Note: Descriptions are shown in the official language in which they were submitted.
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DESCRIPTION
SPUTTERING TARGET AND METHOD FOR PRODUCING THE SAME
TECHNICAL FIELD
[0001]
The present invention relates to a sputtering target which enables a uniform
semiconductor film, a protective film for a metal thin film, or the like to be
stably formed
of a ZnSn oxide by direct-current (DC) sputtering, and a method for producing
the same.
Priority is claimed on Japanese Patent Application No. 2013-163051, filed
August 6, 2013, and Japanese Patent Application No. 2014-157914, filed August
1, 2014,
the contents of which are incorporated herein by reference.
BACKGROUND ART
[0002]
In a liquid crystal display, a solar cell, or the like, it is suggested to
use, as the
material of an electrode which is electrically-conductive and transparent to
allow light to
pass through, a mixture (ZnSn oxide (ZTO)) of zinc oxide (ZnO) and tin oxide
(Sn02).
Furthermore, since both of ZnO and SnO2 are semiconductors, ZTO can be used as
not
only a transparent electrode but also as an oxide semiconductor (for example,
refer to
PTL 1). Particularly, a Zn2SnO4 thin film, which is a semiconductor having a
practical
mobility, can be formed at room temperature using a ZTO sputtering target.
This may
be formed on, for example, an organic film to be used as the material of a
thin-film
transistor (TFT). In this case, unlike the case of the transparent electrode
mentioned
above, the conductivity of the sputtering target is not allowed to be high.
Therefore,
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film formation is generally carried out according to a radio-frequency (RF)
sputtering
method instead of a direct-current (DC) sputtering method.
[0003]
In addition, since the Zn2SnO4 thin film is transparent and has a highly
refractive
property, the Zn2SnO4 thin film is used as the protective film of a
transparent far-infrared
reflective film formed of a metal film such as an Au thin film, an Ag thin
film, or a Cu
thin film. In order to obtain good far-infrared reflection performance while
ensuring a
high transmittance, for example, the Zn2SnO4 thin film as a transparent and
highly
refractive film is laminated on the Ag thin film. For the lamination, a
sputtering method
is also employed.
[0004]
As described above, since Zn2SnO4 itself has a high resistance, a sputtering
target formed of Zn2SnO4 does not reach such a conductivity that enables DC
sputtering.
In order to form the Zn2SnO4 thin film using the sputtering target, the RF
sputtering
method has to be employed, and this results in a low film-forming rate. Here,
in order
to decrease the resistance of the sputtering target for forming the Zn2SnO4
thin film,
allowing ZnSnO3 to be a primary phase, or adding a dopant to decrease the
resistance of
the sputtering target and enable DC sputtering, is suggested (for example,
refer to PTLs 2
to 4).
CITATION LIST
PATENT LITERATURE
[0005]
[PTL 1] Japanese Unexamined Patent Application, First Publication No.
2010-037161
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[PTL 2] Japanese Unexamined Patent Application, First Publication No.
2007-277075
[PTL 3] Japanese Unexamined Patent Application, First Publication No.
2007-314364
[PTL 4] Japanese Unexamined Patent Application, First Publication No.
2012-121791
SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0006]
As described above, in a ZTO sputtering target containing ZnSnO3 as a primary
phase suggested in PTLs 2 and 3, the specific resistance of the target can be
decreased.
Nevertheless, a sputter-deposited film formed by using the ZTO sputtering
target has a
high carrier concentration and a low resistance and is not appropriate as a
semiconductor
film.
[0007]
On the other hand, it is suggested to treat a sputtering target containing
Zn2Sna4
under a reducing atmosphere and accelerate an increase in oxygen deficiency in
a ZnSn
oxide in order to realize a decrease in resistance. However, this method
increases the
number of processes, resulting in poor productivity. Furthermore, even when
the
sputtering target having a high density is subjected to a reducing treatment,
the reduction
does not progress through the inside of the target although the increase in
oxygen
deficiency in the surface of the target is accelerated, which results in
variation in the
reduced state in the thickness direction of the target. Therefore, the
increase in the
oxygen deficiency in the center portion of the target cannot be expected.
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[0008]
For example, when a ZTO sputtering target having a greater size than a
diameter
of 100 mm and a thickness of 10 mm is manufactured, a phase in which the
effect of
reduction is insufficient remains toward the inside of the target although the
surface of
the target is sufficiently reduced. Therefore, variation in the specific
resistance occurs
in the thickness direction of the sputtering target. When sputtering is
carried out using
the sputtering target, the surface of the target has a low specific resistance
and thus DC
sputtering is enabled. However, when the inside of the target is sputtered as
the
sputtering proceeds, a portion having a high specific resistance is exposed to
the surface,
and thus abnormal discharge frequently occurs. Therefore, the sputtering
cannot be
stably carried out, and the film-forming rate is also changed. As described
above, there
are problems in that DC sputtering cannot be stably carried out, and a uniform
film
cannot be formed.
