U.S. patent application number 12/996949 was filed with the patent office on 2011-05-26 for high purity copper and method of producing high purity copper based on electrolysis.
This patent application is currently assigned to JX NIPPON MINING & METALS CORPORATION. Invention is credited to Atsushi Fukushima, Susumu Shimamoto, Yuichiro Shindo.
Application Number | 20110123389 12/996949 |
Document ID | / |
Family ID | 42073406 |
Filed Date | 2011-05-26 |
United States Patent
Application |
20110123389 |
Kind Code |
A1 |
Shindo; Yuichiro ; et
al. |
May 26, 2011 |
High Purity Copper and Method of Producing High Purity Copper Based
on Electrolysis
Abstract
High purity copper having a purity of 6N or higher, wherein
content of each of the respective components of P, S, 0, and C is 1
ppm or less, and nonmetal inclusions having a particle size of 0.5
.mu.m or more and 20 .mu.m or less contained in the copper are
10,000 inclusions/g or less. As a result of using high purity
copper or high purity copper alloy as the raw material from which
harmful P, S, C, 0-based inclusions have been reduced and
controlling the existence form of nonmetal inclusions, it is
possible to reduce the occurrence of rupture of a bonding wire and
improve the reproducibility of mechanical properties, or reduce the
percent defect of a semiconductor device wiring formed by
sputtering a high purity copper target with favorable
reproducibility.
Inventors: |
Shindo; Yuichiro; (Ibaraki,
JP) ; Shimamoto; Susumu; (Ibaraki, JP) ;
Fukushima; Atsushi; (Ibaraki, JP) |
Assignee: |
JX NIPPON MINING & METALS
CORPORATION
Tokyo
JP
|
Family ID: |
42073406 |
Appl. No.: |
12/996949 |
Filed: |
September 24, 2009 |
PCT Filed: |
September 24, 2009 |
PCT NO: |
PCT/JP2009/066479 |
371 Date: |
January 25, 2011 |
Current U.S.
Class: |
420/499 ;
205/574; 420/469; 420/500 |
Current CPC
Class: |
C22C 9/00 20130101; H01L
2924/0002 20130101; H01L 2924/0002 20130101; C25C 1/12 20130101;
C23C 14/3414 20130101; C25C 7/06 20130101; H01L 2924/00
20130101 |
Class at
Publication: |
420/499 ;
205/574; 420/469; 420/500 |
International
Class: |
C22C 9/00 20060101
C22C009/00; C25C 1/12 20060101 C25C001/12 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2008 |
JP |
2008-253038 |
Claims
1. High purity copper having a purity of 6N or higher, wherein
content of each of the respective components of P, S, O, and C is 1
ppm or less, and nonmetal inclusions having a particle size of 0.5
.mu.m or more and 20 .mu.m or less contained in the copper are
10,000 inclusions/g or less.
2. The high purity copper according to claim 1, wherein inclusions
of carbon or carbide having a particle size of 0.5 .mu.m or more
and 20 .mu.m or less are 5,000 inclusions/g or less.
3. A method of producing high purity copper based on electrolysis,
wherein electrolysis is performed by providing a partition between
a cathode and an anode, and, upon supplying electrolyte extracted
from an electrolytic cell on the anode side or additional
electrolyte to an electrolytic cell on the cathode side, passing
the electrolyte through an activated carbon filter immediately
before supplying it to the electrolytic cell on the cathode side,
and thereafter supplying the electrolyte to the electrolytic cell
on the cathode side.
4. The method of producing high purity copper based on electrolysis
according to claim 3, wherein a purity of 6N or higher, content of
each of the respective components of P, S, O, and C being 1 ppm or
less, and nonmetal inclusions having a particle size of 0.5 .mu.m
or more and 20 .mu.m or less contained in the .copper being 10,000
inclusions/g or less are achieved based on electrolysis.
5. The method of producing high purity copper based on
electrolysis. according to claim 3, wherein inclusions of carbon or
carbide having a particle size of 0.5 .mu.m or more and 20 .mu.m or
less contained in the copper are made to be 5,000 inclusions/g or
less.
Description
TECHNICAL FIELD
[0001] The present invention relates to high purity copper and a
method of producing high purity copper based on electrolysis. The
high purity copper produced with the method of the present
invention can be used to produce high purity copper alloy by adding
the necessary alloy elements. The present invention covers all of
the above. Incidentally, "%" and "ppm" as used in this
specification respectively represent mass % and mass ppm. Moreover,
"purity" represents the purity excluding C, O, N, and H as gas
components.
