U.S. patent application number 13/729721 was filed with the patent office on 2013-11-07 for electroless copper plating bath and electroless copper plating method.
This patent application is currently assigned to C. UYEMURA & CO., LTD.. The applicant listed for this patent is C. UYEMURA & CO., LTD.. Invention is credited to Teruyuki HOTTA, Takahiro ISHIZAKI, Tomoharu NAKAYAMA.
Application Number | 20130295294 13/729721 |
Document ID | / |
Family ID | 49512720 |
Filed Date | 2013-11-07 |
United States Patent
Application |
20130295294 |
Kind Code |
A1 |
ISHIZAKI; Takahiro ; et
al. |
November 7, 2013 |
ELECTROLESS COPPER PLATING BATH AND ELECTROLESS COPPER PLATING
METHOD
Abstract
Provided are an electroless copper plating bath and an
electroless copper plating method using the electroless copper
plating bath, the electroless copper plating bath not containing
formaldehyde; being usable under approximately neutral pH
conditions; improving plating bath stability; and capable of
forming a plating film with a good thickness while controlling
deposition outside a pattern. The electroless copper plating bath
according to the present invention contains a water-soluble copper
salt, and amine borane or a substituted derivative thereof as a
reducing agent; does not contain formaldehyde; and has a pH of 4 to
9, wherein polyaminopolyphosphonic acid as a complexing agent, an
anionic surface-active agent, an antimony compound, and a
nitrogen-containing aromatic compound are contained.
Inventors: |
ISHIZAKI; Takahiro; (Osaka,
JP) ; NAKAYAMA; Tomoharu; (Osaka, JP) ; HOTTA;
Teruyuki; (Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
C. UYEMURA & CO., LTD. |
Osaka-shi |
|
JP |
|
|
Assignee: |
C. UYEMURA & CO., LTD.
Osaka-shi
JP
|
Family ID: |
49512720 |
Appl. No.: |
13/729721 |
Filed: |
December 28, 2012 |
Current U.S.
Class: |
427/437 ;
106/1.23; 427/443.1 |
Current CPC
Class: |
C23C 18/1651 20130101;
C23C 18/1633 20130101; C23C 18/08 20130101; C23C 18/166 20130101;
C23C 18/1605 20130101; C23C 18/40 20130101 |
Class at
Publication: |
427/437 ;
427/443.1; 106/1.23 |
International
Class: |
C23C 18/08 20060101
C23C018/08; C23C 18/16 20060101 C23C018/16 |
Foreign Application Data
Date |
Code |
Application Number |
May 7, 2012 |
JP |
2012-105924 |
Claims
1. An electroless copper plating bath, comprising a water-soluble
copper salt, and amine borane or a substituted derivative thereof
as a reducing agent; not comprising formaldehyde; and having a pH
of 4 to 9, wherein polyaminopolyphosphonic acid as a complexing
agent, an anionic surface active agent, an antimony compound, and a
nitrogen-containing aromatic compound are comprised.
2. The electroless copper plating bath according to claim 1,
wherein a concentration of the polyaminopolyphosphonic acid is 0.01
to 1 mol/L.
3. The electroless copper plating bath according to claim 1,
wherein a concentration of the anionic surface active agent is 0.01
to 2000 mg/L.
4. The electroless copper plating bath according to claim 1,
wherein a concentration of the antimony compound is 0.1 to 20
mg/L.
5. The electroless copper plating bath according to claim 1,
wherein a concentration of the nitrogen-containing aromatic
compound is 0.01 to 1000 mg/L.
6. An electroless copper plating method, wherein a copper plating
film is formed on a base material by using the electroless copper
plating bath according to claim 1.
7. The electroless copper plating method according to claim 6,
wherein the base material is made of aluminum or aluminum alloy, or
magnesium or magnesium alloy.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an electroless copper
plating bath and an electroless copper plating method, more
specifically, an electroless copper plating bath not containing
formaldehyde and being usable at approximately neutral pH, and an
electroless copper plating method using the electroless copper
plating bath.
[0003] The present application asserts priority rights based on JP
Patent Application 2012-105924 filed in Japan on May 7, 2012. The
total contents of disclosure of the patent application of the
senior filing date are to be incorporated by reference into the
present application.
[0004] 2. Description of the Related Art
[0005] Formaldehyde has been used for a conventional electroless
copper plating bath as a reducing agent for copper ions. However,
the vapor pressure of formaldehyde is high, and deterioration of
work environment by the irritating odor and harmful effects on the
human body due to carcinogenicity have been pointed out. In
addition, an electroless copper plating bath using formaldehyde is
strongly alkaline, whereby a material to be plated is damaged and
easily deteriorates, and thus the electroless copper plating bath
can not be effectively used, for example, for metal, such as
aluminum or aluminum alloy, and the use has been limited.
[0006] On the other hand, for example, as disclosed in Japanese
Patent Application Laid-Open No. 2001-131761, an electroless copper
plating bath not containing formaldehyde as a reducing agent, but
containing amine borane or a derivative thereof has been proposed.
Amine borane is usable as a reducing agent under neutral to weakly
alkaline pH conditions, thereby preventing deterioration of a
material to be plated and being usable with high safety.
[0007] However, amine borane has a considerably high reducing
power, and has a problem that a plating bath is easily decomposed.
There has not been an electroless copper plating bath solution
containing amine borane as a reducing agent while having good bath
stability and high practicality.
