TW201435118A - Sputtering target, oxide semiconductor thin film, and production methods for both - Google Patents

Abstract

A sputtering target comprising an oxide containing indium (In), tin (Sn), zinc (Zn), and magnesium (Mg), and including a homologous structure compound indicate by In2O3(ZnO)m (m being 0.1-20) and a spinel structure compound indicated by Zn2SnO4.

Description

Sputtering target, oxide semiconductor film, and manufacturing method thereof

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 film produced using the target, a thin film transistor including the film, and the like.

A field effect transistor such as a thin film transistor (TFT) is widely used as a unit electronic component of a semiconductor memory bulk circuit, a high frequency signal amplifying element, a liquid crystal driving element, etc., and is currently the most practical electronic device. Among them, with the rapid development of display devices in recent years, liquid crystal display devices (LCD), electroluminescence display devices (EL, electroluminescence), field emission displays (FED, field emission display) Among various display devices, a TFT is often used as a switching element that applies a driving voltage to a display element to drive a display device.

As a material of a semiconductor layer (channel layer) which is a main component of a field effect type transistor, a germanium semiconductor compound is most widely used. Usually, a single crystal germanium is used for a high frequency amplifying element or an integrated circuit element which requires high speed operation. On the other hand, an amorphous germanium semiconductor (amorphous germanium) is used for a liquid crystal driving element or the like due to a large area.

Although the film of amorphous germanium can be formed at a relatively low temperature, the switching speed is slower than that of the crystalline thin film. Therefore, when the switching element of the display device is driven, there is a case where the display of the high-speed dynamic picture cannot be followed. Specifically, in a liquid crystal television having a resolution of VGA (Video Graphics Array), an amorphous germanium having a mobility of 0.5 to 1 cm ² /Vs can be used, and if the resolution is SXGA (Super Extended Graphics Array) A graphics array), a UXGA (Ultra Extended Graphics Array), a QXGA (Quantum Extended Graphics Array), or the like, requires a mobility of 2 cm ² /Vs or more. In addition, if the driving frequency is increased in order to improve the image quality, a higher degree of mobility is required.

On the other hand, although the crystalline ruthenium-based film has a high degree of mobility, it has a problem that it requires a large amount of energy and the number of steps at the time of production, or a large area is difficult. For example, in order to crystallize a lanthanide film, a high temperature of 800 ° C or higher or a laser annealing using an expensive apparatus is required. Further, since the crystalline ruthenium-based film is generally configured to limit the element configuration of the TFT to the top gate, it is difficult to reduce the cost of the number of masks.

In order to solve the above problems, a thin film transistor using an oxide semiconductor film containing indium oxide, zinc oxide, and gallium oxide has been studied. Generally, the production of an oxide semiconductor thin film is performed by sputtering using a target (sputter target) containing an oxide sintered body.

For example, a target containing a compound exhibiting a homologous crystal structure represented by the 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 sintered density (relative density) of the target, it is necessary to perform sintering in an oxidizing atmosphere. In this case, in order to lower the electric resistance of the target, it is necessary to carry out a reduction treatment at a high temperature after sintering. Further, when the target is used for a long period of time, there is a problem that the characteristics of the obtained film or the film formation rate vary greatly, and abnormal discharge due to abnormal growth of InGaZnO ₄ or In ₂ Ga ₂ ZnO ₇ during sintering occurs. And when the film is formed, more particles are generated. When the abnormal discharge is frequently caused, the plasma discharge state becomes unstable, and stable film formation cannot be performed, which adversely affects the film characteristics.

On the other hand, a thin film transistor using an amorphous oxide semiconductor film containing no indium oxide and containing zinc oxide has been proposed (Patent Document 4).

However, if the partial pressure of oxygen at the time of film formation is not increased, there is a problem that the normally-off operation of the TFT cannot be achieved.

In addition, a sputtering target for a protective layer of an optical information recording medium containing an additive element such as Ta, Y or Si in an In ₂ O ₃ -SnO ₂ -ZnO-based oxide containing tin oxide as a main component has been studied (Patent Literature) 5 and 6).

However, these targets are not used for an oxide semiconductor, and there is a problem that an aggregate of an insulating substance is easily formed, a resistance value is high, or an abnormal discharge is likely to occur.

Prior technical literature Patent literature

Patent Document 1: Japanese Patent Laid-Open No. Hei 8-245220

Patent Document 2: Japanese Patent Laid-Open Publication No. 2007-73312

Patent Document 3: International Publication No. 2009/084537

Patent Document 4: International Publication No. 2005/088726

Patent Document 5: International Publication No. 2005/078152

Patent Document 6: International Publication No. 2005/078153

An object of the present invention is to provide an oxide containing an indium element (In), a tin element (Sn), a zinc element (Zn), and a magnesium element (Mg), and can achieve high mobility and high reliability. The sputtering target of the TFT.

Further, it is an object of the present invention to provide a sputtering target which can produce a TFT having high mobility and high reliability with high productivity by a back channel etching method.

According to the present invention, the following sputtering targets and the like can be provided.

A sputtering target comprising a homologous structural compound containing an oxide and having In ₂ O ₃ (ZnO) _m (m is 0.1 to 20), and a spinel structure represented by Zn­ ₂ SnO ₄ A compound containing an indium element (In), a tin element (Sn), a zinc element (Zn), and a magnesium element (Mg).

2. The sputtering target according to the above 1, wherein the atomic ratio of the indium element, the tin element, the zinc element, and the 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)

(wherein, In, Sn, Zn, and Mg represent the atomic ratios of the respective elements in the sputtering target, respectively)

3. The sputtering target according to 1 or 2 above, wherein the relative density is 97% or more and the volume specific resistance is 10 m?cm or less.

4. The method for producing a sputtering target according to any one of the above 1 to 3, comprising the step of heating the molded body at a temperature increase rate of 2 ° C /min or less in a temperature range of 300 ° C to 500 ° C. The formed body was sintered by holding it at 1200 ° C to 1650 ° C for 10 to 5 hours.

An oxide semiconductor thin film formed by sputtering using a sputtering target according to any one of the above 1 to 3.

6. The oxide semiconductor thin film according to the above 5, which is insoluble in the phosphoric acid-based etching liquid and soluble in the oxalic acid-based etching liquid.

7. The oxide semiconductor thin film according to the above 6, wherein the etching rate of the phosphoric acid-based etching solution at 35 ° C is 10 nm/min or less, and the etching rate of the oxalic acid etching solution at 35 ° C is 20 nm/min or more.

A method for producing an oxide semiconductor thin film, which is used in an environment containing a mixed gas of one or more selected from the group consisting of water vapor, oxygen, and nitrous oxide gas and a rare gas, and is used as described in the above 1 to 3 A sputtering target is formed by sputtering.

9. The method for producing an oxide semiconductor thin film according to the above 8, wherein the oxide semiconductor thin film is formed in an atmosphere containing at least a mixed gas of water vapor and a rare gas.

10. The method for producing an oxide semiconductor thin film according to the above 8 or 9, wherein the ratio of the water vapor contained in the mixed gas is 0.1% to 25% in terms of a partial pressure ratio.

11. The method of producing an oxide semiconductor thin film according to any one of the above 8 to 10, wherein The ratio of the oxygen contained in the mixed gas is 0.1% to 30% in terms of a partial pressure ratio.

12. The method for producing an oxide semiconductor thin film according to any one of the above 8 to 11, wherein the film formation of the oxide semiconductor film is carried out by a sputtering method in which the substrate is sequentially transferred to and The position of the three or more targets placed side by side in the vacuum chamber at a predetermined interval is opposite to each other, and when the negative potential and the positive potential are alternately applied to the respective targets from the AC power source, the output from the AC power source is turned on. At least one of the branches is switched between the two or more connected targets, and a plasma is generated on the target to form a film on the surface of the substrate.

13. The method for producing an oxide semiconductor thin film according to the above 12, wherein the AC power source has an AC power density of 3 W/cm ² or more and 20 W/cm ² or less.

