Effect of precursor solvent on the copper migration behavior at the (polyimide/copper) interface

Copper (Cu) migration at the interface of (polyimide(PI)/Cu) bilayers prepared from various precursors was investigated on the basis of dynamic secondary ion mass spectroscopic (D-SIMS) analysis. The Cu migration into the PI phase at the (PI/Cu) interface was clearly detected from the D-SIMS profiles. The Cu migration state depended on the presence of carboxyl groups of PI precursor during the interface formation and on the properties of solvents. On the basis of the D-SIMS profiles, a model of the Cu migration state at the (PI/Cu) interface was proposed. The model consisted of an interfacial region formed by the interpercolation of each component and a diffusional region formed by the diffusion of precursor molecules complexed with Cu. The degree of gradual decrease of Cu secondary-ion intensity from the (PI/Cu) interface to the PI surface ((PI/air)interface) depended on the polarity of solvents. The interfacial region as well as the diffusional one was formed for the specimen prepared from the precursor solutions of aprotic polar solvent. On the other hand, only the interfacial region was formed for the specimen prepared from the precursor solutions of protic solvent. Therefore, it was concluded that the Cu migration state mainly depends on the complex formation with Cu and the diffusion capability of the PI precursor, while the contribution of the solvent was very small.