KR20240112815A - Sputtering target material and oxide semiconductor manufacturing method - Google Patents

Abstract

The sputtering 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, and the atomic ratio of each element satisfies all of formulas (1) to (3). ,

The relative density is 95% or more, and an oxide semiconductor of the same composition is manufactured using the sputtering target material.

Description

Sputtering target material and oxide semiconductor manufacturing method

The present invention relates to a sputtering target material. Additionally, the present invention 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 “TFTs”) used in flat panel displays (hereinafter also referred to as “FPDs”), with the increase in functionality of FPDs, In-Ga-Zn composites have replaced conventional amorphous silicon. Oxide semiconductors, represented by oxides (hereinafter also referred to as "IGZO"), are attracting attention, and practical use is progressing. IGZO has the advantage of exhibiting high field effect mobility and low leakage current. In recent years, as FPDs have become more highly functional, materials showing field effect mobility higher than that of IGZO have been proposed.

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

Additionally, flexible displays, one of FPDs, have been attracting attention in recent years because they are said to be capable of wide application development. One of the important members constituting a flexible display is a flexible base material, and among them, plastic film is suitable because it is thin, light, and has excellent flexibility. However, plastic films have problems with heat resistance. In order to form a TFT on a substrate, post-anneal treatment is required to improve electrical properties after film formation. When a substrate with low heat resistance such as a plastic film is used, the post-anneal treatment needs to be performed at a low temperature. However, when a film made of IGZO is post-annealed at a low temperature, the resistance of the film is reduced, making it difficult to function as a semiconductor.

US2013/270109A1 US2014/102892A1

In the technology 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 as a result, abnormal discharge is likely to occur, and cracks are likely to occur in the target material during abnormal discharge. As a result, there are cases where manufacturing high-performance TFTs is hindered.

Additionally, in order to form a TFT on a substrate with low heat resistance, such as a plastic film, it is necessary to perform post-anneal treatment to improve electrical properties after film formation. 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, the object of the present invention is to provide a sputtering target material and a method of manufacturing an oxide semiconductor that can solve the shortcomings of the above-described prior art.

The present inventors conducted intensive studies to solve the above problems. As a result, in the oxide containing the indium (In) element and the zinc (Zn) element as the main elements, the content of the zinc (Zn) is increased and a trace amount of the tantalum (Ta) element is contained, and the relative density is also increased. It was discovered that by increasing , the above-mentioned abnormal discharge 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 equations (1) to (3),

A sputtering target material having a relative density of 95% or more is provided.

In addition, the present invention is a method for manufacturing an oxide semiconductor using the above sputtering target material,

The oxide semiconductor,

It is composed of oxides containing the elements indium (In), zinc (Zn), and tantalum (Ta),

Method for producing an oxide semiconductor manufactured so that the atomic ratio of each element satisfies all of equations (1) to (3)

is to provide.

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 the metal elements constituting it, but may intentionally or unavoidably contain trace elements in addition to these elements as long as the effect of the present invention is not impaired. . Examples of trace elements include elements contained in organic additives described later and media raw materials such as ball mills mixed during target material production. Trace elements in the target material of the present invention include, for example, 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, Nb, Sr and Pb. Their content is preferably 100 mass ppm (hereinafter also referred to as "ppm") or less, respectively, with respect to the total mass of oxides containing In, Zn, and Ta contained in the target material of the present invention, and more preferably 80 ppm or less. More preferably, it is 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 a trace element, the total mass also includes the mass of the trace element.

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

The target material of the present invention preferably has an atomic ratio of the metal elements constituting it, that is, In, Zn, and Ta, in a specific range because the performance of the oxide semiconductor device formed from the target material is improved.

Specifically, it is desirable for In and Ta to satisfy the atomic ratio expressed by the following formula (1).

Regarding Zn, it is desirable to satisfy the atomic ratio expressed by the following formula (2).

Regarding Ta, it is desirable to satisfy the atomic ratio expressed by the following formula (3).