14. The method of producing an oxide semiconductor thin film according to the above 12 or 13, wherein the frequency of the alternating current power source is 10 kHz to 1 MHz.

A thin film transistor having the oxide semiconductor film according to any one of the above 5 to 7 as a channel layer.

16. The thin film transistor according to the above 15, wherein the field effect mobility is 10 cm ² /Vs or more.

A thin film transistor having a protective film containing at least SiN _x (x is an arbitrary number) on the oxide semiconductor thin film according to any one of the above 5 to 7.

A method of producing a thin film transistor, which is the method for producing a thin film transistor using the oxide semiconductor thin film according to any one of the above 5 to 7 as a semiconductor active layer, and comprising the step of not using the semiconductor thin film The etch stop layer is laminated, and the semiconductor thin film and the electrode are patterned using different etching liquids, and the etching liquid directly contacts the semiconductor thin film when the electrodes are patterned.

A display device comprising the thin film transistor according to any one of the above 15 to 17.

According to the present invention, it is possible to provide an oxide containing an indium element (In), a tin element (Sn), a zinc element (Zn), and a magnesium element (Mg), and can achieve higher mobility and higher The reliability of the TFT sputtering target.

In addition, it is possible to provide a sputtering target which can produce a TFT having high mobility and high reliability with high productivity by a back channel etching method.

17a‧‧‧AC power supply

17b‧‧‧AC power supply

17c‧‧‧AC power supply

31a‧‧ Target

31b‧‧‧ target

31c‧‧ Target

31d‧‧‧ target

31e‧‧ Target

31f‧‧‧ target

40a‧‧‧Magnetic field forming mechanism

40b‧‧‧Magnetic field forming mechanism

40c‧‧‧Magnetic field forming mechanism

40d‧‧‧Magnetic field forming mechanism

40e‧‧‧Magnetic field forming mechanism

40f‧‧‧Magnetic field forming mechanism

Fig. 1 is an X-ray chart of the sintered body obtained in Example 1.

2 is an X-ray chart of the sintered body obtained in Example 2.

Fig. 3 is an X-ray chart of the sintered body obtained in Example 3.

Fig. 4 is a view showing a sputtering apparatus used in an embodiment of the present invention.

Hereinafter, the sputtering target, the oxide film, the thin film transistor, the display device, and the like of the present invention will be described in detail, but the present invention is not limited to the following embodiments and examples.

The sputtering target of the present invention comprises a homologous structural compound containing an oxide and having In ₂ O ₃ (ZnO) _m (m is 0.1 to 20), and a spinel structure compound represented by Zn­ ₂ SnO ₄ , The oxide contains an indium element (In), a tin element (Sn), a zinc element (Zn), and a magnesium element (Mg).

The homologous structural compound and the spinel structure compound can be confirmed by X-ray refraction.

The term "homologous structure" refers to a crystal structure including a "natural superlattice" structure having a long period in which a plurality of layers of crystal layers of different substances are overlapped. In the case where the crystal period or the thickness of each film layer is in the degree of nanometer, the chemical composition of each layer or the combination of the thicknesses of the layers is used to obtain a property different from that of a single substance or a mixture of layers uniformly mixed. Inherent characteristics. Further, the crystal structure of the homologous phase can be confirmed, for example, by the fact that the X-ray refracting pattern of the powder obtained by pulverizing the target coincides with the crystal structure X-ray refracting pattern of the homologous phase assumed from the composition ratio. Specifically, it can be based on the JCPDS (Joint Committee of Powder Diffraction Standards) card or ICSD (Inorganic It was confirmed that the crystal structure X-ray refraction patterns of the homologous phases obtained by the Crystal Structure Database were identical.

Regarding the spinel structure, X-ray refraction measurement was performed on the sputtering target, and as a result, the peak of the spinel structure compound was observed, whereby the spinel structure was confirmed.

The spinel structure is described in detail in "Introduction to Western Solid State Chemistry" (Kodansha Technology). According to the above, the spinel structure is as follows.

The spinel has a composition formula of AB ₂ O ₄ , and if classified according to the coordination state of the A ion and the B ion, it can be classified into a spinel structure, a reverse spinel structure, and a structure in between.

The positive spinel has a structure in which one eighth of the tetrahedral gap of the three-dimensional surface-shaped lattice formed by O ^2- is filled with A and one of the octahedral gaps is filled with B. The inverse spinel structure has a structure in which one-eighth of the tetrahedral gap is filled with B and one-half of the octahedral gap is filled with A and B. Although it is usually cubic crystal, there are also cubic crystal deformers.

Further, the spinel structure compound also includes a substituted solid solution in which one of atoms or ions in the crystal structure is substituted by another atom, and an intrusive solid solution in which other atoms are added at an intercrystalline position.

By including a homologous structural compound represented by In ₂ O ₃ (ZnO) _m (m is 0.1 to 20), it is possible to obtain a target in which the relative density of the target is easily increased, the specific resistance is also easily lowered, and abnormal discharge is difficult.

m is, for example, an integer, preferably 0.1 to 10, more preferably 0.5 to 7, and further preferably 2 to 5.

In addition, by including a spinel structure compound represented by Zn­ ₂ SnO ₄ , the Mg element is solid-solved, and even if the content of Mg is large, it is possible to prevent the formation of high-resistance MgO in the target, thereby easily lowering the target resistance. It is easy to suppress abnormal discharge.

In the sputtering target of the present invention, it is preferred 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)

(wherein, In, Sn, Zn, and Mg represent the atomic ratios of the respective elements in the sputtering target, respectively)

In the above formula (1), when the amount of the In element is 0.05 or more, the bulk resistance value of the sputtering target is likely to be low, and DC (Direct Current) sputtering can be easily performed.

On the other hand, when the amount of the In element is 0.70 or less, the carrier concentration of the film produced using the target does not become too high, and it can be used as a film for semiconductor.

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 the Sn element is 0.01 or more, the density of the target is likely to increase, and the volume resistance of the sputtering target is likely to be lowered.

On the other hand, when the amount of the Sn element is 0.35 or less, SnO _{2 which} is a cause of abnormal discharge is not easily precipitated in the target.

According to the above, the concentration of Sn 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 further preferably 0.05 to 0.30.

In the above formula (3), when the amount of the Zn element is 0.01 or more, the target density is likely to increase, and the target resistance is also likely to be low. On the other hand, when the amount of the Zn element is 0.90 or less, ZnO which is a cause of abnormal discharge is not easily precipitated in the target.

According to the above, the concentration of Zn is preferably 0.01 ≦ Zn / (In + Sn + Zn + Mg) ≦ 0.90.

The amount of Zn element [Zn/(In+Sn+Zn+Mg)] is preferably from 0.03 to 0.85, and more preferably from 0.05 to 0.80.

In the above formula (4), when the amount of the Mg element is 0.01 or more, the carrier concentration of the film produced using the target is not easily increased, and it is easy to exhibit good semiconductor characteristics.

On the other hand, when the amount of the Mg element is 0.30 or less, it is less likely to cause a high resistance of the target due to the individual expression of MgO.

From the above, the concentration of Mg 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 further preferably 0.02 to 0.25.

The atomic ratio of each element contained in the sputtering target can be quantitatively analyzed by an inductively coupled plasma-optical emission spectroscop (ICP-AES). Find out.

Specifically, if the solution sample is sprayed into an argon plasma (about 6000 to 8000 ° C) by a sprayer, the element in the sample absorbs thermal energy and is excited, and the orbital electrons move from the ground state to a higher energy. The track of the order. The orbital electrons move to a lower energy orbit for about ^10-7 to ^10-8 seconds. At this time, the energy difference is emitted as light and emits light. This light shows the wavelength (spectral line) inherent to the element, so the presence of the element (qualitative analysis) can be confirmed by the presence or absence of the spectral line.

Further, since the size (emission intensity) of each spectral line is proportional to the number of elements in the sample, the sample concentration (quantitative analysis) can be obtained by comparison with a standard solution of a known concentration.

After specifying the elements contained in the qualitative analysis, the content is determined by quantitative analysis, and based on the results, the atomic ratio of each element can be obtained.

