JP7709480B2 - Electrostatic Chuck - Google Patents

Description

The present invention relates to an electrostatic chuck.

For example, in semiconductor manufacturing equipment such as CVD equipment, an electrostatic chuck is provided as a device for attracting and holding a substrate such as a silicon wafer to be processed. The electrostatic chuck has a dielectric substrate on which an attraction electrode is provided. When a voltage is applied to the attraction electrode, an electrostatic force is generated, and the substrate placed on the dielectric substrate is attracted and held.

As described in the following Patent Document 1, the dielectric substrate may have an RF electrode built in, which is one of a pair of opposing electrodes for generating plasma in a semiconductor manufacturing device. In this case, both the chucking electrode and the RF electrode are built into the dielectric substrate.

Furthermore, dielectric substrates often have through holes formed vertically through the mounting surface. Such through holes are formed, for example, for the purpose of supplying an inert gas such as helium between the dielectric substrate and the substrate. In order to prevent the chucking electrode and the like from being exposed on the inner surface of the through hole, circular openings are formed in the chucking electrode and the RF electrode at the portions that overlap the through hole in top view. The openings are formed so as to be concentric with the through hole and to encompass the through hole.

JP 2011-119654 A

During substrate processing, the chucking electrode is at a high potential, while the RF electrode is kept at a predetermined low potential (for example, the same ground potential as the base plate supporting the dielectric substrate). At this time, a strong electric field is generated in the through-hole from the edge of the chucking electrode opening toward the edge of the RF electrode opening. Since the direction of this electric field is the same as the extension direction of the through-hole, there is a possibility that insulation breakdown will occur along the path through the through-hole.

The present invention was made in consideration of these problems, and its purpose is to provide an electrostatic chuck that can suppress the occurrence of dielectric breakdown through the through holes.

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 in which a through hole is formed perpendicular to the mounting surface, an RF electrode embedded inside the dielectric substrate, and an adsorption electrode embedded inside the dielectric substrate at a position closer to the mounting surface than the RF electrode. When viewed from a direction perpendicular to the mounting surface, the adsorption electrode has a circular first opening formed therein that is concentric with and encompasses the through hole, and the RF electrode has a circular second opening formed therein that is concentric with and encompasses the through hole. In this electrostatic chuck, the radius of the second opening is larger than the radius of the first opening.

In an electrostatic chuck having such a configuration, the edge of the second opening formed in the RF electrode is located farther from the through hole than the edge of the first opening formed in the chucking electrode. In the through hole, the component of the electric field from the edge of the first opening to the edge of the second opening along the direction in which the through hole extends is smaller, so that the possibility of dielectric breakdown occurring through the through hole can be reduced compared to conventional techniques.

In the electrostatic chuck according to the present invention, it is also preferable that the difference between the radius of the second opening and the radius of the first opening is 2.7 mm or less. The larger the radius of the second opening, the farther the edge of the second opening is from the through hole, so the lower the possibility of dielectric breakdown through the through hole. However, if the radius of the second opening is made too large, the electric field around the chucking electrode, which is at a high potential, may affect other parts through the second opening, causing dielectric breakdown in those parts. According to the inventors' experimental confirmation, it has been found that such dielectric breakdown can be prevented by setting the difference between the radius of the second opening and the radius of the first opening to 2.7 mm or less.

In addition, in the electrostatic chuck according to the present invention, it is also preferable that the through-hole is a gas supply hole. When the through-hole is a gas supply hole, the pressure inside the through-hole is a pressure range in which dielectric breakdown is relatively likely to occur. In such a case, the effect of applying the present invention as described above is particularly large.

The present invention provides an electrostatic chuck that can suppress the occurrence of dielectric breakdown through a through hole.

1 is a cross-sectional view illustrating a schematic configuration of an electrostatic chuck according to an embodiment of the present invention. FIG. 2 is an enlarged, detailed cross-sectional view of a portion of the structure shown in FIG. 1; 1A to 1C are diagrams for explaining the relationship between the shape of an RF electrode or the like and the likelihood of dielectric breakdown. 1A to 1C are diagrams for explaining the relationship between the shape of an RF electrode or the like and the likelihood of dielectric breakdown.

