JP2004260088A - Electrostatic chuck - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrostatic chuck which hardly generates defect resulting from thermal expansion difference to an electrode even if a low thermal expansion ceramics is used. <P>SOLUTION: The electrostatic chuck 1 has an electrode 3 and a dielectric ceramics layer 2 which coats the electrode 3 and attracts an attraction object 10 by applying a voltage to the electrode 3. The thermal expansion coefficient in the range of 23±3°C of the ceramics layer 2 is -0.5×10<SP>-6</SP>to 0.5×10<SP>-6</SP>/°C, the volume resistivity is 1×10<SP>9</SP>to 1×10<SP>14</SP>Ωcm, and the electrode 3 is constituted of a wire cloth or a punching metal formed of tungsten or molybdenum. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００４５】
【表２】

【００４６】
【発明の効果】
以上説明したように、本発明によれば、セラミックス層として熱膨張係数が２３±３℃の範囲で−０．５×１０^−６〜０．５×１０^−６／℃という室温付近で低熱膨張係数を示すものを用い、電極として、高融点でかつ金属の中では熱膨張係数の小さいタングステンまたはモリブデン製の金網またはパンチングメタルを用いたので、セラミックス層と電極との間の熱膨張差を極力少なくしつつ、セラミックス層と電極との密着性を良好とすることができ、静電チャックの割れやセラミックス層と電極との間の剥離の問題を生じ難くすることができる。
【図面の簡単な説明】
【図１】本発明の一実施形態に係る静電チャックを示す断面図。
【符号の説明】
１；静電チャック
２，４；セラミックス層
３；電極
５；基台
６；給電部材
１０；被吸着物[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrostatic chuck that attracts and holds a substrate when processing the substrate near room temperature in semiconductor manufacturing or the like.
[0002]
[Prior art]
In recent years, fine processing and measurement are performed in semiconductor manufacturing equipment and measuring equipment, and the parts of such equipment generate less particles than metals and have higher strength than resins. Tall ceramics have become widely used. For example, ceramics such as alumina, aluminum nitride, silicon nitride, and silicon carbide are often used as semiconductor manufacturing device members.
[0003]
As such a semiconductor manufacturing device member made of ceramics, for example, there is an electrostatic chuck that electrostatically holds a silicon wafer as a semiconductor substrate in order to perform processing such as film formation and etching on the silicon wafer.
[0004]
Ceramic electrostatic chucks include high-melting-point metal meshes and foils embedded in a ceramic compact such as aluminum nitride, alumina, silicon carbide, etc., which are fired, and high-melting-point metal paste printed on ceramic green sheets. In addition, a method of sintering after laminating and pressing a sheet is used (for example, Patent Documents 1 and 2).
[0005]
On the other hand, in recent years, as the degree of integration of integrated circuits has increased, the dimensions of patterns to be formed have become smaller, and high-precision pattern formation has been required. Particularly, in the exposure step, high-precision pattern formation is indispensable. If the electrostatic chuck on which the substrate is mounted thermally expands or contracts due to a temperature change, it becomes difficult to form a high-precision pattern, and the yield decreases. In these processes near room temperature, although the temperature inside the processing chamber is controlled, if the sample temperature rises during processing and the heat is transferred to the electrostatic chuck, or if the electrostatic chuck is operating, the There is a problem that heat around the portion is transmitted to the electrostatic chuck and the electrostatic chuck thermally expands or contracts.
[0006]
Therefore, a ceramic electrostatic chuck having a smaller coefficient of thermal expansion than the conventionally used electrostatic chucks made of aluminum nitride, alumina, and silicon carbide has been required. A material having a thermal expansion coefficient of about 0.5 × 10 ^{−6 to} 0.5 × 10 ⁻⁶ / ° C. is required.
