Electrostatic chuck

Abstract

The present invention provides an electrostatic chuck capable of suppressing the occurrence of insulation breakdown in the vicinity of a bonding layer. An electrostatic chuck (10) is provided with: a dielectric substrate (100); a base plate (200) formed of a metal material; and a bonding layer (300) that bonds between the dielectric substrate (100) and the base plate (200). At least a portion of the base plate (200) facing the bonding layer (300) is covered by a ceramic film (231), and the surface of the ceramic film (231) becomes a surface to be bonded (S). The bonded surface (S) satisfies at least one of a first condition: arithmetic average height (Sa) < = 1.5 [mu] m and a second condition: root mean square height (Sq) < = 2.0 [mu] m, and satisfies at least one of a third condition: maximum valley depth (Sv) > = 20.0 [mu] m and a fourth condition: maximum height (Sz) > = 20.0 [mu] m.

Description

Technical Field

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

[0002] For example, in a semiconductor manufacturing device such as an etching device, 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 the following patent document 1, the electrostatic chuck includes: a dielectric substrate provided with an adsorption electrode; and a base plate supporting the dielectric substrate, and has a structure in which these are bonded to each other. For example, the dielectric substrate and the base plate are bonded by a silicone adhesive, i.e., a bonding layer. If a voltage is applied to the adsorption electrode, an electrostatic force is generated to adsorb and hold the substrate placed on the dielectric substrate.

[0003] Patent Literature Patent Document 1: Japanese Patent Application Laid-Open No. 4-287344 Summary of the invention

[0004] When etching or other processes are performed in a semiconductor manufacturing device, the temperature of the substrate rises due to exposure to plasma, and the temperature of the dielectric substrate also rises. On the other hand, since a low-temperature cooling medium is supplied to the base plate, the temperature of the base plate may drop to -60°C or below. Due to the temperature changes of various parts accompanying the substrate processing or the temperature difference between the dielectric substrate and the base plate, the bonding layer and its surrounding parts are subjected to large thermal stress.

[0005] If a part of the bonding layer is peeled off from the surface of the base plate due to thermal stress, the surface of the base plate is exposed, and as a result, insulation breakdown may occur between the exposed part and the surrounding members.

[0006] In addition, the exposed portion of the surface of the base plate due to the peeling of the bonding layer as described above is sometimes covered with a ceramic film formed in advance by thermal spraying. However, such a ceramic film alone may not be able to prevent insulation damage when the bonding layer peels off.

[0007] 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 suppressing the occurrence of insulation breakdown in the vicinity of a bonding layer.

[0008] In order to solve the above problems, the electrostatic chuck involved in the present invention comprises: a dielectric substrate; a base plate formed of a metal material; and a bonding layer for bonding the dielectric substrate and the base plate. At least a portion of the base plate facing the bonding layer is covered with a ceramic film, and the surface of the ceramic film becomes a bonding surface. The joint surface satisfies Condition 1: Arithmetic mean height (Sa) ≤ 1.5 μm, Second condition: RMS height (Sq) ≤ 2.0 μm, At least one of the above conditions 1 and 2 is met, Condition 3: Maximum valley depth (Sv) ≥ 20.0 μm, Condition 4: Maximum height (Sz) ≥ 20.0 μm, At least one of the third and fourth conditions above.

[0009] Among the above-mentioned conditions that the surface shape of the bonded surface should satisfy, the first condition and the second condition both become conditions that stipulate that the bonded surface is smooth. If the bonded surface becomes a smooth surface to the extent that at least one of the first condition and the second condition is satisfied, the thickness of the bonding layer is generally uniform on the whole, and the thermal resistance of the bonding layer is also generally uniform. Therefore, the in-plane temperature distribution of the substrate being processed can be made uniform.

[0010] On the other hand, the third condition and the fourth condition are both conditions that stipulate that a relatively deep recess is formed on the bonded surface. When a recess is formed on the bonded surface to a degree that satisfies at least one of the third condition and the fourth condition, when the dielectric substrate and the base plate are bonded, the uncured adhesive enters the recess and then cures. Since the so-called "anchor effect" becomes larger, the bonding strength between the bonding layer and the bonded surface (that is, the ceramic film) becomes larger.

