JP6141332B2 - Sputtering target, oxide semiconductor thin film, and manufacturing method thereof - Google Patents

Description

  The present invention relates to a sputtering target for producing an oxide thin film such as an oxide semiconductor or a transparent conductive film, a thin film produced using the target, a thin film transistor including the thin film, and a method for producing them.

  Field effect transistors such as thin film transistors (TFTs) are widely used as unit electronic elements, high frequency signal amplifying elements, liquid crystal driving elements, etc. for semiconductor memory integrated circuits, and are currently the most widely used electronic devices. . In particular, with the remarkable development of display devices in recent years, in various display devices such as liquid crystal display devices (LCD), electroluminescence display devices (EL), and field emission displays (FED), a driving voltage is applied to the display elements. TFTs are often used as switching elements for driving display devices.

  As a material for a semiconductor layer (channel layer) which is a main member of a field effect transistor, a silicon semiconductor compound is most widely used. In general, a silicon single crystal is used for a high-frequency amplifying element or an integrated circuit element that requires high-speed operation. On the other hand, an amorphous silicon semiconductor (amorphous silicon) is used for a liquid crystal driving element or the like because of a demand for a large area.

Although an amorphous silicon thin film can be formed at a relatively low temperature, its switching speed is slower than that of a crystalline thin film, so when used as a switching element for driving a display device, it may not be able to follow the display of high-speed movies. is there. Specifically, in a liquid crystal television with a resolution of VGA, amorphous silicon having a mobility of 0.5 to ¹ cm ² / Vs could be used, but when the resolution becomes SXGA, UXGA, QXGA or higher, 2 cm ² / Mobility greater than Vs is required. Further, when the driving frequency is increased in order to improve the image quality, higher mobility is required.

  On the other hand, although the crystalline silicon-based thin film has a high mobility, there are problems such as requiring a large amount of energy and the number of processes for manufacturing, and a problem that it is difficult to increase the area. For example, when annealing a silicon-based thin film, laser annealing using a high temperature of 800 ° C. or higher and expensive equipment is necessary. In addition, since the crystalline silicon-based thin film is normally limited to the top gate configuration of the TFT, the cost reduction such as reduction of the number of masks is difficult.

  In order to solve such a problem, a thin film transistor using an oxide semiconductor film made of indium oxide, zinc oxide, and gallium oxide has been studied. In general, an oxide semiconductor thin film is manufactured by sputtering using a target (sputtering target) made of an oxide sintered body.

For example, a target made of a compound having a homologous crystal structure represented by general formulas In ₂ Ga ₂ ZnO ₇ and InGaZnO ₄ is known (Patent Documents 1, 2, and 3).
However, in order to increase the sintering density (relative density) with this target, it is necessary to sinter in an oxidizing atmosphere. In that case, in order to reduce the resistance of the target, it is necessary to perform a reduction treatment at a high temperature after sintering. was there. In addition, when the target is used for a long period of time, the characteristics and deposition rate of the obtained film change greatly, and abnormal discharge occurs due to InGaZnO ₄ or In ₂ Ga ₂ ZnO ₇ abnormally grown during sintering. There were problems such as generation of particles at times. If abnormal discharge frequently occurs, the plasma discharge state becomes unstable, and stable film formation is not performed, which adversely affects the film characteristics.

On the other hand, a thin film transistor using an amorphous oxide semiconductor film that does not contain gallium and is made of indium oxide and zinc oxide has also been proposed (Patent Document 4).
However, there is a problem that the normally-off operation of the TFT cannot be realized unless the oxygen partial pressure during film formation is increased.

In addition, a sputtering target for a protective layer of an optical information recording medium in which an additive element such as Ta, Y, or Si is added to an In ₂ O ₃ —SnO ₂ —ZnO-based oxide mainly composed of tin oxide has been studied ( Patent Documents 5 and 6).
However, these targets are not for oxide semiconductors, and there are problems that aggregates of insulating materials are easily formed, resistance values are increased, and abnormal discharge is likely to occur.

JP-A-8-245220 JP 2007-73312 A International Publication No. 2009/084537 International Publication No. 2005/088726 International Publication No. 2005/0778152 International Publication No. 2005/078153

The present invention includes an oxide containing indium element (In), tin element (Sn), zinc element (Zn), and magnesium element (Mg), and can realize a TFT having high mobility and high reliability. The aim is to provide a target.
Furthermore, an object of the present invention is to provide a sputtering target capable of manufacturing a TFT having high mobility and high reliability by a back channel etching method with high productivity.

According to the present invention, the following sputtering target and the like are provided.
1. It consists of an oxide containing indium element (In), tin element (Sn), zinc element (Zn), and magnesium element (Mg), and is represented by In ₂ O ₃ (ZnO) _m (m is 0.1 to 20). Sputtering target comprising a homologous structural compound and a spinel structural compound represented by Zn ₂ SnO ₄ .
2. 2. The sputtering target according to 1, wherein an atomic ratio of the indium element, tin element, zinc element and magnesium element satisfies the following formulas (1) to (4).
0.05 ≦ In / (In + Sn + Zn + Mg) ≦ 0.70 (1)
0.01 ≦ Sn / (In + Sn + Zn + Mg) ≦ 0.35 (2)
0.01 ≦ Zn / (In + Sn + Zn + Mg) ≦ 0.90 (3)
0.01 ≦ Mg / (In + Sn + Zn + Mg) ≦ 0.30 (4)
(In the formula, In, Sn, Zn, and Mg each indicate an atomic ratio of each element in the sputtering target.)
3. 3. The sputtering target according to 1 or 2, wherein the relative density is 97% or more and the bulk specific resistance is 10 mΩcm or less.
4). Including heating the molded body at a temperature rising rate of 2 ° C./min or less in a temperature range of 300 ° C. to 500 ° C., holding the molded body at 1200 ° C. to 1650 ° C. for 10 to 50 hours, and sintering. 4. A method for producing a sputtering target according to any one of 3 above.
An oxide semiconductor thin film formed by sputtering using the sputtering target according to any one of 5.1 to 3.
6). 6. The oxide semiconductor thin film according to 5, which is insoluble in a phosphoric acid etching solution and soluble in an oxalic acid etching solution.
7). 7. The oxide semiconductor thin film according to 6, wherein an etching rate at 35 ° C. with the phosphoric acid etching solution is 10 nm / min or less and an etching rate at 35 ° C. with the oxalic acid etching solution is 20 nm / min or more.
8). Oxidation formed by sputtering using a sputtering target according to any one of 1 to 3 in an atmosphere of a mixed gas containing one or more selected from water vapor, oxygen gas and nitrous oxide gas and a rare gas Method for manufacturing a semiconductor thin film.
9. 9. The method for producing an oxide semiconductor thin film according to 8, wherein the oxide semiconductor thin film is formed in an atmosphere of a mixed gas containing at least water vapor and a rare gas.
10. The manufacturing method of the oxide semiconductor thin film of 8 or 9 whose ratio of the water vapor | steam contained in the said mixed gas is 0.1%-25% by partial pressure ratio.
11. The manufacturing method of the oxide semiconductor thin film in any one of 8-10 whose ratio of the oxygen gas contained in the said mixed gas is 0.1%-30% by partial pressure ratio.
12 The oxide semiconductor thin film is formed by sequentially transporting the substrate to a position facing three or more targets arranged in parallel in the vacuum chamber at a predetermined interval, and from each AC power source to each target. In the case of alternately applying a negative potential and a positive potential, at least one of the outputs from the AC power supply is switched between two or more targets that are branched and connected while switching the target to which the potential is applied. The manufacturing method of the oxide semiconductor thin film in any one of 8-11 performed with the sputtering method which generates a plasma on a target and forms into a film on a substrate surface.
13. 13. The method for producing an oxide semiconductor thin film according to 12, wherein the AC power density of the AC power source is 3 W / cm ² or more and 20 W / cm ² or less.
14 The manufacturing method of the oxide semiconductor thin film of 12 or 13 whose frequency of the said alternating current power supply is 10 kHz-1 MHz.
A thin film transistor having the oxide semiconductor thin film according to any one of 15.5 to 7 as a channel layer.
16. 16. The thin film transistor according to 15, wherein the field effect mobility is 10 cm ² / Vs or more.
A thin film transistor having a protective film containing at least SiNx (x is an arbitrary number) on the oxide semiconductor thin film according to any one of 17.5 to 7.
18. A method of manufacturing a thin film transistor using the oxide semiconductor thin film according to any one of 5 to 7 as a semiconductor active layer, wherein the semiconductor thin film and the electrode are different without stacking an etching stopper on the semiconductor thin film. A method of manufacturing a thin film transistor, comprising a step of patterning using an etching solution, and the step of contacting the semiconductor thin film directly with the etching solution when patterning an electrode.
19. A display device comprising the thin film transistor according to any one of 15 to 17.

