Electrostatic chuck

Abstract

The invention provides an electrostatic chuck capable of appropriately maintaining in-plane temperature distribution of a substrate during processing. An electrostatic chuck (10) is provided with: a dielectric substrate (100); a base plate (200) that supports the dielectric substrate (100); and a bonding layer (300) that bonds between the dielectric substrate (100) and the base plate (200). The value of the loss tangent of the bonding layer (300) when the temperature of the bonding layer (300) is 20 DEG C is used as a reference value. In the electrostatic chuck (10), when the temperature of the bonding layer (300) changes from 20 DEG C to-60 DEG C, the range in which the value of the loss tangent of the bonding layer (300) varies is within the range of 50% to 200% of a reference value.

Description

Technical Field

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

[0002] For example, in semiconductor manufacturing apparatuses such as etching apparatuses, an electrostatic chuck is provided as a device for adsorbing and holding a substrate such as a silicon wafer that is an object to be processed. As described in Patent Document 1 below, the electrostatic chuck includes: a dielectric substrate (base material) provided with adsorption electrodes; and a base plate (base portion) that supports the dielectric substrate, and has a structure in which these are joined to each other. When a voltage is applied to the adsorption electrodes, an electrostatic force is generated to adsorb and hold the substrate placed on the dielectric substrate.

[0003] In a process such as etching, it is necessary to maintain 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 the process appropriate, for example, the surrounding arrangement of the cooling medium flow path formed inside the base plate, and the arrangement of the air holes for supplying gas to the back side of the substrate, etc., the structure of each part of the electrostatic chuck is appropriately designed.

[0004] Patent Document Patent Document 1: Japanese Patent Application Laid-Open No. 2015-162490 Summary of the Invention

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

[0006] The present inventors have obtained the following new knowledge: if the temperature of the bonding layer changes corresponding to the operating conditions of the semiconductor manufacturing apparatus, etc., the value of the loss tangent of the bonding layer also changes accordingly. If the value of the loss tangent changes, the calorific value of the bonding layer due to the application of the alternating current electric field also changes, and thus the in-plane temperature distribution of the substrate is affected.

[0007] As described above, in the electrostatic chuck, the surrounding arrangement of the cooling medium flow path, etc. is appropriately designed so that the in-plane temperature distribution of the substrate during the process becomes appropriate. However, if the calorific value of the bonding layer changes greatly due to a change in the operating conditions, etc., the premise of the design is broken, and thus it may also occur that the in-plane temperature distribution of the substrate cannot be appropriately maintained.

[0008] The present invention has been made in view of such problems, and the technical problem to be solved is to provide an electrostatic chuck that can appropriately maintain the in-plane temperature distribution of a substrate during processing.

[0009] 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 loss 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 loss tangent of the bonding layer changes is within the range of 50% to 200% of the reference value.

[0010] In the electrostatic chuck configured in this way, it is configured that even when the temperature of the bonding layer changes from 20°C to -60°C, the change in the value of the loss tangent during that period is within the range of 50% to 200% of the reference value. Even when the temperature of the bonding layer changes, the change in the heat generation amount of the bonding layer is suppressed to be smaller than before, so that the in-plane temperature distribution of the substrate can continue to be appropriately maintained.

[0011] According to the present invention, an electrostatic chuck can be provided that can appropriately maintain the in-plane temperature distribution of a substrate during processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a cross-sectional view schematically showing the structure of the electrostatic chuck according to the present embodiment. Figure 2 It is a graph showing the relationship between the temperature of the bonding layer and the loss tangent. Figure 3 It is a graph showing the relationship between the temperature of the bonding layer and the dielectric constant. Figure 4 It is a graph showing the relationship between the temperature of the bonding layer and the change rate of the loss tangent. Figure 5 It is a graph showing the relationship between the temperature of the bonding layer and the dielectric constant. Figure 6 It is a graph showing the relationship between the temperature of the bonding layer and the volume resistivity. REFERENCE SIGNS 10 - electrostatic chuck; 100 - dielectric substrate; 200 - base plate; 300 - bonding layer. DETAILED DESCRIPTION OF THE EMBODIMENT

