STUDIES ON METAL BENZOCYCLOBUTENE (BCB) INTERFACE AND ADHESION

Abstract

Interfacial characteristics such as chemical reaction. metal diffusion, and morphology were investigated for Cu/BCB, Cr/BCB and Ti/BCB structures. Using Auger and XPS depth profiling, the formation of titanium carbide and chromium oxide was confirmed at the metal/BCB interface. Annealing at 250-degrees-C for extended periods resulted in the diffusion of Cu, Cr and Ti into the BCB and subsequent formation of Cu-Si, CrSi2 and Ti-Si compound precipitates. The reaction is a thermal diffusion controlled process which is dependent on time and temperature. Ar sputtering treatment of BCB film before metallization was found to roughen the surface, resulting in metal spikes which penetrate into the roughened BCB film. However, the peel strength of metals on BCB was only about 177 g cm-1 presumably due to the brittleness of the BCB film. The etch rates of the BCB film in a reactive ion etcher (RIE) and a plasma etcher were measured using Ar, O2, O2 + CF4, and O2 + SF6 gas mixtures. Faster etch rates were obtained when CF4 and SF6 were added to oxygen, since the presence of atomic fluorine enhances the etch rate of organics, while also etching Si and SiO2 formed by exposure of Si-containing BCB film to oxygen gas. Surface compositional changes on the BCB film were observed by XPS after plasma modification. Pure O2 and O2 + CF4 plasmas oxidized the carbo-siloxane linkage (C-Si-O) of the BCB, resulting in the formation of SiO2 on the surface. The O2 + SF6 plasma, however, did not produce the surface SiO2, because of its faster Si and SiO2 etch rates.