JP5279455B2 - Electrostatic chuck - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrostatic chuck which can reduce leakage current flowing in an object to be attracted and reduce the flatness of the object, and generates less particle. <P>SOLUTION: The electrostatic chuck includes: a disc-like ceramic base material whose diameter is at least 200 mm; a plurality of projections formed on one major surface of the ceramics base material; an electrode formed on the major surface between the projections; and a resin covering the electrode and formed between the projections. The flatness of a surface formed at a top part of the plurality of projections is at most 5 &mu;m. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

The present invention relates to an electrostatic chuck having a dielectric layer on an electrode and electrostatically adsorbing an object to be adsorbed such as a silicon wafer or a glass substrate on the dielectric layer by applying a voltage to the electrode.

When manufacturing semiconductor devices and flat panel displays, electrostatic chucks are used to hold silicon wafers, glass substrates, and the like, particularly in a vacuum atmosphere. The dielectric layer of the electrostatic chuck has a specific volume resistance. When a voltage of several hundred volts or more is applied during adsorption, a leakage current corresponding to the volume resistance of the dielectric layer flows.

When the object to be adsorbed is a silicon wafer, this leakage current flows through the inside and the surface of the silicon wafer, and it has become prominent that they adversely affect the manufacture of devices. Leakage current flowing inside the silicon wafer may destroy devices formed on the silicon wafer. In addition, since the current flowing on the surface of the recon wafer affects the magnetic field in an apparatus using an electron beam, for example, it may be difficult to control the electron beam. For these reasons, there has been a strong demand for an electrostatic chuck with a small leakage current flowing through the silicon wafer during adsorption.

Further, as a problem associated with device miniaturization, the flatness of a silicon wafer at the time of adsorption has become a problem. For example, in the CVD process of device manufacturing, if the flatness of the silicon wafer at the time of adsorption is poor, the film quality variation within the silicon wafer surface will increase, and the exposure accuracy will deteriorate in the exposure process. It has become. For these reasons, an electrostatic chuck having a smaller flatness of the attracting portion has been demanded.

Furthermore, with the miniaturization of devices, the demand for particles generated when a silicon wafer is attracted has become stricter. Particles generated at the time of wafer adsorption cause contamination of the process environment and decrease in device yield. For this reason, there has been a strong demand for an electrostatic chuck that generates fewer particles when the wafer is attracted.

From the background as described above, there has been a demand for an electrostatic chuck in which the leakage current flowing through the object to be adsorbed is small, the flatness of the object to be adsorbed can be reduced, and the generation of particles is small.

For example, Patent Document 1 discloses an electrostatic chuck that uses a Johnsen-Rahbek force, and includes a dielectric layer including a ceramic layer and a resin layer formed on the ceramic layer, and generates an electrostatic adsorption force. An electrostatic chuck is described in which the dielectric layer has a protrusion for supporting the substrate, and the resin layer has a thickness of 1 to 30 μm. According to such an electrostatic chuck, since the resin layer on the ceramic layer can suppress the occurrence of excessive leakage current and the resin layer is softer than the ceramic layer, the dielectric layer Can prevent the generation of particles and scratches caused by the protrusions of the substrate rubbing against the substrate

JP 2006-287210 A

Here, in order to reduce the leakage current, it is only necessary to form a dielectric layer with a material having a high volume resistance. In order to develop an adsorption force with an electrostatic chuck using a material with a high volume resistance as a dielectric layer, It is desirable to use a Coulomb force type electrostatic chuck that can obtain an attractive force by thinning the insulating layer.

In the electrostatic chuck disclosed in Patent Document 1, a resin layer having a thickness of 1 to 30 μm is formed as a dielectric layer, but this uses a Johnsenler-Beck force and is not a Coulomb force type electrostatic chuck. The electrostatic chuck using the Johnsen-Rahbek force does not require the strict control of the dielectric layer thickness as the Coulomb force type electrostatic chuck. This is because the electrostatic chuck using the Coulomb force is required to strictly control the thickness of the dielectric layer because the variation in the thickness of the dielectric layer leads directly to the variation in the attractive force.

In addition, when the resin layer is used as a dielectric layer, it is difficult to reduce the flatness of the surface of the dielectric layer, and an electrostatic chuck that attracts a silicon wafer of 8 inches or more, which is currently mainstream, has a flatness of 5 μm or less. It is very difficult to make. Furthermore, since the Young's modulus of polyimide is 2-3 GPa and the Young's modulus of silicon wafer is 130-190 GPa, the polyimide is easily deformed when the silicon wafer is adsorbed. Therefore, there has been a problem that the flatness of the silicon wafer surface at the time of suction is significantly worse than the flatness of the electrostatic chuck surface. Therefore, it has been difficult to form a dielectric layer having a small flatness with a resin layer in an electrostatic chuck using Coulomb force.

