U.S. patent application number 17/041229 was filed with the patent office on 2021-01-14 for co anode, and co electroplating method using co anode.
The applicant listed for this patent is JX Nippon Mining & Metals Corporation. Invention is credited to Takayuki Asano, Kengo Kaminaga, Yoshimasa Koido, Shuhei Murata.
Application Number | 20210010149 17/041229 |
Document ID | / |
Family ID | 1000005164833 |
Filed Date | 2021-01-14 |
United States Patent
Application |
20210010149 |
Kind Code |
A1 |
Murata; Shuhei ; et
al. |
January 14, 2021 |
Co Anode, And Co Electroplating Method Using Co Anode
Abstract
Provided is a novel anode for electroplating, which replaces the
Cu anode and which is capable of suppressing plating defects. The
Co anode has a number of particles with a grain size of 0.5 .mu.m
or more of 6000 particles/g or less, as measured by an in-liquid
particle counter according to JIS B 9925 after dissolving the Co
anode in dilute nitric acid having a nitric acid concentration of
20% by mass.
Inventors: |
Murata; Shuhei; (Ibaraki,
JP) ; Koido; Yoshimasa; (Ibaraki, JP) ; Asano;
Takayuki; (Ibaraki, JP) ; Kaminaga; Kengo;
(Ibaraki, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
JX Nippon Mining & Metals Corporation |
Minato-ku, Tokyo |
|
JP |
|
|
Family ID: |
1000005164833 |
Appl. No.: |
17/041229 |
Filed: |
October 3, 2018 |
PCT Filed: |
October 3, 2018 |
PCT NO: |
PCT/JP2018/037118 |
371 Date: |
September 24, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25D 3/12 20130101; C25D
17/12 20130101 |
International
Class: |
C25D 17/12 20060101
C25D017/12; C25D 3/12 20060101 C25D003/12 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 28, 2018 |
JP |
2018-063008 |
Claims
1. A Co anode for electroplating, the Co anode having a number of
particles with a grain size of 0.5 .mu.m or more of 6000
particles/g or less, as measured by an in-liquid particle counter
according to JIS B 9925 after dissolving the Co anode in dilute
nitric acid having a nitric acid concentration of 20% by mass.
2. The Co anode according to claim 1, wherein the number of
particles with a grain size of 0.5 .mu.m or more is 5000
particles/g or less.
3. The Co anode according to claim 1, wherein the Co anode has a
purity of 3N or more.
4. The Co anode according to claim 3, wherein the purity is 4N or
more.
5. The Co anode according to claim 3, wherein the Co anode has a Fe
concentration of 10 ppm or less.
6. The Co anode according to claim 5, wherein the Fe concentration
is 5 ppm or less.
7. A Co electroplating method using the Co anode according to claim
1.
8. An evaluation method of Co anode for electroplating, the method
comprising the steps of: dissolving the Co anode in dilute nitric
acid having a nitric acid concentration of 20% by mass, measuring
an in-liquid particle in the dilute nitric acid in which the Co
anode is dissolved by an in-liquid particle counter according to
JIS B 9925, and judging good or bad of the Co anode based on the
measurement result by the in-liquid particle counter.
9. The evaluation method of Co anode for electroplating according
to claim 8, wherein the step of judging good or bad of the Co anode
based on the measurement result by the in-liquid particle counter
includes: a step of evaluating if a number of particles with a
grain size greater than or equal to a predetermined grain size of
0.5 .mu.m or more is below a predetermined threshold of 6000
particles/g or less.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a Co anode and a Co
electroplating method using the Co anode.
BACKGROUND OF THE INVENTION
[0002] In general, Cu electroplating is used for forming Cu wiring
in PWBs (printed wiring boards) and the like. Recently, it is also
used for forming Cu wiring of semiconductors. A pure Cu anode or a
phosphorus-containing Cu anode is used as an anode for Cu
electroplating for forming the Cu wiring.
[0003] The pure Cu anode or the phosphorus-containing Cu anode used
for the Cu electroplating is described in, for example, Patent
Literature 1, which discloses that purity is controlled within a
predetermined range and an impurity content is controlled below a
predetermined value, so that adhesion of particles to a
semiconductor wafer manufactured using the pure Cu anode or the
phosphorus-containing Cu anode can be suppressed.
