JP2014095144A - Sputtering target - Google Patents

Abstract

Disclosed is a sputtering target that can suppress generation of abnormal discharge, nodules, and particles, can produce an oxide semiconductor film having a small S value, excellent TFT reliability, and high mobility.
SOLUTION: An oxide including an In element, a Ga element, and a Zn element, and having at least a homologous phase represented by In ₂ Ga ₂ ZnO ₇ as a crystalline phase, a homologous phase represented by InGaZnO ₄ , and In ₂ O _3. The sputtering target containing the sintered compact in which the intensity | strength of each said crystal phase obtained by X-ray-diffraction measurement satisfy | fills following formula (1-1) and (1-2) is included including the bixbite phase represented by these. (In the formula, I (X) represents the strength of the crystal phase of X.)
I (In ₂ Ga ₂ ZnO ₇ )> I (InGaZnO ₄ ) (1-1)
I (In ₂ Ga ₂ ZnO ₇ )> I (In ₂ O ₃ ) (1-2)
[Selection] Figure 1

Description

  The present invention relates to a sputtering target and a manufacturing method thereof.

Oxide thin films made of indium oxide and zinc oxide, indium oxide, gallium oxide and zinc oxide, indium oxide and gallium oxide, etc. have excellent visible light transmission and have a wide range of electrical characteristics from conductors to semiconductors and insulators. Therefore, it attracts attention as a semiconductor film for transparent electrodes and thin film transistors (TFTs).
These transparent oxide thin films can be formed by film forming methods such as sputtering, PLD (pulse laser deposition), and vapor deposition. In particular, a sputtering method capable of uniformly forming a film over a large area has been mainly studied. A sputtering target (target) is used for the sputtering method.

As a target for manufacturing a semiconductor film for TFT, an In—Ga—Zn-based (IGZO-based) oxide semiconductor using indium oxide, gallium oxide, and zinc oxide has been energetically studied.
As the IGZO-based target, a composition containing a known homologous crystal represented by InGaZnO ₄ , In ₂ Ga ₂ ZnO ₇ or the like (Patent Document 1), or a compound having a composition close thereto is being studied.
Also, depending on the composition, it is also a target containing a compound having a bixbyite structure or spinel structure represented by In ₂ O ₃ (Patent Documents 2 to 4) has been studied. Non-Patent Document 1 discloses an oxide represented by InGaO ₃ (ZnO) _m (m = 1 to 20) such as InGaO ₃ (ZnO) ₂ and a synthesis method thereof.

  In addition to the above, Patent Documents 5 and 6 disclose novel crystal structures as IGZO-based sintered bodies and targets. With regard to the study on this IGZO-based oxide semiconductor thin film, studies on thin films having different composition ratios by co-sputtering (a method for producing thin films having various composition ratios using a plurality of targets) have been reported (Patent Document 7). , 8).

JP-A-8-245220 JP 2007-73312 A International Publication No. 2009/084537 Pamphlet International Publication No. 2008/072486 Pamphlet International Publication No. 2011/061930 Pamphlet International Publication No. 2011/061936 Pamphlet JP 2007-281409 A JP 2008-053356 A

N. Kimizuka et al. , Journal of Solid State Chemistry, Vol 116, Issue 1, 1995.

  A target used in the sputtering method is desired to have high conductivity and less generation of abnormal discharge, nodules, and particles, but such a target is not easy to manufacture. The reason is that the properties and state of the target change depending on the manufacturing conditions of the target and the composition of the components, the conductivity changes, and the ease of generation of nodules, abnormal discharge, and particles changes. This is due to the fact that the type and distribution of the crystal structure constituting the manufactured target are affected, and the crystal system that is stably generated differs depending on the composition and manufacturing conditions.

In order to obtain a target with few abnormal discharges, nodules, particles, etc., it is extremely effective to select the crystal phase in the target composition accurately. These occurrences greatly depend on the type of crystal phase constituting the target and its size (crystal grain size). It is important to reduce the number of defects (pores and cracks) in the target and to have a high density in order to suppress abnormal discharge, nodules, and particle generation. If this happens, these will become a problem.
In addition, it is naturally required that a semiconductor thin film manufactured by sputtering exhibits desired performance.

  Thus, it is necessary to improve the performance of the obtained oxide semiconductor thin film and to produce a high-density target with high stability at the time of film formation and few defects even during the production of the target. So far, the studies have not been fully satisfactory.

  An object of the present invention is to provide a sputtering target that can suppress the generation of abnormal discharge, nodules, and particles, can produce an oxide semiconductor film having a small S value, excellent TFT reliability, and high mobility. That is.

