JPH09260473A - Electrostatic chuck - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide durability against plasma gas and to improve adhesion with a wafer and heat conductivity by sequentially providing a first insulating layer made of ceramic on a metal plate, a conductive pattern formed as an electrode on the first layer and a second insulating layer made of an elastic body on the pattern. SOLUTION: The first insulating layer 3 is sequentially provided on the metal plate 5, the conductive pattern 6 on the layer and the second insulating layer 1 on the pattern. It is preferable to use ceramic of high conductivity for those used for the first insulating layer 3 for improving the heat conductivity of an electrostatic chuck. The conductive pattern 6 operates as the electrode for the wafer chuck of an electrostatic chuck. The elastic body of high heat conductivity is used for the second insulating layer 1. It is important to improve the adhesion of the wafer and the second insulating layer 1 and to deteriorate contact heat resistance. Thus, cooling performance and durability can be improved since plasma resistance, adhesibility and heat conductivity are improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic chuck used for holding a substrate in manufacturing a semiconductor integrated circuit.

[0002]

2. Description of the Related Art Conventionally, in a plasma etching process in manufacturing a semiconductor integrated circuit, an electrostatic adsorption method,
Wafer chucks of the Jansen-Rahbek force method, so-called electrostatic chucks are used, but plastic such as polyimide, alumina, or the like is used as an insulating layer of the chuck.
Ceramics such as aluminum nitride and rubber elastic bodies such as silicone rubber have been proposed and put to practical use. On the other hand, in the plasma etching process, the temperature rise of the wafer due to the heat supplied from the plasma is suppressed to make the temperature of the wafer uniform and constant, and a cooling chiller is flown on the back surface of the electrostatic chuck to perform highly accurate etching. A cooling mechanism is provided to cool the wafer, keep the temperature of the wafer uniform, increase the selectivity with respect to the mask material and the base of the etching target, and obtain an anisotropic shape.

[0003]

The electrostatic chuck made of ceramics has been put into practical use because the insulating layer has excellent durability against plasma gas and has high thermal conductivity. Since the layer is hard, the adhesion to the wafer is poor, and the contact heat resistance is large, so that there is a problem that sufficient heat dissipation characteristics cannot be obtained. In order to solve the above problems, a method is generally used in which an inert gas such as helium is flown between the wafer and the insulating layer to mediate heat transfer between the wafer and the insulating layer. However, this method requires fine processing such as providing a groove for flowing a gas on the surface of the insulating layer, which increases the cost of the chuck. Further, there is a problem that the cost becomes high, such as the need for equipment for flowing the inert gas.

Although the electrostatic chuck made of plastic such as polyimide is not sufficiently durable against plasma gas, it is currently most widely used because it is easy to manufacture and is inexpensive. As the electrostatic chuck is low and hard, the adhesiveness to the wafer is poor and the contact thermal resistance is large, like the electrostatic chuck made of ceramics, so that sufficient heat dissipation characteristics cannot be obtained. In addition, JP-A-59-6424
The electrostatic chuck made of silicone rubber disclosed in Japanese Patent Publication No. 5 and the like has good adhesion to the wafer, but does not have sufficient heat dissipation characteristics and has insufficient durability against plasma gas.

[0005]

The inventors of the present invention have completed the present invention as a result of extensive studies in view of the above problems, and the present invention is based on a first insulating layer made of ceramics on a metal plate. A conductive pattern formed on the first insulating layer as an electrode, and a second conductive pattern formed on the conductive pattern.
The purpose of the present invention is to provide an electrostatic chuck characterized by being provided with an insulating layer, which has durability against plasma gas, good adhesion to a wafer, and good thermal conductivity.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to FIGS. 1 and 2 show an example of a bipolar electrostatic chuck of the present invention, which includes a second insulating layer 1, an adhesive layer 2, a first insulating layer 3, an adhesive layer 4, a metal substrate 5, and a conductive layer. The conductive pattern 6 and the lead wire 7 are used to energize the lead wire 7 to attract the wafer to the second insulating layer 1. The metal plate 5 functions as an electrode of a high-frequency power source applied when plasma is generated, and as a material, any material may be used as long as it has durability against plasma gas and does not pollute the semiconductor integrated circuit. Examples include aluminum, alumite, and duralumin.