As described above, the metal element contained in the sputtering target substantially contains In, Sn, Zn, and Mg, and may contain other unavoidable impurities within a range that does not impair the effects of the present invention.

In the present invention, the term "substantially" means that the effect as a sputtering target is caused by the above-mentioned In, Sn, Zn, and Mg, or 95% by weight or more of the metal element of the sputtering target. The weight% or less (preferably 98% by weight or more and 100% by weight or less) is In, Sn, Zn, and Mg.

The sputtering target of the present invention preferably has a relative density of 97% or more. When a large substrate (1G or more) is used to increase the sputtering output and the oxide semiconductor thin film is formed, the relative density is preferably 97% or more. The relative density refers to the density calculated relative to the theoretical density calculated from the weighted average. The density calculated from the weighted average of the densities of the respective raw materials is the theoretical density, which is set to 100%.

If the relative density is 97% or more, a stable sputtering state can be maintained. When a large substrate is used to increase the sputtering output and the film is formed, if the relative density is less than 97%, the target surface may be blackened or abnormal discharge may occur. The relative density is more preferably 98.5% or more, and further preferably 99% or more.

The relative density can be calculated from the measured density and theoretical density measured by the Archimedes method. The relative density is preferably 100% or less. When it is 100% or less, it is not easy to generate metal particles or form a low-order oxide in the sintered body, and the oxygen supply amount can be completed even if the film formation is not strictly adjusted.

Further, after the sintering, the density may be adjusted by performing a post-treatment step such as a heat treatment operation in a reducing environment. The reducing environment may use an environment such as argon gas, nitrogen gas, hydrogen gas, or the like, or a mixed gas atmosphere.

Further, the sputtering target of the present invention preferably has a relative density of 97% or more and a bulk specific resistance of 10 m?cm or less. Thereby, when the sputtering target of the present invention is sputtered, the occurrence of abnormal discharge can be suppressed. The sputtering target of the present invention enables a high quality oxide semiconductor film to be formed efficiently, inexpensively, and energy-savingly.

The bulk specific resistance can be measured, for example, by the method described in the examples.

The maximum particle diameter of the crystal in the sputtering target of the present invention is preferably 8 μm or less. When the particle diameter of the crystal is 8 μm or less, no tuberculosis is likely to occur.

When the target surface is scraped by sputtering, the shaving speed is based on the crystal plane Different from each other, irregularities are generated on the surface of the target. The size of the concavities and convexities depends on the crystal grain size present in the sputtering target. Regarding a target having a large crystal grain size, it is considered that the unevenness thereof is large, and tuberculosis is generated from the convex portion.

The maximum particle diameter of the crystal of the sputtering target is measured for the largest diameter of the particles having the largest diameter observed in the frame of 100 μm square at the following five locations, and is present in the frames of the five locations. The average value of the particle diameters of the largest particles indicates that the five portions are located at the center point of the circle (one portion) and the two center lines orthogonal to the center point when the shape of the sputtering target is circular. The total of the center point and the intermediate point (four parts) of the peripheral portion is five, and when the shape of the sputtering target is a quadrangle, the center point (one part) and the diagonal of the quadrangle The total of the center point and the middle point of the corner (four parts) is five parts in total. The particle size is used to measure the long diameter of the crystal grains. The crystal grains can be observed by a scanning electron microscope (SEM).

The method of manufacturing the sputtering target of the present invention comprises the following two steps.

(1) Step of mixing and shaping a raw material compound to form a shaped body

(2) a step of sintering the above shaped body

Hereinafter, each step will be described.

(1) Step of mixing and shaping a raw material compound to form a shaped body

The raw material compound is not particularly limited as long as it is a compound containing In, Sn, Zn, and Mg and the sintered body may have the following atomic ratio.

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)

(wherein, In, Sn, Zn, and Mg represent the atomic ratios of the respective elements in the sputtering target, respectively)

For example, a combination of indium oxide, tin oxide, zinc oxide, and magnesium oxide can be mentioned. Further, 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.

In the case where a monomer metal is used as the raw material, for example, when a combination of indium oxide, tin oxide, zinc oxide, and monomer Mg is used as the raw material powder, particles of the monomer Mg are sometimes present in the obtained sintered body. The metal particles on the surface of the target are melted during the film formation without being released from the target, and there is a case where the composition of the obtained film differs greatly from the composition of the sintered body.

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

For example, an In ₂ O ₃ powder having an average particle diameter of 0.1 μm to 1.2 μm, a SnO ₂ powder having an average particle diameter of 0.1 μm to 1.2 μm, a ZnO powder having an average particle diameter of 0.1 μm to 1.2 μm, and an average particle diameter are used. The oxide of the MgO powder of 0.1 μm to 1.2 μm is used as a raw material powder, and these are blended in accordance with the ratios satisfying the above formulas (1) to (4).

The mixing and molding method of the step (1) is not particularly limited, and it can be carried out by a known method. For example, an aqueous solvent is prepared in a raw material powder containing a mixed powder of an oxide containing indium oxide powder, tin oxide, zinc oxide, and magnesium oxide powder, and the obtained slurry is mixed for 12 hours or more, followed by solid-liquid separation. Drying ‧ granulation, and then the granules are added to the mold frame for forming.

For mixing, a wet or dry ball mill, a vibrating mill, a bead mill, or the like can be used. In order to obtain uniform and fine crystal grains and pores, it is preferable to use a bead mill mixing method in which the crushing efficiency of the aggregate is high in a short time and the dispersion state of the additive is also good.

The mixing time by the ball mill is preferably set to 15 hours or longer, more preferably 19 hours or longer. The reason for this is that if the mixing time is insufficient, a high-resistance compound such as MgO is formed in the sintered body finally obtained.

The pulverization and mixing time by the bead mill differ depending on the size of the apparatus and the amount of the slurry to be processed, but the particle size distribution in the slurry is all 1 μm or less and becomes uniform. Appropriate adjustment.

Further, it is preferred to add only an arbitrary amount of the binder while mixing, and to carry out mixing at the same time. As the binder, polyvinyl alcohol, vinyl acetate or the like can be used.

Next, a granulated powder is obtained from the raw material powder slurry. In the case of granulation, it is preferred to carry out rapid drying granulation. As a device for performing rapid drying granulation, a spray dryer is widely used. The specific drying conditions are determined according to various conditions such as the slurry concentration of the dried slurry, the hot air temperature used for drying, and the amount of air. Therefore, it is necessary to obtain optimum conditions in advance when performing.

In the case of natural drying, since the precipitation rate differs depending on the difference in specific gravity of the raw material powder, separation of In ₂ O ₃ powder, Sn ₂ O ₂ powder, ZnO powder, and MgO powder may occur, and uniform granulated powder may not be obtained. .

For the granulated powder, the molded body is usually obtained by die pressing or cold isostatic pressing (CIP, cold isostatic pressing) and molding at a pressure of, for example, 1.2 ton/cm ² or more.

(2) Step of sintering the formed body

The obtained molded article can be sintered at a sintering temperature of 1200 to 1650 ° C for 10 to 50 hours to obtain a sintered body.

The sintering temperature is preferably 1300 to 1600 ° C, more preferably 1350 to 1550 ° C, and further preferably 1400 to 1500 ° C. The sintering time is preferably from 12 to 40 hours, more preferably from 13 to 30 hours.

When the sintering temperature is 1200 ° C or higher and the sintering time is 10 hours or longer, a target which does not easily form zinc oxide or magnesium oxide in the target and is less likely to cause abnormal discharge can be obtained. On the other hand, when the sintering temperature is 1650 ° C or less and the sintering time is 50 hours or less, it is possible to suppress an increase in the average crystal grain size or the generation of coarse pores due to the apparent grain growth, and it is difficult to cause the sintered body. Reduced strength or abnormal discharge.

Further, in the process of raising the temperature of the formed body to the above-mentioned sintering temperature, the average temperature increase rate in the temperature range of 300 to 500 ° C is 2 ° C / min or less (preferably 0.05 to 1 ° C / min) The clock is more preferably 0.05 to 0.5 ° C / min).

