U.S. patent application number 15/828286 was filed with the patent office on 2018-12-06 for method and apparatus for remote plasma treatment for reducing metal oxides on a metal seed layer.
The applicant listed for this patent is Lam Research Corporation. Invention is credited to George Andrew Antonelli, Natalia V. Doubina, James E. Duncan, David W. Porter, Jonathan David Reid, Tighe A. Spurlin.
Application Number | 20180350670 15/828286 |
Document ID | / |
Family ID | 51467806 |
Filed Date | 2018-12-06 |
United States Patent
Application |
20180350670 |
Kind Code |
A1 |
Spurlin; Tighe A. ; et
al. |
December 6, 2018 |
METHOD AND APPARATUS FOR REMOTE PLASMA TREATMENT FOR REDUCING METAL
OXIDES ON A METAL SEED LAYER
Abstract
Method and apparatus for reducing metal oxide surfaces to
modified metal surfaces and cooling the metal surfaces are
disclosed. By exposing a metal oxide surface to remote plasma, the
metal oxide surface on a substrate can be reduced to pure metal. A
remote plasma apparatus can treat the metal oxide surface as well
as actively cool, load/unload, and move the substrate within a
single standalone apparatus. The remote plasma apparatus can be
configured to actively cool the substrate during and/or after
reducing the metal oxide to pure metal using an active cooling
system. The active cooling system can include one or more of an
actively cooled pedestal, an actively cooled showerhead, and one or
more cooling gas inlets for delivering cooling gas to cool the
substrate.
Inventors: |
Spurlin; Tighe A.;
(Portland, OR) ; Antonelli; George Andrew;
(Portland, OR) ; Doubina; Natalia V.; (Portland,
OR) ; Duncan; James E.; (Beaverton, OR) ;
Reid; Jonathan David; (Sherwood, OR) ; Porter; David
W.; (Sherwood, OR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lam Research Corporation |
Fremont |
CA |
US |
|
|
Family ID: |
51467806 |
Appl. No.: |
15/828286 |
Filed: |
November 30, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14086770 |
Nov 21, 2013 |
9865501 |
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15828286 |
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14020339 |
Sep 6, 2013 |
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14086770 |
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13787499 |
Mar 6, 2013 |
9070750 |
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14020339 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 21/02063 20130101;
C25D 5/42 20130101; C25D 5/34 20130101; C23C 18/1619 20130101; C23C
18/1851 20130101; C23C 18/1865 20130101; H01L 21/02068 20130101;
H01L 21/76874 20130101; C25D 17/001 20130101; H01L 21/68742
20130101; C25D 5/40 20130101; C23C 18/1868 20130101; H01J 37/32357
20130101; H01L 21/67115 20130101; H01L 21/76873 20130101; H01L
21/76861 20130101; C23C 18/1675 20130101 |
International
Class: |
H01L 21/768 20060101
H01L021/768; C23C 18/16 20060101 C23C018/16; H01J 37/32 20060101
H01J037/32; C23C 18/18 20060101 C23C018/18; C25D 17/00 20060101
C25D017/00; C25D 5/42 20060101 C25D005/42; C25D 5/40 20060101
C25D005/40; C25D 5/34 20060101 C25D005/34; H01L 21/687 20060101
H01L021/687; H01L 21/67 20060101 H01L021/67; H01L 21/02 20060101
H01L021/02 |
Claims
1. A remote plasma apparatus comprising: a processing chamber; a
substrate support for holding a substrate with a metal seed layer
in the processing chamber, wherein a portion of the metal seed
layer of the substrate has been converted to oxide of the metal; a
remote plasma source over the substrate support; a showerhead
comprising a plurality of through-holes and positioned between the
remote plasma source and the substrate support; and a controller
configured with instructions for performing the following
operations: form a remote plasma of a reducing gas species in the
remote plasma source; expose the metal seed layer of the substrate
to the remote plasma in the processing chamber under conditions
that reduce the oxide of the metal; and move the substrate away
from the substrate support and towards the showerhead to position
the substrate closer to the showerhead, wherein the showerhead is
actively cooled to a temperature below about 30.degree. C. so that
a temperature of the substrate is lower when closer to the actively
cooled showerhead than when further away from the actively cooled
showerhead.
2. The remote plasma apparatus of claim 1, further comprising one
or more cooling gas inlets for delivering cooling gas into the
processing chamber, wherein the one or more cooling gas inlets are
positioned above the substrate support.
3. The remote plasma apparatus of claim 2, wherein the controller
is further configured with instructions for flowing the cooling gas
from the one or more cooling gas inlets to cool the substrate after
completion of exposing the metal seed layer to the remote plasma,
wherein flowing the cooling gas cools the substrate to a
temperature of about 30.degree. C. or less.
4. The remote plasma apparatus of claim 2, wherein the cooling gas
includes at least one of argon, helium, or nitrogen.
5. The remote plasma apparatus of claim 2, wherein a temperature of
the cooling gas is between about -270.degree. C. and about
30.degree. C.
6. The remote plasma apparatus of claim 1, further comprising: one
or more movable members in the processing chamber configured to
move the substrate to a plurality of positions between the
showerhead and the substrate support, wherein a distance between
the showerhead and the substrate support for the plurality of
positions is between about 0.05 inches and about 0.75 inches.
7. The remote plasma apparatus of claim 1, wherein the showerhead
is actively cooled during exposure of the metal seed layer to the
remote plasma.
8. The remote plasma apparatus of claim 1, wherein the showerhead
is actively cooled after completion of exposing the metal seed
layer to the remote plasma.
9. The remote plasma apparatus of claim 1, wherein the controller
is further configured with instructions for transferring the
substrate to an electroplating apparatus after cooling the
substrate.
10. The remote plasma apparatus of claim 9, wherein the remote
plasma apparatus is part of the electroplating apparatus.
11. The remote plasma apparatus of claim 1, wherein the substrate
support includes a pedestal with one or more fluid channels to
actively cool or actively heat the pedestal.
12. The remote plasma apparatus of claim 11, wherein the controller
is further configured with instructions for maintaining a
temperature of the pedestal between about -10.degree. C. and about
150.degree. C.
13. A remote plasma apparatus comprising: a processing chamber; a
substrate support for holding a substrate with a metal seed layer
in the processing chamber, wherein a portion of the metal seed
layer of the substrate has been converted to oxide of the metal; a
remote plasma source over the substrate support; one or more
cooling gas inlets above the substrate support in the processing
chamber; a showerhead comprising a plurality of through-holes and
positioned between the remote plasma source and the substrate
support; and a controller configured with instructions for
performing the following operations: form a remote plasma of a
reducing gas species in the remote plasma source; expose the metal
seed layer of the substrate to the remote plasma in the processing
chamber under conditions that reduce the oxide of the metal; and
cool the substrate actively to a temperature of about 30.degree. C.
or less by flowing a cooling gas onto the substrate using the one
or more cooling gas inlets after completion of exposing the metal
seed layer to the remote plasma.
14. The remote plasma apparatus of claim 13, wherein a temperature
of the cooling gas is between about -270.degree. C. and about
30.degree. C., the temperature of the substrate being actively
cooled by the cooling gas to 30.degree. C. or less in a span of
about 100 seconds or less.
15. The remote plasma apparatus of claim 13, wherein the one or
more cooling gas inlets are positioned to provide the cooling gas
through the showerhead and/or from an area peripheral to the
substrate support.
16. The remote plasma apparatus of claim 13, wherein the controller
is further configured with instructions for: maintaining a
temperature of the showerhead below about 30.degree. C. so that a
temperature of the substrate is lower when closer to the showerhead
than when further away from the showerhead; and moving the
substrate towards the showerhead to further cool the substrate
after completion of exposing the metal seed layer to the remote
plasma.
17. The remote plasma apparatus of claim 13, wherein the controller
is further configured with instructions for transferring the
substrate to an electroplating apparatus after cooling the
substrate.
18. The remote plasma apparatus of claim 17, wherein the remote
plasma apparatus is part of the electroplating apparatus.
19. The remote plasma apparatus of claim 13, wherein the substrate
support includes a pedestal with one or more fluid channels to
actively cool or actively heat the pedestal.
20. The remote plasma apparatus of claim 19, wherein the controller
is further configured with instructions for maintaining a
temperature of the pedestal between about -10.degree. C. and about
150.degree. C.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/086,770, titled "METHOD AND APPARATUS FOR
REMOTE PLASMA TREATMENT FOR REDUCING METAL OXIDES ON A METAL SEED
LAYER," which is a continuation-in-part of U.S. patent application
Ser. No. 13/787,499, titled "METHODS FOR REDUCING METAL OXIDE
SURFACES TO MODIFIED METAL SURFACES USING A GASEOUS REDUCING
ENVIRONMENT," filed Mar. 6, 2013, and which is a
continuation-in-part of U.S. patent application Ser. No.
14/020,339, titled "METHOD AND APPARATUS FOR REMOTE PLASMA
TREATMENT FOR REDUCING METAL OXIDES ON A METAL SEED LAYER," filed
Sep. 6, 2013, all of which are incorporated herein by reference for
all purposes.
INTRODUCTION
Field of the Invention
[0002] This disclosure generally relates to reducing metal oxide
surfaces on metal seed layers. Certain aspects of this disclosure
pertain to reducing metal oxide surfaces on metal seed layers using
a remote plasma apparatus.
Background
[0003] Formation of metal wiring interconnects in integrated
circuits (ICs) can be achieved using a damascene or dual damascene
process. Typically, trenches or holes are etched into dielectric
material, such as silicon dioxide, located on a substrate. The
holes or trenches may be lined with one or more adhesion and/or
diffusion barrier layers. Then a thin layer of metal may be
deposited in the holes or trenches that can act as a seed layer for
electroplated metal. Thereafter, the holes or trenches may be
filled with electroplated metal.
[0004] Typically, the seed metal is copper. However, other metals
such as ruthenium, palladium, iridium, rhodium, osmium, cobalt,
nickel, gold, silver, and aluminum, or alloys of these metals, may
also be used.
[0005] To achieve higher performance ICs, many of the features of
the ICs are being fabricated with smaller feature sizes and higher
densities of components. In some damascene processing, for example,
copper seed layers on 2.times.-nm node features may be as thin as
or thinner than 50 .ANG.. In some implementations, metal seed
layers on 1.times.-nm node features may be applied that may or may
not include copper. Technical challenges arise with smaller feature
sizes in producing metal seed layers and metal interconnects
substantially free of voids or defects.
SUMMARY
[0006] This disclosure pertains to a remote plasma apparatus for
treating a substrate with a metal seed layer. The remote plasma
apparatus can include a processing chamber, a substrate support for
holding the substrate in the processing chamber, a remote plasma
source over the substrate support, a showerhead between the remote
plasma source and the substrate support, and one or more movable
members configured to move the substrate between the showerhead and
the substrate support in the processing chamber. The remote plasma
apparatus further includes a controller with instructions to
perform the operations of providing the substrate in the processing
chamber, moving the substrate towards the substrate support in the
processing chamber, forming a remote plasma of a reducing gas
species in the remote plasma source where the remote plasma
includes radicals of the reducing gas species, exposing the metal
seed layer of the substrate to the radicals of the reducing gas
species, and exposing the substrate to a cooling gas.