[0009]
In addition, the ZTO sputtering target disclosed in PTL 3 contains ZnSnO3 as
its
primary phase and also contains a Sn02 phase. When the Sn02 phase is present
in the
sputtering target, the Sn02 phase becomes the cause of abnormal discharge or
the
occurrence of particles in the sputter-deposited film formed by using the DC
sputtering,
and there is a further problem in that the target itself easily cracks.
[0010]
Here, an object of the present invention is to provide a sputtering target
formed
of a ZnSn oxide, which has a further lower target-specific resistance over the
entire
region in a thickness direction, always enables stable DC sputtering until the
end of the
service life of the target, is less likely to crack even during sputtering,
and is suitable for
forming a semiconductor film, a protective film for a metal thin film, or the
like, by
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- uniformly and sufficiently accelerating an increase in the oxygen
deficiency and
accelerating a reduction reaction during sintering in the thickness direction
(erosion depth
direction) of the ZnSn oxide (ZTO) sputtering target, and a method of
manufacturing the
same.
5
SOLUTION TO PROBLEM
[0011]
Paying attention to the fact that, in the above-mentioned ZnSn oxide (ZTO)
sputtering target, the specific resistance of the target is low at the surface
of the target and
is increased toward the inside of the target, it was found that it is
effective to also
decrease the specific resistance of the inside of the target, and as a method
of
uniformizing a change in the specific resistance, it is effective to dry and
granulate a
mixture of predetermined amounts of a zinc oxide (ZnO) powder and a tin oxide
(Sn02)
powder, carry out a heat treatment on the resultant under a reducing
atmosphere, and then
carry out pressing sintering on the resultant in a non-oxidizing atmosphere.
In the heat
treatment, reduction is accelerated to affect the inside of the mixture, the
reduction
proceeds over the entirety of the mixture, and an oxygen-deficient state is
generated.
Accordingly, the specific resistance of the target is decreased over the
entire region in the
thickness direction of the target, and movement of oxygen atoms during
sintering is
accelerated. As a result, the density of a sintered body is enhanced. It was
determined
that a ZTO sputtering target which always enables stable DC sputtering is
obtained
consequently.
[0012]
Here, a mixture obtained by mixing a zinc oxide (ZnO) powder and a tin oxide
(Sn02) powder, which are commercially available, at a mixing ratio of Zn and
Sn of 1:1
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in terms of atomic ratio using a wet type ball mill or a beads mill, was
dried, granulated,
inserted into a carbon crucible, and then subjected to a heat treatment at 800
C for 3
hours in a vacuum. Thereafter, the obtained powder was crushed, subjected to
pressing
sintering under conditions of 900 C, 3 hours, and 29.4 MPa (300 kgf/cm2),
thereby
obtaining a ZnSn oxide (ZTO) sintered body. The ZTO sintered body was machined
to
a predetermined shape and thus a ZTO sputtering target was produced. It was
confirmed that the specific resistance of the target was further decreased
over the entire
region in the thickness direction of the target. It was confirmed that during
formation of
a ZTO film using the ZTO sputtering target, stable DC sputtering is always
enabled.
[0013]
This was achieved by the heat treatment in the reducing atmosphere in a stage
of
the mixture before carrying out the pressing sintering. Therefore, reduction
was
sufficiently carried out over the entire region of the mixture and an oxygen-
deficient state
was achieved over the entire region in the thickness direction to the inside
of the ZTO
sintered body that was subjected to the pressing sintering. It was found that
this
contributes to a further decrease in the specific resistance of the target.
[0014]
Therefore, the present invention has been obtained on the basis of the
above-described finding and employs the following constitutions in order to
solve the
above-described problems.
(1) A sputtering target of the present invention is a sintered body formed of
a
ZnSn oxide which has a composition expressed by a chemical formula: ZnxSny0,
(x+y=2,
and z-=x+2y-a(x+2y)) and which has a deficiency coefficient of a=0.002 to 0.03
and a
fraction of oxygen of z=2.1 to 3.8, in which a variation of specific
resistances with
respect to an average of specific resistances in a thickness direction of the
sintered body
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is 50% or lower.
(2) In the sputtering target of (1), a density ratio is 90% or higher.
(3) In the sputtering target of (1) and (2), a bending strength is 100 N/mm2
or
higher.
