OPTIMIZATION OF OPTICAL-PARAMETERS IN KRF EXCIMER-LASER LITHOGRAPHY FOR QUARTER-MICRON LINES PATTERN

Optical parameters of KrF excimer laser stepper are optimized for 0.25 mum level patterning by means of a light intensity simulation method. The light intensity simulation method is applied in conventional and two modified illuminations (annular and 4-point) to improve the depth of focus (DOF) at 0.25 mum periodic lines and spaces pattern (L & S). Simulation results obtained are; (1) the DOF of conventional illuminat ion is not sufficient even in the optimum condition (NA = 0.5, sigma = 0.8), (2) more than 1.5 mum DOF could be achieved with an annular ill umination, if present resist performance is improved slightly, and (3) wider DOF is obtained in the case of with 4-point illumination. Howev er, the DOF is rather degraded in the specific sized (near double/trip le sized) region and oblique pattern, therefore the application of thi s illumination is restricted into some specific mask layout pattern.