JP7689852B2 - Substrate holding member and method of manufacturing same - Google Patents

Description

The present invention relates to a substrate holding member and a method for manufacturing the same.

Conventionally, substrate holding members that support substrates such as silicon wafers and glass wafers have been used in semiconductor manufacturing equipment and the like. Such substrate holding members support the back side of the substrate, and in the case of a vacuum chuck, for example, the substrate is supported by suction by evacuating the space defined by the front side of the base and the back side of the substrate through an air hole formed on the front side of the base.

In recent years, semiconductor products have become increasingly finer and more precise, and in order to reduce the risk of particles getting caught between the substrate and the base, which could cause the flatness of the substrate to be compromised, substrate holding members are being used that have a substrate supporting area made up of multiple pin-shaped protrusions to reduce the contact area between the substrate and the base.

In addition, as semiconductor products become increasingly fine and highly accurate, the wiring patterns formed on substrates are also becoming finer and more multi-layered. In the exposure process, it is necessary to overlay multiple layers of circuit patterns on the substrate, and the requirements for positioning accuracy (overlay accuracy) between each layer are becoming increasingly strict.

Patent Document 1 discloses an article holding device that forms an amorphous hard carbon film (e.g., DLC film, etc.) on the surface of the substrate holding surface to suppress the generation of particles due to wear of the holding surface, thereby reducing the risk of particles getting caught between the holding surface and the substrate.

Patent Document 2 discloses that scratches are formed in the radial direction on the surface of the chuck that supports the wafer. This reduces the frictional force with the wafer in the radial direction, thereby reducing friction against lateral movement when the wafer is attracted to the chuck, allowing the wafer to be attracted in a flat state.

Japanese Patent Application Publication No. 09-45753 Special table 2018-526822 publication

Due to the miniaturization and multi-layer wiring of wiring patterns formed on substrates, the positioning accuracy of the substrate that is attracted to the substrate holding member (chuck) during exposure processing is extremely important. However, the substrate to be attracted is not necessarily excellent in flatness, and may have concave or convex warping. In this case, the shape of the substrate warping is not constant, so when negative pressure is generated by the suction of the vacuum chuck, or when electrostatic attraction force is generated by the electrostatic chuck, pressure is not necessarily applied evenly to the back surface of the substrate, which may cause the substrate to slip, expand or contract, or become displaced.

The amorphous hard carbon film (DLC film) formed on the surface of the holding surface described in Patent Document 1 has the characteristics of high hardness and high wear resistance, as well as a low coefficient of friction, which causes the substrate to slip during adhesion, making it difficult to position it.

The formation of the scratches described in Patent Document 2 reduces the frictional force with the wafer in the radial direction, which causes the wafer to expand and contract in the radial direction when it is attracted to the wafer, making it difficult to position it.

The present invention was made in consideration of these circumstances, and aims to provide a substrate holding member that can improve the positioning accuracy of the substrate while maintaining a low contact state with the substrate.

(1) In order to achieve the above object, the substrate holding member of the present invention is a substrate holding member comprising a flat base and a plurality of pin-shaped protrusions formed and protruding upward from an upper surface of the base, the upper end surface of the protrusions having fine grooves formed in the circumferential direction of the base, the fine grooves having a width of 1 to 10 μm .

In this way, by having fine grooves formed in the circumferential direction on the upper end surface of the convex portion, radial expansion and contraction and displacement of the substrate are suppressed when the substrate is adsorbed, improving the positioning accuracy of the substrate (overlay accuracy).

(2) In addition, in the substrate holding member of the present invention, the upper end surface of the convex portion is characterized in that the surface roughness Ra along the radial direction of the base is greater than the surface roughness Ra along the circumferential direction of the base.

In this way, the radial surface roughness Ra of the upper end surface of the convex portion is greater than the circumferential surface roughness Ra, which further improves the positioning accuracy of the substrate.

(3) Furthermore, in the substrate holding member of the present invention, when the upper surface is divided into four regions by two straight lines that pass through the center of the base and intersect at right angles, each region includes a convex portion in which the surface roughness Ra of the upper end surface of the convex portion along the radial direction of the base is larger than the surface roughness Ra along the circumferential direction of the base.

This reduces the expansion and contraction and displacement of the board in various radial directions, further improving the positioning accuracy of the board.

(4) Furthermore, in the substrate holding member of the present invention, the surface roughness Ra of the upper end surface of the convex portion along the radial direction of the base is greater than the surface roughness Ra along the circumferential direction of the base, and the surface roughness Ra of the convex portion along the radial direction of the base is 0.04 μm or more and less than 0.15 μm.

This allows the effect of improving the positioning accuracy of the substrate to be fully realized while reducing the risk of particle generation.

(5) In addition, in the substrate holding member of the present invention, at least a portion of the upper end surface of the protrusion is formed of an abrasion-resistant layer.

