JP6277977B2 - Oxide sintered body, sputtering target, and oxide semiconductor thin film obtained using the same - Google Patents

Description

  The present invention relates to an oxide sintered body, a target, and an oxide semiconductor thin film obtained by using the oxide sintered body, and more particularly, an amorphous oxide semiconductor thin film carrier containing indium, gallium, and silicon. Sputtering target enabling concentration reduction, oxide sintered body containing indium, gallium and silicon optimal for obtaining the target, and non-carrier exhibiting low carrier concentration and high carrier mobility obtained by using the same The present invention relates to an oxide semiconductor thin film containing crystalline indium, gallium, and silicon.

  A thin film transistor (hereinafter referred to as TFT) is one type of a field effect transistor (hereinafter referred to as FET). A TFT is a three-terminal element having a gate terminal, a source terminal, and a drain terminal as a basic structure, and a semiconductor thin film formed on a substrate is used as a channel layer through which electrons or holes move, and a voltage is applied to the gate terminal. Is an active element having a function of switching the current between the source terminal and the drain terminal by controlling the current flowing through 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.

With respect to 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 of the oxide. , The composition when crystallized is InGaO ₃ (ZnO) _m (m is a natural number less than 6), 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 · sec) and having a carrier concentration (also referred to as carrier electron concentration) of 10 ¹⁶ / cm ³ or less, and the transparent semi-insulating thin film A thin film transistor characterized by using an insulating amorphous oxide thin film as a channel layer has been proposed.

However, a transparent amorphous oxide thin film (indicated by Patent Document 1), which is formed by a vapor phase film forming method of either sputtering or pulse laser deposition, and is composed of elements of In, Ga, Zn, and O ( It has been pointed out that the carrier electron mobility of the a-IGZO film) remains in the range of approximately 1 to 10 cm ² / (V · sec), and the carrier mobility is insufficient for further high definition display. .

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 is disclosed. However, since the target of Patent Document 2 is a polycrystalline oxide sintered body having a homologous phase crystal structure, the amorphous oxide thin film obtained therefrom has a carrier mobility of about 10 cm ² as in Patent Document 1. / V · s.

As a material for realizing high carrier mobility, in Patent Document 3, gallium is dissolved in indium oxide and the atomic ratio Ga / (Ga + In) is 0.001 to 0.12, and indium with respect to all metal atoms. There has been proposed a thin film transistor characterized by using an oxide thin film having an In ₂ O ₃ bixbite structure with a gallium content of 80 atomic% or more, and gallium is fixed to indium oxide as a raw material. 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 bixbite structure is obtained. An oxide sintered body characterized by having it has been proposed.

  However, when a crystalline oxide semiconductor thin film as proposed in Patent Document 3 is applied to a TFT, variations in TFT characteristics due to crystal grain boundaries are a problem. In particular, it is extremely difficult to form TFTs uniformly on a large glass substrate of the eighth generation or higher.

Patent Document 4 discloses an oxide sintered body having a bixbite structure and containing indium oxide, gallium oxide, and positive trivalent and / or positive tetravalent metal, and has a positive trivalent and / or positive tetravalent metal content. Is a sintered body having a composition range of 100 to 10000 ppm and indium (In) and gallium (Ga) composition ratios satisfying the formula 0.005 <In / (In + Ga) <0.15 in atomic%. In TFT evaluation, an example showing a high mobility of about 60 cm ² / V · s is disclosed.

  However, the oxide semiconductor thin film obtained by the sintered body of Patent Document 4 has a problem that microcrystals and the like are easily generated, and it becomes difficult to form a TFT with a high yield particularly on a large glass substrate. 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 the amorphous film forming 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 the oxide sintered body having substantially only the bigsbite structure of Patent Document 4, the crystallization temperature of the formed amorphous film becomes low, and this is a stage after the film formation. However, there arises a problem that microcrystals are generated and residues are generated in the etching process, or partial crystallization occurs and etching cannot be performed. That is, it becomes difficult to form a desired TFT channel layer pattern by a wet etching method using a photolithography technique or the like, or even if a TFT can be formed, there is a problem that it does not operate stably. .

