Substrate suction apparatus and method for manufacturing the same

Provided is a substrate suction apparatus which has a vacuum suction mechanism and an electrostatic attraction mechanism, and improves planarity of a subject to be processed by improving uniformity in vacuum suction power. A method for manufacturing such substrate suction apparatus is also provided. A substrate suction apparatus (1) is provided with a base board (2), a dielectric body (3), an electrostatic attraction mechanism (4) and a vacuum suction mechanism (5). Specifically, the dielectric body (3) is composed of a downmost dielectric layer (31), an intermediate dielectric layer (32) and a topmost dielectric layer (33). The electrostatic attraction mechanism (4) is composed of attraction electrodes (41, 42) and a direct current power supply. The vacuum suction mechanism (5) is composed of a groove (51), a suction channel (52), a porous dielectric body (3) and the porous attraction electrodes (41, 42). The downmost dielectric layer (31), the intermediate dielectric layer (32) and the topmost dielectric layer (33) are formed by spraying ceramic particles, and the attraction electrodes (41, 42) are formed by spraying tungsten particles. The average pore diameter and porosity of the downmost dielectric layer (31) are set maximum, and those of the topmost dielectric layer (33) are set minimum.

TECHNICAL FIELD

The present invention relates to substrate suction apparatuses for holding and carrying wafers, liquid crystal display substrates and the like utilized in semiconductor manufacturing equipment and liquid crystal display devices, and to a method of manufacturing such substrate suction apparatuses.

BACKGROUND ART

Vacuum chuck apparatuses and electrostatic chuck apparatuses are among this kind of substrate suction apparatuses.

A vacuum chuck apparatus embodies a vacuum suction technology of sucking up a substrate by sucking away the air between the substrate and the chuck apparatus so as to create a negative pressure therebetween. Since the apparatus sucks up the whole surface of a substrate with a strong negative pressure, it is possible to suck up even a substrate easy to warp while restraining it from warping. However, vacuum chuck apparatuses cannot be utilized under a vacuum atmosphere without gas. Therefore, they are not applicable to apparatuses utilizing vacuum such as plasma processing apparatuses, ion implantation apparatuses, ion doping apparatuses, liquid crystal substrate compositing apparatuses, exposure apparatuses of electron beam, EUV and the like, wafer inspection apparatuses, etc.

On the other hand, an electrostatic chuck apparatus can be utilized either under a vacuum atmosphere or under an air atmosphere because it electrostatically attracts up a substrate by virtue of electrostatic force acting between the substrate and the apparatus. Therefore, electrostatic chuck apparatuses are positioned as indispensable in the recent semiconductor manufacturing technologies which employ a great number of apparatuses utilizing vacuum. However, since the electrostatic chuck apparatuses are not provided with a strong suction power, it is more difficult for them than the vacuum chuck apparatuses to deal with warping of the substrates.

In view of the above problems, as disclosed in the following Patent Documents 1 to 4, there are proposed substrate suction apparatuses which include a vacuum suction mechanism and an electrostatic attraction mechanism.

By employing these apparatuses, inside an exposure apparatus and the like, for example, an exposure process and the like can be carried out under a vacuum atmosphere by first flattening a warped substrate through vacuum suction and then switching it to electrostatic attraction.

Patent Document 2: Japanese Patent Application Publication No. 2003-107487;

Patent Document 3: Japanese Patent Application Publication No. 2007-053405;

Patent Document 4: Japanese Patent Application Publication No. 2005-109358; and

Patent Document 5: Japanese Patent Application Publication No. 2004-298970.

DISCLOSURE OF THE INVENTION

Nevertheless, as will be described hereinbelow, there are problems with the aforementioned conventional substrate suction apparatuses.

In recent years, planarity of a substrate and uniformity of suction force have been required at a high level in sucking up the substrate.

This is because there are growing needs to improve performances in cooling the substrate and keeping the apparatus at a constant temperature by uniforming or equalizing the contact pressure between the suction surface of the apparatus and the underside surface of the substrate. Another reason is that it is necessary to flatten the substrates as much as possible for exposure apparatuses and the like because super miniaturizations have been required for wiring patterns on the substrates. Further, the industry is moving in the direction of thinning silicon wafers as a so-called “ecological measure” for silicon resources. A wafer 300 mm long in diameter is 0.8 mm in thickness at the present time, but is expected to be thinned down to approximately 0.2 mm in the future. Further, the movement of thinning substrates is not with respect only to wafers but to liquid crystal display substrates as well. However, thinned substrates become low in rigidity, thereby being subject to influences from the suction surface of the substrate suction apparatus. As a result, they may become easy to deform. Hence, planarity and uniformity in substrate suction are required at a higher level.

