JPH11297804A - Electrostatic chuck - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve adhesibility between an insulating layer and a wafer and to reduce contact resistance, by forming a conductive pattern divided into two areas as electrodes and the elastic insulating layer constituted of the hardened object of a silicon rubber composition, which is installed on the conductive pattern. SOLUTION: A conductive pattern on which copper plating whose film thickness is 20 μm is executed on an insulating alumina substrate, in which through holes are given for take-out electrodes and the take-out electrodes 3b are formed on the inner peripheral faces of the through holes. Silicon adhesive is applied on the elastic insulating layer 1 (silicon rubber sheet containing alumina) by screen printing so that film thickness becomes 25 μm. It is adhered with a conductive pattern side on which the copper plating of the insulating alumina substrate is executed. They are press-adhered with the condition of 0.1 kgf/cm<2> of pressure, 120 deg.C of a temperature and ten minutes. Thus, the adhesibiltiy of the insulating layer and a wafer improves, contact resistance is reduced and cooling ability can considerably be 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 which is used for holding a silicon wafer substrate in the manufacture of a semiconductor integrated circuit, and is particularly useful in an ion implantation process.

[0002]

2. Description of the Related Art Conventionally, in an ion implantation step in a manufacturing process of a semiconductor integrated circuit, a wafer chuck of an electrostatic chuck system or a Johnsen-Rahbek force system, a so-called electrostatic chuck, has been used. As the insulating layer of the electrostatic chuck,
Plastics such as polyimide resin, ceramics such as alumina and aluminum nitride, and rubber elastic bodies such as silicone rubber have been proposed and are all in practical use. On the other hand, in order to keep the wafer temperature uniform and constant by suppressing the temperature rise of the wafer due to the heat given by the implanted ions in the ion implantation process, a cooling mechanism such as flowing a cooling chiller on the back surface of the electrostatic chuck to cool the wafer A method of keeping the temperature of the wafer uniform and constant to prevent thermal degradation of the photoresist of the mask material has been performed.

[0003]

The electrostatic chuck having a ceramic insulating layer has many practical examples because of its excellent durability and high thermal conductivity. However, since the insulating layer is hard, its adhesion to a wafer is poor. There is a problem that sufficient heat radiation characteristics cannot be obtained due to high contact thermal resistance. In order to solve this problem, a method of flowing an inert gas such as helium between the wafer and the insulating layer to improve the heat transfer between the wafer and the insulating layer is generally used. However, this method requires fine processing such as providing a groove for flowing a gas on the surface of the insulating layer, and requires equipment for flowing an inert gas, thereby increasing the manufacturing cost of the electrostatic chuck. There is.

[0004] An electrostatic chuck having an insulating layer made of a polyimide resin is not widely used because it is not durable but easy to manufacture and the manufacturing cost is low. However, since the thermal conductivity is low and hard, the adhesion to the wafer is poor as in the case of the ceramic electrostatic chuck, and there is a problem that sufficient heat radiation characteristics cannot be obtained because of the large contact thermal resistance.

[0005] An electrostatic chuck in which the insulating layer is made of silicone rubber has excellent adhesion to the wafer because the insulating layer is an elastic body, so that there is no need to flow an inert gas such as helium between the wafer and the insulating layer. There is an advantage. Conventionally, as electrostatic chucks using silicone rubber for the insulating layer, those described in Japanese Patent Publication No. 2-55175 and Japanese Patent Publication No. 2-63307 have been proposed. Use a metal with excellent thermal conductivity
An internal electrode is provided between the insulating layer and the second insulating layer. An extraction electrode is required to supply power to the internal electrode of the electrostatic chuck. However, when a metal such as aluminum is used for the substrate, it is necessary to ensure insulation between the extraction electrode and the substrate and the extraction electrode portion. Has a problem that the structure is complicated and the manufacturing cost is increased. The present inventors have previously disclosed in Japanese Patent Application Laid-Open No. 9-260473, a first insulating layer made of ceramics formed on a metal plate, a conductive pattern formed as an electrode on the insulating layer, and a conductive pattern formed on the conductive pattern. Although an electrostatic chuck including the formed elastic second insulating layer has been proposed, this is excellent in heat dissipation, but has a problem that insulation failure may occur.