According to the present invention, it is possible to realize a TFT having high mobility and high reliability, including an oxide containing indium element (In), tin element (Sn), zinc element (Zn), and magnesium element (Mg). A sputtering target can be provided.
Further, it is possible to provide a sputtering target capable of manufacturing a TFT having high mobility and high reliability with high productivity by a back channel etching method.

2 is an X-ray chart of a sintered body obtained in Example 1. 3 is an X-ray chart of a sintered body obtained in Example 2. 4 is an X-ray chart of a sintered body obtained in Example 3. It is a figure which shows the sputtering device used for one Embodiment of this invention.

  Hereinafter, although the sputtering target of this invention, an oxide thin film, a thin-film transistor, a display apparatus, and these manufacturing methods are demonstrated in detail, this invention is not limited to the following embodiment and an Example.

The sputtering target of the present invention is composed of an oxide containing indium element (In), tin element (Sn), zinc element (Zn), and magnesium element (Mg), and In ₂ O ₃ (ZnO) _m (m is 0). 0.1-20) and a spinel structure compound represented by Zn ₂ SnO ₄ .
The presence or absence of the homologous structural compound and the spinel structural compound can be confirmed by X-ray diffraction.

  The homologous structure is a crystal structure composed of a “natural superlattice” structure having a long period obtained by superposing several crystal layers of different substances. When the crystal period or the thickness of each thin film layer is about nanometers, depending on the combination of the chemical composition of each layer and the thickness of the layer, it differs from the properties of a single substance or a mixed crystal in which each layer is uniformly mixed. Unique characteristics can be obtained. The crystal structure of the homologous phase can be confirmed, for example, because the X-ray diffraction pattern of the powder obtained by pulverizing the target matches the crystal structure X-ray diffraction pattern of the homologous phase assumed from the composition ratio. Specifically, it can be confirmed from the coincidence with the crystal structure X-ray diffraction pattern of the homologous phase obtained from JCPDS (Joint Committee of Powder Diffraction Standards) card or ICSD (Inorganic Crystal Structure Database).

The spinel structure can be confirmed by observing the peak of the spinel structure compound as a result of X-ray diffraction measurement of the sputtering target.
The spinel structure is described in detail in “Introduction to West Solid Chemistry” (Kodansha Scientific). According to this, the spinel structure is as follows.

Spinel has a composition formula of AB ₂ O ₄ and is classified into a normal spinel structure, a reverse spinel structure, and an intermediate structure between the two when classified according to the coordination state of A ions and B ions.

The regular spinel has a structure in which A is filled in one-eighth of the tetrahedral gap of the three-dimensional face-centered lattice formed by O ²⁻ and B is filled in one-half of the octahedral gap. The reverse spinel structure has a structure in which one-eighth of the tetrahedral gap is filled with B and half of the octahedral gap is filled with A and B. Generally, it is a cubic crystal, but some of the cubic crystals are distorted.
Also included in the spinel structure compound are substituted solid solutions in which atoms and ions in the crystal structure are partially substituted with other atoms, and interstitial solid solutions in which other atoms are added to interstitial positions.

By including a homologous structure compound represented by In ₂ O ₃ (ZnO) _m (m is 0.1 to 20), the relative density of the target is easily improved, the specific resistance is also easily lowered, and abnormal discharge is caused. It is possible to make it a difficult target.
For example, m is an integer, preferably 0.1 to 10, more preferably 0.5 to 7, and still more preferably 2 to 5.

In addition, by including a spinel structure compound represented by Zn ₂ SnO ₄ , Mg element is dissolved, and even if the content of Mg is large, high resistance MgO is prevented from being generated in the target. It becomes easy to lower the target resistance and to suppress abnormal discharge.

In the sputtering target of the present invention, it is preferable that the atomic ratio of each element satisfies the following formulas (1) to (4).
0.05 ≦ In / (In + Sn + Zn + Mg) ≦ 0.70 (1)
0.01 ≦ Sn / (In + Sn + Zn + Mg) ≦ 0.35 (2)
0.01 ≦ Zn / (In + Sn + Zn + Mg) ≦ 0.90 (3)
0.01 ≦ Mg / (In + Sn + Zn + Mg) ≦ 0.30 (4)
(In the formula, In, Sn, Zn, and Mg each indicate an atomic ratio of each element in the sputtering target.)

In the above formula (1), when the amount of In element is 0.05 or more, the bulk resistance value of the sputtering target tends to be low, and DC sputtering becomes easy.
On the other hand, when the amount of In element is 0.70 or less, the carrier concentration of a thin film produced using the target does not become too high, and can be used as a semiconductor thin film.

  From the above, the concentration of In is preferably 0.05 ≦ In / (In + Sn + Zn + Mg) ≦ 0.70. More preferably, the amount of In element [In / (In + Sn + Zn + Mg)] is 0.10 to 0.60.

In the above formula (2), when the amount of Sn element is 0.01 or more, the density of the target is easily improved, and the bulk resistance value of the sputtering target is easily lowered.
On the other hand, if the amount of Sn element is 0.35 or less, SnO ₂ that causes abnormal discharge is difficult to deposit in the target.
Accordingly, the Sn concentration is preferably 0.01 ≦ Sn / (In + Sn + Zn + Mg) ≦ 0.35.

The amount of Sn element [Sn / (In + Sn + Zn + Mg)] is more preferably 0.03 to 0.35, and still more preferably 0.05 to 0.30.
In the above formula (3), when the amount of Zn element is 0.01 or more, the target density is easily improved and the target resistance is also easily lowered. On the other hand, when the amount of Zn element is 0.90 or less, ZnO that causes abnormal discharge is difficult to deposit in the target.

From the above, the Zn concentration is preferably 0.01 ≦ Zn / (In + Sn + Zn + Mg) ≦ 0.90.
The amount of Zn element [Zn / (In + Sn + Zn + Mg)] is more preferably 0.03 to 0.85, and still more preferably 0.05 to 0.80.
In the above formula (4), when the amount of Mg element is 0.01 or more, the carrier concentration of a thin film manufactured using the target is not easily increased, and good semiconductor characteristics are easily exhibited.

On the other hand, when the amount of Mg element is 0.30 or less, it becomes difficult for the target to have high resistance due to MgO appearing alone.
From the above, the Mg concentration is preferably 0.01 ≦ Mg / (In + Sn + Zn + Mg) ≦ 0.30.
The amount of Mg element [Mg / (In + Sn + Zn + Mg)] is more preferably 0.02 to 0.27, and still more preferably 0.02 to 0.25.

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

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

As described above, the metal element contained in the sputtering target is substantially composed of In, Sn, Zn, and Mg, and may contain other inevitable impurities as long as the effects of the present invention are not impaired.
In the present invention, “substantially” means that the effect as a sputtering target is caused by the above In, Sn, Zn and Mg, or 95% by weight to 100% by weight (preferably 98% by weight) of the metal element of the sputtering target. Means 100% by weight or less), In, Sn, Zn and Mg.

  The sputtering target of the present invention preferably has a relative density of 97% or more. In the case where an oxide semiconductor thin film is formed by increasing the sputtering output on a large substrate (1G size or more), the relative density is preferably 97% or more. 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 is the theoretical density, which is defined as 100%.

  If the relative density is 97% or more, a stable sputtering state is maintained. When forming a film with a large substrate and increasing the sputtering output, the target surface may be blackened or abnormal discharge may occur if the relative density is less than 97%. The relative density is more preferably 98.5% or more, still more preferably 99% or more.

  The relative density can be calculated from the actual density and the theoretical density measured by the Archimedes method. The relative density is preferably 100% or less. If it is 100% or less, it becomes difficult for metal particles to be generated in the sintered body or to form a lower oxide, and it is not necessary to strictly adjust the oxygen supply amount during film formation.

