fraction represents the fraction of the feature that was
filled with copper during deposition. The fill fraction may be
correlated to the fill rate. The features plated in electrolyte
having 40 g/L copper ions show the widest variation in fill
fraction. The uniformity of fill fraction increases slightly for
the features plated in electrolyte having 30 g/L copper ions, and
the uniformity is best for the features plated in electrolyte
having the lowest copper ion concentration at 20 g/L. At the low
copper condition, the fill fraction at the upstream edge was 85% of
that seen at the downstream edge, which is significantly more
uniform than at the 40 g/L copper ion condition where the fill
fraction at the upstream edge was only about 50% of that seen at
the downstream edge. For each set of features, there is a general
trend towards higher fill fraction at the downstream edge (406) as
compared to the upstream edge (402). This may be a result of
different surface concentrations of adsorbed additives.
[0071] Low copper electrolytes are also beneficial because they
increase the cloud point of the suppressor in the electrolyte. As
discussed above, suppressors form agglomerations above certain
temperatures. The temperature at which the agglomerations become
visible is referred to as the cloud point, though it is believed
that such agglomerations begin to form at temperatures lower than
the cloud point. The agglomerations result in significant plating
defects, and therefore, plating should occur at a temperature well
below (e.g., 20.degree. C. or more below) the cloud point of the
electrolyte. The increase in cloud point resulting from the use of
a low copper electrolyte is substantial. For example, the cloud
point of a 2% (vol/vol) suppressor solution may be increased by
about 25.degree. C. when the copper concentration is reduced from
40 to 5 g/L in copper sulfate plating baths. Therefore,
agglomeration defects can be significantly reduced or eliminated
through the use of a low copper electrolyte. The increased cloud
point also makes it possible to use strong suppressors (or higher
suppressor concentrations) that could not be used in higher copper
electrolytes due to their low cloud point. Furthermore, by
increasing the cloud point of the suppressor/electrolyte, a wider
range of process temperatures may be used for plating.
Specifically, plating may occur at higher temperatures than was
otherwise acceptable in conventional plating solutions.
[0072] Table 1 lists the cloud point of solutions of 2% (vol/vol)
commercial suppressor (Extreme Plus from Enthone) in two
electrolytes. The cloud point of the conventional high copper, high
acid electrolyte is 35.degree. C. The cloud point of the low
copper, low acid electrolyte is 25.degree. C. higher at 60.degree.
C. It is believed that all suppressors will exhibit similarly
increased cloud points in electrolytes with low copper ion
concentrations.
TABLE-US-00001 TABLE 1 Electrolyte Composition Cloud Point
(.degree. C.) 40 g/L Cu.sup.2+, 10 g/L acid, 50 ppm Cl.sup.- 35 5
g/L Cu.sup.2+, 5 g/L acid, 50 ppm Cl.sup.- 60
[0073] An additional benefit to using low copper/low acid/high
halide concentration electrolytes is that the impact from the
terminal effect is reduced. When plating begins, there is a
significant potential drop between the edges of a wafer (where the
wafer is connected to the power supply) and its center. The
difference in potential results in faster plating at the edges and
slower plating at the center of the substrate during the initial
plating stage. The resulting film is generally edge-thick and
center-thin, meaning that there may be significant plating
non-uniformities between the different areas on a wafer. However,
the impact of the terminal effect is reduced when a low copper/low
acid/high halide concentration electrolyte is used due to the
higher impedance/lower conductivity of the electrolyte. Because of
the lower electrolyte conductivity (due at least in part to the
lower acid concentration), the voltage drop between the wafer edge
and center due to resistive seed becomes less significant. The
terminal effect is an important consideration when designing
electroplating systems, and will be even more important as the
industry transitions from 300 to 450 mm wafers. Further, the
terminal effect is increasingly important as thinner seed layers
are used to accommodate smaller features because the thinner seed
layers exhibit higher sheet resistance.
[0074] As mentioned above, many electroplating processes utilize
electrolytes having a relatively low concentration of halide ions,
for example about 100 ppm or lower, often 50 ppm or lower, or even
10 ppm or lower in many cases. The halide ions may act as a bridge
between the substrate and the organic plating additives. One reason
that the halide ion concentration is typically kept low is that
high concentrations of chloride ions can result in formation of
CuCl, which precipitates out of the electrolyte and causes poor
plating results. CuCl has a low solubility in aqueous solutions
(solubility product of CuCl, K.sub.sp=1.72.times.10.sup.-7). This
issue is particularly problematic in electrolytes having a high
concentration of copper ions, as the chloride ions are more likely
to form CuCl when more copper ions are available in solution. By
contrast, in a low copper electrolyte, the chloride ion
concentration can be much higher without precipitating CuCl.
Therefore, the use of a high halide concentration as discussed
herein is only beneficial in the context of the low copper
electrolyte. Similarly high halide concentrations would be
detrimental in a conventional high copper electrolyte.
[0075] Another reason that the halide concentration may be kept low
in conventional plating methods is that higher halide ion
concentrations may, in a number of cases, result in higher levels
of roughness and/or impurities in the resulting electroplated film.
However, the low copper/low acid/high halide electrolytes discussed
herein have surprisingly not shown such trends, as discussed in
relation to FIG. 4F, below. Instead, the electrolytes discussed
herein exhibit comparable and commercially acceptable levels of
impurities over a wide range of chloride ion concentrations,
assuming that the electrolyte is provided with appropriate plating
additives, as described herein.
