Electrostatic workpiece-holding method and electrostatic workpiece-holding system

An electrostatic workpiece-holding method includes an initialization step, a static elimination step, a workpiece setting step, a workpiece attracting step, and a workpiece release step. The initialization step is a step of applying a positive voltage to electrode of the electrostatic attracting part while applying a negative voltage to electrode. The static elimination step is a step of removing the static charge on the surface of the electrostatic attracting part. The workpiece setting step is a step of placing the workpiece in contact with the surface of the electrostatic attracting part. The workpiece attracting step is a step of interrupting the application of the positive voltage to electrode of the electrostatic attracting part and the application of the negative voltage to electrode. The workpiece release step is a step of applying the positive voltage to electrode of the electrostatic attracting part while applying the negative voltage to electrode.

RELATED APPLICATIONS

The present application is National Phase of International Application No. PCT/JP2018/027849 filed Jul. 25, 2018, and claims priorities from Japanese Application No. 2017-163798, filed Aug. 28, 2017 and Japanese Application No. 2017-239200, filed Dec. 14, 2017, the disclosure of which is hereby incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention relates to an electrostatic workpiece-holding method and an electrostatic workpiece-holding system for holding a workpiece such as a conductor, a semiconductor, and a dielectric.

BACKGROUND ART

As an electrostatic workpiece-holding technique for holding a workpiece such as a silicon wafer, devices described in Patent Literature 1 and Patent Literature 2 are known, for example.

These devices include an electrostatic attracting part and a voltage controlling part. Specifically, the electrostatic attracting part is formed of a plurality of electrodes giving a pair of positive and negative charges and an insulating layer covering these electrodes. The voltage controlling part can apply a high voltage to the plurality of electrodes of the electrostatic attracting part and discharge the applied voltage.

Thus, an electrostatic attraction force is generated between a workpiece placed on a surface of the electrostatic attracting part and the electrostatic attracting part by applying a high voltage to the electrodes of the electrostatic attracting part by means of the voltage controlling part, and the workpiece is held on the electrostatic attracting part. The application of the high voltage to the electrodes is stopped by the voltage controlling part to eliminate the electrostatic attraction force between the workpiece and the electrostatic attracting part, whereby a release of the workpiece can be performed. That is, these devices function as an electrostatic chuck capable of sucking and holding (chucking) the workpiece by the electrostatic attraction force and also detaching (dechucking) the workpiece at the time of releasing.

CITATION LIST

Patent Literature

SUMMARY OF THE INVENTION

Technical Problem

However, the foregoing conventional technique has the following problems.

More specifically, in the foregoing devices, the high voltage needs to be kept applied to the workpiece in order to generate the electrostatic attraction force between the workpiece and the electrostatic attracting part at the time of holding the workpiece. That is, a cable from a power supply needs to be kept connected to the electrodes in order to keep applying the high voltage to the electrodes at the time of holding the workpiece and carrying the electrostatic attracting part from a certain process to the next process. Where the distance between the processes is long, the workpiece is carried while a long cable is dragged, which is very inconvenient and leads to a reduction in work efficiency.

Further, in a thin-film silicon wafer, cracks or microcracks may be generated on a surface of the silicon wafer when the silicon wafer is peeled off from the electrostatic attracting part and singly conveyed. Thus, the generation of cracks, etc., can be prevented if such a thin-film silicon wafer can be transported in a state of being attracted to the electrostatic attracting part. However, such conveyance has been impossible in the conventional technique requiring the cable connection.

The present invention has been made in order to solve the foregoing problems, and an object thereof is to provide an electrostatic workpiece-holding method and an electrostatic workpiece-holding system capable of holding the workpiece with the voltage application to the electrodes of the electrostatic attracting part interrupted.

Solution to the Problems

In order to solve the foregoing problems, the first aspect of the present invention is an electrostatic workpiece-holding method for holding a workpiece, by an electrostatic attraction force, on a surface of an electrostatic attracting part formed of one or more first electrodes capable of applying a positive voltage, one or more second electrodes capable of applying a negative voltage, and a dielectric covering these first and second electrodes, comprising an initialization step of applying a positive voltage to the first electrode(s) and applying a negative voltage to the second electrode(s), a static elimination step of eliminating charges on the surface of the electrostatic attracting part after the execution of the initialization step, a workpiece setting step of abutting a workpiece against the surface of the electrostatic attracting part after the execution of the static elimination step, a workpiece attracting step of interrupting the application of the positive voltage to the first electrode(s) and the application of the negative voltage to the second electrode(s) after the execution of the workpiece setting step, and a workpiece release step of applying a positive voltage to the first electrode(s) and applying a negative voltage to the second electrode(s) after the execution of the workpiece attracting step.

With this configuration, upon execution of the initialization step, a positive voltage is applied to the first electrode(s) and a negative voltage is applied to the second electrode(s). Whereby, a positive charge corresponding to the positive voltage is charged on the surface of the electrostatic attracting part and at a position immediately above the first electrode(s), and a negative charge corresponding to the negative voltage is charged on the surface of the electrostatic attracting part and at a position immediately above the second electrode(s).

Then, upon execution of the static elimination step, the positive charge and the negative charge charged on the surface of the electrostatic attracting part are eliminated with the positive voltage applied to the first electrode(s) and the negative voltage applied to the second electrode(s), and the surface potential of the electrostatic attracting part becomes zero.

By executing the workpiece setting step in such a state, the workpiece is placed, etc., on the electrostatic attracting part so that the workpiece can be abutted against the surface of the electrostatic attracting part.

