TW201736319A - Oxide sintered body, sputtering target, and methods for making same - Google Patents

Abstract

An oxide sintered body that includes 50 to 500 ppm of zirconium, and satisfies formulas (1) to (3) when the percentages (atom%) of contents of zinc, indium, gallium, and tin with respect to all metal elements excluding oxygen are, respectively, [Zn], [In], [Ga], and [Sn]. 35 atom% ≤ [Zn] ≤ 55 atom% (1) 20 atom% ≤ ([In]+[Ga]) ≤ 55 atom% (2) 5 atom% ≤ [Sn] ≤ 25 atom% (3).

Description

Oxide sintered body and sputtering target and method for producing same

The present invention relates to an oxide semiconductor thin film of a thin film transistor (TFT) used in a display device such as a liquid crystal display or an organic electroluminescence (EL) display by sputtering. The oxide sintered body and the sputtering target used in the present invention and a method for producing the same.

The amorphous (amorphous) oxide semiconductor thin film used in the TFT has high carrier mobility, large optical band gap, and can be compared with general-purpose amorphous silicon (a-Si). Film formation at low temperatures. Therefore, it is expected to be used in a next-generation display that is large-sized, high-resolution, and requires high-speed driving, and is applied to a resin substrate having low heat resistance. As an oxide semiconductor suitable for such applications, an amorphous oxide semiconductor containing In has been proposed. For example, an In-Ga-Zn-based oxide semiconductor has attracted attention.

In the formation of the oxide semiconductor thin film, a sputtering method in which a sputtering target (hereinafter sometimes referred to as a "target") is sputtered is preferably used, and the sputtering target contains the same composition as the thin film. s material.

In the case of the composite oxide sintered body which obtains favorable TFT characteristics, it is described that it contains a group selected from In, Zn, Sn, and X (Mg, Al, Ga, Si, Sc, Ti, Y, Zr, One or more elements X of Hf, Ta, La, Nd, and Sm) include a bixbyite structural compound represented by In ₂ O ₃ and a sputtering target of a spinel structure compound.

In Patent Document 2, as a sintered body of In-Ga-Zn oxide which can be stably sputtered, it is described that InGaZn _m O _{3 + m} (m is an integer of 0.5 or more) An oxide sintered body having an average particle diameter of the source phase and the HfO ₂ phase or the ZrO ₂ phase of 10 μm or less. [Prior Art Document] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. Hei. No. 2014-111818 (Patent Document 2) Japanese Patent Laid-Open Publication No. 2015-189632

[Problem to be Solved by the Invention] The sputtering target is used in a state where the oxide sintered body is welded to the bottom plate. In the step of soldering the oxide sintered body to the substrate, the oxide sintered body is broken.

The production requirements of the display device are always efficient. In addition, in consideration of the productivity, the manufacturing cost, and the like, the sputtering target used for the production of the oxide semiconductor thin film for a display device and the oxide sintered body used as the material thereof are of course required to suppress sputtering at the time of sputtering. The target is broken, and it is required to suppress cracking of the oxide sintered body when the oxide sintered body is welded to the bottom plate.

The embodiment of the present invention has been made in view of the above-described circumstances, and a first object thereof is to provide an oxide sintered body for use in a sputtering target suitable for producing an In-Ga-Zn-Sn-based oxide semiconductor thin film. The sintered In-Ga-Zn-Sn-based oxide used in the present invention can suppress cracking when soldered to the substrate. A second object of an embodiment of the present invention is to provide a method for producing the oxide sintered body. A third object of an embodiment of the present invention is to provide a sputtering target using the oxide sintered body. A fourth object of an embodiment of the present invention is to provide a method for producing a sputtering target. [Means for solving the problem]

In order to solve the problem, the inventors of the present invention have conducted intensive studies. As a result, it has been found that zirconium is contained in a specific range in an oxide sintered body containing an oxide of zinc, indium, gallium, and tin. Thus, an embodiment of the present invention is completed.

According to a first aspect of the present invention, there is provided an oxide sintered body comprising 50 ppm to 500 ppm of zirconium, wherein the ratio of indium, gallium, and tin to the ratio of all metal elements other than oxygen (atomic %) is set. When it is [In], [Ga], and [Sn], the following formula (1) to formula (3) are satisfied: 35 atomic % ≦ [Zn] ≦ 55 atomic % (1) 20 atomic % ≦ ([ In]+[Ga])≦55 atom%・・・(2) 5 atom%≦[Sn]≦25 atom%・・・(3).

Preferably, the oxide sintered body has a relative density of 95% or more.

It is preferred that the pores in the oxide sintered body have a maximum circle-equivalent diameter of 3 μm or less.

The relative ratio of the average equivalent circle diameter of the pores in the oxide sintered body to the maximum circle-equivalent diameter is preferably 0.3 or more and 1.0 or less.

It is preferred that the oxide sintered body has an average crystal grain size of 20 μm or less.

It is preferable that the area ratio of crystal grains having an crystal grain size of more than 30 μm in the oxide sintered body is 10% or less.

The specific resistance of the oxide sintered body is preferably 1 Ω·cm or less.

A second embodiment of the present invention is a sputtering target which is obtained by fixing the oxide sintered body of the first embodiment to a bottom plate by a welding material.

According to a third aspect of the present invention, in a method of producing an oxide sintered body according to the first embodiment, the method includes the steps of: preparing a mixed powder containing zinc oxide, indium oxide, gallium oxide, tin oxide, and zirconium oxide in a predetermined ratio. A step of sintering the mixed powder into a predetermined shape.

The step of preparing the mixed powder includes a step of mixing raw material powders containing zinc oxide, indium oxide, gallium oxide, and tin oxide by using a ball mill or a bead mill using a medium containing zirconia. The step of preparing the mixed powder may include a step of mixing raw material powders containing zinc oxide, indium oxide, gallium oxide, tin oxide, and zirconium oxide by a ball mill or a bead mill instead of the above steps.

The step of sintering may also be hot pressing. That is, in the step of sintering, it may be included in a state where a surface pressure of 10 MPa to 39 MPa is applied to the mixed powder by a molding die, and the sintering temperature is maintained at 900 ° C to 1200 ° C for 1 hour to 12 hours. Hours of steps. Preferably, in the case of hot pressing, the average temperature increase rate up to the sintering temperature is 600 ° C / hr or less.