[0007] In some embodiments, the controller includes instructions
for moving the substrate to the actuated position via the one or
more movable members before exposing the substrate to a cooling
gas. In some embodiments, the controller includes instructions for
heating the substrate support to a processing temperature between
about 0.degree. C. and about 400.degree. C. during the operations
of moving the substrate to the unactuated position through exposing
the metal seed layer of the substrate to the radicals of the
reducing gas species. In some embodiments, exposing the substrate
to the cooling gas includes cooling the substrate to a temperature
below about 30.degree. C. In some embodiments, the remote plasma
apparatus is part of an electroplating apparatus. In some
embodiments, the one or more movable members are configured to move
the substrate between an actuated and an unactuated position, where
the distance between the showerhead and the substrate in the
actuated position is between about 0.05 inches and about 0.75
inches, and the distance between the showerhead and the substrate
in the unactuated position is between about 1 inch and about 5
inches.
[0008] This disclosure also pertains to a method of treating a
substrate with a metal seed layer. The method includes providing
the substrate in a processing chamber, moving the substrate towards
a substrate support in the processing chamber, forming a remote
plasma of a reducing gas species in a remote plasma source where
the remote plasma includes radicals of the reducing gas species,
exposing the metal seed layer of the substrate to the radicals of
the reducing gas species, and exposing the substrate to a cooling
gas.
[0009] In some embodiments, the method further includes heating a
substrate support to a processing temperature between about
0.degree. C. and about 400.degree. C. In some embodiments, the
method further includes maintaining a temperature of the showerhead
below about 30.degree. C. In some embodiments, the method further
includes moving the substrate towards the showerhead via one or
more movable members before exposing the substrate to a cooling
gas. In some embodiments, the method further includes adjusting a
temperature of the substrate, where adjusting the temperature of
the substrate is configured by positioning the substrate via one or
more movable members between a showerhead and the substrate
support.
[0010] This disclosure also pertains to a remote plasma apparatus
for treating a substrate with a metal seed layer. The remote plasma
apparatus includes a processing chamber, a substrate support for
holding the substrate in the processing chamber, a remote plasma
source over the substrate support, a showerhead between the remote
plasma source and the substrate support, and a controller. The
controller includes instructions for performing the operations of
providing the substrate with the metal seed layer in the processing
chamber, where a portion of the metal seed layer has been converted
to oxide of the metal, forming a remote plasma of a reducing gas
species in a remote plasma source, where the remote plasma includes
one or more of: radicals, ions, and ultraviolet (UV) radiation from
the reducing gas species, and exposing the metal seed layer of the
substrate to the remote plasma, where the exposure reduces the
oxide of the metal and reflows the metal in the metal seed
layer.
[0011] In some embodiments, the remote plasma includes at least two
of the following: radicals, ions, and UV radiation from the
reducing gas species. In some embodiments, the remote plasma
further includes neutral molecules of the reducing gas species, and
exposing the metal seed layer to the remote plasma includes
exposing the metal seed layer to neutral molecules of the reducing
gas species. In some embodiments, the showerhead includes a
plurality of holes. The number of holes in the showerhead can be
between about 100 and about 900 holes. The average diameter of the
holes can be between about 0.05 inches and about 0.5 inches. In
some embodiments, the remote plasma apparatus can further include a
UV source, where the controller can further include instructions
for exposing the reducing gas species to UV radiation from the UV
source to form radicals of the reducing gas species.
[0012] This disclosure also pertains to a method of treating a
substrate with a metal seed layer. The method includes providing
the substrate with the metal seed layer in a processing chamber,
where a portion of the metal seed layer has been converted to oxide
of the metal, forming a remote plasma of a reducing gas species in
a remote plasma source, where the remote plasma includes one or
more of: radicals, ions, and UV radiation from the reducing gas
species, and exposing the metal seed layer to the remote plasma,
where exposure reduces the oxide of the metal and reflows the metal
in the metal seed layer.
[0013] In some embodiments, the remote plasma includes radicals,
ions, and UV radiation from the reducing gas species. Exposing the
metal seed layer to the remote plasma includes introducing the
radicals, the ions, and the UV radiation from the reducing gas
species through a showerhead between the remote plasma source and
the processing chamber, where the showerhead includes a plurality
of holes. In some embodiments, the number of holes in the
showerhead is between about 100 and about 900 holes. In some
embodiments, the average diameter of the holes is between about
0.05 inches and about 0.5 inches.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1A shows an example of a cross-sectional schematic of
dielectric layers prior to a via etch in a damascene process.
[0015] FIG. 1B shows an example of a cross-sectional schematic of
the dielectric layers in FIG. 1A after an etch has been performed
in the damascene process.
[0016] FIG. 1C shows an example of a cross-sectional schematic of
the dielectric layers in FIGS. 1A and 1B after the etched regions
have been filled with metal in the damascene process.
[0017] FIG. 2 shows an exemplary flow diagram illustrating a method
of electroplating copper on a substrate.
[0018] FIG. 3 shows an exemplary flow diagram illustrating a method
of reducing metal oxides on a metal seed layer and plating metal on
a substrate.
[0019] FIG. 4A shows an example of a cross-sectional schematic of
an oxidized metal seed layer.
[0020] FIG. 4B shows an example of a cross-sectional schematic of a
metal seed layer with a void due to removal of metal oxide.
[0021] FIG. 4C shows an example of a cross-sectional schematic of a
metal seed layer with reduced metal oxide forming a reaction
product not integrated with the metal seed layer.
[0022] FIG. 4D shows an example of a cross-sectional schematic of a
metal seed layer with reduced metal oxide forming a film integrated
with the metal seed layer.
[0023] FIG. 5 shows an example of a cross-sectional schematic
diagram of a remote plasma apparatus with a processing chamber.
[0024] FIG. 6A shows an exemplary flow diagram illustrating a
method of treating a substrate with a metal seed layer.
[0025] FIG. 6B shows an exemplary flow diagram illustrating another
method of treating a substrate with a metal seed layer.
[0026] FIGS. 7A-7D show examples of cross-sectional schematic
diagrams illustrating various stages of treating a substrate with a
metal seed layer using a remote plasma apparatus.
[0027] FIG. 8A shows an example of a top view schematic of an
electroplating apparatus.
[0028] FIG. 8B shows an example of a magnified top view schematic
of a remote plasma apparatus with an electroplating apparatus.
[0029] FIG. 8C shows an example of a three-dimensional perspective
view of a remote plasma apparatus attached to an electroplating
apparatus.
[0030] FIG. 9 shows a graph illustrating the effects of exposure to
a remote plasma and gains in electrical conductivity for
copper.
[0031] FIG. 10 shows scanning electron microscopy (SEM) images of
seed trench coupons when treated using a remote plasma and when not
treated using a remote plasma.
[0032] FIG. 11 shows a graph illustrating the growth of metal oxide
on a metal seed layer exposed to ambient conditions following a
reduction treatment.
[0033] FIG. 12 shows SEM images of seed trench coupons exposed to
ambient conditions for different durations following a reduction
treatment and when not following a reduction treatment.
[0034] FIG. 13 shows a graph illustrating temperature cooling
profiles over time under different conditions in a processing
chamber.
[0035] FIG. 14 shows a graph illustrating the effects of
temperature and surface roughness of the metal seed layer following
a remote plasma treatment.
[0036] FIG. 15 shows a graph illustrating the effects of
temperature and void reduction in a metal seed layer.
DETAILED DESCRIPTION
[0037] In the following description, numerous specific details are
set forth in order to provide a thorough understanding of the
presented concepts. The presented concepts may be practiced without
some or all of these specific details. In other instances, well
known process operations have not been described in detail so as to
not unnecessarily obscure the described concepts. While some
concepts will be described in conjunction with the specific
embodiments, it will be understood that these embodiments are not
intended to be limiting.
INTRODUCTION
[0038] Although the present invention may be used in a variety of
applications, one very useful application is the damascene or dual
damascene process commonly used in the manufacture of semiconductor
devices. The damascene or dual damascene processes may include
metal interconnects, such as copper interconnects.
[0039] A generalized version of a dual damascene technique may be
described with reference to FIGS. 1A-1C, which depicts some of the
stages of the dual damascene process.
[0040] FIG. 1A shows an example of a cross-sectional schematic of
one or more dielectric layers prior to a via etch in a damascene
process. In a dual damascene process, first and second layers of
dielectric are normally deposited in succession, possibly separated
by deposition of an etch stop layer, such as a silicon nitride
layer. These layers are depicted in FIG. 1A as a first dielectric
layer 103, second dielectric layer 105, and etch stop layer 107.
These are formed on an adjacent portion of a substrate 109, which a
portion may be an underlying metallization layer or a gate
electrode layer (at the device level).
[0041] After deposition of the second dielectric layer 105, the
process forms a via mask 111 having openings where vias will be
subsequently etched. FIG. 1B shows an example of a cross-sectional
schematic of the one or more dielectric layers in FIG. 1A after an
etch has been performed in the damascene process. Next, vias are
partially etched down through the level of etch stop 107. Then via
mask 111 is stripped off and replaced with a line mask 113 as
depicted in FIG. 1B. A second etch operation is performed to remove
sufficient amounts of dielectric to define line paths 115 in second
dielectric layer 105. The etch operation also extends via holes 117
through first dielectric layer 103, down to contact the underlying
substrate 109 as illustrated in FIG. 1B.
[0042] Thereafter, the process forms a thin layer of relatively
conductive barrier layer material 119 on the exposed surfaces
(including sidewalls) of dielectric layers 103 and 105. FIG. 1C
shows an example of a cross-sectional schematic of the dielectric
layers in FIGS. 1A and 1B after the etched regions have been coated
with a conductive barrier layer material and filled with metal in
the damascene process. Conductive barrier layer material 119 may be
formed, for example, of tantalum nitride or titanium nitride. A
chemical vapor deposition (CVD), an atomic layer deposition (ALD),
or a physical vapor deposition (PVD) operation is typically
employed to deposit the conductive barrier layer material 119.
[0043] On top of the conductive barrier layer material 119, the
process then deposits conductive metal 121 (typically, though not
necessarily, copper) in the via holes and line paths 117 and 115.
Conventionally this deposition is performed in two steps: an
initial deposition of a metal seed layer followed by bulk
deposition of metal by plating. However, the present disclosure
provides a pre-treatment step prior to the bulk deposition step, as
described in detail below. The metal seed layer may be deposited by
PVD, CVD, electroless plating, or any other suitable deposition
technique known in the art. Note that the bulk deposition of copper
not only fills line paths 115 but, to ensure complete filling,
covers all the exposed regions on top of second dielectric layer
105. The metal 121 may serve as copper interconnects for IC
devices. In some embodiments, metals other than copper are used in
the seed layer. Examples of such other metals include cobalt,
tungsten, and ruthenium.
[0044] Metal seed layers can readily react with oxygen or water
vapor in the air and oxidize from a pure metal into a mixed film of
a metal oxide and a buried pure metal. While the oxidation under
ambient conditions may be limited to a thin surface layer of some
metals, that thin layer may represent a significant fraction or
perhaps the entire thickness of thin seed layers used in current
technology nodes. The relatively thin layers may be necessitated by
the technology node, such as the 4.times. nm node, the 3.times. nm
node, the 2.times. nm node, and the 1.times. nm node, and less than
10 nm. The height to width aspect ratio of vias and trenches in
technology nodes necessitating relatively thin metal layers can be
about 5:1 or greater. In such technology nodes, the thickness of
the metal seed layer can be less than about 100 .ANG. on average as
a result. In some implementations, the thickness of the metal seed
layer can be less than about 50 .ANG. on average.
[0045] Through the general chemical reactions shown in Equation 1
and Equation 2 below, metals used for seed or barrier layers are
converted to metal oxides (Mox), though the exact reaction
mechanisms between the metal surfaces (M) and ambient oxygen or
water vapor can vary depending on the properties and the oxidation
state.