The workpiece attracting step is executed after the execution of the workpiece setting step, whereby the application of the positive voltage to the first electrode(s) and the application of the negative voltage to the second electrode(s) are interrupted, and a negative charge corresponding to the positive voltage is charged on the surface of the electrostatic attracting part and at a position immediately above the first electrode(s) and a positive charge corresponding to the negative voltage is charged on the surface of the electrostatic attracting part and at a position immediately above the second electrode(s).

As a result, a positive charge is induced on a back surface of the workpiece and at a position corresponding to the first electrode(s), and a negative charge is induced on the back surface of the workpiece and at a position corresponding to the second electrode(s). Whereby, the workpiece is attracted to the surface of the electrostatic attracting part by an electrostatic attraction force by the charges on the back surface of the workpiece and the charges on the surface of the electrostatic attracting part.

By executing the workpiece release step after the execution of the workpiece attracting step, a positive voltage is applied to the first electrode(s) and a negative voltage is applied to the second electrode(s). Whereby, the negative charge charged on the surface of the electrostatic attracting part and at the position immediately above the first electrode(s) and the positive charge charged at the position immediately above the second electrode(s) are cancelled out by the positive voltage and the negative voltage applied to the first and second electrodes. As a result, the electrostatic attraction force between the workpiece and the electrostatic attracting part is released, and the workpiece can be easily peeled off from the surface of the electrostatic attracting part.

The second aspect of the present invention is the electrostatic workpiece-holding method according to the first aspect of the present invention, wherein the static elimination step eliminates the charges on the surface of the electrostatic attracting part by applying a very weak X-ray to a gas around the electrostatic attracting part and ionizing the gas.

With this configuration, upon execution of the static elimination step, a very weak X-ray is applied to the gas around the electrostatic attracting part, and almost the same amount of positive ions and negative ions is produced around the electrostatic attracting part. The positive charge on the surface of the electrostatic attracting part and at the position immediately above the first electrode(s) is then neutralized by the negative ions, and the negative charge immediately above the second electrode(s) is neutralized by the positive ions. As a result, the entire surface of the electrostatic attracting part is charge-neutralized.

The third aspect of the present invention is the electrostatic workpiece-holding method according to the first or second aspect of the present invention, wherein the first and second electrodes of the electrostatic attracting part are either flat plate-shaped electrodes juxtaposed so as to adjoin each other at a predetermined interval or comb-shaped electrodes arranged so as to mesh with each other at a predetermined interval.

With this configuration, the workpiece can be electrostatically attracted by a Coulomb force where the first and second electrodes of the electrostatic attracting part are flat plate-shaped electrodes. Therefore, although a sufficient electrostatic attraction force cannot be obtained for an insulator workpiece on the electrostatic attracting part, a strong electrostatic attraction force by electrostatic induction can be obtained for a conductor workpiece or a semiconductor workpiece such as a silicon wafer, and the workpiece can be held firmly.

Where the first and second electrodes of the electrostatic attracting part are comb-shaped electrodes arranged so as to mesh with each other at a predetermined interval, the workpiece can be electrostatically attracted by a gradient force. Therefore, not only can the conductor or semiconductor workpiece be electrostatically attracted but also a strong electrostatic attraction force due to dielectric polarization can be obtained even for an insulator workpiece such as a glass substrate, and such a workpiece can be held firmly.

The fourth aspect of the present invention is an electrostatic workpiece-holding system including an electrostatic attracting part formed of one or more first electrodes capable of applying a positive voltage, one or more second electrodes capable of applying a negative voltage, and a dielectric covering these first and second electrodes, a power supply part capable of applying a positive voltage to the first electrode(s) and applying a negative voltage to the second voltage(s), a static eliminating part eliminating charges on a surface of the electrostatic attracting part, a workpiece setting part capable of abutting a workpiece against the surface of the electrostatic attracting part and taking out the workpiece from the surface of the electrostatic attracting part, and a control part controlling the workpiece setting part, the static eliminating part, and the power supply part, wherein the control part includes an initializing part turning on the power supply part, a static elimination driving part driving the static eliminating part after the actuation of the initializing part, a workpiece abutting part driving the workpiece setting part to abut the workpiece against the surface of the electrostatic attracting part after the actuation of the static elimination driving part, a workpiece attracting part turning off the power supply part after the actuation of the workpiece abutting part, and a workpiece releasing part turning on the power supply part and driving the workpiece setting part to take out the workpiece from the electrostatic attracting part after the actuation of the workpiece attracting part.

With this configuration, when the power supply part is turned on by the control of the initializing part of the control part, a positive voltage is applied to the first electrode(s) of the electrostatic attracting part and a negative voltage is applied to the second electrode(s). Whereby, a positive charge corresponding to the positive voltage is charged on the surface of the electrostatic attracting part and at a position immediately above the first electrode(s), and a negative charge corresponding to the negative voltage is charged on the surface of the electrostatic attracting part and at a position immediately above the second electrode(s).

Then, when the static eliminating part is driven by the control of the static elimination driving part, the charges on the surface of the electrostatic attracting part are eliminated by the static eliminating part. Whereby, the positive charge and the negative charge charged on the surface of the electrostatic attracting part are eliminated with the positive voltage applied to the first electrode(s) and the negative voltage applied to the second electrode(s), and the surface potential of the electrostatic attracting part becomes zero.

When the workpiece setting part is driven by the control of the workpiece abutting part in such a state, the workpiece is placed, etc., on the electrostatic attracting part by the workpiece setting part, and the workpiece is abutted against the surface of the electrostatic attracting part.

