IMPROVEMENT OF FOCUS AND EXPOSURE LATITUDE BY THE USE OF PHASE-SHIFTING MASKS FOR DUV APPLICATIONS

Three types of phase-shifting mask designs are studied with respect to their suitability to print periodical L/S structures. The evaluation criteria are DOF, exposure latitude, linearity, and image contrast and slope of the intensity profile. Mask-making issues are also taken into account. The investigation is based on both simulations and experimental results. A fully transparent shifter causing an optical shift of 180 degrees is considered. A negative tone photoresist is used for the exposures with a KrF excimer laser stepper (248 nm).