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Quantitative calibration of conductive pattern growth via electroless copper plating at nano-resolution

In compositions of flexible electronics, conductive strands with high flexibility are crucial. Today, electroless plating for metallization of plastic substrates is favourable, due to its low cost, broad material compatibility, high conductivity, and potential for batch process. It is important to investigate the surface chemistry during electroless plating for better quantization of conductive patterns during the growth with nanoscopic resolution. Wherein, time-of-flight secondary ion mass spectrometry (TOF-SIMS) and atomic force microscopy (AFM) are combinatively used to follow surface chemistry of electroless-plated copper layers on a silver-activated polyimide film, in a bath containing mainly a copper source, two chelates and a reducing agent of formaldehyde. TOF-SIMS results show that surface contaminants detected on the copper layers can be traced back to the chemicals used in the plating bath, some of which impact copper purity. Shallow depth profiling of a copper layer reveals the variations of copper oxide and surface contaminants. AFM results innovate the instrumentations for probing surface morphologies in relationship to the electroless plating process as well. The results demonstrated a powerful technique in understanding the surface chemistry of electroless-plated copper layers on an activated insulating substrate and playing a calibration role in next step for industrialization.