JP2019048748A - Electrically conductive ceramics - Google Patents

Abstract

To provide electrically conductive ceramics which are dense and have excellent electrical conduction property.SOLUTION: The electrically conductive ceramics contain alumina and single layer carbon nanotubes, wherein the content of the single layer carbon nanotube is 0.05 vol.% or over and 0.7 vol.% or under and the volume resistivity thereof is 10Ω cm or over and 10Ω cm or under. Herein, the single layer carbon nanotubes have BET specific surface of 800 m/g or over. Moreover, the single layer carbon nanotubes have average diameter of 3 nm or over and 5 nm or under.SELECTED DRAWING: None

Description

  The present invention relates to conductive ceramics.

  Ceramics are excellent in mechanical properties such as wear resistance, corrosion resistance and heat resistance. Therefore, the application of ceramics to members for manufacturing devices for semiconductors and liquid crystal devices, hard disk bearing parts, and the like is expected.

  However, ceramics usually have high electrical insulation. Therefore, in the case where the ceramic is used for a member requiring a countermeasure against static electricity such as a member for a semiconductor manufacturing apparatus, it is required to impart electrical conductivity to the ceramic.

  Therefore, for example, in Patent Document 1, a composite material (conductive ceramic) having improved electrical conductivity is provided by combining alumina, carbon nanohorns, and multi-walled carbon nanotubes.

JP, 2013-107807, A

  However, the above-mentioned conventional conductive ceramics have insufficient electric conductivity. In addition, since the conventional conductive ceramics described above contain a large amount of carbon nanohorns and multi-walled carbon nanotubes in order to enhance the electrical conductivity, the density is low and the strength is not sufficient.

  Then, this invention aims at providing the electroconductive ceramics which are precise | minute and are excellent in electrical conductivity.

  As a result of intensive studies to achieve the above object, the present inventors have found that if single-walled carbon nanotubes are mixed with alumina in a predetermined ratio, conductive ceramics that are compact and have excellent electrical conductivity can be obtained. It has been found that the present invention is complete.

That is, the present invention aims to advantageously solve the above-mentioned problems, and the conductive ceramic of the present invention contains alumina and single-walled carbon nanotubes, and the content ratio of the single-walled carbon nanotubes The volume resistivity is 0.05 volume% or more and 0.7 volume% or less, and the volume resistivity is 10 ⁻² Ω · cm or more and 10 ⁶ Ω · cm or less. As described above, when single-walled carbon nanotubes are contained in the above proportion and the volume resistivity is in the above range, it is possible to obtain a conductive ceramic which is dense and excellent in electric conductivity.
In the present invention, “volume resistivity” refers to the Van der Pauw method (when the volume resistivity is 10 ³ Ω · cm or less) or the DC three-terminal method (when the volume resistivity is more than 10 ³ Ω · cm) Can be measured at room temperature (25.degree. C.).

Here, in the conductive ceramic of the present invention, the BET specific surface area of the single-walled carbon nanotube is preferably 800 m ² / g or more. If single-walled carbon nanotubes having a BET specific surface area of 800 m ² / g or more are used, the electrical conductivity of the conductive ceramic can be favorably improved.
In the present invention, the "BET specific surface area" refers to the nitrogen adsorption specific surface area measured using the BET method.

In the conductive ceramic of the present invention, the single-walled carbon nanotubes preferably have an average diameter of 3 nm or more and 5 nm or less. If single-walled carbon nanotubes having an average diameter of 3 nm or more and 5 nm or less are used, the electrical conductivity of the conductive ceramic can be favorably improved.
In the present invention, the “average diameter” of single-walled carbon nanotubes is determined by measuring the diameter (outer diameter) of 100 randomly selected single-walled carbon nanotubes using a TEM (transmission electron microscope). be able to.

The conductive ceramic of the present invention preferably has an iron content of 5 mass ppm or less. If the content of iron is 5 mass ppm or less, the conductive ceramic can be favorably used as a member for a semiconductor manufacturing apparatus or the like.
In the present invention, “the iron content” can be measured by ICP-AES (high frequency inductively coupled plasma emission spectrometry).

