JP2009117686A - Electrostatic chuck - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrostatic chuck which can provide a uniform film thickness to an insulating layer with an improved attracting force. <P>SOLUTION: An internal electrode 2 is provided therein with a plurality of slits 21a, 21b, etc., extended in the form of a comb in concentric directions of the internal electrode and with slits 23a, 23b, etc. extended linearly in its radius directions, and the slits 21a, 21b, etc., extended in the concentric directions are continuous at their one ends to the slits 23a, 23b, etc., extended in its radius directions. With such an electrode structure, upon sintering, both of expansion of the electrode in its circumferential direction and expansion thereof in the radius direction can be absorbed or reduced and thus an insulating layer can have a uniform film thickness. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrostatic chuck, for example, an electrostatic chuck used for attracting and holding a wafer in a semiconductor manufacturing apparatus.

In manufacturing and inspection processes of semiconductor substrates such as silicon wafers and other various substrates, it is necessary to hold the substrates during various processes, measurements, and conveyances. For example, an etching process for performing microfabrication on a semiconductor wafer in a semiconductor manufacturing process, a film forming process for forming a thin film, an exposure processing process using a photoresist film, etc. are performed under vacuum, so that the wafer is held. An electrostatic chuck is used. For example, an electrostatic chuck uses a top surface of a dielectric layer made of a low thermal expansion ceramic as an adsorption surface of a wafer, and a voltage is applied between the electrostatic adsorption electrode (internal electrode) embedded in the dielectric layer and the wafer. The wafer was held on the suction surface by the obtained electrostatic suction force. (See, for example, Patent Document 1).
JP 2006-40993 A

  In the conventional electrostatic chuck described above, in order to improve the adhesion between the base material and the internal electrode, for example, a mesh electrode provided with an opening formed by overlapping metal meshes, or an opening formed by punching a plate-shaped electrode material A punching metal electrode provided with is used as an internal electrode. When a substrate such as a ceramic with such electrodes embedded is sintered, in the case of a mesh electrode, deformation of the electrode itself is difficult to occur due to its elasticity, but local heat generation due to poor contact between the metal meshes occurs. Product temperature rises and volume resistivity decreases. As a result, there is a risk that the leakage current increases and the device formed on the wafer is destroyed.

  Therefore, there is a method to sinter the base material using a punching metal electrode in order to improve local heat generation. However, the punching metal electrode has a flat plate shape, so it has poor stretchability, and deformation of the electrode such as warpage occurs. There was a problem that it was easy to do. As a result of such deformation of the electrode, peeling occurs and the film thickness of the insulating layer becomes uneven, resulting in variations in characteristics such as adsorption force. Therefore, when such an electrostatic chuck is used in a semiconductor manufacturing process, there is a problem in that the etching rate and the film formation rate also vary.

  The present invention has been made in view of such circumstances, and provides an electrostatic chuck having a flat attracting surface by preventing peeling due to electrode deformation during sintering and eliminating variations in the thickness of the insulating layer. For the purpose.

In order to achieve the above object, an electrostatic chuck according to the present invention is an electrostatic chuck in which an internal electrode having a predetermined shape is disposed in an insulating substrate, and the internal electrode is concentric and spaced apart by a predetermined interval. And a second slit group extending from the center toward the outer edge, and one end of the first slit group is connected to the second slit group. It is characterized by that.
For example, the slit width of the first slit group and the second slit group is 20 μm to 1000 μm, and the electrode width of the internal electrode is 1 mm to 5 mm. Further, for example, the first slit group and the second slit group are arranged in a predetermined outer peripheral region excluding the central region of the internal electrode.
Further, for example, the internal electrode has a substantially circular planar shape, and the first slit group is arranged concentrically while entering a comb shape in opposite directions. Also, for example, the internal electrode has a polygonal planar shape, and the first slit group is arranged coaxially in parallel with the sides of the polygon while entering the comb shape in opposite directions. Features.

  ADVANTAGE OF THE INVENTION According to this invention, the electrostatic chuck which suppressed the deformation | transformation of an internal electrode, prevented peeling and improved the attraction | suction force with respect to a to-be-adsorbed object can be provided.