  In addition, the density can be adjusted by performing a post-treatment step such as a heat treatment operation under a reducing atmosphere after sintering. As the reducing atmosphere, an atmosphere of argon, nitrogen, hydrogen, or a mixed gas atmosphere thereof is used.

The sputtering target of the present invention preferably has a relative density of 97% or more and a bulk specific resistance of 10 mΩcm or less. Thereby, when sputtering the sputtering target of this invention, generation | occurrence | production of abnormal discharge can be suppressed. The sputtering target of the present invention can form a high-quality oxide semiconductor thin film efficiently, inexpensively and with energy saving.
A bulk specific resistance can be measured by the method as described in an Example, for example.

The maximum grain size of the crystal in the sputtering target of the present invention is desirably 8 μm or less. If the crystal has a particle size of 8 μm or less, nodules are hardly generated.
When the target surface is cut by sputtering, the cutting speed varies depending on the direction of the crystal plane, and irregularities are generated on the target surface. The size of the unevenness depends on the crystal grain size present in the sputtering target. In the target having a large crystal grain size, the unevenness is increased, and it is considered that nodules are generated from the convex portion.

  When the shape of the sputtering target is circular, the maximum grain size of these sputtering target crystals is the center point (one place) of the circle and the center point and the peripheral part on two center lines orthogonal to the center point. At a total of five intermediate points (four locations), and when the sputtering target has a quadrangular shape, the central point (one location) and the intermediate point (4) between the central point and the corner on the diagonal of the quadrangle. The maximum diameter of particles having the maximum diameter observed in a 100 μm square frame at a total of five locations is measured, and the average value of the particle sizes of the maximum particles present in each of these five locations is Represent. The particle size is measured for the major axis of the crystal grains. The crystal grains can be observed with a scanning electron microscope (SEM).

The manufacturing method of the sputtering target of the present invention includes the following two steps.
(1) Step of mixing raw material compounds and molding to form a molded body (2) Step of sintering the molded body

Hereinafter, each step will be described.
(1) Step of mixing raw material compounds and forming into a molded body The raw material compound is not particularly limited, and is a compound containing In, Sn, Zn and Mg, and the sintered body has the following atomic ratio. A compound that can be used may be used.
0.05 ≦ In / (In + Sn + Zn + Mg) ≦ 0.70 (1)
0.01 ≦ Sn / (In + Sn + Zn + Mg) ≦ 0.35 (2)
0.01 ≦ Zn / (In + Sn + Zn + Mg) ≦ 0.90 (3)
0.01 ≦ Mg / (In + Sn + Zn + Mg) ≦ 0.30 (4)
(In the formula, In, Sn, Zn, and Mg each indicate an atomic ratio of each element in the sputtering target.)

For example, a combination of indium oxide, tin oxide, zinc oxide and magnesium oxide can be used. The raw material is preferably a powder.
The raw material is preferably a mixed powder of indium oxide, tin oxide, zinc oxide and magnesium oxide.

  When a single metal is used as the raw material, for example, when a combination of indium oxide, tin oxide, zinc oxide and single Mg is used as the raw material powder, single Mg particles are present in the obtained sintered body, In some cases, metal particles on the surface of the target melt in the film and are not released from the target, and the composition of the obtained film and the composition of the sintered body may be greatly different.

  The average particle size of the raw material powder is preferably 0.1 μm to 1.2 μm, more preferably 0.1 μm to 1.0 μm. The average particle diameter of the raw material powder can be measured with a laser diffraction type particle size distribution apparatus or the like.

For example, In ₂ O ₃ powder having an average particle diameter of 0.1 μm to 1.2 μm, SnO ₂ powder having an average particle diameter of 0.1 μm to 1.2 μm, and ZnO powder having an average particle diameter of 0.1 μm to 1.2 μm And the oxide containing the MgO powder whose average particle diameter is 0.1 micrometer-1.2 micrometers is made into raw material powder, and these are prepared in the ratio which satisfy | fills said Formula (1)-(4).

  The mixing and forming method in step (1) is not particularly limited, and can be performed using a known method. For example, an aqueous solvent is blended with a raw material powder containing a mixed powder of oxides containing indium oxide powder, tin oxide, zinc oxide and magnesium oxide powder, and the resulting slurry is mixed for 12 hours or more, followed by solid-liquid separation.・ Dry and granulate, and then put this granulated product into a mold and mold it.

  For mixing, a wet or dry ball mill, vibration mill, bead mill, or the like can be used. In order to obtain uniform and fine crystal grains and vacancies, a bead mill mixing method is most preferable because the crushing efficiency of the agglomerates is high in a short time and the additive is well dispersed.

  The mixing time by the ball mill is preferably 15 hours or more, more preferably 19 hours or more. This is because if the mixing time is insufficient, a high resistance compound such as MgO may be formed in the finally obtained sintered body.

The pulverization and mixing time by the bead mill varies depending on the size of the apparatus and the amount of slurry to be processed, but is appropriately adjusted so that the particle size distribution in the slurry is all uniform at 1 μm or less.
Further, when mixing, it is preferable to add an arbitrary amount of a binder and mix them at the same time. As the binder, polyvinyl alcohol, vinyl acetate, or the like can be used.

  Next, granulated powder is obtained from the raw material powder slurry. In granulation, it is preferable to perform rapid drying granulation. As an apparatus for rapid drying granulation, a spray dryer is widely used. The specific drying conditions are determined by various conditions such as the slurry concentration of the slurry to be dried, the temperature of hot air used for drying, the air volume, etc., and therefore, it is necessary to obtain optimum conditions in advance.

When natural drying is performed, the sedimentation speed varies depending on the specific gravity difference of the raw material powder, so that separation of In ₂ O ₃ powder, Sn ₂ O ₂ powder, ZnO powder and MgO powder occurs, and uniform granulated powder may not be obtained. There is.
The granulated powder is usually molded by a die press or cold isostatic press (CIP) at a pressure of, for example, 1.2 ton / cm ² or more to obtain a molded body.

(2) The process of sintering a molded object The obtained molded object can be sintered for 10 to 50 hours at the sintering temperature of 1200-1650 degreeC, and a sintered compact can be obtained.
The sintering temperature is preferably 1300 to 1600 ° C, more preferably 1350 to 1550 ° C, and still more preferably 1400 to 1500 ° C. The sintering time is preferably 12 to 40 hours, more preferably 13 to 30 hours.

  When the sintering temperature is 1200 ° C. or more and the sintering time is 10 hours or more, zinc oxide or magnesium oxide is hardly formed inside the target, and an abnormal discharge hardly occurs. On the other hand, if the sintering temperature is 1650 ° C. or less and the sintering time is 50 hours or less, the increase in the average crystal grain size due to remarkable crystal grain growth, the generation of coarse pores, etc. can be suppressed, and the strength of the sintered body is reduced. And abnormal discharge can be made difficult to occur.

Further, in the process of raising the temperature of the compact to the above-mentioned sintering temperature, the average temperature rise rate in the temperature range of 300 to 500 ° C. is 2 ° C./min or less (preferably 0.05 to 1 ° C./min, more preferably 0.05 to 0.5 ° C./min).
Magnesium oxide is hygroscopic and dehydration occurs at 300 ° C or higher. By setting the average rate of temperature increase in the temperature range of 300 to 500 ° C. to 2 ° C./min or less, it is possible to prevent a rapid dehydration reaction from occurring and to make a target in which pores are difficult to be formed.

  As a sintering method used in the present invention, a pressure sintering method such as hot press, oxygen pressurization, hot isostatic pressurization and the like can be employed in addition to the normal pressure sintering method. However, it is preferable to employ a normal pressure sintering method from the viewpoints of reducing manufacturing cost, possibility of mass production, and easy production of a large sintered body.

  In the normal pressure sintering method, the compact is sintered in an air atmosphere or an oxidizing gas atmosphere, preferably an oxidizing gas atmosphere. The oxidizing gas atmosphere is preferably an oxygen gas atmosphere. The oxygen gas atmosphere is preferably an atmosphere having an oxygen concentration of, for example, 10 to 100% by volume. In the manufacturing method of the sputtering target of this invention, a sintered compact density can be made higher by introduce | transducing oxygen gas atmosphere in a temperature rising process.

In order to make the bulk resistance of the sintered body obtained in the sintering process uniform over the entire target, a reduction process may be provided as necessary.
Examples of the reduction method 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.

  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 10 hours, preferably 0.05 to 5 hours.

