Reducing proximity effects in optical lithography

Using simulation, the influence of stepper parameters on optical proximity effects is explored. In particular, numerical aperture and partial coherence will be examined for a variety of feature sizes and types. Both one-dimensional and two-dimensional mask features will be studied. The impact of resist contrast will also be explored. In addition to the iso-dense print bias as a metric of proximity effects, the depth of focus as an overlapping of two focus-exposure process windows, one for the isolated line and one for the dense line, will be used. The optimum NA and sigma will give the maximum depth of focus calculated from the overlapped process window. Finally, the statistical CD distribution methodology will be used to find the stepper settings that minimize the linewidth distribution spread for a given process.