JP2000326170A - Elastically deformable electrostatic chuck and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatic chuck having good following ability during elastic deformation and heat radiation ability by embedding a electrically conductive silicone rubber having thermal conductivity higher than a specific value and volume specific resistivity lower than a specific value in a highly-thermal- conductive silicone rubber cured material with thermal conductivity higher than a specific value. SOLUTION: This electrostatic chuck 3 supports the rear surface of a wafer 4 by combination with support projections 2 on a stage 1, and is elastically deformable in the vertical direction. This electrostatic chuck 3 is constructed by embedding an electrically conductive silicone rubber in a high-thermal- conductive silicone rubber cured material. Thermal conductivity of the highly- thermal-conductive silicone rubber cured material is set higher than 0.5 W/m. deg.C, thermal conductivity of the electrically conductive silicone rubber cured material is set higher than 0.5 W/m. deg.C, and volume specific resistivity is lower than 1,000 Ω.cm. The electrostatic chuck 3 is manufactured by thermal compression integral simultaneous molding of an uncured sheet-like pre-form.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic chuck capable of holding a wafer without being deformed, and a method of manufacturing the same.
The present invention relates to an elastically deformable electrostatic chuck used for a wafer holding mechanism capable of efficiently cooling a wafer and a method of manufacturing the same.

[0002]

2. Description of the Related Art In most current semiconductor manufacturing processes, a mechanical chuck or an electrostatic chuck is used because a vacuum chuck cannot be used. In the case of an electrostatic chuck, the wafer is vertically restrained on the surface of the electrostatic chuck by the attraction force. Also, the wafer is restrained in its plane by the frictional force generated when the wafer is pressed against the surface of the electrostatic chuck.

In a general semiconductor process, it is desirable to deform and hold a wafer that is free and warped, such as an electrostatic chuck (hereinafter, referred to as flattening). On the other hand, in a process such as manufacturing a mask for X-ray exposure, holding a wafer in a free state instead of holding it in a deformed state (hereinafter referred to as “non-deformed holding”) is a problem of overlay error and in-film stress. Is required to reduce

[0004]

As such a non-deformation holding mechanism, Japanese Unexamined Patent Publication No. Hei 6-132388 discloses a support projection for supporting the back surface of a wafer, an installation of the support projection, and an elastic deformation in the vertical direction of the wafer surface. There has been proposed a wafer holding mechanism including a thin electrostatic chuck. As specific examples, an electrostatic chuck having a structure in which a thin metal foil and an organic insulator are bonded to each other, an electrostatic chuck having a structure in which an insulating substance is welded to the metal foil, and a metal deposited or deposited on the thin insulator. An electrostatic chuck having a plated structure is exemplified.

However, in any of these cases,
There has been a problem that the ability of the electrodes of the electrostatic chuck to follow deformation during elastic deformation is not sufficient. Further, even in an electron beam lithography apparatus used in a process of manufacturing a mask for X-ray exposure, deformation of the mask substrate due to heat generated on a silicon wafer serving as the mask substrate during the process has become a problem, and heat dissipation performance has been increasing. It became clear that it was necessary to use an electrostatic chuck excellent in the above.

The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems. As a result, when conductive silicone rubber is used as an electrode, the electrostatic chuck has excellent followability during elastic deformation and excellent heat dissipation performance. The inventors have found that the present invention has been achieved. Accordingly, a first object of the present invention is to provide an electrostatic chuck which is used in a wafer holding mechanism capable of efficiently cooling a wafer and has excellent followability during elastic deformation and excellent heat dissipation performance. A second object of the present invention is to provide a method for manufacturing an electrostatic chuck having excellent followability during deformation and excellent heat dissipation performance.

