KR102099197B1 - Oxide sintered bodies and sputtering targets, and methods for manufacturing them - Google Patents

Abstract

It contains 50 to 500 ppm of zirconium, and the ratio (atomic%) of the content of zinc, indium, gallium and tin to all metal elements excluding oxygen, respectively, is [Zn], [In], [Ga] and [Sn] It is said that it is an oxide sintered body satisfying the following formulas (1) to (3).

Description

Oxide sintered bodies and sputtering targets, and methods for manufacturing them

The present disclosure relates to an oxide sintered body and a sputtering target used when forming a thin film transistor (TFT) oxide semiconductor thin film used in a display device such as a liquid crystal display or an organic EL display by a sputtering method. It relates to a manufacturing method.

The amorphous (amorphous) oxide semiconductor thin film used in TFTs has a high carrier mobility, a large optical band gap, and can be formed at a low temperature as compared to general-purpose amorphous silicon (a-Si). Therefore, it is expected to be used in a large-scale, high-resolution, next-generation display requiring high-speed driving, and application to a resin substrate having low heat resistance. As an oxide semiconductor suitable for these applications, an In-containing amorphous oxide semiconductor has been proposed. For example, In-Ga-Zn-based oxide semiconductors are attracting attention.

In forming the oxide semiconductor thin film, a sputtering method of sputtering a sputtering target (hereinafter sometimes referred to as a “target material”) containing a material having the same composition as the thin film is suitably used.

In Patent Document 1, In, Zn and Sn, and group X (Mg, Al, Ga, Si, Sc, Ti, Y, Zr, Hf, Ta, La, Nd, Sm) are obtained as a composite oxide sintered body having good TFT characteristics. A sputtering target comprising a bixbite structured compound represented by In ₂ O ₃ and a spinel structured compound containing at least one element X selected from) is described.

In Patent Document 2, an in-Ga-Zn oxide sintered body capable of stable sputtering, a homologous phase represented by InGaZn _m O _{3 + m} (m is an integer of 0.5 or 1 or more), and a HfO ₂ phase or ZrO ₂ An oxide sintered body having an average particle diameter of 10 µm or less is described.

Japanese Patent Publication No. 2014-111818 Japanese Patent Publication No. 2015-189632

The sputtering target is used in a state in which the oxide sintered body is bonded to the backing plate. In the process of bonding an oxide sintered body to a backing plate, the oxide sintered body may crack.

Efficiency of production of a display device is always required. In addition, in consideration of productivity, manufacturing cost, and the like, the sputtering target used for the production of the oxide semiconductor thin film for display devices and the oxide sintered body of the material are suppressed from cracking of the sputtering target when sputtering, and the oxide sintered body is backed. It is required to suppress cracking of the oxide sintered body when bonding to the plate.

An embodiment of the present invention has been made in view of the above circumstances, and a first object is an In-Ga-Zn-Sn-based oxide sintered body for use in a sputtering target suitable for production of an In-Ga-Zn-Sn-based oxide semiconductor thin film. It is to provide an oxide sintered body that can suppress the occurrence of cracks when bonding to the backing plate.

The 2nd objective of embodiment of this invention is providing the manufacturing method of the oxide sintered body mentioned above.

A third object of the embodiment of the present invention is to provide a sputtering target using the above-described oxide sintered body.

A fourth object of the embodiment of the present invention is to provide a method for producing a sputtering target.

As a result of repeated studies in order to solve the above problems, the inventors found that the above problems can be solved by containing zirconium in a specific range in an oxide sintered body containing oxides of zinc, indium, gallium, and tin, The embodiments of the present invention have been completed.

The first aspect of the present invention is an oxide sintered body,

Contains 50 to 500ppm zirconium,

When the ratio (atomic%) of the content of zinc, indium, gallium and tin to all metal elements excluding oxygen is [Zn], [In], [Ga] and [Sn], respectively, the following formula (1) ) To (3).

It is preferable that the relative density of the oxide sintered body is 95% or more.

It is preferable that the maximum circle equivalent diameter of the pores in the oxide sintered body is 3 µm or less.

It is preferable that the relative ratio of the average circle equivalent diameter to the maximum circle equivalent diameter of the pores in the oxide sintered body is 0.3 or more and 1.0 or less.

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

It is preferable that the oxide sintered body has an area ratio of 10% or less of crystal grains whose crystal grain size exceeds 30 μm.

It is preferable that the oxide sintered body has a specific resistance of 1 Ω · cm or less.

The second aspect of the present invention is a sputtering target,

The oxide sintered body according to the first aspect is made by being fixed on the backing plate with a bonding material.

The third aspect of the present invention is a method for manufacturing the oxide sintered body according to the first aspect,

A process of preparing a mixed powder containing zinc oxide, indium oxide, gallium oxide, tin oxide and zirconium oxide in a predetermined ratio,

And sintering the mixed powder into a predetermined shape.

The process of preparing the mixed powder may include mixing a raw material powder containing zinc oxide, indium oxide, gallium oxide, and tin oxide by a ball mill or bead mill using a medium containing zirconium oxide.

Instead, the step of preparing the mixed powder may include mixing a raw material powder containing zinc oxide, indium oxide, gallium oxide, tin oxide, and zirconium oxide by a ball mill or bead mill.

The sintering process may be hot pressing. That is, in the step of sintering, it may include maintaining the sintering temperature at 900 to 1200 ° C for 1 to 12 hours in a state in which a surface pressure of 10 to 39 MPa is applied to the mixed powder in a mold. In the case of a hot press, it is preferable that the average heating rate up to the sintering temperature is 600 ° C / hr or less.

