JP4052343B2 - Electrostatic chuck - Google Patents

Description

  The present invention relates to an electrostatic chuck that adsorbs a semiconductor substrate, a glass substrate, or the like.

  Electrostatic chucks disclosed in Patent Documents 1 to 4 as means for adsorbing and holding a semiconductor substrate or a glass substrate in a vacuum processing chamber to which processing heat such as plasma for etching, CVD, sputtering, ion implantation, ashing and the like is applied Is used.

  As shown in FIG. 4, the structure of the conventional electrostatic chuck disclosed in Patent Document 1 is a dielectric layer 103 in which an electrode 102 is held on a metal plate 100 via an organic adhesive 101 such as a silicone resin. Are integrated. And as a method of embedding the electrode 102 in the dielectric layer 103, an electrode (tungsten) is printed on the surface of the ceramic green sheet which becomes the dielectric layer by firing, and another ceramic green sheet is further formed thereon. Stacked and fired (hot press). In addition, as disclosed in Patent Document 2, there is an electrostatic chuck having an approximately similar configuration as described above, in which the average particle diameter of ceramic is suppressed to 2 μm or less.

  The electrostatic chuck of the type shown in FIG. 4 is not a simple method for manufacturing because the manufacturing method for embedding the electrode 102 is complicated and the construction period is prolonged. More specifically, in order to insert an electrode inside the dielectric, after two dielectric substrates are fired and molded, the electrode material is sandwiched and integrated by heating and pressing such as hot pressing. It requires a sophisticated and complicated process.

In view of this, an electrostatic chuck of a type in which the process is simplified with respect to the electrostatic chuck in which an electrode is held inside a dielectric having a complicated process has been proposed (Patent Documents 3 and 4).
Patent Document 3 discloses an electrostatic chuck in which an electrode is fixed on the surface of a dielectric substrate so as to face the base plate with an adhesive interposed on a base plate made of a metal material such as aluminum.
Further, Patent Document 4 discloses an electrostatic chuck in which an electrode is formed on the surface of a dielectric layer substrate, and an insulating resin such as polyimide is pasted thereon and bonded to a metal base plate. .
Japanese Patent Laid-Open No. 10-223742 Japanese Patent Laid-Open No. 2003-152065 Japanese Utility Model Publication No. 4-133443 JP 2001-338970 A

However, none of the electrostatic chucks of Patent Documents 3 and 4 has a structure that can sufficiently satisfy the cooling performance while maintaining high insulation reliability.
In the electrostatic chuck of Patent Document 3, if the insulating adhesive interposed between the electrode 2 and the base plate 3 is made sufficiently thick, the insulation reliability can be improved. However, silicone or the like generally used as an adhesive can be improved. The resin has poor thermal conductivity, and in particular, the cooling performance of the wafer to be adsorbed on the surface of the dielectric substrate could not be secured sufficiently.
Further, since the electrostatic chuck of Patent Document 4 uses an insulating resin such as polyimide, the thermal conductivity of the portion is poor, and the wafer cooling performance cannot be secured sufficiently.

  Therefore, in the present invention, an electrostatic chuck that can be manufactured by a simple manufacturing process and has high reliability of electrical insulation between the electrode and the metal plate, between the electrodes, etc., and particularly has high wafer cooling ability. The purpose is to provide.

In the present invention, in order to achieve the above-mentioned object, a metal plate having an electric insulator film formed on the surface by thermal spraying, a relative density of 99% or more with electrodes selectively formed on the surface, and a thermal conductivity of 30 W / mk. The above-mentioned dielectric substrate is bonded with an electric insulating adhesive so that the electrode and the electric insulator film face each other, and the electrode is formed on the surface of the dielectric substrate. Provided is an electrostatic chuck characterized in that the electrical insulating adhesive is interposed between a portion having no electrical insulation and the electrical insulating film, and the thermal conductivity of the electrical insulating adhesive is 1 W / mK or more. To do.
In a preferred embodiment of the present invention, the flexibility of the electrical insulating adhesive is such that the elongation is 30% or more.
In a preferred embodiment of the present invention, the electric insulator film has a thickness of 0.3 mm to 0.6 mm.
In a preferred embodiment of the present invention, the electrical insulating adhesive has a thickness of 0.1 mm or more and 0.3 mm or less.
In a preferred embodiment of the present invention, the thermal conductivity of the electrical insulator film is made larger than the thermal conductivity of the electrical insulating adhesive.

