JP2010030824A - Metal phase-containing indium oxide sintered compact and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an indium oxide sputtering target which can suppress the generation of nodules upon sputtering, and to provide an indium oxide sintered compact and a method for producing the same. <P>SOLUTION: The indium oxide sputtering target is composed of an indium oxide sintered compact having an indium oxide phase and a metal phase. Further, powder obtained by mixing an indium compound and metal fine particles or powder obtained by mixing an indium compound and metal oxide fine particles is subjected to discharge plasma sintering to thereby produce the indium oxide sintered compact having the indium oxide phase and the metal phase. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an indium oxide sintered body (sputtering target) used when forming an oxide film by sputtering.

ITO film made of indium oxide and tin oxide has conductivity and visible light transmission, so it can be used for various applications such as transparent electrodes, switching elements, and drive circuit elements in display devices such as liquid crystal display devices. Has been.
In an ITO target used for forming an ITO film, tin oxide is considered to generate carriers in the ITO target by solid solution dispersion in indium oxide. Thereby, the bulk resistance of the ITO sputtering target is as low as about 0.1 mΩcm.

  In the formation of an ITO film using an ITO target, the generation of nodules during film formation is a problem. A nodule is a black protrusion that appears on the surface of a target during sputtering. When this occurs, particles increase, which causes a defect in the ITO film.

There are the following theories about the cause of nodules.
(1) Theory that lower oxides accumulated in vacancies remain as nuclei (2) Columnar In ₂ O ₃ growth occurs on the target, and the target is excavated using this as a nucleus Theory of remaining (3) Theory that high-resistance particles generated in the sputtering chamber adhere to the target and leave a digging residue as a nucleus. (4) The digging residue occurs due to the incident angle dependence of the sputtering rate. Theory (5) Theory that digging remains with high resistance material generated by abnormal discharge as the core

  In addition, there is an idea that nodules are generated by the presence of tin oxide particles in the ITO target, and a manufacturing method in which tin oxide is completely dissolved in indium oxide has been proposed.

The following measures have been proposed to prevent nodules.
(1) Densification of target (2) Decrease in surface roughness of target surface (3) Integrated molding of target (thing without division)
(4) Preventing adhesion of particles to erosion (5) Preventing arcing at the edge of the target etc. However, it has not yet been achieved to completely suppress the generation of nodules.

As a sputtering target for forming an ITO film, for example, Patent Document 1 describes a target manufactured from a powder mixture or a coprecipitated powder of partially reduced indium oxide-tin oxide.
Further, Patent Document 2 describes a method of producing by hot compression or isostatic hot compression using a raw material powder produced by oxidation of fine metal indium-tin.
In Patent Document 3, at least one metal powder or oxide powder selected from the group consisting of metal silicon, titanium, zinc, gallium, germanium, niobium, molybdenum, ruthenium, tin and tungsten is added to the indium oxide powder. A method for producing a high-density sputtering target by forming and sintering by hot pressing is described. In the examples, only indium oxide and metallic tungsten or tungsten oxide are described.

  However, these techniques cannot control the metal particles to be oxidized or segregated during the sintering of the oxide powder, and the bulk resistance of the sputtered particles generated during sputtering to be lower than the bulk resistance of the sputtering target. The generation of nodules may not be suppressed.

As the discharge plasma sintering method, for example, Patent Document 4 describes a method for producing oxide fine particles and high-density sintered bodies in which oxide fine particles are subjected to discharge plasma sintering.
Patent Document 5 describes a method for producing an indium-tin oxide sintered body in which indium oxide and tin oxide are used as raw materials and a pulse current is applied to conduct current sintering. The density of the sintered body is about 6.5 g / cm ³ (relative density: 92%).
JP-A-8-41634 JP-A-9-170076 Japanese Patent Laid-Open No. 2006-2202 JP-A-10-251070 JP 2003-81673 A

  An object of the present invention is to provide an indium oxide sintered body (sputtering target) that can suppress generation of nodules during sputtering.

As a result of intensive studies, the present inventors have found that generation of nodules can be suppressed in a target made of a sintered body having an indium oxide phase and a metal phase, and completed the present invention.
According to the present invention, the following indium oxide sintered body and the like are provided.
1. An indium oxide sintered body having an indium oxide phase and a metal phase.
2. 2. The indium oxide sintered body according to 1, wherein the content of the metal phase is 1 wt% to 30 wt% of the entire sintered body.
3. 3. The indium oxide sintered body according to 1 or 2, wherein an average particle diameter of the metal phase is less than 20 μm.
4). The indium oxide sintered body according to any one of 1 to 3, wherein the metal phase is composed of metal tin and / or metal zinc.
5). The indium oxide sintered body according to any one of 1 to 4, wherein a part of the indium oxide phase is substituted and dissolved by an oxide of another metal element.
6). The sputtering target which consists of an indium oxide sintered compact in any one of said 1-5.
7). The method for producing an indium oxide sintered body according to any one of claims 1 to 4, wherein a powder obtained by mixing an indium compound and metal fine particles is subjected to discharge plasma sintering.
8). 6. The method for producing an indium oxide sintered body according to any one of 1 to 5, wherein a powder obtained by mixing an indium compound and metal oxide fine particles is subjected to discharge plasma sintering.
9. 7. An oxide thin film obtained by sputtering using the sputtering target according to 6 above at a film forming temperature of 25 to 450 ° C.
10. 10. The oxide thin film according to 9, wherein the oxide thin film is a thin film for a channel layer of a thin film transistor.
11. A method of manufacturing a thin film transistor including an oxide thin film and an oxide insulator layer,
(I) a step of heat-treating the ten oxide thin films in an oxidizing atmosphere; and (ii) a step of forming an oxide insulator layer on the heat-treated oxide thin film;
A method for manufacturing a thin film transistor, comprising:
12 12. A semiconductor device comprising a thin film transistor manufactured by the method for manufacturing a thin film transistor as described in 11 above.

  In the present invention, the density of the indium oxide sintered body is increased, and the bulk resistance value can be controlled to a lower resistance, so that a sputtering target free from nodules can be obtained.

The indium oxide sintered body of the present invention includes an indium oxide phase and a metal phase.
As the metal forming the metal phase, indium (In), tin (Sn), zinc (Zn), gallium (Ga), magnesium (Mg), aluminum (Al), zirconium element (Zr), germanium (Ge), Cerium (Ce), niobium (Nb), tantalum (Ta), molybdenum (Mo), tungsten (W), titanium (Ti), chromium (Cr) manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), or silicon (Si). The metal phase may be composed of these single metals or may be composed of two or more kinds.

It is particularly preferable that the metal forming the metal phase is Sn and / or Zn.
When the sintered body of the present invention contains Sn, the film obtained by sputtering is an ITO film, and when it contains a zinc element, an indium oxide-zinc oxide film (for example, IZO (from Idemitsu Kosan Co., Ltd.) Registered trademark)). Further, when tin and zinc are simultaneously contained, an indium oxide-zinc oxide-tin oxide film can be obtained. Each can be used according to the purpose. Since an indium oxide-zinc oxide-tin oxide film can reduce the amount of indium, it is also effective as an indium-saving transparent conductive film.

The content of the metal phase is preferably 1 wt% to 30 wt% of the entire sintered body, more preferably 1 to 20 wt%, still more preferably 2 to 15 wt%. If it is 1 wt%-30 wt%, since the bulk resistance of a sintered compact can be controlled to an appropriate range and a high-density sintered compact is obtained, it is preferable.
The content of the metal phase can be controlled, for example, by adjusting the blending amount of the metal fine particles that are raw materials.

The average particle size of the metal phase is preferably less than 20 μm, more preferably 0.1 to 15 μm, and particularly preferably 1 to 10 μm.
The average particle diameter of the metal phase is a value measured by surface analysis using an electron beam microanalyzer (EPMA). Specifically, the surface analysis of oxygen and metal in a 50 × 50 micron field is performed, and the major axis of the particle of the metal phase is calculated with the portion containing no oxygen as the metal phase, and the average of the particle diameter in the field of view The value was defined as the average particle size.

