VACUUM-CLAMPING DEVICE USING CERAMIC VACUUM-CLAMPING BOARD

Abstract: A ceramic substrate for hard disks, thin film chip capacitors, and hybrid ICs, of titanium oxide or aluminum oxide, has an extremely small number of pores of larger than 3 µm diameter in the surface. The substrate is fabricated by burning finely powdered high-purity titanium oxide or high-purity aluminum oxide in the air, an inert atmosphere at 1,100-1,300 °C, or a reducing atmosphere at 1,200-1,400 °C and then, subjecting it to an HIP process.

Description: The present invention relates to a ceramic wafer-chucking device. In particular, the present invention relates to a substrate chucking device comprising a wafer-chucking substrate for chucking and transporting or suction chucking and fixing a wafer, and in particular, to a substrate chucking device in association with a wafer hand and a wafer holder for suction chucking and transporting or fixing a wafer such as a semiconductor wafer etc. Background Art Conventionally, Winchester discs have been known as a representative of magnetic disc memory devices (hard disc drives) which uses a non-magnetic metal disc for a recording magnetic disc. The Winchester disc is a disc memory characterized in that a magnetic hard disc for recording is mounted in an unremovable or hermetically sealed disc pack together with a flying inductive head disposed above the disc surface without physical contact. The above recording magnetic disc uses a flat substrate (a hard disc substrate) with a magnetic material layer coated thereon for recording information. As the hard disc substrates of this kind, metallic substrates made from aluminum, an aluminum alloy or the like have been used conventionally. Recently, development of hard discs of this kind for high-capacity has been actively being pursued, and in order to increase the recording capacity of hard discs, it is necessary to reduce a flying height of the aforementioned head from the disc surface. To reduce the flying height of the head, flatness of the disc substrate needs to be reduced, but the improvement in flatness of the conventionally used metallic substrates of aluminum, an aluminum alloy or the like almost has come to a limit; therefore, it is difficult to fabricate flatter substrates using these materials. As regards flatness, since ceramic substrates can be more easily fabricated than the metallic substrates, hard disc substrates made of ceramics have been desired. It is true that ceramic substrates can be fabricated to have improved flatness, but the ceramic substrates suffer from the occurrence of many pores of 3µm or more in diameter on the surface thereof. Hence, it has been a problem that no ceramic substrate can be obtained without pores present on its surface. A wafer hand as well as a wafer holder built into fabricating apparatuses for semiconductor integrated circuits holds wafers by vacuum suction through a wafer-chucking plate, so as to transfer or fix the wafer by means of vacuum suction. As the wafer-chucking substrate for wafer hands and wafer holders, a wafer-chucking substrate made of alumina, that is, of an insulator, has been used conventionally. Meanwhile, in fabrication lines for ICs, existence of dust is extremely undesirable, so that various measures are taken into consideration against dust. In the case of using a conventional alumina wafer-chucking substrate, this wafer-chucking substrate tends to carry static charges, and therefore has a drawback of being likely to attract dust due to such static charges. In order to eliminate this defect, more specifically, in order to remove the static charges staying on the alumina wafer-chucking plate, some proposals have been made including a method of coating a conductive material on the wafer-chucking plate. This process of coating a conducting material, however, needs complicated procedures and involves a lot of other problems. For this reason, a ceramic wafer-chucking plate which dose not need such a process has been desired. That is, a ceramic-made wafer-chucking substrate has been desired, which, unlike the conventional, insulator-made or alumina-made wafer-chucking plates, has a low specific resistance and therefore will never bear static charges. Alternatively, in a case where many pores exist on the surface of a wafer-chucking substrate, especially when a lot of large-sized pores (e.g., pores with diameters of 3µm or more) exist, the following problems occur: (a) the pores attract dust and dirt, and the thus adhered dust and dirt may cause problems such as of contaminating the semiconductor fabrication line; and (b) gases and the like may adsorb into the pores, thereby deteriorating the efficiency of suction and holding thin plates, such as semiconductor wafers. Accordingly, nowadays, a wafer-chucking substrate satisfying the aforementioned demand and capable of eliminating the above