U.S. patent application number 14/010404 was filed with the patent office on 2015-02-26 for bottom-up fill in damascene features.
This patent application is currently assigned to Lam Research Corporation. The applicant listed for this patent is Lam Research Corporation. Invention is credited to Jonathan D. Reid, Huanfeng Zhu.
Application Number | 20150053565 14/010404 |
Document ID | / |
Family ID | 52479389 |
Filed Date | 2015-02-26 |
United States Patent
Application |
20150053565 |
Kind Code |
A1 |
Zhu; Huanfeng ; et
al. |
February 26, 2015 |
BOTTOM-UP FILL IN DAMASCENE FEATURES
Abstract
The embodiments herein relate to methods and apparatus for
filling features with copper by a bottom-up fill mechanism without
the use of organic plating additives. In some cases, filling occurs
directly on a semi-noble metal layer, without the deposition of a
copper seed layer. In other cases, the filling occurs on a copper
seed layer. Factors such as the polarization of electrolyte, the
use of a complexing agent, electrolyte pH, electrolyte temperature,
and the waveform used to deposit material may contribute to
promoting the bottom-up fill.
Inventors: |
Zhu; Huanfeng; (West Linn,
OR) ; Reid; Jonathan D.; (Sherwood, OR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lam Research Corporation |
Fremont |
CA |
US |
|
|
Assignee: |
Lam Research Corporation
Fremont
CA
|
Family ID: |
52479389 |
Appl. No.: |
14/010404 |
Filed: |
August 26, 2013 |
Current U.S.
Class: |
205/122 ;
204/229.4 |
Current CPC
Class: |
C25D 3/38 20130101; C25D
17/001 20130101; C25D 5/18 20130101; C25D 21/12 20130101; C25D
7/123 20130101 |
Class at
Publication: |
205/122 ;
204/229.4 |
International
Class: |
C25D 3/38 20060101
C25D003/38 |
Claims
1. A method of performing a one step electrofill process to fill
features on a partially fabricated integrated circuit, comprising:
(a) receiving a substrate having an exposed semi-noble metal layer
and a plurality of features thereon; (b) contacting the substrate
with electrolyte comprising: (i) between about 1-100 mM copper
cations; and (ii) a complexing agent that forms a complex with the
copper cations, wherein the electrolyte is substantially free of
suppressors, accelerators and levelers; and (c) while contacting
the electrolyte, electroplating copper into the features by a
bottom-up fill mechanism at a substrate potential for
electrodeposition between about 0.03 and 0.33 V versus an NHE
reference electrode.
2. The method of claim 1, wherein no suppressor, accelerator, or
leveler substantially contributes to the bottom-up fill
mechanism.
3. The method of claim 1, wherein the bottom-up fill is conducted
directly on the semi-noble metal layer, without first forming a
seed layer.
4. The method of claim 1, wherein electroplating copper in
operation (c) comprises applying a modulated waveform that
alternately pulses current at a first level that deposits copper on
the substrate and a second level that etches copper from copper
that was previously electroplated on the substrate.
5. The method of claim 4, wherein the second level of current that
etches copper has an absolute value between about 0.05-0.3
mA/cm.sup.2, and wherein the pulses of current alternate between
the first current level and second current level with a frequency
between about 100-1000 Hz.
6. The method of claim 1, wherein the complexing agent is selected
from the group consisting of ethylenediaminetetraacetic acid
(EDTA), nitrilotriacetic acid (NTA), citric acid, and glutamic
acid.
7. The method of claim 6, wherein the complexing agent is
ethylenediaminetetraacetic acid (EDTA).
8. The method of claim 1, wherein, during electroplating, the
electrolyte is held at a temperature between about 20-80.degree.
C.
9. The method of claim 8, wherein, during electroplating, the
electrolyte is held at a temperature between about 50-70.degree.
C.
10. The method of claim 1, wherein, during electroplating, the
electroplating surface of the substrate experiences a current
density of between about 0.1 and 2 mA/cm.sup.2.
11. The method of claim 1, wherein a pH of the electrolyte is
between about 1-5.
12. The method of claim 1, wherein the semi-noble metal layer
comprises a material selected from the group consisting of
ruthenium, tungsten, cobalt, osmium, platinum, palladium, aluminum,
gold, silver, iridium and rhodium.
13. The method of claim 12, wherein the semi-noble metal layer
comprises ruthenium.
14. The method of claim 1, wherein at least some of the features
have a width of about 100 nm or less.
15. The method of claim 14, wherein at least some of the features
have a width of about 20 nm or less.
16. The method of claim 1, wherein the electrolyte comprises about
2 ppm or less dissolved oxygen.
17. A method of performing a one step electrofill process to fill
features on a partially fabricated integrated circuit, comprising:
(a) receiving a substrate having an exposed semi-noble metal layer
and a plurality of features thereon; (b) contacting the substrate
with electrolyte comprising between about 1-100 mM copper cations,
wherein the electrolyte is substantially free of suppressors,
accelerators and levelers; and (c) while contacting the substrate
with electrolyte, applying a modulated waveform that alternately
pulses current at a first level that deposits copper on the
substrate and a second level that etches copper from copper that
was previously electroplated on the substrate, to thereby
electroplate copper into the features by a bottom-up fill mechanism
at a substrate potential for electrodeposition between about 0.03
and 0.33 V versus an NHE reference electrode.
