TEM-EDX Characterization of Immersion Pd & Pd-MoOx on Cu & NiP

Immersion palladium (Pd) alloyed with molybdenate (MoOx) is developed and coated on copper (Cu) to reduce the Cu diffusion into Pd. The level of Cu diffusion was compared with immersion Pd. The Pd and Pd-MoOx layer coated on top of Cu and the layers’ interface are characterized using Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray (EDX) line scan. Approximate 55 - 60 atomic% of Cu diffusion into the Pd layer is observed for immersion Pd (70 nm) coating on Cu. While immersion Pd-MoOx provides a Pd layer of 37nm thickness with less Cu diffusion (appx. 40%). Immersion Pd and Pd-MoOx were also performed on sample with electroless nickel phosphorous (NiP) layer. Significant crystalline structure of immersion Pd layer with approx. 45nm thickness is observed. The grain size of crystalline structure of Pd-MoOx (58 nm) on NiP is smaller compared to the one of Pd only. With the integration of MoOx and oxide into the Pd layer, it is expected that the density of the film will be greatly reduced. Finally, the NiP samples coated with Pd and Pd-MoOx were dipped into immersion gold (Au) solution for 10 minutes respectively, where both samples show Au thickness of approximately 70 nm, with no black pad (phosphorous left over) are observed. Immersion Pd and Pd-MoOx can be used to prevent black pad during Au plating on NiP. In this case, immersion Pd-MoOx utilize less Pd (lower cost) compared to immersion Pd for this purpose.