In this way, at least a portion of the upper end surface of the convex portion is formed from an abrasion-resistant layer, which can suppress the generation of particles during repeated use.

(6) The method for manufacturing a substrate holding member of the present invention is characterized in that it includes a base preparation step of preparing a flat base made of a ceramic sintered body, a convex portion forming step of forming a plurality of convex portions protruding from the upper surface of the base, a lapping step of lapping the upper end surfaces of the plurality of convex portions, and a texturing step of texturing the upper end surfaces of the plurality of convex portions so that the radial surface roughness Ra is greater than the circumferential surface roughness Ra.

This allows the production of substrate holding members with improved substrate positioning accuracy (overlay accuracy).

The present invention makes it possible to improve the positioning accuracy of the substrate while maintaining a low contact state with the substrate.

3 is a schematic diagram showing an example of an upper surface of a substrate holding member according to an embodiment of the present invention. FIG. 1 is a schematic cross-sectional view showing an example of a substrate holding member according to an embodiment of the present invention. 5A and 5B are schematic perspective views showing a convex portion having no fine grooves formed on the upper end surface of the convex portion and a convex portion having fine grooves formed in the circumferential direction, respectively. 1 is a schematic diagram showing the concept of the upper surface of a substrate holding member having a protruding portion having a narrow groove formed in the circumferential direction arranged over the entire surface thereof; FIG. 1 is a schematic diagram showing the concept of the upper surface of a substrate holding member having a convex portion with a fine groove formed in one direction arranged over the entire surface thereof; 5A and 5B are schematic cross-sectional views showing protruding portions on which an abrasion-resistant layer is formed. 11A and 11B are schematic diagrams illustrating modified examples of the upper surface of a substrate holding member according to an embodiment of the present invention. 10A and 10B are schematic cross-sectional views showing modified examples of a substrate holding member according to an embodiment of the present invention. 1A and 1B are schematic perspective and plan views, respectively, illustrating the process of a texturing process. 4A and 4B are optical microscope photographs of the upper end faces of the convex portions of Example 1 and Comparative Example 1, respectively.

Next, an embodiment of the present invention will be described with reference to the drawings. To facilitate understanding of the description, the same reference numbers are used for the same components in each drawing, and duplicate descriptions will be omitted. Note that in the configuration diagrams, the size of each component is shown conceptually and does not necessarily represent the actual dimensional ratio.

[Embodiment]
A substrate holding member according to an embodiment of the present invention will be described with reference to Fig. 1 and Fig. 2. Fig. 1 is a schematic diagram showing an example of the upper surface of a substrate holding member according to an embodiment of the present invention. Fig. 2 is a schematic cross-sectional diagram showing an example of a substrate holding member according to an embodiment of the present invention. The substrate holding member 100 according to this embodiment includes a flat base 10 for suction-holding a substrate (wafer) W.

The base 10 is made of a ceramic sintered body and is formed into a flat plate shape. The base 10 may be in various shapes, such as a circular plate, a polygonal plate, an elliptical plate, or the like, depending on the shape of the substrate to be attracted. The ceramic sintered body forming the base ₁₀ may be made of various materials depending on the application. For example, SiC, _Al2O3 , _Si3N4 , AlN, cordierite, lithium aluminosilicate _, etc. may be used.

The base 10 has a plurality of protrusions 20 formed to protrude upward from the upper surface 12. The shape of the plurality of protrusions 20 is appropriately selected from cylindrical shapes such as a cylinder or a prismatic shape, a cone shape such as a pyramid shape, a truncated cone shape, a truncated pyramid shape with the top portion cut off, and the like. The shape of the plurality of protrusions 20 may be a stepped shape in which the cross-sectional area of the upper portion is smaller than that of the lower portion. In other words, the plurality of protrusions 20 are a plurality of pin-shaped protrusions.

The arrangement of the multiple protrusions 20 is not particularly limited. It may be in a known form or a similar form, and may be, for example, a regular arrangement such as concentric circles, a square lattice, or a triangular lattice as shown in FIG. 1, or an irregular arrangement with localized sparseness and denseness. It is preferable that the center-to-center distance between adjacent protrusions 20 is 8 mm or less.

The multiple protrusions 20 support the substrate W. The upper ends 22 of the multiple protrusions are formed to be approximately flush. That is, a plane (reference plane) 30 is determined by the upper ends 22 of the multiple protrusions. This causes the upper ends 22 of the multiple protrusions to abut against the substrate W, thereby supporting the substrate W. Note that, among the multiple protrusions 20, some may have upper ends that do not abut against the substrate W. This is because, even if such protrusions exist, it is possible to support the substrate W depending on the arrangement of the surrounding protrusions 20.

The height of the protrusions 20 is preferably 50 μm or more and 300 μm or less. The height of the protrusions 20 refers to the distance from the upper surface 12 of the base 10 to the upper end 22 of the protrusions.

