JP2007214288A - Electrostatic chuck - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Coulomb force type electrostatic chuck capable of acquiring a sufficient chucking force and preventing cracks during processing. <P>SOLUTION: The electrostatic chuck includes a dielectric substrate 24 for an electrostatic chuck made of a polysilicon alumina containing 99.9 wt.% or more of alumina, and having a bulk density of 3.98 or more, a Vickers hardness of 17 GPa, a flexural strength of 400 MPa or more, and a volume resistivity of 10<SP>14</SP>Ω cm or more at a room temperature. The dielectric substrate 24 has a thickness of not less than 0.2 mm and also less than 0.5 mm. Further, a plurality of concave portions are formed and a ratio of the total area of the top surface of the concave portions to the area of the surface of the dielectric substrate 24 is ≥0.001% and also <0.5%. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrostatic chuck for attracting and fixing an object to be adsorbed such as a semiconductor wafer and a glass substrate for FPD by electrostatic force.

  As means for adsorbing and holding a semiconductor substrate or a glass substrate in a plasma processing chamber that performs etching, CVD, sputtering, ion implantation, ashing, and the like, electrostatic chucks disclosed in Patent Documents 1 to 3 are used.

  As a recent trend in the industry for etching copper wiring devices and the like, there is a demand for an apparatus that can handle plasma powers of different sizes. In this case, although the plasma power is different, the temperature of the wafer at the time of etching is fixed at around 80 ° C. Therefore, the temperature of the wafer is changed by changing the temperature of the electrostatic chuck portion according to the magnitude of the plasma power. Must be constant.

The electrostatic chuck is classified into a so-called Johnsen-Rahbek type electrostatic chuck in which the dielectric layer has a volume resistivity of 1 × 10 ¹³ Ωcm or less at the operating temperature, and the dielectric layer has a volume resistivity of 1 × at the operating temperature. There is a so-called Coulomb force type electrostatic chuck of 10 ¹⁴ Ωcm or more. However, when the electrostatic chuck temperature is changed as described above, the volume resistivity of the dielectric substrate due to the temperature change is reduced. It is desirable to use a Coulomb force type electrostatic chuck in which the change does not significantly affect the electrostatic chuck adsorption / release characteristics and leakage current. However, since the electrostatic chuck of the Coulomb force type is weaker than the Johnsen-Rahbek force type, it is desired to increase the adsorption force. In the Coulomb force type electrostatic chuck, it is known that the thinner the dielectric, the stronger the attractive force. However, when the dielectric substrate is thin, there is a problem that cracks are likely to occur during processing.

  The cracks during the processing can be processed to be thinner by increasing the strength of the dielectric substrate. For this reason, single crystal alumina can be used as the dielectric substrate, but in order to obtain single crystal alumina, it is necessary to use a special method called single crystal pulling method from the melt. Has a problem that the production process takes a long time and the productivity is low. (For example, Patent Document 4)

Japanese Patent No. 3084869 Japanese Utility Model Publication No. 4-133443 JP 2001-338970 A JP-A-7-29959

  The present invention is based on the premise of adopting a general sintering method without using a special method such as the above-described single crystal pulling method. It is to provide a Coulomb force type electrostatic chuck that does not occur.

In order to achieve the above object, in the present invention, dielectric for electrostatic chuck comprising polycrystalline alumina having 99.9 wt% or more of alumina, 3.98 or more in bulk density, and 10 ¹⁴ Ωcm or more in volume resistivity at room temperature. Disclosed is an electrostatic chuck comprising a substrate, wherein the dielectric substrate has a thickness of 0.2 mm or more and less than 0.5 mm. As a result, it is possible to provide a coulomb force type electrostatic chuck that can obtain a sufficient attracting force and does not cause cracks during processing.

The volume resistivity of the dielectric substrate is preferably 1 × 10 ¹⁴ Ωcm or more at room temperature. By making the volume resistivity as described above, the so-called Coulomb force type electrostatic chuck in which the change in volume resistivity due to the temperature change of the dielectric substrate hardly affects the adsorption / desorption characteristics of the substrate and the leakage current. It can be.

