JP2007031786A - Sputtering target, manufacturing method therefor and transparent electroconductive film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sputtering target which provides a transparent electroconductive film with low electric resistance even though containing a reduced amount of indium, and to provide a method for manufacturing the sputtering target. <P>SOLUTION: The sputtering target includes zinc oxide and stannic oxide, or includes zinc oxide, stannic oxide and indium oxide; and makes a metal or an alloy dispersed in the whole sputtering target. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a sputtering target, a manufacturing method thereof, and a transparent conductive film. More specifically, the present invention relates to a sputtering target that does not reduce or use indium which is a rare resource.

  Liquid crystal displays (LCD) and organic electroluminescence (EL) displays occupy the mainstream as display devices for mobile phones, personal digital assistants (PDAs), personal computers, laptop computers, televisions, etc., from the viewpoint of display performance and energy saving. Has reached. As a transparent conductive film used in these devices, an indium tin oxide (hereinafter referred to as ITO) film dominates. However, the ITO film uses a large amount of indium (usually about 90% by mass). Since indium is a scarce resource and is uneasy to supply, and has some toxicity, development of a transparent conductive film with a small amount of indium is important for further spread of display devices using transparent electrodes.

As a transparent conductive film in which indium is not reduced or used, a transparent conductive film mainly composed of zinc oxide-tin oxide has been studied (for example, see Patent Document 1).
Although this transparent conductive film has problems such as high resistance and large in-plane distribution of resistance, no study has been made to solve these problems.

As a sputtering target of ITO, it has been disclosed that the resistance can be reduced by setting the oxygen amount to a certain level or more (see, for example, Patent Document 2).
However, the oxygen content of the sputtering target with reduced indium has not been studied.

Further, a sputtering target composed of a metal oxide portion and a metal portion is disclosed (for example, see Patent Document 3).
However, the influence on the target with reduced indium has not been studied. In addition, a sputtering target consisting of a metal oxide part and a metal part is a composite of a metal oxide target and a metal target or a metal wire. However, the discharge during sputtering is not stable and the sputtering speed is slow.
JP-A-8-171824 JP 2000-256842 A JP 2004030934 A

  This invention is made | formed in view of the above-mentioned problem, and it aims at providing the manufacturing method of a sputtering target and a sputtering target with which a low-resistance transparent conductive film is obtained even if indium is reduced.

  As a result of intensive studies to overcome the above problems, the present inventors have determined that the stoichiometry of the metal atoms and the oxygen atoms constituting the sputtering target is the number of oxygen atoms when the metal atoms constitute the oxide. It has been found that a transparent conductive film having a low resistance can be obtained even if indium is reduced by making the amount less than the amount. Further, the present inventors have completed the present invention by discovering that a non-oxidized metal or alloy can be dispersed in a sputtering target to stably produce a target having a small amount of oxygen and to reduce the resistance of the target.

According to this invention, the following sputtering targets, its manufacturing method, a transparent conductive film, and a transparent electrode are provided.
1. A sputtering target containing zinc oxide and tin oxide, or zinc oxide, tin oxide and indium oxide, wherein a metal or an alloy is dispersed throughout the sputtering target.
2. The sputtering target according to 1, which satisfies the following (1) and (2).
_{0.65 ≦ M Zn / (M Zn} + M Sn) ≦ 0.9 (1)
0 ≦ M _In / (M _Zn + M _Sn + M _In ) ≦ 0.7 (2)
[ _Wherein , M _Zn , M _Sn and M _In represent the number of atoms of Zn, Sn and In in the sputtering target, respectively. ]
3. Furthermore, the sputtering target according to 1 or 2, which satisfies the following (3).
M _o / (M _Zn + M _Sn × 2 + M _In × 1.5) ≦ 0.99 (3)
[ _Wherein , M _Zn , M _Sn , _Mo and M _In represent the number of atoms of Zn, Sn, O and In in the sputtering target, respectively. ]
4). The sputtering target in any one of 1-3 which contains 0.1-6 mass% of said metals or alloys.
5. Hexagonal phase layered compound made of indium oxide-zinc oxide _{(In 2 O 3 (ZnO)} m: m is an integer from 3 to 20) The sputtering target according to any one of 1 to 4, including a.
6). The sputtering target according to any one of 1 to 5, wherein the bulk resistance is less than 100 mΩcm.
7). The sputtering target according to any one of 1 to 6, having a density of 5.3 to 7.2 g / cm ³ .
8). The method for producing a sputtering target according to any one of 1 to 7, comprising a step of mixing a metal oxide powder and a metal powder.
9. The transparent conductive film produced using the sputtering target in any one of said 1-7.
10. 10. A transparent electrode prepared by etching the transparent conductive film according to 9 above.

