U.S. patent application number 10/717774 was filed with the patent office on 2004-11-04 for electroplating bath.
This patent application is currently assigned to Shipley Company, L.L.C.. Invention is credited to Mikkola, Robert D., Wang, Deyan, Wu, Chunyi.
Application Number | 20040217009 10/717774 |
Document ID | / |
Family ID | 32233682 |
Filed Date | 2004-11-04 |
United States Patent
Application |
20040217009 |
Kind Code |
A1 |
Mikkola, Robert D. ; et
al. |
November 4, 2004 |
Electroplating bath
Abstract
Copper electroplating baths containing one or more suppressor
compounds capable of providing copper filled sub-micron sized
apertures free of pits and voids are provided. Such copper
electroplating baths are useful in the manufacture of electronic
devices, such as printed wiring boards and integrated circuits.
Inventors: |
Mikkola, Robert D.;
(Grafton, MA) ; Wang, Deyan; (Hudson, MA) ;
Wu, Chunyi; (Westford, MA) |
Correspondence
Address: |
EDWARDS & ANGELL, LLP
P.O. Box 9169
Boston
MA
02209
US
|
Assignee: |
Shipley Company, L.L.C.
Marlborough
MA
|
Family ID: |
32233682 |
Appl. No.: |
10/717774 |
Filed: |
November 20, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60428161 |
Nov 21, 2002 |
|
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|
60435920 |
Dec 20, 2002 |
|
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Current U.S.
Class: |
205/296 |
Current CPC
Class: |
H05K 3/423 20130101;
C25D 3/38 20130101; H01L 21/2885 20130101 |
Class at
Publication: |
205/296 |
International
Class: |
C25D 003/38 |
Claims
What is claimed is:
1. A composition comprising one or more sources of copper ions, an
electrolyte and one or more poly(alkylene oxide) random copolymers
comprising as polymerized units two or more alkylene oxide
monomers.
2. The composition of claim 1 wherein the poly(alkylene oxide)
random copolymer is an ethylene oxide /propylene oxide random
copolymer.
3. The composition of claim 2 wherein the ethylene oxide/propylene
oxide random copolymer has the formula HO--(A).sub.n--(B).sub.m--H
wherein each of A and B are selected from ethyleneoxy and
propyleneoxy groups provided that A and B are different; and n and
m are the number of A and B repeat units, respectively, in the
copolymer.
4. The composition of claim 1 wherein the poly(alkylene oxide)
random copolymer is a linear copolymer or a star copolymer.
5. The composition of claim 1 wherein the poly(alkylene oxide)
random copolymer has a molecular weight of 500 to 20,000.
6. The composition of claim 1 further comprising one or more
brighteners.
7. The composition of claim 1 further comprising one or more
leveling agents.
8. The composition of claim 1 wherein the electrolyte is
acidic.
9. A method of depositing a layer of copper on a substrate
comprising the steps of contacting the substrate with the
composition of claim 1 and applying current density for a period of
time sufficient to deposit a layer of copper on the substrate.
10. The method of claim 9 wherein the substrate is a printed wiring
board, lead frame or an integrated circuit.
11. The method of claim 9 wherein the poly(alkylene oxide) random
copolymer is an ethylene oxide/propylene oxide random
copolymer.
12. The method of claim 11 wherein the ethylene oxide /propylene
oxide random copolymer has the formula HO--(A).sub.n--(B).sub.m--H
wherein each of A and B are selected from ethyleneoxy and
propyleneoxy groups provided that A and B are different; and n and
m are the number of A and B repeat units, respectively, in the
copolymer.
13. The method of claim 9 wherein the substrate has one or more
apertures having a width of .ltoreq.1 .mu.m.
14. A method of manufacturing an electronic device comprising the
step of depositing a layer of copper on an electronic device
comprising the steps of contacting the electronic device substrate
with the composition of claim 1 and applying current density for a
period of time sufficient to deposit a layer of copper on the
electronic device.
15. The method of claim 14 wherein the substrate is a printed
wiring board, lead frame or an integrated circuit.
16. The method of claim 14 wherein the poly(alkylene oxide) random
copolymer is an ethylene oxide/propylene oxide random
copolymer.
17. The method of claim 16 wherein the ethylene oxide /propylene
oxide random copolymer has the formula HO--(A).sub.n--(B).sub.m--H
wherein each of A and B are selected from ethyleneoxy and
propyleneoxy groups provided that A and B are different; and n and
m are the number of A and B repeat units, respectively, in the
copolymer.
18. The method of claim 14 wherein the substrate has one or more
apertures having a width of .ltoreq.1 .mu.m.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to the field of
electroplating. In particular, the present invention relates to the
field of electroplating copper on a substrate.
[0002] Methods for electroplating articles with metal coatings
generally involve passing a current between two electrodes in a
plating solution where one of the electrodes is the article to be
plated. A typical acid copper plating solution comprises dissolved
copper (usually copper sulfate), an acid electrolyte such as
sulfuric acid in an amount sufficient to impart conductivity to the
bath, and proprietary additives to improve the uniformity of the
plating and the quality of the metal deposit. Such additives
include brighteners, levelers, surfactants, suppressors, and the
like.
[0003] Electrolytic copper plating solutions are used for many
industrial applications. For example, they are used in the
automotive industry to deposit base layers for subsequently applied
decorative and corrosion protective coatings. They are also used in
the electronics industry, particularly for the fabrication of
printed circuit boards and integrated circuits. For circuit board
fabrication, copper is electroplated over selected portions of the
surface of a printed circuit board and onto the walls of through
holes passing between the surfaces of the circuit board base
material. The walls of a through hole are first metallized to
provide conductivity between the board's circuit layers. For
semiconductor fabrication, copper is electroplated over the surface
of a wafer containing a variety of features such as vias, trenches
or a combination thereof. The vias and trenches are metallized to
provide conductivity between various layers of the semiconductor
device.
