U.S. patent application number 11/915628 was filed with the patent office on 2009-11-05 for ultrahigh-purity copper and process for producing the same, and bonding wire comprising ultrahigh-purity copper.
This patent application is currently assigned to NIPPON MINING & METALS CO., LTD.. Invention is credited to Yuichiro Shindo, Kouichi Takemoto.
Application Number | 20090272466 11/915628 |
Document ID | / |
Family ID | 37532091 |
Filed Date | 2009-11-05 |
United States Patent
Application |
20090272466 |
Kind Code |
A1 |
Shindo; Yuichiro ; et
al. |
November 5, 2009 |
Ultrahigh-Purity Copper and Process for Producing the Same, and
Bonding Wire Comprising Ultrahigh-Purity Copper
Abstract
Provided is ultrahigh purity copper having a hardness of 40 Hv
or less, and a purity of 8N or higher (provided that this excludes
the gas components of O, C, N, H, S and P). With this ultrahigh
purity copper, the respective elements of O, S and P as gas
components are 1 wtppm or less. Also provided is a manufacturing
method of ultrahigh purity copper based on two-step electrolysis
using an electrolytic solution comprised of copper nitrate
solution, including the procedures of adding hydrochloric acid in
an electrolytic solution comprised of copper nitrate solution;
circulating the electrolytic solution; and performing two-step
electrolysis while eliminating impurities with a filter upon
temporarily setting the circulating electrolytic solution to a
temperature of 10.degree. C. or less. The present invention
provides a copper material that is compatible with the thinning
(wire drawing) of the above, and is capable of efficiently
manufacturing ultrahigh purity copper having a purity of 8N
(99.999999 wt %) or higher, providing the obtained ultrahigh purity
copper, and providing a bonding wire for use in a semiconductor
element that can be thinned.
Inventors: |
Shindo; Yuichiro; (Ibaraki,
JP) ; Takemoto; Kouichi; (Ibaraki, JP) |
Correspondence
Address: |
HOWSON & HOWSON LLP
501 OFFICE CENTER DRIVE, SUITE 210
FORT WASHINGTON
PA
19034
US
|
Assignee: |
NIPPON MINING & METALS CO.,
LTD.
Tokyo
JP
|
Family ID: |
37532091 |
Appl. No.: |
11/915628 |
Filed: |
April 24, 2006 |
PCT Filed: |
April 24, 2006 |
PCT NO: |
PCT/JP2006/308521 |
371 Date: |
June 17, 2009 |
Current U.S.
Class: |
148/432 ;
205/98 |
Current CPC
Class: |
C22B 15/0089 20130101;
H01L 2924/01208 20130101; C22B 15/0084 20130101; H01L 24/45
20130101; H01L 2924/14 20130101; C22B 15/0073 20130101; H01L 24/43
20130101; H01L 2224/45147 20130101; H01L 2224/45015 20130101; H01L
2224/43848 20130101; H01L 2224/45565 20130101; Y02P 10/236
20151101; H01L 2924/01105 20130101; H01L 2224/456 20130101; C25C
1/12 20130101; H01L 2224/48624 20130101; H01L 2224/43 20130101;
H01L 2224/05624 20130101; C22C 9/00 20130101; C25C 7/06 20130101;
H01L 2924/10253 20130101; H01L 2924/00011 20130101; Y02P 10/20
20151101; H01L 2224/45144 20130101; H01L 2224/45147 20130101; H01L
2924/01008 20130101; H01L 2224/45147 20130101; H01L 2924/01015
20130101; H01L 2224/45147 20130101; H01L 2924/01016 20130101; H01L
2224/45147 20130101; H01L 2924/01205 20130101; H01L 2924/01046
20130101; H01L 2924/00011 20130101; H01L 2224/05624 20130101; H01L
2924/00014 20130101; H01L 2224/45565 20130101; H01L 2224/45147
20130101; H01L 2224/45647 20130101; H01L 2224/45147 20130101; H01L
2924/01208 20130101; H01L 2224/48824 20130101; H01L 2924/00
20130101; H01L 2224/48624 20130101; H01L 2924/00 20130101; H01L
2224/45144 20130101; H01L 2924/00015 20130101; H01L 2224/45147
20130101; H01L 2924/013 20130101; H01L 2924/00 20130101; H01L
2224/45015 20130101; H01L 2924/00 20130101; H01L 2224/43848
20130101; H01L 2924/20105 20130101; H01L 2224/43848 20130101; H01L
2924/20106 20130101; H01L 2224/43848 20130101; H01L 2924/20107