problems (a) and (b), or more specifically, a ceramic-made wafer-chucking substrate which has a low specific resistance and an extremely small number of pores on its surface has been strongly desired. It is therefore the object of the present invention to provide a substrate chucking device comprising a ceramic wafer-chucking substrate satisfying the above demands. In detail, it is an object of the present invention to provide a substrate chucking device equipped with a ceramic wafer-chucking substrate having a low specific resistance and an extremely small number of pores on the surface thereof, as well as to provide a substrate chucking device equipped with a ceramic wafer-chucking substrate which allows easy prevention against static charges, and is able to largely contribute to high-integration as well as a high yield of semiconductor devices. Disclosure of Invention The present invention is characterized in that: a wafer-chucking plate made of titanium oxide is used as a ceramic wafer-chucking substrate; the wafer-chucking substrate has a specific resistance of 1.0Ω·cm or less; and the number of pores with diameters of 3µm or more on the surface thereof is 100 pores or less per 1mm 2 . With this configuration, the present invention is to provide a substrate chucking device for achieving the above objects. That is, a gist of the present invention resides in a substrate chucking device comprising a wafer-chucking substrate for suction chucking and transporting or fixing a wafer, being characterized in that the wafer-chucking substrate is made of titanium oxide and has a specific resistance of 1.0 Ω·cm or less and the number of pores with diameters of 3µm or more on the surface thereof is 100 pores or less per 1mm 2 . Best Mode for Carrying Out the Invention Details of a carrier which can suction chuck substrates according to the present invention will be described. The inventors of the invention have earnestly studied the producing process of flat ceramics having a low specific resistance and an extremely small number of pores on the surface thereof, and as a result they found the fact that, in accordance with the following producing processes (1) to (3), it is possible to obtain a targeted ceramic wafer-chucking substrate, thus having completed the present invention. (1) A process comprising the steps of molding highly purified titanium oxide fine powder, baking the molding in the air or an inert atmosphere, and further subjecting the baked molding to a hot isostatic pressing (HIP) treatment. (2) A process comprising the steps of molding highly purified titanium oxide fine powder, and baking the molding in a reducing atmosphere. (3) A process comprising the steps of molding highly purified titanium oxide fine powder, baking the molding in a reducing atmosphere, and further subjecting the baked molding to a hot isostatic pressing (HIP) treatment. That is, the technical subject of the present invention is to provide a ceramic wafer-chucking substrate having both a first feature of the present invention that the specific resistance is extremely low, and a second feature of the present invention that the surface has an extremely small number of pores. Then, the present inventors found that, in accordance with the aforementioned producing processes (1) to (3), a titanium oxide sintered body having both the first and second features, more specifically, a titanium oxide sintered body which has a specific resistance of 1.0Ω·cm or less and in which the number of pores with diameters of 3µm or more on the surface thereof is 100 pores or less per 1mm 2 can be obtained, thus having completed the present invention using the sintered titanium oxide body as the wafer-chucking substrate for substrate chucking devices. In the above producing processes (1) to (3), a highly purified titanium oxide fine powder used as a starting material preferably has a high purity of 99% or more. If the purity is less than 99%, it is hardly possible to obtain the second feature of the present invention, that is, a sintered body with an extremely small number of pores on the surface thereof (a sintered body in which the number of pores having diameters of 3µm or more is 100 pores per 1mm 2 or less), thus presenting undesirable outcome (see comparative examples 26 and 27 described below). The average particle size of the above starting fine powder is preferably 1µm or less. If any powder having a size exceeding 1µm is used, it is difficult to obtain the same second feature of the present invention, or a sintered body with an extremely small number of pores on the surface thereof, thus resulting in undesirable outcome (see comparative examples 8 described below). As referring to further details as to the highly purified titanium oxide fine powder used as a starting powder, if the starting powder has a purity of less than 99%, or if the average particle