Evaluation of 3D alternating PSM structures using mask topography simulation and AIMS at λ=193nm

The extendibility of alternating aperture phase shifting, masks (AAPSM) is investigated using reticle topography simulation. Aerial image measurements with an ArF AIMS tool are used to calibrate the simulated performance of the AAPSM. Simulations are performed for several illumination conditions through pitch allowing understanding of reticle performance that will be required to reach the 70nm node. Simulation convergence, speed, and memory requirements are also reported on for Solid CM. Experimental AIMS data are analyzed to extract the effective phase through pitch for several etch targets. These phase measurements are compared to simulations using AFM characterization of the same mask. Simulated aerial images through pitch are directly compared to those measured on AIMS. Qualitative agreement between AIMS and simulated images is obtained, but the contrast of the AIMS images is consistently lower. Image balance sensitivity, phase error sensitivity, and quartz sidewall angle sensitivity are defined and examined to identify performance limiting aspects of implementing AAPSM for the 70nm node over a range of pitches. Example phase sensitivity values are derived using mask topography simulation and used to define phase error specifications. AIMS and mask topography simulation show that smaller pitches and spaces are more sensitive to etch depth variation. Simulation also reveals quartz sidewall angle variation results in an apparent phase error where an under-cut behaves like an over-etch and inward sloping sidewalls behave like an under-etch. A correction to the well known etch target formula is proposed to account for sidewall angle variation.