Holding table

Abstract

To provide a holding table capable of preventing electrostatic charge of a workpiece and facilitating grasping of a position of an outer edge of the workpiece.SOLUTION: The holding table comprises a body having an annular or square annular groove formed on a holding surface and a communication path formed therein to communicate with the groove, and is used for sucking an annular or square annular workpiece overlapping the entire region of the groove but not overlapping an outer surface of the body when placed on the holding surface through the communication path and the groove. The body includes a conductive first non-metal part, and an insulating second non-metal part provided to surround the first non-metal part with its outer surface set as the outer surface. The groove is positioned in an outer region of the first non-metal part or an inner region of the second non-metal part or between the outer region and the inner region.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a holding table that is used to hold a workpiece by suction. [Background technology]

[0002] Chips of devices such as ICs (Integrated Circuits) are essential components in various electronic devices such as mobile phones and personal computers. Such chips are manufactured, for example, by grinding the back side of a workpiece such as a wafer having a plurality of devices on its front side until the workpiece has a desired thickness, and then cutting the workpiece so that the workpiece is divided along the boundaries of the plurality of devices.

[0003] When a workpiece is processed in this way, stress is concentrated on its outer edge, which easily causes cracks. Therefore, in the chip manufacturing process, the outer edge of the workpiece is often chamfered, that is, a chamfer is formed on the outer edge of the workpiece, prior to various processes. However, when the back side of a workpiece having a chamfer on its outer edge is ground, the outer edge becomes shaped like a knife edge.

[0004] If the outer edge of the workpiece is shaped like a knife edge, stress will concentrate on this outer edge, making it more likely to crack. For this reason, in the chip manufacturing process, a part of the front side of the chamfer formed on the outer edge of the workpiece is removed (hereinafter also referred to as "edge trimming"), and then the back side of the workpiece is ground to remove the remaining part of the chamfer (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2000-173961 A Summary of the Invention [Problem to be solved by the invention]

[0006] Edge trimming is generally performed while the workpiece is held on the holding surface of a holding table by suction, and the edge trimming is performed after determining the position of the outer edge of the workpiece by referring to an image formed by imaging the holding table from above, which holds the workpiece on the holding surface.

[0007] To make it easier to grasp this position, it is necessary to increase the contrast between the outer edge of the workpiece and the surface of the holding table. For example, if the workpiece is dark in color (e.g., gray), it is necessary to use a holding table whose holding surface is light in color (e.g., white).

[0008] Furthermore, during edge trimming, static electricity may be generated between the cutting blade for cutting the workpiece and the workpiece, causing the workpiece to become charged. If the workpiece becomes charged, there is a risk that multiple devices formed on the surface side of the workpiece may be damaged.

[0009] In order to prevent such damage to the multiple devices, it is necessary to ground the workpiece during edge trimming. The workpiece is grounded, for example, via a holding table made of a conductive material. However, if the holding table is made of a metal material, there is a risk that the workpiece will be contaminated by fine particles of this metal material.

[0010] On the other hand, if the holding table is made of a conductive nonmetallic material (e.g., conductive polyetheretherketone (PEEK)), the holding surface of the holding table tends to have the same color (e.g., gray) as the workpiece. In this case, the contrast between the outer edge of the workpiece and the surface of the holding table is small. Therefore, in this case, it may be difficult to accurately grasp the position of the outer edge of the workpiece prior to edge trimming.

[0011] In view of these points, an object of the present invention is to provide a holding table that can prevent the workpiece from becoming charged and that can make it easier to grasp the position of the outer edge of the workpiece. [Means for solving the problem]

[0012] According to the present invention, there is provided a holding table having a main body with a circular or rectangular groove formed on its holding surface and a communicating passage formed inside that communicates with the groove, and which is used to hold a disk-shaped or rectangular plate-shaped workpiece by suction through the communicating passage and the groove, which overlaps the entire area of ​​the groove when placed on the holding surface but does not overlap the outer surface of the main body, the main body including a conductive first non-metallic part and an insulating second non-metallic part arranged to surround the first non-metallic part and whose outer surface becomes the outer surface of the main body, and the groove is located in the outer region of the first non-metallic part, the inner region of the second non-metallic part, or between the outer region and the inner region.