  According to the present invention, an electrostatic chuck that can be manufactured by a simple manufacturing process and has a high electrical insulation reliability between the electrode and the metal plate, between the electrodes, etc., and particularly has a high wafer cooling capability. It becomes possible to provide.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an overall view of a plasma processing apparatus incorporating an electrostatic chuck according to the present invention, FIG. 2 is a cross-sectional view of the electrostatic chuck, and FIG. 3 is a diagram illustrating an assembly procedure of the electrostatic chuck.

  In the plasma processing apparatus, an upper electrode 10 for generating plasma and an electrostatic chuck 20 are disposed in a chamber 1. The ceiling of the chamber 1 is formed with a reaction gas introduction port 2 such as CF4 or O2 and an exhaust port 3 connected to a decompression device.

  The basic structure of the electrostatic chuck 20 is that an insulator film 22 is formed on the surface of a metal plate 21 by thermal spraying. A dielectric substrate 24 is bonded to the insulator film 22 via an insulating adhesive layer 23, and the surface of the dielectric substrate 24 is used as a mounting surface for an object W to be adsorbed such as a semiconductor wafer. Are provided with electrodes 25, 25. Lead wires 26 and 26 for supplying power to the electrodes 25 and 25 extend downward through the metal plate 21. The lead wire 26 and the metal plate 21 are insulated.

  In order to assemble the electrostatic chuck 20, as shown in FIG. 3, a metal plate 21 on which an insulator film 22 is formed in advance and a dielectric substrate 24 on which an electrode 25 is formed are prepared. The insulating film 22 of 21 and the electrode 25 of the dielectric substrate 24 are bonded to each other through an insulating adhesive 23 so as to face each other.

  The metal plate 21 is made of a metal having excellent thermal conductivity such as an aluminum alloy or copper, and a coolant passage 21a is formed inside.

  The insulator film 22 is required to have electrical insulation between the electrode and the metal plate and heat transfer to transfer the processing heat to the metal plate. As a material of the insulator film 22, a material having a thermal conductivity larger than that of the insulating adhesive is preferable, and an inorganic material, for example, ceramic such as alumina (Al2O3) is most preferable.

  By providing an insulator film made of a material having a thermal conductivity larger than the thermal conductivity of such an insulating adhesive with a thickness of 0.6 mm or less, the insulating adhesive layer alone can be secured while ensuring insulation reliability. The thermal conductivity becomes better than the case, and the cooling efficiency of the wafer is improved. Moreover, by forming by a thermal spraying method, the said insulator film can be formed, without producing heat deterioration of a plate and using an extra adhesive agent.

  The insulating film is preferably 2 W / mK or more. By doing so, the thermal conductivity becomes sufficiently better than the case of the insulating adhesive layer alone, and the cooling efficiency of the wafer is further improved.

  Further, the thickness of the insulator film is preferably as thin as possible in order to increase the cooling efficiency, and as thick as possible in order to ensure insulation against the voltage applied for substrate adsorption. The thickness of the insulator film that achieves both of these is 0.3 mm or more and 0.6 mm or less.

  The insulating adhesive 23 has an electrical insulation between the electrodes and between the electrodes and the outside, a heat transfer property that transfers processing heat to the cooling plate, and a difference in linear expansion coefficient between the dielectric layer substrate and the metal plate on which the insulating film is formed by thermal spraying. Flexibility is required to relieve the shearing stress caused by.

  The insulating adhesive 23 preferably has a thermal conductivity of 1 W / mk or more, more preferably 1.6 W / mK or more. The insulating adhesive having the thermal conductivity can be obtained by adding alumina or aluminum nitride as a filler to a silicone resin, for example.

