JP2010235394A - Porous ceramics - Google Patents

Abstract

To obtain porous ceramics having continuous open pores that are closer to black and have electrical resistivity that can be an ESD countermeasure.
The problem has been solved by producing porous ceramics mainly composed of alumina and mullite and titania and titanium carbide as subcomponents. By controlling the composition of the starting material and the sintering atmosphere, etc., the ceramic with continuous open pores has a sufficiently low surface roughness, semi-conductivity that does not cause ESD, and black that is a countermeasure against halation in optical equipment. A close color tone can be given.
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Description

  The present invention relates to a porous sintered body made of alumina, mullite, titanium carbide, titania having continuous open pores in a main body, and a vacuum chuck using the porous ceramic.

  Many porous sintered bodies such as alumina and mullite have been proposed so far.

Patent Document 1 discloses a method of producing an Al ₂ O ₃ and Al ₂ O ₃ —MgO-based porous sintered body using powder having two average particle diameter peaks.

  Patent Document 2 discloses porous ceramics mainly composed of oxide ceramics including alumina.

Patent Document 3 discloses a dark porous sintered body having continuous open pores containing 0.1 to 10% by mass of TiO _X (1.5 ≦ x <2.0) and the balance being Al ₂ O _3. It is shown. The purpose of darkening is to prevent halation.

Patent Documents 4 and 5 disclose porous ceramics in which components overlap with those of the porous ceramics of the present invention, but no details are disclosed as disclosed in the present invention.

JP 2004-315358 A JP 62-82047 A JP 2006-182595 A Japanese Patent Publication No. 6-85026 Japanese Patent Publication No. 6-72667

Since the alumina-based material is basically a material based on white, it is difficult to distinguish wafers, elements, powder, dust, and the like having a color close to white with the naked eye and a sensor. In addition, since white reflects most of the light without absorbing it, it is difficult to detect the region. Although visual detection is also difficult, it is not suitable for causing halation particularly when detecting the boundary of an object with an optical sensor using a CCD camera.
In addition, the electrical resistance may be destroyed by various devices when static electricity is generated. Therefore, it is best not to be insulating or conductive, but to be semiconductive located in the middle. The range of semiconductivity is roughly 1 × 10 ² to 1 × 10 ¹¹ (Ω · cm), although it varies depending on the type of device and element and the standards of each company.

  The technique disclosed in Patent Document 2 can produce a brown cordierite sintered body, but adds oxides of Fe, Mn, and Co that are inferior in corrosion resistance, chemical resistance, and wear resistance. Further, it is not desirable to use it for a filter for filtering acidic or alkaline chemicals and a film forming jig.

  With the technique disclosed in Patent Document 3, a dark porous material can be obtained. However, some sensors discriminate white, and problems remain. From the viewpoint of countermeasures against static electricity, it is almost an insulator, so that it is difficult to use as a member that needs countermeasures against ESD (electrostatic discharge).

  Patent Document 4 discloses a rotating polygon mirror having ceramics in which open pores are filled with a lubricant. In this document, alumina, mullite, titania and titanium carbide, which are essential components of the present invention, are listed in claim 2, but there is no description of these systems.

  Cited Document 5 shows a valve body in which carbon having a open pore of 5 to 55% is filled with carbon fluoride. In this document, alumina, mullite, titania, and titanium carbide, which are essential components of the present invention, are listed in claim 2, but there is no description of these systems.

Accordingly, an object of the present invention is to obtain an alumina or mullite-based porous ceramic that is closer to black and can be used as an ESD countermeasure.

  In the present invention, the first component of alumina and mullite is at least 5% by mass and 50 to 98% by mass in total, titanium carbide and titania are 2 to 50% by mass in total, and the mass of titania is the sum of titania and titanium carbide. Porous ceramics having continuous open pores composed of the second component whose value divided by mass is in the range of 0.001 to 0.5, or a part of alumina and mullite as the first component is 0.01 It is the same porous ceramic substituted with ˜20% silicon oxide.