  In order to use the Coulomb force type electrostatic chuck with a sufficient attracting force in a practical voltage range (± 1 kV to ± 5 kV, more preferably ± 2 kV to ± 5 kV), the thickness of the dielectric substrate is set to 0. It is desirable to be less than 5 mm. On the other hand, a thickness of 0.2 mm or more, more preferably 0.3 mm or more is required so as not to cause cracks in the dielectric substrate during processing. Therefore, a desired electrostatic chuck can be provided by setting the thickness of the dielectric substrate to 0.2 mm or more and less than 0.5 mm, more preferably 0.3 mm or more and less than 0.5 mm.

  The polycrystalline alumina of the dielectric substrate is preferably 99.9 wt% or more and a bulk density of 3.98 or more. By setting the purity and bulk density as described above, a sufficient withstand voltage can be ensured even when the thickness of the dielectric substrate is 0.2 mm or more and less than 0.5 mm.

In another embodiment of the present invention, an electrostatic material comprising alumina of 99.9 wt% or more, a bulk density of 3.98 or more, a Vickers hardness of 17 GPa or more, and a volume resistivity of 10 ¹⁴ Ωcm or more at room temperature. An electrostatic chuck comprising a dielectric substrate for chuck and having a thickness of 0.2 mm or more and less than 0.5 mm is disclosed. As a result, it is possible to provide a coulomb force type electrostatic chuck that can obtain a sufficient attracting force and does not cause cracks during processing.

  The polycrystalline alumina of the dielectric substrate preferably has a Vickers hardness of 17 GPa or more, more preferably 18 GPa or more. By setting the Vickers hardness as described above, the thickness can be processed to 0.2 mm or more and less than 0.5 mm without causing cracks in the dielectric substrate during processing.

In another embodiment of the present invention, electrostatic is composed of polycrystalline alumina having alumina of 99.9 wt% or more, bulk density of 3.98 or more, bending strength of 400 MPa or more, and volume resistivity of 10 ¹⁴ Ωcm or more at room temperature. An electrostatic chuck comprising a dielectric substrate for chuck and having a thickness of 0.2 mm or more and less than 0.5 mm is disclosed. As a result, it is possible to provide a coulomb force type electrostatic chuck that can obtain a sufficient attracting force and does not cause cracks during processing.

  It is desirable that the polycrystalline alumina of the dielectric substrate has a bending strength of 400 MPa or more, more preferably 500 MPa or more. By setting the bending strength as described above, the thickness can be processed to 0.2 mm or more and less than 0.5 mm without causing cracks in the dielectric substrate during processing.

  By making the thickness of the dielectric substrate 0.2 mm or more and less than 0.5 mm, a large attracting force can be generated, and as a result, a convex portion can be provided on the surface of the Coulomb force type electrostatic chuck. The contact area with the object to be adsorbed can be reduced to 1 to 10% with respect to the area of the adsorption surface.

  Further, by making the height of the convex portion provided on the surface 5 to 15 μm, the attracting force can be exerted even in the contacted portion. As a result, the area of the convex portion can be made 0.001% or more and less than 0.5% with respect to the area of the suction surface. Since the temperature of the object to be adsorbed is transferred through the contact portion as the contact area of the convex portion becomes small, even if the structure of the convex portion is eroded by plasma, the influence is small. Therefore, an electrostatic chuck with little change with time can be realized as a result of increasing plasma resistance and minimizing contact with the object to be adsorbed.

  In a preferred embodiment of the present invention, a plurality of convex portions are formed, and the dielectric substrate has a smooth surface on which the object to be adsorbed is placed on the upper surface of the convex portions. The ratio with respect to the area of the dielectric substrate surface is 0.001% or more and less than 0.5%, and the height of the convex portion is 5 to 15 μm. Disclosed an electrostatic chuck. As a result, it is possible to minimize the influence of the change in the adsorption state on the object to be adsorbed due to the influence of surface roughness due to the erosion by the plasma at the contact portion with the object to be adsorbed. At this time, if the ratio of the contact area is 0.001% or less, the size per one convex portion becomes too fine, and the processing becomes difficult. On the other hand, if it exceeds 1%, the influence of erosion on the plasma on the surface of the convex portion that comes into contact with the adsorbed body cannot be ignored.

  The average particle diameter of the polycrystalline alumina constituting the dielectric substrate is preferably 4 μm or less, more preferably 2 μm or less in terms of improving plasma resistance. By setting the average particle size to 4 μm or less, more preferably 2 μm or less, it is possible to provide an electrostatic chuck with a small change in the attracting surface roughness of the dielectric substrate even when wafer rescreening is repeated.

  According to the present invention, it is possible to obtain a sufficient attracting force and to produce a Coulomb force type electrostatic chuck that does not cause cracks during processing.