As described above, resins such as polyimide generally have a low Young's modulus, and it is difficult to perform high flatness processing. In order to obtain an electrostatic chuck having a surface with high flatness, it is most preferable to use a ceramic dielectric layer. If the dielectric layer is ceramic, a flatness of 5 μm or less can be achieved with an electrostatic chuck of 8 inches or more. It is not difficult to do.

However, when the dielectric layer is formed of ceramics, much more particles are generated than polyimide. For example, when an alumina electrostatic chuck and a polyimide electrostatic chuck having the same contact area with a silicon wafer and exhibiting the same adsorption force are compared, the number of particles of an alumina electrostatic chuck is 100 times that of a polyimide electrostatic chuck. That's it. Therefore, in the case of an electrostatic chuck using ceramic as a dielectric layer, a type in which pins are formed in order to reduce an adsorption area with a silicon wafer and contacted on the pin surface is the mainstream.

However, in order to realize the number of particles similar to or less than that of the polyimide electrostatic chuck, for example, the contact area ratio needs to be 1% or less. However, in the case of such a contact area ratio, although depending on the pin area and pin height, in the case of many ceramics such as alumina and aluminum nitride, sufficient adsorption is required unless the dielectric layer thickness is 10 μm or less. I can't get power. It is very difficult to manufacture a dense ceramic plate having a pin with such a thickness of 8 inches or more, particularly 12 inches or more.

The present invention has been made in view of these problems, and provides an electrostatic chuck in which leakage current flowing through an object to be adsorbed is small, flatness of the object to be adsorbed can be reduced, and generation of particles is small. Is.

In order to solve these problems, the present invention provides a disk-shaped ceramic substrate having a diameter of 200 mm or more, a plurality of protrusions formed on one main surface of the ceramic substrate, and a main portion between the protrusions. An electrode provided on a lower surface than the top of the protrusion, and a resin that covers the electrode and is formed between the protrusions, and the distance between the side surface of the protrusion and the electrode is The electrostatic chuck is at least larger than the height difference between the top of the protrusion and the electrode .

As described above, in an electrostatic chuck having a diameter of 8 inches (200 mm) or more, particularly 12 inches (300 mm) or more, an electrostatic chuck that keeps the flatness of an object to be adsorbed and generates less particles is manufactured. Was difficult. The present invention provides a high-performance electrostatic chuck having such a size that has been difficult in the past.

In the present invention, the electrode is formed on the main surface between the plurality of protrusions formed on one main surface of the substrate. This is to form a dielectric layer made of resin so as to cover the electrodes. In a conventional structure in which electrodes are embedded in a ceramic sintered body, it is necessary to thinly process the ceramic dielectric layer as described above, and cracks are likely to occur. Therefore, since a certain thickness is required, it becomes difficult to develop an adsorption force due to the Coulomb force. In the present invention, since the electrodes are formed on the main surface of the substrate, a dielectric layer made of resin can be easily formed, and the thickness thereof can be controlled by the height of the protrusions. Note that the electrode formed on the main surface of the protrusion is covered with a resin and thus does not appear on the surface of the electrostatic chuck.

Also, if the structure is such that the electrode is covered and the resin formed between the protrusions is a dielectric layer, the thickness of the protrusion can be made uniform by making the height of the protrusion uniform, so the dielectric layer is made of resin. Even if it is formed, the in-plane variation of the attractive force can be kept small. Further, by filling the space between the protrusions with the resin, there is an effect of reducing the impact when the object to be adsorbed is placed on the protrusions and suppressing the generation of particles.

Furthermore, it is desirable that the flatness of the surface formed by the tops of the plurality of protrusions is 5 μm or less. By using ceramics as the protrusions, it is possible to achieve high flatness, and by forming a resin between the protrusions, generation of particles can be suppressed. If the resin is formed up to the top of the protrusion, the flatness is remarkably lowered, which is not preferable. Further, since the resin at the top of the protrusion is easily peeled off, it is difficult to prepare the surface by surface grinding. Here, the plurality of protrusions on the surface formed by the tops of the plurality of protrusions means all protrusions that come into contact with the object to be adsorbed. Unless protrusions having different heights that are not intended to come into contact with the object to be adsorbed are formed, all protrusions formed on the main surface.