20130101; H01L 2224/43848 20130101; H01L 2924/2011 20130101; H01L
2224/43848 20130101; H01L 2924/20111 20130101; H01L 2924/00011
20130101; H01L 2924/01033 20130101; H01L 2224/45147 20130101; H01L
2924/01001 20130101; H01L 2224/45147 20130101; H01L 2924/01006
20130101; H01L 2224/45147 20130101; H01L 2924/01007 20130101 |
Class at
Publication: |
148/432 ;
205/98 |
International
Class: |
C22C 9/00 20060101
C22C009/00; C25D 21/06 20060101 C25D021/06; C25D 3/38 20060101
C25D003/38 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 15, 2005 |
JP |
2005-174896 |
Claims
1. Ultrahigh purity copper having a hardness of 40 Hv or less, and
a purity of 8N or higher (provided that this excludes the gas
components of O, C, N, H, S and P).
2. The ultrahigh purity copper according to claim 1, wherein the
respective elements of O, S and P as gas components are 1 wtppm or
less.
3. The ultrahigh purity copper according to claim 1 or claim 2,
wherein the recrystallization temperature is 200.degree. C. or
less.
4. A bonding wire comprised of the ultrahigh purity copper
according to any one of claims 1 to 3.
5. A manufacturing method of ultrahigh purity copper based on
two-step electrolysis using an electrolytic solution comprised of
copper nitrate solution, including the procedures of adding
hydrochloric acid in an electrolytic solution comprised of copper
nitrate solution; circulating the electrolytic solution; and
performing two-step electrolysis while eliminating impurities with
a filter upon temporarily setting the circulating electrolytic
solution to a temperature of 10.degree. C. or less.
6. The manufacturing method of ultrahigh purity copper according to
any one of claims 1 to 3 based on two-step electrolysis using an
electrolytic solution comprised of copper nitrate solution,
including the procedures of adding hydrochloric acid in an
electrolytic solution comprised of copper nitrate solution;
circulating the electrolytic solution; and performing two-step
electrolysis while eliminating impurities with a filter upon
temporarily setting the circulating electrolytic solution to a
temperature of 10.degree. C. or less.
Description
TECHNICAL FIELD
[0001] The present invention relates to ultrahigh purity copper
having a purity of 8N (99.999999 wt %) or higher that can be
subject to thinning without breaking, and the manufacturing method
of such ultrahigh purity copper. The present invention also relates
to a bonding wire comprised of such ultrahigh purity copper.
BACKGROUND ART
[0002] Conventionally, a gold wire has been used as the bonding
wire for electrically connecting a silicon chip as the
semiconductor element and the lead frame. Nevertheless, from the
perspective that a gold wire is expensive and the strength thereof
is inferior to copper, proposals have been made for switching to a
copper wire (Non-Patent Documents 1 and 2).
[0003] High purity copper is characterized in that it is soft since
the recrystallization temperature is low, it has favorable
workability since there is hardly any brittleness in the
intermediate temperature range, and it has high thermal
conductivity since the electrical resistance is small at ultracold
temperatures. It is also characterized by characteristic
improvement due to addition of infinitesimal quantity of elements
and great impact of impurity contamination on the
characteristics.
[0004] The foregoing conventional technologies utilize such
characteristics of high purity copper to manufacture a bonding wire
for semiconductor elements.
[0005] Nevertheless, a copper wire also entails several drawbacks;
for instance, a copper wire is easily oxidized when forming the tip
thereof into a ball shape, and there is a problem in that the
silicon chip will be damaged when the ball shape is inferior or
because the ball is too hard.
