Thick selective electroless-plated cobalt-nickel alloy contacts to cosi2: I. Material properties

Thick (>1 (µm) selective electroless plating of Co, Ni, and their alloys is used to provide ‘plug’ contacts to shallow junctions below CoSi2. After a brief discussion of the electroless plating procedure and material characteristics, we concentrate on plating uniformity relating to substrate doping and window definition by reactive ion etching. Optical and scanning electron microscopy correlates the plating uniformity with the reactive ion etch chemistries used to pattern windows in a deposited dielectric to CoSi2. The plating yield is poor when only a brief dilute HF pretreatment is used to remove residues remaining on CoSi2 after a CHF3/CO2 reactive ion overetch. Appropriate pretreatment is suggested after determining the chemical nature of the modified CoSi2 surface with x-ray photoemission spectroscopy. We discuss the thermal stability of the Al/Co-Ni/CoSi2/Si metallization for various hydrogen anneal cycles up to 450°C. The Co-Ni plug metallization can be annealed at ~400°C without any Co/CoSi2/Si interaction. A Co-W alloy extends the thermal stability to ~450°C. Al/Co interact at ^400°C. Data are derived from Rutherford backscattering and Auger electron spectroscopies and cross-sectional transmission and scanning electron microscopies. The data indicate that an appropriate low-stress electroless plated alloy, deposited on a properly pretreated surface, provides a good plug process for multilevel metallization of shallow junctions.