[0007]
[Patent Document 1]
JP-A-7-273164 [Patent Document 2]
JP-A-2-160444
[Problems to be solved by the invention]
However, if such ceramics having a small coefficient of thermal expansion are used as the ceramics constituting the electrostatic chuck, if the electrodes are formed in an inner layer and fired in the same manner as the conventional ceramics electrostatic chucks, the ceramics and the electrodes are not heated. There is a problem that cracks are likely to occur due to the difference in thermal expansion between them. In order to reduce this cracking, it is conceivable to use an electrode having a low coefficient of thermal expansion as much as possible as an electrode to be interpolated and adopt a method of applying pressure from outside the ceramic such as hot pressing or HIP firing as a firing method. Depending on the shape of the electrode to be formed, the occurrence of cracks may not be solved even if such measures are taken. Further, even if firing is completed without cracking, stress during firing is released at the time of processing, and there is a problem that the ceramic layer is particularly separated from the electrode.
[0009]
The present invention has been made in view of such circumstances, and it is an object of the present invention to provide an electrostatic chuck in which a defect due to a difference in thermal expansion from an electrode is unlikely to occur even when using low thermal expansion ceramics. .
[0010]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention is an electrostatic chuck having an electrode, and a dielectric ceramic layer which covers the electrode and which applies a voltage to the electrode to adsorb the object to be adsorbed. The ceramic layer has a coefficient of thermal expansion in the range of 23 ± 3 ° C. of −0.5 × 10 ^{−6 to} 0.5 × 10 ⁻⁶ / ° C., and a volume resistivity of 1 × 10 ⁹ to 1 × 10 ¹⁴ Ω. Cm, wherein the electrode is made of a metal mesh or punched metal made of tungsten or molybdenum.
[0011]
According to the present invention, a ceramic layer having a low coefficient of thermal expansion near room temperature of -0.5 × 10 ^{−6 to} 0.5 × 10 ⁻⁶ / ° C. in a range of 23 ± 3 ° C. is used. In the previous electrostatic chuck, tungsten or molybdenum with a high melting point and a small coefficient of thermal expansion was used as the electrode, and the shape of the electrode was a wire mesh or punched metal. Adhesion between the ceramic layer and the electrode can be improved while minimizing the difference in expansion, and problems such as cracking of the electrostatic chuck and peeling between the ceramic layer and the electrode can be prevented.
[0012]
In the above-mentioned electrostatic chuck, the thickness of the ceramic layer is 0.5 mm or more, the wire diameter is 0.5 mm or less when the electrode is a wire mesh, and the thickness is 0 mm when the electrode is a punched metal. It is preferably not more than 0.5 mm. Further, it is preferable that the porosity of the electrode is 25 to 80%.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a sectional view showing an electrostatic chuck according to one embodiment of the present invention.
The electrostatic chuck 1 is fixedly provided on a base 5 made of aluminum or the like. The electrostatic chuck 1 includes an electrode 3, a dielectric ceramic layer 2 provided so as to cover the electrode 3, and an insulating ceramic layer 4 provided below the electrode 3. . That is, the electrode 3 is buried between the ceramic layers 2 and 4. A power supply member 6 is connected to the electrode 3, and a DC voltage is applied to the electrode 3 from a DC power supply (not shown) via the power supply member 6. By applying the DC voltage to the electrode 3 as described above, the object to be sucked 10, for example, a silicon wafer, is sucked onto the suction surface 2 a of the ceramic layer 2.
[0014]
The ceramic layer 2 has a coefficient of thermal expansion in the range of 23 ± 3 ° C. from −0.5 × 10 ^{−6 to} 0.5 × 10 ⁻⁶ / ° C., and a volume resistivity of 1 × 10 ⁹ to 1 × 10 ¹⁴ Ω. -Consists of ceramics of cm.
[0015]
The coefficient of thermal expansion in the range of 23 ± 3 ° C. of the ceramic layer 2 is set to −0.5 × 10 ^{−6 to} 0.5 × 10 ⁻⁶ / ° C., for example, in consideration of application to a semiconductor exposure apparatus. If the temperature is out of this range, a slight temperature change is applied to the mounting stage, which causes deformation of the sample mounting stage, which not only reduces the exposure accuracy but also causes friction with the silicon wafer as the object to be attracted. This is because particles are generated.