18. The method of claim 17, wherein the second level of current
that etches copper has an absolute value between about 0.05 and 0.3
mA/cm.sup.2, and wherein the pulses of current alternate between
the first current level and second current level with a frequency
between about 100-1000 Hz.
19. A method of depositing copper in a feature on a partially
fabricated integrated circuit, comprising: (a) receiving a
substrate having a plurality of features and a copper seed layer
thereon; (b) contacting the substrate with electrolyte comprising
between about 1-100 mM copper cations, wherein the electrolyte is
substantially free of suppressors, accelerators and levelers; and
(c) electroplating copper into the feature by a bottom-up fill
mechanism at a potential between about 0.03 and 0.33 V versus an
NHE reference electrode.
20. The method of claim 19, wherein, during electroplating, the
electrolyte is held at a temperature between about 20-80.degree.
C.
21. The method of claim 20, wherein, during electroplating, the
electrolyte is held at a temperature between about 20-50.degree.
C.
22. The method of claim 19, wherein, during electroplating, the
electroplating surface of the substrate has a current density of
between about 0.1-2 mA/cm.sup.2.
23. The method of claim 19, wherein a pH of the electrolyte is
between about 1-5.
24. The method of claim 19, at least some of the features have a
width of about 100 nm or less.
25. The method of claim 24, at least some of the features have a
width of about 20 nm or less.
26. The method of claim 19, wherein electroplating copper in
operation (c) comprises applying a galvanostatically controlled
current to the substrate.
27. An apparatus for electroplating copper into features on a
substrate, comprising: (a) one or more electroplating baths
configured to contain electrolyte; (b) a substrate supporter; and
(c) a controller having a set of instructions comprising
instructions for: receiving electrolyte into the one or more
electroplating baths; immersing the substrate in electrolyte;
maintaining a substrate potential between about 0.03-0.33 V versus
an NHE reference electrode to thereby electroplate copper into the
features by a bottom-up fill mechanism that does not substantially
rely on the presence of suppressor, accelerator or leveler.
Description
BACKGROUND
[0001] In damascene processing, copper is deposited into features
on a partially fabricated semiconductor substrate. The conventional
copper deposition typically occurs in two steps. First, a copper
seed layer is deposited on the substrate using a physical vapor
deposition (PVD) process. Next, copper is electroplated on the seed
layer to fill the features. As the critical dimension of damascene
interconnects decreases over time, it is increasingly difficult to
obtain uniform copper coverage over all surfaces when depositing
the seed layer through the PVD process. Non-uniform seed layer
coverage is problematic because thin copper seed areas are
especially susceptible to oxidation and dissolution in electrolyte
during the initial stages of the electroplating process. In other
words, areas of the seed which are thinner (e.g., on the sidewall
of a feature) tend to dissolve in electrolyte to yield a
discontinuous metal seed layer. When electroplating takes place on
the discontinuous seed layer, the plating results are non-uniform
and defects may be introduced.
[0002] Certain techniques (e.g., immersion at high voltage initial
plating conditions, seed pre-treatment, etc.) may be used to reduce
seed dissolution. However, some amount of seed dissolution is
expected, even when these techniques are fully utilized. As such,
there exists a need for a method of depositing copper in
semiconductor features that does not require deposition of a copper
seed layer.
[0003] One technique that has been developed avoids the use of PVD
to deposit the copper seed by directly electroplating the copper
seed layer on a semi-noble surface such as a layer of ruthenium.
However, the process used to electroplate the seed layer and the
process used to subsequently fill the feature require substantially
different electrolytes, and the copper electroplating must
therefore occur over two discrete processes.
[0004] Electrolytes used in electroplating copper onto the seed
layer in 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, which encourage a conventional bottom-up
fill mechanism, described below.
[0005] In conventional electroplating of copper, the organic
additives are critical to achieving the desired metallurgy, film
uniformity, defect control and fill performance. However, the
concentration of organic additives can change over time, and
careful attention must be paid to tracking the electrolyte
composition to ensure proper plating results. The concentration of
the additives is very low in many cases, and it is difficult to
accurately track the electrolyte composition within the relevant
tolerances. Because of this difficulty, a certain portion of
substrates may be plated in baths that do not have a proper balance
of additives, and may not be suitable for further use. Thus, there
exists a need for a method of electroplating copper into
semiconductor features that does not employ conventional organic
additives such as suppressors, accelerators or levelers.
SUMMARY
[0006] Certain embodiments herein relate to methods and apparatus
for performing bottom-up fill in a feature on a substrate. In one
aspect of the embodiments herein, a method is provided for
performing a one step electrofill process to fill features on a
partially fabricated integrated circuit. The method may include (a)
receiving a substrate having an exposed semi-noble metal layer and
a plurality of features thereon; (b) contacting the substrate with
electrolyte having (i) between about 1-100 mM copper cations; and
(ii) a complexing agent that forms a complex with the copper
cations, where the electrolyte is substantially free of
suppressors, accelerators and levelers; and (c) while contacting
the electrolyte, electroplating copper into the features by a
bottom-up fill mechanism at a substrate potential for
electrodeposition between about 0.03 and 0.33 V versus an NHE
reference electrode.
[0007] In various embodiments, no suppressor, accelerator, or
leveler substantially contributes to the bottom-up fill mechanism.
