JPH0547909A - Wafer chuck - Google Patents

Abstract

PURPOSE:To improve durability and prevent adhesion of foreign matters, by using a ceramic having high hardness and endurance as the matrix, and coating the surface with material having hardness larger than a wafer and the matrix, and structure which is not non-uniform. CONSTITUTION:Negative pressure trenches 2 are formed on the surface 1 of a chuck, and a wafer is vacuum-sucked by supplying negative pressure. The matrix of the chuck is porous Al2O3 based ceramic, whose hardness is larger than or equal to a wafer. The surface 1 of the chuck is coated. A coat is arranged on the retaining surface side of the wafer. The material of the coat is high-molecular compound softer than the wafer. After the coat is formed, grinding and lapping are performed in order to obtain flatness of the chuck surface 1. The chuck surface 1 is finished to be equivalent to the wafer surface roughness, and thinly machined in order to avoid breaking due to the difference of the thermal expansion coefficient from the matrix.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface structure of a chuck which holds a wafer and straightens it in an exposure apparatus for manufacturing semiconductor circuit elements, and a base material thereof.

[0002]

2. Description of the Related Art Conventionally, the material of a wafer supporting chuck used for manufacturing a semiconductor element is an aluminum-based metal plated with alumite (trade name). Other than that, stainless steel and alumite ceramics were used.

[0003]

However, in the aluminum of the above-mentioned conventional example, which is anodized, the base material is softer than silicon, which is the main material of the semiconductor element, so that it has scratches and dents and has a long durability. I had a problem with. The chuck made of stainless steel had the same drawbacks as aluminum. Therefore, recently, in order to improve durability, ceramics, which is a hard material, has been used. However, in the manufacturing process of ceramics,
Since uniform particles (size of several μm) are baked and solidified, they have a heterogeneous structure. In this case, even if the surface is finished by grinding or lapping, the surface becomes uneven. Foreign matter such as the photosensitive material on the back surface of the wafer easily enters the concave shape. Due to this foreign matter, the flatness of the wafer cannot be properly corrected. In this case, the foreign matter once entered cannot be easily removed due to the uneven shape. Further, since the uneven shape loses the smoothness of the surface, the wafer cannot be transferred smoothly.

The present invention has been made in view of the above-mentioned drawbacks of the prior art, and an object of the present invention is to provide a wafer chuck capable of improving durability, preventing foreign matter from adhering, and performing stable wafer straightening.

[0005]

In order to achieve the above object, according to the present invention, a ceramic having high hardness and durability is used as a base material, and its surface has a hardness higher than that of a wafer and a mother material. It is coated with a material that is harder than the material and does not have a heterogeneous structure such as ceramics.

The inhomogeneous structure of this ceramic has several μm to several tens of μ at grain boundaries when a polycrystalline state is obtained as a result of sintering.
Since it has a step and a size of m, it is difficult to remove it during the ceramics sintering process. Therefore, when forming the overcoat layer, the vacuum heating vapor deposition method,
Although the CVD method or the like is used, it is difficult to form a thin film of, for example, several tens of μm with a metal or a metal oxide on the surface of a ceramic having a large step. Therefore, in the present invention, when forming the overcoat layer, such an inorganic material is not used, but in the case of a ceramic having a large step, an organic overcoat material is used. As a result, a large step can be easily flattened. Further, in the case of the organic overcoat material, not only flatness but also smoothness can be improved. Examples of such organic overcoat materials include vinyl resins such as polytetrafluoroethylene (trade name, Teflon) and polyvinyl chloride, and silicone resins such as polysiloxane and polydimethylsiloxane,
2-4 thermosetting urea resin such as dichlorophenoxyacetic acid,
Polyethylene terephthalate and other known photoresists are effectively used. However, for the purposes of the present invention, Teflon (trade name, American EI du Pon
(Polyethylene fluoride fiber manufactured by tde Numours & Co. Inc.)
Is available in the most suitable form. The reason is that not only the flatness but also the smoothness is excellent, and the curability of the resin is great and the abrasion resistance is also good. Good heat resistance and chemical resistance are also advantages that metal overcoat materials do not have.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention is shown in FIGS. FIG. 1 shows the external appearance of a chuck for holding and flattening a wafer, and FIG. 2 shows its cross section. Reference numeral 1 denotes a chuck surface that contacts the wafer, and a wafer (not shown) is placed on the surface 1. The wafer is held by the negative pressure groove 2
Done by The negative pressure is supplied from the chuck back surface 6 through the hole 4. Further, the plane correction of the wafer is performed by the chuck surface 1 by vacuum suction through the groove 2. The chuck surface 1 is covered with a coat 3. The feature of the present invention is the coat 3, which is arranged on the wafer holding surface side. As the material of the coat 3, a polymer compound softer than the wafer, particularly Teflon (trade name, manufactured by DuPont) is effective. The Teflon film is formed by a pressure molding firing method and an extrusion molding method. It has excellent electrical properties, is stable at high temperatures (325 ° C), and does not exhibit thermoplasticity. Further, the surface has a small coefficient of friction and thus has excellent smoothness. The thickness of the coat layer is 10
μm to 60 μm, which is the thickness including the amount of grinding and lapping for obtaining the flatness of the chuck surface 1 after forming the coat. The coat thickness after grinding and lapping is 5 μm ~
The thickness of the chuck is 30 μm, and the surface of the chuck is finished to have the same roughness as the surface of the wafer. The negative pressure groove 2 is processed after grinding and lapping the chuck.
The material of the chuck base material 5 is mainly a porous structure A
It is an l ₂ O ₃ series ceramics. It is desirable that the base material 5 has a hardness equal to or higher than that of the wafer and a difference in coefficient of thermal expansion from the coat of 10 ppm or less.

A cross section of another embodiment of the present invention is shown in FIG.
In this embodiment, coat 7 covers the entire chuck surface, not just the surface that contacts the wafer. The coat 7 is formed after processing the groove 2 of the chuck, and after coating, grinding and lapping are performed. The structure of FIG. 3 has a characteristic that the coat layer is less likely to be peeled from the base material when the area in contact with the wafer is 1 mm ² or less or the width is 0.5 mm or less, as compared with the structure of FIG. ..

[0009]

As described above, the durability is improved by using ceramics as the base material of the wafer chuck, the surface of which has a hardness slightly lower than that of the wafer and does not have a non-homogeneous structure, and has a heat treatment with the base material. It is possible to prevent foreign matters from adhering to the chuck by coating the polyethylene-based fibers (particularly Teflon) having a small difference in expansion coefficient by an extrusion molding method, and further improve smoothness and flatness. As a result, it is possible to perform a stable flat surface correction of the wafer which is durable and has no foreign matter attached.

[Brief description of drawings]

FIG. 1 is an external view of a wafer chuck according to the present invention.

2 is a partial cross-sectional view of the wafer chuck of FIG.

FIG. 3 is a cross-sectional view of another embodiment of the present invention.

[Explanation of symbols]

1; chuck surface, 2; negative pressure groove, 3; coat, 4; negative pressure supply hole, 5; chuck base material, 6; back surface, 7; coat.

Claims (2)

[Claims] 1. A wafer chuck having a negative pressure groove for adsorbing a wafer on the wafer mounting surface side and a base material made of ceramics, wherein the surface of the ceramic base material is overcoated with a polymer compound. Wafer chuck to do. 2. The wafer chuck according to claim 1, wherein the polymer compound is made of polyfluoroethylene fiber.