JP2012206917A - Binder, power feeding unit of electrostatic chuck using the same and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a binder, a power feeding unit of an electrostatic chuck using the binder, and a manufacturing method therefor in which a precise binding layer can be formed without cracking in a binding part of ceramics and a metal when manufacturing a power feeding unit of the electrostatic chuck.SOLUTION: The binder includes tungsten, active silver solder and an organic binder. After removing the organic binder by heating, the binder contains tungsten at 20 to 50 vol.% and the remaining part is comprised of the active silver solder. A hole 4 of a ceramics structure in which a base material 1, an internal electrode 2 and a dielectric 3 are disposed in order is filled with the binder, and a metal electrode 5 is inserted thereinto and bonded by heating, thereby forming a power feeding unit of an electrostatic chuck.

Description

  The present invention relates to a bonding agent used for bonding ceramics and metal when manufacturing an electrostatic chuck or the like, a power feeding unit of an electrostatic chuck using the same, and a manufacturing method thereof.

  An electrostatic chuck has a dielectric layer on a base material, a voltage is applied to the dielectric layer, and an electrostatic chucking force generated between a target object such as a wafer placed on the dielectric layer and the dielectric. To adsorb the wafer. As the material for the electrostatic chuck, ceramics with high wear resistance are often used. An electrostatic chuck is composed of a dielectric and an insulator serving as a base material. To apply a voltage to the dielectric, an internal electrode is provided between the dielectric and the base material, and the voltage is applied to the internal electrode. It is necessary to apply. In order to apply a voltage to the internal electrode sandwiched between the dielectric and the base material, it is a simple method to establish conduction on the side surface of the electrostatic chuck, but there is a problem that the leakage current generated on the dielectric side increases. There is. In order to solve this problem, a hole extending from the bottom surface (exposed surface) of the base material opposite to the dielectric to the internal electrode is provided, and a metal electrode is inserted into the hole so as to be electrically connected to the internal electrode. It will be necessary.

  When ceramics and metal are joined, a joined body can be obtained by using active silver solder as a joining agent. However, in joining with active silver solder, it is necessary to heat the active silver solder at a temperature equal to or higher than the melting point of the active silver solder to melt the active silver solder. It arises from the problem of stress and cracking. In particular, as described above, when a metal is joined into a hole provided in the base material ceramics, it becomes a constrained structure, so stress is likely to concentrate on the corners of the hole and cracks may occur. It is extremely difficult to suppress.

  Various methods have been studied in the past as methods for relieving thermal stress due to thermal expansion differences in bonding ceramics and metals.

  Patent Document 1 discloses a technique for reducing the thermal expansion of an active brazing material using a thermal expansion reducing agent made of one or a mixture of two or more selected from molybdenum powder, tungsten powder and ceramic powder. ing.

In Patent Document 2, in order to reduce thermal stress, an alloy of 80 to 98% by mass of Ag consisting of 60 to 80% by mass of Ag and 20 to 40% by mass of Cu, and 1 to 10% by mass of hydride of Ti or Ti In addition, a brazing material for ceramic-metal bonding comprising Mo or W particles of 1 to 10% by mass with a specific surface area of 2000 to 10000 cm ² / g is disclosed.

  In Patent Document 3, in order to solve the problem that the brazing material breaks the tool, a sintered body portion containing 20% by volume or more of diamond and / or cubic boron nitride includes a tool base material via a bonding layer. In the hard sintered body cutting tool that is directly bonded to the bonding layer, the bonding layer is composed of 2 to 15 mass% of particles consisting of at least one of W or Mo with respect to the entire bonding layer, and the entire bonding layer. 1 to 10% by mass of a hard sintered body cutting tool comprising at least one of Ti or Zr, the balance consisting of at least one of Ag or Cu, and inevitable impurities is disclosed.

  In Patent Document 4, irregularities and voids are likely to be generated on the surface of the brazing material due to the influence of high melting point metal powders such as Mo and W. Therefore, moisture in the atmosphere enters into the irregularities and voids on the surface of the brazing material. In order to solve the problem that corrosion is likely to occur, a ceramic-metal bonded structure in which the bonding surface between the ceramic and the metal is bonded with a brazing material made of an Ag-Cu alloy containing at least one of Ti, Zr, and Hf. The brazing material discloses a ceramic-metal bonding structure in which Mo or W is contained only in the central region of the bonding surface.

