JP5403390B2 - Oxides containing indium, gallium and zinc - Google Patents

Description

The present invention relates to an oxide containing an oxide crystal phase containing indium element (In), gallium element (Ga), and zinc element (Zn) and represented by (Ga, In) ₂ O ₃ . In particular, the present invention relates to a sputtering target having a good appearance including the oxide as a main component.

Oxide semiconductor films composed of several metal complex oxides have high mobility and visible light transmission, so liquid crystal display devices, thin film electroluminescence display devices, electrophoretic display devices, powder transfer methods It is used for a wide variety of applications such as switching elements and drive circuit elements for display devices. In particular, an oxide semiconductor film containing indium oxide-zinc oxide has attracted attention from the viewpoint of ease of manufacture, cost, and excellent characteristics. Among these, an oxide containing indium oxide-gallium oxide-zinc oxide or an oxide semiconductor film containing these as a main component has an advantage of higher mobility than an amorphous silicon film. Such an oxide semiconductor is usually manufactured by a sputtering method using a sputtering target made of each oxide, for example, indium oxide-gallium oxide-zinc oxide (Patent Documents 1 and 2).
However, a sputtering target made of indium oxide-gallium oxide-zinc oxide used for forming such an oxide semiconductor film cannot obtain a sufficiently low resistance target. For example, a sputtering target composed of indium oxide-gallium oxide-zinc oxide using a compound of InGaO ₃ (ZnO) _m (a polycrystalline oxide sintered body showing a homologous phase crystal structure) is used for InGaO when sputtering is performed. _The compound represented by ₃ (ZnO) _m abnormally grows to cause abnormal discharge, resulting in a defect in the resulting film (Patent Document 2). Moreover, as a sputtering target consisting of indium oxide-gallium oxide-zinc oxide, A _X B _Y O _{(KaX + KbY ) / 2} (ZnO) _m (1 <m, X ≦ m, 0 <Y ≦ 0.9, A target containing a compound containing zinc oxide as a main component satisfying X + Y = 2) is also known (Patent Document 3). However, this sputtering target has a defect in appearance such as irregularities generated on a target surface called a white spot. Easily generated, slow sputtering rate, sputtered material dust generation (particles), arc discharge (arcing), nodules (lumps formed on the sputtering target surface), relative density and bulk resistance There were problems such as a large variation in quality such as difficulty in uniformly forming a large area.

On the other hand, a sputtering target having an (Ga ₂ , In) ₂ O ₃ phase using an oxide composed of gallium oxide and indium oxide has been studied (Patent Document 3). This sputtering target can obtain an oxide film having high light transmittance in the near ultraviolet region. However, when an oxide consisting of only gallium and indium is used to produce a thin film transistor (TFT) using a sputtering target, there is a disadvantage that the crystallization temperature of the oxide film is lowered and crystallization is facilitated, and the TFT characteristics are low. .

JP-A-8-245220 JP 2007-73312 A Japanese Unexamined Patent Publication No. 2007-210823

A first object of the present invention is to provide a sputtering target having no white spots on the surface.
The second object of the present invention is to provide a target having a high sputtering rate.
The third object of the present invention is that direct current (DC) sputtering is possible when forming a film by sputtering, arcing, particles (dust generation) and nodule generation during sputtering are small, and high density and quality are achieved. It is an object of the present invention to provide a sputtering target that has little variation and can improve mass productivity.
A fourth object of the present invention is to provide an oxide particularly suitable for the sputtering target.
A fifth object of the present invention is to provide a thin film obtained by using the sputtering target, preferably a protective film, and a method for forming a thin film transistor including the film.

As a result of intensive research, the inventors of the present invention have included indium, gallium, and zinc at a specific composition ratio and sintered under specific conditions, thereby producing an oxide exhibiting a (Ga ₂ , In) ₂ O ₃ phase. The inventors have found that it can be produced, and have completed the present invention.

The present invention
[1] An oxide comprising an oxide crystal phase containing indium element (In), gallium element (Ga), and zinc element (Zn) and represented by (Ga, In) ₂ O ₃ .
[2] The oxide according to [1], wherein the oxide crystal phase represented by (Ga, In) ₂ O ₃ is 50% by mass or more with respect to the entire crystal phase contained in the oxide. .
[3] The atomic ratio of each element with respect to the sum of the indium element (In), the gallium element (Ga), and the zinc element (Zn) (In + Ga + Zn) satisfies the relationships of the following formulas (1) to (3): ] Or the oxide according to [2].
0.05 ≦ In / (In + Ga + Zn) ≦ 0.9 (1)
0.05 ≦ Ga / (In + Ga + Zn) ≦ 0.9 (2)
0.05 ≦ Zn / (In + Ga + Zn) ≦ 0.9 (3)
[4] The oxide according to any one of [1] to [3], further including a positive tetravalent or higher-valent metal element (X).
[5] The positive tetravalent or higher metal element (X) is one or more elements selected from tin, zirconium, germanium, cerium, niobium, tantalum, molybdenum, tungsten, and titanium [4] ] About the oxide as described in.
[6] Atoms of the positive tetravalent or higher metal element (X) with respect to the sum (In + Ga + Zn + X) of the indium element (In), gallium element (Ga), zinc element (Zn), and the positive tetravalent or higher metal element (X) It is related with the oxide as described in [4] or [5] whose ratio satisfy | fills the relationship of following formula (4) or (5).
0.0001 ≦ X / (In + Ga + Zn + X) <0.05 (4)
0.05 ≦ X / (In + Ga + Zn + X) ≦ 0.4 (5)
[7] The oxide according to any one of [1] to [6], which has a bulk resistance of 0.1 to 17 mΩcm and a relative density of 80% or more.
[8]
(a) a step of weighing, mixing and grinding indium oxide, gallium oxide and zinc oxide;
(b) mixing the obtained pulverized product with a medium and drying to obtain a mixed powder; and
(c) It is related with the oxide preparation method as described in any one of [1]-[7] including the process of sintering the obtained mixed powder.
[9] The present invention relates to a sputtering target made of the oxide according to any one of [1] to [7].
[10] A method for forming an amorphous oxide thin film by a sputtering method,
(i) a step of performing sputtering at a film formation temperature of 25 to 450 ° C. using the sputtering target according to [9],
And forming the amorphous oxide thin film having an electron carrier concentration of less than 1 × 10 ¹⁸ / cm ³ .
[11] The method according to [10], wherein the amorphous oxide thin film is used as a channel layer of a thin film transistor.