[0006]

The present invention solves these conventional problems at once. That is, an electrostatic chuck comprising an insulating ceramic substrate, a conductive pattern formed by dividing the substrate into two regions as electrodes, and an elastic insulating layer provided on the conductive pattern. .

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. Insulating ceramics used for the substrate in the present invention,
In order to increase the thermal conductivity of the electrostatic chuck, those having high thermal conductivity are preferable. It is preferable that the thermal conductivity is 0.05 cal / cm · sec · ° C. or more, and by setting such thermal conductivity, the temperature rise of the wafer due to the heat given by the ions is suppressed and the photoresist is deteriorated. The wafer temperature can be kept lower than the temperature. Thermal conductivity 0.05 cal / cm ・ sec
If the temperature is lower than ℃, the cooling efficiency of the wafer decreases, the temperature of the wafer increases, and it becomes impossible to control the temperature to a constant temperature. As the insulating ceramic in the present invention, aluminum nitride, alumina, boron nitride, silicon nitride and the like are suitable. The thickness of the insulating ceramic in the present invention is 0.1
If the thickness is less than 0.1 mm, the withstand voltage is insufficient, and the electrostatic chuck is liable to cause dielectric breakdown, which may deteriorate the yield of semiconductor devices. On the other hand, if the thickness exceeds 100 mm, the heat radiation property is reduced, so that the cooling efficiency of the wafer is deteriorated and the yield of semiconductor devices may be deteriorated.

In the present invention, the conductive pattern functions as an electrode for attracting a wafer to the electrostatic chuck. The conductive pattern may be made of copper, aluminum, nickel,
Silver, metal-based conductors such as tungsten and ceramics-based conductors such as titanium nitride, resin-based conductors such as conductive silicone rubber and conductive epoxy resin are used,
The thickness is preferably from 1 to 100 μm, and more preferably from 5 to 50 μm. If it is less than 1 μm, the mechanical strength of the conductive pattern is reduced, and the reliability is reduced. Even if the thickness exceeds 100 μm, the mechanical strength and the electrical performance of the conductive pattern are not improved, and the material cost increases. The shape of the conductive pattern is roughly classified into two types, a monopolar type (generally a positive electrode) and a bipolar type. In the present invention, the bipolar type (a positive electrode and a negative electrode are uniformly applied) is particularly preferred. This is preferable because the throughput becomes faster. Usually, the throughput of the bipolar type is 10 seconds / sheet, while the throughput of the monopolar type is 60 seconds / sheet. One example of the conductive pattern according to the present invention is shown in FIG. 1 (see Example).

As the elastic insulating layer in the first aspect of the present invention, an elastic material having a high thermal conductivity is used. Examples of the elastic material include silicone rubber, ethylene propylene rubber, fluorine rubber, acrylic rubber, and styrene butadiene rubber. , Natural rubber and the like. Among these elastic bodies, a cured product of the silicone rubber composition (silicone rubber) has a small amount of conductive impurities and outgassing components, and is therefore most suitable for use in a semiconductor integrated circuit manufacturing process. Here, the thermal conductivity of the elastic insulating layer is 0.001 cal / cm
When the temperature is 0.0015 cal / cm · sec · ° C or higher, the wafer temperature can be kept lower than the photoresist deterioration temperature (generally less than 100 ° C) by suppressing the wafer temperature rise due to the heat supplied from the ions. It is preferred. In addition, in order to improve the adhesion between the wafer and the insulating layer and reduce the contact thermal resistance, the surface shape of the elastic insulating layer is deformed so that the surface shape of the elastic insulating layer easily follows the back surface shape of the wafer by the electrostatic attraction force acting on the wafer. It is preferable to be able to. For this purpose, the hardness of the elastic insulating layer in the present invention is set to 30 ° to 90 °, particularly 40 ° to 85 ° (JIS).
-AZ) is preferable. If the hardness is less than 30 °,
The adhesion between the front surface of the elastic insulating layer and the back surface of the wafer may be too high, and it may be difficult to peel the wafer from the electrostatic chuck after the plasma etching process. On the other hand, if the angle exceeds 90 °, the deformation of the elastic insulating layer due to the attraction force is reduced, the ability of the elastic insulating layer to follow the rear surface of the wafer is reduced, and the contact thermal resistance may be increased.