  In the indium oxide sintered body of the present invention, the bulk resistance value of the sintered body obtained by dispersing the metal phase in indium oxide is compared with the bulk resistance value of indium oxide in which the oxide is substituted and dissolved, Highly controllable. Thereby, the bulk resistance of sputtered particles generated during sputtering becomes lower than the bulk resistance of the sputtering target, and the sputtered particles deposited on the sputtering target can be re-sputtered. Thereby, a sputtering target in which nodules are not generated is obtained.

The density of the indium oxide sintered body is preferably 6.580~7.3014g / cm ^3, more preferably, 6.890~7.2014g / cm ^3, more preferably from 6.95 to 7.14. 6.580 g / cm ³ or more is preferable because stable sputter discharge is possible. In particular, the true density of indium oxide of 7.2 g / cm ³ or less is preferable because indium oxide itself is not converted into metallic indium and abnormal discharge such as a splash phenomenon can be suppressed.
Splash refers to a phenomenon in which a low-melting-point substance deposited on the surface of a sputtering target becomes small liquid droplets and adheres to a glass substrate. The main factors are the presence of micropores, abnormal discharge due to coarse crystal grains, and abnormal discharge due to the presence of oxides.
A density is the value which measured the sintered compact sample piece about 20 * 20 * 20 mm in size by the Archimedes method.

In the sintered body of the present invention, a part of the indium oxide phase may be substituted and solid solution by an oxide of another metal (R).
Examples of the other metal element (R) include one or more metal elements selected from zinc, tin, yttrium, zirconium, germanium, cerium, niobium, tantalum, molybdenum, tungsten, titanium, aluminum, silicon, and lanthanoid. Can be mentioned.
The lanthanoid is Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu.

  Here, the indium oxide phase in which another metal (R) oxide is dissolved can be confirmed by a change in lattice constant (interstitial distance) calculated from X-ray diffraction or a structural analysis using high-intensity synchrotron radiation. . Specifically, it can be judged from the peak shift of the X-ray diffraction pattern by the change in the axial length of the crystal structure. When the axial length is shortened by substitutional solid solution, the peak of the X-ray diffraction pattern is shifted to the high angle side. Further, the lattice constant is obtained using Rietveld analysis.

In the case of containing an oxide of another metal element (R), the sintered body of the present invention is particularly suitable for each element of indium element (In), other metal element (R), and metal phase metal (M). It is preferable that the atomic ratio satisfy the relationships of the following formulas (1) to (3).
0.33 ≦ In / (In + R + M) <0.99 (1)
0.01 ≦ M / (In + R + M) ≦ 0.50 (2)
0.00 <R / (In + R + M) ≦ 0.10 (3)
In particular, it is preferable to satisfy the relationships of the following formulas (1) ′ to (3) ′.
0.50 ≦ In / (In + R + M) <0.95 (1) ′
0.05 ≦ M / (In + R + M) ≦ 0.30 (2) ′
0.00 <R / (In + R + M) ≦ 0.05 (3) ′

The sintered body of the present invention preferably further contains a metal element (X) having a positive tetravalence or higher.
The positive tetravalent or higher metal element (X) is preferably at least one element selected from, for example, tin, zirconium, germanium, cerium, niobium, tantalum, molybdenum, tungsten, and titanium.

  The content (atomic ratio) of the positive tetravalent or higher metal element (X) is preferably 10 to 10000 ppm, more preferably 100 to 5000 ppm, particularly preferably 200 to 1000 ppm, based on the total number of atoms of the sintered body excluding oxygen atoms. preferable. If it is 10 ppm or more, the relative density can be improved, the bulk resistance can be lowered, and the bending strength can be sufficiently improved. If it is 10000 ppm or less, a crystal type other than the rare earth oxide C type can be obtained. Since there is also no possibility of precipitation, it is preferable.

The indium oxide sintered body of the present invention can be produced by, for example, discharge plasma sintering of a powder in which an indium compound and metal fine particles are mixed (first production method). FIG. 1 is a process diagram of the first manufacturing method of the present invention.
In the first manufacturing method, calcination may be performed before spark plasma sintering. FIG. 2 is a process diagram when a calcination process is employed in the first manufacturing method of the present invention.

Moreover, the raw material which mixed the compound of an indium compound, the compound of a metal element (R), and / or the compound of a metal element (X) is sintered (pre-sintering), and the pulverized material and metal fine particle of the obtained sintered compact were used. The mixed raw material mixture can be produced by spark plasma sintering (second production method).
FIG. 3 is a process diagram of the second manufacturing method of the present invention. Hereinafter, two manufacturing methods will be described.

(A) 1st manufacturing method The 1st manufacturing method of this invention includes the following processes (a)-(c).
(A) Step of mixing raw material compound powder and metal particles (b) Step of forming mixed powder (c) Step of sintering the obtained raw material mixture using a discharge plasma sintering (pulse current sintering) method

(A) Mixing step In this step, the raw material compound powder and the metal particles, which are raw material powders, are mixed.
Examples of the raw material compound powder include a compound that forms an indium oxide phase by sintering, a compound that contains a metal element (R) that dissolves and replaces part of the indium oxide phase, a compound that contains a metal element (X) having a positive tetravalent or higher valence, etc. Is mentioned.

Examples of the indium compound that forms the indium oxide phase include indium oxide and indium hydroxide. The oxide is not limited to indium oxide alone, but it is also possible to use a raw material obtained by reacting indium oxide with one or more oxide-added elements.
Note that indium oxide may be solid solution substituted with a metal element (R). In this case, the content of the metal element (R) is preferably 0.01 <R / (In + R) <0.1 in terms of atomic ratio with the indium element (In).

Examples of the compound containing the metal element (R) and the compound containing the metal element (X) having a positive tetravalence or more include oxides and hydroxides of the metal element (R) or the metal element (X).
As each compound, an oxide is preferable because of ease of sintering and generation of by-products.

  There is no restriction | limiting in particular as a metal particle, The metal particle which forms the metal phase mentioned above can be used. Instead of metal particles, a compound that becomes a single metal by reduction or the like may be used. The metal particles become fine particles by a subsequent mixing step.

  The above raw materials are mixed and pulverized by known mixing and pulverizing means. The purity of each raw material is usually 99.9% by mass (3N) or more, preferably 99.99% by mass (4N) or more, more preferably 99.995% by mass or more, particularly preferably 99.999% by mass (5N). That's it. If the purity of each raw material is 99.9% by mass (3N) or more, the semiconductor characteristics are not deteriorated by impurities such as Fe, Al, Si, Ni, Cu, and the reliability can be sufficiently maintained. In particular, it is preferable that the Na content is less than 100 ppm because reliability is improved when a thin film transistor is manufactured.

  The average particle size of the metal element (R) or metal element (X) compound powder used as a raw material is preferably smaller than the average particle size of the indium compound powder. The average particle diameter of the raw material metal compound powder can be measured by the method described in JIS R 1619.

  It is preferable to use powders having the same specific surface area for each raw material powder. Thereby, it can pulverize and mix more efficiently. Specifically, the ratio of the specific surface area is preferably within a range of 1/4 to 4 times, and more preferably within a range of 1/2 to 2 times.

The raw material compound powder and the metal particles are preferably mixed and pulverized uniformly using an ordinary mixing and pulverizing machine such as a wet ball mill, a bead mill or an ultrasonic device. The average particle size of the mixture obtained after mixing and pulverization is preferably 0.5 to 20 μm, more preferably 0.5 to 15 μm. If the average particle size is in the range of 0.5 to 20 μm, the generation of nodules can be suppressed, the dispersion becomes uniform, and the variation in resistance value in the large sintered body is reduced, so that abnormal discharge can also be suppressed. Therefore, it is preferable.
Here, the average particle diameter can be measured by the method described in JIS R 1619.