  The thickness of the insulating adhesive is preferably as thin as possible in order to increase the cooling efficiency, and the shear stress due to the difference in linear expansion coefficient between the metal plate having the insulating film formed on the surface by thermal spraying and the dielectric substrate. On the other hand, in order to prevent the insulating adhesive layer from being peeled off, it is desirable that it is as thick as possible. The thickness of the adhesive layer that balances these becomes 0.1 mm or more and 0.3 mm or less.

  The flexibility of the insulating adhesive is preferably 30% or more. Adhesion sufficient to prevent exfoliation of the insulating adhesive layer against shear stress due to the difference in linear expansion coefficient between the metal plate on which the insulating film is formed and the dielectric substrate if there is more flexibility than this Sex can be obtained.

The material used for the dielectric substrate 24 is selected according to various requirements required for the electrostatic chuck, but it is preferable to use a ceramic sintered body in consideration of thermal conductivity, reliability of withstand voltage, and the like.
The ceramic sintered body may be any of alumina, yttria, silicon carbide, aluminum nitride and the like.

  The volume resistivity of the ceramic sintered body may be 10 14 cmΩ or more (Coulomb type electrostatic chuck) at the use temperature, or 10 8 to 10 11 cmΩ (Johnsen-Rahbek type electrostatic chuck) at the use temperature. .

  In the case of a Coulomb force type electrostatic chuck, in order to use it in a practical voltage range (± 1000 V to ± 5000 V, preferably ± 2000 V to ± 5000 V), the thickness of the dielectric substrate is 0 in order to secure an attractive force. The thickness of the dielectric substrate that can be manufactured as a structure is preferably 0.2 mm or more (preferably 0.3 mm or more).

  In order to use a Johnsen-Rahbek type electrostatic chuck in a practical voltage range (± 500 V to ± 2000 V), the thickness of the dielectric substrate is preferably 1.5 mm or less, and can be manufactured as a structure. The thickness of the dielectric substrate is preferably 0.2 mm or more (preferably 0.3 mm or more).

As the particles constituting the dielectric substrate, those having an average particle diameter of 2 μm or less are preferable for improving the plasma resistance. By setting the average particle diameter to 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.

  In addition, the electrode 25 is obtained by grinding the surface of the dielectric substrate 24, forming a conductive film such as TiC or Ti by CVD or PVD, and obtaining a predetermined electrode pattern by sandblasting or etching the conductive film. Can do.

  The most important role required for electrostatic chucks used in semiconductor manufacturing equipment is to efficiently dissipate processing heat generated during wafer processing to a coolant, cool the wafer below the desired temperature, and make the temperature in the wafer surface uniform. Is to control. In an apparatus that generates plasma such as a dry etching apparatus, a plasma CVD apparatus, or a plasma ashing apparatus, it is necessary to release the heat generated by the plasma. Even in an apparatus that does not generate plasma, such as a sputtering apparatus or an ion implantation apparatus. It is necessary to release the processing heat generated during wafer processing. Semiconductor manufacturing apparatuses are always required to reduce the processing time per wafer called throughput. Therefore, every time a new generation of a semiconductor processing apparatus is used, the plasma power and the amount of processing heat are increased in order to reduce the throughput. Therefore, in the electrostatic chuck, improvement in cooling efficiency is always required. The present invention can be said to be an electrostatic chuck that can meet the above requirements at a relatively low manufacturing cost.

  Hereinafter, the dielectric substrate manufacturing method of the electrostatic chuck according to the present invention will be exemplified for the case of the Coulomb force type electrostatic chuck and the Johnsen-Rahbek type electrostatic chuck.

