U.S. patent application number 09/772070 was filed with the patent office on 2001-06-28 for aluminum or aluminum alloy sputtering target and method for manufacturing the same.
This patent application is currently assigned to Kabushiki Kaisha Kobe Seiko Sho (aka Kobe Steel, Ltd.). Invention is credited to Kusamichi, Tatsuhiko, Mizuno, Masao, Nishi, Seiji, Onishi, Takashi, Suemitsu, Toshihisa, Takahara, Teruyuki, Yoshikawa, Kazuo.
Application Number | 20010004856 09/772070 |
Document ID | / |
Family ID | 12582796 |
Filed Date | 2001-06-28 |
United States Patent
Application |
20010004856 |
Kind Code |
A1 |
Nishi, Seiji ; et
al. |
June 28, 2001 |
Aluminum or aluminum alloy sputtering target and method for
manufacturing the same
Abstract
The sputtering target is manufactured by adjusting the ratio of
the gas flow volume (Nm.sup.3)/molten liquid flow mass (kg) to 5
Nm.sup.3/kg or more in the gas atomizing step of the spray forming
method using an Al or Al alloy sputtering target material in which
the maximum length of all the inclusions is 20 .mu.m or less.
Inventors: |
Nishi, Seiji; (Kobe-shi,
JP) ; Kusamichi, Tatsuhiko; (Kobe-shi, JP) ;
Onishi, Takashi; (Kobe-shi, JP) ; Mizuno, Masao;
(Kobe-shi, JP) ; Takahara, Teruyuki; (Kobe-shi,
JP) ; Suemitsu, Toshihisa; (Kobe-shi, JP) ;
Yoshikawa, Kazuo; (Kobe-shi, JP) |
Correspondence
Address: |
REED SMITH HAZEL THOMAS LLP
Suite 1400
3110 Fairview Park Drive
Falls Church
VA
22042
US
|
Assignee: |
Kabushiki Kaisha Kobe Seiko Sho
(aka Kobe Steel, Ltd.)
|
Family ID: |
12582796 |
Appl. No.: |
09/772070 |
Filed: |
January 30, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09772070 |
Jan 30, 2001 |
|
|
|
09253727 |
Feb 22, 1999 |
|
|
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Current U.S.
Class: |
75/338 |
Current CPC
Class: |
B22F 2999/00 20130101;
B22F 3/115 20130101; C23C 14/3414 20130101; B22F 2999/00 20130101;
B22F 9/082 20130101; B22F 2201/02 20130101 |
Class at
Publication: |
75/338 |
International
Class: |
B22F 009/12 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 23, 1998 |
JP |
HEI 10-40520 |
Claims
What is claimed is:
1. A method for manufacturing an aluminum or aluminum alloy
sputtering target material comprising aluminum or aluminum alloy
containing inclusions having a maximum length of 20 .mu.m, wherein
the ratio of the gas volume (Nm.sup.3)/the liquid mass (kg) is 5
Nm.sup.3/kg or more in a spray forming method including the step of
obtaining an aluminum or aluminum alloy ingot by a gas atomizing
step of a molten liquid having aluminum or aluminum alloy.
2. A method for manufacturing an aluminum or aluminum alloy
sputtering target material according to claim 1, wherein the ratio
of the gas volume (Nm.sup.3)/the liquid mass (kg) is adjusted to be
10 Nm.sup.3/kg or more.
3. A method for manufacturing an aluminum or aluminum alloy
sputtering target material according to claim 2, wherein nitrogen
gas is used for atomizing gas in the gas atomizing step.
4. A method for manufacturing an aluminum or aluminum alloy
sputtering target material comprising aluminum or aluminum alloy
containing inclusions having a maximum length of 20 .mu.m
comprises: melting an material having aluminum or aluminum alloy
ingot into a liquid flow; atomizing a gas flow; spraying the liquid
flow onto a surface by means of said gas flow, wherein the ratio of
the gas flow volume (Nm.sup.3)/the liquid flow mass (kg) is 5
Nm.sup.3/kg or more; and depositing on said surface an aluminum or
aluminum alloy sputtering target material comprising aluminum or
aluminum alloy containing inclusions having a maximum length of 20
.mu.m.
5. A method for manufacturing an aluminum or aluminum alloy
sputtering target material according to claim 4, wherein the ratio
of the gas flow volume (Nm.sup.3)/the liquid flow mass (kg) is
adjusted to be 10 Nm.sup.3/kg or more.
6. A method for manufacturing an aluminum or aluminum alloy
sputtering target material according to claim 5, wherein nitrogen
gas is used for the gas flow.
