JP2019077594A - Oxide sintered body, sputtering target, 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 ensuring the strength of a target even with a composition in which Y (yttrium) is added to indium oxide. SOLUTION: The atomic composition ratio of the Y element is the following formula (1), which contains an In element, a Zn element, a Sn element and a Y element, and contains a big bite structure represented by In2O3 and a pyrochlor structure represented by Y2Sn2O7. An oxide sintered body characterized by satisfying the above range. 0.03 ≤ Y / (In + Sn + Zn + Y) ≤ 0.08 ... (1) [Selection diagram] None

Description

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

  An amorphous oxide semiconductor used for a thin film transistor (Tin Film Transistor, hereinafter abbreviated as TFT) has high carrier mobility and a large optical band gap as compared with general-purpose amorphous silicon (a-Si), It is possible to form a film 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 oxide semiconductor thin film. This is because the thin film formed by the sputtering method is superior to the thin film formed by the ion plating method, the vacuum evaporation method, or the electron beam evaporation method in uniformity of the composition, film thickness and the like. Moreover, it is because the thin film of the component composition same as a sputtering target can be formed.

In Patent Document 1, an oxide consisting of In, Y and O, wherein Y / (Y + In) is 2.0 atomic% or more and 40 atomic% or less, and volume resistivity is 5 × 10 ⁻² Ωcm or less The use of a sintered body as a target is described. The content of Sn element is described as Sn / (In + Sn + all other metal atoms) of 2.8 atomic% or more and 20 atomic% or less.

  Patent Document 2 describes an oxide sintered body composed of In, Sn, Y and O, wherein Y / (In + Sn + Y) is 0.1 or more and 2.0 atomic% or less, and a sputtering target using the same. ing. It is described that a thin film obtained from this target constitutes an apparatus such as a flat panel display and a touch panel.

Patent Document 3 describes a sintered body having a lattice constant intermediate between lattice constants of YInO ₃ and In ₂ O ₃ and using this as a sputtering target. In addition, a sintered body containing In ₂ O ₃ and Y ₂ Sn ₂ O ₇ in a composition comprising indium oxide, yttrium oxide and tin oxide is described. In addition, a sintered body is described which is made of yttrium oxide, tin oxide and zinc oxide and contains Y ₂ Sn ₂ O ₇ and ZnO or Zn ₂ SnO ₄ .

Patent Document 4 contains one or more elements selected from the group consisting of Mg, Si, Al, Sc, Ti, Y, Zr, Hf, Ta, La, Nd and Sm in In, Sn and Zn. An oxide sintered body and its use as a sputtering target are described. This sintered body is a sintered body containing In ₂ O ₃ and Zn ₂ SnO ₄ .

  In Patent Document 5, an element selected from Mg, Al, Ga, Si, Ti, Y, Zr, Hf, Ta, La, Nd, and Sm is added to In, Sn, and Zn to form a bixbyite structure and spinel. Sputtering targets that include structures are described.

In Patent Document 6, an element selected from Hf, Zr, Ti, Y, Nb, Ta, W, Mo, and Sm is added to In, Sn, and Zn, and an In ₂ O ₃ structure, a spinel structure, X ₂ A sintered body is described which comprises one or more structures selected from the Sn ₂ O ₇ structure (pyrochlore structure) and ZnX ₂ O ₆ .

Japanese Patent Application Laid-Open No. 09-209134 JP 2000-169219 A International Publication No. 2010/032432 International Publication No. 2012/153507 JP, 2014-111818, A JP, 2015-214436, A

However, the techniques described in Patent Document 1 to Patent Document 6 have the following problems.
The targets described in Patent Document 1 and Patent Document 2 are targets for obtaining a transparent conductive film, and this composition has a problem that a semiconductor film can not be obtained.
Although the targets described in Patent Documents 3 to 6 can obtain a semiconductor film, the sintering density is increased when an element having a large atomic radius such as yttrium is added to a target material based on indium oxide. In some cases, the strength of the target material may be reduced, microcracks may be generated due to thermal stress during sputtering at high power, or abnormal discharge may occur due to chipping. These phenomena cause defects in the thin film and cause deterioration in TFT performance. In addition, there is a problem that the mobility of the semiconductor film is lowered when yttrium is added.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an oxide sintered body and a sputtering target which can ensure the strength of the target even with a composition in which yttrium is added to indium oxide.
Another object of the present invention is to provide an amorphous oxide semiconductor thin film having excellent characteristics, particularly, high mobility 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] A bixbyite structure represented by In ₂ O ₃ containing an In element, a Sn element, a Zn element and a Y element, and a pyrochlore structure represented by Y ₂ Sn ₂ O ₇ The oxide sintered body characterized in that the composition ratio is a range satisfying the following formula (1).
0.03 ≦ Y / (In + Sn + Zn + Y) ≦ 0.08 (1)
[2] A bixbyite structure represented by In ₂ O ₃ containing an In element, a Sn element, a Zn element, and a Y element, and a pyrochlore structure represented by Y ₂ Sn ₂ O ₇ , Zn ₂ SnO ₄ And the hexagonal layer structure represented by In ₂ O ₃ (ZnO) _m (where m is an integer of 1 to 20), and the atomic composition ratio of Y element is represented by the following formula An oxide sintered body characterized in that it is a range satisfying (2).
0.03 ≦ Y / (In + Sn + Zn + Y) ≦ 0.08 (2)
[3] The oxide sintered body according to [1] or [2], wherein the atomic composition ratio of Y element to Sn element is a range satisfying the following formula (3).
0.2 ≦ Y / Sn ≦ 0.5 (3)
[4] The atomic composition ratio of the In element, the Sn element, and the Zn element is in a range satisfying the following formulas (4) to (6), described in any one of [1] to [3] Oxide sintered body.
0.50 ≦ In / (In + Sn + Zn + Y) ≦ 0.93 (4)
0.03 ≦ Sn / (In + Sn + Zn + Y) ≦ 0.30 (5)
0.01 ≦ Zn / (In + Sn + Zn + Y) ≦ 0.15 (6)

According to the present invention, the following sputtering target is provided.
[5] A sputtering target comprising the oxide sintered body according to any one of [1] to [4].

According to the present invention, the following oxide semiconductor thin film is provided.
[6] An oxide semiconductor thin film comprising an In element, a Sn element, a Zn element, and a Y element, and having an atomic composition ratio satisfying the following formulas (7) to (10).
0.50 ≦ In / (In + Sn + Zn + Y) ≦ 0.93 (7)
0.03 ≦ Sn / (In + Sn + Zn + Y) ≦ 0.30 (8)
0.01 ≦ Zn / (In + Sn + Zn + Y) ≦ 0.15 (9)
0.03 ≦ Y / (In + Sn + Zn + Y) ≦ 0.08 (10)
[7] The oxide semiconductor thin film according to [6], wherein the atomic composition ratio of Y element to Sn element is a range satisfying the following formula (11).
0.2 ≦ Y / Sn ≦ 0.5 (11)
[8] The oxide semiconductor thin film according to [6] or [7], which is amorphous.

According to the present invention, the following thin film transistor is provided.
[9] A thin film transistor comprising the oxide semiconductor thin film according to any one of [6] to [8].

According to the present invention, the following electronic device is provided.
[10] An electronic device comprising the thin film transistor according to [9].