The present invention provides an oxide containing (Ga ₂ , In) ₂ O ₃ phase oxide crystal containing indium, gallium and zinc, and using the oxide as a sputtering target, thereby reducing the bulk resistance value, It is possible to provide a sputtering target with improved fold strength (JIS R1601), improved relative density, and no appearance defects such as white spots.
A sputtering target including an oxide including an indium, gallium, and zinc and including an oxide crystal phase represented by (Ga ₂ , In) ₂ O _{3 according} to the present invention includes a sputtering target made of a conventional InGaZnO ₄ type oxide, Compared with a sputtering target made of an In ₂ Ga ₂ ZnO ₇ type oxide, particles (dust generation) generated at the time of sputtering can be suppressed to a low level, thereby improving the yield of a thin layer transistor (TFT) panel obtained from the sputtering target. Can do. In addition, by using the oxide of the present invention, nodules (lumps) generated on the surface of the sputtering target can be reduced, and the folding strength (JIS R1601) of the sputtering target can be improved. Moreover, since the sputtering target using the oxide of the present invention can achieve a high degree of uniformity, by using the sputtering target, abnormal discharge during sputtering can be suppressed, and as a result, the thin film formed by sputtering can be made uniform. Can be realized.
By using an oxide containing indium, gallium and zinc and containing a (Ga ₂ , In) ₂ O ₃ phase oxide crystal of the present invention, a target suitable for manufacturing an oxide semiconductor or a TFT can be provided.

(1) Oxide The oxide of the present invention includes indium element (In), gallium element (Ga), and zinc element (Zn), and includes an oxide crystal phase represented by (Ga, In) ₂ O _3. . The oxide of the present invention preferably further contains a metal element (X) having a positive tetravalence or higher.
(1-1) Containing Element The oxide of the present invention contains indium element (In), gallium element (Ga), and zinc element (Zn). More preferably, a positive tetravalent or higher metal element (X) is included. Examples of the positive tetravalent or higher metal element (X) include one or more elements selected from tin, zirconium, germanium, cerium, niobium, tantalum, molybdenum, tungsten, and titanium. By adding these metal elements (X) to the oxide of the present invention, the bulk resistance value of the oxide itself can be reduced, and the occurrence of abnormal discharge occurring on the sputtering target when the oxide is sputtered can be suppressed. I can do it.
The oxide thin film obtained from the sputtering target using the oxide of the present invention is an amorphous film, and the added positive tetravalent metal has no doping effect, and a film having a sufficiently reduced electron density is obtained. Can do. Therefore, when the oxide film is used as an oxide semiconductor film, Vth shift due to bias stress is suppressed, and the operation as a semiconductor becomes stable. Here, Vth refers to a voltage when the drain current rises when a gate voltage (drain voltage) is applied. The Vth shift is a change in Vth that occurs when a gate voltage (drain voltage) is applied. If the Vth shift is small, it can be said that the operation as a semiconductor is stable.

The atomic ratio of each element of indium element (In), gallium element (Ga), and zinc element (Zn) preferably satisfies the relationships of the following formulas (1) to (3).
0.05 ≦ In / (In + Ga + Zn) ≦ 0.9 (1)
0.05 ≦ Ga / (In + Ga + Zn) ≦ 0.9 (2)
0.05 ≦ Zn / (In + Ga + Zn) ≦ 0.9 (3)
In the formula, “In”, “Ga”, and “Zn” are the numbers of atoms of indium element (In), gallium element (Ga), and zinc element (Zn), respectively.
If In / (In + Ga + Zn) is larger than 0.05, the carrier mobility of a thin layer transistor (TFT) obtained from the oxide can be improved, and if it is smaller than 0.9, the off-current is high. It is preferable because it never happens.
If Ga / (In + Ga + Zn) is larger than 0.05, the off current does not increase, and if it is smaller than 0.9, the carrier mobility can be improved, which is preferable.
If Zn / (In + Ga + Zn) is larger than 0.05, there is no influence on wet etching, and if it is smaller than 0.9, it is preferable because it does not become chemically unstable.

More preferably
0.25 ≦ In / (In + Ga + Zn) ≦ 0.5 (1)
0.25 ≦ Ga / (In + Ga + Zn) ≦ 0.5 (2)
0.15 ≦ Zn / (In + Ga + Zn) ≦ 0.4 (3)
And particularly preferably,
0.3 ≦ In / (In + Ga + Zn) ≦ 0.5 (1)
0.3 ≦ Ga / (In + Ga + Zn) ≦ 0.5 (2)
0.15 ≦ Zn / (In + Ga + Zn) ≦ 0.25 (3)
It is. Within the above range, (Ga, In) ₂ O ₃ is formed.

In the case where the oxide of the present invention contains a metal element (X) having a positive tetravalence or more, the sum of indium element (In), gallium element (Ga), zinc element (Zn), and metal element (X) having a positive tetravalence or more ( It is preferable that the atomic ratio of the positive tetravalent or higher metal element (X) to In + Ga + Zn + X) satisfies the relationship of the following formula (4) or (5).
0.0001 ≦ X / (In + Ga + Zn + X) <0.05 (4)
0.05 ≦ X / (In + Ga + Zn + X) ≦ 0.4 (5)
Note that in the formula, “In”, “Ga”, “Zn”, and “X” represent indium element (In), gallium element (Ga), zinc element (Zn), and a metal element (X ) Number of atoms.
Here, in Formula (4), 0.0001 ≦ X / (In + Ga + Zn + X) <0.05 is preferable, and 0.0003 ≦ X / (In + Ga + Zn + X) ≦ 0.02 is particularly preferable. If it is 0.0001 or more, the effect of the addition of the metal element (X) having a positive tetravalence or more can be sufficiently exerted, and the production of (Ga, In) ₂ O ₃ is not affected. On the other hand, if it is smaller than 0.05, the decrease in mobility and the increase in S value due to scattering of the metal element (X) are preferable.
Here, the S value (Swing Factor) is a value indicating the steepness of the drain current that rapidly rises from the off state to the on state when the gate voltage is increased from the off state. As defined by the following equation, an increment of the gate voltage when the drain current increases by one digit (10 times) is defined as an S value.
S value = dVg / dlog (Ids)
The smaller the S value, the sharper the rise ("All about Thin Film Transistor Technology", Ikuhiro Ukai, 2007, Industrial Research Committee). When the S value is large, it is necessary to apply a high gate voltage when switching from on to off, and power consumption may increase.
The S value is preferably 0.8 V / dec or less, more preferably 0.3 V / dec or less, further preferably 0.25 V / dec or less, and particularly preferably 0.2 V / dec or less. If it is greater than 0.8 V / dec, the drive voltage may increase and power consumption may increase. In particular, when used in an organic EL display, it is preferable to set the S value to 0.3 V / dec or less because of direct current drive because power consumption can be greatly reduced.

