U.S. patent application number 10/816168 was filed with the patent office on 2005-04-07 for copper plating bath and plating method.
This patent application is currently assigned to EBARA CORPORATION. Invention is credited to Kimizuka, Ryoichi, Kobayashi, Takeshi, Mishima, Koji, Nakada, Tsutomu, Sahoda, Tsuyoshi.
Application Number | 20050072683 10/816168 |
Document ID | / |
Family ID | 34396826 |
Filed Date | 2005-04-07 |
United States Patent
Application |
20050072683 |
Kind Code |
A1 |
Nakada, Tsutomu ; et
al. |
April 7, 2005 |
Copper plating bath and plating method
Abstract
An acid copper plating solution comprises copper ions, an
organic acid or an inorganic acid, chloride ions, a high molecular
weight surfactant that controls the electrodeposition reaction, and
a sulfur-containing saturated organic compound that promotes the
electrocoating rate. The high molecular weight surfactant comprises
two or more types of surfactants with different hydrophobicities.
The plating solution is used for forming a plating film on a
conductor layer.
Inventors: |
Nakada, Tsutomu; (Tokyo,
JP) ; Sahoda, Tsuyoshi; (Tokyo, JP) ; Mishima,
Koji; (Tokyo, JP) ; Kimizuka, Ryoichi;
(Kanagawa, JP) ; Kobayashi, Takeshi; (Kanagawa,
JP) |
Correspondence
Address: |
BROWDY AND NEIMARK, P.L.L.C.
624 NINTH STREET, NW
SUITE 300
WASHINGTON
DC
20001-5303
US
|
Assignee: |
EBARA CORPORATION
Tokyo
JP
EBARA-UDYLITE CO., LTD.
Tokyo
JP
|
Family ID: |
34396826 |
Appl. No.: |
10/816168 |
Filed: |
April 2, 2004 |
Current U.S.
Class: |
205/296 ;
106/1.18 |
Current CPC
Class: |
C25D 5/18 20130101; H05K
3/423 20130101; C25D 3/38 20130101 |
Class at
Publication: |
205/296 ;
106/001.18 |
International
Class: |
C25D 003/38 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 3, 2003 |
JP |
2003-100374 |
Jun 6, 2003 |
JP |
2003-161666 |
Oct 27, 2003 |
JP |
2003-366162 |
Claims
1. An acid copper plating solution comprising copper ions, an
organic acid or an inorganic acid, chloride ions, high molecular
weight surfactant which controls the electrodeposition reaction,
and a sulfur-containing saturated organic compound which promotes
the electrocoating rate, wherein the high molecular weight
surfactant comprises at least two types with different
hydrophobicities.
2. The acid copper plating solution according to claim 1, wherein
all of the at least two types of high molecular weight surfactants
with different hydrophobicities are nonionic surfactants and the
concentration of a surfactant having comparatively strong
hydrophobicity is less than the concentration of a surfactant
having comparatively weak hydrophobicity.
3. The acid copper plating solution according to claim 1, wherein
among the at least two types of high molecular weight surfactants
with different hydrophobicities, the concentration of a nonionic
surfactant having comparatively strong hydrophobicity is equal to
or less than the critical micelle concentration in the acid copper
plating solution.
4. The acid copper plating solution according to claim 1, wherein
among the at least two types of high molecular weight surfactants
with different hydrophobicities, the concentration of a nonionic
surfactant having comparatively weak hydrophobicity is equal to or
more than the critical micelle concentration in the acid copper
plating solution.
5. The acid copper plating solution according to claim 1, wherein
among the at least two types of high molecular weight surfactants
with different hydrophobicities, the concentration of a nonionic
surfactant having comparatively strong hydrophobicity is equal to
or less than the critical micelle concentration in the acid copper
plating solution and the concentration of a nonionic surfactant
having comparatively weak hydrophobicity is equal to or more than
the critical micelle concentration in the acid copper plating
solution.
6. The acid copper plating solution according to claim 1, wherein
the at least two types of high molecular weight surfactants with
different hydrophobicities comprise a nonionic surfactant and a
surfactant other than the nonionic surfactant, and the
concentration of the nonionic surfactant is higher than the
concentration of the surfactant other than the nonionic
surfactant.
7. The acid copper plating solution according to claim 1, wherein
the at least two types of high molecular weight surfactants with
different hydrophobicities comprise a nonionic surfactant and a
surfactant other than the nonionic surfactant, and the surfactant
other than the nonionic surfactant is a cationic surfactant, a
surfactant which is nonionic but exhibits cationic properties under
strong acidic conditions, or an amphoteric surfactant.
8. The acid copper plating solution according to claim 1, wherein
the at least two types of high molecular weight surfactants with
different hydrophobicities comprise a nonionic surfactant and a
surfactant other than the nonionic surfactant, and the
concentration of the surfactant other than the nonionic surfactant
is equal to or lower than the critical micelle concentration.
9. The acid copper plating solution according to claim 1, wherein
the at least two types of high molecular weight surfactants with
different hydrophobicities comprise a nonionic surfactant and a
surfactant other than the nonionic surfactant, and the
concentration of the nonionic surfactant is equal to or higher than
the critical micelle concentration.
10. The acid copper plating solution according to claim 1, wherein
the at least two types of high molecular weight surfactants with
different hydrophobicities comprise a nonionic surfactant and a
surfactant other than the nonionic surfactant, and the
concentration of the nonionic surfactant is equal to or higher than
the critical micelle concentration and the concentration of the
surfactant other than the nonionic surfactant is equal to or lower
than the critical micelle concentration.
11. An electrolytic plating method comprising performing plating at
a cathode current density in the range of 0.1-30 mA/cm.sup.2 using
the acid copper plating solution of claim 1.
12. A plating method for forming a plating film on a conductor
layer, which is formed on at least a part of a structural object
having a concave-convex pattern on a semiconductor substrate,
comprising providing a cathode potential to the conductor layer and
supplying a plating solution which electrically connects an anode
with the conductor layer, wherein the plating solution contains
25-75 g/l of copper ion and 0.4 mol/l of an organic acid or
inorganic acid and an electric resistor is installed between the
conductor layer and the anode.
13. The plating method according to claim 12, carried out at an
electrical conductivity of 3 S/m or less.
14. The plating method according to claim 12, wherein the organic
acid or inorganic acid is sulfuric acid, alkane sulfonic acid, or
alkanol sulfonic acid.
15. The plating method according to claim 12, wherein a copper
compound selected from the group consisting of copper sulfate,
copper oxide, copper chloride, copper carbonate, copper
pyrophosphate, copper alkane sulfonate, copper alkanol sulfonate,
and organic acid copper is used as a copper ion source.
16. The plating method according to claim 12, wherein the organic
acid or inorganic acid is sulfuric acid and the copper ion source
is copper sulfate.
17. The plating method according to claim 12, wherein the organic
acid or inorganic acid is sulfuric acid, the copper ion source is
copper sulfate, and the copper ion concentration is 58 g/l or
less.
18. The plating method according to claim 12, wherein the
concave-convex pattern formed on a semiconductor substrate
comprises a pattern with a wiring width or via of 0.1 .mu.m or
less.
19. A plating method for forming a wiring circuit on an electronic
circuit substrate having fine holes and trenches, comprising
forming a plating film on a conductor layer, which is formed on at
least a part of the substrate, and filling the holes and trenches
with copper, wherein the plating film is formed by using an acid
copper plating solution containing copper ions, organic or
inorganic acid, chloride ions, sulfur-containing saturated organic
compound, and high molecular weight surfactant controlling
electrocoating at a concentration of 500 ppm or more.