The specific surface area of each raw material powder, for example, 2 to 10 m ² / g, preferably it is appropriate to be 4 to 8 m ² / g. The difference in specific surface area between the raw material powders is 5 m ² / g or less, preferably 3 m ² / g or less. The smaller the difference in specific surface area, the more preferable the raw material powder can be efficiently pulverized and mixed. The specific surface area can be determined by the BET method.

The specific surface area after pulverization is such that the specific surface area of the raw material mixed powder before pulverization is increased by 1.0 to 3.0 m ² / g, or the average median diameter (d50) after pulverization is 0.6 to 1 μm. It is preferable to grind to the extent. By using the raw material mixed powder prepared in this way, a high-density 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 pulverized raw material mixed powder is 1 μm or less because the sintered density is 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, the contamination (impurity contamination amount) from the pulverizer during pulverization is Since it does not increase, it is preferable.
Here, the specific surface area of the powder is a value measured by the BET method. The median diameter of the particle size distribution of the 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.

During mixing and grinding, water added with about 1% by volume of polyvinyl alcohol (PVA), ethanol, or the like may be used as a medium.
The median diameter (d50) of each raw material powder 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, it is possible to prevent the formation of voids in the sintered body and prevent the sintered density from being lowered. This is preferable because an increase in particle size can be prevented.

(A ′) Calcination step After the step (a), a calcination step (a ′) may be performed.
In the calcining step, the raw material mixed powder obtained in the step (a) is calcined. By performing the calcination, it becomes easy to increase the density of the finally obtained sintered body in order to remove excess moisture, organic matter, and the like.
In the calcination step, the mixture obtained in step (a) is heat-treated at a temperature of 200 to 600 ° C., preferably 400 to 550 ° C. for 1 to 100 hours, preferably 2 to 50 hours. preferable. Heat treatment conditions of 200 ° C. or higher and 1 hour or longer are preferable because evaporation and thermal decomposition of moisture and organic substances are sufficiently performed. If the heat treatment conditions are 600 ° C. or less and 100 hours or less, the particles are not coarsened, which is preferable.

Furthermore, it is preferable to pulverize the raw material mixed powder obtained after calcination here before the subsequent sintering step. The mixture after calcination is suitably pulverized using a ball mill, roll mill, pearl mill, jet mill or the like. The average particle size of the mixture after calcination obtained after pulverization is, for example, 0.01 to 3.0 μm, preferably 0.1 to 2.0 μm. If the average particle size of the obtained mixture after calcining is 0.01 μm or more, the bulk specific gravity of the mixture can be sufficiently increased, and the handling becomes easy. If the average particle size of the calcined product is 3.0 μm or less, it is easy to increase the density of the finally obtained sintered body.
The average particle size of the calcined product can be measured by the method described in JIS R 1619.

(B) Molding In the discharge plasma sintering, the raw material mixed powder is put into a carbon die or an alumina die of a discharge plasma sintering apparatus and pressed from both directions to be molded.

(C) Sintering process A sintering process is a process of carrying out discharge plasma sintering of the raw material mixed powder obtained at the said process (the mixture after calcination when the said calcination process is provided).
In order to improve the performance of the target, it is important to control the structure such as the size of the particle diameter in the sintered body. As one of them, it is possible to control the resistance of the target by suppressing the particle growth during sintering and forming a structure composed of fine particles of several micrometers or less. Moreover, by sintering while conducting electricity in a vacuum, the growth of metal fine particles can be suppressed and the oxidation reaction can be suppressed.

In the discharge plasma sintering, the raw material mixed powder is put into a carbon die or alumina die of a discharge plasma sintering apparatus, pressurized in both directions in a vacuum (inert atmosphere or in the atmosphere), and the die is pressed. (Sample) is subjected to direct current pulse current, and heat is generated by the generated discharge plasma to perform sintering.
The pressure during spark plasma sintering is preferably 10 to 100 MPa, more preferably 30 to 90 MPa, and particularly preferably 40 to 80 MPa.
The sintering time is preferably 1 minute to 10 hours, more preferably 3 minutes to 5 hours, and particularly preferably 5 minutes to 2 hours.
The sintering temperature is preferably 600 ° C to 1300 ° C, more preferably 700 ° C to 1200 ° C, and particularly preferably 800 ° C to 1150 ° C.
The applied current voltage is preferably controlled automatically by temperature from 1 KA to 200 KA, 1 V to 10 V. More preferably, they are 1.5KA-100KA, 1V-10V, Most preferably, 1.5KA-100KA, 1V-10V.

  Under the above sintering conditions, it is possible to easily produce a sintered body containing the metal fine particles, that is, while maintaining the particle diameter of the raw material mixed powder. In addition, the sintering temperature can be lowered and the sintering time can be shortened as compared with normal atmospheric pressure sintering and hot press sintering.

The indium oxide particles and the metal fine particles in the sintered body form a structure composed of fine particles of several micrometers. Thereby, segregation of the metal fine particles during sintering of the raw material mixed powder can be suppressed, and a high-density indium oxide sintered body can be produced. Thereby, the difference in bulk resistance between the flakes generated during sputtering and the target can be controlled to be small, and generation of nodules can be suppressed.
In addition, by using a discharge plasma sintering method, the metal oxide-containing indium oxide sintered body can be produced at a low temperature and in a short time by reducing the metal oxide.

(B) Second Manufacturing Method The second manufacturing method of the present invention includes the following steps (a) to (f).
(A) Step of mixing raw material compound powder (b) Step of shaping the obtained mixture and sintering (pre-sintering) (c) Step of pulverizing the sintered body (d) Step of mixing metal fine particles (e) Step of forming mixed powder (f) Step of sintering raw material mixed powder using discharge plasma sintering (pulse current sintering) method

(A) Mixing step This step is the same as the mixing step of the first manufacturing method described above, except that metal fine particles are not used and two or more raw material compounds are used. The same applies to the calcination step (a ′).
Examples of the two or more kinds of raw material compounds include a combination of indium oxide and one or more kinds of compounds selected from a compound containing the metal element (R) and a compound containing a metal element (X) having a positive tetravalence or more. .

(B) Molding / Pre-sintering process (b-1) Molding The molding process is performed by placing the raw material mixture (or mixture after calcining if the above calcining process is provided) into a mold and press molding. It is a process of making a body. By this step, the mixture (or the mixture after calcination) is formed into a shape suitable as a sputtering target. When the calcination step is provided, the obtained fine powder of the mixture after calcination can be formed into a desired shape.
As the molding process that can be used in this step, for example, press molding, uniaxial pressing, pressure molding, cold isostatic pressing, mold molding, and casting molding injection molding can be employed. Various shapes can be used as the mold. 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.
In the molding process, SiNx, carbon or the like may be used as a release agent.

As the press molding, a known molding method such as a cold press method or a hot press method can be used. For example, the obtained mixed powder is filled in a mold and pressure-molded with a cold press machine. Pressure molding, for example, room temperature (25 ° C.) under, 100~100000kg / cm ^2, preferably, at a pressure of from 500~10000kg / cm ^2. 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 rate of temperature rise is 30 ° C./hour or more, the decomposition of the oxide does not proceed and no pinholes are generated. In addition, if the cooling rate during cooling is 30 ° C./hour or more, the composition ratio of In or the like does not change.

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.

  As the wet-type cold press, for example, a filtration molding method (see JP-A-11-286002) is preferably used. 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 filtering mold that drains the 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, and this slurry was poured into a filter-type mold, and the molded body was produced by draining the water in the slurry under reduced pressure only from the filter surface side.燥脱 sintering after the fat.

(B-2) Pre-sintering process At this process, the obtained molded object is sintered (pre-sintering).
Sintering is performed at atmospheric pressure or under pressure in an oxygen gas atmosphere or a nitrogen gas atmosphere.
Sintering in an oxygen gas atmosphere is preferable because the density of the sintered body tends to increase and the occurrence of abnormal discharge during sputtering can be suppressed. The oxygen gas atmosphere refers to an atmosphere having an oxygen concentration of, for example, 10 to 100%. Calcination can be performed under atmospheric pressure or under pressure. The pressurization is, for example, 98 KPa to 1 MPa, preferably 0.1 to 5 MPa.

