JP2018103270A - Multilayer porous plate and method for producing multilayer porous plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vacuum chuck having both partial adsorption performance and wet use performance. SOLUTION: A porous plate 20 of a vacuum chuck 10 is provided with a surface porous layer 21 for holding a work W on a surface 21a and a base material porous layer laminated on the back surface 21b side of the surface porous layer 21. 22 and. The average pore size of the surface porous layer 21 is smaller than the average pore size of the base material porous layer 22. The average pore size of the surface porous layer 21 and the average pore size of the base material porous layer 22 are large enough to allow the treatment liquid of the work W to permeate. The thickness of the surface porous layer 21 is smaller than the thickness of the base material porous layer 22. [Selection diagram] Fig. 1

Description

  The present invention relates to a multilayer porous plate for vacuum-holding and holding a workpiece and a method for producing the multilayer porous plate.

  Conventionally, a vacuum chuck has been used to evacuate and hold a workpiece by suction. A vacuum chuck using a porous plate sucks and holds the workpiece by evacuating the workpiece on the surface of the porous plate from the back side. In such a case, since the workpiece can be adsorbed and held uniformly in the surface, the vacuum chuck using the porous plate is particularly useful for a thin workpiece.

  A porous plate used for a normal vacuum chuck has an average pore diameter of about 50 μm to 60 μm and a low pressure loss. In such a case, for example, when the size of the workpiece becomes smaller than the surface of the porous plate, air flows into the porous plate from the part not holding the workpiece, and as a result, the degree of vacuum decreases and the workpiece is adsorbed. It may not be possible to keep it. In the following description, such a state in which the workpiece is sucked and held by a part of the porous plate is referred to as partial suction. In view of this, for example, Non-Patent Document 1 proposes a vacuum chuck in which the pressure loss of the porous plate is increased and the partial adsorption performance is improved by reducing the average pore diameter of the porous plate to about several μm. .

  On the other hand, for example, there is a demand to perform a predetermined process using a processing liquid on a work that is sucked and held by a vacuum chuck. In the following description, using a vacuum chuck under such a condition of using a processing liquid is called wet use. However, as described above, when a porous plate having an average pore diameter as small as about several μm is used, if the treatment liquid enters the pores of the porous plate, it will not be properly discharged and will become clogged. The work cannot be evacuated properly and cannot be held by suction. Thus, for example, Non-Patent Document 2 proposes a vacuum chuck that can be used for wet use by increasing the average pore diameter of the porous plate to 10 μm.

“Porous ceramic vacuum chuck”, [online], Nippon Tungsten Co., Ltd. [searched July 11, 2016] Internet <URL: http://www.nittan.co.jp/products/ceramic_chuck_001_018.html> “Introduction of Porous Ceramic Vacuum Chuck”, [online], Nippon Tungsten Co., Ltd. [searched July 11, 2016] Internet <URL: http://www.nittan.co.jp/tech/gihou/takoushitu_ceramics_066. html>

  However, when a porous plate with an average pore diameter of 10 μm described in Non-Patent Document 2 is used, the vacuum chuck is compatible with wet use and has some partial adsorption performance, but still exhibits sufficient partial adsorption performance. do not do. In particular, if the size of the workpiece is reduced, this vacuum chuck cannot be held by suction. Therefore, there is a limit to satisfy both conflicting partial adsorption performance and wet use performance only by adjusting the pore diameter of the porous plate.

  This invention is made | formed in view of this point, and it aims at providing the vacuum chuck which makes a partial adsorption | suction performance and wet use performance compatible.

  In order to achieve the above object, the present invention provides a multilayer porous plate for evacuating and holding a workpiece by suction, a surface porous layer holding the workpiece on the surface, and a back surface of the surface porous layer Substrate porous layer provided on the side, and the average pore diameter of the surface porous layer is smaller than the average pore diameter of the substrate porous layer, the average of the surface porous layer The pore diameter and the average pore diameter of the substrate porous layer are characterized in that each has a size that allows the treatment liquid of the workpiece to pass therethrough.