When the atomic ratios of In, Zn, and Ta satisfy all of the above equations (1) to (3), a semiconductor device having an oxide thin film formed by sputtering using the target material of the present invention can be produced at a low temperature of less than 250°C. Even with the post-annealing treatment performed, it exhibits 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 the following formulas (1-2) to (1-5) are satisfied for In and Ta.

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

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

The target material of the present invention is characterized by a high relative density in addition to the atomic ratio of In, Zn, and Ta. In detail, 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 preferable because it becomes possible to suppress the generation of particles when sputtering is performed using the target material of the present invention. From this point of view, the relative density of the target material of the present invention is more preferably 97% or more, more preferably 98% or more, even more preferably 99% or more, particularly preferably 100% or more, and more preferably more than 100%. This is particularly preferable. The target material of the present invention having such a relative density is suitably manufactured by the method described later. Relative density is measured according to Archimedes' method. The specific measurement method will be explained in detail in the examples described later.

The target material of the present invention is also characterized by high strength. In detail, the target material of the present invention preferably exhibits a high transverse strength of 100 MPa or more. By exhibiting such a high transverse strength, when sputtering is performed using the target material of the present invention, it is preferable because it becomes difficult for cracks to occur in the target material even if unintended abnormal discharge occurs during sputtering. From this viewpoint, the target material of the present invention has a transverse strength of more preferably 105 MPa or more, and even more preferably 110 MPa or more. In addition, it is preferable that the upper limit of the transverse strength is, for example, 300 MPa from the viewpoint of the toughness of the target material, etc. The target material of the present invention having such a breaking strength is suitably manufactured by the method described later. The transverse strength is measured based on JIS R1601. The specific measurement method will be explained in detail in the examples described later.

The target material of the present invention is also characterized by low bulk resistivity. A low bulk resistivity is advantageous in that DC sputtering is possible using the target material. From this point of view, the bulk resistivity of the target material of the present invention is preferably 100 mΩ·cm or less at 25°C, more preferably 50 mΩ·cm or less, more preferably 30 mΩ·cm or less, and even more preferably 20 mΩ·cm or less. , it is further preferably 15 mΩ·cm or less, particularly preferably 12 mΩ·cm or less, particularly more preferably 10 mΩ·cm or less, and even more preferably 5 mΩ·cm or less. In addition, the lower the bulk resistivity, the more desirable it is, and the lower limit is not particularly set, 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 later. Bulk resistivity is measured by the direct current probe method. The specific measurement method will be explained in detail in the examples described later.

As described above, the target material of the present invention is composed of an oxide containing In, Zn, and Ta. This oxide may be an oxide of In, an oxide of Zn, or an oxide of Ta. Alternatively, this oxide may be a composite oxide of any two or more elements selected from the group consisting of In, Zn, and Ta. Specific examples of the complex oxide include, but are not limited to, In-Zn complex oxide, Zn-Ta complex oxide, In-Ta complex oxide, and In-Zn-Ta complex oxide.

In the target material of the present invention, it is preferable that the In/Zn atomic ratio in the same plane is homogeneous during cross-sectional observation by SEM at a magnification of 200 times. It is preferable that the In/Zn atomic ratio is uniform because when a thin film is formed by sputtering, there is no bias in the composition and the film characteristics do not change.

Evaluation of the homogeneous state of the In/Zn atomic ratio is performed 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 × 625 μm at a magnification of 200 times and a randomly selected cross section of the target material. Next, the field of view is equally divided into 4 vertically and 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 defined as the dispersion rate (%). Evaluate the degree of homogeneity of the In/Zn atomic ratio based on the size of . 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, especially preferably 3% or less, and 2% or less. The following values are particularly more preferable.

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

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

It is suitable to use oxide powder or hydroxide powder as the above raw material powder. As the oxide powder, In oxide powder, Zn oxide powder, and Ta oxide powder are used. As In oxide, For example, In ₂ O ₃ can be used. As the Zn oxide, for example, ZnO can be used. As a powder of Ta oxide, Ta ₂ O ₅ can be used, for example.

The amount of In oxide powder, Zn oxide powder, and Ta oxide powder used is preferably adjusted so that the atomic ratio of In, Zn, and Ta in the target material satisfies the above-mentioned range.

