JP7576019B2 - IGZO sputtering target - Google Patents

Description

The present invention relates to an IGZO sputtering target.

Traditionally, α-Si (amorphous silicon) has been used for the TFTs (thin film transistors) on the backplane of FPDs (flat panel displays). However, α-Si does not provide sufficient electron mobility, and in recent years, research and development has been conducted on TFTs that use In-Ga-Zn-O oxide (IGZO), which has higher electron mobility than α-Si. Some next-generation high-performance flat panel displays using IGZO-TFTs have been put into practical use and are attracting attention.

Here, the IGZO film can be obtained by DC sputtering a sputtering target made from an IGZO sintered body, and sputtering targets capable of obtaining IGZO films of higher quality are being investigated (for example, Patent Document 1).

International Publication No. 2017/131111

The IGZO sintered body for the sputtering target can be manufactured by producing an oxide sintered body by sintering a molded body obtained by mixing and molding the desired metal oxides, and then cutting the molded body into the desired shape and dimensions. However, even if the oxide sintered body after sintering the molded body has highly uniform properties, the oxide sintered body after cutting into the desired shape and dimensions in the process of manufacturing the sputtering target may have reduced uniformity in at least one property selected from the number of microcracks in the structure, the number of voids in the sintered body structure, and surface roughness. In such cases, there was a concern that the amount of particles generated during sputtering using the sputtering target would increase, making it difficult to obtain a high-quality IGZO film.

Therefore, the present invention aims to provide an IGZO sputtering target that can improve the uniformity of at least one characteristic selected from the number of microcracks in the structure, the number of voids in the sintered body structure, and surface roughness.

As a result of intensive research to solve the above-mentioned problems of the conventional technology, the present inventors have found that in an oxide sintered body obtained by firing and cutting, differences in characteristics, particularly differences in the lightness L* of the surface of the sintered body, may occur depending on the position in the sintered body. The inventors have found that this is because at least one of the number of microcracks in the structure or the voids in the structure of the sintered body increases locally at the end of the oxide sintered body due to processing damage during cutting of the oxide sintered body after firing, or the surface roughness increases. Furthermore, as a result of the change at the end, it has been found that the lightness L* at the end is increased relative to the lightness L* at the center. In addition, it has been found that if the density of the oxide sintered body is reduced too much in order to reduce the amount of cracks present in the oxide sintered body, nodules that are generated on the oxide sintered body and lead to a deterioration in the quality of the IGZO film are more likely to occur, and this has led to the completion of the present invention.
That is, the present invention is as follows.

In one embodiment, the IGZO sputtering target of the present invention is a sputtering target having an oxide sintered body made of indium (In), gallium (Ga), zinc (Zn) and unavoidable impurities, and on the surface of the oxide sintered body, ΔL* obtained by subtracting the brightness Lc* at the center of the surface from the brightness Le* at a position 10 mm from the edge of the surface toward the center satisfies ΔL* < 3.0, and the relative density of the oxide sintered body is 97.0% or more.

According to one embodiment of the present invention, it is possible to provide an IGZO sputtering target that can improve the uniformity of at least one characteristic selected from the number of microcracks in the structure, the number of voids in the sintered compact structure, and the surface roughness.

The following describes in detail an embodiment of the present invention (hereinafter, "the present embodiment"); however, the present invention is not limited to the present embodiment.

The IGZO sputtering target of this embodiment (hereinafter also referred to as "sputtering target") is an IGZO sputtering target having an oxide sintered body consisting of indium (In), gallium (Ga), zinc (Zn) and unavoidable impurities. The sputtering target of this embodiment can be used to form a semiconductor film, specifically, it can be used to form TFTs (thin film transistors) for FPDs (flat panel displays) such as organic electroluminescence (EL) and flexible displays, transparent semiconductor films for semiconductor products, etc.

