JP2017168572A - Oxide semiconductor thin film, oxide sintered compact, thin film transistor and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a crystalline transparent oxide semiconductor thin film having a high electron carrier mobility, of which the carrier concentration is reduced to such an extent that it can be used as a channel layer of a thin film transistor; and a thin film transistor including the thin film.SOLUTION: An oxide semiconductor thin film according to the present invention comprises a crystalline material including indium and yttrium, in which the content of the yttrium is 0.05-0.12 in Y/(In+Y) atomic number ratio, a crystal phase is constituted by only an indium oxide phase of a bixbyite type structure, the carrier concentration is 7.0×10cmor less, and the carrier mobility is 5 cmVsecor more. It is preferable that the content of the yttrium is 0.08-0.10 in Y/(In+Y) atomic number ratio.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an oxide semiconductor thin film, an oxide sintered body, a thin film transistor, and a display device. More specifically, an oxide semiconductor thin film that is crystalline and has high carrier mobility and reduced carrier electron concentration, an oxide sintered body for obtaining an oxide semiconductor thin film, and the oxide semiconductor thin film were used. The present invention relates to a thin film transistor and a display device using the thin film transistor.

  A thin film transistor (Thin Film Transistor) is one type of field effect transistor. The field effect transistor is a three-terminal element including a gate terminal, a source terminal, and a drain terminal as a basic configuration. In this field effect transistor, a semiconductor thin film formed on a substrate is used as a channel layer in which electrons or holes move, a voltage is applied to the gate terminal to control a current flowing in the channel layer, and a source terminal and a drain terminal It is an active element which has the function to switch the electric current between.

As a channel layer of a field effect transistor, a polycrystalline silicon film or an amorphous silicon film is currently widely used. In particular, amorphous silicon has been widely used as a channel layer for liquid crystal panels because it can be uniformly formed on a large-area 10th generation glass substrate. However, since the mobility of electrons as carriers (hereinafter referred to as “carrier mobility”) is as low as 1 cm ² / Vsec or less, application to high-definition panels is becoming difficult. With the demand for higher definition of liquid crystal, high-speed driving has been required. However, in order to realize high-speed driving, a carrier mobility is higher than at least 1 cm ² / Vsec of amorphous silicon. It is necessary to use a thin film for the channel layer.

Since the polycrystalline silicon film exhibits a high carrier mobility of about 100 cm ² / Vsec, it has sufficient characteristics as a channel layer material for a high-definition panel. However, since polycrystalline silicon has low carrier mobility at grain boundaries, the in-plane uniformity of the substrate is poor and its characteristics vary. In the manufacturing process of polycrystalline silicon, it is necessary to form amorphous silicon at a relatively low temperature of 300 ° C. or lower and then crystallize it by an annealing process. In this annealing process, an excimer laser annealing method or the like is applied, so that the running cost increases. Furthermore, since the size of the glass substrate that can be handled is limited to about the fifth generation, there is a limit to cost reduction and product development is also limited. That is, there is a demand for a channel layer material that combines the uniform film formability and low cost provided by amorphous silicon and the high carrier mobility provided by polycrystalline silicon.

In Patent Document 1, the composition when crystallized is InGaO ₃ (ZnO) _m (m is a natural number of less than 6), a transparent amorphous oxide thin film formed by a vapor deposition method, and this thin film as a channel layer A thin film transistor used as has been proposed. This transparent amorphous oxide thin film is semi-insulating with an electron mobility exceeding 1 cm ² / (V · sec) and an electron carrier concentration of 10 ¹⁶ / cm ³ or less.

However, although this transparent amorphous oxide thin film (a-IGZO film) exhibits a relatively high electron carrier mobility in a range of approximately 1 to 10 cm ² / Vsec, the amorphous oxide thin film inherently tends to generate oxygen vacancies. In addition, it is a problem that the behavior of electrons as carriers is not always stable against external factors such as heat and the like, which has an adverse effect, and the operation is often unstable. In addition, when a negative bias is continuously applied to the element under visible light irradiation unique to an amorphous film, a phenomenon in which the threshold voltage shifts to the negative side (light negative bias deterioration) occurs. In this way, when the threshold voltage shifts, current flows at a voltage that originally does not flow between the source terminal and the drain terminal, causing screen flickering and malfunctioning. It has been pointed out that it becomes a serious problem in applications.

  Against this background, in recent years, a crystalline film is being studied as a channel layer used in a thin film transistor, not an amorphous film.

For example, in Patent Document 2, 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 bixbyte. An oxide thin film having a structure has been proposed. However, in any of the examples, the carrier concentration of the oxide semiconductor thin film exceeds 1 × 10 ¹⁸ cm ⁻³ , and the carrier concentration is too high to be used as the channel layer of the thin film transistor. Ratio cannot be achieved.

In Patent Document 3, the crystal structure is substantially composed of indium oxide having a bixbite structure, the atomic ratio Ga / (Ga + In) is 0.10 to 0.15, and the indium oxide having the bixbite structure is used. An oxide semiconductor thin film and a thin film transistor using the oxide semiconductor thin film as a channel layer are disclosed. Since this thin film transistor has a higher gallium atomic ratio in the oxide sintered body and the oxide semiconductor thin film than the thin film transistor of Patent Document 2 described above, the oxide semiconductor thin film disclosed in the example of Patent Document 3 Although the carrier concentration is lower than that of the oxide thin film disclosed in the example of Patent Document 2, it exceeds 3 × 10 ¹⁷ cm ⁻³ , so that it can be further applied to a practical thin film transistor. The concentration needs to be lowered.

  Thus, the carrier concentration is high in the crystalline oxide semiconductor thin film, and a thin film transistor having an on / off ratio sufficient for use as a channel layer cannot be obtained.

On the other hand, for example, in Patent Document 4, an indium oxide is formed by forming a film-formed body by a DC sputtering method at a water pressure of 3 × 10 ^{−4 to} 5 × 10 ⁻² Pa in the system and crystallization. A method for manufacturing an oxide semiconductor having a bixbyite structure is disclosed. According to this method, the carrier concentration in the obtained thin film transistor can be reduced to 10 ¹⁵ cm ⁻³ . However, it is difficult to control the moisture pressure during sputtering, which leads to an increase in running cost. Moreover, the crystallization temperature of the oxide thin film rises due to the presence of water during sputtering. This raises the heat treatment temperature and requires a large amount of heating.

  As described above, an oxide semiconductor with low carrier concentration and high carrier mobility is required as a crystalline oxide semiconductor to be applied to a thin film transistor. However, a semiconductor that sufficiently satisfies this requirement has not been obtained. .

JP 2010-182924 A International Publication No. 2010/032422 JP 2011-146571 A JP 2011-222557 A

  The present invention has been made in view of such problems, and has a high electron carrier mobility and a crystalline oxide semiconductor thin film having a carrier concentration reduced to such an extent that it can be used as a channel layer of a thin film transistor. It is providing the thin-film transistor comprised by providing.