2M.sub.(s)+O.sub.2(g).fwdarw.2MOx.sub.(s) Equation 1:
2M.sub.(s)+H.sub.2O.sub.(g).fwdarw.M.sub.2Ox+H.sub.2(g) Equation
2:
[0046] For example, copper seed deposited on substrates is known to
rapidly form copper oxide upon exposure to the air. A copper oxide
film can form a layer that is approximately 20 .ANG. and upwards to
50 .ANG. thick on top of underlying copper metal. As metal seed
layers become thinner and thinner, the formation of metal oxides
from oxidation in ambient conditions can pose significant technical
challenges.
[0047] Conversion of pure metal seed to metal oxide can lead to
several problems. This is true not only in current copper damascene
processing, but also for electrodeposition processes that use
different conductive metals, such as ruthenium, cobalt, silver,
aluminum, and alloys of these metals. First, an oxidized surface is
difficult to plate on. Due to different interactions that
electroplating bath additives can have on metal oxide and pure
metal, non-uniform plating may result. As a result of the
differences in conductivity between a metal oxide and a pure metal,
non-uniform plating may further result. Second, voids may form in
the metal seed that may make portions of the metal seed unavailable
to support plating. The voids may form as a result of dissolution
of metal oxide during exposure to corrosive plating solutions. The
voids also may form on the surface due to non-uniform plating.
Additionally, plating bulk metal on top of an oxidized surface can
lead to adhesion or delamination problems, which can further lead
to voids following subsequent processing steps, such as chemical
mechanical planarization (CMP). Voids that result from etching,
non-uniform plating, delamination, or other means may make the
metal seed layer discontinuous, and unavailable to support plating.
In fact, because modern damascene metal seed layers are relatively
thin, such as about 50 .ANG. or thinner, even a little oxidation
may consume an entire layer thickness. Third, metal oxide formation
may impede post-electrodeposition steps, such as capping, where the
metal oxide may limit adhesion for capping layers.
[0048] After depositing a metal seed layer but prior to
electroplating a bulk metal on the seed layer, it may be difficult
to avoid formation of metal oxide on the metal seed layer. Various
steps occur prior to electroplating the metal that may expose the
metal seed layer to oxygen or water vapor in ambient conditions.
For example, FIG. 2 shows an exemplary flow diagram illustrating a
method of electroplating copper on a substrate. The process 200 may
begin at step 205, where a process chamber or deposition chamber
receives a substrate such as a semiconductor wafer. A metal seed
layer such as a copper seed layer may be deposited on the substrate
using a suitable deposition technique such as PVD.
[0049] At optional step 210, the substrate with the metal seed
layer may be rinsed and dried. For example, the metal seed layer
may be rinsed with de-ionized water. The rinsing step may be
limited to a time, for example, of between about 1 and 10 seconds,
but may take a longer or shorter time. Subsequently, the substrate
may be dried, which can be between about 20 and 40 seconds, though
the drying step may take a longer or shorter time. During this
step, the metal seed layer may be exposed to oxidation.
[0050] At step 215, the substrate with the metal seed layer is
transferred to the electroplating system or bath. During this
transfer, the metal seed layer may be exposed to ambient conditions
such that the metal seed layer may rapidly oxidize. In some
embodiments, the duration of this exposure may be anywhere between
about 1 minute and about 4 hours, between about 15 minutes and
about 1 hour, or more. At step 220, bulk metal may be electroplated
on the substrate. A substrate with a copper seed layer, for
example, may be immersed in an electroplating bath containing
positive ions of copper and associated anions in an acid solution.
Step 220 of FIG. 2 can involve a series of processes that is
described in U.S. Pat. No. 6,793,796, filed Feb. 28, 2001 (attorney
docket no. NOVLP073), the entirety of which is hereby incorporated
by reference. The reference describes at least four phases of the
electrofilling process and discloses controlled current density
methods for each phase for optimal filling of relatively small
embedded features.
[0051] With various steps that may expose the metal seed layer to
oxidation between deposition of the metal seed layer and
electroplating, a technique for reducing the negative effects of
the metal oxide surfaces is needed. However, some of the current
techniques may have drawbacks. Typically, the use of hydrogen-based
plasmas may reduce thick metal oxides, but such techniques add
substantial costs and utilize substantially high temperatures
(e.g., at least over 200.degree. C.) that can badly damage a thin
metal seed layer resulting in high void counts within features. A
thermal forming gas anneal to reduce thick metal oxides uses a
forming gas (e.g., mixture of hydrogen and nitrogen gas) at
temperatures higher than 150.degree. C., which can cause metal seed
to agglomerate and also lead to increased voiding. The use of acids
or other chemical reagents may dissolve or etch thick metal oxides,
but removal of such oxides results in increased void formation in
regions where metal cannot be plated on, due to the creation of
regions with insufficient seed layer where metal cannot be plated
on.
[0052] The present disclosure provides methods for reducing metal
oxide surfaces to modified metal surfaces. The method of reducing
the metal oxide surfaces provides a substantially clean metallic
surface that is substantially free of oxide when a substrate is
introduced into the electroplating bath. The substrate that is
substantially free of oxide may also be introduced into an
electroless plating system or other metal deposition system. In
addition, the method of reducing the metal oxide operates in
relatively low temperatures, and the reduced metal oxide converts
to metal to form a continuous film that is integrated with the
metal seed layer and adherent to the underlying seed or substrate.
Further, the method for reducing metal oxide surfaces can reflow
the metal to reduce voids and gaps in the metal seed layer.
Reflowing the metal can mobilize metal and redistribute atoms in
the seed layer to improve seed coverage and/or smoothness, thereby
forming a more uniform and continuous seed layer.
Method of Reducing Metal Oxides on a Metal Seed Layer
[0053] A method of preparing a substrate with a metal seed layer
using a remote plasma can be disclosed. The substrate is maintained
at a temperature below a temperature that produces agglomeration of
the metal seed layer during exposure to the reducing gas
atmosphere. The method further includes transferring the substrate
to a plating bath containing a plating solution, and plating metal
onto the metal seed layer using the plating solution.
[0054] FIG. 3 shows an exemplary flow diagram illustrating a method
of reducing oxides on a metal seed layer and plating metal on a
substrate. The process 300 can begin with step 305 where a metal
seed layer such as a thin copper layer is deposited on a substrate.
This provides a substrate having the metal seed layer on a plating
surface of the substrate. The substrate may have recesses having
height to width aspect ratios of greater than about 3:1 or greater
than about 5:1.
[0055] In some embodiments, the metal seed layer can include a
semi-noble metal layer. The semi-noble metal layer may be part of a
diffusion barrier or serve as the diffusion barrier. The semi-noble
metal layer can include a semi-noble metal, such as ruthenium.
Aspects of the semi-noble metal layer can be further described in
U.S. Pat. No. 7,442,267 (attorney docket no. NOVLP350), U.S. Pat.
No. 7,964,506 (attorney docket no. NOVLP272), U.S. Pat. No.
7,799,684 (attorney docket no. NOVLP207), U.S. patent application
Ser. No. 11/540,937 (attorney docket no. NOVLP175), U.S. patent
application Ser. No. 12/785,205 (attorney docket no. NOVLP272X1),
and U.S. patent application Ser. No. 13/367,710 (attorney docket
no. NOVLP272X2), each of which is incorporated in its entirety by
reference. Step 305 can occur in a deposition apparatus such as a
PVD apparatus. The process 300 can continue with step 310 where the
substrate is transferred to a chamber or apparatus having a
substantially reduced pressure or vacuum environment. The chamber
or apparatus can include a reducing gas species. In some
embodiments, the reducing gas species can include hydrogen
(H.sub.2), ammonia (NH.sub.3), carbon monoxide (CO), diborane
(B.sub.2H.sub.6), sulfite compounds, carbon and/or hydrocarbons,
phosphites, and/or hydrazine (N.sub.2H.sub.4). During the transfer
in step 310, the substrate may be exposed to ambient conditions
that can cause the surface of the metal seed layer to oxidize.
Thus, at least a portion of the metal seed layer may be converted
to an oxidized metal.
[0056] At step 315, while the substrate is in the reduced or vacuum
environment, the reducing gas species may be exposed to a remote
plasma. The remote plasma may generate radicals of the reducing gas
species, such as, for example, H*, NH.sub.2*, or N.sub.2H.sub.3*.
The radicals of the reducing gas species react with the metal oxide
surface to generate a pure metallic surface. As demonstrated below,
Equation 3 shows an example a reducing gas species such as hydrogen
gas being broken down into hydrogen radicals. Equation 4 shows the
hydrogen radicals reacting with the metal oxide surface to convert
the metal oxide to metal. For hydrogen gas molecules that are not
broken down or hydrogen radicals that recombine to form hydrogen
gas molecules, the hydrogen gas molecules can still serve as a
reducing agent for converting the metal oxide to metal, as shown in
Equation 5.
H.sub.2.fwdarw.2H.sup.* Equation 3:
(x)2H*+MOx.fwdarw.M+(x)H.sub.2O Equation 4:
xH.sub.2+MOx.fwdarw.M+xH.sub.2O Equation 5:
[0057] The radicals of the reducing gas species, ions from the
reducing gas species, ultraviolet (UV) radiation from the reducing
gas species, or the reducing gas species itself reacts with the
metal oxide under conditions that convert the metal oxide to metal
in the form of a film integrated with the metal seed layer, as
shown in step 320. Characteristics of the film integrated with the
metal seed layer are discussed in further detail with respect to
FIG. 4D below.
[0058] The remote plasma may generate and include ions and other
charged species of the reducing gas species. The ions and charged
species of the reducing gas species may move to the surface of the
substrate to react or otherwise contact the metal seed layer. The
ions or charged species may freely drift toward the surface of the
substrate or be accelerated toward the surface of the substrate
when an oppositely charged bias is provided on a substrate support.
The ions or charged species may react with the metal oxide to
reduce the metal oxide. In some implementations, the ions or
charged species in the remote plasma can include, for example,
H.sup.+, NH.sub.2.sup.+, NH.sub.3.sup.+, and H.sup.-. Ions or
charged species may be advantageous for reducing oxide on metal
seed layers depending on a thickness and nature of the oxide
layers, which can form on cobalt, ruthenium, palladium, rhodium,
iridium, osmium, nickel, gold, silver, aluminum, tungsten, and
alloys thereof. For example, the ions or charged species may be
beneficial for treatment of a seed layer containing cobalt.
[0059] The remote plasma may also generate and include UV radiation
from the reducing gas species. Excitation of the reducing gas
molecules from the remote plasma may cause emission of photons. The
emitted photons may lead to one of several effects. First, the
emitted photons in the UV spectrum may heat the surface of the
substrate to activate the metal oxide surface so that radicals,
ions, and other charged species can more readily react with the
metal oxide surface. Second, reducing gas species may absorb the
emitted photons and generate radicals of the reducing gas species.
The generated radicals may react with the metal oxide surface to
reduce the metal oxide. Third, the emitted photon may have
sufficient energy to cause reduction of the metal oxide itself.
[0060] The process conditions for converting the metal oxide to
metal in the form of a film integrated with the metal seed layer
can vary depending on the choice of metal and/or on the choice of
the reducing gas species. In some embodiments, the reducing gas
species can include at least one of H.sub.2, NH.sub.3, CO, carbon
and/or hydrocarbons, B.sub.2H.sub.6, sulfite compounds, phosphites,
and N.sub.2H.sub.4. In addition, the reducing gas species can be
combined with mixing gas species, such as relatively inert gas
species. Examples of relatively inert gas species can include
nitrogen (N.sub.2), helium (He), neon (Ne), krypton (Kr), xenon
(Xe), radon (Rn), and argon (Ar). The flow rate of the reducing gas
species can vary depending on the size of the wafer for processing.
