Study of Ti/TiN bump defect formation mechanism and elimination by etch process optimization

Subtle Ti/TiN bump defects are observed after thermal annealing in the development step of a back-end-of-line (BEOL) via metallization. It disturbs the endpoint detection of a sequential tungsten (W) chemical-mechanical planarization (CMP) process and results in W residue on the surface of the wafer. SIMS analysis conducted before Ti/TiN deposition indicates the presence of high concentrations of fluorine (F) atoms that have already doped into the oxide film after the via hole plasma etching process, even in the presence of an amorphous carbon hard-mask. The doped F species could diffuse out of the surface region, and then react with as-deposited Ti/TiN to form volatile TiF4 during high-temperature annealing. As a result, severe metallic bump-like defects are observed. In this study, we report that the formation of the metallic bump defect is correlated to both the RF bias frequency, and the RF bias power applied in the capacitive-coupled fluorocarbon plasma via feature etching.