  The present inventors have made various studies in order to obtain an oxide semiconductor thin film having a relatively high electron carrier mobility and a low carrier concentration. As a result, it has been found that the carrier concentration is effectively reduced in an oxide thin film crystallized by forming an amorphous oxide semiconductor thin film by a sputtering method and then annealing at a specific temperature.

(1) A first aspect of the present invention is a crystalline oxide semiconductor thin film containing indium and yttrium, wherein the yttrium content is 0.05 or more and 0.12 in terms of the Y / (In + Y) atomic ratio. The crystal phase is composed only of an indium oxide phase having a bixbite structure, the carrier concentration is 7.0 × 10 ¹⁵ cm ⁻³ or less, and the carrier mobility is 5 cm ² V ⁻¹ sec ⁻¹ or more. It is a certain oxide semiconductor thin film.

  (2) The second invention of the present invention is the oxide semiconductor thin film according to the first invention, wherein the yttrium content is 0.08 or more and 0.10 or less in terms of Y / (In + Y) atomic ratio.

(3) The third invention of the present invention is the oxide semiconductor thin film according to the first or second invention, wherein the carrier concentration is 1.0 × 10 ¹⁵ cm ⁻³ or less.

(4) A fourth invention of the present invention is the oxide semiconductor thin film according to any one of the first to third inventions, wherein the carrier mobility is 5 cm ² V ⁻¹ sec ⁻¹ or more.

  (5) According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the oxidation is obtained by sputtering a sputtering target obtained by sintering a metal source having an average particle size of 1 μm or less. A semiconductor thin film.

(6) A sixth invention of the present invention is an oxide sintered body containing indium and yttrium, wherein the yttrium content is 0.05 to 0.12 in terms of the Y / (In + Y) atomic ratio. In other words, the oxide phase is an oxide sintered body whose main component is an In ₂ O ₃ phase having a bixbite structure.

(7) The seventh invention of the present invention is an oxide sintered body containing indium and yttrium, wherein the yttrium content is 0.05 to 0.12 in terms of Y / (In + Y) atomic ratio. There is a sputtering target whose main component is an In ₂ O ₃ phase having a bixbite type crystal phase.

  (8) An eighth invention of the present invention is a thin film transistor including a source electrode, a drain electrode, a gate electrode, a channel layer, and a gate insulating film, wherein the channel layer is related to any one of the first to fifth inventions. The thin film transistor is formed using an oxide semiconductor thin film.

  (9) A ninth invention of the present invention is a display device comprising the thin film transistor according to the eighth invention.

  (10) A tenth aspect of the present invention is a method for producing an oxide semiconductor thin film, comprising sintering a metal source having an average particle size of 1 μm or less to obtain an oxide sintered body, A film forming step of forming an amorphous thin film on a substrate having a temperature lower than the crystallization temperature of the oxide semiconductor using the oxide sintered body; And an annealing step of annealing at a temperature equal to or higher than the crystallization temperature of the oxide semiconductor.

  (11) The eleventh invention of the present invention is the method for producing a thin film of an oxide semiconductor according to the tenth invention, wherein in the annealing step, the thin film is annealed at 350 ° C. or higher and 400 ° C. or lower.

According to the present invention, the crystalline oxide semiconductor thin film made of indium and yttrium according to the present invention exhibits a relatively high carrier mobility and reduces the carrier concentration to 7.0 × 10 ¹⁵ cm ⁻³ or less. Can do. By applying this oxide semiconductor thin film to the channel layer, a thin film transistor with an excellent on / off ratio can be realized.

It is a schematic diagram of the cross section of a bottom gate top contact type thin film transistor.

  Specific embodiments of the present invention (hereinafter referred to as “present embodiments”) will be described in detail below. Note that the present invention is not limited to the following embodiment, and can be implemented with appropriate modifications within the scope of the object of the present invention.

<< 1. Oxide semiconductor thin film >>
The oxide semiconductor thin film according to this embodiment is a crystalline oxide semiconductor thin film containing indium and yttrium, and the content of yttrium is 0.05 or more and 0.12 in terms of the Y / (In + Y) atomic ratio. The crystal phase is composed only of an indium oxide phase having a bixbite structure, the carrier concentration is 7.0 × 10 ¹⁵ cm ⁻³ or less, and the carrier mobility is 5 cm ² V ⁻¹ sec ⁻¹ or more. is there.

Here, when the carrier concentration of the oxide semiconductor thin film is 7.0 × 10 ¹⁵ cm ⁻³ or less, even if there is an increase in the carrier concentration due to the thermal history or the like in the process of manufacturing the thin film transistor device, The carrier concentration of the oxide semiconductor thin film in a simple device can be suppressed to 1.0 × 10 ¹⁶ cm ⁻³ or less.

  As described above, the oxide semiconductor thin film according to this embodiment is an oxide semiconductor thin film having both a low carrier concentration and a high carrier mobility. Although this oxide semiconductor thin film is crystalline, it has a low carrier concentration. This shows a good on / off ratio. In addition, a device with high performance and low power consumption can be configured by having high carrier mobility.

  The amount of yttrium contained in the oxide semiconductor thin film is 0.05 or more in terms of the atomic ratio of yttrium atoms to the total amount of indium atoms and yttrium atoms contained in the oxide semiconductor thin film (Y / (In + Y)), preferably Is 0.07 or more, more preferably 0.08 or more. When the atomic ratio (Y / (In + Y)) of yttrium is 0.05 or more, oxygen vacancies disappear due to the high oxygen affinity of yttrium, and the carrier concentration can be reduced.

  The amount of yttrium contained in the oxide semiconductor thin film is 0.12 or less, preferably 0.11 or less, more preferably 0.10 or less in terms of the yttrium atomic ratio (Y / (In + Y)). It is. When the atomic ratio of yttrium is 0.12 or less, the crystallization temperature of the oxide semiconductor thin film can be maintained so as not to be too high, and an oxide semiconductor thin film with high crystallinity can be obtained. In addition, it is possible to suppress a decrease in carrier mobility in the oxide semiconductor thin film due to an impurity scattering factor generated by containing yttrium.

  The oxide semiconductor thin film is a crystalline oxide semiconductor thin film containing indium and yttrium, and the crystal phase thereof is composed only of an indium oxide phase having a bixbyite structure. By using an oxide semiconductor thin film having such a crystal phase, the carrier concentration can be effectively reduced.

  It does not specifically limit as a film thickness of an oxide thin film, It can set suitably by a use. Specifically, for example, the thickness is preferably 10 nm to 500 nm, more preferably 20 nm to 300 nm, and still more preferably 30 nm to 100 nm. When the film thickness is 10 nm or more, the crystallinity is high and high carrier mobility can be realized. On the other hand, when the film thickness is 500 nm or less, coloring of the film can be prevented.