The step of sintering may also be atmospheric pressure sintering. In the atmospheric pressure sintering, a step of pre-forming the mixed powder is included after the step of preparing the mixed powder and before the step of sintering. Further, in the step of sintering, the step of holding the preformed molded body under normal pressure at a sintering temperature of 1,450 ° C to 1,600 ° C for 1 hour to 5 hours is also included. It is preferable that in the case of normal pressure sintering, the average temperature increase rate up to the sintering temperature is 100 ° C / hr or less.

According to a fourth aspect of the present invention, there is provided a method of producing a sputtering target according to the second embodiment, which comprises the oxide sintered body according to the first embodiment or the production method according to the third embodiment. The step of bonding the produced oxide sintered body to the substrate. [Effects of the Invention]

According to the embodiment of the present invention, it is possible to provide an oxide sintered body capable of suppressing cracking when soldered on a substrate, and a sputtering target using the oxide sintered body, and an oxide sintered body and a sputtering target. .

<Oxide sintered body> First, an oxide sintered body according to an embodiment of the present invention will be described in detail. The oxide sintered body of the embodiment of the present invention contains an oxide of zinc, indium, gallium, and tin. Here, in order to manufacture a sputtering target which can form an oxide semiconductor thin film having an effect of excellent TFT characteristics, it is necessary to appropriately control the content of the metal element contained in the oxide sintered body used in the sputtering target.

Therefore, the oxide sintered body according to the embodiment of the present invention contains 50 ppm to 500 ppm of zirconium, and the content of zinc, indium, gallium, and tin contained in the oxide sintered body is relative to all metal elements other than oxygen. When the ratio (atomic %) is set to [Zn], [In], [Ga], and [Sn], respectively, the following formulas (1) to (3) are satisfied. 35 atom% ≦[Zn]≦55 atom%・・・(1) 20 atom%≦([In]+[Ga])≦55 atom%・・・(2) 5 atom%≦[Sn]≦25 atom %・・・(3)

The "all metal elements other than oxygen contained in the oxide sintered body" are zinc, indium, gallium, tin, and zirconium, and may contain metal impurities which are unavoidable in production. Here, since zirconium and unavoidable metal impurities are in a small amount, the influence on the ratio of the metal element in the oxide sintered body is small. Therefore, "all metal elements other than oxygen contained in the oxide sintered body" are substantially zinc, indium, gallium, and tin.

Therefore, in the present specification, the content of zinc, indium, gallium, and tin in the oxide sintered body is expressed by the number of atoms, and the content of zinc can be changed to "[Zn] with respect to the total amount (total number of atoms). ]], the content of indium is referred to as "[In]", the content of gallium is referred to as "[Ga]", and the content of tin is referred to as "[Sn]". Further, it becomes [Zn] + [In] + [Ga] + [Sn] = 100 atom%. The content ratio (atomic %) ([Zn], [In], [Ga], and [Sn]) of each element of zinc, indium, gallium, and tin defined as described above satisfies the above formula (1) to The way of (3) controls the content of each element.

The content ratio (atomic %) of each element of zinc, indium, gallium, and tin will be described in detail below. Further, the content of each element is mainly set in consideration of the characteristics of the oxide semiconductor thin film formed by sputtering the target.

Zinc content: 35 atom% ≦ [Zn] ≦ 55 atom% Zinc improves the stability of the amorphous structure of the oxide semiconductor film. The content of zinc is preferably 37 atom% ≦[Zn]≦54 atom%, more preferably 40 atom% ≦[Zn]≦53 atom%.

Indium and gallium content: 20 atom% ≦ ([In] + [Ga]) ≦ 55 atom% Indium increases the carrier mobility of the oxide semiconductor film. Gallium increases the reliability of optical stress, that is, the deviation of the threshold value of the oxide semiconductor film. Indium and gallium are Group III elements that interact in imparting these properties. Therefore, in order to appropriately exhibit the respective characteristics of indium and gallium, it is desirable to appropriately control the total amount of them. The total content of indium and gallium is preferably 25 atom% ≦ ([In] + [Ga]) ≦ 54 atom%, more preferably 30 atom% ≦ ([In] + [Ga]) ≦ 53 atom%.

Tin content: 5 atom% ≦ [Sn] ≦ 25 atom% Tin improves the etch resistance of the oxide semiconductor film. The content of tin is preferably 7 atom% ≦ [Sn] ≦ 22 atom%, more preferably 9 atom% ≦ [Sn] ≦ 20 atom%.

In the oxide sintered body of the embodiment of the present invention, the content of zirconium is controlled to 50 ppm to 500 ppm from the viewpoint of controlling the physical properties of the oxide sintered body and controlling the physical properties of the oxide semiconductor thin film. By adding zirconium to the oxide sintered body, the relative density of the oxide sintered body is increased, and the strength of the oxide sintered body is improved. When the oxide sintered body is welded to the bottom plate, the oxide sintered body receives stress due to impact or heat history, but the strength of the oxide sintered body can be improved by containing zirconium, so that the oxide sintered body can be suppressed. rupture. By setting the amount of zirconium to 50 ppm or more, the effect of suppressing cracking can be sufficiently exhibited. The amount of zirconium is preferably 60 ppm or more, more preferably 70 ppm or more.

On the other hand, zirconium exists as zirconia (zirconium) in the oxide sintered body. Since zirconia is an insulator, it can cause abnormal discharge during sputtering. In addition, when an oxide sintered body containing a large amount of zirconia is used for film formation, the carrier characteristics are deteriorated due to zirconia in the obtained oxide semiconductor thin film. By setting the amount of zirconium to 500 ppm or less, abnormal discharge at the time of sputtering can be suppressed, and the carrier characteristics of the oxide semiconductor thin film formed by sputtering can be maintained high. The amount of zirconium is preferably 450 ppm or less, more preferably 400 ppm or less.

The content of zirconium (the amount of zirconium) in the present specification is the average amount of zirconium measured by the following method. The entire surface of the oxide sintered body was subjected to a grinding process of 0.5 mm or more to remove the black skin on the surface. Next, about 5 g of the oxide sintered body was taken and quantitatively analyzed by Inductively Coupled Plasma (ICP) analysis. The same measurement was performed a plurality of times (for example, three times). The average value of the obtained amount of zirconium was determined. In the present specification, the term "zirconium amount" means the average zirconium amount unless otherwise specified.

