Systematic Design of Phase-Shifting Masks with Extended Depth of Focus and/or Shifted Focus Plane

We propose an optimization based algorithm for designing phase-shifting masks. Our approach is an extension of our previous work [1]-[3] in the sense that the intensity image is optimized at a number of optical planes rather than just the focus plane. In addition, our algorithm can be used to design masks with shifted focus plane and/or extended depth of focus. We also propose the concept of “dual mask” and show its consequences to practical phase-shifting mask design. Finally we show examples of our proposed design techniques for single line phase connectors, cross phase connectors, contact holes and bright lines. Simulation and experimental results verify the capability of our design technique to extend depth of focus and shift the focus plane.