JP2004335742A - Electrostatic chuck - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrostatic chuck wherein no breakage occurs in a carbon jig or the body of itself in a sintering process and has a low thermal expansion, as an electrostatic chuck having such a structure that an electrode is located between two low-thermal-expansion ceramic base materials. <P>SOLUTION: A paste containing conductive ceramic of low thermal expansion is applied on one surface of one low-thermal-expansion ceramic base material to form the electrode. Then, the other low-thermal-expansion ceramic base material is so joined to the low-thermal-expansion ceramic base material as to cover the electrode using a bonding material made of low-thermal-expansion ceramic having a melting point lower than that of the base material. Thus, the electrostatic chuck having such a structure that the electrode is located between the two low-thermal-expansion ceramic base materials can be obtained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrostatic chuck used for a semiconductor manufacturing apparatus or the like, and more particularly, to an electrostatic chuck made of a low thermal expansion ceramic base material.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as an electrostatic chuck for attracting and holding a semiconductor wafer or the like in a semiconductor manufacturing process, for example, an electrostatic chuck using aluminum nitride as a base material has been used. (For example, see Patent Document 1)
[0003]
However, in recent years, semiconductor circuits have tended to become more and more fine, and in conventional electrostatic chucks based on aluminum nitride, a decrease in product yield has been caused due to thermal expansion deformation due to a change in ambient temperature. A low thermal expansion material containing cordierite as a main component has been used as a constituent member of a manufacturing apparatus. (For example, see Patent Document 2)
[0004]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2000-44345 [Patent Document 2]
JP-A-11-79830
[Problems to be solved by the invention]
2. Description of the Related Art A conventional electrostatic chuck is manufactured by a hot press method in which electrodes are provided inside ceramic powder constituting an electrostatic chuck body. In hot pressing, ceramic powder and electrodes are placed in a carbon jig and sintering is performed at a high temperature while applying a load.However, in the case of low thermal expansion ceramics, since the thermal expansion is smaller than that of the carbon jig, the ceramic is fired by the carbon jig during cooling. There was a problem that the compact was compressed and the carbon jig or the sintered body was damaged.
[0006]
The electrodes to be provided are made of a conductive material such as tungsten or molybdenum having a large coefficient of thermal expansion as an electrode material. Although some measures have been taken to mitigate the problem, it is difficult to maintain the thermal expansion of the suction surface of the electrostatic chuck at a very low level, so that flatness accuracy cannot be maintained and the product yield is reduced. was there.
[0007]
The present invention has been made in view of such circumstances, and even when an electrostatic chuck having a structure in which an electrode is disposed between two low thermal expansion ceramic base materials is used, a carbon jig is used in a sintering process. Alternatively, it is another object of the present invention to provide an electrostatic chuck characterized in that the ceramic base material is not damaged and the suction surface has a low coefficient of thermal expansion.
[0008]
[Means for Solving the Problems]
The object of the present invention is achieved by the following (1) to (4).
(1) An electrostatic chuck having a structure in which an electrode is disposed between two low-thermal-expansion ceramic base materials, wherein the electrode has conductive low-thermal-expansion ceramic on one surface of one low-thermal-expansion ceramic base material. A low-thermal-expansion ceramic material having a lower melting temperature than the base material so that another low-thermal-expansion ceramic base material covers the electrode. An electrostatic chuck, comprising:
(2) An electrostatic chuck having a structure in which an electrode is disposed between two low thermal expansion ceramic base materials, wherein the electrode is a sintered body made of conductive low thermal expansion ceramic, and Characterized by being sandwiched between two low-thermal-expansion ceramic base materials and bonded to each other with a bonding material made of low-thermal-expansion ceramics having a lower melting temperature than the base material.
(3) In the above (1) and (2), the composite material constituting the low thermal expansion ceramic matrix is at least one material selected from lithium aluminosilicate and cordierite, and silicon carbide, boron carbide, An average coefficient of thermal expansion of the low thermal expansion ceramic base material at 20 to 30 ° C., comprising at least one material selected from silicon nitride, sialon, alumina, zirconia, mullite, zircon, aluminum nitride, and calcium silicate. Is -1 × 10 ⁻⁶ to 1 × 10 ⁻⁶ / ° C.
(4) In the above (1), (2) and (3), the composite material constituting the conductive low thermal expansion ceramic is at least one material selected from lithium aluminosilicate and cordierite, and silicon carbide. And at least one material selected from boron carbide, titanium carbide, titanium boride, and tungsten carbide, and the conductivity of the conductive low thermal expansion ceramic is 10 ⁻⁶ to 10 ⁻² S / cm. An electrostatic chuck characterized in that:
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
The electrostatic chuck according to the present invention is an electrostatic chuck having a structure in which electrodes are disposed between two low thermal expansion ceramic base materials.
