JP7422269B2 - Sputtering target material and method for producing oxide semiconductor - Google Patents

Description

The present invention relates to sputtering target materials. The present invention also relates to a method for manufacturing an oxide semiconductor using the sputtering target material.

In the technical field of thin film transistors (hereinafter also referred to as "TFT") used in flat panel displays (hereinafter also referred to as "FPD"), In-Ga is replacing the conventional amorphous silicon as FPDs become more sophisticated. Oxide semiconductors represented by -Zn composite oxide (hereinafter also referred to as "IGZO") are attracting attention and are being put into practical use. IGZO has the advantage of exhibiting high field effect mobility and low leakage current. In recent years, as FPDs have become more sophisticated, materials have been proposed that exhibit field-effect mobility even higher than that of IGZO.

For example, Patent Documents 1 and 2 propose an oxide semiconductor for a TFT using an In-Zn-X composite oxide consisting of an indium (In) element, a zinc (Zn) element, and an arbitrary element X. According to this document, this oxide semiconductor is formed by sputtering using a target material made of In--Zn--X composite oxide.

Furthermore, flexible displays, which are one type of FPD, have been attracting attention in recent years as they can be used in a wide range of applications. One of the important members constituting a flexible display is a flexible base material, and among them, plastic films are suitable because they are thin, lightweight, and have excellent flexibility. However, plastic films have problems with heat resistance. In order to form a TFT on a substrate, post-annealing treatment is required to improve electrical properties after film formation, but when using a substrate with low heat resistance such as a plastic film, post-annealing treatment is performed at a low temperature. It is necessary to do so. However, when a film made of IGZO is post-annealed at a low temperature, the resistance of the film decreases, making it difficult to function as a semiconductor.

US2013/270109A1 US2014/102892A1

In the techniques described in Patent Documents 1 and 2, the target material is manufactured by a powder sintering method. However, the target material manufactured by the powder sintering method generally has a low relative density, and due to this, abnormal discharge is likely to occur, and cracks are likely to occur in the target material during abnormal discharge. As a result, it may be difficult to manufacture high-performance TFTs.

Furthermore, in order to form a TFT on a substrate with low heat resistance such as a plastic film, it is necessary to perform post-annealing treatment after film formation to improve electrical characteristics. However, for example, if a film made of IGZO is post-annealed at a low temperature of less than 250° C., the resistance of the film decreases, making it difficult to function as a semiconductor.
Therefore, an object of the present invention is to provide a sputtering target material and a method for manufacturing an oxide semiconductor that can eliminate the drawbacks of the prior art described above.

The present inventors conducted extensive studies to solve the above problems. As a result, in an oxide containing indium (In) element and zinc (Zn) element as main elements, the content of zinc (Zn) is increased, a trace amount of tantalum (Ta) element is included, and the relative density is lowered. It has been found that by increasing the temperature, the abnormal discharge described above can be suppressed, and an oxide semiconductor that can function as a semiconductor can be obtained even by post-annealing treatment performed at a low temperature of less than 250°C.

That is, the present invention is composed of an oxide containing an indium (In) element, a zinc (Zn) element, and a tantalum (Ta) element,
The atomic ratio of each element satisfies all of formulas (1) to (3),
0.1≦(In+Ta)/(In+Zn+Ta)<0.4 (1)
0.6<Zn/(In+Zn+Ta)≦0.9 (2)
0.001≦Ta/(In+Zn+Ta)<0.014 (3)
A sputtering target material having a relative density of 95% or more is provided.

The present invention also provides a method for manufacturing an oxide semiconductor using the above sputtering target material, comprising:
The oxide semiconductor is
It is composed of an oxide containing indium (In) element, zinc (Zn) element and tantalum (Ta) element,
Method for manufacturing an oxide semiconductor manufactured such that the atomic ratio of each element satisfies all of formulas (1) to (3) 0.1≦(In+Ta)/(In+Zn+Ta)<0.4 (1)
0.6<Zn/(In+Zn+Ta)≦0.9 (2)
0.001≦Ta/(In+Zn+Ta)<0.014 (3)
It provides:

FIG. 1 is a schematic diagram showing the structure of a thin film transistor manufactured using the sputtering target material of the present invention.