For example, the flow rate of the reducing gas species can be
between about 10 standard cubic centimeter per minute (sccm) and
about 100,000 sccm for processing a single 450 mm wafer. Other
wafer sizes can also apply. For example, the flow rate of the
reducing gas species can be between about 500 sccm and about 30,000
sccm for processing a single 300 mm wafer.
[0061] Processing conditions such as temperature and pressure in
the reducing chamber can also be controlled to permit conversion of
the metal oxide to metal in the form of a film integrated with the
metal seed layer. In some embodiments, the temperature of the
reducing chamber can be relatively high to permit the dissociation
of reducing gas species into radicals. For example, the reducing
chamber can be anywhere between about 10.degree. C. and about
500.degree. C., such as between about 50.degree. C. and about
250.degree. C. Higher temperatures may be used to speed up metal
oxide reduction reactions and shorten the duration of exposure to
the reducing gas atmosphere. In some embodiments, the reducing
chamber can have a relatively low pressure to substantially remove
any oxygen from the reducing gas atmosphere, as minimizing the
presence of oxygen in the atmosphere can reduce the effects of
reoxidation. For example, the reducing chamber can be pumped down
to a vacuum environment or a reduced pressure of between about 0.1
Torr and about 50 Torr. The increased temperature and/or the
reduced temperature can also increase reflow of metal atoms in the
metal seed layer to create a more uniform and continuous metal seed
layer.
[0062] Although the reducing chamber can have a relatively high
temperature to permit the dissociation of reducing gas species into
radicals, the temperature of the substrate itself may be separately
controlled to avoid or reduce damage to the metal seed layer.
Depending on the type of metal in the metal seed layer, the metal
can begin to agglomerate above a threshold temperature. The effects
of agglomeration is more pronounced in relatively thin seed layers,
especially in seed layers having a thickness less than about 100
.ANG.. Agglomeration includes any coalescing or beading of a
continuous or semi-continuous metal seed layer into beads, bumps,
islands, or other masses to form a discontinuous metal seed layer.
This can cause the metal seed layer to peel away from the surface
upon which it is disposed and can lead to increased voiding during
plating. For example, the temperature at which agglomeration begins
to occur in copper is greater than about 100.degree. C. Different
agglomeration temperatures may be appropriate for different
metals.
[0063] To control the temperature of the substrate and avoid or
reduce the effects of agglomeration, a cooling system such as an
actively cooled pedestal and/or gas flow cooling apparatus in the
reducing chamber can be used to keep the local area of the
substrate at temperatures below the agglomeration temperature. In
some embodiments, the substrate may be supported upon and directly
in contact with the pedestal. In some embodiments, a gap may exist
between the pedestal and the substrate. Heat transfer can occur via
conduction, convection, radiation, or combinations thereof.
[0064] In some implementations, an actively cooled pedestal
provides a heat transfer element with resistive heating elements,
cooling channels, or other heat sources or sinks embedded within
the pedestal. For example, the pedestal can include cooling
elements that permit a fluid such as water to circulate within the
pedestal and actively cool the pedestal. In some embodiments, the
cooling elements can be located outside the pedestal. In some
embodiments, the cooling fluid can include a low-boiling fluid,
such as glycols. Embodiments that include such cooling elements can
be described in U.S. Pat. No. 7,327,948 (attorney docket no.
NOVLP127X1), issued Feb. 5, 2008; U.S. Pat. No. 7,941,039 (attorney
docket no. NOVLP127X3), issued Jan. 5, 2011; U.S. patent
application Ser. No. 11/751,584 (attorney docket no. NOVLP127X2),
filed May 21, 2007; U.S. patent application Ser. No. 13/370,579
(attorney docket no. NOVLP127C1), filed Feb. 10, 2012; and U.S.
Pat. No. 8,137,465 (attorney docket no. NOVLP127), issued Mar. 20,
2012, each of which are incorporated herein by reference in its
entirety and for all purposes. Temperature in the pedestal can be
actively controlled using a feedback loop.
[0065] In some implementations, a gap can exist between the
pedestal and the substrate, and a conductive media such as gas can
be introduced between the pedestal and the substrate to cool the
substrate. In some embodiments, the conductive media can include
helium. In some embodiments, the pedestal can be convex or concave
to promote uniform cooling across the substrate. Examples of
pedestal profiles can be described in U.S. patent application Ser.
No. 11/129,266 (attorney docket no. NOVLP361), filed May 12, 2005;
U.S. patent application Ser. No. 11/546,189 (attorney docket no.
NOVLP198), filed Oct. 10, 2006; and U.S. patent application Ser.
No. 12/749,170 (attorney docket no. NOVLP361D1), filed Mar. 29,
2010, each of which is incorporated herein by reference in its
entirety and for all purposes.
[0066] Different configurations can be utilized to efficiently cool
and to maintain a substantially uniform temperature across the
substrate. Some implementations of an active cooling system include
a pedestal circulating water within the pedestal coupled with a
uniform gas flow across the substrate. Other implementations
include a pedestal resistively heated coupled with a uniform gas
flow across the substrate. Other configurations and/or additions
may also be provided with the active cooling system. For example, a
removable ceramic cover can be inserted between the pedestal and
the substrate to promote substantially uniform temperature across
the substrate, as described in U.S. patent application Ser. No.
13/086,010 (attorney docket no. NOVLP400), filed Apr. 13, 2011,
which is incorporated herein by reference in its entirety and for
all purposes. In some embodiments, gas flow can be controlled with
minimum contact supports to rapidly and uniformly cool the
substrate, as described in U.S. Pat. No. 8,033,771 (attorney docket
no. NOVLP298), issued Oct. 11, 2011, which is incorporated herein
by reference in its entirety and for all purposes. In some
embodiments, the heat transfer coefficient of the conductive media
can be adjusted by varying the partial pressure of the conductive
media as described in U.S. Pat. No. 8,288,288 (attorney docket no.
NOVLP232), issued Oct. 12, 2012, which is incorporated herein by
reference in its entirety and for all purposes. Other
configurations for a localized cooling system for maintaining a
relatively low substrate temperature can be utilized as is known in
the art.
[0067] The temperature of the substrate can be maintained at a
temperature below the agglomeration temperature of the metal using
any of the cooling systems discussed earlier herein or as is known
in the art. In some embodiments, the substrate can be maintained at
a temperature between about -10.degree. C. and about 150.degree. C.
In copper seed layers, for example, the substrate can be maintained
at a temperature between about 75.degree. C. and about 100.degree.
C. In cobalt seed layers, the substrate can be maintained at a
temperature greater than about 100.degree. C.
[0068] The duration of exposure to the reducing gas atmosphere can
vary depending on the other process parameters. For example, the
duration of exposure to the reducing gas atmosphere can be
shortened by increasing remote plasma power, temperature of the
reducing chamber, etc. In certain embodiments, the duration of the
exposure to reduce the metal oxide surfaces to pure metal in an
integrated film with the metal seed layer can be between about 1
second and about 60 minutes. For example, for pretreatment of
copper seed layers, the duration of the exposure can between about
10 seconds and about 300 seconds.
[0069] While most reducing treatments may require that the
substrate be rinsed and dried prior to plating in order to clean
the substrate surface, the substrate as exposed to a reducing gas
atmosphere need not be rinsed and dried prior to plating. Thus,
reducing metal oxide surfaces using a reducing gas atmosphere can
avoid the additional step of rinsing and drying the substrate
before plating, which can further reduce the effects of
reoxidation.
[0070] In some implementations, the metal in the metal seed layer
may be reflowed as a result of exposure to one or more of increased
temperature, reduced pressure, UV radiation from a UV source, UV
radiation from the remote plasma, and radicals, ions, and other
charged species from the remote plasma. Such exposure can lead to
atoms in the metal seed layer to enter a more excited state and
become more mobile. The atoms can move around on an underlying
layer to reduce voids/gaps. As a result, a more uniform and
continuous metal seed layer can be created. In some
implementations, the reflow and the reduction treatment can occur
simultaneously.
[0071] At step 325 in FIG. 3, the substrate may be transferred
under ambient conditions or under a blanket of inert gas to the
electroplating system, electroless plating system, metal deposition
system, or pretreating apparatus. Though metal oxides in the metal
seed layer have been substantially reduced by exposing the metal
oxide surfaces to a reducing gas atmosphere, performing step 325
may present an additional challenge of reoxidation from exposure to
the ambient environment. In some embodiments, exposure to ambient
conditions may be minimized using techniques such as shortening the
duration of transfer or controlling the atmosphere during transfer.
Additionally or alternatively, the transfer is conducted in a
controlled environment that is less oxidizing than ambient
conditions. To control the atmosphere during transfer, for example,
the atmosphere may be substantially devoid of oxygen. The
environment may be substantially inert and/or be low pressure or
vacuum. In some embodiments, the substrate may be transferred under
a blanket of inert gas. As discussed below, the transfer in step
325 may occur from a remote plasma apparatus to an electroplating
system, where the remote plasma apparatus is integrated or
otherwise connected to the electroplating system. At step 330,
metal may be electroplated on to the substrate.
[0072] FIGS. 4A-4D show examples of cross-sectional schematics of a
metal seed layer deposited on a conductive barrier layer. FIG. 4A
shows an example of a cross-sectional schematic of an oxidized
metal seed layer deposited over a conductive barrier layer 419. As
discussed earlier herein, the metal seed layer 420 may be oxidized
upon exposure to oxygen or water vapor in ambient conditions, which
can convert metal to a metal oxide 425 in a portion of the metal
seed layer 420.
[0073] FIG. 4B shows an example of a cross-sectional schematic of a
metal seed layer with a void due to removal of metal oxide. As
discussed earlier herein, some solutions treat the metal oxide 425
by removal of the metal oxide 425, resulting in voids 426. For
example, the metal oxide 425 can be removed by oxide etching or
oxide dissolution by an acid or other chemical. Because the
thickness of the void 426 can be substantially large relative to
the thinness of the metal seed layer 420, the effect of the void
426 on subsequent plating can be significant.
[0074] FIG. 4C shows an example of a cross-sectional schematic of a
metal seed layer with reduced metal oxide forming a reaction
product not integrated with the metal seed layer. As discussed
earlier herein, some solutions reduce the metal oxide 425 under
conditions that agglomerate metal with the metal seed layer 420. In
some embodiments, reducing techniques generate metal particles 427,
such as copper powder, that can agglomerate with the metal seed
layer 420. The metal particles 427 do not form an integrated film
with the metal seed layer 420. Instead, the metal particles 427 are
not continuous, conformal, and/or adherent to the metal seed layer
420.
[0075] FIG. 4D shows an example of a cross-sectional schematic of a
metal seed layer with reduced metal oxide forming a film integrated
with the metal seed layer. In some embodiments, radicals from a
reducing gas species, ions from the reducing gas species, UV
radiation from the reducing gas species, or the reducing gas
species itself can reduce the metal oxide 425. When process
conditions for the reducing gas atmosphere are appropriately
adjusted, the metal oxide 425 in FIG. 4A may convert to a film 428
integrated with the metal seed layer 420. The film 428 is not a
powder. In contrast to the example in FIG. 4C, the film 428 can
have several properties that integrate it with the metal seed layer
420. For example, the film 428 can be substantially continuous and
conformal over the contours metal seed layer 420. Moreover, the
film 428 can be substantially adherent to the metal seed layer 420,
such that the film 428 does not easily delaminate from the metal
seed layer 420.