  The average transmittance of the oxide thin film is not particularly limited, but in the visible region (400 to 800 nm), it is preferably 80% or more, more preferably 85% or more, and 90% or more. Further preferred. When the average transmittance is 80% or more, the light extraction efficiency of a liquid crystal element or an organic EL element is improved.

  As a constituent element of the oxide thin film, in addition to indium and yttrium, other elements can be included so as not to affect the characteristics.

  On the other hand, it is preferable that zinc is not substantially contained as a constituent element of the oxide thin film. Here, “substantially does not contain” means that a trace amount of unavoidable impurities derived from raw materials, production equipment, and the like is allowed. Specifically, the number of atoms of these metals is It means 100 ppm or less relative to the number of atoms of all metals. Thus, when the oxide thin film does not substantially contain zinc as a constituent element, the absorption of light on the short wavelength side of the visible region can be reduced and the transmittance can be increased. For example, this oxide thin film has an extinction coefficient of 0.05 or less at a wavelength of 400 nm. Such an oxide thin film has high transmittance of blue light, enhances color development of a liquid crystal element, an organic EL element, and the like, and can be suitably used as a material for a channel layer of a TFT of these elements. On the other hand, for example, since the a-IGZO film described in Patent Document 1 contains zinc, the absorption of light particularly on the short wavelength side of the visible region is large.

≪2. Method for manufacturing oxide semiconductor thin film >>
The method for manufacturing an oxide semiconductor thin film according to this embodiment uses a raw material sintering step for obtaining an oxide sintered body by sintering a metal source having an average particle size of 1 μm or less, and the oxide sintered body. A film forming step of forming an amorphous thin film on a substrate having a temperature lower than the crystallization temperature of the oxide semiconductor, and annealing for annealing the amorphous thin film at a temperature equal to or higher than the crystallization temperature of the oxide semiconductor. Process.

<2-1. Raw material sintering process>
The raw material sintering step is a step in which a metal source having an average particle size of 1 μm or less is sintered to obtain an oxide sintered body that is a raw material for the oxide semiconductor thin film. The oxide sintered body obtained in this step can be used as it is as a raw material for producing an oxide semiconductor thin film in a subsequent film formation step. Further, it can be processed and used as a sputtering target.

  Thus, by using a metal source having an average particle size of 1 μm or less as a raw material for producing an oxide sintered body, the oxide sintered body and the entire sputtering target obtained by processing the oxide sintered body are covered. An oxide sintered body and a sputtering target having a uniform composition can be obtained with no uneven composition. Thus, if the composition of the oxide sintered body is uniform, a micro arc that causes defects in the oxide film does not occur when the sputtering process is performed.

  In the raw material sintering step, it is preferable that a metal source having an average particle diameter of 1 μm or less is subjected to wet ball mill treatment or wet bead mill treatment, and sufficiently mixed to make uniform. This makes it possible to prepare a raw material powder for obtaining an oxide sintered body having a uniform composition more efficiently. At this time, for example, after the mixed powder is obtained as a slurry, it can be subjected to a treatment such as filtration, drying and granulation.

  Here, as the metal source, a compound containing at least an indium-containing compound and a compound containing yttrium, and a compound containing other metals can be further included. The type of the metal source is not particularly limited as long as it forms an oxide by sintering. For example, an oxide or a metal salt such as chloride, nitrate, sulfate, etc. can be used. More specifically, for example, it is preferable to use indium oxide as the indium source and yttrium oxide as the yttrium source.

  Although it does not specifically limit as sintering temperature, Specifically, it is preferable that it is 1000 degreeC or more, for example, It is more preferable that it is 1100 degreeC or more, It is further more preferable that it is 1200 degreeC or more. It is particularly preferably 1300 ° C. or higher. If it is 1000 degreeC or more, a metal source will fully sinter.

  The sintering atmosphere is not particularly limited as long as it is an oxidizing atmosphere. Here, the “oxidizing atmosphere” refers to an atmosphere in which oxidation is promoted. Specifically, it refers to an atmosphere containing any one or more of oxygen, ozone, water vapor, and nitrogen oxide. An atmosphere with added oxygen can be applied.

  The sintering time is not particularly limited and can be appropriately adjusted depending on the sintering temperature. Specifically, for example, it is preferably 10 hours or more, and preferably 15 hours or more. It is more preferable. When heated for 10 hours or more, the metal source is sufficiently sintered. Moreover, as an upper limit of sintering time, it is preferable that it is 50 hours or less, and it is more preferable that it is 30 hours or less. When heated for about 50 hours, an oxide sintered body is generally formed.

  By processing the oxide sintered body produced by such a method, a sputtering target for use in a film forming process described later can be obtained. When sputtering is performed using this sputtering target, generation of micro arc is suppressed and a homogeneous oxide semiconductor thin film is obtained.

<2-2. Film formation process>
The film forming process uses an oxide sintered body obtained in the raw material sintering process, and is a precursor of an oxide semiconductor thin film on a substrate having a temperature lower than the crystallization temperature of the oxide semiconductor. This is a step of forming a porous thin film.

  In the film forming step, an amorphous oxide semiconductor thin film is obtained by various film forming methods such as sputtering and ion plating using the oxide sintered body obtained in the raw material sintering step. Among these, it is particularly preferable to use a sputtering method. Specific examples of the sputtering method include RF magnetron sputtering, DC magnetron sputtering, AC magnetron sputtering, and pulsed DC magnetron sputtering. In addition, when using sputtering method, the above-mentioned oxide sintered compact is processed and used for a sputtering target.

Here, the oxide sintered body and the sputtering target obtained by processing the oxide sintered body are obtained by using a metal source having an average particle diameter of 1 μm or less as a raw material, and thus have a uniform composition. Thus, the micro arc discharge during sputtering is suppressed by using the oxide sintered compact or sputtering target with a uniform composition. Thereby, generation | occurrence | production of the defect in the oxide semiconductor thin film by micro arc discharge can be suppressed, and the raise of the carrier concentration derived from the defect can be suppressed. As a result, an oxide semiconductor thin film having a carrier concentration of 7.0 × 10 ¹⁵ cm ⁻³ or less can be obtained as the crystalline oxide semiconductor thin film after the annealing step.

  In order to form an amorphous oxide semiconductor thin film by a 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. Moreover, it is preferable to perform sputtering by setting the pressure in the chamber of the sputtering apparatus to 0.1 to 1 Pa, preferably 0.2 to 0.8 Pa.

  The substrate is not particularly limited as long as it can withstand the heat treatment in the film forming step and the annealing step. Specifically, for example, a glass substrate, a resin plate, a resin film, or the like is used. Can do.

