JP2009155177A - Metallic tin-containing indium oxide sintered compact, sputtering target, and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sputtering target suppressing the generation of nodules during sputtering. <P>SOLUTION: The indium oxide sintered compact contains metallic tin, and the metallic tin is dispersed in the sintered compact. It is preferable that the bulk resistance thereof is ≥0.5 mΩcm and the density thereof is ≥6.8 g/cm<SP>3</SP>. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a metal tin-containing indium oxide sintered body (target) used when forming an ITO film (Indium-Tin Oxide film) by sputtering.

ITO film made of indium oxide and tin oxide has conductivity and visible light transmission, so it can be used for various applications such as transparent electrodes, switching elements, and drive circuit elements in display devices such as liquid crystal display devices. Has been.
In an ITO target used for forming an ITO film, tin oxide is considered to generate carriers in the ITO target by being dissolved in indium oxide.

  In the formation of an ITO film using an ITO target, the generation of nodules during film formation is a problem. A nodule is a black protrusion that appears on the surface of a target during sputtering. If this occurs, particles increase or abnormal discharge tends to occur, which causes a defect in the ITO film.

There are the following theories about the cause of nodules.
(1) Theory that lower oxides accumulated in vacancies remain as nuclei (2) Columnar In ₂ O ₃ growth occurs on the target, and the target is excavated using this as a nucleus Theory of remaining (3) Theory that high-resistance particles generated in the sputtering chamber adhere to the target and leave a digging residue as a nucleus. (4) The digging residue occurs due to the incident angle dependence of the sputtering rate. Theory (5) Theory that digging remains with high resistance material generated by abnormal discharge as the core

  In addition, there is an idea that nodules are generated by the presence of tin oxide particles in the ITO target, and a manufacturing method in which tin oxide is completely dissolved in indium oxide has been proposed.

The following measures have been proposed to prevent nodules.
(1) Densification of target (2) Decrease in surface roughness of target surface (3) Integrated molding of target (thing without division)
(4) Preventing adhesion of particles to erosion (5) Preventing arcing at the edge of the target etc. However, it has not yet been achieved to completely suppress the generation of nodules.

There have been several proposals for ITO targets used for sputtering. For example, Patent Document 1 describes an ITO target manufactured by a hot press method.
However, in the target manufactured by this method, the surface part of the target that is in contact with the graphite mold in a vacuum is reduced, and the composition differs between the inside and the surface, and the sputtering conditions are precisely controlled during sputtering. Furthermore, the hot press method has a high manufacturing cost and is not suitable for mass production.

Moreover, what has a metal phase in a target is proposed.
For example, Patent Document 2 discloses a target that is thought to produce metal indium and metal tin by depositing metal by reducing a mixture of indium oxide and tin oxide with hydrogen.
In Patent Document 3, a mixed melt of metal indium and metal tin is sprayed in an oxygen-containing atmosphere, and a target is manufactured by hot compression or isostatic hot compression from a metal powder whose surface is oxidized. A method is described. Also in this document, the metal phase is a mixed phase of metal indium and metal tin.

In the case where ITO is obtained by sintering tin oxide and indium oxide, the tin oxide is dissolved in indium oxide and dispersed uniformly in indium oxide, and does not exist as a single tin oxide. In this case, the crystal of indium oxide may grow abnormally and become a huge crystal. In addition, the enormous crystal particles may be left behind during sputtering and may be a starting point for nodules.
JP-A-56-54702 JP-A-8-41634 JP-A-9-170076

In the target having the metal phase described in Patent Documents 2 and 3 described above, metal indium is included, but since metal indium has a low melting point and is present in the target as it is, it melts and scatters during sputtering. It could cause foreign matter. In addition, when indium oxide and metallic indium are present in the target, lower indium oxide (In ₂ O) or the like is generated, but this lower oxide is an insulator and causes nodule generation. Therefore, nodule generation could not be suppressed when metallic indium was present.

