Patent Number: 061608653
Section: summary

FIELD OF THE INVENTION AND RELATED ART This invention relates to a synchrotron radiation intensity measuring system for measuring the intensity of synchrotron radiation and also to an X-ray exposure apparatus wherein the exposure amount is controlled on the basis of measurement by such measuring system. In another aspect, the invention is concerned with a device manufacturing method which uses such exposure apparatus. In X-ray exposure apparatuses for use in an X-ray lithographic process in one field of use of synchrotron radiation, since the synchrotron radiation has a shape of sheet-like beam and sufficient exposure region is not provided, an X-ray mirror is used to expand the sheet-like beam in a direction perpendicular to the synchrotron orbit. It is an important factor to maintain uniform exposure amount upon the surface of a substrate such as a wafer, irradiated thereby. To this end, it is required to precisely control the attitude of or relative position of the X-ray mirror with respect to the sheet-like beam, emitted from a synchrotron ring. Further, if during the X-ray exposure process the relative positional relation between the X-ray mirror and the sheet-like beam varies due to vibration, temperature change or fluctuation of the sheet-like beam, uniformness of exposure amount can not be retained, and non-uniform exposure results. In consideration of this, it is desired that the synchrotron ring, the X-ray mirror and the X-ray exposure apparatus are mounted very precisely. Additionally, use of some mechanism for cancelling any external vibration is desired. U.S. Pat. No. 5,448,612 shows an apparatus wherein a beam position detector is provided on a support member for an X-ray mirror to detect relative positional deviation of the X-ray mirror relative to the beam. Driving means controls the attitude of the X-ray mirror on the basis of the result of detection by the detector. A dual-element detector disposed in a vertical direction are used to control the attitude of an X-ray mirror so that the outputs of the detector elements are balanced. Also, on the basis of the sum signal of the outputs of the two detector elements or of an output of one of them, the intensity of synchrotron radiation is calculated. Although in the above-described example the intensity of synchrotron radiation can be calculated on the basis of an output signal of a detector, if the intensity distribution in a direction perpendicular to the synchrotron radiation varies as a result of a change in accumulated current of a synchrotron ring, for example, the intensity of synchrotron radiation and the output signal of the detector are not exactly proportionally correlated with each other. Thus, in that occasion, an error occurs in calculation of the synchrotron radiation intensity. If the exposure amount is controlled on the basis of it, there may occur an error in exposure amount. SUMMARY OF THE INVENTION It is an object of the present invention to provide a synchrotron radiation intensity measuring system by which the intensity of synchrotron radiation can be measured precisely and quickly with simple procedure. It is another object of the present invention to provide an X-ray exposure apparatus by which exposure amount can be controlled precisely on the basis of measurement made by use of such intensity measuring system. In accordance with an aspect of the present invention, there is provided a synchrotron radiation measuring system, comprising: an X-ray detector movable in a direction of intensity distribution of synchrotron radiation to follow shift of the synchrotron radiation; and computing means for reserving therein one of (i) a relation between a signal of said X-ray detector and the intensity of synchrotron radiation and (ii) a relation among a signal of said X-ray detector, the level of vacuum at a synchrotron ring and the intensity of synchrotron radiation; wherein the intensity of synchrotron radiation is measured through said computing means on the basis of an output signal of said X-ray detector. In one preferred form of this aspect of the present invention, said computing means reserves therein a relation between a signal of said X-ray detector and the intensity of synchrotron radiation, and, when the intensity of synchrotron radiation is I and the output of said X-ray detector is v, the relation satisfies a condition: EQU I(v)=a.sub.0 +a.sub.1 v+a.sub.2 v.sup.2 +a.sub.3 v.sup.3 + . . . In another preferred form of this aspect of the present invention, said computing means reserves therein a relation among a signal of said X-ray detector, the level of vacuum at the synchrotron ring and the intensity of synchrotron radiation, and, when the intensity of synchrotron radiation is I and the output of said X-ray detector is v, the relation satisfies a condition: EQU I(v)=a.sub.0 (p)+a.sub.1 (p)v+a.sub.2 (p)v.sup.2 +a.sub.3 (p)v.sup.3 + . . . where a.sub.0, a.sub.1, a.sub.3, . . . , are coefficients which are a function of vacuum level p of the synchrotron ring. In a further preferred form of this aspect of the present invention, said X-ray detector has two elements which are disposed in array along the direction of intensity distribution of the synchrotron radiation. In accordance with another aspect of the present invention, there is provided an X-ray exposure apparatus, comprising: a synchrotron radiation intensity measuring system as recited above; and control means for controlling exposure amount on the basis of measurement by said measuring system. In one preferred form of this aspect of the present invention, said control means comprises means for controlling exposure time. In another preferred form of this aspect of the present invention, said exposure time controlling means comprises shutter control means for controlling a driving speed or a driving pattern for a shutter thereby to control the exposure time. Use of computing means which reserves therein one of (i) a relation between a signal of said X-ray detector and the intensity of synchrotron radiation and (ii) a relation among a signal of said X-ray detector, the level of vacuum at a synchrotron ring and the intensity of synchrotron radiation, enables high precision and high speed calculation of the intensity of synchrotron radiation on the basis of an output of the X-ray detector which detects a sheet-like beam of synchrotron radiation. Further, because of capability of high precision and high speed calculation of synchrotron radiation intensity, exposure time can be controlled through control of a driving speed or driving pattern for a shutter on the basis of the result of calculation. Thus, high precision exposure amount control is assured. 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.