The oxide sintered body contains oxides of zinc, indium, gallium, and tin. Specifically, it has a constituent phase mainly composed of a Zn ₂ SnO ₄ phase, an InGaZnO ₄ phase, an InGaZn ₂ O ₅ phase, an In ₂ O ₃ phase, and a SnO ₂ phase. Further, it may include impurities such as oxides which are inevitably mixed or formed in the production.

Preferably, the oxide sintered body has a relative density of 95% or more. Thereby, the strength of the oxide sintered body can be increased, and the crack of the oxide sintered body when welded to the bottom plate can be effectively suppressed. The relative density is more preferably 97% or more, and still more preferably 99% or more.

The relative density in this specification can be obtained as follows. The oxide sintered body prepared as a sample for measurement is cut at an arbitrary position in the thickness direction, and mirror-polished at any position of the cut surface. Next, a photograph is taken at a suitable magnification (for example, a magnification of 1000 times) using a scanning electron microscope (SEM), and the area ratio (%) of the pores in a region of 100 μm square is measured as "porosity (%). )". In the same sample, the same porosity measurement was performed on the cut surface of 20 points, and the average value of the porosity obtained by 20 measurements was taken as the average porosity (%) of the sample. The value obtained by [100-average porosity] is referred to as "relative density (%)" in the present specification.

An example of a secondary electron image (magnification: 1,000 times) of the oxide sintered body is shown in Fig. 2 . In Fig. 2, the black dot portion is a pore. The pores can be easily identified with other metal structures in any of the SEM photographs and the secondary electron images.

Regarding the pores in the oxide sintered body, it is preferable that not only the porosity is low but also the size of the pores is small. When the molded body including the pores is sintered, the small pores disappear due to sintering, but the large pores do not disappear and remain in the inside of the oxide sintered body. The pores in the oxide sintered body exist in a state in which the gas is compressed. Further, there is a phenomenon in which Sn, Ga, or the like in the molded body is decomposed during sintering, and pores are generated inside the oxide sintered body. A compressed gas may also be present inside the pores produced as described above. When the pores containing the compressed gas are present in the oxide sintered body, the internal stress is increased, and the mechanical strength and thermal shock resistance of the oxide sintered body are lowered.

The larger the pores are, the higher the rupture of the oxide sintered body is due to the pores. Therefore, by suppressing the size of the pores in the oxide sintered body to be small, the mechanical strength of the oxide sintered body can be improved, and the crack of the oxide sintered body can be suppressed. By setting the maximum equivalent circle diameter D _{max of the} pores to 3 μm or less, the internal stress can be sufficiently reduced. The maximum equivalent circle diameter of the porosity is preferably 2 μm or less.

Further, the relative equivalent diameter D _ave (μm) of the pores in the oxide sintered body is preferably 0.3 or more and 1.0 or less relative to the maximum equivalent circle diameter D _max (μm) (that is, 0.3 ≦ D _ave / D _{max ).} ≦ 1.0). When the relative ratio is 1.0, it becomes a circle, and as the relative ratio becomes smaller, it becomes a flat elliptical shape. When the shape of the pores is elliptical, the oxide sintered body having reduced mechanical strength is more likely to be broken than in the case of a circular shape. In particular, the tendency becomes more flat as the ellipse becomes flatter. Therefore, by making the relative ratio 0.3 or more, the strength of the oxide sintered body can be increased. The relative ratio is more preferably 0.5 or more.

The maximum equivalent circle diameter and the average circle equivalent diameter of the pores in the present specification can be obtained as follows. The oxide sintered body prepared as a sample for measurement is cut at an arbitrary position in the thickness direction, and mirror-polished at any position of the cut surface. Next, a photograph is taken at a suitable magnification (for example, a magnification of 1000 times) using a scanning electron microscope (SEM), and the circle-equivalent diameter of all the pores existing in a region of 100 μm square is obtained. In the same sample, the circle-equivalent diameters of all the pores were obtained in the same manner on the cut surfaces of the 20 portions. The largest equivalent circle diameter among all the circle-equivalent diameters obtained in the 20 measurements is taken as the "maximum equivalent circle diameter of the pores" of the oxide sintered body, and the average value of all the circle-equivalent diameters is taken as the oxide sintered body. "Average equivalent circle diameter of pores".

When the crystal grains of the oxide sintered body are made fine, the effect of suppressing cracking of the oxide sintered body when welded to the bottom plate can be improved. The average grain size of the crystal grains is preferably 20 μm or less, whereby the effect of suppressing cracking of the oxide sintered body can be further enhanced. The average grain size is more preferably 17 μm or less, and further preferably 15 μm or less. On the other hand, the lower limit of the average grain size is not particularly limited, but a preferable lower limit of the average grain size is about 0.05 μm from the viewpoint of the balance between the average grain size and the production cost.

The average grain size of the crystal grains can be measured as described below. The oxide sintered body prepared as a sample for measurement is cut at an arbitrary position in the thickness direction, and mirror-polished at any position of the cut surface. Next, a photograph is taken on the tissue of the cut surface at a suitable magnification (for example, a magnification of 400 times) using a scanning electron microscope (SEM). On the photographed photograph, a line corresponding to the measured length of 100 μm in length (that is, "corresponding to the measured length of 100 μm") is drawn in an arbitrary direction, and the number of crystal grains existing on the straight line is obtained (N ). The value calculated by [100/N] (μm) is taken as the "grain degree on a straight line". Further, 20 straight lines corresponding to an actual measurement length of 100 μm were formed on the photograph, and the crystal grain size on each straight line was calculated. In addition, the value calculated by [(the total of the crystal grains on each straight line) / 20] is the "average grain size of the oxide sintered body" in the present specification.

Further preferably, in addition to controlling the average grain size of the oxide sintered body grains, the particle size distribution is also suitably controlled. In particular, coarse crystal grains having a grain size of more than 30 μm cause cracking of the oxide sintered body during welding, and thus can be as small as possible. The coarse crystal grains having a crystal grain size of more than 30 μm are preferably 10% or less, more preferably 8% or less, still more preferably 6% or less, still more preferably 4% or less, and most preferably 0. %.