Here, it is preferable that the average thermal expansion coefficient of the low thermal expansion ceramic base material at 20 to 30 ° C. is −1 × 10 ⁻⁶ to 1 × 10 ⁻⁶ / ° C. The reason is that within this range, when used as a member of a semiconductor manufacturing apparatus, it can be adapted to refinement of a semiconductor circuit.
In addition, as electrostatic adsorption, adsorption by Coulomb force, adsorption by Johnsen-Lahbek force, and adsorption in which these are combined are also possible.
Conventional electrostatic chucks using low-thermal-expansion ceramics use tungsten or molybdenum with a large thermal expansion coefficient for the electrodes, so stress remains in the low-thermal-expansion ceramics during the manufacture of the electrostatic chuck, and a Coulomb force is developed. Therefore, when the thickness of the low thermal expansion ceramic is reduced to 0.1 to 0.5 mm, there is a problem that the low thermal expansion ceramic insulating layer is damaged. However, in the present invention, since the conductive low thermal expansion ceramic is used as the electrode, no stress remains in the low thermal expansion ceramic when the electrostatic chuck is manufactured. It has the effect that the layer is not damaged.
The Johnsen-Rahbek force may be developed by controlling the conductivity of the low thermal expansion ceramic base material to 10 ⁻¹⁴ to 10 ⁻⁸ S / cm.
[0010]
Next, as a composite material constituting the low thermal expansion ceramic base material, at least one first material selected from lithium aluminosilicate and cordierite, and silicon carbide, boron carbide, silicon nitride, sialon, alumina, zirconia It is preferable to use one or more second materials selected from, mullite, zircon, aluminum nitride, and calcium silicate. Of these constituent materials, the first material has a very low thermal expansion, and the second material has a higher thermal expansion coefficient than the first material but a higher Young's modulus. This is because a material having both high rigidity can be obtained.
As the first material, β-eucryptite or spodumene, which is lithium aluminosilicate, is preferable. Among them, β-eucryptite exhibits a negative thermal expansion. Therefore, by combining it with a second material exhibiting a positive thermal expansion, it is possible to obtain an extremely low thermal expansion coefficient. It is possible to adjust the thermal expansion coefficient in a wide range from minus to plus by adjusting. In addition, lithium aluminosilicate represented by β-eucryptite and spojumen forms a solid solution with other components such as Ca, Mg, Fe, K, Ti, and Zn. In the present invention, such a solid solution is also applied. It is possible.
[0011]
Next, according to the present invention, there is provided an electrostatic chuck having a structure in which an electrode is disposed between two low thermal expansion ceramic base materials, wherein the electrode is electrically conductive on one surface of one low thermal expansion ceramic base material. It is obtained by applying a paste containing low thermal expansion ceramics and then sintering, and has a lower melting temperature than that of another low thermal expansion ceramic base material so as to cover the electrode. An electrostatic chuck characterized by being joined with a joining material made of low thermal expansion ceramics has been proposed.
[0012]
Here, the composite material forming the electrode is selected from one or more first materials selected from lithium aluminosilicate and cordierite, and selected from silicon carbide, boron carbide, titanium carbide, titanium boride, and tungsten carbide. Those comprising one or more second materials are preferred. Of these constituent materials, the first material has a very low thermal expansion, and the second material has a higher thermal expansion coefficient than the first material but a higher electrical conductivity. And a material having both electric conductivity.
As the second material, β-silicon carbide is preferable. Since β-silicon carbide has a relatively low coefficient of thermal expansion compared to other materials and has higher conductivity, it is possible to obtain an electrode material having an extremely low coefficient of thermal expansion.
Further, the average thermal expansion coefficient of the composite material constituting the electrode at 20 to 30 ° C. is preferably −1.5 × 10 ^{−6 to} 1.5 × 10 ⁻⁶ / ° C. This is because if it is in this range, it can be adapted to the refinement of the semiconductor circuit without affecting the low thermal expansion ceramic base material.
Further, the conductivity of the composite material constituting the electrode is desirably 10 ⁻⁶ S / cm or more. The upper limit is not particularly limited, but is desirably 10 ⁻² S / cm or less. If it is less than 10 ⁻⁶ S / cm, the conductivity is too low to function as an electrode. Further, when the content is 10 ⁻² S / cm or more, the amount of the second material added as the conductive material increases, and a low coefficient of thermal expansion cannot be maintained.
