JP2000277596A - Electrostatic chuck - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reinforce a chuck force by a method wherein a cavity part intervenes between chuck electrode layers of different poles disposed adjacently in the direction of an insulating substrate face. SOLUTION: An insulating substrate 2 constituting an electrostatic chuck 1 is composed of an aluminum nitride sintered compact of a dielectric. Since the insulating substrate 2 chucks simultaneously a plurality of silicon wafers W1 as matters to be attracted, it is formed so as to have an area several times that of the silicon wafer W1. As a surface roughness of a chuck face S1 of the insulating substrate 2 decreases, a Johnson-Rahbeck power increases. The insulating substrate 2 has a multilayer structure, and is formed internally with chuck electrode layers 3, 4, and a heater electrode layer. The chuck electrode layer 3 of a positive pole and the chuck electrode layer 4 of a negative pole are together positioned in a layer close to the chuck face S 1. The respective chuck electrode layers 3, 4 are connected as interlayers to a non-chuck face S2, respectively. A plus side of a chucking DC power source 5 is connected correspondingly to the chuck electrode layer 3 of a positive pole via a wiring. A shielding material layer 6 intervenes between the different-pole chuck electrode layers 3 and 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic chuck.

[0002]

2. Description of the Related Art In a semiconductor manufacturing process, processes such as etching and sputtering are performed while a semiconductor wafer made of silicon or the like is fixed. In such a case, a fixing means called a chuck device is usually used. In particular, in recent years, a ceramic electrostatic chuck that attracts a semiconductor wafer by using the force of static electricity has been proposed.

In this type of conventional electrostatic chuck,
Positive and negative chuck electrode layers are formed inside the insulating base material. Both chuck electrode layers have a comb shape and are arranged alternately. When a direct current is applied to both chuck electrode layers, a suitable electric field is formed in the outer region of the chuck surface, and as a result, the semiconductor wafer is electrostatically attracted to the same surface.

[0004]

In the manufacture of semiconductors, for example, there are cases where it is desired to chuck a large-diameter wafer, or when a large number of wafers are to be chucked. In these cases, it is necessary to securely fix the wafer with a strong chucking force and to prevent the occurrence of displacement, dropping, and the like.

However, if the voltage applied to the chuck electrode layer is increased to increase the chucking force, dielectric breakdown occurs at a place where the adjacent different-sized chuck electrodes are insulated from each other. There is a possibility that current leaks in between. Therefore, conventionally, the applied voltage can be set only within a range not exceeding the dielectric strength of the ceramic used for the insulating base material. That is, it was actually difficult to obtain a sufficient chucking force by a method of increasing the applied voltage.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an electrostatic chuck having a strong chucking force.

[0007]

In order to solve the above-mentioned problems, according to the first aspect of the present invention, an object to be attracted is electrostatically charged on the chuck surface of the insulating base material by energizing the chuck electrode layer. The gist of the electrostatic chuck to be attracted is that a cavity is interposed between chuck electrode layers of different polarities arranged adjacent to each other in the substrate surface direction.

According to a second aspect of the present invention, in the first aspect, the hollow portion is a shielding groove that opens on the chuck surface side. According to a third aspect of the present invention, in the second aspect, the bottom surface of the shielding groove is located closer to the inner layer than the lower surface of the chuck electrode layer.

The "action" of the present invention will be described below. According to the first aspect of the present invention, the chuck electrode layers having different polarities arranged adjacent to each other are shielded by the air layer in the hollow portion. The insulation at the location is less likely to be destroyed. As a result, there is no fear that a current leaks between the two chuck electrodes. As a result, an electric field is less likely to be formed in the insulating base material, and conversely, an electric field is more likely to be formed in a region outside the chuck surface. Therefore, a strong chucking force can be obtained by increasing the applied voltage.

According to the second aspect of the present invention, since a shielding groove which is opened on the chuck surface side can be formed relatively easily, it becomes difficult to manufacture the electrostatic chuck and to increase the cost. Will not be accompanied.

