Etching of Magnetic Tunnel Junction Materials Using Reactive Ion Beam

Abstract

agnetic tunnel junction (MTJ) materials such as CoPt, CoFeB, and MgO and the hard mask material such as W were etched with a reactive ion beam system using Ar, NF3, CH3OH, and CO/NH3 as etch gases. The effects of etch gas and the energy of the ion beam on the etch characteristics were then investigated. When the MTJ materials were etched with an Ar ion beam, the etch selectivities of the MTJ materials over W and the etch profiles of the etched MTJ patterns masked with W were generally poor, possibly due to the nonselective etching, physical sputtering without chemical reaction, and severe redeposition of the nonvolatile etch residues on the sidewall of the etched features. The use of NF3 -> CH3OH -> CO/NH3 reactive ion beam showed better etch selectivities over W and better etch profiles due to the higher etch selectivities of MTJ materials over W and less sidewall deposition. For reactive gases such as CH3OH and CO/NH3, the use of higher ion energy by increasing the 1st grid voltage of the ion beam up to +250 V also improved the MTJ etch profiles, possibly due to the increased effective chemical assisted physical sputtering of the etch products and the minimization of sidewall etch residues by removing etch products more effectively.