Patent Number: 051538989
Section: summary

FIELD OF THE INVENTION AND RELATED ART The present invention relates to a projection exposure apparatus, more particularly to an X-ray reduction projection exposure system of the reflection type and an X-ray reduction imaging system particularly usable for effecting high resolution printing. In the field of semiconductor circuit manufacturing, exposure apparatuses such as mask aligners and steppers are widely used to print a circuit pattern from a mask or reticle onto a wafer. The recent trend to the high density of the semiconductor chips such as IC and LSI increases the need for an exposure apparatus capable of very high resolution printing. Various researches and developments are being made to provide an exposure apparatus which can replace the recently used deep UV light. In general, in the exposure apparatuses of this type, more particularly to projection exposure apparatuses such as steppers, the minimum line width which is printable by the apparatus, represented by resolution power, is determined by wavelength of light used and a numerical aperture of the projection optical system. As regards the numerical aperture, the resolution increases with increase of the numerical aperture, but the increase of the numerical aperture leads to shorter depth of focus, with the result that the image to be printed or transferred is blurred due to very small defocusing. For this reason, it is considered from the standpoint of optical design that obtaining high resolution by changing the numerical aperture is difficult. In view of this, efforts have been made to accomplish high resolution by using as the projection energy ray, a beam produced by an excimer laser or the like and X-rays which are relatively short in wavelength. Particularly, the X-ray exposure apparatus is expected as an exposure apparatus of the next generation, and an X-ray exposure apparatus in a proximity type has been proposed. However, the currently proposed proximity type X-ray exposure is still not satisfactory in that the resolution is not enough for an ultra LSI such as 64 mega bit DRAM or higher density requiring very high resolution on the order of submicrons. Another problem is that a highly accurate pattern must be formed on a mask. SUMMARY OF THE INVENTION Accordingly, it is a principal object of the present invention to provide an X-ray reduction projection exposure system of reflection type and an X-ray reduction projection imaging system of reflection type, not the conventional proximity type. It is another object of the present invention to provide an X-ray reduction projection exposure system of reflection type capable of printing images in high resolution on the order of submicrons. It is a further object of the present invention to provide an X-ray reduction projection exposure system of reflection type capable of effecting printing in very high resolution. According to an embodiment of the present invention, there is provided a system comprising means for directing X-rays to a mask and a projection imaging system for forming an image of a mask pattern in a predetermined reduced magnification or scale. Therefore, the pattern of the mask can be transferred in a reduced scale onto a wafer disposed at an imaging position by way of a projection exposure system. These and other objects, features and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.