[0011] Thus, in the electrostatic chuck of the above structure, the shape of the bonded surface of the ceramic film is made into a shape that satisfies the specified conditions, thereby suppressing the unevenness of the thickness of the bonding layer and fully improving the bonding strength between the bonding layer and the bonded surface based on the anchor effect.

[0012] In the processing of the substrate, when it is assumed that the bonding layer and its vicinity are subjected to large thermal stress, the bonding layer peels off at the interface on the dielectric substrate side before peeling off at the interface on the ceramic film side, or breaks inside the bonding layer. In either case, the bonded surface of the ceramic film continues to be covered by the bonding layer as a whole, so it will not be exposed to the outside due to the peeling of the bonding layer. Therefore, it is possible to suppress the occurrence of insulation breakdown near the bonding layer, and specifically, it is possible to fully suppress the occurrence of insulation breakdown through the exposed portion of the ceramic film.

[0013] According to the present invention, it is possible to provide an electrostatic chuck capable of suppressing the occurrence of insulation breakdown in the vicinity of a bonding layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a cross-sectional view schematically showing the structure of the electrostatic chuck according to the present embodiment. Figure 2This is a diagram schematically showing the cross-sectional shape of the surface to be joined in the ceramic film. Figure 3 It is a diagram for explaining the peeling of the bonding layer. Explanation of symbols 10-electrostatic chuck; 100-dielectric substrate; 200-base plate; 210-surface; 230, 231-ceramic film; 300-joining layer; S-joined surface. DETAILED DESCRIPTION

[0015] Hereinafter, the present embodiment will be described with reference to the drawings. In order to facilitate the description, the same components are denoted by the same reference numerals as much as possible in each of the drawings, and repeated descriptions are omitted.

[0016] The electrostatic chuck 10 according to the present embodiment absorbs and holds a substrate W to be processed by electrostatic force in a semiconductor manufacturing device (not shown), such as an etching device. The substrate W is, for example, a silicon wafer. The electrostatic chuck 10 can also be used in devices other than semiconductor manufacturing devices.

[0017] Figure 1 , the structure of the electrostatic chuck 10 in a state of sucking and holding the substrate W is shown as a schematic cross-sectional view. The electrostatic chuck 10 includes a dielectric substrate 100 , a base plate 200 , and a bonding layer 300 .

[0018] The dielectric substrate 100 is a roughly disk-shaped member composed of a ceramic sintered body. The dielectric substrate 100 contains, for example, high-purity aluminum oxide (Al2O3), but may also contain other materials. The purity and type of ceramics in the dielectric substrate 100, additives, etc. may be appropriately set in consideration of the plasma resistance required of the dielectric substrate 100 in the semiconductor manufacturing device.

[0019] In the dielectric substrate 100, Figure 1 The upper surface 110 in the dielectric substrate 100 is a "placing surface" on which the substrate W is placed. Figure 1 The lower surface 120 in the middle is a surface to be bonded to the base plate 200 by a bonding layer 300 described later.

[0020] An adsorption electrode 130 is embedded inside the dielectric substrate 100. The adsorption electrode 130 is a thin, flat layer formed of a metal material such as tungsten, and is built into the dielectric substrate 100 in a state parallel to the surface 110. As a material for 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, 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 only one so-called "monopolar" electrode as in the present embodiment, or two so-called "bipolar" electrodes can be provided.

[0021] like Figure 1 As shown in FIG. 1 , a space SP is formed between the dielectric substrate 100 and the substrate W. When etching or other processing 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 making the helium gas exist between the dielectric substrate 100 and the substrate W, the thermal resistance between the two is adjusted, so that the temperature of the substrate W is maintained at an appropriate temperature. In addition, the gas for temperature adjustment supplied to the space SP may be a gas of a different type from helium.

[0022] A sealing ring 111 , a dot 112 , and the like are provided on the surface 110 which is the placement surface, and the above-mentioned space SP is formed around these surfaces.

[0023] The sealing ring 111 is a wall that divides the space SP at the position that becomes the outermost periphery. The upper end surface of the sealing ring 111 becomes a part of the surface 110 and abuts against the substrate W. In addition, a plurality of sealing rings 111 may be provided in a manner that divides the space SP. With such a structure, the pressure of the helium gas in each space SP can be adjusted separately, and the surface temperature distribution of the substrate W can be made uniform during processing.

