JP2014065635A - Low thermal expansion ceramics and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide low thermal expansion ceramics in which a size of cracks can be miniaturized and changes of flatness of surfaces processed with high accuracy can be prevented even under circumstance having temperature changes, and to provide its manufacturing method.SOLUTION: Low thermal expansion ceramics contains β-eucryptite and one or more kinds selected from silicon carbide and silicon nitride, and has a relative density of 99% or more, an average particle diameter of a sintered body of 0.5 μm or less, and an average thermal expansion coefficient at 20°C or higher and 30°C or lower of -1×10/°C or more and 1×10/°C or less. In the low thermal expansion ceramics, a size of microcracks can be miniaturized and changes of flatness of surfaces processed with high accuracy can be prevented because its sintered body has the average particle diameter of 0.5 μm or less. Therefore, it is suitably used for example as a mirror for positioning of a semiconductor manufacturing apparatus.

Description

  The present invention relates to a low thermal expansion ceramic comprising β-eucryptite and one or more materials selected from silicon carbide and silicon nitride, and a method for producing the same.

Conventionally, low thermal expansion ceramics have high rigidity in addition to low thermal expansion, and are therefore used as positioning mirrors and stage members for semiconductor manufacturing equipment. As the low thermal expansion ceramics, one made of eucryptite and one or more materials selected from silicon carbide, silicon nitride and the like is known (see Patent Document 1). The low thermal expansion ceramic described in Patent Document 1 has an average thermal expansion coefficient at 20 to 30 ° C. of −1 × 10 ⁻⁶ to 1 × 10 ⁻⁶ / ° C.

  On the other hand, ceramics formed by blending β-eucryptite and β-wollastonite with an average crystal grain size of 2 μm or less are disclosed (see Patent Document 2). The ceramic described in Patent Document 2 has been developed for the purpose of improving workability.

JP 2004-224607 A JP 2000-1386 A

  As described above, low thermal expansion ceramics are excellent in low thermal expansion properties and high rigidity, and are used for mirror members, etc., but in particular, in composite material ceramics, a plane processed with high accuracy causes a change over time. There are circumstances that make it easy.

  Eucryptite constituting a composite material-based low thermal expansion ceramic is a negative expansion ceramic, and one factor that develops negative expansion is microcracks existing in the particles of the sintered body structure. The low thermal expansion ceramic as described above achieves zero expansion at 23 ± 3 ° C. by adding silicon carbide and silicon nitride which are positive expansion to eucryptite which is negative expansion and adjusting the blending thereof. .

  However, in an environment of 5 ° C. or lower, the flatness of the surface processed with high accuracy may change due to microcracks present in the sintered particles. For example, when the flatness of the mirror part of a φ300 disk mirror member is processed to 0.060 μm, the flatness of the mirror part changes to 0.200 μm when exposed to an environment of −5 ° C. for a certain period of time. . This change in accuracy becomes fatal for a positioning mirror of a semiconductor manufacturing apparatus. In addition, strict temperature control is required also in the transportation and storage methods of materials.

  The present invention has been made in view of such circumstances, and has a low thermal expansion capable of minimizing the size of a crack and preventing a change in flatness of a surface processed with high accuracy even in an environment where there is a temperature change. An object of the present invention is to provide ceramics and a method for producing the same.

(1) In order to achieve the above object, the low thermal expansion ceramic of the present invention is a low thermal expansion ceramic composed of β-eucryptite and one or more materials selected from silicon carbide and silicon nitride, and has a relative density. Is 99% or more, the average particle diameter of the sintered body is 0.5 μm or less, and the average thermal expansion coefficient at 20 ° C. or more and 30 ° C. or less is −1 × 10 ⁻⁶ / ° C. or more and 1 × 10 ⁻⁶ / ° C. or less. It is characterized by being.

  Thus, since the low thermal expansion ceramic of the present invention has an average particle size of 0.5 μm or less of the sintered body, the size of the microcrack can be reduced and the flatness of the surface processed with high precision can be prevented. . Therefore, it can be suitably applied to, for example, a positioning mirror of a semiconductor manufacturing apparatus.

  (2) In addition, the low thermal expansion ceramic of the present invention is characterized in that the number of pores of 10 μm or more is 1 per field or less on average in 10 fields when observed with a 500 × field of view with an electron microscope. . Since the number of large pores is reduced as described above, it is possible to prevent a change in flatness of a surface processed with high accuracy.

  (3) Further, the low thermal expansion ceramic of the present invention is characterized in that the number of microcracks having a length of 10 μm or more is 1 or less in total in 10 fields when observed with an electron microscope at a magnification of 3000 times. It is said. Thereby, since the number of large cracks is reduced, a change in flatness of the surface processed with high accuracy can be prevented.