It is desirable that the height difference between the electrode and the top of the protrusion is 100 μm or less. The adsorption force per unit area in the Coulomb force type electrostatic chuck is expressed by the following equation. According to this equation, the thickness of the dielectric layer in the case where polyimide (dielectric constant 3 to 4) is used as the resin layer needs to be 100 μm or less.
F = 1/2 · ε · (V / d) ²
ε: Dielectric constant of dielectric layer V: Applied voltage d: Dielectric layer thickness In the present invention, by adjusting the height of the protrusion, the thickness of the resin layer as the dielectric layer may be 100 μm or less. It is possible to obtain an electrostatic chuck having a sufficient attractive force and a small leakage current. Further, by adjusting this distance, the suction force can also be adjusted. Therefore, if it is desired to increase the suction force at a specific location in the plane, the distance of that portion may be shortened.

The volume resistivity of the resin is desirably 1 × 10 ¹⁵ Ωcm or more, and the volume resistivity of the ceramic substrate is desirably 1 × 10 ¹² Ωcm or more. The reason why the volume resistivity of the resin is 1 × 10 ¹⁵ Ωcm or more is to reduce the leakage current. By forming the dielectric layer with a material having a high volume resistance, a Coulomb force type electrostatic chuck with little leakage current can be obtained. The reason why the volume resistivity of the ceramic base material is set to 1 × 10 ¹² Ωcm or more is that a leakage current passing through the protrusions may flow slightly from the ceramic base material. This 1 × 10 ¹² Ωcm is the upper limit value of the volume resistivity of the dielectric layer in the Johnsen-Lehbeck force type electrostatic chuck, and below this value, the leakage current increases rapidly.

It is desirable that the surface of the resin and the surface formed at the top of the protrusion are substantially flush. By adopting such a structure, it is difficult for particles to be generated even if the ceramic protrusion comes into contact with the object to be adsorbed. The generation of particles is due to the occurrence of degreasing of the ceramics when the object to be adsorbed hits the protrusions or is strongly pressed. In the present invention, a resin is formed between the protrusions and is made to be substantially flush with the surface formed at the top of the protrusion, thereby reducing the impact when the object to be adsorbed is placed on the protrusion and reducing the particle size. Occurrence is suppressed.

Here, that the surface of the resin and the surface formed by the top of the protrusion are substantially flush includes the case where the surfaces are coincident or the surface of the resin is slightly higher. The height of the surface of the resin can be adjusted within a range in which when the object to be adsorbed is adsorbed, the resin is deformed and the object to be adsorbed comes into contact with the protrusion. This is because if there is a space between the object to be adsorbed and the resin, the withstand voltage of the resin layer is lowered, and the effect of suppressing the impact of the silicon wafer is lost, so that the effect of suppressing the generation of particles is reduced. Moreover, since the dielectric constant of space is 1 with respect to the dielectric constants 3-4 of polyimide, the electric charge induced to a silicon wafer will reduce, and the adsorption | suction power of a part with space will fall. Further, in an environment where a corrosive gas is used, since the exposed area is large, corrosion of the dielectric layer proceeds.

Provided is an electrostatic chuck in which leakage current flowing through an object to be adsorbed is small, flatness of the object to be adsorbed can be reduced, and particles are not generated.

Hereinafter, the electrostatic chuck of the present invention will be described in more detail.

FIG. 1 is a schematic view showing an electrostatic chuck of the present invention. A disk-shaped ceramic substrate 11 having a diameter of 200 mm or more, a protrusion 12 formed on one main surface 11a of the ceramic substrate 11, an electrode 13 formed on the main surface 11a between the protrusions 12, and an electrode 13 The resin 14 is covered and formed between the protrusions 12.

The material of the ceramic substrate 11 is desirably higher in rigidity than a silicon wafer that is a typical object to be adsorbed. Further, the volume resistivity of the substrate is desirably 1 × 10 ¹² Ωcm or more. Specifically, alumina, aluminum nitride, silicon nitride, spinel, yttria, cordierite, or the like can be used.

Since the protrusion 12 is formed by processing a ceramic substrate, the material thereof can be the same as that of the ceramic substrate. As the protrusion, a pin type or a rib type can be applied. The pin type can adopt various shapes such as a cylinder, a prism, and a hemispherical type, and the rib type can also have various shapes such as a ring shape. Further, the arrangement of pins and ribs is not particularly limited, and various patterns such as a lattice shape and a radial shape can be adopted. The total area of the tops of the protrusions in contact is preferably 20% or less, more preferably 10% or less, of the total area of the main surface and the tops of the protrusions.

