JP7580191B2 - Electrostatic Chuck - Google Patents

Description

The present invention relates to an electrostatic chuck used to electrostatically attract insulating substrates in semiconductor manufacturing processes, etc.

Conventionally, an electrostatic chuck for attracting insulating substrates has been disclosed in which a pair of electrodes are arranged in a linear or circumferential pattern facing each other on the opposite sides of the attracting surface, and are arranged in an alternating intertwined pattern (see, for example, Patent Document 1).

Patent No. 3805134

It is said that exerting Coulomb force and gradient force is effective for electrostatically adsorbing insulating substrates such as glass substrates. In this case, Coulomb force is achieved by electrostatic force between the electrode and the substrate, relying on the slight conductivity of the insulating substrate, while gradient force is achieved when an insulating substrate placed in an electric field formed by a pair of electrodes becomes polarized, and a force acts in the direction of the gradient of the electric field strength. In other words, adsorption by Coulomb force is not possible for substrates with high insulation properties.

In the electrode pattern of the electrostatic chuck for attracting insulating substrates described in Patent Document 1, the electrodes are arranged to effectively exert a gradient force, and the gradient force appears mainly at the space between the pair of electrodes. For example, in the electrode pattern shown in Figure 4 of Patent Document 1, on the x-y plane, a periodic force is exerted along the x-axis along the direction in which the linear patterns of the pair of electrodes face each other, and a uniform force is exerted along the y-axis along the direction in which the linear patterns of the pair of electrodes extend.

When adsorbing and fixing an insulating substrate, it is desirable to uniformly correct the plane of the entire substrate on the adsorption surface and adsorb and fix the substrate without distorting the substrate. However, when a force acts only on a specific area on the adsorption surface, as in the electrostatic chuck of Patent Document 1, there is a problem that the substrate may be adsorbed with a slight localized distortion when adsorbed. In particular, such distortion may be observed when the opposing direction of a pair of electrode patterns is uniform and the opposing pair of electrode patterns is long in a specific direction, as in the electrode patterns of the electrostatic chuck of Patent Document 1.

The present invention was made with a focus on these issues, and aims to provide an electrostatic chuck that can suppress localized distortion of the substrate when it is attracted to the substrate and correct the flatness.

In order to achieve the above object, an electrostatic chuck according to the present invention has an insulating base and a pair of first and second electrodes, the insulating base is plate-shaped and has a mounting surface for mounting an insulating substrate and a back surface opposite to the mounting surface, the first electrode and the second electrode are provided inside or on the back surface of the insulating base so as to electrostatically attract the substrate to the mounting surface, the first electrode has a first main electrode and a plurality of first sub-electrodes, the first main electrode extends in a first direction, each of the first sub-electrodes has a base end and a tip end, is connected to the first main electrode at the base end of the first sub-electrode and extends linearly in a second direction different from the first direction, the second electrode has a second main electrode and a plurality of first sub-electrodes, and a second sub-electrode, the second main electrode extends in a third direction, each second sub-electrode has a base end and a tip end, is connected to the second main electrode at the base end of the second sub-electrode, and extends linearly in the fourth direction different from the third direction, each first sub-electrode and each second sub-electrode has a width of 0.3 to 2.0 mm, each first sub-electrode faces the adjacent second sub-electrode with a space of 0.3 to 2.5 mm in the width direction, the tip end of each first sub-electrode faces the second main electrode with a space of 0.3 to 2.5 mm, and the tip end of each second sub-electrode faces the first main electrode with a space of 0.3 to 2.5 mm, ² ≦W1×L1≦50 ^mm2 and 5 ^mm2 ≦W2×L2 ≦50 ^mm2 are satisfied.

The electrostatic chuck according to the present invention functions by applying a voltage from an external power source to the first electrode and the second electrode. Each first sub-electrode faces the second sub-electrode while being spaced apart in the width direction, and a potential difference is generated between them. By setting the electrode width and the spaced apart distance within the above-mentioned predetermined range, a gradient force can be effectively exerted on the substrate placed on the mounting surface, and the substrate can be electrostatically attracted. In this case, the gradient force is mainly manifested in the spaced apart area in the electrode width direction.

