Patent Number: 051951134
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS For a better understanding of the present invention, a conventional X-ray exposure apparatus will be first described with reference to FIGS. 3 and 4. Referring to FIG. 3, X-ray beams 1 irradiated from a synchrotrons, are reflected by a reflecting mirror M. The X-ray beams 1 enter a chamber 5 defined by a casing 5a of an exposure apparatus body 4 through a port 2 under an extremely high vacuum state and an X-ray take-out window 3 formed at a front end of the port 2. The interior of the chamber 5 is of a helium atmosphere for preventing the X-ray beams 1 from being attenuated, and in the inside of the chamber 5 are accommodated a mask stage 7 holding an X-ray mask 6 to be movable, a wafer stage 9 holding a semiconductor wafer 8 to be movable and an alignment optical system 10 for detecting a positional offset between patterns described on the X-ray mask 6 and the semiconductor wafer 8. According to this structure of the X-ray exposure apparatus, the X-ray beams 1 entering the chamber 5 of the exposure apparatus body 4 are irradiated on the X-ray mask 6, through which then irradiated on the surface of the semiconductor wafer 8 thereby to expose a circuit pattern of the X-ray mask 6 onto the semiconductor wafer 8. The exposure apparatus body 4 is mounted on an oscillation removing table 12 which is set on a floor 13 as a reference base through an elastic member such as an air spring 11, thus effectively preventing the exposure apparatus body 4 from being oscillated or affected by external shock or the like from the floor 13. The X-ray beams 1 obtained by a synchrotron orbit radiation (SOR) constitute horizontal linear beams irradiated in a horizontal direction. In order to enlarge an irradiated area for carrying out an exposure transfer of the circuit pattern of the X-ray mask 6 onto the semiconductor wafer 8, the X-ray reflecting mirror M is arranged between the synchrotrons and the exposure apparatus body 4, and the X-ray beams 1 are swinged by swinging the reflecting mirror. The reflected X-ray beams 1 from the X-ray reflecting mirror M have an angle twice the incident angle .alpha. of the incident X-ray beams 1 with respect to the incident X-ray beams 1. Furthermore, in order to transfer the circuit pattern on the X-ray mask 6 onto the semiconductor wafer 8 in a precisely overlapped manner, it is required that the alignment optical system 10 and the exposure optical system for the transfer be stably constructed with a predetermined performance. This requirement, in one example, is achieved by assembling, for adjustment with mechanically high precision, the mask stage 7, the wafer stage 9 and the alignment optical system 10 as the exposure apparatus body. For the reason described above, in the X-ray exposure apparatus utilizing the SOR, the adjustment of the axes of the X-ray beams 1 and the alignment optical system 10 are required to have high precision. In other words, as shown in FIG. 4, in order to carry out the transferring, in a precisely overlapped state the circuit pattern on the X-ray mask 6 to the semiconductor wafer 8 on which a resist 14 is coated, it is necessary to adjust the positions of the X-ray mask 6 and the semiconductor wafer 8 so as not to have a positional offset between a position of a mask pattern and a position of a pattern to be formed on the semiconductor wafer 8. Namely, the precise coincidence of the optical axis 1a of the X-ray beams 1 with an optical axis 10a, as measurement reference, of the alignment optical system 10 is required. In the case of no coincidence, a positional offset is caused in an amount such as shown by the following equation, EQU .delta.=G.times..DELTA..theta. in which G is a gap between the X-ray mask 6 and the semiconductor wafer 8, and .DELTA..theta. is an angular difference between the axis la of the beam 1 and the axis 10a of the alignment optical system 10, and .delta. is an amount of positional offset. As described above, the X-ray beams 1 are reflected by the reflecting mirror and then enter the exposure apparatus body 4, so that the X-ray beams 1 are not ordinarily parallel to the floor 13 on which the X-ray exposure apparatus is settled and has an inclination of several angles. On the contrary, since the exposure apparatus body 4 is precisely assembled with a horizontal plane as the reference level, the optical axis 10a of the alignment optical system 10 as the measurement reference is made substantially horizontal. For this reason, in the prior art, in order to make the axis 1a of the X-ray beams 1 coincident with the optical axis 10a of the alignment optical system 10 as the measurement reference, there is provided a method wherein two parallel X-ray reflecting mirrors are arranged with a predetermined distance therebetween between the synchrotron and the exposure apparatus body to thereby reflect the X-ray beams twice by the two reflecting mirrors