Sputtering target and oxide semiconductor

Abstract

The sputtering target is composed of an oxide containing indium (In), zinc (Zn), and an additive element (X). The additive element (X) is composed of at least one element selected from tantalum (Ta), strontium (Sr), and niobium (Nb). The atomic ratios of the elements in the sputtering target satisfy equations (1) to (3). The relative density of the sputtering target is 95% or higher. 0.4≤(In+X) / (In+Zn+X)≤0.8(1), 0.2≤Zn / (In+Zn+X)≤0.6(2), 0.001≤X / (In+Zn+X)≤0.015(3).

Description

Technical Field

[0001] This invention relates to sputtering targets. Furthermore, this invention relates to oxide semiconductors formed using sputtering targets. Background Technology

[0002] In the field of thin-film transistors (TFTs) used in flat panel displays (FPDs), with the increasing functionality of FPDs, oxide semiconductors, represented by In-Ga-Zn composite oxides (IGZO), are attracting attention and are driving practical applications, replacing the previously used amorphous silicon. IGZO has the advantage of exhibiting high field-effect mobility and low leakage current. In recent years, with the continuous development of higher functionality in FPDs, materials exhibiting even higher field-effect mobility than that shown by IGZO have been proposed.

[0003] For example, Patent Documents 1 and 2 propose oxide semiconductors for TFTs using an In-Zn-X composite oxide composed of indium (In), zinc (Zn), and any element X. According to these documents, the oxide semiconductor is formed by sputtering using a target material composed of the In-Zn-X composite oxide.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: US2013 / 2701091A1

[0007] Patent Document 2: US2014 / 1028921A1 Summary of the Invention

[0008] In the technologies described in Patent Documents 1 and 2, the target material is manufactured using a powder sintering method. However, targets manufactured by powder sintering typically have a low relative density, which makes them prone to particle generation and cracking during abnormal discharges. As a result, this can sometimes hinder the manufacture of high-performance TFTs.

[0009] Furthermore, in the field of TFT technology, oxide semiconductors that exhibit higher field-effect mobility than those shown by IGZO are desired.

[0010] Furthermore, in the field of TFT technology, it is desirable for oxide semiconductors to exhibit a threshold voltage close to 0V.

[0011] Therefore, the objective of this invention is to provide a sputtering target and an oxide semiconductor that can overcome the disadvantages of the prior art described above.

[0012] The present invention solves the aforementioned problems by providing the following sputtering target:

[0013] The aforementioned sputtering target is composed of an oxide containing indium (In), zinc (Zn), and additive element (X).

[0014] The added element (X) consists of at least one element selected from tantalum (Ta), strontium (Sr), and niobium (Nb).

[0015] The atomic ratios of each element satisfy equations (1) to (3) (where X is the sum of the contents of the aforementioned added elements).

[0016] 0.4≤(In+X) / (In+Zn+X)≤0.8 (1)

[0017] 0.2≤Zn / (In+Zn+X)≤0.6 (2)

[0018] 0.001≤X / (In+Zn+X)≤0.015 (3)

[0019] The relative density is over 95%.

[0020] The present invention also provides an oxide semiconductor, which is an oxide semiconductor formed using the aforementioned sputtering target.

[0021] The aforementioned oxide semiconductor is composed of an oxide containing indium (In), zinc (Zn), and an additive element (X).

[0022] The added element (X) consists of at least one element selected from tantalum (Ta), strontium (Sr), and niobium (Nb).

[0023] The atomic ratios of each element satisfy equations (1) to (3) (where X is the sum of the contents of the aforementioned added elements).

[0024] 0.4≤(In+X) / (In+Zn+X)≤0.8 (1)

[0025] 0.2≤Zn / (In+Zn+X)≤0.6 (2)

[0026] 0.001≤X / (In+Zn+X)≤0.015 (3)

[0027] The present invention also provides a thin-film transistor having an oxide semiconductor and a field-effect mobility of 45 cm⁻¹. 2 / Vs or more,

[0028] The aforementioned oxide semiconductor is composed of an oxide containing indium (In), zinc (Zn), and an additive element (X).

[0029] The added element (X) consists of at least one element selected from tantalum (Ta), strontium (Sr), and niobium (Nb).

[0030] The atomic ratios of each element satisfy equations (1) to (3) (where X is the sum of the contents of the aforementioned added elements).

[0031] 0.4≤(In+X) / (In+Zn+X)≤0.8 (1)

[0032] 0.2≤Zn / (In+Zn+X)≤0.6 (2)

[0033] 0.001≤X / (In+Zn+X)≤0.015 (3). Attached Figure Description

[0034] Figure 1 This is a schematic diagram illustrating the structure of a thin-film transistor manufactured using the sputtering target of the present invention.

[0035] Figure 2 This is a graph showing the results of X-ray diffraction measurements of the sputtering target obtained in Example 1.

[0036] Figure 3 This is a scanning electron microscope image of the sputtering target obtained in Example 1.

[0037] Figure 4 This is a scanning electron microscope image of the sputtering target obtained in Example 1.

[0038] Figure 5 These are the qualitative analysis charts and quantitative analysis results of the In2O3 phase of the sputtering target obtained in Example 1 from EDX analysis.

[0039] Figure 6 This is a scanning electron microscope image of the sputtering target obtained in Example 1.

[0040] Figure 7 These are qualitative analysis charts and quantitative analysis results of the Zn3In2O6 phase of the sputtering target obtained in Example 1, obtained through EDX analysis.

[0041] Figure 8 Image (a) shows the EDX analysis results of the sputtering target obtained in Example 1. Figure 8 (b) is an image showing the EDX analysis results of the sputtering target obtained in Comparative Example 1. Detailed Implementation

[0042] The present invention will now be described based on its preferred embodiments. The present invention relates to sputtering targets (hereinafter also referred to as "targets"). The target of the present invention is composed of an oxide comprising indium (In), zinc (Zn), and an additive element (X). The additive element (X) is composed of at least one element selected from tantalum (Ta), strontium (Sr), and niobium (Nb). The target of the present invention comprises In, Zn, and the additive element (X) as metallic elements constituting the target. In addition to these elements, trace elements may be intentionally or unavoidably included, without impairing the effects of the present invention. Examples of trace elements include, for example, elements contained in organic additives described later, and media raw materials such as those from ball mills incorporated during the manufacture of the target. Examples of trace elements in the target material of the present invention include Fe, Cr, Ni, Al, Si, W, Zr, Na, Mg, K, Ca, Ti, Y, Ga, Sn, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Pb. Their content, relative to the total mass of oxides containing In, Zn, and X contained in the target material of the present invention, is generally preferably 100 ppm (hereinafter also referred to as "ppm") or less, more preferably 80 ppm or less, and even more preferably 50 ppm or less, respectively. The total amount of these trace elements is preferably 500 ppm or less, more preferably 300 ppm or less, and even more preferably 100 ppm or less. When the target material of the present invention contains trace elements, the aforementioned total mass also includes the mass of the trace elements.

[0043] The target material of the present invention is preferably composed of a sintered body containing the above-mentioned oxides. The shape of the sintered body and the sputtering target material is not particularly limited, and conventionally known shapes such as flat plates and cylindrical shapes can be used.