JP 2010-219538 A JP 2007-0773312 A WO2010 / 032422 WO2011 / 152048

  An object of the present invention is to provide a sputtering target capable of forming an amorphous oxide semiconductor thin film exhibiting good wet etching properties and high carrier mobility, an oxide sintered body optimal for obtaining the target, and a sputtering target thereof. Another object of the present invention is to provide an oxide semiconductor thin film having a low carrier concentration and a high carrier mobility obtained by using the above-described metal.

The inventors of the present invention are oxide sintered bodies made of indium, gallium, and silicon, and the gallium content is 0.08 to 0.49 in terms of Ga / (In + Ga) atomic ratio, and the silicon content There Si / (in + Ga + Si ) 0.25 less than 0.0001 or more in atomic ratio is the oxide sintered body of the _in 2 _{O 3} phase bixbite type structure, as a generation phase other than _in 2 _{O 3} phase β-Ga ₂ O ₃ -type GaInO ₃ phase, or β-Ga ₂ O ₃ -type GaInO ₃ phase and (Ga, In) ₂ O ₃ phase, and tortobitite-type In ₂ (Si ₂ O ₇ ) Amorphous oxide semiconductor thin film prepared by using the above-mentioned oxide sintered body, when composed of a phase, newly exhibits good wet etchability, low carrier concentration and high carrier mobility. Found in It was.

  That is, the first of the present invention contains indium, gallium and silicon as oxides, and the gallium content is 0.08 or more and 0.49 or less in terms of Ga / (In + Ga) atomic ratio, The oxide sintered body is characterized in that the content is 0.0001 or more and less than 0.25 in terms of Si / (In + Ga + Si) atomic ratio.

The second of the present invention is a bixbite type In ₂ O ₃ phase and a β-Ga ₂ O ₃ type GaInO ₃ phase or β-Ga ₂ O ₃ type as a production phase other than the In ₂ O ₃ phase. The oxide sintered body according to the first aspect of the present invention, which is constituted by a GaInO ₃ phase having a structure and a (Ga, In) ₂ O ₃ phase.

The third aspect of the present invention is an oxide sintered body according to the first or second invention, characterized in that it comprises an In ₂ Si ₂ O ₇ phase Toruto by tight structure.

  A fourth aspect of the present invention is the oxide sintered body according to any one of the first to third aspects, wherein the silicon content is 0.01 or more and 0.20 or less in terms of Si / (In + Ga + Si) atomic ratio.

  A fifth aspect of the present invention is the oxide sintered body according to any one of the first to fourth aspects, wherein the gallium content is in a Ga / (In + Ga) atomic ratio of 0.20 to 0.45. .

  The sixth of the present invention is a sputtering target obtained by processing the oxide sintered body according to any one of the first to fifth inventions.

  A seventh aspect of the present invention is an amorphous oxidation characterized by being formed on a substrate by a sputtering method using the sputtering target according to the sixth aspect of the present invention and then subjected to a heat treatment in an oxidizing atmosphere. A semiconductor thin film.

An eighth aspect of the present invention is the oxide semiconductor according to the seventh aspect, wherein the carrier concentration is less than 4.0 × 10 ¹⁸ cm ⁻³ and the carrier mobility is 10 cm ² / V · s or more. It is a thin film.

A ninth aspect of the present invention is the oxide semiconductor thin film according to the eighth aspect, wherein the carrier concentration is 6.0 × 10 ¹⁷ cm ⁻³ or less.

A tenth aspect of the present invention is the oxide semiconductor thin film according to the eighth or ninth aspect, wherein the carrier mobility is 15 cm ² / V · s or more.

