Electroless nickel ternary alloy deposition on SiO₂ for application to diffusion barrier layer in copper interconnect technology

Electroless NiWP and NiReP films were investigated with the aim of application to barrier and capping layers in interconnect technology. These alloys containing a refractory metal with a high melting point were expected to have the ability to avoid diffusion of Cu into the interlevel dielectric. The composition and resistivity of these films were investigated first in order to know the relation between the composition and its thermal stability. The thermal stability was investigated by measuring the sheet resistance and the cross-sectional observation with field emission scanning electron microscope. Additionally, an electroless Ni alloy deposition on the SiO₂ layer without a sputtered seed layer was also examined by utilizing a self-assembled monolayer (SAM) as an adhesion and catalytic layer. Since an alkaline solution damaged the SiO₂ surface, a two-step process, which consists of a nucleation step performed in an acid electroless deposition bath and a barrier layer formation step carried out in an alkaline bath, is employed in order to fabricate a consistently uniform barrier film on the SAM/SiO₂ surface. It was found that the NiReP films formed on SAM/SiO₂ surfaces were stable up to 400°C, and are feasible for the barrier layer for the Cu interconnect technology.