size is greater than 1µm, low temperature sintering properties fail as will be described later and consequently the sintered density can not be enough raised. Therefore, if the powder is sintered at high-temperatures (exceeding 1,300°C which is defined by the present invention, e.g.,1,400°C, 1,600°C) in order to raise the sintered density, grains tend to grow large and pores become large and rough (see comparative examples 22 to 28 described below). Accordingly, in the present invention, it is preferable to use as the starting material a highly purified titanium oxide fine powder which has an average particle size of not more than 1µm and is highly purified 99% or more, and it is more preferable to use a titanium oxide powder which has an average particle size of not more than 0.5µm and is highly purified 99.8% or more. In the present invention, the above starting fine powder is formed into ceramic green sheets by a typical CIP forming process, the Doctor-blade process, the extrusion process or the like. The thus obtained ceramic green sheet molded by the Doctor-blade process or the extrusion process, is subjected, as required, to a treatment for burning out binder. Next, the starting material is baked to produce a targeted titanium oxide substrate having both the aforementioned first and second features by adopting any one of the following processes (1) to (3): (1) A process comprising the steps of baking in the air or an inert atmosphere, and further conducting a HIP treatment; (2) A process comprising the step of baking in a reducing atmosphere; and (3) A process comprising the steps of baking in a reducing atmosphere, and further conducting a HIP treatment. In the aforementioned processes (1) to (3), the baking in the air or a reducing atmosphere is preferably conducted at a temperature of 1,100 to 1,300°C, and more preferably at 1,200°C and thereabout. If the baking is conducted at a lower temperature than 1,100°C, sintering itself is unlikely to proceed and therefore well-sintered body is difficult to obtain. On the other hand, if the baking temperature exceeds 1,300°C, it is difficult to obtain the second feature of the present invention, that is, a sintered body with an extremely small number of pores on the surface thereof (a sintered body in which the number of pores having diameters of 3µm or more is 100 pores per 1mm 2 or less), thus presenting undesirable result (refer to comparative example 2, described below). Referring further to the aforementioned baking temperature, the starting material in the present invention is baked in the air, an inert atmosphere or a reducing atmosphere at lower temperatures of 1,100 to 1,300°C than a typical baking temperature (1,350°C) at which titania ceramics are formed. And, a baking temperature exceeding 1,300°C, excessively promotes grain growth (or crystal growth), causing pores to move to the grain boundary phase and making pores rough and large as the grains grow large, thereby bringing about undesirable result. Accordingly, in the present invention, in order to facilitate the starting material to be sintered at low temperatures (that is, in order to make the low temperature sintering properties effective), the aforementioned highly purified titanium oxide fine powder having an average particle size of not more than 1µm and being highly purified 99% or more, is to be used as the starting material. In the aforementioned process (1), the baking in the air or inert atmosphere alone, cannot provide the first feature of the present invention a sintered body with a low specific resistance (a sintered body having a specific resistance of 1.0Ω·cm or less) (refer to comparative example 2, described below). Therefore, when this baking process in the air or an inert atmosphere is adopted, it is necessary that the resultant sintered body is further HIP-treated in order to provide the aforesaid first feature a feature of low specific resistance. By this HIP treatment, for example, a HIP treatment using a carbon heater, the titanium oxide sintered body having been baked in the air or an inert atmosphere becomes semiconductive, thus presenting a desirable specific resistance of 1.0Ω·cm or less. It should be noted that, besides the function of reducing specific resistance, the HIP treatment also has a function of lessening pores on the surface. The HIP treatment is preferably conducted at 800 to 1,100°C, or a temperature not higher than the aforementioned baking temperature (1,100 to 1,300°C), in view of preventing pores from becoming large due to the grain growth. The pressure during the HIP treatment is preferably 500kg/cm 2 or more. A more preferable HIP condition is 1,000°C, 1,500kg/cm 2 . In the aforementioned process (2) of baking in a reducing atmosphere, the baking in a reducing atmosphere causes titanium oxide to be partly reduced and become semiconductive, whereby the resultant