Electrostatic chuck

Abstract

To provide an electrostatic chuck which can keep an appropriate in-plane temperature distribution of a substrate during a process.SOLUTION: An electrostatic chuck 10 includes a dielectric substrate 100, a base plate 200 which supports the dielectric substrate 100, and a joining layer 300 which joins the dielectric substrate 100 and the base plate 200. A value of a dielectric tangent of the joining layer 300 when a temperature of the joining layer 300 is 20°C is set as a reference value. In the electrostatic chuck 10, when the temperature of the joining layer 300 changes from 20°C to -60°C, the range in which the value of the dielectric tangent of the joining layer 300 fluctuates falls within the range from 50% to 200% of the reference value.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] For example, in semiconductor manufacturing equipment such as an etching device, an electrostatic chuck is provided as a device for attracting and holding a substrate such as a silicon wafer to be processed. As described in Patent Document 1 below, an electrostatic chuck includes a dielectric substrate (base material) provided with an attraction electrode and a base plate (base portion) for supporting the dielectric substrate, which are joined together. When a voltage is applied to the attraction electrode, an electrostatic force is generated, and a substrate placed on the dielectric substrate is attracted and held.

[0003] During processing such as etching, it is necessary to maintain the temperature of each part of the substrate at an appropriate temperature. To ensure an appropriate in-plane temperature distribution of the substrate during processing, the configuration of each part of the electrostatic chuck, such as the layout of the coolant flow passage formed inside the base plate and the arrangement of gas holes for supplying gas to the back side of the substrate, is appropriately designed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2015-162490 A Summary of the Invention [Problem to be solved by the invention]

[0005] When generating plasma in a semiconductor manufacturing device, a high-frequency voltage is applied between a pair of electrodes. This applies an AC electric field to each part of the electrostatic chuck. The above-mentioned Patent Document 1 shows a configuration example in which a part of the electrostatic chuck (e.g., a base plate) is used as one of the electrodes. In particular, in such a configuration, the AC electric field applied to each part of the electrostatic chuck becomes large.

[0006] The present inventors have found that when the temperature of the bonding layer changes depending on the operating conditions of the semiconductor manufacturing equipment, the dielectric tangent value of the bonding layer also changes accordingly. When the dielectric tangent value changes, the amount of heat generated by the bonding layer due to the application of an AC electric field also changes, and the in-plane temperature distribution of the substrate is affected by this.

[0007] As described above, in the electrostatic chuck, the layout of the coolant flow path and the like are appropriately designed so that the in-plane temperature distribution of the substrate during processing is appropriate. However, if the amount of heat generated by the bonding layer changes significantly due to a change in the operating conditions, etc., the design premise is lost, and it may become impossible to maintain the in-plane temperature distribution of the substrate appropriately.

[0008] The present invention has been made in view of the above problems, and an object of the present invention is to provide an electrostatic chuck capable of maintaining an appropriate in-plane temperature distribution of a substrate during processing. [Means for solving the problem]

[0009] In order to solve the above problems, an electrostatic chuck according to the present invention includes a dielectric substrate, a base plate that supports the dielectric substrate, and a bonding layer that bonds between the dielectric substrate and the base plate. When the value of the dielectric tangent of the bonding layer when the temperature of the bonding layer is 20° C. is taken as a reference value, in this electrostatic chuck, when the temperature of the bonding layer changes from 20° C. to −60° C., the range in which the value of the dielectric tangent of the bonding layer varies falls within a range of 50% to 200% of the reference value.