  Alumina and mullite, which are the first components, are chemically stable oxides, and raw materials such as alumina, mullite, silicon oxide, and titania are stably available and are not expensive. Moreover, even if it is used as a porous ceramic, a certain strength can be maintained.

The reason why the lower limit of each component of alumina and mullite is 5% by mass is that solid solution and dispersion strengthening are performed with two oxides to ensure strength. Further, the total amount is set to 50 to 98 mass because if the content is smaller than this range, the second component becomes the main phase, so that it becomes difficult to obtain continuous open pores, and the characteristics of titanium carbide and titania become strong. This is because it is difficult to obtain the values required in terms of strength and electrical resistivity.

The second component is composed of titania and titanium carbide and occupies 2 to 50% by mass of the porous ceramic. Titanium carbide is a conductor and has a volume electrical resistivity of about 1 × 10 ⁻³ (Ω · cm). Although titania is not as good as titanium carbide, it has electrical conductivity. Further, titania is generally represented by TiO ₂ , but the composition of the present invention has a small amount of TiO x (x ≠ 2) deviating from the stoichiometric ratio in addition to TiO ₂ . Since titania exists even in a small amount in the sintered body, it has a function of reducing the surface roughness after grinding. Titanium carbide is an important element in forming the porous ceramics of the present invention because of its high conductivity and strong black color. However, since its own sinterability is not good, it contains more than 50% and is porous. The quality ceramic cannot obtain sufficient strength and becomes brittle. The titania / titanium carbide ratio shows a kind of equilibrium movement, but there is oxygen exchange between titania, mullite, and titanium carbide, and it is stable in a region with a large amount of titanium carbide. In this case, the amount of titania is preferably in the range of 0.001 to 0.5 with respect to the sum of titanium carbide and titania. If it is smaller than 0.001, the above-mentioned surface roughness characteristics after grinding cannot be seen. In addition, since the amount of titania exceeds 0.5 when the sintering is completed, sintering is not stable with titanium carbide in the process of sintering to cooling, so that it is difficult to obtain a uniform composition as a whole. And uniformity of pores are difficult to obtain, which is not preferable in terms of strength and scientific stability. This second component occupies 2 to 50% by mass of the porous ceramic, but if it is less than 2% by mass, it is subjected to sintering only by necking between mullite and alumina, and therefore has continuous pores. It is difficult to obtain sufficiently strong porous ceramics. On the other hand, if the amount is more than 50% by mass, the amount of titanium carbide is excessively increased, so that the sintering is extremely difficult to proceed within the sintering temperature range assumed in the present invention.

The present invention described in claim 2 is the porous ceramic according to claim 1, wherein a part of alumina and mullite as the first component is substituted with 0.01 to 20% by mass of silicon oxide. Silicon oxide can be added as a starting material, but silicon and oxygen constitute part of mullite, so that part or all of it decomposes and becomes part of mullite after sintering. If silicon oxide exceeding the amount that becomes part of mullite is added, it remains in the porous ceramic as silicon oxide. This amount is different depending on the atmosphere and sintering conditions. If 0.01% or more of the silicon oxide in the porous ceramics remains, it has a function of promoting the sintering of the porous ceramics, which facilitates production. If it is less than that, the work which advances sintering is not seen. On the other hand, if it exceeds 20% by mass, the silicon oxide itself is fragile and the porous ceramic is liable to break down. Accordingly, an appropriate amount of silicon oxide is 0.01% by mass to 20% by mass.

The present invention described in claim 3 is the porous ceramic according to claim 1 or 2, wherein the porosity is 15 to 45%. As the porosity of the porous ceramic becomes smaller, the mechanical strength becomes stronger. However, the amount of movement of gas or liquid using the pores at that time becomes smaller. For example, when used as a vacuum chuck, the suction force becomes relatively weak. Therefore, the use of porous ceramics having a porosity of less than 15% is limited. Moreover, if the porosity is high, the movement of gas or liquid can be increased. On the other hand, since the mechanical strength of the porous ceramics is lowered, the objects that can still be used are limited. This tendency increases rapidly when the porosity exceeds 45%. Therefore, it can be said that 15 to 45% of the porosity is a more appropriate range.