The electrode 13 can be a metal such as copper or nickel, or a compound such as titanium carbide or tungsten carbide. It is better that there is no conductor to be an electrode on the side or periphery of the protrusion. Further, it is preferable that a gap be provided at least for the height difference between the electrode 13 and the top 12a of the protrusion. This is because the risk of creeping discharge between the electrode and the silicon wafer is reduced. The thickness of the electrode is not particularly limited as long as the height difference from the top of the protrusion can be adjusted to 100 μm or less. For example, if the distance between the electrode and the silicon wafer (dielectric layer thickness) is designed to be 20 μm, and the electrode thickness is 2 μm, the protrusion is formed at 22 μm.

It is necessary to use a highly insulating resin 14. For example, since the volume resistance of polyimide is 1 × 10 ¹⁵ Ωcm or more, it can be said that it is a suitable material for the purpose of the present invention. Although polyimide is taken as an example, polyethylene, polycarbonate, neoprene, etc. can be formed by a predetermined method. As long as the particles can be sufficiently reduced and the flatness at the time of desired adsorption can be obtained, the resin does not necessarily have to reach the top of the protrusion, but it is desirable that the resin be substantially flush as described above.

Next, the manufacturing method of the electrostatic chuck of this invention is demonstrated. FIG. 2 is a schematic diagram showing the flow of the manufacturing method.

FIG. 2A shows a state in which the protrusions 22 are formed on one main surface 21 a of the ceramic substrate 21. The ceramic substrate 21 is obtained by molding by a known method such as CIP or casting, and firing by a known method such as normal pressure or hot pressing. The protrusion 22 can be formed by processing one surface of the ceramic substrate such as blasting, a machining center, or chemical etching. The method for processing the protrusion is not particularly limited. The surface of the protrusion thus obtained is lapped so that the flatness of the surface formed by the top portions 22a of the plurality of protrusions is 5 μm or less. By doing so, the flatness of the wafer surface during adsorption can be improved.

Next, as a method for forming the electrode, a method corresponding to the material of the electrode may be appropriately selected, and examples thereof include plating, CVD, sputtering, and brazing. The material of the electrode is not limited to one type. Since ceramics do not wet well with metal, a conductor made of another material may be formed on the conductor after a conductor that wets well with ceramic is disposed on the base.

When the electrode requires a specific pattern, for example, when it is a bipolar comb-like pattern, the pattern may be formed according to the film forming method. A method of forming a pattern by blasting after film formation on the entire surface, or a method of removing the mask 25 after plating with the mask 25 as shown in FIGS. 2B to 2D may be used.

In order to form the resin, it is possible to employ a method of pasting a film from which the protrusions have been deleted in advance, or a method of filling and solidifying a liquid resin other than the protrusions. Further, it can be filled by a vapor phase method. When filled with a liquid resin or a vapor phase method, the resin may adhere to the protrusions 22 or become higher than the protrusions as shown in FIG. 2E. In this case, the protrusion can be exposed by lapping the surface. Since the resin is relatively soft and easily peeled off from the substrate, it was difficult to increase the flatness. However, in the present invention, since the resin 24 is formed between the protrusions, the resin is hardly peeled off and the flatness is low. Secured by the top of the protrusion. Also in this case, the flatness of the surface formed by the top portions 22a of the plurality of protrusions is set to 5 μm or less.

EXAMPLES Hereinafter, the Example of this invention is specifically given with a comparative example, and this invention is demonstrated in detail.

An alumina sintered body (purity 99.5%) having a diameter of 200 mm and a thickness of 10 mm was used as the ceramic substrate. The alumina sintered body was granulated by spray-drying alumina powder, CIP molded, and then fired in the atmosphere. Thereafter, a surface grinding process or the like was applied to obtain a ceramic substrate.

On one surface of the obtained ceramic substrate, a blast mask extracted in a pin pattern of 60 ° staggered with φ 1 mm and pitch 10 mm was placed, and projections were formed by sand blasting. The height of the protrusion was 52 μm.