[0008] In the case where formaldehyde is used as a reducing agent,
the formaldehyde shows a strong reduction power selectively over
the surface of metal, such as palladium and copper, while has a
weak reducing action in a plating bath, and therefore deposition
does not take place easily on a portion other than a pattern
(metal). On the other hand, a borane compound, such as
dimethylamine borane, has a reducing power strong enough to reduce
water to hydrogen, thereby reducing metal ions to metal not only on
a metal but also in a plating bath, and therefore there has been a
problem that the selectivity onto a pattern is low, and accordingly
deposition takes place outside a pattern. [0009] PTL 1: Japanese
Patent Application Laid-Open No. 2001-131761
[0010] The present invention is proposed in view of such
conventional actual circumstances, and the purpose of the present
invention is to provide an electroless copper plating bath and an
electroless copper plating method using the electroless copper
plating bath, the electroless copper plating bath not containing
formaldehyde; being usable under approximately neutral pH
conditions; improving plating bath stability; and being capable of
forming a plating film with a good thickness while controlling
deposition outside a pattern.
SUMMARY OF THE INVENTION
[0011] The present inventors earnestly studied to achieve the
above-mentioned purpose, and, as a result, found that, in a
formaldehyde-free electroless copper plating bath, controlling the
balance of promotion and inhibition of plating deposition enabled
deposition outside a pattern to be effectively controlled while
enabled a plating film with a good thickness to be formed, and
completed the present invention.
[0012] In other words, an electroless copper plating bath according
to the present invention is an electroless copper plating bath
containing a water-soluble copper salt, and amine borane or a
substituted derivative thereof as a reducing agent; not containing
formaldehyde; and having a pH of 4 to 9, wherein
polyaminopolyphosphonic acid as a complexing agent, an anionic
surface-active agent, an antimony compound, and a
nitrogen-containing aromatic compound are contained.
[0013] An electroless copper plating method according to the
present invention is characterized in that a copper plating film is
formed on a substrate by using the above-mentioned electroless
copper plating bath.
[0014] According to the present invention, the electroless copper
plating bath can be used under approximately neutral pH conditions,
and plating treatment can be performed for a material to be plated
without causing damage. In addition, plating deposition outside a
pattern can be effectively controlled, and a plating film with a
good thickness can be formed. Thus, plating treatment is performed
simply and easily without providing a barrier layer or the like for
a base material made of aluminum, aluminum alloy, or the like, and
the electroless copper plating bath can be suitably used for
manufacturing of semiconductor wafers and the like.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a graph showing a relationship between an antimony
concentration in an electroless copper plating bath and a
deposition film thickness.
[0016] FIG. 2 is a graph showing a relationship between an antimony
concentration in an electroless copper plating bath and a
deposition film thickness.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] A specific embodiment of an electroless copper plating bath
and an electroless copper plating method according to the present
invention (hereinafter, referred to as the present embodiment) will
be described in detail in the following order.
[0018] 1. Electroless Copper Plating Bath
[0019] 2. Electroless Copper Plating Method
[0020] 3. Examples
1. ELECTROLESS COPPER PLATING BATH
[0021] The electroless copper plating bath according to the present
embodiment is an electroless copper plating bath, not containing
formaldehyde, that is, what is called a formaldehyde- (formalin-)
free plating bath; containing a water-soluble copper salt, and
amine borane or a substituted derivative thereof as a reducing
agent; and having a pH of 4 to 9. The electroless copper plating
bath is characterized in that polyaminopolyphosphonic acid as a
complexing agent, an anionic surface active agent, an antimony
compound, and a nitrogen-containing aromatic compound are
contained.
[0022] As mentioned above, the electroless copper plating bath
according to the present embodiment does not contain a reducing
agent, such as formaldehyde or glyoxylic acid, which is used under
strongly alkaline pH conditions, but contains amine borane or a
substituted derivative thereof as a reducing agent, which can be
used under neutral to weakly alkaline pH conditions. Thus, unlike
the case of a plating bath of strongly alkaline pH in which
formaldehyde or the like is used as a reducing agent, a metal base
material used as a material to be plated is not damaged. Therefore,
the electroless copper plating bath according to the present
embodiment can be suitably used, for example, as a plating bath to
form a plating film for a semiconductor wafer made of aluminum,
aluminum alloy, or the like, and can form a good plating film.
[0023] In the case where amine borane or a substituted derivative
thereof is used as a reducing agent, there is a problem that, due
to the very strong reducing power, a plating bath easily
decomposes, and deposition outside a pattern formed on a base
material to be plated is produced, and thus the pattern selectivity
is low. However, the electroless copper plating bath according to
the present embodiment contains polyaminopolyphosphonic acid as a
complexing agent, an anionic surface active agent, an antimony
compound, and a nitrogen-containing aromatic compound, as mentioned
above, whereby stability of the plating bath can be increased and
the balance of promotion and inhibition of plating deposition can
be controlled, and, with a higher pattern selectivity, a plating
film with a good thickness can be formed.
[0024] Such electroless copper plating bath can simply and easily
form a good plating film having no plating protrusion on a metal
base material, such as aluminum or aluminum alloy, or magnesium or
magnesium alloy, without providing a barrier layer or the like
thereon to prevent deposition outside a pattern, and can be
suitably used, for example, in manufacturing of semiconductor
wafers.
[0025] <Water-Soluble Copper Salt>
[0026] Examples of a water-soluble copper salt include copper
sulfate, copper nitrate, copper chloride, copper acetate, copper
citrate, copper tartrate, and copper gluconate, and these
water-soluble copper salts may be used alone or two or more kinds
of these may be mixed at an arbitrary ratio and used.
[0027] As a concentration of the water-soluble copper salt, for
example, a copper concentration may be 0.005 to 0.5 mol/L,
preferably 0.01 to 0.5 mol/L, more preferably 0.05 to 0.1 mol/L.