Then, when the power supply part is turned off by the control of the workpiece attracting part, the application of the positive voltage to the first electrode(s) and the application of the negative voltage to the second electrode(s) are interrupted. Whereby, a negative charge corresponding to the positive voltage is charged on the surface of the electrostatic attracting part and at a position immediately above the first electrode(s) and a positive charge corresponding to the negative voltage is charged on the surface of the electrostatic attracting part and at a position immediately above the second electrode(s).

As a result, a positive charge is induced on a back surface of the workpiece and at a position corresponding to the first electrode(s), and a negative charge is induced on the back surface of the workpiece and at a position corresponding to the second electrode(s). The workpiece is attracted to the surface of the electrostatic attracting part by an electrostatic attraction force by the charges on the back surface of the workpiece and the charges on the surface of the electrostatic attracting part.

When the control by the workpiece attracting part of the control part is completed, the power supply part is turned on by the control of the workpiece releasing part, and a positive voltage is applied to the first electrode(s) and a negative voltage is applied to the second electrode(s). Whereby, the negative charge charged on the surface of the electrostatic attracting part and at the position immediately above the first electrode(s) and the positive charge charged at the position immediately above the second electrode(s) are cancelled out by the positive voltage and the negative voltage applied to the first and second electrodes. As a result, the electrostatic attraction force between the workpiece and the electrostatic attracting part is released.

The workpiece setting part is driven by the control of the workpiece releasing part in such a state, and the workpiece is peeled off from the electrostatic attracting part.

The fifth aspect of the present invention is the electrostatic workpiece-holding system according to the fourth aspect of the present invention, wherein the static eliminating part is a static eliminator for eliminating the charges on the surface of the electrostatic attracting part by applying a very weak X-ray to a gas around the electrostatic attracting part and ionizing the gas.

With this configuration, when the static eliminator which is the static eliminating part is driven by the control of the static elimination driving part, a very weak X-ray output from the static eliminator is applied to the gas around the electrostatic attracting part, and almost the same amount of positive ions and negative ions is produced around the electrostatic attracting part. The positive charge on the surface of the electrostatic attracting part and at the position immediately above the first electrode(s) is neutralized by the negative ions, and the negative charge immediately above the second electrode(s) is neutralized by the positive ions. As a result, the entire surface of the electrostatic attracting part is charge-neutralized.

The sixth aspect of the present invention is the electrostatic workpiece-holding system according to the fourth or fifth aspect of the present invention, wherein the first and second electrodes of the electrostatic attracting part are either flat plate-shaped electrodes juxtaposed so as to adjoin each other at a predetermined interval or comb-shaped electrodes arranged so as to mesh with each other at a predetermined interval.

Effects of the Invention

As described above in detail, according to the present invention, the workpiece can be held by the electrostatic attracting part without applying the voltage to the first and second electrodes of the electrostatic attracting part. Therefore, the electrostatic attracting part can be carried without connecting the cable from the power supply to the electrostatic attracting part. As a result, there are excellent effects that the efficiency of the carrying operation can be increased and the electric power consumption can be reduced.

Even in the case of a workpiece such as a thin-film silicon wafer in which cracks or microcracks are likely to occur, there is an effect that only the electrostatic attracting part holding the workpiece can be conveyed safely without connecting the power supply cable.

Further, according to the third or sixth aspect of the present invention, there is an effect that the conductor workpiece or the semiconductor workpiece such as the silicon wafer can be held firmly by the Coulomb force, or not only the conductor or semiconductor workpiece but also the insulator workpiece can be held by the gradient force.

Further, according to the second and fifth aspects of the present invention, the surface of the electrostatic attracting part is configured to be charge-neutralized by applying a very weak X-ray to the gas around the electrostatic attracting part. Therefore, the surface can be charge-neutralized without bringing a static eliminating member, etc., into contact with the electrostatic attracting part. As a result, there is no occurrence such as wear or contamination of the surface of the electrostatic attracting part and generation of particles caused by a contact type static eliminating means. Thus, using these aspects of the present invention is particularly effective when charge-neutralizing a semiconductor substrate in which contamination by particles poses a problem.

Further, the amount of static elimination per unit time is larger than that of an ionizer which is the same non-contact type static eliminating means. Thus, the static elimination operating time can be shortened.

Furthermore, a wide-angle application of a very weak X-ray is possible. Accordingly, the static elimination processing becomes possible with respect to a large number of electrostatic attracting parts. As a result, the static elimination processing on a batch basis becomes possible, and the work efficiency can be improved.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, the best modes of the present invention will be described with reference to the drawings.

First Embodiment

FIG. 1is a flow diagram showing an electrostatic workpiece-holding method according to the first embodiment of the present invention.FIG. 2is a schematic diagram showing a device for implementing the electrostatic workpiece-holding method of this embodiment.

The electrostatic workpiece-holding method of this embodiment is a method for holding or releasing a workpiece on or from an electrostatic attracting part. This method includes an initialization step S1, a static elimination step S2, a workpiece setting step S3, a workpiece attracting step S4, and a workpiece release step S5, as shown inFIG. 1.

A device for performing these steps is constituted of an electrostatic attracting part1for electrostatically attracting a workpiece W and a power supply part2for supplying a predetermined high voltage to this electrostatic attracting part1, as shown inFIG. 2.

The electrostatic attracting part1has such a structure that an electrode11as a first electrode and an electrode12as a second electrode are covered with a dielectric10.

FIG. 3is a plan view of the electrostatic attracting part1shown with a pair of the electrodes11,12exposed.