[0044] From the viewpoint of improving the performance of oxide semiconductor devices formed from the target material of the present invention, it is preferable that the atomic ratio of the metal elements constituting the target material, namely In, Zn and X, is within a specific range.

[0045] Specifically, for In and X, the atomic ratio shown in Equation (1) is preferred (where X is the sum of the contents of the aforementioned added elements. The same applies to Equations (2) and (3) below).

[0046] 0.4≤(In+X) / (In+Zn+X)≤0.8 (1)

[0047] For Zn, the atomic ratio shown in equation (2) is preferred.

[0048] 0.2≤Zn / (In+Zn+X)≤0.6 (2)

[0049] For X, the atomic ratio shown in equation (3) is preferred.

[0050] 0.001≤X / (In+Zn+X)≤0.015 (3)

[0051] By satisfying the aforementioned equations (1) to (3) with the atomic ratio of In, Zn, and X, semiconductor devices having oxide thin films formed by sputtering using the target material of the present invention exhibit high field-effect mobility, low leakage current, and a threshold voltage close to 0V. For In and X, from the viewpoint of making these advantages even more significant, it is more preferable to satisfy the following equations (1-2) to (1-5).

[0052] 0.43≤(In+X) / (In+Zn+X)≤0.79 (1-2)

[0053] 0.48≤(In+X) / (In+Zn+X)≤0.78 (1-3)

[0054] 0.53≤(In+X) / (In+Zn+X)≤0.75 (1-4)

[0055] 0.58≤(In+X) / (In+Zn+X)≤0.70 (1-5)

[0056] For Zn, from the same point of view as above, it is more preferable to satisfy the following equations (2-2) to (2-5), and for X, it is even more preferable to satisfy the following equations (3-2) to (3-5).

[0057] 0.21≤Zn / (In+Zn+X)≤0.57 (2-2)

[0058] 0.22≤Zn / (In+Zn+X)≤0.52 (2-3)

[0059] 0.25≤Zn / (In+Zn+X)≤0.47 (2-4)

[0060] 0.30≤Zn / (In+Zn+X)≤0.42 (2-5)

[0061] 0.0015≤X / (In+Zn+X)≤0.013 (3-2)

[0062] 0.002<X / (In+Zn+X)≤0.012 (3-3)

[0063] 0.0025≤X / (In+Zn+X)≤0.010 (3-4)

[0064] 0.003≤X / (In+Zn+X)≤0.009 (3-5)

[0065] As described above, one or more elements selected from Ta, Sr, and Nb can be used as the additive element (X). These elements can be used individually or in combination of two or more. In particular, from the viewpoint of the overall performance of the oxide semiconductor device manufactured from the target material of the present invention, and from the viewpoint of the economy in manufacturing the target material, the use of Ta as the additive element (X) is preferred.

[0066] In addition to satisfying the relationships (1) to (3) above, from the viewpoint of further improving the field-effect mobility of the oxide semiconductor device formed by the target of the present invention and exhibiting a threshold voltage close to 0V, the atomic ratio of In to X of the target of the present invention preferably satisfies the following formula (4).

[0067] 0.970≤In / (In+X)≤0.999 (4)

[0068] As can be seen from equation (4), in the target material of the present invention, by using a very small amount of X relative to the amount of In, the field-effect mobility of the oxide semiconductor device formed by the target material is increased. This is a first discovery by the inventors. In the prior art known to date (e.g., the prior art described in Patent Documents 1 and 2), the amount of X used relative to the amount of In is greater than that of the present invention.

[0069] From the viewpoint that the field-effect mobility of the oxide semiconductor formed by the target material is further increased, and from the viewpoint that it exhibits a threshold voltage close to 0V, it is more preferable that the atomic ratio of In to X satisfies the following equations (4-2) to (4-4).

[0070] 0.980≤In / (In+X)≤0.997 (4-2)

[0071] 0.990≤In / (In+X)≤0.995 (4-3)

[0072] 0.990<In / (In+X)≤0.993 (4-4)

[0073] From the perspective of enhancing the functionality of FPDs due to the improved transfer characteristics of TFTs as oxide semiconductor elements, it is preferable to have a high field-effect mobility for oxide semiconductor elements formed from a target. Specifically, for a TFT equipped with an oxide semiconductor element formed from a target, its field-effect mobility (cm²) is preferred. 2 / Vs) is preferably 45cm 2 / Vs or higher, and preferably 50cm 2 / Vs or more, preferably 60cm 2 / Vs or higher, further preferably 70cm 2 / Vs or higher, with an even better option of 80cm 2 / Vs or higher, with a further preferred value of 90cm 2 / Vs or more, especially preferred is 100cm 2 / Vs or higher. From the perspective of high functionalization of FPD, a higher field-effect mobility value is preferred, and if the field-effect mobility reaches 200cm... 2 With a value of approximately / Vs, the performance can be adequately satisfied.

[0074] The proportions of each metal contained in the target material of the present invention can be determined, for example, by ICP emission spectroscopy.

[0075] The target material of the present invention is characterized not only by the atomic ratio of In, Zn, and X, but also by its high relative density. Specifically, the target material of the present invention exhibits a relatively density preferably of 95% or higher. Because of this high relative density, the generation of particulate matter can be suppressed during sputtering using the target material of the present invention, which is therefore preferred. From this viewpoint, the target material of the present invention is further preferably characterized by a relative density of 97% or higher, more preferably 98% or higher, even more preferably 99% or higher, particularly preferably 100% or higher, and extremely preferably exceeding 100%. The target material of the present invention having such a relative density can be suitably manufactured by the method described later. The relative density is determined according to the Archimedes method. Specific determination methods will be described in detail in the examples described later.

[0076] The target material of the present invention is further characterized by its small pore size and low number of pores. Specifically, for the target material of the present invention, the number of pores with an area equivalent circle diameter of 0.5 μm or more and 20 μm or less is 5 per 1000 μm. 2 The following is a preferred method. When using a sputtering target with low porosity, the generation of microparticles can be suppressed. From this viewpoint, the target material of the present invention is further preferably characterized by an area equivalent circle diameter of 0.5 μm or more and 20 μm or less, and a porosity of 3 pores per 1000 μm. 2 The following, and more preferably, are 2 per 1000 μm 2 The following, and more preferably, is 1 per 1000μm 2 The following, particularly preferred, is 0.5 particles / 1000μm. 2 The following, and most preferably, is 0.1 particles / 1000μm 2 The target material of the present invention, with its low pore number, can be suitably manufactured by the methods described later. Specific measurement methods will be described in detail in the examples described later.

[0077] The target material of the present invention is further characterized by its high strength. Specifically, the target material of the present invention exhibits a high flexural strength, preferably 100 MPa or more. Because it exhibits such high flexural strength, even if an abnormal discharge occurs unexpectedly during sputtering, the target material is less prone to cracking, which is therefore preferable. From this viewpoint, the target material of the present invention is further preferably characterized by a flexural strength of 120 MPa or more, more preferably 150 MPa or more. The target material of the present invention having this flexural strength can be suitably manufactured by the method described later. The flexural strength is measured according to JIS R1601. The specific measurement method will be described in detail in the examples described later.

