JP2824928B2 - Electrostatic suction device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

 The present invention relates to an electrostatic chuck.

[Prior art]

For example, in a vacuum processing apparatus such as an ion implantation apparatus or a sputtering apparatus in a semiconductor manufacturing apparatus, it is necessary to hold and convey a wafer as an object to be processed in a vacuum to process the wafer. Vacuum suction means widely used as suction holding means in the atmosphere cannot be used. For this reason, for example, in the ion implantation apparatus, the periphery of the wafer is held by the holding claws, but there is a problem of generation of particles due to contact between the wafer and the claws. Therefore, an electrostatic suction device has been proposed as a suction holding means in a vacuum (JP-A-59-79545, JP-B-1-36707, etc.). In one of these electrostatic suction devices, the suction surface of the wafer of the suction holding table is formed of a dielectric, and a dielectric electrode layer is formed under the dielectric or in the dielectric over an area approximately equal to the suction surface. And a DC voltage is applied between the electrode layer and the wafer. In this method, an electrostatic attraction force (Coulomb force) is generated between the electric charge of the electrode layer accumulated through the dielectric by the application of the DC voltage and the electric charge of the wafer different from the electric charge, and the wafer is attracted and held. Is held by suction. In the case of this method, since the electrode is brought into contact with the wafer, there is still a problem of generation of particles. Another method of the electrostatic attraction device proposed above is to provide first and second suction portions on the suction surface of the holding table, and apply a DC voltage between the electrode layers of the first and second suction portions. This is the method of applying. In this method, since the wafer is a conductor, different kinds of electric charges appear on the wafer due to electrostatic induction on the wafer due to electrostatic induction, and an electrostatic attraction force is generated between this electric charge and the electric charge generated by applying a voltage to the electrode layer. Is caused. According to this method, the electrodes are not brought into contact with the wafer, so that the generation of particles is reduced. In addition, in the above-mentioned publication, between the electrode layer and the wafer, or in the first and second layers,
A method of applying a single-phase alternating current between the electrodes of the adsorption section is also described.

[Problems to be solved by the invention]

By the way, in the case of a method in which a DC voltage is applied between the wafer and the electrode or between the two electrodes, the attractive force (Coulomb force) is strong, but dielectric polarization occurs on the dielectric material on the adsorption surface.
Even if the application of the voltage is stopped, the electric charge remains, so that there is a disadvantage that the object to be adsorbed is hard to be detached from the adsorption holding table. In addition, there is a disadvantage that dust and the like easily adhere to the object to be adsorbed. On the other hand, if an AC voltage is applied instead of a DC voltage, dust can be reduced from adhering to the object to be adsorbed, and dielectric polarization does not occur in the dielectric. It can be immediately removed from the suction holding table. However, in the case of the prior art described in the above-mentioned publication, since a single-phase AC voltage is applied, a sufficient attractive force cannot be obtained. That is, in the single-phase AC voltage, the applied instantaneous voltage always becomes zero volt in a constant cycle, and at the instantaneous voltage, the attractive force also becomes zero. In view of the above, an object of the present invention is to provide an electrostatic attraction device that can use an AC voltage as an applied voltage and has a large attractive force.

According to the present invention, a surface to be brought into contact with an object to be adsorbed is made of a dielectric, and an electrode is provided below or in the dielectric, and an AC voltage is applied to the electrode. In the electrostatic attraction device for applying and attracting the object to be attracted by an electrostatic attraction force, a period in which an AC voltage applied to the electrode becomes zero voltage is eliminated. Further, three or more electrodes are provided, and alternating voltages having phases shifted from each other are applied between the electrodes. When there are three electrodes, each of the electrodes may be formed in a sector shape having an angular interval of 120 degrees.

[Action]

According to the present invention, an AC voltage of three or more layers having a phase shift is applied between three or more electrodes for electrostatic attraction, so that the instantaneous value of the attraction applied voltage does not become zero and a relatively large static voltage is applied. Electro-attraction is obtained.