As a result of intensive studies by the present inventors, a sputtering target in which a homologous compound represented by In ₂ Ga ₂ ZnO ₇ is present in a larger amount than a homologous compound represented by InGaZnO ₄ is acceptable for manufacturing conditions even when applied to an industrial process. The present inventors have found that the width is wide, that is, generation of abnormal discharge, nodules and particles during the formation of an oxide semiconductor thin film can be suppressed, and the resulting oxide thin film has excellent TFT characteristics.
According to the present invention, the following sputtering target and the like are provided.
1. It includes an oxide containing In element, Ga element and Zn element, and is represented by a homologous phase represented by at least In ₂ Ga ₂ ZnO ₇ as a crystal phase, a homologous phase represented by InGaZnO ₄ , and In ₂ O _3. A sputtering target comprising a sintered body containing a bixbite phase, wherein the strength of each crystal phase obtained by X-ray diffraction measurement satisfies the following formulas (1-1) and (1-2).
I (In ₂ Ga ₂ ZnO ₇ )> I (InGaZnO ₄ ) (1-1)
I (In ₂ Ga ₂ ZnO ₇ )> I (In ₂ O ₃ ) (1-2)
(In the formula, I (X) represents the strength of the crystal phase of X.)
2. The sputtering target according to 1, wherein the intensity of the homologous phase represented by the In ₂ Ga ₂ ZnO ₇ is 1.2 times or more larger than the intensity of the homologous phase composed of the InGaZnO ₄ .
3. _3. The sputtering target according to 1 or 2, wherein the intensity of the homologous phase represented by the In ₂ Ga ₂ ZnO ₇ is 1.2 times or more larger than the intensity of the bixbite phase composed of In ₂ O ₃ .
4). A bixbite phase containing an oxide containing In element, Ga element and Zn element and having at least a homologous phase represented by In ₂ Ga ₂ ZnO ₇ as a crystalline phase, a homologous phase represented by InGaZnO ₄ , and an In ₂ O ₃ A sputtering target including a sintered body satisfying the following formulas (2-1) and (2-2) in which the cross-sectional area of each crystal phase measured by observation with a scanning electron microscope (SEM) is included.
S (In ₂ Ga ₂ ZnO ₇ )> S (InGaZnO ₄ ) (2-1)
S (In ₂ Ga ₂ ZnO ₇ )> S (In ₂ O ₃ ) (2-2)
(In the formula, S (X) represents the cross-sectional occupation area of the crystal phase of X)
5. 5. The sputtering target according to ₄ , wherein a cross-sectional occupation area of a homologous phase represented by the In ₂ Ga ₂ ZnO ₇ is 1.5 times or more larger than a cross-sectional occupation area of a homologous phase composed of the InGaZnO ₄ .
6). The sputtering target according to 4 or 5, wherein a cross-sectional occupation area of the homologous phase represented by the In ₂ Ga ₂ ZnO ₇ is 1.5 times or more larger than a cross-sectional occupation area of the bixbite phase represented by In ₂ O ₃ .
7). The sputtering target according to any one of 1 to 6, wherein an atomic ratio of the sintered body satisfies the following formulas (3-1) to (3-3).
0.45 <In / (In + Ga + Zn) <0.70 (3-1)
0.20 <Ga / (In + Ga + Zn) <0.45 (3-2)
0 <Zn / (In + Ga + Zn) <0.15 (3-3)
8). 8. The sputtering target according to 7, wherein the formula (3-1) is the following formula (3-1 ′).
0.47 <In / (In + Ga + Zn) <0.68 (3-1 ′)
9. The sputtering target according to 7 or 8, wherein the formula (3-2) is the following formula (3-2 ′).
0.22 <Ga / (In + Ga + Zn) <0.43 (3-2 ′)
10. The sputtering target according to any one of 7 to 9, wherein the formula (3-3) is the following formula (3-3 ′).
0.01 <Zn / (In + Ga + Zn) <0.15 (3-3 ′)
11. The sputtering target according to any one of 1 to 10, wherein the sintered body does not contain a spinel structure compound.
12 The manufacturing method of the sputtering target in any one of 1-11 which sinters the molded object containing the raw material containing In element, Ga element, and Zn element at 1300-1500 degreeC for 1-180 hours.
13. 13. The method for producing a sputtering target according to 12, wherein the molded body is sintered in an atmosphere having an oxygen concentration of 50% by volume or more.
14. A field effect thin film transistor having, as a channel layer, an oxide thin film manufactured using the sputtering target according to any one of 14.1 to 11.
15. A display device comprising the field effect thin film transistor according to 15.14.

  ADVANTAGE OF THE INVENTION According to this invention, the sputtering target which can suppress the generation | occurrence | production of abnormal discharge, a nodule, and a particle, can manufacture an oxide semiconductor film with small S value, excellent TFT reliability, and high mobility can be provided. .

2 is a SEM image of a cross-sectional crystal phase of a sintered body produced in Example 1. 4 is a SEM image of a cross-sectional crystal phase of a sintered body produced in Example 2. 4 is a SEM image of a cross-sectional crystal phase of a sintered body produced in Example 3. 6 is a SEM image of a cross-sectional crystal phase of a sintered body produced in Example 4. 4 is a SEM image of a cross-sectional crystal phase of a sintered body produced in Comparative Example 2. It is a schematic sectional drawing of the thin-film transistor produced by the Example and the comparative example.

The first sputtering target of the present invention includes a sintered body, the sintered body includes an oxide including an In element, a Ga element, and a Zn element, and a homologous phase represented by at least In ₂ Ga ₂ ZnO ₇ as a crystal phase. , A homologous phase represented by InGaZnO ₄ , and a bixbite phase represented by In ₂ O ₃ .
Moreover, the intensity | strength obtained by carrying out X-ray diffraction measurement of said crystalline phase contained in a sintered compact satisfy | fills following formula (1-1) and (1-2).
I (In ₂ Ga ₂ ZnO ₇ )> I (InGaZnO ₄ ) (1-1)
I (In ₂ Ga ₂ ZnO ₇ )> I (In ₂ O ₃ ) (1-2)
(In the formula, I (X) represents the strength of the crystal phase of X.)

It can be confirmed by X-ray diffraction measurement that it has a homologous phase represented by In ₂ Ga ₂ ZnO ₇ , a homologous phase represented by InGaZnO ₄ , and a bixbite phase represented by In ₂ O ₃ . Specifically, the X-ray diffraction measurement can be performed by the method described in the examples.

The crystal structure can be confirmed, for example, because the X-ray diffraction pattern of the target (sintered body) matches the assumed crystal structure X-ray diffraction pattern.
Specifically, it can be confirmed from the coincidence with a crystal structure X-ray diffraction pattern obtained from a JCPDS (Joint Committee of Powder Diffraction Standard) card or an ICSD (The Inorganic Crystal Structure Database).

The homologous phase represented by In ₂ Ga ₂ ZnO ₇ exhibits a peak pattern of 38-1097 in the JCPDS database or a similar (shifted) pattern by X-ray diffraction. The homologous phase X-ray diffraction represented by InGaZnO ₄ shows the peak pattern of 38-1104 of the JCPDS database, or a similar (shifted) pattern.

  A crystal phase derived from a homologous structure is a crystal having a “natural superlattice” structure having a long period in which several crystal layers of different substances are stacked. When the crystal cycle or thickness of each thin film layer is on the order of nanometers, depending on the combination of the chemical composition of these layers and the thickness of the layers, it differs from the properties of a single crystal or a mixed crystal in which each layer is uniformly mixed. May show unique characteristics.

The crystal structure of the homologous phase can be confirmed, for example, because the X-ray diffraction pattern measured for the target pulverized product or the cut piece matches the crystal structure X-ray diffraction pattern of the homologous phase assumed from the composition ratio. Specifically, it can be confirmed from the coincidence with the crystal structure X-ray diffraction pattern of the homologous phase obtained from the JCPDS card.
In the sintering process, a clear crystal structure may not be exhibited depending on the composition. This is thought to be due to the case where the crystal phase is in the process of transition or unclear ordering. In such a case, the composition ratio of the raw materials mixed with the composition ratio of the crystal phase does not necessarily match, and there are cases where the peak is not observed or the peak is not observed. In the present invention, in these cases, it is assumed that it can be ignored within a range that does not particularly deteriorate the performance.

