JP2019038735A - Oxide sintered body, oxide sintered body manufacturing method, sputtering target, and amorphous oxide semiconductor thin film - Google Patents

Abstract

An oxide sintered body capable of forming an amorphous oxide semiconductor thin film stably exhibiting a low carrier concentration and a high carrier mobility is provided. An oxide sintered body containing In, Si, and Sn as constituent elements, including an In2O3 phase having a bixbite type structure and an In4Sn3O12 phase having a fluorite type structure, the sum of In and Si The content of Si with respect to the atomic ratio is 0.05 ≦ Si / (In + Si) ≦ 0.3, and the content of Sn with respect to the sum of In, Si, and Sn is 0.1 ≦ Sn / ( In + Si + Sn) ≦ 0.2 is satisfied. [Selection figure] None

Description

  The present invention relates to an oxide sintered body mainly containing indium, silicon, and tin, a method for producing the oxide sintered body, a sputtering target, and an amorphous oxide semiconductor thin film.

  A thin film transistor (TFT) is a kind of a field effect transistor (FET). A TFT is a three-terminal element having a gate terminal, a source terminal, and a drain terminal as a basic configuration. A semiconductor thin film formed on a substrate is used as a channel layer in which electrons or holes move, and a voltage is applied to the gate terminal. This is an active element having a function of switching the current between the source terminal and the drain terminal by applying and controlling the current flowing in the channel layer. A TFT is an electronic device that is most frequently put into practical use, and a typical application is a liquid crystal driving element.

  Currently, the most widely used TFT is a metal-insulator-semiconductor-FET (MIS-FET) using a polycrystalline silicon film or an amorphous silicon film as a channel layer material. Since the MIS-FET using silicon is opaque to visible light, a transparent circuit cannot be formed. For this reason, when the MIS-FET is applied as a switching element for liquid crystal driving of a liquid crystal display, the device has a small aperture ratio of display pixels.

  In recent years, with the demand for higher definition of liquid crystal, high-speed driving has been required for liquid crystal driving switching elements. In order to realize high-speed driving, it has become necessary to use a semiconductor thin film in which the mobility of electrons or holes as carriers is at least higher than that of amorphous silicon for the channel layer.

For such a situation, Patent Document 1 discloses a transparent amorphous oxide thin film formed by vapor phase film formation and composed of elements of In, Ga, Zn, and O. The composition is InGaO ₃ (ZnO) _m (m is a natural number less than 6) when crystallized, and the carrier mobility (also referred to as carrier electron mobility) is 1 cm ² // without adding impurity ions. A transparent semi-insulating amorphous oxide thin film characterized by having a semi-insulating property exceeding (V · s) and having a carrier concentration (also referred to as carrier electron concentration) of 10 ¹⁶ / cm ³ or less, and this transparent semi-insulating material A thin film transistor characterized by using a conductive amorphous oxide thin film as a channel layer has been proposed.

  Patent Document 2 discloses a sputtering target for forming the amorphous oxide thin film described in Patent Document 1, that is, a sintered body target containing at least In, Zn, and Ga, and the composition thereof is A sputtering target including In, Zn, and Ga, having a relative density of 75% or more and a resistance value ρ of 50 Ωcm or less has been proposed.

In Patent Document 3, as a material that realizes high carrier mobility, gallium is dissolved in indium oxide, the atomic ratio Ga / (Ga + In) is 0.001 to 0.12, and all metal atoms A thin film transistor characterized by using an oxide thin film having an indium and gallium content of 80 atomic% or more and an In ₂ O ₃ bixbyite structure has been proposed. It is a solid solution in indium, the atomic ratio Ga / (Ga + In) is 0.001 to 0.12, the content ratio of indium and gallium with respect to all metal atoms is 80 atomic% or more, and the In ₂ O ₃ bix An oxide sintered body characterized by having a bite structure has been proposed.

Patent Document 4 discloses an oxide sintered body having a bixbite structure and containing indium oxide, gallium oxide, and a positive trivalent and / or positive tetravalent metal, and is a positive trivalent and / or positive tetravalent. Sintering in which the metal content is 100 to 10,000 ppm, and the composition amount of indium (In) and gallium (Ga) is in the composition range satisfying the equation 0.005 <In / (In + Ga) <0.15 in atomic%. The body is described, and the TFT evaluation discloses an example showing a high mobility of about 60 cm ² / V · s.

  Patent Document 5 proposes a transparent conductive thin film having a high transmittance, which is manufactured by doping indium oxide as a main component, doping silicon, and further doping with tin or tungsten.

JP 2010-219538 A JP 2007-0773312 A International Publication No. 2010/032422 International Publication No. 2011/152048 JP 2004-087451 A

However, in Patent Document 1, a transparent amorphous oxide thin film (a−) formed by vapor phase film formation of either sputtering or pulse laser vapor deposition and composed of elements of In, Ga, Zn, and O is used. The IGZO film) has a carrier electron mobility in the range of approximately 1 to 10 cm ² / (V · sec), and there is a possibility that the carrier mobility is insufficient for further high definition display.

In addition, since the target described in Patent Document 2 is a polycrystalline oxide sintered body having a homologous phase crystal structure, the amorphous oxide thin film obtained by this target has a carrier mobility as in Patent Document 1. However, it is only about 10 cm ² / V · s.