  In the film formation step, the substrate temperature is set lower than the crystallization temperature of the oxide semiconductor. By doing so, the oxide semiconductor film deposited on the surface does not exceed the crystallization temperature, so that it is not crystallized and an amorphous thin film is obtained. Specifically, for example, the temperature is preferably 100 ° C. or lower.

Pre-sputtering can also be performed as a pretreatment for sputtering. Specifically, as a pre-sputtering method, for example, after evacuating to 2 × 10 ⁻⁴ Pa or less, a mixed gas composed of argon and oxygen is introduced, the gas pressure is set to 0.2 to 1.0 Pa, and the target The plasma can be generated by applying power so that the power with respect to the surface area, that is, the power density is in the range of about 1 to 3 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.

  The amorphous oxide semiconductor thin film thus obtained is finely processed by wet etching or dry etching as necessary. Since it is amorphous, processing by wet etching using a weak acid is easy. Although the weak acid used for this etching is not specifically limited, The weak acid which has oxalic acid as a main component is preferable, Specifically, Kanto Chemical ITO-06N etc. can be used, for example. In the case of dry etching, processing can be performed using an appropriate etching gas.

<2-3. Annealing process>
The annealing step is a step of annealing the amorphous oxide semiconductor thin film obtained in the film forming step at a temperature equal to or higher than the crystallization temperature of the oxide semiconductor in an oxidizing atmosphere.

  An oxide semiconductor thin film can be obtained by annealing the amorphous oxide semiconductor thin film obtained in the film formation step in an oxidizing atmosphere. Here, the “oxidizing atmosphere” refers to an atmosphere in which oxidation is promoted, and specifically refers to an atmosphere containing any one or more of oxygen, ozone, water vapor, and nitrogen oxide.

The amorphous oxide semiconductor thin film obtained in the film formation step has a crystallization temperature higher than 200 ° C., and can maintain an amorphous state even in a temperature range exceeding 200 ° C. On the other hand, the oxidation of an amorphous oxide easily proceeds in a temperature range exceeding 200 ° C. until the crystallinity is improved. Therefore, an oxide semiconductor having a crystallization temperature higher than 200 ° C. is once formed as an amorphous thin film, and then the oxide semiconductor thin film is heated to exceed 200 ° C. to be crystallized so that oxidation proceeds. Oxygen deficiency can be eliminated. Thereby, carrier concentration can be suppressed to 7.0 * 10 < ¹⁵ > cm < ^-3 > or less.

  The annealing temperature is not particularly limited as long as it is higher than the crystallization temperature. For example, when an oxide semiconductor thin film having a crystallization temperature of 255 ° C. is sintered, the temperature is preferably 255 ° C. or higher. In order to obtain a highly crystalline thin film, the temperature is preferably 350 ° C. or higher. On the other hand, when the distortion of the glass substrate is taken into consideration, the annealing temperature is preferably 400 ° C. or lower. Note that rapid heating treatment using lamp heating can also be performed like RTA. In the case where only the extreme surface is rapidly heated using a flash lamp in a very short time, it may be possible to perform annealing at a temperature exceeding 400 ° C.

≪3. Thin film transistor and manufacturing method thereof >>
The thin film transistor according to this embodiment is a thin film transistor including three electrodes of a source electrode, a drain electrode, and a gate electrode, a channel layer, and a gate insulating film, and an oxide semiconductor thin film is used as the channel layer.

  As the thin film transistor, for example, the bottom gate / top contact type thin film transistor 1 having the configuration shown in FIG. 1 can be exemplified. In the thin film transistor 1 of FIG. 1, a gate insulating film 12 is provided on a gate electrode 11, a channel layer 13 is stacked on the surface, and a source electrode 14 and a drain electrode 15 are further disposed on the surface. Further, there is no gap between these components, and the components are in close contact.

In the thin film transistor 1 of FIG. 1, a Si substrate is used as the gate electrode 11. The surface of the gate electrode 11 is changed to SiO ₂ by thermal oxidation to constitute a gate insulating film 12. As described above, the gate electrode 11 and the gate insulating film 12 are composed of a single substrate as the SiO ₂ / Si substrate. As the channel layer 13, an oxide semiconductor thin film is used. Furthermore, Au / Ti laminated electrodes are used as the source electrode 14 and the drain electrode 15.

The substrate is not limited to the SiO ₂ / Si substrate, and a conventionally known substrate for an electronic device such as a transistor can be used. Specifically, for example, a glass substrate such as alkali-free glass or quartz glass can be used in addition to the above-described SiO ₂ / Si substrate or Si substrate. In addition, various metal substrates, plastic substrates, non-transparent heat-resistant polymer film substrates such as polyimide can be used.

The gate electrode 11 is not limited to Si. Specifically, for example, metals such as Mo, Al, Ta, Ti, Au, and Pt, alloys, conductive metal oxides, metal nitrides, metals An oxynitride, various conductive polymer materials, or the like can be used. These materials can also be used as a thin film. In the case of a transparent thin film transistor, a transparent conductive film such as ITO can be used. Note that a transparent conductive film having the same metal composition as that of the oxide semiconductor thin film forming the channel layer 13 can also be used. The gate electrode 11 is required to have good conductivity. Specific resistance of the electrode is ^{preferably 10} -6 ~10 ^-1 Ω · ^cm, and more preferably ¹⁰ -6 ~10 ^-3 Ω · cm.

As the gate insulating film 12, an insulating polymer material such as a metal oxide thin film such as SiO ₂ , Y ₂ O ₃ , Ta ₂ O ₅ , or Hf oxide, a metal nitride thin film such as SiN _x , or polyimide is used. Etc. can be used. The specific resistance of the gate insulating film 12 is preferably 1 × 10 ⁶ to 1 × 10 ¹⁵ Ω · cm, and more preferably 1 × 10 ¹⁰ to 1 × 10 ¹⁵ Ω · cm.

As the channel layer 13, an oxide semiconductor thin film manufactured by the above-described method for manufacturing an oxide semiconductor thin film is used. The specific resistance of the channel layer 13 is not particularly limited, but is preferably 10 ⁻¹ to 10 ⁶ Ω · cm, and more preferably 10 ⁰ to 10 ³ Ω · cm. The specific resistance of the oxide semiconductor thin film used for the channel layer 13 can be controlled by selecting film forming conditions such as sputtering and ion plating and heat treatment conditions.

As the source electrode 14 and the drain electrode 15, the same material as that of the gate electrode 11 can be used. Specifically, for example, metals such as Mo, Al, Ta, Ti, Au, and Pt, alloys, conductive metal oxides, metal nitrides, metal oxynitrides, or various conductive polymer materials are used. be able to. These materials can also be used as a thin film. In the case of a transparent thin film transistor, a transparent conductive film such as ITO can be used. Moreover, these thin films can also be laminated. The source electrode 14 or the drain electrode 15 is required to have good conductivity. The resistivity of these ^electrodes, preferably from ¹⁰ -6 ~10 ^-1 Ω · ^cm, and more preferably ¹⁰ -6 ~10 ^-3 Ω · cm.