  As a result of extensive studies by the inventors, it has been found that when the porous plate is made thin, clogging by the treatment liquid can be suppressed even if the average pore diameter is small. That is, when the porous plate is thinned, both the partial adsorption performance and the wet use performance can be achieved. This reason will be described in an embodiment described later.

  However, even if the thickness of the porous plate is reduced, there are structural limitations in terms of strength and accuracy. Therefore, in the present invention, the porous plate has a multilayer structure. In the surface porous layer, the average pore diameter can be reduced to increase the pressure loss, and the workpiece can be partially adsorbed. On the other hand, the substrate porous layer that supports the surface porous layer can make the surface porous layer thin, and the average pore size of the surface porous layer is such that the treatment liquid can permeate. The clogging can be suppressed by appropriately discharging the treatment liquid from the surface porous layer. Therefore, by using the vacuum chuck provided with the multilayer porous plate of the present invention, both the partial adsorption performance and the wet use performance can be achieved.

  In addition, since the average pore diameter of the substrate porous layer is large and the average pore diameter of the substrate porous layer is a size that allows the treatment liquid to pass through, the treatment liquid is appropriately removed from the substrate porous layer. Can be discharged.

  The thickness of the surface porous layer may be smaller than the thickness of the substrate porous layer.

  The ratio of the average pore diameter of the surface porous layer to the average pore diameter of the substrate porous layer is preferably 1/20 to 1/10.

  The porosity of the surface porous layer and the porosity of the substrate porous layer are preferably 30% to 50%, respectively.

  One or more intermediate porous layers are provided between the surface porous layer and the substrate porous layer, and the average pore diameter of the intermediate porous layer is larger than the average pore diameter of the surface porous layer. It may be larger and smaller than the average pore size of the porous substrate layer.

  Another aspect of the present invention is a method for producing a multilayer porous plate for evacuating and holding a workpiece by vacuum suction, wherein the back surface of the surface porous layer is a surface porous layer that holds the workpiece on the surface. The substrate porous layer is laminated on the side, the average pore diameter of the surface porous layer is smaller than the average pore diameter of the substrate porous layer, and the average pore diameter of the surface porous layer and the substrate porosity The multilayer porous plate is manufactured such that the average pore diameter of the porous layer is such that each of the workpiece treatment liquids can pass therethrough.

  The surface porous layer and the substrate porous layer may be bonded to each other by applying at least heat or pressure to the surface porous layer and the substrate porous layer. Alternatively, the surface porous layer may be formed by applying a coating solution on the surface of the substrate porous layer. Alternatively, the surface porous layer may be formed by spraying a thermal spray material on the surface of the substrate porous layer.

  The multilayer porous plate may be manufactured such that the thickness of the surface porous layer is smaller than the thickness of the substrate porous layer.

  The multilayer porous plate is preferably manufactured such that the ratio of the average pore diameter of the surface porous layer to the average pore diameter of the substrate porous layer is 1/20 to 1/10.

  The multilayer porous plate is preferably manufactured so that the porosity of the surface porous layer and the porosity of the base porous layer are 30% to 50%, respectively.

  One or more intermediate porous layers are provided between the surface porous layer and the substrate porous layer, and the average pore diameter of the intermediate porous layer is larger than the average pore diameter of the surface porous layer, And the said multilayer porous board may be manufactured so that it may become smaller than the average hole diameter of the said base material porous layer.

  By using the vacuum chuck provided with the multilayer porous plate of the present invention, it is possible to achieve both partial adsorption performance and wet use performance.

It is a longitudinal cross-sectional view which shows the outline of a structure of the vacuum chuck provided with the porous board concerning this Embodiment. It is explanatory drawing for demonstrating the structure of a porous board. It is explanatory drawing for demonstrating the structure of a porous board. It is explanatory drawing for demonstrating the structure of a porous board. It is a graph for demonstrating the design method of a porous board. It is a longitudinal cross-sectional view which shows the outline of a structure of the vacuum chuck provided with the porous board concerning other embodiment.