[0004] Further, as a similar art for suppressing the adhesion of
particles to the semiconductor wafer manufactured using the
phosphorus-containing Cu anode, Patent Literature 2 discloses that
when subjecting the semiconductor wafer to the Cu electroplating, a
fine crystal layer having a crystal grain size controlled within a
predetermined range is previously formed on a surface of the
phosphorus-containing Cu anode.
CITATION LIST
Patent Literatures
[0005] [Patent Literature 1] Japanese Patent No. 5066577 B [0006]
[Patent Literature 2] Japanese Patent No. 4076751 B
SUMMARY OF THE INVENTION
[0007] In recent years, semiconductor devices have been required to
have higher performance and lower power consumption, and as wiring
becomes finer, measures against electromigration (EM) deterioration
which would affect the reliability of wiring and decreasing wiring
resistance which would cause signal delay have been required. The
arts described in Patent Literature 1 and Patent Literature 2 are
to suppress the particles generated when forming Cu wiring or the
like by the Cu electroplating as described above, thereby improving
plating defects to provide Cu wiring useful for finer wiring.
However, there is room for improvement of the electroplating using
such a conventional Cu anode, in terms of EM resistance and
decreased wiring resistance. Therefore, there would be a need for
development of a novel electroplating anode which replaces the Cu
anode, and which is capable of suppressing the conventional problem
of plating defects.
[0008] Therefore, an object of an embodiment of the present
invention is to provide a novel anode for electroplating, which
replaces the Cu anode and which is capable of suppressing plating
defects.
[0009] As a result of various studies to solve such problems, the
present inventors have focused on the fact that, in a technical
field of forming fine wiring, replacement of Cu wiring to Co wiring
has been attempted in advanced local wiring having narrow wiring
and a relatively short wiring distance. The present inventors have
found that the Co wiring has better EM resistance than that of the
Cu wiring and can achieve wiring resistance which is lower than
that of the Cu wiring by a thinner barrier metal layer, when the
wiring distance is shorter.
[0010] Therefore, the present inventors have found that an anode
for electroplating, which is capable of suppressing plating
defects, can be obtained by producing a Co anode in place of the
conventional Cu anode and controlling the number of particles
having a predetermined grain size or more in the Co anode.
[0011] In an aspect, an embodiment of the present invention
completed on the basis of the above findings relates to a Co anode,
the Co anode having a number of particles with a grain size of 0.5
.mu.m or more of 6000 particles/g or less, as measured by an
in-liquid particle counter according to JIS B 9925 after dissolving
the Co anode in dilute nitric acid having a nitric acid
concentration of 20% by mass.
[0012] In another aspect, an embodiment of the present invention
relates to a Co electroplating method using the Co anode according
to the embodiment of the present invention.
[0013] According to an embodiment of the present invention, it is
possible to provide a novel anode for electroplating, which
replaces the Cu anode and which is capable of suppressing plating
defects.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1(a) shows SEM images of Example 5 (purity: 3N,
magnification: 300 times); FIG. 1(b) shows images of Example 3
(purity: 4N, magnification: 300 times); and FIG. 1(c) shows images
of Example 1 (purity: 5N, magnification: 300 times);
[0015] FIG. 2(a) shows SEM images of Example 5 (purity: 3N,
magnification: 15000 times); FIG. 2(b) shows SEM images of Example
3 (purity: 4N, magnification: 30000 times); and FIG. 2(c) shows SEM
images of Example 1 (purity: 5N, magnification: 15000 times);
[0016] FIG. 3(a) shows a graph of an EDX spectrum of Example 5;
[0017] FIG. 3(b) shows a graph of an EDX spectrum of Example 3;
and
[0018] FIG. 3(c) is a graph of an EDX spectrum of Example 1.
DETAILED DESCRIPTION OF THE INVENTION
[Structure of Co Anode]
[0019] A Co anode according to an embodiment of the present
invention has a number of particles with a grain size of 0.5 .mu.m
or more of 6000 particles/g or less, as measured by an in-liquid
particle counter according to JIS B 9925 after dissolving the Co
anode in dilute nitric acid having a nitric acid concentration of
20% by mass. The Co anode has better EM resistance than that of the
Cu anode, and can achieve wiring resistance which is lower than
that of the Cu wiring by a thinner barrier metal layer, when a
wiring distance is shorter. Further, since the number of particles
with a grain size of 0.5 .mu.m or more is controlled to 6000
particles/g or less, any occurrence of abnormal deposition of
plating can be suppressed when electroplating is performed using
the Co anode, thereby resulting in good suppression of plating
defects.