According to the third aspect of the present invention, since the bottom surface of the shielding groove is located closer to the inner layer than the lower surface of the chuck electrode layer, a more reliable shielding effect can be obtained. Therefore, it is possible to withstand a larger applied voltage and to realize a stronger chucking force.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a bipolar type electrostatic chuck 1 according to an embodiment of the present invention will be described in detail with reference to FIGS.

FIGS. 1 and 2 schematically show an electrostatic chuck 1 according to this embodiment. The insulating base material 2 constituting the electrostatic chuck 1 is made of a sintered body of aluminum nitride which is a suitable dielectric. Here, a disk-shaped insulating substrate having a thickness of about several mm is used. The insulating substrate 2 of the present embodiment is formed to have an area several times larger than that of the silicon wafer W1 so that a plurality of silicon wafers W1 to be adsorbed can be simultaneously chucked. The surface roughness Ra of the chuck surface S1 (the upper surface in FIG. 1) of the insulating base material 2 is 0.07 .mu.m or less, more preferably 0.07 .mu.m or less.
It is good to set it to 5 μm or less, most preferably to 0.03 μm or less. The reason is that the Johnson-Rahbek force increases as the flatness of the chuck surface S1 increases, that is, as the surface roughness Ra decreases.

The insulating substrate 2 of the present embodiment has a multilayer structure, in which chuck electrode layers 3 and 4 and a heater electrode layer (not shown) are formed. The chuck electrode layer 3 of the positive electrode and the chuck electrode layer 4 of the negative electrode are both located near the chuck surface S1. The depth from the chuck surface S1 to the lower surfaces of the chuck electrode layers 3 and 4 is set to about 0.3 mm. The heater electrode layer is located below the chuck electrode layers 3 and 4. Each of the electrode layers 3 and 4 is formed by printing using a conductive paste P1 such as a tungsten paste. The printing thickness of each of the electrode layers 3 and 4 is set to about several tens of μm.

As shown in FIG. 2, the chuck electrode layer 3 of the positive electrode includes a semicircular portion located on the outer periphery of the insulating base material 2 and a number of straight lines extending from the semicircular portion in parallel and at equal intervals. And a portion 3a. Accordingly, the chuck electrode layer 3 has a comb-like shape as a whole. The negative electrode chuck electrode layer 4 also includes a semicircular arc-shaped portion and a large number of linear portions 4a, and also has a comb-like shape. In the present embodiment, the shape and size of these two chuck electrode layers 3 and 4 are substantially equal.

The two linear portions 3a and 4a are connected to each other in FIG.
Are staggered as shown in FIG. That is, the linear portions 3a and 4a of the chuck electrode layers 3 and 4 having different polarities are
They are arranged adjacent to each other in the substrate surface direction. The distance L1 between the adjacent linear portions 3a and 4a may be set to 5 mm or more, preferably 10 mm or more. The reason is to secure a sufficient insulating region between the linear portions 3a and 4a.

Each of the chuck electrode layers 3 and 4 is interlayer-connected to the non-chuck surface (lower surface in FIG. 1) S2 by separate through holes T1 and T2. The plus side of the DC power supply 5 for chucking is connected to the lower end surface of the through hole T1 corresponding to the chuck electrode layer 3 of the positive electrode via a wiring. On the other hand, the lower side of the through hole T2 corresponding to the negative electrode chuck electrode layer 4 is connected to the minus side of the DC power supply 5 via a wiring.

As shown in FIGS. 1 and 2, the electrostatic chuck 1 has a shielding groove 6 as a cavity. The shielding groove 6 is open on the chuck surface S1 side of the insulating base material 2. The shielding groove 6 in the present embodiment is elongated and continuous, and has a substantially rectangular cross-sectional shape. The shield layer 6 is composed of the linear portions 3 of the chuck electrode layers 3 and 4 having different polarities.
a, 4a. The shield layer 6 has a positional relationship such that it does not overlap with the chuck electrode layers 3 and 4 when the insulating substrate 2 is projected from the substrate thickness direction. Further, the shield layer 6 of the present embodiment has a depth of about 0.4 mm to 0.6 mm, and is formed deeper than the chuck electrode layers 3 and 4. That is, the bottom surface of the shielding groove 6 is located closer to the inner layer than the lower surfaces of the chuck electrode layers 3 and 4.