20. The plating method according to claim 19, wherein a cathode
potential is applied to a conductor layer when the electronic
circuit substrate on which the conductor layer has been formed is
put into the plating bath.
21. The plating method according to claim 20, wherein a cathode
potential is applied at a constant current or constant voltage to a
conductor layer when the electronic circuit substrate on which the
conductor layer has been formed is put into the plating bath.
22. The plating method according to claim 19, wherein the fine
holes and trenches formed on an electronic circuit substrate
comprise a copper seed layer with a thickness of 1-100 nm, the
holes and trenches having an opening width of 1 .mu.m or less and
an aspect ratio of 5 or more.
23. A plating method comprising producing a plating film with a
thickness of 10-100 nm on a conductive layer which is formed on at
least a part of an electronic circuit substrate having fine holes
and trenches using an acid copper plating solution containing
copper ions, organic or inorganic acid, chloride ions,
sulfur-containing saturated organic compound, and high molecular
weight surfactant controlling electrocoating at a concentration of
500 ppm or more, and further plating until the fine holes and
trenches are filled with copper using an acid copper plating
solution containing copper ions, organic or inorganic acid,
chloride ions, sulfur-containing saturated organic compound, and
high molecular weight surfactant controlling electrocoating at a
concentration of 10-100 ppm.
24. The plating method according to claim 23, wherein the fine
holes and trenches formed on an electronic circuit substrate
comprise a copper seed layer with a thickness of 1-100 nm, the
holes and trenches having an opening width of 1 .mu.m or less and
an aspect ratio of 5 or more.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an acid copper plating
solution and a plating method. More particularly, the present
invention relates to an acid copper plating solution for plating
the surface of wafers, which are electronic materials, in
particular, for plating wafer surfaces having submicron-level gaps
to produce fine copper circuits.
[0003] The present invention further relates to a method for
plating a substrate to form circuit patterns on semiconductor
substrates and the like using a metal plating technique such as a
copper plating technique, particularly to a copper plating method
for plating wafer surfaces having submicron-level gaps to produce
fine copper circuits while ensuring excellent plating film
uniformity and filling performance.
[0004] The present invention also relates to a plating method
capable of depositing copper in fine holes and trenches in
electronic circuit substrates such as semiconductor substrates and
printed boards which are miniaturized due to increased integration
to the extent that it is difficult to form a satisfactory seed
layer.
[0005] 2. Description of Related Art
[0006] A copper sulfate plating solution has long been used as an
acid copper plating solution and is used for plating wafers in a
recent technology (Japanese Patent Application Laid-open No.
2000-248397).
[0007] In a wafer processing method, a fine circuit pattern is
formed on the wafer surface, followed by copper plating of the
wafer surface. The fine circuit pattern formed on this wafer
surface has very fine submicron-level gaps, for example.
[0008] To uniformly plate copper on a wafer surface having such
very fine gaps, the electrocoating conditions must be separately
controlled for the area in which copper is plated with comparative
ease and the area in which it is difficult to uniformly plate
copper by electrocoating, such as the inside of the fine gaps.
[0009] Low-k/Cu damascene wiring in logic devices is an important
technique for implementing highly integrated/high performance
multilayer wiring. Requirements for copper wiring are particularly
stringent. In the wake of the era in which a circuit width of 65 nm
or less was demanded, more excellent filling performance for fine
damascene structures, superior in-plane uniformity for 300 mm
wafers, and a further reduction of step difference after plating
have been desired. In addition, since barrier metal/seed layers are
expected to become markedly thin after the 65 nm generation,
satisfying these requirements involves further difficulty.
[0010] In fact, in conventional cup-type plating apparatuses, the
electric resistance of the seed film itself increases due to the
decrease in the seed layer thickness. For this reason, there have
been occasions in which in-plane uniformity is impaired due to a
decrease in the film thickness from the edge toward the center of
the wafers. As a measure for avoiding this phenomenon, a method of
controlling the electric field uniformly using an electric field
adjuster (a shield plate), a partition anode, and the like is
conceivable. This method, however, may require a complicated
operation to process a variety of samples when parts and recipes
vary according to the types of plating solution and the seed film
thickness.
[0011] Another possible measure is to increase the electric
resistance between the anode and cathode (wafer) to the extent that
the electric resistance of the seed film itself is no longer
predominant over the uniformity of plane.
[0012] Based on this idea, a method of increasing the resistance of
the plating solution itself by decreasing the sulfuric acid
concentration in the plating solution (see U.S. Pat. No. 6,350,366,
for example) and a method of increasing the electric resistance
between the electrodes by inserting specific resistors between the
electrodes (see M. Tsujimura et al., "A Novel Compact ECD Tool for
ULSI Cu Metallization", Proc. ISSM, 2000, pp. 106-109, for example)
have been invented and put into practice.
[0013] A conventional method for forming a wiring circuit by
forming fine trenches and holes in the form of the wiring circuit
on an electronic circuit substrate, plating the substrate with
copper to fill the trenches and holes with copper, and removing the
copper deposited on unnecessary parts has also been a problem.
[0014] Specifically, forming wiring by copper plating using the
above method may also cause difficult problems, since the wiring
width formed by such fine trenches is anticipated to become as
small as 0.1 .mu.m or less in the future due to the increasing
wiring density in electronic equipment. One problem is that a thin
copper seed layer formed in the fine trenches and holes on the
sidewall or bottom may dissolve before the plate film is
produced.
[0015] Specifically, in a typical method of plating an electronic
circuit substrate, a barrier layer is first formed and a copper
layer, called a seed layer, functioning as a conductive layer is
formed on the barrier layer by sputtering or chemical vapor
deposition.
[0016] However, even if a copper seed film on the surface of the
substrate has a thickness of about 100 nm, the seed film thickness
in vias, with a diameter of 0.1 .mu.m (100 nm) and an aspect ratio
of about 5, is 10 nm or less due to poor sputter coverage. The seed
film thickness in the sidewalls of vias is particularly small.
[0017] The present invention has been completed in view of the
above situation. Specifically, an object of the present invention
is to provide an acid copper plating solution which can be applied
to the surface of a wafer or the like having submicron-level gaps
to completely fill the gaps with copper plating and, at the same
time, form highly uniform copper plating and an electroplating
method using the acid copper plating solution.
[0018] Another object of the present invention is to provide a
plating method which can provide a thin seed layer with excellent
in-plane uniformity and outstanding capability of filling fine
damascene structures.
[0019] Still another object of the present invention is to provide
a plating method capable of producing uniform plating on an
extremely thin part of a copper seed film on sidewalls and bottom
of vias to produce voidless filling, which has been very difficult
to attain using present technologies.
SUMMARY OF THE INVENTION
[0020] The present inventors have conducted studies on the
components for an acid copper plating solution with an objective of
obtaining a copper plating solution which, when applied to the
surface of a wafer or the like having submicron-level gaps, can
completely fill the gaps with copper plating and, at the same time,
can form highly uniform copper plating.