  The present invention according to claim 4 is the porous ceramic according to any one of claims 1 to 3, wherein the average pore diameter is 2 to 20 μm. The pore diameter is a value measured by a mercury intrusion method. If the average pore diameter is small, a material having a relatively high mechanical strength can be obtained, but the amount of movement of gas or liquid using the pores is small as in the case of a material having a low porosity. Moreover, although the average pore diameter is as large as 20 μm or more, depending on the application, surface irregularities become severe and the surface roughness cannot be lowered. One object of the porous ceramic of the present invention is to obtain a material that can be used in a vacuum chuck or the like that requires smoothness. In such applications, the average pore diameter is 2 to 20 μm as described above. It is desirable that Of course, when the application does not require a certain surface roughness, the range is not limited to this range.

  According to the fifth aspect of the present invention, the color tone represented by the L * a * b * color system is such that the absolute value of the product of a * and b * is 10 or less, and L * is 45 or less. The porous ceramic according to any one of claims 1 to 4, wherein the porous ceramic is characterized. The L * a * b * color system is a value representing a color defined in JIS Z 8729 in the Japanese Industrial Standard.

  The absolute value of the product of a * and b * is 10 or less is a range having no particular feature such as red and blue as the color tone. Since the porous ceramics of the present invention are composed of ceramic particles such as white, black, and gray, most fall within this range. Further, the value of L * is 45 or less, and together with the above-described values of a * and b *, it indicates a range from dark gray to black.

  For the inspection of electronic parts and the measurement of dimensions by using optical equipment, the more easily the color difference between the background (for example, the suction member) and the object to be inspected (for example, the electronic part), the easier it is to detect. The error can be reduced. Up to now, white and dark ceramic vacuum chucks have been mainly used, but these can be further improved.

It is the content of titanium carbide that has the greatest influence on the color tone (blackening). When used in such applications, it is desirable to contain titanium carbide within the scope of claim 1.

The present invention described in claim 6 has a volume electrical resistivity in the range of 1 × 10 ² to 1 × 10 ¹¹ (Ω · cm), according to any one of claims 1 to 5. Porous ceramics. The range shown in this claim is the range of the electrical resistivity of the porous ceramics as a measure against ESD (electrostatic discharge). The value is indicated by volume resistivity. When various members are insulators, static electricity is generated due to friction and peeling during manufacturing and inspection, which may directly damage and destroy various elements. Further, an unintended abnormal current may occur even if it is not static electricity, and various elements may be destroyed through the conductor. For such destruction of an electrical element, it is desirable that an object in contact with the element has “semi-conductivity” that conducts electricity to some extent. If the electrical resistivity is smaller than this range, the damage when a large current is directly hit is large. Conversely, if the electrical resistivity is large, the electrostatic charge itself is easily charged.
Therefore, it is preferable that a member in contact with various elements has a certain electric resistivity and can pass a current little by little. The range of 1 × 10 ² to 1 × 10 ¹¹ (Ω · cm) given in the present invention follows this range.

The present invention according to claim 7 is a vacuum chuck made of the porous ceramic according to any one of claims 1 to 6. The characteristics required for the vacuum chuck are its surface roughness, adsorption force, color tone, antihalation characteristics, electrical characteristics, and the like. The porous ceramics according to the first to sixth aspects of the present invention can select desired characteristics for surface roughness, adsorption force, and the like. Further, by adjusting the amount of titanium carbide and the like, the anti-halation characteristic, the color tone is selected from a range from gray to black, and the electrical resistivity is selected from a region including a range of 1 × 10 ² to 1 × 10 ¹¹ (Ω · cm). Can be used for more vacuum chuck applications.