At least some of the multiple protrusions 20 have the upper ends 22 of the protrusions formed as a surface (upper end surface). At least some of the protrusions 20 having the upper ends 22 of the protrusions formed as a surface have fine grooves 26 formed in the upper end surface 24 of the protrusions in the circumferential direction of the base 10. In this way, by having the fine grooves 26 formed in the upper end surface 24 of the protrusions in the circumferential direction of the base 10, radial expansion and contraction and displacement of the substrate W during suction are suppressed, improving the positioning accuracy (overlay accuracy) of the substrate W. It is preferable that the maximum diameter of the upper end surface 24 of the protrusions of the protrusions 20 having the upper ends 22 of the protrusions formed as a surface is 500 μm or less.

Figures 3(a) and (b) are schematic perspective views showing a convex portion 20 in which no fine grooves 26 are formed on the upper end surface 24 of the convex portion, and a convex portion 20 in which fine grooves 26 are formed in the circumferential direction, respectively. The fine grooves 26 may or may not be continuous from one end of the upper end surface 24 of the convex portion to the other. The width of the fine grooves 26 is preferably 1 μm or more and 10 μm or less. The depth of the fine grooves 26 is preferably 0.2 μm or more and 2 μm or less.

The substrate holding member 100 of the present invention preferably has a narrow groove 26 as shown in FIG. 4 as a whole, due to the convex portion 20 on which the narrow groove 26 is formed in the circumferential direction. FIG. 4 is a schematic diagram showing the concept of the upper surface of the substrate holding member 100 on which the convex portion 20 on which the narrow groove 26 is formed in the circumferential direction is disposed over the entire surface. FIG. 5 is a schematic diagram showing the concept of the upper surface of the substrate holding member on which the convex portion on which the narrow groove is formed in one direction is disposed over the entire surface. Note that the convex portion 20 is omitted in FIGS. 4 and 5.

As shown in FIG. 4, a substrate holding member 100 having a protrusion 20 with narrow grooves 26 formed in the circumferential direction arranged over the entire surface can suppress slippage, expansion/contraction, and displacement in all radial directions from the center of the substrate W. On the other hand, as shown in FIG. 5, a substrate holding member having a protrusion with narrow grooves formed in one direction arranged over the entire surface can suppress slippage, expansion/contraction, and displacement in a certain radial direction from the center of the substrate W, but cannot suppress slippage, expansion/contraction, and displacement in a different radial direction. For this reason, it is preferable that the substrate holding member of the present invention has multiple protrusions 20 with narrow grooves 26 formed in the circumferential direction, and it is even more preferable that they are arranged over the entire surface.

However, since the convex portion 20 having the narrow groove 26 formed in the circumferential direction can suppress radial slippage, expansion/contraction, and displacement of the substrate W at the location where it is arranged, even if some of the convex portions 20 have narrow grooves 26 formed in the circumferential direction and the remaining convex portions 20 do not have narrow grooves 26 formed therein, this is still within the scope of the present invention.

It is preferable that the surface roughness Ra of the upper end surface 24 of the convex portion along the radial direction of the base 10 is larger than the surface roughness Ra of the upper end surface 24 of the convex portion along the circumferential direction of the base 10. In this way, the positioning accuracy of the substrate W is further improved by the surface roughness Ra of the upper end surface 24 of the convex portion being larger than the surface roughness Ra of the circumferential direction. Note that the radial direction and circumferential direction of the substrate 10 refer to the radial direction and circumferential direction of a circle whose center is the center 16 of the substrate when the center 16 of the substrate is set on the upper surface 12 of the substrate 10. It is preferable that the center 16 of the substrate is set near the center of the substrate W when the substrate W of the maximum diameter that can be placed on the substrate holding member 100 is placed. Near the center refers to a range within 0.2 mm from the center of the substrate W of the maximum diameter.

The surface roughness Ra of the upper end surface 24 of the convex portion along the radial direction of the base 10 is preferably 0.04 μm or more. If the surface roughness Ra along the radial direction is too small, the effect of suppressing the expansion and contraction and displacement of the substrate W in the radial direction when the substrate W is adsorbed is reduced. In addition, the surface roughness Ra of the upper end surface 24 of the convex portion along the radial direction of the base 10 is preferably less than 0.15 μm, and more preferably 0.1 μm or less. If the surface roughness Ra along the radial direction is too large, the risk of particle generation increases.

The surface roughness Ra of the upper end surface 24 of the convex portion along the radial direction of the base 10 is larger than the surface roughness Ra of the upper end surface 24 of the convex portion along the circumferential direction of the base 10. The surface roughness Ra of the convex portion 20 along the circumferential direction of the base 10 is preferably 0.001 μm or more and 0.08 μm or less.

The surface roughness Ra of the upper end faces 24 of the convex portions along the radial direction of the substrate 10 and the surface roughness Ra of the substrate 10 along the circumferential direction can be determined by scanning the amount of unevenness of the upper end faces 24 of the convex portions three-dimensionally without contact using a white light interferometer, creating a 2D chart on a radial straight line or a circumferential curve on the scanned 3D height map, and using the created 2D chart. It is preferable to determine the surface roughness Ra as the average value of the upper end faces 24 of multiple convex portions.