7. A method for manufacturing an aluminum or aluminum alloy
sputtering target material comprising aluminum or aluminum alloy
containing inclusions having a maximum length of 10 .mu.m
comprises: melting an material having aluminum or aluminum alloy
ingot into a liquid flow; atomizing a gas flow; spraying the liquid
flow onto a surface by means of said gas flow, wherein the ratio of
the gas flow volume (Nm.sup.3)/the liquid flow mass (kg) is 5
Nm.sup.3/kg or more; and depositing on said surface an aluminum or
aluminum alloy sputtering target material comprising aluminum or
aluminum alloy containing inclusions having a maximum length of 10
.mu.m.
8. A method for manufacturing an aluminum or aluminum alloy
sputtering target material according to claim 7, wherein the ratio
of the gas flow volume (Nm.sup.3)/the liquid flow mass (kg) is
adjusted to be 10 Nm.sup.3/kg or more.
9. A method for manufacturing an aluminum or aluminum alloy
sputtering target material according to claim 8, wherein nitrogen
gas is used for the gas flow.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a sputtering target
material comprising aluminum or an aluminum alloy (referred to an
aluminum or aluminum alloy sputtering target hereinafter), and a
method for manufacturing the same. The present invention especially
relates to an aluminum or aluminum alloy sputtering target material
for use in forming semiconductor electrode films and a method for
manufacturing the same, relating among all to an aluminum or
aluminum alloy sputtering target for forming semiconductor
electrode films being advantageous as liquid crystal display
electrodes (thin film wiring and the electrode itself) and a method
for manufacturing the same.
[0003] 2. Description of the Related Art
[0004] Use of liquid crystal displays (abbreviated as LCD
hereinafter) has been recently expanded since it can be made thin
and lightweight besides consuming small amount of electric power
while maintaining high resolution as compared with conventional
cathode-ray tubes (CRT). The LCDs having a structure in which
semiconductor devices such as thin film transistors (abbreviated as
TFT hereinafter) are integrated as switching elements have been
recently proposed and widely used in order to enhance image
quality. The TFT as used herein refers to an active element
produced by connecting semiconductor electrodes comprising a thin
metal film to a semiconductor film formed on an insulation
substrate made of, for example, a glass. The semiconductor
electrode is defined as an electrode to be used as a part of the
TFT including a thin film wiring and the electrode itself. Once the
active element is formed into the TFT, the wiring and the electrode
itself are put into electrical continuity with each other.
[0005] Among various characteristics required for the LCD as
described above, making electrical resistivity small for preventing
signal delay is being one of the most crucial characteristics in
compliance with the trends toward large size or highly
sophisticated LCDs.
[0006] The semiconductor electrode for use in the LCD is produced
by a sputtering method in which a sputtering target is used for
sputtering. The sputtering target serves as a sputtering source for
forming the semiconductor electrode on a substrate by sputtering,
usually comprising a circular or rectangular plate. Atoms
constituting the sputtering target are emitted into the space and
deposited on the confronting substrate by exchange of kinetic
momentum when accelerated particles collide with the surface of the
sputtering target during sputtering.
[0007] High melting point metals such as Ta, Mo, Cr, Ti, W, Zr and
Nb have been used for sputtering target materials for forming these
semiconductor electrodes for use in the LCD. However, since the
high melting point metals such as Ta, Mo, Cr, Ti, W, Zr and Nb have
so high specific resistivity when they are formed into thin films
that their application for the foregoing object have became
difficult, because currently used LSIs are so highly integrated
that a wiring width of as fine as 1 .mu.m is required for the
circuit. In other words, resistivity of the semiconductor electrode
manufactured by using the sputtering target material comprising the
foregoing high melting point metals is so high that the material
became hardly compatible with fine wiring width as described above.
Accordingly, development of semiconductor electrode materials
having low resistivity as substitutes of the foregoing high melting
point metals is desired.
[0008] Examples of the semiconductor electrode materials with
desirable low resistivity include Au, Cu and Al. However, Au does
not exhibit suitable etching characteristic, besides it is
expensive, required for forming into a desired pattern after
depositing a sheet of electrode, or an electrode film (a wiring
film). Cu has some problems in adhesive property and corrosion
resistance while Al has so poor heat resistance that minute hills
called hillocks appear on the surface during the heating step (at
about 250 to 400.degree. C.), an inevitable production process of
the TFT, after forming the electrode film. Because the electrode
film is formed at the lowermost layer in the TFT-LCD, other films
can not be laminated thereon when these hillocks are generated.
[0009] An electrode film comprising an Al alloy containing the
alloy components as disclosed in Japanese Unexamined Patent
Publication No. 7-45555 which is hereby fully incorporated by
reference, and an Al alloy sputtering target for forming such Al
alloy electrode film are proposed as a means for avoiding the
hillock problems in the Al electrode film.
[0010] However, there arise another problems that particles and
splashes are appeared to generate when the semiconductor electrode
is formed on the substrate by sputtering using the sputtering
target materials comprising the Al or Al alloys as described above.