The bottom-up fill may be conducted directly on the semi-noble
metal layer, without first forming a seed layer. Various different
waveforms may be used. In some cases, electroplating copper in
operation (c) includes applying a modulated waveform that
alternately pulses current at a first level that deposits copper on
the substrate and a second level that etches copper from copper
that was previously electroplated on the substrate. The second
level of current that etches copper may have an absolute value
below about 0.1 mA for a 300 mm diameter wafer. In certain
embodiments, the pulses of current alternate between the first
current level and the second current level with a frequency between
about 100-1000 Hz. In these or other cases, the electroplating
surface of the substrate may experience a current density of
between about 0.004-0.4 mA/cm.sup.2.
[0008] A number of different complexing agents may be used. In some
implementations, the complexing agent is selected from the group
consisting of ethylenediaminetetraacetic acid (EDTA),
nitrilotriacetric acid (NTA), citric acid, and glutamic acid. In a
particular case, the complexing agent is EDTA. The electrolyte may
be at or above about room temperature. In one embodiment, the
electrolyte is held at a temperature between about 20-80.degree.
C., for example between about 50-70.degree. C. The pH of the
electrolyte may be between about 1-5 in some cases between about
1.5-3.5. The dissolved oxygen content of the electrolyte may be
about 2 ppm or lower.
[0009] The methods herein may be used to plate on a variety of
different metals. In some cases, the semi-noble metal layer
includes a material selected from the group consisting of
ruthenium, tungsten, cobalt, osmium, platinum, palladium, aluminum,
gold, silver, iridium, and rhodium. In a particular case the
semi-noble metal layer is ruthenium. In some embodiments, at least
some of the features on the semiconductor substrate have an opening
width of about 100 nm or less. For instance, in some cases the
features have a width of about 20 nm or less.
[0010] In another aspect of the disclosed embodiments, a method of
depositing copper in a feature on a partially fabricated integrated
circuit is provided. The method may include (a) receiving a
substrate having a plurality of features and a copper seed layer
thereon; (b) contacting the substrate with electrolyte having
between about 1-100 mM copper cations, where the electrolyte is
substantially free of suppressors, accelerators and levelers; and
(c) electroplating copper into the feature by a bottom-up fill
mechanism at a potential between about 0.03-0.33 V versus an NHE
reference electrode.
[0011] In some embodiments, the electrolyte is held at a
temperature between about 20-80.degree. C. during electroplating,
for example between about 20-50.degree. C. The electroplating
surface of the substrate may experience a current density of
between about 0.004-0.4 mA/cm.sup.2. In certain implementations, a
pH of the electrolyte may be between about 1-5, for example between
about 1.5-3.5. The disclosed methods may be used to fill relatively
small features. In some cases, at least some of the features have a
width of about 100 nm or less, for example between about 20 nm or
less. In certain embodiments, electroplating copper in operation
(c) includes applying a galvanostatically controlled current to the
substrate.
[0012] These and other features will be described below with
reference to the associated drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 shows a flowchart for a method of electroplating
copper into a feature on a substrate having an exposed semi-noble
layer.
[0014] FIG. 2 shows a flowchart for a method of electroplating
copper into a feature on a substrate having an exposed copper seed
layer.
[0015] FIG. 3 depicts an exemplary multi-station apparatus in
accordance with the disclosed embodiments.
[0016] FIG. 4 depicts an alternative implementation of a
multi-station apparatus in accordance with the disclosed
embodiments.
[0017] FIG. 5 is a graph depicting the relative polarization effect
of different complexing agents in electrolyte.
[0018] FIG. 6 is a graph showing the relative polarization effect
of different copper cation concentrations and different pH levels
in electrolyte.
[0019] FIG. 7 is a graph showing the relative polarization effect
of different electrolyte temperatures.
[0020] FIGS. 8A-8C show SEM images of ruthenium seeded trench
coupons plated at 0.4 mA (FIG. 8A), 0.6 mA (FIG. 8B), and 1 mA
(FIG. 8C).
[0021] FIGS. 9A-9C show SEM images of ruthenium seeded trench
coupons plated using modulated waveforms at room temperature (FIG.
9A), 50.degree. C. (FIG. 9B), and 70.degree. C. (FIG. 9C).
[0022] FIGS. 10A and 10B show SEM images of ruthenium seeded trench
coupons plated in electrolytes containing NTA (FIG. 10A) and
glutamic acid (FIG. 10B) as complexing agents.
[0023] FIGS. 11A-11C and 12A-12C show cross-sectional (FIGS.
11A-11C) and top-down (FIGS. 12A-12C) SEM images of copper seeded
trench coupons plated at different temperatures.
[0024] FIG. 13 depicts a TEM image of a copper seeded trench coupon
plated in electrolyte lacking a complexing agent.
DETAILED DESCRIPTION
[0025] 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. A wafer or
substrate used in the semiconductor device industry typically has a
diameter of 200 mm, or 300 mm, or 450 mm. Further, the terms
"electrolyte," "plating bath," "bath," and "plating solution" are
used interchangeably. 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.
[0026] 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.
[0027] As mentioned above, conventional copper deposition processes
typically utilize organic additives such as suppressors,
accelerators and levelers to achieve a bottom-up fill. Though the
embodiments herein do not require the use of these additives, and
often benefit from their absence, the additives will be discussed
below for the purpose of comparison to the disclosed
implementations.
Suppressors
[0028] 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. 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.
