| In order to increase speed and functionality, computer chip technology continues its evolution towards higher device density and reduced feature size. As interconnect signal delay has become prohibitively high for traditional Al/SiO2 architectures, there is a pressing need to pursue integration of low-k materials into back-end-of-the-line interconnect architectures.; To this end, polytetrafluoroethylene (PTFE) was integrated with aluminum, implementing titanium nitride as a barrier layer. SPEEDFILM, a version of PTFE, has a low dielectric constant of 1.9–2.0. With the use of an adhesion promoter, SPEEDFILM can be easily spun-cast onto patterned aluminum substrates, allowing for implementation into existing interconnect process flows.; CVD aluminum/PVD TiN binary stacks have been successfully grown on spin-cast films of PTFE. Elemental analysis revealed compositionally pure aluminum, showing virtually no fluorine contamination in as-deposited and annealed binary stacks, and resistivity as low as 3.2 μΩ-cm have been obtained. Thermal annealing studies indicate titanium nitride is an effective barrier against thermally-driven fluorine diffusion from PTFE.; A fabrication flow for a two-level Al/PTFE test structure was identified in order to examine key integration issues and produce an electrically testable demonstration vehicle. Many integration milestones have been met. In particular, XPS studies of plasma-treated PTFE surfaces demonstrated that an NH3 plasma can defluorinate the PTFE surface, allowing sufficient adhesion of a subsequently-deposited SiO2 cap to survive chemical-mechanical polishing. First pass work also indicated promising etching and photoresist stripping results of SiO2/PTFE stacks, which are designed for use at the via level of this two-level structure. This is a particularly useful result since low-k dielectrics are often difficult to pattern due to their degradation upon exposure to traditional photoresist stripping chemistries.; Finally, in-depth thermal stability studies of PVD TiN and TaN barriers on PTFE were performed. TaN was found to be more chemically stable with PTFE compared to TiN, where post-annealed bulk fluorine contents were <1 at% and 3 at% respectively by XPS for 32.5 nm barriers. Both barriers exhibited the presence of surface fluorocarbons after annealing, although their origin has not been determined. Potential extension of this work to copper metallization is discussed. |