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

The organic additives described above are substances used to appropriately adjust the properties of the slurry or molded body. Examples of organic additives include binders, dispersants, and plasticizers. Binder is added to increase the strength of the molded body. As the binder, a binder commonly used when obtaining a molded body in a known powder sintering method can be used. Examples of the binder include polyvinyl alcohol. A dispersant is added to increase the dispersibility of the raw material powder in the slurry. Examples of dispersants include polycarboxylic acid-based dispersants and polyacrylic acid-based dispersants. Plasticizers are added to increase the plasticity of the molded body. Examples of plasticizers include polyethylene glycol (PEG) and ethylene glycol (EG).

There is no particular limitation on the dispersion medium used when producing a slurry containing raw material powder and organic additives, and depending on the purpose, it can be appropriately selected from water-soluble organic solvents such as water and alcohol. There is no particular limitation on the method of producing a slurry containing raw material powder and organic additives. For example, a method of placing raw material powder, organic additives, dispersion medium, and zirconia balls in a pot and mixing them by ball mill can be used.

Once the slurry is obtained in this way, this slurry is poured into a mold, and the dispersion medium is then removed to produce a molded body. Examples of molds that can be used include metal molds, plaster molds, and resin molds that are pressurized to remove the dispersion medium.

On the other hand, in the CIP molding method, a slurry similar to the slurry used in the injection molding method is spray dried to obtain dry powder. The obtained dry powder is filled into a mold and CIP molding is performed.

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 prior art, for example, the technology described in Patent Document 2, firing is performed after mixing ₃ minutes of In ₂ O and ₅ minutes of Ta ₂ O, and then the obtained firing component is mixed with the ZnO component and firing is performed again. . In this method, the particles constituting the powder are aggregated by prior firing, so it is not easy 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 all mixed and molded at room temperature, and then fired, so that a dense target material with a high relative density can be easily obtained. . Firing of the molded body can generally be carried out in an oxygen-containing atmosphere. In particular, firing in an atmospheric atmosphere is easy. 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 to 100 hours, more preferably 2 hours to 50 hours, and even more preferably 3 hours to 30 hours. 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 even more preferably 20°C/hour or more and 100°C/hour or less.

In the firing of the molded body, it is desirable to maintain the temperature at which a complex oxide of In and Zn, for example, the phase of Zn ₅ In ₂ O _{8 ,} is generated for a certain period of time from the viewpoint of promoting sintering and producing a dense target material during the firing process. do. Since volumetric diffusion progresses and densification is promoted when the Zn ₅ In ₂ O ₈ phase is generated, it is desirable to reliably generate the Zn ₅ In ₂ O ₈ phase. From this point of view, in the process of increasing the temperature of firing, it is desirable 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 of one specific point, and may be a temperature range with a certain width. Specifically, when T (°C) is a specific temperature selected from the range of 1000°C to 1250°C, it may be, for example, T±10°C, as long as it is within the range of 1000°C to 1250°C, Preferably it is T±5°C, more preferably it is T±3°C, and even more preferably it is T±1°C. The time for maintaining this temperature range is preferably 1 hour or more and 40 hours or less, and more preferably 2 hours or more and 20 hours or less.

The target material obtained in this way can be processed into a predetermined size by grinding processing or the like. A sputtering target is obtained by bonding this to a substrate. The sputtering target obtained in this way is suitably used in the production of oxide semiconductors. For example, the target material of the present invention can be used in the production of TFT. Figure 1 schematically shows one embodiment of a TFT device.

The TFT element 1 shown in the figure is formed on one surface of the substrate 10. A channel layer 20, a source electrode 30, and a drain electrode 31 are disposed on one side of the substrate 10, and a gate insulating film 40 is formed to cover them. A gate electrode 50 is disposed on the gate insulating film 40. And 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 composed of an oxide containing an indium (In) element, a zinc (Zn) element, and a tantalum (Ta) element. ) The atomic ratio satisfies the above-mentioned equation (1). Additionally, the above-mentioned equations (2) and (3) are satisfied.