[0078] The target material of the present invention is further characterized by its low volume resistivity. From the viewpoint that this target material can be used for DC sputtering, low volume resistivity is advantageous. From this viewpoint, the target material of the present invention preferably has a volume resistivity of 100 mΩ·cm or less at 25°C, more preferably 50 mΩ·cm or less, even more preferably 10 mΩ·cm or less, even more preferably 5 mΩ·cm or less, even more preferably 4 mΩ·cm or less, particularly preferably 3 mΩ·cm or less, extremely preferably 2 mΩ·cm or less, and especially preferably 1.5 mΩ·cm or less. The target material of the present invention having this volume resistivity can be suitably manufactured by the method described later. The volume resistivity is measured using the DC four-probe method. Specific measurement methods will be described in detail in the embodiments described later.

[0079] The target material of the present invention is further characterized by small deviations in the number of pores and volume resistivity within the same surface of the target material. Specifically, for the target material of the present invention, the absolute value obtained by dividing the difference between the values ​​of the number of pores and volume resistivity measured at any five points on the same surface and the arithmetic mean of the five points by the arithmetic mean of the five points and then multiplying by 100 is 20% or less. When sputtering is performed using such a target material with small deviations within the same surface, the film properties do not change due to the relative positions of the glass substrates during sputtering, which is therefore preferable. From this viewpoint, the aforementioned absolute values ​​of the target material of the present invention are further preferably 15% or less, even more preferably 10% or less, even more preferably 5% or less, particularly preferably 3% or less, and extremely preferably 1% or less. The target material of the present invention with such small deviations in the number of pores and volume resistivity can be suitably manufactured by the method described later.

[0080] Furthermore, the target material of the present invention is characterized by small deviations in the number of pores and volume resistivity in the depth direction of the target material. Specifically, for the target material of the present invention, a surface is obtained by grinding 1 mm at a time along the depth direction from the surface. The absolute value of the difference between the value of the number of pores and the volume resistivity of this surface and the arithmetic mean of five points, divided by the arithmetic mean of the five points and then multiplied by 100, is 20% or less. From the same point of view as above, the aforementioned absolute values ​​of the target material of the present invention are further preferably 15% or less, even more preferably 10% or less, even more preferably 5% or less, particularly preferably 3% or less, and extremely preferably 1% or less. This target material of the present invention, with its small deviations in the number of pores and volume resistivity, can be suitably manufactured by the method described later.

[0081] The target material of the present invention preferably has a standard deviation of Vickers hardness of 50 or less in the same plane. When this value meets the above conditions, it is preferred as a target material because there is no deviation in density, grain diameter, and composition. The standard deviation of Vickers hardness in the same plane is preferably 40 or less, more preferably 30 or less, even more preferably 20 or less, and even more preferably 10 or less. The target material of the present invention having this Vickers hardness can be suitably manufactured by the method described later. Vickers hardness is measured according to JIS-R-1610:2003. The specific measurement method will be described in detail in the examples described later.

[0082] The arithmetic mean roughness Ra (JIS-B-0601:2013) of the target material surface of the present invention can be appropriately adjusted by means of the numbering of the grinding stone during grinding. When using a target material with a small arithmetic mean roughness Ra for sputtering, abnormal discharge can be suppressed during sputtering, which is therefore preferable. From this viewpoint, the target material of the present invention preferably has an arithmetic mean roughness Ra of 3.2 μm or less, more preferably 1.6 μm or less, even more preferably 1.2 μm or less, even more preferably 0.8 μm or less, particularly preferably 0.5 μm or less, and extremely preferably 0.1 μm or less. The arithmetic mean roughness Ra can be measured using a surface roughness measuring instrument. Specific measurement methods will be described in detail in the embodiments described later.

[0083] The target material of the present invention preferably has a maximum color difference ΔE* of 5 or less on its surface. Furthermore, the maximum color difference ΔE* in the depth direction of the target material is also preferably 5 or less. "Color difference ΔE*" is a numerical indicator of the difference between two colors. When this value meets the above conditions, it is preferred as a target material because there are no deviations in density, grain diameter, and composition. The maximum color difference ΔE* in the overall surface and depth direction is preferably 4 or less, more preferably 3 or less, even more preferably 2 or less, and even more preferably 1 or less. The target material of the present invention having this maximum color difference ΔE* can be suitably manufactured by the method described later. Specific measurement methods will be described in detail in the examples described later.

[0084] As described above, the target material of the present invention is composed of an oxide containing In, Zn, and X. This oxide can be an oxide of In, an oxide of Zn, or an oxide of X. Alternatively, the oxide can be a composite oxide selected from any two or more elements chosen from In, Zn, and X. Specific examples of composite oxides include: In-Zn composite oxides, Zn-Ta composite oxides, In-Ta composite oxides, In-Nb composite oxides, Zn-Nb composite oxides, In-Nb composite oxides, In-Sr composite oxides, Zn-Sr composite oxides, In-Sr composite oxides, In-Zn-Ta composite oxides, In-Zn-Nb composite oxides, In-Zn-Sr composite oxides, etc., but are not limited to these.

[0085] For the target material of the present invention, in particular, from the viewpoint of improving the density and strength of the target material and reducing its resistivity, it is preferable to include an oxide of In, namely the In2O3 phase, and a composite oxide of In and Zn, namely the Zn3In2O6 phase. The fact that the target material of the present invention contains both the In2O3 and Zn3In2O6 phases can be determined by measuring whether the In2O3 and Zn3In2O6 phases are observable using X-ray diffraction (hereinafter also referred to as "XRD") on the target material of the present invention. It should be noted that the In2O3 phase in the present invention may contain trace amounts of Zn.

[0086] Specifically, in XRD measurements using CuKα rays as the X-ray source, the In₂O₃ phase main peak was observed in the range of 2θ = 30.38° to 30.78°. The Zn₃In₂O₆ phase main peak was observed in the range of 2θ = 34.00° to 34.40°.

[0087] Furthermore, in the target material of the present invention, X is preferably contained in both the In2O3 phase and the Zn3In2O6 phase. In particular, when X is homogeneously dispersed and contained throughout the target material, the oxide semiconductor formed from the target material of the present invention also contains X, and a homogeneous oxide semiconductor film can be obtained. The presence of X in both the In2O3 phase and the Zn3In2O6 phase can be determined by, for example, energy-dispersive X-ray spectroscopy (hereinafter also referred to as "EDX"). Specific determination methods will be described in detail in the embodiments described later.

[0088] When the In2O3 phase is observed in the target material of the present invention by XRD measurement, from the viewpoint of improving the density and strength of the target material of the present invention and reducing the resistivity, the grain size of the In2O3 phase preferably meets a specific range. Specifically, the grain size of the In2O3 phase is preferably 3.0 μm or less, more preferably 2.7 μm or less, and even more preferably 2.5 μm or less. The smaller the grain size, the more preferred; the lower limit is not particularly limited, and it is usually 0.1 μm or more.

[0089] When the Zn3In2O6 phase is observed in the target material of the present invention by XRD measurement, from the viewpoint of improving the density and strength of the target material of the present invention and reducing the resistivity, the grain size of the Zn3In2O6 phase preferably meets a specific range. Specifically, the grain size of the Zn3In2O6 phase is preferably 3.9 μm or less, more preferably 3.5 μm or less, further preferably 3.0 μm or less, even more preferably 2.5 μm or less, even more preferably 2.3 μm or less, particularly preferably 2.0 μm or less, and extremely preferably 1.9 μm or less. Smaller grain size is more preferred, and the lower limit is not particularly limited, but is generally 0.1 μm or more.