Moreover, Formula (5) is
0.05 ≦ X / (In + Ga + Zn + X) ≦ 0.4 is preferable, and 0.07 ≦ X / (In + Ga + Zn + X) ≦ 0.2 is particularly preferable.
If it is 0.05 or more, it is preferable because the chemical resistance of the thin film can be improved when a thin film is produced as a sputtering target. If it is 0.4 or less, the bulk resistance does not increase, the relative density of the sputtering target does not decrease, and the bending strength of the sputtering target can be maintained, and (Ga, In) ₂ This is preferable because it does not affect the generation of O ₃ .
Here, the reason is not necessarily elucidated, but within the range of the above formula (4), the positive tetravalent or higher-valent metal element X is substituted into indium oxide to generate a carrier, and (Ga, In) ₂ It is considered that the O ₃ structure is easily generated and the crystal is strengthened. In addition, within the range of the above formula (5), a positive tetravalent or higher-valent metal element (X) existing between crystal lattices changes the crystallization temperature of (Ga, In) ₂ O ₃ , and (Ga, In) _This is thought to facilitate the generation of the ₂ O ₃ structure.
Further, the reason why it is a requirement to satisfy either one of the formulas (4) and (5), instead of setting one range combining the formulas (4) and (5) as a preferable range is effect valence more metal elements (X) is, (4) in the range of working as an effect of lowering the (Ga, an in) ₂ O ₃ itself resistance, range in (Ga, an in) of ₂ O ₃ (5) This is because it is considered to work to promote the generation itself.

(1-2) oxides of structure present invention the crystalline phase has a (Ga, In) ₂ O ₃ oxide crystal phase represented ((Ga, In) ₂ O ₃ -type structure). The fact that the oxide of the present invention includes an oxide crystal phase represented by (Ga, In) ₂ O ₃ indicates that the X-ray diffraction pattern of the oxide of the present invention is known (Ga, In) ₂ O ₃ . This can be judged from the coincidence with the X-ray diffraction pattern (JCPDS card No. 14-0564) of the oxide crystal phase represented. Although the exact structure of the oxide crystal phase represented by (Ga, In) ₂ O ₃ is not known, it has a structure similar to kappa alumina, β-Ga ₂ O ₃ type structure, bixbite type The structure is different from the corundum structure.
In addition to the indium element (In) and the gallium element (Ga), the oxide of the present invention includes a zinc element (Zn) and optionally a metal element (X) having a positive tetravalent or higher value. It is not known how these zinc element (Zn) and optionally a metal element (X) having a positive tetravalence or more exist in the oxide crystal phase represented by (Ga, In) ₂ O _3. However, as described above, when the metal element (X) satisfies the formula (4), it exists between the crystal lattices of (Ga, In) ₂ O ₃ , and the metal element (X) represents the formula (5). When satisfy | filling, it is thought that at least one part has substituted Ga or In.
Moreover, the average particle diameter measured by the X-ray microanalyzer (EPMA) of the crystal of (Ga, In) ₂ O ₃ is 40 μm or less, preferably 30 μm or less, more preferably 10 to 0.1 μm. Is appropriate. Here, the average particle diameter is preferably the average particle diameter of the maximum particle diameter measured by an X-ray microanalyzer (EPMA). The maximum particle size is, for example, obtained by embedding the obtained sintered body in a resin and polishing the surface with alumina particles having a particle size of 0.05 μm, and then XX-ray microanalyzer (EPMA) JXA-8621MX (Japan) The maximum diameter of (Ga, In) ₂ O ₃ crystal particles observed in a 50 μm × 50 μm square frame on the surface of the sintered body magnified by 5,000 times is measured at five locations. The average of the maximum value of the maximum diameter at each location (the maximum diameter of the largest particle at each location) is taken as the average particle size of the maximum particle size. Here, the diameter of the circumscribed circle (the longest diameter of the particles) is the maximum diameter.

Usually, during sintering of an oxide, depending on the content ratio of components contained in the oxide and the sintering conditions, a gallium oxide phase having a β-Ga ₂ O ₃ type structure (β-Ga ₂ O ₃ phase), β -Ga ₂ O ₃ -type structure gallium indium oxide phase (β-GaInO ₃ phase), (Ga ₂ , In) ₂ O ₃ -type structure (Ga ₂ , In) ₂ O ₃ phase, bixbite-type structure oxidation It is known to form an indium phase (In ₂ O ₃ phase). However, an oxide having a β-Ga ₂ O ₃ type structure has a high bulk resistance, and this oxide is not suitable as a sputtering target. In addition, oxides with a bixbite type structure tend to form nodules, and perform sputtering continuously for a long time due to abnormal phenomena such as abnormal discharge and generation of particles (dust generation). Is difficult. Therefore, it is preferable that the oxide of the present invention does not have these structures. In particular, in the sputtering target containing the oxide of the present invention, at least the β-Ga ₂ O ₃ type crystal phase is 10% by mass or less, preferably 5% by mass or less, with respect to the entire crystal phase contained in the sputtering target. It is appropriate to be.

(1-3) Ratio of Crystal Phase The oxide of the present invention contains an oxide crystal phase represented by (Ga, In) ₂ O ₃ as a main component. Specifically, the oxide of the present invention has an oxide crystal phase represented by (Ga, In) ₂ O ₃ with respect to the entire crystal phase contained in the oxide of the present invention, and a peak intensity ratio of 50% or more. It is preferable to contain 70% or more, more preferably 90% or more. Here, the content of the specific oxide crystal phase in the oxide can be obtained by analysis by X-ray diffraction. Specifically, the peak intensity of each crystal phase is measured by X-ray diffraction to determine the peak intensity ratio. For example, the oxide is subjected to X-ray analysis using an X-ray analyzer of Rigaku Corporation, model number Ultimatema-III. The peak intensity is obtained assuming that the peak at 2θ≈33 ° is the peak of the oxide crystal phase (Ga, In) ₂ O ₃ phase of the present invention. Then, the maximum one (Ga, an In) those which show the greatest strength in JCPDS card of identified peaks in addition ₂ O ₃ phase (Ga, an In) in the peak intensity of the other ₂ O ₃ phase. From the following formula (A), the peak intensity ratio of the oxide crystal phase of the present invention ((Ga, In) ₂ O ₃ phase) to the entire crystal phase contained in the oxide of the present invention can be determined.

(A) X-ray diffraction peak intensity ratio (%) = [peak intensity of (Ga, In) ₂ O ₃ phase] /
{[Peak intensity of the highest peak intensity other than [Ga, In) ₂ O ₃ phase] + [peak intensity of (Ga, In) ₂ O ₃ phase]} × 100

(1-4) Physical properties of oxides
(a) Size of pinhole The surface of the oxide of the present invention preferably has no pinhole. Pinholes are voids formed between the powders when the oxide powder is sintered to produce the oxide of the present invention. The presence or absence of pinholes can be evaluated using the horizontal ferret diameter. Here, the horizontal ferret diameter refers to an interval between two parallel lines in a certain direction sandwiching a particle when the pinhole is regarded as a particle. The horizontal ferret diameter can be measured, for example, by observation with an SEM image. Here, the horizontal ferret diameter of the surface of the oxide of the present invention is such that the number of pinholes having a ferret diameter of 2 μm or more per unit area (1 mm × 1 mm) is 50 / mm ² or less. Preferably, it is 20 pieces / mm ² or less, more preferably 5 pieces / mm ² or less. If the number of pinholes with the ferret diameter of 2 μm or more is 50 / mm ² or less, when the oxide of the present invention is used as a sputtering target, abnormal discharge does not occur during sputtering, and the smoothness of the resulting sputtered film It is also preferable because it can be improved.