The area ratio of crystal grains having a grain size of more than 30 μm can be measured as shown below. In the measurement of the "average grain size of crystal grains", when a line corresponding to a length of 100 μm is drawn, a crystal grain having a length of 30 μm or more cut out from the straight line is referred to as a "coarse grain". On the straight line having a length of 100 μm, the length occupied by the coarse particles (that is, the length of the portion transverse to the coarse particles in a straight line) was taken as L (μm). The value of L (μm) divided by 100 (μm) is taken as the ratio R (%) of the coarse particles on the straight line. R (%) = (L (μm) / 100 (μm)) × 100 (%) Further, in the case where a plurality of coarse particles are present on a straight line having a length of 100 μm, the length of the portion of each coarse particle is transversely cut. In total, L (μm) is obtained, and the ratio R (%) of the coarse particles is obtained. In each of the 20 straight lines drawn in the measurement of the average crystal grain size of the crystal grains, the ratio R (%) of the coarse particles was determined, and the average value thereof was defined as the ratio of the coarse particles of the sintered body.

The specific resistance of the oxide sintered body is preferably 1 Ω·cm or less, more preferably 10 ^-1 Ω·cm or less, still more preferably 10 ^-2 Ω·cm or less. As described later, the oxide sintered body is fixed to the bottom plate to form a sputtering target. When the sputtering target is used, the specific resistance of the oxide sintered body is suppressed to be low, whereby abnormal discharge during sputtering can be suppressed, and cracking of the oxide sintered body due to abnormal discharge can be suppressed. Thereby, the film formation cost of the oxide semiconductor thin film using the sputtering target can be suppressed. Further, it is possible to suppress film formation failure due to abnormal discharge during sputtering, whereby an oxide semiconductor film having uniform and excellent characteristics can be produced. For example, in the production line for manufacturing a display device, by using a sputtering target to produce an oxide semiconductor thin film of a TFT, the manufacturing cost of the TFT can be suppressed, and the manufacturing cost of the display device can be suppressed. Further, an oxide semiconductor thin film exhibiting good TFT characteristics can be formed, whereby a high-performance display device can be manufactured.

The specific resistance of the oxide sintered body can be measured by a four-probe method. Specifically, the specific resistance of the oxide sintered body can be measured using a known specific resistance measuring instrument (for example, Loresta GP manufactured by Mitsubishi Chemical Analytech Co., Ltd.). In addition, the specific resistance of this specification is obtained by measuring the distance between each terminal as 1.5 mm. The specific resistance is measured a plurality of times (for example, four times) at different positions, and the average value thereof is taken as the specific resistance of the oxide sintered body.

<Sputter Target> Next, a sputtering target using an oxide sintered body will be described. FIG. 1 is a schematic cross-sectional view of a sputtering target 1. The sputtering target 1 includes a bottom plate 20 and an oxide sintered body 10 fixed to the bottom plate 20 by a solder material 30. The oxide sintered body of the embodiment of the present invention is used in the oxide sintered body 10. Therefore, when welded to the bottom plate 20 by the welding material 30, the oxide sintered body is hard to be broken, and the sputtering target 1 can be produced with good yield.

<Manufacturing Method> Next, an oxide sintered body and a method of producing a sputtering target according to an embodiment of the present invention will be described.

The oxide sintered body according to the embodiment of the present invention can be obtained by sintering a mixed powder containing zinc oxide, indium oxide, gallium oxide, tin oxide, and zirconium oxide. The sputtering target of the embodiment of the present invention can be obtained by fixing the obtained oxide sintered body to a substrate. More specifically, the oxide sintered body can be produced by the following steps (a) to (e). The sputtering target can be produced by the following steps (f) and (g). Step (a): mixing and pulverizing the powder of the oxide (b): drying the obtained mixed powder, granulating step (c): pre-forming the granulated mixed powder (d): The preformed molded body is subjected to a degreasing step (e): sintering the degreased molded body to obtain an oxide sintered body step (f): processing the obtained oxide sintered body (g): processing is performed The oxide sintered body is welded to the bottom plate to obtain a sputtering target

In the embodiment of the present invention, in the step (a), the control is carried out in such a manner that an appropriate amount of zirconia is contained in the mixed powder. Further, in the step (e), the sintering conditions are controlled such that the oxide sintered body has a density higher than a predetermined density. Further, in the step (e), it is preferred to control the sintering conditions in such a manner that the grain size enters a preferable range. The step (b) to the step (d), the step (f), and the step (g) are not particularly limited as long as the oxide sintered body and the sputtering target can be produced, and can be suitably used in an oxide sintered body and a sputtering target. The steps commonly used in the manufacture of materials. Hereinafter, each step will be described in detail, but the embodiment of the present invention is not limited to the gist of the steps.

(Step (a): Mixing and pulverizing the oxide powder) The zinc oxide, the indium oxide powder, the gallium oxide powder, and the tin oxide powder are blended in a predetermined ratio, and mixed and pulverized. The purity of each raw material powder used is preferably about 99.99% or more. This is because if a small amount of an impurity element is present, there is a possibility that the semiconductor characteristics of the oxide semiconductor thin film are impaired. The "predetermined ratio" of each raw material powder means the content of zinc, indium, gallium, and tin contained in the oxide sintered body obtained after sintering, and all metal elements other than oxygen removal (zinc, indium, gallium, and The ratio of tin) is a ratio within the range of the following formulas (1) to (3). 35 atom% ≦[Zn]≦55 atom%・・・(1) 20 atom%≦([In]+[Ga])≦55 atom%・・・(2) 5 atom%≦[Sn]≦25 atom %・・・(3)

In general, the contents of zinc, indium, gallium, and tin contained in the mixed powder obtained by mixing the respective raw material powders (zinc oxide, indium oxide powder, gallium oxide powder, and tin oxide powder) with respect to oxygen removal The raw material powder may be blended so that the ratio of all the metal elements is within the range of the above formulas (1) to (3).

In the mixing and pulverization, it is preferred to use a ball mill or a bead mill. The raw material powder and water are put into a polishing apparatus, and the raw material powder is pulverized and mixed, whereby a mixed powder can be obtained. In this case, the raw material powder may be uniformly mixed, and the dispersion material may be added and mixed, or a binder may be added and mixed in order to facilitate the formation of the molded body later.