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

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

[0015] Figure 1 FIG. 4 shows a cross-sectional view of the electrostatic chuck 10 in a state of adsorbing and holding the substrate W as a patterned cross-sectional view. 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. Although the dielectric substrate 100 contains, for example, high-purity alumina (Al 2 O 3 ), it may also contain other materials. Considering the plasma resistance and the like required for the dielectric substrate 100 in a semiconductor manufacturing apparatus, the purity, type, and additives of the ceramic in the dielectric substrate 100 can be appropriately set.

[0017] In the dielectric substrate 100, Figure 1 the upper surface 110 therein becomes the "placement surface" for placing the substrate W. Further, in the dielectric substrate 100, Figure 1 the lower surface 120 therein becomes the "surface to be joined" that is joined to the base plate 200 via the joining layer 300. Hereinafter, the viewpoint when observing the electrostatic chuck 10 from the surface 110 side in a direction perpendicular to the surface 110 is also referred to as "top view observation".

[0018] Inside the dielectric substrate 100, an adsorption electrode 130 is embedded. The adsorption electrode 130 is, for example, a thin plate-shaped layer formed of a metal material such as tungsten and is disposed parallel to the surface 110. As the material of the adsorption electrode 130, in addition to tungsten, molybdenum, platinum, palladium, etc. can also be used. If a voltage is applied to the adsorption electrode 130 from the outside through a power supply circuit (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 structure of the above-mentioned power supply circuit, various known structures can be adopted. The adsorption electrode 130 can be provided as a so-called "single-pole" electrode, i.e., only one, as in the present embodiment, or can be provided as a so-called "bipolar" electrode, i.e., two.

[0019] As Figure 1As shown, a space SP is formed between the dielectric substrate 100 and the substrate W. When performing processes such as etching in a semiconductor manufacturing apparatus, helium for temperature adjustment is supplied from the outside to the space SP through air holes (not shown). By having helium present between the dielectric substrate 100 and the substrate W, the thermal resistance between the two is adjusted, and thus the temperature of the substrate W is maintained at an appropriate temperature. Also, the gas for temperature adjustment supplied to the space SP can be a gas of a different type from helium.

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

[0021] The seal ring 111 is a wall that divides the space SP at the outermost peripheral position. The upper end of the seal ring 111 becomes a part of the surface 110 and abuts against the substrate W. Also, a plurality of seal rings 111 can be provided in a manner that divides the space SP. With such a structure, the pressure of the helium in each space SP can be adjusted individually, and the surface temperature distribution of the substrate W can be made uniform during the process.

[0022] Figure 1 In the figure, the portion marked with the 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 and the dots 112 described below are formed as a result of digging 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 approximately evenly on the placement surface of the dielectric substrate 100. The upper end of each dot 112 becomes a part of the surface 110 and abuts against the substrate W. By providing a plurality of such dots 112, warping 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. In the base plate 200, Figure 1 the upper-side surface 210 in the figure becomes the "surface to be joined" that is joined to the dielectric substrate 100 through 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 a layer formed by curing an adhesive made of an insulating material. As the above-mentioned adhesive, for example, silicone adhesives, epoxy adhesives, polyimide adhesives, etc. can be used. The joining layer 300 can also be a layer formed by curing other types of adhesives. In any case, it is preferable to use a material with as high a thermal conductivity as possible as the material of the joining 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-based adhesive were fabricated respectively. In each embodiment, hereinafter, the electrostatic chuck 10 having the bonding layer 300 formed of a silicone adhesive will be referred to as "Embodiment 1". Hereinafter, the electrostatic chuck 10 having the bonding layer 300 formed of a polyimide-based adhesive will be referred to as "Embodiment 2".