substance presents a desirable specific resistance of 1.0Ω·cm or less. The reducing atmosphere may be any reducing atmosphere in which titanium oxide can become semiconductive during the baking. For example, it is preferable to perform the baking in nitrogen atmosphere using a carbon heater etc. The process (2) of baking at 1,100 to 1,300°C in a reducing atmosphere can provide a titanium oxide sintered body having both the first targeted feature of the present invention, the specific resistance is extremely low and the second targeted feature of the present invention, the surface has a very small number of pores. Additionally, in order to lessen the pores on surface much more, it is possible to further subject the resultant titanium oxide sintered body obtained in the aforementioned process (2) to a HIP treatment using for example a carbon heater. The HIP treatment is preferably conducted, similarly to the HIP treatment in the above (1), at a baking temperature of 800 to 1,100°C under a pressure of 500Kg/cm 2 or more, and more preferably conducted at 1,000°C under 1,500kg/cm 2 . In the present invention, the thus obtained titanium oxide substrates by the above processes (1) to (3) can be surface ground or subjected to the surface lapping, as required. Then, a sucking hole is drilled in this titanium oxide substrate to thereby provide a wafer-chucking substrate of titanium oxide. Next, a carrier which can chuck substrates according to the present invention will be further described in detail referring to examples of the present invention together with comparative examples. Examples 1 to 8 serve illustrative purposes and are not within the scope of the claims. (Examples 1 to 4) Polyvinyl butyral and ethyl alcohol were added to titanium oxide powder having a purity of 99.8% with an average particle size of 0.25µm and mixed so as to be slurried. Then, a green sheet was prepared from the slurry by the Doctor-blade process. After being subjected to the treatment for burning out binder, the green sheet was baked under a normal pressure sintering condition (at a temperature of 1,200°C in the air atmosphere or nitrogen atmosphere) as shown in Table 1. Further, in examples 2 and 4, the thus baked sheet was HIP treated in a HIP heater having a carbon heater under argon atmosphere in a HIP treatment condition (at a temperature of 1,000°C under a pressure of 1,500kg/cm 2 ) as shown in Table 1. Next, the thus treated material was heat-treated in the air atmosphere at a temperature of 700 to 900°C in examples 2 to 4 other than example 1. The number of pores having diameters of 1µm or more was counted as to each of the thus obtained titanium oxide substrates. The result is shown in Table 1. In these cases, no pore having a diameter of 30µm or more was observed on the surface of each substrate. Each surface of the substrates to be measured was observed and photographed by a scanning electron microscope and the thus obtained photography was used to estimate the number and diameter of pores on the surface of the substrate. (Example 5) Polyvinyl butyral and ethyl alcohol were added to titanium oxide powder having a purity of 99.2% with an average particle size of 0.7µm and mixed so as to be slurried. Then, a green sheet was prepared from the slurry by the Doctor-blade process. After being subjected to the treatment for burning out binder, the green sheet was baked under a normal pressure sintering condition (at a temperature of 1,200°C in the air atmosphere) as shown in Table 1. Further, the thus baked sheet was HIP treated under argon atmosphere in a HIP treatment condition (of the same HIP treatment as in the above examples 2 and 4) as shown in Table 1. Thereafter, the treated sheet was heat-treated in the air atmosphere at a temperature of 700 to 900°C. The number of pores was counted as to the thus obtained titanium oxide substrate in the same manner as in examples 1 to 4. The result is shown in Table 1. In this case, no pore having a diameter of 30µm or more was observed on the surface of the substrate. (Examples 6 to 9) Polyvinyl butyral and ethyl alcohol were added to aluminum oxide powder having a purity of 99.9% with an average particle size of 0.25µm and mixed so as to be slurried. Then, a green sheet was prepared from the slurry by the Doctor-blade process. After being subjected to the treatment for burning out binder, the green sheet was baked under a normal pressure sintering condition (at a temperature of 1,400°C in the air atmosphere or nitrogen atmosphere) as shown in Table 1. Further, in examples 7 and 9, the thus baked sheet was HIP treated under argon atmosphere in a HIP treatment condition (at a temperature of 1,350°C under a pressure of 1,800kg/cm 2 ) as shown in Table 1. The number of pores was counted as to each of the thus obtained aluminum oxide substrates in the same manner as in examples 1 to 4. The result is