Electrostatic chuck

Abstract

To provide an electrostatic chuck which has a configuration with a flange section provided on a dielectric substrate and can ensure the strength of the flange section.SOLUTION: An electrostatic chuck 10 includes a dielectric substrate 100 and a base plate 200 joined to the dielectric substrate 100. The dielectric substrate 100 is provided with a flange section 150, which is a portion protruding outward along an entire periphery of a portion of a side surface of the dielectric substrate on the base plate 200 side. The base plate 200 has a surface 210 which is closest to the dielectric substrate 100, and a portion of which is joined to the dielectric substrate 100. When viewed from above, a portion of surface 210 which is not joined to the dielectric substrate 100, surrounds the flange section 150 along the entire periphery.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an electrostatic chuck. [Background technology]

[0002] For example, semiconductor manufacturing equipment such as etching equipment is provided with an electrostatic chuck as a device for attracting and holding a substrate, such as a silicon wafer, to be processed. The electrostatic chuck includes a dielectric substrate provided with an attracting electrode and a base plate that supports the dielectric substrate, which are joined together. When a voltage is applied to the attracting electrode, an electrostatic force is generated, and the substrate placed on the dielectric substrate is attracted and held.

[0003] The outer shape of the dielectric substrate, as viewed from above, is often the same as the outer shape of the mounting surface on which the substrate is placed. That is, the dielectric substrate is often thin and cylindrical. However, in such a configuration, the side of the bonding layer bonding the dielectric substrate to the base plate is exposed directly below the outer edge of the mounting surface. It is not desirable to expose the bonding layer, which is, for example, a cured silicone adhesive, near the substrate on the mounting surface.

[0004] Therefore, as described in Patent Document 1 below, for example, a configuration in which a flange is provided on the dielectric substrate is sometimes adopted. The flange is a portion of the side surface of the dielectric substrate that protrudes outward around the entire periphery on the base plate side. In the configuration described in Patent Document 1 below, the flange extends to a position that covers the entire top surface of the base plate.

[0005] When the flange is provided on the dielectric substrate, the side surface of the bonding layer is exposed at a position further outward than the outer periphery of the mounting surface, and therefore the exposed portion of the bonding layer can be placed farther away from the substrate than when the dielectric substrate does not have a flange. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2022 / 255118 Summary of the Invention [Problem to be solved by the invention]

[0007] In recent years, with the miniaturization and high performance of semiconductor devices, the demands for cooling performance, etc. of electrostatic chucks have increased dramatically. Accordingly, dielectric substrates have become thinner than before, with some measuring less than 4 mm in thickness.

[0008] If a flange is provided on the dielectric substrate, the thickness of the flange must be even thinner, for example, 1.5 mm or less. Since it is expected that dielectric substrates will continue to become thinner in the future, it may become difficult to ensure sufficient strength depending on the shape of the flange.

[0009] The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an electrostatic chuck that has a flange portion on a dielectric substrate and yet can ensure the strength of the flange portion. [Means for solving the problem]

[0010] In order to solve the above problems, the electrostatic chuck according to the present invention includes a dielectric substrate having a mounting surface on which an object to be attracted is placed, and a base plate joined to the dielectric substrate. The dielectric substrate is provided with a flange, which is a portion of its side surface that faces the base plate and protrudes outward around the entire periphery. The base plate has a flat surface that is closest to the dielectric substrate, a portion of which is joined to the dielectric substrate. When viewed from a direction perpendicular to the mounting surface, the portion of the flat surface that is not joined to the dielectric substrate surrounds the flange around the entire periphery.

