KR20170101981A - An oxide sintered body, a target for sputtering, and an oxide semiconductor thin film obtained by using the same - Google Patents

Abstract

A target for sputtering capable of forming an amorphous oxide semiconductor thin film exhibiting good wet etching properties and high carrier mobility, an oxide sintered body optimum for obtaining the oxide target, and an oxide semiconductor thin film exhibiting a low carrier density and a high carrier mobility, .
Ga / (In + Ga) atom ratio of 0.08 or more to 0.49 or less, and the content of silicon is 0.0001 or more and 0.25 or less in terms of Si / (In + Ga + Si) atomic ratio, By mass of the oxide-sintered body.

Description

An oxide sintered body, a target for sputtering, and an oxide semiconductor thin film obtained by using the same

The present invention relates to an oxide-sintered body, a target, and an oxide semiconductor thin film obtained by using the oxide-sintered body, a target, and more particularly, to a thin oxide semiconductor thin film formed by sputtering for reducing carrier concentration of an amorphous oxide semiconductor thin film by containing indium, gallium, An oxide sintered body containing indium, gallium, and silicon, which is optimum for obtaining a target, and an oxide semiconductor thin film containing amorphous indium, gallium, and silicon, which exhibit a low carrier concentration and a high carrier mobility obtained using the oxide sintered body, .

BACKGROUND ART Thin film transistors (hereinafter, referred to as TFTs) are a type of field effect transistors (hereinafter, referred to as FETs). A TFT is a three-terminal element having a gate terminal, a source terminal, and a drain terminal as a basic structure, and uses a semiconductor thin film formed on a substrate as a channel layer in which electrons or holes move, And controls the current flowing in the channel layer and switches the current between the source terminal and the drain terminal. The TFT is the most widely used electronic device at present, and there is a liquid crystal driving element as a typical application thereof.

At present, the most widely used TFT is a metal-insulator-semiconductor-FET (MIS-FET) having a polycrystalline silicon film or an amorphous silicon film as a channel layer material. Since a MIS-FET using silicon is opaque to visible light, a transparent circuit can not be formed. Therefore, when the MIS-FET is applied as a switching element for liquid crystal driving of a liquid crystal display, the aperture ratio of the display pixel becomes small.

In addition, in recent years, as the liquid crystal is required to have a high resolution, high-speed driving is required for the liquid crystal driving switching element. In order to realize high-speed driving, it has been necessary to use a semiconductor thin film having a mobility of electrons or holes as a carrier 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 a vapor phase film formation method and composed of elements of In, Ga, Zn, and O, wherein the composition of the oxide is such that the composition when crystallized is InGaO ₃ (ZnO) _m (m is a natural number less than 6), without the addition of the impurity ions, and the carrier mobility (also referred to as electron carrier mobility) is more than 1 cm ² V ^-1 sec ^-1, and carrier concentration (carrier (Hereinafter also referred to as " electron concentration ") of 10 ¹⁶ cm ^-3 or less, and a thin film transistor characterized in that the transparent semi-insulating amorphous oxide thin film is a channel layer .

However, the transparent amorphous oxide thin film (a-IGZO film) which is proposed by Patent Document 1 and is formed by any one of the vapor phase film formation method of the sputtering method and the pulse laser vapor deposition method and composed of the elements of In, Ga, Zn and O, Carrier electron mobility is in the range of approximately 1 to 10 cm ² / (V · sec), indicating that the carrier mobility is insufficient for better flatness of the display.

Patent Document 2 discloses a sputtering target for forming an amorphous oxide thin film described in Patent Document 1, that is, a sintered product target containing at least In, Zn, and Ga, and has a composition of In, Zn, Ga , And a relative density of 75% or more and a resistance value (?) Of 50 Ωcm or less. However, since the target of Patent Document 2 is a polycrystalline oxide sintered body showing a crystalline structure on the homologous phase, the amorphous oxide thin film obtained therefrom has a carrier mobility of about 10 cm ² V ^{- 1} sec ^{- It} stays at about ^one degree.

As a material for realizing a high carrier mobility, Patent Document 3 discloses a material in which gallium is solid-solved in indium oxide, atomic ratio Ga / (Ga + In) is 0.001 to 0.12, indium A thin film transistor characterized by using an oxide thin film having a content of gallium of 80 atomic% or more and having a Big bite structure of In ₂ O ₃ is proposed. As a material of the thin film transistor, gallium is dissolved in indium oxide, There is proposed an oxide sintered body characterized in that Ga / (Ga + In) is 0.001 to 0.12, indium and gallium content to all metal atoms is 80 atomic% or more, and has a Bigbite structure of In ₂ O ₃ .