The present invention will be described below based on its preferred embodiments. The present invention relates to a sputtering target material (hereinafter also referred to as "target material"). The target material of the present invention is composed of an oxide containing an indium (In) element, a zinc (Zn) element, and a tantalum (Ta) element. The target material of the present invention contains In, Zn, and Ta as its constituent metal elements, but in addition to these elements, trace amounts may be intentionally or unavoidably contained within the range that does not impair the effects of the present invention. May contain elements. Examples of trace elements include elements contained in organic additives to be described later, and media raw materials such as ball mills that are mixed in during the production of the target material. 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, Examples include Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Nb, Sr, and Pb. It is preferable that their content is usually 100 mass ppm (hereinafter also referred to as "ppm") or less, based on the total mass of oxides containing In, Zn, and Ta contained in the target material of the present invention, and more preferably Preferably it is 80 ppm or less, more preferably 50 ppm or less. 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 total mass also includes the mass of the trace elements.

The target material of the present invention is preferably composed of a sintered body containing the above-mentioned oxide. There is no particular restriction on the shape of the sintered body and sputtering target material, and conventionally known shapes, such as a flat plate shape and a cylindrical shape, can be adopted.

In the target material of the present invention, the atomic ratio of the metal elements constituting the target material, that is, In, Zn, and Ta, is within a specific range, since this improves the performance of the oxide semiconductor device formed from the target material. preferable.
Specifically, it is preferable that In and Ta satisfy the atomic ratio expressed by the following formula (1).
0.1≦(In+Ta)/(In+Zn+Ta)<0.4 (1)
Regarding Zn, it is preferable that the atomic ratio expressed by the following formula (2) is satisfied.
0.6<Zn/(In+Zn+Ta)≦0.9 (2)
Regarding Ta, it is preferable that the atomic ratio expressed by the following formula (3) is satisfied.
0.001≦Ta/(In+Zn+Ta)<0.014 (3)

Since the atomic ratio of In, Zn, and Ta satisfies all of the above formulas (1) to (3), a semiconductor element having an oxide thin film formed by sputtering using the target material of the present invention can be heated to temperatures below 250°C. Post-annealing performed at a low temperature also results in high field-effect mobility, low leakage current, and a threshold voltage close to 0V. From the viewpoint of making these advantages even more remarkable, it is more preferable that In and Ta satisfy the following formulas (1-2) to (1-5).
0.12≦(In+Ta)/(In+Zn+Ta)≦0.38 (1-2)
0.14≦(In+Ta)/(In+Zn+Ta)≦0.35 (1-3)
0.16≦(In+Ta)/(In+Zn+Ta)≦0.31 (1-4)
0.20≦(In+Ta)/(In+Zn+Ta)≦0.30 (1-5)

From the same viewpoint as above, it is more preferable that Zn satisfies the following formulas (2-2) to (2-5), and Ta satisfies the following formulas (3-2) to (3-5). More preferably.

0.62≦Zn/(In+Zn+Ta)≦0.88 (2-2)
0.65≦Zn/(In+Zn+Ta)≦0.86 (2-3)
0.69≦Zn/(In+Zn+Ta)≦0.84 (2-4)
0.70≦Zn/(In+Zn+Ta)≦0.80 (2-5)
0.0015≦Ta/(In+Zn+Ta)≦0.013 (3-2)
0.002<Ta/(In+Zn+Ta)≦0.012 (3-3)
0.0025≦Ta/(In+Zn+Ta)≦0.010 (3-4)
0.003≦Ta/(In+Zn+Ta)≦0.009 (3-5)

The proportion of each metal contained in the target material of the present invention is measured, for example, by ICP emission spectrometry.

In addition to the atomic ratio of In, Zn, and Ta, the target material of the present invention is also characterized by a high relative density. Specifically, the target material of the present invention preferably exhibits a high relative density of 95% or more. By exhibiting such a high relative density, it is possible to suppress the generation of particles when performing sputtering using the target material of the present invention, which is preferable. From this point of view, the relative density of the target material of the present invention is more preferably 97% or more, even more preferably 98% or more, even more preferably 99% or more, and even more preferably 100% or more. It is particularly preferable that it is more than 100%. The target material of the present invention having such a relative density is suitably manufactured by the method described below. Relative density is measured according to the Archimedes method. A specific measuring method will be explained in detail in the examples described later.