The bixbite phase represented by In ₂ O ₃ can be confirmed by observing the peak of the bixbite structure compound as a result of X-ray diffraction measurement of the sintered body.

Bixbyte is also referred to as rare earth oxide C-type or Mn 2 O 3 (I) -type oxide. As disclosed in “Technology of Transparent Conductive Films” (Ohm Publishing Co., Ltd., Japan Society for the Promotion of Science, Transparent Oxide / Optoelectronic Materials 166th Committee, 1999), the stoichiometric ratio is M ₂ X ₃ (M is a cation, X is an anion, usually an oxygen ion), and one unit cell is composed of 16 molecules of M ₂ X ₃ , a total of 80 atoms (M is 32, X is 48) Yes.

The bixbite structure is X-ray diffraction, and is No. of JCPDS database. A peak pattern of 06-0416 or a similar (shifted) pattern is shown.
The bixbite structure compound also includes a substitutional solid solution in which atoms and ions in the crystal structure are partially substituted with other atoms, and an interstitial solid solution in which other atoms are added to interstitial positions.

The sintered body may include a crystal phase other than a homologous phase represented by In ₂ Ga ₂ ZnO ₇ , a homologous phase represented by InGaZnO ₄ , and a bixbite phase represented by In ₂ O _3. Is preferably free of a spinel structure compound, and substantially includes a homologous phase represented by In ₂ Ga ₂ ZnO ₇ , a homologous phase represented by InGaZnO ₄ , and a bixbite phase represented by In ₂ O _3. More preferably.
The “substantially” means that the homologous phase represented by In ₂ Ga ₂ ZnO ₇ , the homologous phase represented by InGaZnO ₄ , and the bixbite phase represented by In ₂ O ₃ in the sintered body. , 95 atomic% or more, 97 atomic% or more, 98 atomic% or more, or 99 atomic% or more. “Substantially” includes “consisting only of”.

The spinel structure is an ionic crystal having a composition of AB ₂ O ₄ when A is a divalent cation and B is a trivalent cation, and is a tetrahedral gap of a three-dimensional face-centered lattice formed by O ²⁻ . One-eighth is filled with A and half of the octahedral gap is filled with B. The reverse spinel structure is an ionic crystal having a composition of AB ₂ O ₄ like the spinel structure. B is filled in one-eighth of the tetrahedral gap and A and B are filled in one-half of the octahedral gap. Has a structured.

In the first sputtering target (sintered body) of the present invention, when the existence ratio of the In ₂ Ga ₂ ZnO ₇ homologous structure is larger than the InGaZnO ₄ homologous structure, an oxide thin film is produced using a conventional sputtering apparatus. It is possible to manufacture suitably. Specifically, abnormal discharge, nodules, and generation of particles can be suppressed.
Further, since the presence ratio of the In ₂ Ga ₂ ZnO ₇ homologous structure is larger than that of the In ₂ O ₃ bixbyite structure, generation of particles can be effectively suppressed during production of the oxide thin film, and abnormal discharge associated therewith can be suppressed. .

  The intensity of the crystal phase can be determined from the height of the main peak of each crystal phase obtained by X-ray diffraction measurement. Specifically, it can be measured by the method described in the examples.

In the sintered body, I (In ₂ Ga ₂ ZnO ₇ ) is larger than I (InGaZnO ₄ ), preferably 1.2 times or more. Further, I (In ₂ Ga ₂ ZnO ₇ ) is larger than I (In ₂ O ₃ ), preferably 1.2 times or more.

In the sintered body used for the first sputtering target of the present invention, it is preferable that the atomic ratio of each atom satisfies the following formulas (3-1) to (3-3).
0.45 <In / (In + Ga + Zn) <0.70 (3-1)
0.20 <Ga / (In + Ga + Zn) <0.45 (3-2)
0 <Zn / (In + Ga + Zn) <0.15 (3-3)

In the above formula (3-1), when the amount of In element exceeds 0.45, a homologous structure represented by In ₂ Ga ₂ ZnO ₇ can be efficiently constructed. Moreover, the production | generation of a bixbyte structure can be suppressed as it is less than 0.70.
The atomic ratio of In more preferably satisfies the following formula (3-1 ′).
0.47 <In / (In + Ga + Zn) <0.68 (3-1 ′)

In the above formula (3-2), when the amount of Ga element is more than 0.20, stability (reliability during driving and optical reliability) when applied as an oxide semiconductor can be obtained. Further, if it is less than 0.45, an increase in resistance value during the formation of a thin film can be suppressed, and good semiconductor characteristics can be obtained.
The atomic ratio of Ga more preferably satisfies the following formula (3-2 ′).
0.22 <Ga / (In + Ga + Zn) <0.43 (3-2 ′)

In the above formula (3-3), the amount of Zn elements to suppress the formation of InGaZnO ₄ is less than _0.15, the In ₂ Ga ₂ ZnO ₇ can be efficiently configured.
The atomic ratio of Zn more preferably satisfies the following formula (3-3 ′).
0.01 <Zn / (In + Ga + Zn) <0.15 (3-3 ′)

The atomic ratio of each element contained in the sintered body can be determined by quantitatively analyzing the contained elements with an inductively coupled plasma emission spectrometer (ICP-AES).
Specifically, when a solution sample is atomized with a nebulizer and introduced into an argon plasma (about 6000 to 8000 ° C.), the element in the sample is excited by absorbing thermal energy, and orbital electrons are excited from the ground state. Move to the orbit. These orbital electrons move to a lower energy level orbit in about 10 ⁻⁷ to 10 ⁻⁸ seconds. At this time, the energy difference is emitted as light to emit light. Since this light shows a wavelength (spectral line) unique to the element, the presence of the element can be confirmed by the presence or absence of the spectral line (qualitative analysis).

