Au-Sn alloys, with a range of compositions, can be successfully pulse plated onto blank wafers and patterned wafers using a slightly acidic, chloride based solution. However, the plating solutions have limited stability (about two to three days), after which deposit compositions are not controllable. The aim of this work was to employ a number of characterization techniques to study the degradation of the plating solution in an effort to develop an understanding of the causes and mechanisms associated with instability. The techniques employed include scanning and transmission electron microscopy (SEM/TEM), x-ray diffraction (XRD), ultraviolet/visible (UV/Vis) spectroscopy and turbidity measurements. Nano-sized Au particles (<10 nm), were present in freshly mixed solutions. These increased in number over time, peaking out after about two days, before agglomerating into visible particles. UV/Vis spectroscopic analysis showed that ascorbic acid (present in the electroplating solution) acted as a reducing agent for the ionic complexes of gold.
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