U.S. patent application number 14/333589 was filed with the patent office on 2014-11-20 for sputtering target and oxide semiconductor film.
This patent application is currently assigned to IDEMITSU KOSAN CO., LTD.. The applicant listed for this patent is IDEMITSU KOSAN CO., LTD.. Invention is credited to Kazuyoshi INOUE, Futoshi UTSUNO, Koki YANO.
Application Number | 20140339073 14/333589 |
Document ID | / |
Family ID | 39511509 |
Filed Date | 2014-11-20 |
United States Patent
Application |
20140339073 |
Kind Code |
A1 |
INOUE; Kazuyoshi ; et
al. |
November 20, 2014 |
Sputtering Target and Oxide Semiconductor Film
Abstract
A sputtering target containing oxides of indium (In), gallium
(Ga) and zinc (Zn), which includes a compound shown by
ZnGa.sub.2O.sub.4 and a compound shown by InGaZnO.sub.4.
Inventors: |
INOUE; Kazuyoshi; (Chiba,
JP) ; YANO; Koki; (Chiba, JP) ; UTSUNO;
Futoshi; (Chiba, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
IDEMITSU KOSAN CO., LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
IDEMITSU KOSAN CO., LTD.
Tokyo
JP
|
Family ID: |
39511509 |
Appl. No.: |
14/333589 |
Filed: |
July 17, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14018606 |
Sep 5, 2013 |
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14333589 |
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12518988 |
Jan 19, 2010 |
8784700 |
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PCT/JP2007/073134 |
Nov 30, 2007 |
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14018606 |
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Current U.S.
Class: |
204/192.25 |
Current CPC
Class: |
C04B 2235/3287 20130101;
C04B 2235/80 20130101; C23C 14/3414 20130101; H01J 37/3429
20130101; C23C 14/086 20130101; C04B 2235/77 20130101; C04B
2235/5445 20130101; C04B 2235/3256 20130101; C04B 2235/3293
20130101; C04B 2235/3284 20130101; C04B 2235/604 20130101; C04B
2235/5436 20130101; C04B 2235/6586 20130101; H01J 2237/332
20130101; C04B 35/62625 20130101; C04B 2235/3244 20130101; C04B
35/01 20130101; C04B 35/64 20130101; C04B 2235/3258 20130101; C04B
2235/3286 20130101; C04B 2235/3229 20130101; H01L 21/02565
20130101; C04B 2235/5409 20130101; C04B 2235/6585 20130101; C04B
35/6261 20130101; C04B 2235/725 20130101; C04B 35/453 20130101;
H01L 21/02631 20130101; C01G 15/00 20130101; C04B 35/62655
20130101; C04B 2235/3251 20130101 |
Class at
Publication: |
204/192.25 |
International
Class: |
H01J 37/34 20060101
H01J037/34; C23C 14/08 20060101 C23C014/08; H01L 21/02 20060101
H01L021/02; C01G 15/00 20060101 C01G015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 13, 2006 |
JP |
2006-335817 |
Jan 5, 2007 |
JP |
2007-000417 |
Jan 5, 2007 |
JP |
2007-000418 |
Mar 5, 2007 |
JP |
2007-054185 |
Claims
1.-23. (canceled)
24. A method for DC sputtering which comprises subjecting a
sputtering target to DC sputtering to produce an oxide
semiconductor film: wherein the sputtering target comprises a
compound shown by InGaZnO.sub.4 as a main component, which further
contains a metal element with an atomic valency of positive
tetravalency or higher, wherein the content of the metal element
with an atomic valency of positive tetravalency or higher is 100
ppm to 10000 ppm relative to the total metal elements in the
sputtering target, and wherein the sputtering target has a bulk
resistance of less than 5.times.10.sup.-3 .OMEGA.cm.
25. The method according to claim 24, wherein the content of the
metal element with an atomic valency of positive tetravalency or
higher in the sputtering target is 200 ppm to 5000 ppm relative to
the total metal elements in the sputtering target.
26. The method according to claim 24, wherein the content of the
metal element with an atomic valency of positive tetravalency or
higher in the sputtering target is 500 ppm to 2000 ppm relative to
the total metal elements in the sputtering target.
27. The method according to claim 24, wherein the sputtering target
has a bulk resistance of less than 2.times.10.sup.-3 .OMEGA.cm.
28. The method according to claim 24, wherein the sputtering target
has a bulk resistance of less than 1.times.10.sup.-3 .OMEGA.cm.
29. The method according to claim 24, wherein the metal element
with an atomic valency of positive tetravalency or higher in the
sputtering target is at least one element selected from the group
consisting of tin, zirconium, germanium, cerium, niobium, tantalum,
molybdenum and tungsten.
30. The method according to claim 24, wherein the metal element
with an atomic valency of positive tetravalency or higher in the
sputtering target is at least one element selected from the group
consisting of tin, cerium and zirconium.
31. The method according to claim 24, wherein the presence of no
structure other than InGaZnO.sub.4 in the sputtering target is
confirmed by the X-ray diffraction analysis, or, if a structure
other than InGaZnO.sub.4 in the sputtering target is confirmed by
the X-ray diffraction analysis, the intensity thereof is smaller
than that of InGaZnO.sub.4.
32. The method according to claim 24, wherein the sputtering target
has a sintered body density of 6.0 g/cm.sup.3 or more.
Description
TECHNICAL FIELD
[0001] The invention relates to a sputtering target and an oxide
semiconductor film,
BACKGROUND ART
[0002] An oxide semiconductor film comprising a metal complex oxide
has a high degree of mobility and visible light transmission, and
is used as a switching device, a driving circuit device or the like
of a liquid crystal display, a thin film electroluminescence
display, an electrophoresis display, a moving particle display or
the like.
[0003] Examples of an oxide semiconductor film comprising a metal
complex oxide include an oxide semiconductor film comprising an
oxide of In, Ga and Zn (IGZO). An oxide semiconductor film obtained
by using an IGZO sputtering target has an advantage that it has a
higher mobility than that of an amorphous silicon film, and hence
has been attracting attention (see Patent Documents 1 to 10).
[0004] An IGZO target is known to be composed mainly of a compound
shown by InGaO.sub.3(ZnO).sub.m (wherein m is an integer of 1 to
20). However, if sputtering (DC sputtering, for example) is
conducted by using an IGZO sputtering target, a problem arises that
the compound shown by InGaO.sub.3(ZnO).sub.m grows abnormally to
cause abnormal discharge, leading to the formation of a defective
film.
[0005] Furthermore, an IGZO sputtering target is produced by mixing
raw material powder to form a mixture, prefiring, pulverizing,
granulating and molding the mixture to form a molded product, and
sintering and reducing the molded product. However, due to a large
number of steps, this process has a disadvantage that the
productivity of a sputtering target is lowered, resulting in an
increased production cost.
[0006] Therefore, it is preferable to omit even one of these steps.
However, no improvement has heretofore been made on the production
process, and an IGZO target is being produced by a conventional
process.
[0007] In addition, the sputtering target obtained by conventional
processes has a conductivity of about 90 S/cm (specific bulk
resistance: 0.011 .OMEGA.cm); in other words, has a high
resistance. It is difficult to obtain by conventional processes a
target which does not suffer from cracking or other problems during
sputtering.
[0008] Compounds, which are contained in an IGZO target and shown
by InGaO.sub.3(ZnO).sub.2, InGaO.sub.3(ZnO).sub.3,
InGaO.sub.3(ZnO).sub.4, InGaO.sub.3(ZnO).sub.5 and
InGaO.sub.3(ZnO).sub.7, as well as the production method thereof
are disclosed in Patent Documents 11 to 15.
[0009] However, compounds shown by ZnGa.sub.2O.sub.4 and
InGaZnO.sub.4 are not obtained in Patent Documents 11 to 15. As for
the particle size of the raw material powder used in Patent
Documents 11 to 15, these patent documents only state that a
particularly preferred particle size is 10 m or less. Furthermore,
although these patent documents state that these compounds can be
used in a semiconductor device, no statement is made on the
specific resistance value thereof and the use thereof in a
sputtering target. [0010] Patent Document 1: JP-A-H8-295514 [0011]
Patent Document 2: JP-A-H8-330103 [0012] Patent Document 3:
JP-A-2000-044236 [0013] Patent Document 4: JP-A-2006-165527 [0014]
Patent Document 5: JP-A-2006-165528 [0015] Patent Document 6:
JP-A-2006-165529 [0016] Patent Document 7: JP-A-2006-165530 [0017]
Patent Document 8: JP-A-2006-165531 [0018] Patent Document 9:
JP-A-2006-165532 [0019] Patent Document 10: JP-A-2006-173580 [0020]
Patent Document 11: JP-A-S63-239117 [0021] Patent Document 12:
JP-A-S63-210022 [0022] Patent Document 13: JP-A-S63-210023 [0023]
Patent Document 14: JP-A-S63-210024 [0024] Patent Document 15:
JP-A-S63-265818
DISCLOSURE OF THE INVENTION
[0025] An object of the invention is to provide a sputtering target
which can suppress abnormal discharge which occurs during formation
of an oxide semiconductor film by the sputtering method, and is
capable of forming an oxide semiconductor film which is improved in
surface smoothness without film quality disorders.
[0026] Another object of the invention is to provide a sputtering
target which maintains the properties of an IGZO sputtering target,
has a low bulk resistance, a high density, and more
uniform-fine-particle-size structure, as well as a high degree of
transverse rupture strength.
[0027] Still another object of the invention is to provide a
sputtering target which can suppress occurrence of abnormal
discharge even though it is an IGZO sputtering target and is used
in DC sputtering.
[0028] Further another object of the invention is to provide a
method for producing a sputtering target which can shorten the
production process without impairing the properties of an IGZO
sputtering target.
[0029] The inventors have found that, in an IGZO sputtering target
which contains an oxide of indium (In), gallium (Ga) and zinc (Zn),
a compound shown by ZnGa.sub.2O.sub.4 inhibits abnormal growth of a
compound shown by InGaO.sub.3(ZnO).sub.m (wherein m is an integer
of 2 to 20), whereby abnormal discharge during sputtering can be
suppressed, and a compound shown by InZnGaO.sub.4 inhibits abnormal
growth of a compound shown by InGaO.sub.3(ZnO).sub.m (wherein m is
an integer of 2 to 20), whereby abnormal discharge during
sputtering can be suppressed.
[0030] In addition, the inventors have found that, the bulk
resistance of a sputtering target itself can be reduced by adding a
metal element with an atomic valency of positive tetravalency or
higher, whereby abnormal discharge can be suppressed (First
Invention).