  In addition, when the crystalline oxide semiconductor thin film described in Patent Document 3 is applied to a TFT, variations in TFT characteristics due to crystal grain boundaries are a problem, particularly on a large glass substrate of the eighth generation or higher. It is extremely difficult to form TFTs uniformly. That is, in order to suppress variation in TFT characteristics, there is a demand for an oxide semiconductor thin film to be in an amorphous state.

  In addition, the oxide semiconductor thin film obtained by the sintered body described in Patent Document 4 has a problem that microcrystals and the like are easily generated, and in particular, a TFT can be formed on a large glass substrate with a high yield. It becomes difficult. In general, in the manufacturing process of an oxide semiconductor thin film transistor, an amorphous film is once formed, and an amorphous or crystalline oxide semiconductor thin film is obtained by subsequent annealing. After this amorphous film formation step, wet etching with a weak acid such as an aqueous solution containing oxalic acid or hydrochloric acid is performed in order to perform patterning into a desired channel layer shape. However, in the case of using an oxide sintered body having substantially only a bigsbite structure in Patent Document 4, the crystallization temperature of the formed amorphous film is lowered, and this is a stage after the film formation. In this case, microcrystals are generated, and therefore, there is a problem that a residue is generated in the etching process, or that it is partially crystallized and cannot be etched. That is, it becomes difficult to form a desired TFT channel layer pattern by a wet etching method using photolithography technology or the like, or even if a TFT can be formed, there is a problem that it does not operate stably. End up.

  Moreover, in the transparent conductive thin film described in Patent Document 5, the crystallization temperature is crystallized at a relatively low temperature of 180 ° C. or higher. There is a problem in that microcrystals are already generated at the stage after film formation and residues are generated in the etching process, or it is partially crystallized and cannot be etched. As in the above-mentioned Patent Document 4, it becomes difficult to form a desired TFT channel layer pattern, or even if a TFT can be formed, there is a problem that it does not operate stably.

  Furthermore, when an amorphous oxide semiconductor thin film is used for a TFT, it is required to exhibit a low carrier concentration in order to increase the on / off of the TFT. An oxide sintered body capable of forming a simple oxide semiconductor thin film is not described.

  Accordingly, the present invention has been devised in view of the above-mentioned problems of the prior art, suppresses variations in TFT characteristics, has good wet etching properties, and exhibits high carrier mobility at a low carrier concentration. A novel and improved oxide sintered body capable of forming an amorphous oxide semiconductor thin film, a method for producing the oxide sintered body, a sputtering target, and an amorphous oxide semiconductor thin film The purpose is to provide.

That is, in order to achieve the above object, an oxide sintered body according to one aspect of the present invention is an oxide sintered body containing In, Si, and Sn as constituent elements, and is a bixbite type. The In ₂ O ₃ phase having a structure and the In ₄ Sn ₃ O ₁₂ phase having a fluorite structure, and the content of Si with respect to the sum of In and Si is 0.05 ≦ Si / (In + Si ) ≦ 0.3, and the content of Sn with respect to the sum of In, Si, and Sn satisfies the relational expression of 0.1 ≦ Sn / (In + Si + Sn) ≦ 0.2 in terms of atomic ratio. And

In one embodiment of the present invention, it is preferable that an In ₂ (Si ₂ O ₇ ) phase having a tortuitite structure is further included.

  In one embodiment of the present invention, it is preferable that the content of Si with respect to the sum of In and Si satisfies a relational expression of 0.1 ≦ Si / (In + Si) <0.2 in terms of an atomic ratio.

  In another aspect of the present invention, there is provided a method for manufacturing the above-described oxide sintered body, wherein the content of Si with respect to the sum of In and Si is 0.05 ≦ Si / (In + Si) ≦ in atomic ratio. Indium oxide so that the content of Sn with respect to the sum of In, Si, and Sn satisfies the relational expression of 0.1 ≦ Sn / (In + Si + Sn) ≦ 0.2 in terms of atomic ratio A mixing step of mixing powder, silicon dioxide powder, and tin oxide powder; a forming step of forming the mixed powder obtained in the mixing step; and a firing step of firing the molded body obtained in the forming step. It is characterized by that.

  A sputtering target according to another aspect of the present invention is characterized by comprising the above-described oxide sintered body.

In another aspect of the present invention, an amorphous oxide semiconductor thin film composed of an oxide sintered body containing In, Si, and Sn as constituent elements, wherein the In ₂ O has a bixbite structure. ₃ phase and an In ₄ Sn ₃ O ₁₂ phase having a fluorite structure, and the content of Si with respect to the sum of In and Si is 0.05 ≦ Si / (In + Si) ≦ 0.3 in atomic ratio. In addition, the content of Sn with respect to the sum of In, Si, and Sn satisfies the relational expression of 0.1 ≦ Sn / (In + Si + Sn) ≦ 0.2 in terms of atomic ratio, and the carrier concentration is 9.8 × It is 10 ¹⁸ cm ⁻³ or less, and carrier mobility is 5.8 cm ² / V · s or more.

In another aspect of the present invention, it is preferable that the carrier concentration is 9.0 × 10 ¹⁷ cm ⁻³ or less and the carrier mobility is 10 cm ² / V · s or more.

  According to the present invention, it is possible to stably form an amorphous oxide semiconductor thin film having good wet etching properties and high carrier mobility at a low carrier concentration.