(4) In the sputtering target of (1) to (3), the specific resistance is 1 acm
or
lower.
(5) The present invention is a method for producing the sputtering target of
(1)
to (4), and the manufacturing method includes a heat treatment process of
drying and
granulating a mixture of predetermined amounts of a zinc oxide powder and a
tin oxide
powder and thereafter heating the mixture in a reducing atmosphere; and a
sintering
process of carrying out pressing sintering on the mixture subjected to the
heat treatment
in a non-oxidizing atmosphere to obtain a sintered body, in which an oxygen-
deficiencies
are increased in the heat treatment process.
(6) In the producing method of (5), the heat treatment process and the
sintering
process are continuously carried out in a heating furnace.
ADVANTAGEOUS EFFECTS OF INVENTION
[0015]
As described above, in the sintered body of the ZnSn oxide (ZTO) sputtering
target of the present invention, the oxygen-deficient state remains, and the
oxygen-deficiencies are increased over the entire region of the inside of the
sintered body.
Therefore, the specific resistance is decreased over the entire region in the
thickness
direction (erosion depth direction) of the target to a level such that DC
sputtering is
enabled. Furthermore, a variation in the specific resistance in the thickness
direction of
the target is decreased. As a result, DC sputtering can be stably carried out
until the end
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of the service life of the target, and cracking of the target during the
sputtering can also
be suppressed. Furthermore, a uniform film can be formed.
[0016]
In addition, the producing method of the present invention includes the heat
treatment process of drying and granulating the mixture of the predetermined
amounts of
the zinc oxide powder and the tin oxide powder and thereafter heating the
mixture in the
reducing atmosphere; and the sintering process of carrying out pressing
sintering on the
mixture subjected to the heat treatment in the non-oxidizing atmosphere to
obtain the
sintered body. Therefore, an increase in the oxygen-deficiencies is
accelerated in the
heat treatment process, and the sintering is carried out while the oxygen-
deficient state
remains in the sintering process. As a result, a state in which reduction
proceeds to the
inside of the sintered body is achieved, and the oxygen-deficiencies are
uniformly
increased over the entire region of the inside of the sintered body. According
to the
producing method of the present invention, a ZTO sputtering target in which
the specific
resistance is low over the entire region in the thickness direction of the
target and a
variation in the specific resistance is small can be produced.
[0017]
Therefore, according to the sputtering target of the present invention, since
the
specific resistance of the target is low over the entire region in the
thickness direction of
the target and is uniform in the target plane, stable DC sputtering is always
enabled,
which contributes to the enhancement of productivity.
BRIEF DESCRIPTION OF DRAWINGS
[0018]
FIG. 1 is a view illustrating measurement of a specific resistance in a
sputtering
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in-plane direction of a sputtering target.
DESCRIPTION OF EMBODIMENTS
[0019]
Next, an oxide sputtering target according to an embodiment of the present
invention, and an embodiment of a method for producing the same will be
described.
The sputtering target of the embodiment is formed of a sintered body formed of
a ZnSn oxide having a composition expressed by the chemical formula: ZnxSnyOz.
The
composition of zinc (Zn) and tin (Sn) is set such that x+y=2 is satisfied and
that the
fractions thereof are in the range of those in a ZnSn oxide film to be formed.
Furthermore, since Zn2SnO4 itself has a high specific resistance, the specific
resistance of
the target is decreased by making the ZnSn oxide (Zn2Sn04) to be in an oxygen-
deficient
state. It is preferable that the fraction z of oxygen (0) in the ZnSn oxide
which is in the
oxygen-deficient state be z=2.1 to 3.8.
[0020]
Here, when a deficiency coefficient representing the acceleration of an
increase
in the oxygen-deficiencies is referred to as a, the fraction z of oxygen in
the chemical
formula: ZnxSnyOz of the ZnSn oxide of which the oxygen-deficiencies are
increased can
be expressed as z=x+2y-a(x+2y). A ZnO powder and an SnO2 powder are mixed so
as
to satisfy the conditions of x+y=2, and the mixture is subjected to a heat
treatment,
thereby adjusting the deficiency coefficient a of the mixture and the fraction
of oxygen is
changed. When the mixture of which the deficiency coefficient a is adjusted is
subjected to hot pressing under a non-oxidizing atmosphere, a sintered body
formed of
the ZnSn oxide of which the oxygen-deficiencies are increased can be obtained.
In
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addition, the fraction of oxygen of z=2.1 to 3.8 is achieved as a range of the
deficiency
coefficient of a=0.002 to 0.03.