[0007]

SUMMARY OF THE INVENTION A first object of the present invention is to:
An electrostatic chuck in which a conductive silicone rubber is embedded inside a cured product of a high thermal conductive silicone rubber, which is used in combination with a support projection for supporting a back surface of a wafer and is elastically deformable in a vertical direction of the back surface of the wafer. The cured product of the high thermal conductive silicone rubber has a thermal conductivity of 0.5 W / m · ° C. or more, and the cured product of the conductive silicone rubber has a thermal conductivity of 0.5 W / m · ° C. or more and has a specific volume. A second object is to provide an elastically deformable electrostatic chuck having a resistivity of 1,000 Ω · cm or less and a thermal conductivity after curing of 0.5 W / m · ° C. or more. It functions as an electrode having a thermal conductivity of 0.5 W / m · ° C. or more and a volume resistivity of 1,000 Ω · cm or less on an uncured sheet preform of a high thermal conductive silicone rubber compound. After placing an uncured sheet preform or sheet-like cured product of silicone rubber compound, it is heated and pressurized and integrally molded together, then cured or uncured sheet-shaped preform on the previously cured electrode The method for manufacturing an elastically deformable electrostatic chuck according to claim 1 is characterized in that, after being installed, it is heated and pressed to be integrally molded simultaneously.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a conceptual diagram of a wafer support mechanism in which an electrostatic chuck 3 of the present invention and a support projection 2 supporting the back surface of a wafer 4 are combined. FIG. 1A is a plan view of FIG.
The figure is a sectional view taken along line AA.

In the present invention, the thermal conductivity of the high thermal conductive silicone rubber is preferably 0.5 W / m · ° C. or more, so that the temperature of the wafer is prevented from rising due to heat, and the temperature of the wafer is made uniform and constant to achieve high precision. It is necessary to enable drawing of. Since it is important to improve the adhesion to the wafer and reduce the contact thermal resistance, the surface shape of the elastic body, which is the electrostatic chuck, easily follows the back surface shape of the wafer due to the suction force acting on the wafer. It is necessary to deform.

Accordingly, the elastic body on the surface of the electrostatic chuck (ie,
Hardness of high thermal conductive silicone rubber) is 20 ~
It is preferably 90 (JIS-A). If it is less than 20, the adhesiveness between the surface of the cured product of the high thermal conductive silicone rubber and the back surface of the wafer becomes high, and when the wafer is peeled off from the electrostatic chuck, the wafer is strongly adhered to the electrostatic chuck due to the adhesive force, so the peeling is not performed. There is a problem that it becomes difficult. On the other hand, when it exceeds 90, the deformation of the cured product of the silicone rubber composition due to the adsorption force decreases, the followability to the back surface of the wafer decreases, and the contact thermal resistance increases, which is not preferable.

The properties of the silicone rubber compound before curing may be either a millable type or a liquid type, and the curing form may be a peroxide curing type, an addition reaction curing type, a condensation curing type, an ultraviolet curing type, or the like. Various curing types can be used. In the present invention, a millable peroxide-curable or addition-reaction-curable compound is particularly suitable.

The filler for imparting high thermal conductivity to the silicone rubber compound may be a high thermal conductive ceramic powder such as alumina powder, aluminum nitride powder, boron nitride powder, silicon nitride powder, magnesium oxide powder or silica powder. Is preferred. The content of the above filler is 0.5W / m
-It is an amount necessary to provide thermal conductivity of at least ° C. The thickness is preferably as thin as possible from the viewpoint of heat dissipation,
From the viewpoint of the performance as an electrostatic chuck, those having a range of 50 to 500 μm are preferable. When the thickness is less than 50 μm, the withstand voltage decreases, and the probability that the electrostatic chuck causes dielectric breakdown increases, which is disadvantageous. On the other hand, if it exceeds 500 μm, the heat radiation property is reduced, and the cooling efficiency of the wafer is deteriorated, which is disadvantageous.