[0004] It is well known in certain areas of plating, such as in
electroplating of electronic devices, that the use of additives in
the electroplating bath can be crucial in achieving a uniform and
defect-free metal deposit on a substrate surface. For example,
conventional electrochemical metallization processes for advanced
interconnects use an electroplating bath containing sulfuric acid
(10-100 g/L H.sub.2SO.sub.4), cupric ions (30-50 g/L), and chloride
ions (50-70 mg/L). An organ additive package is used to assist in
the development of bottom-up fill, and to promote a uniform
thickness of copper across the wafer. Such additive package
typically includes accelerators, suppressors and levelers and may
optionally include surfactants, defoamers, or ductilizers for the
purpose of modifying the properties of the plating bath or the
resultant metal deposits. A balance must be struck between the use
of such accelerators, suppressors, levelers, and other additives to
achieve the desired level of copper fill of apertures without void
formation. If such balance is not achieved, then the plating across
the wafer may occur much faster than plating within the aperture,
resulting in void formation within the apertures.
[0005] Plating a substrate having sub-micron sized apertures, such
as those found in integrated circuits, can pose particular
difficulties using such electroplating baths. During the filling of
such sub-micron sized apertures with copper using an electroplating
bath containing suppressors, defects, such as pits or voids often
result. For example, when conventional polyethylene glycols are
used as suppressors, the resulting copper deposits typically
contain defects protruding upward from the surface of the deposit
("protrusions"). Copper deposits obtained from electroplating baths
containing ethylene oxide/propylene oxide block copolymers
typically contain pits or lines of pits on the surface of the
deposit. Such defects can lead to electrical shorts and reliability
problems in electronic devices. There is a need for copper
electroplating baths containing suppressors that provide copper
deposits, particularly copper filled sub-micron sized apertures,
free of defects.
SUMMARY OF THE INVENTION
[0006] It has been surprisingly found that the elimination of
defects in copper deposits and particularly in copper deposits
within sub-micron sized apertures can be accomplished by
modification of the organic additive package used in the copper
electroplating bath. Such organic additive package modification is
achieved by the use of certain suppressor compounds.
[0007] The present invention provides an electroplating bath
including a source of metal ions, an electrolyte and one or more
suppressor compounds, wherein the one or more suppressor compounds
is capable of providing a copper filled, sub-micron sized aperture
free of pits and voids. Also provided by the present invention is a
composition including one or more sources of copper ions, an
electrolyte and one or more polyalkylene oxide random copolymers
comprising as polymerized units two or more alkylene oxide
monomers. Preferably, the suppressor compounds are ethylene
oxide-propylene oxide random copolymers.
[0008] Further provided by the present invention is a method of
depositing a metal layer on a substrate including the steps of: a)
contacting a substrate with the electroplating bath described
above; and b) subjecting the electroplating bath to a current
density sufficient to deposit the metal layer. Still further, the
present invention provides a method of depositing a layer of copper
on a substrate including the steps of contacting the substrate with
the composition described above and applying current density for a
period of time sufficient to deposit a layer of copper on the
substrate.
[0009] The present invention additionally provides a method of
manufacturing an electronic device including the steps of: a)
contacting an electronic device with the electroplating bath
described above; and b) subjecting the electroplating bath to a
current density sufficient to deposit the metal layer on the
electronic device. Also provided by the present invention is a
method of manufacturing an electronic device including the step of
depositing a layer of copper on an electronic device substrate
including the steps of contacting the electronic device substrate
with the composition described above and applying current density
for a period of time sufficient to deposit a layer of copper on the
electronic device substrate.
[0010] The invention also includes articles of manufacture,
including electronic devices such as printed circuit boards,
multichip modules, integrated circuits and the like that contain a
copper deposit produced from a plating solution of the invention.
In addition, the present invention provides an article of
manufacture including an electronic device containing one or more
apertures, each aperture containing an electrolytic copper deposit
obtained from the electroplating bath described above.
[0011] Further, the present invention provides a method for
removing excess material from a semiconductor wafer by using a
chemical mechanical planarization process which includes contacting
the semiconductor wafer with a rotating polishing pad thereby
removing the excess material from the semiconductor wafer; wherein
the semiconductor wafer has been prior electroplated by the copper
electroplating bath described above.
[0012] Still further, the present invention provides a method for
removing excess material from a semiconductor wafer by using a
chemical mechanical planarization process which includes contacting
the semiconductor wafer with a rotating polishing pad thereby
removing the excess material from the semiconductor wafer; wherein
the semiconductor wafer has been prior electroplated using the
copper electroplating bath described above.
DETAILED DESCRIPTION OF THE INVENTION
[0013] As used throughout the specification, the following
abbreviations shall have the following meanings, unless the context
clearly indicates otherwise: nm=nanometers; g/L=grams per liter;
mA/cm.sup.2=milliamperes per square centimeter; M=molar;
.mu.m=micron=micrometer; ppm=parts per million, mL=milliliter;
.degree. C.=degrees Centigrade; g=grams; RPM=revolutions per
minute; and .ANG.=angstroms.
[0014] As used throughout the specification, "feature" refers to
the geometries on a substrate, such geometries may be recessed or
protruding. "Apertures" refer to recessed features, such as vias
and trenches. The term "small features" refers to features that are
one micron or smaller in size. "Very small features" refers to
features that are one-half micron or smaller in size. Likewise,
"small apertures" refer to apertures that are one micron or smaller
in size and "very small apertures" refer to apertures that are
one-half micron or smaller in size. As used throughout this
specification, the term "plating" refers to copper electroplating,
unless the context clearly indicates otherwise. "Deposition" and
"plating" are used interchangeably throughout this specification.
