JP6166207B2 - Oxide sintered body and sputtering target - Google Patents

Description

  The present invention relates to an oxide sintered body and a sputtering target comprising the same.

An oxide film formed using a sputtering target is used for a transparent electrode such as a liquid crystal display device or an organic electroluminescence display device, a semiconductor layer of a thin film transistor (TFT), or the like (for example, see Patent Documents 1 to 5). .)
For example, a thin film transistor using an In—Ga—Zn oxide semiconductor has favorable switching characteristics.

In order to increase the mobility of the TFT to 20 cm ² / Vs or more, it is necessary to increase the In content of the semiconductor layer. In this case, the target crystal phase is a homologous phase (InGaZn _m O _{3 + m} ; m is 0.5 or an integer of 1 or more), a spinel phase such as ZnGa ₂ O ₄ , and an In ₂ O ₃ phase.

JP-A-8-245220 Japanese Patent Laid-Open No. 11-213763 JP-A-8-295514 JP 2012-144410 A JP 2013-1592 A

  In forming an oxide film by a sputtering method, it is important to perform sputtering in a stable state in which abnormal discharge or the like does not occur in order to stabilize the quality of the obtained oxide film. For example, when there is a small hole (pore) in the oxide sintered body constituting the sputtering target, the sputtering becomes unstable. Therefore, in an In-Sn oxide (ITO) sintered body or the like, the pores in the sintered body are made as small as possible by increasing the firing temperature or lengthening the firing time to complete grain growth. The number is decreasing.

On the other hand, some In—Ga—Zn oxide sputtering targets contain a crystal structure of a homologous phase (InGaZn _m O _{3 + m} ; m is an integer of 0.5 or 1 or more). InGaZn _m O _{3 + m} shows a crystal structure and does not show the composition itself. The homologous phase forms twins, but cracks easily occur at the grain boundaries. When the particle size of the homologous phase is increased, the grain boundary is also increased, so that there is a possibility that a large crack is generated during sputtering. When cracking occurs, the debris particles adhere to the target surface and cause arcing. As a result, there is a possibility that semiconductor films having locally different characteristics may be produced.
Therefore, an oxide sintered body capable of stable sputtering could not be obtained simply by setting the sintering conditions to promote grain growth like ITO.
In addition, there is a method of accelerating firing by ordinary atmospheric pressure firing such as hot pressing, but in that case, there is a problem that the manufacturing cost increases.

  An object of the present invention is to provide an In—Ga—Zn oxide sintered body capable of stable sputtering.

In the In—Ga—Zn oxide sintered body having a homologous phase and an In ₂ O ₃ phase, and the In ₂ O ₃ phase containing a predetermined metal element, the present inventors It has been found that even if the firing temperature is lowered and the firing time is shortened, cracks in the pores and twin grain boundaries can be suppressed, and the present invention has been completed.
According to the present invention, the following oxide sintered bodies and the like are provided.
1. Containing a homologous phase represented by In ₂ O ₃ phase and InGaZn _m O _{3 + m} (m is an integer of 0.5 or 1 or more), and the In ₂ O ₃ phase is Hf, Zr, Ti, Y, Containing one or more elements X selected from the group consisting of Ge, Ta, Nb and lanthanoid elements, the number of twin cracks having a length of 10 μm or more is 1 or less in a field of view of 40 × 25 μm square, An oxide sintered body having a density of 95% or more and an average particle diameter of the In ₂ O ₃ phase and the homologous phase of 10 μm or less.
2. 2. The oxide sintered body according to 1, wherein the element X is one or more elements selected from Hf, Zr, Ti, Y, Ta, and Sm.
3. The oxide sintered body according to 1 or 2, wherein m is 1 or 2.
4). The oxide sintered body according to 1 or 2, wherein m is 2.
5. 5. The oxide sintered body according to any one of 1 to 4, wherein X is dissolved in the In ₂ O ₃ phase.
6). The oxide sintered body according to any one of 1 to 5, wherein the In ₂ O ₃ phase is a bixbite phase.
7). 7. The oxide sintered body according to any one of 1 to 6, wherein the resistance value is 50 mΩcm or less.
8). 8. The oxide sintered body according to any one of 1 to 7, wherein the number of pores having a diameter of 1 μm or more is 9 or less in a field of view of 40 × 25 μm square.
9. 9. The oxide sintered body according to any one of 1 to 8, wherein the number of twin cracks having a length of 10 μm or more is 0 in a 40 × 25 μm square field of view.
10. The oxide sintered body according to any one of 1 to 9, wherein the atomic ratio [X / (In + Ga + Zn + X)] of the element X is 0.001 to 0.2.
11. A sputtering target obtained by processing the oxide sintered body according to any one of 1 to 10 above.
12 12. An oxide thin film formed using the sputtering target according to 11 above.
13. 13. The oxide thin film according to 12, which is an amorphous film.
14 14. A thin film transistor comprising the oxide thin film according to 12 or 13 as a channel layer.

