Atomic layer deposition of cobalt using H\u3csub\u3e2\u3c/sub\u3e-, N\u3csub\u3e2\u3c/sub\u3e-, and NH\u3csub\u3e3\u3c/sub\u3e-based plasmas:on the role of the Co-reactant

\u3cp\u3eThis work investigates the role of the co-reactant for the atomic layer deposition of cobalt (Co) films using cobaltocene (CoCp\u3csub\u3e2\u3c/sub\u3e) as the precursor. Three different processes were compared: an AB process using NH\u3csub\u3e3\u3c/sub\u3e plasma, an AB process using H\u3csub\u3e2\u3c/sub\u3e/N\u3csub\u3e2\u3c/sub\u3e plasma, and an ABC process using subsequent N\u3csub\u3e2\u3c/sub\u3e and H\u3csub\u3e2\u3c/sub\u3e plasmas. A connection was made between the plasma composition and film properties, thereby gaining an understanding of the role of the various plasma species. For NH\u3csub\u3e3\u3c/sub\u3e plasma, H\u3csub\u3e2\u3c/sub\u3e and N\u3csub\u3e2\u3c/sub\u3e were identified as the main species apart from the expected NH\u3csub\u3e3\u3c/sub\u3e, whereas for the H\u3csub\u3e2\u3c/sub\u3e/N\u3csub\u3e2\u3c/sub\u3e plasma, NH\u3csub\u3e3\u3c/sub\u3e was detected. Moreover, HCp was observed as a reaction product in the precursor and co-reactant subcycles. Both AB processes showed self-limiting half-reactions and yielded similar material properties, that is, high purity and low resistivity. For the AB process with H\u3csub\u3e2\u3c/sub\u3e/N\u3csub\u3e2\u3c/sub\u3e, the resistivity and impurity content depended on the H\u3csub\u3e2\u3c/sub\u3e/N\u3csub\u3e2\u3c/sub\u3e mixing ratio, which was linked to the production of NH\u3csub\u3e3\u3c/sub\u3e molecules and related radicals. The ABC process resulted in high-resistivity and low-purity films, attributed to the lack of NH\u3csub\u3ex,x≤3\u3c/sub\u3e species during the co-reactant exposures. The obtained insights are summarized in a reaction scheme where CoCp\u3csub\u3e2\u3c/sub\u3e chemisorbs in the precursor subcycle and NH\u3csub\u3ex\u3c/sub\u3e species eliminate the remaining Cp in the consecutive subcycle.\u3c/p\u3