The ceramic used for the first insulating layer 3 is preferably one having high thermal conductivity in order to enhance the thermal conductivity of the electrostatic chuck, and the thermal conductivity is 0.05 cal / cm · sec · ° C.
The above is preferable and is selected from aluminum nitride, alumina, boron nitride, and silicon nitride. When the thermal conductivity of ceramics is 0.05 cal / cm · sec · ° C or more, the temperature rise of the wafer due to the heat supplied from the plasma can be suppressed to make the wafer temperature uniform and constant, and highly accurate etching can be performed. However, if it is less than 0.05 cal / cm · sec · ° C, the cooling efficiency of the wafer is lowered, the wafer temperature rises, the temperature cannot be controlled to a constant temperature, and the yield of integrated circuits deteriorates. The thickness of the ceramics layer is preferably 100 to 2000 μm. If the thickness is less than 100 μm, the dielectric strength is insufficient and the electrostatic chuck is more likely to cause dielectric breakdown, which is disadvantageous in the yield of semiconductor devices. If it exceeds the above range, the heat radiation property is deteriorated, so that the wafer cooling efficiency is deteriorated, which is disadvantageous in the yield of semiconductor devices.

The conductive pattern 6 acts as an electrode for attracting the wafer of the electrostatic chuck, and the material thereof is a metal-based conductor such as copper, aluminum, nickel, silver or tungsten, or titanium nitride or the like. A ceramic-based conductor is exemplified, and the film thickness may be 1 to 100 μm, preferably 5 to 50 μm. 1 μm
If less than, the mechanical strength of the conductive pattern is reduced, and damage may occur due to the printing pressure of the soldering iron when the second insulating layer is laminated or when the lead wire for voltage supply is joined to the conductive pattern with solder or the like. If a problem occurs, and if it exceeds 100 μm, the mechanical strength and electric performance of the conductive pattern become constant, and further improvement does not occur, which is disadvantageous in terms of material cost.
The shape of the conductive pattern may be a known shape, and it is roughly classified into two types, a unipolar type (generally serving as a positive electrode) and a bipolar type (wherein the positive electrode and the negative electrode are applied uniformly). Any type may be used. An example of the bipolar conductive pattern is shown in FIG.

As the second insulating layer, an elastic body having high thermal conductivity is used, and the thermal conductivity is preferably 0.0005 cal / cm · sec · ° C. or higher, and more preferably 0.0001 cal / cm · sec · ° C. or higher. If the thermal conductivity is 0.0005 cal / cm · sec · ° C or higher, the temperature rise of the wafer due to the heat supplied from the plasma can be suppressed to make the temperature of the wafer uniform and constant, and highly accurate etching can be performed. If it is less than 0.0005 cal / cm · sec · ° C, the cooling efficiency of the wafer decreases, the wafer temperature rises, it becomes impossible to control the temperature to a constant temperature, and the yield of integrated circuits deteriorates. It should be noted that the higher the thermal conductivity, the more preferable, but this depends on the amount of the filler, and the larger the amount, the greater the thermal conductivity. However, if the amount of the filler is increased, the hardness of the elastic body becomes hard and exceeds 90 °. It is difficult to set the temperature to 0.05 cal / cm · sec · ° C or higher because of the problem of poor adhesion with As the filler for imparting high thermal conductivity to the elastic body composition, alumina powder, aluminum nitride powder, boron nitride powder, silicon nitride powder, magnesium oxide powder,
High thermal conductivity ceramic powder such as silica powder is preferable,
The amount of the filler to be blended is an amount necessary to impart a thermal conductivity of 0.0005 cal / cm · sec · ° C. or higher, and they are mixed by a known method.

Further, as the second insulating layer, it is important to improve the adhesion between the wafer and the second insulating layer to reduce the contact thermal resistance, and the surface shape of the elastic body can be easily made by the attraction force acting on the wafer. It is necessary to deform so as to follow the shape of the back surface. Therefore, the hardness of the elastic body is preferably 30 to 90 ° according to JIS-A, and if it is less than 30 °, the adhesion between the surface of the second insulating layer and the back surface of the wafer becomes high, and the wafer remains static after the plasma etching process. When peeling from the electric chuck, the wafer adheres strongly due to the adhesive force, which causes a problem that the peeling becomes difficult. Further, when the angle exceeds 90 °, the deformation of the cured product of the second insulating layer due to the adsorption force decreases, There is a problem that the followability to the back surface is reduced and the contact thermal resistance is increased.

As the elastic body, silicone rubber, EPD
Examples include M, fluororubber, nitrile rubber, natural rubber and the like. Among them, a cured product of the silicone rubber composition has less conductive impurities and outgas components, and is preferable for use in the process of semiconductor integrated circuits. As the silicone rubber composition, the property before curing may be either a millable solid type or a liquid type, and the curing method may be a peroxide curing type, an addition reaction curing type, a condensation curing type, an ultraviolet curing type or the like. Anything is fine.