The sintering step may be atmospheric pressure sintering. In normal pressure sintering, after the step of preparing the mixed powder, and before the step of sintering, a step of preforming the mixed powder is included. In the sintering step, the preformed molded body may include maintaining the sintering temperature at 1450 to 1600 ° C for 1 to 5 hours under normal pressure. In the case of normal pressure sintering, it is preferable that the average temperature increase rate up to the sintering temperature is 100 ° C / hr or less.

The 4th aspect of this invention is a manufacturing method of the sputtering target which concerns on a 2nd aspect, and the oxide sintered body which concerns on 1st aspect or the oxide sintered body produced by the manufacturing method which concerns on 3rd aspect is bonded on a backing plate. And a step of joining with ash.

According to the embodiment of the present invention, it is possible to provide an oxide sintered body capable of suppressing the occurrence of cracking when bonding to a backing plate, a sputtering target using the oxide sintered body, and a method for manufacturing the oxide sintered body and sputtering target .

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

<Oxide sintered body>

First, the oxide sintered body according to the embodiment of the present invention will be described in detail.

The oxide sintered body of the embodiment of the present invention contains oxides of zinc, indium, gallium, and tin. Here, in order to manufacture a sputtering target capable of forming an oxide semiconductor thin film having an excellent TFT characteristic effect, it is necessary to appropriately control the content of metal elements contained in the oxide sintered body used for the sputtering target, respectively.

So, the oxide sintered body of the embodiment of the present invention,

Contains 50 to 500ppm zirconium,

When the ratio (atomic percent) of zinc, indium, gallium and tin content to all metal elements excluding oxygen contained in the oxide sintered body is [Zn], [In], [Ga] and [Sn], respectively , It satisfies the following formulas (1) to (3).

The term "all metal elements except oxygen contained in the oxide sintered body" is zinc, indium, gallium, tin, and zirconium, and may contain metal impurities that are inevitable in production.

Here, since zirconium and unavoidable metal impurities are in trace amounts, the influence in defining the proportion of metal elements in the oxide sintered body is small. Therefore, "all metal elements except 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 in terms of the number of atoms, and the content of zinc relative to the total amount (total number of atoms) is "[Zn]", and the content of indium is "[ In] ", the content of gallium can be replaced by" [Ga] "and the content of tin by" [Sn] ". Then, [Zn] + [In] + [Ga] + [Sn] = 100 atomic%. The content (atomic percent) of each element of zinc, indium, gallium, and tin ([Zn], [In], [Ga], and [Sn]) defined as described above is expressed by the above formulas (1) to (3). To satisfy, the content of each element is controlled.

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

Content rate of zinc: 35 atomic% ≤ [Zn] ≤55 atomic%

Zinc improves the stability of the amorphous structure of the oxide semiconductor thin film. The content rate of zinc is preferably 37 atomic% ≤ [Zn] ≤ 54 atomic%, more preferably 40 atomic% ≤ [Zn] ≤ 53 atomic%.

Indium and gallium content: 20 atomic% ≤ ([In] + [Ga]) ≤55 atomic%

Indium increases the carrier mobility of the oxide semiconductor thin film.

Gallium improves the light stress reliability of the oxide semiconductor thin film, that is, the threshold bias shift.

Indium and gallium are the same group III elements and interact with each other in imparting the above properties. Therefore, in order to properly exhibit the properties of indium and gallium, it is preferable to appropriately control their total amount. The total content of indium and gallium is preferably 25 atomic% ≤ ([In] + [Ga]) ≤54 atomic%, more preferably 30 atomic% ≤ ([In] + [Ga]) ≤53 Atomic%.

Content rate of tin: 5 atomic% ≤ [Sn] ≤25 atomic%

Tin improves the etchant resistance of the oxide semiconductor thin film. The content rate of tin is preferably 7 atomic% ≤ [Sn] ≤ 22 atomic%, more preferably 9 atomic% ≤ [Sn] ≤ 20 atomic%.

In the oxide sintered body of the embodiment of the present invention, the zirconium content is controlled to 50 to 500 ppm from both viewpoints of controlling the physical properties of the oxide sintered body and controlling the physical properties of the oxide semiconductor thin film.

When zirconium is added 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 bonding the oxide sintered body to the backing plate, the oxide sintered body is subjected to stress due to impact or thermal history, but since the strength of the oxide sintered body is improved by including zirconium, cracking of the oxide sintered body can be suppressed.

When the amount of zirconium is 50 ppm or more, the effect of suppressing cracking can be sufficiently exhibited. The amount of zirconium is preferably 60 ppm or more, and more preferably 70 ppm or more.

On the other hand, zirconium exists as zirconium oxide (zirconia) in an oxide sintered body. Since zirconium oxide is an insulator, it may cause abnormal discharge during sputtering. In addition, when a film is formed by using an oxide sintered body containing a large amount of zirconium oxide, carrier properties are deteriorated by zirconium oxide in the resulting 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 carrier characteristics of the oxide semiconductor thin film formed by sputtering can be kept high. The amount of zirconium is preferably 450 ppm or less, and more preferably 400 ppm or less.

Content (zirconium amount) of zirconium in this specification is an average amount of zirconium measured by the following method.

The entire surface of the oxide sintered body is ground by 0.5 mm or more to remove the black skin on the surface. Next, about 5 g of an oxide sintered body is collected, and quantitative analysis is performed by ICP analysis. The same measurement is performed multiple times (for example, 3 times). The average value of the amount of zirconium obtained was determined. In the present specification, unless otherwise specified, the "amount of zirconium" means the average amount of zirconium.