Here, the oxide sintered body of the sputtering target of this embodiment is composed of a composite oxide containing In ₂ O ₃ --Ga ₂ O ₃ --ZnO as a main component.
More specifically, for example, in a composition in which the target Ga content and the target Zn content are each 100 when the In content in the oxide sintered body is taken as 100, it is preferable that the atomic ratio of Ga is 100±30 and that of Zn is 100±30. The contents of In, Ga, and Zn in the oxide sintered body can be measured by a method such as fluorescent X-ray or ICP-AES.

In this embodiment, the oxide sintered body may further contain other additive elements in addition to indium (In), gallium (Ga), and zinc (Zn), and may contain at least one selected from the group consisting of Sn, Zr, Mg, Al, Si, Y, and Ti. The total amount of these other additive elements is preferably 50 to 1000 mass ppm, and more preferably 100 to 500 mass ppm. By setting the total amount of these other additive elements to 1000 mass ppm or less, a sintered body having a desired grain size and sintered body density can be obtained, and by setting the total amount to 50 mass ppm or more, the effect of adding the additive elements can be fully obtained. The additive elements here also include unavoidable impurities due to grinding media wear.
In this embodiment, when the oxide sintered body further contains other additive elements, it is preferable that the oxide sintered body contains at least tin (Sn), which can control the grain size and the resistance to microcracks in the structure. When the oxide sintered body contains at least tin, the content of tin is preferably 1000 mass ppm or less, more preferably 500 mass ppm or less.

In addition, inevitable impurities are generally those that are present in the raw materials of metal or metal oxide products or that are inevitably mixed in during the manufacturing process, such as media used when grinding raw powder. Although they are essentially unnecessary, they are tolerated because they are present in trace amounts and do not affect the properties of the metal or metal oxide product. In the sputtering target according to this embodiment, the total amount of inevitable impurities is generally 1000 ppm by mass or less, typically 500 ppm by mass or less, and more typically 200 ppm by mass or less.

In this embodiment, when the lightness at a position 10 mm from the end of the surface of the oxide sintered body of the sputtering target is Le*, the lightness at the center of the surface of the oxide sintered body is Lc*, and the lightness difference obtained by subtracting Lc* from the lightness Le* is ΔL*, the lightness difference ΔL* satisfies ΔL* < 3.0.
Here, the lightness (L*) belongs to one of the three elements of the color system defined in JIS Z 8729, and as the lightness increases, the color becomes brighter and closer to white. In other words, the greater the lightness of the surface of the oxide sintered body, the greater the diffuse reflection of visible light, indicating that at least one of microcracks in the sintered body structure and voids in the sintered body structure is present in large numbers, or that the surface roughness is large. In this embodiment, the sputtering target satisfies the lightness difference ΔL* of ΔL*<3.0, so that there is no significant difference between the end and center of the oxide sintered body of the sputtering target in terms of at least one characteristic selected from the number of microcracks in the structure, the number of voids in the sintered body structure, and the surface roughness. Therefore, the sputtering target of this embodiment has an oxide sintered body with less processing damage during cutting and improved uniformity. It is estimated that a high-quality IGZO film can be formed by sputtering using a sputtering target having such an oxide sintered body.
From the same viewpoint, in this embodiment, the sputtering target preferably satisfies the difference in brightness ΔL*<2.5, and more preferably ΔL*<2.0.

In this specification, the lightness can be measured by polishing the surface of the oxide sintered body of the sputtering target with a grindstone of #80 to #800, and then measuring with a simplified spectrophotometer (manufactured by Nippon Denshoku Industries Co., Ltd., model number: NF333).
The surface of the oxide sintered body of the sputtering target, which is the measurement target for the lightness Le* and Lc*, is the surface of the oxide sintered body on the side to be sputtered when the sputtering target is used. Specifically, if the oxide sintered body is, for example, disk-shaped or rectangular, the surface is, for example, the surface (flat surface) of the oxide sintered body on the opposite side to the bonding surface with the backing plate, and if the oxide sintered body is cylindrical, the outer circumferential surface of the cylinder.
More specifically, the lightness Le* is an arithmetic average of values measured at three positions on the surface of the oxide sintered body of the sputtering target, the positions being 10 mm away from the end of the oxide sintered body toward the center, and the end of the oxide sintered body refers to an end formed by cutting the oxide sintered body after firing, among the ends of the oxide sintered body of the sputtering target. Moreover, the term "from the end to the center" refers to a direction perpendicular to the outline of the end.
More specifically, the lightness Lc* is an arithmetic average of values measured at three locations in the center of the surface of the oxide sintered body of the sputtering target, and the center of the surface of the oxide sintered body refers to a region of the surface of the oxide sintered body of the sputtering target that is located more than 10 mm away from the end of the oxide sintered body (including an end formed by cutting the oxide sintered body after firing and an end not cut) toward the center.