[0021] During the course of the study, the inventors have found
that, among high molecular weight surfactants (components for
controlling electrodeposition reaction) and sulfur-containing
saturated organic compounds (components for promoting
electrocoating rate) which are contained in common acid copper
plating solutions, the high molecular weight surfactants are
adsorbed in the area exposed to the plating solution on the surface
to be plated having very small gaps and control the
electrodeposition reaction in that area. However, in wafers having
submicron-level gaps, such high molecular weight surfactants were
found to have a tendency of concentrating the plating current in
the edges, particularly, in the edges on the surface side on which
extremely minute gaps are formed.
[0022] The inventors have further found that, to control the
electrodeposition reaction in the edges to a great extent, it is
desirable to cause a highly hydrophobic and strongly adsorptive
high molecular weight surfactant to be adsorbed in the edges and to
cause another, less adsorptive and less hydrophobic, high molecular
weight surfactant exhibiting relatively small controlling power to
be adsorbed in the other areas.
[0023] The inventors also found that if two or more high molecular
weight surfactants with different hydrophobicities are used while
controlling their concentrations, it is possible to approximate the
electrocoating rates in the area in which electrocoating of copper
plating occurs comparatively easily and in the area in which
electrocoating of copper plating proceeds only unevenly, such as
inside the very minute gaps, thereby obtaining uniform plating.
[0024] The inventors have conducted further extensive studies on a
plating method which can provide a thin seed layer with excellent
in-plane uniformity and an outstanding capability of filling fine
damascene structures and, as a result, have found that plating
exhibiting both excellent in-plane uniformity and outstanding
filling capability can be achieved using a plating bath containing
an acid at a concentration above a specific level and by inserting
an electric resistor between the wafer and anode.
[0025] The inventors have further studied a method for uniformly
producing acid copper plating when the copper seed film is
extremely thin and found that if the high molecular weight
surfactant is added to an acid copper plating solution at a higher
concentration, dissolution of copper in the area in which the
copper seed layer is thin, such as the bottom of vias, can be
prevented, and voidless filling is possible.
[0026] The inventors have further found that an acid copper plating
solution containing an organic acid or an inorganic acid at a
concentration of 0.4 mol/l is useful to directly plate copper on a
substrate of another metal such as Ta, Ti, Al, Ru, Pt, or Ir,
without a copper seed film.
[0027] Specifically, the present invention provides an acid copper
plating solution comprising copper ions, an organic acid or an
inorganic acid, chloride ions, high molecular weight surfactant
which controls the electrodeposition reaction, and a
sulfur-containing saturated organic compound which promotes the
electrocoating rate, wherein the high molecular weight surfactant
comprises at least two types with different hydrophobicities.
[0028] Moreover, the present invention provides an electrolytic
plating method characterized by performing plating at a cathode
current density in the range of 0.1-30 MA/cm.sup.2 using any one of
the above-mentioned acid copper plating solutions.
[0029] The present invention further provides a plating method for
forming a plating film on a conductor layer, which is formed on at
least a part of a structural object having a concave-convex pattern
on a semiconductor substrate, comprising providing a cathode
potential to the conductor layer and supplying a plating solution
which electrically connects an anode with the conductor layer,
wherein the plating solution contains 25-75 g/l of copper ion and
0.4 mol/l or more of an organic acid or inorganic acid and an
electric resistor is installed between the conductor layer and the
anode.
[0030] The present invention further provides a plating method for
forming a wiring circuit on an electronic circuit substrate having
fine holes and trenches, comprising forming a plating film on a
conductor layer, which is formed on at least a part of the
substrate, and filling the holes and trenches with copper, wherein
the plating film is formed by using an acid copper plating solution
containing copper ions, organic or inorganic acid, chloride ions,
sulfur-containing saturated organic compound, and high molecular
weight surfactant controlling electrocoating at a concentration of
500 ppm or more.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a chart showing the relationship between the
porosity and electric conductivity, wherein Type A indicates SiC
and Type B indicates Al.sub.2O.sub.3.
[0032] FIG. 2 is a chart showing the relationship between the pore
size and electric conductivity.
[0033] FIG. 3 is a drawing schematically showing an embodiment of a
first plating method, wherein 1 indicates a plating cell, 2
indicates a wafer, 3 indicates an anode, 4 indicates an electric
resistor, 5 indicates a wafer seal, and 6 indicates a cathode.
[0034] FIG. 4 shows a result of measuring a film thickness
distribution along the diameter of a 200 mm wafer, wherein A and B
indicate the results respectively when the seed layer is 20 nm or
60 nm.
[0035] FIG. 5 shows a result of measuring a film thickness
distribution along the diameter of a 300 mm wafer, wherein A and B
indicate the results respectively when the seed layer is 20 nm or
60 nm.
[0036] FIG. 6 is a drawing showing the thickness distribution when
plating is carried out in different plating thicknesses, wherein A,
B, and C respectively indicate the thicknesses of 0.5 .mu.m, 1.0
.mu.m, and 2.5 .mu.m.
[0037] FIG. 7 is a chart showing the relationship between the
sulfuric acid concentration in a usual copper sulfate plating
solution and the electric conductivity.
[0038] FIG. 8 is a drawing showing the calculation result of the
electric conductivity and thickness distribution when the seed
layer is varied by the finite element method (FEM).
[0039] FIG. 9 is a drawing schematically showing a chip testing
instrument used in Examples, wherein 11 indicates a plating bath,
12 indicates a substrate, 13 indicates an anode, 14 indicates a
plating solution, 15 indicates a stirrer, 16 indicates a substrate
holder, and 17 indicates an electric source.
[0040] FIG. 10 is a drawing showing an embodiment of electric
current control.
[0041] FIG. 11 is a drawing showing another embodiment of electric
current control.
DETAILED DESCRIPTION OF THE INVENTION
[0042] A first embodiment of the present invention is an acid
copper plating solution comprising copper ions, an organic acid or
an inorganic acid, chloride ions, high molecular weight surfactant
which controls an electrodeposition reaction, and a
sulfur-containing saturated organic compound which promotes the
electrocoating rate, wherein the high molecular weight surfactant
comprises at least two types with different hydrophobicities (this
embodiment hereinafter referred to from time to time as "acid
copper plating solution").
[0043] The second embodiment of the present invention is a plating
method for forming a plating film on a conductor layer, which is
formed on at least a part of a structural object having a
concave-convex pattern on a semiconductor substrate, comprising
providing a cathode potential to the conductor layer and supplying
a plating solution which electrically connects an anode with the
conductor layer, wherein the plating solution contains 25-75 g/l of
copper ion and 0.4 mol/l or more of an organic acid or inorganic
acid and an electric resistor is installed between the conductor
layer and the anode (this embodiment hereinafter referred to from
time to time as "first plating method"). The third embodiment of
the present invention is a plating method for forming a wiring
circuit on an electronic circuit substrate having fine holes and
trenches, comprising forming a plating film on a conductor layer,
which is formed on at least a part of the substrate, and filling
the holes and trenches with copper, wherein the plating film is
formed by using an acid copper plating solution containing a copper
ion source, organic or inorganic acid, chloride ions,
sulfur-containing saturated organic compound, and high molecular
weight surfactant controlling electrocoating at a concentration of
500 ppm or more (this embodiment hereinafter referred to from time
to time as "second plating method"). These embodiments will now be
described.
[0044] The acid copper plating solution of the first embodiment
comprises copper ions, an organic acid or an inorganic acid, and
chloride ions as essential components. An example of the inorganic
acid in the acid copper plating solution is sulfuric acid and
examples of the organic acid include alkane sulfonic acids such as
methansulfonic acid, and pyrophosphoric acid.