(b) Bulk resistance The bulk resistance of the oxide of the present invention is measured according to, for example, JISR1637. The value of the bulk resistance is, for example, 0.1 to 17 mΩcm, preferably 0.2 to 10 mΩcm, and more preferably Ωcm 0.3 to 5 mΩcm. If the bulk resistance is 0.1 mΩcm or more, abnormal discharge does not occur between the particles of the sputtering material existing at the time of sputtering, which is preferable. Moreover, if it is 17 mΩcm or less, even if the oxide of the present invention is used as a sputtering target, the target is not cracked, discharge becomes unstable, and particles are not increased.
Further, it is appropriate that the range of variation in bulk resistance in the oxide is within 3%, preferably within 1%. Here, the variation is a value indicated by the size of the standard deviation with respect to the average value of the bulk resistance. The bulk resistance is obtained, for example, by measuring 50 or more oxide surfaces at equal intervals by a four-probe method using Loresta (manufactured by Mitsubishi Chemical Corporation).
(c) Relative density The relative density of the oxide of the present invention is, for example, 75% or more, usually 80% or more, preferably 90% or more, more preferably 95% or more, and particularly preferably 99% or more. is there. If it is 75% or more, even if the oxide of the present invention is used as a sputtering target, the target is not cracked and abnormal discharge does not occur. Here, the relative density is a density calculated relative to the theoretical density calculated from the weighted average. The density calculated from the weighted average of the density of each raw material powder is the theoretical density, which is defined as 100%.
Further, it is appropriate that the range of variation in relative density in the oxide is within 3%, preferably within 1%. Here, the variation is a value indicated by the standard deviation with respect to the average value, and 20 or more pieces of oxide are cut out and the density is measured to obtain the average and standard deviation.

(d) Variation of positive elements The oxide of the present invention has a variation range of positive metal elements other than zinc contained in the oxide within 0.5%, preferably within 0.1%. Is preferably suitable. Here, the variation means the size of the standard deviation with respect to the average value. For this variation, 20 or more pieces of oxide are cut out, the content of each positive metal element other than zinc is measured by ICP or the like, and the average and standard deviation are obtained.

(1-5) Method for Producing Oxide The oxide of the present invention is suitably produced by the following method.
(a) a step of weighing, mixing, and pulverizing oxides of indium oxide, gallium oxide, zinc oxide, and any metal element (X) having a positive tetravalence or higher;
(b) mixing the obtained pulverized product with a medium and drying to obtain a mixed powder; and
(c) A step of sintering the obtained mixed powder.

Step (a)
The raw materials, that is, indium oxide, gallium oxide, zinc oxide, and an oxide of any positive tetravalent or higher metal element (X) are in an atomic ratio of indium: gallium: zinc: metal element (X) of 5 to 90: 5. It is weighed so that it will be -90: 5-90, Preferably, it will be 20-60: 10-60: 10-60.
The above raw materials are mixed and pulverized by known mixing and pulverizing means. The purity of each raw material is usually 99.9% (3N) or higher, preferably 99.99% (4N) or higher, more preferably 99.995% or higher, and particularly preferably 99.999% (5N) or higher. If the purity of each raw material is 99.9% (3N) or more, the semiconductor characteristics are not deteriorated by impurities, and the reliability can be sufficiently maintained. In particular, when the Na content is less than 100 ppm, reliability is improved when a thin film transistor is manufactured, which is preferable.
For the raw material, indium oxide powder having a specific surface area of 3~16m ² / g, gallium oxide powder, wherein zinc powder or a composite oxide powder, mixed powder specific surface area of the entire powder is 3~16m ² / g Is preferably used as a raw material. In addition, it is preferable to use the powder whose specific surface area of each oxide powder is substantially the same. Thereby, it can pulverize and mix more efficiently. Specifically, the ratio of the specific surface area is preferably 1/4 to 4 times or less, particularly preferably 1/2 to 2 times or less.

The mixed powder is mixed and ground using, for example, a wet medium stirring mill. At this time, the specific surface area after pulverization is increased by 1.0 to 3.0 m ² / g from the specific surface area of the raw material mixed powder, or is pulverized so that the average median diameter after pulverization is 0.6 to 1 μm. It is preferable to do. By using the raw material powder thus adjusted, a high-density oxide sintered body can be obtained without requiring a calcination step at all. Moreover, a reduction process is also unnecessary.
In addition, it is preferable that the increase in the specific surface area of the raw material mixed powder is 1.0 m ² / g or more, or the average median diameter of the raw material mixed powder after pulverization is 1 μm or less, because the sintered density becomes sufficiently large. On the other hand, if the increase in the specific surface area of the raw material mixed powder is 3.0 m ² / g or less or the average median diameter after pulverization is 0.6 μm or more, contamination (impurity contamination) from the pulverizer during pulverization Is preferable because it does not increase.
Here, the specific surface area of each powder is a value measured by the BET method. The median diameter of the particle size distribution of each powder is a value measured with a particle size distribution meter. These values can be adjusted by pulverizing the powder by a dry pulverization method, a wet pulverization method or the like.
The median diameter (d50) of these raw material powders is, for example, 0.5 to 20 μm, preferably 1 to 10 μm. If the median diameter (d50) of the raw material powder is 0.5 μm or more, pinholes (vacuum) can be formed in the sintered body and the sintering density can be prevented from decreasing. This is preferable because an increase in the particle size in the aggregate can be prevented.

(a) 'Calcination process
A step of calcining the mixture obtained in the step (a) may be included between the steps (a) and (b). The calcination step is a step of calcination of the mixture obtained in step (a) to sufficiently oxidize lower oxides and non-oxidized components. In the calcination step, the metal oxide mixture is preferably heat-treated at 500 to 1200 ° C. for 1 to 100 hours. If the heat treatment conditions are 500 ° C. or higher or 1 hour or longer, the indium compound, the zinc compound, and the tin compound are sufficiently thermally decomposed. On the other hand, the case of 1200 ° C. or less or 100 hours or less is preferable because the particles are not coarsened.
Therefore, it is particularly preferable to perform heat treatment (calcination) in the temperature range of 800 to 1200 ° C. for 2 to 50 hours.