As shown inFIG. 3, the electrodes11,12are two flat plate-shaped electrodes and arranged so as to adjoin each other at an interval d1.

As a material for such electrodes11,12, carbon ink was applied. As a material for the dielectric10covering the electrodes11,12, polyimide resin was applied.

As shown inFIG. 2, the power supply part2includes a power supply21capable of applying a positive voltage of, for example, +2000 V (bolt) to the electrode11and a power supply22capable of applying a negative voltage of, for example, −2000 V to the electrode12. Specifically, the power supply21whose negative pole is grounded is electrically connected to the electrode11through a switch SW1and a connector13, and the power supply22whose positive pole is grounded is electrically connected to the electrode12through a switch SW2and a connector14.

FIG. 4is a schematic diagram showing the device in a state in which the initialization step S1has been executed.

The initialization step S1is a step of applying a positive voltage to the electrode11of the electrostatic attracting part1and applying a negative voltage to the electrode12.

Specifically, the switches SW1, SW2of the power supply part2are both turned on, as shown inFIG. 4.

Whereby, the positive voltage of +2000 V is applied to the electrode11and the negative voltage of −2000 V is applied to the electrode12. As a result, a positive charge corresponding to +2000 V is charged on a surface1aof the electrostatic attracting part immediately above the electrode11and a region of the surface1aconcerned comes to have a potential of almost +2000 V. A negative charge corresponding to −2000 V is charged on the surface1aof the electrostatic attracting part immediately above the electrode12and a region of the surface1aconcerned comes to have a potential of almost −2000 V.

FIG. 5is a schematic view showing the device in a state in which the static elimination step S2has been executed.

The static elimination step S2is a step of eliminating the charges on the surface1aof the electrostatic attracting part1, and this step is executed after the execution of the above initialization step S1.

Specifically, as shown inFIG. 5, an anti-static brush15grounded is brought into contact with almost the entire surface1aof the electrostatic attracting part1with the switches SW1, SW2of the power supply part2turned on. Thereafter, this anti-static brush15is moved away from the electrostatic attracting part1to cut off the contact with the electrostatic attracting part1.

Whereby, the positive charge and the negative charge charged on the surface1aof the electrostatic attracting part1are eliminated, and the potential of the surface1aof the electrostatic attracting part1becomes almost 0 V.

FIG. 6is a schematic view showing the device in a state in which the workpiece setting step S3has been executed.

The workpiece setting step S3is a step of abutting the workpiece W against the surface1aof the electrostatic attracting part1, and this step is executed after the execution of the above static elimination step S2.

Specifically, as shown inFIG. 6, the workpiece W is placed on the electrostatic attracting part1with the switches SW1, SW2of the power supply part2turned on, and the workpiece W is abutted against the surface1a. At this moment, the surface1aof the electrostatic attracting part1has been charge-neutralized by the above static elimination step S2, although the electrodes11,12are maintained at +2000 V and −2000 V. Accordingly, an electrostatic attraction force by the charges is not generated between the workpiece W and the electrostatic attracting part1. As a result, the workpiece W can be smoothly placed at any place on the surface1aof the electrostatic attracting part1.

FIG. 7is a schematic view showing the device in a state in which the workpiece attracting step S4has been executed.FIG. 8is a schematic view showing a state in which the electrostatic part1is removed from the power supply part2.

The workpiece attracting step S4is a step of interrupting the application of the positive voltage to the electrode11of the electrostatic attracting part1and the application of the negative voltage to the electrode12, and this step is executed after the execution of the workpiece setting step S3.

Specifically, as shown inFIG. 7, the switches SW1, SW2of the power supply part2are both turned off with the workpiece W placed on the electrostatic attracting part1.

Whereby, the application of the positive voltage to the electrode11and the application of the negative voltage to the electrode12are interrupted, and the potentials of the electrodes11,12are both changed to 0 V. Simultaneously, the surface1aof the electrostatic attracting part immediately above the electrode11comes to have a potential of −2000 V, and the surface1aof the electrostatic attracting part immediately above the electrode12comes to have a potential of +2000 V. That is, a negative charge corresponding to −2000 V is charged on the surface1aof the electrostatic attracting part immediately above the electrode11and a positive charge corresponding to +2000 V is charged on the surface1aof the electrostatic attracting part immediately above the electrode12.

As a result, a positive charge is charged on a back surface Wa location of the workpiece W immediately above the electrode11and a negative charge is charged on the back surface Wa location of the workpiece W immediately above the electrode12, so that an electrostatic attraction force by these charges is generated. By this electrostatic attraction force, the workpiece W is attracted to the surface1aof the electrostatic attracting part1.

Meanwhile, the electrodes11,12are flat plate-shaped electrodes arranged side by side as shown inFIG. 3, so that the workpiece W is electrostatically attracted by the Coulomb force.

That is, where the workpiece W is a conductor or a semiconductor such as a silicon wafer, the workpiece W is brought into an electrostatic induction state in which an internal electric field is zero, by an external electric field between the positive and negative charges on the surface1aof the electrostatic attracting part. Therefore, the workpiece W is attracted to the surface1aof the electrostatic attracting part by a strong electrostatic attraction force. Moreover, since the unit area of the electrodes11,12per unit area of the workpiece is large, a large attraction force can be obtained in this regard as well.

In this manner, the workpiece W can be held by the electrostatic attracting part1with the power supply part2being turned off by executing the workpiece attracting step S4. Thus, as shown inFIG. 8, the workpiece W is kept attracted to the electrostatic attracting part1even if a male connector13aand a female connector13bof the connector13are detached and a male connector14aand a female connector14bof the connector14are detached. Accordingly, only the electrostatic attracting part1attracting the workpiece W can be carried to a predetermined place without connecting the cable from the power supply part2to the electrostatic attracting part1.

