Impact of source polarization on the imaging of line and space features at 45nm half pitch node

Polarization studies become increasingly important as optical lithography is being pushed into 45nm half pitch node. Some image simulations and experimental exposure results confirmed the advantage of the polarized illumination for high NA imaging of dense line/space (L/S) patterns. However, the imaging of semi-dense and isolated features with polarized illumination has not yet been fully investigated. In this paper the imaging of L/S patterns with different duty cycles was fully studied at 45nm half pitch node for varied polarized illumination modes. The lithography performances were then analyzed. The results show that the use of polarization that is parallel to the line orientation, i.e. the Y direction, improves lithography performances, while the use of polarization that is perpendicular to the line orientation, i.e. the X direction, deteriorates lithography performances. It is especially true for not only dense but also semi-dense and isolated features. The use of TE or TM polarization will not result in remarkable improvements of lithography performance when employing a combination of conventional illumination (CI) and alternative phase mask (altPSM). In case of the combination of dipole or cross-quasar (C-Quad) illumination and attenuated phase mask (attPSM), however, TE polarization will behave like Y polarization and TM polarization behave like X polarization. Compared with the imaging of dense and isolated features, the imaging of semidense features can have better process capability. The total image performance will be more desirable in the case applying CI and altPSM (or dipole and attPSM) than that in the case applying C-Quad and attPSM.