Indium oxide and tin oxide are known to produce In ₄ Sn ₃ O ₁₂ at a temperature of 1200 ° C. or higher. This is thought to be due to the reaction of tin oxide above the solid solubility limit with indium oxide. In general, it is said that the solid solution limit of indium oxide and tin oxide is less than 5% by weight (“Transparent Conductive Film Technology” Japan Society for the Promotion of Science, Transparent Oxide Optical / Electronic Materials 166th Committee, p91. ). The above In ₄ Sn ₃ O ₁₂ can be confirmed by setting the addition amount of tin oxide to 30% by weight or more, but in general ITO, the addition amount of tin oxide is 3 to 20% by weight, Preferably, it is 5 to 15% by weight. In this region, it was considered that tin oxide was dissolved in indium oxide.
In practice, however, In ₄ Sn ₃ O ₁₂ was often generated. In this case, a portion where tin oxide is completely _dissolved, the In ₄ Sn _{3 O 12} becomes crystalline regions have different resistance _values, the resistance value of In ₄ Sn _{3 O 12} is increased more than one order of magnitude. This also causes nodules and abnormal discharge.

  An object of the present invention is to provide a sputtering target capable of suppressing the generation of nodules during sputtering.

As a result of intensive studies, the present inventors have found that generation of nodules can be suppressed in a target made of a sintered body in which metallic tin is dispersed in indium oxide, and the present invention has been completed.
According to the present invention, the following indium oxide sintered body and the like are provided.
1. A sintered body containing metal tin and indium oxide, wherein the metal tin is dispersed in the sintered body.
2. 2. The indium oxide sintered body according to 1, having a bulk resistance of 0.5 mΩcm or more and a density of 6.8 g / cm ³ or more.
3. A sputtering target comprising the indium oxide sintered body according to 1 or 2 above.
4). It has a step of pulverizing and mixing indium oxide and metal tin, a step of molding the powder obtained in the above step, and a step of sintering the molded body, and the sintering temperature in the sintering step is 700 to 1200 ° C. The method for producing an indium oxide sintered body according to 1 or 2, wherein the sintering pressure is 100 MPa to 300 MPa, and the sintering time is 5 hours or more.

  The present invention can provide an indium oxide target that can suppress the generation of nodules during sputtering.

The indium oxide sintered body of the present invention is characterized in that metallic tin is dispersed. As a result, metallic tin can be present between the lattices of indium oxide and at the crystal grain boundaries, and generation of an extra compound represented by In ₄ Sn ₃ O ₁₂ can be reduced.
The content of metal tin in the indium oxide sintered body is 1% by weight to 30% by weight. Preferably they are 3 weight%-20 weight%, Especially preferably, they are 5 weight%-15 weight%.
The structure of the indium oxide sintered body can be identified by analyzing a chart measured by X-ray diffraction. Further, the dispersion means that the metal tin particles themselves are distributed almost uniformly in the sintered body. The state of dispersion can be discriminated by measuring zinc and oxygen with EPMA, and the average particle diameter is obtained from the image data of EPMA. The average particle size of metallic tin is preferably 10 microns or less, more preferably 5 microns or less, and even more preferably 3 microns or less.

  The indium oxide sintered body of the present invention preferably has a bulk resistance of 0.5 mΩcm or more. If the bulk resistance of the sintered body is less than 0.5 mΩcm, the generation of nodules may increase drastically. Preferably, it is 0.8 mΩcm or more, more preferably 1 mΩcm. On the other hand, the upper limit of the bulk resistance is not particularly limited, but is preferably 15 mΩcm or less, preferably 10 mΩcm, more preferably 5 mΩcm or less. When it is larger than 15 mΩcm, nodule generation is small, but abnormal discharge may occur during DC sputtering.

In the case of the present invention, the yellow flakes from which the formed film has been peeled off, or the resistance value of the deposit formed by depositing particles protruding from the target on the target is approximately the same as the resistance value of the formed film. Conceivable. Further, the relationship between the bulk resistance of the sintered body (target) and the formed film is considered as follows.
Bulk resistance of target> Bulk resistance of yellow flake or particle deposit

  In the case of the present invention, since the bulk resistance of the deposit is smaller than the bulk resistance of the target, even if it contacts the plasma during sputtering, it is re-sputtered and formed into a thin film, so that no nodules are formed.

