KrF excimer laser lithography with a dummy diffraction mask

In this paper, we report the sub-quarter-micron lithography of a KrF excimer laser stepper with a dummy diffraction mask (DDM). A homemade KrF excimer laser stepper (N.A.=0.42, sigma=0.34) was used as the exposure tool, and an L/S-phase-grating-type DDM was adopted. The result for the resolution limit of a conventional mask was 0.34 mu m L/S with a 1.5 mu m depth of focus while that of the DDM was improved to 0.2 mu m L/S with a 0.9 mu m depth of focus. The DDM consist of a 0.5 mu m L/S phase grating, and it enhance not only the resolution but also the depth of focus for the L/S patterns. This result was consistent with a simulation obtained by using a homemade simulator.