[0006] Proposals have been made to overcome the foregoing problems
that arise during the shaping of the ball and with regard to the
hardness of copper; namely, employing a protective atmosphere
(reduction or inert atmosphere), and realizing copper having a
purity level of 4N to 6N by eliminating impurities so as to soften
such copper.
[0007] As conventional technologies of copper bonding wires,
numerous documents have been disclosed; for instance, a copper
bonding wire wherein the impurities are 10 ppm or less (refer to
Patent Document 1), a copper bonding wire wherein the impurities
containing B are 50 ppm or less (refer to Patent Document 2), a
bonding wire for use in a semiconductor element wherein the copper
purity is 99.999% or higher and the S content is 0.0005% or less
(refer to Patent Document 3), a copper bonding wire comprised of
high purity copper subject to annealing during the wire drawing
process (refer to Patent Document 4), a bonding wire for use in a
semiconductor device wherein the total content of impurities is 5
ppm or less, and the rupture strength is 18 to 28 kg/mm.sup.2
(refer to Patent Document 5), a copper bonding wire with adjusted
crystal grains wherein the impurities are 10 ppm or less (refer to
Patent Document 6), a bonding wire for use in a semiconductor
element wherein the copper purity is 99.999% or higher, the S
content is 0.0005% or less, and 0.02% of In, Hf and Mg is added
thereto (refer to Patent Document 7), a bonding wire for use in a
semiconductor element wherein the copper purity is 99.999% or
higher, the S content is 0.0005% or less, and the alkali metals
elements and alkali earth metal elements are 0.0001% or less (refer
to Patent Document 8), a bonding wire for use in a semiconductor
element wherein the copper purity is 99.999% or higher, the S
content is 0.0005% or less, In and Mg are less than 0.02%, and Be,
B, Zr, Y, Ag, Si, Ca and rare earths are added thereto (refer to
Patent Document 9), a bonding wire for use in a semiconductor
element wherein the coefficient of extension during rupture is 3%
to 15% (refer to Patent Document 10), a metal wire for wire bonding
wherein a gold plating layer is provided on the copper wire (refer
to Patent Document 11), a copper thin wire superior in ultrasonic
weldability wherein the copper purity is 99.999% or higher, and the
tensile strength is less than 23 kg/mm.sup.2 (refer to Patent
Document 12), a bonding wire containing additive elements in an
amount of 10 ppm or less (refer to Patent Document 13), a bonding
wire for use in a semiconductor integrated circuit element wherein
the copper purity of the core is 99.99% to 99.999%, and the coating
layer is 99.999% or higher (refer to Patent Document 14), a copper
alloy ultrathin wire for use in a semiconductor device wherein the
copper purity is 99.9999% or higher, the content of Fe and Ag is
0.1% to 3.0%, and containing Mg in an amount of 0.5 to 400 ppm
(refer to Patent Document 15), a copper bonding wire wherein the
copper purity is 99.9999% or higher, and containing rare earths or
Zr in an amount of 0.0002% to 0.002% (refer to Patent Document 16),
and a copper bonding wire that does not damage the electrode tip
using a porous metal (refer to Patent Document 17), among
others.
[0008] Nevertheless, all of these conventional technologies relate
to a purity level of 5N to 6N. With that said, it should be known
that it is not technically easy to industrially manufacture the
foregoing high purity copper having a purity level of 5N to 6N.
These technologies conform to the objective of conventional bonding
wires.
[0009] In recent years, there are demands of copper bonding subject
to thinning. Nevertheless, even with the foregoing high purity
copper having a purity level of 5N to 6N, there is a problem in
that the copper itself has a higher hardness in comparison to gold,
and will rupture during the wire drawing process. In order to
overcome this problem, the copper must possess a certain level of
softness (low hardness). In addition, a high purity copper bonding
wire having a purity level of 5N to 6N also had the problem of
generating cracks in the silicon under the Al pad during
adhesion.
[0010] Accordingly, practically speaking, the conventional
technologies had problems in not being able to obtain a copper
bonding wire that supersedes the performance of Au.
