JP2000277599A - Electrostatic chuck - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make scanty the occurrence amount of particles even when applying a high voltage and when used at high temperatures by a method wherein a chuck face of an insulating substrate composed of a ceramic sintered compact is coated with a porous ceramic easy-to-break layer of low hardness. SOLUTION: An insulating substrate 2 of an aluminum nitride sintered compact 7 having superior heat-resistance, heat conductivity, and plasma-resistance is used. As a plurality of silicon wafers W1 as an object to be attracted are simultaneously chucked, the insulating substrate 2 is formed in an area several times that of the silicon wafer W1. Furthermore, the substrate 2 has a multilayer structure, and chuck electrode layers 3, 4 are internally formed. The chuck electrode layers 3, 4 of position and negative poles are together positioned in a layer close to a chuck face S1. The chuck electrode layer 3 of the positive pole is constituted by a semicircular-arc-like part positioned in an outer periphery of the insulating substrate 2 and a plurality of straight line part 3a extending at equal intervals and in parallel to the part. The chuck electrode layer 4 of the negative pole comprises also a straight line part 4a. A porous silica layer 6 as a porous ceramic easy-to-break layer is uniformly covered on all surfaces of the insulating substrate 2.

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 electrostatic chuck, by supplying a current to a chuck electrode in an insulating substrate made of dielectric ceramic, a wafer as an object to be attracted is electrostatically attracted to the chuck surface. Has become.

[0004]

However, in the conventional ceramic electrostatic chuck, the sintered body and the wafer are in direct contact with each other. Shear stress occurs. Then, under the influence of the shear stress, the aluminum nitride particles in the surface layer easily fall off, and there is a possibility that the aluminum nitride particles mainly become particles and adhere to the back surface of the semiconductor wafer.

It is also known that when the temperature during use is increased or when the applied voltage is increased to increase the chucking force, the generated shear stress increases, and as a result, the falling off of the aluminum nitride particles is promoted. I have.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an electrostatic chuck that generates a small amount of particles even when a high voltage is applied or when a high temperature is used.

[0007]

According to the first aspect of the present invention, an object is electrostatically adsorbed on a chuck surface of an insulating base made of a ceramic sintered body. The gist of the invention is an electrostatic chuck characterized in that at least a chuck surface of the insulating base material is covered with a porous ceramic easily breakable layer having a lower hardness than the insulating base material.

According to a second aspect of the present invention, in the first aspect, the porous ceramic easily breakable layer is a porous silica layer. According to a third aspect of the present invention, in the second aspect, the thickness of the porous silica layer is 1 μm to 10 μm.

The "action" of the present invention will be described below. According to the first aspect of the present invention, at the time of chucking, the object to be adsorbed is supported in a state of being in contact with the porous ceramic easily breakable layer having a lower hardness than the insulating base material. For this reason, the object to be adsorbed does not come into direct contact with the ceramic sintered body that is relatively hard and the surface crystal grains are likely to fall off. Therefore, the ceramic sintered body is not directly affected by the shear stress. Of course, the porous ceramic easily breakable layer itself has a low hardness, so that even if the porous ceramic easily breakable layer comes into contact with the object, it is unlikely to damage the object. As a result, the amount of particles generated due to falling off of surface crystal particles of the ceramic sintered body constituting the insulating base material is extremely reduced.

Further, since the ceramic easily breakable layer is a porous body, unlike a dense body, it is easily broken by contact with an object to be adsorbed. On the other hand, even if particles derived from the porous ceramic easily breakable layer adhere to the object to be adsorbed, it can be removed without difficulty. Therefore, the problem is not as serious as when particles derived from a hard material such as a ceramic sintered body constituting the insulating base material adhere.

According to the second aspect of the present invention, when the porous ceramic easily destructible layer is a porous silica layer, for example, when the substance to be adsorbed is made of silicon, the difference in thermal expansion coefficient from that is very small. Become. For this reason, the magnitude of the generated shear stress becomes extremely small, so that the amount of generated particles can be further reduced.

