Mitigation of mask three dimensional induced phase effects by absorber optimization in ArFi and extreme ultraviolet lithography
Abstract. We will summarize our work on mask topography induced effects over the last 5 years. We will give a full physical explanation of the effects that can be observed from exposed wafers in state of the art immersion and extreme ultraviolet photolithography. The mask topography induced phase leads to vertical and lateral displacements of the aerial image, resulting in feature dependent best focus and position. The feature dependency has been studied for gratings through pitch and size and for two trench arrangements. The physical explanation involves the analysis and quantification of phase effects in a similar way as was done for projection lens aberrations one decade ago. Phase effects, derived both from rigorous simulations and an analytical model, will be compared with exposure figure or merits (e.g. best focus per feature) and correlate well. Therefore, the analysis of mask topography induced phase and the reduction thereof by absorber thickness optimization can be used to drive lithography improvements.