  Patent Document 5 discloses a method of joining a ceramic member and a metal member, and in the case of heterogeneous joining with a structure in which a concave portion and a convex portion are fitted, the residual stress tends to concentrate on the corner portion, and a crack is generated. In order to eliminate the point, a ceramic member having a concave portion, a metal member having a convex portion that fits into the concave portion, a concave bottom surface portion of the ceramic member, and a convex tip end portion of the metal member are joined, and A hard soldering material covering a corner between the tip portion and the side surface portion of the metal member, a first bonding agent containing a particulate material and porous; a concave side surface portion of the ceramic member; and a convex portion of the metal member A bonding member having a second bonding agent containing a hard brazing material that bonds the side surface portion is disclosed.

  However, the conventional techniques aiming at joining in a plane as in Patent Documents 1 to 4 cannot solve the problem that a crack occurs in the joint when the power feeding part of the electrostatic chuck is manufactured. In addition, as in the technique disclosed in Patent Document 5, it is difficult to solve a problem such as a decrease in the strength of the joint portion by a method of reducing thermal stress by providing a porous brazing material portion. .

Japanese Patent Laid-Open No. 03-080160 Japanese Patent Laid-Open No. 11-343179 Japanese Patent Laid-Open No. 11-188510 Japanese Patent Laid-Open No. 11-335184 JP 2004-273736 A

  The problem to be solved by the present invention is to use a bonding agent capable of forming a dense bonding layer that does not cause cracks in a bonding portion between a ceramic and a metal, and the bonding agent in manufacturing a power feeding portion of an electrostatic chuck. An object of the present invention is to provide a power feeding unit for an electrostatic chuck and a manufacturing method thereof.

  As a result of earnest research and development, the inventors focused on using a bonding agent composed of tungsten, active silver wax, and an organic binder, and blended tungsten and active silver wax after the organic binder was removed by heating. However, it has been discovered that when 20 to 50% by volume of tungsten and the balance is activated silver brazing, cracks do not occur and a dense joint can be obtained.

The gist of the present invention is as follows.
(1) A bonding agent for bonding ceramic and metal, which is composed of tungsten, active silver brazing, and an organic binder, and contains 20% by volume to 50% by volume of tungsten after the organic binder is removed by heating. A bonding agent, the balance of which is made of active silver wax.
(2) A hole extending from the exposed surface of the base material of the ceramic structure in which the base material, the internal electrode, and the dielectric are sequentially arranged to the internal electrode is formed, and the bonding agent according to (1) is provided inside the hole. A power feeding part of the electrostatic chuck to which the metal electrode is joined via.
(3) An electrostatic chuck in which a hole extending from the exposed surface of the base material of the ceramic structure in which the base material, the internal electrode, and the dielectric are sequentially arranged to the internal electrode is formed, and the metal electrode is bonded to the inside of the hole In the method for manufacturing the power feeding unit, the method for manufacturing the power feeding unit of the electrostatic chuck in which the bonding agent according to (1) is loaded in the hole, and the metal electrode is inserted and heat-bonded.

  Cracks do not occur in the power feeding portion of the electrostatic chuck manufactured using the bonding agent of the present invention. In addition, since the connecting portion is dense, it has excellent bonding strength and is reliable and can be mass-produced.

An example of an electrostatic chuck having a power feeding unit is shown. The crack which arose in the metal electrode junction part is shown.

(First embodiment)
The first embodiment is a bonding agent for bonding ceramics and metal, and is composed of tungsten, active silver wax, and an organic binder. After the organic binder is removed by heating, 20 vol% to 50% of tungsten is removed. The bonding agent is contained in volume% and the balance is made of active silver wax.

  The bonding agent according to the present invention can be obtained by mixing tungsten powder, active silver wax powder, and an organic binder. By mixing these together into a paste, a highly fluid bonding agent can be obtained, and the bonding agent can be tightly filled into a narrow gap when a metal electrode is inserted into a hole provided in an electrostatic chuck. It becomes. When using a mixture of only tungsten powder and active silver brazing powder as the bonding agent, it is difficult to obtain a dense bonding part because the bonding agent cannot be tightly filled in the narrow gap between the hole and the metal electrode. is there. Also, in the method of filling the gap between the hole and the metal electrode with tungsten powder and melting the active silver solder from the top, it is difficult to infiltrate the active silver solder between the tungsten powder, and a dense joint is obtained. I can't.