Since the tip of the first sub-electrode faces the second main electrode at the above-mentioned specified distance, a potential difference occurs between the tip of the first sub-electrode and the second main electrode. Also, since the tip of the second sub-electrode faces the first main electrode at the above-mentioned specified distance, a potential difference also occurs between the tip of the second sub-electrode and the first main electrode. As a result, a gradient force is also generated in the regions of the tips of the first sub-electrode and the second sub-electrode.

By setting the product of the width and length of the first sub-electrode and the product of the width and length of the second sub-electrode within the above specified range, the areas of the tips of the first sub-electrode and the second sub-electrode are increased in the plane on which the electrodes are arranged, so that the gradient force can be effectively exerted not only in the areas spaced apart in the width direction of the sub-electrodes but also in the tip areas, making it possible to apply the gradient force more evenly over the entire surface of the substrate.
As a result, local distortion of the substrate during substrate chucking can be suppressed, and the substrate can be electrostatically chucked in a state in which the substrate has been flattened by a uniform force.

In the electrostatic chuck according to the present invention, it is preferable that the first electrode includes a plurality of the first main electrodes, and the second electrode includes a plurality of the second main electrodes.
In this case, it becomes easier to balance the area spaced apart in the width direction of the sub-electrode with the area at the tip, making it less likely that local distortion will occur in the substrate when it is attracted to the substrate, and allowing the substrate to be electrostatically attracted in a more flat and corrected state.

In the electrostatic chuck according to the present invention, it is preferable that the first direction and the third direction are radial directions of the same circle, the second direction and the fourth direction are circumferential directions along the circumference of the same circle, and the first main electrode and the second main electrode are arranged alternately in the circumferential direction.
In this case, the circular mounting surface makes it easier to balance the areas spaced apart in the width direction of the sub-electrode and the area at the tip, making it less likely that local distortion will occur in the substrate when it is attracted to the circular mounting surface, and allowing the substrate to be electrostatically attracted in a more flat and corrected state.

The present invention provides an electrostatic chuck that can suppress localized distortion of a substrate when the substrate is attracted and can correct the flatness.

1A is a plan view showing a schematic configuration of an electrostatic chuck according to an embodiment of the present invention, and FIG. 1B is a vertical sectional view showing the same. FIG. 2 is a plan view showing a part of an electrode pattern of the electrostatic chuck shown in FIG. 1 . 3A is an explanatory diagram showing a preferable example, (B) an unsuitable example 1, and (C) an unsuitable example 2 of the electrode pattern shown in FIG. 2. 1. FIG. 4 is a plan view showing another electrode pattern of the electrostatic chuck shown in FIG. FIG. 1 is a plan view showing a part of an electrode pattern of a conventional electrostatic chuck.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in Fig. 1, an electrostatic chuck according to an embodiment of the present invention has an insulating base 1 and a pair of a first electrode 2 and a second electrode 3. The insulating base 1 is formed by providing an insulating layer 12 on a disk-shaped base 11. The insulating base 1 has a mounting surface 1a for mounting an insulating substrate and a back surface 1b opposite to the mounting surface 1a. The first electrode 2 and the second electrode 3 are connected to a DC power source or an AC power source by terminals 4. The first electrode 2 and the second electrode 3 are provided inside the insulating base 1 or on the back surface 1b so as to electrostatically attract the substrate to the mounting surface 1a.

The first electrode 2 has a plurality of first main electrodes 21 and a plurality of first sub-electrodes 22. The first main electrodes 21 extend linearly in the radial direction (first direction) from the center of a concentric circle along the outer periphery of the disk-shaped insulating base 1. Each first sub-electrode 22 has a base end 22a and a tip end 22b, and is connected to both sides of the width direction of the first main electrode 21 by the base end 22a of the first sub-electrode 22, and extends linearly in a second direction different from the first direction. The second direction is the circumferential direction along the circumference of the same circle that is a concentric circle along the outer periphery of the disk-shaped insulating base 1.

