Molecular dynamics simulation of damage formation in Ni due to H⁺ ion bombardment

Abstract

In the manufacturing of magnetoresistive random access memories (MRAMs), etching processes are used to form magnetic tunneling junction (MTJ) cells and damages formed by energetic ion bombardment on the side walls of MTJ cells can deteriorate their memory performance. Especially if reactive ion etching (RIE) is used and the etching gas contains hydrogen, as in the case of CO/NH₃ plasmas or CH₃OH plasmas, H⁺ ions generated in the plasma may collide with the surface of MTJ sidewalls and penetrate into the magnetic material, causing damages to the metal crystalline structure. Dislocations of the metal and deposited hydrogen atoms may migrate and reach the interface between the metal and insulator (such as MgO), where interfacial defects can adversely affect the magnetization properties of the MTJ cell. In this study, we have selected nickel (Ni) as a sample magnetic metal and examined the damage formation of a Ni substrate by the irradiation of H⁺ ions with an energy up to 500 eV at various angles of incidence, using molecular dynamics (MD) simulation. It has been found that H⁺ ions penetrate much more deeply into Ni than typical heavy ions (such as Ar+ ions) and dislocation of Ni by H⁺ ion incidence are also distributed deeply, even at large oblique angles of incidence.