According to the third aspect of the present invention, by setting the thickness of the porous silica layer within the above preferred range,
A sufficient effect by coating the porous silica layer can be obtained while avoiding an increase in cost.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a bipolar 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 an aluminum nitride sintered body 7 which is a suitable dielectric. The reason why the aluminum nitride sintered body 7 was selected as the ceramic sintered body is that it is excellent in heat resistance, thermal conductivity, plasma resistance and the like, and is extremely convenient as a material for the electrostatic chuck 1. Here, a disk-shaped insulating substrate having a thickness of about several mm is used. In addition, the insulating base material 2 of this embodiment is formed so as to have an area several times as large as that of the silicon wafer W1 in order to simultaneously chuck a plurality of silicon wafers W1 as the objects to be attracted.

The insulating substrate 2 of the present embodiment has a multilayer structure, in which chuck electrode layers 3 and 4 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. Each of the chuck electrode layers 3 and 4 is formed by printing using a conductive paste P1 such as a tungsten paste.

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 plurality 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 shapes and sizes 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 positive side of the DC power supply 5 for chucking is connected to the chuck electrode layer 3 of the positive electrode via through holes and wiring (not shown). Similarly, the negative side of the DC power supply 5 is connected to the negative-electrode chuck electrode layer 4 through a through hole and a wiring (not shown).

As shown in FIGS. 1 and 2, a porous silica layer (porous SiO ₂ layer) 6 as a porous ceramic easily breakable layer is formed on the insulating base material 2 of the electrostatic chuck 1. ing. The porous silica layer 6 of the present embodiment covers the entire surface of the insulating substrate 2 with a substantially uniform thickness. Since the porous silica layer 6 is porous, the aluminum nitride sintered body 7 is a dense body and has almost no pores.
Is relatively low in hardness as compared with Therefore, the porous silica layer 6 has a property that it is relatively easily broken at the time of contact with the silicon wafer W1 as compared with the aluminum nitride sintered body 7.

The thickness of the porous silica layer 6 is 1 μm to 10 μm.
m, more preferably 4 μm to 7 μm.
If the porous silica layer 6 is too thin, the effect obtained by coating may be insufficient. Conversely, even if the porous silica layer 6 is made thicker than necessary, the effect is not expected to increase much, and the cost may be increased.

The porosity of the porous silica layer 6 is 10% to 70%.
%, Preferably 20% to 60%, more preferably 30%
% To 50%. If the porosity is too small,
It becomes dense and no longer an easily breakable layer. On the other hand, if the porosity is too large, it becomes too brittle more than necessary, which is not preferable.

Next, an example of a procedure for manufacturing the electrostatic chuck 1 of the present embodiment will be introduced. The green sheet to be used as the material of the insulating base material 2 is produced by forming a sheet of a slurry containing aluminum nitride powder as a main component and a sintering aid such as yttria by a doctor blade method. At a predetermined position of the obtained green sheet, if necessary,
Holes for forming through holes are formed by drilling or punching.

On the green sheet that has been punched, a conductive paste P1 containing tungsten particles as conductive particles, a dispersion solvent, a dispersant, and the like is printed in the next paste printing step.

In this step, first, the green sheet having undergone the perforating step is set in a printing apparatus, and a metal mask is arranged on the printing surface. By printing in this state,
The conductive paste P1 is filled in the through hole. Next, the green sheet on which through-hole printing or the like 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 and 4 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 of the vacuum pressing, the green sheets are integrated to form a green sheet laminate.

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
Before the main firing step, degreasing and preliminary firing are performed in a non-oxidizing atmosphere in advance. 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 as needed. The crucible in this state is set in a firing furnace, and the crucible is placed in a conventional manner.
Hot press firing is performed at a temperature of 0 ° C. or higher for a predetermined time and a predetermined pressure. As a result, the aluminum nitride and the conductive paste P1 are completely co-sintered, and the insulating substrate 2 made of the aluminum nitride sintered body 7 is formed.