When the concentration of the water-soluble copper salt is less
than 0.005 mol/L, a deposition rate is slower and a plating time is
longer, which is not economical. On the other hand, when the
concentration exceeds 0.5 mol/L, an amount of pumping increases and
a cost rises, and in addition, a plating solution is unstable.
Furthermore, nodules and roughness are easily formed and pattern
characteristics are lowered.
[0028] <Reducing Agent>
[0029] Examples of amine borane or a substituted derivative thereof
as a reducing agent include dimethylamine borane, tert-butylamine
borane, triethylamine borane, and trimethylamine borane.
[0030] Amine borane or a substituted derivative thereof is a
reducing agent which is usable at neutral to weakly alkaline pH.
Accordingly, amine borane or a substituted derivative thereof is
not used for a plating bath having a strongly alkaline pH, such as
a plating bath using an aldehyde reducing agent, such as
formaldehyde and glyoxylic acid, and therefore damage to a metal
base material or the like to be plated is controlled, and
deterioration thereof can be prevented. In addition, unlike an
aldehyde reducing agent, amine borane or a substituted derivative
thereof can exclude deterioration of work environment and harmful
effects on the human body, whereby safety can be improved.
[0031] A concentration of amine borane or a substituted derivative
thereof as a reducing agent is preferably 0.01 to 0.5 mol/L.
[0032] <Complexing Agent>
[0033] The electroless copper plating bath according to the present
embodiment contains polyaminopolyphosphonic acid as a complexing
agent.
[0034] Polyaminopolyphosphonic acid can easily complex copper ions
efficiently at approximately neutral pH, and control decomposition
of a plating bath and improve the stability.
[0035] Specific examples of polyaminopolyphosphonic acid include
N,N,N',N'-ethylenediaminetetrakis(methylene phosphonic acid),
nitrilotris(methylene phosphonic acid), diethylenediamine
penta(methylene phosphonic acid), diethylenetriamine
penta(methylene phosphonic acid), bis(hexamethylene triamine
penta(methylene phosphonic acid)), and glycine N,N-bis(methylene
phosphonic acid).
[0036] A concentration of polyaminopolyphosphonic acid as a
complexing agent is not particularly limited, but preferably 0.01
to 1 mol/L. When the concentration is less than 0.01 mol/L, copper
ions cannot fully be complexed and a plating bath could become
unstable. On the other hand, when the concentration exceeds 1
mol/L, an amount of pumping increases and a cost rises. In
addition, a deposition rate of copper is slower and a plating time
is longer, which is not economical. Furthermore, a base film could
be damaged and degraded.
[0037] <Anionic Surface Active Agent>
[0038] The electroless copper plating bath according to the present
embodiment contains an anionic surface active agent. When an
anionic surface active agent is made to be contained, stability of
a plating bath can be improved.
[0039] A detailed mechanism which improves stability of a plating
bath is not certain, but, it is presumed that, when an anionic
surface active agent is added, the anionic surface active agent
adsorbs to metal particles produced in a plating bath, thereby
inhibiting the particles from further growing, and thus there is an
effect that dissolution of the particles by the above-mentioned
complexing agent and other additives is promoted. Furthermore, as a
factor in improvement of bath stability, it also can be presumed
that the dispersion effect by the anionic surface active agent
inhibits the metal particles formed in a plating bath from
agglomerating and growing.
[0040] On the other hand, adsorptivity of a cationic surface active
agent to the surfaces of metal particles is too high, and therefore
plating deposition is inhibited (Once a cationic surface active
agent adsorbs to the surfaces, it is difficult to separate the
cationic surface active agent from the surfaces.). Compared with an
anionic surface active agent or a cationic surface active agent, a
nonionic surface active agent has lower adsorptivity to metal
particles and lower effects in improving bath stability. The
electroless copper plating bath has a high salt concentration,
whereby a cloud point of a nonionic surface active agent is lowered
and turbidity is easily produced. Furthermore, when a concentration
of a nonionic surface active agent is made high, the nonionic
surface active agent has a high foaming property, whereby it
becomes difficult to raise the concentration in order to improve
bath stability.