In addition, since the magnitude (luminescence intensity) of each spectral line is proportional to the number of elements in the sample, the sample concentration can be obtained by comparing with a standard solution having a known concentration (quantitative analysis).
After identifying the elements contained in the qualitative analysis, the content is obtained by quantitative analysis, and the atomic ratio of each element is obtained from the result.

The sintered body used for the first sputtering target of the present invention may contain a metal element other than the above-described In, Ga and Zn as long as the effects of the present invention are not impaired. You may consist only of In, Ga, and Zn or only In, Ga, and Zn.
Examples of metal elements other than In, Ga, and Zn include Sn, Mg, Ti, Al, Si, and the like.

Here, “substantially” means that the effect as a sputtering target is caused by the above In, Ga and Zn, or 95% by weight to 100% by weight (preferably 98% by weight or more) of the metal element of the sintered body. 100% by weight or less) is In, Ga and Zn.
The sintered body used in the present invention may contain inevitable impurities in addition to In, Zn and Ga as long as the effects of the present invention are not impaired.

When used for DC sputtering, the first sputtering target of the present invention preferably has a specific resistance value of 1.0 × ⁻⁴ Ωcm or less, more preferably 5.0 × ⁻⁵ Ωcm or less. Since the specific resistance value of the target is related to the target density, it is desirable to sinter to a high density state.
The first sputtering target of the present invention preferably has a relative density of 95% or higher, more preferably 98% or higher.

The second sputtering target of the present invention includes a sintered body, the sintered body includes an oxide including In element, Ga element, and Zn element, and is represented by a homologous phase represented by at least In ₂ Ga ₂ ZnO ₇ as a crystal phase. , A homologous phase represented by InGaZnO ₄ , and a bixbite phase represented by In ₂ O ₃ .
In the sintered body, the area occupied by the cross section of the crystal phase determined from observation with a scanning electron microscope (SEM) satisfies the following formulas (2-1) and (2-2).
S (In ₂ Ga ₂ ZnO ₇ )> S (InGaZnO ₄ ) (2-1)
S (In ₂ Ga ₂ ZnO ₇ )> S (In ₂ O ₃ ) (2-2)
(In the formula, S (X) represents the cross-sectional area occupied by the crystal phase of S).

The second sputtering target (sintered body) of the present invention has a larger proportion of the In ₂ Ga ₂ ZnO ₇ homologous structure (occupied area in the cross section of the sintered body) than the InGaZnO ₄ homologous structure. In the case of producing an oxide thin film by using, it can be suitably produced. Specifically, abnormal discharge, nodules, and generation of particles can be suppressed.
In addition, since the presence ratio of the In ₂ Ga ₂ ZnO ₇ homologous structure is larger than that of the In ₂ O ₃ bixbyite structure, generation of particles can be effectively suppressed during production of the oxide thin film, and abnormal discharge associated therewith can also be suppressed. .

The observation of the crystal phase in the cross section of the sintered body can be performed as follows. That is, after the sintered body is polished, it is appropriately cut, embedded and polished to obtain an observation sample. Each crystal phase can be identified by observing this observation sample with SEM at 1000 times.
In SEM observation, the surface irregularities are usually imaged by detecting secondary electrons. However, if the surface is smooth, it is possible to confirm the image by forming a contrast due to the difference in conductivity. The presence of each crystal phase can be identified by SEM observation of a sample having a smooth surface produced by embedded polishing.

In the above sintered body, S (In ₂ Ga ₂ ZnO ₇ ) is larger than S (InGaZnO ₄ ), preferably 1.5 times or more. Further, S (In ₂ Ga ₂ ZnO ₇ ) is larger than S (In ₂ O ₃ ), preferably 1.5 times or more.

  Other conditions in the second sputtering target of the present invention are the same as those of the first sputtering target of the present invention.

The first and second sputtering targets of the present invention (sputtering target of the present invention) can be produced, for example, by sintering raw material powder containing each metal element.
Specifically, the raw material powder is mixed and pulverized using a pulverizer such as a ball mill or a bead mill, then granulated by a spray dryer or the like, uniaxial press such as HP or CP, cold isostatic pressure (CIP), hot static It is obtained by molding and baking by an isotropic press such as water pressure (HIP).
The raw material is not particularly limited as long as the target to be obtained can form the target crystal phase, but the particle size and specific surface area are appropriately selected and blended so as not to generate defects such as aggregation, cracks and pores.

Each step will be described below.
(1) Compounding step In the compounding step, the compound of the metal element contained in the sputtering target of the present invention is mixed.
As a raw material, an In compound powder, a Ga compound powder, a Zn compound powder, or the like can be used. Examples of the In compound include indium oxide and indium hydroxide. Examples of the Ga compound include gallium oxide and gallium hydroxide. Examples of the Zn compound include zinc oxide and zinc hydroxide. As each compound, it is preferable to apply an oxide from the viewpoint of easiness of sintering, residual byproducts, and the like.

When using oxides, the surface area of the indium oxide and gallium (BET surface area) are each usually 3~18m ² / g, and preferably 7~16m ² / a, more preferably 7~15m ² / g. The surface area of the zinc oxide (BET surface area) is usually 3~18m ² / g, preferably from 3 to 10 m ² /, more preferably 4~10m ² / g. When the specific surface area is 3 m ² / g or more, aggregates of the respective elements grow in the sintered body, the crystal form of the raw material powder remains, an unexpected crystal form is generated, and the properties change. The problem can be prevented. When the specific surface area is 18 m ² / g or less, problems such as generation of unexpected crystal phases and changes in properties, poor dispersion, appearance defects, and uneven characteristics can be prevented.

  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 is hardly lowered, and impurities can be prevented from entering the liquid crystal and baking.

(2) Molding process In the molding process, it is molded into a shape suitable as a target. Examples of the molding process include press molding (uniaxial molding), mold molding, casting molding, injection molding, and the like. In order to obtain a target having a high sintered density, cold isostatic pressing (CIP) or the like. It is preferable to mold with.
In the case of simple press molding (uniaxial press), uneven pressure is generated, and there is a risk of unexpected generation of crystal types and deformation of crystals.
Moreover, after press molding (uniaxial press), cold isostatic pressure (CIP), hot isostatic pressure (HIP), etc. may be performed and the molding process of two or more steps may be provided.

