Reticle Critical Dimension Latitude for Fabrication of 0.18 µm Line Patterns

The reticle critical dimension (CD) latitude of 0.18 µm line patterns with various pitches was investigated from the standpoint of mask linearity, optical proximity effect (OPE) and depth of focus (DOF). We propose a global reticle CD latitude which is defined by the common range of allowable reticle CDs for various pitches. The global reticle CD latitude was enhanced under illumination conditions in which the OPE was suppressed, e.g., conventional illumination, and at the optimum numerical aperture (NA) which gave a wider DOF, especially for isolated lines. We found experimentally that the global reticle CD latitude (on x4 reticle, range) of 0.18 µm line patterns was 20 nm at NA=0.60 and σ=0.75 conventional illumination. Furthermore, from aerial image simulation results, the global reticle CD latitude was expected to be enhanced at the optimum NA (~0.68) by KrF, and at 0.60 NA by ArF lithography.