WO2017142063A1

WO2017142063A1 - Oxide sintered body and production method for same

Info

Publication number: WO2017142063A1
Application number: PCT/JP2017/005908
Authority: WO
Inventors: 原浩之; 伊藤謙一; 原慎一
Original assignee: 東ソー株式会社
Priority date: 2016-02-18
Filing date: 2017-02-17
Publication date: 2017-08-24
Also published as: TW201800364A; JP6705202B2; JP2017145179A

Abstract

The purpose of the present invention is to inexpensively provide an oxide sintered body which is formed of a niobium oxide and which has high strength, and to provide a production method with which the oxide sintered body can be easily obtained, without employing an HP method, by use of inexpensive equipment. According to the present invention, a compact undergoes firing at a temperature elevation rate of not lower than 400ºC/hour.

Description

Oxide sintered body and manufacturing method thereof

The present invention relates to an oxide sintered body used for a sputtering target for forming a thin film such as a high refractive index film, and a method for producing the same.

In recent years, high refractive index films are being adopted for refractive index adjustment in portable displays and building glass. Sputtering is generally used for the production of high refractive index films, but niobium oxide and titanium oxide used for high refractive index materials have extremely slow film formation speeds, and high productivity is required from the viewpoint of productivity. Film formation is desired. However, niobium oxide, which is a typical high-refractive index material, has a problem that the strength is low when the atmospheric pressure sintering method is used, and the sputtering target breaks when a film is formed under high output. The reason for the low strength of niobium oxide is due to the following two reasons. The first point is that the coefficient of thermal expansion differs in the a-axis, b-axis, and c-axis directions of the crystal orientation. Due to the anisotropy of the thermal expansion coefficient, stress is applied during the production of the sintered body (temperature lowering step), and if the sintered body has a large particle size, microcracks are generated, resulting in a decrease in strength.

Therefore, in Patent Documents 1 and 2, manufacturing is performed by a hot press (HP) method. However, when the HP method is used, a large press mechanism is required for manufacturing a large target, which is not a realistic process. Is small and limited to a simple shape such as a flat plate type, and a complicated shape such as a large area or a cylindrical shape cannot be obtained.

Secondly reason for niobium oxide is low intensity niobium oxide _Nb 2 _{O 5} phase (density 4.542g / cm ³⁾ is likely to be reduced, a reducing atmosphere firing NbO _2-phase (density 5.916g / ^cm 3) It is a point of forming different crystal phases. When different crystal phases are formed, internal stress and microcracks are inherent in the sintered body due to the difference in density, and the strength of the sintered body is reduced. In some cases, cracks are generated.

Therefore, in the hot isostatic pressing (HIP method) described in Patent Documents 3 and 4, since another crystal phase is formed, the strength of the sintered body is reduced, and cracks are generated particularly in a large sintered body. There was a problem that it was easy.

Japanese Unexamined Patent Publication No. 2005-256175 Japanese Laid-Open Patent Publication No. 2004-059965 Japanese Patent Laid-Open No. 2002-338354 Japanese Patent Application Laid-Open No. 2014-194072

An object of the present invention is to provide a high-strength oxide sintered body made of niobium oxide at low cost, and to provide a manufacturing method that can be easily obtained with inexpensive equipment regardless of the HP method. .

As a result of intensive studies on the manufacturing process of a sintered body made of niobium (V) oxide in the stoichiometric composition, the present inventors have obtained a high-strength sintered body using the atmospheric pressure sintering method. As a result, the present invention has been completed.

That is, the present invention resides in the following [1] to [5].
[1] The sintered body density is 95% or more, the sintered body particle size is 5.5 μm or less, niobium (IV) oxide attributed to the NbO ₂ phase does not exist by X-ray diffraction, A niobium oxide sintered body having a strength of 100 MPa or more.
[2] The niobium oxide sintered body according to [1], which has a cylindrical shape.
[3] The niobium oxide sintered body according to [1], wherein the shape is a flat plate and the area between the targets is 1000 cm ² or more.
[4] The method for producing a niobium oxide sintered body according to [1] to [3], wherein firing is performed at a temperature rising rate of 400 ° C./hour or more.
[5] The method for producing a niobium oxide sintered body according to [4], wherein firing is performed using electromagnetic heating.