An oxide sintered body comprising indium, gallium, and silicon according to the present invention, wherein the gallium content is 0.08 or more and 0.49 or less in terms of Ga / (In + Ga) atomic ratio, and the silicon content is Si / The atomic ratio of (In + Ga + Si) is 0.0001 or more and less than 0.25, and the In ₂ O ₃ phase of the bixbite structure and the β-Ga ₂ O ₃ type structure as a generation phase other than the In ₂ O ₃ phase If GaInO ₃ phase, or _beta-Ga 2 _{O 3} -type structure GaInO ₃ phase and the (Ga, _{an in)} oxide sintered body containing 2 _{O 3} phase, for example used as a sputtering target, sputtering The amorphous oxide semiconductor thin film of the present invention can be obtained by the subsequent heat treatment. The thin film formed by the above-described sputtering film formation has a desired shape by wet etching because it does not generate microcrystals due to the effect of containing a predetermined amount of gallium and silicon and has sufficient amorphousness. Can be patterned. In addition, due to the same effect, the amorphous oxide semiconductor thin film of the present invention exhibits low carrier concentration and high carrier mobility. Therefore, when the amorphous oxide semiconductor thin film of the present invention is applied to a TFT, on / off of the TFT can be increased. Therefore, the oxide sintered body, the target, and the oxide semiconductor thin film obtained using the oxide sintered body of the present invention are extremely useful industrially.

It is the figure which showed the X-ray-diffraction measurement result spectrum of the oxide sintered compact of Example 5,10,11. It is the crystal grain photograph of the oxide sintered compact of Example 11 image | photographed using the scanning transmission electron microscope.

  Below, the oxide sintered compact of this invention, the target for sputtering, and the oxide semiconductor thin film obtained using it are demonstrated in detail.

(1) Oxide sintered body (a) Composition The oxide sintered body of the present invention is an oxide sintered body made of indium, gallium and silicon, and the gallium content is Ga / (In + Ga) atoms. The ratio is 0.08 or more and 0.49 or less, and the silicon content is 0.0001 or more and less than 0.25 by Si / (In + Ga + Si) atomic ratio.

  The gallium content is Ga / (In + Ga) atomic ratio of 0.08 or more and 0.49 or less, and more preferably 0.15 or more and 0.45 or less. Gallium has the effect of increasing the crystallization temperature of the amorphous oxide semiconductor thin film of the present invention. Further, gallium has a strong bonding force with oxygen and has an effect of reducing the amount of oxygen vacancies in the amorphous oxide semiconductor thin film of the present invention. When the gallium content is less than 0.08 in terms of the Ga / (In + Ga) atomic ratio, these effects cannot be obtained sufficiently. On the other hand, when it exceeds 0.49, sufficiently high carrier mobility cannot be obtained as the oxide semiconductor thin film.

  The oxide sintered body of the present invention contains silicon in addition to indium and gallium in the composition range specified as described above. The silicon content is 0.0001 or more and less than 0.25, preferably 0.01 or more and 0.20 or less in terms of the atomic ratio of Si / (In + Ga + Si). Silicon has the effect of increasing the crystallization temperature of the amorphous oxide semiconductor thin film of the present invention. In addition, the addition of silicon suppresses the carrier concentration of the amorphous oxide semiconductor thin film of the present invention. However, when it is 0.25 or more, the bulk resistance value of the sputtering target is increased, and the carrier concentration is increased during sputtering. A homogeneous film cannot be obtained due to abnormal discharge such as arc discharge (arcing) during film formation.

  This effect makes it possible to increase the on / off of the TFT when the amorphous oxide semiconductor thin film of the present invention is applied to the TFT.

(B) Sintered body structure The oxide sintered body of the present invention is composed of an In ₂ O ₃ phase having a bixbite type structure and a GaInO ₃ phase having a β-Ga ₂ O ₃ type structure. (Ga, In) ₂ O ₃ phase may be included to some extent. Furthermore, it may contain an In ₂ (Si ₂ O ₇ ) phase having a tortovite structure.

Here, it is preferable that gallium is dissolved in the In ₂ O ₃ phase having a bixbite structure or constitutes a GaInO ₃ phase having a β-Ga ₂ O ₃ structure. Basically, gallium, which is a positive trivalent ion, replaces the lattice position of indium, which is also a positive trivalent ion, when it is dissolved in the In ₂ O ₃ phase having a bixbite structure. When a GaInO ₃ phase and a (Ga, In) ₂ O ₃ phase having a β-Ga ₂ O ₃ type structure are formed, Ga basically occupies the original lattice position, but the In lattice position is a defect. It may be a slightly substituted solid solution. In addition, gallium is hardly dissolved in the In ₂ O ₃ phase of the bixbite type structure or the β-Ga ₂ O ₃ type GaInO ₃ phase and (Ga, In) ₂ due to reasons such as sintering not progressing. O ₃ phase is not easily generated, as a result, forming a _Ga 2 _{O 3} phase of _beta-Ga 2 _{O 3} -type structure is not preferable. Since the Ga ₂ O ₃ phase has poor conductivity, it causes abnormal discharge. Further, in the case where it is dissolved in In ₂ (Si ₂ O ₇ ) having a tortuitite structure, it is basically replaced with a lattice position of In or Si. It is not preferable to produce a large amount of In ₂ (Si ₂ O ₇ ) having a tortuitite structure because it has poor conductivity and may cause abnormal discharge.

