Design and Analysis of Multi-Mirror Soft X-Ray Projection Lithography Systems

Recently, there have been a number of reports where two-mirror inverted Schwarzschild microscopes, which were coated with appropriate multilayers, have been used in soft x-ray projection lithography experiments and have obtained resolutions as small as 50 nm [1-3]. A projection optics design survey [4] reported that the Schwarzschild type optics will have a field of view less than 1 mm with a resolution of 0.1 microns. However, it has been demonstrated [4,5] that four-mirror projection systems can be designed by conventional techniques to have a resolution less than 0.1 micron over a 20 mm field of view with distortion limiting system performance. Canon has disclosed [6] a number of three- and four-mirror projection lithography systems which are reported to yield 0.25 micron resolution over large fields of view.