JPH074718B2 - Electrostatic adsorption device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic chucking device for holding a conductive substance such as a semiconductor wafer in a vacuum, and in particular, reverses the applied voltage polarity during the chucking of an object to be attracted. Accordingly, the present invention relates to an electrostatic adsorption device that improves the reproducibility of the adsorption force and reduces the residual adsorption force when loading and unloading an object to be attracted.

[Prior Art] In recent years, semiconductor manufacturing processes have rapidly become dry, and samples are processed in a vacuum of 10 torr or less by etching equipment, ashing equipment, ion implantation equipment, plasma CVD equipment, electron beam lithography, X-ray lithography, etc. Things to do are increasing.

Conventionally, mechanical chucks and vacuum chucks by mechanical methods have been widely used for holding the sample, but the mechanical chuck cannot hold the entire sample uniformly in the holder and may damage the sample. There was a drawback. Further, since the vacuum chuck utilizes the pressure difference from the atmosphere, it cannot be used in the vacuum chamber of the dry process apparatus.

Further, in an ion beam etching apparatus, a magnetron reactive ion etching apparatus, and an ion implantation apparatus, the sample is exposed to high-speed ions, so that the temperature thereof rises and the resist or the like is damaged by heat. Further, in a CVD apparatus, it is often necessary to adjust the temperature of the sample, for example, the temperature of the sample strongly affects the generation rate and properties of the formed film.

Therefore, electrostatic adsorption using electrostatic force capable of making uniform thermal contact between the sample and the holder in vacuum is very advantageous.

FIG. 3 shows the principle of this electrostatic attraction. In the figure,
Reference numeral 1 is an electrode, 2 is an insulator, 3 is an object to be adsorbed made of a conductive substance, 4 is a switch, and 5 is a DC power source.

In the above structure, when the object to be adsorbed 3 is placed on the electrode 1 via the insulator 2, the switch 4 is turned on and a voltage is applied between the electrode 1 and the object to be adsorbed 3 by the power supply 5, the electrode 1 and the object to be adsorbed are An adsorbing force of F ( _N ) = 1/2 · εoεs (V / d) ² S is generated between the adsorbates 3. Here, εo is the permittivity in vacuum, εs is the relative permittivity of the insulator 2, V is the voltage of the power source 5, and d
Is the thickness of the insulator 2 and S is the area of the electrode 1.

However, in the conventional electrostatic attracting device, when the attracted object 3 is attracted, the electric charge remains in the insulator 2 even if the switch 4 is turned off,
The adsorption power remains for a long time. In addition, there is a problem that the time for which the suction force is reduced varies.

In the device of FIG. 3, after actually turning off the switch 4,
The time until the adsorption force was reduced to 1 g / cm ² was measured. At this time, the insulator 2 is an Al ₂ O ₃ sprayed film having a thickness of 50 μ / m.

As mentioned above, it takes a very long time.

[Object of the Invention] The present invention has been made in view of the problems of the above-described conventional example, and makes it possible to quickly reduce the residual attraction force in the electrostatic attraction device, and to quickly perform the attachment / detachment operation of the object to be attracted. The purpose is to be able to do.

[Summary of the Invention] In order to achieve this object, an electrostatic attraction device of the present invention is configured to generate an insulating layer having a placement surface on which an object to be attracted is placed, and to generate polarized charges on the placement surface of the insulating layer. A pair of electrodes, a DC power supply that generates a voltage applied to the electrodes, a first switch means that is switched to apply a voltage from the DC power supply to the electrodes, and the first switch means applies a voltage. It has a second switch means that is switched to reverse the polarity of the applied voltage at least once more while it is switched to the side.

According to this, since the polarity of the applied voltage is inverted at least once by the second switch means while the first switch means is being switched to the voltage application side, the insulation is maintained even after the voltage applied to the electrodes is cut off. The residual adsorptive force (residual charge) remaining between the layer and the object to be adsorbed is reduced, and the object to be adsorbed is quickly attached and detached. Further, destabilization of the adsorption force at the time of adsorption after the next time due to the residual charge is also avoided. Furthermore, since the adsorption force does not continue to increase during the adsorption of the adsorption target, even when the adsorption target is adsorbed for a long time, the adsorption force will destroy the adsorption target or the insulating layer. There is no fear.

Embodiments Embodiments of the present invention will be described below with reference to the drawings. It should be noted that parts that are the same as or correspond to those in the conventional example are denoted by the same reference numerals.

