A new methodology for completely phase-shifting a poly layout without creating local phase conflicts was proposed for lithographic techniques combining one phase-shifting mask and one binary mask exposure. Critical and non-critical areas of the layout are identified and phase conflicts are avoided by splitting the shifter regions from non-critical areas to non-critical areas without crossing critical areas. The out-of-phase splits of the shifter regions are removed using the binary exposure.
Simulation results and experimental data collected for 90nm technology node show no sign of process latitude loss around the areas where the shifters are split. The overlay latitude is commensurate with 90nm technology scanner requirements (tool to itself).
For 65nm node, we have identified certain types of cuts that will be forbidden (or at least highly undesirable) during the generation of the phase-shifting layout; this is primarily the case for cuts in “elbow” structures which exhibit limited process latitude. Other cuts like line-end cuts will have to be modified.
Mask corner rounding effects were evaluated. Up to 80nm rounding does not create any significant change (below 2nm CD change at 1X) in the aerial image simulation as compared to the case where no rounding is assumed.