JP2012012659A - Sputtering target - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sputtering target which suppresses a nodule generated at sputter deposition, and can stably obtain an oxide semiconductor film with high reproducibility.SOLUTION: The sputtering target consists of a metal oxide sintered compact that contains an In element, a Cu element, and a Ga element in an atom ratio of Cu/(Cu+In+Ga)=0.001-0.09 and Ga/(Cu+In+Ga)=0.001-0.90.

Description

  The present invention relates to a sputtering target containing a trace amount of Cu used for manufacturing an oxide semiconductor thin film, an oxide semiconductor thin film obtained by using the sputtering target, a thin film transistor, and a display device.

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 one, so when used as a switching element to drive 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, a crystalline silicon-based thin film is difficult to reduce costs such as a reduction in the number of masks because the element configuration of a TFT is usually limited to a top gate configuration.

In order to solve such a problem, a thin film transistor (TFT) 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 the general formulas In ₂ Ga ₂ ZnO ₇ and InGaZnO ₄ is disclosed (Patent Documents 1, 2, and 3). An oxide semiconductor thin film formed using a target including In, Ga, and Zn has a hole concentration of 10 cm ² / Vs at a carrier concentration of 10 ¹⁷ cm ⁻³ .

  In Patent Document 4, a thin film transistor using an oxide doped with Ni or Cu as a dopant in a channel layer is disclosed. In the example of Patent Document 4, a TFT using an oxide made of Zn, In, and Ni is disclosed, and good TFT characteristics are obtained. Here, the contents of Zn, In, and Ni are Zn: In: Ni = 1: 1.0121: 0.0079 (atomic ratio).

  In general, a sputtering method or a CVD method is used as a means for forming an oxide semiconductor. Among these, the sputtering method uses a sputtering target formed from a sintered body having a composition corresponding to the composition of the thin film. In the sputtering target to which Ni or Cu is added, there is a risk that the target resistance increases and nodules are generated during sputtering. As described above, a study on a target used when an oxide semiconductor film is formed by a sputtering method has not been sufficient.

  Here, the nodule means a black precipitate (projection) generated when the target is being sputtered except for a very small portion of the deepest erosion portion in the erosion portion of the target surface. Nodules cause abnormal discharge, and abnormal discharge is suppressed by reducing the nodules. Therefore, an oxide target in which nodules are not generated is preferable.

JP-A-8-245220 JP 2007-73312 A International Publication No. 09/088453 Pamphlet JP 2009-10348 A

  An object of the present invention is to provide a sputtering target capable of suppressing nodules generated during sputtering film formation and obtaining an oxide semiconductor film stably and with good reproducibility.

In the metal oxide sputtering target in which Cu and Ga are added to In, the inventors prepared a thin film using a sputtering method and examined the occurrence of nodules. As a result, the formation of a compound of In ₂ Ga ₂ CuO ₇ having a hexagonal crystal structure and / or InGaCuO ₄ having a rhombohedral crystal structure suppresses precipitation of a Cu ₂ In ₂ O ₅ phase that is a high resistance phase. Therefore, it was found that generation of nodules is suppressed, and the present invention has been completed.

According to the present invention, the following sputtering target and the like are provided.
1. The sputtering target which consists of a metal oxide sintered compact containing In element, Cu element, and Ga element by the atomic ratio of following (1) and (2).
Cu / (Cu + In + Ga) = 0.001 to 0.09 (1)
Ga / (Cu + In + Ga) = 0.001 to 0.90 (2)
2. _2. The sputtering target according to 1, wherein the metal oxide sintered body contains a compound having a bixbyite structure represented by In ₂ O ₃ .
3. 3. The sputtering according to 2, wherein the metal oxide sintered body further includes a compound having a hexagonal crystal structure represented by In ₂ Ga ₂ CuO ₇ and / or a compound having a rhombohedral crystal structure represented by InGaCuO _4. target.
4). The sputtering target according to any one of 1 to 3, substantially consisting of an oxide of a Cu element, an In element, and a Ga element.
5. Formula represented by _(3), the Cu 2 _{an In} 2 _{O 5} phase (0 1 2) the area ratio of the X-ray diffraction peaks of 1 to 4 comprising a metal oxide sintered body is not more than 11% of any A sputtering target according to claim 1.
I ₁ / (I ₁ + I ₂ + I ₃ + I ₄ ) × 100 (%) (3)
I ₁ : (0 1 2) peak area of Cu ₂ In ₂ O ₅ phase showing monoclinic structure I ₂ : (2 2 2) peak area of In ₂ O ₃ phase showing bixbite structure I ₃ : diamond 5. (1 0 1) peak area I _{4 of} InGaCuO ₄ phase exhibiting a tetrahedral structure: (1 0 5) peak area of In ₂ Ga ₂ CuO ₇ phase exhibiting a hexagonal structure The metal oxide sintered body consists essentially of _In 2 _{O 3} showing the bixbyite structure, or _In 2 _Ga 2 CuO ₇ shows the _In 2 _{O 3} and hexagonal structure showing a bixbyite structure and / or sputtering target according to any one of 1 to 5 consisting essentially of InGaCuO ₄ showing the rhombohedral structure.
The oxide semiconductor thin film obtained by forming by sputtering method using the sputtering target in any one of 7.1-6.
A thin film transistor in which the oxide semiconductor thin film according to 8.7 is a channel layer.
A display device comprising the thin film transistor according to 9.8.