[0016]
Adjusting the volume resistivity of the ceramic layer 2 to 1 × 10 ⁹ to 1 × 10 ¹⁴ Ω · cm is within this range so that the ceramic layer 2 has a realistic thickness and has a higher adsorption due to the Johnson-Rahbek force. This is because you can gain strength. In the case of adsorption by Coulomb force, the thickness of the ceramic layer 2 must be extremely thin, about 0.1 mm, which makes processing very difficult. On the other hand, if the volume resistivity is in the range of 1 × 10 ⁹ to 1 × 10 ¹⁴ Ω · cm, the electric charge can be obtained without causing a circuit breakage due to a large leak current flowing through the silicon wafer as the object to be adsorbed. And the Johnson-Rahbek force acts effectively, so that a sufficient attraction force can be obtained even if the thickness of the ceramic layer 2 is about 1 mm or more. Of course, if the thickness of the ceramics layer 2 is made thinner, Coulomb force will be developed, and the attraction force can be further increased.
[0017]
Examples of ceramics satisfying such characteristics include lithium aluminosilicate represented by eucryptite and spodumene, cordierite, zirconyl phosphate, and potassium zirconium phosphate. In addition to these materials alone, as long as the above characteristics are satisfied, other materials can be used without any problem depending on the purpose of use.
[0018]
For example, it can be composed of a composite material of low thermal expansion ceramics and high Young's modulus ceramics. By thus combining the low thermal expansion ceramics and the high Young's modulus ceramics, the rigidity can be further increased while maintaining the desired low thermal expansion, and the deformation can be maintained even when mechanical or thermal stress is applied. It is preferable because it hardly occurs.
[0019]
As such a composite material, specifically, one or more selected from lithium aluminosilicate, potassium zirconium phosphate, and cordierite are used as low thermal expansion ceramics, and silicon carbide, silicon nitride is used as high Young's modulus ceramics. It is preferable to use at least one selected from sialon, alumina, zirconia, mullite, zircon, aluminum nitride, calcium silicate, and B ₄ C. These combinations have little mutual reaction and maintain the independence of each material, so that a mixing law is established for the coefficient of thermal expansion and the Young's modulus. A composite material combining these can satisfy a high Young's modulus of 120 GPa or more while satisfying a thermal expansion coefficient of -0.5 × 10 ^{−6 to} 0.5 × 10 ⁻⁶ / ° C. in a range of 23 ± 3 ° C. It is. Further, since the composition is a composite material, the coefficient of thermal expansion and the volume resistivity can be controlled by adjusting the composition.
[0020]
As the low thermal expansion ceramics constituting the composite material, lithium aluminosilicate β-eucryptite and spodumene are preferable. Among them, β-eucryptite exhibits a negative thermal expansion, and therefore, it is possible to obtain an extremely low thermal expansion coefficient close to 0 by combining it with a high Young's modulus ceramic exhibiting a positive thermal expansion. Further, by adjusting the composition, the thermal expansion coefficient can be adjusted in a wide range from minus to plus. 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.
[0021]
Among such composite materials, a combination of β-eucryptite and silicon carbide or silicon nitride is more preferable. As described above, β-eucryptite has a negative coefficient of thermal expansion, and silicon carbide and silicon nitride have positive coefficients of thermal expansion. Therefore, extremely low thermal expansion can be realized. Silicon carbide and silicon nitride exhibit high rigidity. Therefore, these composite materials have both desired low thermal expansion and high Young's modulus. Further, by changing the mixing ratio, it is possible to arbitrarily change the coefficient of thermal expansion from minus expansion to plus expansion.
[0022]
When the ceramic layer 2 is made of a composite material, a combination of a plurality of materials can be used as the low thermal expansion ceramic as long as no substantial chemical reaction occurs. Similarly, a high Young's modulus ceramic can be used in combination of a plurality of materials if a substantial chemical reaction does not occur.
