Growth mode of copper films electrodeposited on silicon from sulfate and pyrophosphate solutions

The electrodeposition of thin copper films on silicon substrates from copper pyrophosphate and copper sulfate solutions, without the addition of additives or hydrofluoric add, is presented. The copper films obtained from these two solutions have different characteristics. Cyclic voltammetry was performed in order to investigate the silicon/electrolyte interface. This provides an explanation why the copper pyrophosphate solution is more favorable for electrodepositing copper on a semiconductor substrate. The copper films obtained with the pyrophosphate solution, having thicknesses ranging from 20 to 280 nm, were characterized in detail. They are homogeneous, exhibit a metallic luster, and show good adhesion. The topography was examined by atomic force microscopy, providing the root-mean-square roughness and the average grain size on the surface. The grain size values are compared with the average value of the scattering coherence length determined by X-ray diffraction. The kinetic roughening of the copper deposits was investigated by dynamic scaling behavior and compared to previous studies.