JP5421092B2 - Alumina sintered body - Google Patents

Description

  The present invention relates to an alumina sintered body, and in particular, a member such as an inner wall material (chamber) of a semiconductor manufacturing apparatus, a microwave introduction window, a shower head, a focus ring, a shield ring, or a stage of a liquid crystal manufacturing apparatus. The present invention relates to an alumina sintered body for a corrosion-resistant member that can be suitably used for mirrors, mask holders, mask stages, chucks, reticles, and the like.

  Conventionally, alumina sintered bodies are excellent in heat resistance, chemical resistance, and plasma resistance, and have a low dielectric loss tangent (tan δ) in the high frequency region, so they have been used for semiconductors and high frequency plasma device members for liquid crystals. ing.

  Semiconductor and liquid crystal manufacturing equipment members are in contact with highly reactive halogen-based corrosive gases used for etching and cleaning, and their plasmas, so high corrosion resistance is required. Generally, 99.0% by mass or more There is a need for a high-purity alumina sintered body. On the other hand, the dielectric loss tangent increases from the viewpoint of sinterability as it becomes a high-purity alumina sintered body, which decreases the high-frequency transmittance in the MHz band, increases energy loss, breaks the member due to heat generation, etc. Problems are known to occur.

For reducing the loss of the alumina sintered body, SiO ₂ , CaO, and MgO are included as sintering aids, and the content is controlled to be within a certain range. There is known an alumina sintered body with improved sinter (see, for example, Patent Document 1).

In Patent Document 1, and 99.8 to 99.9 wt% alumina, the balance is composed of a _SiO 2, CaO, grain boundary phase component composed of MgO having a predetermined ratio, Q value at a measuring frequency 8GHz 10,000 or more ( It is described that an alumina sintered body for a microwave resonator having a dielectric loss tangent of 0.0001 or less was obtained.

  However, the alumina sintered body of Patent Document 1 has a large dielectric loss tangent in the MHz band. For example, when used for a member for a high-frequency plasma device for semiconductors that uses a high frequency in the MHz band, The high-frequency transmittance is reduced, causing problems such as an increase in energy loss and breakage of members.

  In response to this problem, the dielectric loss tangent at a measurement frequency of 1 MHz to 8.5 GHz can be obtained by generating a crystal phase containing 99.3% by mass of alumina and containing Si, Al, Sr, and O elements at the grain boundaries. An alumina sintered body that is further reduced in size and improved in dielectric properties is known (see Patent Document 2).

In Patent Document 2, alumina is contained in an amount of 99.3% by mass or more, and a crystal phase containing Si, Al, Sr, and O elements is formed at grain boundaries, so that a dielectric at a measurement frequency of 1 MHz to 8.5 GHz is obtained. It is described that an alumina sintered body having a tangent of 5 × 10 ⁻⁴ or less was obtained.

JP-A-6-16469 International Publication No. 2009/069770 Pamphlet

However, in the alumina sintered body described in Patent Document 2, the average particle diameter of the alumina crystal particles is 20 μm or more in order to make the dielectric loss tangent at a measurement frequency of 1 MHz to 8.5 GHz 5 × 10 ⁻⁴ or less. In this case, there is a problem that the three-point bending strength is as low as 350 MPa or less, and such an alumina sintered body having a low three-point bending strength has a limitation in application development to various uses.

  An object of the present invention is to provide a high-strength alumina sintered body that can reduce the dielectric loss tangent at MHz to GHz.

The alumina-based sintered body of the present invention contains 99.3% by mass or more of Al as an element in terms of Al ₂ O ₃ , and Si and M (M is at least one of Mg, Ca, Sr and Ba) as other elements. Seed) containing alumina crystal particles as main crystal particles, the alumina crystal particles having an average particle size of 20 μm or more in terms of volume distribution average and a particle size of 10 μm or more. The triple point composed of large particles composed of crystal particles has a structure in which a plurality of small particle particles composed of the alumina crystal particles having a particle size of 5 μm or less are assembled, and the triple point is represented by MAl ₂ Si ₂ O ₈ . It is present compound, and a dielectric loss tangent 5 × ^{10 -4} or less at a measuring frequency 1 MHz, and a dielectric loss tangent 5 × ^{10 -4} or less at a measuring frequency 12 MHz, measuring Dielectric loss tangent in the frequency 8.5GHz is at 5 × ^{10 -4} or less, three-point bending strength is equal to or not less than 380 MPa.