FIG. 9is a schematic view showing the device in a state in which the workpiece release step S5has been executed.

The workpiece release step S5is a step of applying a positive voltage to the electrode11of the electrostatic attracting part1and applying a negative voltage to the electrode12, and this step is executed after the execution of the workpiece attracting step S4.

Specifically, a predetermined processing is carried out on the workpiece W in the state shown inFIG. 7or the electrostatic attracting part1shown inFIG. 8is connected to the power supply part2of the conveyance destination via the connectors13,14, thereafter the switches SW1, SW2of the power supply part2are both turned on.

Whereby, a positive voltage of +2000 V is applied to the electrode11and a negative voltage of −2000 V is applied to the electrode12. As a result, the negative charge (seeFIG. 7) having been charged on the surface1aof the electrostatic attracting part immediately above the electrode11is eliminated and a region of the surface1aconcerned comes to have a potential of almost 0 V. The positive charge (seeFIG. 7) having been charged on the surface1aof the electrostatic attracting part immediately above the electrode12is eliminated and a region of the surface1aconcerned also comes to have a potential of 0 V. As a result, the electrostatic attraction force between the workpiece W and the electrostatic attracting part1is released, and the workpiece W can be easily peeled off from the surface1aof the electrostatic attracting part1as shown by a chain double-dashed line.

Second Embodiment

Next, the second embodiment of the present invention will be described.

FIG. 10is a schematic view of a device showing a main part of an electrostatic workpiece-holding method according to the second embodiment of the present invention.FIG. 11is a plan view of an electrostatic attracting part1shown with a pair of electrodes11′,12′ exposed.

The electrostatic workpiece-holding method of this embodiment differs from the foregoing first embodiment in that comb-shaped electrodes11′,12′ are used as the first and second electrodes.

Specifically, as shown inFIG. 10andFIG. 11, the electrodes11′,12′ covered with a dielectric10of the electrostatic attracting part1are both formed in a comb shape and arranged so as to mesh with each other at an interval d2.

With this configuration, a workpiece W is electrostatically attracted by a gradient force.

That is, upon execution of a workpiece attracting step S4, a positive charge is charged on a surface1aof the electrostatic attracting part immediately above each tooth part11a′ of the electrode11′ and a negative charge is charged on the surface1aof the electrostatic attracting part immediately above each tooth part12a′ of the electrode12′, as shown inFIG. 10. As a result, charges having polarities opposite to those of these charges are alternately charged on a back surface Wa of the workpiece W. That is, the back surface Wa of the workpiece W is brought into a dielectric polarization state. Thus, when an insulator such as a glass substrate is used as the workpiece W, the inside of the workpiece W comes into the dielectric polarization state and the workpiece W is reliably attracted to the electrostatic attracting part1. That is, since the flat plate-shaped electrodes11,12are used in the electrostatic attracting part1of the foregoing first embodiment, the insulator such as the glass substrate in which the Coulomb force is not generated cannot be used as the workpiece W. However, the insulator is such that dielectric polarization is caused inside by an external electric field. Therefore, when this insulator workpiece W is placed on the electrostatic attracting part1in which the positive and negative charges are alternately arranged as in this embodiment, the workpiece W is attracted firmly to the electrostatic attracting part1by the gradient force. That is, the insulator workpiece W can be electrostatically attracted by using the electrostatic workpiece-holding method of this embodiment.

It is a matter of course that the workpiece W is attracted to the electrostatic attracting part1even when the workpiece W is a conductor or a semiconductor. However, the electrodes11′,12′ of this embodiment have a unit area of the electrode per unit area of the workpiece being almost half of that of the electrodes11,12of the foregoing first embodiment. Therefore, it is understood that the attraction force is reduced to about half as compared with the electrodes11,12of the first embodiment.

Other configurations, operations and effects are the same as those of the foregoing first embodiment, and thus their description is omitted.

Third Embodiment

Next, the third embodiment of the present invention will be described.

FIG. 12is a block diagram showing an electrostatic workpiece-holding system according to the third embodiment of the present invention.

The electrostatic workpiece-holding system of this embodiment is a system capable of automatically implementing the electrostatic workpiece-holding method of the foregoing first embodiment.

This electrostatic workpiece-holding system includes the electrostatic attracting part1exemplified in the first embodiment, a power supply part2′, a static eliminating part3, a workpiece setting part4, and a control part5, as shown inFIG. 12.

The power supply part2′ is a part capable of applying a positive voltage to an electrode11of the electrostatic attracting part1and applying a negative voltage to an electrode12, and has the same function with the power supply part2of the foregoing first embodiment.

Specifically, the power supply part2′ includes an AC/DC converting circuit23, an inverting circuit24, a booster circuit25, and switches SW1, SW2.

The AC/DC converting circuit23is a circuit that converts an input commercial alternating current power supply of +100 V to a direct current voltage of, for example, +24 V and outputs the direct current voltage from output terminals23a,23b, respectively.

The output terminal23aof the AC/DC converting circuit23is directly connected to the booster circuit25, and the output terminal23bis connected to the booster circuit25through the inverting circuit24. That is, the direct current voltage of +24 V having been output from the output terminal23aof the AC/DC converting circuit23is directly input to the booster circuit25as is. On the other hand, the direct current voltage of +24 V having been output from the output terminal23bis inverted to a direct current voltage of −24 V by the inverting circuit24, and then is directly input to the booster circuit25.