The thickness of the elastic insulating layer in the present invention is preferably as thin as possible in order to improve heat dissipation.
Those having a range of 50 to 1,000 μm are preferred. If the thickness is less than 50 μm, the dielectric breakdown voltage is reduced, so that the electrostatic chuck is likely to cause dielectric breakdown, and the yield of semiconductor devices may be deteriorated. On the other hand, if the thickness exceeds 1,000 μm, the heat radiation property is reduced, so that the cooling efficiency of the wafer is deteriorated and the yield of the integrated circuit may be deteriorated. Also, the flatness and surface roughness of the elastic insulating layer surface affect the adhesion to the wafer and the contact thermal resistance between the wafer and the insulating layer surface. It is suitable for improving the adhesion. If it exceeds 50 μm, the adhesiveness to the wafer will be reduced, and the heat radiation will be reduced, so that the cooling efficiency of the wafer will be reduced and the yield of the integrated circuit may be reduced. The surface roughness (Ra) is preferably set to 10 μm or less in order to improve the adhesion to the wafer. When the thickness exceeds 10 μm, the heat radiation property is reduced, so that the cooling efficiency of the wafer is deteriorated and the yield of the integrated circuit may be deteriorated.

According to the third aspect of the present invention, the silicone rubber composition for forming the elastic insulating layer may be of a millable type or a liquid type, and the curing method may be a peroxide catalyst. And various curing methods such as curing by addition reaction, addition reaction curing, condensation reaction curing, and ultraviolet curing. In the silicone rubber composition forming the elastic insulating layer according to the invention of claim 3 of the present invention, alumina powder, aluminum nitride powder, boron nitride powder, silicon nitride powder, High thermal conductive ceramic powder such as magnesium oxide powder and silica powder is added. The amount of the filler is the amount necessary to give the thermal insulation of 0.001 cal / cm-sec- ° C or more to the elastic insulating layer. If the thermal conductivity is less than 0.001 cal / cm-sec- ° C, the Cooling efficiency decreases, the wafer temperature rises, and it becomes impossible to control the temperature to a constant temperature, and the yield of integrated circuits may deteriorate.

Since the elastic insulating layer according to the third aspect of the present invention is in direct contact with the wafer, the content of impurities in the silicone rubber composition forming the elastic insulating layer which affects the insulating property is minimized. It is preferable to reduce the content of heavy metals such as alkali metals, alkaline earth metals, iron, nickel, copper, and chromium.
It is optional to add various fillers, coloring agents, and flame retardants for adjusting the strength and hardness of the cured product of the silicone rubber composition.

In the present invention, the conductive pattern is formed on the insulating ceramic substrate by a method such as printing or plating a conductive paste or by bonding a conductive metal film. Further, an electrode may be directly formed on the elastic insulating layer. In this case, a conductive liquid silicone rubber composition containing carbon or metal is printed on the insulating layer by screen printing or the like, and then the conductive liquid silicone rubber composition is formed. Allow the object to cure. The extraction electrode is used to connect to a power supply to apply a voltage to the conductive pattern. This is a combination of metal plating inside the through hole opened in the ceramic substrate and insertion of metal pins and soldering. What is necessary is just to join to a conductive pattern by methods, such as.

[0014]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto. (Silicone rubber sheets 1 to 4) Silicone rubber compositions 1 to 4 in which the following raw materials A to F were blended at the ratios shown in Table 1 were pressed under a pressure of 5 kg / cm ² , a temperature of 170 ° C., and 30 minutes. Press molding was performed to produce silicone rubber sheets 1 to 4 for an insulating layer. A: An average degree of polymerization of 99.85 mol% of dimethylsiloxane units and 0.15 mol% of methylvinylsiloxane units 8,000
Methylvinylpolysiloxane [Shin-Etsu Chemical Co., Ltd.
B: di-t-butyl peroxide [Nippon Yushi Co., Ltd.
C: Alumina powder / AL24 [trade name of Showa Denko KK] D: Aluminum nitride powder / XUS-35548 [Dow Chemical product name] E: Boron nitride powder / KBN- (h) 10 [Shin-Etsu Chemical Co., Ltd.] F: Silica powder / crystallite [Trade name of Tatsumori Co., Ltd.]