[0041] Specific examples of the anionic surface active agent
include an alkyl carboxylic acid surface active agent; naphthalene
sulfonate formaldehyde condensate, such as sodium salt of
.alpha.-naphthalenesulfonic acid formalin condensate (for example,
DEMOL N manufactured by Kao Corp., and LAVELIN series manufactured
by Dai-Ichi Kogyo Seiyaku Co., Ltd.); polyoxy alkylene ether
sulfate, such as sodium polyoxyethylene lauryl ether sulfate (for
example, EMAL 20C manufactured by Kao Corp.) and polyoxyethylene
alkyl ether sulfate triethanolamine (for example, EMAL 20T
manufactured by Kao Corp.); higher alcohol sulfuric ester or its
salt, such as sodium dodecyl sulfate (for example, EMAL 10G
manufactured by Kao triethanolamine dodecyl sulfurate (for example,
EMAL TD manufactured by Kao Corp.), and dodecyl ammonium sulfate
(for example, EMAL AD-25 manufactured by Kao Corp.); alkylbenzene
sulfonic acid or its salt, such as sodium dodecyl benzene sulfonate
(for example, NEOPELEX GS manufactured by Kao Corp., UPON LH-200
manufactured by Lion Corp., and MONOGEN Y-100 manufactured by
Dai-Ichi Kogyo Seiyaku Co., Ltd.), and linear alkyl benzene
sulfonate sodium (for example, NEOGEN S-20F manufactured by
Dai-Ichi Kogyo Seiyaku Co., Ltd.); an alkyl sulfosuccinate ester
surface active agent, such as sodium dialkyl sulfosuccinate (for
example, PELEX OT-P manufactured by Kao Corp., ADEKA COL EC-series
manufactured by ADEKA Corp.), disodium lauryl sulfosuccinate (for
example, NEO-HITENOL LS manufactured by Dai-Ichi Kogyo Seiyaku Co.,
Ltd.), and sodium dioctyl sulfosuccinate (for example, NEOCOL SW-C
manufactured by Dai-Ichi Kogyo Seiyaku Co., Ltd.); polyoxyethylene
alkyl sulfosuccinic acid or its salt (for example, NEO-HITENOL S-70
manufactured by Dai-Ichi Kogyo Seiyaku Co., Ltd.); monoalkyl
phosphoric ester or its salt (for example, ADEKA COL
PS/CS/TS-series manufactured by ADEKA Corp., and Phosphanol series
manufactured by Toho Chemical Industry Co., Ltd.); polyoxyethylene
alkyl ether phosphoric acid or its salt, such as polyoxyethylene
tridecyl ether phosphoric ester (for example, PLYSURF A212C
manufactured by Dai-Ichi Kogyo Seiyaku Co., Ltd.) and
polyoxyethylene lauryl ether phosphoric ester (for example, PLYSURF
A208B manufactured by Dai-Ichi Kogyo Seiyaku Co., Ltd.); and
.alpha.-olefin sulfonic acid or its salt (for example, NEOGEN AO-90
manufactured by Dai-Ichi Kogyo Seiyaku Co., Ltd.).
[0042] A concentration of the anionic surface active agent is not
particularly limited, but preferably 0.01 to 2000 mg/L. When the
concentration is less than 0.01 mg/L, an effect as a stabilizer is
not fully obtained and a plating bath could become unstable.
Furthermore, nodules and roughness are easily formed. On the other
hand, when the concentration exceeds 2000 mg/L, a foaming property
is too high. Furthermore, water washability in a downstream process
falls, and treatment of waste liquid and waste water becomes
difficult.
[0043] <Antimony Compound>
[0044] The electroless copper plating bath according to the present
embodiment contains an antimony compound. Thus, when an antimony
compound is added, an effect of promotion of plating deposition by
underpotential deposition phenomenon and an effect of deposition
inhibition by a catalyst poison effect accompanying adsorption of
antimony are balanced, whereby an effect of improvement in
deposition rate and an effect of inhibition of plating protrusion
can be obtained.
[0045] Note that the underpotential deposition phenomenon means a
phenomenon in which, at the time when an element (antimony) to be
added is redissolved as an ion immediately after being reduced,
electrons are emitted, whereby deposition of target metal (copper)
is promoted, and thus metal deposits at an electric potential lower
than a theoretically-calculated deposition potential.
[0046] Specifically, in antimony compounds, the influence of a
concentration thereof on deposition rate of the plating metal can
be expressed graphically as a curve protruding upward, in other
words, in both cases where the concentration is too low and too
high, a deposition rate is slower, and there is a concentration at
which a deposition rate is maximum. Thus, it is presumed that the
inhibition appears at a pattern end portion (edge portion) to which
antimony easily adsorbs, while, mainly the promotion appears at
portions, other than the edge portion, to which antimony hardly
adsorbs, whereby, even if a deposition rate is high, spread of
plating deposition outside a pattern can be controlled.
[0047] Here, a relationship between a deposition rate of plating
metal and a concentration of an antimony compound will be
specifically explained with reference to specific experiment
examples.
[0048] First, in Experiment Example 1, a sample was obtained in
such manner that, on an Al--Si alloy sputtered film formed on a
silicon wafer, a pattern was formed with a TiN film, and then a
double zincate treatment was performed in accordance with the usual
method, and the sample was immersed in an electroless copper
plating bath having the following composition for 1 hour to perform
electroless copper plating treatment, whereby a copper plating film
was formed on the pattern.
[0049] (Composition of Electroless Copper Plating Bath)
[0050] Ethylene diamine tetra(methylene phosphonic acid): 0.08
mol/L
[0051] Copper (copper sulfate pentahydrate): 0.063 mol/L (4 g/L as
a copper concentration)
[0052] Dimethylamine borane: 8 g/L
[0053] Sodium lauryl sulfate: 20 mg/L
[0054] o-phenanthroline: 4 mg/L
[0055] Antimony oxide: refer to Table 1 below. (as an antimony
concentration)
[0056] pH: 7.7
[0057] Bath temperature: 60 degrees C.
[0058] Then, a film thickness of the formed plating film, an amount
of deposition outside the pattern (a protrusion amount), and
plating appearance were examined. Table 1 below shows each
measurement result. FIG. 1 shows variations of deposition film
thickness with respect to a concentration of antimony in the
electroless copper plating bath. Note that, in Table 1 below,
"bridge" in the evaluation of plating protrusion represents a state
in which patterns are connected each other by plating protrusion,
while "occurrence of edge thinning" in the evaluation of appearance
represents a phenomenon in which a film thickness of a periphery
portion of a substrate/pad is thinner. Note that a minus value of
plating protrusion represents a state in which plating does not
deposit at a pattern edge portion due to occurrence of edge
thinning, whereby the base is exposed.
