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 illumination 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 illumination, if present resist performance is improved slightly, and (3) wider DOF is obtained in the case of with 4-point illumination. However, the DOF is rather degraded in the specific sized (near double/triple sized) region and oblique pattern, therefore the application of this illumination is restricted into some specific mask layout pattern.