[0023]
The thickness of the ceramic layer 2 is preferably 0.5 to 3 mm. If it is less than 0.5 mm, the withstand voltage is poor, and if it exceeds 3 mm, the attraction force due to the Johnson-Rahbek force becomes insufficient, and the performance of adsorbing and desorbing an object to and from the electrostatic chuck may decrease.
[0024]
The ceramic layer 4 only needs to have a function of insulating the base 5 and the electrode 3 from each other. However, the ceramic layer 4 is preferably made of the same material as the ceramic layer 2 from the viewpoint of the matching of the thermal expansion coefficient and the ease of manufacturing. preferable.
[0025]
The electrode 3 is made of tungsten or molybdenum. As a material of the electrode, a material having a coefficient of thermal expansion close to the coefficient of thermal expansion of the thermally expandable ceramic constituting the ceramic layer 2 is preferable, and a material having a high melting point is preferable because the ceramic is inserted into the ceramic and fired. From such a point, tungsten and molybdenum, which have a particularly low thermal expansion coefficient and a high melting point, are selected as electrode materials.
[0026]
However, the thermal expansion coefficient of tungsten is 4.5 × 10 ⁻⁶ (0 to 100 ° C.), and the thermal expansion coefficient of molybdenum is 5.1 × 10 ⁻⁶ (0 to 100 ° C.). The coefficient of thermal expansion between −0.5 × 10 ^{−6 and} 0.5 × 10 ⁻⁶ / ° C. is still large, and even if the electrode material is selected in this way, cracks may still occur due to the difference in thermal expansion. May occur. Further, even if the firing is completed without the occurrence of cracks, the stress during firing is released during processing, and the ceramic layer 2 may be peeled from the electrode 3. In particular, when the ceramic layer 2 is made of a low thermal expansion ceramic alone such as lithium aluminosilicate or cordierite, cracking or peeling is liable to occur due to low mechanical strength such as Young's modulus.
[0027]
In order to avoid such a situation, a wire mesh or a punched metal is used as the form of the electrode 3. By using a wire mesh and punching metal, such a difference in thermal expansion can be reduced, and the adhesion between the ceramic layer 2 and the electrode 3 can be improved. The problem of separation between the electrodes can be reduced.
[0028]
As the wire mesh, a woven wire mesh, a turtle wire mesh, a rhombus wire mesh, and the like are known. However, molybdenum and tungsten constituting the electrode 3 are difficult to process, so that the process is relatively easy to process. It is preferred to use a twill wire mesh.
[0029]
When the electrode 3 is a wire mesh, particularly in the case of a plain weave wire mesh, the wire diameter is preferably 0.5 mm or less. If the thickness of the ceramic layer 2 is 0.5 mm or more and the linear shape of the wire mesh constituting the electrode 3 exceeds 0.5 mm, cracks occur in the ceramic layer 2 regardless of the value of the porosity. Easier to do.
[0030]
It is desirable that the opening of the wire mesh is not less than the wire diameter, and the opening ratio of the wire mesh is not less than 25%. If the porosity is less than 25%, the adhesion between the electrode 3 and the ceramic layer 2 is deteriorated, and the electrode 3 and the ceramic layer 2 are likely to peel off. The increase in the porosity greatly contributes to the reduction of cracks. However, if the porosity exceeds 80%, the electrode area becomes very small and the adsorbing power decreases, so the porosity should be 80% or less. Is preferred. However, even if the porosity exceeds 80%, a desired adsorption force can be obtained by means such as lowering the volume resistivity of the ceramic or increasing the voltage applied to the electrodes.
[0031]
Punching metal is a metal material obtained by punching a metal material to form a plurality of holes in a predetermined shape and arrangement. The holes are staggered at 45 degrees, at 60 degrees at staggered holes, and at 90 degrees in series. A series of square holes, a staggered square hole, a staggered long hole, a series of long holes, and the like are generally used. The punching metal used as the electrode 3 is not particularly limited, and may be appropriately determined in consideration of the adhesion and the like.
