Atomic layer etching of Sn by surface modification with H and Cl radicals

Sn is the one of the materials that can be used for next generation extreme ultraviolet (EUV) mask material having a high absorption coefficient and, for the fabrication of the next generation EUV mask, a precise etching of Sn is required. In this study, the atomic layer etching (ALE) process was performed for the precise etch thickness control and low damage etching of Sn by the formation SnH_xCl_y compounds on the Sn surface using with H and Cl radicals during the adsorption step and by the removal of the compound using Ar⁺ ions with a controlled energy during the desorption step. Through this process, optimized ALE conditions with different H/Cl radical combinations that can etch Sn at ∼2.6 Å cycle⁻¹ were identified with a high etch selectivity over Ru which can be used as the capping layer of the EUV mask. In addition, it was confirmed that not only the Sn but also Ru showed almost no physical and chemical damage during the Sn ALE process.