In addition, the oxygen concentration when forming the channel layer 20 is preferably, for example, 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%. It is more preferable that it is below.

When an oxide semiconductor layer is formed by sputtering, it is preferable to anneal the oxide semiconductor layer. The purpose of the annealing treatment is to provide the desired performance to the oxide semiconductor layer. For this purpose, the temperature of the annealing treatment is preferably 20°C or more and less than 250°C, more preferably 20°C or more and 200°C or less, still more preferably 20°C or more and 180°C or less, and more preferably 20°C or more and 150°C or less. It is even more desirable. Additionally, the temperature of the annealing treatment may be 50°C or higher, and may also be 80°C or higher. The annealing time 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 atmosphere for annealing is preferably an oxygen atmosphere containing atmospheric pressure.

Annealing treatment for the oxide semiconductor layer can be performed immediately after formation of the oxide semiconductor layer. Alternatively, after forming the oxide semiconductor layer, one or more layers may be formed, and annealing may be performed thereafter.

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

In addition, it is preferable that the field effect mobility of the oxide semiconductor element formed from the target material is large in terms of higher functionality of the FPD due to improved transmission characteristics of the TFT element, which is an oxide semiconductor element. In detail, the TFT including the oxide semiconductor element formed from the target material preferably has a field effect mobility (cm2/Vs) of 1 cm2/Vs or more, more preferably 2 cm2/Vs or more, and 3 cm2/Vs. It is more preferable that it is Vs or more, it is still more preferable that it is 5 cm2/Vs or more, it is even more preferable that it is 10 cm2/Vs or more, it is even more preferable that it is 20 cm2/Vs or more, and it is especially preferable that it is 30 cm2/Vs or more. The larger the value of the field effect mobility, the more desirable it is in terms of higher functionality of the FPD. However, if the field effect mobility is as high as about 200 cm2/Vs, sufficient performance can be obtained.

Example

Hereinafter, the present invention will be described in more detail through examples. However, the scope of the present invention is not limited to these examples.

[Example 1]

In ₂ O ₃ powder with an average particle diameter D ₅₀ of 0.6 μm, ZnO powder with an average particle diameter D ₅₀ of 0.8 μm, and Ta ₂ O ₅ powder with an average particle diameter D ₅₀ of 0.6 μm were mixed in a ball mill dry manner using zirconia balls. Thus, mixed raw material powder was prepared. The average particle diameter D ₅₀ 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 measurement was performed at a refractive index of 2.20 of the measured substance. The mixing ratio of each powder was set so that the atomic ratios of In, Zn, and Ta were the values shown in Table 1 below.

To the pot where the mixed raw material powder was prepared, 0.2% by mass of a binder based on the mixed raw material powder, 0.6% by mass of a dispersant based on the mixed raw material powder, and 20% by mass of water based on the mixed raw material powder were added, and then added to the zirconia ball. A slurry was prepared by mixing with a ball mill.

The prepared slurry was poured into a metal mold with a filter in between, and water in the slurry was then discharged to obtain a molded body. This molded body was fired to produce a sintered body. The firing was carried out in an atmosphere with 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 decrease rate of 50°C/hour. During firing, the temperature was maintained at 1100°C for 6 hours to promote the production of Zn ₅ In ₂ O ₈ .

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

[Examples 2 to 5]

In Example 1, each raw material powder was mixed so that the atomic ratios of In, Zn, and Ta were the values shown in Table 1 below. Other than that, a target material was obtained in the same manner as in Example 1.

[Comparative Example 1]

In ₂ O ₃ powder with an average particle diameter D ₅₀ of 0.6 ㎛ and Ta ₂ O ₅ powder with an average particle diameter D ₅₀ of 0.6 ㎛, the atomic ratio of the In element to the sum of the In element and the Ta element [In/(In+ Ta)] was mixed so that it was 0.983. The mixture was supplied to a wet ball mill and mixed and ground for 12 hours.

The obtained mixed slurry was taken out, filtered, and dried. This dried powder was charged into a kiln and heat-treated at 1000°C for 5 hours in an air atmosphere.