However, when a crystalline oxide semiconductor thin film proposed in Patent Document 3 is applied to a TFT, the deviation of TFT characteristics caused by grain boundaries is a problem. In particular, it is very difficult to uniformly form TFTs on a large glass substrate of the eighth generation or more.

Patent Document 4 discloses an oxide sintered body having a Bigbite structure and containing indium oxide, gallium oxide, and a positive trivalent and / or tetravalent metal, wherein the positive and negative valence metal contents are 100 (In + Ga) < 0.15 in terms of atomic%, and in the TFT evaluation, a sintered body having a composition ratio of indium (In) and gallium cm ² V ^{- 1} is disclosed embodiment showing a high degree of mobility of sec ^-1.

However, in the oxide semiconductor thin film obtained by the sintered body of Patent Document 4, microcrystalline or the like is liable to be generated, and in particular, it is difficult to form a TFT on a large glass substrate with good yield. Generally, in an oxide semiconductor thin film transistor manufacturing process, 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 process, wet etching is performed with a weak acid such as an aqueous solution containing oxalic acid, hydrochloric acid, or the like, in order to perform patterning in the shape of a desired channel layer. However, in the case of using an oxide-sintered body consisting essentially of the Bigbite structure of Patent Document 4, the crystallization temperature of the formed amorphous film is lowered, so that microcrystalline is already generated at the stage after the film formation to generate a residue in the etching process, There arises a problem that it is crystallized and can not be etched. That is, it is difficult to form a desired TFT channel layer pattern by a wet etching method using a photolithography technique or the like, or a problem arises such that stable operation can not be performed even if a TFT can be formed.

Patent Document 1: JP-A-2010-219538 Patent Document 2: JP-A 2007-073312 Patent Document 3: WO2010 / 032422 Patent Document 4: 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 optimum for obtaining the same, and a low carrier concentration and high carrier mobility And to provide an oxide semiconductor thin film which exhibits a high degree of crystallinity.

The present inventors have found that an oxide sintered body made of indium, gallium and silicon has a gallium content of not less than 0.08 and not more than 0.49 in terms of Ga / (In + Ga) atomic ratio and having a silicon content of Si / (In + Ga + Si) 0.0001 0.25 lower than the oxide-sintered body with a defense, and Biggs byte structure of in ₂ O ₃ phase (相), in ₂ O of the ₃ β-Ga ₂ O ₃ structure a generation phase other than the phase GaInO ₃ phase, or β -Ga ₂ O ₃ in the case of the structure GaInO ₃ phase and (Ga, in) ₂ O ₃ phase, soil Stuttgart composed of the phase of the tight structure by _{in 2 (Si 2 O 7)} , using the oxide-sintered body The amorphous oxide semiconductor thin film produced by the present invention has a good wet etching property, a low carrier concentration and a high carrier mobility.

That is, the first aspect of the present invention is a nitride semiconductor device comprising indium, gallium, and silicon as oxides, wherein the content of gallium is 0.08 or more and 0.49 or less in terms of Ga / (In + Ga) atomic ratio, + Ga < + > Si) atomic ratio of from 0.0001 to less than 0.25.

Claim 2 of the present invention, Biggs byte structure of In ₂ O ₃ phase and, In ₂ O of the ₃ β-Ga ₂ O ₃ structure a generation phase other than the phase GaInO ₃ phase, or a β-Ga ₂ O ₃ type (Ga, In) ₂ O ₃ phase of a GaInO ₃ phase structure of the first aspect of the present invention.

A third aspect of the present invention is the oxide-sintered body according to the first or second invention, characterized in that it comprises an In ₂ Si ₂ O ₇ phase of a tort-

A fourth aspect of the present invention is the oxide-sintered body according to any one of the first to third inventions, wherein the content of silicon is 0.01 to 0.20 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 content of gallium is in a range of Ga / (In + Ga) atomic ratio of 0.20 to 0.45.

A sixth aspect of the present invention is a sputtering target obtained by processing the oxide-sintered body according to any one of the first to fifth aspects of the invention.

A seventh aspect of the present invention is an amorphous oxide semiconductor thin film, which is 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.

Claim 8 of the present invention, the carrier concentration is less than 4.0 × 10 ¹⁸ cm ^-3, and the carrier mobility is 10 cm ² V ^- an oxide semiconductor thin film according to the seventh invention, characterized in that not less than ¹ sec ^-1.