The booster circuit25is a circuit that amplifies the direct current voltage of +24 V from the AC/DC converting circuit23to, for example, +2000 V and outputs it from an output terminal25aand also amplifies the direct current voltage of −24 V from the inverting circuit24to, for example, −2000 V and outputs it from an output terminal25b.

The output terminal25aof the booster circuit25is connected to the electrode11of the electrostatic attracting part1through the switch SW1, and the output terminal25bis connected to the electrode12through the switch SW2.

That is, in the power supply part2′, the output terminal23aof the AC/DC converting circuit23and the booster circuit25correspond to the power supply21of the power supply part2of the foregoing first embodiment, and the output terminal23bof the AC/DC converting circuit23, the inverting circuit24, and the booster circuit25correspond to the power supply22of the power supply part2of the foregoing first embodiment.

The switches SW1, SW2are the same switches as those of the foregoing first embodiment, and their on and off operations are controlled by the control part5.

The static eliminating part3is a part that eliminates the charges charged on the electrostatic attracting part1by moving an anti-static brush15while contacting the anti-static blush15with the surface1aof the electrostatic attracting part1, and the moving operation of this static eliminating part3is controlled by the control part5.

The workpiece setting part4is a part that places a workpiece W located at a predetermined place S onto the surface1aof the electrostatic attracting part1or takes out the workpiece W placed on the electrostatic attracting part1and returns the workpiece W to the predetermined place S. This workpiece setting part4is controlled by the control part5.

The control part5is a part that controls the power supply part2′, the static eliminating part3, and the workpiece setting part4. This control part5includes a computer and its program. Specifically, the control part5includes an initializing part51, a static elimination driving part52, a workpiece abutting part53, a workpiece attracting part54, and a workpiece releasing part55as functional blocks.

The initializing part51has a function of sending an ON control signal C1to the power supply part2′ to turn on the switches SW1, SW2and outputting a command signal Q1to the static elimination driving part52.

The static elimination driving part52has a function of outputting a control signal C3to the static eliminating part3to drive the static eliminating part3upon input of the command signal Q1from the initializing part51and outputting a command signal Q2to the workpiece abutting part53.

The workpiece abutting part53has a function of outputting a control signal C4to the workpiece setting part4to control the placing operation of the workpiece setting part4upon input of the command signal Q2from the static elimination driving part52and outputting a command signal Q3to the workpiece attracting part54. The workpiece abutting part53also has a function of outputting a control signal C5to the workpiece setting part4to control the taking-out operation of the workpiece setting part4upon input of a command signal Q5from the workpiece releasing part55described later.

The workpiece attracting part54has a function of sending an OFF control signal C2to the power supply part2′ to turn off the switches SW1, SW2upon input of the command signal Q3from the workpiece abutting part53and outputting a command signal Q4to the workpiece releasing part55after an elapse of a predetermined time.

The workpiece releasing part55has a function of sending an ON control signal C1to the power supply part2′ to turn on the switches SW1, SW2upon input of the command signal Q4from the workpiece attracting part54and outputting a command signal Q5to the workpiece abutting part53.

Next, the operation shown by the electrostatic workpiece-holding system of this embodiment will be described.

Upon actuation of the control part5, first, the initializing part51functions, and the power supply part2′ having received the ON control signal C1from the initializing part51is turned on, and the electrostatic attracting part1is brought into a voltage state and an electrically charged state as shown inFIG. 4(execution of the initialization step S1).

Thereafter, the static elimination driving part52having input the command signal Q1from the initializing part51functions, and the static eliminating part3having input the control signal C3from the static elimination driving part52charge-neutralizes the surface1aof the electrostatic attracting part1by using the anti-static brush15of the electrostatic attracting part1. As a result, the electrostatic attracting part1is brought into a voltage state and an electrically charged state as shown inFIG. 5(execution of the static elimination step S2).

Then, the workpiece abutting part53having input the command signal Q2from the static elimination driving part52functions, and the workpiece setting part4having input the control signal C4from the workpiece abutting part53places the workpiece W on the electrostatic attracting part1(execution of the workpiece setting step S3).

In this state, the workpiece attracting part54inputs the command signal Q3from the workpiece abutting part53and functions, and the power supply part2′ having received the OFF control signal C2from the workpiece attracting part54is turned off. As a result, the electrostatic attracting part1and the workpiece W are brought into a voltage state and an electrically charged state shown inFIG. 7, and the workpiece W is attracted to the surface1aof the electrostatic attracting part1(execution of the workpiece attracting step S4).

Thereafter, when a predetermined time elapses and the processing of the workpiece W is completed, the workpiece releasing part55having input the command signal Q4from the workpiece attracting part54functions and the power supply part2′ is turned on. Then, the electrostatic attracting part1and the workpiece W are brought into a voltage state and an electrically charged state shown inFIG. 9. The workpiece abutting part53having input the command signal Q5from the workpiece releasing part55then outputs the control signal C5to the workpiece setting part4to control the taking-out operation of the workpiece setting part4. Whereby, the workpiece W having been processed is returned onto the predetermined place S (execution of the workpiece release step S5).

By the above, one cycle of the operation by the electrostatic workpiece-holding system of this embodiment is completed.

Other configurations, operations and effects are the same as those of the foregoing first and second embodiments, and thus, their description is omitted.

Fourth Embodiment

Next, the fourth embodiment of the present invention will be described.