[Non-Patent Document 1] "Practical Application Technology of Copper
Wire Bonding" (No. 42, 1989) pages 77 to 80 [Non-Patent Document 2]
"Development of Copper Bonding Wire" Electronics Special Feature
(No.10, 1991-1) pages 53 to 56 [Patent Document 1] Japanese Patent
Laid-Open Publication No. S61-251062 [Patent Document 2] Japanese
Patent Laid-Open Publication No. S61-255045 [Patent Document 3]
Japanese Patent Laid-Open Publication No. S62-104061 [Patent
Document 4] Japanese Patent Laid-Open Publication No. S62-20858
[Patent Document 5] Japanese Patent Laid-Open Publication No.
S62-22469 [Patent Document 6] Japanese Patent Laid-Open Publication
No. S62-89348 [Patent Document 7] Japanese Patent Laid-Open
Publication No. S62-127436 [Patent Document 8] Japanese Patent
Laid-Open Publication No. S62-216238 [Patent Document 9] Japanese
Patent Laid-Open Publication No. S62-127438 [Patent Document 10]
Japanese Patent Laid-Open Publication No. S63-3424 [Patent Document
11] Japanese Patent Laid-Open Publication No. S63-56924 [Patent
Document 12] Japanese Patent Laid-Open Publication No. S63-72858
[Patent Document 13] Japanese Patent Laid-Open Publication No.
S63-3424 [Patent Document 14] Japanese Patent Laid-Open Publication
No. S63-236338 [Patent Document 15] Japanese Patent Laid-Open
Publication No. H3-291340 [Patent Document 16] Japanese Patent
Laid-Open Publication No. H4-247630
[Patent Document 17] Japanese Patent Laid-Open Publication No.
2003-174057
DISCLOSURE OF THE INVENTION
[0011] An object of the present invention is to obtain a copper
material that is compatible with the thinning (wire drawing) of the
above. The conventional high purity copper having a purity level of
5N to 6N, which in itself is extremely high purity copper, was able
to achieve a certain degree of softness by eliminating impurities
as much as possible.
[0012] Nevertheless, although it cannot necessarily be said that
the further purification of copper will lead to the reduction of
hardness that will be compatible with thinning or the like, the
present invention attempted to achieve higher purification of the
high purity copper having a purity level of 5N to 6N. In other
words, the present invention aims to develop technology for
efficiently manufacturing ultrahigh purity copper having a purity
of 8N (99.999999 wt %) or higher, and provide extremely soft
ultrahigh purity copper obtained thereby which in particular
enables thinning. The present invention also aims to provide a
bonding wire for use in a semiconductor element capable of
preventing the generation of cracks in the silicon during bonding,
inhibiting the heat generation caused by the low resistivity of
wires, and preventing oxidization during heat treatment.
[0013] In order to achieve the foregoing objects, the present
invention, based on the premise of realizing high purification
through electrolytic refining, provides ultrahigh purity copper
having a hardness of 40 Hv or less, and a purity of 8N or higher
(provided that this excludes the gas components of O, C, N, H, S
and P). If the hardness is 40 Hv or less, it is possible to prevent
the generation of cracks in the silicon during bonding and enable
thinning. The ultrahigh purity copper of this invention is able to
achieve this object.
[0014] It is desirable that the respective elements of O, S and P
as gas components are 1 wtppm or less. These gas components
(impurities) create a compound with Cu, and become deposited as a
heterophase in the Cu. Although such heterophase deposits are
extremely trivial in the ultrahigh purity copper, rupture will
occur during the thinning process with such heterophase deposits as
the origin. In addition, since the Cu will harden, cracks will
easily occur in the silicon during bonding. Accordingly, it is
necessary to reduce the foregoing gas components as much as
possible.
[0015] Moreover, with the ultrahigh purity copper of the present
invention, it is possible to achieve a recrystallization
temperature of 200.degree. C. or less. Thus, annealing can be
performed at low temperatures during the manufacture process such
as the wire drawing process, and it is thereby possible to lower
the hardness even further.
[0016] As a result of the foregoing configuration, thinning is
enabled, and it is possible to obtain ultrahigh purity copper that
is soft and suitable as a bonding wire.