As shown in FIG. 2, a plating mask was used, and the main surface between the protrusions was plated with copper to form a bipolar electrode (thickness: 2 μm). After the mask was removed by etching, polyimide varnish (Upicote (registered trademark) manufactured by Ube Industries) was filled by screen printing in an amount sufficient to fill the space between the protrusions and solidified. Thereafter, the polyimide varnish on the protrusions was removed by lapping, and an electrostatic chuck according to the present invention in which the flatness of the surface formed by the tops of the plurality of protrusions was 5 μm or less was obtained. In addition, the power supply to the electrode can be performed by taking out the power supply line connected to the electrode from the side surface of the electrostatic chuck and connecting it to an external power source.

For comparison, an electrostatic chuck using alumina as a dielectric layer and a polyimide electrostatic chuck were prepared.

The production of an alumina electrostatic chuck will be described. An alumina base material having a diameter of 200 mm and a thickness of 10 mm and an alumina sintered body having a diameter of 200 mm and a thickness of 3 mm (purity 99.5%) are prepared, and a mask is formed so that a bipolar electrode is formed on one side of the alumina sintered body. Then, 2 μm thick copper plating was applied to obtain a bipolar electrode. Thereafter, the plated surface of the alumina base material and the alumina sintered body was fixed with a silicon adhesive. In the electrostatic chuck of the above embodiment according to the present invention, the polyimide dielectric layer has a thickness of 50 μm. However, in order to obtain an equivalent adsorption force at the same applied voltage with an alumina electrostatic chuck, the dielectric constant of alumina is 6. Therefore, it is necessary to make the dielectric thickness of alumina of 100 μm. Therefore, when an attempt was made to grind a 3 mm alumina sintered body to a thickness of 100 μm by grinding, cracks occurred when the thickness was 400 μm. Therefore, an alumina electrostatic chuck could not be obtained.

The production of a polyimide electrostatic chuck will be described. An alumina sintered body (purity 99.5%) having a diameter of 200 mm and a thickness of 10 mm was used as the ceramic substrate. By lapping one main surface of this base material, the flatness is set to 5 μm, and the main surface is masked to be an electrode having the same shape as the above-described embodiment, and copper plating with a thickness of 2 μm is applied to form a bipolar type. An electrode was obtained. A polyimide film having a thickness of 50 μm (Upilex (registered trademark) manufactured by Ube Industries Co., Ltd.) was attached thereon to obtain a polyimide electrostatic chuck.

A silicon wafer (diameter 200 mm, thickness 725 μm, thickness variation ± 1 μm) was placed on the electrostatic chuck produced as described above, and ± 1000 V was applied to the bipolar electrode for adsorption.

The flatness of the electrostatic chuck before the suction, that is, the flatness of the surface composed of the tops of the plurality of protrusions, and the flatness of the silicon wafer attracted to the electrostatic chuck were measured at 30 points on any protrusion position using a three-dimensional measuring machine. . For the polyimide electrostatic chuck, the same 30 points on the polyimide were measured. Further, the number of particles having a size of 0.2 μm or more was evaluated on the surface of the silicon wafer adsorbed on the electrostatic chuck using a laser scattering type particle counter.

The electrostatic chuck of the present invention had a low flatness, and the flatness of the adsorbed silicon wafer was also good. The number of particles was equivalent to that of the electrostatic chuck made of polyimide. On the other hand, the flatness of the electrostatic chuck made of polyimide was worse than that of the electrostatic chuck of the present invention.

It is a section schematic diagram of an electrostatic chuck. It is the schematic which shows the manufacturing method of an electrostatic chuck.

Explanation of symbols

10, 20 Electrostatic chuck 11, 21 Ceramic substrate 12, 22 Protrusion 13, 23 Electrode 14, 24 Resin 25 Mask

Claims (5)

A disk-shaped ceramic substrate having a diameter of 200 mm or more;
A plurality of protrusions formed on one main surface of the ceramic substrate;
An electrode formed on a main surface between the protrusions and provided at a position lower than the top of the protrusions ;
A resin that covers the electrode and is formed between the protrusions;
Consists of
The electrostatic chuck is such that the distance between the side surface of the protrusion and the electrode is at least larger than the height difference between the top of the protrusion and the electrode. The electrostatic chuck according to claim 1, wherein the flatness of the surface formed by the tops of the plurality of protrusions is 5 μm or less. The electrostatic chuck according to claim 1, wherein a difference in height between the electrode and the top of the protrusion is 100 μm or less. The electrostatic chuck according to claim 1, wherein the resin has a volume resistivity of 1 × 10 ¹⁵ Ωcm or more, and the ceramic substrate has a volume resistivity of 1 × 10 ¹² Ωcm or more. The electrostatic chuck according to claim 1, wherein a surface of the resin and a surface formed by a top portion of the protrusion are substantially flush.

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