Sacrificial adhesion promotion layer for Cu deposition in supercritical carbon dioxide

Interfacial adhesion of Cu film to adjacent layers is a critical aspect in metallization for advanced integrated circuits (ICs). We report an ultra-thin poly(acrylic acid) (PAA) layer can dramatically enhance the adhesion of Cu films on Si substrates with or without barrier layers. Cu films were deposited by the H-2-assisted reduction of bis(2,2,7-trimethyloctane-3,5-dionato)copper in supercritical carbon dioxide. The deposited films and the Cu/substrate interface information were collected by using X-ray photoelectron spectroscopy (XPS), electron microscopy, atomic force microscopy, and variable angle spectroscopic ellipsometry. The adhesion layer was found to be sacrificial at the deposition conditions. At the interface, Cu was present primarily as Cu-0, while the layer oxides were dramatically reduced. Additionally, we demonstrate that similar improvements can be achieved by using simple acrylic acid vapor exposure or UV polymerization of acrylic acid, suggesting the technique can be extended to patterned substrates.