However, the vacuum suction mechanism in the aforementioned conventional substrate suction apparatuses is of such a structure as a plurality of holes are drilled on the suction surface of the apparatus, so as to suck up the substrate with a vacuum force created by sucking away the air through the holes. Hence, the suction force on the substrate is strong around the holes whereas weak off the holes, thereby lacking in uniformity. Therefore, it was concerned that a thinned substrate and the like might degrade in planarity because they would get dented in the hole portions.

To address the above problem, there is also proposed a vacuum chuck apparatus with improved uniformity in suction force by forming the suction surface out of a porous material such as ceramics and the like (for example, see Patent Document 5).

However, in this case, since the porous material is formed by sintering granular substances such as ceramics and the like, pore size and distribution are not uniformed but varied and biased. Further, since the material is formed through sintering, it is not possible to control the pores to be formed uniformly in size and distribution. Therefore, it is practically impossible to make up a porous material which has a porosity from 5% to 25%, a small average pore diameter, and a nearly uniform pore distribution. In reality, a usable porous material can only be made with a porosity not lower than 30%. Consequently, applying a porous material with a great average pore diameter to the suction surface of the vacuum suction mechanism cannot acquire uniformity of the suction force and thereby cannot secure planarity of the substrate.

The present invention is made to solve the above problems and has as its object the provision of an substrate suction apparatus and a method for manufacturing such substrate suction apparatus which includes a vacuum suction mechanism and an electrostatic attraction mechanism for improving uniformity in vacuum suction force so as to upgrade planarity of a work piece.

In order to solve the above problems, an aspect of the present invention as set forth in claim1provides a substrate suction apparatus including: a base, a dielectric body being provided on the base and having a surface employed as a suction surface for a work piece, an electrostatic attraction mechanism for attracting up the work piece on the suction surface with an electrostatic force between the work piece and an attraction electrode provided inside the dielectric body, and a vacuum suction mechanism for sucking up the work piece on the suction surface by creating a negative pressure between the work piece and the suction surface of the dielectric body; the vacuum suction mechanism is composed of a suction portion opening on the base surface for sucking in a gas on the base surface side, the porous dielectric body formed on the base through spraying, and the porous attraction electrode formed inside the dielectric body through spraying.

By virtue of this configuration, with the work piece being placed on the suction surface of the dielectric body, when the vacuum suction mechanism is put into function to suck in the gas from the suction portion of the base, the gas between the suction surface and the work piece is sucked away through the pores in the dielectric body and attraction electrode, thereby creating a negative pressure between the suction surface and the work piece. As a result, the work piece is sucked up on the suction surface with its warped surface flattened.

In this state, as the electrostatic attraction mechanism is put into function after the vacuum suction mechanism is stopped, the work piece can be attracted up on the suction surface by an electrostatic force between the attraction electrode and the work piece. As a result, even under a vacuum atmosphere, a predetermined process can be carried out with respect to the work piece with its surface flattened.

However, if the vacuum suction mechanism is put into function to suck up an ultrathin work piece on the suction surface, the work piece may get dented in the pore portions to form numerous convexoconcaves on its underside surface and thereby degrade in planarity.

Therefore, in the substrate suction apparatus of the present invention, the vacuum suction mechanism is composed of a suction portion for sucking in a gas on the base surface side, a porous dielectric body formed on the base through spraying, and a porous attraction electrode formed inside the dielectric body through spraying, whereby pores can be uniformly distributed in the dielectric body and the attraction electrode. Further, spray particles small in average particle diameter are utilized to acquire a small average pore diameter.

In this manner, by virtue of spraying, pores small in average pore diameter are formed and distributed uniformly in the dielectric body and attraction electrode. Then, the ultrathin work piece is placed and sucked up on the suction surface of the dielectric body including the small pores in diameter, thereby allowing its entire underside surface to be uniformly sucked by virtue of the numerous small pores. Hence, even an ultrathin work piece will not get dented due to the pores. That is, since the work piece is sucked up uniformly by virtue of the small pores in diameter, its planarity is thus secured.