According to the present invention, the following oxide sintered body is provided.
[11] A bixbyite structure represented by In ₂ O ₃ containing an In element, Sn element, Zn element, Y element and Al element, and a pyrochlore structure represented by Y ₂ Sn ₂ O ₇ An oxide sintered body characterized in that the atomic composition ratio of is a range satisfying the following formula (12).
0.03 ≦ Y / (In + Sn + Zn + Y + Al) ≦ 0.20 (12)
[12] A bixbyite structure represented by In ₂ O ₃ containing an In element, a Sn element, a Zn element, a Y element, and an Al element, and a pyrochlore structure represented by Y ₂ Sn ₂ O _{7 The} spinel structure represented by ₂ SnO ₄ and the hexagonal layer structure represented by In ₂ O ₃ (ZnO) _m (where m is an integer of 1 to 20) are not included, and the atomic composition ratio of Y element The range is such that the following formula (13) is satisfied.
0.03 ≦ Y / (In + Sn + Zn + Y + Al) ≦ 0.20 (13)
[13] The oxide sintered body according to [11] or [12], which is a range in which the atomic ratio of Al element satisfies the following formula (14).
0.005 ≦ Al / (In + Sn + Zn + Y + Al) ≦ 0.10 (14)
[14] The oxide sintered body according to any one of [11] to [13], wherein the atomic composition ratio of the Y element and the Sn element satisfies the following formula (15).
0.2 ≦ Y / Sn ≦ 0.5 (15)
[15] The atomic composition ratio of the In element, the Sn element, and the Zn element is a range satisfying the following formulas (16) to (18): described in any one of [10] to [14] Oxide sintered body.
0.50 ≦ In / (In + Sn + Zn + Y + Al) ≦ 0.93 (16)
0.03 ≦ Sn / (In + Sn + Zn + Y + Al) ≦ 0.30 (17)
0.01 ≦ Zn / (In + Sn + Zn + Y + Al) ≦ 0.15 (18)

According to the present invention, the following sputtering target is provided.
[16] A sputtering target comprising the oxide sintered body according to any one of [11] to [15].

According to the present invention, the following oxide semiconductor thin film is provided.
[17] An oxide semiconductor thin film containing an In element, a Sn element, a Zn element, a Y element, and an Al element, and having an atomic composition ratio satisfying the following formulas (19) to (23).
0.50 ≦ In / (In + Sn + Zn + Y + Al) ≦ 0.93 (19)
0.03 ≦ Sn / (In + Sn + Zn + Y + Al) ≦ 0.30 (20)
0.01 ≦ Zn / (In + Sn + Zn + Y + Al) ≦ 0.15 (21)
0.03 ≦ Y 2 /(In+Sn+Zn+Y+Al)≦0.20 (22)
0.005 ≦ Al / (In + Sn + Zn + Y + Al) ≦ 0.10 (23)
[18] The oxide semiconductor thin film according to [17], wherein the atomic composition ratio of Y element to Sn element is a range satisfying the following formula (24).
0.2 ≦ Y / Sn ≦ 0.5 (24)
[19] The oxide semiconductor thin film according to [17] or [18], which is amorphous.

According to the present invention, the following thin film transistor is provided.
[20] A thin film transistor comprising the oxide semiconductor thin film according to any one of [17] to [19].

According to the present invention, the following electronic device is provided.
[21] An electronic device comprising the thin film transistor according to [20].

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 the thin film transistor concerning this embodiment, and (A) is a top view, (B) is a figure showing a circuit of a pixel part applicable to a pixel of a VA type liquid crystal display. (C) is a figure which shows the circuit of the pixel part of the display apparatus using organic EL element. FIG. 2 is a diagram showing a circuit of a pixel unit 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, The lower part is a value of a pure substance (ICDD, the standard substance recorded 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 lower stage is a value of a pure substance (ICDD, standard substance recorded in International Center for Diffraction Data). It is a figure which shows the XRD diffraction pattern of the oxide sinter of Example 3, Comprising: The upper stage is a measured value, and the lower stage is a value 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 4, Comprising: The upper stage is a measured value, and the lower stage is a value of a pure substance (ICDD, standard substance recorded on International Center for Diffraction Data). It is a figure which shows the XRD diffraction pattern of the oxide sinter of Example 5, Comprising: The upper stage is a measured value, and the lower stage is a value of a pure substance (ICDD, standard substance recorded in International Center for Diffraction Data). It is a figure which shows the XRD diffraction pattern of the oxide sinter of Example 6, Comprising: The upper stage is a measured value, and the lower stage is a value of a pure substance (ICDD, the standard substance recorded 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 1, Comprising: The upper stage is a measured value, the lower part is a value of a pure substance (ICDD, standard substance recorded 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 2, Comprising: The upper stage is a measured value, the lower part is a value 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.
When an element having a large atomic radius such as yttrium is added to a target material based on indium oxide, the strength of the target decreases and it is difficult to increase the mobility of a semiconductor thin film manufactured using the target. Is known.
In order to solve this problem, the inventors of the present invention are oxide semiconductors containing indium (In), tin (Sn), zinc (Zn), and oxygen (O) (In-Sn-Zn-O, hereinafter “ It was thought that if the composition was obtained by adding yttrium (Y) to “ITZO” (abbreviated as “ITZO”), the target strength and the mobility of the semiconductor thin film could be improved.
This is because ITZO can realize relatively high carrier mobility and etching rate by using inexpensive Sn and Zn as a raw material of an oxide semiconductor. In addition, ITZO itself tends to be a conductor, but it is thought that addition of Y makes it easy to make a semiconductor.
Then, when the inventors added a small amount of Y to ITZO, the strength of the sintered body was improved. It was also confirmed that the semiconductor characteristics did not deteriorate and the mobility improved. On the other hand, since it was also confirmed that such an effect appears strongly when the addition amount of Y is small to some extent, the present invention has been made.
The above is 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.
The oxide sintered body according to the first aspect of the present embodiment includes an In element, an Sn element, a Zn element, and a Y element, and has a bixbye structure represented by In ₂ O ₃ , and Y ₂ Sn ₂ O It is a range including the pyrochlore structure represented by ₇ , and in which the atomic composition ratio of Y element satisfies the following formula (1).
0.03 ≦ Y / (In + Sn + Zn + Y) ≦ 0.08 (1)

In Formula (1), when the Y element is 0.03 or more, the thin film formed by the sputtering target manufactured from the sintered body becomes a semiconductor, and the characteristics as a semiconductor are also stabilized. By setting the Y element to 0.08 or less, it is possible to prevent the thin film from becoming an insulator. The effect of improving mobility is also strongly exhibited, and the formation of a hexagonal layered structure can also be prevented.
In formula (1), Y is preferably 0.03 or more and 0.07 or less.

  The content (atomic ratio) of each metal element of the oxide sintered body can be determined by measuring the abundance of each element by ICP (Inductive Coupled Plasma) measurement. The ICP measurement can use an inductive plasma emission analyzer.

When the oxide sintered body contains a bixbite structure represented by In ₂ O ₃ , the bulk resistance is reduced, and the oxide sintered body can be suitably used as a sputtering target. The mobility of the thin film formed by the sputtering target can be easily improved.
By including the pyrochlore structure in which the oxide sintered body is represented by Y ₂ Sn ₂ O ₇ , the thermal conductivity is improved, and the sputtering target using the oxide sintered body and the oxide sintered body is at the time of sputtering. It becomes hard to break.
Whether or not the oxide sintered body contains a bixbite structure or a pyrochlore structure can be confirmed by examining the crystal structure with an X-ray diffractometer (XRD).

