JP2009051674A - Manufacturing method of ceramics - Google Patents

Abstract

In ceramic production, ceramics with a uniform density distribution are required for quality stabilization. Especially in the ceramic production method by electromagnetic wave heating, the density difference between the part in contact with the setter and other parts is reduced. It is requested to do.
In a method for producing ceramics, in which a compact of a ceramic raw material powder such as ITO or AZO is sintered by electromagnetic heating, a setter for placing the compact is made of a ceramic having a porous structure.
[Selection figure] None

Description

  The present invention relates to a method for producing ceramics by electromagnetic wave heating.

  Conventionally, ceramic firing methods include atmospheric firing method, hot pressing method, HIP method, etc., but these firings are heated and sintered by an external heat source, so it takes a long time to obtain a uniform fired product. It is a manufacturing method that requires firing and consumes a lot of energy. In recent years, self-heating type sintering using electromagnetic waves such as microwaves and millimeter waves has been studied for ceramic materials such as alumina from the viewpoint of uniform heating by self-heating and energy saving effect by shortening the firing time (see Non-Patent Document 1, for example). ).

  Heating using electromagnetic waves is sintering using self-heating of the object to be fired, and heat is transferred from the inside of the object to be fired to the outside, and the surface temperature of the object to be fired is lower than the inside. If this temperature difference is large, the material to be fired may be damaged during firing. As a countermeasure, the concept of an isothermal heat insulating wall has been proposed as a method for maintaining the surface temperature of the object to be fired at the same level as the inside, and ceramic firing by electromagnetic wave heating has become possible (for example, see Patent Document 1).

  On the other hand, in the sintered body obtained by electromagnetic wave heating, there are cases where the density is different from the whole only in the vertical direction of the sintered body, particularly around the portion in contact with the setter. The regions with different densities are regions up to about 2 mm from the contact surface with the setter to the top. In the case of normal external heating, the rate of temperature increase was not fast, and the temperature difference between the object to be fired and the setter was not large. On the other hand, firing of ceramics by electromagnetic wave heating is self-heating, so that it is presumed that a temperature difference between the upper and lower sides of the object to be fired is induced when the electromagnetic wave absorption rate of the object to be fired differs greatly from that of the setter. As a result, when a setter having a porosity of about 10% that is normally used is used, the density of the sintered body in the portion in contact with the setter becomes higher or lower than the other portions.

  The reason for the high density is not clear, but the temperature at the part in contact with the setter tends to rise because the release of heat to the surface is suppressed, and the setter becomes hotter than the object to be fired, and the bottom of the object to be fired Is estimated to have become hot. If the temperature rises too much, the setter may react with the setter and the product may not be taken out. If the part in contact with the setter is hot, the baking temperature is adjusted to the part in contact with the setter. In some cases, the overall density of the object is lowered. It is also speculated that the cause of the lower density is that the setter is deprived of heat of the object to be fired because the setter absorbs less electromagnetic waves than the object to be fired.

  Such a phenomenon has a great influence particularly when baking an object to be fired having a large contact area with a setter or a thin product. Examples of such products include ceramic sputtering targets made of an ITO (Indium Tin Oxide) sintered body, an AZO (Aluminum Zinc Oxide) sintered body, and the like. Sputtering targets have become larger as panel manufacturing equipment such as liquid crystals grows in size. For example, the ceramic sintered body has a length of about 80 cm, a width of about 30 cm, a thickness of about 5 mm to 15 mm, and a flat shape, and the presence of a density distribution in the thickness direction is unfavorable because it affects quality. .

  The ITO / AZO sputtering target is a sputtering target for producing an ITO / AZO thin film. ITO and AZO thin films have characteristics such as high conductivity and high transmittance, and because they can be easily finely processed, they can be used in a wide range of fields such as display electrodes for flat panel displays, window materials for solar cells, and antistatic films. It is used across. In particular, in the field of flat panel displays such as liquid crystal display devices, the increase in size and definition has progressed in recent years, and the demand for ITO and AZO thin films as display electrodes has also increased rapidly.