[0090] To set the grain size of the In2O3 phase and the Zn3In2O6 phase to the above range, the target material can be manufactured, for example, by the method described later.

[0091] The grain size of the In2O3 phase and the grain size of the Zn3In2O6 phase can be determined by observing the target material of the present invention using a scanning electron microscope (hereinafter also referred to as "SEM"). The specific measurement method will be described in detail in the following embodiments.

[0092] In relation to the aforementioned grain size, from the viewpoint of reducing the resistivity of the target material of the present invention, it is also preferable that the proportion of the In2O3 phase per unit area (hereinafter also referred to as "In2O3 phase area ratio") is within a specific range. Specifically, the In2O3 phase area ratio is preferably 10% or more and 70% or less, more preferably 20% or more and 70% or less, even more preferably 30% or more and 70% or less, and even more preferably 35% or more and 70% or less.

[0093] On the other hand, the proportion of the area occupied by the Zn3In2O6 phase per unit area (hereinafter also referred to as "Zn3In2O6 phase area ratio") is preferably 30% or more and 90% or less, more preferably 30% or more and 80% or less, even more preferably 30% or more and 70% or less, and even more preferably 30% or more and 65% or less.

[0094] To set the In2O3 phase area fraction and Zn3In2O6 phase area fraction within the aforementioned range, the target material can be manufactured, for example, by the method described later. The In2O3 phase area fraction and Zn3In2O6 phase area fraction can be determined by observing the target material of the present invention using SEM. The specific measurement method will be described in detail in the embodiments described later.

[0095] In the target material of the present invention, the In2O3 phase and the Zn3In2O6 phase are preferably homogeneously dispersed. If they are homogeneously dispersed, the composition will not deviate and the film properties will not change when the film is formed by sputtering, which is therefore preferred.

[0096] The dispersion state of the crystalline phases was evaluated using EDX. Based on a randomly selected magnification of 200x and a field of view of 437.5 μm × 625 μm from the target material, the overall In / Zn atomic ratio of the field of view was obtained using EDX. Next, this field of view was divided into equal vertical × horizontal sections of 4, and the In / Zn atomic ratio in each section was obtained. The absolute value of the difference between the In / Zn atomic ratio in each section and the overall In / Zn atomic ratio of the field of view was divided by the overall In / Zn atomic ratio of the field of view and multiplied by 100. The resulting value was defined as the dispersion rate (%). The degree of homogeneity of the In₂O₃ and Zn₃In₂O₆ phases was evaluated based on the magnitude of the dispersion rate. The closer the dispersion rate is to zero, the more homogeneous the In₂O₃ and Zn₃In₂O₆ phases are. The maximum value of the dispersion rate at point 16 is preferably 10% or less, more preferably 5% or less, even more preferably 4% or less, even more preferably 3% or less, particularly preferably 2% or less, and extremely preferably 1% or less.

[0097] Next, a suitable manufacturing method for the target material of the present invention will be described. In this manufacturing method, oxide powder, which is the raw material for the target material, is shaped into a predetermined shape to obtain a shaped body, and the shaped body is calcined to obtain a target material formed from a sintered body. In order to obtain the shaped body, methods known in the art to date can be used. In particular, from the viewpoint of being able to manufacture dense target materials, casting forming or CIP forming is preferred.

[0098] The slip casting method is also known as the slurry casting method. To perform slip casting, firstly, a slurry containing raw material powder and organic additives must be prepared using a dispersion medium.

[0099] As the aforementioned raw material powders, oxide powders, hydroxide powders, and carbonate powders are suitable. As oxide powders, powders of In oxide, Zn oxide, and X oxides are used. For example, In₂O₃ can be used as an In oxide. For example, ZnO can be used as a Zn oxide. For example, Ta₂O₅, SrO, and Nb₂O₅ can be used as X oxide powders. It should be noted that although SrO exists in the air as SrCO₃ by combining with carbon dioxide, carbon dioxide separates from SrCO₃ during calcination to form SrO.

[0100] In this manufacturing method, all the raw material powders are mixed and then calcined. In contrast, in the prior art, such as the technology described in Patent Document 2, In₂O₃ powder and Ta₂O₅ powder are mixed and calcined, and then the resulting calcined powder is mixed with ZnO powder and calcined again. This method, by performing pre-calcination, results in coarse particles forming the powder, making it difficult to obtain a target material with a high relative density. In contrast, this manufacturing method preferably mixes, shapes, and calcines all the powders of In oxide, Zn oxide, and X oxide at room temperature, thus easily obtaining a dense target material with a high relative density.

[0101] The amounts of In oxide powder, Zn oxide powder, and X oxide powder used are preferably adjusted such that the atomic ratio of In, Zn, and X in the target material satisfies the above-mentioned range.

[0102] The particle size of the raw material powder is the volumetric particle size D, measured using laser diffraction scattering particle size distribution determination method, at a cumulative volume of 50% of capacity. 50 The particle size is preferably 0.1 μm or larger and 1.5 μm or smaller. By using raw material powder with a particle size within this range, it is possible to easily obtain a target material with a high relative density.

[0103] The aforementioned organic additives are substances used to suitably adjust the properties of the slurry and the molded body. Examples of organic additives include binders, dispersants, and plasticizers. Binders are added to improve the strength of the molded body. Binders commonly used in powder sintering processes to obtain molded bodies can be used as binders. Polyvinyl alcohol is an example of a binder. Dispersants are added to improve the dispersibility of the raw material powder in the slurry. Examples of dispersants include polycarboxylic acid dispersants and polyacrylic acid dispersants. Plasticizers are added to improve the plasticity of the molded body. Examples of plasticizers include polyethylene glycol (PEG) and ethylene glycol (EG).

[0104] There are no particular limitations on the dispersion medium used when preparing slurries containing raw material powders and organic additives. Water-soluble organic solvents such as water and alcohol can be appropriately selected and used, depending on the purpose. There are also no particular limitations on the method for preparing slurries containing raw material powders and organic additives. For example, a method can be used where the raw material powders, organic additives, dispersion medium, and zirconia balls are placed in a container and ball-milled for mixing.

[0105] After obtaining the slurry, the slurry is poured into a mold, and then the dispersion medium is removed to form a molded body. Examples of molds that can be used include metal molds, plaster molds, and resin molds that remove the dispersion medium by applying pressure.

[0106] In the CIP molding method, the same slurry used in the casting molding method is spray-dried to obtain a dried powder. The obtained dried powder is then filled into a mold and CIP molding is performed.

[0107] After obtaining the shaped body, it is then fired. Firing of the shaped body can generally be carried out in an oxygen-containing atmosphere. Firing in an atmospheric atmosphere is particularly convenient. The firing temperature is preferably 1200°C or higher and 1600°C or lower, more preferably 1300°C or higher and 1500°C or lower, and even more preferably 1350°C or higher and 1450°C or lower. The firing time is preferably 1 hour or higher and 100 hours or lower, more preferably 2 hours or higher and 50 hours or lower, and even more preferably 3 hours or higher and 30 hours or lower. The heating rate is preferably 5°C / hour or higher and 500°C / hour or lower, even more preferably 10°C / hour or higher and 200°C / hour or lower, and even more preferably 20°C / hour or higher and 100°C / hour or lower.

