JP7150510B2 - electrostatic chuck - Google Patents

Description

The present invention relates to electrostatic chucks.

An electrostatic chuck is used as a wafer stage in a semiconductor manufacturing process performed under a reduced pressure environment. In recent years, with the increase in the number of processes in the semiconductor manufacturing process, there has been a demand for shortening the time taken to remove the wafer from the electrostatic chuck. As a countermeasure against this, in addition to reducing the volume resistivity of the insulating layer of the electrostatic chuck, a convex portion is provided on the surface of the electrostatic chuck to reduce the contact area with the wafer, thereby reducing the total pressure of the adsorption force and reducing the residual pressure. A technique has been proposed in which a countermeasure is taken such as reducing the adsorption force to be applied (Patent Document 1).

Japanese Patent No. 4407793

However, in the technique disclosed in Patent Document 1, the electrostatic attraction electrode is embedded inside the dielectric, and the contact interface between the wafer and the surface of the electrostatic chuck is caused by a minute current flowing between the electrostatic attraction electrode and the wafer during use. The microelectrodes flow due to polarization. For this reason, the so-called Johnsen-Rahbek effect occurs between the electrostatic chuck and the wafer, and even if the attraction power supply for supplying power to the electrostatic attraction electrode is turned off, the attraction force remains transiently for a certain period of time. Further improvements are required to reduce the residual adsorption force.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an electrostatic chuck capable of reducing the residual attraction force after the attraction power supply is turned off.

[1] To achieve the above object, the electrostatic chuck of the present invention comprises:
an insulating substrate having insulation;
an electrostatic adsorption electrode embedded in the insulating substrate along the surface of the insulating substrate;
a plurality of protrusions provided on the surface;
An electrostatic chuck comprising:
the electrostatic attraction electrode is spaced apart from the region overlapping the convex portion in the thickness direction of the insulating substrate,
a distance T in the thickness direction of the insulating substrate from the surface of the insulating substrate to the electrostatic attraction electrode is 2×10 −3 (m) or less;
a first vector extending from the end of the electrostatic adsorption electrode closest to the protrusion toward the lower end of the protrusion closest to the end of the electrostatic adsorption electrode; An angle θ formed between the first vector and a second vector formed by projecting the first vector onto a plane on which the electrostatic attraction electrode is arranged is 10.6° to 45° .

According to this configuration, the distance (thickness) T in the thickness direction of the insulating substrate from the surface of the insulating substrate to the electrostatic attraction electrode is 2×10 ⁻³ (m) or less. Further, a first vector extending from the end of the electrostatic attraction electrode closest to the projection toward the bottom end of the projection closest to the end of the electrostatic attraction electrode, and a first vector along the thickness direction of the insulating substrate to the second vector formed by projecting onto the plane on which the electrostatic adsorption electrodes are arranged is 45° or less.

For this reason, the electrostatic chucking electrode is spaced apart from the region overlapping the convex portion in the thickness direction of the insulating substrate, from the end portion of the electrostatic chucking electrode closest to the convex portion to the convex portion closest to the end portion of the electrostatic chucking electrode. distance increases. Since the distance from the end of the electrostatic attraction electrode closest to the projection to the projection closest to the edge of the electrostatic attraction electrode increases, the edge of the electrostatic attraction electrode on the insulating substrate (dielectric) of the electrostatic chuck The electric resistance R2 from the ridge to the top surface of the ridge increases. Due to the electrical resistance R2 in the insulating substrate (dielectric) of the electrostatic chuck, the current density (electric lines of force) flowing from the electrostatic attraction electrode to the wafer via the projections is reduced.

Although the electrical resistance R1 at the contact interface between the convex portion and the wafer does not change, the current density (electric line of force) flowing through the convex portion to the wafer becomes smaller, so the potential difference V1 at the contact interface between the convex portion and the wafer becomes smaller. Become. Since the potential difference V1 decreases while the capacitance C1 formed at the contact interface between the convex portion and the wafer remains unchanged, the amount of electricity at the contact interface decreases. As a result, the amount of electricity remaining at the time of dechucking is reduced, so that the remaining attraction force due to the Johnsen-Rahbek effect is reduced, and the detachment time of the wafer from the electrostatic chuck can be shortened.

[2] Further, in the electrostatic chuck of the present invention, it is preferable that the height H of the convex portion is 3 to 15 (μm).