When using CIP (cold hydrostatic pressure or hydrostatic pressure press), the surface pressure is preferably maintained for 0.5 to 60 minutes at a surface pressure of 800 to 4000 kgf / cm ² , and 2 to ² at a surface pressure of 2000 to 3000 kgf / cm ² . It is more preferable to hold for 30 minutes. Within this range, it is expected that the compositional unevenness in the molded body will be reduced and uniformized.

Further, if the surface pressure is 800 kgf / cm ² or more, the density after sintering is likely to increase, and the resistance is difficult to increase. When the surface pressure is 4000 kgf / cm ² or less, the apparatus does not become too large and is economical. If the holding time is 0.5 minutes or more, the density after sintering tends to increase. If it is 60 minutes or less, it is economical without taking too much time.
In the molding process, molding aids such as polyvinyl alcohol, methylcellulose, polywax, and oleic acid may be used.

(3) Firing step The firing step is a step of firing the molded body obtained in the molding step. Firing can be performed by hot isostatic pressure (HIP) firing or the like.
As baking conditions, it is 1100-1600 degreeC normally, Preferably it is 1300-1500 degreeC, More preferably, it is 1400-1450 degreeC, Usually 30 minutes-360 hours, Preferably it is 1-180 hours, More preferably, it bakes for 12 to 96 hours. . When the firing temperature is 1100 ° C. or higher, the density of the target increases, and it does not take too much time for sintering. Moreover, if it is 1600 degrees C or less, a composition shift by vaporization of a component will not generate | occur | produce and a furnace will not be damaged.
If the burning time is 30 minutes or more, the density of the target is increased, and if it is 360 hours or less, the high cost due to the manufacturing time can be suppressed and there is a possibility of practical use.

Firing is usually performed in a normal pressure atmosphere containing oxygen, such as an air atmosphere, or a method of forming an atmosphere having an oxygen concentration of 50% by volume or more, preferably 80% by volume or more. The method is preferred. These atmospheric conditions can be appropriately selected depending on the properties of the target to be obtained, but it is preferable to carry out in an oxygen stream for the purpose of suppressing the transpiration of Zn and the purpose of suppressing the formation of nitrides.
When firing in an atmosphere containing oxygen, oxygen defects are suppressed in the vicinity of the target surface, and the possibility that nitrides are generated is suppressed.

The temperature rising rate during firing is usually 8 ° C./min or less, preferably 4 ° C./min or less, more preferably 2 ° C./min or less. If it is 8 ° C./min or less, cracks are unlikely to occur when the temperature falls.
Moreover, the temperature-fall rate at the time of baking is 4 degrees C / min or less normally, Preferably it is 2 degrees C / min or less. If it is 4 ° C./min or less, cracks are unlikely to occur when the temperature falls.

(4) Polishing Step The oxide sintered body can be processed into a desired shape as necessary.
The processing may be performed to cut the oxide sintered body into a shape suitable for mounting on the sputtering apparatus and to attach a mounting jig such as a backing plate. When the oxide sintered body is used as a sputtering target, the sintered body is ground by, for example, a surface grinder so that the average surface roughness Ra is 5 μm or less. Further, the sputter surface of the sputtering target may be mirror-finished so that the average surface roughness Ra is 1000 mm or less. For this mirror finishing (polishing), known polishing techniques such as mechanical polishing, chemical polishing, and mechanochemical polishing (a combination of mechanical polishing and chemical polishing) can be used. For example, by polishing to # 2000 or more with a fixed abrasive polisher (polishing liquid: water), or lapping with loose abrasive lapping (abrasive: SiC paste, etc.) and then lapping the abrasive instead of diamond paste Can be obtained. Such a polishing method is not particularly limited.

It is preferable to clean the target after polishing. For the cleaning treatment, air blow or running water cleaning can be used. When removing foreign matter by air blow, it is possible to remove the foreign matter more effectively by suctioning with a dust collector from the opposite side of the nozzle. In addition, since the above air blow and running water cleaning have a limit, ultrasonic cleaning etc. can also be performed. This ultrasonic cleaning is effective by performing multiple oscillations at a frequency of 25 to 300 KHz. For example, it is preferable to perform ultrasonic cleaning by causing multiple oscillations of 12 types of frequencies at intervals of 25 KHz between frequencies of 25 to 300 KHz.
The obtained sputtering target is bonded to a backing plate. The thickness of the target is usually 2 to 20 mm, preferably 3 to 12 mm, particularly preferably 4 to 10 mm. Further, a plurality of targets may be attached to one backing plate to substantially serve as one target.

An oxide thin film can be formed by sputtering an object such as a substrate using the target of the present invention.
The oxide thin film can be used for a transparent electrode, a semiconductor layer of a thin film transistor, an oxide thin film layer, and the like. Among these, it can be suitably used as a semiconductor layer (channel layer) of a thin film transistor.

  If the thin-film transistor of this invention has said oxide thin film, the element structure will not be specifically limited, Various well-known element structures are employable. The thin film transistor of the present invention preferably has the above oxide thin film as a channel layer.

  The film thickness of the channel layer in the thin film transistor of the present invention is usually 10 to 300 nm, preferably 20 to 250 nm, more preferably 30 to 200 nm, still more preferably 35 to 120 nm, and particularly preferably 40 to 80 nm. When the film thickness of the channel layer is 10 nm or more, the film thickness is uniform even when the film is formed in a large area, and the characteristics of the manufactured TFT are easily made uniform in the plane. On the other hand, when the film thickness is 300 nm or less, the film formation time is appropriate and industrially preferable.

  The channel layer in the thin film transistor of the present invention is usually used in an N-type region, but a PN junction transistor or the like in combination with various P-type semiconductors such as a P-type Si-based semiconductor, a P-type oxide semiconductor, and a P-type organic semiconductor. It can be used for various semiconductor devices.

The thin film transistor of the present invention preferably includes a protective film on the channel layer. The protective film in the thin film transistor of the present invention preferably contains at least SiN _x . Since SiN _x can form a dense film as compared with SiO ₂ , it has an advantage of a high TFT deterioration suppressing effect.

In addition to SiN _x , the protective film may be, for example, SiO ₂ , 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, It may contain oxides such as Sc ₂ O ₃ , Y ₂ O ₃ , HfO ₂ , CaHfO ₃ , PbTi ₃ , BaTa ₂ O ₆ , Sm ₂ O ₃ , SrTiO _3, or AlN, but substantially SiN _x. It is preferable that it consists only of. Here, “consisting essentially of SiN _x ” means that 70 wt% or more, preferably 80 wt% or more, more preferably 85 wt% or more of the thin film constituting the protective layer in the thin film transistor of the present invention is SiN _x. Means.