[0027] An insulating film may also be formed on the surface of the base plate 200. As the insulating film, for example, a film of aluminum oxide formed by sputtering can be used. By covering the surface of the base plate 200 with the insulating film, the withstand voltage of the base plate 200 can be improved accordingly.

[0028] Inside the base plate 200, a coolant flow path 250 for allowing a coolant to pass through is formed. When performing a process such as etching in a semiconductor manufacturing apparatus, the coolant is supplied from the outside to the coolant flow path 250 to cool the base plate 200. During the process, the heat generated on the substrate W is transferred to the coolant 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 coolant.

[0029] However, when performing a process such as etching in a semiconductor manufacturing apparatus, it is necessary to maintain the temperature of each part of the substrate W at an appropriate temperature. In an electrostatic chuck, usually, the structure of each part is appropriately designed so that the in-plane temperature distribution of the substrate W during the process becomes appropriate. Among the above-mentioned "structures" that may affect the in-plane temperature distribution of the substrate W, for example, it includes the surrounding arrangement of the coolant flow path 250 formed inside the base plate 200, the configuration of the air holes (not shown) for supplying gas to the space SP, and the shape or configuration of the point 112 or the seal ring 111 in the dielectric substrate 100, etc. In addition, when a heater for heating the dielectric substrate 100 is provided in the electrostatic chuck 10, the performance or configuration of the heater, etc. is also included in the above-mentioned "structure".

[0030] When plasma is generated 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 10. For example, one of the above electrodes is disposed at a position above the substrate W (the opposite side of the electrostatic chuck 10). As the other of the above electrodes, although the base plate 200 is often used, a member other than the base plate 200 can also be used. In any case, a relatively large alternating electric field is applied to each member constituting the bonding layer 300 of the electrostatic chuck 10, etc.

[0031] If an alternating current electric field is applied to the bonding layer 300, a part of the energy of the alternating current electric field is converted into heat, and the temperature of the bonding layer 300 rises. In order to confirm the influence of such an alternating current electric field, the present inventors investigated the loss tangent of the material constituting the bonding layer 300.

[0032] The results of this investigation will be described. Figure 2 and Figure 3 shows an example of the relationship between the temperature of the bonding layer 300 (horizontal axis) and the value of the loss tangent of the bonding layer 300 (vertical axis).

[0033] Figure 2 Each data plotted with triangular points in is the result obtained by forming the bonding layer 300 using a normal silicone adhesive and measuring the value of the loss tangent of the bonding layer 300 at each temperature, and is data shown as a "comparative example" of the present embodiment. Each data is measured in a state where an alternating current electric field of 400 kHz is applied to the bonding layer 300.

[0034] In this comparative example, when the temperature of the bonding layer 300 was lowered from 20 °C, it was confirmed that the value of the loss tangent of the bonding layer 300 changed accordingly. Hereinafter, the value of the loss tangent of the bonding layer 300 when the bonding layer 300 is at 20 °C will also be referred to as the "reference value". In this comparative example, as the temperature of the bonding layer 300 decreased from 20 °C, the value of the loss tangent of the bonding layer 300 decreased from the reference value (which is 0.0006 in this comparative example). Starting from around when the temperature of the bonding layer 300 was lower than -40 °C, the value of the loss tangent increased sharply, and at the moment when the temperature reached -60 °C, the value of the loss tangent rose to about 220% of the reference value.

[0035] In this way, it was found that if the temperature of the bonding layer 300 changes, the value of the loss tangent of the bonding layer 300 also changes accordingly. If the value of the loss tangent changes, the amount of heat generated in the bonding layer 300 due to the application of the alternating current electric field also changes, and thus the in-plane temperature distribution of the substrate W is affected by this. If the value of the loss tangent exceeds 200% of the reference value, the influence on the temperature of the substrate W is so large that it cannot be ignored.