[0013] It is preferable that when visible light is irradiated onto the holding surface, the proportion of the visible light specularly reflected by the first non-metallic part is different from the proportion of the visible light specularly reflected by the second non-metallic part. It is also preferable that the main body is cylindrical or rectangular. It is also preferable that the main body further comprises a conductive base having a recess in which the main body is housed, and the base is electrically connected to the first non-metallic part. In addition, it is preferable that the main body is fixed to the recess of the base by using a conductive screw. Alternatively, it is preferable that the main body is fixed to the recess of the base by using a conductive adhesive. Effect of the Invention

[0014] In the holding table of the present invention, the groove that overlaps with the workpiece when the workpiece is placed on the holding surface is located in the outer region of the conductive first non-metallic part, in the inner region of the insulating second non-metallic part that is provided so as to surround the first non-metallic part, or between the outer region and the inner region. In this case, the part of the workpiece that is located inside the groove in a plan view comes into contact with the first non-metallic part. Therefore, when the workpiece is held on the holding surface of the holding table of the present invention, it is possible to ground the workpiece via the first non-metallic part, that is, to prevent the workpiece from becoming charged.

[0015] In addition, in the holding table of the present invention, the outer surface of the insulating second non-metallic part becomes the outer surface of the main body. The insulating second non-metallic part has a higher degree of freedom in material selection than the conductive first non-metallic part. Therefore, in the holding table of the present invention, it is possible to select a material for the second non-metallic part so as to increase the contrast with the workpiece, making it easier to grasp the position of the outer edge of the workpiece. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1(A) is a top view that typically shows an example of a workpiece, and FIG. 1(B) is a cross-sectional view that typically shows the workpiece shown in FIG. 1(A). [Diagram 2] FIG. 2 is a perspective view that illustrates an example of a cutting device capable of edge trimming of a workpiece. [Diagram 3] FIG. 3(A) is a perspective view that illustrates an example of a holding table, and FIG. 3(B) is a cross-sectional view that illustrates the holding table illustrated in FIG. 3(A). [Figure 4] FIG. 4 is a cross-sectional view that illustrates a state in which a workpiece is held on the holding surface of the holding table illustrated in FIG. [Diagram 5] FIG. 5 is a perspective view that typically shows the cutting blade and the like shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] An embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1(A) is a top view showing an example of a workpiece, and Fig. 1(B) is a cross-sectional view showing the workpiece shown in Fig. 1(A). The workpiece 11 shown in Fig. 1(A) and Fig. 1(B) is, for example, a wafer made of silicon (Si).

[0018] A plurality of devices 13 are formed on the front surface 11a side of the workpiece 11. Each of the plurality of devices 13 includes, for example, an element for constituting an IC, a semiconductor memory, or a CMOS (Complementary Metal Oxide Semiconductor) image sensor. The boundaries of the plurality of devices 13 extend, for example, in a lattice pattern.

[0019] In addition, the outer edge of the workpiece 11 is chamfered, that is, a chamfered portion is formed on the outer edge of the workpiece 11. In other words, the side surface 11b of the workpiece 11 is curved so as to be convex outward.

[0020] There is no limitation on the material, shape, structure, size, etc. of the workpiece 11. The workpiece 11 may be made of a semiconductor material other than silicon (e.g., silicon carbide (SiC) or gallium nitride (GaN), etc.). Similarly, there is no limitation on the type, number, shape, structure, size, arrangement, etc. of the device 13.

[0021] Fig. 2 is a perspective view showing a schematic example of a cutting device capable of edge trimming of a workpiece 11. Note that the X-axis direction and the Y-axis direction shown in Fig. 2 are directions perpendicular to each other on a horizontal plane, and the Z-axis direction is a direction (vertical direction) perpendicular to each of the X-axis direction and the Y-axis direction.

[0022] The cutting device 2 shown in Fig. 2 includes a base 4 that supports each of the components. A recess 4a extending along the X-axis direction is formed on the top surface of the base 4. Inside the recess 4a, a flat table cover 6 and a bellows-like dust-proof and drip-proof cover 8 that expands and contracts as the table cover 6 moves are provided.

[0023] Moreover, a cylindrical holding table 10 with a bottom is provided above the table cover 6. Fig. 3(A) is a perspective view that typically shows the holding table 10, and Fig. 3(B) is a cross-sectional view that typically shows the holding table 10.