shown in Table 1. In these cases, no pore having a diameter of 30µm or more was observed on the surface of each substrate. (Example 10) Polyvinyl butyral and ethyl alcohol were added to aluminum oxide powder having a purity of 99.2% with an average particle size of 0.6µm and mixed so as to be slurried. Then, a green sheet was prepared from the slurry by the Doctor-blade process. After being subjected to the treatment for burning out binder, the green sheet was baked under a normal pressure sintering condition (at a temperature of 1,400°C in the air atmosphere) as shown in Table 1. Further, the thus baked sheet was HIP treated under argon atmosphere in a HIP treatment condition (at a temperature of 1,350°C under a pressure of 1,800kg/cm 2 ) as shown in Table 1. The number of pores was counted as to the thus obtained aluminum oxide substrate in the same manner as in examples 1 to 4. The result is shown in Table 1. In this case, no pore having a diameter of 30µm or more was observed on the surface of the substrate. (Comparative Examples 1 to 8) With titanium oxide powders each having a purity and an average particle size as shown in Table 2, green sheets were prepared in the same manner as in the above examples 1 to 4. After being subjected to the treatment for burning out binder, each green sheet was baked under a normal pressure sintering condition and HIP treated in a HIP condition shown in Table 2. Further, each of the thus treated sheets other than comparative examples 1, 5 and 7, was heat-treated in the similar manner to the above example. The number of pores was counted in the same manner as in examples 1 to 4 as to each of the thus obtained titanium oxide substrates. The result is shown in Table 2. (Comparative Examples 9 to 16) With aluminum oxide powders each having a purity and an average particle size as shown in Table 2, green sheets were prepared in the same manner as in the above examples 6 to 9. After being subjected to the treatment for burning out binder, each green sheet was baked under a normal pressure sintering condition and HIP treated in a HIP condition shown in Table 2. The number of pores was counted in the same manner as in examples 1 to 4 as to each of the thus obtained aluminum oxide substrates. The result is shown in Table 2. As apparent from Table 1 above, in examples 1 and 3 in which titanium oxide powder having a purity of 99.8% with an average particle size of 0.25µm was molded, thereafter baked at 1,200°C in the air or nitrogen gas, substrates having 70 pores/mm 2 were obtained. In examples 2 and 4 in which the sintered bodies obtained in examples 1 and 3 were further HIP treated, substrates having 34 pores/mm 2 and 38 pores/mm 2 , respectively were obtained . From the result, it can be understood that additionally conducted HIP treatment will extremely lessen the pores present on the substrate surface and therefore create more preferable hard disc substrates. Similarly, in examples 6 and 8 in which aluminum oxide powder having a purity of 99.9% with an average particle size of 0.25µm was molded, thereafter baked at 1,400°C in the air or nitrogen gas, substrates having 85 pores/mm 2 and 82 pores/mm 2 , respectively were obtained. In examples 7 and 9 in which the sintered bodies obtained in examples 6 and 8 were further HIP treated, substrates having 48 pores/mm 2 and 40 pores/mm 2 , respectively were obtained. From the result, it can be understood that, as in the cases of the above titanium oxide substrate, additionally conducted HIP treatment will also extremely lessen the pores present on the aluminum oxide substrate surface and therefore create more preferable hard disc substrate, thin film chip capacitor and a ceramic substrate for hybrid ICs. In example 5 in which titanium oxide powder having a purity of 99.2% with an average particle size of 0.7µm (a starting material which has an average diameter of greater and a purity lower than those in example 2 but both falling within the scope of the present invention) was used, as well as in example 10 in which aluminum oxide powder having a purity of 99.2% with an average particle size of 0.6µm (a starting material which has an average diameter of greater and a purity lower than those in example 7 but both falling within the scope of the present invention) was used, substrates having 92 pores/mm 2 and 96 pores/mm 2 (both of which fall within a target value of the present invention, i.e., 100 pores) were obtained, respectively, though the numbers of pores were greater than those of examples 2 and 7. Therefore, both of them can be used as a hard disc substrate, thin film chip capacitor and a ceramic substrate for hybrid ICs. As is apparent from the Table 2 above, in contrast with the above examples 1 to 10, in the cases where, even with starting powder having a purity of 99% or more with an average particle size of 1µm or less, both of which