It is a flowchart which shows the outline of the manufacturing method of the oxide sintered compact which concerns on one Embodiment of this invention. It is a characteristic view which shows the X-ray-diffraction pattern of Example 7 and the oxide sintered compact of Comparative Examples 3 and 4 obtained by X-ray-diffraction measurement.

  Hereinafter, preferred embodiments of the present invention will be described in detail. The present embodiment described below does not unduly limit the contents of the present invention described in the claims, and all the configurations described in the present embodiment are essential as means for solving the present invention. Not necessarily.

[1. Oxide sintered body]
First, the composition of the oxide sintered body according to one embodiment of the present invention will be described. This oxide sintered body contains indium (In), silicon (Si), and tin (Sn) as constituent elements, and the content of Si with respect to the total of In and Si is 0.05 ≦ number by atomic ratio. Si / (In + Si) ≦ 0.3, and the Sn content with respect to the sum of In, Si, and Sn satisfies the relational expression of 0.1 ≦ Sn / (In + Si + Sn) ≦ 0.2 in terms of atomic ratio. It is characterized by.

  The Si content relative to the total of In and Si satisfies the relational expression of 0.05 ≦ Si / (In + Si) ≦ 0.3, preferably 0.1 ≦ Si / (In + Si) <0. 2 is satisfied, more preferably 0.12 ≦ Si / (In + Si) ≦ 0.15. This is because silicon has a strong bonding force with oxygen and has the effect of reducing the amount of oxygen vacancies in the amorphous oxide semiconductor thin film according to the present embodiment, which will be described later. It is because a thing with high is obtained. When Si / (In + Si) is less than 0.05, the amount of oxygen vacancies in the amorphous oxide semiconductor thin film cannot be reduced, so that these effects cannot be obtained sufficiently. On the other hand, when Si / (In + Si) exceeds 0.3, the bulk resistance value of the sputtering target becomes high, and a homogeneous film cannot be obtained due to abnormal discharge such as arc discharge (arcing) during sputtering.

  The oxide sintered body according to the present embodiment contains Sn in addition to In and Si in the composition range defined as described above. The Sn content relative to the total of In, Si, and Sn satisfies the relational expression 0.1 ≦ Sn / (In + Si + Sn) ≦ 0.2, preferably 0.1 ≦ Sn / ( In + Si + Sn) ≦ 0.17 is satisfied. Sn has the effect of increasing the crystallization temperature of the amorphous oxide semiconductor thin film according to this embodiment described later. Due to this effect, when the amorphous oxide semiconductor thin film according to this embodiment is applied to a TFT, it is possible to increase the on / off of the TFT. When Sn / (In + Si + Sn) is less than 0.1, there is no effect of suppressing the carrier concentration, the carrier concentration becomes high, and the TFT may not be turned on / off. Further, since the crystal structure of the thin film after the heat treatment includes a microcrystalline portion, there is a possibility that a residue is generated when etching is performed. On the other hand, if Sn / (In + Si + Sn) exceeds 0.2, the carrier concentration is suppressed, but the bulk resistance value of the sputtering target becomes high, and a homogeneous film is formed by abnormal discharge such as abnormal discharge (arcing) during sputtering. You will not be able to get.

  Next, the sintered body structure of the oxide sintered body according to this embodiment will be described. In this embodiment, in order to raise the crystallization temperature of the amorphous oxide semiconductor thin film obtained using the sputtering target which uses an oxide sintered compact as a raw material, the sintered compact structure of an oxide sintered compact is important. It is.

The oxide sintered body according to the present embodiment is configured by an In ₂ O ₃ phase having a bixbite structure and an In ₄ Sn ₃ O ₁₂ phase having a fluorite structure as an intermediate compound other than the In ₂ O ₃ phase. The In this embodiment, the oxide semiconductor thin film obtained has a high crystallization temperature by including the In ₂ O ₃ phase having a bixbyite structure and the In ₄ Sn ₃ O ₁₂ phase having a fluorite structure. In particular, an oxide thin film obtained by an oxide sintered body including an In ₄ Sn ₃ O ₁₂ phase having a fluorite structure has a high crystallization temperature, that is, a crystallization temperature of 300 ° C. or higher, and is stable amorphous. Become. Such an amorphous oxide thin film exhibits good etching properties because no etching residue remains in patterning processing by wet etching in TFT manufacturing.

Further, in the present embodiment may further comprise _In 2 _(Si 2 _{O 7)} phase Toruto by tight structure. As a result, the crystallization temperature of the amorphous oxide semiconductor thin film can be further increased, so that etching residues can be more reliably suppressed during high-temperature processing, and there is no yield in mass production. However, if a large amount of In ₂ (Si ₂ O ₇ ) phase having a tortuitite structure is included, this In ₂ (Si ₂ O ₇ ) phase is poor in conductivity and may cause abnormal discharge during sputtering. There is.

[2. Manufacturing method of oxide sintered body]
Next, the manufacturing method of the oxide sintered compact concerning one embodiment of the present invention is explained using a drawing. FIG. 1 is a flowchart showing an outline of a method for producing an oxide sintered body according to an embodiment of the present invention. As shown in FIG. 1, the method for manufacturing an oxide sintered body according to this embodiment includes a mixing step S1, a forming step S2, and a sintering step S3.

  First, the mixing step S1 is a step of mixing raw material powder containing In, Si, and Sn.

