Ion-assisted plasma etch modeling of L10 phase FePt magnetic media fabrication with embedded mask patterning method

Embedded Mask Patterning (EMP) method uses a plasma etching process to form ultra-small but thermally stable isolated L1₀-FePt magnetic grains with embedded Ru hardmask^1,2. It has been demonstrated as a promising and highly cost effective solution to fabricate the ultra-high density magnetic media for the next generation hard-disk drive technology, such as heat-assisted magnetic recording (HAMR). EMP process can produce recording media with extremely small and tunable grain size with narrow grain boundary thickness¹. For example, at 10 Tbit/in² recording density the required aspect ratio of vertically etched L1₀-FePt bit is estimated as high as 4:1 with bit diameter ~4-5nm and grain boundary ~2-3nm. In this simulation study, we investigated manufacturability of formation of these nanometer size features in a CH₃OH/Ar plasma etch process which is used to etch FePt through narrow Ru mask opening and to form volatile Fe-carbonyl product. With addition of Ar gas the etch selectivity of hard mask and magnetic material can be significantly improved³. In order to account for re-deposition of etch product, based on the ion-neutral synergy model^4,5,6 we have formed a new chemical-physical etch rate model that also includes the effect of re-deposited etch product by calculating the re-deposition flux distribution in addition to neutral and ion flux coverage over the etch surface. Our simulation shows that the re-deposition rate can increase as etch progresses deeper into the substrate. It significantly reduces the etch rate more inside the higher aspect ratio (AR) features and produces non-uniform etched patterns across the grain boundary distribution, which may degrade media magnetic properties. The etch rate model is combined with a developed 2-D level set computational program to track the moving etch front at different etch time interval with the real-time etch rate distribution calcu- ation. As the result, the simulation allow us to gain insights into the etch process characteristics and to help find optimal etch parameters using the EMP process to fabricate high density recording media.