  As a method of manufacturing the dielectric substrate 24 of the Coulomb force type electrostatic chuck, for example, an acrylic binder is added to an alumina raw material powder having an average particle diameter of 0.1 μm and a purity of 99.99% or more, and granulated by a spray dryer after adjustment. And granule powder is prepared. Then, after forming CIP (rubber press) or mechanical press, it is processed into a predetermined shape and fired in an air atmosphere at 1250 to 1450 ° C. Further, HIP processing (hot isostatic pressing) is performed. The HIP condition is Ar gas of 1000 atm or higher, and the temperature is 1250 to 1450 ° C. which is the same as the firing temperature. Under such conditions, the particles are extremely dense and have an average particle diameter of 2 μm or less, a volume resistivity of 1014 Ωcm or more at 20 ± 3 ° C., a relative density of 99% or more, and a thermal conductivity of 30 W / mK or more. A dielectric substrate 24 is obtained.

  As a method for manufacturing the dielectric substrate 24 of the Johnsen-Rahbek type electrostatic chuck, for example, an alumina raw material powder having an average particle diameter of 0.1 μm and a purity of 99.99% or more is used as a main component. A large, 0.6 wt% or less titanium oxide (TiO2) is mixed and pulverized, an acrylic binder is added, and after adjustment, the mixture is granulated with a spray dryer to produce granulated powder. Then, after forming CIP (rubber press) or mechanical press, it is processed into a predetermined shape and fired in a reducing atmosphere at 1150 to 1350 ° C. Further, HIP processing (hot isostatic pressing) is performed. The HIP condition is Ar gas of 1000 atm or higher, and the temperature is 1150 to 1350 ° C. which is the same as the firing temperature. Under such conditions, the particles are extremely dense, the average particle diameter of the constituent particles is 2 μm or less, the volume resistivity is 108 to 10 11 Ωcm or more at 20 ± 3 ° C., the relative density is 99% or more, and the thermal conductivity is 30 W / mK. The above dielectric substrate 24 is obtained.

In addition, the average particle diameter shown here is a particle diameter calculated | required with the following planimetric methods. First, take a picture of the dielectric substrate with SEM, draw a circle with a known area (A) on this picture, and calculate the unit area from the number of particles nc in the circle and the number of particles ni on the circumference by equation (1). Find the number of particles per particle NG.
NG = (nc + 1/2 ni) / (A / m2) (1)
M shown here is the magnification of the photograph. Since 1 / NG is the area occupied by one particle, the particle diameter can be obtained as 2 / √ (π NG).

Overall view of a plasma processing apparatus incorporating an electrostatic chuck according to the present invention Cross section of the electrostatic chuck The figure explaining the assembly procedure of the electrostatic chuck Cross section of conventional electrostatic chuck

Explanation of symbols

      DESCRIPTION OF SYMBOLS 1 ... Chamber, 2 ... Reaction gas introduction port, 3 ... Exhaust port, 10 ... Upper electrode, 20 ... Electrostatic chuck, 21 ... Metal plate, 21a ... Refrigerant passage, 22 ... Insulator film, 23 ... Insulating adhesive layer 24 ... dielectric substrate, 25 ... electrode, 26 ... lead wire, 100 ... metal plate, 101 ... organic adhesive, 102 ... electrode, 103 ... dielectric layer, W ... adsorbed material.

Claims (5)

A metal plate having an electrical insulator film formed on the surface by thermal spraying, and a dielectric substrate having a relative density of 99% or more and a thermal conductivity of 30 W / mk or more selectively formed on the surface, the electrode and the An electrical insulating adhesive is interposed so as to face the electrical insulator film, and the portion of the surface of the dielectric substrate where the electrode is not formed and the electrical insulator film The electrostatic chuck is characterized in that the electrical insulating adhesive is interposed, and the thermal conductivity of the electrical insulating adhesive is 1 W / mK or more. 2. The electrostatic chuck according to claim 1, wherein the flexibility of the electrically insulating adhesive is an elongation rate of 30% or more. 3. The electrostatic chuck according to claim 1, wherein a thickness of the electric insulator film is not less than 0.3 mm and not more than 0.6 mm. 4. 4. The electrostatic chuck according to claim 1, wherein the thickness of the electrically insulating adhesive is 0.1 mm or more and 0.3 mm or less. 5. The electrostatic chuck according to claim 1, wherein a thermal conductivity of the electrical insulator film is larger than a thermal conductivity of the electrical insulating adhesive. 6.

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