BACKGROUND ART
[0002] Conventionally, if the aim is to produce high purity copper,
emphasis was primarily placed on eliminating metal elements
(excluding copper) and nonmetal elements, which are recognized as
impurities, and limiting gas components to a constant amount of
several ppm to several 100 ppm.
[0003] Thus, trace amounts of inclusions that existed in the high
purity copper were not acknowledged as a problem, and no
consideration was given for eliminating or reducing the same.
Moreover, even in cases where gas components are limited as much as
possible, there was no concern with respect to the mode of
existence of the inclusions arising therefrom.
[0004] Nevertheless, if there are inclusions other than copper in
the high purity copper, even minute and trace amounts, for example,
may cause disconnection with such inclusions as the source in the
thinning process of the copper bonding wire or problems may arise
regarding mechanical properties such as tensile properties, and
adverse effects may also be inflicted on the reproducibility of
such properties.
[0005] In addition, when preparing a high purity copper sputtering
target for use in semiconductor devices, protrusions (nodules)
would arise on the target surface in the process of forming a thin
film by way of sputtering, and particles would arise due to the
rupture or the like of the protrusions (nodules) caused by an
abnormal discharge. Generation of particles causes the percent
defective of the semiconductor device to deteriorate.
[0006] Conventionally, the recognition was that other causes had a
greater influence on the generation of the foregoing particles or
the rupture of the bonding wire, and the recognition that minute
and trace amounts of inclusions existing in the high purity copper
target were the cause was low.
[0007] Nevertheless, as the conventionally recognized sources of
particles and causes of rupture of the bonding wire become
clarified and subsequently solved, the new recognition is that
other sources of particles exist and that, unless they are solved,
it is not possible to realize high quality deposition or obtain a
bonding wire that will not rupture easily.
[0008] To put it differently, existing sputtering targets and
bonding wires for forming copper wiring for use in semiconductors
are based on the foregoing sophisticated technology level. It
should be easy to understand that the high purity copper of the
present invention can be applied to all materials that use high
purity copper in addition to the use in sputtering targets or
bonding wires.
[0009] Although the deposition technology of copper wirings or
bonding wires for use in semiconductors is well known technology,
the principle of the sputtering method, which is sometimes slightly
difficult to understand, is briefly explained below.
[0010] The sputtering method forms a film on a substrate by
utilizing the phenomenon where atoms configuring the target are
discharged into space and accumulated on the opposing substrate
based on the momentum exchange that occurs when the accelerated
charged particles collide with the target surface.
[0011] The sputtering target is usually in the shape of a discoid
or rectangular plate, and is used as the sputter source for
forming, by way of sputtering, an electrode, gate, element,
insulating film, protective film and the like of various
semiconductor devices.
[0012] Generally, as the sputtering target, an aluminum and
aluminum alloy target, a copper and copper alloy target, a high
melting point metal and alloy target, a metal silicide target and
the like are used.
[0013] Among the foregoing targets, an important target is a copper
and copper alloy target that is used in forming a copper wiring as
an alternative of a conventional aluminum wiring.
[0014] Meanwhile, during the deposition based on sputtering,
protrusions having a size of several .mu.m to several mm referred
to as nodules sometimes arise on the eroded portion of the
sputtering target. There is a problem in that such nodules will
burst as a result of colliding with the charged particles in the
sputtering process, and thereby cause to generate particles
(cluster-shaped coarse fragments) on the substrate.
[0015] The generation of particles will increase in proportion to
the number of nodules on the eroded surface of the target, and a
major issue is to prevent the generation of nodules in order to
reduce the problematic particles.
[0016] In the recent circumstances where LSI semiconductor devices
are subject to higher integration and the linewidth thereof being
miniaturized to 0.25 .mu.m or less, the generation of particles
caused by the foregoing nodules is now being considered a major
problem.
[0017] Specifically, particles directly adhere to the thin film
that is formed on the substrate, or once adhere to and accumulate
on the circumferential wall or component of the sputtering device
and thereafter flake off and adhere to the thin film again, and
cause problems such as the disconnection or short circuit of the
wiring. The generation of particles is becoming a major problem
pursuant to the advancement of higher integration and
miniaturization of the electronic device circuit as described.
[0018] As described above, causes of the conventionally recognized
sources of particles and rupture of the bonding wire are being
clarified and many of them have been solved, but the current
situation is that it is still insufficient. With the foregoing
problems unsolved, it is not possible to achieve high quality
deposition or obtain a bonding wire that will not rupture
easily.
[0019] Conventional technologies are now introduced. Nevertheless,
the following conventional technologies have no concern regarding
the mode and influence of the minute and trace amounts of
inclusions existing in the high purity copper, and do not provide
any kind of specific solution therefor.
[0020] Patent Document 1 describes cleaning electrolyte based on
solvent extraction.