The terms used in this specification will be explained below.
(Slurry adjustment, granulation, raw processing)
An acrylic binder was added to the alumina raw material powder, and after adjustment, the mixture was granulated with a spray dryer to prepare granule powder. The granulated powder was processed into a predetermined shape after CIP (rubber press) molding or mechanical press molding. In CIP molding, the granulated powder was packed in a rubber mold and then subjected to a pressure of 1 ton / cm 2 to produce an ingot, which was then processed into a predetermined shape to produce a formed shape.
(Baking)
The raw processed body was fired in the air or in a nitrogen or hydrogen gas reducing atmosphere. Example 1 was fired in a reducing atmosphere, and Examples 2 and 3 were fired in air. The firing temperature was 1250 to 1450 ° C., the firing time was 1 to 8 hours, and the conditions with the highest bulk density were selected.
(HIP processing)
Further, HIP treatment was performed to produce a dielectric substrate. The HIP conditions were Ar gas of 1000 atm or higher and the temperature was 1250 to 1450 ° C.
(Electrode production)
After grinding the surface of the dielectric substrate, a conductive film such as TiC or Ti was formed on one side by CVD or PVD, and this conductive film was sandblasted or etched to obtain a predetermined electrode pattern.
(Joining)
The dielectric substrate on which the electrodes are formed is placed on a metal plate on which an insulator film has been previously formed by alumina spraying so that the insulator film on the metal plate and the electrode on the dielectric substrate face each other via an insulating adhesive. Both were joined.
(Surface pattern production)
The dielectric substrate bonded to the metal plate was ground so as to have a predetermined thickness of 0.2 mm or more and less than 0.5 mm, and then a convex portion having a predetermined size and height was formed on the surface by sandblasting.

(Physical property measurement)
What was obtained by the HIP treatment was subjected to firing bulk density, average particle size measurement by observation of the fired body structure SEM, bending strength, Vickers hardness, volume resistivity measurement, and friction force measurement in vacuum. The bending strength was measured by room temperature three-point bending strength according to JIS R1601. The measuring machine was a small table tester Easy Graph manufactured by Shimadzu Corporation. The test piece dimensions were 4 mm wide, 3 mm thick, 40 mm long, and the length between the lower fulcrums was 30 mm. Vickers hardness was measured by measuring room temperature Vickers hardness according to JIS R1610. The measuring machine used was a Vickers hardness tester HV-113 manufactured by Akashi, and the test load was 9.807 N, the test force speed was 100 μm / s, and the holding time was 15S.
Moreover, plasma was actually irradiated and the change in the surface roughness (centerline average roughness Ra) of the ceramic was measured. In the initial state, the surface roughness was Ra 0.02 μm or less. The plasma was a reactive ion etching apparatus, and the etching gas was CF4 + O2 at 1000 W for 30 hours for plasma discharge.

(Comparative product)
For comparison, alumina ceramics produced by a conventional manufacturing method is illustrated. The composition is 99.7 wt% of alumina having an average particle size of 0.5 μm and the firing temperature is 1580 ° C. The comparative product is not HIP processed. The plasma irradiation was the same as in the example, and the surface roughness was Ra 0.02 μm or less in the initial state. The dielectric substrate of this comparative example was bonded to a metal plate, and the dielectric substrate was ground to a predetermined thickness of 0.2 mm or more and less than 0.5 mm.

上記試験の結果を表１に示す。実施例の誘電体基板は全て、金属プレートに接合した後、誘電体基板厚みを０．２ｍｍまで研削加工でき、さらに表面に凸部を形成してもクラック等の発生はなかった。ただし、０．２ｍｍより薄くすると基板にクラックが発生した。一方、比較例では厚み０．５ｍｍまでは加工できたが、それ以下の厚みではクラックが発生した。この違いは基板の強度の差によるものと考えられた。すなわち、研削加工時の応力に対して基板の強度が弱い場合にクラックが発生する。本実施例のように金属プレートに接合した後で研削加工する場合には、曲げ強度で４００ＭＰａ以上が必要であることがわかった。また、曲げ強度とビッカース硬度には相関があることが知られており、同じようにビッカース硬度で１７ＧＰａ以上が必要であることがわかった。

The results of the above test are shown in Table 1. All of the dielectric substrates of the examples could be ground to a thickness of 0.2 mm after being bonded to a metal plate, and no cracks or the like were generated even if convex portions were formed on the surface. However, when the thickness was less than 0.2 mm, cracks occurred in the substrate. On the other hand, in the comparative example, processing was possible up to a thickness of 0.5 mm, but cracks occurred at a thickness less than that. This difference was thought to be due to the difference in strength of the substrates. That is, cracks occur when the strength of the substrate is weak against the stress during grinding. When grinding was performed after joining to a metal plate as in this example, it was found that a bending strength of 400 MPa or more was necessary. Further, it is known that there is a correlation between the bending strength and the Vickers hardness, and similarly, it was found that a Vickers hardness of 17 GPa or more is necessary.

