U.S. patent application number 12/911260 was filed with the patent office on 2012-04-26 for method for copper electrodeposition.
This patent application is currently assigned to UNIVERSITEIT GENT. Invention is credited to Tanya A. Atanasova, Margalit Nagar, Aleksandar Radisic, Philippe M. Vereecken.
Application Number | 20120097547 12/911260 |
Document ID | / |
Family ID | 45972039 |
Filed Date | 2012-04-26 |
United States Patent
Application |
20120097547 |
Kind Code |
A1 |
Vereecken; Philippe M. ; et
al. |
April 26, 2012 |
Method for Copper Electrodeposition
Abstract
The present invention is related to a method for electroplating
a copper deposit onto a substrate, wherein the method comprises the
steps of: a) immersing the substrate into an electroplating bath
having a copper ion concentration comprised between 0.5
mmoll.sup.-1 and 50 mmoll.sup.-1, and an acid concentration
comprised between 0.05% and 10% per volume of said electroplating
bath; and wherein the method further comprises the step of b)
electroplating the copper deposit from the electroplating bath onto
the substrate. In particular, the present invention is directed to
an improved method for the manufacture of semiconductor integrated
circuit (IC) devices provided with sub-100 nm features.
Inventors: |
Vereecken; Philippe M.;
(Liege, BE) ; Atanasova; Tanya A.; (Leuven,
BE) ; Nagar; Margalit; (Zichem, BE) ; Radisic;
Aleksandar; (Leuven, BE) |
Assignee: |
UNIVERSITEIT GENT
Gent
BE
IMEC
Leuven
BE
|
Family ID: |
45972039 |
Appl. No.: |
12/911260 |
Filed: |
October 25, 2010 |
Current U.S.
Class: |
205/157 ;
205/291 |
Current CPC
Class: |
C25D 7/123 20130101;
H01L 21/2885 20130101; C25D 3/38 20130101; H01L 21/76877
20130101 |
Class at
Publication: |
205/157 ;
205/291 |
International
Class: |
C25D 3/38 20060101
C25D003/38; C25D 7/12 20060101 C25D007/12 |
Claims
1. A method for electroplating a copper deposit onto a substrate,
wherein the method comprises the steps of: a. immersing said
substrate into an electroplating bath having a copper ion
concentration comprised between about 0.5 mmoll.sup.-1 and about 50
mmoll.sup.-1, and an acid concentration comprised between about
0.05% and about 10% per volume of said electroplating bath; and b.
electroplating the copper deposit from said electroplating bath
onto said substrate.
2. A method according to claim 1, wherein the pH of the
electroplating bath is acidic, preferably the pH is comprised
between about -0.3 and about 3.0, more preferably between about
-0.2 and about 2.0.
3. A method according to claim 1, wherein the electroplating bath
has a chloride ion concentration comprised between about 0.1 ppm
and about 10 ppm, preferably between about 0.5 ppm and about 8 ppm,
more preferably between about 1 ppm and about 5 ppm, even more
preferably between about 1 ppm and about 3 ppm, still more
preferably between about 1.5 ppm and about 2.5 ppm, most preferably
between about 1.8 ppm and about 2.2 ppm.
4. A method according to claim 1, wherein the substrate is provided
with at least one feature opening, preferably selected from the
group of trenches and vias, wherein said feature opening has a
width below about 100 nm, preferably below about 70 nm, more
preferably below about 50 nm, even more preferably below about 35
nm.
5. A method according to claim 1, wherein the substrate is provided
with a copper seed having a thickness below about 60 nm, preferably
below about 50 nm, more preferably below about 30 nm, even more
preferably below about 20 nm, still more preferably below about 10
nm, most preferably below about 8 nm.
6. A method according to claim 5, wherein the electroplating bath
has an acid concentration comprised between about 0.05% and about
1%, preferably between about 0.05% and about 0.7%, more preferably
between about 0.05% and about 0.5%, even more preferably between
about 0.05% and about 0.3%, most preferably between about 0.05% and
about 0.15% per volume of said electroplating bath.
7. A method according to claim 5, wherein the electroplating bath
comprises sulfuric acid, preferably in a concentration comprised
between about 10 mmoll.sup.-1 and about 200 mmoll.sup.-1, more
preferably between about 10 mmoll.sup.-1 and about 100
mmoll.sup.-1, even more preferably between about 15 mmoll.sup.-1
and about 50 mmoll.sup.-1, most preferably between about 15
mmoll.sup.-1 and about 25 mmoll.sup.-1.
8. A method according to any of claim 1, wherein the substrate is
provided with a seed layer made from a seed material not comprising
copper; and wherein the seed material preferably comprises
ruthenium.
9. A method according to claim 8, wherein the electroplating bath
has an acid concentration comprised between about 5% and about 10%,
preferably between about 6% and about 9.5%, even more preferably
between about 7% and about 9%, most preferably between about 8% and
about 9% per volume of said electroplating bath.
10. A method according to claim 8, wherein the electroplating bath
comprises sulfuric acid, preferably in a concentration comprised
between about 1 moll.sup.-1 and about 2 moll.sup.-1, more
preferably between about 1.2 moll.sup.-1 and about 1.9 moll.sup.-1,
even more preferably between about 1.4 moll.sup.-1 and about 1.8
moll.sup.-1, most preferably between about 1.6 moll.sup.-1 and
about 1.8 mmoll.sup.-1.
11. A method according to claim 1, wherein the electroplating bath
has a copper ion concentration comprised between about 0.5
mmoll.sup.-1 and about 30 mmoll.sup.-1, preferably between about
0.5 mmoll.sup.-1 and about 20 mmoll.sup.-1, more preferably between
about 1.0 mmoll.sup.-1 and about 20 mmoll.sup.-1, even more
preferably between about 1.0 mmoll.sup.-1 and about 10
mmoll.sup.-1.
12. A method according to claim 1, wherein the electroplating bath
further comprises an organic additive system comprising a
suppressor of copper deposition on copper and/or an accelerator of
copper deposition on copper.
13. A method according to claim 12, wherein the electroplating bath
comprises a suppressor of copper deposition, which is preferably
polyethylene glycol, in a concentration comprised between about 20
ppm and about 500 ppm, more preferably between about 50 ppm and
about 120 ppm, even more preferably between about 70 ppm and about
115 ppm, still more preferably between about 90 ppm and about 110
ppm; most preferably in a concentration of about 100 ppm; and
wherein the electroplating bath comprises an accelerator of copper
deposition, which is preferably bis-(sodium sulfopropyl)-disulfide,
in a concentration comprised between about 0.02 ppm and about 2
ppm, preferably between about 0.1 ppm and about 1.5 ppm, more
preferably between about 0.5 ppm and about 1.3 ppm, most preferably
between about 0.7 ppm and about 1.0 ppm.
14. A method for the preparation of an electroplating bath suitable
for electroplating a copper deposit onto a substrate, wherein the
method comprises the step of: a. providing a concentrate
composition comprising a source of copper ion and a source of acid;
and b. diluting said concentrate composition into a solution
comprising deionized water, thereby forming an electroplating bath
as described in claim 1.
15. The concentrate composition as defined in claim 14.
16. The concentrate composition according to claim 15, which
further comprises a source of chloride ion, preferably in such an
amount as to form an electroplating bath having a chloride ion
concentration comprised between about 0.1 ppm and about 10 ppm,
preferably between about 0.5 ppm and about 8 ppm, more preferably
between about 1 ppm and about 5 ppm, even more preferably between
about 1 ppm and about 3 ppm, still more preferably between about
1.5 ppm and about 2.5 ppm, most preferably between about 1.8 ppm
and about 2.2 ppm, when said concentrate composition is diluted
into a solution comprising deionized water.