"Defects" refer to surface defects of a copper layer, such as
protrusions and pits, as well as defects within a copper layer,
such as voids.
[0015] The term "alkyl" includes linear, branched and cyclic alkyl.
"Brightener" refers to an organic additive that increases the
plating rate of a metal during electroplating. The terms
"brightener" and "accelerator" are used interchangeable throughout
this specification. "Suppressors" refer to organic additives that
suppress the plating rate of a metal during electroplating.
"Leveler" refers to an organic additive that is capable of
providing a substantially planar metal layer. The terms "leveler"
and "leveling agent" are used interchangeably through this
specification. The term "halide" refers to fluoride, chloride,
bromide and iodide.
[0016] All percentages and ratios are by weight unless otherwise
indicated. All ranges are inclusive and combinable in any order
except where it is clear that such numerical ranges are constrained
to add up to 100%.
[0017] Electroplating solutions of the present invention generally
include at least one source of copper ions such as a soluble copper
salt, an electrolyte, and a suppressor compound capable of
providing a copper filled, sub-micron sized aperture free of pits
and voids. The electroplating solutions of the present invention
may optionally contain one or more additives, such as halides,
accelerators or brighteners, other suppressors, levelers, grain
refiners, wetting agents, surfactants, defoamers, ductilizers, and
the like.
[0018] A variety of copper salts may be employed in the present
electroplating baths, including for example copper sulfate, copper
sulfonate, copper acetate, copper gluconate, copper fluoroborate,
cupric nitrate, copper alkanesulfonates and copper arylsulfonates.
Suitable copper alkanesulfonates include copper methane sulfonate
and copper ethanesulfonate. Suitable copper arylsulfonates include
copper phenylsulfonates and copper tolylsulfonate. Copper sulfate
pentahydrate is a particularly preferred copper salt. Mixtures of
copper salts may also be used. The copper salt may be used in the
present electroplating baths in a relatively wide concentration
range. Typically, the copper salt is present in an amount
sufficient to provide an amount of copper ion of 10 to 180 g/L in
the plating bath. More typically, the amount of copper salt
provides 15 to 65 g/L of copper ions in the plating bath. The
copper plating bath may also contain amounts of other alloying
elements, such as, but not limited to, tin, zinc, indium, antimony,
and the like. Such alloying elements are added to the
electroplating baths in the form of any suitable bath-solution
salt. Thus, the copper electroplating baths useful in the present
invention may deposit copper or copper alloy.
[0019] Plating baths useful in the present invention employ an
electrolyte. Any suitable electrolyte may be used such as acidic or
alkaline, and typically the electrolyte is acidic. When the
electrolyte is acidic, the acid may be inorganic or organic.
Suitable inorganic acids include, but are not limited to, sulfuric
acid, phosphoric acid, nitric acid, hydrogen halide acids such as
hydrochloric acid, sulfamic acid, fluoroboric acid and the like.
Suitable organic acids include, but are not limited to,
alkylsulfonic acids, aryl sulfonic acids such as phenylsulfonic
acid and tolylsulfonic acid, carboxylic acids such as formic acid,
acetic acid and propionic acid, halogenated acids such as
trifluoromethylsulfonic acid and haloacetic acid, and the like.
Particularly suitable organic acids include
(C.sub.1-C.sub.10)alkylsulfon- ic acids, such as methansulfonic
acid, ethanesulfonic acid and propanesulfonic acid. Other suitable
electrolytes include pyrophosphate.
[0020] It will be appreciated by those skilled in the art that a
combination of two or more acids may be used as the electrolyte.
Particularly suitable combinations of acids include one or more
inorganic acids with one or more organic acids or a mixture of two
or more organic acids. Typically, the two or more acids may be
present in any ratio. For example, when two acids are used, they
may be present in any ratio from 99:1 to 1:99. Typically, the two
acids are present in a ratio from 90:10 to 10:90, specifically from
80:20 to 20:80, more specifically from 75:25 to 25:75, and even
more specifically from 60:40 to 40:60.
[0021] In one embodiment, the acids suitably used as the
electrolyte include sulfuric acid, nitric acid, methanesulfonic
acid, phenylsulfonic acid, mixtures of sulfuric acid and
methanesulfonic acid, mixtures of methanesulfonic acid and
phenylsulfonic acid, and mixtures of sulfuric acid, methanesulfonic
acid and phenylsulfonic acid.
[0022] The total amount of added acid electrolyte used in the
present electroplating baths may be from 0 to 100 g/L, and
typically from 0 to 60 g/L, although higher amounts of acid may be
used for certain applications, such as up to 225 g/L or even 300
g/L. It will be appreciated by those skilled in the art that by
using copper sulfate, a copper alkanesulfonate or a copper
arylsulfonate as the copper ion source, an acidic electrolyte can
be obtained without any added acid.
[0023] In another embodiment, such as in the plating of wafers
having very small apertures, electroplating baths having a low
total amount of added acid may be used. By "low acid" is meant that
the total amount of added acid in the electrolyte is less than 40
g/L, typically less than 30 g/L, and more typically less than 20
g/L.
[0024] The electrolyte may optionally contain one or more halides,
and generally does contain at least one halide. Any halide may be
used with chloride and bromide being the typical halides, and
chloride being preferred. A wide range of halide ion concentrations
(if a halide ion is employed) may be suitably utilized, e.g. from 0
(where no halide ion employed) to 100 ppm of halide ion in the
plating solution. Other suitable ranges of halide ions include from
5 to 75 ppm, and more typically from 10 to 75 ppm. A particularly
useful range of chloride ion is from 5 to 50 ppm.