to obtain horizontal light beams. In another method, an angle of the X-ray reflecting mirror is generally adjusted in accordance with the arranged position and the inclination of the exposure apparatus body. The conventional X-ray beam exposure apparatus and method, however, has the defects or drawbacks as described hereinbefore. The present invention conceived for eliminating these defects or drawbacks will be described hereunder with reference to FIGS. 1 and 2. A synchrotron S is utilized for generating X-ray beams and a reflecting mirror M is disposed at a portion suitable for reflecting the X-ray beams from the synchrotron S towards the exposure apparatus body. The exposure apparatus body 4 comprises an X-ray beam guide port 2 under extremely high vacuum state and a casing 5a defining an exposure chamber 5 which is communicated with the port 2 through a window 3 formed at a front end of the port 2. Accordingly, the X-ray beams 1 reflected by the mirror M is guided into the port 2 and then enters the exposure chamber 5 through the window 3. In the interior of the exposure chamber 5, are accommodated a mask stage 7 holding an X-ray mask 6 to be movable, a wafer stage 9 holding a semiconductor wafer 8 and an alignment optical system 10, which have substantially the same structures and functions as those described with reference to FIGS. 3 and 4. Accordingly, the X-ray beams 1 are horizontally irradiated from the synchrotron S and reflected by the reflecting mirror M with an optimum reflecting angle, i.e. the beams 1 are incident on the exposure apparatus body 4 with an incident angle .alpha. with respect to the horizontal plane. As described, in this embodiment, it is necessary to make an optical axis 1a of the X-ray beams 1 coincident with an optical axis 10a, as measurement reference, of the alignment optical system 10. As shown in FIG. 1, a distance between the synchrotron S and the reflecting mirror M is L.sub.1, a distance between the reflecting mirror M and the semiconductor wafer 8 is L.sub.2, and a major axis of the synchrotron S are D. In general, L.sub.1 =2-10 m, L.sub.2 =5-15 m, and the incident angle .alpha. of the beams 1 on the exposure apparatus body 4=40-50 mrad. In FIG. 1, for example, when L.sub.2 =10 m, the incident angle .alpha.=50 mrad, and D=20 m, a height difference .DELTA.H between the reflecting mirror M and the semiconductor wafer 8=500 mm, an inclination of the exposure apparatus body 4 (i.e. a height difference .DELTA.h between a front height h.sub.1 and a rear height h.sub.2)=50 mm. On the other hand, an irradiated area of the semiconductor wafer is (20-30 mm).sup.2 and an adjusted amount of the beams 1 is usually less than 1 mm. As the adjusted amount of the beams 1 is too small in comparison with the distance between the synchrotron S and the exposure apparatus body 4, it is difficult to adjust the beams 1. When the exposure apparatus body 4 is installed on the floor 13, for example as a reference base, the exposure apparatus body 4 is supported by an oscillation removing or absorbing table 12 which is set on the floor 13 through air springs 11. According to the present invention, a floating or raising mechanism and a securing mechanism are disposed between the exposure apparatus body 4 and the oscillation removing table 12. The raising mechanism comprises four air cushions 15 for raising the exposure apparatus body 4 in a floating manner and for adjusting the height position and inclination of the exposure apparatus body 4. The securing mechanism comprises adjusting bolts 16 and clamping bolts 17 for fixing the exposure apparatus body 4 on the oscillation removing table 12 after adjusting the height position and inclination thereof, by means of the air cushions 15. In more detail, the four air cushions 15 are disposed on the upper surface of the oscillation removing table 12 at four corner portions of the lower surface of the exposure apparatus body 4. Each cushion 15 is individually swollen so as to expand in the vertical direction in an installed state by supplying air in the cushion 15 to thereby adjust the height of the air cushion 15. In this way, the four air cushion 15 may adjust the position and inclination of the exposure apparatus body 4. As shown in FIG. 5, the air cushion 15 has an upper plate 25, a lower plate 26, and a rubber side portion 27 connecting the upper plate 25 and the lower plate 26. Air pipes 22 are connected to the lower plates 26. In FIG. 1, each air pipe 22 connected to the air cushion 15 has an adjusting valve 23. A front height sensor 20a and a rear height sensor 20b for measuring the front height and the rear height of the exposure apparatus body 4 are provided on the front portion and the rear portion of the oscillation removing table 12. The front height sensor 20a and the rear height sensor 20b are connected to a controller 21 which independently controls the adjusting valves 23. The adjusting bolts 16 are secured to the