KR100279149B1 - Blackout chuck - Google Patents

Abstract

The present invention discloses an electrostatic chuck having a heat transfer layer composed of a solid solution particle composed of alumina and a transition metal oxide having a corundum structure and a glass component present in the solid solution particle boundary. The transition metal oxide is a transition metal oxide capable of forming a solid solution with alumina, in particular chromia (Cr ₂ O ₃ ), and its crystal structure is similar to that of alumina having a corundum structure. The electrostatic chuck may exhibit stable electrostatic performance regardless of the operating temperature.

Description

Blackout chuck

1 is a diagram showing an equivalent circuit of electrostatic chuck.

2 is an enlarged schematic view of the insulating layer.

3 is a state diagram of alumina (Al ₂ O ₃ ) -chromia (Cr ₂ O ₃ ).

4 is a graph showing the relationship between the addition ratio of chromia in solid solution weight and the volume specific resistance.

5 is a graph showing the relationship between the volume specific resistance and the electric field strength.

6 is an enlarged schematic view of an insulating layer according to another embodiment.

7 is a graph showing the relationship between the concentration of titania (TiO ₂ ) and the volume specific resistance.

8 is a graph showing the relationship between the concentration of titanium (TiO ₂ ), the volume intrinsic resistance of the insulator and the electric field strength.

* Explanation of symbols for main parts of the drawings

1 substrate 2 insulation layer

3: electrode 21: solid solution particles

22: glass 23: precipitate

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chuck for adsorbing and fixing an adsorbate, such as a semiconductor wafer, with electrostatic force.

When the semiconductor wafer is subjected to plasma etching, CVD, ion plating, or the like in a reduced pressure atmosphere, an electrostatic chuck in which an internal electrode is provided between the substrate and the insulating layer (dielectric layer) is used as the wafer fixing jig.

The characteristics required for this electrostatic chuck are to generate a large adsorption force when a voltage is applied, to prevent the adsorbed product from dropping, and to release the adsorbed product so that the adsorbed product can be easily dropped by quickly removing the applied voltage. .

As means for increasing the adsorption force, means for increasing the dielectric constant of the insulating layer (Japanese Patent Laid-Open Nos. 60-59104 and 62-19060), means for controlling the thickness of the insulating layer (Japanese Patent Laid-Open No. 57-64950), Means for making the volume specific resistance of the insulating layer within a predetermined range (Japanese Patent Publication No. 61-14660 and Japanese Patent Publication No. 2-22166) can be cited. Means for blowing helium gas into and between the adsorbed material (Japanese Utility Model Publication No. 2-120831) and a means for applying a voltage of reverse polarity to the voltage at the time of adsorption (Japanese Patent Publication No. 2-63304) Etc. can be mentioned.

In the conventional method described above, the means for increasing the adsorption force is focused only on the insulating layer, and even if the adsorption force is high, the residual adsorption force tends to be large. In addition, since it takes 60 seconds or more for the adsorbate to drop easily due to attenuation of the residual adsorptive force, even if the adsorbed product is dropped immediately after the processing, it is not possible to cope with it. There is a disadvantage in that a new operation must be added in addition to the device and the normal operation, and there is a problem in use at low temperatures.

Here, the inventors of the present invention, as shown in Figure 1, the electrostatic chuck according to the present invention forms an insulating layer (2) on the substrate 1, between the substrate 1 and the insulating layer (2) ), The electrode 3 is connected to the DC power supply 5 via the lead wire 4, and the semiconductor wafer W is directly connected to the ground or is electrically connected by plasma. From the equivalent circuit of this electrostatic chuck, i) the decay time t _S (the time at which the residual constant power decays 98% of the saturated electrostatic power), ii) the volume resistivity of the insulating layer at the working temperature of the electrostatic chuck ρ ( M), iii) the dielectric constant of the insulating layer ε _r at the operating temperature of the electrostatic chuck, iv) the distance d (m) between the internal electrode and the surface of the insulating layer, and (v) between the adsorbate and the surface of the insulating layer. The relationship between the gap δ (m) of This relationship is shown by the following formula.

t _S = 1.731 × 10 ^-11 ρ (ε _r + d / δ)

Where

P is the volume specific resistance (Ωm) of the insulating layer

ε _r is the dielectric constant of the insulating layer at the working temperature of the electrostatic chuck

d is the distance in m between the internal electrode and the surface of the insulating layer (ie, the thickness of the insulating layer),

δ is the gap between the adsorbate and the surface of the insulating layer.

