Capability of etched multilayer EUV mask fabrication

Recently, development of next generation extremely ultraviolet lithography (EUVL) equipment with high-NA (Numerical Aperture) optics for less than hp10nm node is accelerated. Increasing magnification of projection optics or mask size using conventional mask structure has been studied, but these methods make lithography cost high because of low through put and preparing new large mask infrastructures. To avoid these issues, etched multilayer EUV mask has been proposed. As a result of improvement of binary etched multilayer mask process, hp40nm line and space pattern on mask (hp10nm on wafer using 4x optics) has been demonstrated. However, mask patterns are easily collapsed by wet cleaning process due to their low durability caused by high aspect ratio. We propose reducing the number of multilayer pairs from 40 to 20 in order to increase durability against multilayer pattern collapse. With 20pair multilayer blank, durable minimum feature size of isolated line is extended from 80nm to 56nm. CD uniformity and linearity of 20pair etched multilayer pattern are catching up EUV mask requirement of 2014.