Particles scattering from the target are turned into clusters that
directly adhere to the thin film on the substrate, or adhered or
deposited layers on the surrounding wall or components is peeled
off to adhere to the thin film on the substrate (so-called particle
problem). Otherwise, droplets of the target material are scattered
and adhere to the thin film on the substrate (so-called splash
problem).
[0011] While the problems of particle and splash generation has
been solved by decreasing the content of inclusion in the
sputtering target materials as small as possible, it was pointed
out in Japanese Unexamined Patent Publication No. 9-25564 which is
hereby fully incorporated by reference that the utmost number of
the inclusions having a mean particle size of 10 .mu.m or more in
the target should be reduced to less than 40 particles/cm.sup.2.
However, the countermeasure as described above was proved to be
insufficient for solving the problems of particle and splash
generation.
[0012] Among the problems of particle and splash generation, the
crucial problem that is urgently to be solved is that generation of
splash provides serious obstacle on the performance of the thin
film on the substrate or of the semiconductor electrode formed
thereon. Splashes tend to be formed especially when an Al alloy
sputtering target is used in order to prevent hillocks from
appearing on the Al electrode film.
[0013] Splashes are generated not only in forming the foregoing
semiconductor electrode for use in LCDs, but also in forming wiring
of semiconductor integrated circuits and reflection layers of
magnetic recording and photomagnetic recording media by sputtering
as well.
SUMMARY OF THE INVENTION
[0014] Accordingly, the object of the present invention is to
provide an aluminum or aluminum alloy sputtering target material
hardly generating splashes when used for sputtering, and a method
for manufacturing the same.
[0015] In a first aspect, the present invention provides an
aluminum or aluminum alloy sputtering target comprising aluminum or
an aluminum alloy containing inclusions having a maximum length of
20 .mu.m or less.
[0016] The sputtering target material as described above allows
splashes to be suppressed from generating during sputtering. The
maximum length of the inclusions is limited to 20 .mu.m or less
because the inclusions with a maximum length of more than 20 .mu.m
makes the splashes to be readily generated owing to these
inclusions, insufficiently suppressing generation of the
splashes.
[0017] It is advantageous that all the inclusions have a maximum
length of 10 .mu.m or less.
[0018] The sputtering target material with the maximum length of
the inclusions as described above allows the splashes to be hardly
generated, more securely suppressing splash generation.
[0019] In a preferred embodiment, the present invention provides a
method for fabricating an Al or Al alloy sputtering target material
by a spray forming method, wherein the ratio of the gas flow volume
(Nm.sup.3)/molten liquid flow mass (kg) in a gas atomizing step of
the spray forming method is adjusted to 5 Nm.sup.3/kg or more.
[0020] In the method described above, the molten liquid of the Al
or Al alloy is atomized to be dispersed into molten or semi-molten
small particles as well as crashing the inclusion into small pieces
in the atomizing step of the spray forming method. These small
particles of semi-molten Al or Al alloy are successively deposited
by spraying onto a bottom floor or in a mold, thereby forming the
Al or Al alloy sputtering target material. When the ratio of the
gas flow volume (Nm.sup.3)/molten liquid flow mass (kg) in the gas
atomizing step of the spray forming method is adjusted to 5
Nm.sup.3/kg or more, the size (the maximum length) of all the
inclusions after crushing becomes 20 .mu.m or less, making it
possible to obtain the Al or Al alloy sputtering target material in
which the size of all the inclusions is 20 .mu.m or less.
[0021] It is also advantageous to adjust the ratio of the gas flow
volume (Nm.sup.3)/molten liquid flow mass (kg) to 10 Nm.sup.3/kg or
more.
[0022] When the ratio of the gas flow volume (Nm.sup.3)/molten
liquid flow mass (kg) is adjusted to 10 Nm.sup.3/kg or more, an Al
or Al alloy sputtering target material in which the size (the
maximum length) of all the inclusions is 10 .mu.m or less.
[0023] It is also advantageous to use nitrogen gas for the
atomizing gas in the gas atomizing step along with adjusting the
ratio of the gas flow volume (Nm.sup.3)/molten liquid flow mass
(kg) to 10 Nm.sup.3/kg or more.