  According to the present invention, an In—Ga—Zn oxide sintered body capable of stable sputtering can be provided.

2 is a SEM photograph of a cross section of an oxide sintered body produced in Example 1. It is the figure which showed the distribution state of In atom in the visual field of the SEM photograph of FIG. 1 by SEM-EDS. It is the figure which showed the distribution state of Sm atom in the visual field of the SEM photograph of FIG. 1 by SEM-EDS. It is the photograph which showed the EDS spectrum measurement location in the SEM photograph of FIG. It is an EDS spectrum of the phase of point A shown in FIG. It is an EDS spectrum of the phase of the point B shown in FIG. 4 is a SEM photograph of a cross section of an oxide sintered body produced in Example 4. 4 is a SEM photograph of a cross section of an oxide sintered body produced in Example 21. FIG. 4 is a SEM photograph of a cross section of an oxide sintered body produced in Comparative Example 1. 4 is a SEM photograph of a cross section of an oxide sintered body produced in Comparative Example 2. 5 is a SEM photograph of an oxide sintered body produced in Comparative Example 3. 3 is an X-ray diffraction pattern of an oxide sintered body produced in Example 3. FIG. 4 is an X-ray diffraction pattern of an oxide sintered body produced in Example 4. 3 is an X-ray diffraction pattern of an oxide sintered body produced in Example 12. FIG. 4 is an X-ray diffraction pattern of an oxide sintered body produced in Example 23. FIG.

The oxide sintered body of the present invention contains an In ₂ O ₃ phase and a homologous phase represented by InGaZn _m O _{3 + m} (m is an integer of 0.5 or 1 or more), and the In ₂ O ₃ phase Contains one or more elements X selected from the group consisting of Hf, Zr, Ti, Y, Ge, Ta, Nb and a lanthanoid element (Ln). The average particle size of _In 2 _{O 3} phase and homologous phase, characterized in that at 10μm or less.
By adding the compound of element X to the raw material of the oxide sintered body, the temperature during firing can be lowered, and the firing time can be shortened. As a result, an oxide sintered body having a homologous phase with few pores and a small twin grain boundary can be produced. The sputtering target made of this oxide sintered body is capable of stable discharge with little arcing such as micro arc besides stable arc such as so-called fireball discharge. Can be made.

It can be confirmed by an X-ray diffraction method that the sintered body of the present invention contains a homologous phase represented by InGaZn _m O _{3 + m} (m is an integer of 0.5 or 1 or more). Specifically, it can be confirmed by comparing the X-ray diffraction result with an ICDD (International Center for Diffraction Data) card. For example, a homologous phase in which m is 1 is an ICDD card No. The pattern of 20-1439 is shown. The homologous phase where m is 2 is the ICDD card no. The pattern of 40-252 is shown.
Similarly, it can be confirmed by the X-ray diffraction method that the oxide sintered body has an In ₂ O ₃ phase. The oxide sintered body of the present invention may contain a phase other than the In ₂ O ₃ phase and the homologous phase described above.
In addition, confirmation of the particles of In ₂ O ₃ phase and homologous phase can also be performed by SEM-EDS. Elemental distribution is measured by mapping using each characteristic X-ray by EDS, and particles comprising 70% or more of In and O are defined as In ₂ O ₃ particles, and contain In, Ga and Zn. The particles are defined as particles of an In—Ga—Zn oxide homologous phase. Furthermore, simple quantification is performed on each particle by EDS point element quantitative analysis to confirm the phase.

The elements contained in the phase (particles) present in the oxide sintered body are specified by a scanning electron microscope and an energy dispersive X-ray spectrometer (SEM-EDS). Specifically, the position and shape of the particles are confirmed by observing a mirror-polished sintered body with an SEM, and the elements contained in the particles are identified by EDS for each particle.
Part of the element X may be dissolved in the homologous phase particles. Other compound phases may be formed.