Another aspect of the present invention as set forth in claim2provides the substrate suction apparatus according to claim1, wherein the suction portion of the vacuum suction mechanism is composed of a plurality of grooves recessed on the base surface and one or more suction channel(s) provided inside the base.

By virtue of this configuration, the gas is sucked into the plurality of grooves from the pores of the dielectric body, and then pumped to the outside through the suction channel.

Yet another aspect of the present invention as set forth in claim3provides the substrate suction apparatus according to claim1, wherein the base is formed of a porous material, and its side surfaces and bottom surface are covered in an airtight manner with a nonporous member; the suction portion of the vacuum suction mechanism is composed of numerous pores of the base and a suction channel provided to the nonporous member.

By virtue of this configuration, a suction portion with a desired suction force may be formed without bringing complicated processes to the base, thereby facilitating reduction in manufacturing cost.

Yet another aspect of the present invention as set forth in claim4provides the substrate suction apparatus according to any one of claims1to3, wherein the dielectric body is composed of a downmost dielectric layer formed as a lamina on the base through spraying, one or more intermediate dielectric layer(s) formed as a lamina on the downmost dielectric layer through spraying, and a topmost dielectric layer being formed as a lamina in the topmost position through spraying and having a surface employed as the suction surface; the average pore diameter and porosity of the downmost dielectric layer is set maximum whereas those of the topmost dielectric layer is set minimum.

By virtue of this configuration, the average pore diameter and porosity are diminished in a gradual manner upwardly from the downmost dielectric layer toward the topmost dielectric layer, whereby a smooth suction function becomes possible.

Yet another aspect of the present invention as set forth in claim5provides the substrate suction apparatus according to claim4, wherein the average pore diameter and porosity of the pores in the downmost dielectric layer are set to 20 μm to 200 μm and 25% to 60%, respectively; those of the pores in the one or more intermediate dielectric layer(s) and attraction electrode are set to 10 μm to 150 μm and 20% to 50%, respectively; and those of the pores in the topmost dielectric layer are set to 5 μm to 20 μm and 5% to 25%, respectively.

Yet another aspect of the present invention as set forth in claim6provides the substrate suction apparatus according to any one of claims1to5, wherein the dielectric body is formed by spraying ceramic particles; the attraction electrode is formed by spraying tungsten particles, molybdenum particles or nickel aluminum particles.

By virtue of this configuration, it is possible to easily form the dielectric body and attraction electrode with a desired average pore diameter and porosity.

Yet another aspect of the present invention as set forth in claim7provides a method for manufacturing the substrate suction apparatus, the method including: a base forming process for forming a base including a suction portion for sucking in a gas on its surface side, and a potential supply terminal projecting out of its surface from inside; an under layer forming process for forming a downmost dielectric layer maximum in average pore diameter and porosity as a lamina on the base through spraying; an electrode forming process for forming an attraction electrode smaller than the downmost dielectric layer in average pore diameter and porosity as a lamina on the downmost dielectric layer and on the end of the potential supply terminal through spraying; an intermediate layer forming process for forming one or more intermediate dielectric layer(s) nearly equal to the attraction electrode in average pore diameter and porosity as a lamina on the downmost dielectric layer in such a manner as to cover the attraction electrode through spraying; and an upper layer forming process for forming a topmost dielectric layer being minimum in average pore diameter and porosity and having a surface employed as a suction surface for a work piece as a lamina on the one or more intermediate dielectric layer(s) through spraying.

By virtue of this configuration, the base forming process is carried out to form a base including a suction portion for sucking in a gas on its surface side, and a potential supply terminal projecting out of its surface from inside; and the under layer forming process is carried out to form a downmost dielectric layer maximum in average pore diameter and porosity as a lamina on the base through spraying. Further, the electrode forming process is carried out to form an attraction electrode smaller than the downmost dielectric layer in average pore diameter and porosity as a lamina on the downmost dielectric layer and on the end of the potential supply terminal through spraying. Further, the intermediate layer forming process is carried out to form one or more intermediate dielectric layer(s) nearly equal to the attraction electrode in average pore diameter and porosity as a lamina on the downmost dielectric layer in such a manner as to cover the attraction electrode through spraying. Furthermore, the upper layer forming process is carried out to form a topmost dielectric layer being minimum in average pore diameter and porosity and having a surface employed as a suction surface for a work piece as a lamina on the one or more intermediate dielectric layer(s) through spraying.