[0045] In addition, at least a high molecular weight surfactant,
which inhibits the electrodeposition reaction, and
sulfur-containing saturated organic compound, which promotes the
electrocoating rate, are added to and used in the acid copper
plating of the present invention.
[0046] As the high molecular weight surfactant, compounds
consisting of a hydrophilic moiety (group) and a hydrophobic moiety
(group) can be given, for example. As examples of the hydrophilic
moiety of the high molecular weight surfactant, a polyhydric
alcohol residue, polyethylene glycol residue, amine group,
quaternary ammonium group, pyridinium group, sulfonium group,
phosphonium group, polyethylene polyamine group, carboxyl group,
sulfonic acid group, sulfate group, phosphate group, phosphonic
acid group, amino acid residue, betaine, amino sulfate group, and
sulfobetaine can be given. As examples of the hydrophobic moiety,
moieties of a triglyceride, fatty acid, fatty alcohol, resin acid,
n-paraffin, naphthenic acid, .alpha.-olefin, alkyl benzene, alkyl
phenol, polyoxyalkylene glycol, completely fluorinated fatty acid
and fatty alcohol, partially fluorinated fatty acid and fatty
alcohol, polysiloxane, and the like can be given. Of the above
hydrophilic moieties, the polyhydric-alcohol residue is preferably
selected from the group consisting of a glycerol residue, glucose
residue, sucrose residue, and amino alcohol residue.
[0047] As more specific examples of the high molecular weight
surfactant, a fatty acid salt, rosin acid salt, alkyl
polyoxyethylene sulfate, .alpha.-olefin sulfonate, alkyl
naphthalene sulfonate, lignin sulfonate, alkyl phosphate, primary
amine salt, alkyl trimethyl ammonium salt, alkyl polyoxyethylene
amine, N-alkyl .beta.-aminopropionic acid, N-alkyl sulfobetaine,
N-alkylhydroxylsulfobetaine, lecithin, silkyl polyoxyethylene
ether, fatty acid polyoxyethylene ester, fatty acid sorbitan ester,
fatty acid sucrose ester, 1,3-dioxalane polymer, polypropylene
glycol, polypropylene propanol, polyethylene glycol, polyethylene
glycol derivative, oxylalkylene polymer, copolymer of ethylene
oxide and propylene oxide, and fatty acid polyglycerol ester can be
given.
[0048] In the acid plating solution of the present invention, two
or more high molecular weight surfactants with different
hydrophobicities must be selected and used. There are two cases for
the selection. In one case, the two or more high molecular weight
surfactants are nonionic surfactants. In the other case, among the
two or more high molecular weight surfactants, one or more are
nonionic surfactants, and one or more are different surfactants,
i.e. an anionic surfactant, cationic surfactant, or amphoteric
surfactant.
[0049] When two or more high molecular weight surfactants are
nonionic surfactants, a nonionic surfactant with comparatively
strong hydrophobicity must be used at a concentration lower than
the concentration of a nonionic surfactant with comparatively weak
hydrophobicity. The reason is that although it is desirable to use
a strongly adsorptive nonionic surfactant with strong
hydrophobicity for the edge parts to significantly control the
electrodeposition reaction and to use a less hydrophobic nonionic
surfactant with a smaller controlling effect for the other parts to
cause copper to deposit, the nonionic surfactant with strong
hydrophobicity must be used at a concentration lower than the
concentration of the nonionic surfactant with weak hydrophobicity
because the total area of the edge parts is smaller than the total
area of other parts.
[0050] Although there are no specific limitations to the
concentration of these nonionic surfactants, the concentration of
the nonionic surfactant with strong hydrophobicity is preferably
not more than the critical micelle concentration in an acid copper
plating solution, and the concentration of the nonionic surfactant
with weak hydrophobicity is preferably not less than the critical
micelle concentration in the acid copper plating solution. In
particular, it is preferable that both the concentration of the
nonionic surfactant with strong hydrophobicity is not more than the
critical micelle concentration in an acid copper plating solution,
and the concentration of the nonionic surfactant with weak
hydrophobicity is not less than the critical micelle concentration
in the acid copper plating solution. Controlling the concentrations
in this manner ensures accurate and fine copper plating inside very
small gaps.
[0051] A micelle herein refers to an aggregate of molecules or ions
which a surfactant at a concentration greater than a certain level
forms in a solution and a critical micelle concentration (cmc)
indicates the concentration at which such a micelle is formed.
Although the critical micelle concentrations of many surfactants in
aqueous solutions are known, it is necessary in the present
invention to determine the critical micelle concentration in the
acid copper plating solution and to control copper plating
operations on the basis of such a concentration. To determine the
critical micelle concentration, a surfactant is added to an acid
plating solution having the same concentration as the acid copper
plating solution to be used to make various concentrations and the
concentration at which the physicochemical characteristics greatly
change is determined. As examples of the physicochemical
characteristics used for detecting the critical micelle
concentration, detergency, surface tension, interfacial tension,
osmotic pressure, equivalent conductance, and high frequency
conductivity can be given.
[0052] When one of the two or more high molecular weight
surfactants is a nonionic surfactant and one or more are different
surfactants (a cationic surfactant, a nonionic surfactant
exhibiting cationic properties under highly acidic conditions (e.g.
at pH 4 or less), or an amphoteric surfactant), the concentration
of the nonionic surfactant must be higher than the concentration of
the other surfactants. Specifically, the ionic surfactant other
than the nonionic surfactant (e.g, a cationic surfactant, a
nonionic surfactant exhibiting cationic properties under highly
acidic conditions, and an amphoteric surfactant) is preferably used
at a low concentration because these surfactants are preferentially
adsorbed in edge parts with a small total area by controlling the
current and voltage.
[0053] Although there are no specific limitations to the
concentrations of the nonionic surfactants and other surfactants,
the concentration of the surfactant other than the nonionic
surfactant is preferably less than the critical micelle
concentration in an acid copper plating solution, and the
concentration of the nonionic surfactant is preferably more than
the critical micelle concentration in the acid copper plating
solution. In particular, it is preferable that both the
concentration of the nonionic surfactant is more than the critical
micelle concentration in an acid copper plating solution, and the
concentration of the other surfactant is less than the critical
micelle concentration in the acid copper plating solution.
Controlling the concentrations in this manner ensures accurate and
fine copper plating inside very small gaps.
[0054] The reasons for causing a surfactant with a small
electrodeposition controlling effect (a nonionic surfactant with
comparatively low hydrophobicity in the former case and a nonionic
surfactant in the latter case) to be adsorbed in very small gaps
are to obtain a more precise and fine plating film using the effect
of a later-described sulfur-containing organic compound and to
control dissolution of the copper seed layer by chlorine, acids,
and the like contained in the plating solution.
[0055] In the acid copper plating solution of the present
invention, a sulfur-containing organic compound is used as an
additive in addition to the high molecular weight surfactant. The
sulfur-containing organic compound promotes the rate of
electrocoating copper onto the plated surface. Since the
sulfur-containing organic compound has a molecular weight
comparatively smaller than the high molecular weight surfactant,
the sulfur-containing organic compound can easily enter very small
gaps, thereby promoting the electrocoating rate of copper plating
inside the small gaps. The sulfur-containing organic compound may
be added in an amount of 0.1-200 mg/l.
