JP2019064859A - Oxide sintered body, sputtering target, amorphous oxide semiconductor thin film, and thin film transistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxide sintered body and a sputtering target capable of forming an amorphous oxide semiconductor thin film having excellent TFT performance and ensuring strength when a light rare earth element is added. SOLUTION: The atomic ratios of In element, Zn element, Sn element and light rare earth element (hereinafter referred to as LREE: X) satisfy the formulas (1) to (4), and the main component is a big bite structure represented by In2O3. Oxide sintered body. 0.55 ≤ In / (In + Sn + Zn) ≤ 0.90 ... (1), 0.05 ≤ Sn / (In + Sn + Zn) ≤ 0.25 ... (2), 0.05 ≤ Zn / (In + Sn + Zn) ≤ 0.20 ... (3), 0.05 ≦ X / (In + Sn + Zn + X) ≦ 0.25 ... (4). However, the light rare earth element is one or more elements selected from La, Nd, Sm, and Eu. [Selection diagram] None

Description

  The present invention relates to an oxide sintered body, a sputtering target, an amorphous oxide semiconductor thin film, and a thin film transistor.

  An amorphous oxide semiconductor used for a thin film transistor has higher carrier mobility than general-purpose amorphous silicon (a-Si), has a large optical band gap, and can be formed at a low temperature. Therefore, the application to the next-generation display in which large size, high resolution, and high speed driving are required, resin substrate with low heat resistance, etc. is expected.

  Sputtering is preferably used to form the amorphous oxide semiconductor thin film. The thin film formed by the sputtering method has a component composition in the film surface direction (in the film surface), a film thickness, etc. as compared with the thin film formed by the ion plating method, the vacuum evaporation method or the electron beam evaporation method. It is because it is excellent in uniformity. Moreover, it is because the thin film of the component composition same as a sputtering target can be formed.

  Among oxide semiconductors, amorphous oxide semiconductors (In-Sn-Zn-O, hereinafter abbreviated as "ITZO") consisting of indium, zinc, tin and oxygen are inexpensive zinc as a raw material of oxide semiconductors. And tin can realize relatively high carrier mobility and etching rate with organic acids such as boric acid, and it does not dissolve in mixed acid of phosphoric acid, acetic acid and nitric acid which is an etching solution for metal wiring. Attention is focused on the possibility of selective etching of metal wirings and oxide semiconductor films.

  Patent Document 1 discloses a sputtering target containing at least one metal selected from indium, zinc and tin as a component, and at least selected from the group consisting of hafnium, tantalum, bismuth, or a lanthanoid metal as a third component. It is described that the sputtering target is characterized in that it contains one or more metals. It is described that this target is suitably used to obtain a transparent conductive film.

Patent Document 2 discloses the sintering of an oxide containing InSmO ₃ and / or Sn ₂ Sm ₂ O ₇ consisting of a sintered body of an oxide mainly composed of In and Sm and consisting of InSmO ₃ and indium oxide. There is a description about the body.

Patent Document 3 discloses a group consisting of Mg, Si, Al, Sc, Ti, Y, Zr, Hf, Ta, La, Nd and Sm in order to lower the oxygen partial pressure during sputtering to In, Sn and Zn. An oxide sintered body containing one or more selected elements, and a sputtering target using the same are described. This sintered body is a sintered body containing In ₂ O ₃ and Zn ₂ SnO ₄ .

  In Patent Document 4, Mg, Al, Ga, Si, Ti, Y, Zr, Hf, Ta, Mg, Al, Ga, Si, Ti, Y, Zr, Hf, Ta, and the like are used in the oxide sintered body containing In, Sn, and Zn so as not to crystallize even if the amount of In is increased. It is described that an element selected from La, Nd, and Sm is added. The oxide sintered body is described to include a bixbite structure and a spinel structure.

In Patent Document 5, an oxide sintered body containing In, Sn, and Zn is selected from Hf, Zr, Ti, Y, Nb, Ta, W, Mo, and Sm to prevent cracking during sputtering. The addition of the element X is exemplified, and it has one or more layers selected from In ₂ O ₃ structure, spinel structure, X ₂ Sn ₂ O ₇ structure (pyrochlore structure), ZnX ₂ O _{6 and} has a resistance value of 2 mΩcm or more The sintered body which is 50 mΩcm or less is described. As for the lanthanoid element, Zn / (In + Sn + Zn + Sm) = 0.35 and 0.3 are described when the Sm content: Sm / (In + Sn + Zn + Sm) = 0.05 and 0.1. When converted to Zn / (In + Sn + Zn), the value exceeds 0.3.
Patent Document 6 also discloses a solid-state imaging device and an image sensor in which an oxide semiconductor is combined with a photoelectric conversion element.

JP 2004-68054 A International Publication No. 2007/010702 International Publication No. 2012/153507 JP, 2014-111818, A JP 2015-214436 A JP, 2017-135410, A

However, the techniques described in Patent Document 1 to Patent Document 5 have the following problems.
The target described in Patent Document 1 is a target for obtaining a conductive film, and has a problem that an amorphous oxide semiconductor thin film can not be obtained.
The target described in Patent Document 2 is also a target for obtaining a transparent conductive film, and there is a problem that an amorphous oxide semiconductor thin film can not be obtained. Moreover, since the target of patent document 2 does not contain zinc, there also existed a problem that it could not apply to ITZO.

Although the techniques described in Patent Document 3 to Patent Document 5 add a rare earth element to a target material based on indium oxide, a light rare earth element having a large atomic radius among rare earths, such as a samarium element, is particularly used. When it is added, the lattice constant of the bixbite structure of indium oxide changes, the sintering density does not increase, the strength of the target material decreases, or micro cracks occur due to thermal stress during sputtering at high power, or chipping occurs. In some cases, abnormal discharge may occur. These phenomena may also cause defects in the formed semiconductor thin film and cause deterioration of TFT performance.
Moreover, in patent document 3, there existed a problem that the addition amount of rare earth elements can be contained only about 0.048 atomic ratio with respect to the atomic ratio of the whole metal element. In Patent Document 3, the control of etching is difficult because the content of zinc is too large.
Furthermore, in Patent Document 5, it is necessary to contain a large amount of zinc in order to reduce bulk resistance, and the content of zinc is too large, which makes it difficult to control etching.
Further, Patent Document 6 shows an example in which an oxide semiconductor is used for a transfer transistor and a reset transistor of a CMOS image sensor, and a transistor with a small off current is required.

This invention is made in view of the said subject, and even when it is a case where light rare earth elements are added, intensity | strength can be ensured and the oxide baking which can form into a film the amorphous oxide semiconductor thin film excellent in TFT performance. It aims at provision of a solid body and a sputtering target.
Another object of the present invention is to provide an amorphous oxide semiconductor thin film having excellent characteristics when used for a thin film transistor, and a thin film transistor including the thin film.

According to the present invention, the following oxide sintered body is provided.
[1] The atomic ratio of In element, Zn element, Sn element and light rare earth element (described as LREE: light rare earth element: X) satisfies the following formulas (1) to (4), and In ₂ O ₃ An oxide sintered body comprising a bixbite structure represented as a main component.
0.55 ≦ In / (In + Sn + Zn) ≦ 0.90 (1)
0.05 ≦ Sn / (In + Sn + Zn) ≦ 0.25 (2)
0.05 ≦ Zn / (In + Sn + Zn) ≦ 0.20 (3)
0.05 ≦ X / (In + Sn + Zn + X) ≦ 0.25 (4)
However, the light rare earth element is one or more elements selected from La, Nd, Sm, and Eu.
[2] The oxide sintered body according to [1], wherein the ratio of the content of Sn element to all metals and the ratio of the content of light rare earth elements to all metals satisfies the following formula (5).
1.2 ≦ (Sn / all metal elements) / (X / all metal elements) ≦ 3.5 (5)
[3] The oxide sintered body according to [1] or [2], which has a bixbite structure represented by In ₂ O ₃ as a main component and further contains a pyrochlore structure.
[4] The oxide sintered body according to [3], wherein the pyrochlore structure is a pyrochlore structure represented by X ₂ Sn ₂ O ₇ .
[5] The oxide sinter according to any one of [1] to [4], which contains In, Zn, Sn and a light rare earth element, the balance being oxygen and unavoidable impurities. Body.
[6] The oxide sintered body according to any one of [1] to [5], which has a bulk resistance value of 1.4 mΩcm or less.

According to the present invention, the following sputtering target is provided.
[7] A sputtering target comprising the sintered body according to any one of [1] to [6].

According to the present invention, the following amorphous oxide semiconductor thin film is provided.
[8] The atomic ratio of In element, Zn element, Sn element and light rare earth element (abbreviated as LREE: light rare earth element: X) is a range satisfying the following formulas (6) to (10) Amorphous oxide semiconductor thin film.
0.55 ≦ In / (In + Sn + Zn) ≦ 0.90 (6)
0.05 ≦ Sn / (In + Sn + Zn) ≦ 0.25 (7)
0.05 ≦ Zn / (In + Sn + Zn) ≦ 0.20 (8)
0.05 ≦ X / (In + Sn + Zn + X) ≦ 0.25 (9)
1.2 ≦ (Sn / all metal elements) / (X / all metal elements) ≦ 3.5 (10)
However, the light rare earth element is one or more elements selected from La, Nd, Sm, and Eu.
[9] The amorphous oxide semiconductor thin film according to [8], containing an In element, a Zn element, a Sn element and a light rare earth element, with the balance being oxygen and unavoidable impurities.

According to the present invention, the following thin film transistor is provided.
[10] A thin film transistor comprising the amorphous oxide semiconductor thin film according to [9].