  The best mode for carrying out the present invention will be described below in detail with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing the configuration of an electrostatic chuck (substrate holder) according to an embodiment of the present invention. As shown in FIG. 1, an electrostatic chuck 10 according to an embodiment of the present invention is embedded in a plate-like body (ceramic sintered body) 1 composed of a dielectric material to be described later and the plate-like body 1. A bipolar internal electrode 2 composed of two electrodes 2a and 2b spaced apart by a predetermined distance, and a dielectric layer formed on the upper surface of the plate-like body 1 so as to cover these electrodes 2a and 2b ( The surface of the dielectric layer 4 is an adsorption surface 5 for adsorbing and holding an object to be adsorbed.

  In the electrostatic chuck 10 shown in FIG. 1, a DC voltage is applied to the electrodes 2a and 2b by a power source (not shown), and an electrostatic force generated thereby causes Wafer W is adsorbed. For convenience, the portion from the internal electrode 2 to the adsorption surface 5 is referred to as a dielectric layer 4. Here, illustration of a lift pin for detaching the wafer W from the electrostatic chuck 10 and a through-hole capable of moving the lift pin in the vertical direction is omitted.

  The plate-like body 1 and the dielectric layer 4 of the electrostatic chuck 10 according to the embodiment of the present invention are ceramic sintered bodies made of alumina, aluminum nitride, magnesia spinel, or the like, for example. In the embodiment of the present invention, a plate-like body is produced by hot press firing or the like, for example, in order to form the above-mentioned material in a mold having a predetermined shape and to make it dense. The internal electrode 2 is an electrode made of a metal material such as molybdenum or tungsten, for example, and is formed in a state of being embedded in the plate-like body 1 as described above. The internal electrode 2 and the plate-like body 1 are fired simultaneously, and the upper and lower surfaces of the obtained sintered body are ground so that the plate-like body 1 and the dielectric layer 4 have a predetermined thickness. The electrostatic chuck 10 is produced.

  Next, the internal electrodes characteristic of the electrostatic chuck according to the embodiment of the present invention will be described in detail. FIG. 2 is a plan view showing an example of an electrode pattern of the electrostatic chuck according to the embodiment of the present invention. The internal electrode 2 shown in FIG. 2 is an example of a round electrode in a bipolar electrostatic chuck, and includes electrodes 2a and 2b that bisect the internal electrode 2 in a semicircular shape. Each of the electrodes 2a and 2b is provided with a plurality of slits 21a and 21b and the like which are inserted in a comb shape (comb shape) while maintaining a predetermined interval in the concentric direction, and one end portion thereof is It has a structure connected to slits 23a, 23b and the like extending linearly in the radial direction. As a result, the individual electrode portions 25a, 25b, etc. of the electrodes 2a, 2b also have a structure that enters the comb shape by the interposition of these slits 21a, 21b.

  The electrodes 2a and 2b constituting the bipolar internal electrode 2 are arranged apart from each other by a predetermined interval s as shown in FIG. By adopting such an arrangement structure, a predetermined electrical dielectric strength is obtained between the electrodes 2a and 2b. In the example shown in FIG. 2, the electrode portions 25a, 25b, etc. and the slits 21a, 21b, etc. are surrounded by a plurality of slits 23a, 23b, etc. extending in the radial direction. It can be seen that it is divided into two blocks. Therefore, although not shown, a power supply terminal to the internal electrode 2 may be provided in units of the electrodes 2a and 2b, or may be provided for each of these blocks. Note that the number of blocks is not limited to four.

  The width of the slits 21a, 21b, etc. of the internal electrode 2 is, for example, 20 μm to 1000 μm, the width of the electrode portions 25a, 25b, etc. is, for example, 1 mm to 5 mm, and the thickness is, for example, 50 μm to 100 μm. . These slits 21a, 21b and the like are formed using, for example, electric discharge machining, laser machining, or the like. Here, if the width of the slit is, for example, less than 20 μm, a problem in processing the electrode may occur, and a portion that does not become a slit may occur. Further, when the slit width exceeds 1000 μm, there arises a problem that the adsorptive power is reduced as much as the total area of the electrode is reduced.

  In the electrostatic chuck according to the embodiment of the present invention, the base material and the electrode are in close contact after sintering by filling the slit material with the base material in the manufacturing process. Therefore, if the slit width is less than 20 μm, the degree of adhesion may be reduced.

  On the other hand, if the width of the electrode exceeds 5 mm, for example, peeling from the base material of the plate-like body is likely to occur during thermal expansion in the firing step, and if the electrode width is less than 1 mm, the electrode is handled when handling the electrode alone. May be deformed. In addition, when the diameter of the internal electrode 2 is less than 100 mm, for example, there is a problem that the effect of uniforming the thickness of the insulating layer cannot be expected.