Magnesium oxide is hygroscopic and causes a dehydration reaction above 300 °C. By setting the average temperature increase rate in the temperature range of 300 to 500 ° C to 2 ° C / min or less, it is possible to produce a target which is capable of preventing a rapid dehydration reaction and which is less likely to cause pores.

As the sintering method used in the present invention, in addition to the normal pressure sintering method, a pressure sintering method such as hot pressing, oxygen pressurization, or hot pressurization pressurization may be employed. Among them, from the viewpoints of reduction in manufacturing cost, possibility of mass production, and easy production of a large sintered body, a normal pressure sintering method is preferably employed.

The normal pressure sintering method sinters the formed body in an atmosphere or an oxidizing gas atmosphere, preferably an oxidizing gas atmosphere. The oxidizing gas environment is preferably an oxygen atmosphere. The oxygen atmosphere is preferably an environment having an oxygen concentration of, for example, 10 to 100% by volume. In the method for producing a sputtering target of the present invention, the density of the sintered body can be further increased by introducing an oxygen atmosphere during the temperature increase.

In order to homogenize the bulk resistance of the sintered body obtained in the above sintering step in the entire target, a reduction step may be provided as needed.

Examples of the reduction method include a method using a reducing gas, or a method using vacuum calcination or reduction of an inert gas. In the case of reduction treatment using a reducing gas, hydrogen, methane, carbon monoxide, or a mixed gas of such a gas and oxygen may be used. In the case of a reduction treatment by calcination in an inert gas, nitrogen gas, argon gas, or a mixed gas of such gas and oxygen or the like can be used.

The temperature during the reduction treatment is usually from 100 to 800 ° C, preferably from 200 to 800 ° C. Further, the time of the reduction treatment is usually from 0.01 to 10 hours, preferably from 0.05 to 5 hours.

In summary, for example, a sintered body can be obtained by disposing an aqueous solvent in a raw material powder containing a mixed powder of indium oxide powder, tin oxide powder, zinc oxide powder, and magnesium oxide powder, and mixing the obtained slurry. 12 hours or more, followed by solid-liquid separation, drying, granulation, and then the granules are added to the mold frame for forming. Thereafter, the temperature increase rate in the temperature range of 300 to 500 ° C is set to 2 ° C / min or less in an oxygen atmosphere, and the obtained molded product is calcined at 1200 to 1650 ° C for 10 to 50 hours.

The sputtering target of the present invention can be produced by processing the sintered body obtained as described above. Specifically, the sintered target can be formed into a sputtering target by cutting the sintered body into a shape suitable for mounting on a sputtering apparatus, and then adhering the target to the backing plate.

In order to form the sintered body into a target, the sintered body is shaved by, for example, a surface grinding disc to obtain a material having a surface roughness Ra of 0.5 μm or less. Here, the sputter surface of the target may be mirror-finished to have an average surface roughness Ra of 1000 angstroms or less.

The mirror processing (polishing) can be performed by a known grinding technique such as mechanical polishing, chemical polishing, or mechanical chemical polishing (combination of mechanical polishing and chemical polishing). For example, it can be obtained by polishing with a fixed abrasive grain polisher (polishing liquid: water) to #2000 or more, or by using free abrasive grain polishing (abrasive material: SiC paste, etc.), and then grinding the abrasive material into a diamond paste for grinding. . The polishing method is not particularly limited.

The surface of the target is preferably processed by a diamond grinding wheel of 200 to 10,000, and is preferably processed by a diamond grinding wheel of 400 to 5,000. If a diamond grinding wheel larger than 200 and smaller than 10,000 is used, the target becomes less susceptible to cracking.

It is preferable that the target has a surface roughness Ra of 0.5 μm or less and a non-directional polishing surface. When Ra is 0.5 μm or less and there is no directionality on the polished surface, abnormal discharge or generation of fine particles is less likely to occur.

Next, the obtained target is subjected to purification treatment. The purification treatment can be performed by using blast or running water. When the foreign matter is removed by air blowing, if the dust collector is used to inhale from the opposite side of the nozzle, it can be removed more effectively.

Furthermore, there is a limit to the above blast or running water cleaning, so that ultrasonic cleaning or the like can be further performed. For this ultrasonic cleaning, it is more effective to perform the method of multiple vibrations at a frequency of 25 to 300 kHz. For example, ultrasonic cleaning is preferably performed at a frequency of 25 to 300 kHz with 12 types of frequencies per 25 kHz.

The thickness of the target is usually 2 to 20 mm, preferably 3 to 12 mm, and more preferably 4 to 6 mm.

The sputtering target can be obtained by bonding the target obtained as described above to the liner. Alternatively, a plurality of targets may be mounted on one of the liners to form substantially one target.

The oxide semiconductor thin film of the present invention is obtained by forming a film by a sputtering method using the sputtering target of the present invention described above.

The oxide semiconductor thin film of the present invention contains indium, tin, zinc, magnesium, and oxygen, and generally has an atomic ratio of (1) to (4): 0.05 ≦ In / (In + Sn + Zn + Mg) ≦ 0.70 (1)

0.015≦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 respectively represent the atomic ratio of each element in the oxide semiconductor thin film).

In the above formula (1), when the amount of the In element is 0.05 or more, the degree of mobility is easily improved when the film formed film is applied to the channel layer of the TFT. On the other hand, when the amount of the In element is 0.70 or less, when the film to be formed is applied to the channel layer of the TFT, it is difficult to be a characteristic of constant conduction, and it is easy to exhibit good characteristics as a TFT.

In the above formula (2), when the amount of the Sn element is 0.01 or more, the obtained film is not excessively fast in dissolution rate with respect to wet etching, and is easily subjected to wet etching. On the other hand, when the amount of the Sn element is 0.35 or less, the residue does not easily remain even after the wet etching.

In the above formula (3), when the amount of the 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 the Zn element is 0.90 or less, the obtained film is not excessively fast in dissolution rate with respect to wet etching, and is easily subjected to wet etching.

In the above formula (4), if the amount of the Mg element is 0.01 or more, the carrier concentration in the film is not It will become too high to prevent the TFT characteristics from becoming a constant conduction. On the other hand, when the amount of the Mg element is 0.30 or less, the mobility is not easily lowered.

The sputtering target of the present invention has high conductivity, so that a DC sputtering method with a faster film formation speed can be used.

In addition to the above-mentioned DC sputtering method, the sputtering target of the present invention can also be applied to RF (Radio Frequency) sputtering, AC (Alternating Current) sputtering, and pulsed DC sputtering. Sputter without abnormal discharge.

The oxide semiconductor thin film can also be produced by a vapor deposition method, an ion plating method, a pulsed laser vapor deposition method, or the like using the above-described sputtering target.

As the sputtering gas (environment), a mixed gas of a rare gas such as argon gas 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 the group consisting of water vapor, oxygen, 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 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 , and 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, occurrence of electric leakage or TFT characteristics can be prevented from being normally conducted. Further, when the carrier concentration is 10 ¹³ cm ^-3 or more, it is easy to exhibit good characteristics as a TFT.

The carrier concentration of the oxide semiconductor film can be measured by a Hall effect measurement method.

The oxygen partial pressure at the time of sputtering film formation is preferably set to 0.1% to 30%. When the oxygen partial pressure ratio is 30% or more, the carrier concentration of the film is greatly lowered and the carrier concentration is less than 10 ¹³ cm ^-3 .

More preferably 0.1% to 20%.

The partial pressure ratio of water vapor (water molecules) contained in the sputtering gas (environment) when the oxide film of the present invention is deposited, that is, [water vapor (H ₂ O)] / ([water vapor (H ₂ O)] +[rare gas]+[other gas molecules]) is preferably 0.1 to 25%.

Further, when the partial pressure ratio of water is 25% or less, the decrease in the film density can be prevented, and the repetition of In on the 5 s orbit does not become small, so that the mobility is not easily lowered. The partial pressure ratio of water in the environment at the time of sputtering is preferably 0.7 to 13%, 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 less, the absorption of oxygen or the like introduced during film formation is not easily reduced, and even after heating, the carrier concentration of the film is likely to be 10 ¹⁹ cm ^-3 or less. Further, if the substrate temperature at the time of film formation is higher than 25 ° C, the film density of the film is increased, and the mobility of the TFT is not easily lowered.