fall within the limitation of the present invention, if the material had been baked at a temperature beyond the scope of the baking temperatures (the sintering temperature: 1,100 to 1,300°C for titanium oxide powder; and 1,200 to 1,400°C for aluminum oxide powder) limited by the present invention, particularly when, as in comparative examples 1 to 4 and 9 to 12, the material was baked at a temperature of 1,600°C, which exceeds the upper boundary of the limitation; substrates obtained had at least about 500 pores/mm 2 to about 1,000 pore/mm 2 on the surface thereof even though the material was HIP treated. Accordingly, these substrates were inappropriate as a hard disc substrate, thin film chip capacitor and a ceramic substrate for hybrid ICs. Further, with starting powder having a purity of less than 99% as seen in comparative examples 5, 6 and comparative examples 13, 14, or with starting powder having an average particle size of more than 1µm as seen in comparative examples 7, 8 and comparative examples 15, 16, the material had to be baked above the baking temperature defined by the present invention. As a result, a lot of pores appeared on the surface of resulting substrates. Therefore, these substrates were again inappropriate as a hard disc substrate, thin film chip capacitor and a ceramic substrate for hybrid ICs. (Example 11) Polyvinyl butyral and ethyl alcohol were added to titanium oxide powder having a purity of 99.8% with an average particle size of 0.25µm and mixed so as to be slurried. Then, a green sheet was prepared from the slurry by the Doctor-blade process. After being subjected to the treatment for burning out binder, the green sheet was baked at a temperature of 1,200°C in the air atmosphere. Next, the thus sintered body was HIP treated in a HIP heater having a carbon heater under argon atmosphere at a temperature of 1,000°C under a pressure of 1,500kg/cm 2 . The specific resistance and the number of pores as to the thus obtained titanium oxide substrate were measured. The result is shown in Table 3. In this case, no pore having a diameter of 30µm or more was observed on the surface of the substrate. The aforementioned specific resistance was measured by the four probe method (1V, 1kHz). The surface of the substrate to be measured was observed and photographed by a scanning electron microscope and the thus obtained photography was used to estimate the number and diameter of pores on the surface of the substrate. Here, specific resistance values in Table 1 were the measurements at 25°C while numbers of pores are the counts of pores with an average diameter of 3µm or more per millimeter square. (Example 12) Polyvinyl butyral and ethyl alcohol were added to titanium oxide powder having a purity of 99.8% with an average particle size of 0.25µm and mixed so as to be slurried. Then, a green sheet was prepared from the slurry by the Doctor-blade process. After being subjected to the treatment for burning out binder, the green sheet was baked at a temperature of 1,200°C in nitrogen atmosphere by a carbon heater. The specific resistance and the number of pores as to the thus obtained titanium oxide substrate were measured in the same manner as in example 1. The result is shown in Table 3. In this case, no pore having a diameter of 30µm or more was observed on the surface of the substrate. (Example 13) The sintered body obtained in example 2 was HIP-treated in a HIP furnace having a carbon heater in argon atmosphere at a temperature of 1,000°C under a pressure of 1,500kg/cm 2 as in the same manner as in the above example 1. The specific resistance and the number of pores as to the thus obtained titanium oxide substrate were measured in the same manner as in example 11. The result is shown in Table 3. In this case, no pore having a diameter of 30µm or more was observed on the surface of the substrate. (Example 14) A titanium oxide substrate was prepared by the same means as in example 11 except in that titanium oxide powder having a purity of 99.2% with an average diameter of 0.7µm was used. The specific resistance and the number of pores as to the thus obtained titanium oxide substrate were measured in the same manner as in example 11. The result is shown in Table 3. In this case, no pore having a diameter of 30µm or more was observed on the surface of the substrate. (Comparative Examples 21 to 28) For the purpose of comparison, with titanium oxide powders each having a purity and an average particle size as shown in Table 3, green sheets were prepared in the same manner as in the above example 1. After being subjected to the treatment for burning out binder, each green sheet was baked under a normal pressure sintering condition shown in the same Table 1 (for comparative examples 23, 25, 27 and 28, further HIP treated in HIP conditions shown in Table 1). The specific resistance and the number of pores as to