[0021] Patent Document 2 describes eliminating Sb and Bi with
chelate resin.
[0022] Patent Document 3 describes adding a diaphragm and glue in
copper electrolysis to smooth the electrolyzed surface, and thereby
reducing the uptake of impurities.
[0023] Patent Document 4 describes causing anolite to come in
contact with activated carbon in copper electrolysis to eliminate
glue.
[0024] Patent Document 5 describes performing electrolysis once
again in copper electrolysis.
[0025] Patent Document 6 describes smoothing the electrode surface
based on periodic reverse current electrolysis in copper
electrolysis to prevent the inclusion of suspended matter and
electrolyte.
[0026] Patent Document 7 describes adding a macromolecular additive
to improve the surface condition in copper electrolysis and using
electrolyte containing urea to produce high purity copper with a
low silver and sulfur content.
[0027] Patent Document 8 describes that the three metallurgical
characteristics of a sputtering target that affect the performance
of a target are the uniformity of the material (no precipitate,
void, inclusion and other defects), crystal particle size (finer
crystal particle size is generally more preferable than coarse
crystal particle size), and texture (texture relates to the
strength of a specific crystallographic orientation; a "weak"
texture includes substantially random distribution of the
crystallographic orientation, and a "strong" texture includes a
preferential crystallographic orientation in the distribution of
the crystallographic orientation), and further states that,
generally speaking, it is necessary to reduce defects such as
inclusions in the target.
[0028] Patent Document 9 describes a titanium sputtering target in
which the number of inclusions of 1 .mu.m or more existing at the
crystal grain boundary of titanium configuring the target is 100
inclusions or less per 1 cm.sup.2 of the target plane, and
additionally describes that the inclusions existing at the crystal
grain boundary of titanium are a composite compound based on a
combination of one or more types among oxides, nitrides, carbides,
sulfides, and hydrides of metal components of titanium or iron,
nickel, chromium, aluminum, silicon, tungsten, and molybdenum, and
that the oxides can be decomposed by heat treatment.
[0029] Patent Document 10 and Patent Document 11 describe reducing
the number of inclusions in an aluminum or aluminum alloy target to
be 40 inclusions/cm.sup.2 or less per unit area, that splashes can
be reduced by causing the maximum length of the inclusions to be 20
.mu.m or less, that reducing the inclusions in the sputtering
target is particularly important in order to inhibit the generation
of particles and splashes, and reducing inclusions by filtering
molten metal with a ceramic filter.
[0030] Patent Document 12 described a method of producing a high
purity copper or copper alloy sputtering target having an oxygen
content of 100 ppm or less, carbon content of 150 ppm or less,
nitrogen [content] of 50 ppm or less, and sulfur content of 200 ppm
or less, wherein used is a high purity copper or copper alloy ingot
in which the oxygen content in the target is 100 ppm or less, the
carbon content is 150 ppm or less, the nitrogen [content] is 50 ppm
or less, and the sulfur content is 200 ppm or less, or the number
of indications having a flat bottom hole diameter of 0.5 mm or more
is 0.014 indications/cm.sup.2 or less in an ultrasonic inspection
performed from the target surface, and obtained by melting and
casting based on electron beam melting or vacuum induction skull
melting. However, the large inclusions detected in the ultrasonic
inspection are not observed in current high purity copper
targets.
[0031] Patent Document 13 describes that the gas components of
oxygen, nitrogen, and carbon contained in the copper alloy
sputtering target form inclusions at the crystal grain boundary and
cause the generation of particles, and that it is desirable to
reduce such gas components as much as possible since they cause the
unexpected generation of particles during the sputter life, and
unavoidable impurities excluding gas components are reduced to 10
wtppm or less.
[0032] [Patent Document 1] Japanese Published Unexamined Patent
Application No.H11-106842
[0033] [Patent Document 2] Japanese Published Unexamined Patent
Application No.2000-107596
[0034] [Patent Document 3] Japanese Published Unexamined Patent
Application No. S63-297583
[0035] [Patent Document 4] Japanese Published Unexamined Patent
Application No. S64-55394
[0036] [Patent Document 5] Japanese Published Unexamined Patent
Application No. H1-152291
[0037] [Patent Document 6] Japanese Published Unexamined Patent
Application No. S64-8289
[0038] [Patent Document 7] Japanese Published Unexamined Patent
Application No. 2005-307343
[0039] [Patent Document 8] Japanese Published Examined Patent
Application No.2004-513228
[0040] [Patent Document 9] Japanese Published Unexamined Patent
Application No. H5-214519
[0041] [Patent Document 10] Japanese Published Unexamined Patent
Application No. H9-25564
[0042] [Patent Document 11] Japanese Published Unexamined Patent
Application No. H11-315373
[0043] [Patent Document 12] Japanese Published Unexamined Patent
Application No.2000-239836
[0044] [Patent Document 13] W02004/083482
DISCLOSURE OF INVENTION
[0045] In light of the foregoing circumstances, an object of this
invention is to use high purity copper or high purity copper alloy
from which harmful P, S, C, 0-based inclusions have been reduced as
the raw material and controlling the existence form of nonmetal
inclusions, and thereby reduce the occurrence of rupture of a
bonding wire and improve the reproducibility of mechanical
properties, or reduce the percent defect of a semiconductor device
wiring formed by sputtering a high purity copper target with
favorable reproducibility.