[0025] The suppressor compounds useful in the present invention are
those capable of providing a metal filled, such as copper filled,
sub-micron sized aperture substantially free of defects,
particularly pits and voids, and typically free of such defects. By
"substantially free" of defects it is meant that the metal filled
apertures contain less than 0.25 microprotrusions/cm.sup.2 and
preferably also show no evidence of pitting defects. Particularly
suitable suppressor compounds are poly(alkylene oxide) random
copolymers including as polymerized units two or more alkylene
oxide monomers. Mixtures of such suppressor compounds may be used.
Such random copolymers may be linear, star-shaped or the like. By
"random copolymer" it is meant a copolymer having its repeat units
randomly distributed along the copolymer chain.
[0026] A wide variety of alkylene oxide monomers may be used, such
as, but not limited to, ethylene oxide, propylene oxide, butylene
oxide, styrene oxide and the like. Typically, the poly(alkylene
oxide) random copolymer is an ethylene oxide ("EO")/propylene oxide
("PO") random copolymer. Exemplary EO/PO random copolymers are
those having the formula HO--(A).sub.n--(B).sub.m--H wherein each
of A and B are selected from ethyleneoxy and propyleneoxy groups
provided that A and B are different; and n and m are the number of
A and B repeat units, respectively, in the copolymer. "Ethyleneoxy"
refers to moieties having the formula --(CH.sub.2-CH.sub.2--O)--.
"Propyleneoxy" refers to moieties having the formula
--(CH(CH.sub.3)--CH.sub.2--O)-- or --(O--CH(CH.sub.3)--CH.sub.2)--
-. Typically, n is in the range of 1 to 250 and specifically 10 to
170. Typically, m is in the range of 1 to 250 and specifically 10
to 90. Particularly useful EO/PO random copolymers are those having
the formula
HO(CH.sub.2CH.sub.2O).sub.x(CH.sub.2CHCH.sub.3O).sub.yH. In
general, the ratio of x:y is from 10:90 to 95:5 and specifically
from 50:50 to 75:25. It will be appreciated by those skilled in the
art that the solubility of such EO/PO copolymers can be adjusted by
changing the number of EO groups, PO groups or both groups.
[0027] Such poly(alkylene oxide) random copolymers may be linear or
star-shaped copolymers. Such star copolymers are poly(alkylene
oxide) random copolymers having 3 or more terminal hydroxyl groups.
In general, each arm of the star shape terminates in a hydroxyl
group. Typically, such star random copolymers have 3 or 4 terminal
hydroxyl groups, although copolymers having a greater number of
terminal hydroxyl groups may be employed.
[0028] In general, the present suppressor compounds have a
molecular weight of 500 to 20,000. Typically, the molecular weight
of the present suppressor compounds is from 700 to 15,000 and more
typically from 1000 to 12,000. Although poly(alkylene oxide) random
copolymers having a molecular weight that is lower or higher than
these ranges may still be suitably employed.
[0029] The amount of such suppressors present in the electroplating
baths is typically in the range of from 0.1 to 10,000 ppm. More
typically, the suppressor compounds are present in an amount of
from 0.5 to 1,000 ppm, and even more typically from 1 to 500 ppm.
It will be appreciated by those skilled in the art that one or more
other conventional suppressors may be used in combination with the
suppressors of the present invention. Such combination may have
advantages under certain circumstances where a balance of
suppression characteristics is desired.
[0030] A wide variety of brighteners (or accelerators), including
known brightener agents, may be employed in the copper
electroplating compositions of the invention. Such brighteners may
be used alone or as a mixture of two or more. Typical brighteners
contain one or more sulfur atoms, and typically without any
nitrogen atoms and a molecular weight of 1000 or less. Brightener
compounds that have sulfide and/or sulfonic acid groups are
generally preferred, particularly compounds that comprise a group
of the formula R'--S--R--SO.sub.3X, where R is an optionally
substituted alkyl (which include cycloalkyl), optionally
substituted heteroalkyl, optionally substituted aryl group, or
optionally substituted heteroalicyclic; X is a counter ion such as
sodium or potassium; and R' is hydrogen or a chemical bond
(i.e.--S--R--SO.sub.3X or substituent of a larger compound).
Typically alkyl groups will have from one to 16 carbons, more
typically one to 8 or 12 carbons. Heteroalkyl groups will have one
or more hetero (N, O or S) atoms in the chain, and typically have
from 1 to 16 carbons, more typically 1 to 8 or 12 carbons.
Carbocyclic aryl groups are typical aryl groups, such as phenyl and
naphthyl. Heteroaromatic groups also will be suitable aryl groups,
and typically contain 1 to 3 N, O or S atoms and 1 to 3 separate or
fused rings and include e.g. coumarinyl, quinolinyl, pyridyl,
pyrazinyl, pyrimidyl, furyl, pyrrolyl, thienyl, thiazolyl,
oxazolyl, oxidizolyl, triazole, imidazolyl, indolyl, benzofuranyl,
benzothiazol, and the like. Heteroalicyclic groups typically will
have 1 to 3 N, O or S atoms and from 1 to 3 separate or fused rings
and include e.g. tetrahydrofuranyl, thienyl, tetrahydropyranyl,
piperdinyl, morpholino, pyrrolindinyl, and the like. Substituents
of substituted alkyl, heteroalkyl, aryl or heteroalicyclic groups
include e.g. C.sub.1-8 alkoxy; C.sub.1-8 alkyl, halogen,
particularly F, C1 and Br; cyano, nitro, and the like.