Hereinafter, the present invention will be described in detail.

The present invention is a sintered body made of niobium oxide, having a sintered body density of 95% or more, a sintered body particle size of 5.5 μm or less, and presence of niobium (IV) oxide by X-ray diffraction. It is an oxide sintered body characterized by not.

The sintered body density of the present invention is characterized by a relative density of 95% or more. When the sintered body density is lower than 95%, the strength decreases. Furthermore, since the frequency of arcing increases when used as a sputtering target, it is preferably 97% or more, more preferably 98% or more.

Further, the particle size of the sintered body of the present invention is 5.5 μm or less. If it exceeds 5.5 μm, stress is applied to the grain boundary due to the anisotropy of the coefficient of thermal expansion of the crystal orientation, and microcracks are generated, so that the strength sharply decreases. In order to stably obtain high strength, the particle size of the sintered body is preferably 5 μm or less, and more preferably 4.5 μm or less.

Furthermore, the crystalline phase of the present invention is characterized by the absence of a niobium (IV) oxide phase in XRD. Niobium oxide (V) (density 4.542 g / cm ³ ) and niobium oxide (IV) (density 5.916 g / cm ³ ) have a large density difference. Internal stresses and microcracks are inherent in the body, and particularly large sintered bodies are easily cracked, making it impossible to produce sintered bodies with good yield. In addition, when such a sintered body is used and high power is applied by sputtering, it is not preferable because cracks are likely to occur during discharge and cause the productivity of the film forming process to be reduced.

The bending strength of the present invention is preferably 100 MPa or more. If the strength of the sintered body is high, cracks are less likely to occur in the grinding process and bonding process, and the yield is high, so the productivity is good. Especially when the shape is cylindrical, depending on the material of the backing tube and the thickness of the solder, a stress of 50-80 MPa is applied in the bonding process, so if the bending strength is less than 100 MPa, the sintered body may crack. High nature. Furthermore, even when high power is applied during sputtering, the problem of cracking is unlikely to occur.

Further, since the oxide sintered body of the present invention does not use the HP method, the area of the target surface can be 500 cm ² or more. The area of the target surface here refers to the area of the surface of the sintered body on the side to be sputtered. In the case of a multi-divided target composed of a plurality of sintered bodies, the area of the surface of the sintered body on the side to be sputtered in each sintered body is the largest and the area of the target surface in the multi-divided target To do. There is no restriction | limiting in particular in the shape of a sintered compact, There is no problem even if either a flat plate shape or a cylindrical shape. In the case of a flat plate-shaped sintered body, those having a target surface area of 1000 cm ² or more can be produced, and those having a surface of 2000 cm ² or more can be produced.

The niobium oxide sintered body of the present invention can be fired using electromagnetic heating.

In the case of external heating such as in an electric furnace, since sintering proceeds from the outer surface of the sintered body, closed pores tend to remain at the center of the sintered body, and in particular, a single composition such as niobium oxide remains. In the case of materials, since sintering between crystal grains is fast and grain growth is easy, it is difficult to obtain a sintered body having a high density and a fine structure.

On the other hand, in the case of self-heating by electromagnetic wave heating, the sintered body itself is heated from the inside, and sintering proceeds uniformly from the center of the sintered body in an open pore state, and the pores are discharged out of the sintered body. Ideal sintering is possible. In addition, since electromagnetic heating is heated by self-heating from the inside of the sintered body itself even if heated rapidly, the temperature distribution is small even in large-sized products, it is difficult to crack during firing, and it is heated uniformly by self-heating. Therefore, it is not necessary to consider the thermal diffusion in the sintered body, the firing time can be shortened, and the grain growth of crystal grains can be suppressed.