Thus, the conductive low thermal expansion ceramic powder of the present invention can be obtained by appropriately selecting the second material constituting the electrode so that the thermal expansion coefficient and the electrical conductivity are in the desired ranges.
[0013]
Next, a method for forming an electrode will be described. First, the above-mentioned conductive low thermal expansion ceramic powder is kneaded with an appropriate binder to form a paste having adhesive properties, and this paste is applied to one surface of one of the low thermal expansion ceramic base materials. Next, the bonding material paste prepared by a method described later is applied to the surface of the low thermal expansion ceramic base material on which the electrodes are formed and the surface of another low thermal expansion ceramic base material, and degreased. The surfaces of the base materials to which the bonding material is applied are brought into close contact with each other, and heat treatment is performed at a temperature at which the bonding material melts but the base material does not melt. As a result, the bonding material is melted, and a part of the bonding material is diffused into the base material, so that the base material and the electrode material can be bonded to each other.
As the heat treatment atmosphere at this time, an air atmosphere can be used as long as all the materials are oxide-based, but a non-oxidation atmosphere can be used when non-oxide-based materials are included. preferable.
[0014]
Here, the composite material forming the bonding material is at least one first material selected from lithium aluminosilicate and cordierite, and silicon carbide, boron carbide, silicon nitride, sialon, alumina, zirconia, mullite, and zirconium. , Aluminum nitride, and one or more second materials selected from calcium silicate. At this time, the second material forming the joining material is appropriately selected from the above materials so that the melting temperature of the joining material is lower than the melting temperature of the base material.
Next, a method for adjusting the bonding material paste will be described.
The bonding material paste of the present invention is prepared by kneading the bonding material powder with an appropriate binder to form a paste having a sticky property. The base materials are bonded to each other through this paste, and the bonding material is melted but the base material is heat-treated at a temperature that does not melt, so that the bonding material is melted and partly diffused into the base material to join the base materials together. You can do it.
[0015]
Note that in the composite material forming the electrode, the bonding material, and the base material, a plurality of materials can be used in combination as the first material unless a substantial chemical reaction occurs. Similarly, the second material can be used in combination of a plurality of materials as long as no substantial chemical reaction occurs.
Here, it is preferable that at least one of the constituent materials of the composite material forming the base material is the same as the constituent material of the composite material forming the joining material. Thereby, the common constituent material is easily diffused and can be firmly joined.
In this case, the composition of the base material is 50 to 95% by mass of β-eucryptite and 5 to 50% by mass of silicon carbide, and the composition of the bonding material is 40 to 85% by mass of β-eucryptite and silicon nitride. It is preferably 15 to 60% by mass.
By using a low thermal expansion ceramic having a lower melting temperature than the base material as the joining material, the joining material is heated at a temperature higher than the melting temperature of the joining material and lower than the melting temperature of the base material during joining. Only the base material can be melted and joined together. In this case, since the joining material is a low thermal expansion ceramic, the stress remaining in the joining portion is small, and the rigidity of the joining portion is high, so that the rigidity of the entire material is high and the joining strength of the joining portion itself is large.
[0016]
Next, according to the present invention, there is provided an electrostatic chuck having a structure in which an electrode is provided between two low thermal expansion ceramic base materials, wherein the electrode is a sintered body made of conductive low thermal expansion ceramic, In addition, an electrostatic chuck characterized in that the electrode is sandwiched between two low thermal expansion ceramic base materials and bonded to each other with a bonding material made of low thermal expansion ceramic having a lower melting temperature than the base material. are doing.
[0017]
Here, as the composite material forming the base material, the electrode, and the bonding material, the same materials as those described above can be used.
Next, as a method for producing the low thermal expansion ceramic base material and the conductive low thermal expansion ceramics to be electrodes, general ceramic molding and sintering methods can be applied.
Also, the same method as described above can be applied to the method of adjusting the bonding material paste and the bonding method.
[0018]
Hereinafter, examples of the present invention will be described.
(Example 1)
β-eucryptite and silicon carbide were mixed in a pot mill at a mass ratio of 65:35 and dried to prepare a raw material mixed powder for a low thermal expansion ceramic base material. The mixed powder was uniaxially pressed to form a disc-shaped molded body, and the molded body was subjected to a CIP treatment at 150 MPa.
The thus obtained molded body was fired at 1380 ° C. in a nitrogen atmosphere to obtain a ceramic base material composed of a disc-shaped sintered body having a diameter of 200 mm × thickness of 10 mm and a diameter of 200 mm × thickness of 6 mm.