  To summarize the above, for example, an aqueous solvent is blended with a raw material powder containing a mixed powder of indium oxide powder, tin oxide powder, zinc oxide powder and magnesium oxide powder, and the resulting slurry is mixed for 12 hours or more. Liquid separation, drying, and granulation are performed, and then this granulated product is put into a mold and molded. Thereafter, the obtained molded product is heated in an oxygen atmosphere at a temperature rise rate of 300 to 500 ° C. at 2 ° C. / Min or less, and a sintered body can be obtained by firing at 1200 to 1650 ° C. for 10 to 50 hours.

  It can be set as the sputtering target of this invention by processing the sintered compact obtained above. Specifically, a sputtering target material can be obtained by cutting the sintered body into a shape suitable for mounting on a sputtering apparatus, and a sputtering target can be obtained by bonding the target material to a backing plate.

  In order to use the sintered body as a target material, the sintered body is ground with, for example, a surface grinder to obtain a material having a surface roughness Ra of 0.5 μm or less. Here, the sputter surface of the target material may be further mirror-finished so that the average surface roughness Ra may be 1000 angstroms or less.

  For the mirror surface processing (polishing), known polishing techniques such as mechanical polishing, chemical polishing, and mechanochemical polishing (a combination of mechanical polishing and chemical polishing) can be used. For example, polishing to # 2000 or more with a fixed abrasive polisher (polishing liquid: water), or lapping with loose abrasive lapping (abrasive: SiC paste, etc.), and then lapping by changing the abrasive to diamond paste Can be obtained. Such a polishing method is not particularly limited.

  The surface of the target material 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. When a diamond grindstone larger than No. 200 and smaller than No. 10,000 is used, the target material becomes difficult to break.

  It is preferable that the target material has a surface roughness Ra of 0.5 μm or less and has a non-directional ground surface. If Ra is 0.5 μm or less and there is no directionality on the polished surface, abnormal discharge or particles are unlikely to occur.

  Next, the obtained target material is cleaned. Air blow or running water washing can be used for the cleaning treatment. 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 oscillating 12 types of frequencies in 25 kHz increments between frequencies 25 to 300 kHz.

The thickness of the target material is usually 2 to 20 mm, preferably 3 to 12 mm, particularly preferably 4 to 6 mm.
A sputtering target can be obtained by bonding the target material obtained as described above to a backing plate. Further, a plurality of target materials may be attached to one backing plate to substantially serve as one target.

The oxide semiconductor thin film of the present invention can be obtained by forming a film by a sputtering method using the above-described sputtering target of the present invention.
The oxide semiconductor thin film of the present invention is composed of indium, tin, zinc, magnesium, and oxygen, and usually has an atomic ratio of (1) to (4).

0.05 ≦ In / (In + Sn + Zn + Mg) ≦ 0.70 (1)
0.01 ≦ Sn / (In + Sn + Zn + Mg) ≦ 0.35 (2)
0.01 ≦ Zn / (In + Sn + Zn + Mg) ≦ 0.90 (3)
0.01 ≦ Mg / (In + Sn + Zn + Mg) ≦ 0.30 (4)
(In the formula, In, Sn, Zn, and Mg each indicate an atomic ratio of each element in the oxide semiconductor thin film.)

  In the above formula (1), when the amount of In element is 0.05 or more, the mobility is easily improved when the formed film is applied to the channel layer of the TFT. On the other hand, when the amount of In element is 0.70 or less, when the formed film is applied to the channel layer of the TFT, normally-on characteristics are hardly obtained, and favorable characteristics as the TFT are easily exhibited.

  In the above formula (2), when the amount of Sn element is 0.01 or more, the resulting thin film does not have a too high dissolution rate with respect to the wet etchant, and it becomes easy to perform wet etching. On the other hand, if the amount of Sn element is 0.35 or less, it is difficult for residues to remain even after wet etching.

  In the above formula (3), when the amount of Zn element is 0.01 or more, the obtained film is easily stabilized as an amorphous film. On the other hand, when the amount of Zn element is 0.90 or less, the resulting thin film does not have an excessively high dissolution rate with respect to the wet etchant, and it becomes easy to perform wet etching.

  In the above formula (4), when the amount of Mg element is 0.01 or more, it is possible to prevent the TFT characteristics from being normally on without excessively increasing the carrier concentration in the film. On the other hand, when the amount of Mg element is 0.30 or less, the mobility is hardly lowered.

Since the sputtering target of the present invention has high conductivity, a DC sputtering method having a high film formation rate can be applied.
The sputtering target of the present invention can be applied to an RF sputtering method, an AC sputtering method, and a pulsed DC sputtering method in addition to the DC sputtering method, and enables sputtering without abnormal discharge.

The oxide semiconductor thin film can also be manufactured by a vapor deposition method, an ion plating method, a pulse laser vapor deposition method, or the like using the above sputtering target.
As the sputtering gas (atmosphere), a mixed gas of a rare gas such as argon and an oxidizing gas can be used. Examples of the oxidizing gas include O ₂ , CO ₂ , O ₃ , water vapor (H ₂ O), and N ₂ O. The sputtering gas is preferably a mixed gas containing a rare gas and one or more selected from water vapor, oxygen gas, and nitrous oxide gas, and more preferably a mixed gas containing at least a rare gas and water vapor.

The carrier concentration of the oxide semiconductor thin film is usually 10 ¹⁹ cm ⁻³ or less, preferably 10 ¹³ to 10 ¹⁸ cm ⁻³ , more preferably 10 ¹⁴ to 10 ¹⁸ cm ⁻³ , particularly preferably 10. ¹⁵ to 10 ¹⁸ cm ⁻³ .
When the carrier concentration of the oxide layer is 10 ¹⁹ cm ⁻³ or less, when an element such as a thin film transistor is formed, generation of leakage current and TFT characteristics can be prevented from being normally on. Furthermore, when the carrier concentration is 10 ¹³ cm ⁻³ or more, good characteristics as a TFT are easily exhibited.

The carrier concentration of the oxide semiconductor thin film can be measured by a Hall effect measurement method.
The oxygen partial pressure ratio during sputtering film formation is preferably 0.1% to 30%. A thin film manufactured under a condition where the oxygen partial pressure ratio is 30% or more has a possibility that the carrier concentration is significantly reduced and the carrier concentration is less than 10 ¹³ cm ⁻³ .

More preferably, it is 0.1% to 20%.
The partial pressure ratio of water vapor (water molecules) contained in the sputtering gas (atmosphere) during oxide thin film deposition in the present invention, that is, [water vapor (H ₂ O)] / ([water vapor (H ₂ O)] + [rare gas] ] + [Other gas molecules]) is preferably 0.1 to 25%.

  Moreover, if the partial pressure ratio of water is 25% or less, the film density can be prevented from decreasing, and the overlap of the 5s orbitals of In will not be reduced. The partial pressure ratio of water in the atmosphere during sputtering is more preferably 0.7 to 13%, and particularly preferably 1 to 6%.

The substrate temperature at the time of film formation by sputtering is preferably 25 to 120 ° C, more preferably 25 to 100 ° C, and particularly preferably 25 to 90 ° C. When the substrate temperature at the time of film formation is 120 ° C. or lower, the incorporation of oxygen or the like introduced at the time of film formation is difficult to decrease, and the carrier concentration of the thin film is easily reduced to 10 ¹⁹ cm ⁻³ or lower even after heating. In addition, when the substrate temperature during film formation is higher than 25 ° C., the film density of the thin film is improved, and the mobility of the TFT is hardly lowered.

  It is preferable to anneal the oxide thin film obtained by sputtering at 150 to 500 ° C. for 15 minutes to 5 hours. The annealing temperature after film formation is more preferably 200 ° C. or higher and 450 ° C. or lower, and further preferably 250 ° C. or higher and 350 ° C. or lower. By performing the annealing, semiconductor characteristics can be obtained.

The atmosphere during heating is not particularly limited, but from the viewpoint of carrier controllability, an air atmosphere or an oxygen circulation atmosphere is preferable.
In the post-treatment annealing step of the oxide thin film, a lamp annealing device, a laser annealing device, a thermal plasma device, a hot air heating device, a contact heating device, or the like can be used in the presence or absence of oxygen.