  In the electrostatic chuck according to the embodiment of the present invention, the slits 21a, 21b and the like are disposed only in the outer peripheral portion of the electrode 2 as shown in FIG. The structure is not provided at the center of the electrode 2. This is because, as will be described later, in the central region of the insulating layer, there is almost no influence of electrode deformation during sintering, and the effect of forming a slit in the central portion cannot be confirmed. Further, when the slits are arranged in a predetermined region (radial direction of 50 mm or more) on the outer peripheral portion of the electrode 2 in this way, there is an advantage that it is easy to take out a power supply terminal for supplying power to the electrode. On the other hand, when the slits 21a, 21b, etc. are disposed only in the region of the electrode outer periphery, for example, in the radial direction of 50 mm or less, it has been found that the expansion of the electrode during the sintering cannot be absorbed and the effect of the slit cannot be expected.

  As described above, in the electrostatic chuck according to the present embodiment, a plurality of slits entering the comb shape and the slits extending linearly in the radial direction are arranged in the concentric direction, and these concentric direction slits are arranged. By forming an electrode structure in which one end of the electrode is connected to a slit in the radial direction, a structure having excellent stretchability can be realized as the whole electrode. During sintering, expansion in the circumferential direction indicated by arrow A in FIG. It can absorb and relieve both the radial expansion indicated by. As a result, the deformation of the internal electrode 2 is reduced during sintering, and the peeling of the electrode from the base material can be prevented, and the thickness of the insulating layer on the electrode can be made uniform and the film thickness can be made uniform. There is an excellent effect that the attracting surface becomes flat and the electrostatic attracting force is improved.

  Further, as illustrated in FIG. 2, each of the bipolar electrodes 2a and 2b is a single electrode, and the electrodes facing each other across the slit have the same potential. Therefore, even if the width of the slit is narrow, The internal discharge (discharge between the electrodes) that has been a problem with the mesh electrode does not occur.

  In addition, since the attractive force in the electrostatic chuck is proportional to the area of the electrode, the electrode area can be increased by arranging a narrow slit in the electrode in a comb shape. Can be improved compared to punching metal electrodes and mesh electrodes. In addition, as an attraction force of the electrostatic chuck, there is one using a Coulomb force or a Johnsen-Rahbek force, but the electrostatic chuck according to this embodiment can be applied to any of them. Electrostatic chucks that are attracted by Coulomb force generally have a high dielectric resistance, and it is necessary to apply a higher voltage than electrostatic chucks that use the Johnsen-Rahbek force to obtain the required attracting force. There is.

Next, the electrostatic chuck according to the present invention will be described in more detail with reference to examples and comparative examples. Here, an electrostatic chuck was manufactured by the following manufacturing method. That is, after a raw material (aluminum nitride) is filled in a predetermined mold, uniaxial pressing is performed at 100 kg / cm ² , and a slit mold that has been prepared (preliminarily molded) in advance at a predetermined position of the obtained molded product The electrode was installed. Here, molybdenum was employed as the electrode material.

Then, the raw material was filled again so as to cover the installed electrode, the electrode was embedded, and hot press firing was performed at 1900 ° C. for 2 hours while performing uniaxial pressing at 100 kg / cm ² . Then, the upper and lower surfaces were ground until the obtained sintered body had a predetermined thickness, and a test electrostatic chuck was formed. In this example, grinding was performed until the thickness of the insulating layer (dielectric layer) of the obtained sintered body was about 1 mm.

  Tables 1 to 3 below show the results of comparing the film thickness of the insulating layer between the conventional product and the product of the present invention. Specifically, the product No. 1 in which the electrode width of the slit-type electrode of the electrostatic chuck according to the present invention was changed. 1-No. 6 and the conventional product using a punching metal electrode, the thickness of the insulating layer at six locations was measured with an eddy current film thickness meter for each of the outer circumference, middle and inner circumference of the insulating layer. Table 1 shows the measurement results of the outer peripheral film thickness, Table 2 shows the measurement of the intermediate film thickness, and Table 3 shows the measurement results of the inner peripheral film thickness. In addition, the slit width of the electrode used in each implementation product is 1 mm.