[0021]
In the sputtering target of this embodiment, the deficiency coefficient is in
a
5 range of a=0.002 to 0.03. When the deficiency coefficient a is higher
than 0.03, a
portion of tin oxide (Sn02) in the structure is reduced, and there is a
possibility that metal
tin (Sn) may be eluted. When Sn is eluted, Sn adheres to a furnace during
producing,
which results in not only damage to the furnace but also a reduction in
productivity due
to the need for cleaning of the furnace. In addition, there is a problem of a
variation in
10 the composition of the sputtering target due to the eluted portion of
Sn. On the other
hand, when the deficiency coefficient a is lower than 0.002, since the
specific resistance
of the target is not reduced, and it becomes difficult to carry out DC
sputtering. Here, in
this embodiment, the deficiency coefficient a is in a range of 0.002 to 0.03.
In addition,
the deficiency coefficient a is more preferably 0.008 to 0.02, and is not
limited thereto.
When the fraction z of oxygen is lower than 2.1, the ratio of the ZnO powder
becomes too high, and thus there is concern that the film-forming rate may be
lowered.
On the other hand, when the fraction z of oxygen is higher than 3.8, the ratio
of the Sn02
powder becomes too high, and there is concern that an increase in the specific
resistance,
an increase in abnormal discharges, cracking during sputtering, or the like
may easily
occur. Here, in this embodiment, the fraction z of oxygen is in a range of 2.1
to 3.8.
In addition, the fraction z of oxygen is more preferably 2.7 to 3.6, and is
not limited
thereto.
[0022]
Furthermore, in the sputtering target of this embodiment, a variation with
respect
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to the average of the specific resistance in the thickness direction of the
sintered body is
50% or lower. The reason for this limitation is that when the variation
exceeds 50%,
stable DC sputtering cannot be carried out, and a uniform film cannot be
formed. By
decreasing the variation in the specific resistance in the thickness direction
of the target,
DC sputtering can be stably carried out until the end of the service life of
the target, and a
uniform film can be formed. Moreover, cracking of the target can be suppressed
during
sputtering. It is more preferable that a variation with respect to the average
of the
specific resistance in the thickness direction of the sintered body be 30% or
lower.
[0023]
Here, in the sputtering target of this embodiment, in a case where the density
ratio is 90% or higher, cracking is less likely to occur during sputtering,
and it becomes
possible to improve the film-forming rate. In order to reliably exhibit the
operational
effect, the density ratio is preferably 95% or higher.
[0024]
In addition, in the sputtering target of this embodiment, in a case where the
bending strength is 100 Nimm2 or higher, cracking is less likely to occur
during
sputtering, and it becomes possible to enhance the film-forming rate. In order
to
reliably exhibit the operational effect, the bending strength is preferably
130 I\l/nun2 or
higher.
[0025]
Moreover, in the sputtering target of this embodiment, in a case where the
specific resistance is 1Q=cm or lower, DC sputtering can be stably carried
out, and it
becomes possible to improve the film-forming rate. In order to reliably
exhibit the
operational effect, the specific resistance is preferably 0.1 SI=cm or lower.
[0026]
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In addition, an object of the producing method of this embodiment is to obtain
a
ZTO sputtering target which enables DC sputtering, obtains an appropriate
target-specific
resistance for formation of a semiconductor film or a metal thin film
protective film, and
has a decreased variation in the specific resistance in the thickness
direction of the target.
In addition, the producing method of this embodiment includes a heat treatment
process
of drying and granulating a mixture of predetermined amounts of a zinc oxide
(ZnO)
powder and a tin oxide (Sn02) powder and thereafter heating the mixture in a
reducing
atmosphere, and a sintering process of carrying out pressing sintering on the
mixture
subjected to the heat treatment in a non-oxidizing atmosphere to obtain a
sintered body.
The oxygen-deficient state of ZnO is promoted in the heat treatment process.
The
deficiency coefficient a that represents the oxygen-deficient state is changed
according to
the temperature and the treatment time of a reducing treatment in the heat
treatment
process and is increased as the temperature is increased or the time is
lengthened.