The thickness of the second insulating layer is preferably as thin as possible from the viewpoint of heat dissipation, and is preferably in the range of 50 to 1000 μm. If the thickness is less than 50 μm, the dielectric breakdown voltage is lowered, so that the electrostatic chuck has a high probability of causing dielectric breakdown, which is disadvantageous in the yield of semiconductor devices, and if it exceeds 1000 μm, the heat dissipation is lowered, so that the wafer cooling efficiency is reduced. Is worse, which is a disadvantage in terms of integrated circuit yield. Further, the flatness and surface roughness of the surface of the second insulating layer affect the adhesion to the wafer and the contact thermal resistance between the wafer and the surface of the second insulating layer, but the flatness should be 50 μm or less. However, it is preferable for improving the adhesion to the wafer. If it exceeds 50 μm, the adhesion to the wafer will be reduced and the heat dissipation will be reduced.
The wafer cooling efficiency deteriorates, which is disadvantageous in terms of integrated circuit yield. The surface roughness (Ra) is preferably less than 10 μm in order to improve the adhesion to the wafer. 10μ
If it exceeds m, the heat dissipation is deteriorated, so that the wafer cooling efficiency is deteriorated, which is disadvantageous in the yield of the integrated circuit.

In addition, since the cured product of the above rubber composition is in direct contact with the wafer, it is preferable that the conductive impurities are as small as possible, and alkali metal, alkaline earth metal and heavy metals such as iron, nickel, copper and chromium are contained. The amount is preferably 1 ppm or less, and it is necessary that these impurity components do not migrate to the wafer.

For the purpose of adjusting the strength and hardness of the cured product of the rubber composition, various known fillers, colorants, flame retardants and the like can be added to the rubber composition.

Each layer of the electrostatic chuck of the present invention may be laminated by adhesion or adhesion, but an adhesive is preferably used, and a known silicone rubber adhesive is preferable as the adhesive. The conductive pattern can be formed on the first insulating layer by printing a conductive paste, plating, or by bonding a conductive metal film. The lead wire is installed for connecting to the power source to apply voltage to the conductive pattern,
It may be attached to the conductive pattern by soldering or the like. Further, electrical insulation between the lead wires and between the lead wires and the metal substrate may be performed by a known silicone-based sealing material or epoxy-based sealing material.

[0016]

EXAMPLES Next, examples and comparative examples of the present invention will be explained, but these do not limit the present invention. Composition Examples 1 to 4 Composition Examples 1 to 1 shown in Table 1 in which raw materials are selected from the following A to F
The silicone rubber composition of No. 4 was blended with a roll and press-molded under the conditions of a pressing pressure of 5 kg / cm ² , a temperature of 170 ° C. and a time of 30 minutes to prepare a sheet. Using the obtained silicone rubber sheet, an electrostatic chuck was manufactured with the constitution shown in Table 2.

A: methylvinylpolysiloxane having an average degree of polymerization of 8000, consisting of dimethylsiloxane unit 99.85 mol% and methylvinylsiloxane unit 0.15 mol% B: di-t-butyl peroxide C: alumina powder (AL24, Showa Denko KK) Product name D: Aluminum nitride powder (XUS-35548, product name of Dow Chemical Co., Ltd.) E: Boron nitride powder (KBN (h) 10, product name of Shin-Etsu Chemical Co., Ltd.) F: Silica powder (Crystallite, Tatsumori) Company product name)

[0018]

[Table 1]

Example 1 An electrostatic chuck having the structure shown in Table 2 is manufactured. That is,
Alumina plate of the first insulating layer is plated with copper to a film thickness of 20μ
m to form the bipolar electrode pattern shown in FIG.
A silicone adhesive KE1801 (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.) is applied to the silicone rubber sheet of composition example 1 of the insulating layer by screen printing so as to have a film thickness of 25 μm, and is bonded to the copper pattern side of the alumina plate, and the pressure is 0.1 kgf. / cm ² , temperature 120
Press bonding was carried out under the conditions of ° C and time of 10 minutes. Next, screen-print the silicone adhesive KE on the aluminum substrate.
1801 (described above) is applied to a film thickness of 10 μm, and the above alumina plate /
Copper pattern / composition example 1 Alumina side of composite sheet of silicone rubber sheet is stuck together, pressure 0.01kgf / cm ² ,
Press bonding was performed under the conditions of a temperature of 120 ° C. and a time of 10 minutes. Two
This lead wire is soldered from a copper pattern and sealed with a silicone potting agent KJR632 (trade name of Shin-Etsu Chemical Co., Ltd.) to insulate the lead wires from each other and between the aluminum substrate and the lead wire. The electrostatic chuck shown in was obtained.