each of the thus obtained titanium oxide substrates were measured in the same manner as in example 11. The result is shown in Table 1. (Comparative Example 29) Further, for the purpose of comparison, aluminum oxide powder having a purity of 99.8% with an average diameter of 0.6µm was used to form a green sheet in the same manner as in the above example 11. Then, after being subjected to the treatment for burning out binder, the green sheet was baked at 1,600°C in the air. The specific resistance and the number of pores as to the thus obtained aluminum oxide substrate were measured in the same manner as in example 11. The result is shown in Table 1. As is apparent from Table 3, in example 11 in which titanium oxide powder having a purity of 99.8% with an average particle size of 0.25µm was molded and the molding was baked at 1,200°C in the air and the baked molding was further HIP-treated in a reducing atmosphere at 1,000°C under a pressure of 1,500kg/cm 2 , a substrate having a specific resistance of 0.7Ω·cm with 34 pores/mm 2 was obtained. In example 12 in which the same material as in example 11 was baked in nitrogen atmosphere at 1,200°C, a substrate having a specific resistance of 0.9Ω·cm with 70 pores/mm 2 was obtained. In example 13 in which the substrate obtained in example 12 was further HIP-treated, a substrate having a specific resistance of 0.7Ω·cm with 38 pores/mm 2 was obtained. From this result, it can be understood that the HIP-treatment will improve the specific resistance as well as the number of pores (specific resistance: 0.9 to 0.7; number of pores: 70 to 38). Further, in example 14 in which titanium oxide powder having a purity of 99.2% with an average particle size of 0.7µm (a starting material which has an average diameter of greater and a purity lower than those in example 11 but both falling within the scope of the present invention) was molded and the molding was baked in the air in the same manner as in example 11 and further HIP-treated, a substrate having a specific resistance of 0.7 Ω·cm which is as low as in example 11, with 92 pores/mm 2 , which falls within a range designated by the present invention, i.e., not more than 100 pores/mm 2 , although it is greater than that in example 11. In contrast, in comparative example 11 in which the material was processed in the same condition as in example 11 but was not subjected to a HIP treatment, obtained was a substrate with 70 pores/mm 2 but having a high specific resistance as of 10 12 Ω·cm, (as compared to 0.7Ω·cm in example 11). That is, this comparative example could not produce a sintered body having a low specific resistance (a sintered body having a specific resistance of not more than 1.0Ω·cm) to be targeted by the present invention. In comparative example 12 in which the material was processed in the same manner as in example 11 except in that baking was conducted at a temperature of 1,600°C in the air with no HIP treatment done, and in comparative example 23 in which the substrate obtained in comparative example 22 was HIP-treated (at 1,400°C under 1,500kg/cm 2 ), both comparative examples 22 and 23 only produced substrates having high specific resistances (10 12 Ω·cm) with 840 pores/mm 2 and 480 pores/mm 2 , respectively. Further, in comparative example 24 in which the material was processed in the same manner as in example 12 except in that baking was conducted at a temperature of 1,600°C in nitrogen atmosphere with no HIP treatment done, and in comparative example 25 in which the substrate obtained in comparative example 14 was HIP-treated (at 1,400°C under 1,500kg/cm 2 ), both comparative examples 24 and 25 produced substrates having low specific resistances (0.8Ω·cm) but having as much pores as 920 pores/mm 2 and 770 pores/mm 2 , respectively. In comparative example 26, in which a molding made of a starting material with an average diameter of 0.7µm as is equivalent to that of example 14 and therefore belongs to the scope of the invention, but having a purity of 92.0% which is beyond the scope of the invention, was baked at 1,400°C in the air, a substrate having as a high specific resistance as 10 12 Ω·cm with 960 pores/mm 2 was obtained. In comparative example 27 in which a molding of the same starting material used in the above comparative example 26 was baked in the air and further HIP-treated (at 1,200°C under 1,800kg/cm 2 ), the specific resistance of a resultant substrate was 0.8Ω·cm because of the implementation of the HIP treatment, but the number of pores was as much as 550 pores/mm 2 because the purity of the starting material was low (92.0%) and the baking was conducted in the air at a temperature (1,400°C), which is beyond the scope of the present invention. Further, in comparative example 28 in which a molding of a starting material having a purity of 99.2% which falls within the scope of the invention, with an average