  The distance between the target and the substrate during sputtering is preferably 1 to 15 cm, more preferably 2 to 8 cm in the direction perpendicular to the film formation surface of the substrate. If this distance is 1 cm or more, the kinetic energy of the particles of the target constituent element that reaches the substrate does not become too large, so that in-plane distribution of film thickness and electrical characteristics is unlikely to occur. On the other hand, if the distance between the target and the substrate is 15 cm or less, the kinetic energy of the particles of the target constituent element that reaches the substrate does not become too small, the film density is unlikely to decrease, and good semiconductor characteristics are easily obtained. .

  The oxide thin film is preferably formed by sputtering in an atmosphere having a magnetic field strength of 300 to 1500 gauss. When the magnetic field strength is 300 gauss or more, the plasma density can be increased, so that even a high resistance sputtering target can be sputtered without problems. On the other hand, when it is 1500 gauss or less, the film thickness and the electrical characteristics in the film can be easily controlled.

  The pressure of the gas atmosphere (sputtering pressure) is not particularly limited as long as the plasma can be stably discharged, but is preferably 0.1 to 3.0 Pa, more preferably 0.1 to 1.5 Pa. Particularly preferred is 0.1 to 1.0 Pa. If the sputtering pressure is 3.0 Pa or less, the mean free path of sputtered particles can be lengthened and the density of the thin film can be easily improved. Moreover, when the sputtering pressure is 0.1 Pa or more, it becomes easy to prevent the formation of microcrystals in the film during film formation. The sputtering pressure refers to the total pressure in the system at the start of sputtering after introducing a rare gas such as argon, water vapor, oxygen gas or the like.

Alternatively, the oxide semiconductor thin film may be formed by AC sputtering as described below.
The substrate is sequentially transported to a position facing three or more targets arranged in parallel at a predetermined interval in the vacuum chamber, and negative and positive potentials are alternately applied to each target from an AC power source. Then, plasma is generated on the target to form a film on the substrate surface.

  At this time, at least one of the outputs from the AC power supply is performed while switching a target to which a potential is applied between two or more targets that are branched and connected. That is, at least one of the outputs from the AC power supply is branched and connected to two or more targets, and film formation is performed while applying different potentials to adjacent targets.

  Note that when an oxide semiconductor thin film is formed by AC sputtering, for example, sputtering is performed in an atmosphere of a mixed gas containing a rare gas and one or more selected from water vapor, oxygen gas, and nitrous oxide gas. It is particularly preferable to perform sputtering in an atmosphere of a mixed gas containing at least a rare gas and water vapor.

When the film is formed by AC sputtering, an oxide layer having industrially excellent large area uniformity can be obtained, and improvement in the utilization efficiency of the target can be expected.
Further, when sputtering film formation is performed on a large-area substrate having a side exceeding 1 m, it is preferable to use an AC sputtering apparatus for large-area production as described in JP-A-2005-290550, for example.

  Specifically, the AC sputtering apparatus described in JP-A-2005-290550 includes a vacuum chamber, a substrate holder disposed inside the vacuum chamber, and a sputtering source disposed at a position facing the substrate holder. . FIG. 4 shows a main part of the sputtering source of the AC sputtering apparatus. The sputter source has a plurality of sputter units, each of which has plate-like targets 31a to 31f, and the surfaces to be sputtered of the targets 31a to 31f are sputter surfaces. It arrange | positions so that it may be located in. Each target 31a to 31f is formed in an elongated shape having a longitudinal direction, each target has the same shape, and the edge portions (side surfaces) in the longitudinal direction of the sputtering surface are arranged in parallel at a predetermined interval. Therefore, the side surfaces of the adjacent targets 31a to 31f are parallel.

  AC power supplies 17a to 17c are arranged outside the vacuum chamber, and one of the two terminals of each AC power supply 17a to 17c is connected to one of the two adjacent electrodes, The other terminal is connected to the other electrode. Two terminals of each of the AC power supplies 17a to 17c output voltages having different polarities, and the targets 31a to 31f are attached in close contact with the electrodes, so that the two adjacent targets 31a to 31f are adjacent to each other. AC voltages having different polarities are applied from the AC power sources 17a to 17c. Accordingly, when one of the targets 31a to 31f adjacent to each other is placed at a positive potential, the other is placed at a negative potential.

  Magnetic field forming means 40a to 40f are arranged on the surface of the electrode opposite to the targets 31a to 31f. Each of the magnetic field forming means 40a to 40f includes an elongated ring-shaped magnet whose outer periphery is substantially equal to the outer periphery of the targets 31a to 31f, and a bar-shaped magnet shorter than the length of the ring-shaped magnet.

  Each ring-shaped magnet is arranged in parallel with the longitudinal direction of the targets 31a to 31f at a position directly behind the corresponding one of the targets 31a to 31f. As described above, since the targets 31a to 31f are arranged in parallel at a predetermined interval, the ring-shaped magnets are also arranged at the same interval as the targets 31a to 31f.

The AC power density when an oxide target is used in AC sputtering is preferably 3 W / cm ² or more and 20 W / cm ² or less. When the power density is 3 W / cm ² or more, the deposition rate can be increased, which is economical in production. It can prevent that a target breaks that it is 20 W / cm < ² > or less. More preferred power density is ^{3W / cm 2 ~15W / cm 2} .

The frequency of AC sputtering is preferably in the range of 10 kHz to 1 MHz. By exceeding 10 kHz, the problem of noise hardly occurs. If it does not exceed 1 MHz, it is possible to prevent the plasma from spreading too much, and it is possible to prevent the sputtering from being performed at a position other than the desired target position and the uniformity to be lost. A more preferable frequency of AC sputtering is 20 kHz to 500 kHz.
What is necessary is just to select suitably the conditions at the time of sputtering other than the above from what was mentioned above.

  The oxide semiconductor thin film of the present invention is insoluble in a phosphoric acid etching solution and soluble in an oxalic acid etching solution. Thus, by having selectivity with respect to the etching solution, the oxide thin film is etched by oxalic acid-based etching, and the electrode formed on the oxide thin film is formed with a phosphoric acid-based etching solution. And patterning can be performed.

  Preferably, the etching rate at 35 ° C. by the phosphoric acid etching solution is 10 nm / min or less, and the etching rate at 35 ° C. by the oxalic acid etching solution is 20 nm / min or more. When the etching rate is in the above range, the selectivity of the etching solution can be exhibited, and a TFT can be manufactured by back channel etching.

  Examples of the oxalic acid-based etching solution include ITO-06N (manufactured by Kanto Chemical Co., Inc.). Preferably, the one containing 0.5 to 10 wt% oxalic acid is good. However, in addition to oxalic acid, carboxylic acid such as malonic acid, succinic acid, and acetic acid and other acids may be included, and oxalic acid is not necessarily included.

  Examples of the phosphoric acid etching solution include a PAN etching solution containing phosphoric acid, acetic acid, and nitric acid. The PAN-based etching solution is preferably in the range of 45 to 95 wt% phosphoric acid, 3 to 50 wt% acetic acid, and 0.5 to 5 wt% nitric acid.

The oxide semiconductor thin film of the present invention can be used for a thin film transistor, and can be particularly suitably used as a channel layer.
If the thin-film transistor of this invention has the oxide semiconductor thin film of this invention demonstrated above as a channel layer, the element structure will not be specifically limited, Various well-known element structures are employable.

  The film thickness of the channel layer in the thin film transistor of the present invention is usually 10 to 300 nm, preferably 20 to 250 nm, more preferably 30 to 200 nm, still more preferably 35 to 120 nm, and particularly preferably 40 to 80 nm. When the thickness of the channel layer is 10 nm or more, the non-uniformity of the film thickness when the film is formed in a large area can be reduced, and the characteristics of the manufactured TFT can be prevented from becoming non-uniform in the plane. On the other hand, if the film thickness is 300 nm or less, the film formation time does not become too long, which is industrially advantageous.

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

Field effect mobility of the thin film transistor of the present invention is preferably 10 cm ² / Vs or more, more preferably 11 c ^m 2 / Vs or more.

The thin film transistor of the present invention preferably includes a protective film on the channel layer. The protective film in the thin film transistor of the present invention preferably contains at least SiN _x . Since SiN _x can form a dense film as compared with SiO ₂ , it has an advantage of a high TFT deterioration suppressing effect.
Note that x is an arbitrary number, and the stoichiometric ratio of SiN _x may not be constant.