Yet another aspect of the present invention as set forth in claim8provides the method according to claim7further including a grinding process for grinding the surface of the downmost dielectric layer so as to flush the end of the potential supply terminal into the surface of the downmost dielectric layer prior to the electrode forming process.

By virtue of this configuration, the grinding process is carried out prior to the electrode forming process to grind the surface of the downmost dielectric layer so as to flush the end of the potential supply terminal into the surface of the downmost dielectric layer.

Yet another aspect of the present invention as set forth in claim9provides the method according to claim7or8, wherein the average particle diameter of the spray particles utilized in each of the processes is set such that: the average pore diameter and porosity of the pores in the downmost dielectric layer are 20 μm to 200 μm and 25% to 60%, respectively; those of the pores in the one or more intermediate dielectric layer(s) and attraction electrode are 10 μm to 150 μm and 20% to 50%, respectively; and those of the pores in the topmost dielectric layer are 5 μm to 20 μm and 5% to 25%, respectively.

Yet another aspect of the present invention as set forth in claim10provides the method according to any one of claims7to9, wherein the downmost dielectric layer, the intermediate dielectric layer and the topmost dielectric layer are formed as laminas by spraying ceramic particles; the attraction electrode is formed as a lamina by spraying tungsten particles, molybdenum particles or nickel aluminum particles.

As described above in detail, according to the substrate suction apparatus of the present invention as set forth in claims1to6, by virtue of the small pores in diameter formed on the suction surface of the dielectric body, the work piece can be sucked up uniformly to secure its planarity. Thereby, an excellent effect is available in improving uniformity of the vacuum suction force so as to upgrade planarity of the work piece. As a result, it is possible to equally secure planarity of the work piece under both air and vacuum atmospheres.

Especially, according to the substrate suction apparatus of the present invention, as set forth in claim3, reduction in manufacturing cost can be expected; as set forth in claim4, there is an effect in achieving a smooth suction function.

Further, according to the substrate suction apparatus of the present invention as set forth in claim6, there is an effect in easily forming the dielectric body and attraction electrode with a desired average pore diameter and porosity.

According to the method for manufacturing the substrate suction apparatus of the present invention as set forth in claims7to10, there are formed through spraying the downmost dielectric layer, the attraction electrode, the intermediate dielectric layer, and the topmost dielectric layer as laminas on the base. The average pore diameter and porosity of the pores in those laminas are diminished in a gradual manner upwardly from the downmost dielectric layer toward the topmost dielectric layer, whereby the vacuum suction force is high enough in uniformity to manufacture a substrate suction apparatus capable of securing planarity of the work piece. That is, by regulating the spray particles in average particle diameter, temperature, spraying velocity and the like, it is possible to easily and correctly control the average pore diameter and porosity of each layer or electrode. Thereby, an excellent effect is available in easily and correctly manufacturing the substrate suction apparatus with a desired vacuum suction performance.

Especially, according to the method of the present invention as set forth in claim8, the end of the potential supply terminal is flushed or ground into the surface of the downmost dielectric layer, whereby it is possible to connect the attraction electrode to the potential supply terminal in a flat state.

DESCRIPTION OF NOTATIONS

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments will be described with reference to the drawings.

First Embodiment

FIG. 1is a perspective view showing a substrate suction apparatus with a fractured portion in accordance with a first embodiment of the present invention;FIG. 2is a plan view of the substrate suction apparatus;FIG. 3is a cross-sectional view of the substrate suction apparatus, viewed along arrows A-A inFIG. 2; andFIG. 4is a plan view showing the substrate suction apparatus with a fractured portion.

As shown inFIG. 1, in this embodiment, a substrate suction apparatus1is a apparatus for rectangular ultrathin substrates. The substrate suction apparatus1is provided with a base2, a dielectric body3, an electrostatic attraction mechanism4, and a vacuum suction mechanism5.