Step (b) The pulverized product obtained in step (a) is mixed with a medium. A commercially available apparatus such as a bead mill, a ball mill, a roll mill, a planetary mill, or a jet mill can be used as the wet medium stirring mill. When a bead mill is used, the pulverizing medium (beads) is preferably zirconia, alumina, quartz, silicon nitride, stainless steel, mullite, glass beads, SiC or the like, and the particle size is preferably 0.1 to 2 mm. Particularly preferred is a solid particle zirconia bead. By mixing with the medium, the specific surface area of the obtained mixed powder can be increased by, for example, 0.5 to ⁴ m ² / g, preferably 1 to ³ m ² / g, compared with that before mixing with the medium. The reason why the specific surface area is increased by using the medium is to improve the density of the sintered body.
When solid particles are used as the medium, the median diameter (d50) of the particles is, for example, preferably 0.5 to 3 μm, preferably 1 to 2 μm, more preferably 1 μm. The medium is suitably 0.5 to 30 parts by mass, preferably 1 to 20 parts by mass when the total mass of the raw material powder is 100 parts by mass.
The obtained mixture is dried with a spray dryer or the like to obtain a mixed powder.

Step (c)
The mixed powder obtained in step (b) is sintered.
For the sintering, a known sintering method can be used. For example, it is appropriate to sinter using an electric furnace or the like. Sintering may be performed, for example, in the presence of air, preferably in an oxygen atmosphere, and more preferably in an oxygen atmosphere by circulating oxygen. More preferably, sintering is performed under pressure. Thereby, transpiration of zinc can be suppressed, and a sintered body free from voids (voids) can be obtained. Since the sintered body manufactured in this manner has a high density and generates less nodules and particles during use, an oxide semiconductor film having excellent film characteristics can be manufactured. The surface temperature of the mixed powder to be sintered is 400 to 3000 ° C., preferably 600 to 1800 ° C., more preferably 1000 to 1600 ° C. for 1 to 96 hours, preferably 2 to 24 hours. .
In addition, the mixed powder may be arbitrarily shaped before sintering to have a desired sputtering target shape. For the molding, a known molding method such as pressure molding, a cold press method or a hot press method can be used, but pressure molding is preferable. For example, the obtained mixed powder is filled in a mold and pressure-molded with a cold press machine. The pressure molding is performed at a pressure of 100 to 100,000 kg / cm ² , preferably 500 to 10,000 kg / cm ² , for example, at normal temperature (25 ° C.). Further, in the temperature profile, it is preferable that the temperature increase rate up to 1000 ° C. is 30 ° C./hour or more, and the temperature decrease rate during cooling is 30 ° C./hour or more. If the temperature rising rate is 30 ° C./hour or more, the decomposition of the oxide does not proceed and no pinholes are generated. Further, if the cooling rate during cooling is 30 ° C./hour or more, the composition ratio of In and Ga does not change.

The cold press method and the hot press method will be described in detail. In the cold press method, the mixed powder is filled in a mold to produce a molded body and sintered. In the hot press method, the mixed powder is directly sintered in a mold.
As a dry-type cold press method, the raw material after the pulverization step is dried with a spray dryer or the like and then molded. For the molding, known methods such as pressure molding, cold isostatic pressing, mold molding, and cast molding injection molding can be employed. In order to obtain a sintered body (sputtering target) having a high sintered density, it is preferable to form by a method involving pressurization such as cold isostatic pressure (CIP). In the molding process, molding aids such as polyvinyl alcohol, methylcellulose, polywax, and oleic acid may be used.
As the wet method, for example, it is preferable to use a filtration molding method (see JP-A-11-286002). This filtration molding method is a filtration molding die made of a water-insoluble material for obtaining a molded body by draining water from a ceramic raw material slurry under reduced pressure, and a lower molding die having one or more drain holes And a water-permeable filter placed on the molding lower mold, and a molding mold clamped from the upper surface side through a sealing material for sealing the filter, the molding lower mold, Forming mold, sealing material, and filter are assembled so that they can be disassembled respectively. Using a filtration mold that drains water in the slurry under reduced pressure only from the filter surface side, mixed powder, ion-exchanged water and organic A slurry made of an additive was prepared, this slurry was poured into a filtration mold, and the molded body was produced by draining the water in the slurry under reduced pressure only from the filter surface side. After drying degreasing, and firing.

  In order to make the bulk resistance of the sintered body obtained by a dry method or a wet method uniform as a whole oxide, a reduction step is preferably further included. Examples of the reduction method that can be applied include a method using a reducing gas, vacuum firing, or reduction using an inert gas. In the case of reduction treatment with a reducing gas, hydrogen, methane, carbon monoxide, a mixed gas of these gases and oxygen, or the like can be used. In the case of reduction treatment by firing in an inert gas, nitrogen, argon, a mixed gas of these gases and oxygen, or the like can be used. In addition, the temperature in a reduction process is 300-1200 degreeC normally, Preferably it is 500-800 degreeC. The reduction treatment time is usually 0.01 to 10 hours, preferably 0.05 to 5 hours.

The obtained oxide is appropriately processed.
The processing step is to cut the sintered body obtained by sintering as described above into a shape suitable for mounting on a sputtering apparatus, and to attach a mounting jig such as a backing plate, It is a process provided as needed. Since the thickness of the sputtering target is usually 2 to 20 mm, preferably 3 to 12 mm, particularly preferably 4 to 6 mm, it is appropriate that the oxide of the present invention is also processed to the thickness. Alternatively, a plurality of oxides may be attached to one backing plate (support) to form a substantially single sputtering target. The surface is preferably finished with a diamond grindstone of No. 200 to 10,000, and particularly preferably finished with a diamond grindstone of No. 400 to 5,000. Use of a diamond grindstone of No. 200 to No. 10,000 is preferable because the oxide does not break.

  After the oxide is processed into the shape of the sputtering target, it is bonded to a backing plate (support) to obtain a sputtering target that can be used by being attached to a film forming apparatus. The backing plate is preferably made of oxygen-free copper. It is preferable to use indium solder for bonding.

(2) Sputtering target The sputtering target of this invention consists of an oxide of this invention. Here, the sputtering target is an oxide lump used for sputtering film formation, and as described above, a backing plate (support) such as oxygen-free copper can be attached to the sputtering target. It is common.
The sputtering target of the present invention is preferably a sintered body of the oxide of the present invention prepared by the above-described oxide preparation method. By using such an oxide sintered body, it is usually necessary to increase the density of the sintered body and improve the uniformity. Firing below) can be omitted.

  In order to obtain the sputtering target of the present invention from the oxide of the present invention, the oxide of the present invention is ground with, for example, a surface grinder so that the average surface roughness (Ra) is 0.5 μm or less, and further the sputtering target. It is preferable that the surface to be sputtered is mirror-finished so that the average surface roughness (Ra) is 100 nm 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. More specifically, polishing is performed with a fixed abrasive polisher (polishing liquid: water) to # 2000 mesh (inch standard) or more, or lapping with loose abrasive lapping (abrasive: SiC paste, etc.) and then abrasive. Can be polished by lapping instead of diamond paste. Such a polishing method is not particularly limited.

  Next, the oxide polished as described above is cleaned. For the cleaning process, 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 multiplying twelve types of frequencies at 25 KHz intervals between frequencies of 25 to 300 KHz.