A static eliminating means for executing the static elimination step in the electrostatic workpiece-holding method of the present invention includes a contact type static eliminating means which brings a static eliminating member into contact with the electrostatic attracting part to eliminate charges on the surface of the electrostatic attracting part and a non-contact type static eliminating means which eliminates charges on the surface of the electrostatic attracting part without bringing the static eliminating member into contact with the electrostatic attracting part.

The contact type static eliminating means includes static eliminating equipment such as an anti-static cord, and one that a conductor such as a conductor metal plate or a conductor rubber sheet or a conductor material is made into an earth plate, other than the anti-static brush15applied in the foregoing embodiment. In addition, a method of applying a liquid such as isopropyl alcohol or ethyl alcohol to the electrostatic attracting part or bringing a gas such as argon gas into contact with the electrostatic attracting part can also be applied as the contact type static eliminating means.

The contact type static eliminating means can completely eliminate static electricity from the electrostatic attracting part in a low voltage state to the electrostatic attracting part in a high voltage state. Moreover, the contact type static eliminating means is an excellent static eliminating means since the static elimination time is short and the amount of static elimination per unit time is large. However, in this static eliminating means, the static eliminating member is brought into contact with the surface of the electrostatic attracting part, so that the electrostatic attracting part may be worn out or contaminated and in which particles may be generated around the electrostatic attracting part may occur. In the case of a semiconductor substrate such as a silicon wafer, it is not preferable that these do not occur at the time of static elimination. Therefore, the semiconductor substrate such as the silicon wafer cannot be used in the electrostatic workpiece-holding method including the contact type static elimination step.

On the other hand, the non-contact type static eliminating means includes an ionizer. A static elimination method by this ionizer is such that a high voltage is applied into the air to generate corona discharge and the electrostatic attracting part is charge-neutralized by using ions having been produced by this discharge. This static eliminating means is superior in not causing occurrences such as wear or contamination of the electrostatic attracting part and the generation of particles. However, this static eliminating means has disadvantages that the static elimination time is long and the amount of static elimination per unit time is small. Further, reverse charging is easily caused on the electrostatic attracting part, and static elimination control is difficult. Furthermore, since the static elimination range is narrow, a large number of electrostatic attracting parts cannot be subjected to the static elimination processing at one time. Thus, there is also a disadvantage that this static eliminating means is inferior in work efficiency as well.

Thus, in this embodiment, an electrostatic workpiece-holding method including a static elimination step in which the static elimination time is short, the amount of static elimination per unit time is large, the static elimination control is easy, and a large number of electrostatic attracting parts can be subjected to the static elimination processing at one time (batch processing), in spite of being non-contact will be exemplified.

FIG. 13is a perspective view showing the electrostatic workpiece-holding method according to the fourth embodiment of the present invention.FIG. 14is a schematic view showing an arrangement of a static eliminator at the time of an initialization step.

A static elimination step S2applied in this embodiment is a step of eliminating charges on a surface1aof an electrostatic attracting part1using a static eliminator16.

Specifically, the static eliminator16is a device capable of applying a very weak X-ray to a gas around the electrostatic attracting part1at the time of actuation and ionizing the gas. As the static eliminator16, “Photo Ion Bar L12536”, “Photo Ionizer L12645”, and “Photo Ionizer L11754” of Hamamatsu Photonics K.K. can be applied for example.

Such a static eliminator16is arranged immediately above the electrostatic attracting part1and has an output window16afacing the surface1aof the electrostatic attracting part1, as shown inFIG. 13andFIG. 14.

Whereby, upon actuation of the static eliminator16, a very weak X-ray is applied from the output window16aof the static eliminator16toward the surface1aof the electrostatic attracting part1.

When an initialization step S1is executed in the electrostatic workpiece-holding method of this embodiment, a positive voltage of +2000 V is applied to an electrode11and a negative voltage of −2000 V is applied to an electrode12in the same manner as the foregoing first embodiment. As a result, a positive charge corresponding to +2000 V is charged on the surface1aof the electrostatic attracting part immediately above the electrode11and a negative charge corresponding to −2000 V is charged on the surface1aof the electrostatic attracting part immediately above the electrode12, as shown inFIG. 14.

FIG. 15is a schematic view showing a state in which the static elimination step has been executed.FIG. 16is a schematic view for explaining a static elimination action in the static elimination step.FIG. 17is a schematic view showing a workpiece setting step.

After the execution of the initialization step S1, the static elimination step S2is executed. That is, as shown inFIG. 15, the static eliminator16is actuated to apply a very weak X-ray toward the surface1aof the electrostatic attracting part1from the output window16a.

Neutral particles P such as oxygen molecules and nitrogen molecules are present around the electrostatic attracting part1. Thus, when a very weak X-ray is applied therearound from the static eliminator16, as shown inFIG. 16, the neutral particles P within the application area of a very weak X-ray are separated into positive ions P+and negative ions P−and the same number of positive ions P+and negative ions P−is produced within the application area of a very weak X-ray.

Then, a positive charge Q+charged immediately above the electrode11is electrically bonded with a nearby negative ion P−and disappears, and a negative charge Q−charged immediately above the electrode12is electrically bonded with a nearby positive ion P+and disappears.

As a result, as shown inFIG. 17, the positive charge Q+ and the negative charge Q− charged on the surface1aof the electrostatic attracting part1are all eliminated and the potential of the surface1aof the electrostatic attracting part1becomes almost 0 V.

After an elapse of a predetermined time, the static elimination step S2is completed by stopping the operation of the static eliminator16. The workpiece setting step S3is executed, and the workpiece W can be placed on the surface1aof the electrostatic attracting part1in the non-electrically charged state.

