IGZO sputtering target

Abstract

To provide an IGZO sputtering target with high relative density while suppressing arcing and particle increase during sputtering. [Solution] An IGZO sputtering target containing indium (In), gallium (Ga), zinc (Zn), zirconium (Zr), and oxygen (O), with the remainder being unavoidable impurities, containing less than 20 ppm by mass of Zr, and having a relative density of 95% or more.

Description

[Technical Field]

[0001] This invention relates to an IGZO sputtering target, and more particularly to an IGZO sputtering target that can achieve a high relative density while reducing the zirconium content. [Background technology]

[0002] Traditionally, amorphous silicon (α-Si) has been used for the TFTs (thin-film transistors) in the backplane of flat panel displays (FPDs). However, α-Si does not provide sufficient electron mobility, and in recent years, research and development has been conducted on TFTs using In-Ga-Zn-O oxide (IGZO), which has higher electron mobility than α-Si. Next-generation high-performance flat panel displays using IGZO-TFTs have been partially commercialized and are attracting attention.

[0003] IGZO films are primarily deposited by sputtering a target made from a sputtering target such as an IGZO sintered body. When forming thin films by sputtering, particle generation can cause pattern defects and other problems. The most common cause of these particle generation is abnormal discharge (arking) that occurs during sputtering. In particular, when arcing occurs on the target surface, the target material around the arcing site is ejected from the target in clusters (clumps). This clustered target material then adheres to the substrate.

[0004] Furthermore, due to the precision requirements of displays in recent years, the particles produced during sputtering have become more stringent than before. To address these sputtering challenges, attempts have been made to improve the density of the target and control the crystal grain size to obtain high-strength targets.

[0005] Patent Document 1 (Japanese Patent Application Publication No. 2014-024738) discloses an oxide sintered body containing In, Ga, and Zn, having a homologous crystalline structure represented by InGaZnO4, and characterized by containing zirconium in a weight ratio of 20 ppm or more and less than 100 ppm. It is disclosed that by adding zirconium in a weight ratio of 20 ppm or more and less than 100 ppm to a sintered body having a homologous crystalline structure represented by InGaZnO4, the relative density of the sintered body can be increased to 95% or more, and the flexural strength can be increased to 100 MPa or more. Furthermore, it is disclosed that an IGZO film obtained by sputtering using this sintered body exhibits superior transmittance compared to one without added zirconium.

[0006] Furthermore, Patent Document 2 (Japanese Patent Publication No. 2015-024944) discloses an oxide sintered body containing at least In, Ga, and Zn, having a homologous crystalline structure represented by InGaZnO4, characterized in that the grain size of the oxide sintered body is 5 μm or less, the relative density is 95% or more, and the flexural strength of the oxide sintered body is 100 MPa or more. The patent document describes how controlling the grain size, relative density, and flexural strength of the sintered body to constant values ​​improves the yield in the production of large-sized targets required by mass production equipment, and also improves crack occurrence during sputtering even when used as a cylindrical sputtering target that can be subjected to high power.

[0007] Furthermore, Patent Document 3 (Japanese Unexamined Patent Publication No. 2007-223849) describes GaInM x O yA gallium oxide-based sintered body is disclosed, characterized by being expressed by the formula (where M is a metal element with a valency of +2 or higher, x is an integer from 1 to 3, and y is an integer from 4 to 8), having a sintered body density of 95% or more in relative density, the absence of an insulating phase of Ga2O3, and an average crystal grain size of 10 μm or less. When this gallium oxide-based sintered body is used, the occurrence of cracks and nodules in the sputtering target during DC sputtering is suppressed, and the occurrence of abnormal discharges is also reduced, making it possible to deposit high-quality transparent thin films efficiently, inexpensively, and with energy savings. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2014-024738 [Patent Document 2] Japanese Patent Publication No. 2015-024944 [Patent Document 3] Japanese Patent Publication No. 2007-223849 [Overview of the project] [Problems that the invention aims to solve]

[0009] Sputtering targets made of IGZO sintered bodies are obtained by controlling the particle size of the raw material powder, the maximum sintering temperature, the holding time, and the sintering atmosphere so that the crystal grain size is below a certain level and the relative density is above a certain level. IGZO sintered bodies can usually be made denser and their density improved by bead milling the raw material powders of In2O3, ZnO, and Ga2O3 to a fine particle size. However, zirconia beads are usually used for bead milling, and these zirconia beads wear down during the bead milling process, inevitably becoming mixed into the raw material powder as impurities. The inclusion of impurities (contamination) may cause an increase in particles due to arcing during sputtering, a decrease in the transmittance of the IGZO film, and a decrease in the mobility of the TFT element.

