Patent Number: 06078640&
Section: summary

FIELD OF THE INVENTION AND RELATED ART This invention relates to an X-ray exposure apparatus for use in the manufacture of semiconductor devices, for example. Miniaturization of circuit patterns has been enhanced for an increase of operation speed and integration of a solid device such as LSI. For formation of a circuit pattern in LSI manufacturing processes, as a future exposure technique, a fine pattern forming process which is based on high luminance X-rays from a synchrotron orbit radiation (SOR), for example, is attractive. Generally, X-ray exposure methods include a proximity unit-magnification X-ray exposure method which uses those of soft X-rays having a wavelength of 0.5-2 nm, and a reduction projection exposure method which uses a reflection type mask and a wavelength of 4-20 nm. An example of the former is proposed in Japanese Laid-Open Patent Application, Laid-Open No. 100311/1990. In this method, because of a short exposure wavelength, in principle, there is a possibility of high resolution not larger than 0.1 micron. The proximity unit-magnification X-ray exposure method uses a transmission type mask, called a "unit-magnification X-ray mask". The portion of such a unit-magnification X-ray mask through which X-rays are transmitted is made of a light element material such as SiN.multidot.SiC, called a "membrane". It comprises a thin film having a thickness of about 2 microns, and a size 35 mm square. As for an X-ray absorbing portion of the unit-magnification X-ray mask, a circuit pattern made of heavy metal such as Ta or W, called an "absorptive material", having a thickness of about 0.5-1.0 micron, is formed on the membrane. Also, an optical system in the proximity unit-magnification X-ray exposure method serves to enlarge X-rays from a light source into a predetermined field size by use of an X-ray mirror, and through the X-ray mask it serves to transfer the pattern onto a wafer substrate, disposed opposed to the X-ray mask. However, an apparatus to be used in the proximity unit-magnification X-ray exposure method such as described above differs from a conventional optical exposure apparatus using ultraviolet rays, for example, and it is difficult to variably set the exposure transfer magnification, to be transferred onto a wafer substrate, by use of the X-ray optical system. More specifically, it is difficult to correct magnification with the X-ray optical system, whereas the magnification in an optical exposure apparatus can be corrected with an optical system having lens groups. As for correction of magnification in X-ray exposure apparatuses, a method has been proposed in which a mask substrate is positively deformed to thereby control the pattern magnification on a membrane. For example, an example wherein a plane stress is applied to a mask substrate is disclosed in Japanese Published Patent Application, Publication No. 66095/1992. In this method, a clamping mechanism for a mask chuck is provided with mechanical means (electrostrictive device) and, as a result of application of deformation to a mask supporting frame, the mask substrate on the supporting frame is elongated or contracted. With the pattern magnification correcting mechanism for an X-ray exposure apparatus such as described above, however, a stress along a plane or not along a plane is applied to the mask to press the mask against a reference surface, for example, to thereby cause deformation of it and correct the pattern magnification. This causes positional deviation of the pattern, and it raises a problem of degradation of pattern registration precision. SUMMARY OF THE INVENTION It is an object of the present invention to provide an X-ray exposure apparatus by which high precision exposure is assured regardless of mask magnification correction. These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.