Alumina ceramics, titanium, aluminum, aluminum alloys and the like may be utilized as a material for the base2. In the embodiment, the base2is formed of a rectangular board shaped up out of bulk alumina ceramics and, as shown inFIG. 3, is provided with cooling water passages20therein.

The dielectric body3is a laminate provided on the base2with its surface as a suction surface3afor sucking up a substrate W as its work piece. The dielectric body3is composed of a downmost dielectric layer31, an intermediate dielectric layer32and a topmost dielectric layer33which are formed by spraying. These layers31to33, as will be described hereinafter, are formed of ceramics different in porosity, respectively.

The electrostatic attraction mechanism4is configured to attract up the substrate W on the suction surface3awith electrostatic force, and is composed of attraction electrodes41,42provided between the layers of the dielectric body3, and a DC power supply43.

Inparticular, the attraction electrodes41,42are rectangular bipolar electrodes formed by spraying tungsten on the downmost dielectric layer31. These attraction electrodes41,42are connected to potential supply terminals44,45, respectively. The potential supply terminals44,45are connected to the two electrodes of the DC power supply43via a switch46.

The vacuum suction mechanism5is configured to suck up the substrate W on the suction surface3aby creating a negative pressure between the substrate W and the suction surface3aof the dielectric body3. This vacuum suction mechanism5is composed of grooves51and a suction channel52as a suction portion for sucking in a gas on the surface side of the base2, the porous dielectric body3, and the porous attraction electrodes41,42.

As shown inFIG. 1, the grooves51are provided as recessed portions on the surface of the base2. Concentric circles, spiral patterns, lattice shapes and the like may be applied to the shape of the grooves51. In the embodiment, a lattice shape is applied.

In particular, the grooves51are formed by connecting four longitudinal grooves51aapproximately 1 mm deep and approximately 3 cm wide with four transverse grooves51bapproximately 0.5 mm deep and approximately 3 cm wide into a lattice. Then, as shown inFIG. 3, a suction channel52is provided in the base2with its upper end in communication with the longitudinal grooves51aand its lower end in connection with a suction pump50.

The porous dielectric body3is, as described above, composed of the downmost dielectric layer31, the intermediate dielectric layer32and the topmost dielectric layer33which are formed on the base2by spraying ceramic particles.

In particular, the downmost electric layer31is formed on a surface2aof the base2in a state of filling in the grooves51, and its thickness is set to 300 μm above the surface2a. Further, the average pore diameter of the downmost electric layer31is set to a maximum value of 40 μm. Furthermore, the porosity is set to approximately 30%.

Then, the attraction electrodes41,42are formed by spraying tungsten particles on the downmost dielectric layer31, and their thickness is set to 20 μm to 50 μm. Further, the average pore diameter of the attraction electrodes41,42is set to 20 μm which is smaller than that of the downmost electric layer31. Furthermore, the porosity is set to approximately 20%.

The intermediate dielectric layer32is formed on the downmost electric layer31to cover the attraction electrodes41,42, and its thickness is set to approximately 250 μm. Further, the average pore diameter of the intermediate dielectric layer32is set to 20 μm which is substantially equal to that of the attraction electrodes41,42. Furthermore, the porosity is also set to approximately 20%.

The topmost dielectric layer33is formed on the intermediate electric layer32, and its thickness is set to 50 μm. Further, the average pore diameter of the topmost dielectric layer33is set to a minimum value of 10 μm. Furthermore, the porosity is set to approximately 5%.

FIG. 5is a schematic cross-sectional view for describing porosity and the like of each layer.

As described above, the average pore diameter and porosity of the downmost dielectric layer31are of maximum values, those of the topmost dielectric layer33are of minimum values, and those of the intermediate dielectric layer32and the attraction electrodes41,42are of medium values thereof.

That is, to describe the pores of each layer in a schematic manner, as shown inFIG. 5, pores56, the thickest, are formed in the downmost dielectric layer31uniformly in a predetermined number; pores57, approximately half as thick as the pores56, are formed in the intermediate dielectric layer32and the attraction electrodes41,42uniformly in the aforementioned predetermined number; and pores58, approximately one-fourth as thick as the pores56, are formed in the topmost dielectric layer33uniformly in the aforementioned predetermined number. Accordingly, these pores56to58are in communication with each other, whereby the gas on the suction surface3aof the topmost dielectric layer33is sucked into the minute pores58which open uniformly on the suction surface3a, passes through the pores57,56, and is sucked smoothly into the grooves51shown inFIG. 3.