For example, if there are convex portions 20 on the entire upper surface 12 of the base 10, in which the surface roughness Ra of the upper end surface 24 of the convex portion along the radial direction of the base 10 is larger than the surface roughness Ra along the circumferential direction of the base 10, four circles of arbitrary radius centered on the center 16 of the base are set, and a total of 12 convex points in three directions at equal intervals of 120° in the rotational direction are selected as observation positions, and the surface roughness Ra along the radial direction of the base 10 and the surface roughness Ra along the circumferential direction of the base 10 of all selected convex portions 20 are calculated, and the average values thereof can be used as the surface roughness Ra along the radial direction of the base 10 and the surface roughness Ra along the circumferential direction of the base 10, respectively.

In addition, when the upper surface 12 is divided into four regions by two straight lines that pass through the center 16 of the base and intersect at right angles, it is preferable that each region includes a convex portion 20 in which the surface roughness Ra of the upper end surface 24 of the convex portion along the radial direction of the base 10 is greater than the surface roughness Ra along the circumferential direction of the base 10. This suppresses expansion/contraction and displacement of the substrate in various radial directions, thereby further improving the positioning accuracy of the substrate.

For example, it is sufficient that all of the protrusions 20 in the region inside a circle of a predetermined radius centered on the center 16 of the base are protrusions 20 whose surface roughness Ra of the upper end surface 24 of the protrusions in the radial direction of the base 10 is larger than the surface roughness Ra of the upper end surface 24 of the protrusions in the circumferential direction of the base 10. Also, for example, it is sufficient that all of the protrusions 20 in a doughnut-shaped region surrounded by two circles of different predetermined radii centered on the center 16 of the base are protrusions 20 whose surface roughness Ra of the upper end surface 24 of the protrusions in the radial direction of the base 10 is larger than the surface roughness Ra of the upper end surface 24 of the protrusions in the circumferential direction of the base 10.

As described above, it is preferable that all of the convex portions 20 formed on the substrate 10 have fine grooves 26 formed in the circumferential direction. It is also preferable that all of the convex portions 20 formed on the substrate 10 are convex portions 20 in which the surface roughness Ra of the upper end surface 24 of the convex portion along the radial direction of the substrate 10 is larger than the surface roughness Ra along the circumferential direction of the substrate 10.

At least a part of the upper end 22 of the convex portion or at least a part of the upper end surface 24 of the convex portion is preferably formed of an abrasion-resistant layer 28. By forming at least a part of the upper end surface 24 of the convex portion with the abrasion-resistant layer 28, the generation of particles during repeated use can be suppressed. FIGS. 6(a) and 6(b) are schematic cross-sectional views showing the convex portion 20 on which the abrasion-resistant layer 28 is formed. As shown in FIG. 6(a), the abrasion-resistant layer 28 may be formed on all or at least a part of the upper end 22 of the convex portion or the upper end surface 24 of the convex portion. Also, as shown in FIG. 6(b), it may be formed on the upper end 22 of the convex portion or the upper end surface 24 of the convex portion, its side surface, and the upper surface 12 of the base body 10.

The wear-resistant layer 28 can be formed from a DLC (diamond-like carbon) film or a SiC film formed by physical vapor deposition (PVD method), chemical vapor deposition (CVD method), ionization deposition method, etc.

The convex portion 20, at least a part of whose upper end surface 24 is formed of the wear-resistant layer 28, preferably has fine grooves 26 formed in the circumferential direction. In addition, the convex portion 20, at least a part of whose upper end surface 24 is formed of the wear-resistant layer 28, preferably has a surface roughness Ra of the upper end surface 24 of the convex portion along the radial direction of the substrate 10 that is greater than the surface roughness Ra of the upper end surface 24 along the circumferential direction of the substrate 10. This is because, when at least a part of the upper end surface 24 of the convex portion is formed of the wear-resistant layer 28, slippage, expansion/contraction, displacement, etc. of the substrate are likely to occur.

The substrate holding member 100 may be provided with electrodes, terminals, terminal holes, lift pin holes, etc. (not shown). When used as a vacuum chuck, it may be provided with ventilation holes, annular protrusions, etc. When used as an electrostatic chuck, it may be provided with electrodes for electrostatic adsorption, etc.

Figure 7 is a schematic diagram showing a modified top surface of a substrate holding member according to an embodiment of the present invention. Also, Figure 8 is a schematic cross-sectional view showing a modified substrate holding member according to an embodiment of the present invention. Figures 7 and 8 assume that the substrate holding member 100 is used as a vacuum chuck.