[0076] FIG. 4B illustrates current density vs. time over the first
second of electroplating, when the additives initially adsorb onto
the substrate. Five different electrolytes were tested, with halide
(chloride) ion concentrations ranging from about 50 ppm to about
400 ppm. The electrolytes each had about 5 g/L copper ions and 10
g/L acid. A constant potential of about -0.8V was applied to the
substrates during immersion, and the substrates were rotated at
about 300 RPM. The current density increased (became more negative)
much more quickly in the cases where higher concentrations of
halide ion were used. This indicates that the additives quickly
adsorbed onto the substrate to establish bottom-up fill when higher
concentrations of halide ion were used. By contrast, where a
concentration of only 50 ppm halide ions was used, the current
density increased (became more negative) much more slowly, and
never reached the same level as the other electrolytes tested.
These results indicate that the use of a high halide ion
concentration can help establish a desired bottom-up plating regime
more rapidly than a low halide ion concentration, at least where a
low copper/low acid electrolyte is used. Because of the issues
mentioned above with respect to a short filling timeframe, rapid
additive adsorption/establishment of bottom-up fill is highly
beneficial. The initial additive adsorption strongly affects the
quality of feature fill, and rapid adsorption/establishment of
bottom-up fill results in high quality deposits.
[0077] FIG. 4C depicts the polarization rate vs. halide ion
concentration for the electrolytes tested in FIG. 4B. The
polarization rate (sometimes referred to as the additive adsorption
rate) was calculated based on the rate of change of the current
density over an initial plating period (e.g., about 50 ms), for the
electrolytes described in relation to FIG. 4B. The polarization
rate first increases with increasing halide ion concentration,
reaching a maximum polarization rate at about 300 ppm. At halide
ion concentrations above 300 ppm, the rate of polarization begins
to decrease.
[0078] FIG. 4D illustrates the steady state polarization achieved
for six different electrolytes having different halide (chloride)
ion concentrations ranging from about 50 ppm to about 400 ppm. The
electrolytes included about 5 g/L copper ions and 10 g/L acid. A
constant current density of about 10 mA/cm.sup.2 was applied to the
substrates, which were rotated at about 300 RPM. FIG. 4E depicts
the polarization strength of the steady state polarization (taken
at about 60 seconds from FIG. 4D) for the different electrolytes
tested in relation to FIG. 4D. Notably, the polarization strength
increases (becomes more negative) when increasing from about 50 to
about 300 ppm halide ions. Above 300 ppm halide ions, the steady
state polarization strength begins to decrease.
[0079] The results in FIGS. 4B-4E suggest that the rate of
polarization and strength of polarization can be maximized by
controlling the concentration of halide ions between about 150-400
ppm, for example between about 150-300 ppm, or between about
200-300 ppm. Halide ion concentrations below or above these ranges
may result in slower and less significant polarization, and
therefore lower quality plating results. While the optimal halide
concentration for a particular application may depend on the exact
composition of the electrolyte, it has been found that halide
concentrations within the disclosed ranges produce significant and
unexpected benefits, particularly for low copper/low acid
electrolytes. One surprising result illustrated in FIGS. 4B-4E is
that the increase in polarization rate and polarization strength
was not monotonic with increasing halide concentration. In other
words, the benefits related to increased halide ion concentration
were only relevant within a certain range of halide ion
concentrations. Above this concentration (e.g., about 300 ppm
halide ions), additional halide ions begin to result in slower and
lower degrees of polarization.
[0080] FIG. 4F depicts four graphs describing the composition of
films deposited using electrolytes having halide ion concentrations
ranging between about 50-300 ppm. Each graph relates to a different
element (C, Cl, S, and N). Notably, the increasing halide
concentration did not have a significant impact on the
incorporation of impurities into the electroplated film. This
result was surprising. It was expected that higher chloride
concentrations would result in higher film impurities, for example
due to incorporation of chloride (or other species) from the
electrolyte into the plated film. However, the data show that this
was not the case, and film impurities were fairly stable over a
wide range of chloride concentrations. Because it was expected that
film impurities would increase with increasing chloride ion
concentrations, this result was unexpected.
[0081] FIG. 4G presents the data of FIG. 4F at a film depth of
about 0.7 .mu.m. As explained in relation to FIG. 4F, the film
impurities were not significantly affected by the increasing halide
ion concentration.
[0082] FIG. 4H presents defect maps for a variety of substrates
electroplated in different electrolytes using different defect
inspection recipes. The electrolytes included between about 50-300
ppm halide (chloride) ions. Three inspection recipes were used:
Recipe A, Recipe P, and Recipe F. Recipe A is tuned to pick out
general defects that are about 0.16 um and larger. Recipe P and
Recipe F have higher sensitivity than Recipe A, and are tuned to
pick out smaller defects that Recipe A may not be able to detect.
Recipe P is specifically tuned to detect small pits and/or voids in
addition to larger defects. Recipe F is tuned to detect more
surface topography related small defects such as surface roughness,
small protrusions, and fine particles. The substrates tested were
blanket wafers. The electrolytes tested each included 5 g/L copper
ions, 10 g/L acid, 90 ppm or mg/L Cobra accelerator, 160 ppm or
mg/L Cobra suppressor, and 16 ppm or mg/L Cobra leveler. The number
on the bottom right portion of each defect map indicates the number
of defects detected on that wafer. For each recipe, there was not a
clear trend between halide ion concentration and the number of
defects produced. In other words, the inclusion of relatively high
levels of halide ions (e.g., up to about 300 or 400 ppm) does not
result in increased defects on the substrate. Based on prior
results in the context of conventional (high copper) electrolytes,
this result was unexpected. In high copper electrolytes, increasing
chloride concentration is known to increase the risk of forming
CuCl, which can precipitate out of solution and cause defects on
the wafer. The reflectivity of each wafer described in relation to
FIG. 4H was also tested. The reflectivity was comparable for all of
the substrates, indicating that increasing halide ion concentration
does not have a negative effect on reflectivity.