According to such a configuration, when the object to be attracted to the electrostatic chuck is a semiconductor such as a silicon wafer, a Coulomb force effect is also generated at the height H which is the gap between the surface of the insulating substrate and the silicon wafer. Express. The distance (thickness) T from the electrostatic adsorption electrode to the surface of the insulating substrate is very small, and the input voltage input between the electrostatic adsorption electrode and the silicon wafer is the gap between the surface of the insulating substrate and the silicon wafer. is divided into portions of height H where . If the height H is smaller than 3 (μm), manufacturing becomes difficult. Also, if the height H is made larger than 15 (μm), an excessive voltage is required to obtain a sufficient attracting force. Therefore, by setting the height H to 3 to 15 (μm) so that the attraction force due to the Coulomb force effect is dominant, the current density (electric line of force) flowing from the electrostatic attraction electrode to the wafer via the projections can be reduced. It is possible to reduce the residual electrostatic adsorption force.

[3] Further, in the electrostatic chuck of the present invention, the capacitance of a parallel plate capacitor formed between the electrostatic chucking electrode and the chucking object placed on the convex portion is calculated as the electrostatic capacitance per square meter. The value converted to capacity is preferably 1×10 ⁻⁸ (F) or more. According to such a configuration, an object to be attracted can be attracted with a sufficient attraction force as an electrostatic chuck.

1 is a cross-sectional view showing an electrostatic chuck of the present invention; FIG. FIG. 2 is a cross-sectional view taken along the line II-II of FIG. 1; 2 is an enlarged view of a main portion showing the electrostatic chuck of FIG. 1; FIG. 2 is an equivalent circuit diagram showing the electrostatic chuck of FIG. 1; FIG. FIG. 5A is a working diagram of the electrostatic chuck of the embodiment of the present invention. FIG. 5B is an action diagram of the electrostatic chuck of the comparative example. FIG. 5C is a working diagram of an electrostatic chuck of a further comparative example.

Embodiments of the present invention will be described below with reference to the drawings. The drawings conceptually (schematically) show the electrostatic chuck 1 .

As shown in FIGS. 1 and 2, the electrostatic chuck 1 includes an insulating substrate 2 having insulating properties, an electrostatic attraction electrode 4 embedded in the insulating substrate 2 along a surface 3 of the insulating substrate 2, and an electrostatic chuck electrode 4 embedded in the insulating substrate 2. and a plurality of protrusions 5 provided on the . A height H of the projection 5 is 3 to 15 (μm), and a wafer 11 as a semiconductor is placed on the projection 5 . An opening 6 is formed in the electrostatic attraction electrode 4 , and the electrostatic attraction electrode 4 is separated from the region S<b>1 overlapping the protrusion 5 in the thickness direction of the insulating substrate 2 .

As shown in FIGS. 2 and 3, the distance T in the thickness direction of the insulating substrate 2 from the surface 3 of the insulating substrate 2 to the electrostatic attraction electrode 4 is set to 2×10 ⁻³ (m) or less. A dielectric 7 is provided between the surface 3 of the insulating substrate 2 and the electrostatic attraction electrode 4 .

From the end A of the opening 6 of the electrostatic adsorption electrode 4 closest to the protrusion 5 of the insulating substrate 2 toward the bottom end B of the protrusion 5 closest to the end A of the opening 6 of the electrostatic adsorption electrode 4 The angle θ between the extending first vector AB and the second vector AC formed by projecting the first vector AB along the thickness direction of the insulating substrate 2 onto the plane on which the electrostatic attraction electrode 4 is arranged is It is set at 45° or less. Point C is a projection point obtained by projecting the lower end portion B of the projection 5 onto the plane on which the electrostatic attraction electrode 4 is provided in the thickness direction of the insulating substrate 2 .

Next, the electrostatic chuck 1 will be described using an equivalent circuit as well.

As shown in FIG. 4 , the electrostatic chuck 1 schematically shown on the left side of the drawing is supplied with power from a power source 12 via lead wires 13 to the electrostatic attraction electrodes 4 embedded in the insulating substrate 2 . A wafer 11 is placed on the convex portion 5 of the insulating substrate 2 as an object to be adsorbed. Thus, the electrostatic chuck 1 has a configuration like a parallel plate capacitor.

The attraction force of the electrostatic chuck 1 is composed of the Johnsen-Rahbek force f(j) generated at the interface between the projections 5 of the electrostatic chuck 1 and the wafer 11 and the Coulomb force generated between the electrostatic attraction electrode 4 and the wafer 11. f(c), and can be expressed as attraction force=f(j)+f(c).

The Johnsen-Rahbek force f(j) is abruptly generated by the resistance R1 of the contact portion between the convex portion 5 and the wafer 11 when a voltage is applied to the convex portion 5 and the wafer 11, which are objects in contact with each other. It is a force due to a phenomenon in which an electric charge is accumulated between contact surfaces due to a voltage drop, and an attractive force is generated between objects.