17. The method of use according to claim 1 for the manufacture of a
semiconducting device, preferably a semiconductor integrated
circuit (IC) device.
18. The method of use according to claim 17 for the manufacture of
semiconducting devices features, preferably for the manufacture of
interconnections having a width which is preferably below about 100
nm, more preferably below about 70 nm, even more preferably below
about 50 nm, most preferably below about 35 nm.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention is related to the field of
semiconductor processing, and in particular the field of
semiconductor integrated circuit (IC) device manufacturing. More
specifically, the present invention is directed to a method for
copper electrodeposition onto a substrate provided with sub-100 nm
features.
[0003] 2. Description of Related Art
[0004] The demand for manufacturing semiconductor integrated
circuit (IC) devices such as computer chips with high circuit
speed, high packing density and low power dissipation requires the
downward scaling of feature sizes in ultra-large-scale integration
(ULSI) and very-large-scale integration (VLSI) structures. The
trend to smaller chip sizes and increased circuit density requires
the miniaturization of interconnect features which severely
penalizes the overall performance of the structure because of
increasing interconnect resistance and reliability concerns such as
electromigration.
[0005] Traditionally, such structures had used aluminum and
aluminum alloys as the metallization on silicon wafers with silicon
dioxide being the dielectric material. In general, openings are
formed in the dielectric layer in the shape of vias and trenches
after metallization to form interconnects. Increased
miniaturization is reducing the openings to submicron, and even
sub-100 nm sizes.
[0006] To achieve further miniaturization of the device, copper has
been introduced instead of aluminum as the metal to form the
connection lines and interconnects in the chip. Copper has a lower
resistivity than aluminum and the thickness of a copper line for
the same resistance can be thinner than that of an aluminum line.
Also, copper has excellent electromigration resistance.
[0007] Copper can be deposited on substrates by plating
(electroless or electrolytic), sputtering, physical vapor
deposition (PVD), and chemical vapor deposition (CVD). It is
generally recognized that electrochemical deposition is the most
suitable method to apply copper to semiconductor devices since high
deposition rates are typically achieved and the associated tool
costs may be kept to a minimum. However, plating methods shall meet
the stringent requirements of the semiconductor industry. As a way
of example, the copper deposits shall be uniform and capable of
flawlessly filling the extremely small trenches and vias of the
device.
[0008] The deposition of copper from acid cooper baths is
recognized in the electronics industry as the leading candidate to
copper plate integrated circuit devices. The integration of copper
into the IC manufacturing process may be e.g. implemented by
damascene plating techniques where electrodeposition is used for
fabricating the wiring structures. In that context, a successful
integration of the copper into the wiring structures requires
depositing a continuous copper seed layer as a conductive layer on
top of a highly resistive barrier liner which covers the underlying
substrate such as a patterned wafer, and which is aimed at
preventing copper from diffusing into the underlying substrate. The
copper seed layer is deposited to ensure good electrical contact
and improved adhesion to the diffusion barrier layer.
[0009] As the feature sizes of interconnects decrease and aspect
ratios increase, copper electrodeposition becomes even more
challenging. Due to the dimensional shrinkage, the thickness of the
barrier/copper seed layers becomes significantly bigger with
respect to the trench/via opening. As a result, the available space
for copper deposition decreases dramatically which can lead to
pinch off of the feature openings and void formation in the inlaid
trench and via features. In order to compensate for the dimensional
shrinkage, the thicknesses of the barrier and copper seed layers
have to be scaled down as well.
[0010] However, scaling down of the copper seed layer thickness is
stringently limited due to the so-called terminal effect. The
terminal effect, which is particularly severe for very thin copper
seeds, leads to the applied current or voltage dropping off
drastically within a short distance from the edge of the wafer,
where the electrical contact is made (as described below). As a
result of this severe terminal effect, copper deposition will only
occur near the edge of the substrate and copper plating will only
take place at the edge of the substrate. At most, a delay in
plating of the center of the processed wafer is observed. As a
result of this "non-instant plating", corrosion of the copper seed
occurs in the center of the wafer. The terminal effect is therefore
a key limitation for the integration of copper plating performed on
very thin copper seed (having thicknesses typically below 20 nm) in
the manufacture of chip semiconductor integrated circuit (IC)
devices comprising very narrow interconnect features (having
typically a width below 100 nm).
[0011] Conventional methods for overcoming the terminal effects for
these seed layers include low platting current, segmented anode
configuration, high copper concentration and low conductivity (low
acid concentration) copper plating baths which improve the current
distribution and result in a more uniform film thickness. However,
these techniques may not be applicable for very thin seed layers
having thicknesses typically below 20 nm or in the absence of seed
layer due to the extreme severity of the terminal effect.
[0012] One partial solution to problem of achieving acceptable
filling of very narrow feature openings (trench or via) throughout
the entire processed wafer is allegedly disclosed in
US-A1-2004/0069648 which describes a method for electroplating an
electrically conductive material onto a platable resistive metal
barrier layer located on a substrate, which method comprises
contacting the substrate with a plating bath and applying changing
current or voltage as a function of the area of plated metal, and
wherein the method does not require the pre-deposition of a seed
layer.
[0013] Another partial solution to have very narrow features filled
with standard copper electrochemical deposition (ECD) techniques is
allegedly disclosed in US-A1-2002/0153259 which describes a method
of forming a copper-containing layer on a substrate, wherein the
method comprises electroplating the substrate in an electroplating
bath comprising a source of copper ions and a specific complexing
agent for complexing the copper ions. However no enabling teaching
of narrow features filling is described whatsoever.
[0014] US-A1-2003/0168343 discloses a method for electroplating a
copper deposit onto a semiconductor integrated circuit device
substrate having submicron-sized features with allegedly fewer
defects and improved surface morphology. The disclosed method
involves immersing the substrate into an electroplating bath
including ionic copper and an effective amount of a defect reducing
agent.
[0015] Despite the progress in the art, there is still need for an
efficient method for the integration of copper plating onto a
substrate provided with very narrow feature openings (such as
trenches or vias), in particular sub-100 nm feature openings.
[0016] Advantageously, the method of the present invention may be
performed on a substrate provided with very thin copper seeds which
typically have thicknesses below 20 nm.
[0017] Advantageously still, the method of the invention is
applicable to direct (seedless) copper plating with direct (super)
filling of very narrow feature openings.
[0018] Other advantages of the invention will be immediately
apparent to those skilled in the art from the following
description.
SUMMARY OF THE INVENTION
[0019] It is against the above background that the present
invention provides certain advantages and advancements over the
prior art.
[0020] According to one aspect of the present invention, it is
provided a method for electroplating a copper deposit onto a
substrate, wherein the method comprises (or consists of) the steps
of:
[0021] immersing the substrate into an electroplating bath having a
copper ion concentration comprised between about 0.5 mmoll.sup.-1
and about 50 mmoll.sup.-1, and an acid concentration comprised
between about 0.05% and about 10% per volume of the electroplating
bath solution; and
[0022] electroplating the copper deposit from the electroplating
bath onto the substrate.
[0023] Preferably, in the method of the invention as described
above, the copper ion is a copper (II) cation.
[0024] Preferably, in the method of the invention as described
above, the pH of the electroplating bath is acidic. Preferably, the
pH is below about 6, more preferably below about 4, even more
preferably below about 3, still more preferably below about 2.