The oxide sintered body according to the second aspect of the present embodiment includes an In element, a Sn element, a Zn element and a Y element, and has a bixbye structure represented by In ₂ O ₃ and Y ₂ Sn ₂ O _7. And a spinel structure represented by Zn ₂ SnO ₄ , and a hexagonal layered structure represented by In ₂ O ₃ (ZnO) _m (wherein m is an integer of 1 to 20). And the atomic ratio of Y element is a range satisfying the following formula (2).
0.03 ≦ Y / (In + Sn + Zn + Y) ≦ 0.08 (2)
The effect of satisfying the equation (2) is the same as that of the equation (1). Preferred ranges are also the same.
The term "does not contain" the spinel structure and the hexagonal layered structure means that the existence of the crystal structure can not be confirmed by examining the crystal structure with an X-ray diffractometer (XRD).
The effects including the bixbite structure and the pyrochlore structure are also the same as in the first aspect.

By not including the spinel structure and the hexagonal layered structure, the strength of the sintered body can be improved. This is due to the following reasons.
The spinel structure and the hexagonal layered structure each have a crystal structure having anisotropy, and the expansion coefficients may differ in the direction of the anisotropy of the crystals. Due to the difference in the expansion coefficient, anisotropy occurs in the shrinkage direction of the target during temperature rise, temperature decrease or sintering of the oxide sintered body, and the oxide sintered body is cracked or sputtered. The thermal stress may cause cracks. On the other hand, the bixbite structure and the pyrochlore structure are cubic crystals and there is no anisotropy of the crystal, so cracking during the production of the oxide sintered body and occurrence of hairline cracks during sputtering at high power As a result, a target with high yield can be manufactured, and stable sputtering can be performed even at high power.

The oxide sintered body of the present embodiment preferably has a bixbyite structure as a main component. “The bixbite structure is the main component” means that the abundance ratio of the bixbite structure is 50% by mass or more in the oxide sintered body.
By having the bixbite structure as the main component, the bulk resistance of the sintered body is reduced, and the sintered body can be suitably used as a sputtering target. In addition, the mobility of the semiconductor thin film obtained from the sputtering target can be easily improved.
Furthermore, since the pyrochlore structure is dispersed in a sintered body having a bixbite structure as a main component, application to a fluorescent material other than the target material can be expected by doping a rare earth element or the like.
The abundance ratio of the bixbite structure in the oxide sintered body is preferably 50% by mass or more and 95% by mass or less, and more preferably 60% by mass or more and 95% by mass or less.

In the bixbite structure represented by In ₂ O ₃ , it is preferable that any one or more of Y element and Zn element is in interstitial solid solution or / and substitutional solid solution.
The interstitial solid solution of Zn in the bixbite structure represented by In ₂ O ₃ means that the lattice constant of the bixbyte 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, the substitutional solid solution of Y element in the bixbyite structure represented by In ₂ O ₃ means that the lattice constant of the bixbye structure of indium oxide in the sintered body is more than the lattice constant of only indium oxide It can confirm by having become large.
The interstitial solid solution and / or the substitutional solid solution of the Zn element and the Y element can be adjusted by the addition amount of yttrium oxide used in the production of the sintered body. By making the addition amount of yttrium oxide small, it is possible to generate indium oxide of the bixbite structure in which Zn element is interstitial solid solution, and by increasing the addition amount of yttrium oxide, the substitution type solid solution of Y element is formed. It can produce indium oxide having a bite structure. In this case, the interstitial Zn solid element is separated from the indium oxide crystal, and further reacts with the indium oxide to form a hexagonal layered compound represented by In ((Zn ₃ In) O ₆ ). And so on.
Here, 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 pure substance bixbite structure is 10.118 × 10 ^-10 m. The pure substance mentioned here means a standard substance recorded in ICDD (International Center for Diffraction Data).

In all of the oxide sintered bodies of the first aspect, the second aspect and the third aspect to be described later, the atomic ratio of the Y element to the Sn element is preferably in the range satisfying the following formula (3).
0.2 ≦ Y / Sn ≦ 0.5 (3)
By satisfying the formula (3), the effect of improving the stability and mobility of the semiconductor film can be strongly expressed by containing Y.
In Formula (3), Y / Sn is preferably 0.26 or more and 0.41 or less.

In the first aspect and the second aspect, the atomic ratio of the In element, the Sn element, the Zn element, and the Y element is preferably in a range satisfying the following formulas (4) to (6).
0.50 ≦ In / (In + Sn + Zn + Y) ≦ 0.93 (4)
0.03 ≦ Sn / (In + Sn + Zn + Y) ≦ 0.30 (5)
0.01 ≦ Zn / (In + Sn + Zn + Y) ≦ 0.15 (6)

In Formula (4), when In is 0.50 or more, the bulk resistance of a sintered compact can be made low and the abnormal discharge at the time of sputter | spatter can be prevented. In addition, the effect of increasing the mobility of the oxide semiconductor can be obtained by the addition of In. By setting the thickness to 0.93 or less, the thin film can be prevented from becoming a conductor.
In Formula (4), In is more preferably 0.50 or more and 0.87 or less.

In Formula (5), the bulk resistance of a target can be reduced by Sn being 0.03 or more. Furthermore, when Sn is 0.03 or more, the density of the sintered body can also be improved, and the strength, the linear expansion coefficient, and the thermal conductivity can also be made suitable.
In addition, when the semiconductor thin film of the TFT is formed with a target using a sintered body because Sn is 0.03 or more, the mixed acid consisting of phosphoric acid, nitric acid, and acetic acid, which is an etching solution for wiring metal, is used. The semiconductor thin solid solution film does not dissolve, and a back channel TFT can be formed.
In Formula (5), when Sn is 0.30 or less, the fall of a sintered compact density can be prevented. When a semiconductor layer of a thin film transistor is formed using a sputtering target manufactured from a sintered body, the semiconductor layer can be etched with an organic acid such as boric acid, which facilitates formation of a TFT.
In the formula (5), Sn is more preferably 0.05 or more and 0.15 or less, still more preferably 0.08 or more and 0.15 or less, and still more preferably 0.10 or more and 0.15 or less.

In the formula (6), when Zn is 0.01 or more, a high density sintered body can be obtained. Moreover, when Zn is 0.01 or more, when forming a semiconductor thin film of TFT with a target using a sintered body, there is an effect that the obtained oxide semiconductor thin film is stably kept amorphous. And etching with an organic acid such as boric acid. In Formula (6), when Zn is 0.15 or less, it is possible to prevent the Zn element from being precipitated as zinc oxide or precipitated as a hexagonal layered structure. Moreover, when Zn is 0.15 or less, when forming a semiconductor thin film of TFT with a target using a sintered body, resistance to mixed acid such as phosphoric acid, acetic acid, nitric acid is maintained, and thin film transistors It can be easily formed.
In the formula (6), Zn is more preferably 0.03 or more and 0.15 or less, still more preferably 0.05 or more and 0.15 or less, and still more preferably 0.08 or more and 0.15 or less.

The oxide sintered body according to the third aspect of the present embodiment is a range in which the atomic composition ratio satisfies the following formulas (7) to (10), including In, Sn, Zn and Y elements. .
0.50 ≦ In / (In + Sn + Zn + Y) ≦ 0.93 (7)
0.03 ≦ Sn / (In + Sn + Zn + Y) ≦ 0.30 (8)
0.01 ≦ Zn / (In + Sn + Zn + Y) ≦ 0.15 (9)
0.03 ≦ Y / (In + Sn + Zn + Y) ≦ 0.08 (10)
The effects of satisfying the expressions (7) to (10) are the same as those of the expressions (4) to (6) and the expression (1). Preferred ranges are also the same.

