JPH0152899B2 - - Google Patents

Description

[Detailed description of the invention]

Mechanical chucks are usually used as a method of holding and fixing objects, so-called chucks, but when this is not possible or desirable, vacuum chucks,
Methods such as electrostatic chuck have been proposed. Among these, electrostatic chuck is a method based on electrostatic attraction,
It is relatively lightweight and is advantageous for applications that require operation in a vacuum. An example of a case where an electrostatic chuck is particularly useful is the semiconductor device manufacturing process. For example, vapor deposition,
Processes such as CVD and etching are performed in vacuum or under extremely low pressure, so a vacuum chuck cannot be used. In addition, in any form of mechanical chuck, a part of the surface is covered by the chucking arm, and it is not possible to fabricate semiconductor devices on that part of the wafer, which is not a desirable method. In addition, in a mechanical chuck, the chucking force is only applied to a small portion of the chuck, so it is not suitable for purposes such as pressing a wafer to correct warpage and flatten the wafer. Electrostatic chucks can be used even in a vacuum, do not require a chuck arm, and apply a uniform chuck force, so they are always advantageous as a chuck method in these processes. By the way, the following two types of electrostatic chucks, that is, electrostatic chuck devices have already been proposed. One is as shown in Figure 1,
An object to be attracted 3 is placed on an electrode 1 on a plane through an insulator 2.
is installed, and a voltage is applied between the electrode 1 and the object to be attracted 3 to cause the object to be attracted. The adsorption force F obtained in this way is expressed by the following equation (1). F=1/2·ε·V ² /d ² ·S (1) Here, ε is the dielectric constant, V is the applied voltage, d is the thickness of the insulator layer, and S is the electrode area. In this method, it is necessary to make electrical contact with the attracting object in order to apply a voltage between the attracting object 3 and the electrode 1. For this reason, the objects to be attracted 3 that can be used are limited to conductors, semiconductors, or objects whose surface portions are electrically conductive. Therefore, it cannot be used for semiconductor wafers whose surfaces are covered with an insulating material such as SiO ₂ film.
Another example is shown in FIGS. 2 and 3. An object to be attracted 3 is placed on a pair of comb-shaped electrodes 4 and 5 with an insulating material 2 interposed therebetween, and the object 3 is attracted thereto.It was proposed to attract an insulating material such as paper. This is designed to make the distance between the pair of electrodes extremely narrow, so
During this time, a strong electric field is created. This induces a polarized charge on the object 3', and the adsorption is based on the attractive force generated between the polarized charge and the charge on the electrode. This method can be applied to conductive objects, so it can be said to have a wide range of applications, but the adsorption force is weaker than the method shown in FIG. The present invention can be applied to both conductive objects (including conductors and semiconductors) such as semiconductor wafers and conductive objects whose surfaces are covered with a thin insulating film, has stronger adsorption force, and is easier to use. The object of the present invention is to provide an electrostatic adsorption device having the following structure. The electrostatic adsorption device of the present invention is characterized in that a conductive object is placed on a pair of flat electrodes via an insulator, and a voltage is applied between the electrodes to electrostatically adsorb the object onto the electrodes. It is characterized by The present invention will be described in detail below with reference to the drawings. FIG. 4 shows a cross section and wiring of the electrostatic chuck device according to the present invention, and FIG. 5 shows a plan view of the electrode section. Approximately 1000 ~ between a pair of flat electrodes 4 and 5
The object to be attracted 3 can be attracted by applying a voltage of about 5000V. The electrodes 4 and 5 may be made of aluminum, for example, and the insulator 2 may be made of polyethylene, for example. The thickness d of the insulator 2 is preferably about 50 to 200 microns. Here, the principle of the electrostatic chuck device of the present invention will be explained. FIG. 8 is a diagram in which FIG. 4 is replaced with an electrical equivalent circuit. Since the adsorbed object 2 is conductive,
Since there is a capacitance C ₁ C ₂ between this and the electrodes 4 and 5, it can be considered that the adsorbed object and the electrodes form a capacitor. Further, this capacitor is connected in series by the wiring and the object to be attracted 3 shown in FIG. Here, if the potentials of electrodes 4 and 5 are V ₁ and V ₂ , respectively, and the potential of the adsorbed object is V ₁₂ , then V ₁₂ = C ₁ /C ₁ +C ₂ V ₁ +C ₂ /C ₁ +C ₂ V ₂ (2) becomes. It is known that when voltage is applied to a capacitor, electrostatic attraction occurs, and its magnitude is expressed by equation (1). Therefore, now two capacitors
The voltages acting on C ₁ C ₂ are (V ₁₂ −V ₁ ) and (V ₁₂ −
V ₂ ) and the area of each electrode is S ₁ S ₂ , the electrostatic adsorption force F (C ₁ C ₂ ) of the present invention is F (C ₁ C ₂ )=1/2ε/d ² {V ₁₂ −V ₁ ) ² S ₁ + (V ₁₂ −V ₂ ) ² S ₂ } (3). Here, by substituting C ₁ = εS ₁ /α, C ₂ = εS ₂ /α (4) into equation (2), and substituting equation (2) into equation 3, we end up with F(C ₁ C ₂ )=1/ 2ε/d ₂ S ₁ S ₂ /S ₁ +S ₂ (V ₂ −V ₁ ) ² = 1/2ε/d ² S ₁ S ₂ /S ₁ +S ₂ V ² (5) where V=|V ₁ − V ₂ | (6) From equation (5), the adsorption force is proportional to the dielectric constant of the insulator and the electrode area, proportional to the square of the voltage, and 2 of the thickness of the insulator.
It can be seen that it is inversely proportional to the power of Note that F(C ₁ , C ₂ ) is maximum when S ₁ = S ₂ = S ₁ + S ₂ /2 = S/2, and in this case F(C ₁ , C ₂ ) is F(C ₁ C ₂ ). =ε/8V ² /α ² ·S (7). Below, the performance of the conventional electrostatic adsorption device and the electrostatic adsorption device of the present invention will be compared based on experimental results. In the experiment, an electrostatic adsorption device with an adsorption area of 100 cm ² and an insulating layer thickness of 100 μm was prepared, and the three examples described above were compared. Polyethylene was used as the material for the insulating layer, and the objects to be adsorbed were an aluminum plate Si wafer, a Si wafer with a 1 μm SiO ₂ film, and a quartz plate. Note that the applied voltage was 1000V. The experimental results of the electrostatic adsorption device conducted as described above are shown in the table.