According to the present invention, even when a light rare earth element is added, it is possible to provide an oxide sintered body and a sputtering target capable of securing strength and capable of forming an amorphous semiconductor thin film excellent in TFT performance.
It is also possible to provide an amorphous oxide semiconductor thin film having excellent properties when used for a thin film transistor, and a thin film transistor provided with the thin film.

BRIEF DESCRIPTION OF THE DRAWINGS The perspective view which shows the shape of the target which concerns on this embodiment. FIG. 1 is a longitudinal sectional view showing a thin film transistor according to the present embodiment. FIG. 1 is a longitudinal sectional view showing a thin film transistor according to the present embodiment. It is a figure showing a display using thin film transistors concerning this embodiment, and (A) is a top view, (B) is a figure showing a pixel circuit applicable to a pixel of a VA type liquid crystal display, (C Fig. 6 shows a pixel structure of a display device using an organic EL element. FIG. 2 is a view showing a pixel circuit of a solid-state imaging device using a thin film transistor according to the embodiment. It is a figure which shows the XRD diffraction pattern of the oxide sinter of Example 1, Comprising: The upper stage is a measured value, and the middle and lower stages are the values of a pure substance (ICDD, the standard substance contained in International Center for Diffraction Data). It is a figure which shows the XRD diffraction pattern of the oxide sinter of Example 2, Comprising: The upper stage is a measured value, and the middle and lower stages are the values of a pure substance (ICDD, the standard substance contained in International Center for Diffraction Data). It is a figure which shows the XRD diffraction pattern of the oxide sintered compact of the comparative example 3, Comprising: The upper stage is a measured value, and the middle and lower stages are the values of a pure substance (ICDD, standard substance recorded in International Center for Diffraction Data). (A) a longitudinal sectional view showing a state of forming an oxide film on a glass substrate, the (B) is a longitudinal sectional view showing a state in, it is further formed an SiO ₂ film (A).

<Background of the Invention>
First, the background of the present invention will be briefly described.
It is well known that the addition of a light rare earth element to an oxide sintered body based on indium oxide changes the lattice constant of the bixbite structure of indium oxide and the strength of the target material decreases without increasing the sintering density. is there.
For example, in order to increase the target strength, it is necessary to increase the In content, but on the other hand, in the case of an oxide semiconductor based on indium oxide, zinc oxide, and tin oxide, when the content of indium oxide is increased, transparent conductive It is known that it becomes a film composition and does not become semiconductor.
In addition, in the manufacture of thin film transistors, there is a demand for a semiconductor with less deterioration in semiconductor characteristics (CVD resistance) due to heating or the like when forming a protective film or an insulating film by chemical vapor deposition (CVD).

  On the other hand, the present inventors examined whether there is a condition that the strength can be secured even if the light rare earth element is added. In addition, we examined whether there were conditions not only for securing the strength but also for the characteristics as a semiconductor without conducting.

Under the present circumstances, the present inventors paid attention to the reaction which a pyrochlore structure produces. Since the pyrochlore structure is a structure represented by X ₂ Sn ₂ O ₇ when the light rare earth element is X, if the added light rare earth element is consumed to form the pyrochlore structure, a bixbite structure is obtained. It is because it thought that it did not affect. On the other hand, since the pyrochlore structure also contains Sn, it was considered to be influenced by the addition amount of Sn.

  Therefore, the present inventors examined the conditions under which the light rare earth element is consumed in the pyrochlore structure. As a result, by setting the In element, the Zn element, the Sn element and the light rare earth element in a predetermined composition range, in particular by increasing the content of Sn more than before, the light rare earth element is consumed in the pyrochlore structure We found a composition range that does not affect the structure.

Also, conventionally, it is known that when the Sn content is increased, the bulk resistance of the sintered body is increased, but since Sn is also consumed in the pyrochlore structure in the composition range, even if Sn is increased It has been found that the bulk resistance is very low, and the present invention has been achieved.
The preceding is an explanation of the background of the present invention.

<Structure of oxide sinter>
Next, the structure of the oxide sintered body according to the present embodiment will be described.
In the oxide sintered body according to the present embodiment, the atomic ratio of In element, Zn element, Sn element and light rare earth element (described as light rare earth element: LREE) has the following formulas (1) to (4) Meet).
0.55 ≦ In / (In + Sn + Zn) ≦ 0.90 (1)
0.05 ≦ Sn / (In + Sn + Zn) ≦ 0.25 (2)
0.05 ≦ Zn / (In + Sn + Zn) ≦ 0.20 (3)
0.05 ≦ X / (In + Sn + Zn + X) ≦ 0.25 (4)
However, the light rare earth element is one or more elements selected from La, Nd, Sm, and Eu.

In Formula (1), when In is less than 0.55, the bulk resistance of a sintered compact may become high and may become a cause of abnormal discharge. In addition, the effect of increasing the mobility of an oxide semiconductor with indium can not be obtained, and only an oxide semiconductor with low mobility may be obtained. If it exceeds 0.90, the thin film may be crystallized to become a conductor.
Within the range of Formula (1), the amount may be defined from the addition amount of each additive element in consideration of the required TFT characteristics.
The atomic ratio represented by In / (In + Sn + Zn) is more preferably 0.55 or more and 0.85 or less, and still more preferably 0.60 or more and 0.80 or less.

In the formula (2), when Sn is less than 0.05, the resistance value of the target does not decrease or the sintered density does not increase, and the strength of the subsequent sintered body does not increase, or the linear expansion coefficient or thermal conductivity May have adverse effects. In addition, when a semiconductor thin film of a thin film transistor is formed using a sputtering target manufactured from a sintered body of less than 0.05, it is dissolved in a mixed acid consisting of phosphoric acid, nitric acid and acetic acid which is an etching solution of wiring metal. Become. This may make it difficult to form a back channel TFT. On the other hand, if it exceeds 0.25, when the semiconductor layer of the thin film transistor is formed using a sputtering target manufactured from a sintered body, etching may not be possible with an organic acid such as boric acid, making it difficult to form a TFT. There is a case.
In the formula (2), Sn is more preferably 0.07 or more and 0.25 or less, and still more preferably 0.10 or more and 0.22 or less.

In the formula (3), when the atomic ratio represented by Zn / (In + Sn + Zn) is less than 0.05, the obtained thin film semiconductor may be crystallized to be a conductor. If it exceeds 0.20, zinc can not form a solid solution in the indium oxide or pyrochlore structure, and precipitates as zinc oxide or a spinel structure made of Zn ₂ SnO ₄ or the like appears to lower the density of the sintered body or strength May decrease. When the thickness exceeds 0.20, when a semiconductor layer of a thin film transistor (TFT) is formed using a sputtering target manufactured from a sintered body, only a TFT lacking in stability may be obtained.
The atomic ratio represented by Zn / (In + Sn + Zn) is preferably 0.08 or more and 0.20 or less, and more preferably 0.10 or more and 0.18 or less.

In the formula (4), when the content of the light rare earth element is less than 0.05, the carrier concentration may be too high in the step of forming the SiO ₂ film by the CVD process which is a step of forming a protective film. In this case, the carrier concentration may not be reduced even by the subsequent heat treatment, and the semiconductor may not act as a conductor. Also, if it exceeds 0.25, the carrier concentration may be too low, and it may not operate as a semiconductor, or its mobility may be small even if it operates. The content of the light rare earth element may be adjusted in accordance with the content of indium oxide. As the content of indium oxide increases, the amount of oxygen deficiency in the thin film tends to increase, and the content of the light rare earth element needs to be increased. On the other hand, as the content of indium oxide decreases, the amount of oxygen deficiency in the thin film tends to decrease, and the content of the light rare earth element needs to be reduced. It may be appropriately selected according to the content of indium oxide. In the formula (4), the content of the light rare earth element is more preferably 0.06 or more and 0.23 or less, still more preferably 0.07 or more and 0.20 or less.
The light rare earth element is preferably at least one selected from La, Nd, and Sm. More preferably, it is Sm. The reason is that natural abundance is also large, and procurement of materials is easy in industrial use.

In the oxide sintered body, the ratio of the content of the tin element to the total metal and the content of the light rare earth element to the total metal element preferably satisfies the following formula (5).
1.2 ≦ (Sn / all metal elements) / (X / all metal elements) ≦ 3.5 (5)
By satisfying the lower limit of the formula (5), the light rare earth element is consumed in the pyrochlore structure, so it does not affect the structure of the bixbite structure and does not adversely affect the semiconductor characteristics.
By satisfying the upper limit of Expression (5), it is possible to prevent the bulk resistance from deteriorating.

  The content (atomic ratio) of each metal element in the sintered body can be determined by measuring the abundance of each element by ICP (Inductive Coupled Plasma) measurement.

The oxide sintered body of the present invention may contain indium element, zinc element, tin element and light rare earth element, and may substantially consist of indium element, zinc element, tin element and light rare earth element.
"Substantial" means that the content ratio of the indium element, the zinc element, the tin element and the light rare earth element in the metal element contained in the oxide sintered body is 90 atm% or more. 95 atm% or more and 98 atm% or more are preferable, 99 atm% or more is more preferable, and 100 atm% is more preferable.
The oxide sintered body of the present invention may contain a gallium element as a metal element other than the indium element, the zinc element, the tin element and the light rare earth element as long as the effects of the present invention are not impaired.

However, it is preferable that the composition contains an indium element, a zinc element, a tin element and a light rare earth element, and the balance (an element other than the indium element, the zinc element, the tin element and the light rare earth element) consists of oxygen and unavoidable impurities. Elements other than indium element, zinc element, tin element and light rare earth element are oxide sinter, and semiconductor thin film produced by using the oxide sinter as the remainder is oxygen and an unavoidable impurity Can be minimized.
An unavoidable impurity is an element which is not intentionally added, and means an element which is mixed in the raw material or the manufacturing process. The same applies to the following description.

