Patent Number: 051724022
Section: summary

FIELD OF THE INVENTION AND RELATED ART This invention relates to an exposure apparatus and, more particularly, to an exposure apparatus for transferring and printing an image of an original, such as a mask, onto a workpiece such as a semiconductor wafer, with high precision. With the increasing degree of integration of semiconductor integrated circuits, in an exposure apparatus (aligner) for manufacture of the same, further enhancement of transfer precision is required. As an example, for an integrated circuit of a 256 megabit DRAM, an exposure apparatus capable of printing a pattern of a linewidth of 0.25 micron order is necessary. As such super-fine pattern printing exposure apparatus, an exposure apparatus which uses orbit radiation light (SOR X-rays) has been proposed. The orbit radiation light has a sheet beam shape, uniform in a horizontal direction. Thus, for exposure of a plane of a certain area, many proposals have been made, such as: (1) a scan exposure method wherein a mask and a wafer are moved in a vertical direction whereby the surface is scanned with X-rays of sheet beam shape in a horizontal direction; PA1 (2) a scan mirror exposure method wherein X-rays of a sheet beam shape are reflected by an oscillating mirror whereby a mask and a wafer are scanned in a vertical direction; and PA1 (3) a simultaneous exposure method wherein X-rays of a sheet beam shape in a horizontal direction are diverged in a vertical direction by an X-ray mirror having a reflection surface machined into a convex shape, whereby an exposure region as a whole is irradiated simultaneously. The inventors of the subject application have cooperated to devise such a simultaneous exposure type X-ray exposure apparatus, which is disclosed in Japanese Laid-Open Patent Application No. 243519/1989. In this type of exposure apparatus, exposure light (X-ray) has uniform illuminance in a horizontal direction (hereinafter "X direction"). However, in a vertical direction (hereinafter "Y direction"), it has non-uniform illuminance such as depicted by an illuminance distribution curve 1i in FIG. 3A, for example, wherein the illuminance is high at a central portion and decreases sway from the central portion. In the proposed apparatus, a blocking member having a rectangular opening (shutter aperture) is used, and the relationship of the time moment (t) of passage and the position in the Y direction of each of two edges, of four edges defining the opening, is controlled independently as depicted in FIG. 3B, whereby the exposure time (.DELTA.T) at each portion in an exposure region is controlled, as depicted in FIG. 3C. More specifically, the time period from the passage of a leading edge 1a of the blocking member (the preceding one of the two edges with respect to the movement direction of the blocking member), for allowing transmission of the exposure light (X-rays), to the passage of a trailing edge 1b of the opening of the blocking plate (the succeeding edge with respect to the movement direction of the blocking member), for interception of the exposure light, is controlled to thereby attain correct and uniform exposure of the whole exposure region. In that case, the exposure quantity control is effected on the basis of an X-ray illuminance distribution curve (hereinafter "profile") in the Y direction, such as depicted in FIG. 3A, as measured in the exposure region. SUMMARY OF THE INVENTION In this X-ray exposure apparatus, however, any deviation between the aforementioned profile and an edge drive curve produces a non-negligible effect upon the transfer precision. For example, if edge drive curves as depicted by solid lines 1a and 1b. in FIG. 3B, corresponding to the profile of solid line 1i in FIG. 3A, shift by .DELTA.y to the positions of broken lines 2a and 2b in FIG. 3B, respectively, corresponding to the profile of broken line 2i in FIG. 3A, then the illuminance I of the exposure light at a position y changes by "(dI/dy) .times..DELTA.y". Accordingly, in order to suppress the change in illuminance I to a quantity not greater than 0.1%, the following relation has to be satisfied: ##EQU1## More particularly, if the view-angle size of the exposure region in the Y direction is 30 mm, if the profile such as depicted by the solid line 1i in FIG. 3A is represented by a quadratic function which is vertically symmetric with respect to a center line and if the lowest illuminance is 80% of the highest illuminance, then it follows that: EQU .DELTA.y&lt;(1/1000).times.[1/(0.4/15)].perspectiveto.0.04(mm) Thus, it is seen that, in order to suppress non-uniformness in illuminance to a quantity not greater than 0.1%, the shift .DELTA.y in relative position of the exposure light to the exposure region has to be kept at a quantity not greater than 40 microns. A deviation in the edge drive curve or profile may result from a change in the relative attitude of a SOR device and a major assembly of the exposure apparatus, in a case of SOR X-ray exposure apparatus, and, generally, it may be attributable to an error between coordinate axes of a wafer stage and an edge driving system. It is accordingly an object of the present invention to provide an exposure apparatus by which an exposure quantity error .DELTA.I attributable to a relative deviation .DELTA.y between the edge drive curve and the profile can be reduced to thereby enhance transfer precision. In accordance with an aspect of the present invention, to achieve this object, there is provided an exposure apparatus, comprising: a radiation source with non-uniformness in illuminance generally in one-dimensional direction with respect to a predetermined exposure region; illuminance measuring means for measuring an illuminance distribution in the one-dimensional direction in the exposure region and in an area adjacent thereto; shutter means having a leading edge effective to start exposure in the exposure region and a trailing edge effective to stop the exposure; a memory with a drive table for setting a drive curve for the leading and trailing edges in accordance with the measured illuminance distribution; shutter driving means for causing the leading and trailing edges to move through the exposure region in the one-dimensional direction, independently of each other, in accordance with the drive table; edge position detecting means for detecting, with an illuminance detector of