[Table] Conventional Example (2) The one in Figure 2 As can be seen from the results in the table, the electrostatic adsorption device of the present invention can be applied to conductors, semiconductors, and materials with a thin insulating film on their surfaces. The adsorption force is weaker than that shown in Fig. 1 compared to conventional ones, but it is about twice as strong as that shown in Figs. 2 and 3. Judging from the characteristics described above, it is the most advantageous among the three examples above as an electrostatic adsorption device for semiconductor wafers whose surfaces are covered with insulating films such as SiO ₂ and SiO ₃ N ₄ . It is also advantageous in terms of production because of its simple structure. Furthermore, FIGS. 6 and 7 show other embodiments of the electrostatic adsorption device of the present invention in which the electrode shape is changed, and FIG. 6 shows an example in which the electrode is divided into four parts and the electrodes 4 and 5 are point symmetrical. , FIG. 7 shows an electrostatic adsorption device having concentric electrodes 4 and 5. In FIG.

[Brief explanation of drawings]

1 and 2 and 3 are explanatory diagrams of a conventional electrostatic chuck device, and FIGS. 4 and 5 are explanatory diagrams of an electrostatic chuck device of the present invention. 6 and 7 show another form of the present invention, and FIG. 8 shows an equivalent circuit of FIG. 4. In the figure, 3 and 3' are objects to be attracted, 2 is an insulator,
1, 4, and 5 represent electrodes.

Claims (1)

[Claims] 1. A conductive object or a conductive object whose surface is covered with an insulating film is placed on a pair of electrodes via an insulator, and a voltage is applied between the electrodes to cause the object to In an electrostatic adsorption device that electrostatically adsorbs onto an electrode, the electrode is a planar electrode with no irregularities on its outer periphery, and when the object is adsorbed, the total of the pair of planar electrodes facing the object An electrostatic adsorption device characterized in that the area is approximately equal to the contact area between the object and the insulator.