Means for Solving the Problems
[0046] As a result of intense study to solve the foregoing
problems, the present inventors made the following discovery.
Specifically, the inventors discovered that, by reducing as much as
possible the abundance of nonmetal inclusions having a particle
size of 0.5 .mu.m or more and 20 .mu.m or less existing in the high
purity copper and causing such amount to be 10,000 inclusions/g or
less, it is possible to reduce the occurrence of rupture of a
bonding wire, or reduce the percent defect of a semiconductor
device wiring formed by sputtering a high purity copper or copper
alloy target with favorable reproducibility.
[0047] Based on the foregoing discovery, the present invention
provides:
1) High purity copper having a purity of 6N or higher, wherein
content of each of the respective components of P, S, 0, and C is 1
ppm or less, and nonmetal inclusions having a particle size of 0.5
.mu.m or more and 20 .mu.m or less contained in the copper are
10,000 inclusions/g or less; and 2) The high purity copper
according to 1) above, wherein inclusions of carbon or carbide
having a particle size of 0.5 .mu.m or more and 20 .mu.m or less
are 5,000 inclusions/g or less.
[0048] The present invention additionally provides:
3) A method of producing high purity copper based on electrolysis,
wherein electrolysis is performed by providing a partition between
a cathode and an anode, and, upon supplying electrolyte extracted
from an electrolytic cell on the anode side or additional
electrolyte to an electrolytic cell on the cathode side, passing
the electrolyte through an activated carbon filter immediately
before supplying it to the electrolytic cell on the cathode side,
and thereafter supplying the electrolyte to the electrolytic cell
on the cathode side; 4) The method of producing high purity copper
based on electrolysis according to 3) above, wherein a purity of 6N
or higher, content of each of the respective components of P, S, 0,
and C being 1 ppm or less, and nonmetal inclusions having a
particle size of 0.5 .mu.m or more and 20 .mu.m or less contained
in the copper being 10,000 inclusions/g or less are achieved based
on electrolysis; and 5) The method of producing high purity copper
based on electrolysis according to 3) above, wherein inclusions of
carbon or carbide having a particle size of 0.5 .mu.m or more and
20 .mu.m or less contained in the copper are made to be 5,000
inclusions/g or less.
Effect of the Invention
[0049] Accordingly, as a result of using high purity copper as the
raw material from which harmful P, S, C, O-based inclusions have
been reduced and controlling the existence form of nonmetal
inclusions, it is possible to reduce the occurrence of rupture of a
bonding wire and improve the reproducibility of the mechanical
strength, or inhibit the generation of particles upon sputtering a
high purity copper or high purity copper target, and a superior
effect of being able to reduce the percent defective of the
semiconductor device wiring is yielded.
BEST MODE FOR CARRYING OUT THE INVENTION
[0050] P, S, O, and C are particularly problematic as impurities
that cause the generation of inclusions. Since the meltability of
these elements in copper is extremely low, the bulk thereof becomes
inclusions in copper. Particularly, in order to achieve the high
purity of copper according to the present invention, it is taboo to
add organic additives such as glue or polymer for smoothing or the
like which have been conducted conventionally. This is because the
addition of such additives will increase the existence of P, S, O,
and C.
[0051] Moreover, electrolyte of a sulfuric acid system that
particularly causes nonmetal inclusions, in particular S, to get
mixed in was not used, but nitric or hydrochloric electrolyte was
used. Nevertheless, even upon taking the foregoing measures, the
inclusion of large amounts of P, S, O, and C as impurities was
acknowledged. Thus, it was necessary to seek the cause of increase
in impurities elsewhere; that is, other than the electrolyte
itself.
[0052] Thus, through the intense study of the source of inclusions,
it has been confirmed that such sources include SiO.sub.2, C, and
AS.sub.2O.sub.3 which are contained in the electrolyte upon
performing electrolysis to copper as a result of organic matter
eluting from the electrolytic device, particularly piping or the
like for supplying and circulating the electrolyte, environment in
which the electrolytic device is placed, and as a result of being
adhered to the anode.