Remote Plasma Apparatus
[0076] A remote plasma apparatus for treating a substrate with a
metal seed layer is disclosed. The remote plasma apparatus includes
a processing chamber, a substrate support for holding the substrate
in the processing chamber, a remote plasma source over the
substrate support, a showerhead between the remote plasma source
and the substrate support, one or more movable members in the
processing chamber, and a controller. The one or more movable
members may be configured to move the substrate to positions
between the showerhead and the substrate support. The controller
may be configured to perform one or more operations, including
providing the substrate in the processing chamber, moving the
substrate towards the substrate support, forming a remote plasma of
a reducing gas species in the remote plasma source where the remote
plasma includes radicals of the reducing gas species, exposing the
metal seed layer of the substrate to the radicals of the reducing
gas species, and exposing the substrate to an inert gas.
[0077] The remote plasma apparatus can be configured to perform a
plurality of operations that is not limited to treating a substrate
with a remote plasma. The remote plasma apparatus can be configured
to transfer (such as load/unload) a substrate efficiently to and
from an electroplating apparatus, electroless plating apparatus, or
other metal deposition apparatus. The remote plasma apparatus can
be configured to efficiently control the temperature of the
substrate by positioning the substrate using movable members and/or
the using substrate support. The remote plasma apparatus can be
configured to efficiently control the temperature of the substrate
by controlling the temperature of the substrate support and the
temperature of the showerhead. The remote plasma apparatus can be
configured to tune the rate of reduction reaction and the
uniformity of the reduction reaction by positioning the substrate
support relative to the showerhead. The remote plasma apparatus can
be configured to control the environmental conditions surrounding
the substrate by controlling the gases and flow rates of the gases
delivered into the processing chamber. Such operations can improve
the processing of the substrate while also integrating additional
operations into a single standalone apparatus. Thus, a single
apparatus can be used for treating and cooling the substrate,
rather than using two separate modules. Furthermore, by configuring
the remote plasma apparatus to be able to perform some of the
operations described above, the remote plasma apparatus can reduce
potential oxidation of the metal seed layer before, during, and
after processing of the substrate.
[0078] In some implementations, the remote plasma apparatus can
include a processing chamber, a substrate support for holding a
substrate having a metal seed layer in the processing chamber, a
remote plasma source over the substrate support, a showerhead
between the remote plasma source and the substrate support, and a
controller. The controller may be configured to perform one or more
operations, including providing the substrate with the metal seed
layer in the processing chamber, where a portion of the metal seed
layer has been converted to oxide of the metal, forming a remote
plasma in the remote plasma source, where the remote plasma
includes one or more of: radicals, ions, and UV radiation from the
reducing gas species, and exposing the metal seed layer of the
substrate to the remote plasma, where exposure reduces the oxide of
the metal and reflows the metal in the metal seed layer.
[0079] In some implementations, the remote plasma apparatus can
further include a UV source. The UV source can include UV broadband
lamps such as mercury lamps, UV excimer lamps, UV excimer lasers,
and other appropriate UV sources. Aspects of the UV source can be
described in U.S. patent application Ser. No. 13/787,499 (attorney
docket no. LAMRP027), filed Mar. 6, 2013, which is incorporated
herein by reference in its entirety and for all purposes. In some
implementations, the reducing gas species can be exposed to UV
radiation from the UV source to form radicals and other charged
species of the reducing gas species, which can react with a metal
oxide surface of a metal seed layer to reduce metal oxide.
[0080] FIG. 5 shows an example of a cross-sectional schematic
diagram of a remote plasma apparatus with a processing chamber. The
remote plasma apparatus 500 includes a processing chamber 550,
which includes a substrate support 505 such as a pedestal, for
supporting a substrate 510. The remote plasma apparatus 500 also
includes a remote plasma source 540 over the substrate 510, and a
showerhead 530 between the substrate 510 and the remote plasma
source 540. A reducing gas species 520 can flow from the remote
plasma source 540 towards the substrate 510 through the showerhead
530. A remote plasma may be generated in the remote plasma source
540 to produce radicals of the reducing gas species 520. The remote
plasma may also produce ions and other charged species of the
reducing gas species. The remote plasma may further generate
photons, such as UV radiation, from the reducing gas species. For
example, coils 544 may surround the walls of the remote plasma
source 540 and generate a remote plasma in the remote plasma source
540.
[0081] In some embodiments, the coils 544 may be in electrical
communication with a radio frequency (RF) power source or microwave
power source. An example of a remote plasma source 540 with an RF
power source can be found in the GAMMA.RTM., manufactured by Lam
Research Corporation of Fremont, Calif. Another example of an RF
remote plasma source 540 can be found in the Astron.RTM.,
manufactured by MKS Instruments of Wilmington, Mass., which can be
operated at 440 kHz and can be provided as a subunit bolted onto a
larger apparatus for processing one or more substrates in parallel.
In some embodiments, a microwave plasma can be used with the remote
plasma source 540, as found in the Astex.RTM., also manufactured by
MKS Instruments. A microwave plasma can be configured to operate at
a frequency of 2.45 GHz.
[0082] In embodiments with an RF power source, the RF generator may
be operated at any suitable power to form a plasma of a desired
composition of radical species. Examples of suitable powers
include, but are not limited to, powers between about 0.5 kW and
about 6 kW. Likewise, the RF generator may provide RF power of a
suitable frequency, such as 13.56 MHz for an inductively-coupled
plasma.
[0083] Reducing gas species 520 are delivered from a gas inlet 542
and into an internal volume of the remote plasma source 540. The
power supplied to the coils 544 can generate a remote plasma with
the reducing gas species 520 to form radicals of the reducing gas
species 520. The radicals formed in the remote plasma source 540
can be carried in the gas phase towards the substrate 510 through
the showerhead 530. An example of a remote plasma source 655 with
such a configuration can be described in U.S. Pat. No. 8,084,339
(attorney docket no. NOVLP414), issued Dec. 27, 2011, which is
incorporated herein by reference in its entirety and for all
purposes. The radicals of the reducing gas species 520 can reduce
metal oxides on the surface of the substrate 510.
[0084] In addition to radicals of the reducing gas species, the
remote plasma can also generate and include ions and other charged
species of the reducing gas species 520. In some embodiments, the
remote plasma may include neutral molecules of the reducing gas
species 520. Some of the neutral molecules may be recombined
molecules of charged species from the reducing gas species 520. The
neutrals or recombined molecules of the reducing gas species 520
can also reduce metal oxides on the surface of the substrate 510,
though they may take longer to react and reduce the metal oxides
than the radicals of the reducing gas species 520. The ions may
drift to the surface of the substrate 510 and reduce the metal
oxides, or the ions may be accelerated toward the surface of the
substrate 510 to reduce the metal oxides if the substrate support
505 has an oppositely charged bias. Having species with higher ion
energies can allow deeper implantation into the metal seed layer to
create metastable radical species further from the surface of the
substrate 510. For example, if the substrate 510 has high aspect
ratio features, such as between about 10:1 and about 60:1, ions
with higher ionic energies may penetrate deeper into such features
to provide reduction of the metal oxide more throughout the
features. In contrast, some of the radicals of the reducing gas
species 520 from remote plasma generation may recombine in the
field or near the top of the features. The ions with higher ionic
energies (such as 10 eV-100 eV) can also be used to re-sputter and
reflow the metal in the metal seed layer, which can result in a
more uniform seed coverage and reduce the aspect ratio for
subsequent plating or metal deposition (such as PVD, CVD, ALD).
[0085] In FIG. 5, the remote plasma apparatus 500 may actively cool
or otherwise control the temperature of the substrate 510. In some
embodiments, it may be desirable to control the temperature of the
substrate 510 to control the rate of the reduction reaction and the
uniformity of exposure to the remote plasma during processing. It
may also be desirable to control the temperature of the substrate
510 to reduce the effects of oxidation on the substrate 510 before,
during, and/or after processing.
[0086] In some embodiments, the remote plasma apparatus 500 can
include movable members 515, such as lift pins, that are capable of
moving the substrate 510 away from or towards the substrate support
505. The movable members 515 may contact the lower surface of the
substrate 510 or otherwise pick up the substrate 510 from the
substrate support 505. In some embodiments, the movable members 515
may move the substrate 510 vertically and control the spacing
between the substrate 510 and the substrate support 505. In some
embodiments, the movable members 515 can include two or more
actuatable lift pins. The movable members 515 can be configured to
extend between about 0 inches and about 5 inches, or more, away
from the substrate support 505. The movable members 515 can extend
the substrate 510 away from a hot substrate support 505 and towards
a cool showerhead 530 to cool the substrate 510. The movable
members 515 can also retract to bring the substrate 510 towards a
hot substrate support 505 and away from a cool showerhead 530 to
heat the substrate 510. By positioning the substrate 510 via the
movable members 515, the temperature of the substrate 510 can be
adjusted. When positioning the substrate 510, the showerhead 530
and the substrate support 505 can be held at a constant
temperature.
[0087] In some embodiments, the remote plasma apparatus 500 can
include a showerhead 530 that allows for control of the showerhead
temperature. An example of a showerhead configuration that permits
temperature control can be described in U.S. Pat. No. 8,137,467
(attorney docket no. NOVLP246), issued Mar. 20, 2012, and U.S.
Patent Publication No. 2009/0095220 (attorney docket no.
NOVLP246X1), published Apr. 16, 2009, both of which are
incorporated herein by reference in their entirety and for all
purposes. Another example of a showerhead configuration that
permits temperature control can be described in U.S. Patent
Publication No. 2011/0146571 (attorney docket no. NOVLP329),
published Jun. 23, 2011, which is incorporated herein by reference
in its entirety and for all purposes. To permit active cooling of
the showerhead 530, a heat exchange fluid may be used, such as
deionized water or a thermal transfer liquid manufactured by the
Dow Chemical Company in Midland, Mich. In some embodiments, the
heat exchange fluid may flow through fluid channels (not shown) in
the showerhead 530. In addition, the showerhead 530 may use a heat
exchanger system (not shown), such as a fluid heater/chiller to
control temperature. In some embodiments, the temperature of the
showerhead 530 may be controlled to below about 30.degree. C., such
as between about 5.degree. C. and about 20.degree. C. The
showerhead 530 may be cooled to reduce damage to the metal seed
layer that may result from excess heat during processing of the
substrate 510. The showerhead 530 may also be cooled to lower the
temperature of the substrate 510, such as before and after
processing the substrate 510.
[0088] In some embodiments, the showerhead 530 may include a
plurality of holes. Increasing the size and number of holes in the
showerhead 530 and/or decreasing the thickness of the showerhead
530 may permit greater flow of radicals, ions, and UV radiation
from the reducing gas species 520 through the showerhead 530.
Exposing the metal seed layer to more radicals, ions, and UV
radiation can provide more UV exposure and energetic species to
reduce metal oxide in the metal seed layer. In some embodiments,
the showerhead 530 can include between about 100 and about 900
holes. In some embodiments, an average diameter of the holes can be
between about 0.05 and about 0.5 inches. This can result in an open
area in the showerhead 530 due to holes of between about 3.7% and
about 25%. In some embodiments, the showerhead 530 can have a
thickness between about 0.25 and about 3.0 inches.