  In the present invention, as the organic binder, it is preferable to use a resin component such as cellulose resin mixed with an alcohol such as ethanol, an organic solvent such as aromatic hydrocarbon, or an oil component of turpentine oil. When these organic binder components are removed by heating, residual components such as carbon do not remain and are decomposed and removed at a temperature lower than the temperature at which the active silver wax melts for bonding, and the active silver wax is melted and bonded. The residual component does not remain at the temperature to be applied. If a binder component that generates a residual component such as carbon is used, the residual component remains as a defect in the joint, or the active silver wax reacts with the residual component to form a compound in the joint layer, thereby strengthening the joint. It will cause the decrease.

  That is, the bonding agent of the present invention is a mixture of tungsten powder and active silver wax powder in an organic binder that decomposes below the bonding temperature and has no residual components. That is, the bonding agent of the present invention after the organic binder is removed by heating is composed of tungsten and active silver solder. However, this is a concept that includes, in addition to tungsten and active silver wax, residual components of organic binders and inevitable impurities can be contained at an impurity level (3% by mass or less).

(Reason for limiting numerical values of ingredients)
The reason why the tungsten powder is 20 to 50% by volume after the organic binder is removed by heating is that when the amount is less than 20% by volume, the thermal expansion coefficient of the bonding agent is large. In the cooling process after melting, the thermal stress due to the thermal expansion difference from the dielectric or base material of the electrostatic chuck increases, and the electrostatic chuck cracks. This is because there are few active silver brazing components filling the gap, so that a dense joint cannot be obtained.

  It is preferable to use a tungsten powder having an average particle diameter of 1 to 100 μm. When a powder of less than 1 μm is used, the viscosity of the paste-like bonding agent obtained by mixing an organic binder, active silver brazing powder, and tungsten powder increases, so that the bonding agent is a gap between the electrostatic chuck hole and the metal electrode. This is because it is difficult to densely fill the film and defects are likely to remain after bonding. In addition, when a powder larger than 100 μm is used, the powder is too large with respect to the gap between the hole and the metal electrode, so that it is difficult to fill the powder. Moreover, it is preferable to use two types of tungsten powders having different average particle diameters. This is because the filling rate is improved by filling the gaps between the large powders with a small powder, so that the bonding agent can be densely filled and the bonded portion after bonding becomes dense.

  As the active silver wax, silver alloy powder mixed with silver, copper or titanium can be used. In order to reduce the thermal stress at the time of joining, it is preferable to lower the joining temperature. Therefore, 60-80% by mass of silver, 20-40% by mass of copper, and 1% of titanium, which are compositions with which a low melting point alloy is obtained. It is preferable to use an alloy of 10 to 10% by mass. Moreover, since it can join at a low temperature of 850 degrees C or less by using the alloy of 68-75 mass% of silver from which melting | fusing point of an alloy will be 800 degrees C or less, copper 25-32 mass%, and titanium 1-5 mass%, it is still more preferable. .

(Second Embodiment)
In the second embodiment, a hole is formed from the exposed surface of the base material of the ceramic structure in which the base material, the internal electrode, and the dielectric are sequentially arranged to the internal electrode, and the first embodiment is formed inside the hole. It is the electric power feeding part of the electrostatic chuck to which the metal electrode is joined via the bonding agent explained in 1.

  As shown in FIG. 1, the electrostatic chuck has a structure in which a base material 1, an internal electrode 2, and a dielectric 3 are arranged in this order. In forming the power feeding portion in the electrostatic chuck, a hole 4 extending from the bottom surface (exposed surface) to the internal electrode 2 is formed in the base material 1. At this time, the hole 4 is formed so that the internal electrode 2 is exposed on the end face or side face of the hole. The shape of the hole 4 is matched with the shape of the metal electrode 5 inserted into the hole 4. For example, when a cylindrical metal electrode is used, a cylindrical hole is formed. At this time, it is preferable to form the hole 4 so that the gap becomes 100 μm or more so that the gap between the metal electrode 5 and the inner wall of the hole 4 is easily filled with the paste-like bonding agent. Moreover, since the thermal stress which generate | occur | produces will become large when the thickness of a bonding agent becomes thick, it is preferable to form the hole 4 so that a clearance gap may be 500 micrometers or less.

  Next, the power feeding portion constituted by the metal electrode 5 and the dielectric 3 are joined through the hole 4. As a bonding method, a paste-like bonding agent is loaded into the holes 4. The amount of the bonding agent is sufficient to fill the gap between the hole 4 and the metal electrode 5 and the dielectric 3 when the metal electrode 5 is inserted. After the bonding agent is loaded into the hole 4, the metal electrode 5 is inserted into the hole 4, and the metal electrode 5 is pushed toward the dielectric 3 and installed. As a result, the bonding agent can be filled in the gap between the hole 4 and the metal electrode 5 and the dielectric 3 without any gap.