[0017] Upon manufacturing the ultrahigh purity copper of the
present invention, electrolytic solution comprised of copper
nitrate solution added with hydrochloric acid is used, and
electrolysis is performed with two-step electrolysis. The
electrolytic solution is circulated. The liquid temperature of the
circulated solution is temporarily set to be 10.degree. C. or less,
and impurities such as AgCl are deposited and eliminated with a
filter so as to obtain a further purified electrolytic solution.
The electrolysis temperature is set to be 10 to 70.degree. C. Like
this, by performing electrolysis more than twice, it is possible to
obtain high purity copper having a purity level of 8N or higher. If
the electrolysis temperature is less than 10.degree. C., impurities
such as oxygen will increase and the electrodeposited Cu will
become brittle. If the electrolysis temperature exceeds 70.degree.
C., the evaporation of the electrolytic solution will become a
significant loss. Accordingly, it is desirable to set the
electrolysis temperature to 10 to 70.degree. C.
[Effect of the Invention]
[0018] As described above, the present invention yields a
significant effect of being able to efficiently manufacture
ultrahigh purity copper having a purity level of 8N (99.999999 wt
%) or higher. It is thereby possible to reduce the hardness and
obtain a copper material that is compatible with thinning (wire
drawing).
[0019] In particular, thinning of a bonding wire for a
semiconductor element is enabled. In addition, the present
invention yields a superior effect of being able to prevent the
generation of cracks in the silicon during bonding, inhibit the
heat generation caused by the low resistance of the wires, and
prevent the oxidization during heat treatment.
[0020] Since the improvement of corrosion resistance (oxidation
resistance) will not require the heating atmosphere to be a strict
Ar+H.sub.2 atmosphere, an additional effect is yielded in that the
labor efficiency is also favorable.
BEST MODE FOR CARRYING OUT THE INVENTION
[0021] A bulk copper raw material having a purity level of 4N was
used as the anode, a copper plate was used as the cathode, and an
electrolytic solution comprised of copper nitrate solution was used
to perform electrolysis based on two-step electrolysis. Since only
a purity level of 5 to 7N can be obtained in the first step,
electrolysis must be performed with two or more steps. The copper
raw material (4N) primarily contains large amounts of O, P and
S.
[0022] In the primary electrolysis, the bath temperature was set to
15.degree. C. or less, a nitric acid series electrolytic solution
was used, and hydrochloric acid was added to the electrolytic
solution in an amount of 0.1 to 100 ml/L. This is in order to
eliminate Ag as AgCl.
[0023] Then, electrolysis was performed at pH of 0 to 4, and
current density of 0.1 to 10 A/dm.sup.2. The electrolytic solution
was circulated, the electrolytic solution of the circuit was cooled
with a cooler to a temperature of 10.degree. C. or less to deposit
AgCl, and a filter was used to eliminate such AgCl and the like. It
is thereby possible to obtain high purity copper having a purity
level of 5N to 6N.
[0024] Subsequently, this copper having a purity level of 5N to 6N
was used to perform electrolysis once again under the same
electrolytic conditions as those described above. The electrolytic
solution was similarly circulated, the electrolytic solution of the
circuit was cooled with a cooler to a temperature of 10.degree. C.
or less to deposit AgCl, and a filter was used to eliminate such
AgCl and the like.
[0025] According to the foregoing process, it was possible to
obtain electrodeposited copper (deposited on the cathode) having a
purity level of 8N or higher. In other words, it was possible to
realize a purity level of 8N (99.999999 wt %) or higher excluding
gas components, and to make all metallic component as impurities to
be 0.01 wtppm or less.
[0026] In addition, the electrodeposited copper obtained by the
foregoing electrolysis may also be subject to vacuum melting such
as by electron beam melting. As a result of performing such vacuum
melting, it is possible to effectively eliminate alkali metals such
as Na and K and other volatile impurities, as well as gas
components such as Cl. As a result of performing degasification
with reducible gas as necessary, it is possible to eliminate and
reduce the gas components.