The Coulomb force f(c) is a force acting on the electrostatic attraction electrode 4 and the wafer 11 between charged objects. The magnitude of the Coulomb force f(c) is proportional to the amount of each charge and inversely proportional to the square of the distance between the electrostatic attraction electrode 4 and the wafer 11 .

In FIG. 4, R1 is the electric resistance of the contact portion between the projection 5 and the wafer 11 relating to the Johnsen-Rahbek force. C1 is the capacitance of the gap δ portion between the convex portion 5 and the wafer 11 relating to the Johnsen-Rahbek force. V1 is the potential difference at the gap δ portion between the projection 5 and the wafer 11 relating to the Johnsen-Rahbek force.
Also, R2 is the electrical resistance between the electrostatic attraction electrode 4 and the wafer 11 with respect to the Coulomb force, C2 is the capacitance of the insulator 7 immediately above the electrostatic attraction electrode 4 with respect to the Coulomb force, and V2 is the potential difference between the electrostatic attraction electrode 4 and the contact portion of the projection 5 with the wafer 11 with respect to the Johnsen-Rahbek force. The overall voltage V0 can be expressed as V0=V1+V2.

When a voltage V0 is applied to the electrostatic chuck 1, a Johnsen-Rahbek force f(j) corresponding to the magnitude of the potential difference V1 and a Coulomb force f(c) corresponding to the magnitude of the potential difference V0 are generated.

Here, the Johnsen-Rahbek effect is to polarize the contact interface between the wafer 11 and the projections 5 of the electrostatic chuck 1 by a minute current flowing between the electrostatic attraction electrode 4 and the wafer 11. Since the electrode 4 is separated from the region S1 overlapping the protrusion 5 in the thickness direction of the insulating substrate 2 and has a large electric resistance R2, the electric current flowing between the electrostatic chuck 1 and the wafer 11 is suppressed, and the Johnsen-Rahbek effect is reduced. be done.

On the other hand, between the electrostatic adsorption electrode 4 and the wafer 11, the area other than the protrusions 5 in the thickness direction of the insulating substrate 2 corresponds to the thickness T of the dielectric 7 which is an insulating layer and the height H of the protrusions 5. Since the electrostatic attraction electrode 4 and the wafer 11 are opposed to each other with a space therebetween, a parallel plate capacitor is formed between the electrostatic attraction electrode 4 and the wafer 11. Coulomb force is generated by adding a potential difference V0 to the combined capacitance C0 of the capacitance of the space corresponding to the height H of the projection 5, and the wafer 11 is attracted to the electrostatic chuck 1. FIG.

At this time, a small amount of current flows to the wafer 11 through the protrusions 5, but almost no current flows in most regions other than the protrusions 5 due to the dielectric 7 and the space above it. Therefore, the Johnsen-Rahbek effect is minimized and the detachability of the wafer 11 can be improved. Thus, in the present invention, it is possible to reduce the residual attraction force after the attraction power supply is turned off.

As shown in FIGS. 2 to 4, the electrostatic chucking electrode 4 is separated from the region S1 overlapping the convex portion 5 in the thickness direction of the insulating substrate 2, and is separated from the end of the electrostatic chucking electrode 4 closest to the convex portion 5. The distance to the projection 5 closest to the end of the electrostatic attraction electrode 4 is increased. Compared to the distance from the electrostatic adsorption electrode 4 to the protrusion 5 closest to the electrostatic adsorption electrode 4 when the electrostatic adsorption electrode 4 is arranged immediately below the protrusion 5, the electrostatic adsorption closest to the protrusion 5 is Since the distance from the edge of the electrode 4 to the projection 5 closest to the edge of the electrostatic attraction electrode 4 increases, the distance from the edge of the electrostatic attraction electrode 4 on the insulating substrate (dielectric) 2 of the electrostatic chuck 1 increases. The electric resistance R2 up to the top surface of the projection 5 is increased.

Due to the electrical resistance R2 in the insulating substrate 2 of the electrostatic chuck 1, the current density (electric line of force) flowing from the electrostatic attraction electrode 4 to the wafer 11 via the projections 5 is reduced. Although the electrical resistance R1 at the contact interface between the projections 5 and the wafer 11 does not change, the electrical resistance R2 is large, so the current density (electric line of force) flowing through the projections 5 to the wafer 11 is reduced. and the wafer 11, the potential difference V1 at the contact interface becomes smaller. Since the potential difference V1 decreases while the capacitance C1 formed at the contact interface between the convex portion 5 and the wafer 11 remains unchanged, the amount of electricity at the contact interface decreases. This reduces the amount of electricity that remains after the power supply for attraction is turned off, so that the remaining attraction force due to the Johnsen-Rahbek effect is reduced, and the detachment time of the wafer 11 from the electrostatic chuck 1 can be shortened.