The oxide sintered body of the present embodiment mainly has a bixbyite structure represented by In ₂ O ₃ .
Thereby, since the oxide sintered body exhibits a high density, the bulk resistance is reduced, and a stable sputtering state can be maintained.
That the oxide sintered body is composed of a bixbite structure represented by In ₂ O ₃ can be confirmed by examining the crystal structure with an X-ray diffraction measurement apparatus (XRD).
The term "main component" as used herein means that in the oxide sintered body, the bixbite structure is 70% by mass or more. Preferably, it is 75% by mass or more, more preferably 78% by mass or more, and still more preferably 80% by mass or more.

In the bixbite structure, it is preferable that any one or more of the light rare earth element, the Sn element, and the Zn element is in interstitial solid solution and / or substitutional solid solution.
The interstitial solid solution of zinc element in the bixbite structure represented by In ₂ O ₃ means that the lattice constant of the bixbite structure of indium oxide in the sintered body is smaller than the lattice constant of only indium oxide It can be confirmed by In addition, substitution of the light rare earth element in the bixbite structure represented by In ₂ O ₃ indicates that the lattice constant of the bixbyte structure of indium oxide in the sintered body is the lattice constant of only indium oxide. It can confirm by becoming larger. In addition, the interstitial type of tin element in the bixbite structure represented by In ₂ O ₃ means that the lattice constant of the bixbite structure of indium oxide in the sintered body is more than that of only indium oxide. It can confirm by having become large. By the lead belt analysis, the solid solution state can be grasped more reliably. On the other hand, the bixbyite structure represented by In ₂ O ₃ can be easily determined by XRD measurement.
The interstitial solid solution of zinc element in the pyrochlore structure means that the lattice constant of the pyrochlore structure represented by X ₂ Sn ₂ O ₇ in the sintered body is represented by X ₂ Sn ₂ O ₇ It can be confirmed by the fact that it is smaller than the lattice constant of. In addition, the interstitial solid solution and / or substitutional solid solution of the indium element in the pyrochlore structure represented by X ₂ Sn ₂ O ₇ means that the lattice constant of the pyrochlore structure in the sintered body is X ₂ by is smaller than the pyrochlore structure represented by sn ₂ O _7, it can be confirmed. By the lead belt analysis, the solid solution state can be grasped more reliably. On the other hand, the pyrochlore structure represented by X ₂ Sn ₂ O ₇ can be easily determined by XRD measurement.

The "lattice constant" is defined as the length of the lattice axis of the unit cell and can be determined by X-ray diffraction. The lattice constant of the bixbite structure of indium oxide of a pure substance (here, the standard substance contained in ICDD) is 10.118 × 10 ⁻¹⁰ m.
For the pyrochlore structure represented by X ₂ Sn ₂ O ₇ in a pure substance, for example, the lattice constant of the pyrochlore structure of Sm ₂ Sn ₂ O ₇ is 10.51005 × 10 ⁻¹⁰ m.

The oxide sintered body preferably includes a pyrochlore structure represented by X ₂ Sn ₂ O ₇ . By including the pyrochlore structure, the thermal conductivity is improved and it becomes difficult to be broken.

The oxide sintered body may include structures other than the bixbite structure and the pyrochlore structure.
For example, it may include a hexagonal layered structure represented by In ₂ O ₃ (ZnO) _m (where m is an integer of 1 or more and 20 or less).
However, it is desirable not to include the spinel structure made of Zn ₂ SnO ₄ . By not containing the spinel structure, it is possible to prevent the density of the sintered body from being reduced and the strength from being reduced.
<Physical properties of oxide sinter>
The oxide sintered body according to the present embodiment preferably has a relative density of 95% or more.
By setting the relative density to 95% or more, it is possible to suppress the generation of cracks and nodules at the time of film formation, and it is possible to prevent the deterioration of the performance of the obtained thin film transistor, the decrease of yield, and the decrease of film density. Further, the film formation temperature in the CVD apparatus can be raised. The relative density is preferably 96% or more, more preferably 97% or more.
The relative density can be calculated, for example, by dividing the measured density of the oxide sintered body measured by the Archimedes method by the theoretical density of the oxide sintered body as a percentage.
As a method of measuring the actual measurement density, measure the volume of the oxide sintered body using Archimedes method (apparent density) and measure the volume of the oxide sintered body using a caliper, measure the mass of the oxide sintered body with a meter, and measure the density There is a method (bulk density) to calculate.
As the theoretical density of the oxide sintered body, for example, when using the oxide A, the oxide B, the oxide C, and the oxide D as a raw material powder of the oxide sintered body, the oxide A, the oxide B The theoretical density can be calculated as follows by assuming that the amounts used (charge amounts) of oxide C and oxide D are a (g), b (g), c (g) and d (g), respectively. It can be calculated.
Theoretical density = (a + b + c + d) / ((a / density of oxide A) + (b / density of oxide B) + (c / density of oxide C) + (d / density of oxide D))
In addition, since the density and specific gravity of each oxide are almost the same, using the specific gravity value of the oxide described in the Chemical Handbook, Basic Edition I, Nippon Chemical Edited Second Edition (Maruzen Co., Ltd.) Good. The theoretical density can also be calculated as follows using the mass ratio of each oxide.
Theoretical density = 1 / ((mass ratio of oxide A / density of oxide A) + (mass ratio of oxide B / density of oxide B) + (mass ratio of oxide C / density of oxide C) + (Mass ratio of oxide D / density of oxide D))

The oxide sintered body according to the present embodiment preferably has a bulk resistance of 1.4 mΩcm or less, more preferably 1.2 mΩcm or less, still more preferably 1.0 mΩcm or less, and 0.8 mΩcm or less And even more preferred.
By setting the bulk resistance to 1.4 mΩcm or less, it is possible to prevent the target from being charged and causing abnormal discharge or unstable plasma state and generation of spark during film formation with high power.

The bulk resistance value can be measured based on the four-probe method (JIS R 1637) using a known resistivity meter. There are about five measurement points, and the average value is preferably taken as the bulk resistance value.
When the planar shape of the oxide sintered body is a square, it is preferable that the number of measurement points be five points in total: four points at the center and at four points between the four corners and the center.
In the case where the oxide sintered body has a circular planar shape, it is preferable that a total of five points be provided at the center of the square inscribed in the circle and at four points between the four corners of the square and the center.

The oxide sintered body according to the present embodiment preferably has a three-point bending strength of 120 MPa or more, more preferably 140 MPa or more, and still more preferably 150 MPa or more.
When sputtering deposition is performed with high power if the three-point bending strength is 120 MPa or more, the target may be cracked or chipped, and the solid may be scattered on the target to reduce the possibility of causing an abnormal discharge.
The three-point bending strength can be evaluated according to JIS R 1601 "room temperature bending strength test of fine ceramics". Specifically, first, a standard test piece having a width of 4 mm, a thickness of 3 mm, and a length of 40 mm is placed on two supporting points arranged at a constant distance (30 mm). Next, a crosshead speed of 0.5 mm / min is applied from the center between the fulcrums, and the bending strength is calculated from the maximum load when broken.

The oxide sintered body according to the present embodiment preferably has a linear expansion coefficient of 8.0 × 10 ⁻⁶ (K ⁻¹ ) or less, and 7.5 × 10 ⁻⁶ (K ⁻¹ ) or less More preferably, it is further preferably 7.0 × 10 ⁻⁶ (K ⁻¹ ) or less.
If the linear expansion coefficient is 8.0 × 10 ^-6 (K ^-1 ) or less, it is heated during sputtering with high power, the target expands, and deformation occurs with the bonded copper plate, causing stress There is little risk of causing an abnormal discharge due to micro cracks in the target, cracking or chipping.
The linear expansion coefficient is set, for example, at a heating rate of 5 ° C./min using a standard test piece of 5 mm in width, 5 mm in thickness and 10 mm in length, and displacement detection due to thermal expansion when reaching 300 ° C. is detected It can be evaluated by using a machine.

The oxide sintered body according to the present embodiment preferably has a thermal conductivity of 5.0 (W · m ⁻¹ · K ⁻¹ ) or more, and 5.5 (W · m ⁻¹ · K ⁻¹ ) It is more preferable that it is the above, more preferable to be 6.0 (W · m ⁻¹ · K ⁻¹ ) or more, and most preferable to be 6.5 (W · m ⁻¹ · K ⁻¹ ) or more.
If the thermal conductivity is 5.0 (W · m ⁻¹ · K ⁻¹ ) or more, the temperature of the sputtered surface and the bonded surface differ when sputtering film formation is performed with high power, and the internal stress causes There is little risk of micro cracks, cracks and chipping.
The thermal conductivity can be calculated, for example, by using a standard test piece with a diameter of 10 mm and a thickness of 1 mm to determine the specific heat capacity and the thermal diffusivity by the laser flash method, and multiplying this by the density of the test piece.
The above is the description of the oxide sintered body according to the present embodiment.

Next, the manufacturing method of the oxide sinter which concerns on this embodiment is demonstrated.
Although the manufacturing method is not particularly limited as long as the oxide sintered body according to the present embodiment can be manufactured, a manufacturing method including the following steps (a) to (c) can be exemplified.
(A) A step of mixing the raw material compound powders to prepare a mixture.
(B) molding the mixture to prepare a molded body.
(C) a step of sintering the molded body.

(1) Step (a): Compounding Step The compounding step is a step of mixing the raw materials of the oxide sintered body.
As a raw material, a powder of an indium compound, a powder of a tin compound, a powder of a zinc compound, and a powder of a light rare earth compound are used. Examples of compounds of indium, tin and zinc include oxides and hydroxides. The compounds of light rare earth elements include oxides. The oxide is preferable from the ease of sintering and the difficulty of remaining by-products.