In such an alumina sintered body, since it contains 99.3% by mass or more of alumina, it is possible to maintain the original excellent corrosion resistance, mechanical properties, and electrical properties of alumina, The average particle size is 20 μm or more in terms of volume distribution average, and small particles made of alumina crystal particles having a particle size of 5 μm or less are included in the triple point composed of large particles made of alumina crystal particles having a particle size of 10 μm or more. The presence of a compound having a plurality of aggregated structures and represented by MAl ₂ Si ₂ O ₈ at the triple point makes it possible to reduce the dielectric loss tangent in the high frequency region and simultaneously achieve high strength.

  In addition, the alumina sintered body of the present invention is characterized in that the average particle diameter of the alumina crystal particles is 10 μm or less in terms of number distribution average. In such an alumina sintered body, it means that there are a large number of small-diameter particles composed of alumina crystal particles having a particle diameter of 5 μm or less, present at the triple point composed of large-diameter particles, thereby further increasing the strength. It can be improved.

The alumina sintered body of the present invention is characterized in that the bulk density is 3.84 g / cm ³ or more .

Furthermore, the alumina sintered body of the present invention is characterized in that the amount of Na ₂ O is 0.05% by mass or less. By setting the amount of Na ₂ O in the porcelain to 0.05% by mass or less, the dielectric loss tangent can be stably achieved at 5 × 10 ⁻⁴ or less between 1 MHz and GHz.

  Further, the alumina sintered body of the present invention is characterized in that glass containing M, Al and Si is present at the three points. In such an alumina sintered body, the bonding between crystal grains is reinforced by glass, and higher strength can be promoted.

  The member for a semiconductor manufacturing apparatus and the member for a liquid crystal panel manufacturing apparatus of the present invention are characterized by comprising the above-mentioned alumina sintered body. In such a member for a semiconductor manufacturing apparatus and a member for a liquid crystal panel manufacturing apparatus, since the dielectric loss tangent is small in the frequency range between MHz and GHz, the high frequency transmittance in the MHz to GHz band can be improved and the energy loss is reduced. In addition, damage to the member due to heat generation can be suppressed, and since the strength of the alumina sintered body is high, it can be practically used for various applications.

In the alumina sintered body of the present invention, the dielectric loss tangent in a wide frequency range of MHz to GHz band can be reduced to 5 × 10 ⁻⁴ or less, and an alumina sintered body having high strength can be obtained. Therefore, by using the alumina sintered body of the present invention as a corrosion-resistant member used as a member for semiconductor and liquid crystal manufacturing equipment, it has high corrosion resistance against highly reactive halogen-based corrosive gases and their plasmas. In addition, since the alumina sintered body has a low loss in the MHz to GHz band, it can improve the high frequency transmittance in the MHz to GHz band, reduce energy loss, and suppress damage to the member due to heat generation. it can. Further, due to the improvement in strength, it is possible to suppress damage to parts due to handling during assembly.

It is a schematic sectional drawing of the structure | tissue of an alumina sintered body.

(Form 1)
The alumina-based sintered body of the present invention contains 99.3% by mass or more of Al as an element in terms of Al ₂ O ₃ , and Si and M (M is at least one of Mg, Ca, Sr and Ba) as other elements. Seeds). In other words, it contains 99.3% by mass or more of alumina and 0.7% by mass or less of other subcomponents. By containing 99.3% by mass or more of alumina, it becomes possible to maintain the excellent corrosion resistance, mechanical properties, and electrical properties of alumina.

  On the other hand, when the amount of the auxiliary component is 0.7% by mass or more, it leads to a decrease in mechanical and electrical characteristics and a decrease in corrosion resistance. Therefore, alumina is 99.3% by mass or more, and the auxiliary component is 0.7% by mass or less. Furthermore, in order to be applied as a member for a semiconductor or liquid crystal manufacturing apparatus, it is necessary to have excellent corrosion resistance to halogen-based plasma, so that alumina is 99.5% by mass or more and subcomponents are 0.5% by mass or less. Is preferred.

The alumina sintered body of the present invention comprises alumina crystal particles having alumina crystal particles as main crystal particles, the alumina crystal particles having an average particle size of 20 μm or more in terms of volume distribution average, and a particle size of 10 μm or more. It has a structure in which a plurality of small-diameter particles made of alumina crystal particles having a particle size of 5 μm or less are gathered at the three major points of the large-sized particles, and MAl ₂ Si ₂ O ₈ (M is Mg, Ca). , At least one of Sr and Ba). FIG. 1 shows a schematic cross-sectional view of an alumina sintered body. Reference numeral 1 is a large-diameter particle made of alumina crystal particles, reference numeral 2 is a small-diameter particle made of alumina crystal particles, reference numeral R is a triple point, and reference numeral 4 is a void.