Next, the outer shape of the insulating base material 2 is cut and exposed by grinding using a grinder or the like. Further, a porous silica layer 6 having a predetermined thickness is formed on the entire surface of the aluminum nitride sintered body 7 by a conventionally known film forming method such as a spin coating method or a printing method. Note that CVD or PVD may be performed instead of these methods.

Thereafter, coating and I
By performing various steps such as brazing of / O pins, a desired electrostatic chuck 1 as shown in FIGS. 1 and 2 is completed.
When a direct 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 on the chuck 1. As a result, the silicon wafer W1 is placed on the chuck surface S1 side.
Is attracted to fix the silicon wafer W1. At this time, the silicon wafer W1 is supported in contact with the porous silica layer 6 located on the surface.

[0030]

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 each consist of an insulating substrate 2 made of dense aluminum nitride having an outer diameter of 190 mm and a thickness of 1.5 mm. A porous silica layer 6 is formed by a coating method. Then, the thickness and porosity of the porous silica layer 6 are
Samples 1 to 3 were set to 6 μm and 30%, sample 4 was set to 3 μm and 30%, sample 5 was set to 6 μm and 10%, and sample 6 was set to 6 μm and 70%. On the other hand, Samples 7, 8, and 9, which are Comparative Examples 1 to 3, had no porous silica layer 6 formed. [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
A silicon wafer W1 having a diameter of 20 mm was placed thereon, and energization was performed under vacuum conditions. Then, the silicon wafer W1 is
After chucking for 0 second, the operation of peeling off the silicon wafer W1 was performed five times. In this state, the number (particles / cm ² ) of particles having a diameter of 0.2 μm or more per unit area adhered to the back surface of the wafer was counted. Table 1 shows the results.
In the same table, the applied voltage (V) and the operating temperature (° C.) set for each of the samples 1 to 9 are also shown. [Conclusion] As is clear from Table 1, when the examples in which the applied voltage and the use temperature are set equal in each example and each comparative example are compared, the amount of generated particles of the sample of the example is smaller. I understand. Further, in the electrostatic chucks 1 of these examples, the amount of generated particles was small even when a high voltage was applied or when a high temperature was used.

[0033]

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

(1) Electrostatic chuck structured as described above
In the case of 1, the silicon wafer W1 is
It is supported in a state of being in surface contact with the porous silica layer 6 having a lower hardness than the insulating substrate 2. For this reason, the back surface of the silicon wafer W1 does not come into direct contact with the aluminum nitride sintered body 7 which is relatively hard and the surface layer crystal particles tend to fall off. Therefore, the aluminum nitride sintered body 7 is not directly affected by shear stress. Of course, the hardness of the porous silica layer 6 itself, which is the porous ceramic easily breakable layer, is as low as that of silicon.
Even if it comes in contact with, it is hard to damage the back surface. As a result, the amount of particles generated due to the falling off of the surface crystal grains of the aluminum nitride sintered body 7 constituting the insulating base material 2 is extremely small. As is clear from the above, according to the present embodiment, it is possible to realize an excellent electrostatic chuck 1 that can cope with high voltage application and high temperature use.

(2) Since the silica layer 6 is a porous body, unlike a dense body, it is easily broken by contact with the silicon wafer W1. On the other hand, even if particles derived from the porous silica layer 6 adhere to the silicon wafer W1, it can be removed without difficulty. Therefore, the problem is not as serious as when particles derived from a hard material such as the aluminum nitride sintered body 7 adhere.

(3) Since the porous ceramic easily breakable layer in the present embodiment is the porous silica layer 6, the difference in thermal expansion coefficient from the silicon wafer W1 is extremely small. Therefore, the magnitude of the generated shear stress is extremely small, so that the amount of generated particles can be further reduced.

(4) In this embodiment, since the thickness of the porous silica layer 6 is set within the above-mentioned preferred range, a sufficient effect can be obtained by coating the porous silica layer 6 while avoiding an increase in cost. be able to. Therefore, it is possible to more reliably reduce the amount of generated particles.

