We perform 3D lithography simulations by using a finite-element solver. To proof applicability to real 3D problems we investigate DUV light propagation through a structure of size 9 μm × 4 μm × 65 nm. On this relatively large computational domain we perform rigorous computations (No Hopkins) taking into account a grid of 11 × 21 source points with two polarization directions each. We obtain well converged results with an accuracy of the diffraction orders of about 1%. The results compare well to experimental aerial imaging results. We further investigate the convergence of 3D solutions towards quasi-exact results obtained with different methods.