The purity of the raw material is usually 2N (99% by mass) or more, preferably 3N (99.9% by mass) or more, particularly preferably 4N (99.99% by mass) or more. By setting the purity to 2 N or more, the durability can be secured, and when used in a liquid crystal display, the possibility of the occurrence of baking due to the entry of impurities on the liquid crystal side can be reduced.
The average particle diameter of the raw material powder is preferably 0.1 μm or more and 2 μm or less, more preferably 0.5 μm or more and 1.5 μm or less. The average particle size of the raw material powder can be measured by a laser diffraction type particle size distribution apparatus or the like.

There are no particular limitations on the method of mixing and molding the raw materials, and it can be carried out using known methods. In addition, when mixing, a binder may be added.
The mixing of the raw materials can be performed using a known apparatus such as, for example, a ball mill, a bead mill, a jet mill or an ultrasonic device. The conditions such as the grinding time may be appropriately adjusted, but are preferably 6 hours or more and 100 hours or less.

The blended raw materials may be calcined. In the calcination, a mixture of compounds that are raw materials of the sputtering target is obtained, and then the mixture is calcined, which is an optional step.
Although it is easy to increase the density of the obtained sintered body by calcination, which is preferable, the cost may be increased. Therefore, it is more preferable to increase the density without performing calcination.

In the calcination, the raw material mixture is preferably heat-treated at 500 ° C. or more and 1200 ° C. or less for 1 hour or more and 100 hours or less. By heat treatment at 500 ° C. or more for one hour or more, the thermal decomposition of the indium compound, the tin compound, the zinc compound, and the light rare earth compound becomes sufficient. On the other hand, coarsening of particles can be prevented by setting the heat treatment conditions to 1200 ° C. or less and 100 hours or less.
The calcination is preferably performed in a temperature range of 800 ° C. or more and 1200 ° C. or less for 2 hours or more and 50 hours or less.
It is preferable to grind | pulverize the obtained calcination thing before the following shaping | molding process and baking process.
(2) Step (b): Forming Step The forming step is a step of pressing and forming the raw material mixture (in the case where the above-mentioned calcination step is provided, the calcined material) to form a formed body. By this process, it is molded into a shape suitable as a target. When the calcining step is provided, the obtained fine powder of the calcined product is granulated, and then can be molded into a desired shape by press molding.

  5.5 mm or more is preferable, as for the average thickness of a molded object, 6 mm or more is more preferable, 8 mm or more is more preferable, and 12 mm or more is especially preferable. If it is 5.5 mm or more, it can be expected that the temperature gradient in the thickness direction of the molded body is reduced, and the variation of the combination of the surface and deep crystal types is unlikely to occur.

  As a shaping | molding process which can be used at this process, press molding (uniaxial press), metal mold | die molding, cast molding, injection molding etc. are mentioned, for example. In order to obtain a sintered body (target) having a high sintered density, it is preferable to perform molding by cold isostatic pressure (CIP) or the like.

In addition, two or more stages of forming processes may be provided so as to form by cold isostatic pressure (CIP), hot isostatic pressure (HIP) or the like after press forming (uniaxial press).
When using a cold hydrostatic pressure or hydrostatic pressure device, the surface pressure is 78.5 MPa (800 kgf / cm ² converted to SI unit) or more, and 392.4 MPa (4000 kgf / cm ² converted to SI unit) is 0. It is preferable to hold for 5 minutes or more and 60 minutes or less. It is more preferable to hold | maintain 2 minutes or more and 30 minutes or less by surface pressure 196.2 Mpa or more and 294.3 Mpa or less. It is expected that the composition nonuniformity etc. inside a molded object will reduce and be uniform as it is in the said range. By setting the surface pressure to 78.5 MPa or more, the density after sintering decreases and the resistance also decreases. By setting the surface pressure to 392.4 MPa or less, molding can be performed without increasing the size of the apparatus. It can prevent that the density and resistance after sintering become high as holding time is 0.5 minutes or more. If it takes less than 60 minutes, it will take too long to prevent it from becoming uneconomical.
In the molding process, a molding auxiliary such as polyvinyl alcohol, methyl cellulose, poly wax, oleic acid, etc. may be used.
(3) Step (c): Sintering Step The sintering step is an essential step of firing the molded body obtained in the above-mentioned forming step.
The sintering temperature is preferably 1350 ° C. or more and 1600 ° C. or less, more preferably 1400 ° C. or more and 1600 ° C. or less, and still more preferably 1450 ° C. or more and 1600 ° C. or less.
The sintering time is preferably 10 hours to 50 hours, more preferably 12 hours to 40 hours, and further preferably 13 hours to 30 hours.
If the sintering temperature is 1200 ° C. or more and the sintering time is 10 hours or more, sintering proceeds sufficiently, the electrical resistance of the target is sufficiently lowered, and abnormal discharge hardly occurs. If the firing temperature is 1650 ° C. or less and the firing time is 50 hours or less, significant grain growth can prevent the increase in average grain size and the generation of coarse pores, and the strength of the sintered body can be reduced and abnormal discharge Is less likely to occur.

  In the pressureless sintering method, the molded body is sintered in an air atmosphere or an oxygen gas atmosphere. The oxygen gas atmosphere is preferably an atmosphere having an oxygen concentration of, for example, 10% by volume or more and 50% by volume or less. The sintered body density can be increased by performing the temperature raising process in the air atmosphere.

Furthermore, as for the temperature rising rate at the time of sintering, it is preferable to be from 0.1 ° C./min to 2 ° C./min from 800 ° C. to the sintering temperature.
In the sintered body according to the present embodiment, the temperature range above 800 ° C. is the range in which sintering progresses most. Excessive crystal grain growth can be suppressed as the temperature rising rate in this temperature range is 0.1 ° C./min or more, and high densification can be achieved. When the temperature rise rate is 2 ° C./min or less, temperature distribution occurs in the molded body, and it is possible to suppress that the sintered body is warped or broken.
The temperature raising rate at a sintering temperature from 800 ° C. is preferably 0.5 ° C./min or more and 2.0 ° C./min or less, more preferably 1.0 ° C./min or more and 1.8 ° C./min or less .

<Sputtering target>
Next, the sputtering target according to the present embodiment will be described with reference to FIG.
The sputtering target according to the present embodiment includes the oxide sintered body according to the present embodiment.

  Specifically, the sputtering target includes an oxide sintered body, and a cooling and holding member such as a backing plate provided on the oxide sintered body as necessary.

The oxide sintered body is a film material to be deposited by sputtering. The shape is not particularly limited, but may be plate-like as shown by symbol 1 in FIG. 1 (A) or cylindrical as shown by symbol 1A in FIG. 1 (B). In the case of the plate shape, the planar shape may be a rectangle as shown by symbol 1 in FIG. 1 (A) or a circle as shown by symbol 1B in FIG. 1 (C). The oxide sintered body may be integrally formed, or may be a multi-division type in which the oxide sintered body (symbol 1B) divided into plural pieces is fixed to the backing plate 3 as shown in FIG. 1 (D).
The backing plate is a member for holding and cooling the oxide sintered body. The material is preferably a material excellent in thermal conductivity such as copper.

The sputtering target is manufactured, for example, by the following process.
(D) grinding the surface of the oxide sintered body.
(E) bonding the oxide sintered body to the backing plate.
Each step is specifically described below.
(4) Step (d): Grinding Step The grinding (processing) step is a step of cutting the sintered body into a shape suitable for mounting on a sputtering apparatus.
The sintered body surface often has a sintered part in a highly oxidized state, and the surface is often uneven, and it is necessary to cut and process it into a specified size.
The surface of the sintered body is preferably ground by 0.3 mm or more. The grinding depth is preferably 0.5 mm or more, and particularly preferably 2 mm or more. By grinding 0.3 mm or more, it is possible to remove the fluctuation part of the crystal structure near the surface.

For example, it is preferable to grind the oxide sintered body with a surface grinder to obtain a material having an average surface roughness Ra of 5 μm or less. Further, the sputtering surface of the sputtering target may be mirror-polished to have an average surface roughness Ra of 1000 × 10 ⁻¹⁰ m or less. This mirror surface process (polishing) can use known polishing techniques such as mechanical polishing, chemical polishing, mechanochemical polishing (combination of mechanical polishing and chemical polishing). For example, polishing may be performed using a fixed abrasive polisher (water is used as the polishing liquid) to # 2000 or more, and after lapping with a free abrasive wrap (an abrasive material such as SiC paste), the abrasive material is changed to diamond paste, You may wrap it. The polishing method is not limited to these methods. The abrasives include # 200, # 400, and even # 800.

  It is preferable to clean the oxide sintered body after the grinding process by air blowing, running water washing or the like. When foreign matter is removed by air blowing, it can be more effectively removed by suctioning air from the side opposite to the nozzle with a dust collector. In addition, since there is a limit in air blow and running water cleaning, ultrasonic cleaning can also be performed. The ultrasonic cleaning is preferably performed by performing multiple oscillation at a frequency of 25 kHz or more and 300 kHz or less. For example, ultrasonic cleaning may be performed by performing multi-oscillation of 12 kinds of frequencies in 25 kHz steps at a frequency of 25 kHz or more and 300 kHz.

(5) Step (e): Bonding Step Step (e) is a step of bonding the sintered body after grinding to a backing plate with a low melting point metal such as metallic indium.
The above is the description of the sputtering target.

