Reflectance coatings for the vacuum/extreme ultraviolet region

A theoretical examination has been undertaken to evaluate the performance of reflective coatings at normal incidence in the spectral region 40-70nm for applications in lithographic imaging systems. Aluminium based multilayer structures were found to offer the highest theoretical reflectance values in this region but due to the presence of surface oxide layers are of little practical value. Alternative multilayer structures based on silicon are offered as an alternative, were it is suggested that oxide formation may be more easily controlled.