[0027]
In the heat treatment process, a mixture, which is obtained by mixing a ZnO
powder and a Sn02 powder to satisfy x+y=2 in a composition expressed by the
chemical
formula: ZnõSnyOz using a wet type ball mill or a beads mill, is dried,
granulated,
inserted into a carbon crucible, and subjected to a heat treatment in a
vacuum. By the
heat treatment, oxygen deficiency is accelerated, and a range of the
deficiency coefficient
of oxygen (0) of a=0.002 to 0.03 can be realized. In the subsequent sintering
process,
the obtained mixture is subjected to pressing sintering under conditions of
800 C to
980 C, 2 hours to 9 hours, and 9.8 MPa to 49 MPa (100 kgf/cm2 to 500 kgf/cm2),
specifically, conditions of 900 C, 3 hours, and 29.4 MPa (300 kgf/cm2),
thereby
obtaining a ZnSn oxide (ZTO) sintered body. In the sintered body obtained in
this
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sintering process, the oxygen-deficient state remains over the entire region
in the
thickness direction even after the sintering. The sintered body is naturally
cooled and
taken out of the furnace. Then, the sintered body is machined and adhered to a
backing
plate, thereby producing a ZTO sputtering target. As a result, a variation in
the specific
resistance in the thickness direction of the target can be decreased, and DC
sputtering can
be stably carried out until the end of the service life of the target.
[0028]
In addition, in the above description, a case of producing the sintered body
by
using different heating furnaces for the heat treatment process and the
sintering process is
described. However, the heat treatment process and the sintering process may
also be
continuously carried out by using the same heating furnace. For example,
sintering may
also be carried out by filling a carbon mold with granulated powder, heating
the powder
to 900 C in a vacuum, and in this state, carrying out hot pressing of the
heated powder at
a pressing pressure of 29.4 MPa (300 kgf/cm2) for 3 hours. Here, an increase
in the
oxygen-deficiencies is accelerated by the heating in the stage prior to
applying the
pressing pressure to the powder. After the oxygen-deficiencies are increased,
the
sintering proceeds. Therefore, even after the sintering, the oxygen-deficient
state
remains over the entire region in the thickness direction, and the sintered
body similar to
that in a case of using different heating furnaces is obtained.
[0029]
Next, the sputtering target according to the embodiment of the invention and
the
method of producing the same will be described in detail with reference to
Examples.
[0030]
EXAMPLES
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First, a zinc oxide (ZnO) powder having a 4N purity and an average particle
size
of D50=1.0 pm, and a tin oxide (Sn02) powder having a 4N purity and an average
particle
size of D50=1511M were prepared. The powders were weighed to achieve the
compositions shown in Table 1. The weighed powders as the raw material and
zirconia
balls (with a diameter of 5 mm and a diameter of 10 mm having the same weight)
that
weighed three times the weight of the powders (ratio by weight) were put into
a plastic
container and subjected to wet mixing in a ball mill device for 24 hours,
thereby
obtaining a mixed powder. As the solvent used at this time, for example,
alcohol is
used. In addition, instead of the above-mentioned zirconia balls, by using
zirconia
beads (with a diameter of 0.5 mm) and carrying out mixing in a bead mill
device, a
mixed powder may also be obtained.
[0031]
A slurry obtained through ball mill mixing (or bead mill mixing) was dried,
granulated, and loaded into a heating furnace. Here, heating was started and
transitioned to the heat treatment process. In the heat treatment process, the
temperature
was increased to 800 C in a vacuum and an increase in the oxygen-deficient
state was
accelerated. Thereafter, the temperature of the heating furnace was further
increased to
be transitioned to the sintering process. In Examples 1 to 7, sintering was
carried out
through hot pressing at a temperature of 900 C and a pressing pressure of 29.4
MPa (300
kgf/cm2) for 3 hours. In Example 8, sintering was carried out through hot
pressing at a
temperature of 930 C and a pressing pressure of 34.3 MPa (350 kgf/cm2) for 3
hours.
In Example 9, sintering was carried out through hot pressing at a temperature
of 900 C
and a pressing pressure of 34.3 MPa (350 kgf/cm2) for 3 hours. In Example 10,
sintering was carried out through hot pressing at a temperature of 850 C and a
pressing
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pressure of 29.4 MPa (300 kgf/cm2) for 3 hours. In addition, the sintering
process was
carried out in a vacuum.
The sintering process finished, and the obtained sintered bodies were taken
out
of the heating furnace and then were machined, thereby producing ZTO
sputtering targets
5 of Examples 1 to 10 having a diameter of 125 mm.
[0032]
COMPARATIVE EXAMPLE
For comparison of the ZTO sputtering targets of Examples described above,
10 ZTO sputtering targets of Comparative Examples 1 to 4 shown in Table 1
were prepared.
Hot pressing conditions were the same as those of Example 1. In all of
Comparative
Examples 1 to 4, similar to the case of each of Examples, a mixed powder was
obtained
by mixing the ZnO powder and the Sn02 powder. However, in Comparative Example
1,
the Sn02 powder was mixed in a large proportion, and thus the fraction z of
oxygen was
15 higher than 3.8. In Comparative Example 2, the ZnO powder was mixed in a
large
proportion, and thus the fraction z of oxygen was lower than 2.1. In addition,
in
Comparative Examples 3 and 4, mixing of the ZnO powder and the Sn02 powder was
carried out in the same manner as in Examples 3 and 6 to 10. However, in both
of
Comparative Examples 3 and 4, the deficiency coefficient a that represents the
oxygen-deficient state was outside the range of this embodiment.