In addition, it is preferable that silicon is dissolved in a Bixbite type In ₂ O ₃ phase or a β-Ga ₂ O ₃ type GaInO ₃ phase. Basically, silicon, which is a cation, replaces the lattice position of indium, which is a cation, when it dissolves in the In ₂ O ₃ phase having a bixbite structure. When a solid solution is formed in the GaInO ₃ phase and the (Ga, In) ₂ O ₃ phase of the β-Ga ₂ O ₃ type structure, the substitution is basically made at the lattice position of In or Ga. Further, when forming In ₂ (Si ₂ O ₇ ) having a tortuitite structure, Si basically occupies the original lattice position, but is slightly substituted and dissolved as a defect in the In lattice position. It doesn't matter.

The oxide sintered body of the present invention is composed of at least a bixbite type In ₂ O ₃ phase, and includes a β-Ga ₂ O ₃ type GaInO ₃ phase and a (Ga, In) ₂ O ₃ phase. In some cases, the crystal grains of these phases preferably have an average particle size of 5 μm or less. Since the crystal grains of these phases are less likely to be sputtered than the In ₂ O ₃ phase crystal grains having a bixbite type structure, nodules are generated when left unexposed, which may cause arcing.

(2) Method for producing oxide sintered body In producing the oxide sintered body of the present invention, it is preferable to use an oxide powder composed of indium oxide powder and gallium oxide powder, and silicon dioxide powder as raw material powders. Silicon monoxide powder or metal silicon powder may be used.

  In the manufacturing process of the oxide sintered body of the present invention, these raw material powders are mixed and then molded, and the molded product is sintered by a normal pressure sintering method. The production phase of the oxide sintered body structure of the present invention strongly depends on the production conditions in each step of the oxide sintered body, for example, the particle size of the raw material powder, the mixing conditions, and the sintering conditions.

The structure of the oxide sintered body of the present invention is that each crystal grain of an In ₂ O ₃ phase having a bixbite type structure, a GaInO ₃ phase having a β-Ga ₂ O ₃ type structure, and a (Ga, In) ₂ O ₃ phase is formed. The average particle size of the raw material powder is more preferably 3.0 μm or less, and even more preferably 1.0 μm or less.

  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.

  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.

  However, in the case of gallium oxide powder, since the amount used is still small compared to indium oxide powder, it may be difficult to obtain a raw material powder having an average particle size of 1.0 μm or less. When only coarse gallium oxide powder is available, it is necessary to grind to an average particle size of 1.0 μm or less.

  In the sintering step of the oxide sintered body of the present invention, it is preferable to apply the 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.

When using the normal pressure sintering method, a molded body is first prepared as described above. The raw material powder is put in a resin pot and mixed with a binder (for example, PVA) or the like by a wet ball mill or the like. The oxide sintered body of the present invention is composed of a bixbite type In ₂ O ₃ phase, or a bixbite type In ₂ O ₃ phase and a β-Ga ₂ O ₃ type GaInO ₃ phase, Although it may contain a Ga, In) ₂ O ₃ phase, it is preferable that the crystal grains of these phases are finely dispersed with an average grain size of 5 μm or less. _{Further, (Ga, In) 2 O} 3 generation of phase are preferably as much as possible suppressed. In addition, it is necessary not to generate a Ga ₂ O ₃ phase having a β-Ga ₂ O ₃ type structure that causes arcing in addition to these phases. In order to satisfy these requirements, the ball mill mixing is preferably performed for 18 hours or more. At this time, a hard ZrO ₂ ball may be used as the mixing ball. After mixing, the slurry is taken out, filtered, dried and granulated. 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.