  Such ITO and AZO thin film production methods can be broadly classified into chemical film formation methods such as spray pyrolysis and CVD, and physical film formation methods such as electron beam evaporation and sputtering. Among these, the sputtering method is used in various fields because it is a film forming method that can easily increase the area and obtain a high-performance film.

  When manufacturing an ITO or AZO thin film by a sputtering method, as the sputtering target to be used, in the case of ITO, a composite oxide target (hereinafter abbreviated as ITO target) composed of indium oxide and tin oxide is used. Similarly, the AZO target is used for the AZO thin film.

  Regarding the quality of the ITO sputtering target and the AZO sputtering target, there are problems associated with the occurrence of arcing during film formation.

  When ITO or AZO film formation is carried out by sputtering, if arcing occurs frequently, foreign particles and defects derived from particles are generated in the formed thin film. This causes a decrease in manufacturing yield in flat panel displays such as liquid crystal display devices, and a sputtering target that can suppress arcing is strongly desired.

  In order to reduce arcing, it is effective to improve the density of ITO sintered bodies and AZO sintered bodies used for sputtering targets. For example, high density ITO having a sintered density of 98% to 100% and a sintered particle diameter of 1 μm to 20 μm. A sintered body is described (see, for example, Patent Document 2). Moreover, as a manufacturing method of a high-density sintered body, for example, a method of performing oxygen pressure sintering is known (see, for example, Patent Document 3).

  Thus, it is important to manufacture a high-density sintered body with respect to the quality of the ceramic sputtering target.

  When manufacturing a ceramic sputtering target by electromagnetic wave heating, the temperature at the part in contact with the setter rises or falls, and there is a problem that a density difference tends to occur in the vertical direction, and the production is not stable.

Japanese Patent No. 3845777 Japanese Patent No. 3457969 JP-A-3-207858 Toyota Central R & D Review Vol. 30 NO. 4 (1995)

  In the production of ceramics, ceramics with a uniform density distribution are required for quality stabilization. In particular, the method of producing ceramics by electromagnetic wave heating can reduce the density difference between the part in contact with the setter and other parts. It has been demanded.

  As a result of diligent research to solve the above problems, by using a setter made of ceramics having a porous structure, it is possible to suppress increase / decrease in the density of the lower part of the object to be fired in contact with the setter, and to reduce the density difference in the vertical direction. As a result, the present invention was completed.

  That is, the present invention relates to a method for producing ceramics in which a molded body of ceramic raw material powder is sintered by electromagnetic heating, wherein a setter made of ceramics having a porous structure is used as a setter for placing the molded body. It is. Hereinafter, the present invention will be described in detail.

The ceramic produced in the present invention is not particularly limited as long as it can be sintered by electromagnetic heating. For example, structural materials such as alumina, zirconia, titania, SiC, ITO (In ₂ O ₃ —SnO ₂ ), AZO (Al ₂ O ₃ —ZnO ₂ ), In ₂ O ₃ —ZnO, Ga ₂ O ₃ —ZnO , TiO ₂ -α (α: positive pentavalent ions such as Ta), SnO ₂ -β (β: positive pentavalent ions such as Sb), and the like, BaTiO ₃ , PZT And functional ceramics.

  The ceramic setter having a porous structure used in the present invention is a ceramic setter having pores, and the porosity is 20% or more, preferably 30% or more. The larger the porosity, the lower the calorific value of the setter itself, and the lower the heat transfer between the object to be fired and the setter, so that the thermal influence on the object to be fired is alleviated.

  Further, the pore size of the ceramic setter having the porous structure of the present invention is not particularly limited, but is preferably 10 nm to 10 mm, and the one in which the structure such as the pore size does not change at the firing temperature of the sintered body is selected. For example, when firing at a high temperature, a setter or the like having a pore size of about 1 mm and a mesh-like material forming the skeleton is preferable because deformation at high temperature is small.

  Moreover, the shape of the ceramic setter having a porous structure of the present invention may be any shape as long as the object to be fired can be loaded. For example, a plate-like thing, a wave-like thing, and a block-like thing can be illustrated.