Next, a method for manufacturing the substrate suction apparatus1will be described.

Besides, the manufacturing method of the embodiment is a specific implementation of the method for manufacturing the substrate suction apparatus of the present invention.

FIG. 6is process flow diagram showing abase forming process, an under layer forming process and a grinding process, andFIG. 7is process flow diagram showing an electrode forming process, an intermediate layer forming process and an upper layer forming process.

The method for manufacturing the substrate suction apparatus1is accomplished by carrying out a base forming process S1, an under layer forming process S2, a grinding process S3, an electrode forming process S4, an intermediate layer forming process S5, and an upper layer forming process S6.

The base forming process S1will be carried out. This base forming process S1is a process to form the base2.

In particular, as shown inFIG. 6(a), through the base forming process S1, a rectangular base2is formed out of bulk alumina ceramics, and is provided therein with cooling water passages20and grooves51which are composed of longitudinal grooves51aapproximately 1 mm deep and transverse grooves51bapproximately 0.5 mm deep. A suction channel52is provided through the base2to be in communication with a longitudinal groove51awhile through holes21,22are provided in nearly the center portion of the base2.

Then, as shown inFIG. 6(b), the potential supply terminals44,45are inserted through the through holes21,22, and their ends44a,45aare projected out of the surface2aof the base2. In this state, nonporous ceramic isolation bushes47,48are provided inside the through holes21,22to finish the base forming process S1.

Next, the under layer forming process S2will be carried out. This under layer forming process S2is a process to form the downmost dielectric layer31as a lamina on the base2.

In particular, as shown inFIG. 6(c), ceramic particles of 99.9% purity are sprayed to substantially fill in the grooves51, and then further sprayed to form a lamina approximately 300 μm thick on the surface2aof the base2to accomplish the downmost dielectric layer31.

As a spraying method, plasma spraying, arc spraying, laser spraying and the like may be applied. In the embodiment, plasma spraying is adopted, utilizing ceramic particles which are 120 μm in average particle diameter to form the downmost dielectric layer31which is 40 μm in average pore diameter and approximately 30% in porosity.

When the under layer forming process S2is finished, projections34a,34bwill appear on the surface of the downmost dielectric layer31due to the ends44a,45aof the potential supply terminals44,45.

At this stage, the grinding process S3will be carried out. This grinding process S3is a process to flush or grind the ends of the potential supply terminals44,45into the surface of the downmost dielectric layer31.

In particular, as shown inFIG. 6(d), ceramic particles are sprayed from above the downmost dielectric layer31to forma sacrifice layer34approximately 20% in porosity as a lamina thereon. Then, as shown inFIG. 6(e), the sacrifice layer34and the downmost dielectric layer31are ground away approximately 10 μm to 20 μm in thickness from its top surface to form a flattened surface31cof the downmost dielectric layer31. Thereby, the ends44a,45aof the potential supply terminals44,45are flushed or ground into the surface31cof the downmost dielectric layer31.

Then, the electrode forming process S4will be carried out. This electrode forming process S4is a process to form the attraction electrodes41,42on the downmost dielectric layer31.

In particular, as shown inFIG. 7(a), tungsten particles are sprayed respectively on the potential supply terminals44,45exposed on the surface31cof the downmost dielectric layer31to form 20 μm to 50 μm thick attraction electrodes41,42as laminas on the downmost dielectric layer31. Thereby, the attraction electrodes41,42are in electric connection with the potential supply terminals44,45in a flat state, respectively.

The same spraying method is adopted as for the aforementioned downmost dielectric layer31and the sacrifice layer34to form the attraction electrodes41,42which are 20 μm in average pore diameter and approximately 20% in porosity by utilizing tungsten particles which are 100 μm in average particle diameter.

Next, the intermediate layer forming process S5will be carried out. This intermediate layer forming process S5is a process to form the intermediate dielectric layer32on the downmost dielectric layer31.

In particular, as shown inFIG. 7(b), ceramic particles of 99.9% purity are sprayed from above the attraction electrodes41,42on the surface31cof the downmost dielectric layer31to form the intermediate dielectric layer32which is approximately 250 μm thick to cover the attraction electrodes41,42on the downmost dielectric layer31as a lamina.