[0083] FIG. 5A is a graph illustrating the fill fraction for
substrates plated in various electrolytes having between 50-300 ppm
halide (chloride) ions. Each electrolyte also included Cobra
accelerator, Cobra suppressor, and Cobra leveler at 90 ppm, 160
ppm, and 16 ppm or mg/L, respectively. Each substrate was patterned
with 56 nm pitch trenches, and plating occurred at about 6.7
mA/cm.sup.2, for a duration of about 1 second. Because plating
occurred for only 1 second in each case, the fill fraction also
represents the fill rate. While higher halide concentrations
slightly decreased the fill fraction/fill rate, this decrease was
very small. Based on previous experience, it was expected that the
increasing halide concentration would decrease the fill
fraction/fill rate to a much greater extent. Advantageously, this
was not the case. At high halide ion concentrations, the features
are filled sufficiently slowly to produce high quality plating
results, but not too slow to be commercially feasible. While the
decrease in fill fraction/fill rate at high halide concentrations
was insignificant, this may not be the case for all features. For
example, where large features (e.g., 1 .mu.m features) are filled,
the plating time is much longer, which may render even small
changes in plating rate significant. However, for various
embodiments herein, the features are sufficiently small (e.g.,
10-20 nm) and fill sufficiently quickly that the decreased fill
rate at higher halide ion concentrations is insignificant.
[0084] FIG. 5B is a graph illustrating the fill fraction for
substrates plated in various electrolytes having between 50-300 ppm
halide (chloride) ions. The electrolytes had the same
accelerator/suppressor/leveler concentrations as described in
relation to FIG. 5A. Plating occurred at about 6.7 mA/cm.sup.2 for
a duration of about 2 seconds. Because each substrate was plated
for the same amount of time, the fill fraction also represents the
fill rate. Each substrate was patterned with 50 or 60 nm dual
damascene structures (trenches and vias). Two different substrate
structures were tested, and Structure 1 had larger features than
Structure 2. Like the results in FIG. 5A, the increased halide ion
concentration did not have a large result on fill fraction/fill
rate. The results in FIGS. 5A and 5B show that high halide
concentrations can effectively be used to electroplate copper into
various kinds of features without unacceptably slowing or stopping
the feature fill.
[0085] FIG. 6 is a graph describing the voided fraction within a
feature vs. chloride ion concentration for substrates plated in
electrolytes having a range of chloride ion concentrations between
about 50-300 ppm. The substrates plated in relation to FIG. 6
included a patterned array of 48 nm trenches, and had relatively
poor seed layers deposited in/on the trenches (120 nm seed). The
poor or discontinuous seed coverage was intentionally created to
act as a test vehicle for copper nucleation, seed dissolution, or
sidewall void study on thin/discontinuous seed. The seed coverage
of commercial products is typically much better, and void formation
is therefore much less likely/significant than is presented in
relation to FIG. 6. Each electrolyte further included accelerator,
suppressor, and leveler at the concentrations described in relation
to FIG. 5A. The voided fraction was evaluated at both the center
and edge of the array of features. Near the edge of the array, the
halide ion concentration did not have much effect on the voided
fraction within the feature. However, near the center of the array,
increasing the halide ion concentration from about 50 to 300 ppm
results in a substantial decrease in the voided fraction within the
feature. In other words, the relatively higher halide ion
concentration ranges described herein can result in significant
improvements in feature fill near the center of a substrate/array
of features. These improvements may relate to formation of features
that have fewer and less extensive voids (if any) compared to
substrates plated in electrolytes having conventional (e.g., 100
ppm or lower) halide ion concentrations. This decrease in voided
fraction where a poor seed layer is used is a substantial
benefit.
[0086] Without wishing to be bound by theory or mechanism of
action, it is believed that the halide ion concentration ranges
described herein promote improved nucleation on the seed layer
(e.g., compared to lower/conventional halide ion concentrations).
This factor is especially beneficial in cases where the seed layer
is poor (e.g., oxidized, discontinuous, or otherwise poor
quality).
[0087] In another experiment, a number of blanket substrates were
electroplated in low copper (5 g/L), low acid (10 g/L), high halide
ion (200 ppm chloride ion) electrolytes. The concentration of
accelerator was varied between about 60-200 ppm or mg/L (Cobra
accelerator), and the concentration of suppressor was varied
between about 100-240 ppm or mg/L (Cobra suppressor). Additionally,
the electrolytes included about 16 ppm or mg/L Cobra leveler. Each
substrate was tested for defects and reflectivity. The defect and
reflectivity behavior was comparable for the various electrolytes.
These results indicate that electrolytes having the described
composition have a reasonably wide process window in terms of
additive concentrations. In other words, the use of a relatively
high halide ion concentration does not unacceptably limit the
concentration of the additives in the electrolyte. Experiments
performed on patterned substrates similarly show that there is a
reasonably wide process window for additive concentrations in cases
where the substrate is patterned. Generally, higher suppressor
concentrations (e.g., 200 ppm and above) may result in a slightly
slower fill rate compared to lower suppressor concentrations in
cases where a low copper/low acid/high halide ion electrolyte is
used. In some cases, the benefits described herein are most
prevalent where the concentration of accelerator is about 90 ppm or
above.
[0088] The use of a relatively high concentration of halide ions
(within the ranges described herein) can have significant benefits
in terms of void formation, especially in cases where the seed
coverage is poor. The high concentration of halide ions does not
substantially/unacceptably decrease the fill rate, nor does it
substantially/unacceptably increase defects or film impurities or
limit the process window in terms of additive concentrations. The
improved void formation may be a result of the increased rate at
which suppression occurs in the electrolyte during and shortly
after immersion. The high halide ion concentration may allow the
additives (e.g., suppressor and others) to quickly adsorb onto the
substrate at appropriate locations to quickly establish bottom-up
fill and reduce the likelihood that a void will form.