In the present embodiment, a method for making the difference ΔL* in lightness of the oxide sintered body in the sputtering target satisfy ΔL*<3.0 includes reducing processing damage during cutting of the oxide sintered body, specifically, reducing the cutting speed during cutting and using a fine grindstone. However, from the viewpoint of ensuring the productivity of the sputtering target, it is also preferable that the oxide sintered body itself has strength against such processing damage during cutting.
An oxide sintered body having strength against processing damage during cutting can be obtained by adjusting the firing temperature of the oxide sintered body, the holding time at the maximum firing temperature, and the atmosphere during firing. Specifically, when the firing temperature is relatively high, microcracks may occur throughout the structure of the oxide sintered body. In this case, the residual stress in the sintered body structure is relaxed, and the microcracks tend not to progress significantly due to damage during cutting, so the difference ΔL* between the lightness Le* near the end of the oxide sintered body and the lightness Lc* at the center of the oxide sintered body is unlikely to become large.
On the other hand, when the firing temperature is relatively low, the particles in the structure of the oxide sintered body can be made strong, so that during cutting, microcracks that may occur due to processing damage can be reduced throughout the structure, and even when cutting is performed, the difference ΔL* between the lightness Le* near the end of the oxide sintered body and the lightness Lc* at the center of the oxide sintered body tends to be small. Furthermore, when the grain size in the structure at this time is small, the structure itself becomes even stronger, microcracks due to damage during cutting hardly progress, and the difference ΔL* between the lightness Le* near the end of the oxide sintered body and the lightness Lc* at the center of the oxide sintered body tends to be smaller.
Furthermore, when the sintering temperature is moderate, there may be no cracks in the entire structure of the oxide sintered body after sintering, or even if there are, there may be only a few cracks. However, in this case, it is considered that there is residual stress in the sintered body structure generated during the sintering process, and microcracks are likely to progress due to damage during cutting processing, and as a result, the difference ΔL* between the lightness Le* near the target end and the lightness Lc* at the center may become large.

Next, a method for improving strength against damage during cutting by adjusting the holding time of the maximum firing temperature will be described. In an oxide sintered body, the longer the holding time of the maximum firing temperature, the more likely it is that microcracks will occur throughout the structure after firing. However, when the holding time is relatively long, even if microcracks develop due to damage during cutting, the difference ΔL* between the lightness Le* near the end of the oxide sintered body and the lightness Lc* at the center of the oxide sintered body is unlikely to become large.
Furthermore, when the holding time is relatively short, the occurrence of cracks throughout the structure can be reduced, and even when cutting is performed, the difference ΔL* between the lightness Le* near the end of the oxide sintered body and the lightness Lc* at the center of the oxide sintered body tends to be small.
Furthermore, when the holding time is intermediate, there are no cracks in the entire structure of the oxide sintered body after sintering, or if there are any, they are very few. However, in this case, it is considered that there is residual stress in the sintered body structure generated during the firing process, and microcracks are likely to progress due to damage during cutting processing, so that the difference ΔL* between the lightness Le* near the target end and the lightness Lc* at the center may become large.

Next, it is preferable to use an oxygen atmosphere for the sintering atmosphere when obtaining an oxide sintered body, as using an oxygen atmosphere increases the sinterability and tends to increase the difference in brightness ΔL* compared to sintering in an air atmosphere.