However, electromagnetic heating is not applicable to any material and depends on the electromagnetic wave absorption characteristics of the material to be heated. The electromagnetic wave absorption characteristics are better for a material having a large dielectric loss, and a material having a small dielectric loss does not absorb the electromagnetic wave and cannot heat the electromagnetic wave. Although the dielectric loss is determined by each material, the dielectric loss is temperature-dependent, and depending on the material, the electromagnetic wave absorption characteristics vary greatly depending on the temperature, and niobium oxide is one of them. Niobium oxide has an oxygen-deficient structure at a high temperature, and the oxygen vacancy tends to cause vibration, rotation, collision, and friction of the dipole inside the material, and is heated by self-heating. Further, since niobium oxide does not sinter from room temperature to 600 ° C., the above-mentioned formation of closed pores does not occur.

That is, it is possible to perform baking by external heating with a substance that absorbs electromagnetic waves well, such as SiC, and easily self-heats in the range from room temperature to low temperature, and heats at a high temperature by heating by self-heating of niobium oxide. In spite of the sufficient firing temperature necessary for increasing the density, it is possible to obtain a sintered body having a high density and a high strength by suppressing the growth of crystal grains with rapid heating and a short holding time.

As electromagnetic waves used in the present invention, continuous or pulsed microwaves such as 2.45 GHz generated from magnetron or gyrotron, millimeter waves such as 28 GHz, or submillimeter waves can be used. As for the selection of the frequency of the electromagnetic wave, an appropriate one can be selected from the electromagnetic wave absorption characteristics of the object to be fired. However, in consideration of economics such as the cost of the oscillator, a microwave of 2.45 GHz is preferable.

Hereinafter, the manufacturing method of the niobium oxide sintered body of the present invention will be described for each step.

(1) Raw material adjustment process Niobium oxide (V) powder is used as the raw material powder. The purity of the raw material powder is preferably 99.9% or more, more preferably 99.99% or more. If impurities are included, it causes abnormal grain growth in the firing process.

The raw material powder is preferably subjected to compaction, pulverization, and granulation for improving moldability. The consolidation and pulverization are not particularly limited, and examples thereof include dry and wet media stirring mills and mechanical stirring mills using balls and beads such as zirconia, alumina, and nylon resin. Specifically, a ball mill, a bead mill, an attritor, a vibration mill, a planetary mill, a jet mill, a biaxial planetary agitation mixer, and the like can be given. When a wet ball mill, bead mill, attritor, vibration mill, planetary mill, jet mill or the like is used, it is necessary to dry the pulverized slurry. Although this drying method is not specifically limited, For example, filtration drying, fluidized-bed drying, spray drying, etc. can be illustrated and it can granulate simultaneously with drying.

The niobium (V) oxide powder finally obtained preferably has a BET specific surface area of 4 to 15 m ² / g. When the BET specific surface area is less than 4 m ² / g, the density of the sintered body is difficult to increase, and when it exceeds 15 m ² / g, the formability is deteriorated and the handling of the powder becomes difficult due to aggregation or the like. In consideration of moldability, molding aids such as polyvinyl alcohol, acrylic polymer, methylcellulose, waxes, oleic acid and the like may be added to the raw material powder.

(2) Molding process The molding method is not particularly limited, and a molding method capable of molding the raw material powder into a desired shape can be appropriately selected. Examples thereof include a press molding method, a casting molding method, and an injection molding method.

The molding pressure is not particularly limited as long as it does not cause cracks in the molded body and has a strength that can be handled, but it is preferable to increase the molding density as much as possible. Therefore, it is also possible to use a method such as cold isostatic pressing (CIP) molding. CIP pressure is preferably for 1 ton / cm ² or more to obtain a sufficient consolidation effect, more preferably 2 ton / cm ² or more, especially preferably ² ~ 3ton / cm 2.

(3) Firing step Next, the obtained molded body is put into an electromagnetic wave firing furnace and fired. As a firing furnace to be used, various firing furnaces such as a batch type, a continuous type, and a hybrid type with an external heating type can be used.

In the case of firing by electromagnetic waves, the molded body is placed on a setter and surrounded by a heat insulating material. In this case, an isothermal barrier can be installed inside the heat insulating material. The material of the setter and the isothermal barrier may be appropriately selected in consideration of the heat resistance at the firing temperature and the electromagnetic wave absorption characteristics of each material, and examples thereof include alumina, mullite, zirconia, and SiC. As the setter, SiC having good electromagnetic wave absorption at a low temperature is particularly preferable.