The oxide sintered body contains oxides of zinc, indium, gallium, and tin. Specifically, Zn ₂ SnO ₄ phase, InGaZnO ₄ phase, InGaZn ₂ O ₅ phase, In ₂ O ₃ phase, and SnO ₂ phase are the main constituent phases. In addition, impurities such as oxides which are inevitably mixed or produced during production may be included.

It is preferable that the relative density of the oxide sintered body is 95% or more. Thereby, the strength of the oxide sintered body increases, and cracking of the oxide sintered body when bonding to the backing 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 is calculated | required as follows.

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

2 shows an example of a secondary electron phase (magnification of 1000 times) of the oxide sintered body. In Fig. 2, the black dotted portion is pores. The pores can be easily distinguished from other metal structures in any of the SEM photograph and the secondary electron image.

As for the pores in the oxide sintered body, not only the porosity is low, but the smaller pore size is preferable.

When the molded body containing pores is sintered, small pores disappear by sintering, but large pores do not disappear and remain inside the oxide sintered body. In the pores in the oxide sintered body, the gas is present in a compressed state. In addition, Sn, Ga, etc. in the molded body may be decomposed during sintering, and pores may be generated inside the oxide sintered body. Compressed gas may also exist inside the pores generated as described above. In the oxide sintered body, when pores containing compressed gas are present, the internal stress increases, and the mechanical strength and thermal shock resistance of the oxide sintered body decrease.

The crack of the oxide sintered body resulting from the pore tends to increase as the pore size increases. Therefore, the mechanical strength of the oxide sintered body is improved by suppressing the size of pores in the oxide sintered body to be small, and cracking of the oxide sintered body can be suppressed. By setting the maximum circle equivalent diameter D _max of the pores to 3 µm or less, the internal stress can be sufficiently low. It is more preferable that the maximum equivalent circle diameter of porosity is 2 µm or less.

Further, it is preferable that the relative ratio of the average circle equivalent diameter D _ave (µm) to the maximum circle equivalent diameter D _max (µm) of the pores in the oxide sintered body is 0.3 or more and 1.0 or less (ie, 0.3 ≤ D _ave / D _max ≤ 1.0). . When the relative ratio is 1.0, it is circular, and the smaller the relative ratio, the more flat the oval.

When the shape of the pore is elliptical, mechanical strength is lowered compared to the circular shape, and the oxide sintered body tends to crack. In particular, the more flat the ellipse, the more pronounced the tendency. Therefore, the strength of the oxide sintered compact can be increased by setting the relative ratio to 0.3 or more. It is more preferable that the relative ratio is 0.5 or more.

The maximum circle equivalent diameter and average circle equivalent diameter of pores in this specification are calculated as follows.

The oxide sintered body prepared as a sample for measurement is cut at an arbitrary position in the thickness direction, and the arbitrary position of the cut surface is mirror-polished. Next, a photograph was taken at an appropriate magnification (for example, 1000 times magnification) using a scanning electron microscope (SEM), and a circle equivalent diameter of all pores present in a square region having one side of 100 µm was determined. In the same sample, the circle equivalent diameters of all pores were similarly obtained from 20 cut surfaces. Of all the circle equivalent diameters obtained in 20 measurements, the largest circle equivalent diameter is referred to as the "maximum circle equivalent diameter of the pores" of the oxide sintered body, and the average value of all circle equivalent diameters is the "average circle of pores of the oxide sintered body." Equivalent diameter ”.

When the crystal grain of the oxide sintered body is refined, the effect of suppressing the crack of the oxide sintered body when bonding to the backing plate can be enhanced. The average grain size of the crystal grains is preferably 20 µm or less, whereby the crack suppression effect of the oxide sintered body can be further improved. The average crystal grain size is more preferably 17 μm or less, and even more preferably 15 μm or less.

On the other hand, the lower limit of the average crystal grain size is not particularly limited, but from the balance of miniaturization of the average crystal grain size and production cost, the preferred lower limit of the average crystal grain size is about 0.05 µm.

The average crystal grain size of the crystal grains is measured as follows.

The oxide sintered body prepared as a sample for measurement is cut at an arbitrary position in the thickness direction, and the arbitrary position of the cut surface is mirror-polished. Next, the tissue on the cut surface is photographed at an appropriate magnification (for example, 400 times magnification) using a scanning electron microscope (SEM). On the photographed photograph, in a certain direction, a straight line having a length corresponding to 100 µm in length (that is, "equivalent to 100 µm in length") is drawn as an actual value, and the number N of crystal grains present on the straight line is determined. The value calculated by [100 / N] (µm) is defined as the “crystal grain size on a straight line”. In addition, 20 straight lines corresponding to the actual length of 100 µm are created on the photograph, and crystal grain sizes on each straight line are calculated. And the value calculated by [(the sum of the crystal grain sizes on each straight line) / 20] was referred to as "the average crystal grain size of the oxide sintered body" in this specification.

In addition to controlling the average grain size of the crystal grains of the oxide sintered body, it is more preferable to appropriately control the particle size distribution. Particularly, coarse crystal grains having a grain size of more than 30 µm are the cause of cracking of the oxide sintered body at the time of bonding. The coarse crystal grains having a crystal grain size of more than 30 µm are preferably 10% or less, more preferably 8% or less, more preferably 6% or less, still more preferably 4% or less, most preferably in an area ratio. Is 0%.

The area ratio of the crystal grains whose crystal grain diameter exceeds 30 µm is measured as follows.