The present embodiment will be described below with reference to the attached drawings. To facilitate understanding of the description, the same components in each drawing are denoted by the same reference numerals as much as possible, and duplicate descriptions will be omitted.

The electrostatic chuck 10 according to this embodiment is configured to attract and hold a substrate W to be processed by electrostatic force inside a semiconductor manufacturing apparatus (not shown), such as a CVD film forming apparatus. The substrate W is, for example, a silicon wafer. The electrostatic chuck 10 may also be used in apparatus other than semiconductor manufacturing apparatus.

Figure 1 shows a schematic cross-sectional view of the configuration of an electrostatic chuck 10 when it attracts and holds a substrate W. The electrostatic chuck 10 includes a dielectric substrate 100, a base plate 200, and a bonding layer 300.

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 (Al ₂ O ₃ ), but may 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.

The upper surface 110 of the dielectric substrate 100 in FIG. 1 is a "mounting surface" on which the substrate W, which is the object to be attracted, is placed. The lower surface 120 of the dielectric substrate 100 in FIG. 1 is a "bonding surface" that is bonded to the base plate 200 via a bonding layer 300 described below. The viewpoint when the electrostatic chuck 10 is viewed from the surface 110 side along a direction perpendicular to the surface 110 is hereinafter also referred to as "top view."

An adsorption electrode 130 is embedded inside the dielectric substrate 100. The adsorption electrode 130 is a thin, flat layer made of a metal material such as tungsten, and is arranged parallel to the surface 110. The material of the adsorption electrode 130 may be tungsten, molybdenum, platinum, palladium, or the like. When a voltage is applied to the adsorption electrode 130 from the outside via the power supply line 13, an electrostatic force is generated between the surface 110 and the substrate W, thereby adsorbing and holding the substrate W. The adsorption electrode 130 may be a so-called "monopolar" electrode, as in this embodiment, and only one electrode 130 may be provided, but may also be two electrodes, as so-called "bipolar" electrodes.

1, the entire power supply path 13 is depicted in a simplified form. The portion of the power supply path 13 inside the dielectric substrate 100 is configured, for example, as a long and narrow via (hole) filled with a conductor, and an electrode terminal (not shown) is provided at the lower end. The portion of the power supply path 13 that penetrates the base plate 200 is a conductive metal member (e.g., a bus bar) with one end connected to the electrode terminal. The base plate 200 is formed with a through hole (not shown) for inserting the power supply path 13. For example, a cylindrical insulating member may be provided between the inner surface of the through hole and the power supply path 13.

In addition to the above-mentioned chucking electrode 130, an RF electrode 140 is also embedded inside the dielectric substrate 100. The RF electrode 140 is provided as one of a pair of opposing electrodes for generating plasma in the semiconductor manufacturing apparatus. The other of the opposing electrodes 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 140, like the adsorption electrode 130, is a thin, flat layer made of a metal material such as tungsten. In addition to tungsten, molybdenum, platinum, palladium, etc. may be used as the material of the RF electrode 140. The RF electrode 140 is embedded at a position closer to the surface 120 than the adsorption electrode 130. In other words, the adsorption electrode 130 is embedded at a position closer to the surface 110 than the RF electrode 140. Like the adsorption electrode 130, the RF electrode 140 is arranged so as to be parallel to the surface 110 and the adsorption electrode 130. The RF electrode 140 is a single electrode that is approximately circular when viewed from above.

An opening 143 is formed in the RF electrode 140 in a portion that overlaps with the power supply line 13 in a top view. By forming the opening 143, insulation between the power supply line 13 and the RF electrode 140 is ensured.