[0031] Furthermore, the inventors have found that, occurrence of
abnormal discharge during sputtering can be suppressed by adding to
an IGZO sputtering target which comprises InGaZnO.sub.4 as a main
component a metal element with an atomic valency of positive
tetravalency or higher (Second Invention).
[0032] In addition, the inventors have found that, in the method
for producing an IGZO sputtering target, the prefiring step and the
reduction step can be omitted by mixing/pulverizing, according to a
specific mixing/pulverizing method, indium oxide, gallium oxide and
zinc oxide, or raw material powder containing them as main
components, thereby to adjust the specific surface area or the
median diameter of the raw material mixed powder and the powder
after pulverization (Third Invention).
[0033] The invention provides the following sputtering target or
the like.
First Invention
First Embodiment
[0034] 1. A sputtering target containing oxides of indium (In),
gallium (Ga) and zinc (Zn), which comprises a compound shown by
ZnGa.sub.2O.sub.4 and a compound shown by InGaZnO.sub.4. 2. The
sputtering target according to 1, wherein an atomic ratio shown by
In/(In+Ga+Zn), an atomic ratio shown by Ga/(In+Ga+Zn) and an atomic
ratio shown by Zn/(In+Ga+Zn) satisfy the following
relationship:
0.2<In/(In+Ga+Zn)<0.77
0.2<Ga/(In+Ga+Zn)<0.50
0.03<Zn/(In+Ga+Zn)<0.50.
3. The sputtering target according to 1 or 2, wherein the atomic
ratio shown by In/(In+Ga+Zn) and the atomic ratio shown by
Ga/(Tn+Ga+Zn) satisfy the following relationship:
In/(In+Ga+Zn)>Ga/(In+Ga+Zn).
4. The sputtering target according to any one of 1 to 3, wherein
the sputtering target comprises a metal element with an atomic
valency of positive tetravalency or higher, and the content of the
metal element with an atomic valency of positive tetravalency or
higher relative to the total metal elements [metal element with an
atomic valency of positive tetravalency or higher/total metal
elements:atomic ratio] is 0.0001 to 0.2. 5. The sputtering target
according to 4, wherein the metal element with an atomic valency of
positive tetravalency or higher is one or more elements selected
from tin, zirconium, germanium, cerium, niobium, tantalum,
molybdenum and tungsten. 6. The sputtering target according to any
one of 1 to 5, which has a bulk resistance of less than
5.times.10.sup.-3 .OMEGA.cm. 7. An oxide semiconductor film which
is obtained by film formation by sputtering using the sputtering
target according to any one of 1 to 6.
First Invention
Second Embodiment
[0035] 1. A sputtering target containing oxides of indium (In),
gallium (Ga) and zinc (Zn), which comprises a homologous structure
compound shown by InGaO.sub.3(ZnO).sub.m (wherein m is an integer
of 1 to 20) and a spinel structure compound shown by
ZnGa.sub.2O.sub.4. 2. The sputtering target according to 1, which
comprises at least a homologous structure compound shown by
InGaZO.sub.4. 3. The sputtering target according to 1 or 2, wherein
the spinel structure compound shown by ZnGa.sub.2O.sub.4 has an
average particle diameter of 10 .mu.m or less. 4. The sputtering
target according to any one of 1 to 3, which has a sintered body
density of 6.0 g/cm.sup.3 or more. 5. The sputtering target
according to any one of 1 to 4, which has a surface roughness (Ra)
of 2 .mu.m or less and an average transverse rupture strength of 50
MPa or more. 6. The sputtering target according to any one of 1 to
5, wherein the content of each of Fe, Al, Si, Ni and Cu is 10 ppm
(weight) or less. 7. A method of producing a sputtering target
according to any one of 1 to 6 comprising the steps of:
[0036] pulverizing and mixing/granulating indium oxide, gallium
oxide and zinc oxide to prepare a mixture:
[0037] molding the mixture to obtain a molded product; and
[0038] sintering the molded product in an oxygen stream or under an
oxygen pressure at a temperature of 1250.degree. C. or higher and
lower than 1450.degree. C.
8. An oxide semiconductor film which is obtained by film formation
by sputtering using the sputtering target according to any one of 1
to 6.
Second Invention
[0039] 1. A sputtering target comprising a compound shown by
InGaZnO.sub.4 as a main component, which further contains a metal
element with an atomic valency of positive tetravalency or higher.
2. The sputtering target according to 1, wherein the content of the
metal element with an atomic valency of positive tetravalency or
higher is 100 ppm to 10000 ppm relative to the total metal elements
in the sputtering target. 3. The sputtering target according to 1,
wherein the content of the metal element with an atomic valency of
positive tetravalency or higher is 200 ppm to 5000 ppm relative to
the total metal elements in the sputtering target. 4. The
sputtering target according to 1, wherein the content of the metal
element with an atomic valency of positive tetravalency or higher
is 500 ppm to 2000 ppm relative to the total metal elements in the
sputtering target. 5. The sputtering target according to any one of
1 to 4, which has a bulk resistance of less than 1.times.10.sup.-3
.OMEGA.cm. 6. The sputtering target according to any one of 1 to 5,
wherein the metal element with an atomic valency of positive
tetravalency or higher is at least one element selected from the
group consisting of tin, zirconium, germanium, cerium, niobium,
tantalum, molybdenum and tungsten.
Third Invention
[0040] 1. A method for producing a sputtering target comprising the
steps of:
[0041] preparing, as raw material powder, mixed powder containing
indium oxide powder having a specific surface area of 6 to 10
m.sup.2/g, gallium oxide powder having a specific surface area of 5
to 10 m.sup.2/g and zinc oxide powder having a surface area of 2 to
4 m.sup.2/g, the specific surface area of the entire mixed powder
being 5 to 8 m.sup.2/g;
[0042] mixing/pulverizing the raw material powder by means of a wet
medium stirring mill to increase the specific surface area of the
entire mixed powder by 1.0 to 3.0 m.sup.2/g;
[0043] molding the raw material powder to obtain a molded product;
and
[0044] sintering the molded product in an oxygen atmosphere at a
temperature of 1250 to 1450.degree. C.
2. A method for producing a sputtering target comprising the steps
of:
[0045] preparing, as raw material powder, mixed powder containing
indium oxide powder having a median diameter of particle size
distribution of 1 to 2 .mu.m, gallium oxide powder having a median
diameter of particle size distribution of 1 to 2 .mu.m and zinc
oxide powder having a median diameter of particle size distribution
of 0.8 to 1.6 .mu.m, the median diameter of particle size
distribution of the entire mixed powder being 1.0 to 1.9 .mu.m;
[0046] mixing/pulverizing the raw material powder by means of a wet
medium stirring mill to allow the raw material powder to have a
median diameter of 0.6 to 1 .mu.m;
[0047] molding the raw material powder to obtain a molded product;
and
[0048] sintering the molded product in an oxygen atmosphere at a
temperature of 1250 to 1450.degree. C.
3. The method for producing a sputtering target according to 1 or
2, wherein the sintering is performed without conducting prefiring.
4. The method for producing a sputtering target according to any
one of 1 to 3, wherein the density of a sintered body obtained in
the sintering step is 6.0 g/cm.sup.3 or more.
[0049] According to the invention, it is possible to provide a
sputtering target which can suppress abnormal discharge which
occurs when an oxide semiconductor film is formed by the sputtering
method and is capable of forming an oxide semiconductor film which
is free from film quality disorders and has improved surface
smoothness.
BRIEF DESCRIPTION OF THE DRAWINGS
[0050] FIG. 1 is an X-ray chart of a target prepared in Example
1;
[0051] FIG. 2 is an X-ray chart of a target prepared in Example
2;
[0052] FIG. 3 is an X-ray chart of a target prepared in Example
3;
[0053] FIG. 4 is an X-ray chart of a target prepared in Comparative
Example 1;
[0054] FIG. 5 is a graph showing the relationship between the
amount of a metal with an atomic valency of positive tetravalency
or higher and the bulk resistance of a sintered body;
[0055] FIG. 6 is an X-ray diffraction chart of a target prepared by
adding tin;
[0056] FIG. 7 is an X-ray diffraction chart of a sintered body
prepared in Example 8;
[0057] FIG. 8 is a graph showing the relationship between the
amount of a tin element and the bulk resistance of a sintered body,
and
[0058] FIG. 9 is a graph showing the relationship between the
amount of a metal element with an atomic valency of positive
tetravalency or higher and the bulk resistance of a sintered
body.
BEST MODE FOR CARRYING OUT THE INVENTION
First Invention
First Embodiment
[0059] The sputtering target of the invention (hereinafter often
referred to as "the target of the invention") contains oxides of
indium (In), gallium (Ga) and zinc (Zn), and comprises a compound
shown by ZnGa.sub.2O.sub.4 and a compound shown by
InGaZnO.sub.4.
[0060] By allowing a compound shown by ZnGa.sub.2O.sub.4 and a
compound shown by InGaZnO.sub.4 to be generated in a sputtering
target, abnormal growth of a compound shown by
InGaO.sub.3(ZnO).sub.m (wherein m is an integer of 2 to 20) can be
suppressed, and abnormal discharge of the sputtering during
sputtering can be suppressed. In addition, since the crystal
particle size can be reduced, oxygen deficiency is generated in the
crystal interface, whereby bulk resistance can be reduced.
[0061] In addition, the sputtering target of the invention contains
a plurality of crystal systems such as a compound shown by
InGaO.sub.3(ZnO).sub.m (wherein m is an integer of 2 to 20) and a
compound shown by ZnGa.sub.2O.sub.4, oxygen deficiency occurs due
to the incommensuration of crystals in the crystal grain boundary,
and as a result, carriers are generated in the target. These
carriers lower the resistance of the target, whereby abnormal
discharge during sputtering can be suppressed.
[0062] In the sputtering target of the invention, it is preferred
that an atomic ratio shown by In/(In+Ga+Zn), an atomic ratio shown
by Ga/(In+Ga+Zn) and an atomic ratio shown by Zn/(In+Ga+Zn) satisfy
the following relationship:
0.2<In/(In+Ga+Zn)<0.77
0.2<Ga/(In+Ga+Zn)<0.50
0.03<Zn/(In+Ga+Zn)<0.50.
[0063] The above-mentioned atomic ratios are obtained by adjusting
the mixing ratio of the indium compound, the gallium compound and
the zinc compound before sintering, which will be mentioned
later.