Claim 9 of the present invention, an oxide semiconductor thin film according to the eighth invention, characterized in that the carrier concentration is not more than 6.0 × 10 ¹⁷ cm ^-3.

Claim 10 of the present invention is that the carrier mobility of 15 cm ² V ^- an oxide semiconductor thin film according to the eighth or ninth aspect of the invention less than ¹ sec ^-1.

The oxide-sintered body made of indium, gallium, and silicon according to the present invention is characterized in that the content of gallium is 0.08 or more and 0.49 or less in terms of Ga / (In + Ga) atom number ratio and the content of silicon is in the range of atomic ratio of Si / (In + Ga + Si) to less than 0.0001 0.25, Biggs byte structure of in ₂ O ₃ phase and, in ₂ O of the ₃ β-Ga ₂ O ₃ structure a generation phase other than the phase GaInO ₃ phase, or a β-Ga ₂ O ₃ type the structure of GaInO ₃ phase and (Ga, in) is formed by a case of use as a target for the ₂ O ₃ onto the oxide-sintered body containing, for example, sputtering, sputtering deposition, being that after the heat treatment, the amorphous oxide of the present invention A semiconductor thin film can be obtained. The thin film formed by the above sputtering film formation can be patterned into a desired shape by wet etching because the thin film formed by the sputtering film has sufficient amorphism without producing microcrystalline or the like due to the effect of containing a predetermined amount of gallium and silicon . Further, according to this effect, the amorphous oxide semiconductor thin film of the present invention exhibits a low carrier concentration and a 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 industrially very useful.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram showing spectra of X-ray diffraction measurement results of oxide-sintered bodies of Examples 5, 10 and 11. FIG.
2 is a photograph of the crystal grains of the oxide-sintered body of Example 11 taken using a scanning transmission electron microscope.

Hereinafter, the oxide-sintered body of the present invention, the target for sputtering, and the oxide semiconductor thin film obtained by using the same will be described in detail.

(1) Sintered oxide

(a) composition

The oxide-sintered body of the present invention is an oxide-sintered body made of indium, gallium, and silicon, wherein the content of gallium is 0.08 or more and 0.49 or less in terms of Ga / (In + Ga) atomic ratio and the content of silicon is Si / (In + Ga + Si ) Atomic ratio of 0.0001 or more and less than 0.25.

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

The oxide-sintered body of the present invention contains silicon in addition to indium and gallium in the composition ranges as described above. It is preferable that the content of silicon is 0.0001 or more and less than 0.25, and more preferably 0.01 or more and 0.20 or less in atomic ratio of Si / (In + Ga + Si). Silicon has an effect of raising the crystallization temperature of the amorphous oxide semiconductor thin film of the present invention. Further, by adding silicon, the carrier concentration of the amorphous oxide semiconductor thin film of the present invention is suppressed, but when it is 0.25 or more, the bulk resistance value of the sputtering target becomes high, and when the film is deposited during sputtering, A homogeneous film can not be obtained.

With this effect, when the amorphous oxide semiconductor thin film of the present invention is applied to a TFT, on / off of the TFT can be increased.

(b) Sintered body structure

The oxide-sintered body of the present invention is constituted by a GaInO ₃ phase of In ₂ O ₃ phase and a β-Ga ₂ O ₃ type structure of a Bigbyte type structure, but additionally contains a (Ga, In) ₂ O ₃ phase Maybe. Further, it may contain an In ₂ (Si ₂ O ₇ ) phase of a tort-veit type structure.

It is preferable that gallium is dissolved in the In ₂ O ₃ phase of the Bigbyte type structure or the GaInO ₃ phase of the β-Ga ₂ O ₃ type structure. Gallium, which is basically a trivalent ion, replaces the lattice position of indium, which is also a tetravalent ion, when it is solid in the In ₂ O ₃ phase of the Bigbyte type structure. In the case of constituting the GaInO ₃ phase and the (Ga, In) ₂ O ₃ phase of the β-Ga ₂ O ₃ structure, Ga is basically occupied at the original lattice position. However, It does not matter. Further, gallium is difficult to solidify in the In ₂ O ₃ phase of the Big-Byte structure, or the GaInO ₃ phase of the β-Ga ₂ O ₃ type structure and the (Ga, In) ₂ O ₃ phase is difficult to be formed. As a result, it is not preferable to form a Ga ₂ O ₃ phase of a β-Ga ₂ O ₃ type structure. Since the Ga ₂ O ₃ phase lacks conductivity, it causes an abnormal discharge. When the compound is dissolved in In ₂ (Si ₂ O ₇ ) of the tort-tote type structure, it is basically substituted into the lattice position of In or Si. Since In ₂ (Si ₂ O ₇ ) of the tort-buttite structure has insufficient conductivity and may cause an abnormal discharge, it is not preferable to generate a large amount of In ₂ (Si ₂ O ₇ ).