[0020]

[Table 2]

Next, in the cooling performance tester 15 shown in FIG.
The electrostatic chuck 9 was mounted and the cooling performance of the electrostatic chuck was tested. As the test method, an electrostatic chuck was mounted in a chamber under a reduced pressure of 0.01 Torr, and DC + 0.
5 kV is supplied from the power supply 14, the wafer 10 is electrostatically attracted and fixed to the electrostatic chuck 9, and the wafer 11 is heated by the heater 11.
Is heated to 150 ° C., and then cooling water 13 at 4 ° C. is circulated,
The temperature when the temperature of the wafer 10 was in the equilibrium state was measured by the surface thermometer 12. The results are also shown in Table 2,
From this result, the wafer temperature was 50 ° C., and it was confirmed that the electrostatic chuck was excellent in cooling performance.

Example 2 A bipolar electrode pattern shown in FIG. 3 was coated on a first insulating layer aluminum nitride plate with a silver paste for conductive printing to a film thickness of 10 μm by screen printing, and then a furnace temperature was set to 800.
Formed by baking at 3 ° C. for 3 hours. Then, a silicone adhesive KE44 (trade name of Shin-Etsu Chemical Co., Ltd.) is applied to the silicone rubber sheet of Composition Example 2 of the second insulating layer by screen printing so as to have a film thickness of 20 μm, and is bonded to the silver pattern side of the aluminum nitride plate, Pressure 0.1kgf / cm ² , temperature 20 ℃,
Press bonding was performed under the condition of time of 48 hours. Next, screen-print the silicone adhesive KE44 on the aluminum substrate.
(Above) is applied to a film thickness of 10 μm, and the aluminum nitride plate side of a composite sheet made of the above aluminum nitride plate / silver pattern / composition example 2 silicone rubber sheet is bonded,
Press bond under conditions of pressure 0.01 kgf / cm ² , temperature 20 ° C., time 48 hours, and pull out two lead wires by soldering from the silver pattern to insulate the lead wires and between the aluminum substrate and the lead wires. For this purpose, it was sealed with an epoxy potting agent Semi-coat 114 (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.) to obtain the electrostatic chuck shown in FIG. The electrostatic chuck was tested for cooling performance in the same manner as in Example 1. The results are also shown in Table 2, and the wafer temperature was 30 ° C., and it was confirmed that the obtained electrostatic chuck had excellent cooling performance.

Example 3 A tungsten nitride plate for conductive printing was applied by screen printing to a film thickness of 15 μm on a boron nitride plate of a first insulating layer, and then baked at a furnace temperature of 1000 ° C. for 3 hours, and The bipolar electrode pattern shown in 3 was formed. Then, a silicone adhesive KE1801 (described above) was applied to the silicone rubber sheet of Composition Example 3 of the second insulating layer by screen printing to a film thickness of 2
It is applied to 0 μm and attached to the tungsten pattern side of the aluminum nitride plate, pressure 0.1 kgf / cm ² , temperature 12
Press bonding was performed under conditions of 0 ° C. and time of 10 minutes. Next, screen-print the silicone adhesive KE18 on the duralumin substrate.
01 (above) is applied to a film thickness of 10 μm, and the boron nitride plate side of a composite sheet made of the above boron nitride plate / tungsten pattern / composition example 3 silicone rubber sheet is bonded,
In order to insulate between the lead wires and between the duralumin board and the lead wires, press-bond them at a pressure of 0.01 kgf / cm ² , at a temperature of 120 ° C. for 10 minutes, and pull out the two lead wires from the tungsten pattern by soldering. Sealing with the silicone potting agent KJR632 (described above) gave the electrostatic chuck shown in FIG. This electrostatic chuck was tested for cooling performance in the same manner as in Example 1. The results are also shown in Table 2. The wafer temperature was 40 ° C., and it was confirmed that the obtained electrostatic chuck had excellent cooling performance.

