Electroless Plating Ni-based Barrier Layers for 3D Interconnection

Cu is the key material for both on-chip and inter-chip interconnections. It is the major interconnect material in packaging level, especially in through wafer electrical interconnection (TWEI). Barrier layer is necessary as Cu is easy to diffuse into Si, SiO₂ and other dielectrics. Comparing with traditional Ta and Ti based barrier layers, electroless plating NiMoP film has many advantages, such as seedless, low cost, lower resistivity, etc. Electroless plating NiMoP was investigated on SiO₂/Si. The plating solution was made up in house. Nickel sulfate and sodium molybdate were the sources of nickel and molybdenum. The effects of [MoO₄ ^2-]/[Ni²⁺] on the deposition rate of NiMoP and the film composition, electricity property, surface morphology & crystal structure were investigated. The deposition rate of NiMoP would be stable when the ratio of [MoO₄ ^2-]/[Ni²⁺] is higher than 0.08. The atom percentage of Mo in NiMoP film increases with the increasing of [MoO₄ ^2-]/[Ni²⁺]initially and then reaches a saturation amount at about 10 at%, while the concentration of P decreases with the increasing [MoO₄ ^2-]/[Ni²⁺]. The resistivity of NiMoP film can be as low as 70.2 muOmegacm. The optimized deposition condition for a low resistivity NiMoP barrier is with the pH value of 9.0-10.0, plating temperature in the range of 85-90degC and [MoO₄ ^2-]/[Ni²⁺]of around 0.043. With Auger analysis, the deposited NiMoP film can be the effective diffusion barrier layers after 400degC annealing. A demonstration of 3D interconnection with electroless NiMoP barrier layer has been fabricated.