[0053] Moreover, P, S, and O that are contained in the electrolyte
exist as the suspended solids of CuP, CuS, and CuO, and it has also
been discovered that the cathode sometimes causes these suspended
solids to be included in the copper during the electrolysis, and
that these suspended solids are the primary cause of
contamination.
[0054] In particular, in cases where the impurities are organic
matter, if the electrolytic copper containing organic matter of
several ppm or more in a high concentration is to be melted by way
of high frequency melting in order to achieve high purity, carbon
(C) that is formed as a result of the decomposition of the organic
matter will get mixed in as is in the melted copper.
[0055] In light of the above, it is important to avoid adding
additives to the electrolyte, separate the cathode and the anode
with a diaphragm, and pass activated carbon through a filter
immediately before supplying the electrolyte to the cathode in
order to eliminate the organic matter and suspended solids, and it
has been discovered that the foregoing process is effective in
reducing inclusions.
[0056] There are SiO.sub.2, C, Al.sub.2O.sub.3, CuP, CuS, CuO and
the like as the foregoing impurities, but CuP, CuS, and CuO are
copper compounds that hardly become a solid solution in Cu.
Meanwhile, C solid matter (graphite), SiO.sub.2, and
Al.sub.2O.sub.3 exist as dust, and these exist as solid matter in
the copper structure.
[0057] The term "nonmetal inclusions" as used in this specification
refers to the solid matter existing in the copper structure. Once
these solid matters get mixed in, they cannot be eliminated
sufficiently in the melting process. Among the above, carbon or
carbide having carbon as its component is particularly harmful. In
addition, when carbon or carbide having carbon as its component get
mixed in upon becoming a bonding wire or in the semiconductor
production process, it becomes extremely difficult to eliminate
such carbon or carbide.
[0058] These impurities cause defects in the bonding wire or
semiconductor equipment and become even a greater problem pursuant
to the miniaturization of such semiconductor equipment.
[0059] In light of the above, when producing high purity copper
based on electrolysis, upon providing a partition between the anode
and the cathode and supplying the electrolyte extracted from the
anode-side electrolytic cell (anode box) or the additional
electrolyte to the cathode-side electrolytic cell (cathode box), an
important process is to pass the electrolyte through an activated
carbon filter immediately before supplying such electrolyte to the
cathode-side electrolytic cell, and thereafter supplying the
electrolyte to cathode-side electrolytic cell to perform
electrolysis.
[0060] In the foregoing case, for example, the inclusions cannot be
eliminated if a standard polypropylene filter is used.
Specifically, this means that the elimination of inclusions will be
difficult depending on the type of filter. Moreover, if the
electrolyte is supplied from the anode box to the cathode box
through introduction using a piping or a pump, the reduction of
inclusions is similarly difficult.
[0061] This is because the use of a piping or a pump in itself
becomes the contamination source. Although these may seem to be
innocent processes, in order to prevent the deterioration of
characteristics caused by the existence of trace amounts of minute
nonmetal inclusions, utmost attention must also be given even in
the foregoing electrolysis process.
[0062] The electrolytic production process for producing the high
purity copper was described above, and the high purity copper of
the present invention can only be obtained with the foregoing
process. As the starting material, a commercially available high
purity copper material having a purity level of 5N or less can be
used. Nevertheless, this starting material contains metal
components other than Cu, nonmetal components, P, S, O, C and their
compounds (SiO.sub.2, Al.sub.2O.sub.3, CuP, CuS, CuO and so on)
each in the amount of several ppm to several 1000 ppm.
[0063] Although the high purity copper of the present invention
uses the foregoing starting material as the raw material,
desirably, the high purity copper raw material has a purity of 6N
or higher, content of the respective components of P, S, O, and C
is 1 ppm or less, and nonmetal inclusions having a particle size of
0.5 .mu.m or more are 10,000 inclusions/g or less.
[0064] The foregoing nonmetal inclusions or the carbon system
inclusions of carbon or carbide were measured with the "light
scattering automatic particle counter for liquid" (manufactured by
Kyushu RION Corporation). The measurement method is based on
sorting the particle size in the liquid and measuring the particle
concentration and particle count. The foregoing measuring equipment
is also known as a "liquid particle counter" and is based on JIS B
9925 (this measuring equipment is hereinafter referred to as the
"liquid particle counter").
[0065] To explain the specific measurement method, 5 g [of the raw
material] were sampled and slowly melted in 200 cc of acid so that
the inclusions will not melt, diluted with deionized water to be
500 cc, and 10 cc of this was taken and measured with the liquid
particle counter. For example, if the number of inclusions is 800
inclusions/cc, this means that 0.1 g of the sample was analyzed in
10 cc, and the number of inclusions will be 8000 inclusions/g.