In the oxide sintered body of the present invention, the average particle diameter of the In ₂ O ₃ phase and the homologous phase is 10 μm or less. By suppressing the grain growth so that the average particle diameter is 10 μm or less, abnormal discharge due to twin cracks can be suppressed. The average particle size of the homologous phase is preferably 8 μm or less, and particularly preferably 6 μm or less.
The average particle size is measured by observing a mirror-polished sintered body with a scanning electron microscope (SEM). When the shape of the surface of the sintered body is circular, the square inscribed in the circle is divided into 16 equal areas, and when the surface shape of the sintered body is square, the surface is divided into 16 equal areas. Each of 16 samples is prepared and measured. Details of the measurement are given in the examples.

The element X is one or more elements selected from Hf, Zr, Ti, Y, Ge, Ta, Nb, and Ln. Lanthanoid (Ln) is a general term for La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. These elements are dissolved in the In ₂ O ₃ phase. As a result, calcination can be improved by promoting intragranular diffusion of oxygen in the In ₂ O ₃ phase.
The element X is preferably one or more elements selected from Hf, Zr, Ti, Y and Sm.
In the present invention, the element X is preferably dissolved in the In ₂ O ₃ phase. The fact that the element X is dissolved in the In ₂ O ₃ phase can be confirmed by a change in the lattice constant of X-ray diffraction and composition analysis of SEM-EDS particles, or a broad X-ray absorption fine structure (EXAFS) measurement.

In addition, although the method of adding an additive to In-Ga-Zn oxide sintered compact is known, in order to suppress the pore in a sintered compact and to reduce twin crack like the present invention, it is the above-mentioned. There is no example of adding the element X. For example, when Mg or Al is added in place of the element X, they are not dissolved in the In ₂ O ₃ phase, and thus there is no effect of improving the sinterability and there are many pores.

In the present invention, _m in the homologous phase [InGaZn _m O _{3 + m} ] is preferably 1 (IGZO 111 phase) or 2 (IGZO 112 phase), and m is particularly preferably 2. Since the IGZO 112 phase has a larger amount of Zn than the IGZO 111 phase, Zn is likely to evaporate when the firing temperature is raised, and the structure control effect due to the addition of the element X is more remarkable.

The In ₂ O ₃ phase is preferably a bixbite phase. In this case, since the resistance value becomes low, sputtering becomes more stable.
The fact that the In ₂ O ₃ phase shows a bixbite phase (rare earth oxide C-type crystal structure) indicates that the ICDD card no. This can be confirmed by showing a pattern of 6-0416.

In the oxide sintered body of the present invention, the number of twin cracks having a length of 10 μm or more is 1 or less in a visual field of 40 × 25 μm square. Preferably 0. If the number of twin cracks of 10 μm or more is one or less, the occurrence of arcing can be suppressed, and the destruction of the target due to twin cracks can be prevented. Thereby, abnormal discharge during sputtering can be significantly suppressed.
Note that a twin crystal is a state in which grains having a homologous structure are joined to each other, and crystal grains having different crystal orientations are in contact with each other at a grain boundary (GB). It means that two crystals are combined so as to be symmetrical.
The twin crystal crack means a crack generated at a crystal grain boundary between the two crystals. The length and number of twin cracks are measured by preparing a sample in the same manner as the average particle diameter from a sintered body mirror-polished with abrasive grains such as colloidal silica, and observing it with an SEM. Details of the measurement are given in the examples.
In addition, there is a method to make it easy to observe the grain boundary by heat-treating the polished sample or chemically etching with nitric acid or the like. In these cases, however, twinning cracks and small pores may not be observed by the treatment. is there. Therefore, it is necessary to observe a sample which has been surface-finished by mirror polishing without performing the above treatment.

The relative density of the oxide sintered body is 95% or more. 97% or more is preferable, and 98% or more is particularly preferable. If it is 95% or more, the target is difficult to break and abnormal discharge can be further suppressed.
The relative density is a percentage obtained by dividing the actual density measured by the Archimedes method by the theoretical density calculated from the arithmetic average of the true density of the raw material.

The resistance value of the oxide sintered body is preferably 50 mΩcm or less, more preferably 30 mΩcm or less, and particularly preferably 20 mΩcm or less. If it is 50 mΩcm or less, an arcing abnormal discharge is less likely to occur, which is preferable. When it is 30 mΩcm or less, normal DC sputtering is possible. When it is 20 mΩcm or less, weak magnetic field magnetron sputtering is possible.
The resistance value can be measured by a low resistivity meter “Lorestar EP” (based on JIS K 7194) manufactured by Mitsubishi Chemical Corporation. Details of the measurement are given in the examples.