  On the other hand, in the case of a normal ITO target, the bulk resistance is about 0.1 mΩcm or less. In this case, the bulk resistance of the yellow flake or particle deposit is greater than 0.1 mΩcm, and the bulk resistance of the deposit is greater than the bulk resistance of the target. Therefore, the deposit is reduced by the plasma during sputtering, and the bulk resistance of the deposit is further increased. At the same time, it blackens and grows into nodules.

The indium oxide sintered body of the present invention preferably has a density of 6.8 g / cm ³ or more. When the density of the sintered body is less than 6.8 g / cm ³ , the target may be damaged or the deposition rate may be reduced during sputtering. Density, more ^preferably from ^{6.8g / cm 3 ~7.2g / cm 3} , particularly ^preferably from ^{7.0g / cm 3 ~7.2g / cm 3} .

The indium oxide sintered body of the present invention can be obtained, for example, by a production method having the following steps using indium oxide and metal tin as starting materials.
(1) Step of grinding and mixing indium oxide and metal tin (2) Step of molding the mixed powder (3) Step of sintering the molded body

In the step (1), indium oxide and metal tin which are starting materials are pulverized and mixed. The means for pulverization / mixing is not particularly limited, and means known in the art can be employed. For example, a dry pulverizer such as a ball mill can be used.
About indium oxide and metallic tin, there is no restriction | limiting in particular and what can be obtained industrially can be used.

The amount of indium oxide added to the starting material is preferably 70% by weight to 99% by weight, and particularly preferably 80% by weight to 95% by weight.
Moreover, the addition amount of metal tin is preferably 1% by weight to 30% by weight, and particularly preferably 5% by weight to 15% by weight.
The starting material is metal zinc, metal gallium, metal germanium, metal aluminum, metal copper, metal cobalt, metal nickel, metal titanium, metal niobium, metal tantalum, metal tungsten, to the extent that the effects of the present invention are not impaired. Metallic molybdenum and oxides thereof, and lanthanoid oxides (cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, diprosium, holonium, erbium, thulium, ytterbium, lutetium) and the like may be added.

  In the step (2), the mixed raw material is formed. The means for molding is not particularly limited, and means known in this technical field can be adopted. For example, a hydrostatic press can be used.

In the step (3), the molded product obtained in the step (2) is sintered.
In the present invention, metallic tin is used as a raw material. However, since the melting point of metallic tin is as low as 230 ° C., high-density crystals cannot be obtained by methods such as atmospheric pressure sintering and atmospheric sintering. Therefore, in the present invention, the molding is sintered in a state where pressure is applied.
Specifically, in the present invention, the sintering pressure is set to 100 MPa to 300 MPa. Preferably, it is set to 120 MPa to 200 MPa. Thereby, a high-density sintered body can be obtained. If the sintering pressure is less than 100 MP, the sintering time may be too long. On the other hand, if it exceeds 300 MPa, the apparatus may be expensive.

  The temperature at the time of sintering shall be 700-1200 degreeC. Preferably it is 800 to 1100 degreeC. If the sintering temperature is less than 700 ° C., the sintering may not proceed. On the other hand, if it exceeds 1200 ° C., the metal tin may ooze out.

  The sintering time is preferably 5 hours or more and less than 100 hours. If it is less than 5 hours, the sintered density may not be improved, and if it is 100 hours or more, it is not economical. The sintering time is preferably 8 to 40 hours, more preferably 10 to 25 hours.

In order to disperse the metal tin particles in the sintered body and improve the sintering rate, the particle size of the indium oxide powder and metal tin to be used may be adjusted. Specifically, the average particle size of the indium oxide powder is preferably 0.5 μm to 1 μm, and the average particle size of metal tin is preferably 0.5 μm to 1 μm.
The average particle diameter is a value calculated from the following formula by measuring the specific surface area by the BET specific surface area measurement method by nitrogen adsorption.
Average particle diameter (μm) = 6 / (density × specific surface area)
The particle size can be controlled in the above step (1).

It is important that metal tin is dispersed in the sintered body so as to exist in the lattice of indium oxide and in the crystal grains. In particular, it is preferable to disperse at crystal grain boundaries (triple points). Dispersing them at the triple point results in suppressing the abnormal grain growth of indium oxide and further suppressing the generation of nodules.
Whether metal tin is present in the lattice of indium oxide, in crystal grains, or at triple points can be determined by EPMA analysis of indium, tin, and oxygen.
In the sintered body obtained by the production method of the present invention, metallic tin is present at the above position.