  In the method for manufacturing an oxide sintered body according to this embodiment, these raw material powders are mixed and then molded, and the molded body is sintered by a normal pressure sintering method. Therefore, the generation phase of the structure of the oxide sintered body is the manufacturing conditions in each step S1 to S3 of the method for manufacturing the oxide sintered body according to the present embodiment, for example, the particle size of the raw material powder, the mixing conditions, and the sintering. Strongly dependent on conditions.

As the raw material powder, indium oxide powder, silicon dioxide powder, and tin oxide are preferably used, but silicon monoxide powder or metal silicon powder may be used. For example, raw material powder is put into a resin pot and mixed with a binder (for example, PVA) or the like by a wet ball mill or the like. In order to control each crystal grain of the sintered body to 5 μm or less, it is preferable to perform the ball mill mixing for 18 hours or more. At this time, hard ZrO ₂ balls may be used as the mixing balls used in the ball mill.

The sintered body structure of the oxide sintered body obtained in the present embodiment has a bixbite type In ₂ O ₃ phase and an intermediate compound other than the In ₂ O ₃ phase, In ₄ Sn ₃ O having a fluorite type structure. It is composed of ₁₂ phases, and in some cases includes an In ₂ (Si ₂ O ₇ ) phase having a tortuitite structure, but it is preferable to control the average grain size of each crystal grain to be 5 μm or less. For this reason, it is preferable that the average particle diameter of the indium oxide powder, the silicon dioxide powder, and the tin oxide that are raw material powders is 3.0 μm or less, and more preferably 1.0 μm or less, respectively. The average particle size indicates a volume-based particle size distribution obtained by a laser diffraction method.

  Indium oxide powder is a raw material of ITO (tin-added indium oxide), and development of fine indium oxide powder excellent in sinterability has been promoted along with improvement of ITO. Since indium oxide powder has been continuously used in large quantities as a raw material for ITO, it is possible to obtain a raw material powder having an average particle size of 1.0 μm or less recently. Moreover, since silicon dioxide powder is widely used as a raw material for ceramics and glass, it is possible to obtain a raw material powder having an average particle size of 1.0 μm or less. Furthermore, tin oxide powder is a raw material for ITO (tin-added indium oxide), and development of fine tin oxide powder excellent in sinterability has been promoted along with improvement of ITO. Since tin oxide powder has been used continuously as a raw material for ITO like indium oxide, it is possible to obtain a raw material powder having an average particle size of 1.0 μm or less recently.

Next, the molding step S2 is a step of molding the mixed powder obtained in the mixing step S1. That is, after mixing the raw material powder, the slurry is taken out and granulated by a spray dryer or the like. Thereafter, the granulated product obtained was molded by applying a pressure of about ^{9.8MPa (0.1ton / cm 2) ~294MPa} (3ton / cm 2) cold isostatic pressing, the molded body.

  Next, the sintering step S3 is a step of sintering the molded body obtained in the molding step S2. As the sintering means, it is preferable to apply an atmospheric pressure sintering method. The atmospheric pressure sintering method is a simple and industrially advantageous method, and is also a preferable means from the viewpoint of low cost.

  In sintering process S3, it is preferable to set it as the atmosphere where oxygen exists, and it is more preferable that the oxygen volume fraction in atmosphere exceeds 20%. In particular, when the oxygen volume fraction exceeds 20%, the oxide sintered body is further densified. Due to the excessive oxygen in the atmosphere, the sintering of the surface of the compact proceeds first in the early stage of sintering. Subsequently, sintering in a reduced state inside the molded body proceeds, and finally a high-density oxide sintered body is obtained.

  In an atmosphere in which oxygen does not exist, sintering of the surface of the molded body does not precede, and as a result, the density of the sintered body does not increase. If oxygen is not present, indium oxide is decomposed and metal indium is generated particularly at about 900 to 1000 ° C., so that it is difficult to obtain a target oxide sintered body.

As for the temperature range of atmospheric pressure sintering, 1200-1550 degreeC is preferable, More preferably, it is 1350-1450 degreeC. When the sintering temperature is less than 1200 ° C., the sintering reaction does not proceed sufficiently, the density of the sintered body is not increased, and an In ₄ Sn ₃ O ₁₂ phase having a fluorite structure is not generated. On the other hand, even if the sintering temperature exceeds 1550 ° C., it is difficult to increase the density, while the sintering furnace member and the oxide sintered body react to obtain the desired oxide sintered body. It becomes impossible. In particular, in the above-described oxide sintered body, the Si content with respect to the sum of In and Si is atomic ratio of Si / (In + Si) being 0.05 or more, so the sintering temperature is 1450 ° C. or less. Is more preferable. This is because in the temperature range around 1500 ° C., the In ₂ O ₃ phase may be remarkably generated. A small amount of In ₂ O ₃ phase is not a problem, but a large amount of In ₂ O ₃ phase is not preferable because it may cause a decrease in film formation rate or arcing. The sintering time is preferably 10 to 30 hours, more preferably 15 to 25 hours.

  The heating rate up to the sintering temperature is preferably in the range of 0.2 to 5 ° C./min in order to prevent cracking of the sintered body and advance the binder removal. If it is this range, you may heat up to sintering temperature combining a different temperature increase rate as needed. In the temperature raising process, the binder may be held for a certain time at a specific temperature for the purpose of progressing debinding and sintering. After sintering, it is preferable to stop introducing oxygen when cooling and to lower the temperature up to 1000 ° C. at a rate of 0.2 to 5 ° C./min, particularly 0.2 ° C./min to 1 ° C./min.