It is also preferable that the silicon is dissolved in the In ₂ O ₃ phase of the Bigbyte type structure or the GaInO ₃ phase of the β-Ga ₂ O ₃ type structure. Basically, the cationic silicon replaces the lattice position of indium, which is a cation, when it is solid on the In ₂ O ₃ phase of the Bigbyte type structure. In the case of solid solution in the GaInO ₃ phase and (Ga, In) ₂ O ₃ phase of the? -Ga ₂ O ₃ structure, basically, it is substituted at the lattice position of In or Ga. When In ₂ (Si ₂ O ₇ ) having a tobitite structure is to be formed, Si may inherently occupy the lattice position, but it may be slightly substituted as a defect at the lattice position of In.

The oxide-sintered body of the present invention is constituted by an In ₂ O ₃ phase of at least a Big-Byte structure and includes a GaInO ₃ phase and a (Ga, In) ₂ O ₃ phase of a β-Ga ₂ O ₃ structure , But the crystal grains of these phases preferably have an average particle diameter of 5 mu m or less. The crystal grains of these phases are difficult to be sputtered compared with the crystal grains of the In ₂ O ₃ phase of the Bigbyte type structure, so that the crystal grains are left as they are, resulting in generation of nodules and arcing.

(2) Manufacturing method of oxide sintered body

In the production of 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 a silicon dioxide powder as raw material powders, but silicon monoxide powder or metal silicon powder may also be used.

In the production process of the oxide-sintered body of the present invention, these raw material powders are mixed and then molded, and the formed product is sintered by a normal-pressure sintering method. The generation 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 powder, the mixing condition and the sintering condition.

Organization of the oxide-sintered body of this invention ₃ In ₂ O of Biggs byte structure phase, β-Ga ₂ O of the _3-like structure GaInO ₃ phase, and (Ga, In) of each crystal grain on the ₂ O ₃ a is less than or equal to 5 ㎛ It is preferable to control the average particle diameter of the raw material powder to 3.0 탆 or less, more preferably 1.0 탆 or less.

The indium oxide powder is a raw material for ITO (indium-tin-doped indium oxide), and the development of fine indium oxide powder excellent in sintering property has been progressed with improvement of ITO. Since indium oxide powder is 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 탆 or less in recent years.

Since the 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 diameter of 1.0 mu m or less.

However, in the case of the gallium oxide powder, since the amount of the gallium oxide powder to be used is still smaller than that of the indium oxide powder, it is sometimes difficult to obtain a raw material powder having an average particle diameter of 1.0 mu m or less. In the case where only coarse gallium oxide powder can be obtained, it is necessary to crush to an average particle size of 1.0 탆 or less.

In the sintering step of the oxide-sintered body of the present invention, application of the pressure-sintering method is preferable. The atmospheric pressure sintering method is a simple and industrially advantageous method, and is a preferable means from the viewpoint of low cost.

In the case of using the normal-pressure sintering method, as described above, a formed body is first produced. The raw material powder is put into a resin port and mixed with a binder (for example, PVA) or the like with a wet ball mill or the like. The oxide sintered body of the present invention is constituted by the VIX-byte structure of In ₂ O ₃ phase, or Biggs byte structure of In ₂ O ₃ phase and a β-Ga ₂ O ₃ structure of GaInO _3, also (Ga, In) ₂ O ₃ phase, it is preferable that the crystal grains of these phases are finely dispersed in an average particle diameter of 5 μm or less. In addition, it is preferable that the formation of the (Ga, In) ₂ O ₃ phase is inhibited as much as possible. In addition, in addition to these phases, it is necessary not to generate the Ga ₂ O ₃ phase of the β-Ga ₂ O ₃ -type structure which causes the arcing. In order to satisfy these requirements, it is preferable to mix the ball mill for 18 hours or more. At this time, as the mixing ball, a hard ZrO ₂ ball may be used. After mixing, the slurry is extracted, filtered, dried and granulated. Thereafter, the obtained assembly is molded by applying a pressure of about 9.8 MPa (0.1 ton / cm ² ) to 294 MPa (3 ton / cm ² ) using a cold isostatic press.