The sputtering target of the present invention can be produced by polishing the sintered body of the present invention. By bonding the obtained sputtering target to a backing plate, the sputtering target can be mounted and used.
The film formed by sputtering the target of the present invention is basically an ITO film, and a low resistance film similar to a normal ITO film can be obtained.

Example 1
Raw material is 255 g of indium oxide powder having an average particle size of 1 μm or less and a BET surface area of 5 to 12 m ² / g and metal tin 23 g (metal tin content: 9 wt%) having an average particle size of 0.5 to 3 μm. It was. These mixtures were mixed and pulverized by a dry pulverizer.
The obtained powder was molded by a uniaxial press and then molded by a hydrostatic press at 50 MPa to 400 MPa.
The molded product was vacuum-sealed in a tantalum capsule, the pressure was 250 MPa, the sintering temperature was 800 ° C., and the sintered body was obtained by sintering for 20 hours.

This sintered body was subjected to X-ray diffraction. An X-ray chart of the sintered body is shown in FIG.
In this chart, an indium oxide peak and a metal tin peak were observed, but a tin oxide peak and a peak attributed to In ₄ Sn ₃ O ₁₂ were not observed.
The peak pattern shown at the bottom of the chart is quoted from the JCPDS database.
When the microstructure of the sintered body was examined by EPMA analysis within a 30 micron square field of view, it was confirmed that metal tin was uniformly dispersed, and the average particle diameter was 1 μm.

The sintered body was ground to 4 mm in diameter and 5 mm thick, and bonded to a copper plate with metallic indium to obtain a target.
The density of the obtained target was 6.85 g / cm ³ , and the bulk resistance was 5.3 mΩcm.
The density of the target was calculated from the weight of the target cut out to a certain size and the external dimensions. The bulk resistance was measured by a four-probe method using a resistivity meter Loresta (manufactured by Mitsubishi Chemical Corporation).

A nodule generation test was performed on this target. Specifically, using a sputtering apparatus (HSM-552) manufactured by Shimadzu Corporation, sputtering was continued for 25 hours (10 kWhr), and then the target surface was observed to confirm the occurrence of nodules. In the test, the sputtering pressure was 0.3 Pa (under 100% argon atmosphere), the output was 400 W, and DC sputtering was used.
As a result, no nodules could be confirmed. FIG. 2 shows a photograph of the sputtering target after the test.

Subsequently, deposits deposited around the target and yellow flakes deposited in the apparatus were adhered onto the target, and sputtering was continued for 4 hours in this state to observe the state of the deposit.
FIG. 3A is a photograph in a state where yellow flakes and the like are attached to the target. FIG. 3B is a photograph of the target after sputtering.
Sputtering was performed by DC sputtering with a sputtering pressure of 0.3 Pa (under 100% argon atmosphere) and an output of 200 W.
As a result, arcing was observed at the beginning of the test, but after a while arcing was not observed. When the target surface was confirmed after completion, the deposited deposits and yellow flakes were both resputtered and disappeared, and no nodules were observed.

  Next, a film was formed using the target of Example 1. The sputtering conditions were a sputtering pressure of 0.3 Pa (under an atmosphere of 98% argon and 2% oxygen), DC sputtering with an output of 400 W, and film formation on a glass substrate heated to 250 ° C. As a result, a thin film having a thickness of 150 nm was formed. The obtained substrate with a thin film had a light transmittance (wavelength of 550 nm) of 90%, and the specific resistance of the thin film was 167 μΩcm.

Example 2
A sputtering target was prepared and evaluated in the same manner as in Example 1 except that the content of metal tin was 5 wt%.
The density of the obtained target was 6.82 g / cm ³ . The bulk resistance was 4.2 mΩcm. The specific resistance of the transparent conductive film was 190 μΩcm.
As in Example 1, the microstructure of the sintered body was examined by EPMA analysis within a 30 micron square field of view. As a result, it was confirmed that the tin metal was uniformly dispersed, and the average particle size was 0.9 μm. It was.