[0015]

[Table 1]

Example 1 A 20 μm-thick copper-plated conductive pattern and an extraction electrode shown in FIG. 1 were placed on the inner peripheral surface of a through-hole on an insulating alumina substrate having a through-hole for an extraction electrode. A silicone adhesive (KE1801) is applied to the elastic insulating layer (alumina-containing silicone rubber sheet 1) by screen printing so as to have a film thickness of 25 μm, and this is adhered to the copper-plated conductive pattern side of the alumina substrate. bonding, pressure 0.1 kgf / cm ^2, temperature 120
Press bonding was performed at 10 ° C. for 10 minutes. The completed electrostatic chuck is shown in FIG. Next, the obtained electrostatic chuck 9 was attached to the cooling performance tester 8 shown in FIG. 5, and the cooling performance of the electrostatic chuck was measured. That is, in a chamber under a reduced pressure of 0.01 Torr, DC ± 0.5 KV was supplied to the electrostatic chuck from the power supply 14, the wafer 10 was electrostatically attracted and fixed to the electrostatic chuck 9, and the wafer 10 was heated to 150 ° C. by the heater 11. Thereafter, cooling water of 4 ° C. was circulated through the tube 13, and the temperature when the temperature of the wafer 10 became equilibrium was measured by the surface thermometer 12. The results are shown in Table 2. The wafer temperature was cooled to 55 ° C., and it was confirmed that the electrostatic chuck obtained in Example 1 had excellent cooling performance.

(Example 2) FIG. 2 (1) shows an insulating aluminum nitride substrate in which platinum pins are embedded as extraction electrodes in advance.
Film thickness of the conductive printing silver paste shown in
After coating to a thickness of 10 μm (corresponding to (1) 3a in FIG. 2), baking was performed in a reducing atmosphere at a furnace temperature of 800 ° C. for 3 hours to form a conductive pattern. Next, a silicone adhesive KE44 having a film thickness of 20 μm was screen-printed on the insulating layer (aluminum nitride-containing silicone rubber sheet 2) [FIG.
(1) 2), and bonded to the silver conductive pattern side of the insulating aluminum nitride substrate.
Press bonding was performed under the conditions of 1 kgf / cm ² , a temperature of 20 ° C. and 48 hours.
The cooling performance of the obtained electrostatic chuck shown in (1) of FIG. 2 was confirmed in the same manner as in Example 1.
It was 50 ° C, and it was confirmed that the cooling performance was excellent.

Example 3 A conductive printing tungsten paste shown in (1) of FIG. 2 was applied by screen printing to a thickness of 15 μm on an insulating boron nitride substrate in which tungsten pins were embedded as extraction electrodes in advance. After that, baking was performed at a furnace temperature of 1,000 ° C. for 3 hours to form a conductive pattern. Next, a silicone-based adhesive (KE1801) is applied to the insulating layer (boron nitride-containing silicone rubber sheet 3) by screen printing so as to have a thickness of 20 μm, and is adhered to the tungsten pattern side of the boron nitride substrate, and the pressure is 0.1 kgf / cm ^2. Press bonding was performed at a temperature of 120 ° C. for 10 minutes. When the cooling performance of the obtained electrostatic chuck shown in FIG. 2A was confirmed in the same manner as in Example 1, the wafer temperature was 40 ° C., and it was confirmed that the cooling performance was excellent.

(Example 4) A conductive liquid silicone rubber adhesive (KE3491) is applied to the upper insulating layer (silica-containing silicone rubber sheet 4) by screen printing so as to have a film thickness of 20 μm, and left at room temperature in the air for 48 hours. Then, the adhesive was cured to form a conductive pattern shown in FIG. Next, a silicone adhesive (KE44) is applied by screen printing to an alumina substrate in which copper pins are embedded as extraction electrodes in advance so as to have a thickness of 20 μm without covering the copper pins.
Next, a conductive liquid silicone rubber adhesive (KE3491) is applied onto the copper pins, and then bonded to the conductive pattern side of the insulating layer on which the conductive pattern is formed, at a pressure of 0.1 kgf / c.
Press bonding was performed under the conditions of m ² , temperature of 25 ° C. and 48 hours. The cooling performance of the obtained electrostatic chuck shown in (1) of FIG. 2 was confirmed in the same manner as in Example 1.
It was 65 ° C, and it was confirmed that the cooling performance was excellent. The electrostatic chucks obtained in Examples 1 to 4 were mounted on an ion implantation apparatus, and the ion implantation energy was 200 KV and the beam current was 1,000.
μA, ion implantation dose 2 × 10 ¹⁵ ions / cm ² , wafer 1
200,000 silicone wafers were processed under the condition that the processing time per wafer was 250 seconds. However, no increase in the temperature of the wafer and no variation in the temperature distribution were observed, and no inconvenience such as deterioration of the resist occurred.