  With the sputtering target of the present invention, a transparent conductive film having a low resistance can be obtained even if indium is reduced.

Hereinafter, the sputtering target of the present invention will be specifically described.
The sputtering target of the present invention has a form in which a metal or an alloy is dispersed throughout an oxide containing at least zinc oxide and tin oxide. Thereby, even if indium is reduced, a low-resistance transparent conductive film can be obtained. Moreover, the resistance of a target can be reduced by disperse | distributing the metal or alloy which is not oxidized in a sputtering target.

As a metal or an alloy, it can use without a restriction | limiting especially in the range which does not impair the performance of this invention. A metal or alloy having a melting point of 1300 ° C. or lower, preferably 1000 ° C. or lower, more preferably 800 ° C. or lower, and even more preferably 600 ° C. or lower is usually used. If the melting point is 1300 ° C. or lower, the target melts at the time of sintering and the density of the target increases, so that the resistance of the target tends to decrease.
Moreover, what a metal oxide shows electroconductivity is also preferable. As such, Zn, Sn, In, Ga, Ge, Cd, Nd, Sm, Ce, Eu, Ag, Au, Al, and alloys containing them as main components can be preferably used. In particular, Zn, Sn, or In is preferable. In addition, you may use these metals or alloys in mixture.

The metal or alloy is preferably dispersed in the target as aggregates of 500 μm or less. More preferably, it is 100 micrometers or less, More preferably, it is 10 micrometers or less, Most preferably, it is 5 micrometers or less.
The presence of the metal or alloy can be judged from the peak of X-ray diffraction. In addition, the dispersion state can be confirmed by the presence of an agglomerated part or a low oxygen part of metal atoms by surface analysis with an X-ray microanalyzer (EPMA). Further, “dispersed throughout” means a state in which one or more metals or alloys of 500 μm or less can be confirmed in an arbitrary 5000 μm square region.
In addition, the form in which the metal or alloy is dispersed can be realized by a manufacturing method described later.

The metal or alloy content in the sputtering target is preferably 0.1 to 6% by mass, more preferably 0.2 to 4% by mass, and particularly preferably 0.3 to 3% by mass. If the amount is less than 0.1% by mass, the effect of the present invention may not be exhibited, or white spots may be formed. If the amount is more than 6% by mass, oxygen may be insufficient, and resistance may increase or transparency may decrease. There is.
Whether the sputtering target contains an unoxidized metal or alloy can be confirmed by X-ray diffraction (XRD).

The sputtering target of the present invention preferably satisfies the following (1) and (2).
0.65 ≦ M _Zn / (M _Zn + M _Sn ) ≦ 0.9 (1)
0 ≦ M _In / (M _Zn + M _Sn + M _In ) ≦ 0.7 (2)
[ _Wherein , M _Zn , M _Sn and M _In represent the number of atoms of Zn, Sn and In in the sputtering target, respectively. ]
The value [ _MZn / ( _MZn + _MSn )] of the above formula (1) defines the abundance ratio of Zn and Sn in the sputtering target. When this value is smaller than 0.65, the amount of Sn occupying the target increases and SnO ₂ aggregates and may be charged during film formation to cause abnormal discharge. On the other hand, when it is larger than 0.9, the acid resistance may be lowered. M _Zn / (M _Zn + M _Sn ) is preferably 0.7 to 0.85, more preferably 0.7 to 0.8.

Equation (2) defines the amount of In in the sputtering target. In consideration of the object of the present invention, it is preferable that the amount of In used is small, but by adding In, the resistance of the target and the thin film after film formation can be reduced. M _In / (M _Zn + M _Sn + M _In ) is preferably 0.05 to 0.6, more preferably 0.1 to 0.45, still more preferably 0.15 to 0.35, and particularly preferably 0.00. 25-0.35.

The sputtering target of the present invention preferably further satisfies the following (3).
_{M o / (M Zn + M} Sn × 2 + M In × 1.5) ≦ 0.99 (3)
[ _Wherein , M _Zn , M _Sn , _Mo and M _In represent the number of atoms of Zn, Sn, O and In in the sputtering target, respectively. ]
Equation (3) defines the amount of oxygen atoms (O) in the sputtering target. The denominator of the formula (3) means the number of oxygen atoms when each metal atom forms an oxide (ZnO, SnO ₂ , In ₂ O ₃ ). If the ratio of the value of formula (3), that is, the number of oxygen atoms contained in the sputtering target and the number of oxygen atoms when all of the metal atoms constitute an oxide is 0.99 or less, In Even if it does not reduce or use, it becomes a sputtering target from which a low-resistance transparent conductive film is obtained. In addition, the value of Formula (3) becomes like this. Preferably it is 0.8-0.98, More preferably, it is 0.9-0.97. If it is less than 0.8, the conductive film after film formation may be colored.