By setting the average particle diameter of the large-diameter particles 1 made of alumina crystal particles to 20 μm or more in terms of volume distribution average, the grain boundary can be reduced as much as possible, and the dielectric loss tangent can be stably reduced. From the viewpoint of further stabilizing the low dielectric loss tangent, the volume distribution average particle diameter D ₅₀ of the alumina crystal particles is preferably 25 μm or more, particularly preferably 30 μm or more. On the other hand, the volume distribution average particle diameter D ₅₀ of the alumina crystal particles is desirably 70 μm or less, particularly 50 μm or less, from the viewpoint of mechanical properties.

Further, the alumina sintered body of the present invention has a small diameter particle 2 made of alumina crystal particles having a particle size of 5 μm or less at a triple point R constituted by large particle 1 made of alumina crystal particles having a particle size of 10 μm or more. And a structure in which a compound represented by MAl ₂ Si ₂ O ₈ exists in the triple point R, the strength at the triple point R composed of the large-diameter particles 1 is improved. In addition to suppressing the propagation of cracks in the alumina sintered body and improving the bending strength of the alumina sintered body, MAl ₂ Si ₂ O ₈ (M is Mg, Ca, Sr) having a low dielectric loss tangent at the grain boundary. And (at least one of Ba) compounds are formed, and the dielectric loss tangent can be lowered.

The MAl ₂ Si ₂ O ₈ compound exists at the triple point R composed of the large-diameter particles 1 made of alumina crystal particles having a particle size of 10 μm or more. Exists in the world. The MAl ₂ Si ₂ O ₈ compound inhibits the sintering of the small diameter particles 2 during sintering.

  Further, it is desirable from the viewpoint of improving the bending strength that the number of the small-diameter particles 2 made of alumina crystal particles having a particle diameter of 5 μm or less present at the triple point R is 5 or more.

From the viewpoint of lowering the dielectric loss tangent, the texture composed of a plurality of small-diameter particles 2, in other words, the triple point R, is preferably 30% or less in volume ratio with respect to the porcelain. The MAl ₂ Si ₂ O ₈ compound may be slightly deviated from the stoichiometric composition. M is preferably Mg, Ca, or Sr from the viewpoints of dielectric properties and sinterability. Among these, Sr is particularly preferable from the viewpoint of low dielectric loss tangent.

In the present invention, the compound represented by MAl ₂ Si ₂ O ₈ is a concept including a compound in which a part of the constituent element of M is replaced with another element.

  The triple point R composed of the large-diameter particles 1 made of alumina crystal particles is a grain boundary formed by three or more large-diameter particles 1 and between two surfaces composed of two large-diameter particles 1. Different from grain boundaries.

The volume distribution mean particle diameter D ₅₀ of the alumina crystal grain in the total volume of the particle, when the calculated distribution of the volume ratio with particle size occupies refers to the particle size at 50% accumulation from fine side of the cumulative particle size distribution.

In the alumina sintered body of the present invention configured as described above, the average particle diameter of the alumina crystal particles is 20 μm or more in terms of volume distribution average, and the large-diameter particles 1 made of alumina crystal particles having a particle diameter of 10 μm or more. A compound represented by MAl ₂ Si ₂ O ₈ exists in the triple point R having a structure in which a plurality of small-diameter particles 2 made of alumina crystal particles having a particle diameter of 5 μm or less are assembled. By doing so, the dielectric loss tangent in the high frequency region can be lowered, and at the same time high strength can be achieved.

That is, since a compound represented by MAl ₂ Si ₂ O ₈ (M is at least one of Mg, Ca, Sr, and Ba) has a low dielectric loss tangent in the MHz to GHz band, it has a low dielectric constant in the MHz and GHz bands. A tangential alumina sintered body can be obtained, and since the average particle size of the alumina crystal particles is as large as 20 μm or more in terms of volume distribution average, the dielectric loss tangent at MHz to GHz can be reduced.

  On the other hand, when the average particle size of the alumina crystal particles is increased, the strength tends to decrease. In the present invention, however, the triple point R composed of the large-diameter particles 1 made of alumina crystal particles having a particle size of 10 μm or more is used. Since it has a structure in which a plurality of small-diameter particles 2 made of alumina crystal particles having a diameter of 5 μm or less are gathered, the strength of the alumina sintered body can be improved.