  According to the present invention, it is possible to obtain a conductive ceramic which is dense and excellent in electric conductivity.

Hereinafter, embodiments of the present invention will be described in detail.
Here, the conductive ceramic of the present invention is not particularly limited, and is used, for example, as a member for a semiconductor manufacturing apparatus or an electronic component manufacturing member. Parts for semiconductor manufacturing equipment: Stages for plasma treatment where volume resistivity of 10 ⁶ Ω · cm or less, preferably 10 ⁵ Ω · cm or more and 10 ⁶ Ω · cm or less is required, Volume resistivity of 10 Ω · cm or less It includes the counter electrode for high frequency generation, the heating element, etc. Moreover, as an electronic component manufacturing member, in order to prevent static electricity, that is, to prevent damage to the sample due to electrostatic discharge, a volume resistance of 10 ⁶ Ω · cm or less, preferably 10 ⁵ Ω · cm or more and 10 ⁶ Ω · cm or less Transport rail components for transporting electronic components, vacuum chucks, etc. And the electroconductive ceramics of this invention can be manufactured, for example using the manufacturing method of electroconductive ceramics mentioned later.

(Conductive ceramics)
The conductive ceramic of the present invention contains alumina and single-walled carbon nanotubes, and optionally further contains an additive such as an additive that can be blended in the conductive ceramic and an impurity such as iron. In the conductive ceramic of the present invention, the content ratio of single-walled carbon nanotubes is 0.05% by volume or more and 0.7% by volume or less, and the volume resistivity is 10 ⁻² Ω · cm or more and 10 ⁶ Ω · It is characterized by being less than cm.

  And, in the conductive ceramic of the present invention, since single-walled carbon nanotubes are used, the blending amount of single-walled carbon nanotubes is 0.05 volume% or more and 0.7 volume as compared with the case where multi-walled carbon nanotubes are used. Even if it is as low as% or less, the electrical conductivity of the conductive ceramic can be sufficiently enhanced. Therefore, the conductive ceramic of the present invention is dense and excellent in electric conductivity.

<Alumina>
Alumina is a material to be a base material of conductive ceramics. The conductive ceramic contains alumina as a main component.
In addition, "it contains as a main component" shows that a content rate is more than 50 volume%. And the content rate of the alumina in electroconductive ceramics can be measured using a fluorescent X ray spectroscopy.

Here, as alumina contained in the conductive ceramic, α-alumina, γ-alumina, or a mixture thereof can be used. Among them, as alumina contained in the conductive ceramic, α-alumina is preferable.
The "alumina" in the present invention, mullite _{(Al 6 O} 13 Si ₂₎ and, spinel (MgAl ₂ O ₄₎ is also intended to be that contained.

<Single-walled carbon nanotube>
As the single-walled carbon nanotube (hereinafter sometimes referred to as “SWCNT”), SWCNT synthesized by an arbitrary method such as a chemical vapor deposition (CVD) method, an arc discharge method, or a laser evaporation method can be used. Among them, as SWCNTs, when a raw material compound and a carrier gas are supplied onto a substrate having a catalyst layer for producing carbon nanotubes on the surface, and CNTs are synthesized by a chemical vapor deposition method (CVD method), Single layer produced by using the method (super growth method; see WO2006 / 011655) of dramatically improving the catalytic activity of the catalyst layer by the presence of a trace amount of an oxidizing agent (catalyst activating material) in the Carbon nanotubes are preferred.

  Here, the SWCNTs preferably have an average length of 300 μm or more at the time of synthesis. If the average length at the time of synthesis of SWCNTs is 300 μm or more, the conductive path can be favorably formed in the conductive ceramic even with a small compounding amount, and the electrical conductivity of the conductive ceramic can be sufficiently enhanced. It is. In addition, the average length at the time of synthesis of SWCNT can be set to 600 μm or less from the viewpoint of productivity and the like.

  The SWCNTs contained in the conductive ceramic preferably have an average diameter of 3 nm or more and 5 nm or less. If the average diameter of the SWCNTs is within the above range, the electrical conductivity of the conductive ceramic can be favorably improved.