[0027] The ultrahigh purity copper having a purity level of 8N or
higher manufactured as described above satisfies the condition of
having a hardness of 40 Hv or less, and it is also possible to
achieve a recrystallization temperature of 200.degree. C. or
less.
EXAMPLES
[0028] Examples of the present invention are now explained. These
Examples merely illustrate a preferred example, and the present
invention shall in no way be limited thereby. In other words, all
modifications, other embodiments and modes covered by the technical
spirit of the present invention shall be included in this
invention.
Example 1
[0029] A bulk copper raw material having a purity level of 4N was
used as the anode, and a copper plate was used as the cathode to
perform electrolysis. The content of raw material impurities is
shown in Table 1. As shown in Table 1, the copper raw material (4N)
primarily contained large amounts of O, P and S. Table 1 also shows
the hardness and recrystallization temperature at this impurity
level. The hardness at a purity level of 4N was 45 Hv, and the
recrystallization temperature was 450.degree. C. The diameter of
the wire rod capable of being subject to thinning was 200 .mu.m.
The wires at this level were hard and generated cracks in the
silicon during bonding (adhesion).
[0030] A nitric acid series electrolytic solution having a bath
temperature of 30.degree. C. was used, and 1 ml/L of hydrochloric
acid was additionally added thereto. Electrolysis was performed at
a pH of 1.3, and a current density of 1 A/dm.sup.2. The
electrolytic solution was circulated, the electrolytic solution of
the circuit was temporarily cooled with a cooler to a temperature
of 2.degree. C., and a filter was used to eliminate the deposited
AgCl and the like. Thereby, as shown in Table 1, it was possible to
obtain high purity copper having a purity level of 6N. Table 1
shows the hardness and recrystallization temperature of copper
having a purity level of 6N. Hardness of the 6N copper was 42 Hv,
and the recrystallization temperature was reduced to 230.degree. C.
The diameter of the wire rod capable of being subject to thinning
was 40 .mu.m. Some cracks were generated in the silicon during
bonding (adhesion), but this was not as significant as the 4N
Cu.
[0031] Subsequently, this copper having a purity level of 6N was
used to perform electrolysis once again under the same electrolytic
conditions as those described above. The electrolytic solution was
similarly circulated, the electrolytic solution of the circuit was
temporarily cooled with a cooler to a temperature of 0.degree. C.,
and a filter was used to eliminate the deposited AgCl and the like.
Thereby, as shown in Table 1, it was possible to obtain ultrahigh
purity copper having a purity level of 9N.
[0032] Table 1 shows the hardness and recrystallization temperature
of copper having a purity level of 9N. The hardness was 38 Hv, and
the recrystallization temperature decreased to 150.degree. C. The
diameter of the wire rod capable of being subject to thinning was 2
.mu.m, and improved significantly. No cracks were generated in the
silicon during bonding (adhesion).
[0033] Example 1 achieved all conditions of the present invention;
namely, the hardness being 40 Hv or less and the recrystallization
temperature being 200.degree. C. or less.
TABLE-US-00001 TABLE 1 (O, P, S: wtppm) Recrystal- Hard- lization
Existence Pu- ness Temperature Thinning of Si rity Hv O P S
(.degree. C.) Diameter Cracks 4N 45 10 0.2 8.6 450 200 .mu.m Many
6N 42 <1 0.01 0.02 230 40 .mu.m Few 9N 38 <1 <0.005
<0.005 150 2 .mu.m None
Example 2
[0034] A bulk copper raw material having a purity level of 4N level
was used as the anode, and a copper plate was used as the cathode
to perform electrolysis. The content of raw material impurities is
shown in Table 2. As shown in Table 2, the copper raw material (4N)
primarily contained large amounts of O, P and S. Table 2 also shows
the hardness and recrystallization temperature at this impurity
level. The hardness at a purity level of 4N was 47 Hv, and the
recrystallization temperature was 450.degree. C. The diameter of
the wire rod capable of being subject to thinning was 200
.mu.m.