  Furthermore, at least one of Mg, Sr, Ca and Ba functions as a sintering aid, can improve the sinterability of the alumina sintered body, and can reduce voids and defects. A low-loss alumina sintered body can be obtained in the band, and the sinterability is improved. For example, the central portion in the thickness direction of the thick sintered body is sufficiently sintered. The mechanical strength of the entire thick sintered body can be improved.

In the alumina sintered body of the present invention, it is desirable that the average particle diameter of the alumina crystal particles is 10 μm or less in terms of number distribution average. Thereby, the three-point bending strength can be improved. From the viewpoint of improving the strength, the number distribution average particle diameter D ₅₀ is preferably 7 μm or less. On the other hand, the number distribution average particle diameter D ₅₀ is preferably 2 μm or more for the reason of lower loss in the MHz band.

Here, the number distribution average particle diameter D _50, when determined the distribution of particle sizes in the total number of particles of the alumina crystal grain in an arbitrary cross-section, refers to a particle size in a cumulative 50% fine particle side of the cumulative particle size distribution.

The alumina sintered body of the present invention has a measurement frequency of 1 MHz by setting the dielectric loss tangent at a measurement frequency of 1 MHz to 5 × 10 ⁻⁴ or less and the dielectric loss tangent of a measurement frequency of 8.5 GHz to 5 × 10 ⁻⁴ or less. Even in the frequency region between ˜8.5 GHz, the dielectric loss tangent can be expected to be 5 × 10 ⁻⁴ or less. From the viewpoint of expecting a lower dielectric loss tangent of 2 × 10 ⁻⁴ or less in the above frequency range, the dielectric loss tangent of the measurement frequency 1 MHz is 2 × 10 ⁻⁴ or lower and the dielectric loss tangent of 8.5 GHz is 2 × 10 ⁻⁴ or lower. It is preferable that

That is, by measuring the dielectric loss tangent of the alumina sintered body at a frequency of 1 MHz and confirming that it is 5 × 10 ⁻⁴ or less, there is no increase in dielectric loss tangent due to space charge polarization, interface polarization, and dipole polarization. I can confirm that. Moreover, since the peak due to the increase of the dielectric loss tangent due to these factors is in a frequency band lower than 1 MHz or in the frequency of several MHz nearby, by confirming that it is 5 × 10 ⁻⁴ or less at 1 MHz, up to around 1 GHz It can be expected that there is no increase in dielectric loss tangent due to these factors.

Moreover, it can be confirmed that there is no increase in the dielectric loss tangent due to ion polarization by confirming that the dielectric loss tangent at 8.5 GHz is 5 × 10 ⁻⁴ or less. Moreover, it is confirmed that the peak due to the increase of the dielectric tangent due to ion polarization occurs in a frequency band higher than 8.5 GHz or a frequency of several GHz near 8.5 GHz and is 5 × 10 ⁻⁴ or less at 8.5 GHz. By doing so, it can be expected that the dielectric loss tangent does not increase due to the ion polarization factor up to around 1 GHz. Therefore, by confirming that it is 5 × 10 ⁻⁴ or less at 1 MHz and 5 × 10 ⁻⁴ or less at 8.5 GHz, in the frequency region between 1 MHz and 8.5 GHz, particularly between 10 MHz and 1 GHz. Can be expected to have a dielectric loss tangent of 5 × 10 ⁻⁴ or less.

Furthermore, the alumina sintered body of the present invention desirably has an amount of Na ₂ O in the porcelain of 0.05% by mass or less. Thereby, there is almost no influence on the interface polarization and space charge polarization, the dielectric loss tangent in the several MHz band can be made small, and the influence on the ion polarization is hardly made, and the dielectric loss tangent in the GHz band can be made small. A dielectric loss tangent of 5 × 10 ⁻⁴ or less can be stably achieved. In particular, the amount of Na ₂ O is preferably 0.03% by mass or less from the viewpoint of low dielectric loss tangent. To reduce the Na ₂ O content in the porcelain, to reduce the Na ₂ O content in the raw material.

Incidentally, the alumina sintered body of the present invention, the dielectric loss tangent, in view of the strength bulk density of the sintered ceramic is 3.84 g / cm ³ or more, and particularly preferably at 3.85 g / cm ³ or more.

  Similarly, from the viewpoint of dielectric loss tangent and strength, the void ratio inside the porcelain is preferably 5% or less, the number distribution average void diameter is 5 μm or less, and the maximum void diameter is 20 μm or less.