As shown in FIG. 1, the RF electrode 140 is connected to the power supply line 14. The power supply line 14 is an electric path provided to match the potential of the RF electrode 140 with the potential of the base plate 200 when a high-frequency AC voltage is applied between the RF electrode 140 and the other opposing electrode. In FIG. 1, the entire power supply line 14 is illustrated in a simplified form. The power supply line 14 is configured, for example, as an electrode terminal having one end connected to the RF electrode 140 and the other end formed to protrude downward from the surface 120. The protruding portion of the power supply line 14 as described above is embedded in a recess (not shown) formed in the surface 120 of the base plate 200 and is connected to a metal portion of the base plate 200.

A space SP is formed between the dielectric substrate 100 and the substrate W. When processing such as film formation is performed in the semiconductor manufacturing device, helium gas for temperature adjustment is supplied to the space SP from the outside through a gas hole 150 described below. 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. The temperature adjustment gas supplied to the space SP may be a type of gas other than helium.

A seal ring 111 and dots 112 are provided on the surface 110, which is the adsorption surface, and a space SP is formed around these.

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 helium gas pressure in each space SP and make the surface temperature distribution of the substrate W during processing more uniform.

The portion marked with the reference symbol "116" in FIG. 1 and other figures 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 as a result of digging down a portion of the surface 110 to the position of the bottom surface 116.

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 adsorption surface of the dielectric substrate 100. The upper end of each dot 112 forms part of the surface 110 and abuts against the substrate W. By providing a plurality of such dots 112, deflection of the substrate W is suppressed.

A groove 113 is formed in the bottom surface 116 of the space SP. The groove 113 is formed so as to retreat further from the bottom surface 116 toward the surface 120. The groove 113 is formed for the purpose of quickly diffusing the helium gas supplied from the gas hole 150 into the space SP and making the pressure distribution in the space SP approximately uniform within a short period of time.

The dielectric substrate 100 has gas holes 150 extending vertically from the surface 120 toward the surface 110, and the gas holes 150 are connected to the space SP via the through holes 151 shown in FIG. 2. Multiple gas holes 150 are formed, but only one of them is shown in FIG. 1.

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 such as aluminum. The upper surface 210 of the base plate 200 in FIG. 1 is a "bonded surface" that is bonded to the dielectric substrate 100 via a bonding layer 300.

An insulating film 230 is formed on almost the entire surface of the base plate 200, except for the surface 220 on the lower side in FIG. 1. The insulating film 230 is a film made of an insulating material such as alumina, and is formed, for example, by thermal spraying. The surface 210 mentioned above is entirely on the surface of the insulating film 230. The range of the base plate 200 on which the insulating film 230 is formed may be a range different from that shown in FIG. 1. For example, the insulating film 230 may be formed only on the surface 210, which is the surface to be joined.

A coolant flow path 270 for flowing a coolant is formed inside the base plate 200. When a process such as film formation is performed in the semiconductor manufacturing device, a coolant is supplied to the coolant flow path 270 from the outside, thereby cooling the base plate 200. Heat generated in the substrate W during processing is transferred to the coolant via the helium gas in the space SP, the dielectric substrate 100, and the base plate 200, and is discharged to the outside together with the coolant.

Gas holes 250 are formed in the base plate 200, extending vertically from the surface 210 toward the surface 220. The gas holes 250 are formed at positions that overlap the gas holes 150 of the dielectric substrate 100 in a top view, and are connected to the gas holes 150 via through holes provided in the bonding layer 300. The gas holes 250, together with the gas holes 150 of the dielectric substrate 100, form part of a path for supplying helium gas toward the space SP.

The gas holes 250 may be formed so as to extend linearly as in this embodiment, but may be formed so as to bend on the way to the surface 220. In addition, the multiple gas holes 250 on the surface 210 side may be aggregated into a small number of flow paths inside the base plate 200, and the flow paths may be configured to extend to the surface 220 side.

The bonding layer 300 is a layer provided between the dielectric substrate 100 and the base plate 200, and bonds the two together. The bonding layer 300 is made by hardening an adhesive made of an insulating material. For example, a silicone-based adhesive can be used as such an adhesive.