  Embodiments of the present invention will be described below. In addition, this invention is not limited by embodiment shown below.

<1. Vacuum chuck>
First, the structure of the vacuum chuck provided with the multilayer porous board concerning this Embodiment is demonstrated. FIG. 1 is a longitudinal sectional view showing an outline of the configuration of the vacuum chuck 10. The vacuum chuck 10 sucks and holds a plurality of workpieces W smaller than the suction portion of the vacuum chuck 10 by vacuuming.

  The vacuum chuck 10 has a porous plate 20 and a main body portion 30 provided on the back side of the porous plate 20. The porous plate 20 has a two-layer structure in which a surface porous layer 21 and a substrate porous layer 22 are laminated. The detailed configuration of the porous plate 20 will be described later.

  A suction space 31 is formed between the main body 30 and the porous plate 20. A suction tube 40 is connected to the suction space 31, and the suction tube 40 is connected to a vacuum pump 41, for example. When the vacuum pump 41 is operated, the plurality of workpieces W placed on the surface 21 a of the surface porous layer 21 are evacuated from the suction pipe 40 through the suction space 31 and the porous plate 20, and the vacuum chuck 10. Are held together.

  When the vacuum chuck 10 is used in a wet manner, when the vacuum pump 41 is operated, the processing liquid is discharged from the suction tube 40 through the porous plate 20 and the suction space 31. Then, the processing liquid in the suction pipe 40 is collected in a drain tank (not shown) connected to the suction pipe 40.

<2. Configuration of multilayer porous plate>
Next, the configuration of the porous plate 20 described above will be described. The porous plate 20 is configured to achieve both the partial adsorption performance and the wet use performance of the vacuum chuck 10. As a result of intensive studies, the inventors have arrived at the multilayer porous plate 20 based on the following knowledge. It was. The explanation of the knowledge will be described using the porous plate 100 shown in FIGS.

  In order to exhibit the partial adsorption performance of the vacuum chuck 10, it is necessary to use a porous plate 100 having a reduced average pore diameter as shown in FIG. When the average pore diameter is reduced, the pressure loss of the porous plate 100 is increased. In such a case, when the plurality of workpieces W on the surface of the porous plate 100 are evacuated by operating the vacuum pump 41, a negative pressure is generated on the back surface of the workpiece W, and the pressure difference from the atmospheric pressure on the surface of the workpiece W The workpiece W is sucked and held. Therefore, the partial suction performance of the vacuum chuck 10 is exhibited by reducing the average pore diameter of the porous plate 100.

  However, if the average pore diameter of the porous plate 100 is simply reduced, the vacuum chuck 10 may not be used wet even if the average pore diameter is a size that allows the treatment liquid to pass therethrough.

  As shown in FIG. 3, when the processing liquid L is supplied to the surface 100 a of the porous plate 100, the processing liquid L enters the porous plate 100 and is discharged from the back surface 100 b of the porous plate 100. At this time, for example, when the size of the workpiece W1 is large, the treatment liquid L penetrates to some extent below the workpiece W1 in the porous plate 100, but is discharged from the back surface 100b of the porous plate 100. That is, the processing liquid L does not completely block the back surface 100b of the porous plate 100 below the workpiece W1. Therefore, the workpiece W1 can be vacuumed and held by suction.

  On the other hand, for example, when the size of the workpiece W2 is small, the processing liquid L permeates below the workpiece W2 in the porous plate 100, and the back surface 100b below the workpiece is clogged by the processing liquid L. For this reason, the workpiece W2 cannot be evacuated and cannot be sucked and held.

  Therefore, the porous plate 100 is thinned as shown in FIG. In such a case, the processing liquid L is discharged from the back surface 100b of the porous plate 100 with respect to the work W2 having a small size, and does not completely block the back surface 100b of the porous plate 100 below the work W2. Therefore, the workpiece W2 can be vacuumed and held.

