Ceramic sintered product and process for producing the same

Abstract

Low thermal expansion ceramics contains a cordierite crystal phase, wherein a phase of a crystalline compound containing at least one element selected from the group consisting of an alkaline earth element other than Mg, a rare earth element, Ga and In, is precipitated in the grain boundaries of said crystal phase, said ceramics has a relative density of not smaller than 95%, a coefficient of thermal expansion of not larger than 1×10−6 / ° C. at 10 to 40° C., and a Young's modulus of not smaller than 130 GPa. That is, the ceramics has a small coefficient of thermal expansion, is deformed very little depending upon a change in the temperature, has a very high Young's modulus and is highly rigid and is resistance against external force such as vibration. Accordingly, the ceramics is very useful as a member for supporting a wafer or an optical system is a lithography apparatus that forms high resolution circuit patterns on a silicon wafer.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to ceramics that thermally expands little containing cordierite as a main crystal phase. In particular, the invention relates to ceramics that thermally expands little and is adapted for use in various devices used for a process for producing semiconductors, such as a semiconductor wafer support fitting like a vacuum chuck, succeptor, electrostatic chuck, or a stage or a member for supporting an optical element in a lithography apparatus.[0003]2. Description of the Prior Art[0004]The cordierite-type sintered product has heretofore been known as ceramics that thermally expands little, and has been used for filters, honeycombs and refractories. The cordierite-type sintered product is obtained by using a cordierite powder or a powder in which is mixed MgO, Al2Do3 and SiO2 in amounts capable of forming cordierite, by adding, to this powder, a sintering assistant such as an oxide of a rare earth...

AI Technical Summary

Benefits of technology

[0008]The object of the present invention, therefore, is to provide ceramics that thermally expands little and has a high rigidity (high Young's modulus) and a process for producing the same.

Problems solved by technology

With such ceramics, a change of 0.1° C. in the temperature of the atmosphere results in the deformation of about several hundred nanometers, making it no longer possible to satisfy the above-mentioned requirement of precision.

This sintered product, however, has low rigidity which is a defect.

The drop in the precision of exposure becomes conspicuous as the lines of the circuit formed by exposure to light become fine, casting a fatal problem from the standpoint of forming high resolution circuits.

When the exposure is effected relying upon such optical elements, therefore, the light beam vibrates causing the focal point to be blurred or deviated and, eventually, causing the precision of exposure to be greatly deteriorated.

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