In the sintering step of the atmospheric pressure sintering method, the atmosphere is preferably in the presence of oxygen, and more preferably the volume fraction of oxygen in the atmosphere exceeds 20%. Particularly, when the oxygen volume fraction exceeds 20%, the oxide sintered body is further densified. Owing to the excess oxygen in the atmosphere, the sintering of the surface of the molded body proceeds at an early stage of sintering. Subsequently, sintering in a reduced state inside the formed body proceeds, and finally a high-density oxide sintered body is obtained.

In an atmosphere in which oxygen is not present, sintering of the surface of the formed body is not preceded, and consequently, the density of the sintered body is not progressively increased. If oxygen is not present, indium oxide is decomposed at a temperature of about 900 to 1000 占 폚 to produce metal indium. Therefore, it is difficult to obtain an intended oxide sintered body.

The temperature range of the pressure-sintering is preferably 1200 to 1550 DEG C, and more preferably 1350 to 1450 DEG C in an atmosphere for introducing oxygen gas 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 in the above range, and the oxide powder, and silicon dioxide powder is made of the adjustment to less than the average particle size of 1.0 ㎛ indium powder and a gallium oxide powder as the raw material powder, mainly Biggs byte structure In ₂ O ₃ and is a β-Ga ₂ O ₃ structure of the GaInO ₃ or (Ga, in) composed of the phase ₂ O _3.

When the sintering temperature is lower than 1200 캜, the sintering reaction does not proceed sufficiently. On the other hand, when the sintering temperature exceeds 1550 DEG C, the increase in density is difficult to proceed, while the sintering furnace member and the oxide sintered body are reacted with each other, and the intended oxide sintered body can not be obtained. In particular, since the content of gallium in the oxide-sintered body of the present invention is 0.08 or more in terms of Ga / (In + Ga) atomic ratio, the sintering temperature is preferably 1450 占 폚 or lower. This is because the formation of the (Ga, In) ₂ O ₃ phase may be conspicuous in the temperature region around 1500 ° C. A small amount of the (Ga, In) ₂ O ₃ phase does not interfere, but in a large amount, the film formation rate may be lowered or arcing may be caused.

The rate of temperature rise up to the sintering temperature is preferably set in the range of 0.2 to 5 占 폚 / min so that the sintered body is prevented from cracking and the binder is advanced. If it is within this range, different temperature raising rates may be combined to raise the sintering temperature, if necessary. For the purpose of advancing the binder removal or sintering in the heating step, it may be maintained at a specific temperature for a certain period of time. At the time of cooling after the sintering, it is preferable to stop the introduction of oxygen and to lower the temperature to 1000 占 폚 at a rate of 0.2 to 5 占 폚 / min, particularly 0.2 占 폚 / min to 1 占 폚 / min.

(3) Target

The target of the present invention is obtained by processing the oxide-sintered body of the present invention to 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. In the case of using a cylindrical target, it is desirable to suppress the generation of particles due to the rotation of the target. Further, the oxide-sintered body can be processed into, for example, a columnar shape to form a tablet, and can be used for film formation by a vapor deposition method or an ion plating method.

When used as a target for sputtering, the density of the oxide-sintered body of the present invention is preferably 6.3 g / cm ³ or more, and more preferably 6.7 g / cm ³ or more. If the density is less than 6.3 g / cm < ³ >, it causes nodule generation at the time of mass production. When used as a tablet for ion plating, it is preferably less than 6.3 g / cm ^3, more preferably from 3.4 to 5.5 g / cm ³ . In this case, it may be preferable to set the sintering temperature to less than 1200 캜.

(4) Oxide semiconductor thin film and method for forming the same

The amorphous oxide semiconductor thin film of the present invention is obtained mainly by forming the amorphous oxide thin film on the substrate by the sputtering method using the above sputtering target and then performing the annealing treatment.

The target for sputtering is obtained from the oxide-sintered body of the present invention. The oxide-sintered body structure, the In ₂ O ₃ phase and the? -Ga ₂ O ₃ -type GaInO ₃ phase of the Bigbyte type structure or the? -Ga ₂ O ₃ this type of structure GaInO ₃ and the tissue, which is the default configuration by a (Ga, in) ₂ O ₃ 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, as well as In ₂ O ₃ phase of Biggs byte structure, β-Ga ₂ O of the _3-like structure GaInO ₃ phase or a β-Ga ₂ O of the _3-like structure GaInO ₃ phase and ( Ga, In) ₂ O ₃ phase, 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 becomes stable amorphous. In addition, when the In ₂ (Si ₂ O ₇ ) phase of the tort-butite structure is included, the crystallization temperature is higher and the amorphous state becomes more stable. On the other hand, when the oxide-sintered body is composed only of the In ₂ O ₃ phase having a Big-Byte structure, the oxide thin film obtained from the oxide-sintered body has a low crystallization temperature of about 200 캜 and is not amorphous. In this case, after the film formation, microcrystallization is already generated and the amorphous state is not maintained, making it difficult to perform patterning processing by wet etching.