[0032]
When the electrode 3 is a punched metal, its thickness is preferably 0.5 mm or less. If the thickness of the punching metal constituting the electrode 3 exceeds 0.5 mm when the ceramic layer 2 is 0.5 mm or more, cracks occur in the ceramic layer 2 regardless of the value of the porosity. It will be easier.
[0033]
It is desirable that the porosity of the punched metal is 25% or more. If the porosity is less than 25%, the adhesion between the electrode 3 and the ceramic layer 2 is deteriorated, and the electrode 3 and the ceramic layer 2 are likely to peel off. In the case of punching metal as well, the increase in the opening ratio greatly contributes to the reduction of cracks. However, when the opening ratio exceeds 80%, the electrode area becomes very small, and the attraction force is reduced. It is preferably 80% or less. However, even if the porosity exceeds 80%, a desired adsorption force can be obtained by means such as lowering the volume resistivity of the ceramic or increasing the voltage applied to the electrodes.
[0034]
Next, a method for manufacturing the electrostatic chuck will be described.
As described above, the thermal expansion coefficient of tungsten is 4.5 × 10 ⁻⁶ (0 to 100 ° C.) and the thermal expansion coefficient of molybdenum is 5.1 × 10 ⁻⁶ (0 to 100 ° C.). Since the difference in thermal expansion between -0.5 × 10 ^{−6 and} 0.5 × 10 ⁻⁶ / ° C. is large, the electrodes are embedded in the ceramic raw material powder and fired while applying pressure from the outside. It is preferable to perform firing using a hot press firing method, HIP, or gas pressure firing method. For example, in the case of hot press firing,
(1) Preliminary molding of the raw material powder into a predetermined shape (2) Arranging an inner layer electrode on the preformed body (3) Covering the powder so as to cover the electrode and molding (4) It is produced by a procedure such as hot press firing of the molded body. The obtained sintered body is processed into a predetermined shape to produce an electrostatic chuck.
[0035]
That is, when such a metal electrode having a higher coefficient of thermal expansion than the ceramic layer is embedded in the ceramic raw material powder and fired in a normal atmospheric pressure atmosphere, cracking occurs even when a wire mesh or punching metal is used as the electrode shape. Although it is difficult to completely prevent the occurrence, this baking while applying pressure from the outside, together with the use of wire mesh or punching metal for the electrode, more reliably prevents cracking and peeling can do.
[0036]
The structure of the electrostatic chuck is not particularly limited. In addition to the structure shown in FIG. 1, a dielectric layer having an electrode formed on one surface is attached to a ceramic plate or an aluminum base with an adhesive. Various structures such as a structure can be adopted. The electrode structure is not particularly limited, and may be a monopolar electrode or a bipolar electrode, and the overall shape is not limited.
[0037]
【Example】
Hereinafter, examples of the present invention will be described.
78 parts by mass of a commercially available high-purity β-eucryptite powder having an average particle size of 4 μm or less, which is lithium aluminosilicate, and 22 parts by mass of α-SiC having an average particle size of 1.0 μm or less were mixed to form a mixed powder. This mixed powder was uniaxially pressed at 100 kg / cm ² to obtain a molded body of φ200 × 10 mm. Next, a tungsten wire mesh (Nos. 1 to 9) of various forms shown in Table 1 or a punching metal of various forms shown in Table 2 to be a single-electrode electrostatic chuck electrode having a diameter of 190 mm is formed on the compact. (Nos. 11 to 16) were placed, and these were charged in a carbon jig. The same mixed powder was charged above the electrodes in a carbon jig in the same mass, and the mixture was further uniaxially pressed to obtain a molded body of φ200 × 20 mm. This compact was subjected to hot press sintering at a firing temperature of 1350 ° C., a firing time of 3 hours, and a press pressure of 100 kg / cm ² , to obtain a sintered body having two ceramic layers with an electrode interposed therebetween.