【Example】

An embodiment in which the electrostatic chuck according to the present invention is applied to a high current type ion implanter will be described below with reference to the drawings. As shown in FIG. 4, a high current type ion implantation apparatus is provided on a disk 1 arranged in a vacuum chamber along a plurality of circumferences in order to reduce heat generated by ion implantation. A semiconductor wafer holding section 2 is provided, the semiconductor wafer 3 is held by the holding section 2, and the disk 1 is rotated in a direction indicated by an arrow 4 around the center position thereof as a rotation axis. A configuration is adopted in which ions are collectively implanted into a plurality of semiconductor wafers 3 by reciprocating linear motion in the direction shown. Each holding unit 2 has an electrostatic attraction mechanism. As shown in the sectional view of FIG. 2, a dielectric 22 made of a plastic such as polyimide is provided on a base 21 made of, for example, silicon rubber. Can be As means for eliminating the wafer suction period and the instantaneous period during which the suction applied voltage becomes zero in the dielectric 22, for example, as shown in FIG. Three electrode layers 23
A, 23B and 23C are embedded and have a sandwich-like structure. In the case of this example, the thickness of the dielectric 22 including the electrode layer is, for example, about 25 μm. Then, from each of the electrode layers 23A, 23B, 23C, terminals 24A, 24B, 2
4C is derived. Then, the AC voltage shown in FIG. 3A is applied between the terminals 24A and 24B of all the holding portions 2 on the disk 1.
A series circuit of a power supply 25U for generating EU and a switch 26U is connected, and an AC voltage EV shown in FIG. 3B is connected between terminals 24B and 24C.
Power supply 2 that generates (120 ° phase different from AC voltage EU)
A series circuit of 5V and switch 26V is connected, and terminals 24C and
AC voltage EW shown in Fig. 3C (AC voltage EU is 2
A series circuit of a power supply 25W for generating a phase difference of 40 °) and a switch 26W is connected. As the power supply 25U, 25V, 25W,
A commercial three-phase AC power supply can be used. In this case, the switches 26U, 26V, 26W are interlocked with each other, and when the wafer 3 is placed on the holder 2,
Turned on. When the switches 26U, 26V, 26W are turned on, the AC voltages EU, EV, EW are applied between the electrode layers 23A, 23B, 23C. Then, electric charges appear on the wafer 3 which is a conductor through the dielectric 22 by electrostatic induction, and are attracted to the holding unit 2 by the coulomb force. In this case, the voltage applied to the electrode layers 23A, 23B, 23C is
As shown in FIG. 3, since the three-phase AC voltage is used, the instantaneous value does not become zero unlike a single-phase AC voltage, and a sufficient electrostatic attraction force can be obtained. Note that the base 21 of the holding unit 2 can be made of aluminum or ceramic. However, as in the example above,
When the base 21 is made of an elastic material such as silicon rubber, when the wafer 3 is warped or the like, the dielectric 22 has the same structure as an extremely thin flexible substrate. The base 21 is deformed according to. Therefore, even if the wafer 3 is deformed such as warpage, no gap is formed between the wafer 3 and the holding portion 2, and a suction force of a predetermined value or more can be held. Note that the number of electrodes and the number of AC voltages out of phase may be three or more. Further, in the above embodiment, an example was described in which the electrostatic chucking voltage application region of the wafer was set to three regions. However, even if a multi-phase AC voltage was applied with one electrode, the applied chucking voltage was zero with respect to the wafer. It is sufficient that there is no period. Further, a DC bias may be provided. In this case, the DC bias voltage is preferably a low voltage. In the above example, the electrostatic adsorption device according to the present invention is applied to an ion implantation device. However, as described at the beginning, the present invention includes a sputtering device, another vacuum processing device, and a vacuum transfer device. Needless to say, it can be applied to Further, the present invention can be applied to holding and transporting an object to be adsorbed in the atmosphere without being limited to a vacuum. Further, the object to be adsorbed is not limited to a semiconductor wafer, but may be any object that is conductive.

【The invention's effect】

As described above, according to the present invention, since an AC voltage is applied between the electrodes, adhesion of dust to an object to be adsorbed is reduced. Further, when the applied voltage is cut off, no charge remains on the dielectric, so that the object to be adsorbed can be easily separated. In the present invention, a multi-phase AC voltage of three or more phases is
Since the voltage is applied between a plurality of electrodes, a predetermined electrostatic attraction force can be secured.

[Brief description of the drawings]

FIG. 1 is a plan view of an embodiment of the electrostatic chuck according to the present invention, FIG. 2 is a cross-sectional view taken along line AA, FIG. 3 is a diagram showing an example of a plurality of AC voltages having different phases, FIG. 4 is a diagram for explaining a main part of an ion implantation apparatus to which the present invention is applied. 2: Wafer holder 3; Semiconductor wafer 21; Base 22; Dielectric 23A, 23B, 23C; Electrode layer 24A, 24B, 24C; Terminal 25U, 25V, 25W; 3-phase AC power supply EU, EV, EW; 3 Phase AC voltage

Claims (4)

(57) [Claims] 1. A surface to be brought into contact with an object to be adsorbed is made of a dielectric, and an electrode is provided below or inside the dielectric, and an AC voltage is applied to the electrode to cause the object to be adsorbed. Wherein the instantaneous value of the AC voltage applied to the electrode is zero in a zero-voltage period. 2. The electrostatic attraction device according to claim 1, wherein three or more electrodes are provided, and alternating voltages having phases shifted from each other are applied between the electrodes. 3. The electrostatic attraction device according to claim 2, wherein the number of the electrodes is three, and each of the electrodes has a sector shape with an angular interval of 120 degrees. 4. A series circuit of a source of a single-phase AC voltage having a different phase between the electrodes and a switch means is connected between the electrodes, and the switch is connected to the switch when the object is electrostatically attracted. The electrostatic attraction device according to claim 2 or 3, wherein said means is turned on in conjunction with said means.