Still more preferably, the pH of the electroplating bath is
comprised between about -0.3 and about 3.0, more preferably between
about -0.25 and about 2.0, even more preferably between about -0.25
and about 2.0.
[0025] Preferably, in the method of the invention as described
above, the electroplating bath has a chloride ion concentration
comprised between about 0.1 ppm and about 10 ppm, preferably
between about 0.5 ppm and about 8 ppm, more preferably between
about 1 ppm and about 5 ppm, even more preferably between about 1
ppm and about 3 ppm, still more preferably between about 1.5 ppm
and about 2.5 ppm, still more preferably between about 1.8 ppm and
about 2.2 ppm, most preferably the electroplating bath has a
chloride ion concentration of about 2.0 ppm.
[0026] Preferably, in the method of the invention as described
above, the source of chloride ion in the electroplating bath is
selected from the group consisting of hydrochloric acid, potassium
chloride, sodium chloride, and any combinations or mixtures
thereof. Preferably, the source of chloride ion in the
electroplating bath is selected to comprise hydrochloric acid.
[0027] Preferably, in the method of the invention as described
above, the substrate comprises a semiconductor material which is
preferably selected from the group consisting of silicon,
germanium, silicon on insulator (SOI), and any combinations or
mixtures thereof. More preferably, in the method according to the
invention, the substrate is a silicon wafer.
[0028] Preferably, in the method of the invention as described
above, the substrate is provided with at least one feature opening,
preferably selected from the group of trenches and vias, wherein
the feature opening has a width below about 100 nm, preferably
below about 70 nm, more preferably below about 50 nm, even more
preferably below about 35 nm.
[0029] According to one preferred aspect, in the method of the
invention as described above, the substrate is provided with a
copper seed having a thickness below about 60 nm, preferably below
about 50 nm, more preferably below about 30 nm, even more
preferably below about 20 nm, still more preferably below about 10
nm, most preferably below about 8 nm.
[0030] Preferably, in the method of the invention as described
above, the copper seed layer at least partly covers the sidewalls
and the bottom of the feature opening. More preferably, the copper
seed layer fully covers the sidewalls and the bottom of the feature
opening, without fully filling the feature opening.
[0031] Preferably, the method of the invention as described above
further comprises the step of providing the substrate with a copper
seed layer having a thickness preferably below about 60 nm, more
preferably below about 50 nm, even more preferably below about 20
nm, still more preferably below about 10 nm, most preferably below
about 8 nm. Preferably, the copper seed layer is deposited using
Physical Vapor Deposition (PVD) techniques.
[0032] Preferably, in the method of the invention as described
above, the substrate is further provided with a diffusion barrier
layer, whereby the copper seed layer is preferably deposited onto
the diffusion barrier layer.
[0033] Preferably, in the method of the invention as described
above, the source of acid concentration in the electroplating bath
is selected to comprise sulfuric acid.
[0034] According to one preferred aspect of the method of the
invention, whereby the substrate is provided with a copper seed,
the electroplating bath preferably has an acid concentration
comprised between about 0.05% and about 1%, more preferably between
about 0.05% and about 0.7%, even more preferably between about
0.05% and about 0.5%, still more preferably between about 0.05% and
about 0.3%, most preferably between about 0.05% and about 0.15% per
volume of the electroplating bath.
[0035] Still according to the preferred aspect of the method of the
invention, whereby the substrate is provided with a copper seed,
the electroplating bath preferably comprises sulfuric acid, more
preferably in a concentration comprised between about 10
mmoll.sup.-1 and about 200 mmoll.sup.-1, more preferably between
about 10 mmoll.sup.-1 and about 100 mmoll.sup.-1, even more
preferably between about 15 mmoll.sup.-1 and about 50 mmoll.sup.-1,
most preferably between about 15 mmoll.sup.-1 and about 25
mmoll.sup.-1.
[0036] According to another preferred aspect of the method of the
invention, the substrate is provided with a seed layer made from a
seed material not comprising copper. In a preferred aspect, the
seed material comprises a metal selected from the group consisting
of ruthenium, tantalum, cobalt, and any combinations or mixtures
thereof. More preferably, the seed material comprises
ruthenium.
[0037] According to another aspect of the invention, the seed layer
not comprising copper may also further act as a diffusion barrier
layer.
[0038] According to one preferred aspect of the method of the
invention, whereby the substrate is provided with a seed layer made
from a seed material not comprising copper, the electroplating bath
preferably has an acid concentration comprised between about 5% and
about 10%, more preferably between about 6% and about 9.5%, even
more preferably between about 7% and about 9%, most preferably
between about 8% and about 9%, per volume of said electroplating
bath.
[0039] Still according to the preferred aspect of the method of the
invention, whereby the substrate is provided with a seed layer made
from a seed material not comprising copper, the electroplating bath
preferably comprises sulfuric acid, more preferably in a
concentration comprised between about 1 moll.sup.-1 and about 2
moll.sup.-1, more preferably between about 12 moll.sup.-1 and about
1.9 moll.sup.-1, even more preferably between about 1.4 moll.sup.-1
and about 1.8 moll.sup.-1, most preferably between about 1.0
moll.sup.-1 and about 1.8 moll.sup.-1.
[0040] Preferably, in the method of the invention as described
above, the electroplating bath has a copper ion concentration
comprised between about 0.5 mmoll.sup.-1 and about 30 mmoll.sup.-1,
preferably between about 0.5 mmoll.sup.-1 and about 20
mmoll.sup.-1, more preferably between about 1.0 mmoll.sup.-1 and
about 20 mmoll.sup.-1, even more preferably between about 1.0
mmoll.sup.-1 and about 10 mmoll.sup.-1.
[0041] Preferably, in the method of the invention as described
above, the source of copper ion concentration in the electroplating
bath is selected from the group consisting of copper sulfate,
copper nitrate, copper carbonate, copper phosphate, and any
combinations or mixtures thereof. More preferably, the source of
copper ion concentration in the electroplating bath is selected to
comprise copper sulfate.
[0042] Preferably, in the method of the invention as described
above, the electroplating bath further comprises an organic
additive system comprising a suppressor of copper deposition on
copper and an accelerator of copper deposition on copper.
[0043] Preferably, in the method of the invention as described
above, the suppressor of copper deposition is selected from the
group consisting of polyethylene glycol, polypropylene glycol,
block copolymer of polyethylene glycol-polypropylene
glycol-polyethylene glycol, and any combinations or mixtures
thereof; and the accelerator of copper deposition is preferably
selected to comprise (or consist of) bis-(sodium
sulfopropyl)-disulfide.
[0044] Preferably, in the method of the invention as described
above, the electroplating bath comprises a suppressor of copper
deposition, which is preferably polyethylene glycol, in a
concentration preferably comprised between about 20 ppm and about
500 ppm, more preferably between about 50 ppm and about 120 ppm,
even more preferably between about 70 ppm and about 115 ppm, still
more preferably between about 90 ppm and about 110 ppm; most
preferably the electroplating bath comprises a suppressor of copper
deposition in a concentration of about 100 ppm.
[0045] Preferably, in the Method of the invention as described
above, the electroplating bath further comprises an accelerator of
copper deposition, which is preferably bis-(sodium
sulfopropyl)-disulfide, in a concentration preferably comprised
between about 0.02 ppm and about 2 ppm, more preferably between
about 0.1 ppm and about 1.5 ppm, even more preferably between about
0.5 ppm and about 1.3 ppm, most preferably between about 0.7 ppm
and about 1.0 ppm.