[0024] The Al or Al alloy sputtering target material in which the
size (the maximum length) of all the inclusions is 10 .mu.m or
less, along with containing 0.1 mass % or less of nitrogen, can be
obtained to allow splashes to be hardly generated during
sputtering, thereby enabling to form an Al or Al alloy thin film
with small specific resistivity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 denotes a table indicating the sputtering conditions
described in the Examples;
[0026] FIG. 2 denotes a table indicating the manufacturing
conditions of the sputtering target material according to Examples
1 to 4, and the results of investigations on the size of the
inclusion, the number of the splash having a size of 10 .mu.m or
more, and the oxygen content;
[0027] FIG. 3 denotes a table indicating the manufacturing
conditions of the sputtering target according to Examples 5 to 9,
and the results of investigations on the size of the inclusion, the
number of the splash having a size of 10 .mu.m or more, and the
oxygen content;
[0028] FIG. 4 denotes a table indicating the sputtering conditions
of the sputtering target material according to Example 10;
[0029] FIG. 5 denotes a table showing the relation between the
maximum length of the inclusion and the number of the splash having
a size of 10 .mu.m or more with respect to the Al or Al alloy
sputtering target material according to Example 4;
[0030] FIG. 6 denotes a graph showing the relation between the
maximum length of the inclusion and the number of the splash having
a size of 10 .mu.m or more with respect to the Al or Al alloy
sputtering target material according to Example 4; and
[0031] FIG. 7 denotes a graph showing the relation between the
nitrogen content and electrical resistivity of the thin film
obtained with respect to the sputtering target material according
to Example 10.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0032] The Al or Al alloy sputtering target material according to
the preferred embodiment of the present invention and the method
for fabricating the same will be described hereinafter.
[0033] The present invention was completed based on the results
obtained through intensive studies for developing the Al or Al
alloy sputtering target material that hardly generates
splashes.
[0034] The inventors of the present invention have manufactured the
Al sputtering target material and Al alloy sputtering target
material having various size of inclusion. The behavior of these
sputtering target materials during sputtering has been fully
investigated using these materials as sputtering targets.
[0035] The results indicated that the splash is generated when
cooling of the target material is partially inhibited around the
inclusion, especially at just above the inclusion, in the
sputtering target material. In other words, it was found that the
site around the inclusion is melted by plasma heating during
sputtering and the splash is generated by allowing the molten layer
to scatter by electromagnetic force forming droplets, that the
splash is largely correlated with the size of the inclusion rather
than the amount of the inclusion as described in Japanese
Unexamined Patent Publication No. 9-25564, and that generation of
the splash can be suppressed when the size (the maximum length, or
the length of the portion having the maximum length) of the
inclusion is 20 .mu.m or less, or little splashes are generated
when the size of the inclusion is 10 .mu.m or less.
[0036] The size of the portion where cooling is inhibited by the
inclusion during sputtering becomes small in the Al sputtering
target material and Al alloy sputtering target material having the
inclusion with a size (the maximum length) of 20 .mu.m or less and
the molten layer is hardly formed. Accordingly, the scattering
frequency of the molten layer as droplets, or the frequency of
splash generation, is so markedly decreased to sufficiently
suppress generation of the splash. Especially, when the size of all
the inclusion is 10 .mu.m or less, the splash is substantially not
generated.
[0037] In the first step of the method for manufacturing the Al or
Al alloy sputtering target material according to the present
invention, a ingot is produced by a spray forming method using a
molten liquid. The molten liquid of Al or an Al alloy is deposited
by gas atomizing to obtain a ingot. The ratio of the gas flow
volume (Nm.sup.3)/molten liquid flow mass (kg) in the gas atomizing
step of the spray forming method is adjusted to 5 Nm.sup.3/kg or
more, thereby enabling to obtain the Al or Al alloy sputtering
target material according to the present embodiment, or the
sputtering target material comprising the Al or Al alloy having the
maximum length of all the inclusions of 20 .mu.m or less. The ratio
of the gas flow volume (Nm.sup.3)/molten liquid flow mass (kg) in
the gas atomizing step of the spray forming method is adjusted to 5
Nm.sup.3/kg or more because, when the ratio is less than 5
Nm.sup.3/kg, a substantial number of inclusions having the maximum
length of more than 20 .mu.m are included in the Al or Al alloy
sputtering target material, the inclusion serving as trigger points
for generating the splashes during sputtering in the sputtering
target material as described above.
[0038] The Al or Al alloy sputtering target material obtained by
the spray forming method as described above contains a higher
concentration of oxygen in the material than the Al or Al alloy
sputtering target material obtained by the vacuum melting method.
However, the splashes are hardly generated in the former material
as compared with the latter material during sputtering, in spite of
the fact that the former contains larger amount of the inclusions
in the material than the latter. This is because the former
contains smaller size of inclusions than the latter. In other
words, the large number of the inclusions have little influence
when the size of the inclusion is small as in the former case,
hardly generating the splashes. In the melting methods in vacuum or
in the air, so many inclusions having a size of more than 20 .mu.m
are formed that they serve as trigger points of splash
generation.
[0039] Nitrogen concentration in the Al or Al alloy sputtering
target material becomes high when nitrogen gas is used for the
atomizing gas in the atomizing step of the spray forming method in
manufacturing the Al or Al alloy sputtering target material by the
spray forming method. The Al or Al alloy thin film for the Al
electrode, manufactured by sputtering using the sputtering target
material containing a high concentration of nitrogen as described
above, naturally contains a high concentration of nitrogen, showing
high specific resistivity by being influenced by included nitrogen.