  In the sintering step of the normal pressure sintering method, an atmosphere in which oxygen is present is preferable, and the oxygen volume fraction in the atmosphere is more preferably more than 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.

  The temperature range of atmospheric pressure sintering is preferably 1200 to 1550 ° C., and more preferably 1350 to 1450 ° C. in an atmosphere in which oxygen gas is introduced into the atmosphere in the sintering furnace. The sintering time is preferably 10 to 30 hours, more preferably 15 to 25 hours.

By using the sintering temperature within the above range and the oxide powder composed of indium oxide powder and gallium oxide powder adjusted to the average particle size of 1.0 μm or less, and silicon dioxide powder as the raw material powder, the bixbite type is mainly used. _in 2 _{O 3} phase and the _β-Ga 2 GaInO _{3-phase O 3} -type structure of structure, or (Ga, _{an in)} composed of a 2 _{O 3} phase.

When the sintering temperature is less than 1200 ° C., the sintering reaction does not proceed sufficiently. On the other hand, when 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. Disappear. In particular, since the oxide sintered body of the present invention has a gallium content of 0.08 or more in terms of a Ga / (In + Ga) atomic ratio, the sintering temperature is preferably 1450 ° C. or less. This is because in the temperature range around 1500 ° C., the formation of (Ga, In) ₂ O ₃ phase may be remarkable. A small amount of the (Ga, In) ₂ O ₃ phase is not a problem, but a large amount is not preferable because it may cause a decrease in film formation rate or arcing.

  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, when introducing oxygen, the introduction of oxygen is stopped, and the temperature can be lowered to 1000 ° C. at a rate of 0.2-5 ° C./min, particularly 0.2 ° C./min to 1 ° C./min. preferable.

(3) Target The target of the present invention is obtained by processing the oxide sintered body of the present invention 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 oxide sintered body of the present invention is preferably 6.3 g / cm ³ or more, 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 6.3 g / cm ^3, more preferably if 3.4~5.5g / cm ^3. In this case, the sintering temperature may be better than 1200 ° C.

(4) Oxide semiconductor thin film and method for forming the same The amorphous oxide semiconductor thin film of the present invention is mainly an amorphous oxide once formed on a substrate by sputtering using the above sputtering target. It is obtained by forming a thin film and then applying an annealing treatment.

The sputtering target is obtained from the oxide sintered body of the present invention, and the oxide sintered body structure, In ₂ O ₃ phase of bixbite type structure and GaInO ₃ phase of β-Ga ₂ O ₃ type structure Alternatively _beta-Ga 2 _{O 3} -type structure GaInO ₃ phase and the (Ga, _in) tissue being basic structure by 2 _{O 3} phase is important. In order to obtain the amorphous oxide semiconductor thin film of the present invention, it is important that the crystallization temperature of the amorphous oxide semiconductor thin film is high, which is related to the oxide sintered body structure. . That is, as in the oxide sintered body of the present invention, not only the _In 2 _{O 3} phase bixbyite structure, the _β-Ga 2 _{O 3} type GaInO ₃ phase or _β-Ga 2 _{O 3} -type structure of structure When the GaInO ₃ phase and the (Ga, In) ₂ O ₃ phase are also included, the oxide thin film obtained therefrom exhibits a high crystallization temperature, that is, a crystallization temperature of 300 ° C. or higher, more preferably 350 ° C. or higher, and is stable. Becomes amorphous. In addition, when it contains an In ₂ (Si ₂ O ₇ ) phase having a tortuitite structure, it exhibits a higher crystallization temperature and becomes more stable amorphous. On the other hand, when the oxide sintered body is constituted only by the In ₂ O ₃ phase having a bixbite type structure, the oxide thin film obtained therefrom has a low crystallization temperature of around 200 ° C. and is amorphous. Is not. In this case, microcrystals are already generated after the film formation and the amorphousness is not maintained, and patterning processing by wet etching becomes difficult.