[0011] In an electrostatic chuck having such a configuration, the flange of the dielectric substrate does not extend to a position where it covers the entire flat surface of the base plate. In other words, the amount of protrusion of the flange toward the outer periphery is limited to the extent that the flat surface is exposed so as to surround the periphery of the flange. This configuration makes it possible to ensure the strength of the flange compared to a configuration in which the flange protrudes to a position where it covers the entire flat surface. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide an electrostatic chuck in which the flange portion is provided on the dielectric substrate and yet the strength of the flange portion can be ensured. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view schematically illustrating a configuration of an electrostatic chuck according to an embodiment of the present invention. [Figure 2] FIG. 3 is a cross-sectional view showing in detail the configuration of the flange and its surrounding area. [Figure 3] FIG. 3 is a cross-sectional view showing in detail the configuration of the flange and its surrounding area. [Figure 4] 3A and 3B are diagrams illustrating the configuration of a coolant flow path formed in a base plate. [Figure 5] FIG. 10 is a cross-sectional view showing in detail the configuration of a flange portion and its vicinity of an electrostatic chuck according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, the present embodiment will be described with reference to the accompanying drawings. To facilitate understanding of the description, the same components in the drawings will be denoted by the same reference numerals as much as possible, and duplicated descriptions will be omitted.

[0015] The electrostatic chuck 10 according to this embodiment is configured to electrostatically attract and hold a substrate W to be processed inside a semiconductor manufacturing apparatus (not shown), such as an etching apparatus. The substrate W to be attracted is, for example, a silicon wafer. The electrostatic chuck 10 may also be used in apparatuses other than semiconductor manufacturing apparatuses.

[0016] 1 is a schematic cross-sectional view showing the configuration of an electrostatic chuck 10 in a state where the electrostatic chuck 10 attracts and holds a substrate W. The electrostatic chuck 10 includes a dielectric substrate 100 and a base plate 200.

[0017] The dielectric substrate 100 is a substantially disk-shaped member made of a sintered ceramic body. The dielectric substrate 100 contains, for example, high-purity aluminum oxide (Al2O3), but may also contain other materials. The purity, type, and additives of the ceramics in the dielectric substrate 100 can be appropriately set in consideration of the plasma resistance and other properties required of the dielectric substrate 100 in semiconductor manufacturing equipment.

[0018] The upper surface 110 of the dielectric substrate 100 in FIG. 1 is a "mounting surface" on which the substrate W is placed. The lower surface 120 of the dielectric substrate 100 in FIG. 1 is a "bonded surface" that is bonded to the base plate 200 via a bonding layer 300. The viewpoint when the electrostatic chuck 10 is viewed from the surface 110 along a direction perpendicular to the surface 110 will hereinafter be referred to as a "top view." The diameter of the surface 110 is, for example, 290 to 300 mm. The overall thickness of the dielectric substrate 100 is, for example, 1 to 5 mm.

[0019] An attraction electrode 130 is embedded inside the dielectric substrate 100. The attraction electrode 130 is a thin, flat layer made of a metal material such as tungsten, and is disposed parallel to the surface 110. The attraction electrode 130 may be made of a material other than tungsten, such as molybdenum, platinum, or palladium. When a voltage is applied to the attraction electrode 130 from the outside via a power supply path (not shown), an electrostatic force is generated between the surface 110 and the substrate W, thereby attracting and holding the substrate W. The power supply path may be configured in any of various well-known ways. The attraction electrode 130 may be provided as a single so-called "monopolar" electrode as in this embodiment, or as two so-called "bipolar" electrodes.

[0020] The depth at which the chucking electrode 130 is disposed, i.e., the distance from the bottom surface 116 (described later) to the chucking electrode 130, is, for example, 0.1 to 0.5 mm. The distance from the outer peripheral end of the chucking electrode 130 to the outer surface of the dielectric substrate 100 (the outer surface of the portion excluding the flange portion 202) is, for example, 0.1 to 3 mm.

[0021] In addition to the above-described chucking electrode 130, an RF electrode may be embedded inside the dielectric substrate 100. The RF electrode is provided as one of a pair of opposing electrodes for generating plasma in a semiconductor manufacturing apparatus. The other opposing electrode is provided at a position above the electrostatic chuck 10 in the semiconductor manufacturing apparatus. When a high-frequency AC voltage is applied between these opposing electrodes, plasma is generated above the substrate W, and is used for processing such as film formation and etching on the substrate W. The RF electrode is preferably embedded at a position that is 0.1 to 4.5 mm away from the surface 120. The distance from the chucking electrode 130 to the RF electrode is preferably 0.2 to 2 mm. The distance from the outer peripheral end of the RF electrode to the outer surface of the dielectric substrate 100 is preferably about 0.1 to 5 mm.

