Effects of phase shift masks on across field linewidth control

The concept of the iso-aberration dose is introduced and defined as the dose where the "depth of aberration" is at a maximum. By allowing patterning of small isolated lines closer to the isoaberration dose, the use of phase shift masks (PSMs) improves critical dimension (CD) sensitivity to lithographic tool aberrations. The use of specialized photo-resist and mask assist features is also found to improve isolated line CD sensitivity to aberrations. The improvement in aberration sensitivity from PSM results in improved across field linewidth control for some lithographic systems but causes degraded CD control for other tools which are optimized for operation with standard binary reticles. Simulations show that the trim mask PSM approach has superior aberration sensitivity for patterning 100nm than multi-phase PSM approaches when the allowed phasewidth is restricted to a maximum value.