  The alumina-based sintered body of the present invention is used as a part for industrial machinery, and can be suitably used as a large and thick member used particularly for a semiconductor manufacturing apparatus or a liquid crystal manufacturing apparatus. The member for a semiconductor manufacturing apparatus in the present invention means an inner wall material (chamber), a microwave introduction window, a shower head, a focus ring, a shield ring, or the like of the semiconductor manufacturing apparatus. The liquid crystal manufacturing apparatus member means a stage, a mirror, a mask holder, a mask stage, a chuck, a reticle, and the like.

Preparation of the alumina sintered body of the present invention, for example, aluminum oxide powder of about D ₅₀ of 2μm in volume distribution, in a mixture of aluminum oxide powder of less than D ₅₀ of 1μm in volume distribution, Si source and alkaline earth A raw material powder mixed with a metal source and heat-treated is mixed, and after the mixed powder is formed, it is fired at 1500 to 1800 ° C.

Raw material powder obtained by mixing and heat-treating an alkaline earth metal (at least one of Mg, Sr, Ca and Ba) source and Si source generates MAl ₂ Si ₂ O ₈ from the Si source and alkaline earth metal source It is a powder obtained by mixing at a predetermined ratio and heat-treating at 500-1400 ° C. Thus, by using the raw material powder obtained by mixing the alkaline earth metal (at least one of Mg, Sr, Ca and Ba) source and the Si source at a ratio to produce MAl ₂ Si ₂ O ₈ and heat-treating it, A compound represented by MAl ₂ Si ₂ O ₈ can be generated. The Si source and alkaline earth metal source here may be any of salts such as metals, oxides, hydroxides, carbonates, nitrates and the like. By using the raw material powder of Si and alkaline earth metal, the distribution of Si and alkaline earth metal in the alumina sintered body can be made uniform, and the non-uniform sintered structure can be eliminated.

  In addition, it is possible to preferentially cause a reaction between Si and an alkaline earth metal, and to generate a crystal having a low dielectric loss tangent composed of Si, an alkaline earth metal, Al, and O element between alumina crystal particles.

  In some cases, the aluminum oxide powder is mixed with a raw material powder obtained by mixing and heat-treating the alkaline earth metal source and the Si source, and a raw material powder containing the Mg source, followed by firing. As the Mg source, it is possible to use salts such as metals, metal oxides, metal hydroxides, and metal carbonates as powders or aqueous solutions.

  For molding, a molding method such as press molding, casting, cold isostatic pressing, or cold isostatic pressing can be used. Next, the obtained molded body is fired in a temperature range of 1500 to 1800 ° C. As a result, a sintered body having a high density and a crystal phase formed of a compound containing Si, an alkaline earth metal, Al, and an O element is produced between the alumina crystal particles.

Next, by measuring the dielectric loss tangent of the sintered body at a measurement frequency of 1 MHz and 8.5 GHz, and using a non-defective product that is 5 × 10 ⁻⁴ or less at 1 MHz and 5 × 10 ⁻⁴ or less at 8.5 GHz. The dielectric loss tangent can be expected to be 5 × 10 ⁻⁴ or less even in the frequency region between the measurement frequencies of 1 MHz to 8.5 GHz. For this measurement, it is possible to use a high-precision capacitance meter and network analyzer with respect to the dielectric loss tangent, and it is possible to design a low dielectric loss tangent material in the 1 MHz to 8.5 GHz band that cannot be guaranteed by a conventional impedance analyzer. The frequency measured by the network analyzer may deviate from 8.5 GHz depending on the size of the measurement sample. For example, when the thickness of the measurement sample is 1 to 2 mm, the measurement frequency varies by about 7 to 8.5 GHz.

That is, conventionally, the dielectric loss tangent at a measurement frequency of 1 MHz is measured using a capacitance meter (HP-4278A), and the dielectric loss tangent at a measurement frequency of 8.5 GHz is measured using a cavity resonator method (network analyzer 8722ES), resulting in measurement errors. Are known to obtain accurate dielectric loss tangents of ± 2 × 10 ⁻⁴ or less and ± 0.1 × 10 ⁻⁴ or less, respectively, but 1 MHz to 8 required for semiconductor and liquid crystal manufacturing apparatus members .5 GHz, especially in the frequency range of 10 MHz to 1 GHz, there is only measurement with an impedance analyzer (HP-4291A), and the measurement error is about ± 30 × 10 ⁻⁴ at most, and the dielectric loss tangent of 5 × 10 ⁻⁴ or less The measurement accuracy is very low.