It is desirable that the clearance between the shielding groove 6 and the chuck electrode layers 3 and 4 is at least 0.1 mm or more, preferably 0.5 mm or more. In view of such circumstances, the separation width L between the linear portions 3a, 4a
In this embodiment where 1 is set to 10 mm, the width of the shielding groove 6 is set to about 1 mm to 8 mm.

Next, an example of a procedure for manufacturing the electrostatic chuck 1 of the present embodiment will be introduced. The green sheet as a material of the insulating base material 2 is produced by forming a slurry containing a ceramic powder as a main component into a sheet by a doctor blade method. At predetermined positions of the obtained green sheet, through-hole forming holes are formed as necessary by drilling or punching.

As the ceramic powder for the green sheet, a powder of aluminum nitride, high-purity alumina, boron nitride, silicon nitride or the like is used. Among them, it is particularly desirable to select aluminum nitride powder. This is because a sintered body made of aluminum nitride is not only excellent in heat resistance, but also excellent in thermal conductivity and plasma resistance, and is therefore extremely convenient as a material for the electrostatic chuck 1.

The green sheet having been drilled has tungsten (W) particles as conductive particles, a dispersion solvent,
The conductive paste P1 containing a dispersant or the like is printed. However, instead of W particles, tungsten monocarbide (WC)
The conductive paste P1 containing particles may be used.

In the subsequent paste printing step, first, the green sheets having undergone the perforating step are set one by one in a printing apparatus, and a metal mask is arranged on the printing surface. In this state, the above-mentioned conductive paste P1 is printed to form through holes. Next, the green sheet on which the through-hole printing has been performed is set on a screen printing machine this time, and a screen mask is arranged on a printing surface. In this state, the above-mentioned conductive paste P1 is pattern-printed to form chuck electrode layers 3, 4 and a heater electrode layer on the surface of the green sheet.

Next, a plurality of green sheets having undergone the paste printing step are positioned and superimposed, and a vacuum press is performed at a predetermined pressure in this state. As a result, the green sheets are integrated, and a green sheet laminate is formed.
Then, the obtained green sheet laminate is dried by heating at a temperature of several tens of degrees C. to one hundred and several tens degrees C. for a predetermined time under normal pressure. The drying step may be performed before performing the laminating step.

The green sheet laminate after the drying step is
Prior to the main sintering step, by performing the following heat treatment step in advance, degreasing and temporary sintering are performed in a non-oxidizing atmosphere.

Thereafter, the green sheet calcined body obtained through the heat treatment step is placed in a crucible, and the periphery thereof is surrounded by a setter if necessary. The crucible in this state is set in a firing furnace, and hot press firing is performed at a temperature of 1700 ° C. or higher for a predetermined time and at a predetermined pressure according to a conventional method. As a result, the aluminum nitride and the conductive paste P1 are co-sintered completely, and an insulating substrate 2 made of aluminum nitride and having the chuck electrode layers 3, 4 and the like is formed.

After that, the outer shape processing and the surfacing processing of the insulating base material 2 are performed by using a grinding machine or the like, and thereby the chuck surface S
The surface roughness Ra of 1 is adjusted within a predetermined range. Next, a shielding groove 6 having a predetermined width and a predetermined depth is formed on the chuck surface S1 of the insulating base material 2 by performing a conventionally known groove processing.
The groove processing may be performed at the same time as the outer shape processing before the surfacing processing. After that, various processes such as coating and brazing of I / O pins are performed according to a conventional method.
A desired electrostatic chuck 1 as shown in FIG. 2 is completed.