[0035] A nitric acid series electrolytic solution having a bath
temperature of 25.degree. C. was used, and 1 ml/L of hydrochloric
acid was additionally added thereto. Electrolysis was performed at
a pH of 2.0, and a current density of 1.5 A/dm.sup.2. The
electrolytic solution was circulated, and, as with Example 1, the
electrolytic solution of the circuit was temporarily cooled with a
cooler to a temperature of 5.degree. C., and a filter was used to
eliminate the deposited AgCl and the like. Thereby, as shown in
Table 2, it was possible to obtain high purity copper having a
purity level of 5N5. Table 2 shows the hardness and
recrystallization temperature of copper having a purity level of
5N5. Hardness of the 5N5 copper was 43 Hv, and the
recrystallization temperature was reduced to 280.degree. C. The
diameter of the wire rod capable of being subject to thinning was
50 .mu.m.
[0036] Subsequently, this copper having a purity level of 5N5 was
used to perform electrolysis once again under the same electrolytic
conditions as those described above. The electrolysis was performed
by setting the electrolytic solution to a temperature of 20.degree.
C. The electrolytic solution was similarly circulated, the
electrolytic solution of the circuit was temporarily cooled with a
cooler to a temperature of 3.degree. C., and a filter was used to
eliminate the deposited AgCl and the like. Thereby, as shown in
Table 2, it was possible to obtain ultrahigh purity copper having a
purity level of 8N.
[0037] Table 2 shows the hardness and recrystallization temperature
of copper having a purity level of 8N. The hardness was 40 Hv, and
the recrystallization temperature decreased to 180.degree. C. The
diameter of the wire rod capable of being subject to thinning was 5
.mu.m, and improved significantly.
[0038] Example 2 achieved all conditions of the present invention;
namely, the hardness being 40 Hv or less and the recrystallization
temperature being 200.degree. C. or less.
TABLE-US-00002 TABLE 2 (O, P, S: wtppm) Recrystal- Hard- lization
Existence Pu- ness Temperature Thinning of Si rity Hv O P S
(.degree. C.) Diameter Cracks 4N 47 30 1.0 12 480 200 .mu.m Many
5N5 43 <1 0.1 0.6 280 50 .mu.m Few 8N 40 <1 <0.01 <0.01
180 5 .mu.m None
Comparative Example 1
[0039] A bulk copper raw material having a purity level of 4N was
used as the anode, and a copper plate was used as the cathode to
perform electrolysis. The content of raw material impurities is
shown in Table 3. As shown in Table 3, the copper raw material (4N)
primarily contained large amounts of O, P and S. Table 3 also shows
the hardness and recrystallization temperature at this impurity
level. The hardness at a purity level of 4N was 45 Hv, and the
recrystallization temperature was 450.degree. C. The diameter of
the wire rod capable of being subject to thinning was 200
.mu.m.
[0040] A nitric acid series electrolytic solution having a bath
temperature of 20.degree. C. was used, and 1 ml/L of hydrochloric
acid was additionally added thereto. Electrolysis was performed at
a pH of 1.3, and a current density of 1 A/dm.sup.2. The
electrolytic solution was circulated but not cooled, and used as
the electrolytic solution as is. Thereby, as shown in Table 3, it
was possible to obtain high purity copper having a purity level of
4N5. Table 3 shows the hardness and recrystallization temperature
of copper having a purity level of 4N5. Hardness of the 4N5 copper
was 44 Hv. The recrystallization temperature was 430.degree. C.,
and did not decrease significantly. The diameter of the wire rod
capable of being subject to thinning was 150 .mu.m, but not very
effective.
[0041] Subsequently, this copper having a purity level of 4N5 was
used to perform electrolysis once again under the same electrolytic
conditions as those described above. Thereby, as shown in Table 3,
it was possible to obtain high purity copper having a purity level
of 5N.
[0042] Table 3 shows the hardness and recrystallization temperature
of copper having a purity level of 5N. The hardness was high at 43
Hv, and the recrystallization temperature decreased to 420.degree.
C. The diameter of the wire rod capable of being subject to
thinning was 120 .mu.m, and insufficient.
