JP2008087987A - Nitride composite ceramic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitride composite ceramic which can be used in the electrical discharge machining of Si<SB>3</SB>N<SB>4</SB>or AlN. <P>SOLUTION: A technique of giving conductivity by adding a metal carbide or nitride as an accessory component has been proposed. A conductive ceramic in an amount of 1 to 35 vol% is finely dispersed in carbide or nitride (Si<SB>3</SB>N<SB>4</SB>or AlN) to prepare a nitride composite ceramic sintered compact having a texture which contains no coarse particles having a particle size of 5 μm or more formed by the aggregation of the conductive ceramic. The nitride composite ceramic sintered compact is suitable for semiconductor-holding equipment, a reflecting mirror for optical position measurement, an implement for precision component processing, a precision press, a stamping die, a heat-dissipating member and a heat conduction member, a heater and an electrostatic chuck. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a composite ceramic made of nitride and carbide having a fine structure.

Conventionally, Si ₃ N ₄ is generally mass-produced as a cutting tool, a pipe-making roll, a wear-resistant member, a heat-resistant member, etc. due to its hardness, high fracture toughness, wear resistance and the like. Si ₃ N ₄ itself is a hard-to-sinter material, and for materials that are mass-produced, several percent of sintering aids such as Al ₂ O ₃ , Y ₂ O ₃ , AlN, TiN are added to Si ₃ N _4. It is a general composition. Whether the auxiliary material present in the grain boundary of _Si 3 _{N 4,} make some solid solution and _Si 3 _{N 4,} lowering the sintering temperature.

AlN has no special mention in mechanical performance, but its thermal conductivity is higher than that of other ceramics and is 150 to 250 W / m · K. Because of its high heat resistance, it is used as a heat conducting material or heat radiating member at high temperatures.

Since Si ₃ N ₄ and AlN are insulators having a single electrical resistivity of 1 × 10 ¹² (Ω · cm) or more, electric discharge machining cannot be performed and the shape of the sintered body is limited. was there.

There are various advantages of compounding Si ₃ N ₄ , AlN and a conductive additive, but the most important point is the electrical characteristics. Other advantages include adjustment of the coefficient of thermal expansion, suppression of Si ₃ N ₄ and AlN grain growth, improvement of strength and toughness due to crack growth inhibition effect, and prevention of cracks, chips and chipping associated therewith.

A number of composite materials have been proposed in which the toughness, strength, chipping resistance and sinterability of the material are combined by combining such Si ₃ N ₄ and AlN with conductive additives. Representative documents on Si ₃ N ₄ are cited from Patent Document 1 and Patent Document 2.

In Patent Document 1, 0.5 to 30% of a 4a to 6a group metal compound is added to Si ₃ N ₄ , and electric discharge is less than 10 ⁻³ (Ω ⁻¹ · cm ⁻¹ ). Possible sintered bodies have been proposed. The raw material powder has an average particle size of 1 μm or less.
In Patent Document 2, 0.05 to 5% of an oxide sintering aid and 1 to 25% by volume of a compound of Ti, Ta, Hf, W, Mo, Zr, and Cr are added to Si ₃ N ₄ powder. A conductive Si ₃ N ₄ material is disclosed.

Further, AlN is cited from Patent Document 3 and Patent Document 4.
Patent Document 3 proposes a heater having an AlN resistor in which AlN is a main component and Ti and Zr compounds are dispersed by 0.1% or more. There is a description that this heater has an electrical resistivity of 1 (Ω · cm) or less.
Patent Document 4 discloses a ceramic composite containing AlN of a nonconductive ceramic as a main component and containing a group 4a-6a metal compound.

Japanese Patent Laid-Open No. 57-200265 JP 58-041771 A Japanese Patent Laid-Open No. 04-308680 JP, 01-133968, A Composite ceramic is usually manufactured by the following method. Mixing is performed using a ball mill, an attritor, a blast mill, etc., and both powders need to be mixed uniformly. Drying and granulation are generally performed using stationary drying or a spray dryer. The press molding uses a die press or a cold isostatic press (CIP) method. If necessary, intermediate processing is performed on the green compact thus obtained. The conventional method of sintering green compacts is to use an atmospheric furnace, vacuum furnace, pressure furnace, atmospheric furnace, hot press furnace, etc., but new sintering methods such as energized plasma sintering have become common. ing. In order to obtain a higher density, hot isostatic pressing (HIP) may be performed after this sintering step. The above is the most common process for obtaining composite ceramics.

In recent years, applications that cannot be solved by the technique described in the prior art have become conspicuous.
For example, Si ₃ N ₄ -based ceramics are actively used for semiconductor holding devices, optical position measuring reflectors, jigs for processing precision parts, precision presses, punching dies, and the like. Among these, particularly when used as a mold, a complicated shape is often required. Si ₃ N ₄ alone is an insulator and cannot be subjected to electric discharge machining, and is hard and mechanically difficult to machine because it is hard and tough.