[0029] Although suppressors adsorb onto a substrate surface, it is
believed that they are not incorporated into the deposited film and
may slowly degrade over time. Compounds which do not principally
act by adsorbing onto a substrate surface are not considered
suppressors. 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
[0030] 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. Compounds which do not principally act by adsorbing
onto a substrate surface are not considered to be accelerators.
Levelers
[0031] 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
adsorbed. 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.
[0032] 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. Compounds which do not
principally act by adsorbing onto a substrate surface are not
considered levelers. 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 Promoted by Organic Additives
[0033] In a 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. In
conventional applications, the three types of additives described
above are necessary in accomplishing bottom-up fill, each working
to selectively increase or decrease the polarization at the
substrate surface.
[0034] 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.
[0035] 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.
[0036] 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 is conventionally 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. In conventional applications, a feature may
tend to overfill and produce a bump in the absence of leveler.
Therefore, in the later stages of conventional bottom-up fill
plating, levelers are beneficial in producing a relatively flat
deposit.
[0037] The use of suppressor, accelerator and leveler, in
combination, allow a feature to be filled without voids from the
bottom-up and from the sidewalls-inward, 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 Without Organic Additives
[0038] One aspect of the disclosed embodiments is a method of
electroplating copper into features on a semiconductor substrate
having an exposed semi-noble metal liner. In this embodiment,
copper is electroplated directly onto the semi-noble liner, rather
than on a copper seed layer. While the electrolyte in this
implementation may include a complexing agent that complexes with
copper in the solution, the electrolyte is substantially free of
organic additives such as suppressor, accelerator and leveler.
Where some small amount of organic additives are present, it may be
the case that the organic additives do not substantially contribute
to the bottom-up fill mechanism. In other words, the bottom-up fill
would occur even in the absence of the organic additives, when
plating under otherwise identical plating conditions. Another
aspect of the disclosed embodiments is a method of electroplating
copper into features on a semiconductor substrate having an exposed
copper seed layer. As with the previous embodiment, this method may
be performed with electrolyte that is substantially free of
suppressor, accelerator and leveler. Despite the absence of organic
additives, the disclosed methods achieve a bottom-up fill mechanism
to fill the features.
Methods
Plating on a Semi-Noble Metal Layer
[0039] In one embodiment, copper is electroplated on an exposed
semi-noble metal liner layer. The semi-noble metal liner layer may
be ruthenium, cobalt, tungsten, osmium, platinum, palladium,
aluminum, gold, silver, iridium, rhodium, or a combination thereof.
A substrate having an exposed semi-noble layer is provided in an
electroplating cell and immersed in electrolyte having particular
characteristics, as discussed below. Current is applied to the
substrate to promote nucleation, followed by Volmer-Weber growth,
to thereby form three-dimensional copper islands. The copper
islands continue to grow until they coalesce into a continuous
copper film. The applied current depends on the composition of the
electrolyte, but is generally controlled to provide a voltage
between about 0 and 4V versus a normal hydrogen electrode (NHE), or
between about 0.03 and 0.33 V versus the NHE.
[0040] The electrolyte may be designed to help promote a high
nucleation density. One way to promote high nucleation density is
to use conditions that result in a relatively more polarized
electrolyte. Increased electrolyte polarization can be achieved by
using certain complexing agents such as ethylenediaminetetraacetic
acid (EDTA), nitrilotriacetic acid (NTA), citric acid, glutamic
acid, etc. in combination with low copper concentrations. These
complexing agents form complexes with copper ion dissolved in the
electrolyte. Complexing agents bind with copper ions by, e.g.,
electrostatic interactions and form a soluble complex. In various
examples, complexing agents are shaped to partially enclose
complexed copper ions and partially shield the copper ions.
Complexing agents do not appreciably adsorb onto the surface of the
substrate, at least not to the extent of conventional plating
additives such as suppressors, accelerators, and levelers. Thus,
the complexing agents employed herein are not suppressor compounds
(or accelerators or levelers). The polarization effects of
complexers such as those mentioned above are illustrated below in
the Experimental section.
[0041] The complexing agents promote high nucleation density.
Although the complexing agents are not suppressors (because they
principally act by forming complexes with copper in solution,
rather than acting by adsorbing onto the substrate surface), the
complexing agents do serve a suppressor-like function to increase
the overpotential of the copper electrodeposition. In some
embodiments, the concentration of complexing agent is between about
1-100 mM, for example between about 1-20 mM or between about 5-10
mM. The concentration of complexing agent may be substantially
similar (e.g., within about 30%) to the concentration of copper
cations, as measured in molar concentration. In some cases, these
concentrations are substantially equimolar (e.g., within about 10%,
or within about 5%). In a particular case, the concentration of
complexing agent and the concentration of copper cations are
exactly equimolar. Equimolar concentrations of copper cations and
complexing agents may be beneficial as the copper and complexing
agents together form a complex in a 1:1 ratio. In other cases,
these concentrations vary more considerably. In some embodiments,
the concentration of complexing agent may be higher than the
concentration of copper cations. Having a stoichiometric excess of
complexing agent may be beneficial in certain embodiments, as this
may help achieve a higher fraction of complexed copper cations,
which may contribute to achieving a high nucleation density on a
semi-noble metal surface.
[0042] In some embodiments, the complexing agent may be omitted.
When plating on a semi-noble metal layer without a complexing
agent, a modulated waveform may be used to help promote bottom-up
plating. Modulated waveforms are discussed further below.