From the above equation, it can be seen that the detachability of the adsorbed material at the use temperature of the electrostatic chuck is largely dependent on the volume resistivity of the insulating layer. That is, in order to exhibit stable electrostatic characteristics despite the use temperature, it is necessary to arbitrarily and widely adjust the volume intrinsic resistance of the insulating layer when fabricating the charge chuck.

However, the material constituting the insulating layer (dielectric layer) of the conventional electrostatic chuck cannot arbitrarily adjust its volume resistivity. For example, it has been proposed to add titania as a transition metal oxide to alumina. However, when the amount of titania is increased, composite oxide particles precipitated between alumina particles increase, and the dependence of the electric field strength of electrical conductivity characteristics is remarkable. do. As a result, the volume specific resistance decreases rapidly at the boundary of a certain electric field, so that a predetermined electrostatic characteristic cannot be maintained.

In order to achieve the above object, the electrostatic chuck according to the present invention is characterized in that the insulating layer of the electrostatic chuck is a glass present in the grain boundary of the solid solution particles and the solid solution particles, or the particles of the glass and solid solution particles present in the grain boundary of the solid solution particles and the solid solution particles. It is composed of a transition metal oxide of 2% by weight or less, and the solid solution particles are made of alumina and a transition metal oxide of corundum structure.

When the corundum structure is made of a transition metal oxide, the corundum structure becomes similar to the crystal structure of alumina, and thus forms a solid solution easily with alumina.

Embodiments of the present invention will be described with reference to the accompanying drawings.

In the electrostatic chuck according to the present invention, as shown in FIG. 1, an insulating layer 2 is formed on a substrate 1, and an electrode 3 is formed between the substrate 1 and the insulating layer 2, and The electrode 3 is connected to the DC power supply 5 via the lead wire 4, and the semiconductor wafer W is directly connected to the ground or is electrically connected by plasma.

And the insulating layer 2 is comprised from the solid solution particle 21 which consists of an alumina and a transition metal oxide, and the glass 22 which exists in the grain boundary of a solid solution particle, as revealed from the enlarged schematic diagram of FIG. Here, as the transition metal oxide, a solid solution is formed between alumina and chromia (Cr ₂ O ₃ ), which is a crystal structure having a corundum structure similar to that of alumina, is preferable. Further, in addition to chromia, Ga ₂ O ₃ , Fe ₂ O ₃ , V ₂ O ₃ , Rh ₂ O ₃ and Ti ₂ O ₃ may be mentioned, but chromia (Cr ₂ O ₃ ) is particularly preferable. 3 is a state diagram of alumina (Al ₂ O ₃ ) and chromia (Cr ₂ O ₃ ), and it can be seen that the solution is completely dissolved, as is apparent from this drawing.

By the way, it is assumed that the volume specific resistance of alumina is 10 ¹² Ω · m or more, and the volume specific resistance of chromia has a volume specific resistance of 10 ⁴ Ω · m or less, and as described above, alumina and chromia Since is completely solid solution, the volume specific resistance of the insulating layer 2 can be adjusted by changing the addition ratio of chromia. 4 is a graph showing the relationship between the addition ratio of chromia in solid solution weight and its volume specific resistance, and it can be seen from this graph also that the volume specific resistance of the insulating layer 2 can be arbitrarily adjusted within a predetermined range.

In addition, since the insulating layer 2 having the structure as shown in the enlarged schematic diagram of FIG. 2 has a lower resistance than the glass 922 at the grain boundary of the solid solution particles 21, the charge is in the solid solution particles 21. It is evangelized through. In this case, as shown in FIG. 5, even if the electric field strength becomes large, the current follows Ohm's law. Thus, breakdown due to rapid current increase does not occur, and damage on the silicon wafer can be prevented.

6 is an enlarged schematic diagram of an insulating layer according to another embodiment of the present invention. In this embodiment, alumina and chromia (a transition metal oxide having a corundum structure), solid solution particles 21, and solid particles present at grain boundaries are present. The insulating layer 2 is formed of the glass 22 and the precipitate 23 of titania (a transition metal oxide having no corundum structure).

FIG. 7 is a graph showing the relationship between the concentration of TiO ₂ and the volume specific resistance, and FIG. 8 is a graph showing the relationship between the TiO ₂ concentration and the volume intrinsic resistance and electric field strength of an insulator. When titania (TiO ₂ ) is added, it is difficult to control the volume specific resistance within the range of 10 ⁶ Ω · m to 10 ¹⁰ Ω · m unless the concentration of 2 wt% or less is large. As a result, dielectric breakdown due to a sudden increase is likely to occur.