[0010] In an electrostatic chuck having such a configuration, the variation in the dielectric tangent value during the temperature change of the bonding layer from 20° C. to −60° C. is within a range of 50% to 200% of the reference value. Even if the temperature of the bonding layer changes, the variation in the amount of heat generated by the bonding layer is suppressed to a smaller value than in the past, so that the in-plane temperature distribution of the substrate can be maintained appropriately. Effect of the Invention

[0011] According to the present invention, it is possible to provide an electrostatic chuck capable of appropriately maintaining the in-plane temperature distribution of a substrate during processing. [Brief description of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view illustrating a schematic configuration of an electrostatic chuck according to an embodiment of the present invention. [Diagram 2] FIG. 13 is a diagram showing the relationship between the temperature and the dielectric tangent of the bonding layer. [Diagram 3] FIG. 4 is a diagram showing the relationship between the temperature and the relative dielectric constant of the bonding layer. [Figure 4] FIG. 13 is a diagram showing the relationship between the temperature of the bonding layer and the rate of variation of the dielectric tangent. [Diagram 5] FIG. 4 is a diagram showing the relationship between the temperature and the relative dielectric constant of the bonding layer. [Figure 6] FIG. 4 is a diagram showing the relationship between the temperature and the volume resistivity of the bonding layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, the present embodiment will be described with reference to the accompanying drawings. In order to facilitate understanding of the description, the same components in each drawing are denoted by the same reference numerals as much as possible, and duplicated description will be omitted.

[0014] 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 be used in an apparatus other than a semiconductor manufacturing apparatus.

[0015] 1 shows, in a schematic cross-sectional view, the configuration of an electrostatic chuck 10 in a state in which the electrostatic chuck 10 attracts and holds a substrate W. The electrostatic chuck 10 includes a dielectric substrate 100 and a base plate 200.

[0016] The dielectric substrate 100 is a substantially disk-shaped member made of a sintered ceramic body. The dielectric substrate 100 is made of, 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, etc. required for the dielectric substrate 100 in the semiconductor manufacturing equipment.

[0017] 1 of the dielectric substrate 100 is a "mounting surface" on which the substrate W is placed. Also, a lower surface 120 of the dielectric substrate 100 in FIG. 1 is a "joined surface" that is joined to the base plate 200 via a joining layer 300. The viewpoint when the electrostatic chuck 10 is viewed from the side of the surface 110 along a direction perpendicular to the surface 110 will hereinafter be referred to as a "top view".

[0018] 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 molybdenum, platinum, palladium, or the like, in addition to tungsten. When a voltage is applied to the adsorption 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 adsorbing and holding the substrate W. As the configuration of the power supply path, various known configurations can be adopted. The adsorption electrode 130 may be provided as a so-called "monopolar" electrode as in this embodiment, or may be provided as two so-called "bipolar" electrodes.

[0019] 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 apparatus, helium gas for temperature adjustment is supplied from the outside to the space SP 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, and the temperature of the substrate W is thereby maintained at an appropriate temperature. The temperature adjustment gas supplied to the space SP may be a type of gas other than helium.

[0020] A seal ring 111 and dots 112 are provided on a surface 110 serving as a mounting surface, and the above-mentioned space SP is formed around these.

[0021] 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 a plurality of 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.

[0022] 1, the portion marked with the reference symbol "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 part of the surface 110 to the position of the bottom surface 116.

[0023] The dots 112 are circular protrusions protruding 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 abuts against the substrate W. By providing a plurality of such dots 112, bending of the substrate W is suppressed.

[0024] 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 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.

[0025] 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 hardening an adhesive made of an insulating material. Examples of the adhesive that can be used include a silicone adhesive, an epoxy adhesive, and a polyimide adhesive. The bonding layer 300 may be formed by hardening another type of adhesive. In any 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 that the thermal resistance between the dielectric substrate 100 and the base plate 200 is small.

[0026] In this embodiment, an electrostatic chuck 10 using a silicone adhesive as the bonding layer 300 and an electrostatic chuck 10 using a polyimide adhesive are manufactured. Of the respective embodiments, the electrostatic chuck 10 having the bonding layer 300 made of a silicone adhesive is also referred to as "Present Embodiment 1" below. The electrostatic chuck 10 having the bonding layer 300 made of a polyimide adhesive is also referred to as "Present Embodiment 2" below.

[0027] An insulating film may be formed on the surface of the base plate 200. For example, an alumina film formed by thermal spraying can be used as the insulating film. By covering the surface of the base plate 200 with the insulating film, the dielectric strength of the base plate 200 can be increased.