[0036] As described above, in the electrostatic chuck 10, the surrounding arrangement of the cooling medium flow path 250 and the like are appropriately designed so that the in-plane temperature distribution of the substrate W becomes appropriate during processing. However, for example, if the amount of heat generated in 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 it may also be the case that the in-plane temperature distribution of the substrate W cannot be appropriately maintained.

[0037] Regarding the bonding layer 300 according to Embodiment 1, the bonding layer 300 according to Embodiment 2, and the bonding layer 300 according to the comparative example, Figure 5 Examples showing the results of measuring the relationship between the temperature (horizontal axis) and the dielectric constant (vertical axis) thereof are respectively presented. The dielectric constant is data measured under a state where an AC electric field of 400 KHz is applied to the bonding layer 300.

[0038] In addition, regarding the bonding layer 300 according to Embodiment 1 and the bonding layer 300 according to the comparative example, Figure 6 Examples showing the results of measuring the relationship between the temperature (horizontal axis) and the volume resistivity (vertical axis) thereof are respectively presented. Figure 6 The vertical axis is a logarithmic axis.

[0039] As shown in these figures, it is known that if the temperature of the bonding layer 300 changes, its dielectric constant and volume resistivity also change significantly. Such variations in various physical property values are the main reasons that make it difficult to design the electrostatic chuck 10 for making the in-plane temperature distribution of the substrate W appropriate. Among various operating conditions of the semiconductor manufacturing apparatus, in order to design the electrostatic chuck 10 to properly exhibit its cooling performance, it is preferable to minimize the number of physical property values that vary with temperature as much as possible.

[0040] Then, the inventor of the present invention tried to suppress the temperature dependence of the loss tangent for the bonding layer 300 of the present embodiment, for example, by appropriately selecting its material such as an adhesive. Regarding the sample cut out from the bonding layer 300 of Embodiment 1, Figure 2 Each data depicted by circular dots represents the result of measuring (or calculating by simulation) the value of the loss tangent at each temperature. Similar to the above-described comparative example, each data is data measured under a state where an AC electric field of 400 KHz is applied to the bonding layer 300.

[0041] In Embodiment 1, the value of the loss tangent at 20°C of the bonding layer 300, that is, the "reference value", is 0.0007. In the electrostatic chuck 10 according to Embodiment 1, even if the temperature of the bonding layer 300 is changed from 20°C to -60°C, almost no change in the value of the loss tangent is observed during this period, and a value substantially equal to the reference value is maintained.

[0042] Regarding the sample cut out from the bonding layer 300 of Embodiment 2, Figure 3 Each data depicted by circular dots represents the result of measuring (or calculating by simulation) the value of the loss tangent at each temperature. Similar to Figure 2 each data shown, each data is data measured under a state where an AC electric field of 400 KHz is applied to the bonding layer 300.

[0043] In Embodiment 2, the value of the loss tangent of the bonding layer 300 at 20°C, i.e., the "reference value", is 0.0081. The value of the loss tangent of the bonding layer 300 at -40°C is 0.0086, and the value of the loss tangent of the bonding layer 300 at -60°C is 0.0076. Thus, in the electrostatic chuck 10 according to 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 loss tangent during this period is relatively small, and a value approximately equal to the reference value is maintained.

[0044] Figure 4 shows how the loss tangent of the bonding layer 300 changes from the reference value as the temperature decreases in the above various samples. The vertical axis of this figure represents the change rate of the loss tangent value, which is expressed as a percentage by taking the value of the loss tangent at 20°C (i.e., the reference value) as 100%.

[0045] As described above, in the comparative example, starting from around when the temperature of the bonding layer 300 is lower than -40°C, the value of the loss tangent rises sharply, and at the moment when the temperature reaches -60°C, the value of the loss tangent rises 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 is changed from 20°C to -60°C, the change in the value of the loss tangent of the bonding layer 300 is suppressed to an unobservable level, and 100% of the approximate reference value is continuously maintained.