[0056] The acid copper plating solution of the present invention
may further contain a nitrogen-containing saturated organic
compound or an organic dye compound for controlling the leveling of
copper plating. Although the effect of these compounds is small at
the start of the plating operation, i.e. at an early stage of
plating electrocoating, the compounds play a role of providing
uniform copper electrocoating irrespective of the plating surface
configuration after the copper plating electrocoating has proceeded
to some extent. This ensures that the final copper plating is
highly leveled. Although one or more types of nitrogen-containing
saturated organic compounds or organic dye compounds may be added
in an amount of 0.01-20 mg/l, these nitrogen-containing saturated
organic compounds or organic dye compounds may not be required
according to the high molecular weight surfactant and the
sulfur-containing organic compound selected.
[0057] Although there are no specific limitations to the
concentrations of copper ions, the organic acid or inorganic acid,
and chloride ions which are the basic components of the acid copper
plating solution of the present invention, preferable concentration
ranges for ensuring copper plating with excellent uniformity and
filling properties are as follows.
[0058] Specifically, when copper sulfate is used as a copper ion
source, for example, the amount of the copper sulfate, as
pentahydrate, is preferably in the range of 100-240 g/l. If the
concentration of copper sulfate is less than 100 g/l, the amount of
copper ions supplied to the plated surface is insufficient,
resulting in inadequate filling of very small gaps; if more than
240 g/l, copper precipitate tends to be produced. The concentration
of sulfuric acid is preferably 10-100 g/l. If the sulfuric acid
concentration is less than 10 g/l, the voltage is high and burnt
plating tends to occur; if more than 100 g/l, leveling and filling
properties decrease. The concentration of chlorine is preferably
10-90 mg/l. If the chlorine concentration is less than 10 mg/l,
uniform electrocoating is impossible; if more than 90 mg/l, copper
chloride tends to precipitate.
[0059] Copper plating using the acid copper plating solution of the
present invention can be carried out under conventional plating
conditions without any specific limitations. Specifically, the
plating can be carried out at a liquid temperature of about
18-30.degree. C. and a cathode current density of 0.1-30
mA/cm.sup.2.
[0060] The concentration of the high molecular weight surfactant in
the plating solution must be controlled as mentioned above. The
concentration can be controlled according to a known method by
appropriately adding the high molecular weight surfactant while
monitoring its concentration.
[0061] Control by means of the critical micelle concentration can
be carried out by preparing a test solution with the same
composition as the copper sulfate plating solution to be used. The
critical micelle concentration of this solution is determined to
control the operation based on this concentration.
[0062] The first plating method of the second embodiment of the
present invention is a plating method for forming a plating film on
a conductor layer, which is formed on at least a part of a
structural object having a concave-convex pattern on a
semiconductor substrate, comprising providing a cathode potential
to the conductor layer and supplying a plating solution which
electrically connects the anode to the conductor layer, wherein the
plating solution contains 25-75 g/l of copper ion, 0.4 mol/l or
more of an organic acid or inorganic acid, and an electric resistor
is installed between the conductor layer and the anode.
[0063] The copper plating solution used in the first plating method
contains 25-75 g/l of copper ion and 0.4 mol/l or more of an
organic acid or inorganic acid.
[0064] As examples of the copper ion source used for the copper
plating solution, copper compounds selected from the group
consisting of copper sulfate, copper oxide, copper chloride, copper
carbonate, copper pyrophosphate, copper alkane sulfonate, copper
alkanol sulfonate, and organic acid copper can be given.
[0065] As examples of the organic acid or inorganic acid
(hereinafter referred to as "acids"), sulfuric acid, alkane
sulfonic acid, and alkanol sulfonic acid can be given.
[0066] The concentration of these acids is 0.4 mol/l or more. If
the concentration is lower than 0.4 mol/l, the filling properties
may be impaired. A preferable concentration of the acids is 0.4-1.0
mol/l.
[0067] The addition of an organic acid or an inorganic acid at a
concentration of 0.4 mol/l or more is preferable to directly plate
copper on a substrate of another metal such as Ta, Ti, Al, Ru, Pt,
or Ir, without a copper seed film.
[0068] A particularly preferable combination of the acid and copper
ion source used in the first plating method of the present
invention is the combination of sulfuric acid and copper sulfate,
particularly, a combination in which the copper ion concentration
is 58 g/l or less.
[0069] In the first plating method, an electric resistor must be
inserted between the wafer and anode. As the electric resistor,
ceramic porous materials such as SiC and Al.sub.2O.sub.3, PTFE
filter, and porous plastics such as polyethylene in the form of a
sheet can be used.
[0070] Preferable electric resistors are those capable of reducing
the electric conductivity during the plating operation to one half
or less of the electric conductivity during a normal plating
operation, for example, 3 s/m or less.
[0071] Other than the above features, conventionally known methods
are appropriately employed in the first plating method of the
present invention. For example, chloride ions and additives at
suitable concentrations can be added to the plating bath. As the
additives, high molecular weight surfactants for controlling
electrodeposition reaction, sulfur-containing saturated organic
compounds for promoting the electrocoating rate,
nitrogen-containing saturated organic compounds for controlling
leveling, organic dye compounds, and the like can be used either
individually or in combination of two or more.
[0072] As the anode for plating, commonly known soluble electrodes
and insoluble electrodes can be used. Also, the wafers to be plated
may be those formed with a barrier layer or a seed layer according
to a conventional method. Furthermore, it is possible to use
various types of plating apparatuses, such as a face-up type
apparatus, face-down type apparatus, and vertical-type
apparatus.
[0073] The second plating method of the third embodiment of the
present invention is a plating method for forming a wiring circuit
on an electronic circuit substrate having fine holes and trenches,
comprising forming a plating film on a conductor layer, which is
formed on at least a part of the substrate, and filling the holes
and trenches with copper, wherein the plating film is formed by
using an acid copper plating solution containing copper ions,
organic or inorganic acid, chloride ions, sulfur-containing
saturated organic compound, and high molecular weight surfactant
controlling electrocoating at a concentration of 500 ppm or
more.
[0074] The second plating method utilizes the effect of the high
molecular weight surfactant used as the additive for controlling
electrocoating in an acid copper plating solution to prevent
dissolution of copper by an acid and to protect a thin copper seed
film from the action of the acid contained in the acid copper
plating solution.
[0075] The high molecular weight surfactants used in the second
plating method may be those used as the additive for controlling
electrocoating, for example, polyethylene glycol with a molecular
weight of 1,000-5,000 and polypropylene glycol with a molecular
weight of 500-1, 000 (such a high molecular weight surfactant is
hereinafter referred to as "a polymer component").
[0076] The polymer component, however, must be added in an amount
far greater than the amount used for conventional acid copper
plating solutions. Specifically, the polymer component, which is
used in an amount of about 50-300 ppm in conventional acid copper
plating solutions, must be used in an amount of 2-20 times that
amount, i.e. about 500-1,000 ppm in the second plating method.
[0077] Except for using the polymer component in the above
concentration, the acid copper plating solution of the second
plating method is prepared according to the same composition as the
known acid copper plating solutions.
[0078] For example, copper ions can be supplied from copper
compounds such as copper sulfate and copper alkane sulfonate, and
sulfuric acid and alkane sulfonic acid can be used as an anion
component. Moreover, the acid copper plating solution preferably
contains chloride ions. As additives, sulfur-containing saturated
organic compounds such as bis(3-sulfopropyl)disulfide (SPS) and
mercaptopropane sulfonic acid (MPS) and nitrogen-containing
polymers such as a quaternary salt of polydialkylaminoethyl
acrylate, polydiallyldimethylammonium chloride, polyethylene imine,
quaternary salt of polyvinyl pyridine, polyvinyl amidine, polyallyl
amine, and polyamine sulfonic acid can be used.
