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 Art

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

[0003] During processing such as etching, it is necessary to keep the temperature of each part of the substrate at an appropriate temperature. In order to make the in-plane temperature distribution of the substrate during processing appropriate, for example, the layout of the refrigerant flow path formed inside the base plate and the arrangement of the gas holes for supplying gas to the back surface side of the substrate, etc., the configuration of each part of the electrostatic chuck is appropriately designed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When generating plasma in a semiconductor manufacturing apparatus, a high-frequency voltage is applied between a pair of electrodes. As a result, an alternating electric field is applied to each part of the electrostatic chuck. Patent Document 1 above shows a configuration example in the case where a part of the electrostatic chuck (for example, the base plate) is used as one of the electrodes. In particular, in such a configuration, the alternating electric field applied to each part of the electrostatic chuck becomes large.

[0006] The inventors have obtained new findings that when the temperature of the bonding layer changes according to the operating conditions of the semiconductor manufacturing apparatus or the like, the value of the dielectric tangent of the bonding layer also changes accordingly. When the value of the dielectric tangent changes, the amount of heat generated in the bonding layer due to the application of an alternating electric field also changes, so the in-plane temperature distribution of the substrate is affected by this.

[0007] As described above, in an electrostatic chuck, the routing of the refrigerant flow path and the like are appropriately designed so that the in-plane temperature distribution of the substrate during processing becomes appropriate. However, if the amount of heat generated in the bonding layer changes significantly due to a change in operating conditions or the like, the premise of the design is broken, so there may be a case where the in-plane temperature distribution of the substrate cannot be maintained appropriately.

[0008] The present invention has been made in view of such problems, and an object thereof is to provide an electrostatic chuck capable of appropriately maintaining the in-plane temperature distribution of a substrate during processing.

Means for Solving the Problems

[0009] In order to solve the above problems, the 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 at a temperature of 20°C of the bonding layer is used 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 fluctuates falls within the range from 50% to 200% of the reference value.

[0010] In the electrostatic chuck having such a configuration, even when the temperature of the bonding layer changes from 20°C to -60°C, the fluctuation of the value of the dielectric tangent during that time is configured to fall within the range from 50% to 200% of the reference value. Even when the temperature of the bonding layer changes, the fluctuation of the amount of heat generated in the bonding layer can be suppressed to be smaller than before, so the in-plane temperature distribution of the substrate can continue to be maintained appropriately.

Effects 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

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0013] Hereinafter, the present embodiment will be described with reference to the accompanying drawings. For ease of understanding the description, the same reference numerals are attached to the same components in each drawing as much as possible, and duplicate descriptions are omitted.

[0014] The electrostatic chuck 10 according to the present embodiment adsorbs and holds a substrate W to be processed by electrostatic force inside a semiconductor manufacturing apparatus (not shown) such as an etching apparatus. The substrate W to be adsorbed is, for example, a silicon wafer. The electrostatic chuck 10 may be used in an apparatus other than a semiconductor manufacturing apparatus.

[0015] FIG. 1 shows, as a schematic cross-sectional view, the configuration of the electrostatic chuck 10 in a state where the substrate W is adsorbed and held. 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 ceramic sintered 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, additives, etc. of the ceramics in the dielectric substrate 100 can be appropriately set in consideration of the plasma resistance required for the dielectric substrate 100 in a semiconductor manufacturing apparatus.

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

[0018] An adsorption electrode 130 is embedded inside the dielectric substrate 100. The adsorption electrode 130 is a thin flat plate-shaped layer formed of a metal material such as tungsten, for example, and is arranged to be parallel to the surface 110. As the material of the adsorption electrode 130, in addition to tungsten, molybdenum, platinum, palladium, etc. may be used. When a voltage is applied to the adsorption electrode 130 from the outside through a power supply path (not shown), an electrostatic force is generated between the surface 110 and the substrate W, and thereby the substrate W is adsorbed and held. As the configuration of the above power supply path, various known configurations can be adopted. The adsorption electrode 130 may be provided only one as a so-called "unipolar" electrode as in the present embodiment, or may be provided two as a so-called "bipolar" electrode.

[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 interposing helium gas between the dielectric substrate 100 and the substrate W, the thermal resistance between the two is adjusted, and thereby the temperature of the substrate W is maintained at an appropriate temperature. Note that the gas for temperature adjustment supplied to the space SP may be a gas of a type different from helium.