[0022] As shown in Fig. 1, a space SP is formed between the dielectric substrate 100 and the substrate W. When a process such as etching is performed in the semiconductor manufacturing equipment, helium gas for temperature adjustment is supplied to the space SP from the outside through a gas hole (not shown). By providing helium gas between the dielectric substrate 100 and the substrate W, the thermal resistance between them is adjusted, thereby maintaining the temperature of the substrate W at an appropriate temperature. Note that the temperature adjustment gas supplied to the space SP may be a gas other than helium.

[0023] A seal ring 111 and dots 112 are provided on a surface 110 that is a mounting surface, and the space SP is formed around these.

[0024] The seal ring 111 is a wall that divides the space SP at the outermost position. The upper end of the seal ring 111 forms part of the surface 110 and abuts against the substrate W. Note that multiple seal rings 111 may be provided to divide the space SP. With this configuration, it is possible to individually adjust the pressure of the helium gas in each space SP and make the surface temperature distribution of the substrate W during processing more uniform.

[0025] 1, the portion marked with the reference numeral "116" is the bottom surface of the space SP. Hereinafter, this portion will also be referred to as the "bottom surface 116." The seal ring 111, together with the dots 112 described below, is formed by digging down a portion of the surface 110 to the position of the bottom surface 116.

[0026] The dots 112 are circular protrusions that protrude from the bottom surface 116. A plurality of dots 112 are provided, and are distributed approximately evenly on the mounting surface of the dielectric substrate 100. The upper end of each dot 112 forms part of the surface 110 and comes into contact with the substrate W. By providing a plurality of such dots 112, bending of the substrate W is suppressed.

[0027] The dielectric substrate 100 is provided with a flange 150. The flange 150 is a portion of the side surface of the dielectric substrate 100 that faces the base plate 200 and protrudes outward around the entire periphery. Therefore, the overall shape of the dielectric substrate 100 is not a simple (thin) cylindrical shape. Due to the provision of the flange 150, the surface 120, which is the surface to be joined, is larger than the surface 110, which is the mounting surface. When viewed from above, the centers of the surfaces 110 and 120 are aligned. The outer shape of the surface 120, when viewed from above, is aligned with the outer shape of the flange 150, when viewed from above. The thickness of the flange 150 is, for example, 0.5 to 4 mm.

[0028] The base plate 200 is a substantially disk-shaped member that supports the dielectric substrate 100. The base plate 200 is formed of a metal material such as aluminum. The base plate 200 is bonded to the surface 120 of the dielectric substrate 100 via a bonding layer 300. A portion of the surface 210 of the base plate 200 on the upper side in FIG. 1 serves as a "bonded surface" that is bonded to the dielectric substrate 100. The overall thickness of the base plate 200 is, for example, 30 to 40 mm.

[0029] The bonding layer 300 is a layer provided between the dielectric substrate 100 and the base plate 200, and bonds them together. The bonding layer 300 is formed by curing an adhesive made of an insulating material. In this embodiment, a silicone adhesive is used as the adhesive. However, the bonding layer 300 may be formed by curing another type of adhesive. In either case, it is preferable to use a material with as high a thermal conductivity as possible as the material for the bonding layer 300 so as to reduce the thermal resistance between the dielectric substrate 100 and the base plate 200.

[0030] The surface 210 of the base plate 200 is a "flat surface" of the base plate 200 that is closest to the dielectric substrate 100. In this embodiment, the shape of the base plate 200 is approximately cylindrical. Therefore, the entire surface of the base plate 200 that faces the dielectric substrate 100 is the surface 210, which is a flat surface. In other words, the outer shape of the surface 210 (flat surface) when viewed from above matches the outer shape of the base plate 200 when viewed from above. The diameter of the surface 210 is, for example, 300 to 360 mm.