[0108] In the calcination of the shaped body, from the viewpoint of promoting sintering and generating a dense target material, it is preferable to maintain the temperature at which the composite oxide of In and Zn, such as Zn5In2O8, is formed for a certain period of time during the calcination process. Specifically, when the raw material powder contains In2O3 powder and ZnO powder, they react with increasing temperature to form the Zn5In2O8 phase, then the Zn4In2O7 phase, and finally the Zn3In2O6 phase. In particular, volume diffusion intensifies during the formation of the Zn5In2O8 phase, promoting densification; therefore, it is preferable to reliably form the Zn5In2O8 phase. From this viewpoint, it is preferable to maintain the temperature in the range of 1000°C to 1250°C for a certain period of time during the calcination heating process, more preferably in the range of 1050°C to 1200°C for a certain period of time. The maintained temperature is not necessarily limited to a specific temperature point, but can be a temperature range with a certain degree of amplitude. Specifically, when a specific temperature selected from the range of 1000°C to 1250°C is defined as T (°C), as long as it is within the range of 1000°C to 1250°C, it can be, for example, T ± 10°C, preferably T ± 5°C, more preferably T ± 3°C, and even more preferably T ± 1°C. The time for maintaining this temperature range is preferably 1 hour or more and 40 hours or less, and even more preferably 2 hours or more and 20 hours or less.

[0109] The resulting target material can be processed into specified dimensions by grinding or other methods. It is then bonded to a substrate to obtain a sputtering target. The sputtering target thus obtained is suitable for the manufacture of oxide semiconductors. For example, the target material of this invention can be used in the manufacture of TFTs. Figure 1 An example of a TFT element 1 is schematically shown in the figure. The TFT element 1 shown in the figure is formed on one side of a glass substrate 10. A gate electrode 20 is disposed on one side of the glass substrate 10, and a gate insulating film 30 is formed to cover the gate electrode 20. A source electrode 60, a drain electrode 61, and a channel layer 40 are disposed on the gate insulating film 30. An etch barrier layer 50 is disposed on the channel layer 40. Furthermore, a protective layer 70 is disposed at the top. In the TFT element 1 having this structure, the target material of the present invention can be used, for example, to form the channel layer 40. In this case, the channel layer 40 is composed of an oxide containing indium (In), zinc (Zn), and an additive element (X), the atomic ratio of indium (In), zinc (Zn), and additive element (X) satisfying the above formula (1). In addition, formulas (2) and (3) above are also satisfied.

[0110] For oxide semiconductor devices formed from the target material of the present invention, from the viewpoint of improving the performance of the device, an amorphous structure is preferred.

[0111] Example

[0112] The present invention will now be described in more detail through embodiments. However, the scope of the present invention is not limited to these embodiments. Unless otherwise specified, "%" means "mass %".

[0113] [Example 1]

[0114] Zirconia spheres were used to measure the average particle size D. 50 In₂O₃ powder with a particle size of 0.6 μm and an average particle size D 50 ZnO powder with a particle size of 0.8 μm and an average particle size D 50 To prepare a mixed raw material powder, 0.6 μm Ta₂O₅ powder was dry-mixed by ball milling. The average particle size D of each powder was determined. 50 The particle size distribution was measured using a MicrotracBEL MT3300EXII particle size analyzer manufactured by MicrotracBEL Co., Ltd. Water was used as the solvent during the measurement, and the refractive index of the measured substance was 2.20. The mixing ratio of each powder was set such that the atomic ratios of In, Zn, and Ta reached the values ​​shown in Table 1 below.

[0115] Add 0.2% binder, 0.6% dispersant, and 20% water relative to the mixed raw material powder to a container, and then ball mill the mixture using zirconia balls to prepare a slurry.

[0116] The prepared slurry is poured into a metal mold sandwiched with a filter, and then the water in the slurry is drained to obtain a shaped body. This shaped body is then calcined to produce a sintered body. Calcination is carried out in an atmosphere with an oxygen concentration of 20% by volume at a calcination temperature of 1400°C, a calcination time of 8 hours, a heating rate of 50°C / hour, and a cooling rate of 50°C / hour. During calcination, the temperature is maintained at 1100°C for 6 hours to promote the formation of Zn₅In₂O₈.

[0117] The sintered body thus obtained was machined to obtain an oxide sintered body (target) with a width of 210 mm × length of 710 mm × thickness of 6 mm. The machining was performed using a #170 grinding stone.

[0118] For the obtained target material, the number of pores and the deviation of volume resistivity in the same plane and in the depth direction are calculated using the above method.

[0119] The deviations in the number of pores within the same surface calculated for any five points on the target material were 5.7%, 0.4%, 1.4%, 6.8%, and 2.2%, respectively. The deviations in volume resistivity within the same surface were 3.5%, 5.3%, 3.5%, 5.3%, and 3.5%, respectively.

[0120] The deviations in the number of pores in the depth direction calculated for any five points on the target material were 4.6%, 0.2%, 1.6%, 1.6%, and 1.6%, respectively. The deviations in the volume resistivity in the depth direction were 3.5%, 3.5%, 5.3%, 5.3%, and 3.5%, respectively.

[0121] The obtained target material was measured per 1000 μm using the following method. 2 The number of pores, arithmetic mean roughness Ra, maximum surface color difference ΔE*, and maximum color difference ΔE* in the depth direction. Per 1000 μm 2 The number of pores is 1.2. The arithmetic mean roughness Ra is 1.0 μm. The maximum color difference ΔE* on the surface is 1.1, and the maximum color difference ΔE* in the depth direction is 1.0.

[0122] [Examples 2 to 8]

[0123] In Example 1, the raw material powders were mixed in such a manner that the atomic ratios of In, Zn, and Ta were as shown in Table 1 below. Otherwise, the target material was obtained in the same manner as in Example 1.

[0124] [Comparative Example 1]

[0125] Average particle size D 50 In₂O₃ powder with a particle size of 0.6 μm and an average particle size D 50 Ta₂O₅ powder with a particle size of 0.6 μm was mixed with an atomic ratio of In to the sum of In and Ta elements [In / (In+Ta)] of 0.993. The mixture was fed into a wet ball mill and mixed and pulverized for 12 hours.

[0126] The resulting slurry was removed, filtered, and dried. The dried powder was then placed in a calcining furnace and heat-treated at 1000°C for 5 hours in an atmospheric atmosphere.

[0127] Through the above process, a mixed powder containing In and Ta elements is obtained.

[0128] Mix the average particle size D into the mixed powder 50 ZnO powder with a particle size of 0.8 μm was prepared to achieve an atomic ratio [In / (In+Zn)] of 0.698. The mixed powder was fed into a wet ball mill and mixed and pulverized for 24 hours to obtain a slurry of the raw material powder. The slurry was then filtered, dried, and granulated.

[0129] The obtained granules are pressed into shape and then subjected to a further application of 2000 kgf / cm². 2 The pressure is applied and the material is formed by cold isostatic pressing.

[0130] The shaped body was placed in a calcining furnace and calcined at 1400℃ for 12 hours under atmospheric pressure and with oxygen flowing in, to obtain a sintered body. The heating rate from room temperature to 400℃ was set to 0.5℃ / min, and the rate from 400℃ to 1400℃ was set to 1℃ / min. The cooling rate was set to 1℃ / min.