Preferably, the oxide film obtained by sputtering is further subjected to an annealing treatment at 150 to 500 ° C for 15 minutes to 5 hours. The annealing treatment temperature after film formation is more preferably 200 ° C or more and 450 ° C or less, and further preferably 250 ° C or more and 350 ° C or less. Semiconductor characteristics are obtained by performing the above annealing.

Further, the environment at the time of heating is not particularly limited, and from the viewpoint of carrier controllability, it is preferably an atmospheric environment or an oxygen circulation environment.

In the post-treatment annealing step of the oxide 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 at the time of sputtering is preferably 1 to 15 cm in the vertical direction with respect to the film formation surface of the substrate, and more preferably 2 to 8 cm. When the distance is 1 cm or more, the kinetic energy of the particles reaching the target constituent elements of the substrate does not become excessively large, so that it is less likely to cause an in-plane distribution of film thickness or electrical characteristics. On the other hand, when the distance between the target and the substrate is 15 cm or less, the kinetic energy of the particles reaching the target constituent elements of the substrate does not become excessively small, the film density is not easily lowered, and good semiconductor characteristics are easily obtained.

The film formation of the oxide film is preferably in the environment of a magnetic field strength of 300 to 1500 gauss. Sputtering is performed. When the magnetic field strength is 300 gauss or more, the plasma density can be increased, and even if it is a high-resistance sputtering target, sputtering can be performed without any problem. On the other hand, when it is 1500 gauss or less, it is easy to control the film thickness and the electrical characteristics in a film.

The pressure of the gas atmosphere (sputtering pressure) is not particularly limited as long as it is a range in which the plasma can be stably discharged, and is preferably 0.1 to 3.0 Pa, more preferably 0.1 to 1.5 Pa, and particularly preferably 0.1 to 1.0 Pa. If the sputtering pressure is 3.0 Pa or less, the average free step of the sputtered particles can be lengthened, and the density of the film can be easily increased. Further, when the sputtering pressure is 0.1 Pa or more, it is easy to prevent the formation of microcrystals in the film during film formation. In addition, the sputtering pressure is a system-controlled total pressure at the start of sputtering after introduction of a rare gas such as argon gas, water vapor, or oxygen.

Further, film formation of the oxide semiconductor thin film can also be carried out by the following alternating current sputtering.

The substrate is sequentially transported to a position opposite to three or more targets placed in a vacuum chamber at a predetermined interval, and a negative potential and a positive potential are alternately applied to the respective targets from the AC power source to generate plasma on the target. Film formation on the surface of the substrate.

At this time, at least one of the outputs from the AC power source is branched while switching between the two or more connected targets. In other words, at least one of the outputs from the AC power source is branched and connected to two or more targets, and a film is formed while applying a different potential to the adjacent targets.

Further, in the case of forming an oxide semiconductor thin film by alternating current sputtering, for example, it is preferably an environment containing a mixed gas of a rare gas and one or more selected from the group consisting of water vapor, oxygen, and nitrous oxide gas. Sputtering is carried out, and it is particularly preferable to perform sputtering in an environment containing at least a mixed gas of a rare gas and water vapor.

In the case of film formation by AC sputtering, an oxide layer excellent in industrial area uniformity is obtained, and an improvement in utilization efficiency of the target can be expected.

In the case of performing sputtering on a large-area substrate having a side of more than 1 m, for example, an AC sputtering apparatus for large-area production as described in JP-A-2005-290550 is preferably used.

The AC sputtering apparatus described in Japanese Laid-Open Patent Publication No. 2005-290550 specifically includes a vacuum chamber, a substrate holder disposed inside the vacuum chamber, and a sputtering source disposed at a position facing the substrate holder. The main part of the sputtering source of the AC sputtering apparatus is shown in FIG. The sputtering source has a plurality of sputtering portions each having a plate-shaped target 31a to 31f. When the sputtering surface of each of the targets 31a to 3tf is a sputtering surface, the sputtering surface is disposed on the same plane. Each sputter part. Each of the targets 31a to 31f is formed to have an elongated shape in the longitudinal direction, and each of the targets has the same shape, and the edge portions (side surfaces) in the longitudinal direction of the sputtering surface are arranged in parallel with each other at a predetermined interval. Therefore, the side faces of the adjacent targets 31a to 31f become parallel.

The AC power sources 17a to 17c are disposed outside the vacuum chamber, and one of the two terminals of the AC power sources 17a to 17c is connected to one of the adjacent two electrodes, and the other terminal is connected to the other electrode. The two terminals of the AC power supplies 17a to 17c output voltages of different positive and negative polarities, and the targets 31a to 31f are attached so as to be in close contact with the electrodes. Therefore, the adjacent two targets 31a to 31f are mutually applied from the AC power sources 17a to 17c. AC voltages of different polarities. Therefore, one of the targets 31a to 31f adjacent to each other is at a positive potential and the other is at a negative potential.

The electrode targets 31a to 31f mean that the magnetic field forming mechanisms 40a to 40f are disposed on the opposite side. Each of the magnetic field forming mechanisms 40a to 40f has an elongated annular magnet having an outer circumference substantially equal to the outer circumference of the targets 31a to 31f, and a shorter rod-shaped magnet having a shorter length than the annular magnet.

Each of the annular magnets is disposed in parallel with the longitudinal direction of the targets 31a to 31f at the front and back sides of 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 annular magnets are also disposed at the same interval as the targets 31a to 31f.

The AC power density in the case where an oxide target is used in AC sputtering is preferably 3 W/cm ² or more and 20 W/cm ² or less. If the power density is 3 W/cm ² or more, the film formation speed can be increased, which is economical in production. When it is 20 W/cm<^2> or less, damage of a target can be prevented. More preferably, the power density is from 3 W/cm ² to 15 W/cm ² .

The frequency of AC sputtering is preferably in the range of 10 kHz to 1 MHz. With more than 10 kHz, noise is less likely to occur. If it does not exceed 1 MHz, it is possible to prevent the plasma from excessively expanding and sputtering outside the desired target position to impair uniformity. The better AC sputtering frequency is 20kHz~500kHz.

The conditions and the like at the time of sputtering other than the above may be appropriately selected in accordance with the above.

The oxide semiconductor film of the present invention is insoluble in a phosphoric acid-based etching liquid and is soluble in an oxalic acid-based etching liquid. As described above, the etching liquid is selective, whereby the oxide film can be etched by oxalic acid etching, and the electrode formed on the oxide film can be patterned by using a phosphoric acid etching solution.

Preferably, the etching rate of the phosphoric acid-based etching solution at 35 ° C is 10 nm/min or less, and the etching rate at 35 ° C of the oxalic acid-based etching liquid is 20 nm/min or more. When the etching rate is within the above range, the selectivity of the etching liquid can be exhibited, and the TFT can be formed by post-channel etching.

ITO-06N (manufactured by Kanto Chemical Co., Ltd.) is exemplified as the oxalic acid-based etching liquid. It is preferably 0.5 to 10% by weight of oxalic acid. However, in addition to oxalic acid, carboxylic acid or other acid such as malonic acid or succinic acid or acetic acid may be contained, and oxalic acid is not necessarily contained.

Examples of the phosphoric acid-based etching liquid include a PAN (Polyacrylonitrile)-based etching liquid containing phosphoric acid, acetic acid, and nitric acid. The PAN-based etching liquid is preferably in the range of 45 to 95% by weight of phosphoric acid, 3 to 50% by weight of acetic acid, and 0.5 to 5% by weight of nitric acid.

The oxide semiconductor film of the present invention can be used for a thin film transistor, and particularly preferably used as a channel layer.

The thin film transistor of the present invention is not particularly limited as long as it has the above-described oxidized semiconductor thin film of the present invention as a channel layer, and can be formed by various known elements.