The oxide sintered body according to the fourth aspect of the present embodiment includes an In element, a Sn element, a Zn element, a Y element and an Al element, and has a bixbye structure represented by In ₂ O ₃ and Y ₂ Sn. The atomic composition ratio of the Y element is a range that satisfies the following formula (12), including a pyrochlore structure represented by ₂ O ₇ .
0.03 ≦ Y / (In + Sn + Zn + Y + Al) ≦ 0.20 (12)
In Formula (12), when the Y element is 0.03 or more, the thin film formed by the sputtering target manufactured from the sintered body becomes a semiconductor, and the characteristics as a semiconductor are also stabilized. When the Y element is 0.20 or less, the thin film can be prevented from becoming insulator.

The oxide sintered body according to the fifth aspect of the present embodiment includes an In element, a Sn element, a Zn element, a Y element, and an Al element, and has a bixbye structure represented by In ₂ O ₃ and Y ₂ It includes a pyrochlore structure represented by Sn ₂ O ₇ and a spinel structure represented by Zn ₂ SnO ₄ and is represented by In ₂ O ₃ (ZnO) _m (where m is an integer of 1 to 20) It is a range which does not contain a hexagonal layered structure, and the atomic composition ratio of Y element satisfy | fills following formula (13).
0.03 ≦ Y / (In + Sn + Zn + Y + Al) ≦ 0.20 (13)
The effect of satisfying the equation (13) is the same as that of the equation (12).
In the oxide sintered bodies of the fourth and fifth aspects, the atomic ratio of the Al element is preferably in the range satisfying the following formula (14).
0.005 ≦ Al / (In + Sn + Zn + Y + Al) ≦ 0.10 (14)
In Formula (14), when Al is 0.005 or more, the off current can be 10 ⁻¹² A or less. When Al is 0.10 or less, the saturation mobility of the TFT can be maintained at 10 cm ² / V · s or more. Al is more preferably 0.01 or more and 0.08 or less.
In all of the oxide sintered bodies of the fourth and fifth aspects, the atomic ratio of the Y element to the Sn element is preferably in the range satisfying the following formula (15).
0.2 ≦ Y / Sn ≦ 0.5 (15)
The effect of satisfying the equation (15) is the same as that of the equation (3). Preferred ranges are also the same.
In the oxide sintered bodies of the fourth and fifth aspects, the atomic ratio of In element, Sn element, Zn element, Y element, and Al element satisfies the following formulas (16) to (18): Is preferred.
0.50 ≦ In / (In + Sn + Zn + Y + Al) ≦ 0.93 (16)
0.03 ≦ Sn / (In + Sn + Zn + Y + Al) ≦ 0.30 (17)
0.01 ≦ Zn / (In + Sn + Zn + Y + Al) ≦ 0.15 (18)
The effects of satisfying the expressions (16) to (18) are the same as those of the expressions (4) to (6). The values in the preferred range are also the same.

In the oxide sintered bodies according to the first to fifth aspects, the In element, the Sn element, the Zn element, the Y element, and, if necessary, the Al element may be included, substantially the In element, the Sn element, It may be made of Zn element and Y element (and Al element).
"Substantial" means that the content ratio of In element, Sn element, Zn element, Y element (and Al element) to metal elements contained in the oxide sintered body is 90 atm% or more. . 95 atm% or more is preferable, 98 atm% or more is more preferable, 99 atm% or more is more preferable, and 100 atm% is even more preferable.

However, it contains In element, Sn element, Zn element, Y element (and Al element), and the balance (elements other than In element, Sn element, Zn element, Y element (and Al element)) is only oxygen and unavoidable impurities The composition consisting of Elements other than In element, Sn element, Zn element, Y element (and Al element) were manufactured using oxide sinter or oxide sinter as the balance is oxygen and unavoidable impurities The influence on the characteristics of the semiconductor thin film 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.

<Physical properties of oxide sinter>
The sintered oxide bodies of the first to fifth aspects preferably have a relative density of 95% or more.
When the relative density is 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.
For example, when oxide A, oxide B, oxide C and oxide D are used as raw material powders of oxide sintered body, oxide A, oxide B, oxide C and oxide D are used. The theoretical density can be calculated by applying as follows if the amounts used (amounts charged) are a (g), b (g), c (g) and d (g), respectively.
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))

In the oxide sintered bodies of the first to fifth aspects, the bulk resistance is preferably 10 mΩcm or less, more preferably 8 mΩcm or less, and still more preferably 5 mΩcm or less.
By setting the bulk resistance to 10 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 lower limit of the bulk resistance is not particularly specified, but is, for example, 1 mΩcm or more.

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 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 to set a total of five points: a center of a square inscribed in the circle and four points at four corners of the square and a midpoint between the centers.

The oxide sintered bodies of the first to fifth aspects preferably have a 3-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 the standard test piece breaks.

The oxide sintered bodies according to the first to fifth aspects preferably have a linear expansion coefficient of 8.0 × 10 ⁻⁶ (K ⁻¹ ) or less, and 7.5 × 10 ⁻⁶ (K ⁻¹⁾ Or less), and more 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. It can be evaluated by using a machine.

The oxide sintered bodies of the first to fifth aspects preferably have a thermal conductivity of 5.0 (W · m ⁻¹ · K ⁻¹ ) or more, and 5.5 (W · m ^{−1) -It} is more preferable that it is K- ¹ ) or more, It is further more preferable that it is 6.0 (W * m- ¹ * K- ¹ ) or more, It is 6.5 (W * m- ¹ * K- ¹ ) or more And most preferred.
If the thermal conductivity is 5.0 (W · m ⁻¹ · K ⁻¹ ) or more, the temperature of the sputtered surface and the temperature of the bonded surface differ when sputtering film formation is performed with high power, and the internal stress is There is little risk of micro cracks, cracks and chipping in the target.
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, powder of In compound, powder of Sn compound, powder of Zn compound, and powder of Y compound are used. When adding Al, a powder of an Al compound is also used. The compounds of In, Sn and Zn include, for example, oxides and hydroxides. The compounds of Y and Al include oxides. The oxide is preferable in terms of the easiness 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. When the purity is 2N or more, the durability of the oxide sintered body can be ensured, 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 to the raw material mixture.
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.

(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, after press molding (uniaxial press), 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.
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 1200 ° C. or more and 1650 ° C. or less, more preferably 1350 ° C. or more and 1600 ° C. or less, still 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 setting the temperature raising process under the 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, as shown in FIG. 1 (D), may be a multi-division type in which the oxide sintered body (code 1C) divided into plural pieces is fixed to the backing plate 3 respectively.
The backing plate 3 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 it into a predetermined 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 fluctuating 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. For mirror surface processing (polishing), known polishing techniques such as mechanical polishing, chemical polishing, and mechanochemical polishing (combination of mechanical polishing and chemical polishing) can be used. 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 cleanliness in air blow or 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.
The oxide semiconductor thin film according to the first aspect of the present embodiment includes the In element, the Sn element, the Zn element, and the Y element, and the atomic composition ratio is a range satisfying the following formulas (7) to (10). .
0.50 ≦ In / (In + Sn + Zn + Y) ≦ 0.93 (7)
0.03 ≦ Sn / (In + Sn + Zn + Y) ≦ 0.30 (8)
0.01 ≦ Zn / (In + Sn + Zn + Y) ≦ 0.15 (9)
0.03 ≦ Y / (In + Sn + Zn + Y) ≦ 0.08 (10)

  Outside the composition range shown in Formula (7) to Formula (10), the carrier concentration of the semiconductor portion of the thin film transistor increases during processing in the CVD film forming apparatus used in the step of forming the thin film transistor, and the annealing thereafter occurs. The treatment may not lower the carrier concentration. In this case, it may not operate as a transistor. In that case, the film formation temperature of the CVD apparatus 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 apparatus, the TFT characteristics having poor durability There are cases where you can only get.

