JP2000272951A - Production of alumina ceramic sintered compact having low dielectric loss - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a high-purity/dense alumina ceramic sintered compact having low dielectric loss useful for a semiconductor production apparatus and a liquid crystal producing apparatus, etc., requiring electrical insulating properties in a high high-frequency electric field. SOLUTION: A powdery raw material comprising 99.5-99.9 wt.% of an alumina raw material in which >=95 wt.% based on the whole alumina amount of alumina raw material powder having 0.1-3.0 μm as its particle diameter distribution exists and 20-45 wt.% of the whole alumina particles having 0.1-1.07 μm, 1.0-2.0 μm and 2.0-3.0 μm particle diameters exist and 0.1-0.5 wt..% of the rest of at least one or more sintering auxliaries selected from SiO2, MgO and rare earth element oxides is formulated with a dispersion medium composed of water, a dispersant, a pH adjuster and a binder and subjected to slip casting to give a molding product, which is retained at 1,550-1,650 deg.C maximum temperature for >=2 hours and sintered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to high-purity alumina ceramics, and more particularly to the manufacture of dense low dielectric loss alumina ceramics used for semiconductor manufacturing equipment and liquid crystal manufacturing equipment requiring electrical insulation. About the method.

[0002]

2. Description of the Related Art A high-purity dense alumina sintered body has heat resistance, chemical resistance, plasma resistance, etc., and has a large electric resistance and excellent electric insulation. Applications are being developed mainly for liquid crystal manufacturing equipment. When applied to these members, the required characteristics include a high-purity, dense sintered body structure and 1 MHz
It is required that the dielectric consumption energy associated with the dielectric polarization generated by a high-frequency AC electric field exceeding the above (low dielectric loss) is small. As a cause of increasing the dielectric loss, there is an alkali metal contained in the sintered body.

A large amount of alkali metal is contained in the alumina-based sintered body because it is contained in the raw material to be used and the sintered body such as pulverization, molding, molding (substrate) processing, firing, etc. It is conceivable that it is mixed during the manufacturing process. In order to avoid these problems, Japanese Patent Application Laid-Open No.
No. 61, the content of alkali metal is 1
It was necessary to use a high-purity (99.9% or more) alumina raw material having a low soda content of less than 000 ppm (= 0.1% by weight). Therefore, there has been a problem that a large increase in cost is required to obtain a low-soda (low alkali) alumina-based sintered body.

[0004]

According to the present invention, a low soda alumina raw material having a low content of alkali metal oxides such as Na and K is used as the alumina raw material, and the alumina purity is 99.
It is an object of the present invention to provide a low dielectric loss alumina ceramic which is as high as 5% or more and can greatly reduce the production cost in the working steps from raw material preparation to molding to sintering.

[0005]

According to the present invention, the alumina raw material powder has a particle diameter distribution of 0.1 to 3.0 μm in which 95% by weight or more of the total alumina amount is present, and the particle diameter is 0.1 to 1.
99.5 to 99.9% by weight of the alumina raw material having 20 to 45% by weight of the total amount of alumina in each range of 0 μm, 1.0 to 2.0 μm, and 2.0 to 3.0 μm, with the balance being Si
A powder raw material comprising 0.1 to 0.5% by weight of at least one sintering aid selected from O ₂ , MgO, CaO and rare earth oxides is prepared from water, a dispersant, a pH adjuster and a binder. This is a method for producing an alumina-based ceramics sintered body in which a dense molded body is obtained by mixing with a dispersing medium and cast-molded, and then held and sintered at a maximum temperature of 1550 to 1650 ° C. for 2 hours or more.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION When the alumina material powder has a particle size distribution of less than 95% by weight of the total amount of alumina in 0.1 to 3.0 μm, when the number of particles less than 0.1 μm is excessive, the casting time during casting is reduced. It is not preferable because the fluidity of the slurry is lowered. If the particle size is more than 3.0 μm, it is not suitable because it becomes difficult to densify at the time of sintering. When the alumina particle diameter is less than 20% by weight in the range of 0.1 to 1.0 μm, the sinterability is deteriorated and a high-density sintered body cannot be obtained. And it is difficult to increase the concentration. About alumina particle diameter
If the range of 0 to 2.0 μm is less than 20% by weight, the sinterability is reduced and a high-density sintered body cannot be obtained, and if it exceeds 45% by weight, it is difficult to make the compact at the time of casting. Therefore, it is not suitable. If the alumina particle size in the range of 2.0 to 3.0 μm is less than 20% by weight, it is difficult to densify the compact at the time of casting. It is unsuitable because no aggregate can be obtained. In the case where the alumina raw material in which each of these ranges contains 20 to 45% by weight of the total amount of alumina, including all other alumina particles, is less than 99.5% by weight of the entire powder raw material constituting the slurry, A high-purity and low dielectric loss alumina ceramic sintered body cannot be obtained, and if it exceeds 99.9% by weight, the amount of the sintering aid is limited to less than 0.1% by weight. This is not preferable because a decrease in sinterability cannot be avoided.