FIG. 1 shows a main configuration of an electrostatic chucking device according to an embodiment of the present invention. In the figure, 2a is a chuck body for supporting a wafer, and as shown in the figure, it contains an insulator 2 and an electrode 1. An electrode 3a is installed on the upper part of the insulator 2 and on the outer periphery of the upper part of the chuck body 2a so as to be in contact with the wafer 3 when the wafer 3 is placed. Therefore, when the wafer 3 is placed, the electrode 3a and the wafer 3 always maintain the same potential. That is, in this embodiment, the DC power supply 5 applies a voltage directly to the electrode 1 and the wafer 3. A first switch 6 turns the applied voltage on and off. Reference numeral 7 denotes an auxiliary switch, which is interlocked with the first switch 6, and when the first switch 6 is on (closed), the auxiliary switch 7 is off (open) and the first switch 6 is turned on. When it is off, the auxiliary switch 7 is on. Reference numeral 8 denotes a second switch, which is a timer switch for reversing the voltage polarity between the electrode 1 and the object to be adsorbed 3 at regular intervals.

In the above structure, the wafer to be attracted 3 is placed on the insulator 2 and the first switch 6 is turned on. Then, a voltage is applied from the DC power supply 5 to the electrode 1 and the wafer 3. At this time, the auxiliary switch 7 is turned off. Second after a certain period of time determined by the applied voltage and the type of insulator
The switch 8 operates to reverse the polarity of the voltage applied to the electrode 1 and the wafer 3. After that, the polarity of the applied voltage is inverted by the second switch 8 at regular intervals.

When the wafer 3 is desired to be removed, the first switch 6 is turned off, and the auxiliary switch 7 interlocking with the first switch 6 short-circuits the electrode 1 and the wafer 3 to reduce the attraction force.

The following table is obtained as a result of conducting an experiment in this embodiment, and is required for each applied voltage when the time until the adsorption force becomes substantially zero after the switch 6 is turned off is 1 second. It shows the minimum voltage polarity reversal time.

The above values are obtained when the dielectric 2 of the electrostatic attraction device is a plasma sprayed film of Al ₂ O ₃ having a thickness of 50 μm, which is similar to that shown in FIG.

During attraction, the attraction force momentarily decreases when the voltage polarity is reversed, but the attraction force returns within about 1 second.

FIG. 2 shows a main configuration of an electrostatic attraction device according to another embodiment of the present invention. The apparatus shown in the figure is different from the apparatus shown in FIG. 1 in that a pair of electrodes 1a and 1b are arranged on the surface opposite to the mounting surface with respect to the insulator 2 and a voltage is applied to these electrodes 1a and 1b. I am trying. The operation is exactly the same as in the case of the device shown in FIG.

Further, when the conventional electrostatic adsorption device is used, the reproducibility of the adsorption force is very poor due to the residual electric charge of the insulator 2, and in order to solve this problem, “each time the object to be attracted is adsorbed once, The polarity of the applied voltage is reversed. "
58-114437). However, although this method can stabilize the adsorption force, it is difficult to reduce the adsorption force at any time and quickly remove the object to be adsorbed.

In this embodiment, since the polarity of the applied voltage is reversed at a predetermined time interval during the adsorption of the object to be adsorbed, it is possible to obtain a high reproducibility of the adsorption force.

Although the sprayed film of aluminum oxide was used as the insulating material in the above-described embodiments, the present invention is not limited to this, and other edge materials can be used.

[Effects of the Invention] As described above, according to the present invention, by reversing the polarity of the applied voltage during the adsorption of the object to be adsorbed, the object to be adsorbed can be quickly desorbed and the adsorption force can be improved. Stabilization can be obtained.

[Brief description of drawings]

FIG. 1 is a main part configuration diagram of an electrostatic adsorption device according to an embodiment of the present invention, FIG. 2 is a main part configuration diagram of an electrostatic adsorption device according to another embodiment of the present invention, and FIG. FIG. 4 is a configuration diagram of a main part of a conventional electrostatic attraction device. 1,1a, 1b: Electrode, 2: Insulator, 3: Adsorbed object, 5: DC power supply, 6:
First switch, 7: auxiliary switch, 8: second switch.

Claims (5)

[Claims] 1. An insulating layer having a mounting surface on which an object to be attracted is mounted, a pair of electrodes for generating polarized charges on the mounting surface of the insulating layer, and a voltage applied to the electrode. Direct current power supply, a first switch means that is switched to apply a voltage from the direct current power supply to the electrode, and a polarity of the applied voltage while the first switch means is switched to the voltage application side. An electrostatic adsorption device comprising a second switch means that is switched to reverse at least once. 2. The electrostatic attraction device according to claim 1, wherein the second switch means has a timer switch that is switched at predetermined time intervals. 3. The claim 1 according to claim 1, wherein one of the electrodes is in contact with the object to be adsorbed when the object to be adsorbed is placed on the mounting surface of the insulating layer. Electrostatic adsorption device. 4. The static electrode according to claim 1, wherein each of the electrodes is arranged so as to face the object to be adsorbed on a surface opposite to a mounting surface of the insulating layer. Electroadsorption device. 5. The electrostatic adsorption device according to claim 1, wherein the insulating layer is a sprayed film of aluminum oxide.