As a result, a mixed powder containing the In element and the Ta element was obtained.

Into this mixture, ZnO powder with an average particle diameter D ₅₀ of 0.8 μm was mixed so that the atomic ratio [In/(In+Zn)] was 0.296. The mixed powder was supplied to a wet ball mill and mixed and ground for 24 hours to obtain a slurry of raw material powder. This slurry was filtered, dried and granulated.

The obtained granulated product was press molded and further molded using a cold isostatic press by applying a pressure of 2000 kgf/cm2.

The molded body was charged into a sintering 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 from room temperature to 400°C was 0.5°C/min, and from 400 to 1400°C, it was 1°C/min. The temperature lowering rate was 1°C/min.

Other than these, the target material was obtained in the same manner as in Example 1.

[Comparative Example 2]

In ₂ O ₃ powder with an average particle diameter D ₅₀ of 0.6 ㎛ and Ta ₂ O ₅ powder with an average particle diameter D ₅₀ of 0.6 ㎛, the atomic ratio of the In element to the sum of the In element and the Ta element [In/(In+ Ta)] was mixed so that it was 0.975. The mixture was supplied to a wet ball mill and mixed and ground for 12 hours.

The obtained mixed slurry was taken out, filtered, and dried. This dried powder was charged into a kiln and heat-treated at 1000°C for 5 hours in an air atmosphere.

As a result, a mixed powder containing the In element and the Ta element was obtained.

Into this mixture, ZnO powder with an average particle diameter D ₅₀ of 0.8 μm was mixed so that the atomic ratio [In/(In+Zn)] was 0.196. The mixed powder was supplied to a wet ball mill and mixed and ground for 24 hours to obtain a slurry of raw material powder. This slurry was filtered, dried and granulated. Otherwise, the target material was obtained in the same manner as in Comparative Example 1.

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

[Evaluation 1]

For the target materials obtained in the examples and comparative examples, the relative density, transverse strength, and bulk resistivity were measured by the following methods.

[Relative density]

The air mass of the target material is divided by the volume (submerged mass of the target material/specific gravity of water at the measured temperature), and the percentage value for the theoretical density ρ (g/cm3) based on the following equation (i) is calculated as the relative density (unit: %).

(In the formula, Ci represents the content (mass%) of the constituent materials of the target material, and ρi represents the density (g/cm3) of each constituent material corresponding to Ci.)

In the case of the present invention, the content (mass %) of the constituent materials of the target material is considered to be In ₂ O ₃ , ZnO, and Ta ₂ O ₅ , for example

C1: Mass% of In ₂ O ₃ in target material

ρ1: Density of In ₂ O ₃ (7.18g/㎤)

C2: Mass% of ZnO in target material

ρ2: Density of ZnO (5.60g/㎤)

C3: Mass% of Ta ₂ O ₅ of target material

ρ3: Density of Ta ₂ O ₅ (8.73 g/cm3)

The theoretical density ρ can be calculated by applying to equation (i).

The mass % of In ₂ O ₃ , the mass % of ZnO, and the mass % of Ta ₂ O ₅ can be obtained from the analysis results of each element of the target material by ICP emission spectroscopy.

〔Strength of section〕

Measurement was performed using Autograph (registered trademark) AGS-500B manufactured by Shimadzu Seisakusho. Using a sample piece (overall length 36 mm, width 4.0 mm, thickness 3.0 mm) cut from the target material, measurement was performed according to the three-point bending strength measurement method of JIS-R-1601 (Fine ceramics bending strength test method). did.

[Bulk resistivity]

It was measured by the JIS standard direct current probe method using Loresta (registered trademark) HP MCP-T410 manufactured by Mitsubishi Chemical. A probe (series 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 5 locations near the center of the target material and at the four corners, and the arithmetic average of each measured 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.

Reached vacuum: 1×10 ^-5 [Pa]

Sputter pressure: 0.50[Pa]

Argon gas flow rate: 32[cc]

Oxygen gas flow rate: 8[cc]

Input power: 3[W/㎠]

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

[Evaluation 3]

Using the target materials of Examples and Comparative Examples, the TFT element 1 shown in FIG. 1 was produced by photolithography.