  Next, heat treatment is performed to remove the organic binder in the bonding agent. The heat treatment is performed at a temperature at which the organic binder component is completely decomposed and removed. The heat treatment is performed in the air, in an inert gas atmosphere such as Ar, or in a vacuum. In order to prevent oxidation of the metal electrode, it is preferably performed in an inert gas atmosphere or in a vacuum.

  After removing the organic binder, heat treatment is performed to realize bonding with the bonding agent. The heat treatment for bonding is performed at a temperature equal to or higher than the melting point of the active silver wax in the bonding agent, but is performed at a temperature 50 to 100 ° C. higher than the melting point at which the active silver wax becomes a viscosity suitable for melting and bonding. It is preferable. The heat treatment for bonding is performed in an inert gas atmosphere or in vacuum, but is preferably performed in vacuum in order to reduce voids in the bonded portion after bonding. Moreover, the heat treatment for decomposing and removing the organic binder and the heat treatment for bonding can be performed in the same step.

  By the above method, it is possible to form a power feeding portion in which a crack is not generated and the joint portion is dense. Then, by applying a voltage to the dielectric 3 through the power supply unit, the Si wafer is generated by the electrostatic attraction force generated between the dielectric 3 and an object to be adsorbed such as the Si wafer 8 placed on the dielectric 3. 8 can be adsorbed.

  A hole having a diameter of 8.5 mm and a depth of 5 mm reaching the internal electrode from the base material side was formed in an electrostatic chuck manufactured using alumina as a base material and alumina added with titanium oxide as a dielectric. In this hole, an active silver wax powder made of an alloy powder of 70.1% by weight of silver, 27.9% by weight of copper, and 2.0% by weight of titanium, an organic powder made of tungsten powder, turpentine oil, petroleum naphtha and cellulose resin. A mixture with a binder was loaded, and a titanium electrode having a diameter of 8 mm and a height of 4.5 mm was inserted into the hole to form a power feeding portion. This was heat treated in vacuum at 600 ° C., and then heat treated at 850 ° C. in vacuum for 30 minutes for bonding.

  After cutting the part of the obtained power feeding part and mirror polishing the cross section, the presence of cracks was confirmed by observation with a scanning electron microscope, and the porosity was measured by measuring the cross-sectional area of the gap in the joint did.

  Table 1 shows the presence / absence of cracks in the joint portion of each power feeding portion and the porosity of the joint portion when the composition of tungsten and active silver wax after the organic binder is removed by heating is changed.

  In Examples 1 to 5 in which the volume percent of tungsten after the organic binder was removed by heating was 20, 30, 35, 40, and 50, no crack occurred in the joint portion of the power feeding portion.

  However, in Comparative Example 1 in which the volume percentage of tungsten after removing the organic binder by heating was 15, a crack occurred in the joint portion of the power feeding portion (reference numeral 8 in FIG. 2 is a crack). Further, in Comparative Example 2 in which the volume percentage of tungsten after the organic binder was removed by heating was 55, a void of 36% was generated at the joint portion of the power feeding portion.

DESCRIPTION OF SYMBOLS 1 Base material 2 Internal electrode 3 Dielectric body 4 Hole 5 Metal electrode 6 Binder 7 Crack 8 Si wafer (adsorbed body)

Claims (3)

A bonding agent for bonding ceramic and metal,
A bonding agent comprising tungsten, active silver wax, and an organic binder, and containing 20% by volume to 50% by volume of tungsten after the organic binder is removed by heating, with the balance being made of active silver wax.   A hole extending from the exposed surface of the base material of the ceramic structure in which the base material, the internal electrode, and the dielectric are sequentially arranged to the internal electrode is formed, and a metal is formed in the hole via the bonding agent according to claim 1. Electrostatic chuck power supply unit to which electrodes are joined. Electrostatic chuck power supply unit in which a hole extending from the exposed surface of the base material of the ceramic structure in which the base material, the internal electrode, and the dielectric are sequentially arranged to the internal electrode is formed, and the metal electrode is bonded to the inside of the hole In the manufacturing method of
The manufacturing method of the electric power feeding part of the electrostatic chuck which fills the inside of the said hole with the bonding | jointing agent of Claim 1, and inserts the said metal electrode and heat-joins.