The target material of the invention is also characterized by high strength. Specifically, the target material of the present invention preferably exhibits a high bending strength of 100 MPa or more. By exhibiting such high flexural strength, when performing sputtering using the target material of the present invention, even if abnormal discharge occurs unintentionally during sputtering, cracks are less likely to occur in the target material, which is preferable. From this viewpoint, the target material of the present invention preferably has a bending strength of 105 MPa or more, and even more preferably 110 MPa or more. Note that the upper limit of the bending strength is preferably 300 MPa, for example, from the viewpoint of the toughness of the target material. The target material of the present invention having such a bending strength is suitably manufactured by the method described below. The bending strength is measured in accordance with JIS R1601. A specific measuring method will be explained in detail in the examples described later.

The target material of the invention is also characterized by a low bulk resistivity. A low bulk resistivity is advantageous in that it allows DC sputtering using the target material. From this point of view, the target material of the present invention preferably has a bulk resistivity of 100 mΩ·cm or less at 25°C, more preferably 50 mΩ·cm or less, even more preferably 30 mΩ·cm or less, It is more preferably 20 mΩ·cm or less, even more preferably 15 mΩ·cm or less, particularly preferably 12 mΩ·cm or less, particularly preferably 10 mΩ·cm or less, and particularly preferably 5 mΩ·cm or less. It is particularly preferred that there be. Note that the lower the bulk resistivity is, the more preferable it is, and the lower limit is not particularly determined, but is usually 0.01 mΩ·cm or more. The target material of the present invention having such a bulk resistivity is suitably manufactured by the method described below. Bulk resistivity is measured by the DC four-probe method. A specific measuring method will be explained in detail in the examples described later.

As described above, the target material of the present invention is made of an oxide containing In, Zn, and Ta. This oxide can be an oxide of In, an oxide of Zn or an oxide of Ta. Alternatively, this oxide may be a composite oxide of two or more arbitrary elements selected from the group consisting of In, Zn, and Ta. Specific examples of composite oxides include, but are not limited to, In-Zn composite oxide, Zn-Ta composite oxide, In-Ta composite oxide, In-Zn-Ta composite oxide, etc. It's not a thing.

In the target material of the present invention, it is preferable that the In/Zn atomic ratio in the same plane is homogeneous in cross-sectional observation using a SEM at a magnification of 200 times. It is preferable that the In/Zn atomic ratio be homogeneous because when a thin film is formed by sputtering, the composition will be uniform and the film properties will not change.

The homogeneity state of the In/Zn atomic ratio is evaluated by energy dispersive X-ray spectroscopy (hereinafter also referred to as "EDX"). The In/Zn atomic ratio of the entire field of view is obtained by EDX from a range of 437.5 μm x 625 μm randomly selected at a magnification of 200 times in the cross section of the target material. Subsequently, the same field of view is equally divided into 4 vertically x 4 horizontally, and the In/Zn atomic ratio in each divided field of view is obtained. The absolute value of the difference between the In/Zn atomic ratio in each divided field of view and the In/Zn atomic ratio in the entire field of view is divided by the In/Zn atomic ratio in the entire field of view, and the value multiplied by 100 is called the dispersion rate (%). The degree of homogeneity of the In/Zn atomic ratio is evaluated based on the magnitude of the dispersion rate. The closer the dispersion rate is to zero, the more homogeneous the In/Zn atomic ratio is. The maximum value of the dispersion rate at 16 locations is preferably 10% or less, more preferably 8% or less, even more preferably 6% or less, even more preferably 4% or less, It is particularly preferably 3% or less, particularly preferably 2% or less.

Next, a preferred method for manufacturing the target material of the present invention will be described. In this manufacturing method, oxide powder, which is a raw material for a target material, is molded into a predetermined shape to obtain a molded body, and this molded body is fired to obtain a target material made of a sintered body. In order to obtain the molded body, methods known so far in the technical field can be employed. In particular, it is preferable to employ the cast molding method or the CIP molding method because a dense target material can be manufactured.

The casting method is also called the slip casting method. To carry out the cast molding method, first, a slurry containing raw material powder and organic additives is prepared using a dispersion medium.

As the raw material powder, it is preferable to use oxide powder or hydroxide powder. As the oxide powder, In oxide powder, Zn oxide powder, and Ta oxide powder are used. For example, In ₂ O ₃ can be used as the In oxide. For example, ZnO can be used as the Zn oxide. For example, Ta ₂ O ₅ can be used as the Ta oxide powder.