The second electrode 3 has a plurality of second main electrodes 31 and a plurality of second sub-electrodes 32. The second main electrodes 31, like the first main electrodes 21, extend linearly in the radial direction (third direction) from the center of a concentric circle along the outer periphery of the disk-shaped insulating base 1. Each of the first main electrodes 21 and each of the second main electrodes 31 are alternately arranged at equal intervals in the circumferential direction of the same circle.

Each second sub-electrode 32 has a base end 32a and a tip end 32b. Each second sub-electrode 32 is connected to both sides of the second main electrode 31 in the width direction at the base end 32a of the second sub-electrode 32 and extends linearly in a fourth direction different from the third direction. The fourth direction is a circumferential direction along the circumference of a circle that is a concentric circle along the outer periphery of the disk-shaped insulating base 1. Each first sub-electrode 22 and each second sub-electrode 32 are alternately arranged at equal intervals in the radial direction of the circle.

Each of the first sub-electrodes 22 and each of the second sub-electrodes 32 has a width of 0.3 to 2.0 mm. Each of the first sub-electrodes 22 faces the adjacent second sub-electrodes 32 with a widthwise separation of 0.3 to 2.5 mm. Each of the first sub-electrodes 22 faces the second main electrode 31 with a tip 22b spaced apart by 0.3 to 2.5 mm. Each of the second sub-electrodes 32 faces the first main electrode 21 with a tip 32b spaced apart by 0.3 to 2.5 mm. When the width and length of the first sub-electrode 22 are W1 and L1, respectively, and the width and length of the second sub-electrode 32 are W2 and L2, respectively, the following conditions are satisfied: 5 mm ² ≦W1×L1≦50 mm ² and 5 mm ² ≦W2×L2≦50 mm ² .

Next, the operation will be described.
The electrostatic chuck functions by applying a voltage from an external power source to the first electrode 2 and the second electrode 3. Each of the first sub-electrodes 22 faces each of the second sub-electrodes 32 while being spaced apart in the width direction, and a potential difference is generated between them. By setting the electrode width and the spaced apart distance within the above-mentioned predetermined range, a gradient force can be effectively exerted on the substrate placed on the placement surface 1a, and the substrate can be electrostatically attracted. At this time, the gradient force is generated in the spaced area between the first sub-electrode 22 and the second sub-electrode 32.

Since the tip 22b of the first sub-electrode 22 faces the second main electrode 31 at the above-mentioned specified distance, a potential difference occurs between the tip 22b of the first sub-electrode 22 and the second main electrode 31. Furthermore, since the tip 32b of the second sub-electrode 32 faces the first main electrode 21 at the above-mentioned specified distance, a potential difference also occurs between the tip 32b of the second sub-electrode 32 and the first main electrode 21. As a result, a gradient force is also generated in the gap region between the tips 22b, 32b of the first sub-electrode 22 and the second sub-electrode 32 and the first main electrode 21 and the second main electrode 31.

In the formulas 5 mm2 ^≦ W1 × L1 ≦ 50 ^mm2 and 5 mm2 ^≦ W2 × L2 ≦ 50 ^mm2 , when the length L1 of the first sub-electrode 22 or the length L2 of the second sub-electrode 32 is reduced, the number of regions of the tip ends 22b, 32b of the first sub-electrode 22 and the second sub-electrode 32 increases over the entire insulating base 1. As a result, many gradient forces are generated in the separation regions between the tip ends 22b, 32b of each sub-electrode 22, 32 and the first main electrode 21 or the second main electrode 31 facing them on their extension lines, and the electrostatic adsorption force becomes stronger.

However, when the product of the length L1 and width W1 of the first sub-electrode 22 or the product of the length L2 and width W2 of the second sub-electrode 32 (i.e., equivalent to the electrode area) exceeds 50 ^mm2 , the effect of the Coulomb force becomes large while the gradient force becomes relatively small, which is not preferable for adsorption of an insulating substrate.
Furthermore, if the width W1 of the first sub-electrode 22 or the width W2 of the second sub-electrode 32 is too large, the number of separation regions between the adjacent and opposing first sub-electrodes 22 and second sub-electrodes 32 will be reduced over the entire insulating base 1. As a result, the gradient force itself will not work sufficiently, and the substrate will not be able to be electrostatically attracted sufficiently.