The number of pores having a diameter of 0.5 μm or more and less than 1 μm in the oxide sintered body is preferably 20 or less in a 40 × 25 μm square field of view.
Thereby, the abnormal discharge resulting from a pore can be suppressed significantly. The number of pores is preferably 15 or less, and particularly preferably 10 or less.
The pore is a hole formed between particles observed on the surface of the sintered body by SEM observation. A pore having a diameter of less than 1 μm is a pore that is likely to be formed in a triple point of the grain or grain boundary.

In the oxide sintered body of the present invention, the number of pores having a diameter of 1 μm or more is preferably 9 or less in a field of view of 40 × 25 μm square. Thereby, the abnormal discharge resulting from a pore can be suppressed significantly. The number of pores is preferably 5 or less, and particularly preferably 2 or less. A pore having a diameter of 1 μm or more is a remaining pore due to insufficient firing.
The number of pores is measured by SEM observation by preparing a sample in the same manner as the average particle size of the homologous phase described above. Details of the measurement are given in the examples.

  Regarding the composition of the oxide sintered body of the present invention, the atomic ratio of element X [X / (In + Ga + Zn + X)] is preferably 0.001 to 0.2. If it is this range, the improvement effect of the calcination property by adding element X will be acquired, and the characteristic of the oxide film obtained will be hard to change. The atomic ratio of the element X is preferably 0.005 to 0.15, and particularly preferably 0.01 to 0.1.

The In atomic ratio [In / (In + Ga + Zn)] is preferably 0.4 to 0.8. Most preferably, it is 0.5-0.7.
The atomic ratio [Ga / (In + Ga + Zn)] of Ga is preferably 0.1 to 0.4. Most preferably, it is 0.1-0.3.
The atomic ratio [Zn / (In + Ga + Zn)] of Zn is preferably 0.1 to 0.5. Especially preferably, it is 0.15-0.4.

The atomic ratio of each metal element in the oxide sintered body can be controlled by the blending amount of the raw materials. Further, the atomic ratio of each element can be obtained by quantitative analysis of the contained elements using an inductively coupled plasma emission spectrometer (ICP-AES).
Specifically, in the analysis using ICP-AES, a solution sample obtained by dissolving a powder obtained by pulverizing an oxide sintered body to 10 μm or less in an acid or the like is atomized with a nebulizer, and argon plasma (about 6000 to 8000 ° C.) is obtained. ), The element in the sample absorbs thermal energy and is excited, and the orbital electrons move from the ground state to a higher energy level orbit. These orbital electrons move to a lower energy level orbit in about 10 ⁻⁷ to 10 ⁻⁸ seconds. At this time, the energy difference is emitted as light to emit light. Since this light shows a wavelength (spectral line) unique to the element, the presence of the element can be confirmed by the presence or absence of the spectral line (qualitative analysis).

In addition, since the magnitude (luminescence intensity) of each spectral line is proportional to the number of elements in the sample, the sample concentration can be obtained by comparing with a standard solution having a known concentration (quantitative analysis).
After identifying the elements contained in the qualitative analysis, the content is obtained by quantitative analysis, and the atomic ratio of each element is obtained from the result.

  In addition, in this invention, in the range which does not impair the effect of this invention, you may contain other metal elements other than In, Ga, Zn, and X mentioned above. In the present invention, the metal element contained in the target may be substantially only In, Ga, Zn, and X. Note that “substantially” means that no elements other than impurities, which are inevitably included due to raw materials, manufacturing processes, and the like are not included.

The oxide sintered body of the present invention can be produced, for example, by firing a raw material powder containing each metal element. Hereinafter, the manufacturing process will be described.
(1) Compounding Process The compounding process of raw materials is an essential process for mixing the metal element compound contained in the oxide of the present invention.
As the raw material, powders such as indium compound powder, gallium compound powder, zinc compound powder, and element X compound powder are used. Examples of the indium compound include indium oxide and indium hydroxide. Examples of the zinc compound include zinc oxide and zinc hydroxide. As each compound, an oxide is preferable from the viewpoint of easiness of firing and the difficulty of leaving a by-product.

As the compound of the element X, in particular, Y ₂ O ₃ , TiO ₂ , Sm ₂ O ₃ , ZrO ₂ , HfO ₂ , GeO ₂ , Ta ₂ O ₅ or Nb ₂ O ₅ are In ₂ O ₃ in the slurry dispersion, Aggregation of Ga ₂ O ₃ and ZnO can be suppressed, and the uniformity of the composition in the powder after granulation is improved, which is preferable.
The particle diameter of the primary particles of the raw material is preferably 3 μm or less, more preferably 1 μm or less, and more preferably 0.5 μm or less. In particular, when the particle size of the element X compound is large, segregation may occur, so that it is preferably 0.3 μm or less.