The annular protrusion 40 is formed in a ring shape along the outer periphery of the upper surface 12 of the base 10. For example, when the base 10 is formed in a disk shape, the annular protrusion 40 is preferably formed in a continuous ring shape when viewed from above, at a position along the outer periphery of the upper surface of the base 10 or at a position a predetermined width away from the outer periphery and toward the center. When the annular protrusion 40 is formed in a ring shape, it is preferable that its center coincides with the center 16 of the base.

The upper end 42 of the annular convex portion is preferably closer to the upper surface 12 of the base 10 than the upper ends 22 of the multiple convex portions. In other words, the height of the annular convex portion 40 is preferably lower than the height of the multiple convex portions 20. This allows air to always flow in from the outside of the base 10 during the suction operation of the substrate W, and the Bernoulli effect can be exerted near the annular convex portion 40 to suppress sinking of the edge of the substrate W. In addition, the contact area with the substrate W can be reduced, reducing the risk of particle generation. Note that by forming the annular convex portion 40 a certain amount lower than the upper ends of the multiple convex portions 20, outside air is always introduced from the outer periphery when the substrate W is suctioned, but this does not matter as long as the interval is large enough to obtain a sufficient vacuum for suction of the substrate W due to the generation of a pressure gradient.

The height of the annular protrusion 40 refers to the distance from the upper surface 12 of the base 10 to the upper end 42 of the annular protrusion. The height of the annular protrusion 40 is preferably 1 μm or more and 10 μm or less lower than the height of the multiple protrusions 20. For example, when the height of the multiple protrusions 20 is 100 μm, the height of the annular protrusion 40 is preferably 90 μm or more and 99 μm or less.

The width of the annular convex portion 40 is preferably 0.1 μm or more and 8 mm or less. In addition, the width of the annular convex portion 40 is preferably equal to or less than the distance between the centers of the adjacent convex portions 20. The cross-sectional shape of the annular convex portion 40 may be rectangular, trapezoidal, hemispherical, or other various shapes, but it is preferable that the upper end 42 of the annular convex portion is formed as a flat surface. In this case, it is preferable that the surface roughness of the flat surface of the upper end 42 of the annular convex portion (the upper end surface 44 of the annular convex portion) is Ra 0.20 μm or less.

In the case of a so-called Bernoulli-type vacuum chuck in which the upper end 42 of the annular convex portion is located closer to the upper surface 12 of the substrate 10 than the upper ends 22 of the multiple convex portions, the upper end surface 44 of the annular convex portion does not come into contact with the substrate W, so there is no need to form a fine groove on the upper end surface 44 of the annular convex portion. On the other hand, in the case of a vacuum chuck in which the upper end 42 of the annular convex portion is formed substantially flush with the upper ends 22 of the multiple convex portions, the upper end surface 44 of the annular convex portion comes into contact with the substrate W, so the fine groove 26 may be formed on the upper end surface 44 of the annular convex portion.

The base 10 is formed with one or more ventilation holes 50 opening on the upper surface 12. When multiple ventilation holes 50 are formed, the multiple ventilation holes 50 may be connected via an air passage passing through the inside of the base 10. The ventilation hole 50 is connected to a vacuum suction device (not shown). The position, shape, and size of the ventilation hole 50 vary depending on the design of the substrate holding device, such as the shape of the suction surface area, the shape and type of the substrate W, and the suction force when vacuum suctioned.

[Method of manufacturing the substrate holding member]
Next, a method for manufacturing a substrate holding member according to an embodiment of the present invention will be described. The method for manufacturing a substrate holding member according to an embodiment of the present invention includes a base preparation step, a convex portion formation step, a lapping step, and a texturing step. Each step will be described below.

In the base preparation step, a flat-plate base made of a ceramic sintered body is prepared. A flat-plate-shaped compact is produced from raw material powder by a known method, and a _flat -plate-shaped ceramic sintered body is obtained by firing the compact. The ceramic sintered body is SiC, _Al2O3 , _Si3N4 , AlN, cordierite, lithium aluminosilicate _, etc. The raw material powder may contain a sintering aid. Although a disk-shaped substrate holder is illustrated in FIG. 1, etc., any shape may be used, such as a polygonal shape or an elliptical shape.

In the convex portion forming process, multiple convex portions are formed that protrude from the upper surface of the base. In other words, multiple convex portions are formed on the surface that will become the upper surface of the ceramic sintered body. In addition, ventilation holes, annular convex portions, etc. are formed as necessary. Forming methods that can be used include blasting, milling, laser processing, etc.

The arrangement of the multiple protrusions is not particularly limited. It may be in a known form or a form similar thereto. For example, the arrangement may be a regular arrangement such as a triangular lattice, a square lattice, or a concentric circle arrangement, or may be an irregular arrangement with localized sparseness and density.