[0031] More specifically, useful brighteners include those of the
following formulae:
XO.sub.3 S--R--SH;
XO.sub.3S--R--S--S--R--SO.sub.3 X; and
XO.sub.3S--Ar--S--S--Ar--SO.sub.3X;
[0032] wherein R in the above formulae is an optionally substituted
alkyl group, and typically is an alkyl group having from 1 to 6
carbon atoms, more typically is an alkyl group having from 1 to 4
carbon atoms; Ar is an optionally substituted aryl group such as
optionally substituted phenyl or naphthyl; and X is a suitable
counter ion such as hydrogen, sodium or potassium.
[0033] Some specific suitable brighteners include e.g.
N,N-dimethyl-dithiocarbamic acid-(3-sulfopropyl)ester;
3-mercapto-propylsulfonic acid-(3-sulfopropyl)ester;
3-mercapto-propylsulfonic acid (sodium salt); carbonic
acid-dithio-o-ethylester-s-ester with 3-mercapto-1 -propane
sulfonic acid (potassium salt); bissulfopropyl disulfide;
3-(benzthiazolyl-s-thio)propy- l sulfonic acid (sodium salt);
pyridinium propyl sulfobetaine;
1-sodium-3-mercaptopropane-1-sulfonate; sulfoalkyl sulfide
compounds disclosed in U.S. Pat. No. 3,778,357; the peroxide
oxidation product of a dialkyl
amino-thiox-methyl-thioalkanesulfonic acid; and combinations of the
above. Additional suitable brighteners are also described in U.S.
Pat. Nos. 3,770,598, 4,374,709, 4,376,685, 4,555,315, and
4,673,469. Particularly preferred brighteners for use in the
plating compositions of the invention are
N,N-dimethyl-dithiocarbamic acid-(3-sulfopropyl)ester and
bis-sodium-sulfonopropyl-disulfide.
[0034] The amount of such brighteners present in the electroplating
baths is typically from 0.1 to 1000 ppm. More typically, the
brightener compounds are present in an amount of from 0.5 to 300
ppm, still more typically from 1 to 100 ppm, and even more
typically from 2 to 50 ppm.
[0035] Levelers may optionally be added to the present
electroplating baths. It is preferred that one or more leveler
components is used in the present electroplating baths. Such
levelers may be used in a wide range of amounts, such as from 0.01
to 50 ppm or greater. Examples of suitable leveling agents are
described and set forth in U.S. Pat. Nos. 3,770,598, 4,374,709,
4,376,685, 4,555,315 and 4,673,459. In general, useful leveling
agents include those that contain a substituted amino group such as
compounds having R--N--R', where each R and R' is independently a
substituted or unsubstituted alkyl group or a substituted or
unsubstituted aryl group. Typically the alkyl groups have from 1 to
6 carbon atoms, more typically from 1 to 4 carbon atoms. Suitable
aryl groups include substituted or unsubstituted phenyl or
naphthyl. The substituents of the substituted alkyl and aryl groups
may be, for example, alkyl, halo and alkoxy.
[0036] More specifically, suitable leveling agents include, but are
not limited to, 1-(2-hydroxyethyl)-2-imidazolidinethione;
4-mercaptopyridine; 2-mercaptothiazoline; ethylene thiourea;
thiourea; alkylated polyalkyleneimine; phenazonium compounds
disclosed in U.S. Pat. No. 3,956,084; N-heteroaromatic rings
containing polymers; quatemized, acrylic, polymeric amines;
polyvinyl carbamates; pyrrolidone; and imidazole. An exemplary
leveler is 1-(2-hydroxyethyl)-2-imidazolidinethio- ne, although
other suitable levelers may be employed.
[0037] Other suitable levelers are reaction products of an amine
with an epihalohydrin, and preferably epichlorohydrin. Suitable
amines include, but are not limited to, primary, secondary or
tertiary amines, cyclic amines, aromatic amines and the like.
Exemplary amines include, without limitation, dialkylamines,
trialkylamines, arylalylamines, diarylamines, imidazole, triazole,
tetrazole, benzimidazole, benzotriazole, piperidine, morpholine,
piperazine, pyridine, oxazole, benzoxazole, pyrimidine, quinoline,
isoquinoline, and the like. Imidazole being more preferred. Such
amines may be substituted or unsubstituted. By "substituted", it is
meant that one or more of the hydrogens are replaced by one or more
substituent groups, such a alkyl, aryl, alkoxy, halo, alkenyl, and
the like. Other suitable reaction products of amines with
epichlorohydrin are those disclosed in U.S. Pat. No. 4,038,161
(Eckles et al.). Such reaction products are generally commercially
available, such as from Raschig, or may be prepared by methods
known in the art.
[0038] When present, the leveling agents are typically used in an
amount of 0.5 to 1000 ppm. More typically, the leveling agents are
used in the range of 0.5 to 500 ppm, still more typically from 1 to
250 ppm, and even more typically from 1 to 50 ppm.
[0039] Exemplary electroplating baths of the present invention
include 0 to 100 g/L, typically 0 to 6 g/L, of sulfuric acid; 10 to
65 g/L copper ions and typically 10 to 45 g/L of copper ions; 35 to
50 ppm of chloride ion; and 1 to 1,000 ppm of suppressor compound.
More particularly, suitable baths further include 0 to 1000 ppm of
brightener compound and 0.5 to 500 ppm of leveling agent.
[0040] The present invention is useful for depositing a layer of
copper on a variety of substrates, particularly those substrates
used in the manufacture of electronic devices. The present
invention is particularly useful in the manufacture of printed
wiring boards and integrated circuits. Accordingly, the present
invention provides a method of depositing a copper layer on a
substrate including the steps of: a) contacting a substrate with
the copper plating bath described above; and b) applying a current
density for a period time sufficient to deposit a layer of copper
on the substrate.