Furthermore, an oxide sintered body that has strength against processing damage during cutting can also be obtained by adjusting the density (relative density) of the sintered body structure. Generally, if the density of a sputtering target is low, it can cause nodules to form, but if the density of the oxide sintered body of an IGZO target is too high, local stress within the structure is not alleviated and cracks are likely to develop, although the mechanism is not clear. On the other hand, if the density is too low, microcracks are unlikely to develop, but there is a higher concern about nodule formation.

That is, in this embodiment, from the viewpoint of suppressing the generation of nodules, the relative density is 97.0% or more, and preferably 98.0% or more, whereas from the viewpoint of suppressing the growth of microcracks, the relative density is preferably 99.3% or less.
The relative density is determined by the ratio of the Archimedes density to the theoretical density, which is determined by the composition.

Here, the theoretical density is a density value calculated from the theoretical density of the oxide of each element of the oxide sintered body of the sputtering target, excluding oxygen. The theoretical density is calculated by performing a component analysis of the oxide sintered body, and using the oxide mass ratio (mass%) calculated by converting the atomic ratio (at%) of In, Ga, and Zn to the total of 100 at% of the constituent elements In, _Ga , and Zn, and the simple substance densities of _In2O3 , _{Ga2O3 ,} and ZnO. Specifically, the density of _In2O3 is 7.18 ⁽ g/ _cm3 ), the density of _Ga2O3 is 5.95 (g/ _cm3 ), the density of ZnO is 5.61 (g/ ^cm3 ), the mass ratio of _In2O3 is ^WIn2O3 (mass%), the mass ratio of _{Ga2O3 is WGa2O3 (} mass%), and the mass ratio of _ZnO is _WZnO ( _mass %), and the theoretical density (g/ ^cm3 ) is calculated as (7.18 x _WIn2O3 + 5.95 x _WGa2O3 + 5.61 x _WZnO )/100.

Note that this relative density is based on the theoretical density calculated by assuming that the sintered body of the sputtering target is a mixture of _In2O3 , _Ga2O3 , and _{ZnO .} Since the true value of the density of the target sintered body may be higher than the theoretical density, the relative density referred to here may exceed 100%.

The relative density of the oxide sintered body of the sputtering target of this embodiment can be controlled within the above range by adjusting the maximum firing temperature, firing holding time, firing atmosphere, etc.

In this embodiment, the grain size of the oxide sintered body is preferably 1.5 μm or more and 15 μm or less, and more preferably 3.0 μm or more and 10 μm or less. If the grain size is large, exceeding 15 μm, there is a concern that coarse particles may be generated during sputtering. If the grain size is less than 1.5 μm, there is a concern that sintering may be insufficient and sufficient density may not be obtained.

The grain size is measured by the code method. The grain size is measured by cutting a sample for observation from the target, mirror-polishing the surface of the sample, taking a structural photograph of the mirror-polished sample surface in five fields of view at a magnification of 1000 times with a scanning electron microscope (SEM), drawing two straight lines on the photographed image, and measuring the arithmetic mean value of the lengths at which each straight line intersects with a crystal grain, and the arithmetic mean value is taken as the grain size (crystal grain size).
The grain size of the oxide sintered body measured by the cord method can be controlled by adjusting the maximum sintering temperature, sintering holding time, sintering atmosphere, and the like.

Here, in this embodiment, the oxide sintered body can be a part of a sputtering target, and can be bonded to a backing plate with a bonding material as necessary, and the oxide sintered body in the sputtering target can be in the shape of a circular plate, a rectangular plate, or a cylindrical shape.
The thickness of the oxide sintered body in the sputtering target can be 18 mm or less, preferably 15 mm or less. The thickness is preferably 3 mm or more, more preferably 6 mm or more. By making the thickness 3 mm or more, the usage period of the target can be extended, the downtime of the sputtering device can be reduced, and the productivity can be improved. If the thickness of the target is too thick, there is a tendency that sufficient density cannot be obtained during sintering, so the thickness is preferably 18 mm or less.