In the production of the TFT element 1, a polyethylene naphthalate film (Teonex (registered trademark) manufactured by Toyobo Corporation) (glass transition point: 155°C) was used as the substrate 10. On the substrate 10, a Mo thin film was deposited as the source electrode 30 and the drain electrode 31 using a DC sputtering device, and the target material obtained by the above-described method was used to form the film by sputtering under the following conditions. Then, a channel layer 20 with a thickness of approximately 30 nm was formed.

・Film formation device: DC sputtering device SML-464 manufactured by Toki Co., Ltd.

·Achieved vacuum degree: less than 1×10 ^-4 Pa

·Sputter gas: Ar/O ₂ mixed gas

·Sputter gas pressure: 0.4Pa

·O ₂ gas concentration: As shown in Table 1 below.

·Substrate temperature: room temperature

·Sputtering power: 3W/㎠

Next, a SiOx thin film was formed as the gate insulating film 40 under the following conditions.

・Film formation device: Plasma CVD device PD-2202L manufactured by Samco Co., Ltd.

·Film forming gas: SiH ₄ /N ₂ O/N ₂ mixed gas

·Film formation pressure: 110Pa

·Substrate temperature: 150℃

Next, a Mo thin film was formed as the gate electrode 50 using the DC sputtering device.

As the protective layer 60, a SiOx thin film was formed using the above plasma CVD device. Finally, annealing treatment was performed at 150°C. The annealing time was set to 60 minutes. In this way, the TFT element 1 was manufactured.

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

For the TFT element 1 thus obtained, the transfer characteristics were measured at a drain voltage Vd = 5V. The measured transfer characteristics are field effect mobility μ (cm2/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, Inc. The measurement results are shown in Table 1. Additionally, although not shown in the table, the present inventor confirmed through XRD measurement that the channel layer 20 of the TFT element 1 obtained in each example had an amorphous structure.

Field-effect mobility is the channel mobility obtained from the change in drain current with respect to the gate voltage when the drain voltage is kept constant in the saturation region of MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) operation. The larger the value, the higher the value. Transmission characteristics are good.

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 at which the drain current flows and becomes 1 nA when a constant voltage is applied to the drain electrode and a positive or negative voltage is applied to the gate electrode, and the value is preferably close to 0V. In detail, it is more preferable that it is -2V or more, it is still more preferable that it is -1V or more, and it is even more preferable that it is 0V or more. Moreover, it is more preferable that it is 3V or less, it is still more preferable that it is 2V or less, and it is even more preferable that it is 1V or less. Specifically, it is more preferable that it is -2V or more and 3V or less, it is still more preferable that it is -1V or more and 2V or less, and it is still more preferable that it is 0V or more and 1V or less.

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

[Evaluation 3]

For 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 16 locations was 3.9% at the maximum, and it was proven 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 heterogeneous In/Zn atomic ratio.

In addition, although not shown in the table, the present inventor confirmed that the dispersion rate at 16 locations was 10% or less at most 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 (TFTs) used in flat panel displays (FPDs). In addition, conventional IGZO required post-annealing treatment at a high temperature of 250°C or higher, but in the present invention, it can be made to function as a semiconductor even by post-annealing treatment at a low temperature of less than 250°C. Therefore, the energy required for manufacturing can be reduced, leading to sustainable management, efficient use and decarbonization of natural resources.

Claims (4)

It is composed of an oxide containing an indium (In) element, a zinc (Zn) element, and a tantalum (Ta) element, and the atomic ratio of each element satisfies all of formulas (1) to (3),

A sputtering target material with a relative density of 95% or more. According to paragraph 1,
A sputtering target material with a fracture strength of 100 MPa or more. According to claim 1 or 2,
A sputtering target material with a bulk resistivity of 100mΩ·cm or less at 25°C. 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 oxides containing the elements indium (In), zinc (Zn), and tantalum (Ta),
A method for producing an oxide semiconductor, wherein the atomic ratio of each element is manufactured so as to satisfy all of equations (1) to (3).