Fig. 3A shows a preferred example of an electrostatic chuck according to an embodiment of the present invention. In Fig. 3A to Fig. 3C, a dashed line region 5 indicates a separation region in the width direction between the first and second sub-electrodes 22 and 32, and a dashed line region 6 indicates a separation region between the tips 22b and 32b of the first and second sub-electrodes 22 and 32. As shown in Fig. 3A, by setting the product of the width and length of the first and second sub-electrodes 22 and 32 to the above-mentioned predetermined range, the region of the tips 22b and 32b of the first and second sub-electrodes 22 and 32 is increased on the plane on which the electrodes are arranged, so that the gradient force is effectively exerted not only in the region separated in the width direction of the sub-electrodes 22 and 32 but also in the region of the tips 22b and 32b, and the gradient force can be exerted more uniformly over the entire surface of the substrate.
As a result, local distortion of the substrate during substrate chucking can be suppressed, and the substrate can be electrostatically chucked in a state in which the substrate has been flattened by a uniform force.

In contrast, in the unsuitable example 1 shown in FIG. 3(B), the balance between the widthwise separation area (dashed line area 5) of the first and second sub-electrodes 22 and 32 and the separation area (dashed line area 6) between the tips of the first and second sub-electrodes 22 and 32 and the first and second main electrodes 21 and 31 is poor, so local distortion is likely to occur. In addition, in the unsuitable example 2 shown in FIG. 3(C), the widths of the first and second sub-electrodes 22 and 32 are too wide, so the number of areas where the gradient force acts is reduced, and the electrostatic adsorption force is weak.

In the electrostatic chuck according to the embodiment of the present invention, in particular, the first electrode 2 has a plurality of first main electrodes 21, and the second electrode 3 has a plurality of second main electrodes 31, so that it is easier to balance the separation area between adjacent first and second sub-electrodes 22 and 32 and the area between the tip portions 22b, 32b and the first and second main electrodes 21 and 31, making it difficult for local distortion to occur in the substrate when it is attracted, and the substrate can be electrostatically attracted in a more flat and corrected state.

In addition, the directions in which the first main electrode 21 and the second main electrode 31 extend (first direction, third direction) are radial directions of the same circle, the directions in which the first sub-electrode 22 and the second sub-electrode 32 extend (second direction, fourth direction) are circumferential directions along the circumference of the same circle, and the first main electrode 21 and the second main electrode 31 are arranged alternately in the circumferential direction, so that it is easy to balance the space between the sub-electrodes 22, 32 and the space between the tip portions 22b, 32b and the main electrodes 21, 31 on the circular mounting surface 1a. This makes it difficult for local distortion to occur when the substrate is attracted to the circular mounting surface 1a, and allows the substrate to be electrostatically attracted in a more flat and corrected state.

As shown in FIG. 4, connection lines 23 connecting the plurality of first main electrodes 21 to each other and/or connection lines 33 connecting the plurality of second main electrodes 31 to each other may be provided.
Furthermore, the electrode pattern is not limited to the patterns shown in FIGS. 2 and 4, and may be other patterns.
The first sub-electrode 22 and/or the second sub-electrode 32 may be in a straight line, a bent shape, or a branched shape in addition to the arc shape.
Regardless of their shapes, the first main electrode 21, the second main electrode 31, the first sub-electrode 22 and the second sub-electrode 32 are preferably arranged approximately evenly in approximately the same area as the mounting surface 1a.