[0031] As described above, a portion of surface 210 is bonded to dielectric substrate 100 via bonding layer 300. In top view, the center of surface 210 and the center of surface 110 coincide with each other. The outer shape of surface 210 in top view is larger than the outer shape of flange portion 150 in top view. Therefore, in top view, the portion of surface 210 that is not bonded to dielectric substrate 100 surrounds flange portion 150 from the outside all around.

[0032] In this embodiment, an insulating film 230 (not shown in FIG. 1, see FIG. 2) is formed on the surface of the base plate 200. The insulating film 230 may be, for example, an alumina film formed by thermal spraying. By covering the surface of the base plate 200 with the insulating film 230, the dielectric strength of the base plate 200 can be increased.

[0033] The insulating film 230 is preferably formed so as to cover at least the entire surface of the base plate 200 that faces the dielectric substrate 100. In this embodiment, the entire surface 210, which is the "surface of the base plate 200 closest to the dielectric substrate 100," forms the surface of the insulating film 230. The thickness of the insulating film 230 is, for example, 1 mm or less. The thickness of the insulating film 230 may be uniform throughout, or may vary depending on the location. For example, the thickness of the portion of the insulating film 230 that contacts the bonding layer 300 may be thinner than the thickness of the insulating film 230 around it.

[0034] If the occurrence of dielectric breakdown can be prevented by other methods, the insulating film 230 does not need to be formed on the base plate 200. In this case, the surface 210, which is the "surface of the base plate 200 closest to the dielectric substrate 100," is the surface of the metal part of the base plate 200.

[0035] A coolant flow path 250 for passing a coolant is formed inside the base plate 200. When a process such as etching is performed in the semiconductor manufacturing equipment, a coolant is supplied to the coolant flow path 250 from the outside, thereby cooling the base plate 200. Heat generated in the substrate W during the process is transferred to the coolant via the helium gas in the space SP, the dielectric substrate 100, and the base plate 200, and is then discharged to the outside together with the coolant. The coolant is supplied to and discharged from the coolant flow path 250 through openings 255 and 256 (not shown in FIG. 1, see FIG. 4) formed on the surface 220 of the base plate 200 opposite the surface 210. The specific configuration of the coolant flow path 250 will be described later.

[0036] When processing a substrate W in a semiconductor manufacturing apparatus, a focus ring (not shown in FIG. 1) is installed on a portion of surface 210 that is not bonded to dielectric substrate 100. In FIG. 2, the dotted line marked with the symbol "FR" indicates the portion where the focus ring is installed. A focus ring installed in this position will hereinafter also be referred to as a "focus ring FR." The focus ring FR is an annular, plate-shaped member made of an insulating material such as quartz, and is installed to adjust the distribution of plasma during processing. Substantially the entire dielectric substrate 100 is surrounded by the focus ring FR from the outer periphery.

[0037] In this embodiment, the diameter of surface 210 is relatively large, and substantially the entire focus ring FR is supported from below by surface 210. Coolant flow path 250 is formed not only in the area directly below surface 110, which is the mounting surface, but also in the area directly below focus ring FR. The portion of substrate W near the outer edge is cooled not only via dielectric substrate 100 but also via focus ring FR. To ensure efficient cooling of focus ring FR by base plate 200, it is preferable to interpose a heat-transfer gel between surface 210 of base plate 200 and focus ring FR.

[0038] For ease of explanation, the edge on the outer periphery of surface 110, which is the mounting surface, will hereinafter also be referred to as "edge E1." Edge E1 has a circular ridgeline when viewed from above, but a portion of the ridgeline (for example, the orientation flat portion) may be a ridgeline that is not circular.

[0039] Furthermore, the portion of the bonding layer 300 that is exposed to the outside at the outermost end will also be referred to as an "exposed portion E2" below.

[0040] When the substrate W is subjected to a process such as etching, the end of the bonding layer 300 may be exposed to plasma, deteriorate, and fly apart, adversely affecting the substrate W being processed. For example, if the dielectric substrate 100 does not have a flange 150, the exposed portion E2 of the bonding layer 300 will be exposed at a position directly below the end E1. The relatively short distance from the exposed portion E2 to the end E1 may increase the impact on the substrate W as described above.