  Thus, by controlling the oxygen content in the target, the resistance of the sputtering thin film can be reduced, but the exact reason has not been elucidated. However, in the conventional method, it is presumed that oxygen in the film is excessive because Zn atoms that are lighter than Sn and In are exhausted without reverse sputtering or film formation.

  In addition, the value of Formula (1)-(3) mentioned above is computable from the value of the abundance ratio of each atom obtained by composition-analyzing a sputtering target using an X-ray microanalyzer (EPMA).

As a method for producing the sputtering target of the present invention, for example, there is a method in which a mixed powder of each metal oxide is further mixed with a metal or alloy powder and sintered. By using the metal powder, the oxygen content in the target can be easily controlled. Further, since the resistance of the target itself is reduced, the sputtering rate is increased and stable sputtering can be performed. Furthermore, it seems that the metal powder has a function of stabilizing oxygen defects in the film and reducing the resistance by generating carriers.
In order to adjust the difference depending on the sputtering apparatus and the sputtering conditions, a small amount of oxidizing gas may be introduced and adjusted at the time of sputtering in a slightly oxygen-deficient state at the time of sintering.

When a metal or alloy powder is mixed with each metal oxide powder and sintered, the particle size of the powder is 500 μm or less, preferably 100 μm or less, more preferably 10 μm or less, and particularly preferably 5 μm or less. . If it is larger than 500 μm, it is not uniformly mixed with other raw material powders, so that the metal or alloy may not be dispersed in the target or the resistance of the target may be increased.
The particle diameter is a value measured by a light scattering equivalent diameter (JIS R 1629).

  In the present invention, in addition to the above metal oxide powders and metal powders, sintering aids (yttria, magnesia, etc.), dispersants (polyammonium acrylate) are within the range not impairing the object of the present invention. Etc.), a binder, a lubricant (such as a stearic acid emulsion) and the like may be added.

The sputtering target of the present invention preferably contains a hexagonal phase layered compound (In ₂ O ₃ (ZnO) m: m is an integer from 3 to 20) composed of indium oxide and zinc oxide. By including these structures, the sintering density increases and the resistance of the target is likely to decrease.
Such a structure can be obtained by the manufacturing method described above. The structure is analyzed by X-ray diffraction (XRD).

The sputtering target of the present invention preferably has a bulk resistance of 0.2 to less than 100 mΩcm. Satisfying this value stabilizes the discharge during sputtering and increases the sputtering rate. More preferably, it is 0.4-20 mΩcm or less, Most preferably, it is 0.6-10 mΩcm or less.
The density of the sputtering target is preferably 5.3~7.2g / cm ^3, is preferably further 6.2~7.0g / cm ^3, in particular, 6.4～6.8G it is preferably / cm ^3. By satisfying this value, the discharge during sputtering can be stabilized and the film formation rate can be improved.

  The transparent conductive film of the present invention can be obtained by sputtering the above-described sputtering target of the present invention by a conventional method. Moreover, a transparent electrode can be obtained by etching this transparent conductive film with an etching solution such as a mixed acid containing oxalic acid or phosphoric acid.

Hereinafter, the present invention will be described more specifically with reference to examples. The particle diameter is a value measured by a laser diffraction scattering method.
Example 1
Zinc oxide powder (particle size of 1 μm or less), tin oxide powder (particle size of 0.4 μm or less) and metal zinc powder (particle size of 5 μm or less) are put in a polyethylene pot at the blending ratio shown in Table 1 and dried using a dry ball mill. The mixed powder was manufactured by mixing for 72 hours.
This mixed powder was put into a mold and pressed at a pressure of 300 kg / cm ² to obtain a molded body. This compact was subjected to densification treatment by CIP (cold isostatic pressing) molding at a pressure of 3 ton / cm ² . Next, this compact was placed in a pure oxygen atmosphere sintering furnace and sintered under the following conditions.

(Sintering conditions)
Sintering temperature: 1450 ° C., heating rate: 25 ° C./Hr, sintering time: 6 hours, introduction gas to the sintering furnace: oxygen, introduction gas pressure: 30 mmH ₂ O (gauge pressure), introduction gas linear velocity: 2.6 cm / min, preparation weight / gas flow rate: 0.4 kg · min / L, gas introduction start temperature (at the time of temperature rise): 400 ° C., gas introduction stop temperature (at the time of temperature fall): 400 ° C.

The density of the sintered body was measured by Archimedes method was 5.5 g / cm ^3.
The composition of the sintered body was analyzed using an X-ray microanalyzer (EPMA). As a result, the oxygen atom number ratio (O / (Zn + Sn + In)) to the total number of metal atoms was 1.18. Moreover, the bulk resistance of the target measured by the four probe method was 80 mΩcm.
Furthermore, when the target was analyzed by X-ray diffraction (XRD), a peak derived from Zn metal could be confirmed.
Further, by surface analysis of EPMA, it was confirmed that metal atoms of 5 to 50 μm aggregated in a 5000 μm square region and 100 or more portions having low oxygen were dispersed.