[0019]
Here, a test piece was cut out from the sintered body obtained by firing in the same manner, and the thermal expansion coefficient at room temperature was determined using a laser interference type thermal expansion measurement device (LIX-1 manufactured by ULVAC-RIKO). The average coefficient of thermal expansion at 20 to 30 ° C. was 0.4 × 10 ⁻⁶ / ° C., which was low. When the Young's modulus was measured by the resonance method, the rigidity was 170 GPa, which was high. On the other hand, when the conductivity of the ceramic base material was determined by the three-terminal method, it was 6.4 × 10 ⁻¹⁰ S / cm.
[0020]
Next, β-eucryptite powder and silicon nitride were mixed in a pot mill at a mass ratio of 40:60 and dried to prepare a mixed powder for a bonding material. This mixed powder was mixed with a 15% α-terpineol solution of ethyl cellulose so as to have an inorganic content of 30% by volume, and a three-roll roll was used to obtain a bonding material paste.
A sintered body having the same composition was prepared for this joining material, and the thermal expansion coefficient was determined in the same manner as described above. As a result, the average coefficient of thermal expansion at 20 to 30 ° C. was 0.65 × 10 ⁻⁶ / ° C., and the Young's modulus was 200 GPa.
[0021]
Further, β-eucryptite powder and β-silicon carbide were mixed in a pot mill at a mass ratio of 65:35 and dried to prepare a mixed powder for an electrode. This mixed powder was made into a paste as described above. A sintered body having the same composition as the mixed powder for an electrode was prepared, and the thermal expansion coefficient and the electrical conductivity were determined in the same manner as described above. As a result, the average thermal expansion coefficient at 20 to 30 ° C. was 1.38 × 10 ⁻⁶ / ° C., which was a low thermal expansion. Further, the conductivity was 2.5 × 10 ⁻² S / cm, and it was confirmed that the ceramic was a conductive low thermal expansion ceramic.
[0022]
The conductive low thermal expansion ceramic powder paste thus obtained was printed on one surface of one of the low thermal expansion ceramic base materials (200 mm in diameter × 10 mm in thickness) to a thickness of 80 μm using a screen mask. Next, the bonding material paste is applied to the surface of the low-thermal-expansion ceramic base material on which the electrodes are formed and the surface of another low-thermal-expansion ceramic base material (200 mm in diameter x 6 mm in thickness), and has a thickness of 80 μm on one side using a screen mask. And forcibly dried, and then degreased at 500 ° C. Next, the surfaces of the base materials to which the bonding material is applied are brought into close contact with each other, and heat treatment is performed at a temperature of 1340 ° C. in a nitrogen atmosphere to melt the bonding material and bond the surfaces of the base materials. An electrostatic chuck having a structure disposed between ceramic base materials was obtained.
[0023]
FIG. 1 shows a schematic sectional view of the electrostatic chuck obtained in this embodiment.
Here, 1 is a base made of a low thermal expansion ceramic base material, 2 is a chuck portion made of a low thermal expansion ceramic base material, and 3 is an electrode. Reference numeral 4 denotes a joining portion in which the base and the chuck portion are joined with a joining material.
In this embodiment, the method of forming an electrode on the base and then joining the chuck portion to obtain an electrostatic chuck has been described. However, the electrodes are formed on the chuck portion and then the base is joined and the electrostatic chuck is joined. You may get.
[0024]
The electrostatic chuck obtained in this embodiment has a structure in which electrodes are disposed between two low thermal expansion ceramic base materials, and the electrodes are obtained by applying a paste containing conductive low thermal expansion ceramics. In addition, since the base materials are joined to each other by a joining material made of low thermal expansion ceramics having a lower melting temperature than the base material, the overall thermal expansion coefficient can be reduced. Further, since the difference in thermal expansion between the base material and the joining material was extremely small, there was no crack at the joining portion. In addition, it was confirmed that the joint material had a large joint strength that maintained the rigidity of the base material and did not cause a significant decrease in the strength of the base material.
[0025]
(Example 2)
A disc-shaped molded body was obtained in the same procedure as in Example 1 and fired at 1380 ° C. in a nitrogen atmosphere to obtain a low-thermal-expansion ceramic base material having a diameter of 200 mm × thickness of 10 mm and a diameter of 200 mm × thickness of 6 mm. Obtained.
Next, β-eucryptite powder and α-silicon carbide are mixed in a pot mill at a mass ratio of 60:40 and dried to prepare a mixed powder for an electrode, and a sintered body is prepared by firing at 1380 ° C. in a nitrogen atmosphere. did. When the coefficient of thermal expansion and the electrical conductivity of the test piece obtained in the same manner as in Example 1 were determined, the average coefficient of thermal expansion at 20 to 30 ° C. was 1.48 × 10 ⁻⁶ / ° C., and the electrical conductivity was 1.2 × 10 ⁻³ S / cm. Therefore, it was confirmed that the obtained electrode was a conductive low thermal expansion ceramic within the scope of the present invention.