When the Al alloy thin film is formed using a sputtering target
material comprising an Al--Ti alloy (Al alloy containing Ti) for
example, electrical resistivity of the Al thin film becomes higher
as the nitrogen concentration in the sputtering target obtained is
higher as shown in FIG. 7. Accordingly, a lower nitrogen
concentration in the Al or Al alloy sputtering target material is
preferable from the view point of specific resistivity of the Al or
Al alloy sputtering target material, a content of 0.1 mass % or
less being desirable.
[0040] The upper limit of the nitrogen concentration was set to 0.1
mass % or less because a material having resistivity comparable to
that of the material containing 0% of nitrogen is urgently desired
from the view point of suppressing increase of specific resistivity
due to increase of the nitrogen concentration.
[0041] Accordingly, the inventors of the present invention have
carried out intensive studies for developing the technology by
which the nitrogen concentration of the Al or Al alloy sputtering
target material obtained can be reduced especially to 0.1 mass % or
less when nitrogen gas is used for the atomizing gas in the gas
atomizing step of the spray forming method. It was found from the
results of the investigation that, when the ratio of the gas flow
volume (Nm.sup.3)/molten liquid flow mass (kg), or the ratio of
nitrogen gas flow volume Nm.sup.3)/molten liquid flow mass (kg), is
adjusted to 10 Nm.sup.3/kg or more, an Al or Al alloy sputtering
target material containing 0.1 mass % or less of nitrogen can be
obtained.
[0042] The size (the maximum length) of all the inclusions is 10
.mu.m or less in the Al or Al alloy sputtering target material
obtained by the method as hitherto described, hardly generating the
splashes during sputtering since the material was obtained by the
manufacturing method having basically the same construction as that
of the manufacturing method according to the present invention.
[0043] Accordingly, the Al or Al alloy sputtering target material
in which the size (the maximum length) of all the inclusions is 10
.mu.m or less along with containing 0.1 mass % or less of nitrogen
can be obtained when nitrogen gas is used for the atomizing gas in
the gas atomizing step of the spray forming method for producing
the Al or Al alloy sputtering target material, wherein the ratio of
the gas flow volume (Nm.sup.3)/molten liquid mass (kg) is adjusted
to 10 Nm.sup.3/kg or more. The splashes are hardly generated during
sputtering in the Al or Al alloy sputtering target material
obtained by the method as described above, making it possible to
form the Al or Al alloy thin film having low specific
resistivity.
[0044] When the ratio of the gas flow volume (Nm.sup.3)/molten
liquid flow mass (kg), or the nitrogen gas flow volume
(Nm.sup.3)/molten liquid flow mass (kg), in the gas atomizing step
is adjusted to 10 Nm.sup.3/kg or more, the Al or Al alloy
sputtering target material containing 0.1 mass % or less of
nitrogen can be obtained by using nitrogen gas for the atomizing
gas in the gas atomizing step of the spray forming method as
hitherto described. This is because, after allowing droplets
(molten or semi-molten small particles) to deposit on the bottom
floor or in the mold, the droplets are quickly solidified by
nitrogen gas, hardly inducing a reaction between Al and N to reduce
the amount of nitride formed.
[0045] When the ratio of the nitrogen gas flow volume
(Nm.sup.3)/molten liquid flow mass (kg) described above is less
than 10 Nm.sup.3/kg, cooling of the droplets deposited on the
bottom floor or in the mold, especially at the center of the
deposit (deposited layer of the droplets) becomes insufficient,
making the reaction of Al with N relatively easy to form a lot of
nitride by the reaction, thereby increasing the nitrogen
concentration in the Al or Al alloy sputtering target material
obtained to more than 0.1 mass %.
[0046] The maximum length of the inclusion refers to the length of
the largest part in the inclusion in the present invention. For
example, the maximum length corresponds to the diameter when the
inclusion assumes a spherical shape or to the maximum side length
when the inclusion assumes a nearly rectangular shape. The term
that the maximum length of all the inclusions is 20 .mu.m or less
means that all the inclusions in the material have a maximum length
of 20 .mu.m or less.
[0047] The flow mass of the molten liquid in the gas atomizing step
of the spray forming method refers to a mass of the molten liquid
per unit time flowing out of the molten liquid exit of the vessel
containing the molten liquid. The gas flow volume in the step
refers to the volume per unit time flowing out of the gas exit of
the atomizing gas source for gas atomizing the flowing molten
liquid.