[0033]
<Deficiency Coefficient a>
Here, the deficiency coefficient a of the ZnSn oxide that forms the obtained
ZTO sputtering targets of Examples and Comparative Examples was calculated in
the
following procedure.
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(Procedure 1) A ZnSn oxide powder obtained by crushing the target was heated
at 100 C for 1 hour and dried.
(Procedure 2) 1 g of the ZnSn oxide powder after being dried was weighed and
was put into a crucible that was subjected to a heat treatment in advance to
have a
constant weight. Here, the weight of the ZnSn oxide powder after being dried
is
referred to as a, and the weight of the crucible is referred to as b.
(Procedure 3) In an electric furnace, the powder was heated at 800 C for 2
hours,
and the heated powder was naturally cooled for 30 minutes to 60 minutes in a
desiccator
and then was precisely weighed. This was repeated until a constant weight was
achieved. The weight of the ZnSn oxide powder and the crucible after the heat
treatment is referred to as c.
(Procedure 4) The deficiency coefficient a of oxygen was calculated according
to the following calculation expression. In addition, the atomic weight of
oxygen is
referred to as [0], the atomic weight of Zn is referred to as [Zn], and the
atomic weight
of Sn is referred to as [Sn].
[0034]
[Expression 1]
(c ¨ b ¨ a) 1(c ¨ b) = [0] x a(x + 2 y)
[Zn]x x +[Sn]x y + [0]x (x + 2 y)
[0035]
Procedures 1 to 4 were repeated three times, and the average value of the
obtained deficiency coefficients a is shown in Table 1.
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= [0036]
[Table 1]
ZnõSny0, composition
Deficiency
X Y z
coefficient a
' _ -
Example 1 0.2 1.8 3.793 0.01
Example 2 0.4 1.6 3.594 0.01
Example 3 1 1 2.994 0.01
Example 4 1.6 0.4 2.395 0.01
Example 5 1.8 0.2 2.195 0.01
Example 6 1 1 2.999 = 0.002
Example 7 1 1 2.982 0.03
Example 8 1 1 2.994 0.01
Example 9 1 1 2.994 0.01
Example 10 1 1 2.994 0.01
Comparative
0.1 1.9 3.893 0.01
Example 1
Comparative
1.9 0.1 2.095 0.01
Example 2
Comparative 1 1 Higher than Lower than
Example 3 2.999 0.001
Comparative
1 1 2.976 0.04
Example 4
[0037]
<Measurement of Specific Resistance>
For the obtained ZTO sputtering targets of Examples and Comparative
Examples, the specific resistance was measured by a resistance-measuring
apparatus.
Here, a ZTO sputtering target having a diameter of 125 mm and a thickness of
mm was produced by the above-described producing method and was cut to 2 nun
and
10 5 mm from the surface (0 mm) in an erosion depth direction (thickness
direction of the
target), and the specific resistances at the positions were measured. A
variation in the
specific resistance in the thickness direction was expressed as a percentage
of a variation
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=
18
= coefficient. In addition, the variation coefficient was obtained by
dividing the standard
deviation of the specific resistances in the thickness direction of the target
by the average
value of the specific resistances in the thickness direction of the target.
[0038]
In addition, at the positions of the surface (0 mm) of the ZTO sputtering
target of
Examples and Comparative Examples, and 2 mm and 5 mm from the surface (0 mm),
for
five (A to E) measurement points in a sputtered target plane shown in FIG 1,
the specific
resistances were measured. The average value of the measured specific
resistances in
the plane is shown in Table 2. As the measurement points A to E, on the XY
coordinates having the center of the sputtered surface as the origin, there
were A (X=0
mm, Y=55 mm), B (X=-55 mm, Y=0 mm), C (X=0 mm, Y=0 mm), D (X=55 nun, Y=0
mm) and E (X=0 mm, Y=-55 mm).
During this measurement, the specific resistance (Q=cm) was measured by a
four-probe method using a low-resistivity meter (Loresta-GP) manufactured by
Mitsubishi Chemical Corporation as the resistance-measuring apparatus. During
the
measurement, the temperature was 23 5 C, and the humidity was 50 20%.
[0039]
<Density Ratio>
For each of the obtained ZTO sputtering targets of Examples and Comparative
Examples, the density ratio was obtained.