Method of Electroplating with Low Copper/High Halide
Electrolyte
[0089] The electrolyte used in embodiments herein may contain
copper ions, acid, water, halide ions, and organic additives such
as suppressors, accelerators and levelers. The composition of the
electrolyte is described in more detail below. The temperature of
the electrolyte during deposition may be between about
25-40.degree. C., for example 30.degree. C., to achieve a
reasonable deposition rate and temperature control.
[0090] In some embodiments, before a wafer enters the electrolyte,
a constant potential is applied to the wafer in order to prevent
seed dissolution or corrosion when the wafer first enters the
electrolyte. The constant potential entry is further described in
U.S. Pat. No. 6,551,483, issued Apr. 22, 2003, and incorporated by
reference herein. In other embodiments, the potential is dynamic
during the initial immersion period. Generally, a high potential is
desired during entry in order to provide better seed protection,
especially where thin copper seed layers are used. During the entry
phase, the copper plating is conformal (i.e., the copper deposition
rate is the same at all locations such as the field, sidewalls and
bottom of features). In conventional methods, where the entry
potential is too high, or where the potential is applied for too
long, excessive conformal plating inside the features may lead to
seam voids. However, low copper electrolytes allow for high
potential entry without causing excessive conformal plating inside
the substrate's features because a lower current density may be
used. The minimum current density required to support plating in a
particular electrolyte at a given mass transfer rate is
proportional to the copper concentration of bulk solution. The high
constant potential entry voltage followed by plating at a low
current density in low copper electrolyte provides better seed
protection, fill efficiency and uniformity, and process
consistency.
[0091] In many embodiments herein, after the initial (often
potentiostatic) immersion period, a substrate is plated at a
relatively low constant current or current density as the features
are filled. For example, the substrate may be plated at a current
density between about 0.5-5 mA/cm.sup.2 during this fill stage. In
some cases the current density during this fill stage is about 5
mA/cm.sup.2 or less, or about 3 mA/cm.sup.2 or less (e.g., between
about 3-5 mA/cm.sup.2). In certain implementations the current
density during the bottom-up fill stage is higher, for example,
about 10 mA/cm.sup.2 or less (e.g., between about 0.5-10
mA/cm.sup.2). The higher current densities can be used when the
mass transfer to the substrate is relatively higher. A high mass
transfer rate is beneficial during the fill stage in order to avoid
copper depletion inside the features, especially at relatively
higher current densities. Higher mass transfer rates may be
achieved by increasing the flow rate of the electrolyte, as well as
by increasing the rotation speed of the electrode, which increases
convection to the substrate surface. The mass transfer rate should
generally be sufficiently high such that the electrodeposition
reaction is kinetically controlled, not mass transfer controlled.
In certain embodiments, the current or current density may be
dynamic over time. Many suitable electroplating processes and
systems may be used to implement the embodiments described herein.
Examples of such processes and systems are described in the
following U.S. patents and U.S. patent applications, each
incorporated herein by reference in its entirety: U.S. Pat. Nos.
6,333,275 and 8,308,931, and U.S. Patent Application No.
61/315,679, filed Mar. 19, 2010 and titled "Electrolyte Loop with
Pressure Regulation for Separated Anode Chamber of Electroplating
System."
[0092] After plating is complete, the substrate may be removed from
the electrolyte, rinsed, dried and processed for further use.
[0093] FIG. 7 shows an example of a method of electroplating copper
700 according to the embodiments described herein. The plating
process may be divided into the following basic stages: immersion,
fill, overburden and removal. In the immersion stage beginning at
block 701, a negative bias is applied to the wafer. At block 703,
the biased wafer is immersed into a low copper concentration
electrolyte at an angled orientation. The wafer enters the plating
bath at a high constant potential between about 1-2V, depending on
seed thickness. A higher potential may be applied when the seed is
thinner or when the sheet resistance of the seed is higher. The
wafer enters the plating bath at an angle (e.g., 2-4 degrees) with
respect to the surface of the plating solution in order to avoid
trapping air bubbles on the wafer surface. The entry angle may be
fixed, or it may be dynamic as the wafer becomes more fully
immersed. The vertical speed of the wafer during immersion may be
between about 5-300 mm/s, between about 5-200 mm/sec, or between
about 100-300 mm/sec in certain implementations. The vertical speed
should be relatively fast in order to achieve uniform initial
plating across the wafer, but should not be so fast as to cause
defect issues due to splashing. The rotation speed of the electrode
may be optimized such that there is (1) a low limiting current at
high entry voltage during potentiostatic entry, and (2) a uniform
initial plating rate across the wafer. A low rotation speed is
generally beneficial where there is a low limiting current, while a
high rotation speed is generally beneficial to promote uniform
initial plating across the wafer. Thus, the entry rotation speed of
the electrode should be set at an intermediate level, for example,
between about 30-120 RPM. The flow rate of plating solution during
the initial immersion stage may be relatively low (e.g., between
about 3-6 LPM). After the wafer is fully immersed in the plating
bath, the wafer is set to a tilt angle of 0.
[0094] During the fill stage of plating at block 705, the features
on the substrate undergo bottom-up fill as described herein. The
current density during the fill stage may be relatively low (e.g.,
between about 0.5-5 mA/cm.sup.2, though it may be higher, e.g., up
to about 10 mA/cm.sup.2 in some cases). Further, the mass transfer
rate during the fill stage may be relatively low in order to avoid
diffusion of leveler into the features. For example, the flow rate
of electrolyte may be about 6 LPM during this stage. The electrode
rotation speed may be relatively low during the fill stage (e.g.,
between about 12-30 RPM).