On the other hand, AlN is lower in hardness and toughness than Si ₃ N ₄ and is a flaw-working material, but conversely, the end portion of the sintered body tends to cause chipping and chipping during processing and use. AlN is also not electroprocessable like Si ₃ N ₄ . As the use of AlN, in addition to a heat radiating member and a heat conducting member, application examples to a heater and an electrostatic chuck are increasing.

Therefore, as described in the cited document, a technique for imparting conductivity by adding metal carbide or nitride as a subsidiary component has been proposed, but carbide or nitride as a conductive additive has coarse particles. In this case, carbide / nitride particles frequently fall off during processing and use. This is noticeable when the carbide / nitride coarse particles exceed 5 μm.

The problem to be solved by the present invention is to make these nitride ceramics conductive enough to be electroprocessed and to prevent the formation of coarse particles of conductive carbide / nitride.

An object of the present invention is to obtain a material having the following characteristics with respect to Si ₃ N ₄ and AlN ceramics which are nitrides.
1. It must have conductivity (1 × 10 ⁻¹ (Ω · cm) or less) to the extent that electrical processing can be performed by adding a conductive additive.
2. The maximum particle diameter and major axis of the conductive additive in the sintered body are 5 μm or less. The major axis in this case refers to the longest distance of non-spherical particles.

If explanation is added about these, it will become as follows.
1. The content of the conductive additive needs to be mixed within a range where the characteristics of the sintered body can be obtained. However, the bonding between the particles of carbide and nitride, which are conductive additives, easily causes separation, and this tendency becomes stronger as the particle diameter increases. Therefore, the carbide / nitride needs to be more finely dispersed.
As for the composition, it is difficult to obtain sufficient conductivity when the conductive additive is added in an amount of 1% by volume or less, and if it is added in an amount exceeding 35% by volume, not only the advantages of Si ₃ N ₄ and AlN can be utilized. In other words, the conductive particles tend to be coarse crystals, and the desired properties cannot be obtained. As the conductive additive, it is particularly suitable to select one or more of TiN, TiC, TaC, NbC, WC, Cr ₃ C ₂ and VC.
2. Carbides and nitrides, which are conductive additives, frequently fall out of carbide / nitride particles during processing and use when the particles become coarse. This is seen when the carbide / nitride coarse particles exceed 5 μm (diameter or major axis). Therefore, as a method in which the conductive additive of 5 μm or more is not generated, the average particle diameter of the raw material powder of the conductive additive is set to 200 nm or less.

Techniques for imparting conductivity by adding metal carbide or nitride as a subsidiary component have been proposed, but 1 to 35% by volume in the carbide or nitride (Si ₃ N ₄ or AlN) that is a conductive additive. By obtaining a sintered body having a structure free from coarse particles of 5 μm or more in which the conductive ceramics are aggregated in the structure, a semiconductor holding device, a reflector for optical position measurement, a jig for processing precision parts Thus, it was possible to obtain a nitride sintered body suitable for precision presses, punching dies, heat radiating members, heat conducting members, heaters and electrostatic chucks.

Hereinafter, embodiments of the present invention will be described based on examples.

(Raw material / powder)
As raw material powders of Si ₃ N ₄ and AlN as the main components, raw material powders having an average particle size of 1.0 μm or less, more preferably 0.5 μm or less are prepared. Further, fine powders having an average particle diameter of 10 nm to 200 nm are used as the carbide and nitride which are conductive additives occupying 1 to 35% by volume.
The conductive additive particles grow during sintering (conversely, densification does not proceed sufficiently under the condition that the conductive additive does not grow). In anticipation of grain growth of carbide particles during sintering, the raw material powder must be in the above range. Within this average particle size range, the maximum particle size of the conductive particles after sintering can be controlled to 5 μm or less even after sintering and densification have sufficiently proceeded at about 1500 ° C. to 1900 ° C. . If a raw material powder exceeding 200 nm is used, when it is made a sufficiently dense sintered body (theoretical density ratio 99% or more), the conductive additive takes an overall continuous structure, so that it is controlled to 5 μm or less. Is impossible.
Since the raw material powder of conductive additive particles of less than 10 nm is very difficult to obtain, it is difficult to use industrially (this particle diameter is not excluded). The method for producing fine powder of conductive additive is a method in which an organic metal-containing material is liquefied with a solvent, and a carbon source / nitrogen source is added thereto and carbonized in a furnace, mechanical milling, jet pulverization, etc. Any means can be used as long as a sufficient particle size can be obtained.
Tables 1 and 2 show the experimental conditions obtained by changing the particle diameter and composition of the conductive additive material. The sintering temperature is a temperature at which a high density is obtained by changing various temperature conditions.