[0048] The ratio of the gas flow volume (Nm.sup.3)/molten liquid
flow mass (kg) in the gas atomizing step of the spray foing method
refers to the ratio between the gas flow volume and molten liquid
flow mass when the molten liquid flow mass is expressed by kg/unit
time and the gas flow volume is expressed by Nm.sup.3/unit time, or
the ratio of the gas flow volume (Nm.sup.3/unit time)/molten liquid
flow mass (kg/unit time). The definition of the unit time should be
the same in the expression of the molten liquid flow mass and gas
flow volume. The gas flow volume (Nm.sup.3)/molten liquid flow mass
(kg) described above is also referred to the gas/metal ratio.
[0049] For example, when the gas flow volume is 40 Nm.sup.3/min and
the molten liquid flow mass is 4 kg/min, the ratio of the gas flow
volume (Nm.sup.3)/molten liquid flow mass (kg) is expressed by 40
(Nm.sup.3/min)/4 (kg/min) or 40 (Nm.sup.3)/4 (kg), or 10
Nm.sup.3/min.
EXAMPLES
Example 1 to 3
[0050] An Al--Nd alloy containing 2 at % (atomic percentage) of Nd
(Al--Nd (2 at %) alloy) was melted and a ingot was made using the
alloy by the spray forming method. The molten liquid of the Al--Nd
(2 at %) alloy was subjected to gas atomization to deposit in the
mold, thereby obtaining a ingot of the Al--Nd (2 at %) alloy.
Nitrogen gas was used as the atomizing gas in the gas atomizing
step of the spray forming method. The ratios of the nitrogen gas
flow volume (Nm.sup.3)/molten liquid mass (kg) were adjusted to 6
Nm.sup.3/kg, 10 Nm.sup.3/kg or 15 Nm.sup.3/kg, respectively, in the
gas atomizing step of the spray forming method. The method for
making the ingot of the Al--Nd (2 at %) alloy (the sputtering
target material) described above corresponds to the production
method in the present embodiment.
[0051] After forging and rolling of the ingot, a disk of the
sputtering target material of the Al--Nd (2 at %) alloy with a
diameter of 4 inches was manufactured by machining.
[0052] The size (the maximum diameter) of the inclusion and oxygen
content, as well as the frequency of generation of the splashes,
were investigated with respect to the sputtering target material of
the Al--Nd (2 at %) alloy fabricated as described above.
[0053] Samples for microscopic measurement of the size of the
inclusions were taken from the sputtering target material and,
after polishing the samples, were observed under an optical
microscope to measure the size of the inclusion. Oxygen content was
determined by gas analysis of the sample taken from the sputtering
target material.
[0054] For the purpose of investigating the frequency of splash
generation, the sputtering target material was subjected to
sputtering for 1 hour under the sputtering conditions listed in
FIG. 1. After forming a thin film of the Al--Nd (2 at %) alloy on
the substrate, the surface of this thin film was observed under an
optical microscope to count the number of the splashes having a
size (the maximum length) of 10 .mu.m or more, since the splash
having a size of 10 .mu.m or more causes a severe problem on the
performance of the thin film.
[0055] The results of measurements with respect to the size of the
inclusion, oxygen content and the number of splashes having a size
of 10 .mu.m or more are listed in FIG. 2.
[0056] It was shown in FIG. 2 that all the sizes of the inclusions
were 20 .mu.m or less in Examples 1 to 3. The maximum length of the
inclusion in the Al--Nd (2 at %) sputtering target material,
obtained by adjusting the ratio of the nitrogen gas flow volume
(Nm.sup.3)/molten liquid mass (kg) to 6 Nm.sup.3/kg, was 16 .mu.m,
the maximum length of the inclusion in the Al--Nd (2 at %)
sputtering target material, obtained by adjusting the ratio of the
nitrogen gas flow volume (Nm.sup.3)/molten liquid mass (kg) to 10
Nm.sup.3/kg, was 8 .mu.m, and the maximum length of the inclusion
in the Al--Nd (2 at %) sputtering target material, obtained by
adjusting the ratio of the nitrogen gas flow volume
(Nm.sup.3)/molten liquid mass (kg) to 15 Nm.sup.3/kg, was 4 .mu.m.
These Al--Nd (2 at %) sputtering target materials refer to the
sputtering target material according to Example 1, the sputtering
target material according to Example 2 and the sputtering target
material according to Example 3, respectively, in the order of the
above description hereinafter.
[0057] The numbers of splashes having a size (the maximum length)
of 10 .mu.m or more were 10, 5 and 3 in the sputtering target
materials according to Example 1, Example 2 and Example 3,
respectively. The frequencies of slush generation with a size of 10
.mu.m or more that adversely affect the performance of the thin
film were very small in Examples 1 to 3. When the number of the
splashes having a size of 10 .mu.m or more is adjusted to 10 or
less, a significant technical achievement that allows the problem
of making the wiring width very fine to be solved would be
attained.