  As described above, when the porous plate 100 is thinned, the clogging of the porous plate 100 by the processing liquid L can be suppressed even when the average pore diameter is small, that is, the partial adsorption performance and the wet use performance of the vacuum chuck 10 are improved. Both can be achieved. However, in order to reduce the thickness of the porous plate 100, there are structural limitations in terms of strength and accuracy. Specifically, for example, when the porous plate 100 has a circular shape with a diameter of 300 mm in plan view, a thickness of 2 mm is a structural limit, although it depends on use conditions.

  In order to improve the partial suction performance when the vacuum chuck 10 is used in a wet manner, it is conceivable to increase the diameter of the suction tube 40 or to improve the capacity (capacity) of the vacuum pump 41. However, adjusting the diameter of the suction tube 40 and the capacity of the vacuum pump 41 has structural and theoretical limitations, and the partial suction performance of the vacuum chuck 10 cannot be sufficiently improved.

  Based on the above knowledge, as shown in FIG. 1, in the present embodiment, the porous plate 20 has a two-layer structure of a surface porous layer 21 and a substrate porous layer 22. That is, the average pore diameter of the surface porous layer 21 is reduced, and the surface porous layer 21 is thinned. Further, the base porous layer 22 is laminated on the back surface 21b side of the surface porous layer 21 in order to compensate for the lack of strength due to the thinning of the surface porous layer 21.

  The average pore diameter of the surface porous layer 21 is, for example, 1 μm to 10 μm. The average pore diameter needs to be large enough to allow the treatment liquid L to pass through. For this purpose, an average pore diameter of 1 μm or more is required. On the other hand, the surface porous layer 21 needs to have a sufficient pressure loss in order to ensure partial adsorption performance. For this purpose, it is necessary that the average pore diameter is 10 μm or less.

  The porosity of the surface porous layer 21 is, for example, 30% to 50%. The porosity affects the pressure loss of the surface porous layer 21. The smaller the porosity, the larger the pressure loss, and the partial adsorption performance improves as in the case where the average porosity is reduced. However, 30% to 50% is a limit in production.

  The surface porous layer 21 can be made sufficiently thin as long as it is supported by the substrate porous layer 22, and the thickness of the surface porous layer 21 is, for example, 50 μm to 0.5 mm. The surface porous layer 21 needs to have a sufficient pressure loss. For this purpose, for example, a thickness of 50 μm or more is required for an average pore diameter of 1 μm. On the other hand, the surface porous layer 21 needs to suppress clogging by the processing liquid L. For this purpose, for example, when the processing liquid L is pure water and the size of the workpiece W is 5 mm × 5 mm, the thickness is 0. It is desirable that it is 5 mm or less.

  The surface porous layer 21 is made of ceramic such as alumina ceramics or SiC (silicon carbide).

  The average pore diameter of the substrate porous layer 22 is larger than the average pore diameter of the surface porous layer 21. Of course, this is a size through which the treatment liquid L can permeate. Specifically, the ratio of the average pore diameter of the surface porous layer 21 to the average pore diameter of the substrate porous layer 22 is 1/20 to 1/10, and the average pore diameter of the substrate porous layer 22 is Is, for example, 10 μm to 230 μm. In such a case, the pores of the surface porous layer 21 and the pores of the substrate porous layer 22 are continuous in the thickness direction, and the flow of air and the processing liquid L from the surface porous layer 21 to the substrate porous layer 22 is performed. I can't interfere.

  The porosity of the base porous layer 22 is, for example, 30% to 50%, similarly to the porosity of the surface porous layer 21. This is a production limit.

  Since the substrate porous layer 22 supports the surface porous layer 21, the substrate porous layer 22 is preferably thicker, and the thickness of the substrate porous layer 22 is larger than the thickness of the surface porous layer 21. Specifically, the base porous layer 22 is 2 mm to 10 mm, for example.

  The base porous layer 22 is made of ceramic such as alumina ceramics or SiC (silicon carbide).

  At the joint surface between the surface porous layer 21 and the base material porous layer 22, the air holes in the surface layer porous layer 21 and the air holes in the base material porous layer 22 are visible in order to appropriately flow air and the processing liquid L. Closely joined without clogging.