[0041] The present copper electroplating compositions are suitably
used in similar manner to prior copper electroplating baths.
Plating baths of the invention may be employed at below room
temperature, such as about 15.degree. C., at room temperature or
above room temperature, such as up to 65.degree. C. and greater.
Typically, the plating baths are operated at a temperature in the
range of 20 to 25.degree. C. The plating composition is generally
agitated during use such as by air sparger, work piece agitation,
impingement or other suitable method. Plating is typically
conducted at a current density ranging from 1 to 100 mA/cm.sup.2,
and more typically from 1 to 60 mA/cm.sup.2, depending upon
substrate characteristics. Plating time may range from about 2
minutes to 1 hour or more, depending on the difficulty of the work
piece.
[0042] The present electroplating baths not only provide good fill
of small apertures, e.g. 0.18 .mu.m and smaller, but may, in an
alternative embodiment, provide in-situ repair of a seed layer. The
present copper plating baths are suitable for applying copper to an
electrically conductive layer. Thus, an underlying conductive seed
layer, typically a metal seed layer such as copper, is generally
applied to the substrate prior to electrochemically depositing
copper. Such seed layers may be applied by a variety of methods,
such as physical vapor deposition ("PVD"; which includes
sputtering, evaporation, or deposition from ionized metal plasma of
hollow cathode magnetron sources) and chemical vapor deposition
("CVD", which includes deposition from metal or organometallic
precursors comprising one of more metal atoms in combination with
inorganic or organic ligands such as halides, pseudohalides,
carbonyls, nitrites, alkyls, olefins, allyls, arenes, phosphines,
amines, and the like).
[0043] Typically, seed layers are thin in comparison to other metal
layers, such as from 50 to 1500 angstroms thick. Such seed layers
are typically deposited by PVD techniques which deposits the copper
seed layer in a line-of-sight fashion. Accordingly, discontinuities
in the seed layer may exist when the substrate contains very small
features. Such discontinuities in the seed layer may be problematic
for subsequent electroplating to fill the features. It is desirable
to repair or enhance such seed layers to remove any
discontinuities. The present electroplating baths may be used to
enhance such discontinuous seed layers. Accordingly, the present
invention provides a method of repairing a seed layer including the
steps of: a) contacting a substrate including a seed layer having
discontinuities; b) contacting the substrate with the
electroplating bath described above; and c) subjecting the
electroplating bath to a current density sufficient to deposit
sufficient copper to provide a uniform seed layer. By "uniform seed
layer" it is meant a seed layer that has reduced discontinuities as
compared to the number of discontinuities present prior to such
treatment.
[0044] Exposure of marginally thin copper seed to highly acidic
conventional electrolyte results in removal of the thin conductive
copper oxide layer on the seed layer, exposing the underlying
agglomerated copper seed layer (copper islands). When used to
enhance seed layers containing oxidized copper, the present
electroplating bath compositions are typically selected such that
they are less acidic than conventional copper electroplating baths.
Such less acidic baths have reduced copper oxide removal and copper
seed layer corrosion than conventional plating baths. While not
intending to be bound by theory, it is believed that the
suppression provided by the present suppressors enhances the
selective nucleation of the thin copper seed along the lower
sidewalls of the apertures during the initial seconds of
electroplating. The present compositions are believed to have
higher copper nucleation rates within apertures than conventional
electroplating baths.
[0045] Once the seed layer has been rendered continuous by the
present method, the electroplating fill sequence proceeds by the
normal bottom-up fill sequence. It will be appreciated by those
skilled in the art that the use of a hot entry step in the plating
waveform will further ensure the reduction or elimination of void
formation on the thin copper seed layer. The choice of the
particular waveform will depend upon the a number of factors known
to those skilled in the art.
[0046] A wide variety of substrates may be plated with the
compositions of the invention, as discussed above. The compositions
of the invention are particularly useful to plate electronic
devices, including without limitation, printed circuit board
substrates such as printed circuit board inner layers and outer
layers, flexible circuits and the like, integrated circuit ("IC")
devices such as wafers used in IC manufacture having small
apertures, semiconductor packaging such as lead frames, and the
like.
[0047] The compositions of the invention are particularly suitable
for plating substrates having apertures having a wide variety of
dimensions. Typically, such substrates have one or more apertures
having a size, such as a width, of .ltoreq.1 .mu.m. Other suitable
aperture sizes (widths) include, but are not limited to, 200 nm,
180 nm, 150 nm, 135 nm, 100 nm, 90 nm, 45 nm or even smaller. Such
apertures may have a wide variety of aspect ratios, such as 1.5:1
or greater, and typically aspect ratios of 2:1, 3:1, 4:1, 5:1, 6:1,
7:1, 10:1 or greater, and even up to about 15:1 or greater. The
present compositions can be used to effectively fill such apertures
without defects (e.g. no voids or inclusions by ion beam
examination).
[0048] The present invention provides a method of manufacturing an
electronic device including the step of depositing a layer of
copper on an electronic device including the steps of: a)
contacting the electronic device with the electroplating bath
described above; and b) applying current density for a period of
time sufficient to deposit a layer of copper on the electronic
device. Accordingly, the present invention also provides an article
of manufacture including an electronic device containing a layer of
copper deposited using the electroplating bath described above.