[0043] As described above, Comparative Example 1 did not satisfy
all conditions of the present invention; namely, the hardness being
40 Hv or less and the recrystallization temperature being
200.degree. C. or less, and did not achieve sufficient softness for
realizing the thinning of a bonding wire. In addition, numerous
cracks were generated in the silicon under the Al pad during heat
bonding.
TABLE-US-00003 TABLE 3 (O, P, S: wtppm) Recrystal- Hard- lization
Existence Pu- ness Temperature Thinning of Si rity Hv O P S
(.degree. C.) Diameter Cracks 4N 45 10 0.2 8.6 450 200 .mu.m Many
4N5 44 10 0.1 2.0 430 150 .mu.m Yes 5N 43 10 0.1 1.0 420 120 .mu.m
Yes
Comparative Example 2
[0044] A bulk copper raw material having a purity level of 4N level
was used as the anode, and a copper plate was used as the cathode
to perform electrolysis. The content of raw material impurities is
shown in Table 4. As shown in Table 4, the copper raw material (4N)
primarily contained large amounts of O, P and S. Table 4 also shows
the hardness and recrystallization temperature at this impurity
level. The hardness at a purity level of 4N was 45 Hv, and the
recrystallization temperature was 450.degree. C. The diameter of
the wire rod capable of being subject to thinning was 200
.mu.m.
[0045] A nitric acid series electrolytic solution having a bath
temperature of 35.degree. C. was used, and 1 ml/L of hydrochloric
acid was additionally added thereto. Electrolysis was performed at
a pH of 1.3, and a current density of 1 A/dm.sup.2. The
electrolytic solution was only circulated. Thereby, as shown in
Table 4, it was possible to obtain high purity copper having a
purity level of 4N5. Table 4 shows the hardness and
recrystallization temperature of copper having a purity level of
4N5. Hardness of the 4N5 copper was 44 Hv. The recrystallization
temperature decreased to 430.degree. C. The diameter of the wire
rod capable of being subject to thinning was 150 .mu.m.
[0046] Subsequently, this copper having a purity level of 4N5 was
used to perform electrolysis once again under the same electrolytic
conditions as those described above. In addition, the electrolytic
solution of the circuit was temporarily cooled with a cooler to a
temperature of 15.degree. C., and a filter was used to eliminate
the deposited AgCl and the like. Thereby, as shown in Table 4, it
was possible to obtain high purity copper having a purity level of
6N.
[0047] Table 4 shows the hardness and recrystallization temperature
of copper having a purity level of 6N. The hardness was high at 42
Hv, and the recrystallization temperature decreased to 230.degree.
C. The diameter of the wire rod capable of being subject to
thinning was 40 .mu.m, and insufficient.
[0048] As described above, Comparative Example 2 did not satisfy
the conditions of the present invention; namely, the hardness being
40 Hv or less and the recrystallization temperature being
200.degree.0 C. or less, and did not achieve sufficient softness
for realizing the thinning of a bonding wire. In addition, numerous
cracks were generated in the silicon under the Al pad during heat
bonding.
TABLE-US-00004 TABLE 4 (O, P, S: wtppm) Recrystal- Hard- lization
Existence Pu- ness Temperature Thinning of Si rity Hv O P S
(.degree. C.) Diameter Cracks 4N 45 10 0.2 8.6 450 200 .mu.m Many
4N5 44 10 0.1 2.0 430 150 .mu.m Yes 6N 42 <1 0.01 0.02 230 40
.mu.m Yes
INDUSTRIAL APPLICABILITY
[0049] As described above, the present invention yields a
significant effect of being able to efficiently manufacture
ultrahigh purity copper having a purity of 8N (99.999999 wt %) or
higher. It is thereby possible to obtain a copper material with
reduced hardness and compatible with thinning (wire drawing). In
particular, thinning of a bonding wire for a semiconductor element
is enabled. In addition, the present invention yields a superior
effect of being able to prevent the generation of cracks in the
silicon during bonding, inhibit the heat generation caused by the
low resistance of the wires, and prevent the oxidization during
heat treatment.
[0050] Accordingly, the present invention is suitable for a copper
bonding wire for a semiconductor element that requires
thinning.
* * * * *