[0010] The invention described in Patent Document 1 aims to obtain an IGZO sintered body having high density and flexural strength, and less cracking when used as a sputtering target, by incorporating zirconium at a weight ratio of 20 ppm to less than 100 ppm in an IGZO sintered body having a homologous crystalline structure represented by InGaZnO4. However, because zirconia (Zr) is deliberately added as an impurity to obtain the relative density and strength of the sintered body, arcing and particle generation during sputtering are expected. If the Zr content is reduced, the effect of relative density and strength will be lost.

[0011] Furthermore, in the invention described in Patent Document 1, since dispersion treatment is performed using zirconia beads in a wet bead mill, it is considered that, as mentioned above, zirconia beads inevitably become mixed into the raw material powder as impurities.

[0012] This invention was completed in view of the above-mentioned problems, and in one embodiment, the objective is to provide an IGZO sputtering target with high relative density while suppressing arcing and particle increase during sputtering. [Means for solving the problem]

[0013] As a result of diligent research, the inventors have found that by devising a method for grinding the raw material powder of the IGZO sputtering target, it is possible to obtain an IGZO sputtering target with high relative density while suppressing the inclusion of Zr. The present invention was completed based on this finding and is illustrated below.

[0014] [1] An IGZO sputtering target containing indium (In), gallium (Ga), zinc (Zn), zirconium (Zr), and oxygen (O), with the remainder consisting of unavoidable impurities, containing less than 20 ppm by mass of Zr, and having a relative density of 95% or more. [2] An IGZO sputtering target as described in [1], having a relative density of 98% or higher. [3] The IGZO sputtering target according to [1] or [2], having a bulk resistance of 100 mΩ·cm or less. [4] The IGZO sputtering target according to any one of [1] to [3], having an average crystal grain size of 30 μm or less. [5] The IGZO sputtering target according to [4], having an average crystal grain size of 12 μm or less. [6] The IGZO sputtering target according to any one of [1] to [5], having a flexural strength of 100 MPa or more. [7] The IGZO sputtering target according to any one of [1] to [6], being in a disk shape, a rectangular plate shape, or a cylindrical shape. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide an IGZO sputtering target having a high relative density while suppressing arcing and an increase in particles during sputtering. [Modes for Carrying Out the Invention]

[0016] Next, embodiments of the present invention will be described in detail with reference to the drawings. It should be understood that the present invention is not limited to the following embodiments, and design changes, improvements, etc. can be appropriately made based on the ordinary knowledge of those skilled in the art without departing from the gist of the present invention.

[0017] (1. Composition) In one embodiment, the IGZO sputtering target according to the present invention contains indium (In), gallium (Ga), zinc (Zn), zirconium (Zr), and oxygen (O), the balance being composed of inevitable impurities, and contains Zr in an amount of less than 20 mass ppm.

[0018] Unavoidable impurities are those present in the raw materials or inevitably introduced during the manufacturing process. While they are inherently unwanted, they are acceptable because they are present in trace amounts and do not significantly adversely affect the product's characteristics. In the IGZO sputtering target according to the present invention, typical unavoidable impurities include those contained in the raw materials In2O3 powder, Ga2O3 powder, and ZnO powder, those introduced during the grinding process, and those contained in the molding aid. In the IGZO sputtering target according to the present invention, the total concentration of unavoidable impurities can be, for example, 100 ppm by mass or less, preferably 50 ppm by mass or less, and more preferably 30 ppm by mass or less. There is no particular lower limit to the total concentration of unavoidable impurities, but from the viewpoint of manufacturing costs, it can be, for example, 10 ppm by mass or more, and typically 30 ppm by mass or more. By keeping the total concentration of unavoidable impurities in the IGZO sputtering target low, it is possible to prevent adverse effects on the properties (conductivity, transparency, etc.) of the IGZO film obtained by sputtering it.