[0024] The holding table 10 has a conductive base 12 made of a metal material such as stainless steel. The base 12 has a disk-shaped bottom wall 12a and a cylindrical side wall 12b extending upward from the outer periphery of the bottom wall 12a. The inner diameter of the side wall 12b, i.e., the diameter of the cylindrical recess defined by the bottom wall 12a and the side wall 12b of the base 12, is longer than the diameter of the workpiece 11.

[0025] The recess accommodates a main body 14 having a height roughly equal to that of the side wall 12b of the base 12. The main body 14 has a conductive first non-metallic part 16. The first non-metallic part 16 is made of, for example, a conductive plastic such as conductive PEEK, or an alumina-based or zirconia-based conductive ceramic. The first non-metallic part 16 has a cylindrical shape with an outer diameter shorter than the diameter of the workpiece 11.

[0026] A plurality of screw holes are formed in the lower surface of the first non-metallic part 16, and the main body 14 is fixed to the recess of the base 12 by using conductive screws 18 that are screwed into each of the plurality of screw holes. Specifically, each screw 18 is made of, for example, a metal material, and passes through one of a plurality of through holes formed in the bottom wall 12a of the base 12, and is screwed into a screw hole formed in the lower surface of the first non-metallic part 16 so as to press the base 12 against the main body 14. The base 12 and the first non-metallic part 16 are electrically connected via the plurality of screws 18.

[0027] The inner surface of an insulating second non-metallic part 20 is fixed to the outer surface of the first non-metallic part 16. The second non-metallic part 20 is made of, for example, insulating plastic such as insulating PEEK, or insulating ceramics such as alumina or zirconia. The second non-metallic part 20 has a cylindrical shape with an inner diameter shorter than the diameter of the workpiece 11 and an outer diameter longer than the diameter of the workpiece 11. The outer surface of the second non-metallic part 20 becomes the outer surface of the main body 14 and is in contact with the inner surface of the side wall 12b of the base 12.

[0028] The upper surface of the first non-metallic part 16 and the upper surface of the second non-metallic part 20 become the holding surfaces of the holding table 10 when holding the workpiece 11. Therefore, from the viewpoint of not damaging the workpiece 11, it is preferable that the first non-metallic part 16 is made of conductive plastic and the second non-metallic part 20 is made of insulating plastic.

[0029] Furthermore, when visible light is irradiated onto the holding surface of the holding table 10, the proportion of visible light that is specularly reflected by the first non-metallic portion 16 differs from the proportion of visible light that is specularly reflected by the second non-metallic portion 20.

[0030] For example, the first non-metallic portion 16 has a dark color (e.g., gray), and the second non-metallic portion 20 has a light color (e.g., white). In this case, when visible light is irradiated onto the holding surface, the proportion of visible light absorbed by the first non-metallic portion 16 is higher than the proportion of visible light absorbed by the second non-metallic portion 20. As a result, in this case, the proportion of visible light specularly reflected by the first non-metallic portion 16 is lower than the proportion of visible light specularly reflected by the second non-metallic portion 20.

[0031] Furthermore, the surface roughness of the first non-metallic part 16 may be greater than the surface roughness of the second non-metallic part 20. In this case, when visible light is irradiated onto the holding surface, the proportion of visible light that is diffusely reflected by the upper surface of the first non-metallic part 16 is higher than the proportion of visible light that is diffusely reflected by the upper surface of the second non-metallic part 20. As a result, in this case, the proportion of visible light that is specularly reflected by the first non-metallic part 16 is lower than the proportion of visible light that is specularly reflected by the second non-metallic part 20.

[0032] Furthermore, an annular groove 20a is formed in the inner region of the second non-metallic part 20 on the holding surface of the holding table 10, the groove 20a being concentric with the inner and outer diameters of the first non-metallic part 16 and the second non-metallic part 20. The inner region of the second non-metallic part 20 is a region located inside an imaginary ring located at the center in the width direction of the second non-metallic part 20. A communication passage 20b is formed inside the second non-metallic part 20, and the groove 20a communicates with a suction source (not shown) via the communication passage 20b and a communication passage 12c formed in the bottom wall 12a of the base 12.