The sintering temperature is preferably 900 to 1650 ° C, more preferably 1000 to 1550 ° C. When the sintering temperature is 900 ° C. or higher, the density of the sputtering target is easily increased, and sintering can be performed within an appropriate time. If it is 1650 degrees C or less, since a component does not vaporize, zinc evaporates and the composition of a sintered compact changes and / or there is no possibility that a void (void | void) will generate | occur | produce in a target, It is suitable.
The sintering time is preferably 30 minutes to 360 hours, more preferably 1 to 100 hours, and particularly preferably 1 to 30 hours. If the sintering time is 30 minutes or more, the density of the sintered body is likely to increase, and if it is 360 hours or less, sintering can be performed within an appropriate time.
Further, the heating rate during sintering is usually 20 ° C./min or less, preferably 8 ° C./min or less, more preferably 4 ° C./min or less, further preferably 2 ° C./min or less, particularly preferably 0.5. C / min or less. If it is 20 degrees C / min or less, it can sinter without destroying a sintered compact.

(C) Step of pulverizing the sintered body The pre-sintered body obtained in (b) is suitably pulverized using a ball mill, roll mill, pearl mill, jet mill or the like. By pulverization, the average particle size is preferably 0.01 to 3.0 μm, particularly preferably 0.1 to 2.0 μm.
The average particle diameter can be measured by the method described in JIS R 1619.

  The pre-sintering and pulverization may be repeated a plurality of times, for example, three times or more.

(D) Step of mixing pulverized product of sintered body and metal fine particles obtained The mixing of the pulverized product of sintered body and metal fine particles may be performed in the same manner as the mixing step of the first manufacturing method described above.

(E) Molding and (f) Spark Plasma Sintering (Pulsed Current Sintering) Step Using the raw material mixed powder obtained in the above step (d), the sintering step (b) ( What is necessary is just like c).

The first and second manufacturing methods described above may further include the following steps as post-steps.
(G) Step of further sintering after spark plasma sintering (post-sintering step)
(H) Step of reducing the obtained sintered body (reduction step)
(I) Process of processing a sintered body into a shape suitable for mounting on a sputtering apparatus (processing process)

(G) Post-sintering step As the post-sintering conditions, the heat treatment temperature is preferably 900 to 1650 ° C, and more preferably 1000 to 1550 ° C in an oxygen gas atmosphere or a nitrogen gas atmosphere under atmospheric pressure or pressure. The sintering time is preferably 30 minutes to 360 hours, more preferably 1 to 100 hours, and particularly preferably 1 to 30 hours. When the sintering temperature is 900 ° C. or higher, the density of the sputtering target is easily increased, and sintering can be performed within an appropriate time. When the temperature is 1650 ° C. or lower, the components are not vaporized, the zinc is evaporated, the composition of the sintered body is changed, and / or voids (voids) are not generated in the target. Furthermore, if the sintering time is 30 minutes or more, the density of the sputtering target is likely to increase, and if it is 360 hours or less, sintering can be performed within an appropriate time. Further, it is preferable to perform sintering in an oxygen gas atmosphere or an oxygen gas atmosphere because the density of the sputtering target is easily increased and the occurrence of abnormal discharge during sputtering can be suppressed. The oxygen gas atmosphere refers to an atmosphere having an oxygen concentration of, for example, 10 to 100%. Sintering can be performed under atmospheric pressure or under pressure. The pressurization is, for example, 98 KPa to 1 MPa, preferably 0.1 to 5 MPa.
Further, the heating rate during sintering is usually 20 ° C./min or less, preferably 8 ° C./min or less, more preferably 4 ° C./min or less, further preferably 2 ° C./min or less, particularly preferably 0.5. C / min or less. If it is 20 degrees C / min or less, it can sinter without destroying a sintered compact.

(H) Reduction process The reduction process is an optional process in which a reduction treatment is performed in order to uniformize the bulk specific resistance of the sintered body obtained in the sintering process as the entire sintered body.
Examples of the reduction method that can be applied in this step include a method of circulating a reducing gas, a method of baking in a vacuum, and a method of baking in an inert gas.
As the reducing gas, for example, hydrogen, methane, carbon monoxide, a mixed gas of these gases and oxygen, or the like can be used.
As the inert gas, nitrogen, argon, a mixed gas of these gases and oxygen, or the like can be used.
In addition, the temperature at the time of a reduction process is 100-800 degreeC normally, Preferably it is 200-800 degreeC. The reduction treatment time is usually 0.01 to 5 hours, preferably 0.05 to 1 hour.
The pressure of the reducing gas or the inert gas is, for example, 9.8 to 1000 KPa, preferably 98 to 500 KPa. In the case of sintering in vacuum, the vacuum specifically refers to about 10 ⁻¹ to 10 ⁻⁸ Pa, preferably about 10 ⁻² to 10 ⁻⁵ Pa, and the residual gas is argon, nitrogen, or the like.

(I) Processing Step 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 mount a backing plate or the like. It is the process provided as needed for attaching a tool.
The thickness of the sputtering target is usually 2 to 20 mm, preferably 3 to 12 mm, particularly preferably 4 to 6 mm. The surface of the sputtering target 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. It is preferable to use a diamond grindstone of No. 200 to No. 10,000 because the sputtering target will not break. Further, a plurality of sputtering targets may be attached to one backing plate to substantially form one target. Examples of the backing plate include those made of oxygen-free copper.

The oxide thin film of the present invention is obtained by sputtering at the film forming temperature of 25 to 450 ° C. using the above-described sputtering target of the present invention. Thus, the amorphous oxide thin film of the electron carrier concentration less than 1 × ¹⁰ 18 / cm ³ (the oxide semiconductor), or an electron carrier concentration of 1 × ¹⁰ 20 / cm ³ or more amorphous oxide thin film (transparent conductive film) Can be formed.
Examples of the sputtering method include a DC (direct current) sputtering method, an AC (alternating current) sputtering method, an RF (high frequency) magnetron sputtering method, an electron beam evaporation method, and an ion plating method. DC (direct current) sputtering and RF (high frequency) sputtering are preferably used.
The film forming temperature during sputtering varies depending on the sputtering method, but is suitably 25 to 450 ° C., preferably 25 to 300 ° C., and more preferably 25 to 250 ° 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 DC (direct current) sputtering, 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 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 to 80: 0 to 20, preferably 99.5 to 90: 0.5 to 10. Is appropriate.

Prior to sputtering, the sputtering target is bonded (bonded) to the support. This is for fixing the target to the sputtering apparatus.
Sputtering is performed using the bonded sputtering target to obtain an oxide thin film containing In and Zn oxides as main components on the substrate. Here, “main component” means that the sum of atomic ratios of elements excluding oxygen is 100%, and that each element of In and Zn is included by 50% or more in atomic ratio.
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 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 density of the oxide thin film obtained is 6.0 g / cm ³ or more, preferably, suitably be a 6.1~7.2g / cm ^3. With such a density, even in the obtained oxide thin film, generation of nodules and particles is small, and an oxide thin film having excellent film characteristics can be obtained.

The oxide thin film of the present invention can be used as it is or after heat treatment as a semiconductor film such as a thin film transistor, a channel layer, a solar cell and a gas sensor, a display element such as a touch panel, and a transparent conductive film such as a solar cell. . In particular, a thin film transistor channel layer (semiconductor layer) is suitable as a semiconductor film, and a transparent electrode for a flat panel is suitable as a transparent conductive film.
Hereinafter, an example in which the oxide thin film of the present invention is applied to a channel layer of a thin film transistor will be described.

FIG. 4 is a schematic cross-sectional view of an example of a thin film transistor.
In this thin film transistor, a gate electrode 2 is formed on a substrate 1 such as a glass substrate. A gate insulating film 3 is provided so as to cover the gate electrode 2, and a channel layer 4 is provided thereon. Either one of the source electrode 5 and the drain electrode 6 is formed at both ends of the channel layer 4. A protective film 7 is formed except for part of the source electrode 5 and the drain electrode 6.