Further, the surface roughness of the thermally conductive silicone rubber surface affects the adhesion to the wafer and the contact thermal resistance between the wafer and the thermally conductive silicone rubber surface, but the maximum surface roughness (Ry) Is preferably less than 20 μm in order to improve the adhesion between the electrostatic chuck and the wafer. 20
If it exceeds μm, the heat radiation property is reduced, and the cooling efficiency of the wafer is deteriorated, which is disadvantageous. For the purpose of adjusting the strength and hardness of the cured product of the high thermal conductive silicone rubber, various fillers such as a coloring agent and a flame retardant may be added.

The properties of the conductive silicone rubber compound as an electrode of the electrostatic chuck before curing may be either a millable type or a liquid type. As the curing mode, various curing types such as a peroxide curing type, an addition reaction curing type, a condensation curing type, and an ultraviolet ray curing type can be used. In the present invention, millable peroxide-curable and addition-reaction-curable compounds are particularly preferred.

Examples of the conductive filler include carbon black, acetylene black, conductive furnace black, superconductive furnace black,
Conductive carbon powder such as extra-conductive furnace black, conductive channel black, furnace black or channel black heat-treated at a high temperature of about 1500 ° C, or metal powder such as gold, silver, steel, nickel, or their metals Examples thereof include beads and the like.

The amount of the conductive filler added is such that the thermal conductivity after curing is 0.5 W / m · ° C. or more and the volume specific resistivity is
What is necessary is just to mix | blend the quantity used as 1,000 ohm * cm or less. Also,
From the point of heat dissipation, it is advantageous that the thickness is as thin as possible.
Those having a range of μm are preferred. If it is less than 1 μm, the film strength is disadvantageously reduced. On the other hand, when the thickness exceeds 500 μm, heat dissipation and flexibility are reduced, and the cooling efficiency of the wafer is deteriorated, which is disadvantageous.

Next, a method of manufacturing the elastically deformable electrostatic chuck of the present invention will be described. Step (1): As shown in FIG. 2, the thermal conductivity after curing is
An addition-curable or peroxide-curable high-thermal-conductivity silicone rubber compound adjusted to 0.5 W / m · ° C. or more is calender-molded or coated on a plastics resin film as a process paper to a thickness of 0.05 to 5 mm. 0.
It is formed as a sheet-like preform with a uniform thickness in the range of 5 mm.

The process paper used in the present invention is made of plastic, and the material thereof is polyethylene terephthalate, polyethylene naphthalate, nylon,
Polyethylene, polypropylene, PTFE, FEP, PFA, ETF
E, polyimide and the like. The thickness is preferably from 25 to 150 μm. If the thickness is less than 25 μm, the strength may be insufficient, and it may be damaged during the process. On the other hand, if it exceeds 150 μm, the flexibility is impaired, so that problems may occur in calender molding.

Step (2): As shown in FIG. 3, an addition in which the thermal conductivity after curing to be an electrode is 0.5 W / m · ° C. or more and the volume resistivity is adjusted to 1000 Ω · cm or less. A curable or peroxide-curable conductive silicone rubber compound is calendered or coated on a plastic resin film, which is process paper, to a thickness of 0.05.
It is formed as a sheet-shaped preform with a uniform thickness in the range of 0.5 mm. In the present invention, a cured sheet obtained by previously curing the conductive silicone rubber may be used. Use a mold to make a cured sheet, 100-200 ° C, 1-80
It may be hot-pressed for 1 to 30 minutes under the condition of kgf / m ² or heated for 1 to 30 minutes under hot air at 150 ° C.

Step (3): As shown in FIG. 4, the sheet-like preform lined with the process paper obtained in the steps (1) and (2) is laminated and put into a mold.
2), 100 ℃ ~200 ℃, 1~30 under a pressure 1~80kgf / ^{m 2}
(4-3) to produce a laminated sheet (4-4) of high thermal conductive silicone rubber and conductive silicone rubber. At this time, each sheet-shaped preform is
As shown in 5, it is preferable to perform a die cutting process on a plastic resin film as a process paper with a predetermined planar contour shape. Further, it is preferable that the contour dimension of the sheet-shaped preform of the conductive silicone be smaller than the contour dimension of the sheet-shaped preform of the highly heat-conductive silicone.

