Optimizing edge topography of alternating phase shift masks using rigorous mask modelling

This paper describes mask topography effects of alternating phase shift masks for DUV lithography. First two options to achieve intensity balancing are discussed. Global phase errors of +-10° cause a CD change of 3 nm and 8 nm CD placement errors. The CD placement appears to be the parameter affected most by phase errors. A sloped quartz edge with an angle of 3° causes a CD change of 10 nm. The CD sensitivity on local phase errors, i. e. quartz bumps or holes was also studied. The critical defect size of a quartz bump was seen to be 180 nm (5 x) for 150 nm technology. For the investigation the recently developed topography simulator T-Mask was used. The simulator was first checked against analytical tests and experimental results.