[0046] Preferably still, the method of the invention further
comprises the step of performing a surface pre-treatment of the
substrate before the step of electroplating the copper deposit,
more preferably before the step of immersing the substrate into the
electroplating bath. More preferably, the surface pre-treatment
consists of an electrochemical clean.
[0047] According to another aspect, the present invention is
directed to a method for the preparation of a electroplating bath
suitable for electroplating a copper deposit onto a substrate,
wherein the method comprises the step of:
[0048] providing a concentrate composition comprising a source of
copper ion and a source of acid; and
[0049] diluting the concentrate composition into a solution
comprising deionized water, thereby forming an electroplating bath
having a copper ion concentration comprised between about 0.5
mmoll.sup.-1 and about 50 mmoll.sup.-1, and an acid concentration
comprised between about 0.05% and about 10% per volume of the
electroplating bath.
[0050] According to still another aspect, the present invention is
directed to a method for the preparation of a electroplating bath
suitable for electroplating a copper deposit onto a substrate,
wherein the method comprises the step of:
[0051] providing a concentrate composition comprising a source of
copper ion and a source of acid; and
[0052] diluting the concentrate composition into a solution
comprising deionized water, thereby forming an electroplating bath
as described above.
[0053] According to still another aspect, the present invention is
directed to a concentrate composition as defined above. Preferably,
the concentrate composition further comprises a source of chloride
ion, preferably in such an amount as to form an electroplating bath
having a chloride ion concentration comprised between about 0.1 ppm
and about 10 ppm, more preferably between about 0.5 ppm and about 8
ppm, even more preferably between about 1 ppm and about 5 ppm,
still more preferably between about 1 ppm and about 3 ppm, still
more preferably between about 1.5 ppm and about 2.5 ppm, still more
preferably between about 1.8 ppm and about 2.2 ppm, most preferably
of about 2.0 ppm, when the concentrate composition is diluted into
a solution comprising deionized water.
[0054] According to yet another aspect, the present invention is
directed to the use of the method as described above for the
manufacture of a semiconducting device, preferably a semiconductor
integrated circuit (IC) device.
[0055] According to a preferred aspect, the present invention is
directed to the use of the method as described above for the
manufacture of semiconducting devices features, preferably for the
manufacture of interconnections having a width which is preferably
below about 100 nm, more preferably below about 70 nm, even more
preferably below about 50 nm, most preferably below about 35
nm.
[0056] Accordingly, the present invention is further directed to a
method for the superfilling of a feature opening provided in a
substrate, wherein the feature opening is preferably selected from
the group of trenches and vias, and wherein the feature opening has
a width below about 100 nm, preferably below about 70 nm, more
preferably below about 50 nm, even more preferably below about 35
nm.
BRIEF DESCRIPTION OF THE DRAWINGS
[0057] All figures/drawings are intended to illustrate some aspects
and embodiments of the present invention. Devices are depicted in a
simplified way for reason of clarity. Not all alternatives and
options are shown and therefore the invention is not limited to the
content of the given drawings.
[0058] FIG. 1 graphically represents the radial profiles of
substrates containing copper deposits with increasing thicknesses
plated on a 5 nm thin copper seed with an ultra-high copper ion
concentrated electroplating bath.
[0059] FIG. 2 graphically represents semi-logarithmic plot of the
measured current density vs. the sample's potential measured with
respect to saturated mercurous sulphate electrode (SMSE) for:
[0060] i. a highly concentrated copper-acid electroplating bath
(250 mmoll.sup.-1 CuSO.sub.4) (.box-solid.) (full square); and
[0061] ii. an ultra-lowly concentrated copper-acid electroplating
bath (10 mmoll.sup.-1 CuSO.sub.4) (.tangle-solidup.) (full
triangle).
[0062] FIG. 3 graphically represents a simulated comparative
current distribution over a wafer while using ultra-lowly
concentrated copper-acid electroplating bath (10 mmoll.sup.-1
CuSO.sub.4+0.1% H.sub.2SO.sub.4) and highly copper ion and acid
concentrated electroplating bath (160 mmoll.sup.-1 CuSO.sub.4+0.5%
H.sub.2SO.sub.4).
[0063] FIG. 4 shows SEM images of copper islands electrodeposited
on a Ru based substrate from solutions containing 1.8 M
H.sub.2SO.sub.4, 50 ppm HCl and different copper concentrations (10
mM to 600 mM CuSO.sub.4.5H.sub.2O) at different current
densities.
[0064] FIG. 5 shows the respective island density values as
obtained from the SEM images shown in FIG. 4.
[0065] FIG. 6 shows top-down SEM images of copper islands deposited
from solutions containing 1.8 moll.sup.-1 H.sub.2SO.sub.4, 50 ppm
HCl and different CuSO.sub.4.5H.sub.2O concentrations (50 to 600
mM) with and without the addition of 300 ppm PEG. The depositions
are performed at current density of -2.5 mAcm.sup.-2 for 4
seconds.
[0066] FIG. 7 shows top-down SEM images of copper islands deposited
on a Ru based substrate from solutions containing 10 mmoll.sup.-1
CuSO.sub.4.5H.sub.2O, 1.8 mmoll.sup.-1 H.sub.2SO.sub.4, 2 ppm HCl
and different PEG concentrations (0 ppm to 1000 ppm).
[0067] FIG. 8 shows top-down SEM images of copper islands deposited
on a Ru based substrate from solutions containing 10 mmoll.sup.-1
CuSO.sub.4.5H.sub.2O, 1.8 moll.sup.-1 H.sub.2SO.sub.4, 500 ppm PEG
and different HCl concentrations (0 ppm to 50 ppm).
[0068] FIG. 9 shows the chloride concentration as a function of the
normalized charge (Q/Q.sub.o) calculated from data for the measured
current density after copper depositions on Cu-seed layers from two
electroplating baths according to the invention, and comprising
ultra-low copper ion concentration (10 mmoll.sup.-1 CuSO.sub.4), 2
ppm HCl, 100 ppm PEG 4000, 1 pmm SPS and H.sub.2SO.sub.4. A
comparison between ( ) 18 mmoll.sup.-1 H.sub.2SO.sub.4 and
(.diamond-solid.) 1.8 moll.sup.-1 H.sub.2SO.sub.4 is made and the
most appropriate chloride concentrations for each of the two
electrolytes are indicated in the graph. The smallest normalized
charge indicates the strongest suppression; hence, the optimum
working condition.
[0069] FIG. 10 represents schematically a profile of a damascene
structure (trench) in a silicon substrate, with a diffusion barrier
(1.5 nm TaN/Ta) and a copper seed layer.
[0070] FIG. 11 is a cross-sectional SEM image of 90 nm wide
trenches, with 60 nm thick initial copper seed layer, filled with
copper according to the method of the invention using
electroplating baths comprising various ultra-low copper ion
concentrations and adjusted additives concentrations.
DETAILED DESCRIPTION OF THE INVENTION
[0071] According to one aspect of the present invention, it is
provided a method for electroplating a copper deposit onto a
substrate, wherein the method comprises the steps of:
[0072] immersing the substrate into an electroplating bath solution
having a copper ion concentration comprised between 0.5
mmoll.sup.-1 and 50 mmoll.sup.-1, and an acid concentration
comprised between 0.05% and 10% per volume of the electroplating
bath solution; and
[0073] electroplating the copper deposit from the electroplating
bath onto the substrate.