The film thickness of the channel layer in the thin film transistor of the present invention is usually 10 to 300 nm, preferably 20 to 250 nm, more preferably 30 to 200 nm, still more preferably 35 to 120 nm, and particularly preferably 40 to 80 nm. When the film thickness of the channel layer is 10 nm or more, the unevenness of the film thickness at the time of film formation in a large area can be reduced, and the characteristics of the produced TFT can be prevented from becoming uneven in the plane. On the other hand, when the film thickness is 300 nm or less, the film formation time is not excessively extended, which is industrially advantageous.

The channel layer in the thin film transistor of the present invention is generally used in an N-type region, and may be used 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 for a PN junction type transistor. Various semiconductor devices.

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

The thin film transistor of the present invention preferably has 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 finer film than SiO ₂ , it has an advantage that the deterioration suppression effect of the TFT is high.

Furthermore, x is an arbitrary number, and the stoichiometric ratio of SiN _x may not be fixed.

The protective film may contain, 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 in} addition to SiN _x . An oxide such as 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 AlN.

The oxide semiconductor thin film containing the indium element (In) tin element (Sn), the zinc element (Zn), and the magnesium element (Mg) of the present invention contains a Mg element, so the CVD (Chemical Vapor Deposition) process The reduction resistance is improved, and it is not easy to reduce the back channel side by the process of producing a protective film, and SiN _x can be used as a protective film.

Before forming the protective film, it is preferred to perform ozone treatment, oxygen plasma treatment, nitrogen dioxide plasma treatment or nitrous oxide plasma treatment on the channel layer. If the above treatment is performed after the formation of the channel layer and before the formation of the protective film, it may be performed at any timing, but it is preferably formed immediately. It is carried out before the protective film. By performing the above pretreatment, the generation of oxygen defects in the channel layer can be suppressed.

Further, when hydrogen in the oxide semiconductor film is diffused during driving of the TFT, there is a possibility that the threshold voltage is shifted to lower the reliability of the TFT. By performing ozone treatment, oxygen plasma treatment, or nitrous oxide plasma treatment on the channel layer, the bonding of the In-OH can be stabilized in the thin film structure to suppress the diffusion of hydrogen in the oxide semiconductor film.

The thin film transistor generally 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 material which is usually used 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, or the like can be used. 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 or AlN. 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, for example, by a plasma CVD (Chemical VaPor Deposttion) method.

When a gate insulating film is formed by a plasma CVD method and a channel layer is formed thereon, hydrogen in the gate insulating film is diffused to the channel layer, resulting in a decrease in film quality of the channel layer or a decrease in reliability of the TFT. Hey. In order to prevent the film quality of the channel layer from decreasing or the reliability of the TFT from being lowered, it is preferred to perform ozone treatment, oxygen plasma treatment, nitrogen dioxide plasma treatment or nitrous oxide on the gate insulating film before film formation of the channel layer. Slurry treatment. By performing the above pretreatment, the film quality of the channel layer can be prevented from being lowered or the reliability of the TFT can be lowered.

Further, the oxygen number of the above oxide is not necessarily the same as the stoichiometric ratio, and may be, for example, SiO ₂ or SiO _x .

The gate insulating film may also be a junction of an insulating film containing two or more layers of different materials. Structure. Further, the gate insulating film may be any of crystalline, polycrystalline, and amorphous, but is preferably polycrystalline or amorphous which is industrially easy to manufacture.

The material for forming the electrodes of the drain electrode, the source electrode, and the gate electrode in the thin film transistor of the present invention is not particularly limited, and a material which is generally used can be arbitrarily selected. For example, a transparent electrode such as indium tin oxide (ITO), indium zinc oxide, ZnO, or SnO ₂ or a metal electrode such as Al, Ag, Cu, Cr, Ni, Mo, Au, Ti, or Ta, or the like may be used. Metal electrodes of these alloys.

The thin film transistor of the present invention can be produced by etching an etchant of an oxide film without forming an etch stop layer on the oxide film as an active layer, and etching by a back channel.

When a thin film transistor in which a normal oxide semiconductor thin film such as IGZO is used for the active layer is used, the etching liquid for etching the electrode can also etch the oxide semiconductor thin film, so that it is necessary to form an oxide for the oxide. An etch stop layer such as SiO _x or the like which is prevented from being etched on the semiconductor film. Productivity is reduced due to the step of forming an etch stop layer.

However, the oxide semiconductor thin film of the present invention can be formed by appropriately selecting an etching liquid for patterning a semiconductor thin film and an electrode when a thin film transistor is formed, and can be completed without forming an etch stop layer, so that productivity is improved.

That is, the thin film transistor using the oxide semiconductor thin film of the present invention as the semiconductor active layer can be produced by a manufacturing method including the step of laminating an etch stop layer on the semiconductor thin film and using a different etching liquid to make the semiconductor The film and the electrode are patterned to directly contact the semiconductor film with the etching liquid when patterning the electrode.

Specifically, when the oxide semiconductor thin film is patterned, an etching solution such as an oxalic acid etching solution or the like is used, and when the electrode is patterned, indium zinc oxide, ZnO, SnO ₂ or the like is used. a transparent conductive oxide or a metal such as Al, Ag, Cu, Cr, Ni, Mo, Ti, or Ta, or an electrode material such as an alloy thereof, which is etched and is not easily etched by the oxide semiconductor film, for example, a phosphoric acid type etching. Thereby, even if the etching liquid of the electrode is directly in contact with the semiconductor film, the semiconductor film is not etched, so that it is not necessary to form an etch stop layer.

Each of the electrodes of the drain electrode, the source electrode, and the gate electrode may be formed in a multilayer structure in which two or more different conductive layers are laminated. In particular, the source ‧thole electrode has a strong requirement for low-resistance wiring, and can be used by laminating a good conductor such as Al or Cu with a metal having excellent adhesion such as Ti or Mo.

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

The composition of the thin film transistor of the present invention can be made without any limitation by a known configuration such as a bottom gate, a bottom contact, and a top contact.

In particular, the bottom gate constitutes a higher performance than a thin film transistor of amorphous germanium or ZnO, and thus is advantageous. The bottom gate structure is preferable because it is easy to reduce the number of masks at the time of manufacture and to easily reduce the manufacturing cost of a large-sized display or the like.

The thin film transistor of the present invention can be preferably used for a display device.

As a large-area display application, a thin film transistor composed of a channel-etched bottom gate is particularly preferable. The channel etching type bottom gate constitutes a thin film electro-crystal system. In the photolithography step, the number of masks is small, and the panel for display can be manufactured at low cost. Among them, the thin film transistor composed of the bottom gate structure and the top contact of the channel etching type is particularly preferable because of good characteristics such as mobility and ease of industrialization.

Example Example 1~3

[Manufacture of sintered body]

As the raw material powder, the following oxide powder was used. Furthermore, the oxide powder level The average particle diameter was measured by a laser refractive particle size distribution measuring apparatus SALD-300V (manufactured by Shimadzu Corporation), and the average particle diameter was a median diameter D50.

Indium oxide powder: average particle size 0.98μm

Tin oxide powder: average particle size 0.96μm

Zinc oxide powder: average particle size 0.98μm

Magnesium oxide powder: average particle size 0.98μm

The powder was weighed so as to have an atomic ratio (percentage) shown in Table 1, uniformly finely pulverized and mixed, and then a molding binder was added thereto to carry out granulation. Next, the raw material pellets were uniformly filled in a mold, and subjected to press molding at a press pressure of 140 MPa by a cold press.

The formed body obtained in this manner is sintered. First, the formed body was placed in a sintering furnace, and oxygen gas was introduced at a rate of 5 liters per minute per 0.1 m ^{3 of the} inside of the sintering furnace. In this environment, sintering was carried out under the conditions described in Table 1 (temperature rising rate of 300 to 500 ° C, sintering holding temperature, and sintering time). Further, the temperature increase rate from 500 ° C to 100 ° C was set to 0.5 ° C / min, and the temperature increase rate from 800 ° C to the sintering hold temperature was set to 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. With respect to the sintered bodies of Examples 1 to 3, it was confirmed that the relative density was 97% or more.