[0033] 4 is a cross-sectional view showing a schematic state of the workpiece 11 being held on the holding surface of the holding table 10. When holding the workpiece 11 on the holding surface of the holding table 10, first, the workpiece 11 is placed on the holding surface so that the surface 11a faces upward and the center of the workpiece 11 is positioned directly above the center of the bottom wall 12a of the base 12. As a result, the workpiece 11 overlaps the entire area of ​​the groove 20a but does not overlap the outer surface of the main body 14, and is surrounded by the second non-metallic portion 20 in a plan view.

[0034] In this state, the suction source communicating with the groove 20a is operated. This causes a suction force generated from the suction source to act on the outer periphery of the workpiece 11. As a result, the workpiece 11 is held on the holding surface of the holding table 10. The holding table 10 is also connected to an X-axis direction moving mechanism (not shown) and a rotation drive source (not shown) provided inside the recess 4a shown in FIG. 2.

[0035] The X-axis direction moving mechanism includes, for example, a ball screw and a motor connected to the ball screw. When the X-axis direction moving mechanism is operated, the holding table 10 moves along the X-axis direction. In addition, in accordance with this movement, the table cover 6 moves along the X-axis direction and the dust-proof / water-proof cover 8 expands and contracts.

[0036] The rotary drive source includes, for example, a pulley and a motor connected to the pulley. When the rotary drive source is operated, the holding table 10 rotates around a rotation axis that passes through the center of the upper surface of the holding table 10 and is aligned along the Z-axis direction. However, in association with this rotation, the table cover 6 does not rotate around a rotation axis that is aligned along the Z-axis direction.

[0037] A support structure 22 is provided in a region near the recess 4a on the upper surface of the base 4. The support structure 22 has an erected portion 22a erected from the upper surface of the base 4, and an arm portion 22b extending along the Y-axis direction from the upper end of the erected portion 22a so as to cross the recess 4a. A Y-axis direction moving mechanism 24 is provided on the front side of the arm portion 22b.

[0038] The Y-axis direction moving mechanism 24 is fixed to the front surface of the arm portion 22b and has a pair of Y-axis guide rails 26 extending along the Y-axis direction. A Y-axis moving plate 28 is provided on the front surface side of the pair of Y-axis guide rails 26 in a manner that allows it to slide along the pair of Y-axis guide rails 26.

[0039] A Y-axis screw shaft 30 extending along the Y-axis direction is disposed between the pair of Y-axis guide rails 26. A motor (not shown) for rotating the Y-axis screw shaft 30 is connected to one end of the Y-axis screw shaft 30. A nut (not shown) for accommodating a large number of balls that roll on the surface of the rotating Y-axis screw shaft 30 is provided on the surface of the Y-axis screw shaft 30 on which a spiral groove is formed, thereby forming a ball screw.

[0040] That is, when the Y-axis screw shaft 30 rotates, many balls circulate inside the nut, and the nut moves along the Y-axis direction. The nut is fixed to the rear side of the Y-axis moving plate 28. Therefore, when the Y-axis screw shaft 30 is rotated by a motor connected to one end of the Y-axis screw shaft 30, the Y-axis moving plate 28 moves along the Y-axis direction together with the nut.

[0041] A Z-axis direction moving mechanism 32 is provided on the front side of the Y-axis moving plate 28. This Z-axis direction moving mechanism 32 is fixed to the front side of the Y-axis moving plate 28 and has a pair of Z-axis guide rails 34 extending along the Z-axis direction. A Z-axis moving plate 36 is connected to the front side of the pair of Z-axis guide rails 34 in a manner that allows it to slide along the pair of Z-axis guide rails 34.

[0042] A Z-axis screw shaft 38 extending along the Z-axis direction is disposed between the pair of Z-axis guide rails 34. A motor 40 for rotating the Z-axis screw shaft 38 is connected to one end (upper end) of the Z-axis screw shaft 38. A nut (not shown) for accommodating a large number of balls that roll on the surface of the rotating Z-axis screw shaft 38 is provided on the surface of the Z-axis screw shaft 38 on which a spiral groove is formed, thereby forming a ball screw.

[0043] That is, when the Z-axis screw shaft 38 rotates, many balls circulate inside the nut, and the nut moves along the Z-axis direction. The nut is fixed to the rear side of the Z-axis moving plate 36. Therefore, when the Z-axis screw shaft 38 is rotated by the motor 40, the Z-axis moving plate 36 moves along the Z-axis direction together with the nut.