In addition to SiN _x , the protective film may be, for example, SiO ₂ , Al ₂ O ₃ , Ta ₂ O ₅ , TiO ₂ , MgO, ZrO ₂ , CeO ₂ , K ₂ O, Li ₂ O, Na ₂ O, Rb ₂ O, Sc ₂ O ₃ , Y ₂ O ₃ , HfO ₂ , CaHfO ₃ , PbTiO ₃ , BaTa ₂ O ₆ , Sm ₂ O ₃ , SrTiO _3, or an oxide such as AlN can be included.

The oxide semiconductor thin film containing indium element (In) tin element (Sn), zinc element (Zn), and magnesium element (Mg) according to the present invention contains Mg element, so the reduction resistance by CVD process is improved. In addition, the back channel side is not easily reduced by the process of forming the protective film, and SiN _x can be used as the protective film.

  Before forming the protective film, the channel layer is preferably subjected to ozone treatment, oxygen plasma treatment, nitrogen dioxide plasma treatment, or nitrous oxide plasma treatment. Such treatment may be performed at any timing after the channel layer is formed and before the protective film is formed, but is preferably performed immediately before the protective film is formed. By performing such pretreatment, generation of oxygen defects in the channel layer can be suppressed.

  Further, when hydrogen in the oxide semiconductor film diffuses during driving of the TFT, a threshold voltage shift may occur and the reliability of the TFT may be reduced. By performing ozone treatment, oxygen plasma treatment, or nitrous oxide plasma treatment on the channel layer, the In—OH bond is stabilized in the thin film structure, and diffusion of hydrogen in the oxide semiconductor film can be suppressed. .

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

The material for forming the gate insulating film in the thin film transistor of the present invention is not particularly limited, and a commonly used material can be arbitrarily selected. Specifically, for _{example, SiO 2, SiN x, Al} 2 O 3, Ta 2 O 5, TiO 2, MgO, ZrO 2, CeO 2, K 2 O, Li 2 O, Na 2 O, Rb 2 O, Compounds such as Sc ₂ O ₃ , Y ₂ O ₃ , HfO ₂ , CaHfO ₃ , PbTiO ₃ , BaTa ₂ O ₆ , SrTiO ₃ , Sm ₂ O ₃ , and AlN can be used. Among these, SiO ₂ , SiN _x , Al ₂ O ₃ , Y ₂ O ₃ , HfO ₂ and CaHfO ₃ are preferable, and SiO ₂ , SiN _x , HfO ₂ and Al ₂ O ₃ are more preferable.

The gate insulating film can be formed by, for example, a plasma CVD (Chemical Vapor Deposition) method.
When a gate insulating film is formed by plasma CVD and a channel layer is formed on the gate insulating film, hydrogen in the gate insulating film may diffuse into the channel layer, leading to deterioration in channel layer quality and TFT reliability. is there. In order to prevent deterioration in channel layer quality and TFT reliability, the gate insulating film may be subjected to ozone treatment, oxygen plasma treatment, nitrogen dioxide plasma treatment or nitrous oxide plasma treatment before forming the channel layer. preferable. By performing such pretreatment, it is possible to prevent deterioration of the channel layer film quality and TFT reliability.

Note that the number of oxygen in the oxide does not necessarily match the stoichiometric ratio, and may be, for example, SiO ₂ or SiO _x .
The gate insulating film may have a structure in which two or more insulating films made of different materials are stacked. The gate insulating film may be crystalline, polycrystalline, or amorphous, but is preferably polycrystalline or amorphous that can be easily manufactured industrially.

There are no particular limitations on the material for forming each of the drain electrode, the source electrode, and the gate electrode in the thin film transistor of the present invention, and a commonly used material can be arbitrarily selected. For example, transparent electrodes such as indium tin oxide (ITO), indium zinc oxide, ZnO, SnO ₂ , metal electrodes such as Al, Ag, Cu, Cr, Ni, Mo, Au, Ti, Ta, or these An alloy metal electrode can be used.

  The thin film transistor of the present invention can be produced by back channel etching without forming an etching stopper on the oxide thin film which is an active layer, utilizing the etching solution selectivity of the oxide thin film.

  Thin-film transistors using an active layer of a normal oxide semiconductor thin film such as an IGZO system prevent etching on the oxide semiconductor thin film because the oxide semiconductor thin film is also etched against the etchant used to etch the electrodes. For this purpose, it is necessary to form an etching stopper such as SiOx. Productivity has been reduced by including a step of forming an etching stopper.

However, the oxide semiconductor thin film of the present invention has a high productivity because it is not necessary to form an etching stopper by appropriately selecting an etching solution for patterning the semiconductor thin film and the electrode when a thin film transistor is manufactured. improves.
That is, in the thin film transistor using the oxide semiconductor thin film of the present invention as the semiconductor active layer, the semiconductor thin film and the electrode are patterned using different etching solutions without stacking the etching stopper on the semiconductor thin film, and the electrode is patterned. In this case, it can be manufactured by a manufacturing method including a step in which the etching solution directly contacts the semiconductor thin film.

Specifically, when patterning an oxide semiconductor thin film, an etchable solution such as an oxalic acid-based etchant is used, while when patterning an electrode, indium zinc oxide, ZnO, SnO ₂ or the like is used. Etching is possible for electrode materials such as transparent conductive oxides, metals such as Al, Ag, Cu, Cr, Ni, Mo, Ti, Ta, or alloys containing these, and for oxide semiconductor thin films Etching is difficult. For example, by using phosphoric acid etching, the semiconductor thin film is not etched even when the electrode etchant directly contacts the semiconductor thin film, so that it is not necessary to form an etching stopper.

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

The thin film transistor of the present invention can be applied to various integrated circuits such as a field effect transistor, a logic circuit, a memory circuit, and a differential amplifier circuit. Further, in addition to the field effect transistor, it can be applied to an electrostatic induction transistor, a Schottky barrier transistor, a Schottky diode, and a resistance element.
As the structure of the thin film transistor of the present invention, known structures such as a bottom gate, a bottom contact, and a top contact can be adopted without limitation.

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

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

Examples 1-3
[Production of sintered body]
The following oxide powder was used as a raw material powder. The average particle size of the oxide powder was measured with a laser diffraction particle size distribution analyzer SALD-300V (manufactured by Shimadzu Corporation), and the median particle size D50 was employed.
Indium oxide powder: average particle size 0.98 μm
Tin oxide powder: Average particle size 0.96μm
Zinc oxide powder: Average particle size 0.98μm
Magnesium oxide powder: Average particle size 0.98 μm

  The above powder was weighed so as to have the atomic ratio (percentage) shown in Table 1, and after uniformly pulverizing and mixing, a molding binder was added and granulated. Next, the raw material grains were uniformly filled in a mold and subjected to pressure molding with a cold press machine at a press pressure of 140 MPa.

The obtained molded body was sintered as follows. First, the compact was placed in a sintering furnace, and oxygen was introduced at a rate of 5 liters / minute per volume of 0.1 m ³ in the sintering furnace. In this atmosphere, sintering was performed under the conditions shown in Table 1 (a heating rate of 300 to 500 ° C., a sintering holding temperature, and a sintering time). The temperature rising rate from 500 ° C. to 800 ° C. was 0.5 ° C./min, and the temperature rising rate from 800 ° C. to the sintering holding temperature was 1 ° C./min.

The relative density of the obtained sintered body was calculated from the measured density and the theoretical density measured by the Archimedes method. It was confirmed that the sintered bodies of Examples 1 to 3 had a relative density of 97% or more.
Further, the bulk specific resistance (conductivity) of the obtained sintered body was measured based on the four-probe method (JIS R 1637) using a resistivity meter (Made by Mitsubishi Chemical Corporation, Loresta). The results are shown in Table 1. As shown in Table 1, the bulk specific resistance of the sintered bodies of Examples 1 to 3 was 10 mΩcm or less.

[Analysis of sintered body]
ICP-AES analysis was performed on the obtained sintered body, and the atomic ratio shown in Table 1 was confirmed.
In addition, the crystal structure of the obtained sintered body was examined using an X-ray diffraction measurement apparatus (XRD). The measurement conditions of XRD are as follows.

・ Device: ULTIMA-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

The X-ray diffraction charts of the sintered bodies obtained in Examples 1 to 3 are shown in FIGS. As a result of analyzing the chart, in the sintered body of Example 1, a homologous structure of In ₂ Zn ₄ O ₇ and a spinel structure of Zn ₂ SnO ₄ were observed.
The crystal structure can be confirmed with a JCPDS card or ICSD.
The homologous structure of In ₂ Zn ₄ O ₇ is ICSD # 162451, and the spinel structure of Zn ₂ SnO ₄ is JCPDS card no. 24-1470.