[0020] The particles are solid inclusions present in the structure
of the Co anode, and refer to those which are not dissolved in
dilute nitric acid in the implementation of an in-liquid particle
counter as described later. Impurities in the Co anode also include
substances that are dissolved in dilute nitric acid (for example,
metals having strong ionization tendency). However, even if such
substances are present as coarse structures in the Co anode, they
are ionized in a process of electroplating, and thus are
incorporated into a plated film in a very finer form at an ion
level. On the other hand, the inclusions (particles) that are not
dissolved in dilute nitric acid are electrochemically stable, and
thus are incorporated into the plated film while maintaining the
forms close to those present in the Co anode. Therefore, even if Co
anodes have the same purity, a Co anode having higher proportion of
the particles among the impurities results in a larger size of
impurities incorporated into the plated film, so that the plating
defects tend to occur. The present invention focuses on this point,
and provides the Co anode in which the number of particles having
the predetermined grain size or more is controlled, among the
particles being solid inclusions that are not dissolved in dilute
nitric acid.
[0021] The particles mainly originate from impurities contained in
a Co raw material, or impurities or products contaminated in a
production step. The particles are, for example, one or more
selected from the group consisting of metals, metal oxides, carbon,
carbon compounds, and chlorine compounds. Further, the particles
may be one or more metals selected from the group consisting of Fe,
Mg, Cr, Ni, Si, and Al, or oxides thereof (including cobalt
oxide).
[0022] Furthermore, the present inventors have focused on density
of the number of particles having a grain size of 0.5 .mu.m or more
because the particles having such a grain size are not dissolved in
an electrolytic solution and are likely to cause abnormal
deposition of plating by being incorporated into the plated film,
and found that by controlling the density of the number to 6000
particles/g or less, the generation of the particles in the plated
film produced by electroplating can be suppressed very well,
resulting in suppression of the generation of abnormal deposition
of plating. The present inventors have also found that when
comparing a case where the impurities are not detected as the
particles with a case where the impurities are detected, the
detected particles have an adverse effect on the plating step, and
in particular, a Co wiring formed using the Co anode is often
utilized as finer wiring, which will make such an adverse effect
remarkable. From this viewpoint, the present invention controls the
number of particles having the grain size of 0.5 .mu.m or more. In
the Co anode according to the embodiment of the present invention,
the number of particles having the grain size of 0.5 .mu.m or more
is preferably 5000 particles/g or less, and more preferably 4000
particles/g or less.
[0023] The grain size of the particles is determined by measurement
with a "light scattering type automatic particle counter for
liquid" (from Kyushu Rion Co., Ltd.). This measuring method is to
select the sizes of particles in a liquid and measure the particle
concentration and the number of particles, and is based on JIS B
9925 (as used herein, the measurement is referred to as "in-liquid
particle counter").
[0024] The procedure for carrying out the in-liquid particle
counter will be specifically described. One gram of a sample was
taken and slowly dissolved in 150 ml of dilute nitric acid (an
aqueous solution of 20% by mass nitric acid) so as not to dissolve
the particles, and left for 24 hours and then diluted with pure
water to 500 ml, 10 ml of which is taken and measured with the
in-liquid particle counter. For example, when the number of
particles is 1000 particles/ml, 0.02 g of the sample will be
measured in 10 ml of the solution, so that the number of particles
will be 500000 particles/g.
[0025] It should be noted that the measurement of the number of
particles is not limited to the measurement with the in-liquid
particle counter, and other means may be used as long as the number
of the particles can be measured in the same manner.