[0043] The low copper concentration further contributes to the
relatively high polarization of the electrolyte. In some
embodiments, the concentration of copper cations is between about
1-100 mM, for example between about 1-20 mM, or between about 5-10
mM. The effect of different copper concentrations on the
polarization of solution is further discussed below in the
Experimental section.
[0044] Another factor affecting the polarization of the electrolyte
is the pH. Generally, electrolytes having higher pH are more
polarized. In certain embodiments, the pH of the electrolyte is
between about 1-5, for example between about 1.5-3.5. The effect of
different electrolyte pH is further discussed below in the
Experimental section.
[0045] The polarization of the electrolyte is also affected by the
temperature of the electrolyte. Generally, lower temperatures
result in higher electrolyte polarization. However, lower
temperatures also result in lower deposition rates and more
conformal films. In the context of bottom-up fill, conformal films
are undesirable because they can lead to the incorporation of
seams/voids inside features. As such, the increased polarization
benefits at low temperatures should be balanced against the high
temperature advantages of increased deposition rate and less
conformal films. In some embodiments, deposition occurs at a
temperature between about 20-80.degree. C., for example between
about 50-70.degree. C. Conventional bottom-up fill processes
typically occur at about 20-25.degree. C. One benefit of the
disclosed embodiments is that where filling occurs at an elevated
temperature, the deposition rate may be higher than in the
conventional processes, which generally take place at lower
temperatures.
[0046] The waveform applied to drive electrodeposition may also
have an effect on the fill mechanism. In some embodiments, a DC
current is used (e.g., with galvanostatic or galvanodynamic
control). In other embodiments, a modulated waveform is used (e.g.,
with current alternating between deposition and etching currents).
The use of a modulated waveform may result in a film that is less
conformal, which is beneficial in the context of bottom-up
fill.
[0047] As known to those of skill in the art, the maximum current
used for deposition (the limiting current) is affected by the
availability of copper at the substrate-electrolyte interface. If
the current goes above an acceptable level, the electrolyte may
experience copper depletion, resulting in poor deposition results.
In other words, there may be an insufficient amount of copper at
the interface to sustain the reduction reaction at the relevant
level of current. Instead, a parasitic reaction may 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, causing non-uniform plating and in some
cases the formation of nodular growths on the substrate. The
maximum current during etching is typically limited only by
hardware limitations, though care should be taken to ensure that
the current is not so high as to fully remove the previously
deposited metal.
[0048] In some embodiments, a current level used to deposit
material is between about 0.001-1.5 A, for example between about
0.05-1.4 A, or between about 0.05-1 A (based on a 300 mm wafer). In
these or other embodiments, the absolute value of a current level
used to etch material is between about 0.035-0.25 A, for example
between about 0.04-0.2 A, or below about 0.1 A (based on a 300 mm
wafer). In various cases, the current used to etch material is
negative. The current density during electroplating may be between
about 0.1-2 mA/cm.sup.2. The current density during etching may be
between about 0.05-0.3 mA/cm.sup.2. In implementations using a
modulated waveform (e.g., a square waveform), a frequency of the
waveform may be between about 100-1000 Hz. In other words, the
waveform may alternate between a deposition current and an etching
current at the disclosed frequency. The effect of different
waveforms on plating results is further discussed below in the
Experimental section.
[0049] Without wishing to be bound by a particular theory or
mechanism of action, it is believed that when a modulated waveform
is used, it may result in a redistribution of material on and in
the feature. During the etching portion of the waveform, copper may
be selectively etched near the top portion of the feature. The
copper farther down in the feature, near the feature bottom, is
less likely to be etched away. This selective etching may
effectively reduce the surface area of copper within the feature
that is available (and favorable) for plating. During a subsequent
deposition portion of the waveform, copper may tend to deposit more
toward the bottom of the feature, where the remaining copper is
concentrated, as the energy required to deposit in this region may
be lower than in regions near the top of the feature. While both
the deposition and etching operations act on all portions of the
feature, the deposition may occur more heavily near the feature
bottom as compared to the feature top, and the etching may occur
more heavily near the feature top as compared to the feature
bottom. Through repeated cycles of deposition and etching, copper
may be redistributed within the feature to achieve bottom-up fill.
Another factor which may contribute to the bottom-up fill mechanism
is the relatively low deposition rate. Because plating occurs over
a longer period of time, the copper has more time to redistribute
in the feature to provide a good fill result.
[0050] Where a DC waveform is used, the mechanism of action that
promotes bottom-up fill may be somewhat different. When copper is
combined with a complexing agent, e.g., a relatively weak
complexing agent such as NTA and/or glutamic acid, and is plated at
a low deposition rate, the fill mechanism may become less
conformal, leading to a bottom-up fill of the feature. The choice
of complexing agent, the concentration of copper in electrolyte,
the electrolyte pH and the electrolyte temperature all affect the
polarization of the solution. Bottom-up fill has been shown to
reliably occur where the substrate is maintained at a potential
between about 0.03 to 0.33 V vs. an NHE reference electrode. This
voltage range has been shown to be successful in promoting
bottom-up fill. If the voltage is significantly below this range,
the plating current is too low and very little copper will be
deposited; if the voltage is above this range, the fill behavior is
observed to be conformal, rather than bottom-up. By applying
current in such a way that the voltage falls within the cited
range, bottom up fill may be achieved. In certain embodiments, this
voltage corresponds to a potential between about -0.3 to -0.6 V
(e.g., about -0.4 to -0.5 V) vs. a mercury sulfate reference
electrode (MSE), as used in the experiments described below. By
maintaining the voltage in this range, in combination with the
electrolyte conditions described above, bottom-up fill is achieved
without the use of organic additives such as suppressors,
accelerators and levelers. In some cases, the electrolyte may
contain trace amounts of organic additives, but the additives do
not substantially contribute to the bottom-up fill mechanism.