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

[0021] The seal ring 111 is a wall that partitions the space SP at the outermost peripheral position. The upper end of the seal ring 111 is a part of the surface 110 and abuts on the substrate W. Note that a plurality of seal rings 111 may be provided so as to divide the space SP. With such a configuration, the pressure of the helium gas in each space SP can be individually adjusted, and the surface temperature distribution of the substrate W during processing can be made closer to uniform.

[0022] The portion labeled with reference numeral “116” in FIG. 1 is the bottom surface of the space SP. Hereinafter, this portion is also 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 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 arranged substantially evenly and dispersedly on the mounting surface of the dielectric substrate 100. The upper end of each dot 112 is a part of the surface 110 and abuts on the substrate W. By providing a plurality of such dots 112, the deflection 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, for example. Among the surfaces of the base plate 200, the upper surface 210 in FIG. 1 serves as a "surface to be joined" that is joined to the dielectric substrate 100 via the joining layer 300.

[0025] The joining layer 300 is a layer provided between the dielectric substrate 100 and the base plate 200 and joins the two. The joining layer 300 is obtained by curing an adhesive made of an insulating material. As the above-mentioned adhesive, for example, a silicone-based adhesive, an epoxy-based adhesive, a polyimide-based adhesive, or the like can be used. The joining layer 300 may be obtained by curing other types of adhesives. In any case, as the material of the joining layer 300, it is preferable to use a material with as high a thermal conductivity as possible so that the thermal resistance between the dielectric substrate 100 and the base plate 200 is reduced.

[0026] In this embodiment, an electrostatic chuck 10 using a silicone adhesive as the joining layer 300 and an electrostatic chuck 10 using a polyimide-based adhesive are each manufactured. Among the respective embodiments, the electrostatic chuck 10 provided with the joining layer 300 made of a silicone adhesive is hereinafter also referred to as "Embodiment 1". The electrostatic chuck 10 provided with the joining layer 300 made of a polyimide-based adhesive is hereinafter also referred to as "Embodiment 2".

[0027] An insulating film may be formed on the surface of the base plate 200. As the insulating film, for example, an alumina film formed by spraying can be used. By covering the surface of the base plate 200 with an insulating film, the dielectric breakdown voltage of the base plate 200 can be increased.

[0028] Inside the base plate 200, a refrigerant flow path 250 for passing refrigerant is formed. When a process such as etching is performed in the semiconductor manufacturing apparatus, refrigerant is supplied from the outside to the refrigerant flow path 250, and thereby the base plate 200 is cooled. The heat generated in the substrate W during the process is transmitted to the refrigerant through 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 refrigerant.

[0029] By the way, when a process such as etching is being performed in the semiconductor manufacturing apparatus, it is necessary to keep the temperature of each part of the substrate W at an appropriate temperature. In general, in the electrostatic chuck, the configuration of each part is appropriately designed so that the in-plane temperature distribution of the substrate W during the process becomes appropriate. The above-mentioned "configuration" that can affect the in-plane temperature distribution of the substrate W includes, for example, the routing of the refrigerant 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. Further, 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 the semiconductor manufacturing apparatus, a high-frequency voltage is applied between a pair of electrodes. As a result, an alternating electric field is applied to each part of the electrostatic chuck 10. For example, one of the above electrodes is arranged at a position above the substrate W (opposite to the electrostatic chuck 10). As the other of the above electrodes, the base plate 200 is often used, but a member other than the base plate 200 may be used. In any case, a relatively large alternating electric field is applied to each member such as the bonding layer 300 constituting the electrostatic chuck 10.

[0031] When an alternating electric field is applied to the bonding layer 300, a part of the energy of the alternating electric field changes to heat and raises the temperature of the bonding layer 300. In order to confirm the influence of such an alternating electric field, the present inventors investigated the dielectric tangent of the material constituting the bonding layer 300.

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

[0033] Each data plotted as triangular dots in FIG. 2 shows the results obtained by forming the bonding layer 300 using a general silicone adhesive and measuring the value of the dielectric loss tangent of the bonding layer 300 at each temperature, as the "comparative example" of the present embodiment. Each data was measured with an AC electric field of 400 KHz applied to the bonding layer 300.