Also in Examples 2 to 3, as shown in Table 1, a homologous structure of In ₂ O ₃ (ZnO) _m and a spinel structure of Zn ₂ SnO ₄ were observed.
In Examples 2-3, the homologous structure of In ₂ Zn ₇ O ₁₀ is ICSD # 162453, the homologous structure of In ₂ Zn ₃ O ₆ is ICSD # 162450, and the spinel structure of Zn ₂ SnO ₄ is JCPDS card No. . 24-1470.

[Manufacture of sputtering target]
The surfaces of the sintered bodies obtained in Examples 1 to 3 were ground with a surface grinder, the side edges were cut with a diamond cutter, and bonded to a backing plate to prepare sputtering targets each having a diameter of 4 inches.
In addition, six targets each having a width of 200 mm, a length of 1700 mm, and a thickness of 10 mm were prepared for AC sputtering film formation.

[Check for abnormal discharge]
The obtained sputtering target having a diameter of 4 inches was mounted on a DC sputtering apparatus, a mixed gas in which water vapor was added to argon gas at a partial pressure ratio of 2% as an atmosphere, a sputtering pressure of 0.4 Pa, a substrate temperature of room temperature, DC 10 kWh continuous sputtering was performed at an output of 400 W. Voltage fluctuations during sputtering were accumulated in a data logger, and the presence or absence of abnormal discharge was confirmed. The results are shown in Table 1.

  The presence or absence of the abnormal discharge was detected by monitoring the voltage fluctuation and detecting the abnormal discharge. Specifically, the abnormal discharge was determined when the voltage fluctuation generated during the measurement time of 5 minutes was 10% or more of the steady voltage during the sputtering operation. In particular, when the steady-state voltage during sputtering operation varies by ± 10% in 0.1 second, a micro arc, which is an abnormal discharge of the sputter discharge, has occurred, and the device yield may decrease, making it unsuitable for mass production. is there.

[Check for nodule occurrence]
In addition, using the obtained sputtering target having a diameter of 4 inches, using a mixed gas obtained by adding 3% of hydrogen gas to argon gas at a partial pressure ratio, sputtering was performed continuously for 40 hours, and no nodules were generated. It was confirmed.

As a result, no nodules were observed on the surfaces of the sputtering targets of Examples 1 to 3.
The sputtering conditions were a sputtering pressure of 0.4 Pa, a DC output of 100 W, and a substrate temperature of room temperature. Hydrogen gas was added to the atmospheric gas to promote the generation of nodules.

Nodules are measured after sputtering at a total of five points: the center point (one place) of the circular sputtering target and the center point (four places) between the center point and the peripheral part on two center lines orthogonal to the center point. A method of measuring the number average of nodules having a major axis of 20 μm or more generated in a visual field of 9 mm ² was adopted by observing the change of the target surface 50 times with a stereomicroscope. Table 1 shows the number of nodules generated.

Comparative Examples 1-2
Raw material powders were mixed at an atomic ratio (percentage) shown in Table 1, and a sintered body and a sputtering target were produced and evaluated in the same manner as in Example 1. The results are shown in Table 1.

In Comparative Examples 1 and 2, the homologous structure of In ₂ O ₃ (ZnO) _m and the spinel structure of Zn ₂ SnO ₄ were not observed simultaneously.
The spinel structure of MgIn ₂ O ₄ is ICSD # 24992, and the rock salt structure of MgO is JCPDS card no. 45-0946, and the rutile structure of SnO ₂ is JCPDS card no. It corresponded to 00-1024, respectively.

In Comparative Examples 1 and 2, the density was 90% or less, and the density was low. This is presumably because the moisture rising rate of MgO rapidly desorbed and a large number of pores were generated because the temperature rising rate at 300 ° C. to 500 ° C. was as fast as 2.5 ° C./min.
In the sputtering target of Comparative Example 1, abnormal discharge occurred during sputtering, and nodules were observed on the target surface. Comparative Example 2 had high resistance and could not be discharged.

Examples 4-6
[Manufacture of oxide semiconductor thin films]
A 4-inch target having the composition shown in Table 2 prepared in Examples 1 to 3 was mounted on a magnetron sputtering apparatus, and a slide glass (# 1737 manufactured by Corning) was mounted as a substrate. An amorphous film having a thickness of 50 nm was formed on the slide glass by a DC magnetron sputtering method. At the time of film formation, Ar gas, O ₂ gas, and water vapor were introduced at a partial pressure ratio (%) shown in Table 2.

The sputtering conditions are as follows.
-Substrate temperature: 25 ° C (however, Example 6 is 100 ° C)
-Ultimate pressure: 8.5 × 10 ⁻⁵ Pa
Atmospheric gas: Ar gas, O ₂ gas, water vapor (see Table 2 for partial pressure ratio)
・ Sputtering pressure (total pressure): 0.4 Pa
-Input power: DC100W
・ S (substrate) -T (target) distance: 70 mm

The crystal structure of the thin film formed on the glass substrate was examined using an X-ray diffraction (XRD) measuring device (Rigaku's Ultimate-III).
In Examples 4 to 6, it was confirmed that a diffraction peak was not observed immediately after deposition of the thin film and the film was amorphous.
The measurement conditions of XRD are as follows.

・ Device: ULTIMA-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

Next, the substrate on which the amorphous film was formed was heated in the atmosphere at the annealing temperature shown in Table 2 for the annealing time to form an oxide semiconductor film. The substrate formed on this glass substrate was set as a ResiTest 8300 type (manufactured by Toyo Technica Co., Ltd.) using the Hall effect measurement element, and the Hall effect was evaluated at room temperature.
ICP-AES analysis confirmed that the atomic ratio of each element contained in the oxide semiconductor thin film was the same as that of the sputtering target.

[Manufacture of thin film transistors]
As the substrate, a conductive silicon substrate with a thermal oxide film having a thickness of 100 nm was used. The thermal oxide film functions as a gate insulating film, and the conductive silicon portion functions as a gate electrode.

  A 50 nm-thick amorphous thin film was formed by sputtering on the gate insulating film. OFPR # 800 (manufactured by Tokyo Ohka Kogyo Co., Ltd.) was used as a resist, and coating, pre-baking (80 ° C., 5 minutes), and exposure were performed. After development, it was post-baked (120 ° C., 5 minutes), etched with oxalic acid, and patterned into a desired shape. Thereafter, heat treatment (annealing treatment) was performed in the hot air heating furnace at the annealing temperatures shown in Table 2 for the annealing time.

Thereafter, Mo (100 nm) was deposited by sputtering using a lift-off method, and the source / drain electrodes were patterned into a desired shape. Further, a nitrous oxide plasma treatment was performed on the oxide semiconductor film as a treatment before the formation of the protective film. After that, a protective film by forming a SiO _x by plasma CVD (PECVD). A contact hole was opened using hydrofluoric acid to produce a thin film transistor.

[Evaluation of etching rate]
The etching rate was evaluated using the oxide semiconductor thin films of Examples 4 to 6 formed under the same conditions except that the thickness of the amorphous film was 100 nm.

  ITO-06N (Kanto Chemical Co., Ltd.), which is an oxalic acid-based etching solution, was set to 35 ° C., the oxide semiconductor thin film was immersed, and the etching rate was calculated from the immersion time and the film thickness before and after the immersion.

  Further, a PAN etching solution (phosphoric acid 91.4 wt%, nitric acid 3.3 wt%, acetic acid 5.3 wt%) is set to 35 ° C., and the oxide semiconductor thin film is immersed, and the immersion time is as follows: The etching rate was calculated from the film thickness before and after the immersion.

[Evaluation of Thin Film Transistor]
The thin film transistors manufactured in Examples 4 to 6 were evaluated for field effect mobility (μ), S value, and threshold voltage (Vth). These characteristic values were measured using a semiconductor parameter analyzer (4200SCS manufactured by Keithley Instruments Co., Ltd.) at room temperature in a light-shielding environment (in a shield box). Vth is the gate voltage (Vg) when the drain current (Id) is 1 nA.

