Electromagnetic phenomena in advanced photomasks

The adoption of resolution enhancement techniques (RET) for subwavelength lithography relies on performing accurate simulation of mask effects. Although topography effects have been successfully used in RET flows, the impact of electromagnetic effects such as surface plasmons tend to be ignored. It is known, however, from the performance of “C-shaped” apertures that extraordinary transmission and opacity can be achieved using these electromagnetic effects. We have examined simulations for representative 45 nm features using both conventional and novel finite difference time domain simulators. When the mask material is assumed to be conducting chromium, we found that electromagnetic effects appear to be significant and highly dependent on polarization. This may place additional constraints on the specification of mask material composition for these integrated circuit generations.