<Oxide semiconductor thin film>
Next, the amorphous oxide semiconductor thin film according to the present embodiment will be described.
In the oxide semiconductor thin film according to the present embodiment, the atomic ratio of In element, Zn element, Sn element and light rare earth element X satisfies the following formulas (6) to (10).
0.50 ≦ In / (In + Sn + Zn) ≦ 0.85 (6)
0.10 ≦ Sn / (In + Sn + Zn) ≦ 0.45 (7)
0.05 ≦ Zn / (In + Sn + Zn) ≦ 0.25 (8)
0.05 ≦ X / (In + Sn + Zn + X) ≦ 0.25 (9)
1.2 ≦ (Sn / all metal elements) / (X / all metal elements) ≦ 3.5 (10)

Outside the composition range shown in Formula (6) to Formula (10), the carrier concentration of the semiconductor portion of the thin film transistor is increased during processing in the CVD film forming apparatus used in the step of forming the thin film transistor, and the annealing thereafter is performed. The treatment may not lower the carrier concentration. In this case, the off current does not decrease and there is a possibility that the transistor does not operate. Alternatively, when it is used as a transfer transistor or a reset transistor of a CMOS image sensor, the sensitivity may decrease or the function as a sensor may decrease.
In addition, the film formation temperature of the CVD device was lowered to suppress the rise of the carrier concentration, and the TFT characteristics were expressed. However, by reducing the film formation temperature of the CVD device, only the TFT characteristics having poor durability. It may not be obtained.

  Specific grounds of upper and lower limits of Formula (6) to Formula (10) and more preferable ranges are the same as specific bases of upper and lower limits of Formula (1) to Formula (5) and more preferable range It is.

The elements other than the In element, the Zn element, the Sn element, and the light rare earth element are not particularly limited.
However, it is preferable that the oxide semiconductor thin film according to the present embodiment includes an In element, a Zn element, an Sn element, and a light rare earth element, and the balance be oxygen and an unavoidable impurity. When the balance is oxygen and an unavoidable impurity, the influence of elements other than In, Zn, Sn, and light rare earth elements on the characteristics of the oxide semiconductor thin film can be minimized.

The carrier density of the oxide semiconductor thin film is usually preferably 1 × 10 ¹⁸ (cm ⁻³ ) or less, preferably 1 × 10 ¹² (cm ⁻³ ) or more, and more preferably 1 × 10 ¹⁷ (cm ⁻³ ) or less And more preferably 1 × 10 ¹³ (cm ⁻³ ) or more.

If the carrier density of the heat-treated oxide layer after film deposition is 1 × 10 ¹⁸ (cm ⁻³ ) or less, the leakage current when forming an element such as a thin film transistor, the normally on, or the on-off ratio A drop can be prevented, and good transistor performance can be exhibited. If the carrier concentration is 1 × 10 ¹³ (cm ⁻³ ) or more, the transistor is driven without problems.
The carrier density of the oxide semiconductor thin film can be measured by the Hall effect measurement method.

The mobility of the oxide semiconductor thin film 1.0cm ² / V · s or more, preferably not more than 50.0cm ² / V · s. A liquid crystal display can be driven by setting it as 1.0 cm < ² > / V * s or more. By setting the density to 50.0 cm ² / V · s or less, the off current can be reduced to 10 ⁻¹² A or less, and the on / off ratio can be increased to 10 ⁸ or more. Thereby, the transfer transistor and the reset transistor of the CMOS image sensor can be driven.
The mobility is determined by a Hall effect / resistivity measuring device.

The oxide semiconductor thin film is amorphous. By making it amorphous, it is possible to prevent the effect of adding tin from becoming too strong, and to prevent the thin film from becoming conductive.
Whether it is amorphous or not can be judged by whether or not the peak of XRD, in particular, the peak appears at 30 to 40 ° at 2θ.

<Method of manufacturing amorphous oxide semiconductor thin film>
Next, a method of manufacturing the amorphous oxide semiconductor thin film according to the present embodiment will be described.
The manufacturing method is not particularly limited as long as the amorphous oxide semiconductor thin film according to the present embodiment can be manufactured. Specifically, the following manufacturing method can be exemplified.

  Sputtering is preferably used to form the amorphous oxide semiconductor thin film. This is because the uniformity of the composition, film thickness, and the like is excellent as compared with the thin film formed by the ion plating method, the vacuum evaporation method, or the electron beam evaporation method. Moreover, it is because the thin film of the component composition same as a sputtering target can be formed.

Among sputtering methods, a DC sputtering method which can form a large-area film and has a high film formation rate is preferable. Other sputtering methods such as RF sputtering and AC sputtering may be used.
By using the sputtering target according to the present embodiment as the sputtering target, an oxide semiconductor thin film satisfying the conditions shown in Formulas (6) to (10) can be obtained.

The atmosphere of sputtering is preferably an oxidative atmosphere. By sputtering in an oxidizing atmosphere, the oxidizing gas reduces oxygen vacancies in the semiconductor thin film, so that the carrier concentration can be adjusted. The oxidizing atmosphere is an atmosphere containing an oxidizing gas. The oxidizing gas means an oxygen atom-containing gas such as O ₂ , H ₂ O, CO, CO _{2 and the} like. The concentration of oxidizing gas is optimized under the conditions of use such as equipment, substrate temperature, sputtering pressure and the like.

  In the film formation using the sputtering target according to the present embodiment, the oxygen partial pressure at the time of film formation may be about 1%. This is because the light rare earth element has a high effect of suppressing the generation of oxygen vacancies, and therefore, the necessity of adding oxygen at the time of film formation is low. Since the generation of nodules and the like during sputtering is suppressed as the oxygen partial pressure of the oxidizing gas is lower, the sputtering target according to the present embodiment is also useful in this respect.

Power density during sputtering (divided by the area of the surface of the input power target), 1.0 W / cm ² or more, is preferably 5.0 W / cm ² or less. By setting the concentration to 1.0 W / cm ² or more, the discharge is stabilized and a desired sputtering rate can be obtained. By setting the power to 5.0 W / cm ² or less, it is possible to prevent the target from cracking by generated heat.
The pressure (sputtering pressure) of the gas atmosphere is not particularly limited as long as the plasma can be stably discharged, but is preferably 0.05 Pa or more and 5 Pa or less.

  Examples of the substrate to be film-formed include silicon wafers, glasses, ceramics, plastics, metals and the like. The substrate temperature during film formation is not particularly limited, but is preferably 300 ° C. or less in that an amorphous film can be easily obtained. In addition, the substrate temperature may be around room temperature, in particular, when intentional heating is not performed.

After film formation, the substrate can be post-heated (heat treatment). The heat treatment densifies the film and lowers the resistance value.
The heat treatment is preferably performed at 60 ° C. or more and 400 ° C. or less in the air. By setting the temperature to 60 ° C. or higher, the effect of the heat treatment is exhibited. By setting the temperature to 400 ° C. or less, it is possible to prevent the resistance value from increasing.
The above is the description of the method for manufacturing an amorphous oxide semiconductor thin film.

<Thin film transistor>
Next, the structure of the thin film transistor according to the present embodiment will be described.
The thin film transistor according to the present embodiment includes the amorphous oxide semiconductor thin film according to the present embodiment, and the structure is not particularly limited as long as it functions as a transistor.
Specific examples of the thin film transistor include a back channel etch type transistor, an etch stopper type transistor, a top gate type transistor, and the like.

Specific examples of thin film transistors are shown in FIGS. 2 and 3.
As shown in FIG. 2, the thin film transistor 100 includes a silicon wafer 20, a gate insulating film 30, an oxide semiconductor thin film 40, a source electrode 50, a drain electrode 60, and interlayer insulating films 70 and 70A.

The silicon wafer 20 is a gate electrode. The gate insulating film 30 is an insulating film that blocks conduction between the gate electrode and the oxide semiconductor thin film 40, and is provided on the silicon wafer 20.
The oxide semiconductor thin film 40 is a channel layer and is provided on the gate insulating film 30. For the oxide semiconductor thin film 40, the amorphous oxide semiconductor thin film according to the present embodiment is used.

The source electrode 50 and the drain electrode 60 are conductive terminals for flowing a source current and a drain current to the oxide semiconductor thin film 40, and are provided so as to be in contact with the vicinity of both ends of the oxide semiconductor thin film 40.
The interlayer insulating film 70 is an insulating film that blocks conduction between the source electrode 50 and the drain electrode 60 and the oxide semiconductor thin film 40 except for the contact portion.
The interlayer insulating film 70A is an insulating film that blocks conduction between the source electrode 50, the drain electrode 60, and the oxide semiconductor thin film 40 except for the contact portion. It is also an insulating film that blocks the conduction between the source electrode 50 and the drain electrode 60. It is also a channel layer protective layer.

  As shown in FIG. 3, the structure of the thin film transistor 100A is the same as that of the thin film transistor 100, but the source electrode 50 and the drain electrode 60 are provided in contact with both the gate insulating film 30 and the oxide semiconductor thin film 40. The point is different. Another difference is that an interlayer insulating film 70B is integrally provided to cover the gate insulating film 30, the oxide semiconductor thin film 40, the source electrode 50, and the drain electrode 60.

The thin film transistor preferably has the following characteristics.
Saturation mobility of the thin film transistor is 1.0cm ² / V · s or more, preferably not more than 50.0cm ² / V · s. By setting the area to 1.0 cm ² / V · s or more, the transfer transistor, the reset transistor, and the liquid crystal display of the CMOS image sensor can be driven. By setting the density to 50.0 cm ² / V · s or less, the off current can be reduced to 10 ⁻¹² A or less, and the on / off ratio can be increased to 10 ⁸ or more. Thereby, the transfer transistor and the reset transistor of the CMOS image sensor can be driven.

  The saturation mobility is obtained from the transfer characteristics when a drain voltage of 20 V is applied. Specifically, a graph of the transfer characteristic Id-Vg is created, the transconductance (Gm) of each Vg is calculated, and the saturation mobility is determined by the equation of the saturation region. Id is a current between the source and drain electrodes, and Vg is a gate voltage when a voltage Vd is applied between the source and drain electrodes.