The purity of the raw material is usually 2N (99% by mass) or more, preferably 3N (99.9% by mass) or more, particularly preferably 4N (99.99% by mass) or more. If the purity is lower than 2N, the durability may be lowered, or impurities may enter the liquid crystal side and baking may occur.
It is preferable to mix the raw materials used for the production of the target such as metal oxide and uniformly mix and pulverize them using an ordinary mixing and pulverizing machine such as a wet ball mill, a bead mill or an ultrasonic device.
In order to improve the density of the molded body in the molding process described below or to suppress cracking of the molded body, molding aids such as polyvinyl alcohol (PVA), methylcellulose, polywax, oleic acid, etc. may be mixed. Furthermore, you may mix the mold release agent from a metal mold | die at the time of shaping | molding.
For example, when PVA is used as the dispersant, the amount of PVA used is preferably 5% by weight or less, more preferably 3% by weight or less and 2% by weight or less of the total amount of raw materials. If the amount of the dispersant is large, the zinc compound or the gallium compound is segregated, and there is a possibility that a highly resistant ZnGa ₂ O ₄ phase precipitates or coarse particles of a homologous phase are generated.
For example, stearic acid may be used as the mold release agent.

(2) Calcining step In the calcining step, the mixture obtained in the above step is calcined. In addition, this process is a process provided as needed. The calcining step makes it easy to increase the oxide density, but the production cost may increase. Therefore, it is more preferable that the density can be increased without performing calcination.
In the calcination step, it is preferable to heat-treat the above mixture at 500 to 1500 ° C. for 1 to 100 hours.

(3) Molding process The molding process is an indispensable process for pressure-molding the mixture obtained in the above-described blending process (or calcined product when the calcining process is provided) to form a compact. By this process, it is formed into a shape suitable as a target. When the calcination step is provided, the obtained calcined fine powder can be granulated and then molded into a desired shape by a molding process.
Examples of the molding process include press molding (uniaxial molding), mold molding, cast molding, injection molding, and the like. In order to obtain a target having a high firing density, molding is performed by cold isostatic pressure (CIP) or the like. It is preferable to do this.
In the case of simple press molding (uniaxial press), uneven pressure is generated, and an unexpected crystal form may be generated.
Moreover, after press molding (uniaxial pressing), cold isostatic pressure (CIP), hot isostatic pressure (HIP), etc. may be performed to provide two or more molding processes.

(4) Firing step The firing step is an essential step of firing the molded body obtained in the molding step.
Firing can be performed by atmospheric pressure firing or hot isostatic pressure (HIP) firing.
As firing conditions, it is preferable to obtain a step of degreasing moisture and molding aid in the molded body at 120 to 400 ° C. for 0.5 to 6 hours after the molded body is placed in the sintering furnace.
Thereafter, the temperature was raised to 800 to 1200 ° C. at a temperature raising rate of 0.5 to 5 ° C./min, and then reached a firing temperature of 1300 to 1500 ° C. at a rate of 0.1 to 3 ° C./min slower than the temperature rising rate of the previous period. To do. The firing holding time is 5 to 72 hours, preferably 8 to 48 hours, and more preferably 10 to 36 hours.
In the temperature lowering process after firing, the temperature is decreased from 0.1 to 5 ° C./min up to 1000 to 1200 ° C. The temperature is preferably lowered at 0.2 to 3 ° C, more preferably 0.2 to 1 ° C / min. Further, the temperature is lowered at 1 to 5 ° C./min up to 300 to 500 ° C., and further cooled to the room temperature at a temperature lowering rate of 3 ° C./min or less.
The atmosphere to be baked may be air under atmospheric pressure, air circulation, oxygen circulation system, or oxygen pressurization. An atmosphere in an oxygen flow system is preferable because pores in the sintered body are reduced. The oxygen flow rate is preferably 0.1 to 100 L / min per 1 m ^{3 of} the furnace volume, although it depends on the furnace volume and the method of installing the molded body. In particular, when oxygen flows in a baking process at 1000 ° C. or higher, pores are reduced, which is effective.