[0028] 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 apparatus, 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 discharged to the outside together with the coolant.

[0029] Meanwhile, when a process such as etching is performed in a semiconductor manufacturing apparatus, it is necessary to keep the temperature of each part of the substrate W at an appropriate temperature. In an electrostatic chuck, the configuration of each part is generally designed appropriately so that the in-plane temperature distribution of the substrate W during processing is appropriate. The above-mentioned "configuration" that may affect the in-plane temperature distribution of the substrate W includes, for example, the routing of the coolant flow path 250 formed inside the base plate 200, the arrangement of gas holes (not shown) for supplying gas to the space SP, the shape and arrangement of the dots 112 and the seal ring 111 in the dielectric substrate 100, and the like. In addition, when a heater for heating the dielectric substrate 100 is provided in the electrostatic chuck 10, the performance and arrangement of the heater may also be included in the above-mentioned "configuration".

[0030] When generating plasma in a semiconductor manufacturing apparatus, a high-frequency voltage is applied between a pair of electrodes. As a result, an AC electric field is applied to each part of the electrostatic chuck 10. For example, one of the electrodes is disposed at a position above the substrate W (opposite the electrostatic chuck 10). The other electrode is often the base plate 200, but a member other than the base plate 200 may also be used. In either case, a relatively large AC electric field is applied to each member such as the bonding layer 300 constituting the electrostatic chuck 10.

[0031] When an AC electric field is applied to the bonding layer 300, part of the energy of the AC electric field is converted into heat, increasing the temperature of the bonding layer 300. In order to confirm the effect of such an AC electric field, the present inventors investigated the dielectric loss tangent of the material constituting the bonding layer 300.

[0032] The results of the investigation will be described below. An example of the relationship between the temperature of the bonding layer 300 (horizontal axis) and the dielectric tangent value of the bonding layer 300 (vertical axis) is shown in Fig. 2 and Fig. 3.

[0033] 2, the data plotted with triangular dots are the results obtained by forming the bonding layer 300 using a general silicone adhesive and measuring the dielectric tangent value of the bonding layer 300 at each temperature, and are shown as "Comparative Examples" of this embodiment. Each data was measured in a state where an AC electric field of 400 KHz was applied to the bonding layer 300.

[0034] In this comparative example, it was confirmed that the value of the dielectric tangent of the bonding layer 300 changes as the temperature of the bonding layer 300 is lowered from 20°C. The value of the dielectric tangent of the bonding layer 300 when the bonding layer 300 is at 20°C is also referred to as the "reference value" below. In this comparative example, as the temperature of the bonding layer 300 is lowered from 20°C, the value of the dielectric tangent of the bonding layer 300 decreases from the reference value (0.0006 in this comparative example). When the temperature of the bonding layer 300 falls below -40°C, the value of the dielectric tangent increases rapidly, and when the temperature reaches -60°C, the value of the dielectric tangent increases to about 220% of the reference value.

[0035] Thus, it was found that when the temperature of the bonding layer 300 changes, the value of the dielectric tangent of the bonding layer 300 also changes accordingly. When the value of the dielectric tangent changes, the amount of heat generated by the bonding layer 300 due to the application of an AC electric field also changes, and this affects the in-plane temperature distribution of the substrate W. When the value of the dielectric tangent exceeds 200% of the reference value, the effect on the temperature of the substrate W becomes too large to be ignored.

[0036] As described above, in the electrostatic chuck 10, the layout of the coolant flow passage 250 and the like are appropriately designed so as to maintain an appropriate in-plane temperature distribution of the substrate W during processing. However, for example, if the amount of heat generated by the bonding layer 300 changes significantly due to a change in the operating conditions of the semiconductor manufacturing device, the design premise is lost, and it may become impossible to maintain an appropriate in-plane temperature distribution of the substrate W.

[0037] 5 shows an example of the results of measuring the relationship between temperature (horizontal axis) and relative dielectric constant (vertical axis) for each of the bonding layer 300 according to the first embodiment, the bonding layer 300 according to the second embodiment, and the bonding layer 300 according to the comparative example. The relative dielectric constant was measured in a state where an AC electric field of 400 KHz was applied to the bonding layer 300.