The amounts of In oxide powder, Zn oxide powder, and Ta oxide powder used are preferably adjusted so that the atomic ratio of In, Zn, and Ta in the intended target material satisfies the above range. .

The particle size of the raw material powder is preferably 0.1 μm or more and 1.5 μm or less, expressed as volume cumulative particle size D ₅₀ at 50 volume % cumulative volume measured by laser diffraction scattering particle size distribution measurement method. By using a raw material powder having a particle size within this range, a target material with a high relative density can be easily obtained.

The above-mentioned organic additives are substances used to suitably adjust the properties of slurries and molded bodies. Examples of organic additives include binders, dispersants, and plasticizers. A binder is added to increase the strength of the molded body. As the binder, it is possible to use a binder that is normally used when obtaining a molded body in a known powder sintering method. Examples of the binder include polyvinyl alcohol. The dispersant is added to improve the dispersibility of the raw material powder in the slurry. Examples of the dispersant include polycarboxylic acid dispersants and polyacrylic acid dispersants. A plasticizer is added to increase the plasticity of the molded article. Examples of the plasticizer include polyethylene glycol (PEG) and ethylene glycol (EG).

There are no particular restrictions on the dispersion medium used when producing the slurry containing the raw material powder and organic additives, and the dispersion medium can be appropriately selected from water and water-soluble organic solvents such as alcohol depending on the purpose. can. There are no particular limitations on the method for producing the slurry containing the raw material powder and organic additives, and for example, a method may be used in which the raw material powder, organic additive, dispersion medium, and zirconia balls are placed in a pot and mixed in a ball mill.

Once the slurry is obtained in this way, this slurry is poured into a mold, and then the dispersion medium is removed to produce 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.

On the other hand, in the CIP molding method, a dry powder is obtained by spray drying a slurry similar to the slurry used in the cast molding method. The obtained dry powder is filled into a mold and subjected to CIP molding.

Once the molded body is obtained in this way, it is then fired. As described above, in this manufacturing method, firing is performed after all the raw material powders are mixed. In contrast, in the conventional technology, for example, the technology described in Patent Document 2, firing is performed after mixing In ₂ O ₃ powder and Ta ₂ O ₅ powder, and then the obtained fired powder and ZnO powder are mixed. The mixture is then mixed and fired again. In this method, the particles constituting the powder become coarse particles due to the prior firing, making it difficult to obtain a target material with a high relative density.

On the other hand, in this manufacturing method, preferably, the In oxide powder, Zn oxide powder, and Ta oxide powder are mixed at room temperature, molded, and then fired, so that the powder has a high relative density. Dense target material can be easily obtained. Firing of the compact can generally be carried out in an oxygen-containing atmosphere. In particular, it is convenient to perform firing in an air atmosphere. The firing temperature is preferably 1200°C or more and 1600°C or less, more preferably 1300°C or more and 1500°C or less, and even more preferably 1350°C or more and 1450°C or less. The firing time is preferably 1 hour or more and 100 hours or less, more preferably 2 hours or more and 50 hours or less, and even more preferably 3 hours or more and 30 hours or less. The temperature increase rate is preferably 5°C/hour or more and 500°C/hour or less, more preferably 10°C/hour or more and 200°C/hour or less, and 20°C/hour or more and 100°C/hour or less. is more preferable.

When firing a compact, maintaining a temperature at which a complex oxide of In and Zn, for example, a phase of Zn ₅ In ₂ O ₈ is generated during the firing process, for a certain period of time promotes sintering and creates a dense target material. Preferable from the viewpoint of production. When the Zn ₅ In ₂ O ₈ phase is generated, volume diffusion progresses and densification is promoted, so it is preferable to reliably generate the Zn ₅ In ₂ O ₈ phase. From this point of view, in the heating process of firing, it is preferable to maintain the temperature in the range of 1000° C. or more and 1250° C. or less for a certain period of time, and it is more preferable to maintain the temperature in the range of 1050° C. or more and 1200° C. or less for a certain period of time. The temperature to be maintained is not necessarily limited to the temperature at one specific point, but may be within a temperature range having a certain degree of width. Specifically, when T (°C) is a specific temperature selected from the range of 1000°C to 1250°C, as long as it is within the range of 1000°C to 1250°C, for example T ± 10°C. It is preferably T±5°C, more preferably T±3°C, and still more preferably T±1°C. The time for maintaining this temperature range is preferably 1 hour or more and 40 hours or less, more preferably 2 hours or more and 20 hours or less.