Next, a detailed configuration for minimizing the Johnsen-Rahbek effect and improving the detachability of the wafer 11 will be described. As an example, a plurality of types of electrostatic chucks 1 were produced as follows and evaluated by the following methods.

[Configuration of Electrostatic Chuck 1]
The outer diameter of the electrostatic chuck 1 is φ298 mm. On the surface 3 of the electrostatic chuck 1, a columnar protrusion 5 having a diameter of φd/m and a height H of 10 μm is formed. The protrusions 5 are arranged on the entire surface 3 of the insulating substrate 2 so as to be continuous with the vertexes of equilateral triangles having a pitch of P/m on one side.

The electrostatic attraction electrode 4 is of a bipolar type (half-moon shape), and is spaced apart so as not to overlap the protrusions 5 formed on the surface 3 and the insulating substrate 2 in the thickness direction, forming a circular space (opening 6) of φD/m. to form

[Production method]
A disk-shaped insulating layer is made of a ceramic sintered body. A molybdenum electrostatic adsorption electrode 4 is embedded in aluminum nitride (AlN) and hot-press fired (1800° C., 10 MP, 8 hours firing). Note that the thickness of the electrostatic chuck 1 is 15 mm.

A plurality of electrostatic chucks 1 are manufactured in which the dielectric 7 of the insulating substrate 2 has a thickness T of 0.3 to 3 mm. The electrostatic adsorption electrode 4 is produced by forming an opening 6 of φDm at a predetermined position in a molybdenum foil (diameter 290 mm, thickness 0.1 mm). The ceramic sintered body after sintering is processed to adjust the thickness T of the dielectric 7 which is an insulating layer and to process the protrusions 5 on the surface 3 .

Note that the manufacturing method is not limited to the above method, and for example, the dielectric 7 to be the insulating layer may be manufactured by thermal spraying. In this case, an alumina substrate (φ298 mm, thickness 15 mm) is plasma-sprayed with tungsten and patterned into a predetermined shape by sandblasting to form the electrostatic attraction electrode 4 . The electrostatic attraction electrode 4 is made of tungsten and has a thickness of 30 μm. Granular powder of alumina added with 25 wt % TiO ₂ is plasma-sprayed thereon as dielectric 7 . After forming the dielectric 7 as an insulating layer to a thickness of 500 μm, it is processed to a predetermined thickness.

As another manufacturing method, a film of titanium and chromium is formed on an alumina substrate (290 mm in diameter and 15 mm in thickness) by PVD, and patterned into a predetermined shape by etching to form the electrostatic attraction electrode 4 . The thickness of the electrostatic attraction electrode 4 is set to 5 μm, and a sintered compact made by adding 3 wt % TiO ₂ to alumina as the dielectric 7 is sputtered thereon as a target. At this time, after forming the dielectric 7 as an insulating layer to a thickness of 60 μm, it is processed to a predetermined thickness.

[Evaluation method]
The electrostatic chuck 1 thus produced was subjected to measurement of residual adsorption force in a vacuum apparatus. The test condition is that the wafer 11 as an attraction object is a silicon wafer (having an insulating film of 500 nm formed on the attraction surface side), and is placed on the electrostatic chuck 1 . The applied voltage was ±1000 V, the application time was 60 seconds, and the wafer was released from the electrostatic chuck 1 5 seconds after the end of the voltage application. When the load was 10 N or less, the wafer 11 jumped up during release, and was judged to be good "O".

The table below shows the above evaluation results.

Referring to Table 1, in Examples 1 to 12, the (insulating layer) thickness T of the dielectric 7 is 2 mm or less and the angle θ between the first vector AB and the second vector AC is 45° or less. In this case, the load at the time of detachment of the wafer 11 was 10 N or less, and the residual attracting force was even smaller than in Comparative Examples 1 to 8, indicating that the detachability was good (good).
The combined capacitance C0 shown in Table 1 indicates a value obtained by converting the capacitance of the parallel plate capacitor formed between the electrostatic attraction electrode 4 and the wafer 11 into capacitance per square meter. The larger the combined capacitance C0, the larger the attracting force, which is preferable for the function of the electrostatic chuck. For good adsorption, the combined capacity C0 is preferably 1×10 ⁻⁸ F or more, more preferably 1×10 ⁻⁷ F or more.