[0024] Figure 1 In FIG. 1 , the portion marked with the symbol “116” is the bottom surface of the space SP. Hereinafter, this portion is also referred to as “bottom surface 116”. The sealing ring 111 is formed as a result of digging out a portion of the surface 110 to the position of the bottom surface 116 together with the point 112 described below.

[0025] The dots 112 are circular protrusions protruding from the bottom surface 116. A plurality of dots 112 are provided and are dispersed 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 contacts the substrate W. By providing a plurality of such dots 112, the substrate W is prevented from being bent.

[0026] 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. Figure 1 The upper surface 210 in the bonding layer 300 is a portion facing the bonding layer 300. However, in the present embodiment, the surface 210 and the bonding layer 300 are not directly bonded, but a ceramic film 230 is interposed therebetween.

[0027] The ceramic film 230 is an insulating film formed so as to cover the surface of the base plate 200. As the insulating film, for example, a film of aluminum oxide formed by thermal spraying can be used. By covering the surface of the base plate 200 with the ceramic film 230, the insulation withstand voltage of the base plate 200 can be improved.

[0028] The ceramic film 230 covers not only the surface 210 of the base plate 200 but also the side surfaces connected to the surface 210. Among the surfaces of the base plate 200, only the surface 220 on the opposite side of the surface 210 is not covered by the ceramic film 230. Instead of such a configuration, only the surface 210 may be covered by the ceramic film 230.

[0029] In the following, the portion of the ceramic film 230 covering the surface 210 is also referred to as "ceramic film 231". The outer surface of the ceramic film 231 is bonded to the dielectric substrate 100 via the bonding layer 300. This surface is also referred to as "bonded surface S".

[0030] As described above, in the present embodiment, at least the portion (surface 210 ) of the base plate 200 facing the bonding layer 300 is covered with the ceramic film 231 , and the surface of the ceramic film 231 serves as the surface S to be bonded.

[0031] A cooling medium flow path 250 for flowing a cooling medium is formed inside the susceptor plate 200. When etching or other processing is performed in the semiconductor manufacturing apparatus, a cooling medium is supplied from the outside to the cooling medium flow path 250, thereby cooling the susceptor plate 200. During the processing, heat generated on the substrate W is transferred to the cooling medium via the helium gas in the space SP, the dielectric substrate 100, and the susceptor plate 200, and is discharged to the outside together with the cooling medium.

[0032] The bonding layer 300 is a layer provided between the dielectric substrate 100 and the base plate 200, and the two are bonded. The bonding layer 300 is a layer formed by curing an adhesive material composed of an insulating material. In the present embodiment, a silicone adhesive is used as the above-mentioned adhesive. However, the bonding layer 300 can also be a layer formed by curing other types of adhesives. In either case, it is preferred to use a material with a higher thermal conductivity as much as possible as the material of the bonding layer 300 so that the thermal resistance between the dielectric substrate 100 and the base plate 200 is small.

[0033] In the present embodiment, the shape of the surface S to be joined in the ceramic film 231 is studied, thereby improving the bonding strength between the bonding layer 300 and the surface S to be joined. Figure 2 , the cross-sectional shape of the surface S to be joined and its vicinity in the ceramic film 231 is schematically shown. The ceramic film 231 of this embodiment is a film formed by thermal spraying. Therefore, countless concavoconvex parts are formed on the surface S to be joined. The joined surface S is formed so as to satisfy at least one of the following first and second conditions. Condition 1: Arithmetic mean height (Sa) ≤ 1.5 μm Second condition: RMS height (Sq) ≤ 2.0 μm

[0034] The "arithmetic mean height (Sa)" of the first condition is the concept of expanding the arithmetic mean height (Ra) from a line to a surface. For the average surface of the joined surface S, the arithmetic mean height (Sa) can be calculated as the absolute average value of the height difference at each position of the joined surface S. For the average surface of the joined surface S, the "root mean square height (Sq)" of the second condition can be calculated as the standard deviation of the height (distance) at each position of the joined surface S. As the respective definitions and measurement methods of the above arithmetic mean height (Sa) and root mean square height (Sq), the definitions and measurement methods specified in ISO25178 of the International Organization for Standardization can be adopted.