The inventor carried out the following measurements to confirm such effects.

FIG. 18is a schematic view showing an experimental device.FIG. 19is a diagram showing experimental results.

As shown inFIG. 18, the experimental device included an electrostatic attracting part1to which a power supply part2is connected, a static eliminator16, a surface potential meter100, and an X-ray shielding box101in this experiment.

Specifically, the static eliminator16was arranged beside the electrostatic attracting part1and near the boundary between the electrodes11,12, and the surface potential meter100was arranged close to the surface1aof the electrostatic attracting part1. The electrostatic attracting part1, the static eliminator16, and the surface potential meter100were covered with the X-ray shielding box101.

At this time, a PI-bipolar electrostatic carrier with a diameter of 300 mm manufactured by Creative Technology Corporation was used as the electrostatic attracting part1, and a high voltage power supply for an electrostatic chuck (CTPS-3KV2AF) capable of applying a maximum direct current voltage of ±3 KV and manufactured by Creative Technology Corporation was used as the power supply part2. “Photo Ionizer L12645” of Hamamatsu Photonics K.K. was used as the static eliminator16. A digital low voltage static meter (MODEL KSD-3000) manufactured by KASUGA DENKI, Inc. was used as the surface potential meter100, and a box made of PVC (polyvinyl chloride) was used as the X-ray shielding box101.

In the experiment, a predetermined voltage was applied to the electrodes11,12of the electrostatic attracting part1from the power supply part2, and the static eliminator16was operated for 5 minutes, and a change in surface potential of the surface1aof the electrostatic attracting part1was measured by the surface potential meter100.

As the first experimental measurement, the surface potential immediately above the positive electrode11and the surface potential immediately above the negative electrode12were measured for 5 minutes with voltages of ±300 V applied to the electrodes11,12of the electrostatic attracting part1.

According to this measurement result, as shown by a curve R1ofFIG. 19, the surface potential immediately above the positive electrode11was initially +240 V but gradually decreased to −60 V after 5 minutes. As shown by a curve R2ofFIG. 19, the surface potential immediately above the negative electrode12was initially −330 V but gradually increased to −40 V after 5 minutes.

As the second experimental measurement, the surface potential immediately above the negative electrode12was measured for 5 minutes with voltages of ±500 V applied to the electrodes11,12. As shown by a curve R3ofFIG. 19, the surface potential immediately above the negative electrode12was initially −530 V but gradually increased to −70 V after 5 minutes.

Thereafter, as the third, fourth, and fifth experimental measurements, voltages of ±1000 V, ±1500 V, and ±2000 V were respectively applied to the electrodes11,12. In each voltage state, the surface potential immediately above the negative electrode12was measured for 5 minutes.

Then, in the third experimental measurement, a result was obtained that the surface potential immediately above the negative electrode12was gradually increased from −1040 V to −90 V as shown by a curve R4. Results were obtained that, in the fourth experimental measurement, the surface potential immediately above the negative electrode12was gradually increased from −1600 V to −150 V as shown by a curve R5, and in the fifth experimental measurement, the surface potential immediately above the negative electrode12was gradually increased from −1980 V to −290 V as shown by a curve R6.

From the foregoing experimental results, the inventor has confirmed that a desired amount of static elimination can be obtained in a short time by using the static elimination method using the static eliminator16. That is, according to this method, the amount of static elimination per unit time is large, so that the static elimination operating time can be shortened.

Further, occurrences such as wear or contamination of the surface1aof the electrostatic attracting part1and the generation of particles did not occur during the experiment. From this point, it has been confirmed that even the semiconductor substrate in which contamination by particles becomes a problem can be charge-neutralized reliably by using this static elimination method.

In the static eliminator16applied to the electrostatic workpiece-holding method of this embodiment, as shown inFIG. 20, a very weak X-ray can be applied at a wide angle to subject a large number of electrostatic attracting parts1to static elimination processing. That is, the static elimination processing on a batch basis becomes possible and work efficiency can be improved.

Further, the static eliminator16applied in this embodiment can be applied to an electrostatic workpiece-holding system. Specifically, as shown inFIG. 21, the static eliminator16is used as the static eliminating part3, and the control signal C3is output from the static elimination driving part52of the control part5to the static eliminator16, whereby the static eliminator16is controlled.

Other configurations, operations and effects are the same as those of the foregoing first to third embodiments, and their description is omitted.

The present invention should not be limited to the foregoing embodiments, and various modifications and changes can be made within the scope of the gist of the present invention.

For example, the electrodes11,12,11′,12′ are made of carbon ink in the foregoing embodiments. However, without being limited thereto, the electrodes11,12,11′,12′ can be made of, for example, a conductive material (foil or paste) having copper, SUS, iron, nickel, silver, or platinum, etc., as the main component or mixed therewith.

Further, polyimide resin is applied as the material of the dielectric10in the foregoing embodiments. However, without being limited thereto, resin such as vinyl chloride and ceramic such as alumina or aluminum nitride can also be applied as the material of the dielectric10.

Furthermore, the electrostatic attracting part1having one electrode11(11′) as the first electrode and one electrode12(12′) as the second electrode is exemplified in the foregoing embodiments. However, the number of the first and second electrodes should not be limited to one each. An electrostatic attracting part1with a plurality of electrodes11and a plurality of electrodes12arranged side by side as shown inFIG. 22, and an electrostatic attracting part1with a plurality of electrodes12arranged on both sides of one electrode11as shown inFIG. 23are also included in the scope of the present invention.

REFERENCE SIGNS LIST