[0131] In addition, the target material was obtained in the same manner as in Example 1.

[0132] [Comparative Example 2]

[0133] In Example 1, Ta₂O₅ powder was not used. The raw material powders were mixed in such a way that the atomic ratio of In to Zn was as shown in Table 2 below. Otherwise, the target material was obtained in the same manner as in Example 1.

[0134] [Examples 9 to 13]

[0135] In Example 1, the raw material powders were mixed in such a manner that the atomic ratios of In, Zn, and Ta were as shown in Table 2 below. Otherwise, the target material was obtained in the same manner as in Example 1.

[0136] [Example 14]

[0137] In Example 1, the average particle size D was used. 50 0.7 μm Nb₂O₅ powder was used instead of Ta₂O₅ powder. The raw material powders were mixed in such a manner that the atomic ratios of In, Zn, and Nb were as shown in Table 2 below. Otherwise, the target material was obtained in the same manner as in Example 1.

[0138] [Example 15]

[0139] In Example 1, the average particle size D was used. 50 1.5 μm SrCO3 powder was used instead of Ta2O5 powder. The raw material powders were mixed in such a manner that the atomic ratios of In, Zn, and Sr were as shown in Table 2 below. Otherwise, the target material was obtained in the same manner as in Example 1.

[0140] [Example 16]

[0141] In Example 1, Ta₂O₅ powder, Nb₂O₅ powder, and SrCO₃ powder were mixed to replace Ta₂O₅ powder in such a way that the atomic ratios of In, Zn, Ta, Nb, and Sr were as shown in Table 2 below. The molar ratio of Ta, Nb, and Sr was set to Ta:Nb:Sr = 3:1:1. Otherwise, the target material was obtained in the same manner as in Example 1.

[0142] The proportions of each metal contained in the targets obtained in the examples and comparative examples were determined by ICP emission spectroscopy. It was confirmed that the atomic ratios of In, Zn, and Ta were the same as those of the raw materials shown in Table 1.

[0143] [Evaluation 1]

[0144] For the targets obtained in the examples and comparative examples, the relative density, flexural strength, volume resistivity, and Vickers hardness were measured using the following methods. For the targets obtained in the examples and comparative examples, XRD measurements were performed under the following conditions to confirm the presence or absence of the In2O3 and Zn3In2O6 phases. Furthermore, SEM observation was performed on the targets obtained in the examples and comparative examples, and the grain size of the In2O3 phase, the grain size of the Zn3In2O6 phase, the area fraction of the In2O3 phase, and the area fraction of the Zn3In2O6 phase were measured using the following methods. Furthermore, EDX was used to determine whether the In2O3 and Zn3In2O6 phases confirmed by SEM observation contained added elements (X). These results are shown in Tables 1 and 2 below. Figures 2 to 7 .

[0145] [Relative density]

[0146] The air mass of the target is divided by its volume (mass of the target in water / specific gravity of water at the measurement temperature), and then compared with the theoretical density ρ (g / cm³) based on the following formula (i). 3 The percentage value of ) is taken as the relative density (unit: %).

[0147] ρ={Σ((Ci / 100) / ρi)} -1 ···(i)

[0148] (In the formula, Ci represents the content (mass%) of the constituent substances of the target material, and ρi represents the density (g / cm³) of each constituent substance corresponding to Ci.) 3 ). )

[0149] In the present invention, the content (mass %) of the constituent substances of the target material is considered to include In2O3, ZnO, Ta2O5, Nb2O5, and SrO, for example, […].

[0150] C1: Mass % of In2O3 in the target material

[0151] ρ1: Density of In₂O₃ (7.18 g / cm³) 3 )

[0152] C2: % by mass of ZnO in the target material

[0153] ρ2: Density of ZnO (5.60 g / cm³) 3 )

[0154] C3: Mass % of Ta2O5 in the target material

[0155] ρ3: Density of Ta2O5 (8.73 g / cm³) 3 )

[0156] C4: Mass % of Nb2O5 in the target material

[0157] ρ4: Density of Nb₂O₅ (4.60 g / cm³) 3 )

[0158] C5: Mass % of SrO from the target material

[0159] ρ5: Density of SrO (4.70 g / cm³) 3 )

[0160] This is applied to equation (i), which allows us to calculate the theoretical density ρ.

[0161] The mass percentages of In2O3, ZnO, Ta2O5, Nb2O5, and SrO can be determined based on the analytical results of each element of the target material obtained by ICP emission spectroscopy.

[0162] [per 1000μm] 2 Number of pores

[0163] The target material was cut to obtain a cross-section, which was then graded and ground using sandpaper of #180, #400, #800, #1000, and #2000 grits. Finally, it was polished to achieve a mirror finish. The mirror-finished surface was then observed using SEM. Five fields of view were randomly selected at 400x magnification, covering a 218.7μm × 312.5μm area, to obtain the SEM images.

[0164] The obtained SEM images were analyzed using the image processing software ImageJ 1.51k (http: / / imageJ.nih.gov / ij / , provided by the National Institutes of Health (NIH)). The specific process is as follows.

[0165] For the obtained image, the pores are first depicted. After all depictions are completed, particle analysis (Analyze→Analyze Particles) is performed to obtain the number of pores and the area of ​​each pore. Then, the area equivalent circle diameter is calculated based on the area of ​​each pore. The number of pores is obtained by dividing the sum of the area equivalent circle diameters of 0.5 μm to 20 μm identified in the five fields of view by the total area of ​​the five fields of view, and then converted to a value per 1000 μm. 2 .

[0166] Flexural strength

[0167] The measurements were performed using an AutoGraph (registered trademark) AGS-500B manufactured by Shimadzu Corporation. The measurements were performed using a sample cut from the target material (over 36 mm in length, 4.0 mm in width, and 3.0 mm in thickness) according to the three-point bending strength determination method in JIS-R-1601 (Test Method for Bending Strength of Fine Ceramics).

[0168] [Volume Resistivity]

[0169] The Loresta HP MCP-T410 (registered trademark) manufactured by Mitsubishi Chemical was used for the measurement via the JIS standard DC four-probe method. The probes (tandem four-probe type ESP) were placed against the surface of the processed target material, and the measurement was performed in AUTO RANGE mode. The measurement positions were set at five locations: near the center of the target material and at the four corners. The arithmetic mean of the measured values ​​was taken as the volume resistivity of the target material.

[0170] Arithmetic mean roughness Ra

[0171] The surface roughness was measured using a surface roughness measuring instrument (SJ-210 / Mitutoyo Co., Ltd.). Measurements were taken at five points on the sputtering surface of the target, and the arithmetic mean was taken as the arithmetic mean roughness Ra of the target.

[0172] [Maximum color difference]

[0173] The in-surface color difference ΔE* is measured and evaluated as follows: Using a colorimeter (Konica Minolta, CR-300 colorimeter), measurements are taken at 50mm intervals along the x and y axes on the surface of the machined target material. The L*, a*, and b* values ​​at each measured point are evaluated using the CIE 1976 L*a*b* color space. Then, based on the differences ΔL*, Δa*, and Δb* between the L*, a*, and b* values ​​of two points measured at each point, the color difference ΔE* is calculated using the combination of all two points and the following formula (ii). The maximum value of the calculated multiple color differences ΔE* is taken as the maximum in-surface color difference ΔE*.