Before forming the protective film, the channel layer is preferably subjected to ozone treatment, oxygen plasma treatment, nitrogen dioxide plasma treatment, or nitrous oxide plasma treatment. Such treatment may be performed at any timing after the channel layer is formed and before the protective film is formed, but is preferably performed immediately before the protective film is formed. By performing such pretreatment, generation of oxygen defects in the channel layer can be suppressed.
Further, when hydrogen in the oxide semiconductor film diffuses during driving of the TFT, a threshold voltage shift may occur and the reliability of the TFT may be reduced. By performing ozone treatment, oxygen plasma treatment, or nitrous oxide plasma treatment on the channel layer, the bond of In—OH is stabilized in the crystal structure, and diffusion of hydrogen in the oxide semiconductor film can be suppressed. it can.

  A thin film transistor usually includes a substrate, a gate electrode, a gate insulating layer, an organic semiconductor layer (channel layer), a source electrode, and a drain electrode. The channel layer is as described above, and a known material can be used for the substrate.

The material for forming the gate insulating film in the thin film transistor of the present invention is not particularly limited, and a commonly used material can be arbitrarily selected. 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, A compound such as Sc ₂ O ₃ , Y ₂ O ₃ , HfO ₂ , CaHfO ₃ , PbTi ₃ , BaTa ₂ O ₆ , SrTiO ₃ , Sm ₂ O ₃ , or AlN can be used. Among them, preferred are _{SiO 2, SiN x, Al 2} O 3, Y 2 O 3, HfO 2, CaHfO 3, more preferably _{SiO 2, SiN x, HfO 2} , Al 2 O 3.

The gate insulating film can be formed by, for example, a plasma CVD (Chemical Vapor Deposition) method.
When a gate insulating film is formed by plasma CVD and a channel layer is formed on the gate insulating film, hydrogen in the gate insulating film may diffuse into the channel layer, leading to deterioration in channel layer quality and TFT reliability. is there. In order to prevent deterioration in channel layer quality and TFT reliability, the gate insulating film may be subjected to ozone treatment, oxygen plasma treatment, nitrogen dioxide plasma treatment or nitrous oxide plasma treatment before forming the channel layer. preferable. By performing such pretreatment, it is possible to prevent deterioration of the channel layer film quality and TFT reliability.
Note that the number of oxygen in the oxide does not necessarily match the stoichiometric ratio, and may be, for example, SiO ₂ or SiO _x .

  The gate insulating film may have a structure in which two or more insulating films made of different materials are stacked. The gate insulating film may be crystalline, polycrystalline, or amorphous, but is preferably polycrystalline or amorphous that can be easily manufactured industrially.

There are no particular limitations on the material for forming each of the drain electrode, the source electrode, and the gate electrode in the thin film transistor of the present invention, and a commonly used material can be arbitrarily selected. For example, a transparent electrode such as ITO, IZO, ZnO, or SnO ₂ , a metal electrode such as Al, Ag, Cu, Cr, Ni, Mo, Au, Ti, or Ta, or a metal electrode made of an alloy containing these may be used. it can.

  Each of the drain electrode, the source electrode, and the gate electrode can have a multilayer structure in which two or more different conductive layers are stacked. In particular, since the source / drain electrodes have a strong demand for low-resistance wiring, a good conductor such as Al or Cu may be sandwiched with a metal having excellent adhesion such as Ti or Mo.

  The thin film transistor of the present invention can be applied to various integrated circuits such as a field effect transistor, a logic circuit, a memory circuit, and a differential amplifier circuit. Further, in addition to the field effect transistor, it can be applied to an electrostatic induction transistor, a Schottky barrier transistor, a Schottky diode, and a resistance element.

  As the structure of the thin film transistor of the present invention, known structures such as a bottom gate, a bottom contact, and a top contact can be adopted without limitation.

  In particular, the bottom gate structure is advantageous because high performance can be obtained as compared with thin film transistors of amorphous silicon or ZnO. The bottom gate configuration is preferable because it is easy to reduce the number of masks at the time of manufacturing, and it is easy to reduce the manufacturing cost for uses such as a large display.

  For large-area displays, a channel-etched bottom gate thin film transistor is particularly preferable. A channel-etched bottom gate thin film transistor has a small number of photomasks at the time of a photolithography process, and can produce a display panel at a low cost. Among them, a channel-etched bottom gate structure and a top contact structure thin film transistor are particularly preferable because they have good characteristics such as mobility and are easily industrialized.

  The thin film transistor of the present invention can be suitably used for a display device such as a liquid crystal display or an organic EL display.

  Examples of the sputtering target of the present invention are shown below. The following examples are examples that can be applied in carrying out the present invention, and the present invention is not limited to the examples as long as the object of the present invention is not impaired.

Example 1
(1) Production of oxide sintered body As raw materials, In ₂ O ₃ (purity 4N, manufactured by Asian Physical Materials Company), Ga ₂ O ₃ (purity 4N, manufactured by Asian Physical Materials Company) and ZnO (purity 4N, high purity) Chemical Co., Ltd.) was used and weighed so that the atomic ratio was In: Ga: Zn = 60: 35: 5. The weighed raw materials were mixed and ground in a planetary ball mill with an integrated power of 500 kWhr, and then pulverized by a wet medium stirring mill using 0.5 mmφ zirconia beads as the medium. Next, it was dried and granulated with a spray dryer. The obtained granulated powder was filled in a mold, uniaxially pressed, and further held at a cold isostatic pressure (CIP) at a surface pressure of 2200 kgf / cm ² for 5 minutes, followed by pressure molding to produce a molded body.