The shape of the multiple protrusions is appropriately selected from cylindrical, prismatic, and other columnar shapes, conical, and other pyramidal shapes, and shapes with the top of a pyramid, such as a truncated cone shape or a truncated pyramid shape, etc. The shape of the multiple protrusions 20 may be a stepped shape in which the cross-sectional area of the upper part is smaller than that of the lower part. At least some of the protrusions are formed with the upper end of the protrusion as a surface. In other words, it is preferable that the shape of at least some of the protrusions is a columnar, prismatic, and other columnar shape, or a truncated cone shape or a truncated pyramid shape, such as a truncated cone shape or a truncated pyramid shape, with the top part cut off.

The upper ends of the multiple protrusions are formed to be approximately flush. The multiple protrusions are preferably designed according to the conditions of the substrate to be adsorbed, for example, with a protrusion amount of 50 μm to 500 μm and a spacing between the multiple protrusions in the range of 1.5 mm to 8 mm. In addition, the diameter of the upper end surface of the protrusions formed as a surface is preferably 100 μm to 500 μm.

In the lapping process, the upper end faces of the multiple protrusions are lapped. The surfaces of the protrusions are lapped using free abrasive grains to a surface roughness Ra of preferably 0.05 μm or less, more preferably 0.04 μm or less.

In the texturing process, the upper end surfaces of the multiple protrusions are textured so that the surface roughness Ra in the radial direction is greater than the surface roughness Ra in the circumferential direction. Specifically, the surfaces of the protrusions are textured to form fine grooves along the circumferential direction. At this time, it is preferable that the surface roughness Ra along the radial direction of the base is 0.04 μm or more and less than 0.15 μm. The texturing process is carried out, for example, as follows. Figures 9(a) and (b) are schematic perspective and plan views, respectively, showing the process of the texturing process.

The texturing process is carried out, for example, by scanning a dense ceramic sintered body piece on the surface of the multiple protrusions. The ceramic piece is made of oxide ceramics such as _Al2O3 or _ZrO2 , and is formed in a disk or square shape, and the surface roughness Ra _of the surface that contacts the substrate holding member (multiple protrusions) is preferably 0.1 μm or more and 0.5 μm or less. If Ra exceeds 0.5 μm, there is a risk of particles being generated due to wear of the multiple protrusions, and the flatness of the substrate holding member being deteriorated. Also, if it is less than 0.1 μm, adhesion with the multiple protrusions occurs, making it difficult to scan the ceramic piece, and there is a risk of applying more force than necessary and damaging the protrusions.

To prevent dust generation from the ceramic pieces themselves, it is preferable that the purity of the ceramic pieces is high. For example, it is preferable that the purity is 95% or more, and more preferably 99% or more.

Diamond paste is applied thinly and evenly to the surface of the ceramic piece, which is then placed on the surfaces of multiple convex parts and scanned in the circumferential direction of the substrate holding member with a pressure of 1 KPa or less (the weight of the piece itself). In order to form fine grooves along the circumferential direction, the ceramic piece is scanned only in a fixed direction. For example, after scanning the outer periphery of the substrate holding member for 1 to 3 revolutions, the ceramic piece is offset inward and scanned in the same way for 1 to 3 revolutions. The surface roughness is then measured, and if the value is not satisfactory, the same scan is repeated to perform surface texturing.

The surface roughness Ra of the upper end surface of the convex portion along the radial direction of the base and the surface roughness Ra of the base along the circumferential direction can be determined by scanning the unevenness of the upper end surface of the convex portion three-dimensionally without contact using a white light interferometer, creating a 2D chart on a straight line in the radial direction or a curve in the circumferential direction on the scanned 3D height map, and using the created 2D chart. It is preferable to determine the surface roughness Ra as the average value of the upper end surfaces of multiple convex portions.

In addition, an abrasion-resistant layer forming process may be performed before or after the texturing process, in which an abrasion-resistant layer is formed on at least a portion of the upper end surface of the multiple protrusions. In the abrasion-resistant layer forming process, a DLC film (diamond-like carbon) or SiC film is formed by physical vapor deposition (PVD method), chemical vapor deposition (CVD method), ionization vapor deposition method, or the like on the substrate holding member on which multiple protrusions have been formed and lapped, to form an abrasion-resistant layer.

The abrasion-resistant layer forming process may be performed either before or after the texturing process if the thickness of the abrasion-resistant layer to be formed is thinner than the depth of the fine grooves formed in the texturing process. If the thickness of the abrasion-resistant layer to be formed is equal to or greater than the depth of the fine grooves formed in the texturing process, it is preferable to perform the abrasion-resistant layer forming process after the texturing process.

The substrate holding member of the present invention can be manufactured by the above process.

[Examples and Comparative Examples]
Example 1
A substantially disk-shaped base body made of sintered silicon carbide with a diameter of φ310 mm and a thickness of t1.5 mm was prepared, and blast processing was used to form vent holes, multiple convex portions, and annular convex portions. The multiple convex portions were formed to have a height of 150 μm, a diameter of φ300 μm, and a triangular lattice shape with a center-to-center distance of 4 mm between each convex portion. The annular convex portion was formed to have a width of 200 μm, and was formed by additional processing so that it was 3 μm lower than the multiple convex portions.