  Specific grounds of upper and lower limits of Formula (7) to Formula (10) and more preferable ranges are the same as specific bases of upper and lower limits of Formula (1) to Formula (6) and more preferable range It is.

A range in which the oxide semiconductor thin film according to the second aspect of the present embodiment includes In element, Sn element, Zn element, Y element, and Al element, and the atomic composition ratio satisfies the following formulas (19) to (23): It is.
0.50 ≦ In / (In + Sn + Zn + Y + Al) ≦ 0.93 (19)
0.03 ≦ Sn / (In + Sn + Zn + Y + Al) ≦ 0.30 (20)
0.01 ≦ Zn / (In + Sn + Zn + Y + Al) ≦ 0.15 (21)
0.03 ≦ Y 2 /(In+Sn+Zn+Y+Al)≦0.20 (22)
0.005 ≦ Al / (In + Sn + Zn + Y + Al) ≦ 0.10 (23)
Specific grounds of upper and lower limits of Formula (19) to Formula (23), and more preferable ranges are the same as specific bases of upper and lower limits of Formula (14) to Formula (18), and more preferable range It is.

In the oxide semiconductor thin film according to the first aspect and the second aspect of the present embodiment, the atomic ratio of Y element to Sn element is preferably in the range satisfying the following formula (24).
0.2 ≦ Y / Sn ≦ 0.5 (24)
The specific basis and the more preferable range of the upper and lower limits of Formula (24) are the same as the specific basis and the more preferable range of the upper and lower limits of Formula (3).

The content (atomic ratio) of each metal element in the oxide semiconductor thin film can be determined by measuring the abundance of each element by ICP (Inductive Coupled Plasma) measurement or XRF (X-ray Fluorescence) measurement. The ICP measurement can use an inductive plasma emission analyzer. A thin film fluorescent X-ray analyzer (AZX400, manufactured by Rigaku Corporation) can be used for XRF measurement.
In addition, the content (atomic ratio) of each metal element in the oxide semiconductor thin film can be analyzed with the same accuracy as inductive plasma emission analysis even by using a sector type dynamic secondary ion mass spectrometer SIMS analysis. The source / drain electrode is formed of the same material as the TFT element with a channel length on the top surface of a standard oxide thin film whose atomic ratio of metal elements is known by inductive plasma emission analysis or thin film fluorescent X-ray analysis. As a standard material, analysis of the oxide semiconductor layer is performed with a sector type dynamic secondary ion mass spectrometer SIMS (IMS 7f-Auto, manufactured by AMETEK) to obtain mass spectral intensities of each element, known element concentrations and mass spectral intensities Prepare a standard curve of Next, when the atomic ratio is calculated from the spectral intensity of the oxide semiconductor film portion of the actual TFT element by the sector type dynamic secondary ion mass spectrometer SIMS analysis using the above-mentioned calibration curve, the calculated atomic ratio is It can be confirmed that it is within 2 atomic% of the atomic ratio of the oxide semiconductor film which is separately measured by a thin film fluorescent X-ray analyzer or inductive plasma emission analyzer.

  The oxide semiconductor thin film according to the first aspect and the second aspect is preferably amorphous. By making amorphous, it is possible to prevent the effect of adding Sn from becoming too strong, and to prevent the thin film from becoming conductive.

The oxide semiconductor thin film according to the first aspect and the second aspect preferably has a band gap of 3.0 eV or more. When the band gap is 3.0 eV or more, the oxide semiconductor thin film does not absorb light at a wavelength of around 420 nm to the long wavelength side. As a result, the oxide semiconductor thin film does not absorb light from the light source of the organic EL or TFT-LCD, and when used as a channel layer of the TFT, there is no malfunction due to the light of the TFT, etc. It is possible to improve the quality. The band gap of the oxide semiconductor thin film is preferably 3.1 eV or more, more preferably 3.3 eV or more.
The band gap is determined by measuring the transmission spectrum of the sample, fitting it to the portion where the absorption rises, and using the energy (eV) value at which the spectrum crosses the baseline as the band gap.

In general, the carrier density of the oxide semiconductor thin film according to the first aspect and the second aspect is preferably 1 × 10 ¹⁸ (cm ⁻³ ) or less, preferably 1 × 10 ¹² (cm ⁻³ ) or more, and more preferably It is 1 × 10 ¹⁷ (cm ⁻³ ) or less, more preferably 1 × 10 ¹³ (cm ⁻³ ) or more.

When the carrier density of the oxide semiconductor thin film is 1 × 10 ¹⁸ (cm ⁻³ ) or less, leakage current, normally on, and reduction in on-off ratio can be prevented when a device such as a thin film transistor is formed. , Good transistor performance can be exhibited. If the carrier concentration is 1 × 10 ¹² (cm ⁻³ ) or more, the transistor can be driven without problems. When the carrier density is 1 × 10 ¹⁶ (cm ⁻³ ) or less, the off current can be 10 ⁻¹² A or less, and the on / off ratio can be 10 ⁸ or more. Thereby, the transfer transistor and the reset transistor of the CMOS image sensor can be driven.
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 according to the first aspect and the second aspect is 1.0 cm 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.
The mobility is determined by a Hall effect / resistivity measuring device.
The oxide semiconductor thin film according to the first aspect and the second aspect preferably has an amorphous structure. Whether or not it has an amorphous structure can be judged by whether or not a peak appears at an XRD peak, particularly at 30 to 40 ° at 2θ. Whether or not it has an amorphous structure can be judged by whether or not a peak appears at an XRD peak, particularly at 30 to 40 ° at 2θ.

<Method of manufacturing oxide semiconductor thin film>
Next, the manufacturing method of the oxide semiconductor thin film which concerns on this embodiment is demonstrated.
The manufacturing method is not particularly limited as long as the 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 oxide semiconductor thin film. This is because the uniformity of the composition, the 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 pulsed DC sputtering may be used.
An oxide semiconductor thin film satisfying the conditions represented by the equations (7) to (10) or the conditions represented by the equations (19) to (23) by using the sputtering target according to the present embodiment as the sputtering target Is 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 or H ₂ O. The concentration of oxidizing gas is optimized at the conditions used, such as equipment, substrate temperature, and sputtering pressure.

  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 Y has a high effect of suppressing the generation of oxygen vacancies, so that 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 power density to 1.0 W / cm ² or more, the discharge is stabilized and a desired sputter rate can be obtained. By setting the power density to 5.0 W / cm ² or less, it is possible to prevent the target from being broken by the heat generated at the time of sputtering.
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.

  The substrate to be film-formed includes silicon wafer, glass, ceramics, plastics, metal 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 for heat treatment to 60 ° C. or higher, the effect of the heat treatment is exhibited. By setting the temperature for heat treatment 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 the 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 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, and a top gate type transistor.