[0074] In the context of the present invention, it has been
surprisingly discovered while performing the method of the
invention, efficient integration of copper plating onto a substrate
provided with very narrow feature openings (such as trenches or
vias) may be achieved. More specifically, efficient (e.g. void
free) filling of narrow feature openings, having typically a width
which is below 100 nm, preferably below 70 nm, more preferably
below 50 nm, even more preferably below 35 nm may be unexpectedly
achieved. This is surprising result in view of the ultra low copper
ion concentration of the electroplating bath for use in the method
of the invention.
[0075] Without wishing to be bound by theory, it is believed that
the low copper ion concentration of the electrolytic bath provides
the following effects: 1) the relative potential drop over the thin
seed layer is considerably reduced by lowering the deposition
current (and exchange current density); 2) the potential window for
copper plating is enlarged by the presence of a diffusion limited
current region, which further counters the terminal effect; 3)
improvement in current distribution over the substrate during
electroplating.
[0076] FIG. 1 graphically represents the radial profiles (on a 300
mm wafer) of substrates containing copper deposits with increasing
thicknesses electroplated on a 5 nm thin copper seed with an
ultra-high copper ion concentrated electroplating bath, and thereby
depicts the severe terminal effect experienced by very thin copper
seeds. For the first 10 to 20 nm of electroplated copper, the
plating rate is near zero in the center and fast around the edge of
the wafer.
[0077] FIG. 2 graphically represents semi-logarithmic plot of the
measured current density vs. the sample's potential measured with
respect to saturated mercurous sulfate electrode (SMSE) for: [0078]
i. a highly concentrated copper-acid electroplating bath (250
mmoll.sup.-1 CuSO.sub.4) (.box-solid.) (full square); and [0079]
ii. an ultra-lowly concentrated copper-acid electroplating bath (10
mmoll.sup.-1 CuSO.sub.4) (.tangle-solidup.) (full triangle).
[0080] FIG. 2 clearly shows that by lowering the copper
concentration, the relative potential drop over the thin seed layer
is considerably reduced by lowering the deposition current (and
exchange current density).
[0081] FIG. 3 graphically represents a simulated comparative
current distribution over a wafer while using ultra-lowly
concentrated copper-acid electroplating bath (10 mmoll.sup.-1
CuSO.sub.4+0.1% H.sub.2SO.sub.4) and highly copper ion and acid
concentrated electroplating bath (160 mmoll.sup.-1 CuSO.sub.4+0.5%
H.sub.2SO.sub.4). FIG. 3 clearly shows the drastic improvement in
current distribution for ultra-low copper concentrations.
[0082] Advantageously and no less surprisingly, the method of the
present invention may be performed on a substrate provided with
very thin copper seeds which typically have thicknesses below 20
nm.
[0083] Preferably, in the method of the invention as described
above, the copper ion is a copper (II) cation.
[0084] Preferably, in the method of the invention as described
above, the pH of the electroplating bath is acidic. Preferably, the
pH is below 6, more preferably below 4, even more preferably below
3, still more preferably below 2. Still more preferably, the pH of
the electroplating bath is comprised between -0.3 and 3.0, more
preferably between -0.25 and 2.0, even more preferably between
-0.25 and 2.0.
[0085] Preferably, in the method of the invention as described
above, the electroplating bath comprises chloride ion, preferably
in a concentration comprised between 0.1 ppm and 10 ppm, more
preferably between 0.5 ppm and 8 ppm, even more preferably between
1 ppm and 5 ppm, still more preferably between 1 ppm and 3 ppm,
still more preferably between about 1.5 ppm and about 2.5 ppm,
still more preferably between about 1.8 ppm and about 2.2 ppm, most
preferably the electroplating bath has a chloride ion concentration
of about 2.0 ppm.
[0086] As will be easily apparent to those skilled in the art of
electrochemistry in the light of the present description, the
optimum value for the pH and the chloride ion concentration of the
electroplating bath will depend on the particular composition of
the electroplating bath.
[0087] Preferably, in the method of the invention as described
above, the source of chloride ion in the electroplating bath is
selected from the group consisting of hydrochloric acid, potassium
chloride, sodium chloride, and any combinations or mixtures
thereof. Preferably, the source of chloride ion in the
electroplating bath is selected to comprise hydrochloric acid.
Advantageously, according to the preferred aspect of the invention
where hydrochloric acid is used as the source of chloride ion in
the electroplating bath, the latter is typically used in such a
very low concentration that the addition of hydrochloric acid does
not substantially affect the pH of the resulting electroplating
bath.
[0088] Preferably, in the method of the invention as described
above, the substrate comprises a semiconductor material which is
preferably selected from the group consisting of silicon,
germanium, silicon on insulator (SOI), and any combinations or
mixtures thereof. More preferably, in the method according to the
invention, the substrate is a silicon wafer.
[0089] Preferably, in the method a of the invention as described
above, the substrate is provided with at least one feature opening,
preferably selected from the group of trenches and vias, wherein
the feature opening has a width below 100 nm, preferably below 70
nm, more preferably below 50 nm, even more preferably below 35
nm.
[0090] According to one preferred aspect, in the method of the
invention as described above, the substrate is provided with a
copper seed having a thickness below about 60 nm, preferably below
about 50 nm, more preferably below about 30 nm, even more
preferably below about 20 nm, still more preferably below about 10
nm, most preferably below about 8 nm.
[0091] Preferably, in the method of the invention as described
above, the copper seed layer at least partly covers the sidewalls
and the bottom of the feature opening. More preferably, the copper
seed layer fully covers the sidewalls and the bottom of the feature
opening, without fully filling the feature opening.
[0092] Preferably, the method of the invention as described above
further comprises the step of providing the substrate with a copper
seed layer having a thickness preferably below 60 nm, more
preferably below 50 nm, even more preferably below 20 nm, still
more preferably below 10 nm, most preferably below 8 nm.
Preferably, the copper seed layer is deposited using Physical Vapor
Deposition (PVD) techniques.
[0093] Preferably, in the method of the invention as described
above, the substrate is further provided with a diffusion barrier
layer, whereby the copper seed layer is preferably deposited onto
the diffusion barrier layer.
[0094] Preferably, in the method of the invention as described
above, the source of acid concentration in the electroplating bath
is selected to comprise or consist of sulfuric acid. However, the
invention is not that limited as other suitable sources of acid
concentration in the electroplating bath will be easily identified
by those skilled in the art in the light of the present
description.
[0095] According to one preferred aspect of the method of the
invention, whereby the substrate is provided with a copper seed,
the electroplating bath preferably has an acid concentration
comprised between 0.05% and 1%, more preferably between 0.05% and
0.7%, even more preferably between 0.05% and 0.5%, still more
preferably between 0.05% and 0.3%, most preferably between 0.05%
and 0.15% per volume of the electroplating bath.
[0096] Still according to the preferred aspect of the method of the
invention, whereby the substrate is provided with a copper seed,
the electroplating bath preferably comprises sulfuric acid, more
preferably in a concentration comprised between 10 mmoll.sup.-1 and
200 mmoll.sup.-1, more preferably between 10 mmoll.sup.-1 and 100
mmoll.sup.-1, even more preferably between 15 mmoll.sup.-1 and 50
mmoll.sup.-1, most preferably between 15 mmoll.sup.-1 and 25
mmoll.sup.-1.
[0097] According to another preferred aspect of the method of the
invention, the substrate is provided with a seed layer made from a
seed material not comprising copper. In a preferred aspect, the
seed material comprises a metal selected from the group consisting
of ruthenium, tantalum, cobalt, and any combinations or mixtures
thereof. More preferably, the seed material comprises ruthenium.
Exemplary seed materials for use herein include, but are not
limited to, Ru-containing alloys, such as e.g. RuTa. In one
preferred aspect, the seed material comprises or consists of
RuTa.