[0066] Note that the number of nonmetal inclusions or the carbon
system inclusions of carbon or carbide was measured with the liquid
particle counter as described above. However, it should be easily
understood that it does not matter upon using other means if
similar analysis of the number of inclusions can be performed.
[0067] The components of P, S, O, and C all become impurities in
copper and form phosphides, sulfides, carbides, and oxides that do
not become a solid solution in the copper, and may cause the
formation of nonmetal inclusions. Thus, reducing these components
to be 1 ppm or less will reduce the nonmetal inclusions and improve
the characteristics of high purity copper.
[0068] The nonmetal inclusions having a particle size of 0.5 .mu.m
or more and 20 .mu.m or less contained in the copper are made to be
10,000 inclusions/g or less in the present invention, and the
amount of such nonmetal inclusions is the problem. If the number of
nonmetal inclusions exceeds 10,000 inclusions/g or less, they will
become foreign matter in the thinned bonding wire, and it becomes
easier for rupture to occur with such foreign matter as the
source.
[0069] In addition, the nonmetal inclusions in the target will
reach a level of becoming problematic, become protrusive foreign
matter during the erosion of the target, and abnormal discharge is
easily generated to such protrustive foreign matter. This causes
the generation of particles during sputtering.
[0070] In a bonding wire or a sputtering target, the numerical
value of nonmetal inclusions having a particle size of 0.5 .mu.m or
more and 20 .mu.m or less being 10,000 inclusions/g or less is not
necessarily a large amount. This numerical value cannot be achieved
simply by reducing the content of impurity elements configuring the
nonmetal inclusions to be 1 ppm or less.
[0071] Nevertheless, this is important in order to reduce the
occurrence of rupture of a bonding wire and improve the
reproducibility of the mechanical strength, reduce the percent
defective of the semiconductor device wiring that is formed by
sputtering a high purity copper target. It is necessary to
recognize the importance of this fact as the latest technology.
[0072] In particular, the existence of inclusions of carbon or
carbide is harmful, and it is desirable to reduce the carbon or
carbide having a particle size of 0.5 .mu.m or more and 20 .mu.m or
less to be 5,000 inclusions/g or less. Since the carbon or carbide
is often a result of contamination from organic matter as described
above, the use of organic matter in electrolysis must be
avoided.
[0073] A high purity copper alloy bonding wire or sputtering target
can be produced by additionally adding an alloy element with the
foregoing high purity copper as the base material.
[0074] Although there is no particular limitation as the alloy
element, the sputtering target may be used upon adding 10% or less
of one type or two types or more among the normally added elements
of Al, Ag, B, Cr, Ge, Mg, Mn, Nd, Si, Sn, Ti, and Zr to the high
purity copper.
[0075] Commercially available copper raw materials and alloy
component materials may be used as the raw material for producing
the high purity copper or high purity copper alloy of the present
invention. However, it is desirable to reduce, as much as possible,
the impurity content of radioactive elements, alkali metals,
transition metals, heavy metals and the like which have an adverse
effect on electronic devices or the like especially when using the
obtained high purity copper or high purity copper alloy as the raw
material of a sputtering target.
[0076] In particular, with semiconductor equipment, radioactive
elements such as U and Th as impurities affect the MOS with their
radiation, alkali metals and alkali earth metals such as Na and K
deteriorate the MOS interface characteristics, and transition
metals or heavy metals such as Fe, Ni, and Co generate an interface
state or cause a junction leak, and these elements may contaminate
the semiconductor equipment through the copper film.
[0077] In light of the above, it is desirable to reduce the total
amount of alkali metals and alkali earth metals to be 5 ppm or
less, the total amount of radioactive elements to be 1 ppb or less,
and the total amount of heavy metals and light metals contained as
impurities other than the alloy elements to be 10 ppm or less.
[0078] A target is usually prepared by melting and casting the raw
material, performing such plastic forming processes as forging and
rolling as well as heat treatment in order to achieve the
appropriate crystal structure, particle size and the like of the
cast material, and performing finish processing to obtain the final
target size in the shape of a disk or the like.
[0079] The quality of the target such as its crystal orientation
can be adjusted by appropriately combining the plastic forming
process such as forging and rolling, and the heat treatment
process.