Thereafter, the obtained molded body was sintered in an electric furnace. The sintering conditions were as follows.
Temperature increase rate: 2 ° C / min Sintering temperature: 1400 ° C
Sintering time: 5 hours Sintering atmosphere: Oxygen inflow / fall time: 72 hours

(2) Production of sputtering target After sintering, a sintered body having a thickness of 6 mm was ground and polished to a thickness of 5 mm and a diameter of 4 inches. A sintered body for target was cut out from this sintered body. The side of the sintered body was cut with a diamond cutter, and the surface was ground with a surface grinder so that the surface roughness Ra was 0.5 μm or less.
Next, the surface was blown with air, and further, 12 types of frequencies were oscillated in 25 kHz increments between frequencies 25 to 300 kHz and ultrasonically cleaned for 3 minutes to obtain a target material.
Thereafter, the target material was bonded to an oxygen-free copper backing plate with indium solder to obtain a sputtering target. The surface roughness of the target was Ra ≦ 0.5 μm and had a ground surface with no directionality.

(3) Evaluation of sputtering target The following evaluation was performed about the obtained target (sintered body). The results are shown in Table 1.

(A) Ratio of metal elements (composition: atomic ratio)
The analysis was performed using an inductively coupled plasma emission analyzer (ICP-AES, manufactured by Shimadzu Corporation).

(B) Crystal structure, crystal phase strength The sample after polishing the sintered body was determined by performing X-ray diffraction measurement (XRD) under the following conditions. Each peak was identified by powder X-ray diffraction pattern comprehensive analysis software JADE. The observed crystal phase is shown in Table 1.
In addition, when the crystal phase was observed, “◯”, when the peak was observed but a minute peak that was not a main crystal or sub-crystal, “Δ”, and when not observed, “-”. . In addition, when there was a peak that could not be identified in the JCPDS database, “◯” was marked.
In Table 1, I (In ₂ Ga ₂ ZnO ₇ ), I (InGaZnO ₄ ) and I (In ₂ O ₃ ) are counts obtained from the main peak height of each crystal phase.
・ Equipment: Rigaku Corporation Ultimate-III
-X-ray: Cu-Kα ray (wavelength 1.5406mm, monochromatized with graphite monochromator)
・ 2θ-θ reflection method, continuous scan (1.0 ° / min)
・ Sampling interval: 0.02 °
・ Slit DS, SS: 2/3 °, RS: 0.6 mm

(C) Observation of cross section of sintered body The crystal phase in the cross section of the sintered body was observed as follows. That is, after the sintered body was polished, it was appropriately cut, embedded and polished to obtain an observation sample, and this observation sample was observed by SEM in the range of 1000 times, specifically 104 μm × 86 μm, to identify each crystal phase. The area occupied by the cross-sectional crystal phase is measured with the SEM observation image in several fields (10 fields), and the density is calculated by image processing software (manufactured by Innotech Co., Ltd., image processing measurement software). did.

The SEM images used for the observation of Examples 1 to 4 and Comparative Example 2 are shown in FIGS.
In this SEM image, the whitest region has an In ₂ O ₃ bixbite structure, the gray portion is identified as a homologous phase represented by In ₂ Ga ₂ ZnO ₇ , and the darker gray portion is represented by a homologous phase represented by InGaZnO ₄ Identified. This identification was carried out based on the element density by electron beam microanalyzer (EPMA) measurement.
Moreover, the black part in the visual field is a hole, and it was deleted from the calculation of the occupied area without being recognized at the time of image processing. The occupying area per field of view was calculated by clarifying the boundary from the shading in the field of view of the SEM image and calculating the area of the recognized area. Thereafter, the occupied area was similarly measured over the entire visual field, and the average values were taken as S (In ₂ Ga ₂ ZnO ₇ ), S (InGaZnO ₄ ), and S (In ₂ O ₃ ).

(C) Target Characteristics (a) Relative Density From the theoretical density calculated from the density of the raw material powder and the density of the sintered body measured by the Archimedes method, the calculation was performed according to the following formula.
Relative density (%) = (density measured by Archimedes method) ÷ (theoretical density) x 100
(B) Bulk resistivity (specific resistance)
About the target after sintering polishing, it measured based on the four-probe method (JIS R1637) using a resistivity meter (Mitsubishi Chemical Co., Ltd., Loresta), and measured the average value of the measurement values at any 10 locations. Rate.

(C) Nodule The produced target was mounted on a DC sputtering film forming apparatus. In an Ar atmosphere of 0.3 Pa, continuous sputtering was performed at a DC output of 200 W for 100 hours, and nodules generated on the target surface were visually observed.

(D) Abnormal discharge The produced sputtering target is attached to a DC sputtering apparatus, Ar is used as a sputtering gas, and 10 kWhr continuous sputtering is performed at 0.3 Pa and DC output 200 W, and voltage fluctuation during sputtering is a data logger. And the presence or absence of abnormal discharge was confirmed. The presence or absence of abnormal discharge was detected by monitoring voltage fluctuation and detecting abnormal discharge. When the voltage fluctuation generated during the measurement time of 5 minutes was 10% or more of the steady voltage during the sputtering operation, it was regarded as abnormal discharge, and the number of times was measured.

(E) Particles Particles deposited on a non-erosion portion when the produced sputtering target is attached to a DC sputtering apparatus and Ar is used as a sputtering gas at 0.3 Pa and DC output 200 W for 100 hr continuous sputtering. The amount of powder present (the area and thickness of the existing region) was visually compared and judged.

(4) Production of Thin Film Transistor (TFT) A channel stopper type thin film transistor (reverse stagger type thin film transistor) shown in FIG. 6 was produced and evaluated.

As the substrate 10, a glass substrate (Corning 1737) was used. First, 10 nm thick Mo, 80 nm thick Al, and 10 nm thick Mo were laminated in this order on the substrate 10 by electron beam evaporation. A laminated film was formed on the gate electrode 20 by using a photolithography method and a lift-off method.
A 200 nm thick SiO 2 film was formed on the gate electrode 20 and the substrate 10 by the TEOS-CVD method to form the gate insulating layer 30. The gate insulating layer may be formed by sputtering, but is preferably formed by a CVD method such as a TEOS-CVD method or a PECVD method. In the sputtering method, off current may be increased.

Subsequently, a 40 nm-thick semiconductor film 40 (channel layer) was formed by RF sputtering using the target produced in Example 1. A SiO ₂ film was deposited on the semiconductor film 40 as an etching stopper layer 60 (protective film) by sputtering. The protective film may be formed by a CVD method.