Comparative Example 1
[0058] A disk shaped Al--Nd (2 at %) sputtering target material
(referred to the sputtering target material according to
Comparative Example 1 hereinafter) with a diameter of 4 inches was
manufactured by machining after melting the Al--Nd (2 at %) alloy
in the air followed by casting and rolling.
[0059] The maximum length of the inclusion and other
characteristics in the sputtering target material according to
Comparative Example 1 were investigated by the same method as in
Examples 1 to 3. The results are listed in FIG. 2. It is evident
from FIG. 2 that the maximum length of the inclusion in the
sputtering target material according to Comparative Example 1 was
60 .mu.m, along with showing the number of the splashes with a size
of 10 .mu.m or more of as large as 54.
Comparative Example 2
[0060] A disk shaped Al--Nd (2 at %) sputtering target material
(referred to the sputtering target material according to
Comparative Example 2 hereinafter) with a diameter of 4 inches was
manufactured by machining after melting the Al--Nd (2 at %) alloy
in vacuum followed by casting and rolling.
[0061] The maximum length of the inclusion and other
characteristics in the sputtering target material according to
Comparative Example 2 were investigated by the same method as in
Examples 1 to 3. The results are listed in FIG. 2. It is evident
from FIG. 2 that the maximum length of the inclusion in the
sputtering target material according to Comparative Example 2 was
30 .mu.m, along with showing the number of the splashes with a size
of 10 .mu.m or more of as large as 25.
[0062] The results in Comparative examples 1 and 2 clearly shows
that the size of all the inclusions can not be adjusted to 20 .mu.m
or less when the alloy is melted in the air or in vacuum.
Comparative Example 3
[0063] A disk shaped (4 inches in diameter) Al--Nd (2 at %) alloy
sputtering target material (referred to the sputtering target
material according to Comparative Example 3 hereinafter) was
manufactured by the same method in Examples 1 to 3, except that the
ratio of the nitrogen gas flow volume (Nm.sup.3)/molten liquid flow
mass (kg) in the gas atomizing step of the spray forming method was
adjusted to 4 Nm.sup.3/kg as shown in FIG. 2.
[0064] The maximum length of the inclusion and other
characteristics in the sputtering target material according to
Comparative Example 3 were investigated by the same method as in
Examples 1 to 3. The results are listed in FIG. 2. It is evident
from FIG. 2 that the maximum length of the inclusion in the
sputtering target material according to Comparative Example 3 was
25 .mu.m, along with showing the number of the splashes with a size
of 10 .mu.m or more of as large as 20.
Example 4
[0065] An Al--Nd (2 at %) alloy sputtering target material was
manufactured by the same method as in Examples 1 to 3. The ratio of
the nitrogen gas flow volume (Nm.sup.3)/molten liquid flow mass
(kg) in the gas atomizing step of the spray forming method was used
as variable parameters in order to allow the maximum length of the
inclusion in the sputtering target material to change.
[0066] The maximum length of the inclusion and the number of
splashes having a size of 10 .mu.m or more generated during
sputtering in the sputtering target material described above were
investigated by the same method as in Examples 1 to 3. The relation
between the maximum length of the inclusion and the number of
splashes with a size of 10 .mu.m or more, obtained based on the
investigations above, is shown in FIG. 6.
[0067] It can be seen from FIG. 6 that, while the number of
splashes with a size of 10 .mu.m or more rapidly increases as the
maximum length of the inclusion is increased in the region where
the maximum length of the inclusion is more than 20 .mu.m, little
number of splashes with a size of 10 .mu.m or more are found in the
region where the maximum length of the inclusion is 20 .mu.m or
less, indicating that splashes are hardly generated.
[0068] Although the results as hitherto described in Examples 1 to
4 and in Comparative Example 3 are obtained by using nitrogen gas
as the atomizing gas in the gas atomizing step of the spray forming
method, the same results can be obtained when other atomizing gases
such as argon gas are used instead of nitrogen gas.
Examples 5 to 7
[0069] An Al--Ti alloy (Al alloy containing Ti) was melted to make
a ingot by the spray forming method. Nitrogen gas was used as the
atomizing gas in the gas atomizing step of the spray forming
method. The ratios of the nitrogen gas flow volume
(Nm.sup.3)/molten liquid flow mass (kg) in this gas atomizing step
were changed to 14.3 Nm.sup.3/kg, 12.9 Nm.sup.3/kg and 10.0
Nm.sup.3/kg as shown in FIG. 3.