Furthermore, SWCNT contained in the conductive ceramic has a ratio (3σ) of the standard deviation of diameter (σ: sample standard deviation) multiplied by 3 to the average diameter (Av) of 0. More than 20 and less than 0.60 is preferable, 3σ / Av is more preferably more than 0.25, and 3σ / Av is more preferably more than 0.50. The use of SWCNTs in the above range of 3σ / Av makes it possible to favorably improve the electrical conductivity of the conductive ceramic.
The average diameter (Av) and standard deviation (σ) of SWCNTs may be adjusted by changing the production method or production conditions of SWCNTs, or by combining a plurality of types of SWCNTs obtained by different production methods. You may

The SWCNT contained in the conductive ceramic preferably has a BET specific surface area of 800 m ² / g or more. If the BET specific surface area of the SWCNTs is equal to or more than the above lower limit value, the electrical conductivity of the conductive ceramic can be favorably improved. The BET specific surface area of the SWCNTs is usually 2000 m ² / g or less, preferably 1800 m ² / g or less, and more preferably 1600 m ² / g or less. If the BET specific surface area of the SWCNTs is equal to or less than the above upper limit value, the SWCNTs can be favorably dispersed in the conductive ceramic.

  And the content rate of SWCNT mentioned above needs to be 0.05 volume% or more and 0.7 volume% or less, and it is preferable that it is 0.1 volume% or more, and is 0.2 volume% or more Is more preferred. If the content ratio of SWCNTs is less than 0.05% by volume, the electrical conductivity of the conductive ceramic can not be sufficiently improved. In addition, when the content ratio of SWCNTs is more than 0.7% by volume, while the ratio of improving the electrical conductivity decreases due to the increase of the compounding amount of SWCNTs, the conductive ceramics As the density decreases, the amount of impurities in the conductive ceramic increases.

  The conductive ceramic may contain multi-walled carbon nanotubes in addition to the single-walled carbon nanotubes described above, but from the viewpoint of enhancing the compactness and electrical conductivity of the conductive ceramic, it is included in the conductive ceramic. The proportion of single-walled carbon nanotubes in the total carbon nanotubes is preferably 90% by mass or more.

<Additives>
The additive that the conductive ceramic may optionally contain is not particularly limited, and examples thereof include silicon carbide particles, boron carbide particles, boron nitride particles, titanium nitride particles, titanium carbide particles, monazite particles, and zircon particles. Ceramic particles other than alumina particles; metal particles such as cobalt particles, nickel particles, copper particles, titanium particles, molybdenum particles and tungsten particles; and stabilizers.
The content ratio of the additive in the conductive ceramic is usually 30% by volume or less.

<Impurity>
In addition, the conductive ceramic may contain impurities such as iron. Specifically, the conductive ceramic may contain, for example, impurities such as iron used as a catalyst at the time of synthesis of SWCNTs.

  Here, in the case where the conductive ceramic is used as a member for a semiconductor manufacturing apparatus or the like, the content of iron in the conductive ceramic is preferably 5 mass ppm or less.

<Physical properties>
And, the conductive ceramic of the present invention needs to have a volume resistivity within a predetermined range, and preferably has the following physical properties.

[Volume resistivity]
The volume resistivity of the conductive ceramic is 10 ⁻² Ω · cm or more and 10 ⁶ Ω · cm or less. When the volume resistivity exceeds the upper limit value of the above numerical range, the electrical conductivity of the conductive ceramic can not be sufficiently secured. When the volume resistivity is less than the lower limit of the above numerical range, it is necessary to mix a large amount of a conductive substance such as SWCNT, so the density of the conductive ceramic can not be sufficiently increased.

[Bending strength]
Furthermore, the conductive ceramic preferably has a flexural strength of 300 MPa or more, more preferably 500 MPa or more, and still more preferably 900 MPa or more. If the bending strength is at least the above lower limit value, the strength of the conductive ceramic can be sufficiently increased.
The "bending strength" can be measured in accordance with JIS R1601.

  And the magnitude | size of the bending strength of electroconductive ceramics is not specifically limited, For example, it can adjust by adjusting content of SWCNT, the manufacturing conditions of electroconductive ceramics, etc.