The input RF power was 200 W. The atmosphere during film formation was a total pressure of 0.4 Pa, and the gas flow rate ratio at that time was Ar: O ₂ = 92: 8. The substrate temperature was 70 ° C. The deposited oxide semiconductor film and protective film were processed into appropriate sizes by a photolithography method and an etching method.

After the formation of the etching stopper layer 60, Mo having a thickness of 5 nm, Al having a thickness of 50 nm, and Mo having a thickness of 5 nm were laminated in this order, and the source electrode 50 and the drain electrode 52 were formed by photolithography and dry etching. .
After that, heat treatment was performed in the atmosphere at 300 ° C. for 60 minutes to manufacture a transistor with a channel length of 10 μm and a channel width of 100 μm.

(5) Evaluation of TFT The following evaluation was performed about the produced thin-film transistor. The results are shown in Table 2.
(A) Mobility (field effect mobility (μ)), S value and on / off ratio Measurement was performed using a semiconductor parameter analyzer (Keutley 4200) at room temperature in a light-shielded environment.
(B) Threshold voltage (Vth)
From the result of the transfer characteristics, a graph of √Id−Vg was prepared and obtained from the x intercept.
(C) Reliability evaluation The following DC bias stress test was performed. The change in threshold voltage was measured before and after applying DC stress (stress temperature of 80 ° C.) of Vg = 15V and Vd = 15V for 10,000 seconds. The case where the absolute value of the threshold voltage change was less than 0.3 V was evaluated as “◯”, the case of 0.3 to 1.0 V as “Δ”, and the case of exceeding 1.0 V as “X”. The results are shown in Table 2.
It can be seen that the TFT of the present invention has a very small threshold voltage variation and is hardly affected by DC stress, that is, high reliability.

Examples 2-5, Comparative Examples 1-3
A sputtering target and a TFT were manufactured and evaluated in the same manner as in Example 1 except that the raw material atomic ratio (In: Sn: Zn) at the time of preparing the oxide sintered body was changed as shown in Table 1. The results are shown in Tables 1 and 2.

  The sputtering target of this invention can be used for preparation of oxide thin films, such as an oxide semiconductor and a transparent conductive film. The oxide thin film of the present invention can be used for a transparent electrode, a semiconductor layer of a thin film transistor, an oxide thin film layer, and the like.

DESCRIPTION OF SYMBOLS 10 Substrate 20 Gate electrode 30 Gate insulating film 40 Semiconductor film 50 Source electrode 52 Drain electrode 60 Etch stopper

Claims (15)

It includes an oxide containing In element, Ga element and Zn element, and is represented by a homologous phase represented by at least In ₂ Ga ₂ ZnO ₇ as a crystal phase, a homologous phase represented by InGaZnO ₄ , and In ₂ O _3. A sputtering target comprising a sintered body containing a bixbite phase, wherein the strength of each crystal phase obtained by X-ray diffraction measurement satisfies the following formulas (1-1) and (1-2).
I (In ₂ Ga ₂ ZnO ₇ )> I (InGaZnO ₄ ) (1-1)
I (In ₂ Ga ₂ ZnO ₇ )> I (In ₂ O ₃ ) (1-2)
(In the formula, I (X) represents the strength of the crystal phase of X.) The sputtering target according to claim 1, wherein the intensity of the homologous phase represented by In ₂ Ga ₂ ZnO ₇ is 1.2 times or more larger than the intensity of the homologous phase composed of InGaZnO ₄ . The sputtering target according to claim 1 or 2, wherein the strength of the homologous phase represented by the In ₂ Ga ₂ ZnO ₇ is 1.2 times or more larger than the strength of the bixbite phase composed of the In ₂ O ₃ . A bixbite phase containing an oxide containing In element, Ga element and Zn element and having at least a homologous phase represented by In ₂ Ga ₂ ZnO ₇ as a crystalline phase, a homologous phase represented by InGaZnO ₄ , and an In ₂ O ₃ A sputtering target including a sintered body satisfying the following formulas (2-1) and (2-2) in which the cross-sectional area of each crystal phase measured by observation with a scanning electron microscope (SEM) is included.
S (In ₂ Ga ₂ ZnO ₇ )> S (InGaZnO ₄ ) (2-1)
S (In ₂ Ga ₂ ZnO ₇ )> S (In ₂ O ₃ ) (2-2)
(In the formula, S (X) represents the cross-sectional occupation area of the crystal phase of X) The sputtering target according to claim ₄ , wherein a cross-sectional occupation area of a homologous phase represented by the In ₂ Ga ₂ ZnO ₇ is 1.5 times or more larger than a cross-sectional occupation area of a homologous phase composed of the InGaZnO ₄ . The sputtering target according to claim 4 or 5, wherein a cross-sectional occupation area of the homologous phase represented by the In ₂ Ga ₂ ZnO ₇ is 1.5 times or more larger than a cross-sectional occupation area of the bixbite phase represented by In ₂ O ₃ . The sputtering target according to any one of claims 1 to 6, wherein an atomic ratio of the sintered body satisfies the following formulas (3-1) to (3-3).
0.45 <In / (In + Ga + Zn) <0.70 (3-1)
0.20 <Ga / (In + Ga + Zn) <0.45 (3-2)
0 <Zn / (In + Ga + Zn) <0.15 (3-3) The sputtering target according to claim 7, wherein the formula (3-1) is the following formula (3-1 ′).
0.47 <In / (In + Ga + Zn) <0.68 (3-1 ′) The sputtering target according to claim 7 or 8, wherein the formula (3-2) is the following formula (3-2 ').
0.22 <Ga / (In + Ga + Zn) <0.43 (3-2 ′) The said formula (3-3) is following formula (3-3 '), The sputtering target in any one of Claims 7-9.
0.01 <Zn / (In + Ga + Zn) <0.15 (3-3 ′)   The sputtering target according to any one of claims 1 to 10, wherein the sintered body does not contain a spinel structure compound.   The manufacturing method of the sputtering target in any one of Claims 1-11 which sinter the molded object containing the raw material containing In element, Ga element, and Zn element at 1300-1500 degreeC for 1-180 hours.   The manufacturing method of the sputtering target of Claim 12 which sinters a molded object in the atmosphere whose oxygen concentration is 50 volume% or more.   A field effect thin film transistor having, as a channel layer, an oxide thin film produced using the sputtering target according to claim 1.   A display device comprising the field-effect thin film transistor according to claim 14.