  (4) Further, the low thermal expansion ceramic of the present invention is characterized in that the Young's modulus is 140 GPa or more. Thereby, it can use suitably for the member of a semiconductor manufacturing apparatus, etc. as a low thermal expansion ceramics which has high rigidity.

  (5) Further, the low thermal expansion ceramic of the present invention is characterized in that the three-point bending strength is 250 MPa or more. Thereby, low thermal expansion ceramics having high strength can be realized.

  (6) The method for producing a low thermal expansion ceramic of the present invention is a method for producing a low thermal expansion ceramic comprising β-eucryptite and one or more materials selected from silicon carbide and silicon nitride, A pulverization step in which a raw powder of eucryptite and a raw material powder of one or more materials selected from silicon carbide and silicon nitride are mixed and pulverized to have an average primary particle size of 0.25 μm or less, and obtained by the pulverization step. A molding step for pressure-molding the powder, a firing step for firing the molded body obtained in the molding step at 1200 to 1315 ° C., and an HIP treatment for performing HIP processing at 100 MPa or more and 1150 to 1300 ° C. And a process.

  As described above, since the method for producing the low thermal expansion ceramic of the present invention is mixed and pulverized to have an average primary particle diameter of 0.25 μm or less, it is processed with high accuracy by reducing the size of cracks in the sintered body. The change in flatness of the surface can be prevented.

  According to the present invention, it is possible to reduce the size of a crack and prevent a change in flatness of a surface processed with high accuracy even in an environment where there is a temperature change.

(A), (b) is a 500 times SEM photograph of an Example and a comparative example, respectively. (A), (b) It is the SEM photograph of 1500 times of an Example and 3000 times of a comparative example, respectively.

(Configuration of low thermal expansion ceramics)
The low thermal expansion ceramic (hereinafter, low thermal expansion ceramic) of the present invention is composed of β-eucryptite and one or more materials selected from silicon carbide and silicon nitride. β-eucryptite has the characteristic of negative expansion that contracts with increasing temperature, and one or more materials selected from silicon carbide and silicon nitride have the characteristic of positive expansion that expands with increasing temperature. doing.

By constituting a composite material with a composition in which these cancel each other's expansion, they are configured as low thermal expansion materials. The average coefficient of thermal expansion of the low thermal expansion ceramics thus configured at 20 ° C. or higher and 30 ° C. or lower is −1 × 10 ⁻⁶ / ° C. or higher and 1 × 10 ⁻⁶ / ° C. or lower.

  Further, the low thermal expansion ceramic is densified to a relative density of 99% or more, and the average particle size of the sintered body is 0.5 μm or less. The β-eucryptite constituting the low thermal expansion ceramic has microcracks, and the microcracks function to cause negative expansion characteristics.

  However, on the other hand, the flatness of the processed surface is likely to change due to the presence of microcracks. On the other hand, in the low thermal expansion ceramic of the present invention, the structure of the sintered body is controlled to reduce the particle size. Specifically, by reducing the size of the sintered particles of the sintered body (particle diameter: 0.5 μm or less), the number of microcracks themselves existing in the particles is reduced, and further the size of the cracks is reduced. It is miniaturized. Thereby, the change of the flatness of the surface processed with high precision can be prevented. This can be suitably applied, for example, as a positioning mirror of a semiconductor manufacturing apparatus.

  When the low thermal expansion ceramic is observed with an electron microscope in a 3000-fold field of view, the number of microcracks having a length of 10 μm or more is preferably 1 or less in total for 10 fields of view. Thereby, since the number of large cracks can be reduced, a change in the flatness of the surface processed with high accuracy can be prevented.

  Further, when the low thermal expansion ceramic is observed with an electron microscope in a field of magnification of 500 times, the number of pores of 10 μm or more is preferably 1 per field or less on average in 10 fields of view. When the number of microcracks is reduced, the number of pores is also reduced, and a change in flatness of the processed surface can be prevented.

  The low thermal expansion ceramic preferably has a Young's modulus of 140 GPa or more. Thereby, it becomes suitable for the member of a semiconductor manufacturing apparatus etc. as a low thermal expansion ceramics which has high rigidity. Further, the three-point bending strength is preferably 250 MPa or more. This can be applied to low thermal expansion ceramics having high strength.

(Production method of low thermal expansion ceramics)
A method for producing the low thermal expansion ceramics configured as described above will be described. First, β-eucryptite powder and powder of one or more materials selected from silicon carbide and silicon nitride are mixed and ground. The blending ratio at that time is a predetermined blending ratio designed so that the thermal expansion coefficient is low. In this way, a powder having an average primary particle size of 0.25 μm or less is obtained (pulverization step).

