Effect of a Ti interlayer on the bond strength and thermal stability of the Cu/benzocyclobutene-divinyl tetramethyldisiloxane interface

A series of experiments were carried out to investigate the adhesion properties and thermal stability of Cu/benzocyclobutene-divinyl tetramethyldisiloxane (BCB-DVS) interfaces by a stud pull test and cross-sectional transmission electron microscopy (TEM), respectively. Multilayered specimens were prepared by spin-coating a layer of BCB-DVS onto a Si wafer and subsequently a layer of Cu was deposited on the BCB-DVS by electron beam evaporation. It was found that the average bond strength of the Cu/BCB-DVS interface was improved slightly by either Ar ion bombardment of the BCB-DVS surface or a Ti interlayer between Cu and BCB-DVS. A significant improvement was obtained by a combination of Ar ion bombardment and a Ti interlayer, and resulted in the formation of titanium carbides or oxides between Ti and BCB-DVS. Upon annealing the specimens at 260°C in vacuum for 18 h, interdiffusion of Cu into BCB-DVS to form clusters was observed, by cross-sectional TEM, for specimens with a 5 nm Ti interlayer, whereas the Cu island was not present in specimens with a 20 nm Ti interlayer. Interfacial reactions upon annealing were demonstrated by the formation of Cu3TiO5 and Cu-Ti intermetallics, identified by selected area diffraction.