[0047] In addition, in Embodiment 2 (epoxy adhesive), if the temperature of the bonding layer 300 is changed from 20°C to -40°C, the value of the loss tangent of the bonding layer 300 rises to about 106% of the reference value. After that, if the temperature of the bonding layer 300 is changed to -60°C, the value of the loss 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 loss 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 loss tangent of the bonding layer 300 accompanying temperature change is suppressed to be smaller than before. Even when the temperature of the bonding layer 300 changes during the processing of the substrate W due to a change in the operating conditions of the semiconductor manufacturing apparatus or the like, the value of the loss tangent of the bonding layer 300 maintains a value approximately close to the reference value. Since the heat generation amount in the bonding layer 300 is almost the same as before the change in the operating conditions, the electrostatic chuck 10 exhibits the cooling performance as designed initially, and appropriately maintains the in-plane temperature distribution of the substrate W.

[0049] Preferably, the variation in the value of the loss tangent of the bonding layer 300 when the temperature of the bonding layer 300 changes from 20 °C to -60 °C is at least in the range of 50% to 200% of the reference value. If the change in the value of the loss tangent is suppressed to the above-described extent, the variation in the calorific value of the bonding layer 300 is suppressed to be smaller than before, and thus the in-plane temperature distribution of the substrate W can be continuously and appropriately maintained.

[0050] As in Embodiments 1 and 2, more preferably, the variation in the value of the loss tangent when the temperature of the bonding layer 300 changes from 20 °C to -60 °C is in the range of 90% to 110% of the reference value. If the change in the value of the loss tangent is suppressed within the range of ±10% of the reference value, the variation in the calorific value of the bonding layer 300 can be suppressed to a negligible level.

[0051] As in Embodiment 1, preferably, the value of the loss tangent of the bonding layer 300 is always less than 0.0008 when the temperature changes from 20 °C to -60 °C. By adopting such a configuration, not only can the variation range of the calorific value of the bonding layer 300 during processing be sufficiently and significantly suppressed, but also the absolute value of the calorific value can be sufficiently and significantly suppressed.

[0052] As the adhesive for the bonding layer 300, an adhesive is preferably selected such that the variation in the value of the loss tangent when the temperature drops is within the above range. In addition, by adding a filler to an existing adhesive, the variation in the value of the loss tangent when the temperature drops can also be made to be 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 loss tangent can be adjusted. At this time, it has been found that the smaller the value of the loss tangent and the smaller the change amount of the loss tangent at low temperatures, the more the addition amount of the filler increases. However, when the dispersibility of the filler is poor and agglomeration occurs, the value of the loss tangent becomes larger instead. Therefore, it is necessary to add the filler while paying attention to agglomeration.

[0053] The above has described the present embodiment with reference to specific examples. However, the present invention is not limited to these specific examples. Regarding these specific examples, as long as they have the features of the present invention, the techniques appropriately designed and modified by those skilled in the art are also included in the scope of the present invention. The elements, their configurations, conditions, shapes, etc. possessed by the foregoing specific examples are not limited to the illustrated content, but can be appropriately changed. As long as there is no technical contradiction, the elements possessed by the foregoing specific examples can be appropriately combined and changed.

Claims

1. An electrostatic chuck, characterized in that: Possessing: a dielectric substrate; a base plate supporting the dielectric substrate; and a bonding layer for bonding the dielectric substrate and the base plate, When the value of the loss 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 loss tangent value of the bonding layer changes is within a range of 50% to 200% of the reference value.

2. The electrostatic chuck according to claim 1, characterized in that: When the temperature of the bonding layer changes from 20° C. to −60° C., the range in which the loss tangent value of the bonding layer changes is within a range of 90% to 110% of the reference value.

3. 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 loss tangent of the bonding layer may have a value less than 0.0008.

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