Impact of source pupil shapes on process windows in EUV lithography

Abstract

International Technology Roadmap for Semiconductors (ITRS) report proposes extreme ultraviolet (EUV) lithography to be the key candidate of lithography tools to manufacture devices at the 22nm node and beyond. The image effects on wafer critical dimensions (CDs) in the EUV lithography are different from the effects in the conventional lithography caused by the off-axis illumination and refelective optics design. This research investigates process windows of line/space (L/S) with the target CD 22nm and contact hole (CH) features with the target CD 35nm illuminated by the conventional, annular, dipole, and quasor source shapes. The diffraction amplitudes by the EUV mask are summarized. The research suggests that the dipole is the better illumination source shape to print L/S features and the quasor is the better one for CH features. In addition, the research reports the best dipole illumination setting for the L/S features and the best quasor illumination setting for the CH features. The exposure latitude and depth of focus (DOF) for L/S feature illuminated by the dipole to print the target CD 22nm are 4% and 100nm respectively. The exposure latitude and DOF for CH feature illuminated by the quasor to print the target CD 35nm are 24% and 300nm respectively. Full field analysis of CH CDs displays the minimized CD error through slit due to the quasor illumination in the EUV lithography.