[0049] In a further embodiment, a copper diffusion barrier is
selectively deposited on the surface of the copper deposited
according to the present invention. Such selective deposition may
be performed by a variety of means, such as immersion plating, or
electroless plating. Any conducting material that inhibits or
reduces copper migration into the adjoining dielectric layers may
be used. Suitable diffusion barrier materials include, but are not
limited to, nickel, chromium, cobalt, cobalt-tungsten-phosphide,
silver, gold, palladium, platinum, ruthenium and the like. In
immersion or displacement plating, metal deposition occurs when the
dissolved metal ions in a plating bath are displaced by a more
active (less noble) metal that is contacted with the plating bath.
Immersion plating is particularly suitable it will not deposit
metal on the surrounding dielectric, only on the exposed copper
surfaces. In an alternate embodiment, a copper colloid composition,
such as that disclosed in European Patent Application No. 0 707 093
A1, may be used to selectively deposit a platable colloid, followed
by electrolessly or electrolytically plating metal on the platable
colloid. A variety of electroless metal plating baths are suitable.
Such copper diffusion barriers are particularly useful in the
manufacture of integrated circuits.
[0050] An integrated circuit device (e.g. a semiconductor wafer) is
generally plated with excess copper. During the process of
manufacturing an integrated circuit, a semiconductor wafer is often
polished to remove the excess unwanted materials on the surface of
the wafer. Polishing generally takes the form of
chemical-mechanical planarization ("CMP") wherein a chemically
active slurry is used in conjunction with a polishing pad. Thus,
once a semiconductor wafer is plated according to the present
invention, the wafer is typically subjected to CMP. A CMP procedure
can be conducted in accordance with the invention as follows.
[0051] The wafer is mounted in a wafer carrier which urges the
wafer against the surface of a moving polishing pad. The polishing
pad can be a conventional smooth polishing pad or a grooved
polishing pad. Examples of a grooved polishing pad are described in
U.S. Pat. Nos. 5,177,908; 5,020,283; 5,297,364; 5,216,843;
5,329,734; 5,435,772; 5,394,655; 5,650,039; 5,489,233; 5,578,362;
5,900,164; 5,609,719; 5,628,862; 5,769,699; 5,690,540; 5,778,481;
5,645,469; 5,725,420; 5,842,910; 5,873,772; 5,921,855; 5,888,121;
5,984,769; and European Patent 806267. The polishing pad can be
located-on a conventional platen that can rotate the polishing pad.
The polishing pad can be held on the platen by a holding means such
as, but not limited to, an adhesive, such as, double-faced tape
having adhesive on both sides.
[0052] A polishing solution or slurry is fed onto the polishing
pad. The wafer carrier can be at different positions on the
polishing pad. The wafer can be held in position by any suitable
holding means such as, but is not limited to, a wafer holder,
vacuum or liquid tensioning such as, but not limited to a fluid
such as, but not limited to water. If the holding means is by
vacuum then there is generally a hollow shaft which is connected to
the wafer carrier. Additionally, the hollow shaft could be used to
regulate gas pressure, such as, but not limited to air or an inert
gas or use a vacuum to initially hold the wafer. The gas or vacuum
would flow from the hollow shaft to the carrier. The gas can urge
the wafer against the polishing pad for the desired contour. The
vacuum can initially hold the wafer into position in the wafer
carrier. Once the wafer is located on top of the polishing pad the
vacuum can be disengaged and the gas pressure can be engaged to
thrust the wafer against the polishing pad. The excess or unwanted
copper is then removed. The platen and wafer carrier can be
independently rotatable. Therefore, it is possible to rotate the
wafer in the same direction as the polishing pad at the same or
different speed or rotate the wafer in the opposite direction as
the polishing pad.
[0053] Thus, the present invention provides a method for removing
excess material from a semiconductor wafer by using a chemical
mechanical planarization process which includes contacting the
semiconductor wafer with a rotating polishing pad thereby removing
the excess material from the semiconductor wafer; wherein the
semiconductor wafer has been prior electroplated by the copper
electroplating composition described above.
[0054] In another embodiment, the present plating bath may be used
with advanced plating hardware (such as that available from NuTool,
Inc., Milpitas, Calif.) where the anode and cathode are in intimate
contact, being separated by a porous membrane. Under such plating
conditions, the surface of the resulting electrodeposited copper
layer will be defect free and extremely level over narrow and wide
features (0.1 to 100 .mu.m wide). When using such advanced plating
hardware, minimal copper deposition is required. In addition, such
advanced plating hardware allows for minimizing the CMP
planarization process.
[0055] While the present invention has been described with respect
to copper electroplating baths, it will be appreciated by those
skilled in the art that the present suppressor compounds may be
used with a variety of plating baths, such as copper alloy, tin,
tin alloy, nickel, nickel-alloy, and the like.
EXAMPLES 1 to 18
[0056] Copper electroplating baths are prepared by combining 35 g/L
copper ion added as copper sulfate, 45 g/L sulfuric acid and 45 ppm
chloride ion, 10 mL/L of a conventional brightener, and
approximately 4 to 10 mL/L of a poly(alkylene oxide) random
copolymer indicated in Table 1. A leveling agent, a reaction
product of diethylene glycol, imidazole and epichlorohydrin
(0.5:1:1), is also added to each bath in an amount of 5 to 10
ppm.
