In a STEM image from a uniform region, we could clearly identify the electroplated Ni layer, with a thickness of approximately 180 nm. Above this Ni layer, we observed a uniform electroless plated Cu layer, with an average thickness of 220 nm. The cross-sectional STEM image from a non-uniform region clearly showed that the electroplated Ni layer was uniform (Figure ). The observed non-uniformity originated from the electroless plating step. Figure revealed that the electroless plated Cu layer was non-uniform, with variations in thickness ranging from approximately ~130 nm to ~400 nm. Additional top-view and cross-sectional SEM images of both uniform and non-uniform regions are presented in Figures A cross-sectional sample from a non-uniform region was prepared to verify the existence, extent, and efficiency of the electroless-plated layer in areas where irregular growth was observed, and to compare it with data obtained from uniform regions (Figure ). Figure shows the STEM bright-field (BF) image of the typical multilayer arrangement present in the uniform region. As described in the fabrication process, the successive layers of Ti and Cu on top of Si are evident in the elemental maps in Figure . The presence of oxygen below the metals aligns with a native The electroless process is autocatalytic, meaning that the metal being deposited acts as a catalyst to promote its own deposition . Mechanistically, electroless copper deposition proceeds in two steps: the thin-film stage (up to 3 µm) and the bulk stage (often 1-15 µm). In this work, the electroless deposited Cu was less than 500 nm and thus well within the thin-film range.