Investigation of mask defectivity in full field EUV lithography

Abstract

A detailed defect printability analysis is reported for conditions that are fully representative for the world's first full field EUV scanner, using 4X reticles, as obtained by simulation. For absorber type defects the historical rule of thumb underestimates the printability. An opaque defect located in a space within a 40nm lines and space pattern can already cause more than a 10% change in the space width from 80% of the space width onwards (>32nm at mask scale, >8 nm at wafer scale) depending on its location. Absorber type clear defects start affecting line width in 40nm lines and spaces from about twice the size of an opaque defect. Particles simulated as carbon cubes have a similar effect as absorber type opaque defects provided that they are about 50% larger. Other possible particle materials are investigated as well. Local carbon deposition, which may originate from SEM inspection, can cause a printing effect already at a thickness of only 2nm. Multilayer or substrate type defects require surface smoothing to less than about 2nm, as to keep the impact of so-called phase defects under control. Experimental plans for comparison of simulations to exposures on the ASML Alpha Demo Tool installed at IMEC are included.