[0051] FIG. 1 provides a flowchart depicting a method of filling a
feature on a semiconductor substrate having an exposed semi-noble
metal layer. The process 100 begins at block 101, where a substrate
having an exposed semi-noble metal layer is received/provided in an
electrodeposition chamber. The substrate typically has features
thereon which are to be filled through the electrodeposition
process. In some cases, the features may be trenches that are
between about 10-100 nm wide, for example between about 50-100 nm
wide. In these or other cases, the feature may have a width of
about 100 nm or less, for example about 20 nm or less. Next, at
block 103 the substrate is contacted with electrolyte that is
substantially free of suppressor, accelerator and leveler
compounds. The electrolyte may have the characteristics described
above such as a complexing agent, a low concentration of copper
cations, and a particular pH and/or temperature. These factors may
contribute to a relatively highly polarized electrolyte. At block
105, current is applied to the substrate. The applied current may
be a direct current or a modulated current, and is designed to
maintain a substrate potential between about 0.03-0.33 V vs. an NHE
reference electrode. This substrate potential, in combination with
the disclosed electrolyte, promotes bottom-up fill without the use
of organic plating additives.
Plating on a Copper Seed Layer
[0052] The method disclosed above relating to electrodeposition of
copper on a semi-noble metal layer may be extended to plating on a
copper seed layer. While this embodiment may not achieve the
benefit of a one-step fill (as the copper seed layer is deposited
separately from the copper fill material), this embodiment does
capture the advantage of electroplating copper through bottom-up
fill without the use of organic plating additives.
[0053] Generally, the teachings disclosed above related to
electrolyte composition/pH/temperature/waveform apply to plating on
copper seed layers, as well. However, some of the considerations
above are less important when plating on a copper seed layer, and
other considerations may be more important. For example, where
plating occurs on a copper seed layer, the complexing agent may be
omitted from the electrolyte. The complexing agent may be more
important in the context of plating on a semi-noble metal layer, as
the degree of polarization necessary to achieve proper plating
results may be higher when plating on semi-noble layers as compared
to plating on copper.
[0054] Further, when plating on a copper seed layer, the use of a
modulated waveform is somewhat more complicated. As with plating on
a semi-noble metal, the applied current may be galvanostatic or
galvanodynamic. The extra complication arises because there is a
chance that in some region on the substrate, all of the copper
(including the copper seed layer) could be dissolved during an
etching portion of a modulated waveform. If this occurs, then there
will be no appropriate surface on which to electroplate in this
region, and the plating results will be poor. While bottom-up fill
may be achieved using the disclosed method with a modulated
waveform, care should be taken to avoid seed dissolution.
Therefore, the etching portion of a waveform may be delayed until a
sufficient amount of copper is plated in an initial portion of the
plating sequence. Plating on a copper seed layer may also be
accomplished using a direct current waveform.
[0055] The optimal deposition temperature may be lower in the
embodiment employing a copper seed layer as compared to the
embodiment where plating occurs directly on a semi-noble metal
layer. In some cases, when plating on a copper seed, the
temperature is maintained between about 20-80.degree. C., for
example between about 20-50.degree. C.
[0056] Without wishing to be bound by any mechanism of action, it
is believed that the mechanism for bottom-up fill on copper seed
may be similar to the bottom-up fill mechanism described above in
relation to plating on a semi-noble metal layer such as ruthenium.
However, in various cases when plating on copper seed, it is not
necessary to use a complexing agent or a modulated waveform to
promote nucleation on the copper seed layer.
[0057] FIG. 2 provides a flowchart for a method of electroplating
copper onto a copper seed layer. The process 200 begins at block
201, where a substrate having an exposed layer of copper seed is
received/provided in an electrodeposition chamber. The substrate
will generally have features thereon which are to be filled through
the electrodeposition process. In some cases, the features may be
trenches that are between about 10-100 nm wide, for example between
about 50-100 nm wide. Next, at block 203 the substrate is contacted
with electrolyte that is substantially free of suppressor,
accelerator and leveler compounds. The electrolyte may have the
characteristics described above such as a complexing agent, a low
concentration of copper cations, and a particular pH and/or
temperature. In certain embodiments employing a copper seed layer,
no complexing agent is used. At block 205, current is applied to
the substrate. The applied current may be a direct current or a
modulated current, and is designed to maintain a substrate
potential between about 0.03-0.33 V vs. an NHE reference electrode.
This substrate potential, in combination with the disclosed
electrolyte, promotes bottom-up fill without the use of organic
plating additives.
Apparatus
[0058] 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.
[0059] 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.
[0060] 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. 3
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.
[0061] 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 electrolyte components 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.
[0062] 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.
[0063] 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 relatively high
overpotential associated therewith. For example, the system control
logic may be configured to provide a relatively low current density
during a bottom-up fill. 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 a bottom-up fill stage than during an
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, or the pH of the electrolyte,
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 1-100 mM. In
another example, the system control logic may be configured to
apply current so as to maintain the substrate at a potential
between about 0.03-0.33 V vs. an NHE electrode. 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.
