Nanoscale patterning of Ru. II. Anisotropy and selectivity

A cyclic process consisting of plasma nitridation, hydrogen plasma reduction, and etching by oxygen plasma was developed, achieving an etch rate of 3.6 or 0.2 nm per cycle, with and without ions, respectively (Part I). In this work, the ion-dependent etch was confirmed from etching nanoscale patterned ruthenium samples. Oxygen plasma produced an etch profile with undercut and an etch anisotropy of 4 and a selectivity of 27 with respect to the hard mask, SiO2. The N2/O2 cyclic process increased the anisotropy to 10, but the etch profile was slightly tapered due to passivation by RuN. The N2/H2/O2 cyclic process maintained an anisotropy of 10 and achieved more vertical etched profiles with no redeposition on the hard mask sidewalls and a selectivity of 16. On features with a pitch as low as 35 nm, the cyclic process resulted in an anisotropic etch profile and less aspect ratio dependence while maintaining a high selectivity versus the hard mask.