The present invention according to claim 8 is a halation countermeasure member made of the porous ceramic according to any one of claims 1 to 6. As described above, in the present invention, the color tone can be changed from gray to black by adjusting the composition within the scope of the claims. Therefore, it is possible to select an appropriate color according to the object to be inspected and take measures against halation. Of course, the anti-halation member can be used as the vacuum chuck.

  The present invention solves at least one of the following problems.

1. 1. It is possible to obtain porous ceramics having continuous open pores, mainly composed of alumina and mullite, which can easily reduce the roughness of the processed surface. The electrical resistivity can be controlled, and a porous ceramic having continuous open pores as an ESD countermeasure can be obtained.

3. Ceramics with continuous open pores whose color tone is close to black can be obtained.

  An example of the manufacturing method of the porous ceramics of this invention is shown.

  First, a total of 50 to 98% by mass of alumina powder and mullite powder are prepared as starting materials. In order to control the porosity and the pore diameter after obtaining continuous open pores, the average particle size of these powders is preferably about 10 to 200 μm. Further, the shape of the powder is preferably close to a sphere that easily leaves open pores.

  Titanium carbide and titania are added in a total amount of 2 to 50% by mass. The average particle diameter is suitably about 0.1 to 4 μm.

  When silicon oxide is added, 0.01 to 20% by weight of the total amount is added so as to replace alumina and mullite. The average particle size is suitably about 0.1 to 3 μm.

  The large change in the average particle size as described above prevented the overall densification by having small powder (titania, titanium carbide, silicon oxide) take charge of necking between larger powders (alumina, mullite). This is to obtain continuous open pores.

  If possible, these powders are uniformly mixed with a ball mill, an attritor, a raking machine or the like under a wet condition in which water or alcohol is added. After adding 1-10 external mass% organic binder for shaping | molding to the obtained slurry, it dries and granulates by stationary drying, a spray dryer, a sieve net, etc. The mixed powder is obtained as described above.

  Next, the obtained mixed powder is press-molded at a pressure of 30 to 300 MPa, and if necessary, intermediate processing is performed.

  After the intermediate processing, the organic binder is degreased at 300 to 700 ° C. in a reducing or vacuum atmosphere. At this time, since the press body contains titanium carbide, degreasing in an oxidizing atmosphere and an air atmosphere is inappropriate.

  Next, the degreased body is sintered. Sintering can be performed in any one of a reducing atmosphere using carbon derived from a furnace wall or a jig, a reducing atmosphere using a reducing gas or an inert gas, or a vacuum atmosphere. The appropriate temperature is 1400 ° C to 1700 ° C.

  About the composition of the obtained sintered compact, the chemical change had occurred unlike the time of raw material powder injection | throwing-in. Specifically, alumina and titania, the oxide components of silicon oxide when added, decreased and the amount of mullite increased instead. In addition, some titania was reduced by the generation of mullite, and the carbon in the atmosphere was taken in to generate titanium carbide.

Porous ceramics are obtained after sintering. This porous ceramic is characterized by titania, so that the surface accuracy can be increased, and it is well suited for use in handling precision members. At the same time, it is possible to obtain a porosity of 10 to 45% with an average pore diameter of 2 to 20 μm for those having a color tone close to black, semiconductivity, and pores by controlling the components and the production method. It is.

Example 1
As starting materials, 70% by mass of alumina powder having an average particle size of 68 μm, 20% by mass of mullite powder having an average particle size of 45 μm, 5% by mass of titanium carbide powder having an average particle size of 1 μm, and titania 2 having an average particle size of 1 μm Mass% and 3% by mass of silicon oxide having an average particle diameter of 1 μm were put into a ball mill and mixed for 10 hours in a wet manner using alumina balls. After mixing, polyethylene glycol having a molecular weight of about 20,000 as an organic binder for molding was granulated with a spray dryer together with an external fraction of 3% by mass to obtain granulated powder.

  Next, the granulated powder was pressed and molded at 100 MPa with a mold to obtain a disk-shaped green body. The green body was degreased in a carbon atmosphere and then placed in a sintering furnace, and sintered at 1500 ° C. in a reducing atmosphere with an argon gas flow while interposing the carbon.