[0095] After the features are filled, an overburden stage occurs at
block 707. During the overburden stage, a higher current and/or
current density is applied (e.g., between about 10-15 mA/cm.sup.2),
and a higher rate of mass transfer is used (e.g., an electrolyte
flow rate between about 12-20 LPM, and an electrode rotation speed
between about 60-120 RPM). Next, at block 709 the wafer may be
removed from the electrolyte. At block 711 the wafer may be
optionally rinsed, dried and processed for further use. Next, at
block 713 the wafer is planarized to remove overburden. Operations
711 and 713 may occur in either order.
[0096] FIG. 8 shows the fill of 48 nm trenches (i.e., features)
plated in two-component plating solutions in three different
electrolyte compositions. "Two-component plating solution" means
that the electrolyte included both accelerator and suppressor. The
left panel of FIG. 8 corresponds to trenches filled in a high
copper/high acid electrolyte having 40 g/L Cu.sup.2+, 10 g/L acid,
50 ppm Cl.sup.-, 40 ppm or mg/L accelerator, and 200 ppm or mg/L
suppressor. The middle panel corresponds to trenches filled in a
low copper/high acid electrolyte having 5 g/L Cu.sup.2+, 10 g/L
acid, 50 ppm Cl.sup.-, 20 ppm or mg/L accelerator, and 100 ppm or
mg/L suppressor. The right panel corresponds to trenches filled in
a low copper/low acid electrolyte having 5 g/L Cu.sup.2+, 5 g/L
acid, 50 ppm Cl.sup.-, 20 ppm or mg/L accelerator, and 100 ppm or
mg/L suppressor. Each set of trenches was plated for 0.15 seconds
in a beaker with a potentiostatic entry at 1V as compared to an
Hg/HgSO.sub.4 reference electrode, followed by plating at a
constant current density of 3 mA/cm.sup.2. The rotation speed of
the electrode during plating was 100 RPM. The trenches filled in
the high copper/high acid solution (FIG. 8, left panel) show
conformal plating with significant seam void defects, while the
trenches plated in the low copper solutions (FIG. 8, center and
right panels) show no such defects. The use of the low copper
electrolyte substantially reduced the number and severity of
plating defects seen in the features and appears to have eliminated
such defects altogether. FIG. 8 focuses on the benefits of low
copper and low acid electrolytes, and does not examine the effect
of high halide ion concentrations.
Composition of Electrolyte
[0097] Electrolytes used in the embodiments disclosed herein may
contain copper ions, acid, water, halide ions, and organic
additives such as suppressors, accelerators and levelers. The
concentration of copper ions (Cu.sup.2+) in the electrolyte may be
between about 4-10 g/L, in some cases between about 4-8 g/L or
between about 4-5 g/L. The copper ions are typically provided in
the form of a copper salt. Example copper salts include, but are
not limited to, copper sulfate, copper methanesulfonate, copper
pyrophosphate, copper propanesulfonate, etc. The copper
concentrations cited herein include only the mass of the copper
cations and do not include the mass of any associated anions. The
concentration of acid in the electrolyte may be less than about 10
g/L acid. In some cases, the acid concentration is between about
2-15 g/L acid, though in certain implementations the concentration
is limited to between about 5-10 g/L. Other implementations of the
invention may utilize acid concentrations above 15 g/L. Example
acids include, but are not limited to, sulfuric acid and
methanesulfonic acid. The acid will dissociate into cations and
anions, and the anions are typically the same species as anions
formed from the copper salt. The acid concentrations cited herein
include the mass of both the hydrogen cation and the associated
anion in solution. The acid concentration may be varied to control
the conductivity of the plating bath. In addition to increasing the
polarization of the electrolyte as described above, low acid
electrolytes may be further beneficial because they use less acid
(reducing cost), are safer to use, and are easier on the plating
equipment (causing less equipment damage over time).
[0098] The electrolytes used herein are typically aqueous and
generally contain halide ions. Example halide ions include, but are
not limited to, chloride ions, bromide ions, iodide ions, and
combinations thereof. It is believed that halide ions act as
bridges to assist the adsorption of organic additives on the copper
surface to achieve bottom-up fill of the features. The
concentration of halide ions may range between about 150-400 ppm,
in some cases between about 150-300 ppm, or between about 200-300
ppm, or between about 250-300 ppm. The halide ion concentrations
cited herein include the mass of the halide anions, and do not
include the mass of any associated cations. In certain embodiments,
the oxygen level of the electrolyte is less than about 1-2 ppm in
order to minimize seed oxidation/corrosion in the electrolyte.
[0099] Next, the electrolyte may contain organic additives such as
suppressors, accelerators and/or levelers. A detailed description
of the function, interaction and identity of these additives is
included above. The concentration of organic additives in the
electrolyte may range between about 10-500 mg/L. This concentration
corresponds to the mass of active components in the additives and
does not include the mass of non-active components. The use of a
low copper electrolyte allows plating to occur at relatively low
suppressor concentrations as compared to conventional
electroplating electrolytes. In certain embodiments, the
concentration of suppressor is between about 50-200 ppm, between
about 50-300 ppm, and/or below about 200 ppm. Because the
concentration of suppressor is relatively low, the electrolyte will
tend to have a cloud point that is relatively high. In some
embodiments, the cloud point of the electrolyte is between about
40-100.degree. C., between about 50-100.degree. C., or between
about 60-100.degree. C.
[0100] Three example electrolyte compositions are shown in Table 2.
These compositions are included for exemplary purposes only, and
should not be construed as limiting. Electrolyte 1 has a high
chloride ion concentration as described herein.
