Atomic Layer Deposition of Cobalt Using H(2)-, N(2)-, and NH(3)-Based Plasmas: On the Role of the Co-reactant

[Image: see text] This work investigates the role of the co-reactant for the atomic layer deposition of cobalt (Co) films using cobaltocene (CoCp(2)) as the precursor. Three different processes were compared: an AB process using NH(3) plasma, an AB process using H(2)/N(2) plasma, and an ABC process using subsequent N(2) and H(2) 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(3) plasma, H(2) and N(2) were identified as the main species apart from the expected NH(3), whereas for the H(2)/N(2) plasma, NH(3) 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(2)/N(2), the resistivity and impurity content depended on the H(2)/N(2) mixing ratio, which was linked to the production of NH(3) molecules and related radicals. The ABC process resulted in high-resistivity and low-purity films, attributed to the lack of NH(x,x≤3) species during the co-reactant exposures. The obtained insights are summarized in a reaction scheme where CoCp(2) chemisorbs in the precursor subcycle and NH(x) species eliminate the remaining Cp in the consecutive subcycle.