JPS62287950A - Electrostatic attracting device - Google Patents

Abstract

PURPOSE:To enable attracting force to be stabilized, by providing a switch applying power supply voltage and disconnecting it, a switch short-circuiting paired electrodes, when the power supply voltage is disconnected, and a switch inverting polarity of the applied voltage during attraction. CONSTITUTION:An attracted material 3 is placed on an insulating material 2, and the first switch 6 is turned on. Then voltage is applied to an electrode 1 and the attracted material 3 from a DC power supply 5. Here the second switch 7 is left as turned off. After a fixed length of time, determined by the applied voltage and the kind of the insulating material, the third switch 8 operates inverting polarity of the voltage applied to the electrode 1 and the attracted material 3. Thereafter, the polarity of the applied voltage is inverted by the third switch 8 in every fixed time. When the attracted material 3 is desired to be removed, attracting force is reduced by short-circuiting the electrode 1 and the attracted material 3 through the second switch 7 interlocking to the first switch 6 if it is turned off.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field to which the invention pertains] The present invention relates to an electrostatic adsorption device that holds a conductive material such as a semiconductor wafer in vacuum, and particularly relates to an electrostatic adsorption device that holds a conductive material such as a semiconductor wafer in vacuum, and in particular, The present invention relates to an electrostatic chucking device that improves the reproducibility of chucking force by reversing the polarity of the applied voltage and reduces the residual chucking force when loading and unloading an object.

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

Conventionally, mechanical chucks and vacuum chucks have been used to hold samples, but mechanical chucks cannot immerse the entire sample evenly in the holder, and there is a risk of damaging the sample. There was a drawback that there was. Furthermore, since the vacuum chuck utilizes a pressure difference with the atmosphere, it is impossible to use it within the vacuum chamber of the dry process apparatus.

Furthermore, in an ion beam etching device, a magnetron reactive ion etching device, or an ion implantation device, the sample is exposed to high-speed ions, so the temperature rises, causing thermal damage to resists and the like. Furthermore, in a CVD apparatus, it is often necessary to adjust the temperature of the sample, as the rate of production and properties of the film are strongly affected by the temperature of the sample.

Therefore, electrostatic adsorption using electrostatic force is very advantageous because it allows uniform thermal contact between the sample and the holder in a vacuum.

FIG. 3 shows the principle of this electrostatic adsorption. In the same figure,
1 is an electrode, 2 is an insulator, 3 is an object made of a conductive material, 4 is a switch, and 5 is a DC power source.

In the above configuration, when the object 3 to be attracted is placed on the electrode 1 via the insulator 2 and the switch 4 is turned on to apply a voltage from the power source 5 between the voltage ff11 and the object 3 to be attracted, the voltage ff1
F(N>=1/2 ・ε0εS
An adsorption force of (V/d)2S is generated. Here, ε
O is the dielectric constant in vacuum, εS is the relative permittivity of the insulator 2, ■ is the voltage of the power source 5, d is the thickness of the insulator 2, and S is the electrode 1
is the area of

However, in the conventional electrostatic adsorption device, when the object to be adsorbed 3 is adsorbed, an electric charge remains on the insulator 2 even if the switch 4 is turned off.
Adsorption power remains for a long time.

Further, there were problems such as variations in the time taken for the adsorption force to decrease.

In the device shown in FIG. 3, after actually turning off the switch 4,
The time required for the adsorption force to decrease to 1 Q/ci was measured.

The insulator 2 at this time was a ΔJ203 sprayed film with a thickness of 50 μ/m.

As mentioned above, it takes a very long time.

[Objective of the Invention 1] The present invention has been made in view of the problems of the prior art described above, and has an object to quickly reduce the residual adsorption force in an electrostatic adsorption device and to quickly carry out the operation of attaching an object to be adsorbed. The purpose is to

[Embodiments] A detailed description of the present invention will be given below from 1 to 1 with reference to the drawings. Components that are the same as or correspond to those of the conventional example are designated by the same reference numerals.