[0079] The amounts of each component for the acid copper plating
solution of the second plating method can be appropriately
selected. A preferable compositional range for copper sulfate
plating, for example, is as follows.
1 Particularly Preferable range preferable range Copper sulfate
100.about.250 g/l 180.about.230 g/l pentahydrate Sulfuric acid
10.about.100 g/l 10.about.60 g/l Chlorine 50.about.70 ppm
55.about.65 ppm Polymer component 500.about.1500 ppm 700.about.1200
ppm Sulfur-containing 1.about.5 ppm 1.about.3 ppm organic compound
Nitrogen-containing 1.about.100 ppm 1.about.50 ppm polymer
[0080] To perform the second plating method, a barrier layer and
copper seed layer (conductor layer) are first formed on an
electronic circuit substrate having fine holes and trenches
according to a conventional method and the electronic circuit
substrate is then dipped in the acid copper plating solution
containing copper ions, an organic or inorganic acid, chloride
ions, and the polymer component at a concentration of 500 ppm or
more, whereupon copper is plated.
[0081] In plating copper, although it is possible to pass an
electric current after the plated material has been entirely
dipped, amore preferable method is applying a cathode potential to
the seed layer (conductor layer) when the material is dipped.
Either a constant voltage or a constant current may be used for
applying the cathode potential when dipping. A combination of these
and a combination of an additional means such as a pulse current or
PR current can also be used.
[0082] Next, an example of the electric potential controlling
method for plating will now be described. FIG. 10 shows a
controlling method of plating, consisting of a constant voltage
control and a two stage constant current control, using an
apparatus (for example, a chip tester shown in FIG. 9) having a
plating power supply 7, of which the cathode is connected to a
substrate 2 secured by a substrate holder 6 to function as a
cathode electrode and the anode is connected to an anode electrode
3.
[0083] In the example of the control shown in FIG. 10, the
substrate 2 is put into a plating bath 1 while applying a constant
voltage control between the cathode electrode and the anode
electrode (t.sub.0-t.sub.1), a low constant current i.sub.1 is
applied to gradually grow a plating film (t.sub.1-t.sub.2), then,
when the plating film has grown to a certain thickness, a high
constant current i.sub.2 (i.sub.2>i.sub.1) is applied to rapidly
grow the plating film and fill copper.
[0084] FIG. 3 shows another example of the control for the plating,
which initially employs a constant voltage control, followed by a
constant low current control, a constant current control after
reversing the anode and cathode, and finally a constant high
current control.
[0085] In the example of the control shown in FIG. 11, after
putting the substrate 2 into the plating bath while controlling at
a constant voltage, a low constant current i.sub.3 is passed to
gradually grow the plating film. Then, the current (voltage) is
switched to reverse the cathode electrode into the anode and the
anode electrode into the cathode, and a constant current (-i.sub.4)
is applied (t.sub.5-t.sub.6). After switching the direction of the
current (voltage), a high constant current i.sub.2
(i.sub.2>i.sub.1) is applied to rapidly grow the plating film
and fill copper. In this manner, the plated film near the openings
on the substrate surface in which the plated film becomes thick
faster than in the bottoms of the holes and trenches is etched
while the holes and trenches are filled, whereby flatness of the
resulting plated film can be improved.
[0086] Although the plating may be completed using the acid copper
plating solution containing 500 ppm or more of the above polymer
component, it is possible to fill the holes and trenches after
switching the acid copper plating solution to a conventional acid
copper plating solution containing a smaller amount (10-100 ppm) of
the polymer component.
[0087] In this instance, it is preferable to use the acid copper
plating solution containing 500 ppm or more of the above polymer
component until the plated film thickness on the substrate surface
becomes about 50-200 nm and to plate copper for the plated film
thickness from 200 nm to 2,000 nm using a conventional acid copper
plating solution containing a smaller amount (10-100 ppm) of the
polymer component.
[0088] Various plating apparatuses, such as a face-up type plating
apparatus (impregnation plating apparatus), a face-down type
plating apparatus (DMP: damascene metal plating), and a test
machine in a chip level, can be used for the second plating
method.
[0089] Plating conditions that can be employed are a current
density of 1-50 mA/cm.sup.2 and a plating solution temperature of
15-30.degree. C., while stirring by means of substrate rotation,
jet stream, or air bubbling.
[0090] As a typical example of the substrate on which uniform
plating is formed while preventing formation of voids using the
above-described second plating method, a semiconductor substrate
having holes and/or trenches with vias or an opening width of 1
.mu.m or less, preferably 0.1-0.2 .mu.m, an aspect ratio of 4 or
more, preferably 5 or more, and provided with a copper seed film of
about 1-100 nm on the surface can be given.
[0091] When significantly controlling the electrodeposition
reaction in the edge parts by using a strongly adsorptive
surfactant with strong hydrophobicity and controlling deposition of
copper on the other parts by using a less hydrophobic surfactant
with a smaller controlling effect, the surfactant with strong
hydrophobicity is used at a concentration lower than the
concentration of the surfactant with weak hydrophobicity in the
acid copper plating solution of the present invention taking into
consideration that the total area of the edge parts is smaller than
the total area of the other parts.
[0092] As a result of decreasing the concentration of the
surfactant with strong hydrophobicity, deposition is controlled
mainly in the edge parts by the acid copper plating solution of the
present invention, allowing less hydrophobic surfactants and other
additives to invade gaps to form uniform plating, not only on the
surface of the wafers but also in the gaps.
[0093] In the first plating method of the present invention,
filling properties are promoted by increasing the acid
concentration in the plating bath to 0.4 ml/l or more and, at the
same time, excellent in-plane uniformity is ensured by inserting an
electric resistance between the anode and the wafer.
[0094] The combination of these features has satisfied the two
contradictory characteristics of excellent in-plane uniformity and
excellent filling of fine circuit trenches and vias.
EXAMPLES
[0095] The present invention will be described in more detail by
way of Examples, Comparative Examples, and Reference Examples.
However, these examples should not be construed as limiting the
present invention.
[0096] The critical micelle concentration of the high molecular
weight surfactants used in the examples was determined as a value
saturating the surface tension of the copper sulfate plating
solution of the following composition obtained by measuring the
surface tension using a Traube's stalagmometer (the value is
hereinafter referred to as "measured cmc").
2 (Copper sulfate plating solution composition) Copper sulfate (as
pentahydrate) 180 g/l Sulfuric acid 25 g/l Chlorine 60 ppm
Example 1
[0097] Plating Test Using a Combination of Two Nonionic
surfactants
[0098] Polypropylene glycol (PPG) with a molecular weight of about
3,000 (as a nonionic surfactant with high hydrophobicity) and
polyethylene glycol (PEG) with a molecular weight of about 3, 000
(as a nonionic surfactant with low hydrophobicity) were added to
the above copper sulfate plating solution in amounts to provide
concentrations of 5 mg/l and 20 mg/l, respectively. As another
additive, 5 mg/l of bis(3-sulfopropyl)disulfide (SPS) was
added.
[0099] A test piece provided with fine trenches with a width of 180
nm and an aspect ratio of 5, made electrically conductive by a
known method, was plated using this copper-sulfate plating solution
under the following conditions.