[0080] The primary inclusions in the copper and copper alloy are
oxides, nitrides, carbides, and sulfides, and they are generated in
the process of melting and casting the raw material. Thus, melting
and casting are performed in a nonoxidizing atmosphere, or
preferably in a vacuum for efficiently eliminating oxygen,
nitrogen, and sulfur as the inclusion sources. As the melting
method, electron beam melting using a water-cooled copper crucible,
vacuum induction skull melting, or the use of a water-cooled copper
mold is suitable for avoiding the contamination of carbon and
oxygen from the graphite crucible used in conventional high
frequency melting.
[0081] When the copper or copper alloy target from which the
foregoing impurities and inclusions were reduced is sputtered, the
reduction of impurities and inclusions of the target is reflected
in the thin film, and it is possible to form a semiconductor device
wiring and thin film having the same level of impurities and
inclusions.
EXAMPLES
[0082] The Examples and Comparative Examples of the present
invention are now explained. These Examples are merely
illustrative, and the present invention shall in no way be limited
thereby. In other words, various modifications and other
embodiments based on the technical spirit claimed in the claims
shall be included in the present invention as a matter of
course.
Example 1
[0083] 4N--Cu was used as the raw material anode and electrolysis
was performed using nitric electrolyte. Here, electrolysis was
performed by separating the cathode and the anode with a diaphragm,
extracting the Cu ion-containing electrolyte that was eluted from
the anode, and passing it through an activated carbon filter with a
sieve opening of approximately 0.1 .mu.m immediately before being
placed in the cathode box.
[0084] As a result of subjecting the obtained electrolytic copper
to vacuum induction skull melting and measuring the obtained high
purity copper with a liquid particle counter, approximately 4,000
inclusions/g of nonmetal inclusions having a particle size of 0.5
.mu.m or more and 20 .mu.m or less were detected. In addition, the
P, S, O, and C contained in the electrodeposited copper were all 1
ppm or less. Moreover, the inclusions of carbon or carbide were
approximately 600 inclusions/g. These all sufficiently satisfied
the conditions of the present invention.
[0085] Based on the production conditions of the present invention,
Example 1 is able to produce high purity copper having a purity of
6N or higher, wherein content of each of the respective components
of P, S, O, and C is 1 ppm or less, and nonmetal inclusions having
a particle size of 0.5 .mu.m or more and 20 .mu.m or less contained
in the copper are 10,000 inclusions/g or less. However, if the
foregoing conditions cannot be achieved, the electrolyte may be
additionally passed through the activated carbon filter as
needed.
[0086] This is because the ultimate objective is to produce a
sputtering target that is free from the generation of particles or
a bonding wire that will not rupture by using the high purity
copper of the present invention.
Comparative Example 1
[0087] Under the same conditions as Example 1, filtering was
performed with a standard polypropylene filter (filtering rate of
0.5 .mu.m). As a result of subjecting the obtained electrolytic
copper to vacuum induction skull melting and measuring the obtained
high purity copper with a liquid particle counter, approximately
20,000 inclusions/g of nonmetal inclusions having a particle size
of 0,5 .mu.m or more and 20 .mu.m or less were detected. In
addition, the P, S, O, and C contained in the electrodeposited
copper were 2 ppm, 6 ppm, 10 ppm, and 10 ppm, respectively.
Moreover, the inclusions of carbon or carbide were approximately
8,400 inclusions/g.
[0088] None of these satisfied the conditions of the present
invention.
Comparative Example 2
[0089] The conditions were the same as Example 1, but the Cu
ion-containing electrolyte that was eluted from the anode was
extracted without using a filter and placed in the cathode box.
[0090] As a result of subjecting the obtained electrolytic copper
to vacuum induction skull melting and measuring the obtained high
purity copper with a liquid particle counter, approximately 52,000
inclusions/g of nonmetal inclusions having a particle size of 0.5
.mu.m or more and 20 .mu.m or less were detected. In addition, the
P, S, O, and C contained in the electrodeposited copper were
respectively 4 ppm, 8 ppm, 20 ppm, and 20 ppm. Moreover, the
inclusions of carbon or carbide were approximately 25,000
inclusions/g. None of these satisfied the conditions of the present
invention.
Comparative Example 3
[0091] Under the same conditions as Example 1, the activated carbon
filter was placed immediately after the anode box and the
electrolyte was passed therethrough, and returned to the cathode
box via a piping and a pump.
[0092] As a result of subjecting the obtained electrolytic copper
to vacuum induction skull melting and measuring the obtained high
purity copper with a liquid particle counter, approximately 12,000
inclusions/g of nonmetal inclusions having a particle size of 0.5
.mu.m or more and 20 .mu.m or less were detected. In addition, the
P, S, O, and C contained in the electrodeposited copper were
respectively 1 ppm, 4 ppm, 2 ppm, and 3 ppm. Moreover, the
inclusions of carbon or carbide were approximately 6,500
inclusions/g. Although the results showed fewer inclusions and
impurities of P, S, O, C in comparison to Comparative Example 1 or
Comparative Example 2, they increased in comparison to Example
1.
