Acid-base properties of copper oxides and fluorides by means of band calculations: Relevance to metal-polymer adhesion

Classification of acids and bases in the Lewis sense implies electronic participation and it is extendable to non-protonic solvent interactions as well as solventless reactions. In many microelectronic applications, interfacial interactions between a polymer and a metal occur and contribute to the resulting adhesion of the bond. In the practical sense, metal surfaces are either oxidized or can be chemically altered by process conditions; therefore, the interaction is through a modified surface. The present study shows how tight binding calculations of the extended Hückel type can be used to estimate the relative acid strengths of copper, its oxides and fluorides. The trends obtained from bulk and surface layers in each case were related to the Fermi level of the crystal and the number of empty states derived from the copper 3d orbitals. Our results show the relative acid strengths follow the trend: CuF2 > CuO > CuF ~ Cu2O > Cu The methods used here can be directly applicable to classify the relative acid strengths of other metal-based substrates.