  Among the products shown in Table 1 and Table 2 above, those marked with * and having electrode widths of 10 mm and 8 mm (No. 1 and No. 2) have the maximum film thickness at the outer and intermediate measurement points. Since the difference between the value and the minimum value exceeds 200 μm, it was excluded from the scope of the present invention as not being a preferable example. In Table 3, when the measurement location is the inner peripheral film thickness and the electrode width is 10 mm and 8 mm (No. 1 and No. 2 marked with *), the difference between the maximum value and the minimum value is other. It was excluded from the scope of the present invention. As shown in Table 3, even in the products with electrode widths of 10 mm and 8 mm, the difference between the maximum value and the minimum value of the inner peripheral film thickness is not significantly different from other products. In the product of the present invention, it can be seen that the distortion is small in the inner circumference of the insulating layer at any electrode width. For this reason, in the electrostatic chuck according to the embodiment of the present invention, as described above, a slit is provided only in a predetermined region of the outer peripheral portion of the electrode, and a slit is not provided in the central portion of the electrode with small distortion. It was.

  Table 4 shows a comparison result of characteristics (temperature distribution and adsorption force) between the conventional product and the practical product. Here, regarding the temperature distribution, the electrostatic chuck is heated to 400 ° C. in a vacuum, and when it reaches a steady state, a voltage of 1000 V is applied between predetermined electrode terminals to adsorb the wafer, The temperature distribution was measured with an infrared camera (thermograph). Similarly, with respect to the suction force, when the electrostatic chuck is heated to 400 ° C. in a vacuum and becomes a steady state, a voltage of 1000 V is applied between predetermined electrode terminals to suck the wafer, and from the back surface of the wafer. Helium (He) gas was pressurized and the pressure when the wafer was removed was measured.

  As shown in Table 4, when comparing the attractive force of the conventional product (electrostatic chuck with punching metal electrode) and the actual product (electrostatic chuck with slit-type electrode), In the case where the electrode width is 1 mm to 5 mm, and the electrode width is 8 mm or 10 mm (marked with an asterisk), some peeling is observed between the insulating layer and the electrode. It was equivalent or less.

  The present invention is not limited to the above-described embodiment, and various modifications can be made. The planar shape of the slit-type electrode is not limited to the circular shape described above. For example, as shown in FIG. 3, a rectangular internal electrode 3 composed of bipolar electrodes 3 a and 3 b may be used. It may be a polygon. When the planar shape of the electrode is a quadrangle or polygon, the shape of the slit itself is also a square (straight) arranged coaxially in parallel with the sides of the square or polygon. Also in the example shown in FIG. 3, as in the case where the electrode shape is circular, the slit is provided only in the outer peripheral portion of the electrode 3, for example, in a region of d = 50 mm or more, and is not provided in the central portion of the electrode 3. And

  In the above-described example, the bipolar electrode that bisects the internal electrode in a semicircular shape is taken as an example of the electrode configuration, but the number of divided electrodes is not limited to this. Furthermore, the electrode configuration is not limited to the bipolar electrode, and the electrostatic chuck according to the present embodiment can be applied to a single electrode.

It is sectional drawing which shows typically schematic structure of the electrostatic chuck which concerns on the example of embodiment of this invention. It is a top view which shows an example of the electrode pattern of the electrostatic chuck which concerns on the embodiment of this invention. It is a top view which shows the other example of the electrode pattern of the electrostatic chuck which concerns on the embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Plate-like body 2,3 Internal electrode 2a, 2b, 3a, 3b Electrode 4 Dielectric layer (insulating layer)
5 Suction surface 10 Electrostatic chuck 21 a, 21 b, 23 a, 23 b,... Slit 25 a, 25 b,.

Claims (5)

  An electrostatic chuck in which an internal electrode having a predetermined shape is disposed in an insulating base material, wherein the internal electrode is concentric and arranged at a predetermined interval, and an outer edge portion from a center portion And an end of the first slit group connected to the second slit group. 2. An electrostatic chuck, comprising: a second slit group extending toward the first slit group;   2. The electrostatic chuck according to claim 1, wherein a slit width of each of the first slit group and the second slit group is 20 μm to 1000 μm, and an electrode width of the internal electrode is 1 mm to 5 mm.   The electrostatic chuck according to claim 1, wherein the first slit group and the second slit group are arranged in a predetermined outer peripheral area excluding a central area of the internal electrode.   4. The electrostatic chuck according to claim 3, wherein the internal electrode has a substantially circular planar shape, and the first slit group is arranged concentrically while entering a comb shape in opposite directions. 5.   The planar shape of the internal electrode is polygonal, and the first slit group is arranged coaxially in parallel with the sides of the polygon while entering a comb shape in opposite directions. Item 4. The electrostatic chuck according to Item 3.

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