Therefore, in the present invention, the dielectric loss tangent at the measurement frequencies of 1 MHz and 8.5 GHz is indirectly measured without directly measuring the dielectric loss in the frequency region of 1 MHz to 8.5 GHz with an impedance analyzer with low measurement accuracy, If the dielectric loss tangent at a measuring frequency 1MHz and 8.5GHz in the range of 5 × ^{10 -4} or less, the dielectric loss tangent is 5 × ^{10 -4} or less in the frequency domain between the measured frequency 1MHz~8.5GHz The dielectric loss tangent at the measurement frequency of 1 MHz to 8.5 GHz can be estimated easily and accurately.
(Form 2)
The alumina sintered body of the present invention has a plurality of small-diameter particles 2 made of alumina crystal particles having a particle size of 5 μm or less at a triple point R constituted by large-diameter particles 1 made of alumina crystal particles having a particle size of 10 μm or more. In addition to having an aggregated structure, a compound represented by MAl ₂ Si ₂ O ₈ is present at the triple point R, and a glass containing M, Al, and Si is present at the triple point R.

  The presence of glass at the triple point R can be confirmed from an electron beam diffraction pattern by observation with a transmission electron microscope (TEM).

In other words, the triple point R includes small-diameter particles 2, a compound represented by MAl ₂ Si ₂ O ₈ and glass containing M, Al, and Si. The glass containing M, Al, and Si exists between the three-point R small-diameter particles 2 (three-point of the small-diameter particles 2), and liquid-phase sintering the small-diameter particles 2 with each other. This can be further improved. Although the presence of glass containing M, Al and Si may affect the dielectric loss tangent, particularly the dielectric loss tangent in the GHz band, the amount of glass in the sintered body is at most 0.07% by mass. Since the amount of glass containing M, Al, and Si is very small, the dielectric loss tangent in the GHz band hardly changes.

  In such an alumina sintered body, the dielectric loss in the frequency region at 1 MHz to 8.5 GHz can be reduced, and the bonding between the crystal particles is reinforced with glass, and higher strength can be promoted.

Such preparation of alumina sintered body, for example, aluminum oxide powder of about D ₅₀ of 2μm in volume distribution, in a mixture of aluminum oxide powder of less than D ₅₀ of 1μm in volume distribution, Si source and alkaline earth A raw material powder (not heat-treated) mixed with a metal source at a predetermined ratio for producing MAl ₂ Si ₂ O ₈ is mixed, and the mixed powder is molded and then fired at 1500 to 1800 ° C.

By using a mixed powder (raw material powder that has not been heat-treated) in which Si and an alkaline earth metal are mixed at a predetermined ratio that generates MAl ₂ Si ₂ O ₈ , the distribution of Si and the alkaline earth metal is uniform. In the part, the reaction between Si and alkaline earth metal preferentially occurs, and crystals with a low dielectric loss tangent composed of MAl ₂ Si ₂ O ₈ (Si and alkaline earth metals, Al, O elements) are generated between the alumina crystal particles. In addition, an amorphous phase (glass) is generated in a portion where the distribution of Si and alkaline earth metal is non-uniform, and liquid particles can be sintered with small-diameter particles in glass, thereby improving the strength. .

Furthermore, the alumina sintered body of the present invention desirably has an MgO content of 0.06% by mass or less. In such an alumina sintered body, since the MgO content is 0.06% by mass or less, the sinterability can be improved and the dielectric loss tangent at 1 MHz can be further reduced. MgO has the function of a sintering aid, but if it exceeds 0.06% by mass, spinel (MgAl ₂ O ₄ ) precipitates in the alumina grains and at the grain boundaries. Alumina crystal particles tend to be smaller and tan δ in the MHz band tends to be higher.

First, powders of SiO ₂ and SrCO ₃ , CaCO ₃ , and BaCO ₃ are weighed and mixed so as to have the compositions shown in Table 1 in terms of SiO ₂ , SrO, CaO, and BaO, respectively, to obtain a mixed powder. It was. This powder was heat-treated at 1000 to 1300 ° C. and pulverized in an alumina ball mill for 48 to 72 hours to produce a raw material powder.

The _Al 2 _{O 3} powder having a purity value indicating _{D 50} of Table 1 99.9 wt%, the _Al 2 _{O 3} powder of purity is _{D 50} 99.5 wt% values shown in Table 1 in a weight ratio of The raw material powders such as Si and Sr and the Mg (OH) ₂ powder were added at the ratios shown in Table 1 in terms of MgO, and a predetermined amount of water was added thereto. In addition, it was mixed for 48 hours in an alumina ball mill to form a slurry. The slurry is added to the slurry, dried, granulated, and the mixed powder is molded at a pressure of 1 t / cm ² to produce a cylindrical molded body (diameter 60 mm × height 30 mm). Then, firing was performed in the air to obtain an alumina sintered body having a diameter of 50 mm and a height of 25 mm.

