Mask and wafer topography effects in immersion lithography

The paper investigates the application of different modeling approaches for mask diffraction and wafer exposure analysis in the hyper imaging NA regime. Immersion lithography implies larger angles of incidence of the light which illuminates the mask. This effect limits the validity of the so called Hopkins approach for the rigorous simulation of light diffraction from the mask. It is demonstrated that strong phase shifting techniques in combination with off-axis illumination are not adequately modeled by the Hopkins approach. Moreover, the application of immersion lithography results in larger light propagation angles inside the resist/wafer stack. The application of rigorous electromagnetic field (EMF) simulation for the description of the wafer side light propagation demonstrates the limitation of the performance of single antireflective coatings (ARC). Rigorous EMF wafer simulations are also used to explore the printability of small air bubbles in the immersion liquid, which stick to the surface of the resist. Finally, a new approach (RENFT) for efficient rigorous EMF wafer simulations is proposed.