As the balls or granules used in the ball mill and the bead mill (referred to as "medium"), those containing zirconia can be used. When mixing and pulverizing, a trace amount of zirconia is added to the mixed powder due to wear of the surface of the medium. In this method, if the mixing time is long, the amount of wear of the medium (i.e., the amount of addition of zirconia) increases. Therefore, by adjusting the mixing time, the amount of zirconia added in the mixed powder can be adjusted relatively accurately.

As the medium used in the ball mill and the bead mill, a nylon or alumina can also be used. In this case, zirconia powder is added as a raw material powder so that a predetermined amount of zirconia is contained in the mixed powder. In this case, since the mixed powder containing the predetermined zirconia can be obtained irrespective of the mixing time, the mixing time can be arbitrarily set. A nylon container, an alumina container, and a zirconium container can be used for the container used in the ball mill and the bead mill.

Further, zirconia powder may be added as a raw material powder, and a medium made of zirconia may be further used as a medium. In this case, a part of the amount of zirconia desired is added as a raw material powder, and the remainder is added by abrasion of the medium.

The mixing time of the ball mill or the bead mill is preferably 3 hours or longer, more preferably 10 hours or longer, and still more preferably 20 hours or longer.

(Step (b): Drying and granulating the mixed powder) The mixed powder obtained in the step (a) is preferably granulated by drying by, for example, a spray dryer or the like.

(Step (c): Pre-forming the granulated mixed powder) It is preferred to fill the granulated mixed powder in a metal mold of a predetermined size, and apply a predetermined pressure (for example, about 49 MPa by pressing with a metal mold). The pressure is pre-formed into a predetermined shape at a pressure of about 98 MPa. In the case of performing the sintering in the step (e) by hot pressing, the step (c) may be omitted, or the mixed powder may be filled in a sintering mold to perform pressure sintering to produce a dense oxide. Sintered body. Further, in order to facilitate the operation, the preform may be placed in a molding die for sintering and subjected to hot pressing after pre-forming by the step (c). On the other hand, in the case where the sintering in the step (e) is carried out by normal pressure sintering, a dense oxide sintered body can be produced by performing preforming in the step (c).

(Step (d): Degreasing the preformed molded body) In the step (a), when a dispersion material and/or a binder is added to the mixed powder, it is preferred to heat the molded body to form the molded body. The dispersing material and the binder are removed (ie, degreased). The heating conditions (heating temperature and holding time) are not particularly limited as long as the temperature and time at which the dispersion material and the binder can be removed. For example, the shaped body can be held in the atmosphere at a heating temperature of about 500 ° C for about 5 hours. In the step (a), the step (d) may be omitted in the case where the dispersion material and the binder are not used. In the case where the step (c) is omitted, that is, in the case where the step (e) is performed by hot pressing and the formed body is not formed, the mixed powder may be heated to disperse the mixed powder. And the binder is removed (degreasing).

(Step (e): Sintering the formed body to obtain an oxide sintered body) The molded body after degreasing is sintered under predetermined sintering conditions to obtain an oxide sintered body. As the sintering method, any of hot pressing and normal pressure sintering can be used. Hereinafter, sintering conditions and the like will be described with respect to each of hot pressing and normal pressure sintering.

(i) Hot pressing In the hot press, the molded body is placed in a sintering mold while being placed in a sintering mold, and sintering is performed under pressure. When a pressure is applied to the formed body to face the formed body, sintering can be suppressed to a relatively low temperature to obtain a dense oxide sintered body. In the hot pressing, a molding die for sintering for pressurizing the formed body is used. As the molding die for sintering, any of a mold (metal mold) and a graphite mold (graphite mold) can be used depending on the sintering temperature. It is particularly excellent for graphite molds with excellent heat resistance and can withstand temperatures up to 900 °C.

The pressure applied to the forming mold is not particularly limited, and the surface pressure (pressing pressure) is preferably 10 MPa to 39 MPa. If the pressure is too high, there is a possibility that the graphite die for sintering is broken, and a large pressing apparatus is required. In addition, when the thickness exceeds 39 MPa, the densification promoting effect of the sintered body is saturated, so that there is little interest in pressurizing at a pressure higher than the above. On the other hand, when the pressure is less than 10 MPa, it is difficult to sufficiently perform densification of the sintered body. More preferred pressurization conditions are from 10 MPa to 30 MPa.

The sintering temperature can be set to a temperature higher than the sintering temperature of the mixed powder in the molded body. For example, if the sintering is performed at a surface pressure of 10 MPa to 39 MPa, the sintering temperature is preferably 900 ° C to 1200 ° C. When the sintering temperature is 900 ° C or more, sintering is sufficiently performed, and the density of the obtained oxide sintered body can be increased. The sintering temperature is more preferably 920 ° C or higher, and still more preferably 940 ° C or higher. In addition, when the sintering temperature is 1200 ° C or lower, grain growth during sintering is suppressed, and the grain size in the oxide sintered body can be reduced. The sintering temperature is more preferably 1100 ° C or lower, further preferably 1000 ° C or lower.

The time (holding time) of holding at a predetermined sintering temperature is sufficient for sintering of the mixed powder, and the density of the obtained oxide sintered body becomes a predetermined density or more. For example, when the sintering temperature is from 900 ° C to 1200 ° C, the holding time is preferably from 1 hour to 12 hours. When the holding time is 1 hour or longer, the structure in the obtained oxide sintered body can be made uniform. The holding time is more preferably 2 hours or more, and still more preferably 3 hours or more. In addition, when the holding time is 12 hours or less, grain growth during sintering can be suppressed, and the grain size in the oxide sintered body can be made small. The holding time is more preferably 10 hours or less, further preferably 8 hours or less.

The average temperature increase rate up to the sintering temperature affects the size of the crystal grains in the oxide sintered body and the relative density of the oxide sintered body. The average temperature increase rate is preferably 600 ° C / hr or less, and since it is difficult to cause abnormal growth of crystal grains, the ratio of coarse crystal grains can be suppressed. Further, when the temperature is 600 ° C / hr or less, the relative density of the sintered oxide body after sintering can be increased. The average temperature increase rate is more preferably 400 ° C / hr or less, further preferably 300 ° C / hr or less. The lower limit of the average temperature increase rate is not particularly limited, and is preferably 50° C./hr or more, and more preferably 100° C./hr or more from the viewpoint of productivity.