  The material of the ceramic setter having a porous structure according to the present invention is not particularly limited as long as it is a material that does not deform or change its composition at the firing temperature of the material to be fired and does not react with the material to be fired. A material having characteristics similar to the electromagnetic wave absorption characteristics of the object to be fired is more preferable. For example, alumina, mullite, zirconia, SiC, silica-alumina and the like can be exemplified.

  In the setting method of the setter having a porous structure according to the present invention, it is essential that the object to be fired is placed on the setter having the porous structure, and the object to be fired is placed on the setter having the porous structure. Alternatively, a method of placing a porous setter on a normal setter having a low porosity and placing an object to be fired thereon may be used.

  Next, the method for producing the ceramic of the present invention will be described by taking the production of an ITO or AZO sintered body as an example.

First, raw material powders of ITO and AZO sintered bodies are mixed at a predetermined mixing ratio. For example, in the case of an ITO sintered body, the content of tin oxide is 8% by weight or more and 15% by weight or less in SnO ₂ / (In ₂ O ₃ + SnO ₂ ) whose specific resistance decreases when a thin film is produced by a sputtering method. It is preferable that Further, for example, in the case of AZO, the content of aluminum oxide is desirably 1% by weight or more and 5% by weight or less at which the specific resistance decreases when a thin film is produced by a sputtering method.

  A binder or the like may be added to the raw material powder. Mixing is performed by a ball mill, a jet mill, a cross mixer, or the like.

  The obtained raw material powder is molded by a molding method such as a press method or a casting method to produce a target molded body. At this time, if the average particle size of the powder used is large, the density after sintering may not be sufficiently increased. Therefore, the average particle size of the powder used is desirably 1 μm or less, more preferably 0.1 μm. ˜1 μm. By doing so, it becomes possible to obtain a sintered body having a small sintered particle size and a high sintered density.

Next, consolidation processing such as CIP is performed on the obtained molded body as necessary. Here CIP pressure to obtain a sufficient compaction effect 1 ton / cm ² or higher, preferably 2 ton / cm ² or more, more preferably from 2~3ton / cm ^2. Here, when the first molding is performed by a casting method, the binder may be removed for the purpose of removing moisture remaining in the molded body after CIP and organic substances such as a binder. Even when the first molding is performed by a press method, the same debinding process can be performed when a binder is used during molding.

  Next, the thus obtained molded body is sintered by electromagnetic wave heating. The present invention is not particularly limited as long as it is a sintering method heated using electromagnetic waves, but as electromagnetic waves, 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. The frequency of the electromagnetic wave can be selected appropriately from the sintering behavior of ceramics.

  As the electromagnetic wave 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.

  The obtained molded body is placed on a ceramic setter having a porous structure. In the case of ITO, the sintering holding temperature is 1300 ° C. or higher and lower than 1650 ° C., and in the case of AZO, it is 1200 ° C. or higher and lower than 1550 ° C. Therefore, the ceramic setter having a porous structure is made of alumina, mullite, SiC Select a material with high heat resistance such as

  The molded body and the setter are surrounded by a heat insulating material. At this time, it is also possible to install a material for the isothermal barrier inside the heat insulating material. As the isothermal heat insulating wall, a material having high heat resistance such as alumina, mullite, SiC or the like is preferable.

  The temperature raising rate during firing is not particularly limited, but is preferably 100 to 600 ° C./hour, and more preferably 200 to 600 ° C./hour. For example, in the case of ITO, the sintering holding temperature is 1300 ° C. or higher and lower than 1650 ° C., preferably 1400 ° C. or higher and 1600 ° C. or lower. Moreover, in the case of AZO, it is 1200 degreeC or more and less than 1550 degreeC, Preferably it is 1300 degreeC or more and 1500 degrees C or less.