The embodiment of the present invention may be modified as follows. -Like another example of the electrostatic chuck 11 shown in FIG.
The porous silica layer 6, which is a porous ceramic easily breakable layer,
The aluminum nitride sintered body 7 may be formed not on the entire surface but on a part thereof, for example, only on the chuck surface S1. Further, another example of the electrostatic chuck 21 shown in FIG.
As described above, the porous silica layer 6 may be formed in a projection shape or a stripe shape. In the case shown in FIG. 4, there is no possibility that cracks are caused due to a difference in shrinkage ratio when the easily breakable layer is formed, and the electrostatic chuck 21 can be easily manufactured.

It is permissible to change the porous ceramic easily breakable layer to a porous layer made of an oxide of a substance other than silicon, instead of a layer made of a porous silicon oxide as in the embodiment. Is done.

In manufacturing the insulating base material 2, a material other than the aluminum nitride sintered body 7 may be used as a ceramic sintered body. For example, boron nitride, silicon nitride, high-purity alumina, beryllia, magnesia, etc. A sintered body can be selected.

The object to be adsorbed is not limited to a silicon wafer, but may be another object such as a gallium arsenide wafer. In the above embodiments and other examples, the present invention is embodied as bipolar electrostatic chucks 1, 11, 21. However, the present invention may be embodied as a single-pole electrostatic chuck.

Next, in addition to the technical ideas described in the claims, the technical ideas grasped by the above-described embodiments are listed below together with their effects. (1) The porosity of the porous silica layer according to claim 2 or 3, which is preferably 10% to 70% (preferably 20% to 60%).
That.

(2) In any one of the first to third aspects and the technical idea 1, the ceramic sintered body is an aluminum nitride sintered body. Therefore, according to the invention described in the technical idea 2, a suitable electrostatic chuck having excellent heat resistance, thermal conductivity, plasma resistance, and the like can be obtained.

(3) Claims 1 to 3, technical idea 1,
2. In any one of 2., the porous ceramic easily-breakable layer is formed so as to cover the entire surface of the insulating base material.

(4) In any one of claims 1 to 3 and technical ideas 1 to 3, the porous ceramic easily breakable layer is formed in a projection shape or a stripe shape. Therefore, according to the invention described in the technical idea 4, there is no possibility that a crack is generated due to a difference in shrinkage ratio when the easily breakable layer is formed.

[0046]

As described above in detail, according to the first to third aspects of the present invention, it is possible to provide an electrostatic chuck which generates a small amount of particles even when a high voltage is applied or when a high temperature is used. Can be.

According to the second aspect of the invention, for example, when the object to be adsorbed is made of silicon, the amount of generated particles can be further reduced. According to the third aspect of the invention, a sufficient effect can be obtained by coating the porous silica layer while avoiding an increase in cost.
It is possible to more reliably reduce the amount of generated particles.

[Brief description of the drawings]

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

FIG. 2 is a plan view of the electrostatic chuck according to the embodiment.

FIG. 3 is a schematic cross-sectional view of another example of an electrostatic chuck.

FIG. 4 is a schematic cross-sectional view of another example of an electrostatic chuck.

[Explanation of symbols]

1,11,21 ... electrostatic chuck, 2 ... insulating base material, 6 ... porous silica layer as porous ceramic easily breakable layer, 7 ...
Aluminum nitride sintered body as ceramic sintered body, S
1: chuck surface, W1: silicon wafer as an object to be adsorbed.

Claims (3)

[Claims] 1. An electrostatic chuck wherein an object to be attracted is electrostatically attracted to a chuck surface of an insulating base made of a ceramic sintered body, wherein at least the chuck surface of the insulating base is higher than the insulating base. An electrostatic chuck, wherein the electrostatic chuck is covered with a low-hardness porous ceramic easily breakable layer. 2. The electrostatic chuck according to claim 1, wherein said porous ceramic easily breakable layer is a porous silica layer. 3. The porous silica layer has a thickness of 1 μm to 10 μm.
The electrostatic chuck according to claim 2, wherein the thickness is μm.