Next, a method for producing the sputtering target of this embodiment will be described.
The sputtering target of this embodiment can be produced through the steps of mixing and pulverizing raw materials, a granulating step, a molding step, and a firing step.
In the mixing and grinding step, indium oxide (In ₂ O ₃ ) powder, gallium oxide (Ga ₂ O ₃ ) powder, and zinc oxide (ZnO) powder are prepared as raw material powders.
It is preferable to use indium oxide powder with a median diameter (D50) of 0.5 to 3 μm and a specific surface area of 4 to 10 ^m2 /g, gallium oxide powder with a median diameter (D50) of 0.5 to 4 μm and a specific surface area of 6 to 30 ^m2 /g, and zinc oxide powder with a median diameter (D50) of 0.1 to 2 μm and a specific surface area of 2 to 20 ^m2 /g.

Next, the raw powders are weighed to obtain the desired composition ratio, and then mixed and pulverized. There are various pulverization methods depending on the desired particle size and the material to be pulverized, and wet or dry ball mills, vibration mills, bead mills, etc. can be used. To obtain uniform and fine crystal particles, the bead mill mixing method is preferred, as it has high efficiency in breaking down aggregates in a short time and also provides good dispersion of additives.

Next, in the granulation process, the finely ground slurry is granulated. This is to improve the fluidity of the powder by granulation, which allows the powder to be filled evenly into a mold during the next process of press molding, resulting in a homogeneous molded body. There are various methods of granulation, but one method for obtaining granulated powder suitable for press molding is to use a spray drying device (spray dryer). This method makes the powder into a slurry, disperses it as droplets in hot air, and dries it instantly, allowing for the continuous production of spherical granulated powder of 10 to 500 μm.

When drying with a spray dryer, it is important to control the inlet and outlet temperatures of the hot air. If the temperature difference between the inlet and outlet is large, the amount of dry material per unit time increases, improving productivity, but if the inlet temperature is too high, the powder and any added binders may be altered by the heat, and the desired characteristics may not be obtained. Also, if the outlet temperature is too low, the granulated powder may not be dried sufficiently.

The strength of the molded body can be improved by adding a binder such as polyvinyl alcohol (PVA) to the slurry and incorporating it into the granulated powder. The amount of PVA added can be 50 to 250 cc/kg of an aqueous solution containing 6% by mass of PVA relative to the raw powder. Furthermore, the crushing strength of the granulated powder during press molding can be adjusted by adding a plasticizer suitable for the binder. Another method for improving the strength of the molded body is to add a small amount of water to the obtained granulated powder to moisten it.

Next, in the molding step, the granulated powder is pressed by a die or cold isostatic press (CIP) at a pressure of, for example, 1 ton/cm ² or more for 1 to 3 minutes to obtain a molded body.

Next, in the sintering process, for example, an electric furnace can be used, and in addition to atmospheric sintering, pressure sintering methods such as hot pressing, oxygen pressure, and hot isostatic pressure can also be used. However, from the viewpoints of reducing manufacturing costs, the possibility of mass production, and the ease of manufacturing large sintered bodies, it is preferable to use atmospheric sintering.

The firing atmosphere in the firing step preferably contains oxygen, and more preferably is an oxygen atmosphere. By containing oxygen, the bulk resistance of the oxide sintered body can be easily adjusted to a desired range.
In the normal pressure sintering method, the molded body is usually sintered by firing in the air, and when oxygen is introduced for firing, the flow rate of oxygen is preferably 5 to 2000 L/min.

The maximum firing temperature in the firing step can be 1200 to 1500° C., and preferably 1220 to 1360° C. By setting the maximum firing temperature within this range, the difference in lightness ΔL* satisfies ΔL*<3.0, and the relative density of the oxide sintered body can be easily set within a predetermined range.
The holding time at the maximum firing temperature can be 5 to 100 hours, preferably 10 to 100 hours, and more preferably 20 to 80 hours. By setting the holding time at the maximum firing temperature within this range, the difference in lightness ΔL* satisfies ΔL*<3.0, and the relative density of the oxide sintered body can be easily set within a predetermined range.