TABLE-US-00002 TABLE 2 Electrolyte 1 Electrolyte 2 Electrolyte 3
Copper ion concentration 4-20 4-20 4-20 (g/L) Sulfuric acid
concentration 5-10 5-10 5-10 (g/L) Halide ion concentration 150-400
10-100 10-100 (mg/L) mg/L Cl- mg/L Cl.sup.-; mg/L Br.sup.-; 0.5-25
mg/L Br.sup.- Organic additive 10-500 10-500 10-500 concentration
(mg/L)
Apparatus for Plating
[0101] Many apparatus configurations may be used in accordance with
the embodiments described herein. One example apparatus includes a
clamshell fixture that seals a wafer's backside away from the
plating solution while allowing plating to proceed on the wafer's
face. The clamshell fixture may support the wafer, for example, via
a seal placed over the bevel of the wafer, or by means such as a
vacuum applied to the back of a wafer in conjunction with seals
applied near the bevel.
[0102] The clamshell fixture should enter the bath in a way that
allows good wetting of the wafer's plating surface. The quality of
substrate wetting is affected by multiple variables including, but
not limited to, clamshell rotation speed, vertical entry speed, and
the angle of the clamshell relative to the surface of the plating
bath. These variables and their effects are further discussed in
U.S. Pat. No. 6,551,487, incorporated by reference herein. In
certain implementations, the electrode rotation rate is between
about 5-125 RPM, the vertical entry speed is between about 5-300
mm/s, and the angle of the clamshell relative to the surface of the
plating bath is between about 1-10 degrees. One of the goals in
optimizing these variables for a particular application is to
achieve good wetting by fully displacing air from the wafer
surface.
[0103] The electrodeposition methods disclosed herein can be
described in reference to, and may be employed in the context of,
various electroplating tool apparatuses. One example of a plating
apparatus that may be used according to the embodiments herein is
the Lam Research Sabre tool. Electrodeposition, including substrate
immersion, and other methods disclosed herein can be performed in
components that form a larger electrodeposition apparatus. FIG. 9
shows a schematic of a top view of an example electrodeposition
apparatus. The electrodeposition apparatus 900 can include three
separate electroplating modules 902, 904, and 906. The
electrodeposition apparatus 900 can also include three separate
modules 912, 914, and 916 configured for various process
operations. For example, in some embodiments, one or more of
modules 912, 914, and 916 may be a spin rinse drying (SRD) module.
In other embodiments, one or more of the modules 912, 914, and 916
may be post-electrofill modules (PEMs), each configured to perform
a function, such as edge bevel removal, backside etching, and acid
cleaning of substrates after they have been processed by one of the
electroplating modules 902, 904, and 906.
[0104] The electrodeposition apparatus 900 includes a central
electrodeposition chamber 924. The central electrodeposition
chamber 924 is a chamber that holds the chemical solution used as
the electroplating solution in the electroplating modules 902, 904,
and 906. The electrodeposition apparatus 900 also includes a dosing
system 926 that may store and deliver additives for the
electroplating solution. A chemical dilution module 922 may store
and mix chemicals to be used as an etchant. A filtration and
pumping unit 928 may filter the electroplating solution for the
central electrodeposition chamber 924 and pump it to the
electroplating modules.
[0105] A system controller 930 provides electronic and interface
controls required to operate the electrodeposition apparatus 900.
The system controller 930 (which may include one or more physical
or logical controllers) controls some or all of the properties of
the electroplating apparatus 900. The system controller 930
typically includes one or more memory devices and one or more
processors. The processor may include a central processing unit
(CPU) or computer, analog and/or digital input/output connections,
stepper motor controller boards, and other like components.
Instructions for implementing appropriate control operations as
described herein may be executed on the processor. These
instructions may be stored on the memory devices associated with
the system controller 930 or they may be provided over a network.
In certain embodiments, the system controller 930 executes system
control software.
[0106] The system control software in the electrodeposition
apparatus 900 may include instructions for controlling the timing,
mixture of electrolyte components (including the concentration of
one or more electrolyte components), inlet pressure, plating cell
pressure, plating cell temperature, substrate temperature, current
and potential applied to the substrate and any other electrodes,
substrate position, substrate rotation, and other parameters of a
particular process performed by the electrodeposition apparatus
900. The system control logic may also include instructions for
electroplating under conditions that are tailored to be appropriate
for a low copper concentration electrolyte and the high
overpotential associated therewith. For example, the system control
logic may be configured to provide a relatively low current density
during the bottom-up fill stage and/or a higher current density
during the overburden stage. The control logic may also be
configured to provide certain levels of mass transfer to the wafer
surface during plating. For example, the control logic may be
configured to control the flow of electrolyte to ensure sufficient
mass transfer to the wafer during plating such that the substrate
does not encounter depleted copper conditions. In certain
embodiments the control logic may operate to provide different
levels of mass transfer at different stages of the plating process
(e.g., higher mass transfer during the bottom-up fill stage than
during the overburden stage, or lower mass transfer during the
bottom-up fill stage than during the overburden stage). Further,
the system control logic may be configured to maintain the
concentration of one or more electrolyte components within any of
the ranges disclosed herein. As a particular example, the system
control logic may be designed or configured to maintain the
concentration of copper cations between about 1-10 g/L. System
control logic may be configured in any suitable way. For example,
various process tool component sub-routines or control objects may
be written to control operation of the process tool components
necessary to carry out various process tool processes. System
control software may be coded in any suitable computer readable
programming language. The logic may also be implemented as hardware
in a programmable logic device (e.g., an FPGA), an ASIC, or other
appropriate vehicle.
[0107] In some embodiments, system control logic includes
input/output control (IOC) sequencing instructions for controlling
the various parameters described above. For example, each phase of
an electroplating process may include one or more instructions for
execution by the system controller 930. The instructions for
setting process conditions for an immersion process phase may be
included in a corresponding immersion recipe phase. In some
embodiments, the electroplating recipe phases may be sequentially
arranged, so that all instructions for an electroplating process
phase are executed concurrently with that process phase.
