X-ray lithography

X-ray lithography with wavelengths between 0.2 and 2 nm provides a structural resolution as good as 0.1 micrometer under optimized conditions even in the case of high proximity gaps of 50 micrometers which are needed in practical applications. But the high performance of x-ray lithography can only be realized by parallel and highly intensive radiation. The wavelength distribution has to be tuned properly to the absorption properties of a special set of mask substrate, absorber and window material. As there are no suitable optics for x-rays in order to fabricate a condensator for a homogeneous illumination of mask and wafer, the type of x-ray source used is the most decisive parameter with respect to both resolution and wafer throughput. Comparing various x-ray sources, such as x-ray tubes, storage rings, and plasma sources, the conclusion is that at present synchrotron radiation offers most advantages. However, the existence of low cost compact storage rings especially designed for the lithography purposes is a precondition for an industrial application.