 The resolution limit may also originate from stochastic effects, as in the case of EUV.Consequently, 20 nm linewidth still requires EUV double patterning, due to larger defectivity at larger pitches.It is well-established that dense two-dimensional patterns, which are formed from the interference of two or three beams along one direction, as in quadrupole or QUASAR illumination, are subject to significant rounding, particularly at bends and corners.