FIG. 1 shows the main structure of an electrostatic adsorption 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, an insulator 2 and an electrode 1 are built in. On the upper part of the insulator 2 and on the upper outer periphery of the chuck body 2a, there is an electrode 3a installed so as to be in contact with the wafer 3 when the wafer 3 is placed thereon. Therefore, wafer 3
When placed, the electrode 3a and the wafer 3 always maintain the same potential. That is, in this embodiment, the DC type m5 applies voltage directly to the electrode 1 and the wafer 3. A first switch 6 turns on and off the applied voltage. 7 is the second switch,
When the first switch 6 is on (closed), the second switch 7 is off (closed).
When the first switch 6 is off, the second switch 7 is on. 8 is the third switch,
This is a timer switch that reverses the voltage polarity between the electrode 1 and the object to be attracted 3 at regular intervals.

In the above configuration, a wafer, which is an object 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 second switch 7 is turned off. After a certain period of time determined by the applied voltage and the type of insulator, the third
The switch 8 is operated to invert the polarity of the voltage applied to the electrode 1 and the wafer 3. Thereafter, the polarity of the applied voltage is reversed by the third switch E8 at regular intervals.

When it is desired to remove the wafer 3, the first switch 6 is turned off, and the second switch 7, which operates in conjunction with the first switch 6, short-circuits the electrode 1 and the wafer 3, reducing the adsorption force.

The table below shows the results of the experiment conducted in this example (LI), and shows the values for each applied voltage when the time from when the switch 6 is turned off until the adsorption force becomes substantially zero is 1 second. Indicates the minimum required voltage polarity reversal time.

The above values indicate that the dielectric 2 of the electrostatic adsorption device is a plasma sprayed film of AJ203 with a thickness of 50 μm, similar to the one in Fig. 3.
It is from the time of.

During adsorption, the adsorption force momentarily decreases when the voltage polarity is reversed, but J
3. The adsorption force will be restored within about 1 second.

FIG. 2 shows a main part configuration of an electrostatic adsorption device according to another embodiment of the present invention. The device shown in the figure is different from the device shown in FIG.
b+,: Voltage is applied.

Its operation is exactly the same as that of the device shown in FIG. 1 described above.

Furthermore, when using a conventional electrostatic adsorption device, the reproducibility of the adsorption force is very poor due to the residual charge in the insulator 2. It has been proposed (Japanese Unexamined Patent Publication No. 114437/1983) to reverse the polarity of the applied voltage. However, although this method stabilizes the adsorption force, it may decrease the adsorption force at any time.
It was difficult to quickly remove the adsorbed object.

In this embodiment, since the polarity of the applied voltage is reversed at predetermined time intervals while the object to be attracted is being attracted, it is possible to obtain high reproducibility with respect to this attraction force.

In the above-described embodiments, a sprayed film of aluminum oxide was used as the insulator, but the present invention is not limited to this, and other insulators may also be used.

[Effects of the Invention] As explained above, according to the present invention, the polarity of the applied voltage is reversed while the object to be attracted is being attracted, and furthermore, when the object to be attracted is removed, the electrode and the object to be attracted are short-circuited. Through this operation, the adsorbed object can be quickly desorbed and the adsorption force can be stabilized.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of main parts of an electrostatic chuck device according to an embodiment of the present invention, FIG. 2 is a block diagram of main parts of an electrostatic chuck device according to another embodiment of the present invention, and FIG. 1 is a schematic diagram of the main part 1f4 of a conventional electrostatic adsorption device. 1.1a, Ib: Electrode, 2: Insulator, 3: Adsorbed object, 5
: DC power supply, 6: first switch, 7: second switch, 8: third switch.

Claims (1)

[Claims] 1. An insulating layer having a surface on which an object to be attracted is placed, a pair of electrodes that generate polarized charges on at least the above-mentioned surface of the insulating layer, and between the pair of electrodes. a DC power supply that applies a voltage; a first switch that applies and cuts off the power supply voltage; a second switch that short-circuits the pair of electrodes when the first switch is cut off; and the object to be attracted. and a third switch for reversing the polarity of the applied voltage at least once during adsorption. 2. The electrostatic adsorption device according to claim 1, wherein the third switch is a timer switch that reverses the polarity of the applied voltage at predetermined intervals. 3. The electrostatic adsorption device according to claim 1 or 2, wherein one of the pair of electrodes is the object to be adsorbed itself. 4. Claim 1 or 2, wherein the pair of electrodes comprises one or more pairs of electrodes arranged facing the object to be attracted on a surface opposite to the mounting surface of the insulating layer. electrostatic adsorption device. 5. The electrostatic adsorption device according to any one of claims 1 to 4, wherein the insulating layer is a sprayed film of aluminum oxide.