[0019] In one embodiment of the present invention, the total concentration of unavoidable impurities refers to the total concentration of Li, Be, B, Na, Mg, Al, Si, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Y, Nb, Mo, Cd, Sb, Ba, Hf, W, Pb, and Bi. Zr can also be considered an unavoidable impurity, but since the concentration of Zr is particularly controlled in this invention, it is discussed separately for convenience.

[0020] In the IGZO sputtering target according to the present invention, the Zr concentration can be, for example, less than 20 ppm by mass, preferably 19 ppm by mass or less, more preferably 18 ppm by mass or less, even more preferably 17 ppm by mass or less, even more preferably 16 ppm by mass or less, even more preferably 15 ppm by mass or less, even more preferably 14 ppm by mass or less, even more preferably 13 ppm by mass or less, even more preferably 12 ppm by mass or less, even more preferably 11 ppm by mass or less, and even more preferably 10 ppm by mass or less. By controlling the Zr concentration to a low level, arcing and particle increase during sputtering can be suppressed.

[0021] While no lower limit is set for Zr concentration, it is generally set at 1 ppm by mass or higher, typically 5 ppm by mass or higher, due to the trade-off with the cost of completely eliminating Zr.

[0022] The concentration of Zr is measured by inductively coupled plasma emission spectrometry (ICP-OES), and each metallic element is analyzed using a measurement solution pre-treated with a portion of the sputtering target material as a sample. The concentrations of other unavoidable impurities are measured by glow discharge mass spectrometry (GDMS), and various elements are analyzed using the Ta electrode method, in which high-purity Ta is discharged together with the measurement sample.

[0023] (2. Relative density) The relative density of the sputtering target is desirable to be high because it affects the generation of arcing and particles during sputtering. A higher relative density of the sputtering target is also preferable from the viewpoint of suppressing the occurrence of cracks and fissures in the sputtering target. In one embodiment, the IGZO sputtering target according to the present invention has a relative density of 95% or more. The relative density is preferably 98% or more, more preferably 99% or more, even more preferably 99.5% or more, and even more preferably 99.6% or more. There is no particular upper limit to the relative density, but depending on the balance with manufacturing costs, it can be, for example, 99.99% or less, or 99.9% or less.

[0024] In this invention, "relative density" is expressed as relative density = (measured density / theoretical density) × 100 (%). Theoretical density is the density value calculated from the theoretical density of the oxides of the elements excluding oxygen for each constituent element of the sintered body. In the case of the IGZO sputtering target in this invention, indium oxide (In2O3), gallium oxide (Ga2O3), and zinc oxide (ZnO) are used as oxides of the elements excluding O among the constituent elements In, Ga, Zn, and O to calculate the theoretical density. The elemental analysis values ​​(at%, or mass%) of In, Ga, and Zn of the IGZO sputtering target are converted to the mass ratio of indium oxide (In2O3), gallium oxide (Ga2O3), and zinc oxide (ZnO). The density of each oxide is In2O3: 7.18 g / cm³. 3 Ga2O3: 5.88 g / cm³ 3 ZnO: 5.61 g / cm³ 3 This method is used. On the other hand, the measured density is the value obtained by dividing the weight by the volume. In the case of a sintered body, the volume is determined by the Archimedes method and then calculated.

[0025] (3. Bulk Resistor) To enable stable DC sputtering, it is preferable that the bulk resistance of the IGZO sputtering target be sufficiently low. In one embodiment, the IGZO sputtering target of the present invention has a bulk resistance of 100 mΩ·cm or less. This enables stable DC sputtering and suppresses abnormal discharge during sputtering. From this viewpoint, the bulk resistance of the IGZO sputtering target is preferably 80 mΩ·cm or less, and more preferably 60 mΩ·cm or less.