[0026] The Co anode according to an embodiment of the present
invention preferably has a purity of 3N or more. The purity of the
Co anode of 3N (a purity of 99.9% by mass) or more can more
effectively suppress the generation of the particles in the plated
film produced by electroplating using the Co anode, resulting in
better suppression of the generation of abnormal deposition. The Co
anode according to the embodiment of the present invention
preferably has a purity of 4N (purity of 99.99% by mass) or more,
and more preferably 5N (purity of 99.999% by mass) or more. With
regard to the "higher purity" as used herein, for example, a purity
of 5N (99.999%) means that the total amount of all metal elements
other than elements below lower detection limit and Co, such as Be,
Na, Mg, Al, Si, P, S, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Zr,
Mo, Cd, Sn, Sb, Hg, Pb, Bi, Th, and U are less than 10 ppm, when
analyzing a dissolved Co ingot by glow discharge mass spectrometry
(GDMS: Glow Discharge Mass Spectrometry).
[0027] It should be noted that, as shown in Examples and
Comparative Example as described later, the "higher purity" does
not necessarily mean that the number of particles is lower, and the
Co anode having higher purity may exhibit a larger number of
particles in the present invention than the Co anode having lower
purity.
[0028] The Co anode according to an embodiment of the present
invention preferably has a Fe concentration controlled to 10 ppm or
less. Since Fe is difficult to be dissolved in an acidic solution,
the contamination of Fe in the Co anode tends to easily form the
particles. When comparing Co anodes having the same purity, the Co
anode having the Fe concentration controlled to 10 ppm or less
produces fewer particles in the plated film than the Co anode
having the Fe concentration of more than 10 ppm, resulting in
further suppression of the generation of abnormal deposition of
plating. In the Co anode according to the embodiment of the present
invention, the Fe concentration is controlled to more preferably 8
ppm or less, and even more preferably 5 ppm or less, and still more
preferably 3 ppm or less, and still more preferably 1 ppm or less,
and still more preferably 0 ppm.
[Method for Producing Co Anode]
[0029] A method for producing the Co anode according to the
embodiment of the present invention will be described in detail.
First, Co, a raw material, is melted in a certain container.
Examples of the Co raw material to be used include Co having a
purity of 3N (a purity of 99.9% by mass) or more.
[0030] As described above, the particles that are problematic
during electroplating are grains of compounds of Fe, Mg, Cr, Ni,
Si, Al and the like, and these grains cause the particles generated
in the plated film. In order to prevent these particles from mixing
into the Co anode, a surface roughness of a portion in contact with
the Co material in the container, piping and mold may be
controlled. Further, based on the findings that these particles
tend to float on a slag side, a stirring time of a molten metal may
be increased to distribute the particles of compounds of Fe, Mg,
Cr, Ni, Si, and Al each having a grain size of more than 0.5 .mu.m
to the slag side.
[0031] The melted Co raw material is then fed to a mold and forged,
and then subjected to rolling, a heat treatment, and further
surface cutting to produce a Co anode.
[Co Electroplating Method]
[0032] Co electroplating using the Co anode according to the
embodiment of the present invention can lead to very good
suppression of the generation of the particles in a plated film to
be produced, resulting in suppression of the generation of abnormal
deposition of plating.
[0033] In the Co electroplating method according to an embodiment
of the present invention, for example, an appropriate amount of
cobalt sulfate: 10 to 30 g/L (Co) or cobalt chloride 5 to 15 g/L
may be used as a plating bath, although not particularly limited
thereto. A pH is from 2.5 to 3.5.
[0034] In addition, a plating bath temperature can be from 25 to
60.degree. C., a cathode current density can be from 0.5 to 10
A/dm.sup.2, and an anode current density can be from 0.5 to 10
A/dm.sup.2, although those conditions are not necessarily limited
to thereto. The plating bath may contain a brightening
agent/complexing agent, a pH buffering agent, a surfactant and the
like.
EXAMPLES
[0035] Examples are provided below for better understanding of the
present invention and its advantages, but the present invention is
not limited to these Examples.
[Preparation of Co Anode]
[0036] For each of Examples 1 to 5 and Comparative Example 1, a Co
raw material having the predetermined purity was melted under
vacuum to prepare an ingot, which was then melted. The Co raw
material having purity of 3N was a commercially available cobalt
material, and the Co raw materials having purity of 4N and 5N were
obtained by electrolytic refining.
[0037] The melted Co raw material was then fed to the mold and
forged, and subjected to rolling at a rolling reduction rate of
from 30 to 50%, followed by a heat treatment at 300.degree. C. to
600.degree. C. and further surface cutting, to produce a Co
anode.