(Manufacturing method using green sheet molding)
For example, an electrostatic chuck was produced by the ceramic green sheet molding method disclosed in Japanese Patent Application Laid-Open No. 2008-147549.
The ceramic green sheet is preferably composed mainly of Al ₂ O ₃ and AlN. In this embodiment, Al ₂ O ₃ with a purity of 99.5% was used as the raw material powder. The Al ₂ O ₃ , binder, plasticizer, dispersant, and solvent were mixed to form a slurry, and the green sheet was formed using a doctor blade. The thickness of the green sheet to be formed is preferably 0.5 to 2 mm. In this embodiment, the thickness was 0.65 mm.

A pair of layered electrodes was formed by printing a W (tungsten) paste on a ceramic green sheet using a screen mask. The design of the screen mask was appropriately adjusted so that the printed pattern would be the pattern shown in FIG.
For comparison, a printed electrode pattern of the conventional example was also produced, as shown in Fig. 5. The conventional electrode pattern has a first main electrode 41 and a second main electrode 51 extending radially in opposite directions from the center of the circle, and has a shape in which first sub-electrodes 42 and second sub-electrodes 52 each having an arc shape formed by cutting out a portion of a plurality of concentric circles with a common center are alternately connected to the first main electrode 41 and the second main electrode 51.

The prepared ceramic green sheet was laminated with other ceramic green sheets (including via holes filled with W paste as via conductors) so that a pair of electrodes was sandwiched between the two ceramic green sheets to form a laminate. If necessary, blind holes were machined on the back surface of the laminate to insert terminals that conduct with the electrodes through the via conductors, and W paste was applied to the surface that defines the holes. Then, the laminate was fired at 1600°C for 3 hours in a reducing atmosphere to obtain a ceramic sintered body. Then, the outer shape was machined.
A terminal (made of Kovar) for connecting to an external power source was inserted into a blind hole on the back surface of the ceramic sintered body, and the electrode and the terminal were joined by silver brazing to complete an electrostatic chuck. At this time, the center line diameter of the outermost periphery of the electrode pattern of the electrostatic chuck was 300 mm, the thickness of the insulating layer was 0.1 mm, and the surface roughness Ra of the mounting surface was 0.1 μm.

In the electrode pattern of the conventional example, the sub-electrode 42 branches off from the main electrode 41 that extends in the 12 o'clock direction. Also, the sub-electrode 52 branches off from the main electrode 51 that extends in the 6 o'clock direction on the opposite side of the main electrode 41. The length of the sub-electrodes 42, 52 is approximately 1/2 the circumference. The gradient force is mainly manifested in the space between the electrodes. Therefore, the gradient force is periodically unevenly distributed in the radial direction.

In this embodiment, twelve first main electrodes 21 and twelve second main electrodes 31 extending in the radial direction from the center of the circle are arranged alternately in the circumferential direction. The first sub-electrodes 22 and the second sub-electrodes 32 extend from the first main electrode 21 and the second main electrode 31 on both sides along the circumference of a plurality of concentric circles with a common center, and are arranged alternately at equal intervals in the radial direction of the same circle. The patterns of the first sub-electrodes 22 and the second sub-electrodes 32 are arc-shaped, each of which is obtained by dividing a plurality of concentric circles into 24. The sub-electrodes 22 and 32 branch out in the circumferential direction from the main electrodes 21 and 31 extending in the radial direction. The length of the sub-electrodes 22 and 32 is approximately the length of the arc obtained by dividing the circumference into 24. The gradient force is mainly manifested in the space between the electrodes.

In the electrode pattern of this embodiment shown in FIG. 2, the length L from the branched position (base end 22a, 32a) of the sub-electrodes 22, 32 to one tip 22b, 32b is shorter than in the conventional electrode pattern shown in FIG. 5, and the number of one tip 22b, 32b of the sub-electrodes 22, 32 is increased. One tip 22b, 32b of the sub-electrodes 22, 32 is surrounded by the opposing electrode, and the electric field of the tip 22b, 32b of the sub-electrodes 22, 32 is formed mainly between the opposing electrode (second main electrode 31, first main electrode 21) existing on the extension line of the tip of the sub-electrode, and a gradient force is generated.