[0034] In this comparative example, it was confirmed that as the temperature of the bonding layer 300 was decreased from 20°C, the value of the dielectric loss tangent of the bonding layer 300 fluctuated accordingly. The value of the dielectric loss tangent of the bonding layer 300 when the bonding layer 300 is at 20°C is also referred to as the "reference value" hereinafter. In this comparative example, as the temperature of the bonding layer 300 decreased from 20°C, the value of the dielectric loss tangent of the bonding layer 300 decreased from the reference value (0.0006 in this comparative example). When the temperature of the bonding layer 300 dropped below -40°C, the value of the dielectric loss tangent increased rapidly, and when the temperature reached -60°C, the value of the dielectric loss tangent increased 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 loss tangent of the bonding layer 300 also changes accordingly. When the value of the dielectric loss tangent changes, the amount of heat generated in the bonding layer 300 due to the application of the AC electric field also changes, so the in-plane temperature distribution of the substrate W is affected. When the value of the dielectric loss tangent exceeds 200% of the reference value, the influence on the temperature of the substrate W becomes so large that it cannot be ignored.

[0036] As described above, in the electrostatic chuck 10, the routing of the refrigerant flow path 250 and the like are appropriately designed so that the in-plane temperature distribution of the substrate W during processing becomes appropriate. However, for example, if the heat generation amount of the bonding layer 300 changes significantly due to a change in the operating conditions of the semiconductor manufacturing apparatus or the like, the premise of the design is broken, and thus there may be a case where the in-plane temperature distribution of the substrate W cannot be appropriately maintained.

[0037] FIG. 5 shows an example of the results of measuring the relationship between the temperature (horizontal axis) and the relative permittivity (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 permittivity was measured with an AC electric field of 400 KHz applied to the bonding layer 300.

[0038] Further, FIG. 6 shows an example of the results of measuring the relationship between the temperature (horizontal axis) and the volume resistivity (vertical axis) for each of 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, it can be seen that when the temperature of the bonding layer 300 changes, the relative permittivity and the volume resistivity also change significantly. Such fluctuations in various physical property values are factors that make it more difficult to design the electrostatic chuck 10 so that the in-plane temperature distribution of the substrate W is appropriate. In order to perform a design that appropriately exhibits the cooling performance of the electrostatic chuck 10 under various operating conditions of the semiconductor manufacturing apparatus, it is preferable to minimize the number of physical property values that vary with temperature.

[0040] Therefore, the inventors of the present invention attempted to suppress the temperature dependence of the dielectric tangent as described above by appropriately selecting, for example, the adhesive which is the material of the bonding layer 300 in the present embodiment. Each data plotted as a circular dot in FIG. 2 shows the result of measuring (or calculating by simulation) the value of the dielectric tangent at each temperature for a sample obtained by cutting out the bonding layer 300 of the first embodiment. Each data was measured or the like with an AC electric field of 400 KHz applied to the bonding layer 300 in the same manner as in the above-described comparative example.

[0041] The value of the dielectric tangent when the bonding layer 300 was at 20° C., that is, the “reference value”, was 0.0007 in the first embodiment. In the electrostatic chuck 10 according to the first embodiment, even when the temperature of the bonding layer 300 was changed from 20° C. to -60° C., almost no variation in the value of the dielectric tangent was observed during that period, and a value approximately equal to the reference value was maintained.

[0042] Each data plotted as a circular dot in FIG. 3 shows the result of measuring (or calculating by simulation) the value of the dielectric tangent at each temperature for a sample obtained by cutting out the bonding layer 300 of the second embodiment. Each data was measured or the like with an AC electric field of 400 KHz applied to the bonding layer 300 in the same manner as each data shown in FIG. 2.

[0043] The value of the dielectric tangent when the bonding layer 300 was at 20° C., that is, the “reference value”, was 0.0081 in the second embodiment. The value of the dielectric tangent when the bonding layer 300 was at -40° C. was 0.0086, and the value of the dielectric tangent when the bonding layer 300 was at -60° C. was 0.0076. Thus, in the electrostatic chuck 10 according to the second embodiment, even when the temperature of the bonding layer 300 was changed from 20° C. to -60° C., the variation in the value of the dielectric tangent during that period was relatively small, and a value approximately equal to the reference value was maintained.