ADVANTAGE OF THE INVENTION According to this invention, generation | occurrence | production of the nodule at the time of forming an oxide thin film by sputtering method can be suppressed, and the target which can perform sputtering stably can be provided.
Further, by forming a film using a target in which Cu and Ga are added to In, the carrier concentration of the oxide semiconductor thin film can be easily adjusted.

3 is a diagram showing a chart obtained by X-ray diffraction in Example 1. FIG. 6 is a diagram showing a chart obtained by X-ray diffraction of Example 2. FIG. 6 is a diagram showing a chart obtained by X-ray diffraction in Example 3. FIG. 6 is a view showing a chart obtained by X-ray diffraction in Example 4. FIG. 6 is a diagram showing a chart obtained by X-ray diffraction in Example 5. FIG. 6 is a diagram showing a chart obtained by X-ray diffraction in Example 6. FIG. 6 is a diagram showing a chart obtained by X-ray diffraction in Example 7. FIG. 10 is a diagram showing a chart obtained by X-ray diffraction in Example 8. FIG. 10 is a diagram showing a chart obtained by X-ray diffraction in Example 9. FIG. 10 is a view showing a chart obtained by X-ray diffraction in Example 10. FIG. 10 is a view showing a chart obtained by X-ray diffraction in Example 11. FIG. It is a figure which shows the chart obtained by the X-ray diffraction of the comparative example 1.

The sputtering target of the present invention comprises a metal oxide sintered body containing In element, Cu element and Ga element. In element, Cu element and Ga element in the metal oxide sintered body have the following atomic ratio (1): And (2) is satisfied.
Cu / (Cu + In + Ga) = 0.001 to 0.09 (1)
Ga / (Cu + In + Ga) = 0.001 to 0.90 (2)

In a sputtering target obtained by adding a Cu element to In ₂ O ₃ , a Cu ₂ In ₂ O ₅ phase having a monoclinic structure may be precipitated. If a high resistance phase such as Cu ₂ In ₂ O ₅ is contained in the In ₂ O ₃ crystal in a large amount, nodules are generated during sputtering and abnormal discharge is likely to occur. The reason is estimated as follows.
Abnormal discharge occurs due to uneven targets and locally different portions of specific resistance, and the impedance of the discharge system including the target fluctuates during sputtering. The portion where the specific resistance is locally different is a high resistance phase such as a Cu ₂ In ₂ O ₅ phase. Therefore, reducing the size and number density of this portion is effective in suppressing abnormal discharge.
The crystal structure can be confirmed by X-ray diffraction.

When the atomic ratio Cu / (Cu + In + Ga) exceeds 0.09, the atomic ratio Cu / (Cu + In + Ga) in the oxide semiconductor thin film obtained by forming the target of the present invention exceeds 0.09, and the carrier concentration is There is a possibility that it will not operate as a TFT because it is 10 ¹³ cm ⁻³ or less. On the other hand, when the atomic ratio Cu / (Cu + In + Ga) is less than 0.001, the TFT element including the oxide semiconductor thin film obtained by forming the target of the present invention has a thin film carrier concentration of 10 ¹⁸ cm ^−3. There is a possibility that the order will be higher than the order, and with the occurrence of leakage current, the normally-on and on-off ratio may become small, and good transistor performance may not be exhibited.

  From the above viewpoint, the atomic ratio Cu / (Cu + In + Ga) is preferably 0.003 to 0.08, and more preferably 0.005 to 0.06.

When the atomic ratio (Ga / (Cu + In + Ga)) is less than 0.001, formation of In ₂ Ga ₂ CuO ₇ which is a compound having a hexagonal crystal structure and InGaCuO ₄ which is a compound having a rhombohedral crystal structure is inhibited. There is a fear. On the other hand, if the atomic ratio (Ga / (Cu + In + Ga)) exceeds 0.90, the resulting thin film has a carrier concentration of 10 ¹³ cm ⁻³ or less and may not operate as a TFT.
From the above viewpoint, the atomic ratio Ga / (Cu + In + Ga) is preferably 0.01 to 0.60, and more preferably 0.03 to 0.40.

The atomic ratio of each element contained in the oxide sintered body can be determined by analyzing the contained elements using an inductively coupled plasma emission spectrometer (ICP-AES).
For example, in the case of analysis using ICP-AES, 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 are generated. Move from the ground state to a high energy 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). Thus, the atomic ratio of each element can be calculated | required by specifying the element contained by qualitative analysis and calculating | requiring content by quantitative analysis.

The metal oxide sintered body constituting the target of the present invention preferably contains a compound having a bixbyite structure represented by In ₂ O ₃ .
The metal oxide sintered body is preferably a compound having a bixbyite structure represented by In ₂ O ₃ , a compound having a hexagonal structure represented by In ₂ Ga ₂ CuO ₇ , and / or InGaCuO. ₄ including a compound having a rhombohedral crystal structure represented by ₄ ;

The metal oxide sintered body is preferably substantially composed of oxides of In element, Cu element and Ga element.
In the present invention, “substantially” means that the effect as a target results from the composition of the metal element constituting the metal oxide sintered body, or 95 weight of the metal oxide constituting the metal oxide sintered body. % To 100% by weight (preferably 98% to 100% by weight) means the oxide of the metal element.
The metal oxide sintered body is a sintered body obtained by adding a Cu metal element and a Ga metal element to In ₂ O _3. However, if the metal oxide sintered body is mainly composed of the above elements, it contains other inevitable impurities. You may go out.