the illuminance measuring means and at different two points spaced in the one-dimension direction, a position of a shadow of one of said leading and trailing edges; and coordinate conversion means for effecting conversion of a coordinate system of the drive table and a coordinate system for the positioning of the illuminance detector during the illuminance distribution measurement, in accordance with results of the edge position detection. With this structure, the position of the shadow of the edge as detected by the illuminance distribution measuring means with respect to at least two points, spaced in the direction of illuminance distribution, does correspond to the position of the edge, designated in terms of the coordinate system of the drive table, as projected upon the coordinate system used for the measurement of the illuminance distribution. Accordingly, it is possible to detect the relationship between the coordinate system of the drive table and the coordinate system in the measurement of illuminance distribution and, by converting the coordinate system for the illuminance distribution measurement into the coordinate system of the drive table, an error between the coordinate systems of the illuminance distribution measurement and the drive table can be corrected and, as a result, non-uniformness in exposure (exposure quantity error) .DELTA.I attributable to such error can be reduced. The inventors of the subject application have made investigations into an exposure apparatus of the aforementioned type to attain further enhancement of the transfer precision, and have found that a change in the relative position of the exposure region and the exposure light provides a non-negligible effect on the transfer precision. Particularly, in the proximity exposure process, a change in the angle of incidence of the exposure light to the exposure region results in degradation of the superposing precision. For example, if the proximity gap G between a mask and a wafer is 50 microns, then, in order to suppress a superposition error .DELTA..delta. due to a change in the angle of incidence to a quantity not greater than 0.002 micron, the change .DELTA..theta. in the angle of incidence has to be suppressed to satisfy: EQU .DELTA..theta.=.DELTA..delta./G&lt;0.002/50=4.times.10.sup.-5 (rad) Namely, it has to be suppressed to a quantity not greater than 4.times.10.sup.-5 rad. Further, if the exposure light has a divergent angle, the angle of incidence of the exposure light to the exposure region changes with the shift .DELTA.y of the relative position as described above. If the interval between the surface to be exposed and the point of divergence (e.g. the position of incidence of X-rays upon a divergence convex mirror of a SOR X-ray exposure apparatus) is 5 m, then the quantity .DELTA..theta. of change in the angle of incidence is given by: EQU .DELTA..theta.=.DELTA.y/5000&lt;4.times.10.sup.-5 (rad) From this change .DELTA..theta. in the angle of incidence, the above-described superposition error .DELTA..delta. results. The superposition error .DELTA..delta. in this case appears at different portions of the surface to be exposed, as a run-out error of distributed transfer magnifications. From the above equation, it is seen that the change .DELTA.y in the relative position has to be suppressed to a quantity not greater than 0.2 mm. Further, if in the positional relationship between the exposure light and the exposure region there occurs a rotational deviation .DELTA..omega..sub.z about an axis (Z axis) of the path of the exposure light, then, at a position (X, Y) on the X-Y plane having an origin on that axis, there are caused an error .DELTA..theta. in the angle of incidence as well as an illuminance change .DELTA.I and an error .DELTA..delta., equivalently as there is caused a change .DELTA.y wherein .DELTA.y=Y. cos .omega..sub.z. As regards the variations such as the relative positional deviation .DELTA.y and .DELTA..omega..sub.z, one of which is attributable to an attitude change of the exposure apparatus resulting from movement of a wafer stage of about 200 microns, a displacement resulting from a temperature change may be of about 10 microns and a displacement resulting from vibration of a floor may be about 2 microns. It is another object of the present invention to provide an exposure apparatus by which an exposure quantity error .DELTA.I and a superposition error .DELTA..delta. attributable to the rotational deviation .DELTA..omega..sub.z can be reduced, to thereby attain further enhancement of the transfer precision. In accordance with another aspect of the present invention, to achieve this object, there is provided an exposure apparatus, comprising: a radiation source with non-uniformness in illuminance generally in a one-dimension direction with respect to a predetermined exposure region; exposure quantity correcting means for setting an exposure time distribution in accordance with the non-uniformness in illuminance so as to assure a substantially uniform exposure quantity in the exposure region; illuminance distribution measuring means for measuring an illuminance distribution in the exposure region; computing means for calculating a constant-illumination line on the basis of a measured data of the measuring means; and paralleling means for making the constant-illumination line and a constant-exposure-time line of said exposure quantity correcting means parallel. In this structure, the illuminance distribution measuring means serves to measure an illuminance distribution in the exposure region and an area adjacent thereto, the computing means serves to calculate a constant-illuminance line on the basis of a measured illuminance distribution data, and the paralleling means serves to execute an operation making the calculated constant-illuminance line and a constant-exposure-time line determined by the exposure quantity correcting means parallel. By this paralleling operation, the rotational deviation .omega..sub.z can be corrected and, therefore, the exposure quantity error .DELTA.I and the superposition error .DELTA..delta. attributable to such rotational deviation .omega..sub.z can be reduced. It is a further object of the present invention to provide an exposure method and apparatus by which uniform exposure is attained and, thus, a resist pattern of uniform linewidth 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.