The specific configuration of the upper end of the gas hole 150 and its surrounding area will be described. FIG. 2 shows the configuration of this area as a schematic cross-sectional view. As shown in the figure, the gas hole 150 is formed at a position directly below the groove 113, extending from the surface 120 toward the groove 113, but does not reach the bottom surface of the groove 113. The gas hole 150 and the space SP are connected by a through hole 151.

The through hole 151 is a circular through hole formed to extend linearly from the upper end of the gas hole 150 to the bottom surface of the groove 113. The radius of the through hole 151 is smaller than the radius of the gas hole 150. The central axis AX of the through hole 151 coincides with the central axis of the gas hole 150. In other words, the through hole 151 extends in a direction perpendicular to the surface 110. The helium gas that passes through the gas hole 150 is supplied from the through hole 151 to the space SP. The through hole 151 can be said to be the part of the gas hole 150 that is the through hole closest to the surface 110, that is, the gas outlet part.

As described above, by making the radius of the gas outlet portion of the gas hole 150 small, it is possible to make it difficult for insulation breakdown to occur through the gas hole 150. Alternatively, the gas hole 150 may extend directly to the bottom surface of the groove 113.

2, a porous plug 155 is disposed inside the gas hole 150. The porous plug 155 is a substantially cylindrical member formed of a porous material having gas permeability. A space PN is formed between the upper end of the porous plug 155 and the upper end of the gas hole 150. The arrangement of the porous plug 155 can further reduce the occurrence of dielectric breakdown between the substrate W and the base plate 200. Similarly, a porous plug for preventing dielectric breakdown may also be disposed in the portion of the gas hole 250 that is adjacent to the bonding layer 300.

An opening 131 is formed in the adsorption electrode 130 in a portion that overlaps with the through hole 151 and the gas hole 150 in a top view. In a top view, the opening 131 is a circular opening, and its center is on the central axis AX. In addition, the radius R1 of the opening 131 is larger than the radius R0 of the through hole 151. In other words, the opening 131 is a circular opening that is concentric with the through hole 151 in a top view and includes the through hole 151.

An opening 141 is formed in the RF electrode 140 at a portion that overlaps with the through hole 151 and the gas hole 150 in a top view. In a top view, the opening 141 is a circular opening, and its center is on the central axis AX. In addition, the radius R2 of the opening 141 is larger than the radius R0 of the through hole 151. In other words, the opening 141 is a circular opening that is concentric with the through hole 151 in a top view and includes the through hole 151.

Opening 131 corresponds to the "first opening" in this embodiment. Opening 141 corresponds to the "second opening" in this embodiment. The formation of openings 131 and 141 prevents the chucking electrode 130 and the RF electrode 140 from being exposed on the inner surface of the through hole 151.

In this embodiment, the radius R2 of the second opening, opening 141, is larger than the radius R1 of the first opening, opening 131.

The reason for this configuration will be explained below. Figure 3(B) shows the configuration of the portion of the electrostatic chuck according to the comparative example that corresponds to Figure 2. In this comparative example, the radius R1 of the opening 131 and the radius R2 of the opening 141 are the same (approximately the same as the radius R1 in Figure 3).

During processing of the substrate W, the chucking electrode 130 is at a high potential, while the RF electrode 140 is maintained at a predetermined low potential (the same potential as the base plate 200, for example, ground potential). Each arrow shown in FIG. 3B shows a schematic representation of the electric field lines in the vicinity of the opening 141 and the edge of the opening 131. Each electric field line extends from the edge of the opening 131 to the edge of the opening 141. When the radius R1 of the opening 131 and the radius R2 of the opening 141 are equal to each other, as in this comparative example, the direction of the electric field in the through hole 151 (i.e., the direction of the electric field lines) is approximately the same as the direction in which the through hole 151 extends. Therefore, in the configuration of this comparative example, there is a possibility that insulation breakdown may occur along the path through the through hole 151.