[3. Sputtering target]
The sputtering target according to the present embodiment is made of the oxide sintered body described above. This sputtering target is obtained by processing an oxide sintered body into a predetermined size. When used as a target, the surface can be further polished and adhered to a backing plate. The target shape is preferably a flat plate shape, but may be a cylindrical shape. When a cylindrical target is used, it is preferable to suppress particle generation due to target rotation. Further, the oxide sintered body can be processed into, for example, a cylindrical shape to form a tablet, which can be used for film formation by vapor deposition or ion plating.

When used as a sputtering target, the density of the above-described oxide sintered body is preferably 6.3 g / cm ³ or more, and more preferably 6.7 g / cm ³ or more. When the density is less than 6.3 g / cm ³ , it causes nodules during mass production. When used as an ion plating tablet is preferably less than ^{6.3g / cm 3, 3.4~5.5g / cm} 3 is more preferable.

[4. Amorphous oxide semiconductor thin film]
The amorphous oxide semiconductor thin film according to this embodiment is composed of the oxide sintered body described above, and has a predetermined carrier concentration and carrier mobility.

The structure of the oxide sintered body included in the sputtering target is an In ₂ O ₃ phase having a bixbite structure, and an In ₄ Sn ₃ O ₁₂ phase having a fluorite structure as an intermediate compound other than the In ₂ O ₃ phase. In some cases, it may further include an In ₂ (Si ₂ O ₇ ) phase having a tortuitite structure.

In order to obtain the amorphous oxide semiconductor thin film according to the present embodiment, it is important that the crystallization temperature of the amorphous oxide semiconductor thin film is high. Is related. That is, when the In ₄ Sn ₃ O ₁₂ phase having a fluorite structure is included as in the oxide sintered body according to the present embodiment described above, the oxide semiconductor thin film obtained thereby has a high crystallization temperature, That is, it exhibits a crystallization temperature of 300 ° C. or higher, preferably 350 ° C. or higher, and becomes a stable amorphous material. In addition, when it further contains an In ₂ (Si ₂ O ₇ ) phase having a tortuitite structure, it exhibits a higher crystallization temperature and becomes a more stable amorphous material. Thus, since the oxide semiconductor thin film is stable and amorphous, variation in TFT characteristics can be suppressed.

On the other hand, an oxide sintered body constituted only by an In ₂ O ₃ phase having a bixbite structure, or an In ₂ O ₃ phase having a bixbite structure and an in ₂ (Si ₂ O structure) having a tortobitite structure. ₇ ) An oxide thin film obtained from an oxide sintered body constituted by a phase has a low crystallization temperature, the film is crystallized or a part of microcrystals are formed, and is not amorphous. In such a film, an etching residue may remain by patterning by wet etching.

Therefore, in the present embodiment, the In ₂ O ₃ phase having a bixbite type structure and the In ₄ Sn ₃ O ₁₂ phase having a fluorite type structure, or In ₂ (Si ₂ O _{7 having a} tortobitite type structure are used. ) Phase further includes a high crystallization temperature, and thus becomes stable and amorphous. Such an oxide thin film does not leave an etching residue by patterning by wet etching. Etching includes dry etching using plasma in addition to wet etching. However, since dry etching generally uses a vacuum apparatus, the cost is higher than that of wet etching. Therefore, since the oxide semiconductor thin film as in this embodiment can be applied to wet etching, patterning can be performed at low cost in the manufacture of a TFT substrate.

  The composition of In, Si, and Sn of the amorphous oxide semiconductor thin film is substantially the same as the composition of the oxide sintered body according to the present embodiment described above. That is, it is an amorphous oxide burned semiconductor thin film containing In and Si as oxides and Sn. The content of Si with respect to the sum of In and Si is 0.05 ≦ Si / (In + Si) ≦ 0.3 in atomic ratio, and the content of Sn with respect to the sum of In, Si, and Sn is 0.1 in atomic ratio. ≦ Sn / (In + Si + Sn) ≦ 0.2 is satisfied.

The amorphous oxide semiconductor thin film according to this embodiment is formed by using an oxide sintered body whose composition and structure are controlled as described above as a sputtering target and the like, and heat-treated under the appropriate conditions described above. Thus, the carrier concentration is reduced to 9.8 × 10 ¹⁸ cm ⁻³ or less, and the carrier mobility is 5.8 cm ² / V · s or more. Among these, it is more preferable that the carrier concentration is 9.0 × 10 ¹⁷ cm ⁻³ or less and the carrier mobility is 10 cm ² / V · s or more.

  The amorphous oxide semiconductor thin film according to this embodiment is subjected to fine processing necessary for applications such as TFTs by wet etching or dry etching. Fine processing by wet etching can be performed. As the etching solution (etchant), any weak acid can be used. However, a weak acid mainly composed of oxalic acid or hydrochloric acid is preferable, and commercially available products such as ITO-06N manufactured by Kanto Chemical Co., Ltd. can be used. Note that dry etching may be selected depending on the configuration of the TFT.

  The thickness of the amorphous oxide semiconductor thin film according to this embodiment is not limited, but is 10 to 500 nm, preferably 20 to 300 nm, and more preferably 30 to 100 nm. If the film thickness is less than 10 nm, sufficient semiconductor characteristics cannot be obtained, and as a result, high carrier mobility cannot be realized. On the other hand, if the film thickness exceeds 500 nm, productivity problems occur, which is not preferable.