[0026] In this invention, bulk resistance is calculated using the four-probe method by summing the measurement results of samples taken at three locations separated from each other from the IGZO sputtering target, and dividing by the number of measurement locations to obtain the average value.

[0027] (4.Average grain size) The IGZO sputtering target of the present invention preferably has an average crystal grain size of 30 μm or less. By keeping the average crystal grain size within the above numerical range, the mechanical strength can be increased. From this viewpoint, the average crystal grain size of the IGZO sputtering target is more preferably 20 μm or less, even more preferably 15 μm or less, even more preferably 12 μm or less, and even more preferably 10 μm or less.

[0028] The method for measuring the average grain size is as follows: The IGZO sputtering target is observed using FE-SEM, the grain size is measured, and the average value is calculated. The coding method is used to measure the average grain size. The coding method involves drawing straight lines from grain boundary to grain boundary in any direction on the SEM image, and the average length of the line crossing a single particle is taken as the average grain size. On the SEM image, an arbitrary straight line (from grain boundary to grain boundary) is drawn, the number of intersections with the grain boundaries is counted, and the average grain size is calculated using the following (Equation 1). Average grain size = length of the line / number of intersections (Equation 1)

[0029] Specifically, at a magnification of 2000x, three parallel lines of arbitrary length are drawn in each of the six fields of view of the SEM image. The average grain size is then calculated from the average of the total length of these lines and the total number of intersections with grain boundaries.

[0030] The sample will be mirror-polished. SEM images will be taken using an FE-SEM (manufactured by JEOL Ltd.). The sample will be taken from the center of the sintered body, measuring 10 mm x 10 mm x thickness. When the sample size is given as length (Y mm) x width (X mm) x thickness (Z mm), the following points will be measured using the 1 / 2 position of both the length and width as a reference. Select two points from the intersections of the Y / 4mm axis with the X / 4, X / 2, and 3X / 4mm axes, two points from the intersections of the Y / 2mm axis with the X / 4, X / 2, and 3X / 4mm axes, and two points from the intersections of the 3Y / 4mm axis with the X / 4, X / 2, and 3X / 4mm axes.

[0031] (5. Flexural strength) The IGZO sputtering target of the present invention preferably has a flexural strength of 100 MPa or more. By having a flexural strength of 100 MPa or more, the phenomenon of cracking occurring in the sputtering target during sputtering can be suppressed. From this viewpoint, the flexural strength of the IGZO sputtering target is more preferably 120 MPa or more, and even more preferably 140 MPa or more.

[0032] The bending strength will be measured by a three-point bending test in accordance with JIS R1601:2008. Specifically, the sample length will be 40 mm ± 0.1 mm, width 4 mm ± 0.1 mm, thickness 3 mm ± 0.1 mm, distance between supports 30 mm ± 0.1 mm, and crosshead speed 0.5 mm / min.

[0033] (6. Manufacturing method) The following describes, in principle, a preferred method for manufacturing an IGZO sputtering target according to the present invention. [1] Powder Powders containing In, Ga, and Zn can be used. More specifically, powders of In compounds, powders of Ga compounds, and powders of Zn compounds can be used. Alternatively, powders containing combinations of these elements may be used. Examples of In compound powders include indium oxide (In2O3) and indium hydroxide. Examples of Ga compound powders include gallium oxide (Ga2O3) and gallium nitrate. Examples of Zn compound powders include zinc oxide (ZnO) and zinc hydroxide. The amount of each compound should be such that the desired atomic ratio of In, Ga, and Zn is achieved.

[0034] [2] Grinding and mixing Next, these raw material powders are finely ground and mixed. The fine grinding and mixing of the raw material powders can be done using either a dry or wet method. Dry methods include those using balls or beads made of zirconia, alumina, nylon resin, etc. Wet methods include media-stirring mills using the aforementioned balls or beads. Furthermore, wet methods include media-less container rotation type, mechanical stirring type, and airflow type wet methods. Generally, wet methods have superior fine grinding and mixing capabilities compared to dry methods. Therefore, it is preferable to perform fine grinding and mixing using a wet method.

