Patent Number: 048521337
Section: summary

BACKGROUND OF THE INVENTION The present invention relates to an X-ray pattern transfer apparatus also referred to as the X-ray lithography apparatus for transferring a fine pattern formed in a mask to a wafer by using a soft X-ray. As a hitherto known X-ray lithography apparatus, there can be mentioned the one disclosed in Japanese Patent Application Laid-Open No. 169242/1982 (JP-A-57-169242) which corresponds to U.S. Pat. No. 4,403,336. Referring to FIG. 3 of the accompanying drawings, this known X-ray lithography apparatus includes a gas chamber having an X-ray receiving window which is disposed on a side of an X-ray generating unit 1 where an X-ray exit window is provided. The gas chamber 2 accommodates therein a gaseous medium having a high transmissivity to the X-ray. A mask 3 having a desired pattern formed therein is mounted on the X-ray lithography apparatus 1 so as to cover an aperture formed in a wall of the gas chamber 2 at a position opposite to the X-ray receiving window. A wafer stage 5 is provided outside of the gas chamber 2 for holding a wafer 4 in an ambient atmosphere so as to be exposed to the X-ray through the mask 3, while allowing the wafer 4 to be moved relative to the mask 3. Disposed within the gas chamber 2 is an optical system 6 which serves to aid positional alignment to be attained between the pattern of the mask and the wafer through visual observation. With a view to preventing the purity of helium gas filling the gas chamber 2 from being degraded due to admixing of the air possibly occurring upon replacement of the mask, a helium gas cylinder (bomb) 7 is provided in communication with the gas chamber 2 so that an amount of helium gas is constantly supplied to the chamber 2 with a corresponding amount of gas being discharged through a drain duct 8. However, the flow of helium gas within the chamber 2 is extremely small and can thus be neglected. Further disposed within the gas containing chamber 2 are a light source for illumination of the viewing or detecting optics 6, a television camera 9, an optics positioning mechanism 10, a mask positioning device 11 and other. These components constitute heat generating sources within the gas chamber 2. Additionally, thermal flux produced by the soft X-ray generating unit 1 may flow into the gas chamber 2 through the X-ray exit window 12. In the case of the hitherto known X-ray lithography apparatus reviewed above, no consideration is paid to removal of heat generated within the gas chamber 2 by the imager system and others mentioned above. Consequently, thermal distortion or deformation is likely to occur in the viewing or detecting optics, which results in occurrence of a drift of the detected values representative of the relative positions of the mask 3 and the wafer 4, giving rise to a problem that the accuracy of positional alignment is undesirably degraded. Under the circumstance, the X-ray lithography apparatus known heretofore can be used only after a warm-up operation which is continued until the temperature rise due to the heat generation has attained a saturated state. This warm-up operation usually takes several hours or more. Consequently, the X-ray lithography apparatus has to be operated continuously day and night in order to ensure a high working ratio. Further, such drift can occur when the operating condition is changed. Parenthetically, it is noted that an X-ray lithography apparatus including means for preventing the temperature of a mask from being raised is disclosed in Japanese Patent Application Laid-Open No. 191433/1983 (JP-A-58-191433). SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an X-ray lithography apparatus which is protected against occurrence of drifts in the optically detected position due to temperature rise brought about by positional alignment detecting/imaging means and others and which can be operated with a high accuracy even a short time after power-on of the apparatus. In view of the above object, it is proposed according to an aspect of the present invention an X-ray lithography apparatus which includes a gas chamber filled with a gas such as helium gas for preventing attenuation of X-ray and has a mask mounted at a position to be irradiated with the X-ray, imaging means disposed within the gas chamber for detecting an alignment mark used for alignment of a wafer with the mask, a gas discharge port provided in the gas chamber in the vicinity of the imaging means, a gas recharging port provided at such a position where the cooled gas such as helium gas or the like is circulated uniformly within the gas chamber, and a blower and a heat exchanger both provided between the gas discharge port and the gas recharging port to circulate and cool the gas such as helium gas, to thereby prevent the detecting optics from undergoing thermal deformation due to heat generated by the imaging means. With the arrangement described above, heat generated by the imaging means is prevented from being transmitted to the interior of the gas chamber and bringing about thermal deformation of the detecting optics and other elements, whereby the mask and the wafer can be aligned with each other at an improved accuracy without being accompanied with drifts in the detected position signal.