[0038]
Thereafter, the upper and lower surfaces of the obtained sintered body were ground. At this time, since the electrode is located at the center in the thickness direction of the sintered body, an arbitrary surface is used as a suction surface of the electrostatic chuck and the ceramic layer including the suction surface is ground so as to have a thickness of 0.5 mm. Then, an electrostatic chuck was used.
[0039]
For comparison, an electrostatic chuck manufactured in the same manner as described above except that a solid tungsten plate having a thickness of 0.5 mm was used as an electrode was prepared (No. 10).
[0040]
The ground surfaces of these electrostatic chucks were observed to check for cracks and peeling. The evaluation criterion was evaluated as ○ when there was no crack or peeling, Δ when crack or peeling was slightly present, and × when crack or peeling was clearly present. The results are shown in Tables 1 and 2.
[0041]
As shown in Tables 1 and 2, No. 1 was a comparative example using a solid tungsten plate as an electrode. In No. 10, the electrode and the ceramic layer were clearly peeled off. Nos. 1 to 9 and 11 to 16 had no clear cracks or peeling.
[0042]
In Example No. 1 using a wire mesh as an electrode. No. 1 to No. 9 No. 6 has a hole area ratio of 20.9% out of the preferred range. In No. 9, since the wire diameter was out of the preferable range of 0.6 mm, the peeling occurred very slightly, but the other wires satisfied the preferable range of the wire diameter of 0.5 mm or less and the porosity of 25 to 80%. No cracking or peeling was present.
[0043]
In Example No. 1 using a punching metal as an electrode. No. 11 to No. 16 No. 13 has a hole area ratio of 19.6% out of the preferable range. No. 16 had a very small peeling because the plate thickness was out of the preferable range of 0.6 mm, but the other parts satisfied the preferable ranges of the plate thickness of 0.5 mm or less and the porosity of 25 to 80%. No cracking or peeling was present.
[0044]
[Table 1]

[0045]
[Table 2]

[0046]
【The invention's effect】
As described above, according to the present invention, the ceramic layer has a low thermal expansion coefficient of about -0.5 × 10 ^{−6 to} 0.5 × 10 ⁻⁶ / ° C. at a room temperature of 23 ± 3 ° C. The electrode used is a metal wire or punched metal made of tungsten or molybdenum, which has a high melting point and a small thermal expansion coefficient among metals, as the electrode, so that the difference in thermal expansion between the ceramic layer and the electrode is minimized. It is possible to improve the adhesion between the ceramic layer and the electrode while reducing the number thereof, and it is possible to prevent the problem of cracking of the electrostatic chuck and peeling between the ceramic layer and the electrode.
[Brief description of the drawings]
FIG. 1 is a sectional view showing an electrostatic chuck according to one embodiment of the present invention.
[Explanation of symbols]
Reference Signs List 1: electrostatic chucks 2, 4; ceramic layer 3; electrode 5; base 6; power supply member 10;

Claims (3)

An electrostatic chuck having an electrode and a dielectric ceramic layer which covers the electrode and applies a voltage to the electrode to adsorb the object to be adsorbed, wherein the electrostatic chuck has a temperature range of 23 ± 3 ° C. of the ceramic layer. Has a thermal expansion coefficient of −0.5 × 10 ^{−6 to} 0.5 × 10 ⁻⁶ / ° C., a volume resistivity of 1 × 10 ⁹ to 1 × 10 ¹⁴ Ω · cm, and the electrode is made of tungsten or molybdenum. An electrostatic chuck comprising a wire mesh or punched metal. The thickness of the ceramic layer is 0.5 mm or more, and the wire diameter is 0.5 mm or less when the electrode is a wire mesh, and the thickness is 0.5 mm or less when the electrode is a punched metal. The electrostatic chuck according to claim 1, wherein 3. The electrostatic chuck according to claim 2, wherein the porosity of the electrode is 25 to 80%.

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