In the thin film transistor shown in FIG. 4, the protective film 7 is formed after the source electrode 5 and the drain 6 electrode are formed. However, the present invention is not limited to this, and the thin film transistor shown in FIG.
In the thin film transistor of FIG. 5, a gate electrode 12 is formed on a substrate 11 such as a glass substrate. A gate insulating film 13 is provided so as to cover the gate electrode 12, and a channel layer 14 is provided thereon. A protective film 15 (etching stopper) is formed on the channel layer 14, and then a source electrode / drain electrode 17 is formed (FIG. 5 (1)). Thereafter, the source electrode / drain electrode 17 is patterned by etching or the like (FIG. 5B).
The oxide thin film of the present invention can be suitably used as the channel layers 4 and 14.

When the oxide thin film of the present invention is used as the channel layer 4, it is preferable that the oxide thin film and the oxide insulator layer have a laminated structure and are manufactured by a method including the following steps.
(I) A step of heat-treating the oxide thin film of the present invention in an oxidizing atmosphere (ii) A step of forming an oxide insulator layer on the heat-treated oxide thin film

In the step (i), the oxide thin film is heat-treated in an oxidizing atmosphere. The oxidizing atmosphere may be, for example, an oxygen gas atmosphere.
Moreover, heat processing is 100-450 degreeC, for example, Preferably it is 150-350 degreeC, for 0.1 to 10 hours, Preferably, it performs for 0.5 to 2 hours. Thereby, the semiconductor characteristics of the oxide thin film can be stabilized.

In the step (ii), an oxide insulator layer is formed on the heat-treated oxide thin film. The oxide insulator layer functions as a semiconductor protective film.
Examples of the method for the oxide insulator layer include a CVD method and a sputtering method.
Examples of the oxide insulator layer include SiO ₂ , SiNx, Al ₂ O ₃ , Ta ₂ O ₅ , TiO ₂ , MgO, ZrO ₂ , CeO ₂ , K ₂ O, Li ₂ O, Na ₂ O, and Rb _2. O, Sc ₂ O ₃ , Y ₂ O ₃ , Hf ₂ O ₃ , CaHfO ₃ , PbTi ₃ , BaTa ₂ O ₆ , SrTiO ₃ , AlN, or the like can be used. Among _{these, SiO 2, SiNx, Al 2} O 3, Y 2 O 3, Hf 2 O 3, it is preferable to use CaHfO _3, more preferably _{SiO 2, SiNx, Y 2 O} 3, Hf 2 O 3 , CaHfO ₃ , and oxides such as SiO ₂ , Y ₂ O ₃ , Hf ₂ O ₃ , and CaHfO ₃ are particularly preferable. The number of oxygen in these oxides does not necessarily match the stoichiometric ratio (for example, it may be SiO ₂ or SiO x). SiNx may contain a hydrogen element.

The oxide insulator layer may have a structure in which two or more different insulating films are stacked.
Further, it may be any of crystalline, polycrystalline, and amorphous, but it is preferably polycrystalline or amorphous that is easy to industrially manufacture, and is preferably amorphous. . If it is an amorphous film, the smoothness of the interface will be good, high carrier mobility can be maintained, and the threshold voltage and S value will not become too large.
The S value (Swing Factor) is a value indicating the steepness of the drain current that rises sharply 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.

Hereinafter, the field effect transistor of the present invention will be described with respect to constituent members.
1. Substrate There is no restriction | limiting in particular as a board | substrate, A well-known thing can be used in this technical field. For example, glass substrates such as alkali silicate glass, non-alkali glass and quartz glass, silicon substrates, resin substrates such as acrylic, polycarbonate and polyethylene naphthalate (PEN), polymer film bases such as polyethylene terephthalate (PET) and polyamide Materials can be used. As for the thickness of a board | substrate or a base material, 0.1-10 mm is common, and 0.3-5 mm is preferable. In the case of a glass substrate, those chemically or thermally reinforced are preferred. When transparency and smoothness are required, a glass substrate and a resin substrate are preferable, and a glass substrate is particularly preferable. When weight reduction is required, a resin substrate or a polymer material is preferable.

2. Semiconductor layer (channel layer)
As described above, the semiconductor layer can be produced by forming an oxide thin film using the sputtering target of the present invention.
In the present invention, the semiconductor layer is preferably an amorphous film. By being an amorphous film, adhesion with an insulating film and a protective film is improved, and uniform transistor characteristics can be easily obtained even in a large area. Here, whether or not the semiconductor layer is an amorphous film can be confirmed by X-ray crystal structure analysis. The case where no clear peak is observed is amorphous.
The band gap is preferably 2.0 to 6.0 eV, and more preferably 2.8 to 5.0 eV. If the band gap is 2.0 eV or more, the visible light is absorbed and there is no possibility that the field effect transistor malfunctions. On the other hand, if it is 6.0 eV or less, it is difficult for carriers to be supplied and the field-effect transistor is less likely to fail.
The semiconductor layer is preferably a non-degenerate semiconductor exhibiting a thermal activation type. In the case of a non-degenerate semiconductor, disadvantages such as an increase in off current and gate leakage current due to too many carriers, a negative threshold value and normally on can be avoided. Whether or not the semiconductor layer is a non-degenerate semiconductor can be determined by measuring temperature changes in mobility and carrier density using the Hall effect. In addition, the semiconductor layer can be made a non-degenerate semiconductor by adjusting the oxygen partial pressure during film formation and performing post-processing to control the amount of oxygen defects and optimize the carrier density.

The surface roughness (RMS) of the semiconductor layer is preferably 1 nm or less, more preferably 0.6 nm or less, and particularly preferably 0.3 nm or less. If it is 1 nm or less, there is no possibility that the mobility is lowered.
The semiconductor layer is preferably an amorphous film that maintains at least part of the edge sharing structure of the bixbite structure of indium oxide. Whether or not the amorphous film containing indium oxide maintains at least a part of the edge sharing structure of the bixbite structure of indium oxide is determined by small angle incident X-ray scattering (GIXS) using high-intensity synchrotron radiation or the like. It can be confirmed that the peak representing In-X (X is In, Zn) is between 0.30 and 0.36 nm by the radial distribution function (RDF) obtained by F. Utsuno, et al., Thin Solid Films, Volume 496, 2006, Pages 95-98).
Furthermore, when the maximum value of RDF between the interatomic distances of 0.30 and 0.36 nm is A, and the maximum value of RDF between the interatomic distances of 0.36 and 0.42 is B, A / B> 0.7 is preferably satisfied, A / B> 0.85 is more preferable, A / B> 1 is further more preferable, and A / B> 1.2 is particularly preferable.
If A / B is 0.7 or more, when the semiconductor layer is used as an active layer of a transistor, there is no possibility that the mobility is lowered or the threshold value or the S value becomes too large. It is considered that the small A / B reflects the poor short-range order of the amorphous film.
Further, the average In—In bond distance is preferably 0.3 to 0.322 nm, and particularly preferably 0.31 to 0.32 nm. The average bond distance of In—In can be determined by X-ray absorption spectroscopy. The measurement by X-ray absorption spectroscopy shows an X-ray absorption wide-area microstructure (EXAFS) that has spread to a high energy as high as several hundred eV from the rise. EXAFS is caused by backscattering of electrons by atoms around the excited atom. Interference effect between the flying electron wave and the back-scattered wave occurs. Interference depends on the wavelength of the electronic state and the optical path length to and from surrounding atoms. A radial distribution function (RDF) is obtained by Fourier transforming EXAFS. The average bond distance can be estimated from the RDF peak.

  The film thickness of the semiconductor layer is usually 0.5 to 500 nm, preferably 1 to 150 nm, more preferably 3 to 80 nm, and particularly preferably 10 to 60 nm. If it is 0.5 nm or more, it is possible to form an industrially uniform film. On the other hand, if it is 500 nm or less, the film formation time will not be too long. Moreover, when it exists in the range of 3-80 nm, TFT characteristics, such as a mobility and an on / off ratio, are especially favorable.