[0064] If the In/(In+Ga+Zn) is 0.77 or more, the conductivity of
the resulting oxide semiconductor film may be increased, making it
difficult to be used as a semiconductor. If the In/(In+Ga+Zn) is
0.2 or less, the oxide semiconductor film obtained by film
formation may have a lowered carrier mobility when used as a
semiconductor.
[0065] If the Ga/(In+Ga+Zn) is 0.5 or more, when used as a
semiconductor, the carrier mobility of the oxide semiconductor film
obtained by film formation may be lowered. On the other hand, if
the Ga/(In+Ga+Zn) is 0.2 or less, the conductivity of the oxide
semiconductor film obtained by film formation may be increased,
making it difficult to be used as a semiconductor. In addition, the
semiconductor properties may be varied or the threshold voltage
(Vth) shift may be increased due to disturbance such as
heating.
[0066] If the Zn/(In+Ga+Zn) is 0.03 or less, the oxide
semiconductor film may be crystallized. On the other hand, if the
Zn/(In+Ga+Zn) is 0.5 or more, the oxide semiconductor film itself
may not have sufficient stability, resulting in an increased Vth
shift.
[0067] The atomic ratio of each element in the above-mentioned
target can be obtained by measuring the amount of each element by
ICP (Inductively Coupled Plasma).
[0068] In the sputtering target of the invention, the atomic ratio
shown by In/(In+Ga+Zn) and the atomic ratio shown by Ga/(In+Ga+Zn)
preferably satisfy the following formula:
In/(In+Ga+Zn)>Ga/(In+Ga+Zn).
[0069] The sputtering target satisfying this formula is capable of
producing an oxide semiconductor film which has a high degree of
stability, the suppressed Vth shift, and long-term stability,
[0070] The sputtering target of the invention preferably contains a
metal element with an atomic valency of positive tetravalency or
higher, and the content of the metal element with an atomic valency
of positive tetravalency or higher relative to the total metal
elements [metal element with an atomic valency of positive
tetravalency or higher/total metal elements:atomic ratio] is 0.0001
to 0.2.
[0071] Since the sputtering target contains a metal element with an
atomic valency of positive tetravalency of higher, the target
itself has a reduced bulk resistance, whereby occurrence of
abnormal discharge during sputtering by the target can be
suppressed.
[0072] If the content ratio [metal element with an atomic valency
of positive tetravalency or higher/total metal elements:atomic
ratio] is less than 0.0001, the effects of decreasing the bulk
resistance may be small. On the other hand, if the content ratio
[metal element with an atomic valency of positive tetravalency or
higher/total metal elements:atomic ratio] exceeds 0.2, the
stability of the oxide semiconductor film may be lowered.
[0073] Examples of preferred metal element with an atomic valency
of positive tetravalency or higher include tin, zirconium,
germanium, cerium, niobium, tantalum molybdenum and tungsten. Of
these, tin, cerium and zirconium are more preferable.
[0074] The above-mentioned metal element with an atomic valency of
positive tetravalency or higher is added, for example, as a metal
oxide, to the raw materials of the sputtering target such that the
content of metal element falls within the above-mentioned
range.
[0075] In addition to the above-mentioned metal element with an
atomic valency of positive tetravalency or higher, the sputtering
target of the invention may contain, for example, hafnium, rhenium,
titanium, vanadium or the like within an amount range which does
not impair the advantageous effects of the invention.
Second Embodiment
[0076] The sputtering target of the invention (hereinafter often
referred to as the target of the invention) contains oxides of
indium (In), gallium (Ga) and zinc (Zn), and comprises a homologous
compound shown by InGaO.sub.3(ZnO).sub.m (m is an integer of 1 to
20) and a spinel structure compound shown by ZnGa.sub.2O.sub.4.
[0077] The homologous compound is a compound having a homologous
phase.
[0078] The homologous phase (Homologous Series) is, for example, a
magneli phase shown by a compositional formula Ti.sub.nO.sub.2,
taking n as a natural number. In such a phase, there are a series
of compounds in which n varies continuously.
[0079] Specific examples of the homologous compound include
In.sub.2O.sub.3(ZnO).sub.m (wherein m is an integer of 2 to 20),
InGaO.sub.3(ZnO).sub.m (wherein m is an integer of 2 to 20), or the
like.
[0080] As described in "Crystal Chemistry" (Mitsuoki Nakahira,
Kodansha, 1973) or the like, an AB.sub.2X.sub.4 type or an
A.sub.2BX.sub.4 type is called a spinel structure, and a compound
having such a crystal structure is generally called a spinel
structure compound.
[0081] In a common spinel structure, anions (usually oxygen) are
filled by cubic closest packing with cations being present in part
of tetrahedron or octahedron clearances.
[0082] A substituted-type solid solution in which some of the atoms
and ions in the crystal structure are replaced with other atoms and
an interstitial solid solution in which other atoms are added to
the sites between gratings are also included in the spinel
structure compounds.
[0083] The crystal conditions of the compound in the target can be
judged by observing a sample extracted from the target (sintered
body) by the X-ray diffraction method.
[0084] The spinel structure compound constituting the target of the
invention is a compound shown by ZnGa.sub.2O.sub.4. That is, in the
X-ray diffraction, the compound shows a peak pattern of No. 38-1240
or an analogous (shifted) pattern of the Joint Committee on Powder
Diffraction Standards (JCPDS) database.
[0085] By allowing a compound shown by ZnGa.sub.2O.sub.4 to be
formed in the sputtering target, abnormal growth of a compound
shown by InGaO.sub.3(ZnO).sub.m (wherein m is an integer of 2 to
20) can be suppressed, whereby abnormal discharge of a target
during sputtering can be suppressed. Preferably, by allowing a
compound shown by InGaZnO.sub.4 to be formed, abnormal growth of a
compound shown by InGaO.sub.3(ZnO).sub.m (wherein m is an integer
of 2 to 20) can be further suppressed.
[0086] By suppressing abnormal growth of a compound shown by
InGaO.sub.3(ZnO).sub.m (wherein m is an integer of 2 to 20), it is
possible to increase the transverse rupture strength of the target,
whereby cracking of the target during sputtering can be
suppressed.
[0087] Since the sputtering target of the invention contains a
plurality of crystal systems of the homologous structure compound
shown by InGaO.sub.3(ZnO).sub.m (wherein m is an integer of 1 to
20) and the spinel structure compound shown by ZnGa.sub.2O.sub.4,
oxygen deficiency occurs due to the incommensuration of the
crystals in the crystal grain boundary, and as a result, carriers
are generated in the target. These carriers lower the resistance of
the target, whereby abnormal discharge during sputtering can be
suppressed.
[0088] In the target of the invention, the average particle size of
the spinel structure compound shown by ZnGa.sub.2O.sub.4 is
preferably 10 .mu.m or less, more preferably 5 .mu.m or less.
[0089] By allowing the average particle size of the spinel
structure compound shown by ZnGa.sub.2O.sub.4 to be 10 .mu.m or
less, the particle growth of the compound shown by
InGaO.sub.3(ZnO).sub.m (wherein m is an integer of 2 to 20) can be
more surely suppressed, and the transverse rupture strength of the
target can be increased, whereby cracking of the target during
sputtering is suppressed.
[0090] The average particle size of the above-mentioned spinel
structure compound shown by ZnGa.sub.2O.sub.4 can be evaluated by
observing a secondary electron image of a scanning electron
microscope (SEM), for example.
[0091] The sputtering target of the above-mentioned first and
second embodiments preferably has a bulk resistance of less than
5.times.10.sup.-3 .OMEGA.cm, more preferably less than
2.times.10.sup.-3 .OMEGA.cm. If the bulk resistance is
5.times.10.sup.-3 .OMEGA.cm or more, abnormal discharge may be
induced during sputtering and foreign matters (nodules) may be
generated.
[0092] The bulk resistance of the target of the invention can be
measured by the four probe method.
[0093] The sputtering target of the invention preferably has a
sintered body density of 6.0 g/cm.sup.3 or more.
[0094] By allowing the density of a sintered body of the target to
be 6.0 g/cm.sup.3 or more, the transverse rupture strength of the
target can be increased, thereby suppressing cracking of the target
during sputtering. On the other hand, if the density of a sintered
body of the target is less than 6.0 g/cm.sup.3, the target surface
may be blackened to cause abnormal discharge.
[0095] In order to obtain a high-density sintered body, it is
preferable to perform molding by the cold isostatic press (CIP)
method, the hot isostatic press (HIP) method, or the like.
[0096] It is preferred that the target of the invention have a
surface roughness (Ra) of 2 .mu.m or less and an average transverse
rupture strength of 50 MPa or more. More preferably, the target of
the invention has a surface roughness (Ra) of 0.5 .mu.m or less and
an average transverse rupture strength of 55 MPa or more.
[0097] By allowing the surface roughness (Ra) of the target to be 2
.mu.m or less, the average transverse rupture strength of the
target can be maintained 50 MPa or more, whereby cracking of the
target during sputtering can be suppressed.
[0098] The surface roughness (Ra) can be measured by the AFM method
and the average rupture transverse strength can be measured
according to JIS R 1601.
[0099] It is preferred that the target of the invention contain Fe,
Al, Si, Ni and Cu in an amount of 10 ppm (weight) or less.
[0100] Fe, Al, Si, Ni and Cu are the impurities of the target of
the invention. By allowing the content of each of Fe, Al, Si, Ni
and Cu to be 10 ppm (weight) or less, variation in the threshold
voltage of an oxide semiconductor film obtained by film formation
using this target can be suppressed, whereby stable operation
conditions can be obtained.
[0101] The content of the above-mentioned impurity elements can be
measured by the inductively coupled plasma (ICP)
spectrophotometry.
[0102] In addition to oxides of indium (In), gallium (Ga) and zinc
(Zn), the sputtering target of the invention may contain a metal
element with an atomic valency of positive tetravalency within an
amount range which does not impair the advantageous effects of the
invention.
[0103] An oxide semiconductor film obtained by using the sputtering
target of the invention is amorphous, and exhibits stable
semiconductor properties without the effects of carrier generation
(doping effects) even though a metal element with an atomic valency
of positive tetravaleny is contained.
[0104] Method for Producing a Sputtering Target
[0105] The sputtering target of the above-mentioned first and
second embodiments can be produced, for example, by pulverizing and
mixing/granulating indium oxide, gallium oxide and zinc oxide to
prepare a mixture, molding the mixture to obtain a molded product,
and subjecting the molded product to a heat treatment in an oxygen
stream or under an oxygen pressure at a temperature of 1250.degree.