The target material obtained in this way can be processed into predetermined dimensions by grinding or the like. A sputtering target can be obtained by bonding this to a base material. The sputtering target obtained in this way is suitably used for manufacturing oxide semiconductors. For example, the target material of the present invention can be used for manufacturing TFTs. FIG. 1 schematically shows one embodiment of a TFT element.

The TFT element 1 shown in the figure is formed on one surface of a base material 10. A channel layer 20, a source electrode 30, and a drain electrode 31 are arranged on one surface of the base material 10, and a gate insulating film 40 is formed to cover them. A gate electrode 50 is arranged on the gate insulating film 40. A protective layer 60 is disposed at the top. In the TFT element 1 having this structure, for example, the channel layer 20 is composed of an oxide semiconductor layer. In the TFT element 1 having this structure, for example, the channel layer 20 can be formed using the target material of the present invention. In that case, the channel layer 20 is made of an oxide containing indium (In), zinc (Zn), and tantalum (Ta). The atomic ratio of Ta) satisfies the above-mentioned formula (1). Moreover, the above-mentioned equations (2) and (3) are satisfied.
The oxygen concentration when forming the channel layer 20 is, for example, preferably 10 volume% or more and 40 volume% or less, more preferably 12 volume% or more and 37 volume% or less, and 15 volume% or more and 35 volume% or less. It is more preferable that it is the following.

After the oxide semiconductor layer is formed by a sputtering method, it is preferable to perform an annealing treatment on the oxide semiconductor layer. The purpose of the annealing treatment is to impart desired performance to the oxide semiconductor layer. For this purpose, the temperature of the annealing treatment is preferably 20°C or higher and lower than 250°C, more preferably 20°C or higher and 200°C or lower, even more preferably 20°C or higher and 180°C or lower, and even more preferably 20°C or higher and lower than 200°C. It is even more preferable that the temperature is 150° C. or higher and 150° C. or lower. Further, the temperature of the annealing treatment may be 50°C or higher, or may be 80°C or higher. The time for the annealing treatment is preferably 1 minute or more and 180 minutes or less, more preferably 2 minutes or more and 120 minutes or less, and even more preferably 3 minutes or more and 60 minutes or less. The annealing atmosphere is preferably an oxygen atmosphere containing atmospheric pressure.
Annealing treatment for the oxide semiconductor layer can be performed immediately after the oxide semiconductor layer is formed. Alternatively, after forming the oxide semiconductor layer, one or more other layers may be formed, and then annealing treatment may be performed.

It is preferable that the oxide semiconductor device formed from the target material of the present invention has an amorphous structure from the viewpoint of improving the performance of the device.

Note that the large value of field effect mobility of the oxide semiconductor element formed from the target material is due to the improvement in the transfer characteristics of the TFT element, which is an oxide semiconductor element. preferred. In detail, the field effect mobility (cm ² /Vs) of a TFT including an oxide semiconductor element formed from a target material is preferably 1 cm ² /Vs or more, and preferably 2 cm ² /Vs or more. is more preferably 3 cm ² /Vs or more, even more preferably 5 cm ² /Vs or more, even more preferably 10 cm ² /Vs or more, and even more preferably 20 cm ² /Vs or more. is even more preferable, and particularly preferably 30 cm ² /Vs or more. The larger the value of the field effect mobility, the more preferable it is from the standpoint of improving the functionality of the FPD, but if the field effect mobility is as high as about 200 cm ² /Vs, a sufficiently satisfactory level of performance can be obtained.

Hereinafter, the present invention will be explained in more detail with reference to Examples. However, the scope of the invention is not limited to such examples.

[Example 1]
In ₂ O ₃ powder whose average particle size D ₅₀ is 0.6 μm, ZnO powder whose average particle size D ₅₀ is 0.8 μm, and Ta ₂ O ₅ powder whose average particle size D ₅₀ is 0.6 μm. were dry mixed using a zirconia ball in a ball mill to prepare a mixed raw material powder. The average particle diameter _D50 of each powder was measured using a particle size distribution measuring device MT3300EXII manufactured by Micro Track Bell Co., Ltd. During the measurement, water was used as a solvent and the refractive index of the substance to be measured was 2.20. The mixing ratio of each powder was such that the atomic ratio of In, Zn, and Ta was as shown in Table 1 below.