[0089] In some embodiments, the substrate support 505 may be
configured to move to and away from the showerhead 530. The
substrate support 505 may extend vertically to control the spacing
between the substrate 510 and the showerhead 530. When reducing
metal oxides on the substrate 510, the uniformity as well as the
rate of the reduction on the substrate 510 may be tuned. For
example, if the substrate support 505 is closer to the showerhead
530, reduction of the metal oxide on the surface of the substrate
510 may proceed faster. However, the center of the substrate 510
may get hotter than the edges of the substrate 510, which can
result in a less uniform reduction treatment. Accordingly, the
spacing between the substrate 510 and the showerhead 530 can be
adjusted to obtain a desired rate and uniformity for processing the
substrate 510. In some embodiments, the substrate support 505 can
be configured to extend between about 0 inches and about 5 inches,
or greater than about 5 inches, from the showerhead 530.
[0090] In some embodiments, the temperature of the substrate
support 505 may also be adjusted. In some embodiments, the
substrate support 505 can be a pedestal with one or more fluid
channels (not shown). The fluid channels may circulate a heat
transfer fluid within the pedestal to actively cool or actively
heat the pedestal, depending on the temperature of the heat
transfer fluid. Embodiments that include such fluid channels and
heat transfer fluids can be described in actively cooled pedestal
systems discussed earlier herein. The circulation of the heat
transfer fluid through one or more fluid channels can control the
temperature of the substrate support 505. Temperature control of
the substrate support 505 can control the temperature of the
substrate 510 to a finer degree. In some embodiments, the
temperature of the substrate support 505 can be adjusted to be
between about 0.degree. C. and about 400.degree. C.
[0091] In some embodiments, the remote plasma apparatus 500 can
include one or more gas inlets 522 to flow cooling gas 560 through
the processing chamber 550. The one or more gas inlets 522 may be
positioned above, below, and/or to the side of the substrate 510.
Some of the one or more gas inlets 522 may be configured to flow
cooling gas 560 in a direction that is substantially perpendicular
to the surface of the substrate 510. In some embodiments, at least
one of the gas inlets 522 may deliver cooling gas 560 through the
showerhead 530 to the substrate 510. Some of the one or more gas
inlets 522 may be parallel to the plane of the substrate 510, and
may be configured to deliver a cross-flow of cooling gas 560 across
the surface of the substrate 510. In some embodiments, the one or
more gas inlets 522 may deliver cooling gas 560 above and below the
substrate 510. The flow of cooling gas 560 across the substrate 510
can enable rapid cooling of the substrate 510. Rapid cooling of the
substrate 510 can reduce the oxidation of the metal seed layer in
the substrate 510. Such cooling of the substrate 510 may take place
before and after processing of the substrate 510. The flow rate of
the cooling gas 560 for cooling can be between about 0.1 standard
liters per minute (slm) and about 100 slm.
[0092] Examples of cooling gas 560 can include a relatively inert
gas, such as nitrogen, helium, neon, krypton, xenon, radon, and
argon. In some embodiments, the cooling gas 560 can include at
least one of nitrogen, helium, and argon.
[0093] In some embodiments, the cooling gas 560 can be delivered at
room temperature, such as between about 10.degree. C. and about
30.degree. C. In some embodiments, the cooling gas 560 can be
delivered at a temperature less than room temperature. For example,
a cold inert gas may be formed by expanding a cold liquid to gas,
such as liquid argon, helium, or nitrogen. Thus, the temperature
range of the cooling gas 560 used for cooling can be broadened to
be anywhere between about -270.degree. C. and about 30.degree.
C.
[0094] In some embodiments, the remote plasma apparatus 500 may be
part of or integrated with an electroplating apparatus (not shown).
This can be shown in FIGS. 8B and 8C, which is discussed in more
detail below. Oxidation of the metal seed layer in the substrate
510 can occur rapidly during exposure to ambient conditions. By
attaching or otherwise connecting the remote plasma apparatus 500
to the electroplating apparatus, the duration of exposure to
ambient conditions of the substrate 510 can be reduced. For
example, the transfer time between the remote plasma apparatus
following treatment and the electroplating apparatus can be between
about 15 seconds and about 90 seconds, or less than about 15
seconds.
[0095] Table I summarizes exemplary ranges of process parameters
that can be used with certain embodiments of a remote plasma
apparatus 500.
Table I
TABLE-US-00001 [0096] TABLE I Parameter Parameter Range Pedestal
Temperature 0.degree. C.-400.degree. C. Showerhead Temperature
5.degree. C.-30.degree. C. Pedestal Dropping Vertical Travel
0''-5'' Lift Pins Raising Vertical Travel 0''-5'' Cooling Gas Flow
(N.sub.2/Ar/He - pure or mixture) 0.1-100 slm Cooling Gas
Temperature -270.degree. C.-30.degree. C. Process Gas Flow
(H.sub.2/He/NH.sub.3 - pure or mixture) 0.5 slm-30 slm Process
Pressure 0.5-6 Torr Venting Gas Flow Nominally same as cooling gas
Venting Gas Nominally same as cooling gas RF Plasma Power 0.5-6 kW
Remote Plasma Apparatus to Electroplating 15-90 seconds Apparatus
Transfer Time Showerhead hole number 100-900 Showerhead thickness
0.25''-3.0'' Showerhead hole diameter 0.05''-0.5'' Showerhead open
area due to holes 3.7%-25%
[0097] A controller 535 may contain instructions for controlling
parameters for the operation of the remote plasma apparatus 500.
The controller 535 will typically include one or more memory
devices and one or more processors. The processor may include a CPU
or computer, analog and/or digital input/output connections,
stepper motor controller boards, etc. Aspects of the controller 535
may be further described with respect to the controller in FIGS. 8A
and 8B.
[0098] FIG. 6A shows an exemplary flow diagram illustrating a
method of treating a substrate with a metal seed layer. FIGS. 7A-7D
show examples of cross-sectional schematic diagrams illustrating
various stages of treating a substrate with a metal seed layer
using a remote plasma apparatus. Some of the steps discussed in
FIG. 6A may be discussed with respect to a corresponding
cross-sectional schematic diagram in FIGS. 7A-7D.
[0099] In FIG. 6A, the process 600a can begin with step 605a where
a substrate is provided in a processing chamber. The substrate can
include a metal seed layer, where a portion of the metal seed layer
has been converted to oxide of the metal. Prior to treatment of the
substrate by a remote plasma, the substrate can be loaded into a
processing chamber of a remote plasma apparatus. In some
embodiments, the substrate can be provided on one or more movable
members in an actuated position. In some embodiments, inert gas may
be flowed through the processing chamber to cool the substrate
during loading. This can reduce additional oxidation of the
substrate during loading. In some embodiments, upon loading the
substrate into the processing chamber, the processing chamber can
be closed and pumped down to vacuum or to a reduced pressure. This
can provide an environment that is substantially free of oxygen.
The pressure of the processing chamber can be between about 0.5
Torr and about 6 Torr, such as between about 0.5 Torr and 3 Torr.
Reduced pressures can reduce the presence of oxygen in the
environment. Thus, loading the substrate into the processing
chamber in such conditions can reduce additional oxidation of the
metal seed layer.
[0100] FIG. 7A shows an example of a cross-sectional schematic
diagram of a remote plasma apparatus 700 at one of the stages of
treating a substrate with a metal seed layer (such as at step
605a). The remote plasma apparatus 700 includes a substrate support
705 in a processing chamber 750, a remote plasma source 740 over
the substrate support 705, and a showerhead 730 between the remote
plasma source 740 and the substrate support 705. Movable members
715 may extend from the substrate support 705 towards the
showerhead 730 to position the substrate 710. Examples of movable
members can include lift pins and peripheral grips. The substrate
710 may include a metal seed layer, where the metal seed layer
includes at least one of Cu, Co, Ru, Pd, Rh, Ir, Os, Ni, Au, Ag,
Al, and W. In some embodiments, the thickness of the metal seed
layer can be less than about 100 .ANG..
[0101] In FIG. 7A, the movable members 715 in a processing chamber
750 may position a substrate 710 in an actuated position. The
actuated position can place the substrate 710 at a distance A.sub.1
closer to the showerhead 730 than an unactuated position (as
illustrated in FIG. 7B). In the actuated position, the distance
A.sub.1 between the substrate 710 and the showerhead 730 can be
between about 0.05 inches and about 0.75 inches. A distance B.sub.1
between the substrate 710 and the substrate support 705 can be any
desired distance. For example, the distance B.sub.1 can be greater
than about 1 inch, such as between about 1 inch and about 5 inches.
The showerhead 730 can be maintained at a relatively cool
temperature, such as less than about 30.degree. C.
[0102] Returning to FIG. 6A, at step 610a, the substrate is moved
towards a substrate support in the processing chamber. In some
embodiments, the substrate can be moved via the movable members to
an unactuated position. The unactuated position is further from a
showerhead in the processing chamber than the actuated position. In
some embodiments, the substrate in the unactuated position may be
in contact with the substrate support. For example, the movable
members may be retracted so that the substrate can rest on the
substrate support. In some embodiments, a gap can exist between the
substrate support and the substrate, and heat transfer can occur
via conduction, convection, radiation, or combinations thereof. The
substrate support can be heated, which in turn can heat the
substrate. The substrate support may be heated to a processing
temperature, such as a temperature between about 0.degree. C. and
about 400.degree. C. The temperature of the substrate support can
depend on the metal seed layer of the substrate. For example, the
substrate support can be heated between about 250.degree. C. and
about 300.degree. C. for cobalt, and between about 75.degree. C.
and about 100.degree. C. for copper. Higher temperatures of the
substrate can speed up the metal oxide reduction reactions.
However, the temperature may be selected to not exceed an
agglomeration temperature of the metal seed layer. When the
substrate is heated, the substrate may be exposed to a remote
plasma treatment.
[0103] FIG. 7B shows an example of a cross-sectional schematic
diagram of a remote plasma apparatus 700 at one of the stages of
treating a substrate with a metal seed layer (such as at step
610a). The remote plasma apparatus 700 includes a substrate 710
over the substrate support 705, where the substrate 710 is in the
unactuated position. In the unactuated position, the substrate 710
is positioned at a distance A.sub.2 from the showerhead 730 and is
further away from the showerhead 730 than in the actuated position.
The distance A.sub.2 between the showerhead 730 and the substrate
710 can be greater than about 1 inch, such as between about 1 inch
and about 5 inches. The substrate 710 and the substrate support 705
can be in contact with each other, or a distance B.sub.2 between
the substrate 710 and the substrate support 705 can be relatively
small so as to allow efficient heat transfer between the substrate
710 and the substrate support 705. In some embodiments, the
distance B.sub.2 can be between about 0 inches and about 0.5
inches. In some embodiments, the movable members 715 can be
retracted so that the substrate 710 rests on the substrate support
705. The substrate support 705 can position the substrate 710
relative to the showerhead 730 by vertically moving the substrate
support 710. The showerhead 730 can be maintained at a relatively
cool temperature, such as less than about 30.degree. C.
[0104] The distance A.sub.2 can be adjusted and can tune the rate
of reaction and the uniformity of reaction during processing of the
substrate. For example, where the substrate support 705 is closer
to the showerhead 730, the rate of reduction may proceed faster but
achieve less uniform results. The distance A.sub.2 can be adjusted
by vertical movement of the substrate support 705. In some
embodiments, the substrate support 705 may move from a first
position to a second position in the processing chamber, where a
distance between the first position and the second position is
greater than about 1 inch. An increased degree of freedom for
positioning the substrate support 705 provides greater flexibility
in tuning the rate and uniformity of the subsequent reduction
treatment.
[0105] Returning to FIG. 6A, at step 615a, a remote plasma can be
formed of a reducing gas species in a remote plasma source, where
the remote plasma includes radicals of the reducing gas species.