[0064] 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.
[0065] 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.
[0066] 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.
[0067] In some embodiments, parameters adjusted by the system
controller 930 may relate to process conditions. Non-limiting
examples include bath conditions (temperature, composition, pH,
flow rate, etc.), substrate position (rotation rate, linear
(vertical) speed, angle from horizontal, etc.) and electrical
conditions (current, potential, etc.) 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.
[0068] 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.
[0069] 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.
[0070] 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.
[0071] 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.
[0072] 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.
[0073] 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.
[0074] An alternative embodiment of an electrodeposition apparatus
1000 is schematically illustrated in FIG. 4. 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. 4, 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. 3D tool, can have
two or more levels "stacked" on top of each other, each potentially
having identical or different types of processing stations.
[0075] Referring once again to FIG. 4, 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.
[0076] Lithographic patterning of a film typically comprises some
or all of the following steps, each step enabled with a number of
possible tools: (1) application of photoresist on a workpiece,
e.g., a substrate having a silicon nitride film formed thereon,
using a spin-on or spray-on tool; (2) curing of photoresist using a
hot plate or furnace or other suitable curing tool; (3) exposing
the photoresist to visible or 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 or a spray developer; (5) transferring the resist pattern
into an underlying film or workpiece 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. In some
embodiments, an ashable hard mask layer (such as an amorphous
carbon layer) and another suitable hard mask (such as an
antireflective layer) may be deposited prior to applying the
photoresist.
[0077] 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.
[0078] 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.
Experimental
[0079] Several experimental studies have shown that the disclosed
methods can be used to achieve bottom-up fill in the absence of
organic plating additives. The initial results provided in this
section relate to cyclic voltammetry (CV) scans showing the effect
that different parameters (e.g., the identity of a complexing
agent, concentration of copper cations, solution pH and solution
temperature) have on polarization. The latter results provided in
this section show fill results for features filled according to
different plating conditions. All of the results presented in this
section were generated without the use of organic plating
additives. Where coupons were used for plating, the coupons had a
plating area of about 1 cm.sup.2.
[0080] FIG. 5 shows CV results illustrating the relative effect of
different complexing agents on the polarization of the electrolyte.
The tested electrolytes contained 5 mM copper cations and 5 mM of
the relevant complexing agents. The CVs were collected on a
platinum rotating disk electrode (RDE) in a beaker with a scan rate
of 10 mV/s at a rotation speed of 200 RPM, with a mercury sulfate
reference electrode (MSE). Dissolved oxygen was controlled to be
about 1 ppm, and the pH was adjusted by tetramethylammonium
hydroxide (TMAH) or sulfuric acid to a pH of about 3. The
ethylenediaminetetraacetic acid (EDTA) solution was the most
strongly polarized, and the sulfate (SO.sub.4) solution was the
least polarized. The sulfate solution was the least polarized
because in that case, the copper only formed complexes with
water.
[0081] FIG. 6 shows CV results illustrating the relative effects of
different copper ion concentrations and pH levels on the
polarization of solutions containing EDTA as a complexing agent.
For each of these solutions, the concentration of copper cations
and the concentration of EDTA were equimolar. The results were
collected on a platinum RDE, with a scan rate of 10 mV/s at a
rotation speed of 200 RPM, with pH adjusted by TMAH or sulfuric
acid to the designated level. The reference electrode was an MSE
electrode. Lower copper concentrations and higher pH levels result
in more polarized solutions.
[0082] FIG. 7 shows CV results depicting the effect of electrolyte
temperature on the polarization of solutions containing 10 mM
copper cations and 10 mM EDTA. The data were collected on PVD
copper seed coupon attached on a RDE electrode at different
temperatures, with a scan rate of 10 mV/s at a rotation rate of 200
RPM. The reference electrode in this case was MSE, the level of
dissolved oxygen was around 1 ppm, and the pH was adjusted by TMAH
or sulfuric acid to about 2.3. The scans show that lower
temperatures result in more highly polarized solutions.
[0083] FIGS. 8A-8C depict scanning electron microscope (SEM) images
showing the resulting fill for ruthenium seeded trench coupons
attached to an RDE electrode after plating in electrolyte having 10
mM copper cations and 10 mM EDTA. The pH of each electrolyte was
adjusted by TMAH or sulfuric acid to a pH of about 2.3. The
dissolved oxygen level of each electrolyte was around 1 ppm. The
temperature of each electrolyte was about 70.degree. C. In this
case, the trenches had a width of about 80 nm, though the
techniques may also be applied to narrower trenches (e.g., about 20
nm wide trenches). The speed of rotation of the RDE was about 200
RPM, and the reference electrode was an MSE electrode. Each of the
coupons shown in FIGS. 8A-8C was plated under galvanostatic
conditions. The coupon shown in FIG. 8A was plated at 0.4 mA, 8B
was plated at 0.6 mA, and 8C was plated at 1 mA.
[0084] Void free bottom-up fill was achieved in the 80 nm trenches
for the coupons plated at 0.4 and 0.6 mA. However, when the DC
current was increased to 1 mA, seams were observed, as indicated in
FIG. 8C by the white arrows. The quality of the fill was also
checked after an annealing operation, and no voids were observed in
the coupons plated at 0.4 and 0.6 mA (i.e., the coupons shown in
FIGS. 8A and 8B). Experiments performed over a wide range of
conditions showed that void free bottom-up fill can be achieved
where the applied voltage is maintained between about -0.3 to -0.6
V (e.g., -0.4 to -0.5 V) vs. an MSE reference electrode. Because
MSE electrodes are not standard and can produce different potential
readings depending on the particular filling of the electrode, the
results are also reported in terms of the potential vs. a standard
NHE electrode. As compared to an NHE electrode, void free bottom-up
fill may be achieved where the voltage is maintained in the range
of about 0.03-0.33 V. At voltages outside this range, seams were
observed.
