Patent Number: 048872822
Section: summary

BACKGROUND OF THE INVENTION 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. SUMMARY OF THE INVENTION The object of the present invention is to provide a method and arrangement for an x-ray lithography with which changes of the imaging scale can be undertaken in synchroton lithography. This object is achieved by an improvement in a method for changing the imaging scale and x-ray lithography wherein at least one part of the surface of an object to be structured is subjected with collimated radiation passing through a mask preceding the object. The improvement is that the object is deformed, at least in the region to be structured, and that the radius of curvature produced by individual surface points of the deformation is kept constant during the irradiation of the object. The improvement in the apparatus for changing imaging scales in x-ray lithography comprises an improvement in an apparatus having a radiation source for generating a collimated x-radiation, a mask, and means for positioning or holding an object in the x-ray beam and aligned with the mask. One of the improvements is that the means for positioning or holding the object includes means for curving the surface of the object facing the mask. This means for curving the surface can include a holder having a curved surface having grooves connected to a suction or vacuum pump means or the holder having elastic walls which engage the object to apply pressure on a back surface of the object to cause bending thereof. The advantage obtainable with the invention is especially that the changes in the rated size of the mask and wafer can be compensated by adaptation of the imaging scale. Other features and objects of the invention will be readily apparent from the following description of the preferred embodiments, the drawings and claims.