In the film formation process of the amorphous oxide semiconductor thin film of the present invention, a general sputtering method is used, but in particular, the direct current (DC) sputtering method is industrially advantageous because thermal effect at the time of film formation is small and high speed film formation is possible. In order to form the oxide semiconductor thin film of the present invention by DC sputtering, it is preferable to use a mixed gas of inert gas and oxygen, particularly argon and oxygen, as the sputtering gas. In addition, it is preferable to perform sputtering in the chamber of the sputtering apparatus at a pressure of 0.1 to 1 Pa, particularly 0.2 to 0.8 Pa.

As the substrate, a glass substrate is typical and an alkali-free glass is preferable, but any resin plate or resin film that can withstand the above process conditions can be used.

In the amorphous oxide thin film forming step, for example, after evacuation to 2 x 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. DC power is applied so that the power, that is, the DC power density is in the range of about 1 to 7 W / cm ² , to generate DC plasma and perform free sputtering. It is preferable that the free sputtering is carried out for 5 to 30 minutes, then the substrate position is adjusted as necessary, and then sputtering is performed.

In the sputtering film formation in the above-described film formation step, in order to improve the film formation speed, the DC power to be injected is increased.

The amorphous oxide semiconductor thin film of the present invention can be obtained by depositing the above-mentioned amorphous oxide thin film and annealing it. As one of the methods up to the annealing process, an amorphous oxide thin film is first formed at a low temperature, for example, near room temperature, and then annealed at a temperature lower than the crystallization temperature to obtain an oxide semiconductor thin film while maintaining the amorphous state. As another method, an amorphous oxide semiconductor thin film is formed by heating the substrate to a temperature lower than the crystallization temperature, preferably 100 to 300 캜. Subsequently, further annealing may be performed. The heating temperature in these two methods should be about 600 DEG C or less, and can be made to be not more than the distortion point of the alkali-free glass substrate.

The amorphous oxide semiconductor thin film of the present invention is obtained by forming an amorphous oxide thin film once and then annealing the amorphous oxide semiconductor thin film. The annealing 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 占 폚, preferably 300 to 500 占 폚. The annealing time is preferably from 1 to 120 minutes, and preferably from 5 to 60 minutes, at the annealing temperature.

The compositions of indium, gallium, and silicon of the amorphous oxide thin film and the amorphous oxide semiconductor thin film are almost the same as those of the oxide sintered body of the present invention. That is, it is an amorphous oxide semiconductor thin film containing indium and gallium as oxides and further containing silicon. The content of gallium is 0.08 or more and 0.49 or less in terms of Ga / (In + Ga) atom number ratio, and the content of Si is 0.0001 or more and less than 0.25 in terms of Si / (In + Ga + Si) atom number ratio.

The amorphous oxide semiconductor thin film of the present invention can be formed by depositing an oxide sintered body having the above-described composition and structure controlled using a sputtering target or the like and annealing under the appropriate conditions as described above to obtain a carrier concentration of 4.0 x 10 ¹⁸ cm ^-3 And the carrier mobility is more than 10 cm ² V ^{- 1} sec ^-1 . More preferably, the carrier mobility of 15 cm ² V ^-1 sec ^-1 or more, and particularly preferably 20 cm ² V ^- a ¹ sec ^-1 or higher are obtained.

The amorphous oxide semiconductor thin film of the present invention is subjected to micromachining required for applications such as TFTs by wet etching or dry etching. Usually, a suitable substrate temperature is selected at a temperature lower than the crystallization temperature, for example, from room temperature to 300 ° C to form an amorphous oxide thin film, followed by micro-processing by wet etching. As the etching agent, a weak acid mainly composed of oxalic acid or hydrochloric acid is preferable, although it can be used generally as a weak acid. 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.

The film thickness of the amorphous oxide semiconductor thin film of the present invention is not limited, but is 10 to 500 nm, preferably 20 to 300 nm, more preferably 30 to 100 nm. When the thickness is less than 10 nm, sufficient semiconductor characteristics can not be obtained, and as a result, high carrier mobility can not be realized. On the other hand, if it exceeds 500 nm, the problem of productivity tends to occur, which is not preferable.