When a DC current is applied to the two chuck electrode layers 3 and 4 of the electrostatic chuck 1 manufactured as described above, an electric field is formed in an outer region of the chuck surface S1, and as a result, the silicon wafer W1 An electrostatic force acts between the electrostatic chuck 1 and the electrostatic chuck 1. As a result, the silicon wafer W1 is attracted to the chuck surface S1, and the silicon wafer W1 is fixed. At this time, due to the shielding effect provided by the shielding groove 6, a current leak between the chuck electrode layers 3 and 4 having different polarities is prevented beforehand, and dielectric breakdown at the location is avoided. In FIG. 3, a leakage current between the chuck electrode layers 3 and 4 having different polarities is assumed, and the flow is represented by A1.
Is conceptually shown in FIG. That is, in the present embodiment, since the air layer 7 existing in the shielding groove 6 is in the way between the chuck electrodes 3 and 4 having different polarities, the leak current flows through the insulating base material 2 side. Hateful. Therefore, the leakage current is exclusively generated outside the insulating base material 2, that is, the chuck surface S
1 would have to flow through the outer region. Accordingly, it is considered that an electric field is not easily formed in the insulating base material 2, but an electric field is easily formed in a region outside the chuck surface S <b> 1.

[0029]

EXAMPLES AND COMPARATIVE EXAMPLES [Preparation of Samples] Here, the following nine types of subject samples were prepared in advance.

Samples 1 to 6 of Examples 1 to 6 were made of an insulating substrate 2 made of aluminum nitride having an outer diameter of 190 mm and a thickness of 1.5 mm, and had a chuck surface S1 having a surface roughness Ra of 0 mm. 0.03 μm. For these samples 1 to 6, the shielding groove 6 having the above-described shape was provided at a predetermined position. Then, the porosity of the aluminum nitride sintered body constituting the insulating base material 2 is set to 2% in the sample 1, 3% in the sample 2, 5% in the sample 3, and 10% in the sample 4. 5 for 15
% And 20% for sample 6.

In Samples 7 to 9, which are Comparative Examples 1 to 3,
No shielding groove 6 was provided (see FIG. 4). Then, the porosity of the aluminum nitride sintered body constituting the insulating base material 2 was set to 3% or less for Sample 7, 5% for Sample 8, and 10% for Sample 9.

The green sheet or the conductive paste P
Regarding the composition and the like of 1, samples 1 to 7 were completely the same. [Comparative test and its results] The following comparative tests were performed on these nine types of samples.

That is, the chuck surface S1 of each electrostatic chuck 1
Then, a silicon wafer W1 of 20 mmφ is placed under high temperature conditions (specifically, 600 ° C.) and energization is started at a predetermined applied voltage (specifically, 1000 V) to chuck the silicon wafer W1 in the presence of air. I let it. After a lapse of a predetermined time from the start of chucking, the silicon wafer W
1 was pulled in the vertical direction, and the magnitude (kg / cm ² ) of the force required to peel it was measured. Table 1 shows the results. [Conclusion] As is clear from Table 1, in Examples 1 to 6, although the porosity of the sintered body exceeded 3%, a strong chucking force comparable to Comparative Example 1 could be obtained. . In other words, it can be concluded that dielectric breakdown did not occur even when a large DC voltage was applied to achieve the predetermined chucking force.
On the other hand, in Comparative Examples 2 and 3, the chucking force was significantly reduced as compared to Comparative Example 1, and as a result, as indicated conceptually in FIG. .

[0034]

[Table 1] When the above results are combined, according to the present embodiment, the following effects can be obtained.

(1) In this electrostatic chuck 1, the chuck electrode layers 3, 4 of different polarities arranged adjacent to each other are connected to the shielding grooves 6.
It is shielded by the air layer 7 inside. Therefore, even when the applied voltage is set to a large value, the insulation at the insulating portion between the chuck electrode layers 3 and 4 is hardly broken. As a result, there is no fear of current leaking between the two chuck electrode layers 3 and 4, and as a result, an electric field is less likely to be formed in the insulating base material 2,
Conversely, an electric field is likely to be formed in a region outside the chuck surface S1. Therefore, a strong chucking force can be obtained by increasing the applied voltage.

According to this embodiment, the porosity is 3%.
Since it is not particularly necessary to improve the dielectric strength such as the following, there is an advantage that the applicable range of the ceramic material that can be used is wider than before.

(2) The hollow portion of the electrostatic chuck 1 is a shielding groove 6 opened on the chuck surface side S1. Therefore, with such a groove structure, it is possible to form the groove relatively easily and inexpensively by performing conventionally known groove processing after the firing step as described above. Therefore, there is an advantage that the manufacturing of the electrostatic chuck is not made difficult and the cost is not increased.