[5. Method for depositing amorphous oxide semiconductor thin film]
The method for forming an amorphous oxide semiconductor thin film according to this embodiment is mainly to form an amorphous oxide semiconductor thin film on a substrate by a sputtering method using the sputtering target, and then perform a predetermined process. The heat treatment is performed under the heat treatment conditions.

In the method for forming an amorphous oxide semiconductor thin film according to this embodiment, a general sputtering method is used. In particular, in the case of a direct current (DC) sputtering method, there is little thermal influence during film formation, Since high-speed film formation is possible, it is industrially advantageous. In the method for forming an amorphous oxide semiconductor thin film, for example, after evacuating to 2 × 10 ⁻⁴ Pa or less, a mixed gas composed of argon and oxygen is introduced, and the gas pressure in the chamber is set to 0.1 to 10 ° C. The pressure is 1 Pa, particularly 0.2 to 0.8 Pa, the direct current power with respect to the area of the target, that is, the direct current power is applied so that the direct current power density is in the range of about 1 to 7 W / cm ² to generate direct current plasma, Pre-sputtering can be performed. After performing this pre-sputtering for 5 to 30 minutes, it is preferable to perform sputtering after correcting the substrate position if necessary.

  In the sputtering film formation in the above film formation method, the DC power to be input is increased in order to improve the film formation speed.

  The substrate is typically a glass substrate and is preferably alkali-free glass, but may be used as long as it can withstand the above process conditions among a resin plate and a resin film.

  The heat treatment condition is a temperature lower than the crystallization temperature in an oxidizing atmosphere. As the oxidizing atmosphere, an atmosphere containing oxygen, ozone, water vapor, nitrogen oxide, or the like is preferable. The heat treatment temperature is 300 to 600 ° C, preferably 300 to 500 ° C. The heat treatment time is 1 to 120 minutes, preferably 5 to 60 minutes, which is maintained at the heat treatment temperature.

[6. Summary]
As described above, the oxide sintered body according to the present embodiment contains In, Si, and Sn as constituent elements, and has an In ₂ O ₃ phase with a bixbite structure and an In with a fluorite structure. ₄ Sn ₃ O ₁₂ phase, the content of Si with respect to the sum of In and Si is 0.05 ≦ Si / (In + Si) ≦ 0.3 in atomic ratio, and Sn with respect to the sum of In, Si, and Sn In the atomic ratio, the relational expression 0.1 ≦ Sn / (In + Si + Sn) ≦ 0.2 is satisfied.

  In addition, the method for manufacturing an oxide sintered body according to the present embodiment is a method for manufacturing an oxide sintered body to which In, Si, and Sn are added as constituent elements, and Si is based on the sum of In and Si. The content of Sn is 0.05 ≦ Si / (In + Si) ≦ 0.3 by atomic ratio, and the content of Sn with respect to the sum of In, Si, and Sn is 0.1 ≦ Sn / (In + Si + Sn) ≦ Obtained by mixing step of mixing indium oxide powder, silicon dioxide powder and tin oxide powder, forming step of forming mixed powder obtained by mixing step, and forming step so as to satisfy the relational expression of 0.2 And a firing step for firing the formed body.

  Such an oxide sintered body stably suppresses variation in TFT characteristics, stably has an amorphous oxide semiconductor thin film having good wet etching properties and high carrier mobility at a low carrier concentration. Can be formed. Therefore, it is very useful as a target material during sputtering.

Furthermore, the amorphous oxide semiconductor thin film according to the present embodiment is composed of an oxide sintered body containing In, Si, and Sn as constituent elements. It contains an In ₂ O ₃ phase having a bite structure and an In ₄ Sn ₃ O ₁₂ phase having a fluorite structure, and the Si content relative to the total of In and Si is 0.05 ≦ Si / (In + Si) ≦ 0.3, and the Sn content with respect to the sum of In, Si, and Sn satisfies the relational expression of 0.1 ≦ Sn / (In + Si + Sn) ≦ 0.2 in terms of atomic ratio, and the carrier concentration is 9.8 × 10 ¹⁸ cm ⁻³ or less and carrier mobility is 5.8 cm ² / V · s or more.

  Such an amorphous oxide semiconductor thin film exhibits a low carrier concentration and a high carrier mobility as described above. The amorphous oxide semiconductor thin film has a good etching property that there is no etching residue and does not affect the film quality even when patterning is performed by wet etching. For this reason, this amorphous oxide semiconductor thin film has a very high industrial significance because a TFT substrate can be manufactured without yield at the TFT manufacturing site.

  Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited to these examples.

<Method for evaluating oxide sintered body>
The composition analysis of the oxide sintered body was performed by ICP emission spectroscopy, and the formation phase was identified by a powder method using an X-ray diffractometer (manufactured by Philips).

<Evaluation method of oxide semiconductor thin film>
The film thickness of the oxide semiconductor thin film was measured with a surface roughness meter (manufactured by Tencor), and the carrier concentration and carrier mobility were determined with a Hall effect measuring device (manufactured by Toyo Technica). The formation phase of the film was identified by X-ray diffraction measurement. Further, ITO-06N (manufactured by Kanto Chemical Co., Ltd.), which is an oxalic acid-based etching solution, was heated at 30 ° C., and the oxide semiconductor thin film was immersed for 1 minute for etching. In order to confirm an etching residue, it observed with the microscope.