[0026]
The same bonding material paste as in Example 1 was printed to a thickness of 80 μm on one side using a screen mask on each bonding surface of the two low thermal expansion ceramic base materials and on both surfaces of the conductive low thermal expansion ceramics serving as electrodes at 500 ° C. Defatted.
Next, the electrodes are sandwiched between two low-thermal-expansion ceramic base materials, the printed surfaces of the bonding materials are closely adhered to each other, a load of 0.5 g / mm2 is applied, and heat treatment is performed at a temperature of 1340 ° C. in a nitrogen atmosphere. Was melted, and the two low thermal expansion ceramic base materials and the electrode were joined to each other to obtain an electrostatic chuck.
FIG. 2 shows a schematic sectional view of the electrostatic chuck obtained in this embodiment.
Here, 1 is a base made of a low thermal expansion ceramic base material, 2 is a chuck portion made of a low thermal expansion ceramic base material, and 3 is an electrode. Reference numeral 4 denotes a joining portion in which the base, the electrode, and the chuck portion are joined to each other with a joining material.
[0027]
The electrostatic chuck obtained in the present embodiment has a structure in which electrodes are disposed between two low thermal expansion ceramic base materials, and the electrodes are sintered bodies made of conductive low thermal expansion ceramics, and Since the electrodes are sandwiched between two low-thermal-expansion ceramic base materials and bonded to each other with a bonding material made of low-thermal-expansion ceramics having a lower melting temperature than the base material, the overall thermal expansion coefficient can be reduced. . Further, since the difference in thermal expansion between the base material and the joining material was extremely small, there was no crack at the joining portion. In addition, it was confirmed that the base material had a large joint strength that maintained the rigidity of the base material and did not cause a significant decrease in the strength of the base material. Furthermore, it was confirmed that cracks did not occur near the electrodes.
[0028]
【The invention's effect】
As described above, according to the present invention, since the average thermal expansion coefficient at 20 to 30 ° C. of the joining material is substantially the same as that of the electrode and the low thermal expansion ceramic base material, the joining portion of the base material has no crack. In addition, it is possible to obtain a large joint strength that maintains the rigidity of the base material and does not cause a significant decrease in the strength of the base material. Further, it is possible to obtain an electrostatic chuck in which cracks do not occur near the electrodes.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of an electrostatic chuck according to a first embodiment of the present invention.
FIG. 2 is a schematic sectional view of an electrostatic chuck according to a second embodiment of the present invention.
[Explanation of symbols]
1 Base 2 Chuck 3 Electrode 4 Joint

Claims (4)

An electrostatic chuck having a structure in which an electrode is disposed between two low-thermal-expansion ceramic base materials, wherein the electrode comprises a paste containing conductive low-thermal-expansion ceramic on one surface of one low-thermal-expansion ceramic base material. And a second low-thermal-expansion ceramic base material joined by a bonding material made of low-thermal-expansion ceramic having a lower melting temperature than the base material so as to cover the electrode. An electrostatic chuck characterized in that: An electrostatic chuck having a structure in which an electrode is disposed between two low thermal expansion ceramic base materials, wherein the electrode is a sintered body made of conductive low thermal expansion ceramic, and the two electrodes are An electrostatic chuck comprising a low-thermal-expansion ceramic base material and a low-thermal-expansion ceramic base material having a lower melting temperature than the base material. The composite material constituting the low thermal expansion ceramic matrix is one or more materials selected from lithium aluminosilicate and cordierite, and silicon carbide, boron carbide, silicon nitride, sialon, alumina, zirconia, mullite, zircon, It is made of at least one material selected from aluminum nitride and calcium silicate, and the low thermal expansion ceramic base material has an average thermal expansion coefficient at 20 to 30 ° C. of −1 × 10 ⁻⁶ to 1 × 10 ^−6. The electrostatic chuck according to claim 1 or 2, wherein the temperature is / ° C. The composite material constituting the conductive low thermal expansion ceramic is at least one material selected from lithium aluminosilicate and cordierite, and one or more materials selected from silicon carbide, boron carbide, titanium carbide, titanium boride, and tungsten carbide. 4. The electrostatic device according to claim 1, wherein the material is made of at least one kind of material, and the conductivity of the conductive low thermal expansion ceramic is 10 ⁻⁶ to 10 ⁻² S / cm. 5. Chuck.

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