Furthermore, the heating rate during sintering is preferably 0.1 to 5°C/min, more preferably 0.3 to 3°C/min, and even more preferably 0.5 to 2°C/min, in a temperature range of 1000°C or higher. A heating rate of 5°C/min or higher in this temperature range is not preferred from the viewpoint of process stability during mass production. Also, a heating rate of 0.1°C/min or lower in this temperature range is not preferred from the viewpoint of productivity.
Furthermore, the rate of temperature increase outside the above-mentioned predetermined temperature range is not particularly limited and can be any rate of temperature increase.

Furthermore, the temperature of the molded body (sintered body) after sintering can be decreased at a rate of 10°C/min or less in a temperature range of 600°C or more. By decreasing the rate of temperature decrease to 10°C/min or less, cracking of the sintered body due to thermal stress can be suppressed. The reason why the temperature range in which the rate of temperature decrease is 10°C/min or less is set to 600°C or more is that thermal stress tends to increase in the sintered body at 600°C or more when the sintered body is decreased in temperature.
The temperature drop rate is preferably 5° C./min or less, more preferably 3° C./min or less. From the viewpoint of productivity, the temperature drop rate is preferably 0.1° C./min or more, more preferably 0.5° C./min or more.
Furthermore, the temperature decreasing rate outside the above-mentioned predetermined temperature range is not particularly limited and can be any desired temperature decreasing rate.

In the sputtering target manufacturing method of this embodiment, the sintered body obtained through the above-mentioned firing process can be processed into a desired shape using a processing machine such as a surface grinder, a cylindrical grinder, or a machining machine, as necessary, to produce a sputtering target. There are no particular restrictions on the shape of the sputtering target. For example, it can be disk-shaped, rectangular, cylindrical, etc. If necessary, the sputtering target may be bonded to a backing plate using a bonding material.

The oxide sintered body can be cut using a cutting wheel. The wheel is preferably made of a metal material, and the grain size is preferably #60 to #400, and more preferably #80 to #280. When the oxide sintered body has a cylindrical shape, it can be cut by cutting into the outer periphery of the oxide sintered body at a speed of 0.1 to 10 mm/min while rotating the oxide sintered body around its axis at, for example, 5 to 200 rpm. When the oxide sintered body has a disk or rectangular shape, it can be cut by cutting into the surface of the oxide sintered body at a speed of 0.1 to 100 mm/min.

Although the embodiments of the present invention have been described above, the sputtering target of the present invention is not limited to the above examples and can be modified as appropriate.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

(Preparation of sputtering target)
As raw material powders of the oxide sintered bodies of the sputtering targets of Examples 1 to 31 and Comparative Examples 1 to 9, indium oxide (In ₂ O ₃ ) powder, gallium oxide (Ga ₂ O ₃ ) powder, and zinc oxide (ZnO) powder were prepared.
In the sputtering targets of Examples 1, 3 to 7, 9, 11, 13 to 20, 22 to 30 and Comparative Examples 1, 2, 4, 5, 8, and 9, indium oxide powder with a median diameter (D50): 1.6 μm and specific surface area: 4.2 ^m2 /g, gallium oxide powder with a median diameter (D50): 1.7 μm and specific surface area: 11.7 ^m2 /g, and zinc oxide powder with a median diameter (D50): 0.6 μm and specific surface area: 3.9 ^m2 /g were used.
In the sputtering targets of Examples 2, 8, 10, 12, 21, and 31 and Comparative Examples 3, 6, and 7, the indium oxide powder had a median diameter (D50) of 1.4 μm and a specific surface area of 5.0 m ² /g, the gallium oxide powder had a median diameter (D50) of 1.7 μm and a specific surface area of 11.7 m ² /g, and the zinc oxide powder had a median diameter (D50) of 0.6 μm and a specific surface area of 3.9 m ² /g. In Examples 2, 8, 10, 12, 21, and 31 and Comparative Examples 3, 6, and 7, tin oxide (SnO ₂ ) powder was also contained as a raw material in the amount shown in Table 1 (Table 1 shows the content of tin atoms), and the tin oxide powder had a median diameter (D50) of 1.5 μm and a specific surface area of 5.7 m ² /g.