In the pot in which the mixed raw material powder was prepared, 0.2% by mass of binder with respect to the mixed raw material powder, 0.6% by mass of a dispersant with respect to the mixed raw material powder, and 20% by mass with respect to the mixed raw material powder. of water and mixed in a ball mill using a zirconia ball to prepare a slurry.

The prepared slurry was poured into a metal mold sandwiching a filter, and then water in the slurry was drained to obtain a molded body. This molded body was fired to produce a sintered body. The firing was performed in an atmosphere having an oxygen concentration of 20% by volume at a firing temperature of 1400°C, a firing time of 8 hours, a temperature increase rate of 50°C/hour, and a temperature fall rate of 50°C/hour. During the firing, the temperature was maintained at 1100° C. for 6 hours to promote the formation of Zn ₅ In ₂ O ₈ .

The sintered body thus obtained was cut to obtain an oxide sintered body (target material) with a width of 210 mm, a length of 710 mm, and a thickness of 6 mm. A #170 grindstone was used for cutting.

[Example 2 to 5]
In Example 1, each raw material powder was mixed so that the atomic ratios of In, Zn, and Ta were as shown in Table 1 below. A target material was obtained in the same manner as in Example 1 except for this.

[Comparative example 1]
The atomic ratio of _{In element} to _the total of In _element and Ta _{element is} They were mixed so that [In/(In+Ta)] was 0.983. The mixture was fed into a wet ball mill and mixed and ground for 12 hours.
The resulting mixed slurry was taken out, filtered, and dried. This dry powder was charged into a firing furnace and heat-treated at 1000° C. for 5 hours in an air atmosphere.
Through the above process, a mixed powder containing In element and Ta element was obtained.

ZnO powder having an average particle diameter _D50 of 0.8 μm was mixed into this mixed powder so that the atomic ratio [In/(In+Zn)] was 0.296. The mixed powder was supplied to a wet ball mill and mixed and pulverized for 24 hours to obtain a slurry of raw material powder. This slurry was filtered, dried and granulated.
The obtained granules were press-molded and further molded using a cold isostatic press while applying a pressure of 2000 kgf/cm ² .
The molded body was charged into a firing furnace and fired at 1400° C. for 12 hours under atmospheric pressure and oxygen gas inflow conditions to obtain a sintered body. The temperature increase rate was 0.5°C/min from room temperature to 400°C, and 1°C/min from 400 to 1400°C. The temperature decreasing rate was 1°C/min.
A target material was obtained in the same manner as in Example 1 except for the above.

[Comparative example 2]
The atomic ratio of _{In element} to _the total of In _element and Ta _{element is} They were mixed so that [In/(In+Ta)] was 0.975. The mixture was fed into a wet ball mill and mixed and ground for 12 hours.
The resulting mixed slurry was taken out, filtered, and dried. This dry powder was charged into a firing furnace and heat-treated at 1000° C. for 5 hours in an air atmosphere.
Through the above process, a mixed powder containing In element and Ta element was obtained.

ZnO powder having an average particle diameter _D50 of 0.8 μm was mixed into this mixed powder so that the atomic ratio [In/(In+Zn)] was 0.196. The mixed powder was supplied to a wet ball mill and mixed and pulverized for 24 hours to obtain a slurry of raw material powder. This slurry was filtered, dried and granulated. A target material was obtained in the same manner as in Comparative Example 1 except for this.

The proportion of each metal contained in the target materials obtained in Examples and Comparative Examples was measured by ICP emission spectrometry. It was confirmed that the atomic ratios of In, Zn, and Ta were the same as the raw material ratios shown in Table 1.

[Rating 1]
Relative density, bending strength, and bulk resistivity of the target materials obtained in Examples and Comparative Examples were measured using the following methods.

