Nanoscale patterning of Ru. I. Effect of plasma nitridation and hydrogen reduction

For ruthenium to be a viable replacement for copper interconnects at the sub-10 nm scale, an anisotropic and selective etching process is required. A cyclic chemical process with sequential exposure to N2, H2, and O2 plasmas was developed to circumvent the isotropic etch profile by O2 plasma alone, tailoring the reactions for anisotropy and selectivity. RuN was formed in N2 plasma to act as a passivation layer against O2 plasma etching of Ru. A hydrogen plasma was able to reduce RuN to Ru, with low energy hydrogen ions enhancing the reduction. A cyclic process with sequential exposure to N2, H2, and O2 plasmas, where ions are present, yielded an etch rate of 3.6 nm per cycle. When ions were excluded, the etch rate was reduced to 0.2 nm per cycle, signifying the importance of ions in nitridation and reduction processes. Since ion bombardment on the sidewall of an evolving feature is much less than that on the feature bottom, this difference suggests that a greater etch anisotropy and selectivity can be achieved by this cyclic process, as detailed in Part II.