[0098] In the context of the present invention, it has been
surprisingly discovered that the method of the invention is
advantageously applicable to direct (seedless) copper plating with
direct (super)filling of very narrow feature openings. In the
context of the present invention, the term "seedless or direct
plating" is meant to refer to copper plating and filling on a seed
material not comprising copper, which may also be referred to
throughout the description as alternative seed layer. According to
this particular aspect, the need for a copper seed layer, and as a
consequence the problem of copper seed corrosion due to terminal
effect in acid copper electroplating bath, may be advantageously
obviated.
[0099] In another aspect of the invention, the seed layer not
comprising copper may also further act as a diffusion barrier
layer. According to this particular aspect of the invention, it
derives that the method of the invention is also applicable to
direct plating and filling directly onto the diffusion barrier
layer.
[0100] According to one preferred aspect of the method of the
invention, whereby the substrate is provided with a seed layer made
from a seed material not comprising copper, the electroplating bath
preferably has an acid concentration comprised between 5% and 10%,
more preferably between 6% and 9.5%, even more preferably between
7% and 9%, most preferably between 8% and 9%, per volume of said
electroplating bath.
[0101] Still according to the preferred aspect of the method of the
invention, whereby the substrate is provided with a seed layer made
from a seed material not comprising copper, the electroplating bath
preferably comprises sulfuric acid, more preferably in a
concentration comprised between 1 moll.sup.-1 and 2 moll.sup.-1,
more preferably between 1.2 moll.sup.-1 and 1.9 moll.sup.-1, even
more preferably between 1.4 moll.sup.-1 and 1.8 moll.sup.-1, most
preferably between 1.6 moll.sup.-1 and 1.8 moll.sup.-1.
[0102] While electrodeposition of copper on copper typically
follows layer-by-layer type of growth, copper electrodeposition on
seed layer made from a seed material not comprising copper proceeds
through nucleation and specific growth process. Accordingly, in the
context of the particular aspect of the invention whereby the
substrate is provided with a seed layer made from a seed material
not comprising copper, the present invention has required extensive
experiments so as to achieve a profound understanding of the
nucleation and growth mechanism. In that context, the Applicant has
found that the copper growth process proceeds through forming and
growing of three dimensional (3D) islands until they coalesce into
a continuous film. Since the coalescence thickness is determined by
the island density, it alters according to the shape of the islands
(sphere to hemisphere and disk), i.e. quasi 2D growth leads to a
thinner coalescence thickness. In order to fill small features, the
coalescence shall be fast and followed by preferably by bottom-up
superfilling, which is indistinguishable from growth on a
conventional copper seed layer. In order to achieve the first
copper layer in the small features, high island density shall be
achieved with consequently fast coalescence in the features with
thickness smaller than the features size. In the context of the
invention, the critical importance of achieving high enough island
density while trying to achieve efficient (i.e. void- and
defect-free) filling of small features has been identified. In
order to achieve high island density of copper electrodeposition,
the nucleation and growth mechanism has been elucidated at a
fundamental level and the influence of each component of the
electroplating bath has been extensively studied.
[0103] Preferably, in the method of the invention as described
above, the electroplating bath has a copper ion concentration
comprised between 0.5 mmoll.sup.-1 and 30 mmoll.sup.-1, preferably
between 0.5 mmoll.sup.-1 and 20 mmoll.sup.-1, more preferably
between 1.0 mmoll.sup.-1 and 20 mmoll.sup.-1, even more preferably
between 1.0 mmoll.sup.-1 and 10 mmoll.sup.-1.
[0104] In the context of the present invention, it has been
surprisingly discovered that copper island density directly
increases with lower copper concentration. Also, it has been no
less surprisingly discovered that copper island density directly
increases with higher applied deposition current.
[0105] FIG. 4 shows SEM images of copper islands electrodeposited
on a Ru based substrate from solutions containing 1.8 M
H.sub.2SO.sub.4, 50 ppm HCl and different copper concentrations (10
mM to 600 mM CuSO.sub.4.5H.sub.2O) at different current densities.
The experiments were terminated at the same charge, Q=0.01 C
cm.sup.-2.
[0106] FIG. 5 shows the respective island density values as
obtained from the SEM images shown in FIG. 4.
[0107] In the context of the present invention still, it has been
unexpectedly found that copper islands coalesce faster with
decreasing copper concentration.
[0108] Preferably, in the method of the invention as described
above, the source of copper ion concentration in the electroplating
bath is selected from the group consisting of copper sulfate,
copper nitrate, copper carbonate, copper phosphate, and any
combinations or mixtures thereof. More preferably, the source of
copper ion concentration in the electroplating bath is selected to
comprise or consist of copper sulfate.
[0109] Preferably, in the method of the invention as described
above, the electroplating bath further comprises an organic
additive system comprising a suppressor of copper deposition on
copper and an accelerator of copper deposition on copper.
[0110] Preferably, in the method of the invention as described
above, the suppressor of copper deposition is selected from the
group consisting of polyethylene glycol, polypropylene glycol,
block copolymer of polyethylene glycol-polypropylene
glycol-polyethylene glycol, and any combinations or mixtures
thereof; and the accelerator of copper deposition is preferably
selected to comprise or consist of bis-(sodium
sulfopropyl)-disulfide. More preferably, the suppressor of copper
deposition for use herein is selected from the group consisting of
PEG8000, PEG4000, EPE2000, and any combinations or mixtures
thereof. Even more preferably, the suppressor of copper deposition
for use herein is selected to comprise or to consist of
PEG4000.
[0111] Preferably, in the method of the invention as described
above, the electroplating bath comprises a suppressor of copper
deposition, which is preferably polyethylene glycol, in a
concentration preferably comprised between about 20 ppm and about
500 ppm, more preferably between about 50 ppm and about 120 ppm,
even more preferably between about 70 ppm and about 115 ppm, still
more preferably between about 90 ppm and about 110 ppm; most
preferably the electroplating bath comprises a suppressor of copper
deposition in a concentration of about 100 ppm.
[0112] In the context of the present invention, it has been
surprisingly discovered that the addition of a suppressor, such as
e.g. polyethylene glycol, in the electroplating bath having a low
copper concentration, increases the copper island density.
[0113] FIG. 6 shows top-down SEM images of copper islands deposited
from solutions containing 1.8 moll.sup.-1 H.sub.2SO.sub.4, 50 ppm
HCl and different CuSO.sub.4.5H.sub.2O concentrations (50 to 600
mM) with and without the addition of 300 ppm PEG. The depositions
are performed at current density of -2.5 mAcm.sup.-2 for 4
seconds.
[0114] FIG. 7 shows top-down SEM images of copper islands deposited
on a Ru based substrate from solutions containing 10 mmoll.sup.-1
CuSO.sub.4.5H.sub.2O, 1.8 moll.sup.-1 H.sub.2SO.sub.4, 2 ppm HCl
and different PEG concentrations (0 ppm to 1000 ppm). The
depositions are performed at current density of -0.5 mAcm.sup.-2
for 20 seconds.
[0115] It has also been discovered that the addition of chloride
ion may, in some selected conditions, participate in increasing the
copper island density.
[0116] FIG. 8 shows top-down SEM images of copper islands deposited
on a Ru based substrate from solutions containing 10 mmoll.sup.-1
CuSO.sub.4.5H.sub.2O, 1.8 moll.sup.-1 H.sub.2SO.sub.4, 500 ppm PEG
and different HCl concentrations (0 ppm to 50 ppm). The depositions
are performed at current density of -0.5 mAcm-2 for 20 seconds.
