[20p-438-1~21] 8.2 Plasma deposition of thin film, plasma etching and surface treatment

▲ [20p-438-3] Atomic-layer etching (ALE) of magnetic films by Hexafluoroacetylacetone (HFAC) molecules

〇(D)Abdulrahman Hikmat Basher¹, Michiro Isobe¹, Tomoko Ito¹, Masato Kiuchi², Take Takeuchi³, Kazuhiro Karahashi¹, Ikutaro Hamada¹, Yoshitada Morikawa¹, Satoshi Hamaguchi¹ (1.Osaka Univ., 2.AIST, 3.Nara Womens Univ.)

Keywords:ALE, organic etchants, magnetic martial etching

Manufacturing of nanometer-scale MRAM devices is still a challenge due to the difficulties in atomic-scale patterning of (MTJ) stacks used to store data. The development of controllable etching processes for nanometer-scales patterning with high anisotropy and low damage formation is required for the manufacturing for such devices. Each MTJ stack consists two ferromagnetic layers separated by a dielectric barrier layer and highly controllable etching processes may be established by using organic etchants. One of the organic etchants that may be used for such processes is (hfac), which can form volatile metal complexes from a metal surface and therefore etch the surface. A typical sequence of hfac etching of a metal surface may be the following: (1)a metal (or its oxidized) surface is to hfac, (2)under certain conditions, volatile organometallic compounds are formed on the surface, (3)volatile organometallic compounds is removed when the surface temperature is increased. In this process, if the metal surface is completely covered by hfac molecules, a single metal layer is expected to be removed. By repeating this process, ALE of a metal surface is established. For example, in the case of a nickel (Ni) surface, hfac can form Ni(hfac)2 as a volatile molecule. Similar etching processes may be developed for other magnetic martials such as Fe and Co with the use of different etchants such as (acac) and (fa). In this study, we performed first-principles QM calculations to study the interaction of a Ni surface with hfac molecules. Experimentally it has been observed that slight oxidation of Ni will increase the probability of the formation of Ni(hfac)2 on a Ni surface exposed to hfac. It has been found that a decomposition of an hfac molecule can be energetically preferred when an hfac molecule is placed on a metallic Ni surface whereas an hfac molecule can be stably adsorbed on a NiO surface because hfac can be deprotonated and form a metal complex with a surface Ni.