In the measurement of the "average crystal grain size of the crystal grain" described above, when a straight line corresponding to a length of 100 µm is drawn, a crystal grain whose length cut by the straight line becomes 30 µm or more is referred to as "coarse particles". On a straight line having a length of 100 µm, the length occupied by the coarse particles (that is, the length of the portion of the straight line crossing the coarse particles) is called L (µm). The value obtained by dividing L (µm) by 100 (µm) was referred to as the ratio R (%) of coarse particles on the straight line.

R (%) = (L (µm) / 100 (µm)) × 100 (%)

In addition, when there are a plurality of coarse particles on a straight line having a length of 100 µm, the sum of the lengths of the portions crossing each coarse particle is referred to as L (µm), and the ratio R (%) of the coarse particles is determined.

In each of the 20 straight lines drawn in the measurement of the average grain size of the crystal grains, the ratio R (%) of the coarse particles was determined, and the average value was taken as the ratio of the coarse particles in the sintered body.

Resistivity of the oxide sintered body is preferably 1Ω and ㎝, more preferably at most 10 ^-1 Ω and ㎝ or less, more preferably 10 ^{- 2} Ω and ㎝ below. As described later, the oxide sintered body is fixed to the backing plate to form a sputtering target. When using this sputtering target, by suppressing the specific resistance of the oxide sintered body low, abnormal discharge during sputtering can be suppressed, and furthermore, cracking of the oxide sintered body caused by the abnormal discharge can be suppressed. Thereby, the film formation cost of the oxide semiconductor thin film using a sputtering target can be suppressed. In addition, since defects in film formation due to abnormal discharge during sputtering can be suppressed, an oxide semiconductor thin film having uniform and good properties can be produced.

For example, in a production line for manufacturing a display device, by manufacturing an oxide semiconductor thin film of a TFT using a sputtering target, the manufacturing cost of the TFT, and furthermore, the manufacturing cost of the display device can be suppressed. Further, an oxide semiconductor thin film showing good TFT characteristics can be formed, and a high-performance display device can be manufactured.

The specific resistance of the oxide sintered body was measured by a four-probe method. Specifically, the specific resistance of the oxide sintered body can be measured using a known specific resistance meter (for example, Mitsubishi Chemical Corporation Lloresta GP, etc.). In addition, the specific resistance of this specification points out what was obtained by measuring the distance between each terminal as 1.5 mm. The specific resistance was measured multiple times (for example, 4 times) at different places, and the average value was used as the specific resistance of the oxide sintered body.

<Sputtering target>

Next, a sputtering target using an oxide sintered body will be described.

1 is a schematic cross-sectional view of the sputtering target 1. The sputtering target 1 includes a backing plate 20 and an oxide sintered body 10 fixed with a bonding material 30 on the backing plate 20.

An oxide sintered body according to an embodiment of the present invention is used for the oxide sintered body 10. Therefore, when bonding with the bonding material 30 to the backing plate 20, the oxide sintered body is hard to crack, and the sputtering target 1 can be manufactured with good yield.

<Manufacturing method>

Next, a method of manufacturing the oxide sintered body and the sputtering target of the embodiment of the present invention will be described.

The oxide sintered body of the embodiment of the present invention is 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 is obtained by fixing the obtained oxide sintered body on a backing plate.

More specifically, the oxide sintered body is produced by the following steps (a) to (e). The sputtering target is produced by the following steps (f) and (g).

Step (a): The powder of the oxide is mixed and pulverized.

Step (b): The obtained mixed powder is dried and granulated.

Step (c): pre-molding the assembled powder mixture

Step (d): degrease the preformed molded body

Step (e): sintering the degreased molded body to obtain an oxide sintered body

Process (f): The obtained oxide sintered body is processed

Process (g): The processed oxide sintered body is bonded to a backing plate to obtain a sputtering target.

In the embodiment of the present invention, in the step (a), the mixed powder is controlled to contain an appropriate amount of zirconium oxide. In addition, in step (e), the sintering conditions are controlled so that the oxide sintered body has a density higher than a predetermined density. In addition, in step (e), sintering conditions are preferably controlled so that the crystal grain size falls within a desirable range. Steps (b) to (d), (f), and (g) are not particularly limited as long as an oxide sintered body and a sputtering target can be produced, and steps commonly used in the production of oxide sintered bodies and sputtering targets can be appropriately applied. You can. Hereinafter, each process will be described in detail, but it is not intended to limit the embodiments of the present invention to these processes.

(Process (a): Powder of oxide is mixed and pulverized)

Zinc oxide, indium oxide powder, gallium oxide powder and tin oxide powder are blended in a predetermined ratio, mixed and pulverized. The purity of each raw material powder used is preferably about 99.99% or more, respectively. This is because the presence of a trace amount of impurity elements may impair the semiconductor properties of the oxide semiconductor thin film.

The "predetermined ratio" of each raw material powder is less than the ratio of the content of zinc, indium, gallium and tin to all metal elements (zinc, indium, gallium and tin) excluding oxygen contained in the oxide sintered body obtained after sintering. It is a ratio within the range of equations (1) to (3).

Usually, the content of zinc, indium, gallium, and tin content for all metal elements excluding oxygen contained in the mixed powder after mixing each raw material powder (zinc oxide, indium oxide powder, gallium oxide powder, and tin oxide powder) Each raw material powder may be compounded so that the ratio is within the range of the above formulas (1) to (3).

It is preferable to use a ball mill or bead mill for mixing and grinding. The mixed powder can be obtained by injecting the raw material powder and water into a mill and crushing and mixing the raw material powder. At this time, for the purpose of uniformly mixing the raw material powder, a dispersing material may be added and mixed, or a binder may be added and mixed to facilitate forming a molded body later.