[0117] FIG. 9 represents the chloride concentration as a function
of the normalized charge (Q/Q.sub.o) calculated from data for the
measured current density after copper depositions on Cu-seed layers
from two different electroplating baths according to the invention,
and comprising ultra-low copper ion concentrations (10 mmoll.sup.-1
CuSO.sub.4), 2 ppm HCl, 100 ppm PEG 4000, 1 pmm SPS and
H.sub.2SO.sub.4. A comparison between ( ) 18 mmoll.sup.-1
H.sub.2SO.sub.4 and (.diamond-solid.) 1.8 moll.sup.-1
H.sub.2SO.sub.4 is made and the most appropriate chloride
concentrations for each of the two electrolytes are indicated in
the graph. The smallest normalized charge indicates the strongest
suppression, and therefore the optimum working condition.
[0118] Preferably, in the method of the invention as described
above, the electroplating bath further comprises an accelerator of
copper deposition, which is preferably bis-(sodium
sulfopropyl)-disulfide, in a concentration preferably comprised
between 0.02 ppm and 2 ppm, more preferably between 0.1 ppm and 1.5
ppm, even more preferably between 0.5 ppm and 1.3 ppm, most
preferably between 0.7 ppm and 1.0 ppm.
[0119] According to another preferred aspect, the method of the
invention further comprises the step of performing a surface
pre-treatment of the substrate before the step of electroplating
the copper deposit, more preferably before the step of immersing
the substrate into the electroplating bath. More preferably, the
surface pre-treatment consists of an electrochemical clean.
[0120] According to another aspect, the present invention is
directed to a method for the preparation of a electroplating bath
suitable for electroplating a copper deposit onto a substrate,
wherein the method comprises the step of:
[0121] providing a concentrate composition comprising a source of
copper ion and a source of acid; and
[0122] diluting the concentrate composition into a solution
comprising deionized water, thereby forming an electroplating bath
having a copper ion concentration comprised between 0.5
mmoll.sup.-1 and 50 mmoll.sup.-1, and an acid concentration
comprised between 0.05% and 10% per volume of the electroplating
bath.
[0123] According to still another aspect, the present invention is
directed to a method for the preparation of a electroplating bath
suitable for electroplating a copper deposit onto a substrate,
wherein the method comprises the step of:
[0124] providing a concentrate composition comprising a source of
copper ion and a source of acid; and
[0125] diluting the concentrate composition into a solution
comprising deionized water, thereby forming an electroplating bath
as described above.
[0126] According to still another aspect, the present invention is
directed to a concentrate composition as defined above. Preferably,
the concentrate composition further comprises a source of chloride
ion, preferably in such an amount as to form an electroplating bath
having a chloride ion concentration comprised between 0.1 ppm and
10 ppm, more preferably between 0.5 ppm and 8 ppm, even more
preferably between 1 ppm and 5 ppm, still more preferably between 1
ppm and 3 ppm, still more preferably between 1.5 ppm and 2.5 ppm,
still more preferably between 1.8 ppm and 2.2 ppm, most preferably
of about 2.0 ppm, when the concentrate composition is diluted into
a solution comprising deionized water.
[0127] The methods and concentrate composition according to the
present invention may find particular use in the manufacture of a
semiconducting device. Accordingly, the present invention is
further directed to the use of the method as described above for
the manufacture of a semiconducting device, preferably a
semiconductor integrated circuit (IC) device.
[0128] According to a preferred aspect, the present invention is
directed to the use of the method as described above for the
manufacture of semiconducting devices features, preferably for the
manufacture of interconnections having a width which is preferably
below 100 nm, more preferably below 70 nm, even more preferably
below 50 nm, most preferably below 35 nm. FIG. 10 represents
schematically a profile of a damascene structure (trench) in a
silicon substrate, with a diffusion barrier (1.5 nm TaN/Ta) and a
copper seed layer.
[0129] Accordingly, the present invention is further directed to a
method for the (super)filling of a feature opening provided in a
substrate, wherein the feature opening is preferably selected from
the group of trenches and vias, and wherein the feature opening has
a width below 100 nm, preferably below 70 nm, more preferably below
50 nm, even more preferably below 35 nm.
[0130] FIG. 11 is a cross-sectional SEM image of 90 nm wide
trenches, with 60 nm thick initial copper seed layer, filled with
copper from an electroplating bath according to the invention, and
comprising ultra-low copper ion concentrations (10 mmoll.sup.-1 or
1 mmoll.sup.-1 CuSO.sub.4) and adjusted additives concentrations,
as follows: [0131] a. 10 mmoll.sup.-1 CuSO.sub.4+18 mmoll.sup.-1
H.sub.2SO.sub.4+2 ppm HCl+100 ppm PEG4000+1 ppm SPS, where PEG4000
is polyethylene glycol with average molecular weight Mw=4000
gmol.sup.-1, [0132] b. 10 mmoll.sup.-1 CuSO.sub.4+18 mmoll.sup.-1
H.sub.2SO.sub.4+2 ppm HCl+200 ppm EPE2000+0.04 ppm SPS, where
EPE2000 is a block copolymer of polyethylene glycol-polypropylene
glycol-polyethylene glycol with average molecular weight MW=2000
gmol.sup.-1, and [0133] c. 1 mmoll.sup.-1 CuSO.sub.4+18
mmoll.sup.-1 H.sub.2SO.sub.4+0.7 ppm HCl+200 ppm EPE2000+0.02 ppm
SPS.
[0134] With all three electroplating baths, very good quality
trench-filling with copper are obtained, i.e. without any voids or
defects.
[0135] While the present invention has been described and
illustrated with reference to specific illustrative embodiments
thereof, it will be recognized by those skilled in the art that
variations and modifications may be made without departing from the
spirit and scope of the present invention. It is therefore intended
to include within the present invention all such variations and
modifications that fall within the scope of the appended claims and
equivalents thereof.
EXAMPLES
[0136] One exemplary method of the invention is described below
with full details. The examples herein are meant to exemplify the
present invention but are not necessarily used to limit or
otherwise define the scope of the present invention.
Example 1
Preparation of the Make-Up Solutions
[0137] The make-up solutions are prepared from CuSO.sub.4.5H.sub.2O
(>98%, Sigma Aldrich), H.sub.2SO.sub.4 (96%, Assay, Baker), and
deionized water (DI water). HCl (Assay, Baker) is added to vary the
chloride ions concentration between 0 and 10 ppm (10 ppm=10
mgl.sup.-1 Cl.sup.-). The suppressor, polyethylene glycol with
molecular weight 4000 (PEG 4000; Sigma Aldrich), is added to the
make-up solutions in concentrations between 10 and 1000 ppm (1000
ppm=1000 mgl.sup.-1=1 gl.sup.-1 PEG). The accelerator,
bis-(3-sodiumsulfopropyl) disulfide (SPS) is added in
concentrations between 0.02 and 2.0 ppm (0.02 ppm=20 ppb=0.02
mgl.sup.-1 SPS).
[0138] The steps for preparing 1.0 liter of copper plating solution
(electrolyte) with a composition 10 mmoll.sup.-1 CuSO.sub.4+18
mmoll.sup.-1 H.sub.2SO.sub.4+2 ppm+300 ppm PEG+1 ppm SPS are as
follows: [0139] a. Measuring on analytical scale the amount of
CuSO.sub.4.5H.sub.2O needed. The amount needed is calculated
according to the formula: m(g)=c(moll.sup.-1)Mm(gmol.sup.-1)V(I).