After the sintered body was machined to predetermined dimensions, the bulk
density thereof was obtained by measuring the weight thereof and was divided
by a
theoretical density pfn, thereby calculating the density ratio. In addition,
the theoretical
density pfr, was calculated by the following expression on the basis of the
weight of the
CA 02918933 2016-01-20
s
19
_
raw material. In addition, the density of Sn02 is referred to as pl, the mass%
of Sn02 is
referred to as C1, the density of ZnO is p2, and the mass% of ZnO is referred
to as C2.
[0040]
[Expression 2]
1
P fn = (Ci 1100 C2 /100
+
PI P2
[0041]
<Bending Strength>
According to the same method as that of the ZTO sputtering targets of Examples
and Comparative Examples shown in Table 1, each of test pieces (3 mmx4 mmx35
mm)
corresponding to each composition was produced, a stress curve thereof was
measured at
a pushing speed of 0.5 mm/min using Autograph AG-X manufactured by Shimadzu
Corporation, the maximum point stress in an elastic region was obtained, and
this was
determined as the bending strength.
CA 02918933 2016-01-20
4
_
. [0042]
[Table 2]
Specific resistance in thickness direction of Variation
target (.cm) in specific
resistance Density Bending
Cutting Cutting Cutting in ratio strength
amount amount amount thickness (%) (N/mm2)
0 mm 2 mm 5 mm direction
(%)
Example 1 0.19 0.35 0.18 32 90
101
Example 2 0.15 0.25 0.19 21 93
103
, Example 3 0.11 0.15 , 0.08 25 92
123
Example 4 0.18 0.22 0.25 13 92
110
Example 5 0.08 0.02 0.09 49 94
112
Example 6 0.75 0.63 0.52 15 93
128
Example 7 0.04 0.08 0.05 30 93
126
Example 8 0.04 0.03 0.05 20 97
141
Example 9 0.05 0.06 0.08 20 95
130
Example 10 0.06 0.07 0.11 27 87
89
Comparative
1.5 3.2 2.1 31 92
103
Example 1
Comparative
0.05 0.04 0.09 36 88 105
Example 2
Outside of Outside of Outside of
Comparative
measurement measurement measurement - 93
110
Example 3
range range range
Comparative
0.03 0.05 0.05 22 94 87
Example 4
[0043]
5 Next, for the obtained ZTO sputtering target of Examples and
Comparative
Examples, the number of times of occurrences of abnormal discharge during
sputtering,
the film-forming rate, and the presence or absence of cracking of the target
during
sputtering were measured.
[0044]
10 <Number of Times of Abnormal Discharge>
CA 02918933 2016-01-20
21
Next, for the obtained ZTO sputtering target of Examples and Comparative
Examples, the number of times of occurrences of abnormal discharge during
sputtering
was measured in the following procedure.
By using the ZTO sputtering targets of Examples and Comparative Examples, a
film-forming test was carried out under the following film-forming conditions.
= Power supply: two conditions of DC800W/DC1200W
= Total pressure: 0.4 Pa
= Sputtering gas: Ar=28.5 sccm, 02=1.5 sccm
= Target-substrate (TS) distance: 70 mm
Sputtering was carried out for 1 hour under the above film-forming conditions,
and the number of times of occurrences of abnormal micro-arc discharge was
automatically measured by an arcing counter attached to a sputtering power
supply
device. The measurement results are shown in Table 3.
[0045]
<Measurement of Film-Forming Rate>
For the measurement of the film-forming rate, sputtering was carried out for
100
seconds under the above-described film-forming conditions to allow a target
material to
be deposited on a glass substrate subjected to masking, and the height of a
stepped
portion formed after removing the masking was measured by using a step
profiler,
thereby calculating the film-forming rate. The measurement results are shown
in Table
3.
[0046]
<Observation of Target Cracking>
After measuring the number of times of occurrences of abnormal discharge
CA 02918933 2016-01-20
it
22
.
described above, the target surface was visually observed, and the presence
or absence of
cracking was checked. The observation results are shown in Table 3. In Table
3, a
case where cracking of the target was confirmed is represented by "present",
and a case
where cracking of the target was not confirmed is represented by "absent".