[0035] The first condition and the second condition mentioned above are conditions for specifying that the bonded surface S is a surface that is smooth to a certain extent. The bonded surface S may satisfy both the first condition and the second condition, or may satisfy only one of the first condition and the second condition. If the bonded surface S is a smooth surface to the extent that at least one of the first condition and the second condition is satisfied, the thickness of the bonding layer 300 located directly above it is generally uniform, and the thermal resistance of the bonding layer 300 is also generally uniform. Therefore, the in-plane temperature distribution of the substrate W being processed can be made uniform.

[0036] The joined surface S is further formed so as to satisfy at least one of the following third and fourth conditions. Condition 3: Maximum valley depth (Sv) ≥ 20.0 μm Condition 4: Maximum height (Sz) ≥ 20.0 μm

[0037] The "maximum valley depth (Sv)" of the third condition can be calculated as the absolute value of the minimum value of the height at each position of the joined surface S for the average surface of the joined surface S. The "maximum height (Sz)" of the fourth condition can be calculated as the distance from the highest point to the lowest point at each position of the joined surface S (the distance along the direction perpendicular to the surface of the average surface of the joined surface S). As the respective definitions and measurement methods of the above maximum valley depth (Sv) and maximum height (Sz), the definitions and measurement methods specified in ISO25178 of the International Organization for Standardization can be adopted.

[0038] The third and fourth conditions described above are conditions that define the formation of a deep recess on the joined surface S. Figure 2 In the example of , such recesses are formed at the positions indicated by arrows on the joined surface S. In view of the fact that the joined surface S satisfies the first condition or the second condition, a plurality of recesses are usually spaced apart from each other and are arranged at a point.

[0039] When a recessed portion is formed on the bonded surface S to a degree satisfying at least one of the third condition and the fourth condition, when the dielectric substrate 100 and the base plate 200 are bonded, the uncured adhesive enters the recessed portion and then cures. Since the so-called "anchor effect" is increased, the bonding strength between the bonding layer 300 and the bonded surface S is increased.

[0040] As described above, in the electrostatic suction cup 10 involved in this embodiment, the shape of the bonding surface S of the ceramic film 231 is made to satisfy the various conditions described previously, thereby suppressing the unevenness of the thickness of the bonding layer 300 while fully improving the bonding strength between the bonding layer 300 and the bonding surface S based on the anchoring effect.

[0041] When the bonding layer 300 and its vicinity are subjected to large thermal stress during processing of the substrate W, there is a concern that the bonding layer 300 may be partially peeled off at the interface on either the dielectric substrate 100 side or the ceramic film 231 side. Figure 3 (A) schematically depicts an example in which the bonding layer 300 peels off at the interface on the ceramic film 231 side. At this time, since a small gap G1 is formed between the bonding layer 300 and the ceramic film 231, a part of the bonded surface S is exposed to the outside through the gap G1. As a result, insulation breakdown may occur between this part and surrounding components (for example, a part of a semiconductor manufacturing device).

[0042] Therefore, in the electrostatic chuck according to the present embodiment, the bonded surface S is formed in a manner that satisfies the above-mentioned conditions, thereby improving the bonding strength between the bonding layer 300 and the bonded surface S. If the bonding layer 300 and its vicinity are subjected to large thermal stress, the bonding layer 300 of the present embodiment may be peeled off at the interface on the dielectric substrate 100 side before being peeled off at the interface on the ceramic film 231 side, or may be broken inside the bonding layer 300. Figure 3 (B) schematically depicts an example in which the bonding layer 300 peels off at the interface on the dielectric substrate 100 side. At this time, although a small gap G2 is formed between the bonding layer 300 and the dielectric substrate 100, the bonded surface S of the ceramic film 231 is still in a state where the entirety is covered by the bonding layer 300. Even when a fracture occurs inside the bonding layer 300, the same state is achieved, so the bonded surface S of the ceramic film 231 is not exposed to the outside due to the peeling of the bonding layer 300. Therefore, it is possible to suppress the occurrence of insulation breakdown near the bonding layer 300, and specifically, it is possible to fully suppress the occurrence of insulation breakdown through the exposed portion of the ceramic film 231.