Step (4): As shown in FIG. 6, the process paper of the laminated sheet obtained in step (4) is peeled off (4-
5) The conductive silicone rubber surface and the preform (5-4) of the high heat conductive silicone obtained in the same manner as in the step (1) are put in a mold in a state where they are attached to each other.
2), 100 ℃ ~200 ℃, 1~30 under a pressure 1~80kgf / ^{m 2}
(6-3) to produce a laminated sheet having a structure in which conductive silicone rubber is sandwiched between highly thermally conductive silicone rubber layers (6-4). Finally, the electrostatic chuck 22 is obtained by peeling the process paper. At this time, the contour dimension of the sheet-like preform of high thermal conductive silicone is determined by the process.
It is preferable that the contour dimensions are the same as those of the sheet-shaped preform of the highly heat-conductive silicone of No. 3.

[0022]

According to the electrostatic chuck of the present invention, since all of the electrodes and the insulating layer are made of silicone rubber elastic material, it is suitable for a non-deformable holding mechanism having support projections, and is capable of following heat radiation during elastic deformation. An electrostatic chuck with excellent characteristics. Further, the method for manufacturing an electrostatic chuck of the present invention can improve the handling workability of a sheet-shaped preform of a silicone compound by using a plastic film as a process paper in the process, and furthermore, the process paper can be used. By charging the preform in the mold with the backing, it is possible to prevent the mold from being stained with silicone.

[0023]

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.

Composition Examples 1-4. A: average degree of polymerization composed of 99.85 mol% of dimethylsiloxane units and 0.15 mol% of methylvinylsiloxane units
8,000 methyl vinyl polysiloxane B: di-t-butyl peroxide C: alumina powder (AS23: trade name, manufactured by Showa Denko KK) D: aluminum nitride powder (XUS-35548: trade name, manufactured by Dow Chemical Co., Ltd.) E: Boron nitride powder (KBN- (h) 10: Shin-Etsu Chemical Co., Ltd.)
Product name) F: Silica powder (Crystalite: product name, manufactured by Tatsumori Co., Ltd.) Using the raw materials selected from A to F above, high thermal conductive silicone rubbers of composition examples 1 to 4 shown in Table 1 A compound was prepared. Next, using a calender roll, a sheet was formed on a 100 μm-thick polyethylene terephthalate film, which is a process paper.

[0025]

[Table 1]

Composition Examples 5 and 6 G: average degree of polymerization composed of 99.85 mol% of dimethylsiloxane units and 0.15 mol% of methylvinylsiloxane units
8,000 methylvinylpolysiloxane H: di-t-butyl peroxide I: orthomethylbenzoyl peroxide J: acetylene black (manufactured by Denki Kagaku Kogyo KK) K: silver powder AgC-BO (Fukuda Metal Foil Powder Co., Ltd.) L) Fumed silica surface-treated with hexamethyldisilazane (specific surface area: 200 m ² / g)

Using the raw materials selected from G to L, conductive silicone rubber compounds shown in Table 2 were prepared.

[Table 2]

The conductive silicone rubber compound of Composition Example 5 was formed into a sheet-shaped preform on a polyethylene terephthalate film (film thickness: 100 μm) as process paper using a calender roll. Further, the conductive silicone rubber compound of Composition Example 6 was diluted with xylene so as to be 50% by weight in terms of a solid component weight ratio, coated on a polyethylene terephthalate film (100 μm thick), and dried to obtain a sheet-like preform. Made and further
Hot press molding was performed at 170 ° C. and 20 kgf / cm ² for 10 minutes.