C. or higher and lower than 1450.degree. C.
[0106] The raw materials of the sputtering target of the invention
are indium oxide, gallium oxide and zinc oxide. Preferably, the raw
materials of the sputtering target are indium oxide powder with a
specific area of 6 to 10 m.sup.2/g, gallium oxide powder with a
specific area of 5 to 10 m.sup.2/g and zinc oxide powder with a
specific area of 2 to 4 m.sup.2/g, or indium oxide powder with a
median diameter of 1 to 2 .mu.m, gallium oxide powder with a median
diameter of 1 to 2 .mu.m and zinc oxide powder with a median
diameter of 0.8 to 1.6 .mu.m.
[0107] The purity of each of the above-mentioned raw materials is
normally 2N (99 mass %) or more, preferably 3N (99.9 mass %) or
more, and more preferably 4N (99.99 mass %) or more. If the purity
is lower than 2N, a large amount of impurities such as Fe, Al, Si,
Ni and Cu may be contained. Due to the presence of these
impurities, troubles occur that the operation of an oxide
semiconductor film prepared by using this target becomes unstable
or the like.
[0108] A common pulverizer may be used for pulverizing the
above-mentioned raw materials. For example, the raw materials can
be uniformly mixed and pulverized by means of a wet medium stirring
mill, a beads mill, or an ultrasonic apparatus.
[0109] The raw materials are weighed such that the mixing ratio
In:Ga:Zn becomes 45:30:25 in weight ratio (In:Ga:Zn=1:1:1 in molar
ratio) or In.sub.2O.sub.3:Ga.sub.2O.sub.3:ZnO becomes 51:34:15 in
weight ratio (In.sub.2O.sub.3:Ga.sub.2O.sub.3:ZnO=1:1:1 in molar
ratio).
[0110] The raw materials are mixed such that, in the sputtering
target of the invention, an atomic ratio shown by In/(In+Ga+Zn), an
atomic ratio shown by Ga/(In+Ga+Zn) and an atomic ratio shown by
Zn/(In+Ga+Zn) satisfy the following formulas, for example.
0.2<In/(In+Ga+Zn)<0.77
0.2<Ga/(In+Ga+Zn)<0.50
0.03<Zn/(In+Ga+Zn)<0.50
[0111] The mixed powder is prepared such that the specific surface
area of each of the raw materials is increased by 1.0 to 2.5
m.sup.2/g or such that the average median diameter of each of the
raw materials becomes 0.6 to 1.0 .mu.m after pulverization and
mixing/granulation.
[0112] If the specific surface area of each of the raw materials is
increased by less than 1.0 m.sup.2/g or the average median diameter
of each of the raw materials is increased by less than 0.6 .mu.m,
the amount of impurities which are admixed from a pulverizer or the
like during pulverization and mixing/granulation may be
increased.
[0113] In the above-mentioned pulverization and mixing/granulation,
if the specific surface areas of indium oxide and gallium oxide
before pulverization and mixing/granulation are almost the same,
pulverization and mixing/granulation can be performed more
effectively. It is preferred that the difference in specific
surface area between indium oxide and gallium oxide before
pulverization and mixing/granulation be 3 m.sup.2/g or less. If the
difference in specific surface area is outside the above-mentioned
range, pulverization and mixing/granulation cannot be performed
efficiently. As a result, gallium oxide particles may remain in the
resulting sintered body.
[0114] If the median diameter of indium oxide and the median
diameter of gallium oxide before pulverization and
mixing/granulation are almost the same, pulverization and
mixing/granulation can be performed more efficiently. It is
preferred that the difference in median diameter between indium
oxide and gallium oxide before pulverization and mixing/granulation
be 1 .mu.m or less. If the difference in median diameter is not
within this range, gallium oxide particles may remain in the
resulting sintered body.
[0115] As the molding treatment for molding the above-mentioned
mixture, die molding, cast molding, injection molding, and the like
can be given. In order to obtain a sintered body having a high
degree of density, it is preferable to mold by CIP (isostatic
press) or the like.
[0116] For the molding treatment, a molding aid such as polyvinyl
alcohol, methyl cellulose, polywax, oleic acid or the like may be
used.
[0117] It is possible to produce a sintered body for the sputtering
target of the invention by subjecting a molded product obtained by
the above-mentioned method to firing.
[0118] The temperature for firing is 1250.degree. C. or higher and
lower than 1450.degree. C., preferably 1300.degree. C. or higher
and lower than 1450.degree. C. The firing time is normally 2 to 100
hours, preferably 4 to 40 hours.
[0119] If the firing temperature is lower than 12500.degree. C., a
resulting sintered body may not have an increased density. If the
firing temperature is 1450.degree. C. or higher, zinc is
evaporated, whereby the composition of the sintered body varies
and/or voids are generated in the target.
[0120] It is preferred that the above-mentioned firing be performed
in an oxygen stream or under an oxygen pressure. By performing
firing in an oxygen atmosphere, evaporation of zinc can be
suppressed, whereby a sintered body having no voids can be
produced. InGaZnO.sub.4 and ZnGa.sub.2O.sub.4 are formed in this
sintered body. Formation of InGaZnO.sub.4 and ZnGa.sub.2O.sub.4 can
be confirmed by the X-ray diffraction method.
[0121] The sputtering target of the invention can be produced by
subjecting the sintered body after firing to, for example,
polishing to have a desired surface roughness.
[0122] For example, the above-mentioned sintered body is ground by
means of a surface grinder to allow the average surface roughness
(Ra) to be 5 .mu.m or less, preferably 2 .mu.m or less.
Furthermore, the sputtering surface is then subjected to mirror
finishing, whereby the average surface roughness (Ra) can be to
1,000 angstroms or less.
[0123] There are no restrictions on the type of mirror finishing
(polishing). Known polishing technologies such as mechanical
polishing, chemical polishing, and mechanochemical polishing
(combination of mechanical polishing and chemical polishing) can be
used. For example, it is possible to polish to a roughness of #2000
or more by using a fixed abrasive polisher (polishing solution:
water), or, after lapping by means of a free abrasive lap
(abrasive: SiC paste or the like), it is possible to lap by using
diamond paste instead of the abrasive.
[0124] In the method for producing the sputtering target of the
invention, it is preferred that the resulting sputtering target be
subjected to a cleaning treatment.
[0125] Examples of the cleaning treatment include air blowing and
washing with running water. If cleaning (removal of foreign
matters) is performed by air blowing, foreign matters can be
effectively removed by absorbing the air by means of a dust
collector facing the nozzle.
[0126] After the above-mentioned cleaning treatments such as air
blowing and washing with running water, it is preferred that
ultrasonic cleaning or the like be further conducted. It is
effective to conduct this ultrasonic cleaning by generating
multiple oscillation within a frequency of 25 to 300 KHz. For
example, ultrasonic cleaning may be performed by generating
multiple oscillation of 12 kinds of frequencies of from 25 to 300
KHz every 25 KHz.
[0127] After bonding to a backing plate, the sputtering target can
be installed in a sputtering apparatus.
[0128] According to the method for producing the sputtering target
of the invention, it is possible to obtain a high-density sintered
body for a sputtering target without the need of a prefiring step.
In addition, it is possible to obtain a sintered body with a low
bulk resistance with the need of a reduction step. The sputtering
target of the invention can be produced with a high degree of
productivity since the production thereof does not require the
above-mentioned prefiring and reduction steps.
[0129] An oxide semiconductor film can be formed by using the
target of the invention. As the film forming method, the RF
magnetron sputtering method, the DC magnetron sputtering method,
the electron beam deposition method, the ion plating method or the
like can be used. Of these, the RF magnetron sputtering method can
preferably be used. If the bulk resistance of the target exceeds 1
.OMEGA.cm, a stable sputtering state can be maintained without
causing abnormal discharge if the RF magnetron sputtering method is
used. If the bulk resistance of the target is 10 m.OMEGA.cm or
less, the DC magnetron sputtering method, which is industrially
advantageous, can also be used.
[0130] As a result, a stable sputtering state can be maintained
without suffering from abnormal discharge, and stable film
formation can be performed continuously on the industrial
scale.
[0131] An oxide semiconductor film formed by using the sputtering
target of the invention generates only a small amount of nodules or
particles due to the high density of the sputtering target, and
hence, is improved in film properties (excellent surface smoothness
with no film quality disorders).
Second Invention
[0132] The sputtering target of the invention is an IGZO sputtering
target which is produced mainly from indium oxide, gallium oxide
and zinc oxide, comprises a compound shown by InGaZnO.sub.4 as a
main component and further contains a metal element with an atomic
valency of positive tetravalency or higher. In an IGZO sputtering
target to which a metal element with an atomic valency of positive
tetravalency or higher is added, the bulk resistance of the target
itself can be reduced and the occurrence of abnormal discharge
during DC sputtering can be suppressed.
[0133] Furthermore, in the production process of the target, it is
possible to omit a reduction step for reducing the bulk resistance
of the target. Therefore, productivity can be improved with a
reduced production cost.
[0134] The presence of a compound (crystal) shown by InGaZnO.sub.4
as a main component means that a structure other than InGaZnO.sub.4
cannot be confirmed by the X-ray diffraction analysis, or means
that, even though a structure other than InGaZnO.sub.4 is
confirmed, the intensity thereof is smaller than that of
InGaZnO.sub.4.
[0135] In the sputtering target of the invention, the amount
(weight) of the metal element with an atomic valency of positive
tetravalency or higher relative to the total metal elements in the
target is preferably 100 ppm to 10000 ppm. If the amount is less
than 100 ppm, the effects of adding a metal element with an atomic
valency of positive tetravalency or higher may be small, and if the
amount exceeds 10000 ppm, an oxide thin film may have an
insufficient stability or may have a lowered carrier mobility. The
amount of a metal element with an atomic valency of positive
tetravalency or higher is preferably 200 ppm to 5000 ppm, more
preferably 500 ppm to 2000 ppm.
[0136] In the sputtering target of the invention, it is preferred
that the bulk resistance of the target be less than
1.times.10.sup.-3 .OMEGA.cm. If the bulk resistance is
1.times.10.sup.-3 .OMEGA.cm or more, when DC sputtering is
conducted for a long period of time, spark is generated due to
abnormal discharge to cause the target to be cracked or the
properties of the resulting film as an oxide semiconductor film may
be lowered due to the adhesion of] particles which have jumped out
from the target by spark to a formed film on a substrate.
