When considered from a spatial frequency standpoint, that attenuated phase shift mask and assist bar OPC perform functions that can be compared to frequency filtering. The combination of these two resolution enhancement techniques can be evaluated from this perspective and they can be optimized together to produce maximum desired effects. We will describe a simple method of RET analysis and introduce a new concept to assist bar OPC where non-zero transmission of the bar is allowed. Gray assist bar OPC can offer for significant control over imaging performance.
Bruce W. Smith, Bruce W. Smith,
"Spatial filtering effects of the attenuated PSM and assist bar OPC", Proc. SPIE 4404, Lithography for Semiconductor Manufacturing II, (26 April 2001); doi: 10.1117/12.425233; https://doi.org/10.1117/12.425233