Characterization of Pd-free electroless Co-based cap selectively deposited on Cu surface via borane-based reducing agent

In this work, a highly selective and self-activated (Pd-free) Co-based deposition process for capping of Cu-lines is presented. TEM images of the cross-section of capped Cu-lines show no extraneous deposition, which translates to selectivity and direct deposition of Co-based alloy on the Cu surface without Pd-activation as a pretreatment step in conventional electroless deposition. Furthermore, an 8.6% increase in the sheet resistance(Rs) via Pd-activation process which is higher than that of the Co-based self-activated process indicates that Pd may diffuse into Cu line and induce Rs increase. Results from grazing incidence X-ray diffraction (GIXRD) analysis on as-deposited Co-based films reveal that it has a nano-crystalline structure. Such structure changes very little after annealing over 400 °C for 30 min. AES depth profiles also reveal a uniform distribution of the elemental components and extremely low B content. Additionally, Cu was not detected on Co cap film, indicating such films could serve as diffusion barrier layers to inhibit Cu diffusion.