JP7828225B2 - Electrostatic chuck and manufacturing method thereof - Google Patents

Description

The present invention relates to an electrostatic chuck that is attached to the surface of a base and attracts and holds an object to be attracted, and a method for manufacturing the same.

For example, in the manufacturing process of flat panel displays, relatively large substrates made of glass, quartz, or resin are subjected to various vacuum processes, such as film formation using a plasma atmosphere, ion implantation, and etching. Vacuum processing equipment for performing such vacuum processes generally includes a stage equipped with an electrostatic chuck that positions and holds the substrate within a vacuum chamber in a vacuum atmosphere. During vacuum processing, the substrate, which serves as an object attracted to the electrostatic chuck, may be cooled and maintained at a predetermined temperature or below through heat exchange with the stage. This requires that the electrostatic chuck be able to attract and hold the substrate in close contact with the entire surface until the vacuum processing is completed.

This type of electrostatic chuck is known, for example, from Patent Document 1. This chuck has a dielectric layer (holding base) made of a ceramic material whose main component is Al ₂ O ₃ (alumina) and whose volume resistivity is in the range of 10 ⁸ Ωcm to 10 ¹⁴ Ωcm, and a pair of positive and negative electrode layers are incorporated therein. The dielectric layer has its substrate attracting surface facing up, and the portion of the dielectric layer located above the electrode layer is made thinner, so that an attracting force dominated by the Johnsen-Rahbek force is exerted to attract the substrate. In this case, the electrode layer can be configured so that each electrode exerts a gradient force in addition to the Johnsen-Rahbek force.

With the above configuration, for example, when forming a conductive film on the surface of an insulating substrate through a film-forming process, the substrate, which is less likely to polarize before the start of vacuum processing, can be attracted by an attraction force dominated by gradient forces. Once the conductive film is formed on the substrate surface, the substrate can be maintained in a held state by an attraction force dominated by Johnsen-Rahbek forces. However, if attraction forces based on both Johnsen-Rahbek forces and gradient forces can be generated, and the portion of the dielectric layer located above the electrode layer is made of the same ceramic material, there is a problem in that when an attraction force dominated by either Johnsen-Rahbek forces or gradient forces is generated, the attraction force cannot be effectively strengthened.

Patent No. 4976911

The present invention has been developed in consideration of the above points, and its objective is to provide an electrostatic chuck and a method for manufacturing the same that always produces a uniform attracting force when attracting an object by generating an attracting force dominated by the Johnsen-Rahbek force or gradient force.

In order to solve the above problems, the electrostatic chuck of the present invention is provided on a surface of a base and attracts an object to be attracted. The electrostatic chuck includes a dielectric layer having a volume resistivity of ¹⁰ Ωcm or more and an electrode layer incorporated in the dielectric layer, the electrode layer having a flat first electrode portion and a pair of positive and negative second electrode portions having a line width narrower than that of the first electrode portion and arranged in close proximity to each other, and is characterized in that, with the attracting surface side of the dielectric layer facing up toward the object to be attracted, a portion of the dielectric layer located above the first electrode portions is composed of a low volume resistivity layer having a locally reduced volume resistivity.

Based on the above, for example, when a conductive film is formed on an insulating substrate such as glass as an object to be attracted, after placing the substrate on the electrostatic chuck, applying a DC voltage (e.g., 1 kV to 5 kV) between the positive and negative electrodes of the second electrode unit causes an attracting force dominated by gradient force to be exerted, and the substrate is attracted to the upper surface of the dielectric layer. Then, once a conductive film is formed on the surface of the substrate, applying a DC voltage (e.g., 10 V to 10,000 V) to the first electrode unit causes an attracting force dominated by Johnsen-Rahbek force to be exerted, maintaining the substrate attracted to the upper surface of the dielectric layer. Thus, by adopting a configuration in which the portions of the dielectric layer located above the first and second electrode units have different volume resistivities, the present invention can consistently obtain a uniform attracting force, even when an attracting force dominated by Johnsen-Rahbek force or gradient force is exerted to attract an object to be attracted. Therefore, the substrate Sw can be attracted and held with a substantially constant attracting force during the formation of a conductive film on the substrate. In this case, if the volume resistivity of the dielectric layer located above the second electrode unit is less than ¹⁰ Ωcm, a strong adsorptive force dominated by gradient forces will not be exhibited even if the DC voltage applied between the positive and negative electrodes is increased. On the other hand, if the volume resistivity of the dielectric layer located above the first electrode unit is also outside the range of ¹⁰ Ωcm to ¹⁰ Ωcm, a strong adsorptive force dominated by Johnsen-Rahbek forces will not be exhibited. Note that the first electrode unit is typically composed of a pair of electrodes having equal areas (bipolar type), but may be a monopolar type when a film formation process is performed using a plasma atmosphere.