The same spraying method is adopted as for the aforementioned downmost dielectric layer31and the sacrifice layer34to form the intermediate dielectric layer32which is 20 μm in average pore diameter and approximately 20% in porosity by utilizing ceramic particles which are 100 μm in average particle diameter.

After the intermediate layer forming process S5is finished, the upper layer forming process S6will be carried out. This upper layer forming process S6is a process to form the topmost dielectric layer33on the intermediate dielectric layer32.

In particular, as shown inFIG. 7(c), ceramic particles of 99.9% purity are sprayed on the intermediate dielectric layer32to form the topmost dielectric layer33which is approximately 50 μm thick as a lamina.

The same spraying method is adopted as for the aforementioned downmost dielectric layer31and the intermediate dielectric layer32to form the topmost dielectric layer33which is 10 μm in average pore diameter and approximately 5% in porosity by utilizing ceramic particles which are 50 μm in average particle diameter.

Then, as shown inFIG. 7(d), the suction surface3aof the topmost dielectric layer33is ground or polished into a flat surface with a grinder100to finish the whole manufacturing process.

FIG. 8is a partially enlarged schematic cross-sectional view for describing a relationship between the average pore diameter and porosity, and the average particle diameter, with respect to each layer.

In the above manufacturing method, the average pore diameter and porosity of each layer are diminished in a gradual manner by diminishing the average particle diameter in the order of the downmost dielectric layer31, the intermediate dielectric layer32and attraction electrodes41,42, and the topmost dielectric layer33.

That is, as shown inFIG. 8, of the downmost dielectric layer31laminated inside the groove51and on the base2, the particles31dare sized greatest in such a manner as the porosity is set to approximately 30% while the average pore diameter defined by the clearance between the particles31dis set to 40 μm. Further, of the attraction electrodes41,42and the intermediate dielectric layer32laminated on the downmost dielectric layer31, the particles32dare sized smaller than the particles31din such a manner as the porosity is set to approximately 20% while the average pore diameter defined by the clearance between the particles32dis set to 20 μm. Furthermore, of the topmost dielectric layer33laminated in the topmost position, the particles33dare sized smallest in such a manner as the porosity is set to approximately 15% while the average pore diameter defined by the clearance between the particles33dis set to 10 μm.

In this manner, by spraying ceramic particles to form laminas, the pores defined by the clearance between the particles31dof the downmost dielectric layer31, the pores defined by the clearance between the particles32dof the intermediate dielectric layer32and attraction electrodes41,42(seeFIG. 3), and the pores defined by the clearance between the particles33dof the topmost dielectric layer33are in communication with each other. As a result, as shown in the schematic view ofFIG. 5, there is thus obtained the dielectric body3including pores which are uniformly distributed and diminish in average pore diameter from the lower layer up to the upper layer in a gradual manner.

That is, according to the manufacturing method of the embodiment, by regulating the ceramic particles in average particle diameter, temperature, spraying velocity and the like, it is possible to easily and correctly control the pores of the downmost dielectric layer31, the intermediate dielectric layer32, the attraction electrodes41,42, and the topmost dielectric layer31in average pore diameter and porosity. Hence, by forming the dielectric body3having a desired average pore diameter and porosity, and pores uniformly distributed therein, it is possible to easily and correctly manufacture a substrate suction apparatus having a desired vacuum suction performance.

Next, a description will be made with respect to the function and effect manifested by the substrate suction apparatus1of the embodiment.

FIG. 9is a schematic diagram showing an example of utilizing the substrate suction apparatus andFIG. 10is schematic cross-sectional view for schematically describing a vacuum suction function.

When it is necessary to carry out a process with respect to the substrate W under a vacuum atmosphere such as plasma etching and the like, as shown inFIG. 9, the substrate W is placed on the suction surface3aof the substrate suction apparatus1which is installed inside a chamber200, and the vacuum suction mechanism5is put into function under an air atmosphere.

That is, the suction pump50is actuated to suck out the air inside the grooves51through the suction channel52. Then, as shown inFIGS. 5 and 8, the air between the substrate W and the suction surface3ais sucked away through the pores56to58defined by the clearances between the particles31dto33dof the dielectric body3, so as to create a negative pressure between the substrate W and the suction surface3a. As a result, as shown with the two-dot chain lines inFIG. 9, the warped and swelled ultrathin substrate W is sucked up on the suction surface3awith its surface flattened.