One or more sintering aids selected from among SiO ₂ , MgO, CaO and rare earth oxides are added in an amount of 0.1
If the amount is less than 10% by weight, it is not preferable because the effect of adding the auxiliary agent at the time of alumina sintering cannot be avoided as described above.
Addition of more than 0.5% by weight is not suitable because the resulting alumina-based ceramics sintered body loses the characteristics of high purity and low dielectric loss. Water, dispersant, pH
With respect to mixing and casting in a dispersion medium consisting of a modifier and a binder, water is preferably deionized water or purified water because the pH can be easily controlled, and the dispersant is not particularly limited. An aqueous solution of an ammonium carboxylate is preferably used, and one containing no Na or K is particularly suitable. Although the pH adjuster is not particularly limited, ammonium chloride, diethylamine, etc. are typical, and here, those containing no Na, K or the like are suitable. As the binder, either a water-soluble or emulsion type can be used, but in order to improve the durability of the casting mold at the time of casting, a water-soluble binder is not easily clogged easily, and an acrylic emulsion is preferably used. .

As the molding method of the present invention, there is used a known casting method in which the material is dispersed and suspended in a dispersion medium, injected into a water absorbing mold, and dehydrated and solidified. Next, as a firing method, use a gas-fired shuttle kiln furnace or a resistance heating type electric furnace at a maximum temperature of 15 ° C.
Hold at 50 to 1650 ° C. for 2 hours or more. Fifteen
If the temperature is lower than 50 ° C., the densification does not proceed sufficiently, and 1650 ° C.
If it is excessively large, abnormal grain growth occurs and the density of the sintered body decreases, which is not preferable. Baking for less than 2 hours is not preferred because thick or large-sized products are more likely to cause burn unevenness. As the slurry for casting, the amount of the dispersion medium is 13 to
17% by weight is preferred. This is because it is difficult to prepare a slurry of less than 13% by weight, and it is difficult for solidification to proceed with a dispersion medium amount of more than 17% by weight.

[0009] Unlike ordinary high-purity and easily sintered alumina raw materials, 95% by weight or more of the total alumina used in a particle size distribution of 0.1 to 3.0 µm is present, and the particle size is 0.1%. ~ 1.0 μm, 1.0 ~ 2.0 μm, 2.0 ~
20 to 45% by weight of the total amount of alumina in each range of 3.0 μm
99.5 to 99.9% by weight of alumina containing particles of
And a sintering aid having a balance of at least one selected from SiO ₂ , MgO, CaO and rare earth oxides.
By using the powder raw material of 5% by weight, it is possible to easily prepare a thick slurry for use in casting. According to the compounding diameter of the present invention, the effect of mixing fine powder and coarse particles having a particle diameter of about 5 to 10 times is produced, the fluidity of the slurry is excellent, and the obtained compact density is high, Linear shrinkage can also be reduced. On the other hand, even under the same sintering conditions, since at least 20% by weight of a relatively coarse alumina raw material of 2.0 to 3.0 μm is included, the growth rate of each grain in the sintered body structure can be increased.
As a result, the free-cutting property at the time of processing the sintered body is ensured, and the relative dielectric constant (ε _r ) and the dielectric loss (ta) are also reduced with respect to the electrical insulating property because the specific surface area of all the constituent particles of the sintered body is reduced.
nδ) can be easily reduced.

[0010]

Embodiments of the present invention will be described below.