(a) Surface Roughness The surface roughness (Ra) of the sputtering target of the present invention is suitably Ra ≦ 0.5 μm, preferably Ra ≦ 0.3 μm, and more preferably Ra ≦ 100 nm. It is preferable that the polished surface has no directivity because generation of abnormal discharge and generation of particles can be suppressed. A surface roughness (Ra) of 0.5 μm or less is preferable because abnormal discharge during sputtering can be suppressed and generation of particles (particles) of the sputtered material can be suppressed. Here, the surface roughness means the centerline average roughness.
(b) bending strength of the sputtering target of the bending strength present invention, for example, 4 kg / mm ² or more preferably, 6 kg / mm ² or more, more preferably, 8 kg / mm ² or more is particularly preferable. Here, the bending strength is also called bending strength, and is evaluated based on JIS R1601 using a bending tester. When the bending strength is 4 kg / mm ² or more, the sputtering target is not cracked during sputtering, and when the backing plate as a support for the sputtering target is bonded to the sputtering target or when the sputtering target is transported, There is no fear that the sputtering target is broken, which is preferable.

(3) Method for forming thin film An amorphous oxide thin film can be formed on a substrate by sputtering using the sputtering target of the present invention. In particular,
(i) a step of performing sputtering at a film forming temperature of 25 to 450 ° C. using the sputtering target of the present invention; and
(ii) forming an amorphous oxide thin film having an electron carrier concentration of less than 1 × 10 ¹⁸ / cm ³ ;
including.
Examples of the sputtering method include DC (direct current) sputtering, AC (alternating current) sputtering, RF (radio frequency) sputtering, magnetron sputtering, ion beam sputtering, ECR sputtering, and counter target sputtering. A (direct current) sputtering method and an RF (high frequency) sputtering method are preferably used.
The film formation temperature during sputtering varies depending on the sputtering method, but is suitably 25 to 450 ° C., preferably 30 to 250 ° C., more preferably 35 to 150 ° C., for example. Here, the film formation temperature is the temperature of the substrate on which the thin film is formed.
The pressure in the sputtering chamber during sputtering varies depending on the sputtering method. For example, in the case of the DC (direct current) sputtering method, the pressure is 0.1 to 2.0 MPa, preferably 0.3 to 0.8 MPa. In the case of the (high frequency) sputtering method, it is 0.1 to 2.0 MPa, preferably 0.3 to 0.8 MPa.
The power output input during sputtering varies depending on the sputtering method. For example, in the case of DC (direct current) sputtering method, it is 10 to 1000 W, preferably 100 to 300 W, and in the case of RF (high frequency) sputtering method, It is 10 to 1000 W, preferably 50 to 250 W.
The substrate-target distance (ST distance) during sputtering is usually 150 mm or less, preferably 110 mm, and particularly preferably 80 mm or less. If the ST distance is short, the substrate is exposed to plasma during sputtering, so that a high deposition rate can be expected. Moreover, if it is 150 mm or less, sufficient film-forming speed | velocity can be anticipated.

The power supply frequency in the case of RF (high frequency) sputtering is, for example, 50 Hz to 50 MHz, preferably 10 k to 20 MHz.
The carrier gas at the time of sputtering varies depending on the sputtering method, and examples thereof include oxygen, helium, argon, xenon, and krypton. A mixed gas of argon and oxygen is preferable.
When a mixed gas of argon and oxygen is used, the flow ratio of argon: oxygen is Ar: O ₂ = 100-80: 0-20, preferably 99.5-90: 0.5-10. Is appropriate.

Prior to sputtering, the sputtering target is bonded (bonded) to the support. This is for fixing the sputtering target to the sputtering apparatus.
Sputtering is performed using the bonded sputtering target to obtain an amorphous oxide thin film containing In, Ga and Zn oxides as main components on the substrate. Here, “main component” means containing 60% or more of In, Ga, and Zn in atomic ratio excluding oxygen.
As the substrate, glass, resin (PET, PES, or the like) can be used.
The thickness of the obtained amorphous oxide thin film varies depending on the film formation time and the sputtering method, but is, for example, 5 to 300 nm, preferably 10 to 90 nm.
The electron carrier concentration of the obtained amorphous oxide thin film is, for example, less than 1 × 10 ¹⁸ / cm ³ , and preferably 5 × 10 ¹⁷ to 1 × 10 ¹² / cm ³ .
Furthermore, the relative density of the obtained amorphous oxide thin film is 6.0 g / cm ³ or more, preferably 6.1 to 7.2 g / cm ³ . With such a high density, even in the obtained oxide thin film, the generation of nodules and particles is small, and an oxide thin film having excellent film characteristics can be obtained.

(4) Use of thin film The amorphous oxide thin film thus obtained can be used as it is or as a semiconductor film for a thin film transistor, a solar cell, a gas sensor or the like by heat treatment.
Here, the heat treatment is preferably performed at 100 to 450 ° C., preferably 150 to 350 ° C. for 0.1 to 10 hours, preferably 0.5 to 2 hours, from the viewpoint of stabilizing semiconductor characteristics. is there.
Here, a thin film transistor will be described as an example with reference to FIG.
A substrate (1) such as a glass substrate is prepared, and Ti (adhesion layer) having a thickness of 1 to 100 nm, Au (connection layer) having a thickness of 10 to 300 nm, and a thickness of 1 to 100 nm are formed on the substrate by electron beam evaporation. Ti (adhesion layer) are laminated in this order. A gate electrode (2) is formed on the laminated film by using a photolithography method and a lift-off method.
Further, a SiO ₂ film having a thickness of 50 to 500 nm is formed thereon by a TEOS-CVD method to form a gate insulating film (3). The gate insulating film (3) may be formed by a sputtering method, but a CVD method such as a TEOS-CVD method or a PECVD method is preferable.

Subsequently, an amorphous oxide thin film made of an In—Ga—Zn—O oxide having a thickness of 5 to 300 nm as a channel layer (4) is formed by RF sputtering using the sputtering target made of the oxide of the present invention as a target. Semiconductor) is deposited. The device on which the obtained thin film is deposited is appropriately cut to a desired size and then heat-treated at 100 to 450 ° C. for 6 to 600 minutes under atmospheric pressure. The obtained element was further laminated with Ti (adhesion layer) having a thickness of 1 to 100 nm, Au (connection layer) having a thickness of 10 to 300 nm and Ti (adhesion layer) having a thickness of 1 to 100 nm in this order, A source electrode (5) and a drain electrode (6) are formed by a lithography method and a lift-off method. Further, a SiO ₂ film of 50 to 500 nm is deposited thereon as a protective film (7) by sputtering. The film formation method of the protective film (7) may be a CVD method. Note that the process may be changed, and the production of the protective film (etching stopper) as shown in FIGS. 7A and 7B may be performed prior to the production of the source electrode and the drain electrode.
Examples of the present invention will be described below, but the present invention is not limited to the embodiments of the following examples.