As a ball mill or beads used in a ball mill and a bead mill (these are referred to as "media"), one containing zirconium oxide is used. When mixing and pulverizing, the surface of the media wears, so that trace amounts of zirconium oxide can be added to the mixed powder. In this method, the amount of wear of the media (ie, the amount of zirconium oxide added) increases as the mixing time increases. Therefore, by adjusting the mixing time, the amount of zirconium oxide added to the mixed powder can be adjusted with relatively high precision.

As the media used in the ball mill and bead mill, a nylon or alumina-made one may be used. In this case, zirconium oxide powder is added as a raw material powder so that a predetermined amount of zirconium oxide is included in the mixed powder. In this case, regardless of the mixing time, since a mixed powder containing a predetermined zirconium oxide can be obtained, the mixing time can be set arbitrarily.

For the pod used for the ball mill and the beads mill, nylon pod, alumina pod, and zirconia pod can be used.

Further, a zirconium oxide powder may be added as a raw material powder, and a zirconium oxide material may be used as the medium. In this case, part of the desired amount of zirconium oxide is added as a raw material powder, and the rest is added by abrasion of the media.

The mixing time by the ball mill or bead mill is preferably 3 hours or more, more preferably 10 hours or more, and even more preferably 20 hours or more.

(Process (b): dry powder is assembled)

It is preferable that the mixed powder obtained in step (a) is dried by, for example, a spray dryer or the like to granulate.

(Process (c): Pre-molding the assembled powder mixture)

It is preferable to preform into a predetermined shape by filling the mixed powder after granulation into a mold having a predetermined size and applying a predetermined pressure (for example, about 49 MPa to about 98 MPa) with a mold press.

When the sintering in the step (e) is performed by hot pressing, the step (c) may be omitted, and a dense oxide sintered body can be produced by loading and sintering the mixed powder in a sintering die. In addition, in order to facilitate handling, after preforming in step (c), the molded body may be placed in a mold for sintering and hot pressed.

On the other hand, when sintering in step (e) is performed by atmospheric pressure sintering, a dense oxide sintered body can be produced by preforming in step (c).

(Step (d): Degrease the preformed molded body)

In the step (a), when a dispersant and / or a binder is added to the mixed powder, it is preferable to heat the molded body to remove (ie degrease) the dispersant and the binder in the molded body. The heating condition (heating temperature and holding time) is not particularly limited as long as it is a temperature and time at which the dispersant and the binder can be removed. For example, the molded body is kept in the atmosphere at a heating temperature of about 500 ° C for about 5 hours.

In the step (a), when the dispersant and the binder are not used, the step (d) may be omitted.

When the step (c) is omitted, that is, in the case of sintering by hot pressing in the step (e), and the molded body is not formed, the mixed powder is heated to remove the dispersant and binder in the mixed powder (degreasing). You may do it.

(Step (e): sintering the molded 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 a sintering method, both hot press and normal pressure sintering can be used. The sintering conditions and the like will be described below for each of hot pressing and normal pressure sintering.

(i) hot press

In a hot press, the molded body is placed in a sintering furnace in a state in which it is placed in a sintering mold, and sintering is performed in a pressurized state. By sintering the molded body while applying pressure to the molded body, a dense oxide sintered body can be obtained while suppressing the sintering temperature relatively low.

In a hot press, a molding mold for sintering for pressing the molded body is used. As a sintering mold, both a metal mold (mold) and a graphite mold (graphite) can be used depending on the sintering temperature. In particular, a graphite type having excellent heat resistance is preferable, and can withstand high temperatures of 900 ° C or higher.

The pressure applied to the molding die is not particularly limited, but a surface pressure (pressurizing pressure) of 10 to 39 MPa is preferable. If the pressure is too high, there is a possibility that the graphite type for sintering is broken, and a large press equipment is also required. Moreover, when it exceeds 39 kPa, since the effect of accelerating densification of the sintered body is saturated, there is little benefit to pressurize at more pressure. On the other hand, when the pressure is less than 10 kPa, the densification of the sintered body is difficult to proceed sufficiently. More preferable pressurization conditions are 10 to 30 MPa.

The sintering temperature is set to be at least the temperature at which sintering of the mixed powder in the molded body proceeds, and for example, if it is sintering under a pressure of 10 to 39 MPa, the sintering temperature is preferably 900 to 1200 ° C.

When the sintering temperature is 900 ° C or higher, sintering proceeds sufficiently, and the density of the resulting oxide sintered body can be increased. The sintering temperature is more preferably 920 ° C or higher, and still more preferably 940 ° C or higher. Moreover, when the sintering temperature is 1200 ° C or less, grain growth during sintering is suppressed, and the crystal grain size in the oxide sintered body can be reduced. The sintering temperature is more preferably 1100 ° C or lower, and still more preferably 1000 ° C or lower.

The time to hold at the predetermined sintering temperature (retention time) is a time during which the sintering of the mixed powder proceeds sufficiently and the density of the obtained oxide sintered body becomes greater than or equal to the predetermined density. For example, if the sintering temperature is 900 to 1200 ° C, the holding time is preferably 1 to 12 hours.

When the holding time is 1 hour or more, 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, if the holding time is 12 hours or less, grain growth during sintering can be suppressed, and the crystal grain size in the oxide sintered body can be reduced. The holding time is more preferably 10 hours or less, and still more preferably 8 hours or less.

The average heating rate up to the sintering temperature can affect the size of the crystal grains in the oxide sintered body and the relative density of the oxide sintered body. The average heating rate is preferably 600 ° C./hr or less, and since abnormal growth of crystal grains is unlikely to occur, the proportion of coarse grains can be suppressed. Moreover, when it is 600 degrees C / hr or less, the relative density of the oxide sintered body after sintering can be made high. The average heating rate is more preferably 400 ° C / hr or less, and even more preferably 300 ° C / hr or less.