[0108] The control logic may be divided into various components
such as programs or sections of programs in some embodiments.
Examples of logic components for this purpose include a substrate
positioning component, an electrolyte composition control
component, a pressure control component, a heater control
component, and a potential/current power supply control
component.
[0109] In some embodiments, there may be a user interface
associated with the system controller 930. The user interface may
include a display screen, graphical software displays of the
apparatus and/or process conditions, and user input devices such as
pointing devices, keyboards, touch screens, microphones, etc.
[0110] In some embodiments, parameters adjusted by the system
controller 930 may relate to process conditions. Non-limiting
examples include bath conditions (temperature, composition, and
flow rate), substrate position (rotation rate, linear (vertical)
speed, angle from horizontal) at various stages, etc. These
parameters may be provided to the user in the form of a recipe,
which may be entered utilizing the user interface.
[0111] Signals for monitoring the process may be provided by analog
and/or digital input connections of the system controller 930 from
various process tool sensors. The signals for controlling the
process may be output on the analog and digital output connections
of the process tool. Non-limiting examples of process tool sensors
that may be monitored include mass flow controllers, pressure
sensors (such as manometers), thermocouples, optical position
sensors, etc. Appropriately programmed feedback and control
algorithms may be used with data from these sensors to maintain
process conditions.
[0112] In one embodiment, the instructions can include inserting
the substrate in a wafer holder, tilting the substrate, biasing the
substrate during immersion, and electrodepositing a copper
containing structure on a substrate.
[0113] A hand-off tool 940 may select a substrate from a substrate
cassette such as the cassette 942 or the cassette 944. The
cassettes 942 or 944 may be front opening unified pods (FOUPs). A
FOUP is an enclosure designed to hold substrates securely and
safely in a controlled environment and to allow the substrates to
be removed for processing or measurement by tools equipped with
appropriate load ports and robotic handling systems. The hand-off
tool 940 may hold the substrate using a vacuum attachment or some
other attaching mechanism.
[0114] The hand-off tool 940 may interface with a wafer handling
station 932, the cassettes 942 or 944, a transfer station 950, or
an aligner 948. From the transfer station 950, a hand-off tool 946
may gain access to the substrate. The transfer station 950 may be a
slot or a position from and to which hand-off tools 940 and 946 may
pass substrates without going through the aligner 948. In some
embodiments, however, to ensure that a substrate is properly
aligned on the hand-off tool 946 for precision delivery to an
electroplating module, the hand-off tool 946 may align the
substrate with an aligner 948. The hand-off tool 946 may also
deliver a substrate to one of the electroplating modules 902, 904,
or 906 or to one of the three separate modules 912, 914, and 916
configured for various process operations.
[0115] An example of a process operation according to the methods
described above may proceed as follows: (1) electrodeposit copper
onto a substrate to form a copper containing structure in the
electroplating module 904; (2) rinse and dry the substrate in SRD
in module 912; and, (3) perform edge bevel removal in module
914.
[0116] An apparatus configured to allow efficient cycling of
substrates through sequential plating, rinsing, drying, and PEM
process operations may be useful for implementations for use in a
manufacturing environment. To accomplish this, the module 912 can
be configured as a spin rinse dryer and an edge bevel removal
chamber. With such a module 912, the substrate would only need to
be transported between the electroplating module 904 and the module
912 for the copper plating and EBR operations.
[0117] In some implementations, a controller (e.g., system
controller 930) is part of a system, which may be part of the
above-described examples. Such systems can comprise semiconductor
processing equipment, including a processing tool or tools, chamber
or chambers, a platform or platforms for processing, and/or
specific processing components (a wafer pedestal, a gas flow
system, etc.). These systems may be integrated with electronics for
controlling their operation before, during, and after processing of
a semiconductor wafer or substrate. The electronics may be referred
to as the "controller," which may control various components or
subparts of the system or systems. The controller, depending on the
processing requirements and/or the type of system, may be
programmed to control any of the processes disclosed herein,
including the delivery of processing gases, temperature settings
(e.g., heating and/or cooling), pressure settings, vacuum settings,
power settings, radio frequency (RF) generator settings, RF
matching circuit settings, frequency settings, flow rate settings,
fluid delivery settings, positional and operation settings, wafer
transfers into and out of a tool and other transfer tools and/or
load locks connected to or interfaced with a specific system.
[0118] Broadly speaking, the controller may be defined as
electronics having various integrated circuits, logic, memory,
and/or software that receive instructions, issue instructions,
control operation, enable cleaning operations, enable endpoint
measurements, and the like. The integrated circuits may include
chips in the form of firmware that store program instructions,
digital signal processors (DSPs), chips defined as application
specific integrated circuits (ASICs), and/or one or more
microprocessors, or microcontrollers that execute program
instructions (e.g., software). Program instructions may be
instructions communicated to the controller in the form of various
individual settings (or program files), defining operational
parameters for carrying out a particular process on or for a
semiconductor wafer or to a system. The operational parameters may,
in some embodiments, be part of a recipe defined by process
engineers to accomplish one or more processing steps during the
fabrication of one or more layers, materials, metals, oxides,
silicon, silicon dioxide, surfaces, circuits, and/or dies of a
wafer.