EPMA and XRD were measured under the following conditions.
・ EPMA
Equipment used: Shimadzu Corporation, Electron Beam Microanalyzer EPMA-2300
Acceleration voltage: 15 kV, sample current: 0.05 μm, Beam Size: 1 μm, Area Size: 68.4 × 68.4 μm, Step Size: 0.2 μm × 0.2 μm, measurement elements: Zn, Sn, O, SBSE ( Backscattered electron image)
・ XRD
Equipment used: Rigaku Corporation, Ultimate-III
X-ray: Cu—Kα ray (wavelength 1.5406 mm, monochromatized with graphite monometer), measured by 2θ-θ reflection method, continuous scan (1.0 ° / min), sampling interval: 0.02 °, Slit: DS, SS, 2/3 °, RS: 0.6mm

This sintered body was processed into a sintered body having a thickness of 6 mm by a wet processing method, and bonded to a backing plate made of oxygen-free copper using indium solder to obtain a target.
Using this target, a transparent conductive film was formed by sputtering on a 0.7 mm thick glass substrate (Corning, # 7059). The sputtering conditions were as follows.
(Sputtering conditions)
RF power: 110 W, gas pressure: 0.3 Pa, sputtering gas: Ar, 100%, film thickness: 100 nm, substrate temperature: 200 ° C.

The specific resistance of the obtained conductive film measured by the four-terminal method was 50 mΩ · cm. The light transmittance at a wavelength of 550 nm was 90%. The transmittance was measured as the transmittance including the glass substrate using air as a reference.
Table 1 shows the raw material composition of the sputtering target, composition analysis, sputtering conditions, the composition and properties of the transparent conductive film, and the like.

Examples 2 and 3: Comparative Examples 1 to 3
A target was produced and sputtered in the same manner as in Example 1 except that the composition ratio of the raw materials was changed as shown in Table 1.
The results are shown in Table 1.

Evaluation Example In the raw material composition of the sputtering target, the target was prepared in the same manner as in Example 3 except that the amount of Zn metal powder was changed from 0 to 4 wt%, and the amount of ZnO powder was adjusted accordingly. did.
About the obtained transparent conductive film, the relationship between the amount of Zn metal powder and the bulk resistance value of the target, and the amount of Zn metal powder and the specific resistance value of the transparent conductive film were evaluated. Each result is shown in FIG.1 and FIG.2.

  The transparent conductive film formed using the sputtering target of the present invention can be suitably used as a transparent electrode for various display devices such as liquid crystal display devices and EL display devices.

It is a graph which shows the relationship between the quantity of Zn metal powder, and the bulk resistance of a target. It is a graph which shows the relationship between the quantity of Zn metal powder, and the specific resistance value of a transparent conductive film.

Claims (10)

  A sputtering target containing zinc oxide and tin oxide, or zinc oxide, tin oxide and indium oxide, wherein a metal or an alloy is dispersed throughout the sputtering target. The sputtering target of Claim 1 which satisfy | fills following (1) and (2).
0.65 ≦ M _Zn / (M _Zn + M _Sn ) ≦ 0.9 (1)
0 ≦ M _In / (M _Zn + M _Sn + M _In ) ≦ 0.7 (2)
[ _Wherein , M _Zn , M _Sn and M _In represent the number of atoms of Zn, Sn and In in the sputtering target, respectively. ] Furthermore, the sputtering target of Claim 1 or 2 which satisfy | fills following (3).
M _o / (M _Zn + M _Sn × 2 + M _In × 1.5) ≦ 0.99 (3)
[ _Wherein , M _Zn , M _Sn , _Mo and M _In represent the number of atoms of Zn, Sn, O and In in the sputtering target, respectively. ]   The sputtering target in any one of Claims 1-3 containing 0.1-6 mass% of said metals or alloys. Hexagonal phase layered compound made of indium oxide-zinc oxide _{(In 2 O 3 (ZnO)} m: m is an integer from 3 to 20) The sputtering target according to claim 1 comprising a.   The sputtering target according to claim 1, wherein the bulk resistance is less than 100 mΩcm. The sputtering target according to any one of claims 1 to 6, wherein the density is 5.3 to 7.2 g / cm ³ .   The method for producing a sputtering target according to claim 1, comprising a step of mixing a metal oxide powder and a metal powder.   The transparent conductive film produced using the sputtering target in any one of Claims 1-7. A transparent electrode produced by etching the transparent conductive film according to claim 9.

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