(Method of manufacturing conductive ceramics)
One example of the method for producing a conductive ceramic of the present invention is a step of sintering a solid mixture containing alumina and single-walled carbon nanotubes having a content ratio of 0.05% to 0.7% by volume (sintering (sintering) Preparing a ceramic slurry composition including alumina, single-walled carbon nanotubes, and a dispersion medium (slurry preparation process), and optionally including the process (A), and the ceramic slurry composition. And the step of obtaining the solid mixture (solid mixture preparation step).

<Slurry preparation process>
In the slurry preparation step, a ceramic slurry composition is prepared, which contains alumina, single-walled carbon nanotubes, and a dispersion medium, and optionally further contains additives and impurities.
The ceramic slurry composition may contain a known dispersant such as sodium dodecylbenzene sulfonate.

  Here, as the alumina, the single-walled carbon nanotube, the additive and the impurity, the same as those described above as those which can be contained in the conductive ceramic of the present invention may be mentioned. It is similar.

  Also, the dispersion medium is not particularly limited, and water; methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, Alcohols such as amyl alcohol; Ketones such as acetone, methyl ethyl ketone and cyclohexanone; esters such as ethyl acetate and butyl acetate; ethers such as diethyl ether, dioxane and tetrahydrofuran; N, N-dimethylformamide, N-methylpyrrolidone and the like Amide-based polar organic solvents; aromatic hydrocarbons such as toluene, xylene, chlorobenzene, ortho-dichlorobenzene, para-dichlorobenzene and the like; and the like can be used. One of these may be used alone, or two or more may be mixed and used.

  And a ceramic slurry composition can be prepared by mixing the components mentioned above and performing a dispersion process arbitrarily.

  Here, mixing of the components mentioned above can be performed in arbitrary order. Among them, in the ceramic slurry composition, after preparing a dispersion liquid in which SWCNTs are dispersed in a dispersion medium, alumina and an arbitrary additive are added to the dispersion liquid, and an arbitrary mixed liquid is obtained. It is preferable to prepare by performing a dispersion process.

  In addition, the dispersion treatment of the dispersion liquid and the mixture liquid is not particularly limited, and can be performed using, for example, the method described in WO 2014/097626 or WO 2016/013219. .

<Solid mixture preparation process>
In the solid mixture preparation step, the dispersion medium is removed from the ceramic slurry composition obtained in the slurry preparation step, and alumina and single-walled carbon nanotubes having a content ratio of 0.05% to 0.7% by volume are contained. A solid mixture is obtained.

Here, as a method of removing the dispersion medium, a known drying method can be adopted. Examples of the drying method include a heat drying method, a hot air drying method, a vacuum drying method, a heat roll drying method, an infrared irradiation method and the like. Specifically, the removal of the dispersion medium can be carried out, for example, by heating the ceramic slurry composition under an argon atmosphere at 600 ° C. for 1 hour.
In addition, the removal of the dispersion medium may be performed while subjecting the ceramic slurry composition to a dispersion treatment. Specifically, all or part of the dispersion medium may be removed, for example, by heating the ceramic slurry composition while irradiating ultrasonic waves in an ultrasonic water bath.

<Sintering process>
In the sintering step, a solid mixture containing alumina and 0.05% to 0.7% by volume of single-walled carbon nanotubes, optionally further containing an additive and an impurity, is sintered to form a volume. A conductive ceramic having a resistivity of 10 ⁻² Ω · cm or more and 10 ⁶ Ω · cm or less is obtained.

  Here, the sintering is not particularly limited, and can be performed using, for example, a pressure sintering method or a pressureless sintering method under a vacuum pressure reduction or an inert gas atmosphere.

  Then, as the inert gas, for example, nitrogen gas, helium gas, argon gas, neon gas or the like can be used.

  Further, the sintering temperature can be, for example, 1300 ° C. or more and 1500 ° C. or less. Furthermore, the sintering time can be, for example, 50 minutes or more and 90 minutes or less. In addition, even in the case of a sintered body with a low relative density, if the open porosity is 0%, under argon pressure at a temperature of 1300 ° C. to 1500 ° C. and a pressure of 150 to 200 MPa using a hot isostatic press (HIP) sintering machine By sintering for 1 hour, a dense sintered body having a relative density of 99.9% or more can be produced.