[0035] However, in order to keep the amount of Zr contained in the IGZO sputtering target below 20 ppm by mass, at least the Ga compound powder, preferably all of the raw material powders, must be pulverized using a media-free dry grinding apparatus. Examples of media-free dry grinding apparatuses include compressed air dry grinding apparatuses and superheated steam dry grinding apparatuses. By using a media-free dry grinding apparatus, the use of zirconia beads can be avoided, and therefore, contamination due to wear of zirconia beads can be prevented, thus reducing the amount of Zr contained in the IGZO sputtering target.

[0036] In this specification, a superheated steam dry grinding apparatus is a dry grinding apparatus that, by using superheated steam, can generate higher collision energy compared to compressed air, and can also prevent the inclusion of zirconia beads.

[0037] While there are no particular limitations on the particle size after grinding, smaller sizes are preferable because finer grinding of the raw material powder yields a high-density sintered body, enabling high electrical conductivity and suppression of nodules during sputtering. Therefore, the volume-based median diameter (D50) of the raw material powder after grinding, determined by laser diffraction / scattering, is preferably 1.0 μm or less, and more preferably 0.5 μm or less. Furthermore, if grinding is insufficient, the components will segregate within the manufactured target, resulting in the presence of high-resistivity and low-resistivity regions. This can cause abnormal discharges such as arcing due to charging in the high-resistivity regions during sputtering. Therefore, sufficient mixing and grinding are necessary.

[0038] [3] Granulation When mixing is performed using a wet method, a molding aid is added to the mixed powder slurry obtained in the above process, and then granulated powder is produced using a spray dryer. By improving the fluidity of the powder through granulation, the powder can be uniformly filled into the mold during the subsequent press molding process, resulting in a homogeneous molded body. There are various methods for granulation, but the method using a spray dryer is preferred. This method disperses the slurry as droplets in hot air and dries them instantaneously, allowing for the continuous production of spherical granulated powder. The granulated powder preferably has a volume-based median diameter (D50) determined by laser diffraction and scattering, of 35 to 65 μm, more preferably 40 to 60 μm, and even more preferably 45 to 55 μm.

[0039] The addition ratio of the forming aid shall be appropriately 50 to 250 cc per 1 kg of the mixed powder slurry. In order to obtain sufficient strength of the formed body, the addition ratio of the forming aid is preferably 100 cc or more, more preferably 120 cc or more per 1 kg of the mixed powder slurry. Since the forming aid inhibits sintering and causes low density of the sintered body, the addition ratio of the forming aid is preferably 175 cc or less, more preferably 150 cc or less per 1 kg of the mixed powder slurry.

[0040] [4] Forming Next, the mixed powder is filled into a mold and uniaxially pressed under the conditions of a surface pressure of 400 to 1000 kgf / cm 2 for 1 to 3 minutes to obtain a formed body. If the surface pressure is less than 400 kgf / cm 2 , a formed body with sufficient density cannot be obtained. Also, a surface pressure exceeding 1000 kgf / cm 2 is not particularly required in production. That is, even if an excessive surface pressure is applied, it is difficult for the density of the formed body to improve beyond a certain value. Further, when a surface pressure exceeding 1000 kgf / cm 2 is applied, a density distribution is likely to occur in the formed body in principle during uniaxial pressing, which causes deformation and cracking during sintering.

[0041] Next, this formed body is double vacuum-packed with vinyl and subjected to CIP (Cold Isostatic Pressing) under the conditions of a pressure of 1500 to 4000 kgf / cm 2 for 1 to 3 minutes. If the pressure is less than 1500 kgf / cm 2 , a sufficient CIP effect cannot be obtained. On the other hand, even if a pressure exceeding 4000 kgf / cm 2 is applied, it is difficult for the density of the formed body to improve beyond a certain value. Therefore, a surface pressure exceeding 4000 kgf / cm 2 is not particularly required in production. Regarding the size of the formed body, there is no particular regulation, but if the thickness is too large, it becomes difficult to obtain a sintered body with a high relative density. Therefore, it is preferable to adjust the thickness of the formed body so that the thickness of the sintered body is 15 mm or less.