The above results show that when the angle θ formed by the first vector AB and the second vector AC becomes larger than 45°, the residual attracting force increases, but the current density between the electrostatic attracting electrode 4 and the wafer increases. It is presumed that this is because the Johnsen-Rahbek effect occurs at the contact surface of the convex portion 5 .

In Comparative Example 9, the angle θ between the first vector AB and the second vector AC is 45° or less, but the thickness T of the dielectric 7 (insulating layer) is greater than 2 mm, and the static electricity of the insulating layer itself is low. The electrostatic capacity is small, and as a result, the combined capacity C0 is as small as less than 1×10 ⁻⁸ F, so that the adsorption force (Coulomb force) itself becomes small, making it unsuitable for the function of an electrostatic chuck.

Next, the effects of Examples and Comparative Examples will be described.

FIG. 5A is a diagram showing the action of one example of Examples 1 to 12. Since the angle θ between the first vector AB and the second vector AC is 45° or less, the electrostatic attraction electrode 4 is insulated. It is separated from the region S<b>1 overlapping the convex portion 5 in the thickness direction of the substrate 2 .

Therefore, the distance from the end of the electrostatic attraction electrode 4 on the side of the opening 6 to the contact portion between the convex portion 5 and the wafer 11 is large, and the resistance is large. ) becomes smaller, and the remaining adsorption force due to the Johnsen-Rahbek effect can be made smaller.

FIG. 5B is a diagram showing an example of the action of Comparative Examples 1 to 7. Although the electrostatic attraction electrode 4 is separated from the region S1 overlapping the convex portion 5, the first vector AB and the second vector AC are separated from each other. is greater than 45°.

Therefore, compared to the case where the angle θ formed by the first vector AB and the second vector AC is 45° or less (Examples 1 to 12), from the end of the electrostatic attraction electrode 4 on the opening 6 side, The distance to the contact portion between the convex portion 5 and the wafer 11 is small, and the resistance is small. Therefore, compared to Examples 1 to 12, the current density (lines of electric force) in the convex portion 5 is increased, and the remaining attractive force due to the Johnsen-Rahbek effect is increased.

FIG. 5C is a diagram showing an example of the action of Comparative Example 8, in which the electrostatic chucking electrode 4 has no opening and is also arranged in the region S1 where the electrostatic chucking electrode 4 overlaps the convex portion 5. FIG.

For this reason, the current density (lines of electric force) in the convex portion 5 increases compared to the case where there is no electrostatic adsorption electrode 4 in the region S1 overlapping the convex portion 5 (the region immediately below the convex portion 5). The residual adsorption force due to the Rabeck effect increases.

In addition, in the embodiment, the convex portion 5 has a columnar shape, but it is not limited to this, and the convex portion 5 may have a prismatic shape. Further, in the embodiment, the shape of the opening 6 of the electrostatic attraction electrode 4 is circular, but it is not limited to this. The electrostatic adsorption electrode 4 is separated from the region S1 overlapping the convex portion 5 in the thickness direction of the insulating substrate 2, the distance T is 2×10 ⁻³ (m) or less, and the first vector AB and the second vector AC If the angle .theta.

REFERENCE SIGNS LIST 1 : electrostatic chuck 2 : insulating substrate 3 : surface 4 : electrostatic attraction electrode 5 : convex portion 11 : wafer S1 : area overlapping with convex portion H : height of convex portion T : distance in thickness direction of dielectric θ : The angle between the first vector and the second vector

Claims (3)

an insulating substrate having insulation;
an electrostatic adsorption electrode embedded in the insulating substrate along the surface of the insulating substrate;
a plurality of protrusions provided on the surface;
An electrostatic chuck comprising:
the electrostatic adsorption electrode is separated from the region overlapping the convex portion in the thickness direction of the insulating substrate,
a distance T in the thickness direction of the insulating substrate from the surface of the insulating substrate to the electrostatic attraction electrode is 2×10 −3 (m) or less;
a first vector extending from the end of the electrostatic adsorption electrode closest to the protrusion toward the lower end of the protrusion closest to the end of the electrostatic adsorption electrode; An electrostatic chuck, wherein an angle θ between the first vector and a second vector formed by projecting the first vector onto a plane on which the electrostatic attraction electrode is arranged is 10.6° to 45°. . The electrostatic chuck of claim 1, comprising:
The electrostatic chuck, wherein the height H of the convex portion is 3 to 15 (μm). The electrostatic chuck according to claim 1 or 2,
The value obtained by converting the capacitance of the parallel plate capacitor formed between the electrostatic attraction electrode and the attraction placed on the convex portion to the capacitance per square meter is 1×10 −8 (F). ) above.

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