  And the powder obtained at the crushing process is pressure-molded (molding process). Next, the molded body obtained in the molding step is fired at a firing temperature of 1200 ° C. or higher and 1315 ° C. or lower (firing step). Finally, the HIP treatment is performed at 100 MPa or higher and 1150 ° C. or higher and 1300 ° C. or lower (HIP processing step).

  As mentioned above, the average primary particle size of the raw material is 0.25 μm or less during mixing and grinding, so the size of the cracks in the sintered body is miniaturized and changes in the flatness of the surface processed with high precision are prevented. it can. The use of fine powder is one point for reducing the size of the sintered particles of the sintered body, but it is also a point to sinter at the lowest possible temperature.

  If the primary particle diameter of the raw material powder is 1.0 μm, it can be densified to a relative density of 98% or more in the range of 1280 to 1380 ° C. However, since the grains grow in the high temperature region, the sintered particle diameter is about 3 to 4 μm.

  By controlling the primary particle diameter of the raw material powder to 0.25 μm or less, the firing temperature can be lowered, and the relative density becomes 98% at 1250 to 1380 ° C. Furthermore, when the densification range is expanded to a relative density of 95% or more, the temperature becomes 1200 to 1380 ° C. However, even if the raw material powder is atomized, if sintered in a high temperature region, the particle size of the sintered body becomes 0.5 μm or more.

  Therefore, it can be seen that 1200 to 1315 ° C. is a firing temperature at which the particle diameter of the sintered body particles is 0.5 μm or less and the relative density is 95% or more. After that, by carrying out HIP treatment at 1150 to 1300 ° C. at an atmospheric pressure of 100 MPa or higher in Ar, the sintered compact particles can be densified to a relative density of 99% while maintaining the particle diameter of 0.5 μm or less. it can.

(Production conditions of the examples)
The low thermal expansion ceramic of the example was produced by the above production method. Add 22% by mass of silicon carbide powder and 1% by mass of silicon nitride to 77% by mass of β-eucryptite powder, add this together with ethanol solvent and alumina balls into a ball mill, and mix and pulverize for 5 to 48 hours in a wet manner. Was done.

The mixed pulverized powder thus obtained was dried and pulverized, and then the primary particle size was measured using a laser scattering particle size distribution analyzer. As a result, a raw material powder having an average primary particle size of 0.22 to 0.24 μm was obtained. The obtained mixed pulverized powder was uniaxially pressed at 100 kg / cm ² for 1 minute, and then subjected to cold isostatic pressing at 1200 kg / cm ² for 1 minute to produce a molded body. The molded body was fired at a firing temperature of 1200 to 1315 ° C. in a nitrogen atmosphere. The fired body was further subjected to HIP treatment at 1150 to 1300 ° C. under an atmospheric pressure of 100 MPa or more in Ar (Sample Nos. 1 to 4).

(Production conditions for the comparative example)
As a comparative example, β-eucryptite and silicon carbide were mixed and pulverized to obtain a raw material powder having an average primary particle diameter of 2 μm, which was molded under the same conditions as in the above examples, and a firing temperature of 1200 ° C. in a nitrogen atmosphere. Baked in. Furthermore, HIP treatment was performed at 1150 ° C. in Ar at an atmospheric pressure of 100 MPa or more (Sample No. 5).

  In addition, the mixture was pulverized under the same conditions as in the above example, and a raw material powder having an average primary particle size of 0.25 μm was molded under the same conditions as in the above example, and the firing temperature was 1320 ° C. in a nitrogen atmosphere. Baked in. Further, HIP treatment was performed at 1300 ° C. under an atmospheric pressure of 100 MPa or more in Ar (sample No. 6).

In addition, the mixture was pulverized under the same conditions as in the above example, a raw material powder having an average primary particle size of 0.25 μm was used, and it was molded under the same conditions as in the above example. Baked in. Furthermore, HIP treatment was performed at 1100 ° C. under an atmospheric pressure of 100 MPa or more in Ar (sample No. 7). The following table shows the production conditions of the samples of the examples and comparative examples.

(Evaluation results)
The relative density of each sintered body thus obtained was measured by the Archimedes method. Also, the surface of each ceramic sintered body is processed, the surface is observed with a scanning electron microscope (SEM), and the number of pores when the surface is observed with a microscope at an average particle diameter of 500 times, 3000 times. The number of microcracks when the surface was observed with a microscope was measured.

(SEM observation)
1 (a) and 1 (b) show sample Nos. Of Examples. 1 and Comparative Sample No. 5 is an SEM photograph 500 times as large as 5; As shown to Fig.1 (a), the surface of the low thermal expansion ceramic of the Example was uniform, and the pore was not found from the visual field. The average of 10 fields was 1 per field or less. Further, as shown in FIG. 1B, two pores 10 having a diameter of about 10 μm were found on the surface of the ceramic of the comparative example. The average of 10 fields was 2.2 / field.