[0093] Although the use of a piping and a pump was merely added, it
was not possible to achieve the objective of reducing the
inclusions or impurities.
(Evaluation of target based on nonmetal inclusions)
[0094] Subsequently, the high purity copper of Example 1 prepared
as described above was melted to produce a target.
[0095] As a result of measuring this target with a liquid particle
counter, the nonmetal inclusions having a particle size of 0.5
.mu.m or more and 20 .mu.m or less were approximately 6,500
inclusions/g. The increase of nonmetal inclusions was acknowledged
at the stage of producing the target. However, the amount was
small.
[0096] This is considered to be a result of the number of nonmetal
inclusions contained in the raw material itself to be melted being
small. Accordingly, as explained below, upon sputtering this
target, the result was the generation of few particles.
[0097] As a result of performing electrolytic etching to this
target and analyzing the protrusive nonmetal inclusions that
appeared on the surface using FIB-AES, 40% of the overall nonmetal
inclusions was carbon-based inclusions (carbon and carbide), and
the number of carbon-based inclusions having a particle size of 0.5
.mu.m or more and 20 .mu.m or less was approximately 3,500
inclusions/g.
[0098] As a result of sputtering this target and depositing a
copper thin film on a 300 mm wafer, the number of particles having
a particle size of 0.05 .mu.m or more was 17 particles/square inch,
and it was possible to obtain a favorable sputtered film.
(Application to a bonding wire)
[0099] Upon producing a bonding wire, the processes of melting the
high purity copper of Example 1, and additionally subjecting this
to casting, forging, heat treatment and rolling (drawing) are
performed. The process is basically the same as producing the
foregoing target. Accordingly, it is effective to use the cold
crucible melting method in order to prevent the inclusion of
impurities in the melting process and obtain an ingot.
[0100] As a result of similarly performing electrolytic etching to
the bonding wire and analyzing the protrusive nonmetal inclusions
that appeared on the surface using FIB-AES, 40% of the overall
nonmetal inclusions was carbon-based inclusions (carbon and
carbide), and the number of carbon-based inclusions having a
particle size of 0.5 .mu.m or more and 20 .mu.m or less was
approximately 4,200 inclusions/g.
[0101] The existence of few nonmetal inclusions as described above
is able to effectively inhibit the rupture of the bonding wire.
(Evaluation of Comparative Example 1 to Comparative Example 3)
[0102] The foregoing high purity copper was processed and subject
to heat treatment to produce a target. As a result of measuring the
target with a liquid particle counter, the number of nonmetal
inclusions having a particle size of 0.5 .mu.m or more and 20 .mu.m
or less was approximately 30,000 inclusions/g or more.
[0103] At the stage of producing this target, the increase of
nonmetal inclusions was acknowledged in proportion to the raw
material. Moreover, the amount of increase was significant. This
may be caused by a result that the number of nonmetal inclusions
contained in the raw material itself to be melted is great.
[0104] Accordingly, upon sputtering this target, the result was the
proportional increase in the generation of particles.
(Application of Comparative Example 1 to Comparative Example 3 to a
bonding wire)
[0105] This is also similar to the production process of the target
as described above. As a result of measuring the bonding wire with
a liquid particle counter, the number of nonmetal inclusions having
a particle size of 0.5 .mu.m or more and 20 .mu.m or less was
similarly approximately 30,000 inclusions/g or more. At the stage
of producing this bonding wire, the increase of nonmetal inclusions
was acknowledged in proportion to the raw material. Moreover, the
amount of increase was significant.
[0106] Accordingly, the rupture off the bonding wire increased in
proportion to the abundance of nonmetal inclusions.
INDUSTRIAL APPLICABILITY
[0107] Provided is a high purity copper from which harmful P, S, C,
O inclusions have been reduced. As a result of controlling the
existence form and amount of nonmetal inclusions, it is possible to
reduce the occurrence of rupture of a bonding wire and improve the
reproducibility of the mechanical strength, or inhibit the
generation of particles upon sputtering a high purity copper or
high purity copper target, and a superior effect of being able to
reduce the percent defective of the semiconductor device wiring is
yielded.
[0108] Accordingly, under the recent circumstances where LSI
semiconductor devices are subject to higher integration and the
linewidth thereof being miniaturized to 0.25 .mu.m or less, the
present invention is effective as a high purity copper and high
purity copper alloy target and a bonding wire that will not rupture
easily which are suitable for forming a copper wiring or the like
that is capable of preventing problems such as short circuits and
disconnections.
* * * * *