particle size of 2.1µm which falls beyond the scope of the invention, was baked in the air (at 1,400°C), and further HIP-treated (at 1,200°C under 1,800kg/cm 2 ), a substrate having a specific resistance of 0.8Ω·cm but having as much pores as 310 pores/mm 2 was obtained. Moreover, in comparative example 29 in which an alumina sintered body was formed by baking in the air a starting material having a purity of 99.8% with an average particle size of 0.6 µm, the obtained substrate not only exhibited as a high specific resistance as 10 14 Ω·cm but also had as much pores as 1,000 pores/mm 2 . Thus, as has been apparent from examples 11 to 14 and comparative examples 21 to 29 in Table 3, the present invention can be understood that a targeted titanium oxide substrate having an extremely small number of pores on the surface thereof and a low specific resistance, or specifically, a titanium oxide substrate in which the specific resistance is 1.0 Ω·cm or less and the number of pores with diameters of 3µm or more on the surface thereof is not more than 100 pores or less per 1mm 2 , is obtained only: 1) by using a highly purified titanium oxide fine powder having a purity of 99% or more with an average particle size of 1µm or less; and 2) baking the material at 1,100 to 1300°C in the air or a reducing atmosphere; and 3) requiring a HIP treatment (for example, a HIP treatment in a HIP furnace having a carbon heater) in the case where the baking is conducted in the air. Further, it is also understood that 4) in the case where the baking (sintering) is conducted in a reducing atmosphere in the above 2), the HIP treatment following will improve the factors of the specific resistance and the number of pores much more; and 5) the HIP treatment mentioned in 3) will also improve the factor of the number of pores. Industrial Applicability As has been detailed above, since a carrier which can chuck the substrate according to the present invention is a substrate chucking device using a wafer-chucking substrate made of titanium oxide which has an extremely low specific resistance of 1.0Ω·cm or less and in which the number of pores with diameters of 3µm or more on the surface thereof is 100 pores or less per 1mm 2 , it is easy to prevent the wafer-chucking substrate from bearing static charges, and therefore no dust etc. brought by the static charges adsorbs to the substrate. In addition, since there are extremely rare pores with no pore having a diameter of 30µm or more thereon, no gas etc. will not adsorb thereto, thereby providing remarkable effects, such as making the device free from deterioration of the functions for chucking and holding semiconductor wafers or any other wafers. Further, it is possible to desirably apply the substrate chucking device of the present invention to a wafer hand or a wafer holder built in a semiconductor integrated circuit fabrication apparatus and it is possible to largely contribute to the increased integration and improved yield of semiconductor devices.

Claims: A wafer chucking device comprising a wafer-chucking substrate for suction chucking and transporting or fixing a wafer, being characterized in that said wafer-chucking substrate is made of titanium oxide and has a specific resistance of 1.0 Ω·cm or less, and the number of pores with diameters of 3 µm or more on the surface thereof is 100 pores or less per 1 mm 2 . A wafer chucking device according to Claim 1 wherein said wafer-chucking substrate made of titanium oxide is formed by molding titanium oxide powder having a purity of 99% or more with an average particle size of 1µm or less, baking the molding in the air atmosphere or an inert atmosphere at a temperature of 1,100 to 1,300°C, and further subjecting the baked molding to a hot isostatic pressing (HIP) treatment under a pressure of 500kg/cm 2 or more. A wafer chucking device according to Claim 1 wherein said wafer-chucking substrate made of titanium oxide is formed by molding titanium oxide powder having a purity of 99% or more with an average particle size of 1µm or less, and baking the molding in a reducing atmosphere at a temperature of 1,100 to 1,300°C. A wafer chucking device according to Claim 1 wherein said wafer-chucking substrate made of titanium oxide is formed by molding titanium oxide powder having a purity of 99% or more with an average particle size of 1µm or less, baking the molding in a reducing atmosphere at a temperature of 1,100 to 1,300°C, and further subjecting the baked molding to a hot isostatic pressing (HIP) treatment under a pressure of 500kg/cm 2 or more.

Inventors: KAMIAKA HIDETO, KISHI YUKIO, KAMIAKA, HIDETO, KISHI, YUKIO, KAMIAKA, HIDETO, A-202, MEZON ASANO UMEGAOKA, KISHI, YUKIO, 302, KOKUTO FUNABASHI HAITSU
Applicants: NIHON CEMENT, NIHON CEMENT CO., LTD.
Application year: 1993
Main classification: G11B5
IPC codes: G11B5, C04B35, H01L23, H01G4, H05K1, H01L21