  2 (a) and 2 (b) are SEM photographs of 1500 times of the example and 3000 times of the comparative example, respectively. As shown in FIG. 2 (a), the low thermal expansion ceramic of the example is composed of particles having an average particle diameter of 0.5 μm, and no microcracks of about several μm were found even in a total of 10 fields of view. Further, as shown in FIG. 2B, the ceramic of the comparative example is composed of particles having an average particle diameter of 5 μm, and two cracks 20 of about 10 μm were found. In addition, a total of 12 fields were found.

In addition, the thermal expansion coefficient, Young's modulus, bending strength, and accuracy change were evaluated for each sample. The Young's modulus was evaluated by a bending resonance method using a measuring device (room temperature Young's modulus measuring machine / JE-RT3 manufactured by Nippon Techno Plus Co., Ltd.) in accordance with “JISR1602 Fine Ceramic Elasticity Test Method”. The bending strength was evaluated using a measuring device (Autograph AG-2000B / manufactured by Shimadzu Corporation) based on “JIS R1601 Fine Ceramics Room Temperature Bending Strength Test Method”. The accuracy change was evaluated according to the following procedure. That is, a φ200 × 10t material was prepared from each sintered body sample, and the upper surface was lapped after surface grinding of the upper and lower surfaces, and the flatness was finished to 0.05 μm. And it preserve | saved for 24 hours in -5 degreeC environment, and measured the flatness of the upper surface with the optical surface property measuring machine (zygo). The following table summarizes the evaluation results.

  As a result of the above evaluation, sample No. 1 to 4 sufficiently cleared the specified values in all items. There was no problem with the change in accuracy, with a change in flatness of ± 0.02 μm or less. On the other hand, sample No. 5 has a relative density of less than 99%, an average particle diameter of the sintered body is larger than 0.5 μm, the number of pores is greater than 1 / field of view, the number of microcracks is greater than 1, and the accuracy changes. Also, there was a change of +0.100 μm or more, and the prescribed value was not satisfied.

  Sample No. 6 had a relative density of 99% or more, but the average particle size of the sintered body was larger than 0.5 μm. Further, although the number of pores was 1 / viewing field or less, the number of microcracks was more than 1, and the change in accuracy was +0.100 μm or more, and the specified value was not satisfied.

  Sample No. 7 had a relative density of less than 99% and an average particle size of the sintered body of less than 0.5 μm. Further, the number of pores was greater than 1 per field of view, the number of microcracks was greater than 1, and the change in accuracy was measured by +0.100 μm or more, and the prescribed value was not satisfied.

  As described above, in the ceramic sintered body of the comparative example, it was found that pores and cracks were generated on the processed surface, and the flatness thereof was easily changed.

  In contrast, the low thermal expansion ceramic sintered body of the example has an average particle size of 0.5 μm or less, no pores or cracks of several μm, and it has been found that changes in flatness of the processed surface can be prevented.

10 pore 20 micro crack

Claims (6)

A low thermal expansion ceramic comprising β-eucryptite and one or more materials selected from silicon carbide and silicon nitride,
The relative density is 99% or more, the average particle size of the sintered body is 0.5 μm or less,
A low thermal expansion ceramic characterized in that an average thermal expansion coefficient at 20 ° C. or higher and 30 ° C. or lower is −1 × 10 ⁻⁶ / ° C. or higher and 1 × 10 ⁻⁶ / ° C. or lower.   2. The low thermal expansion ceramic according to claim 1, wherein the number of pores of 10 μm or more is 1 per field or less on average in 10 fields when observed with an electron microscope at a magnification of 500 times.   3. The low thermal expansion according to claim 1, wherein the number of microcracks having a length of 10 μm or more is 1 or less in total when viewed with an electron microscope at a magnification of 3000 times. Ceramics.   The low thermal expansion ceramic according to any one of claims 1 to 3, wherein Young's modulus is 140 GPa or more.   The low thermal expansion ceramic according to any one of claims 1 to 4, wherein a three-point bending strength is 250 MPa or more. A method for producing a low thermal expansion ceramic comprising β-eucryptite and one or more materials selected from silicon carbide and silicon nitride,
a crushing step of mixing and crushing a raw powder of β-eucryptite and a raw material powder of one or more materials selected from silicon carbide and silicon nitride so as to have an average primary particle size of 0.25 μm or less;
A molding step of pressure-molding the powder obtained in the pulverization step;
A firing step of firing the molded body obtained in the molding step at 1200 ° C. or higher and 1315 ° C. or lower;
And a HIP processing step of performing HIP processing at 100 MPa or higher and 1150 ° C. or higher and 1300 ° C. or lower.