In the sintering step, in order to suppress oxidation and disappearance of the graphite die for sintering, it is preferred to set the sintering environment to an inert gas atmosphere. A suitable inert environment can be applied, for example, to an inert gas such as Ar gas or N ₂ gas. For example, the sintering environment can be adjusted by introducing an inert gas into the sintering furnace. Further, from the viewpoint of suppressing vapor evaporation of a metal having a high vapor pressure, it is preferable to set the pressure of the ambient gas to atmospheric pressure or to vacuum (that is, a pressure lower than atmospheric pressure).

(ii) Normal Pressure Sintering In the normal pressure sintering, the formed body is placed in a sintering furnace and sintered at normal pressure. Further, in the normal pressure sintering, since no pressure is applied at the time of sintering, sintering is difficult, and therefore, sintering is usually performed at a sintering temperature higher than the hot pressure.

The sintering temperature is not particularly limited as long as it is at least the temperature at which the mixed powder in the molded body is sintered. For example, the sintering temperature can be set to 1450 ° C to 1600 ° C. When the sintering temperature is 1450 ° C or more, sintering is sufficiently performed, and the density of the obtained oxide sintered body can be increased. The sintering temperature is more preferably 1500 ° C or higher, and still more preferably 1550 ° C or higher. In addition, when the sintering temperature is 1600 ° C or lower, grain growth during sintering can be suppressed, and the grain size in the oxide sintered body can be made small. The sintering temperature is more preferably 1580 ° C or lower, further preferably 1550 ° C or lower.

The holding time is not particularly limited as long as the density of the obtained oxide sintered body is sufficiently sintered, and the obtained oxide sintered body has a predetermined density or more. For example, it can be 1 hour to 5 hours. When the holding time is 1 hour or longer, the structure in the obtained oxide sintered body can be made uniform. The holding time is more preferably 2 hours or more, and still more preferably 3 hours or more. In addition, when the holding time is 5 hours or less, grain growth during sintering can be suppressed, and the crystal grain size in the oxide sintered body can be made small. The holding time is more preferably 4 hours or less, further preferably 3 hours or less.

The average temperature increase rate is preferably 100 ° C / hr or less, and since it is difficult to cause abnormal growth of crystal grains, the ratio of coarse crystal grains can be suppressed. Moreover, when it is 100 ° C / hr or less, the relative density of the oxide sintered body after sintering can be improved. The average temperature increase rate is more preferably 90 ° C / hr or less, further preferably 80 ° C / hr or less. The lower limit of the average temperature increase rate is not particularly limited, and is preferably 50° C./hr or more, and more preferably 60° C./hr or more from the viewpoint of productivity.

The sintering environment is preferably an atmosphere or an oxygen-rich environment. It is particularly desirable that the oxygen concentration in the environment is 50% by volume to 100% by volume.

As described above, the oxide sintered body can be produced by the steps (a) to (e).

(Step (f): Processing of Oxide Sintered Body) The obtained oxide sintered body can also be processed into a shape suitable for a sputtering target. The processing method of the oxide sintered body is not particularly limited, and can be processed into a shape corresponding to various uses by a known method.

(Step (g): Welding the oxide sintered body to the bottom plate) As shown in Fig. 1, the processed oxide sintered body 10 is joined to the base plate 20 by the welded material 30. Thereby, the sputtering target 1 is obtained. The material of the bottom plate 20 is not particularly limited, and is preferably pure copper or a copper alloy excellent in thermal conductivity. Various known welding materials having conductivity, for example, an In-based solder material, a Sn-based solder material, or the like can be used for the solder material 30. The joining method is not particularly limited as long as it is a method of joining the bottom plate 20 and the oxide sintered body 10 by the welded material 30 to be used. As an example, the oxide sintered body 10 and the bottom plate 20 are heated to a temperature at which the solder material 30 is dissolved (for example, from about 140 ° C to about 220 ° C). After the molten solder material 30 is applied onto the solder surface 23 of the substrate 20 (the surface of the oxide sintered body 10, that is, the upper surface of the bottom plate 20), the oxide sintered body 10 is placed on the solder surface 23. By cooling the bottom plate 20 in a state in which the oxide sintered body 10 is pressure-bonded, the welded material 30 can be solidified, and the oxide sintered body 10 is fixed to the welded surface 23. [Examples]

In the following, the embodiments of the present invention will be more specifically described by the examples, but the present invention is not limited to the following examples, and may be appropriately modified and implemented within the scope of the gist of the present invention. It is included in the technical scope of the present invention.

<Example 1> (Preparation of sputtering target) In the atomic ratio (atomic %) shown in Table 1, zinc oxide powder (ZnO) having a purity of 99.99% and indium oxide powder having a purity of 99.99% (In ₂ O) were prepared. ₃ ) A gallium oxide powder (Ga ₂ O ₃ ) having a purity of 99.99% and a tin oxide powder (SnO ₂ ) having a purity of 99.99% as a raw material powder. Water and a dispersing agent (ammonium polycarboxylate) were added and mixed and pulverized by a ball mill for 20 hours. In this embodiment, a ball mill using a nylon container and a zirconia ball as a medium is used. Next, the mixed powder obtained in the above step is dried and granulated.

[Table 1] (Table 1)

The mixture was pressed with a metal mold and pressurized at a pressure of 1.0 ton/cm ² , and the obtained mixed powder was formed into a disk-shaped molded body having a diameter of 110 mm × a thickness of 13 mm. The molded body was heated to 500 ° C under a normal pressure and an atmospheric atmosphere, and kept at this temperature for 5 hours to carry out degreasing. The degreased molded body was placed in a graphite mold and hot pressed under the following conditions. At this time, N ₂ gas was introduced into the hot press furnace, and sintering was performed in an N ₂ atmosphere. Maintaining temperature: 920 ° C Holding time: 3 hours until the average temperature of the sintering temperature: 200 ° C / hr Surface pressure: 30 MPa

The obtained oxide sintered body was machined to have a diameter of 100 mm × a thickness of 5 mm to obtain a sintered body for measurement. After the oxide sintered body for measurement and the bottom plate made of Cu were heated to 180° C. for 10 minutes, the lower surface of the oxide sintered body was welded to the upper surface of the base plate using a solder material (indium) to prepare a sputtering target.