In the present invention, the semiconductor layer is preferably an amorphous film, and the energy width (E ₀ ) of the delocalized level is preferably 14 meV or less. The energy width (E ₀ ) of the delocalized level of the semiconductor layer is more preferably 10 meV or less, further preferably 8 meV or less, and particularly preferably 6 meV or less. When the energy width (E ₀ ) of the delocalized level is 14 meV or less, when the semiconductor layer is used as the active layer of the transistor, there is no possibility that the mobility is lowered or the threshold value or the S value is too large. It is considered that the large energy width (E ₀ ) of the delocalized level of the semiconductor layer reflects the poor short-range order of the amorphous film.

3. Protective film of semiconductor layer The protective film of the semiconductor layer is an oxide insulator layer formed on the above-described oxide thin film. If there is a protective film for the semiconductor, oxygen in the surface layer of the semiconductor is not desorbed in a vacuum or under a low pressure, and there is no possibility that the off current becomes high or the threshold voltage becomes negative. Further, there is no influence of ambient conditions such as humidity even in the atmosphere, and there is no possibility that variations in transistor characteristics such as threshold voltage will increase.

The protective film of the semiconductor layer is preferably an amorphous oxide or an amorphous nitride, and particularly preferably an amorphous oxide. In addition, when the protective film is an oxide, oxygen in the semiconductor does not move to the protective film side, the off-current does not increase, and the threshold voltage becomes negative and there is no possibility of showing normally-off.
An organic insulating film such as poly (4-vinylphenol) (PVP) or parylene may be further used as a protective film for the semiconductor layer. Furthermore, the protective film of the semiconductor layer may have a laminated structure of two or more layers of an inorganic insulating film and an organic insulating film.

4). Gate insulating film There is no particular limitation on the material for forming the gate insulating film. What is generally used can be arbitrarily selected as long as the effects of the present invention are not lost. For _{example, SiO 2, SiNx, Al 2} O 3, Ta 2 O 5, TiO 2, MgO, ZrO 2, CeO 2, K 2 O, Li 2 O, Na 2 O, Rb 2 O, Sc 2 O 3, Y ₂ O ₃ , Hf ₂ O ₃ , CaHfO ₃ , PbTi ₃ , BaTa ₂ O ₆ , SrTiO ₃ , AlN, or the like can be used. Among _{these, SiO 2, SiNx, Al 2} O 3, Y 2 O 3, Hf 2 O 3, it is preferable to use CaHfO _3, more preferably _{SiO 2, SiNx, Y 2 O} 3, Hf 2 O 3 , CaHfO ₃ . The number of oxygen in these oxides does not necessarily match the stoichiometric ratio (for example, it may be SiO ₂ or SiO x). SiNx may contain a hydrogen element.
Such a gate insulating film may have a structure in which two or more different insulating films are stacked. The gate insulating film may be crystalline, polycrystalline, or amorphous, but is preferably polycrystalline or amorphous that is easy to manufacture industrially.
The gate insulating film may be an organic insulating film such as poly (4-vinylphenol) (PVP) or parylene. Further, the gate insulating film may have a stacked structure of two or more layers of an inorganic insulating film and an organic insulating film.
The gate insulating film preferably has a thickness of 50 to 500 nm. The gate insulating film may be formed by a sputtering method, but a CVD method such as a TEOS-CVD method or a PECVD method is preferable.

5). Electrode There are no particular limitations on the material for forming each of the gate electrode, the source electrode, and the drain electrode, and any material that is generally used can be selected as long as the effects of the present invention are not lost.
For example, transparent electrodes such as indium tin oxide (ITO), indium zinc oxide, ZnO, SnO ₂ , metal electrodes such as Al, Ag, Cr, Ni, Mo, Au, Ti, Ta, Cu, or these An alloy metal electrode can be used. Moreover, it is preferable to laminate two or more layers to reduce the contact resistance or improve the interface strength. In order to reduce the contact resistance of the source electrode and the drain electrode, the resistance of the interface with the semiconductor electrode may be adjusted by plasma treatment, ozone treatment or the like.

  The laminated electrode is formed by, for example, using an electron beam evaporation method to form 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. And the laminated film can be processed by a photolithography method and a lift-off method.

  The thin film transistor of the present invention preferably has a structure for shielding the semiconductor layer. If there is a structure that shields the semiconductor layer (for example, a light shielding layer), when light enters the semiconductor layer, there is no possibility that the carrier electrons are excited and the off-current increases. The light shielding layer is preferably a thin film having absorption at 300 to 800 nm. The light shielding layer may be either the upper part or the lower part of the semiconductor layer, but is preferably on both the upper part and the lower part. Further, the light shielding layer may also be used as a gate insulating film, a black matrix, or the like. When the light shielding layer is on only one side, it is necessary to devise a structure so that light is not irradiated onto the semiconductor layer from the side where the light shielding layer is not present.

In the thin film transistor of the present invention, a contact layer may be provided between the semiconductor layer and the source / drain electrodes. The contact layer preferably has a lower resistance than the semiconductor layer. As a material for forming the contact layer, a composite oxide having the same composition as that of the semiconductor layer described above can be used. That is, the contact layer preferably contains each element such as In, Zn, and Zr. When these elements are included, there is no movement of elements between the contact layer and the semiconductor layer, and there is no possibility that the shift of the threshold voltage becomes large when a stress test or the like is performed.
There are no particular restrictions on the method for forming the contact layer, but a contact layer having the same composition ratio as the semiconductor layer can be formed by changing the film formation conditions, a layer having a composition ratio different from that of the semiconductor layer can be formed, or a semiconductor electrode The contact portion may be formed by increasing the resistance by plasma treatment or ozone treatment, or a layer having a higher resistance may be formed by film formation conditions such as oxygen partial pressure when forming the semiconductor layer. The thin film transistor of the present invention preferably includes an oxide resistance layer having a higher resistance than the semiconductor layer between the semiconductor layer and the gate insulating film and / or between the semiconductor layer and the protective film. If there is an oxide resistance layer, no off-current is generated, the threshold voltage becomes negative and normally on, and the semiconductor layer changes in quality during post-processing steps such as protective film formation and etching, resulting in deterioration of characteristics. There is no risk of doing so.

The following can be illustrated as an oxide resistance layer.
・ Amorphous oxide film with the same composition as the semiconductor layer deposited at a higher oxygen partial pressure than when the semiconductor film was deposited ・ Amorphous oxide film with the same composition as the semiconductor layer but with a different composition ratio An amorphous oxide film containing In and Zn and containing an element X different from the semiconductor layer. A polycrystalline oxide film containing indium oxide as a main component. Indium oxide as a main component, Zn, Cu, Co, Ni, Mn, An amorphous oxide film having the same composition as the polycrystalline oxide film semiconductor layer doped with one or more positive divalent elements such as Mg, but with a different composition ratio, and an element X containing In and Zn and different from the semiconductor layer In the case of the amorphous oxide film that is included, the In composition ratio is preferably smaller than that of the semiconductor layer. Moreover, it is preferable that the composition ratio of the element X is larger than that of the semiconductor layer.
The oxide resistance layer is preferably an oxide containing In and Zn. In the case of including these, there is no movement of elements between the oxide resistance layer and the semiconductor layer, and there is no possibility that the shift of the threshold voltage becomes large when a stress test or the like is performed.

Each component (layer) of the above-described thin film transistor can be formed by a method known in this technical field.
Specifically, as a film formation method, a chemical film formation method such as a spray method, a dip method, or a CVD method, or a physical film formation method such as a sputtering method, a vacuum evaporation method, an ion plating method, or a pulse laser deposition method. The method can be used. Since the carrier density is easily controlled and the film quality can be easily improved, a physical film formation method is preferably used, and a sputtering method is more preferably used because of high productivity.
In sputtering, a method using a sintered complex oxide target, a method using co-sputtering using a plurality of sintered targets, a method using reactive sputtering using an alloy target, and the like can be used. Preferably, a composite oxide sintered target is used. Although well-known things, such as RF, DC, or AC sputtering, can be utilized, DC or AC sputtering is preferable from the viewpoint of uniformity and mass productivity (equipment cost).