TABLE-US-00001 TABLE 1 Antimony Deposition Film Plating
Concentration Thickness Protrusion [mg/L] [um/hrs] [um] Appearance
0 1.9 Bridge Normal 1 4.7 20 Normal 2 5.3 5 Normal 3 5.9 5 Normal 4
9.4 0 Occurrence of Edge Thinning 5 7.5 -10 Occurrence of Edge
Thinning 10 6.8 -15 Occurrence of Edge Thinning 20 No Deposition No
Deposition No Deposition
[0059] It is understood that, when plating treatment is performed
under the above-mentioned conditions of the plating bath
composition and the base in Experiment Example 1, as shown in Table
1, in the cases of no addition and a lower concentration of
antimony and a higher concentration of antimony, a plating
deposition rate is slower, and a plating film thickness is thinner
while abnormalities in deposition at a pattern edge portion are
caused. On the other hand, it is understood that, when an antimony
concentration is in the approximately middle of a concentration
range shown in Table 1, a plating film with a good thickness is
formed, and spread of plating deposition outside a pattern and
occurrence of edge thinning are controlled.
[0060] Next, in Experiment Example 2, a sample was obtained in such
manner that, in accordance with the usual method, a palladium
substitution treatment was performed for a ceramic substrate on
which a pattern was formed with a nickel film, and the sample was
immersed in an electroless copper plating bath having the same
composition as in Experiment Example 1 for 1 hour to perform an
electroless copper plating treatment, whereby a copper plating film
was formed on the pattern. In other words, there was examined a
relationship between a deposition rate of plating metal and a
concentration of an antimony compound in the case of changing
conditions of the base for which plating treatment is to be given.
Note that a concentration of antimony oxide which was one of
compositions of the plating bath (as an antimony concentration) was
changed as shown in Table 2 below.
[0061] Then, a film thickness of the formed plating film, an amount
of deposition outside the pattern (a protrusion amount), and
plating appearance were examined. Table 2 below shows each
measurement result. FIG. 2 shows variations of deposition film
thickness with respect to a concentration of antimony in the
electroless copper plating bath. Note that terms used for the
evaluation shown in Table 2 below represent the same as those used
in Table 1 above.
TABLE-US-00002 TABLE 2 Antimony Deposition Film Plating
Concentration Thickness Protrusion [mg/L] [um/hrs] [um] Appearance
0 2.8 Bridge Normal 0.5 3.2 12 Normal 1 5.0 28 Normal 2 6.5 20
Normal 3 7.5 15 Normal 4 9.4 8 Normal 5 9.5 10 Normal 8 10.4 -5
Occurrence of Edge Thinning 10 10.2 -10 Occurrence of Edge Thinning
20 8.5 -30 No Deposition at Edge Portion
[0062] As shown in Table 2, it is understood that, also in the case
of changing conditions of the base, both when antimony is not added
and when a concentration of antimony is low or high, a plating
deposition rate is slower, and a plating film thickness is thinner
while abnormalities in deposition at a pattern edge portion are
caused. On the other hand, it is understood that, when an antimony
concentration is in the approximately middle of a concentration
range shown in Table 2, a plating film with a good thickness is
formed, and spread of plating deposition outside a pattern and
occurrence of edge thinning are controlled.
[0063] As shown in Experiment Examples 1 and 2 mentioned above, it
is clearly understood that, although depending on conditions of a
plating bath composition and a plating base, stirring conditions,
and the like, a deposition rate is slower in both cases where an
antimony concentration is too low and too high, and there is a
concentration range in which a plating deposition rate is maximum.
And it is understood that, in the concentration range in which a
plating deposition rate is maximum, the inhibition of plating
deposition appears at a pattern end portion (edge portion) to which
antimony easily adsorbs, while mainly the promotion of plating
deposition appears at portions, other than a pattern edge portion,
to which antimony hardly adsorbs, whereby a plating film with good
thickness is formed while spread (plating protrusion) of plating
deposition outside a pattern can be controlled.
[0064] Therefore, by thus adding a predetermined concentration of
an antimony compound to a plating bath, an effect of improvement in
a deposition rate and an effect of inhibition of plating protrusion
can be obtained based on the balance between an effect of promotion
of plating deposition and an effect of deposition inhibition by an
catalyst poison effect accompanying adsorption of antimony, whereby
pattern selectivity can be increased, and a plating film with a
good film thickness in which plating protrusion is controlled can
be formed.
[0065] As mentioned above, a specific amount (concentration) of an
antimony compound added is different depending on conditions of
other composition components of plating bath (plating composition)
and a base, stirring conditions, and the like, thereby being
preferably suitably changed in accordance with those conditions,
but, for example, may be 0.1 to 20 mg/L, preferably 0.5 to 10 mg/L,
more preferably 1 to 4 mg/L.
[0066] The antimony compound is not limited so far as it is a
water-soluble compound which dissolves in a plating bath, and for
example, antimony oxide, antimony chloride, and the like may be
used.
[0067] <Nitrogen-Containing Aromatic Compound>
[0068] The electroless copper plating bath according to the present
embodiment contains a nitrogen-containing aromatic compound.
[0069] Conventionally, a nitrogen-containing aromatic compound,
such as example 2,2'-bipyridyl and 1,10-phenanthroline, has been
used as a stabilizer or an agent to improve film
physical-properties, of a plating bath. However, although a
detailed mechanism is not certain, when a nitrogen-containing
aromatic compound is added to the electroless copper plating bath
according to the present embodiment, the nitrogen-containing
aromatic compound comes to act as an promoter which promotes metal
plating.