Embodiment 1 Sheet-shaped preform of high thermal conductive silicone rubber compound of composition example 1 and composition example 5
After using the sheet-shaped preform of the conductive silicone rubber compound of Example 1 and laminating it by the production method shown in Steps 1 to 4, the high thermal conductive silicone rubber layer of Composition Example 1 was applied to the conductive silicone rubber surface in accordance with Steps 5 and 6. Were further laminated to produce an electrostatic chuck. Using the obtained electrostatic chuck, an X-ray exposure mask was manufactured by an electron beam lithography system having a wafer holding mechanism shown in FIG. 1, and as a result, the position of the wafer could be prevented from being shifted, and the heat generated on the wafer could be prevented. It was confirmed that cooling was also possible efficiently. The obtained mask was a good X-ray exposure mask.

Embodiments 2-4. An electrostatic chuck was manufactured in exactly the same manner as in Example 1 except that the high thermal conductive silicone rubber compound of Composition Examples 2 to 4 was used instead of the high thermal conductive silicone rubber compound of Composition Example 1. Using the obtained electrostatic chuck, a mask for X-ray exposure was manufactured by an electron beam lithography apparatus having a wafer holding mechanism shown in FIG. 1. It was confirmed that cooling was also possible efficiently. The obtained mask was a good X-ray exposure mask.

Embodiment 5 FIG. An electrostatic chuck was manufactured in exactly the same manner as in Example 1, except that the conductive silicone rubber cured sheet of Composition Example 6 was used instead of the conductive silicone rubber compound sheet-like preform of Composition Example 5. Using the obtained electrostatic chuck, a mask for X-ray exposure was manufactured by an electron beam lithography apparatus having a wafer holding mechanism shown in FIG. 1. It was confirmed that cooling was also possible efficiently. The obtained mask was a good X-ray exposure mask.

Embodiments 6-8. An electrostatic chuck was manufactured in exactly the same manner as in Example 2-4 except that the conductive silicone rubber cured product sheet of Composition Example 6 was used instead of the conductive silicone rubber compound sheet-shaped preform of Composition Example 5. . Using the obtained electrostatic chuck, an X-ray exposure mask was manufactured using an electron beam lithography system having a wafer holding mechanism shown in FIG. 1. It was confirmed that cooling was possible efficiently. The obtained mask was a good X-ray exposure mask.

Comparative Example 1 A 12 μm steel foil as an electrode was sandwiched and laminated between polyimide films each having a thickness of 25 μm to manufacture an electrostatic chuck having the same contour dimensions as the example.
Using the obtained electrostatic chuck, as a result of manufacturing a mask for X-ray exposure with an electron beam drawing apparatus having a wafer holding mechanism shown in FIG. The heat generated on the wafer could not be cooled, and a mask for X-ray exposure could not be manufactured.

Comparative Example 2 A copper foil of 12 μm was sandwiched and laminated between the thermally conductive silicone rubber layers used in Composition Example 1 to manufacture an electrostatic chuck having the same contour dimensions as the example. Using the obtained electrostatic chuck, a mask for X-ray exposure was manufactured by an electron beam lithography apparatus having a wafer holding mechanism shown in FIG. 1. The heat could not be cooled, and an X-ray exposure mask could not be manufactured.

Embodiment 6 FIG. As a result of manufacturing the electrostatic chuck without using the process paper used in the process of Example 1, the manufacturing time was about three times as long as the process paper was used. In addition, the mold was stained. The dimensions of the obtained electrostatic chuck varied greatly. Using the obtained electrostatic chuck, an X-ray exposure mask was manufactured by an electron beam lithography system having a wafer holding mechanism shown in FIG. 1, and as a result, it was impossible to prevent the displacement of the wafer and to cool the heat generated on the wafer. The production yield of the mask for X-ray exposure was not good.

By using a plastic film as a process paper as in Examples 1 to 5, the workability of handling a sheet-shaped preform of a silicone rubber compound is improved, and the process paper is attached to a mold. It was confirmed that by charging the preform, it was possible to prevent the mold from being stained by silicone. Further, since each rubber layer is integrated by a cross-linking reaction in the lamination process of each silicone rubber layer, there is no need to use a primer, an adhesive or the like, so that the manufacturing process is simplified, thereby reducing costs. be able to. Furthermore, the electrostatic chuck of the present invention has excellent flexibility, not only can hold the wafer without deformation, but also has excellent heat dissipation, so that the wafer can be efficiently cooled. Has been demonstrated.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a wafer support mechanism having a support protrusion. (1-1) is a plan view, and (1-2) is a sectional view taken along the line AA.