[Preparation of sintered oxide and target]
Indium oxide powder, silicon dioxide powder, and tin oxide powder were each adjusted to have an average particle size of 1.0 μm or less to obtain raw material powder. In Examples 1 to 28 and Comparative Examples 1 to 7, these raw material powders were prepared so as to have an atomic ratio of Si / (In + Si) and Sn / (In + Si + Sn) shown in Tables 1 and 2 below. It put into the pot made and mixed with the wet ball mill. At this time, hard ZrO ₂ balls were used as wet ball mill conditions, and the mixing time was 18 hours. After mixing these, the produced | generated slurry was taken out and granulated with the spray dryer. The obtained granulated product was molded by applying a pressure of 294 MPa (3 ton / cm ² ) with a cold isostatic press to produce a molded body.

Next, the obtained molded body was sintered. Sintering was performed at a sintering temperature of 1350 to 1450 ° C. for 20 hours in an atmosphere in which oxygen was introduced into the atmosphere in the sintering furnace at a rate of 5 liters / minute per 0.1 m ^{3 of the} furnace volume. At this time, the temperature was raised at 1 ° C./min. And in cooling after sintering, oxygen introduction was stopped and the temperature was lowered to 1000 ° C. at 1 ° C./min.

  Next, the obtained oxide sintered body was processed into a diameter of 152 mm and a thickness of 5 mm, and the sputtering surface was polished with a cup grindstone so that the maximum height Rz was 3.0 μm or less. The processed oxide sintered body was bonded to a backing plate made of oxygen-free copper using metallic indium to obtain a sputtering target.

[Evaluation of sintered oxide]
In Examples 1 to 28 and Comparative Examples 1 to 7, when composition analysis was performed using the obtained oxide sintered compact, the metal element was almost the same as the charged composition at the time of blending the raw material powder. I confirmed that there was.

FIG. 2 shows an example of the result of identifying the phase of the oxide sintered body by X-ray diffraction using CuKα rays with respect to the powder of the oxide sintered body obtained by pulverization. In Comparative Example 1-7, the oxide sintered body, _{an In} 2 _O bixbite type structure ₃ Aitansho or bixbite type structure _In 2 _{O 3} phase and Toruto by tight structure _{In 2,} (Si 2 whereas and a O ₇₎ phase, in example 1-28, the oxide sintered body, _in 4 _Sn 3 _{O 12} phase of _in 2 _{O 3} phase and a fluorite structure bixbite type structure Of In ₂ O ₃ phase of bixbite type structure, In ₄ Sn ₃ O ₁₂ phase of fluorite type structure, and In ₂ (Si ₂ O ₇ ) phase of tortovite type structure Confirmed that it has been.

[Preparation of oxide semiconductor thin film]
Using sputtering targets obtained in Examples 1 to 28 and Comparative Examples 1 to 7 and an alkali-free glass substrate (Corning EagleXG), film formation by direct current sputtering was performed under the conditions shown in Tables 1 and 2. The sputtering target was attached to the cathode of a DC magnetron sputtering apparatus (manufactured by Anelva) equipped with a DC power supply without an arcing suppression function. At this time, the distance between the target and the substrate (holder) was fixed to 60 mm. After evacuating to 2 × 10 ⁻⁴ Pa or less, a mixed gas of argon and oxygen is introduced so as to have an appropriate oxygen ratio according to the amount of silicon and tin of each target, and the gas pressure is set to 0.6 Pa. It was adjusted. A DC plasma was generated by applying a DC power of 300 W (1.64 W / cm ² ). After pre-sputtering for 10 minutes, an oxide semiconductor thin film having a thickness of 50 nm was formed by placing the substrate directly above the sputtering target, that is, at a stationary facing position.

  In Examples 1 to 28 and Comparative Examples 1 to 7, the formed oxide semiconductor thin films were heat-treated at 300 to 600 ° C. in oxygen as described in Table 1. In addition, Table 1 shows manufacturing conditions and evaluation results of Examples 1 to 28. In addition, Table 2 shows manufacturing conditions and evaluation results of Comparative Examples 1 to 7.

[Evaluation results of oxide semiconductor thin film]
In the oxide semiconductor thin films of Examples 1 to 28, the oxide sintered body as a raw material includes an In ₂ O ₃ phase having a bixbite structure and an In ₄ Sn ₃ O ₁₂ phase having a fluorite structure, and In and The content of Si with respect to the total of Si is 0.05 ≦ Si / (In + Si) ≦ 0.3 in atomic ratio, and the content of Sn with respect to the total of In, Si, and Sn is 0.1 ≦ in atomic ratio. By satisfying the relational expression of Sn / (In + Si + Sn) ≦ 0.2, the carrier concentration is 9.8 × 10 ¹⁸ cm ⁻³ or less and the carrier mobility is 5.8 cm ² / V · s or more. It was confirmed that no etching residue was generated in the etching test because the film quality was also amorphous.