Further, the specific resistance (electrical conductivity) of the obtained sintered body was measured using a resistivity meter (manufactured by Mitsubishi Chemical Corporation, Loresta) and based on a four-probe method (JIS R 1637). The results are shown in Table 1. As shown in Table 1, the specific electrical resistance of the sintered bodies of Examples 1 to 3 was 10 mΩcm or less.

[Analysis of sintered body]

The obtained sintered body was subjected to ICP-AES analysis and confirmed to have the atomic ratio shown in Table 1.

In addition, the obtained sintered body is examined by an X-ray refraction measuring device (XRD). Check the crystal structure. The measurement conditions of XRD are as follows.

‧Device: Ultima-III manufactured by Rigaku Co., Ltd.

‧X-ray: Cu-Kα ray (wavelength 1.5406Å, monochromated with graphite monochromator)

‧2θ-θ reflection method, continuous scanning (1.0°/min)

‧Sampling interval: 0.02°

‧Slit DS, SS: 2/3°, RS: 0.6mm

The X-ray refraction diagrams of the sintered bodies obtained in Examples 1 to 3 are shown in Figs. 1 to 3. The chart was analyzed, and as a result, the homologous structure of In ₂ Zn ₄ O ₇ and the spinel structure of Zn ₂ SnO ₄ were observed in the sintered body of Example 1.

The crystal structure can be confirmed by 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.

With respect to Examples 2 to 3, the homology structure of In ₂ O ₃ (ZnO) _m and the spinel structure of Zn ₂ SnO _{4 were} also observed as shown in Table 1.

In Examples 2 to 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 shaved by a flat grinding disc, and the side edges were cut and attached to the backing plate using a diamond cutter to prepare a sputtering target having a diameter of 4 inches. .

Further, six targets having a width of 200 mm, a length of 1,700 mm, and a thickness of 10 mm for AC sputtering were separately prepared.

[Confirmation of abnormal discharge]

The obtained 4 inch diameter sputtering target is mounted in a DC sputtering device as a ring In a argon gas, a mixed gas of water vapor was added at a partial pressure ratio of 2%, and continuous sputtering was performed at a sputtering temperature of 0.4 Pa, a substrate temperature of room temperature, and a DC output of 400 W. Store the voltage fluctuations during sputtering in the data logger to check for abnormal discharge. The results are shown in Table 1.

In addition, the presence or absence of the abnormal discharge is confirmed by observing the voltage fluctuation and detecting the abnormal discharge. Specifically, the case where the voltage generated in the measurement time of 5 minutes is changed to 10% or more of the constant voltage during the sputtering operation is assumed to be abnormal discharge. In particular, when the constant voltage during the sputtering operation is changed by ±10% within 0.1 second, there is a micro-arc which causes abnormal discharge of the sputtering discharge, and the yield of the element is lowered, which is not suitable for mass production.

[Is there a confirmation of tuberculosis]

In addition, a sputtering target having a diameter of 4 inches was used, and a mixed gas containing hydrogen gas at a partial pressure of 3% in argon was used as an environment, and sputtering was continuously performed for 40 hours to confirm whether or not nodules were generated.

As a result, no nodules were observed on the surface of the sputtering target of Examples 1 to 3.

Further, the sputtering conditions were set to a sputtering pressure of 0.4 Pa, a DC output of 100 W, and a substrate temperature of room temperature. Hydrogen is added to the ambient gas to promote the production of nodules.

The tuberculosis system adopts the following method: the method is at the center point (one part) of the circular sputtering target, and the intermediate point (four parts) between the center point and the peripheral portion on the two center lines orthogonal to the center point The total of the five sites was magnified to 50 times by a stereoscopic microscope to observe the change in the target surface after sputtering, and the number of tuberculosis measurements having a long diameter of 20 μm or more generated in a field of 9 mm ² was averaged. The number of tuberculosis produced is shown in Table 1.

Comparative example 1~2

The 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 at the same time.

The spinel structure of MgIn ₂ O ₄ corresponds to ICSD #24992, the rock salt type structure of MgO corresponds to JCPDS card No. 45-0946, and the rutile structure of SnO ₂ corresponds to JCPDS card No. 00-1024.

In Comparative Examples 1 and 2, the density was 90% or less and the density was low. The reason for this is considered to be that the temperature increase rate at 300 ° C to 500 ° C is faster than 2.5 ° C / min or more, so that moisture absorbed by MgO rapidly desorbs to form a plurality of pores.

In the sputtering target of Comparative Example 1, abnormal discharge occurred during sputtering, and nodules were observed on the surface of the target. In Comparative Example 2, the electric resistance was high and it was impossible to discharge.

Example 4~6

[Manufacture of oxide semiconductor film]

A 4 inch target having the composition shown in Table 2 prepared in Examples 1 to 3 was attached to the magnetron sputtering apparatus, and a glass slide (#1737 manufactured by Corning Incorporated) was attached as a substrate. An amorphous film having a film thickness of 50 nm was formed on a glass slide by DC magnetron sputtering. At the time of film formation, argon gas, oxygen 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 (where example 6 is 100 ° C)

‧ Arrival pressure: 8.5×10 ^-5 Pa

‧Environmental gases: argon, oxygen, water vapor (partition ratio is shown in Table 2)

‧ Sputtering pressure (total pressure): 0.4Pa

‧Input power: DC100W

‧S (substrate)-T (target) distance: 70mm

The film structure was examined by an X-ray refraction (XRD) measuring apparatus (Ultima-III manufactured by Rigaku) on a film formed on a glass substrate.

In Examples 4 to 6, it was confirmed that no refractive index was observed after the film was deposited, and it was amorphous.

The measurement conditions of XRD are as follows.

‧Device: Ultima-III manufactured by Rigaku Co., Ltd.

‧X-ray: Cu-Kα ray (wavelength 1.5406Å, monochromated with graphite monochromator)

‧2θ-θ reflection method, continuous scanning (1.0°/min)

‧Sampling interval: 0.02°

‧Slit DS, SS: 2/3°, RS: 0.6mm

Next, the substrate on which the amorphous film was formed was heated in the atmosphere at the annealing temperature shown in Table 2 during the annealing time to form an oxide semiconductor film. Used in the glass The substrate on which the film was formed on the glass substrate was used as a Hall effect measuring element, and was placed on a Resi Test 8300 (manufactured by Toyo Denki Co., Ltd.) to evaluate the Hall effect at room temperature.

Further, it was confirmed by ICP-AES analysis 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 transistor]

As the substrate, a conductive germanium substrate to which a thermal oxide film having a film thickness of 100 nm was attached was used. The thermal oxide film functions as a gate insulating film, and the conductive crotch functions as a gate electrode.

A sputtering film was formed on the gate insulating film to form an amorphous film having a film thickness of 50 nm. Coating, prebaking (80 ° C, 5 minutes), and exposure were carried out using OFPR #800 (manufactured by Tokyo Ohka Kogyo Co., Ltd.) as a resist. After development, post-baking (120 ° C, 5 minutes) was carried out and etched with oxalic acid to pattern according to the desired shape. Thereafter, heat treatment (annealing treatment) was performed in the hot air heating furnace at the annealing temperature shown in Table 2 during the annealing time.

Thereafter, Mo (100 nm) was formed into a film by sputtering, and the source/drain electrodes were patterned in a desired shape according to the lift-off method. Further, as the treatment in the stage before the formation of the protective film, the oxide semiconductor film is subjected to nitrous oxide plasma treatment. Thereafter, SiO _{x is} formed into a film by a plasma CVD method (PECVD) to form a protective film. A thin film transistor was formed by opening a contact hole with hydrofluoric acid.

[Evaluation of etching speed]

The etching rate of the oxide semiconductor thin films of Examples 4 to 6 which were formed under the same conditions except that the film thickness of the amorphous film was changed to 100 nm was used.

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

In addition, a PAN etching solution (91.4 wt% of phosphoric acid, 3.3 wt% of nitric acid, and 5.3 wt% of acetic acid) as a phosphoric acid-based etching liquid was set to 35 ° C, and an oxide semiconductor thin film was immersed in accordance with the impregnation. The etching rate was calculated by the film thickness before and after the immersion.

