Optimization of mask absorber stacks and illumination settings for contact hole imaging
This paper reports on the mutual optimization of the mask geometry, mask absorber stack, and illumination settings for arrays of non-quadratic contact holes with different pitches. In contrast to previous work in this field, mask topography effects are fully taken into account. The proposed procedure is enabled by significant performance improvements implemented in the rigorous Waveguide EMF solver and by the application of global optimization techniques. In order to allow for a flexible and efficient interaction, all models and algorithms have been integrated into the Fraunhofer IISB development and research lithography simulation environment Dr.LiTHO. To demonstrate the flexibility of our optimization approaches, we have optimized the imaging of dense and semi-dense arrays of 65nm×90nm c ontact holes with a 1.35NA water immersion ArF scanner. The process performance is evaluated in terms of overlapping process windows of all relevant feature sizes.