  A sample having a thickness of 1 mm was cut out from the center in the height direction of the obtained sintered body, and the density and dielectric loss tangent were measured. The density was measured by the Archimedes method.

The dielectric loss tangent is measured at 1 MHz, 12 MHz, and 8.5 GHz, and measured using a capacitance meter (HP-4278A), impedance analyzer (HP-4291A), cavity resonator method; network analyzer (8722ES), respectively. Was done. Although the measurement error of the capacitance meter is ± 2 × 10 ⁻⁴ or less and the measurement error of the cavity resonator method is ± 0.1 × 10 ⁻⁴ or less, the measurement error of the impedance analyzer is ± 30 × 10 ^−4. Therefore, when the 12 MHz dielectric loss tangent by the impedance analyzer is less than 5 × 10 ⁻⁴ , it is described in Table 1 as <5.

  First, using a network analyzer, a sample having a diameter of 50 mm × thickness 1 mm is sandwiched by a jig to obtain a dielectric loss tangent at 8.5 GHz. Next, using an impedance analyzer, the sample having a diameter of 50 mm × thickness 1 mm is cured. The electrode was formed on the upper and lower surfaces of the sample having a diameter of 50 mm and a thickness of 1 mm based on JIS C2141, and the dielectric loss tangent at 1 MHz was obtained with a capacitance meter. .

Moreover, the analysis of the crystal phase in each sintered body is performed by energy dispersive X-ray spectroscopy (EDS) and limited-field electron diffraction using a transmission electron microscope (TEM), and Si, Al, M ( Table 2 shows the presence or absence of MAl ₂ Si ₂ O _8, which is a low-loss crystal phase composed of a compound containing M = Mg, Ca, Sr, Ba) and O elements. Table 2 shows the presence or absence of glass containing Si, Al, M (M = Mg, Ca, Sr, Ba), and O elements at the triple point.

Further, the average particle diameter D ₅₀ of the alumina crystal particles is a Mac View image in the range of 0.04 mm ² (0.2 mm × 0.2 mm) with respect to the scanning electron micrograph (500 times SEM photograph) of the sample. The diameter of each crystal particle was obtained with an analyzer, and the average particle diameter was calculated from the volume distribution and number distribution.

The number of small-diameter particles having a particle size of 5 μm or less at the triple point composed of large-diameter particles made of alumina crystal particles having a particle size of 10 μm or more was determined in the range of 0.04 mm ² for the SEM photograph. For large diameter particles made of alumina crystal particles having a particle size of 10 μm or more, and for small diameter particles made of alumina crystal particles having a particle size of 5 μm or less, the maximum diameter of the particles is obtained from the SEM photograph, and the maximum diameter is 10 μm or more. Or 5 μm or less. As a result, in the sample of the present invention, 5 or more small-sized particles having a particle size of 5 μm or less were present at the triple point composed of large-sized particles made of alumina crystal particles having a particle size of 10 μm or more. Table 2 shows the presence or absence of small-diameter particles at the triple point.

  The three-point bending strength of the alumina sintered body was measured according to JIS R1601, and listed in Table 2.

From Tables 1 and 2, in the sample of the present invention containing Si, M (M = Mg, Ca, Sr, Ba) and O elements as auxiliary components in addition to alumina, between the small-diameter particles of alumina crystal, MAl ₂ Si ₂ O ₈ (M is at least one of Mg, Ca, Sr and Ba) is produced, and the dielectric loss tangent is 5 × 10 ⁻⁴ or less at 8.5 GHz and 1 MHz 5 × ^{10 -4} or less, it can be seen that a low loss of 5 × ^{10 -4} or less in 12MHz in. It can also be seen that the three-point bending strength is 380 MPa or more.

On the other hand, Sample No. Samples 6, 11, and 14 were prepared as follows. The Al ₂ O ₃ powder having a purity of 99.9% by mass was mixed with SiO ₂ powder, SrCO ₃ powder, CaCO ₃ powder, and Mg (OH) ₂ powder in Sample No. 6, 11, and 14 were added at a ratio, and a predetermined amount of water was added thereto and mixed in a ball mill for 48 hours to form a slurry. A binder is added to the slurry, dried, granulated, and the mixed powder is molded at a pressure of 1 t / cm ² to produce a molded body (diameter 60 mm × height 30 mm) and fired at 1665 ° C. Was done.