  The type of thin film transistor is not limited to the bottom gate / top contact type shown in FIG. 1, but other shapes such as a bottom gate / bottom contact type, a top gate / bottom contact type, a top gate / top contact type, etc. Can also be configured.

  Hereinafter, an example of a method for manufacturing the thin film transistor according to this embodiment will be described.

First, the n-type Si surface of the substrate of highly doped, the _SiO 2 / Si wafers SiO ₂ film is formed by thermal oxidation of the substrate. After holding this substrate at, for example, 100 ° C. or lower, an amorphous thin film having a predetermined thickness is formed on the SiO ₂ film on the surface by a direct current magnetron sputtering method. By using a mask when forming the amorphous film, or by performing an etching process using a photolithography technique or the like after the amorphous film is formed, the amorphous thin film has a desired channel length and channel width. Process to the shape you have.

  Next, the amorphous thin film is annealed at a temperature of 400 ° C. or lower, for example, to obtain a channel layer made of a crystalline oxide semiconductor thin film having a predetermined channel length and channel width. A source electrode and a drain electrode are formed at two locations on the channel layer by sequentially laminating a Ti thin film having a thickness of about 5 nm and an Au thin film having a thickness of about 100 nm using a mask. In forming the source electrode and the drain electrode, an etching process may be performed using a photolithography technique or the like to obtain a predetermined shape. Through such a process, a thin film transistor using an oxide semiconductor thin film can be obtained.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

<Example 1: Preparation of oxide thin film and Hall effect characteristics>
In accordance with the procedures of Examples 1-1 to 1-6 and Comparative Examples 1-1 to 1-6, oxide thin films were prepared, and the thin films were evaluated using the following method.

  Table 1 shows the charge ratio of raw materials (Y / (In + Y)) in each of Examples 1-1 to 1-6 and Comparative Examples 1-1 to 1-6, and whether or not micro arc discharge occurs during crystallization. , Shows the film thickness, crystallization temperature, carrier concentration, and carrier mobility of the thin film. In Table 1, in the column of “micro arc”, “◯” indicates that no micro arc occurred during the formation of the oxide thin film, and “×” indicates that micro arc occurred during the formation of the oxide thin film. Indicates.

[Evaluation of sintered oxide]
Using the oxide sintered compacts obtained in Examples 1-1 to 1-6 and Comparative Examples 1-1 to 1-6, using an X-ray diffractometer (manufactured by Philips) and using a powder method The product phase was identified.

[Basic characteristics evaluation of oxide thin film]
The compositions of the oxide thin films obtained in Examples 1-1 to 1-6 and Comparative Examples 1-1 to 1-6 were examined by ICP emission spectroscopy. The film thickness of the oxide thin film was measured with a surface shape measuring device (manufactured by Tencor). The film formation rate was calculated from the film thickness and the film formation time. The carrier concentration and specific resistance of the oxide thin film were measured with a Hall effect measuring device (manufactured by Toyo Technica), and the carrier mobility was calculated from these values. The film formation phase was identified by the above X-ray diffraction measurement.

  The characteristics of the obtained thin film transistor were evaluated using a semiconductor parameter analyzer 4200SCS (manufactured by Keithley).

(Example 1-1)
An oxide thin film was formed using a sputtering target made of an oxide sintered body containing indium and yttrium as oxides.

Indium oxide powder and yttrium oxide powder were adjusted to have an average particle size of 1 μm or less to obtain raw material powder. These powders were prepared so that the atomic ratio (Y / (In + Y)) of yttrium was 0.08, put into a resin pot together with water, and mixed by 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.

Subsequently, the compact was sintered for 20 hours at a sintering temperature of 1400 ° C. 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 heating rate was 1 ° C./min. During cooling after sintering, oxygen introduction was stopped and the temperature was lowered to 1000 ° C. at 10 ° C./min. 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. An oxide sintered body was bonded to a backing plate made of oxygen-free copper using metallic indium to obtain a sputtering target.

When the end material of the oxide sintered body was crushed and subjected to composition analysis by ICP emission spectroscopy, it was confirmed that it was the same as the charged composition of the raw material powder. As a result of the X-ray diffraction measurement, it was confirmed that the oxide sintered body was mainly composed of an In ₂ O ₃ phase having a big Svit type structure.

The obtained sputtering target was attached to a cathode for a non-magnetic target of a DC magnetron sputtering apparatus (manufactured by Tokki) equipped with a DC power supply having no arcing suppression function. As the substrate, an alkali-free glass substrate (Corning EAGLE XG) was used, and the target-substrate distance was fixed to 60 mm. After evacuating to 2 × 10 ⁻⁴ Pa or less, a mixed gas of argon and oxygen was introduced so that the ratio of oxygen was 0.5%, and the gas pressure was adjusted to 0.6 Pa.

A direct-current power of 300 W (1.64 W / cm ² ) was applied to generate direct-current plasma for film formation. After pre-sputtering for 10 minutes, a substrate was placed immediately above the sputtering target, that is, at a stationary facing position, and sputtering was performed at room temperature without heating to form an oxide thin film having a thickness of 50 nm. It was confirmed that the composition of the obtained oxide semiconductor thin film was the same as the composition of the oxide sintered compact target. As a result of X-ray diffraction measurement, it was confirmed that the oxide semiconductor thin film was amorphous.

  Moreover, when another film-forming sample was prepared by the same method and high temperature X-ray diffraction measurement was performed, the crystallization temperature was 255 degreeC. At this time, the number of occurrences of microarcs during the formation of the oxide thin film was measured using a microarc monitor (manufactured by Landmark Technology), but no microarc discharge occurred during the formation of the oxide thin film.

Next, this amorphous oxide semiconductor thin film was annealed in the atmosphere at 360 ° C. for 30 minutes to obtain a crystalline thin film. As a result of X-ray diffraction measurement, the obtained thin film was confirmed to be a single phase of indium oxide having a bixbite structure having a peak derived from (222) of In ₂ O ₃ as a main peak.

The Hall effect of the crystalline oxide semiconductor thin film thus obtained was measured. As a result, the carrier concentration was 3.8 × 10 ¹⁵ cm ⁻³ and the carrier mobility was 6.7 cm ² / Vsec.

(Example 1-2)
An oxide semiconductor thin film was produced in the same manner as in Example 1-1 except that the annealing temperature of the oxide semiconductor thin film was changed to 400 ° C., and its characteristics were evaluated.