The metal oxide sintered body has an area ratio of the X-ray diffraction peak of (0 1 2) of the Cu ₂ In ₂ O ₅ phase showing a monoclinic structure defined by the following formula (3) of 11% or less. It is preferable. The area ratio is more preferably 0.5 to 9%, particularly preferably 1 to 7%. As described above, since the Cu ₂ In ₂ O ₅ phase is a high resistance phase, when this increases, that is, when the area ratio of the X-ray diffraction peak of the Cu ₂ In ₂ O ₅ phase exceeds 11%, the target surface Nodules may occur and abnormal discharge may occur.
I ₁ / (I ₁ + I ₂ + I ₃ + I ₄ ) × 100 (%) (3)
I ₁ : (0 1 2) peak area of Cu ₂ In ₂ O ₅ phase showing monoclinic structure I ₂ : (2 2 2) peak area of In ₂ O ₃ phase showing bixbite structure I ₃ : diamond (1 0 1) peak area I _{4 of the} InGaCuO ₄ phase exhibiting a plane crystal structure I ₄ : (1 0 5) peak area of the In ₂ Ga ₂ CuO ₇ phase exhibiting a hexagonal crystal structure

By using a JCPDS (Joint Committee of Powder Diffraction Standards) card, a Cu ₂ In ₂ O ₅ phase showing a monoclinic structure, an In ₂ O ₃ phase showing a bixbite structure, and an InGaCuO ₄ phase showing a rhombohedral structure And an In ₂ Ga ₂ CuO ₇ phase exhibiting a hexagonal crystal structure can be confirmed.

The Cu ₂ In ₂ O ₅ phase exhibiting a monoclinic structure is a JCPDS card no. 30-0479, the peak representing the (0 1 2) plane is the maximum peak of the phase.
In ₂ O ₃ phase having a bixbyite structure is JCPDS card no. The peak representing the (2 2 2) plane is the maximum peak of the phase.
The InGaCuO ₄ phase having a rhombohedral crystal structure is a JCPDS card no. It can be confirmed at 38-0839, and the peak representing the (1 0 1) plane is the maximum peak of the phase.
The In ₂ Ga ₂ CuO ₇ phase having a hexagonal crystal structure is JCPDS card no. 38-0840, and the peak representing the (1 0 5) plane is the maximum peak of the phase.

Metal oxide sintered body is preferably and _In 2 _Ga 2 CuO ₇ shows the _In 2 _{O 3} and the hexagonal structure showing substantially consisting or bixbyite structure from _In 2 _{O 3} showing the bixbyite structure / Or substantially composed of InGaCuO ₄ exhibiting a rhombohedral crystal structure.
Incidentally, when the metal oxide sintered body consists of _In 2 _{O 3} showing the bixbyite structure substantially, Cu element and Ga element is dissolved in the _In 2 _{O 3.}

The crystal structure of the target can be analyzed by XRD (X-ray diffraction) measurement. When X-rays enter a crystal in which atoms are regularly arranged, a diffraction phenomenon occurs in which strong X-rays are observed in a specific direction. If the optical path difference of the X-rays scattered at each position is an integral multiple of the wavelength of the X-rays, the wave phase matches and the wave amplitude increases, which explains the diffraction phenomenon.
Since each substance forms crystals having specific regularity, the type of compound can be examined by X-ray diffraction. It is also possible to evaluate the size of the crystal (order of the crystal), the distribution of crystal orientations in the material (crystal orientation), and the residual stress applied to the crystal.

The density of the metal oxide sintered body is preferably 6.0 g / cm ³ or more, more preferably 6.2 g / cm ³ or more.
When the density is less than 6.0 g / cm ^3, the surface of the sputtering target formed from the oxide sintered body may be blackened to induce abnormal discharge and reduce the sputtering rate. In the sputtering target, it is desirable that the oxide sintered body has a higher density.
The density of the metal oxide sintered body is particularly preferably 6.0 g / cm ³ or more and 7.1 g / cm ³ or less.

The maximum grain size of the crystals in the sintered body is desirably 5 μm or less. If the crystal grain size grows over 5 μm, it may cause nodules.
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 sintered body. In a target made of a sintered body 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 crystals is the center point (one place) of the circle and the midpoint between the center point on the two center lines orthogonal to the center point and the peripheral part ( 4 points) and when the shape of the sputtering target is a square, the sum of the center point (1 place) and the midpoint (4 places) between the center point and the corner on the diagonal of the square. The maximum diameter of the largest particles observed in a frame of 100 μm square at five locations is measured, and the average value of the particle diameters of the largest particles present in each of these five frames.

The sputtering target of this invention can be manufactured as follows.
An aqueous solvent is blended with the raw material powder obtained by mixing CuO powder, In ₂ O ₃ powder and Ga ₂ O ₃ powder, and the resulting slurry is mixed for 12 hours or more, then solid-liquid separation, drying and granulating, The granulated product is placed in a mold and molded. Thereafter, the obtained molded product is fired at 900 to 1600 ° C. for 5 to 50 hours in an oxygen atmosphere to obtain an oxide sintered body.