3 (Plating conditions) Plating temperature: 25.degree. C. Current
density: 10 mA/cm.sup.2 Plating time: 1 minute
[0100] After plating, the fine trenches were cut and the copper
filling conditions were inspected using a microscope to confirm
that the copper was completely filled in without any voids.
[0101] Although the measured cmc of the PPG used was 20 mg/l and
that of the PEG was 20 mg/l, excellent filling of the fine trenches
was achieved by using PPG with high hydrophobicity at a
comparatively low concentration and PEG with low hydrophobicity at
a low concentration.
[0102] The reason is presumed to be as follows. PPG used at a low
concentration no greater than the measured cmc is preferentially
adsorbed near the openings of vias and can be adsorbed only with
difficulty to the bottom of the fine trenches, whereas PEG used at
a high concentration no lower than the measured cmc can be adsorbed
both to the bottom and openings of the fine trenches due to the
high concentration. As a result, both the PPG and PEG are adsorbed
near the openings of vias to significantly control plating.
Therefore, plating from the bottom of trenches without blocking the
openings is possible.
[0103] It is possible to use a suitable combination of nonionic
surfactants with different hydrophilicities and hydrophobicities
selected from the group consisting of natural lauryl alcohol,
natural alcohol, natural oleyl alcohol, synthetic primary alcohol,
nonylphenol ethoxylate, octylphenol ethoxylate, and special phenol
ethoxylate.
Example 2
[0104] Plating Test Using a Combination of a Nonionic Surfactant
and Another Surfactant
[0105] A combination of 20 mg/l of PEG with a molecular weight of
about 3,000 (as a nonionic surfactant) and 5 mg/l of
polyoxyethylene dimethyl ammonium chloride which is a cationic
surfactant (as another surfactant) was added to the above copper
sulfate plating solution. As another additive, 5 mg/l of SPS was
added.
[0106] The same plating test as in Example 1 was carried out to
examine the copper filling conditions in fine trenches. As a
result, excellent copper filling without voids was confirmed.
[0107] Although the measured cmc of the PEG used was 20 mg/l and
that of the polyoxyethylene dimethyl ammonium chloride was 20 mg/l
in this Example, excellent filling of fine holes was achieved by
using PEG which is a nonionic surfactant at a comparatively high
concentration of more than the measured cmc and polyoxyethylene
dimethyl ammonium chloride which is a cationic surfactant at a low
concentration below the measured cmc.
[0108] The same reason as in Example 1 is presumed for this
excellent filling. Specifically, polyoxyethylene dimethyl ammonium
chloride which is a cationic surfactant is preferentially adsorbed
near the opening of the fine trenches, but can be adsorbed only
with difficulty to the bottom of the vias, whereas PEG is adsorbed
both to the bottom and opening of the fine trenches. As a result,
both the polyoxyethylene dimethyl ammonium chloride and PEG are
adsorbed near the openings of the vias to significantly control
plating. Therefore, plating from the bottom of trenches without
blocking the openings is possible.
[0109] In addition to the above effects, the combination of a
nonionic surfactant at a comparatively high concentration and a
cationic surfactant at a comparatively low concentration exhibits
an effect of producing uniform plating in coarse and dense patterns
formed from fine holes and trenches.
[0110] Wafers and the like on which fine circuit patterns are
formed have an area with densely formed fine circuits and an area
with only sparsely formed circuits. The current supplied per unit
area is higher in the area in which fine circuits are densely
formed, whereas a cationic surfactant with a higher plating control
effect is attracted to the area with densely formed fine circuits
having a higher current value. As a result, a uniform plating
control effect can be obtained as a whole.
[0111] As other nonionic surfactants, a mono-long-chain alkyl-type
surfactant, di-long-chain alkyl-type surfactant, diamide quaternary
cationic surfactant, diester quaternary cationic surfactant,
alkylamine oxide, dimethyl diallyl ammonium chloride polymer,
polyoxypropylene diethyl methyl ammonium chloride, and the like can
be used.
Example 3
[0112] Plating Test Using a Combination of a Nonionic Surfactant
and Another Nonionic Surfactant Exhibiting Cationic Properties
Under Strongly Acidic Conditions
[0113] A mixture of 20 mg/l of PEG with a molecular weight of about
3,000 as a nonionic surfactant and 5 mg/l of an ethylenediamine
polyoxyethylene polyoxypropylene block polymer as another nonionic
surfactant exhibiting cationic properties under strongly acidic
conditions (pH<4) was added to the above copper sulfate plating
solution. As another additive, 5 mg/l of SPS was added.
[0114] The same plating test as in Example 1 was carried out to
examine the copper filling conditions in fine trenches. As a
result, excellent copper filling without voids was confirmed.
[0115] An amphoteric surfactant such as lauryl amide propyl acetic
acid betaine, lauryl aminoacetic acid betaine, or the like may be
used instead of the nonionic surfactant exhibiting cationic
properties under strongly acidic conditions.
Comparative Example 1
[0116] Plating Test Using a Combination of Two Nonionic
Surfactants
[0117] A plating solution was prepared in the same manner as in
Example 1, except that PPG as a nonionic surfactant with high
hydrophobicity and PEG as a nonionic surfactant with low
hydrophobicity were added to the copper sulfate plating solution in
amounts to provide concentrations of 20 mg/l and 5 mg/l,
respectively.
[0118] After plating, fine trenches were cut and the copper filling
conditions were inspected using a microscope to confirm that there
were seams and voids.
[0119] The reason for the occurrence of seams and voids is presumed
to be that the highly hydrophobic PPG is adsorbed onto the bottom,
in addition to the opening area, due to its high concentration of
the above measured cmc and exhibits the same plating control effect
on the opening area and the bottom to cause conformal deposition of
plating metal.
[0120] Production of seams and voids in fine trenches were also
confirmed in a plating test in which polyoxyethylene
dimethylammonium chloride, a cationic surfactant, was used instead
of PPG.
Reference Example 1
[0121] Selection of Electric Resistor
[0122] The electric resistor was selected from porous materials
which can allow impregnation of the plating solution thereinto.
Since the current between the electrodes flows through the plating
solution filled into the hollow parts of the electric resistor,
suitable selection of the electric resistor in respect of the
material quality, porosity, and pore size is essential. Therefore,
two types of materials, SiC and Al.sub.2O.sub.3, each having
different porosity and pore sizes were prepared. These materials
were inserted between the electrodes in an electroplating bath
filled with a plating solution. The electric current and voltage
were measured during a plating operation to determine the
resistance.
[0123] The resistance under the conditions in the absence of an
electric resistor was subtracted from the measured resistance. The
electric conductivity of the electric resistor was determined from
the resulting difference in resistance. The relation between
porosity and the electric conductivity and the relation between the
pore size and the electric conductivity are shown respectively in
FIG. 1 and FIG. 2. The electric conductivity tends to increase in
proportion to the porosity and as the pore size increases below a
certain value. Also, there was no impact on the quality of the
materials.
[0124] In view of the above results, the electric resistor having a
porosity and pore size respectively within the dotted lines shown
by the graphs was used. In regard to the material, SiC was selected
in view of its porosity with a good pore size distribution in the
plane.