Further, although not specifically described in the table, Si ₃ N ₄ and AlN in this case are not limited to pure nitrides, but include MgO, Y ₂ O ₃ , SiO ₂ , CaO, TiO ₂ , It should be noted that substances used as sintering aids for known oxides, such as rare earth oxides, are within the scope of the present invention if the amount is not particularly large (3% by volume or less of the total). .
In addition, the average particle diameter of the raw material powders of Si ₃ N ₄ and AlN is unified at 0.5 μm.

(Molding / Sintering)
The molding can be performed by press molding to obtain a desired shape. Intermediate processing can also be performed on the green compact with a machine tool. The obtained molded body can be sintered at about 1500 to 1900 ° C. in a non-reducing atmosphere furnace. More preferably, the atmosphere is pressurized at about 10 atm using N ₂ gas or non-oxidizing gas. This experiment is the result of adjusting the sintering temperature, searching for a condition that provides a sufficient density with the theoretical density ratio, and sintering at that temperature.
Further, if the object is a flat plate, it is possible to simultaneously perform molding and sintering using HP (hot press). The temperature at this time was 1400 to 1800 ° C., and the atmosphere was an N ₂ atmosphere. The pressure of the hot press was unified at 300 MPa.
Furthermore, in any of the above cases, pores can be further reduced by performing HIP treatment after sintering.
The relative density (ratio to theoretical density) and electric resistivity of the sintered body sintered under the composition and sintering conditions shown in Table 1 and Table 2 were measured. Moreover, the presence or absence of coarse particles (thickness exceeding 5 μm) was determined by observation. The maximum distance was performed by observing lapping cross-section with an optical microscope, a 1 mm ^2.
These results are shown in Tables 3 and 4.

The numbers marked with * in the samples of Tables 1 to 4 are comparative examples outside the scope of the present invention.

(Evaluation organization and lapping surface roughness)
In the samples of the present invention shown in Table 3 and Table 4, coarse particles of a conductive additive of 5 μm or more are not observed, and the electric resistivity is 1 × 10 ⁻² (Ω · cm) or less, which is a stable type. Carved electrical discharge machining and wire electrical discharge machining were possible.

On the other hand, the comparative example which gave "*" to the sample number is outside the scope of the present invention.
* Since Sample 1 had a small amount of conductive additive (TaC), a dense sintered body without coarse particles was obtained, but the sintered body was not conductive.
* In Sample 6, since the amount of the conductive additive (TaC) was too large, the conductive additive continued throughout, and coarse particles exceeding 20 μm were generated.
* Sample 14 was too large at the time of powder of the conductive additive, so that coarse particles exceeding 20 μm were generated, but conductivity was not obtained.
* Sample 16 and * Sample 19 are obtained by adding the same conductive particles as Sample 17 and Sample 20, respectively, but the sintering conditions are different. * Sample 16 and * Sample 19 were insufficient for densification of the sintering conditions, so that a sufficiently dense structure could not be obtained. This occurs because the additive fine particles are insufficiently sintered, and the electric resistivity is also high.
Moreover, in all the samples of the Example of this invention, the distance of electroconductive particle and the other electroconductive particle nearest to it was 2 micrometers or less, and it turned out that the fine particle is disperse | distributing uniformly. From a microscopic point of view, the structure is homogeneous, which can be expected to improve surface roughness. Further, since it is homogeneous, there is no portion that is weak in strength and becomes the starting point of destruction, and therefore physical properties are also improved. Furthermore, the voltage value in electric discharge machining is constant, and inconvenience such as cutting of the machining wire does not occur.

In the nitride-based composite ceramics of the present invention, Si ₃ N ₄ composite ceramics are free from defects such as chipping, cracking and grain removal, and are used for holding devices for semiconductors, reflecting mirrors for optical position measurement, and jigs for processing precision parts. It was suitable as a material for precision presses, punching dies, etc., and was capable of electrical discharge machining.
Moreover, the AlN composite ceramics are sufficiently resistant to use in heaters and electrostatic chucks in addition to heat radiating members and heat conducting members, and can be subjected to electric discharge machining.

The present invention can be used for the following applications.
Lens molding die, semiconductor manufacturing jig, electrostatic chuck, cutting tool, blade, voltage nonlinear resistor, vacuum chuck, semiconductor holder, heating element, heat sink, sliding member, precision mold, optical reflector, High temperature members, wear resistant members, sliding members, bearings, gas sensors, piezoelectric elements, molten metal containers, sliding nozzles, immersion nozzles, etc.

Claims (1)

A nitride-based composite ceramic in which 1 to 35% by volume of a conductive ceramic (electric resistivity is 1 × 10 ⁻² (Ω · cm) or less) is finely dispersed in Si ₃ N ₄ or AlN,
There is no coarse grain of 5μm or more in which the conductive ceramics aggregate in the structure,
Nitride-based composite ceramics characterized by being capable of electric discharge machining.