Example 1
Raw material powder as a specific surface area of 6 m ² / g indium oxide powder having a specific surface area of gallium oxide powder and the specific surface area is 6 m ² / g and zinc oxide powder is 5 m ² / g, indium, gallium, zinc atom Weighed to a ratio of 2: 2: 1. The weighed raw material powder was mixed and ground using a wet medium stirring mill. Here, 1 mmφ zirconia beads were used as the medium, and the specific surface area after mixing with the medium was increased by 2 m ² / g from the specific surface area before mixing with the medium. The obtained mixture was further pressure-molded at a pressure of 3000 kg / cm ² using a spray dryer. The pressure-molded body was sintered for 2 hours at a surface temperature of 1500 ° C. in an oxygen atmosphere while flowing pure oxygen. The relative density of the obtained oxide (sintered body) was 98%.
(Examples 2 to 15)
Except for changing the atomic ratio of sintering temperature, indium element (In), gallium element (Ga), zinc element (Zn), and metal element (X) having a positive tetravalence or more as shown in Table 1, Examples In the same manner as in Example 1, an oxide sintered body was prepared.
(Comparative Examples 1-11)
An oxide sintered body was prepared in the same manner as in Example 1 except for the composition ratio and the sintering temperature.

[Evaluation of oxides]
Composition The atomic ratio of elements of indium element (In), gallium element (Ga), zinc element (Zn), and metal element (X) having a positive tetravalence or higher contained in the oxides of Examples and Comparative Examples is determined by the ICP method. It was obtained by calculation from the atomic ratio by composition analysis using.
-Crystal phase The crystal phase of the obtained oxide was confirmed by X-ray diffraction. The measurement conditions for X-ray diffraction are as follows.
・ Device: Ultimate-III manufactured by Rigaku Corporation
-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
As typical X-ray diffraction charts, the X-ray diffraction charts of Example 1, Example 14, and Comparative Examples 1 to 3 are shown in FIGS. In Example 1, the presence of crystals other than the oxide crystals represented by (Ga, In) ₂ O ₃ could not be confirmed, and the peak intensity ratio was 100%. In Example 14, in about 71 percent (Ga, an In) ₂ O ₃ was the main component ((Ga, In) peak intensity of ₂ O ₃ is 2000 cps, other peak intensity 800 cps).

-Bulk resistance The bulk resistance of the oxide of the present invention was measured 20 times by a four probe method using a resistivity meter (Mitsubishi Chemical, Loresta) based on JIS R1637, and the average was obtained.
-Relative density The relative density of the oxide of the present invention was calculated as follows 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.
Relative density = (density measured by Archimedes method) ÷ (theoretical density) x 100 (%)
-Folding strength The bending strength of the oxide of the present invention (ie, sputtering target) was measured based on JISR1601.

-Pinhole The presence or absence of pinholes was evaluated using the horizontal ferret diameter. Specifically, the oxides obtained in Examples and Comparative Examples were pulverized, and the fractured surface was polished to a mirror surface state using a # 2000 sandpaper using a rotary grinder, and the fractured surface was magnified 100 times. An SEM image of is obtained. This SEM image was subjected to binary image processing to identify pinholes, and the number of pinholes having a horizontal ferret diameter of 2 μm or more existing at 1 mm × 1 mm was counted using image processing software (Particle Analysis III: manufactured by AISoft). .
・ Appearance (white spot)
When observed with the naked eye and a white spot can be observed: x, when a white spot can be partially observed: Δ, when a white spot cannot be observed: ○

The evaluation results are summarized in Table 1 and Table 2 below.

As shown in Tables 1 and 2, it can be confirmed that the oxide of the present invention includes an oxide crystal phase represented by (Ga, In) ₂ O ₃ . The X-ray diffraction chart is shown in FIG. Since the crystal type containing Zn could not be confirmed, it was estimated that Zn was dissolved in the (Ga, In) ₂ O ₃ crystal. The average particle diameter of the maximum particle size of the X-ray micro the analyzer (EPMA) is JXA-8621MX Analysis by (manufactured by JEOL Ltd.) (Ga, an In) of ₂ O ₃ crystal can be confirmed that at 20μm or less It was. Here, the maximum particle diameter is embedded in the resin and the surface is polished with alumina particles having a particle diameter of 0.05 μm, and then multiplied by 5,000 times by the X-ray microanalyzer (EPMA). The maximum diameter of (Ga, In) ₂ O ₃ crystal particles observed in a 50 μm × 50 μm square frame on the surface of the expanded sintered body was measured at five locations. The average of the maximum value of the maximum diameter at each location (the maximum diameter of the largest particle at each location) was taken as the average particle size of the maximum particle size. Here, the diameter of the circumscribed circle (the longest diameter of the particles) was taken as the maximum diameter.

[Preparation of amorphous oxide thin film]
Using the oxides of Examples and Comparative Examples, a continuous film formation test by DC sputtering was performed to obtain an amorphous oxide thin film.
The semiconductor film was formed on a glass substrate (Corning 1737) by being mounted on a DC magnetron sputtering film forming apparatus which is one of the DC sputtering methods.
As sputtering conditions here, substrate temperature: 25 ° C., ultimate pressure: 1 × 10 ⁻⁶ Pa, atmospheric gas: Ar 99.5% and oxygen 0.5%, sputtering pressure (total pressure): 2 × 10 ⁻¹ Pa, input power 100 W, film formation time 8 minutes, ST distance 100 mm.

[Evaluation]
-Abnormal discharge (arcing) occurrence frequency The number of abnormal discharges that occurred every 3 hours was measured.
-Particle (dust generation) amount A slide glass was placed in the chamber, and the density of particles of 1 μm or more adhered to the slide glass after continuous film formation for 96 hours was measured using a microscope.
As a result, in order from the smallest number of particles, 1 piece / cm ^{2 or} less: ◎, 10 ² pieces / cm ^{2 or} less: ○, 10 ⁴ pieces / m ^{2 or} less: Δ, more than 10 ⁴ pieces / m ² : x Evaluation was made in 4 stages.
-Nodule generation density The area covered with the nodule was calculated from the photograph of the sputtering target after film formation after continuous film formation for 96 hours, and the generation density was calculated by the following formula.
Nodule generation density = nodule generation area ÷ sputtering target area As a result, in order from the smallest nodule, 10 ^{−4 or} less: ◎, 10 ^{−2 or} less: ○, 10 ^{−1 or} less: Δ, more than 10 ⁻¹ : × Evaluation was made in 4 stages.
-Continuous film-forming stability The ratio (1st batch / 20th batch) of the average field effect mobility of the 1st batch and 20th batch in 20 continuous batches was measured. As a result, the TFT characteristics were evaluated in four stages in order from those with good reproducibility of TFT characteristics: 1.10 or less: 、, 1.20 or less: ○, 1.50 or less: Δ, greater than 1.50: x.
-In-plane uniformity The ratio (maximum value / minimum value) of the maximum value and minimum value of specific resistance in the same plane was measured. As a result, evaluation was made in four stages in order from the one with the better uniformity of specific resistance: within 1.05: 、, within 1.10: ○, within 1.20: Δ, greater than 1.20: ×.