Example

Hereinafter, the present invention will be described in more detail with reference to 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. The resulting oxide sintered body was used to identify the product phase by the 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 Corporation) and subjected to energy-dispersive X-ray analysis (manufactured by Hitachi High-Technologies Corporation) To investigate the composition of each crystal grain.

≪ Evaluation of basic characteristics 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 by a surface roughness machine (manufactured by Tencor Corporation). The deposition rate was calculated from the film thickness and the film deposition time. The carrier concentration and the mobility of the oxide thin film were determined by a Hall effect measuring apparatus (manufactured by Toyota Technica). The formation phase of the film was identified by X-ray diffraction measurement.

&Quot; Preparation of oxide-sintered body and oxide thin film "

The indium oxide powder, the gallium oxide powder, and the silicon dioxide powder were adjusted so as to have an average particle diameter of 1.0 占 퐉 or less to obtain a raw material powder. These raw material powders were combined so as to have an atomic ratio of Ga / (In + Ga) and an atomic ratio of Si / (In + Ga + Si) in Examples and Comparative Examples in Table 1 and Table 2, Placed in a pot and mixed with a wet ball mill. At this time, a hard ZrO ₂ ball was used and the mixing time was 18 hours. After mixing, the slurry was extracted, filtered, dried and assembled. The assembly was molded by applying a pressure of 3 ton / cm ^{2 using} a cold isostatic press.

Next, the formed body was sintered as follows. And sintered at a sintering temperature of 1350 to 1450 캜 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 占 폚 / min. During the cooling after sintering, the introduction of oxygen was stopped and the temperature was lowered to 1000 占 폚 at 1 占 폚 / min.

The composition of the obtained oxide-sintered body was analyzed by ICP emission spectroscopy. As a result, it was confirmed that the metal element had almost the same composition as that of the raw material powder.

Next, crystal grains are observed by means of X-ray diffraction (XRD) phase identification of the oxide-sintered body and scanning transmission electron microscope (STEM), and energy-dispersive X- dispersive X-ray spectrometry (EDX) analysis. The results are shown in Table 1.

The results of X-ray diffraction measurements of Examples 5, 10 and 11 are shown in Fig. 1, and the results of observation of a scanning transmission electron microscope of Example 11 are shown in Fig. In the scanning transmission electron microscope observation, the presence of two types of crystal grains, that is, a whitened crystal grain and a black crystal grain, was confirmed. From the results of the X-ray diffraction measurement and the energy dispersive X-ray analysis, it was found that the whitened crystal grains were In ₂ O ₃ phase of bixbyite structure and the black grains were GaInO ₃ phase of β-Ga ₂ O ₃ type structure .

The oxide sintered body was machined to a size of 152 mm in diameter and 5 mm in thickness, and the sputtering surface was polished with a cup stone so that the maximum height (Rz) was 3.0 m or less. The processed oxide sintered body was bonded to a backing plate made of oxygen-oxygen copper using metal indium to obtain a target for sputtering.

Film formation was carried out by DC sputtering at the substrate temperatures shown in Table 2 using the target and non-alkali glass substrates for sputtering (Corning Eagle XG) of Examples and Comparative Examples. The sputtering target was attached to the cathode of a DC magnetron sputtering apparatus (Toki) equipped with a direct current power source having no arcing suppression function. At this time, the distance between the target and the substrate (holder) was fixed at 60 mm. After vacuum evacuation to 2 x 10 < ^-4 > Pa or less, a mixed gas of argon and oxygen was introduced so as to have a suitable oxygen ratio according to the amount of gallium and the amount of silicon of each target, and the gas pressure was adjusted to 0.6 Pa. DC power of 300 W (1.64 W / cm ² ) was applied to generate a DC plasma. After 10 minutes of free sputtering, the substrate was placed immediately above the sputtering target, that is, at the stationary opposed position, to form an oxide semiconductor thin film with a film thickness of 50 nm. At this time, presence or absence of arcing was confirmed. 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 deposited oxide semiconductor thin film was subjected to a heat treatment in oxygen at 300 to 500 占 폚 for 30 to 60 minutes to examine the crystallinity of the oxide semiconductor thin film after the heat treatment by X-ray diffraction measurement . As a result, the oxide semiconductor thin films of Comparative Examples 1 and 2 were crystallized and an In ₂ O ₃ phase of a Bigbyte type structure was produced, but in the Examples and Comparative Examples except for this, the amorphous state was maintained. Further, with respect to the crystallized oxide semiconductor thin film, the crystal phase constituting the oxide semiconductor thin film was identified. The hole effect of the oxide semiconductor thin film was measured for Examples and Comparative Examples except for Comparative Examples 1, 2, 4 to 6 and 8 to determine the carrier concentration and the carrier mobility. The evaluation results obtained are collectively shown in Table 2.