Hence, m(g)=0.01(moll.sup.-1)249.684(gmol.sup.1)1(l)=2.4968 g.
[0140] b. Quantitative transfer of the proper amount of
CuSO.sub.4.5H.sub.2O measured on the analytical scale into a
measuring glass with exact volume of 1 liter. Quantitative transfer
means that the transfer of all the quantity of a chemical compound
is assisted by 2-3 portions of deionized water (DI water) in small
quantities. [0141] c. Addition of H.sub.2SO.sub.4 in a quantity
found according to the formula:
V.sub.initial(l)=V.sub.needed(l)c.sub.needed(moll.sup.-1)/c.sub.initial(m-
oll.sup.-1). As the initial concentration of 96% H.sub.2SO.sub.4
corresponds to 18 moll.sup.-1, the formula is expressed as:
V.sub.initial(l)=1(l)0.018(moll.sup.-1)/18(moll.sup.-1)=1.10.sup.-4
l=1000 .mu.l. [0142] d. Filling the measuring glass with DI water
until volume of 1 liter is obtained. [0143] e. Chloride ions are
added to the make-up electrolyte in micro-liter amounts of 0.14
moll.sup.-1 HCl previously prepared. For example, to obtain a
concentration of 2 ppm Cl.sup.- in the electrolyte, 400 .mu.l of
0.14 mll.sup.1HCl is added. [0144] f. PEG is measured on analytical
scale and added in the amount needed prior to each experiment. For
example, to obtain a concentration of 300 ppm PEG in the
electrolyte, 0.3 g of PEG is added to 1 L of electrolyte. [0145] g.
As a source of SPS, a solution of 1 g SPS in 100 ml DI water (10000
ppm SPS) is used. For example, to obtain a concentration of 1 ppm
SPS in the electrolyte, 100 .mu.l of SPS solution (10000 ppm) were
added to 1 L of electrolyte.
[0146] The different solution compositions tested are listed in
Table 1 below:
TABLE-US-00001 TABLE 1 Composition of the make-up solutions tested.
[CuSO.sub.4], [H.sub.2SO.sub.4], mmol l.sup.-1 mmol l.sup.-1 [Cl],
ppm [PEG], ppm [SPS], ppm 10.0, 18 0.0, 0.2, 0.4, 10, 100, 200,
0.02, 0.04, 0.06, 1.0, 1800 0.6, 1.0, 1.5, 300, 500, 0.1, 0.2, 0.4,
0.5 2.0, 4.0 1000 0.6, 1.0, 2.0
Example 2
Substrate
[0147] The substrate is a patterned wafer (wafer with trenches)
with a diameter of 300 mm. Two types of structures (trenches) are
examined, i.e. trenches with width 90 nm and depth of about 208 nm
and trenches with width 35 nm and depth of about 80 nm.
[0148] The aspect ratio, which is the ratio between depth and
width, is 2.3 for both structures. The aspect ratio is obtained
after patterning the wafer to achieve the required shape and size
of the trenches and deposition of a barrier layer made of a low-k
dielectric material. In the case of Damascene copper plating with
copper seed, the barrier layer is 1.5 nm of tantalum
nitride/tantalum (TaN/Ta).
[0149] At the surface of the wafer, including both the surface
between the trenches and the surface of the trench bottom and side
walls, a thin copper seed layer is previously deposited by means of
physical vapor deposition (PVD) as schematically shown in FIG. 10.
The thickness of the copper seed layer is 60 nm for 90 nm wide
trenches and 20 nm for 35 nm wide trenches. Coupons with size about
2.times.2 cm are cut manually from the wafer with a diamond
tip.
[0150] Alternatively, on other samples, an alternative seed layer
(such as e.g. Ru, RuTa, Co, etc.) may be deposited instead of the
copper seed layer.
Example 3
Electrochemical Step
[0151] All tests are performed at room temperature using a glass
three-electrode electrochemical cell wherein the three electrodes
and the plating bath are placed. The counter electrode is separated
from the working electrode compartment with a porous glass frit.
The working electrode is a coupon of a patterned wafer (a sample)
with dimensions around 2.times.2 cm, placed in a sample holder. The
area of the sample exposed therefore to the plating bath (working
area) was of 1.54 cm.sup.2. All tests are performed keeping the
working electrode at a rotation rate of 500 rpm. Before each test,
a copper tape is placed at the edges of the sample connecting the
front and the back side of the sample in order to ensure an
electrical contact between the working sample area (front part) and
the electrode connection at the back side of the sample.
[0152] As a reference electrode a saturated mercurous sulfate
electrode (SMSE) is used to avoid leakage of chloride ions into the
electrolyte, which can be the case when using silver/silver
chloride or calomel electrodes. This is important since the
[Cl.sup.-] concentration is always in the range of few ppm. The
potential of the SMSE is measured with respect to a silver/silver
chloride standard reference electrode (3 mmoll.sup.-1 KCl, 0.210 V
vs. SHE) in a solution of 5 wt. % H.sub.2SO.sub.4 (0.94
moll.sup.-1) and 10 vol. % HCl (1.20 moll.sup.-1). A stable and
reproducible value of 0.485 V for the potential of the SMSE is
observed. Considering the potential of silver/silver chloride
standard reference electrode vs. SHE, the potential of SMSE vs. SHE
is calculated to be 0.695 V.
[0153] The SMSE is connected to the plating cell via a Luggin
capillary placed about 0.5 cm from the working electrode. All
potentials are referred to the SMSE. The counter electrode
consisted of a platinum rod cleaned in a solution of hydrogen
peroxide and sulfuric acid in range
H.sub.2O.sub.2:H.sub.2SO.sub.4=1:3 before the tests.
[0154] Cyclic voltammetry measurements are performed at a step
potential of 0.001 V and a scan rate of 0.020 Vs.sup.-1 for the
different solution compositions examined. In this case, potential
is applied between the working electrode (blanket copper sample)
and the counter electrode (Pt). This potential is the driving force
of the electrodeposition process. In order to obtain the range when
copper deposition occurs, the applied potential is changed to more
negative values with a step of 0.001 V as described above. The
change in the potential of the working electrode (blanket copper
sample) is monitored with respect to the reference electrode (SMSE)
and recorded versus the measured current, flowing between the
working electrode (blanket copper sample) and the counter electrode
(Pt). The results of these measurements are represented in the
current-voltage curve shown in FIG. 2.
[0155] Apart from the cyclic voltammetry measurements,
electrochemical copper depositions at patterned samples (coupons of
patterned wafers) are performed. For this goal, a constant current
or a constant potential, chosen from the current-voltage curves, is
applied for a time long enough to obtain surface charge of Q=0.830
C which corresponds to a copper deposit with thickness about 200
nm.
[0156] All electrochemical steps are performed using a potentiostat
from Metrohm Ltd., which controls the applied current or voltage,
in the case of copper electrodeposition, or applies potential and
measures the current, in the case of cyclic voltammetry
measurements.
Example 4
Quality of the Deposits
[0157] After electrochemical deposition of copper, the patterned
samples are examined using a scanning electron microscope (SEM).
For this purpose, a FIB tool with a beam of Ga.sup.+ ions is first
used to provide with uniform cut through the middle of the trenches
ensuring that the deposited copper will not be pulled out of the
trenches during a mechanical cleaving. After the FIB cut, the
samples are examined by SEM and images of the samples at different
magnification are recorded. The appearance or absence of voids
(defects in the copper deposit) is observed. Copper deposit with a
good quality is the one without voids (defects).
* * * * *