(3) In this electrostatic chuck 1, the shielding groove 6
Is located on the inner layer side with respect to the lower surfaces of the chuck electrode layers 3 and 4. Therefore, a more reliable shielding effect can be obtained. Therefore, it is possible to withstand a larger applied voltage and to realize a stronger chucking force.

The embodiment of the present invention may be modified as follows. -Like another example of the electrostatic chuck 11 shown in FIG.
The shielding groove 6 which is a cavity may be formed shallower than that of the embodiment.

Another example of the electrostatic chuck 2 shown in FIG.
1, an elongated shielding space 2 not communicating with the chuck surface S1.
As in the case of 2, a cavity without a groove structure may be formed. In this case, as in the electrostatic chuck 31 of FIG. 7, the elongated shielding space 22 may be made thinner and formed so as to be located on the same layer as the chuck electrode layers 3 and 4.

The shielding groove 6 and the elongated shielding space 22 which are cavities are not limited to the case where they are elongated and continuously formed as in the embodiment and other examples. For example, even if it is formed discontinuously or intermittently, a certain shielding effect can be expected.

The formation of the cavity may be performed not only after the firing step but also before the firing step. Specifically, a predetermined portion of a green sheet in which a hollow portion is to be formed is punched out in advance, and these are stacked, degreased and pre-fired, and then fired as usual.

The cross-sectional shape of the shielding groove 6 as a cavity is not limited to a rectangular shape, but may be, for example, an inverted V-shape or a semicircle. Next, in addition to the technical ideas described in the claims, technical ideas grasped by the above-described embodiments are listed below together with their effects.

(1) The device according to any one of claims 1 to 3, wherein a separation width between the chuck electrode layers having different polarities is at least 10 mm or more, and the cavity and the chuck electrode layers interposed therebetween. The clearance between must be at least 0.5 mm.

(2) In claim 1, the hollow portion is an elongated shielding space not communicating with the chuck surface, and the lower end portion is formed at least on the inner layer side from the position where the chuck electrode layer is located. . Therefore, according to the invention described in the technical idea 2, a more reliable shielding effect can be obtained.

[0046]

As described in detail above, according to the first to third aspects of the present invention, an electrostatic chuck having a strong chucking force can be provided.

According to the second aspect of the present invention, even in the case where the hollow portion is provided, it is possible to avoid the difficulty in manufacturing and the increase in cost. According to the third aspect of the present invention, a more reliable shielding effect can be obtained, so that an electrostatic chuck having a strong chucking force can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an electrostatic chuck according to an embodiment.

FIG. 2 is a sectional view taken along line AA of FIG. 1;

FIG. 3 is an enlarged sectional view of a main part of the electrostatic chuck according to the embodiment.

FIG. 4 is an enlarged sectional view of a main part of an electrostatic chuck of a comparative example.

FIG. 5 is an enlarged sectional view of a main part of another example of an electrostatic chuck.

FIG. 6 is an enlarged sectional view of a main part of another example of an electrostatic chuck.

FIG. 7 is an enlarged sectional view of a main part of another example of an electrostatic chuck.

[Explanation of symbols]

1, 11, 21, 31 ... electrostatic chuck, 2 ... insulating base material,
3, 4 ... chuck electrode layer, 6 ... shielding groove as cavity,
22: elongated shield space as a cavity, S1: chuck surface, W1: semiconductor wafer as an object to be adsorbed.

Claims (3)

[Claims] In an electrostatic chuck in which an object to be attracted is electrostatically attracted to a chuck surface of an insulating base material by energizing a chuck electrode layer, a different electrode arranged adjacent to the base material surface direction. An electrostatic chuck characterized in that a cavity is interposed between the chuck electrode layers. 2. The electrostatic chuck according to claim 1, wherein the cavity is a shielding groove that opens on the chuck surface side. 3. The electrostatic chuck according to claim 2, wherein a bottom surface of the shielding groove is located closer to an inner layer than a lower surface of the chuck electrode layer.