[0137] The bulk resistance is a value which is measured by means of
a resistivity meter according to the four probe method.
[0138] The sputtering target of the invention can be produced by
mixing all powder of indium oxide, gallium oxide, zinc oxide and a
material containing a metal element with an atomic valency of
positive tetravalency or higher to form a mixture and pulverizing
and sintering the mixture.
[0139] As the raw material containing a metal element with an
atomic valency of positive tetravalency or higher, a simple metal
element or a metal oxide can be used. As the metal element with an
atomic valency of positive tetravalency or higher, one or a
plurality of metal elements may be appropriately selected from tin,
zirconium, germanium, cerium, niobium, tantalum, molybdenum and
tungsten.
[0140] As for the raw material powder, it is preferred that the
specific surface area of the indium oxide powder be 8 to 10
m.sup.2/g, the specific surface area of the gallium oxide powder be
5 to 10 m.sup.2/g, and the specific surface area of the zinc oxide
powder be 2 to 4 m.sup.2/g. It is preferred that the median
diameter of the indium oxide powder be 1 to 2 .mu.m, the median
diameter of the gallium oxide powder be 1 to 2 .mu.m and the median
diameter of the zinc oxide powder be 0.8 to 1.6 .mu.m.
[0141] Furthermore, it is preferable to use powder in which the
specific surface area of the indium oxide powder and the specific
surface area of the gallium oxide powder are almost the same. By
using such powder, pulverization and mixing can be conducted more
efficiently. Specifically, it is preferable to make a specific
surface area difference 3 m.sup.2/g or less. If the specific
surface area is significantly different between the indium oxide
powder and the gallium oxide powder, pulverization and mixing may
not be conducted efficiently, and as a result, gallium oxide
particles may remain in the resulting sintered body.
[0142] In the raw material powder, the indium oxide powder, the
gallium oxide powder and the zinc oxide powder are mixed such that
the mixing ratio thereof (indium oxide powder:gallium oxide
powder:zinc oxide powder) becomes about 45:30:25 (In:Ga:Zn=1:1:1 in
molar ratio) or about 51:34:15
(In.sub.2O.sub.3:Ga.sub.2O.sub.3:ZnO=1:1:1).
[0143] It is preferred that the amount of the material containing
the metal element with an atomic valency of positive tetravalency
or higher be 100 ppm to 10000 ppm relative to the total metal
elements in the target. The amount of the material containing the
metal element with an atomic valency of positive tetravalency or
higher is appropriately adjusted based on the amounts of the indium
oxide powder, the gallium oxide powder and the zinc oxide
powder.
[0144] As long as the mixed powder containing the indium oxide
powder, the gallium oxide powder, the zinc oxide powder and the
material containing a metal element with an atomic valency of
positive tetravalency or higher is used, other components for
improving the properties of the sputtering target may be added.
[0145] The mixed powder is pulverized by means of a wet medium
stirring mill, for example. At this time, it is preferred that
pulverization be performed such that the specific area of the mixed
powder is increased by 1.5 to 2.5 m.sup.2/g after pulverization, or
such that the average median diameter becomes 0.6 to 1 .mu.m after
pulverization. By using the thus adjusted raw material powder, it
is possible to obtain a high-density sintered body for an IGZO
sputtering target without conducting the prefiring step. Also, the
reduction step becomes unnecessary.
[0146] If an increase in the specific area of the raw material
mixed powder is less than 1.0 m.sup.2/g or if the average median
diameter of the raw material mixed powder after pulverization
exceeds 1 .mu.m, the sintered density may not be sufficiently
large. If an increase in the specific surface area of the raw
material mixed powder exceeds 3.0 m.sup.2/g or the average median
diameter after pulverization is less than 0.6 .mu.m, the amount of
contaminants (the amount of admixed impurities) from a pulverizer
or the like at the time of pulverization may be increased.
[0147] Here, the specific area of each powder is a value measured
by the BET method. The median diameter of particle distribution of
each powder is a value measured by means of a particle size
distribution meter. These values can be adjusted by pulverizing the
powder by a dry pulverizing method, a wet pulverizing method or the
like.
[0148] After drying the raw material after pulverization by means
of a spray dryer or the like, the raw material is then molded.
Molding can be conducted by a known method such as the pressure
molding method and the isostatic press method.
[0149] Then, the resulting molded product is sintered to obtain a
sintered body. It is preferred that sintering be performed at 1500
to 1600.degree. C. for 2 to 20 hours. As a result, a sintered body
for an IGZO sputtering target with a sintered body density of 6.0
g/cm.sup.3 or more can be obtained. If the sintering temperature is
lower than 1500.degree. C., density may not be improved. If the
temperature exceeds 1600.degree. C., zinc may be evaporated,
whereby the composition of a sintered body is varied or voids are
generated in a sintered body due to evaporation.
[0150] It is preferred that sintering be performed in an oxygen
atmosphere by circulating oxygen or under a pressure. By this
sintering method, zinc evaporation can be suppressed, whereby a
sintered body having no voids can be obtained.
[0151] A sintered body produced by the above-mentioned method has a
density as high as 6.0 g/cm.sup.3 or more. Therefore, only a small
amount of nodules or particles are generated during use, and hence,
an oxide semiconductor film improved in film properties can be
prepared.
[0152] In the resulting sintered body, InGaZnO.sub.4 is generated
as a main component. Generation of InGaZnO.sub.4 can be confirmed
by identifying the crystal structure by the X-ray diffraction
method.
[0153] A sputtering target can be obtained by subjecting the
resulting sintered body to polishing, cleaning or the like as in
the case of the above-mentioned first invention.
[0154] By conducting sputtering using a sputtering target after
bonding, an IGZO oxide semiconductor film containing oxides of In,
Ga and Zn as main components can be formed on an object such as a
substrate.
[0155] An oxide thin film obtained by using the target of the
invention is an amorphous film, and since the metal element with an
atomic valency of tetravalency or higher which has been added does
not demonstrate doping effects (effects of carrier generation), it
is fully satisfactory as a film of which the electron density is
reduced. Therefore, when used as an oxide semiconductor film, it
exhibits a high degree of stability, and operates stably as a
semiconductor due to a suppressed Vth shift.
Third Invention
[0156] In the method for producing the sputtering target of the
invention, mixed powder of indium oxide powder, gallium oxide
powder and zinc oxide powder, or powder containing indium oxide,
gallium oxide and zinc oxide as main components is used as a raw
material. One of the characteristic features of the invention is to
use each raw material having a prescribed specific surface area or
a specific median diameter of particle diameter distribution.
[0157] Furthermore, the method of the invention is characterized in
that it comprises the step of pulverizing the above-mentioned raw
material powder by means of a wet medium stirring mill to adjust
the specific surface area or the median diameter of particle size
distribution, the step of molding the pulverized raw material to
form a molded product and the step of sintering the molded product
in an oxygen atmosphere at 1250 to 1450.degree. C.
[0158] The method (1), in which the specific surface area is
adjusted, and the method (2), in which the median diameter of
particle size distribution is adjusted, will be described
below.
(1) Production Method in which the Specific Surface Area is
Adjusted
[0159] In this method, mixed powder containing the following powder
(a) to (c) is used as the raw material powder.
(a) Indium oxide powder with a specific surface area of 6 to 10
m.sup.2/g (b) Gallium oxide powder with a specific surface area of
5 to 10 m.sup.2/g (c) Zinc oxide powder with a specific surface
area of 2 to 4 m.sup.2/g
[0160] As mentioned later, in addition to the components (a) to
(c), a fourth component may be added. In this case, it is preferred
that the total amount of the three kinds of powder accounts for 90
wt % or more of the amount of entire raw material.
[0161] The specific surface area of the entire raw material mixed
powder is 5 to 8 m.sup.2/g.
[0162] By allowing the specific surface area of each oxide to be
within the above-mentioned range, mixing/pulverization can be
conducted more efficiently.
[0163] The specific surface area of each raw material powder is a
value measured by the BET method. The specific surface area can be
adjusted by pulverizing the powder by a dry pulverizing method, a
wet pulverizing method, or the like.
[0164] In the invention, it is preferred that the specific surface
area of indium oxide and the specific surface area of gallium oxide
be almost the same. This enables more efficient pulverization and
mixing. It is preferred that the difference in specific surface
area among the raw material powder be 3 m.sup.2/g or less. If the
difference in specific surface area is large, effective
pulverization and mixing may not be conducted, and gallium oxide
powder may remain in the resulting sintered body.
[0165] The amount ratio of indium oxide and gallium oxide can be
appropriately adjusted according to application or the like. In
order to reduce the bulk resistance of the target and to conduct
stable sputtering, the amount ratio (molar ratio) of indium oxide
and gallium oxide is adjusted such that the amount of indium oxide
and the amount of gallium oxide become the same or such that the
amount of indium oxide is larger than the amount of gallium oxide.
If the molar ratio of gallium oxide becomes larger than the molar
ratio of indium oxide, abnormal discharge may be caused since
excessive gallium oxide particles may be present in the target.
[0166] The amount of zinc oxide is preferably the same as or
smaller than the total amount (molar ratio) of indium oxide and
gallium oxide.
[0167] Specifically, it is preferred that indium oxide, gallium
oxide and zinc oxide be weighed such that indium oxide:gallium
oxide:zinc oxide (weight ratio) be almost 45:30:25 (In:Ga:Zn=1:1:1,
molar ratio) or 50:35:15
(In.sub.2O.sub.3:Ga.sub.2O.sub.3:ZnO=1:1:1, molar ratio).
[0168] By mixing and pulverizing the above-mentioned raw material
powder by means of a wet medium stirring mill, the specific surface
area of the raw material powder is increased by 1.0 to 3.0
m.sup.2/g than the specific surface area of the raw material powder
before pulverization. Due to such adjustment, a high-density
sintered body for an IGZO sputtering target can be obtained without
the need of the prefiring step.
[0169] If an increase in specific surface area after pulverization
is less than 1.0 m.sup.2/g, the density of a sintered body after
the sintering step is not increased. If the specific surface area
is increased by an amount exceeding 3.0 m.sup.2/g, the amount of
admixed impurities (contaminants) from a pulverizer or the like at
the time of pulverization is increased. An increase in specific
surface area after pulverization is preferably 1.5 to 2.5
m.sup.2/g.
[0170] Here, the specific surface area of the raw material mixed
powder before pulverization means the specific surface area
measured in the state where each oxide powder has been mixed.