Next, a method of manufacturing the electrostatic chuck according to the present invention will be described.

First, as a raw material, alumina powder and a transition metal oxide (chromia, Cr ₂ O ₃ ) having a corundum structure, titania (TiO ₂ ) and a sintering aid for forming a glass component in the final product are prepared. These were weighed, mixed and ground by a ball mill, a binder such as polyvinyl butyral (PVB) and a solvent such as toluene, isopropyl alcohol or n-butanol were added, degassed, aged and molded to form a green sheet, An electrode layer printed with tungsten, molybdenum or the like was laminated on the green sheet on a substrate such as microporous Al ₂ O ₃ (the same material used for the insulating layer), and then reduced to 1,500 ° C to 1,650 ° C (typically about 1,600 ° C). ), The electrostatic chuck can be obtained by firing for about 1 to 7 hours (usually 2 hours).

Here, alumina is added in an amount of 41 to 91% by weight. A transition metal oxide having a corundum structure is added in an amount of 1 to 50% by weight. The reason is that if it is added in an amount of less than 1% by weight, it is ineffective, and if it is 50% by weight or more, it cannot be satisfactorily fired. As firing aids, carbonates or nitrates of alkali earth metals such as silica sand, clay, glass frit, MgCO ₃ , CaCO ₃ , SiCO ₃ or BaCO ₃ can be used, which must be added in amounts of 5-12% by weight. . The reason is that less than 5% by weight, the shrinkage of the ceramics is lowered, causing a drop in the breakdown voltage. If the content exceeds 12% by weight, a liquid layer is formed at low temperature, and sufficient baking cannot be achieved.

Table 1 shows the volume specific resistance, desorption time, and leakage (when adsorbing a 6-inch wafer) of the electrostatic chuck according to the present invention and the insulating layer of the conventional electrostatic chuck were measured with an electric field strength of 1.67 × 10 ⁶ V / m. Value. In addition, the electrostatic chuck used in the measurement was alumina, chromia (Cr 2 O ₃ ) and titania (TiO ₂ ) and 9 wt% of MgO and CaO as oxides as a firing aid in the amount (weight%) shown in Table 1. After mixing and pulverizing, PVB as a binder and toluene and butyl acetate as a solvent are added and aged, followed by molding to form a green sheet, and the green sheet is laminated on a substrate made of Al ₂ O ₃ , and tungsten thereon. The prepared electrode layer was printed and calcined at 1,600 ° C. for 2 hours under reduced pressure of a hydrogen-nitrogen mixed gas.

Y: the present invention

As is apparent from Table 1, the electrostatic chuck according to the present invention comprises: i) an insulating layer composed of a glass component present in the grain boundary of solid solution particles and solid solution particles composed of a transition metal oxide having alumina and corundum structure, or ii) alumina; The volume of the insulating layer at the time of fabrication is composed of solid solution particles of the transition metal oxide having a corundum structure, glass component present in the particle weight of the solid solution particles, and transition metal oxide of 2% by weight or less applied to the particle boundary of the solid solution particles. Since the resistivity can be arbitrarily controlled in a wide range, an electrostatic chuck exhibiting stable electrostatic characteristics in accordance with the operating temperature is obtained.

Claims (5)

In the electrostatic chuck provided with an internal electrode in the insulating layer, The insulating layer is composed of a solid solution particles made of alumina and a corundum transition metal oxide and glass present in the grain boundary of the solid solution particles, and the transition metal oxide of the electric corundum structure is chromia (Cr ₂ O ₃ ). Characteristic of electrostatic chuck. In the electrostatic chuck provided with an internal electrode in the insulating layer, The insulating layer is composed of a solid metal particles consisting of a transition metal oxide of alumina and corundum structure and less than 2% by weight of a transition metal oxide precipitated in the particle boundary of the glass and solid solution particles present in the particle boundary of the solid solution particles Blackout chuck. The electrostatic chuck according to claim 2, wherein the transition metal oxide is titania (TiO ₂ ). The electrostatic chuck according to claim 1 or 2, wherein the insulating layer has a volume specific resistance of 10 ^11? M or less. The electrostatic chuck according to claim 2, wherein the transition metal oxide is present in the grain boundary of the particles of the solid solution.