1TABLE 1 Poly(alkylene oxide) Random Example Copolymer 1
H(CH.sub.2CH.sub.2O).sub.11(CH- .sub.2CHCH.sub.3O).sub.26H 2
HO(CH.sub.2CH.sub.2O).sub.22(CH.sub.2C- HCH.sub.3O).sub.52H 3
HO(CH.sub.2CH.sub.2O).sub.34(CH.sub.2CHCH.sub- .3O).sub.78H 4
HO(CH.sub.2CH.sub.2O).sub.46(CH.sub.2CHCH.sub.3O).su- b.103H 5
HO(CH.sub.2CH.sub.2O).sub.57(CH.sub.2CHCH.sub.3O).sub.129H 6
HO(CH.sub.2CH.sub.2O).sub.68(CH.sub.2CHCH.sub.3O).sub.135H 7
HO(CH.sub.2CH.sub.2O).sub.23(CH.sub.2CHCH.sub.3O).sub.17H 8
HO(CH.sub.2CH.sub.2O).sub.46(CH.sub.2CHCH.sub.3O).sub.35H 9
HO(CH.sub.2CH.sub.2O).sub.68(CH.sub.2CHCH.sub.3O).sub.52H 10
HO(CH.sub.2CH.sub.2O).sub.91(CH.sub.2CHCH.sub.3O).sub.103H 11
HO(CH.sub.2CH.sub.2O).sub.114(CH.sub.2CHCH.sub.3O).sub.86H 12
HO(CH.sub.2CH.sub.2O).sub.136(CH.sub.2CHCH.sub.3O).sub.103H 13
HO(CH.sub.2CH.sub.2O).sub.34(CH.sub.2CHCH.sub.3O).sub.9H 14
HO(CH.sub.2CH.sub.2O).sub.68(CH.sub.2CHCH.sub.3O).sub.17H 15
HO(CH.sub.2CH.sub.2O).sub.102(CH.sub.2CHCH.sub.3O).sub.26H 16
HO(CH.sub.2CH.sub.2O).sub.136(CH.sub.2CHCH.sub.3O).sub.35H 17
HO(CH.sub.2CH.sub.2O).sub.170(CH.sub.2CHCH.sub.3O).sub.43H 18
HO(CH.sub.2CH.sub.2O).sub.204(CH.sub.2CHCH.sub.3O).sub.52H
[0057] Layers of copper are electroplated onto wafer substrates by
contacting a spinning wafer (25 to 200 RPM) with one of the above
electroplating baths at 25.degree. C. A current density of up to 60
mA/cm.sup.2 is applied and a copper layer is deposited on each
wafer to a desired thickness, e.g., 1 .mu.m. The layers of copper
are analyzed by AFM to determine the surface roughness of the
copper deposit. The copper deposit was also evaluated to determine
its reflectivity ("Rf"). In addition, the copper deposit was
evaluated by scanning electron microscopy ("SEM") and fast ion
bombardment ("FIB"). The reflectivity value is relative to a
polished silicon wafer having an Rf value of 100.
EXAMPLES 19-36
[0058] Each of Examples 1-18 is repeated except that the copper
electroplating bath contains 40 g/L copper as copper ions, 10 g/L
sulfuric acid and 20 ppm chloride ion.
EXAMPLES 37-54
[0059] Each of Examples 1-18 is repeated except that the copper
electroplating bath contains 40 g/L copper as copper ions, 60 g/L
sulfuric acid and 20 ppm chloride ion.
EXAMPLE 55 - Comparative
[0060] The copper plating bath of Example 1 is repeated except that
the poly(alkylene oxide) copolymer is polyethylene glycol having a
formula HO(CH.sub.2CH.sub.2O).sub.45H and a molecular weight of
approximately 2,000. A layer of copper is deposited using this
electroplating bath and the conditions described in Example 1. A
visual inspection of the copper deposit shows numerous protrusions
extending from the surface of the deposit. The surface of the
deposit is analyzed and is found to have a lower Rf than the
deposits obtained from Examples 1 to 54.
EXAMPLE 56
[0061] Two copper electroplating baths are prepared by combining 40
g/L copper ion added as copper sulfate, 10 g/L sulfuric acid and 50
ppm chloride ion, 10 mL/L of a conventional brightener, and<10
ppm of a leveling agent which is a reaction product of diethylene
glycol, imidazole and epichlorohydrin (0.5:1:1). To the first bath
(Bath 1--Comparative) is added an ethylene oxide /propylene oxide
tri-block copolymer of the formula
HO(CH.sub.2CH.sub.2O).sub.5(CH.sub.2CHCH.sub.3O)-
.sub.32(CH.sub.2CH.sub.2O).sub.5H having a molecular weight of
approximately 2,360 at a concentration of 4 mL/L as a suppressor.
To the second bath (Bath 2--Invention) is added an ethylene oxide
/propylene oxide random copolymer having a molecular weight of
approximately 2400 and an EO:PO ratio of approximately 75:25. A
layer of copper is deposited on a semiconductor substrate using
each electroplating bath and the conditions described in Example
1.
[0062] An inspection of the layer of copper deposited from Bath 1
shows numerous defects, such as pits, on the surface of the
deposit. The surface of the layer of copper deposited from Bath 2
shows a very smooth (defect-free) surface. The surfaces of the
deposits are analyzed by AFM and FIB to determine the root mean
square roughness ("Rs"), arithmetic average roughness ("Ra") and
height differential ("Z"). These results are reported in Table
2.
2TABLE 2 Ra Rs Z Bath Suppressor (nm) (nm) (nm) 1-Comparative EO/PO
block copolymer 4.5 5.7 50 2-Invention EO/PO random copolymer 3.9
4.9 42
[0063] The lower the values of Ra and Rs are, the smoother the
surface is. Lower values of Z indicate a more uniform surface
height across the evaluated area. Thus, layers of copper having low
Ra, Rs and Z-values are desired. As can be seen from the above
data, the poly(alkylene oxide) random copolymer suppressor agents
provide copper deposits having smoother surfaces as compared to
conventional suppressors.
EXAMPLES 57-74
[0064] Each of Examples 1-18 is repeated except that the layers of
copper are electroplated onto printed wiring board substrates. The
printed wiring board substrates typically have one or more through
holes, via holes or both though holes and via holes that need to be
electroplated with copper.
* * * * *