Efficient light scattering modeling for alignment, metrology, and resist exposure in photolithography

In previous work, a two-dimensional waveguide model has been developed and examined extensively so that rigorous light scattering calculations for photolithography-related processes, such as stepper alignment, linewidth and overlay measurements, and resist bleaching, can be performed. The computation, however, is expensive if the wafer topography involved is complicated or if resist bleaching problems are involved. Numerical techniques that reduce CPU usage by approximately an order of magnitude are reported. These techniques make the waveguide model more practical to use. Typically, for each polarization state, it takes 10 to 200 s to simulate a static case (e.g. linewidth measurement), and it is projected that it will take 7 to 70 min to simulate a dynamic case (e.g. resist bleaching under 13 incoherent illumination point sources and ten exposure steps) on a high-speed workstation such as an IBM RISC/6000 Model 530