Paper PS-TuP7
Molecular Dynamics Simulation of Ni Self-sputtering and Modeling of Interatomic Potential Functions

Tuesday, October 31, 2017, 6:30 pm, Room Central Hall

Plasma etching techniques have been widely used to manufacture semiconductor devices. Typical device scales of silicon (Si)-based field effect transistors (FET) are now approaching atomic scales. For the further development of plasma etching techniques to fabricate such small devices, a good understanding of plasma-surface interactions is indispensable. For example, during a plasma etching process with energetic ion bombardment, damages may be induced and lead to the formation of non-functional regions inside the created device structures. Therefore plasma-induced damages have to be avoided as much as possible.

In the production of magnetoresistive random-access memories (MRAM), stacks of thin layers of magnetic metals and insulators are deposited and etched to form magnetic tunnel junction (MTJ) cells. In typical manufacturing processes of MTJ cells, ion milling with energetic Ar+ ions are used. However, to further miniaturize MTJ cells and increase the MRAM integration, one would need less damaging and more selective etching processes for magnetic materials and insulators. The ultimate goal of this study is to establish reactive ion etching (RIE) processes for MTJ cells and we approach this goal by examining etching characteristics of magnetic materials with various reactive ions theoretically, using molecular dynamics (MD) simulations and first-principle quantum mechanical (QM) simulations. In this study, we take nickel (Ni) as a sample magnetic material.

In classical MD simulations, the interatomic potential models must be selected from the existing models or created based on QM simulation. It has been found that, with most existing interatomic potential models for Ni, the physical sputtering yields of Ni obtained from ion beam experiments for high ion incident energies cannot be reproduced by MD simulation. Therefore, in this study, we have focused on self-sputtering of Ni and examined the dependence of the self-sputtering yield on the interatomic potential functions. Since the Ni self-sputtering yield at a high ion incident energy sensitively depend on the short-range repulsive atomic interaction, we have determined the short-range interatomic functions based on experimentally observed Ni self-sputtering yields. It has been found that the newly adjusted interatomic potential model for Ni, which is based on the embedded atom model (EAM), can reproduce experimentally obtained Ni self-sputtering yields over a wide range of ion incident energy. Using the newly created interatomic potential model, we have also determined the dependence of the Ni self-sputtering yield on the ion incident angle.