  The obtained porous ceramic as a sintered body was a porous body having a dark gray appearance close to black and having continuous open pores. As a result of analysis, the sintered body was changed to a composition containing 68% by mass of alumina, 25% by mass of mullite, 6% by mass of titanium carbide, 1% by mass of titania, and 0% of silicon oxide. This is probably because mullite was newly generated from a part of alumina and silicon oxide, and a reaction in which a part of titania changed to titanium carbide occurred. This sample is designated as Sample 1.

When the sample 1 was investigated, it had the following characteristics.

Porosity The porosity was determined from the dimensions and weight, and was 58% of the completely sintered ideal sintered body, and the porosity was 42%. The average pore diameter was 18 μm as measured by mercury porosimetry.
It was L * = 35.0 a * =-0.8 b * = 1.5 when it measured with the color chromaticity meter.
Electrical resistivity When the volume resistivity was measured, it was 2 × 10 ⁸ (Ω · cm).

  Next, the composition of the starting material was changed to make Samples 2 to 114, and the production and measurement were performed with the starting material and the manufacturing method basically the same as those of Sample 1. The compositions of the starting materials are shown in Tables 1-3, the compositions after sintering are shown in Tables 4-6, and the characteristic values are shown in Tables 7-9.

Those with * in Table 3 are comparative samples outside the scope of the present invention.

Those with * in Table 6 are comparative samples outside the scope of the present invention.

In Table 9, the numbers marked with * are comparative samples outside the scope of the present invention.

  In the examples, the three samples with the number “T” are samples aiming at a relatively small pore diameter, with the average particle diameter of the raw material powder of alumina and mullite being 10 μm.

The samples of the present invention had no problem in normal handling of the mechanical properties of all samples including Sample 1. Specifically, no cracking or chipping occurred, there was no separation of particles from the surface, and the color tone was constant regardless of the position of the sample. The three-point bending strength was at least 40 MPa.

  In many cases, the composition was different from the input material. This is mainly due to the generation of mullite during sintering, and since the components of Al, Si, O are deprived from alumina and silicon oxide, the amount of alumina and silicon oxide is reduced, and mullite is generated or formed. There seems to be an increasing response. At this time, both the case where the silicon oxide completely became a part of mullite and the case where it remained were observed. In addition, titania decreased in all Examples. This is considered to be caused by the presence of carbon in the atmosphere and the supply of O to the mullite. Depending on the amount of raw material input, change to mullite, titanium carbide, etc., it may be reduced to a very small amount of 0.1% or less. When a part of titania changed to titanium carbide, there was a tendency that the high electrical conductivity and the blackening function that are characteristic of titanium carbide appeared more remarkably.

Regarding the influence of surface roughness on the presence or absence of titania, a sample in which 1% of titania in sample 30 was made of titanium carbide could be obtained by increasing the high temperature maintenance time of sintering. This sample is referred to as a comparative sample * 112, and both are compared. Since the average pore diameter of these samples is as relatively large as 16 μm, a normal surface roughness meter cannot be measured as it is because terminals once entering the pores cannot return along the surface. For that purpose, a polymer sheet having a thickness of 20 μm was laid between the sample and the terminal, which was held in a state of being evacuated from the back surface, and the measurement was performed therethrough. Since the maximum height and the like cannot be measured, the comparison was performed using the center line average roughness Ra (1982 version JIS) by the same method.
In the test, a sample obtained by grinding both samples simultaneously with a surface grinder using a # 200 diamond grindstone was used. As a result, the Ra of the sample 30 was 0.5 (μm), whereas the equivalent value of the comparative sample * 112 was 2.3 (μm). It was confirmed that the surface roughness after processing was suppressed to a low value depending on the presence or absence of titania.

Regarding the sample of the present invention, the samples having a volume resistivity of 1 × 10 ² to 1 × 10 ¹¹ (Ω · cm) (Claim 6) are Samples 1 to 7 and Samples 21 to 30. there were. Other samples are considered difficult to use as ESD countermeasure members.