There are no particular restrictions on the rate of temperature increase of the object to be fired, but in order to obtain a high-strength sintered body, 400 to 800 ° C./hour, preferably 500 to 800 ° C./hour, more preferably 600 to 800 ° C./hour. And Since firing by electromagnetic waves is heating by self-heating, the temperature distribution in the material to be fired is small, and even when a large-sized fired material is heated at a high temperature increase rate, the occurrence of cracks is very small. In the case of a molded body containing moisture and a binder, the molded body may be cracked if it is accompanied by a rapid volume expansion when the moisture and the binder component are volatilized particularly in a large molded body. For this reason, it is preferable to set the rate of temperature increase to 20 to 100 ° C./hour in a temperature range where moisture and binder components are volatilized, for example, in a temperature range of 100 to 400 ° C.

The firing temperature is 1320 ° C to 1400 ° C. The holding time at the baking temperature is sufficient within one hour, but when the baking temperature is 1370 to 1400 ° C., the holding time is preferably about 10 to 30 minutes. The temperature lowering rate is not particularly limited, and can be appropriately determined in consideration of the capacity of the sintering furnace, the size and shape of the sintered body, the ease of cracking, and the like.

Although the firing atmosphere is not particularly limited, it is preferably an air or oxygen atmosphere. Further, for the purpose of suppressing uneven color on the surface of the sintered body and lowering the specific resistance of the sintered body, it is possible to create a non-oxidizing atmosphere such as nitrogen when the temperature is lowered from the firing temperature.

(4) Targeting process The obtained sintered body is formed into a desired shape such as a plate shape, a circular shape, or a cylindrical shape by using a machining machine such as a surface grinder, a cylindrical grinder, a lathe, a cutting machine, or a machining center. To grind. Furthermore, a sputtering target using the sintered body of the present invention as a target material is obtained by bonding (bonding) a backing plate made of oxygen-free copper, titanium, or the like to the backing tube or backing tube using indium solder or the like as necessary. Can do.

According to the present invention, since a sintered body can be manufactured using a conventionally known atmospheric pressure sintering method, a large target can be manufactured. In the case of a flat plate-type sputtering target, a large-sized sintered body having a target surface area of 1000 cm ² or more can be produced, and a cylindrical sputtering target having a more complicated shape can also be produced.

The niobium oxide sintered body of the present invention has high strength, and when used as a sputtering target, there is no cracking even under high output, and high productivity can be obtained. Furthermore, it is used for large-sized and cylindrical sputtering targets. Is possible.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto. In addition, each measurement in a present Example was performed as follows.
(1) Density of Sintered Body The relative density of the sintered body was determined by measuring the bulk density by the Archimedes method in accordance with JIS R 1634 and dividing by the true density. The true density of the sintered body was 4.542 (g / cm ³ ).
(2) X-ray diffraction test An X-ray diffraction pattern in the range of 2θ = 20 to 70 ° of the mirror-polished sintered sample was measured.
Scanning method: Step scan method (FT method)
X-ray source: CuKα
Power: 40kV, 40mA
Step width: 0.01 °
(3) Sintered body particle size The sintered body sample which was mirror-polished and thermally etched was observed with a scanning electron microscope, and the sintered body particle diameter was measured by the diameter method from the obtained sintered body structure image. At least three arbitrary points were observed, and 300 or more particles were measured.
(Thermal etching conditions)
Temperature: 900 ° C
Time: 30 minutes (observation conditions of scanning electron microscope)
Acceleration voltage: 10 kV
(4) Folding strength Measured according to JIS R 1601.
(Measurement conditions of bending strength)
Test method: 3-point bending test fulcrum distance: 30 mm
Sample size: 3 x 4 x 40 mm
Head speed: 0.5 mm / min.

(Example 1)
A niobium (V) oxide powder having a BET specific surface area of 7.56 m ² / g was subjected to cold isostatic pressing (CIP) molding at a pressure of 3 ton / cm ² to prepare a molded body of about 390 mm × 770 mm × 12 mmt.