Example 4
[0125] In-plane uniformity and filling performance in the case of
using an electric resistor were tested using the cell schematically
shown in FIG. 3. In the Figure, 1 indicates a plating cell, 2
indicates a wafer, 3 indicates an anode, 4 indicates an electric
resistor, 5 indicates a wafer seal, and 6 indicates a cathode. A
silicon wafer with a size of 200 mm.times.300 mm treated with
SiO.sub.2, TaN, Ta, and Cu in that order was used. Thicknesses of
20 nm and 60 nm were used for the copper seed layer.
[0126] The wafer was mounted on a stage with the process plane
upward. An SiC foil with a thickness of 10 mm was disposed between
the anode and the wafer. A seal for preventing leakage of the
plating solution and a cathode contact point were disposed on the
periphery of the wafer. The plating solution was introduced into
the space between the electric resistor and the wafer. The
composition of the plating solution and the plating conditions were
as follows.
4 (Plating solution composition) Copper sulfate pentahydrate 225
g/l Sulfuric acid 55 g/l Chlorine 60 ppm Additive (PEG) 22 ml/l
(Plating conditions) Current: Direct current Current density: 20
mA/cm.sup.2 Bath temperature: 25.degree. C. Plating time: 2
minutes
[0127] (Measuring Method)
[0128] The film thickness after plating was determined by measuring
the sheet resistance of the copper film using the direct-current
four-probe method and converting the resistance into the film
thickness using a known resistance-thickness conversion rate. The
in-plane distribution and uniformity of the film thickness were
determined by measuring the thickness at 355 points within 4 mm
inside the edge in the diameter direction.
[0129] (Test Result)
[0130] FIG. 4 shows a result of measuring a film thickness
distribution in the periphery of a 200 mm wafer and FIG. 5 shows a
result of measuring a film thickness distribution in the periphery
of a 300 mm wafer. The in-plane distribution in the case of the
seed film thickness of 20 nm was almost the same as that in the
case of the seed film thickness of 60 nm. No tendency of a film
thickness increase in the edge portion was identified. The in-plane
uniformity (3.sigma.) obtained when plating a 300 mm substrate to
produce a 1.0 .mu.m plating film was 3% or less.
Example 5
[0131] A substrate with a thickness of 300 mm with a 60 nm copper
seed layer formed thereon (pretreated in the same manner as in
Example 1) was plated under the following conditions for a period
of time to produce films with an average thickness of 0.5 .mu.m,
1.0 .mu.m, and 2.5 .mu.m. After plating, the film thickness
distribution was measured. The results are shown in FIG. 6. In any
of the cases of an average thickness of 0.5 .mu.m, 1.0 .mu.m, and
2.5 .mu.m, the in-plane uniformity (3.sigma.) was 2.2-3.3%,
indicating that there was no significant thickness change in the
in-plane distribution.
5 (Plating solution composition) Copper sulfate pentahydrate 225
g/l Sulfuric acid 55 g/l Chlorine 60 ppm Additive (PEG) 22 ml/l
(Plating conditions) Current: Direct current Current density: 20
mA/cm.sup.2 Bath temperature: 25.degree. C.
[0132] The relation between the sulfuric acid concentration and
electric conductivity of the copper sulfate plating solution is
shown in FIG. 7, which shows that conventional plating without
using an electric resistor was effected at the sulfuric acid
concentration in the range of 10-60 g/l and the electric
conductivity in the range of 6-20 S/m. In contrast, based on the
fact that plating was possible at the electric conductivity of 3
S/m or less as shown in FIGS. 2 and 3, it can be judged that
excellent in-plane uniformity was achieved when an electric
resistor was used.
[0133] FIG. 8 shows the calculation result of the electric
conductivity and thickness distribution (recess conditions in the
center of the wafer) when the seed layer was varied by the finite
element method (FEM). The result also shows the effect of the seed
film thickness on the electric conductivity and film thickness
distribution.
Example 6
[0134] A barrier layer and copper seed layer (with a seed layer
thickness of 80 nm near the vias) were formed according to a
conventional method on a semiconductor silicon substrate having
vias with an opening of 0.14 .mu.m and an aspect ratio of 5 formed
thereon to prepare a test sample. This test sample was used for a
plating test using the acid copper plating solution 1 having the
composition shown below and a chip testing instrument (liquid
volume: 1 1) schematically shown in FIG. 9. Plating was carried out
at a current density of 3 mA/cm.sup.2, a plating bath temperature
of 25.degree. C., and mechanical stirring using a stirrer at no
more than 400 rpm for 3 minutes.
6 (Composition of plating solution 1) CuSO.sub.4.5H.sub.2O 200 g/l
H.sub.2SO.sub.4 10 mol/l Cl.sup.- 60 ppm PEG (molecular weight:
about 3,000) 1,000 ppm SPS 5 ppm Polyethylene imine 1 ppm
[0135] The section of vias after plating was inspected by a
scanning electron microscope (SEM) to confirm that there were no
voids produced.
Example 7
[0136] A plating test was carried out on the sample of Example 6
using the plating solution 1 of Example 6 and the following plating
solution 2 in two chip testing instruments. Plating was carried out
at a current density of 15 mA/cm.sup.2 for 5 seconds using the
plating solution 1, then at a current density of 6 mA/cm.sup.2 for
3 minutes using the plating solution 2. The plating bath
temperature was 25.degree. C.
7 (Composition of plating solution 2) CuSO.sub.4.5H.sub.2O 200 g/l
H.sub.2SO.sub.4 10 mol/l Cl.sup.- 60 ppm PEG (molecular weight:
about 3,000) 200 ppm SPS 5 ppm Polyethylene imine 1 ppm
[0137] The section of vias after plating was inspected by SEM to
confirm that there were no voids produced.
Comparative Example 2
[0138] A plating test was carried out in the same manner as in
Example 6 using the same sample of Example 6, except that the
plating solution 3 with the following composition was used.
8 (Composition of plating solution 3) CuSO.sub.4.5H.sub.2O 200 g/l
H.sub.2SO.sub.4 10 mol/l Cl.sup.- 60 ppm PEG (molecular weight:
about 3,000) 200 ppm SPS 5 ppm Polyethylene imine 1 ppm
[0139] The section of vias after plating was inspected by SEM to
confirm that there were no voids produced.
INDUSTRIAL APPLICABILITY
[0140] The acid copper plating solution of the present invention
can be applied to the surface of wafers or the like having
submicron-level gaps to completely fill the gaps with copper
plating and, at the same time, form highly uniform copper plating
at a higher electrocoating speed.
[0141] According to the first plating method of the present
invention, copper plating with excellent in-plane thickness
uniformity can be obtained without being affected by the seed film
thickness and plating thickness by using a plating bath with a
specific acid concentration and inserting an electric resistor
between the electrodes. In particular, because excellent filling
can be ensured even in the case in which a concave-convex pattern
on a semiconductor substrate contains circuit trenches or vias with
a width of 0.1 .mu.m or less, the method is expected as a useful
means for achieving excellent in-plane uniformity in the copper
wiring plating after the 65 nm generation.
[0142] According to the second plating method of the present
invention, uniform plating can be ensured while preventing void
formation, even in very small holes and trenches where the copper
seed film is extremely thin without causing copper to be dissolved
in the plating solution.
[0143] Therefore, the present invention is extremely useful as a
technology for plating the surface of wafers, which are
semiconductor materials, particularly for forming circuit patterns
having submicron-level trenches on electronic circuit substrates
such as wafers, semi-conductor substrates, or printed boards by
using metal plating such as copper plating. The present invention
can therefore be used with advantage for manufacturing next
generation electronic circuit boards with an increasing density of
wiring circuits.
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