Example 4 A silicone adhesive KE1825 (trade name of Shin-Etsu Chemical Co., Ltd.) was applied to the silicone rubber sheet of Composition Example 4 of the second insulating layer by screen printing so as to have a film thickness of 20 μm, and then a thickness of 35 μm.
The copper foil of No. 1 was attached to the coated surface, and press-bonded under the conditions of pressure 0.1 kgf / cm ² , temperature 120 ° C. and time 10 minutes. Then, a bipolar electrode pattern shown in FIG. 3 was formed by a chemical etching process. Next, apply a silicone adhesive KE1825 (previously described) to the quartz plate of the first insulating layer by screen printing to a film thickness of 20 μm, and bond it to the copper pattern side of the second insulating layer, and pressure 0.1 kgf / cm ² , Temperature 120 ℃, time 10
Press bonding was performed under the conditions of minutes. Next, a silicone adhesive KE1825 (described above) is applied to the duralumin substrate by screen printing, and the quartz sheet / copper pattern / silicone rubber sheet of Composition Example 4 is attached to the quartz sheet side with a pressure of 0.01 kgf. Press-bonding was performed under the conditions of / cm ² , temperature of 120 ° C., and time of 10 minutes. Then, two lead wires are pulled out from the copper pattern by soldering and sealed with silicone potting agent KJR632 (described above) to insulate the lead wires and the duralumin board from the lead wires, as shown in Fig. 1. An electrostatic chuck was obtained. This electrostatic chuck was tested for cooling performance in the same manner as in Example 1. The results are also shown in Table 2, and the wafer temperature was 65 ° C., and it was confirmed that the obtained electrostatic chuck had excellent cooling performance.

The electrostatic chucks produced in Examples 1 to 4 were mounted on a plasma etching apparatus, and CF was used as a reaction gas.
₄ , O ₂ (oxygen partial pressure = 0.1) was used, and 4000 silicon wafers were processed under the conditions of a temperature of 70 ° C, a pressure of 0.8 Torr, a microwave input of 400 W, and a processing time of 60 seconds per wafer. It was confirmed that the temperature rise of the wafer and the variation of the temperature distribution were not observed in any of the electrostatic chucks, and that the electrostatic chuck of the present invention was excellent in durability because it could be processed into a good anisotropic shape. It was

Comparative Example 1 For comparison, a polyimide electrostatic chuck was prepared under the same conditions as in Example 4 except that the structure shown in Comparative Example 1 column in Table 3 was used, and the cooling performance was tested. , Wafer temperature is 1
It was 20 ° C., and it was confirmed that the cooling performance was poor.

[0027]

[Table 3]

Comparative Example 2 Example 1 except that the structure shown in the column of Comparative Example 2 in Table 3 was used.
Under the same conditions as above, an integrally baked alumina electrostatic chuck with a built-in conductive pattern was produced and the cooling performance was tested.
The wafer temperature was 110 ° C., and it was confirmed that the cooling performance was poor.

Comparative Example 3 Example 4 except that the structure shown in the column of Comparative Example 3 in Table 3 was used.
Under the same conditions as above, a silicone rubber electrostatic chuck was produced and the cooling performance was tested. As a result, it was confirmed that the wafer temperature was 90 ° C. and the cooling performance was poor.

[0030]

According to the present invention, the plasma resistance is good,
Since the adhesiveness to the wafer is good and the thermal conductivity is good, an electrostatic chuck having excellent cooling performance and high durability is provided.

[Brief description of drawings]

FIG. 1 is a schematic side view of an embodiment of an electrostatic chuck of the present invention.

FIG. 2 is a schematic side view of another embodiment of the electrostatic chuck of the present invention.

FIG. 3 is a schematic top view of an example of a conductive pattern according to the present invention.

FIG. 4 is a schematic sectional view of a cooling performance tester.

[Explanation of symbols]

1 ... 2nd insulating layer 2 ... adhesive layer 3 ... 1st insulating layer 4 ... adhesive layer 5 ... metal substrate 6 ... conductive pattern 7 ... lead wire 8 Sealant 9 Electrostatic chuck 10 Wafer 11 Heater 12 Surface thermometer 13 Cooling water 14 Power supply 15 Cooling performance tester

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsutomu Yoneyama 1 Hitomi, Osamu Matsuida-cho, Usui-gun, Gunma 10 Shin-Etsu Chemical Co., Ltd. Silicone Electronic Materials Research Laboratory

Claims (4)

[Claims] 1. A first insulating layer made of ceramics on a metal plate, a conductive pattern formed as an electrode on the first insulating layer, and a second elastic layer formed on the conductive pattern.
An electrostatic chuck comprising an insulating layer. 2. The electrostatic chuck according to claim 1, wherein the first insulating layer made of ceramics is selected from aluminum nitride, alumina, boron nitride, and silicon nitride. 3. The second insulating layer made of an elastic material has a thermal conductivity of 0.0005 cal / cm · sec · ° C. or more and a hardness according to JIS-A of 30 to 90 °. The electrostatic chuck described in. 4. The electrostatic chuck according to claim 1, wherein the second insulating layer made of an elastic body is made of a cured product of a silicone rubber composition.