[0174] ΔE*=((ΔL*) 2 +(Δa*) 2 +(Δb*) 2 ) 1 / 2 ··(ii)

[0175] Furthermore, the maximum color difference ΔE* in the depth direction is measured and evaluated as follows: A 1mm cut is made at any position on the machined target material, and measurements are taken at various depths up to the center of the target material using a colorimeter. The L*, a*, and b* values ​​at each measured point are evaluated using the CIE 1976 L*a*b* color space. Then, based on the differences ΔL*, Δa*, and Δb* between the L*, a*, and b* values ​​of two points, the color difference ΔE* is calculated using all combinations of the two points. The maximum value of the calculated color differences ΔE* is taken as the maximum color difference ΔE* in the depth direction.

[0176] [Vickers Hardness]

[0177] The Vickers hardness was measured using a Vickers MHT-1 hardness tester from Isozawa Corporation. The target material was cut to obtain a cross-section, which was then graded and ground using sandpaper of grits #180, #400, #800, #1000, and #2000. Finally, it was polished to a mirror finish and used as the testing surface. Additionally, the opposite side, viewed from the testing surface, was ground using the same grit sandpaper in a parallel manner to the testing surface, to obtain a test piece. Using this test piece, the Vickers hardness was measured under a load of 1 kgf according to the hardness testing method in JIS-R-1610:2003 (Test Method for Hardness of Fine Ceramics). Measurements were taken at 10 different locations on one test piece, and the arithmetic mean was taken as the Vickers hardness of the target material. Furthermore, the standard deviation of the Vickers hardness was calculated based on the obtained measurement values.

[0178] [XRD Measurement Conditions]

[0179] SmartLab (registered trademark) of Rigaku Co., Ltd. was used. The measurement conditions are as follows. The XRD measurement results for the target material obtained in Example 1 are shown below. Figure 2 .

[0180] • Source: CuKα rays

[0181] • Tube voltage: 40kV

[0182] Tube current: 30mA

[0183] • Scanning speed: 5 degrees / minute

[0184] Stride length: 0.02 degrees

[0185] • Scanning range: 2θ = 5 degrees to 80 degrees

[0186] [Grain size of In2O3 phase, grain size of Zn3In2O6 phase, area fraction of In2O3 phase and area fraction of Zn3In2O6 phase]

[0187] The surface of the target material was observed using a Hitachi SU3500 scanning electron microscope manufactured with advanced technology, and the structural phase or crystal shape of the crystals was evaluated.

[0188] Specifically, the target material was cut to obtain a cross-section, which was then graded and ground using sandpaper of #180, #400, #800, #1000, and #2000 grits. Finally, it was polished to achieve a mirror finish. The mirror-finished surface was then observed using SEM. For the evaluation of crystal morphology, ten fields of view were randomly selected from 1000x magnification, 87.5μm × 125μm range (BSE-COMP image), resulting in SEM images.

[0189] The obtained SEM images were analyzed using the image processing software ImageJ 1.51k (http: / / imageJ.nih.gov / ij / , provided by the National Institutes of Health (NIH)). The specific process is as follows.

[0190] The sample used for SEM image acquisition was subjected to thermal etching at 1100℃ for 1 hour, and the results were obtained through SEM observation. Figure 3 The image shown depicts the grain boundaries. For the obtained image, first along the In₂O₃ phase (…). Figure 3 The grain boundaries of the whitish region A were depicted. After all depictions were completed, particle analysis (Analyze→AnalyzeParticles) was performed to obtain the area of ​​each particle. Then, the area equivalent circle diameter was calculated based on the area of ​​each particle. The arithmetic mean of the area equivalent circle diameters of all particles calculated in 10 fields of view was taken as the grain size of the In2O3 phase. Next, along the Zn3In2O6 phase ( Figure 3 The grain boundaries of region B, which appears blackish, were depicted, and the area of ​​each grain was obtained through the same analysis. Based on this, the area equivalent circle diameter was calculated. The arithmetic mean of the area equivalent circle diameters of all grains calculated from 10 fields of view was taken as the grain size of the Zn3In2O6 phase.

[0191] Furthermore, by performing particle analysis on BSE-COMP images without grain boundaries before thermal etching, the ratio of the In2O3 phase area in the total area was calculated. The arithmetic mean of all particles calculated in 10 fields of view was taken as the In2O3 phase area ratio. Additionally, the Zn3In2O6 phase area ratio was calculated by subtracting the In2O3 phase area ratio from 100.

[0192] It should be noted that, Figure 4 and Figure 6 yes Figure 3 A magnified image.

[0193] [The presence or absence of element (X) and its quantitative determination]

[0194] The Octane Elite Plus energy-dispersive X-ray analyzer manufactured by EDAX was used to obtain spectral information of the In2O3 and Zn3In2O6 phases identified in the aforementioned SEM observations based on point analysis at arbitrary locations, to confirm the presence of added elements (X). The results are presented below. Figure 5 and Figure 7 .

[0195] [Evaluation 2]

[0196] The targets used in the examples and comparative examples were fabricated by photolithography. Figure 1 The TFT element 1 shown is shown.

[0197] In the fabrication of TFT element 1, firstly, a Mo thin film is formed on a glass substrate (NEC-10, manufactured by NEC Glass Co., Ltd.) 10 as a gate electrode 20 using a DC sputtering apparatus. Next, a SiOx thin film is formed as a gate insulating film 30 under the following conditions.

[0198] Film formation apparatus: Plasma CVD apparatus, manufactured by SAMCO Corporation, PD-2202L

[0199] Film-forming gas: SiH4 / N2O / N2 mixed gas

[0200] Film-forming pressure: 110 Pa

[0201] Substrate temperature: 250~400℃

[0202] Next, using the target material obtained in the examples and comparative examples, the channel layer 40 was sputtered to form a film with a thickness of about 10 to 50 nm under the following conditions.

[0203] • Film deposition apparatus: DC sputtering apparatus, manufactured by Tokki Corporation, SML-464

[0204] • Ultimate vacuum degree: less than 1×10 -4 Pa

[0205] Sputtering gas: Ar / O2 mixture

[0206] Sputtering gas pressure: 0.4 Pa

[0207] O2 partial pressure: 50%

[0208] ·Substrate temperature: room temperature

[0209] Sputtering power: 3W / cm 2

[0210] Next, a SiOx thin film is formed using the aforementioned plasma CVD apparatus to serve as an etch barrier layer 50. Then, a Mo thin film is formed using the aforementioned DC sputtering apparatus to serve as a source electrode 60 and a drain electrode 61. A SiOx thin film is formed using the aforementioned plasma CVD apparatus to serve as a protective layer 70. Finally, a heat treatment is performed at 350°C.

[0211] The transfer characteristics of the TFT element 1 obtained in this way were measured at a leakage voltage Vd = 5V. The measured transfer characteristics are the field-effect mobility μ (cm²). 2 The values ​​of V / Vs, SS (subthreshold swing) (V / dec), and threshold voltage Vth (V) were measured. The transfer characteristics were measured using a Semiconductor Device Analyzer B1500A manufactured by Agilent Technologies, Inc. The measurement results are shown in Tables 1 and 2. It should be noted that although not shown in the tables, the inventors confirmed through XRD measurements that the channel layer 40 of the TFT element 1 obtained in each embodiment is an amorphous structure.

