The impact of the mask stack and its optical parameters on the imaging performance

Rigorous electromagnetic field (EMF) simulations of light diffraction from the mask in combination with vector imaging simulation are used to explore the impact of the optical mask parameters on the diffraction and imaging performance. Optical mask parameters and mask stack configurations are varied over a wide range and independently from the presently used materials. The results are evaluated in terms of diffraction efficiencies and typical lithographic performance criteria such as iso-dense bias, mask error enhancement factor (MEEF), sidelobe-printability, and (overlapping) process windows. Both local and global optimization techniques are used to identify optimum parameter settings. The results are compared with the performance of standard mask stacks and parameters.