[0042] [5] Sintering Next, the molded body is sintered at a temperature of 1300 to 1500°C (preferably 1350 to 1450°C) for 5 to 24 hours (preferably 10 to 22 hours, more preferably 15 to 21 hours) in an air or oxygen atmosphere to obtain a sintered body. If the sintering temperature is lower than 1300°C, a sintered body with sufficient density cannot be obtained. Also, a sufficient amount of the crystalline phase InGaZnO4 cannot be obtained. If the sintering temperature is higher than 1500°C, the size of the crystal grains in the sintered body becomes too large, which may reduce the mechanical strength of the sintered body. Furthermore, if the time is less than 5 hours, a sintered body with sufficient density cannot be obtained, and if the time is longer than 24 hours, it is undesirable from the viewpoint of production cost.

[0043] The heating rate in the sintering process is preferably 1 to 10°C / min. This is because if the heating rate is too slow, grain growth will occur before sufficient densification can be achieved, resulting in insufficient density. Furthermore, the heating rate in the sintering process is preferably 3 to 8°C / min, and more preferably 4 to 6°C / min. Additionally, the cooling rate in the sintering process is preferably 20°C / min or less, and more preferably 10°C / min or less. This is because if the cooling rate is too fast, the sintered body may be damaged by thermal shock.

[0044] Furthermore, in addition to the methods described above, HP (hot pressing) and HIP (hot isostatic pressing) can also be used in the molding and sintering process.

[0045] [6] Grinding The sintered body obtained through the above process can be processed into the desired shape using a surface grinder, cylindrical grinder, machining center, or other processing machine as needed to create an IGZO sputtering target. There are no particular restrictions on the shape of the IGZO sputtering target, but it can be, for example, a disc, a rectangular plate, or a cylindrical shape. The IGZO sputtering target may be used alone or, as appropriate, joined to a backing plate. As for methods of joining to a backing plate, for example, an indium-based alloy or the like can be bonded to a copper backing plate as a bonding metal.

[0046] By following the above steps, the IGZO sputtering target intended by the present invention can be obtained. [Examples]

[0047] The following explanation is based on examples and comparative examples. However, these examples are merely illustrative, and the present invention is not limited to these examples.

[0048] In2O3 powder, Ga2O3 powder, and ZnO powder were weighed so that the composition ratio of the sintered body was approximately 1:1:1 in terms of the atomic ratios of In, Ga, and Zn. These raw material powders were then finely ground and mixed according to the conditions shown in Table 1. Subsequently, the mixed raw material powders were dispersed in pure water to prepare a slurry with a solid content of 45-50% by mass. This slurry was then dried and granulated using a spray dryer (manufactured by Okawara Chemical Machinery Co., Ltd., device name: FOC-25E) to obtain a mixed powder. Next, this mixed powder was subjected to a surface pressure of 400-1000 kgf / cm². 2 A disc-shaped molded body with a diameter of 280 mm was obtained by uniaxial pressing. Next, the obtained molded body was sintered under the conditions shown in Table 1.

[0049] As methods for finely grinding and mixing the raw material powder, a wet bead mill or a superheated steam dry grinding apparatus was employed, as shown in Table 1. The conditions for each were as follows:

[0050] (Conditions for a wet bead mill) Raw material powders were prepared and dispersed in pure water to create a slurry with a solid content of 45% by mass (for Comparative Example 1, only Ga2O3 powder was used). Next, the mixture was placed in a bead mill (manufactured by Ashizawa Finetech Co., Ltd., device name: LMZ) using ZrO2 beads as the grinding medium, and grinding was carried out until the median diameter (D50) of the mixed powder reached the value shown in Table 1 according to the test number, thereby obtaining the mixed powder slurry corresponding to each test number.

[0051] (Conditions for a superheated steam dry grinding apparatus) Ga2O3 powder was prepared and ground at a grinding steam pressure of 3.8 MPa, a classifier speed of 7000 rpm, and a grinding steam temperature of 250-340°C until the median diameter (D50) of the Ga2O3 powder reached the values ​​listed in Table 1 according to the test number, thereby obtaining ground Ga2O3 powder.