(5) Reduction process The reduction process is for uniformizing the bulk resistance of the sintered body obtained in the above firing process over the entire target, and is a process provided as necessary. Examples of the reduction method that can be used include a method using a reducing gas, vacuum baking, or reduction using an inert gas.
In the case of reduction treatment with a reducing gas, hydrogen, methane, carbon monoxide, a mixed gas of these gases and oxygen, or the like can be used.
In the case of reduction treatment by firing in an inert gas, nitrogen, argon, a mixed gas of these gases and oxygen, or the like can be used.
The temperature at the time of a reduction process is 100-800 degreeC normally, Preferably it is 200-800 degreeC. The reduction treatment time is usually 0.01 to 10 hours, preferably 0.05 to 5 hours.

The sputtering target of the present invention is obtained by processing the oxide sintered body into a desired shape as necessary.
The processing is performed to cut the oxide sintered body into a shape suitable for mounting on a sputtering apparatus and to attach a mounting jig such as a backing plate. In order to use the oxide sintered body as a sputtering target, the sintered body is ground with a surface grinder, for example, to have a surface roughness Ra of 5 μm or less. Further, the sputter surface of the sputtering target may be mirror-finished so that the average surface roughness Ra is 1000 angstroms or less. For this mirror finishing (polishing), a known polishing technique such as mechanical polishing, chemical polishing, mechanochemical polishing (a combination of mechanical polishing and chemical polishing) can be used. For example, polishing to # 2000 or more with a fixed abrasive polisher (polishing liquid: water) or lapping with loose abrasive lapping (abrasive: SiC paste, etc.), and then lapping by changing the abrasive to diamond paste Can be obtained by: Such a polishing method is not particularly limited.

  The obtained sputtering target is bonded to a backing plate. Further, a plurality of targets may be attached to one backing plate to make a substantially single target.

After polishing, the target is washed. For the cleaning treatment, air blow or running water cleaning can be used. When removing foreign matter by air blow, it is possible to remove the foreign matter more effectively by suctioning with a dust collector from the opposite side of the nozzle. In addition, since the above air blow and running water cleaning have a limit, ultrasonic cleaning etc. can also be performed. This ultrasonic cleaning is effective by performing multiple oscillations at a frequency of 25 to 300 KHz. For example, it is preferable to perform ultrasonic cleaning by causing multiple oscillations of 12 types of frequencies at intervals of 25 KHz between frequencies of 25 to 300 KHz.
After washing, it is preferable to dry sufficiently at a temperature of 110 ° C. or less for 0.5 to 48 hours.

  The oxide thin film of the present invention is obtained by forming a film by a sputtering method using the above-described sputtering target of the present invention. The oxide thin film can also be manufactured by a vapor deposition method, an ion plating method, a pulse laser vapor deposition method, or the like using a sputtering target.

The oxide thin film of the present invention is preferably an amorphous film because electric characteristics, optical characteristics, and etching characteristics are uniform over a large area.
The fact that the oxide thin film is an amorphous film can be confirmed by the fact that the measurement result by X-ray diffraction does not show a specific crystal peak.
In addition, by adding any element selected from Zr, Hf, Ti, Y, Ta, and Nb, chemical resistance is improved, and back channel etching utilizing a difference in etching rate with the electrode is possible. Become. In particular, Ta or Nb has a remarkable improvement in acid resistance. For example, etching resistance to PAN (mixed acid of phosphoric acid, acetic acid, and nitric acid) used in an etchant for Al wiring is improved.

  The oxide thin film of the present invention can be used for a thin film transistor (TFT). In particular, it can be used as a channel layer. The TFT of the present invention only needs to have the oxide thin film of the present invention as a channel layer, and known components can be appropriately employed as the TFT structure and electrodes.

Example 1
Weigh 99.99% pure indium oxide powder, 99.99% pure gallium oxide powder, 99.99% pure zinc oxide powder, and samarium oxide powder so that the atomic ratio of each metal element satisfies the following. Wet mixed and pulverized using a planetary ball mill.
[In / (In + Ga + Zn + Sm)] = 0.5
[Ga / (In + Ga + Zn + Sm)] = 0.1
[Zn / (In + Ga + Zn + Sm)] = 0.3
[Sm / (In + Ga + Zn + Sm)] = 0.1
In addition, several kinds of zirconia beads having different particle diameters of 0.2 to 1 mmφ were used as the medium of the wet medium stirring mill. Moreover, 1 mass% of polyvinyl alcohol (PVA) was used as a shaping | molding adjuvant.
After mixing and grinding, it was dried with a spray dryer. A mixed powder obtained by classifying coarse particles of 0.5 μm or more was filled in a mold, and uniaxial pressing and CIP molding were performed to produce a molded body (diameter 101.6 mm, thickness 8 mm).
The obtained molded body was dried and degreased at 300 ° C. for 2 hours in an oxygen stream of 1 L / min, and fired at 1430 ° C. for 20 hours to produce an oxide sintered body. The heating rate was 1 ° C./min up to 1000 ° C., and then the temperature was raised at 0.5 ° C./min to reach the firing temperature. The temperature was lowered to 1000 ° C. at 0.5 ° C./min, 1 ° C./min to 500 ° C., and then cooled to room temperature at 0.6 ° C./min in an air atmosphere in the furnace.