  The holding time during sintering is not particularly limited, but 5 hours or less is sufficient. Further, the temperature lowering rate is not particularly defined, but for example, in the case of an ITO sintered body, it is 100 ° C./hour or more, preferably 200 ° C./hour or more up to 1200 ° C. The upper limit value of the temperature lowering rate from 1200 ° C. to room temperature is not particularly specified, but is preferably 100 ° C./hour or less. The setting of the temperature for lowering the temperature lowering rate and the selection of the temperature lowering rate may be appropriately determined in consideration of the capacity of the sintering furnace, the size and shape of the sintered body, ease of cracking, and the like. The atmosphere during sintering is arbitrarily selected according to the type of ceramic. For example, in the case of an ITO sintered body, an oxygen atmosphere is preferable. In the case of an AZO sintered body, the atmosphere during sintering is preferably air or an inert atmosphere.

  After grinding the ITO and AZO sintered bodies obtained in this way to a desired shape, they are bonded to a backing plate made of oxygen-free copper or the like using indium solder or the like, if necessary. An ITO or AZO sputtering target can be obtained.

  The obtained target is placed in a sputtering apparatus, and sputtering is performed by applying a dc or rf electric field by using an inert gas such as argon and oxygen gas as a sputtering gas as necessary, and applying a dc or rf electric field. In addition, an ITO or AZO thin film can be formed. At this time, the effect of the present invention that the amount of arcing is reduced is exhibited.

  The method for producing ceramics according to the present invention is also effective for ceramics to which a third element is added for the purpose of imparting an additional function to the ceramics. Examples of the third element include Mg, Al, Si, Ti, Zn, Ga, In, Ge, Y, Zr, Nb, Hf, and Ta. The amount of addition of these elements is not particularly limited, but in order not to deteriorate the excellent electro-optical characteristics of ceramics, (total of oxides of third elements) / (ceramics + oxides of third elements) The total is preferably more than 0% by weight and 20% by weight or less (weight ratio).

  By the manufacturing method of the present invention, ceramics with high density and low density distribution can be easily obtained, and the quality of the product is stabilized. Therefore, by using the ceramic of the present invention as a target material, since it has a high density and a small density distribution, the occurrence of arcing is extremely low, and an excellent sputtering target with a low occurrence of arcing over a long period of time up to the target life. Can be obtained.

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) Sintered body density: Measured by Archimedes method.
Note that the relative density (D), for example, in the case of ITO sintered body, indicating the relative value to the _In 2 _{O 3} and the theoretical density determined from the true density of the arithmetic mean of SnO _{2 (d ITO).} The theoretical density (d) obtained from the arithmetic mean is the true density of 7.18 when the mixing amount of In ₂ O ₃ and SnO ₂ powder is a (g) and b (g) in the target composition. Using (g / cm ³ ) and 6.95 (g / cm ³ ), it was obtained by d = (a + b) / ((a / 7.18) + (b / 6.95)). When the measured density of the sintered body is d1, the relative density D is obtained by D = d1 / _dITO × 100 (%).

Also, for example, in the case of AZO sintered body, the relative density (D), shows a relative value with respect to the theoretical density determined from the true density of the arithmetic mean of ZnO and _{Al 2 O 3 (d AZO)} . The theoretical density (d) obtained from the arithmetic mean is the true density of 5.68 when the mixing amount of ZnO and Al ₂ O ₃ powder is x (g) and y (g) in the target composition. Using (g / cm ³ ) and 3.987 (g / cm ³ ), d = (x + y) / ((x / 5.68) + (y / 3.987)). When the density of the actually obtained sintered body is d2, the relative density D is obtained by D = d2 / _dAZO × 100.

(2) Density in the thickness direction of the sintered body: As a result of observing the structure in the thickness direction of the sintered body obtained by electromagnetic wave heating, the structure from the setter contact surface to about 2 mm is changed compared to other parts. Since it was large, the density at around 2 mm from the setter contact surface was measured.
The density was measured for the upper density (upper surface to 2 mm above the setter contact surface) and lower density (from the setter contact surface to 2 mm above) in the thickness direction of the sintered body.
The density of the lower part was calculated by the following formula from the density measured value by the Archimedes method before and after grinding the sintered body by 2 mm above the setter contact surface by plane research.
Lower density = {(weight before grinding) − (weight after grinding)} / {(weight before grinding) / (density before grinding) − (weight after grinding) / (density after grinding)}
The density of the upper part was determined by a usual method from the sintered body after grinding.