[0171] As the wet medium stirring mill, a commercially available
apparatus, such as a beads mill, a ball mill, a roll mill, a
planetary mill and a jet mill, can be used.
[0172] If a beads mill is used, as a pulverizing medium (beads), it
is preferable to use zirconia, alumina, quartz, titania silicon
nitride, stainless steel, mullite, glass beads, SiC or the like,
and the particle diameter thereof is preferably about 0.1 to 2
mm.
[0173] In order to allow the specific surface area of the mixed
powder to be increased by 1.0 to 3.0 m.sup.2/g than the specific
surface area of the raw material mixed powder before pulverization,
the treatment time, the type of beads, the particle diameter or the
like may be appropriately adjusted. These conditions are required
to be adjusted by means of an apparatus used.
[0174] The raw material after the above-mentioned pulverization is
dried by means of a spray dryer or the like, followed by molding.
The molding is performed by a known method, such as pressure
molding and cold isostatic pressing.
[0175] Then, the resulting molded product is sintered to obtain a
sintered body.
[0176] The sintering temperature is controlled to 1250.degree. C.
to 1450.degree. C., preferably 1350.degree. C. to 1450.degree. C.
By circulating oxygen or under an oxygen pressure, sintering is
performed in an oxygen atmosphere. If the sintering temperature is
lower than 1250.degree. C., the density of the sintered body may
not be increased. If the sintering temperature exceeds 1450.degree.
C., the composition of the sintered body may vary or voids may be
generated in a sintered body due to evaporation. The sintering time
is 2 to 72 hours, preferably 20 to 48 hours.
[0177] Evaporation of zinc can be suppressed by conducting
sintering in an atmosphere of oxygen, whereby a sintered body
having no voids can be obtained. As a result, the density of a
sintered body can be 6.0 g/cm.sup.3 or more.
[0178] In addition, it is possible to obtain a sintered body having
a bulk resistance of less than 5 m.OMEGA.cm without the reduction
step. If a sintered body has a bulk resistance of 5 m.OMEGA.cm or
more, abnormal discharge may be induced or foreign matters
(nodules) may be generated during sputtering.
(2) Production Method in which the Median Diameter is Adjusted
[0179] In this method, the mixed powder containing the following
powder (a') to (c') is used.
(a') Indium oxide powder with a median diameter of particle size
distribution of 1 to 2 .mu.m (b') Gallium oxide powder with a
median diameter of particle size distribution of 1 to 2 .mu.m (c')
Zinc oxide powder with a median diameter of particle size
distribution of 0.8 to 1.6 .mu.m
[0180] In addition to the components (a) to (c), a fourth component
may be added. In this case, it is preferred that the total of the
three kinds of powder accounts for 90 wt % or more of the entire
raw material.
[0181] The median diameter of particle size distribution of the
mixed powder as a raw material is 1.0 to 1.9 .mu.m.
[0182] By allowing the specific surface area of each oxide to be
within the above-mentioned range, mixing/pulverization can be
conducted more efficiently.
[0183] Here, the median diameter of particle size distribution is a
value measured by means of a particle distribution meter. The
median diameter can be adjusted by classification after performing
dry pulverization and wet pulverization.
[0184] It is preferable to use powder in which the median diameter
of indium oxide and the median diameter of gallium oxide are almost
the same. As a result, mixing/pulverization can be performed more
efficiency. It is preferred that the difference in median diameter
among the raw material powder be 1 .mu.m or less. If the difference
in median diameter is large, efficient mixing/pulverization may not
be performed, and as a result, gallium oxide particles may remain
in the resulting sintered body.
[0185] The amount ratio of indium oxide and gallium oxide, and the
pulverization step are the same as mentioned in (1) above.
[0186] By the pulverization step, the median diameter after
pulverization becomes 0.6 to 1 .mu.m. It is preferred that the
median diameter of the raw material be changed before and after
pulverization by 0.1 .mu.m or more. By using the thus-prepared raw
material powder, it is possible to obtain a high-density IGZO
sputtering target without the need of the prefiring step. If the
median diameter after pulverization exceeds 1 .mu.m, the density of
a sintered body does not increase. If the median diameter after
pulverization is less than 0.6 .mu.m, the amount of impurities from
a pulverizer or the like during pulverization increases.
[0187] Here, the median diameter after pulverization means the
median diameter of the entire mixed powder.
[0188] The raw material after pulverization is molded and sintered
to produce a sintered body. The molding and sintering may be
performed in the same manner as in (1) mentioned above.
[0189] The sintered body prepared in (1) or (2) as mentioned above
is then subjected to polishing, cleaning or the like as in the
above-mentioned first invention, whereby a sputtering target is
obtained.
[0190] By conducting sputtering using a sputtering target after
bonding, it is possible to obtain an oxide semiconductor film
containing oxides of In, Ga and Zn as main components. According to
the production method of the invention, not only the productivity
of the sputtering target is improved, but also the density of the
resulting sputtering target can be as high as 6.0 g/cm.sup.3 or
more. Therefore, an oxide semiconductor film excellent in film
properties, suffering from only a small amount of nodules or
particles, can be obtained. Although depending on the composition,
the upper limit of the density of the sputtering target is about
6.8 g/cm.sup.3.
[0191] In the invention, in order to further decrease the bulk
resistance of the sputtering target, a metal element with an atomic
valency of tetravalency or higher may be contained in an amount of
200 to 5000 ppm (atomic ratio) in a sintered body. Specifically, in
addition to indium oxide, gallium oxide and zinc oxide. SnO.sub.2,
ZrO.sub.2, CeO.sub.2, GeO.sub.2, TiO.sub.2, HfO.sub.2 or the like
may be added.
[0192] In the production method according to the invention, as far
as indium oxide, gallium oxide and zinc oxide are contained as main
components, other components for improving the properties of the
sputtering target may be contained in the raw material powder. For
example, a lanthanoid-based element with an atomic valency of
positive trivalency may be added, for example.
[0193] The resulting oxide semiconductor film is amorphous, and
exhibits stable semiconductor properties with no carrier generation
effects (doping effects) even though a metal element with an atomic
valency of tetravalency or higher is added.
EXAMPLES
[0194] The invention will be explained by way of examples while
comparing them with comparative examples. The following examples
only show preferable examples, and the invention are by no ways
limited by these examples. Therefore, various modifications based
on the technical concept of the invention or other examples are
included in the invention.
First Invention
[0195] The method for measuring the properties of the sputtering
target prepared in examples and comparative examples will be shown
below.
(1) Density Density was calculated from the weight and external
dimension of a target which has been cut out with a specific
dimension. (2) Bulk Resistance of Target Bulk resistance was
measured by the four probe method by means of a resistivity meter
(Rhoresta, manufactured by Mitsubishi Chemical Corporation).
(3) Structure of Oxide Present in Target
[0196] The structure of an oxide was identified by analyzing a
chart obtained by the X-ray diffraction method.
(4) Specific Surface Area of Raw Material Powder
[0197] The specific surface area of the raw material powder was
measured by the BET method.
(5) Median Diameter of Raw Material Powder
[0198] The median diameter of the raw material powder was measured
by means of a particle size distribution measuring apparatus.
(6) Average Transverse Rupture Strength
[0199] The average transverse rupture strength was measured by the
three-point bending test.
(7) Weibull Modulus of Sputtering Target
[0200] By the median rank method, the cumulative probability of
failure against the bending strength and the Weibull plot in the
single mode were obtained, whereby a Weibull modulus (m value)
showing the variation of probability of failure was obtained. The
Weibull modulus (m value) was obtained by using the linear
regressive line.
Example 1
[0201] 99.99%-pure indium oxide powder with a specific surface area
of 6 m.sup.2/g, 99.99%-pure gallium oxide powder with a specific
surface area of 6 m.sup.2/g, and 99.99%-pure zinc oxide powder with
a specific surface area of 3 m.sup.2/g were weighed such that the
weight ratio of In.sub.2O.sub.3:Ga.sub.2O.sub.3:ZnO became
45:30:25. The powder was then subjected to mixing/pulverization by
means of a wet medium stirring mill. As the medium of the wet
medium stirring mill, zirconia beads with a diameter of 1 mm were
used.
[0202] After the mixing/pulverization, the specific surface area of
each raw material powder was increased by 2 m.sup.2/g. The raw
material powder was then dried by means of a spray dryer. The
resulting mixed powder was placed in a mold, and then subject to
pressure molding by means of a cold pressing machine, whereby a
molded product was produced.
[0203] The resulting molded product was sintered for 4 hours at a
high temperature of 1400.degree. C. in an oxygen atmosphere by
circulating oxygen. As a result, a sintered body for an IGZO
sputtering target (sputtering target) having a density of 6.06
g/cm.sup.3 was obtained without conducting the prefiring step. The
X-ray diffraction analysis confirmed the presence of crystals of
ZnGa.sub.2O.sub.4 and InGaZnO.sub.4 in the sintered body. FIG. 1
shows an X-ray diffraction analysis chart.
[0204] The sintered body had a bulk resistance of 4.2 m.mu.cm.
[0205] The amount of impurities in this sintered body was measured
by the ICP analysis. The results showed that the content of each of
Fe, Al, Si, Ni and Cu was less than 10 ppm.
Example 2
[0206] Indium oxide powder with a median diameter of 1.5 .mu.m,
gallium oxide powder with a median diameter of 2.0 .mu.m, and zinc
oxide powder with a median diameter of 1.0 .mu.m were weighed such
that the weight ratio of In.sub.2O.sub.3:Ga.sub.2O.sub.3:ZnO became
almost 55:25:20. The powder was then subjected to
mixing/pulverization by means of a wet medium stirring mill. As the
medium of the wet medium stirring mill, zirconia beads with a
diameter of 1 mm were used.
[0207] After the mixing/pulverization, the average median diameter
of each raw material was allowed to be 0.8 .mu.m. The raw material
powder was then dried by means of a spray dryer. The resulting
mixed powder was placed in a mold, and then subject to pressure
molding by means of a cold pressing machine, whereby a molded
product was produced.
[0208] The resulting molded product was sintered for 4 hours at a
high temperature of 1400.degree. C. in an oxygen atmosphere by
circulating oxygen. As a result, a sintered body for an IGZO
sputtering target having a density of 6.14 g/cm.sup.3 was obtained
without conducting the prefiring step. The X-ray diffraction
analysis confirmed the presence of crystals of ZnGa.sub.2O.sub.4,
InGaZnO.sub.4 and In.sub.2O.sub.3 (ZnO).sub.4 in the sintered body.