[0212] Field-effect mobility refers to the channel mobility in the saturation region of a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) based on the change in leakage current relative to the gate voltage that keeps the leakage voltage constant. A higher value indicates better transfer characteristics.

[0213] The SS value refers to the gate voltage required to increase the leakage current by one order of magnitude near the threshold voltage. The smaller the value, the better the transfer characteristics.

[0214] The threshold voltage refers to the voltage at which the leakage current reaches 1 nA when a positive voltage is applied to the drain electrode and either a positive or negative voltage is applied to the gate electrode. Preferably, the value is close to 0V. More specifically, it is further preferably -2V or higher, more preferably -1V or higher, and even more preferably 0V or higher. Additionally, it is further preferably 3V or lower, more preferably 2V or lower, and even more preferably 1V or lower. Specifically, it is further preferably -2V or higher and 3V or lower, more preferably -1V or higher and 2V or lower, and even more preferably 0V or higher and 1V or lower.

[0215] [Table 1]

[0216]

[0217] [Table 2]

[0218]

[0219] As shown in Tables 1 and 2, the TFT elements fabricated using the targets obtained in each embodiment exhibit excellent transfer characteristics. (Per 1000 μm) 2 The number of pores, the deviation of the volume resistivity, the arithmetic mean roughness Ra, the maximum color difference, and the In / Zn atomic ratio are not shown in Tables 1 and 2, but the targets obtained in Examples 2 to 16 yielded the same results as in Example 1.

[0220] Moreover, from Figure 2 The results show that the target material obtained in Example 1 contains both In2O3 and Zn3In2O6 phases. Although not illustrated, the targets obtained in Examples 2 to 16 also yielded the same results.

[0221] Moreover, from Figure 5 and Figure 7 The results show that the In2O3 phase and Zn3In2O6 phase contained in the target material obtained in Example 1 both contain Ta. Although not illustrated, the same results were obtained for the targets obtained in Examples 2 to 16.

[0222] [Evaluation 3]

[0223] For the targets obtained in Example 1 and Comparative Example 1, the dispersion rates of the In2O3 phase and the Zn3In2O6 phase were determined using the method described above. The results are shown in Table 3 below. Figure 8 (a) and Figure 8 (b)

[0224] [Table 3]

[0225]

[0226] from Figure 8 As shown in (a), the In2O3 and Zn3In2O6 phases in the target material obtained in Example 1 are homogeneously dispersed. As shown in Table 3, in Example 1, the dispersion rate at position 16 is the highest at 3.3%, confirming that the In2O3 and Zn3In2O6 phases are homogeneously dispersed.

[0227] In contrast, from Figure 8 As shown in (b), the In2O3 phase and Zn3In2O6 phase in the target material obtained in Comparative Example 1 are heterogeneously dispersed.

[0228] It should be noted that, although not shown in the table, the inventors have confirmed that, for the targets obtained in Examples 2 to 16, the dispersion at point 16 is at most less than 10%.

[0229] Industrial availability

[0230] As detailed above, by using the sputtering target of the present invention, particulate matter can be suppressed, and cracking caused by abnormal discharge can be suppressed. As a result, TFTs with high field-effect mobility can be easily manufactured.

Claims

1. A sputtering target, It is composed of an oxide containing indium (In), zinc (Zn), and added element X. The added element X consists of at least one element selected from tantalum (Ta), strontium (Sr), and niobium (Nb). The atomic ratios of each element satisfy equations (1) to (4), where X is the sum of the contents of the added elements. 0.4≤(In+X) / (In+Zn+X)≤0.75 (1) 0.25≤Zn / (In+Zn+X)≤0.6 (2) 0.001≤X / (In+Zn+X)≤0.015 (3) 0.992≤In / (In+X)≤0.996 (4) The flexural strength is above 100MPa. The relative density is over 95%.

2. The sputtering target according to claim 1, wherein, Add element X as tantalum (Ta).

3. The sputtering target according to claim 1 or 2 has a volume resistivity of less than 100 mΩ·cm at 25°C.

4. The sputtering target according to claim 1 or 2, comprising an In2O3 phase and a Zn3In2O6 phase.

5. The sputtering target according to claim 4, wherein, Both the In2O3 phase and the Zn3In2O6 phase contain the added element X.

6. The sputtering target according to claim 4, wherein, The grain size of the In₂O₃ phase is greater than 0.1 μm and less than 3.0 μm. The grain size of the Zn3In2O6 phase is greater than 0.1 μm and less than 3.9 μm.

7. The sputtering target according to claim 1 or 2, wherein, The standard deviation of Vickers hardness measured according to JIS-R-1610:2003 is less than 50.

8. The sputtering target according to claim 1 or 2, wherein, The maximum value of the dispersion of the sputtering target, as determined by the following method, is less than 10%. The method for determining the dispersion rate is as follows: Based on a range of 200x magnification and 437.5μm×625μm randomly selected from the sputtering target, the In / Zn atomic ratio of the entire field of view is obtained by EDX. The field of view is divided into equal vertical × horizontal 4 sections to obtain the In / Zn atomic ratio in each section. The absolute value of the difference between the In / Zn atomic ratio in each section and the In / Zn atomic ratio of the entire field of view is divided by the In / Zn atomic ratio of the entire field of view and then multiplied by 100. The obtained value is defined as the dispersion rate of each section, and the maximum value is defined as the maximum dispersion rate.

9. An oxide semiconductor, which is an oxide semiconductor formed using any one of the sputtering targets according to claims 1 to 8. The oxide semiconductor is composed of an oxide containing indium (In), zinc (Zn), and additive element X. The added element X consists of at least one element selected from tantalum (Ta), strontium (Sr), and niobium (Nb). The atomic ratios of each element satisfy equations (1) to (4), where X is the sum of the contents of the added elements. 0.4≤(In+X) / (In+Zn+X)≤0.75 (1) 0.25≤Zn / (In+Zn+X)≤0.6 (2) 0.001≤X / (In+Zn+X)≤0.015 (3) 0.992≤In / (In+X)≤0.996 (4).

10. A thin-film transistor having an oxide semiconductor and a field-effect mobility of 45 cm⁻¹ 2 / Vs or more, The oxide semiconductor is composed of an oxide containing indium (In), zinc (Zn), and additive element X. The added element X consists of at least one element selected from tantalum (Ta), strontium (Sr), and niobium (Nb). The atomic ratios of each element satisfy equations (1) to (4), where X is the sum of the contents of the added elements. 0.4≤(In+X) / (In+Zn+X)≤0.75 (1) 0.25≤Zn / (In+Zn+X)≤0.6 (2) 0.001≤X / (In+Zn+X)≤0.015 (3) 0.992≤In / (In+X)≤0.996 (4).

11. The thin-film transistor of claim 10, wherein, The oxide semiconductor has an amorphous structure.

12. The thin-film transistor according to claim 10 or 11, wherein the field-effect mobility is 70 cm⁻¹. 2 / Vs and above.

13. The thin-film transistor according to claim 10 or 11, wherein the threshold voltage is above -2V and below 3V.

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