[0070] Specific examples of the nitrogen-containing aromatic
compound include imidazole or a substituted derivative thereof;
pyrazole or a substituted derivative thereof; oxazole or a
substituted derivative thereof; thiazole or a substituted
derivative thereof; pyridine or a substituted derivative thereof;
pyrazine or a substituted derivative thereof; pyrimidine or a
substituted derivative thereof; pyridazine or a substituted
derivative thereof; triazine or a substituted derivative thereof;
benzothiophene or a substituted derivative thereof; benzothiazole
or a substituted derivative thereof; pyridine or a substituted
derivative thereof, such as 2,2'-dipyridyl, 4,4'-dipyridyl,
nicotinic acid, nicotinamide, picoline, or lutidine; quinoline or a
substituted derivative thereof, such as hydroxyquinoline; acridine
or a substituted derivative thereof, such as
3,6-dimethylaminoacridine, proflavine, acridine acid, or
quinoline-1,2-dicarboxylic acid; pyrimidine or a substituted
derivative thereof, such as uracil, uridine, thymine, 2-thiouracil,
6-methyl-2-thiouracil, or 6-propyl-2-thiouracil; phenanthroline or
a substituted derivative thereof, such as 1,10-phenanthroline,
neocuproine, or bathophenanthroline; and purine or a substituted
derivative thereof, such as aminopurine, adenine, adenosine,
guanine, hydantoin, adenosine, xanthin, hypoxanthine, caffeine,
theophylline, theobromine, or aminophylline.
[0071] A concentration of the nitrogen-containing aromatic compound
is not limited, but preferably 0.01 to 1000 mg/L. When the
concentration is less than 0.01 mg/L, an effect as a promoter is
not obtained, and a deposition rate is slower and a plating time is
longer, which is not economical. Furthermore, deposition of copper
at an initial stage is poorer, whereby a base material could be
damaged and an undeposited portion could be produced. On the other
hand, when the concentration exceeds 1000 mg/L, a deposition rate
is too high, so that a rough film is produced. In addition, nodules
and roughness are easily formed, and pattern characteristics are
lowered. Furthermore, a plating bath could become unstable.
[0072] <Other Conditions>
[0073] The plating bath has a pH of 4.0 to 9.0, preferably a pH of
5.0 to 9.0, more preferably a pH of 6.0 to 8.0. As mentioned above,
the electroless copper plating bath according to the present
embodiment contains, as a reducing agent, amine borane or a
substituted derivative thereof, which is usable under neutral to
alkaline pH conditions. Thus, the electroless copper plating bath
can be used in a range of pH 4.0 to pH 9.0, and plating treatment
can be performed without giving damage to a base material to be
plated.
[0074] Here, when the pH is less than 4.0, natural consumption of
the reducing agent increases, thereby leading to an increase in
cost, and the plating bath becomes unstable. On the other hand,
when the pH is more than 9.0, damage to the base material to be
plated increases.
[0075] The pH of the plating bath can be adjusted, for example, by
making a pH adjustor, such as sodium hydroxide, potassium
hydroxide, or tetramethyl ammonium hydroxide, contained.
[0076] A temperature of the plating bath is not particularly
limited, but 20 to 90 degrees C., preferably 40 to 80 degrees C.,
more preferably 60 to 70 degrees C. When the bath temperature is
less than 20 degrees C., a deposition rate is slower and a plating
time is longer, which is not economical. On the other hand, when
the bath temperature exceeds 90 degrees C., a deposition rate is
too high, so that a rough film is produced, and in addition, a warp
of a base material sometimes occurs due to heat shrinkage of a film
after plating. In addition, nodules and roughness are easily
formed, and pattern characteristics are lowered. Furthermore, a
plating bath could become unstable, and natural consumption of a
reducing agent increases, thereby leading to an increase in
cost.
[0077] As mentioned above, the electroless copper plating bath
according to the present embodiment is an electroless copper
plating bath containing amine borane or a substituted derivative
thereof as a reducing agent, and not containing formaldehyde,
wherein polyaminopolyphosphonic acid as a complexing agent, an
anionic surface active agent, an antimony compound, and a
nitrogen-containing aromatic compound are contained. This
electroless copper plating bath is usable at approximately neutral
pH, and therefore, without giving damage to a material to be
plated, good plating treatment can be performed, for example, for a
material to be plated which easily deteriorates, such as
aluminum.
[0078] Furthermore, the electroless copper plating bath can improve
the stability of the plating bath, and also can control the balance
between promotion and inhibition of plating deposition, thereby
effectively controlling the plating protrusion outside a pattern
while not making a thinner edge and the like occur, and a desired
plating film with a good thickness can be formed.
[0079] Thus, for example, a good plating film without plating
protrusion can be simply and easily formed on aluminum or aluminum
alloy, or magnesium or magnesium alloy, without providing a barrier
layer or the like to prevent deposition outside a pattern, and the
electroless copper plating bath can be suitably used, for example,
in manufacturing of semiconductor wafers.
[0080] Furthermore, as mentioned above, since the balance between
promotion and inhibition of plating deposition can be controlled, a
plating film to be formed is smooth, for example, peel strength of
wire bonding can be improved. Moreover, the appearance of the
plating film is excellent.
2. ELECTROLESS COPPER PLATING METHOD
[0081] Next, an electroless copper plating method using the
above-mentioned electroless copper plating bath will be explained.
A well-known method may be used as the electroless copper plating
method. Also, in the case where catalyst addition treatment or the
like is required as pretreatment, a well-known method may be
applied as the catalyst addition treatment.
[0082] When electroless copper plating treatment is performed, as
mentioned above, a bath temperature of the electroless copper
plating bath is controlled to be 20 to 90 degrees C., preferably 40
to 80 degrees C., more preferably 60 to 70 degrees C.