As a raw material of alumina ceramics, the purity is 99.5%, the average particle size is 1.4 μm, and the particle size is 0.1 to 0.1%.
1.0 μm, 1.0 to 2.0 μm, 2.0 to 3.0 μm
25, 40, and 33% by weight of the total amount of alumina exist in each range, and 99.75% by weight of an alumina raw material containing 0.2% by weight of Na ₂ O and 0.20% by weight of SiO ₂
A composition in which 0.05% by weight of MgO and MgO were added as a sintering aid was used. As a molding method, a known casting method was used.
A gypsum mold having a slurry concentration of 84% by weight and a porosity of 40% by volume as a water-absorbing mold was used to obtain a molded product of □ 200 × t30 mm. The compact density was 2.71 g / cm ³ . This is kept in a resistance heating type electric furnace at 1620 ° C. × 4 hours, and □ 1
A sound sintered body of 78 × t26 mm was obtained. The physical properties of the sintered body include a three-point flexural strength of 360 MPa, a Young's modulus of 375 GPa, and a bulk density of 3.000 according to JIS-R1601.
88 g / cm ^3, the coefficient of thermal expansion 7.5 × 10 ^-6 / K, was 0.02% water absorption. The resistance value at the time of grinding was 500 N, which was in a range that would not hinder normal processing of a sintered body of alumina ceramics. Here, the resistance during grinding was performed under the following workability evaluation conditions. Cutting speed 60mm / mi
n. , Diamond whetstone roughness # 120, whetstone diameter φ8mm
Core drill, whetstone peripheral speed 60 m / min. The total depth of cut was 10 mm depth and 10 continuous holes. The stress applied to the Kistler dynamometer at this time was averaged three times and measured.

The electrical characteristics of the sintered body include:
At an AC frequency of 10 MHz, the relative permittivity ε _r = 8.5,
The dielectric loss tan δ was 0.0040. 100MH
In the AC high frequency region of z, the relative dielectric constant ε _r = 8.
5, a low value of dielectric loss tan δ = 0.0050 was obtained, and it was also confirmed that the value did not depend on the frequency.

As comparative examples, the purity is 99.8%, the average particle diameter is 0.6 μm, the particle diameter is 0.1 to 1.0 μm,
Raw soda (containing 0.06% by weight of Na ₂ O) alumina raw material in which 75, 10, and 5% by weight of the total amount of alumina are present in the respective ranges of 2.0 μm and 2.0 to 3.0 μm 9
9.75% by weight and 0.20% by weight of SiO ₂
And MgO as a sintering aid of 0.05% by weight. As a molding method, the granules after spray granulation were filled in rubber or the like and subjected to hydrostatic pressure to obtain a molded body having the same shape as described above. This was held at 1620 ° C. × 4 hours in an electric furnace and fired to obtain a sintered body (□ 162 × t24 mm). As a result of measuring the physical properties of the sintered body, a three-point bending strength of 240 MPa and a Young's modulus of 360 G according to JIS-R1601 were obtained.
Pa, bulk density 3.88 g / cm ³ , coefficient of thermal expansion 7.8 × 1
0 ^-6 / K, water absorption 0.06%. The resistance during grinding was determined under the same conditions as in the above example, but the grinding wheel was broken at the fifth hole during the continuous processing of 10 holes. The average resistance value up to that time was as high as 750 N, and it was a resistance that required careful setting of the feed speed at the time of cutting and the life of the grindstone during processing.
As electrical characteristics, at an AC frequency of 10 MHz, the relative permittivity ε _r = 9.8 and the dielectric loss tan δ = 0.0110
showed that. In an AC high frequency region of 100 MHz, the relative dielectric constant ε _r = 9.4 and the dielectric loss tan δ = 0.0
All of them showed a high value of 160, and varied greatly depending on the frequency.

From the above, the relative permittivity and the dielectric loss in the frequency range of 10 and 100 MHz in the above-described embodiment are significantly lower than those in the comparative example, and good results were obtained.

[0015]

According to the present invention, low dielectric loss alumina ceramics can achieve electrical insulation and reduction of dielectric energy consumption in an AC high frequency electric field while securing stable productivity during sintering and processing. Was. As a result, the manufacturing cost was also reduced.

Claims (1)

[Claims] 1. A particle diameter distribution of 0.1 to 3.0 μm in which 95% by weight or more of all alumina particles are present and a particle diameter of 0.1 to 1.0 μm, 1.0 to 2.0 μm, .0
99.5% to 99.9% by weight of alumina in which 20 to 45% by weight of the total alumina particles are present in each range of 3.0 μm, and the remainder is selected from among SiO ₂ , MgO, CaO, and rare earth oxides. A powdered raw material comprising 0.1 to 0.5% by weight of a sintering aid composed of at least one kind was mixed with water, a dispersant, a dispersion medium composed of a pH adjuster and a binder, and then cast and molded. A method for producing an alumina ceramic sintered body, comprising sintering a molded body at a maximum temperature of 1550 to 1650 ° C. for 2 hours or more.