In the present invention, the volume low efficiency is 10 ¹⁴ Ωcm or more under all firing conditions, and it was found that the volume resistivity at room temperature of 10 ¹⁴ Ωcm or more required for a dielectric for a Coulomb chuck was satisfied. Furthermore, by setting the thickness of the dielectric substrate to 0.2 mm or more and less than 0.5 mm, a sufficient attracting force could be generated even when a convex portion was formed on the surface of the dielectric substrate.

  Furthermore, by setting the alumina purity of the dielectric substrate to 99.9 wt% or more and the bulk density to 3.98 or more, a sufficient withstand voltage can be secured even when the thickness of the dielectric substrate is 0.2 mm or more and less than 0.5 mm.

  In the present invention, by using a fine alumina raw material having an average particle diameter of less than 0.2 μm and a purity of 99.9% or more, firing can be performed at a firing temperature of 1450 ° C. or lower, which is significantly lower than the comparative example. It became possible to fire at. It is considered that the bending strength and the Vickers hardness are greatly improved by firing at such a low temperature, with the particle size being small and uniform firing. In this example, an alumina raw material having an average particle diameter of 0.1 μm and a purity of 99.99% or more was used.

Convex part of electrostatic chuck having a smooth surface on which a plurality of convex parts are formed and an object to be adsorbed placed on the upper surface of the convex part, and including a dielectric for electrostatic chuck having a volume resistivity of 10 ¹⁴ Ωcm or more An electrostatic chuck in which the ratio of the total area of the upper surface to the area of the dielectric surface was 0.089% was produced. At this time, convex portions having a diameter of 0.25 mm are continuously arranged on the surface of each apex of a regular triangle having a side of 8 mm. The height of the convex portion is 10 μm.

As a result, the change in temperature during processing of the silicon wafer that is the object to be adsorbed overlaps with the fact that the change in surface roughness after plasma irradiation is small and the contact area with the object to be adsorbed is very small. Could be very little.

It is a figure showing the electrostatic chuck of this invention. It is an enlarged view of the surface pattern of the electrostatic chuck of this invention.

Explanation of symbols

21 ... Metal plate, 21a ... Refrigerant passage, 22 ... Insulator film, 23 ... Insulating adhesive layer, 24 ... Dielectric substrate, 25 ... Electrode, 26 ... Lead wire,

Claims (4)

An electrostatic chuck dielectric substrate made of polycrystalline alumina having an alumina content of 99.9 wt% or more, a bulk density of 3.98 or more, and a volume resistivity of 10 ¹⁴ Ωcm or more at room temperature, and the thickness of the dielectric substrate is 0 An electrostatic chuck characterized by being 2 mm or more and less than 0.5 mm. A dielectric substrate for an electrostatic chuck comprising alumina of 99.9 wt% or more, a bulk density of 3.98 or more, a Vickers hardness of 17 GPa or more, and a volume resistivity of 10 ¹⁴ Ωcm or more at room temperature; An electrostatic chuck characterized in that the thickness of the body substrate is 0.2 mm or more and less than 0.5 mm. A dielectric substrate for electrostatic chuck comprising alumina of 99.9 wt% or more, bulk density of 3.98 or more, bending strength of 400 MPa or more, and volume resistivity of 10 ¹⁴ Ωcm or more at room temperature, An electrostatic chuck characterized in that the thickness of the body substrate is 0.2 mm or more and less than 0.5 mm. A plurality of convex portions are formed, and the dielectric substrate has a smooth surface on which the adherend is placed on the upper surface of the convex portion. The total area of the upper surfaces of the plurality of convex portions and the area of the dielectric substrate surface The electrostatic chuck according to claim 1, wherein the ratio is 0.001% or more and less than 0.5%, and the height of the convex portion is 5 to 15 μm.

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