By adding a Cu metal element and a Ga metal element to In ₂ O ₃ , a compound of In ₂ Ga ₂ CuO ₇ having a hexagonal crystal structure or InGaCuO ₄ having a rhombohedral crystal structure is preferably formed. As a result, precipitation of the Cu ₂ In ₂ O ₅ phase, which is a high resistance phase, can be suppressed, and nodules generated during sputtering can be suppressed.
In the present _invention, by In ₂ Ga ₂ CuO _7-phase and InGaCuO ₄ phase is stably formed, would be able to suppress the formation of _Cu 2 _In 2 _{O 5} phase is monoclinic structure.

The average particle size of the raw material powder is desirably 1.2 μm or less. Preferably, In ₂ O ₃ powder having an average particle size of 1.2 μm or less, CuO powder having an average particle size of 1.2 μm or less, and Ga ₂ O ₃ powder having an average particle size of 1.2 μm or less are used as raw material powders, The ratio is such that the value of the atomic ratio indicated by Cu / (In + Ga + Cu) is 0.001 to 0.09 and the atomic ratio indicated by Ga / (In + Ga + Cu) is 0.001 to 0.90.
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 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, precipitation of Cu ₂ In ₂ O ₅ phase or the like may become remarkable in the finally obtained oxide 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 adjusted so that the particle size distribution in the slurry is all uniform at 1 μm or less.

  Further, when mixing, an arbitrary amount of binder may be added and mixed 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 the In ₂ O ₃ powder, the CuO powder, and the Ga ₂ O ₃ powder may be separated and a uniform granulated powder may not be obtained.

The granulated powder is molded at a pressure of 1.2 ton / cm ² or more by, for example, a die press or a cold isostatic press (CIP) to obtain a molded body.

  As a sintering method for obtaining the sputtering target of the present invention, a pressure sintering method such as hot pressing, oxygen pressurization, hot isostatic pressing, etc. can be employed in addition to the atmospheric pressure sintering method. However, it is preferable to employ a normal pressure sintering method from the viewpoints of reducing manufacturing costs, possibility of mass production, and easy production of large sintered bodies.

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 an atmosphere having an oxygen concentration of, for example, 10 to 100 vol%. By introducing an oxygen gas atmosphere in the temperature raising process, the oxide sintered body density can be further increased.

The firing temperature is, for example, 900 to 1600 ° C. The firing time is, for example, 5 to 50 hours. When the firing temperature is less than 900 ° C. or the firing time is less than 5 hours, a Cu ₂ In ₂ O ₅ phase or the like may be precipitated, and abnormal discharge may occur. On the other hand, when the firing temperature exceeds 1600 ° C. or the firing time exceeds 50 hours, the average crystal grain size increases due to remarkable crystal grain growth and the generation of coarse pores, resulting in a decrease in the strength of the sintered body or abnormalities. Cause discharge.
The firing temperature is preferably 1000 to 1600 ° C, more preferably 1000 to 1450 ° C, and particularly preferably 1000 to 1350 ° C. The firing time is preferably 8 to 50 hours, more preferably 10 to 40 hours, and particularly preferably 10 to 30 hours.

  Furthermore, it is preferable that the temperature increase rate in baking shall be 1-15 degrees C / min in the temperature range of 500-1500 degreeC. The temperature range of 500 to 1500 ° C. is the range in which sintering proceeds most. When the rate of temperature increase in this temperature range is slower than 1 ° C./min, crystal grain growth becomes remarkable and high density can be achieved. Can not. On the other hand, when the rate of temperature rise is higher than 15 ° C./min, the soaking property in the sintering furnace is lowered, and as a result, the shrinkage amount during the sintering is distributed, and the sintered body may be cracked.

The reduction step is for making the bulk resistance of the sintered body obtained in the firing step uniform over the entire target, and is a step provided as necessary.
Examples of the reduction method that can be applied in this step 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 reduction treatment temperature is usually 100 to 800 ° C, preferably 200 to 800 ° C. The reduction treatment time is usually 0.01 to 10 hours, preferably 0.05 to 5 hours.

By controlling the various conditions in the production process of the sintered body as described above, an oxide sintered body having a density of 6.0 g / cm ³ or more and an average crystal grain size of 10 μm or less can be obtained. .

It can be set as a sputtering target by processing the manufactured oxide sintered compact. Specifically, a sputtering target can be obtained by cutting the oxide sintered body of the present invention into a shape suitable for mounting on a sputtering apparatus.
In order to target the oxide sintered body, the sintered body is ground with, for example, a surface grinder to obtain a material having a surface roughness Ra of 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 this mirror finishing (polishing), a known polishing technique 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 by: 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. If a diamond grindstone smaller than 200 or larger than 10,000 is used, the target material may be easily broken.

  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 larger than 0.5 μm or the polished surface has directivity, abnormal discharge may occur or particles may be generated.

  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 causing multiple oscillations of 12 types of frequencies at intervals of 25 KHz between frequencies of 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.

  The sputtering target of the present invention made of an oxide sintered body 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 make substantially one target.

