Patterned FePt media solutions, such as Bit-Patterned Media (BPM) and Embedded Hardmask Patterning (EMP), have been proposed as alternative methods to improve Heat-Assisted Magnetic Recording areal density. Understanding etching mechanism of FePt material is important to warrent the low damage to the magnetic properties caused by micro-fabrication process. In this research, Reactive Molecular Dynamics (MD) modeling is carried out to study methanol (MeOH) plasma etch on L10-FePt media. The atomistic-level etch simulation process is divided into two sequential MD simulation steps: the radical-based reactive treatment step, followed by the ion-based physical etch step. Carbon-monoxide (CO) and H2 molecules are identified as the main etch precursors in methanol plasma interacting with substrate. Reactive interaction between CO/H2 radicals and Fe/Pt atoms is studied using bond-order ReaxFF force field with atomic charge calculation. Bond energy calculation shows the positively charged Fe and Pt and the negatively charged C atoms in CO molecules can form ionic carbonyl bonds that are shown more stable than Fe-Pt metallic bonds. As the result, it is found that the number of Fe(CO) and Pt(CO) carbonyl bonds are dominated among the new bonds produced after the reactive-treatment process. In the following physical etch step simulated with Ar or He ion bombardment, in comparison with FePt surface without CO/H2 treatment, the sputter yield of FePt can significantly improve by 2-4X on the samples with the CO/H2-treatment step.
1 H. Wang, H. Zhao, P. Quarterman, and J.-P. Wang, Appl. Phys. Lett., vol. 102, no. 5, p. 052406, 2013
2 Patent: US10,347,467B2, J.-P. Wang, P. Quarterman and J. Zhu
3 LAMMPS - A flexible simulation tool for particle-based materials modeling at the atomic, meso, and continuum scales, Comp. Phys. Comm. (accepted 09/2021), DOI:10.1016/j.cpc.2021.108171
4 J. Zhu, P. Quarterman, J.-P. Wang, AIP Advances 2017, 7 (5) , 056507. https://doi.org/10.1063/1.4977223
Figure 1. Number and types of carbonyl bonds created on FePt surface after CO/H2 exposure
Figure 2. FePt sputter yield ( with Ar ions) comparison on CO/H2-treated and non-treated surface