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 the 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. The oxide semiconductor thin film according to the present embodiment is used as the oxide semiconductor thin film 40.

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. The interlayer insulating film 70A is also an insulating film that blocks the conduction between the source electrode 50 and the drain electrode 60. The interlayer insulating film 70A 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.

There are no particular limitations on the materials for forming the drain electrode 60, the source electrode 50, and the gate electrode, and commonly used materials can be arbitrarily selected. In the example mentioned in FIG. 2 and FIG. 3, although a silicon wafer is used as a substrate and a silicon wafer also works as an electrode, an electrode material is not limited to silicon.
For example, transparent electrodes such as indium tin oxide (ITO), indium zinc oxide (IZO), ZnO, and SnO ₂ , metal electrodes such as Al, Ag, Cu, Cr, Ni, Mo, Au, Ti, and Ta, Alternatively, metal electrodes or laminated electrodes of alloys containing these can be used.
Further, in FIGS. 2 and 3, the gate electrode may be formed on a substrate such as glass.

The material for forming the interlayer insulating films 70, 70A, 70B is not particularly limited, and a commonly used material can be arbitrarily selected. As a material for forming the interlayer insulating films 70, 70A, 70B, specifically, for example, SiO ₂ , SiN _x , Al ₂ O ₃ , Ta ₂ O ₅ , TiO ₂ , MgO, ZrO ₂ , CeO ₂ , K ₂ O, Li ₂ O, Na ₂ O, Rb ₂ O, Sc ₂ O ₃ , Y ₂ O ₃ , Y ₂ O ₃ , HfO ₂ , CaHfO ₃ , PbTiO ₃ , PbTa ₂ O ₆ , SrTiO ₃ , Sm ₂ O ₃ , and AlN etc. Compounds can be used.

  When the thin film transistor according to this embodiment is a back channel etch type (bottom gate type), it is preferable to provide a protective film on the drain electrode, the source electrode, and the channel layer. By providing the protective film, the durability can be easily improved even when the TFT is driven for a long time. In the case of a top gate TFT, for example, a gate insulating film is formed on a channel layer.

  The protective film or the insulating film can be formed by, for example, CVD, but it may result in a process due to high temperature. Further, the protective film or the insulating film often contains an impurity gas immediately after deposition, and it is preferable to perform heat treatment (annealing treatment). By removing the impurity gas by heat treatment, a stable protective film or insulating film can be obtained, and a highly durable TFT element can be easily formed.

  By using the oxide semiconductor thin film according to the present embodiment, the TFT characteristics are hardly affected by the influence of the temperature in the CVD process and the heat treatment thereafter, so that the TFT characteristics can be obtained even when the protective film or the insulating film is formed. Stability can be improved.

The thin film transistor preferably has the following characteristics.
Mobility of the thin film transistor is 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.

  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 can be calculated 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 V or less, more preferably -2.0 V or more and 2.0 V or less, and still more preferably -1.0 V or more and 1.0 V or less. When the threshold voltage (Vth) is -3.0 V or more, a thin film transistor with high mobility can be obtained. When the threshold voltage (Vth) is 3.0 V or less, a thin film transistor having a small off current and a large on / off ratio can be obtained.

The threshold voltage (Vth) can be 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 ¹⁰ or less. When the on-off ratio is 10 ⁶ or more, the liquid crystal display can be driven. When the on-off ratio is 10 ¹² or less, driving of the organic EL with large contrast can be performed. 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 ratio [On current value / Off current value] with 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. .
The off current value is preferably 10 ^-10 A or less, more preferably 10 ^-11 A or less, and still more preferably 10 ^-12 A or less. When the Off current value is 10 ^-10 A or less, driving of the organic EL with large contrast can be performed. In addition, when used as a transfer transistor or a reset transistor of a CMOS image sensor, the image holding time can be extended 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.

<Use of thin film transistor>
The thin film transistor according to the present 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, and can be applied to electronic devices and the like. Furthermore, the thin film transistor according to the present embodiment can be applied to an electrostatic induction transistor, a Schottky barrier transistor, a Schottky diode, and a resistor in addition to the field effect transistor.
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 circuit of a pixel portion in the case where a liquid crystal element is applied to the pixel portion of the display device of one embodiment of the present invention. FIG. 4C is a circuit diagram for describing a circuit of a pixel portion in the case of applying an organic EL element to the pixel portion of the 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 circuit of a pixel portion which can be applied to a pixel portion of a VA liquid crystal display device is shown.

  The circuit of this pixel portion can be applied to a configuration 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 portion 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 portion illustrated in FIG. 4B.

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

  FIG. 4C is a diagram illustrating an example of a circuit of the applicable pixel portion 320. 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. Digital time grayscale driving can be applied to the circuit of the pixel portion.

  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 circuit of the pixel portion 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 circuit in the pixel portion 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.

  As described above, 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, preferred embodiments of the present invention will be described in more detail based on examples, but the present invention is not limited to the examples.

<Strength test of sintered body and target>
First, an oxide sintered body satisfying the conditions 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 In, Sn, Zn, and Y were prepared as Example 1 to Example 3. As Example 4 to Example 6, samples of compositions containing In, Sn, Zn, Y, and Al were prepared.
As Comparative Example 1 and Comparative Example 2, although In, Sn, and Y were contained, Zn and Al were not contained, and Y prepared the sample out of the upper limit of Formula (1). As Comparative Example 3 and Comparative Example 4, a sample containing In, Sn, Zn, and Y but not containing Al, and Y being out of the upper limit of Formula (1) 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
Yttrium: Y ₂ O ₃
Aluminum: Al 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 + Y ₂ O ₃ + Al ₂ O ₃ )
Tin mass ratio: SnO ₂ / (In ₂ O ₃ + ZnO + SnO ₂ + Y ₂ O ₃ + Al ₂ O ₃ )
Zinc mass ratio: ZnO / (In ₂ O ₃ + ZnO + SnO ₂ + Y ₂ O ₃ + Al ₂ O ₃ )
Yttrium mass ratio: Y ₂ O ₃ / (In ₂ O ₃ + ZnO + SnO ₂ + Y ₂ O ₃ + Al ₂ O ₃ )
Aluminum mass ratio: Al ₂ O ₃ / (In ₂ O ₃ + ZnO + SnO ₂ + Y ₂ O ₃ + Al 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 49 MPa (converted to 500 kg / cm ² ). The compact was densified by CIP (Cold Isostatic Pressing) at a pressure of 196 MPa (converted to 2000 kg / cm ² ). Next, this molded body is 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 1450 ° C. for 20 hours. Then left to cool.

Next, the crystal structure of the obtained sintered body, the lattice constant of the crystal structure, the atomic composition ratio, the relative density, the bulk resistance, and the abundance ratio of each crystal layer were determined. Furthermore, a film formation test was performed using the obtained sintered body as a sputtering target.
Specific conditions are as follows.

<Crystal structure>
About the obtained sintered compact, X-ray diffraction (XRD) was measured on X-ray-diffraction measuring device Smartlab on condition of the following. The obtained XRD chart was analyzed by JADE 6 to determine the crystal structure of the sintered body.
Device: Smartlab (made by Rigaku Corporation)
X-ray: Cu-Kα ray (wavelength 1.5418 × 10 ^-10 m, monochromated with graphite monochromator)
2θ-θ reflection method Continuous scan (2.0 ° / min)
Sampling interval: 0.02 °
Slit DS (divergent slit), SS (divergent slit), RS (receiving slit): 1 mm

<Lattice constant>
The obtained XRD pattern was analyzed by full pattern fitting (WPF) using JADE 6 (powder X-ray diffraction pattern general analysis software; manufactured by Rigaku Corporation), and each crystal component contained in the XRD pattern was identified and obtained. The lattice constant of the In ₂ O ₃ crystal structure in the oxide sintered body was calculated.

