Impact of HF-based cleaning solutions on via resistance for sub-10 nm BEOL structures
In this work, ultra-dilute HF systems with the addition of functional hydrocarbon as an additive at elevated temperatures were evaluated to remove the post reactive ion etching (RIE) residues in a controlled chamber with ambient O2 concentration < 30 ppb. Controlling the HF and additive concentration was critical to achieve minimum dielectric loss (< 2 Å) and to suppress the formation of copper oxides while effectively removing post etch residues (PER). Cu 2p XPS peaks confirmed the removal of residues from the Cu and ULK sidewalls. An oxide free Ta/TaN liner and Cu surface was achieved and confirmed using time of flight secondary ion mass spectroscopy (TOF-SIMS). In addition, the impact of HF solution was electrically evaluated by measuring via resistance and yield. A clear trend in via resistance reduction and yield improvement (40%) was observed with applying the optimized cleaning conditions when compared to the control samples.