"evaluation"

From the results shown in Table 1, it can be seen that in Examples 1 to 19, the gallium content is 0.08 or more and 0.49 or less in terms of the Ga / (In + Ga) atom number ratio and the silicon content is 0.0001 or more in terms of the Si / (In + Ga + 0.25 include, in Biggs byte structure in ₂ O ₃ phase and a β-Ga ₂ O of the _3-like structure GaInO _3-phase, β-Ga ₂ O of the _3-like structure GaInO ₃ phase and (Ga, in) of less than ₂ O ₃ Or In ₂ (Si ₂ O ₇ ) of the tortbite type. On the other hand, in Comparative Examples 1 to 3, the content of gallium or silicon in the oxide-sintered body is less than the range of the present invention. In Comparative Examples 1 and 2, an oxide sintered body composed of only the In ₂ O ₃ phase of the Bigbyte type structure was formed. In Comparative Examples 3 to 6 and 8, since the silicon content was excessive, arcing occurred during the sputtering film formation, and a homogeneous film could not be obtained, and the oxide-sintered object of the present invention was not obtained.

The result of Table 2 shows that the amorphous oxide semiconductor thin film made of indium, gallium and silicon has a gallium content of 0.08 or more and 0.49 or less in terms of Ga / (In + Ga) atomic ratio and a silicon content of Si / + Si) atomic ratio of 0.0001 to less than 0.25.

It can be seen that the oxide semiconductor thin films of Examples are all amorphous. In addition, the embodiment of the oxide semiconductor thin film, the carrier concentration is 4.0 × 10 ¹⁸ cm ^-3 or less, and the carrier mobility is 10 cm ² V ^- it can be seen that exhibit excellent characteristics than ¹ sec ^-1.

On the other hand, in Comparative Examples 1 and 2, the oxide semiconductor thin film after annealing was crystallized, and an In ₂ O ₃ phase of a Bigbyte type structure was produced and was not amorphous. In the oxide semiconductor thin films of Comparative Examples 3 to 6 and 8, the silicon content exceeded the range of the present invention. As a result, arcing occurred and a homogeneous film was not obtained. Therefore, evaluation of carrier concentration and carrier mobility Did not. In the oxide semiconductor of Comparative Example 7, since the above-mentioned Ga / (In + Ga) exceeds the upper limit, the carrier mobility is less than 10 cm ² V ^-1 sec ^-1 .

Claims (10)

Indium, gallium and silicon as oxides,
Wherein the content of gallium is 0.08 or more and 0.49 or less in terms of Ga / (In + Ga) atomic ratio,
Wherein the content of silicon is 0.0001 or more and less than 0.25 in terms of Si / (In + Ga + Si) atomic ratio. The method of claim 1 wherein the VIX-byte structure of In ₂ O ₃ phase (相) as a main phase, and, In ₂ O of β-Ga ₂ O ₃ Type ₃ structure as a phase other than the phase generated the GaInO ₃ or β- Ga ₂ O ₃ -type GaInO ₃ phase and a (Ga, In) ₂ O ₃ phase. The oxide-sintered body according to any one of claims 1 to 3, comprising an In ₂ (Si ₂ O ₇ ) phase of a toite bitite structure. The oxide-sintered body according to any one of claims 1 to 3, wherein the content of silicon is 0.01 to 0.20 in terms of Si / (In + Ga + Si) atomic ratio. The oxide-sintered body according to any one of claims 1 to 4, wherein the content of gallium is 0.15 or more and 0.45 or less in terms of Ga / (In + Ga) atomic ratio. A sputtering target obtained by processing the oxide-sintered body according to any one of claims 1 to 5. 7. An amorphous oxide semiconductor thin film formed on a substrate by a sputtering method using the sputtering target according to claim 6 and then subjected to a heat treatment in an oxidizing atmosphere. The oxide semiconductor thin film according to claim 7, wherein the carrier concentration is less than 4.0 x 10 ¹⁸ cm ^-3 and the carrier mobility is 10 cm ² V ^-1 sec ^-1 or more. The method of claim 8, wherein the carrier concentration is 6.0 × 10 ¹⁷ cm ^-3 oxide semiconductor thin film, characterized in that not more than. Claim 8 or claim 9, wherein the carrier mobility is 15 cm ² V ^{- 1} sec ^-1 than the oxide semiconductor thin film.

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