[0047]
[Table 3]
DC800W DC1200W
Number of Number of
times of Cracking of Film-forming times of Cracking of Film-forming
occurrences target during rate occurrences target
during rate
of abnormal sputtering (nm/sec) of abnormal sputtering
(nm/sec)
discharge discharge
Example 1 35 Absent 4.8 42 Present
6.6
Example 2 20 Absent 4.3 25 Present
6.4
Example 3 0 Absent 4.1 2 Present
6.2
Example 4 2 Absent 3.5 5 Present
4.9
Example 5 1 Absent 2.6 3 Present
3.6
Example 6 2 Absent 3.8 2 Present
5.4
Example 7 1 Absent 4.4 5 Present
6.2
Example 8 1 Absent 4.2 1 Absent
6.3
Example 9 1 Absent 4.2 2 Absent
6.3
Example 10 154 Absent 4.0 389 Present
5.8
Unable to
Unable to
Comparative measure due
measure due
5489 Present 9345 Present
Example 1 to abnormal to
abnormal
discharge
discharge
Comparative
2 Absent 2.0 45 Present 2.8
Example 2
Comparative
Example 3 Unable to carry out DC sputtering Unable to carry
out DC sputtering
Comparative
Unable to evaluate due to elution of Sn Unable to evaluate due to elution of
Sn
Example 4
[0048]
According to the results shown in each of the tables above, it was found that
in
all of the ZTO sputtering targets of Examples, the deficiency coefficient a
was in a range
of 0.002 to 0.03, a decrease in resistance could be achieved over the entire
region in the
CA 02918933 2016-01-20
=
23
= target thickness direction, and a variation in the thickness direction of
the target was
small. Moreover, during sputtering carried out using the ZTO sputtering
targets of
Examples described above, the occurrence of abnormal discharge can be
significantly
reduced, and furthermore, cracking of the target was not confirmed under the
conditions
of DC800W. Therefore, since the specific resistance of the target could be low
over the
entire region in the thickness direction of the target, stable DC sputtering
was always
enabled, and thus a uniform film could be formed while improving the film-
forming rate.
[0049]
In addition, in Example 10 in which the density ratio was 87% and the bending
strength was 891=1/mm2, cracking of the target was not confirmed under the
conditions of
DC800W, but cracking of the target was confirmed under the conditions of
DC1200W.
In addition, the number of times of abnormal discharge was slightly high.
In contrast, in Example 8 in which the density ratio was 97% and the bending
strength was 141 Nimm2, and in Example 9 in which the density ratio was 95%
and the
bending strength was 130 Nimm2, it was confirmed that cracking of the target
was not
confirmed even under the conditions of DC1200W, and the number of times of
occurrences of abnormal discharge was suppressed.
[0050]
On the other hand, in all of the ZTO sputtering targets of Comparative
Examples,
similar to Examples, a mixed powder was obtained by mixing the ZnO powder and
the
SnO2 powder. In Comparative Example 1, since the Sn02 powder was mixed in a
large
proportion and thus the fraction z of oxygen was higher than 3.8, the specific
resistance
was high, and the number of times of abnormal discharge was also high.
Moreover,
since cracking was confirmed during sputtering, film formation could not be
carried out.
In Comparative Example 2, since the ZnO powder was mixed in a large proportion
and
CA 02918933 2016-01-20
1
24
thus the fraction z of oxygen was lower than 2.1, the film-forming rate was
not enhanced.
In Comparative Examples 3 and 4, the deficiency coefficient a that represents
the
oxygen-deficient state was outside a range of 0.002 to 0.03. In Comparative
Example 3,
the deficiency coefficient a was too low, the conductivity was low, and thus
the specific
resistance in the thickness direction of the target was so high as to be
outside the
measurement range, and thus DC sputtering could not be carried out. In
Comparative
Example 4, since the deficiency coefficient a was too high, metal (Sn) was
eluted in the
sputtering target, and thus sputtering could not be carried out.
[0051]
As described above, according to the present invention, the specific
resistance
was lowered over the entire region in the thickness direction of the ZTO
sputtering target,
and the variation in the target could be decreased. This effect is similarly
applied even
when the target shape is flat (flat plate shape) or cylinder. In addition,
although the
reducing atmosphere is achieved by carrying out the heat treatment process of
the present
invention in a vacuum by using the carbon crucible, a reducing gas such as CO,
SO2, or
H2 may also be used. In addition, although the sintering process in Examples
and
Comparative Examples is carried out in a vacuum, the same effect is obtained
as long as
the non-oxidizing atmosphere is achieved.
INDUSTRIAL APPLICABILITY
[0052]
According to the sputtering target of the present invention, a semiconductor
film,
a protective film for a metal thin film, or the like can be stably formed by
direct-current
(DC) sputtering until the end of the service life of the target. In addition,
according to
the method of manufacturing the sputtering target of the present invention, a
sputtering
CA 02918933 2016-01-20
target, which enables a semiconductor film, a protective film for a metal thin
film, or the
like to be stably formed by direct-current (DC) sputtering until the end of
the service life
of the target, can be produced.
