Patent Number: 051724030
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, denoted at 50 is an X-ray source accommodating chamber for accommodating an X-ray source therein. Barrel 5 is coupled to the X-ray source accommodating chamber and, to this barrel 5, a stage accommodating chamber 19 is coupled. The barrel 5 is equipped with a beryllium blocking window 6 through which the X-rays produced by the X-ray source are introduced into the stage accommodating chamber 19 along the z-axis direction. The stage accommodating chamber 19 accommodates therein a mask 13, a mask chuck 14 for holding the mask 13, a semiconductor wafer 15, a wafer chuck 16 for holding the wafer 15, a wafer stage 18 which is movable along the x-axis, y-axis and z-axis directions as well as in rotational directions about these axes, respectively, and an optical system 17 for the alignment of the mask and the wafer with respect to each of the x-axis, y-axis and z-axis directions. More particularly, the optical system 17 is operable to detect any positional deviation between alignment marks provided on the mask and the wafer. The wafer stage 18 can be moved stepwise in each of the x-axis and y-axis directions, for printing a circuit pattern formed on the mask 13 upon different shot areas on the wafer 15. By exposing the wafer 15 with the x-rays through the mask 13, the pattern of the mask 13 can be printed on a particular shot area of the wafer 15. Thus, the above-described structure constitutes what can be called an "X-ray stepper". To the barrel 5, a high vacuum pump 51 such as a turbo molecular pump, for example, is coupled, for vacuum-evacuation thereof. To the stage accommodating chamber 19, a low vacuum pump 11 such as an oil rotation pump, for example, is coupled by way of a discharging port 12 and a variable valve 10. The discharging port 12 is coupled to the same side of the stage accommodating chamber 19, to which the barrel 5 is coupled. However, the discharging port may be coupled to the wall of the stage accommodating chamber 19 on the opposite side remote from the barrel 5, as in the FIG. 6 example. The variable valve 10 is adapted to change the opening thereof automatically in response to a signal from a controller 9. The stage accommodating chamber 19 is equipped with an opening 31 for passage of X-rays, on the side of which opening a pressure detecting port 7 is provided to detect the pressure in an X-ray projection path 30 between the beryllium blocking window 6 and the mask 13. On the basis of the pressure detected by the pressure sensor 8, the controller 9 controls the opening of the variable valve 10. By this, the pressure in the stage accommodating chamber 19, more particularly, the pressure in the X-ray projection path (passageway) 30, can be controlled and maintained constant. The flow of helium gas from a tank 1 is adjusted by a manual adjusting valve 2 to a predetermined flow rate and, through a helium supply port 3 disposed just after (wafer 15 side) the beryllium blocking window 6 of the barrel 5, the helium gas is supplied into the stage accommodating chamber 19 through the X-ray projection path 30. The mask chuck 14 is provided with a helium discharging port 4 for discharging the supplied helium gas in the X-ray projection path 30 into the stage accommodating chamber 19. The helium discharging port 4 is arranged to avoid vibration or flexure of the mask 13 due to the gas flow of helium. FIG. 2 is a sectional view of the helium supply port 3, taken on line A--A in FIG. 1. FIG. 3 is a sectional view of the helium discharging port 4, taken on line B--B in FIG. 1. As seen in these drawings, in the neighborhood of the portion of the barrel 5 to which the helium supply port 3 is coupled, an inner cylinder 40 is provided in a concentric relationship with the barrel 5. The inner cylinder 40 has twelve (12) bores 41 formed equidistantly along the circumference of the cylinder 40. The helium introduced into the barrel 5 from the helium supply port 3, is then introduced into the X-ray projection path 30 through these bores 41 of the inner cylinder 40. Also, as best seen in FIG. 3, the mask chuck 14 has eight (8) helium discharging ports 4 which are formed equidistantly around the X-ray projection path 30, as passageways extending radially outwardly from the center of the X-ray projection path 30. The helium introduced into the X-ray projection path 30, is then introduced into the stage accommodating chamber 19 through these discharging ports 4. By introducing and discharging the helium gas radially inwardly and outwardly in the manner described above, it is possible to obtain a uniform or homogeneous helium ambience. For the exposure process in the X-ray exposure apparatus of the structure described above, first the inside atmosphere in the stage accommodating chamber 19 is replaced by a helium gas of a predetermined pressure. Then, in accordance with the quantity of impure gas introduction (leakage) into the stage accommodating chamber 19 (for example, the introduction of air through seal means), a constant amount of helium necessary for retaining the purity of helium in the stage accommodating chamber 19 is supplied continuously from the helium supply port 3. Additionally, the opening of the variable valve 10 coupled to the vacuum pump 10 is controlled continuously on the basis of the output of the pressure sensor 8. By this, the pressure in the X-ray projection path 30 can be controlled and maintained constant. Referring