Among them, the atomic ratio of Si / (In + Si) is 0.12 to 0.15, Sn / (In + Si + Sn) is 0.1 to 0.17, and the oxygen concentration is 2% (volume fraction). In Examples 4 to 6 and Examples 13 to 21 heat-treated at 400 ° C., oxygen deficiency can be suppressed, the carrier mobility is 10 cm ² / V · s or more, and the carrier concentration is 9.0 × 10 ¹⁷ cm. ^-3 or less. Therefore, it was confirmed that the obtained amorphous oxide semiconductor thin film exhibited excellent characteristics. In particular, the amorphous oxide semiconductor thin films obtained in Examples 18 and 19 in which the atomic ratio of Si / (In + Si) is 0.15 and Sn / (In + Si + Sn) is 0.12, the heat treatment temperature is 320. It was also confirmed that the carrier mobility was 15 cm ² / V · s or more and the carrier concentration was 7.0 × 10 ¹⁶ cm ⁻³ or less, and excellent characteristics were exhibited by adjusting the temperature to from 350 ° C. to 350 ° C.

  On the other hand, in Comparative Examples 1, 3, and 4, since Sn is not doped, the carrier concentration cannot be suppressed, and when the thin film is used as a liquid crystal driving switching element, an OFF current cannot be obtained and switching is performed. Operation becomes difficult. In addition, microcrystals were generated by the heat treatment, and etching residues were generated.

In addition, the oxide semiconductor thin film obtained in Comparative Example 2 was crystallized, and the In ₂ O ₃ phase and In ₂ (Si ₂ O ₇ ) having a bixbite structure were generated. Crystals were formed and etching residues were generated.

  Further, in Comparative Example 5, Si / (In + Si) is 0.3 or more as the atomic ratio with respect to the Si content, and when a voltage is applied to the target at the time of sputtering film formation, the resistance value is high and arcing occurs. As a result, unstable discharge occurred, and an oxide semiconductor thin film for evaluation could not be obtained.

  In Comparative Examples 6 and 7, by adding a small amount of Sn, the carrier concentration was suppressed, and an oxide semiconductor thin film with high carrier mobility was achieved while having a low carrier concentration. However, etching residue was generated in the obtained oxide semiconductor thin film because microcrystals were generated by the heat treatment.

Furthermore, in Example 7, as shown in FIG. 2, a diffraction peak derived from the In ₄ Sn ₃ O ₁₂ phase having a fluorite structure was identified at diffraction angles 2θ = 30 ° and around 35 °. On the other hand, in Comparative Examples 3 and 4, unlike Example 7, a diffraction peak derived from the In ₄ Sn ₃ O ₁₂ phase having a fluorite structure was not identified in the vicinity of diffraction angles 2θ = 30 ° and 35 °. That is, as a result of comparison between Example 7 and Comparative Examples 3 and 4, the oxide semiconductor thin film obtained in Example 7 is an In ₄ Sn ₃ O ₁₂ phase having a fluorite structure in an oxide sintered body as a raw material. The reason for this is that the crystallization temperature rises and the amorphous state is obtained.

  S1 mixing process, S2 molding process, S3 sintering process

Claims (7)

An oxide sintered body containing In, Si, and Sn as constituent elements,
A bixbite type structure In ₂ O ₃ phase and a fluorite type structure In ₄ Sn ₃ O ₁₂ phase,
The content of Si with respect to the sum of In and Si is 0.05 ≦ Si / (In + Si) ≦ 0.3 in atomic ratio, and the content of Sn with respect to the sum of In, Si, and Sn Satisfies the relational expression of 0.1 ≦ Sn / (In + Si + Sn) ≦ 0.2 in terms of the atomic ratio. The oxide sintered body according to claim 1, further comprising an In ₂ (Si ₂ O ₇ ) phase having a tortuitite structure.   3. The oxidation according to claim 1, wherein the Si content with respect to the sum of In and Si satisfies a relational expression of 0.1 ≦ Si / (In + Si) <0.2 in atomic ratio. Sintered product. A method for producing an oxide sintered body according to any one of claims 1 to 3,
The content of Si with respect to the sum of In and Si is 0.05 ≦ Si / (In + Si) ≦ 0.3 in atomic ratio, and the content of Sn with respect to the sum of In, Si, and Sn Mixing the indium oxide powder, the silicon dioxide powder, and the tin oxide powder such that the atomic ratio satisfies the relational expression of 0.1 ≦ Sn / (In + Si + Sn) ≦ 0.2,
A molding step of molding the mixed powder obtained in the mixing step;
A method for producing an oxide sintered body, comprising: a firing step of firing the compact obtained in the molding step.   A sputtering target comprising the oxide sintered body according to any one of claims 1 to 3. An amorphous oxide semiconductor thin film composed of an oxide sintered body containing In, Si, and Sn as constituent elements,
The oxide sintered body includes an In ₂ O ₃ phase having a bixbite structure and an In ₄ Sn ₃ O ₁₂ phase having a fluorite structure,
The content of Si with respect to the sum of In and Si is 0.05 ≦ Si / (In + Si) ≦ 0.3 in atomic ratio, and the content of Sn with respect to the sum of In, Si, and Sn Satisfies the relational expression of 0.1 ≦ Sn / (In + Si + Sn) ≦ 0.2 in terms of atomic ratio,
An amorphous oxide semiconductor thin film characterized by having a carrier concentration of 9.8 × 10 ¹⁸ cm ⁻³ or less and a carrier mobility of 5.8 cm ² / V · s or more. The carrier concentration is 9.0 × 10 ¹⁷ cm ⁻³ or less,
The amorphous oxide semiconductor thin film according to claim 6, wherein the carrier mobility is 10 cm ² / V · s or more.

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