Crystal growth on novel Cu electroplating using suspension of supercritical CO2 in electrolyte with Cu particles

This paper reports an electroplating method with supercritical carbon dioxide (sc-CO2) emulsion (EP-SCE) on hole test element group (TEG), which has an integrated structure of Cu seed layer on TiN barrier layer sputtered on Si substrates. The reaction is carried out in an emulsion of sc-CO2 in copper-sulfate-based electrolyte with surfactants. It was reported that Ni film obtained by EP-SCE is uniform and without pinhole, because sc-CO2 has low viscosity and compatibility of hydrogen. Thus, this method is applicable in fine Cu wiring, but dissolution of Cu seed layer in EP-SCE was observed. Therefore, Cu particle was added to form a suspension. An electroplating method with sc-CO2 suspension (EP-SCS) is proposed to inhibit dissolution of Cu seed layer. Electroplated Cu film obtained by this method was a smooth film without pinhole. Moreover, we applied EP-SCS technique into filling of hole TEG with holes having 60 and 70 nm in diameter, and complete filling of all the holes with electrodeposited Cu without any void was obtained. The Cu filled into the holes was found to be single crystal or had only a few twin boundaries parallel to the surface of TEG. We suggest that crystal growth in EP-SCS could be bottom-up growth along [111] crystallographic orientation of Cu.