[0085] FIGS. 9A-9C show SEM images illustrating fill results for
ruthenium seeded trench coupons attached to a RDE and plated using
a modulated waveform at different temperatures, currents, and
plating times. Each electrolyte used to plate in FIGS. 9A-9C had 10
mM copper cations and 10 mM EDTA, was adjusted by TMAH or sulfuric
acid to have a pH of about 2.3, and also had a dissolved oxygen
content of about 1 ppm. The rotation speed for each case was about
200 RPM, and the reference electrode was an MSE electrode. For each
case, the modulated waveform was a square wave that alternated
between a deposition current and an etching current at a frequency
of about 100 Hz (frequencies between about 50-1000 Hz have been
tested and showed good fill results). For each deposition, the
etching current was set to -0.05 mA, and voltage was maintained
between about -0.4 to -0.5 V vs. the MSE electrode.
[0086] The coupon shown in FIG. 9A was electroplated for 20 minutes
at room temperature, with a deposition current level of 0.45 mA.
The coupon shown in FIG. 9B was electroplated for 20 minutes at
50.degree. C., with a deposition current of 0.5 mA. The coupon
shown in FIG. 9C was electroplated for 8 minutes at 70.degree. C.,
with a deposition current of 1.4 mA. Void free bottom-up fill was
achieved in each case shown in FIGS. 9A-9C, though the fill
happened more quickly at the higher temperatures. In fact, the fill
rate was about 10.times. higher at 70.degree. C. as compared to the
room temperature case.
[0087] FIGS. 10A-10B illustrate SEM images for ruthenium seeded
trench coupons attached on an RDE and plated in electrolytes having
different complexing agents. The coupon shown in FIG. 10A was
plated in an electrolyte having 5 mM copper cations and 5 mM NTA,
with pH adjusted by TMAH or sulfuric acid to about 3.1, and with a
dissolved oxygen content of about 1 ppm. The coupon shown in FIG.
10B was plated in electrolyte having 10 mM copper cations and 10 mM
glutamic acid, with a pH adjusted to about 3.1 and a dissolved
oxygen content of about 1 ppm. For each case, the rotation rate was
about 200 RPM, the temperature was room temperature, the reference
electrode was an MSE electrode, and the waveform used to drive
deposition was galvanostatic (0.1 mA for FIG. 10A/NTA, and 0.6 mA
for FIG. 10B/glutamic acid). Good quality bottom-up fill was
achieved in both cases.
[0088] In another experiment, bottom-up fill was achieved on a
ruthenium seeded coupon plated in an electrolyte having no
complexing agent. In this case, the electrolyte included 10 mM
CuSO.sub.4 at a pH of 2.3. A modulated waveform was used to plate
the copper, the modulated waveform being similar to those used in
relation to FIGS. 9A-9C.
[0089] The remaining experiments relate to plating that occurred on
coupons having a copper seed layer. FIGS. 11A-11C show SEM
cross-section images of copper seeded coupons filled at various
temperatures, and FIGS. 12A-12C show SEM top-down views of these
same coupons (after chemical mechanical polishing), respectively.
The copper seeded coupons were attached to an RDE and plated in an
electrolyte having 10 mM copper cations and 10 mM EDTA, with a
dissolved oxygen level of about 1 ppm, pH adjusted by TMAH or
sulfuric acid to 2.3, at a rotation speed of 200 RPM, with an MSE
reference electrode. The coupons shown in FIGS. 11A-11C and 12A-12C
were plated through a process having a 0.25 s triggered
potentiostatic entry into electrolyte at -0.5V open circuit
potential, followed by galvanostatic deposition at a current of 0.2
mA. The trenches in the coupons were about 50 nm wide. The coupon
shown in FIGS. 11A and 12A was plated at room temperature, while
the coupon shown in FIGS. 11B and 12B was plated at 50.degree. C.
and the coupon shown in FIGS. 11C and 12C were plated at 70.degree.
C. Good quality, void-free bottom-up fill was achieved at room
temperature. However, at the higher temperature of 70.degree. C.,
seed dissolution and a lack of growth appears to occur at the
relatively low current density (0.2 mA) chosen for this particular
test. As such, the benefit of higher plating rates at higher
temperatures should be balanced against the increased possibility
of seed dissolution at these higher temperatures.
[0090] FIG. 13 shows a transmission electron microscope (TEM) image
of a copper seeded trench coupon that was plated in electrolyte
lacking a complexing agent. The electrolyte in this case included
10 mM copper cations, around 1 ppm dissolved oxygen, and a pH of
2.3. The rotation speed was 200 RPM, and the reference electrode
was an MSE electrode. A 0.25 s triggered potentiostatic entry into
electrolyte at -0.5 V vs. the open circuit potential was used,
followed by galvanostatic plating at a current of 1.2 mA. Good
quality bottom-up fill was achieved, as illustrated in FIG. 13. As
such, in some embodiments the complexing agent may be omitted from
the electrolyte.
* * * * *