FIG. 2 shows the X-ray diffraction analysis chart.
[0209] The sintered body had a bulk resistance of 3.8
m.OMEGA.cm.
Example 3
[0210] Indium oxide powder with a median diameter of 1.5 .mu.m,
gallium oxide powder with a median diameter of 2.0 .mu.m, and zinc
oxide powder with a median diameter of 1.0 .mu.m were weighed such
that the weight ratio of In.sub.2O.sub.3:Ga.sub.2O.sub.3:ZnO became
almost 35:25:40. The powder was then subjected to
mixing/pulverization by means of a wet medium stirring mill. As the
medium of the wet medium stirring mill, zirconia beads with a
diameter of 1 mm were used.
[0211] After the mixing/pulverization, the average median diameter
of each raw material was 0.8 .mu.m. The raw material powder was
then dried by means of a spray dryer. The resulting mixed powder
was placed in a mold, and then subject to pressure molding by means
of a cold pressing machine, whereby a molded product was
produced.
[0212] The resulting molded product was sintered for 4 hours at a
high temperature of 1400.degree. C. in an oxygen atmosphere by
circulating oxygen. As a result, a sintered body for an IGZO
sputtering target having a density of 6.02 g/cm.sup.3 was obtained
without conducting the prefiring step. The X-ray diffraction
analysis confirmed that crystals of ZnGa.sub.2O.sub.4 and
InGaZnO.sub.4 were present in the sintered body. FIG. 3 shows an
X-ray diffraction analysis chart.
[0213] The sintered body had a bulk resistance of 4.9
m.OMEGA.cm.
Comparative Example 1
[0214] Indium oxide powder with a median diameter of 1.5 .mu.m,
gallium oxide powder with a median diameter of 2.0 .mu.m, and zinc
oxide powder with a median diameter of 1.0 pun were weighed such
that the weight ratio of In.sub.2O.sub.3:Ga.sub.2O.sub.3:ZnO became
almost 34:46:20. The powder was then subjected to
mixing/pulverization by means of a wet medium stirring mill. As the
medium of the wet medium stirring mill, zirconia beads with a
diameter of 1 mm were used.
[0215] After the mixing/pulverization, the average median diameter
of each raw material was allowed to be 0.8 .mu.m. The raw material
powder was then dried by means of a spray dryer. The resulting
mixed powder was placed in a mold, and then subject to pressure
molding by means of a cold pressing machine, whereby a molded
product was produced.
[0216] The resulting molded product was sintered for 4 hours at a
high temperature of 1200.degree. C. in an oxygen atmosphere by
circulating oxygen. As a result, a sintered body for an IGZO
sputtering target having a density of 5.85 g/cm; was obtained
without conducting the prefiring step. As a result of the X-ray
diffraction analysis, it was confirmed that, although crystals of
ZnGa.sub.2O.sub.4 were present in the sintered body,
InGaO.sub.3(ZnO).sub.m was not generated. FIG. 4 shows an X-ray
diffraction analysis chart.
[0217] The sintered body had a bulk resistance of 450
m.OMEGA.cm.
Examples 4 and 5
[0218] Then, the sintered body for an IGZO sputtering target
produced in Example 1 was subjected to fine polishing (Example 4:
fine polishing, Example 5: surface grinding in the longitudinal
direction), whereby a sputtering target was produced. As for the
structure of the thus-produced sputtering target, the target
surface was analyzed by observing a secondary electron image of a
scanning electron microscope (SEM). As a result, the average
particle diameters of ZnGa.sub.2O.sub.4 crystals in the targets in
Examples 4 and 5 were found to be 4.4 .mu.m. The surface roughness
was measured by means of a surface roughness meter. As a result, it
was found that the surface roughness Ra of the target in Example 4
was 0.5 .mu.m and the surface roughness Ra of the target in Example
5 was 1.8 .mu.m.
Comparative Example 2
[0219] The sintered body for an IGZO sputtering target produced in
Comparative Example 1 was subjected to fine polishing (surface
grinding in the longitudinal direction), whereby a sputtering
target was produced. As for the structure of the thus produced
sputtering target, the target surface was analyzed by observing a
secondary electron image of a scanning electron microscope (SEM).
The average particle diameter of ZnGa.sub.2O.sub.4 crystals in the
target was 14 .mu.m. The surface roughness was measured by means of
a surface roughness meter. As a result, it was found that the
surface roughness Ra of the target was 3.5 .mu.m.
[0220] Then, as for each of the sputtering targets obtained in
Examples 4 and 5, and Comparative Example 2, the Weibull modulus
and the average transverse rupture strength were evaluated. The
results are shown in Table 1.
TABLE-US-00001 TABLE 1 Average Surface Weibull transverse Grinding
roughness modulus rupture strength condition Ra (.mu.m) [--] [MPa]
Example 4 Polishing 0.5 10.4 58 Example 5 Surface grinding 1.8 10.2
54 in the longitudinal direction Comparative Surface grinding 3.5
9.1 46 Example 2 in the longitudinal direction
[0221] A larger Weibull modulus value means that no variation can
be observed in the maximum value of the non-destructive stress.
From the results shown in Table 1, it was confirmed that the
sputtering target of the invention was a stable target suffering
from only a small degree of variation.
[0222] The surface roughness after surface grinding normally
corresponds to the particle diameter of the crystals. If the
particle diameter is not uniform, Ra tends to increase. The
transverse rupture strength is lowered with an increase in Ra.
[0223] From the results shown in Table 1, it was confirmed that the
sputtering target of the invention has a high quality since it has
a small crystal particle diameter and a small surface
roughness.
Example 6
[0224] The target produced in Example 4 (diameter: 4 inches,
thickness: 5 mm) was bonded to a backing plate, and then installed
in a DC sputtering film formation apparatus. Under an argon
atmosphere of 0.3 Pa, continuous sputtering was conducted at 100 W
for 100 hours. Nodules generated on the target surface were
observed. As a result of the observation, no nodules were generated
on the surface.
Comparative Example 3
[0225] The target produced in Comparative Example 2 (diameter: 4
inches, thickness: 5 mm) was bonded to a backing plate, and then
installed in a DC sputtering film formation apparatus. Under an
argon atmosphere of 0.3 Pa, continuous sputtering was conducted at
100 W for 100 hours. Nodules generated on the target surface were
observed. It was found that nodules were generated on almost half
of the target surface.
Example 7
[0226] A sintered body was prepared in the same manner as in
Example 1, except that tin oxide, zirconium oxide, germanium oxide,
cerium oxide, niobium oxide, tantalum oxide, molybdenum oxide or
tungsten oxide (an oxide of a metal element with an atomic valency
of positive tetravalency or higher) was added. The bulk resistance
of the sintered body was measured. The relationship between the
amount of a metal element with an atomic valency of positive
tetravalency or higher and the bulk resistance of the sintered body
is shown in FIG. 5. A sintered body for an IGZO sputtering target
was obtained by using tin as the metal element with an atomic
valency of positive tetravalency or higher and by adding tin such
that [tin element/total metal elements:atomic ratio] became 0.001.
The X-ray diffraction chart of the resulting sintered body for an
IGZO sputtering target is shown in FIG. 6.
[0227] As is apparent from FIG. 5, by adding a metal element with
an atomic valency of positive tetravalency or higher, the bulk
resistance was lowered.
Second Invention
Example 8
[0228] Indium oxide powder with a specific surface area of 6
m.sup.2/g, gallium oxide powder with a specific surface area of 6
m.sup.2/g, and zinc oxide powder with a specific surface area of 3
m.sup.2/g were weighed such that the weight ratio became 45:30:25.
Furthermore, as the metal element with an atomic valency of
positive tetravalency or higher, SnO.sub.2 was added such that the
content of an Sn element relative to the total metal elements
[Sn/(In+Ga+Zn+Sn):weight ratio] became 600 ppm.
[0229] The raw material mixed powder was subjected to
mixing/pulverization by means of a wet medium stirring mill. As the
medium, zirconia beads with a diameter of 1 mm were used. After the
mixing/pulverization, the specific surface area of the raw material
powder was increased by 2 m.sup.2/g. The raw material powder was
then dried by means of a spray dryer.
[0230] The resulting mixed powder was placed in a mold, and then
subject to pressure molding by means of a cold pressing machine,
whereby a molded product was produced. The resulting molded product
was sintered at 1550.degree. C. for 8 hours in an oxygen atmosphere
by circulating oxygen. As a result, a sintered body for an IGZO
sputtering target having a density of 6.12 g/cm.sup.3 was obtained
without conducting the prefiring step.
[0231] The density of the sintered body was calculated from the
weight and the external dimension of a sintered body which had been
cut out into a specific size.
[0232] The sintered body was analyzed by the X-ray diffraction
method. FIG. 7 is an X-ray diffraction chart of the sintered body.
From FIG. 7, presence of crystals of InGaZnO.sub.4 could be
confirmed. Since a peak derived from a metal oxide other than
InGaZnO.sub.4 could not be observed, it was confirmed that a
sintered body containing InGaZnO.sub.4 as main components was
obtained.
[0233] The bulk resistance of the thus obtained sintered body was
measured by the four probe method by means of a resistivity meter
(Rhoresta, manufactured by Mitsubishi Chemical Corporation). It was
found that the bulk resistance was 0.95.times.10.sup.-3
.OMEGA.cm.
Comparative Example 4
[0234] A sintered body was produced in the same manner as in
Example 8, except that a metal oxide which contained a metal
element with an atomic valency of positive tetravalency or higher
(tin oxide) was not added.
[0235] The density of this sintered body was found to be 5.98
g/cm.sup.3. As a result of the X-ray diffraction analysis, it was
confirmed that a sintered body containing InGaZnO.sub.4 as a main
component was obtained, since crystals of InGaZnO.sub.4 were
present and a peak derived from a metal oxide other than
InGaZnO.sub.4 was not observed.
[0236] The bulk resistance of this sintered body was 0.018 cm.
[0237] FIG. 8 is a graph showing the relationship between the
amount of a tin element and the bulk resistance of the sintered
body. FIG. 8 shows the bulk resistances of sintered bodies prepared
in the same manner as in Example 8 except that the amount of the
tin oxide powder was varied to 500 ppm, 800 ppm and 1000 ppm and
the bulk resistance of a sintered body prepared in Comparative
Example 4 (the amount of a tin element was 0 ppm). As is apparent
from FIG. 8, by adding a tin element which is a metal element with
an atomic valency of tetravalency or higher, the bulk resistance of
a sintered body could be reduced.