The center part (thickness 1 mm) in the height direction of the obtained sintered body was cut out, and the density and dielectric properties were measured by the same method as in the above Examples. As a result of analysis, sample No. In FIG. 6, a crystal phase composed of a compound represented by MAl ₂ Si ₂ O ₈ was formed between the aluminum oxide crystal particles, but no texture of small-diameter particles was present. For this reason, the dielectric loss tangent showed a low value, but the three-point bending strength was as low as 290 MPa.

Sample No. of Comparative Example In No. 11, no crystal composed of a compound represented by MAl ₂ Si ₂ O ₈ was produced, but a texture of small-diameter particles was formed. Therefore, the three-point bending strength was as high as 380 MPa, but the dielectric loss tangent values were as high as 20 × 10 ⁻⁴ and 7.3 × 10 ^{−4 at} 1 MHz and 8.5 GHz, respectively.

Sample No. of Comparative Example In No. 14, crystals composed of a compound represented by MAl ₂ Si ₂ O ₈ were not generated, and there was no texture of small-diameter particles. Therefore, the three-point bending strength was as high as 400 MPa, but the dielectric loss tangent values were as high as 40 × 10 ⁻⁴ and 6.2 × 10 ⁻⁴ at 1 MHz and 8.5 GHz, respectively.

First, powders of SiO ₂ , SrCO ₃ , CaCO ₃ , and BaCO ₃ were weighed so as to have the compositions shown in Table 13 in terms of SiO ₂ , SrO, CaO, and BaO, and 48 to 72 using an alumina ball mill. Time mixing was performed to prepare a raw material powder.

The _Al 2 _{O 3} powder having a purity of the values shown in _{D 50} of Table 3 with 99.9 wt%, the _Al 2 _{O 3} powder of purity is _{D 50} 99.5 wt% values shown in Table 3 in a weight ratio The raw material powders such as Si and Sr, and Mg (OH) ₂ powder were added at the ratios shown in Table 3 in terms of MgO, and a predetermined amount of water was added thereto. Was added and mixed with an alumina ball mill for 48 hours to form a slurry. The slurry is added to the slurry, dried, granulated, and the mixed powder is molded at a pressure of 1 t / cm ² to produce a cylindrical molded body (diameter 60 mm × height 30 mm). Then, firing was performed in the air to obtain an alumina sintered body having a diameter of 50 mm and a height of 25 mm.

  Each item in Table 4 was measured in the same manner as in Example 1 and listed in Table 4.

  From Tables 3 and 4, the presence of glass containing Si, Al, M (M = Mg, Ca, Sr, Ba), and O elements at the three points improves the three-point bending strength to 400 MPa or more, Although the dielectric loss at 1 MHz decreases, it can be seen that the dielectric loss at 8.5 GHz is slightly higher.

1 ... large particle 2 ... small particle

4 ... Void R ... 3 points

Claims (7)

Alumina sintered body containing 99.3% by mass or more of Al as an element in terms of Al ₂ O _{3 and} containing Si and M (M is at least one of Mg, Ca, Sr and Ba) as other elements Because
Alumina crystal particles are used as main crystal particles, and the average particle size of the alumina crystal particles is 20 μm or more in terms of volume distribution average, and the triple point is composed of large-diameter particles made of the alumina crystal particles having a particle size of 10 μm or more. And having a structure in which a plurality of small-diameter particles composed of the alumina crystal particles having a particle size of 5 μm or less are aggregated, and a compound represented by MAl ₂ Si ₂ O ₈ is present at the three points ,
The dielectric loss tangent at a measurement frequency of 1 MHz is 5 × 10 ⁻⁴ or less, the dielectric loss tangent at a measurement frequency of 12 MHz is 5 × 10 ⁻⁴ or less, and the dielectric loss tangent at a measurement frequency of 8.5 GHz is 5 × 10 ⁻⁴ or less. An alumina-based sintered body having a three-point bending strength of 380 MPa or more .   2. The alumina sintered body according to claim 1, wherein an average particle diameter of the alumina crystal particles is 10 μm or less in terms of number distribution average. The alumina sintered body according to claim 1 or 2, wherein a bulk density is 3.84 g / cm ³ or more . The alumina sintered body according to any one of claims 1 to 3, wherein the amount of Na ₂ O is 0.05% by mass or less.   5. The alumina sintered body according to claim 1, wherein a glass containing M, Al, and Si exists at the three points.   A member for a semiconductor manufacturing apparatus, comprising the alumina sintered body according to any one of claims 1 to 5.   A member for a liquid crystal panel manufacturing apparatus, comprising the alumina sintered body according to any one of claims 1 to 5.

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