  In the film formation process of the amorphous oxide semiconductor thin film of the present invention, a general sputtering method is used. In particular, in the case of a direct current (DC) sputtering method, there is little thermal influence at the time of film formation, and high-speed formation is achieved. Since a film is possible, it is industrially advantageous. In order to form the oxide semiconductor thin film of the present invention by a direct current sputtering method, it is preferable to use a mixed gas composed of an inert gas and oxygen, particularly argon and oxygen, as a sputtering gas. Further, it is preferable to perform sputtering in a chamber of the sputtering apparatus at a pressure of 0.1 to 1 Pa, particularly 0.2 to 0.8 Pa.

  The substrate is typically a glass substrate and is preferably alkali-free glass, but any substrate that can withstand the above process conditions can be used.

In the amorphous oxide thin film forming step, 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 is set to 0.2 to 0.8 Pa. Pre-sputtering can be performed by applying DC power to generate DC plasma such that the DC power with respect to the target area, that is, the DC power density is in the range of about 1 to 7 W / cm ² . 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 film formation step, the direct-current power to be input is increased in order to improve the film formation speed.

  The amorphous oxide semiconductor thin film of the present invention can be obtained by forming the amorphous oxide thin film and annealing it. As one of the methods up to the annealing treatment, for example, an amorphous oxide thin film is once formed at a low temperature such as near room temperature, and then an annealing treatment is performed at a temperature lower than the crystallization temperature to maintain the amorphous state. A physical semiconductor thin film is obtained. As another method, the substrate is heated to a temperature lower than the crystallization temperature, preferably 100 to 300 ° C., to form an amorphous oxide semiconductor thin film. This may be followed by further annealing. The heating temperature in these two methods may be about 600 ° C. or less, and can be made below the strain point of the alkali-free glass substrate.

  The amorphous oxide semiconductor thin film of the present invention can be obtained by forming an amorphous oxide thin film and then annealing it. The annealing 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 annealing temperature is 200 to 600 ° C, preferably 300 to 500 ° C. The annealing time is 1 to 120 minutes, preferably 5 to 60 minutes, which is maintained at the annealing temperature.

  The composition of indium, gallium, and silicon of the amorphous oxide thin film and the amorphous oxide semiconductor thin film is substantially the same as the composition of the oxide sintered body of the present invention. That is, it is an amorphous oxide-baked semiconductor thin film containing indium and gallium as oxides and containing silicon. The gallium content is 0.08 or more and 0.49 or less in Ga / (In + Ga) atomic ratio, and the silicon content is 0.0001 or more and less than 0.25 in Si / (In + Ga + Si) atomic ratio. .

The amorphous oxide semiconductor thin film of the present invention is formed by using an oxide sintered body whose composition and structure are controlled as described above as a sputtering target, etc., and annealed under the appropriate conditions described above. Thus, the carrier concentration decreases to 4.0 × 10 ¹⁸ cm ⁻³ or less, and the carrier mobility is 10 cm ² / V · s or more. More preferably, the carrier mobility is 15 cm ² / V · s or more, and particularly preferably 20 cm ² / V · s or more.

The amorphous oxide semiconductor thin film of the present invention is subjected to fine processing necessary for applications such as TFTs by wet etching or dry etching. Usually, after forming an amorphous oxide thin film once by selecting an appropriate substrate temperature from a temperature lower than the crystallization temperature, for example, a range from room temperature to 300 ° C., fine processing by wet etching can be performed. As the etchant, any weak acid can be used, but a weak acid mainly composed of oxalic acid or hydrochloric acid is preferred. For example, commercially available products such as ITO-06N manufactured by Kanto Chemical Co., Ltd. can be used. Depending on the configuration of the TFT, dry etching may be selected.
Although the film thickness of the amorphous oxide semiconductor thin film of this invention is not limited, It is 10-500 nm, Preferably it is 20-300 nm, More preferably, it is 30-100 nm. If the 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 it exceeds 500 nm, a problem of productivity occurs, which is not preferable.

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

<Evaluation of oxide sintered body>
The composition of the metal element of the obtained oxide sintered body was examined by ICP emission spectroscopy. Using the end material of the obtained oxide sintered body, the generated phase was identified by a powder method using an X-ray diffractometer (manufactured by Philips). The obtained oxide sintered body was thinned using a focused ion beam apparatus, and crystal grains were observed with a scanning transmission electron microscope (manufactured by Hitachi High-Technologies), and energy dispersive X-ray analysis (Hitachi High) The composition of each crystal grain was examined by Technologies).