oscillation removing table 12 and extend upwardly in a manner where the projecting amounts of the adjusting bolts 16 are adjustable. The upper end portions thereof are formed in spherical shapes so as to be capable of carrying the bottom of the exposure apparatus body 4 by using wider areas of the upper end portions. Otherwise, the upper end portions of the adjusting bolts 16 may be movable in a spherical motion manner. The four adjusting bolts 16 are, for example, arranged in an equilateral triangle in a plan view so that one bolt 16 is arranged at each of two points of the triangle shape and two bolts 16 are arranged at another one point thereof. Namely, the bottom of the exposure apparatus body 4 is supported at more than three supporting portions to restrict the vertical motion of the exposure apparatus body 4. The clamping bolts 17 are engaged with a bracket 18 disposed in a standing manner on the oscillation removing table 12 at a circumferential portion of the exposure apparatus body 4. The clamping bolts 17 are screwed horizontally to clamp the lower side portions of the exposure apparatus body 4 to thereby restrict the back and forth and lateral motions thereof. That is, the clamping bolts 17 prevent the exposure apparatus body 4 from moving in a horizontal plane. The operation of positioning the exposure apparatus body 4 is as follows. First, the air is supplied into the respective air cushions 15 through the air pipes 22 in order to raise the exposure apparatus body 4 in a floating manner. Next, the height position and the inclination of the exposure apparatus body are adjusted by controlling the air amounts supplied into the respective air cushions 15, to the desirable height position and inclination where the optical axis 10a of the alignment optical system 10 substantially coincides with the axis 1a of the X-ray beams 1. The adjustment of the exposure apparatus body 4 will be described in detail. The X-ray beams 1 are actually irradiated from the synchrotron S. Next, heights H.sub.1 and H.sub.2 from the oscillation removing table 12 to the beams 1 at two optional positions are measured by suitable measuring means such as a fluorescence plate or an X-ray monitor. After that, the heights H.sub.1 and H.sub.2 are inputted to the controller 21, and then a height H.sub.3 from the oscillation removing table 12 to an exposure point of the semiconductor wafer 8 is calculated on the basis of the heights H.sub.1 and H.sub.2. At the same time, in the controller 21 the front height h.sub.1 and the rear height h.sub.2 of the exposure apparatus body 4 are calculated on the basis of the heights H.sub.1 and H.sub.2 so that the optical axis 10a of the alignment Optical system 10 coincides with the axis 1a of the X-ray beams 1. On the other hand, the front height h.sub.1 and the rear height h.sub.2 measured by the front height sensor 20a and the rear height sensor 20b are inputted to the controller 21. Then, the respective adjusting valves 23 are controlled by the controller 21 on the basis of the calculated values and the measured values of the front height h.sub.1 and the rear heights h.sub.2. Thereafter, as shown in FIG. 2, the exposure apparatus body 4 is secured to the height position and the inclination adjusted in the previous step by means of the securing mechanism comprising the adjusting bolts 16 and the clamping bolts 17. Air bleeding from the respective air cushions 15 is then performed. In this case, as shown in FIG. 4, it is possible to check whether or not the coincidence between the optical axis 10a as the measurement reference of the alignment optical system 10 and the axis 1a of the X-ray beams 1 has been adjusted to be within a required range. In the case of not being adjusted, the raising mechanism, i.e. air cushions 15 are again operated to carry out the readjustment of the coincidence of the optical axes 1a and 10a. This adjustment can be carried out easily, however. Accordingly, as described hereinbefore, according to the present invention, the exposure apparatus body which is arranged independently from the synchrotron as X-ray generating source, can have vertical and horizontal positions adjusted so as to make coincident between the axis of the X-ray beams from the synchrotron and the axis of the alignment optical system without adversely affecting on the function of the exposure apparatus as a whole. In the described embodiment, the air cushions are utilized for raising the exposure apparatus body, but any other means such as hydraulic jack means may be utilized. Furthermore, securing members each having a tapered upper end may be substituted for the adjusting bolts having top spherical shapes and adjusting bolts may be also substituted for the clamping bolts. It is to be understood that the present invention is not limited to the described preferred embodiment and many other changes and modifications may be made without departing from the scope of the appended claims.