As a result of evaluating the obtained oxide sintered body by X-ray diffraction, it was confirmed that a homologous phase (IGZO112 phase) in which _m of InGaZn _m O _{3 +} m was 2 and an In ₂ O ₃ phase were present in the sintered body. It was done.

1 is a SEM photograph of a cross section of the oxide sintered body produced in Example 1. FIG. 2 and 3 are diagrams showing the distribution states of In atoms and Sm atoms in the field of view of the SEM photograph of FIG. 1 by SEM-EDS, respectively. In each figure, the bright portion indicates a region where the concentration of each atom is high.
From this figure, it can be confirmed that Sm exists in the phase with high In concentration, that is, the In ₂ O ₃ phase.

FIG. 4 is a photograph showing the EDS spectrum measurement points on the same SEM photograph as FIG. 5 and 6 are EDS spectra at points A and B shown in FIG. 4, respectively.
The EDS spectrum at point A corresponds to the In ₂ O ₃ phase in which Sm is dissolved, and the EDS spectrum at point B corresponds to the homologous phase (IGZO 112 phase).
The resistance value of the oxide sintered body, the density, the average particle diameter of the ZrO ₂ phase, the average particle diameter of the ZrO ₂ phase, the number of twins cracking, average diameter, the number of the above pore diameter 1μm pore, a diameter less than 1μm Tables 1 and 2 show the number of pores. Moreover, it shows in Table 1 and 2 about the crystal phase which an oxide sintered compact has.

The evaluation was carried out by the following method.
(1) Resistance value Measured with a low resistivity meter “Lorestar EP” (based on JIS K 7194) manufactured by Mitsubishi Chemical Corporation. Measurements were made at a total of 5 points, the intersection of two perpendicular diameters of the obtained circular sintered body, and the intersection and the middle point of the end, and the average value was taken as the resistance value.
(2) Relative Density The sample obtained by polishing the upper and lower surfaces of the obtained circular sintered body by 1 mm and further shaping the central part into a 2 × 2 × 0.5 cm rectangular parallelepiped was measured for the measured density by the Archimedes method. The relative density was calculated by dividing by the theoretical density.
(3) Average particle diameter of In ₂ O ₃ phase and homologous phase The upper and lower surfaces of the obtained circular sintered body were polished to a thickness of 5 mm. Furthermore, it shape | molded in diameter 101.6mmphi with the water jet cutting machine. The square inscribed in the circle is divided into 16 equal areas, and each center part is molded into a 1 × 1 × 0.5cm rectangular parallelepiped, embedded in resin and mirror-polished, and 16 pieces are used as samples. It was. The mirror polishing was performed until there were no cutting traces on the surface of the observation portion generated during sampling of the sintered body or polishing traces during rough cutting. The sample was coated with osmium for charge removal. An observation image having a size of 40 × 25 μm square (rectangular) is taken in a 3,000-times field of view by measurement with SEM observation (JSM-6390A manufactured by JEOL Ltd., acceleration voltage 15 kV), and observed within the range. The particle diameter of the particles was measured, and the average value of the particle diameters of the 16 sample frames was determined as the average particle diameter. The particle diameter was measured based on JIS R 1670 with crystal grains as equivalent circle diameters.
Confirmation of particles of In ₂ O ₃ phase and homologous phase was performed by an energy dispersive X-ray analyzer EDS apparatus (manufactured by JEOL Ltd., EX-2300) attached to the SEM. The element distribution is measured by mapping using each characteristic X-ray by EDS, and particles comprising 70% or more of In and O are defined as In ₂ O ₃ particles, and contain In, Ga, and Zn. The particles are defined as particles of In—Ga—Zn homologous phase. Furthermore, simple quantification was performed on each particle by EDS point element quantitative analysis to confirm the phase.
(4) Number of twin cracks Using the same sample as in (3) above, similarly, an observation image having a size of 40 × 25 μm square was taken in a 3000 × field of view by measurement with SEM. A linear space observed between them is defined as a twin crack, and the number of cracks having a length of 10 μm or more among the cracks in the observed range is measured, and within the frame of the 16 samples. The average value of the number of cracks was determined and used as the number of twin cracks of 10 μm or more.
(5) Number of pores Using the same sample as in (3) above, similarly, an observation image having a size of 40 × 25 μm in a 3,000 × field of view is taken by SEM, and there are no particles observed in the field of view. A void having an equivalent circle diameter of 0.5 μm or more measured based on JIS R 1670 was defined as a pore. The number of pores having an equivalent circle diameter of 1 μm or more was counted as pores having a diameter of 1 μm or more, and the average of the 16 samples was defined as the number of pores having a diameter of 1 μm or more. Similarly, the number of pores having a diameter of less than 1 μm was also measured.
(6) Crystal phase Determined by X-ray diffraction measurement (XRD).
・ Device: ULTIMA-III manufactured by Rigaku Corporation
-X-ray: Cu-Kα ray (wavelength 1.5406mm, monochromatized with graphite monochromator)
・ 2θ-θ reflection method, continuous scan (1.0 ° / min)
・ Sampling interval: 0.02 °
・ Slit DS, SS: 2/3 °, RS: 0.6 mm