[0044] A cutting unit 42 is fixed to the lower part of the Z-axis moving plate 36. This cutting unit 42 has a cylindrical spindle housing 44 extending along the Y-axis direction, and a cutting blade 46 exposed from the spindle housing 44. Fig. 5 is a perspective view showing the cutting blade 46 and the like.

[0045] A cylindrical spindle 48 extending along the Y-axis direction is housed in the spindle housing 44 of the cutting unit 42. The spindle 48 is rotatably supported by the spindle housing 44. The tip of the spindle 48 protrudes outside the spindle housing 44, and an annular cutting blade 46 is attached to the tip.

[0046] The cutting blade 46 includes a cutting edge formed of an electroformed grindstone in which abrasive grains made of diamond or cubic boron nitride (cBN) are fixed with a binder such as nickel. Furthermore, the base end of the spindle 48 is connected to a motor built into the spindle housing 44.

[0047] When the motor is operated, the cutting blade 46 rotates together with the spindle 48 around a straight line along the Y-axis direction as a rotation axis. The cutting blade 46 is attached to the spindle 48 so that the rotation axis of the spindle 48 passes through the center of the cutting blade 46.

[0048] 2, an imaging unit 50 is provided on the side of the cutting unit 42. The imaging unit 50 includes, for example, an objective lens and an imaging element such as a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal Oxide Semiconductor) image sensor, and captures an image of a structure present below.

[0049] Furthermore, when the motor connected to one end of the Y-axis screw shaft 30 is operated, the cutting unit 42 and the imaging unit 50 move along the Y-axis direction. Furthermore, when the motor 40 connected to one end of the Z-axis screw shaft 38 is operated, the cutting unit 42 and the imaging unit 50 move along the Z-axis direction.

[0050] When performing edge trimming of the workpiece 11 held on the holding surface of the holding table 10, first, the holding table 10 is moved along the X-axis direction and / or the cutting unit 42 and the imaging unit 50 are moved along the Y-axis direction so that the workpiece 11 is positioned directly below the imaging unit 50.

[0051] Next, the workpiece 11 and the holding table 10 are imaged by the imaging unit 50 to form an image. Next, the holding table 10 is moved along the X-axis direction and / or the cutting unit 42 and the imaging unit 50 are moved along the Y-axis direction so that the lower end of the cutting blade 46 is positioned directly above the end in the Y-axis direction of the outer edge of the workpiece 11 grasped with reference to this image.

[0052] Next, while rotating the cutting blade 46 together with the spindle 48, the cutting unit 42 and the imaging unit 50 are lowered so that the lower end of the cutting blade 46 is positioned lower than the front surface 11a of the workpiece 11 and higher than the back surface 11c. This causes the cutting blade 46 to cut into the outer edge of the workpiece 11.

[0053] Next, the holding table 10 is rotated at least once while the cutting blade 46 is kept rotating. As a result, the upper side of the outer edge of the workpiece 11 is cut and removed by the cutting blade 46. As a result, the edge trimming of the workpiece 11 is completed.

[0054] In the above-described holding table 10, the groove 20a that overlaps with the workpiece 11 when the workpiece 11 is placed on the holding surface is located in an inner region of the second non-metallic portion 20 that is provided to surround the first non-metallic portion 16. In this case, the portion of the workpiece 11 that is located on the inner side of the groove 20a in a plan view comes into contact with the first non-metallic portion 16. Therefore, when the workpiece 11 is held on the holding surface of the holding table 10, it is possible to ground the workpiece 11 via the first non-metallic portion 16, that is, to prevent the workpiece 11 from being charged.

[0055] In addition, in the holding table 10, the outer surface of the second non-metallic part 20 becomes the outer surface of the main body 14. In addition, the insulating second non-metallic part 20 has a higher degree of freedom in material selection compared to the conductive first non-metallic part 16. Therefore, in the holding table 10, it is possible to select a material for the second non-metallic part 20 so as to increase the contrast with the workpiece 11, making it easier to grasp the position of the outer edge of the workpiece 11.

[0056] For example, when the workpiece 11 is made of silicon or the like, the workpiece 11 has a dark color (e.g., gray). In this case, a material having a light color (e.g., white) is selected as the material of the second non-metallic part 20. When the workpiece 11 is made of quartz glass or the like, the workpiece 11 is transparent and its outer edge has a light color (e.g., white). In this case, a material having a dark color (e.g., black) is selected as the material of the second non-metallic part 20.

