Electrodeposition of Ni in Submicrometer Trenches

A survey of the effect of cationic, anionic, and nonionic surfactants on the rate and morphological evolution of nickel electrodeposition is presented. Attention is given to the prospect for void-free filling of submicrometer trenches. Cationic species such as polyethyleneimine (PEI) and cetyl-trimethyl-ammonium yield significant inhibition of nickel deposition. For a range of concentrations the single cationic surfactant systems exhibit hysteretic voltammetric curves that, when corrected for ohmic electrolyte losses, reveal an S-shaped negative differential resistance. Void-free bottom-up superconformal feature filling is observed when operating at potentials within the hysteretic regime whereby metal deposition begins preferentially in the most densely patterned regions of the wafer followed by propagation of the growth front laterally across the wafer surface. In contrast, at low overpotentials and concentrations, sulfur-bearing additives such as thiourea (TU) exert a depolarizing effect on nickel deposition and negligible hysteresis. When PEI and TU are both present, the suppression provided by PEI is diminished and feature filling leads to uniform deposition on the wafer scale. Suitable combinations of PEI and TU enable near void-free filling of wide trenches with sloping sidewalls. Initial conformal growth is followed by geometric leveling once the deposits on the sloping sidewalls meet.