[Relative density]
The mass of the target material in the air is divided by the volume (mass of the target material in water/specific gravity of water at the measurement temperature), and the percentage value for the theoretical density ρ (g/cm ³ ) based on the following formula (i) is calculated as the relative density (unit: %).
...(i)
(In the formula, Ci indicates the content (mass%) of the constituent substances of the target material, and ρi indicates the density (g/cm ³ ) of each constituent substance corresponding to Ci.)
In the case of the present invention, the content (mass%) of the constituent substances of the target material is considered to be In ₂ O ₃ , ZnO, Ta ₂ O ₅ , for example, C1: mass % of In ₂ O ₃ of the target material.
ρ1: Density of In ₂ O ₃ (7.18 g/cm ³ )
C2: Mass% of ZnO in target material
ρ2: Density of ZnO (5.60g/cm ³ )
C3: Mass% of Ta ₂ O ₅ in target material
ρ3: Density of Ta ₂ O ₅ (8.73 g/cm ³ )
The theoretical density ρ can be calculated by applying ρ to equation (i).
The mass % of In ₂ O ₃ , the mass % of ZnO, and the mass % of Ta ₂ O ₅ can be determined from the analysis results of each element of the target material by ICP emission spectrometry.

[Folding strength]
Measurement was performed using Autograph (registered trademark) AGS-500B manufactured by Shimadzu Corporation. Using a sample piece cut out from the target material (total length 36 mm or more, width 4.0 mm, thickness 3.0 mm), according to the three-point bending strength measurement method of JIS-R-1601 (bending strength test method for fine ceramics). It was measured.

[Bulk resistivity]
The measurement was performed using Loresta (registered trademark) HP MCP-T410 manufactured by Mitsubishi Chemical by the JIS standard DC four-probe method. A probe (series four-probe probe TYPE ESP) was brought into contact with the surface of the target material after processing, and measurement was performed in AUTO RANGE mode. The measurement points were a total of five locations near the center and the four corners of the target material, and the arithmetic mean value of each measurement value was taken as the bulk resistivity of the target material.

[Evaluation 2]
Abnormal discharge was evaluated using the target materials of Examples and Comparative Examples. DC sputtering was performed under the following conditions using a DC magnetron sputtering device (high rate sputtering device manufactured by Shinku Kikai Kogyo Co., Ltd.), an exhaust system cryopump, and a rotary pump.
Ultimate vacuum: 1×10 ^-5 [Pa]
Sputtering pressure: 0.50 [Pa]
Argon gas flow rate: 32 [cc]
Oxygen gas flow rate: 8 [cc]
Input power: 3 [W/cm ² ]
Time: 48 hours The number of occurrences of abnormal discharge was evaluated as follows using an arcing counter (model: μArc Monitor MAM Genesis MAM Data Collector Ver. 2.02 (manufactured by LANDMARK TECHNOLOGY)).
A: Less than 50 times B: More than 50 times

[Rating 3]
Using the target materials of Examples and Comparative Examples, a TFT element 1 shown in FIG. 1 was manufactured by photolithography.
In producing the TFT element 1, a polyethylene naphthalate film (Teonex (registered trademark) manufactured by Toyobo Co., Ltd.) (glass transition point: 155° C.) was used as the base material 10. A Mo thin film was formed as a source electrode 30 and a drain electrode 31 on the base material 10 using a DC sputtering device, and sputtering film formation was performed under the following conditions using the target material obtained by the above method. A channel layer 20 having a thickness of about 30 nm was formed.
・Film forming equipment: DC sputtering equipment SML-464 manufactured by Tokki Co., Ltd.
・Ultimate vacuum: less than 1×10 ⁻⁴ Pa ・Sputter gas: Ar/O ₂ mixed gas ・Sputter gas pressure: 0.4 Pa
・_O2 gas concentration: As shown in Table 1 below.
・Substrate temperature: Room temperature ・Sputtering power: 3W/ ^cm2

Next, a SiOx thin film was formed as the gate insulating film 40 under the following conditions.
・Film deposition equipment: Plasma CVD equipment Samco Co., Ltd. PD-2202L
・Film-forming gas: SiH ₄ /N ₂ O/N ₂ mixed gas ・Film-forming pressure: 110 Pa
・Substrate temperature: 150℃
Next, a Mo thin film was formed as the gate electrode 50 using the DC sputtering apparatus.
As the protective layer 60, a SiOx thin film was formed using the plasma CVD apparatus described above. Finally, annealing treatment was performed at 150°C. The annealing treatment time was 60 minutes. In this way, TFT element 1 was manufactured.

The present inventor has confirmed by X-Ray Photoelectron Spectroscopy (XPS) that the composition of the channel layer 20 in the obtained TFT element 1 is the same as the composition of the target material (see below). The same applies to Examples and Comparative Examples.) XPS is a measurement method that can analyze the constituent elements of a sample and their electronic states by measuring the photoelectron energy generated by irradiating the sample surface with X-rays. Therefore, the composition of each element shown in Table 1 is the same in the channel layer 20 and the target material.