Next, lapping was performed using free abrasive grains, and finishing was performed so that the surface roughness Ra of the multiple protrusions was approximately 0.03 μm.

Next, as a surface texturing process, a diamond paste with a particle size of 0.5 μm was applied to a ceramic piece (φ130 mm × t15 mm) made of aluminum oxide with a relative density of 99% and a surface roughness Ra of 0.3 μm, and the piece was scanned in the circumferential direction to produce the substrate holding member of Example 1. After the texturing process, the surface roughness Ra along the radial direction of the base for the 12 convex portions was measured to be 0.04 μm. Furthermore, the surface roughness Ra along the circumferential direction of the base for the same 12 convex portions was 0.03 μm.

The surface roughness Ra of the convex parts before texturing in the examples and comparative examples was measured as follows. Four circles of arbitrary radius centered on the center of the substrate were set (in this example, φ20 mm, φ110 mm, φ200 mm, and φ298 mm), and a total of 12 convex parts in three directions were selected as observation positions at equal intervals of 120° in the rotation direction. Next, the unevenness of the upper end surface of the selected convex parts was scanned three-dimensionally without contact using a white light interferometer (AMETEK Talor Hobson: CCI-HD). Next, a 2D chart was created on an arbitrary straight line on the scanned 3D height map, and the surface roughness Ra of each convex part was determined using the created 2D chart. Then, the surface roughness Ra of the substrate holding member was determined by calculating the average value of the surface roughness Ra of the 12 convex parts.

In addition, the surface roughness Ra of the convex portion along the radial direction of the substrate and along the circumferential direction of the substrate after the texturing process in the embodiment were measured as follows. Four circles of arbitrary radius centered on the center of the substrate were set (in this embodiment, φ20 mm, φ110 mm, φ200 mm, and φ298 mm), and a total of 12 convex portions in three directions were selected as observation positions at 120° equal intervals in the rotation direction. Next, the unevenness of the upper end surface of the selected convex portions was scanned three-dimensionally without contact using a white light interferometer (AMETEK Talor Hobson: CCI-HD). Next, a 2D chart was created on the scanned 3D height map on a straight line in the radial direction or a curved line in the circumferential direction, and the surface roughness Ra of each convex portion along the radial direction of the substrate and the surface roughness Ra of each convex portion along the circumferential direction of the substrate were obtained using the created 2D chart. Then, the average surface roughness Ra of the 12 protrusions along the radial direction of the base and the average surface roughness Ra of the 12 protrusions along the circumferential direction of the base were calculated to determine the surface roughness Ra of each base holding member along the radial direction of the base and the surface roughness Ra of the base along the circumferential direction of the base. In Comparative Example 2, only the surface roughness along the X direction was calculated.

Example 2
In Example 2, a substrate holding member was manufactured under the same conditions as in Example 1, except that the number of circumferential scans in the texturing process was increased compared to Example 1. After the texturing process, the surface roughness Ra of the 12 protrusions measured along the radial direction of the base was 0.10 μm. The surface roughness Ra of the same 12 protrusions measured along the circumferential direction of the base was 0.03 μm.

Example 3
In Example 3, a substrate holding member was manufactured under the same conditions as in Example 1, except that the number of circumferential scans in the texturing process was increased further than in Example 2. After the texturing process, the surface roughness Ra measured in the radial direction of the base for the 12 protrusions was 0.15 μm. The surface roughness Ra measured in the circumferential direction of the base for the same 12 protrusions was 0.03 μm.

Example 4
In Example 4, a substrate holder was manufactured under the same conditions as in Example 1, except that a wear-resistant layer made of a DLC film having a thickness of 0.5 μm was formed by PVD on the surface of the multiple protrusions after lapping, and then texturing was performed. After texturing, the surface roughness Ra of the 12 protrusions measured along the radial direction of the base was 0.06 μm. The surface roughness Ra of the same 12 protrusions along the circumferential direction of the base was 0.03 μm.

(Comparative Example 1)
In Comparative Example 1, a substrate holding member was manufactured by performing lapping using free abrasive grains, finishing so that the surface roughness Ra of the multiple convex portions was approximately 0.03 μm, and no surface texturing was performed.

(Comparative Example 2)
In Comparative Example 2, a substrate holder was manufactured by performing lapping using free abrasive grains, finishing such that the surface roughness Ra of the multiple protrusions was about 0.03 μm, and texturing such that the scanning direction of the ceramic piece was only in the Y direction. After texturing, the surface roughness Ra of the 12 protrusions along the X direction was measured and was 0.10 μm.

(Comparative Example 3)
In Comparative Example 3, a substrate holding member was manufactured by performing lapping using free abrasive grains, finishing processing so that the surface roughness Ra of the multiple convex portions was approximately 0.03 μm, and forming a wear-resistant layer made of a DLC film having a thickness of 0.5 μm by a PVD method on the surface of the multiple convex portions after lapping.

