Combined Application of AFM-XRD-SIMS to Characterize Crystal Properties in Electroless Nickel Metal Induced by Trace Contaminants

The crystal properties of electroless nickel (EN) film plated on copper (Cu) bond pad (on wafer) can be differentiated by AFM (Atomic Force Microscopy) for its surface roughness and XRD (X-ray Diffraction) for its crystal orientation. The EN film deposited during the clean bath (CB) shows higher roughness under AFM and more oriented crystals under XRD, when comparing to the one from contaminated bath (COB). COB was CB pre-treated with small amount of Cu ²⁺ and OH ^- . Applying Secondary Ions Mass Spectroscopy (SIMS), Cu and hydrogen (H) contaminants were found to be higher in COB processed EN film compared to the one from CB. The H contaminant in COB EN film is due to its high plating rate (with more OH ^- ) resulting in more hydrogen gas by-product accumulation from the EN catalytic reaction. The presence of these 2 contaminants have potentially caused the change of crystal properties of the EN layer as detected by AFM and XRD.