In the present invention, the low volume resistivity layer is preferably formed by doping the dielectric layer with a dopant, and the dielectric layer and the low volume resistivity layer are preferably formed as thermally sprayed films. Here, for example, when forming the dielectric layer from a material primarily composed of Al ₂ O ₃ , a sintering method may be used for its manufacture. However, such a sintering method makes it difficult to form layers with different volume resistivities and uniform interfaces due to thermal expansion and contraction during sintering, resulting in problems such as dielectric breakdown. In contrast, forming the dielectric layer and the low volume resistivity layer as thermally sprayed films is advantageous because it makes it easy to form layers with different volume resistivities and uniform interfaces. Furthermore, when the dielectric layer is primarily composed of Al ₂ O ₃ , a dielectric layer with a volume resistivity in the range of ¹⁰ Ωcm to ¹⁰ Ωcm can be easily achieved by using at least one dopant selected from the group consisting of TiO ₂ , Cr, Ca, Mg, SiO ₂ , and C.

In order to solve the above-mentioned problems, a manufacturing method of an electrostatic chuck of the present invention, which is provided on the surface of a base and attracts and holds an object to be attracted, includes the following steps: a first step of forming a first dielectric layer portion having a volume resistivity of 10 ^Ωcm or more on the surface of the base by thermal spraying; a second step of forming, on the surface of the first dielectric layer portion, a flat first electrode portion and a pair of positive and negative second electrode portions having a line width narrower than that of the first electrode portion and arranged closely to each other; and a third step of forming, on the surface of the first dielectric layer portion by thermal spraying, a second dielectric layer portion having a volume resistivity equivalent to that of the first dielectric layer portion so as to cover the second electrode portion, and a third dielectric layer portion having a volume resistivity lower than that of the first dielectric layer portion so as to cover the first electrode portion.

In the present invention, it is preferable to use the same dielectric material as the spray material for the first dielectric layer portion and the second dielectric layer portion, and to use the dielectric material doped with a dopant at a predetermined weight ratio as the spray material for the third dielectric layer portion. When the dielectric layer is mainly composed of _Al2O3 , the _dopant can be at least one selected from _TiO2 , Cr, Ca, Mg, _SiO2 and C.

FIG. 2 is a schematic cross-sectional view showing the electrostatic chuck of the present embodiment in a state where a substrate is attracted to the electrostatic chuck; FIG. 2 is a cross-sectional view taken along line II-II in FIG. 2A to 2D are diagrams showing a manufacturing procedure for the electrostatic chuck shown in FIG. 1 . 10 is a graph showing experimental results illustrating the effects of the present invention.

Hereinafter, with reference to the drawings, an embodiment of an electrostatic chuck and a manufacturing method thereof of the present invention for adsorbing a glass substrate (hereinafter referred to as "substrate Sw") to a substrate Sw in a vacuum chamber not shown will be described. In the following, terms indicating directions such as up, down, left, and right refer to Figure 1.

1 and 2 , the electrostatic chuck EC of this embodiment includes a dielectric layer 1 provided on the upper surface of a base Bp made of a metal such as titanium or aluminum, which has a rectangular outline corresponding to the substrate Sw and a flat upper surface, and an electrode layer 2 incorporated in the dielectric layer 1. The dielectric layer 1 is formed of a sprayed film having a thickness of ⁵⁰ μm or more, which is formed by spraying a dielectric material such as Al ₂ O ₃ (alumina), AlN (aluminum nitride), or SiC (silicon carbide) as a spray material so as to have a volume resistivity of 10 Ω cm or more. Note that a known spraying device can be used to form the sprayed film, and therefore a detailed description thereof will be omitted here.