[0070] The content of nitrogen (nitrogen concentration) in the
ingot above was measured by nitrogen gas analysis of the samples
taken from the ingot for the nitrogen gas analysis sample. After
forging and rolling of the ingot, a disk of the sputtering target
material of the Al--Ti alloy with a diameter of 4 inches was
manufactured by machining. Next, a thin film of the Al--Ti alloy
was formed on the substrate by sputtering under the sputtering
condition shown in FIG. 4 using the sputtering target material
described above. After a conventional heat treatment, the electric
resistivity of this thin film was measured. The thin film was
processed by photolithography as a resistivity measuring pattern
with a dimension of 100 .mu.m in width and 10 .mu.m in length and
specific resistivity was measured by a four point probe method. The
results of measurements are shown in FIG. 3. The nitrogen contents
were as low as 0.015, 0.018 and 0.027 mass %, respectively, all
being 0.1 mass % or less, allowing the increase of the electrical
resistivity ascribed to respective nitrogen contents (0.1 mass % or
less) to be suppressed below 0.11 .mu..OMEGA..cm, 0.13
.mu..OMEGA..cm and 0.20 .mu..OMEGA..cm.
Examples 8 and 9
[0071] An Al--Ti alloy was melted to make an ingot by the spray
forming method. Nitrogen gas was used as the atomizing gas in the
gas atomizing step of the spray forming method. The ratios of the
nitrogen gas flow volume (Nm.sup.3)/molten liquid flow mass (kg) in
this gas atomizing step were changed to 14.3 Nm.sup.3/kg and 10.0
Nm.sup.3/kg as shown in FIG. 3.
[0072] The content of nitrogen in the ingot in Examples 8 and 9 was
measured by the same method as in Examples 5 to 7. The results of
measurements are shown in FIG. 3. The nitrogen contents were as low
as 0.012 and 0.020 mass %.
[0073] While a smaller nitrogen content is preferable for reducing
electrical resistivity, the nitrogen content will be discussed in
Reference examples 1 to 4 below.
Reference Examples 1 and 2
[0074] Al--Ti alloy ingot were made by the same method as in
Examples 5 to 7, except that the ratios of the nitrogen gas flow
volume (Nm.sup.3)/molten liquid flow mass (kg) were adjusted to
8.88 and 8.93 Nm.sup.3/kg as shown in FIG. 3.
[0075] Nitrogen contents of the ingot in Reference Example 1 and 2
were measured by the same method as in Examples 5 to 7. The results
of the measurements are shown in FIG. 3. The nitrogen contents in
respective samples are 0.13 and 0.41 mass %, all exceeding 0.1 mass
%.
Reference Examples 3 and 4
[0076] Al--Ti alloy ingots were made by the same method as in
Examples 8 and 9, except that the ratios of the nitrogen gas flow
volume (Nm.sup.3)/molten liquid flow mass (kg) were adjusted to 9.0
and 8.9 Nm.sup.3/kg as shown in FIG. 3.
[0077] Nitrogen contents of the ingots in Reference Example 3 and 4
were measured by the same method as in Examples 5 to 7. The results
of the measurements are shown in FIG. 3. The nitrogen contents in
respective samples are 0.11 and 0.33 mass %, all exceeding 0.1 mass
%.
Example 10
[0078] An Al alloy sputtering target material was manufactured by
the same method as in Examples 1 to 3 by using an Al--Ti alloy
instead of the Al--Nd alloy as the Al alloy. The ratio of the
nitrogen gas flow volume (Nm.sup.3)/molten liquid flow mass (kg) in
the gas atomizing step of the spray forming method was used as
variable parameters in order to allow the nitrogen content in the
sputtering target material to change.
[0079] A thin film of the Al--Ti alloy was formed on the substrate
by sputtering under the sputtering condition shown in FIG. 4 using
the sputtering target material described above. After a
conventional heat treatment, the electric resistivity of this thin
film was measured. The thin film was processed by photolithography
as a resistivity measuring pattern with a dimension of 100 .mu.m in
width and 10 .mu.m in length and specific resistivity was measured
by a four point probe method.
[0080] The nitrogen content in the sputtering target material
according to Example 10 was measured by the same method as in
Examples 5 to 7.
[0081] The relation between the nitrogen content in the sputtering
target material and electrical resistivity of the thin film
obtained was determined based on the results of measurements
described above. The results are shown in FIG. 7. FIG. 7 shows that
the electrical resistivity of the Al alloy thin film formed becomes
smaller as the nitrogen content in the sputtering target material
is lower.
[0082] While the results as hitherto described are obtained by
using the Al--Nd alloy and Al--Ti alloy as the Al alloy in Examples
1 to 10, Comparative examples 1 to 3 and Reference Examples 1 to 4,
the same tendency may be obtained using Al--Ta, Al--Fe, Al--Co,
Al--Ni and Al--REM (rare earth metal) alloys instead of these Al
alloys.
[0083] While the invention has been described in detail and with
reference to specific embodiments thereof, it will be apparent to
those skilled in the art that various changes and modifications can
be made therein without departing from the spirit and the scope
thereof.
[0084] The entire disclosure of Japanese Patent Application No.
10-40520 filed on Feb. 23, 1998 including specification, claims,
drawings and summary are incorporated herein by reference in its
entirety.
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