The transfer characteristics of the TFT element 1 thus obtained were measured at a drain voltage of Vd=5V. The measured transfer characteristics are field effect mobility μ (cm ² /Vs), SS (Subthreshold Swing) value (V/dec), and threshold voltage Vth (V). The transfer characteristics were measured using Semiconductor Device Analyzer B1500A manufactured by Agilent Technologies. The measurement results are shown in Table 1. Although not shown in the table, the inventor has confirmed by XRD measurement that the channel layer 20 of the TFT device 1 obtained in each example has an amorphous structure.
Field-effect mobility is the channel mobility determined from the change in drain current with respect to gate voltage when the drain voltage is constant in the saturation region of MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) operation. , the larger the value, the better the transfer characteristics.
The SS value is the gate voltage required to increase the drain current by one order of magnitude near the threshold voltage, and the smaller the value, the better the transfer characteristics.
The threshold voltage is the voltage when a drain current flows and becomes 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, and the value is preferably close to 0 V. . Specifically, it is more preferably -2V or more, even more preferably -1V or more, and even more preferably 0V or more. Further, it is more preferably 3V or less, even more preferably 2V or less, and even more preferably 1V or less. Specifically, it is more preferably -2V or more and 3V or less, even more preferably -1V or more and 2V or less, and even more preferably 0V or more and 1V or less.

As is clear from the results shown in Table 1, it can be seen that the TFT devices manufactured using the target materials obtained in each example have excellent transfer characteristics even after the post-annealing treatment performed at a low temperature of 150°C. .

[Rating 3]
Regarding the target materials obtained in Example 1 and Comparative Example 1, the dispersion rate of the In/Zn atomic ratio was measured by the method described above. The results are shown in Table 2 below.

As shown in Table 2, in Example 1, the dispersion rate at the 16 locations was 3.9% at most, proving that the In/Zn atomic ratio was homogeneous. On the other hand, it can be seen that the target material obtained in Comparative Example 1 has a non-uniform In/Zn atomic ratio.
Although not shown in the table, the present inventor has confirmed that the dispersion rate at 16 locations was also 10% or less at maximum for the target materials obtained in Examples 2 to 5.

The sputtering target of the present invention can be suitably used in the technical field of thin film transistors (TFT) used in flat panel displays (FPD). Furthermore, while conventional IGZO requires post-annealing at a high temperature of 250° C. or higher, the present invention allows it to function as a semiconductor even with post-annealing at a low temperature of less than 250° C. Therefore, the energy required for manufacturing can be reduced, leading to sustainable management of natural resources, efficient use, and achieving carbon neutrality.

Claims (6)

It is composed of an oxide containing indium (In) element, zinc (Zn) element and tantalum (Ta) element,
The atomic ratio of each element satisfies all of formulas (1) to (3),
0.1≦(In+Ta)/(In+Zn+Ta)<0.4 (1)
0.6<Zn/(In+Zn+Ta)≦0.9 (2)
0.001≦Ta/(In+Zn+Ta)<0.014 (3)
The relative density is 95% or more,
A sputtering target material having a bending strength of 100 MPa or more . The sputtering target material according to claim 1 , having a bulk resistivity of 100 mΩ·cm or less at 25°C. The sputtering target material according to claim 1 or 2, having a relative density of 98% or more. The sputtering target material according to claim 1 or 2, comprising an oxide consisting of indium (In) element, zinc (Zn) element, tantalum (Ta) element, and inevitable trace elements. The relative density is 98% or more,
The sputtering target material according to claim 1 or 2, comprising an oxide consisting of indium (In) element, zinc (Zn) element, tantalum (Ta) element, and inevitable trace elements. A method for manufacturing an oxide semiconductor using the sputtering target material according to claim 1 or 2,
The oxide semiconductor is
It is composed of an oxide containing indium (In) element, zinc (Zn) element and tantalum (Ta) element,
A method for producing an oxide semiconductor in which the atomic ratio of each element satisfies all of formulas (1) to (3).
0.1≦(In+Ta)/(In+Zn+Ta)<0.4 (1)
0.6<Zn/(In+Zn+Ta)≦0.9 (2)
0.001≦Ta/(In+Zn+Ta)<0.014 (3)