[0041] Therefore, in the electrostatic chuck 10 according to this embodiment, the flange portion 150 is provided on the dielectric substrate 100. As a result of the exposed portion E2 being disposed at a position closer to the outer periphery than directly below the end E1, the distance from the exposed portion E2 to the end E1 becomes longer, and therefore the above-described influence on the substrate W can be suppressed.

[0042] It is also conceivable to extend flange 150 to a position overlapping the outer peripheral edge of surface 210 in a top view so that the entire surface 210 is covered with dielectric substrate 100. However, with such a configuration, it becomes difficult to ensure sufficient strength of flange 150, and there is a possibility that flange 150 may be damaged due to thermal expansion.

[0043] As mentioned above, the overall thickness of the dielectric substrate 100 is approximately 1 to 5 mm, and the thickness of the collar portion 150 is only approximately 0.5 to 4 mm. In recent years, the requirements for cooling performance and the like of the electrostatic chuck 10 have been increasing, and it is expected that the thicknesses of the dielectric substrate 100 and the collar portion 150 will continue to decrease in the future. Therefore, if the collar portion 150 is extended significantly toward the outer periphery, the possibility of damage to the collar portion 150 as described above will become even higher. In addition, machining the collar portion 150 will also become more difficult.

[0044] Therefore, in the electrostatic chuck 10 according to this embodiment, the collar portion 150 does not extend to a position where it covers the entire surface 210 (flat surface) of the base plate 200. In other words, the amount of protrusion of the collar portion 150 toward the outer periphery is limited to the extent that the surface 210 is exposed so as to surround the periphery of the collar portion 150. With this configuration, it is possible to ensure the strength of the collar portion 150 compared to a configuration in which the collar portion 150 protrudes to a position where it covers the entire surface 210.

[0045] 3 is a diagram in which the focus ring FR is omitted from FIG. 2 and instead dimensions "L1" and "L2" are depicted. "L1" shown in FIG. 3 represents the radial length of flange portion 150, i.e., the amount of projection of flange portion 150 toward the outer periphery. "L2" shown in the same figure represents the radial length of the portion of surface 210 (flat surface) that is not joined to dielectric substrate 100.

[0046] In this embodiment, the flange portion 150 is provided such that the length (L1) along the radial direction of the flange portion 150 is shorter than the length (L2) along the radial direction of the portion of the surface 210 that is not joined to the dielectric substrate 100. L1 is, for example, 1 to 10 mm. L2 is, for example, 20 to 30 mm.

[0047] The reason will be explained. As shown in FIG. 2, in this embodiment, a part of the focus ring FR is arranged at the position directly above the flange portion 150. As described above, it is preferable to interpose a heat transfer gel between the surface 210 of the base plate 200 and the focus ring FR. On the other hand, it is often difficult to interpose a heat transfer gel between the flange portion 150 and the focus ring FR arranged directly above it. Since no gel is interposed, the thermal resistance between the two remains large, so there may be a case where the portion arranged directly above the flange portion 150 cannot be sufficiently cooled. As a result, the temperature of the focus ring FR may locally increase.

[0048] Therefore, in this embodiment, as described above, the length along the radial direction of the flange portion 150 is minimized so that L1 < L2. The area directly above the flange portion 150, that is, the area where it is difficult to sufficiently cool through the flange portion 150 becomes narrower, so that the temperature of the member arranged directly above the flange portion 150 can be adjusted more stably.

[0049] Note that what is arranged directly above the flange portion 150 may be a part of the focus ring FR as in this embodiment, or may be a member different from the focus ring FR. In any case, by forming the flange portion 150 so as to satisfy the condition of L1 < L2, it becomes possible to more stably control the temperature of the flange portion 150 and the member arranged directly above it.

[0050] 4 is a schematic top view of the configuration of coolant flow path 250 formed inside base plate 200. As described above, openings 255 and 256 are provided on surface 220 of base plate 200. Coolant flow path 250 is formed along a path connecting openings 255 and 256. For example, opening 255 is used as an inlet for the coolant, and opening 256 is used as an outlet for the coolant.