[0083] Electroless copper plating treatment time is not
particularly limited, and may be suitably set so as to obtain a
desired film thickness. Specifically, the time may be, for example,
approximately 30 seconds to 15 hours.
[0084] When the electroless copper plating treatment is performed,
as the plating treatment progresses, copper ions are reduced to
copper metal by a reducing agent and deposit on a base material,
and as a result, a concentration of copper ions and a concentration
of a reducing agent in a plating solution decrease, and the pH of
the plating solution also varies. Therefore, it is preferable that
a water-soluble copper salt as a source of copper ions, a reducing
agent, a complexing agent, and other additives are supplied into
the electroless copper plating solution continuously or
periodically to maintain those concentrations in a predetermined
concentration range.
[0085] Moreover, the electroless copper plating bath is preferably
stirred by air bubbling or the like, as needed.
[0086] Specifically, the electroless copper plating method using
the electroless copper plating bath is such that, for example,
without providing a barrier layer, zincate treatment (zinc
substitution) is performed for a base material made of aluminum or
aluminum alloy, or magnesium or magnesium alloy, and then
electroless copper plating treatment is performed using the
above-mentioned electroless copper plating bath. By the electroless
copper plating method according to the present embodiment,
deposition outside a pattern can be controlled effectively as
mentioned above, and therefore a good plating film can be formed
simply and easily without providing a barrier layer or the
like.
[0087] Another example of the electroless copper plating method is
such that activation treatment is performed for a thin film
containing copper, nickel, palladium, platinum, tungsten,
molybdenum, rhodium, titanium, tantalum, and the like, by
substitution for palladium, platinum, copper, and the like, and
then, electroless copper plating treatment is performed using the
above-mentioned electroless copper plating bath.
[0088] Another example of the electroless copper plating method is
such that, after the above-mentioned activation treatment,
reduction treatment is performed by a treatment solution containing
borane or a substituted derivative thereof, and then electroless
copper plating treatment is performed using the above-mentioned
electroless copper plating bath.
3. EXAMPLES
[0089] Hereinafter, specific Examples according to the present
invention will be described. Note that the present invention is not
limited to any of the following Examples.
[0090] <Examination of Composition of Electroless Copper Plating
Bath>
[0091] First, in Example 1 to Example 2, and Comparative Example 1
to Comparative Example 10, which are shown below, a film thickness
of a plating film and a deposition amount outside a pattern (a
plating protrusion amount) were examined by changing the
composition of an electroless plating bath.
Example 1
[0092] (Composition of Electroless Copper Plating Bath)
[0093] Ethylene diamine tetra(methylene phosphonic acid): 0.08
mol/L
[0094] Copper (copper sulfate pentahydrate): 0.063 mol/L (4 g/L as
a copper concentration)
[0095] Dimethylamine borane: 8 g/L
[0096] Sodium lauryl sulfate: 20 mg/L
[0097] o-phenanthroline: 4 mg/L
[0098] Antimony oxide: 2 mg/L as an antimony concentration
[0099] pH: 7.7
[0100] Bath temperature: 60 degrees C.
[0101] (Electroless Copper Plating Method)
[0102] A sample was obtained in such manner that, on an Al--Si
alloy sputtered film formed on a silicon wafer, a pattern was
formed with a TiN film, and then double zincate treatment was
performed in accordance with the usual method, and the sample was
immersed in an electroless copper plating bath having the
above-mentioned composition for 1 hour to perform electroless
copper plating treatment, whereby a copper plating film was formed
on the pattern.
[0103] (Evaluation)
[0104] For the formed plating film, difference in height between
before and after the plating treatment was measured with a laser
microscope to measure a plating film thickness. As a result, it was
found that the formed plating film had a good film thickness,
namely a film thickness of 5.3 .mu.m, and there was almost no
plating protrusion outside the pattern, namely 5 .mu.m of plating
protrusion.
Example 2
[0105] (Composition of Electroless Copper Plating Bath)
[0106] Glycine N,N-bis(methylenephosphonic acid): 0.13 mol/L
[0107] Copper (copper sulfate pentahydrate): 0.063 mol/L (4 g/L as
a copper concentration)
[0108] Dimethylamine borane: 8 g/L
[0109] Sodium lauryl sulfate: 20 mg/L
[0110] 2,9-dimethyl-1,10-phenanthroline: 2 mg/L
[0111] Antimony oxide: 2 mg/L as an antimony concentration
[0112] pH: 7.7
[0113] Bath temperature: 60 degrees C.
[0114] (Electroless Copper Plating Method)
[0115] A sample was obtained in such manner that, on an Al--Si
alloy sputtered film formed on a silicon wafer, a pattern was
formed with a TiN film, and then double zincate treatment was
performed in accordance with the usual method, and the sample was
immersed in an electroless copper plating bath having the
above-mentioned composition for 1 hour to perform electroless
copper plating treatment, whereby a copper plating film was formed
on the pattern.
[0116] (Evaluation)
[0117] For the formed plating film, difference in height between
before and after the plating treatment was measured with a laser
microscope to measure a plating film thickness. As a result, it was
found that the formed plating film had a good film thickness,
namely a film thickness of 5.3 .mu.m, and there was almost no
plating protrusion outside the pattern, namely 5 .mu.m of plating
protrusion.
Comparative Example 1
[0118] Electroless copper plating treatment was performed to form a
copper plating film on a pattern in the same manner as in Example
1, except that an antimony compound was not contained in the
composition of the electroless copper plating bath.
[0119] As a result, the formed plating film had a thickness of 2.6
.mu.m and was thinner than those of Examples 1 and 2, and an amount
of plating protrusion outside the pattern was 15 .mu.m. Thus,
plating deposition was inhibited while a large amount of protruding
deposition was produced, and accordingly pattern selectivity was
very low.