Although the lower limit of the average heating rate is not particularly limited, from the viewpoint of productivity, it is preferably 50 ° C / hr or more, and more preferably 100 ° C / hr or more.

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

(ii) atmospheric pressure sintering

In normal pressure sintering, the molded body is placed in a sintering furnace and sintered at normal pressure. In addition, in normal pressure sintering, since sintering is difficult to proceed because pressure is not applied during sintering, it is usually sintered at a sintering temperature higher than that of a hot press.

The sintering temperature is not particularly limited as long as the sintering of the mixed powder in the molded body proceeds, and for example, the sintering temperature can be 1450 to 1600 ° C.

When the sintering temperature is 1450 ° C or higher, sintering proceeds sufficiently, and the density of the resulting oxide sintered body can be increased. The sintering temperature is more preferably 1500 ° C or higher, and still more preferably 1550 ° C or higher. Moreover, when the sintering temperature is 1600 ° C or less, grain growth during sintering can be suppressed, and the crystal grain size in the oxide sintered body can be reduced. The sintering temperature is more preferably 1580 ° C or lower, and still more preferably 1550 ° C or lower.

The holding time is not particularly limited as long as the sintering of the mixed powder proceeds sufficiently and the density of the obtained oxide sintered body becomes equal to or higher than a predetermined density, and can be, for example, 1 to 5 hours.

When the holding time is 1 hour or more, 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 reduced. The holding time is more preferably 4 hours or less, and still more preferably 3 hours or less.

The average heating rate is preferably 100 ° C./hr or less, and since abnormal growth of crystal grains is unlikely to occur, the proportion of coarse grains can be suppressed. Moreover, if it is 100 degrees C / hr or less, the relative density of the oxide sintered body after sintering can be made high. The average heating rate is more preferably 90 ° C / hr or less, and even more preferably 80 ° C / hr or less.

Although the lower limit of the average heating rate is not particularly limited, from the viewpoint of productivity, it is preferably 50 ° C / hr or more, and more preferably 60 ° C / hr or more.

The sintering atmosphere is preferably an atmosphere or an oxygen-rich atmosphere. In particular, it is preferable that the oxygen concentration in the atmosphere is 50 to 100% by volume.

In this way, the oxide sintered body can be produced by steps (a) to (e).

(Process (f): Process the oxide sintered body)

The obtained oxide sintered body may be processed into a shape suitable for a sputtering target. The method for processing the oxide sintered body is not particularly limited, and may be processed into a shape according to various uses by a known method.

(Process (g): Bonding the oxide sintered body to the backing plate)

As shown in Fig. 1, the processed oxide sintered body 10 is bonded to the backing plate 20 by a bonding material 30. Thereby, the sputtering target 1 is obtained. The material of the backing plate 20 is not particularly limited, but pure copper or copper alloy having excellent thermal conductivity is preferred. As the bonding material 30, various known bonding materials having conductivity can be used, and for example, In-based solder materials, Sn-based solder materials, and the like are suitable. The bonding method is not particularly limited as long as the backing plate 20 and the oxide sintered body 10 are joined by the bonding material 30 used. As an example, the oxide sintered body 10 and the backing plate 20 are heated to a temperature at which the bonding material 30 is dissolved (for example, about 140 ° C to about 220 ° C). After the molten bonding material 30 is applied to the bonding surface 23 of the backing plate 20 (the surface where the oxide sintered body 10 is fixed, that is, the upper surface of the backing plate 20), the bonding surface 23 is applied. The oxide sintered body 10 is loaded. By cooling in a state where the backing plate 20 and the oxide sintered body 10 are compressed, the bonding material 30 is solidified, and the oxide sintered body 10 is fixed on the bonding surface 23.

Example

Hereinafter, the embodiment of the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples, and can be carried out by appropriately changing it within a range suitable for the gist of the present invention. , All of them are included in the technical scope of the present invention.

<Example 1>

(Production of sputtering target)

99.99% purity zinc oxide powder (ZnO), 99.99% purity indium oxide powder (In ₂ O ₃ ), 99.99% purity gallium oxide powder (Ga ₂ O ₃ ), 99.99% purity tin oxide powder (SnO ₂ ) Was blended at an atomic ratio (atomic%) shown in Table 1 to prepare a raw material powder. Water and a dispersant (ammonium carboxylate) were added, mixed and crushed in a ball mill for 20 hours. In this example, a nylon pod and a ball mill using zirconia balls as media were used. Next, the mixed powder obtained in the above step was dried to granulate.

The obtained mixed powder was pressurized at a pressure of 1.0 ton / cm 2 using a mold press to prepare a disk-shaped molded body having a diameter of 110 mm and a thickness of 13 mm. The molded body was heated to 500 ° C under normal pressure and atmospheric atmosphere, and held at that temperature for 5 hours to degrease. The molded body after degreasing was set in a graphite mold, and hot pressing was performed under the following conditions. At this time, N ₂ gas was introduced into the hot press furnace and sintered under an N ₂ atmosphere.

Holding temperature: 920 ℃

Holding time: 3 hours

Average heating rate up to sintering temperature: 200 ℃ / hr

Surface pressure: 30㎫

The obtained oxide sintered body was machined and finished to a diameter of 100 mm x a thickness of 5 mm to obtain an oxide sintered body for measurement. After heating the oxide sintered body for measurement and the backing plate made of Cu to 180 ° C. over 10 minutes, the lower surface of the oxide sintered body was bonded to the upper surface of the backing plate using a bonding material (indium) to produce a sputtering target.