On the other hand, samples outside the scope of the present invention will be described.
Comparative Samples * 103, * 104, and * 105 have a total amount of alumina and mullite exceeding 98% by mass, and the progress of sintering starts from necking of alumina and mullite with large particles, resulting in very large and continuous open pores. Was obtained, but the overall strength was very weak and processing was impossible.

  Comparative samples * 101, * 102, * 109, and * 110 are samples in which the total amount of alumina and mullite is lower than 50% by mass (including silicon oxide if included). In this state, the structure is such that titania or titanium carbide enters the gap between alumina and mullite having a large particle diameter without gap. Titanium carbide, unlike alumina and mullite, has a high sintering temperature. Therefore, in this state, sintering did not proceed sufficiently and the sample did not have sufficient strength.

Comparative samples * 106 and * 107 are samples in which titania is 0% by mass. As described above, titania is TiO ₂ or, in some cases, carbonated TiCO. If this is contained in the sintered body, the surface roughness of the surface can be significantly reduced during machining. There is also a theory that it plays the role of a dress for machining tools. For this reason, this comparative example is not sufficient in surface roughness by machining, and departs from the spirit of the present invention.

  The comparative sample * 8 had a structure in which the amount of titania was larger than the amount of titanium carbide and was not stable. For this reason, portions with different color unevenness and surface roughness are conspicuous throughout.

The comparative sample * 111 contains 21% by mass of silicon oxide. Since silicon oxide is brittle compared to other components, sintering tends to proceed when the amount increases, but the entire sample becomes brittle. This comparative sample could easily be folded by hand.

(Example 2) Example to vacuum chuck After performing machining and sealing using the sample * 4 described in Example 1, the pump for controlling the gas and the joint are disassembled to form a vacuum. A chuck was produced. This vacuum chuck showed a necessary and sufficient suction force. Also, there was no problem such as destruction of the structure on the chuck surface or discoloration even after cleaning.

Further, this vacuum chuck exhibits semiconductivity of 4 × 10 ⁷ (Ω · cm), and can be used simultaneously as an ESD countermeasure member. Further, the color tone was close to black with L * of 37, and the discrimination was made accurately by visual inspection of the adsorbed white or light-colored object to be inspected (represented as “element etc.”) and discrimination with an inspection apparatus.

  This is the range of the electrical resistance value that allows electricity to flow gradually, such as when an element is adsorbed or released on this vacuum chuck, if friction occurs on the chuck, or if an unintended current flows on the vacuum chuck. In addition, there is no electrical breakdown of the device.

  Furthermore, this vacuum chuck can keep the surface roughness sufficiently low. For this reason, there is no damage to the element or the like during adsorption or release, and the life is long because it is ceramic.

  Therefore, it can be suitably used as a vacuum chuck for various applications such as wafers, chips, capacitors, glass plates, films as well as various elements.

Claims (8)

Alumina and mullite, which are the first components, are at least 5% by mass, and 50 to 98% by mass in total
The balance is titanium carbide and titania, and the second component is a value obtained by dividing the mass of titania by the total mass of titania and titanium carbide in the range of 0.001 to 0.5.
Porous ceramics with continuous open pores. The porous ceramic according to claim 1, wherein a part of alumina and mullite as the first component is substituted with 0.01 to 20% silicon oxide. The porous ceramic according to claim 1 or 2, wherein the porosity is 15 to 45%. The porous ceramics according to any one of claims 1 to 3, wherein an average pore diameter is 2 to 20 µm. The color tone shown in the L * a * b * color system has an absolute value of a product of a * and b * of 10 or less, and L * is 45 or less. 5. The porous ceramic according to any one of 4 above. 6. The porous ceramic according to claim 1, wherein the volume electrical resistivity is in a range of 1 × 10 ² to 1 × 10 ¹¹ (Ω · cm). A vacuum chuck made of the porous ceramic according to claim 1. A halation countermeasure member comprising the porous ceramic according to any one of claims 1 to 6.