The oxide semiconductor thin film of the present invention can be produced by the vapor deposition method, the sputtering method, the ion plating method, the pulse laser vapor deposition method or the like using the above oxide sintered body.
Since the oxide sintered body has high conductivity, a DC sputtering method having a high film formation rate can be applied. Further, in addition to the DC sputtering method, it can be applied to an RF sputtering method, an AC sputtering method, and a pulsed DC sputtering method, and sputtering without abnormal discharge is possible.

As a sputtering gas, a mixed gas of argon and an oxidizing gas can be used. Examples of the oxidizing gas include O ₂ , CO ₂ , O ₃ , H ₂ O, and the like.
When oxygen is used as the oxidizing gas, the oxygen partial pressure during sputtering film formation is preferably 5% to 40%. A thin film manufactured under a condition where the oxygen partial pressure is less than 5% has conductivity and may be difficult to use as an oxide semiconductor. Preferably, the oxygen partial pressure is 10 or more and 40% or less.

The substrate temperature during film formation or the annealing temperature after film formation is, for example, 500 ° C. or less. The substrate temperature during film formation is preferably 10 ° C. or higher and 400 ° C. or lower, more preferably 20 ° C. or higher and 350 ° C. or lower, and particularly preferably 80 ° C. or higher and 300 ° C. or lower.
The annealing temperature after film formation is preferably 100 ° C. or higher and 500 ° C. or lower, more preferably 150 ° C. or higher and 400 ° C. or lower, and particularly preferably 200 ° C. or higher and 350 ° C. or lower.

  Further, the heating atmosphere is not particularly limited, but an air atmosphere and an oxygen circulation atmosphere are preferable from the viewpoint of carrier controllability.

  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.

Ga doping has the effect of reducing the lattice constant of indium oxide, and it is expected that the 5s orbital overlap between the indiums in the crystal will increase and the mobility will be improved. Further, Cu doping has an effect of reducing the carrier concentration of the thin film, and the carrier concentration of the semiconductor thin film can be adjusted to 10 ¹⁸ cm ⁻³ or less.

The atomic ratio of the oxide semiconductor thin film of the present invention is usually the same as that of the above metal oxide sintered body.
If the atomic ratio Cu / (In + Ga + Cu) of the oxide semiconductor thin film is less than 0.001, the carrier concentration may exceed the order of 10 ¹⁸ cm ⁻³ , and leakage current may be generated when a thin film transistor is formed. When the transistor is normally on or the on-off ratio is decreased, good transistor performance may not be exhibited.

In a thin film formed using a sputtering target having an atomic ratio Cu / (In + Ga + Cu) of more than 0.09, the carrier concentration may be on the order of 10 ¹³ cm ⁻³ or less, and the TFT characteristics may not be exhibited.

  The oxide thin film of the present invention can be used for a thin film transistor. In particular, it can be used as a channel layer.

  The thin film transistor of the present invention may be a channel etch type. Since the thin film of the present invention is durable, in the manufacture of a thin film transistor using the thin film of the present invention, a photolithography process for forming a source / drain electrode and a channel portion by etching a metal thin film such as Al becomes possible. From the viewpoint of durability of the thin film, it is desirable that the thin film is crystallized.

  The thin film transistor of the present invention may be an etch stopper type. In the thin film of the present invention, the etch stopper can protect the channel portion made of the semiconductor layer, and oxygen can be taken into the semiconductor layer in a large amount from the outside through the etch stopper layer during film formation. Need not be supplied. In addition, it is possible to produce an amorphous film immediately after film formation, and etching a metal thin film such as Al to form source / drain electrodes and a channel portion, and at the same time, the semiconductor layer can be etched to shorten the photolithography process. Is also possible.

Examples 1-11
[Manufacture of target]
An In ₂ O ₃ powder with an average particle size of 0.98 μm, a CuO powder with an average particle size of 0.96 μm, and a Ga ₂ O ₃ powder with an average particle size of 0.96 μm were weighed so as to have the target composition ratio shown in Table 1. After uniformly pulverizing and mixing, a molding binder was added and granulated. Next, this raw material mixed powder was uniformly filled into a mold, and pressure-molded with a cold press machine at a press pressure of 140 MPa. The molded body thus obtained was fired in a sintering furnace at the firing temperature and firing time shown in Table 1 to produce a sintered body.
The firing atmosphere was an oxygen atmosphere during the temperature increase, and the other was in the air (atmosphere). The firing was performed at a temperature increase rate of 1 ° C./min and a temperature decrease rate of 15 ° C./min.
The average particle size of the raw material oxide powder used was measured with a laser diffraction particle size distribution analyzer SALD-300V (manufactured by Shimadzu Corp.), and the median particle size D50 was used.

The crystal structure of the obtained sintered body was examined using an X-ray diffraction measurement apparatus (Rigaku's Ultimate-III). The X-ray charts of the sintered bodies of Examples 1 to 11 are shown in FIGS.
As a result of analyzing the chart, in the sintered bodies of Examples 1 to 11, a Bixbite structure of In ₂ O ₃ , a hexagonal crystal structure of In ₂ Ga ₂ CuO ₇ , and a rhombohedral crystal structure of InGaCuO ₄ were observed. The crystal structure can be confirmed with a JCPDS card. The In ₂ O ₃ big byte structure is JCPDS card no. 06-0416, the hexagonal structure of In ₂ Ga ₂ CuO ₇ is JCPDS card no. 38-0840, the rhombohedral structure of InGaCuO ₄ is JCPDS card no. 38-0839.
In Example 11, since the Ga and Cu in a solid solution to the In site of _In 2 _{O 3,} only bixbyite structure of _In 2 _{O 3} was observed.
As a result of X-ray diffraction, the monoclinic structure of Cu ₂ In ₂ O ₅ was not observed in the sintered bodies obtained in Examples 1 to 11.

