Simulation of light scatter from defects in EUV mask blanks

Using light scatter simulations, we have predicted the PSL-equivalent sensitivity needed for mask blank inspection. The simulation procedure has two steps. First, the electromagnetic field scattered off a feature is calculated by solving Maxwell´s equations with a time-domain finite-element method. Then, the resultant near field is extrapolated to the far field using the Kirchhoff diffraction formula. We performed two-dimensional simulations at a wavelength of 488 nm (Ar laser). The mask blank is illuminated by an s-polarized plane wave at normal incidence. We also discuss the angular distribution of scattered intensity, as well as the effects of incident angle and wavelength on light scattering.