EXAMPLES Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples.
In Examples and Comparative Examples, the content of iron in the conductive ceramic, the bending strength, the volume resistivity, and the relative density were measured by the following methods.

<Content of iron>
The produced sintered body (conductive ceramic) was crushed. Then, 0.5 g of the crushed sintered body is weighed in a sealed Teflon (registered trademark) container, 10 ml of (1 + 3) sulfuric acid is added, the container is sealed, and pressure decomposition is performed at 230 ° C. for 16 hours. After that, it was diluted to 100 ml with pure water to make an analysis sample. Then, the amount of iron in the analysis sample was measured by ICP-AES (high frequency inductively coupled plasma emission spectrometry) to calculate the amount of iron contained in the sintered body (conductive ceramic).
<Volume resistivity>
After grinding both sides of the produced sintered body (conductive ceramic) with a diamond grindstone of grain size # 100 and # 800 to a thickness of 1 mm, a square (10 mm square) test piece is cut out from the central portion and a measurement sample And
And, for a measurement sample with a volume resistivity of 10 ³ Ω · cm or less, the volume is measured at room temperature (25 ° C.) by the Van der Pauw method using a resistivity / hole measurement system (Toyo Technica Co., Ltd., Resi Test 8308 type) The resistivity was determined. Here, calculation of volume resistivity by Van der Pauw method is to obtain sheet resistance Rs by calculating resistance between four terminals by giving four small ohmic resistances around the measurement sample of thickness t. According to the equation: volume resistivity == Rs × t.
When the volume resistivity of the sample to be measured is more than 10 ³ Ω · cm, an electrometer (Keithley 6517A, measurement software 6524) provided with a guard electrode around the electrode with a diameter of 6 mm is used, and the DC three-terminal method The volume resistivity was determined by
<Relative density>
First, the bulk density of the produced sintered body (conductive ceramic) was determined by the Archimedes method in toluene under the condition of a temperature of 25 ° C.
Further, by using the theoretical density 3.97 g / cm ³ and the theoretical density of 2.0 g / cm ³ of single-walled carbon nanotubes of alumina _(Al 2 _{O 3)} at a temperature 25 ° C., the theoretical density of the sintered body from the blending ratio The relative density (= (bulk density / theoretical density) × 100%) was calculated as the ratio of the bulk density of the sintered body to the theoretical density.
<Bending strength>
The measurement of the bending strength σf at room temperature (25 ° C.) of the produced sintered body (conductive ceramic) was measured by the three-point bending test method in accordance with JIS R1601. For measurement, a three-point bending test was performed under the conditions of a span length of 30 mm and a crosshead speed of 0.5 mm / min using an AG-C universal tester (Autograph) manufactured by Shimadzu Corporation. The bending strength was calculated by the following equation.
σ f = 3 PL / ( ² b · d ² )
σ f: bending strength (Pa)
P: Maximum load when the test piece breaks (N)
L: Distance between lower fulcrums (m)
b: Specimen width (m)
d: Specimen thickness (m)

