Effect of Mask Erosion on Patterning of FePt for Heat-Assisted Magnetic Recording Media Using Embedded Mask Patterning

The embedded mask patterning (EMP) process provides a potential L1₀-FePt media solution for 1-10 Tbit/in² magnetic recording areal density level. Methanol/Ar reactive ion etch process of FePt media (Ru 2 nm/FePt 8 nm) in EMP is investigated using an ion-neutral-redep synergy etch rate model with the consideration of sputtered redeposition. It has been found that etching of high aspect ratio features spacing that is largely limited by its low etch rate due to high redeposition rate; etching of small size grains is mostly limited by hard mask erosion through the etching process. This would cause etch non-uniformity within the grain size and grain spacing distribution. The hard mask on top of the small size grains (i.e., less than 3 nm) erodes much faster than the larger size gains, resulting in a completely consumed mask before the underlying layers are reached. It is important to reduce local ion sputtering in order to minimize mask erosion for the small grains. We have found that a higher chemical etch selectivity (>30:1) is essential to minimize mask erosion on the grains of 2 nm or larger. We also report that when sputter yield of Ru mask and FePt is adjusted from 10^-1 to 10^-2 level, further improvement is observed with the patterned grain size down to 2.5 nm and spacing down to 1.5 nm, and we suggest that the use of etch gas chemistry with a lighter atomic weight (such as He instead of Ar) would allow for sub-10 nm grain patterning.