<Comparative Example 1> A sputtering target of Comparative Example 1 was produced in the same manner as in Example 1 except that the mixing time was changed to 1 hour.

(Zirconium Amount) Each of the examples and the comparative examples was measured as follows to measure the amount of zirconium of the oxide sintered body. First, the entire upper surface of the oxide sintered body fixed to the bottom plate is subjected to a polishing process of 0.5 mm or more to remove the black skin on the surface. Next, about 5 g of the oxide sintered body was taken out from the upper surface of the oxide sintered body, and quantitative analysis of the amount of zirconium was carried out by ICP analysis. The same measurement was performed 3 times. The average of the three measured values of the amount of zirconium is shown in Table 2.

(Measurement of Relative Density) The relative density of the oxide sintered bodies of the respective Examples and Comparative Examples can be determined by using the porosity measured as described below. The oxide sintered body is cut at an arbitrary position in the thickness direction, and the position of the cut surface is mirror-polished. Next, a photograph was taken at a magnification of 1000 times using a scanning electron microscope (SEM), and the area ratio (%) of the pores in the region of 100 μm square was measured as "porosity (%)". In the same sample, the same porosity measurement was performed on the cut surface of 20 points, and the average value of the porosity obtained by 20 measurements was taken as the average porosity (%) of the sample. The value obtained by [100-average porosity] is referred to as "relative density (%)" in the present specification. The measurement results of the relative density are shown in Table 2.

(Average Grain Size) The "average grain size (μm)" of the oxide sintered bodies of the respective Examples and Comparative Examples was measured as follows. First, at any position of the oxide sintered body, it is cut in the thickness direction, and mirror-polished at any position on the cut surface. Next, a photograph was taken of the tissue of the cut surface at a magnification of 400 times using a scanning electron microscope (SEM). On the photograph taken, a line corresponding to a length of 100 μm is drawn in an arbitrary direction, and the number of crystal grains (N) existing on the straight line is obtained. The value calculated by [100/N] (μm) is taken as the "grain degree on a straight line". Further, 20 straight lines corresponding to a length of 100 μm were formed on the photograph, and the crystal grain size on each straight line was calculated. Further, when a plurality of straight lines are drawn, in order to avoid counting the same crystal grains a plurality of times, a straight line is formed so that the distance between adjacent straight lines becomes at least 20 μm (corresponding to the particle diameter of the coarse crystal grains). In addition, the value calculated by [(the total of the crystal grains on each straight line) / 20] is referred to as "the average grain size of the oxide sintered body". The measurement results of the average grain size are shown in Table 2.

(Fracture at the time of welding) Regarding the oxide sintered bodies of the respective Examples and Comparative Examples, it was investigated whether or not cracking occurred when welded to the base plate by the welded material. After the mechanically sintered oxide sintered body was welded to the bottom plate under the above conditions, it was visually confirmed whether or not cracking occurred on the surface of the oxide sintered body. When a crack having a length of more than 1 mm was observed on the surface of the oxide sintered body, it was judged that "cracking occurred", and when it was not possible to confirm a crack having a length of more than 1 mm, it was judged as "no crack occurred". In each of the examples and the comparative examples, 10 pieces of the sintered oxide body which was machined were prepared, and the operation of welding to the bottom plate was performed 10 times. In the case where one of the oxide sintered bodies is cracked, it is described as "rupture" in Table 2. In the case where all of the 10 pieces have not been broken, they are described as "none" in Table 2.

(Abnormal discharge) The oxide sintered bodies of the respective Examples and Comparative Examples were processed into a shape having a diameter of 100 mm and a thickness of 5 mm, and welded to a base plate to obtain a sputtering target. The sputtering target obtained as described above was mounted on a sputtering apparatus to perform direct-current (DC) magnetron sputtering. The sputtering conditions were a DC sputtering power of 200 W, an Ar-O ₂ environment (Ar/O ₂ = 10% by volume in terms of volume ratio), and a pressure of 1 mTorr. In this case, the number of arc generations per 100 min. was counted, and the case of less than three times was regarded as pass, and is shown as "OK" in Table 2. Further, in Comparative Example 1, the oxide sintered body was broken when welded to the substrate, and thus the sputtering target could not be produced. Therefore, in Comparative Example 1, an experiment regarding abnormal discharge was not performed.

[Table 2] (Table 2)

In Examples 1 to 6 having the composition within the range specified in the embodiment of the present invention and the amount of zirconium, no crack was generated when the oxide sintered body was welded to the substrate. Further, sputtering was performed using the sputtering targets of Examples 1 to 6, and as a result, no abnormal discharge occurred during sputtering, and cracking did not occur in the oxide sintered body during sputtering.

On the other hand, in Comparative Example 1 in which the amount of zirconium was smaller than the lower limit of the range defined in the embodiment of the present invention, when the oxide sintered body was welded to the bottom plate, all of the 10 pieces were cracked.