[0038] 6 shows an example of the results of measuring the relationship between temperature (horizontal axis) and volume resistivity (vertical axis) for the bonding layer 300 according to the first embodiment and the bonding layer 300 according to the comparative example. The vertical axis in FIG. 6 is a logarithmic axis.

[0039] As shown in these figures, when the temperature of the bonding layer 300 changes, the dielectric constant and the volume resistivity also change significantly. Such variations in various physical properties make it more difficult to design the electrostatic chuck 10 to provide an appropriate in-plane temperature distribution of the substrate W. In order to design the electrostatic chuck 10 so as to provide an appropriate cooling performance under various operating conditions of the semiconductor manufacturing equipment, it is preferable to minimize the number of physical properties that change with temperature.

[0040] Therefore, the present inventors have attempted to suppress the temperature dependency of the dielectric tangent of the bonding layer 300 of this embodiment by, for example, appropriately selecting the adhesive, which is the material of the bonding layer 300. Each piece of data plotted with circular dots in Fig. 2 indicates the result of measuring (or calculating by simulation) the value of the dielectric tangent at each temperature for a sample cut out from the bonding layer 300 of this embodiment 1. Each piece of data was measured or otherwise obtained in a state where an AC electric field of 400 KHz was applied to the bonding layer 300, as in the above comparative example.

[0041] The value of the dielectric tangent when the bonding layer 300 was at 20° C., i.e., the “reference value”, was 0.0007 in the present embodiment 1. In the electrostatic chuck 10 according to the present embodiment 1, even when the temperature of the bonding layer 300 was changed from 20° C. to −60° C., almost no fluctuation in the value of the dielectric tangent was observed during the change, and the value was maintained approximately equal to the reference value.

[0042] 3, each piece of data plotted with circular dots indicates the result of measuring (or calculating by simulation) the value of the dielectric tangent at each temperature for a sample cut out from the bonding layer 300 of the present embodiment 2. Each piece of data was measured or otherwise obtained in a state where an AC electric field of 400 KHz was applied to the bonding layer 300, similar to each piece of data shown in FIG.

[0043] In the present embodiment 2, the value of the dielectric tangent when the bonding layer 300 is at 20° C., i.e., the “reference value”, is 0.0081. When the bonding layer 300 is at −40° C., the value of the dielectric tangent is 0.0086, and when the bonding layer 300 is at −60° C., the value of the dielectric tangent is 0.0076. Thus, in the electrostatic chuck 10 according to the present embodiment 2, even when the temperature of the bonding layer 300 is changed from 20° C. to −60° C., the change in the value of the dielectric tangent during the change is relatively small, and the value is maintained approximately equal to the reference value.

[0044] 4 shows how the dielectric tangent of the bonding layer 300 in each sample changes from the reference value as the temperature decreases. The vertical axis of the figure shows the variation in the dielectric tangent value expressed as a percentage, i.e., the rate of variation, with the dielectric tangent value at 20°C (i.e., the reference value) being taken as 100%.

[0045] As mentioned above, in the comparative example, the dielectric tangent value increases rapidly when the temperature of the bonding layer 300 falls below -40°C, and when the temperature reaches -60°C, the dielectric tangent value increases to approximately 220% of the reference value.

[0046] On the other hand, in this embodiment 1 (silicone adhesive), even when the temperature of the bonding layer 300 changed from 20°C to -60°C, the fluctuation in the dielectric tangent value of the bonding layer 300 was kept so small that it could not be observed, and remained approximately at 100% of the reference value.

[0047] Furthermore, in the present embodiment 2 (epoxy adhesive), when the temperature of the bonding layer 300 changed from 20° C. to −40° C., the value of the dielectric tangent of the bonding layer 300 increased to about 106% of the reference value. After that, when the temperature of the bonding layer 300 changed to −60° C., the value of the dielectric tangent of the bonding layer 300 decreased to about 94% of the reference value. Thus, in the bonding layer 300 according to the present embodiment 2, the fluctuation of the value of the dielectric tangent was within the range of 94% to 106% of the reference value.