[0057] The above-described holding table 10 is one aspect of the present invention, and the holding table of the present invention is not limited to the above-described holding table 10. For example, in the holding table 10, the main body 14 may be replaced with one having a cylindrical, i.e., solid, first non-metallic part. However, from the viewpoint of not damaging the back surface 11c of the workpiece 11, it is preferable that the main body included in the holding table 10 has a cylindrical, i.e., hollow, first non-metallic part 16 like the main body 14.

[0058] Furthermore, in the holding table 10, the main body 14 may be fixed to the recess of the base 12 by any method as long as the communication path 12c formed in the base 12 communicates with the groove 20a and the communication path 20b formed in the second non-metallic portion 20 and the base 12 and the first non-metallic portion 16 are electrically connected. For example, the main body 14 may be fixed to the recess of the base 12 by using a conductive adhesive.

[0059] Furthermore, in the holding table 10, as long as the workpiece 11 can be held by applying a suction force to the workpiece 11 through the groove formed in the holding surface, the groove may be formed in any position. For example, in the holding table 10, the groove may be formed not in the inner region of the second non-metallic part 20 but in the outer region of the first non-metallic part 16, or between the outer region of the first non-metallic part 16 and the inner region of the second non-metallic part 20. The outer region of the first non-metallic part 16 is a region located outside a virtual ring located at the center in the width direction of the first non-metallic part 16.

[0060] The holding table 10 may be used to hold a rectangular plate-shaped workpiece instead of the circular plate-shaped workpiece 11. In this case, the holding table 10 may be provided with a main body, instead of the main body 14, in which a rectangular annular groove smaller than the rectangular plate-shaped workpiece is formed on the holding surface and a communication passage communicating with the rectangular annular groove is formed inside. In this case, the main body may be prismatic or cylindrical.

[0061] The holding table 10 may also be used to hold the workpiece 11 in a processing device other than a cutting device (for example, a laser processing device). In addition, the structures and methods according to the above-described embodiments can be appropriately modified and implemented without departing from the scope of the present invention. [Explanation of symbols]

[0062] 2:Cutting device 4: Base 6: Table cover 8: Dust-proof and water-resistant cover 10: Holding table 11: Workpiece (11a: front surface, 11b: side surface, 11c: back surface) 12: Base (12a: bottom wall, 12b: side wall, 12c: communication path) 13: Device 14: Main body 16: 1st non-metallic part 18: Screw 20: Second non-metallic part (20a: groove, 20b: communication path) 22: Support structure (22a: standing part, 22b: arm part) 24:Y-axis direction movement mechanism 26: Y-axis guide rail 28: Y-axis moving plate 30: Y-axis screw shaft 32:Z-axis direction movement mechanism 34: Z-axis guide rail 36: Z-axis moving plate 38: Z-axis screw shaft 40: Motor 42: Cutting unit 44: Spindle housing 46: Cutting blade 48: Spindle 50: Imaging unit

Claims

1. A holding table comprising a main body having a circular or rectangular groove formed on a holding surface and a communication passage formed therein communicating with the groove, the holding table being utilized for holding a disk-shaped or rectangular plate-shaped workpiece by suction through the communication passage and the groove, the disk-shaped or rectangular plate-shaped workpiece overlapping the entire area of ​​the groove when placed on the holding surface but not overlapping an outer surface of the main body, The body includes: a conductive first non-metallic portion; a second non-metallic portion that is insulating and that is provided so as to surround the first non-metallic portion and has an outer surface that corresponds to the outer surface of the main body; The groove is a holding table located in the outer region of the first non-metallic portion, the inner region of the second non-metallic portion, or between the outer region and the inner region.

2. 2. The holding table according to claim 1, wherein when visible light is irradiated onto the holding surface, a proportion of the visible light specularly reflected by the first non-metallic portion differs from a proportion of the visible light specularly reflected by the second non-metallic portion.

3. 2. The holding table according to claim 1, wherein the main body is cylindrical or rectangular.

4. a conductive base having a recess in which the main body is received; 4. The holding table according to claim 1, wherein the base is electrically connected to the first non-metallic portion.

5. 5. The holding table according to claim 4, wherein the main body is fixed to the recess of the base by utilizing a conductive screw.

6. 5. The holding table according to claim 4, wherein the main body is fixed to the recess of the base by utilizing a conductive adhesive.

Images