As a result of X-ray diffraction measurement, this oxide semiconductor thin film was confirmed to be a single phase of indium oxide having a bixbite structure having a peak derived from the (222) plane of In ₂ O ₃ as a main peak.

The Hall effect of the crystalline oxide semiconductor thin film thus obtained was measured. As a result, the carrier concentration was 1.1 × 10 ¹⁴ cm ⁻³ and the carrier mobility was 6.1 cm ² / Vsec.

(Example 1-3)
An oxide semiconductor thin film was produced in the same manner as in Example 1 except that the atomic ratio (Y / (In + Y)) of yttrium charged as the raw material for the oxide sintered body was changed to 0.10, and its characteristic evaluation Went.

When the end material of the oxide sintered body was crushed and subjected to composition analysis by ICP emission spectroscopy, it was confirmed that it was the same as the charged composition of the raw material powder. As a result of X-ray diffraction measurement, it was confirmed that this oxide sintered body was composed of an In ₂ O ₃ phase having a big Svit type structure.

  Sputtering was performed under the same conditions as in Example 1-1 to form an oxide semiconductor thin film with a thickness of 50 nm. It was confirmed that the composition of the obtained oxide semiconductor thin film was the same as the composition of the oxide sintered compact target. As a result of X-ray diffraction measurement, it was confirmed that the oxide semiconductor thin film was amorphous.

  Moreover, when another film-forming sample was prepared by the same method and high temperature X-ray diffraction measurement was performed, the crystallization temperature was 285 degreeC. At this time, the number of occurrences of microarcs during the formation of the oxide thin film was measured using a microarc monitor (manufactured by Landmark Technology), but no microarc discharge occurred during the formation of the oxide thin film.

Next, this amorphous oxide semiconductor thin film was annealed in the atmosphere at 360 ° C. for 30 minutes to obtain a crystalline thin film. As a result of X-ray diffraction measurement, this oxide semiconductor thin film was confirmed to be a single phase of indium oxide having a bixbite structure having a peak derived from the (222) plane of In ₂ O ₃ as a main peak.

The Hall effect of the oxide semiconductor thin film thus crystallized was measured. As a result, the carrier concentration was 1.5 × 10 ¹⁵ cm ⁻³ and the carrier mobility was 6.5 cm ² / Vsec.

(Example 1-4)
An oxide semiconductor thin film was produced in the same manner as in Example 1-3, except that the annealing temperature of the amorphous oxide semiconductor thin film obtained by sputtering film formation was changed to 400 ° C. went.

As a result of X-ray diffraction measurement, this oxide semiconductor thin film was confirmed to be a single phase of indium oxide having a bixbite structure having a peak derived from the (222) plane of In ₂ O ₃ as a main peak.

The Hall effect of the crystalline oxide semiconductor thin film thus obtained was measured. As a result, the carrier concentration was 5 × 10 ¹⁴ cm ⁻³ and the carrier mobility was 5.1 cm ² / Vsec.

(Example 1-5)
An oxide semiconductor thin film was produced in the same manner as in Example 1-1, except that the yttrium atomic ratio (Y / (In + Y)) of the raw material charge ratio of the oxide sintered body was changed to 0.05. The characteristics were evaluated.

When the end material of the oxide sintered body was crushed and subjected to composition analysis by ICP emission spectroscopy, it was confirmed that it was the same as the charged composition of the raw material powder. As a result of the X-ray diffraction measurement, it was confirmed that this oxide sintered body was mainly composed of an In ₂ O ₃ phase having a big Svit type structure.

  Sputtering was performed in the same manner as in Example 1-1 to form an oxide semiconductor thin film with a thickness of 50 nm. It was confirmed that the composition of the obtained oxide semiconductor thin film was the same as that of the oxide sintered compact target. As a result of X-ray diffraction measurement, it was confirmed that the oxide semiconductor thin film was amorphous.

  Moreover, when another film-forming sample was prepared by the same method and high temperature X-ray diffraction measurement was performed, the crystallization temperature was 225 degreeC. At this time, the number of occurrences of microarcs during the formation of the oxide thin film was measured using a microarc monitor (manufactured by Landmark Technology), but no microarc discharge occurred during the formation of the oxide thin film.

Next, this amorphous oxide semiconductor thin film was annealed in the atmosphere at 360 ° C. for 30 minutes to obtain a crystalline thin film. As a result of X-ray diffraction measurement, the obtained thin film was confirmed to be a single phase of indium oxide having a bixbite structure having a peak derived from the (222) plane of In ₂ O ₃ as a main peak.

The Hall effect of the crystalline oxide semiconductor thin film thus obtained was measured. As a result, the carrier concentration was 6.5 × 10 ¹⁵ cm ⁻³ and the carrier mobility was 7.1 cm ² / Vsec.

(Example 1-6)
An oxide semiconductor thin film was prepared in the same manner as in Example 1-1, except that the yttrium atomic ratio (Y / (In + Y)) of the raw material charge ratio of the oxide sintered body was changed to 0.12. The characteristics were evaluated.

When the end material of the oxide sintered body was crushed and subjected to composition analysis by ICP emission spectroscopy, it was confirmed that it was the same as the charged composition of the raw material powder. As a result of X-ray diffraction measurement, it was confirmed that the obtained thin film was mainly composed of an In ₂ O ₃ phase having a big Svit type structure.

  Sputtering was performed under the same conditions as in Example 1 to form an oxide semiconductor thin film with a thickness of 50 nm. It was confirmed that the composition of the obtained oxide semiconductor thin film was the same as that of the oxide sintered compact target. As a result of X-ray diffraction measurement, it was confirmed that the oxide semiconductor thin film was amorphous.

  Moreover, when another film-forming sample was prepared by the same method and the high temperature X-ray diffraction measurement was performed, the crystallization temperature was 300 degreeC. At this time, the number of occurrences of microarcs during the formation of the oxide thin film was measured using a microarc monitor (manufactured by Landmark Technology), but no microarc discharge occurred during the formation of the oxide thin film.

Next, this amorphous oxide semiconductor thin film was annealed in the atmosphere at 360 ° C. for 30 minutes to obtain a crystalline thin film. As a result of X-ray diffraction measurement, the obtained thin film was confirmed to be a single phase of indium oxide having a bixbite structure having a peak derived from the (222) plane of In ₂ O ₃ as a main peak.

The Hall effect of the crystalline oxide semiconductor thin film thus obtained was measured. As a result, the carrier concentration was 8.5 × 10 ¹⁴ cm ⁻³ and the carrier mobility was 6.3 cm ² / Vsec.

(Comparative Example 1-1)
An oxide semiconductor thin film was prepared in the same manner as in Example 1-1 except that the yttrium atomic ratio (Y / (In + Y)) in the raw material charge ratio of the oxide sintered body was changed to 0.04. The characteristics were evaluated.