Examples 2-36, Comparative Examples 1-5
An oxide sintered body was prepared and evaluated in the same manner as in Example 1 except that the oxide of the element X shown in Table 1 or 2 was used and the atomic ratio of each metal atom and the firing conditions were changed. The results are shown in Tables 1-4.
FIG. 7 shows an SEM photograph of the cross section of the oxide sintered body produced in Example 4 (Ti), and FIG. 8 shows an SEM photograph of the cross section of the oxide sintered body produced in Example 21 (Y). Shows an SEM photograph of a cross section of the oxide sintered body produced in Comparative Example 1 (Al). FIG. 10 shows an SEM photograph of a cross section of the oxide sintered body produced in Comparative Example 2 (Mg). FIG. 11 shows an SEM photograph of a cross section of the oxide sintered body produced in Comparative Example 3.
12 to 15 are X-ray diffraction patterns of the oxide sintered bodies produced in Example 3, Example 4, Example 12 and Example 23, respectively.

As a result of evaluating the oxide sintered body obtained in Examples 2-36 in the same manner as in Example 1, the sintered body contained a homologous phase and an In ₂ O ₃ phase in which _m of InGaZn _m O _{3 +} m was 1 or 2. It was confirmed to exist. It was also confirmed that element X was present in the In ₂ O ₃ phase.

  The oxide sintered body of the present invention can be used as a sputtering target. A thin film formed using the sputtering target of the present invention can be used for a thin film transistor.

Claims (14)

Containing a homologous phase represented by In ₂ O ₃ phase and InGaZn _m O _{3 + m} (m is an integer of 0.5 or 1 or more),
The In ₂ O ₃ phase contains one or more elements X selected from the group consisting of Hf, Zr, Ti, Y, Ge, Ta, Nb and lanthanoid elements;
The number of twin cracks having a length of 10 μm or more is 1 or less in a 40 × 25 μm square field of view,
The relative density is 95% or more,
An oxide sintered body, wherein the In ₂ O ₃ phase and the homologous phase have an average particle size of 10 μm or less.   2. The oxide sintered body according to claim 1, wherein the element X is one or more elements selected from Hf, Zr, Ti, Y, Ta, and Sm.   The oxide sintered body according to claim 1 or 2, wherein m is 1 or 2.   The oxide sintered body according to claim 1 or 2, wherein m is 2. The oxide sintered body according to any one of claims 1 to 4, wherein X is dissolved in the In ₂ O ₃ phase. The oxide sintered body according to any one of claims 1 to 5, wherein the In ₂ O ₃ phase is a bixbite phase.   The oxide sintered body according to any one of claims 1 to 6, wherein a resistance value is 50 mΩcm or less.   The oxide sintered body according to any one of claims 1 to 7, wherein the number of pores having a diameter of 1 µm or more is 9 or less in a field of 40 x 25 µm square.   9. The oxide sintered body according to claim 1, wherein the number of twin cracks having a length of 10 μm or more is 0 in a field of 40 × 25 μm square.   The oxide sintered body according to any one of claims 1 to 9, wherein an atomic ratio [X / (In + Ga + Zn + X)] of the element X is 0.001 to 0.2.   A sputtering target obtained by processing the oxide sintered body according to claim 1.   An oxide thin film formed using the sputtering target according to claim 11.   The oxide thin film according to claim 12, which is an amorphous film. A thin film transistor comprising the oxide thin film according to claim 12 as a channel layer.