Next, each raw material powder was weighed to have the composition ratio (atomic ratio) shown in Table 1, and then wet mixed and ground in a bead mill. Note that the particle size of each raw material powder in the slurry after grinding was 0.6 μm. Next, the ground slurry was granulated. For granulation, the powder was made into a slurry, dispersed as droplets in hot air using a spray dryer, and instantly dried to continuously obtain 49 μm spherical granulated powder.

Next, for Examples 5, 11 to 14, 16 to 21, 23, 25 to 31, and Comparative Examples 3 to 7, the granulated powder was filled into a mold, and a pressure of 1800 kgf/cm ² was held for 1 minute to mold the powder, and a disk-shaped molded body having a diameter of 130 mm and a thickness of 21 mm was obtained. For Examples 3, 15, and 24, and Comparative Examples 1, 2, and 9, the granulated powder was filled into a mold, and a pressure of 1800 kgf/cm ² was held for 1 minute to mold the powder, and a cylindrical molded body having an axial length of 1600 mm, an outer diameter of 197 mm, and an inner diameter of 157 mm was obtained. For Examples 1, 2, 4, 6 to 10, and 22, and Comparative Example 8, the granulated powder was filled into a mold, and after cold pressing, a pressure of 1800 kgf/cm ² was held for 1 minute to mold the powder, and a rectangular molded body having a width of 550 mm, a length of 595 mm, and a thickness of 16 mm was obtained.
These molded bodies were then fired in an electric furnace under the atmosphere shown in Table 1 to obtain oxide sintered bodies. Specifically, the molded bodies were heated under the conditions shown in Table 1, and then fired at the sintering temperature and time shown in Table 1. The heating rate from 1000°C to the maximum temperature was 1°C/min, and after the maximum temperature was maintained, the heating rate was 1.5°C/min until the temperature was cooled to 600°C.

Next, for Examples 5, 11 to 14, 16 to 21, 23, 25 to 31, and Comparative Examples 3 to 7, the obtained oxide sintered bodies were processed into disks having a diameter of 100 mm and a thickness of 15 mm. The oxide sintered bodies were cut by applying a metal #140 cutting wheel grindstone to the surface of the oxide sintered bodies at a speed of 50 mm/min.
In addition, for Examples 3, 15, and 24 and Comparative Examples 1, 2, and 9, the obtained oxide sintered bodies were processed into a cylindrical shape with an axial length of 50 mm, an outer diameter of 153 mm, and an inner diameter of 135 mm. The oxide sintered bodies were cut by using a metal #140 cutting wheel grindstone and rotating the oxide sintered bodies in the axial direction at 20 rpm, while applying the grindstone to the surface of the oxide sintered bodies at a speed of 1 mm/min.
In addition, for Examples 1, 2, 4, 6 to 10, and 22 and Comparative Example 8, the obtained oxide sintered bodies were processed into a rectangular shape with a width of 450 mm, a length of 450 mm, and a thickness of 10 mm. The oxide sintered bodies were cut by applying a metal #140 cutting wheel grindstone to the surface of the oxide sintered bodies at a speed of 50 mm/min.
The oxide sintered body after processing as described above was subjected to surface finishing with an abrasive having a grain size shown in Table 1. The oxide sintered body subjected to surface finishing was subjected to the evaluation described below.

In firing each molded body, an electric furnace with a furnace volume of 2.2 ^m3 (referred to as "large furnace" in Table 1) and an electric furnace with a furnace volume of 0.06 ^m3 (referred to as "small furnace" in Table 1) were used.