Therefore, in the electrostatic chuck 10 according to this embodiment, the radius R2 of the opening 141 is made larger than the radius R1 of the opening 131, as described above, thereby preventing the above-mentioned dielectric breakdown.

In FIG. 3(A), the cross section of this embodiment is the same as in FIG. 2, but arrows indicating electric field lines are shown in the same manner as in FIG. 3(B). In this embodiment, the radius R2 of the opening 141 is increased, so that only the edge of the opening 141 is moved away from the through hole 151. As a result, in the through hole 151, the component of the electric field from the edge of the opening 131 toward the opening 141 along the direction in which the through hole 151 extends is reduced, so that the possibility of dielectric breakdown occurring through the through hole 151 can be reduced compared to the conventional case.

The larger the radius R2 of the opening 141, the lower the possibility of dielectric breakdown occurring in the through hole 151. Figure 4(B) shows a comparative example in which the radius R2 is extremely large. Figure 4(A) shows the same embodiment as Figure 3(A).

When the radius R2 is made too large, as in the comparative example of FIG. 4B, some of the electric field lines extending from the chucking electrode 130, which is at a high potential, may affect the lower portion through the opening 141. For example, the electric field lines indicated by the arrow AR1 in FIG. 4B are not blocked by the RF electrode 140 and cause a potential difference in the vicinity of the bonding layer 300. As a result, there is a possibility that dielectric breakdown may occur along the inner surface of the through hole formed in the bonding layer 300 (the portion marked with the reference symbol "301" in FIG. 4B).

The inventors have confirmed through experiments and the like that if the difference between the radius R2 of the opening 141 and the radius R1 of the opening 131 is set to 2.7 mm or less, the occurrence of such dielectric breakdown can be sufficiently prevented. For this reason, it is preferable to not make the radius R2 too large, but to keep it at radius R1 + 2.7 mm or less.

The difference between radius R2 and radius R0 is preferably in the range of 1.6 mm or more and 5.4 mm or less. Also, radius R2 is preferably in the range of 1.75 mm or more and 5.35 mm or less.

The openings 141 and 131 as described above may be formed in the dielectric substrate 100 at positions that overlap with through holes provided for a purpose other than the through holes 151 in a top view. For example, the dielectric substrate 100 may be formed with lift pin holes for inserting lift pins (not shown) provided in a semiconductor manufacturing device. Even if openings 141 and 131 similar to those in this embodiment are formed at positions that overlap with the lift pin holes in a top view, the same effects as those described above can be achieved.

However, the pressure inside the through hole 151, which is a gas supply hole, tends to be in a pressure range where insulation breakdown is relatively likely to occur. For this reason, the effect of applying the shapes of the opening 141 and opening 131 described above is particularly large at the position of the through hole 151.

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 are also included within the scope of the present disclosure as long as they have the features of the present disclosure. The elements of each of the above-mentioned 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 each of the above-mentioned specific examples can be combined in different ways as appropriate, as long as no technical contradictions arise.

W: Substrate 10: Electrostatic chuck 100: Dielectric substrate 110: Surface 130: Adsorption electrode 131: Opening 140: RF electrode 141: Opening 151: Through hole

Claims (3)

a dielectric substrate having a mounting surface on which an object to be attached is placed and having a through hole formed perpendicular to the mounting surface;
an RF electrode embedded within the dielectric substrate;
an attraction electrode embedded inside the dielectric substrate at a position closer to the placement surface than the RF electrode;
When viewed from a direction perpendicular to the placement surface,
a first circular opening is formed in the chucking electrode, the first circular opening being concentric with the through hole and including the through hole;
a second circular opening is formed in the RF electrode and is concentric with and encompasses the through hole;
The electrostatic chuck, wherein the second opening has a larger radius than the first opening. The electrostatic chuck of claim 1, characterized in that the difference between the radius of the second opening and the radius of the first opening is 2.7 mm or less. The electrostatic chuck according to claim 1 or 2, characterized in that the through holes are gas supply holes.