Material and process studies in the integration of plasma-promoted chemical-vapor deposition of aluminum with benzocyclobutene low-dielectric constant polymer

Abstract
The integration of low-temperature plasma-promoted chemical-vapor deposition (PPCVD) of aluminum, using dimethylethylamine-alane (DMEAA) as the source precursor, with benzocyclobutene (BCB) low-k polymers has been investigated to explore the feasibility of BCB-based Al metallization for sub-quarter-micron integrated circuitry. The study examined the thermal, chemical, and structural compatibility of PPCVD Al interconnects with the BCB polymer, including the feasibility of barrierless aluminum–BCB multilevel metallization stacks. Studies were conducted on a range of BCB surfaces, consisting of untreated (UNT), reactive-ion etched (RIE), and SiO2-capped BCB (SiO2–BCB) surfaces. The purpose was to mimic the actual BCB surfaces encountered during damascene processing. Each BCB surface was treated with argon or hydrogen plasma prior to aluminum processing to ensure reduction in the barrier to aluminum formation, leading potentially to enhanced Al nucleation mechanisms. In all cases, the direct deposition of Al on BCB films via PPCVD was successfully demonstrated, with the RIE-BCB substrate providing the best Al nucleation characteristics. Compositional analyses of the Al films indicated that carbon and nitrogen contaminants, which could have resulted from the dissociation reaction of the DMEAA molecule, were below the detection limits of the techniques used. Alternatively, oxygen inclusion was highly dependent on the chemical state and type of plasma treatment of the BCB surface, with only the PPCVD Al on plasma pretreated RIE BCB exhibiting bulk oxygen levels below the detection limits of x-ray photoelectron spectroscopy. Oxygen incorporation in the PPCVD Al films on UNT BCB and SiO2–BCB could be attributed to the diffusion of oxygen through intergranular voids upon air exposure, resulting in increased Al film resistivity. In all cases, the study indicated that an appropriate diffusion barrier/adhesion promoter is required to ensure viable BCB integration in Al metallization schemes.