The measurement conditions for the X-ray diffraction measurement (XRD) are as follows.
Device: Rigaku Ultima-III
X-ray: Cu-Kα ray (wavelength 1.5406mm, monochromatized with graphite monochromator)
2θ-θ reflection method, continuous scan (1.0 ° / min)
Sampling interval: 0.02 °
Slit DS, SS: 2/3 °, RS: 0.6 mm

  The density of the obtained sintered body was calculated from the weight and outer dimensions of the sintered body cut into a certain size. The results are shown in Table 1.

  About the obtained sintered compact, dispersion | distribution of Cu element was investigated by EPMA (electron-beam microanalyzer) measurement. As a result, an aggregate of Cu atoms of 1 μm or more was not observed, and it was found that the sintered bodies of Examples 1 to 11 were extremely excellent in the dispersibility and uniformity of the Cu element.

The measurement conditions for EPMA are as follows.
Device name: JXA-8200 (manufactured by JEOL Ltd.)
Acceleration voltage: 15 kV
Irradiation current: 50 nA
Irradiation time (per point): 50mS

  The surfaces of the oxide sintered bodies obtained in Examples 1 to 11 were ground with a surface grinder, the side edges were cut with a diamond cutter, and bonded to a backing plate to obtain 4 inch φ sputtering targets.

The obtained sputtering target is mounted on a DC sputtering apparatus, and argon is used as a sputtering gas, sputtering pressure is 0.4 Pa, substrate temperature is room temperature, DC output is 400 W, 10 kWh is continuously sputtered, and voltage fluctuation during sputtering. Was stored 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 performed 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.

In addition, using the sputtering targets of Examples 1 to 11, a mixed gas in which 3% hydrogen gas was added to argon gas was used as the atmosphere, and sputtering was performed continuously for 30 hours to check whether nodules were generated. did. As a result, no nodules were observed on the surfaces of the sputtering targets of Examples 1 to 11. The reason why hydrogen gas is added to the atmospheric gas is to promote the generation of nodules.
The sputtering conditions were a sputtering pressure of 0.4 Pa, a DC output of 100 W, and a substrate temperature: room temperature.
For the nodules, a change in the target surface after sputtering was observed 50 times with a stereomicroscope, and a method of measuring the number average of nodules of 20 μm or more generated in a visual field of 3 mm ² was adopted. Table 1 shows the number of nodules generated.

Example 12
[Formation of oxide semiconductor thin film and manufacture of thin film transistor]
Using the target (Cu / (In + Ga + Cu) = 0.03, Ga / (In + Ga + Cu) = 0.03) obtained in Example 1 on a glass substrate and a silicon substrate with a thermal oxide film (SiO ₂ ) having a thickness of 100 nm, respectively. A thin film having a thickness of 50 nm was formed by a DC magnetron sputtering method.
The sputtering was performed at room temperature at a sputtering output of 100 W while evacuating until the back pressure reached 5 × 10 ⁻⁴ Pa, adjusting the pressure to 0.4 Pa while flowing argon at 9 sccm and oxygen at 1 sccm.

The glass substrate on which this thin film was formed was put into a heating furnace heated to 300 ° C. in the air and treated for 1 hour. When the carrier concentration and mobility of the thin film after the annealing treatment were evaluated by Hall effect measurement, the carrier concentration was 3.21 × 10 ¹⁴ cm ⁻³ and the hole mobility was 13.2 cm ² / Vs.

The Hall measuring device and the measurement conditions are as follows.
-Hall measuring device manufactured by Toyo Technica: Resi Test 8310
・ Measurement conditions Measurement temperature: Room temperature (25 ℃)
Measurement magnetic field: 0.45T
Measurement current: 10 ⁻¹² to 10 ⁻⁴ A
Measurement mode: AC magnetic field hall measurement

  The thin film formed on the silicon substrate was formed by placing a metal mask on the conductive silicon substrate, forming a channel portion of L: 200 μm, W: 1000 μm, and depositing gold as a source / drain electrode. The element was placed in a heating furnace heated to 300 ° C., and a thin film transistor was manufactured by performing treatment for 1 hour.

  As a result, the manufactured thin film transistor was a thin film transistor having normally-off characteristics, and the output characteristics showed clear pinch-off. The measurement was performed using a semiconductor parameter analyzer (Keutley 4200) at room temperature, in the air, and in a light-shielding environment.

Example 13
Using the target (Cu / (In + Ga + Cu) = 0.01, Ga / (In + Ga + Cu) = 0.03) obtained in Example 11 on a glass substrate and a silicon substrate with a thermal oxide film (SiO ₂ ) having a thickness of 100 nm, respectively. A thin film having a thickness of 50 nm was formed by a DC magnetron sputtering method.
The above sputtering is performed at room temperature with a sputtering output of 100 W while evacuating until the back pressure becomes 5 × 10 ⁻⁴ Pa, adjusting the pressure to 0.4 Pa while flowing argon at 8.5 sccm and oxygen at 1.5 sccm. It was.

