Image Simulation of Extreme Ultraviolet Lithography Optics: Effect of Multilayer Coatings

Multilayer deposition technology is indispensable to the production of extreme ultraviolet (EUV) optics. However, the criteria of the multilayer d-spacing control techniques that are needed from the viewpoint of ULSI lithography has not yet been made clear. We have numerically evaluated EUV lithography optics in terms of the imaging performance and pattern placement accuracy. The tolerance of d-spacing distribution error for a two-mirror imaging optics was derived from a simulation method that takes multilayer reflectance and phase shift into consideration. Also, an image-contrast enhancement technique based on the d-spacing distribution is proposed for a three-mirror imaging optics.