<Evaluation of basic properties of oxide thin film>
The composition of the obtained oxide thin film was examined by ICP emission spectroscopy. The film thickness of the oxide thin film was measured with a surface roughness meter (manufactured by Tencor). The film formation rate was calculated from the film thickness and the film formation time. The carrier concentration and mobility of the oxide thin film were determined by a Hall effect measuring device (manufactured by Toyo Technica). The formation phase of the film was identified by X-ray diffraction measurement.

“Preparation of sintered oxide and oxide thin film”
Indium oxide powder, gallium oxide powder, and silicon dioxide powder were adjusted to an average particle size of 1.0 μm or less to obtain raw material powder. These raw material powders were prepared so that the Ga / (In + Ga) atom number ratio and Si / (In + Ga + Si) atom number ratio in the examples and comparative examples in Tables 1 and 2 were as shown in FIG. And mixed with a wet ball mill. At this time, hard ZrO ₂ balls were used and the mixing time was 18 hours. After mixing, the slurry was taken out, filtered, dried and granulated. The granulated product was molded by applying a pressure of 3 ton / cm ² with a cold isostatic press.

Next, the compact was sintered as follows. 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. When cooling after sintering, the introduction of oxygen was stopped, and the temperature was lowered to 1000 ° C. at 1 ° C./min.

  When the composition analysis of the obtained oxide sintered body was performed by ICP emission spectroscopy, it was confirmed in any of the Examples that the metal element was almost the same as the charged composition at the time of blending the raw material powder.

  Next, phase identification of the oxide sintered body by X-ray diffraction measurement (X-ray diffraction, XRD), observation of crystal grains by a scanning transmission electron microscope (STEM), and energy dispersive X-ray Table 1 shows the results of the compositional analysis of each crystal grain by (Energy dispersive X-ray spectroscopy, EDX) analysis.

The results of phase identification with the X-ray diffraction measurement results of Examples 5, 10, and 11 are shown in FIG. 1, and the observation results of the scanning transmission electron microscope of Example 11 are shown in FIG. Observation with a scanning transmission electron microscope confirmed the presence of two types of crystal grains: white crystal grains and black crystal grains. Furthermore, from the results of X-ray diffraction measurement and energy dispersive X-ray analysis, the crystal grains that appear white are In ₂ O ₃ phases with a bixbite structure, and the crystal grains that appear black are GaInO ₃ phases with a β-Ga ₂ O ₃ type structure It can be seen that it is.

  The oxide sintered body was processed into a size of 152 mm in diameter and 5 mm in thickness, 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.

Using the sputtering targets of Examples and Comparative Examples and an alkali-free glass substrate (Corning EagleXG), film formation by direct current sputtering was performed at the substrate temperatures shown in Table 2. The sputtering target was attached to the cathode of a DC magnetron sputtering apparatus (manufactured by Tokki) equipped with a DC power supply having no 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 gallium and silicon in each target, and the gas pressure is adjusted to 0.6 Pa. did. 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. At this time, it was confirmed whether or not arcing occurred. It was confirmed that the composition of the obtained oxide semiconductor thin film was almost the same as that of the target.

As shown in Table 2, the oxide semiconductor thin film thus formed was subjected to heat treatment at 300 to 500 ° C. for 30 to 60 minutes in oxygen, and the crystallinity of the oxide semiconductor thin film after heat treatment was determined by X-ray diffraction measurement. Examined. As a result, the oxide semiconductor thin films of Comparative Examples 1 and 2 were crystallized, and the In ₂ O ₃ phase having a bixbite structure was formed. Was. For the crystallized oxide semiconductor thin film, the crystal phase constituting the oxide semiconductor thin film was identified. The Hall effect measurement of the oxide semiconductor thin film was performed about the Example and Comparative Example except Comparative Examples 1, 2, 4-6, and 8, and carrier concentration and carrier mobility were calculated | required. The evaluation results obtained are summarized in Table 2.