Comparative Example 2
[0120] Electroless copper plating treatment was performed to form a
copper plating film on a pattern in the same manner as in Example
1, except that 2 mg/L of lead was added in place of 2 mg/L of
antimony in the composition of the electroless copper plating
bath.
[0121] As a result, the formed plating film had a thickness of 2.2
.mu.m and was thinner than those of Examples 1 and 2, and an amount
of plating protrusion outside the pattern was 12 .mu.m. Thus,
plating deposition was inhibited while a large amount of protruding
deposition was produced, and accordingly pattern selectivity was
very low.
Comparative Example 3
[0122] Electroless copper plating treatment was performed to form a
copper plating film on a pattern in the same manner as in Example
1, except that 0.3 mg/L of thallium was added in place of 2 mg/L of
antimony in the composition of the electroless copper plating
bath.
[0123] As a result, the formed plating film had a thickness of 1.8
.mu.m and was considerably thinner than those of Examples 1 and 2.
In addition, there was a large amount of plating protrusion outside
the pattern, and the plating protrusion caused a connection between
patterns (bridge), and therefore the amount of the plating
protrusion could not be measured. Thus, plating deposition was
inhibited while a large amount of protruding deposition was
produced, and accordingly pattern selectivity was very low.
Comparative Example 4
[0124] Electroless copper plating treatment was performed to form a
copper plating film on a pattern in the same manner as in Example
1, except that sodium lauryl sulfate was not contained in the
composition of the electroless copper plating bath.
[0125] In Comparative Example 4, the plating bath decomposed during
the plating treatment, whereby the plating treatment was not
performed properly.
Comparative Example 5
[0126] Electroless copper plating treatment was performed to form a
copper plating film on a pattern in the same manner as in Example
1, except that o-phenanthroline was not contained in the
composition of the electroless copper plating bath.
[0127] As a result, although an amount of plating protrusion
outside the pattern was small, namely 0.5 .mu.m, a plating film
thickness was considerably thinner, namely 1.2 .mu.m, and a plating
rate remarkably decreased.
Comparative Example 6
[0128] Electroless copper plating treatment was performed to form a
copper plating film on a pattern in the same manner as in Example
1, except that 0.5 g/L of polyethylene glycol (PEG) #1000 was added
in place of 20 mg/L of sodium lauryl sulfate in the composition of
the electroless copper plating bath.
[0129] In Comparative Example 6, the plating bath decomposed during
the plating treatment, whereby the plating treatment was not
performed properly.
Comparative Example 7
[0130] Electroless copper plating treatment was performed to form a
copper plating film on a pattern in the same manner as in Example
1, except that 2 mg/L of bismuth was added in place of 2 mg/L of
antimony in the composition of the electroless copper plating
bath.
[0131] As a result, the formed plating film had a good film
thickness, namely a film thickness of 4.4 .mu.m, but, due to
plating protrusion outside the pattern, a connection between
patterns (bridge) was produced, and therefore an amount of the
plating protrusion could not be measured.
Comparative Example 8
[0132] Electroless copper plating treatment was performed to form a
copper plating film on a pattern in the same manner as in Example
1, except that 0.08 ml/L of diethylene triamine pentaacetic acid
was added in place of 0.08 mol/L of ethylene diamine
tetra(methylene phosphonic acid) in the composition of the
electroless copper plating bath.
[0133] In Comparative Example 8, copper plating was not deposited,
and corrosion of the Al--Si alloy sputtered film constituting the
pattern occurred.
Comparative Example 9
[0134] Electroless copper plating treatment was performed to form a
copper plating film on a pattern in the same manner as in Example
1, except that an electroless copper plating bath having the
following composition was used.
[0135] (Composition of Electroless Copper Plating Bath)
[0136] Ethylene diamine tetraacetic acid: 0.08 mol/L
[0137] Copper (copper sulfate pentahydrate): 0.0315 mol/L (2 g/L as
a copper concentration)
[0138] Formaldehyde: 2 g/L
[0139] Polyethylene glycol (PEG) #1000:1 g/L
[0140] 2,2'-dipyridyl: 20 mg/L
[0141] pH: 13.2 (adjusted with NaOH)
[0142] Bath temperature: 60 degrees C.
[0143] In Comparative Example 9, the Al--Si alloy sputtered film
dissolved, whereby the plating treatment was not performed
properly. This is considered because the plating bath contained
formaldehyde as a reducing agent, which was highly alkaline,
thereby causing serious damage to a base material.
Comparative Example 10
[0144] Electroless copper plating treatment was performed to form a
copper plating film on a pattern in the same manner as in Example
1, except that an electroless copper plating bath having the
following composition was used.
[0145] (Composition of Electroless Copper Plating Bath)
[0146] Ethylene diamine tetraacetic acid: 0.08 mol/L
[0147] Copper (copper sulfate pentahydrate): 0.0315 mol/L (2 g/L as
a copper concentration)
[0148] Glyoxylic acid: 6 g/L
[0149] Polyethylene glycol (PEG) #1000:1 g/L
[0150] 2,2'-dipyridyl: 20 mg/L
[0151] pH: 13.2 (adjusted with NaOH)
[0152] Bath temperature: 60 degrees C.
[0153] In Comparative Example 10, the Al--Si alloy sputtered film
dissolved, whereby the plating treatment was not performed
properly. This is considered because the plating bath contained
glyoxylic acid as a reducing agent, which was highly alkaline, as
is the case with formaldehyde, thereby causing serious damage to a
base material.
* * * * *