The electrode layer 2 has a pair of positive and negative first electrode portions 21a, 21b provided on both sides of the dielectric layer 1 in the longitudinal direction (left-right direction in FIG. 1 ), and a pair of positive and negative second electrode portions 22a, 22b provided in a central region located between the first electrode portions 21a, 21b. The first electrode portions 21a, 21b, each having the same area, are each composed of a metal film having a thickness of 1 μm or more, which is formed into a flat plate shape by vacuum deposition or sputtering using a high-melting-point material with relatively high electrical conductivity, such as tungsten or molybdenum. The area of the first electrode portions 21a, 21b (line width: width in the left-right direction in FIG. 1 ) is set appropriately taking into consideration the area of the substrate Sw, the chucking force required to chucking the substrate Sw, the thickness and volume resistivity of the low volume resistivity layer described below, and the like. The second electrodes 22a, 22b are also composed of a metal film with a thickness of 1 μm or more, formed in a predetermined pattern by vacuum deposition, sputtering, or CVD using a high-melting-point material with relatively high electrical conductivity, such as tungsten or molybdenum. In this embodiment, the positive second electrode 22a and the negative second electrode 22b are formed in a pattern in which they are alternately arranged at close intervals so as to extend linearly and face each other with a line width narrower (thinner) than that of the first electrodes 21a, 21b, so that an electric field is efficiently generated when a voltage is applied. In this case, the line length is preferably set to 5 cm/ ^cm² or less. Note that the pattern of the positive second electrode 22a and the negative second electrode 22b is not limited to this, and may be curved, comb-like, or circumferential, as long as it can increase the length of the facing surfaces.

The thickness of the dielectric layer 1 located above the first electrode portions 21a, 21b and the second electrode portions 22a, 22b is set to, for example, 50 μm or more, taking into consideration that the chucking force dominated by the Johnsen-Rahbek force varies with the square of the distance between the substrate Sw and the first electrode portions 21a, 21b. In addition, the portion of the dielectric layer 1 located above the first electrode portions 21a, 21b is formed as a low-volume resistivity layer (the third dielectric layer portion 1c described below) with locally reduced volume resistivity. The volume resistivity of the low-volume resistivity layer 1c is set to a range of 10 ^Ωcm to 10 ^Ωcm to effectively strengthen the chucking force when the chucking force dominated by the Johnsen-Rahbek force is exerted. When a predetermined voltage (e.g., 10 V to 10,000 V) is applied between the pair of positive and negative first electrode portions 21a, 21b by a DC power supply E1, a chucking force dominated by the Johnsen-Rahbek force is exerted. On the other hand, when a predetermined voltage (for example, 1 kV to 5 kV) is applied between the pair of positive and negative second electrodes 22a, 22b by the DC power supply E2, an attraction force dominated by gradient force is generated.

Here, if the volume resistivity of the dielectric layer 1 (specifically, the portion located above the region where the second electrode portions 22a and 22b are formed) is less than ¹⁰ Ωcm, an attractive force dominated by the gradient force cannot be effectively exerted even if the DC voltage applied to the second electrode portions 22a and 22b is increased. Similarly, if the volume resistivity of the low volume resistivity layer is outside the range of ¹⁰ Ωcm to 10 ^Ωcm , an attractive force dominated by the Johnsen-Rahbek force cannot be exerted. Furthermore, the low volume resistivity layer 1c can be formed, for example, by thermally spraying a thermal spray material obtained by doping (adding) a predetermined dopant to the above-mentioned dielectric material. When the dielectric material is primarily composed of Al ₂ O ₃ , the dopant can be at least one selected from TiO ₂ , Cr, Ca, Mg, SiO ₂ , and C. The method for forming the low volume resistivity layer 1 c is not limited to this, and for example, a dopant material may be doped (injected) using an ion implantation device. An example of a method for manufacturing the electrostatic chuck EC of this embodiment will be described below with reference to FIG.

A dielectric material primarily composed of _Al2O3 ( _alumina ) is used as the spray material, and a known thermal spraying device is used to spray the entire upper surface of the base Bp as shown in Figure 3(a) to form a dielectric layer (referred to as the first dielectric layer 1a) with a predetermined thickness and a volume resistivity of ¹⁰¹² Ωcm or more (Step 1). Next, a metal material primarily composed of molybdenum is used as the sputtering target, and a known sputtering device is used to simultaneously pattern a pair of positive and negative first electrodes 21a, 21b and a pair of positive and negative second electrodes 22a, 22b on the upper surface of the first dielectric layer 1a as shown in Figure 3(b) (Step 2). For the patterning, a mask plate having openings corresponding to the first electrodes 21a, 21b and the second electrodes 22a, 22b may be used.