The threshold voltage (Vth) is preferably -3.0 V or more and +3.0 or less, and more preferably -2.5 or more and +2.5 V or less. When the voltage is -3.0 V or more and +3.0 or less, a thin film transistor with a small off current and a large on / off ratio can be formed, and can be driven in combination with a circuit formed of a bulk silicon wafer.

The threshold voltage (Vth) was defined as Vg at Id = 10 ⁻⁹ A from the graph of transfer characteristics.
The on-off ratio is preferably 10 ⁶ or more and 10 ¹² or less, more preferably 10 ⁷ or more and 10 ¹¹ or less, and still more preferably 10 ⁸ or more and 10 ¹¹ or less. If it is 10 ⁶ or more, the liquid crystal display can be driven. If it is 10 ¹² or less, driving of the organic EL panel with large contrast becomes possible. In addition, the off current can be reduced to 10 ⁻¹² A or less, and when it is used for a transfer transistor or a reset transistor of a CMOS image sensor, the image retention time can be extended or the sensitivity can be improved.

The on-off ratio can be obtained by setting the value of Id of Vg = −10 V as the Off current value and determining the value of Id of Vg = 20 V as the On current value to determine the ratio [On / Off].
The off current value is preferably 10 ⁻¹¹ A or less, more preferably 10 ⁻¹² A or less. The off current can be 10 ^-11 A or less, and when used for a transfer transistor or a reset transistor of a CMOS image sensor, the image retention time can be lengthened or the sensitivity can be improved.

The defect density of the amorphous oxide semiconductor thin film according to this embodiment, which is used for the semiconductor layer of the thin film transistor, is preferably 5.0 × 10 ¹⁶ cm ⁻³ or less, and more preferably 1.0 × 10 ¹⁶ cm ⁻³ or less preferable. Due to the decrease in defect density, the mobility of the thin film transistor is further enhanced, the stability upon light irradiation and the stability to heat are enhanced, and the TFT operates stably.

The thin film transistor according to this embodiment can be applied to various integrated circuits such as a field effect transistor, a logic circuit, a memory circuit, and a differential amplifier circuit. Furthermore, in addition to the field effect transistor, the present invention can be applied to an electrostatic induction transistor, a Schottky barrier transistor, a Schottky diode, and a resistor.
The thin film transistor according to the present embodiment can be suitably used for a display device, a solid-state imaging device, and the like. Hereinafter, the case where the thin film transistor according to the present embodiment is used for a display device and a solid-state imaging device will be described.

First, the case where the thin film transistor according to the present embodiment is used for a display device will be described with reference to FIG.
FIG. 4A is a top view of a display device of one embodiment of the present invention. FIG. 4B is a circuit diagram for describing a pixel circuit in the case of applying a liquid crystal element to a pixel of a display device of one embodiment of the present invention. FIG. 4C is a circuit diagram for describing a pixel circuit in the case where an organic EL element is applied to a pixel of a display device of one embodiment of the present invention.

  The thin film transistor according to this embodiment can be used as the transistor provided in the pixel portion. Since the thin film transistor according to this embodiment can easily be an n-channel transistor, part of a driver circuit that can be formed using an n-channel transistor is formed over the same substrate as the transistor in the pixel portion. By using the thin film transistor described in this embodiment for the pixel portion and the driver circuit, a highly reliable display device can be provided.

  An example of a top view of the active matrix display device is illustrated in FIG. A pixel portion 301, a first scan line driver circuit 302, a second scan line driver circuit 303, and a signal line driver circuit 304 are formed over a substrate 300 of a display device. In the pixel portion 301, a plurality of signal lines are extended from the signal line driver circuit 304, and a plurality of scan lines are extended from the first scan line driver circuit 302 and the second scan line driver circuit 303. Be placed. Pixels each having a display element are provided in a matrix at intersections of the scan lines and the signal lines. The substrate 300 of the display device is connected to a timing control circuit (also referred to as a controller or a control IC) through a connection portion such as a flexible printed circuit (FPC).

  In FIG. 4A, the first scan line driver circuit 302, the second scan line driver circuit 303, and the signal line driver circuit 304 are formed over the same substrate 300 as the pixel portion 301. Therefore, the number of parts such as a drive circuit provided outside is reduced, so that cost can be reduced. Further, in the case where a driver circuit is provided outside the substrate 300, it is necessary to extend the wiring, which increases the number of connections between the wirings. In the case where the driver circuit is provided over the same substrate 300, the number of connections between the wirings can be reduced, which can improve the reliability or the yield.

  In addition, an example of a circuit configuration of a pixel is illustrated in FIG. Here, a pixel circuit which can be applied to a pixel of a VA liquid crystal display device is shown.

  This pixel circuit can be applied to a structure having a plurality of pixel electrodes in one pixel. Each pixel electrode is connected to a different transistor, and each transistor is configured to be driven by different gate signals. Thus, signals applied to individual pixel electrodes of multi-domain designed pixels can be controlled independently.

  The gate wiring 312 of the transistor 316 and the gate wiring 313 of the transistor 317 are separated so as to be supplied with different gate signals. On the other hand, the source electrode or drain electrode 314 which functions as a data line is used in common by the transistor 316 and the transistor 317. The transistor according to this embodiment can be used as the transistor 316 and the transistor 317. Thus, a highly reliable liquid crystal display device can be provided.

  A first pixel electrode is electrically connected to the transistor 316, and a second pixel electrode is electrically connected to the transistor 317. The first pixel electrode and the second pixel electrode are separated. The shapes of the first pixel electrode and the second pixel electrode are not particularly limited. For example, the first pixel electrode may be V-shaped.

  The gate electrode of the transistor 316 is connected to the gate wiring 312, and the gate electrode of the transistor 317 is connected to the gate wiring 313. Different gate signals can be supplied to the gate wiring 312 and the gate wiring 313, operation timings of the transistor 316 and the transistor 317 can be different, and alignment of liquid crystals can be controlled.

  In addition, a storage capacitor may be formed of the capacitor wiring 310, a gate insulating film functioning as a dielectric, and a capacitor electrode electrically connected to the first pixel electrode or the second pixel electrode.

  The multi-domain structure includes a first liquid crystal element 318 and a second liquid crystal element 319 in one pixel. The first liquid crystal element 318 is composed of a first pixel electrode, a counter electrode, and a liquid crystal layer in between, and the second liquid crystal element 319 is composed of a second pixel electrode, a counter electrode, and a liquid crystal layer in between .

  The pixel circuit is not limited to the configuration shown in FIG. A switch, a resistor, a capacitor, a transistor, a sensor, or a logic circuit may be added to the pixel illustrated in FIG. 4B.

  Another example of the circuit configuration of the pixel is shown in FIG. Here, a pixel structure of a display device using an organic EL element is shown.

  In the organic EL element, when a voltage is applied to the light emitting element, electrons are injected from one of the pair of electrodes and holes from the other of the pair of electrodes are injected into the layer containing the light emitting organic compound, and current flows. The recombination of electrons and holes causes the light-emitting organic compound to form an excited state, and light is emitted when the excited state returns to the ground state. From such a mechanism, such a light emitting element is referred to as a current excitation light emitting element.

  FIG. 4C illustrates an example of an applicable pixel circuit. Here, an example in which two n-channel transistors are used in one pixel is shown. The oxide semiconductor film of this embodiment can be used for a channel formation region of an n-channel transistor. The pixel circuit can apply digital time gray scale driving.

  The configuration of the applicable pixel circuit and the operation of the pixel when digital time gray scale drive is applied will be described.

  The pixel 320 includes a switching transistor 321, a driving transistor 322, a light emitting element 324, and a capacitor element 323. In the switching transistor 321, the gate electrode is connected to the scan line 326, the first electrode (one of the source electrode and the drain electrode) is connected to the signal line 325, and the second electrode (the other of the source electrode and the drain electrode) Are connected to the gate electrode of the driving transistor 322. The gate electrode of the driving transistor 322 is connected to the power supply line 327 through the capacitor 323, the first electrode is connected to the power supply line 327, and the second electrode is a first electrode of the light emitting element 324 (pixel electrode Connected to). The second electrode of the light emitting element 324 corresponds to the common electrode 328. The common electrode 328 is electrically connected to a common potential line formed on the same substrate.

  The thin film transistor according to this embodiment can be used as the switching transistor 321 and the driving transistor 322. Thereby, a highly reliable organic EL display device can be provided.

The configuration of the pixel circuit is not limited to the configuration shown in FIG. A switch, a resistor, a capacitor, a sensor, a transistor, or a logic circuit may be added to the pixel circuit illustrated in FIG.
The above is the description in the case where the thin film transistor according to the present embodiment is used for a display device.

  Next, the case where the thin film transistor according to the present embodiment is used for a solid-state imaging device will be described with reference to FIG.

  A CMOS (Complementary Metal Oxide Semiconductor) image sensor is a solid-state imaging device that holds a potential in a signal charge storage unit and outputs the potential to a vertical output line through an amplification transistor. If there is a leakage current in the reset transistor and / or the transfer transistor included in the CMOS image sensor, the leakage current causes charging or discharging, and the potential of the signal charge storage portion changes. When the potential of the signal charge storage portion changes, the potential of the amplification transistor also changes, resulting in a value deviated from the original potential, and the captured image is degraded.

  The effect of the operation when the thin film transistor according to the present embodiment is applied to the reset transistor and the transfer transistor of the CMOS image sensor will be described. The amplification transistor may be either a thin film transistor or a bulk transistor.