The formed film can be patterned by various etching methods.
In the present invention, the semiconductor layer is preferably formed by DC or AC sputtering using the target of the present invention. By using DC or AC sputtering, damage during film formation can be reduced as compared with RF sputtering. For this reason, in the field effect transistor, effects such as a reduction in threshold voltage shift, an improvement in mobility, a reduction in threshold voltage, and a reduction in S value can be expected.

Moreover, in this invention, it is preferable to heat-process at 70-350 degreeC after semiconductor layer film-forming. In particular, heat treatment is preferably performed at 70 to 350 ° C. after the semiconductor layer and the semiconductor protective film are formed. If it is 70 degreeC or more, sufficient thermal stability and heat resistance of the transistor obtained can be hold | maintained, sufficient mobility can be hold | maintained, and there is no possibility that S value may become large and a threshold voltage may become high. On the other hand, if it is 350 degrees C or less, a board | substrate without heat resistance can also be used, and there is no possibility that the installation expense for heat processing may start.
The heat treatment temperature is more preferably 80 to 260 ° C, further preferably 90 to 180 ° C, and particularly preferably 100 to 150 ° C. In particular, a heat treatment temperature of 180 ° C. or lower is preferable because a resin substrate having low heat resistance such as PEN can be used as the substrate.
The heat treatment time is usually preferably 1 second to 24 hours, but is preferably adjusted by the treatment temperature. For example, at 70 to 180 ° C., 10 minutes to 24 hours are more preferable, 20 minutes to 6 hours are more preferable, and 30 minutes to 3 hours are particularly preferable. In 180-260 degreeC, 6 minutes to 4 hours are more preferable, and 15 minutes to 2 hours are still more preferable. At 260 to 300 ° C., 30 seconds to 4 hours is more preferable, and 1 minute to 2 hours is particularly preferable. At 300 to 350 ° C., 1 second to 1 hour is more preferable, and 2 seconds to 30 minutes is particularly preferable.
The heat treatment is preferably performed in an inert gas in an environment where the oxygen partial pressure is 10 ⁻³ Pa or less, or after the semiconductor layer is covered with a protective film. Reproducibility is improved under the above conditions.

In the thin film transistor obtained by the manufacturing method of the present invention, mobility is preferably at least ^{1 cm} 2 / Vs, more preferably at least ^{3 cm} 2 / Vs, and particularly preferably equal to or greater than ^{8 cm} 2 / Vs. If it is 1 cm ² / Vs or more, the switching speed does not slow down and it is optimal for use in a large-screen high-definition display.
The on / off ratio is preferably 10 ⁶ or more, more preferably 10 ⁷ or more, and particularly preferably 10 ⁸ or more.
The off current is preferably 2 pA or less, and more preferably 1 pA or less. When the off-current is 2 pA or less, sufficient contrast is obtained when used as a TFT of a display, and good screen uniformity is obtained.
The gate leakage current is preferably 1 pA or less. If it is 1 pA or more, good contrast can be obtained when used as a TFT of a display.
The threshold voltage is usually 0 to 10V, preferably 0 to 4V, more preferably 0 to 3V, and particularly preferably 0 to 2V. If it is 0 V or higher, normally-on is not required, and it is not necessary to apply a voltage at the time of off, so that power consumption can be kept low. If it is 10 V or less, the drive voltage does not increase, the power consumption can be kept low, and the mobility can be kept low.
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 0.8 V / dec or less, the drive voltage can be kept low, and the power consumption can also be suppressed. 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.

Further, the shift amount of the threshold voltage before and after being applied for 100 hours at a DC voltage of 10 μA at 50 ° C. is preferably 1.0 V or less, and more preferably 0.5 V or less. When the voltage is 1.0 V or less, the image quality does not change when used as a transistor of an organic EL display.
Further, it is preferable that the hysteresis is small when the gate voltage is raised or lowered on the transfer curve.
The ratio W / L of the channel width W to the channel length L is usually 0.1 to 100, preferably 0.5 to 20, and particularly preferably 1 to 8. If W / L is 100 or less, the leakage current does not increase and the on / off ratio may decrease. If it is 0.1 or more, the field effect mobility does not decrease and pinch-off becomes clear. The channel length L is usually 0.1 to 1000 μm, preferably 1 to 100 μm, and more preferably 2 to 10 μm. If it is 0.1 μm or more, it is difficult to produce industrially and there is no fear that the leakage current increases, and if it is 1000 μm or less, the device does not become too large.

  The thin film transistor produced by the production method of the present invention is suitable, for example, for TFTs for flat panel displays, particularly for devices such as liquid crystal panels.

Example 1
As the discharge plasma sintering machine, a discharge plasma sintering machine (SPS-3.20MK-IV) manufactured by Izumi Tech Co., Ltd. was used. As the sintering jig, a cylindrical one made of graphite and having a diameter of 10 cm was used.

This sintered jig was mixed with indium oxide (In ₂ O ₃ ) having an average particle diameter of 1.5 μm and metal Sn having an average particle diameter of 3.3 μm (In ₂ O ₃ approximately 92 g, metal Sn approximately 8 g, tin A mixture in which the content was about 10 atomic%, that is, In / (Sn + In) = about 0.9) was mixed uniformly, a pressure of about 30 MPa was applied, and the inside of the sintering chamber was deaerated to about 10 Pa.
Next, a DC pulse current having a peak current value of about 1000 A (pulse width 2.4 milliseconds, period 30 Hz) was passed through the jig, and the periphery of the sample was heated at a temperature increase rate of about 50 ° C./min. Finally, the peak current value was increased to about 6000 A, heated to 850 ° C. or 950 ° C., and held at this temperature (sintering temperature) for 5 minutes. Thereafter, energization and pressurization were stopped, the sample was cooled to room temperature, and the inside of the sintering chamber was returned to atmospheric pressure.
The sintered body taken out in this state was a disk having a diameter of about 10 cm and a thickness of about 5 mm. Table 1 shows the sintering conditions and the properties of the obtained sintered body.
The bulk resistance was measured with Loresta (Mitsubishi Chemical). Further, the density was measured by Archimedes method using a sample piece cut into a 2 cm square size using water as a solvent.

The result of X-ray diffraction of the sintered body 2 is shown in FIG.
An indium oxide peak and a metal Sn peak were observed. Further, FIG. 7 shows the results of surface analysis of an electron beam microanalyzer (EPMA). It was found that metal Sn exists with a particle size of about 7.2 μm. The content of metal Sn was the same as the mixing ratio of the raw materials. The same applies to other embodiments.

The obtained sintered body was ground and then bonded to a Cu backing plate with metallic indium to obtain a sputtering target. This was installed in a sputtering apparatus manufactured by Shimadzu Corporation, DC plasma sputtering output: 400 W, sputtering gas Ar: 99%, O ₂ : 1%, continuous sputtering for 25 hours (10 kWhr = 25 hr × 400 W) on the surface The generated nodules were observed. As a result, no nodules were observed.

Example 2
A sintered body was produced and evaluated in the same manner as in Example 1 except that metal zinc was used instead of metal tin and the sintering temperature was changed to the temperature shown in Table 2. The metal atom ratio [In / (In + Zn)] was 0.83.
The results are shown in Table 2.

The result of the X-ray diffraction of the sintered body 4 is shown in FIG.
An indium oxide peak and a metal Zn peak were observed. Moreover, the result of having performed the surface analysis of EPMA is shown in FIG. Zn was found to be present with a particle size of about 10 μm.

  About the obtained sintered compact, processing of the sputtering target and observation of a nodule were performed similarly to Example 1. As a result, no nodules were observed.

Example 3
A sintered body was produced and evaluated in the same manner as in Example 1 except that metal zinc and metal tin were used instead of metal tin and the sintering temperature was changed to the temperature shown in Table 3. The atomic ratio of metal atoms was as follows.
In / (In + Zn + Sn) = 0.80
Zn / (In + Zn + Sn) = 0.11
Sn / (In + Zn + Sn) = 0.09
The results are shown in Table 3.