[Evaluation of Thin Film Transistors]

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

Further, with respect to the manufactured transistor, the transfer characteristics were evaluated by setting the gate voltage (Vd) to 5 V and the gate voltage (Vg) to -15 to 25 V. The results are shown in Table 2. Further, the field effect mobility (μ) is calculated based on the linear mobility and is defined by the maximum value of Vg-μ.

Next, DC bias stress tests were performed on the TFTs of Examples 4 to 6. Table 2 shows the amount of change ΔVth of Vth before and after applying a DC stress of Vg = 15 V and Vd = 15 V (at a stress temperature of 80 ° C) for 10,000 seconds. Regarding the TFT of the present invention, it is known that the variation of the threshold voltage is extremely small and is not easily affected by the 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 formation conditions, annealing conditions, and results are shown in Table 2.

As shown in Table 2, it was found that the field effect mobility of the element system of Comparative Example 3 was less than 10 cm ² /Vs, which was significantly lower than that of Examples 4 to 6.

Further, the TFT of Comparative Example 3 was subjected to a DC bias stress test. Table 2 shows the amount of change ΔVth of Vth before and after applying a DC stress of Vg = 15 V and Vd = 15 V (at a stress temperature of 80 ° C) for 10,000 seconds.

Examples 7-9

A thin film transistor was produced by subjecting a 4-inch target having the composition shown in Table 3 produced in Examples 1 to 3 to AC sputtering using a film forming apparatus disclosed in Japanese Laid-Open Patent Publication No. 2005-290550. The film formation conditions and the heating (annealing) conditions of the amorphous film are shown in Table 3. A thin film transistor was produced and evaluated in the same manner as in Example 4 except that the source ‧ drain pattern was patterned by dry etching. The results are shown in Table 3.

Further, it was confirmed by ICP-AES analysis that the atomic ratio of each element contained in the oxide film was the same as that of the sputtering target.

AC sputtering was performed using the apparatus shown in FIG.

As shown in Fig. 4, six targets 31a to 31f having a width of 200 mm, a length of 1,700 mm, and a thickness of 10 mm, which were produced in Examples 1 to 3, were arranged at intervals of 2 mm so as to be parallel to each other in the longitudinal direction. The widths of the magnetic field forming mechanisms 40a to 40f are the same as those of the targets 31a to 31f and are 200 mm. From the gas supply system, Ar as a sputtering gas, water vapor, and/or O ₂ are introduced into the system, respectively.

For example, in the seventh embodiment, the film formation environment is set to 0.5 Pa, the power of the alternating current power source is set to 3 W/cm ² (= 10.2 kW / 3400 cm ² ), and the frequency is set to 10 kHz.

Under the above conditions, the film formation rate is 54 nm/min and it is high speed, which is suitable for mass production.

Comparative example 4

An oxide semiconductor was produced in the same manner as in Example 7 except that six sputtering targets having a width of 200 mm, a length of 1,700 mm, and a thickness of 10 mm, which were produced in Comparative Example 1, were used, and the sputtering conditions were changed to those shown in Table 3. Films and thin film transistors were evaluated. The results are shown in Table 3.

As shown in Table 3, it was found that the field mobility of the element of Comparative Example 4 was less than 10 cm ² /Vs, and the field effect mobility was significantly lower than that of Examples 7 to 9.

Example 10~12

A TFT was fabricated under the same conditions as in Examples 4 to 6 except that patterning of Mo was performed by channel etching using an etching solution of PAN (91.4 wt% of phosphoric acid, 3.3 wt% of nitric acid, and 5.3 wt% of acetic acid). The results are shown in Table 4.

It can be seen that good TFT characteristics can also be obtained by etching through the back channel.

[Industrial availability]

The sputtering target of the present invention can be used for the production of an oxide film such as an oxide semiconductor or a transparent conductive film. Further, the oxide 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, or the like.

The embodiments and/or the embodiments of the present invention are described in detail hereinabove, and the embodiments and/or embodiments of the present invention are susceptible to the embodiments and/or embodiments of the present invention. A variety of changes. Accordingly, such various modifications are intended to be included within the scope of the present invention.

The contents of the Japanese application specification which is the basis of the priority of the present application are all incorporated herein.

Claims (19)

A sputtering target comprising a homologous structural compound containing an oxide and having In ₂ O ₃ (ZnO) _m (m is 0.1 to 20), and a spinel structure compound represented by Zn ₂ SnO ₄ , The oxide contains an indium element (In), a tin element (Sn), a zinc element (Zn), and a magnesium element (Mg). The sputtering target according to claim 1, wherein the atomic ratio of the indium element, the tin element, the zinc element, and the magnesium element satisfies the following formula (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) (wherein, In, Sn, Zn, and Mg respectively represent the 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 volume specific resistance is 10 m Ωcm or less. A method for producing a sputtering target according to any one of claims 1 to 3, comprising the steps of: heating a molded body at a temperature increase rate of 2 ° C /min or less in a temperature range of 300 ° C to 500 ° C, and The formed body was sintered at 1200 ° C to 1650 ° C for 10 to 50 hours. An oxide semiconductor thin film formed by sputtering using a sputtering target according to any one of claims 1 to 3. The oxide semiconductor thin film according to claim 5, which is insoluble in the phosphoric acid-based etching liquid and soluble in the oxalic acid-based etching liquid. The oxide semiconductor thin film according to claim 6, wherein the etching rate of the phosphoric acid-based etching solution at 35 ° C is 10 nm/min or less, and the oxalic acid etching solution is used. The etching rate at 35 ° C is 20 nm / min or more. A method for producing an oxide semiconductor thin film, which is used in an environment containing a mixed gas of one or more selected from the group consisting of water vapor, oxygen, and nitrous oxide gas and a rare gas, using any one of claims 1 to 3 The sputtering target of the item is formed by sputtering. The method for producing an oxide semiconductor thin film according to claim 8, wherein the oxide semiconductor thin film is formed in an atmosphere containing at least a mixed gas of water vapor and a rare gas. The method for producing an oxide semiconductor thin film according to claim 8 or 9, wherein the ratio of the water vapor contained in the mixed gas is 0.1% to 25% in terms of a partial pressure ratio. The method for producing an oxide semiconductor thin film according to claim 8, wherein the ratio of the oxygen contained in the mixed gas is 0.1% to 30% in terms of a partial pressure ratio. The method for producing an oxide semiconductor thin film according to claim 8, wherein the film formation of the oxide semiconductor thin film is carried out by a sputtering method in which the substrates are sequentially transferred to a predetermined interval and arranged side by side. When three or more targets in the vacuum chamber are opposed to each other, when a negative potential and a positive potential are alternately applied to the respective targets from the AC power source, at least one of the outputs from the AC power source is branched and connected. When two or more targets are switched between the targets to which the potential is applied, plasma is generated on the target to form a film on the surface of the substrate. The method of producing an oxide semiconductor thin film according to claim 12, wherein the AC power source has an AC power density of 3 W/cm ² or more and 20 W/cm ² or less. The method of manufacturing an oxide semiconductor thin film according to claim 12 or 13, wherein the frequency of the alternating current power source is 10 kHz to 1 MHz. A thin film transistor having the oxide semiconductor film according to any one of claims 5 to 7 as a channel layer. The thin film transistor of claim 15, wherein the field effect mobility is 10 cm ² /Vs or more. A thin film transistor having a protective film containing at least SiN _x (x is an arbitrary number) on the oxide semiconductor thin film according to any one of claims 5 to 7. A method of producing a thin film transistor using the oxide semiconductor thin film according to any one of claims 5 to 7 as a method of manufacturing a thin film transistor of a semiconductor active layer, comprising the steps of: laminating no layer on the semiconductor thin film The termination layer is etched, and the semiconductor thin film and the electrode are patterned using different etching liquids, and the etching liquid directly contacts the semiconductor thin film when the electrode is patterned. A display device comprising the thin film transistor according to any one of claims 15 to 17.