[0043] Furthermore, when the electrostatic chuck 10 is mounted in a semiconductor manufacturing apparatus, the portion of the ceramic film 230 other than the ceramic film 231 is covered from the outside by other structural members (eg, a focus ring, etc.), so the possibility of dielectric breakdown occurring in this portion is low.

[0044] If the value of the maximum valley depth (Sv) of the third condition or the maximum height (Sz) of the fourth condition is increased, the bonding strength between the bonding layer 300 and the bonded surface S based on the anchoring effect can be further improved. However, if these values ​​are made too large, the concave portion of the bonded surface S is further deepened, and the porosity of the ceramic film 230 is increased, so that insulation breakdown may occur easily through the ceramic film 230. In addition, there is a concern that helium may leak through the ceramic film 230.

[0045] Therefore, it is preferable that the joined surface S is formed so as to further satisfy at least one of the fifth and sixth conditions below. Condition 5: Maximum valley depth (Sv) ≤ 100.0 μm Condition 6: Maximum height (Sz) ≤ 100.0 μm

[0046] When the joined surface S is formed as described above, the recessed portion does not become too deep, and thus insulation breakdown and the like via the ceramic film 230 can be sufficiently suppressed.

[0047] The parameters of the arithmetic mean height (Sa) in the first condition, the maximum valley depth (Sv) in the second condition, the root mean square height (Sq) in the third condition, and the maximum height (Sz) in the fourth condition can be obtained by measuring the entire specified area of ​​the joint surface S as a "surface" using a roughness measuring device. As the above-mentioned "specified area", it is preferred to have a surface with a thickness of 350,000 μm. 2 By measuring the above parameters in such an area as a target and making the shape of the joined surface S a shape satisfying the first condition, etc., the occurrence of insulation breakdown can be sufficiently suppressed without being affected by measurement errors.

[0048] In the technical field of forming a ceramic film by spraying, it is known that the porosity of the ceramic film changes according to various film forming conditions. For example, the porosity of the formed ceramic film changes according to the spraying method such as high-speed flame spraying or plasma spraying and the size of the particle size of the spraying material. By appropriately selecting such film forming conditions, the ceramic film 231 can be formed in a manner that satisfies the third condition or the fourth condition and satisfies the fifth condition or the sixth condition. Thereafter, the surface S to be joined is ground as needed, so that a shape that satisfies the first condition or the second condition can be formed.

[0049] Above, the present embodiment has been described with reference to specific examples. However, the present invention is not limited to these specific examples. With regard to these specific examples, as long as they have the characteristics of the present invention, the technology that is appropriately designed and changed by those skilled in the art is also included in the scope of the present invention. The various elements and their configurations, conditions, shapes, etc. possessed by the aforementioned specific examples are not limited to the illustrated contents, but can be appropriately changed. As long as there is no technical contradiction, the various elements possessed by the aforementioned specific examples can be appropriately changed and combined.

Claims

1. An electrostatic chuck, characterized in that: Possessing: a dielectric substrate; a base plate formed of a metal material; and a bonding layer for bonding the dielectric substrate and the base plate, At least a portion of the base plate facing the bonding layer is covered with a ceramic film, and a surface of the ceramic film serves as a bonding surface. The joined surfaces satisfy, Condition 1: Arithmetic mean height Sa ≤ 1.5 μm, Second condition: RMS height Sq ≤ 2.0 μm, At least one of the above conditions 1 and 2 is met, Condition 3: Maximum valley depth Sv ≥ 20.0 μm, Condition 4: Maximum height Sz ≥ 20.0 μm, At least one of the third and fourth conditions above.

2. The electrostatic chuck according to claim 1, characterized in that: The joined surfaces satisfy, The fifth condition: the maximum valley depth Sv ≤ 100.0 μm, Condition 6: Maximum height Sz ≤ 100.0 μm, At least one of the above conditions 5 and 6.

3. The electrostatic chuck according to claim 1, wherein: The ceramic film is a film formed by sputtering.

4. The electrostatic chuck according to claim 1, wherein: The arithmetic mean height Sa in the first condition is: The maximum valley depth Sv in the second condition is, The root mean square height Sq in the third condition is, And the maximum height Sz in the fourth condition, The bonding surface has a thickness of 350000 μm. 2 The value is obtained by measuring the entire area of ​​the above width.

Images