[0044] FIG. 4 shows how the dielectric tangent of the bonding layer 300 in each of the above samples changes from the reference value as the temperature decreases. The vertical axis in this figure represents the percentage change in the dielectric tangent value, that is, the rate of change, with the dielectric tangent value at 20°C (i.e., the reference value) being set as 100%.

[0045] As described above, in the comparative example, when the temperature of the bonding layer 300 drops below -40°C, the value of the dielectric tangent rises sharply. When the temperature reaches -60°C, the value of the dielectric tangent has risen to about 220% of the reference value.

[0046] On the other hand, in Embodiment 1 (silicone adhesive), even when the temperature of the bonding layer 300 changes from 20°C to -60°C, the change in the value of the dielectric tangent of the bonding layer 300 is suppressed to such a small extent that it is hardly observable, and it remains generally at 100% of the reference value.

[0047] Also, in Embodiment 2 (epoxy adhesive), when the temperature of the bonding layer 300 changes from 20°C to -40°C, the value of the dielectric tangent of the bonding layer 300 rises to about 106% of the reference value. Then, when the temperature of the bonding layer 300 changes to -60°C, the value of the dielectric tangent of the bonding layer 300 decreases to about 94% of the reference value. Thus, in the bonding layer 300 according to Embodiment 2, the change in the value of the dielectric tangent is within the range of 94% to 106% of the reference value.

[0048] As described above, in the electrostatic chuck 10 according to Embodiments 1 and 2, the change in the value of the dielectric tangent of the bonding layer 300 due to temperature change is suppressed to be smaller than in the prior art. Even when the temperature of the bonding layer 300 changes during the processing of the substrate W due to, for example, a change in the operating conditions of the semiconductor manufacturing apparatus, the value of the dielectric tangent of the bonding layer 300 is maintained at a value generally 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] When the temperature of the bonding layer 300 changes from 20°C to -60°C, the variation in the value of the dielectric tangent of the bonding layer 300 preferably falls within at least the range from 50% to 200% of the reference value. If the change in the value of the dielectric tangent is suppressed to the above extent, the variation in the heat generation amount of the bonding layer 300 can be suppressed to be smaller than before, so that the in-plane temperature distribution of the substrate W can be continuously maintained appropriately.

[0050] When the temperature of the bonding layer 300 changes from 20°C to -60°C, the variation in the value of the dielectric tangent preferably more preferably falls within the range from 90% to 110% of the reference value as in Embodiments 1 and 2. If the change in the value of the dielectric tangent is suppressed within the range of ±10% of the reference value, the variation in the heat generation amount of the bonding layer 300 can be suppressed to be negligibly small.

[0051] When the temperature of the bonding layer 300 changes from 20°C to -60°C, the value of the dielectric tangent is preferably always less than 0.0008 as in Embodiment 1. With such a configuration, not only the variation range of the heat generation amount of the bonding layer 300 during processing but also the absolute value of the heat generation amount can be sufficiently suppressed to be small.

[0052] As the adhesive used for the bonding layer 300, it is preferable to select one in which the variation in the value of the dielectric tangent when the temperature drops falls within the above range. Also, by adding a filler to an existing adhesive, it is possible to keep the variation in the value of the dielectric tangent when the temperature drops within the above range. For example, by adding an inorganic material such as alumina as a filler, the variation range of the value of the dielectric tangent can be adjusted. In this case, it has been found that the value of the dielectric tangent decreases and the change amount of the dielectric tangent at low temperatures also decreases as the addition amount of the filler increases. However, when the dispersibility of the filler is poor and it aggregates, the value of the dielectric tangent may conversely increase, so it is necessary to add the filler while paying attention not to aggregate.

[0053] The above-described embodiments have been explained with reference to specific examples. However, the present disclosure is not limited to these specific examples. As long as those skilled in the art appropriately make design changes to these specific examples and have the features of the present disclosure, they are included in the scope of the present disclosure. Each element, its arrangement, conditions, shape, etc. included in each of the above-described specific examples are not limited to those illustrated and can be appropriately changed. Each element included in each of the above-described specific examples can be appropriately combined as long as no technical contradiction occurs.

Explanation of Reference Numerals

[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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