The present invention is directed to a method and apparatus for changing the imaging scale in x-ray lithography. The apparatus includes a source for generating a collimated beam of radiation, means for positioning a mask in the beam of radiation before an object to be structured, an adjustment or mounting unit for positioning the object in the beam and for alignment of the object relative to the mask.
The progressive miniaturization of micro-electronic components places an extremely high demand on the performance capability of the lithographic methods. Thus, it is currently possible to routinely generate structures having dimension in a micrometer range (d=2-4 .mu.m), with a light-optical projection predominantly utilized in very large scale integration (VLSI) fabrication.
It has been suggested, as a further improvement in light optical methods, to utilize short-wave ultraviolet light having a wavelength .tau..apprxeq.200-300 nm. However, the utilization of very short-wave ultraviolet light has a lot of technical problems so that the theoretical limit of resolution of about 0.5-0.8 .mu.m can probably not be achieved.
One is, therefore, forced to develop new lithographic methods for producing structures in the sub-micron region. For example, see an article by H. Schaumburg "Neue Lithografieverfahren in der Halbleitertechnik", Elektronik 1978, No. 11, pp. 59-66. X-ray lithographic methods have, therefore, achieved special significance and their resolution is not limited by diffraction effects as a consequence of the short wavelength of the radiation, which wavelength is approximately .tau..apprxeq.0.5-4 nm, but by the range of electrons in the photoresist emitted from the layer to be structured. X-ray lithographic equipment having a conventional radiation source for a whole-wafer exposure of wafers are disclosed, for example, in an article by J. Lyman, "Lithography steps ahead to meet VLSI challenge", Electronics, July 1983, pp. 121-28. In these apparatus, the transfer of the prescribed structure onto the semiconductor wafer occurs on the basis of a shadow imaging in that the adjustment mask-wafer pairs are exposed with an x-radiation coming from a nearly punctiform source. The imaging of the mask structure onto the wafer surface corresponding to a conical projection occurs with a magnification scale M=1: (1+P/L), which is defined by the distance P (P.apprxeq.30 .mu.m) between the mask and wafer and the distance L (L.apprxeq.30 cm) between the x-ray source and the wafer. The changes in the rated size of the mask and the wafer, which changes occur during the manufacturing process as a consequence of thermal expansion and warping, can be compensated in a simple way in that the conical projection by the imaging scale is correspondingly adapted by changing what is referred to as the proximity distance P. This known method, however, fails when electron synchrotons or, respectively, electron storage rings are utilized as high-intensity x-ray sources. As a consequence of the high collimation degree of the synchroton radiation emitted by the electrons circulating on the circular path, the exposure of the mask-wafer pair arranged at a distance of several meters from the source or storage ring occurs on the basis of nearly exact parallel projection and, thus, L.apprxeq..infin.. In order to also guarantee a high overlay degree in the synchroton lithography, it must be assured that size variations of mask and wafer can be compensated by adapting the imaging scale.