Next, as shown in FIG. 3( c), a mask plate Mp1 having an area equivalent to the top surface of the first dielectric layer portion 1a and an opening Mo vertically aligned with the area where the second electrode portions 22a, 22b are formed is placed on the first dielectric layer portion 1a on which the first electrode portions 21a, 21b and the second electrode portions 22a, 22b are formed. In this state, the same dielectric material as used in the first step is used as the thermal spray material, and a known thermal spraying device is used to thermally spray the top surface of the first dielectric layer portion 1a so as to cover the area where the second electrode portions 22a, 22b are formed, thereby forming a dielectric layer (referred to as the second dielectric layer 1b) with a predetermined thickness and a volume resistivity of ¹⁰ Ωcm or more. At this time, the thermal spray material is also filled between the adjacent first electrode portions 21a, 21b and second electrode portions 22a, 22b (in the horizontal direction in FIG. 1 ).

Next, as shown in FIG. 3(d), a plate Mp2 having an area matching the upper surface of the second dielectric layer portion 1b is placed on the second dielectric layer portion 1b. In this state, a thermal spray material, which is a conductive material used in the first step plus a dopant at a predetermined weight ratio, is used as the thermal spray material. Using a known thermal spraying device, the thermal spray material is sprayed onto the upper surface of the first dielectric layer portion 1a so as to cover the area where the first electrodes ^21a and ^21b are formed. This forms a dielectric layer (referred to as the third dielectric layer portion 1c) with a predetermined thickness as a low-resistivity layer with a volume resistivity ranging from 10 Ωcm to 10 Ωcm (step 3). The dopant is at least one selected from TiO ₂ , Cr, Ca, Mg, SiO ₂ , and C, and is added at a predetermined weight ratio. Finally, the upper surfaces of the second dielectric layer portion 1b and the third dielectric layer portion 1c are machined to flatten them.

According to the above embodiment, when a conductive film is formed on a substrate Sw, after the substrate is placed on the electrostatic chuck Ec, a DC voltage is applied between the pair of positive and negative second electrodes 22a, 22b by the first power supply E1, causing an attraction force dominated by gradient force to occur, and the substrate Sw is attracted to the upper surface of the dielectric layer 1. Then, once a conductive film has been formed on the surface of the substrate Sw, a DC voltage is applied between the first electrodes 21a, 21b, causing an attraction force dominated by Johnsen-Rahbek force to occur, maintaining the substrate Sw attracted to the upper surface of the dielectric layer 1. In this manner, in the electrostatic chuck EC of this embodiment, the portions of the dielectric layer located above the first electrode portions 21a, 21b and the second electrode portions 22a, 22b are composed of the second dielectric layer portion 1b and the third dielectric layer portion 1c having different volume resistivities. This allows for a constant, uniform attracting force to be obtained even when the substrate Sw is attracted by an attracting force dominated by the Johnsen-Rahbek force or the gradient force. This allows the substrate Sw to be attracted and held with a substantially constant attracting force while a conductive film is being formed on the substrate Sw. Furthermore, by forming the second dielectric layer 1b and the third dielectric layer 1c by thermal spraying, the second dielectric layer 1b and the third dielectric layer 1c are formed with a uniform interface in the vertical direction and different volume resistivities, preventing problems such as dielectric breakdown. The interface between the second dielectric layer 1c and the third dielectric layer 1b is preferably located along a vertical line passing through substantially the midpoint between the adjacent first electrode portions 21a, 21b and second electrode portions 22a, 22b.

Next, to confirm the effects of the present invention, an electrostatic chuck ₍ invention product) manufactured by the above-described manufacturing method was used. The dielectric material was primarily composed of _Al2O3 , and the dielectric material constituting the low volume resistivity layer was the same as that used in the first step, with _TiO2 added at a predetermined weight ratio. The clamping force was measured when clamping a substrate Sw. As a comparison product, a dielectric layer was formed integrally over the entire surface of the first dielectric layer 1c using a known thermal spraying device, using the same dielectric material as used in the first step as the spray material in the third step. As shown in FIG. 4, the clamping force of the comparison product was approximately 500 Pa when a voltage of 3 V was applied to the first electrodes 21a and 21b by the DC power supply E1. In contrast, the clamping force of the invention product increased as the voltage applied to the first electrodes 21a and 21b by the DC power supply E1 increased, and a strong clamping force of approximately 2000 Pa was obtained at a voltage of 3 V.