Next, this molded body was placed on an alumina setter in a microwave firing furnace (frequency = 2.45 GHz), sandwiched between SiC plates, and fired under the following conditions to obtain a sintered body.
(Baking conditions)
Firing furnace: Microwave furnace Heating rate: 600 ° C / hour Heating atmosphere: air atmosphere Firing temperature: 1350 ° C
Firing time: 30 minutes A sintered body having a size of 323 mm × 637 mm × 10 mmt (2057 cm ² ) without microcracks was obtained. The sintered body characteristics are shown in Table 1.

(Examples 2 to 8)
A sintered body was produced in the same manner as in Example 1 except that the firing conditions were changed. Table 1 shows the sintered body characteristics of the sintered body.

Example 9
A sintered body was produced in the same manner as in Example 1 except that the size of the compact was changed to a cylindrical shape having an outer diameter of 180 mm, an inner diameter of 157 mm, and a length of 300 mm. Table 1 shows the sintered body characteristics of the sintered body.

(Example 10)
A sintered body was produced in the same manner as in Example 1 except that the compact size was about 400 × 1300 × 12 mmt. A sintered body having a size of 331 mm × 1076 mm × 10 mmt (3561 cm ² ) without microcracks was obtained. Table 1 shows the sintered body characteristics of the sintered body.

(Example 11)
A sintered body was produced in the same manner as in Example 1 except that the compact size was about 250 × 600 × 12 mmt. A sintered body having a size of 207 mm × 497 mm × 10 mmt (1029 cm ² ) having no microcracks was obtained. Table 1 shows the sintered body characteristics of the sintered body.

(Comparative Example 1)
A sintered body was produced in the same manner as in Example 1 except that the firing conditions were changed to the following. Table 1 shows the sintered body characteristics of the sintered body.
(Baking conditions)
Firing furnace: Electric furnace Heating rate: 100 ° C / hour Heating atmosphere: air atmosphere Firing temperature: 1400 ° C
Firing time: 180 minutes.

(Comparative Examples 2-3)
A sintered body was produced in the same manner as in Comparative Example 1 except that the firing conditions were changed. Table 1 shows the sintered body characteristics of the sintered body.

(Comparative Examples 4 to 7)
A sintered body was produced in the same manner as in Example 1 except that the firing conditions were changed. Table 1 shows the sintered body characteristics of the sintered body.

(Comparative Example 8)
A sintered body produced by the same method as in Comparative Example 1 was placed on an alumina setter, placed in a hot isostatic press (HIP) apparatus, and subjected to HIP treatment under the following conditions.
(HIP processing conditions)
Temperature rising rate: 100 ° C./hour Temperature rising atmosphere: Argon atmosphere Pressure: 2000 atmospheres Heating temperature: 1200 ° C.
Heating time: 3 hours Temperature decreasing rate: 100 ° C./hour Temperature decreasing atmosphere: Argon atmosphere NbO ₂ phase was detected by identification by X-ray diffraction. The sintered body characteristics are shown in Table 1.

(Comparative Example 9)
A sintered body was produced in the same manner as in Comparative Example 8 except that the firing conditions were changed. Table 1 shows the sintered body characteristics of the sintered body.

Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.

The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2016-029316 filed on Feb. 18, 2016 are cited here as disclosure of the specification of the present invention. Incorporated.

The niobium oxide sintered body according to the present invention has high strength, and when used as a sputtering target, there is no cracking even under high output, and high productivity can be obtained. Further, it is used for a large-sized or cylindrical sputtering target. Expected to be.

Claims

The sintered body density is 95% or more, the sintered body particle size is 5.5 μm or less, niobium (IV) oxide attributed to the NbO 2 phase does not exist by X-ray diffraction, and the bending strength is 100 MPa. A niobium oxide sintered body characterized by the above.
The niobium oxide sintered body according to claim 1, wherein the shape is cylindrical.
The niobium oxide sintered body according to claim 1, wherein the niobium oxide sintered body has a flat plate shape and an area between the targets of 1000 cm 2 or more.
4. The method for producing a niobium oxide sintered body according to claim 1, wherein firing is performed at a temperature rising rate of 400 ° C./hour or more.
The method for producing a niobium oxide sintered body according to claim 4, wherein firing is performed using electromagnetic heating.