The disclosed invention includes the following embodiments. Embodiment 1 An oxide sintered body containing 50 ppm to 500 ppm of zirconium, wherein the ratio of zinc, indium, gallium, and tin to the ratio of all metal elements other than oxygen (atomic %) is set to [ When Zn], [In], [Ga], and [Sn], the following formula (1) to formula (3) are satisfied: 35 atomic % ≦ [Zn] ≦ 55 atom% (1) 20 atom% ≦ ([In]+[Ga])≦55 atom%・・・(2) 5 atom%≦[Sn]≦25 atom%・・・(3). [Embodiment 2] The oxide sintered body according to the first aspect, wherein the relative density is 95% or more. The oxide sintered compact according to the first or second aspect, wherein the pores of the oxide sintered body have a maximum circle-equivalent diameter of 3 μm or less. The oxide sintered body according to any one of the first to third aspects, wherein the average circular equivalent diameter (μm) of the pores in the oxide sintered body is relative to the maximum equivalent circle diameter ( The relative ratio of μm) is 0.3 or more and 1.0 or less. The oxide sintered compact according to any one of the first to fourth aspects, wherein the average grain size is 20 μm or less. The oxide sintered compact according to any one of the first to fifth aspects, wherein an area ratio of crystal grains having a crystal grain size of more than 30 μm is 10% or less. The oxide sintered compact according to any one of the first to sixth aspects, wherein the specific resistance is 1 Ω·cm or less. (Embodiment 8) A sputtering target which is obtained by fixing the oxide sintered body according to any one of Embodiments 1 to 7 to a bottom plate by a welding material. Embodiment 9: A method for producing an oxide sintered body, which is a method for producing the oxide sintered body according to any one of Embodiments 1 to 7, comprising the steps of: preparing to contain zinc oxide in a predetermined ratio And a step of sintering the mixed powder into a predetermined shape by a step of mixing a powder of indium oxide, gallium oxide, tin oxide, and zirconium oxide. Embodiment 10: The manufacturing method according to Embodiment 9, wherein the step of preparing the mixed powder comprises containing zinc oxide, indium oxide, gallium oxide by using a ball mill or a bead mill using a medium containing zirconia. And a step of mixing the raw material powder of tin oxide. Embodiment 11: The manufacturing method according to Embodiment 9, wherein the step of preparing the mixed powder comprises: using a ball mill or a bead mill, a raw material containing zinc oxide, indium oxide, gallium oxide, tin oxide, and zirconium oxide. The step of mixing the powder. The manufacturing method according to any one of Embodiments 9 to 11, wherein the step of sintering is performed by applying 10 MPa to 39 MPa to the mixed powder by a forming die. In the state of the surface pressure, the sintering temperature is maintained at 900 ° C to 1200 ° C for 1 hour to 12 hours. The production method according to the twelfth aspect, wherein in the step of sintering, the average temperature increase rate up to the sintering temperature is 600 ° C / hr or less. The production method according to any one of Embodiments 9 to 11, further comprising, after the step of preparing the mixed powder, before the step of sintering, pre-forming the mixed powder In the step of sintering, the step of holding the preformed molded body under normal pressure at a sintering temperature of 1,450 ° C to 1,600 ° C for 1 hour to 5 hours is included. The production method according to the fourteenth aspect, wherein in the step of sintering, the average temperature increase rate up to the sintering temperature is 100 ° C / hr or less. Embodiment 16: A method of producing a sputtering target, comprising: the oxide sintered body according to any one of Embodiments 1 to 7 or by Embodiment 9 to Embodiment The step of bonding the oxide sintered body produced by the production method according to any one of the above 15 to the substrate.

Japanese Patent Application No. Hei. No. 2016-80333, filed on Apr. 13, 2016, and Japanese Patent Application No. Hei. Number is the priority of the application. Japanese Patent Application No. 2016-80333 and Japanese Patent Application No. 2017-7848 are incorporated herein by reference.

1‧‧‧Splating target
10‧‧‧Oxide sintered body
20‧‧‧floor
23‧‧‧welding surface
30‧‧‧welding materials

Fig. 1 is a schematic cross-sectional view showing a sputtering target according to an embodiment of the present invention. 2 is a secondary electron image of an oxide sintered body.

1‧‧‧Splating target

10‧‧‧Oxide sintered body

20‧‧‧floor

23‧‧‧welding surface

30‧‧‧welding materials

Claims (16)

An oxide sintered body containing 50 ppm to 500 ppm of zirconium, and the ratio (atomic %) of zinc, indium, gallium, and tin to all metal elements other than oxygen is set to [Zn], respectively. In the case of In], [Ga], and [Sn], the following formula (1) to formula (3) are satisfied: 35 atomic % ≦ [Zn] ≦ 55 atomic % (1) 20 atomic % ≦ ([In] +[Ga])≦55 atom%・・・(2) 5 atom%≦[Sn]≦25 atom%・・・(3). The oxide sintered body according to claim 1, wherein the relative density is 95% or more. The oxide sintered body according to claim 1, wherein the oxide sintered body has a maximum circle-equivalent diameter of pores of 3 μm or less. The oxide sintered body according to the first aspect of the invention, wherein the relative ratio of the average equivalent circle diameter (μm) of the pores in the oxide sintered body to the maximum equivalent circle diameter (μm) is 0.3 or more, 1.0 or less. The oxide sintered body according to claim 1, wherein the average grain size is 20 μm or less. The oxide sintered compact according to any one of the first to fifth aspects of the present invention, wherein an area ratio of crystal grains having a crystal grain size of more than 30 μm is 10% or less. The oxide sintered body according to the first aspect of the invention, wherein the specific resistance is 1 Ω·cm or less. A sputtering target which is obtained by fixing an oxide sintered body according to claim 1 to a base plate by a welding material. A method for producing an oxide sintered body, which is a method for producing an oxide sintered body according to claim 1, which comprises the steps of: preparing zinc oxide, indium oxide, gallium oxide, tin oxide in a predetermined ratio And a step of mixing the powder of zirconia, the step of sintering the mixed powder into a predetermined shape. The method for producing an oxide sintered body according to claim 9, wherein the step of preparing the mixed powder comprises containing zinc oxide and oxidizing by using a ball mill or a bead mill using a medium containing zirconia. A step of mixing raw material powders of indium, gallium oxide and tin oxide. The method for producing an oxide sintered body according to claim 9, wherein the step of preparing the mixed powder comprises containing zinc oxide, indium oxide, gallium oxide, tin oxide, and the like by a ball mill or a bead mill. The step of mixing the raw material powder of zirconia. The method for producing an oxide sintered body according to any one of the preceding claims, wherein the step of sintering includes applying 10 MPa to the mixed powder by a forming die. In the state of the surface pressure of 39 MPa, the sintering temperature is maintained at 900 ° C to 1200 ° C for 1 hour to 12 hours. The method for producing an oxide sintered body according to claim 12, wherein in the step of sintering, the average temperature increase rate up to the sintering temperature is 600 ° C / hr or less. The method for producing an oxide sintered body according to any one of the items 9 to 11, further comprising, after the step of preparing the mixed powder, before the step of sintering, the mixed powder The step of pre-forming comprises the step of maintaining the preformed shaped body at a normal temperature and a sintering temperature of 1450 ° C to 1600 ° C for 1 hour to 5 hours. The method for producing an oxide sintered body according to claim 14, wherein in the step of sintering, the average temperature increase rate up to the sintering temperature is 100 ° C / hr or less. A method for producing a sputtering target, comprising the use of a solder material, the oxide sintered body according to claim 1 or the manufacture of the oxide sintered body according to claim 9 The oxide sintered body produced by the method is bonded to the substrate.