[Evaluation]
(Evaluation of Particles)
[0038] The particle size and number of the particles were measured
with a "light scattering type automatic particle counter for
liquid" (from Kyushu Rion Co., Ltd.). Specifically, 1 g of a Co
anode was sampled and slowly dissolved in 150 ml of dilute nitric
acid (an aqueous solution of 20% by mass nitric acid) so as not to
dissolve the particles, and left for 24 hours, and further diluted
with pure water to 500 ml, 10 ml of which was taken and measured
with the in-liquid particle counter. An average value obtained by
repeating this procedure three times was determined to be the
number of particles. The particle size of the particles was
evaluated by a SEM image. FIG. 1(a) shows a SEM image of Example 5
(purity: 3N, magnification: 300 times), FIG. 1(b) shows a SEM image
of Example 3 (purity: 4N, magnification: 300 times), and FIG. 1(c)
shows a SEM image of Example 1 (purity: 5N, magnification: 300
times. Further, FIG. 2(a) shows a SEM image of Example 5 (purity:
3N, magnification: 15000 times), FIG. 2(b) shows a SEM image of
Example 3 (purity: 4N, magnification: 30000 times), and FIG. 2(c)
shows a SEM image of Example 1 (purity: 5N, magnification: 15000
times). Furthermore, in FIG. 1, the particles (inclusions) having a
grain size of 0.5 .mu.m or more are shown by surrounding them by
frame lines.
(Evaluation of Fe Concentration)
[0039] The concentration of Fe contained in the Co anode was
evaluated by GDMS. Further, the particle components remaining on a
filter when measuring the particle size and number of particles
were evaluated using energy dispersive X-ray analysis (EDX: Energy
Dispersive X-ray Spectrometry). FIG. 3(a) shows an EDX spectrum
graph of Example 5, FIG. 3(b) shows an EDX spectrum graph of
Example 3, and FIG. 3(c) shows an EXD spectrum graph of Example
1.
(Evaluation of Number of Abnormal Electrodepositions)
[0040] On a wafer having a diameter of 300 mm, Co electroplating
was performed under the same conditions using each of the Co anodes
of Examples 1 to 5 and Comparative Example 1 to form a Co plated
film having a thickness of 10 nm. The number of defects (the number
of abnormal electrodepositions) generated in the Co plated film was
evaluated.
[0041] Table 1 shows the results of the above Examples and
Comparative example.
TABLE-US-00001 TABLE 1 Comparative Example 1 Example 2 Example 3
Example 4 Example 5 Example 1 Purity 5N 5N 4N 4N 3N 3N Fe
Concentration (ppm) 0.8 7 1.2 6 4.1 12 Particles Having Grain Size
1200 2900 3700 5900 4800 9700 of 0.5 .mu.m or more (particles/g)
Number of Abnormal 0 0 0 0 0 1 Electrodepositions per a Wafer in Co
Plating Having Thickness of 10 nm
(Evaluation Results)
[0042] Each of Examples 1 to 5 could produce a Co anode in which
the number of particles having a grain size of 0.5 .mu.m or more
was 6000 particles/g or less. However, Comparative Example 1
produced a Co anode in which the number of particles having a grain
size of 0.5 .mu.m or more was more than 6000 particles/g.
[0043] Further, Example 1 and Example 2, Example 3 and Example 4,
and Example 5 and Comparative Example 1 used Co anodes having the
same purity, respectively, but they had different Fe
concentrations, resulting in a difference in the number of
particles having a grain diameter of 0.5 .mu.m or more. It is
understood from this result that if the Co anodes have the same
purity, a Co anode having a lower Fe concentration can decrease a
larger number of particles having a grain size of 0.5 .mu.m or
more.
[0044] In addition, Example 4 where the purity was 4N had a larger
number of particles having a grain size of 0.5 .mu.m or more than
that of Example 5 where the purity was 3N. Thus, the "higher
purity" does not necessarily lead to the lower number of particles,
and the Co anode having higher purity may have the larger number of
particles according to the present invention than that of the Co
anode having lower purity.
[0045] Further, in the Co plated film formed using each of the Co
anodes of Examples 1 to 5, the number of abnormal
electrodepositions was zero, and the plating defects were well
suppressed. In the Co plated film formed using the Co anode of
Comparative Example 1, the abnormal electrodeposition was confirmed
and plating defects were generated.
* * * * *