In this state, the electrostatic attraction mechanism4is put into function after the vacuum suction mechanism5is stopped.

That is, by turning on a switch46to apply a DC power to the attraction electrodes41,42from the DC power supply43, an electrostatic force is generated between the substrate W and the attraction electrodes41,42to attract up the substrate W on the suction surface3a.

In this state, by utilizing a vacuum pump201to pump out the air inside the chamber200, it is possible to carry out a plasma etching process and the like with respect to the substrate W under a vacuum atmosphere.

However, if the vacuum suction mechanism5is put into function to suck up an ultrathin substrate Won the suction surface3a, depending on the pore size and distribution, the substrate W may get dented or bent in the pore portions.

For example, as shown inFIG. 10(a), if there is too great an average pore diameter of the pores58which open on the suction surface3aof the dielectric body3, the substrate W may be sucked into the pores58, thereby forming numerous convexoconcaves thereon due to the pores58.

Further, as shown inFIG. 10(b), pores58are small in average pore diameter. However, if they are biased to the left, for example, on the suction surface3ain distribution or density, the substrate W may roll back on the right due to the insufficient suction force on the right side of the substrate W.

However, in the embodiment, as shown inFIG. 10(c), the substrate suction apparatus1is configured such that numerous pores58small in average pore diameter are distributed uniformly on the suction surface3a, whereby the substrate W is uniformly sucked up on the suction surface3awithout getting dented into the pores58or rolling back. That is, the substrate W is uniformly sucked up by virtue of the numerous pores58small in diameter, whereby its planarity is secured.

Second Embodiment

FIG. 11is a cross-sectional view showing a substrate suction apparatus in accordance with the second embodiment of the present invention.

This embodiment is different from the aforementioned first embodiment in the aspect that the base is also formed of a porous material.

In particular, a base2′ is formed of ceramics which is approximately 30% to 50% in porosity, and its side surfaces and bottom surface are covered in an airtight manner with a nonporous metallic wall6formed of aluminum, titanium and the like. Then, the suction channel52is fitted to the bottom of the metallic wall6to be communicated with the pores of the base2′.

Thereby, a suction portion is formed of the suction channel52and the numerous pores of the base2′.

By virtue of this configuration, by putting the vacuum suction mechanism5into function, it is possible to pump the gas sucked in through the pores of the dielectric body3to the outside through the numerous pores of the base2′ and the suction channel52.

According to the embodiment, it is possible to form a suction portion with a desired suction force without bringing complicated processes to the base such as forming the grooves51and the like, thereby facilitating reduction in manufacturing cost.

Other configurations, functions and effects are similar to those of the aforementioned first embodiment; hence, it should be appreciated that descriptions therefor are omitted.

Further, it is to be understood that the present invention is not limited to the aforementioned embodiments; various modifications and variations are possible within the true spirit and scope of the invention.

For example, in the aforementioned embodiments, bipolar attraction electrodes41,42were applied. However, without being limited to this, a monopolar attraction electrode may, of course, be applied as the attraction electrode as well.

Further, in the aforementioned embodiments, an example was given to show that the dielectric body3was formed as a laminate by spraying ceramic particles. However, spray materials are not limited to ceramics; vitreous or resinous particles, for example, may also be sprayed to form the dielectric body3as a laminate.

Further, in the aforementioned embodiments, the average pore diameter was set to 40 μm, 20 μm, and 10 μm for the downmost dielectric layer31, the attraction electrodes41,42and the intermediate dielectric layer32, and the topmost dielectric layer33, respectively. However, without being limited to this, the average pore diameter may also be set to the ranges of 20 μm to 200 μm, 10 μm to 150 μm, and 5 μm to 20 μm for the downmost dielectric layer31, the attraction electrodes41,42and the intermediate dielectric layer32, and the topmost dielectric layer33, respectively.

Furthermore, in the aforementioned embodiments, an example was given to show that the attraction electrodes41,42were formed as laminas by spraying tungsten particles. However, without being limited to this, the attraction electrode may also be formed by spraying molybdenum particles or nickel aluminum particles.