The obtained oxide sintered body was evaluated as follows. The evaluation results are shown in Table 2.
(1) Density and relative density of oxide sintered body In accordance with JIS R 1634, the bulk density was calculated from the volume and dry weight of the sintered body calculated by the Archimedes method using the following formula, and the bulk density was divided by the theoretical density to obtain the relative density.
Volume of sintered body = (weight of hydrated body - weight in water) / density of water The theoretical density of the sintered body was calculated using the mass ratios of _In2O3 W _In2O3 (mass %), the mass ratio of _Ga2O3 W _Ga2O3 (mass %), and the mass ratio of ZnO W _ZnO (mass %), which were calculated by converting the atomic ratios (at %) of In, _Ga , and _Zn to the total of 100 at % of the constituent _{elements In} , Ga, and Zn, as well as the elemental densities of _In2O3 (7.18 (g/ ^cm3 ), _Ga2O3 (5.95 (g/ ^cm3 ), and ZnO (5.61 (g/ ^cm3 )), using the following formula:
Theoretical density (g/cm ³ ) = (7.18×W _In2O3 +5.95×W _Ga2O3 +5.61×W _ZnO )/100

(2) Grain size of the oxide sintered body measured by the code method The grain size of the oxide sintered body measured by the code method was measured by cutting out an observation sample from the oxide sintered body after surface finishing with an abrasive having a grain size shown in Table 1, and mirror polishing the surface of the cut sample. A micrograph of the surface of the mirror polished sample was taken in five fields of view at a magnification of 1000 times with a scanning electron microscope (SEM), and the crystal grain size (grain size of the grain) of multiple fields of view (five fields of view) was calculated as an arithmetic average value by the evaluation method of the code method. In the code method, two straight lines of arbitrary length were drawn on each surface texture photograph, the length of the straight lines was divided by the number of grains crossed by the straight lines, and this value was converted by applying it to the scale of the surface texture photograph, and the arithmetic average grain size was calculated based on the value obtained from a total of 10 straight lines.

(3) Lightness Le* and Lc*
The lightness Le* and Lc* of the oxide sintered bodies that had been surface-finished with the abrasives having the grain sizes shown in Table 1 were measured using a simplified spectrophotometer (NF333, manufactured by Nippon Denshoku Industries Co., Ltd.).

As shown in Table 2, the lightness Le*, lightness Lc*, lightness difference ΔL*, and relative density of the oxide sintered body could be adjusted to be within the desired range by sintering the raw material molded body to obtain the oxide sintered body under a high oxygen partial pressure, adjusting the firing temperature, firing time, firing atmosphere, and temperature increase/decrease rate, performing an annealing treatment after firing, fine-tuning the composition, and the like.
In Examples 1 to 31, in which the lightness difference ΔL* of the oxide sintered body and the relative density are set within a predetermined range, it is possible to provide an IGZO sputtering target having improved uniformity in at least one property selected from the number of microcracks in the structure, the number of voids in the sintered body structure, and the surface roughness, and it is presumed that this makes it possible to obtain a high-quality IGZO film.

The present invention provides an IGZO sputtering target that can improve the uniformity of at least one characteristic selected from the number of microcracks in the structure, the number of voids in the sintered body structure, and surface roughness.

Claims (6)

A sputtering target having an oxide sintered body composed of indium (In), gallium (Ga), zinc (Zn) and inevitable impurities and cut after sintering,
In the surface of the oxide sintered body, ΔL* obtained by subtracting the lightness Lc* at the center of the surface from the lightness Le* at a position 10 mm from the end of the surface toward the center satisfies ΔL*<3.0,
The relative density of the oxide sintered body is 97.0% or more,
The IGZO sputtering target, wherein the surface of the oxide sintered body is flat. The IGZO sputtering target according to claim 1, wherein the grain size of the oxide sintered body is 1.5 to 15 μm. The IGZO sputtering target according to claim 1 or 2, wherein the relative density of the oxide sintered body is 99.3% or less. The IGZO sputtering target according to any one of claims 1 to 3, wherein the oxide sintered body has a circular plate shape or a rectangular plate shape . The IGZO sputtering target according to any one of claims 1 to 4, in which the atomic ratio of Ga is 100±30 and Zn is 100±30 when the In content in the oxide sintered body is 100. The IGZO sputtering target according to any one of claims 1 to 5, wherein the thickness of the oxide sintered body is 15 mm or less.