[0052] (Median diameter (D50)) Furthermore, for each raw material powder after grinding, the cumulative distribution of particle size based on volume was measured using a laser diffraction / scattering particle size analyzer (Horiba, Ltd., model name: LA-960) to determine the median diameter (D50). Alcosol was used as a dispersant, and the measurement was performed with a refractive index of 1.9. In cases where "None" is indicated as the grinding method, the median diameter (D50) of the raw material powder is directly shown. In cases where "Wet bead mill" is indicated as the grinding method, the median diameter (D50) of the mixed powder slurry of In2O3, ZnO, and Ga2O3 after fine grinding and mixing was measured. In cases where "Wet bead mill (Note)" is indicated as the grinding method, the grinding time was halved compared to the "Wet bead mill," and the median diameter (D50) of the mixed powder slurry of In2O3 and ZnO after fine grinding and mixing was measured. In each example and comparative example, Ga2O3 powder with a median diameter (D50) of 2.17 μm was used.

[0053] (Relative density) The measured density of the IGZO sputtering targets for each test number obtained above was determined by the Archimedes method, and the relative density was calculated according to the method described above: relative density = measured density / theoretical density × 100 (%). The results are shown in Table 1.

[0054] (Average grain size) The average crystal grain size of the IGZO sputtering targets for each test number obtained above was measured according to the method described above. The results are shown in Table 1.

[0055] (Bulk resistance) The bulk resistance of the IGZO sputtering targets corresponding to each test number obtained above was measured according to the method described above. The results are shown in Table 1.

[0056] (flexural strength) For Example 7, the flexural strength of the IGZO sputtering target corresponding to each test number obtained above was measured according to the method described above. As a result, the flexural strength of Example 7 was 160.9 MPa.

[0057] (Zr content) The Zr concentration in the IGZO sputtering targets corresponding to each test number obtained above was measured by inductively coupled plasma emission spectrometry (ICP-OES) under the conditions described above. The results are shown in Table 1. In the table, "<" indicates that the concentration is below the detection limit.

[0058] [Table 1]

[0059] (Consideration) As can be seen from Table 1, in each example, by grinding the Ga2O3 powder in a superheated steam dry grinding device instead of a wet bead mill, the inclusion of Zr was suppressed, and as a result the Zr content of the obtained IGZO sputtering targets was less than 20 ppm by mass. Furthermore, the IGZO sputtering targets in each example had a relative density of 95% or more, a bulk resistance of 100 mΩ·cm or less, and an average crystal grain size of 30 μm or less.

[0060] On the other hand, when Ga2O3 powder was ground using a wet bead mill, the Zr content of the resulting IGZO sputtering target increased significantly (Comparative Example 1). When the IGZO sputtering target was prepared without grinding the Ga2O3 powder at all, it was possible to prevent Zr contamination, but because the particle size of the raw material powder was high, it was not possible to achieve a relative density of 95% or higher (Comparative Examples 2-5).

Claims

1. An IGZO sputtering target containing indium (In), gallium (Ga), zinc (Zn), zirconium (Zr), and oxygen (O), with the remainder consisting of unavoidable impurities, containing less than 20 ppm by mass of Zr, and having a relative density of 95% or more.

2. The IGZO sputtering target according to claim 1, wherein the relative density is 98% or higher.

3. An IGZO sputtering target according to claim 1 or 2, wherein the bulk resistance is 100 mΩ·cm or less.

4. An IGZO sputtering target according to any one of claims 1 to 3, wherein the average crystal grain size is 30 μm or less.

5. The IGZO sputtering target according to claim 4, wherein the average crystal grain size is 12 μm or less.

6. An IGZO sputtering target according to any one of claims 1 to 5, wherein the bending strength is 100 MPa or more.

7. An IGZO sputtering target according to any one of claims 1 to 6, which is disc-shaped, rectangular plate-shaped, or cylindrical.

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