Computation of reflected images from EUV masks

The reflective mask used in Extreme Ultraviolet Lithography is based on a m ultilayer stack reflector, over-coated with a suitable absorber. We show th at in order to predict correctly the reflected field it is necessary to des cribe in detail the diffraction and multiple reflection processes that the propagating field undergoes in the multilayer stack. The effects of absorbe r thickness, mask bias and partial spatial coherence are shown through seve ral examples using numerical calculations.