<Atom composition ratio>
The elemental composition in the sintered body was measured by an inductive plasma emission analyzer (ICP-AES, manufactured by Shimadzu Corporation).

<Relative density>
The relative density is calculated using the value obtained by dividing the actual density measured by the Archimedes method for the obtained oxide sintered body by the theoretical density calculated from the density and mass ratio of the oxides of the constituent elements as a percentage. did. In addition, since the density and specific gravity of each raw material powder are almost the same, the value of the specific gravity of the oxide described in the Chemical Handbook, Basic Edition I, Nippon Chemical Edition, Rev. 2 (Maruzen Co., Ltd.) was used. .

<Bulk resistance>
The bulk resistance (mΩcm) of the obtained oxide sintered body was measured based on the four-point probe method (JIS R 1637) using a resistivity meter Loresta (Loresta AX MCP-T370 manufactured by Mitsubishi Chemical Corporation) did.
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.

<Abundance ratio of crystal layer>
From the obtained XRD pattern, it calculated | required as an abundance ratio (a unit is mass%) by the all pattern fitting (WPF) method.

<Deposition durability evaluation test>
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 continuously for 10 hours. 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. In Comparative Examples 2 to 4, since the bulk resistance of the sintered body was too high to be used for DC magnetron sputtering, the film formation durability evaluation test was not conducted.

  The above results are shown in Table 1. Among the obtained XRD charts, those of Examples 1 to 6 and Comparative Examples 1 to 2 are shown in FIG. 6 to FIG. 6 to 13 also show the angle of the crystal structure corresponding to the predetermined peak.

As shown in Table 1 and FIGS. 6 to 13, in Examples 1 to 6 and Comparative Examples 1 to 4, the bixbyte structure represented by In ₂ O ₃ is the main component, and Y ₂ It contained a pyrochlore structure represented by Sn ₂ O ₇ . For Examples 1 to 6, the spinel structure and the hexagonal layered structure were not measured.
In Examples 1 to 6 and Comparative Examples 3 and 4, the lattice constant of the bixbite structure represented by In ₂ O ₃ is based on the lattice constant of a pure substance (10.118 × 10 ⁻¹⁰ m). Since it is also small, it is understood that Zn element is in interstitial solid solution in the bixbite structure represented by In ₂ O ₃ .
The relative density of the oxide sintered bodies of Examples 1 to 6 was 95% or more for all the samples, and the bulk resistance was 20 mΩcm or less.

  In Examples 1 to 6, no significant change was observed on the surface of the target after film formation, except for the occurrence of erosion. On the other hand, in Comparative Example 1, a large amount of black foreign matter was observed in the erosion portion on the surface of the target after film formation. Also, hairline cracks were observed. Furthermore, when the number of times of abnormal discharge was measured with a micro arc counter, with the targets using the sintered bodies of Example 1 to Example 6, the arc could not be measured substantially, but the sintered body of Comparative Example 1 was used. There were many frequent occurrences of arcs on the target.

From this result, ITZO containing Y within the range satisfying the formula (1), the formula (2), the formula (12), and the formula (13) is represented by the formula (1) as in the configurations of Example 1 to Example 6. It was found that the strength against sputtering of the sintered body and the sputtering target was higher as compared with the case where the formula (2), the formula (12) and the formula (13) were not satisfied. Moreover, all of Example 1 to Example 6 satisfied the formula (3) and the formula (15).
In addition, when it bakes under atmospheric pressure, a sintering density does not become high easily compared with the technique which used HIP, discharge plasma sintering (SPS), or an oxygen atmosphere calcination furnace. However, as shown in Table 1, even if it is simple atmospheric pressure baking, it turns out that Example 1 to Example 6 are high density.

<Evaluation test of semiconductor thin film>
Next, using the sputtering targets of Example 1 to Example 6, 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 produced in Examples 1 to 6 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 sputtering target produced as shown in FIG. The sample which formed the film was manufactured.
The film formation conditions are as follows.
Atmosphere gas: mixed gas of high purity Ar and high purity O ₂ 1% by volume Back pressure before film formation: 5 × 10 ^-4 Pa
Sputtering pressure during film formation: 0.5 Pa
Substrate temperature during film formation: room temperature (24 ° C.)
Oxygen partial pressure during film formation: Example A, B: 20%, Example C, F: 30%, Example D, E: 10%

(2) Heat Treatment Step Next, the obtained sample was heated at 350 ° C. in the air at a temperature rising rate of 10 ° C./minute for 60 minutes.

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.
In addition, as a result of analyzing the obtained oxide semiconductor thin film 83 with an inductive plasma emission analyzer (ICP-AES, manufactured by Shimadzu Corporation), the atomic ratio of the obtained oxide semiconductor thin film is the production of the oxide semiconductor thin film. It confirmed that it was the same as the atomic ratio of the sintered compact used for 4.

In Examples 1 to 3, a SiO ₂ film 85 was further formed on the oxide semiconductor thin film 83 of the above-described sample for Hall effect measurement by a CVD apparatus at a substrate temperature of 250 ° C. as shown in FIG. After that, the same Hall effect measurement as described above was performed. In Examples 1 to 3, the sample on which the SiO ₂ film was formed under the conditions shown in Table 2 was subjected to heat treatment at 350 ° C. for 60 minutes in the air atmosphere, and the semiconductor thin film of the obtained sample was The same Hall effect measurement was performed. At this time, the measuring needle was pierced into the SiO ₂ film until reaching the gold layer formed on the oxide semiconductor thin film 83 to make contact.

<Crystal characteristics of semiconductor thin film>
X-ray diffraction (X-ray diffraction) 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 thin film 83 It evaluated by the XRD) measurement. As a result, it was amorphous before heating and was amorphous after heating.

<Band gap of semiconductor thin film>
The transmission spectrum of the sample heat-treated under the heat treatment conditions shown in Table 2 is measured for the sample consisting of the glass substrate 81 and the oxide semiconductor thin film 83, and the wavelength of the horizontal axis is energy (eV) and the transmittance of the vertical axis is Converted to the equation (25) of
Transmittance = (α h ² ) ² (25)
Here, α, h and ν are as follows.
α: Absorption coefficient h: Planck constant :: frequency In the converted graph, fitting was performed to a portion where the absorption rises, and an energy value (eV) at which the graph intersects with the baseline was calculated as a band gap.

<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 having a thickness of 50 nm was formed on a silicon wafer 20 as a gate electrode with a thermal oxide film (gate insulating film 30) via a metal mask. Other conditions were the same as in the case where the oxide semiconductor thin film 83 was formed on the glass substrate 81.

(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 Regarding Examples 1 to 3, on the semiconductor thin film of the thin film transistor before forming the protective insulating film obtained in (2), chemical vapor deposition (CVD) at a substrate temperature of 300 ° C. A SiO ₂ film (protective insulating film; interlayer insulating film 70 B) 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.