The remote plasma can be formed by exposing the reducing gas
species to a source of energy. The energy source can produce
radicals, ions, and other charged species that can be flowed
towards the substrate. In some embodiments, the energy source can
be an RF discharge. When the remote plasma is formed, the substrate
can be or is already heated to a desired processing temperature. In
some embodiments, a showerhead is connected to the remote plasma
source and filters out the ions so that the radicals of the
reducing gas species can be flowed towards the substrate in the
processing chamber.
[0106] At step 620a, the metal seed layer of the substrate is
exposed to the radicals of the reducing gas species. A portion of
the metal seed layer can include an oxide of the metal seed layer.
Ions, radicals, and other charged species formed in the remote
plasma flow through the showerhead, and ions and other charged
species can be filtered out so that the substrate is substantially
exposed to radicals of the reducing gas species. The metal oxide
can react with the radicals of the reducing gas species or the
reducing gas species itself to convert the metal oxide to metal.
The reaction takes place under conditions that convert the metal
oxide to metal. The metal oxide in the metal seed layer is reduced
to form a film integrated with the metal seed layer. Reduction of a
metal oxide in a metal seed layer using a reducing gas species can
be described in U.S. application Ser. No. 13/787,499 (attorney
docket no. LAMRP027), filed Mar. 6, 2013, which is incorporated
herein by reference in its entirety and for all purposes. In some
embodiments, radicals of the reducing gas species flow through the
showerhead when the showerhead is maintained at a temperature below
about 30.degree. C.
[0107] FIG. 7C shows an example of a cross-sectional schematic
diagram of a remote plasma apparatus 700 at one of the stages of
treating a substrate with a metal seed layer (such as at steps 615a
and 620a). The remote plasma apparatus 700 includes a remote plasma
source 740 over the substrate 710 and one or more coils 744
surrounding the walls of the remote plasma source 740. A gas inlet
742 can be connected to the remote plasma source 740 to deliver a
reducing gas species 720 into an internal volume of the remote
plasma source 740. The reducing gas species 720 can be flowed at a
flow rate between about 500 sccm and about 30,000 sccm, which can
be applicable to any substrate size. In some embodiments, the
reducing gas species 720 can include at least one of H.sub.2,
NH.sub.3, CO, B.sub.2H.sub.6, sulfite compounds, carbon and/or
hydrocarbons, phosphites, and N.sub.2H.sub.4. Power supplied to the
one or more coils 744 can generate a remote plasma of the reducing
gas species 720 in the remote plasma source 740. RF plasma power
supplied to the coils 744 can be between about 0.5 kW and about 6
kW. The remote plasma can include radicals of the reducing gas
species 720, such as H*, NH*, NH.sub.2*, or N.sub.2H.sub.3*. The
remote plasma can also include ions and other charged species, but
the showerhead 730 can filter them out so that the radicals of the
reducing gas species 720 arrive at the substrate 710. The radicals
of the reducing gas species 720 flow from the remote plasma source
740 through the showerhead 730 and onto the surface of the
substrate 710 in the processing chamber 750. The showerhead 730 can
be maintained at a relatively cool temperature, such as less than
about 30.degree. C. The cooled showerhead 730 can limit excess heat
from reaching the substrate 710 and avoid damaging the metal seed
layer in the substrate 710.
[0108] In FIG. 7C, the substrate 710 can remain in an unactuated
position. A distance A.sub.3 between the substrate 710 and the
showerhead 730 can be adjusted by moving the substrate support 705.
Adjusting the distance A.sub.3 can tune the rate of reduction
reaction and the uniformity of the reduction reaction occurring at
the substrate 710. For example, a shorter distance A.sub.3 can lead
to faster conversion of metal oxide but less uniformity, while a
longer distance A.sub.3 can lead to slower conversion of metal
oxide but greater uniformity. In some embodiments, the distance
A.sub.3 can be the same as the distance A.sub.2. Movable members
715 can be retracted so that the substrate 710 and the substrate
support 705 remain in contact, or a distance B.sub.3 between the
substrate 710 and the substrate support 705 can be the same as the
distance B.sub.2 in FIG. 7B.
[0109] The temperature of the substrate support 705 can be adjusted
via an active heating or active cooling system. The temperature can
be tuned according to the metal seed layer in the substrate 710
being treated. For example, the temperature of the substrate
support 705 can be changed when switching between two different
metal seed layers that require operating in two different
temperature regimes. For example, the substrate support 705 can be
heated between about 250.degree. C. and about 300.degree. C. for a
cobalt seed layer, and switched to be between about 75.degree. C.
and about 100.degree. C. for a copper seed layer.
[0110] Returning to FIG. 6A, at step 625a, the substrate is exposed
to a cooling gas. The cooling gas can include at least one of
argon, helium, and nitrogen. In some embodiments, the cooling gas
can be produced by expanding a cold liquid to a gas. Exposing the
substrate to the cooling gas can cool the substrate to a
temperature below about 30.degree. C. Thus, the cooling gas can be
delivered at a temperature below ambient conditions to cool the
substrate. In some embodiments, the substrate can be moved to an
actuated position via the movable members prior to exposing the
substrate to the cooling gas. The substrate can be exposed to the
cooling gas while in the actuated position for faster cooling. In
some embodiments, the substrate can be transferred to an
electroplating apparatus after exposing the substrate to the
cooling gas. Alternatively, the substrate may be transferred to an
electroless plating or other metal deposition apparatus. In some
embodiments, the processing chamber can be vented to atmospheric
conditions with a venting gas after exposing the substrate to the
cooling gas.
[0111] FIG. 7D shows an example of a cross-sectional schematic
diagram of a remote plasma apparatus 700 at one of the stages of
treating a substrate with a metal seed layer (such as at step
625a). The remote plasma apparatus 700 can include one or more
cooling gas inlets 722 for delivering a cooling gas 760. The
cooling gas inlets 722 may be positioned around the substrate 710,
including above and to the side of the substrate 710. Cooling gas
760 can be directed onto the substrate 710 through the showerhead
730 and perpendicular to the substrate plane. Cooling gas 760 can
also be directed onto the substrate 710 and parallel to the
substrate plane from cooling gas inlets 722 on the sides of the
process chamber 750. The cooling gas 760 can be flowed into the
process chamber 750 at a flow rate between about 0.1 slm and about
100 slm. The cooling gas inlets 722 can flush cooling gas 760
across the substrate 710 to rapidly cool the substrate 710 prior to
transferring the substrate to an electroplating, electroless
plating, or other metal deposition apparatus. In some embodiments,
the substrate 710 can be cooled without turning off or cooling the
substrate support 705. This can enable the substrate 710 to be
treated and cooled within a single process chamber 750 without
having to use a two-chamber design having separate heating and
cooling zones.
[0112] In FIG. 7D, the substrate 710 can be in an actuated
position. A distance A.sub.4 between the showerhead 730 and the
substrate 710 can be between about 0.05 inches and about 0.75
inches. In some embodiments, the distance A.sub.4 can be the same
as the distance A.sub.1 in FIG. 7A. By positioning the substrate
710 closer to a cooled showerhead 730 and away from a hot substrate
support 705, the substrate 710 can be cooled at a faster rate.
Movable members 715 can lift the substrate 710 away from the
substrate support 705 and towards the showerhead 730. A distance
B.sub.4 between the substrate support 705 and the substrate 710 can
be greater than about 1 inch, or between about 1 inch and about 5
inches. In some embodiments, the distance B.sub.4 can be the same
as the distance B.sub.1 in FIG. 7A. In some embodiments, when the
substrate 710 is in the actuated position and cooled to about room
temperature, the process chamber 750 can be vented to atmospheric
conditions and transferred to an electroplating, electroless
plating, or other metal deposition apparatus.
[0113] FIG. 6B shows an exemplary flow diagram illustrating another
method of treating a substrate with a metal seed layer. At step
605b of the method 600b, a substrate with a metal seed layer can be
provided in a processing chamber, as generally described at step
605a of the method 600a. The metal seed layer can have a portion
that has been converted to oxide of the metal.
[0114] At step 610b, a remote plasma of a reducing gas species can
be formed in a remote plasma source, where the remote plasma
includes one or more of: radicals, ions, and UV radiation from the
reducing gas species. The energy of the remote plasma may be
increased to generate higher energy species, including higher
energy ions. Higher energy ions may be produced in high density
plasma (HDP) processing systems and/or sputtering systems. The
remote plasma may also generate UV radiation as a result of
excitation of the reducing gas species. The generated UV radiation
can have a wavelength between about 100 nm and about 700 nm. For
example, the generated UV radiation can include short wavelength UV
light, such as between about 120 nm and about 200 nm, and long
wavelength UV light, such as between about 200 nm and about 700 nm.
In addition, the remote plasma may include neutrals and/or generate
recombined molecules of the reducing gas species.
[0115] At step 615b, the metal seed layer of the substrate is
exposed to the remote plasma, where the exposure reduces the oxide
of the metal and reflows the metal in the metal seed layer. In some
implementations, reflow of the metal and the reduction of the metal
oxide may occur concurrently. In some implementations, the remote
plasma can include radicals, ions, and UV radiation from the
reducing gas species, or some combination thereof. A showerhead
between the remote plasma source and the processing chamber can
have a thickness, a number of holes, and an average diameter of
holes configured to permit radicals, ions, and UV radiation flow or
otherwise travel through the showerhead toward the substrate. The
radicals, ions, and UV radiation may enter the processing chamber
and reduce metal oxide in the metal seed layer. High energy ions
may penetrate further from the surface of the substrate to provide
a reducing chemistry throughout more of the metal seed layer. UV
radiation may activate the metal oxide surface to improve the
thermodynamics of the reduction process, or directly reduce the
metal oxide itself. The UV radiation may also be absorbed by the
reducing gas species and give rise to radicals that can reduce
metal oxide. Furthermore, neutral molecules of the reducing gas
species may further react and reduce metal oxide in the metal seed
layer.
[0116] In some implementations, the metal in the metal seed layer
may be excited and mobilized upon exposure. The metal may be
reflowed to reduce gaps and voids in the metal seed layer, which
can reduce the surface roughness of the metal seed layer. How much
the metal is reflowed can depend on the temperature of the
substrate, the chamber pressure, the reducing gas species, and the
intensity of the UV radiation, for example. As the metal is
reflowed and redistributed on the underlying layer, a more uniform
and continuous metal seed layer can be formed.
[0117] FIG. 8A shows an example of a top view schematic of an
electroplating apparatus. The electroplating apparatus 800 can
include three separate electroplating modules 802, 804, and 806.
The electroplating apparatus 800 can also include three separate
modules 812, 814, and 816 configured for various process
operations. For example, in some embodiments, modules 812 and 816
may be spin rinse drying (SRD) modules and module 814 may be an
annealing station. However, the use of SRD modules may be rendered
unnecessary after exposure to a reducing gas species from a remote
plasma treatment. In some embodiments, at least one of the modules
812, 814, and 816 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 802, 804, and
806.
[0118] The electroplating apparatus 800 can include a central
electroplating chamber 824. The central electroplating chamber 824
is a chamber that holds the chemical solution used as the
electroplating solution in the electroplating modules 802, 804, and
806. The electroplating apparatus 800 also includes a dosing system
826 that may store and deliver additives for the electroplating
solution. A chemical dilution module 822 may store and mix
chemicals that may be used as an etchant. A filtration and pumping
unit 828 may filter the electroplating solution for the central
electroplating chamber 824 and pump it to the electroplating
modules 802, 804, and 806.