When the end material of the oxide sintered body was crushed and subjected to composition analysis by ICP emission spectroscopy, it was confirmed that it was the same as the charged composition of the raw material powder. As a result of the X-ray diffraction measurement, it was confirmed that this oxide sintered body was mainly composed of an In ₂ O ₃ phase having a big Svit type structure.

  Sputtering was performed in the same manner as in Example 1-1 to form an oxide semiconductor thin film with a thickness of 50 nm. It was confirmed that the composition of the obtained oxide semiconductor thin film was the same as that of the oxide sintered compact target. Further, as a result of X-ray diffraction measurement, it was confirmed to be amorphous. Separately, a film formation sample was prepared and subjected to high-temperature X-ray diffraction measurement. As a result, the crystallization temperature was 200 ° C. At this time, the number of occurrences of microarcs during the formation of the oxide thin film was measured using a microarc monitor (manufactured by Landmark Technology), but no microarc discharge occurred during the formation of the oxide thin film.

Next, the amorphous oxide semiconductor thin film was annealed to make it crystalline. The annealing treatment conditions were 360 ° C. and 30 minutes in the atmosphere. As a result of X-ray diffraction measurement, it was confirmed to be a single phase indium oxide having a bixbite structure having a peak derived from the (222) plane of In ₂ O ₃ as a main peak.

The Hall effect of the crystalline oxide semiconductor thin film thus obtained was measured. As a result, the carrier concentration was 5.5 × 10 ¹⁶ cm ⁻³ and the carrier mobility was 7.3 cm ² / Vsec.

(Comparative Example 1-2)
An oxide semiconductor thin film was produced in the same manner as Comparative Example 1-1 except that the annealing temperature of the oxide semiconductor thin film was changed to 400 ° C., and the characteristics were evaluated.

As a result of X-ray diffraction measurement, this oxide semiconductor thin film was confirmed to be a single phase of indium oxide having a bixbite structure having a peak derived from the In ₂ O ₃ (222) plane as a main peak.

Subsequently, Hall effect measurement of the oxide semiconductor thin film was performed. As a result, the carrier concentration was 8.5 × 10 ¹⁵ cm ⁻³ and the carrier mobility was 6.5 cm ² / Vsec.

(Comparative Example 1-3)
An oxide semiconductor thin film was prepared in the same manner as in Example 1-1 except that the yttrium atomic ratio (Y / (In + Y)) of the raw material charge ratio of the oxide sintered body was changed to 0.13. The characteristics were evaluated.

When the end material of the oxide sintered body was crushed and subjected to composition analysis by ICP emission spectroscopy, it was confirmed that it was the same as the charged composition of the raw material powder. As a result of the X-ray diffraction measurement, it was confirmed that this oxide sintered body was mainly composed of an In ₂ O ₃ phase having a big Svit type structure.

  Sputtering was performed in the same manner as in Example 1-1 to form an oxide semiconductor thin film with a thickness of 50 nm. It was confirmed that the composition of the obtained oxide semiconductor thin film was the same as that of the oxide sintered compact target. Further, as a result of X-ray diffraction measurement, it was confirmed to be amorphous.

  Moreover, when another film-forming sample was prepared by the same method and high temperature X-ray diffraction measurement was performed, the crystallization temperature was 315 degreeC. At this time, the number of occurrences of microarcs during the formation of the oxide thin film was measured using a microarc monitor (manufactured by Landmark Technology), but no microarc discharge occurred during the formation of the oxide thin film.

Next, the oxide semiconductor thin film was annealed in the atmosphere at 360 ° C. for 30 minutes. As a result of X-ray diffraction measurement, this oxide semiconductor thin film was confirmed to be a single phase of indium oxide having a bixbite structure having a peak derived from the (222) plane of In ₂ O ₃ as a main peak.

The Hall effect of the crystalline oxide semiconductor thin film thus obtained was measured. As a result, the carrier concentration was 4.5 × 10 ¹⁴ cm ⁻³ and the carrier mobility was 3.7 cm ² / Vsec.

(Comparative Example 1-4)
An oxide semiconductor thin film was prepared in the same manner as in Comparative Example 1 except that the annealing temperature was changed to 400 ° C., and the characteristics were evaluated.

As a result of X-ray diffraction measurement, this oxide semiconductor thin film was confirmed to be a single phase of indium oxide having a bixbite structure having a peak derived from the (222) plane of In ₂ O ₃ as a main peak.

The Hall effect of the crystalline oxide semiconductor thin film thus obtained was measured. As a result, the carrier concentration was 1.5 × 10 ¹⁵ cm ⁻³ and the carrier mobility was 4.8 cm ² / Vsec.

(Comparative Example 1-5)
An oxide semiconductor thin film was prepared in the same manner as in Example 1 except that the atomic ratio (Y / (In + Y)) of yttrium charged as the raw material for the oxide sintered body was changed to 0.20, and its characteristics were evaluated. Went.

  When the end material of the oxide sintered body was crushed and subjected to composition analysis by ICP emission spectroscopy, it was confirmed that it was the same as the charged composition of the raw material powder.

  Sputtering was performed in the same manner as in Example 1-1 to form an oxide semiconductor thin film with a thickness of 50 nm. It was confirmed that the composition of the obtained oxide semiconductor thin film was the same as that of the oxide sintered compact target. As a result of X-ray diffraction measurement, it was confirmed that the oxide semiconductor thin film was amorphous.

  Moreover, when another film-forming sample was prepared by the same method and high temperature X-ray diffraction measurement was performed, the crystallization temperature was 405 degreeC. At this time, the number of occurrences of microarcs during the formation of the oxide thin film was measured using a microarc monitor (manufactured by Landmark Technology), but no microarc discharge occurred during the formation of the oxide thin film.

  Next, this amorphous oxide semiconductor thin film was annealed. The annealing conditions were 400 ° C. and 30 minutes in the atmosphere. As a result of the X-ray diffraction measurement, it was confirmed that this oxide semiconductor thin film did not crystallize even when annealed and was amorphous.

(Comparative Example 1-6)
The yttrium atomic ratio (Y / (In + Y)) charged to the raw material of the oxide sintered body was changed to 0.05, and the indium oxide powder and the yttrium oxide powder were adjusted to have an average particle size of 2 μm or less. In this case, an oxide sintered body was produced in the same manner as in Example 1 except that the mixing time using the hard ZrO ₂ balls was changed to 72 hours, and the characteristics were evaluated.

When the end material of the oxide sintered body was crushed and subjected to composition analysis by ICP emission spectroscopy, it was confirmed that it was the same as the charged composition of the raw material powder. As a result of the X-ray diffraction measurement, it was confirmed that this oxide sintered body was mainly composed of an In ₂ O ₃ phase having a big Svit type structure.