By satisfying the formulas 5 ^mm2 ≦ W1 × L1 ≦ 50 ^mm2 and 5 mm2 ^≦ W2 × L2 ≦ 50 ^mm2 , it is possible to increase the number of separation points between the tips 22b, 32b of the sub-electrodes 22, 32 and the opposing electrodes (second main electrode 31, first main electrode 21) that exist on the extension lines of the tips of the sub-electrodes. This makes it possible to make the points where the gradient force is exerted more uniform than before, and as a result, it becomes possible to adsorb the insulating substrate with less distortion.

(evaluation)
For the electrostatic chuck of this embodiment and the electrostatic chuck of the conventional example, a DC voltage of ±3 kV was applied to a pair of terminals, and an alkali-free glass substrate (diameter 300 mm, thickness 0.7 mm) was electrostatically attracted to the electrostatic chuck, and the results were observed.
The following Examples 1 to 10 and Comparative Examples 1 to 7 are the results of evaluations performed by changing the sub-electrode length L and the sub-electrode width W. The sub-electrode lengths in the table below are the longest in the pattern.

As shown in Table 1, when the product of the sub-electrode length L and the sub-electrode width W is 50 ^mm2 or less, the flatness of the electrostatically attracted substrate is less than 3 μm, which indicates that the local flatness of the substrate is improved.
In addition, in Comparative Example 4, the chucking force was small, and in Comparative Example 5, poor insulation occurred between the electrodes, so that correction of flatness could not be performed, and therefore flatness measurement could not be performed.

REFERENCE SIGNS LIST 1 insulating base 2 first electrode 3 second electrode 11 base 12 insulating layer 1a mounting surface 1b back surface 4 terminal 21 first main electrode 22 first sub-electrode 22a base end 22b tip 31 second main electrode 32 second sub-electrode 32a base end 32b tip

Claims (3)

An electrostatic chuck comprising an insulating base and a pair of first and second electrodes, the insulating base being plate-shaped and having a mounting surface for mounting an insulating substrate thereon and a back surface opposite to the mounting surface, the first electrode and the second electrode being provided inside the insulating base or on the back surface so as to electrostatically attract the substrate to the mounting surface,
The first electrode includes a first main electrode and a plurality of first sub-electrodes, the first main electrode extends in a first direction, each of the first sub-electrodes has a base end and a tip end, is connected to the first main electrode at the base end of the first sub-electrode, and extends linearly in a second direction different from the first direction,
the second electrode has a second main electrode and a plurality of second sub-electrodes, the second main electrode extends in a third direction, each of the second sub-electrodes has a base end and a tip end, is connected to the second main electrode at the base end of the second sub-electrode, and extends linearly in a fourth direction different from the third direction;
Each of the first sub-electrodes and each of the second sub-electrodes has a width of 0.3 to 2.0 mm;
Each of the first sub-electrodes faces the adjacent second sub-electrode at a distance of 0.3 to 2.5 mm in the width direction, and a tip of each of the first sub-electrodes faces the second main electrode at a distance of 0.3 to 2.5 mm,
A tip of each of the second sub-electrodes faces the first main electrode with a distance of 0.3 to 2.5 mm therebetween;
When the width and length of the first sub-electrode are W1 and L1, respectively, and the width and length of the second sub-electrode are W2 and L2, the following conditions are satisfied: 6.9 mm ² ≦W1×L1≦50 mm ² and 6.9 mm ² ≦W2×L2≦50 mm ² ;
The L1 and L2 satisfy 12.6 mm≦L1≦23.1 mm and 12.6 mm≦L2≦23.1 mm, respectively;
The electrostatic chuck is characterized in that the mounting surface has an area equivalent to or larger than an area of a substrate having a diameter of 300 mm . The electrostatic chuck according to claim 1, characterized in that the first electrode has a plurality of the first main electrodes, and the second electrode has a plurality of the second main electrodes. 3. The electrostatic chuck according to claim 2, wherein the first direction and the third direction are radial directions of a same circle, the second direction and the fourth direction are circumferential directions along the circumference of the same circle, and the first main electrodes and the second main electrodes are arranged alternately in the circumferential direction.

Images