Examples 9 to 15
[0238] Sintered bodies were prepared in the same manner as in
Example 8, except that, as the metal oxide containing a metal
element with an atomic valency of tetravalency or higher, a
prescribed amount of an oxide shown in Table 2 was used instead of
tin oxide. The bulk resistances of the sintered body are shown in
Table 2.
TABLE-US-00002 TABLE 2 Bulk Amount added resistance Metal oxide
(weight ppm) (.OMEGA. cm) Example 9 Zirconium oxide 1010 0.94
.times. 10.sup.-3 Example 10 Germanium oxide 1020 0.89 .times.
10.sup.-3 Example 11 Cerium oxide 2000 0.92 .times. 10.sup.-3
Example 12 Niobium oxide 5000 0.95 .times. 10.sup.-3 Example 13
Tantalum oxide 10000 0.96 .times. 10.sup.-3 Example 14 Molybdenum
oxide 1500 0.92 .times. 10.sup.-3 Example 15 Tungsten oxide 1020
0.91 .times. 10.sup.-3
[0239] FIG. 9 shows the results of Examples 9 to 15, specifically,
it is a graph showing the relationship between the amount of the
metal element with an atomic valency of positive tetravalency or
higher and the bulk resistance of the sintered body. As is apparent
from FIG. 9, the bulk resistance is lowered by adding a metal
element with an atomic valency of positive tetravalency or
higher.
Third Invention
Example 16
[0240] The following oxide powder was used and weighed as the raw
material mixed powder. The specific surface area was measured by
the BET method.
(a) Indium oxide powder: 45 wt %, specific surface area: 6
m.sup.2/g (b) Gallium oxide powder: 30 wt %, specific surface area:
6 m.sup.2/g (c) Zinc oxide powder: 25 wt %, specific surface area:
3 m.sup.2/g
[0241] The specific surface area of the entire mix powder
comprising (a) to (c) was 5.3 m.sup.2/g.
[0242] The above-mentioned mixed powder was subjected to
mixing/pulverization by means of a wet medium stirring mill. As the
medium of the wet medium stirring mill, zirconia beads with a
diameter of 1 mm were used. During the pulverization, the specific
surface area of the mixed powder was checked, thereby to allow the
specific surface area to increase by 2 m.sup.2/g.
[0243] The raw material powder was then dried by means of a spray
dryer. The resulting mixed powder was placed in a mold (diameter:
150 mm, thickness: 20 mm), and then subject to pressure molding by
means of a cold pressing machine.
[0244] After the molding, the resulting molded product was sintered
for 40 hours at 1400.degree. C. in an oxygen atmosphere by
circulating oxygen.
[0245] The density of the thus produced sintered body was
calculated from the weight and external dimension of a piece of the
sintered body which had been cut out into a predetermined size. The
results showed that the density of the sintered body was 6.15
g/cm.sup.3. As mentioned hereinabove, a high-density sintered body
for an IGZO sputtering target could be obtained without conducting
the prefiring step.
[0246] As a result of the analysis on the chart obtained by the
X-ray diffraction method, it was confirmed that crystals of
InGaZnO.sub.4 and crystals of Ga.sub.2ZnO.sub.4 were present in the
sintered body.
[0247] The bulk resistance of the sintered body was measured by
means of a resistivity meter (Rhoresta, manufactured by Mitsubishi
Chemical Corporation). It was found that the sintered body had a
bulk resistance of 4.2 m.OMEGA.cm.
Example 17
[0248] As the raw material mixed powder, the following oxide powder
was used and weighed. The median diameter was measured by means of
a particle size distribution meter.
(a') Indium oxide powder: 50 wt %, median diameter: 1.5 .mu.m (b')
Gallium oxide powder: 35 wt %, median diameter: 2.0 .mu.m (c') Zinc
oxide powder: 15 wt %, median diameter: 1.0 .mu.m
[0249] The median diameter of the entire mixed powder comprising
(a') to (c') was 1.6 .mu.m.
[0250] In the same manner as in Example 16, the above-mentioned
mixed powder was subjected to mixing/pulverization by means of a
wet medium stirring mill. During the pulverization, the median
diameter of the mixed powder was checked, thereby to allow the
median diameter to be 0.9 .mu.m.
[0251] In the same manner as in Example 16, the mixed powder was
molded, followed by sintering to produce a sintered body, and the
resulting sintered body was evaluated.
[0252] The results showed that the density of the sintered body was
6.05 g/cm.sup.3. A high-density sintered body for an IGZO
sputtering target could be obtained without conducting the
prefiring step.
[0253] It was confirmed that crystals of InGaZnO.sub.4 and crystals
of Ga.sub.2ZnO.sub.4 were present in the sintered body.
[0254] The bulk resistance of the sintered body was 3.8
m.OMEGA.cm.
Comparative Example 5
[0255] The following oxide powder was used and weighed as the raw
material mixed powder.
(a) Indium oxide powder: 45 wt %, specific surface area: 9
m.sup.2/g (b) Gallium oxide powder: 30 wt %, specific surface area:
4 m.sup.2/g (c) Zinc oxide powder: 25 wt %, specific surface area:
3 m.sup.2/g
[0256] The specific surface area of the entire mixed powder
comprising (a) to (c) was 6 m.sup.2/g.
[0257] The raw material mixed powder was subjected to
mixing/pulverization by means of a wet medium stirring mill in the
same manner as in Example 16. During pulverization, the specific
surface area of the mixed powder was checked, thereby to allow the
specific area of the mixed powder to be increased by 1.4
m.sup.2/g.
[0258] Then, molding of the mixed powder and sintering were
conducted in the same manner as in Example 16, except that the
sintering condition was changed to 40 hours at 1400.degree. C.
under atmospheric conditions.
[0259] The density of the resulting sintered body was 5.76
g/cm.sup.3. That is, in this comparative example, a sintered body
having a low density was obtained.
[0260] In addition, the bulk resistance of the sintered body was
140 m.OMEGA.cm due to the absence of the reduction step.
[0261] In the sintered body, crystals which appeared to be gallium
oxide were present.
Comparative Example 6
[0262] As the raw material mixed powder, the following oxide powder
was used and weighed.
(a') Indium oxide powder: 50 wt %, median diameter: 2.5 .mu.m (b')
Gallium oxide powder: 35 wt %, median diameter: 2.5 .mu.m (c') Zinc
oxide powder: 15 wt %, median diameter: 2.0 .mu.m
[0263] The median diameter of the entire mixed powder comprising
(a') to (c') was 2.4 .mu.m.
[0264] In the same manner as in Example 16, the above-mentioned
mixed powder was subjected to mixing/pulverization by means of a
wet medium stirring mill. During the pulverization, the median
diameter of the mixed powder was checked, there by to allow the
median diameter to be 2.1 .mu.m.
[0265] In the same manner as in Example 16, the mixed powder was
molded, following by sintering to produce a sintered body, and the
resulting sintered body was evaluated, except that the sintering
condition was changed to 10 hours at 1400.degree. C. under
atmospheric conditions.
[0266] The density of the resulting sintered body was 5.85
g/cm.sup.3. That is, in this comparative example, a sintered body
having a low density was obtained.
[0267] In addition, the bulk resistance of the sintered body was
160 m.OMEGA.cm due to the absence of the reduction step.
[0268] In the sintered body, crystals which appeared to be gallium
oxide were present.
Comparative Example 7
[0269] A prefiring step was conducted in Comparative Example 5.
Specifically, the same mixed powder as in Comparative Example 5 was
prefired at 1200.degree. C. for 10 hours. The powder after the
prefiring had a specific surface area of 2 m.sup.2/g.
[0270] The thus prefired powder was pulverized by means of a wet
medium stirring mill, whereby the specific surface area thereof was
increased by 2 m.sup.2/g. Then, the mixed powder was subjected to
drying and pressure molding in the same manner as in Example 16.
Thereafter, the molded product was sintered at 1450.degree. C. for
4 hours in an oxygen atmosphere, whereby a sintered body was
produced.
[0271] The sintered body had a density of 5.83 g/cm.sup.3. As
compared with Comparative Example 5, the density could be
increased. However, as compared with Examples 16 and 17, in which
the prefiring step was not conducted, poorer results were obtained.
In addition, provision of the prefiring step impaired the
productivity of a sintered body.
[0272] This sintered body was subjected to a reduction treatment at
500.degree. C. for 5 hours in a nitrogen stream. As a result, the
bulk density of the sintered body was 23 m.OMEGA.cm.
Comparative Example 8
[0273] The same mixed powder as in Comparative Example 6 was
prefired at 1200.degree. C. for 10 hours. The specific surface area
of the prefired powder was 2 m.sup.2/g.
[0274] The prefired powder was pulverized by means of a wet medium
stirring mill to increase the specific surface area by 2 m.sup.2/g.
Then, the mixed powder was subjected to drying and pressure molding
in the same manner as in Example 16. Thereafter, the molded product
was sintered at 1450.degree. C. for 40 hours in an oxygen
atmosphere, whereby a sintered body was produced.
[0275] The sintered body had a density of 5.94 g/cm.sup.3. As
compared with Comparative Example 6, the density could be
increased. However, as compared with Examples 16 and 17, in which
the prefiring step was not conducted, poorer results were obtained.
In addition, provision of the prefiring step impaired the
productivity of a sintered body.
[0276] This sintered body was subjected to a reduction treatment at
500.degree. C. for 5 hours in a nitrogen stream. The bulk density
of the sintered body was 23 m.OMEGA.cm.
INDUSTRIAL APPLICABILITY
[0277] The target of the invention is suitable as a target to
obtain, by the sputtering method, a transparent conductive film and
an oxide semiconductor film for various applications including a
transparent conductive film for a liquid crystal display (LCD)
apparatus, a transparent conductive film for an electroluminescence
(EL) display apparatus and a transparent conductive film for a
solar cell. For example, it is possible to obtain a transparent
conductive film for an electrode of an organic EL device, a
transparent conductive film for a semi-transmitting/semi-reflecting
LCD, and oxide semiconductor film for driving a liquid crystal
display and an oxide semiconductor film for driving an organic EL
device. Furthermore, it is suitable as a raw material of an oxide
semiconductor film for a switching device, a driving circuit device
or the like of a liquid display apparatus, a thin film
electroluminescence display apparatus, an electrophoresis display
device, a moving particle display device or the like.
[0278] The method for producing a sputtering target of the
invention is an excellent production method which can improve the
productivity of a target, since the prefiring step or the reduction
step is not necessary.
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