This invention relates to an exposure method and, more particularly, to a proximity exposure method using X-rays, for example. The exposure method of the present invention is suitably applicable to the manufacture of various microdevices such as a semiconductor chip (e.g., IC or LSI), a display device (e.g., liquid crystal panel), a detecting device (e.g., magnetic head), and an image pickup device (e.g., CCD), for example.
FIG. 1 shows an example of an X-ray proximity exposure apparatus of a known type (Japanese Laid-Open Patent Application No. 2-100311). Denoted in the drawing at 1 is an X-ray source (light emission point) such as synchrotron orbital radiation (SOR), and denoted at 2 is an SOR X-ray beam being expanded in an X direction into a slit-like shape. Denoted at 3 is a convex mirror, made of SiC, for example, for expanding the slit-like X-ray beam 2 in a Y direction. Denoted at 2a is the X-ray beam having been expanded by the convex mirror 3 into an area shape. Denoted at 7 is a workpiece to be exposed, such as a semiconductor wafer having been coated with a resist, for example. Denoted at 10 is a mask. Denoted at 4 is a beryllium film for isolating an ambience at the SOR side and an ambience at the mask (and workpiece) side from each other. Denoted at 5 is a focal plane type shutter being provided for exposure amount adjustment. In an exposure operation, the mask 10 and the workpiece 7 are placed with a spacing (gap) of about 10 microns maintained therebetween. As the shutter 5 is opened, a slit-like high-luminance X-ray beam 2 from the SOR, for example, and being expanded into an area shape (X-ray beam 2a) by the convex mirror 3, is projected to the mask 10 and then to the workpiece 7, by which a pattern image of the mask 10 is transferred to the workpiece 7 at a unit magnification.
As regards the X-rays in this case, a wavelength of about 0.5-20 nm is used. Therefore, in connection with the wavelength only, theoretically, a very high resolution of 0.05 micron (50 nm) or less will be obtainable. Practically, however, such a high-resolution mask itself is difficult to manufacture. If a mask of a nominal smallest linewidth of 0.05 micron is manufactured by use of a technique for production of a conventional mask of smallest linewidth of 0.1 micron (100 nm), any positional error or any error in the line-and-space (linewidth and spacing) of a pattern produced will be transferred to a workpiece as a mask defect. It will cause a void in the pattern to be formed, or a positional deviation of the pattern. Further, a produced mask pattern may not have a proper linewidth or a sufficient thickness. In these occasions, a sufficient contrast will not be attainable, and the pattern will not be resolved satisfactorily.
It is accordingly an object of the present invention to provide an exposure method by which a pattern can be formed at a higher resolution and a higher precision, on the basis of a currently available X-ray exposure apparatus and a mask which can be produced in accordance with a current technique.
It is another object of the present invention to provide an exposure method which enables accomplishment of resolution even in a strict condition under which the contrast is too low and the resolution is currently difficult to accomplish.