  FIG. 5 is a view showing an example of a pixel configuration of a CMOS image sensor. A pixel is composed of a photodiode 3002 that is a photoelectric conversion element, a transfer transistor 3004, a reset transistor 3006, an amplification transistor 3008, and various wirings, and a plurality of pixels are arranged in a matrix to form a sensor. A selection transistor electrically connected to the amplification transistor 3008 may be provided. “OS” described in the transistor symbol indicates an oxide semiconductor, and “Si” indicates silicon, which represents a preferable material when applied to each transistor. The same applies to the subsequent drawings.

The photodiode 3002 is connected to the source side of the transfer transistor 3004, and a signal charge storage unit 3010 (FD: also referred to as floating diffusion) is formed on the drain side of the transfer transistor 3004. The signal charge storage unit 3010 is connected to the source of the reset transistor 3006 and the gate of the amplification transistor 3008. Alternatively, the reset power supply line 3110 can be eliminated. For example, there is a method of connecting the drain of the reset transistor 3006 to the power supply line 3100 or the vertical output line 3120 instead of the reset power supply line 3110.
The above is the description in the case where the thin film transistor according to the present embodiment is used for a solid-state imaging device.

  Thus, the oxide sintered body of the present embodiment can form an oxide semiconductor thin film having excellent characteristics when used in a thin film transistor, and can suppress generation of cracks and nodules during film formation.

  Hereinafter, the present invention will be described using examples and comparative examples. However, the present invention is not limited to these examples.

<Strength test of sintered body and target>
First, an oxide sintered body satisfying the constituent requirements of the present embodiment was manufactured and processed into a target, and the presence or absence of cracking and generation of nodules during sputtering film formation was tested. The specific procedure is as follows.

  First, samples of compositions containing indium, tin, zinc, and samarium as a light rare earth element were prepared as Example 1 and Example 2. Further, as Comparative Example 1, a sample was prepared in which indium was out of the lower limit of Formula (1) and zinc was out of the upper limit of Formula (3). As Comparative Example 2, a sample having zinc out of the upper limit of Formula (3) was also prepared. As Comparative Example 3, a sample containing no samarium was also prepared.

The raw material of each element had the following composition, and used the oxide powder of purity 99.99 mass%.
Indium: In ₂ O ₃
Tin: SnO ₂
Zinc: ZnO
Samarium: Sm ₂ O ₃
The mass ratio of each element was determined as follows.
Indium mass ratio: In ₂ O ₃ / (In ₂ O ₃ + ZnO + SnO ₂ + Sm ₂ O ₃ )
Tin mass ratio: SnO ₂ / (In ₂ O ₃ + ZnO + SnO ₂ + Sm ₂ O ₃ )
Zinc mass ratio: ZnO / (In ₂ O ₃ + ZnO + SnO ₂ + Sm ₂ O ₃ )
Samarium mass ratio: Sm ₂ O ₃ / (In ₂ O ₃ + ZnO + SnO ₂ + Sm ₂ O ₃ )

Next, the raw material powder was weighed, placed in a polyethylene pot, and mixed and pulverized by a dry ball mill for 72 hours to prepare a mixed powder.
The mixed powder was placed in a mold and made into a press-molded body at a pressure of 500 kg / cm ² . The compact was densified by CIP at a pressure of 2000 kg / cm ² . Next, this molded body was placed in a normal pressure baking furnace, held at 350 ° C. for 3 hours in the air atmosphere, then heated at 100 ° C./hour and sintered at 1480 ° C. for 42 hours . Then, it was left to cool to obtain an oxide sintered body.

The following evaluation was performed about the obtained sintered compact.
(1) Elemental composition ratio (atomic ratio)
The element composition in the sintered body (the middle stage equation sandwiched by the inequality sign of the equation (4)) was determined from the equation (1) using an inductive plasma emission analyzer (ICP-AES).

(2) Crystal structure About the obtained sintered compact, X-ray diffraction (XRD) was measured on condition of the following with X-ray-diffraction measuring device Smartlab. The obtained XRD chart was analyzed by JADE 6 to determine the crystal structure of the sintered body. Furthermore, the composition was determined by mass% from the peak intensity ratio.

In addition, the measurement conditions of XRD are as follows.
-Device: Smartlab (manufactured by Rigaku Corporation)
・ X-ray: Cu-Kα ray (wavelength 1.5418 × 10 ^-10 m)
・ 2θ-θ reflection method, continuous scan (2.0 ° / min)
Sampling interval: 0.02 °
Slit DS (divergent slit), SS (scattering slit), RS (receiving slit): 1 mm

(3) Lattice constant The obtained XRD pattern is subjected to full pattern fitting (WPF) analysis using JADE 6, and each crystal component contained in the XRD pattern is identified, and In ₂ O in the obtained oxide sintered body The lattice constants of the _three crystal structures were calculated.

(4) Relative density For relative density, measure the actual density from the volume and mass in the measurement with a caliper for the oxide sintered body produced, and divide the actual density by the calculated density of the oxide sintered body Calculated by The calculated density was calculated by dividing the total mass of the raw material powder used for producing the oxide sintered body by the total volume of the raw material powder used for producing the oxide sintered body.

(5) Bulk Resistance The bulk resistance (conductivity) of the sintered body was measured based on a four-point probe method using a resistivity meter (Loresta AX MCP-T370, manufactured by Mitsubishi Chemical Corporation).
The measurement points were four points at the center of the oxide sintered body and the midpoint between the four corners of the oxide sintered body and the center, for a total of five points, and the average value of the five points was taken as the bulk resistance value.

  Furthermore, the obtained sintered body was processed into a sputtering target, and a film formation test was performed in the following procedure.

<Deposition durability evaluation>
First, the oxide sintered body was ground and polished, processed into a sputtering target of 4 inches in diameter x 5 mm in thickness, and bonded to a copper backing plate using indium wax.

Next, the backing plate was attached to a DC magnetron sputtering apparatus, and 400 W DC sputtering was performed for 5 hours continuously. The state of the target surface after DC sputtering, specifically, the presence or absence of a crack and the presence or absence of a black foreign matter (nodule) were visually confirmed.
The above results are shown in Table 1. The XRD charts of Example 1, Example 2 and Comparative Example 3 are shown in FIG. 6, FIG. 7 and FIG. FIGS. 6, 7 and 8 also show the angle of the crystal structure corresponding to the given peak.

In the sintered bodies of Example 1 and Example 2, the bixbite structure represented by In ₂ O ₃ was the main component, and the pyrochlore structure represented by Sm ₂ Sn ₂ O ₇ was also observed. The lattice constant of Sm ₂ Sn ₂ O ₇ of Example 1 is 10.50215 × 10 ⁻¹⁰ m, and the lattice constant of Sm ₂ Sn ₂ O ₇ of Example 2 is 10.50397 × 10 ⁻¹⁰ m. there were. Since the lattice constant of Sm ₂ Sn ₂ O _{7 in} the example is smaller than the lattice constant of pure substance Sm ₂ Sn ₂ O ₇ , the elements are closely packed, which is advantageous for heat conduction, and the hairline It is presumed that the resistance to cracking such as cracking and chipping is improved. The hexagonal layered structure represented by In ₂ O ₃ (ZnO) ₃ was also slightly confirmed.

In Comparative Example 1 and Comparative Example 2, the bixbite structure represented by In ₂ O ₃ and the pyrochlore structure represented by Sm ₂ Sn ₂ O ₇ were confirmed. In Comparative Example 2, a spinel structure represented by Zn ₂ SnO ₄ was also confirmed.
In Comparative Example 3, the bixbyite structure represented by In ₂ O ₃ was the main component, and the spinel structure represented by Zn ₂ SnO ₄ was also observed.

In the sintered bodies of Example 1 and Example 2, the lattice constant of the bixbite structure represented by In ₂ O ₃ is smaller than the lattice constant (10.118 × 10 ⁻¹⁰ m) of the bixbite structure of a pure substance. The Therefore, it is considered that the samarium element is not subjected to solid solution substitution in the bixbite structure represented by In ₂ O ₃ .

Furthermore, Example 1 and Example 2 satisfied Formula (5).
The relative density was substantially the same in Examples 1 and 2 and Comparative Examples 1 to 3.
On the other hand, in Examples 1 and 2, the bulk resistance was very low compared to Comparative Examples 1 to 3.

  In Example 1 and Example 2, no crack or nodule was found in the target after film formation. In Comparative Examples 1 to 3, cracks and nodules were observed in the target after film formation.

  From this result, as in the configurations of the first embodiment and the second embodiment, the ITZO satisfying the conditions of the formulas (1) to (4) (and the formula (5)) as compared with the case of not satisfying And the strength of the sputtering target was found to be high. Moreover, it turned out that bulk resistance is also very low.

<Evaluation test of semiconductor thin film>
Next, using the sputtering targets of Example 1, Example 2, and Comparative Example 3, semiconductor thin films were manufactured under the following conditions, and the characteristics were evaluated. The specific procedure is as follows.
In addition, manufacture of a semiconductor thin film was implemented before performing film-forming durability evaluation of a sputtering target.

(1) Film Forming Step The oxide sintered bodies of Example 1 and Example 2 were ground and polished to produce a sputtering target of 4 inches φ × 5 mmt. Only the oxide semiconductor thin film 83 having a film thickness of 50 nm is formed on a glass substrate 81 (ABC-G manufactured by Nippon Electric Glass Co., Ltd.) by DC magnetron sputtering using the produced sputtering target as shown in FIG. The sample which formed the film was manufactured.
The film formation conditions are as follows.
Atmosphere gas: Ar and O ₂
Back pressure before film formation: 5 × 10 ^-4 Pa
Sputtering pressure during film formation: 0.5 Pa
Oxygen partial pressure during film formation: 1%

(2) Heat Treatment Step Next, the obtained sample was heated in the air at 350 ° C. for 30 minutes at a temperature rising rate of 10 ° C./minute.