The upper end surfaces of the convex portions of Example 1 and Comparative Example 1 were observed with an optical microscope. Figures 10(a) and 10(b) are optical microscope photographs of the upper end surfaces of the convex portions of Example 1 and Comparative Example 1, respectively. As shown in Figure 10, a large number of fine grooves were formed along the radial direction on the upper end surface of the convex portion of Example 1.

(Evaluation Method)
The substrate holding members obtained in the examples and comparative examples were installed in an exposure device, and a silicon wafer (substrate) with a diameter of 300 mm and a thickness of 0.7 mm was picked up and evaluated several times. The overall shape of the silicon wafer was compared before and after suction using a Fizeau type laser interferometer (Apre Instruments Inc.: S300HR (SCI)) to confirm the presence or absence of expansion and contraction or displacement in the X and Y directions.

(Evaluation Results)
It was confirmed that the substrate holding members of Examples 1 to 4 suppressed slippage, expansion/contraction, and displacement of the substrate over the entire surface in the X and Y directions, and had high positioning accuracy.

In contrast, in Comparative Example 1, in which surface texturing was not performed, there was variation in the suppression of slippage, expansion/contraction, and displacement of the substrate, and the positioning accuracy was lacking in stability. Furthermore, the substrate release properties after the suction operation was released were poorer than in the Example, which also had the effect of reducing throughput.

In addition, in Comparative Example 2, in which the ceramic piece was scanned only in the Y direction for surface texturing, slippage, expansion and contraction, and displacement of the substrate were observed only in the Y direction, and high positioning accuracy could not be achieved.

In addition, in Comparative Example 3, in which an abrasion-resistant layer was formed but surface texturing was not performed, there was variation in the suppression of slippage, expansion/contraction, and displacement of the substrate, and the positioning accuracy lacked stability. In addition, no directionality was confirmed in the slip direction, and there was a tendency for the position to shift significantly compared to the examples.

In Example 3, in which the surface roughness Ra of the radial direction of the multiple protrusions was set to 0.15 μm by surface texturing, the effect of suppressing slippage, expansion/contraction, and displacement of the substrate was obtained, but the generation of particles was observed over time, and it was confirmed that the flatness precision of the substrate deteriorated. In other words, it is estimated that the lifespan of the substrate holder will be shorter than in Examples 1 and 2.

From the above, it has been confirmed that the substrate holding member of the present invention can improve the positioning accuracy of the substrate while maintaining a low contact state with the substrate. It has also been confirmed that the method for manufacturing the substrate holding member of the present invention can manufacture such a substrate holding member.

The present invention is not limited to the above-described embodiment, and it goes without saying that it covers various modifications and equivalents that fall within the spirit and scope of the present invention. Furthermore, the structure, shape, number, position, size, etc. of the components shown in each drawing are for convenience of explanation and may be changed as appropriate.

10 Base body 12 Upper surface 16 Center of base body 20 Convex portion 22 Upper end of convex portion 24 Upper end surface of convex portion 30 Reference surface 40 Annular convex portion 42 Upper end of annular convex portion 44 Upper end surface of annular convex portion 50 Ventilating hole 100 Substrate holding member W Substrate

Claims (6)

A substrate holding member,
A flat substrate;
a plurality of pin-shaped protrusions formed to protrude upward from the upper surface of the base,
an upper end surface of the protrusion has a fine groove formed in a circumferential direction of the base body;
The substrate holding member is characterized in that the narrow groove has a width of 1 to 10 μm . The substrate holding member according to claim 1, characterized in that the surface roughness Ra of the upper end surface of the convex portion along the radial direction of the base body is greater than the surface roughness Ra along the circumferential direction of the base body. The substrate holding member according to claim 2, characterized in that when the upper surface is divided into four regions by two straight lines that pass through the center of the base and intersect at right angles, each region includes a convex portion in which the surface roughness Ra of the upper end surface of the convex portion along the radial direction of the base is larger than the surface roughness Ra along the circumferential direction of the base. The substrate holding member according to claim 2 or 3, characterized in that the surface roughness Ra of the upper end surface of the convex portion along the radial direction of the base is greater than the surface roughness Ra along the circumferential direction of the base, and the surface roughness Ra of the convex portion along the radial direction of the base is 0.04 μm or more and less than 0.15 μm. The substrate holding member according to any one of claims 1 to 4, characterized in that at least a portion of the upper end surface of the convex portion is formed of an abrasion-resistant layer. A method for manufacturing a substrate holding member, comprising the steps of:
a substrate preparation step of preparing a flat substrate made of a ceramic sintered body;
a convexity forming step of forming a plurality of convexities protruding from an upper surface of the base;
a lapping process for lapping upper end surfaces of the plurality of protrusions;
a texturing process for texturing the upper end surfaces of the plurality of convex portions so that the radial surface roughness Ra is greater than the circumferential surface roughness Ra.