Example 3
A sputtering target was prepared and evaluated in the same manner as in Example 1 except that the content of metal tin was 15 wt%.
The density of the obtained target was 6.86 g / cm ³ . The bulk resistance was 2.5 mΩcm. The specific resistance of the transparent conductive film was 183 μΩcm.
As in Example 1, the microstructure of the sintered body was examined by EPMA analysis within a 30 micron square field of view. As a result, it was confirmed that the metal tin was uniformly dispersed, and the average particle size was 1.2 μm. It was.

  The target produced in Examples 2 and 3 was subjected to a nodule generation test in the same manner as in Example 1. As a result, generation of nodules could not be confirmed for both targets.

Comparative Example 1
A commercially available ITO target (relative density 99.8%, density 7.12 g / cm ³ , bulk resistance 0.1 mΩcm) was mounted on the same apparatus as in Example 1, and generation of nodules was confirmed under the same conditions.
As a result, a large amount of nodules was confirmed. FIG. 4 shows a photograph of the sputtering target after the test.
Further, after removing and cleaning nodules on the target surface, deposits and yellow flakes around the target were adhered to the target surface in the same manner as in Example 1, and sputtering was performed again to confirm the target surface. As a result, a large amount of nodules was generated.
FIG. 5A is a photograph of a state in which yellow flakes and the like are attached to the target. FIG. 5B is a photograph of the target after sputtering.

Evaluation Example The cross section of the ITO target used in Comparative Example 1 was mirror-polished and the composition was analyzed by an electron beam microanalyzer (EPMA). FIG. 6 shows the results of EPMA analysis. As a result, a portion where Sn was segregated was observed.
Further, X-ray diffraction was performed on this target. An X-ray chart of the sintered body is shown in FIG. As a result, it was confirmed that In ₄ Sn ₃ O ₁₂ was present in the target. The segregated Sn was In ₄ Sn ₃ O ₁₂ but had an average particle size of 1.8 μm.
In addition, the same mirror surface portion was observed with a scanning spread resistance microscope (SSRM), and the conductivity of the target structure (crystal particles) was measured. FIG. 8 shows the result of the SSRM analysis. As a result, a portion (island region) having a resistance higher by one digit or more than that of the surrounding region (sea region) was observed. From the results of EPMA analysis and XRD observation, the portion with high resistance can be identified as In ₄ Sn ₃ O ₁₂ .

  The indium oxide sintered body of the present invention is suitable as a sputtering target used when forming a conductive film used in transparent electrodes and semiconductor elements of various display devices.

2 is an X-ray diffraction chart of a sintered body produced in Example 1. FIG. 2 is a photograph of a target after a nodule generation test of Example 1. FIG. FIG. 3A is a photograph observing the state of deposits on the target of Example 1, FIG. 3A is a photograph of a state in which yellow flakes and the like are adhered to the target, and FIG. 3B is a photograph of the target after sputtering. It is a photograph. 6 is a photograph of a target after a nodule generation test of Comparative Example 1. FIG. 5A is a photograph observing the appearance of the target deposit in Comparative Example 1, FIG. 5A is a photograph of a state in which yellow flakes and the like are adhered to the target, and FIG. 5B is a photograph of the target after sputtering. It is a photograph. It is the result of the EPMA analysis of the target used in Comparative Example 1. 3 is an X-ray diffraction chart of a target used in Comparative Example 1. It is a result of the SSRM analysis of the target used in comparative example 1.

Claims (4)

  A sintered body containing metal tin and indium oxide, wherein the metal tin is dispersed in the sintered body. The indium oxide sintered body according to claim 1, wherein the bulk resistance is 0.5 mΩcm or more and the density is 6.8 g / cm ³ or more.   A sputtering target comprising the indium oxide sintered body according to claim 1. Crushing and mixing indium oxide and metallic tin;
A step of molding the powder obtained in the above step;
Having a step of sintering the molded body,
The method for producing an indium oxide sintered body according to claim 1 or 2, wherein a sintering temperature in the sintering step is 700 to 1200 ° C, a sintering pressure is 100 MPa to 300 MPa, and a sintering time is 5 hours or more.