  When the porous plate 20 configured as described above is used, the surface porous layer 21 has a small average pore diameter, and thus has a necessary pressure loss, and appropriately holds the workpiece W by suction even in partial suction use. be able to.

  In addition, when the porous plate 20 is used in a wet manner, when the treatment liquid L permeates the surface porous layer 21, the surface porous layer 21 is thin, so that the treatment liquid L is appropriately discharged to prevent clogging. can do. Furthermore, when the processing liquid L permeates the base material porous layer 22, the processing liquid L can be appropriately discharged because the average pore diameter of the base material porous layer 22 is sufficiently large.

  Therefore, by using the porous plate 20 of the present embodiment, both the partial adsorption performance and the wet use performance of the vacuum chuck 10 can be achieved. Then, the work W having a smaller size can be sucked and held as compared with the case where a single-layer porous plate is used as in the prior art. Specifically, the inventors have confirmed that when the porous plate 20 is used, for example, a workpiece W of 5 mm × 5 mm square can be held even in wet use.

  In addition, since the base plate porous layer 22 is laminated on the surface layer porous layer 21 in the porous plate 20, the structure thereof is stronger than in the case of using a single layer porous plate as in the prior art. Can be. For example, even if a heat load or pressure is applied to the porous plate 20, it can withstand it.

  Furthermore, even when the porous plate 20 is used in a wet manner, the average pore diameter of the surface porous layer 21 is small, so that the processing liquid L hardly penetrates into the surface porous layer 21, and the amount of the processing liquid L used is suppressed. Can do. Furthermore, the diameter of the suction tube 40 can be reduced, and the capacity of the vacuum pump 41 can be reduced.

  Here, the design method of the porous plate 20 of this Embodiment is demonstrated using FIG. FIG. 5 shows the results of experiments conducted by the inventors to verify the performance of the porous plate 20 of the present embodiment and the performance of the porous plates of Comparative Examples 1 and 2. The porous plate of Comparative Example 1 is a porous plate described in Non-Patent Document 2, and is a single-layer porous plate having an average pore diameter of 10 μm. The porous plate of Comparative Example 2 is a single-layer porous plate having an average pore diameter of 1 μm.

  In the experiment, first, the porous plate is evacuated by a vacuum pump in a dry environment, and the pressure loss of the porous plate is measured. Subsequently, the porous plate is immersed in water for 15 seconds, and the porous plate is clogged with water. Thereafter, the porous plate is taken out of water and left in a dry environment. At this time, the porous plate is evacuated by a vacuum pump, the pressure loss of the porous plate is measured every 30 seconds, and the recovery time from clogging, that is, the drainage performance is confirmed. In this experiment, the workpiece W is not placed on the porous plate.

  In FIG. 5, the vertical axis indicates pressure loss, and the horizontal axis indicates time. In Comparative Example 1, since the average pore diameter is large, the return time after clogging is short, and the drainage performance is high. However, the pressure loss of the porous plate is small and the partial adsorption performance is low. In Comparative Example 2, since the average pore diameter is small, the pressure loss of the porous plate is large and the partial adsorption performance is high. However, the recovery time after clogging is long, and the drainage performance is low. Therefore, both the comparative examples 1 and 2 cannot achieve both the partial adsorption performance and the wet use performance.

  On the other hand, in the porous plate 20 of the present embodiment, the pressure loss of the porous plate is large and the partial adsorption performance is high. Moreover, the recovery time after clogging is short, and the drainage performance is high. Therefore, it is possible to achieve both partial adsorption performance and wet use performance.

  In order to optimize the average pore diameter and thickness of the surface porous layer 21 in the porous plate 20, in the graph of FIG. 5, the return time after clogging is increased while increasing the pressure loss as a whole. Should be shortened. That is, it is only necessary to make the slope of the graph as large as possible after the pressure loss is maximized while making the graph as a whole downward.

<3. Manufacturing method of multilayer porous plate>
Next, the manufacturing method of the porous board 20 mentioned above is demonstrated. There are various methods for manufacturing the porous plate 20 and the method is not particularly limited. In the present embodiment, three manufacturing methods will be described.