"Evaluation"
From the result of Table 1, in Examples 1-19, gallium content is 0.08 or more and 0.49 or less in Ga / (In + Ga) atomic ratio, and silicon content is Si / (In + Ga + Si) atomic ratio. If it is less than 0.0001 or more and 0.25 is, _{an in} 2 _{O 3} phase and _beta-Ga 2 GaInO _{3-phase O 3} -type structure bixbite type structure, and GaInO _{3-phase beta-Ga} 2 _{O 3} -type structure It was composed of (Ga, In) ₂ O ₃ phase or tortovite type In ₂ (Si ₂ O ₇ ). On the other hand, in Comparative Examples 1-3, the gallium or silicon content of the oxide sintered body is less than the range of the present invention. In Comparative Examples 1 and 2, for this reason, the oxide sintered body is composed of only the In ₂ O ₃ phase having a bixbite structure. In Comparative Examples 3 to 6 and 8, since the silicon content is excessive, arcing occurs at the time of sputtering film formation, and a homogeneous film cannot be obtained. The body is not obtained.

  From the results shown in Table 2, it is an amorphous oxide semiconductor thin film made of indium, gallium and silicon, and the gallium content is 0.08 or more and 0.49 or less in Ga / (In + Ga) atomic ratio. The characteristics of the oxide semiconductor thin film in which the silicon content was controlled to 0.0001 or more and less than 0.25 in the Si / (In + Ga + Si) atomic ratio were shown.

It can be seen that the oxide semiconductor thin films of the examples are all amorphous. In addition, it can be seen that the oxide semiconductor thin film of Example shows excellent characteristics with a carrier concentration of 4.0 × 10 ¹⁸ cm ⁻³ or less and a carrier mobility of 10 cm ² / V · s or more.

On the other hand, in Comparative Examples 1 and 2, the annealed oxide semiconductor thin film was crystallized, and an In ₂ O ₃ phase having a bixbite structure was generated and was not amorphous. Further, in the oxide semiconductor thin films of Comparative Examples 3 to 6 and 8, since the silicon content exceeded the range of the present invention, arcing occurred and a uniform film was not obtained. Mobility was not evaluated. In the oxide semiconductor of Comparative Example 7, since the above Ga / (In + Ga) exceeds the upper limit, it can be seen that the carrier mobility is less than 10 cm ² / V · s.

Claims (9)

Containing indium, gallium and silicon as oxides,
The gallium content is 0.08 or more and 0.49 or less in Ga / (In + Ga) atomic ratio.
The silicon content is 0.0001 or more and less than 0.25 in terms of Si / (In + Ga + Si) atomic ratio,
And _In 2 _{O 3} phase main phase bixbite type structure, _{an In} 2 GaInO _{3-phase beta-Ga} 2 _{O 3} -type structure as _{O 3} other than the phase generated phase, or _beta-Ga 2 _{O 3} type GaInO structures ₃ An oxide sintered body comprising a phase and a (Ga, In) ₂ O ₃ phase. _2. The oxide sintered body according to claim 1, comprising an In ₂ (Si ₂ O ₇ ) phase having a tortuitite structure.   The oxide sintered body according to claim 1 or 2, wherein the silicon content is 0.01 or more and 0.20 or less in terms of Si / (In + Ga + Si) atomic ratio.   4. The oxide sintered body according to claim 1, wherein the gallium content is 0.15 or more and 0.45 or less in a Ga / (In + Ga) atomic ratio.   A sputtering target obtained by processing the oxide sintered body according to claim 1. A method for producing an amorphous oxide semiconductor thin film , comprising: a sputtering target according to claim 5; and a heat treatment in an oxidizing atmosphere after being formed on a substrate by a sputtering method . The oxide semiconductor thin film according to claim 6, wherein an oxide semiconductor thin film having a carrier concentration of less than 4.0 × 10 ¹⁸ cm ⁻³ and a carrier mobility of 10 cm ² / V · s or more is manufactured. Manufacturing method . The method for producing an oxide semiconductor thin film according to claim 7, wherein an oxide semiconductor thin film having a carrier concentration of 6.0 × 10 ¹⁷ cm ⁻³ or less is produced . The manufacturing method of the oxide semiconductor thin film of Claim 7 or 8 which manufactures the oxide semiconductor thin film whose carrier mobility is 15 cm < ² > / V * s or more.