The glass substrate on which this thin film was formed was put into a heating furnace heated to 300 ° C. in the air and treated for 1 hour. When the carrier concentration and mobility of the thin film after the annealing treatment were evaluated by Hall effect measurement, the carrier concentration was 5.34 × 10 ¹⁶ cm ⁻³ and the hole mobility was 18.1 cm ² / Vs.

  The thin film formed on the silicon substrate was formed by placing a metal mask on the conductive silicon substrate, forming a channel portion of L: 200 μm, W: 1000 μm, and depositing gold as a source / drain electrode. The element was placed in a heating furnace heated to 300 ° C., and a thin film transistor was manufactured by performing treatment for 1 hour.

  As a result, the manufactured thin film transistor was a thin film transistor having normally-off characteristics, and the output characteristics showed clear pinch-off. The measurement was performed using a semiconductor parameter analyzer (Keutley 4200) at room temperature, in the air, and in a light-shielding environment.

Comparative Examples 1-3
In ₂ O ₃ powder with an average particle size of 0.98 μm, CuO powder with an average particle size of 0.96 μm, and ZnO powder with an average particle size of 0.98 μm were weighed so as to have the target composition shown in Table 2, and shown in Table 2 A target was produced and evaluated in the same manner as in Examples 1 to 11 except that firing was performed at the firing temperature and firing time. The results are shown in Table 2.
As can be seen from Table 2, abnormal discharge occurred in the targets of Comparative Examples 1 to 3, and nodules were observed on the target surface.

A chart obtained by X-ray diffraction of the target of Comparative Example 1 is shown in FIG.
In the target of Comparative Example 1, in the X-ray diffraction chart, a bixbite structure of In ₂ O ₃ , a hexagonal structure of Zn ₅ In ₂ O _8, a hexagonal structure of ZnO, and a monoclinic structure of Cu ₂ In ₂ O ₅ Observed.

The crystal structure can be confirmed with a JCPDS card. The In ₂ O ₃ big byte structure is JCPDS card no. The hexagonal structure of 06-0416, Zn ₅ In ₂ O ₈ is JCPDS card no. 20-1440, the hexagonal structure of ZnO is JCPDS card no. The monoclinic structure of 75-0576, Cu ₂ In ₂ O ₅ is JCPDS card no. 30-0479. From the above, when Zn is added, a monoclinic structure of Cu ₂ In ₂ O ₅ is formed, which may cause nodules. Also in the target of Comparative Example 2, formation of Cu ₂ In ₂ O ₅ was observed as in Comparative Example 1.

In Comparative Example 3, bixbyite structure of _In 2 _{O 3} from the results of X-ray diffraction _measurement, monoclinic structure of Cu 2 _In 2 _{O 5} was observed. Formation of a monoclinic structure of Cu ₂ In ₂ O ₅ causes nodules.
Table 2 shows the results of determining the peak area ratio of (0 1 2) X-ray diffraction of the Cu ₂ In ₂ O ₅ phase having a monoclinic structure defined by the following formula (4).
I ₁ / (I ₁ + I ₂ + I ₅ + I ₆ ) × 100 (4)
I ₁ : (0 1 2) peak area of Cu ₂ In ₂ O ₅ phase having a monoclinic structure I ₂ : (2 2 2) peak area of In ₂ O ₃ phase having a bixbite structure I ₅ : Hexagon (1 0 11) peak area I _{6 of} Zn ₅ In ₂ O ₈ phase having a crystal structure: (1 0 1) peak area of ZnO phase having a hexagonal structure

From the above and Table 2, it was found that in Comparative Examples 1 to 3, a monoclinic structure of Cu ₂ In ₂ O ₅ was formed.
The Cu ₂ In ₂ O ₅ phase having a monoclinic structure is a JCPDS card no. 30-0479, the peak representing the (0 1 2) plane is the maximum peak of the phase. In ₂ O ₃ phase having a bixbyite structure is JCPDS card no. The peak representing the (2 2 2) plane is the maximum peak of the phase. The Zn ₅ In ₂ O ₈ phase having a hexagonal crystal structure is a JCPDS card no. 20-1440, and the peak representing the (1 0 11) plane is the maximum peak of the phase. The ZnO phase having a hexagonal crystal structure is a JCPDS card no. 75-0576, and the peak representing the (1 0 1) plane is the maximum peak of the phase.

Comparative Example 4
The same conditions as in Example 12 except that the target (Cu / all metal elements = 0.13) obtained in Comparative Example 1 was used on a glass substrate and a silicon substrate with a thermal oxide film (SiO ₂ ) having a thickness of 100 nm. A thin film was prepared.

The glass substrate on which this thin film was formed was put into a heating furnace heated to 300 ° C. in the air and treated for 1 hour. When the carrier concentration and mobility of the thin film after the annealing treatment were evaluated by Hall effect measurement, the carrier concentration was −10 ¹³ cm ⁻³ or less and below the measurement limit.