[0048] As described above, in the electrostatic chuck 10 according to the first and second embodiments, the fluctuation in the value of the dielectric tangent of the bonding layer 300 caused by the change in temperature is suppressed to a smaller value than in the conventional case. Even if the temperature of the bonding layer 300 during the processing of the substrate W changes due to a change in the operating conditions of the semiconductor manufacturing apparatus or the like, the value of the dielectric tangent of the bonding layer 300 is maintained at a value approximately close to the reference value. Since the amount of heat generated in the bonding layer 300 is almost the same as before the change in the operating conditions, the cooling performance of the electrostatic chuck 10 is exhibited as originally designed, and the in-plane temperature distribution of the substrate W is appropriately maintained.

[0049] It is preferable that the change in the dielectric tangent value of the bonding layer 300 is within a range of at least 50% to 200% of the reference value when the temperature of the bonding layer 300 changes from 20° C. to −60° C. If the change in the dielectric tangent value is suppressed to the above level, the change in the amount of heat generated by the bonding layer 300 can be suppressed to a smaller value than before, so that the in-plane temperature distribution of the substrate W can be maintained appropriately.

[0050] It is more preferable that the variation in the dielectric tangent value when the temperature of the bonding layer 300 changes from 20° C. to −60° C. falls within a range of 90% to 110% of the reference value as in the first and second embodiments. If the variation in the dielectric tangent value is limited to within a range of ±10% of the reference value, the variation in the amount of heat generated by the bonding layer 300 can be kept negligibly small.

[0051] It is preferable that the value of the dielectric tangent when the temperature of the bonding layer 300 changes from 20° C. to −60° C. is always smaller than 0.0008 as in the present embodiment 1. With this configuration, not only the fluctuation range of the amount of heat generated by the bonding layer 300 during processing but also the absolute value of the amount of heat generated can be kept sufficiently small.

[0052] It is preferable to select an adhesive for use in the bonding layer 300 such that the variation in the dielectric tangent value when the temperature is decreased falls within the above range. In addition, by adding a filler to an existing adhesive, it is also possible to keep the variation in the dielectric tangent value when the temperature is decreased within the above range. For example, by adding an inorganic material such as alumina as a filler, the variation range of the dielectric tangent value can be adjusted. In this case, it has been found that the more the amount of filler added, the smaller the dielectric tangent value becomes, and the smaller the change in the dielectric tangent at low temperatures becomes. However, if the filler is poorly dispersed and aggregates, the dielectric tangent value may increase conversely, so it is necessary to add the filler while taking care not to aggregate.

[0053] The present embodiment has been described above with reference to specific examples. However, the present disclosure is not limited to these specific examples. Any design modifications made by a person skilled in the art to these specific examples 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 and their arrangements, conditions, shapes, etc. are not limited to those exemplified and can be changed as appropriate. The combination of each of the elements of each of the above-mentioned specific examples can be changed as appropriate as long as no technical contradiction occurs. [Explanation of symbols]

[0054] 10: Electrostatic chuck 100: Dielectric substrate 200: Base plate 300: Bonding layer

Claims

1. A dielectric substrate; A base plate supporting the dielectric substrate; a bonding layer that bonds the dielectric substrate and the base plate, When the value of the dielectric tangent of the bonding layer when the temperature of the bonding layer is 20° C. is taken as a reference value, When the temperature of the bonding layer changes from 20° C. to −60° C., the range in which the dielectric tangent value of the bonding layer fluctuates falls within a range from 50% to 200% of the reference value.

2. 2. The electrostatic chuck according to claim 1, wherein when the temperature of the bonding layer changes from 20° C. to −60° C., a range in which a value of the dielectric tangent of the bonding layer fluctuates falls within a range from 90% to 110% of the reference value.

3. 2. The electrostatic chuck according to claim 1, wherein when the temperature of the bonding layer is within a range of 20° C. to −60° C., a value of the dielectric tangent of the bonding layer is smaller than 0.0008.

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