Patent Number: 051289750
Section: summary

FIELD OF THE INVENTION AND RELATED ART This invention relates to an X-ray exposure system for use in the manufacture of semiconductor chips and, more particularly, to an X-ray exposure system for exposing a semiconductor wafer to a mask with X-rays contained in synchrotron radiation, to print a pattern of the mask on the wafer. FIG. 4 shows an example of a known type X-ray exposure apparatus. Denoted in this Figure at 37 is a filament for emitting thermoelectrons 39; at 38 is a pulling electrode for drawing the thermoelectrons 39 to a target 40; at 42 is a vacuum chamber by which the filament 37 and the target 40 are kept in a vacuum ambience; and at 43 is a beryllium window which functions as a partition for isolating the vacuum ambience in the vacuum chamber 42 from the atmosphere. X-rays 41 from the target 40 pass through the beryllium window 43 into the atmosphere. Denoted at 44 is a frame for supporting the vacuum chamber 42; at 45 is a mask stage for holding an X-ray mask 1; at 47 is a wafer stage for holding a wafer 46; at 48 is a surface plate which serves as a base for supporting the frame 44, the mask stage 45 and the wafer stage 47; and at 49 is an air spring means provided for vibration isolation of the surface plate 48. The air spring means 49 is effective to suppress the natural vibration frequency of the exposure apparatus as a whole, structured on the surface plate 48, on order of a few Hertz and to render the apparatus as a whole insensitive to high-frequency external vibration. Also, in this apparatus, the entire structure is placed on the surface plate 48, and the relative position of the mask 1 and the illumination area by the X-rays 41 is determined unconditionally. Then, in the illustrated state, the X-rays 41 are projected on the mask 1 and then on the wafer 46, whereby a pattern of the mask 1 is printed on the wafer 46. Another example is an X-ray exposure system having, as an X-ray source, a synchrotron orbit radiation (SOR) ring adapted to produce synchrotron radiation. In this type of exposure system, an SOR ring (X-ray source) is disposed, not on a surface plate such as at 48 in FIG. 4, but on a floor (ground), separately from the surface plate. In an exposure system of the type using synchrotron radiation, in which an illumination system having an exposure energy source is disposed on a floor or otherwise, separately from a stage system for holding a mask and a wafer, there is a possibility of a change in orientation of the mask or the wafer relative to the exposure energy supplied from the illumination system. Therefore, the vibration isolation of the surface plate, such as that made to the surface plate 48 in FIG. 4, is not sufficient to ensure that the pattern of the mask is printed on the wafer without any pattern superposing error. Namely, it is necessary to continuously maintain the attitude of the stage system constant. The attitude of a stage system may be maintained constant, in the FIG. 4 example, by controlling the attitude of the mask 1 and the wafer 46 (lying substantially horizontally) by using the air spring means 49. However, this method cannot be directly applied to an X-ray exposure system using synchrotron radiation. This is because of the fact that the synchrotron radiation is emitted approximately horizontally from the SOR ring and that it is very difficult to change the direction of advancement to a vertical direction as in the FIG. 4 example. Referring to FIG. 5, a possible pattern superposing error in an X-ray exposure system having an SOR ring as a light source, will be explained. Denoted in FIG. 5 at 50 is a point of radiation emission of the SOR ring (or a point of reflection on an X-ray reflecting mirror for reflecting the synchrotron radiation from the SOR ring); at A is the distance from the emission point 50 to a mask 1; at B is the view angle for exposure (X-ray illumination area); at C is the proximity gap between the mask 1 and a wafer 46; at .epsilon.w.sub.x is the quantity of pattern superposing error which occurs when, in a state where there is no relative displacement between the mask 1 and the wafer 46, the mask and the wafer are inclined by .DELTA.w.sub.x from a plane which is perpendicular to the axis of the synchrotron radiation beam; and ".epsilon.1-.epsilon.2" represents the quantity of pattern superposing error which occurs when, in a state where there is no relative displacement between the mask 1 and the wafer 46, both the mask and the wafer are shifted by .DELTA.y from the axis of the synchrotron radiation beam. Assuming in FIG. 5 that: A=4500 (mm) PA1 B=30 (mm) PA1 C=0.05 (mm) PA1 .DELTA.y=1 (mm) PA1 .DELTA.w.sub.x =5.times.10.sup.-4 (rad) then the pattern transfer error (superposing error) .epsilon.y (=.epsilon.1-.epsilon.2) resulting from the shift .DELTA.y can be expressed as follows: ##EQU1## On the other hand, the pattern transfer error (superposing error) .epsilon.w.sub.x resulting from the inclination .DELTA.w.sub.x can be expressed as follows: ##EQU2## It is accordingly an object of the present invention to provide an X-ray exposure system by which the attitude and position of a mask and a wafer relative to a synchrotron radiation beam can be retained at high precision and, as a result, precise pattern printing is ensured. In accordance with an aspect of the present invention, to achieve this object, there is provided an exposure system for exposing a wafer to a mask with X-rays contained in sychrotron radiation to print a pattern of the mask on the wafer, wherein the mask and the wafer are supported by a frame member so that their surfaces are disposed substantially parallel to a vertical direction, wherein the frame member is supported by means of a plurality of vibro-isolating mechanisms so that the former can be displaced relative to the surface of a floor on which the vibro-isolating mechanisms are supported, and wherein these vibro-isolating mechanisms can be controlled and actuated independently of each other, whereby the attitude of the mask and the wafer with respect to the synchrotron radiation beam as well as the position of the frame memh=, with respect to the radiation beam, can be maintained substantially constant. 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.