The thin film formed on the silicon substrate was formed by placing a metal mask on the conductive silicon substrate, forming a channel portion of L: 200 μm, W: 1000 μm, and depositing gold as a source / drain electrode. The element was placed in a heating furnace heated to 300 ° C., and a thin film transistor was manufactured by performing treatment for 1 hour. As a result, the manufactured thin film transistor did not exhibit TFT characteristics because the carrier concentration was as low as 10 ¹³ cm ⁻³ or less.

Comparative Example 5
The same conditions as in Example 12 except that the target (Cu / all metal elements = 0.147) obtained in Comparative Example 3 was used on a glass substrate and a silicon substrate with a thermal oxide film (SiO ₂ ) having a thickness of 100 nm. A thin film was prepared.

The glass substrate on which this thin film was formed was put into a heating furnace heated to 300 ° C. in the air and treated for 1 hour. When the carrier concentration and mobility of the thin film after the annealing treatment were evaluated by Hall effect measurement, the carrier concentration was −10 ¹³ cm ⁻³ or less and below the measurement limit.

The thin film formed on the silicon substrate was formed by placing a metal mask on the conductive silicon substrate, forming a channel portion of L: 200 μm, W: 1000 μm, and depositing gold as a source / drain electrode. The element was placed in a heating furnace heated to 300 ° C., and a thin film transistor was manufactured by performing treatment for 1 hour. As a result, the manufactured thin film transistor did not exhibit TFT characteristics because the carrier concentration was as low as 10 ¹³ cm ⁻³ or less.

Comparative Example 6
Indium oxide powder and gallium oxide powder were weighed so that the atomic ratio Ga / (In + Ga) = 0.01, and a sintered body was manufactured in the same manner as in Example 1 except that copper oxide was not used. Manufactured.
Example 12 A thin film having a thickness of 50 nm was formed by a DC magnetron sputtering method using a target (Ga / (In + Ga) = 0.01) produced on a glass substrate and a silicon substrate with a thermal oxide film (SiO ₂ ) having a thickness of 100 nm. Films were formed under the same conditions as in.

The glass substrate on which this thin film was formed was put into a heating furnace heated to 300 ° C. in the air and treated for 1 hour. When the carrier concentration and mobility of the annealed thin film were evaluated by Hall effect measurement, the carrier concentration was 4.23 × 10 ¹⁸ cm ⁻³ and the hole mobility was 11.2 cm ² / Vs. The annealed thin film was a thin film with a carrier concentration of 10 ¹⁸ cm ⁻³ or more and many oxygen defects, and the carrier concentration was increased as compared with the thin films of Examples 12 and 13.

The thin film formed on the silicon substrate was formed by placing a metal mask on the conductive silicon substrate, forming a channel portion of L: 200 μm, W: 1000 μm, and depositing gold as a source / drain electrode. The element was placed in a heating furnace heated to 300 ° C., and a thin film transistor was manufactured by performing treatment for 1 hour. As a result, the manufactured thin film transistor exhibited normally-on characteristics because the carrier concentration was 10 ¹⁸ cm ⁻³ or more.

  The thin film transistor formed using the sputtering target of the present invention can be used as a unit electronic element, a high frequency signal amplifying element, a liquid crystal driving element or the like of a semiconductor memory integrated circuit.

Claims (9)

The sputtering target which consists of a metal oxide sintered compact containing In element, Cu element, and Ga element by the atomic ratio of following (1) and (2).
Cu / (Cu + In + Ga) = 0.001 to 0.09 (1)
Ga / (Cu + In + Ga) = 0.001 to 0.90 (2) The sputtering target according to claim 1, wherein the metal oxide sintered body includes a compound having a bixbyite structure represented by In ₂ O ₃ . The metal oxide sintered _body, an In ₂ Ga 2 compounds show a hexagonal structure represented by CuO _7, and / or claim 2, further comprising a compound showing a rhombohedral structure represented by InGaCuO ₄ Sputtering target.   The sputtering target according to any one of claims 1 to 3, substantially comprising an oxide of a Cu element, an In element, and a Ga element. It consists of a metal oxide sintered body in which the area ratio of the X-ray diffraction peak of (0 1 2) of the Cu ₂ In ₂ O ₅ phase represented by the following formula (3) is 11% or less. The sputtering target according to any one of the above.
I ₁ / (I ₁ + I ₂ + I ₃ + I ₄ ) × 100 (%) (3)
I ₁ : (0 1 2) peak area of Cu ₂ In ₂ O ₅ phase showing monoclinic structure I ₂ : (2 2 2) peak area of In ₂ O ₃ phase showing bixbite structure I ₃ : diamond (1 0 1) peak area I _{4 of the} InGaCuO ₄ phase exhibiting a plane crystal structure I ₄ : (1 0 5) peak area of the In ₂ Ga ₂ CuO ₇ phase exhibiting a hexagonal crystal structure The metal oxide sintered body consists essentially of _In 2 _{O 3} showing the bixbyite structure, or _In 2 _Ga 2 CuO ₇ shows the _In 2 _{O 3} and hexagonal structure showing a bixbyite structure and / or sputtering target according to claim 1 consisting essentially of InGaCuO ₄ showing the rhombohedral structure.   The oxide semiconductor thin film obtained by forming by sputtering method using the sputtering target in any one of Claims 1-6.   A thin film transistor, wherein the oxide semiconductor thin film according to claim 7 is a channel layer.   A display device comprising the thin film transistor according to claim 8.

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