Effects of surface treatments on the adhesion of Cu and Cr/Cu metallizations to a multifunctional photoresist

Abstract

The effects of chemical, plasma, and reactive ion etching (RIE) treatments on the adhesion of Cu and Cr/Cu to the multifunctional polymer were investigated. The adhesion was measured with the newly developed pull test. The polymer surfaces were characterized by the x-ray photoelectron spectroscopy, atomic force microscopy, and surface free energy measurement. The failure modes were examined with the scanning electron microscopy and energy-dispersive spectroscopy. It was found that the adhesion of Cu and Cr/Cu to the highly functional photoresist was poor, regardless of the chemical, plasma, and reactive ion etching treatment with either O2 or CF4 used. However, the RIE pretreatment with the gas mixture (O2+CF4) of the photoresist surface increased the adhesion of sputtered Cr/Cu to the photoresist remarkably, and the failure mode was cohesive within the photoresist. Furthermore, the RIE pretreatment with pure oxygen gave rise to the needle-like surface together with virtually no introduced reactive functional groups, whereas the RIE with O2-rich gas mixture of O2+CF4 resulted in the relative smooth polymer surfaces and the newly formed C=O/O–C–O and O–C=O functionalities were incorporated on the treated surface with the increased polar surface free energy. The adhesion mechanism based on the experimental adhesion results and the surface characterizations of the polymer is proposed and discussed.