Polarization effects induced by the bi-layer attenuated phase-shift mask and their impacts on near-field distribution

As ArF projection lithography is approaching 45 nm technology node and beyond, polarization effects induced by mask are remarkable. At this mask dimension, traditional Kirchhoff approximation is invalid. Rigorous mask model is needed for accurate evaluation of mask diffraction. In previous works, many researchers are focus on the single grating layer diffraction. In this paper, Lee's formulation based on rigorous coupled wave analysis is applied to simulate the bi-layer grating diffraction in lithography. Then, polarization states as function of mask and incident light properties are evaluated. At last, the impacts on near-field distribution with different polarization state are further investigated. The image quality becomes worse under TE polarization, when Ta thickness becomes 35 nm, where the phase effects are effectively reduced. There should be a tradeoff between them.