<Comparative Example 1>

The 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)

For each of the examples and comparative examples, the amount of zirconium in the oxide sintered body was measured as follows. First, the entire upper surface of the oxide sintered body fixed to the backing plate was ground by 0.5 mm or more to remove the black skin on the surface. Next, about 5 g of the oxide sintered body was scraped off from the top surface of the oxide sintered body, and quantitative analysis of the amount of zirconium was performed by an ICP analysis method. The same measurement was performed 3 times. Table 2 shows the average values of the three measured amounts of zirconium.

(Measurement of relative density)

The relative density of the oxide sintered body of each Example and Comparative Example was calculated | required using the porosity measured as follows.

The oxide sintered body was cut in a thickness direction at an arbitrary position, and an arbitrary position of the cut surface was mirror polished. Next, a photograph was taken at a magnification of 1000 times using a scanning electron microscope (SEM), and the area ratio (%) of pores in a square region having one side of 100 µm was measured and referred to as "porosity (%)". The same porosity was measured on 20 cut surfaces in the same sample, and the average porosity obtained in 20 measurements was referred to as the average porosity (%) of the sample. The value obtained by [100-average porosity] was referred to as "relative density (%)" in this specification. Table 2 shows the measurement results of the relative density.

(Average crystal grain size)

The "average crystal grain size (µm)" of the oxide sintered body of each Example and Comparative Example was measured as follows. First, the oxide sintered body was cut in a thickness direction at an arbitrary position, and an arbitrary position of the cut surface was mirror polished. Next, the tissue on the cut surface was photographed at a magnification of 400 times using a scanning electron microscope (SEM). On a photographed photograph, a straight line having a length of 100 µm was drawn in an arbitrary direction, and the number (N) of crystal grains present on the straight line was determined. The value calculated by [100 / N] (µm) was referred to as the “crystal grain size on a straight line”. In addition, 20 straight lines having a length of 100 µm were formed on the photograph, and crystal grain sizes on each straight line were calculated. In addition, when drawing a plurality of straight lines, in order to avoid counting the same grains multiple times, a straight line was drawn so that the distance between adjacent straight lines was at least 20 µm (equivalent to the grain size of coarse grains).

In addition, the value calculated by [(the sum of the crystal grain sizes on each straight line) / 20] was referred to as "average crystal grain size of the oxide sintered body". Table 2 shows the measurement results of the average crystal grain size.

(Cracking when bonding)

For the oxide sintered body of each of Examples and Comparative Examples, it was investigated whether cracking occurred when bonding the bonding material to the backing plate.

After bonding the machined oxide sintered body to the backing plate under the above-described conditions, it was visually confirmed whether cracks did not occur on the surface of the oxide sintered body. When a crack exceeding 1 mm in length was found on the surface of the oxide sintered body, it was judged that "crack occurred", and when a crack exceeding 1 mm in length could not be confirmed, "crack did not occur" was determined. .

For each of the Examples and Comparative Examples, 10 sheets of machined oxide sintered bodies were prepared, and the operation of bonding to the backing plate was performed 10 times. When a crack occurred even in one oxide sintered body, it was described as "crack" in Table 2. When cracks did not occur in all 10 sheets, Table 2 described "no".

(Abnormal discharge)

The oxide sintered bodies of Examples and Comparative Examples were processed into a shape having a diameter of 100 mm and a thickness of 5 mm, and bonded to a backing plate to obtain a sputtering target. The sputtering target thus obtained was installed in a sputtering apparatus, and DC (direct current) magnetron sputtering was performed. The conditions of sputtering were DC sputtering power of 200 W, Ar-O ₂ atmosphere (Ar / O ₂ = 10% by volume by volume ratio), and pressure of 1 mTorr. At this time, the number of occurrences of arcing per 100 min. Is counted, and the case of less than 3 times is referred to as a pass, and Table 2 lists "OK".

In addition, in Comparative Example 1, the sputtering target could not be produced because the oxide sintered body cracked when bonding to the backing plate. Therefore, in the comparative example 1, the experiment about abnormal discharge was not performed.

In Examples 1 to 6 having a composition within the range specified in the embodiments of the present invention and a zirconia amount, cracking did not occur when the oxide sintered body was bonded to the backing plate. In addition, as a result of sputtering using the sputtering targets of Examples 1 to 6, no abnormal discharge was generated even during sputtering, and no cracks were generated in the oxide sintered body during sputtering.

On the other hand, in Comparative Example 1 in which the amount of zirconia was smaller than the lower limit of the range specified in the embodiment of the present invention, when bonding the oxide sintered body to the backing plate, cracks occurred in all 10 sheets.

The present disclosure includes the following aspects.

Aspect 1:

Contains 50 to 500ppm zirconium,

When the ratio (atomic%) of the content of zinc, indium, gallium and tin to all metal elements excluding oxygen is [Zn], [In], [Ga] and [Sn], respectively, the following formula (1) ) To (3).

Aspect 2:

The oxide sintered body according to embodiment 1, wherein the relative density is 95% or more.

Aspect 3:

The oxide sintered body according to aspect 1 or 2, wherein the maximum circle equivalent diameter of the pores in the oxide sintered body is 3 µm or less.

Aspect 4:

The oxide sintered body according to any one of embodiments 1 to 3, wherein a relative ratio of the average circle equivalent diameter (µm) to the maximum circle equivalent diameter (µm) of the pores in the oxide sintered body is 0.3 or more and 1.0 or less.

Aspect 5:

The oxide sintered body according to any one of embodiments 1 to 4, wherein the average crystal grain size is 20 µm or less.