[Preparation of Thin Film Transistor]
The amorphous oxide thin film obtained by sputtering the oxides of Examples and Comparative Examples obtained as described above was used as a channel layer of the thin film transistor, and the thin film transistor (reverse stagger type TFT element, hereinafter referred to as TFT) shown in FIG. May be omitted). Specifically, first, a glass substrate (Corning 1737 manufactured by Corning) was prepared as a substrate. On this substrate, Ti (adhesion layer) having a thickness of 5 nm, Au having a thickness of 50 nm, and Ti having a thickness of 5 nm were laminated in this order by an electron beam evaporation method. A gate electrode was formed on the stacked films by using a photolithography method and a lift-off method. A SiO ₂ film having a thickness of 200 nm was formed on the upper surface of the obtained gate electrode by TEOS-CVD to form a gate insulating film.
Subsequently, an amorphous oxide thin film (In—Ga—Zn—O oxide semiconductor) having a thickness of 30 nm was deposited as a channel layer by RF sputtering using the sintered body as a target. Here, the output of the input RF power source was 200 W. During film formation, the total pressure was 0.4 Pa, and the gas flow rate ratio was Ar: O ₂ = 95: 5. The substrate temperature was 25 ° C.
Using the deposited amorphous oxide thin film, an element having W = 100 μm and L = 20 μm was manufactured by using a photolithography method and an etching method. The obtained element was heat-treated at 300 ° C. for 60 minutes under atmospheric pressure.
After the heat treatment, 5 nm thick Ti, 50 nm thick Au and 5 nm Ti are laminated in this order on each element, and a source electrode and a drain electrode are formed by a photolithography method and a lift-off method, A thin film transistor was obtained. Further, a 200 nm thick SiO ₂ film was deposited as a protective film on the device by sputtering.

[Evaluation]
Using a semiconductor parameter analyzer (Keutley 4200), transmission characteristics and output characteristics were measured in a dry nitrogen atmosphere, at room temperature (25 ° C.), and in a light-shielding environment. A favorable transistor with a mobility of 17 cm / Vs, a threshold voltage (Vth) = 0.6 V, and an on / off ratio of 10 ⁹ was obtained.

In addition, the following points were evaluated about the state of RF sputtering at the time of thin-film transistor manufacture.
-Abnormal discharge (arcing) occurrence frequency The number of abnormal discharges that occurred every 3 hours was measured.
-In-plane uniformity The ratio (maximum value / minimum value) of the maximum value and minimum value of specific resistance in the same plane was measured. As a result, evaluation was made in four stages in order from the one with the better uniformity of specific resistance: within 1.05: 、, within 1.10: ○, within 1.20: Δ, greater than 1.20: ×.
-TFT panel evaluation The yield and uniformity of the obtained TFT were evaluated in four stages: ◎: very good, ◯: good, △: some problematic, ×: problematic.

2 is an X-ray diffraction chart of the oxide of Example 1. FIG. 14 is an X-ray diffraction chart of the oxide of Example 14. FIG. 6 is an X-ray diffraction chart of the oxide of Comparative Example 1. 6 is an X-ray diffraction chart of the oxide of Comparative Example 2. 10 is an X-ray diffraction chart of the oxide of Comparative Example 3. It is the schematic of a thin layer transistor. FIG. 7A is a schematic diagram of a thin layer transistor (source electrode). FIG. 7B is a schematic diagram of a thin layer transistor (drain electrode).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Gate electrode 3 Gate insulating film 4 Channel layer 5 Source electrode 6 Drain electrode 7 Protective film 11 Substrate 12 Gate electrode 13 Gate insulating film 14 Channel layer 15 Source electrode 16 Drain electrode 17 Protective film

Claims (10)

Indium element (In), gallium element (Ga), and zinc element (Zn) to 78 atomic% or more of the total metal elements include, as a main component an oxide crystal phase represented by (Ga, In) ₂ O ₃ The atomic ratio of each element with respect to the sum of (In + Ga + Zn) of indium element (In), gallium element (Ga), and zinc element (Zn) satisfies the relationship of the following formulas (1) to (3): A sputtering target made of an oxide sintered body.
0.05 ≦ In / (In + Ga + Zn) ≦ 0.9 (1)
0.25 ≦ Ga / (In + Ga + Zn) ≦ 0.9 (2)
0.05 ≦ Zn / (In + Ga + Zn) ≦ 0.9 (3) The oxide crystal phase represented by the (Ga, In) ₂ O ₃ is 50% or more in terms of the XRD peak intensity ratio with respect to the entire crystal phase contained in the oxide sintered body. Sputtering target . Indium element (In), gallium element (Ga), and zinc element (Zn), or indium element (In), gallium element (Ga), zinc element (Zn), and positive tetravalent or higher metal element (X) The sputtering target according to claim 1 or 2. (Ga, In) ₂ O _Three Consisting of an oxide crystal phase represented by (Ga, In) ₂ O _Three And an oxide crystal phase represented by ZnGa ₂ O _Four The sputtering target according to claim 1, comprising an oxide crystal phase represented by: Indium element (In), gallium element (Ga), zinc element (Zn) and positive tetravalent or higher metal element (X), the positive tetravalent or higher metal element (X) is tin, zirconium, germanium, cerium, The sputtering target according to claim 1 , wherein the sputtering target is one or more elements selected from niobium, tantalum, molybdenum, tungsten, and titanium. The atomic ratio of the positive tetravalent or higher metal element (X) to the total (In + Ga + Zn + X) of indium element (In), gallium element (Ga), zinc element (Zn), and higher positive tetravalent metal element (X) is as follows. The sputtering target of Claim 5 which satisfy | fills the relationship of Formula (4) or (5) of these.
0.0001 ≦ X / (In + Ga + Zn + X) <0.05 (4)
0.05 ≦ X / (In + Ga + Zn + X) ≦ 0.4 (5) The sputtering target according to any one of claims 1 to 6, wherein the bulk resistance is 0.1 to 17 mΩcm, and the relative density is 80% or more. (a) a step of weighing, mixing and grinding indium oxide, gallium oxide and zinc oxide;
(b) mixing the obtained pulverized product with a medium and drying to obtain a mixed powder; and
(c) The preparation method of the sputtering target which consists of the oxide sintered compact of any one of Claims 1-7 including the process of sintering the obtained mixed powder. A method for forming an amorphous oxide thin film by sputtering,
(i) a step of performing sputtering at a film forming temperature of 25 to 450 ° C. using the sputtering target according to any one of claims 1 to 7 ;
And forming the amorphous oxide thin film having an electron carrier concentration of less than 1 × 10 ¹⁸ / cm ³ . The method according to claim 9 , wherein the amorphous oxide thin film is used as a channel layer of a thin film transistor.

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