<Evaluation of thin film transistor>
The thin film transistor manufactured, a protective insulating film on the characteristics of the thin film transistor after (SiO ₂ film) formed before the thin film transistor, and forming a protective insulating film (SiO ₂ film) was heated titanium metal measuring needle into the SiO ₂ film Evaluation was done to the layer of. The thin film transistor was evaluated by contacting the source electrode 50 and the drain electrode 60 with a cascade microtech EP 6 probe bar.

<Saturated mobility>
The saturation mobility was determined from the transfer characteristics when a drain voltage of 20 V was applied. 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. In the examples, saturated mobility was evaluated in this way, unless otherwise stated. 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 value>
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 Examples A to F, the thin film and the thin film transistor each had characteristics as a semiconductor. In particular, as a characteristic of the thin film transistor, the off current has a value of the first half of 10 ⁻¹³ A regardless of the negative value of V _th and shows an excellent off current value. This shows that, when applied to a transfer transistor or a cancel transistor for a CMOS image sensor, the potential change of the charge storage portion becomes small, and detection is possible even if the voltage from the photoelectric conversion element is weak. Plasma CVD is generally used to form a protective film for thin film semiconductors for driving LCDs and OLEDs, but in the case of a CMOS image sensor, sputtering, not plasma CVD, is used to form a protective film on a thin film transistor. It is possible to form SiO ₂ . Thus, there is an advantage that a thin film semiconductor can be used without using plasma CVD, and the TFT characteristics after heat treatment can be used as it is.

  From the above results, it was found that the oxide semiconductor thin film formed by using the oxide sintered body having the composition range according to the present embodiment is excellent in the strength of the target, and the saturation mobility of the semiconductor thin film is high.

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 (21)

It contains an In element, a Sn element, a Zn element, and a Y element and includes a bixbite structure represented by In ₂ O ₃ and a pyrochlore structure represented by Y ₂ Sn ₂ O ₇ , and the atomic composition ratio of the Y element is It is a range which satisfy | fills following formula (1), Oxide sinter characterized by the above-mentioned.
0.03 ≦ Y / (In + Sn + Zn + Y) ≦ 0.08 (1) A bixbite structure containing In, Sn, Zn and Y and represented by In ₂ O ₃ and a pyrochlore structure represented by Y ₂ Sn ₂ O ₇ and represented by Zn ₂ SnO ₄ Spinel structure and a hexagonal layered structure represented by In ₂ O ₃ (ZnO) _m (where m is an integer of 1 to 20), and the atomic composition ratio of Y element is represented by the following formula (2) And an oxide sintered body characterized by satisfying the following conditions.
0.03 ≦ Y / (In + Sn + Zn + Y) ≦ 0.08 (2) The oxide sintered body according to claim 1 or 2, wherein the atomic composition ratio of Y element and Sn element is a range satisfying the following formula (3).
0.2 ≦ Y / Sn ≦ 0.5 (3) The oxide according to any one of claims 1 to 3, wherein the atomic composition ratio of In element, Sn element, and Zn element is in a range satisfying the following formulas (4) to (6). Sintered body.
0.50 ≦ In / (In + Sn + Zn + Y) ≦ 0.93 (4)
0.03 ≦ Sn / (In + Sn + Zn + Y) ≦ 0.30 (5)
0.01 ≦ Zn / (In + Sn + Zn + Y) ≦ 0.15 (6)   A sputtering target comprising the oxide sintered body according to any one of claims 1 to 4. What is claimed is: 1. An oxide semiconductor thin film comprising an In element, a Sn element, a Zn element, and a Y element, and having an atomic composition ratio satisfying the following formulas (7) to (10).
0.50 ≦ In / (In + Sn + Zn + Y) ≦ 0.93 (7)
0.03 ≦ Sn / (In + Sn + Zn + Y) ≦ 0.30 (8)
0.01 ≦ Zn / (In + Sn + Zn + Y) ≦ 0.15 (9)
0.03 ≦ Y / (In + Sn + Zn + Y) ≦ 0.08 (10) The oxide semiconductor thin film according to claim 6, wherein the atomic composition ratio of the Y element and the Sn element satisfies the following formula (11).
0.2 ≦ Y / Sn ≦ 0.5 (11)   It is amorphous, The oxide semiconductor thin film of Claim 6 or Claim 7 characterized by the above-mentioned.   A thin film transistor comprising the oxide semiconductor thin film according to any one of claims 6 to 8.   An electronic device comprising the thin film transistor according to claim 9. An atomic composition of Y element including a bixbyite structure represented by In ₂ O ₃ containing an In element, Sn element, Zn element, Y element and Al element and a pyrochlore structure represented by Y ₂ Sn ₂ O ₇ The ratio is a range which satisfy | fills following formula (12), Oxide sinter characterized by the above-mentioned.
0.03 ≦ Y / (In + Sn + Zn + Y + Al) ≦ 0.20 (12) Zn ₂ SnO ₄ containing a bixbyite structure represented by In ₂ O ₃ and an pyrochlore structure represented by Y ₂ Sn ₂ O ₇ containing In, Sn, Zn, Y and Al elements And the hexagonal layer structure represented by In ₂ O ₃ (ZnO) _m (where m is an integer of 1 to 20), and the atomic composition ratio of Y element is represented by the following formula An oxide sintered body characterized in that the range satisfies (13).
0.03 ≦ Y / (In + Sn + Zn + Y + Al) ≦ 0.20 (13) The oxide sintered body according to claim 11 or 12, wherein the atomic ratio of the Al element is in a range satisfying the following formula (14).
0.005 ≦ Al / (In + Sn + Zn + Y + Al) ≦ 0.10 (14) The oxide sintered body according to any one of claims 11 to 13, wherein the atomic composition ratio of the Y element and the Sn element is a range satisfying the following formula (15).
0.2 ≦ Y / Sn ≦ 0.5 (15) The oxide according to any one of claims 10 to 14, wherein the atomic composition ratio of In element, Sn element, and Zn element is in a range satisfying the following formulas (16) to (18). Sintered body.
0.50 ≦ In / (In + Sn + Zn + Y + Al) ≦ 0.93 (16)
0.03 ≦ Sn / (In + Sn + Zn + Y + Al) ≦ 0.30 (17)
0.01 ≦ Zn / (In + Sn + Zn + Y + Al) ≦ 0.15 (18)   A sputtering target comprising the oxide sintered body according to any one of claims 11 to 15. What is claimed is: 1. An oxide semiconductor thin film comprising an In element, a Sn element, a Zn element, a Y element, and an Al element, and having an atomic composition ratio satisfying the following Formulas (19) to (23).
0.50 ≦ In / (In + Sn + Zn + Y + Al) ≦ 0.93 (19)
0.03 ≦ Sn / (In + Sn + Zn + Y + Al) ≦ 0.30 (20)
0.01 ≦ Zn / (In + Sn + Zn + Y + Al) ≦ 0.15 (21)
0.03 ≦ Y 2 /(In+Sn+Zn+Y+Al)≦0.20 (22)
0.005 ≦ Al / (In + Sn + Zn + Y + Al) ≦ 0.10 (23) The oxide semiconductor thin film according to claim 17, wherein the atomic composition ratio of Y element to Sn element is a range satisfying the following formula (24).
0.2 ≦ Y / Sn ≦ 0.5 (24)   The oxide semiconductor thin film according to claim 17, which is amorphous.   A thin film transistor comprising the oxide semiconductor thin film according to any one of claims 17 to 19.   An electronic device comprising the thin film transistor according to claim 20.

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