Aspect 6:

The oxide sintered body according to any one of embodiments 1 to 5, wherein the area ratio of crystal grains having a crystal grain size exceeding 30 µm is 10% or less.

Aspect 7:

The oxide sintered body according to any one of aspects 1 to 6, wherein the specific resistance is 1 Ω · cm or less.

Aspect 8:

A sputtering target comprising the oxide sintered body according to any one of embodiments 1 to 7 fixed on a backing plate with a bonding material.

Aspect 9:

It is the method of manufacturing the oxide sintered body in any one of aspect 1-7,

A process of preparing a mixed powder containing zinc oxide, indium oxide, gallium oxide, tin oxide and zirconium oxide in a predetermined ratio,

Method for producing an oxide sintered body comprising the step of sintering the mixed powder to a predetermined shape.

Aspect 10:

In the step of preparing the mixed powder, in the embodiment 9, the raw material powder containing zinc oxide, indium oxide, gallium oxide and tin oxide is mixed by a ball mill or a bead mill using a medium containing zirconium oxide. The manufacturing method described.

Aspect 11:

The manufacturing method according to Embodiment 9, wherein the step of preparing the mixed powder comprises mixing a raw material powder containing zinc oxide, indium oxide, gallium oxide, tin oxide, and zirconium oxide by a ball mill or a bead mill.

Aspect 12:

In the step of sintering, in the state of applying a surface pressure of 10 to 39 MPa to the mixed powder in a molded form, the preparation according to any one of embodiments 9 to 11, comprising maintaining the sintering temperature at 900 to 1200 ° C for 1 to 12 hours. Way.

Aspect 13:

In the step of sintering, the production method according to aspect 12, wherein the average heating rate up to the sintering temperature is 600 ° C / hr or less.

Aspect 14:

After the step of preparing the mixed powder, and before the step of sintering, further comprising a step of preforming the mixed powder,

In the sintering step, the production method according to any one of Embodiments 9 to 11, comprising maintaining the preformed molded body under normal pressure at a sintering temperature of 1450 to 1600 ° C for 1 to 5 hours.

Aspect 15:

In the step of sintering, the production method according to aspect 14, wherein an average temperature increase rate up to the sintering temperature is 100 ° C / hr or less.

Aspect 16:

A method for producing a sputtering target, comprising the step of bonding the oxide sintered body according to any one of aspects 1 to 7 or the oxide sintered body produced by the manufacturing method according to any one of aspects 9 to 15, with a bonding material on a backing plate.

This application entails a claim of priority based on Japanese Patent Application, Japanese Patent Application No. 2016-80333 whose application date is April 13, 2016, and Japanese Patent Application, Japanese Patent Application No. 2017-7848 which is January 19, 2017. Patent Application Nos. 2016-80333 and 2017-7848 are incorporated herein by reference.

1: Sputtering target
10: oxide sintered body
20: backing plate
30: bonding material

Claims (16)

Contains 50 to 500ppm zirconium,
When the ratio (atomic%) of the content of zinc, indium, gallium and tin to all metal elements excluding oxygen is [Zn], [In], [Ga] and [Sn], respectively, the following formula (1) ) To (3).

According to claim 1,
An oxide sintered body having a relative density of 95% or more. According to claim 1,
An oxide sintered body having a maximum circle equivalent diameter of pores of 3 µm or less in the oxide sintered body. According to claim 1,
An oxide sintered body in which the relative ratio of the average equivalent circle diameter (µm) to the maximum equivalent circle diameter (µm) of the pores in the oxide sintered body is 0.3 or more and 1.0 or less. According to claim 1,
An oxide sintered body having an average crystal grain size of 20 μm or less. The method according to any one of claims 1 to 5,
An oxide sintered body having an area ratio of 10% or less of a crystal grain whose crystal grain size exceeds 30 µm. According to claim 1,
An oxide sintered body having a specific resistance of 1 Ω · cm or less. A sputtering target comprising the oxide sintered body according to claim 1 fixed on a backing plate with a bonding material. A method for producing the oxide sintered body according to claim 1,
A process of preparing a mixed powder containing zinc oxide, indium oxide, gallium oxide, tin oxide and zirconium oxide in a predetermined ratio,
Method for producing an oxide sintered body comprising the step of sintering the mixed powder to a predetermined shape. The method of claim 9,
The process of preparing the mixed powder includes mixing the raw material powder containing zinc oxide, indium oxide, gallium oxide, and tin oxide by a ball mill or bead mill using a medium containing zirconium oxide. The method of claim 9,
The process of preparing the mixed powder includes mixing the raw material powder containing zinc oxide, indium oxide, gallium oxide, tin oxide, and zirconium oxide by a ball mill or a bead mill. The method according to any one of claims 9 to 11,
In the sintering step, a manufacturing method comprising maintaining the sintering temperature at 900 to 1200 ° C for 1 to 12 hours in a state in which a surface pressure of 10 to 39 MPa is applied to the mixed powder in a molding mold. The method of claim 12,
In the sintering step, the average heating rate up to the sintering temperature is 600 ° C / hr or less. The method according to any one of claims 9 to 11,
After the step of preparing the mixed powder, and before the step of sintering, further comprising a step of preforming the mixed powder,
In the sintering step, the production method comprising maintaining the preformed molded body under normal pressure at a sintering temperature of 1450 to 1600 ° C for 1 to 5 hours. The method of claim 14,
In the sintering step, the average heating rate up to the sintering temperature is 100 ° C / hr or less. A method for producing a sputtering target comprising the step of bonding the oxide sintered body according to claim 1 or the oxide sintered body produced by the production method according to claim 9 on a backing plate with a bonding material.

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