The above describes an embodiment of the present invention, but various modifications are possible without departing from the scope of the technical concept of the present invention. In the above embodiment, the first electrodes 21a, 21b are described as being of a so-called bipolar type. However, when applied to a device that performs film formation processing using a plasma atmosphere, they can also be configured as a so-called monopolar type. Furthermore, in the above embodiment, the second electrodes 22a, 22b are described as being arranged in the center, with the first electrodes 21a, 21b on either side. However, this is not limited to this, and the electrode arrangement can be changed as appropriate depending on the size and shape of the substrate Sw to be attracted by exerting an attraction force dominated by Johnsen-Rahbek force or gradient force. Furthermore, the method of forming the first and second electrodes 21a, 21b, 22a, 22b is not limited to the above examples, and they can also be formed by thermal spraying or plating.

EC...electrostatic chuck, 1...dielectric layer, 1a...first dielectric layer portion (constituent element of dielectric layer), 1b...second dielectric layer portion (constituent element of dielectric layer), 1c...third dielectric layer portion (low volume resistivity layer: constituent element of dielectric layer), 2...electrode layer, 21a, 21b...first electrode portion, 22a, 22b...second electrode portion, Bp...base, Sw...substrate.

Claims (8)

1. An electrostatic chuck provided on a surface of a base placed in a vacuum chamber in which a conductive film is formed on a surface of an insulating object to be attracted, the electrostatic chuck attracting the object to be attracted,
A capacitor comprising a dielectric layer having a volume resistivity of 10 ¹² Ωcm or more and an electrode layer incorporated in the dielectric layer, the electrode layer having a flat first electrode portion and a pair of positive and negative second electrode portions having a line width narrower than that of the first electrode portion and arranged close to each other,
a portion of the dielectric layer located above the first electrode portion, with the attracting surface of the dielectric layer facing upward, comprising a low volume resistivity layer having locally reduced volume resistivity ;
an electrostatic chuck configured such that application of a DC voltage between the positive and negative electrodes of a second electrode unit generates an attractive force dominated by a gradient force, thereby attracting the object to the upper surface of the dielectric layer; and when application of a DC voltage to the first electrode unit causes a conductive film to be formed on the surface of the object, application of a Johnsen-Rahbek force dominantly generates an attractive force, thereby attracting the object to the upper surface of the dielectric layer . 2. The electrostatic chuck according to claim 1, wherein the volume resistivity of the low volume resistivity layer is set in the range of 10 ⁶ Ωcm to 10 ¹² Ωcm. 2. The electrostatic chuck of claim 1, wherein the low volume resistivity layer is formed by doping the dielectric layer with a dopant. The electrostatic chuck of claim 3, wherein the dielectric layer and the low volume resistivity layer are formed from thermally sprayed films. _5. The electrostatic chuck according to claim 4 , wherein the dielectric layer is mainly composed of _Al2O3 , and the dopant is at least one selected from the group consisting of _TiO2 , Cr, Ca, Mg, _SiO2 , and C. The method for manufacturing an electrostatic chuck according to any one of claims 1 to 5,
the dielectric layer is composed of a first dielectric layer portion, a second dielectric layer portion, and a third dielectric layer portion, and a first step of forming the first dielectric layer portion having a volume resistivity of 10 ¹² Ωcm or more on the surface of the base by thermal spraying;
a second step of forming the first electrode portion in a flat plate shape and a pair of positive and negative second electrode portions having a line width narrower than that of the first electrode portion and arranged close to each other on the surface of the first dielectric layer portion;
and a third step of forming, by thermal spraying, on a surface of the first dielectric layer portion, the second dielectric layer portion having a volume resistivity equivalent to that of the first dielectric layer portion so as to cover the second electrode portion, and a third dielectric layer portion as the low volume resistivity layer having a volume resistivity lower than that of the first dielectric layer portion so as to cover the first electrode portion. A method for manufacturing an electrostatic chuck according to claim 6, characterized in that the same dielectric material is used as the spray material for the first dielectric layer portion and the second dielectric layer portion, and the same dielectric material doped with a dopant at a predetermined weight ratio is used as the spray material for the third dielectric layer portion. _8. The method for manufacturing an electrostatic chuck according to claim 7, wherein the third dielectric layer portion is mainly composed of _Al2O3 , and the dopant is at least one selected from the group consisting of _TiO2 , Cr, Ca, Mg, _SiO2 , and C.