[0020]

[Table 2]

Comparative Example 1 Using a conductive pattern having the shape shown in FIG. 1, a polyimide electrostatic chuck as shown in FIG. As a result of the cooling performance test, it was confirmed that the cooling performance was poor at a wafer temperature of 120 ° C. (Comparative Example 2) Using the conductive pattern having the shape shown in FIG. 1, an integrally formed alumina electrostatic chuck having a built-in conductive pattern as shown in FIG. As a result of testing the cooling performance by the same method, it was confirmed that the cooling performance was poor at a wafer temperature of 110 ° C. (Comparative Example 3) Using a conductive pattern having the shape shown in FIG. 1, an electrostatic chuck made of integrally molded silicone rubber having a conductive pattern built therein as shown in FIG. As a result of testing the cooling performance in the same way as
It was confirmed that the cooling performance was good at a wafer temperature of 60 ° C,
Manufacturing yield of electrostatic chuck is 50 due to complex structure
% And 100% of Examples 1-4. The cause of the decrease in yield was poor insulation between the lead wires and between the aluminum substrate and the lead wires. (Comparative Example 4) An electrostatic chuck having the structure shown in Table 3 was manufactured using the conductive pattern having the shape shown in FIG. As a result of testing the cooling performance in the same manner as in Example 1, the wafer temperature
Although the cooling performance was confirmed to be good at 50 ° C., there were many defective insulations, and the manufacturing yield of the electrostatic chuck was 60%.
Was bad compared to 100%.

[0022]

[Table 3]

[0023]

According to the structure of the electrostatic chuck of the present invention, the internal electrodes can be laid directly on the insulating ceramics of the substrate, and it is not necessary to insulate and seal the power supply lead-out electrodes unlike the conventional electrostatic chuck. Since it is extremely simple, manufacturing costs can be reduced and reliability can be greatly increased. In addition, by using an elastic silicone rubber for the insulating layer in contact with the wafer, the adhesion between the insulating layer and the wafer is improved, the contact thermal resistance can be reduced, and the cooling performance can be greatly improved. be able to.

[Brief description of the drawings]

FIG. 1 is a schematic view of an example of a conductive pattern according to the present invention.

FIG. 2 is an overall schematic view of the electrostatic chuck of the present invention obtained in 1) Example. 2) It is an enlarged view of an extraction electrode portion of the electrostatic chuck of the present invention obtained in Example 1. 3) It is an enlarged view of an extraction electrode portion of the electrostatic chuck of the present invention obtained in Examples 2 and 3.

FIG. 3 is an overall schematic view of a conventional electrostatic chuck.

FIG. 4 is a schematic view showing a method for measuring the cooling performance of the electrostatic chuck according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 (upper) insulating layer 2 adhesive layer 3a internal electrode 3b extraction electrode 4 insulating ceramic 8 cooling performance measuring instrument 9 electrostatic chuck 10 wafer 11 heater 12 surface thermometer 13 cooling water pipe 14 power supply 31 second insulating layer 32 adhesive Layer 33 First insulating layer 34 Adhesive layer 35 Metal substrate 36 Conductive pattern 37 Lead wire 38 Sealant

Continued on the front page (72) Inventor Ryuichi Handa 1-10 Hitomi, Matsuida-cho, Usui-gun, Gunma Prefecture Inside Silicone Electronic Materials Research Laboratory, Shin-Etsu Chemical Co., Ltd.

Claims (4)

[Claims] 1. An insulating ceramic substrate, comprising: a conductive pattern divided into two regions as electrodes on the substrate; and an elastic insulating layer provided on the conductive pattern. Electrostatic chuck. 2. The thermal conductivity of the insulating ceramic substrate is
2. The electrostatic chuck according to claim 1, wherein the temperature is 0.05 cal / cm.sec..degree. 3. The electrostatic chuck according to claim 1, wherein the elastic insulating layer is a cured product of a silicone rubber composition. 4. The thermal conductivity of the elastic insulating layer is 0.001 cal / cm.
The electrostatic chuck according to any one of claims 1 to 3, wherein the electrostatic chuck has a hardness of 30 ° C or more and a hardness of 30 ° to 90 °.