  From the results of X-ray diffraction of the sintered bodies 6 and 7, the peak of indium oxide and the peaks of metal Zn and metal Sn were observed. Further, when surface analysis of EPMA was performed, it was found that metal Zn and metal Sn exist with a particle size of about 10 μm.

  About the obtained sintered compact, processing of the sputtering target and observation of a nodule were performed similarly to Example 1. As a result, no nodules were observed.

Example 4
A mixed powder (atomic ratio [Sn / (In + Sn)] = 0.05) of tin oxide powder and indium oxide powder was mixed for 24 hours by a wet ball mill. The mixed powder dried with a spray dryer was filled in a mold and pressure-molded with a cold press.
The obtained molded body was sintered at 1450 ° C. for 24 hours. The sintered body was pulverized for 36 hours by a wet ball mill. As a result, an ITO powder having an average particle size of 4.8 μm was obtained.
To this ITO powder, metal Sn (average particle size: 3.3 μm) was mixed so as to be 10 wt% ([In / (Sn + In)] = approximately 0.9) of the entire mixed powder.
This mixed powder was put in a sintering jig and subjected to discharge plasma sintering in the same manner as in Example 1 to obtain a sintered body. The results are shown in Table 4.

  From the results of X-ray diffraction of these sintered bodies, a peak of indium oxide in which tin was dissolved and a peak of metal Sn were observed. Further, when surface analysis of EPMA was performed, it was found that metal Sn exists with a particle size of about 10 μm.

  About the obtained sintered compact, processing of the sputtering target and observation of a nodule were performed similarly to Example 1. As a result, no nodules were observed.

Comparative Example 1
The following commercially available ITO targets A to C were evaluated. The results are shown in Table 5. The tin atom content [Sn / (In + Sn)] is 0.16 (atomic ratio).

FIG. 10 shows the EPMA analysis result (25 μm □ field of view) of the cross section of the target A. Thereby, it turns out that tin oxide exists in the magnitude | size of 1-3 micrometers.
Further, the result of X-ray diffraction is shown in FIG. In this figure, the vertical axis is enlarged 10 times the normal diffraction spectrum. In this spectrum, three peaks characteristic of In ₄ Sn ₃ O ₁₂ appear in a region where 2θ is 19 ° to 24 °. Therefore, dispersion of tin oxide observed in FIG. _10, it is estimated a In ₄ Sn _{3 O 12} compound.

FIG. 12 is a diagram showing a distribution of resistance values when the scanning-type spreading resistance microscope (SSRM) is observed in the same field of view.
It can be seen that there is an island portion having a resistance value that is one digit larger. This part is an In ₄ Sn ₃ O ₁₂ compound.
When a nodule generation test was carried out in the same manner as in Example 1, a large amount of nodules was observed. Thus, a large amount of nodules is generated in the target in which the In ₄ Sn ₃ O ₁₂ compound or the like is dispersed.

Comparative Example 2
A mixed powder in which tin oxide powder and indium oxide powder were mixed so that the atomic ratio [Sn / (In + Sn)] was 0.16 was mixed in a wet ball mill for 24 hours.
The mixed powder dried by the spray dryer was put in a sintering jig, and was subjected to discharge plasma sintering in the same manner as in Example 1 to obtain a sintered body. The sintering temperature was 950 ° C.

The peak of X-ray diffraction of this sintered body was composed of an In ₂ O ₃ phase and a SnO ₂ phase. The density of the sintered body was 6.22 g / cm ³ and the bulk resistance was 0.44 mΩcm.
About the obtained sintered compact, processing of the sputtering target and observation of a nodule were performed similarly to Example 1. As a result, arcing, which is abnormal discharge, occurred during sputter discharge, and a large amount of nodules were observed on the target surface after the discharge experiment was completed. Thus, a large amount of nodules was generated in the target in which SnO ₂ was dispersed.

Example 5
A mixed powder composed of tin oxide powder and indium oxide powder [atomic ratio Sn / (In + Sn) = 0.05] was mixed for 24 hours by a wet ball mill. This was dried with a spray dryer, filled into a mold, and pressure-molded with a cold press.
The obtained molded body was sintered at 1450 ° C. for 24 hours.
The sintered body was pulverized for 36 hours by a wet ball mill. As a result, an ITO powder having an average particle size of 4.8 μm was obtained.
To this ITO powder, metal Sn (average particle size: 0.5 μm, 1 μm, 2 μm, 5 μm) was mixed so as to be 5 wt% of the entire mixed powder.
This mixed powder was put in a sintering jig and subjected to discharge plasma sintering in the same manner as in Example 1 to obtain a sintered body. The sintering temperature was 900 ° C. The results are shown in Table 6.

In each of the sintered bodies, the peak of indium oxide in which tin was dissolved and the peak of metal Sn were observed from the result of X-ray diffraction.
Further, when surface analysis of EPMA was performed, it was found that the average particle diameters of metal Sn were 0.9 μm, 1.2 μm, 3.1 μm, and 7.2 μm, respectively. The bulk resistance of the obtained sintered body changes according to the particle size of the metal Sn particles.

  About the obtained sintered compact, processing of the sputtering target and observation of a nodule were performed similarly to Example 1. As a result, no nodules were observed.

  The indium oxide sintered body of the present invention is suitable as a sputtering target used when forming a semiconductor film used in transparent electrodes and semiconductor elements of various display devices.

It is process drawing of the 1st manufacturing method of this invention. It is process drawing at the time of providing a calcination process in the 1st manufacturing method. It is process drawing of the 2nd manufacturing method of this invention. It is a schematic sectional drawing of an example of a thin-film transistor. It is a schematic sectional drawing of the other example of a thin-film transistor, (1) is the schematic before patterning of a source / drain electrode, (2) is the schematic after patterning of a source / drain electrode. 2 is an X-ray diffraction chart of a sintered body 2 manufactured in Example 1. FIG. It is a result of the EPMA analysis of the sintered compact 2. FIG. 4 is an X-ray diffraction chart of a sintered body 4 manufactured in Example 2. It is a result of the EPMA analysis of the sintered compact 4. FIG. 3 is a result of EPMA analysis of target A evaluated in Comparative Example 1. FIG. 3 is an X-ray diffraction chart of target A. It is a result of SSRM analysis of target A.

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 Protective film 17 Source / drain electrode

Claims (12)

  An indium oxide sintered body having an indium oxide phase and a metal phase.   The indium oxide sintered body according to claim 1, wherein the content of the metal phase is 1 wt% to 30 wt% of the entire sintered body.   3. The indium oxide sintered body according to claim 1, wherein an average particle diameter of the metal phase is less than 20 μm.   The indium oxide sintered body according to any one of claims 1 to 3, wherein the metal phase is composed of metal tin and / or metal zinc.   5. The indium oxide sintered body according to claim 1, wherein a part of the indium oxide phase is substituted and dissolved by an oxide of another metal element.   The sputtering target which consists of an indium oxide sintered compact in any one of Claims 1-5.   The method for producing an indium oxide sintered body according to any one of claims 1 to 4, wherein a powder obtained by mixing an indium compound and metal fine particles is subjected to discharge plasma sintering.   The method for producing an indium oxide sintered body according to any one of claims 1 to 5, wherein a powder obtained by mixing an indium compound and metal oxide fine particles is subjected to discharge plasma sintering.   An oxide thin film obtained by sputtering using the sputtering target according to claim 6 at a film forming temperature of 25 to 450C.   The oxide thin film according to claim 9, wherein the oxide thin film is a thin film for a channel layer of a thin film transistor. A method of manufacturing a thin film transistor including an oxide thin film and an oxide insulator layer,
(I) heat-treating the oxide thin film of claim 10 in an oxidizing atmosphere; and (ii) forming an oxide insulator layer on the heat-treated oxide thin film;
A method for manufacturing a thin film transistor, comprising:   The semiconductor device provided with the thin-film transistor manufactured by the manufacturing method of the thin-film transistor of Claim 11.