FIG. 2 is a diagram showing a relationship between process paper and a high thermal conductive silicone rubber preform. (2-1) is a plan view (2)
-2) FIG.

FIG. 3 is a diagram showing a relationship between process paper and a conductive silicone rubber preform. (3-1) Figure is a plan view, (3-
2) FIG.

FIG. 4 is an explanatory view of a step of laminating a sheet-like preform lined with process paper, placing the preform in a mold, and producing a laminated sheet of a high thermal conductive silicone rubber and a conductive silicone rubber by hot pressing.

FIG. 5 is a diagram illustrating the relationship between the sheet-shaped preform and the size of process paper. (5-1) and (5-2)
When the sheet-shaped preform and the process paper are the same size, (5-
FIGS. 3) and (5-4) show the case where the sheet-shaped preform is smaller than the process paper.

FIG. 6: A preform of high thermal conductive silicone rubber formed on process paper is attached to the surface of the conductive silicone rubber layer of the laminated sheet of high thermal conductive silicone rubber and conductive silicone rubber, and the preform is heated and pressed. It is explanatory drawing of the process of manufacturing the electrostatic chuck of this invention.

[Explanation of symbols]

1． Stage 2. Support projection 3. Electrostatic chuck 4. Wafer 5. Insulating spacer E +. Plus power supply E-. Negative power supply G. Ground 6. Mold 6A. Upper die 6B. Lower mold 7． 7. Conductive silicone rubber sheet preform or conductive silicone rubber cured product sheet Process paper. High thermal conductive silicone rubber or sheet preform 10. Conductive silicone rubber cured product 11A. High thermal conductive silicone rubber cured product 11B. Highly thermally conductive silicone rubber cured product 12. 21. Conductive silicone rubber cured product + high thermal conductive silicone rubber cured product laminated sheet Mold 21A. Upper model 21B. Lower mold 22. Electrostatic chuck reference number P99-818

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Ryuichi Handa 1-10 Hitomi, Matsuida-cho, Usui-gun, Gunma Prefecture F-term in the Silicon Electronics Research Laboratory, Shin-Etsu Chemical Co., Ltd. 3C016 GA10 5F031 CA02 HA02 HA08 HA16 MA27

Claims (3)

[Claims] 1. A statically deformable silicone rubber which is used in combination with a support protrusion for supporting a back surface of a wafer, wherein the conductive silicone rubber is embedded in a cured product of a highly thermally conductive silicone rubber, and which can be elastically deformed in the vertical direction of the back surface of the wafer. An electric chuck, wherein the thermally conductive silicone rubber cured product has a thermal conductivity of 0.5 W / m · ° C. or more, and the conductive silicone rubber cured product has a thermal conductivity of 0.5 W / m · An elastically deformable electrostatic chuck having a volume specific resistivity of 1,000 Ω · cm or less at a temperature of at least ℃. 2. The heat conductivity after curing is 0.5 W / m · ° C.
On the uncured sheet preform of the high thermal conductive silicone rubber compound as described above, a thermal conductivity of 0.5 W /
m · ℃ or higher and volume resistivity is 1,000Ω
Cm or less, an uncured sheet-shaped preform or a sheet-shaped cured product of a silicone rubber compound functioning as an electrode that is not more than cm is placed, and then heat-pressed and integrally molded simultaneously, and then cured, or previously cured. The method for manufacturing an elastically deformable electrostatic chuck according to claim 1, wherein an uncured sheet-shaped preform is placed on the electrode, and then heat pressed and integrally molded at the same time. 3. The method for producing an elastically deformable electrostatic chuck according to claim 2, wherein the uncured sheet-like preform is used while being backed by process paper.