[0051] In Fig. 4, the circular dotted line marked with "DL1" indicates the position of the outer circumferential end of flange 150. The circular dotted line marked with "DL2" indicates the position of the inner circumferential end of flange 150. The region between dotted line DL1 and dotted line DL2 is the region that overlaps with flange 150 in top view. As shown in Fig. 4, a portion of refrigerant flow path 250 (the portion marked with "251") overlaps with flange 150 in top view, and is formed to extend in an arc along flange 150.

[0052] With this configuration, it is possible to efficiently cool the collar 150 using the coolant flow path 250. By sufficiently cooling the collar 150 and the components directly above it, it is possible to suppress a rise in temperature of these components. It is also possible to suppress a rise in temperature of the outer peripheral portion of the substrate W.

[0053] As described above, in this embodiment, the base plate 200 has a substantially cylindrical shape, and the outer shape of the surface 210 (flat surface) in top view matches the outer shape of the base plate 200 in top view. However, the outer shapes of the two may be different from each other.

[0054] 5, the outer shape of surface 210 in a top view may be smaller than the outer shape of base plate 200 in a top view. In the figure, the portion marked with the reference numeral "240" is a portion of base plate 200 on the outer periphery side of surface 210, and is a recess formed so as to recede toward the opposite side from dielectric substrate 100.

[0055] In this modified example, the surface 210 corresponds to the "flat surface" of the base plate 200 that is closest to the dielectric substrate 100. As in the present embodiment, the portion of the surface 210 (flat surface) that is not joined to the dielectric substrate 100 surrounds the entire periphery of the flange portion 150 from the outside when viewed from above. Even with this configuration, the same effects as those described in the present embodiment can be achieved.

[0056] 5, however, it becomes necessary to increase the thickness of the focus ring FR (not shown) directly above the portion indicated by the reference numeral "240." This may make it more difficult to adjust the temperature of the focus ring FR than in this embodiment. In light of this, it is preferable to make the outer shape of the surface 210 (flat surface) in a top view coincide with the outer shape of the base plate 200 in a top view, as in this embodiment.

[0057] The present embodiment has been described above with reference to specific examples. However, the present disclosure is not limited to these specific examples. Design modifications to these specific examples made by a person skilled in the art as appropriate are also included within the scope of the present disclosure as long as they comprise the features of the present disclosure. The elements of the above-described specific examples, as well as their arrangement, conditions, shape, etc., are not limited to those exemplified and can be modified as appropriate. The elements of the above-described specific examples can be combined in various ways as appropriate, as long as no technical contradictions arise. [Explanation of symbols]

[0058] 10: Electrostatic chuck 100: Dielectric substrate 110: Face 150: Tsuba section 200: Base plate 210: Face 250: Refrigerant flow path W: Substrate

Claims

1. a dielectric substrate having a mounting surface on which an object to be attracted is placed; a base plate joined to the dielectric substrate, The dielectric substrate is provided with a flange, which is a portion of a side surface of the dielectric substrate that is on the base plate side and protrudes outward over the entire periphery, the base plate has a flat surface that is closest to the dielectric substrate and a portion of which is joined to the dielectric substrate; When viewed from a direction perpendicular to the placement surface, an electrostatic chuck, characterized in that the portion of the flat surface that is not joined to the dielectric substrate surrounds the entire periphery of the flange portion;

2. When viewed from a direction perpendicular to the placement surface, 2. The electrostatic chuck of claim 1, wherein the outer shape of said flat surface matches the outer shape of said base plate.

3. A coolant flow path for passing a coolant is formed inside the base plate, When viewed from a direction perpendicular to the placement surface, 2. The electrostatic chuck according to claim 1, wherein a portion of the coolant flow path overlaps with the flange portion and extends along the flange portion.

4. The length of the flange portion along the radial direction is 2. The electrostatic chuck according to claim 1, wherein the length of the flat surface is shorter than the length along the radial direction of the portion of the flat surface that is not joined to the dielectric substrate.

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