to FIG. 4 showing a second embodiment of the present invention, helium is supplied through a helium supply port 3 which is provided just before (light source side) the mask 13 held on the mask chuck 14. Additionally, a communication port 20 is formed to provide communication between the stage accommodating chamber 19 and the barrel 5, more particularly, a part of the barrel 5 just after (mask 13 side) of the blocking window 6. The helium gas from the tank 1 flowing through the manual valve 2 flows through the X-ray projection path 30 in a direction from the mask 13 to the blocking window 6 and, thereafter, through the communication port 20 as the helium gas introduced into the stage accommodating chamber 19. As in the first embodiment, the pressure detecting port 7 is provided on the side of the opening 31 of the stage accommodating chamber 19, for passage of X-rays, and it is operable to detect the pressure in the X-ray projection path 30. The remaining structure and operation of this embodiment are substantially the same as those of the first embodiment. Referring to FIG. 5 showing a third embodiment of the present invention, in this embodiment, the first embodiment is modified such that a thin film 21 is added between the mask 13 and the helium discharging port 4 to intercept them. Also, a port 22 is added to provide communication between the stage accommodating chamber 19 and the space which is defined between the thin film 21 and the mask 13. With this arrangement, it is possible to effectively suppress or minimize the vibration or flexure of the mask 13 due to the flow of helium, substantially without decreasing the amount of exposure of the wafer 16 with the X-rays. In FIG. 5, the helium from the tank 1 flowing through the valve 2, is supplied into the stage accommodating chamber 19 from the helium supply port 3 provided just after the blocking window 6 of the barrel 5. More particularly, the helium gas introduced from the helium supply port 3 into the X-ray projection path 30 flows to the discharging ports 4 which are provided just before (blocking window 6 side) the thin film 21, into the stage accommodating chamber. Into the space between the thin film 21 and the mask 13, helium is introduced from the stage accommodating chamber 19 side, through the port 22. The thin film 21 is disposed adjacent the helium discharging ports 4 which are formed in the mask chuck 14 for introduction of the helium gas supplied to the X-ray projection path 30, into the stage accommodating chamber 19. More particularly, it is disposed at one side of the ports 4 facing the mask 13. The communication port 22 provided between the thin film 21 and the mask 13 functions also to prevent the possible flexure or vibration of the thin film 21, due to the gas flow of helium, from adversely affecting the mask 13. Since substantially no differential pressure is produced on the opposite sides of the thin film 21, the thickness thereof may be very small on an order of a few microns. Examples of the material thereof are: an organic material such as polypropylene, polyethylene, polyamide, polycarbonate, vinyl chloride, fluorine plastic or the like; or an inorganic material such as Si.sub.3 N.sub.4, SiC, Be, SiO.sub.2 or the like. As in the first embodiment, the pressure detecting port 7 is provided on the side of the opening 31 of the stage accommodating chamber 19, for passage of X-rays and it is operable to detect the pressure in the X-ray projection path 30. The remaining structure and operation are similar to those of the first embodiment. Also, in the third embodiment, like the second embodiment, the supply port 3 may be provided on the mask chuck side, at a position between the blocking window 6 and the thin film 21, and the communication port 20 (see FIG. 4) may be provided on the barrel 5 side. Whether the structure without a thin film 21 as in the first and second embodiments or the structure with a thin film as in the third embodiment should be selected, may be determined on the basis of various conditions such as, for example, the mechanical structure of the components (such as the barrel 5, the optical system 17, the mask 14, etc.) disposed around the X-ray projection path 30, the flow rate of helium gas as supplied from the helium supply port 3, the material and thickness of the thin film 21, while taking into account the quantity of X-ray attenuation, the effect of vibration or flexure of the mask, and the like. In the preceding three embodiments, the supply and discharge of helium are executed through the ports 3 and 4 provided in the barrel 5 and the mask chuck 14, and the pressure detection is executed through the port 7 provided in the stage accommodating chamber 19. However, the present invention is not limited to such a form. By way of example, the supply port 3 may be provided in the stage accommodating chamber 19 so as to supply helium into the X-ray projection path 30, or the pressure detecting port 7 may be provided in the barrel 5 or the mask chuck 14 so as to detect the pressure in the X-ray projection path 30. Further, the position for the provision of the thin film 21 is not limited to the mask chuck 14. According to the present invention, as described hereinbefore, it is possible to control the helium ambience in the X-ray projection path mainly, to which the control of purity, pressure and the like of the helium gas should actually be executed. While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.