(Examples 1 to 5 and Comparative Examples 1 to 3)
A methyl ethyl ketone dispersion containing 0.35% by mass of long single-walled carbon nanotubes (Zeon Nano Technology, ZEONANO SG101, average diameter: 4 nm, average length: 400 μm, BET specific surface area: 1150 m ² / g) was prepared .
Then, after adding the methyl ethyl ketone dispersion measured so that the amount of single-walled carbon nanotubes contained in the obtained sintered body (conductive ceramic) becomes the ratio shown in Table 1 to 150 mL of ethyl alcohol, an ultrasonic homogenizer ( An ultrasonic wave was applied at an output of 50% for 5 minutes using U200S control (manufactured by IKA Co., Ltd.) to carry out dispersion treatment to obtain a dispersion.
Next, 35 g of alumina powder (TM-DAR, average particle size: 0.1 μm, manufactured by Daimei Chemical Industries, Ltd.) is added to the obtained dispersion, and ultrasonic dispersion is further performed on the obtained mixture The treatment was carried out for 5 minutes at an output of 80% using the same ultrasonic homogenizer as above.
Then, the obtained ceramic slurry composition is subjected to ultrasonic irradiation (frequency: 38 kHz, output: 180 W) in an ultrasonic water bath (ultrasonic cleaning machine US-5KS, manufactured by NSD Co., Ltd.) using a rotary evaporator. While evaporating the ethyl alcohol and methyl ethyl ketone, the solvent was completely removed by further holding in a dryer at 50 ° C. for 12 hours to obtain a solid mixture containing alumina and single-walled carbon nanotubes.
Finally, 10 g of the obtained solid mixture is introduced into a carbon mold with a diameter of 30 mm, and hot pressed and sintered in an argon gas atmosphere using a multipurpose high temperature furnace (manufactured by Fuji Electric Wave Co., Ltd., Hi-Multi 5000) A sintered body (conductive ceramic) of about 4 mm was obtained. In hot-press sintering, the temperature is raised to a temperature of 1100 ° C. under a vacuum reduced pressure of 10 ⁻² Pa or less, thereafter uniaxial pressure of 30 MPa is applied at a temperature of 1100 ° C., and argon gas is introduced. The temperature was raised to ° C. and held for 1 hour.
Then, the iron content, volume resistivity and relative density of the produced sintered body (conductive ceramic) were measured.
Further, for the measurement of bending strength, 26 g of the obtained solid mixture was introduced into a carbon mold of 45 mm in diameter, and a sintered body (conductive ceramic) was obtained in the same procedure as described above. Then, the bending strength of the produced sintered body (conductive ceramic) was measured.
The results are shown in Table 1.

  From Table 1, in Examples 1-5, it turns out that it is precise | minute and the electroconductive ceramic which is excellent in electrical conductivity is obtained.

(Example 6)
Alumina powder having an average particle size of 0.1 μm (TM-DAR manufactured by Daimei Chemical Industries, Ltd., average particle size: 0.1 μm) as alumina powder, and alumina powder having an average particle size of 3 μm (Sumitomo Chemical Co., Ltd. A sintered body (conductive ceramic) in the same manner as in Comparative Example 3 except that 35 g of a mixture of AA-3 and an average particle size of 3 μm (TM-DAR: AA-3 (volume ratio) = 50: 50) was used. Were prepared.
Then, the iron content, volume resistivity, relative density and bending strength of the produced sintered body (conductive ceramic) were measured. The results are shown in Table 2.

  From Table 2, it can be seen that in Example 6, a compact sintered body having excellent conductivity can be obtained.

(Examples 7 to 9)
Solid mixtures were prepared in the same manner as in Examples 1, 2 and 4, respectively.
Then, 10 g of the obtained solid mixture is put in a mold with a diameter of 10 mm and molded with a uniaxial pressure of 10 MPa, and then pressed with a cold isostatic press at a pressure of 200 MPa to sinter powder The body was made. The obtained green compact was put into a BN crucible, and pressureless sintering was performed at a temperature of 1400 ° C. for 1 hour in an argon atmosphere.
Then, the iron content, volume resistivity, relative density and bending strength of the produced sintered body (conductive ceramic) were measured. The results are shown in Table 3.

  It can be seen from Table 3 that a sintered body which is compact and excellent in conductivity can be obtained also in pressureless sintering.

  According to the present invention, it is possible to obtain a conductive ceramic which is dense and excellent in electric conductivity.

Claims (4)

Containing alumina and single-walled carbon nanotubes,
The content ratio of the single-walled carbon nanotube is 0.05% by volume or more and 0.7% by volume or less,
Electroconductive ceramics whose volume resistivity is 10 ^<-2 > ohm * cm or more and 10 ^{< 6} > ohm * cm or less. The conductive ceramic according to claim 1, wherein a BET specific surface area of the single-walled carbon nanotube is 800 m ² / g or more.   The conductive ceramics according to claim 1 or 2 whose mean diameter of said single-walled carbon nanotube is 3 nm or more and 5 nm or less.   Electroconductive ceramics in any one of Claims 1-3 whose content of iron is 5 mass ppm or less.