Atomic Layer Etching of Tantalum with NbCl₅ and O₂

Tantalum has been used in the semiconductor industry as a diffusion barrier for metal interconnects. The current etching processes for this metal are mostly wet etching and reactive ion etching, and also one plasma enhanced atomic layer etching process has been reported. This paper reports development of a thermally activated atomic layer etching (ALE) process based on oxidation with O2 and removal of the oxide with NbCl5. The process was found to be somewhat selective toward the tetragonal β-phase of tantalum over the bcc α-Ta. Phase pure α-Ta films were used to study the ALE process, and EPC of 0.6–5.5 Å was obtained at the temperature range of 200–300 °C. Saturation of the etchant pulses was verified at 250 °C with an EPC of 2.8 Å. Some subsurface oxidation of the tantalum films was seen with XRD after etching at high temperatures, but otherwise, residues from the etching were minimal. The etching mechanism was studied using in vacuo XPS measurements at different stages of the process.