(Example 1)
90 parts by weight of indium oxide powder having an average particle diameter of 0.6 μm and 10 parts by weight of tin oxide powder having an average particle diameter of 0.5 μm were placed in a polyethylene pot and mixed by a dry ball mill for 20 hours to prepare a mixed powder. The tap density of the mixed powder was measured and found to be 2.0 g / cm ³ .

The mixed powder was adjusted in the amount of powder so that a predetermined sintered body thickness was obtained, and placed in a mold, and pressed at a pressure of 300 kg / cm ² to obtain a molded body. This molded body was treated with CIP at a pressure of ² ton / cm ² . Next, the molded body was placed in a microwave baking furnace (frequency = 2.45 GHz) in a mesh setter made of alumina (porosity = 30%, pore size = 1 mm, size 80 × 80 mm, thickness = 10 mm, Al ₂ O ₃ = 99% or more) and sintered under the following conditions.
(Sintering conditions) Temperature rising rate: 300 ° C./hour, sintering holding temperature: 1500 ° C., holding time during sintering: 1 hour, atmosphere: pure oxygen gas from room temperature during temperature rising to 100 ° C. during temperature lowering Introduced into furnace, rate of temperature drop: from sintering holding temperature to 1200 ° C, 200 ° C / hour, thereafter 100 ° C / hour.

  The density of the obtained sintered body and the density in the thickness direction were measured. The results are shown in Table 1. A sintered body having a high sintered body density and a small density difference in the thickness direction of the sintered body was obtained.

(Example 2)
98 parts by weight of zinc oxide powder having an average particle diameter of 0.9 μm and 2 parts by weight of aluminum oxide powder having an average particle diameter of 0.3 μm were placed in a polyethylene pot and mixed for 24 hours by a dry ball mill to prepare a mixed powder. This mixed powder was put into a mold and pressed at a pressure of 300 kg / cm ² to obtain a molded body. This molded body was treated with CIP at a pressure of ² ton / cm ² .

Next, this molded body was placed in a millimeter-wave firing furnace (frequency = 28 GHz) and an alumina porous setter (porosity = 40%, pore size = 3 mm, size 80 × 80 mm, thickness = 10 mm, Al ₂ O ₃ = 99%). ) And sintered under the following conditions.
(Sintering conditions) Temperature rising rate: 300 ° C./hour, sintering holding temperature: 1400 ° C., holding time during sintering: 1 hour, atmosphere: pure nitrogen gas from room temperature during temperature rising to 100 ° C. during temperature lowering Introduced into the furnace, cooling rate: 100 ° C./hour.

  The density of the obtained sintered body and the density in the thickness direction were measured. The results are shown in Table 1. A sintered body having a high sintered body density and a small density difference in the thickness direction of the sintered body was obtained.

(Comparative Example 1)
ITO was fired in the same manner as in Example 1 except that an alumina setter (porosity = 12%, thickness = 10 mm) was used as the setter. The obtained sintered body was welded to the setter, and the product could not be taken out from the setter.

(Comparative Example 2)
ITO was fired in the same manner as in Comparative Example 1 except that the sintering holding temperature was 1450 ° C. The density of the obtained sintered body and the density in the thickness direction were measured. The results are shown in Table 1. The density difference in the thickness direction of the sintered body was large.

(Comparative Example 3)
AZO was fired in the same manner as in Example 2 except that an alumina setter (porosity = 12%, thickness = 10 mm) was used as the setter, and the sintering holding temperature = 1350 ° C. The density of the obtained sintered body and the density in the thickness direction were measured. The results are shown in Table 1. The density difference in the thickness direction of the sintered body was large.

Claims (3)

A ceramic production method for sintering a ceramic raw material powder compact by electromagnetic heating, wherein a setter made of ceramics having a porous structure is used as a setter for placing the compact. The method for producing a ceramic according to claim 1, wherein the produced ceramic is ITO. The method for producing a ceramic according to claim 1, wherein the produced ceramic is AZO.