Next, the following evaluation was performed about the manufactured semiconductor thin film.
<Hall effect measurement>
First, from the sample consisting of the glass substrate 81 and the oxide semiconductor thin film 83, the sample was cut out so that the planar shape became a square of 1 cm square. Next, gold (Au) was formed in four corners of the cut-out sample by an ion coater using a metal mask so as to have a size of 2 mm × 2 mm or less. Next, indium solder was placed on Au metal to improve the contact and to prepare a Hall effect measurement sample.

A sample for Hall effect measurement was set in a Hall effect / specific resistance measurement apparatus (ResiTest Model 8300, manufactured by Toyo Technica Co., Ltd.), the Hall effect was evaluated at room temperature, and the carrier density and mobility were determined.
Further, as a result of analyzing the oxide semiconductor layer of the obtained sample with an inductive plasma emission analyzer (ICP-AES, manufactured by Shimadzu Corp.), the atomic ratio of the obtained oxide semiconductor thin film is the oxide semiconductor thin film. It confirmed that it was the same as the atomic ratio of the sintered compact used for manufacture.
In addition, on the top surface of a standard oxide thin film of which the atomic ratio of metal elements is measured by an inductive plasma emission analyzer, the source / drain electrode is formed of the same material as the TFT element with a channel length as a standard material. Mass spectral intensities of each element are obtained by analysis of the oxide semiconductor layer by a sector type dynamic secondary ion mass spectrometer SIMS (IMS 7f-Auto, manufactured by AMETEK), and calibration curves of known element concentrations and mass spectral intensities are obtained. Made. Next, the atomic ratio of the oxide semiconductor film portion of the actual TFT element was calculated from the spectrum intensity by the sector type dynamic secondary ion mass spectrometer SIMS analysis using the above-mentioned calibration curve. The calculated atomic ratio is within 2 atomic% of the atomic ratio of the oxide semiconductor film measured with a thin film fluorescent X-ray analyzer XRF (AZX400, manufactured by Rigaku Corporation) or inductive plasma emission analyzer separately, and the sector type Dynamic secondary ion mass spectrometry SIMS analysis confirmed that thin film XRF or inductive plasma emission analysis can be performed with the same accuracy.

After a SiO ₂ film 85 is further formed on the oxide semiconductor thin film 83 of the above sample for Hall effect measurement at a substrate temperature of 250 ° C. by a CVD apparatus as shown in FIG. Carried out. Further, the sample on which the SiO ₂ film was formed was further heat-treated in the air atmosphere at a substrate temperature of 350 ° C. for 30 minutes, and the same hole measurement as described above was performed on the obtained semiconductor thin film of the sample. At this time, the measuring needle was pierced to the SiO ₂ film to the gold layer to make contact.

<Crystal characteristics of semiconductor thin film>
X-ray diffraction (XRD) of the crystallinity of the unheated film after sputtering (immediately after film deposition) and the heat treatment after film formation shown in Table 2 for the sample consisting of the glass substrate and the oxide semiconductor layer ) Evaluated by measurement.
Whether it is amorphous or not was judged by whether or not a peak appeared at 30 to 40 ° at 2θ in XRD.
As a result, it was amorphous before heating and was amorphous after heating.

<Production of thin film transistor>
Furthermore, the thin film transistor shown in FIG. 3 using the semiconductor thin film was manufactured in the following procedure.
(1) Film Forming Step An oxide semiconductor thin film 40 of 50 nm was formed via a metal mask on a silicon wafer 20 as a gate electrode with a thermal oxide film (gate insulating film 30). The other conditions were the same as in the case where the semiconductor thin film was formed on the glass substrate.

(2) Formation of Source / Drain Electrode Next, titanium metal was sputtered using a metal mask in the shape of contact holes of source / drain to form titanium electrodes as source electrode 50 and drain electrode 60. The obtained laminate was heat-treated at 350 ° C. for 30 minutes in the air to manufacture a thin film transistor before forming a protective insulating film.

(3) Formation of Protective Insulating Film On the semiconductor thin film of the thin film transistor before forming the protective insulating film obtained in (2), a SiO ₂ film (protective insulating film; chemical vapor deposition (CVD) at a substrate temperature of 300 ° C. An interlayer insulating film 70B was formed. After forming the SiO ₂ film, heat treatment was performed at 350 ° C. for 1 hour in the air to manufacture a thin film transistor provided with a protective insulating film. After that, contact holes were formed at the source and drain portions with the probe pins of the device to make contacts, thereby manufacturing thin film transistors.

<Evaluation of thin film transistor>
The thin film transistor produced, the insulating protective film (SiO ₂ film) formed before the thin film transistor, and the characteristics of the thin film transistor after formation by heating the insulating protective film (SiO ₂ film), a measuring needle into the SiO ₂ film, a source Evaluation was carried out by sticking to the metal titanium layer of the drain electrode.

<Saturated mobility>
The saturation mobility was determined from the transfer characteristics when 20 V was applied to the drain voltage. Specifically, a graph of the transfer characteristic Id-Vg was created, the transconductance (Gm) of each Vg was calculated, and the saturation mobility was derived from the equation of the saturation region. Gm is represented by 表 (Id) / ∂ (Vg), and Vg is applied from −15 V to 25 V, and the maximum mobility in that range is defined as the saturation mobility. The saturation mobility was evaluated by this method unless otherwise specified in the present invention. The above Id is the current between the source and drain electrodes, and Vg is the gate voltage when the voltage Vd is applied between the source and drain electrodes.

<Threshold voltage (Vth)>
The threshold voltage (Vth) was defined as Vg at Id = 10 ⁻⁹ A from the graph of transfer characteristics.

<On-off ratio, Off current>
The on-off ratio was determined using the value of Id of Vg = −10 V as the Off current value and the value of Id of Vg = 20 V as the On current value [On / Off].
The above results are shown in Table 2.

As shown in Table 2, in each of the example A and the example B, the semiconductor thin film and the thin film transistor both had characteristics as a semiconductor. In particular, in a thin film transistor (TFT), when performing the heat treatment after the SiO ₂ film formation, saturation mobility than SiO ₂ deposited before (after heat treatment) was improved.
In Comparative Example A, the thin film became a conductor in any of the thin film and the thin film transistor (TFT), and the characteristics as a semiconductor were not obtained.
From the above results, the oxide semiconductor thin film formed by using the oxide sintered body having the composition range according to the present embodiment is a light rare earth, even if the composition range of indium, tin, and zinc is conventionally made conductive. It was found that the addition of the element made it semiconductive. Furthermore, it was found that the semiconductor characteristics are not deteriorated by heating or the like at the time of formation by a CVD process because the off-state current is small and the saturation mobility is improved even if heat treatment is performed after SiO ₂ film formation.

Reference Signs List 20 silicon wafer (gate electrode) 30 gate insulating film 40 oxide semiconductor thin film 50 source electrode 60 drain electrode 70 interlayer insulating film 70 A interlayer insulating film 70 B interlayer insulating film 81: Glass substrate, 83: Oxide semiconductor thin film, 85: SiO ₂ film, 100: Thin film transistor, 100A: Thin film transistor.

Claims (10)

The atomic ratio of In element, Zn element, Sn element and light rare earth element (described as LREE: light rare earth element: X) satisfies the following formulas (1) to (4) and is represented by In ₂ O ₃ An oxide sintered body comprising a bixbite structure as a main component.
0.55 ≦ In / (In + Sn + Zn) ≦ 0.90 (1)
0.05 ≦ Sn / (In + Sn + Zn) ≦ 0.25 (2)
0.05 ≦ Zn / (In + Sn + Zn) ≦ 0.20 (3)
0.05 ≦ X / (In + Sn + Zn + X) ≦ 0.25 (4)
However, the light rare earth element is one or more elements selected from La, Nd, Sm, and Eu. The oxide sintered body according to claim 1, wherein the ratio of the content of Sn element to the total metal and the content of the light rare earth element to the total metal element satisfies the following formula (5).
1.2 ≦ (Sn / all metal elements) / (X / all metal elements) ≦ 3.5 (5) The oxide sintered body according to claim 1 or 2, which has a bixbite structure represented by In ₂ O ₃ as a main component and further contains a pyrochlore structure. The oxide sintered body according to claim 3, wherein the pyrochlore structure is a pyrochlore structure represented by X ₂ Sn ₂ O ₇ .   The oxide sintered body according to any one of claims 1 to 4, wherein the oxide sintered body contains an In element, a Zn element, a Sn element and a light rare earth element, and the balance is made of oxygen and an unavoidable impurity.   The oxide sintered body according to any one of claims 1 to 5, having a bulk resistance value of 1.4 mΩcm or less.   A sputtering target comprising the sintered body according to any one of claims 1 to 6. Amorphous characterized in that the atomic ratio of In element, Zn element, Sn element and light rare earth element (abbreviated as LREE: light rare earth element: X) is a range satisfying the following formulas (6) to (10) Oxide semiconductor thin film.
0.55 ≦ In / (In + Sn + Zn) ≦ 0.90 (6)
0.05 ≦ Sn / (In + Sn + Zn) ≦ 0.25 (7)
0.05 ≦ Zn / (In + Sn + Zn) ≦ 0.20 (8)
0.05 ≦ X / (In + Sn + Zn + X) ≦ 0.25 (9)
1.2 ≦ (Sn / all metal elements) / (X / all metal elements) ≦ 3.5 (10)
However, the light rare earth element is one or more elements selected from La, Nd, Sm, and Eu.   9. The amorphous oxide semiconductor thin film according to claim 8, comprising In, Zn, Sn and a light rare earth element, with the balance being oxygen and unavoidable impurities.   A thin film transistor comprising the amorphous oxide semiconductor thin film according to claim 9.

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