  The first manufacturing method is a method of preparing a flat surface layer porous layer 21 and a flat substrate porous layer 22 in advance, and joining them. The surface porous layer 21 is prepared to be thicker than a desired thickness. In order to provide continuity of pores at the joint surface between the surface porous layer 21 and the base material porous layer 22, an additive such as an adhesive cannot be used. Therefore, the surface porous layer 21 and the substrate porous layer 22 are joined by applying at least heat or pressure. Thereafter, the surface porous layer 21 is lapped (polished) with the surface porous layer 21 and the substrate porous layer 22 joined to finish the surface porous layer 21 to a desired thickness.

  The second manufacturing method is a method in which a predetermined coating solution is applied to the surface of the flat substrate porous layer 22. As the coating solution, for example, a solution in which ceramic particles are dissolved in a solvent is used. The method for applying the coating liquid to the substrate porous layer 22 is not particularly limited, and for example, a spin coating method is used. In the spin coating method, while rotating the substrate porous layer 22 held by the spin chuck, the coating liquid is supplied to the central portion of the substrate porous layer 22 and the substrate porous layer is utilized using centrifugal force. 22 is a method of diffusing the coating liquid over the entire surface of the surface 22. Thereafter, the coating liquid applied on the substrate porous layer 22 is baked to form the surface porous layer 21.

  The third manufacturing method is a method in which a predetermined thermal spray material, for example, ceramics is sprayed on the surface of the flat substrate-like porous layer 22. For this, a general ceramic spraying method is used. Then, the surface porous layer 21 is formed on the substrate porous layer 22.

  In any of the above cases, the porous plate 20 can be manufactured. In the first manufacturing method, the thickness of the surface porous layer 21 can be arbitrarily adjusted, and a relatively thick layer can be formed. Further, in the second and third production methods, the average pore diameter of the surface porous layer 21 can be arbitrarily adjusted by adjusting the particle size of the coating liquid and sprayed material used.

<4. Other embodiments>
Next, another embodiment of the present invention will be described.

<4-1. Other embodiments>
In the above embodiment, the porous plate 20 has a two-layer structure, but three or more layers may be laminated. As shown in FIG. 6, an intermediate porous layer 23 is provided between the surface porous layer 21 and the substrate porous layer 22. The average pore diameter of the intermediate porous layer 23 is larger than the average pore diameter of the surface porous layer 21 and smaller than the average pore diameter of the base porous layer 22.

  In such a case, the average pore diameter increases in the order of the surface porous layer 21, the intermediate porous layer 23, and the base material porous layer 22, so that air and the treatment liquid L can be more smoothly permeated through the porous plate 20. Can do.

  In particular, when the second coating method and the third thermal spraying method are used in the method for manufacturing the porous plate 20 described above, the particle size of the porous material of the substrate porous layer 22 and the surface porous layer to be formed are formed. When the particle size of 21 is far away, the particles of the surface porous layer 21 enter the pores of the substrate porous layer 22 and the substrate porous layer 22 is clogged or the surface porous layer 21 is clogged. There is a possibility that the thickness of the material becomes non-uniform. For this reason, by providing the intermediate porous layer 23 as in the present embodiment, clogging of the base porous layer 22 and uneven thickness of the surface porous layer 21 can be suppressed.

  A plurality of intermediate porous layers 23 may be provided between the surface porous layer 21 and the substrate porous layer 22. In such a case, the average pore diameter of the plurality of intermediate porous layers 23 increases from the surface porous layer 21 side toward the substrate porous layer 22 side.

<4-2. Other embodiments>
The vacuum chuck 10 of the above embodiment may be provided with a heater (not shown), for example. The heater may be provided inside the porous plate 20 or may be provided outside.