[0119] The controller, in some implementations, may be a part of or
coupled to a computer that is integrated with, coupled to the
system, otherwise networked to the system, or a combination
thereof. For example, the controller may be in the "cloud" or all
or a part of a fab host computer system, which can allow for remote
access of the wafer processing. The computer may enable remote
access to the system to monitor current progress of fabrication
operations, examine a history of past fabrication operations,
examine trends or performance metrics from a plurality of
fabrication operations, to change parameters of current processing,
to set processing steps to follow a current processing, or to start
a new process. In some examples, a remote computer (e.g. a server)
can provide process recipes to a system over a network, which may
include a local network or the Internet. The remote computer may
include a user interface that enables entry or programming of
parameters and/or settings, which are then communicated to the
system from the remote computer. In some examples, the controller
receives instructions in the form of data, which specify parameters
for each of the processing steps to be performed during one or more
operations. It should be understood that the parameters may be
specific to the type of process to be performed and the type of
tool that the controller is configured to interface with or
control. Thus as described above, the controller may be
distributed, such as by comprising one or more discrete controllers
that are networked together and working towards a common purpose,
such as the processes and controls described herein. An example of
a distributed controller for such purposes would be one or more
integrated circuits on a chamber in communication with one or more
integrated circuits located remotely (such as at the platform level
or as part of a remote computer) that combine to control a process
on the chamber.
[0120] Without limitation, example systems may include a plasma
etch chamber or module, a deposition chamber or module, a
spin-rinse chamber or module, a metal plating chamber or module, a
clean chamber or module, a bevel edge etch chamber or module, a
physical vapor deposition (PVD) chamber or module, a chemical vapor
deposition (CVD) chamber or module, an atomic layer deposition
(ALD) chamber or module, an atomic layer etch (ALE) chamber or
module, an ion implantation chamber or module, a track chamber or
module, and any other semiconductor processing systems that may be
associated or used in the fabrication and/or manufacturing of
semiconductor wafers.
[0121] As noted above, depending on the process step or steps to be
performed by the tool, the controller might communicate with one or
more of other tool circuits or modules, other tool components,
cluster tools, other tool interfaces, adjacent tools, neighboring
tools, tools located throughout a factory, a main computer, another
controller, or tools used in material transport that bring
containers of wafers to and from tool locations and/or load ports
in a semiconductor manufacturing factory.
[0122] An alternative embodiment of an electrodeposition apparatus
1000 is schematically illustrated in FIG. 10. In this embodiment,
the electrodeposition apparatus 1000 has a set of electroplating
cells 1007, each containing an electroplating bath, in a paired or
multiple "duet" configuration. In addition to electroplating per
se, the electrodeposition apparatus 1000 may perform a variety of
other electroplating related processes and sub-steps, such as
spin-rinsing, spin-drying, metal and silicon wet etching,
electroless deposition, pre-wetting and pre-chemical treating,
reducing, annealing, photoresist stripping, and surface
pre-activation, for example. The electrodeposition apparatus 1000
is shown schematically looking top down in FIG. 10, and only a
single level or "floor" is revealed in the figure, but it is to be
readily understood by one having ordinary skill in the art that
such an apparatus, e.g. the Novellus Sabre.TM. 3 D tool, can have
two or more levels "stacked" on top of each other, each potentially
having identical or different types of processing stations.
[0123] Referring once again to FIG. 10, the substrates 1006 that
are to be electroplated are generally fed to the electrodeposition
apparatus 1000 through a front end loading FOUP 1001 and, in this
example, are brought from the FOUP to the main substrate processing
area of the electrodeposition apparatus 1000 via a front-end robot
1002 that can retract and move a substrate 1006 driven by a spindle
1003 in multiple dimensions from one station to another of the
accessible stations--two front-end accessible stations 1004 and
also two front-end accessible stations 1008 are shown in this
example. The front-end accessible stations 1004 and 1008 may
include, for example, pre-treatment stations, and spin rinse drying
(SRD) stations. Lateral movement from side-to-side of the front-end
robot 1002 is accomplished utilizing robot track 1002a. Each of the
substrates 1006 may be held by a cup/cone assembly (not shown)
driven by a spindle 1003 connected to a motor (not shown), and the
motor may be attached to a mounting bracket 1009. Also shown in
this example are the four "duets" of electroplating cells 1007, for
a total of eight electroplating cells 1007. The electroplating
cells 1007 may be used for electroplating copper for the copper
containing structure and electroplating solder material for the
solder structure. A system controller (not shown) may be coupled to
the electrodeposition apparatus 1000 to control some or all of the
properties of the electrodeposition apparatus 1000. The system
controller may be programmed or otherwise configured to execute
instructions according to processes described earlier herein.
[0124] The electroplating apparatus/methods described hereinabove
may be used in conjunction with lithographic patterning tools or
processes, for example, for the fabrication or manufacture of
semiconductor devices, displays, LEDs, photovoltaic panels and the
like. Generally, though not necessarily, such tools/processes will
be used or conducted together in a common fabrication facility.
Lithographic patterning of a film generally comprises some or all
of the following steps, each step enabled with a number of possible
tools: (1) application of photoresist on a work piece, i.e., a
substrate, using a spin-on or spray-on tool; (2) curing of
photoresist using a hot plate or furnace or UV curing tool; (3)
exposing the photoresist to visible, UV, or x-ray light with a tool
such as a wafer stepper; (4) developing the resist so as to
selectively remove resist and thereby pattern it using a tool such
as a wet bench; (5) transferring the resist pattern into an
underlying film or work piece by using a dry or plasma-assisted
etching tool; and (6) removing the resist using a tool such as an
RF or microwave plasma resist stripper.
[0125] It is to be understood that the configurations and/or
approaches described herein are exemplary in nature, and that these
specific embodiments or examples are not to be considered in a
limiting sense, because numerous variations are possible. The
specific routines or methods described herein may represent one or
more of any number of processing strategies. As such, various acts
illustrated may be performed in the sequence illustrated, in other
sequences, in parallel, or in some cases omitted. Likewise, the
order of the above described processes may be changed.
[0126] The subject matter of the present disclosure includes all
novel and nonobvious combinations and sub-combinations of the
various processes, systems and configurations, and other features,
functions, acts, and/or properties disclosed herein, as well as any
and all equivalents thereof.
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