[0119] In some embodiments, an annealing station 832 may be used to
anneal substrates as pretreatment. The annealing station 832 may
include a number of stacked annealing devices, e.g., five stacked
annealing devices. The annealing devices may be arranged in the
annealing station 832 one on top of another, in separate stacks, or
in other multiple device configurations.
[0120] A system controller 830 provides electronic and interface
controls required to operate the electroplating apparatus 800. The
system controller 830 (which may include one or more physical or
logical controllers) controls some or all of the properties of the
electroplating apparatus 800. The system controller 830 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 830 or
they may be provided over a network. In certain embodiments, the
system controller 830 executes system control software.
[0121] The system control software in the electroplating apparatus
800 may include electroplating instructions for controlling the
timing, mixture of the 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 performed by the electroplating apparatus 800. System
control software 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.
[0122] In some embodiments, system control software 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 830, and each phase of the
pretreatment or reducing process may include one or more
instructions for execution by the system controller 830. In
electroplating, the instructions for setting process conditions for
an immersion process phase may be included in a corresponding
immersion recipe phase. In pretreatment or reducing, the
instructions for setting process conditions for exposing the
substrate to a remote plasma may be included in a corresponding
reducing phase recipe. In some embodiments, the phases of
electroplating and reducing processes may be sequentially arranged,
so that all instructions for a process phase are executed
concurrently with that process phase.
[0123] Other computer software and/or programs may be employed in
some embodiments. Examples of programs or sections of programs for
this purpose include a substrate positioning program, an
electrolyte composition control program, a pressure control
program, a heater control program, a potential/current power supply
control program. Other examples of programs or sections of this
program for this purpose include a timing control program, movable
members positioning program, a substrate support positioning
program, a remote plasma apparatus control program, a pressure
control program, a substrate support temperature control program, a
showerhead temperature control program, a cooling gas control
program, and a gas atmosphere control program.
[0124] In some embodiments, there may be a user interface
associated with the system controller 830. 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.
[0125] Signals for monitoring the process may be provided by analog
and/or digital input connections of the system controller 830 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, etc. Appropriately
programmed feedback and control algorithms may be used with data
from these sensors to maintain process conditions, such as
temperature of the substrate.
[0126] A hand-off tool 840 may select a substrate from a substrate
cassette such as the cassette 842 or the cassette 844. The
cassettes 842 or 844 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 840 may hold the substrate using a vacuum attachment or some
other attaching mechanism.
[0127] The hand-off tool 840 may interface with the annealing
station 832, the cassettes 842 or 844, a transfer station 850, or
an aligner 848. From the transfer station 850, a hand-off tool 846
may gain access to the substrate. The transfer station 850 may be a
slot or a position from and to which hand-off tools 840 and 846 may
pass substrates without going through the aligner 848. In some
embodiments, however, to ensure that a substrate is properly
aligned on the hand-off tool 846 for precision delivery to an
electroplating module, the hand-off tool 846 may align the
substrate with an aligner 848. The hand-off tool 846 may also
deliver a substrate to one of the electroplating modules 802, 804,
or 806 or to one of the three separate modules 812, 814, and 816
configured for various process operations.
[0128] In some embodiments, a remote plasma apparatus may be part
of or integrated with the electroplating apparatus 800. FIG. 8B
shows an example of a magnified top view schematic of a remote
plasma apparatus with an electroplating apparatus. However, it is
understood by those of ordinary skill in the art that the remote
plasma apparatus may alternatively be attached to an electroless
plating apparatus or other metal deposition apparatus. FIG. 8C
shows an example of a three-dimensional perspective view of a
remote plasma apparatus attached to an electroplating apparatus.
The remote plasma apparatus 860 may be attached to the side of the
electroplating apparatus 800. The remote plasma apparatus 860 may
be connected to the electroplating apparatus 800 in such a way so
as to facilitate efficient transfer of the substrate to and from
the remote plasma apparatus 860 and the electroplating apparatus
800. The hand-off 840 may gain access to the substrate from
cassette 842 or 844. The hand-off tool 840 may pass the substrate
to the remote plasma apparatus 860 for exposing the substrate to a
remote plasma treatment and a cooling operation. The hand-off tool
840 may pass the substrate from the remote plasma apparatus 860 to
the transfer station 850. In some embodiments, the aligner 848 may
align the substrate prior to transfer to one of the electroplating
modules 802, 804, and 806 or one of the three separate modules 812,
814, and 816.
[0129] Operations performed in the electroplating apparatus 800 may
introduce exhaust that can flow through front-end exhaust 862 or a
back-end exhaust 864. The electroplating apparatus 800 may also
include a bath filter assembly 866 for the central electroplating
station 824, and a bath and cell pumping unit 868 for the
electroplating modules 802, 804, and 806.
[0130] In some embodiments, the system controller 830 may control
the parameters for the process conditions in the remote plasma
apparatus 860. Non-limiting examples of such parameters include
substrate support temperature, showerhead temperature, substrate
support position, movable members position, cooling gas flow,
cooling gas temperature, process gas flow, process gas pressure,
venting gas flow, venting gas, reducing gas, plasma power, and
exposure time, transfer time, etc. These parameters may be provided
in the form of a recipe, which may be entered utilizing the user
interface as described earlier herein.
[0131] Operations in the remote plasma apparatus 860 that is part
of the electroplating apparatus 800 may be controlled by a computer
system. In some embodiments, the computer system is part of the
system controller 830 as illustrated in FIG. 8A. In some
embodiments, the computer system may include a separate system
controller (not shown) including program instructions. The program
instructions may include instructions to perform all of the
operations needed to reduce metal oxides to metal in a metal seed
layer. The program instructions may also include instructions to
perform all of the operations needed to cool the substrate,
position the substrate, and load/unload the substrate.
[0132] In some embodiments, a system controller may be connected to
a remote plasma apparatus 860 in a manner as illustrated in FIG. 5.
In one embodiment, the system controller includes instructions for
providing a substrate in a processing chamber, moving the substrate
towards a substrate support in the processing chamber, forming a
remote plasma of a reducing gas species in a remote plasma source,
where the remote plasma includes radicals of the reducing gas
species, exposing a metal seed layer of the substrate to radicals
of the reducing gas species, and exposing the substrate to a
cooling gas. The remote plasma may include one or more of radicals,
ions, neutrals, and UV radiation from the reducing gas species,
resulting in the metal seed layer being exposed to one or more of
radicals, ions, neutrals, and UV radiation from the reducing gas
species. The system controller may further include instructions for
performing operations as described earlier herein with respect to
FIGS. 5, 6A, 6B, and 7A-7D.
[0133] The apparatus/process 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.
Typically, though not necessarily, such tools/processes will be
used or conducted together in a common fabrication facility.
Lithographic patterning of a film typically includes some or all of
the following operations, each operation enabled with a number of
possible tools: (1) application of photoresist on a workpiece,
i.e., 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 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; (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.
[0134] 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.
Examples
[0135] FIG. 9 shows a graph illustrating the effects of exposure to
a remote plasma and gains in electrical conductivity for copper.
Without pretreating the substrate including a copper seed layer
with a remote plasma, the change in electrical conductivity at the
surface of the copper is almost negligible. However, treating the
substrate heated to 75.degree. C. with a remote plasma
substantially increases the electrical conductivity at the surface
of the copper seed layer. The effects remained largely the same
whether the remote plasma treatment occurred from 30 seconds, 60
seconds, and 120 seconds. Therefore, pretreatment with a remote
plasma effectively reduces the presence of copper oxide to pure
metallic copper to increase the electrical conductivity.
[0136] FIG. 10 shows scanning electron microscopy (SEM) images of
seed trench coupons when treated using a remote plasma and when not
treated using a remote plasma. Samples of copper seeded trench
coupons were exposed to a remote plasma to determine the
effectiveness of the remote plasma in reducing copper oxide and
avoiding void formation. Each of the samples of the copper seeded
trench coupons had trenches with a width of about 48 nm each.
Marginal copper seeded trench coupons were utilized where the seed
condition provided thin seed coverage. The marginal copper seeded
trench coupons generally result in very large bottom voids. The
marginal copper seeded trench coupons represent extreme samples
that are typically not found on production wafers, but can more
effectively indicate the ability of reducing agent treatment in
reducing copper oxide and preventing void formation.
[0137] In FIG. 10, the marginal copper seeded trench coupons were
plated with copper without pretreatment by exposure to a remote
plasma. The trench coupons resulted in poor fill and substantially
large bottom void sizes. However, the trench coupons pretreated by
exposure to a remote plasma for 60 seconds at 75.degree. C. prior
to electroplating with copper resulted in trench coupons with
better fill and smaller bottom voids. Therefore, the SEM images of
the trench coupons reveal the improved fill of electroplating
following pretreatment with a remote plasma.
[0138] FIG. 11 shows a graph illustrating the growth of metal oxide
on a metal seed layer exposed to ambient conditions following a
reduction treatment. After a metal seed layer is pretreated with a
remote plasma, exposure to ambient conditions can lead to regrowth
of metal oxide. The graph in FIG. 11 shows that regrowth of metal
oxide occurs rapidly as a function of time. Within the first four
hours, the surface of the metal seed layer can substantially
reoxidize. Therefore, reducing the duration of exposure to ambient
conditions can substantially limit the reoxidation of metal
oxide.
[0139] FIG. 12 shows SEM images of seed trench coupons exposed to
ambient conditions for different durations following a reduction
treatment and when not following a reduction treatment. The first
control condition plated copper without any pretreatment. The
second through last conditions plated copper in trench coupons that
were pretreated with a remote plasma, where each of the conditions
were exposed to ambient conditions for different amounts of time.
The trench coupons under the second condition displayed the best
fill and the smallest bottom voids. The second condition pretreated
the trench coupons with a remote plasma and was exposed to ambient
conditions for the shortest duration of time. Therefore, the SEM
images reveal that reducing the duration of the transfer time
following pretreatment with a remote plasma substantially improves
the fill of electroplating.
[0140] FIG. 13 shows a graph illustrating temperature cooling
profiles over time under different conditions in a processing
chamber. Each of the cooling profiles were obtained by cooling a
substrate from about 85.degree. C. under various flow rates of
cooling gas, distance between the showerhead and the substrate, and
distance between the showerhead and the pedestal. Rapid cooling
rates can be achieved by adjusting the aforementioned parameters.
For example, a substrate can rapidly cool in about 1 minute from
about 85.degree. C. to about room temperature by delivering helium
at 30 slm, positioning the substrate at 1/8 inches from the
showerhead, and positioning the pedestal 3 inches from the
showerhead.
[0141] FIG. 14 shows a graph illustrating the effects of
temperature and surface roughness of the metal seed layer following
a remote plasma treatment. As temperatures of the substrates
increased from about 65.degree. C. to about 100.degree. C., the
average surface roughness of a 50 .ANG. thick metal seed layer
decreased from 0.66 nm root mean square (RMS) to about 0.58 nm RMS.
Thus, the graph in FIG. 14 shows a correlation between increasing
temperature and a smoother metal seed layer. This indicates that
metal seed reflow from the increased temperature may lead to a more
uniform and continuous metal seed layer.
[0142] FIG. 15 shows a graph illustrating the effects of
temperature and void reduction in a metal seed layer. For some seed
layers, such as copper seed layers, lower substrate temperatures
can reduce the percentage of voids on the substrate.
Other Embodiments
[0143] Although the foregoing has been described in some detail for
purposes of clarity and understanding, it will be apparent that
certain changes and modifications may be practiced within the scope
of the appended claims. It should be noted that there are many
alternative ways of implementing the processes, systems, and
apparatus described. Accordingly, the described embodiments are to
be considered as illustrative and not restrictive.
* * * * *