Maximising the process window in sub-half-micron optical lithography.

The effect of resist thickness on depth-of-focus (DOF) is examined. It is s een that for maximum DOF the maximum in-coupling point of the swing curve m ust be selected whether the substrate is highly reflective bare silicon or one utilising a bottom anti-reflective coating (BARC). In addition, it is s hown that the maximum DOF on the BARC-coated substrate exceeds that on any point of the swing curve for the bare silicon substrate. The simulation par ameters used have been highly refined to give excellent correlation with ex periment over a wide range of conditions. Initial practical results are als o presented which tend to confirm these simulated results.