  Sputtering was performed under the same conditions as in Example 1 to form an oxide semiconductor thin film with a thickness of 50 nm. At this time, using a micro arc monitor (manufactured by Landmark Technology), the number of occurrences of micro arc during the formation of the oxide thin film was measured, and 10 micro arc discharges were confirmed during the formation of the oxide thin film. It was.

  It was confirmed that the composition of the obtained oxide semiconductor thin film was the same as that of the oxide sintered compact target. As a result of X-ray diffraction measurement, it was confirmed that the oxide semiconductor thin film was amorphous. Separately, a film formation sample was prepared and subjected to high temperature X-ray diffraction measurement. As a result, the crystallization temperature was 220 ° C.

Next, this amorphous oxide semiconductor thin film was annealed in the atmosphere at 300 ° C. for 30 minutes to obtain a crystalline thin film. As a result of X-ray diffraction measurement, this oxide semiconductor thin film was confirmed to be a single phase of indium oxide having a bixbite structure having a peak derived from the In ₂ O ₃ (222) plane as a main peak.

The Hall effect of the crystalline oxide semiconductor thin film thus obtained was measured. As a result, the carrier concentration was 1.5 × 10 ¹⁶ cm ⁻³ and the carrier mobility was 4.4 cm ² / Vsec.

<Example 2: Evaluation of characteristics of thin film transistor>
According to the procedures of Example 2-1 and Example 2-2, an oxide thin film was prepared, and the thin film was evaluated using the following method. Table 2 shows the yttrium atomic ratio (Y / (In + Y)), presence or absence of micro arc discharge during crystallization, thin film thickness and crystal in Example 2-1 and Example 2-2. The temperature is shown. In Table 2, in the column of “micro arc”, “◯” indicates that no micro arc occurred during the formation of the oxide thin film, and “×” indicates that micro arc occurred during the formation of the oxide thin film. Indicates.

(Example 2-1)
The surface of the Si substrate was thermally oxidized by 300 nm to form a SiO ₂ film. The obtained SiO ₂ / Si substrate was used as a gate insulating film / gate electrode composite.

Next, an oxide thin film as a channel layer was formed on the surface by the same method as in Example 1-1. Specifically, an oxide sintered body was prepared by mixing oxides having a particle size of 1 μm or less so that the atomic ratio (Y / (In + Y)) of charged yttrium was 0.08. This oxide-sintered amorphous oxide semiconductor thin film was formed at room temperature by a direct current magnetron sputtering method so as to have a thickness of 50 nm. Subsequently, the obtained amorphous oxide semiconductor thin film was crystallized in the same manner as in Example 1, that is, by annealing in the atmosphere at 360 ° C. for 30 minutes. The Si substrate, the SiO ₂ film and the crystalline oxide semiconductor thin film were used as a gate electrode, a gate insulating film and a channel layer, respectively.

  Next, on the channel layer, a direct current magnetron sputtering method is used to form a Ti film having a thickness of 5 nm and an Au film having a thickness of 100 nm in order to form a source electrode and a drain electrode made of an Au / Ti laminated film, The bottom gate / top contact type thin film transistor illustrated in FIG. 1 was constructed. The film formation conditions for the source electrode and the drain electrode were the same as the conditions for sputtering the oxide sintered body, except that the sputtering gas was changed to only argon and the DC power was changed to 50 W. When forming the source and drain electrodes, patterning was performed using a metal mask to obtain a thin film transistor having a channel length of 100 μm and a channel width of 450 μm.

  The operating characteristics of the thin film transistor were examined using a semiconductor parameter analyzer 4200SCS (manufactured by Keithley). As a result, good operating characteristics as a thin film transistor were confirmed.

(Example 2-2)
Except that the yttrium atomic ratio (Y / (In + Y)) of the raw material charge ratio of the oxide sintered body was set to 0.10 and the annealing treatment was performed in the atmosphere at 400 ° C. for 30 minutes, A thin film transistor was produced in the same manner as in Example 2-1, except that a crystalline oxide semiconductor thin film made of indium and yttrium was formed, and its characteristics were evaluated.

  When the operating characteristics of the thin film transistor were examined, it was confirmed that the thin film transistor had good operating characteristics.

DESCRIPTION OF SYMBOLS 1 Bottom gate top contact type thin-film transistor 11 Gate electrode 12 Gate insulating film 13 Channel layer 14 Source electrode 15 Drain electrode

Claims (11)

A crystalline oxide semiconductor thin film containing indium and yttrium,
Yttrium content is 0.05 to 0.12 in terms of Y / (In + Y) atomic ratio,
The crystal phase is composed only of an indium oxide phase having a bixbyite structure,
An oxide semiconductor thin film having a carrier concentration of 7.0 × 10 ¹⁵ cm ⁻³ or less and a carrier mobility of 5 cm ² V ⁻¹ sec ⁻¹ or more.   The oxide semiconductor thin film according to claim 1, wherein the content of yttrium is 0.08 or more and 0.10 or less in terms of a Y / (In + Y) atomic ratio. 3. The oxide semiconductor thin film according to claim 1, wherein the carrier concentration is 1.0 × 10 ¹⁵ cm ⁻³ or less. The oxide semiconductor thin film according to claim 1, wherein the carrier mobility is 5 cm ² V ⁻¹ sec ⁻¹ or more. Obtained by sputtering a sputtering target obtained by sintering a metal source having an average particle size of 1 μm or less,
The oxide semiconductor thin film of any one of Claims 1 thru | or 4. An oxide sintered body containing indium and yttrium,
Yttrium content is 0.05 to 0.12 in terms of Y / (In + Y) atomic ratio,
An oxide sintered body whose main component is an In ₂ O ₃ phase having a bixbite type crystal phase. An oxide sintered body containing indium and yttrium,
Yttrium content is 0.05 to 0.12 in terms of Y / (In + Y) atomic ratio,
A sputtering target whose crystal phase is mainly composed of an In ₂ O ₃ phase having a bixbyite structure. A thin film transistor including a source electrode, a drain electrode, a gate electrode, a channel layer, and a gate insulating film,
A thin film transistor in which the channel layer is configured by the oxide semiconductor thin film according to any one of claims 1 to 5.   A display device comprising the thin film transistor according to claim 8. A method of manufacturing a thin film of an oxide semiconductor,
A raw material sintering step of sintering a metal source having an average particle size of 1 μm or less to obtain an oxide sintered body;
A film forming step of forming an amorphous thin film on a substrate having a temperature lower than the crystallization temperature of the oxide semiconductor, using the oxide sintered body;
Annealing the amorphous thin film at a temperature equal to or higher than the crystallization temperature of the oxide semiconductor,
A method for manufacturing a thin film of an oxide semiconductor.   The method for producing a thin film of an oxide semiconductor according to claim 10, wherein in the annealing step, the thin film is annealed at 350 ° C. or more and 400 ° C. or less.