  Moreover, the porous plate 20 (vacuum chuck 10) of the above embodiment is applicable with respect to various processes. For example, it may be applied to a semiconductor manufacturing apparatus or an inspection apparatus. Depending on the processing to be applied, the type of the workpiece W also changes, and the processing liquid L used also changes. Further, for example, as the processing liquid L, a cleaning liquid at the time of manufacturing a semiconductor device may be used. Further, the treatment liquid L may be heated, and in the case of the cleaning liquid described above, for example, it may be heated to about 80 ° C. Furthermore, the planar shape of the porous plate 20 is not particularly limited, and may be, for example, a circular shape or a rectangular shape.

  The preferred embodiments of the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious for those skilled in the art that various modifications or modifications can be conceived within the scope of the idea described in the claims, and these naturally belong to the technical scope of the present invention. It is understood.

DESCRIPTION OF SYMBOLS 10 Vacuum chuck 20 Porous board 21 Surface layer porous layer 22 Base material porous layer 23 Intermediate porous layer 30 Main body part 31 Suction space 40 Suction pipe 41 Vacuum pump L Processing liquid W Workpiece

Claims (13)

A multilayer porous plate for evacuating and holding a workpiece by suction,
A porous surface layer that holds the workpiece on the surface;
A substrate porous layer provided on the back side of the surface porous layer,
The average pore size of the surface porous layer is smaller than the average pore size of the substrate porous layer,
The multilayer porous plate according to claim 1, wherein the average pore diameter of the surface porous layer and the average pore diameter of the substrate porous layer are sizes that allow the workpiece processing liquid to pass through. The multilayer porous plate according to claim 1, wherein the thickness of the surface porous layer is smaller than the thickness of the substrate porous layer. The multilayer porous material according to claim 1 or 2, wherein the ratio of the average pore diameter of the surface porous layer to the average pore diameter of the base porous layer is 1/20 to 1/10. Board. The multilayer according to any one of claims 1 to 3, wherein the porosity of the surface porous layer and the porosity of the porous substrate layer are 30% to 50%, respectively. Porous plate. Between the surface porous layer and the substrate porous layer, one or more intermediate porous layers are provided,
The average pore diameter of the intermediate porous layer is larger than the average pore diameter of the surface porous layer and smaller than the average pore diameter of the base porous layer, 5. The multilayer porous plate according to one item. A method for producing a multilayer porous plate for vacuum-holding and holding a work,
For the surface porous layer that holds the workpiece on the surface, the substrate porous layer is laminated on the back side of the surface porous layer,
The average pore size of the surface porous layer is smaller than the average pore size of the substrate porous layer, and the average pore size of the surface porous layer and the average pore size of the substrate porous layer are respectively A method for producing a multilayer porous plate, comprising producing the multilayer porous plate so as to have a size that allows a treatment liquid to pass therethrough. The multilayer porous body according to claim 6, wherein the surface porous layer and the substrate porous layer are joined by applying at least heat or pressure to the surface porous layer and the substrate porous layer. A manufacturing method of a board. The method for producing a multilayer porous plate according to claim 6, wherein the surface porous layer is formed by applying a coating solution on a surface of the substrate porous layer. The method for producing a multilayer porous plate according to claim 6, wherein the surface porous layer is formed by spraying a thermal spray material on the surface of the substrate porous layer. The multilayer porous plate according to any one of claims 6 to 9, wherein the multilayer porous plate is manufactured so that the thickness of the surface porous layer is smaller than the thickness of the porous substrate layer. A method of manufacturing a slab. The multilayer porous plate is manufactured such that a ratio of an average pore diameter of the surface porous layer to an average pore diameter of the base porous layer is 1/20 to 1/10. The manufacturing method of the multilayer porous board as described in any one of claim | item 6 -10. The multilayer porous plate is manufactured such that the porosity of the surface porous layer and the porosity of the substrate porous layer are 30% to 50%, respectively. The method for producing a multilayer porous plate according to any one of 11. One or more intermediate porous layers are provided between the surface porous layer and the substrate porous layer,
The multilayer porous plate is manufactured such that an average pore diameter of the intermediate porous layer is larger than an average pore diameter of the surface porous layer and smaller than an average pore diameter of the base porous layer. The manufacturing method of the multilayer porous board as described in any one of Claims 6-12.

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