  Further, transfer characteristics of the manufactured transistor were evaluated with a drain voltage (Vd) of 5 V and a gate voltage (Vg) of -15 to 25 V. The results are shown in Table 2. The field effect mobility (μ) was calculated from the linear mobility and defined as the maximum value of Vg−μ.

  Next, a DC bias stress test was performed on the TFTs of Examples 4 to 6. Table 2 shows the amount of change ΔVth in Vth before and after the application of DC stress (stress temperature of 80 ° C.) of Vg = 15 V and Vd = 15 V for 10,000 seconds. It can be seen that the threshold voltage variation of the TFT of the present invention is very small and is hardly affected by DC stress.

Comparative Example 3
An oxide semiconductor thin film and a thin film transistor were produced and evaluated in the same manner as in Example 4 except that the 4-inch target produced in Comparative Example 1 was used. The film forming conditions, annealing conditions, and results are shown in Table 2.

As shown in Table 2, it can be seen that the device of Comparative Example 3 has a field effect mobility of less than 10 cm ² / Vs, which is significantly lower than those of Examples 4-6.
In addition, a DC bias stress test was performed on the TFT of Comparative Example 3. Table 2 shows the amount of change ΔVth in Vth before and after the application of DC stress (stress temperature of 80 ° C.) of Vg = 15 V and Vd = 15 V for 10,000 seconds.

Examples 7-9
Using the film forming apparatus disclosed in Japanese Patent Laid-Open No. 2005-290550, AC sputtering was performed on the 4-inch target having the composition shown in Table 3 manufactured in Examples 1 to 3, and a thin film transistor was manufactured. Deposition conditions and heating (annealing) conditions for the amorphous film are as shown in Table 3. A thin film transistor was fabricated and evaluated in the same manner as in Example 4 except that the source / drain patterning was performed by dry etching. The results are shown in Table 3.
ICP-AES analysis confirmed that the atomic ratio of each element contained in the oxide thin film was the same as that of the sputtering target.

AC sputtering was performed using the apparatus shown in FIG.
Six targets 31a to 31f having a width of 200 mm, a length of 1700 mm, and a thickness of 10 mm prepared in Examples 1 to 3 were arranged at intervals of 2 mm so that the length directions thereof were parallel as shown in FIG. . The widths of the magnetic field forming means 40a to 40f were 200 mm, which is the same as the targets 31a to 31f. Ar, which is a sputtering gas, and water vapor and / or O ₂ were introduced into the system from the gas supply system.

For example, in Example 7, the film formation atmosphere was 0.5 Pa, the power of the AC power source was 3 W / cm ² (= 10.2 kW / 3400 cm ² ), and the frequency was 10 kHz.
Under the above conditions, the film formation rate was as high as 54 nm / min, which was suitable for mass production.

Comparative Example 4
The oxide semiconductor thin film was prepared in the same manner as in Example 7 except that the sputtering conditions were changed to those shown in Table 3 using the six targets 200 mm wide, 1700 mm long and 10 mm thick produced in Comparative Example 1. A thin film transistor was fabricated and evaluated. The results are shown in Table 3.
As shown in Table 3, it can be seen that the device of Comparative Example 4 has a field effect mobility of less than 10 cm ² / Vs, which is significantly lower than those of Examples 7-9.

Examples 10-12
TFT fabricated under the same conditions as in Examples 4 to 6 except that back channel etching with PAN (phosphoric acid 91.4 wt%, nitric acid 3.3 wt%, acetic acid 5.3 wt%) etching solution was used for Mo patterning The characteristic results are shown in Table 4.
It can be seen that good TFT characteristics can also be obtained by back channel etching.

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

Although several embodiments and / or examples of the present invention have been described in detail above, those skilled in the art will appreciate that these exemplary embodiments and / or embodiments are substantially without departing from the novel teachings and advantages of the present invention. It is easy to make many changes to the embodiment. Accordingly, many of these modifications are within the scope of the present invention.
All the contents of the Japanese application specification that is the basis of the priority of Paris in this application are incorporated herein.

Claims (18)

It consists of an oxide containing indium element (In), tin element (Sn), zinc element (Zn), and magnesium element (Mg), and is represented by In ₂ O ₃ (ZnO) _m (m is 0.1 to 20). Sputtering target comprising a homologous structural compound and a spinel structural compound represented by Zn ₂ SnO ₄ . The sputtering target according to claim 1, wherein an atomic ratio of the indium element, tin element, zinc element, and magnesium element satisfies the following formulas (1) to (4).
0.05 ≦ In / (In + Sn + Zn + Mg) ≦ 0.70 (1)
0.01 ≦ Sn / (In + Sn + Zn + Mg) ≦ 0.35 (2)
0.01 ≦ Zn / (In + Sn + Zn + Mg) ≦ 0.90 (3)
0.01 ≦ Mg / (In + Sn + Zn + Mg) ≦ 0.30 (4)
(In the formula, In, Sn, Zn, and Mg each indicate an atomic ratio of each element in the sputtering target.)   The sputtering target according to claim 1 or 2, wherein the relative density is 97% or more and the bulk specific resistance is 10 mΩcm or less.   The method includes heating the molded body at a temperature rising rate of 2 ° C./min or less in a temperature range of 300 ° C. to 500 ° C., and holding and sintering the molded body at 1200 ° C. to 1650 ° C. for 10 to 50 hours. The manufacturing method of the sputtering target in any one of 1-3. The manufacturing method of the oxide semiconductor thin film formed into a film by sputtering method using the sputtering target in any one of Claims 1-3. 6. The oxide according to claim 5, wherein the oxide thin film formed by the sputtering method is insoluble in a phosphoric acid-based etching solution and is soluble in an oxalic acid-based etching solution. A method for manufacturing a semiconductor thin film.   Film formation by sputtering using the sputtering target according to any one of claims 1 to 3, in an atmosphere of a mixed gas containing one or more selected from water vapor, oxygen gas, and nitrous oxide gas and a rare gas. A method for manufacturing an oxide semiconductor thin film. The method for producing an oxide semiconductor thin film according to claim 7 , wherein the oxide semiconductor thin film is formed in an atmosphere of a mixed gas containing at least water vapor and a rare gas. The method for producing an oxide semiconductor thin film according to claim 7 or 8 , wherein a ratio of water vapor contained in the mixed gas is 0.1% to 25% in terms of partial pressure ratio. The method for producing an oxide semiconductor thin film according to any one of claims 7 to 9 , wherein a ratio of oxygen gas contained in the mixed gas is 0.1% to 30% in terms of partial pressure ratio. The oxide semiconductor thin film is formed by sequentially transporting the substrate to a position facing three or more targets arranged in parallel in the vacuum chamber at a predetermined interval, and from each AC power source to each target. In the case of alternately applying a negative potential and a positive potential, at least one of the outputs from the AC power supply is switched between two or more targets that are branched and connected while switching the target to which the potential is applied. The manufacturing method of the oxide semiconductor thin film in any one of Claims 7-10 performed by the sputtering method which produces | generates a plasma on a target and forms into a film on the substrate surface. The method for producing an oxide semiconductor thin film according to claim 11 , wherein the AC power density of the AC power source is 3 W / cm ² or more and 20 W / cm ² or less. The method for producing an oxide semiconductor thin film according to claim 11 or 12 , wherein the frequency of the AC power supply is 10 kHz to 1 MHz. A method for manufacturing a thin film transistor, comprising forming an oxide semiconductor thin film by the method for manufacturing an oxide semiconductor thin film according to claim 5, and using the oxide semiconductor thin film as a channel layer. The method of manufacturing a thin film transistor according to claim 14 , wherein the field effect mobility is 10 cm ² / Vs or more. An oxide semiconductor thin film is formed by the oxide semiconductor thin film manufacturing method according to claim 5, and at least SiNx (x is an arbitrary number) is contained on the oxide semiconductor thin film. A manufacturing method of a thin film transistor for forming a protective film. A method of manufacturing a thin film transistor using the oxide semiconductor thin film manufactured by the method of manufacturing an oxide semiconductor thin film according to claim 5 as a semiconductor active layer, wherein an etching stopper is laminated on the semiconductor thin film. The method for manufacturing a thin film transistor includes a step of patterning the semiconductor thin film and the electrode using different etching solutions, and directly contacting the etching solution with the semiconductor thin film when patterning the electrodes. A method of manufacturing a display device using the thin film transistor, wherein the thin film transistor is manufactured by the method of manufacturing a thin film transistor according to claim 14.

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